eva johansson nr2 - diva...
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DOCTORA L T H E S I S
Department of Civil, Environmental and Natural Resources EngineeringDivision of Mining and Geotechnical Engineering
Technological Properties of Rock Aggregates
Eva Johansson
ISSN: 1402-1544 ISBN 978-91-7439-246-3
Luleå University of Technology 2011
Eva Johansson Technological Properties of R
ock Aggregates
ISSN: 1402-1544 ISBN 978-91-7439-XXX-X Se i listan och fyll i siffror där kryssen är
DOCTORAL THESIS
TECHNOLOGICAL PROPERTIES OF ROCK AGGREGATES
EVA JOHANSSON
LULEÅ UNIVERSITY OF TECHNOLOGY
DEPARTMENT OF CIVIL, ENVIRONMENTAL AND NATURAL RESOURCES ENGINEERING DIVISION OF MINING AND GEOTECHNICAL ENGINEERING
LULEÅ 2011
Printed by Universitetstryckeriet, Luleå 2011
ISSN: 1402-1544 ISBN 978-91-7439-246-3
Luleå 2011
www.ltu.se
DOKTORSAVHANDLING
BERGMATERIALENS MEKANISKA EGENSKAPER
EVA JOHANSSON
LULEÅ TEKNISKA UNIVERSITET
INSTITUTIONEN FÖR SAMHÄLLSBYGGNAD OCH NATURRESURSER AVDELNINGEN FÖR GEOTEKNOLOGI
LULEÅ 2011
To my grandmother, the most admirable woman
I miss you…
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PREFACE
The research in the present thesis was carried out at the Division of Mining and Geotechnical Engineering, Luleå University of Technology. The financial support was provided by the Swedish Transport Administration, the Swedish National Road and the Transport Research Institute and Envix Nord AB.
Many persons have, to a greater or less extent, been engaged in this study and I want to thank all of you; no one mentioned, no one forgotten.
However, there is a group of persons I want to thank in a special way: Sten Fernerud (Managing Director of Envix Nord AB) for your encouragement, support, faith and never ending energy; the project group with Alexander Smekal, Eva-Lotta Olsson, Klas Hermelin, Karl-Johan Loorents (all representing the Swedish Transport Administration) and Håkan Arvidsson (the Swedish National Road and Transport Research Institute) for very good co-operation and feedback; Väglaboratoriet i Norr AB for patience and good service; Lennart, Ralf, Björn, Anders and Tobbe (BBX Entreprenad AB) for the robust action in connection with the sampling; Šárka Lukschová (Charles University in Prague) for your seriousness, tolerance and ability to co-operate; Kerstin Vännman and Gunnar Persson for your quick and invaluable achievements; Richard P ikryl (Charles University in Prague) for your helpful advice; Erling Nordlund and Jenny Greberg (Luleå University of Technology) for the privilege of studying at the Division of Mining and Geotechnical Engineering; Lena Nilsson (Luleå University of Technology) for the financial administration of my project; and finally all colleagues at Envix Nord AB for carrying out the main part of my duties during the most intense time of my studies.
I would like to express my sincere gratitude to my supervisor professor Karel Miškovský, Luleå University of Technology and assistant supervisor PhD Karl-Johan Loorents, the Swedish Transport Administration. Your never-ending encouragement, support, patience, advice and honesty have been the incentive for me and my work. Both of you are the most wonderful, fabulous and warm-hearted persons. You have succeeded in your roles as supervisors without losing our friendship. Send my regards to your lovely families.
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Finally, I want to thank my own wonderful family: my mother Birgit, my father Sonny, my little sister Anna, my nieces Klara and Lovisa and my Loved, and soul mate as well, Inge. Your understanding, support and well-intended words have helped me through doubts, despair, desperation and exhaustion. All of you deserve a star in heaven. By itself the thought leads to my big brother Ove; in spite of your physical absence you are still with me, living in my heart, living in my soul. The most tender dedication I give to my one and only child, my heartily loved daughter and sincere friend Kim; I love you! Umeå, April 2011
Eva Johansson
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ABSTRACT
The commission of technical geology is to apply geological knowledge to the field of constructional engineering, mining technology, environmental protection, architecture etc. The sector of infrastructure is highly dependent on the production of crushed rock materials as the main constituent of e.g. road and railway constructions. The functional properties of crushed rock materials used are of major importance concerning the durability of the construction and they are strongly connected to economic and environmental consequences. The quality of the aggregates is the crucial agent to reach the optimal performance of the infrastructural network. Due to the geological, geographic and climatologic preconditions of Northern Scandinavia, the quality of crushed rock materials is even more important. The Fennoscandian bedrock is dominated by igneous and metamorphic rocks. The access to qualitative rocks for production of aggregates displays considerable regional variation. The oblong geographical extension of the North Scandinavian countries, the fairly low population and the frequent traffic require the widespread infrastructure. The temperate climate characterized by freeze-thaw cycles combined with usage of studded tyres requires a long lasting construction of high sustainability.
In spite of available international standards dealing with the aggregates’ quality, the deterioration of the road constructions is noted in Sweden; it is mostly caused by use of mica-rich, heterogeneous rocks. The utilization of these kinds of rock materials as base courses and bituminous wearing courses results in economic losses and negative environmental consequences.
The aim of the present thesis was to study technological properties of aggregates in a challenge to connect them with the petrographic characteristics of rock materials. The study includes an investigation of enrichment of free mica particles in fine fractions originating from crushed rock aggregates and the development of a scientifically based method for estimation of free mica particles in aggregate fine fractions. The second part of the thesis deals with the influence of petrographic parameters on the mechanical (functional) properties of aggregates. Finally, an interlinking method of drill cuttings analysis is applied as a tool for estimation of rock aggregates’ quality and usability.
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The studies of mica confirmed the enrichment of free mica particles in fine fractions of the crushed rock compared with initial mica content in the rock. The primary grain size of mica in the host rock is suggested to influence the process of enrichment. The evaluation of the developed method for estimation of free mica particles confirms its certainty and repeatability. The petrographic analyses of drill cuttings indicated the compatibility between the content of free mica in fine fractions originating from crushed rock and drill cuttings respectively.
The literature review concerning the correlations between petrographic and mechanical properties of rock materials indicated the necessity to intensify the research on this field. Mineralogical composition, micro-cracks, porosity, grain size, grain shape and the degree of foliation were found to be the most important petrographic parameters influencing the mechanical and technical properties of igneous, metamorphic and sedimentary rocks. The study of the petrographic characteristics of granitoid and gabbroid intrusive rocks as a tool for evaluation of mechanical properties confirmed that grain size, content of mica and frequency of micro-cracks are the main petrographic variables influencing mechanical properties of granitoids. In the case of gabbroid rock types, the mechanical properties generally respond to the mica content and frequency of micro-cracks.
The results of the study of the petrographic and mechanical properties of the rock materials point to the possibility to develop a system for estimation of the mechanical properties of rock materials using their petrographic characteristics. Keywords: crushed rock aggregates, free mica, monomineralic grain, fine fraction, image
analysis, point count method, drill cuttings, mechanical properties, road constructions, rock fabrics, granitoids, gabbroids, intrusive rocks
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SAMMANFATTNING
Den tekniska geologins viktigaste uppgift är att tillämpa geologisk kunskap inom samhällsbyggnadsteknik, gruvteknik, miljö- och naturvård, arkitektur m.m. Infrastruktursektorn är i hög grad beroende av produktion av ballast som är det viktigaste materialet vid byggande av vägar, järnvägar etc. Krossbergets funktionella egenskaper är en avgörande faktor för konstruktionens varaktighet och har därför stor ekonomisk och miljömässig betydelse. Norra Skandinaviens geologiska, geografiska och klimatologiska förutsättningar ställer större kvalitetskrav på bergmaterial jämfört med övriga Europa. Eftersom fennoskandiska berggrunden domineras av djupmagmatiska och metamorfa bergarter, uppvisar tillgången på bergmaterial av lämplig kvalitet stora regionala variationer. De nordskandinaviska ländernas långsträckta geografiska utbredning kräver, i kombination med gles befolkning och tät trafik, ett extensivt infrastrukturnät. Tempererat klimat, karaktäriserat av upprepade frys-/töcykler och användning av dubbdäck, ställer stora krav på infrastrukturens uthållighet och varaktighet.
Trots tillgång till europeiska produktstandarder beträffande kvalitet på ballast, konstaterades förekommande skador på vägkonstruktioner, mestadels orsakade genom användning av glimmerrika, heterogena bergarter i Sverige. Användning av dessa bergmaterial föranleder stora samhällsekonomiska förluster och medför även negativa miljökonsekvenser.
Det föreliggande projektets mål var att studera ballastmaterialens teknologiska egenskaper och försöka sammanföra dessa med bergarternas petrografiska egenskaper. Studiens första del innefattar undersökning av fri glimmers anrikning i finfraktion hos olika typer av glimmerförande krossade bergarter samt utveckling av en vetenskapligt baserad metod för bestämning av andel fri glimmer i finfraktion. Avhandlingens andra del behandlar inverkan av bergarternas petrografiska karaktäristik på mekaniska och funktionella egenskaper för deras krossprodukter.
Resultaten från undersökningen av fri glimmer bekräftade anrikning av fria glimmerpartiklar i finfraktioner jämfört med bergartens ursprungliga glimmerhalt. Anrikningsprocessen påverkas av glimmers ursprungliga kornstorlek i originalbergarten. Petrografiska analyser av borrkax indikerade jämförbara halter av fri glimmer i borrkaxens finfraktion och i finfraktion hos krossat berg.
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Litteraturstudien avseende samband mellan bergmaterialens petrografiska och mekaniska egenskaper pekar på nödvändigheten att intensifiera forskning inom området. Från litteraturstudien framgår att mineralsammansättning, mikrosprickfrekvens, kornstorlek, kornform och foliationsgrad är de viktigaste petrografiska parametrar som påverkar magmatiska, metamorfa och sedimentära bergarters mekaniska egenskaper. Avhandlingens avslutande studie av petrografiska egenskaper hos granitoida och gabbroida intrusivbergarter som verktyg för bedömning av deras mekaniska egenskaper bekräftade att kornstorlek, glimmerhalt och mikrosprickfrekvens är de styrande faktorerna hos granitoida bergarter. Gabbroida bergarters mekaniska egenskaper påverkas huvudsakligen av bergartens glimmerhalt och mikrosprickfrekvens.
Resultat från jämförelser mellan bergmaterialens petrografiska och mekaniska egenskaper visar möjlighet att i framtiden utveckla ett system för bedömning av bergmaterialens mekaniska egenskaper baserat på bergartens petrografiska karaktäristik.
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CONTENTS
1 INTRODUCTION .................................................................................................. 1
1.1 BACKGROUND ............................................................................................. 1
1.2 AIM ............................................................................................................. 2
1.3 ASSUMPTIONS AND APPROACH .................................................................... 3
1.4 DESCRIPTION OF THE TEST METHODS USED FOR TESTING OF ROCK AGGREGATES ............................................................................................... 4
1.4.1 The Los Angeles methods ................................................................ 4
1.4.2 The micro-Deval methods ............................................................... 5
1.4.3 The Studded tyre test method ........................................................... 6
1.4.4 The Impact test method .................................................................... 7
1.5 DISPOSITION OF THE THESIS ........................................................................ 9 2 FREE MICA IN ROCK AGGREGATES ................................................................. 11
2.1 ENRICHMENT OF FREE MICA PARTICLES IN AGGREGATE FINE FRACTIONS ................................................................................................ 11
2.1.1 Samples .......................................................................................... 11
2.1.2 Sample preparation ....................................................................... 12
2.1.3 Content of free mica particles ....................................................... 13
2.1.4 Evaluation ...................................................................................... 14
2.1.5 Remarks ......................................................................................... 15
2.2 A METHOD FOR ESTIMATION OF FREE MICA PARTICLES ............................. 16
2.2.1 Brief description of the testing of the method ............................... 16
2.2.2 Concluding remarks ...................................................................... 18
2.3 ESTIMATION OF FREE MICA CONTENT USING ANALYSIS OF DRILL CUTTINGS ........................................................................................ 18
2.3.1 Approach ....................................................................................... 18
2.3.2 Results from analyses of free mica content ................................... 18
2.3.3 Evaluation ...................................................................................... 19
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2.4 COMPARISON BETWEEN FREE MICA CONTENT IN THE FINE FRACTIONS AND INITIAL MICA CONTENT IN THE HOST ROCK ........................................ 19
2.4.1 Materials and methods .................................................................. 19
2.4.2 Results ............................................................................................ 20
2.4.3 Evaluation ...................................................................................... 21 3 MECHANICAL PROPERTIES OF ROCK AGGREGATES ....................................... 23
3.1 THE LITERATURE REVIEW .......................................................................... 23
3.1.1 Summarized results ........................................................................ 23
3.1.2 Notes .............................................................................................. 23
3.2 INFLUENCE OF PETROGRAPHIC CHARACTERISTICS ON MECHANICAL PROPERTIES ............................................................................................... 24
3.2.1 Methods ......................................................................................... 24
3.2.2 Results ............................................................................................ 25
3.2.3 Evaluation ...................................................................................... 29
3.3 DRILL CUTTINGS USED FOR EARLY ESTIMATION OF ROCK AGGREGATES’ QUALITY .................................................................................................... 30
3.3.1 Implementation .............................................................................. 30
3.3.2 Evaluation ...................................................................................... 31 4 BRIEFING OF THE RESULTS ............................................................................. 33
4.1 ENRICHMENT OF FREE MICA PARTICLES .................................................... 33
4.2 ESTIMATION OF FREE MICA PARTICLES ...................................................... 33
4.3 RELATIONSHIPS BETWEEN PETROGRAPHIC AND MECHANICAL PROPERTIES OF GRANITOID AND GABBROID INTRUSIVE ROCKS .................. 34
4.4 ESTIMATION OF ROCK AGGREGATES’ QUALITY USING DRILL CUTTINGS ........................................................................................ 34 5 DISCUSSION...................................................................................................... 35 6 CONCLUSIONS .................................................................................................. 39 ACKNOWLEDGEMENTS ........................................................................................... 41 REFERENCES ........................................................................................................... 43
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APPENDICES
FREE MICA GRAINS IN CRUSHED ROCK AGGREGATES .................................... PAPER I
A METHOD FOR ESTIMATION OF FREE MICA PARTICLES IN AGGREGATE FINE FRACTION BY IMAGE ANALYSIS OF GRAIN MOUNTS ........... PAPER II
ESTIMATION OF ROCK AGGREGATES QUALITY USING ANALYSES OF DRILL CUTTINGS ........................................................... PAPER III
CORRELATIONS BETWEEN PETROGRAPHIC AND MECHANICAL PROPERTIES OF ROCK MATERIALS: A LITERATURE REVIEW ............................ PAPER IV
PETROGRAPHIC CHARACTERISTICS OF GRANITOID AND GABBROID INTRUSIVE ROCKS AS A TOOL FOR EVALUATION OF MECHANICAL PROPERTIES...................................................................................................... PAPER V
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LIST OF PUBLICATIONS
PAPER I Loorents, K.-J., Johansson, E., Arvidsson, H., 2007. Free mica grains in crushed
rock aggregates, Bulletin of Engineering Geology and the Environment, 66(4), pp. 441-447(7)
PAPER II Johansson, E., Miškovský, K., Loorents, K.-J., Löfgren, O., 2008. A method for
estimation of free mica particles in aggregate fine fraction by image analysis of grain mounts, Journal of Materials Engineering and Performance, 17(2), pp. 250-253(4)
PAPER III Johansson, E., Miškovský, K., Loorents, K.-J., 2009. Estimation of rock aggregates
quality using analyses of drill cuttings, Journal of Materials Engineering and Performance, 18(3), pp. 299-304(6)
PAPER IV Johansson, E., Lukschová, Š., Miškovský, K. Correlations between petrographic
and mechanical properties of rock materials: a literature review, Journal of Materials Engineering and Performance, submitted 10 September 2010
PAPER V Johansson, E., Lukschová, Š., Miškovský, K. Petrographic characteristics of
granitoid and gabbroid intrusive rocks as a tool for evaluation of mechanical properties, Engineering Geology, submitted 15 Mars 2011
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CHAPTER 1 INTRODUCTION
1.1 BACKGROUND
The commission of technical geology is to apply geological knowledge to the field of constructional engineering, mining technology, environmental protection, architecture etc. The sector of infrastructure is highly dependent on the production of crushed rock materials, as the main constituent of e.g. road and railway constructions is aggregates. The functional properties of crushed rock materials used are of major importance concerning the durability of the construction and they are strongly connected to economic and environmental consequences (e.g. Heiniö, 1999; Johansson et al., 2009; Primel and Tourenq, 2000). Hence, the quality of the aggregates is the crucial agent to reach the optimal performance of the infrastructural network.
Rock materials have to meet the constructional, economic and environmental requirements that assume adequate information regarding their petrographic and mechanical properties. The relationships between these properties therefore play an important role concerning sustainable usage of natural resources, appropriate extraction of hard rock and material balance (e.g. Primel and Tourenq, 2000; Smith and Collis, 2001). It is desirable that the matters of extraction should be based on genuine knowledge of different rock materials and their mechanical properties in an effort to reach a rational level of rock material exploitation.
Due to geological, geographical and climatologic preconditions of the Northern Scandinavia, the quality of crushed rock materials is even more important. The Fennoscandian bedrock is dominated by igneous and metamorphic rocks of low to high metamorphoses. The access to qualitative rocks for production of aggregates displays considerable regional variation. The oblong geographical extension of the North Scandinavian countries, the fairly low population and the frequent traffic demand the widespread infrastructure. The temperate climate characterized by freeze-thaw cycles combined with usage of studded tyres requires a long lasting construction of high sustainability.
Despite available international standards dealing with the aggregates’ quality (e.g. the European Committee for Standardization, 1996b; 2002a; 2002b; 2002c; 2002d; 2003), the deterioration of the road constructions is noted in Sweden; it is
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mostly caused by use of mica-rich, heterogeneous meta-sedimentary rocks, i.e. mica-schists, meta-greywackes and sedimentary gneisses. The utilization of these kinds of rock materials as base courses and bituminous wearing courses results in economic losses and negative environmental consequences (e.g. Kondelchuk, 2008; Novikov, 2008).
Smith and Collis (2001) confirm that free mica particles in crushed rock
aggregates intended for constructional purposes affect the quality of the end product. The negative influence of free mica arises in both bounded (e.g. Hakim and Said, 2003) and unbounded (e.g. Nieminen and Uusinoka, 1986) layers of the road. The deterioration of the construction originates from the tendency of mica particles to be released during crushing and to concentrate in the aggregate fine fractions (e.g. Loorents et al., 2007; Loorents and Kondelchuk, 2009; Miškovský, 2004).
Due to high content of free mica in the aggregates, the unbounded base course becomes susceptible to frost weathering, and consequently inclined to crumbling (Nieminen and Uusinoka, 1986), as the free mica particles absorb and hold liquid such as bitumen and water (Miškovský, 2004; Novikov and Miškovský, 2009). Hakim and Said (2003) and Miškovský (2004) show a significant deterioration of the quality of bituminous mixtures related to an increasing amount of free mica in aggregate fine fractions.
In an effort to verify the content of free mica particles in crushed rock aggregates and to limit damage to road constructions related to the mica content, the Swedish Transport Administration established a standard method in 2002 concerning the content of free mica in fine fractions of aggregate products (the Swedish Transport Administration, 2002). The method is based on particle counting (stereoscopic microscope) and provides an approximation of the free mica content. It is mainly suited as an indicative tool, as sample selection and counting may introduce a statistical bias and reproducibility is questionable within the same sample. Thus, the introduction of the standard method demands the development of an effective and scientifically satisfactory method for estimation of free mica particles in fine fractions (Johansson et al., 2008). 1.2 AIM
The aim of the present thesis was to study technological properties of aggregates in an effort to connect them with the intrinsic characteristics of rock materials. The study includes an investigation of enrichment of free mica particles in fine fractions originating from crushed rock aggregates (Paper I) and the development of a scientifically based method for estimation of free mica particles in aggregate fine fractions (Paper II). Finally, the thesis work deals with the influence of petrographic parameters on the mechanical (functional) properties of aggregates
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(Paper IV and V). In an interlinking purpose, analyses of drill cuttings are applied as a tool for estimation of rock aggregates’ quality and usability (Paper III). The method of drill cuttings deals with the occurrence of free mica particles as a quality parameter. The present research focuses on both the free and bounded micas’ influence on the quality of road and railway constructions. The initial mica content in the host rock is one main parameter influencing the mechanical properties of aggregates (Paper V). 1.3 ASSUMPTIONS AND APPROACH
The petrographic properties of rock materials influence the aggregates’ technical properties and their usability as construction materials (e.g. Lindqvist et al., 2007; Ramsay et al., 1974).
Free mica particles tend to be enriched in the fine fractions of crushed rock aggregates. Free mica affects the aggregates’ end products and causes deterioration of the constructions (e.g. Lagerblad, 2005; Miškovský, 2004; Nieminen and Uusinoka, 1986; Smith and Collis, 2001). Furthermore, it is expected that the content of free mica is proportional to the initial mica content in the host rock. In an effort to support the previous research on enrichment of free mica by e.g. Lagerblad (2005) and Miškovský (2004), an investigation concerning the ability of mica to be enriched in fine fractions of crushed rock aggregates was carried out (Paper I).
The increased demand for a reliable method to quantify the content of free mica particles in aggregate fine fractions initiated the development of a robust method (Johansson et al., 2008). The complete description of the method proposed is appended as Paper II.
Geological parameters and mechanical properties are strongly connected (e.g. Brattli, 1992; Räisänen, 2004; Räisänen and Torppa, 2005; Tu rul and Zarif, 1999; Åkesson et al., 2001; 2003). If sufficient petrographic data is acquired, it may be possible to estimate the mechanical properties of the rock materials. With the aim to summarize the current state of the literature concerning rock materials’ petrographic properties and their influences on the mechanical properties, a literature review was carried out (Paper IV). The mechanical properties’ dependence on petrographic variables was evaluated for granitoid and gabbroid intrusive rock types. The selected sample suites were analysed for numerous petrographic and mechanical properties. The intention was to increase the understanding of the performance of rock materials used as aggregates and to initiate an attempt to unify geology and engineering in a common approach to evaluation of rock aggregates’ mechanical properties using petrographic characteristics as key parameters. Paper V deals with the complete study.
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When the petrographic qualities of the rock material are known, it is possible to estimate the mechanical properties of the rock type and its usability as aggregates in various constructions and parts of constructions. The concept of a method for rock aggregates’ quality identification in early constructing stages was developed. The practical implementation of this method was tested by using drill cuttings for estimation of the quality and the usability of rock materials as well as the content of free mica particles in fine fractions (Johansson et al., 2009). Paper III encloses the accomplished study. 1.4 DESCRIPTION OF THE TEST METHODS USED FOR TESTING OF ROCK
AGGREGATES 1.4.1 THE LOS ANGELES TEST METHODS
The Los Angeles test measures the aggregates’ resistance to fragmentation expressed by the LA or the LARB value. The different termed values deal with the aggregate size fractions 10/14 mm or 31.5/50 mm respectively. The Los Angeles test methods are described in accordance with the European Committee for Standardization (2010).
The amount of the fraction 10/14 mm sample is 5,000±5 g, sieved, washed and reduced aggregates. The test apparatus (Figure 1.1) is a steel drum with an inner diameter of 711±5 mm, a length of 508±5 mm and supplied with a lifting beam along the drum. The drum is placed on a machine body directly anchored to a horizontal concrete floor. The aggregates rotate together with 11 steel balls, each with a diameter of 45-49 mm, a weight between 400 and 445 g and a total weight of 4,690-4,860 g. The drum rotates 500 revolutions at a constant velocity of 31-33 min-1. After the test the material is sieved on a 1.6 mm sieve. The amount of material remaining on the 1.6 mm sieve is weighed. The Los Angeles value, LA, is calculated according to the formula:
5,00050
mLA (Equation 1.1)
where: m is the weight of the material remaining on the 1.6 mm sieve, in grams (g) The LA value is reported to the nearest integer in %.
