基于EIS研究镁水泥混凝土中涂层钢筋的耐腐蚀性

通过模拟室内自然状态、氯化镁溶液和水三种工作环境,采用CS350电化学工作站,结合理论与试验分析,对镁水泥混凝土涂层钢筋的交流阻抗谱进行研究。结果表明:通过对交流阻抗谱和涂层电阻的表征分析得出该涂层可以很好地保护镁水泥混凝土中的钢筋免受腐蚀。不同的混凝土保护层厚度对同时期的涂层电阻有一定的影响,涂层电阻的大小随保护层厚度增加而增加。从而得出该涂层对镁水泥钢筋混凝土中的钢筋起到很好的保护作用,进而解决镁水泥钢筋混凝土在盐渍土地区应用易受侵蚀的问题。     

基于氯盐侵蚀的钢筋混凝土桥面板寿命预测

基于考虑温湿度耦合传导下的氯离子在非饱和混凝土内的渗透数值模型,以中国香港沿海处的某座钢筋混凝土高架桥为研究对象,预测临空区桥面板的腐蚀开始时间。系统分析了初始温湿度的变化、水灰比、保护层厚度及矿物掺合料对钢筋腐蚀开始时间的影响。结果表明:较高的初始温度和相对湿度能够延缓结构腐蚀开始时间;混凝土水灰比和保护层厚度是影响构件抗氯离子腐蚀的主要因素;添加粉煤灰或矿渣均能明显提高混凝土抵抗氯离子的侵蚀能力。提出氯盐侵蚀下钢筋混凝土桥面板腐蚀开始时间的简化公式,指出当水灰比小于0.4时,采用年平均值来表征环境变量边界条件的变化是比较合理的。     

混凝土设计参数对氯盐环境下钢筋锈蚀的影响研究

研究了混凝土设计参数包括水胶比、胶凝材料组成、保护层厚度和混凝土氯离子含量等对氯盐环境下混凝土中钢筋锈蚀的影响。通过模拟氯盐环境下混凝土中钢筋所处的锈蚀环境,并以一定的方法加速混凝土中钢筋的锈蚀,采用电化学测试手段(钢筋腐蚀电位和钢筋腐蚀电流密度)来评价各设计参数对钢筋锈蚀的影响。结果表明,水胶比越小、保护层厚度越大、混凝土氯离子含量越小、使用矿物掺合料能有效延缓钢筋开始锈蚀时间,并在不同程度上减小钢筋的锈蚀速率。试件在试验一段时间后被破损,将钢筋周围砂浆制样并进行SEM扫描电镜元素分析试验,进一步验证电化学测试方法的准确性及钢筋的锈蚀程度。     

西部氯盐渍土介质中混凝土的氯离子扩散性

为研究西部氯盐渍土介质中混凝土的氯离子扩散性,采用实验分析、微观扫描、理论预测相结合的方法,分析混凝土中氯离子含量与分布规律、氯离子对流区深度与峰值含量、表层氯离子含量时变规律以及试件表层微观形貌,预测既定混凝土保护层厚度处达到钢筋锈蚀临界氯离子浓度所需时间。研究结果表明,沿扩散深度混凝土中自由氯离子含量与总氯离子含量均呈现出先增长后降低的趋势,二者具有很好的线性关系;存在明显的氯离子含量峰值,随浸泡时间的变化较小;随着浸泡时间的增加,对流区深度逐渐加大,表层氯离子含量逐渐增加,混凝土中Friedel’s和Cl元素逐渐增多。理论分析结果显示,氯离子扩散系数随着扩散深度增加而增大,随浸泡时间增加而减小,使用寿命预测结果与工程实际混凝土结构腐蚀情况吻合较好,预测模型可用于西部氯盐渍土介质中混凝土结构使用寿命预测与分析。     

钢筋混凝土结构中钢筋保护层质量控制的措施

钢筋保护层是保证钢筋混凝土结构物耐久性的重要构造,在精细化施工的今天,不仅要求结构物质量合格,还要求耐久性要好,因此必须控制耐久性指标,包括钢筋保护层、氯离子含量、钢筋锈蚀、混凝土碳化等指标,本文重点论述施工中如何控制钢筋保护层质量,使保护层符合设计要求。笔者通过箱梁预制的施工,总结了一些提高钢筋保护层合格率的经验,以期对今后钢筋保护层合格率的提高提供一些方法和措施。     

