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ImproveRutCharacterisationOfGranularBases-CommissionningOfWheelTracker.docx

Austroads Project No: TT1611

Author(s): Didier Bodin

Reviewed

Project Leader

Didier Bodin

Quality Manager

Michael Moffatt

Technical Editor

Peter Milne

002279 – June 2011

Although the Report is believed to be correct at the time of publication, ARRB Group Ltd, to the extent lawful, excludes all liability for loss (whether arising

under contract, tort, statute or otherwise) arising from the contents of the Report or from its use. Where such liability cannot be excluded, it is reduced to

the full extent lawful. Without limiting the foregoing, people should apply their own skill and judgement when using the information contained in the Report.

Improved Rut Resistance Characterisation of Granular Bases – Manufacture and Commissioning of a Wheel-tracking Device

First Published 2011

© Austroads Inc. 2011

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.


National Library of Australia

Cataloguing-in-Publication data

ISBN

Austroads Project No: TT1611

Austroads Publication No:

Project Manager David Hazell

Prepared by Didier Bodin

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.

IMPROVED RUT RESISTANCE CHARACTERISATION OF GRANULAR

BASES – MANUFACTURE AND COMMISSIONING OF A WHEEL-TRACKING

DEVICE

Sydney 2011

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 Australian state (six) and territory (two) road transport and traffic authorities, the Commonwealth Department of Infrastructure and Transport, the Australian Local Government Association, and the NZ Transport Agency. It is governed by a council consisting of the chief executive officer (or an alternative senior executive officer) of each of its 11 member organisations:

� Roads and Traffic Authority, New South Wales

� Roads Corporation, Victoria (VicRoads)

� Department of Transport and Main Roads, Queensland

� Main Roads Western Australia

� Department for Transport, Energy and Infrastructure, South Australia

� Department of Infrastructure, Energy and Resources, Tasmania

� Department of Lands and Planning, Northern Territory

� ACT Department of Territory and Municipal Services

� Department of Infrastructure and Transport

� Australian Local Government Association

� NZ 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

As part of Austroads research project TT1163 ‘Improved Rut Resistance Characterisation of Granular Bases’ a new large-scale, combined compactor/wheel-tracker machine has been developed to assess granular material performance and characterisation in the laboratory. In addition, the compactor/wheel-tracker is also usable for asphalt characterisation and was designed to meet European standard specifications.

The design and manufacture of the machine were undertaken by IPC Global. The machine was delivered to ARRB Group’s laboratories in May 2011. Commissioning works were undertaken to ensure that the delivered machine met the initial specifications.

This commissioning report contains a description of the machine, its components and the operating control software. Both specimen compaction and wheel-tracking tests conducted during the commissioning works are reported.

The commissioning work presented the first opportunity to operate the machine using real laboratory conditions, and several minor modifications and improvements to the mechanics and software were identified. These have either been addressed or are scheduled to be fixed by IPC Global in the near future.

ACKNOWLEDGEMENTS

We wish to acknowledge IPC Global for the support and reactivity during the wheel-tracking commissioning process.


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CONTENTS

1 INTRODUCTION .................................................................................................................... 1

2 SPECIFICATIONS ................................................................................................................. 2

2.1 General .................................................................................................................................. 2

2.2 Specification for Compaction .................................................................................................. 2

2.3 Specification for Wheel-tracking ............................................................................................. 2

2.3.1 Large Device ............................................................................................................ 2

2.3.2 Extra-large Device .................................................................................................... 3

3 MACHINE DESCRIPTION ..................................................................................................... 4

3.1 Design Concept...................................................................................................................... 4

3.2 Machine Components ............................................................................................................ 4

3.3 Compaction and Tracking Configuration ................................................................................ 6

3.4 Laser Arm .............................................................................................................................. 7

3.5 Transducers ........................................................................................................................... 8

3.5.1 Positioning Transducers ........................................................................................... 8

3.5.2 Force Transducer ..................................................................................................... 8

3.5.3 Displacement Transducer ......................................................................................... 9

3.5.4 Distance Transducer ................................................................................................ 9

3.6 Safety Switches...................................................................................................................... 9

4 SOFTWARE DESCRIPTION ............................................................................................... 11

4.1 Compaction .......................................................................................................................... 11

4.2 Wheel-tracking ..................................................................................................................... 12

5 COMPACTION ASSESSMENT ........................................................................................... 13

5.1 Compaction Procedures ....................................................................................................... 13

5.2 Compaction Control ............................................................................................................. 14

5.3 Compaction Operation on Solid Slab .................................................................................... 15

5.4 Compaction of Granular Materials ........................................................................................ 17

5.5 Conclusions from Compaction Trials .................................................................................... 18

6 LASER MEASUREMENTS ASSESSMENT ........................................................................ 20

6.1 Laser Scanning Measurements ............................................................................................ 20

6.2 Laser Scanning Stability ....................................................................................................... 21

7 WHEEL-TRACKING TESTS ................................................................................................ 25

7.1 First Tracking Tests on Dummy Specimens ......................................................................... 25

7.2 Two Replicates on a Granular Material ................................................................................ 26

8 TROUBLESHOOTING DURING COMMISSIONING ........................................................... 28

9 CONCLUSIONS ................................................................................................................... 29

REFERENCES .............................................................................................................................. 30

APPENDIX A FORMULAS USED IN THE SOFWARE ................................................... 31

APPENDIX B MATERIAL CHARACTERISTICS ............................................................ 32


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TABLES

Table 3.1: Components of machine ........................................................................................... 4

Table 5.1: Compaction parameters ......................................................................................... 17

Table 7.1: Condition used for the first tracking trials on dummy specimens ............................. 25

Table 7.2: Conditions used for the first tracking trials on crushed hornfel specimens .............. 26

Table 8.1: Bugs, mechanical adjustments scheduled on the machine ..................................... 28

FIGURES

Figure 3.1: Schematic of wheel-tracker with all covers removed: front view ................................ 5

