干旱区生态环境知识资源中心

Scaling of concrete surfaces caused by the reversible hydration reactions of highly soluble sodium sulfate in many seaside or desert areas is frequently misdiagnosed as "sulfate attack". While sulfate attack based on chemical reactions of alkali or magnesium sulfates with calcium hydroxide, or the subsequent reaction of the gypsum with monosulfate or hydrated aluminates "left over" in the cement paste, can occur, sodium sulfate often does not usually undergo significant reaction with cement paste components, primarily because the reaction is above ground level where the calcium hydroxide has already carbonated. Further, while the result of sulfate attack is often disintegration of concrete structures due to volume changes, with the exception of minor scaling, sodium sulfate hydration hydrate state changes do not produce significant distress to the concrete. Field experiences and typical scanning electron microscope (SEM) images and X-ray elemental analyses of samples of affected concretes are presented.