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。     

混凝土中氯盐含量与钢筋锈蚀问题

氯盐是引起钢筋锈蚀的主要因素之一,直接影响钢筋混凝土结构物的耐久性,这一事实已越来越引起人们的重视。混凝土中的氯盐主要来源于防冻盐、外加剂(如氯化钙)和含氯盐环境(如海水)等。当混凝土中氯离子达到一定量时,钢筋便开始锈蚀。随着锈蚀的发展和锈蚀产物的聚集,将最终导致混凝土保护层的开裂和剥落,进而危及结构物的安全。国内已陆续出现不少因钢筋锈蚀而导致结构物损坏的实例。关于海工工程的钢筋锈蚀问题,已有一些调查研究报告。值得提及的是,五十年代末期的一些建筑物,因施工过程中不适当地加入氯盐,致使钢筋锈蚀问题不断出现。一些工业、民用建筑,乃至国家重要建筑物,     

关于氯盐对钢筋锈蚀影响的讨论

氯盐能引起混凝土中钢筋锈蚀,从而影响结构物的耐久性,这已是公认的。氯盐对钢筋混凝土的危害作用,越来越引起一些国家的重视。据美国国家标准局统计,美国的年腐蚀损失约占国民经济总产值的3～5％,其中40％是由于混凝土中钢筋锈蚀引起的,而氯盐则是最主要的腐蚀因素。为控制氯盐的腐蚀,一些国家在有关规程、规范中,对混凝土中或使用环境中氯盐的限量做出了相应规定。氯盐主要由两种途径进入到混凝土中,其一是在施工过程中混入氯盐外加剂,拌合水、骨料中含有氯盐等;其二是由使用环     

钢筋混凝土结构冬期施工质量事故分析

一、抗冻外加剂掺量不符合要求而出现质量事故 1.掺氯盐过量造成钢筋锈蚀在混凝土冬施中,掺过量的氯盐,造成“钢筋生锈。由于受锈膨胀力作用,使钢筋保护层处的混凝土被胀裂或脱落。一般在交付使用后两年左右,混凝土构件沿主筋开裂,越裂越严重,最后钢筋周围的混凝土保护层完全脱落,使钢筋外露产生更严重的锈蚀,经数年的锈蚀过程,能使受力钢筋截面减少,从而影响结构的承载能力。     

外加剂与混凝土耐久性（上）

随着外加剂应用的日益广泛,外加剂对混凝土耐久性的影响问题也引起了人们的关注。本文从氯盐对钢筋锈蚀的影响,硫酸盐对混凝土的侵蚀作用,高效减水剂与混凝土耐久性的关系这三个方面,较全面地论述了外加剂与混凝土耐久性的关系问题。     

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     

海砂与钢筋锈蚀

氯盐能引起混凝土中钢筋锈蚀,从而影响钢筋混凝土结构物的耐久性。在此方面,国内外已有不少经验和教训,并有更加严格控制氯盐在混凝土中限量的趋势。氯盐一方面来自于混凝土原材料,如拌合水、海砂及氯盐外加剂等;另一方面来自于使用环境,如海洋及沿海地域的结构物经常受到氯盐的侵蚀。海砂是一种可用的资源,我国海岸线长,目前沿海建设发展迅速,已有一些单位直接使用海砂作为混凝土的细骨料,一方面有就地取材、充分利用资源之便;另一方面也为钢筋锈蚀增加了新的因素,有认真对待     

氯盐对混凝土结构耐久性的危害分析及对策

钢筋锈蚀是影响混凝土结构耐久性的最主要原因,而氯盐又是影响钢筋锈蚀的主要因素之一。因此,本文以氯盐对钢筋混凝土结构腐蚀破坏为研究对象,指出了钢筋锈蚀的机理,钢筋锈蚀对结构性能的影响等,并对防氯盐侵蚀破坏提出了几点措施。     

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.     

