Nanoindentation Characterization of Asphalt Concrete Aging

Asphalt concrete (AC) consists of coarse aggregate, asphalt binder, and fines. The asphalt binder creates an asphalt film around the coarse aggregate and fines. Fines are trapped inside the binder film, which is also known as mastic. Mastic and aggregate govern most of the mechanical properties of AC. Therefore, researchers have performed various tests on mastic to understand macroscale behavior of AC. Nanomechanical characterization is more appropriate for mastic, as the thinness of mastic is approximately 15–20 μm around an aggregate particle. For this paper, the authors conducted nanoindentation tests on mastic and aggregate as integral parts of AC. In particular, they compared the modulus and hardness of oven-aged mastic and aggregate with those of unaged mastic and aggregate. To deal with the heterogeneity of the mastic part, they made hundreds of indents on the mastic part of each AC sample. On the aggregate part, they made 60 indents to determine the mechanical properties of the aggregate of each AC sample. Nanomechanical characterization of the mastic phase of AC showed an excellent agreement with age-hardening behavior of aged AC. The aggregate mechanical property showed insensitivity to long-term oven aging of AC.