海底隧道二衬混凝土寿命预测模型研究

翔安海底隧道设计使用年限100年以上,属一级重要基础设施工程,为了达到设计使用年限,二衬混凝土的寿命研究意义重大.充分考虑技术服役寿命,采用合适的寿命预测方法,建立预测寿命模型,将[Cl-]与[OH-]定为腐蚀变量,对混凝土碳化及氯离子渗透作用于混凝土造成钢筋锈蚀的临界值及其经时变化模型进行分析,计算该结构的使用寿命,...     

氯盐环境下粉煤灰-混凝土中钢筋的锈蚀过程

为分析氯盐环境下粉煤灰对混凝土中钢筋锈蚀过程的影响,设计制作了粉煤灰掺量为0%、10%和20%的水泥净浆-钢筋试件,并在质量分数为3.5%NaCl溶液中进行了钢筋腐蚀过程的电化学测试和水泥浆体的微观测试,获得了不同浸泡时间条件下的Tafel极化曲线、电化学阻抗谱(EIS)曲线、水泥浆体的物相组成和钢筋表面脱钝氯离子阈值,分析了粉煤灰掺量对试件中钢筋腐蚀过程和水泥浆体物相组成的影响.结果表明:用粉煤灰部分替代水泥可以增加混凝土中钢筋的脱钝锈蚀时间,提高水泥浆体中C-S-H凝胶和Friedel's盐的含量,但会降低钢筋表面脱钝氯离子阈值.因此,在混凝土中掺入适量粉煤灰可以提高水泥浆体对氯离子的固化能力,延缓混凝土中氯离子的传输进程,改善氯盐环境下混凝土结构的耐久性能.     

碳化对混凝土钢筋锈蚀的影响

因混凝土碳化引起的钢筋腐蚀造成结构破坏的问题非常普遍和严重。本文研究内容包括在碳化环境下不同品种水泥（普通硅酸盐水泥和石灰石水泥）,不同矿物掺合料,内掺氯盐（试样成型时掺入一定的氯盐）等对钢筋腐蚀速率的影响。试验采用高浓度碳环境使砂浆保护层在较短时间内碳化。实验通过对普通硅酸盐水泥和石灰石水泥的测试得出了他们之间在锈蚀程度上的差异。论文中,主要研究了混凝土用钢筋在碳化条件下的腐蚀性能。     

海洋环境下受荷混凝土中钢筋锈蚀研究

海洋环境下的混凝土结构同时受到二氧化碳和氯离子侵蚀,钢筋锈蚀十分严重。文中通过氯盐浸泡与加速碳化循环的方法来模拟海洋环境,采用螺杆对混凝土进行加载,研究了荷载水平以及矿物掺合料对钢筋锈蚀的影响。试验结果表明:钢筋锈蚀率随着荷载水平的升高而增大,掺入矿物掺合料使钢筋的锈蚀率增大。氯盐浸泡与加速碳化循环的试验方法能表现出自然条件下碳化与氯离子侵蚀时钢筋的锈蚀形态,对模拟真实海洋环境下混凝土中钢筋锈蚀的发展规律具有一定的借鉴意义。     

碱渣用作矿物掺合料对混凝土性能影响的试验研究

碱渣是氨碱法制纯碱排出的废渣,由于含有大量的可溶性氯离子,碱渣直接用作混凝土掺合料时,会导致钢筋锈蚀,从而大大降低建筑物的使用寿命。为解决碱渣应用的难题,对原状碱渣采用工艺处理得到不同氯离子含量的水洗碱渣和除氯碱渣,研究了三种碱渣对混凝土性能的影响。结果表明,碱渣掺入会严重降低混凝土的工作性能,但可以通过增加减水剂掺量的方式调节;在碱渣掺量为10%时,用碱渣等量取代粉煤灰或水泥时混凝土强度均略有增大;较高氯离子含量的原状碱渣和水洗碱渣均会造成钢筋锈蚀,只有氯离子含量低于0.30%的除氯碱渣可作为混凝土矿物掺合料使用,且无需掺加阻锈剂。     

