Production of mortar with calcined alum sludge as partial cement replacement

Alum sludge is a largely generated and disposed waste from water treatment plants. This study aimed to produce mortar using alum sludge calcined at different temperatures (600 – 900 ºC). After the optimal calcination temperature was selected, the calcined alum sludge was used to replace 5, 10, and 15 % of cement by mass in mortar. The performance of the mortars was evaluated based on the workability, compressive strength, flexural strength, porosity, and percentage of water absorption. Mortars with alum sludge calcined at 800 ºC had the highest strength as compared to the other temperatures. The mechanical strength of mortars reduced while the porosity and percentage of water absorbed increased with increasing calcined alum sludge content. Although replacing 5 % of cement with calcined alum sludge would reduce the mechanical strengths by 13 – 15 %, it was still acceptable as it had negligible influence on the porosity and water absorption value of the mortar. In short, the partial substitution of cement with calcined alum sludge should be limited within 5 % to maintain the performance of the mortar.