Performance evaluation of metakaolin based geopolymer binder in binary blended mixes with different aluminosilicate precursor materials

Abstract Geopolymers offer a sustainable alternative to conventional cement by utilizing industrial waste materials rich in silica and alumina. In geopolymer mortar, these minerals react with alkaline solutions to form alumino-silicate gel, which acts as the primary binding phase. This study investigates the performance of ten metakaolin (MK)-based geopolymer mortar mixes with different combinations of silica fume (SF), ground granulated blast furnace slag (GGBS), and rice husk ash (RHA). The mixes were evaluated for standard consistency, initial and final setting times, and compressive strength after 1 and 3 days of curing under three regimes: steam curing at 75 °C, hot air curing at 100 °C, and hot air curing at 200 °C. The results showed that GGBS-based mixes (M5, M6, and M7) achieved the highest compressive strengths. Specifically, Mix M7 (25% MK + 75% GGBS) recorded a maximum 3-day strength of 22.32 MPa under 100 °C curing, a 213.5% increase compared to the control mix (M1). SF-based mixes (M3, M4) showed delayed setting and lower strength, with M4 reaching only 4.95 MPa at 3 days. RHA-based mixes showed moderate improvements; for instance, M8 exhibited a 6.53 MPa strength at 3 days, an 8% decrease compared to M1. Across all mixes, hot air curing at 100 °C consistently produced better strength development, demonstrating its effectiveness in enhancing the geopolymerization process. Scanning Electron Microscopy (SEM) revealed a denser matrix in GGBS-rich mixes with compact C–A–S–H gel formation. In contrast, SF mixes showed unreacted particles and microcracks, indicating incomplete geopolymerization. This study emphasizes the significance of binder composition and optimized curing regimes in tailoring the properties of MK-based geopolymer mortars for enhanced performance in construction applications.