Carbonation curing for recycling and property enhancement of copper slag-based blended mortar

Abstract

This study explores a potential pathway to utilize CO₂ and copper slag (CS) to reduce CO₂ emissions and to enhance the mechanical properties of ordinary Portland cement (OPC)-CS-based cementitious materials. Early age carbonation curing was applied to cure the blended mixtures with varying carbonation durations. The results indicate an improvement in mechanical properties particularly in the early stages. The ultrasonic pulse velocity (UPV) method has proven effective in detecting the subtle changes in microstructure resulting from variations of mixture design and carbonation curing. XRD, TGA, FTIR and SEM were conducted to characterize the influence of carbonation curing on mechanical properties, microstructural development, and their interrelationship. The CS acts as an inert filler in the cement matrix and increases the available surface area and space for the nucleation and formation of carbonation products, in turn leading to a higher CO₂ uptake compared to the OPC reference. Both amorphous and crystalline carbonates contributed to microstructure densification. Moreover, a prolonged carbonation duration modified the silicate structure within C-S-H gel without further reducing the amount of C-S-H, and it did not negatively impact the mechanical properties. Cost and CO₂ emission analyses confirm that adopting CS replacement and carbonation curing can reduce carbon footprint. Besides, the incorporation of CS can reduce the operational cost of carbonation curing, potentially bringing expenses down to levels comparable with those of normal curing.