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Cover of Fatigue Performance Evaluation and Design of Thin Asphalt Surfaced Granular Pavement
Fatigue Performance Evaluation and Design of Thin Asphalt Surfaced Granular Pavement
  • Publication no: AP-T390-26
  • ISBN: 978-1-923617-21-6
  • Published: 9 January 2026

The purpose of this report to improve the design guidelines of thin asphalt-surfaced unbound granular pavements with respect to their susceptibility to asphalt fatigue distress.

The methodology included accelerated pavement testing in the early stage, complemented by a survival analysis of asphalt cracking data. Finally, the reliability level used in the design to predict allowable loading using the Austroads mechanistic empirical procedure was assessed against the field performance-derived reliability.

Asphalt pavement cracking data obtained from the Queensland Department of Transport and Main Roads road network was analysed to evaluate the relative performance of thin asphalt surfacing and assess the reliability of the asphalt in-service performance relationship. In-service performance ratios from PMB asphalt mixes were determined. The observed asphalt fatigue performance exceeded design predictions. This result supports an increase in the shift factor (SF) for the allowable loading calculation of thin asphalt surfacing (thickness ≤ 50 mm) unbound granular pavements in warm climates (WMAPT ≥ 30 ºC).

In addition, this report proposes a mechanistic-empirical framework to evaluate curvature limits at the project level, thereby mitigating the risk of premature fatigue in the asphalt layer.

Watch a recording of the webinar to learn more.

