Development of high strength one-part geopolymer mortar using sodium metasilicate

Abstract

In this study, the solid activator – the synthetic sodium metasilicate pentahydrate – was compared against water and a hybrid sodium silicate and sodium hydroxide activator solution. It was found that the solid activator outperformed the liquid activator as a part of water remained chemically bound to the undissolved particles, thus reducing the apparent water to binder ratio. Contrary to the liquid activator, the increase in activator content past a certain limit did not correspond to improvement in strength. Instead, the compressive strength reduced and the risk of efflorescence increased significantly. Scanning electron microscopy (SEM) analysis showed that the denser reaction products took up less volume and formed a shell as the remaining metasilicate particles gradually dissolved under moisture ingression. This would eventually develop into a void, and cause strength- and durability-related issues. Additionally, fly ash content, microsilica addition, particle size of the activator, binder content, water to binder content and curing condition also played an important role in the hardening and pore refinement of the mixes. The one-part synthesis method could improve the safety and efficiency in geopolymer production.