Two-Step Mixing Process Elaboration of the Hot-Mix Asphalt Mixture Based on Surface Energy Theory

AbstractHot-mix asphalt (HMA) is a multicomponent mixture composed of asphalt, coarse and fine aggregates, fillers, and other necessary additives. The bitumen–aggregate adhesion and performance of HMA are mainly dependent on such factors as mixing temperature and time, raw material characteristics, and mixing sequence of raw materials. The latter factor is the least reported in the literature. In recent years, surface energy theory has significantly been employed as the method for the prediction of bitumen–aggregate adhesion and mixture performance. This paper provides the optimization of the HMA mixing process based on the surface energy theory. A quantitative index called the total adhesion work is proposed from the perspective of energy change, which can be used to determine the two-step adding proportion of fine aggregate. Assuming that asphalt is in the hot-melt state rather than solid-state during the actual mixing process, a method for testing the surface energy components of hot-melt asphalt is proposed. Based on the total adhesion work, several different mixing processes are used to produce HMA, and the optimal one was identified experimentally. It is shown that the asphalt mixture performance can be improved by optimizing the adding sequence and proportion of the fine aggregate. The enhancement of HMA high-temperature performance and water stability is the most pronounced when the total adhesion work ratio of the two-step addition procedure approaches unity.