Investigation of In-Place asphalt film thickness and performance of hot-mix asphalt mixtures

This research work investigates approaches for computing the average asphalt film thickness in asphalt mixtures and examines whether the in-place asphalt film thickness has a rational relationship with the performance of hot-mix asphalt mixtures. Two methods for calculating the aggregate surface areas, the surface area factor and index methods, are discussed in this research and the analytical results show that both the fine aggregate particles and aggregate shapes significantly affect the calculation and should be taken into consideration to obtain greater accuracy for the surface area. A computation method is proposed and significantly improves the current conventional method for the asphalt film thickness calculation by incorporating shape factors and flat surface factors for all sieve sizes. Field performance data from MnROAD and rutting data from laboratory fabricated mixtures, including both coarse and fine gradations, were analyzed to investigate the asphalt film thickness and corresponding performance of asphalt mixtures. Both the field data and laboratory experimental results show that the asphalt film thickness is a significant factor affecting the rutting performance for asphalt mixtures. However, more research work is needed to investigate the relationship between the asphalt film thickness and the other performance parameters of asphalt mixtures, such as fatigue cracking, before a film thickness specification can be proposed.