austroads (2008), ap-t 101-08-the development and evaluation of protocols for the laboratory...

AP-T101/08

The Development and Evaluation of Protocols for the Laboratory

Characterisation of Cemented Materials

AUSTROADS TECHNICAL REPORT

The Development and Evaluation of Protocols for the Laboratory Characterisation of Cemented Materials


First Published August 2008

Austroads Inc. 2008

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without the prior written permission of Austroads.


ISBN 978-1-921329-74-6

Austroads Project No. TT1065

Austroads Publication No. APT101/08

Project Manager Lance Midgley

Prepared by Richard Yeo

Published by Austroads Incorporated Level 9, Robell House 287 Elizabeth Street

Sydney NSW 2000 Australia Phone: +61 2 9264 7088

Fax: +61 2 9264 1657 Email: [email protected]

www.austroads.com.au

Austroads believes this publication to be correct at the time of printing and does not accept responsibility for any consequences arising from the use of information herein. Readers should

rely on their own skill and judgement to apply information to particular issues.

mailto:[email protected]


Sydney 2008

Austroads profile Austroads purpose is to contribute to improved Australian and New Zealand transport outcomes by:

providing expert advice to SCOT and ATC on road and road transport issues facilitating collaboration between road agencies promoting harmonisation, consistency and uniformity in road and related operations undertaking strategic research on behalf of road agencies and communicating outcomes promoting improved and consistent practice by road agencies.

Austroads membership Austroads membership comprises the six state and two territory road transport and traffic authorities, the Commonwealth Department of Infrastructure, Transport, Regional Development and Local Government, the Australian Local Government Association, and New Zealand Transport Agency. It is governed by a council consisting of the chief executive officer (or an alternative senior executive officer) of each of its eleven member organisations:

Roads and Traffic Authority New South Wales Roads Corporation Victoria Department of Main Roads Queensland Main Roads Western Australia Department for Transport, Energy and Infrastructure South Australia Department of Infrastructure, Energy and Resources Tasmania Department of Planning and Infrastructure Northern Territory Department of Territory and Municipal Services Australian Capital Territory Department of Infrastructure, Transport, Regional Development and Local Government Australian Local Government Association New Zealand Transport Agency

The success of Austroads is derived from the collaboration of member organisations and others in the road industry. It aims to be the Australasian leader in providing high quality information, advice and fostering research in the road sector.


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SUMMARY

ARRB Research is currently undertaking a technical research project titled Influence of Vertical Loading on the Performance of Unbound and Cemented Materials for Austroads (Project TT1065). This project involves an investigation of a number of parameters which influence the performance of unbound pavements with thin bituminous surfacings and pavements containing cemented materials. A major investigation of the performance of cement treated pavements was undertaken as part of this project. This report details the laboratory testing of two cemented materials which were subsequently tested under full scale loading using the Accelerated Loading Facility (ALF). The two cemented materials were a crushed hornfels from Lysterfield, Victoria and a crushed quartzite/siltstone from Para Hills, South Australia. The hornfels was stabilised with 3% GP cement while the quartzite/siltstone was stabilised with 4% GP cement by dry mass.

The objectives of the laboratory testing were to:

1. develop standard procedures for strength, modulus and fatigue testing of typical Australian cemented materials

2. determine the strength, modulus and fatigue characteristics of samples taken from the ALF test pavement and samples prepared and cured in the laboratory

3. determine the relationships between the properties of field samples from the ALF test pavement and the laboratory prepared samples

4. develop a suitable definition of the fatigue life of the laboratory samples compared to the observed fatigue life of the ALF test pavements.

In terms of the first objective, test protocols were developed for the assessment of the strength, modulus and fatigue properties of the cemented materials. In developing the procedures, the following observations were made.

Field coring using dry ice and compressed air was moderately successful when sampling weaker materials (for example at an early cure age) although very weak materials could not be retrieved even with dry coring. Wet coring was suitable for coring stronger cemented materials in the field.

The Servopac gyratory compactor was suitable for the preparation of laboratory indirect tensile (IDT) samples.

Wet cutting of field beam samples using a mobile pavement saw provided a practical means of retrieving bound flexural beam samples. A specific saw cut pattern was devised to minimise subsequent cutting in the laboratory and to assist with removal and transport of the field samples. Pavement sawing proved less damaging to the field samples than field coring.

Mixing in a planetary concrete mixer, and laboratory compaction of slabs using the BP slab compactor, proved suitable for the preparation of cemented slabs. Laboratory flexural beams were successfully cut from these slabs, with two beams taken from the mid-section of each slab.

Signal responses during IDT testing were very low and higher applied stresses were required compared to the flexural beam test. It is considered that the IDT test is more appropriate for testing materials of lower stiffness (less than 5,000 MPa).

The flexural beam test proved practical and useful for strength, modulus and fatigue testing of bound cemented materials.


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The MATTA system was suitable for the flexural beam testing as it was capable of applying the required stresses. For the indirect tensile test, the MTS hydraulic machine (actuator capacity of 25 kN or greater) was required as the stresses were much greater than the capacity of the MATTA.

With respect to the second and third objectives, the properties of the cemented materials were assessed using newly-developed draft Austroads test methods for strength, modulus and fatigue involving both the indirect tensile and flexural beam test modes. The factors considered in the study were:

method of sample preparation (samples cut from the field and samples prepared in the laboratory)

curing age (7 days, 28 days, 56 days, 90 days and older, etc.)

material mix type (hornfels with 3% cement and siltstone with 4% cement)

traditional measures such as grading, PI and UCS.

It was found that, whilst the laboratory and field specimens had similar properties, the sample properties were highly dependent on the production and curing characteristics.

The properties of the field samples were more variable than the laboratory samples. For example, samples cut for the ALF test pavement in close proximity to shrinkage cracks tended to be weaker. Cylindrical cored samples tended to be stronger than the saw-cut beams. However, this was influenced by the fact that only strong material could be cored successfully (weaker material tended to fall apart during coring).

Whilst the laboratory samples were more uniform, variations in sample curing processes led to differences in sample properties, particularly for samples cured for an extended period of time, and particularly when samples were allowed to dry out and then wet-up again. Attention to all aspects of the laboratory sample preparation and curing processes would be expected to result in more consistent materials properties.

Because of the dependence of the sample properties on the production and curing processes, with the exception of the UCS test data, no clear trend could be developed between sample strength and modulus and cure age. In any future study of this nature, it would be prudent to take field samples from very similar locations at different cure ages to assess how properties change with curing time. For the laboratory samples, it would be preferable to maintain consistent moist curing conditions for the full curing period. This must be considered in the experimental design stage as the number of samples required for this type of study requires careful consideration in terms of appropriate environmentally controlled storage space.

The hornfels material, with the lower cement content of 3% by mass, had a higher UCS value than the siltstone material with 4% cement. The hornfels material also tended to have a higher IDT modulus than the siltstone material (both field cores and laboratory IDT samples). However, as already noted, the field cores were biased because only strong samples could be successfully cored. While the modulus of initial (28 day) flexural beams of the hornfels material was higher than that of the siltstone material, the modulus of other beam samples was much lower. The field properties of the hornfels material were more variable than the siltstone material.


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Fatigue models were derived for each material. The models indicated that the siltstone material, with 4% binder, had a longer fatigue life than the hornfels material. The difference in fatigue properties based on either IDT fatigue testing at 28 days cure or the long term cure flexural beam fatigue testing, was similar. For the laboratory samples, the slope of the model for the siltstone material between the IDT 28 day testing and the long term cure beam testing was consistent. Both datasets indicated a load-damage exponent of 6.3. The load-damage relationship for the hornfels material for both the IDT and beam fatigue tests was also reasonably consistent (values of 8.8 and 7.9 respectively).

The laboratory testing conducted in this study indicated that the number of cycles of load to half the initial modulus was a suitable definition for the fatigue life of laboratory samples. The results showed that, shortly after the cycles to half the initial modulus was reached, the flexural beam samples typically ruptured. The initial modulus was defined as the mean modulus for the first 50 cycles of the fatigue test while the initial strain was defined as the mean strain during the first 50 cycles of the fatigue test.

The results of this laboratory study will be compared with the results of the full scale accelerated loading testing of the same two materials using ALF. The full scale load performance data will be used to assess the capability of the laboratory test protocols and provide a level of confidence in the laboratory assessment protocols.

