钢筋混凝土界面局部腐蚀发展与抑制机理研究

发布时间：2018-06-12 03:45

本文选题：钢筋混凝土 + 点蚀　；参考：《华中科技大学》2014年博士论文

【摘要】：钢筋混凝土结构受氯盐、CO2、SO42-、氧含量、温湿度、混凝土微观结构和施工缺陷等多方面影响,导致混凝土综合性能劣化,进而造成钢筋表面发生局部或者全面腐蚀。而锈蚀层的发展又会引起混凝土层胀裂,导致结构的强度受损,使服役寿命降低。由于混凝土为高碱性环境,钢筋表面往往优先发生以点蚀为代表的局部腐蚀。尽管工程上为延缓钢筋锈蚀时间,常在新拌混凝土内加入钢筋阻锈剂,但阻锈剂对混凝土下钢筋点蚀的抑制机理目前尚无定论。特别是采用常规电化学方法难以获取混凝土覆盖层下钢筋局部腐蚀的萌发、生长或阻锈剂修复等细节。本文以阻锈剂在混凝土中的扩散以及对钢筋点蚀的抑制机理为研究重点,取得了如下认识： 1)以丝束电极(WBE)技术研究了混凝土下钢筋稳态及亚稳态点蚀的演变过程,模拟了侵蚀性粒子与阻锈剂在钢筋/混凝土界面层内的迁移、竞争吸附行为。研究了烯胺类,醇胺类与无机型亚硝基阻锈剂在模拟孔隙液内和混凝土内对碳钢点蚀的抑制机理,发现二甲基乙醇胺(DMEA)在混凝土中的迁移效率高于三乙烯四胺(TETA),但对钢筋点蚀的抑制作用不及TETA显著。此外,有机型阻锈剂对锈层覆盖下的点蚀修复存在明显滞后,反而会在一定时间内加剧腐蚀的不均匀性。通过WBE表面阳极电流的统计分析,建立了局部腐蚀因子(LF),实现了腐蚀不均匀程度以及阻锈剂对局部腐蚀修复能力的定量表征。 2)干湿循环加速实验表明：在干周期内,氧在混凝土微孔内扩散迅速,并将先期形成的腐蚀产物如FeO和Fe304氧化为FeOOH,而在湿周期,阳极释放的电子将其再还原为Fe(Ⅱ),即锈蚀产物在缺氧条件下代替O2参与了腐蚀的阴极去极化过程,使腐蚀过程得以延续。 3)借助3D显微镜、电化学噪声(ECN)、电化学阻抗和激光拉曼等方法,研究了模拟孔隙液中钢筋表面亚稳态蚀点诱发、生长或死亡的动态过程,探讨了腐蚀产物对亚稳态向稳态蚀点转变的催化机理,原位监测了阻锈剂分子对亚稳态蚀点的阻滞过程,发现亚稳态蚀点产生的电流峰幅值及寿命可反映钝化膜的破裂与修复难易程度,基于噪声峰数值模拟,用钝化膜电容充放电模型解释了亚稳态点蚀电流与电位峰快速上升／缓慢衰减的成因,发展了钢筋锈蚀产物对蚀点生长的促进模型。 4)通过SEM. XPS、AFM、ECN和Mott-Schottky图,研究了阻锈剂分子在裸钢和锈蚀产物表面的吸附行为差异。发现N02-与TEPA均能降低碳钢钝化膜中的载流子浓度,提高钝化膜的抗C1-侵蚀能力。TEPA倾向以钝化膜中氧空位为吸附中心,预膜条件下可增强钢筋的抗点蚀能力,但难以抑制锈层覆盖下的点蚀发展。NO2-离子在混凝土中扩散速率低于有机胺,但它能更快突破腐蚀产物,相比有机胺,表现出对稳态点蚀的快速抑制能力。XPS表明：TETA在金属基体表面存在键合作用,Nls峰显示出明显的化学位移,因而表现出较好的阻锈作用；但在锈蚀层表面,N难以与Fe3+形成有效键合,因而难以抑制锈蚀层下的蚀点发展。
[Abstract]:Reinforced concrete structures are affected by chloride, CO2, SO42-, oxygen content, temperature and humidity, concrete microstructure and construction defects, which lead to the deterioration of the comprehensive performance of concrete, which will cause local or comprehensive corrosion on the surface of the steel bar, and the development of the corrosion layer will cause the swelling of the concrete layer, which leads to the damage of the structure strength and the service life. Life is reduced.
Because the concrete is high alkaline environment, the surface of steel bar often takes precedence of local corrosion represented by pitting corrosion. Although the steel corrosion inhibitor is often added to the fresh concrete in order to postpone the corrosion time of the reinforced bar, the inhibition mechanism of corrosion inhibitor on the pitting corrosion of the reinforced concrete under concrete is not yet conclusive. In order to obtain the details of local corrosion of steel bar under concrete covering layer, growth or rust inhibitor repair, this paper focuses on the diffusion of rust inhibitor in concrete and the inhibition mechanism of pitting corrosion of steel bar.
1) the evolution process of steady and metastable pitting of steel bar under concrete was studied by WBE technique. The migration of corrosive particles and rust inhibitor in the interface layer of reinforced concrete was simulated, and the behavior of competitive adsorption was simulated. The carbon steel points in the simulated pore fluid and in the concrete were studied in the simulated pore fluid and the concrete. The inhibition mechanism of corrosion was found that the transfer efficiency of two methyl ethanolamine (DMEA) in concrete was higher than that of three ethylene four amine (TETA), but the inhibition effect on pitting corrosion