cement-bound road base materials - weinstein.ma delft report on cement-bound road base...

CEMENT-BOUND ROAD BASE MATERIALS Report 7-11-218-1

Prepared by

Pengpeng Wu, MSc

Delft University of Technology

Supervised by

Prof.dr.ir. A.A.A. Molenaar and Ir. L.J.M. Houben

Delft University of Technology

In cooperation with

PowerCem Technologies, Netherlands

July 2011

I

TERM DEFINATION

In this literature study the technical terms are defined as listed below.

Additive A chemical or material applied atop or mixed into amaterial to alter or improve the general quality or tocounteract undesirable properties.

Atterberg limits Soil properties that help to identify a given soil interms of its water retentively and plasticity and theseconsistency limits are Liquid Limit, Plastic Limit andPlasticity Index.

Bitumen Black, viscous liquid to solid obtained as residue frompetroleum coke by preparation or naturally derived.Bitumen is a binder for asphalt mixtures.

California Bearing Ratio A penetration test for evaluation of the load-carryingcapacity (mechanical strength) of soils, expressed as apercentage of a standard.

Characterisation In materials science, it refers to the use of externaltechniques to probe into the internal structure andproperties of a material in form of actual materialstesting, or analysis, for instance in some form ofmicroscope.

Clay A general term for colloid sized (<0.002 mm inequivalent diameter) fine particles of inorganic(mineral) origin in soil that has a high Plasticity Indexin relation to the Liquid Limit.

Crystalline Having a definite form, that is the atoms in a solidmatter are arranged in a regular pattern, and there is assmallest volume element that by repetition in threedimensions describes the crystal.

Capillary Ability of a material to water-sucking and holding itabove the phreatic surface.

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Illite It is a non-expanding, clay-sized, micaceous mineral.A hydrous alluminosilicate clay mineral withstructurally mixed mica and smectite or vermiculite,similar to montmorillonite but containing potassiumbetween the crystal layers. Also referred to as hydrousmica or mica. It has a cation exchange capacity (20-40me/100 g).

Kaolinite It is a layered clay with silicate mineral, with onetetrahedral sheet inked through oxygen atoms to oneoctahedral sheet of alumina octahedral. It has a lowshrink-swell capacity and a low cation exchangecapacity (1-15 me/100 g). Rocks that are rich inkaolinite are known as china clay or kaolin.

Maximum dry density The highest dry density obtainable when using aspecified amount of compaction effort (Standard orModified Proctor) on a soil with various moisturecontents.

Moisture content That portion of the total dry mass of material thatexists as water, expressed in percentage.

Montmorillonite It is a very soft phyllosilicate mineral that typicallyforms in microscopic crystals, forming clay. A memberof the smectite family that is a 2:1 clay, meaning that ithas 2 tetrahedral sheets sandwiching a centraloctahedral sheet. Its water content is variable and itincreases greatly in volume when it absorbs water. Ithas a high cation exchange capacity (60-100 me/100g).

Modulus of elasticity Relationship between a load and the resulting elasticdeformation of the material.

Optimum moisture content The percentage of water (by mass) in material thatallows it to be compacted to the greatest density.

Permeability (Soil) Measure of the ability of a soil to transmit water andair from upper to lower soil layers.

Petroleum An oily flammable bituminous liquid that may varyfrom almost colorless to black, and that is a complex

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mixture of hydrocarbons with small amounts of othersubstances.

Porosity The volume of all the open spaces (pores) between thesolid grains of a soil/material.

Proctor test Standard Proctor compaction effort using a 2,49 kghammer, falling through 305 mm with 3 layers eachcompacted by 55 blows yielding a total energy of 0,15kWh/m3.

Soil Naturally occurring material that is used forconstruction of pavement layers

Soil stabilizer A chemical or material mixed into a material topermanently increase or improve density, compaction,shear strength, and/or changes in plasticitycharacteristics. In addition, a chemical or mechanicaltreatment designed to increase or maintain the stabilityof a mass of soil/material or to otherwise improve itsengineering properties.

Strength (Soil) The capacity of a soil to withstand forces withoutexperiencing failure, whether by rupture,fragmentation, or shear.

Unconfined compressive test In this test, a soil sample is compressed to measure itsstrength. It is a measure of the shearing resistance ofcohesive soils, which may be undisturbed orremoulded samples, using strain-controlled applicationof the axial load. It is also a measure of thecompressive strength of soils, stabilized with bitumen,lime or cement or a combination.

V

LIST OF SYMBOLS

cf Unconfined compressive strength

tf Flexural tensile strength

itf Indirect tensile strength

sE Static modulus of elasticity

dE Dynamic modulus of elasticity

VPulse velocity

NNumber of load repetitions

εApplied strain level

tε Flexural strain at break

σ Applied stress

tσ Ultimate flexural stress (flexural strength)

SN Ratio of applied stress and ultimate stress

η Porosity of specimen

uC Coefficient of uniformity of grain size distribution curve

cC Curvature index of soil distribution curve

Ac Activity of clay

fE Stiffness modulus in flexure

eqN Number of equivalent load repetitions

VII

LIST OF ACRONYMS

OMC Optimum Moisture Content

PI Plasticity Index

PL Plasticity Limit

LL Liquid Limit

SL Shrinkage Limit

UCS Unconfined Compressive Strength

USCS Unified Soil Classification System

AASHTO American Association of State Highway and Transportation Officials

ASTM American Society for Testing and Materials

CBR California Bearing Ratio

NEN European Norms

PCT PowerCem Technologies

MPD Maximum Proctor Density

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LIST OF FIGURES

Fig. 2.1 Liquid limit for stabilized marl samples at different curing time ............. 8Fig. 2.2 Dry and wet CBR values for natural and stabilized marl soil .................. 9Fig. 2.3 Initial strength development of a lime and cement stabilization .............. 9Fig. 2.4 UCS of cement stabilized soil as a function of lime and cement content . 9Fig. 2.5 The compressive strength of cement stabilized and lime stabilized soil .10Fig. 2.6 UCS at optimum water content for cement stabilized fly ash ................. 11Fig. 2.7 Uniaxial compressive strength of fly ash stabilized clay ........................ 11Fig. 2.8 The compressive strength of soil stabilized with multiple soils ..............12Fig. 3.1 Typical soil particle size distribution curves ..........................................16Fig. 3.2 Particle size distribution curves for various soils ...................................17Fig. 3.3 Particle size gradation coefficient ..........................................................17Fig. 3.4 Relationship between clay content and plasticity index .........................19Fig. 3.5 Volume change of a soil specimen during drying ...................................20Fig. 3.6 Phases of soil and Atterberg limits ........................................................20Fig. 3.7 AASHTO plasticity chart ......................................................................22Fig. 3. 8 USCS classification chart .....................................................................22Fig. 3.9 USCS plasticity chart ............................................................................23Fig. 3.10 Effect of addition of cement on the swell ............................................25Fig. 3.11 Reduction of silt-clay content due to cement modification ...................25Fig. 3.12 Comparison of CBR with RoadCem ...................................................30Fig. 4.1 Particle size analysis of coarse grained soils using sieves ......................34Fig. 4.2 Wet sieving for particle size distribution of fine grained materials .........34Fig. 4.3 Cone equipment ....................................................................................35Fig. 4.4 Example of relationship between water content and cone penetration ....35Fig. 4.5 Soil pat after groove closed ...................................................................36Fig. 4.6 Test for Plastic Limit .............................................................................36Fig. 4.7 Moisture-density curves of a cohesive soil for different compaction ......39Fig. 4.8 Effect of compaction methods on the density ........................................39Fig. 4.9 Effect of compaction methods on the compressive strength .................40Fig.4.10 Dry density-moisture curves for sandy clay soil ...................................40Fig. 4.11 Dry Density-Moisture curves for a sand stabilized...............................40Fig. 4.12 Dry density-moisture curves for a range of soil types ..........................41Fig. 4.13 Effect of a time lapse on the dry density and UCS ...............................42Fig. 4.14 Soil gradings for cement-bound mixture..............................................43Fig. 4.15 Coded test conditions for the central composite rotatable design .........44Fig. 4.16 Variation of strength at 1, 7 and 28 curing days of samples ..................46Fig. 4.17 Relationship between UCS and curing temperature .............................46Fig. 5.1 SEM photos of cement stabilized sand specimens after testing ..............50Fig. 5.2 Relationship between UCS and curing period .......................................51Fig. 5.3 Relationship between moisture content and UCS ..................................52

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Fig. 5.4 Relationship between water to cement ratio and UCS............................52Fig. 5.5 28-day strength of cement treated clay ..................................................53Fig. 5.6 Effect of curing age on the unconfined compressive strength ................54Fig. 5.7 Compressive strength for dry and wet specimens at 28 days ..................54Fig. 5. 8 28-day strength variation with number of wetting ................................55Fig. 5.9 Compressive strength of samples at different dry density ......................55Fig. 5. 10 Variation in the 1, 7 and 28 curing days strength of samples ...............56Fig. 5.11 Effect of curing age on compressive strength ......................................56Fig. 5.12 SEM images of RoadCem and Cement treated soil/material ................57Fig. 5.13 Indirect tensile test ..............................................................................58Fig. 5. 14 Effect of cement content on the indirect tensile strength at 28 days ....58Fig. 5.15 Variation of the indirect tensile strength of cement ..............................58Fig. 5.16 Variations of the indirect tensile strength with cement content .............59Fig. 5.17 Relationship between UCS and indirect tensile strength ......................59Fig. 5.18 Flexural tensile strength plotted against compressive strength .............60Fig. 5.19 Typical stress-strain curve for cement stabilized materials ...................61Fig. 5.20 Typical unconfined compressive stress-strain relationships .................61Fig. 5.21 Stress-strain curve for samples under compression ..............................62Fig. 5.22 Influence of clay content on the modulus of elasticity .........................62Fig. 5.23 Cement-bound granular mixtures of tensile strength ............................63Fig. 5.24 Dynamic modulus and pulse velocity ..................................................64Fig. 5.25 28-day compressive strength and dynamic modulus of elasticity .........64Fig. 5.26 Relationship between dynamic modulus and flexural strength .............64Fig. 5. 27 Dynamic modulus and modulus of rupture .........................................65Fig. 5.28 Measurement of dynamic modulus of elasticity ...................................65Fig. 5.29 Comparison of damped harmonic vibration with RoadCem .................66Fig. 5.30 Dynamic flexure tests for 28-day curing time ......................................66Fig. 5.31 Stress ratios versus number of cycles to failure ...................................67Fig. 5.32 General fatigue curves for cement-treated bases ..................................68Fig. 5.33 Effect of loading frequency on stress/life relationship for concrete ......68Fig. 5.34 Fatigue behavior of cement bound materials .......................................69Fig. 5.35 Weight loss in wet-dry testing of soil stabilized cement and lime .......70Fig. 5.36 Change in weight loss with exposure period in the samples tested for .71Fig. 5.37 Effect of cement content on the water permeability .............................71Fig. 5.38 Water absorption versus binder quality for specimens at 28 days .........72Fig. 5.39 Capillary rise with time for 28-days cured specimens ..........................72Fig. 6.1 Reflection cracks ..................................................................................75Fig. 6.2 Cracking as a result of t shrinkage stress, strength and time ..................76Fig. 6.3 Effect of cement content on shrinkage ...................................................77Fig. 6.4 Effect of sand and cement content on the shrinkage ..............................78Fig. 6.5 Development of shrinkage during first 28 days .....................................78Fig. 6.6 Variation of final shrinkage at 28 days with mixing water content .........79Fig. 6.7 Effect of density and moisture on shrinkage ..........................................79Fig. 6.8 7-day UCS vs. beam shrinkage .............................................................80

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Fig. 6.9 Addition of fly ash to reduce drying shrinkage ......................................81Fig. 6.10 Stabilization with RoadCem showing no cracks after 4 years ............82Fig. 6.11 Picture from an electron microscope of the crystalline structure ..........82Fig. 7.1 Comparison of calculation for traditional and RoadCem constructions ..85Fig. 7.2 Strains of the bounded layer over the width of the road .........................87Fig. 7.3 Strains in the bounded layers in the length (X) of the road with .............87Fig. 7.4 Stresses in the bottom of the bounded layers in the width of the road ....88Fig. 7.5 Stresses in the bottom of the bounded layers in the length of the road ...88Fig. 7.6 Deflections in the traditional structure ...................................................90Fig. 7.7 Deflections in the RoadCem structure ...................................................90

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LIST OF TABLES

Table 2.1 Application of traditional stabilization methods ................................... 6Table 2.2 Stabilization methods most suitable for specific applications ............... 6Table 3.1 Particle size ranges in different countries ............................................16

Table 3.2 Indication of uC and cC ....................................................................18

Table 3.3 Three physical states of the soil-aggregate mixtures ............................18Table 3.4 Plasticity and dry strength related to Plasticity Index PI ......................19Table 3.5 Soil classification according to AASHTO ...........................................21Table 3.6 Symbols used in USCS .......................................................................22Table 3.7 Examples of the effect of cement-modification ...................................23Table 3.8 Cement requirement for different soil types ........................................24Table 3. 9 Relationship between shrinkage limit, PI and swell potential .............25Table 3.10 Average change in properties for clay soils .......................................27Table 3.11 Cement requirement of different soils ...............................................28Table 3.12 DCP-CBR strength for stabilized panels with different stabilizers ...30Table 4.1 Cone penetration requirement ............................................................ 35Table 4.2 Summary of sample preparation methods .......................................... 38Table 4.3 Dimensions of the new cylindrical test mould .................................... 38Table 4.4 Summary of the Proctor test and modified Proctor test ...................... 38Table 4.5 Maximum dry density and moisture contents of soil-cement .............. 41Table 4.6 Cement content requirement for soils................................................. 43Table 4.7 Minimum cement content according to the grain sizes ....................... 44Table 4.8 Variables for central composite design ............................................... 44Table 6. 1 Effect of fines content on soil-cement crack pattern ...........................80Table 7.1 Stresses and strains at the bottom of the bounded layers......................87Table 7.2 The results of lifetime for traditional and RoadCem construction ........89

XV

TABLE OF CONTENTS1 INTRODUCTION .................................................................................................. 1

1.1 BACKGROUND .......................................................................................... 11.2 PROBLEMS ................................................................................................. 21.3 OBJECTIVES ............................................................................................... 21.4 CONTENT OF LITERATURE REVIEW ..................................................... 2

2 STABILIZATION AGENT ..................................................................................... 52.1 BITUMEN .................................................................................................... 72.2 LIME ............................................................................................................ 72.3 FLY ASH .....................................................................................................102.4 CEMENT ....................................................................................................122.5 CONCLUSIONS .........................................................................................12

3 MATERIALS FOR CEMENT STABILIZATION ................................................. 153.1 SOIL ............................................................................................................15

3.1.1 Particle size and soil structure.............................................................153.1.2 Atterberg limits ..................................................................................193.1.3 Soil classification ...............................................................................213.1.4 Shrinkage and swell .......................................................................... 243.1.5 Organic content ..................................................................................26

3.2 CEMENT ....................................................................................................273.3 WATER .......................................................................................................283.4 ADDITIVE ..................................................................................................29

3.4.1 Traditional additives ...........................................................................293.4.2 RoadCem ...........................................................................................30

3.5 CONCLUSIONS .......................................................................................................... 314 PRELIMINARY INVESTIGATIONS ................................................................... 33

4.1 SOIL TESTS ................................................................................................334.1.1 Particle size distribution .....................................................................334.1.2 Liquid Limit and Plastic Limit ............................................................344.1.3 Chemical analysis...............................................................................36

4.2 COMPACTION OF MIXTURE ...................................................................374.2.1 Compaction test..................................................................................374.2.2 Factors influencing compaction ..........................................................39

4.3 MIX COMPOSITION..................................................................................424.3.1 Requirements for materials .................................................................424.3.2 Mix design method .............................................................................44

4.4 CURING CONDITIONS .............................................................................454.5 CONCLUSIONS .........................................................................................46

5 MAIN MECHANICAL PROPERTIES ................................................................. 495.1. COMPRESSIVE STRENGTH ....................................................................495.2 TENSILE STRENGTH ................................................................................57

5.2.1 Indirect tensile strength ......................................................................575.2.2 Flexural tensile strength .....................................................................60

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5.3 ELASTIC MODULUS ................................................................................615.3.1 Static modulus ....................................................................................615.3.2 Dynamic modulus ..............................................................................63

5.4 FATIGUE PROPERTIY ...............................................................................665.5 DURABILITY .............................................................................................695.6 WATER PERMEABILITY AND ABSORPTION.........................................715.7 CONCLUSIONS .........................................................................................73

6 CRACKING BEHAVIOR .................................................................................... 756.1 SHRINKAGE ..............................................................................................766.2 FACTORES INFLUNCING SHRINKAGE .................................................776.3 METHODS OF CONTROLLING ...............................................................816.4 CONCLUSIONS .........................................................................................82

7 EFFECTS OF A FLEXURAL STABILIZATION ................................................. 837.1 INTRODUCTION .......................................................................................837.2 ASSUMPTIONS ..........................................................................................837.3 DESIGNS ....................................................................................................847.4 CALCULATION METHOD ........................................................................857.5 DEFLECTIONS ..........................................................................................897.6 CONCLUSIONS ....................................................................................... 90

8 CONCULSIONS AND RECOMMENDATIONS ................................................. 938.1 CONCLUSIONS .........................................................................................938.2 RECOMMENDATIONS..............................................................................94

REFERENCES ........................................................................................................ 95Appendix A ........................................................................................................... 101Appendix B ........................................................................................................... 102Appendix C ........................................................................................................... 107

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CHAPTER 1

INTRODUCTION

1.1 BACKGROUND

High quality road infrastructure is of utmost importance for economic developmentand growth of any country in the world. As a consequence of economic growth, roadtraffic is increasing in vehicle numbers and in truck axle loads. This requiresextension of the road network. Especially for the main road network availability fortraffic should be as high as possible (Molenaar, 2010). Both asphalt and concretepavement structures can be designed and constructed. However, both types ofpavement require a base with good structural performance and a long service lifebelow the asphalt or concrete. Also for the demand of less construction time andresistance to natural disasters, new road materials with environmental friendlytechnology are increasingly required.

For road bases, there is a variety of soils or granular materials available forconstruction, but they may exhibit insufficient properties (e.g. low bearing capacity,susceptibility for frost action), which then results in substantial pavement distress andreduction of the pavement life. However, the properties of soil can be improved byaddition of a stabilizing agent such as cement, bitumen and lime. Among thesedifferent stabilized materials, cement-bound materials develop a quite high stiffnessand strength, and exhibit good performance for pavement serviceability and highdurability.

The soil or granular materials to be stabilized can be almost any combination of sand,silt, clay, gravel, or crushed stone. When there are not many suitable soils availablefor construction, the stabilization of less suitable soil with cement becomes abeneficial option. Also there exists a large amount of waste materials and recycledaggregates which could be widely available near the work sites, which can not onlylower the construction and transportation cost but also save natural resources and

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offer much environmental benefit.

