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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
SUSTAINABILITY
INNOVATION
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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