  • Summary
  • 1. Introduction
    • 1.1 Purpose
    • 1.2 Scope
    • 1.3 Methodology
    • 1.4 Structure of the report
  • 2. Literature and Practice Review
    • 2.1 General
    • 2.2 Background information
      • 2.2.1 Austroads structural design method
      • 2.2.2 Understanding performance of thin asphalt surfacing
    • 2.3 Road agency practice
      • 2.3.1 TMR
      • 2.3.2 MRWA
      • 2.3.3 TfNSW
      • 2.3.4 Waka Kotahi NZTA
      • 2.3.5 Department of Transport and Planning
      • 2.3.6 Pavement construction practice summary
    • 2.4 Performance of thin asphalt surfacing in-service
      • 2.4.1 Department of Transport and Planning research
      • 2.4.2 MRWA pavement performance monitoring
      • 2.4.3 TMR pavement performance monitoring
      • 2.4.4 Performance of thin asphalt surfacing in New Zealand
    • 2.5 Thin asphalt surfacing performance under accelerated loading
      • 2.5.1 Previous ALF trials in Australia
      • 2.5.2 Other Accelerated Pavement Testing of thin asphalt surfacings
      • 2.5.3 Summary
    • 2.6 Reliability of thin asphalt surfacing
    • 2.7 Considering asphalt thickness in the in-service performance relationship
      • 2.7.1 Introduction
      • 2.7.2 Change in mode of loading with pavement thickness and mode factor
      • 2.7.3 South African mechanistic-empirical design method
      • 2.7.4 The AASHTO mechanistic-empirical pavement design approach
  • 3. Summary of the Project Accelerated Pavement Testing Trial
    • 3.1 Introduction
    • 3.2 Test sections and testing program
      • 3.2.1 Experimental test sections
      • 3.2.2 Accelerated pavement testing program
    • 3.3 Summary of the test pavement performance results
      • 3.3.1 Dry testing phase
      • 3.3.2 Wet testing phase
      • 3.3.3 Deflection conditions of the dry and wet testing phase
    • 3.4 Conclusion
  • 4. Relative Cracking Performance of Surfacing Types
    • 4.1 Background
    • 4.2 Field performance data analysed
      • 4.2.1 Data description
      • 4.2.2 Cumulative loading to cracking
    • 4.3 Cracking vs rutting distress mechanism
    • 4.4 Fatigue cracking data analysis methods
      • 4.4.1 General
      • 4.4.2 Cracking performance ratio assessment
      • 4.4.3 Survival probability analysis using the Kaplan-Meier method
      • 4.4.4 Cox proportional hazards regression
      • 4.4.5 Maximum likelihood method using the Weibull distribution
    • 4.5 Survival probability results and discussion
      • 4.5.1 Kaplan-Meier survival probability
      • 4.5.2 Performance ratio based on Cox regression
      • 4.5.3 Performance ratio based on the maximum likelihood method
    • 4.6 Summary
  • 5. Allowable Traffic Loadings Predictions
    • 5.1 Introduction
    • 5.2 Preliminary: Effect of surfacing types on allowable loading
    • 5.3 Allowable loading calculation assumptions
      • 5.3.1 Pavement configuration
      • 5.3.2 Asphalt design moduli
      • 5.3.3 Estimated subgrade design CBR
      • 5.3.4 Traffic load distribution
    • 5.4 Predicted allowable loading
      • 5.4.1 Allowable loading for 50% reliability
      • 5.4.2 Allowable loading for varying reliability levels
      • 5.4.3 Influence of the maximum modulus of granular materials
  • 6. In-service Asphalt Fatigue Relationship and Shift Factor Evaluation
    • 6.1 Introduction
    • 6.2 Reliability-based assessment
    • 6.3 Reliability assessment using the direct counting method
      • 6.3.1 General
      • 6.3.2 Observed reliability for DGA-C320 road sections
      • 6.3.3 Increasing the shift factor to align observed and predicted reliabilities
      • 6.3.4 Reliability assessment for DGA-A15E and SMA-A15E
    • 6.4 Reliability assessment using the survival probability distribution method
      • 6.4.1 Introduction
      • 6.4.2 Method to calculate the distribution of normalised fatigue lives
      • 6.4.3 Shift factor calibration
      • 6.4.4 Proposed shift factor for application in design
    • 6.5 Summary
  • 7. Framework to Assess Minimum Support Conditions for Thin Asphalt Surfaced Granular Pavements
    • 7.1 Introduction
    • 7.2 Variability of specification with pavement structure and climate
      • 7.2.1 Introduction
      • 7.2.2 Thin asphalt on granular pavement parametric study
      • 7.2.3 Relationship between asphalt strain and FWD deflections
      • 7.2.4 Variation of required curvatures with granular and subgrade support
      • 7.2.5 Required curvature with design loading and asphalt design modulus
    • 7.3 Framework to derive road agency specified curvatures for construction specifications
  • 8. Conclusions and Recommendations
    • 8.1 Conclusions
    • 8.2 Recommendations
  • References
  • Appendix A TMR Performance Data Analysis Information and Assumptions
    • A.1 Locations and environmental conditions
    • A.2 Traffic load distribution
    • A.3 Estimated subgrade design CBR
  • Appendix B Performance Ratios of PMB Mixes Based on the Austroads In-service Asphalt Performance Relationship
    • B.1 Introduction
    • B.2 Predicted performance ratio parametric study
  • Appendix C Reliability Assessment with Presumptive CBR values
    • C.1 Introduction
    • C.2 Influence of presumptive subgrade CBR
      • C.2.1 Predicted vs observed loading to cracking of the cracked sections
      • C.2.2 Observed vs predicted reliability comparison – DGA-C320
  • Appendix D Detailed Data for the Reliability Assessment
    • D.1 Observed reliability assessment data
      • D.1.1 DGA-C320 material
      • D.1.2 DGA-A15E material
  • Appendix E Analysis Restricted to Cracked Road Sections
    • E.1 Introduction
    • E.2 Predicted allowable loading vs observed loading to cracking
  • Appendix F Distribution of Normalised Fatigue Lives Compared to AGPT02 Reliability Factor Distribution
  • Appendix G Shift Factor Evaluation Additional Data
    • G.1 Weibull distribution derived optimum shift factors
  • Appendix H Proposed Text for AGPT02
    • H.1 Introduction
    • H.2 Proposed text
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