Ceramics-Silikáty 68, (2) 216 - 224 (2024)

Lower early strength has been one of the bottlenecks of low-carbon supersulfated cement (SSC), consisting of slag (∼85 wt.%), gypsum (∼10 wt.%), and a small amount of an alkali activator (Portland cement (PC), ∼5 wt.%). The work aims at improving the early strength of SSC with the addition of calcium formate (CF). Different dosages (1 wt.%, 2 wt.%, 3 wt.%) of CF were added to the SSC. Then, compressive strength, heat flow, hydration product assemblage, and hydration degree of slag were obtained to reveal the role of CF. The results show that CF would significantly increase the compressive strength of the SSC, and the higher the dosage of CF, the more pronounced the effect is. 3 wt.% of CF would increase the 3-day and 28-day compressive strength of the SSC by 126% and 172%, respectively. CF would accelerate the hydration of slag, increase the hydration degree of slag and production of C-(A)-S-H gels; however, it would inhibit the rapid production of AFt during the first 3 days, and have little influence on the final production of AFt. In addition, the lower the crystal-gel ratio (the ratio between AFt and C-(A)-S-H gel by mass) is, the higher the compressive strength. The enhancement effect of CF was attributed to a more appropriate hydration environment (higher Ca²⁺ concentration and lower pH value), which could promote the precipitation of C-(A)-S-H gels, inhibit the rapid formation of Aft, and reduce the crystal-gel ratio of the system.