Physico-mechanical properties and micromorphology of AAS mortars containing copper slag as fine aggregate at elevated temperature

Copper slag (CS) is an industrial by-product, which is commonly disposed in engineered landfills. Prior studies have successfully incorporated CS as an aggregate phase in cementitious materials. However, the alkali-activated material (AAM) incorporating CS has been scarcely studied. Specifically, the elevated temperature behavior of AAM with CS has not been investigated previously. The present paper aims to study the effects of elevated temperature treatment on the mass loss and residual strength of alkali-activated slag mortars incorporating 0-100% (by volume) of CS with an incremental step of 20% instead of natural sand. The mass loss, compressive and flexural strengths, and microstructure of the mixes before and after exposure to temperatures of 25, 200, 400, 600, and 800 degrees C were evaluated and compared. Results showed that the optimum performance of the mortar at elevated temperatures is achieved by incorporating 20% CS. It led to 24% higher mechanical strength at 800 degrees C than the reference mix. However, mixes with CS content beyond 60% showed inferior mechanical strength at elevated temperatures in comparison to the control mortar. The optimum mortar exhibited improvement in microstructure's density and less micro-cracking based on the results of scanning electron microscopy (SEM) analysis. Finally, the mortar mixes made with CS as fine aggregate were also established to be environmental-friendly and cost-efficient.