钢筋混凝土中氯离子侵蚀探讨

对钢筋锈蚀的发生机理、影响因素进行了探讨，对氯盐引起的钢筋锈蚀现象进行了简要剖析，并着重分析了氯离子在混凝土中的扩散速度公式及钢筋锈蚀的有关临界值，为科研和工程实践提供理论指导。     

Effect of chloride concentration in soil on reinforcement corrosion

This paper presents results of a study conducted to evaluate the effect of chloride concentration in soil on corrosion of reinforcing steel in concrete. Concrete specimens prepared with Type I, Type V and silica fume cements were exposed to soil with a chloride concentration of up to 3%. The effect of chloride concentration in soil on corrosion of reinforcing steel was evaluated by measuring corrosion potentials and corrosion current density. After 18 months of exposure, the concrete specimens were broken and the extent of corrosion of the reinforcing steel was examined and the gravimetric weight loss due to corrosion was assessed. As expected, the degree of corrosion increased with the chloride concentration in the soil. The type of cement also influenced the extent of reinforcement corrosion. For a particular chloride concentration, least reinforcement corrosion was noted in the silica fume cement concrete followed by Type I and Type V cement concrete. Based on the data developed in this study chloride threshold values in soil for the three types of cements investigated are suggested.     

碱矿渣混凝土氯离子渗透及钢筋锈蚀性能

氯离子渗透是造成混凝土中钢筋锈蚀的主要原因之一.采用ASTM C1202规定的氯离子渗透试验方法及浸烘循环试验,研究了矿渣细度、溶矿比对碱矿渣混凝土氯离子渗透及钢筋锈蚀性能的影响,并探讨了碱矿渣混凝土电通量和钢筋失重率之间的关系.研究表明:在其他条件相同时,随矿渣细度增大,碱矿渣混凝土氯离子渗透性降低,抗钢筋锈蚀性能增强;随溶矿比增加,碱矿渣混凝土氯离子渗透性升高,抗钢筋锈蚀性能减弱;且6 h通过碱矿渣混凝土的电通量和钢筋失重率之间存在一定的相关性.     

氯离子侵蚀效应对RC桥墩抗震性能的影响

为研究混凝土桥梁结构在服役期内由于环境氯离子侵蚀效应引起钢筋、混凝土锈蚀退化等导致结构抗震性能退化的规律,以某多跨钢筋混凝土连续梁桥为例,采用OpenSees软件建立非线性动力分析模型,根据已有研究成果并基于概率方法研究了墩柱截面主筋和箍筋锈蚀的开始时间和锈蚀率大小,进而建立了钢筋的直径及屈服强度退化模型;针对考虑纵筋锈蚀、考虑箍筋锈蚀、同时考虑纵筋和箍筋锈蚀3种情况,分别分析了材料退化对桥墩抗震性能的影响。结果表明:同等条件下箍筋锈蚀比纵筋锈蚀更早;随着时间的推移,氯离子侵蚀效应会导致桥墩抗震能力下降,结构的抗震需求明显增加;与以往只考虑纵筋锈蚀的情况相比,同时考虑箍筋和纵筋锈蚀时桥墩抗震性能退化更严重。     

混凝土构件中钢筋锈蚀的中子断层扫描成像

制备了小型混凝土构件,通过三点弯曲诱导裂缝和氯盐溶液干湿循环加速其中钢筋锈蚀,采用自然电位法监测钢筋的腐蚀电位,并采用中子断层扫描成像技术对钢筋锈蚀产物分布进行了分析.结果表明:钢筋混凝土构件经过85次氯盐溶液干湿循环后,采用中子断层扫描成像技术对其进行三维扫描成像,可直观呈现钢筋锈蚀产物分布状况;钢筋锈蚀产物集中分布于裂缝断面钢筋与基体界面的底部区域,并沿界面逐渐向外扩展,符合氯盐诱导钢筋锈蚀的坑蚀规律.这为研究混凝土结构中钢筋的锈蚀机理提供了一种新的试验方法.     

氯盐环境自密实混凝土钢筋腐蚀速率试验

主要研究外渗氯盐侵蚀下的钢筋腐蚀,对比普通混凝土和自密实混凝土内钢筋的腐蚀电流密度时变曲线,对两种混凝土试件中钢筋的腐蚀速率进行分析和研究.试验结果表明:自密实混凝土内钢筋的腐蚀比较迟缓,初始的腐蚀速率较小,但最大腐蚀速率和总体腐蚀规律都与普通混凝土内钢筋基本一致.     