ACKNOWLEDGEMENTS

The laboratory study described in this report was possible because of the support of a number of organisations and individuals. Of particular note are the following:

David Hazell of the Department for Transport Energy and Infrastructure, South Australia who arranged for the supply and transport of the siltstone pavement material

Cameron McInnes of Boral Quarries (Vic) Metro for assistance with sourcing the hornfels material and pugmill mixing of both materials

IPC Global for the supply and support with the laboratory test equipment

Binh Vuong, Ross Luke, David Firth, Stephen OHern, Shannon Lourenz and Lith Choummanivong of the Research Division, ARRB Group.


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CONTENTS

1 INTRODUCTION ............................................................................................................ 1 1.1 Project Objectives for Cemented Materials Research .................................................... 1 1.2 Aims of the Laboratory Study ......................................................................................... 1 2 MATERIAL PROPERTIES............................................................................................. 3 3 LABORATORY TEST METHODS ................................................................................. 5 3.1 Unconfined Compressive Strength (UCS) ...................................................................... 6 3.2 Indirect Tensile (IDT) Test .............................................................................................. 7 3.3 Flexural Beam Test....................................................................................................... 10 4 TEST SAMPLES .......................................................................................................... 13 4.1 Field Samples ............................................................................................................... 13 4.2 Laboratory Mixed and Compacted Samples................................................................. 15

4.2.1 UCS Sample Preparation ............................................................................... 16 4.2.2 IDT Sample Preparation ................................................................................. 17 4.2.3 Flexural Beam Sample Preparation................................................................ 17

4.3 Field Mixed, Laboratory Compacted Samples.............................................................. 18 5 RESULTS..................................................................................................................... 19 5.1 Strength ........................................................................................................................ 19

5.1.1 Unconfined Compressive Strength ................................................................. 19 5.1.2 IDT Strength ................................................................................................... 22 5.1.3 Flexural Beam Strength .................................................................................. 24

5.2 Modulus (IDT and Flexural Beam)................................................................................ 27 5.2.1 IDT Resilient Modulus..................................................................................... 27 5.2.2 Flexural Beam Modulus .................................................................................. 28

5.3 Fatigue (IDT and Flexural Beam) ................................................................................. 32 5.3.1 Fatigue Loading .............................................................................................. 32 5.3.2 Laboratory Samples and Field Samples......................................................... 32 5.3.3 Cure Age for the Fatigue Test ........................................................................ 32 5.3.4 Definition of Fatigue Life ................................................................................. 33 5.3.5 Fatigue Models ............................................................................................... 33 5.3.6 Fatigue Test Results and Models from Indirect Tensile Testing..................... 34 5.3.7 Fatigue Test Results and Models from Flexural Beam Testing ...................... 35

6 DISCUSSION ............................................................................................................... 37 REFERENCES ...................................................................................................................... 41 APPENDIX A PARTICLE SIZE DISTRIBUTION .................................................... 42 APPENDIX B IDT TEST METHOD STRENGTH.................................................. 43 APPENDIX C IDT TEST METHOD MODULUS AND FATIGUE.......................... 47 APPENDIX D FLEXURAL BEAM TEST METHOD - MODULUS AND

FATIGUE .......................................................................................... 55 APPENDIX E UNCONFINED COMPRESSIVE STRENGTH RESULTS ................ 60 APPENDIX F INDIRECT TENSILE TEST RESULTS............................................. 64 APPENDIX G FLEXURAL BEAM RESULTS ......................................................... 70


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TABLES

Table 2.1: Initial characterisation results for each cemented material ............................... 3 Table 5.1: Summary of mean strength data at about 28 days cure age.......................... 19 Table 5.2: Summary of unconfined compressive strength data hornfels ...................... 20 Table 5.3: Summary of unconfined compressive strength data siltstone..................... 21 Table 5.4: Summary of IDT strength data hornfels...................................................... 22 Table 5.5: Summary of IDT strength data siltstone ...................................................... 23 Table 5.6: Summary of flexural beam strength data hornfels ....................................... 25 Table 5.7: Summary of flexural strength data siltstone................................................. 26 Table 5.8: Summary of IDT modulus data hornfels material ....................................... 27 Table 5.9: Summary of IDT modulus data siltstone material ........................................ 28 Table 5.10: Summary of flexural modulus data hornfels material.................................. 29 Table 5.11: Summary of flexural modulus data siltstone material .................................. 30 Table 6.1: Summary of cemented materials strength and modulus................................. 39

FIGURES

Figure 2.1: Particle size distribution for the hornfels and siltstone materials ...................... 4 Figure 3.1: UCS sample in the ARRB compression machine............................................. 6 Figure 3.2: Indirect tensile test for cemented materials using the MATTA (left) and

MTS hydraulic machine (right) .......................................................................... 7 Figure 3.3: Indirect tensile fatigue test ................................................................................ 8 Figure 3.4: Pulse shape and noise from a typical IDT test ................................................. 9 Figure 3.5: Pulse shape and noise from a typical flexural beam test.................................. 9 Figure 3.6: Diagrammatic view of flexural beam testing apparatus (Standards

Australia 2000)................................................................................................ 10 Figure 3.7: Flexural beam test .......................................................................................... 11 Figure 3.8: Flexure beams intact dimensions (left) and beams with some loss of

material (right)................................................................................................. 12 Figure 4.1: Dry coring using dry ice and compressed air.................................................. 13 Figure 4.2: Cutting beam samples from pavement using a mobile diamond-tipped

saw and water................................................................................................. 14 Figure 4.3: Typical layout of sampling locations ............................................................... 15 Figure 4.4: Planetary concrete mixer used to mix cemented material .............................. 15 Figure 4.5: Proctor compaction machine used for UCS samples ..................................... 16 Figure 4.6: Servopac gyratory compaction machine......................................................... 17 Figure 4.7: BP slab compactor with rectangular mould ................................................... 17 Figure 4.8: Wet sawing a flexural beam sample in the laboratory .................................... 18


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Figure 5.1: Unconfined compressive strength hornfels material with 3% GP cement ............................................................................................................ 20

Figure 5.2: Unconfined compressive strength siltstone material with 4% GP cement ............................................................................................................ 21

Figure 5.3: IDT strength hornfels material with 3% GP cement ..................................... 23 Figure 5.4: IDT strength siltstone material with 4% GP cement .................................... 24 Figure 5.5: Flexural beam strength hornfels material with 3% GP cement .................... 25 Figure 5.6: Flexural beam strength siltstone material with 4% GP cement................... 26 Figure 5.7: IDT modulus hornfels material with 3% GP cement .................................... 27 Figure 5.8: IDT modulus siltstone material with 4% GP cement .................................... 28 Figure 5.9: Flexural modulus hornfels material with 3% GP cement ............................. 29 Figure 5.10: Flexural modulus siltstone material with 4% GP cement ............................. 30 Figure 5.11: Variation in flexural modulus with sample density at different cure

periods hornfels material ............................................................................. 31 Figure 5.12: Variations in flexural modulus with sample density at different cure

periods siltstone material ............................................................................. 31 Figure 5.13: Typical flexural beam fatigue test result showing cycles to half initial

modulus .......................................................................................................... 33 Figure 5.14: Summary of fatigue data from indirect tensile testing hornfels material ...... 34 Figure 5.15: Summary of fatigue data from indirect tensile testing siltstone material ...... 35 Figure 5.16: Summary of fatigue data from flexural beam tests hornfels material........... 36 Figure 5.17: Summary of fatigue data from flexural beam tests siltstone material .......... 36 Figure 6.1: Fatigue models for two cemented materials based on laboratory testing....... 40


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1 INTRODUCTION ARRB Research is currently undertaking a national strategic research project titled Influence of Vertical Loading on the Performance of Unbound and Cemented Materials for Austroads (Project TT1065). This project involves the investigation of a number of parameters which influence the performance of pavements. The focus of this research is on unbound pavements with thin bituminous surfacings and pavements containing cemented materials.

The main drivers of the research were the need for an improved understanding of the load-damage relationships currently recommended in the Austroads (2004) Pavement Design Guide, specifically axle load equivalencies for unbound granular materials and the fatigue relationship for cemented materials. Currently, the damage exponent for cemented materials adopted by Austroads is 12 and this was adopted by the National Transport Commission (NTC) as the damage exponent in the performance based standard for pavement vertical loading. If it could be shown that this exponent was too conservative then this would have an obvious influence on design practice.

