Effects of Filler⁻Bitumen Ratio and Mineral Filler Characteristics on the Low-Temperature Performance of Bitumen Mastics

This study analyzed the effects of the filler⁻bitumen interaction of the content and the meso powder characteristics of the mineral filler on the low-temperature performance of bitumen mastics. Control strategies for the mineral filler content (filler⁻bitumen ratio (R_FB)) were also determined. Panjin #90 bitumen and styrene⁻butadiene⁻styrene polymer-modified bitumen were used in the experiment. Four kinds of limestone powder were used, all of which satisfy the Chinese standard for powder particle size but exhibit different meso characteristics. Each kind of limestone powder was used to prepare bitumen mastic samples under five different R_FBs. The meso voids in the unit mass (V_g) of the four kinds of mineral filler were tested on the basis of the principle of the Rigden void ratio. The fixed bitumen⁻free bitumen ratio in the bitumen mastic samples was determined using V_g, bitumen density, and R_FB. The low-temperature cohesive strength of the bitumen mastics was used as the control index for critical failure, whereas variation rates of bending creep stiffness at low temperature were used as the control index for fatigue failure. Results showed that the effects of the filler⁻bitumen interaction of the content and the meso characteristics of the mineral filler are significant and such effects are determined by the fixed bitumen⁻free bitumen ratio. The optimal fixed bitumen⁻free bitumen ratio in the bitumen mastics under two low-temperature conditions (−30 °C and −10 °C) can be determined on the basis of the influence of the fixed bitumen⁻free bitumen ratio on the critical and the failure control indices. Moreover, R_FB can be obtained through reverse calculation. The mineral filler content can therefore be precisely controlled, which is crucial for the rational use of mineral filler and for the improvement of the pavement performance of bitumen mastics at low temperatures.