Effects of multiple precursors on strength, durability, and microstructural properties of ambiently cured geopolymer concrete

Due to increased global warming, the need to find an alternative to conventional cement concrete has increased in the construction industry as cement is known to consume natural resources and lead to higher carbon emissions for its production. This research paper examines the technical feasibility of using silica fume as an admixture to develop the M30, M50 and M70 grade geopolymer (GP) concrete by varying the proportions of industrial wastes such as fly ash (FA) and ground granulated blast furnace slag (GGBS), lowering the concentration of the alkali activator solution and including silica fume (SF) in the fly ash (FA) admixture. Based on their mechanical behaviour, the mix design was optimized for M30, M50 and M70 grade GP concretes. The results demonstrated that the maximum compressive strength (CS) of fly ash and GGBS based GPC at the age of 28 days varies from 38.64 to 57.24 MPa, whereas those of silica fume blended GPC achieved up to 78.57 MPa, was achieved at 70:30 FA:GGBS composition, when the concentration of alkali activator added is 3.5 M and liquid by powder (L/P) ratio is 0.6 for M30 grade GP concrete; at 70:30 FA:GGBS composition, when the concentration of alkali activator added is 5 M and L/P ratio is 0.47 for M50 grade GP concrete; and at 65:30:5 FA:GGBS:SF composition, when the concentration of alkali activator is 5 M and L/P ratio is 0.49 for M70 grade concrete. Using a scanning electron microscope (SEM-EDAX) and X-ray diffraction analysis (XRD), the microstructure of the modified mixtures was analysed and correlated with mechanical properties. Our analysis revealed that the addition of SF enhanced gel formation by increasing the reactivity towards alkali and filling the pores that ultimately resulted in enhanced strength characteristics, which was also confirmed through SEM. It can be concluded from the results that the addition of SF admixture for the strength improvement of GP concrete is technically viable.