1.2 PROBLEMS

In practice, when the granular material is stabilized, the stabilization of soil improvesthe soil gradation, reduces the plasticity index or swelling potential of soil, andincreases the stiffness, strength and durability, which consequently reduces therequired thickness of the pavement structure. However, the hardening cement-boundmaterials exhibit shrinkage cracks and susceptibility to overloading. Cracks due to theshrinkage or overloading result in stress concentration and even base failure andreflective cracking through the overlying layer, which definitely increasesmaintenance and repair costs. Also not all types of soil can be bounded well withcement, like high organic soils and some type of clayey soils. Additives are availablethat can be added to a normal type of cement to reduce or eliminate the disadvantagesof a cement-bound road base (shrinkage, cracks, brittle behavior) (Molenaar, 2010).

1.3 OBJECTIVES

The objectives of this research are to evaluate the properties of cement-boundmaterials in order to design appropriate cement stabilized materials for structuraldesign of pavements. An innovative product RoadCem together with cement has beenproven to be well in all types of granular materials. In this research, the mechanicalproperties to be investigated are not only the stiffness and the strength (compressivestrength and/or indirect tensile strength and/or (fatigue) flexural tensile strength) butalso the thermal cracking, frost thaw behavior and erosion.

RoadCem from PowerCem Technologies is used as additive to improve theperformance of the cement stabilized materials. In this literature review informationwas used from PowerCem Technologies for related soils. However it has to be keptin mind that small differences in soils and test conditions can have a big influence onthe mechanical properties of the stabilized material. The comparison of the test resultsfor soils stabilized with cement and RoadCem and (nearly) the same soil stabilizedwith only cement or another stabilizer therefore is indicative rather than absolute.

1.4 CONTENT OF LITERATURE REVIEW

In this literature review, the properties of cement-bound materials from a number ofresearch studies are summarized. In Chapter 2, various stabilization methods arereviewed, as well as the comparison of the applications of different stabilizing agents.The materials for cement stabilization are described in Chapter 3, including soil,cement, water and additives. The soil properties play a significant role in stabilization.

3

Preliminary tests to indicate the soil properties and mix composition are illustrated inChapter 4. Compaction and curing methods in the laboratory, which significantlycontribute to the strength of samples are also described. Chapter 5 focuses on themechanical properties of cement bound materials, which are summarized fromprevious research results. The cracking behavior, mainly due to the hydraulic reaction,is addressed in Chapter 6. In Chapter 7 the effects of a more flexural stabilization ispresented. Finally in Chapter 8 the conclusions and recommendations are presentedbased on this literature study.

In this review, the units that are used are SI units. During the literature study, someresults were originally mentioned in the British/American units. To prevent the errorsin the interpretation of the results due to the differences in SI and British/Americanunits, everything is converted into the SI system. Due to this conversion the numberscan vary a bit of the original figures. The conversion tables are included in AppendixB. Appendix C gives the translation of general terms mentioned in this review.

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CHAPTER 2

STABILIZATION AGENT

Stabilization of soil is an effective method to improve the soil properties and enhancethe pavement performance. The aims of stabilization are to

(a) Increase stiffness and strength and thus stability and bearing capacity(b) Increase volume stability to control the swell-shrink characteristics caused by

moisture changes(c) Increase durability, resistance to erosion and frost attack(d) Reduce permeability and avoid the intrusion of water

Basically there are five types of traditional stabilization, which are 1) Mechanical stabilization 2) Bitumen stabilization 3) Lime stabilization

4) Fly ash stabilization5) Cement stabilization

Mechanical stabilization means improvement of the grain size distribution by mixingthe soil or gravel with another type of soil, and optimum compaction of materials.

The choice between these types of stabilization is dependent on the nature of the basicmaterial to be stabilized and the desired function of the stabilized layer in thepavement structure (e.g. construction platform or structural layer). The overall costsshould also be taken into account.

There may be more than one candidate stabilizer applicable for one type of soil, whichis indicated in table 2.1. Cement is particularly effective in stabilizing coarse granularmaterial like sands and is not suited to treat fine-grained soil like clay owing to thehigh cement content required. Lime is more efficient to stabilize clay. Table 2.2 listsstabilization methods which are most suitable for specific applications of a particularsoil.

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Table 2.1 Application of traditional stabilization methods (Ingles, 1972)Designation Fine

clayCoarse

clay

Fine

siltCoarse

siltFinesand

Course

sandAggregate

Particle size(mm) <0.006 0.006-0.02 0.02-0.01 0.01-0.06 0.06-0.4 0.2-2 >2.0

Volumestability

Verypoor Fair Fair Good Very good

Lime

Cement

Bitumen

Range of maximum efficiency Effective, difficult quality control

Table 2.2 Stabilization methods most suitable for specific applications (FM 5-410)

Purpose Soil Type Methods

Sub-grade Stabilization

Improves load-carrying andstress-distributioncharacteristics

Fine-grained SA, SC, MB, C

Coarse-grained SA, SC, MB, C

Clays of low PI C, SC, CMS, LMS, SL

Clays of high PI SL, LMS

Reduces frost susceptibility Fine grained CMS, SA, SC, LF

Clays of low PI CMS, SC, SL, LMS

Improves waterproofing andrunoff

Clays of low PI CMS, SA, LMS, SL

Control shrinkage and swell Clays of low PI CMS, SC, C, LMS, SL

Clays of high PI SL

Reduces resiliency Clays of high PI SL, LMS

Elastic silts or clays SC, CMS

Base-course Stabilization

Improves substandard materials

Fine-grained SC, SA, LF, MB

Clays of low PI SC, SL

Improves load-carrying andstress-distributioncharacteristics

Coarse-grained SA, SC, MB, LF

Fine-grained SC, SA, LF, MB

Reduces pumping Fine-grained SC, SA, LF, MB

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The methods of treatment are

C = Compaction MB = Mechanical Blending

LMS = Lime-Modified soil SA = Soil-Cement

LF = Lime-Fly ash SL = Soil-Lime

CMS = Cement-Modified Soil

2.1 BITUMEN

Bitumen is obtained through distillation of crude oil in an oil refinery. It is sensitive totemperature changes. At high temperature it is liquid and deformations (especiallyrutting) can occur. When it becomes hard when temperature lowers, cracks may occur.A bitumen-bound material is a mixture of mineral aggregates (sand, gravel or crushedstone) glued together by the bitumen to form a stable base or wearing course. Bitumenincreases the cohesion and load-bearing capacity of the soil and renders it resistant tothe action of water. There are three types of bituminous stabilized soil:· Sand bitumen. Sand particles are cemented by bitumen to provide a material withincreased stability.· Gravel or crushed aggregate bitumen. A mixture of bitumen and a well-gradedgravel or crushed aggregate that, after compaction, provides a highly stablewaterproof mass of sub-base or base course quality.· Bitumen lime. A mixture of soil, lime and bitumen that, after compaction, mayexhibit the characteristics of any of the bitumen-treated materials indicated above.

The stabilization of soils with bitumen differs greatly from cement and limestabilization. Unlike cement and lime which act chemically with the material beingstabilized, bitumen acts as a binding agent and simply sticks the particles together andprevents the ingress of water (Sherwood, 1993). Freeze-thaw and wet-dry durabilitytests are not applicable for bitumen stabilized mixtures.

2.2 LIME

Lime is most effective in stabilizing soil with a sufficient amount of clay. Lime reactswith medium, moderately fine and fine-grained soil to result in decreased plasticity,improved workability, reduced volume change characteristics and higher resistance tothe damaging effects of moisture. The most substantial improvements in theseproperties are seen in moderately to highly plastic soils, such as heavy clays. Themost commonly used lime products are hydrated lime and quick lime. Dry hydratedlime is effective in drying out soils, but produces a dust problem that makes itundesirable for use in urban areas, and the fast drying action of lime requires anexcess amount of water during hot, dry weather. The quicklime is more economical

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than hydrated lime as it contains approximately 25 percent more available lime, but itrequires more water for stabilization (Sherwood, 1993). The physical properties andchemical composition of quick lime and hydrated lime for soil stabilization shallconform to ASTM C977-89.

The treatment of pavement subgrades with lime can significantly improve theengineering properties of a wide rang of soils. There are many recommendations forsoils to be treated with lime. For example, soils that should be considered for limetreatment include soils with a Plasticity Index (PI) that exceeds 10 and have more than25 percent particles passing the #200 sieve (0.075 mm) (Little, 1995). Lime is used incase the material to be stabilized has a high PI, i.e. above 10 (UFC, 2004).

In stabilizing the clay, lime performs two basic functions: flocculation andcementation. Flocculation reduces the PI of soil, thereby improving the workabilityand reducing the swell potential of the soil. The cementation process is a slowreaction after compaction, which increases the strength and durability of the soil.Cementation also creates a working platform during construction. Lime has also beenused as an admixture to highly plastic materials to facilitate pulverization and mixing,and to increase the compressive strength (Kersten, 1961).

Lime increases the soil strength by pozzolanic action, which results in the formationof cementitious silicates and aluminates. Fly ash is generally high in silicate andalumina, so fly ash can be added to lime stabilized soil to accelerate the pozzolanicaction (Molenaar, 1998). So the lime and fly ash are often used in combination instabilizing cohesive materials successfully. However the material is brittle and has notmuch flexibility especially in clay soils.

Factors influencing the strength of lime-treated soils are similar to those affecting thestrength of cement-treated soils, i.e. the soil type, the amount of lime and thecompacted density (TRH 14, 1985). Yong and Ouhadi (2007) investigated the effectof lime on the properties of marl soil (see Appendix A), which is indicated in Fig. 2.1and Fig. 2.2. I

Fig. 2.1 Liquid limit for stabilized marl samples at different curing time

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Fig. 2.2 Dry and wet CBR values for natural and stabilized marl for lime

Compared with the cement hydration process, the initial stage of lime reaction seemsquite rapid. Fig. 2.3 shows the rapid initial strength development of lime stabilization.lime has a beneficial effect in the form of early hardening of the mixture. Due to thisadvantage, lime can be used for cement stabilized soil to improve the strengthdevelopment.

Fig. 2.3 Initial strength development of a lime stabilizationand cement stabilization (Ingles, 1972)

British studies (Maclean, 1952) have shown that the addition of 2 percent of lime tocement treated soil increased the compressive strength and limited the reduction instrength due to immersion in water. The relationships between lime content and thecompressive strength for cement treated soil with 30% and 15% cement content areshown in Fig. 2.4.

Fig. 2.4 Compressive strength of lime stabilized soil with different cement content

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As can be seen above, the addition of 2 percent of lime can effectively increase thestrength of cement stabilized materials. Based on a study of PowerCem Technologies,the 7-day compressive strength with a mixture of clay1 with 15% cement and 0,15%of RoadCem was 6.4 MPa.

Bnattacharja and Bhatry (2003) investigated the compressive strength of some limeor cement stabilized clay as a function of time, as shown in Fig. 2.5.

(a) Cal soil (sandy clay: A-7-6)(b)

(c) Texas 1 soil (clay: A-7-6)Fig. 2.5 The compressive strength of cement stabilized and lime stabilized soil

As it can be seen in figure 2.5, the strength at all ages of the cement-stabilized soil isgenerally higher than lime-stabilized soil of the same age. Lime-stabilized soil startsweaker but gains strength with time in comparison with this type of soil. So theincrease in strength of lime-stabilized soil is more dependent on the time rather thanon the lime content.

2.3 FLY ASH

Fly ash is the by-product produced by coal-burning electricity generating power plantsthat contains silica, alumina, and calcium-based minerals. Depending upon the sourceand makeup of the coal being burned, the components of fly ash vary considerably,but all fly ash includes substantial amounts of SiO2 and CaO. Research (Kalinski and

1 Clay type of soil was tested in the project RC. 20110607. NL. 0495. PowerCem Technologies,Moerdijk

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Hippley, 2005) evaluated the cement stabilized fly ash. The results show that thecompressive strength of fly ash can be significantly increased by compaction andaddition of cement, as shown in Fig. 2.6.

Fig. 2.6 Unconfined compressive strength at optimum water content for cement stabilized fly ash

For stabilization, fly ash helps to reduce the Plasticity Index and swell and to give thesoil additional strength. Since fly ash begins to hydrate immediately after the additionof water, and the rate of hydration for fly ash is much higher than for Portland cement,the soil strength and density are dependent on the mixing and compaction time.Delays in compaction will decrease the strength and density of the soil dramatically(Ferguson, 1993).

Studies (Kolias, Kasselouri-Rigopoulou et al. 2005) give the effect of addition of flyash on the compressive strength of clay soil (A-6), which indicates that clay combinedwith 20% fly ash produces a high strength, as shown in Fig. 2.7.

Fig. 2.7 Uniaxial compressive strength of fly ash stabilized clay

The properties of fly ash differ significantly due to the production methods. Two majorclasses of fly ash are specified in ASTM C 618 on the basis of their chemicalcomposition resulting from the type of coal burned; these are designated Class F andClass C. Class F is fly ash normally produced from burning anthracite or bituminouscoal, and Class C is normally produced from the burning of subbituminous coal andlignite (Halstead, 1986). Class C fly ash usually has cementitious properties in additionto pozzolanic properties due to free lime, whereas Class F is rarely cementitious whenmixed with water alone. In their studies (Kalinski and Hippley, 2005) state that ClassC fly ash contains sufficient quicklime to be self-cementing, and doesn’t require the

12

addition of a cementing agent such as Portland cement to achieve significant strength.However, addition of cement can increase the strength and accelerate strength gain,because cement hydrates faster than fly ash.

2.4 CEMENT

Cement stabilization has become a popular option to enhance pavement performance.The stabilized base material is stronger, more uniform and more water resistant thanthe un-stabilized base material. Loads are distributed over a larger area and stresses inthe subgrade are reduced (Yoon and Abu-Farsakh, 2009). For stabilizations severaltypes of cement can be used several types of cement. In the world there are differentnames of cement that are used. In the European Union a CEM II Portland fly ashcement (6-35% fly ash and Portland Cement) is often used in stabilizations. CEM IIIBlast furnace cement (36-65% blast furnace slag and 35-64% Portland Clinker) andCEM I (100% Portland Cement) are less frequently used.

Parsons and Milburn (2003) investigated the properties of soil with the addition ofdifferent stabilizers. The improved compressive strength results are indicated in Fig.2.8. The results showed that lime and cement stabilized soils exhibited the mostimprovement in soil performance for multiple soils.

Fig. 2.8 UCS of soil stabilized with multiple soils

In this literature study, the review focuses on the cement stabilization, which isdescribed in the following chapters in detail.

2.5 CONCLUSIONS

In this chapter, various stabilizing agents are briefly described. The addition of astabilizing agent can help to improve the properties of the basic soil (e.g. reduction ofplasticity, increase in bearing capacity) or secondary or primary granular materialsand to obtain a more durable material.

The choice between these types of stabilization is dependent on the nature of the basicmaterial to be stabilized and the desired function of the stabilized layer in the

13

pavement structure. Lime is effective in stabilizing cohesive materials such as clayand silt, while cement is more effective in stabilizing granular materials such asgravel and sand.

15

CHAPTER 3

MATERIALS FOR CEMENT STABILIZATION

Cement-bound materials are defined as mixtures of in-situ and/or secondary soil,cement and water that binds and hardens after compaction and curing to form a strongdurable paving material.

Soils treated with a relatively small proportion of cement (less than that required forthe hardened soil-cement) are commonly classified as cement-modified soil, whichaims to improve the properties of the in-situ soil such as susceptibility for moistureconditions. Soil and/or granular material (crushed aggregates, asphalt…), cement andwater are the three basic materials needed to produce cement stabilized materials.

3.1 SOIL

3.1.1 Particle size and soil structure

Soil used in stabilization contains a wide range of grain sizes, like gravel, sand, siltand clay. The chemical composition of the soil has an important influence on theproperties of the stabilizations. Especially highly organic soils (peat) have a negativeinfluence on the properties of cement stabilizations. With RoadCem also an organicsoil was successfully stabilized2. However, the scope of this study is on inorganic soils.The type of soil is generally specified in terms of the particle size. Soils can begenerally classified into two categories according to the grain size.

a) fine grained soil (mainly clay and silt)

2 Trail on Piako Road, reference number, RC.20100211.NZ.0292, PowerCem Technologies, 2010,Moerdijk

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b) coarse grained soil (sand and gravel predominantly)or in shear strength terms

a) cohesive (e.g. clays, clay silt mixture, organic)b) non-cohesive(e.g. sands and gravels)

The soil types shall be classified according to the detailed particle size and theclassification is different for various countries, which is indicated in Table 3.1.

Table 3.1 Particle size ranges in different countries Range (mm)

Netherlands United kingdom USAClay <0.002 <0.002 <0.005Silt 0.002-0.063 0.002-0.060 0.005-0.075Sand 0.063-2 0.060-2 0.075-4.75Gravel 2-63 2-60 4.75-76.2Cobbles >63 60-200 >76.2Boulders − >200 −

In order to specify the type of soil, the particle size distribution curve is to identify therange of particle sizes. The particle size distribution is usually described in terms ofthe cumulative percentage (by mass) of particles passing each sieve used in theanalysis and may be plotted in the form of a graph. Examples of particle sizedistribution curves are indicated in Fig. 3.1.

Fig. 3.1 Typical soil particle size distribution curves (K.H, 1980)A−uniformly-graded curve (poorly-graded curve)B−well-graded curveC−gap-graded curveThere are three typical types of distributions in Fig.3.1. A well-graded soil ischaracterized by a smooth curve of a wide range of particle sizes. For a gap-gradedsoil, the soil particles are deficient in a certain range of sizes. A uniformly-graded soilconsists of a small range of particle sizes. If the grain size distribution approaches theFuller curve, this means that the densest packing is approached.

Examples of particle size distribution curves of some typical soils are given in Fig.

17

3.2.

Fig. 3.2 Particle size distribution curves for sands and gravels (K.H, 1980)

There are also some specified coefficients to characterize the grading of a soil. The

coefficient of uniformity ( uC ) and the curvature index ( cC ) are used to determine

whether the soil is well graded or poorly graded and they are defined as follows:

60u

10

dCd

= (3-1)

230

C60 10

dC

d d=

´(3-2)

d10 − sieve size through which 10% of material passesd30 − sieve size through which 30% of material passesd60 − sieve size through which 60% of material passesd10, d30, and d60 are shown in Fig. 3.3.

Fig. 3.3 Particle size gradation coefficient

Table 3.2 gives the indication of the coefficients, uC and cC for gravel and sand.

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Table 3.2 Indication of uC and cC

Index Gravel Sand

uC ≥4 ≥6

cC 1-3 1-3

Rating Well graded Well graded

In addition to the particle grain size, the particle arrangements also play an importantrole with respect to the soil properties. Soil consists of particles, voids and moisture.Three typical examples are indicated in table 3.3.

