Design and Analysis System for Thermal Cracking in Asphalt Concrete

Abstract

A reliability based mix design and analysis system for thermal cracking in asphalt concrete pavements is described and demonstrated in this paper. Asphalt-aggregate mixture performance in terms of low temperature cracking and thermal fatigue is assessed independently for each type of cracking in the specified environment. Reliability factors are introduced into this assessment to account for the level of risk assumed by the engineer and the inherent variability in the estimates of mixture resistance to induced thermal stresses and the environmental demand in terms of conditions promoting either type of thermal cracking. Mixture resistance is measured in two laboratory tests, and environmental demand is estimated from predicted surface pavement temperatures. The paper concludes with an example of the analysis described, comparing unmodified and crumb-rubber modified mixture performance at different levels of reliability in a high elevation desert climate. The system presented is recommended as a mix design and analysis tool for evaluating unmodified and modified asphalt-aggregate mixture performance in harsh climates where thermal cracking is of concern.