钢筋混凝土电化学除氯化物试验研究

本文采用钢筋混凝土电化学除氯技术来排出混凝土中的氯盐,由试验发现,电化学除氯处理过程中,除氯处理前期的氯离子排出量远大于中后期,并且随着通电时间的延续递减明显。在试验前期,试验电流密度对氯离子排出量的影响较为显著,2A/m~2电流密度作用下的氯离子排出量约是在1A/m~2作用下的1.4倍;而在除氯处理的后期,电流密度的大小则对氯离子排出量的影响不明显。通过EDAX能谱仪探究除氯处理后不同离子在混凝土中的分布规律。发现电化学除氯处理后,钢筋附近的混凝土与试件表面附近的混凝土相比,结构更加疏松,孔隙率以及裂缝数目较多,试件表面附近的混凝土的结构则比较致密,孔隙率相对较小。     

混凝土在电化学除盐过程中内部离子迁移和结构变化的研究

研究了电化学除盐过程中通电量、电解质溶液的性质等对驱除Cl^-效率的影响，并利用压汞试验方法（NIP）对经电化学脱盐处理的混凝土孔结构进行了分析。结果表明，经电化学除盐后钢筋附近混凝土的总孔隙率增大，其中小于30nm的孔明显增多，而大孔数量则有所减少；远离钢筋的混凝土的孔隙率变化与所用电解质溶液有关，以水作除盐介质时孔隙率增大，而采用饱和Ca（OH）2和饱和Ca（OH）2＋0．001mol／L Li2B4O7溶液时混凝土孔隙率减少。     

电化学除盐对混凝土微观结构的影响

设计了一套钢筋混凝土的电化学除盐循环装置,研究了用0.001 mol/L Li2B4O7 氢氧化钙饱和溶液、氢氧化钙溶液以及蒸馏水作电解液的除盐效率,并用SEM和EDS等方法进行微观结构分析,结果表明:用0.001 mol/L Li2B4O7 氢氧化钙饱和溶液作电解液最有利于混凝土中Cl-的排除,并且经电化学除盐处理后混凝土水化产物中C-S-H凝胶分解,Ca(OH)2增多,并在孔壁形成沉淀,堵塞毛细孔,使表层混凝土孔隙率降低,而钢筋与混凝土界面Ca/Si增大。     

电化学除盐试验研究

电化学除盐是一种针对氯污染混凝土结构物的有效无损修复方法，而我国在电化学除盐防锈技术方面的研究与应用起步较晚，一些技术诀窍尚未完全掌握。本文初步探讨了电解质溶液的种类、浓度及电流密度等对除盐效果的影响。试验结果表明，在通电时间和电流密度一定时，采用不同的电解液，除盐效果有差异：电解液相同时，电流密度越大，除盐速度越快，本试验采用0．0010mol／L Li28407＋饱和Ca（0H）2溶液和2A／m^2的电流密度可以取得较好的除盐效果。     

锈蚀钢筋混凝土梁的新型除氯-加固方法研究

电化学除氯（ECE）可有效去除混凝土中的氯离子,降低钢筋的锈蚀风险。文中采用磷酸镁水泥（MPC）粘结CFRP作为ECE阳极,实现混凝土结构的除氯-加固一体化。主要研究了内掺氯盐的钢筋混凝土梁在不同ECE电流密度下除氯28d后的除氯效率和抗弯承载力。结果显示：与对照组相比,ECE电流密度为1A/m2和3A/m2时,除氯后混凝土梁抗弯极限荷载分别提升了7.99%和3.49%。钢筋-混凝土界面的除氯效率高达70%以上。     

电化学除盐对钢筋——混凝土界面粘结力的影响

应用钢筋混凝土圆柱体试件,研究了电化学除盐对钢筋—混凝土界面粘结力的影响。研究结果表明:除盐电流是导致钢筋—混凝土界面粘结力下降的主要原因,但在采用小电流(1 A/m2~4 A/m2)的情况下,粘结力的损失并不明显。     

电解质溶液对电化学除氯效果的影响

电解质溶液是电化学除盐过程中必备的物质条件之一,着重研究不同电解质对电化学除盐效果的影响。试验结果表明:在0.1mol/LNa3BO3溶液中和饱和Ca(OH)2溶液的除盐效果相差不大,且除盐效率比较好;无论在哪种电解质中进行电化学除盐,混凝土中的Cl-含量以钢筋为中心由内及外呈梯度递增分布;而K+、Na+等阳离子含量则是由内及外呈梯度递减的规律,且内层含量远远高于外层含量。     

