阻锈剂的掺入方式对全珊瑚海水混凝土中钢筋锈蚀的影响

采用线性极化电阻法(LPR)和电化学阻抗谱法(EIS),系统研究了暴露时间、阻锈剂种类及掺入方式对全珊瑚海水混凝土(CASC)中钢筋腐蚀的影响。结果表明:随着暴露时间的延长,不掺及同掺阻锈剂的普通钢筋自腐蚀电位(E_(corr))、极化电阻(R_p)和电荷转移电阻(R_(ct))均逐渐降低;而暴露90 d后,预吸阻锈剂的普通钢筋E_(corr)、R_p和R_(ct)均有增长的趋势,说明以预吸掺入的阻锈剂,不断地由珊瑚骨料向外释放,使得混凝土中有效的阻锈成分不断补充,一定程度上增大了Cl-通过混凝土传到钢筋表面的阻力,延缓了钢筋的锈蚀。此外,无论是掺入亚硝酸钙阻锈剂(CN)还是氨基醇类阻锈剂(AA),对普通钢筋抵抗锈蚀的能力均有不同程度的提高,且随着暴露时间的延长,CN阻锈效果的衰减速率高于AA的。因此,对于海洋岛礁工程中的CASC结构,建议以预吸的方式掺入AA,有利于减弱钢筋对Cl~-腐蚀的敏感性,提高CASC抗Cl~-扩散渗透能力,从而延缓钢筋开始腐蚀时间,降低锈蚀的速率,达到延长CASC结构服役寿命的目的。     

新型复配阻锈剂在混凝土模拟液和试块中对钢筋锈蚀的抑制

利用半电池腐蚀电位、线性极化和电化学交流阻抗技术,分别在混凝土模拟液和干湿循环加速腐蚀混凝土试块中,研究了新型复配有机阻锈剂(IMC-16)对钢筋锈蚀行为的影响,并将其与常规Ca(NO2)2阻锈性能相对比。结果表明,无论在混凝土模拟液中还是在混凝土试块中,空白条件下,随实验时间延长钢筋电极腐蚀电位不断下降,腐蚀电流密度迅速升高,表明在Cl-侵蚀性作用下钢筋表面钝性遭到破坏,并发生严重局部腐蚀;而添加IMC-16阻锈剂后,钢筋电极腐蚀电位升高,阻抗模值增大,腐蚀电流密度与双电层电容显著下降,表明钢筋的锈蚀得到很好的控制。复配阻锈剂对Cl-诱导的钢筋局部腐蚀具有优良的抑制效果,并可有效延缓钢筋的起始锈蚀时间。干湿循环实验结果进一步表明,实验初期Ca(NO2)2虽可较好抑制钢筋的锈蚀,但其后期阻锈性能却明显下降;而复配阻锈剂在实验初期阻锈性能虽不明显,但相同使用浓度下,其后期阻锈效果及稳定性却明显优于Ca(NO2)2。     

利用电渗的方法评价渗透迁移型钢筋阻锈剂的效能

钢筋混凝土阻锈剂是提高钢筋混凝土耐久性的一项重要技术。本工作利用电渗的方法快速评价渗透迁移型钢筋混凝土阻锈剂(MCI)的效能。采用32V的电渗电压促使氯离子快速渗透(ACIM)到钢筋表面并引起钢筋腐蚀,然后采用线性极化法对钢筋腐蚀状态进行测试,最后以阻锈剂的抗氯离子渗透性能和阻锈效能来评价阻锈剂的综合效能。结果表明,氯离子的快速渗透和电化学测试仅需几天的时间,试验结果很好地反映不同阻锈剂掺量的阻锈效能,是一种适合于工程建设需要的快速评价方法。     

