Using Dynamic Modulus Test to Evaluate Moisture Susceptibility of Asphalt Mixtures

Abstract

The stripping in of hot-mix asphalt (HMA) is assessed by AASHTO T283 by means of the indirect tensile strength test. The tensile strength ratio (TSR) is used as the criterion for strength retention after sample conditioning. In recent years, the dynamic modulus ( E*) test, conducted according to AASHTO TP62-03, has gained wider use in the pavement community for two reasons: it is a major input into the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures and is being used as a simple performance test indicator. The objective of this study was to assess whether the E* laboratory test can be used as a replacement test property for indirect tensile strength in AASHTO T283. Because the E* test is nondestructive, unlike the indirect tensile strength test, the advantage would be that the same specimens could be used before and after moisture conditioning. The scope of work in this research included conducting a laboratory testing program on several types of asphalt mixtures by means of both test procedures. All mixtures were obtained from construction projects in the field. A unique aspect of this study was that some of the mixtures failed in the field after stripping. The E* tests were used to determine the percent of retained stiffness, a term referred to as E* stiffness ratio (ESR). Results of both TSR and ESR conducted on the same mixtures were compared and statistically analyzed. The analysis indicated that there was no statistically significant difference between the measured TSR and ESR values for the same mixture. The correlation obtained between the two ratios had good measures of accuracy. It was concluded that the ESR can potentially replace TSR testing to assess field moisture damage for asphalt mixtures. The recommendation was to continue the testing program and expand the database for future analysis.