Sorted municipal solid waste ash as cement substitute: A study on paper ash and food waste ash

This study explores the feasibility of using sorted municipal solid waste, namely waste-derived paper ash (PA) and food waste ash (FWA) as partial cement substitute (0–15%) in both paste and mortar. Although the introduction of PA and FWA into the mortar mix leads to a slight expansion of the blended cement paste, it is still compliant with the requirement of EN 197-1. Notably, PA has a significant impact on both the initial and final setting times of the cement paste, attributed to its high CaO content. On the other hand, FWA demonstrates better promise in term of strength consideration, with a lower extent of 7.2% reduction compared to the control group at a 5% cement substitution level. Besides that, the chloride content of the blended cement paste, with up to 15% PA and FWA substitution, still adheres to the 0.1% limit outlined in EN 196-2. In terms of environmental considerations, the raw materials of PA and FWA exceed the hazardous waste thresholds for certain elements (As, Zn, Pb, Cr, Cu and Sb) as per UNE EN 12457-4 standards. However, when blended into cement mortar at a 15% substitution level, these heavy metals exhibit significantly reduced concentrations, meeting the criteria for non-hazardous and even inert waste. In overall, this study suggests that utilizing sorted PA and FWA as cement substitute can offer a sustainable option. Despite observed reductions in compressive strength, these materials hold potential advantages in terms of environmental impact mitigation and waste management.