Measuring physico-chemical interaction in mastics using glass transition

The current design standard for asphalt mixtures provides guidance on selection of aggregates, asphalt binder and includes requirements for the amount of mineral filler to be included. The amount of filler that can be included is limited to a ratio in the range of 0.6-1.2 by mass of the binder. However, this range is based on experience rather than on scientific evaluation of the interaction between filler and binder. Although many researchers acknowledge the physico-chemical interaction between asphalt binder and the mineral filler, currently a procedure to quantify this interaction, and consider it in selecting favorable filler to binder ratio, is not available. In this paper, the effect of fillers on the glass transition temperature (T-g) of the base binder was used to evaluate the physico-chemical interaction in mastics. The total reinforcement of the filler, which is measured in terms of relative viscosity of the filled binder to the unfilled binder, consists of two parts: mechanical and physico-chemical. The mechanical reinforcement part is calculated based on micromechanical models commonly used in the literature that take into account volume filling effects and particle-to-particle interactions. Physico-chemical reinforcement is estimated based on the change in the T-g in both Williams-Landel-Ferry (WLF) and Arrhenius time-temperature shift models. The concept introduced in this study is evaluated by viscosity and dilatometric T-g testing of three binders mixed with three different fillers, at different concentrations. Results show that the physico-chemical interaction between the mineral filler and the binder can be accurately estimated from the difference in the glass transition temperature of the mastics and the binder.