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

• Published in: Construction & building materials 2018-01, Vol.160, p.487-496
• Main Authors: Stewart, Calvin M., Oputa, Chinedu W., Garcia, Eduardo
• Format: Article
• Language: English
• Subjects: 3D scanning; Analysis; Asphalt; Coefficient of variation; Concrete cracking; Disk-shaped compact tension; Elastic-plastic fracture mechanics; Fracture energy; Fracture toughness; Hot mix asphalt; Linear elastic fracture mechanics; Mechanical properties; Plane-stain; Plane-stress
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2017.11.041

•The plane-strain condition does not exist in 50 mm thick DCT specimen.•Linear elastic fracture mechanics theory can be used to optimize layer thicknesses.•Fracture surfaces do not distinguish between the plane-stress and strain conditions. 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.