一种新型钢筋阻锈剂的阻锈性能

采用硬化砂浆和半电池电位法评价了一种自制的含有氨基和羧基的新型钢筋阻锈剂IH_2的阻锈性能,并采用标准工作曲线法分析了混凝土中钢筋对阻锈剂的吸附性能。结果表明,IH_2钢筋阻锈剂可以延长钢筋发生锈蚀的时间,降低钢筋的腐蚀速率,具有良好的阻锈性能。     

矿物掺合料及腐蚀溶液对混凝土中钢筋的锈蚀行为的影响

采用电化学阻抗谱研究了掺加不同量粉煤灰、矿粉的混凝土中钢筋的锈蚀行为,并探讨了复合盐溶液、海水和单一氯盐溶液对混凝土中钢筋阻抗谱及锈蚀行为的影响。结果表明:掺入30%(与水泥的质量比,下同)粉煤灰以及30%矿粉的C30混凝土,其抗压强度分别下降了45%和35%,且随着矿物掺合料掺量的增加,混凝土抗压强度损失越大。对养护7d的C30混凝土而言,腐蚀溶液导致钢筋锈蚀严重性排序为:复合盐溶液海水氯盐溶液。混凝土中掺入15%~20%矿粉或15%粉煤时,混凝土抵钢筋锈蚀能力最好,但随着矿物掺合料掺量进一步增加,其护筋能力下降。     

混凝土中钢筋腐蚀与防护研究进展

综述了严酷环境下混凝土中钢筋锈蚀的研究现状,论述了钢筋在混凝土碱性环境中的钝化机理,以及碳化和氯盐作用下的钢筋锈蚀机理;讨论了表面防护、阻锈剂、电化学阴极保护和钢筋表面涂镀等钢筋腐蚀防护措施的作用机理及优缺点。     

国内外混凝土钢筋阻锈剂研究进展

混凝土中钢筋的腐蚀是钢筋混凝土建筑过早损坏的主要原因。氯离子的进入是加速此种腐蚀的关键因素。文章着重介绍阻止钢筋混凝土腐蚀的阻锈剂的发展及迁移型阻锈剂的行为特点。阻锈剂技术的发展趋势和今后的研究工作需要进一步的探究。     

新型自修复钢筋涂层的试验研究

将人为损伤的自修复涂层钢筋置于海水中浸泡,通过测量钢筋的自腐蚀电位、涂层下的钢筋腐蚀面积、涂层和钢筋界面间的粘附性,并观察涂层破损处的锈蚀状况,研究自修复涂层中的亚硝酸离子对破损涂层处钢筋腐蚀的抑制效果,及碱性环境对亚硝酸离子抑制效应的影响.结果表明,自修复涂层中的水泥和其碱性环境对抑制腐蚀有促进作用;涂层中添加的亚硝酸盐对钢筋腐蚀有显著的抑制效果;亚硝酸盐和水泥的复合抑制效果优于它们独立的抑制效果,且亚硝酸盐含量越高,腐蚀抑制效果越明显.并对自修复涂层的阻锈机理进行了探讨.     

钢筋阻锈剂阻锈效果的评价

通过半电池电位测量、动电位扫描、恒电位极化等电化学方法和冷热干湿实验评价了自制HP钢筋阻锈剂的阻锈效果,并探讨了其耐蚀机理。实验结果表明,HP阻锈剂是一种阳极型阻锈剂,它通过提高钢筋的半电池电位,促进阳极极化而改善钢筋的耐蚀性能。这种阻锈剂性能稳定,受环境介质变化影响小,对钢筋基体具有良好的保护作用。几种评价方法在实验结果上具有基本规律的一致性,能正确评价钢筋阻锈剂的阻锈效果。     

一种新型钢筋阻锈剂

国内不少工程中使用的钢筋阻锈剂大都含有亚硝酸盐成分,对环境有一定危害作用。由于钼酸盐具有低毒和较好的缓蚀作用,制备了钼酸盐系阻锈剂。采用盐水浸渍试验、干湿冷热循环试验、失重和硬化砂浆等方法,对新型阻锈剂阻锈性能进行系统的评价,并与市售阻锈剂的性能进行了比较。在模拟液中对其阻锈性能作进一步的验证。结果表明,该阻锈剂是一种高效、环保的阻锈剂,在掺量3%时,能发挥最佳阻锈效果。     