外电场作用下混凝土中离子的迁移与分布规律研究

以饱和石灰水为电解液,对外掺3％NaCl的混凝土圆柱体试件进行电化学除氯试验,研究了三种不同电流密度( 1.0 A/m2、2.0 A/m2、3.0 A/m2)作用28d后混凝土中氯离子和钾、钠离子的分布规律.结果表明:电流密度越高时,在距离钢筋越近区域,混凝土中的残余氯离子含量越少;电流密度为2.0 A/m2和3.0A/m2时,可使混凝土中距离钢筋20mm范围内的氯离子含量均降低到水泥用量0.15％(占水泥质量)以下.在电化学除氯电场作用下,大量钾、钠离子向钢筋附近区域迁移和聚集,使混凝土试件内层钠离子含量达到最外层的4.8～17.3倍,钾离子含量达到最外层的3.8～17.5倍,从而增加了混凝土内部发生碱骨科反应破坏的风险,并导致部分水化产物分解,使混凝土与钢筋粘结力显著降低.     

电化学除盐工艺参数优化及工程应用探索

对电化学除盐工艺参数进行了优化,并开展了电化学除盐工程应用探索。结果表明,以0.001mol/LLi2B4O7的饱和Ca(OH)2溶液为电解质溶液、2A/m2的电流密度除盐50d,混凝土内氯离子的排除率可达80%以上,且不会对混凝土抗压强度与抗渗性产生明显影响,取得了良好的修复效果。     

电化学除盐对钢筋与混凝土间黏结力的影响

采用电化学方法对含高氯盐混凝土进行除氯盐试验,在得出除盐效率与除盐后微观结构变化规律的同时,对混凝土中的钢筋进行中心拉拔试验,得出除盐后钢筋与混凝土黏结力变化规律,并对变化原因进行分析,探讨应对不良变化的措施.     

矿物对混凝土中钢筋锈蚀的试验研究

通过检测钢筋电位以及腐蚀电流密度的变化,比较了矿粉、粉煤灰对混凝土中钢筋锈蚀速率的影响.试验结果表明:由于矿粉、粉煤灰能改善混凝土抵抗氯离子渗透的能力,因而能延缓混凝土中钢筋的锈蚀.钢筋电位与腐蚀电流密度的变化情况基本一致,可以作为混凝土中钢筋锈蚀情况的判断依据.     

Effect of rebar coating on corrosion resistance and bond strength of reinforced concrete

The objective of this study is to assess the corrosion resistance of zinc-coated and coating effect on the bond strength between concrete and reinforcing steel. Potentiodynamic polarization method was utilized to determine the corrosion rates of carbon steel and zinc in both pH 12 solution and 3.5 wt% NaCl solution. In addition, cylindrical specimens were cast and exposed to 3.5% NaCl solution and a direct current density (0.5 mA/cm²) was applied to accelerate the corrosion process. Open circuit potential (OCP), direct current polarization resistance were obtained to evaluate the rebar corrosion.Potentiodynamic polarization curves show that the corrosion rate of zinc is higher than carbon steel in pH 12 solution but lower in 3.5% NaCl solution. The bond strength of uncoated rebar is 5–10% less than zinc-coated rebar before aqueous immersion test. The bond strength decreases with an increase in corrosion rate for uncoated rebar and zinc-coated rebar. After 14-days accelerating corrosion process, the reduction ratio of bond strength for zinc-coated rebar is less than uncoated rebar.     

Bond degradation due to the desalination process

In this paper, bond degradation due to the desalination process of chloride-contaminated reinforced concrete is investigated. Four different constant voltages were applied to study the effect of the current on the desalination. Two constant current densities were applied for comparison. Two different electrolytes, NaOH and Ca(OH)₂, were used to examine the effect of electrolyte on the bond characteristics. Pullout specimens were cast and tested, using a single rebar pullout test. Three bond parameters of the bond strength, the critical debonding shear load per unit embedded rebar length and the shear stiffness per unit embedded rebar length were obtained to evaluate the bond quality after desalination. It is found that the bond characteristics decrease dramatically as the duration and/or the voltage of desalination increase. Using Ca(OH)₂ solution as the electrolyte, less bond loss is observed than using NaOH solution. A micro-hardness experiment shows that softening of concrete near the rebar becomes more apparent as the desalination duration and/or desalination voltage increase. A chemical titration experiment indicates that the accumulation of potassium and sodium ions increases as the desalination duration and/or desalination voltage increase. A pH value measurement shows that the desalination current increases the pH value of concrete near the rebar. More than two-thirds of chloride ions migrate out of the rebar–concrete interface in two weeks of desalination with desalination voltage greater than 10 V. Bond strength decreases approximately 40–60%.     

