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 30-60 mu m 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. (C) 2016 American Society of Civil Engineers.