Effect of High Temperatures on the Mechanical Performance of Geopolymer Concrete Incorporating Treated and Untreated Recycled Concrete Aggregates

Abstract

Geopolymer concrete is a sustainable substitute for Portland cement, which can resolve the environmental issues caused by Portland cement. The study aimed to investigate the use of natural aggregates (NA) or recycled coarse aggregates (RCA) in geopolymer system which is seen as greener material. In their study, the authors utilize Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBS), which are industrial waste materials, activated by sodium hydroxide and sodium silicate solution. The research contrasted three different mixes. The mixes that are evaluated are reference R-GNA made with natural aggregate, GTRA geopolymer with treated recycled aggregates, and GUTRA geopolymer with untreated recycled aggregates. One of the focuses of this work is the improvement of RCA quality through a coating process with sodium metasilicate to seal surface pores and micro-fissures. To investigate the thermal stability of these mixtures, they were subjected to a temperature of 700°C for two hours. The Scanning Electron Microscopy (SEM) was used to characterize the microstructural changes and efficiency of the aggregate treatment. The experiment results show that the untreated RCA has high porosity which leads to increased moisture leakage and thereby decreased durability in comparison to natural aggregates. The use of sodium metasilicate enhanced the mechanical performance of recycled aggregate mixtures significantly. Examination of fire injured concrete showed that the treated RCA concrete with TRCA presented with less micro-cracking and gel degradation than untreated RCA concrete which exhibited severe matrix damage. The use of treated recycled aggregates in geopolymer concrete can optimize the compressive strength as well as residual properties after exposure to heat. Thus, it supports sustainable building solutions.