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.     

Utilisation of electrical resistance method for the evaluation of the state of steel reinforcement in concrete and the rate of its corrosion

In this paper, the applications of an electrical resistance method for monitoring of the state of steel reinforcement in concrete and its rate have been described. The following possibilities of the method were shown: an estimation of quantitative data on corroding steel reinforcement, including the values of a cross-sectional decrease, the depth of the corroded layer, the mass loss of steel material due to corrosion; the possibility of the mathematical modelling of the dependence of the rate of steel reinforcement on important factors like ambient relative humidity, concentration of chloride in embedding concrete and others; and obtaining quantitative data on corroding steel reinforcement by means of a potentiodynamic method through the results of the electrical resistance method and the related mathematical relationship.     

普通硅酸盐混凝土中临界氯离子浓度的试验研究

为得到含氯环境下普通硅酸盐混凝土中钢筋的开始腐蚀时间,首先应掌握的一个重要参数是临界氯离子浓度,此参数因受多种因素影响而数值分布较广。本文基于在脱钝过程中钢筋腐蚀电位集中体现了多因素的综合作用的观点,通过以下三部分工作对临界氯离子浓度进行了研究:首先,利用静电位法,在模拟溶液中测试了氯离子浓度与点蚀电位之间的关系,电位的变化范围取-350￣ 100 mV(SCE);然后,将钢筋混凝土试块放置在三种典型环境中(干燥、湿润、浸润环境),分别测试了三种环境下钢筋腐蚀电位的分布范围;最后,基于钢筋脱钝的两个必要条件:足够小的混凝土电阻以及腐蚀电位超越点蚀电位,得到针对三种腐蚀环境的以占水泥用量比例表示的总氯离子浓度取值。     

Performance of generic and proprietary corrosion inhibitors in chloride-contaminated silica fume cement concrete

This paper presents the results of a study conducted to evaluate the improvement in corrosion-resistance of chloride-contaminated silica fume cement concrete due to the use of corrosion inhibitors. Three proprietary and one generic corrosion inhibitors were evaluated for their performance in inhibiting reinforcement corrosion in the silica fume cement concrete specimens contaminated with 0.4%, 1%, and 2% chloride concentration, by weight of cement. Some of the specimens were subjected to wetting and drying cycles and reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. Another batch of concrete specimens was partially immersed in the chloride solution and reinforcement corrosion was accelerated by impressing an anodic potential of 2 V. The extent of corrosion increased with increasing chloride contamination in the concrete specimens. Incorporation of inhibitor generally decreased the rate of reinforcement corrosion. The rate of reinforcement corrosion in the concrete specimens incorporating an organic inhibitor that was added to the concrete during mixing was the least followed by that in the concrete specimens on which a penetrating corrosion inhibitor was applied. Further, the accelerated impressed current technique was noted to be suitable for quickly screening the performance of corrosion inhibitors.     

Performance evaluation of rebar in chloride contaminated concrete by corrosion rate

The presence of chloride ions in reinforced concrete (RC) plays a major role in reinforcement corrosion and hence for the durability and service life of RC structures. With growing concern towards the deterioration of reinforced concrete structures, the use of electrochemical techniques for their performance evaluation has become an important topic of durability study. This paper illustrates the findings of an experimental investigation carried out on large number of specimens for evaluating the performance of different types of rebar in chloride contaminated concrete made with different types of cement through different corrosion rate techniques. The specimens were prepared with three types of cement and three types of steel. From the results of corrosion rate, it was observed that the values of corrosion rate obtained by linear polarization resistance (LPR) technique with guard ring arrangement were in close agreement with those obtained by gravimetric method. On the other hand the corrosion rate values obtained by AC impedance spectroscopy were slightly lower than those obtained by LPR measurement. Further, correlations between different corrosion rate techniques were also obtained. From the results of analysis of variance (ANOVA), it was observed that chloride content has the strongest effect on corrosion rate as compared to other factors.