Study of the Chemical Processes of Combined Sulfate-chloride Attack on Low-carbon Cementitious Materials

Abstract

In marine environments, concrete structures are not only exposed to sulfate ions but also to chloride ones, from an early age. This leads to concrete expansion and cracking as well as steel reinforcements corrosion. However, the coupling effect of sulfate and chloride is still not widely studied. When addressed, some researchers showed that chloride ions mitigate the effect of sulfate while others concluded that it accelerates it and vice versa. Therefore, one of the objectives of this study is to observe both the combined and individual effects of chloride on sulfate attack. The second objective is to perceive the resistance of selected additives (fly ash, blast furnace slag, and metakaolin) to a combined attack. Then, powders of pure cement, binary, ternary, and quaternary blended pastes were immersed in sulfate, chloride, and sulfate-chloride solutions at an early age. Results of the characterization showed that the ettringite formation was delayed due to the presence of chloride. However, the presence of sulfate ions accelerated the chloride effect. The incorporation of more than one additive enhanced the samples’ durability.