Mechanical and physical properties of portland composite cement concrete with basic oxygen furnace slag aggregates for heat reducing rigid pavements

This study investigates basic oxygen furnace (BOF) steel slag aggregates in Portland Composite Cement (PCC) concrete for rigid pavement with a target flexural strength of 4.5 MPa. BOFS replaced fine and coarse aggregates at 0%, 25%, 50%, 75%, and 100% by volume. Tests included material characterization, compressive and flexural strength, thermal conductivity, heating–cooling performance, and skid resistance. Compressive strength showed a non-monotonic response of 34.58–37.27 MPa, peaking at 50% BOFS, while all mixtures exceeded the target flexural strength, reaching 5.11 MPa at 100% BOFS. Thermal conductivity increased by 28.2%, reaching 1.510 W/m·K at 100% BOFS. During heating, BOFS mixtures reduced peak surface temperature by up to 4.3 °C, indicating lower daytime heat accumulation and potential for urban heat island (UHI) mitigation. The maximum vertical temperature gradient decreased from 17.8 °C in the control to 9.5 °C at 75% BOFS, indicating more uniform through-depth temperature distribution and potentially lower temperature-induced stresses. During cooling, surface temperature remained up to 0.7 °C higher than the control, indicating a daytime-nighttime thermal trade-off. Skid resistance decreased from 94.7 BPN for the control to 63.7 BPN at 100% BOFS on the smooth, untreated surface, highlighting the importance of surface texture. Overall, BOFS in PCC concrete can reduce natural aggregate consumption while maintaining the required flexural performance and improving thermal behaviour relevant to heat-reducing rigid pavements and UHI mitigation. BOFS content should therefore balance mechanical, thermal, and skid-resistance performance.