Deterioration mechanism of plain and blended cement mortars partially exposed to sulfate attack

•Durability of cement mortars partially exposed to sulfate attack was investigated.•The upper part mainly suffered physical attack, while the low part suffered chemical attack.•The water-soluble SO42− contents of cement mortars were measured.•SEM, MIP, XRD and X-CT were used to investigate the microstructure changing.

The degradation of cement-based materials partially exposed to sulfate solution are dramatically serious than under ordinary full immersion. To research the damage regime of cement-based materials partially exposed to sulfate attack, the resistance of drying (upper) portion and immersed (lower) portion of both the plain cement mortars as well as fly ash (FA) and grounded blast furnace slag (GBFS) modified cement mortars partially immersed in 10% Na2SO4 solution was investigated in this paper. The mass change, relative dynamic modulus of elasticity, compressive/flexural strength and water-soluble SO42− contents were monitored to show the damage progress. SEM/EDS, XRD, MIP and X-CT were used to investigate the microstructure changing.The research results indicated that the deterioration of cement mortars partially immersed in sulfate solution is not only caused by chemical sulfate attack, but also by physical sulfate attack. The upper part of specimens mainly suffer physical sulfate attack, as well as chemical sulfate attack, while the lower part only suffer chemical sulfate attack. Furthermore, fly ash (FA) have better effect than grounded blast furnace slag (GBFS) on improving the resistance of cement mortars to partially immersed in sulfate solution.