Studies on the microstructure and durability characteristics of ambient cured FA-GGBS based geopolymer mortar

Abstract

The present study involves evolving a mix proportion for geopolymer mortar cured at ambient temperature, utilizing the by-products of industries like fly ash (FA) and ground granulated blast-furnace slag (GGBS) as the binder. The parameters such as proportions of FA and GGBS, molarity of NaOH solution, Na2SiO3 /NaOH ratio, and alkaline liquid/binder ratio were considered. The consistency, setting time, and compressive strength for different percentages of FA replacement with GGBS were studied. It was observed that the addition of GGBS at 10–30 % is suitable for achieving the compressive strength at ambient temperature curing. Hence to assess the practical application of geopolymer mortar, microstructure studies at curing age of 90 days and durability tests over an exposure period of 180 days were conducted on F70:G30, F80:G20, F90:G10 mortar specimens and compared with ordinary Portland cement (OPC) control mixes. SEM, XRD, and FTIR results revealed the polymerization process in the geopolymer and hydration in OPC. Compared to F80:G20 and F90:G10 specimens, the microstructure of F70:G30 specimens containing a more significant proportion of GGBS showed a denser microstructure due to the increased C-A-S-H gel formation. TGA was used to determine the percentage of weight loss with the increase in temperature at curing age of 90 days. It was found that the extent of decomposition of compounds at high temperatures is lower in geopolymer mortar (F70:G30) than in OPC mortar. In addition, it was found that geopolymer mortar (F70:G30) has better resistance to water absorption, sorptivity, acid attack, sulfate attack, marine water attack, and chloride ion penetration and have equivalent mechanical qualities to the OPC control mix.