The principle of testing the 31.5/50 mm fraction is similar to the one testing the fraction 10/14 mm with a few exceptions. The steel balls are 12 in number and with a total weight of 5,210±90 g. The total weight of the sample is 10,000±100 g and the drum rotates 1,000 revolutions instead of 500. The Los Angeles value, LARB, is determined as stated in Equation 1.2.
10,000100RB
mLA (Equation 1.2)
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where: m is the weight of the material remaining on the 1.6 mm sieve, in grams (g) The LARB value is reported to the nearest integer in %.
Figure 1.1 An example of a Los Angeles apparatus
1.4.2 THE MICRO-DEVAL TEST METHODS
The micro-Deval test measures the aggregates’ resistance to wear expressed by the MDE or the MDERB value. Analogous to the Los Angeles methods, the two different terms deal with the size fractions 10/14 mm or 31.5/50 mm respectively. The micro-Deval test methods are described in accordance with the European Committee for Standardization (2011).
The amount of the fraction 10/14 mm sample is 500±2 g, sieved, washed and reduced aggregates. The analysis is performed in a water- and dustproof steel drum with an inner diameter of 200±1 mm and a length of 154±1 mm. The micro-Deval apparatus can consist of 1-4 drums (Figure 1.2). The aggregates rotate together with 5,000±5 g steel balls, 10.0±0.5 mm in diameter, and 2,500±50 ml water added. The drum rotates 12,000±10 revolutions at a velocity of 100±5 min-1. After the test the material is sieved on a 1.6 mm sieve. The amount of material remaining on the 1.6 mm sieve is weighed. Two analyses of the same sample are required. The micro-Deval value, MDE, is calculated with one decimal according to the formula:
500100500DE
mM (Equation 1.3)
Lifting beam
Opening
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where: m is the weight of the material remaining on the 1.6 mm sieve, in grams (g) The result is the mean value of the two analyses performed. The MDE value is reported rounded to the nearest integer in %.
The principle of testing the 31.5/50 mm fraction is similar to the one testing the fraction 10/14 mm with a few exceptions. The length of the drum is 400±2 m, the total weight of the sample is 10,000±100 g and the drum rotates 14,000±10 revolutions. The quantity of water is 2,000±50 ml. No steel balls are used. The micro-Deval value, MDERB, is determined as stated in Equation 1.4.
10,000100DE
mM RB (Equation 1.4)
where: m is the weight of the material remaining on the 1.6 mm sieve, in grams (g) The result is the mean value of the two analyses performed. The MDERB value is reported rounded to the nearest integer in %.
Figure 1.2 A typical micro-Deval apparatus with four drums
1.4.3 THE STUDDED TYRE TEST METHOD
The Studded tyre test value is a measure of the aggregates’ resistance to wear by abrasion from studded tyres, expressed by the AN value. The test method is regularly used in the Nordic countries due to the temperate climate characterized by repeated freeze-thaw cycles, hence the common naming Nordic test. The Studded tyre test method is described in accordance with the European Committee for Standardization (1998).
The analysis is performed in a waterproof, tubular drum, closed in one of the ends and supplied with a water- and dustproof cover in the other (Figure 1.3). The inner diameter of the drum is 206.5±2.0 mm and the length is 335±1 mm. Three ribs, each 333±1 mm long, are regularly distributed around the inner cylinder wall. The size fraction used is 11.2/16 mm, sieved, washed and reduced aggregates to an amount of approximately 1,000 g, dependent on the density of rock. Together with the aggregates 7,000±10 g steel balls (around 500 balls with a diameter of 15.0+0.1/-0.5 mm) and 2,000±10 ml water are added. The drum rotates 5,400±10
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revolutions at a velocity of 90±3 min-1. After the tumbling the material is sieved on the 14.0, 8.0 and 2.0 mm sieves. The amount of material remaining on the sieves is weighed. The procedure has to be repeated for a second sample. The Studded tyre test value, AN, is calculated by the formula:
2( )100 iN
i
m mAm
(Equation 1.5)
where: mi is the dry weight of the sample prior to the analysis, in grams (g) m2 is the sum of the dry weights of the fractions remaining on the sieves 14.0, 8.0
and 2.0 mm, in grams (g) The result is the mean value of the two analyses performed if the deviation is less or equal to 7% of their mean value. If the deviation is higher, it is necessary to analyse two more samples. The AN value is reported with one decimal.
Figure 1.3 A typical apparatus used for the Studded tyre test
1.4.4 THE IMPACT TEST METHOD
The Impact test method measures the aggregates’ resistance to fragmentation by impact expressed by the SZ value. The method described and used for the present study is a Swedish modification (the Swedish Transport Administration, 2001) of the European standardized method for determination of resistance to fragmentation by impact (the European Committee for Standardization, 2010).
The testing machine is an apparatus with a drop hammer, pestle and mortar rigged on a concrete foot with a mass of >100 kg (Figure 1.4). The weight of the drop hammer is 14±0.1 kg and of the pestle 3.7±0.05 kg. The inner diameter of the mortar is 100±0.2 mm and the outside diameter of the pestle’s lower part is 98±0.2 mm. The impact test admits testing of fractions 5.6/8, 8/11.2 or 11.2/16 mm. The preferred size fraction is 11.2/16 mm, sieved, washed and reduced aggregates to an amount of approximately 500 g, dependent on the density of rock. The drop hammer has to be dropped, from a height of 250 mm, 20 times in
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an interval of two seconds. After the test the sample is sieved through the sieve corresponding to the smallest grain size of the sample fraction, in the current study 11.2 mm. The remaining and passed amounts of materials on the sieve are weighed. Two analyses of the same sample are required. The Impact value, SZ, is calculated as formulated in Equation 1.6.
100 p
i
mSZ
m (Equation 1.6)
where: mi is the sample weight, in grams (g) with one decimal mp is the amount of the sample passing the sieve for the smallest grain size of the
sample, in grams (g) with one decimal The SZ value is reported as a mean value of two analyses, rounded to the nearest integer in wt%.
Figure 1.4 An example of a drop hammer apparatus
9
1.5 DISPOSITION OF THE THESIS
The structure of the thesis is based on the chronological order of the obtained results and the published papers. The main features are briefly described in Chapters 2 and 3 respectively. The major results are summarized in Chapter 4 and in Chapter 5 there is a general discussion. The conclusions are presented in Chapter 6. The papers are appended at the end of the thesis.
10
11
CHAPTER 2 FREE MICA IN ROCK AGGREGATES
The first part of the study of technological properties of rock aggregates dealt with free mica content in aggregate fine fractions. Summarily, the research comprised the enrichment of free mica in fine fractions, the development of a robust method for estimation of free mica, the possibility to use drill cuttings for early information on free mica and the content of free mica compared to the initial mica content in host rock. 2.1 ENRICHMENT OF FREE MICA PARTICLES IN AGGREGATE FINE FRACTIONS
The samples used in this study (Paper I) are representative of the common crushed rock aggregates. They were prepared according to the standard laboratory routines and they were analysed for their petrography and the content of free mica particles. 2.1.1 SAMPLES
Rock samples were collected from two areas of the Svecofennian Province granitoids. Samples 1 and 2 were obtained from the same quarry and sample 3 was selected from a road cutting. The samples were all more or less undeformed. Rock samples of comparable microstructural characteristics were preferred to reduce factors that could influence the breakage of the rock (e.g. the release of mica during crushing). The microstructural difference was mainly indicated by the grain size. Samples 1 and 2 had a similar mineralogical composition (Table 2.1), whereas sample 3 was enriched in mica compared with the other samples studied.
Sample 1 was a grey to red, weakly foliated, medium-grained (Gillespie and Styles, 1999) granite (Figure 2.1). As shown in Table 2.1, sample 2 (Figure 2.2) was in general similar to sample 1, although with some differences in mineralogical composition and to a lesser extent in grain size distribution. Sample 3 (Figure 2.3) was a white and black, massive, coarse-grained (Gillespie and Styles, 1999) monzogranite.
12
Figure 2.1 Sample 1 Figure 2.2 Sample 2 Figure 2.3 Sample 3 Table 2.1 Mineralogical composition1 (vol.%) and grain size of the main minerals
2 Qtz Plg K-fsp Bt Cl Ms Opq Acc
Sample 1 40 14 36 3 3 4 0.2 0.2 Grain size (mm) 0.6-1.5 1.4-2.9 1.2-3.7 0.4-0.8 - 0.6-1.6 - -
Sample 2 37 14 37 4 1 7 Trace 1.0 Grain size (mm) 0.7-1.6 1.4-3.2 1.4-2.5 0.6-1.3 - 0.9-1.6 - -
Sample 3 28 25 27 19 - - Trace 1.4 Grain size (mm) 0.9-2.3 1.5-3.2 1.7-2.9 0.9-2.5 - - - -
1 The mineral mode is based on point-counting using a polarization microscope 2 Qtz=quartz; Plg=plagioclase; K-fsp=K-feldspar; Bt=biotite; Cl=chlorite; Ms=muscovite; Opq=opaque;
Acc=accessory 2.1.2 SAMPLE PREPARATION
The breakage of the samples was performed using a primary and a secondary laboratory jaw crusher. For each type of rock a sample similar in shape was used for crushing. The grain size distribution for each crushed sample was obtained by dry sieving (Figure 2.4) in accordance with the European Committee for Standardization (1997; 1999). Additional sieving was made for grains <63 m (Table 2.2). Sieves were weighed before and after the sieving to measure the amount of material that remained on the sieve. Compressed air was used to clean the sieves after each sieving cycle. The following grain size fractions were collected from sieving: <24, 24/42, 42/63 m, 0.063/0.125, 0.125/0.25, 0.25/0.5 and 0.5/1 mm. Table 2.2 Sieving of materials <63 m
Sieve ( m) Passing material (%) Fasten material (g) Sample 1 Sample 2 Sample 3 Sample 1 Sample 2 Sample 3
63 99.6 99.2 99.7 0.07 0.07 0.06 42 72.4 80.6 71.4 0.04 0.03 0.03 24 32.7 40.6 37.1 0.04 0.04 0.05
13
20090634531.51611.285.64210.50.250.1250.063
0.06 0.2 0.6 2 6 20 60Sand Gravelfine medium coarse fine medium coarse
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%Pe
rcen
tage
pas
sing
Particle size (mm)
Sample 1
Sample 2
Sample 3
Figure 2.4 Grain size distributions of the three samples after crushing into two steps
2.1.3 CONTENT OF FREE MICA PARTICLES
The content of free mica particles was estimated generally following RILEM AAR-1 (Sims and Nixon, 2003). For size fractions 0.125/0.25, 0.25/0.5 and 0.5/1 mm grains were grouped and counted (stereoscopic microscope, Technique 1) on the basis of mineralogy into muscovite, biotite and others where appropriate. All grains in the sample were counted (Table 2.3). With Technique 2, a polarizing microscope and the point-count method were used for all fractions collected (Table 2.3). Thin sections were prepared as grain mounts (Nesse, 2004).
14
Table 2.3 Mica content, in particle and vol.%, of sample according to analysed grading fractions together with total number of grains counted
Grain size Bt Ms % mica Count 1 Bt Ms % mica Count Technique 1 Technique 2
Sample 1 0.5/1 (mm) 1 7 8 215 2.8 7.3 10.2 1,704 0.25/0.5 7 5 12 526 5.6 7.6 13.2 1,787 0.125/0.25 8 8 16 571 6.6 7.6 14.1 1,999 0.063/0.125 5.2 8 13.3 2,157 42/63 m 6 9 15 583 24/42 10 14 24 567 <24 14 19 33 525 Sample 2 0.5/1 (mm) 1 6 7 299 4.2 7.1 11.2 1,659 0.25/0.5 3 6 9 467 3.8 8.3 12.0 1,695 0.125/0.25 8 9 17 773 6.4 8.7 15.1 1,925 0.063/0.125 6.9 8.2 15.0 2,022 42/63 m 6 8 14 539 24/42 13 13 26 558 <24 17 17 34 508 Sample 3 0.5/1 (mm) 24 24 368 18.8 18.8 1,834 0.25/0.5 31 31 420 21.8 21.8 1,704 0.125/0.25 22 22 699 19.0 19.0 1,971 0.063/0.125 14.2 2,085 42/63 m 17 17 557 24/42 20 20 568 <24 36 36 536
1 Bt=biotite; Ms=muscovite; % mica=total % mica in sample; Count=total number of grains/points counted 2.1.4 EVALUATION
The three samples used in this study provide a somewhat sparse basis for discussion and a review of literature information on free mica in rock aggregates is justified. However, the current section concerning evaluation is strongly restricted and deals with the data obtained entirely from this study. In Paper I previous research is thoroughly discussed.
The investigation comprised three igneous rock types. Samples 1 and 2 have similar mineralogical compositions and grain sizes, while sample 3 differs mainly in grain size. Samples 1 and 2 are medium-grained and sample 3 is coarse-grained. The trend line of sample 3 (Figure 2.5) generally shows higher amounts of free mica particles for coarser grain fractions, indicating that the amount of free mica depends on the initial mica content and grain size of the host rock.
Figure 2.5 shows the free mica content of the samples. Using grain fraction 0.063/0.125 mm as a divider and comparing the trend lines give quite different associations for the <0.063 and the >0.125 mm grain fractions. For grains >0.125 mm the relationship is less consistent, while for fractions <0.063 mm a
15
uniform tendency towards increase is displayed. The disparity corresponds to the grain size of the host rock and the content of mica. Due to exposure to mechanical breakage of the monomineral in the aggregate, it is presumably that coarser minerals more readily release mica from the mineral aggregate (e.g. >0.125 mm) than fine-grained ones. As the grain fraction gets smaller, the aggregate has to reach a “critical” grain fraction (e.g. <0.063 mm) before further breakage continues.
0
5
10
15
20
25
30
35
40
<24 24-42 42-63 63-125 125-250 250-500 500-1000
Con
tent
of f
ree
mic
a (v
ol.%
)
Grain size fraction ( m)
Sample 1Sample 2Sample 3
Figure 2.5 The content of free mica in the collected grain fractions
Among the samples studied, sample 3 contains the highest initial content of
mica minerals (Table 2.1). The relationship between mica content of the host rock and free mica particle content in the fine fractions correlates well for fractions >0.125 mm (Figure 2.5), while the influence of initial mica content no longer is apparent for grain fractions <0.063 mm. 2.1.5 REMARKS
The issue of the ability of free mica to be enriched in aggregate fine fractions was additionally investigated by Loorents and Kondelchuk (2009). The study dealt with metamorphic rock types and the authors reported that isotrophic source rock, called Type I, exhibits a general increase in the content of free mica towards the finer grain size fractions. Type A, i.e. anisotrophic source rock, shows an increase up to a certain grain fraction, after which the free mica content decreases.
16
2.2 A METHOD FOR ESTIMATION OF FREE MICA PARTICLES
The current study presents a method for estimation of free mica particles in aggregate fine fractions based on a modified point-count approach using micro photos of grain mounts and a software package for analysis and presentation. The method suggested is completely described in Paper II. 2.2.1 BRIEF DESCRIPTION OF THE TESTING OF THE METHOD Samples
The method for estimation of free mica content is applicable to any sample of fine fractions originating from e.g. crushed rock aggregate products or drill cuttings. For testing of the method eleven samples of aggregate products from three different quarries were collected. Preparation
The samples were washed, dried and dry sieved. 5-10 g of each of the size fractions 0.125/0.25, 0.25/0.5 and 0.5/1 mm were collected. The procedure was performed as stated by standard laboratory routines (e.g. the European Committee for Standardization, 1997; 1999). The size fractions were prepared as grain mounts (Nesse, 2004; Sims and Nixon, 2003). A digital single-lens reflex camera (digital SLR) fitted with a macro lens was used for recording images and the image size of 3072×2048 pixels was further reduced to 1810×1810 pixels to meet the requirements of the image analysis software package. Image analysis
The software package, a Microsoft Office Excel add-in (compiled Excel Macro), was used for the image analysis performance. By manually marking grains according to mica minerals and others, the mineralogical composition of the samples was estimated. Identification of the common sheet silicate minerals biotite, muscovite and chlorite is feasible as they are readily distinguished from rock-forming minerals such as quartz and feldspar in polarized micro images. Optical identification of minerals is extensively discussed in the literature (e.g. Deer et al., 1992). Figure 2.6 shows an example of a processed image, in which counting lines and grains marked pursuant to its mineral category are displayed. The software calculates the input and presents the results in tables.
17
Figure 2.6 A segment of a processed image, where blue dots represent mica minerals and red
dots other minerals Evaluation
Estimates of free mica content obtained by image analyses were compared with results acquired by grain count analyses of grain mounts in a polarizing microscope. Eleven samples with various contents of mica were used and in each sample 400-600 grains were counted. No obvious differences between the results obtained by the two methods were observed (Figure 2.7).
0
10
20
30
40
50
60
70
Mic
a co
nten
t (%
)
Microscopic grain count
Image analysis
Figure 2.7 Comparison of mica contents obtained by image analyses and by microscopic grain
count analyses of grain mounts
18
The number of grains counted is crucial to the reliability of the estimates of free mica content in a sample. These problems are dealt with in power analysis, described in many statistics textbooks (e.g. Larsen et al., 1981). For this reason the reliability of 19 samples given by the confidence interval for the estimates of mean mica content was evaluated. The Spearman correlation analysis (e.g. Corder and Foreman, 2009) revealed n=19, r=0.77 and p=<0.005 with 99% confidence interval and significance level alpha=0.01. 2.2.2 CONCLUDING REMARKS
The main advantages of the developed method are: • The method is statistically satisfying from a scientific point of view. • The results are controllable due to the possibility to save the images of the
statistical operation. • The sample can originate from any rock material (e.g. crushed rock, aggregate
products, drill cuttings, natural gravel). 2.3 ESTIMATION OF FREE MICA CONTENT USING ANALYSES OF DRILL CUTTINGS
The Swedish Transport Administration requires limitation of the free mica content in aggregate fine fractions used in unbound base courses and unbound wearing courses (the Swedish Transport Administration, 2009). The content of free mica is therefore a central quality parameter to consider and thus important to verify in early stages of the road project planning. 2.3.1 APPROACH
The development of the method for estimating the quality of rock aggregates using analysis of drill cuttings (Paper III) focused on the methods’ potential to be used for early estimation of the rock materials’ suitability as aggregates for construction purposes and its practical application and efficiency. In additional, it was desirable to observe whether the amount of free mica particles in drill cuttings is comparable to free micas’ occurrence in fine fractions originating from crushed aggregates, i.e. the mica minerals’ ability to be released from the rock by mechanical impact. The fine fractions from drill cuttings and from crushed aggregates were used to estimate the content of free mica particles (Johansson et al., 2008). 2.3.2 RESULTS FROM ANALYSES OF FREE MICA CONTENT
The free mica content in fine fractions of seven samples of drill cuttings and two samples from corresponding aggregates was analysed (Tables 2.4-2.5).
19
Table 2.4 Content of free mica particles in fine fractions (0.125/0.25 mm) originating from drill cuttings
Sample ID Free mica content (%)
P1-1-01 49.5 P1-1-02 36.0 P1-1-03 27.5 P1-1-04 36.0 P1-1-05 29.9 P1-1-06 23.5 P1-1-07 24.6
Table 2.5 Content of free mica particles in fine fractions (0.125/0.25 mm) originating from
corresponding crushed aggregates Sample ID Free mica content (%)
P1-2-01 45.0 P1-2-02 32.6
2.3.3 EVALUATION
The results in Tables 2.4-2.5 indicate a possible relationship between the free mica content in drill cuttings compared with ditto in crushed aggregates. The low number of samples from crushed rock aggregates is a shortage to consider. In order to perform the final estimation further investigations are needed. 2.4 COMPARISON BETWEEN FREE MICA CONTENT IN THE FINE FRACTIONS AND
INITIAL MICA CONTENT IN THE HOST ROCK
With the aim to trace a possible relationship between the free mica content in fine fractions and the content of mica in the host rock, the binary data from the study of the mechanical properties’ dependence on petrographic agents was used and evaluated. The results emerged recently and will be published separately in the future. 2.4.1 MATERIALS AND METHODS
The data used for comparison included 17 granitoid and 9 gabbroid rock types. The fine fraction analysed was 0.125/0.25 mm. The content of mica in the rock was based on point-counting using polarization microscopy and the estimation of free mica particles was performed by means of grain counting and a polarization microscope (modified after Johansson et al., 2008). The results were evaluated statistically using the correlation approach of Pearson and by linear regression analysis (e.g. Montgomery et al., 2006).
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2.4.2 RESULTS
The content of mica in rock and content of free mica in fine fractions are presented in Table 2.6. Table 2.7 and Figure 2.8 show the correlations between the mica contents respectively. Table 2.6 Initial mica content in the rock and content of free mica in the grain size fraction
0.125/0.25 mm Sample ID Mica content in the rock (vol.%) Free mica content in the fine fraction (%)
Granitoids 002 2.1 7.5 005 2.1 2.2 007 29.5 45.0 008 13.1 16.1 010 8.1 16.6 012 8.2 9.7 013 9.6 14.8 014 18.2 20.4 015 18.6 21.6 016 17.0 20.5 018 5.1 17.7 021 20.8 38.5 024 3.0 6.0 027 8.2 6.1 036 10.8 24.6 042 11.0 19.0 043 3.1 8.3 Gabbroids 001 5.0 5.1 003 0.9 3.4 004 1.4 8.1 006 13.3 8.3 011 3.1 10.4 025 6.0 7.6 031 10.7 15.2 038 0.9 6.9 039 0.5 1.3
Table 2.7 The Pearson correlation tests1 of the initial content of mica in rock and the content of
free mica in fine fraction; 99% confidence interval, significance level alpha=0.01 n r p R2
26 0.881 <0.0001 0.776 1 n=number of samples; r=Pearson’s correlation coefficient; p=p-value; R2=coefficient of determination
21
0
5
10
15
20
25
30
35
40
45
50
55
0 5 10 15 20 25 30 35
Free
micaconten
tinthefin
efraction
(%)
Mica content in the rock (vol.%)
Figure 2.8 The content of free mica in fine fraction 0.125/0.25 mm plotted against the initial
content of mica in rock; 99% confidence interval, significance level alpha=0.01 2.4.3 EVALUATION
The statistical evaluation displays a pronounced correlation between the free mica content in fine fractions and its initial content in the host rock. This result supports the suggestion from a previous study (Paper I). The affirmation is applicable merely to granitoids and gabbroids. The host rock - fine fraction mica content needs to be further investigated concerning meta-volcanites and meta-sedimentary rocks, as these types of rocks are frequently used as aggregates for construction purposes.
