The influence of calcium hydroxide on the performance of MK-based geopolymer

Abstract

Zeolite Socony Mobile-5 (ZSM-5) micropores are blocked after repeated use; therefore, their performance is compromised, forming ZSM-5 waste. This work synthesized a new type of multiscale pore structured geopolymer that could be exploited as a zeolite material precursor. The raw materials were metakaolin, calcium hydroxide, and ZSM-5 waste. The action of ZSM-5 waste is synergistic foaming with hydrogen peroxide and as an extra source of silicon in geopolymer generation. The final geopolymer samples were analysed via mechanical performance tests, thermogravimetry, X-ray diffraction, FT-IR spectral analysis, scanning electron microscopy and mercury intrusion methods. The influence of adding calcium hydroxide on the properties of the products was investigated. Metakaolin was replaced by 0, 10, 20 and 30 g of calcium hydroxide. The geopolymer specimens with added calcium hydroxide showed a more compact structure, a higher bulk density and an enhanced compressive strength performance. Moreover, the incorporation of calcium hydroxide increases the geopolymer paste viscosity and limits the foaming action of ZSM-5 waste and hydrogen peroxide, which makes the geopolymer product structure denser. The gel product was significantly associated with the added calcium hydroxide, and the amount of gel product, mainly hydrated calcium aluminosilicate gels (C-(A)-S-H), increased with the incorporation of calcium hydroxide. In general, calcium hydroxide accelerates the geopolymerization process and has a positive impact on the performance of geopolymer products. This study described the influence of calcium hydroxide on multiscale pore structure metakaolin-based geopolymers, and the results can be considered as a reference for the application of multiscale pore structure geopolymers with calcium hydroxide.