混凝土管支架群腐蚀状况的普查、抽检及评价

对某大型石化企业18条管线的在役钢筋混凝土管支架立柱逐一检查外观状况并划分成5个等级,抽检了混凝土强度、保护层厚度、碳化深度、钢筋截面损失率、混凝土pH值和氯离子含量,用EDS结合容量法分析了混凝土和钢筋的腐蚀产物.结果显示,在役支架外观状况与混凝土性能有密切的关系,混凝土强度与外观等级呈反比,而碳化深度则与其呈正比;大多数管支架的混凝土强度虽然能够满足原设计要求,但是碳化深度接近保护层厚度,而且[Cl-]/[OH-]值几乎全都大于0.6,钢筋具备了开始腐蚀的条件;聚酯管线和炼油南管线的管支架腐蚀较为严重,需及时采取有效的防腐蚀和补强措施.     

混凝土内氯离子扩散影响因素的研究综述

随着建筑行业的迅速发展,钢筋混凝土结构得到了广泛应用.但钢筋混凝土结构长期处在氯盐环境中易发生钢筋腐蚀现象,从而降低结构的耐久性.因此,全面系统地认识混凝土内氯离子扩散的影响有助于解决结构氯盐侵蚀问题.氯离子在混凝土中的传输机制极其复杂,其中扩散是氯离子传输的主要机制.文章梳理了国内外近年来关于混凝土内氯离子扩散的研究进展,重点评述了混凝土内氯离子扩散的影响因素,笔者认为低水灰比、加入掺和料、适当增加保护层厚度、限制裂缝宽度等基本措施可以有效减缓钢筋腐蚀.若结构处于恶劣环境中,在采取基本措施的基础上,还需要进一步采取附加措施,主要包括添加缓蚀剂、进行表面涂层、电化学处理等.这些措施得到了一系列的理论及试验验证,为工程应用提供了可行性参考.     

海工结构服役寿命及保护层开裂模式细观数值模拟

通过在钢筋与混凝土交界面处施加时变边界位移建立非均匀锈蚀钢筋锈胀模型,其中混凝土损伤本构采用指数应力软化模型,时变边界位移采用Faraday定律对氯离子浓度积分计算得到.参数化分析保护层厚度、钢筋位置、钢筋直径等因素对服役寿命及保护层开裂模式的影响.研究结果表明,服役寿命随保护层厚度增加而增长,而且增加幅度逐步增大,而钢筋直径变化对服役寿命影响较小,角部钢筋锈蚀则导致结构服役寿命缩短;中部钢筋的锈蚀使得保护层出现三条主裂缝,当保护层较小,保护层破坏模式为凸起式破坏,保护层较大时则将出现层裂;同时,角部钢筋锈蚀将在保护层内形成两条主裂纹,最终导致角部保护层脱落.     

浅谈影响污水处理构筑物质量的主要问题及对策

本文提出了混凝土碱骨料反应和钢筋混凝土保护层厚度不够对污水处理构筑物质量的影响及防治对策。     

浅谈钢筋混凝土保护层质量控制问题

钢筋混凝土保护层能够增强结构耐久性,控制保护层的质量,首先控制混凝土的质量,其次控制保护层的厚度,本文将就混凝土保护层质量控制措施进行简探讨。     

Chloride ingress in microsilica concrete

The paper presents experimental results on chloride ingress and water absorption of microsilica concrete. To investigate the interaction of cement, water and microsilica content on diffusion characteristics and porosity (water absorption), 36 concrete mixes with water/cement ratios ranging from 0·4 to 0·9 and cement contents between 250 and 450 kg/m³ were studied. The microsilica content varied between 5 and 15%. Curing was under two conditions, 20°C, 100% RH and 35°C, 25% RH.

