Effect of Aging on Dynamic Modulus and Fatigue Life of Superpave Mixes

Abstract

In the Mechanistic–Empirical Pavement Design Guide (MEPDG), prediction of flexible pavement response and performance needs an input of dynamic modulus of hot-mix asphalt (HMA) at all three levels of hierarchical inputs. This study investigated the effect of aging on the dynamic modulus and fatigue life of Superpave mixes. Five newly built Superpave pavements for local calibration of MEPDG by the Kansas Department of Transportation (KDOT) were selected as test sections in this study. Volumetric properties of the mixes have been obtained from the mix design database of KDOT. Asphalt concrete (AC) cores were obtained at 30.5 m interval over a 305 m section from all calibration sites and tested in the laboratory for dynamic Moduli. Dynamic modulus was predicted with the Witczak equation. The results show that there is an increase in predicted modulus with an increase in age and frequency of loading. The difference between predicted modulus initially and after 5 years is greater than the difference between the predicted moduli after 5 and 10 years. This shows that the aging process slows down with time. The rate of increase in predicted modulus over the years is higher at 21 o C than at 35 o C. Increase in dynamic modulus with aging results in decrease in tensile strain, but the rate of increase in the predicted number of load repetitions is greater than the allowable number of load repetitions. As a result, fatigue life decreases with time. Laboratory dynamic modulus was comparable for all US routes at 4°C. The variation increased as the test temperature increased. Witczak equation underestimated the dynamic modulus at low temperature and overestimated at high temperature when compared with the laboratory modulus.