Alternation of traditional cement mortars using fly ash-based geopolymer mortars modified by slag

Abstract

The use of local aluminosilicates to serve the local engineering applications could resolve the issue of unpredicted properties of the geopolymer caused by the wide variance in aluminosilicates reactivity. The locally available aluminosilicate byproducts (e.g., fly ash [FA] and granulated ground blast-furnace slag [GGBS]) in Qingdao were used to synthesize geopolymer cement in this study. Six geopolymer cement mortars with different FA/GGBS ratios were compared with ordinary Portland cement (OPC) and magnesium potassium phosphate cement (MKPC) mortars in terms of workability, setting time, strength development, volume stability and chloride permeability. The use of high volume of GGBS equips the geopolymer mortars with fast setting and high early strength despite poor volume stability. Thus, GGBS geopolymer mortars could potentially replace the high-cost MKPC mortar for rapid rehabilitation in construction. The geopolymer cement mortar with a FA/GGBS ratio of 4 behaves similar to OPC mortars in terms of fluidity, setting time, strength development, volume stability and chloride permeability. Therefore, FA-based geopolymer mortar blended with 20% GGBS could be considered as a high-efficiency, low-cost, eco-friendly and sustainable replacement of OPC mortar. Overall, the geopolymer cement properties could be engineered based on the FA/GGBS ratio in order to serve local engineering applications for the maximum utilization in different scenarios.