New Insight into the Role of Alkaline Activator in the Hydration of Supersulfated Cement and the Regulation Effect of Calcium Formate

Abstract

Supersulfated cement (SSC) is a low-carbon cement, but it’s sensitive to alkaline activator dosages inability to achieve high early and late strengths simultaneously. In this study, characterization methods such as hydration heat, phase composition and hydration degree of slag (DoS) from the hydration interactions of aluminum and silicon phases were used to reveal mechanism of this sensitivity and the regulation effect of calcium formate (CF). Results showed that the higher the OPC (ordinary Portland cement) dosage (1 wt.%, 3 wt.% and 5 wt.%), the faster the hydration rate in early stage (1d), the more AFt and C-(A)-S-H gel, and higher early strengths, but lower DoS in late stage (28d), fewer products, and lower strengths. Based on the negative relationship between 1d gel content and 28d strength, it's proposed that early rapid formation of gel covering slag leads to the main reason for slow growth of late strength of SSC with high OPC dosage. CF can increase AFt and gel content, and simultaneously enhance early and late strengths of SSC at each OPC dosages by promoting gel forming in interstitial space of slag. In this paper, a new mechanism is proposed for the role of alkaline activator dosages in strength development of SSC, the over-rapid formation of gel is main reason for poor late hydration hardening performance with excessive alkaline activator, and inducing the precipitation of gel in interstitial space of slag is an effective way of enhancing early and late strengths like the role of CF in this paper.

Keywords: Supersulfated cement, alkaline activator, Calcium formate, Mechanical properties, hydration