Durability assessment of fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates against acid and sulfate attack

Abstract

There is a constant drive to develop high-performance concrete with enhanced mechanical and durability characteristics while incorporating environment-friendly materials. The study investigates the synergistic effects of fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) on the durability characteristics of 100 % recycled aggregate (RA) based geopolymer concrete (GPC) against acid and sulfate attacks. Moreover, its relative performance compared to control samples of ordinary Portland cement (OPC) concrete with natural and recycled aggregates was also assessed. The acid and sulfate resistance were determined by submerging the concrete specimens in the 5 % sulphuric acid (H2SO4), 5 % sodium sulfate (Na2SO4), and 5 % magnesium sulfate (MgSO4) for up to 180 days of exposure duration. The specimens' resistance to chemical attack was assessed by visual observation, changes in weight, and the percentage of compressive strength loss at different time intervals. In addition, the changes in the mineralogical and microstructures of the GPC matrix were also examined using X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) tests. Results indicated that an increased proportion of GGBS and SF positively influenced the durability of GPC, as revealed by reduced mass loss and compressive strength degradation. In addition, the microstructural, mineralogical, and morphological properties depicted enhanced densification and compactness of the GPC matrix due to the formation of CSH, CASH, and NASH gels. GPC-MG15 (FA:GGBS:SF – 35:50:15) yielded the highest strength and durability performance, compensating for the trade-offs of using 100 % RAs in conventional OPC concrete. So, optimized use of these sustainable materials has depicted promising results in aggressive environments while reducing the need for conventional OPC and natural aggregates.