Influence of Water-Glass as an alkali activator on the microstructure and strength characteristics of Geopolymer Concrete

Abstract

This study investigates the influence of water glass as an alkali activator on the microstructure and strength characteristics of geopolymer concrete (GC). Ground granulated blast furnace slag (GGBS) and fly ash (FA) were used as binders, while water glass served as the alkaline activator. The research aimed to evaluate the physical properties of the materials, determine the mechanical properties of various GC grades (M25, M40, and M70), and analyze the GC microstructure using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). The workability of fresh GC was assessed using the slump test, while compressive strength, split tensile strength, and flexural strength were determined at 7 and 28 days. The results showed that increasing the alkali-to-binder ratio from 0.4 to 0.6 improved the mechanical strength parameters of GC for all mixtures. The highest compressive strengths of 28.3, 51.7, and 72.8 N/mm2 were achieved by M25, M40, and M70 grades, respectively, with an alkali-to-binder ratio of 0.6 at 28 days of ambient curing. Microstructure analysis revealed a strong bond between the GGBS-based GC and the reacted FA at the interface, with the M70 grade exhibiting a denser and less porous structure. XRD analysis identified the crystalline phase of FA-GGBS-based GC, while EDS results showed that increasing Si content in M25, M40, and M70 grades led to higher strength and improved geopolymerization. The findings demonstrate the potential of GC as a sustainable alternative to conventional concrete, with water glass as an effective alkali activator for enhancing its mechanical properties and microstructure.