During the period 2002 to 2004, research focussed on the performance of unbound granular pavements. Laboratory testing, together with full scale accelerated pavement testing, was conducted to investigate the effects of different axle loads on the performance of three different unbound basecourse materials surfaced with a thin sprayed bituminous seal. Data gathered from this research has been analysed and reported in Yeo et al. (2007).

Austroads research into the performance of pavements containing cemented materials commenced in 2004/2005. The experimental design for this research is detailed in Yeo (2004).

This report presents draft laboratory test protocols for the characterisation of cemented materials, together with laboratory test results for the two cemented materials tested using the Accelerated Loading Facility (ALF).

1.1 Project Objectives for Cemented Materials Research The aims of the research on the impact of heavy vehicles on cemented materials are to:

assess the relative performance of pavements containing cemented materials under a range of axle loads to provide information relating to the load damage exponent (LDE)

work towards verification of a routine laboratory test protocol for the characterisation of cemented materials in terms of their modulus and fatigue characteristics in order that a wider range of cemented materials may be tested in future to increase understanding of the performance of these materials.

1.2 Aims of the Laboratory Study The aims of the laboratory study were to:

develop standard test procedures for the determination of the strength, modulus and fatigue characteristics of typical Australian cemented materials

determine the strength, modulus and fatigue characteristics of the two cemented materials tested using ALF using samples from the ALF test pavement and samples prepared and cured in the laboratory

investigate the relationship between the properties of the field samples from the ALF test pavement and laboratory-prepared samples


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develop a suitable definition of the fatigue life of the laboratory samples in relation to the observed fatigue life of the ALF test pavements.


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2 MATERIAL PROPERTIES Two cemented base materials were examined in the laboratory study:

Boral hornfels crushed rock (hornfels)

20 mm maximum sized VicRoads Class 3 crushed rock treated with 3% by dry mass of General Purpose (GP) cement binder (supplied by Blue Circle Southern Cement). The source rock was a metamorphic hornfels.

Boral siltstone quarry rubble (siltstone)

20 mm maximum size Department for Transport, Energy and Infrastructure (DTEI) Class 2 PM2/20QG quarry rubble cement treated with 4% by dry mass of GP cement binder (supplied by Blue Circle Southern Cement) according to DTEI Master Specification Part 215. The source rock was a siltstone quartzite.

An initial laboratory characterisation was conducted for each cemented material as follows:

Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) using modified compaction according to AS1289.5.2.1 Standards Australia (2003).

Atterberg Limits (Plastic Limit (PL), Liquid Limit (LL) and Plasticity Index (PI)) according to AS1289.3.3.1 Standards Australia (1995a).

Particle Size Distribution (PSD) according to AS1141.11 Standards Australia (1996a).

Unconfined Compressive Strength (UCS) of the cemented materials at 28 days cure to AS 1141.51 Standards Australia (1996b).

Table 2.1 summarises the MDD, OMC, PI, PL, LL and UCS results for the host crushed rock materials prior to stabilisation while Figure 2.1 shows the Particle Size Distribution (PSD) for both materials (refer Appendix A).

Table 2.1: Initial characterisation results for each cemented material

Material MDD (t/m3) OMC (%) PI PL LL UCS at 96% RC

28 days cure (MPa)

Hornfels with

3% GP cement 2.325 6.1 5 - 22 7.0

siltstone with 4% GP cement 2.070 8.0 6 15 21 6.5

Note: MDD = Maximum Dry Density (modified), OMC = Optimum Moisture Content, RC = Relative Compaction (DD/MDD 100%), PI = Plasticity Index, PL = Plastic Limit, LL = Liquid Limit, UCS = Unconfined compressive strength.


0.075 0.15 0.3 0.425 0.6 1.18 2.36 4.75 6.7 9.5 13.2 190

20

40

60

80

100

Percent Passing

(%)

Hornfels Siltstone

Sieve Size (mm)

Figure 2.1: Particle size distribution for the hornfels and siltstone materials

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3 LABORATORY TEST METHODS The first aim of this part of the project was to develop standard test procedures for the determination of the strength, modulus and fatigue characteristics of the cemented materials.

Whilst the UCS test is a routine and commonly used laboratory test, a standard test for the routine characterisation of the modulus and fatigue properties of cemented materials has not yet been developed. Austroads (2004) lists the following potential methods for determining the modulus of cemented materials: flexural test, direct tension test, indirect tensile test, longitudinal vibration test and the direct compression test. These tests are generally also suitable for determining the fatigue properties of cemented materials with the exception of the last two methods (longitudinal vibration and direct compression).

These tests have been used in various past research studies. For example, Otte (1978) and Litwinowicz and Brandon (1994) developed and used a beam flexure test, while Bullen (1994) proposed the use of the indirect tensile test. Andrews et al. (1998) used a modified repeated load triaxial test for modulus (direct compression) as well as the indirect tensile test. A direct tensile test is routinely used in France (LCPC 1997).

In a review of potential methods for routine testing of cemented materials for strength, modulus and fatigue, Yeo, Vuong and Alderson (2002) proposed the indirect tensile test be adopted on the basis of the wide availability of test machines suitable for this test method (a relatively common test used for asphalt). As indirect tensile samples are cylindrical in shape they are relatively easy to prepare, either in the laboratory using gyratory compaction or field cores.

For the current laboratory program, consideration was given to the definition of design modulus for cemented materials. Austroads (2004) suggested the in situ flexural modulus after 28 days curing was the appropriate design parameter; using this definition, the flexural beam test would be most relevant.

On the basis of this discussion, the following three different test arrangements were adopted for the laboratory assessment of the cemented materials:

UCS test (to enable comparisons with earlier strength studies if required)

indirect tensile (IDT) test

flexural beam test.

It was noted that both the indirect tensile test and the flexural beam test were suitable for estimation of the strength, modulus and fatigue life of cemented materials. A significant development task was undertaken to establish test protocols. Closed loop controllers supplied by IPC were purchased and configured for both the MATTA (pneumatic actuator with a 14 kN capacity) test machine and the ARRB universal testing machine (MTS, hydraulic actuator). The MATTA system was suitable for the flexural beam testing as it was capable of applying the required stresses. For the indirect tensile test the MTS hydraulic machine (actuator capacity of 25 kN or greater) was required as the stresses were much greater than the capacity of the MATTA.

The key features of each of these test arrangements are described in the following sections. Minimal detail is provided for the UCS test as an Australian standard exists for this routine test (Standards Australia 1996b).


3.1 Unconfined Compressive Strength (UCS) The UCS test is a compression test. It involves a cylindrical sample being loaded along its axis until failure. UCS testing was conducted according to AS1141.51-1996 (Standards Australia 1996). The laboratory specimens were manufactured and tested according to the additional requirements in VicRoads Code of Practice RC 500.16 (VicRoads 2007) as follows:

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use of modified compaction

use of a split mould for sample compaction

a sample preconditioning time (or allowable working time) of 2 hours.

The UCS samples were capped with a flyash and sulphur compound in order to provide for uniform load application to the sample. The samples were soaked in water for 4 hours and let stand for 15 minutes before being tested. The load rate was 60 kN/minute as specified in AS1141.51 (Figure 3.1).

In addition to the laboratory prepared specimens, field cored samples were obtained from untrafficked locations of the ALF test pavements for each of the cemented materials. A limited number of samples were also compacted in the laboratory from pugmill mixed material.

UCS samples of both materials were tested at a variety of cure ages in order to observe the effect of curing on the strength of the samples.

Figure 3.1: UCS sample in the ARRB compression machine


3.2 Indirect Tensile (IDT) Test IDT samples are relatively easy to obtain from the field via coring, or to manufacture in the laboratory using a gyratory compactor such as the Servopac. The sample size of the test specimens was nominally 150 mm in diameter and 85 mm thick (the maximum particle size of the two materials was 20 mm). Laboratory samples were manufactured in batches of two to three specimens which would be tested together. Similar to the UCS test, the IDT samples were tested at a variety of cure ages. The IDT test method used was based on AS2891.13.1-1995 (Standards Australia 1995b), modified for cemented materials. Details of the IDT strength test are included in Appendix B and the IDT modulus and fatigue tests are detailed in Appendix C.

