University of Minho Guimarães – Portugal The effect of ... · The effect of using rest periods in 4PB tests on the fatigue life of grouted macadams. Transport Infrastructures Research

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 1

University of Minho Department of Civil Engineering – Transport Infrastructures Research GroupGuimarães – Portugal

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The effect of using rest periods in 4PB tests on the fatigue life of grouted macadams

Joel Oliveira, Jorge Pais, Nick Thom, Salah Zoorob

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 2

Introduction

4 PB Test Apparatus

4 PB Fatigue Test Results on Grouted Macadams

Relationship between laboratory tests and field performance

Laboratory Test Results

Prediction of Grouted Macadam Field Performance

Conclusions

Content

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 3

Introduction

Semi-flexible material comprising an open graded asphalt skeleton with 25 to 30% air voids into which a cementitious grout is poured

What is a grouted Macadam?

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 4

High resistance to rutting;

High resistance to oil and fuel spillage;

High stiffness modulus and strength;

Main properties:

Like Concrete

Like Asphalt

Current applications:Surface course of heavy duty pavements: bus stops, bus lanes, airport aprons and taxiways, distribution centres and industrial pavements.

Flexibility and absence of joints.

Introduction

Need to assess the suitability of using this material in road pavements

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 5

4 PB Test Apparatus

Manufactured during PhD study at University of NottinghamDimensions of Specimen:

- 50 x 50 x 300 mm3;Distance between supports:

- 90 mm.

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 6

Fatigue line of the studied grouted macadam mixture using 4-point bending tests

4 PB Fatigue Test Results on Grouted Macadams

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 7

A major difficulty with fatigue testing is developing a meaningful relationshipbetween the results of laboratory tests and field performance

Factors with influence on the relationship:

Definition of correction factors (known as shift factors) to estimate the field performance from lab results

Different authors have suggested very different values, ranging from 2 to 440, depending on the type of test, mode of loading, testing temperature and type of mixture

Relationship between Laboratory Tests and Field Performance

Mode of loading;Rest periods healing effects;Lateral distribution of loads;Temperature variations.

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 8

A laboratory testing programme was established, focussed mainly on the effect of rest periods on the fatigue life of the standard grouted macadam mixture

Due to limitations of the equipment in controlling the actuator with an intermittent loading pattern (rest periods between loading cycles), the maximum frequency that could be used was 5 Hz

Laboratory Testing Programme

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 9

N1 N3 N4 N5

Influence of rest periods duration on grouted macadam fatigue life

Laboratory Test Results

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 10

N2

Influence of rest periods on the fatigue life of grouted macadams

Laboratory Test Results

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 11

Mode of loading No. of cycles

Shift factor

Continuous fatigue (1) 17739 1.0

1000 cycles + equiv. rest period (2) 40980 2.3

2 cycles + 1 rest period (3) 50823 2.9

1 cycle + 1 rest period (4) 140050 7.9

1 cycle + 2 rest periods (5) 734395 41.4

Shift factor obtained for each fatigue line

9718.39107.2 −− ⋅×= tN ε16.41010169.4 −− ⋅×= tN ε

N = Number of equivalent standard axle loads (ESALs)εt = Tensile strain induced at either surface or underside of bound layers.

Grouted Macadam

Asphalt (traditionally used in the UK)

Shift factor of 45

considering thelateral loaddistribution

Prediction of Grouted Macadam Field Performance

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 12

Fatigue criteria for design of grouted macadams and traditional asphalt layers

Prediction of Grouted Macadam Field Performance

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 13

Conclusions

a shift factor of 45 was determined for grouted macadam mixtures, which should be multiplied by the fatigue life obtained in the laboratory, in order to predict the actual pavement fatigue life more realistically;

the shift factor suggested is still considered a conservative value, since it does not include results from tests with very long rest periods between each load application;

a fatigue criterion was proposed for pavement design when using grouted macadams, which was based on the shift factor determined by using rest periods on four-point bending fatigue tests.

The effect of using rest periods in 4PB testson the fatigue life of grouted macadams

Transport Infrastructures Research GroupDepartment of Civil EngineeringUniversity of Minho - Portugal

2nd Workshop on 4PB – Four Point Bending 14

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