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

Abstract

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.