Once a series of samples was prepared in the laboratory or obtained from the field, the IDT test involved three stages. In the first stage the indirect tensile strength was determined on one of the samples from the series. The second stage involved the determination of the modulus of a second sample from the series, with an indirect tensile stress of typically 40% of the failure stress of the paired sample applied for at least 100 load cycles (Figure 3.2). The relatively low value of 40% of the strength was selected with the aim of testing for modulus within the elastic range of the material (such that no fatigue damage was induced). The resilient modulus was determined from the mean applied stress and the mean resilient strain from the last 50 cycles of the 100 load cycles applied. A pneumatically-controlled MATTA (MATerial Testing Apparatus) system with a 14 kN actuator was used for the early modulus tests. However, as the samples aged and their modulus increased, it was found that a hydraulic machine with a higher load capacity was required as the samples tended to require up to 20 kN for the full test (including the fatigue stage).

Figure 3.2: Indirect tensile test for cemented materials using the MATTA (left) and MTS hydraulic machine (right)

The third stage involved the determination of the fatigue life of the sample. The same samples which had been tested for modulus (within their elastic range) were re-used for the fatigue test. The applied stress was increased to between 60% and 90% of the failure stress to provide a more severe load condition. The cyclic haversine loading was continued using a stress-controlled test until failure was observed.

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Initially samples were cyclically loaded at 1 Hz but, after the first few series of samples was tested, the frequency was increased to 2 Hz to reduce the fatigue test duration. As the fatigue response of the cemented materials was not considered to be time dependent within the 1Hz to 2 Hz cyclic loading frequency, this change was considered appropriate. Figure 3.3 shows a typical fatigue test result for an indirect tensile sample.

One issue with the laboratory test program was the signal to noise ratio of the linear variable differential transformers (LVDT) used to measure the sample response to the applied loading. This was carefully assessed for the IDT test as the measured sample responses were very small, particularly for stiff samples.

Typically electrical and mechanical noise from the test was found to be in the range of 0.1 micron while the sample displacement for the IDT test was in the range of 0.7-1.8 micron for modulus testing (Figure 3.4). Preferably, the signal to noise ratio should exceed 10.

0

5000

10000

15000

20000

25000

30000

0 5000 10000 15000 20000 25000 30000

Cycles

Mod

ulus

(MPa

)

Modulus(MPa)

Half modulus(MPa)

Figure 3.3: Indirect tensile fatigue test

In comparison, the flexural beam tests resulted in a much larger sample displacement of 5 micron to 18 micron for the same 0.1 micron signal noise. As such, the flexural beam tests showed a much better signal to noise ratio than the IDT tests (Figure 3.5). A number of techniques such as grounding the LVDTs were developed which minimised the influence of the signal noise on the IDT modulus and fatigue tests.

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-0.5

0

0.5

1

1.5

5 6 7 8 9 10

Time (s)

Dis

plac

emen

t (m

icro

n)

Axial displ. #1Axial displ. #2

Figure 3.4: Pulse shape and noise from a typical IDT test

-2

0

2

4

6

8

10

12

14

16

5 6 7 8 9 10

Time (s)

Dis

plac

emen

t (m

icro

n)

Axial displ. #1

Figure 3.5: Pulse shape and noise from a typical flexural beam test

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3.3 Flexural Beam Test Austroads (2004) states that third point loading of flexure (beam) specimens (with a span to depth ratio greater than 3) is favoured for modulus characterisation as the test conditions are considered to simulate the stress/strain gradients generated within a pavement layer. As a result, the flexural beam test was also used to estimate the strength, modulus and fatigue properties of the two cemented materials. The geometry of the flexural beams was based on AS1012.11-2000: Methods of testing concrete Method 11: Determination of the modulus of rupture (Standards Australia 2000). The flexural beam test for modulus and fatigue used in this study is detailed as a draft Austroads test method in Appendix D.

Initially, the flexural beam test was not going to be used due to the perceived difficulty of extracting field beam samples from the road bed. However, after some trial and improvement, a routine procedure was developed which enabled beam samples to be readily obtained.

Given the 20 mm maximum aggregate size, the nominal dimensions of the beam samples were 100 mm high by 100 mm wide by 400 mm long. The beam supports were set 300 mm apart to achieve a span to depth ratio of 3. The load positions were at third-points along the sample and the beam displacement was measured at the mid-point as shown in Figure 3.6. A MATTA with a 14 kN pneumatic load actuator was used for the flexural beam tests as the typical loading required was in the range 1 kN to 6 kN for this test (see Figure 3.7).

Prior to testing commencing, pairs of beams were preconditioned in the ARRB fog room for at least 48 hours to ensure a consistent moist condition for all tests. The beams were let stand for approximately 15 minutes while the beam dimensions were measured (to determine the sample volume) and the wet mass of the whole beam was measured (for subsequent determination of the beam moisture content). These details were stored with the results in the test software.

Source: Standards Australia (2000)

Figure 3.6: Diagrammatic view of flexural beam testing apparatus (Standards Australia 2000)

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Figure 3.7: Flexural beam test

One of the paired beams was tested to determine the flexural strength. For the flexural strength test the MATTA was programmed to load the sample with a seating force of 50 N for the first 6 seconds, after which the load was increased at a rate of 3.3 kN per minute until the sample failed as described in AS1012.112000.

The vertical displacement of the beam mid-point was measured using a single LVDT and a reference frame placed on the sample to provide an estimate of the strain at break. The beam deflection data was sampled at a frequency of 100 Hz, together with the applied load.

After the specimen failed, the peak load and approximate location of the break point were recorded. The specimen was weighed, as tested, then dried in an oven to a constant mass for moisture content determination.

Flexural modulus and fatigue testing was then conducted on the matched beam from the pair. The beam was sealed in thin plastic cling wrap to minimise the loss of moisture during the test. A significant loss of moisture could lead to strengthening of the specimen, particularly during a long (more than a few hours duration) fatigue test. Testing was conducted under normal laboratory environment conditions at 23C.

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The modulus test involved the application of cyclic haversine load pulses of 250 ms duration. The beam deflection associated with each load pulse was recorded, together with the seating stress (nominally 50 N) and the peak load. The pulse period was 1 Hz (including a 750 ms rest period between load pulses) and at least 100 load pulses were applied to the sample. The magnitude of the load pulses was about 40% of the breaking load determined from the strength test on the paired beam. As with the IDT test, this load was selected to be low enough not to damage the sample but high enough to produce a sufficient displacement for accurate estimation of tensile strain from the on-sample mid-point deflection measurement, and consequently the resilient modulus.

The fatigue test was initiated straight after the modulus test on the same sample. The peak magnitude of the haversine load pulses was increased to a value in the range of 60% to 90% of the breaking load (based on the paired beam which was tested for strength). A fatigue curve was derived from a series of samples using this stress-controlled test. For each sample, the fatigue load was pulsed at 2 Hz (providing a rest period of 250 ms between load pulses) until the sample failed.

Early in the fatigue testing of some samples, it was clearly apparent that the load being applied was below the fatigue threshold as the modulus was not reducing over time. In some cases the test was re-commenced at an increased load and the results were tagged as having an earlier loading phase. For these tagged tests, the data was generally not used in the analysis. As expected, the fatigue test duration was highly sensitive to the applied load. Samples tested at close to, say, 90% of the estimated strength failed in fatigue within a few hundred cycles while others tested at lower percentages of the strength continued for an extended period (up to over 1 million load cycles or more than 5 days). A range of initial tensile strain values was targeted for the fatigue testing to allow an investigation of the relationship between fatigue life and initial tensile strain. Following the fatigue test, each beam was weighed and then dried in order to determine the moisture content and dry density.

The density and moisture content at the time of testing was estimated from the dry mass and volume of the beam. This method is considered acceptable when the beams are largely intact. However, one source of error in the density estimate occurred when voids were present on the surface of the beam as a result of material lost during the sawing process or due to handling (Figure 3.8). This would tend to cause the estimated density to be lower than the true density.

This issues could have been addressed by determining the sample volume by immersion in water. However, this approach was not considered warranted.

