Calcium formate as a modifier agent for calcium hydroxide-activated slag cement

Abstract Calcium hydroxide (Ca(OH) 2 , or CH) presents a sustainable, cost-effective, and safer alkaline activator for slag compared to traditional activators like NaOH and sodium silicate. However, its application is constrained by the lower mechanical strength of the resulting binder. To address this, calcium formate (CF) was introduced for the first time at varying levels (2–10 wt%, in 2% increments). The effect of different levels of CF on a wide range of slag-CH cement properties was thoroughly investigated. The study applied powerful analytical tools to elucidate the underlying mechanisms. The findings revealed that CF addition reduced flowability and accelerated setting time. Incorporating 2–8% CF enhanced mechanical strength, mitigated the strength degradation after aging, improved transport properties, and reduced drying shrinkage. The optimal dosage of 6% CF was found to promote C-S–H gel formation and refine the pore structure. Conversely, an excessive dosage of 10% CF was detrimental, causing increased porosity and compromising performance.