was not as significant as that of TETA. In addition, there was a significant lag in the repair of pitting corrosion under the rust layer covering the rust layer, and it would increase the inhomogeneity of corrosion in a certain time. Through WBE The local corrosion factor (LF) was established by the statistical analysis of the surface anode current. The uneven corrosion degree and the quantitative characterization of the corrosion resistance of the corrosion inhibitor to the local corrosion repair were realized.
2) the dry and wet cycle accelerated experiments showed that in the dry cycle, oxygen diffused rapidly in the concrete micropores and oxidized the corrosion products such as FeO and Fe304 to FeOOH, while in the wet cycle, the electrons released by the anode reduced them to Fe (II), that is, the corrosion products took part in the corrosion cathodic depolarization process instead of O2 under the condition of hypoxia. The corrosion process continues.
3) by means of 3D microscope, electrochemical noise (ECN), electrochemical impedance and laser Raman, the dynamic process of metastable corrosion point induced, growth or death in the simulated pore fluid is studied. The catalytic mechanism of the metastable corrosion point transition of the corrosion product to metastable steady corrosion point is discussed, and the resistance of the inhibitor to metastable corrosion point is monitored in situ. It is found that the amplitude and life of the current peak produced by the metastable corrosion point can reflect the failure and repair of the passivation film. Based on the numerical simulation of the noise peak, the cause of the rapid rise / slow decay of the metastable pitting current and the potential peak is explained by the passive film capacitance charge discharge model, and the corrosion products of the steel bar are developed to the corrosion point. Promote the model.
4) through the SEM. XPS, AFM, ECN and Mott-Schottky diagrams, the difference of adsorption behavior between the rust inhibitor on the surface of bare steel and corrosion product was studied. It was found that both N02- and TEPA could reduce the carrier concentration in the passivation film of carbon steel and improve the anti C1- erosion ability of the passivation film with the oxygen vacancy in the passivation film as the adsorption center and the pre film conditions could be enhanced. The anti pitting ability of the steel bar is difficult to suppress the pitting corrosion under the rust layer. The diffusion rate of.NO2- ions in the concrete is lower than that of the organic amine, but it can break through the corrosion products faster. Compared with the organic amine, the rapid inhibition ability of the stable pitting.XPS shows that there is a bonding effect of TETA on the surface of the metal matrix, and the Nls peak shows obvious. The chemical displacement shows good corrosion resistance, but on the surface of the corrosion layer, N is difficult to form an effective bond with Fe3+, so it is difficult to inhibit the development of corrosion point under the rust layer.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU375

【参考文献】