Intact beams Beams with some loss of material

Figure 3.8: Flexure beams intact dimensions (left) and beams with some loss of material (right)

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4 TEST SAMPLES

4.1 Field Samples Field cores and slabs were obtained from the ALF test pavements at Dandenong on a number of occasions to enable laboratory testing to be conducted as the pavement aged. The removal of intact, un-damaged cemented samples from the pavements was important if a link between the properties of field and laboratory samples was to be established.

UCS and IDT samples were obtained by coring the pavements with a 100 mm diameter and 150mm diameter diamond tipped core barrel respectively (Figure 4.1). When the materials were at an early cure age (less than 28 days), efforts were made to freeze the upper portion of the cemented layer using dry ice to keep the core barrel cool and enable dry coring. Dry coring was considered desirable in preference to wet coring as water used to cool the barrel and flush out the fines from the cutting process can tend to erode the cemented material and damage the core samples. Once the cemented materials had aged sufficiently, wet coring was used to minimise erosion.

When dry coring was used, compressed air was blown into the barrel to force out the fine grit from the cutting area and prevent the core barrel from jamming. Despite best efforts, it was found that the hornfels material was difficult to core intact at an early age. Wet coring resulted in severe erosion of the cored material. When dry coring was attempted, the samples would often snap off in the barrel. Attempts were made to core the hornfels material from a number of locations until a sufficient number of intact cores were obtained. These samples would therefore be biased towards stronger cemented material.

In contrast, the cemented siltstone was a much softer aggregate type (compared to the hornfels) and it could be successfully wet cored from an early age.

A successful set of cores for UCS and IDT

An unsuccessful core

Figure 4.1: Dry coring using dry ice and compressed air

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In order to obtain the beams to be used for the flexural beam tests, a mobile concrete cutting saw with a diamond tipped blade was used (Figure 4.2). A cutting pattern was established, as shown in Figure 4.3, which enabled a series of paired beams to be obtained from each sample location. The beams had to be cut with water to prevent damage to the diamond-tipped saw blade used. Beam samples were cut at 28 days cure age or greater; they tended not to erode during wet saw-cutting. Field sawing of beams was observed to be a much gentler process for retrieval of samples than the field coring method. This resulted in successful recovery of beams regardless of the sampling location. As a result, the field beams were more representative of both the weak and strong areas of the pavement.

Figure 4.2: Cutting beam samples from pavement using a mobile diamond-tipped saw and water

It was assumed that the cemented material was reasonably homogeneous and, as such, a stratified pattern was established to enable samples to be cut at various cure ages. The pattern allowed for progressive sampling along each test pavement section with a reasonable spacing between locations. While this was satisfactory for the siltstone material, in homogeneity of the hornsfeld material meant that sample properties were found to vary with sampling position. This was particularly the case where some samples were taken in the vicinity of shrinkage cracks while other samples were taken from sound material.

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Figure 4.3: Typical layout of sampling locations

4.2 Laboratory Mixed and Compacted Samples Laboratory samples were prepared from the same bulk materials used for the ALF field trial. The bulk materials were split into representative sub-samples of a suitable mass for each of the test requirements. Prior to the compaction of the samples, a common mixing and conditioning process was used. Batches of the mix were prepared in a motor-driven planetary concrete mixer with a tank size of 800 mm diameter and 350 mm high (Figure 4.4).

Figure 4.4: Planetary concrete mixer used to mix cemented material

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The mixing process was as follows:

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The bulk preconditioned host material was placed into the mixing tank.

The mixer was run for 15 seconds to spread the material evenly in the tank.

The required amount of GP cement was added.

The required amount of water was added.

The mixer was run for 120 seconds then let stand for 120 seconds.

The mixer was run for a further 120 seconds.

Following mixing, the material was placed in containers and covered with a plastic sheet and let stand for a period of time to condition prior to compaction. The intention was to make allowance for the commencement of the cement binder reaction and also to replicate the field placement of cemented materials which can involve quarry mixing and then delivery time prior to placement. The period of time which the material was left to stand was dependent on the sample type being prepared. Typically, for UCS samples, the period was 1.5 hours, with the sample compaction then completed within 2 hours of mixing. For the IDT and flexural beam samples, the standing time was 0.5 hours as, beyond this time, the samples were too difficult to compact due to the initial set of the cement binder in the mix.

4.2.1 UCS Sample Preparation UCS samples were compacted in five layers of pre-determined mass using a Proctor compaction machine (Figure 4.5) and a one-piece split mould (modified compaction as per AS1141.51). A portion of the remaining material was dried in an oven for the determination of moisture content of the sample at the time of compaction. Compacted samples were labelled and taken to the ARRB fog room within an hour for moist curing. Short term samples (less than 4 months cure) were left in the fog room until the time of testing while samples subjected to longer cure periods were removed from the fog room after roughly 1 year and returned to the fog room at least 48 hours prior to testing.

Figure 4.5: Proctor compaction machine used for UCS samples


4.2.2 IDT Sample Preparation The IDT samples were prepared using a Servopac gyratory compactor (Figure 4.6) which was set to compact a cylindrical sample 150 mm in diameter and 80 mm high. Following compaction, the samples were de-moulded and moist cured until the time of testing.

Figure 4.6: Servopac gyratory compaction machine

4.2.3 Flexural Beam Sample Preparation A BP Slab Compactor and a rectangular mould with internal dimensions of 400 mm long x 320 mm wide x 145 mm high was used for slab compaction as shown in Figure 4.7.

Figure 4.7: BP slab compactor with rectangular mould

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A mass of wet material was placed in the mould, spread evenly and tamped manually to commence the compaction process. The material was then compacted in a single layer to the specified height of 100 mm using the slab compactor. The slab compactor was set at an initial vertical pressure of 100 kPa while the curved steel compaction head was rocked over the material. The vertical pressure was increased by 100 kPa for every 10 rocking passes until the pressure reached 600 kPa (near machine capacity). The compaction process was continued until the total number of passes reached 100 (the reduction in height beyond 100 passes had previously been found to be insignificant). The compaction process was refined during the project with the aim of improving the uniformity of the compaction. Initially the curved steel compactor was placed at one end of the mould, the initial vertical pressure was applied and the compaction process commenced. It was observed that this caused the loose material to be shoved across the mould, resulting in one side of the mould having more material and a difference in height and density between the paired beams obtained from the slab. This process was altered with manual tamping added to pre-compact the material and the machine compaction was commenced from the centre of the sample to minimise the amount of material shoved to one side.

The compacted slab was left in the closed mould and covered with a wet cloth and lid to minimise moisture loss and stored at 23C for a minimum of 2 days before being de-moulded and moist cured in the ARRB fog room. Each slab was subsequently cut into two beams after a minimum cure period of 14 days to ensure the slab was strong enough to enable wet cutting with a diamond tipped saw without disintegrating (Figure 4.8).

It was found that there were variations in density between the paired beams from the same slab and that a range of densities around the target density often occurred.

Figure 4.8: Wet sawing a flexural beam sample in the laboratory

4.3 Field Mixed, Laboratory Compacted Samples During the construction of the test pavements for both the hornfels material and the siltstone material at the ALF site at Dandenong, samples of the uncompacted pugmill-mixed cemented material were obtained. This material was brought back to the ARRB laboratory and a limited number of samples were prepared in the same manner as described in Section 4.2 for the UCS and IDT samples. Flexural beam samples were not prepared given the time constraints and mass of material required. UCS samples were not prepared from the siltstone material.

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5 RESULTS

5.1 Strength The cemented material strength was measured using the UCS, IDT and flexural beam test methods described earlier. As there are many test results presented, a brief summary of the strength data from the three test methods is presented in Table 5.1 for samples at about 28 days cure age and about the target density of 96% of modified maximum dry density.

Table 5.1: Summary of mean strength data at about 28 days cure age

Field samples Laboratory samples Field mixed laboratory compacted samples Hornfels Siltstone Hornfels Siltstone Hornfels Siltstone

UCS (MPa) 8.5 7.6 7.1 6.5 8.3 - IDT strength (MPa) 0.67 0.68 0.71 0.81 0.84 0.74 Flexural strength (MPa) 0.97 1.32 1.01 1.13 - -

Table 5.1 indicates that the UCS of the two cemented materials was similar and relatively high at about 6 to 8 MPa, indicating the cemented materials were bound. The IDT strengths were also similar at about 0.7 MPa. The flexural beam test data indicated that the siltstone material had a significantly higher flexural strength than the hornfels material.

