Durability Properties of Ambient Cured Geopolymer Mortar Made from Rice Husk Ash–Based Alkali Activator: A Comparative Study with Conventional Alkali Activator

Abstract

Abstract Geopolymers/alkali-activated materials (AAMs) are widely regarded as ecofriendly and durable alternatives to portland-based cement concrete. However, commercial alkali activators, especially the sodium silicate used to manufacture geopolymers/AAMs, are associated with a significant amount of carbon emission during their production. In this study, the feasibility of using rice husk ash (RHA) as a source for an alternative sustainable alkali activator has been explored at ambient temperature curing, and the durability properties of the geopolymer mortars (GPM) has been investigated. Three different concentrations of sodium hydroxide (SH), i.e., 20, 24, and 27 wt. % solutions, have been taken for the synthesis of RHA alkali activator used in synthesis of GPM, and another GPM with conventional alkali activator has also been synthesized for comparative study. Durability studies such as water absorption, sorptivity, sulfate resistance, and acid resistance were evaluated extensively in terms of change in weight and compressive strength. The experimental results revealed that the GPM made with 24 wt. % SH-RHA–based activator solution (R24) has optimal performance considering all the durability parameters and has a close correlation to the results obtained for the control GPM made with conventional alkali activator (C24). The microstructural studies further revealed that the gel structure of the R24 is compact and homogeneous, similar to that of C24; however, the former has a N-A-S-H–dominated gel matrix and the latter consists of N-(C)-A-S-H–type gels.