Influence of alum sludge ash and ground granulated blast furnace slag on properties of cement mortar

This study aims to investigate the effects of partially carbonized alum sludge ash (ASA) which had been treated at the temperature of 200–300 °C and Ground Granulated Blast Furnace Slag (GGBFS) as supplementary cementitious materials on fresh and hardened properties of cement mortar. In this study, 10 mixtures with maximum replacement levels of ordinary Portland cement (OPC) with ASA and GGBFS up to 6.0 wt% respectively. The setting time and flow table tests were performed on fresh concrete, while the hardened properties (density, compressive strength, flexural strength, water absorption coefficient, porosity and water absorption) were investigated on two concrete curing ages (i.e., after 7 days and 28 days). The results showed that, the mechanical strengths, workability, and density of mortar tended to decrease as the replacement level of OPC with the ASA increase, while the setting time increase with the increase of ASA content. In addition, the ASA and GGBFS enhanced the water absorption coefficient and water absorption properties of concrete at all ages. The highest compressive strength a mortar can be produced from this study after being cured for 28 days is 20.6 MPa 2.0 wt% of ASA and 4.0 wt% of GGBFS were used to partially replace OPC to produce the mortar which had workability of 156 mm. Overall, incorporation of ASA as a partial replacement of cement in mortar production can partly reduce the volume of alum sludge in landfill.