Crack initiation and development in AC layers

An investigation of sub-surface cracks was carried out on Asphaltic Concrete (AC) samples extracted from pavements of various ages, using the Scanning Electron Microscope (SEM). SEM images, of the AC fabric, at 150 times magnification, revealed that the greater majority of nano- and micro-cracks occur along the grain boundary regions between the mineral aggregate and bituminous binder as well as in the binder itself. Analysis of the data obtained from these examinations suggests that these fractures propagate throughout the AC fabric in accordance to linear functions. Also, the composite structure of AC fabric contains many imperfections within its matrix and also within each individual material used in the mix. These flaws support crack growth and further contribute to the deterioration of the fabric and pavement structure. The theory relating to crack initiation in AC layers is addressed in this paper.