钢筋混凝土中氯盐掺量的选定

<正> 建筑系统利用氯盐作为混凝土早强剂和抗冻剂已有二十多年的历史。由于掺量过多,致使钢筋混凝土中的钢筋锈蚀,甚至造成建筑物毁坏。目前有关规范规定氯盐的掺量不超过水泥重量的2％。试验表明,钢筋混凝土中的氯盐掺加量达2％时,能促进钢筋显著锈蚀。本文试图提出氯盐最佳掺量。氯盐对钢筋锈蚀的影响钢筋混凝土中的钢筋产生锈蚀,其影响因素很多,而且     

氯离子侵蚀环境下钢筋混凝土构件的耐久性

钢筋锈蚀是影响钢筋混凝土结构耐久性的最关键问题,也是混凝土结构最常见和量最大的耐久性问题。当混凝土成型时使用了含氯离子的原材料,如海沙、海水或含氯的外加剂等,或混凝土结构处于使用含氯原材料的工业环境、海洋环境、盐渍土与含氯地下水的环境和使用化冰盐的环境中,氯离子通过构件表面侵入到混凝土内部,达到钢筋表面,钝化膜也会提早破坏,钢筋锈蚀就会更严重。随着混凝土保护层的剥落,钢筋锈蚀加速,直到构件破坏。目前对影响钢筋锈蚀的因素、钢筋锈蚀速度、锈蚀后钢筋力学性能的变化、钢筋锈蚀的防护和检测等有较多的研究,但是还没有建立一个公认的钢筋锈蚀量计算模型。     

碳化与氯盐对混凝土孔溶液中钢筋钝化的影响

采用X射线衍射(XRD)、X射线光电子能谱(XPS)和扫描电子显微镜(SEM),研究了碳化与氯盐腐蚀作用下,混凝土孔溶液中钢筋锈蚀物的组成和微结构特征,阐明了腐蚀因素作用下钢筋的腐蚀机理.结果表明:含氯盐混凝土孔溶液中钢筋表面钝化膜和锈蚀物共存,锈蚀物表面较为致密,主要组成为FeOOH和FeO;碳化混凝土孔溶液中钢筋表面有黄黑色锈蚀物生成,锈蚀物呈疏松多孔棒状,主要组成为FeOOH、Fe_3O_4和Fe_2O_3;碳化与氯盐复合混凝土孔溶液中钢筋表面有大量黄褐色锈蚀物生成,锈蚀物表面呈分层剥落状,主要组成为FeOOH、Fe_3O_4和FeCl_3,其中FeOOH含量高达60%以上;从含氯盐混凝土孔溶液到碳化混凝土孔溶液再到碳化与氯盐复合混凝土孔溶液,钢筋锈蚀物中Fe的XPS扫描峰值逐渐增强,Fe的氧化物含量增多,钢筋腐蚀越来越严重.     

氯盐侵蚀下再生混凝土氯离子侵蚀和钢筋锈蚀规律研究

为探究再生混凝土的耐久性能,对氯盐环境下具有类似配合比的再生混凝土和普通混凝土抵抗氯离子侵蚀能力以及内部钢筋锈蚀规律进行对照研究。利用快速氯离子含量检测仪来检测氯离子分布的深度和浓度;采用Reference 600TMPotentiostat/Galvanostat/ZRA电化学工作站,应用线性极化原理对再生混凝土和普通混凝土内部钢筋锈蚀参数进行长期测试。试验结果表明再生混凝土氯盐侵蚀程度及内部钢筋锈蚀均较普通混凝土严重。     

混凝土中钢筋锈蚀的氯离子临界浓度及规范

钢筋锈蚀是钢筋表面的氯离子达到一定浓度时发生的现象,但为防止钢筋锈蚀而设定氯离子临界浓度是很困难的。影响钢筋锈蚀临界浓度的因素很多,目前还没有得到充分解答。本研究通过实际试验,分析研究水泥单位量或种类等因素对氯离子临界浓度的影响,并利用电子探针法实际算出氯离子临界浓度。结果表明:混凝土重量标注的临界浓度,与单位水泥量成正比,用水泥质量标注,与水泥量无关。掺入粉煤灰的水泥钢筋锈蚀临界值,要比掺入普通硅酸盐水泥时低,掺入矿渣水泥时反而临界值增大。因此,要考虑混凝土中钢筋锈蚀机制,确定氯离子相关参数很重要。徐永模     

