Optimization of Hot-Mix Asphalt Surface Course Mix Design for Fatigue Resistance: High-Friction Aggregate and PG Plus

The sensitivity of the fatigue resistance of surface hot-mix asphalt (HMA) mixes is evaluated for three primary design variables. Aggregate type, binder type, and binder content as well as their interaction have been quantified with respect to their effects on HMA fatigue life, rutting resistance, and stiffness. The objective was to optimize the design by extending fatigue performance while reducing the confounded negative effect on rutting resistance. Two aggregate types were used in the evaluation. Two binders of the performance grading (PG) 64-28 were also employed: a modified binder that meets national specifications and an unmodified binder at two binder levels (optimum and optimum plus 0.5%). Aggregate texture was compared visually using high-resolution scanning electron microscopy (SEM) images. The results showed that the value of modifying the binder to produce softer mixes can be compromised when a high-friction aggregate is used due to the irregular shape of the texture, which produces stiffer mixes. A slight adjustment to the amount of binder (+0.5%) can decrease this effect. Superior HMA fatigue performance was exhibited by the regular 12.5 aggregate and the modified binder at the optimum binder content plus the additional 0.5%. This conclusion was reached through the integration of the positive effects of the investigated variables, which revealed only an insignificant reversible impact on rutting resistance. The findings of this study can therefore be considered a guide for designing HMA with superior fatigue performance for use in pavement design.