Sulfate attack of cement matrix containing inorganic alkali-free accelerator

This paper presents an experimental study on the durability of mortar specimens incorporating inorganic alkali-free accelerator (AFA) exposed to external sulfate attack. Visual examination, compressive strength, expansion and density of mortar specimens with or without AFA were monitored up to 360 days of exposure. Additionally, in order to identify the products formed by sulfate attack, mineralogical analysis based on x-ray diffraction (XRD) was also performed on paste samples. Test results confirmed that the mortar specimens with AFA suffered a serious deterioration by sulfate attack, especially in 10% sodium sulfate solution. Furthermore, XRD traces indicated that the formation of ettringite and/or thaumasite is primarily responsible for the sulfate deterioration of mortar specimens. Conclusively, it must be taken a special care when the shotcrete with AFA is applied under the sulfate-bearing environments.