Laboratory-Measured Dynamic Modulus and Predicted Performance of Asphalt Mixtures

Abstract

The dynamic modulus testing of asphalt mixtures is typically conducted by using a specimen 100 mm in diameter and 150 mm tall loaded along its primary axis (axial mode). This specimen orientation can present problems when as-built pavement layers, which are seldom constructed in 150-mm lifts, are evaluated. For this issue to be addressed, dynamic modulus testing in the indirect tension (IDT) loading mode was proposed. The objective of this study was to evaluate the influence of loading mode (axial versus IDT) on the measured dynamic modulus and the effects of the measured difference on pavement performance prediction. For the achievement of these objectives, Superpave® mixtures were collected from Florida, Iowa, Louisiana, Michigan, Minnesota, South Dakota, Virginia, and Wisconsin and were evaluated for the effects of loading mode. Results of the experimental program showed that statistical differences exist between IDT and uniaxial dynamic modulus values measured at different temperatures and frequencies. When the precision of the dynamic modulus test was considered, differences attributable to the loading mode (IDT versus axial) were observed for measurements conducted at all temperatures, with the dynamic moduli measured in the axial loading mode being stiffer than the dynamic moduli measured in the IDT loading mode. Results also showed that performance prediction was significantly affected by the loading mode. Predicted rutting and fatigue cracking in the asphalt layer were the most influenced distresses. Correlation factors were developed to correlate one set of dynamic moduli to the moduli measured in a different loading mode.