【作者】 何富强；

【导师】 史才军；

【作者基本信息】 中南大学 ， 土木工程材料， 2010， 博士

【摘要】 混凝土中的钢筋锈蚀是导致氯离子环境中的钢筋混凝土结构耐久性问题的主要原因,氯离子在水泥基材料中的迁移是氯环境下钢筋混凝土结构耐久性设计考虑的主要因素之一。因此,测量水泥基材料中氯离子的迁移,尤其是用有效的快速法来测量是相当重要的。本文研究了硝酸银显色法的影响因素及其快速测量水泥基材料中氯离子的迁移。基于AgNO3-NaOH-NaCl-H2O四元体系中的局部相平衡规律,推导出了硝酸银显色法测量时水泥基材料试件的变色边界氯离子浓度理论计算公式。结果表明变色边界氯离子浓度取决于测量时硝酸银溶液的浓度及喷洒体积,硝酸银过量时,变色边界氯离子浓度随氢氧根离子浓度线性增大。硝酸银不足量时,氢氧根离子浓度对变色边界氯离子浓度的影响微乎其微,变色边界氯离子浓度随硝酸银物质的量增加而增大。计算的变色边界氯离子浓度解释了文献中变色边界氯离子浓度变化范围很大的原因。依据理论计算与变色边界氯离子浓度影响因素试验研究结果,提出了一种合理的硝酸银显色测量程序。结果表明,采用提出的硝酸银显色法测量程序,变色边界氯离子浓度随水泥基材料水胶比增大而降低。针对不同水胶比水泥基材料试件,选取了变色边界氯离子浓度范围合理的代表值。根据水泥基材料中氯离子吸附双电层模型,通过相关参数的测试与分析,解释了水泥基材料孔溶液中氯离子“浓缩”现象,结果表明水泥基材料中并不存在真正的氯离子浓缩,所谓的氯离子“浓缩”是压滤法测试引起压滤孔溶液中氯离子浓度较孔隙本体溶液氯离子浓度的升高。同时研究了水萃取法测量水泥基材料中自由氯离子浓度,基于水萃取法测量水溶性氯离子的良好重复性及水溶性氯离子与自由氯离子浓度之间良好的截距式线性或幂函数相关性,证明了水萃取法是测量水泥基材料中自由氯离子浓度的有效方法。对用硝酸银显色法测量氯离子非稳态电迁移系数的误差进行了评估,结果表明当氯离子渗透深度较小时,若不限制硝酸银溶液的喷洒量时,变色边界氯离子浓度变异引起的非稳态电迁移系数误差甚至达到200%,而采用本研究提出的硝酸银显色测量程序及选取的变色边界氯离子浓度的代表值,变色边界氯离子浓度变异引起的氯离子非稳态电迁移系数误差可以控制在5%以内。提出并试验论证了硝酸银显色法精确测量氯离子表观扩散系数的关键条件,评估了硝酸银显色法测量氯离子表观扩散系数的灵敏度与误差。结果表明硝酸银显色法测量氯离子表观扩散系数的误差随表面氯离子浓度增大、变色边界氯离子浓度降低而减小。基于本文提出的硝酸银显色测量程序,当表面氯离子浓度与海水中氯离子浓度相同时(0.53mol/L),变色边界氯离子浓度引起的氯离子表观扩散系数的误差小于17.1%,当表面氯离子浓度为2.8mol/L (NT Build443采用的浸泡液氯离子浓度)时,该误差小于2%。当厚度为2mm表面层内平均氯离子浓度与浸泡液氯离子浓度接近时,硝酸银显色法测量的氯离子表观扩散系数与NT Build443法测量的结果十分接近。因此,硝酸银显色法可以快速且较为准确地测量水泥基材料中氯离子表观扩散系数。更多还原

【Abstract】 Chloride corrosion of steel in concrete is a main cause responsible for durability problem of reinforced concrete structures exposed to chloride environment. In that case, migration of chloride ions in cement-based materials is one of the main factors considered for the design of durability of concrete structures. Therefore, investigation on measurement of chloride migration in cement-based materials, especially using quick methods, is rather significant. This study investigated factors affecting AgNO3 colorimetric method and its use for rapid measurement of chloride migration in cement-based materials.Based on phase equilibrium in four-component system of AgNO3-NaOH-NaCl-H2O, equations for calculation of chloride concentration at the color change boundary (Cd) during AgNO3 colorimetric measurement was derived. Results indicated that Cd depended on sprayed concentration and volume of AgNO3 solution. When AgNO3 could react with all Cl- and OH- at the color change boundary, Cd increases linearly with OH- concentration. When AgNO3 react only with partial Cl- and OH- at the color change boundary, OH- has little effect on Cd and Cd increases with molar mass. Calculated range of Cd explained why Cd measured by many researchers change in a broad range.Based on calculation of Cd and investigation on factors influencing Cd, a reasonable AgNO3 colorimetric procedure was proposed and Cd values of cement-based materials were measured according to this procedure. Results indicated that the measured Cd decreased with water/binder ratio. Representative value of Cd was chosen for Cd range of each type of specimen with certain water/binder ratio.Based on diffusion electrical double layer of chloride absorption, chloride ion "condensation" phenomena was explained through measurement and analysis of related parameters. Results showed that there existed real chloride ion "condensation" in cement-based material, so-called chloride ion "condensation" is that chloride ion concentration in expressed pore solution of cement-based materials is higher than that in bulk pore solution owing to expression measurement. Measurement of free chloride in cement-based materials was investigated using water extraction method. Based on good repeatability and good linear or power correlation between water soluble chloride concentrations and free chloride concentration in expressed pore solution, water extraction method could be regarded as an effective procedure for the measurement of free chloride concentration in cement-based materials.Error of electrically accelerated non-steady state chloride ion migration coefficient (Dnssm) using AgNO3 colorimetric method was evaluated. Results indicated that when chloride color change depth was relatively small and sprayed volume of AgNO3 solution was not controlled, error of Dnssm caused by Cd could even reach 200%. When the AgNO3 colorimetric procedure established in this paper was used, error of Dnssm caused by Cd could be less than 5%.Some critical requirements for accurate measurement of chloride apparent coefficient (Dapp) using AgNO3 colorimetric method were proposed and experimentally investigated. The sensitivity and error of Dapp measured by AgNO3 colorimetric method were evaluated. Results indicated that sensitivity and error of Dapp measured by AgNO3 colorimetric method decreased with the increase of surface chloride concentration (Cs) and decrease of Cd. Based on the AgNO3 colorimetric procedure established in this paper, when Cs is equal to 0.53 mol/L (similar chloride ions in seawater) and 2.8 mol/L (chloride ions concentration of immersion solution used in NT build 443), respectively, errors of Dapp measured using AgNO3 colorimetric method caused by Cd changed within 17.1% and 2%, respectively. When average chloride ion chloride concentration in the first 2mm layer of specimens is similar to that in the immersion solution used in NT build 443, Dapp values measured by AgNO3 colorimetric method is very similar with those measured by NT build 443. Therefore, Dapp in cement-based materials can be rapidly and accurately measured by AgNO3 colorimetric method.更多还原