Table 3.3 Three physical states of the soil-aggregate mixtures (Molenaar, 2005)

(a) Aggregate with nofines

(b) Aggregate withsufficient fines

(c)Aggregate with greatamount of fines

Grain-to-grain contact Grain-to-grain contactwith increased resistanceagainst deformation

Grain-to-grain contactdestroyed, aggregate‘floating’ in the soil

Variable density Increased density Decreased densityNon-frost susceptible Frost-susceptible Frost-susceptibleHigh stability if confined,low if unconfined

High stability in confinedand unconfined conditions

Low stability

Not affected by adversewater condition

Not affected by adversewater condition

Greatly affected by adversewater condition

Very difficult to compact Moderately difficult tocompact

Not difficult to compact

It should be noted that the fine particles can cause problems when they interact withthe moisture. An excessive amount of fine particles can lead to loss of stability,susceptibility to frost action, and even mud pumping under traffic loads in practice.Especially, when the fine particles are clay, the soil structure will become strong whenit is dry, and then will lose strength when it becomes wet. So in practice, the finescontent in the soil should be limited as required in the specifications.

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3.1.2 Atterberg limits

In the presence of different amounts of water, cohesive soil can exist in four states:solid, semi-solid, plastic and liquid. The Atterberg Limits are moisture contents whichare used to give empirical information on the soil’s reaction to water. The Atterberglimits comprise the Liquid Limit, Plastic Limit and Shrinkage Limit:

The Liquid Limit (LL) is the water content at which a soil changes from a liquid to aplastic state. The Plastic Limit (PL) is the relatively low water content at which soilchanges from a plastic to a solid state. The range of moisture content between PL andLL is defined as Plasticity Index: PI=LL-PL.

The Plasticity Index (PI) is a measure of the soil’s cohesive properties and isindicative for the amount and nature of the clay minerals in the soil. High PI soilshave the potential for detrimental volume changes during wetting and drying whichsubsequently can lead to pavement roughness. The higher the PI, the more plastic thesoil will be (PCA, 2003).

Depending on the PI value, the soil can be qualified as being more or less plastic,indicated in Table 3.4.

Table 3.4 Plasticity and dry strength related to Plasticity Index PI (Molenaar, 2005)Plasticity Index PI Rate of plasticity Dry strength0-5 Non-plastic Very low, can be crumbed

between thumb and finger6-15 Medium plastic Moderate to low, can be broken

with the hands16-35 Plastic Moderate to low, can hardly be

broken with hands>35 Very plastic Very high, can’t be broken under

the palm of the hand

Clay with a high Plasticity Index (PI) also indicates a high clay content. Fig.3.4 showsthe values of clay content of a wide range of soils, together with the Plasticity Index.

Fig. 3.4 Relationship between clay content and Plasticity Index (Croney, 1977)

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A high clay content can lead to severe volume changes as the moisture contentchanges. A high clay content also requires more cement for stabilization, whichdefinitely results in shrinkage. So it is suggested to first treat clay soil with lime andthen stabilize the clay with less cement to reduce the adverse effects.

The shrinkage limit (SL) indicates a certain moisture content below which the volumeof the soil doesn’t change anymore when it is dried, as indicated in Fig. 3.5.

Fig. 3.5 Volume change of a soil specimen during drying

The shrinkage limit should be higher than the optimum moisture content, which isdetermined in a Proctor density test (see Paragraph 4.2).

Fig. 3.6 gives an overview of the Atterberg limits of soil with the variation of watercontent.

Fig. 3.6 Phases of soil and Atterberg limits (Molenaar, 2005)

Soil with a moisture content greater than the liquid limit has no bearing capacity. Andsoil with a moisture content lower than the plastic limit is difficult to compact. Andsoils with a high PI and LL can experience a large amount of moisture loss andabsorption, which can result in excessive shrinkage or swelling. These volumechanges can result in lower bearing capacity and cause significant damage to thepavement structure. So it is preferred to stabilize a cohesive soil with a low PI-value

21

to decrease the moisture-susceptibility (Molenaar, 2005).

3.1.3 Soil classification

Soil classification systems have been developed based on the particle size distributionand their Atterberg limits. The best known classification systems are the AASHO andUSCS classification systems.

1. AASHTO Soil Classification SystemThe AASHTO system is developed by the Association of American State Highwayand Transportation Officials. The system contains seven classes to identify soils andgranular materials. Materials belonging to the groups A-1 to A-3 are coarse grainedmaterials while materials belonging to the groups A-4 to A-7 are fine grainedmaterials. The A-1 and A-2 groups have a sub-rating. Table 3.5 is an overview of thissystem (Molenaar, 1998).

Table 3.5 Soil classification according to AASHTOMain type Group Symbols Requirement

Coarse-grained(<35% passing 0.075 mm)

A-1A-1-a

<15% passes 0.075 mm,<30% passes0.425 mm.<50% passes 2 mm and PI

<6

A-1-b <25% passes 0.075 mm, <50% passes0.425 mm and PI <6

A-2 <35% passes 0.075 mm, except A-1and A-3

A-2-4 to A-2-7Depending on the plasticity limits ,refer to plasticity chart in Fig. 3.7

A-3<10% passes 0.075 mm, >50%passes

0.425 mm, no plasticFor fined-grained (<35%passing 0.075 mm) A-4

>35% passes 0.075 mm, PI<10 andLL<40

A-5>35% passes 0.075 mm, PI<10 and

LL>40

A-6>35% passes 0.075 mm, PI>10 and

LL<40

A-7>35% passes 0.075 mm, PI>10 and

LL>40

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Fig. 3.7 AASHTO plasticity chart

2. Unified Soil Classification System (USCS)The USCS classification system identifies three major soil divisions: coarse-grainedsoils, fine-grained soils, and highly organic soils. These three divisions are furtherdivided into a total of 15 basic groups. Table 3.6 presents the symbols used in USCS.

Table 3.6 Symbols used in USCSPrimary letter Secondary letter

Coarse-grained soils G=GravelS=Sand

W=Well-gradedP=Poorly graded

Fine-grained soils F=FinesM=SiltC=Clay L=Low plasticity

H=High plasticityOrganic soilsPT=Peat

O=Organic

The USCS classification system is shown in Fig. 3.8 and the fine grained materials areclassified according to the plasticity chart as shown in Fig. 3.9 (ASTM D2487-85).

Fig. 3.8 USCS classification chart

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Fig. 3.9 USCS plasticity chart

The differences between both systems are distinct. The particle size boundary in theAASHTO system used to decide whether a material is coarse or fine grained is ratherlarger than in the USCS system. The AASHTO system can’t indicate whether or notthe material is well graded, while the USCS system doesn’t allow to identify highlyplastic soils (Molenaar, 1998).

Clay can be made to exhibit plasticity within a range of water contents and exhibitsconsiderable strength when air dry. For classification, clay is fine-grained, or thefine-grained portion of a soil, with a plasticity index equal to or greater than 4 (ASTMD2487).

Clay soils present problems of shrinkage and swell under different moistureconditions. The amount and type of clay determine its expansive characteristics. Thereare three main groups of clays: kaolinite, montmorillonite and illite. Soils with morethan 50% clay in the fine fraction are called heavy clay. Clay is the finest of the soilparticles and can actually bond other particles together if sufficient clay and moistureis present (Croney, 1977).

In spite of the high clay content, cement and lime can be used to stabilize clay toreduce its high Plasticity Index and increase the strength. Some typical results areshown in Table 3.7.

Table 3.7 Examples of the effect of cement-modificationon clay soils (PCA, 2003)

Soil No. Cement content (%) Plasticity Index Shrinkage Limit (%)1 None 30 13

3 13 245 12 30

2 None 36 133 21 265 17 32

It is clear that the addition of cement substantially reduces PI and increases the

24

shrinkage limit, which indicates the improvement in the volume change characteristicsand stability.

The term “Activity” (Ac) has been developed to evaluate the activity of clay byconsidering PI and the amount of fine particles.

cPIAC

= (3-3)

Where PI − Plastic Index C − Percentage of particles < 2 µm

cA < 0.75 inactive clay

0.75 < cA < 1.25 normal clay

1.25 < cA < 2 active clay

cA > 2 highly active clay (Molenaar, 1998)

An increasing PI due to a greater activity of the clay leads to a decrease of thecohesion. A very great activity makes the soil unsuitable for application in pavementstructures.

For stabilization, some typical cement contents for sandy clays and non-expansiveclays with low plasticity are shown in Table 3.8 (Lay, 1998).

Table 3.8 Cement requirement for different soil typesClay types Cement requirement by mass of dry soil (%)Well graded sandy clay 2-5Sandy clay 4-6Silty clay 6-8Heavy clay 8-12Very heavy clay 12-15

In this research, the soil to be used for stabilization is mainly sand and clay. Sands inthe Netherlands are usually uniformly graded. The average grain size d50 is mostlybetween 146 and 269 µm and the coefficient of uniformity Cu = d60/d10 is between1.55 and 2.45. The CBR value varies between 10 and 15% (Molenaar, 2001).

3.1.4 Shrinkage and swell

Most soils contain a fraction of clay as a part of their overall composition. Shrinkageand swell of soils containing a relatively large clay fraction (particles < 2 μm) canlead to severe damage on road pavements. Unequal swell can result in serious

25

cracking and unevenness of the pavements (Molenaar, 1998). However, cementmodification can decrease the plasticity and volume change characteristics, increasethe bearing capacity and provide a stable platform for the construction equipment.(PCA, 2003).

The swell potential is dependent on the amount and type of clay in the soil. ThePlasticity Index is a rough measure for the swell potential as PI is determined by thefine fraction of the soil (Donaldl, 1994). Table 3.9 gives the relationship between PIand swell potential (Molenaar, 1998).

Table 3.9 Relationship between shrinkage limit, PI and swell potentialShrinkage limit Plasticity Index Swell potential>18 <15 Small12-18 15-24 Moderate8-12 25-46 Great<8 >46 Great

Fig. 3.10 shows that the swell of a natural clay soil strongly reduces throughstabilization with addition of cement.

Fig. 3.10 Effect of addition of cement on the swell (PCA, 2003)

The tests were performed to evaluate the effect of the addition of cement to amoderately expansive AASHTO Class A-7-6 (16) clay soil. The results showed thatthree percent cement reduced the expansion, as measured in a CBR test, from 3.9% to0.15%.

Fig. 3.11 gives an example of the effect of cement addition on the reduction of thesilt-clay content.

Fig. 3.11 Reduction of silt-clay content due to cement modification (PCA, 1949)

26

As seen above, the silt-clay content of 93% in the untreated soil was reduced to 53%by the addition of 6% cement. A cement content of about 3% or 4% by weight wouldreduce the PI sufficiently to meet the specifications. The cement hydration productsbind some of the particles together to form larger grains in the size ranges of fine sandparticles. The result is that the treated soil contains less silt and clay and more sand,and in addition, the remaining clay has been altered chemically to become a lessexpansive material (PCA, 2003).

3.1.5 Organic content

Organic materials are mostly present in soils like peat and mud and soils with a lowbearing capacity. They can interfere with the hydration of the cement, which willcause a reduction in strength and durability. Sulfate may influence the long-termdurability of the cement-stabilized layer and thus pavement structure.

Soils that do not react with cement may owe to the presence of organic matter whichcauses delayed reaction or to the presence of sulfates that cause swelling or reductionin strength in the presence of water (Kersten, 1961). Kersten investigated the effectof sulfate concentration. Results showed that a sulfate concentration in excess of 0.5to 1.0 percent greatly reduced the strength of the immersed specimens. Research atRRL has shown that for non-cohesive materials the total sulfate content should notexceed 1% (as SO3). For cohesive materials the limit is 0.25%. In order to avoid theadverse effect of organic content and sulfate, a chemical analysis should be done priorto the mixing to determine the content of organic material.

In highly organic soils, the cement reaction will be adversely affected by the presenceof destructive acids, resulting in lower strength gain in mud and peat. Therefore, thisresearch concentrates on inorganic soil rather than organic soil. However, PowerCemTechnologies is contributing to the application of the stabilization of all types of soil(even clay and high organic soils) and contaminated soils3.

Another issue that should be considered in the stabilization of soils is chromium,which is an unavoidable trace element in many raw materials used in industry andmining as well as the manufacturing of Portland cement clinker. Chromium VIcompounds are classified as extremely toxic because of their high oxidation potentialand their ability to penetrate the human skin and many are carcinogenic. For normalstrength concrete the content of Cr VI would be 140 ppb (part per billion), where theacceptable risk limit in South Africa is 200 ppb. For high strength concrete orvariation in the manufacturing of cement, it may lead to an environmental risk whenconsidering the Cr VI. However, tests in PowerCem Technologies have shown that theCr VI content was reduced from 200 000 ppb to 140 ppb using industrial waste from a


27

chrome melter in a concrete matrix with the addition of PowerCem additive (Kurt,2006).

3.2 CEMENT

Cement can be used as an effective stabilizer for a wide range of materials, and it isparticularly effective in stabilizing medium to low plasticity materials. The types ofcement are mainly are Portland, mixed with fly-ash and with high blast furnace slags.Hydraulic cement refers to any cement that sets and hardens after it is combined withwater. Portland cement is hydraulic cement composed primarily of hydraulic calciumsilicates and is the most common used, ranging from TypeⅠto Type Ⅴ. TypeⅠis forgeneral purpose use and TypeⅡis used where precaution against moderate sulfateattack is required. Type Ⅲ cements are chemically and physically similar to TypeⅠexcept they are ground finer to provide the early strength. Blended cement is alsohydraulic cement and is made by mixing two or more types of cement. Usually theprimary materials used in blended cement are Portland cement and slag cement. Thereare two main types of blended cement: Portland blast furnace slag cement andPortland-pozzolan cement.

Soil can be modified by cement to improve its quality or stabilized with a relativelylarger amount of cement to increase the strength and durability. Because when cementis mixed with water, hydration is initiated rapidly. Cement hydration producescementitious material (e.g. C-S-H). Cement develops a high bond strength betweenthe hydrating cement and the soil particles. It also improves the gradation of thestabilized clay soil by forming larger aggregate particles from fined-grained particles.Although it is possible to treat almost any soil with cement to improve its properties,in practice it is difficult to treat fine, clayey materials with cement owing to the highcement content required and the difficulty in pulverizing the soil and mixing thecement (TRH 14, 1985). In general, the soil should have a PI less than 30.

For the plastic materials, the addition of cement reduces their plasticity in terms ofPlasticity Index and increases the shrinkage limit as well as the UCS of the hardenedcement-bound mixture, which is shown in Table 3.10.

Table 3.10 Average change in properties for clay soils% Stabilizer Plasticity Index Shrinkage Limit 7-day UCS 28-day UCS3% Cement -52% 122% 468% 605%3% Lime -55% 123% 183% 348%5% Cement -64% 158% 775% 993%5% Lime -64% 151% 266% 481%

As indicated in table 3.10, cement and lime accomplish a similar reduction in PI andincrease in shrinkage limit at similar content levels. Cement generally produces amuch higher strength than lime at all ages (Kersten, 1961).

28

The cement content plays a significant role in the properties of cement-boundmaterials The selection of the cement content to be used is dependent on the soilclassification and the desired degree of improvement in soil quality. Generally smallamounts of cement are required when it is simply desired to modify the soil propertiessuch as gradation, workability and plasticity. When it is desired to improve thestrength and durability significantly, larger quantities are required (Donaldl, 1994).Table 3.11 shows examples of required cement contents for the different soils.

Table 3.11 Cement requirement of different soils (Molenaar, 1998)Soil type Amount of cement (%)

By weight By VolumeA-1-a 3-5 5-7A-1-b 5-8 7-9A-2 5-9 7-10A-3 7-11 8-11A-4 7-12 8-13A-5 8-13 8-13A-6 9-15 10-14A-7 10-16 10-14

As indicated in the research (Kersten, 1961; Donaldl, 1994; Molenaar, 1998), agood quality mix is obtained with a cement content generally in the range of 8% to14% (depending on the soil type). The compressive strength increases as the cementcontent increases. However, the higher the percentage of cement, not only the higherthe costs but also the more severe the shrinkage cracking.

For the field condition, it is generally accepted that the full-scale field-mixing processis less efficient than the closely controlled laboratory mixing process, and hence it iscommon practice to increase the lab-determined cement content by a multiplicationfactor of about 1.5 to give a cement content appropriate in the field (Guthrie andRogers, 2010).

3.3 WATER

Water serves two purposes for stabilization: it helps to obtain the maximum drydensity during compaction and it is essential for cement hydration. The water contentfor maximum compaction should be at optimum moisture content, for less or morewater will reduce the dry density. For cement hydration, sufficient water contributes tothe complete hydration and to achieve a high strength.

The Optimum Moisture Content (OMC) is the moisture content at which the materialreaches the maximum dry density, which can be obtained by the Proctor test(described in paragraph 4.3). Prior to the mixing, the Proctor test should be performed

29

to get the Optimum Moisture Content, which is an important parameter for thestabilization. After the mixing and compaction, the mixture should be covered toavoid moisture loss. The specimen should be cured in a moist environment to ensurehydration.

3.4 ADDITIVE

Many additives are currently available to improve the performance of the stabilizedmaterial. In this research the effect of additive on the performance of the cementstabilized soil will be investigated. The additive technology for stabilization issummarized in this review.

3.4.1 Traditional additives

(1) Limestone based additivesWhen the soil contains a large amount of clay, the soil particles have a large surfacearea and subsequently adsorb much water. The adsorbed water is strongly bonded tothe clay particles and difficult to remove unless by particular chemicals. Limestonecan be used to remove the bonded water, by ion exchange, which results in a lowerbonded water content.

Based on this, some products were introduced for clay stabilization, which haveadvantages of improving workability, compaction and increase the soil’s shearstrength and bearing capacity, etc. They also can be applied as a stabilizer for sandsand silty soils.

(2) Polymer additivesOrts, Sojka et al. (1999) present a polymer that can be applied for reduction of thesoil erosion. Polymers are brought in the stabilization in a liquid form in order toobtain a more homogeneous mixture (Egyed, 2010).

The product based on polymer technology has been applied as an environmentallysafe stabilizer at various soil conditions. It is reported that it can reduce or eliminatethe following problems: base failure of paved and unpaved roads, dust pollution, soilpermeability and soil erosion. However the lifetime of the polymers in soilstabilization is short.

(3) Enzymes additivesA liquid enzyme stabilizer has been used for soil stabilization, which contributes toincrease in bearing capacity and reduction in soil permeability. Compared withconventional additives, the use of an enzyme additive is more cost effective, and thisprovides a beneficial alternative for road construction. Some additives of enzymeshave been proven to strengthen the road structure and significantly reduce the

30

construction cost.

3.4.2 RoadCem

The RoadCem additive is based on Nano technology and produced by PowerCemTechnologies. It has been used world widely as an additive and specifically designedfor applications in road construction and stabilization. It enhances and increases thestrength and flexibility of stabilized road layers and improves the overall performanceof cement-bound materials used in road construction. This study is intended toevaluate the effect of RoadCem on the performance of cement-bound materials.

The marl soil (see Appendix A) was stabilized with RoadCem–cement to investigatethe effect of the additive. The results in terms of CBR values are shown in Fig. 3.12.

Fig. 3.12 Comparison of CBR values for lime stabilized marl soil

In Fig. 3.12 the CBR values are much higher with RoadCem than only with cement4.

Moloisane (2009) evaluated the strength behavior of unpaved roads stabilized withnon-traditional stabilizers. Table 3.12 presents the DCP-CBR strength of the stabilizedexperimental panels after 8 months. DCP indicates Dynamic Cone Penetrometer.

