Impact of cation type and fly ash on deterioration process of high belite cement pastes exposed to sulfate attack

• DOI: 10.1016/j.conbuildmat.2021.122961
• Publication Date: 2021-03-18T14:36:52Z
• Authors: Chunmeng Jiang; Linhua Jiang; Shuangxi Li; Xinjun Tang; Lei Zhang
• Keywords: 02 engineering and technology; 0210 nano-technology; 6. Clean water

Abstract High belite cement is widely applied in hydraulic concrete, where much attention should be paid to the external sulfate attack. In this paper, high belite cement pastes with and without fly ash were completely exposed in 5% Na2SO4 and MgSO4 solutions, so was the contrastive Portland cement. Mass change, porosity, compressive strength, Vickers hardness and sulfate ion content of all samples were determined at different exposure durations. XRD, TGA and SEM were also conducted to investigate the composition and microstructures of degraded products. Results show that compared with Portland cement, high belite cement has better resistance to sodium sulfate attack owing to its low contents of Ca(OH)2 and aluminum phase in hydrates. Meanwhile, the less formed insoluble Mg(OH)2 contributes to a free diffusion of sulfate ion to some extent, leaving high belite cement a poor attack resistance against magnesium sulfates. Fly ash could effectively improve the anti-corrosion performance of high belite cement immersed in Na2SO4 solution, while reduce that in the MgSO4 solution. Moreover, Vickers hardness is a promising approach to test the deterioration process of sulfate attack, accordingly the paste cross section could be divided into degraded zone, intensified zone, ingressive zone and sound zone.