The data from the field and laboratory samples suggested that the strength properties were similar at the 28 day cure age with the field UCS values slightly higher than the laboratory UCS values. This is discussed in more detail in the following sections together with the mean strength test results for a range of cure ages.

5.1.1 Unconfined Compressive Strength Table 5.2 presents a summary of the UCS data obtained for the hornfels material for the three sample preparation methods while Figure 5.1 displays the results in a graphical form. Similarly, data for the siltstone material is shown in Table 5.3 and Figure 5.2. As expected, the UCS values increased with age with most of the strength gain occurring within the first 28 days curing. More detailed results can be found in Appendix A.

The trend for both materials was that, for a given cure age, the UCS values of the field samples were slightly higher compared to the field mixed laboratory compacted samples or the laboratory samples. The relative compaction between the three sets of data does not, however, explain the higher strength of the field samples as the field samples generally had a lower density than the laboratory samples. As discussed earlier, the field cored samples may be biased towards stronger material as the weaker material could not be successfully cored.

It should also be noted that where the strength of the samples appears to drop with an increased curing time, this was generally found to correspond to differences in density with the older samples having lower density than the younger samples. For the laboratory and field mixed sets of data, only three or less UCS tests were conducted while there were up to six field cores tested for UCS.


Table 5.2: Summary of unconfined compressive strength data hornfels

Field Laboratory Field mixed lab compacted

Age (days)

UCS (MPa)

Relative compaction

(%) Age

(days) UCS

(MPa) Relative

compaction (%)

Age (days)

UCS (MPa)

Relative compaction

(%)

Mean 0.08 0.62 96.6% Std Dev 0.06 0.4%

n 3 3 Mean 7 5.89 96.1% 7 6.46 107.4%

Std Dev 0.77 0.1% 0.92 3.1% n 3 3 3 3

Mean 29 8.48 95.3% 28 7.05 95.9% 28 8.26 96.5% Std Dev 0.42 1.5% 0.23 0.4% 0.64 0.9%

n 5 5 3 3 3 3 Mean 59 7.57 93.3% 56 8.20 96.7% 53 7.23 95.9%

Std Dev 0.81 1.3% 0.69 0.2% 0.58 1.0% n 6 6 3 3 3 3

Mean 90 9.07 96.1% 90 8.44 97.0% Std Dev 1.03 0.6% 1.51 0.6%

n 6 6 3 3 Mean 756 9.85 96.4%

Std Dev 1.30 2.1% n 12 12

0

2

4

6

8

10

12

0 100 200 300 400 500 600 700 800

Sample age (days)

UC

S (M

Pa)

Field cored Field mix lab compacted Lab samples

Figure 5.1: Unconfined compressive strength hornfels material with 3% GP cement

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Table 5.3: Summary of unconfined compressive strength data siltstone

Field Laboratory

Age (days)

UCS (MPa)

Relative compaction

(%) Age

(days) UCS

(MPa) Relative

compaction (%)

Mean 0.08 0.67 96.8% Std Dev 0.10 0.1%

n 3 3 Mean 7 5.78 96.9%

Std Dev 0.28 0.7% n 3 3

Mean 28 7.61 - 28 6.53 95.9% Std Dev 1.25 - 0.38 1.2%

n 6 - 3 3 Mean 57 9.07 - 56 7.90 97.0%

Std Dev 0.57 - 0.27 0.9% n 6 - 3 3

Mean 94 9.77 - 91 7.95 96.7% Std Dev 0.59 - 0.03 0.8%

n 6 - 2 2 Mean 730 8.28 96.8%

Std Dev 1.14 1.4% n 14 14

0

2

4

6

8

10

12

0 100 200 300 400 500 600 700 800

Age (days)

UC

S (M

Pa)

Field cored Lab compacted

Figure 5.2: Unconfined compressive strength siltstone material with 4% GP cement

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5.1.2 IDT Strength Table 5.4 and Figure 5.3 show the IDT strength results for the hornfels material while

Table 5.5 and Figure 5.4 show the results for the siltstone material. More detailed IDT test data are presented in Appendix F.

Similar to the UCS test results, the overall trend was increasing strength with age. However, the IDT strength of the hornfels materials was about 0.7 MPa at 30 or 67 days age then 0.5 MPa at 96 days age. The 96 day cure sample included two very weak samples (0.3 and 0.4 MPa) which reduced the mean (see Figure 5.3).

The IDT strength of the siltstone material increased with cure age, commencing at about 0.7 MPa at 28 days and increasing to over 1 MPa after 56 days. The laboratory samples reached 0.8 MPa at 28 days and had only increased marginally after 58 days.

The sampling technique shown in Figure 4.3 resulted in all samples at a given cure age being taken from a small area of pavement rather than being spread across the test pavement area, the assumption being that the pavement properties would generally be quite uniform. However, it appears that the properties of the hornfels material varied more than those of the siltstone material and this affected the ability to assess changes in properties with cure age for this material. In similar future work, the use of random selection of sampling locations should be considered.

Table 5.4: Summary of IDT strength data hornfels


Age (days)

IDT strength

(MPa)

Relative compaction

(%) Age

(days) IDT

strength (MPa)

Relative compaction

(%) Age

(days) IDT

strength (MPa)

Relative compaction

(%)

Mean 7 0.52 96.1% 7 0.50 97.1% Std Dev 0.06 0.3% 0.06 0.3%

n 3 3 3 3 Mean 30 0.67 97.4% 30 0.71 96.4% 28 0.84 97.6%

Std Dev 0.10 1.5% 0.06 0.4% 0.06 0.4% n 12 9 3 3 3 3

Mean 67 0.65 94.8% 57 0.75 96.2% Std Dev 0.10 1.7% 0.06 1.1%

n 7 7 3 3 Mean 96 0.50 94.5%

Std Dev 0.13 2.3% n 6 3


0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80 100 120 140

Age (days)

IDT

Stre

ngth

(MPa

)

Field cored Field mix, lab compacted Lab samples

Figure 5.3: IDT strength hornfels material with 3% GP cement

Table 5.5: Summary of IDT strength data siltstone


Age (days)

IDT strength

(MPa)

Relative compaction

(%) Age

(days) IDT

strength (MPa)

Relative compaction

(%) Age

(days) IDT

strength (MPa)

Relative compaction

(%)

Mean 7 0.53 95.1% 8 0.46 93.8% Std Dev 0.08 0.4% 0.05 0.8%

n 3 3 3 3 Mean 28 0.68 95.4% 29 0.81 95.0% 28 0.74 -

Std Dev 0.24 3.6% 0.04 0.8% 0.05 - n 14 14 3 3 6 -

Mean 56 1.14 97.4% 58 0.85 94.9% 58 0.87 93.7% Std Dev 0.04 0.6% 0.08 0.1% 0.03 0.6%

n 3 5 2 2 3 3 Mean 102 1.06 98.2% 91 0.80 95.9% 102 0.95 94.8%

Std Dev 0.14 0.7% 0.18 0.2% 0.09 0.2% n 6 12 2 2 3 3

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0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 20 40 60 80 100

Age (days)

IDT

Stre

ngth

(MPa

)

120


Figure 5.4: IDT strength siltstone material with 4% GP cement

5.1.3 Flexural Beam Strength Table 5.6 and Figure 5.5 show the results of the flexural beam strength testing for the hornfels material, while Table 5.7 and Figure 5.6 show the results for the siltstone material. More detailed results are presented in Appendix G.

Like the UCS and IDT strength test results, the overall trend was of increasing strength with age, although the strength of the hornfels field samples again decreased with age. This was again considered to be related to variations in material properties based on the sampling location. The flexural strength of the siltstone beams was significantly higher than that for the hornfels material at each cure age.

