Calcium formate as a modifier agent for fly ash-based geopolymer cement

Calcium formate (CF) is a calcium-based compound often used in Portland cement (PC) systems as an accelerating agent. Class F fly ash (FA), frequently used as a geopolymer precursor, is deficient in calcium. This can slow down the polymerization process and alter the properties of the obtained product. To address this issue, the possible advantages of using CF to increase calcium content in FA geopolymer cement were explored. FA geopolymer was supplemented with varying amounts of CF, from 2 to 10 wt.%. To understand the influence of CF on certain properties of FA geopolymer specimens treated in air and those treated in water, a series of experiments was conducted. Sophisticated analytical techniques were employed to extract deeper insights from the outcomes. The findings showed that adding CF decreased both flowability and setting time. Adding between 2 and 8 wt.% CF improved compressive strength, decreased strength deterioration caused by water curing, increased water resistance (softening coefficient), and decreased transport properties, while adding 10 wt.% CF had adverse consequences. The formation of efflorescence can be inhibited by adding 2-8 wt.% CF. The ideal ratio of CF was 6 wt.%. Adding an appropriate amount of CF can facilitate the formation of C-S-H gel and microstructural densification.