Conversion of local industrial wastes into greener cement through geopolymer technology: A case study of high-magnesium nickel slag

Geopolymer technology has shown the values of converting industrial waste streams into green cements. This 'low temperature' manufacturing technology opens a window to make clink-free concrete. This paper reports the case of using fly ash and a local high-magnesium nickel slag (HMNS) as solid materials to manufacture geopolymer cement under the room temperature conditions. The results show that by using optimal quantities of alkali activator and HMNS, the compressive strengths of resulting geopolymer cements can achieve 60 MPa, which are comparable to hardened Portland cements and adequate for construction purposes. The analysis of carbon emissions and embodied energy indicates that manufacturing 1 t of geopolymer cement paste requires 1.11-1.34 GJ and emits 0.19-0.24 t CO2 at a transportation distance of 50-300 km for solid materials. There is a reduction about 60% in both embodied energy and CO2 emissions compared to manufacturing the same quantity of Portland cement paste. The use of ground HMNS to substitute for fly ash can solve the problem of potential environmental risk of this industrial waste while only increase the environmental footprint of geopolymer cements slightly. The proposed model in this study can be an effective and green process for the management and valuable utilization of local solid industrial wastes with proper compositions and reactivity.