Figure 3.2: Schematic of wheel-tracker with all covers removed: back view ............................... 6

Figure 3.3: Drawing of the carriage in the extra-large configuration: (a) compaction foot presented in compaction position (b) compaction foot lifted up for tracking ..................................................................................................................... 7

Figure 3.4: Drawing of the carriage in the large configuration: (a) compaction foot presented in compaction position (b) compaction foot lifted up for tracking ..................................................................................................................... 7

Figure 3.5: Drawing to illustrate the laser arm use: (a) arm up (home position) laser down (b) arm down laser out .................................................................................... 8

Figure 3.6: Photo from the underneath the bottom plate supporting the mould ........................... 9

Figure 4.1: Example of a compaction in two layers ................................................................... 11

Figure 4.2: Example of a wheel-tracking test parameters as defined in the software ................ 12

Figure 5.1: Compaction sequences for a 300 mm high granular specimen ............................... 14

Figure 5.2: Force measured for the transducer ......................................................................... 15

Figure 5.3: Schematic view of the compaction foot movement: (a) positioned on right edge (b) positioned on left edge..................................................................... 16

Figure 5.4: Height calculated by the software during the compaction of a 100 mm thick MDF reference slab ........................................................................................ 16

Figure 5.5: Compaction of a crushed basalt by using two layers: (a) measurement of the compaction force (b) measurement of the specimen height .............................. 17

Figure 5.6: Compaction of a crushed basalt to a low compaction state: (a) measurement of the compaction force (b) measurement of the specimen height ..................................................................................................................... 18

Figure 6.1: Laser scanning path ............................................................................................... 20

Figure 6.2: Laser measurement stability-check configuration ................................................... 22

Figure 6.3: Initial distance measure from the laser before tracking (cross section X=0 mm) ................................................................................................................. 23

Figure 6.4: Difference between the initial measure (cross section X = 0 mm) ........................... 24

Figure 7.1: Rut depth measurements recorded for the three first tracking tests: (a) linear scale (b) semi-logarithmic scale .................................................................... 26

Figure 7.2: Repeatability results on two crushed hornfel specimens (material 1157): (a) linear scale (b) semi logarithmic scale ............................................................... 27

Figure 7.3: Proportional rut depth results on two crushed hornfel specimens (material 1157) ....................................................................................................... 27


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1 INTRODUCTION

A major finding of Austroads project TT1163 Better basis for bases: optimum use of granular bases (Austroads 2010) was that the existing repeat load triaxial test used for assessing the permanent deformation of unbound granular bases did not correlate well with the shear resistance of materials subjected to full-scale accelerated loading. However, a large-scale laboratory wheel-tracking test ranked the performance of the four test materials similarly to the performance observed under accelerated loading.

The project findings were discussed by various working groups and committees, and it was agreed that a new test for granular base rut resistance needed to be developed, and that it be based on a large-scale wheel-tracking test. Accordingly, in July 2009 Austroads commissioned ARRB to undertake research project TT1611 Improved rut resistance characterisation of granular bases. A worldwide review of existing devices concluded that a new machine design was necessary for compacting the large sized unbound granular samples needed, but that the design should additionally be able to meet existing European standards for both compaction and wheel-tracking of asphalt samples.

The Australian based company IPC Global was engaged to design and construct the machine. IPC has worked collaboratively with Austroads member authorities in developing and supplying laboratory testing machines for pavement materials.

The resulting machine design allows the compaction of specimens from loose granular materials to typical field densities. After compaction, a wheel-tracking test is set up to assess rutting performance of the compacted sample. The surface deformation of the specimen surface is automatically recorded periodically during the tracking process according to a user-defined schedule.

This report documents the commissioning investigations conducted using the prototype manufactured by IPC Global.

The driving need for creation of the machine was to allow study of granular materials but it is also usable for asphalt and could provide a supplement or alternative to the current smaller-scale wheel-tracking tests conducted in Australia and New Zealand. The commissioning works documented in this report focus on the compaction and wheel-tracking of granular materials.

The equipment specifications are presented in Section 2, followed by a brief description of the machine and the controlling software respectively in Section 3 and Section 4. The different commissioning steps to assess the different functionalities of the machine are reported in the followings:

� compaction process (Section 5)

� laser measurements (Section 6)

� wheel-tracking testing (Section 7 )

Finally some enhancement desirable on the prototype were highlighted during the commissioning. The strategy adopted to achieve the prototype is detailed in Section 8.


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2 SPECIFICATIONS

2.1 General

The set of specifications for the wheel-tracker were chosen to be able to meet the requirements of the European standard for compaction (EN 12697 - 33) and wheel-tracking (EN 12697-22). These standards were developed for the testing of asphalt, but provided a good framework to start with for granular material tests. The specifications detailed below build upon these European asphalt standards but include additional requirements to allow the compaction and wheel-tracking of large sized unbound granular samples.

The following specifications were those used to design the prototype device. Commissioning and subsequent use of the prototype device may further refine the specifications for subsequent devices.

In order to minimise laboratory floor space it was specified that a single machine be developed which was able to operate as both a compactor and a wheel-tracker.

2.2 Specification for Compaction

As a compactor the device must be able to compact materials:

� in accordance with EN 12697-33: steel roller method specifications

� with layers in four mould sizes, with the following internal dimensions (± 2 mm):

— 500 x 180 x 50

— 500 x 180 x 100

— 700 x 500 x 300

— 700 x 500 x 200

� in one or more layers, e.g. for 300 mm deep mould, compaction of six 50 mm thick layers

� with provision of a height adjustment to the bottom floor of each mould to enable loose material for each layer to be progressively added

� using either of two smooth steel roller segments:

— track width 180 mm, radius 350 mm

— track width 500 mm, radius 350 mm

� using applied loads ranging from 5 to 28 kN.

2.3 Specification for Wheel-tracking

The device must be able to perform tests in accordance with EN 12697-22: large size and extra-large size specifications.

