Discussion: Three Stages of Permanent Deformation Curve and Rutting Model

Abstract

This paper first discussed the three-stage permanent deformation property of asphalt mixes. Corresponding to the primary, secondary and tertiary stages, there were three physical damage processes: strain hardening, microcracking initiation and propagation, and macrocracking initiation and propagation. After the primary stage, the increased rutting is caused by microcracking and macrocracking initiation and propagation. Rut depths measured in more than 50 pavement structures under accelerated pavement test (APT) were limited to the primary stage, even though the accumulated rut depths of asphalt layer were deeper than 20 mm in some APT sections. Therefore, from the viewpoint of rutting itself, it is, in general, unnecessary to expand the rutting model to characterize the secondary and tertiary stages. In addition, the results of APTs also indicated that the rutting development followed the power law model. Thus, of the existing rutting models, the well-known power law model is commended to predict the rut depth of asphalt concrete, although none of the existing rutting models can characterize the secondary and tertiary stages. It also was discovered that the power law slope, b, is a function of temperature. With increasing temperature, the b value increases. The calculated b value is in the range of 0.16–0.5 based on the results of 41 APT sections.

Keywords:

• Permanent deformation
• Tertiary stage
• Power law model
• APT

Acknowledgements

The authors thank Prof. Robert L. Lytton of Texas A&M University for reviewing the paper and for his valuable comments.