Table 3.12 DCP-CBR strength for stabilized panels with different stabilizers(Moloisane, 2009)

PanelNumber Stabilizer used

In-situ DCP-CBR Soaked DCP-CBRMaximum CBR in

first 5 monthsMaximum CBR in

first 5 months1 Cement 222 1792 Perma-Zyme 11X 152 493 RoadCem and cement 336 2464 Dustex and Bitumen Emulsion 207 755 Dustex 154 1216 Ecobond ((UF) resin) 190 1507 Bitumen Emulsion 222 157

In this research, seven different commercial stabilizer products from five generic


31

group types were applied: one from the electro-chemicals generic group type(Perma-Zyme 11X), and others were from the organic non-petroleum group (Dustex),organic petroleum group (Bitumen Emulsion), polymer group(Ecobond/urea-formaldehyde (UF) resin) and cement catalyst group (RoadCem). Itcan be seen that the soaked CBR strength decreased for every type of stabilizer, butthe RoadCem and Cement treated experimental panel showed the highest strength. Incomparison with the panel with only cement, the panel treated with cement plusRoadCem significantly outperformed in both in-situ and soaked conditions.

Also by environmental investigations and testing on the end-product, RoadCem hasbeen proven to be an environmentally friendly fine-powder substance 5 . 6 . 7

(PowerCem Technologies, 2008).

3.5 CONCLUSIONS

In this chapter, the soil properties (e.g. particle size, classification and swell) arediscussed. Clay has a relative large particle surface area which will results in morecement consumption for stabilization. Sand and gravel are the most suitable forcement stabilization. Clay soil due to the high clay content is reported to besusceptible to volume change. A chemical analysis should be done to determine thecontent of organic material.

The cement content is a significant factor for the properties of stabilized materials.The cement content should be determined to meet the requirement in accordance tothe strength and durability specifications. The water content must be determined bythe Proctor test to obtain the Optimum Moisture Content, which is essential for thecompaction and cement hydration. Compared with traditional additives, RoadCem isreported to be effective in improving the properties of the cement stabilization.

5 Analyses of drilling Invert Cuttings versus PowerCem/OPC modifications and referencemixtures, ref number: 60769/06, UEG, May 2006, Wetzlar (D)6 Material Safety Data Sheet RoadCem,ref. number: 15-9722, Chemwatch , July 2008, Moerdijk7 Immobilization of Cr VI in cement materials using PowerCem, reg.No: 1956/01084/06,Bateman, April 2006, Pretoria (RSA)

33

CHAPTER 4

PRELIMINARY INVESTIGATIONS

The properties of cement-bound materials are dependent on several factors:(a) The nature of the materials whether it is clay, silt, sand or coarse aggregate(b) The proportions of the mix (soil, cement and water)

(c) Degree of compaction and curing conditions (temperature and age)(d) Environmental factors.

In this chapter, the review is mainly about the soil tests and compaction of thesoil-cement mixture.

4.1 SOIL TESTS

Prior to mixing with cement, the following soil tests should be conducted to classifythe soil type and evaluate the soil properties:

· Particle size distribution· Atterberg limits (Plastic Limit, Liquid Limit and Shrinkage Limit)· Maximum Dry Density· Chemical analysis

4.1.1 Particle size distribution

The particle size distribution of soil is investigated by sieving. The soil sample isdistributed through various sieves of decreasing sieve size. The percentage passingthrough every sieve against the sieve size is plotted to get the particle size distribution(see Fig. 3.1). This test is performed based on the standard NEN-EN 933-1. Theequipment for the analysis is shown in Fig. 4.1.

34

Fig. 4.1 Particle size analysis of coarse grained soils using sieves

The smallest sieve size opening generally used is 0.063 mm, and below this thedistribution of silt and clay particles is determined using sedimentation techniques.Wet sieving of the soil particles is the process to separate the fine grained soil fromthe coarse grained soil, which is shown in Fig. 4.2.

Fig. 4.2 Wet sieving for particle size distribution of fine grained materials

4.1.2 Liquid Limit and Plastic Limit

The determination of the Plastic Limit is normally made in conjunction with thedetermination of the Liquid Limit. Standard testing methods for Liquid Limit (LL)and Plastic Limit (PL) are described in ISO/TS 17892-12 and ASTM D4318 -84. BothLL and PL are determined on particles smaller than 0.425 mm.

1. Liquid Limit (LL)

In standards of ISO/TS 17892-12, the cone equipment (shown in Fig. 4.3) is used todetermine the Liquid Limit. The soil sample at its original state is mixed with acertain amount of distilled water and then placed in the cup. The cone is allowed topenetrate and the penetration is recorded, after this the water content is determined.The procedure is repeated at least three times with different water content. For thecalculation of LL, the water content (%) and the cone penetration are plotted on a

35

linear scale (as shown in Fig. 4.4).

1. adjustable stand arm2. plexiglass with graded scale3. cone4. specimen5. mixing cup6. index line

Fig. 4.3 Cone equipment

0

20

40

60

80

100

10 12 14 16 18 20 22 24 26 28

cone penetration/mm

water

con

tent

/%

Fig. 4.4 Example of relationship between water content and cone penetration

The Liquid Limit is the water content determined from the specified penetration,which is dependent on the cone (shown in Table 4.1).

Table 4.1 Cone penetration requirementCone penetration requirements 80g/30º (cone) 60g/60º (cone)Initial penetration about 15 mm about 7 mmPenetration range 15 to 25 mm 7 to 15 mmwL determined from the penetration 20 mm 10 mm

In ASTM 4318-84 the liquid limit is determined by shaking the soil sample. The soilsample is placed in a metal cup and a 2 mm wide groove is made in the center. Thesoil is shocked by dropping the cup at a rate of 2 drops per second and the number ofdrops when the two parts of the soil are drawn together along a distance of 13 mm(shown in Fig. 4.5) is recorded. This procedure is repeated at different water content.Plot a graph of number of drops and water content. The water content at 25 drops is

36

the liquid limit.

Fig. 4.5 Soil pat after groove closed

2. Plastic Limit (PL)For determination of the plastic limit, the methods described in the standards ISO/TS17892-12 and ASTM 4318-84 are similar. In ASTM 4318-84 the Plastic Limit isdetermined by alternately pressing together and rolling into a 3.2 mm diameter thread(shown in Fig. 4.6) a small portion of plastic soil until its water content is reduced to apoint at which the thread crumbles and is no longer able to be pressed together andrerolled. The water content of the soil at this stage is reported as the Plastic Limit.

Fig. 4.6 Test for Plastic Limit

3. Plasticity IndexThe Plasticity Index is calculated as the difference between the Liquid Limit (LL) andPlastic Limit (PL). PI=LL-PL.

4.1.3 Chemical analysis

Soil with a high organic content corresponds to increased water absorption and inmost of the cases a low PH value, both have a big negative influence on the cementreaction. It is essential to detect the presence and content of organic matter.Organic material contains high amounts of carbon compounds, which when heated tohigh temperatures are converted to carbon dioxide and water. In chemical analysis, adry solid sample is heated to a high temperature. The organic matter in the soil is

37

given off as gases. This results in a change in weight which allows for calculation ofthe organic content of the sample.

First dry the granular materials to 100ºC ± 5ºC, so the water evaporates. This must bedone until constant weight to determine the presence of soil and organic material.

To determine the exact amount of organic matter, dry the soil sample for four hours to600ºC and calculate the weight change. Because the organic material starts burning attemperatures > 500ºC.

4.2 COMPACTION OF MIXTURE

Compaction is the process of packing the particles more closely together and reducingthe porosity which can increase the bonding strength and enhance durability. Withgood compaction the materials can also obtain a better resistance to water and anincreased life span. This procedure can be performed according to standard NEN-EN13286-2.

The dry density of the compacted soil is one of the main factors that influence thestrength of the sample. And the optimum moisture content is essential to achieve themaximum dry density and to aid in cement hydration (Yoon and Abu-Farsakh, 2009).There is an optimum moisture content for compaction, above or below which reduceddry densities are obtained (J.Kennedy, 1983). The compaction curves are developedto identify the maximum dry density and the optimum moisture content.

4.2.1 Compaction test

There are two approaches for compacting cement stabilized materials as described inNEN-EN 13286-2, i.e. the standard and modified Proctor compaction test respectively.The tests consist of compacting materials inside moulds with different dimensions(shown in Table 4.2 and 4.3) according to the soil particle sizes, using a hammerweight dropped from a fixed height at a prescribed number of drops. The procedure isrepeated for a sufficient number of water contents. The dry density is then plottedagainst water content and the compaction curve is obtained.

38

Table 4.2 Summary of sample preparation methodsPercentage passing test sieves Mass of sample ( Kg) Proctor

mould16 mm 31.5 mm 63 mm

100 ─ ─15 A

40 B

75 to 100 100 ─ 40 B

<75 75 to 100 100 40 B

─ <75 75 to 100 200 C

Table 4.3 Dimensions of the cylindrical test mould

Proctor mouldDiameter (mm) Height (mm)

Thickness

Wall (mm)Base

plate (mm)

A 100.0±1.0 120.0±1.0 7.5±0.5 11.0±0.5

B 150.0±1.0 120.0±1.0 9.0±0.5 14.0±0.5

C 250.0±1.0 200.0±1.0 14.0±0.5 20.0±0.5

Table 4.4 illustrates the summary of the Proctor test and modified Proctor test.

Table 4.4 Summary of the Proctor test and modified Proctor testTypes of test

Characteristic DimensionProctor mould

A B CProctor test Mass of rammer kg 2.5 2.5 15.0

Diameter of rammer mm 50 50 125.0Height of fall mm 305 305 600

Number of layers - 3 3 3Number of blows per layer - 25 56 22

ModifiedProctor test

Mass of rammer kg 4.5 4.5 15.0Diameter of rammer mm 50 50 125.0

Height of fall mm 457 457 600Number of layers - 5 5 3

Number of blows per layer - 25 56 98

As indicated above, the modified Proctor test corresponds to a larger compactioneffort. Fig. 4.7 gives a comparison of the results of the two compaction methods.

39

1550

1570

1590

1610

1630

1650

1670

1690

0 2 4 6 8 10

Moisture content (%)

Dry

density

(kg/m3)

Modified Proctor

Standard Proctor

Fig. 4.7 Moisture-density curves of a cohesive soil for different compaction (Molenaar, 1998)

It can be noted that Modified Proctor compaction results in a higher dry density due tothe larger compaction effort. For practical use, whether standard or modified, therequired field density for base and sub-base layers is between 95% and 101% of themaximum Proctor density determined in the laboratory.

4.2.2 Factors influencing compaction

1. Compaction methods

Soil is usually compacted by different compaction methods. Bahar, Benazzoug et al.(2004) investigated the effect of different compaction methods on the strength of soilstabilized with cement (5% percent by weight). Compaction was achieved by meansof static, vibratory and dynamic compaction. Static compaction was obtained byapplying a static pressure using a universal compression testing machine. The soil isclassified as moderately plastic clay type A-6 according to the AASHTO system. Theresults are shown in Fig. 4.8 and Fig. 4.9.

Fig. 4.8 presents the compaction curves obtained by different compaction methods. Itcan be observed that the three different methods of compaction used didn’t affectsignificantly the dry density of the soil. The highest density was obtained with thedynamic method when the water content is on the dry side of the curve and with thevibro-compaction method when the water content is on the wetter side.

Fig. 4.8 Effect of compaction methods on the density

40

Fig. 4.9 Effect of compaction methods on the compressive strength

In Fig. 4.9 it can be found that, for dry specimens, dynamic compaction yields thehighest compressive strength for every cement content of the stabilized soil (Bahar,Benazzoug et al. 2004).

Compaction with different energy should result in different dry density-moisturecurves, which is indicated in Fig. 4.10.

Fig. 4.10 Density-moisture curves for sandy clay soil with different compaction effort

It is clearly that the maximum dry density increases and the optimum moisture contentdecreases with increasing compaction effort (Croney, 1977).

2. Cement contentCompared with the compaction of the raw materials, the compaction of the mixture ofsoil-cement may be a little different. Fig. 4.11 gives examples of the compactioncurves obtained for an un-stabilized and cement stabilized sands (A-2, according toAASHTO system) with different cement contents.

Fig. 4.11 Dry Density-Moisture curves for a sand stabilized withdifferent cement contents (Yoon and Abu-Farsakh, 2009)

41

The dry density increases with an increase in cement content. The optimum moisturecontent of the cement stabilized sands (OMC = 10% to 11% ) is slightly lower valuethan that of the un-stabilized sand (OMC = 11.5%).

The optimum moisture content and maximum dry density of compacted soil-cementare approximately the same as those of the raw materials. Some soils do, however,exhibit marked differences in optimum moisture content and maximum dry density,but they are limited in the range of 1 to 3 pcf (pounds per cubic foot) (Kersten, 1961).Table 4.5 gives typical ranges of increases and decreases for different soils stabilizedwith cement.

Table 4.5 Maximum dry density and moisture contents of soil-cement compared to thecorresponding values for the raw soils (Kersten, 1961)

Soil group and type Change in MaximumDensity (in pcf)

Change in OptimumMoisture Content (in

percentage units)A-2 sandy loams 0 to +3 -1 to +1A-3 sands 0 to +6 0 to -1A-4 silts and loams 0 to -6 0 to +3A-5 silts -3 to +1 0 to -3A-6 medium clays 0 to +1 0 to -2A-6 heavy clays -1 to +2 0 to -4

3 Soil typeClay is very difficult to compact when dry or wet. The compaction of clay very muchdepends on the water content. To achieve good results, the water content should staywithin ±2% of the optimum moisture content (Molenaar, 2005). Fig. 4.12 presentsexamples of compaction curves of typical raw soils.

G = gravel S = sandM = silt C = clayW = well graded L = low plasticity H = high plasticity

Fig. 4.12 Dry density-moisture curves for a range of soil types

As shown above, with a decrease in soil particle size, the optimum moisture contentfor a given compaction method is increasing. Clay particles have a relatively large

42

surface, so they need a larger amount of water for compaction.

4. Delayed compaction

In many studies it is found that delayed compaction has a detrimental effect on thecompressive strength and maximum dry density. Because cement begins hydrating assoon as it comes into contact with water, compaction should be performed as soon aspossible after mixing in order to minimize the adverse effect of cement hydration onthe stabilized materials to be compacted.

Fig. 4.13 gives examples of delayed compaction influencing the dry density andstrength (TRH 14, 1985). Fig. 4.13 shows the loss in density and strength withincrease in time between mixing and compaction. So it is essential to perform thecompaction as soon as possible after mixing.

Fig. 4.13 The effect of a time lapse between mixing and compaction on the drydensity and unconfined compressive strength

4.3 MIX COMPOSITION

The proportions of cement, water and soil in the mixture significantly affect theproperties of the stabilized material. Therefore, the mix composition design is animportant process for stabilization.

4.3.1 Requirements for materials

In many studies, there are different requirements for soils suitable for cementstabilization. In a research study (Molenaar, 1998) it is presented that the soil issuited for cement-stabilization if:% < 0.075 mm (#200 sieve): <35%% > 0.075 mm: > 55%Maximum grain-size: <75 mmLL: < 50PL: < 25The specification for soil-cement requires:

43

1. The material should be well-graded with a coefficient of uniformity of not lessthan 5. 2. The material passing the 425 µm sieve should have a Liquid Limit not greaterthan 45 percent and a Plastic Limit not greater than 20 percent (Croney, 1977).

According to NEN-EN 14227-1, the aggregates grading for cement-bound granularmixture is indicated in Fig. 4.14.

Y−Percentage passing by massX−Sieve size, in millimeter (mm)1−Envelope A2−Envelope B

Fig. 4.14 Soil gradings for cement-bound mixture

Fig. 4.14 covers all gradings with which practical experience in cement boundgranular mixtures exists. Gradings characterized by envelope A include sands.Gradings characterized by envelope B include well-graded coarse aggregates withlimited contents of fines < 0.063 mm.

For a given soil that reacts normally with cement, the cement content determines thenature of the cement-stabilized soil. The proportion of cement alters the plasticity,volume change, susceptibility to frost heave, elastic properties, resistance to wet-dryand freeze-thaw cycles (Kersten, 1961).

For stabilization, the quantity of cement required to give the specified strength forsoil-cement varies with the grading of the soil. Table 4.6 gives the ranges of cementcontents likely to be required for different type of soils.

Table 4.6 Cement content requirement for soils (Croney, 1977)Soil Cement content (% by weight)silt-clays 9-12sandy-clays 8-10well-graded sands 5-7sandy gravels 3-5

Standard (NEN-EN 14227-1) gives the minimum cement content required forstabilization (Table 4.7).

44

Table 4.7 Minimum cement content according to the maximum grain sizeMaximum nominal aggregate size (mm) Minimum cement content (% by weight)> 8.0 to 31.5 32.0 to 8.0 4< 2.0 5

For stabilizing soil, the water content of the mixture should be the Optimum MoistureContent obtained by the Proctor test. Water to be used should be clean and free fromdeleterious materials and other organic substances without using RoadCem. Watersuitable for drinking is generally accepted for use.

4.3.2 Mix design method

In this research, the central composite design method is employed for mixcomposition. The two independent variables are the cement content (C) and theadditive content (A). In a PhD thesis (Medani, 2000) the central composite designmethod is described, see Table 4.8 and Fig. 4.15.

Table 4.8 Variables for central composite designTrial Ccoded Acoaded

1234

-1+1-1+1

-1-1+1+1

5678

-ψ+ψ00

00-ψ+ψ

9-13 0 0

Fig. 4.15 Coded test conditions for the central composite rotatable design

As indicated in Table 4.8 and Fig. 4.15, trials 1-4 combine the corner values with thedistance from the center point ±1. Trials 5-8 are called star points, and the distance

45

from the center is ψ, which depends on certain properties desired for the design and

on the number of factors involved. If the value of ψ is set at 2 , the design is called

rotatable. This means that the variance of the predicted response at any point xdepends only on the distance of x from the design center point.

To scale the coded terms of Table 4.7 into values within the range of interest, ψ= 2

is set equal to half the ranges of the variables and the scaling factors for the testsfollow from (Medani, 2000):

scaling max min12 ( )2

C C C= - (4-1)

scaling max min12 ( )2

A A A= - (4-2)

In which

scalingA − scaling factor for additive content

scalingC − scaling factor for cement content

maxA − maximum additive content (kg/m3)

minA − minimum additive content (kg/m3)

maxC − maximum cement content (kg/m3)

minC − minimum cement content (kg/m3)

Finally the experimental values of the cement content and additive content follow from:

max min1 ( )2coded scalingC C C C C= ´ + + (4-3)

max min1 ( )2coded scalingA A A A A= ´ + + (4-4)

4.4 CURING CONDITIONS

The curing condition plays an important role in the properties of cement stabilizedmaterials on the short and long term. Proper curing methods significantly contribute tothe development of the strength of specimens. Appropriate temperature, moistureconditions and time are required for curing.

Fig. 4.16 gives an example of the strength development of samples with differentcement content during the first 28 days. The soil is classified as ML/A-4 according toUSCS/AASHTO.