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Table 5.6: Summary of flexural beam strength data hornfels

Field Laboratory

Age (days)

Flexural strength

(MPa)

Relative compaction

(%) Age

(days) Flexural strength

(MPa)

Relative compaction

(%)

Mean 7 0.72 94.9% Std Dev 0.10 5.1%

n 3 3 Mean 29 0.97 95.8% 28 1.01 95.4%

Std Dev 0.20 1.1% 0.14 1.8% n 6 6 11 11

Mean 71 0.77 95.9% Std Dev 0.26 0.6%

n 6 6 Mean 95 0.64 96.9%

Std Dev 0.11 1.0% n 5 5

Mean 576 1.26 96.7% Std Dev 0.19 1.1%

n 13 13

0.0

0.4

0.8

1.2

1.6

0 100 200 300 400 500 600 700

Age (days)

Flex

ural

stre

ngth

(MP

a)

Field beams Lab beams Figure 5.5: Flexural beam strength hornfels material with 3% GP cement

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Table 5.7: Summary of flexural strength data siltstone

Field Laboratory

Age (days)

Flexural strength

(MPa)

Relative compaction

(%) Age

(days) Flexural strength

(MPa)

Relative compaction

(%)

Mean 7 0.73 92.1% Std Dev 0.17 1.9%

n 3 3 Mean 34 1.32 98.1% 32 1.13 95.8%

Std Dev 0.15 1.0% 0.28 3.2% n 7 7 3 3

Mean 56 1.52 99.4% Std Dev 0.15 0.5%

n 5 5 Mean 97 1.40 97.8%

Std Dev 0.08 0.6% n 6 6

Mean 616 1.06 94.9% Std Dev 0.18 1.1%

n 19 19

0.0

0.4

0.8

1.2

1.6

0 100 200 300 400 500 600 700

Age (days)

Stre

ngth

(MP

a)

Field Beams Lab beams

Figure 5.6: Flexural beam strength siltstone material with 4% GP cement

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5.2 Modulus (IDT and Flexural Beam) 5.2.1 IDT Resilient Modulus The IDT modulus of the field cores was found to be about 17,000-18,000 MPa for the hornfels material and 14,000-17,000 for the siltstone material (refer Table 5.8, Table 5.9, Figure 5.7 and Figure 5.8). For the laboratory samples the modulus of the hornfels material was higher (about 24,000 MPa) while the modulus of the siltstone material was similar to that of the field cores.

Table 5.8: Summary of IDT modulus data hornfels material


Age (days)

IDT resilient modulus

(MPa)

Relative compaction

(%) Age

(days)


(MPa)

Relative compaction

(%) Age

(days)


(MPa)

Relative compaction

(%)

Mean 7 13530 97.1% Std Dev 11070 0.3%

n 3 3 Mean 30 23370 96.8%

Std Dev 2020 1.1% n 6 6

Mean 67 18270 95.2% 57 24260 96.1% Std Dev 6160 0.9% 2600 0.4%

n 4 2 6 6 Mean 101 16030 96.4%

Std Dev 3010 1.4% n 5 2

0

5000

10000

15000

20000

25000

30000

0 20 40 60 80 100 120 140

Age (days)

IDT

mod

ulus

(MP

a)


Figure 5.7: IDT modulus hornfels material with 3% GP cement

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Table 5.9: Summary of IDT modulus data siltstone material

Field Laboratory Field mix, lab compacted

Age (days)


(MPa)

Relative compaction (%)

Age (days)


(MPa)

Relative compaction

(%) Age

(days)


(MPa)

Relative compaction

(%)

Mean 28 13870 95.1% 29 17580 95.0% 28 13890 - Std Dev 5030 3.7% 1320 0.5% 530 -

n 8 8 6 6 3 - Mean 56 16950 97.5% 58 17730 95.2% 58 15600 93.7%

Std Dev 2260 0.2% 1630 0.4% 1890 0.6% n 3 3 5 5 3 3

Mean 102 14330 98.3% 91 21760 95.4% 102 19060 94.8% Std Dev 5300 0.7% 7990 0.2% 2380 0.2%

n 11 11 3 3 3 3

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

0 20 40 60 80 100

Age (days)

IDT

mod

ulus

(MP

a)

120

Field Cored Field mix lab compacted Lab samples

Figure 5.8: IDT modulus siltstone material with 4% GP cement

5.2.2 Flexural Beam Modulus The flexural beam modulus data for the hornfels material contrasted with the IDT modulus data (Table 5.10 and Figure 5.9). The initial beams cut from the test pavements after 30 days cure were found to have a flexural modulus of about 14,000 MPa while the modulus of subsequent field beams cut after 71 and 98 days cure age were much lower, being between 1,000-6,000 MPa. This was considered to be the result of the sample location and variations in the material properties at different locations.

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Table 5.10: Summary of flexural modulus data hornfels material

Field Laboratory

Age (days)

Flexural modulus

(MPa) Relative

compaction (%) Age

(days) Flexural

modulus (MPa) Relative

compaction (%)

Mean 30 14740 96.4% 28 16560 96.4% Std Dev 1150 0.6% 1250 2.5%

n 5 5 11 10 Mean 71 3060 95.9%

Std Dev 1990 1.1% n 6 6

Mean 98 3760 95.7% Std Dev 1650 1.7%

n 8 8 Mean 579 12490 96.8%

Std Dev 1590 1.4% n 18 18

0

5000

10000

15000

20000

0 100 200 300 400 500 600 700

Age (days)

Flex

ural

mod

ulus

(MPa

)

Field beams Laboratory beams

Figure 5.9: Flexural modulus hornfels material with 3% GP cement

With respect to the laboratory-prepared beams, the modulus dropped from about 16,500 MPa after 28 days to 12,500 MPa after 579 days. This is considered to have been related to the curing process. The laboratory samples tested after 28 days were cured in the ARRB fog room (constant high moisture conditions) while the long term cure beams were removed from the fog room after about 3 months (due to space capacity constraints with the fog room) and stored on pallets, causing them to fully dry out. Although the samples were placed back in the fog room for a minimum of 48 hours prior to testing, the wet/dry/wet cycle is thought to have reduced their stiffness properties.

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The flexural modulus of the field beams of the siltstone material was more consistent in terms of variation with cure age and/or sampling location compared to the hornfels material (Table 5.11 and Figure 5.10). The flexural modulus of the field cut beams was consistently about 9,000 MPa, although some values were as high as 14,000 MPa and as low as 5,000 MPa. As was the case with the hornfels material, the difference in modulus was probably related to the sampling location in the road bed. The laboratory flexural beam samples showed a similar variation in modulus to the field beams.

Table 5.11: Summary of flexural modulus data siltstone material

Field Laboratory

Age (days)

Flexural modulus

(MPa) Relative compaction

(%) Age

(days) Flexural modulus

(MPa) Relative

compaction (%)

Mean 34 9220 98.0% 32 11030 94.1% Std Dev 2270 0.8% 2240 3.9%

n 7 7 10 9 Mean 56 12740 98.8% 71 13350 97.0%

Std Dev 1520 0.4% 600 0.0% n 3 2 2 2

Mean 97 9530 98.7% Std Dev 2510 0.8%

n 6 6 Mean 616 6760 94.8%

Std Dev 1470 0.9% n 18 18

0

5000

10000

15000

0 100 200 300 400 500 600 700

Age (days)

Flex

ural

mod

ulus

(MP

a)

Field Beams Lab beams

Figure 5.10: Flexural modulus siltstone material with 4% GP cement

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For the siltstone material, there was a reduction in the laboratory modulus for the samples cured for an extended period (greater than 600 days). As with the hornfels material, this was thought to be related to the curing process. The samples were cured in the ARRB fog room for up to 3 months then removed and stored on pallets where they were allowed to dry out. Again the wet/dry/wet cycle for the long term cure samples was considered to have reduced their stiffness properties compared to the short term cure samples which were always kept moist in the fog room. Comparing Figure 5.11 and Figure 5.12, it would appear that, in general, the flexural modulus of the hornfels material was less sensitive to variations in density than the siltstone material.

y = 32416x - 14674

y = 27211x - 13842

0

5000

10000

15000

20000

91% 92% 93% 94% 95% 96% 97% 98% 99% 100% 101% 102%

Relative compaction (%)

Flex

ural

mod

ulus

(MP

a)

Lab beams, 28 days Lab beams, 579 days Field beams, 71 daysField beams, 30 days Field beams, 98 days

Figure 5.11: Variation in flexural modulus with sample density at different cure periods hornfels material

y = 74338x - 64178

y = 54317x - 40197

0

5000

10000

15000

20000

86% 88% 90% 92% 94% 96% 98% 100% 102%Relative compaction (%)

Flex

ural

mod

ulus

(MPa

)

Lab beams, 34 days Lab beams, 71 days Lab beams, 608 daysField beams, 34 days Field beams, 56 days Field beams, 97 days

Figure 5.12: Variations in flexural modulus with sample density at different cure periods siltstone material

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5.3 Fatigue (IDT and Flexural Beam) The aim of the laboratory fatigue testing was to develop a data set of applied stress or strain (S) against cycles of load until fatigue failure (N). This is often represented as an SN curve in classical materials fatigue assessment.