2.3.1 Large Device

� A device shall be fitted with a 400 x 8 pneumatic tyre without tread pattern (about 425 mm diameter) and having a track width of 80 ± 5 mm.

� Enable to accommodate both asphalt and unbound material materials.

� Rolling vertical load 5.00 ± 0.05 kN or user selectable load.


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� Travel of pneumatic tyre relative to specimen shall be 410 ± 5 mm.

� Frequency of travel 1 ± 0.1 Hz (average speed 0.82 m/s).

� Centre line of tyre track not more than 5 mm from theoretical centre.

� Angle of skew of tyre 0.0±0.5°.

� Temperature control user selectable from room temperature up to 60 °C, such that the temperature within the specimen is maintained at ±2 °C of that set.

� Temperature sensor in accordance with EN 12697-22.

� Displacement measurement device in accordance with EN 12697-22 or better.

2.3.2 Extra-large Device

� A device shall be fitted with a 6.00 –R9 pneumatic tyre without tread pattern (about 550 mm diameter) and having a track width of 110 ± 5 mm.

� Able to accommodate both asphalt and unbound material materials.

� Rolling vertical load 10.00 ± 0.1 kN, or user selectable load.

� Travel of pneumatic tyre relative to specimen shall be 710±5 mm.

� Frequency of travel 0.4 ± 0.08 Hz (average speed 0.57 m/s).

� Centre line of tyre track not more than 10 mm from theoretical centre.

� Angle of skew of tyre 0.0 ± 0.5°.

� Temperature control user selectable from room temperature up to 60 °C, such that the temperature within the specimen is maintained at ±2 °C of that set.

� Temperature sensor in accordance with EN 12697-22.

� Displacement measurement device in accordance with EN 12697-22 or better.


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3 MACHINE DESCRIPTION

3.1 Design Concept

In response to the specifications, IPC Global produced designs for the combination compactor and wheel-tracker. The concept was based on a servo-pneumatic vertical loading ram, with a capacity up to 28 kN to satisfy the requirements for compaction.

The load is applied from below by the pneumatic actuator pushing the specimen onto the compaction plate or wheel. The sideways movement of the mobile carriage supporting the compaction foot and the wheel is achieved by a simple push/pull rod connected to an electric motor via a rotating cam. A computer-controlled system monitors the load being applied, as measured by a load cell, and adjusts the position of the actuator to ensure that the desired test conditions are obtained.

A ventilated enclosure, allowing heating up to 60 ºC, is also incorporated to allow controlled testing conditions for asphalt testing.

An automatic laser scanning system is used to measure rut development on the specimen’s surface.

3.2 Machine Components

Schematic representations of the machine are shown in Figure 3.1 and Figure 3.2, and the descriptions of numbered components of the system shown in these figures are listed in Table 3.1.

Table 3.1: Components of machine

Label Component

1 Machine frame

2 Electric motor

3 Gear box (used to change the speed between compaction and wheel-tracking modes)

4 Speed reducer

5 Cam

6 Rod

7 Mobile carriage holing wheel (78) and the compaction foot (9)

8 Tracking wheel (extra-large configuration shown)

9 Compaction foot (extra-large configuration shown)

10 Mould extension to retain loose material before compaction

11 Mould frames (three extra-large configuration moulds shown for a total depth of 300 mm)

12 Pneumatic actuator

13 Main glass door allowing access to machine and inspection of test being conducted

14 Supporting arms on which to roll the mould from under foot/wheel when preparing or removing the specimen

15 Laser arm support (adjustable in height for different specimen sizes)

16 Laser arm


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Source: IPC Global.

Figure 3.1: Schematic of wheel-tracker with all covers removed: front view

9

8

6

2

11

10

7

3

5

1

4

12

1314


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Source: IPC Global.

Figure 3.2: Schematic of wheel-tracker with all covers removed: back view

3.3 Compaction and Tracking Configuration

The machine was designed to allow both compaction and tracking on the same piece of equipment. To skip from compaction to tracking and vice versa the compaction foot is flipped up to free the wheel as illustrated on Figure 3.3. The wheel, animated by the carriage movement, can then roll freely on the surface of the specimen.

2

3

1

4

6 57

11

10

9

8

12

15 16


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(a) (b)

Source: IPC Global.

Figure 3.3: Drawing of the carriage in the extra-large configuration: (a) compaction foot presented in compaction position (b) compaction foot lifted up for tracking

The same principle is used for the large configuration as illustrated in Figure 3.4. However, the compaction foot is built of one part and is totally flipped up over the wheel in tracking configuration (Figure 3.4b).

(a) (b)

Source: IPC Global.

Figure 3.4: Drawing of the carriage in the large configuration: (a) compaction foot presented in compaction position (b) compaction foot lifted up for tracking

3.4 Laser Arm

The laser arm (numbered 16 in Figure 3.2) at the rear of the machine can flip down above the specimen surface as illustrated on Figure 3.5. Two electric motors allow the laser to be positioned at appropriate X-Y positions for reading.


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(a) (b)

Source: IPC Global.

Figure 3.5: Drawing to illustrate the laser arm use: (a) arm up (home position) laser down (b) arm down laser out

At each X-Y position the distance of the specimen surface to a reference height is recorded. Tracking of the wheel is halted whilst the laser scanning takes place.

3.5 Transducers

The machine is equipped with several transducers all controlled and used by the attached computer. Different types of transducers are used, namely:

� positioning transducer

� force transducer

� displacement transducer

� distance transducer.

3.5.1 Positioning Transducers

A set of position transducers is fitted on the machine. Each has a separate function as follows:

� counting the rotations of the eccentric cam

� detecting the carriage home position

� detecting the carriage central position

� laser arm positioning to detect its home position.