46

Fig. 4.16 Variation of unconfined compressive strength at 1, 7 and 28 curing days ofsamples with different cement contents (Altun, Sezer et al. 2009)

The compressive strength increases rapidly during the first 7 days and after that therate of increase rate is relatively low. After 28 days, the compressive strength almostremains the same.

The strength is also related to the curing temperature, which is essential for thecement hydration. During curing, moisture may be lost by evaporation, which willaffect the cement hydration and reduce the final strength, so the specimen should becured properly to avoid moisture loss. An example of the effect of the curingtemperature on the 7 days compressive strength of cement-stabilized sand (cementcontent 6%) is shown in Fig. 4.17.

Fig. 4.17 Relationship between unconfined compressive strength and curingtemperature for cement stabilized sand (TRH 14, 1985)

As shown in Fig. 4.17, the 7-day strength increases as the temperature increases andthis effect has been used to develop accelerated test methods, i.e. curing at hightemperature, to give an early indication of the long-term strength.

4.5 CONCLUSIONS

For stabilization laboratory soil tests should be performed first to indicate the soilproperties. The tests consist of grain size distribution, Liquid Limit and Plastic Limit,and chemical analyses, which can be performed according to the specified standards.

Proctor test is usually used for laboratory compaction. Also the Proctor compaction isessential to obtain the Optimum Moisture Content for stabilization and the maximumdry density as a reference for field density. Compaction of the soil-cement mixture isessential for stabilization, which can increase the strength and durability of cement

47

stabilized materials. Different soil types result in different compaction curves. Themoisture content for mix design is consequently determined from the optimummoisture content of the curve. The curing condition should also be taken into accountfor the strength development.

The selection of the materials for stabilization should refer to the specifications, andthe quantities of the components are determined according to the guidelines andpractical experiences. In this research, the central composite design method isemployed for the mix composition.

49

CHAPTER 5

MAIN MECHANICAL PROPERTIES

Four major variables control the degree of stabilization with cement:1. The nature of the soil2. The cement content3. The moisture content during compaction4. The dry density attained in the compaction.

If the moisture content and the dry density are controlled according to the standardmethods, and normal mixing and curing procedures are applied, the nature of soil andthe cement content used determine the degree of stabilization (Kersten, 1961).

5.1. COMPRESSIVE STRENGTH

The compressive strength is the most commonly used mechanical property forevaluating cement treated materials, and is extensively used for the mix design andquality control (TRH 14, 1985). The compressive strength is dependent on the soiltype, the amount and type of cement and the degree of compaction. The moisturecontent and curing conditions also affect the compressive strength. These influencingfactors are described hereafter.

1. Cement contentThe cement content has a significant effect on the strength of cement stabilizedmaterials. The strength increases as the cement content increases, because thehydration products fill the pores of the matrix and enhance the bond strength betweenthe particles.

50

Park (2010) has published 12 SEM (Scanning Electron Microscopy) photos ofspecimens after failure, which clearly show the microstructure of the cementstabilized material specimens with different cement content, as presented in Fig. 5.1.

Fig. 5.1 SEM photos of cement stabilized sand specimens after testing (a) 4% cement; (b) 8% cement; (c) 12% cement; (d) 16% cement (Park, 2010)

As shown in the pictures, for the specimens with a cement content of 4 and 8% thesand particles protrude from the mixture, and some voids between these particles canbe observed. However, when the cement ratio was relatively high, such as 12 and 16%,the sand particles are buried into cement and don’t appear.

Examples of the effect of the cement content on the compressive strength arepresented in Fig. 5.2. In this research (TRH 14, 1985) the compressive strength ofdifferent soils stabilized with various cement contents was investigated. Similarresearch results from PowerCem Technologies are also included in Fig. 5.2 to get anindication of the trends. It should be realized that the soils stabilized with cement plusRoadCem are not exactly the same as the soils stabilized with only cement in theeighties.

Furthermore, the test conditions (specimen size, loading rate, etc.) might be different.The strength increases more or less linearly with the cement content but at differentrates for different soils. The larger the particle sizes of the soil, the higher thecompressive strength of the stabilized material. A well-graded particle sizedistribution also results in a better strength. As for the addition of RoadCem, thecompressive curves are all above the curves for the same cement content but withoutadditive, which indicates that Roadcem can improve the compressive strength, whenthe right doses of RoadCem is used, for all types of raw materials.

51

(1) Silty clay

(2) Uniformly graded sand

(3) Well graded sand

(4) GravelFig. 5.2 Relationship between unconfined compressive strength and curing period for

different soils stabilized with various cement content

2. Moisture contentThe water content is also an important factor to determine the compressive strengthbecause the moisture content is essential to achieve the Maximum Dry Density and to

52

hydrate with the cement to gain strength. Yoon and Abu-Farsakh (2009)investigated the effect of the moisture content and the water/cement ratio on thecompressive strength at 7 days, shown in Fig. 5.3 and Fig. 5.4. The soil is classified assilty sand (SM) and A-2 according to the UCCS and AASHTO system, respectively.

Fig. 5.3 Relationship between moisture content and UCS

Fig. 5.4 Relationship between water to cement ratio and UCS

As shown above, the unconfined compressive strength has a positive correlation withthe moisture content at the dry side of the Optimum Moisture Content. The optimumwater to cement ratios that correspond to the highest strength are about 0.75, 1.05 and1.25 for the silty sand sample mixed with 12, 10, and 8% cement, respectively.

Yoon also proposed a correlation model to estimate the unconfined compressivestrength of cement stabilized sand:

0.62( / )

wc a

ini

Cf pe w c

= ´ (5-1)

Where

cf −unconfined compressive strength (kPa)

ap − reference pressure (atmospheric pressure) (kPa)

inie − initial void ratio unit (%)

wC − cement content (%)

The moisture is not only needed for compaction, but must also be sufficient to ensurethe cement hydration. The effect of ratio of water and cement on the compressivestrength was investigated by Yoon, which is shown in Fig. 5.5.

53

01

23

45

67

8

9

0 2 4 6 8 10

Water/Cement Ratio

UnconfinedCompressive

strength(MPa)

soil/cement ratio=0.47



soil/cement ratio=4

Fig. 5.5 28-day strength of cement treated clay

Fig. 5.5 shows the data plotted separately according to the soil-cement ratio. As can beseen, for a given water-cement ratio. This relationship can be expressed in thefollowing equation

( / )

0 ( / )

m s c

c n

ef fw c

= (5-2)

Where

0f , m and n are experimentally assigned values. For the cemented slurry clay

samples, m =0.62, n =3 and 0f = 4,000 kPa for the 7-days strength and 6,000 kPa

for the 28-days strength (Yoon and Abu-Farsakh, 2009).

The experimental work in (Kersten, 1961) showed that the compressive strengthincreases to a maximum at a moisture content slightly less than the optimum moisturecontent for the sandy soil and the silty soil, and at a greater moisture content than theoptimum moisture content for clay soil.

The influence of the moisture content is more related to its ability to improveworkability and facilitate compaction to obtain a coherent mass than that it is to thewater requirement for hydration, because adequate water for compaction ensuresadequate water for hydration provided it is not lost during curing (Kersten, 1961).

3. Curing conditionsAppropriate curing conditions significantly help develop the compressive strength.The curing age is an important factor affecting the strength development. In research(TRH 14, 1985) the effect of the curing age on the compressive strength wasinvestigated for soil stabilized with two types of cement. Based on this result, theeffect of adding Roadcem is included in Fig. 5.6. The curve with RoadCem isobtained from Powercem Technologies. It can be seen that by use of RoadCem, thecompressive strength at 28 days is 20% to 30% higher than the strength only withcement. However, it has to be realized that the soil type and test conditions will havebeen different.

54

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

3 4 5 6 7 8 9 10 11 12 13 14

Cement content (%)

Compressive

strength

(MPa)

112days

56days

28days

14days

7days

4days

2days

1day

112 days withRoadCem

(a) Ordinary Portland Cement

(b) Portland Blast Furnace Cement Fig. 5.6 Effect of curing age on the unconfined compressive strength

Fig.5.6 shows the increase in strength with age. It has been found that the 28-daysstrength is between 1.4 and 1.7 times the 7-days strength. For estimation purposes afactor of 1.5 may be used.

Bahar, Benazzoug et al. (2004) investigated the strength of immersed specimensstabilized with cement (5% percent by weight). The soil is classified as moderatelyplastic clay type A-6 according to the AASHTO system. The compressive strength ofspecimen at dry state and after 48 hours immersion at an age of 28 days are given inFig.5.7.

Fig. 5.7 Compressive strength for dry and wet specimens at 28 days

After immersion in water for 48 hours, the strength of the specimens decreasedsignificantly compared to the dry specimens, because soaking reduces the bondingstrength of the particles. Experiments by Kersten (1961) show that the compressivestrength after 28 days immersion was in all cases lower than after 7 days immersion.

55

In practice the field strength may differ from the laboratory results due to theenvironmental conditions. In order to predict the variations of strength due toenvironmental changes, (Davis, Warr et al. 2007) evaluated the effect of wetting onthe strength of cement-stabilized sand (SP, according to the USCS system) by soaking(1 day) the specimens up to 5 times and measuring the strengths after 28 days curing,as presented in Fig. 5.8.

Fig. 5. 8 28-day strength variation with number of wetting

At low cement ratio (4%) the compressive strength varied a little. But at relativelyhigh cement ratios of 8%, 12% and 16% the strength increased gradually up to threecycles of wetting and drying, and after that it stayed constant or decreased a little.

4 Dry densityThe strength and durability of cement stabilized soil are strongly influenced by the drydensity. The cement stabilized soil samples must be compacted to the maximum drydensity in order to reduce the porosity and enhance the bond strength.

Croney (1977) determined the unconfined compressive strength of cylinders of acohesive soil sample compacted to different dry density. The results in Fig. 5.9 showthat a higher dry density yields a higher compressive strength.

Fig. 5.9 Compressive strength of samples at different dry density (Croney, 1977)

For design purposes, the minimum compressive strength should be specified. In UK,the minimum strength of 2.76 MPa at 7 days is required for moist-cured cylindricalspecimens having a height/diameter ratio of 2:1 (Guthrie and Rogers, 2010).

5. With RoadCemBased on the research (Altun, Sezer et al., 2009) and (Bnattacharja and Bhatry,2003), similar compressive test results from PowerCem Technologies are added in Fig.

56

5.10 and Fig. 5.11. Again it has to be realized that the soil type, the methods ofmanufacturing specimens and the testing conditions might be different.

Fig. 5.10 Variation in the 1, 7 and 28 curing days strength of samples

Fig. 5.11 Effect of curing age on compressive strength

The main observation in Fig. 5.10 and Fig. 5.11 is that due to the addition ofRoadCem the strength keeps on developing during a longer period of time, comparedto cement stabilization only. In this latter case, the gain in strength after 7 days is verylimited.

Fig. 5.12 illustrates the SEM images A–D of the experimental panel treated (stabilized)with RoadCem and Cement, at 5 000 (images A and D), 2 500 (image C), and 1 500(image B) times magnification. Fig. 5.12 (A) and (C) are the images of one month andfive months after construction and show the dense crystalline microstructure(indicated by arrows). It is worth noting that an extended and more profoundcrystalline microstructure formation is visible in image (C). The image in Fig. 5.12 (B)is the image three months after construction and it does not show the microstructureclearly (lowest magnification), hence, it was disregarded for the analysis.

Fig. 5.12 (D) is the image of eight months after construction and it shows adense-cemented matrix in the form of interlocked clusters (indicated by circles), and itis an increase in linking between particles. That contributed to bond strength andstrength gain. The cementitious growths have fully developed between the particlesforming bonds; hence, there is no evidence of shrinkage cracking. This efficiency tofill up the voids improves strength.

The typical needle-like crystals seen in the experimental panel are not visible whenthe soil is stabilized with only cement. Therefore, it looks as if the RoadCem stabilizeraffects conventional cement stabilization. The SEM images show different

57

characteristics because of the different magnifications sizes.

Fig. 5.12 SEM images of RoadCem and Cement treated soil/material(PowerCem Technologies, 2008)

5.2 TENSILE STRENGTH

Sub-bases and bases in pavements structures are subjected to tensile stresses andstrains under applied traffic loads. Therefore the tensile strength of the cement-boundbase material is required for most design methods.

The direct tensile test, the indirect tensile test and the flexural tensile test are threetests that can be used to determine the tensile strength of cement stabilized materials.The indirect tensile test is easy to perform, therefore it is to be preferred to the directtensile test, which is more difficult (TRH 14, 1985). According to NEN-EN 14227-1,

the tensile strength tf can be derived from the indirect tensile strength itf using the

relationship t it0.8f f= . In practice the indirect tensile test and the flexural tensile test

are the two primary types of test utilized to obtain the tensile strength.

5.2.1 Indirect tensile strength

The indirect tensile strength is defined as the stress at failure of a cylindrical specimensubjected to a compression force applied on two opposite directions, shown in Fig.5.13. It can be performed according to the standard NEN-EN 13286-42.

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1 − specimen2 − packing stripsF − load

Fig. 5.13 Indirect tensile test

Kolias, Kasselouri-Rigopoulou et al. (2005) have presented test results on the effectsof the cement content on the indirect tensile strength of cement stabilized clay (soiltype: A-6, according to the AASHTO system), see Fig. 5.14.

Fig. 5. 14 Effect of cement content on the indirect tensile strength at 28 days

The indirect tensile strength increases significantly with the cement content up toabout 10% and beyond that the rate of increase is slower.

Consoli, da Fonseca et al. (2011) have evaluated the effect of the cement content andporosity on the indirect tensile strength. The soil is classified as well graded silty sand(SM). The results of 7-day strength by use of cement (CEM Ⅲ) are presented in Fig.5.15.

Fig. 5.15 Variation of the indirect tensile strength of cement

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As shown in Fig. 5.15, the addition of cement promoted an increase in the indirecttensile strength, and a reduction of the porosity also results in increased indirecttensile strength. Reduction of the porosity results in much more contact between theparticles which enhances the bonding strength.

In this research (Consoli, da Fonseca et al., 2011), the relationship between thevoids/cement ratio and the 7-day indirect tensile strength is also given, as shown inFig. 5.16.

Fig. 5.16 Variations of the indirect tensile strength with cement content and porosity η

It is shown that the voids/cement ratio ( ivη / C ) is an appropriate index parameter to

evaluate the indirect tensile strength.

The relationship between indirect tensile strength and compressive strength has beenevaluated, as shown in Fig. 5.17. It can be seen that a high compressive strengthcorresponds to a high indirect tensile strength.

Fig. 5.17 Relationship between compressive strength and indirect tensile strength(Shacklock, 1974)

In research (Babi, 1987) two linear mathematical models were utilized to define thecorrelation between the compressive strength and the indirect tensile strength.

i t cf af b= + (5-3)

it c'f a f= (5-4)

Where

itf is the indirect tensile strength

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cf is the compressive strength

a , b and 'a are the coefficients

The gradation of the granular materials has practically no influence on the relationship

between itf and cf . The compaction of the mix influences the relationship. With a

degree of compaction of 98%, 95% and 90% (Modified Proctor) the indirect tensilestrength was 11.5%, 13.0% and 15.0% of the compressive strength, respectively.

5.2.2 Flexural tensile strength

The flexural tensile strength is often referred as the modulus of rupture. The flexuraltest simulates the field condition of the cemented layer in a pavement structure whensubjected to a wheel loading, and it is easy and quick to perform, so it is preferred tobe used. The flexural test assumes the applicability of the beam-bending theory andthat the material has the same elastic modulus in compression and tension (Otte,1978)

The flexural tensile strength of cemented materials is about one-third of thecompressive strength for low-strength materials and about one-fifth of thecompressive strength for high-strength materials (TRH 14, 1985). Research (Ronaldet al. 1979) gives an almost linear relationship between the flexural tensile strengthand the compressive strength, indicated in Fig. 5.18.

Fig. 5.18 Flexural tensile strength plotted against compressive strength

In another research (Kersten, 1961) comparable data on unconfined compressivestrength and flexural strength of hardened cement-treated soils shows a nearly linearrelationship at all cement contents and at all ages. The flexural strength wasapproximately 20 percent of the compressive strength.

The strain at break is defined as the strain beyond which the material fails in responseto the applied load. It is a determining factor for calculating the structural thicknessfor static loading or roads with high axle loads. The higher the strain at break, the

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thinner the required pavement structure.

The strain at break can be obtained based on the flexural strength and the deflection.Traditional cement-bound materials like concrete and cement stabilized sand have astrain at break of 150 to 200 µm/m and about 125 µm/m, respectively. Through theaddition of Roadcem the strain at break increases very substantially. So it is possibleto create more flexible cement-bound materials by the addition of RoadCem(PowerCem Technologies, 2008).

5.3 ELASTIC MODULUS

5.3.1 Static modulus

A typical stress-strain curve for an unconfined compression test on a cementedmaterial is shown in Fig. 5.19.

Fig. 5.19 Typical stress-strain curve for cement stabilized materials

The slope of the initial straight line represents the elastic modulus of the cementedmaterial. When concrete and other cemented materials are subjected to tensile stressthe stress-strain relationship becomes non-linear when the applied stress exceeds40-70 percent of the failure stress (Maclean, D.J., Robinson et al. 1952).

The stress-strain relationship can be affected by many factors. Fig. 5.20 gives thecurves for basaltic crushed rock stabilized with different cementitious binders with3% additive content.

Fig. 5.20 Typical unconfined compressive stress-strain relationships for 7-days curedspecimens with different binders (Chakrabarti and Kodikara, 2003)

Fig. 5.21 presents the effect of addition of cement on the elastic modulus of samples

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at the age of 28 days (Bahar, Benazzoug et al. 2004). The soil is classified asmoderately plastic clay type A-6 according to the AASHTO system. In can be seenthat the cement stabilization increases the slope of the curve.

Fig. 5.21 Stress-strain curve for samples under compression

Kersten (1961) investigated the variation of the static modulus of elasticity of cementtreated sand-clay mixtures with the clay content ranging from 0 to 100 percent. Theresults show that the static modulus decreased with increasing clay content, which isshown in Fig. 5.22.

Fig. 5.22 Influence of clay content on the modulus of elasticity (Kersten, 1961)

In order to estimate the elastic modulus of cement stabilized materials, it is usuallyrelated to the strength. TRH 14 (1985) reports the following relations:

Cement-treated crushed stone tE 8 3500f= + (5-5)

Cement-treated natural gravel tE 10 1000f= + (5-6)

Cement-treated crushed stone 0.88cE 4.16( ) 3484f= + (5-7)

Cement-treated natural gravel 0.88cE 5.13( ) 1098f= + (5-8)

Where:

E − static modulus of elasticity (kPa)

cf − unconfined compressive strength (kPa)

tf − flexural tensile strength (kPa)

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Molenaar (2005) reported that the flexural strength and flexural stiffness for cementtreated fine grained, cohesive soils can be estimated using the following equations.

t c0.0042 0.1427f f= - + (5-9)

0.885f cE 1435 f= (5-10)

Where:

cf − compressive strength (MPa)

tf − flexural tensile strength (MPa)

fE − stiffness modulus in flexure (MPa)

According to the standard NEN-EN 14227-1, cement bound granular mixtures shallbe classified by the tensile strength and the elastic modulus, shown in Fig. 5.23.