5.3.1 Fatigue Loading The fatigue testing was conducted in controlled stress mode. This was considered the most appropriate simulation of normal repetitive wheel loads, particularly for a given ALF experiment at a given axle load.

As such, the input for the fatigue test was the peak force (or stress) for the cyclic haversine load pulse. This peak force was initially selected as a percentage of the failure load determined on the paired sample. A number of samples were tested within a range of 60% to 90% of the nominal failure load. However, for some of the paired samples, differences were found in the sample properties. As such, the percentage of the failure load was considered to be a starting point for the selection of the appropriate load to be applied to fatigue a particular beam sample. After applying about 50 pulses of this initial load, the strain was assessed and compared with the target strain for the particular sample. If the strain was acceptable, the cyclic loading was continued until sample failure. However, if, after the initial 50 cycles, the strain was considered too low, the test was stopped and the peak load was increased to ensure the target strain value was achieved. A series of fatigue tests were conducted at a range of initial strain values to develop an S-N curve for each of the two cemented materials.

The process of completing the fatigue test immediately after the modulus test ensured that the sample had been subjected to at least 100 load cycles to shake down the test set-up prior to commencement of the fatigue test. Even with this prior loading, the possibility remained that the first pulse at the increased fatigue test load may be affected by test initialisation issues. To counter this, the initial modulus used in the fatigue life calculations was defined as the mean modulus for the first 50 load cycles applied to the specimen during the fatigue test. Similarly the initial strain used in the fatigue life calculations was defined as the mean tensile strain calculated during the first 50 load cycles applied to the specimen for the fatigue test. The tensile strain was calculated from the peak vertical mid-span beam deflection measured for each load pulse.

5.3.2 Laboratory Samples and Field Samples The focus of the fatigue testing was on the laboratory-prepared samples. As the ALF test pavement was to be assessed using ALF, cutting field beams for laboratory fatigue testing was not of primary interest to the study. The important link sought was between the fatigue performance of the trial pavement under ALF loading and the fatigue performance of the laboratory prepared samples. If a link between the field fatigue performance and the laboratory fatigue performance could be established, then the laboratory test could be more confidently applied to a much wider range of cemented materials to assess relative fatigue properties. Some field cut beams were also tested, but not a sufficient number to compile a full S-N fatigue chart. These data are presented in charts (see Figure 5.16 and Figure 5.17).

5.3.3 Cure Age for the Fatigue Test It was initially assumed that, as the binder used was GP cement, the samples would have reached generally stable material properties after 28 days of curing. The modulus and fatigue testing was therefore commenced after 28 days of curing. However, there were a wide range of fatigue results observed for these early age samples.


A large number of laboratory samples of both materials were therefore left to cure for an extended period while the full scale ALF experiments were undertaken. These samples were subsequently tested for modulus and fatigue and the fatigue results, while still variable, were much more consistent than the early (28 day) fatigue test results. The age of the laboratory samples tested for fatigue was representative of the test pavements during ALF trafficking. The fatigue data for the longer term cure samples was more uniform than the 28 day fatigue data. As a result, it was considered that a cure age of more than six months is required for fatigue testing of cemented materials. It was noted that, in France, cemented materials may be cured for up to 365 days prior to fatigue testing (LCPC 1997).

5.3.4 Definition of Fatigue Life Figure 3.3 shows a typical fatigue data plot for an indirect tensile specimen while Figure 5.13 shows the results of a typical flexural beam fatigue test. In the absence of an established protocol for the identification of the end of fatigue life, cycles to half initial modulus was adopted as the definition of fatigue life for the laboratory fatigue testing. It was found that the cycles of load to half initial modulus were very close to the cycles of load to ultimate failure of the samples for the flexural beam fatigue test (Figure 5.13).

0

2000

4000

6000

8000

0 5000 10000 15000 20000 25000 30000 35000 40000

Cycles

Mod

ulus

(MPa

)

Modulus (MPa) Half initial modulus (MPa)

Figure 5.13: Typical flexural beam fatigue test result showing cycles to half initial modulus

5.3.5 Fatigue Models A number of fatigue tests were conducted at different load pulse magnitudes to derive a dataset of fatigue life against tensile strain induced in the samples. The generic model fitted to the laboratory data is shown in equation (1). This was rearranged as shown in equation (2).

LDE

strainc N

= 1

log (N) = - LDE log (strain) + d 2

where LDE = Load Damage Exponent and c and d are constants.

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5.3.6 Fatigue Test Results and Models from Indirect Tensile Testing The deflections induced in the samples during the indirect tensile testing were very small. It was therefore determined that long term curing was not appropriate as the samples would be expected to become stiffer, resulting in even lower measured deflection responses. Given the signal to noise ratio issues with very stiff specimens (Figure 3.4), indirect tensile fatigue testing was only conducted on the laboratory samples after about 28 days and 56 days curing.

The data from the indirect tensile fatigue test was fitted to equation 2 and the following models were derived for the hornfels material (equation 3) and the siltstone material (equation 4) respectively:

log (N) = -8.84 log (strain) + 14.22 3

(n = 10, R2 = 0.70)

log (N) = -6.32 log (strain) + 12.14 4

(n = 11, R2 = 0.35)

Using equations 3 and 4, the load-damage exponents from the indirect tensile specimens were 8.8 and 6.3 respectively, although the fit of the model for the siltstone material was quite poor (equation 4). The models and the relevant data are shown in Figure 5.14 for the hornfels material and Figure 5.15 for the siltstone material. The axes have been transposed to present the data in the S-N fatigue chart format while the models shown were fitted following the equation 2 format (Log N against Log S).

Lysterfield material - indirect tensile fatigue test

10

100

10 100 1,000 10,000 100,000

Cycles to half initial modulus (N)

Initi

al te

nsile

stra

in (m

icro

stra

in) (

S) Lab IDT, 30 days

Lab IDT, 57 days

Field cores, 70 days

Field cores, 98 days

Lab fatigue model 30and 57 days combined

Figure 5.14: Summary of fatigue data from indirect tensile testing hornfels material

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Para Hills material - indirect tensile fatigue test

10

100

10 100 1,000 10,000 100,000

Cycles to half modulus (N)

Initi

al te

nsile

stra

in (m

icro

stra

in) (

S)

Lab IDT, 28 days

Lab IDT, 56 days

Field core, 108 days

Lab fatigue model 28and 56 days combined

Figure 5.15: Summary of fatigue data from indirect tensile testing siltstone material

5.3.7 Fatigue Test Results and Models from Flexural Beam Testing For the flexural beam testing it was considered appropriate to undertake fatigue testing at an extended cure age to represent the age of the field material test under full scale loading with ALF.

The laboratory fatigue data at an extended cure age (greater than 500 days) was fitted to the equation 2 model. The model fitted to the hornfels fatigue data is shown in equation 5 while equation 6 shows the model fitted to the siltstone data.

log (N) = -7.85 log (strain) + 18.74 5

(n = 12, R2 = 0.96)

log (N) = -6.29 log (strain) + 17.18 6

(n = 11, R2 = 0.63)

More detailed data is provided in Appendix G.

It is interesting to note that, using equations 5 and 6, the load-damage exponents for the hornfels material and the siltstone material were 7.9 and 6.3 respectively which was very similar to the load-damage exponents derived from the indirect tensile fatigue test data.

Figure 5.16 shows the data from the laboratory beams for the hornfels material after 580 days cure together with the model from equation 5 (transposed to fit the S-N format of the chart). The laboratory results for the 28 day fatigue tests are also shown. They tend to indicate a shift in the fatigue properties as the samples aged compared to the fatigue data for the samples cured for 580 days. The fatigue data from the limited number of field beams tested are also shown for comparison. The limited number of field beams, and the high variability in properties noted with the field beams, meant that a fatigue model could not be developed for this dataset. However, as stated earlier, the main focus of the laboratory fatigue assessment was the laboratory specimens as fatigue of the field trial was to be assessed using full scale loading with ALF.

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Lysterfield mat

austroads (2008), ap-t 101-08-the development and evaluation of protocols for the laboratory...

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