Water-quenching blast furnace slag as a by-product of the iron production has caused serious environmental concerns. This paper tried to investigate the feasibility of the blast furnace slag filler (WBFSF) used as an alternative filler to replace the limestone filler (LF) in asphalt mixtures. Specifically, the chemical compositions, morphology characteristics, phase distributions, and thermal properties of two fillers were studied; then rheological properties of asphalt mastics in four filler–asphalt ratios were further studied by the rotational viscosity, temperature sweep, temperature–frequency–sweep (T-f-sweep), and multiple stress creep recovery (MSCR) test. The results show that WBFSF has a larger specific surface area and better-developed mesopores compared with LF. WBFSF asphalt mastic presents a larger complex modulus and a smaller phase angle. Moreover, the MSCR results show that WBFSF improves the elastic recovery and rutting resistance of asphalt mastics. Therefore, WBFSF presents great potential to be used as an alternative filler in asphalt mixtures.
