This study investigates the chemical, physical, and mechanical properties of gasifier slag produced through the coal gasification process. The study focuses on the use of gasifier slag as a full or partial replacement for crushed fine aggregate and/or sand in hot-mix asphalt concrete. Performance of these newly developed slag-asphalt (Slagphalt) mixtures is evaluated in comparison with Control mixes, i.e., conventional mixes without slag. The low cost of slag makes it a viable alternative as a substitute for natural sand. The angularity and relatively narrow particle size distribution of the slag will be attractive in some regions.