Feasibility study of MK-based geopolymer binder for RAC applications: Effects of silica fume and added CaO on compressive strength of mortar samples

The results of a preliminary case study of the effects of silica fume and additional calcium oxide (CaO) on the compressive strength of a metakaolin-based geopolymer binder developed to exhibit appropriate properties for use in recycled aggregate concrete (RAC) are presented. Using recycled aggregates in new concrete has significant environmental benefits but also presents significant challenges to the applicability of the technology, and using geopolymer binders in place of ordinary Portland cement (OPC) has the potential to solve some of these challenges. The study presented in this paper suggests that partial replacement of metakaolin with silica fume results in increased strength while additional CaO may only have limited effectiveness in certain applications. Additionally, it was observed that the activator-to-binder ratio has a much more significant effect on the strength than the water-to-binder ratio. It is concluded that, with some optimization, a geopolymer binder with appropriate strength can be developed for use in RAC applications.