Effect of aluminium phases on thaumasite formation in cement slurries containing limestone powder

Under low-temperature conditions with carbonate, sulfate and abundant water, cement-based materials suffer from a severe thaumasite form of sulfate attack. In this study, the effects of aluminium phases on thaumasite formation in tricalcium silicate (C₃S) slurries containing limestone powder under gypsum solution conditions was examined using X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, nuclear magnetic resonance, Fourier transform infrared spectroscopy and differential thermal gravity analysis. The results indicate the following: the presence and relative amount of tricalcium aluminate (C₃A) are not prerequisites of thaumasite formation; sulfates and carbonates can directly react with the calcium silicate hydrate (C–S–H) gels in cement hydration products, which dissolves the C–S–H gels and produces non-cementitious thaumasite; small amounts of aluminium phases in the reaction are sufficient to accelerate thaumasite formation, and the accelerating effect becomes more noticeable as the aluminium phase content increases. The morphology of erosion products showed that the crystal size become smaller as the C₃A dosage increases.