Effect of a surface protection system on the mechanisms of reinforcement corrosion in cracked, short-term chloride exposed concrete

几十年来，人们一直在研究开裂混凝土中的钢筋锈蚀问题。随着钢筋锈蚀对基础设施和繁荣的负面影响越来越大，钢筋锈蚀的可靠修复理念越来越受到重视。在有裂缝的钢筋混凝土结构中，氯化物等有害物质会在短时间内引起腐蚀。因此，标准要求永久保护此类结构不受氯离子侵入。DBV公告《多层或地下停车场》(2018)建议在裂缝形成完成后，在表面涂抹一层裂缝桥面保护涂料。在以往的研究项目中，对于弯曲裂纹的情况，验证了表面保护涂层对已经引发的宏电池腐蚀的钝化效果。然而，这种效果并不是由于预期的电解液电导率的降低。这种效果显然是由于显著增加了阳极极化电阻。在对涂层混凝土中阳极氧化层的动力学和氯化物的再分布的进一步研究中，没有证实这种阳极极化电阻的增加。此外，即使氯离子污染的时间显著延长，含有横向裂缝的钢筋混凝土试件的宏观和微观单元腐蚀的演化也不是稳定出现的。随后的研究表明，没有稳定的腐蚀并不取决于原电池中的电极表面过程，而是分别来自复杂的裂纹特征和复杂的氯离子迁移。因此，关于间歇性污染开裂钢筋混凝土的腐蚀机理的最初问题仍然没有答案，但可以通过一种允许重复的、统一的裂缝的新的试件设计来回答：·在具有横向裂缝的后续涂层钢筋混凝土试件中，宏观细胞腐蚀是如何发展的？·横向裂缝是否会受到与弯曲裂缝中观察到的相同现象的影响？·质量损失的比例可以追溯到后续涂层混凝土的钢筋腐蚀中的微观细胞腐蚀？新的试件设计使得弯曲裂缝和横向裂缝的起始是一致的。因此，作为衡量钢-混凝土界面处大气状况的裂缝类型可以作为一个奇异参数进行研究。结合电化学腐蚀参数的监测和电致质量损失的最终重量量化，可以对涂层混凝土中的钢筋腐蚀机理进行可重复性的研究。结果表明，该修复方法是有效的，可以更可靠地预测潜在的参数相关性。

Since many decades reinforcement corrosion in cracked concrete is investigated. As a still increasing negative impact on infrastructure and prosperity, reliable repair concepts of reinforcement corrosion gain more and more importance. In cracked reinforced concrete structures, harmful substances like chlorides can induce corrosion within a short period of time. Therefore, standards demand to permanently protect such structures from chloride ingress. The DBV Bulletin “multi-storey or underground car parks” (2018) suggests to apply a crack-bridging surface protection coating after crack formation is finished. In the former research projects, the effectivity of surface protection coatings, to deactivate already initiated macrocell-corrosion was verified for the case of bending cracks. However, the effectivity did not result from the expected reduction of electrolytic conductivity. The effectivity apparently yielded from significantly increasing anodic polarization resistance. In further research on the kinetics of anodic oxide layers and the redistribution of chlorides in coated concrete did not confirm this increase of anodic polarization resistance.Furthermore, the evolution of macro- and microcell corrosion in reinforced concrete specimens with transverse cracks did not emerge steadily even though the period of chloride contamination was extended significantly. Subsequent investigations elucidated, that the absence of stable corrosion did not rely on electrode surfaces processes in the galvanic cell, but from complex crack characteristics and complex chloride migration respectively. Therefore, the initial questions on corrosion mechanisms in intermittently contaminated cracked reinforced concrete are still unanswered, but can be answered via a new specimen design allowing reproducible, uniform cracks:• How does macrocell-corrosion develop in subsequently coated reinforced concrete specimens with transverse cracks?• Are transverse cracks subjected to the same phenomena as observed in bending cracks?• Which proportion of loss of mass traces back to microcell-corrosion within reinforcement corrosion of subsequently coated concrete?The new specimen design enables a congruent initiation of bending cracks as well as transverse cracks. Thereby, the type of crack as a measure of atmospheric situation at the steel concrete interface can be investigated as a singular parameter. In combination with monitoring of the electrochemical corrosion parameters and a concluding gravimetric quantification of the galvanically induced loss of mass, a reproducible investigation on reinforcement corrosion mechanisms in coated concrete is possible. As a conclusion, the effectivity of the repair method can be approved and the underlying parametric correlation can be predicted more reliably.