3.5.2 Force Transducer

The force transducer is located between the end of the actuator rod and the bottom plate supporting the specimen as shown in Figure 3.6. The force transducer signal is used to control the compaction load as well as the wheel-induced load when tracking. To ensure that the weight of the mould and the specimen are not taken into account in the reading, the value is tared when lifting up the specimen before load application.


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Figure 3.6: Photo from the underneath the bottom plate supporting the mould

3.5.3 Displacement Transducer

A displacement transducer is attached between the frame of the machine and the bottom plate supporting the mould. It allows measurement of the vertical position of the specimen. It is mainly used when compacting a specimen. As the compaction foot height is known the position measure is transformed into a measure of the specimen’s height.

3.5.4 Distance Transducer

The laser position on a foldable arm allows measuring of the distance of the specimen surface, from the arm. Subtracting the initial measure (e.g. before load application) to the measured values after a given number of wheel cycles gives the wheel-passes induced deformation. The laser scanning can be performed automatically at different numbers of cycles.

3.6 Safety Switches

Parts or the machine cover and body are removable in order to operate and set up the specimen and testing conditions. Each of them is equipped with a safety switch to stop the machine instantaneously if activated. They feature:

� the main door

Force transducer

Displacement transducerPneumatic actuator

piston rod


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� the gear box cover (the gear box is adjusted to change the speed of tracking from slow compaction to quicker wheel-tracking speed)

� the top cover access to the eccentric cam and rod (this adjusts the wheel travel length between large and extra-large configurations).


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4 SOFTWARE DESCRIPTION

The machine is controlled using a personal computer (PC) operation on a standard Windows XP operating system. The supervision of the tests is done using IPC – UTS 33 software (dedicated to the wheel-tracker device). It allows the definition of the tests, definition of the compaction parameters, and definition of the tracking parameters. Some graphic outputs provide a control during the tests and can be reloaded after completion. The recorded data can be exported to ASCII files for further analysis.

Some of the basics features are briefly presented below. More detail will be found in the forthcoming manual being prepared by IPC. For each operation the user can either use existing templates defined to fit the specifications defined in the standards or use non-standard conditions manually defined in the software.

4.1 Compaction

The compaction process allows manufacturing the specimen from loose material in several layers. For each layer the compaction could comprise several sequences allowing a progressive increase in the compaction load. The example in Figure 4.1 presents six sequences in total. For this example, each layer has been compacted using the following sequences:

� Layer 1: compacted by two sequences to target a height of 50 mm

— 50 cycles at a compaction force of 5 kN

— 50 cycles at a compaction force of 10 kN.

� Layer 2: compacted by four sequences to target a total height of 100 mm




— 50 cycles at a compaction force of 20 kN.

Figure 4.1: Example of a compaction in two layers

The compaction load amplitude and the number of sequences can be adjusted by the user until the compaction requirements are reached. Termination conditions are used to stop the compaction automatically. Compaction can be stopped wether the defined number of passes is reached or the height of the specimen reaches the target during the compaction sequence. When at least one of these is reached the sequence is stopped and the machine is ready to start the new one if needed.

Layer 1 Layer 2


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When compaction of the full depth specimen is achieved, the user can proceed the wheel-tracking testing.

When compacting asphalt specimens, compaction can also be terminated when the target air void content is reached.

4.2 Wheel-tracking

Before starting a wheel-tracking test, the operator defines the general testing conditions. Figure 4.2 gives an overview of the software parameters. Three main sets of parameters are given as follows:

1 Tracking parameters

(a) Frequency: used to adjust the frequency of the sinusoidal movement of the wheel.

(b) Rolling load: used to adjust the value of the load.

(c) Tyre width: used to indicate the width of the track. This input parameter is used by the software when calculating the average of the laser measurement (e.g. only across the wheel track width). Further information is given Appendix A.

2 Termination conditions

(a) Number of cycles: used to define the maximum number of cycles to be applied.

(b) Laser rut depth (mm): used to stop tracking when a given rut depth is reached. This value is be compared to the average rut depth calculated from the data in the tyre width.

3 Laser scanner measurements

(a) Number of cross-sections: from three to seven cross-sections can be defined. They are distributed symmetrically to the centre of the slab. Their positions are given in the ‘Cross-section locations (mm)’ table.

(b) Transverse profile span: defines the width of the laser scanning. It is defined symmetrically to the wheel travel axis. The step between two measures is defined either by its value given in the ‘Spacing between readings (mm)’ box or by the ‘Number of transverse reading’ box.

Figure 4.2: Example of a wheel-tracking test parameters as defined in the software

Each tracking can be preceded by a conditioning sequence. It is used to initialise the testing conditions. It can be a tracking conditioning or a temperature conditioning (mainly useful for asphalt testing in temperature controlled conditions). The tracking conditioning could be used to prepare the specimen, i.e. bedding-in, by applying a few wheel passes before the proper test. When conditioning is defined, the initial specimen’s surface profile is recorded after this conditioning step.


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5 COMPACTION ASSESSMENT

5.1 Compaction Procedures

A full depth granular specimen is generally compacted in different layers to fill the mould at the targeted compaction state progressively and evenly. In accordance with the knowledge and practice in using the New South Wales Roads and Traffic Authority (RTA) wheel-tracker for granular material, 50 mm thick layers should be compacted to reach a sufficient homogeneity of the specimen. Limiting the thickness of the elementary layer will reduce the vertical gradient of density in the final specimen.

The compaction sequences shown in Figure 5.1 present the six sub-layer steps to achieve a 300 mm high specimen. For wheel-tracking using extra-large configuration, the specimen needs to have a minimal height of 200 mm. To test a 100 mm high specimen, a spacer of 100 mm should be placed at the bottom of the mould. The compaction sequence will proceed from configurations 3 to 4 according to Figure 5.1.

Improved Rut Resistance Characterisation of Granular Bas

Figure 5.1: Compaction sequences for a 300 mm high granular specimen

5.2 Compaction Control

The compaction sequences are defined by a pneumatic actuator. The control orod and the bottom plate. The force gaspecimen and the entire mould to the measured force. and there is no friction between the the foot on the material.

