Use of alkali-silica reactive sedimentary rock powder as a resource to produce high strength geopolymer binder

This paper reports on an innovative way to utilize alkali-silica reactive (ASR) rocks as a natural resource to produce high strength geopolymer binder. Excavation of the Jurong rock caverns in Singapore has produced large quantities of sedimentary rocks. These rocks, however, cannot be used for ordinary Portland cement concrete production due to their ASR reactivity. An alternative way to beneficially utilize these rocks is to produce geopolymer binder. The excavated rocks were classified based on petrography into four types and then converted to powder form in a sequence of steps. The rock powders were used to synthesize geopolymers by replacing metakaolin in different replacement ratios. Results showed that geopolymer binder with 67 wt% rock powder and only 33 wt% metakaolin can achieve a high compressive strength of 80 MPa. Incorporation of sedimentary rock powder enhanced the compressive strengths by 15–30% as compared to pure metakaolin geopolymers. Microstructure analysis revealed that the enhancement in compressive strengths were primarily due to the densification of binder by filling the voids in matrix with rock powders.