掺防冻剂混凝土中亚硝酸盐的长期阻锈效果

含防冻剂混凝土加速钢筋腐蚀时确定了氯离子和亚硝酸根的迁移行为，并确定了混凝土中钢筋底部临界NO2^-／Cl^-摩尔比的变化。试验结果表明，含氯盐和亚硝酸盐防冻组分的混凝土由于泌水作用钢筋底部氯离子与亚硝酸根离子浓度较高，而NO2^-／Cl^-摩尔比随龄期变化不大，说明含氯盐混凝土中只要掺入足够NO2^-／Cl^-摩尔比的亚硝酸盐，可以保证亚硝酸盐的长期阻锈效果。     

Assessment of stainless steel reinforcement for concrete structures rehabilitation

The aim of this study was to revise the factors influencing the service life of galvanic coupling between carbon steel and stainless steel reinforcements in simulated concrete pore solution, simulating the condition of a damaged structure repaired with stainless steel reinforcing bars. Numerous investigations have reported that austenitic stainless steel rebar, compared to carbon steel, when embedded in concrete, offer superior corrosion resistance in aggressive environments, especially chloride contaminated concrete. In concrete, contact with other metals should be avoided because of the risk of galvanic corrosion. When passive, both carbon steel and stainless steel have comparable corrosion potentials and the coupling of the two materials is of little effect on the corrosion behavior of either material. Galvanic current values measured between carbon and stainless steel are negligible.     

掺防冻剂混凝土钢筋腐蚀程度的评价

含氯盐及亚硝酸盐混凝土中。通过加速腐蚀试验肉眼观察确定了抑制钢筋腐蚀所需临界摩尔浓度NO^-2／Cl^-比。试验结果表明,随着氯离子含量的增加,抑制钢筋腐蚀所需临界摩尔浓度越高。当氯离子含量达到4kg／m^3时,NO^-2／Cl^-摩尔比约大干1．2时能够完全抑制混凝土中钢筋腐蚀。     

表面防水处理对氯离子侵蚀混凝土中钢筋锈蚀的影响

采用半电池电位法对四种不同条件下钢筋混凝土中的钢筋锈蚀情况进行了测定,分析了硅烷溶液防水剂、Cl-及水胶比对钢筋锈蚀的影响.试验结果表明:水胶比越大,钢筋开始锈蚀的时间越早,锈蚀的程度越严重;对于含有初始氯离子并且锈蚀已经发生的钢筋混凝土,表面防水处理不能够有效控制钢筋锈蚀;对于有外界Cl-侵蚀的钢筋混凝土,硅烷溶液防水剂能有效地降低由于Cl-引起的钢筋锈蚀的概率,并且延缓钢筋锈蚀的时间.     

The impact of fire and fire extinguishing method on the corrosion behavior of the steel bars in concrete pore solution

Exposure of reinforced concrete structural elements to high temperatures, e.g. fire, remains one of the serious potential risks to such structures. This exposure can lead to losses in concrete structural capacity, possible plastic deformation of embedded steel and loss of bond between reinforcing steel and concrete. The level of temperature and the method of extinguishing the fire alter the microstructure of reinforcing steel bars. This microstructure alteration changes the corrosion behavior of steel in such structures, when exposes to chloride ions. The present study was undertaken to determine the impact of exposure of steel to high temperature and the method of extinguishing the fire on its corrosion behavior in alkaline environment of concrete in presence of chloride ions. Results indicated that exposure of steel to high temperatures, regardless of its level; made steel more susceptible to corrosion compared to the reference case, when steel was kept at room temperature. The worst case happened for the steel exposed to 850 °C for an hour, then cooled rapidly in water, where the corrosion rate increased approximately 60% in chloride contaminated concrete pore solution.     

Influence of detection methods on chloride threshold value for the corrosion of steel reinforcement

The aim of this study is to evaluate the influence of depassivation detection methods on chloride threshold value for the corrosion of steel reinforcement in a concrete. The detection methods of depasstivating steel reinforcement have been examined including electrochemical impedance spectra (EIS), potentiodynamic polarization (PP) in a simulated concrete pore solution and half-cell potential, linear polarization (LP) and electrochemical impedance spectra (EIS) in the concrete contaminated by chloride ions. The results have indicated that in a saturated Ca(OH)₂ solution, the chloride threshold value for the corrosion of steel reinforcement concluded by the potentiodynamic polarization is 0.02 mol/L, which is identical with that decided by EIS. However, in the chloride contaminated concrete, no agreement among the chloride threshold values determined by the three detection methods mentioned above can be found. The range of the values decided by half-cell potential is relatively lower than those by the others, besides, the highest values have been obtained by EIS.     

