Characterisation and hydration process of synthetic Sr-bearing ye'elimite

Ye'elimite (C₄A₃$) is the dominant phase in calcium sulfoaluminate cement. Through substitutions of Sr²⁺ ions for Ca²⁺ ions in C₄A₃$, Sr-bearing ye'elimite can be synthesised. In this paper, a kind of Sr-bearing ye'elimite was synthesised with the formula 3CaO·SrO·3Al₂O₃·SO₃ (abbreviated as C₃ŠA₃$); the characterisation and hydration process of C₃ŠA₃$ are reported here. Comparing to C₄A₃$, mineralogical analysis of C₃ŠA₃$ was conducted, and Rietveld quantitative phase analysis was employed to quantify the hydration products of C₃ŠA₃$ and correlate to calorimetric data. Results show that C₃ŠA₃$ accounts for over 93% in the clinker, and the ACn contents are insignificant in terms of amounts. Without gypsum, the hydration process of C₃ŠA₃$ is more retarded and prolonged than C₄A₃$ at an early stage. In the hydration products of C₃ŠA₃$ at 28 d, AFt accounts for 28·2% and AFm occupies 13·4%; CAH₁₀ is quantified to be 5·5%. Compared to C₄A₃$, C₃ŠA₃$ tends to yield more AFt. As regards C₃ŠA₃$ hydrating with a certain amount of gypsum, the hydration rate of C₃ŠA₃$ is accelerated to approach C₄A₃$ blended with gypsum. In the paste of C₃ŠA₃$ blended with gypsum at 28 d, AFt occupies the majority of crystalline phases to take up 42·1%; minor phases AFm and strontium sulfate account for 3·1% and 7·4%, respectively.