2.750 1.257y x
22
23
CHAPTER 3 MECHANICAL PROPERTIES OF ROCK AGGREGATES
The second aim of the thesis was to study the relationships between the petrographic and mechanical properties of rocks. The information and status of previous research were upgraded by means of a literature review (Paper IV). The investigation of petrographic and mechanical properties of granitoid and gabbroid intrusive rocks (Paper V) improved the knowledge concerning the connection between the petrographic and mechanical variables. The results of the prior studies were implemented and tested in the approach to estimation of rock materials’ mechanical properties using the method of drill cuttings. 3.1 THE LITERATURE REVIEW
The literature study (Paper IV) included petrographic influences on both rock mechanical properties (mainly physical variables and tensile and compressive strengths) and mechanical properties tested on rock aggregates (e.g. resistance to fragmentation and wear). 3.1.1 SUMMARIZED RESULTS
The main groups of petrographic variables influencing the mechanical properties found can be divided into: • Mineralogical composition and water content • Micro-cracks and porosity • Grain size and grain shape • Macro-structure (e.g. degree of foliation)
The mineralogical composition and grain size have the strongest impact on igneous rocks, while the influence of foliation increases towards metamorphic rocks. Grain size, pore volume, water content and mineralogical composition appear as the central factors affecting sedimentary rock types. 3.1.2 NOTES
There are a great number of publications dealing with mechanical properties of rock materials, but only some of them focus on petrographic characteristics
24
connected to the mechanical properties. The literature review made the proper basis for the following tasks, in particular concerning the selection and grouping of rock types. 3.2 INFLUENCE OF PETROGRAPHIC CHARACTERISTICS ON MECHANICAL
PROPERTIES
In an effort to examine the mechanical properties’ dependence on petrographic variables, an ample number of rock types were selected and sampled. The sample suite was limited to granitoid and gabbroid igneous intrusive rocks and their metamorphic varieties. The following sections present a short summary of the performance and evaluation. The entire investigation is attached as Paper V. 3.2.1 METHODS
The 26 selected granitoid and gabbroid rock types were sampled from blasted rock segments and in turn laboratory crushed, sieved and reduced in accordance with standard laboratory routines (e.g. the European Committee for Standardization, 1997; 1999).
From each of the collected samples thin sections were prepared and petrographically analysed using polarization microscopy, the point-count method and image analysing technique (Chayes, 1956; Gillespie and Styles, 1999; Glagolev, 1931; Hallsworth and Knox, 1999; Lukschová et al., 2009; Nesse, 2004; P ikryl, 2001; Robertson, 1999; Sigmaplot, 2011; Sims and Nixon, 2003). The main parameters examined were the degree of foliation, grain size, grain size distribution, frequency of micro-cracks and mineralogical composition.
Standard methods for testing of rock aggregates were used to analyse the mechanical properties (the European Committee for Standardization, 1998; 2010; 2011; the Swedish Transport Administration, 2001). The analysed properties were resistance to fragmentation and wear (on two size fractions respectively; 10/14 mm and 31.5/50 mm), resistance to wear by abrasion from studded tyres and resistance to fragmentation by impact.
The results from the petrographic and mechanical analyses were evaluated statistically using the correlation approaches of Spearman and Pearson (e.g. Corder and Foreman, 2009; Montgomery et al., 2006) and by linear regression analyses (e.g. Montgomery et al., 2006). The 95% confidence interval and the significance level alpha=0.05 were applied. The correlation tests of grain size distribution and degree of foliation were performed according to the Spearman rank correlation, as the properties are not quantitatively measured, merely subjectively estimated and ranked. It is not possible to interpret the differences and/or quotients between the
25
values. For the same reason these properties are not analysed for linear regression. The Pearson’s method was used for correlation of the other petrographic parameters. 3.2.2 RESULTS
A generalised adaptation of the results from the petrographic, mechanical and statistical analyses is presented in Tables 3.1-3.5. Figure 3.1 shows examples of some textural properties. The complete results from the analyses are available in Paper V. Table 3.1 Investigated rock types, degree of foliation, grain size and frequency of micro-
cracks Sample ID Rock type Degree of foliation Grain size (mm) Frequency of micro-cracks (mm/mm2)
Granitoids 002 Granodiorite massive 0.5-2 0.3 005 Granite massive 0.2-3 0.2 007 Meta-tonalite strongly foliated 0.5-6 0.4 008 Meta-granite foliated 0.2-1 0.2 010 Granite massive 0.5-1 0.1 012 Granite massive 0.7-5 0.8 013 Granite massive 1-4 0.5 014 Meta-granite foliated 0.3-5 0.4 015 Meta-granodiorite foliated 0.2-3.5 1.3 016 Meta-granodiorite foliated 0.2-3.5 1.1 018 Granodiorite massive 0.4-2 1.2 021 Meta-granodiorite strongly foliated 0.4-4 0.7 024 Aplite massive 0.2-0.3 2.0 027 Quartz porphyry massive - 0.0 036 Granite massive 0.4-80 2.1 042 Aplitic granite massive 0.3 1.8 043 Granite massive 0.4 1.5 Gabbroids 001 Gabbro massive 0.3-4 2.0 003 Diabase massive 0.4-1.5 2.2 004 Olivine-diabase massive 0.3-1.2 1.8 006 Meta-gabbro foliated 0.1-2.5 0.3 011 Olivine-diabase massive 0.5-1.5 1.7 025 Meta-gabbro massive-weakly foliated 0.5-1.5 0.4 031 Meta-gabbro massive-weakly foliated 0.3-1.5 1.8 038 Olivine-diabase massive 1-7 7.1 039 Anorthositic gabbro massive 2-12 9.2
26
Table 3.2 Mineralogical composition1 (vol.%) Sample ID Fsp Qtz Mc Px Amph Ol Ct Opq Oth
Granitoids 002 75.7 22.2 2.1 - - - - - - 005 64.3 32.7 2.1 - - - 0.5 0.4 - 007 46.9 20.5 29.5 - 0.3 - - - 2.8 008 50.1 36.5 13.1 - - - - 0.3 - 010 69.6 22.0 8.1 - - - - - 0.3 012 59.0 32.6 8.2 - - - 0.2 - - 013 59.7 29.1 9.6 - - - - - 1.6 014 55.6 25.5 18.2 - - - - 0.7 - 015 45.9 34.9 18.6 - - - - 0.6 - 016 38.4 43.4 17.0 - - - - 1.2 - 018 58.2 31.9 5.1 - 4.8 - - - - 021 36.6 42.6 20.8 - - - - - - 024 59.9 37.1 3.0 - - - - - - 027 15.8 70.6 8.2 - - - - - 5.4 036 70.2 17.0 10.8 - 1.3 - 0.2 0.3 0.2 042 59.9 29.1 11.0 - - - - - - 043 69.7 26.9 3.1 - - - - - 0.3 Gabbroids 001 57.9 - 5.0 25.6 - 11.5 - - - 003 67.2 - 0.9 20.6 - 7.8 - 3.5 004 60.5 - 1.4 19.1 0.6 12.4 - 6.0 - 006 33.0 6.9 13.3 8.0 37.4 - - - 1.4 011 62.2 - 3.1 11.0 - 20.4 - 3.3 - 025 48.5 - 6.0 26.0 12.5 - - 7.0 - 031 69.1 - 10.7 8.5 10.3 - - 1.4 - 038 54.4 - 0.9 21.3 - 17.8 - 5.6 - 039 84.6 - 0.5 8.1 - 6.6 0.1 - 0.1 1 Fsp=feldspar; Qtz=quartz; Mc=mica; Px=pyroxene; Amph=amphibole; Ol=olivine; Ct=calcite Opq=opaque;
Oth=others
27
Figure 3.1 a) fine-grained granite, b) coarse-grained granite, c) even-grained granite,
d) uneven-grained meta-granodiorite, e) massive gabbro, f) strongly foliated meta-tonalite, g) micro-cracks in pyroxene and olivine, h) micro-cracks in feldspar
28
Table 3.3 Mechanical properties1 (wt.%) Sample ID LARB LA MDERB MDE AN SZ
Granitoids 002 13 23 4 5 12.0 62 005 11 20 3 4 9.7 49 007 - 22 11 14 18.7 42 008 - 21 5 6 10.1 47 010 - 26 5 6 11.1 48 012 12 24 5 7 12.9 49 013 17 39 7 11 19.2 66 014 - 30 9 9 14.7 50 015 17 24 - 9 12.6 40 016 17 25 - 12 13.7 53 018 17 21 - 6 9.8 35 021 19 37 16 18 24.7 51 024 13 19 3 5 7.6 38 027 16 17 4 2 5.6 41 036 34 37 15 13 21.8 53 042 21 24 6 7 10.1 44 043 17 24 4 5 8.9 48 Gabbroids 001 9 15 9 9 13.1 35 003 11 22 9 10 15.2 48 004 9 17 7 8 12.3 49 006 7 15 8 8 11.5 40 011 10 19 8 10 13.5 41 025 11 16 6 7 9.8 34 031 12 15 6 7 9.2 30 038 19 24 11 10 14.6 45 039 16 22 9 11 16.8 50 1 LARB=Los Angeles value fraction 31.5/50 mm; LA=Los Angeles value fraction 10/14 mm; MDERB=micro-Deval
value fraction 31.5/50 mm; MDE=micro-Deval value fraction 10/14 mm; AN=Studded tyre test value fraction 11.2/16 mm; SZ=Impact value fraction 11.2/16 mm
The Los Angeles values LARB (31.5/50 mm) and LA (fraction 10/14 mm) imply
resistance to fragmentation, the micro-Deval values MDERB (fraction 31.5/50 mm) and MDE (fraction 10/14 mm) imply resistance to wear, the Studded tyre test value AN implies resistance to wear by abrasion from studded tyres and the Impact value SZ implies resistance to fragmentation by impact. The interpretations of the results are unanimous for all mechanical methods; the lower the value, the better the mechanical properties (the quality of the rock aggregates).
29
Table 3.4 The Spearman correlation tests of the mechanical properties and grain size distribution and degree of foliation1; 95% confidence interval, values in bold are different from 0 with a significance level alpha=0.05
Property LARB LA MDERB MDE AN SZ r p r p r p r p r p r p
Granitoids n=17 Grain size distribution 0.147 0.628 0.506 0.040 0.589 0.029 0.704 0.002 0.768 0.0005 0.471 0.058 Degree of foliation 0.322 0.279 0.195 0.450 0.592 0.028 0.633 0.007 0.515 0.036 0.011 0.967 Gabbroids n=9 Grain size distribution 0.162 0.678 -0.132 0.744 0.434 0.250 0.133 0.744 0.080 0.843 -0.116 0.776 Degree of foliation -0.552 0.121 -0.420 0.250 -0.070 0.843 -0.211 0.581 -0.274 0.463 -0.137 0.708
1 LARB=Los Angeles value fraction 31.5/50 mm; LA=Los Angeles value fraction 10/14 mm; MDERB=micro-Deval value fraction 31.5/50 mm; MDE=micro-Deval value fraction 10/14 mm; AN=Studded tyre test value fraction 11.2/16 mm; SZ=Impact value fraction 11.2/16 mm; r=Spearman’s rank correlation coefficient; p=p-value; n=number of samples
Table 3.5 The Pearson correlation tests of the mechanical properties and textural properties
and mineralogical composition1; 95% confidence interval, values in bold are different from 0 with a significance level alpha=0.05
Property LARB LA MDERB MDE AN SZ r p r p r p r p r p r p
Granitoids n=17 Mica 0.361 0.226 0.280 0.276 0.704 0.005 0.753 0.0005 0.592 0.012 -0.088 0.736 Quartz -0.309 0.304 -0.344 0.176 -0.221 0.447 -0.239 0.355 -0.358 0.158 -0.289 0.261 Feldspar 0.089 0.773 0.165 0.528 -0.176 0.548 -0.174 0.503 0.006 0.981 0.332 0.207 Grain size -0.512 0.089 -0.810 0.0001 -0.544 0.055 -0.437 0.091 -0.651 0.006 -0.554 0.026 Micro-cracks 0.556 0.049 0.141 0.590 0.189 0.519 0.160 0.541 0.061 0.815 -0.261 0.312 Gabbroids n=9 Mica -0.520 0.151 -0.765 0.016 -0.505 0.166 -0.696 0.037 -0.745 0.021 -0.714 0.031 Pyroxene 0.021 0.958 0.032 0.935 0.140 0.720 -0.120 0.759 -0.041 0.917 -0.072 0.854 Feldspar 0.461 0.212 0.442 0.233 0.094 0.809 0.504 0.166 0.503 0.168 0.332 0.383 Olivine 0.279 0.467 0.516 0.155 0.586 0.097 0.618 0.076 0.535 0.138 0.427 0.252 Grain size -0.453 0.221 -0.293 0.444 -0.537 0.136 -0.419 0.262 -0.375 0.320 -0.117 0.765 Micro-cracks 0.863 0.003 0.762 0.017 0.645 0.061 0.723 0.028 0.741 0.022 0.548 0.126
1 LARB=Los Angeles value fraction 31.5/50 mm; LA=Los Angeles value fraction 10/14 mm; MDERB=micro-Deval value fraction 31.5/50 mm; MDE=micro-Deval value fraction 10/14 mm; AN=Studded tyre test value fraction 11.2/16 mm; SZ=Impact value fraction 11.2/16 mm; r=Pearson’s correlation coefficient; p=p-value; n=number of samples
3.2.3 EVALUATION
The most distinct outcomes from the statistical evaluation of the petrographic and mechanical properties of granitoid rocks are: • Decreasing grain size has a positive effect upon the Los Angeles value
10/14 mm, the Studded tyre test value and the Impact value, i.e. the mechanical properties improve with diminishing grain size.
• Increasing mica content has a negative influence on the micro-Deval values and the Studded tyre test value. A higher amount of mica in the rock causes deterioration of the mechanical properties.
• The Los Angeles value 31.5/50 mm gradually increases with increasing frequency of micro-cracks. Higher frequency of micro-cracks impairs the resistance to fragmentation.
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• Uneven-grained rocks show poorer results for the Los Angeles value 10/14 mm, the micro-Deval values and the Studded tyre test value than even-grained ones, i.e. the mechanical properties are better for even-grained rocks.
• The higher degree of foliation, the higher values regarding the micro-Deval values and the Studded tyre test value. The resistance to wear and resistance to wear by abrasion from studded tyres decrease with increasing degree of foliation.
The corresponding results concerning gabbroid rock types are:
• Increasing mica content improves the Los Angeles value 10/14 mm, the micro-Deval value 10/14 mm, the Studded tyre test value and the Impact value. In contrast to the granitoids, the mechanical properties of gabbroids are better with increasing mica content.
• Increasing frequency of micro-cracks has a negative influence on the Los Angeles values, the micro-Deval value 10/14 mm and the Studded tyre test value, i.e. the mechanical properties impair with higher frequency of micro-cracks.
3.3 DRILL CUTTINGS USED FOR EARLY ESTIMATION OF ROCK AGGREGATES’
QUALITY
Analysis of drill cuttings has a long history as the function of surveying tools extensively used in ore prospecting. Hitherto, the traditional prospecting for aggregates has been based on drill-cores for petrographic and mechanical analyses. The central prerequisite in prospecting of natural resources is the knowledge of the qualities that determine the suitability of rock materials for use as aggregates (e.g. Smith and Collis, 2001). Early information on the quality of the bedrock and its optimal use (i.e. mass and material balance) is required to minimize the environmental consequences and costs for road and railway constructions, and a careful utilization of rock materials on the the construction site is required (e.g. the Swedish Transport Administration, 2004).
With the aim to design a technique for estimation of the rock materials’ suitability as construction materials in early stages of the project planning, the method of drill cuttings was applied. 3.3.1 IMPLEMENTATION
The practical application of the method for estimation of mechanical properties of the rock materials using the petrographic characteristics was adapted in three road projects, located in the north (Project I), central (Project II) and southeast (Project III) regions of Sweden.
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In the first phase, coarse drill cuttings (>4 mm) generated by soil/rock probing in the construction planning stage were collected from all road projects. The samples were prepared through laboratory routines as grain mounts in accordance with standard methods (e.g. the European Committee for Standardization, 1997; 1999; Nesse, 2004; Sims and Nixon, 2003) and petrographically analysed by polarization microscopy and the point-count method (e.g. Chayes, 1956; Gillespie and Styles, 1999; Glagolev, 1931; Hallsworth and Knox, 1999; Nesse, 2004; Robertson, 1999; Sims and Nixon, 2003). By means of the petrographic analyses the rock types and mineralogical compositions were identified. On the basis of known rock types and their petrography, the mechanical properties and the usability were estimated with consideration to each construction project.
To verify the results from the first phase, further sampling of rock materials and crushed aggregates (e.g. the European Committee for Standardization, 1996a), in accessible projects, was carried out after removal of drift materials. The collected samples were analysed for their petrography and mechanical properties. The approach to the petrographic analysis was similar to the former and the mechanical analyses were accomplished as stated by standard laboratory methods (the European Committee for Standardization, 1997; 1998; 1999; 2010; 2011). The main properties tested were resistance to fragmentation (the Los Angeles value 10/14 mm, LA), resistance to wear (the micro-Deval value 10/14 mm, MDE) and resistance to wear by abrasion from studded tyres (the Studded tyre test value AN). 3.3.2 EVALUATION
The mechanical properties estimated from the samples of coarse drill cuttings corresponded well to the results from the mechanical tests performed in the second phase of the study. This confirms the possibility to use drill cuttings for early information on the rock aggregates’ mechanical properties and quality. However, this approach is based on empirical interpretation, which in turn demands long experience of the interpreter. To support the empirical findings and facilitate the interpretation of the mechanical properties, outcomes emerging from the study of the mechanical properties’ dependence on petrographic parameters were successively applied. This strengthens the assumption that petrographic characteristics are strongly connected to the rocks’ mechanical properties.
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CHAPTER 4 BRIEFING OF THE RESULTS
The current chapter deals with the major results from all substudies included in the thesis. 4.1 ENRICHMENT OF FREE MICA PARTICLES
There is a general trend towards enrichment of free mica particles in the aggregates’ smaller fractions (<0.125 mm) of the fine-grained rocks. Regarding coarser grained rocks, the amount of mica generally peaks within the fraction 0.125/0.25 mm. The rock types included are granitoids.
The results from the present study confirm previous research done by e.g. Lagerblad (2005) and Miškovský (2004). A subsequent investigation by Loorents and Kondelchuk (2009) additionally strengthens the assumption that free mica particles tend to be enriched in the aggregate fine fractions. 4.2 ESTIMATION OF FREE MICA PARTICLES
The need to quantify the content of free mica particles in aggregate fine fractions led to the development of a robust analysis method. The developed method is statistically verified and repeatable and the results from the analyses are controllable. This makes the method satisfactory from a scientific point of view.
The concept of using drill cuttings for estimation of free mica in fine fractions was tested with satisfactorily results. The amount of free mica particles in fine fractions originating from drill cuttings is indicated to be comparable to the amount of free mica in fine fractions originating from crushed aggregates. The study reveals that the mica grains are easily released from the rock by mechanical impact.
A strong relationship between free mica content and mica content in the rock was established. The analyses comprised 26 rock types of granitoid and gabbroid composition.
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4.3 RELATIONSHIPS BETWEEN PETROGRAPHIC AND MECHANICAL PROPERTIES OF GRANITOID AND GABBROID INTRUSIVE ROCKS
The study of mechanical properties’ dependence on petrographic characteristics
started with a literature review as a basis for further work. The evaluation of the petrographic parameters’ influences on the mechanical properties showed that the grain size, content of mica and frequency of micro-cracks are the central variables affecting the mechanical properties of granitoid rocks. The grain size distribution and degree of foliation indicate obvious tendencies towards associations. In the case of gabbroids, the mica content and frequency of micro-cracks are the main influencing parameters. The mechanical properties proved to be highly dependent on the intrinsic characteristics of rock materials. 4.4 ESTIMATION OF ROCK AGGREGATES’ QUALITY USING DRILL CUTTINGS
The attempt to use drill cuttings for estimation of the rock aggregates’ quality in early stages of the project planning was a successful approach and the practical application demonstrated the flexibility of the method. However, to turn the petrographic characteristics of the rocks into an estimate of their mechanical properties and to evaluate their suitability as aggregates require long experience of the interpreter. These factors indicate the growing need for a pragmatic tool to support the estimation of the mechanical properties using petrography as input.
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CHAPTER 5 DISCUSSION
The present study is an initial attempt to unify geology and engineering in a common approach to estimation of aggregates’ mechanical properties using petrographic characteristics as key parameters.
In regions dominated by temperate climate and where studded tyres are regularly used, the free mica is to be paid attention to. It is theoretically and practically established that free mica in fine fractions of crushed aggregates affects the quality of the aggregate end products (e.g. Smith and Collis, 2001). The heterogeneous, mica-rich rock types may cause damage to the road construction (e.g. Kondelchuk, 2008; Nieminen and Uusinoka, 1986; Novikov, 2008). In Sweden, demands on limits of the free mica content in fine fractions are established (the Swedish Transport Administration, 2009). These requirements have initiated research on free mica as a quality parameter and the need to develop a user-friendly method to estimate the free mica content in aggregate fine fractions.
Together with previous and subsequent research this work confirms the ability of free mica particles to be released from the rock during crushing and be enriched in the fine fractions. The free micas’ varying enrichment in different parts of fine fractions is suggested to be due to the initial grain size of mica in the host rock. This fact indicates the necessity to carry out petrographic analyses to verify the grain size and content of mica in the original rock. The current investigation focuses on the fine fraction 0.125/0.25 mm, as it is a central sorting with limitation of the free mica content. The rock types studied are of granitoid and gabbroid origin. Additionally research on the free micas’ enrichment in different parts of fine fractions by meta-sedimentary rocks and meta-volcanites is desirable.
The mechanical impact stemming from hammer drilling seems to have a similar effect upon the mica particles’ enrichment in fine fractions as the impact caused by crushing of rock aggregates. This knowledge enables the usage of drill cuttings to estimate the content of free mica. The second applicability of the method of using drill cuttings is to use coarse drill cuttings for estimation of the mechanical properties and the suitability of rocks as construction materials. To turn the petrographic characteristics of rock materials into the estimation of their mechanical properties requires long experience of the interpreter. This fact strengthens the need for tool, practical and easy to use, intended for the purpose.
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The main advantage of the use of drill cuttings is the possibility to obtain early information on the quality of the rock and the limitation of its use. By using drill cuttings from soil/rock probing, the method suggested is applicable in areas where the bedrock is covered with drift materials and therefore highly flexible and cost-effective.
The study of the relationships between petrographic and mechanical properties of granitoid and gabbroid intrusive rocks points to a number of petrographic variables correlating with the mechanical properties. The grain size, content of mica, frequency of micro-cracks, grain size distribution and degree of foliation are the main parameters affecting on the mechanical properties of the rock types examined. The test results obtained showed that the test methods used for evaluation of mechanical properties are influenced by the different petrographic agents.
A decreasing grain size decreases the value of Los Angeles 10/14 mm, the Studded tyre test value and the Impact value, i.e. improves the quality of the aggregate. Regarding the remaining test methods, only a weak positive trend towards diminishing grain size was obtained. A possible explanation is that the micro-Deval method measures wear and that grain size affects wear less than fragmentation. On the other hand, the Los Angeles value tested on size fraction 31.5/50 mm shows no correlation with the variations of grain size. This phenomenon could be caused by the coarse size of the rock fragment tested using steel balls of the same size as the ones used for fraction 10/14 mm. Generally, previous research (e.g. Brattli, 1992; Goswami, 1984; Kazi and Al-Mansour, 1980; Åkesson et al., 2001) proves that decreasing grain size improves the resistance to fragmentation.
Increasing mica content in granitoids shows a negative effect on the quality of the rock material tested, increasing the micro-Deval values and the Studded tyre test value. Concerning gabbroid rocks, the opposite tendency was obtained; the mechanical properties improve with increasing content of mica. One justification is that uniformly distributed mica may have a reinforcing influence on the mechanical strength of gabbroids. Another explanation is related to sericitization of feldspar (e.g. Åkesson et al., 2004), which occurs abundantly in the metamorphic varieties of the gabbroid rocks studied.
As the micro-cracks are expected to represent weak constituents of the rock supporting the propagation of newly formed cracks, it was assumed that it influences all the test methods measuring resistance to fragmentation. However, in the case of granitoid rocks only the Los Angeles value 31.5/50 mm proved to be influenced by the frequency of micro cracks. The resistance to fragmentation gradually becomes poorer with increasing frequency of micro-cracks. Testing gabbroid rocks, the similar phenomenon is exhibited. Increasing frequency of
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micro-cracks impairs the Los Angeles values, the Studded tyre test value and the micro-Deval value 10/14 mm.
