Deterioration mechanism of limestone filler cement mortar exposed to sulfate attack at lower temperature

Cement mortars containing 0 to 30% mass of limestone filler were immersed in 2% magnesium sulfate solution at 5 ± 1°C, their appearance and strength development with immersion times were measured at intervals. X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were used to analyze the mineral composite and microstructure of the mortars after 1 year of immersion. The results show that the addition of a lower content of limestone filler improves the mortar's resistance to sulfate attack at lower temperature. But the sulfate attack of mortar is accelerated when adding a higher content of limestone filler. The surface cracking and spallation occurs in the pure cement mortar specimen after 1 year of immersion to the sulfate solution and a lot of ettringite and gypsum forms in the attacked mortar. On the other hand, the surface layer of the 30% limestone filler mortar becomes soft and mushy, both thaumasite and gypsum were identified in the residual mortar, therefore the mortar undergoes the typical thaumasite form of sulfate attack.