Evaluating Effect of GGBFS in Alkali–Silica Reaction in Geopolymer Mortar with Accelerated Mortar Bar Test

This paper presents the effect of ground granulated blast-furnace slag (GGBFS) content on the alkali–silica reaction (ASR) in geopolymer mortar using the accelerated mortar bar test and scanning electron microscope (SEM) analysis. Three geopolymer mixtures with different fly ash/GGBFS weight ratios (9, 4, and 1) along with one ordinary portland cement (OPC) mixture were considered in this study. Other parameters of the geopolymer mixtures were kept constant. Mortar bar prisms were prepared in accordance with accelerated mortar bar test standards for expansion measurements, and SEM analysis was performed after 21 and 150 days of immersion in 1 M NaOH solution at 80°C. In addition, compressive strengths of mortar cubes were measured up to 29 days. Silica dissolution of the reactive aggregate used in mortar was determined by immersing it in NaOH solutions with different pH values. This study’s results suggest that the ASR in geopolymer is lower than that of OPC and that expansions due to ASR in geopolymer mortar increase with the increase in the GGBFS content in the mix design. Finally, this paper also emphasizes that the standard accelerated mortar bar test needs to be modified before endorsing it for geopolymer mortar.