Role of ITZ in the Degradation Process of Blended Cement Concrete under Magnesium Sulfate Attack

Abstract

Although the importance of the interfacial transition zone (ITZ) to sulfate attack is obvious, the relation between the ITZ and the rate of degradation is still unclear. The impact of ITZ volume content on the degradation of concrete, including length, mass, and elastic dynamic modulus (Ed) variation, fully immersed in magnesium sulfate solution were investigated in this work. The microstructure was analyzed by backscattered electron imaging (BSE) and energy dispersive X-ray spectroscopy (EDX) mapping analysis. The performance of concrete exposed to magnesium sulfate highly depended on the aggregate and the composition of raw materials. There was a trend toward more serious deterioration with increasing ITZ in the reference and limestone filler blended group after 12 months of exposure. The degradation of specimens made with slag was independent of the variation of ITZ content. Gypsum tended to precipitate in the ITZ under magnesium sulfate attack. The EDX analysis confirmed the decomposition of C-S-H, accompanied by the formation of degradation products M-S-H.