The compaction sequence is defined with a number of compaction state in the specimen the user can also define a termination criterion based on the height of the specimen (Figure 4.

The height is back calculated from the displacement measurement at the middle of the bottom plate supporting the mould. The height measurement is set to zero when the compaction foot is

Improved Rut Resistance Characterisation of Granular Bases – Manufacture and Commissioning of a Wheel

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Compaction sequences for a 300 mm high granular specimen

ontrol

The compaction sequences are defined by a vertical force applied at the bottom of the slab by the The control of that force is achieved by measuring the force between the jack

The force gauge is tared to subtract the contribution of the weight of the specimen and the entire mould to the measured force. When friction in the bushes is

between the mould and the frame, this force is equal to the force applied by

sequence is defined with a number of foot passes. To reach the desirethe specimen the user can also define a termination criterion based on the

.1).

The height is back calculated from the displacement measurement at the middle of the bottom The height measurement is set to zero when the compaction foot is

Manufacture and Commissioning of a Wheel-tracking Device

Compaction sequences for a 300 mm high granular specimen

ied at the bottom of the slab by the the force between the jack

ge is tared to subtract the contribution of the weight of the bushes is negligible

this force is equal to the force applied by

To reach the desired the specimen the user can also define a termination criterion based on the

The height is back calculated from the displacement measurement at the middle of the bottom The height measurement is set to zero when the compaction foot is


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touching the top surface of the bottom of the mould. A constant distance parameter is set up in the software to calibrate the specimen’s height from the position of the ram.

For thin specimens, the machine requires the use of a rigid spacer placed at the bottom of the mould. Some medium-density fibreboard (MDF) slabs have been provided for that purpose. When using a spacer during the compaction, the software includes a parameter to define its thickness. This allows data to be presented representing the material specimen thickness.

All these software options allow getting an indirect measurement of the height of the specimen using the displacement transducer at the middle of the specimen. This measure is theoretically equal to the height of the specimen when the compaction foot is positioned vertically above the transducer. When it is on either side of the centre it might be affected by the small rotation of the specimen.

5.3 Compaction Operation on Solid Slab

The compaction process requires a constant vertical load applied to the compaction foot during the passes. As part of the compaction validation, the stability of the load, measured during compaction, has been checked. The European standard specified a compaction load tolerance of 5%. To validate the accuracy of the load, a compaction sequence on two 50 mm thick MDF slabs was performed, specifying a compaction force of 5 kN.

Figure 5.2 shows the recorded force versus the number of passes obtained during the pseudo-compaction process. The load value exhibits some small variations around the average value. During this test, the average force value was 4.98 kN and the variation around the average was lower than 0.15 kN (e.g. 0.3% of the average value), showing that the control of the compaction loads meet the requirements specified in the

Figure 5.2: Force measured for the transducer


Each peak is related with the control of the load when the compaction foot is positioned periodically on the right and left hand side of the mould

(a)

Figure 5.3: Schematic view of the compaction foot movement: (a) positioned on right edge (b) positioned on left edge

Running a compaction process on a solid slab with perfect dimensionheight measurements during the processcompaction process, the height calculated by the software is given the average height is 99.88 mm for a thickness of 100around the average measured along the compaction sequence is less than 0.5

Figure 5.4: Height calculated by


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ak is related with the control of the load when the compaction foot is positioned periodically on the right and left hand side of the mould as shown in Figure 5.4.

(b)

Schematic view of the compaction foot movement: (a) positioned on right edge (b) positioned on left edge

Running a compaction process on a solid slab with perfect dimensions also allowmeasurements during the process. The MDF slab thickness was 100 mm.

he height calculated by the software is given Figure 5.4mm for a thickness of 100 mm measured on the specimen

around the average measured along the compaction sequence is less than 0.5

by the software during the compaction of a 100 mm thick


ak is related with the control of the load when the compaction foot is positioned periodically

Schematic view of the compaction foot movement: (a) positioned on right edge (b) positioned on left edge

also allowed validating the mm. During the . Over the sequence,

mm measured on the specimen. Variation around the average measured along the compaction sequence is less than 0.5 mm.

thick MDF reference slab


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This first validation step using a rigid slab has shown a good control of the load with small variations around the average. The load average value does not differ more than 0.2% from the target. The compaction sequence on a reference slab has also shown that, the measurement of the specimen’s height was performed with an accuracy of 0.5 mm (i.e. 0.5%). However, more investigations are needed to elucidate if the periodic variations shown in Figure 5.4 comes from the loop control of the device or from other phenomena. Regardless, the magnitude of the variation remains very small compared to the measured values

5.4 Compaction of Granular Materials

When compacting granular material, termination of the compaction could be triggered by reaching a predefined number of passes, or alternatively when a targeted height is reached.

The following example illustrates the compaction of a realistic crushed rock specimen in two layers. Two layers of 50 mm have been used to compact the full 100 mm specimen. The compaction parameters are presented in Table 5.1. The compaction load was the same for the two layers, set at 5 kN, for a maximum of 100 passes per sequence. Both compaction force and specimen height are recorded during compaction. Measurements are presented (Figure 5.5) versus the number of compaction passes.

Compaction of both layers was terminated when the maximum number of passes of 100 was reached. The height of layer 1, after 100 passes was only fractionally higher than the target height.

Table 5.1: Compaction parameters

Parameters Layer 1 Sequence 1

Layer 2 Sequence 2

Compaction load (kN) 5 5

Number of passes 100 100

Target height (mm) 50 100

(a) (b)

Figure 5.5: Compaction of a crushed basalt by using two layers: (a) measurement of the compaction force (b) measurement of the specimen height

Compaction layer 1

Compaction layer 2


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The compaction termination condition has been checked in a critical situation by testing a very low compacted the granular material. In order to check the termination of compaction on reaching a targeted height, a specimen was compacted at a 5% lower density than its maximum density measured in the laboratory. The compaction process was expected to be very rapid, requiring just a few compaction passes.