The associations among the grain size distribution and the Los Angeles value 10/14 mm, the micro-Deval values and the Studded tyre test value show that uneven-grained granitoid rocks give a poorer result than even-grained ones, i.e. the quality of even-grained rock types is better. The tendency is similar to the degree of foliation, i.e. the higher degree of foliation, the poorer values regarding mechanical strength. The mechanical properties affected by the degree of foliation are resistance to wear and wear by abrasion from studded tyres.
Beyond the statistically confirmed results there are some notable indications to be discussed. All the mechanical analyses respond positively to increasing content of quartz in granitoids. The quality of the rock materials improves slightly with increasing quartz content. Due to the cleavage of the feldspars it was assumed that the content of feldspar would influence the resistance to fragmentation, as established by e.g. Miškovský et al., 2004 and Brattli, 1992. A deterioration of the resistance to fragmentation in connection with increasing feldspar content was expected. However, the results from the present study did not confirm the expectation.
The somewhat straggling results, partly confirming, partly disaffirming expected results and previous research, may be a consequence of the rather low number of samples, especially concerning the gabbroids. In future research a higher number of samples is required. To explain partial coordination of several petrographic parameters on the single mechanical property, multiple-regression analyses have to be performed.
The methods used for testing of aggregates properties are also to be discussed. The test methods measure the functional properties rather than rock mechanical properties. The functional properties tested have not been fully surveyed. In addition, there is a possibility that the results are dependent on the rock material, i.e. the different rock types. Metamorphic, foliated rocks tend to be favoured, mainly by the methods measuring resistance to fragmentation.
The present investigation reveals dissimilar results for the different size fractions tested by the same method. The disparity is particularly obvious in the case of the Los Angeles method, using the test fractions 10/14 mm and 31.5/50 mm respectively. On the other hand, the results concerning the two size fractions of the micro-Deval method are fully comparable.
The benefit of knowledge regarding the performance of rock materials used for construction purposes can be expressed in environmental, technical and economic terms. Rock is a non-renewable natural resource that requires careful exploitation. Sustainable development is defined as “development which meets the needs of the
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present without compromising the ability of future generations to meet their own needs” (the United Nations, 1987). This expression should constitute the global incentive to reach a high level of knowledge and focus on research of rock materials and their qualification as construction materials. Durable and substantial roads or railways require advanced technique and capable performance. As the main part of the construction consists of aggregates, the appropriate constructional approach should be based on the properties of rocks. Infrastructural constructions designed of deficient materials cause increasing maintenance, which in turn generates high operation costs and environmental impact. To attain the equilibrium in terms of mass and material balance, the use of rock materials of suitable quality adapted to their purpose is necessary.
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CHAPTER 6 CONCLUSIONS
The investigations of mica verified the enrichment of free mica particles in aggregate fine fractions and the assumed correlation between the mica content in the host rock and the free mica content in crushed fine fractions is confirmed for granitoid and gabbroid rock types. The original grain size of mica in the rock is suggested to influence the process of enrichment. The possible compatibility between the content of free mica in fine fractions originating from crushed rock and drill cuttings respectively is indicated, but further affirming studies are needed to establish the results. The evaluation of the developed method for estimation of free mica particles indicates its certainty and repeatability.
The application of the results received from the free mica studies is expected to support the upgrading and correction of the limits of free mica content in fine fractions of aggregate products used as construction materials. The suggested method for estimation of free mica in fine fractions is a user-friendly and an appropriate tool to secure the estimation of free mica with the possibility to make further control of the results.
The literature research resulted in a robust basis for the selection and grouping of rock samples regarding the study of the relationships between the mechanical properties of rock aggregates and their petrography. The investigation of the mechanical properties’ dependence on petrographic variables reveals pronounced influences of the petrographic characteristics on the mechanical properties. The grain size, content of mica and frequency of micro-cracks are the main petrographic variables affecting mechanical properties of granitoids. The grain size distribution and degree of foliation indicate tendencies towards associations. In consideration to gabbroid rock types, the mechanical properties in general respond to the mica content and frequency of micro-cracks.
The approach to using coarse drill cuttings from soil/rock probing, enables the estimation of the rock materials’ suitability for road and railway constructions in the initial stages of the project planning. Early information on the quality of the rock supports the ambition to reach mass and material balance and the rational usage of natural recourses. To transform the petrography of the rock into the mechanical properties requires empirical knowledge of the interpreter. For that
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reason a practical supervision system is needed. The results of the study of the petrographic and mechanical properties of the rock materials point to the possibility to develop the system for estimation of the mechanical properties of rock materials using their petrographic characteristics.
The study of the technological/mechanical and petrographic properties of rock materials has emphasised the importance of thorough understanding of the particular rock type and its intrinsic properties. During the refining process, e.g. blasting and crushing, each rock type is individually affected due to its different susceptibility to mechanical stress. These facts highlight the necessity to adapt the production technology of aggregates to the single rock type processed.
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ACKNOWLEDGMENTS
The present research was financially supported by the Swedish Transport Administration (Trafikverket), the Swedish National Road and Transport Research Institute (VTI) and Envix Nord AB. I wish to express my sincere gratitude; the funding has been invaluable for carrying out the PhD studies.
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FREE MICA GRAINS IN CRUSHED ROCK AGGREGATES
PAPER I
KARL-JOHAN LOORENTS, THE SWEDISH TRANSPORT ADMINISTRATION, BOX 494, 581 06 LINKÖPING, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 31 63 51 65
EVA JOHANSSON, DEPARTMENT OF CIVIL, MINING AND ENVIRONMENTAL ENGINEERING, LULEÅ UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected],
TELEPHONE: +46 920 49 10 21, MOBILE: +46 70 683 03 79 HÅKAN ARVIDSSON, THE SWEDISH NATIONAL ROAD AND TRANSPORT RESEARCH INSTITUTE,
581 95 LINKÖPING, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 13 20 43 57
BULLETIN OF ENGINEERING GEOLOGY AND THE ENVIRONMENT 66(4), NOVEMBER 2007, PP. 441-447
ORIGINAL PAPER
Free mica grains in crushed rock aggregates
Karl-Johan Loorents Æ Eva Johansson ÆHakan Arvidsson
Received: 22 September 2006 / Accepted: 6 January 2007 / Published online: 21 March 2007
� Springer-Verlag 2007
Abstract Enrichment of free mica (i.e. as monomineralic
grains) in the fine fraction of crushed rock aggregates af-
fects the quality of the aggregate end product. Granitoid
rock from the Svecofennian Province were used as being
representative of crushed rock aggregates commonly used
for construction purposes. The results reveal a general trend
of enrichment of mica for finer fractions. For the coarse
grained rock a peak occurs at 0.25–0.5 mm followed by a
decrease in the amount of free mica; for grains <0.063 mm
there is an increase. The general trend and peak are corre-
lated to the microstructural characteristics of the samples.
Keywords Crushed rock aggregates � Free mica �Monomineralic grain
Resume L’enrichissement en micas libres (c.a.d. en
grains mono-mineraux) dans la fraction fine des granulats
de roche concassee affecte la qualite du produit fini. Une
roche granitoıde de la province svecofennienne a ete utili-
see comme representative des granulats de roche concassee
communement utilises pour la construction. Il apparaıt une
tendance generale a l’enrichissement en micas des fractions
fines. Pour la fraction grossiere un pic de concentration en
micas libres apparaıt pour la fraction 0.25–0.50 mm. Puis
cette concentration diminue pour augmenter a nouveau pour
la fraction <0.063 mm. La tendance generale et les pics de
concentration sont correles avec les caracteristiques micro-
structurales des echantillons.
Mots cles Granulats de roche concassee � Micas libres �Grains mono-mineraux
Introduction
Free mica (i.e. monomineralic grains) in crushed rock
aggregates, for construction purposes (Smith and Collis
2001), affects the quality of the aggregate end product.
Nieminen and Uusinoka (1986) show a correlation between
the mineral composition of the fine fraction and the quality of
the unbound base material. Their research points out that an
unbound layer, constructed with a material containing a fine
fraction of a ‘‘larger’’ specific surface area (e.g. clay min-
erals and micas), implies a high risk of constructional dete-
rioration. Hakim and Said (2003) and Miskovsky (2004)
show a material deterioration of bituminous mixtures con-
nected with an increase in the amount of micas in the fine
fraction (<2 mm). A similar relationship has been described
by Lagerblad (2005) for fine fractions used in concrete.
Miskovsky (2004) shows a general trend of increase in
the amount of free mica when comparing narrow grain
fractions, having analysed five samples of granitoid rocks
with varying mica content. Whereas Lagerblad (2005)
states that there is a steady increase in the amount of free
mica with a peak for grain sizes between 0.125 and
0.25 mm, for smaller grains no enrichment was detected.
The study was based on 17 samples of granitoid rocks.
The aim of this study is to enhance an understanding of
how the amount of free mica varies within granitic crushed
rock aggregates, with special attention to the correlation
of the microstructural characteristics of rock samples
K.-J. Loorents (&) � H. ArvidssonVTI, 581 95 Linkoping, Sweden
e-mail: [email protected]
E. Johansson
Department of Civil and Environmental Engineering,
Lulea University of Technology,
971 87 Lulea, Sweden
123
Bull Eng Geol Environ (2007) 66:441–447
DOI 10.1007/s10064-007-0091-4
(Passchier and Trouw 1996; Prikryl 2001). The rock sam-
ples used in this study are representative of the common
crushed rock aggregates used for construction purposes and
have been prepared according to the standard laboratory
routines. The rock samples have been analysed on their
free mica content. The microstructural description of the
rock samples has improved the interpretation of the
behaviour of free mica in crushed rock aggregates.
Materials and methods
Rock samples were collected from two areas of the
Svecofennian Province granitoids. Samples 1 and 2 were
extracted from the same quarry, situated in the south east of
Sweden, and sample 3 was obtained from a road cutting
located in the central part of Sweden.
To limit factors that may influence the breakage of the
rock (e.g. the release of free mica during crushing), rock
samples of similar microstructural characteristics were
preferred. The samples were all more or less undeformed
(microstructurally isotropic). Microstructural difference is
mainly indicated by the grain size distribution and to a
lesser extent by aggregates of grains, grain-size, shape and
boundary (Passchier and Trouw 1996). Samples 1 and 2
had a similar mineralogical composition whereas sample 3
was enriched in mica compared to the other study samples.
Mineral alteration (before the process of weathering;
Delvigne 1998) is mainly limited to serecitic alteration of
feldspars. None of the study samples showed any change
due to weathering.
Sample 1
Sample 1 (granite) was weakly foliated (mineral orientation
defined by small grained biotite), medium grained
(1–2 mm; Gillespie and Styles 1999) and grey to red
(Fig. 1). A complete gradation (seriate) of fine- to medium-
grained grain size distribution with irregular, lobate grain
boundaries (interlobate) describes the microstructure. The
mineralogical composition was quartz > K-feldspar > pla-
gioclase > muscovite > biotite > chlorite with accessory
opaque minerals, apatite, epidote and zircon (Table 1). The
quartz grains had undulose extinction and an anhedral shape
of grains. The K-feldspar (anhedral–subhedral) had well-
developed microcline (scotch plaid) twinning; a few
megacrysts were present. The plagioclase (subhedral–
anhedral) had a fairly well-developed polysynthetic
twinning (albite) and a less common combined albite and
pericline twinning. Some sericite alteration was seen in the
majority of the plagioclase. The muscovite was generally
coarser grained than the biotite; the latter showing some
alteration to chlorite.
Sample 2
As seen in Table 1, sample 2 (Fig. 2) was in general
similar to sample 1 although with some differences in
mineral composition and to a lesser extent grain size dis-
tribution.
Sample 3
Sample 3 (monzogranite) was a white and black, coarse-
grained (>2.5 mm; Gillespie and Styles 1999) massive rock
with a mineralogical composition K-feldspar > quartz >
plagioclase > biotite (Fig. 3). Accessory minerals included
titanite, sericite, kaolinite, zircon, chlorite, opaque and
apatite (Table 1). A seriate distribution of grains with an
interlobate shape of grain aggregates describes the micro-
structure. Plagioclase (subhedral–anhedral) commonly had
well-developed polysynthetic twinning (albite) and less
commonly combined albite and pericline twinning. Some
sericite alteration of the plagioclase was present. K-feld-
spar (subhedral–anhedral) showed sparse intergrowth of
quartz (granophyric texture). Megacrysts of K-feldspar
were present. The quartz grains (anhedral) had undulose
extinction and ‘‘sub grains’’ that may indicate a com-
pressive deformation. The biotite showed a slight alteration
to chlorite.
Sample preparation
Sample breakage was achieved using a primary and a
secondary laboratory jaw crusher. The primary discharge
aperture (setting) was 40 mm and the secondary crusher
had a setting of 15 mm. For each type of rock, a sample
similar in shape was used for crushing with the following
data for weight, density and volume: sample 1—2.58 kg,
2.64 Mg/m3 and 0.98 dm3; sample 2—2.70 kg, 2.64 Mg/m3
Fig. 1 Sample 1
442 K.-J. Loorents et al.
123
and 1.02 dm3; sample 3—2.55 kg, 2.68 Mg/m3 and
0.95 dm3. The grain size distribution for each crushed
sample was obtained by dry sieving according to EN 933-1
(Fig. 4). Additional sieving was undertaken for grains
<63 lm (sample sizes were approximately 20 g). Sieves
were weighed before and after sieving to measure the
amount of material that remained on the sieve (Table 2).
Compressed air was used to clean the sieves between
each sieving cycle. From the sieving, the following
grain size fractions were collected for analysis: 0.5–1,
0.25–0.5, 0.125–0.25, 0.063–0.125 mm, 42–63, 24–42
and <24 lm.
Free mica content
To estimate the amount of free mica in the collected grain
size fractions two methods were used generally following
RILEM AAR (Sims and Nixon 2003).
For size fractions 0.5–1, 0.25–0.5 and 0.125–0.25 mm
samples were collected and an additional quartering
undertaken in order to obtain representative, homogeneous
samples. Grains were grouped and counted (stereoscopic
microscope, Technique 1) on the basis of mineralogy into
muscovite, biotite and others where appropriate. All grains
in the collected and reduced (quartered) sample were
counted (Table 3).
With Technique 2, a polarizing microscope and a point
counting apparatus were used for 0.5–1, 0.25–0.5, 0.125–
0.25, 0.063–0.125 mm, 42–63, 24–42 and <24 lm. Thin
sections were prepared as grain mounts (Nesse 2004) from
2–4 g of crushed sample for each collected grain fraction.
Counting was performed in the same way as for the coarser
grains (Table 3).
Discussion
Prior to sieving, it was not clear whether it would be pos-
sible to obtain/collect representative samples, particularly
for grain fractions <63 lm. However, weighing the sieve
before and after sieving (Table 2) and a microscopic optical
control of the mesh gave a useful and more objective
indication of the material passing through the sieves.
Technique 1 was chosen for certain grain fractions, as
this method ensures that monomineralic material, or
aggregates dominated by one mineral, is properly grouped
Table 1 Mineralogical composition (in vol.%) and grain size distribution of the main minerals
Quartz Plagioclase K-feldspar Biotite Chlorite Muscovite Opaque Assessory
Sample 1 40 14 36 3 3 4 0.2 0.2
Grain size (mm) 0.6–1.5 1.4–2.9 1.2–3.7 0.4–0.8 – 0.6–1.6 – –
Sample 2 37 14 37 4 1 7 Trace 1.0
Grain size (mm) 0.7–1.6 1.4–3.2 1.4–2.5 0.6–1.3 – 0.9–1.6 – –
Sample 3 28 25 27 19 – – Trace 1.4
Grain size (mm) 0.9–2.3 1.5–3.2 1.7–2.9 0.9–2.5 – – – –
The mineral mode is based on point counting using a polarising microscope
Fig. 2 Sample 2 Fig. 3 Sample 3
Free mica grains in crushed rock aggregates 443
123
and counted. Technique 1 is of limited value for coarser
grains, as the power of resolution of the equipment is not
sufficient for the finer fractions analysed in this study.
However, the results from Techniques 1 and 2 are not di-
rectly comparable, as the preparation of the samples and
analysing technique differ. With Technique 1, a sample is
retrieved from the collected batch and should contain a
minimum number of grains to be representative of the
batch; it is also important that all grains of the sample are
counted. Considering mineral separation there is a risk of
biased sampling with this method. For two batches, double
samples were counted to assess precision. This indicated
that the counting varied by up to 10%.
The formation of free mineral phases or monomineralic
grain constituents during breakage by crushing is mainly
dependent on the mineralogical composition (strength of
minerals), grain boundaries and the grain size of the rock.
Thus for a coarse grained rock monomineralic grains will
comprise a larger fraction of ‘‘coarser’’ grains. This rela-
tionship ensures monomineralic grain constituents for
‘‘finer’’ grain fractions and validates the use of Technique
2, especially for medium and coarser grained rocks.
Technique 2 also uses a minimum number of grains to
ensure a statistical significance, but provides a more robust
methodical handling as the sample (thin section) is
impregnated with epoxy resin. With this method (point
counting), counts indicate the presence of a certain mineral
phase, but make no distinction between monomineralic and
aggregate (composed of at least two minerals) grains. The
use of optical microscopy for fractions <63 lm has its
practical limitations, as mineral identification may be hard
to perform. However, as analysing and counting always
started with the coarsest fraction, and the mineralogy of the
sample was well known, the method proved useful.
Thus Technique 1 was used to ensure counting of free
mica grains and partly as a comparison between the
methods. The main emphasis was on Technique 2 as this
provides one ‘‘continuous’’ counting method for all size
fractions analysed in this paper.
The three samples studied are all igneous rocks. Con-
sidering microstructural characteristics, samples 1 and 2
have similar mineral composition and grain size, while
sample 3 differs mainly in grain size. Samples 1 and 2 are
medium grained and sample 3 coarse grained. The trend
line of sample 3 (Fig. 5) generally shows higher amounts
of free mica for coarser grain fractions, indicating that the
amount of free mica depends on initial mineral content and
grain size of the rock.
Figure 5 (see Table 3) depicts the varying free mica
content for the samples, dependent on grain size. Com-
paring the trend lines, using grain fractions 0.063–
0.125 mm as a ‘‘divider’’ gives quite different relation-
ships for the <0.063 and >0.125 mm grain fractions. For
grains >0.125 mm the relationship is less consistent while
for grain fractions <0.063 mm a uniform trend of increase
is displayed. This difference correlates with the initial grain
size of the rock and content (modal vol.%) of mica. It is
suggested that coarse grained rocks follow the trend line of
Table 2 Sieving of materials
<63 lmSieve (lm) Passing material sample (%) Fasten material (g)
1 2 3 1 2 3
63 99.6 99.2 99.7 0.07 0.07 0.06
42 72.4 80.6 71.4 0.04 0.03 0.03
24 32.7 40.6 37.1 0.04 0.04 0.05
coarsemediumfinecoarsemediumfineGravelSand 6020620.60.20.06
10.50.250.1250.063 11.2 20090634531.51685.6420%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Particle size, mm
gnissa
p egat
necreP
Sample 1
Sample 2
Sample 3
Fig. 4 Grain size distribution
of the three samples after
crushing into two steps
444 K.-J. Loorents et al.
123
sample 3 (see Fig. 7), whereas fine to medium grained
rocks are similar to samples 1 and 2. Coarser minerals
more readily release mica from the mineral aggregate (e.g.
>0.125 mm) than small grained minerals, due to exposure
to mechanical breakage of the monomineral in the aggre-
gate. As the grain fraction gets smaller, the aggregate has to
reach a ‘‘critical’’ grain fraction (e.g. <0.063 mm) before
further breakage continues.
Among the studied samples, sample 3 contains the
highest initial content of mica and the coarsest grains
(Table 1). The connection between the initial mineral
content of the rock and the content of free mica in the grain
fractions correlates well for fractions >0.125 mm (Fig. 5).
For grain fractions <0.063 mm the influence of the initial
mica content is no longer perceived. The peak of sample 3
for grains >0.125 mm indicates that there is a relationship
between initial grain size and grain size fraction, based on
the assumption that mica grains are less mechanically
competent than, for instance, quartz and thus break more
readily into ‘‘smaller’’ particles due to mechanical stress.
The three samples used in this study provide a somewhat
sparse basis for reasoning, thus a review of some data in the
literature on free mica in crushed rock aggregates for
construction purposes was motivated. Miskovsky (2004),
using a polarizing microscopy and the point-count method,
showed a general increase in the amount of free mica for
the finer fractions (<0.074, 0.074–0.25 and 0.25–2 mm),
analysing five samples of granitoid rocks with varying
mica content (5.6–33 vol.%; Fig. 6). The result of the
0
5
10
15
20
25
30
35
40
<24 24-42 42-63 63-125 125-250 250-500 500-1000
Grain size fraction, μm
Co
nte
nt
of
free
mic
a (p
arti
cle
and
vo
l %)
Sample 1
Sample 2
Sample 3
Fig. 5 The content of free mica in the collected grain fractions
Table 3 Mica content (in
particle and vol.%) of sample
according to analysed grading
fraction together with total
number of grains counted
Bt biotite, Ms muscovite,
%-Mica total % mica in sample,
Count total number of grains/
points counted
Grain size Bt Ms %-Mica Count Bt Ms %-Mica Count
Technique 1 Technique 2
Sample 1
0.5–1 (mm) 1 7 8 215 2.8 7.3 10.2 1,704
0.25–0.5 7 5 12 526 5.6 7.6 13.2 1,787
0.125–0.25 8 8 16 571 6.6 7.6 14.1 1,999
0.063–0.125 5.2 8 13.3 2,157
42–63 (lm) 6 9 15 583
24–42 10 14 24 567
<24 14 19 33 525
Sample 2
0.5–1 (mm) 1 6 7 299 4.2 7.1 11.2 1,659
0.25–0.5 3 6 9 467 3.8 8.3 12.0 1,695
0.125–0.25 8 9 17 773 6.4 8.7 15.1 1,925
0.063–0.125 6.9 8.2 15.0 2,022
42–63 (lm) 6 8 14 539
24–42 13 13 26 558
<24 17 17 34 508
Sample 3
0.5–1 (mm) 24 24 368 18.8 18.8 1,834
0.25–0.5 31 31 420 21.8 21.8 1,704
0.125–0.25 22 22 699 19 19.0 1,971
0.063–0.125 14.2 2,085
42–63 (lm) 17 17 557
24–42 20 20 568
<24 36 36 536
Free mica grains in crushed rock aggregates 445
123
study suggests the mica enrichment in the grain size frac-
tions: 0.25–2 mm, 8–21.2 vol.%; 0.074–0.25 mm, 9.5–34.6
vol.% and <0.074 mm, 17.8–41.4 vol.%.
Despite the fact that the collected and analysed grain
size fractions of Miskovsky and the present study are not
directly comparable, the two studies show the same tren-
d—an enrichment of mica with finer fractions. Further-
more, the same method is being used (point counting)
which additionally strengthen the results of the studies. In
this kind of study, a narrows grain size fraction is preferred
as this increases the resolution and provides more data on
the behaviour of rock breakage by crushing.
Microstructural comparison between the studies is not
possible as no structural information is provided by Mis-
kovsky (2004) except that the samples were granitoid
rocks.
Lagerblad (2005) states that there is no enrichment of
mica for the finer grain fractions (<0.125 mm) after anal-
ysing 17 samples of granitoid rocks, using X-ray powder
diffraction (XRD) and scanning electron microscope
(SEM) analyses for materials <75 lm (5 samples) and the
point-count method for fractions; 75–125, 125–250, 250–
500, 500–1,000, 1,000–2,000 lm (Fig. 7). Lagerblad’s
study implies a peak in the amount of free mica for the
125–250 lm fraction and then, based on results from the
XRD, SEM and point counting analysis, a possible trend of
lower amounts of free mica with finer fractions.
The point counting method used by Lagerblad and the
present study is similar, thus the results are comparable.