Fig. 5.23 Characterization of cement-bound granular mixtures by the tensile strength (MPa) and modulus of elasticity (MPa)at 28 days

The tensile strength ( tf ) shall be derived from the indirect tensile strength using the

relationship t it0.8f f= . The elastic modulus shall be measured in indirect tension.

5.3.2 Dynamic modulus

The dynamic modulus of elasticity is a material property that indicates how the load isdistributed when the material is dynamically loaded. A model (5-11) was given toindicate the relationship between the pulse velocity and the dynamic modulus (Babic,1987).

dbE aV= (5-11)

Where:V is the pulse velocity (km/s)a and b are coefficients.

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An example of relation (5-11) is given in Fig. 5.24.

Fig. 5.24 Dynamic modulus and pulse velocity

For estimation of the dynamic modulus, Fig. 5.25 gives examples of an experimentalrelationship between the dynamic modulus and compressive strength (Babic, 1987).

Fig. 5.25 28-day compressive strength–dynamic modulus of elasticity correlations

As indicated in Fig. 5.25, the relationship between the compressive strength and thedynamic modulus of elasticity is mostly non-linear. The results can be described by amathematical model of the following form:

d cln( )E a bf c= + (5-12)

The relationship between the compressive strength and the dynamic modulus is basedon experimental results with variable cement content, soil gradation and dry density.No single correlation for all stabilized mixes could be established.

A relationship between the dynamic modulus and the flexural tensile strength is givenin research (Croney, 1977), which is shown in Fig. 5.26.

Fig. 5.26 Relationship between dynamic modulus and flexural tensile strength at 28days for cemented granular materials

At a given flexural tensile strength, the dynamic modulus decreases with increasingfines content in the soil. Clays, sands and gravels show different elastic deformationbehavior under repetitive loading, so when stabilizing with cement the mixtures will

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behave quite differently.

Kersten (1961) presents that the static modulus of elasticity in compression is onaverages slightly more than 60 percent of the static modulus in flexure. In the studythere is presented a linear relationship between the dynamic modulus and the flexuraltensile strength, except for the lower strengths of the silty and clayey soils (Fig. 5.27).The relationship trend also fits for that with compressive strength. This relationshipcan be compared with that in Fig. 5.27, which is not linear.

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20 25 30

Dynamic modulus of elasticity (103 MPa)

Flexural

strength(MPa)

Sand-gravel

Sandy loam

Clayey Sa.Gravel

Silt loam

Fig. 5.27 Dynamic modulus and modulus of rupture (flexural tensile strength)

Croney (1977) presents a relationship between the dynamic and static Young’smodulus for cemented granular materials. The equation is:

d sE =1000+0.88E (5-13)

Where dE and sE are the dynamic and static modulus (MPa), respectively.

In PowerCem Technologies, the dynamic modulus is determined by ultra-waves(nondestructive, Fig. 5.28).

Fig. 5.28 Measurement of dynamic modulus of elasticity

Fig. 5.29 shows the damped harmonic vibration with RoadCem and withoutRoadCem. It can be seen that with the use of RoadCem a higher damping is achieved,which means better harmonic absorption of vibration when there are earthquakes.This means that through the addition of RoadCem the cement-stabilized layer has abetter chance to survive earthquakes without structural damage.

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Fig. 5.29 Comparison of damped harmonic vibration with RoadCemand without RoadCem

5.4 FATIGUE PROPERTIY

Fatigue testing is conducted to determine the lifespan of a material subjected torepeated dynamic loads. Fig. 5.30 shows the variation of the modulus of rupture MOR(also known as flexural tensile strength) with the number of cycles of failure for siltyclay stabilized with cement.

Fig. 5.30 Dynamic flexure tests for 28-day curing time

It can be seen that the flexural tensile strength decreases by about 44%, when around100,000 load cycles are applied. So it was demonstrated that as much as 44%reduction in strength can occur when soil-cement beams are subjected to dynamicflexure (Bhogal, Coupe et al. 1995).

Fatigue damage usually occurs when the applied stress amounts about 35 percent ormore of the strength. The failure starts with micro-cracking and a loss of bond at theinterface between the aggregate and the matrix of fine material. It can be concludedthat the material is able to withstand an unlimited number of load repetitions when thestress ratio remains below 0.35, for the applied stress is then too low to start themicro-cracking. (Otte, 1978)

The stress ratios are plotted against the number of cycles to failure to obtain theso-called S-N curves. Typical S-N relationships for cement stabilized recycledaggregate (SRA) compared with other materials (Sobhan and Das, 2007) are shown

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in Fig. 5.31.

Fig. 5.31 Stress ratios versus number of cycles to failure

As indicated in Fig. 5.30, the performance of SRA is quite similar to these traditionalmaterials.

Generally, the fatigue failure criterion of cement stabilized soil is expressed by theSN-N equation:

log NSN a b= - (5-14)

Where

t

σσ

SN = − Ratio of applied tensile stress and ultimate tensile stress

tσ − ultimate tensile stress

σ− applied tensile stress

In Netherlands, based on laboratory testing, a strain related fatigue curve wasdetermined for a particular sand cement:

log N 10 0.08ε= - (5-15)

Whereε − Flexural tensile strain at the bottom of the sand cement layer (μm/m)

Compared with the laboratory determined fatigue relation, the field fatigue relationcan be written as

log N 8.5 0.034ε= - (5-16)

Where:N − allowable number of 100 kN equivalent single axles,ε − flexural tensile strain at the bottom of the cement treated base (μm/m)

Furthermore it appeared that the chance on fatigue failure is very small if the flexuraltensile strain level is 60 μm/m or less.

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In South Africa, the following relationship for cement treated granular materials isused,

tlog N 9(1- ε / ε )= (5-17)

ε − applied strain level (μm/m)

tε − flexural strain at break (μm/m)

For fresh crushed rock materials the strain at break varies between 100 and 250 μm/m.The mean value was reported to be 160 μm/m (Molenaar, 2005).

In research (Otte, 1978) it is suggested to use strain as the criterion for controllingfracture. Otte proposed 2 relationships between the strain ratio and the number of loadrepetitions expressed as equations (5-18) and (5-19), shown in Fig. 5.32, namely:

fε / 1- 0.11log Nbe = (5-18)

0.079b fε / ε N-= (5-19)

Fig. 5.32 General fatigue curves for cement-treated bases

Croney (1977) performed fatigue tests at various frequencies of loading on twoconcrete grades. The two concrete grades used were 25 MPa and 32 MPa unconfinedcompressive strength at 28 days of curing. The results are shown in Fig. 5.33. CPMindicates cycles per minute.

Fig. 5.33 Effect of loading frequency on stress/life relationship for concrete

The mean relationship shown in Fig. 5.33 can be used for the structural evaluation of

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concrete pavements.

Although there seems to exist a large variation in fatigue relations, the relationbetween applied stress or strain and allowable number of load repetitions alwaysexhibits very high values for the slope, indicating a rather brittle behavior. Comparedto the traditional materials, it has been proven that the addition of a specificPowerCem product (RoadCem) can improve the fatigue property, which is shown inFig. 5.34.

(a) (b)

Ed—dynamic modulusE0—initial dynamic modulus

Fig. 5.34 Fatigue behavior of cement bound materials

From Fig. 5.34, with RoadCem it is clear that at the end of the lifetime the material isnot suddenly breaking. This is due to the higher flexibility of the material withRoadCem. In practice no cracks and no deformation are occuring when execution anddesign is according to the instructions. And the fatigue curves with RoadCem arebetween the asphalt and sand cement. (Birgisson, Egyed et.al. 2008)

5.5 DURABILITY

Durability can be defined as the ability of a material to retain stability and integritywhen exposed to the environmental conditions for many years. This is an importantproperty especially if the material is subjected to severe environmental conditions.

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Durability of the base contributes greatly to the satisfactory performance ofpavements. Two tests are available to evaluate the durability of cement stabilizedsamples, namely, by wetting and drying and by freezing and thawing (NEN-EN12390-9). The freeze/thaw test procedure consists of freezing the cured specimens at-25ºC in a freezer for 24 hours, and then thawing for another 24 hours at atemperature of +22ºC and a relative humidity of approximately 98%.

Both test results are expressed by the loss in weight of a specimen after 12 cycles offreeze/thaw cycles or wet/dry cycles. The suggested allowable material loss values aregiven in Table 5.1.

Table 5.1 Durability requirements for cemented soils (Molenaar, 1998)Soil Allowable loss in weightA-1, A-2-4, A-2-5, A-3 < 14%A-2-6, A-2-7, A-5 < 10%A-6, A-7 < 7%

The durability of stabilized soil on repeated wetting and drying primarily depends onthe pore structure and the tensile strength of the material. Research (Bnattacharjaand Bhatry, 2003) gives an example of wet/dry test results for cement and limestabilized soil.

Fig. 5.35 Weight loss in wet-dry durability testing of soil stabilized with6 and 9% cement and lime

It clearly indicates that cement stabilized soil exhibits superior performance to thatstabilized with hydrated lime.

Shihata and Baghdadi (2001) investigated the effect of the time of exposure to wateron the durability of the specimen (cement content 7%). The soil is A-2-4 according tothe AASHTO classification. Samples were tested after 12 cycles and then exposed tosaline water during different periods of time, which is indicated in Fig. 5.36.

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Fig. 5.36 Change in weight loss with exposure period in the samples tested for (a) Freeze-Thaw and (b) Wet-Dry tests

The results show that both trends of mass loss generally increase sharply up to 90days of exposure after which the rate of increase drops to almost zero. The soil with alarger amount of fines exhibited a larger mass loss in the wet-dry test, which isopposite in the freeze-thaw test.

5.6 WATER PERMEABILITY AND ABSORPTION

Permeability is an important property when materials are exposed to water. Forpractical use, impermeable material may be required to protect the underlyingmaterial to prevent the water intrusion and avoid the strength loss.

Most soils can be made practically impermeable by addition of cement. The reductionin permeability can be attributed to the hydration products filling the voids betweenthe particles. Bahar, Benazzoug et al. (2004) examined the variation of permeabilityof a clay soil (A-6, according to the AASHTO system) by addition of cement and theresult is shown in Fig. 5.37.

Fig. 5.37 Effect of cement content on the water permeability

As shown above, the permeability of soil is closely related to the cement content. The

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addition of cement can reduce the permeability. The stabilization of soil with cementcan lead to a larger mechanical strength and lower permeability and hence betterdurability.

Research (Moloisane, 2009) evaluated the permeability of seven different commercialstabilizer products from the five generic group types, two stabilizers from theelectro-chemicals generic group type (Perma-Zyme 11X and Con-Aid), and otherswere from the organic non-petroleum (Dustex), organic petroleum (BitumenEmulsion), polymer (Ecobond/urea-formaldehyde (UF) resin), cement catalyst(RoadCem). The results show that cement stabilization with RoadCem obtained thelowest permeability.

In-situ soils are sensitive to moisture changes, but by stabilizing them with a binderthe stability can be maintained. Chakrabarti and Kodikara (2003) tested the degreeof water absorption at basaltic crushed rock stabilized with various binder contents.Fig. 5.38 presents the effect of addition of a binder on the water absorption.

GB − general blended cement;GP − general purpose cement;AAS − alkali activated slag.

Fig. 5.38 Water absorption versus binder quality for specimens cured for 28 days

The results clearly show that the water absorption decreases as the binder quantityincreases, particularly for binder quantities > 3%.

Another issue is the potential for capillary rise of water within stabilized materials.Higher water content in pavement material can give rise to excessive water pressuresand associated distress conditions.

Fig. 5.39 Capillary rise with time for 28-days cured specimens

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(Chakrabarti and Kodikara, 2003)

Fig. 5.39 presents the moisture capillary rise as a function of time for basaltic crushedrock stabilized with various contents of general purpose (GP) cement. The resultsshow that the rate of capillary rise decreases with the increase in cement content.

5.7 CONCLUSIONS

Compressive strength is an important property used to characterize cement boundmaterials. Factors influencing the compressive strength are cement content, soil type,curing conditions, and compaction effort, which have been reported in many previousresearch results.

The indirect tensile test and flexural test are commonly used to obtain the tensilestrength. The relationship between compressive strength and tensile strength is nearlylinear and mathematical models have been created to indicate the correlation, but dueto the different compositions and soil type, there is no unique relationship.

For the modulus of elasticity, many relationships have been established to indicate themodulus from the compressive strength or flexural tensile strength. The fatigue failurecriterion of cement stabilized soil is usually expressed by an SN-N equation, whichhas a large variation.

Addition of cement can help reduce the permeability and increase the durability ofin-situ soils. Freeze/thaw and wet/dry tests are used to indicate the durability, which ismainly affected by the cement content.

Addition of RoadCem has been proven to increase compressive strength, bearingcapacity and especially higher breaking strain and fatigue relation and this also withclay soils and soil with organic material.

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CHAPTER 6

CRACKING BEHAVIOR

Failure of a pavement system is sometimes associated with cracking in the bound basecourse (Little, 1987). Cracks may occur in the base course and reflect through the toplayer under loading, resulting in visible surface cracks (as shown in Fig. 6.1), whichare referred as reflection cracks. Reflection cracks may not be a problem. If the cracksare narrow (< 1/8 in. or 3 mm), sufficient load transfer normally exists throughaggregate interlock to keep the pavement structure functioning. However, if widecracks (> ¼ in. or 6 mm) occur at the surface, they will result in poor load transfer andpumping of the subgrade materials due to water intrusion (Halsted, 2007). The severecracking will cause unevenness and structural failure of the pavement and increasedmaintenance and repair costs.

(a) Narrow reflection crack (b) Wide reflection crackFig. 6.1 Reflection cracks (Adaska and Luhr, 2004)

When a cemented material is loaded beyond a certain limit microcracking firstdevelops at the interface between coarse particles and the matrix. The extent of themicrocraking increases upon subsequent loadings, and eventually the microcracks joinup into a macro-crack. Laboratory flexural and compressive tests indicated that

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microcraking occurs at stress levels of about 35 percent and more of the ultimatestrength and strain levels or about 25 percent of more of the strain at break (TRH 14,1985).

6.1 SHRINKAGE

There are generally two types of crack: shrinkage cracks and traffic induced cracks.Drying shrinkage is the main cause of the shrinkage cracks. The final crack widths aremainly dependent on the ultimate shrinkage strain and crack spacing (Halsted, 2007).The degree of shrinkage is affected by various factors, the type of soil, degree ofcompaction, curing, cement content, temperature changes and friction withsurrounding pavement layers.

The other type of cracking is traffic induced cracking. Traffic induced cracking willnot occur in cement treated bases when the strain level remains below 60 / 1.46(environmental factor) = 41 μm/m in cases where the load transfer across transversecracks is poor. When a good load transfer can be guaranteed, this strain level is 50μm/m. These values are proposed to be used as endurance limits for the materialinvestigated (Molenaar, 2001). Cracking due to environmental changes should bedistinguished from subsequent cracking caused by traffic.

When the hydrating cement treated material shrinks, friction develops between thetreated layer and the underlying layer and by consequence internal tensile stresses areinduced. The internal stresses may exceed the tensile strength and cracking occurs. Inresearch (TRH 14, 1985) it is described that the spacing and widths of the cracks aredetermined by the rate of the tensile strength development relative to the shrinkagetensile stress development.

Fig. 6.2 Cracking as a result of the interrelationship between shrinkage stress, strengthand time (TRH 14, 1985)

If the shrinkage stresses exceed the tensile strength at a relatively low strength thenthe cracks will be more numerous, narrower and more closely spaced (shown as

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Material A in Fig. 6.2). Such cracks will vary in width from fine hair cracks to 1 mm,and they are usually up to 2 m apart. If the material develops a greater tensile strengthbefore the shrinkage stress exceeds the tensile strength, there will be fewer cracks, andthey may be 2 to 3 mm wide and 4 to 6 m apart (shown as Material B and C in Fig.6.2).

6.2 FACTORES INFLUNCING SHRINKAGE

The degree of shrinkage is dependent on soil type, cement content, moisture content.

1. Cement contentStabilization of soil with cement can reduce the shrinkage because the cement matrixtends to restrain the soil movement, but the addition of cement doesn’t completelyprevent the shrinkage due to the moisture loss during the hydration. Fig. 6.3 illustratesthe effect of the cement content on the shrinkage of some granular material (A-2-4and A-3, according to the AASHTO system).

Fig. 6.3 Effect of cement content on shrinkage (George, 1968)

As seen above, shrinkage is initially reduced with the addition of a small amount ofcement, but increases steadily as the cement content increases.

The combined effect of cement content and sand percentage was evaluated in research(Kenai, Bahar et al. 2006). Fig. 6.4 shows the effect of the addition of cement, sandand a mixture of cement and sand on the final shrinkage of samples. It can beconcluded that the shrinkage of cement stabilized soil compared to that ofun-stabilized soil was reduced by about 20% and 44% for 6% and 10% of cementcontent, respectively. The addition of sand also reduced the shrinkage about 29% and64% for 10% and 15% of sand content, respectively.

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Fig. 6.4 Effect of sand and cement content on the shrinkage at the age of 28 days

2. Curing timeShrinkage cracks may increase with time. Bahar, Benazzoug et al. (2004)investigated the effect of the curing age on the shrinkage, as shown in Fig. 6.5. Thesoil, classified as moderately plastic clay type A-6 according to the AASHTO system,is stabilized with different cement contents.

Fig. 6.5 Development of shrinkage during first 28 days

It can be clearly seen that shrinkage increases rapidly during the first 4 days, and thenthe rate of increase rate is slow. Hence, curing for the first 4 days will be beneficial inreducing drying shrinkage and cracks.

Rapid moisture loss may also cause much shrinkage and is detrimental to the finalstrength, because when materials dry quickly the volume will change rapidly, whichinevitably results in more shrinkage. Also there will not remain enough moisture tocontinue hydration of the cement which will reduce the final strength. So it is essentialto control the curing environment and avoid rapid moisture loss.

However, due to the unavoidable variations of the environmental conditions, crackingin a cement stabilized layer due to temperature and/or moisture content variation can’tbe avoided and must be accepted.

3. Moisture contentThe shrinkage of stabilized materials mainly results from moisture loss. And moistureloss is mainly caused by the cement hydration and evaporation. Therefore themoisture content is a significant factor for controlling the degree of shrinkage. Fig. 6.6presents the final shrinkage of sand stabilized with cement at variable moisturecontent.

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Fig. 6.6 Variation of final shrinkage at 28 days with mixing water content(Kenai, Bahar et al. 2006)

This figure shows that as the water content increases the shrinkage increases rapidly,due to the loss of excess of water which is not needed for cement hydration. So it isessential to control the water content of the mixture, which is referred as the OptimumMoisture Content obtained by the Proctor test.

Molenaar (1998) reported that the specimens that were compacted at the dry side ofthe optimum moisture content showed lest shrinkage. For practice this means that ifone wants to limit problems due to shrinkage, compaction at a water contentsomewhat lower than the optimum moisture content is recommended.

4. CompactionA tight matrix of a well-compacted soil reduces the shrinkage potential, because thesoil/aggregate particles are packed densely together, resulting in a reduced voidscontent. Good compaction also leads to better aggregate interlock and structuralsupport if a crack does develop (Adaska and Luhr, 2004).

