Evaluation of stray current corrosion resistance of concrete in metro construction

By simulation tests of concrete specimens in saturated Ca(OH)₂ solution and seawater, and based on micro mechanism analysis, this paper evaluates the stray current corrosion resistance of concrete specimens of different mixture ratios, and reaches a conclusion that the capability to resist stray current corrosion of optimally designed concrete mixed with good-quality fly ash and powdered slag is increased by over 5 times more than the reference concrete with the same water to binder ratio, and the service life of such kind of concrete meets the basic requirement of a metro project.     

杂散电流对钢筋混凝土结构耐久性的影响

地铁、轻轨等有杂散电流存在的工程中,杂散电流对钢筋混凝土结构的腐蚀是造成桥梁、隧道等构筑物耐久性下降的主要原因之一.阐述了地铁和轻轨工程中杂散电流的形成,重点分析了杂散电流对混凝土结构中钢筋的腐蚀机理及其危害,探讨了对杂散电流腐蚀的监测方法和防护措施,为今后可能出现杂散电流的混凝土结构工程耐久性设计提供理论依据.     

杂散电流作用下钢筋混凝土腐蚀电流时变规律研究

为研究不同配合比下钢筋混凝土受杂散电流腐蚀作用的时变规律,通过模拟腐蚀试验,探讨了掺合料种类、含量、掺和比例对腐蚀电流的影响。结果表明:钢筋混凝土在杂散电流作用下的锈蚀分为去钝化、裂缝展开、裂缝贯通3阶段。基于采用的配合比,添加掺合料对混凝土的抗杂散电流腐蚀能力有明显提高,开裂时间延缓了2~3倍。单掺时,粉煤灰对于抗杂散电流腐蚀的能力优于矿渣,开裂时间延长约9%。复掺时的抗腐蚀能力优于单掺,在掺和总量不超过50%时,总掺和量越高,其抗腐蚀能力越强。本试验中,复掺25%粉煤灰与25%矿渣时,抗腐蚀能力最强。     

矿物掺合料对混凝土抗杂散电流性能的影响

研究了矿物掺合料对混凝土抗杂散电流性能的影响.结果发现:粉煤灰和矿渣微粉均可以改善混凝土的抗杂散电流性能,并且随着掺量的增加,改善效果逐渐增强.粉煤灰和矿渣微粉复掺后,改善混凝土抗杂散电流的效果最为显著,尤其是复掺总量为20%时,混凝土杂散电流腐蚀开裂时间比基准混凝土延长了28.67%.通过对各配合比混凝土试样进行Si...     

钢纤维混凝土隧道的耐久性能研究

大型土木工程结构中,材料的腐蚀对其结构耐久性具有很大的影响,因而正确分析和认识材料腐蚀的原因至关重要。尤其对于地铁隧道这种特殊地下工程的耐久性能更为重要,针对地铁隧道的杂散电流腐蚀问题,对钢纤维混凝土结构进行了杂散电流腐蚀试验,根据钢筋混凝土腐蚀破坏和钢纤维混凝土腐蚀破坏的等效原理,建立了钢纤维混凝土结构在杂散电流腐蚀作用下结构破坏的预测模型。     

杂散电流影响下海砂混凝土的力学性能以及钢筋锈蚀特征

对杂散电流影响下海砂混凝土的力学性能以及钢筋锈蚀特征进行了研究。结果表明:随着加载电压的增大以及通电时间的延长,其抗压强度和弹性模量明显下降;通过电化学当量和钢筋腐蚀电流密度特征变化,杂散电流对河砂混凝土钢筋锈蚀影响较弱,但会加速海砂混凝土钢筋锈蚀,产生不利影响。     

钢筋混凝土和钢纤维混凝土杂散电流腐蚀实验研究

依据地铁杂散电流对地下金属物质发生阳极氧化的电化学腐蚀机理,模拟了钢筋混凝土和钢纤维混凝土试件的杂散电流腐蚀实验。通过两种不同材料在相同的杂散电流环境中进行模拟腐蚀比较,分析了钢筋混凝土和钢纤维混凝土在抵制杂散电流腐蚀的耐久性和破坏形式方面的异同。结果表明,两种材料的耐久性能差异较大,破坏形式也不同,相同条件下,钢纤维混凝土的耐久性能显著降低。     

地铁迷流腐蚀及其防护技术

论述了地铁迷流的概念，腐蚀机理，国内外迷流控制研究现状等问题，并在此基础上提出了通过增大混凝土材料的阻抗来抑制迷流腐蚀的思路。     

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.     

