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硝酸侵蚀衬砌喷射混凝土中性化过程及机理
王家滨1, 牛荻涛2,3, 何晖1
1.西安工业大学 建筑工程学院, 西安 710021;2.西安建筑科技大学 土木工程学院;3.西部绿色建筑国家重点实验室, 西安 710055
摘要:
以一般大气环境喷射混凝土永久衬砌长大公路隧道为工程背景,开展汽车尾气中氮氧化物对喷射混凝土衬砌结构中性化过程及机理研究。以pH值为2的硝酸溶液为侵蚀介质,对喷射混凝土开展浸泡试验。以侵蚀喷射混凝土的物理力学性能及离子含量为表征指标,分析喷射混凝土中性化过程。采用X射线衍射、热分析及扫描电镜,分析及表征喷射混凝土中性化区的物相组成及微观形貌,研究喷射混凝土中性化发展过程及机理。结果表明,硝酸侵蚀喷射混凝土中性化演化过程可分为中和反应阶段、水化产物分解阶段、混凝土表面剥蚀等3个阶段。期间,喷射混凝土pH值逐渐下降,NO3-含量升高。随着侵蚀的进行,水化硅酸钙及氢氧化钙的含量降低,硝酸钙、硝酸型水化氮铝酸钙及高岭石的相对含量增大,微观结构被破坏,中性化速度加快,物理力学性能降低。
关键词:  隧道工程  衬砌喷射混凝土  硝酸侵蚀  离子含量  侵蚀机理
DOI:10.11835/j.issn.2096-6717.2019.102
分类号:TU528.44
基金项目:国家自然科学基金(51590914);陕西省自然科学基金(2018JQ5032);陕西省教育厅自然科学研究专项(18JK0376);西安工业大学校长基金(XAGDXJJ17019)
Neutralization process and mechanism of nitric acid-exposed-lining shotcrete
Wang Jiabin1, Niu Ditao2,3, He Hui1
1.School of Civil & Architecture Engineering, Xi'an Technological University, Xi'an 710021, P. R. China;2.College of Civil Engineering;3.National Key Laboratory of Green Building in West China, Xi'an University of Architecture and Technology, Xi'an 710055, P. R. China
Abstract:
Neutralization process and mechanism of long highway tunnel shotcrete lining structure in general atmospheric environment which is contacted with nitrogen dioxide in automobile exhaust was analyzed. The neutralization experiment was carried out by nitric acid solution (pH=2) immersion method. Neutralization process of shotcrete was examined via physical and mechanical properties, damage depth and pH value and nitrate ion content of shotcrete. Afterwards, the mineral phases composition and microscopic morphology of neutralization zone were characterized using XRD, TG-DSC and SEM, which investigated the neutralization mechanism of shotcrete. The durability deterioration process of nitric acid exposed shotcrete included three steps of neutralization reaction, hydration products decomposition, and aggregate spalling. The pH value of shotcrete decreased while nitrate ion content increased. With increase of experiment aging, hydration products (calcium silicate hydrate and Ca(OH)2) content decreased while corrosion products (Ca(NO3)2, calcium aluminate nitrogen hydrate and kaolinite) increased. Microstructure of neutralization zone was damaged, which results in a rapid decrase of the physical and mechanical properties.
Key words:  tunnel engineering  lining shotcrete  nitric acid corrosion  ions content  corrosion mechanism
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