Postprocessing Method for Dynamic Modulus Tests of Hot-Mix Asphalt

Abstract

The main objectives of this study are: (1) to develop a postprocessing method for analyzing the dynamic modulus test of compacted asphalt mixtures; (2) to identify optimum regression equations for the compressive stress and its corresponding strains in a dynamic modulus test using this method; and (3) to evaluate the accuracy of the proposed method compared with the method in the current equipment specification. Including the procedure used in the current equipment specifications, two procedures for fitting the dynamic stresses and three procedures for fitting the corresponding strains were employed in the postprocessing method. The coefficients of the regression equations in the five procedures were used to determine the dynamic modulus and phase angle. Uniaxial compressive dynamic modulus tests of 10 asphalt mixtures were conducted at five temperatures and six frequencies with Universal Test Machine (UTM). A total of 1,800 test results were processed with the procedures in the proposed method. On basis of the standard errors of the least square fit, the procedures in the postprocessing method were evaluated. It was found that the procedure in the equipment specification was inaccurate to fit the strains, especially at the higher temperatures and low frequencies. Therefore, correction coefficients were recommended for the measured dynamic modulus and phase angle from the currently used UTM. The potential application of the proposed method is significant since it will improve the degree of accuracy of the dynamic modulus values used in the mechanistic-empirical pavement design procedure.