The measured force and height from this test are presented Figure 5.6. As noticed during the other compaction validations, the load magnitude was very close to the required value parameter of 5 kN (Figure 5.6a). The termination condition was set to target a height of 50 mm. Figure 5.6b shows that the compaction started with a height of 51.7 mm (reached after tamping the specimen and applying a pre-compaction stage) and stopped automatically when it reached a value of 49.8 mm (first measure below the target of 50 mm). The compaction sequence was scheduled for 100 cycles but stopped when reaching the termination criterion with an accuracy of 0.4%. This observation validates the termination criterion implemented in the software.

(a) (b)

Figure 5.6: Compaction of a crushed basalt to a low compaction state: (a) measurement of the compaction force (b) measurement of the specimen height

5.5 Conclusions from Compaction Trials

At this stage, the commissioning of the compaction process using the new laboratory equipment was focused on validating the control of the load magnitude during compaction and evaluating the accuracy of the specimen’s height measurements.

The value recorded for the force transducer is the compaction force assuming there is no friction in the translation guidance of the mould; further investigations will be performed by IPC Global to confirm this assumption. The force magnitude varied very slightly around the average over a compaction sequence. It is well controlled by the software. The average value of the load matched the input parameters with an accuracy below 1% during the validation trials.

Assessment of the compaction height on a rigid slab indicated that the height of the specimen was measured with a good accuracy. Variations of the measurement were found in the range of ±0.5 mm.


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A future validation exercise will be focused on validating the uniformity of density in the manufactured specimen and checking if the material is not affected by significant particle breakdown when compacted.


6 LASER MEASUREMENTS

6.1 Laser Scanning M

To measure rut depth of the specimen the machine operatecycles during the process. The laser scanning sequences described discrete laser measurements of the surface over differenstep in the Y directions. Laser readings arewheelpath.

The laser measures the distance of Scanning the initial profiles allows subsequent data. This gives the wheelscanning at defined numbers of cyclescalculated.


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SER MEASUREMENTS ASSESSMENT

Measurements

To measure rut depth of the specimen the machine operates a laser scanningThe laser scanning sequences described in Figure

discrete laser measurements of the surface over different cross-sections (X positions) ep in the Y directions. Laser readings are generally performed over the tracked area along the

The laser measures the distance of the top surface of the specimen from the laser position. Scanning the initial profiles allows subtracting the initial position of the specimen surface

wheel-induced deformation of the surface. Byning at defined numbers of cycles, the rutting rate with the number of wheel cycles

Figure 6.1: Laser scanning path


a laser scanning, at a fixed number of Figure 6.1 comprise

sections (X positions) with a given he tracked area along the

the top surface of the specimen from the laser position. the initial position of the specimen surface from the

By applying laser wheel cycles can be


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The input parameters for a laser scan are (Figure 4.2):

� Number of cross-sections along x axis. The cross-sections will be symmetrically distributed from each side of the central cross-section for x = 0 mm. For example, the user can set 3 cross-sections positioned at (-150, 0 +150 mm) according the European standard or 5 cross-sections (-150, -75, 0, +75, +150 mm) to provide more refinement.

� Number of measures � or interval between the measures across each cross-section. For a step �� of 1 mm (minimal value for the wheel-tracker) a scanning length of 200 mm across the wheel path will result in 201 data points for each cross-section. Each �th measure will be

positioned at ordinate ��defined by:

�� with

� � � �

� � � � � �

�

1

where

��= transversal position of scanning

��= transversal scanning step.

6.2 Laser Scanning Stability

The laser profile measurement stability was checked by adding a reference beam above the slab placed in the mould. During the laser scan, the reading performed across each cross-section captured the reference beam as illustrated in Figure 6.2. This beam provides reference points at the end of each cross-section. Between tracking sequences, the distance recorded on those points should not change. In addition the beam comprised a step to assess the transversal (e.g. along the

� axis) positioning reliability.

Scanning across the reference beam, the difference between the readings on the beam and on the

step should be 3 mm. If the � positioning is not reliable and stable, a scanning point could be either on the beam or on the step from one scan to another. In that case, readings will exhibit a 3 mm millimetre difference. If it happened, it would show that, the laser was not back it the same position at each laser scanning. The accuracy of the verification would depend on the step �� set up in the scanning parameters.

A wheel-tracking test on solid MDF timber plate was performed to check the stability of the measures.


Figure 6.2:

The stability was checked using parameterssections were defined, positioned at a transversal step, , of 1 mm between each measurement.

The initial profile was recorded firstdistance measured by the laser issection for X = 0 mm is presented. sections. This figure clearly shows the reference beam located approximately at a distance of Y=85 mm from the centre of the crossrecorded data remains below 1 mm.


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: Laser measurement stability-check configuration

parameters providing a high level of refinementns were defined, positioned at -150, -75, 0, 75, 150 mm. The laser scanning was set

mm between each measurement.

itial profile was recorded first, to be subtracted from the other measurementss presented Figure 6.3. In this figure only the middle cross

mm is presented. However, similar plots were obtained on the four other crossThis figure clearly shows the reference beam located approximately at a distance of

of the cross-section. The 3 mm step can also be seen. The scatter of the mm.


providing a high level of refinement. Five cross-. The laser scanning was set up with

ments afterwards. The is figure only the middle cross-

on the four other cross-This figure clearly shows the reference beam located approximately at a distance of

mm step can also be seen. The scatter of the


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Figure 6.3: Initial distance measure from the laser before tracking (cross section X=0 mm)

After the initial measurement, wheel-tracking sequences were applied to the MDF plates in order to check the laser measurement stability after wheel-tracking cycles. Wheel-tracking was conducted to 8 000 cycles, with 11 intermediate laser scanning sequences (at 50, 100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000 and 8000 cycles).