The point counting data from Lagerblad’s study is pre-
sented in Fig. 7, which has been modified and grouped into
fine, medium and coarse grained rock in an attempt to
clarify any microstructural correlations. The (trend) curves
in Fig. 7 verify a peak for medium and coarse grained
rocks, possibly with an initial ‘‘higher’’ content of mica
Fine-grained rock
0
2
4
6
8
10
12
14
16
18
20
Grain size fraction, μm
Medium-grained rock
0
5
10
15
20
25
30
Grain size fraction, μm
Coarse-grained rock
0
5
10
15
20
25
30
35
40
45
50
75-125 125-250 250-500 500-1000 1000-2000
75-125 125-250 250-500 500-1000 1000-2000
75-125 125-250 250-500 500-1000 1000-2000
Grain size fraction, μm
Co
nte
nt
of
free
mic
a (v
ol%
)C
on
ten
t o
f fr
ee m
ica
(vo
l%)
Co
nte
nt
of
free
mic
a (v
ol%
)
Fig. 7 The content of free mica for collected grain fractions for fine,
medium and coarse grained rock (modified after Lagerblad 2005)
0
10
20
30
40
50
60
70
80
74 74-250 250-2000
Grain size fraction, μm
Co
nte
nt
of
free
mic
a (v
ol%
)
33.3 vol%
27.1 vol%
26.8 vol%
21.1 vol%
5.6 vol%
Fig. 6 The content of free mica in the collected fractions; the
samples are sorted into initial content of mica of the uncrushed rock
(modified after Miskovsky 2004)
Table 4 Content of biotite and chlorite (vol.%) for medium and
coarse-grained samples
Medium Coarse Medium Medium Medium
<38 lm
Biotite 16 6.1 11.1 15.6
Chlorite 7.2 1.9 15.6
Grains 188 212 196 206 173
<38–63 lm
Biotite 11 2.3 14.8 11.5
Chlorite 12
Grains 209 219 219 203 209
Grains indicate the total number of counts
446 K.-J. Loorents et al.
123
although Lagerblad gives no information on the initial
mineral composition. The analysis from the present study
verifies a peak for the coarse grained sample 3 (Fig. 3).
Considering the results from Miskovsky (2004), Lagerblad
(2005) and the present study, it is assumed that the position
(grain size fraction) and the height of the peak (content of
free mica) depend on the rock’s initial mineral composition
and mean grain size thus indicating the importance of
microstructural characteristics for the variation in free mica
in crushed rock aggregates.
Lagerblad also carried out SEM analysis on five samples
for fractions <38 and 37–63 lm. As seen in Table 4, the
results do not indicate a uniform ‘‘stronger’’ trend towards
an increase or decrease in the content of mica for the
analysed fractions.
To further understand the variation of free mica for finer
fractions, Lagerblad used semi-quantitative XRD counting
techniques to obtain an indication of the mineral content
for fractions <38 and 37–63 lm. Peak intensities, corre-
lated to SEM analysis (Table 4), were used to assess
mineral variations. As the method is semi-quantitative, any
variations are at best an estimation based on trends, but
appear to show lower amounts of free mica with the finer
fractions.
Conclusion
On the basis of the analytical data presented in this study,
there is a general trend towards the enrichment of mica in
the finer fraction of the fine grained rocks; with medium
and coarse grained rocks, the amount of free mica gener-
ally peaks within the fraction 125–250 lm.
This work has focused on igneous rocks but crushed
rock aggregates come from a wide array of rock types
hence further research is needed to establish if a similar
situation occurs with metamorphic and sedimentary rocks.
Acknowledgments VTI, the Swedish National Road and Transport
Research Institute funded this work.
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A METHOD FOR ESTIMATION OF FREE MICA PARTICLES IN AGGREGATE FINE FRACTION BY IMAGE ANALYSIS OF GRAIN MOUNTS
PAPER II EVA JOHANSSON, DEPARTMENT OF CIVIL, MINING AND ENVIRONMENTAL ENGINEERING, LULEÅ
UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 920 49 10 21, MOBILE: +46 70 683 03 79
KAREL MIŠKOVSKÝ, DEPARTMENT OF CIVIL, MINING AND ENVIRONMENTAL ENGINEERING, LULEÅ UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected],
TELEPHONE: +46 90 14 42 69 KARL-JOHAN LOORENTS, THE SWEDISH TRANSPORT ADMINISTRATION, BOX 494, 581 06 LINKÖPING,
SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 31 63 51 65 OLA LÖFGREN, EKOVISION NORD, GRANVÄGEN 22, 922 32 VINDELN, SWEDEN,
E-MAIL: [email protected], TELEPHONE: +46 933 107 03
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE
17(2), APRIL 2008, PP. 250-253
A Method for Estimation of Free Mica Particlesin Aggregate Fine Fraction by Image Analysis
of Grain MountsEva Johansson, Karel Miskovsky, Karl-Johan Loorents, and Ola Lofgren
(Submitted February 23, 2007; in revised form May 2, 2007)
The need to evaluate free mica grains in fine fraction of aggregate products has initiated the development ofa statistically and scientifically acceptable method. The proposed method is based on a modified point-counting approach using digital micro photos of thin sections of aggregate grains and a software package tosustain sample analysis. A thin section of aggregate grains provides permanent sample documentationreadily available for complimentary or other analysis. Statistical analysis, together with a repeatableanalysis of samples (permanent mounts), confirms the robustness of the method. The method is appropriateas a complementary assessment tool to estimate and trace changes or variations in quality of rockaggregate. Though, the estimation of free mica particles in fine fraction needs to be combined with otheranalyses, e.g., petrographic analysis and analyses of mechanical properties, to assess the quality of any rockmaterial. As the samples can be collected from drill cuttings, i.e., an accessible residual product obtainablefrom surveying or production, the present method is particularly useful as a surveying tool and in pros-pecting and projecting activities.
Keywords aggregates, fine fraction, free mica particles, imageanalysis, point-count method
1. Introduction
The fine fraction of crushed rock aggregates produced frommica carrying rocks can cause considerable damages on roadconstructions, especially within regions dominated by temper-ate climate. The reason for these economically perceptibleproblems is the ability of mica to take up and hold water orbitumen. This ability is partly due to the increased specificsurface area of mica rich aggregates, i.e., stemmed from thegrain shape of micas. The specific surface of a particle is theratio of its surface area to its mass, where the main controllingfactors are particle size and particle geometry. Furthermoreroughness of the external surface, shape, porosity, and miner-alogy may contribute to an increase in the surface area (Ref 1).High water content in unbound application layers may be thebasis for a raised pore water pressure under load, consequentlycausing a lowering of the constructions� bearing capacity. Foran optimum performance, the aggregates surfaces in a mix areintended to be covered by a bitumen film. Substituting the finematerial (i.e., filler) in an asphalt mixture with a material of
dissimilar specific surface area will influence the thickness ofthe bitumen film and thus the asphalt mixture properties, giventhat the binder content is constant. The sorbing ability of micamay accordingly cause an early constructional deterioration(Ref 2-4).
Aggregates for construction purposes extracted from hardrock quarries are tested and sampled according to nationalstandardization programs, e.g., European Committee for Stan-dardization (CEN), by means to certify the aggregate product,i.e., to ensure that the aggregate product meets the qualitydemands for the intended use (e.g., CEN). Still, free micaparticle content or acceptable threshold limit values of freemica particles contained in the aggregate product are notprecisely dealt with in this realm of standards. Furthermore it isnot uncommon, in road construction projects, that a largequantity of materials used for the construction is extractedwithin the construction site. For this sort of materials theaggregate quality assessment may be far less rigorous thancompared to materials extracted and produced from a qualitycertified hard rock quarry. Thus, where applicable, there is arisk that the construction project may not reach a rational usageof natural resources and not limit the impact caused byerroneous usage of materials. A road construction project is onewhere mass and material balance has been achieved. Toaccomplish this, information about the materials quality andpotential use must be obtained early on in the project planning,which calls for evaluations methods fit for field investigations.
In an effort to verify the content of free mica particles incrushed rock aggregates and to limit damages on roadconstructions related to the mica content, the Swedish RoadAdministration (SRA) established a standard method in 2002concerning the content of free mica in fine fraction of aggregateproducts (Ref 5). The method is based on a particle count(stereoscopic microscope) and provides an approximation of
Eva Johansson and Karel Miskovsky, Department of Civil, Miningand Environmental Engineering, Lulea University of Technology, 97187 Lulea, Sweden; Karl-Johan Loorents, Swedish National Road andTransport Research Institute (VTI), 581 95 Linkoping, Sweden; andOla Lofgren, Ekovision nord, Granvagen 22, 922 32 Vindeln,Sweden. Contact e-mail: [email protected].
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the content of free mica for grain size fractions between 0.125-0.25, 0.25-0.5, and 0.5-1 mm. It is mainly suited as anindicative tool as sample selection and counting may introducea statistical bias and reproducibility is questionable within thesame sample. Thus the introduction of the standard methoddemands the development of an effective and from a scientificpoint of view satisfactory method for estimation of free micaparticles in fine fraction.
The present paper presents a method based on a modifiedpoint-count approach using micro photos of grain mounts andan analysis software package. An ample range of field samplescan be used as long as the prerequisite amount and grain sizesare met for analysis. Statistical analysis together with arepeatable analysis of samples provides a robust method formineralogical analysis of the fine fraction.
2. Description of the Method
2.1 Samples
The demonstrated method is applicable to any sample offine-grained rock material originating from, e.g., rock aggregateproducts or drill cuttings from surveying and production. Thefine-grained fraction samples (0.125-0.25, 0.25-0.5 and 0.5-1 mm) used for testing and evaluation of the method arecollected from three different quarries consisting of; mica richmeta-tonalite (five samples), veined meta-greywacke (threesamples), and mica poor granite (three samples).
2.2 Preparation
The sample (ca 500 g) is washed on the sieve 0.63 mm anddried. Following drying the sample is dry sieved and 5-10 g ofeach of the following size fractions are collected; 0.125-0.25,0.25-0.5, and 0.5-1 mm. The procedure is preferentiallyperformed according to standard methods such as EN 932-2:1999 (Ref 6) and EN 933-1:1997 (Ref 7).
From each of the collected size fractions grain mounts isprepared. The collected grain amount (5-10 g) for each sizefraction ensures a high-enough grain frequency on the glassmicroscope slide (Ref 8, 9) and satisfies constrains of thestatistical calculation.
Images may be acquired by using any equipment that havethe utility of using polarized light. In the present work, a digitalsingle-lens reflex camera (digital SLR) fitted with a macro lens
was used for recording images. The photographic setup allowssingle- and cross-polarized light (Fig. 1) to be used. An imagesize of 3072· 2048 pixels was further reduced to1810· 1810 pixels to meet the requirements of the imageanalysis software package.
2.3 Image Analysis
The image analysis is performed by means of a softwarepackage that is a Microsoft Office Excel add-in (compiledExcel Macro). The mineralogical composition of the sample isestimated by manually marking grains according to its sorting(i.e., two categories, mica and others) in the image. Identifi-cation of the common sheet silicate minerals biotite, muscovite,and chlorite is feasible as they are readily distinguished fromrock-forming minerals such as quartz and feldspar in polarizedmicro images. Quartz and feldspar exhibit a low-relief and greycolor, while mica minerals have a higher-relief and show othercolors than grey. Biotite is often brown or greenish andmuscovite varies between red, blue and green color. Thechlorite shows anomaly colors, i.e., it changes from black togrey-blue. If hornblende is present, it may be mistaken forbiotite. In such cases it is recommended to use pleochroiticcolors in single-polarized (plane light) micro photos. In plane-polarized light biotite is brown in color and hornblende green.Optical identification of minerals is extensively discussed in theliterature, e.g., (Ref 10).
An example of a processed image is shown in Fig. 2, inwhich counting lines (scan lines) and grains marked accordingto its mineralogical category by grey or white dots, isdisplayed. As the manual mineral identification is completed,the information is processed and statistics is computed. Theoutcome is presented in tables showing the sum of countedgrains (both mica and others) and the average of mica. Otherstatistical information such as standard deviation, variance,minimum and maximum value, and confidence interval are alsopresented.
3. Discussion and Evaluation
Analyses of fine fractions from drill cuttings have a longhistory as a surveying tool extensively used within oreprospecting. But within the field of prospecting for aggregatesor quarry aggregate quality programs, traditionally surveying
Fig. 1 The photographic set up; (a) digital camera, (b) illuminator equipment with a halogen light, (c) nicoles and (d) a thin-section/sampleholder
Journal of Materials Engineering and Performance Volume 17(2) April 2008—251
uses the more expensive drill-cores for petrological andmechanical analyses. Thus in this context the present workpresents a ‘‘new’’ analysis method as fine fractions from drillcuttings have not, or to a very limited extent, been used inaggregate quality assessment as described in the literature. Themain potential of the proposed analysis method is its time andcost effectiveness, notably capable within; mass- and materialbalance matters (e.g., road and railway cuttings), establishmentof quarries and quarry production control programs. Rockmaterial is a non-renewable natural resource which necessitatesrational usage, thus aggregates must meet the constructoralrequirements otherwise it may cause substantial damages. Asthe samples can be collected from drill cuttings, i.e., anaccessible residual product occurring in several constructingand quarrying stages, the present method is useful as asurveying tool for prospecting and projecting.
One advantage of the photographic hardware used in thecurrent study is the ability to capture the entire thin section inone photographic shot. The photographic equipment is easy tohandle as is any changes of pictures (e.g., produce black andwhite and single-polarized images) or handling due to the useof a digital SLR.
Using samples in the form of a permanent grain mountprovides a great documentation of any aggregate-orientatedactivities. This is especially valuable considering that at any
occasion the thin section can be re-analysed or furtherexamined.
Estimates of free mica particle content in aggregate finefraction obtained by image analysis were compared with resultsobtained by grain count analysis in polarizing microscope alongthe cross line of minimum length of 4 cm. Eleven samples fromthree different localities and with different mica content werecompared. In each sample, 400-600 grains were counted. Noobvious differences between the results obtained by the twomethods could be observed. On the contrary, accordance ofparticle mica content was very good in all samples (Fig. 3).
In order to examine the possible preferred orientation ofmica in the epoxy mould three cross sections of the samesample was produced and analysed. Comparisons of micacontent obtained by analyses of cross-cut sections are given inFig. 4. The results revealed no distinct differences between thetwo methods of cutting.
It is well-known that the number of grains counted is crucialto the reliability of the estimates of free mica content in asample. These problems are dealt with in power analysis, whichis described in many statistics textbooks, e.g., (Ref 11). For thisreason, the reliability of 19 samples given by the confidenceinterval for the estimates of mean mica content was analysed.The results were plotted against the number of grains countedin each sample (Fig. 5). There was a distinct decline in the
Fig. 2 A section of a processed image. White dots represent micaminerals and grey dots other minerals
0
10
20
30
40
50
60
70
Mic
a co
nte
nt
(%)
Microscopic grain count
Image analysis
Fig. 3 Comparison of mica content obtained by image analysis andby microscopic grain count analysis of grain mounts. A confidenceinterval (99%) is established for estimates given by the image analy-sis method
0
10
20
30
40
50
60
70
0.5 0.25 0.125
Fraction (mm)
Mic
a co
nte
nt
(%)
Primary cutting
Transverse cutting
Fig. 4 Comparisons of mica content obtained by image analysis ofcross-cut thin sections. Analyses were performed on three differentfractions. Mean ± 99% confidence interval is given
y = -4.754Ln(x) + 32.972R2 = 0.6334
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0 200 400 600 800 1000
Number of grains counted
Co
nfi
den
ce in
terv
al (
99%
)
Fig. 5 The relationship between confidence interval (99%) of theestimation mean free mica particle content in a sample by imageanalysis and the number of grains counted
252—Volume 17(2) April 2008 Journal of Materials Engineering and Performance
confidence interval with increasing number of grains counted,i.e., the reliability of estimates increased. The relationship wasnot linear and correlation analysis performed with Sperman�sRho revealed r = 0.77, n = 19, and p< 0.005. The best-fit forthe relationship was given by logarithmic regression(R2 = 0.66). The equation for the relationship is given inFig. 5. Furthermore, the results suggest that at least 350 grainsshould be counted to obtain a certainty of 3-4% in the estimateof the average free mica particle content.
The statistical evaluation points out the certainty andrepeatability of the method. Due to the possibility to save theimages of the statistical operation, the results of the method arecontrollable. These factors mentioned make the method satis-factory from a scientific point of view.
4. Conclusion
The need to quantify the content of free mica particles infine fraction of aggregates has initiated the development of ananalysis method that focuses on the estimation of hard rockquality based on image analysis. A further aspect is that, from ascientific point of view, the described method is statisticallysatisfying, thus the present work is a step in the right directionof development.
The sample can originate from any rock material, i.e., notonly from drill cuttings. Hence, the method is appropriate as acomplementary assessment tool to estimate and trace changesor variations in quality of rock aggregate products. Though, theestimation of free mica particles in fine fraction needs to becombined with other analyses, e.g., petrographic analysis andanalyses of mechanical properties, to assess the quality of rockmaterial.
Acknowledgments
This work is funded by the Swedish Road Administration(SRA) and the Swedish National Road and Transport ResearchInstitute (VTI).
References
1. S.L. Brantley and N.P. Mellott, Surface Area and Porosity of PrimarySilicate Minerals, Am. Mineral., 2000, 85, p 1767–1783
2. K. Miskovsky, Enrichment of Fine Mica Originating From RockAggregate Production and Its Influence on the Mechanical Properties ofBituminous Mixtures, J. Mater. Eng. Perform. 2000, 13(5), p 607–611,ASM International
3. H. Hakim and S. Said, Glimmer i bitumenbundna belaggnin-gar—Inverkan av fina, fria glimmerkorn, VTI notat 8-2003, Statensvag-och transportforskningsinstitut (the Swedish National Road andTransport Research Institute), Linkoping, 2003, in Swedish
4. P. Nieminen and R. Uusinoka, Influence of Quality of Fine Fractions onEngineering Geological Properties of Crushed Aggregates, Bull. Int.Assoc. Eng. Geol., 1986, 33, p 97–101
5. ‘‘Bestamning av glimmerhalt i materialets finfraktion’’, VVMB 613,VV Publ nr 2001:100, Swedish Road Administration, Borlange, 2002,6 p, in Swedish http://www.vv.se/filer/publikationer/mb613.pdf
6. ‘‘Tests for General Properties of Aggregates—Part 2: Methods forreducing laboratory samples’’, EN 932-2:1999, European Committeefor Standardization, 1999
7. ‘‘Tests for Geometrical Properties of Aggregates—Part 1: Determina-tion of Particle Size Distribution—Sieving Method’’, EN 933-1:1997,European Committee for Standardization, 1997
8. I. Sims and P. Nixon, RILEM Recommended Test Method AAR-1:Detection of Potential Alkali-Reactivity of Aggregates—PetrographicMethod, Mater. Struct./Mater. Construct., 2003, 36, p 480–496
9. W.D. Nesse, Introduction to Optical Mineralogy, Oxford UniversityPress, 2004, p 348
10. W.A. Deer, R.A. Howie, and J. Zussman, An Introduction to the Rock-Forming Minerals, 2nd ed., Pearson Education Limited, 1992, p 696
11. R.J. Larsen, L. Morris, and I. Marx, An Introduction to MathematicalStatistics and Its Application, Prentice-Hall Inc., 1981, p 536
Journal of Materials Engineering and Performance Volume 17(2) April 2008—253
ESTIMATION OF ROCK AGGREGATES QUALITY USING ANALYSES OF DRILL CUTTINGS
PAPER III EVA JOHANSSON, DEPARTMENT OF CIVIL, MINING AND ENVIRONMENTAL ENGINEERING, LULEÅ
UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 920 49 10 21, MOBILE: +46 70 683 03 79
KAREL MIŠKOVSKÝ, DEPARTMENT OF CIVIL, MINING AND ENVIRONMENTAL ENGINEERING, LULEÅ UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected],
TELEPHONE: +46 90 14 42 69 KARL-JOHAN LOORENTS, THE SWEDISH TRANSPORT ADMINISTRATION, BOX 494, 581 06 LINKÖPING,
SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 31 63 51 65
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE 18(3), APRIL 2009, PP. 299-304
Estimation of Rock Aggregates Quality Using Analysesof Drill Cuttings
Eva Johansson, Karel Miskovsky, and Karl-Johan Loorents
(Submitted May 14, 2008; in revised form July 4, 2008)
There is a need for an effective method to estimate the quality of crushed rock aggregates and its usability inthe early stages of project planning, e.g., for road and railway constructions and quarry prospecting. Theproposed method is based on mineralogical and petrographic analyses of drill cuttings and analysis of thecoarse fraction to estimate the homogeneity/heterogeneity of the bedrock. The geological analyses arefollowed by an estimation of the rock materials� mechanical properties and their potential technicalusability. Development and practical applicability (field and laboratory) of the method have been per-formed and correlated to three road projects from regions of different geological and climatic zones inSweden. The study confirms the capability of the proposed method as a surveying tool.
Keywords aggregates, drill cuttings, mechanical properties,petrographic analysis, road constructions
1. Introduction
To minimize the environmental consequences and costs forroad and railway construction works, a careful use of rockaggregates within the construction site is required (e.g., Ref 1).An early estimation of the quality of the bedrock and itsoptimum use (i.e., mass and material balance) demands anappropriate level of survey. Misjudgments of the use of suchaggregates may cause considerable negative economic andconstruction consequences. The early information concerningthe quality of the bedrock is especially true for areas of lowbedrock exposure covered by drift materials.
In modern society, the attention is paid to economicalprofitability, environmental protection, and a sustainable usageof resources. According to these requisites, the aggregates mustalso meet constructional requirements. In an effort to reach theobject-related volumetric and material equilibrium of rock massfor infrastructure construction, there is a need for a robust toolfor balance calculations.
The central prerequisite in prospecting of natural resourcessuch as rock materials is the knowledge of the qualitiesthat determine the suitability of a material for use as aggregates(Ref 2). The strong relationships between geological properties(e.g., the mineralogical composition and the rock fabrics),mechanical properties, and the rock mass� likely performance asan aggregate in construction must be taken into account whendeciding on new extraction sites for aggregates (Ref 3).
Analysis of drill cuttings is an established surveying toolextensively used in ore prospecting. The traditional prospectingfor crushed rock aggregate quarries is so far based on drill-coresused for petrographic and mechanical analyses. The methodpresented is focused on petrographic analysis of the coarsefraction (>4 mm) of drill cuttings to estimate the homogeneity/heterogeneity of the bedrock and to determine the rock typesincluded. This information in turn admits assessment ofmechanical properties and technical usability in constructionapplications (e.g., roads and railways). The fine fraction (0.125-0.25 mm) is used to estimate the content of free mica particles.It is known that mica-bearing rocks may cause damage in roadconstructions (e.g., Ref 4-6). The deterioration of the construc-tion is related to the ability of mica particles to be releasedduring crushing and to concentrate in the aggregate finefractions. Enrichment of free mica particles in the aggregatefine fractions and its effects on the quality of crushed rockaggregate products applied in constructions are thoroughlydescribed in Ref 4-9.
The purpose of the current study was to examine thepossibility of using drill cuttings for estimation of the qualityof rock aggregates as construction materials. Furthermore, thework is used to develop and test the practical application, and theefficiency of the method, within a number of road projects fromregions of different geological and climatic zones in Sweden.
2. Methods
2.1 Project Design
The practical application of using drill cuttings for estima-tion of the rock aggregates quality was designed according tothree phases; each adapted to the state of the road project.
