Suitability of metakaolin-based geopolymers for underwater applications

The development and use of geopolymers (GPs) considerably increased in the construction industry. This paper assesses the suitability of metakaolin-based GP mortar and concrete mixtures for underwater applications, including the performance comparison to cementitious (CEM)-based materials. Results showed that the flow times and rheological properties of GP mixtures are significantly higher (i.e., about 2 to 5.5-times) than CEM-based ones. This was mostly related to the high viscosity of the alkaline activator that promotes hydrogen bonding and entanglements between interstitial solution and solid particles. The GP mixtures showed no signs of bleeding and remarkably lower levels of washout loss, reflecting excellent stability as well as superior resistance to dilution, erosion, and washout phenomena upon underwater placement. Their residual compressive, flexural, and pull-off bond strengths varied from 65 to 95% (as opposed to 25–70% for CEM-based materials), revealing the suitability of metakaolin-based GPs for underwater placement.