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

Transcription

1 SUSTAINABILITY INNOVATION University of Minho Transport Infrastructures Research Group Guimarães Portugal on the fatigue life of grouted macadams Joel Oliveira, Jorge Pais, Nick Thom, Salah Zoorob 1

2 Content 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 2

3 Introduction What is a grouted Macadam? Semi-flexible material comprising an open graded asphalt skeleton with 25 to 30% air voids into which a cementitious grout is poured 3

4 Introduction Main properties: High resistance to rutting; High resistance to oil and fuel spillage; High stiffness modulus and strength; Flexibility and absence of joints. 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. Need to assess the suitability of using this material in road pavements 4

5 4 PB Test Apparatus Manufactured during PhD study at University of Nottingham Dimensions of Specimen: - 50 x 50 x 300 mm 3 ; Distance between supports: - 90 mm. 5

6 4 PB Fatigue Test Results on Grouted Macadams Fatigue line of the studied grouted macadam mixture using 4-point bending tests 6

7 Relationship between Laboratory Tests and Field Performance A major difficulty with fatigue testing is developing a meaningful relationship between the results of laboratory tests and field performance Factors with influence on the relationship: Mode of loading; Rest periods healing effects; Lateral distribution of loads; Temperature variations. 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 7

8 Laboratory Testing Programme 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 8

9 Laboratory Test Results Influence of rest periods duration on grouted macadam fatigue life N1 N3 N4 N5 9

10 Laboratory Test Results Influence of rest periods N2 10

11 Prediction of Grouted Macadam Field Performance Shift factor obtained for each fatigue line Mode of loading No. of cycles Shift factor Continuous fatigue (1) cycles + equiv. rest period (2) cycles + 1 rest period (3) cycle + 1 rest period (4) cycle + 2 rest periods (5) Shift factor of 45 considering the lateral load distribution N N = εt = εt Grouted Macadam Asphalt (traditionally used in the UK) N = Number of equivalent standard axle loads (ESALs) ε t = Tensile strain induced at either surface or underside of bound layers. 11

12 Prediction of Grouted Macadam Field Performance Fatigue criteria for design of grouted macadams and traditional asphalt layers 12

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. 13

14 Thank You for Your Attention 14