Effect of GGBS Content and Water/Geopolymer Solid Ratio on the Mechanical, Elevated Temperature Resistance, and Sorptivity Properties of FA/GGBS-Based Geopolymer Concrete

This study investigates the effects of water/geopolymer (W/GP) solid ratio and ground granulated blast furnace slag (GGBS) content on the mechanical, elevated temperature resistance, and sorptivity properties of geopolymer concrete (GPC). In this study, two different W/GP solid ratios were used, 0.33 and 0.35, and GPC was produced by replacing fly ash (FA) with 0%, 50%, and 100% GGBS. As a result of physical, mechanical, and nondestructive tests in this GPC; strength performance and durability performance were investigated by finding slump, setting time, compressive strength, elevated temperature resistance, sorptivity, and dynamic modulus of elasticity (DME) via ultrasonic pulse velocity (UPV), a nondestructive test. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses were performed on GPC samples. As the percentage of GGBS in the mixture increased, the slump of GPC decreased but its cohesion increased. The final setting time of GP mortar containing 100% FA is approximately 80 times that of GP mortar containing 100% GGBS for both W/GP solid ratios. When the GGBS percentage in the mixture increased from 0% to 100%, the compressive strength of GPC increased about 4–5 times depending on the W/GP solid ratio. The increase in the GGBS percentage decreased the sorptivity of the GPC up to 6.5 times. The elevated temperature performance of GPC increased with the increase of the FA ratio. SEM analysis showed that a more homogeneous and denser microstructure was obtained with the increase of GGBS content in the mixture.