含亚硝酸盐混凝土中钢筋钝化膜微结构演变机制

Carbonation and chloride corrosion are the main factors that cause the failure of the passive film of steel bar in concrete. The nitrite corrosion inhibitor can improve the surface of steel reinforced concrete and inhibit the corrosion of steel bar caused by carbonation and chloride In view of the facts that the composition and structure of passive film on rebar surface affects the corrosion of rebar in concrete, this project research focuses on the corrosion products of rebar in concrete, taking the corrosion current, electrochemical impedance, corrosion potential, linear polarization, corrosion area rate and weight loss rate as corrosion parameters, adopting XPS、XRD、EPMA and Raman spectra to monitor the compositions, structures, thickness, compactness and stability of the rust layer induced by chloride ion and concrete carbonation, and then explicates the effect of corrosion of carbonation and chloride salt under the steel surface microstructure on the corrosion failure mechanism. Based on above research the mechanism of adsorption and consumption of nitrite ion in concrete was further studied and the influencing factors of free radical nitrite ion content was explored. Next, the microstructure characteristics of the passive film of the steel bar under the influence of nitrite corrosion resistance are interpreted and the relationship between the microstructure characteristics of passive film and the corrosion parameters of steel bar is clarified. Furthermore, the micro-structural evolution of the steel bar surface from passivation to corrosion, and then from corrosion to passivation, is finally defined. The project will reveal the composition and structures of the passive film which is beneficial to the corrosion resistance of steel bars in concrete, and provide theoretical basis and technical support for improving the service life of reinforced concrete structures.

碳化和氯盐侵蚀是引起混凝土中钢筋钝化膜破坏的主要原因，亚硝酸盐阻锈剂能够改善钢筋表面的致钝环境，抑制碳化与氯盐引起的钢筋腐蚀。鉴于钢筋腐蚀的原因归结于钝化膜组成与结构的变化，本项目以混凝土中钢筋腐蚀生成物为研究对象，采用XPS、XRD、EPMA及拉曼光谱等微结构测试手段，对碳化与氯盐引起的钢筋锈蚀物组成、结构、厚度和稳定性等微结构特征进行研究，阐明碳化与氯盐侵蚀作用下钢筋表面微结构特征对腐蚀失效机制的影响。在此基础上，进一步研究亚硝酸根离子在混凝土中吸附和消耗机理，探究游离态亚硝酸根离子含量的影响因素，结合亚硝酸盐阻锈的混凝土中钢筋钝化膜组成和微结构特征分析，明确钝化膜微结构特征与钢筋腐蚀参数之间的相关关系，进而揭示混凝土中钢筋表面从钝化到腐蚀，再从腐蚀到钝化的微结构演变规律。本项目的研究成果将提出有利于混凝土中钢筋表面阻锈的钝化膜组成及结构，为提高钢筋混凝土结构的使用寿命提供理论基础。

本项目采用微结构测试手段，研究了亚硝酸根离子在混凝土中吸附和消耗机理，明确游离态亚硝酸根离子含量的影响因素，结合亚硝酸盐阻锈的混凝土中钢筋钝化膜组成和微结构特征分析，确立钝化膜微结构特征与钢筋腐蚀参数之间的相关关系。结果表明: 从氯盐、碳化到氯盐与碳化复合作用，钢筋锈蚀物中Fe的峰值逐渐增强，Fe的氧化物含量增多，钢筋锈蚀越来越严重，钢筋表面的FeO和Fe3O4等较致密的钝化膜结构会转化为Fe3+，且Fe3+与水泥的水化产物Ca2SiO4形成Fe3+-Ca2SiO4复盐，随着钢筋腐蚀程度的加剧，Fe3+-Ca2SiO4复盐含量逐渐减少，而Fe3+转化为以Fe2O3为主的其他锈蚀物。含亚硝酸盐的水泥浆水化后生成NO2-AFm，并均匀分布于水泥浆内。NO2-AFm 在碳化过程中重新分解生成亚硝酸根离子并向未碳化区扩散，致使碳化区NO2‐含量减少，非碳化区NO2含量增加。由于碳化过程中C-S-H 凝胶分解，吸附于凝胶表面的游离亚硝酸根离子重新转变成游离态，碳化区游离态亚硝酸根离子含量增多。混凝土中养护龄期越长,游离态NO2-含量越低，早期游离态NO2-含量下降速率较快，后期趋于平缓, 且生成NO2-AFm 化合物; 养护温度越高，游离态NO2-含量越低，离子固化率越高，对早期离子固化速率的影响尤为明显；水灰比越大, 游离态NO2-含量越小，水泥浆内的游离态NO2-在养护后期仍持续固化，而水灰比较小的试件在后期固化速率变慢；随着亚硝酸盐掺量的增加，水泥浆体中游离态和固化态的NO2-含量均随之增加，但固化率却随掺量的增加而减少，NaNO2在碱性环境下与Fe元素反应生成中间产物Na2FeO2和(NaFeO2)2，进一步促进Fe3O4的生成，提高了阻锈效果；NaNO2的掺入促进了反应式向正向移动，提高了钝化膜中Fe3O4的含量；当普通碳钢钝化膜内5nm处Fe3+/Fe2+的百分比大于表层的Fe3+/Fe2+百分比时，钝化膜内部的致密性优于表面。NaNO2不参与钝化膜的组成，但参与生成钝化膜的反应过程，该反应过程为缓慢的动态平衡过程，可通过改变反应物的含量控制钝化膜厚度。本项目的研究成果将提出有利于混凝土中钢筋表面阻锈的钝化膜组成及结构，为提高钢筋混凝土结构的使用寿命提供理论基础。