盾构隧道混凝土管片的承载力退化模型

介绍了混凝土结构承载能力的退化模型,基于承载能力限值的混凝土结构耐久性寿命T=t1+t2。确定了退化模型水平段时间(t1),t1=min(TCO2,TCl-,TSO24-,TD),并确定了TCO2,TCl-,TSO24-,TD;建立了锈蚀钢筋混凝土受弯构件正截面承载力计算模型、钢筋锈蚀截面损失率计算模型、杂散电流腐蚀下钢筋锈蚀截面损失率计算模型、腐蚀混凝土轴心抗压强度计算模型,确定了退化模型下降段时间(t2);给出了杂散电流和氯离子与混凝土的力学性能退化关系。     

粉煤灰对地铁杂散电流的抑制作用

本文阐述了地铁轨枕等杂散电流的截流子性质,以及在混凝土中掺加粉煤灰对地铁等杂散电流腐蚀的抑制作用,机理,杂散电流作为离子流,它能破坏钢筋的表面钝化膜,促进钢筋的锈蚀,在混凝土中的掺用粉煤灰抑制了钢筋表面钝化膜的破坏,从而降低了钢筋的杂散电流腐蚀。     

混凝土中掺入粉煤灰对地铁迷流的抑制作用

通过研究建立了符合地铁实际使用情况的模型 ,并由实验方法得出结论 :掺入粉煤灰可有效地提高混凝土的阻抗模和抑制杂散电流腐蚀。粉煤灰对杂散电流的抑制作用随其掺量的增加而增加。但综合考虑强度等其他因素以掺入 30 %粉煤灰为宜。     

Effect of dust in coarse aggregates on reinforcement corrosion in concrete

This paper reports results of a study conducted to investigate the effect of dust, contributed by the coarse aggregates, on the corrosion of reinforcing steel in concrete. The concrete specimens were prepared with up to 10% dust in the coarse aggregates. Two other batches of reinforced concrete specimens were also prepared. In one batch of specimens the aggregates were washed with raw water (total dissolved solids: 3338 ppm) while the dust in the second batch was removed by vacuum suction. Reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. The results indicated that up to 10% dust in the coarse aggregates did not cause any corrosion of the reinforcing steel. Similarly, reinforcement corrosion was not noted in the concrete specimens prepared with coarse aggregates washed with raw water or cleaned with vacuum suction.     

Corrosion of steel reinforcement in concrete of different compressive strengths

Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46 MPa was investigated. Reinforced concrete specimens were immersed in a 3% NaCl solution by weight for 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4 A was applied using portable power supply. Corrosion rate was measured by retrieving electrochemical information of polarization technique. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics.Experimental results showed that corrosion rate of steel bars and bond strength between corroded steel/concrete were dependent on concrete strength and accelerated corrosion period. As concrete strength increased from 20 to 46 MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration caused a slight increase in steel/concrete bond strength, whereas sever corrosion after 7 and 15 days of corrosion acceleration significantly reduced steel/concrete bond strength. Visual and metallographic observation of steel bars removed from concrete samples after testing revealed that the severity of corrosion reactions and reduction of steel bar diameter increased as the corrosion acceleration period increased. Presence of localized corrosion pits as well as severe corrosion grooves of steel bars was confirmed after 7 and 15 days of corrosion acceleration, respectively.     