A mathematical model for prediction of time from corrosion initiation to corrosion cracking in RC structures

Prediction of time from corrosion initiation to corrosion cracking is a crucial factor in evaluating concrete structures' durability and integrity deteriorated by reinforcement corrosion. This paper presents a mathematical model to predict the time from corrosion initiation to corrosion cracking. A dynamic corrosion rate model based on Bulter–Volmer kinetics and a rust expansion model based on Faraday's law are developed. An analytical model is developed to demonstrate the mechanical consequences of rust buildup around the rebar. The time to corrosion cracking is found to be a function of surrounding concrete material properties, chemical composition of rust, ratio of concrete cover thickness to rebar diameter, and corrosion current density. Comparisons with available experimental results are conducted to show the accuracy and reliability of the present model. Further parametric analysis is carried out to show the influences of various parameters included in the model on the time to corrosion cracking.     

混凝土锈胀开裂寿命预测模型及其应用研究

采用圆孔扩张理论对混凝土钢筋锈胀过程进行分析,推导了不同钢筋锈胀量对应的塑性区边界混凝土应力及塑性区半径计算公式,在此基础上建立了混凝土锈胀开裂寿命准则及寿命预测模型。锈胀开裂寿命模型分析表明,预测寿命值与钢筋相对保护层厚度m和混凝土等级有直接关系。随着相对厚度m增加,锈胀开裂预测寿命值增加,并且前期增加较快,后期增加较缓慢。混凝土强度等级对预测寿命值影响显著,随混凝土强度增大,混凝土锈胀开裂寿命增大。工程应用表明,该模型预测寿命可为工程的中度维护提供参考。     

矿物掺合料对钢筋氯盐腐蚀行为的影响及其作用机理

用水泥提取液模拟混凝土孔隙液,用自腐蚀电位、动电位极化和电化学阻抗技术,研究单掺粉煤灰或矿粉、复掺粉煤灰和矿粉对混凝土中钢筋氯盐腐蚀行为的影响.结果表明,粉煤灰和矿粉均能有效降低钢筋受氯离子腐蚀的风险,减小腐蚀速率,并能不同程度地提高钢筋腐蚀的临界氯离子浓度.抑制氯离子腐蚀能力由强到弱依次为:矿粉>矿粉+粉煤灰>粉煤灰>水泥.且随氯离子浓度的增大,矿粉和粉煤灰的阻锈效率会有不同程度的下降.用矿粉和粉煤灰按适当比例复掺的方法来对抗氯离子腐蚀不仅经济,而且有不错的阻锈效果.     

一种新型钢筋阻锈剂的阻锈性能

以极化曲线法、失重法和半电池电位法评价了一种新型钢筋阻锈剂的阻锈性能,并采用EDS手段表征了阻锈剂的渗透性能。结果表明,阻锈剂对混凝土中钢筋有阻锈作用,Cl-含量较低时,阻锈效果明显,缓蚀率达85%;Cl-含量较高时,阻锈效果不明显。阻锈剂通过涂刷方法能够很快渗透到混凝土内部,到达钢筋周围,对在役钢筋混凝土管架有很好的防护作用。     

Effect of surface condition on the initial corrosion of galvanized reinforcing steel embedded in concrete

The present work was aimed at determining the effect of coating surface condition on the initial corrosion of hot-dip galvanized reinforcing steel bar (HDG rebar) in ordinary Portland cement (OPC) concrete. During zinc corrosion in OPC concrete, calcium hydroxyzincate (CHZ) formed on untreated HDG steel provided sufficient protection against corrosion. Therefore, it is concluded that treating HDG rebar with dilute chromic acid is unnecessary as a method of passivating zinc. A layer of zinc oxide and zinc carbonate formed, through weathering, on HDG bars increased the initial corrosion rate and passivation time compared with the non-weathered rebar exposed to concrete. HDG steel with an alloyed coating, i.e. containing only of Fe-Zn intermetallic phases, required a longer time to passivate than those with a pure zinc surface layer. The lower zinc content of the surface limited the rate of CHZ formation; hence, delayed passivation. Regardless of the surface condition, the coating depth loss after two days of embedment in ordinary Portland cement concrete was insignificant.     

