Preservation of α' Dicalcium Silicate (C2S) under SO2-Containing Atmosphere

Mitigating greenhouse gas emissions is one of the main approaches to tackle the current environmental crisis. The decarbonation of the cement industry could significantly lower anthropogenic carbon emissions by limiting the average temperature rise to 2°C. Alternative cement formulations such as calcium
sulfoaluminate (C$A) have great potential in partly replacing the current families of cement due to their lower carbon footprint, rapid strength gain, fast curing time, and lower shrinkage. The eco-friendly characteristics of C$A cement are attributed to reduced amounts of limestone used for production and lower
synthesis temperatures. The challenge facing the production of C$A cement is mainly its requirement of high amounts of alumina which hinders the economic viability at the commercial scale. Alumina is essential for the formation of the ye’elimite phase which heavily contributes to early-age strength development. A
promising technique to improve the process’ economics is to reduce the alumina content requirement while preserving the early-age strength. This can be achieved by stabilizing the high temperature α' polymorphs of dicalcium silicate to ambient conditions. A technique was previously developed wherein elemental sulfur is utilized as a source of fuel and mineralogical control factor that provides the sulfur oxide needed to both preserve α’ dicalcium silicate and form ye’elimite in the clinker. Synthesis of α'C2S was carried out here with a focus on Na, K, B, and P as additives under a sulfur-containing atmosphere. The results display the successful stabilization of about 80% α'C2S upon quantification. Hydration experiments showed that the isothermal heat release of α'C2S deviates significantly from beta-C2S. Highest degree of hydration was
achieved with the boron stabilized α'C2S. Interestingly after 6 days of hydration both investigated α'C2S showed no portlandite formation but only calcium silicate hydrates (C-S-H).