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镀锌钢筋在内掺辅助胶凝材料混凝土中的防腐蚀机理
郑海兵
学位类型博士
导师李伟华
2018-05-10
学位授予单位中国科学院大学
学位授予地点中国科学院海洋研究所
学位专业海洋腐蚀与防护
关键词海洋混凝土结构 辅助胶凝材料 镀锌钢筋 钝化机理 防腐蚀
摘要

镀锌钢筋作为一种经济有效的防腐蚀措施,可用于海洋环境下混凝土结构的腐蚀防护。然而,现在越来越多的辅助胶凝材料(SCMs)被应用于混凝土中,添加SCMs的混凝土中胶凝材料的水化过程与普通水泥混凝土有较大差异,混凝土内部孔溶液的离子成分以及pH值同样会发生变化,而这两个方面是混凝土内镀锌钢筋在腐蚀模型中最关键阶段——钝化阶段的主要影响因素。因此本文主要针对镀锌钢筋在掺加SCMs混凝土中的防腐蚀机理进行了深入和系统的研究。

为了给实际砂浆试验提供理论依据,本文首先进行了镀锌钢筋在混凝土模拟液中的测试,设计了不同的溶液模拟添加不同SCMs的混凝土孔溶液,采用了传统的电化学方法,如开路电位、线性极化阻抗、电化学阻抗谱和循环极化等,研究了不同pH值条件下不同离子对镀锌钢筋钝化的影响机理。其次,本文又选取了两种具有代表性的SCMs添加至砂浆中,一种是最常用的SCMs粉煤灰,另一种是新型的SCMs纳米二氧化硅,采用了水化热测试、ICP测试、pH值测试和差热分析测试对砂浆的孔溶液环境进行了分析,同时采用了电化学方法对镀锌钢筋的钝化过程进行了实时监测,进而深入的分析和探讨了镀锌钢筋在砂浆中钝化机理。最后,本文又采用了电化学方法对镀锌钢筋表面钝化膜的脱钝机理进行了研究。

通过以上研究发现,钙离子对镀锌钢筋的钝化具有显著的促进作用,特别是对于低pH值(12.5)的模拟液,随着钙离子浓度的降低,镀锌层与模拟液的反应逐渐减弱,生成的产物逐渐减少,在饱和氢氧化钙溶液中形成的钝化膜具有最好的腐蚀防护效果;在掺加纳米二氧化硅的砂浆中,由于纳米二氧化硅加速了早期水泥的水化,提高了早期钙离子浓度和pH值,加速了镀锌钢筋的钝化,有利于钝化膜的形成,说明纳米二氧化硅与镀锌钢筋具有较好的兼容性;在添加粉煤灰的砂浆中,镀锌钢筋的钝化过程与普通水泥混凝土中有较大差异,粉煤灰的添加抑制了镀锌钢筋表面钝化膜的形成,形成的钝化膜无法完全覆盖镀锌层表面,其防腐蚀性能也有显著的降低;在模拟液中确定了镀锌钢筋钝化膜的氯离子临界值,其钝化膜层脱钝机理可以用点缺陷模型(PDM)进行解释,当钝化膜发生点蚀后,其腐蚀产物会覆盖于点蚀坑表面,并可以隔离腐蚀介质进一步侵入,从而抑制腐蚀的发展。

其他摘要

As a cost-effective corrosion prevention method, galvanized steel could be used in the marine concrete structures. While more and more supplementary cementitious materials (SCMs) have been used in the concrete and the hydration process of the cement will be different from that of ordinary portland cement. The pH value and the ionic composition of the pore solution will be changed, which are the two main factors affecting the passivation of the galvanized steel bars in concrete. Therefore, the passivation of the galvanized steel in concrete with SCMs was studied in present work.

In order to provide a theoretical basis, the test in the concrete pore solution was firstly conducted. Various solutions were designed to simulate different pore environment of concrete with SCMs. Traditional electrochemical methods were deployed to study the influence of the ion composition at two different pH value on the passivation of the galvanized steel. Secondly, two typical SCMs (fly ash and nanosilica) were selected for addition into mortar. The hydration process, the pH value and the Ca2+ concentration were monitored. Then the passivation process was monitored using electrochemical methods. Finally, the depassivation mechanism of the passive film on the galvanized steel in the presence of the chloride ions was studied.

According to the results, the existence of Ca2+ accelerated the passivation of the galvanized steel in concrete pore solution. The reaction between the galvanized coating and the solution became less vigorous with the reduction of the Ca2+ concentration. The passive film was not integrated when the Ca2+ concentration was low. In the mortar with the addition of the nanosilica, the hydration of the cement was accelerated. The pH value and the Ca2+ concentration were increased at the early age. The passivation process of the galvanized steel was accelerated during the early age of the cement hydration and the properties of the passive film were improved. In the mortar with fly ash, the hydration of cement at the early age was also accelerated. Though the Ca2+ was increased, the pH value was significantly reduced. The passivation was inhibited and the passive film was not integrated when the fly ash was added. The chloride threshold value was defined in the concrete pore solution. The depassivation mechanism could be interpreted by point defect model (PDM). When the pitting corrosion occurred, the corrosion products could cover the pits and inhibit the ingress of the aggressive ions, and thus mitigate the corrosion of the galvanized coating during the protective stage of the corrosion model.

学科门类理学 ; 理学::海洋科学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/154508
专题中国科学院海洋研究所
第一作者单位中国科学院海洋研究所
推荐引用方式
GB/T 7714
郑海兵. 镀锌钢筋在内掺辅助胶凝材料混凝土中的防腐蚀机理[D]. 中国科学院海洋研究所. 中国科学院大学,2018.
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