This study compared the sulphate resistance of deionized water (DI)- and seawater (SW)-mixed cementitious materials based mainly on microstructural observations. The results show that, after a 450-day exposure to 50 g/L Na2SO4 solution, there was an increase in the mean chain length and polymerization degree of the remaining silicate chains in C-S-H gel for both DI- and SW-mixed pastes at a depth of 0–2 mm from the exposed surface. Notably, the Ca leaching of C-S-H gel in the SW-mixed paste at depths larger than 0.3 mm was slightly less than that in the DI-mixed one, despite the Ca leaching in both samples was comparable at a depth of 0.1 mm. For the aluminate phase, the mass loss and length change of the SW-mixed C3A mortar were lower than that of the DI-mixed C3A mortar, after immersing in 50 g/L Na2SO4 solution at different times. It seemed that more expansive product can be accommodated in the SW-mixed C3A matrix. Consequently, fewer cracks deposited by gypsum were observed in SW-mixed paste than in DI-mixed paste. The above were responsible for relatively less compressive strength loss of the SW-mixed mortars suffering from sulphate attack for 450 d.

中文翻译：

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海水混合胶凝材料在硫酸盐侵蚀下的降解机理


本研究主要基于微观结构观察，比较了去离子水 （DI） 和海水 （SW） 混合胶凝材料的硫酸盐电阻。结果表明，在 50 g/L Na2SO4 溶液中暴露 450 天后，在距离暴露表面 0-2 mm 的深度，DI 和 SW 混合糊状物在 C-S-H 凝胶中剩余硅酸盐链的平均链长和聚合度都有所增加。值得注意的是，尽管两个样品在 0.1 mm 深度处的 Ca 浸出量相当，但 SW 混合糊体中 C-S-H 凝胶在深度大于 0.3 mm 的浆料中浸出的 Ca 略小于 DI 混合浆料中的 Ca 浸出。对于铝酸盐相，SW 混合的 C3A 砂浆在不同时间浸泡在 50 g/L Na2SO4 溶液中的质量损失和长度变化均低于 DI 混合的 C3A 砂浆。似乎 SW 混合的 C3A 基质可以容纳更广泛的产物。因此，在 SW 混合浆料中观察到的石膏沉积的裂缝比在 DI 混合浆料中观察到的更少。以上是导致 SW 混合砂浆遭受硫酸盐侵蚀 450 d 的抗压强度损失相对较小的原因。