Estimating Tensile and Compressive Moduli of Asphalt Mixture from Indirect Tensile and Four-Point Bending Tests

An asphalt mixture has different tensile properties as compared with compressive ones due to the combined effect of aggregate interlock, binder stiffness, and aggregate-binder interactions. This study aims to investigate the dynamic tensile and compressive moduli of asphalt mixture through indirect tensile and four-point bending modulus tests. Firstly, methods for determining the tensile moduli of the mixtures in the preceding two tests are developed based on the bimodular theory. Then, the compressive and tensile moduli of one asphalt mixture are determined using the developed methods. It was found that the compressive moduli of the asphalt mixture exceed the tensile ones over the entire frequency domain in both types of test. In general, tensile moduli obtained from indirect tensile and four-point bending tests are in good agreement, especially at the intermediate- to high-frequency domain. The ratios between the compressive moduli and tensile moduli obtained from the two tests are also similar, regardless of test temperature and air-void content. The ratios are about 2.5 at low and intermediate temperatures and increase to approximately 4.0 at high temperatures. The conventional solution for the indirect tensile test based on a single-modulus assumption mainly reflects the compressive properties of the mixture but provides an unrealistic estimation for its Poisson’s ratio. Conversely, in the four-point bending test, the solution based on a single modulus well represents both the tensile and compressive properties of the mixture.