Microstructural investigation of asphalt concrete for performing multiscale experimental studies

In this paper, a microstructural hypothesis for asphalt concrete (AC) is developed in order to provide a basis for a multiscale experimental investigation. The hypothesis is consistent with the belief that AC can be considered as a four-scale assemblage of components with different characteristic length scale, binder, mastic, fine aggregate matrix (FAM) and finally AC. The hypothesis is supported with a series of direct microstructural experiments including morphological observations with digital and scanning electron microscopy as well as quantitative evaluation using a novel meso-gravimetric test method developed specifically for this research. Morphological evaluation shows that asphalt mastic effectively exists as a basic building block for AC. Meso-gravimetric analysis finds that the volumetric composition of this mastic is equal to that found when assuming that mastic contains all of the effective asphalt binder and the filler-sized particles. Other key volumetric properties including FAM gradation and mastic concentration within the FAM and mixture are presented as well.