Time-Dependent Permanent Deformation Models for Asphaltic Mixtures

Abstract

Over the past two decades, a variety of permanent deformation models have been developed to predict rutting in asphalt pavements. Because all of these models are normally based upon laboratory tests in which very short loading and rest times are used, they may not reflect the true actual loading and rest times that may occur in the field service condition. To overcome this limitation, a research study was funded by the Maryland State Highway Administration at the University of Maryland to develop a universal permanent deformation model that could account for both loading and rest times upon its cyclic load behavior. A laboratory testing program was conducted using the cyclic creep test on a single asphalt mixture. The variables considered in the testing program were loading and rest times, both at three levels, and temperature and stress, each at two levels. Two replicate tests per cell were also used, resulting in a total of 72 test specimens being evaluated. Based on the lab test results, two types of empirical permanent deformation models have been calibrated. It was found that the empirical model coefficients, intercept and slope, and permanent deformation parameters, μ and α, were affected by both loading and rest times. Predictive equations were developed for the intercept, slope, μ, and α. The empirical permanent deformation models developed account for both loading and rest times at multiple temperature and stress levels.