氯盐及亚硝酸盐对混凝土钢筋锈蚀的影响

针对在寒冷地区冬季施工中 ,仍然经常使用大量含有氯盐的早强剂和防冻剂这一现实 ,采用钢筋锈蚀快速试验法 ,研究了氯化钠和氯化钙对混凝土中钢筋锈蚀的影响以及亚硝酸盐的阻锈效果。实验结果表明在氯化钠和氯化钙掺量相同时 ,氯化钙对钢筋锈蚀的破坏比氯化钠的更严重。在向混凝土中掺加氯化钠的情况下 ,无论阻锈比 (亚硝酸钠与氯化钠的质量比 )为 1 .2还是 1 .5时 ,亚硝酸钠均有很好的阻锈作用     

Electrochemical chloride removal in reinforced concrete structures: Improvement of effectiveness by simultaneous migration of calcium nitrite

Electrochemical Chloride Extraction (ECE) is becoming a common methodology for repairing reinforced structures. Also the application of corrosion inhibitors on the concrete surface for its penetration its getting more and more interesting as protective method against corrosion of reinforcements. In this sense, the migration of corrosion inhibitors can be promoted by the application of an electric field, enhancing in this way the transport of the inhibitor. In present work, the simultaneous application of both technologies is proposed. The migration of nitrite to the rebar is promoted during the application of an ECE treatment by modifying the classical configuration through the connection of an external cathode to the rebar. The electrochemical response of the rebar after the treatment has been evaluated by corrosion potential and polarization resistance measurements. The efficiency of the treatment was confirmed by the visual inspection of the rebar and the analysis of chloride and nitrite at the level of the rebar.     

Corrosion resistant performance of a chemical quenched rebar in concrete

The corrosion resistance performance of the rebar quenched by a new chemical reagent FM in concrete containing chloride ions was evaluated comparing with bare rebar, water-cooled rebar and air-cooled rebar using electrochemical methods. Two different accelerated corrosion tests (14 cycles of dry/wet alternated corrosion tests and long-term immersion tests) were carried out to accelerate the corrosion process. EIS results of both accelerated corrosion tests showed the corrosion resistance performance of different rebar specimens could be sequenced from high to low as FM-cooled rebar, bare rebar, air-cooled rebar, and water-cooled rebar. It was observed that, after 14 cycles of accelerated corrosion tests, the corrosion degree of FM-cooled rebar is the slightest and most of the initial scale remains undamaged. This result proves that the corrosion resistance of the FM-cooled rebar is much better than the other three kinds of rebar. By using FM-cooling process, the corrosion resistance performance of rebar in concrete has been improved by optimizing the quality of the scale.     

置换混凝土加固含氯离子框架柱

结合工程实例,介绍了框架柱裂缝、钢筋锈蚀的现象和成因,简述了混凝土中氯离子含量偏高是钢筋锈蚀的主因,并提出了用置换混凝土加固法置换柱内全部含氯离子混凝土的加固方案和施工要点。具有一定的参考价值。     

钢筋锈蚀状态的检测与MCI阻锈技术的应用

介绍了如何正确判断混凝土结构中钢筋 (丝 )的锈蚀状态以及如何使用MCI阻锈剂 ,并通过某桥锈蚀的混凝土梁防锈治理后近 1年的电位及电流密度的变化 ,进一步验证了MCI阻锈剂的有效性     

干湿循环条件下钢筋锈蚀的临界氯离子浓度

采用电化学交流阻抗谱研究了干湿循环条件下混凝土中钢筋锈蚀的临界氯离子浓度,深入探讨了混凝土中钢筋锈蚀临界点的判断方法,分析了干湿循环时间比对临界氯离子浓度的影响.结果表明:借助电化学交流阻抗谱法能较为准确地判断钢筋锈蚀临界点;临界氯离子浓度随干湿循环时间比的增加基本呈增大趋势;临界氯离子浓度与干燥结束时混凝土的饱和度之间存在线性关系,且随着干燥结束时混凝土饱和度的增大而降低.     

大气预锈对混凝土模拟液中低合金钢筋腐蚀行为的影响

通过电化学阻抗谱(EIS)、背散射电子(BSE)图像与能谱分析(EDS)研究了大气预锈对低合金钢筋和普通低碳钢筋在混凝土模拟液中氯盐腐蚀行为的影响.结果表明:大气预锈作用影响2种钢筋钝化膜的生成;氯盐侵蚀后,大气预锈作用降低了低碳钢筋的耐蚀性,但低合金钢筋的耐蚀性不受预锈作用影响,原因是低合金钢筋基体与氧化皮间的缝隙内形成了致密的富Cr锈层,抑制了氯盐对钢筋基体的进一步侵蚀.