The first phase is focused on geological map studies, initialfield work, and sampling. Map studies provide indicationsabout the structure of the bedrock and the types of rock. Thefield investigation is aimed toward ocular inspection of theprojecting area. In this stage, the locations and number ofsampling points (i.e., bore holes) are determined. The approximate
Eva Johansson and Karel Miskovsky, Department of Civil, Miningand Environmental Engineering, Lulea University of Technology,971 87 Lulea, Sweden; and Karl-Johan Loorents, The Swedish RoadAdministration, 405 33 Goteborg, Sweden. Contact e-mails: [email protected], [email protected] and [email protected].
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Journal of Materials Engineering and Performance Volume 18(3) April 2009—299
depth of the bore holes is 5 m, which is the regular depthused for soil/rock probing (i.e., geotechnical investigations) foradvanced construction projects (e.g., bridges and under groundconstructions; Ref 10). The depth is selected based on theproperties of the bedrock, and the bore holes may be deeper ifthe geology is complicated or heterogeneous. During thesampling it is of great importance to collect large enoughsamples of coarse drill cuttings for the reliability (statistical) ofthe prediction. The samples are reduced and dry sieved, andnarrow size fractions (0.125-0.25 and >4 mm) are collectedaccording to Ref 11 and 12. From each of the collected sizefractions, thin sections are prepared (Ref 13, 14) and microphotographed to allow for digital analysis. The coarse fractionis used for petrographic analysis while the fine fraction is usedto estimate mineralogical composition (e.g., free mica parti-cles). When the rock type and the mineralogical compositionare known, the quality of the aggregate, aggregate mechanical
properties, and possible usage can be estimated. As a frame-work for construction and material demands, technical norms(Ref 15) for road constructions from the Swedish RoadAdministration are applied.
Within the second phase a complementary field investigationis carried out after drift materials have been cleared and thebedrock exposed. The rock structures are subsequently mappedand samples from the bedrock and from the production (i.e.,crushing) are collected for mechanical and petrographic analy-ses. The outcome is compared with the results from phase 1.
Phase 3 includes functional control of the rock aggregatespertaining to sampling from the construction and testing of therock material. At this stage a final summary comparison of allresults is performed and the method of drill cuttings is evaluatedwith respect to reliability, efficiency, and economic aspects.
Field studies included three road projects that were locatedin the north, central, and southeast regions of Sweden (Fig. 1).Project I comprised phases 1 and 2 while Project II comprisedphase 1. In Project III, phases 1 and 2 were carried outsimultaneously. It was not possible to complete phase 3 in anyof the projects studied, due to time constraints.
2.2 Petrographic Analyses
The analyses of the coarse fraction (>4 mm) were per-formed under a polarizing microscope and the mineralogicalcomposition of the rocks was determined by point-counting(e.g., Ref 13, 16, 17). The estimation of free mica particles inaggregate fine fractions was carried out by image analysis asdescribed in Ref 18. The method used in the present study isbased on a modified point-count approach, using microphotographs of thin sections and a software package foranalysis and presentation of the data.
2.3 Mechanical Analyses
To confirm the validity of the mechanical propertiespredicted in the first phase, samples collected in phase 2 weretested for resistance to wear (micro-Deval value), resistance tofragmentation (Los Angeles value), resistance to wear byabrasion from studded tyres (Nordic test value), and particleshape (flakiness index). All tests were performed by accreditedlaboratories in accordance with Ref 11, 12, 19-23.
3. Results
3.1 Project I
Previous studies of geological maps indicated bedrockdominated by meta-greywacke (sediment-gneisses, veinedFig. 1 The locations of the projects studied
Table 1 Results of the petrographic analyses, Project I, phase 1; rock type and mineralogical composition
Sample ID Rock type Grain size, mm Plagioclase, vol.% Quartz, vol.% Mica, vol.% Others, vol.%
P1-1-01 Mica-schist 0.5 36.6 35.5 27.8 ...P1-1-02 Mica-schist 0.5-1 32.2 48.4 19.4 ...P1-1-03 Mica-schist 0.3-0.5 48.5 31.5 18.0 2.0P1-1-04 Mica-schist 0.3-0.5 30.2 38.2 31.6 ...P1-1-05 Mica-schist 0.3-1 38.5 48.5 13.0 ...P1-1-06 Mica-schist 0.4-5 48.9 38.7 10.6 1.7P1-1-07 Mica-schist 0.2-0.7 38.0 46.9 11.3 3.8
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gneisses, mica-schists, and phyllites) and by limited occurrenceof ortho-gneisses of granitoid composition (Ref 24). The resultsof the petrographic analyses of drill cuttings pointed out adominance of grey to dark grey, strongly foliated, medium-grained mica-schist with the mineralogical composition ofquartz> feldspar (plagioclase)>mica (biotite) (Table 1). Thecontent of free mica particles in the fine fractions varied from24 to nearly 50% (Table 2).
On the basis of the petrographic analyses, the mechanicalproperties and the usability were empirically estimated withconsideration to the project design. The examined rock typeswere considered hardly qualified for use as sub-base coursein unbounded road pavements (Ref 15). Due to theheterogeneity of the bedrock and the high free mica particlecontent in fine fractions, it was estimated that the rockquality would not satisfy the construction demands for thebase course.
The field investigation, the complementary geologicalanalyses, and the mechanical tests in accordance with phase 2confirmed the prognosis given in phase 1. The results of thepetrographic analyses and the geological investigations showedheterogeneous bedrock dominated of coarse-grained, veinedsedimentary gneiss alternating with dark, medium-grainedmica-schist, and dark, medium- to coarse-grained ortho-gneiss(Table 3). All these rock types are mica-rich. The contentof free mica particles in the fine fractions was calculated as33-45% (Table 4). The predicted mechanical properties corre-sponded well with the mechanical tests (Table 5). Because ofthe heterogeneity of the bedrock, the test results should beconsidered as averages. The results from the mineralogical andpetrographic examinations carried out in Project I pointed outthat the rock material within the construction site was notsuitable for use as base course, and as sub-base course it shouldbe used with some reservations.
3.2 Project II
The interpretation of the geological maps indicated thatthe surrounding areas of the road section were comprised ofortho-gneisses of granitoid composition (Ref 24). Thesediment-gneisses, mica-schists and phyllites are subordinate
to the ortho-gneisses. The petrographic analyses of the drillcuttings estimated the rock materials to be composed of greyto light grey to pink, foliated, coarse-grained, irregular-grained ortho-gneiss with feldspar, quartz, and mica (biotite)as the main mineral constituents (Table 6). Some samplesshowed a finer grained ortho-gneiss. The content of free micaparticles in the fine fractions was determined as 19-41%(Table 7).
The rock types investigated were estimated to meet thetechnical demands (Ref 15) for both base course and sub-basecourse in unbounded road pavements. The finer grained ortho-gneisses were considered to display better mechanical proper-ties than the coarse-grained ones. The phase 2 of this projecthas been delayed. Final analysis of the mineral will occur atafter the conclusion of the current project.
3.3 Project III
The geological maps of the area describe a metamorphic,heterogeneous bedrock mainly composed of granofels, includ-ing metamorphic rocks of both sedimentary and igneous origin.The results of the field investigations and the petrographicanalyses (Table 8) of the coarse fraction of the drill cuttingsshowed several rock types:
(i) foliated, medium-grained, mica-rich, biotite-plagioclase-schist,
(ii) dark grey, medium-grained, irregular-grained amphibolite-schist,
(iii) biotite-rich, medium- to coarse-grained ortho-gneiss.
The two first rock types are weakly to medium migmatisedand partly mylonitised; altered into chlorite-schist. The ortho-gneiss is strongly tectonised, exhibiting a high frequency ofmicro-cracks. The analysis of free mica particle content in the
Table 4 Results of the calculations of content of freemica particles in fine fraction (0.125-0.25 mm),Project I, phase 2
Sample ID Mica content, vol.%
P1-2-01 45.0P1-2-02 32.6
Table 3 Results of the petrographic analyses, Project I, phase 2; rock type and mineralogical composition
Sample ID Rock type Grain size, mm Feldspar, vol.% Quartz, vol.% Mica, vol.% Others, vol.%
P1-2-01 Ortho-gneiss 2-3 35.2 28.9 35.9 ...P1-2-02 Migmatite (mica-schist/ortho-gneiss) 0.2 to >2 51.6 31.0 17.4 ...
Table 5 Results of the mechanical analyses,Project I, phase 2
SampleID
Density,Mg/m3
micro-Deval,%
LosAngeles, %
Nordictest, %
Flakinessindex, %
P1-2-01 2.74 19 32 26.2 12P1-2-02 2.71 20 34 30.3 19
Table 2 Results of the calculations of content of freemica particles in fine fraction (0.125-0.25 mm),Project I, phase 1
Sample ID Mica content, vol.%
P1-1-01 49.5P1-1-02 36.0P1-1-03 27.5P1-1-04 36.0P1-1-05 29.9P1-1-06 23.5P1-1-07 24.6
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fine fractions revealed values from 0 to over 50% (Table 9).The amphibolite-schist is lacking mica; all other rocks aremica-rich.
Despite the negative petrographic indications, the mechan-ical tests of the rock samples (Table 10) resulted in valuesapproved for use in base course (Ref 15). The evaluation of theinvestigation presented a general recommendation to limit theconstruction traffic on unbound layers in order to avoidfragmentation.
4. Discussion and Evaluation
The samples of drill cuttings selected in Projects I and IIoriginated from soil/rock probing performed during the plan-ning stage of the road construction project. The analyses of the
drill cutting samples resulted in a prognosis concerning the useof the aggregate for the particular road construction. The latterpetrographic and mechanical analyses of the samples collectedfrom the exposed bedrock and from the crushed aggregateproducts confirmed the primary prognoses based on the
Table 7 Results of the calculations of content of freemica particles in fine fraction (0.125-0.25 mm),Project II, phase 1
Sample ID Mica content, vol.%
P2-1-01 27.1P2-1-02 36.2P2-1-03 28.6P2-1-04 40.7P2-1-05 19.4P2-1-06 30.9P2-1-07 34.7P2-1-08 37.0P2-1-09 27.6
Table 8 Results of the petrographic analyses, Project III, phase 1; rock type and mineralogical composition
Sample ID Rock type Grain size, mm Feldspar, vol.% Quartz, vol.% Mica, vol.% Amphibol, vol.% Others, vol.%
P3-1-01 Mica-schist 0.1-0.7 44.7 21.4 33.8 ... ...P3-1-02 Mica-schist 0.1-0.7 37.8 6.7 55.4 ... ...P3-1-03 Mica-schist 0.1-0.7 49.1 20.6 30.3 ... ...P3-1-04 Mica-schist 0.1-0.7 47.8 17.3 34.9 ... ...P3-1-05 Mica-schist 0.1-0.4 36.0 9.7 53.8 ... 0.4P3-1-06 Amphibolite-schist 0.5-1 39.6 ... ... 59.6 0.8P3-1-07 Amphibolite-schist 0.4-1 39.9 ... ... 57.1 3.0P3-1-08 Amphibolite-schist 0.1-0.2 32.7 ... ... 67.3 ...P3-1-09 Ortho-gneiss 0.1-7 43.7 30.3 26.0 ... ...P3-1-10 Ortho-gneiss 0.1-7 70.8 13.5 15.7 ... ...P3-1-11 Ortho-gneiss 0.1-5 34.6 20.4 45.0 ... ...
Table 6 Results of the petrographic analyses, Project II, phase 1; rock type and mineralogical composition
Sample ID Rock type Grain size, mm Feldspar, vol.% Quartz, vol.% Mica, vol.% Amphibol, vol.% Others, vol.%
P2-1-01 Ortho-gneiss 0.5-4 70.7 17.7 10.5 ... 1.1P2-1-02 Ortho-gneiss 0.5-4 65.4 19.1 10.9 3.5 1.1P2-1-03 Ortho-gneiss 0.2-4 68.3 26.5 3.7 ... 1.5P2-1-04 Ortho-gneiss 0.5-5 67.6 14.5 17.9 ... ...P2-1-05 Ortho-gneiss 1-4 52.0 35.1 11.9 ... 1.0P2-1-06 Ortho-gneiss 1-5 51.0 33.3 11.4 ... 4.3P2-1-07 Ortho-gneiss 1-4 68.9 16.8 12.7 ... 1.6P2-1-08 Ortho-gneiss 0.5-5 68.9 20.2 10.3 ... 0.5P2-1-09 Ortho-gneiss 1-2 60.8 27.6 11.6 ... ...
Table 9 Results of the calculations of content of freemica particles in fine fraction (0.125-0.25 mm),Project III, phase 1
Sample ID Mica content, vol.%
P3-1-01 45.3P3-1-02 46.6P3-1-03 46.3P3-1-04 23.7P3-1-05 50.5P3-1-06 0P3-1-07 0P3-1-08 1.0P3-1-09 44.6P3-1-10 45.4P3-1-11 46.3
Table 10 Results of the mechanical analyses,Project III, phase 2
SampleID
Density,Mg/m3
micro-Deval,%
LosAngeles, %
Nordictest, %
Flakinessindex, %
P3-2-01 2.71 10 21 15.4 14.4P3-2-02 2.97 17 18 20.1 12.9P3-2-03 2.70 20 22 22.6 9.3
302—Volume 18(3) April 2009 Journal of Materials Engineering and Performance
analyses of drill cuttings. The sampling of drill cuttings inProject III was done during production drilling, since phases 1and 2 were carried out simultaneously. However, the results ofthe analyses of drill cuttings and the results of the geologicaland the mechanical analyses of the rock samples and theaggregates produced were well correlated. The differentapproaches of sampling indicate the independence of the fieldsampling technique and stress the flexibility of the drill cuttingmethod and its application as a field method. The utilization ofthe soil/rock probing method provides an opportunity to collectbedrock data during the planning stage of the project with thepossibility of performing a volumetric and quality estimation ofthe rock mass available.
Mechanical properties of rocks are closely connected to theirgeological properties (e.g., Ref 25-30). Thus, mechanicalanalyses used for estimation of the quality of aggregates arenot sufficient to evaluate the usability of crushed rock. On thecontrary, advanced geological analyses do not give informationon the quality or the usability of the rock aggregate, if thegeological parameters are not interpreted into functionalcharacteristics. The interpretation in turn depends on theexperience and the ability of the interpreter to interconnectthe geological and the mechanical properties and to understandthe processing of different rock materials.
The results of this study point out the potential use of thedrill cutting method as a surveying tool for road and railwayconstructions and for quarry establishment. This method iseasily applied even when the bedrock is covered by driftmaterials (i.e., by soil/rock probing). The most desirableadvantage of the method is its timings and cost efficiency.However, the method is also highly flexible and can be used tosupport quality estimation of rock materials. The predictions ofthe quality and the usability of rock materials in the currentinvestigation have been satisfactorily confirmed.
In an effort to further develop and calibrate the method ofdrill cuttings, evaluation of rock aggregate including the phase3 process will be continued. Furthermore, because the inves-tigation deals with metamorphic rocks, further research withindifferent geological environments (i.e., igneous and sedimen-tary rocks) is required.
5. Conclusion
The results from this work confirm the necessity of a quickand reliable method for quality estimation of the rock materialsduring the planning stage of road constructions, quarryprospecting, etc. Using drill cuttings from introductory geo-technical investigations for estimation of the rock materials�mechanical properties is the most efficient method for achievingthis purpose. To turn the petrographic properties of the rocksinto an estimate of their mechanical properties, and to evaluatetheir suitability as aggregates in the different parts of roadconstruction, demands experience of the interpreters.
Acknowledgment
This study was funded by the Swedish Road Administration(SRA) and the Swedish National Road and Transport ResearchInstitute (VTI).
References
1. The Swedish Road Administration, Miljokonsekvensbeskrivning inomvagsektorn, Del 3 Analys och bedomning, Publikation 2002:43,Vagverket (the Swedish Road Administration), Borlange, 2002,p 171 (in Swedish), http://publikationswebbutik.vv.se/upload/1896/2002_43_handbok_miljokonsekvensbeskrivning_inom_vagsektorn_del_3_analys_och_bedomning.pdf (2008-05-14)
2. M.R. Smith and L. Collis, Eds., Aggregates: Sand, Gravel andCrushed Rock Aggregates for Construction Purposes, 3rd edn., vol. 17.Geological Society, London, Engineering Geology Special Publica-tions, 2001, p 339
3. M. Heinio, Ed., Rock Excavation Handbook, Sandvik Tamrock Corp.,1999, p 363
4. H. Hakim and S. Said, Glimmer i bitumenbundna belaggningar -Inverkan av fina, fria glimmerkorn, VTI notat 8-2003, Statens vag- ochtransportforskningsinstitut (the Swedish National Road and TransportResearch Institute), Linkoping, 2003, p 36 (in Swedish), http://www.vti.se/EPiBrowser/Publikationer/N8-2003.pdf (2008-04-03)
5. K. Miskovsky, Enrichment of Fine Mica Originating from RockAggregate Production and its Influence on the Mechanical Propertiesof Bituminous Mixtures, J. Mater. Eng. Perform., 2004, 13(5),p 607–611
6. P. Nieminen and R. Uusinoka, Influence of Quality of Fine Fractions onEngineering Geological Properties of Crushed Aggregates, Bull. Int.Assoc. Eng. Geol., 1986, 33(1), p 97–101
7. S.L. Brantley and N.P. Mellott, Surface Area and Porosity of PrimarySilicate Minerals, Am. Mineral., 2000, 85(11–12), p 1767–1783
8. B. Lagerblad, Krossat berg som ballast i betong, Omrade 2, Projekt nr2,2 Framtida betong, Delprojekt 2,23 Utnyttjande av alternativa typerav ballast i betong, Rapport nr 2:19, MinBaS, Stockholm, 2005, p 68(in Swedish)
9. K.-J. Loorents, E. Johansson, and H. Arvidsson, Free Mica Grains inCrushed Rock Aggregates, Bull. Eng. Geol. Environ., 2007, 66(4),p 441–447
10. The Swedish Geotechnical Society, Geoteknisk falthandbok –Allmanna rad och metodbeskrivningar, SFG Rapport 1:96, SvenskaGeotekniska Foreningen (the Swedish Geotechnical Society), Linko-ping, March, 1996, p 172 (in Swedish), http://www.sgf.net/home/page.asp?sid=862&mid=2&PageId=11564 (2008-05-14)
11. Tests for General Properties of Aggregates – Part 2: Methods forReducing Laboratory Samples, EN 932-2:1999, European Committeefor Standardization, 1999
12. Tests for Geometrical Properties of Aggregates – Part 1: Determinationof Particle Size Distribution – Sieving Method, EN 933-1:1997,European Committee for Standardization, 1997
13. I. Sims and P. Nixon, RILEM Recommended Test Method AAR-1:Detection of Potential Alkali-Reactivity of Aggregates – PetrographicMethod, Mater. Struct./Mater. Construct., 2003, 36(7), p 480–496
14. W.D. Nesse, Introduction to Optical Mineralogy, Oxford UniversityPress, 2004, p 348
15. Allman teknisk beskrivning for vagkonstruktion ATB Vag 2005,Publikation 2005:112, Vagverket (the Swedish Road Administration),Borlange, 2005 (in Swedish), http://www.vv.se/templates/page3____14328.aspx (2008-05-14)
16. F. Chayes, Petrographic Modal Analysis, Wiley, New York, 195617. A.A. Glagolev, Mineralogical Materials, 1931, p 1018. E. Johansson, K. Miskovsky, K.-J. Loorents, and O. Lofgren, A
Method for Estimation of Free Mica Particles in Aggregate FineFraction by Image Analysis of Grain Mounts, J. Mater. Eng. Perform.,2008, 17(2), p 250–253
19. Tests for Mechanical and Physical Properties of Aggregates – Part 1:Determination of the Resistance to Wear (micro-Deval), EN 1097-1:1996, European Committee for Standardization, 1996
20. Test for Mechanical and Physical Properties of Aggregates – Part 2:Methods for the Determination of Resistance to Fragmentation, EN1097-2:1998, European Committee for Standardization, 1998
21. Test for Mechanical and Physical Properties of Aggregates – Part 6:Determination of Particle Density and Water Absorption, EN 1097-6:2000, European Committee for Standardization, 2000
22. Test for Mechanical and Physical Properties of Aggregates – Part 9:Determination of the Resistance to Wear by Abrasion from Studded
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Tyres – Nordic Test, EN 1097-9:1998, European Committee forStandardization, 1998
23. Tests for Geometrical Properties of Aggregate – Part 3: Determinationof Particle Shape – Flakiness Index, EN 933-3:1997, EuropeanCommittee for Standardization, 1997
24. A. Streckeisen, To Each Plutonic Rock Its Proper Name, Earth Sci.Rev., 1976, 12(1), p 1–33
25. B. Brattli, The Influence of Geological Factors on the MechanicalProperties of Basic Igneous Rocks Used as Road Surface Aggregates,Eng. Geol., 1992, 33(1), p 31–44
26. A. Tugrul and I.H. Zarif, Correlation of Mineralogical and TexturalCharacteristics with Engineering Properties of Selected Granitic Rocksfrom Turkey, Eng. Geol., 1999, 51(4), p 303–317
27. U. Akesson, J.E. Lindqvist, M. Goransson, and J. Stigh, RelationshipBetween Texture and Mechanical Properties of Granites, CentralSweden, by Use of Image-Analysing Techniques, Bull. Eng. Geol.Environ., 2001, 60(4), p 277–284
28. U. Akesson, J. Stigh, J.E. Lindqvist, andM. Goransson, The Influence ofFoliation on the Fragility of Granitic Rocks, Image Analysis andQuantitative Microscopy, Eng. Geol., 2003, 68(3–4), p 275–288
29. M. Raisanen, Relationships Between Texture and Mechanical Proper-ties of Hybrid Rocks from the Jaala-Iitti Complex, SoutheasternFinland, Eng. Geol., 2004, 74(3–4), p 197–211
30. M. Raisanen and A. Torppa, Quality Assessment of a GeologicallyHeterogeneous Rock Quarry in Pirkanmaa County, Southern Finland,Bull. Eng. Geol. Environ., 2005, 64(4), p 409–418
304—Volume 18(3) April 2009 Journal of Materials Engineering and Performance
CORRELATIONS BETWEEN PETROGRAPHIC AND MECHANICAL PROPERTIES OF ROCK MATERIALS: A LITERATURE REVIEW
PAPER IV
EVA JOHANSSON, ENVIX NORD AB, KYLGRÄND 6B, 906 20 UMEÅ, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 90 70 67 75, MOBILE: +46 70 388 42 64
ŠÁRKA LUKSCHOVÁ, INSTITUTE OF GEOCHEMISTRY, MINERALOGY AND MINERAL RESOURCES, FACULTY OF SCIENCE, CHARLES UNIVERSITY, ALBERTOV 6, 128 43 PRAGUE 2, CZECH REPUBLIC,
E-MAIL: [email protected], TELEPHONE: +420 774 966 630 KAREL MIŠKOVSKÝ, DEPARTMENT OF CIVIL, ENVIRONMENTAL AND NATURAL RESOURCES
ENGINEERING, LULEÅ UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 90 70 67 73
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE SUBMITTED 10 SEPTEMBER 2010
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Correlations between petrographic and mechanical properties of rock materials: a literature review
Eva Johansson, Envix Nord AB, Kylgränd 6B, 906 20 Umeå, Sweden, e-mail: [email protected], telephone: +46 90 70 67 75, mobile: +46 70 388 42 64,
fax: +46 90 70 67 71
Šárka Lukschová, 1) Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic, 2) Geodynamics,
Institute of Rock Structure and Mechanics, v.v.i., V Holesovickach 41, 181 09 Prague 8, Czech Republic, e-mail: [email protected]
Karel Miškovský, Department of Civil, Mining and Environmental Engineering, Luleå University of Technology, 971 87 Luleå, Sweden, e-mail: [email protected]
Abstract Mechanical and technical properties of rock materials are crucial factors affecting usability of rock aggregates in the construction industry. There is an increase each year in the number of publications focussing on mechanical/technical properties of rock materials. This includes research papers as well as case studies and discussions. However, only a fraction of them deals with mechanical/technical and petrographic properties together. Emphasis in the present literature review was placed on the research papers discussing the specific petrographic parameters and their influences on mechanical/technical properties of rock materials. Mineralogical composition, micro-cracks, porosity, grain size, grain shape, and the degree of foliation are the most important parameters influencing the mechanical and technical properties of igneous, metamorphic, and/or sedimentary rocks. Keywords: rock type, aggregates, petrographic properties, mechanical properties, technical properties, rock fabric Introduction The quality of rock materials used as aggregates is one of the primary variables concerning the costs for maintenance and the durability of road constructions and also an important factor associated with environmental impact (e.g., Ref 1-3). In infrastructure construction nowadays, more emphasis is placed on economical efficiency, protection of the environment and the sustainable use of resources. Rock material is a non-renewable natural resource and therefore calls for rational use. Besides meeting the above requisites aggregates must also meet the constructional requirements. Hence, the appropriate choice of rock material is essential for the production of aggregates for optimum use in infrastructure constructions, e.g., roads, railways, and bridges. The knowledge of the intrinsic properties of rock types (Ref 4-6) is important, not only for the construction industry, but for the processing of aggregates such as drilling, blasting, and crushing. The rock aggregates quality is affected by the many different steps in the production of aggregates, together or severally (e.g., Ref 1, 7-21). For instance, blast-induced micro-cracks (e.g., Ref 22-24), the ability of free mica particles to enrich in crushed aggregates fine fractions (e.g., Ref 25-32), and crushed aggregates particle shape (e.g., Ref 7, 10, 18, 20, 21, 33, 34) are factors strongly impacting the technical and functional properties of the aggregate products.
