Effect of specimen thickness on the fracture resistance of hot mix asphalt in the disk-shaped compact tension (DCT) configuration

In this study, the effect of specimen thickness on the fracture resistance of a dense-graded hot mix asphalt (HMA) is investigated. The fracture toughness, Kc and fracture energy, Gf in triplicate DCT specimens with width-to-thickness ratios ranging from 1.46 to 4.4 is measured at 27 °C. The coefficient of variation (COV) of Kc and Gf is calculated to determine reliability as a function of thickness. Photos of cracked specimens and 3D surface scans are employed to study how the crack path and fracture surface changed with thickness. The ASTM specifications and linear-elastic fracture mechanics theory are applied to show that Kc does not reach a plane-strain condition, Kc≠KIc, for the given ratios. The average Kc increases with thickness while the COV is inconsistent with thickness. The average Gf is independent of thickness but the COV decreases with thickness; thus, Gf is thickness-dependent. The crack path and fracture surface cannot be used to identify the plane-stress or plane-strain condition due to large aggregates dominating the fracture process. A method for estimating the specimen thickness required for the plane-strain condition and a method to estimate the thickness at which fracture toughness is maximized is demonstrated.