The results show that a relationship exists between chloride concentration and W/C ratio, the relationship being different for the various microsilica contents. The effect of high W/C ratios is much more pronounced in low microsilica content mixes (0 and 5% addition). The chloride ingress is also sensitive to cement content in low microsilica contents mixes (0 and 5%), but not in high microsilica content mixes (10 and 15%).

The diffusion coefficient, D_c, is not significantly affected by microsilica content, for mixes made at a constant W/C ratio.     

梯度结构混凝土的传输性能与寿命预测

采用无细观界面过渡区水泥基复合材料制备出梯度结构混凝土的高抗渗保护层,且高抗渗保护层的最佳厚度为10～20mm,可以有效降低GSC的传输性能,大幅降低GSC的Cl-渗透性能,延长其使用寿命.与单层结构的高性能混凝土相比,不同厚度比例组合的GSC的C1-扩散系数DNEL均有不同幅度的下降,且随着MIF在GSC中厚度比例的增加,GSC的DNEL是降低的.当MIF在GSC中的厚度超过10mm时,GSC的DNEL会突降;当MIF在GSC中的厚度增加到25mm时,与HPC的DNEL相比,GSC的DNEL几乎下降了2个数量级,其Cl-渗透性能"极低".根据考虑多种因素作用下的Cl-散理论模型,当GSC的Cl-扩散系数为(2.0～3.0)×1013-13m2/s时,其理论预测使用寿命在1700年以上,可以说是一种超高耐久混凝土--千年混凝土.     

干湿循环作用下水泥基复合材料抗氯离子侵蚀性能及其微观结构变化

为了进一步揭示干湿循环条件下氯离子对水泥基复合材料的侵蚀机制,分别研究了两种水灰比水泥混凝土、砂浆及净浆三种层次试件在干湿循环条件下的抗氯离子侵蚀性能。结果发现,干湿循环作用能促进氯离子入侵速度,增加氯离子入侵深度和浓度,并且水胶比越大,干湿循环作用影响效果越明显;掺入矿粉能增加水泥基复合材料抗氯离子入侵性能,并且降低干湿循环作用的影响效果。净浆样品侵蚀前后的微观结构变化表明,干湿循环作用下,经氯盐侵蚀后水泥基复合材料净浆试件表层明显有Friedel盐生成,而矿粉的加入明显增加了样品中Friedel盐的生成量。     

饱和钢纤维再生混凝土氯离子扩散特性研究

利用废弃骨料制作再生混凝土是建筑固废弃物的再生资源利用途径之一,其在氯盐侵蚀环境条件下的耐久性规律与普通混凝土不同。本文以模拟海洋侵蚀环境,通过改变水灰比及NaCl溶液浓度,分析各因素对钢纤维再生混凝土氯离子扩散行为的影响规律。结果表明:浸泡液浓度越大,进入混凝土内部的氯离子越多,随着深度的增加氯离子含量逐渐减少;较低的水灰比与适量钢纤维的掺入均可以有效降低氯离子扩散系数,提升钢纤维再生混凝土的抗氯盐侵蚀能力;氯离子扩散系数随着NaCl溶液浓度的增加而增大。     

Influence of surface charge on ingress of chloride ion in hardened pastes

The amount of free chloride content in concrete is one of major factors in initiating the corrosion process. The material and environmental factors play a key role in diffusing the chloride ion through the cover concrete to reinforcement. Thus, the electrochemical study is indispensable to understand the mechanism of chloride ingress into concrete. Determination of surface charge and its influence on diffusion of chloride ion into cement matrix of concrete are researched for Ordinary Portland Cement (OPC) paste and cement paste containing Ground Granulated Blastfurnace Slag (GGBS). Different kinds of experiments such as measurement of membrane potential, determination of porosity and pore size distribution, determination of pore solution concentration, and steady state diffusion coefficient of chloride and sodium ions are employed to understand the mechanism of chloride ingress. The obtained results show that the positive surface charge on the pore walls of hardened paste regardless of GGBS’s presents. The surface charge of hardened paste mainly depends on pore solution concentration and cement composition. The physiochemical characteristics of the pores are affecting on transporting ions through it. Hardened paste has greater resistance to diffusing sodium ions than chloride ions. Moreover, there is a strong interaction between transport of chloride ion and surface charge in matured hardened paste.     

