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The long-term failure mechanisms of alkali-activated slag mortar exposed to wet-dry cycles of sodium sulphate
Cement and Concrete Composites ( IF 10.8 ) Pub Date : 2020-12-09 , DOI: 10.1016/j.cemconcomp.2020.103893
Qing Li , Xinyuan Li , Kai Yang , Xiaohong Zhu , Juan Pablo Gevaudan , Changhui Yang , Muhammed Basheer

This study investigates the long-term (570 days) performance of alkali-activated slag (AAS) mortar materials exposed to combined wet-dry cycles and sodium sulphate solutions (i.e. 5 wt% and 10 wt%). Physical and mechanical characteristics of AAS mortars (i.e. visual appearance, compressive/flexural strength, mass change, capillary porosity, water sorptivity) as well as mineralogical and chemical parameters were determined using XRD, FTIR, DSC and BSE. Findings were compared to Portland cement (PC) and high sulphate resistant (HSR) samples. Results indicate that AAS mortars perform better than PC and HSR samples with minimal changes to compressive strength at 570 days (1.7% increasement). The main failure mode for AAS mortar was external spalling, which could be due to the crystallisation/dissolving pressure of sodium sulphate. Moreover, the results indicate key differences in the deterioration mechanism of AAS. Unreacted slag, exposed during sodium sulphate attack under wet-dry cycles, can continue to react in sodium sulphate to form silicon-rich gels. The formation of highly siliceous gel regions has beneficial impacts, such as the increase in flexural strength. While no calcium sulphate phases were detected via XRD and FTIR after 570 days of exposure, it is evident that the molecular changes to the microstructure reveal depolymerisation and enhanced formation of Si–O phases after long-term sodium sulphate exposure. These results are important to understand the long-term degradation mechanisms of AAS materials exposed to sodium sulphate under wet-dry cycles.



中文翻译:

碱活化矿渣砂浆在硫酸钠干湿循环中的长期破坏机理

这项研究调查了碱活化矿渣(AAS)砂浆材料在湿-干循环和硫酸钠溶液(即5 wt%和10 wt%)混合作用下的长期(570天)性能。使用XRD,FTIR,DSC和BSE确定了AAS砂浆的物理和机械特性(即外观,抗压/抗弯强度,质量变化,毛孔孔隙率,吸水率)以及矿物学和化学参数。将结果与波特兰水泥(PC)和高抗硫酸盐(HSR)样品进行了比较。结果表明,AAS砂浆的性能优于PC和HSR样品,在570天时的抗压强度变化很小(增加了1.7%)。AAS砂浆的主要破坏模式是外部剥落,这可能是由于硫酸钠的结晶/溶解压力所致。此外,结果表明,原子吸收光谱的恶化机理存在关键差异。在干湿循环下的硫酸钠侵蚀期间暴露出的未反应炉渣可继续在硫酸钠中反应,形成富含硅的凝胶。高硅质凝胶区域的形成具有有益的影响,例如抗弯强度的增加。虽然在暴露570天后没有通过XRD和FTIR检测到硫酸钙相,但很明显,在长期暴露于硫酸钠后,微观结构的分子变化揭示了解聚和Si-O相形成的增加。这些结果对于了解在干湿循环下暴露于硫酸钠的AAS材料的长期降解机理很重要。在干湿循环下在硫酸钠侵蚀过程中暴露于水中,会继续在硫酸钠中反应形成富硅凝胶。高硅质凝胶区域的形成具有有益的影响,例如抗弯强度的增加。虽然在暴露570天后没有通过XRD和FTIR检测到硫酸钙相,但很明显,在长期暴露于硫酸钠后,微观结构的分子变化揭示了解聚和Si-O相形成的增加。这些结果对于了解在干湿循环下暴露于硫酸钠的AAS材料的长期降解机理很重要。在干湿循环下在硫酸钠侵蚀过程中暴露于水中,会继续在硫酸钠中反应形成富硅凝胶。高硅质凝胶区域的形成具有有益的影响,例如抗弯强度的增加。虽然在暴露570天后没有通过XRD和FTIR检测到硫酸钙相,但很明显,在长期暴露于硫酸钠后,微观结构的分子变化揭示了解聚和Si-O相形成的增加。这些结果对于理解在干湿循环下暴露于硫酸钠的AAS材料的长期降解机理很重要。虽然在暴露570天后没有通过XRD和FTIR检测到硫酸钙相,但很明显,在长期暴露于硫酸钠后,微观结构的分子变化揭示了解聚和Si-O相形成的增加。这些结果对于理解在干湿循环下暴露于硫酸钠的AAS材料的长期降解机理很重要。虽然在暴露570天后没有通过XRD和FTIR检测到硫酸钙相,但很明显,在长期暴露于硫酸钠后,微观结构的分子变化揭示了解聚和Si-O相形成的增加。这些结果对于理解在干湿循环下暴露于硫酸钠的AAS材料的长期降解机理很重要。

更新日期:2020-12-09
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