Time-Temperature and Time-Aggregate Gradation Superposition in Asphalt Mixes

Abstract

ABSTRACT This study was devoted to evaluate the effect of aggregate gradation, temperature, and type of asphalt cement on the permanent deformation of Hot-Mix Asphalt (HMA). An experimental program was conducted to characterize the viscoelastic deformation response of asphalt mixture using the static creep test. The specimen was exposed to a constant vertical stress of 100 KPa and the vertical deformation of the specimen was monitored through linear variable differential transducers (LVDTs). All tests were conducted within a temperature-controlled chamber to keep the temperature constant throughout the test. Time-temperature and time-aggregate gradation shift factors for each evaluated type of HMA were estimated using plots of log time versus log creep compliance. If the deformations under reference temperature or reference gradation are known, those under given temperature or any given gradation can be obtained using shift factor. Also, viscoelastic models were developed to represent the deformation behavior of HMA under constant stress. The collected data was analyzed to study the effects of aggregate gradation, testing temperature, and asphalt consistency on creep behavior. The effect of temperature variation on creep behavior was found to be more significant at low temperatures and long loading time than those at high temperatures and short loading time. Moreover, aggregate gradation found to has a significant effect on creep behavior, the lowest creep deformation was for HMA prepared using ASTM upper limit gradation. While HMA prepared using ASTM mid-limits aggregate gradation was the least affected by temperature variation.