混凝土结构工程除盐的研究与应用

基于氯离子腐蚀混凝土的电化学机理,探讨了用电化学方法反其道而行消除混凝土中氯离子的原理、可行性与工程应用前景。通过除盐试验和除盐后混凝土构件受力性能试验,研究了影响电化学方法除盐效果的各种参数(如碱溶液、电极电位、电流密度、金属网腐蚀牺牲等)及其对混凝土结构性能的影响;分析了除盐后钢筋周围混凝土凝胶体孔隙内碱类物质的积聚,及其对钢筋与混凝土之间粘结力的影响。除盐后的拉拔试验和钢筋混凝土板的弯曲试验表明,除盐后钢筋与混凝土之间的粘结性能会受到损伤,但粘结力的损伤不会对混凝土构件的正常使用性能和承载能力造成显著影响。     

Effectiveness and structural implications of electrochemical chloride extraction from reinforced concrete beams

The overall aim of this paper is to examine the effectiveness and structural implications of electrochemical chloride extraction when applied to reinforced concrete beams containing chlorides as well as chlorides and reactive aggregates. Twelve beams, 100 × 165 × 2300 mm, were altogether cast and tested. The main variables in the beams were water/cement ratio, chloride content and reactive aggregates. Four of the beams contained a reactive aggregate in the concrete mix. All the beams were kept dry, after initial curing, to see if the electrochemical process triggered alkali silica reactivity. The chloride extraction process used an anode system of oxide coated platinised titanium mesh and saturated calcium hydroxide solution as electrolyte. The applied cathodic current density was about 1 A/m². Chloride analysis of the concrete in the beams was carried out before, during and after the electrochemical treatment, and the pH of the electrolyte and any alkali silica reactivity were regularly monitored. The beams were subsequently tested to failure at an age of about 400 days. It is shown that electrochemical treatment is an effective and efficient process to remove chlorides from the cover concrete and from the zone containing steel reinforcement without any adverse effect on structural strength, bond or shear. There was clear evidence that unlike cast-in chlorides, the chloride extraction process will be far more efficient in real structures where the majority of chlorides that would have penetrated into the concrete will be from the outside aggressive environment and which will remain mostly in the concrete cover zone. However, further research is needed to establish the long term effects of alkali silica reactivity initiated by the CE process, and the structural implications of carrying out CE in the field if the dead and live loads carried by the beams are not relieved.     

Influence of aggregate content on the migration coefficient of concrete materials using electrochemical method

In order to investigate the effect of coarse aggregate content on the chloride ion migration coefficient of concrete, specimens with different coarse aggregate volume fractions and two water/cement (w/c) ratios of mortar matrix were used. The chloride ion migration coefficient of concrete is obtained using the electrochemical technique to accelerate chloride ion migration in cement-based material and the experimental results were plotted as a function of the fine aggregate volume fraction. The results are analyzed comparing experimental results and theoretical models that represent the concretes as three-phase composite materials. The three phases are the mortar matrix, the coarse aggregate, and the interfacial transition zone between the two. The chloride ion migration coefficient is used to assess the dilution, tortuosity, interfacial transition zone (ITZ) and, percolation effects of coarse aggregate in concrete. It appears that the dilution and tortuosity effects are a dominant factor affecting the chloride ion migration coefficient of concrete in the low volume fraction of coarse aggregate. As the volume fraction of coarse aggregate increases to 40 and 20% in concrete of w/c ratio 0.35 and 0.45, respectively, the ITZ with percolation effects are significantly.     

Correlation between compressive strength and certain durability indices of plain and blended cement concretes

In this study, plain, silica fume and fly ash cement concrete specimens prepared with varying water to cementitious materials ratio and cementitious materials content were tested for compressive strength, water permeability, chloride permeability, and coefficient of chloride diffusion after 28 days of water curing. The data so developed were statistically analyzed to develop correlations between the compressive strength and the selected durability indices of concrete. Very good correlations were noted between the compressive strength and the selected durability indices, particularly chloride permeability and coefficient of chloride diffusion, irrespective of the mix design parameters. However, these correlations were observed to be dependent on the type of cement.