A mixture design approach for mitigating cracking issue of asphalt concrete pavement

Abstract

The traditional Superpave mixture (SP4) is designed at 4.0% air voids while the mixture is compacted at 7%-8% air voids in the field with the belief that the pavement will achieve its ultimate density after several years. Several studies have reported that the maximum density that a pavement can achieve is about 94%. This higher air voids provide an easy pathway for air into the pavement, which eventually accelerates the aging process and results in premature cracking of the pavement. To this end, this study provides an enhanced mixture design approach in which mixture will be designed at 5% air voids (SP5) and compacted at the same air voids in the field so that the higher in-place density will enhance the fracture strength of the mixture and minimize the aging process. First, the traditional SP4 mixture design has been completed using two different aggregates and binders. Then, the SP5 mixture design is accomplished by reducing the design number of gyrations from 100 to 55 and adjusting the aggregate gradation while keeping the effective binder content the same as SP4. The laboratory Hamburg Wheel Tracking Device (HWTD) and Semi-Circular Bending (SCB) tests have been conducted to evaluate the rutting and fracture properties of the SP4 and SP5 mixtures. In addition, Thermal Stress Restrained Specimen Test (TSRST) has also been conducted to observe the low-temperature cracking performance of the SP4 and SP5 mixtures. The HWTD test results reveal that the SP5 mixture has equal or better rutting resistance properties than the SP4. Based on the fracture energy obtained from SCB test data, the SP5 mixtures exhibit better-cracking resistance than that of SP4 mixtures, which implies that the SP5 mixture will delay in crack initiation and propagation. The TSRST test results show that the SP5 mixture has improved low-temperature cracking property compared to the SP4 mixture. Therefore, the SP5 mixture design procedure will mitigate the cracking issue of asphalt concrete pavement.