The role of temperature in thaumasite formation under the immersion of magnesium sulfate solution

Abstract

To clarify the role of temperature in thaumasite formation of cement mortar under magnesium sulfate solution at two different temperatures, the corrosion products and microstructure of cement-based materials with different amounts and particle sizes of limestone powder were quantitatively analysed by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. At 5°C, the main corrosion products of cement mortar were gypsum and thaumasite. At 20°C, the main corrosion products of cement mortar were gypsum and ettringite. When the temperature increased from 5°C to 20°C, the contents of ettringite, thaumasite and gypsum changed from 0.3, 12.3 and 64.6% to 4.6, 0 and 57.0%, respectively. The formation of thaumasite was the combination of direct reaction with ettringite transformation. The incorporation of limestone powder accelerated the corrosion of mortars, and the change coefficient of compressive strength of mortars decreased from 100% to 47.3% when its content increased from 0% to 30%. Low temperature and incorporation of finer limestone powder enhanced the corrosion of magnesium sulfate solution.