Nanoindentation investigation of asphalt binder and mastic cohesion

A nanoindentation technique for determining the cohesive properties of neat, modified, and aged asphalt binders and mastics with varying filler volumetric concentrations is developed, tested, and verified. Cohesive properties of binder and mastic are critically important to the fracture resistance of asphalt concrete. A new approach to calculate and interpret important cohesive properties from nanoindentation data through low-load sphero-conical (blunt) nanoindentation is presented. Work of effective cohesion values are determined as the average response over multiple possible microstructures for three asphalt binders and 30 different mastics of varying filler volumetric concentrations. Results point to evidence of a critical filler volume fraction beyond which further addition of filler does not affect work of effective cohesion. This plateau in work of effective cohesion values is speculated to be related to the combined effects of volume-filling, particle interactions, and physicochemical interactions. The critical filler volumetric concentrations corresponding to the plateau in work of effective cohesion range between 0.20 and 0.30, which is within the range from literature of 0.15–0.30. Testing of binder and mastic through nanoindentation is an important step toward in situ testing of mastic within asphalt concrete, which is inaccessible using conventional macroscopic experimental methods.