地铁工程用高阻抗混凝土的研制

根据地铁工程对混凝土耐久性和抑制电流腐蚀的特殊要求,研制了高阻抗混凝土,结果表明：在粉煤灰混凝土中掺加由矿粉和胶乳组成的复合阻抗剂,并采用特殊的搅拌工艺,可使混凝土的阻抗得到显著提高,从而满足地铁工程的特殊需要。     

杂散电流对广州地铁混凝土溶蚀性能影响的加速试验研究

通过加速试验方法研究了直流电流作用下混凝土筛余砂浆的溶蚀性能,并建立了其与广州地铁工程混凝土在杂散电流下的溶蚀性能之间的关系.结果表明:当地铁杂散电流为100 mA/m2时,广州地铁工程混凝土抗杂散电流作用下溶蚀能力可以满足100年的安全运行.采用SEM和EDS对电流加速溶蚀试验后的砂浆进行分析,越靠近阴极部位的砂浆,其凝胶产物越松散,水化硅酸钙产物的Ca/Si越为下降;砂浆微观结构越不密实,孔隙越多.溶蚀后的砂浆强度比基准砂浆降低了约10%.     

杂散电流影响下氯离子向混凝土内部的传输特征

利用加载直流电场模拟杂散电流的方法,对杂散电流存在情况下氯离子向混凝土内部的传输特征进行了研究.结果表明:杂散电流的存在会明显加速氯离子向混凝土内部的传输,同时随着杂散电流作用时间的延长和电流强度的增大,杂散电流对氯离子传输的加速作用越发明显.此外,与无杂散电流情况下氯离子在混凝土内部均匀扩散的特点相比,杂散电流的存在使得氯离子在混凝土内部的渗透面变为一个抛物面,并且在垂直钢筋的方向上氯离子侵入深度最大.     

Chloride ingress and macro-cell corrosion of steel in concrete made with recycled brick aggregate

An investigation on chloride ingress and macro-cell corrosion of steel bars in concrete made with recycled brick aggregate (RBA) was carried out. As control cases, virgin brick aggregate (BA) and stone aggregate (SA) were also investigated. Both cylindrical and cracked prism specimens were studied for 16 different cases. The prism specimens were made with a segmented steel bar providing electrical connection from outside of the specimens to measure macro-cell corrosion current continuously under seawater splash exposure for a period of 30 d using a data logger. Cylindrical specimens were submerged in 3% NaCl solution at a temperature of 40°C to investigate chloride ingress in concrete made with RBA, BA, and SA after 120 and 180 d. Half-cell potential, corrosion area, and depths of corrosion were also investigated. The chloride ingress as well as corrosion of steel bars in concrete made with the different types of aggregate is ordered as RBA > BA > SA.     

杂散电流环境下保护层内氯盐传输特性研究

采用电迁移锈蚀法对杂散电流环境下混凝土保护层中氯盐传输特性进行了研究。通过对四组试件在不同电流强度,不同通电时间情况下混凝土保护层内氯离子浓度的变化特征,重点分析了电场作用对保护层内氯离子传输进程和试件表面氯离子浓度的影响规律。结果表明,电场作用下保护层内氯离子浓度在数十小时内便从非稳态传输演变为稳态传输,传输效率较自由扩散高900多倍,但在稳态传输阶段氯离子浓度并非稳定不变,而是随通电时间增加整体呈下降趋势;保护层内氯离子达稳态传输前,混凝土表面氯离子浓度增长规律与一般氯盐环境中明显不同,其随通电时间增长以幂函数形式降低,随电流强度增加呈幂函数形式增长,且受通电时间的影响更为显著。     

Long-term effects of electrochemical realkalization on carbonated concrete

The long-term effects of electrochemical realkalization on carbonated reinforced concrete with a W/C ratio of 0.65 were studied. Fourteen out of 16 carbonated specimens had been subjected to realkalization seven years ago, and the alkalinity of the concrete, the electrochemical characters (corrosion current density and potential) of the specimens and the corrosion conditions of the steel bars were examined. Results of different specimens and also at different time (4, 10, 13 months and 7 years after realkalization) were compared. According to the phenolphthalein and pH meter test, the alkalinity of the concrete had disappeared after seven years. Based on the potentiodynamic polarization test, various corrosion conditions had developed on the steel bars, which was verified by visual observation. All bars were in the depassivated state, and their corrosion current densities increased significantly after seven years. Cracks developed in some of the specimens, and the diverse compactness of concrete and excessive current of realkalization were considered to be possible causes. The effects of the realkalization treatment vanished after seven years.