Effect of low VMA in hot mix asphalt on load-related cracking resistance

Voids in mineral aggregate (VMA) is an important parameter in hot mix asphalt (HMA) mix design. It is believed that a minimum VMA requirement is necessary to ensure adequate binder content and durability for HMA. This paper investigates the effect of lower than typically acceptable VMA on the load-related cracking resistance of four dense-graded asphalt mixes. The mixes were prepared with three aggregate types: limestone, sandstone, and granite. Three different approaches were used to evaluate the cracking resistance of the mixes: the dissipated creep strain energy (DCSE), the fatigue parameter (|E∗|sin φ), and the mechanistic-empirical pavement design guide (M-E PDG) cracking models. The indirect resilient modulus (Mr), indirect tensile strength (ITS), and dynamic modulus (E∗) tests were performed on the mixes. Finite element analysis was used together with the M-E PDG cracking models to predict the expected longitudinal and alligator cracking performance of the mixes when used in a typical pavement structure. Both DCSE and (|E∗| sin φ) results showed that lower VMA decreases the cracking resistance of the mixes. DCSE parameter decreased by 50%, while |E∗| sin φ increased by 12%, for a 3.8% reduction in VMA. The analysis results of M-E PDG cracking models were consistent with the experimental findings. The predicted longitudinal cracking increased by 73%, while the alligator cracking increased by 24% for the same reduction in VMA.