The Effect of Sewage Sludge Ash on Properties of Cement Composites

Abstract

The results of research on sewage sludge ash (SSA) and fly ash (FA) and the effect of these ashes on properties of fresh pastes and hardened mortars have been presented. The chemical composition, specific surface area and grading of SSA were determined. By means of XRD analysis, the occurrence of crystalline materials was detected and by means of SEM the morphology of ashes was investigated. By means of Vicat's softening point the initial and final times of setting were defined. The replacement of cement with 10 or 20% SSA resulted in setting times extension. The chemical composition may suggest that setting times extension was caused by the occurrence of phosphorus in SSA. The standard compressive strength of 10% and 20% SSA mortars were lower. The partial replacement of cements with SSA ash makes the kinetics of strength development slow down. However, the long-term increase in compressive strength of mortar was higher compared to OPC mortar. It means that it was partially similar to the influence of the fly ash.