Insight on the nanoscale chemical degradation mechanism of MgCl2 attack in cement paste
Insight on the nanoscale chemical degradation mechanism of MgCl2 attack in cement paste
复制标题
水泥浆中 MgCl2 侵蚀的纳米级化学降解机制的见解
DOI：
10.1016/j.conbuildmat.2019.117777
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发表时间：
2020-03
影响因子：
7.4
通讯作者：
Hu Hao
中科院分区：
文献类型：
--
作者：
Yang Jun;Hou Dongshuai;Ding Qingjun;Zhang Gaozhan;Zhang Yang;Hu Hao
MgCl 2引起的材料降解是水泥基系统面临的主要耐久性问题。采用X射线衍射（XRD）、Si-29和Al-27核磁共振谱（NMR）、扫描电子显微镜-能谱仪（SEM-EDS）和热力学模型相结合的方法，研究了不同浓度MgCl 2溶液对水泥浆体在纳米尺度下的侵蚀降解机理。X射线衍射（XRD）、扫描电子显微镜（SEMEDS）和核磁共振（NMR）结果表明，水泥净浆暴露于5（相当于15wt%的MgCl 2）中，导致主要水化产物水合铝硅酸钙（C-A-S-H）凝胶、钙钛矿崩解，沿着形成大量的弗里德尔盐、水镁石沉淀和少量的钙矾石。该相转变与MgCl 2侵蚀引起的C-A-S-H凝胶的聚合反应以及低钙环境中硅酸盐平均链长增加和Al[4]/Si比降低的脱铝作用密切相关。此外，热力学模型预测的相图与实验分析吻合较好，为相变提供了补充支持。通过关联相组成的变化和局部结构的铝酸盐物种和聚合的演变，这项研究提供了分子洞察的基本氯化镁诱导降解反应发生在水泥浆体。(C)2019爱思唯尔有限公司版权所有。
The MgCl2 induced material degradation is the major durability issue facing the cement-based system. In this study, the degradation mechanism induced by MgCl2 attack at nanoscale is investigated for cement paste exposed to MgCl2 solution with different concentrations for 28 and 180 days by combing X-ray diffraction (XRD), Si-29 and Al-27 Nuclear Magnetic Resonance Spectroscopy (NMR), Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and thermodynamic modeling. The XRD, SEMEDS and NMR results show that the cement paste exposed to 5 similar to 15 wt% MgCl2 cause disintegration of the main hydration product, calcium aluminosilicate hydrate (C-A-S-H) gel, portlandite, along with the formation of extensive Friedel's salt, brucite precipitation and the small amount of ettringite. The phase transformation is closely related with the polymerization of the C-A-S-H gel and the dealuminization characterized by the increasing mean silicate chain length and reduction of the Al[4]/Si ratio in the low calcium environment induced by MgCl2 attacking. Additionally, the predicted phase diagram from thermodynamic modeling matches well with the experimental analysis and gives a supplement support to the phase transformation. By correlating the phase composition change and the local structure of aluminate species and polymerization evolution, this study provides molecular insight on the fundamental MgCl2 induced degradation reactions happening in cement paste. (C) 2019 Elsevier Ltd. All rights reserved.
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