Rheological Properties of Mineral Filler-Asphalt Mastics and Its Importance to Pavement Performance

Abstract

The rheological and failure properties of eight asphalt-filler mastics were characterized using new testing techniques being developed within the SHRP program for testing asphalt binders. The mastics were prepared using four SHRP core asphalts and two fillers (calcite and quartz). The rheological measurements were used to construct rheological master curves and temperature shift functions. The failure properties were measured at different temperatures and strain rates and were shifted using time-temperature superposition to construct stress and strain-to-failure master curves. A subset of the mastics was also tested after oxidative aging with the pressure aging vessel (PAV) and after isothermal aging at low temperatures. The properties of the mastics were compared with the asphalt binder properties to describe the changes resulting from adding the fillers. The fillers were found to change the shape of the rheological master curves and to significantly increase the failure stress at all combinations of temperatures and loading times. The changes in rheological properties were observed only in the time dependency while the temperature shift functions showed only slight changes at the highest temperatures. The relative stiffening effects were observed to be asphalt-specific, especially at the lower frequencies or higher temperatures. Oxidative aging was shown to change the rheological type of the mastics, to be asphalt-specific, and to be independent of filler type. Physical hardening was observed to result in shifting the master rheological curves to longer loading times without affecting the shape of the master curves. The anticipated influence of mastic properties on the main distress types of asphalt pavements was considered. The influence of fillers on low-temperature cracking was hypothesized to be independent of filler type. Therefore, it is expected that the asphalt binder will control the cracking mechanism. Based on the energy concept, the addition of the filler is expected to improve resistance to stress-controlled fatigue while for strain-controlled fatigue the improvement, if any, is expected to be minimal. Fillers are expected to significantly improve rutting resistance as a result of increasing moduli (viscous component). Effect on rutting is expected to be asphalt-filler-specific.