Reliability-based design method of suppressing chloride ingress for reinforced concrete buildings located in coastal regions of Taiwan

The main purpose of this work is to propose an estimating procedure that building designers can use to choose methods of suppressing chloride ingress, i.e. concrete-cover thickness, concrete-surface coating and concrete mix (water–cement ratio), for reinforced concrete (RC) buildings with a specified durability performance. At first, the authors build equations for estimating airborne chloride concentrations in coastal regions in Taiwan by regressing measurement data. Then, an analytical model incorporates these data into a deterioration model for chloride-induced corrosion and to estimate corrosion of reinforcing steel bars. This work also presents a novel computational procedure to calculate the risk of corrosion for reinforcing steel bars embedded in concrete, while considering uncertainties in environmental conditions, material properties and model error. Using risk curves of corrosion, building designers can set an allowable durable reliability to determine the minimal required concrete-cover thickness for RC members. Finally, this work adopts coastal regions in Taiwan as an example to determine the minimum required concrete-cover thicknesses. Furthermore, reliability-based methods of suppressing chloride ingress for RC buildings are also suggested for each division zone of Taiwan.     

Corrosion rate of ordinary and high-performance concrete subjected to chloride attack by AC impedance spectroscopy

Corrosion of reinforcing steel in concrete is studied by using AC impedance. Subjected to different conditions and chloride concentrations, a laboratory study was conducted to estimate the corrosion rate of reinforcing steel embedded in ordinary Portland concrete (OPC) and high-performance concrete (HPC).One hundred and four OPC and HPC concrete cylinders embedded with a single reinforcing steel bar were exposed to sodium chloride solution with 0%, 1%, 3% and 5% concentrations. Specimens were also subjected to pre-conditioning and drying-wetting cycles.The AC Impedance technique (IS) was used to determine the corrosion rate of the reinforced concrete cylinders. In order to interpret the AC impedance spectra, several electrical equivalent circuits were employed.This investigation aims to compare IS with commonly used corrosion assessment techniques, such as Tafel plot (TP) and linear Polarization (LP).Results confirm that data obtained from AC impedance can be used to calculate the corrosion rate of reinforcing steel. A reasonable agreement with the results of TP and LP techniques is demonstrated. It is found that the corrosion rates obtained by AC impedance technique are lower than TP by 5–20%, while results of LP are 20–30% higher than those of TP.     

混凝土结构钢筋脱钝的随机可靠度分析

根据混凝土临界氯离子浓度和氯离子扩散系数与水灰比、环境温度等的关系式,计算出不同条件下受氯盐侵蚀混凝土结构50年内钢筋表面的氯离子浓度。在分析钢筋混凝土结构钢筋表面氯离子浓度随服役年限关系的基础上,用Monte Carlo方法对钢筋脱钝的随机可靠度进行分析。对保护层厚度、水灰比和环境温度等随机变量对海工混凝土结构钢筋脱钝概率的影响进行探讨。     

钢筋混凝土中钢筋的氯诱导腐蚀

钢筋的氯诱导腐蚀是钢筋混凝土中钢筋腐蚀的最主要的原因之一，它会引起钢筋表面钝化膜的局部破损。混凝土中氯离子来自于采用的受污染的原材料和外界环境中氯离子的渗入。测定氯离子的阀值是众多研究的主要目标之一。由于氯离子阀值受许多因素影响，目前尚无确定的阀值。因此，对受氯离子污染的混凝土来说，对氯离子的活性及钢筋的状态的监测尤其重要。许多电化学方法，例如半电池电势、直流极化电阻、电化学阻抗谱和静电脉冲技术等已经广泛应用于研究和现场监测中，实践证明这些技术也是非常有力的工具。本文对钢筋氯诱导腐蚀的现状作了详细概述。