This study investigates the feasibility of using phosphorus furnace slag as a partial replacement for sand in concrete. Characterization of the chemical and physical properties of the slag showed that air-cooled phosphorus slag, with flat and angular particles, specific gravity of 1360-1440 kg/m3, and low water absorption (1-1.5%), has high abrasion resistance and durability against freeze-thaw cycles and mechanical damage, making it suitable for partial replacement of sand. Compressive strength tests of concrete with 20% sand aggregate replacement showed that the strength decreased by 9.5% at 7 days and only 1.8% at 28 days, indicating that the initial negative effects due to changes in particle arrangement and increase in effective surface area are compensated during continued hydration. The partial pozzolanic activity and filling effect of fine particles also contribute to the densification of the microstructure. Slump tests showed that the slump of concrete increased from 40 mm to 45 mm with the replacement of 20% sand aggregate, indicating improved flowability of fresh concrete due to the presence of finer particles, smoother surfaces, and reduced internal friction. Overall, replacing about 20% of the sand aggregate with phosphorus furnace slag is technically feasible, environmentally and economically beneficial, and does not significantly reduce the mechanical or flow performance of the concrete, making it suitable for many structural applications.