Laboratory Evaluation on Recycling Waste Phosphorus Slag as the Mineral Filler in Hot-Mix Asphalt

Laboratory tests were conducted to evaluate the feasibility of recycling phosphorus slag into hot-mix asphalt (HMA) as mineral fillers. The elemental composition of phosphorus slag was analyzed by energy dispersive spectroscopy (EDS). The pH value, gradation, hydrophilic index, heat stability, and other properties related to mineral filler in asphalt mixture were also tested. The viscoelastic property of asphalt mastics containing phosphorus slag filler was tested by dynamic shear rheometer (DSR). Ground phosphorus slag was added into two HMAs including traditional dense grade mixture and gap-graded stone mastic asphalt (SMA). Moisture susceptibility and rutting potential tests were conducted to investigate the effects of phosphorus slag filler on the mixtures. Tests showed the pH of the slag was alkaline. It was also hydrophobic and stable at high temperature. Thus, it can be potentially used as an antistripping additive in asphalt mixture. The viscoelasticity test showed that phosphorus slag filler improved the stiffness of asphalt in the similar way as the traditional agriculture (Ag) lime mineral additive. The mixture performance tests indicated that phosphorus slag filler significantly increases the resistance of HMAs to rutting and moisture damage.