Degradation of cementitious materials caused by sulfate attack poses a significantly challenge to their durability. Using nano-additives to enhance the mechanical and durability properties of cementitious materials is a promising solution; however, the impact of graphene oxide (GO) on the sulfate resistance is not yet fully understood. While efforts have been made to study the degradation mechanism through accelerated indoor tests with high sulfate concentrations, these methods fail to accurately replicate real-world field exposure conditions. To better understand the degradation mechanism of GO-modified mortars under actual field conditions, this study examines the long-term degradation (over 24 months) of GO-modified mortars exposed to sulfate solutions with varying concentrations: 0 % (reference), 2.1 % (field condition), 5 % (laboratory condition), and 15 % (high-concentration condition). Additionally, a comprehensive chemo-mechanical model that considers multiple factors and time-varying boundary conditions was proposed. The study thoroughly discusses the effects of GO dosage, sulfate concentration, and exposure time on the degradation mechanism. Comparison with experimental data revealed that cement mortar degradation under sulfate attack is primarily driven by the crystallization pressure related to ettringite formation in diluted sulfate solutions, while the precipitation of alkali ions from mortar pore solutions occurs in concentrated sulfate solutions. In real-field conditions, cement mortar degradation primarily involves gypsum precipitation rather than ettringite formation. This study demonstrates that well-dispersed GO nanosheets can significantly enhance durability of cementitious materials against sulfate attack, offering valuable insights for strategic applications of GO nanosheets in cementitious materials.

中文翻译：

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硫酸盐侵蚀下氧化石墨烯纳米片水泥砂浆降解机理的实验与建模


硫酸盐侵蚀导致水泥基材料的降解对其耐用性构成了重大挑战。使用纳米添加剂来增强胶凝材料的机械和耐久性是一种很有前途的解决方案;然而，氧化石墨烯 （GO） 对硫酸根电阻的影响尚不完全清楚。虽然已经努力通过高硫酸盐浓度的加速室内测试来研究降解机制，但这些方法无法准确复制真实世界的现场暴露条件。为了更好地了解 GO 改性砂浆在实际现场条件下的降解机制，本研究检查了暴露于不同浓度硫酸盐溶液的 GO 改性砂浆的长期降解（超过 24 个月）：0 %（参考）、2.1 %（现场条件）、5 %（实验室条件）和 15 %（高浓度条件）。此外，还提出了一个考虑多个因素和时变边界条件的综合化学力学模型。该研究深入讨论了 GO 剂量、硫酸盐浓度和暴露时间对降解机制的影响。与实验数据对比表明，硫酸盐侵蚀下水泥砂浆的降解主要是由稀硫酸盐溶液中钙砾形成相关的结晶压力驱动的，而砂浆孔隙溶液中碱离子的沉淀发生在浓硫酸盐溶液中。在实际田间条件下，水泥砂浆降解主要涉及石膏沉淀，而不是钙矾石的形成。 本研究表明，分散良好的 GO 纳米片可以显著提高胶凝材料对硫酸盐侵蚀的耐久性，为 GO 纳米片在胶凝材料中的战略应用提供有价值的见解。