Nanomechanical properties of constituent phases in bituminous mixtures

This paper presents a nanomechanical test-analysis method to measure the elastic modulus and hardness of constituent phases of bituminous paving mixtures. Quasi-static nanoindentation tests were conducted on small-volume specimens using a Berkovich nanoindenter tip. The elastic modulus and hardness were analyzed from the responses of the material measured during the unloading segment of the nanoindentation tests using a contact mechanics-based analytical model. The correlation of the scanning probe images and nanoindentation results reveal that the aggregates and matrix have the highest and the lowest stiffness-hardness in the mixture as expected, and a gradual change in the elastic modulus and hardness occurs across the aggregate-matrix interphase with an approximate 30-60μm width. This study clearly demonstrates that a nanoindentation approach can be effectively used to characterize the fundamental properties of different phases and critical locations in heterogeneous mixtures using readily available small-volume specimens. The possibility of obtaining more accurate and statistically reliable material properties can improve the accuracy of materials characterization and performance prediction modeling of mixtures and structures.