Study on the expansion of concrete under attack of sulfate and sulfate–chloride ions

This paper describes an experimental study on the expansion and subsequent damage of concrete specimens immersed in pure water, sulfate solutions of different sulfate concentrations, and mixed solutions of different sulfate and chloride concentrations. Based on experimentally obtained results, a theoretical expansion model is proposed for predicting the stresses, strains and volume expansion developed during the process of sulfate attack. The model proposed is based on the assumption that concrete may be treated as a porous visco-elastic material, and was developed by using a micromechanics approach method. The internal expansion force produced by delayed ettringite and gypsum is considered as the main cause of the expansion. The expansion model was validated using the experimental results obtained.

► The higher the concentration of sulfate, the greater the expansion in specimens.
► The higher the water-to-cement ratio used, the more severe the damage found.
► The chloride ions can substantially reduce the sulfate attack.
► The higher the concentration of chloride, the less the expansion in specimens.
► Expansion and damage can be described by a new model based on micromechanics.