A comprehensive model for predicting thermal cracking events in asphalt pavements

Abstract

A compressive model for predicting thermal cracking events in asphalt pavements that accounts for the continuous evolution of the asphalt mixture properties with oxidative ageing over time has been developed. The model also considers temperature-dependent coefficient of thermal contraction (CTC) for the calculation of thermal strain in the asphalt layer. An improved pavement temperature profile estimate has been employed in the model to predict the required hourly pavement temperature data. The temperature data at the desired depth in the asphalt layer are then used in a kinetic-based ageing model to predict growth in the carbonyl (CA) of the asphalt binder over time. Using a refined one-dimensional constitutive linear viscoelastic relationship, the hourly thermal stress is then computed considering the changes in the viscoelastic and thermal contraction properties of the asphalt mixture with the increase in CA of asphalt binder used in the mix. The required age-dependent relaxation modulus is obtained from the dynamic modulus (E^*) of asphalt mixtures (i.e. in complex domain) at various ageing levels. Also, the required age and temperature-dependent CTC is obtained from thermal strain measurements of varied aged asphalt mixtures using the uniaxial thermal stress and strain test (UTSST). The cracking events are detected over the service life by comparing the predicted thermal stress with the age-dependent crack initiation stress (CIS) of the asphalt mixture. The age-dependent CIS is obtained from the UTSST results for different ageing periods. Preliminary analysis of the model revealed the accuracy of the model in a realistic prediction of the accumulative thermal cracking events for the asphalt pavement with different air void levels (4, 7 and 11%) and with unmodified (PG64-22) and polymer-modified (PG64-28) asphalt binders in a selected location.

Keywords:

• Thermal cracking
• oxidative ageing
• carbonyl
• relaxation modulus
• thermal contraction
• crack initiation stress

Acknowledgements

The content of this article is part of the overall effort in the Asphalt Research Consortium (ARC). However, the contents of this report reflect the views of the authors and do not necessarily reflect the official views and policies of the FHWA. The authors gratefully acknowledge the FHWA support.

Notes

¹ E_a: Activation energy, A: Pre-exponential factor.

² HS: Hardening susceptibility, m: hardening function constant.

³ Williams–Landel–Ferry.

⁴ The ageing durations at each temperature for pan-aged binders were as follows: 60, 120, 180 and 240 days at 50 °C; 30, 60, 100 and 160 days at 60 °C; 8, 15, 25 and 40 at 85 °C; and 2, 4, 6 and 10 days at 100 °C.