Bhandari (1973) reported that compacting cement-stabilized soil at modified Proctorcompaction reduced the shrinkage by more than 50% compared to stabilized soilcompacted to standard Proctor density. In addition, the optimum moisture content atModified Proctor compaction is typically less than that at standard Proctorcompaction, which also helps to reduce shrinkage.

Fig. 6.7 Effect of dry density and moisture content on shrinkage (George, 1973)

Fig. 6.7 shows that increased dry density and reduced moisture content result in lessshrinkage of a cement-stabilized A-2-4 granular material.

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The least amount of shrinkage is obtained for the stabilized material at highest densityand lowest moisture content. Many project specifications accept minimum densities of95% of standard Proctor compaction.

5. Soil type

Studies (George, 1968; Nakayama, 1965) show that cement-stabilized fine-grainedsoils (e.g. clays) exhibit more shrinkage than cement-stabilized granular soils. Thereason is that fine-grained soils have larger particle surface areas than granularmaterials and typically require a higher moisture content for compaction and need ahigher cement content to achieve an adequate durability and strength. Both factorscontribute to a high moisture content and consequently a higher drying shrinkage(Adaska and Luhr, 2004).

Research (George, 2002) presents an example of the effect of cement stabilized soilson the crack pattern, as shown in Table 6.1. Clay particles have a large surface arearelative to their weight, so they hold a large amount of water, and have a highoptimum moisture content, so the potential for shrinkage cracking is greater.

Table 6.1 Effect of fines content on soil-cement crack pattern

Type of soilCrack width

when last crackoccurred, mm

Crack spacing, whenlast crack occurred

and later, m

Crack width@ 7days,

mm

Terminal crackwidth, mm

#1 (A-3/SM) 1.5 @ 1.6 days 13.0 3.40 6.0 @ 20.0 days#2 (A-2-6/SC) 2.9 @ 1.2 days 6.0 6.00 10.8 @ 22.0 days

It is clearly that the crack width is substantially affected by the fine content of the soil:the finer the soil, the larger the crack width.

6. Other factors

The factors contributing to the shrinkage are complicated, dependent on the inherentproperties as well as the environmental conditions. Fig. 6.8 presents the shrinkageplotted against UCS for many materials.

Fig. 6.8 7-day UCS vs. beam shrinkage.It shows that there exists an optimum strength that will produce the minimum

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shrinkage and the optimum strength varies depending on the soil type.

6.3 METHODS OF CONTROLLING

Shrinkage is a natural characteristic of all cement-bound materials that should beaccepted. However, proper construction techniques and mix design methods canminimize the adverse effects. With respect to the construction process, following theproper construction techniques and providing good quality control during the fieldoperation can minimize cracking (PCA , 2003).

A number of research studies (PCA, 2003; Cho, Lee et al. 2006; FM 5-410) presentvarious methods to minimize shrinkage cracking, which include altering the mixdesign, proper construction process and techniques, the use of “pre-cracking”, andadding additives. In research (FM 5-410) it is reported that the drying shrinkage ofcement-treated soil can be significantly reduced by replacing a part of the cement withfly ash. Not only the maximum dry shrinkage is reduced, but also the rate of shrinkageis affected by the addition of fly ash. Fig. 6.9 gives an example that the addition of flyash reduces the drying shrinkage (Cho, Lee et al. 2006).

Fig. 6.9 Addition of fly ash to reduce drying shrinkage

PCA (2003) reports that “pre-cracking” is used by applying loading into thesoil-cement layer to obtain a network of closely spaced narrow cracks which acts torelieve the shrinkage stresses and provides a crack pattern to minimize thedevelopment of wide cracks. Research (PCA, 2001) shows that the microcrackingprocess substantially reduces the amount of pavement surface cracking, but notsignificantly affects the base stiffness.

In addition to this, the use of RoadCem from PowerCem Technolygies company incement stabilization may result in no cracks and no deformations. Even when soils areinvolved with a high organic content the cement reaction will get a boost with theaddition of RoadCem. Fig. 6.10 shows a cement stabilization with RoadCem in highorganic soil conditions in a Delta area without cracks after 4 years.

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Fig. 6. 10 Cement stabilization with RoadCem showing no cracks after 4 years(Birgisson, Egyed et al., 2008)

Due to the PowerCem additives a complex chemical reaction with cement, fly-ash,water and granular material is initiated which leads to another mineral structure of thecement bound material and a new type of crystalline structure is formed, which isshown in Fig. 6.11.

Fig. 6.11 Picture from an electron microscope of the crystalline structure(Birgisson, Egyed et al. 2008)

This new crystalline structure formed with addition of RoadCem results in a strongflexural bound material, which efficiently prevents the cracking.

6.4 CONCLUSIONS

Reflection cracks at the surface of pavements are mainly caused by the cracksoccurring in cement-bound bases due to drying shrinkage. Shrinkage is a naturalcharacteristic of cement bound materials, which should be accepted. Cement content,compaction and soil type influence the amount of shrinkage. Many measures can beused to minimize the cracking due to shrinkage, including altering the mixcomposition and following proper construction methods. Use of specific additive is anefficient method. Additive from PowerCem Technologies has been proven to preventcracks.

83

CHAPTER 7

EFFECTS OF A FLEXURAL STABILIZATION

7.1 INTRODUCTION

Based on the specific information of the current stabilization a construction designwas made with RoadCem and without RoadCem.

For this calculation example a traditional asphalt pavement structure is compared witha RoadCem structure. Both structures are assumed to have a similar theoreticallifetime in terms of allowable number of standard axle load repetitions. In thisexample the differences in failure mechanisms and the spreading of the loads to thesubstructure are given in the following paragraphs:

1. Assumptions2. Designs3. Calculations4. Deflections5. Conclusions

7.2 ASSUMPTIONS

The calculation is based on the following assumptions, divided in the following parts:· Traffic· Soil

TrafficThe standard axle load is: 100 kN

84

The axle configuration is 2 times dual tires

SoilAssumptions of the soil:

· Type of soil: clay· Dynamic modulus of elasticity: 25 MPa

7.3 DESIGNS

Fig. 7.1 gives the detailed calculation for the traditional and the RoadCem asphaltpavement structures.

½ x SAL = 50 kN

Front view

Y- axle

Side view

½ x SAL = 50 kN

X- axle

25 kN25 kN

85

Asphalt 40mm Asphalt wearing courseStiffness:Edy n: 6000 Mpa 180 mm

RoadCemStiffness:Edy n = 3500 MPa

Concrete granulateStiffness: 250 mmEdy n = 600 MPa

300 mm

Total thickness structure: 290 mm

Sand sub-baseStiffness:Edy n = 100 MPa

700 mm

Total thickness structure: 1180 mm

Subsoil: ClayStiffness:Edy n: 25 MPa

Traditional structure RoadCem structure

Fig. 7.1 Comparison of traditional and RoadCem asphalt pavement structures

7.4 CALCULATION METHOD

Step 1:

Determine the stresses, strains and deflections in the critical points of the pavementstructures by the linear elastic multilayer program BISAR.

Step 2:

Check the fatigue relationships of the normative asphalt pavement structures:

86

1. Traditional structureNormative failure mechanisms of the traditional structure are given below.

Fatigue relation of the asphalt:

Neq8= EXP(0.33796*LN(Edyn asphalt)^2-7.3642*LN(Edyn) +77.142-5.2438*LN(Strain) (7-1)

OR

Fatigue relation of the top of the unbound base course, which leads to pavementdeformations in the base (which reflects as rutting at the pavement surface):

Neq9 = 10^(-6.211-0.482*0.674-4*LOG(Deflection*0.000001)) (7-2)

The lowest value for Neq will be normative for the lifetime of the traditional structure.

2. RoadCem structure

Fatigue relation of the RoadCem layer:

Neq10 = 7*108*e(-0.027*strain)*0.2 (7-3)

Due to the plastic behavior and the relatively low elastic modulus of the asphalt,deformation could occur in the sub soil and could reflect at the pavement surface asrutting. However, the plastic behavior of the Soil-RoadCem-cement material is lowand the dynamic modulus is relatively high. Due to this behavior the deformation inthe sub soil will NOT lead to deformations at the pavement surface. Just the fatiguerelation of the RoadCem layer will be normative for the lifetime of the RoadCemstructure.

The calculation of the two pavement structures is divided into 2 steps:· Step 1: Calculation of the stresses and strains in the normative layers.· Step 2: Calculation of the lifetime of the structures in terms of allowable

number of 100 kN in standard axle loads (Neq)

Step 1: Calculation of the occurring stresses and strains in the construction.The strains and stresses occurring due to a passing vehicle are given in the tablebelow:

8 F78 asphalt fatigue relation9 Fatigue relation for deformations in the top of unbounded materials, source CROW, publicatie15710 RoadCem fatigue relation, source Project: RC.20100718.CZ.0403 – Brusnice (internal PCT)

87

Table 7.1 Stresses and strains at the bottom of the bound layersConstruction Place Maximum

strainMaximumstress

U-deflection

Traditionalstructure

Bottom Asphaltlayer

93 µm/m 0.65N/mm2

518 µm

RoadCemstructure

Bottom RoadCemlayer

145 µm/m 0.63N/mm2

NA

In the following figures are the strains and stresses (X-axle) and width (Y-axle) of theroad. With herein: Y = 0 is the center of the dual tires. These values are determined bythe calculation in the BISAR program.

Fig. 7.2 Horizontal strains in transverse direction at the bottom of the bound layerover the width of the road due to a 50 kN dual tire load

Fig. 7.3 Horizontal strains in the longitudinal direction at the bottom of bound layersover the length (X) of the road due to a 50 kN dual tire load

In Fig. 7.2 and 7.3 a clear difference is visible between the traditional and theRoadCem pavement structure. The wheel loads in the RoadCem structure will bemore equal spread over the sub-layers. The reason that the strains are higher inRoadCem structure because the material has a lower dynamic elastic modulus than theasphalt of the traditional structure.

88

Fig. 7.4 Horizontal stresses in the transverse direction at the bottom of thebound layers over the width of the road due to a 50 kN dual tire load

Fig. 7.5 Horizontal stresses in the longitudinal direction at the bottom of thebound layers over the length of the road due to a 50 kN dual tire load

The differences in stresses at the bottom of the bound layers are shown in Fig. 7.4 andFig. 7.5. The stresses in the RoadCem structure are spread over a bigger area than thetraditional structure, what leads to a lower peak stress.

89

Step 2: Calculation of the lifetime of the structure:The results of the lifetime of the structure are given in Table 7.2.

Table 7.2 Lifetime of traditional and RoadCem asphalt pavement structureTraditional structure RoadCem structureNormative failure mechanism of thetraditional structure:

Fatigue relation of the asphalt:

Neq = 2.92 x 106

OR

Fatigue relation of the top of theunbounded base course, which leads torutting’s in the asphalt:

Neq = 4.04 x 106

The lowest value for Neq is normativefor the lifetime of the structure.

Normative failure mechanism of theRoadCem structure:

Fatique relation of the RoadCem layer:

Neq = 2.79 x 106

Both structures have indeed about the same theoretical lifetime. It should be realizedthat traffic wander and healing have not been taken into account in the calculation ofthe pavement lifetimes.

7.5 DEFLECTIONS

In the following figures (Fig. 7.6 and Fig. 7.7) the deflections at the top of theunbounded layer (concrete granulate base is the traditional structure and subsoil in theRoadCem structure) are shown in a 3D graphic over the length and the width of theroad:

90

Fig. 7.6 Deflections at the top of the concrete granulate base in the traditionalstructure over the length and the width of the road

Fig. 7.7 Deflections at the top of the subsoil in the RoadCem structure over thelength and the width of the road

The impact area of a passing vehicle on the top of the unbounded layer is in theRoadCem structure much higher than in the traditional structure. This is because thebending stiffness of the total bound layers is much higher in the RoadCem structure.

7.6 CONCLUSIONS

Despite the higher occurring stresses in the RoadCem layer, this structure has acomparable lifespan in terms of allowable number of 100 kN standard axle repetitionswith the traditional asphalt pavement structure.

The main benefit of the use of RoadCem is the limited thickness of the structurewhich saves materials, and labor in the execution. Besides the amount of materialswhich have to be discharged and supplied is limited what makes this type of structurea environmentally friendly technology.

91

The influence of the structure on the subsoil settlements are not included in thisexample, but the limited weight of the pavement structures will definitely lead to lesssettlements in the RoadCem structure in comparison with a traditional structure.

93

·

Chapter 8

CONCULSIONS AND RECOMMENDATIONS

8.1 CONCLUSIONS

This literature review is undertaken to summarize the properties of cement boundmaterials. Based on the literature study, the following conclusions can be given:

1) There is more than one stabilizing agent for every type of soil. The choice isdependent on the nature of the soil and the desired function of the stabilizedlayers as well as the overall cost. In general, lime is more effective to stabilizecohesive soils like silt and clay, while cement is more suitable to stabilizegranular materials like sand and gravel.

2) Prior to soil stabilization, soil tests (Liquid Limit, Plastic Limit, sieve analysis,chemical composition, Proctor test) should be done to obtain the soilproperties. Based on the soil information, the appropriate mix composition canbe determined. The cement content is a significant factor influencing thestrength and the durability.

3) The mechanical properties of cement bound materials are influenced bycement content, soil type, compaction, curing conditions and otherenvironmental factors. It is found that cement content and in-situ material typeare the main factors to control the strength of cement bound materials.

4) Shrinkage cracks in cement bound materials due to drying and moisturechanges can’t be avoided. Many appropriate methods can be used to reducethese cracks and the risk for reflective cracking, like optimum mixcomposition and proper construction technology.

5) For fatigue property, based on stress or strain controlled flexural tests, most ofthe relationships are described by SN-N curves, which exhibit a largevariation.

6) RoadCem has been proven to be a very effective additive for soil stabilization.

94

· Improvement in compressive strength, flexural tensile strength, strain atbreak and fatigue life.

· High resistance against earthquakes and vibrations.· High resistance against erosion and natural disasters.

7) To evaluate the properties and the effect of using RoadCem as additive, acomparison needs to be made for different soil types and mixture.

8.2 RECOMMENDATIONS

Soils stabilized with traditional materials like cement, bitumen and lime, often exhibitinsufficient performance (shrinkage cracks, brittle behavior, etc), which limits theapplications. However, non-traditional stabilizers have been introduced to improve theproperties of soil stabilization.

The product RoadCem, which is based on Nano technology, from PowerCemTechnologies has been widely used in many countries for cement stabilization, and thelaboratory tests and field results show excellent performance (no cracks, high strength,high strain at break, etc). In this review, the comparison of the properties with othertraditional additives has been presented. For the future application, more research inlaboratory and field validation should be undertaken to systematically evaluate theimprovement of Roadcem in the soil stabilization. Based on this, the research willfocus on the effect of RoadCem on the mechanical properties of cement-boundmaterials.

95

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Sherwood, P. (1993). Soil stabilization with cement and lime. Transportation researchlaboratory.

Little, D.N (1995). Handbook for stabilization of pavement subgrades and basecourses with lime. National lime association, Kendall/Hunt Publishing company,Dubuque, Iowa.

Unified Facilities Criteria (UFC). Soil stabilization for pavements. US, 2004.

Kersten, M. S. (1961). Soil Stabilization With Portland Cement. Washington, D. C.,National Academy of Sciences National Research Council

Molenaar, A.A.A. (1998). Road Materials Part 2 Soil stabilization. Lecture notes CT4850, Delft University of Technology, the Netherlands.

TRH 14. (1985). Cementitious Stabilizers in Road Construction South Africa, TRH 14,Pretoria, South Africa.

Yong, R. N. and V. R. Ouhadi (2007). "Experimental study on instability of bases onnatural and lime/cement-stabilized clayey soils." Applied clay science 35(3-4):238-249.

Maclean, D.J., Robinson, P.J.M., and Webb, S.B. (Oct.1952). “An Investigation ofthe Stabilization of heavy clay soil with cement for road base construction .” roadsand road construction (London), 30:358, 287-92

Bnattacharja, S. and J. I. Bhatry (2003). Comparative Performance of PortlandCement and Lime Stabilization of Moderate to High Plasticity Clay Soils, RD125,Portland Cement Association, Skokie, USA.

Head, K.H. Manual of soil laboratory testing. Volume 1: Soil classification andcompaction tests. Pentech Press, Plymouth, 1980.

Kalinski, M. E. and B. T. Hippley (2005). "The effect of water content and cementcontent on the strength of portland cement-stabilized compacted fly ash." Fuel84(14-15): 1812-1819.

Ferguson, G. (1993). Use of self-cementing Fly ashes as a soil stabilization agent. Fly

96

ash for soil improvement. ASCE GSP 36. New York.1-14

Halstead, W. J. 1986. Use of fly ash in concrete. NCHRP 127 (October). Washington:Transportation Research Board, National Research Council.

Yoon, S. and M. Abu-Farsakh (2009). "Laboratory investigation on the strengthcharacteristics of cement-sand as base material." KSCE Journal of Civil Engineering13(1): 15-22.

Justin P. Milburn and Robert L. Parsons, 2004. P.E. Performance of soil stabilizationagents. K-TRAN: KU-01-8.

Molenaar, A.A.A. (2001). Prediction of fatigue cracking in asphalt pavementsTransportation Research Record (pp 155 - 162)

Croney,D. (1977). The Design and Performance of Road pavements. London,Transport and Road Resarech Laboratory, Crowthorne, UK.

PCA (2003). "Properties and Uses of Cement-Modified Soil." Soil-cementInformation 11. Portland Cement Association, Skokie, USA

Donaldl. Basham, J. W. (Oct, 1994). "Soil Stabilization for Pavements." The UnifiedFacilities Criteria.

PCA (2003). "Reflective Cracking in Cement Stabilized Pavements". Portland CementAssociation, Skokie, USA

Special studies No.42 and No.43 (1949) Unpublished report of Portland CementAssociation, Skokie, USA.

Kurt Waelbers, 2006. Immobilization of Cr VI in concrete structures using PowerCem.Bateman Materials Limited Reg. No. 1956/01084/06

Guthrie, W. S. and M. A. Rogers (2010). "Variability in Construction ofCement-Treated Base Layers." Transportation Research Record: Journal of theTransportation Research Board 2186(-1): 78-89.

Orts, W. J., R. E. Sojka, et al. (1999). "Preventing soil erosion with polymeradditives." Polymer News 24: 406-413.

Moloisane, R.Y. (2009). Evaluation of the long-term strength behaviour of unpavedroads stabilized with non-traditional stabilizers. University of Pretoria, South Africa.25 Kennedy, J. (1983). "Cement-bound materials for sub-bases and road bases."

97

Bahar, R., M. Benazzoug, et al. (2004). "Performance of compacted cement-stabilisedsoil." Cement and Concrete Composites 26(7): 811-820.

Molenaar, A.A.A. (2005). Road Materials Part 1 Cohesive and non-cohesive soils andunbound granular materials for bases and sub-bases in roads. Lecture notes CT 4850,Delft University of Technology, Netherlands.