Untrafficked

trafficked

step

beam


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Figure 6.4: Difference between the initial measure (cross section X = 0 mm)

Figure 6.4 shows the differences between the laser measured sequences for the middle cross-section. Similar results were obtained at other cross-sections. Variations of less than ± 1 mm were observed on the timber surface, and significantly less on the reference beam.

This test validates the scanning process stability over a reasonable range of loading cycles. However, the variability observed when scanning over the metal reference beam was smaller than over the timber plate. That raises the question of the effect of material or surface conditions on the measures. Further investigation on the influence of the surface conditions might be needed in the future.

Untrafficked

trafficked

step

beam


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7 WHEEL-TRACKING TESTS

During the commissioning process several wheel-tracking tests were performed. The commissioning started using dummy granular specimens of crushed basalt. In a second stage, a fully characterised granular material was used to get a first estimate of testing repeatability.

7.1 First Tracking Tests on Dummy Specimens

To assess wheel-tracking operation, some tracking tests were performed on the specimen produced when assessing the compaction. A crushed basalt has been used for that purpose. The material optimum moisture content (OMC) was 5.7%. Specimens were manufactured targeting a moisture content (MC) 30% lower than OMC i.e. a MC of 4.0%. Parameters of the tracking tests are listed in Table 7.1.

The first specimen was compacted targeting a lower level of compaction than the two others. The void content was targeted 5% above the modified maximum dry density (MDD). The two others were compacted to their MDD. However, the last two specimens were tested at two different rolling load magnitude.

Table 7.1: Condition used for the first tracking trials on dummy specimens

Name Material Target density Vertical load (kN)

Test slab 1

‘Generic’

crushed basalt

Modified MDD + 5% void 5

Test slab 2 Modified MDD

Test slab 3 7.5

The rut depth measures recorded from the machine are presented in Figure 7.1. In Figure 7.1a plotting in linear scale, the rut depth development exhibits a classical shape with a high rut depth rate at the beginning of the test, after which the rutting process tends to stabilise. The first tests were not performed up the same number of cycles; however, the three curves were well separated. The highest rut depth was obtained for the slab (slab 1) which was voluntarily compacted to a low level of compaction. When loaded at the same loading level of 5 kN, the second slab, compacted at MDD, exhibits a lower rut depth. For the same level of compaction, slab 3 was tested with a higher load. The higher load led to higher rut depth.


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(a) (b)

Figure 7.1: Rut depth measurements recorded for the three first tracking tests: (a) linear scale (b) semi-logarithmic scale

These results obtained during the three first trials gave rut depth consistent with expected trends and consistent with practice. The lowest compacted specimen could have been post-compacted when tracking which led to a higher rut when tested. It is also logical that for the same material, the rut depth increases with an increase of the load.

7.2 Two Replicates on a Granular Material

Further validations of the device were performed using a base quality crushed hornfels material. Before testing, the standard OMC and MDD were evaluated. Results are presented in Appendix B. The same conditions were applied to the two tests to get a first estimate of the test repeatability.

General parameters of the tests are shown in Table 7.2.

Table 7.2: Conditions used for the first tracking trials on crushed hornfel specimens

Specimen number Material type Material number Target density Vertical load (kN)

1167 Crushed

hornfels 1157 Standard MDD 7.5

1170

The rut depth measurements recorded when repeating the tests are presented in Figure 7.2. For these two tests the shapes of the rutting curve were the same, showing a first phase which corresponds to a rapid increase followed by a stabilisation in the second phase. During these two tests the rut nearly plateaus from 15 000 cycles where it reaches stabilisation.

Slab 1

Slab 3

Slab 2

Slab 1

Slab 3

Slab 2


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(a) (b)

Figure 7.2: Repeatability results on two crushed hornfel specimens (material 1157): (a) linear scale (b) semi logarithmic scale

The two curves in Figure 7.2, are not strictly superimposed showing a variation from one specimen to another. In Figure 7.2b the curves are nearly parallel exhibiting similar slope values. However, there is a gap between around 0.5 mm between the two curves. This could be due to the material settlement in the mould from the compaction differing from one specimen to another.

Dividing the rut depth by the thickness of the slab gives the proportional rut depth as defined in the European standard. The proportional rut depth is plotted in Figure 7.3.

Figure 7.3: Proportional rut depth results on two crushed hornfel specimens (material 1157)

The repeatability of proportional between these two tests was found to be below 1.0%. This is encouraging and is in the same range of data produced by asphalt wheel-tracking tests (reported in EN 12697-22) obtained using a large-scale configuration.


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8 TROUBLESHOOTING DURING COMMISSIONING

Before delivery, IPC was not able to validate the device using real test conditions with granular materials. The commissioning process has identified a series of issues which were difficult to anticipate. The main concerns faced were experienced during compaction of granular materials. Other enhancement and changes were also found necessary from mechanical and software point of view. Identified issues are listed in Table 8.1.

Table 8.1: Bugs, mechanical adjustments scheduled on the machine

Type of operation Type of trouble Category Solution

Compacting the top layer to

fill up the mould

The compaction foot rocked over the metal

fence. Then the compaction foot became

uncentered and the compaction sequences

had to be stopped. This problem was not

noticed when performing a compaction for

intermediate layers in the mould because in

that case the extra height of the mould

helps to keep the foot in a central position.

Operating

compaction

The length of the compaction foot has been

slightly reduced of 2 mm. An extra-guide

will also be needed to align the foot when

compacting the last layer of a 300 mm high

specimen. Procedures will have to be well

documented in the machine manual

Compaction and tracking Validation that the load applied at the

bottom of the specimen is fully transferred

to either the compaction foot or the wheel.

Operating

compaction/tracking

The guidance of the mould should limit the

friction as much as possible. The friction

force should be estimated

Compaction and tracking During the commissioning, the mould

tended to rock from one side to another.

This movement could interact with

specimen loading and lead to premature

wear of the equipment.

