Design Process of Asphalt Mixture Incorporating Compaction-Effort Variable

The Superpave mix design is a process of repeatedly optimizing the aggregate gradation and asphalt content in accordance with specified limits. As one of the important design parameters, the number of design gyrations ($N_{\mathrm{des}}$) is adopted empirically to be a fixed number under a specific traffic level. Based on the concept of a performance-oriented approach, this study regarded $N_{\mathrm{des}}$ as a variable design parameter and evaluated the influences of two design cases on the performance of asphalt mixture: $N_{\mathrm{des}}$ variables and asphalt content (gradation unchanged) and $N_{\mathrm{des}}$ variables and aggregate gradation (asphalt content unchanged). Two groups of experiments were designed. The first group used $N_{\mathrm{des}}$ levels of 50, 75, and 100 gyrations, and less asphalt content was adopted with a higher $N_{\mathrm{des}}$. The second group used compaction levels of 50, 75, 100, and 125 gyrations, and coarser aggregate gradation was adopted with a higher $N_{\mathrm{des}}$. Both groups of experiments showed that with an increase in $N_{\mathrm{des}}$, rutting performance was increased and low-temperature performance was decreased. In addition, in the former group of experiments, fatigue performance was decreased with the increase of $N_{\mathrm{des}}$. Following these rules, this paper took Hainan province mix design as a case, and $N_{\mathrm{des}}$ was optimized to meet requirements. It can be seen that regarding $N_{\mathrm{des}}$ as design variable is necessary and can improve flexibility in the design.