The role of chemistry and fineness of metakaolin on the fresh properties and heat resistance of blended fly ash-based geopolymer

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Abstract Sensible thermal energy storage using concrete as a storage medium is a promising technology that helps minimize energy in power plant. The purpose of this study is to evaluate the potential benefits of metakaolin (MK) as a partial substitute for fly ash-based geopolymer for heat resistance. As a partial substitute (5 and 20 wt.%) for fly ash (FA), nine metakaolins containing different alumina contents were selected. In order to assess their potential for storing high-temperature thermal energy, physical and microstructural analyses were performed before and after heat exposure up to 500 °C. Low packing density limits the workability of some metakaolins and increases water demand in pastes. The mechanical properties of geopolymer weaken as the temperature is raised (< 500 °C). The high alumina content of some metakaolins, however, helps to mitigate strength loss during high temperatures. A higher dosage of metakaolin has also shown to prevent this deterioration of strength. A reduction in strength under heating is caused by both dehydration and dehydroxylation. The higher fineness and alumina content of MK have demonstrated significant potential to enhance the heat resistance of FA-based geopolymers. As a result, the geopolymer paste developed is suitable for being used in heat-resistant applications. Article Highlights Fly ash was the main precursor of as prepared alkali-activated binders. Adding metakaolin enhances the resistance of hardened materials under thermal load. The higher the alumina content inside metakaolin is, the higher the performance is.

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