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The selection and preparation of samples or test specimens and experimental factors like non-standardized testing equipment are also of great importance for the results from the tested properties (e.g., Ref 7, 11, 20, 35, 36). Samples and test specimens have to be representative for all rock body, reflecting its main structural, mineralogical, and textural characteristics as described in e.g., Ref 37-43. The rigidity of the test apparatus and the character of the substrate may cause inconsistency into test results (e.g., Ref 7). The purpose of the current study was to summarize the state of the literature concerning the petrographic properties of rock materials and their influences on the mechanical and technical properties. The focus of this work was placed on crucial research results rather than on a comprehensive overview. The mechanical and technical properties are discussed separately due to the functional testing of hard rock and rock aggregates. Mechanical properties The main petrographic factors affecting mechanical properties (tensile and uniaxial compressive strengths) are regarded as the mineralogical composition, the occurrence of micro-cracks and pore voids, and the grain size and grain shape of individual minerals (e.g., Ref 44-51). The mineralogical composition of rocks reflects the proportion of rock forming minerals such as quartz, feldspars, micas, amphiboles, pyroxenes, calcite, and/or clay minerals. The influence of quartz content on rock strength properties is generally explained by quartz hardness, low cleavage and morphology of quartz grains (Ref 45, 49, 52). Tu rul and Zarif (Ref 45) and Goodman (Ref 49) explained the relationship between increasing strength properties and increasing quartz content by quartz anhedral (allotriomorphic) grain shape. Anhedral grains are able to fill the space between euhedral (idiomorphic) grains and decrease rock porosity which increases strength (Ref 45, 49). Increasing content of quartz causes higher degree of interlocking between individual quartz grains which in turn increases strength (Ref 52). Quartz-rich matrix increases the strength in the case of sedimentary rocks (Ref 53, 54). The highest strength observed in sediments cemented by opal-rich matrix is mainly associated with high compactness and low amount of discontinuities in matrix (Ref 54). Feldspar content mainly affects the strength properties due to felspars’ very good cleavage that increases brittleness (Ref 49). Feldspar grains are associated with micro-cracks (fissures) occuring as inter-granular micro-cracks which decrease strength properties (Ref 49, 55, 56). This correlation is typical only for unaltered rocks. Feldspar grains affected by alteration (sericitisation) are less brittle since there is a lower degree of micro-cracking. This causes them to have better resistance to brittle deformation, thus increasing their strength (Ref 57). Amphibole and pyroxene are both mafic minerals belonging to the inosilicate subgroup. However, their influences on strength properties are completely differing. Increase in the strength of rocks is commonly associated with higher pyroxene content and lower amphibole content. (Ref 58). The different effects of amphibole and pyroxene are explained by minerals habitus. Most of the amphiboles exhibit a long, prismatic and sometimes fibrous form, while pyroxene forms short prismatic habitus. A higher content of fibrous minerals increases rock flakiness and brittleness, thus decreasing the rock strength (Ref 55, 58). The effect of mica is well-visible in the case of mica-rich metamorphic rocks in which the mica particles accumulate and form mica-rich bands. Mica preferentially forms flaky particles which in metamorphic rock types are arranged parallel to each other (Ref 59). Rocks exhibit the lowest strength in the direction parallel to the foliation whilst in the direction perpendicular to the foliation they exhibit the highest strength. This strength anisotropy becomes more obvious with
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increasing mica content. In contrast, mica has less effect on samples with homogeneous dispersion of mica particles where isotropic behaviour is characteristic (Ref 59, 60). This phenomenon is typical for igneous rocks. The role of calcite is disputable. Calcite, as a main mineral of limestones, represents very weak material showing negative influence on the strength properties due to its good cleavage and weak inter-crystalline bonds (Ref 61). Marbles compared with limestones show higher strength due to re-crystallization and higher degree of grains interlocking. Calcite also has an ability to fill micro-cracks and cavities typical for rocks with amygdaloidal structure (e.g., volcanites). In this case calcite-filled micro-cracks increase the strength properties of rocks (Ref 61, 62). Clay minerals and other phyllosilicates represent the weakest components of rocks (e.g., Ref 63). They are formed by SiO4
4—tetrahedron and Al-octahedron, arranged in double- or triple-layers. The inter-layer space is filled by cations. The micro-structure of phyllosilicates affects their very low strength. An increase in the amount of phyllosilicates in the rocks (due to alteration) results in a pronounced decrease in their strengths which is demonstrated e.g., in the case of granites, quartzites and basalts (Ref 64, 65), diorites (Ref 58), serpentinites (Ref 63) and schists (Ref 66). The influence of phyllosilicates on strength properties is closely related to water saturation (e.g., Ref 67). The ability of phyllosilicates to absorb water is well-known especially in the case of smectites and mica minerals (Ref 25, 68-71). A small increase in the water content may lead to a marked reduction in strength and deformability (Ref 67, 72). The effect of increasing water content on strength reduction was explained by fracture energy reduction, capillary tension decrease, pore pressure increase, frictional reduction, and chemical and corrosive deterioration (Ref 73). Micro-cracks and connective (micro-) porosity are important parameters when considering the weakening of rocks. The finer pores contain water that is bounded tightly to the material and so the contribution of the finer pores to decrease in strength is limited. Pores coarser than100 m and open cracks increase the content of water and thus decrease the strength properties of rocks. Pre-existing micro-cracks and connective porosity are the initial positions of newly formed cracks propagating due to laboratory stress strain of rock materials (Ref 72, 74-76). Dwivedi et al. (Ref 74) established the dependence of intensity of micro-cracking on uniaxial compressive strength of granitic rocks. The propagation of laboratory induced micro-cracks strongly affected the decrease in strength properties. The influence of micro-cracks and porosity on strength properties is commonly associated with the influence of grain size (e.g., Ref 49, 50). Bagde (Ref 50) found negative correlation between uniaxial compressive strength and porosity in the case of various metamorphic rocks (schists, gneisses and amphibolites). Similar dependence between increasing strength and decreasing porosity combined with decreasing grain size was documented in the case of granitoids (Ref 45, 51, 77, 78), sedimentary rocks (e.g., sandstones and greywackes, Ref 53, 79, 80), and metamorphic rocks (e.g., orthogneisses and marbles, Ref 44, 51, 81). The combination of grain size and micro-cracks and its effect on strength was explained by Eberhardt et al. (Ref 82) and by Yilmaz et al. (Ref 56). The maximum grain size was found significantly controlling the propagation of grain boundaries and pre-existing inter-granular micro-cracks. Thus, the strength decrease is affected by increasing grain size that allows for propagation of micro-cracks. Comparable results were achieved by Vasconcelos et al. (Ref 53), who investigated preferential propagation of pre-existing micro-cracks along clast/matrix boundaries in sedimentary rocks. It confirms that the clast/matrix boundaries and clast/clast boundaries are the weakest parts of rocks.
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Grain size together with grain shape, shape of grain boundaries, and foliation were investigated by Howarth and Rowlands (Ref 47, 48), who included all factors mentioned into the “texture coefficient”. The highest texture coefficient means the highest degree of interlocking of individual grains. Thus, the highest texture coefficients are displayed for igneous intrusive rock types showing a decreasing trend towards igneous effusive, metamorphic, and finally sedimentary rocks. The same coefficient was applied by Azzoni et al. (Ref 83) and Ersoy and Waller (Ref 62) on various rock types including igneous, metamorphic, and sedimentary rocks from Australia and Italy. The texture coefficient was compared with the uniaxial compressive strength of rock samples. This confirmed that rocks with the highest degree of interlocking show the highest uniaxial compressive stress (Ref 48, 62). This can easily be explained by weak bonds between matrix and grains in sedimentary rocks which decrease the texture coefficient and decrease the strength. Plutonic rocks on the other hand are strongly interlocked with strong bonds between individual crystals and so their strength properties are very high (Ref 62, 84, 85). The study of the texture coefficient (Ref 47, 48) was somewhat criticised by Azzoni et al. (Ref 83), who pointed out some inaccuracies within individual groups of rocks; e.g., marbles showed lower texture coefficient (lower degree of grain interlocking) than gneisses. This scepticism decreased the correlation factor between the texture coefficient and the uniaxial compressive strength. Thus, the texture coefficient was assessed to be partly unsatisfactory (Ref 83). The foliation means planar structure in rocks mainly originating due to preferred orientation of pre-existing minerals, by minerals segregation into banding, and/or by preferential growth of newly formed minerals. Foliation causes anisotropic behaviour of rocks (e.g., Ref 59, 86). Shape-preferred orientation may form planes of weakness in a structure. Lower strength properties in the direction parallel to foliation and higher strength in the direction perpendicular to foliation was documented in the case of 18 different samples comprising meta-greywacke, hornblende schist, slate, gneiss, phyllite, hornfels, and amphibolite (Ref 9, 59). Additionally, significant relationship was found between increasing water-saturation and increasing strength anisotropy index (Ref 59). Technical properties This section deals with the definitions used in the European Standards for test methods for aggregates (Ref 87-89). All properties measured using the Los Angeles test are identified as resistance to fragmentation while properties measured with the studded tyre test are identified as resistance to wear by abrasion from studded tyres. Properties named as impact value or brittleness are identified as resistance to fragmentation by impact whilst properties named as abrasion, wear etc. are identified as resistance to wear. These properties are the dominating functional characteristics of rock aggregates tested. An investigation of coarse aggregates consisting of granitoid rocks (Ref 90) established that the resistance to wear is dependent on the content of quartz and feldspar. An increase in quartz content causes an increase in the resistance to wear due to the hardness of the minerals. The hardness of quartz and its influence on wear characteristics is also manifested in Ref 91. The content of feldspar also affects the resistance to fragmentation by impact (Ref 55, 90). Increasing content of feldspar influences negatively on the resistance to fragmentation by impact (Ref 90) and the variations in content of feldspar have a stronger effect on the resistance to fragmentation by impact than on the wearing properties. This was explained as a consequence of
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the feldspars weak bonding along the cleavage planes, which has a greater negative effect on the resistance to fragmentation than on the resistance to wear (Ref 55). For igneous granitoid rocks where mica minerals are uniformly dispersed, it is shown that an increasing content of mica (to about 35 vol.%) has a positive influence on the resistance to fragmentation by impact (Ref 90). In the investigation by Ref 55 it was assumed that the increasing content of mica minerals has a stronger negative effect on the resistance to wear than on the resistance to fragmentation by impact. A study performed by Brattli (Ref 55) showed that an increase in the amount of amphibole, which in this case is an alteration product of pyroxene, results in a negative influence on the resistance to fragmentation by impact, resistance to wear and resistance to wear by abrasion of studded tyres. The samples varied from non-metamorphosed to extremely metamorphosed mafic rock types in a complete gradation. It is shown that an increase in the content of secondary minerals and alteration products causes reduced resistance to fragmentation, resistance to fragmentation by impact, and resistance to wear (Ref 58). In an area where granites are dominant, the technical properties of hybridised and non-hybridised rocks are mainly affected by mineralogical composition and texture (Ref 92). Locally the bedrock is hybridised by means of both mafic and felsic melts are included. The author stated that the hybridised rocks tend to show better technical properties than the hornblende granites due to abundance of fine-grained matrix minerals (hornblende), uniform spatial dispersion of hornblende crystals, low standard deviation of the grain size distribution of hornblende, and intense intergrowth texture with interlocking grain boundaries. He showed that the anhedral rapidly crystallised fine-grained hornblende is intergrown with surrounding grains, which results in a texture with higher resistance to breakage. Increasing number of fine-grained ( 1 mm) hornblende influenced positively on the resistance to fragmentation and on the resistance to wear by abrasion from studded tyres. The frequency of micro-cracks and its influence on resistance to wear by abrasion from studded tyres and flakiness was confirmed in the case of igneous and metamorphic rocks (Ref 90). The authors summarized that the frequency of micro-cracks influences positively on the flakiness but negatively on the resistance to wear by abrasion from studded tyres. A relationship between the occurrence of discontinuities such as micro-cracks and resistance to fragmentation was also shown by Ref 9. The grain size and the volume of pore spaces were established to be the most significant petrographic properties influencing the resistance to fragmentation (Ref 93). The study comprised felsic igneous rocks experimentally treated by sodium sulphate. Decreasing grain size and decreasing volume of pore space had a positive influence on the resistance to fragmentation. Similar results were found by Kazi and Al-Mansour (Ref 94) studying rock types of volcanic and plutonic origins. Considering grain size, there are unanimous results from the research performed. The technical properties of rock aggregates commonly improve as the grain size decreases (e.g., Ref 55, 90, 92, 93, 95). Samples from rocks of igneous and metamorphic origins, felsic and mafic in composition occur in the investigations. Rock texture is of great importance in understanding the technical properties of the rock, documented by the case of felsic rocks dominated by granites (Ref 95). Generally, the samples
6
with the highest perimeter values showed the best resistance to fragmentation and wear by abrasion from studded tyres. The best correlation was detected between the perimeter and the resistance to fragmentation. The study also showed a relationship between the specific surface and the technical properties. In that case, the best correlation was given for the specific surface and the studded tyre test value. The results indicated the technical properties to be dependent not only on the grain size but also on the grain shape and the arrangement of the minerals, particularly concerning the resistance to fragmentation. (Ref 95). The influence of foliation (expressed by the foliation index, FIX) on the resistance to fragmentation was investigated on foliated and non-foliated rocks of granitic composition (Ref 96). The study confirmed the results from a previous investigation (Ref 95), which showed that the perimeter is a parameter able to predict the technical properties. It is also possible to describe the relationship between the texture and the technical properties of foliated samples in a quantitative way if both the perimeter and the foliation index are taken into account (Ref 96). The influence of cataclasis on resistance to wear of granitic rocks was studied in an attempt to find a possible relationship between the degree of ductile deformation and the resistance to wear (Ref 97). With the aim to select samples with various deformations, rocks of quartzo-feldspatic constitution were collected from different thrust/fault zones and an undeformed felsic intrusion. A description between the degree of ductile deformation, expressed by quartz crystallinity index, and the resistance to wear, by a simple linear regression model was failed. This was suggested to at least partly depend on the grain size distribution in the rocks, which has a stronger impact upon the wear properties than the ductile deformation; causing scatter in the regression model. A similar study was carried out by Göransson et al. (Ref 98), who investigated the variation of bedrock quality with increasing ductile deformation of metamorphic and igneous rocks of granitoid, syenitoid and dioritoid composition. Generally the values for the studded tyre test increased with increasing deformation, i.e., the values were lower for massive rocks compared to the foliated varieties (Ref 86, 98). The values for resistance to fragmentation tend to exhibit an analogous trend. The compressive strength values for massive rock types and foliated rocks measured perpendicular to the foliation were comparable and higher than those measured parallel to the foliation. It was concluded that weakly deformed to massive rock types have better properties than the severely deformed ones (Ref 98). Alkali-silica reactivity (ASR), alkali-carbonate reactivity (ACR), resistance to sulphate attack (DEF) and/or frost resistance represent a separate group of technical parameters generally discussed as resistance of aggregates to aggressive environment. Their importance increases with respect to the use of aggregates in concrete constructions. Mineralogical composition is the central parameter affecting all of them (e.g., Ref 99). It is considered that the most important petrographic factors affecting the ASR potential of aggregates are: the presence of amorphous SiO2 (e.g., Ref 100-102), the grain size of quartz (e.g., Ref 103-105), and the texture of quartz-rich aggregates (e.g., Ref 106, 107). The mica and feldspar can release alkalis and support ASR too, but this effect has not been clearly verified (e.g., Ref 108, 109). Alkali-carbonate reaction and DEF are mainly affected by the presence of dolomite and sulphates in rocks (Ref 99, 110-112). Mica and clay minerals strongly influence frost resistance due to their high specific surface and ability to absorb water molecules (Ref 71).
7
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PETROGRAPHIC CHARACTERISTICS OF GRANITOID AND GABBROID INTRUSIVE ROCKS AS A TOOL FOR EVALUATION OF MECHANICAL PROPERTIES
PAPER V
EVA JOHANSSON, ENVIX NORD AB, KYLGRÄND 6B, 906 20 UMEÅ, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 90 70 67 75, MOBILE: +46 70 388 42 64
ŠÁRKA LUKSCHOVÁ, INSTITUTE OF GEOCHEMISTRY, MINERALOGY AND MINERAL RESOURCES, FACULTY OF SCIENCE, CHARLES UNIVERSITY, ALBERTOV 6, 128 43 PRAGUE 2, CZECH REPUBLIC,
E-MAIL: [email protected], TELEPHONE: +420 774 966 630 KAREL MIŠKOVSKÝ, DEPARTMENT OF CIVIL, ENVIRONMENTAL AND NATURAL RESOURCES
ENGINEERING, LULEÅ UNIVERSITY OF TECHNOLOGY, 971 87 LULEÅ, SWEDEN, E-MAIL: [email protected], TELEPHONE: +46 90 70 67 73
ENGINEERING GEOLOGY
SUBMITTED 15 MARS 2011
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Petrographic characteristics of granitoid and gabbroid intrusive rocks as a tool for evaluation of mechanical properties Eva Johansson a, c,*, Šárka Lukschová b, Karel Miškovský c a Envix Nord AB, Kylgränd 6B, 906 20 Umeå, Sweden b Institute of Geochemistry, Mineralogy and Mineral Resources Faculty of Science, Charles
University, Albertov 6, 128 43 Prague 2, Czech Republic c Department of Civil, Environmental and Natural Resources Engineering, Luleå University of
Technology, 971 87 Luleå, Sweden Abstract The evaluation of the mechanical properties’ dependence on petrographic variables comprised 26 rock types divided into two groups, 17 granitoids and 9 gabbroids. The samples were analysed for petrographic characteristics and resistance to fragmentation, wear and wear by abrasion from studded tyres. To identify associations between the petrographic and mechanical properties, statistical correlations and linear regression were performed. The grain size, content of mica and frequency of micro-cracks are the main variables influencing the mechanical properties of granitoids. The grain size distribution and degree of foliation indicate obvious tendencies towards associations. In the case of gabbroid rock types, the mechanical properties generally respond to the mica content and frequency of micro-cracks. The increasing need for knowledge concerning the performance of rock materials used as aggregates initiated an attempt to apply the results obtained to the upcoming development of a tool for estimation of mechanical properties using petrographic parameters as input. Keywords: petrographic properties, mechanical properties, rock aggregate, granitoids, gabbroids, intrusive rocks 1 Introduction The worldwide growing infrastructure needs to be developed for an ecologically sustainable society. The balance between environmental protection and the need for infrastructure is particularly complex and susceptible. The important constituents of the infrastructure, i.e. roads and railways, mostly consist of rock materials such as sand, gravel and crushed rock aggregates (e.g. Primel and Tourenq, 2000; Smith and Collis, 2001). Rock materials have to meet the constructional, economic and environmental requirements that assume knowledge regarding their mechanical properties. This knowledge will ensure sustainable usage of natural resources, rational extraction of hard rock and material balance (e.g. Primel and Tourenq, 2000; Smith and Collis, 2001). The understanding of petrographic and mechanical properties of rock materials and the relationships between these properties also play an important role concerning rock mechanics, mining and tunnelling (e.g. Heiniö, 1999; Johansson et al., 2009). In an effort to reach a rational level of rock material exploitation, it is
* Corresponding author. Telephone: +46 90 70 67 75, Mobile: +46 70 388 42 64, Fax: +46 90 70 67 71 E-mail addresses: [email protected] (E. Johansson), [email protected] (Š. Lukschová), [email protected] (K. Miškovský)
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desirable that the matters of extraction should be based on genuine knowledge of different rock materials and their mechanical properties. The certification (CE marking) of rock aggregates increases due to the free commerce in Europe. Its importance for future more advanced characterizations of rock products will be the guidance for contractors, clients, geology consultants and researchers dealing with the behaviour of rock materials. This indicates an increasing necessity for detailed investigations of petrographic and mechanical properties. The demands for geological information required by the authorities occur sparsely and can be summarized as a simplified petrographic description including the name of the rock type and the mineralogical composition (e.g. European Committee for Standardization, 1996a). Such information is often used as a description of the product without connection to the mechanical properties and technical suitability. This level of knowledge is not adequate to reach a sustainable exploitation of rock materials and the next generations’ requirements. The future development assumes a systematically and relevantly built-up reference source, focusing on technological knowledge of rock materials. The purpose of the present study is to improve the knowledge concerning petrographic characteristics of igneous and metamorphic rocks and their influences on mechanical properties and to increase the understanding of the performance of rock materials used as aggregates. An upcoming intention is to develop a tool for estimation of aggregates’ mechanical properties using petrographic parameters as basic information. 2 Methods In order to evaluate relationships between the petrographic parameters and mechanical properties of common igneous and metamorphic rocks used as aggregates the following methods were applied. 2.1 Materials and sampling The representative rocks samples were selected partly concerning the most frequent rock types used in road and railway constructions within the region of the Baltic Shield, partly regarding the petrographic parameters that according to the literature (e.g. Brattli, 1992; 1994; Goswami, 1984; Göransson et al. 2004: Kazi and Al-Mansour, 1980; Lindqvist et al., 2007); Miškovský, et al. 2004; Persson and Göransson, 2005; Räisänen, 2004; Räisänen and Torppa, 2005; Åkesson et al. 2001; 2003) and practical experience influence the mechanical properties of rock aggregates. The sample suite, represented by 26 rock types, consists of: 1. Granitoid igneous intrusive rock types and their metamorphic varieties, 17 rock types 2. Gabbroid igneous intrusive rock types and their metamorphic varieties, 9 rock types The sampling was performed from blasted rock segments, which in turn were laboratory crushed, reduced and sieved as stated by standard laboratory routines (e.g. European Committee for Standardization, 1997; 1999). 2.2 Microscopic techniques From each of the collected samples thin sections were prepared and the rock types were analysed using polarization microscopy and the point-count method (Chayes, 1956; Gillespie and Styles, 1999; Glagolev, 1931; Hallsworth and Knox, 1999; Nesse, 2004; Robertson, 1999; Sims and Nixon, 2003). Furthermore, the samples were investigated by semi-automatic petrographic image analysing technique (Lukschová et al., 2009; P ikryl, 2001; Sigmaplot, 2011). The central parameters examined were the degree of foliation, texture (grain size, grain size distribution, frequency of micro-cracks) and mineralogical composition.
