Valorization of a region-specific oil shale residue for sustainable high-performance mortars

Driven by the dual challenges of solid waste management and cement industry decarbonization, the sustainable utilization of oil shale residue (OSR) in China remains underexplored due to its regional variations in mineral composition. This study explored the potential of a locally sourced OSR as a supplementary cementitious material (SCM) for low-carbon binder systems. By systematically optimizing the thermal activation temperature (500–850 °C) and replacement levels (10–30%) of calcined oil shale residue (COSR) in Portland cement, this research reveals novel insights into its pozzolanic reactivity, mechanical properties, and environmental benefits. The results demonstrated that thermal activation at 750 °C maximized the pozzolanic reactivity of COSR by significantly increasing the content of reactive tetra-coordinate and penta-coordinate aluminum. Specifically, under these optimized calcination conditions, incorporating COSR at a 20% replacement level yielded the most significant improvement in later-age compressive strength, while viable mechanical performance could still be maintained at a 30% substitution rate. The existence of COSR also refines pore structure and reduces harmful porosity, while significantly lowering carbon emissions without compromising mechanical performance. These findings make a significant contribution to advancing sustainable, high-performance cementitious materials and waste valorization in regions with abundant OSR.