Influence of C₃S/C₂S ratio of Portland cement on the performance of super sulfated cement

Super sulfated cement (SSC), consisting of 1 wt%–5 wt% activator (usually Portland cement), 10 wt%–30 wt% sulfate, and 65 wt%–85 wt% ground granulated blast furnace slag (GGBS), is a low-carbon cementitious material. The activator plays a critical role in the mechanical properties of SSC, and the most commonly used activator, commercial ordinary Portland cement (OPC), usually gives a lower early strength on the premise of higher long-term strength, thus limiting its large-scale application. To obtain the most suitable Portland cement activator for SSC, this paper synthesized three kinds of Portland cement (C₃S/C₂S: 2.75, 0.5, 0.25). The mechanical properties and hydration products of SSC with different dosages of the synthesized Portland cement (0 wt%, 0.5 wt%, 1.1 wt%, 1.8 wt% and 2.5 wt%) were obtained. The results show that it seems to be the C₃S content of the Portland cement that determines the 3-day compressive strength of SSC, and the sample with the optimal C₃S content (0.45 wt%) has the highest hydration degree of GGBS and the most ettringite (AFt) content. However, the 28-day compressive strength is closely related to the C₃S/C₂S ratio of the Portland cement, and the sample with the optimal C₃S/C₂S ratio (0.5) has the highest hydration degree of GGBS and the most C-A-S-H content. This work showed that the total C₃S content and C₃S/C₂S ratio of Portland cement in SSC play a critical role in the early and long-term strength of SSC, respectively, instead of the dosage of Portland cement.