Effects of M-value on long-term microstructural evolution of CSA cement blended with slag

Abstract

In the present study, the effects of the calcium sulfate-to-ye'elimite molar ratio (M-value) on the microstructural evolution of calcium sulfoaluminate (CSA) cement blended with slag during the long-term hydration process were investigated. Blast-furnace slag (BFS) was substituted with a dosage of 50% relative to the binder mass, and anhydrite was used to control it with M-values of 0.75, 1.0, 1.5, and 2.0. The fabricated samples were cured for up to 360 d, and the phase evolution and physicochemical properties were explored using various analytical methods. The test results indicated that the formation of CAH10—a metastable phase—was suppressed at higher M-values, and the formation of strätlingite was suppressed as the M-value increased, owing to the reduced dissolution extent of belite at higher M-values. C-(A)-S-H was produced along with strätlingite after the formation of ettringite and monosulfate in samples with low M-values because belite can be dissolved significantly in the later stage of hydration of CSA cement-based materials. BFS did not substantially affect the microstructural evolution of the samples during long-term hydration, because of its low reaction degree.