Determining effects of moisture in mastic materials using nanoindentation

Asphalt concrete consists of coarse aggregates coated with asphalt binder, matrix, which is a mixture of binder and fine aggregates, and mastic, which is a mixture of asphalt binder and fines passing number 200 sieve (0.075 mm). In this study, nanoindentation tests were conducted on dry and wet mastic materials to determine the contact creep compliance, which is used to examine the effects of moisture in the mastic materials. Indentation creep data were fitted using viscoelastic mechanical models. Results show that the dry mastic materials exhibits viscoelastic behavior, while the wet mastic materials shows less viscoelastic behavior compared to the dry mastic materials. Moisture reduces retardation time significantly in the wet mastic materials. The dry mastic materials follow the linear Burgers viscoelastic model and the wet mastic materials follow the Maxwell viscoelastic model. Stiffness measured on the surface of the wet mastic materials is higher than that of the dry mastic materials. Due to moisture conditioning, mastic sample surface might have eroded that makes it less viscous or become exposed to mastic aggregate, and therefore exhibits high stiffness. Indentation results reveal that the wet mastic is softer below a certain depth from the surface. This study projects that the indenter needs to penetrate more than 4000 nm to reach softer wet mastic materials. Also indentation creep holding time needs be more than 1200 s to reach that target depth in wet mastic materials.