Medani, T.O. and Molenaar, A.A.A. (2000). Estimation of fatigue characteristics ofasphaltic mixes using simple tests. Delft University of Technology, the Netherlands

Park, S. S. (2010). "Effect of Wetting on Unconfined Compressive Strength ofCemented Sands." Journal of geotechnical and geoenvironmental engineering 136(12):1713-1720.

Altun, S., A. Sezer, et al. (2009). "The effects of additives and curing conditions onthe mechanical behavior of a silty soil." Cold Regions Science and Technology56(2-3): 135-140.

Kolias, S., V. Kasselouri-Rigopoulou, et al. (2005). "Stabilisation of clayey soils withhigh calcium fly ash and cement." Cement and Concrete Composites 27(2): 301-313.

Consoli, N. C., A. V. da Fonseca, et al. ( 2011). "Voids/Cement Ratio ControllingTensile Strength of Cement Treated Soils." Journal of geotechnical andgeoenvironmental engineering 1(1): 306.

Shacklock, B.W (1974). Concrete constituents and mix proportions. Cement andConsrete Association, London.

Babic, B. (1987). "Relationships between mechanical properties of cement stabilizedmaterials." Materials and Structures 20(6): 455-460.

E.OTTE, V. W. a. L. I. (1978). "Factors Affecting the Behavior of Cement TreatedLayers in Pavements

Bhogal, B. S., P. S. Coupe, et al. (1995). "Dynamic flexure tests of soil-cementbeams." Journal of materials science letters 14(4): 302-304.

Sobhan, K. and B. M. Das (2007). "Durability of Soil–Cements against FatigueFracture." Journal of materials in civil engineering 19: 26.

Bjorn Birgisson, Christophe Egyed, et al. (2008). New Nano crystalline structureleads to visco-elastic behaviour of cement based materials

Shihata, S. A. and Z. A. Baghdadi (2001). "Long-term strength and durability of soil

98

cement." Journal of materials in civil engineering 13: 161.

Chakrabarti, S. and J. Kodikara (2003). "Basaltic crushed rock stabilized withcementitious additives: compressive strength and stiffness, drying shrinkage, andcapillary flow characteristics." Transportation Research Record: Journal of theTransportation Research Board 1819(-1): 18-26.

Little, W. W. C. a. D. N. (1987). "Tensile Fracture and Fatigue of Cement-StabilizedSoil " Transportation Engineering 113: 26-45.

Halsted, G. E. (2007). "Long-Term Performance of Full-Depth Reclamation withPortland Cement: Research Synopsis." Portland Cement Association, Skokie, USA

Adaska, W. S. and D. R. Luhr (2004). Control of reflective cracking in cementstabilized pavements, RILEM Publications.

George, K.P. (1968), “Shrinkage Characteristics of Soil-Cement Mixtures”, HighwayResearch Record 255, Washington D.C..

Kenai, S., R. Bahar, et al. (2006). "Experimental analysis of the effect of somecompaction methods on mechanical properties and durability of cement stabilizedsoil." Journal of Materials Science 41(21): 6956-6964.

Bhandari, R.K.M. (1973). “Shrinkage of Cement Treated Mixtures”, Journal of theAustralian Road Research Board, Vol. 5, No. 3, October,

George, K.P. (1973), “shrinkage characteristics of soil-cement mixtures”, HighwayResearch Record 255, Washington D.C.

Nakayama, H., and Handy, R.L. (1965) “Factors Influencing Shrinkage ofSoil-Cement”, Highway Research Record 86, Washington, D.C.

George, K. P. (2002). Minimizing cracking in cement-treated materials for improvedperformance, PCA Portland Cement Association, Skokie, USA.

Halsted, G. E. (2006). "Performance of Soil-Cement and Cement-Modified Soil forPavements: Research Synopsis." Portland Cement Association, Skokie, USA.

Cho, Y. H., K. W. Lee, et al. (2006). "Development of cement-treated base materialfor reducing shrinkage cracks." Transportation Research Record: Journal of theTransportation Research Board 1952(-1): 134-143.

FM 5-410. Soil Stabilization for Roads and Airfields.

99

PCA (2001). "Suggested Specifications for Soil-Cement Base Course Construction ".Portland Cement Association, Skokie, USA

PowerCem Technologies (2008). RoadCem Laboratory guide.

“Soil Stabilization with Portland Cement”, Highway Research Board 292, Washington,D.C., 1961.

Galloway, J.W. and H.M.Harding (1976). Elastic modulus of a lean and a pavementquality concrete under uniaxial tension and compression. RILEM. Materials andStrucutre,13-18.

Vertical Drainage (Dutch) Publication CROW (1993) 77, Ede, the Netherlands.

C.R.O.W. 1994. Publication 81. Gefundeerd op weg.

101

Appendix A

Fig. 1 Indication of marl soil in classification

102

Appendix B

CONVERSION TABLES (C.R.O.W. 1994)

Chart B.2.1 Conversion table length.

Chart B.2.2 Conversion table surfaces.0

103

Chart B.2.3 Conversion table volume.

Chart B.2.4 Conversion table mass.

104

Chart B.2.5 Conversion table density.

Chart B.2.6 Conversion table power and weight.

105

Chart B.2.7 Conversion table power and elasticity.

Chart B.2.8 Conversion table permeability

Chart B.2.9 Units

107

Appendix C

TRANSLATION OF TECHNICAL TERMS (C.R.O.W. 1994)

English Francais Deutsch

A aggregate granulat Zuschlagstoff, Gesteinsmaterial

aggressiveness agressivité Aggressivität

aligator cracking faïençage Netzrisse, Elefantenhaut

analysis analyse Untersuchung

analytical model modèle analytique analytisches (Rechen)Modell

articulated lorry camion articulé LKW - Zug

asphalt asphalte Asphalt

asphalt (2nd sense, US) asphalt binder (US) asphalt cement (US)

bitume Bitumen

asphalt concrete béton bitumineux Asphaltbeton

asphalt mixture enrobé asphaltique,materiau bitumineux

Asphaltmischgut

asphalt pavement revêtement bitumineux Asphaltdecke, bituminöserOberbau

assessment of pavementcondition

évaluation de l'état durevêtement (d’une chaussée)

Oberbau-Zustandserfassung

axle essieu Achse

axle load charge par essieu Achslast

axle spacing distance entre essieux Achsabstand

B base course (US) couche de base obere Tragschicht

bearing capacity portance Tragfähigkeit

bedrock bedrock Felsuntergrund

bend courbe, virage Kurve

berm(e) berme Berme

binder liant Bindemittel

bindercontent teneur en liant Bindemittelgehalt

binder course couche de liaison Binderschicht

bitumen bitume Bitumen

bituminous binder liant bitumineux Bitumen, bituminösesBindemittel

bituminous layer couche bitumineuse bituminöse Schicht

bottleneck goulot d'étranglement Engstelle, Engpass

108

C calibration factorcapping layer

coefficient de calagecouche de forme

Anpassungsfaktorverbesserter Unterbau

carriageway chaussée Fahrbahn

canalisation (of traffic) canalisation (des véhicules) Kanalisierung (des Verkehrs)

cement ciment Zement

cement-bound material matériau traité au lianthydraulique

hydraulisch gebundenesMaterial

central reserve terre-plein central Mittelstreifen

clay argile Ton

cohesion cohésion Kohäsion

coarse aggregate granulat grossier Grobkorn

commercial vehicle véhicule commerciale Nutzfahrzeug

compaction compactage Verdichtung

concrete béton Beton

concrete pavement chaussée en béton Betondecke

construction traffic trafic de chantier Baustellenverkehr

core carotte Bohrkern

course couche Schicht

crack longitudinal crack reflection crack transverse crack

fissure fissure longitudinale remontée de fissure fissure transversale

Riß Längsriß Reflektionsriß Querriß

cracking fissuration Rißbildung

structural cracking fissuration structurelle tragfähigkeitsbedingte

surface cracking fissuration superficielle oberflächliche

crazing faïençage feine Netzrisse

cross roads carrefour Kreuzung

cross section, cross profile profil en travers Querschnitt, Querprofil

crossfall pente transversale/dévers Querneigung

crown of a carriageway plateforme Straßenkrone

curb bordure (de trottoir) Bordstein

cycle path (track) piste cyclable Radweg

D debonding décollement d’interface Verlust der Schichthaftung

deflection déflexion Einsenkung

deformationelasticplasticviscous

déformationelastiqueplastiquevisqueux

Verformungelastischeplastischeviskose

delamination délamination Abplatzen, Ablösen einer

109

Schichtdensity masse volumique Dichte

design conception,dimensionnement

Entwurf, Bemessung

design criterie critère de dimensionnement Bemessungskriterien

design life durée de vie Bemessungslebensdauer,Nutzungsdauer

design mix mélange théorique,formule d’ enrobage

Eignungsprüfungsrezeptur

design period période de dimensionnement Bemessungsperiode

design traffic trafic escompté, trafic dedimensionnement

Bemessungsverkehr

deterioration dégradation Schädigung,Schadensentwicklung

distress pavement distress

dégradationdégradation de chaussée

SchadenOberbauschaden

ditch fossé Graben

ditch at top of slope cunette de crête de talus oberer Abfanggraben

ditch at foot of slope fossé de pied de talus unterer Abfanggraben

drainage drainage, évacuation deseaux

Entwässerung

dual carriageway route à double voie zweistreifige Straße

durability durabilité Dauerhaftigkeit

dynamic load charge dynamique dynamische Belastung

E elastic stiffness rigidité élastique elastische Steifigkeit

embankment remblai Damm

empirical model modèle empirique empirisches Verfahren

equivalent standard axleload

essieu standard équivalent äquivalente Standardachslast

eveness uni Ebenheit

F fatigue fatigue Ermüdung

filler filler (fines) Füller

flexible pavement chaussée souple flexibler Oberbau(ungebundene undAsphaltschichten)

footway trottoir, chemin piétonnier Fussweg, Gehweg

forecasting short term long term

prévisionà court termà long term

Vorhersage Kurzzeit- Langzeit-

formation (level) plate-forme Unterbauplanum

110

foundation fondation Gründung

freight transport transport de marchandises Güterverkehr

friction course couche de roulement,couche d’usure

Rauhbelag, Deckschicht

frost-susceptibility gélivité Frostempfindlichkeit

full depth asphaltconstruction

structure bitumineuseépaisse

Vollasphaltoberbau

G global indexgranular layer

indice globalcouche granulaire

globaler (Zustands)wertungebundene Schicht

granular material granulat Gesteinsmaterial

gross vehicle mass masse totale du véhicule Fahrzeuggesamtmasse

gross vehicle weight poids total du véhicule Fahrzeuggesamtgewicht

gussasphalt asphalt coulé Gußasphalt

H hard shoulder for emergencystop

bande d'arrêt d'urgence Standstreifen, befestigterSeitenstreifen

heavy vehicle poids lourd Schwerfahrzeug,Lastkraftwagen

highway route Straße, Fernstraße

I improvement of soil sol traité, sol amélioré Bodenverbesserung

improved subgrade fondation traitée,fondation améliorée

verbesserter Untergrund

interface rough interface smoth interface

interface interface collée interface glissante

Grenzfläche rauhe Grenzfläche glatte Grenzfläche

intersection carrefour routier, intersection Kreuzung

J junction carrefour Knotenpunkt

joint joint Fuge

K kerb bordure Bordstein

L layer couche Lage

levelling course couche de reprofilage Ausgleichsschicht

long-term performance comportement à long terme Langzeit-Gebrauchsverhalten

lorry (UK), truck (US) camion, poids lourd Lastkraftwagen, LKW

lorry with trailer camion avec remorque LKW mit Anhänger

lorry with semi-trailer camion avec semi-remorque LKW mit Sattelanhänger,Sattelzug

load charge Last, Beladung

longitudinal profile profil longitudinal,profil en long

Längsprofil

M macrotexture macrotexture Makrotextur, Grobrauheit

maintenance entretien Erhaltung

111

mastic asphalt mastic, mastic d’ asphalte Asphaltmastix

mechanistic model modèle mechanique mechanistisches(Rechen)Modell

median (US) terre-plein central Mittelstreifen

microtexture microtexture Mikrotextur, Feinrauheit

mix mélange Gemisch

mix design formulation Eignungsprüfung,Rezeptentwurf

mix-in-placemix-in-plant

mélange en placemélange en centrale

BaumischverfahrenZentralmischverfahren

modulus module Modul

modulus of elasticityresilient modulus

module d’elasticitémodule reversible

ElastizitätsmodulVerformungsmodul(Untergrundmodul)

moisture humidité Feuchtigkeit

moisture content teneur en eau Wassergehalt

motorway autoroute Autobahn

O overlay recouvrement,couche de renforcement

Hocheinbau,Verstärkungs-schicht

P particle size distribution granularité, distributiongranules, distributiongranulometrique

Korngrößenverteilung

passenger car véhicule léger, V.L. Personenkraftwagen, PKW

pave recouvrir, revêtir befestigen

pavement chaussée Fahrbahn

pavement flexible pavement

flexible compositepavement

rigid pavement

pavement deterioration

revétement chaussée souple

chaussée semi-rigide, chaussée mixte chaussée rigide revêtement rigidedégradation de chaussée,du revêtement

Oberbauflexibler (bituminöser)Oberbaubit. Oberbau mitzementstab. Tragschichtstarrer Oberbau

Verschlechterung desOberbau-zustandes,Oberbauschädigung

pavement design dimensionnement dechaussée

(Straßen-) Oberbaubemessung

pavement failure rupture de chaussée,dégât de chaussée

Oberbauschaden

pedestrian piéton Fussgänger

112

performance comportement, tenue Gebrauchsverhalten

performance factor facteur de comportement Verhaltenskenngröße(Schadensart)

performance model modèle de comportement Verhaltensmodell

plant-mixed mélange en centrale Zentralmischverfahren

porous asphalt enrobé drainant, enrobéporeux

Drainasphalt, offenporigerAsphalt

pot hole nid de poule Schlagloch

precracking pré-fissuration gezielte Rißbildung

Q quality qualité Qualität

quarry carrière Steinbruch

R raveling arrachement Kornverlust, Kornausbruch

reconstruction reconstruction Erneuerung

regulating course couche de reprofilage Ausgleichsschicht

rehabilitation rehabilitation Instandsetzung

response model modèle de comportement Beanspruchungsmodell

resurfacing rechargement,renouvellement du surface,resurfaçage

Deckschichterneuerung

rigid layer couche rigide starre Schicht

rigid pavement chaussée rigide starrer Oberbau (Beton),Betonstraße

road trunk road toll roadroad base (UK)road construction

route route à grand circulation route à péagecouche de baseconstruction routière

Straße Hauptverkehrsstraße Mautstraßeobere TragschichtStraßenbau

road surface surface de chaussée Straßenoberfläche, Fahrbahn

roller rouleau, cylindre Walze

rut orniére Spurrinne

rutting orniérage Spurrinnenbildung

roughness rugosité Rauhheit, rauhe Stelle

roughness uni Ebenheit

S safety fence (guardrail) glissière de sécurité Schutzplanke(A: Leitschiene, CH:Leitschranke)

screed régle (de finisseur) Bohle, Einbaubohle (Fertiger)

semi-rigid pavement chaussée semi-rigide halbstarrer Oberbau(zement-stabilisierte undAsphaltschichten)

serviceability viabilité Befahrbarkeit

113

shoulder accotement Bankett

shoulder bas-côté Randstreifen

single axle essieu simple Einzelachse

skid resistance adhérence Griffigkeit

slab dalle Platte

slope talus, pente Böschung

soil non-cohesive soil stabilized soil soil cement

sol sol non cohésif sol stabilisé sol ciment, sol stabilisé au ciment

Bodennichtbindiger Bodenverfestigter Bodenmit Bindemittel (Zement)verfestigter Boden

soil mechanics mécanique des sols Bodenmechanik

specification specification Vorschrift, technischeBeschreibung

standard axle essieu standard Standardachse

stiffness rigidité Steifigkeit

stiffness modulus module de rigidité Steifigkeitsmodul

strain allongement, déformationrelative

Dehnung

strength résistance Festigkeit

strengthening,reinforcement

renforcement Verstärkung

stress contrainte Spannung

stripping désenrobage Ablösen(ung)

studded tyres pneus à clous Spikesreifen

subbase couche de fondation untere Tragschicht,Frostschutzschicht

subgrade sol de fondation, sol support Untergrund, Unterbau

surface dressing enduit superficiel bituminöseOberflächen-behandlung

surfacing couche de surface Decke

T tack coat couche d'accrochage bituminöser Haftanstrich,Vorspritzung

tandem axle essieu tandem Tandem- (Doppel)achse

tensile test essai de traction Zugprüfung

test essai Prüfung, Versuch

total land requirement emprise Straßengrund

traffic flow flux de trafic Verkehrsfluß

traffic lane voie de circulation Fahrstreifen

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traffic volume volume de trafic Verkehrsstärke

transverse distribution distribution transversale Querverteilung (des Verkehrs)

transverse profile profil en travers Querprofil

tridem axle essieu tridem Dreifachachse

truck (US) camion, poids lourd Lastkraftwagen, LKW

tyre, tire pneu Reifen

single tire roue simple Einzelreifen

twin tire roues jumelées Zwillingsreifen

U unbound material matériau non traité,matériau non lié

ungebundenes Material

unevenness défaut d'uni Unebenheit

transverse transversal Quer-

longitudinal longitudinal Längs-

V voids content teneur en vides Hohlraumgehalt

W wear usure Abnützung, Abrieb

wearing course couche de roulement Deckschichte

weight poids, charge Gewicht

weigh-in-motion (W.I.M) pesage en marche Wiegen während der Fahrt

wheel roue Rad

wheel assembly roue jumelée Zwillingsrad

wheel base écartement des roues Radstand

wheel load charge par roue Radlast

wheel path frayée, bande de roulement Radspur

widening elargissement Verbreiterung

Parts of the road

total land requirement emprise Straßengrundcrown of a carriageway plate-forme Straßenkronepavement chaussée Fahrbahntraffic lane voie de circulation Fahrstreifenhard shoulder for emergencystop

bande d'arrêt urgence befestigter SeitenstreifenStandstreifen

shoulder accotement Bankettditch fossé Grabenberm(e) berme Bermecentral reservemedian (US)

terre-plein central (TPC) Mittelstreifen

slope talus, pente Böschung

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cycle path (track) piste cyclable Radwegditch at top of cunette de Obererslope crête de talus Abfanggrabenditch at foot of fossé de pied Untererslope de talus Abfanggrabensafety fence glissière de sécurité Schutzplanke

Structure of the pavement

pavementrevêtement (2e sens)

Oberbau

road foundation corps de la chaussée Tragschichten (Oberbau ohneDecke)

subgrade sol de fondation Unterbauroad surface surface de la chaussée

couche de surfaceFahrbahnoberflächeDecke

surface layer,wearing course

couche de roulement Deckschichte

binder course couche de liaison Binderschichtroad base (UK)base course (US)

couche de base (obere) Tragschicht

subbase couche de fondation untere Tragschicht,Frostschutzschicht

capping layer couche de forme verbesserter Unterbaunatural ground terrain naturel Untergrundformation(level) forme Planum (Unterbau-)

cement-bound road base materials - weinstein.ma delft report on cement-bound road base...

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