Operating

compaction

The translation guidance of the specimen

should be upgraded

Removing the specimen The supporting arms provided on the

machine are too short to allow the specimen

to be rolled outside the machine.

Ease of use and

safety

Arms with adjustable length will be provided

on the machine allowing the specimen to

be rolled outside the machine and lifted up

without any cantilever load on the trolley

Rut testing and laser

scanning

The transversal positioning of the specimen

can slightly differ between the initial laser

scanning and subsequent scans

Operating laser

scanning

The specimen should be lifted up and down

before the initial laser scanning

Equipment maintenance

planning

No record of machine use Maintenance

planning

A counter for checking cumulative wheel

passes could help in maintenance planning.

This counter should be independent of the

software


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9 CONCLUSIONS

The new wheel-tracking machine has been developed to improve the characterisation for granular materials. It was designed and manufactured by IPC Global within the framework of current European standard specifications for both compaction and rutting tests of asphalt materials.

IPC facilities did not allow the compaction of granular materials, until it was delivered,. The first compaction trials highlighted some issues and some adjustments were needed. Mechanical and software changes were performed to allow the first validation of the device. Some final modifications are needed and have already been scheduled to finalise the machine.

A set of compaction tests were performed to adjust and finalise the compaction sequence requirements. Tracking tests on 100 mm thick granular materials were performed. Qualitative results of the loading magnitude and material void content were assessed during the first trials. One testing condition was repeated and the repeatability scatter was in the range of what is obtained for asphalt wheel-tracking tests.

The commissioning indicates that the machine appears suitable to assess the rut performance of granular materials. Further investigations will be carried out during the ongoing project to develop the procedures and prepare a standard for granular material characterisation.


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REFERENCES

Austroads 2010, Assessment of Rut-Resistance of Granular Bases using the Repeated Load Triaxial Test,

by G Jameson, B Vuong, MA Moffatt , A Martin , S Lourensz S, AP-R360/10, Austroads, Sydney,

NSW.

Jameson G, 2009, Improved Rut Resistance Characterisation of Granular Bases: Inception Report

RILEM Technical Committee 206-ATB in press ‘RILEM TC 206-ATB: Advanced testing and Characterization

of bituminous materials, by TG3: Mechanical testing of mixtures. French wheel-tracking round robin

test on a polymer modified bitumen mixture’, Materials and Structure, Online First,available online 26

April 2011, DOI: 10.1617/s11527-011-9733-x , 16pp.

European Standards

EN 12697-33: Bituminous mixtures, test methods for hot mix asphalt – part 33: Specimen prepared by roller

compactor.

EN 12697-22: Bituminous mixtures, tests method for hot mix asphalt – part 22: Wheel-tracking.

Australian Standards

AS 1289.5.2.1—2003, Methods of testing soils for engineering purposes: Soil compaction and density

tests—Determination of the dry density/moisture content relation of a soil using modified compactive

effort


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APPENDIX A FORMULAS USED IN THE SOFWARE

A.1 Laser Measurements

The measurements performed to check the stability of laser measurements between the tracking sequences are presented Figure 6.4. The chart shows the difference between the initial profile and

the distance measured after � cycles. Each data point is calculated according the following equation.

��

2

where �� = deformation of the material surface at cycle � at location �� of the

surface

�� = distance measured from the laser after � tracking cycles at location ��

�� = distance measured form the laser on the initial specimen surface for

�=0 at location �� .

A laser scanning will result in a matrix of data point defined for each position �� at each number of cycle �.

A.2 Average Rut Calculation

The performance of a material is characterised by a rutting curve. Several methods could be used to determine the rut depth of a specimen. The European standard generally defines the rut depth as an average of the specimen deformation in the tyre track. The average rut depth provided for a given number of cycle is calculated as follows:

� � �� !�"�

�� 3

where

#$ = average deformation of the material surface at cycle �

�� = deformation of the material surface at cycle � at location �� of the surface

% = width of the wheel path for rut depth calculation


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APPENDIX B MATERIAL CHARACTERISTICS

Part of the commissioning trails have been performed using a standard class 2 crushed Hornfels material. The Victorian crushed hornfels used was obtained from a quarry in the South-Eastern Melbourne suburb of Lysterfield.

The maximum dry density assessed according to test method AS 1289.5.2.1 was found of 2.26 t/m3 with an OMC of 7%.

In the wheel-tracker, the specimens were manufactured targeting a density equal to MDD, but with a moisture content of 70% of OMC i.e. 4.9%.

y = -99.01x2 + 13.933x + 1.773

2.10

2.12

2.14

2.16

2.18

2.20

2.22

2.24

2.26

2.28

2.30

3.00% 4.00% 5.00% 6.00% 7.00% 8.00% 9.00% 10.00%

Dry

Den

sit

y (

t/m

3)

Moisture Content (%)

MDD/OMC Determination Lysterfield Class 2 sample No. 1164


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INFORMATION RETRIEVAL

Austroads, 2011, Improved Rut Resistance Characterisation of Granular Bases – Manufacture and Commissioning of a Wheel-tracking Device, Sydney, A4, pp. 2.

Keywords: wheel-tracking, commissioning, granular materials

Abstract:

To assess permanent deformation of granular materials repeated triaxial tests are currently used. A previous research project highlighted interest in using a wheel-tracking test to obtain a better agreement with field performance.

A new wheel-tracker was developed and manufactured for granular material characterisation. The device also included a compactor to prepare the slab to be tested. The machine was developed and manufactured by IPC Global and delivered to ARRB Group in May 2011.

Commissioning the machine has resulted in testing the ability of the device for compacting granular slabs. The specimens were then used to test the tracking. The trials have highlighted some slight changes needed to the prototype and refinements of the software.

It is concluded that the first trials gave encouraging results for granular material characterisation. Further research will be undertaken to derive a test method and to compare the rutting data with performances obtained previously from experimental pavements.

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