Corrosion Evolution of Steel Reinforced Concrete Under Simulated Tidal and Immersion Zones of Marine Environment

The corrosion evolution processes of steel reinforced concrete under simulated tidal and immersion zones of marine environment were investigated by using electrochemical measurements and corrosion morphology observations.The results indicate that the corrosion of rebar in concrete under both environments experiences the deterioration from passivation to pitting corrosion and then to general corrosion.Specially,the pitting plays the major role only in the early stage of corrosion,and the general corrosion replaces the dominate role of pitting during the long-term corrosion.In addition,both the pitting depth on local surface and the rust thickness on the overall surface of rebar in the tidal condition are larger than those in immersion condition,which is attributed to the faster corrosion rate in tidal zone caused by the concentrated chloride ions and sufficient oxygen supply.     

The influence of cracks on chloride-induced corrosion of steel in ordinary Portland cement and high performance concretes subjected to different loading conditions

Many reinforced concrete structures are subjected to variable loads, but little information is available on the effect of such loading, and the accompanying opening and closing of cracks, on the initiation and propagation of chloride-induced rebar corrosion. The purpose of this paper is to provide that information for reinforced ordinary Portland cement concrete and high performance concrete exposed to static or cyclic three-point bending and exposed to salt solution.It was observed that: (i) corrosion occurred only at intersections of the rebar with cracks in the concrete; (ii) high performance concrete was more protective than ordinary Portland cement concrete and (iii) the type of loading had less impact on corrosion than the type of concrete and exposure conditions.     

Distribution of millscale on corroded steel bars and penetration of steel corrosion products in concrete

This study investigated a reinforced concrete specimen that had deteriorated in an artificial environment for 2 years. The steel/concrete interface and corrosion-induced cracks were observed by SEM to investigate the millscale on the rebar surface and the distribution of rust. The millscale was not further oxidised before the surface cracking of the concrete cover. The penetration of corrosion products into concrete and the formation of a corrosion layer proceeded simultaneously. The rust did not fill the corrosion-induced cracks in concrete. Instead of the three-stage model, a two-stage model is proposed to describe the concrete cracking process induced by steel corrosion.     

Chloride threshold level for corrosion of steel in concrete

The steel rebar inside reinforce concrete structures is susceptible to corrosion when permeation of chloride from deicing salts or seawater results in the chloride content at the surface of the steel exceeding a chloride threshold level (CTL). The CTL is an important influence on the service life of concrete structures exposed to chloride environments. The present study discusses the state of art on the CTL for steel corrosion in concrete, concerning its measurement, representation, influencing factors and methods to enhance the CTL. As the CTL values reported in the majority of previous studies were varied with experimental conditions, corrosion initiation assessment method, the way in which the CTL was represented, direct comparison between the results from different sets and evaluation was subjected to the difficulty. As a result, total chloride by weight of cement or the ratio of [Cl⁻]:[H⁺] is the best presentation of CTL in that these include the aggressiveness of chlorides (i.e. free and bound chlorides) and inhibitive nature of cement matrix. The key factor on CTL was found to be a physical condition of the steel-concrete interface, in terms of entrapped air void content, which is more dominant in CTL rather than chloride binding, buffering capacity of cement matrix or binders. The measures to raise the CTL values using corrosion inhibitor, coating of steel, and electrochemical treatment are also studied.