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The grain size distribution was graded in a range from even-grained, some uneven-grained to uneven-grained. The degree of crystallisation was added as a supplement to the description. The degree of foliation was ranked into three groups: massive to weakly foliated, foliated and strongly foliated. In context with the statistical performance, the groups were given numerical values (i.e. 1, 2 and 3). The grain size was analysed in terms of two approaches: the measured size in an interval (millimetres) and the number of counted grains per 30 millimetres (modified after the method of Chayes, 1956). Regarding foliated rock types, the counting was carried out along two perpendicularly orientated lines and the number of grains was calculated as a mean value of the measurements. The counted values were used for the statistical evaluation and the interval values are included to clarify the rock description. To emphasise the main minerals affecting the mechanical properties of rock materials, the mineralogical composition presented is somewhat generalised. The feldspar content includes K-feldspars and plagioclases as both groups exhibit comparable physical properties. The pyroxene content comprises pyroxene minerals such as augite and diopside. The content of mica is represented by the common sheet minerals biotite, muscovite and chlorite. Chlorite is included due to its similar behaviour to mica minerals. 2.3 Mechanical methods Standard methods for mechanical analyses of rock aggregates preferentially used in Europe and corresponding national standards measure functional properties rather than properties of rock mechanics. The mechanical properties analysed were resistance to fragmentation, wear and wear by abrasion from studded tyres. In the case of resistance to fragmentation two methods were used; the Los Angeles method and a Swedish modification of the European standard EN 1097-2:1998 “Determination of resistance to fragmentation by the impact test method” (European Committee for Standardization, 1998a; the Swedish Transport Administration, 2001). The resistance to fragmentation by the Los Angeles method and the resistance to wear were analysed on two different fractions (10/14 and 31.5/50 millimetres), as the applications and requirements of aggregates in roads versus railways may differ in the view of grain size fractions. The properties for fragmentation and wear are expressed by the Impact, the Los Angeles and the micro-Deval value respectively. The Studded tyre test (STT) value defines the resistance to wear by abrasion from studded tyres. Due to the temperate climate and use of studded tyres, this method is regularly applied in the Nordic countries. The analyses were performed in accordance with standard test methods (European Committee for Standardization, 1996b; 1998a; 1998b; the Swedish Transport Administration, 2001). 2.4 Statistical evaluation The results of the petrographic and mechanical analyses were evaluated statistically partly using the correlation approaches of Spearman (e.g. Corder and Foreman, 2009) and Pearson (e.g. Montgomery et al., 2006), partly by linear regression analyses (e.g. Montgomery et al., 2006). The 95% confidence interval and the significance level alpha=0.05 were applied. The correlation tests of grain size distribution and degree of foliation were performed according to the Spearman rank correlation as the properties are not quantitatively measured, merely subjectively estimated and ranked. It is not possible to interpret the differences and/or quotients between the values. For the same reason these properties are not analysed for linear regression, but only explained with the results from the correlation tests (correlation coefficient and p-value) and explicated as scatter plots against the mechanical properties. The method of Pearson was used for correlation of the other petrographic parameters.
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3 Results 3.1 Petrographic analyses The main results from the petrographic analyses are summarized in Tables 1-3. The image in Fig. 1 shows examples of some textural properties. The mineralogical composition is expressed in volume percent (vol.%). Table 1 The investigated rock types, degree of foliation and frequency of micro-cracks Sample-ID Rock type Degree of foliation Frequency of micro-cracks (mm/mm2)Granitoids 005 Granite massive 0.2 010 Granite massive 0.1 012 Granite massive 0.8 013 Granite massive 0.5 036 Granite massive 2.1 043 Granite massive 1.5 042 Aplitic granite massive 1.8 024 Aplite massive 2.0 002 Granodiorite massive 0.3 018 Granodiorite massive 1.2 008 Meta-granite (ortho-gneiss) foliated 0.2 014 Meta-granite (ortho-gneiss) foliated 0.4 015 Meta-granodiorite (ortho-gneiss) foliated 1.3 016 Meta-granodiorite (ortho-gneiss) foliated 1.1 021 Meta-granodiorite (ortho-gneiss) strongly foliated 0.7 007 Meta-tonalite (ortho-gneiss) strongly foliated 0.4 027 Quartz porphyry massive 0.0 Gabbroids 001 Gabbro massive 2.0 039 Anorthositic gabbro massive 9.2 003 Diabase massive 2.2 004 Olivine-diabase massive 1.8 011 Olivine-diabase massive 1.7 038 Olivine-diabase massive 7.1 006 Meta-gabbro foliated 0.3 025 Meta-gabbro massive-weakly foliated 0.4 031 Meta-gabbro massive-weakly foliated 1.8
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Table 2 The grain size, grain size distribution and degree of crystallisation Sample-ID Grain size Grain size distribution Degree of crystallisation (mm) ( /30 mm)Granitoids 005 0.2-3 86 uneven-grained holocrystalline 010 0.5-1 98 even-grained holocrystalline 012 0.7-5 44 uneven-grained holocrystalline 013 1-4 25 uneven-grained holocrystalline 036 0.4-80 1 uneven-grained holocrystalline 043 0.4 114 even-grained holocrystalline 042 0.3 115 even-grained holocrystalline 024 0.2-0.3 160 even-grained fluidal 002 0.5-2 98 some uneven-grained holocrystalline 018 0.4-2 95 some uneven-grained holocrystalline 008 0.2-1 163 even-grained blastogranitic 014 0.3-5 33 uneven-grained blastoporphyric 015 0.2-3.5 113 uneven-grained blastogranitic 016 0.2-3.5 95 uneven-grained blastoporphyric 021 0.4-4 46 uneven-grained blastogranitic 007 0.5-6 137 uneven-grained blastoporphyric 027 - - porphyric hemicrystalline Gabbroids 001 0.3-4 79 uneven-grained ophitic 039 2-12 10 uneven-grained fluidal 003 0.4-1.5 133 even-grained ophitic 004 0.3-1.2 148 even-grained ophitic 011 0.5-1.5 89 even-grained ophitic 038 1-7 26 uneven-grained ophitic 006 0.1-2.5 25 uneven-grained blasto-ophitic 025 0.5-1.5 96 some uneven-grained blastogranitic 031 0.3-1.5 112 some uneven-grained blasto-ophitic
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Table 3 The mineralogical composition (vol.%)* Sample-ID Fsp Qtz Mc Px Amph Ol Ct Opq Oth Granitoids 005 64.3 32.7 2.1 - - - 0.5 0.4 - 010 69.6 22.0 8.1 - - - - - 0.3 012 59.0 32.6 8.2 - - - 0.2 - - 013 59.7 29.1 9.6 - - - - - 1.6 036 70.2 17.0 10.8 - 1.3 - 0.2 0.3 0.2 043 69.7 26.9 3.1 - - - - - 0.3 042 59.9 29.1 11.0 - - - - - - 024 59.9 37.1 3.0 - - - - - - 002 75.7 22.2 2.1 - - - - - - 018 58.2 31.9 5.1 - 4.8 - - - - 008 50.1 36.5 13.1 - - - - 0.3 - 014 55.6 25.5 18.2 - - - - 0.7 - 015 45.9 34.9 18.6 - - - - 0.6 - 016 38.4 43.4 17.0 - - - - 1.2 - 021 36.6 42.6 20.8 - - - - - - 007 46.9 20.5 29.5 - 0.3 - - - 2.8 027 15.8 70.6 8.2 - - - - - 5.4 Gabbroids 001 57.9 - 5.0 25.6 - 11.5 - - - 039 84.6 - 0.5 8.1 - 6.6 0.1 - 0.1 003 67.2 - 0.9 20.6 - 7.8 - 3.5 - 004 60.5 - 1.4 19.1 0.6 12.4 - 6.0 - 011 62.2 - 3.1 11.0 - 20.4 - 3.3 - 038 54.4 - 0.9 21.3 - 17.8 - 5.6 - 006 33.0 6.9 13.3 8.0 37.4 - - - 1.4 025 48.5 - 6.0 26.0 12.5 - - 7.0 - 031 69.1 - 10.7 8.5 10.3 - - 1.4 - * Fsp=feldspar; Qtz=quar-tz; Mc=mica; Px=pyroxene; Amph=amphibole; Ol=olivine; Ct=calcite; Opq=opaque; Oth=others
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Fig. 1 a) fine-grained granite, b) coarse-grained granite, c) even-grained granite, d) uneven-
grained meta-granodiorite, e) massive gabbro, f) strongly foliated meta-tonalite, g) micro-cracks in pyroxene and olivine, h) micro-cracks in feldspar
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3.2 Mechanical analyses The results from the mechanical tests are given in Table 4. The values are all expressed in weight percent (wt%). Table 4 The mechanical properties (wt%)* Sample-ID LARB LA MDERB MDE AN SZGranitoids 005 11 20 3 4 9.7 49 010 - 26 5 6 11.1 48 012 12 24 5 7 12.9 49 013 17 39 7 11 19.2 66 036 34 37 15 13 21.8 53 043 17 24 4 5 8.9 48 042 21 24 6 7 10.1 44 024 13 19 3 5 7.6 38 002 13 23 4 5 12.0 62 018 17 21 - 6 9.8 35 008 - 21 5 6 10.1 47 014 - 30 9 9 14.7 50 015 17 24 - 9 12.6 40 016 17 25 - 12 13.7 53 021 19 37 16 18 24.7 51 007 - 22 11 14 18.7 42 027 16 17 4 2 5.6 41 Gabbroids 001 9 15 9 9 13.1 35 039 16 22 9 11 16.8 50 003 11 22 9 10 15.2 48 004 9 17 7 8 12.3 49 011 10 19 8 10 13.5 41 038 19 24 11 10 14.6 45 006 7 15 8 8 11.5 40 025 11 16 6 7 9.8 34 031 12 15 6 7 9.2 30 * LARB=Los Angeles value, fraction 31.5/50 mm; LA=Los Angeles value, fraction 10/14 mm; MDERB=micro-Deval value, fraction 31.5/50 mm; MDE=micro-Deval value, fraction 10/14 mm; AN=studded tyre test value, fraction 11.2/16 mm; SZ=impact value, fraction 11.2/16 mm 3.3 Correlation analyses The statistical correlation tests are presented in Tables 5-6. Values in bold are different from 0 with a significance level alpha=0.05. Table 5 The Spearman correlation tests of the mechanical properties and grain size distribution
and degree of foliation* Property LARB LA MDERB MDE AN SZ r p r p r p r p r p r p Granitoids n=17 Grain size distribution 0.147 0.628 0.506 0.040 0.589 0.029 0.704 0.002 0.768 0.0005 0.471 0.058 Degree of foliation 0.322 0.279 0.195 0.450 0.592 0.028 0.633 0.007 0.515 0.036 0.011 0.967 Gabbroids n=9 Grain size distribution 0.162 0.678 -0.132 0.744 0.434 0.250 0.133 0.744 0.080 0.843 -0.116 0.776 Degree of foliation -0.552 0.121 -0.420 0.250 -0.070 0.843 -0.211 0.581 -0.274 0.463 -0.137 0.708 * LARB=Los Angeles value, fraction 31.5/50 mm; LA=Los Angeles value, fraction 10/14 mm; MDERB=micro-Deval value, fraction 31.5/50 mm; MDE=micro-Deval value, fraction 10/14 mm; AN=studded tyre test value, fraction 11.2/16 mm; SZ=impact value, fraction 11.2/16 mm; r=Spearman’s rank correlation coefficient; p=p-value; n=number of samples
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Table 6 The Pearson correlation tests of the mechanical properties and textural properties and mineralogical composition*
Property LARB LA MDERB MDE AN SZ r p r p r p r p r p r p Granitoids n=17 Mica 0.361 0.226 0.280 0.276 0.704 0.005 0.753 0.0005 0.592 0.012 -0.088 0.736 Quartz -0.309 0.304 -0.344 0.176 -0.221 0.447 -0.239 0.355 -0.358 0.158 -0.289 0.261 Feldspar 0.089 0.773 0.165 0.528 -0.176 0.548 -0.174 0.503 0.006 0.981 0.332 0.207 Grain size -0.512 0.089 -0.810 0.0001 -0.544 0.055 -0.437 0.091 -0.651 0.006 -0.554 0.026 Micro-cracks 0.556 0.049 0.141 0.590 0.189 0.519 0.160 0.541 0.061 0.815 -0.261 0.312 Gabbroids n=9 Mica -0.520 0.151 -0.765 0.016 -0.505 0.166 -0.696 0.037 -0.745 0.021 -0.714 0.031 Pyroxene 0.021 0.958 0.032 0.935 0.140 0.720 -0.120 0.759 -0.041 0.917 -0.072 0.854 Feldspar 0.461 0.212 0.442 0.233 0.094 0.809 0.504 0.166 0.503 0.168 0.332 0.383 Olivine 0.279 0.467 0.516 0.155 0.586 0.097 0.618 0.076 0.535 0.138 0.427 0.252 Grain size -0.453 0.221 -0.293 0.444 -0.537 0.136 -0.419 0.262 -0.375 0.320 -0.117 0.765 Micro-cracks 0.863 0.003 0.762 0.017 0.645 0.061 0.723 0.028 0.741 0.022 0.548 0.126 * LARB=Los Angeles value, fraction 31.5/50 mm; LA=Los Angeles value, fraction 10/14 mm; MDERB=micro-Deval value, fraction 31.5/50 mm; MDE=micro-Deval value, fraction 10/14 mm; AN=studded tyre test value, fraction 11.2/16 mm; SZ=impact value, fraction 11.2/16 mm; r=Pearson’s correlation coefficient; p=p-value; n=number of samples 4 Evaluation and discussion The functional properties of the methods used for testing of aggregates are not fully explored. However, some generally premises can be explicated. Resistance to fragmentation by means of the values for LARB, LA and SZ corresponds to impact strength and thus, the intrinsic brittleness of the rock. The ability to resist mechanical abrasion is comparable with resistance to wear by means of the values for MDERB and MDE and it is strongly connected to hardness. The resistance to wear by abrasion of studded tyres by means of the AN value can be explained as a method measuring a combination of impact strength and mechanical abrasion. A common feature of all mechanical methods presented is the interpretation of the results; the lower values, the better mechanical properties (quality of the rock materials). A decreasing grain size has a positive effect upon the Los Angeles value, 10/14 mm, the Studded tyre test value and the Impact value (Tables 2, 4, 6; Fig. 2). On the other hand, only a weak positive trend concerning the influence of diminishing grain size on the other mechanical properties was obtained (Tables 2, 4, 6). Probably, this can be partially explained by the fact that both the micro-Deval values measure wearing and grain size seem to be less susceptible to wear than to fragmentation. Nevertheless, the Los Angeles value tested on fraction 31.5/50 mm shows no associations to the variations of grain size. The influence of grain size on mechanical properties has been thoroughly investigated by several authors (e.g. Brattli; 1992; Goswami, 1984; Kazi and Al-Mansour, 1980; Åkesson et al. 2001) and the results are unanimous; the resistance to fragmentation commonly improves as the grain size decreases.
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Fig. 2 The Los Angeles value, 10/14 mm (LA), the Studded tyre test value (AN) and the Impact
value (SZ) plotted against grain size for granitoid rock types The content of mica in granitoids correlates acceptably with the micro-Deval values and with the Studded tyre test value (Tables 3, 4, 6; Fig. 3). Increasing mica content shows a negative effect upon the resistance to wear and wear by abrasion from studded tyres. However, mica content does not indicate any influence on the Los Angeles values and the Impact value (Tables 3, 4, 6). A study by Miškovský et al. (2004) established the opposite relation between the mica content of granitoid rocks and the Impact value; a rising content of mica improves the resistance to fragmentation by impact. The present study and the one by Miškovský et al. are comparable. The greatest dissimilarity appears in the case of foliation as the investigation by Miškovský et al. is assumed to comprise rock samples with a lower degree of foliation.
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35.636 0.1080.6570.810
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Fig. 3 The micro-Deval value, 31.5/50 mm (MDERB), the micro-Deval value, 10/14 mm (MDE)
and the Studded tyre test value (AN) plotted against mica content for granitoid rock types
The content of quartz (in granitoids) exhibits a positive trend for all the mechanical properties analysed; increasing quartz content results in lower values (Tables 3, 4, 6). As the characteristics of quartz minerals include both high hardness and low cleavage, the tendency obtained was taken into account. However, the analytical results attain too weak associations to establish the results. The contents of quartz are narrowly accumulated and the homogenous input may be one crucial contribution causing failure in the correlation and regression analyses. Due to the cleavage of the feldspars it was assumed that the content of feldspar would play an important role regarding the mechanical properties measuring fragmentation of granitoid rocks. A deterioration of the resistance to fragmentation in connection with increasing feldspar content was expected. However, the results show no relationships between the properties (Table 6). The previous study by Miškovský et al. (2004) stated the assumption that the Impact value is negatively influenced by increasing content of feldspar. Investigating mafic igneous rocks, Brattli (1992) found that the variations in feldspar content have a stronger effect upon the fragmentation than upon the wearing properties. It was explained as a consequence of weakness along the feldspars’ cleavage planes.
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Despite the expectation that every test method measuring resistance to fragmentation should be influenced by the frequency of micro-cracks of granitoid rocks, the Los Angeles test of fraction 31.5/50 mm was the only method corresponding to the variable (Tables 1, 4, 6; Fig. 4). The Los Angeles value gradually becomes higher with increasing frequency of micro-cracks.
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Fig. 4 The Los Angeles value, 31.5/50 mm (LARB) plotted against frequency of micro-cracks
for granitoid rock types The associations among the grain size distribution and the Los Angeles value, 10/14 mm, the micro-Deval values and the Studded tyre test value show that uneven-grained granitoid rocks obtain poorer results from the mechanical analyses than even-grained ones (Tables 2, 4, 5; Fig. 5). The trend is similar to the granitoids’ degree of foliation, i.e. the higher degree of foliation, the poorer values regarding mechanical strength (Table 1, 4, 5; Fig. 6). In this case, the responding mechanical properties are resistance to wear and wear by abrasion from studded tyres.
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Fig. 5 The Los Angeles value, 10/14 mm (LA), the micro-Deval value, 31.5/50 mm (MDERB),
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Fig. 6 The micro-Deval value, 31.5/50 mm (MDERB), the micro-Deval value, 10/14 mm (MDE)
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Correlations among mica content of gabbroids and the Los Angeles value, 10/14 mm, the micro-Deval value, 10/14 mm, the Studded tyre test values and the Impact value are found and presented in Tables 3, 4, 6; Fig. 7. The mechanical properties improve with increasing mica content. This indicates that mica has a reinforcing effect upon the mechanical strength of gabbroids. The mentioned effect is supposed to partially depend on the mica grains’ uniform distribution and the fact that the mica minerals in the sample suite selected are fine-grained and exhibit no preferred orientation. It can also be connected to the sericitization of feldspar (e.g. Åkesson et al., 2004), which occurs abundantly in the metamorphic varieties. The resistance to fragmentation and wear of the coarser fractions show a very slight positive tendency (decreasing) against increasing mica content, but it is too weak to confirm (Tables 3, 4, 6).
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0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14
micro
Devalvalue,10/14mm
(wt%
)
Mica content (vol.%)
0
2
4
6
8
10
12
14
16
18
20
0 2 4 6 8 10 12 14
Stud
dedtyre
testvalue(w
t%)
Mica content (vol.%)
0
5
10
15
20
25
30
35
40
45
50
55
0 2 4 6 8 10 12 14
Impa
ctvalue(w
t%)
Mica content (vol.%)
Fig. 7 The Los Angeles value, 10/14 mm (LA), the micro-Deval value, 10/14 mm (MDE), the
Studded tyre test value (AN) and the Impact value (SZ) plotted against mica content for gabbroid rock types
The frequency of micro-cracks occurring in gabbroid rocks exhibit a negative influence on the Los Angeles values, the micro-Deval value, 10/14 mm and the Studded tyre test value (Tables 1, 4, 6; Fig. 8), while the micro-Deval value, 31.5/50 mm and the Impact value only show a poor traceable trend in the same direction (Tables 1, 4, 6).
2
21.048 0.5860.5850.765
0.016
y xRrp
2
9.904 0.2190.4850.696
0.037
y xRrp
2
14.748 0.4010.5560.745
0.021
y xRrp
2
46.503 1.1160.5100.714
0.031
y xRrp
16
0
2
4
6
8
10
12
14
16
18
20
22
24
0 1 2 3 4 5 6 7 8 9 10
LosAng
eles
value,31
.5/50mm(w
t%)
Frequency of micro cracks (mm/mm2)
024681012141618202224262830
0 1 2 3 4 5 6 7 8 9 10
LosAng
eles
value,10/14mm
(wt%
)
Frequency of micro cracks (mm/mm2)
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8 9 10
micro
Devalvalue,10
/14mm
(wt%
)
Frequency of micro cracks (mm/mm2)
0
2
4
6
8
10
12
14
16
18
20
22
0 1 2 3 4 5 6 7 8 9 10
Stud
dedtyre
testvalue(w
t%)
Frequency of micro cracks (mm/mm2)
Fig. 8 The Los Angeles value, 31.5/50 mm (LARB), the Los Angeles value, 10/14 mm (LA), the
micro-Deval value, 10/14 mm (MDE) and the Studded tyre test value (AN) plotted against frequency of micro-cracks for gabbroid rock types
In efforts to explain partial cooperation of several petrographic agents on the one mechanical property, multiple-regression analyses have to be performed and a higher number of samples is required. The rather low number of samples, especially regarding the gabbroids, is a shortage to consider. This fact can be a contribution to the somewhat straggling results; partly confirming, partly disaffirming expected results and previous research. The disparity of results concerning the different size fractions’ response to the mechanical properties is remarkable. This is particularly obvious in the case of the Los Angeles values using test fractions 10/14 and 31.5/50 mm respectively. On the other hand, the two methods for the micro-Deval value are fully comparable in principle. 5 Conclusions The results of the present study show the complex pattern of associations between the granitoid and gabbroid intrusive rocks’ mechanical properties tested with methods used in the aggregate industry and their petrographic variables.
2
8.442 1.0540.745
0.8630.003
y xRrp
2
15.740 0.8770.580
0.7620.017
y xRrp
2
7.878 0.3420.522
0.7230.028
y xRrp
2
11.115 0.6000.549
0.7410.022
y xRrp
17
The petrographic characteristics of granitoids influencing mechanical properties are mainly grain size, mica content and frequency of micro-cracks. The micro-Deval value, 10/14 mm, the Studded tyre test value and the Impact value represent the properties positively responding to diminishing grain size. Increasing mica content effects the wearing properties and wear by abrasion from studded tyres in a negative way. A rising frequency of micro-cracks deteriorates the Los Angeles value, 31.5/50 mm. Finally, uneven-grained or strongly foliated rock types indicate tendencies to impair the mechanical strength. The mechanical properties of gabbroid rocks seem to be dependent on the content of mica and frequency of micro-cracks. In contrast to the granitoids, an increasing amount of mica improves the Los Angeles and the micro-Deval values, 10/14 mm, the Studded tyre test value and the Impact value. Increasing frequency of micro-crack influences the resistance to fragmentation, wear (for the 10/14 mm fraction) and wear by abrasion from studded tyres negatively. Together with previous studies the present study reveals a base for the future tool to interconnect mechanical properties and technical suitability of rock aggregates with their petrographic properties. It is an effort necessary for the challenge to reach a sustainable usage of natural resources. This motivated the initial attempt to unify geology and engineering in a common approach for evaluation of rock aggregates’ mechanical properties using petrographic characteristics as key parameters. Acknowledgements The authors want to thank the Swedish Transport Administration (STA), the Swedish National Road and Transport Research Institute (VTI), Envix Nord AB and the project No. 103/09/P139, supported by the Czech Science Foundation for good co-operation and support. References Brattli, B., 1992. The influence of geological factors on the mechanical properties of basic
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