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

几十年来，人们一直在研究裂缝混凝土中的钢筋腐蚀问题。钢筋锈蚀对基础设施和繁荣的负面影响日益严重，钢筋锈蚀可靠修复的概念越来越受到重视。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，标准要求永久保护这些结构不受氯化物的侵入。DBV公告“多层或地下停车场”（2018）建议在裂缝形成后应用裂缝桥接表面保护涂层。在之前的研究项目中，对于弯曲裂纹的情况，表面保护涂层对已经引发的宏细胞腐蚀的有效性得到了验证。然而，这种有效性并不是由于预期的电解电导率的降低而产生的。其效率明显来自于阳极极化电阻的显著增加。在进一步的研究中，阳极氧化层的动力学和氯化物在涂层混凝土中的重新分布并没有证实这种阳极极化电阻的增加。此外，尽管氯离子污染时间显著延长，但钢筋混凝土横向裂缝试件的宏、微孔腐蚀演化并不稳定。随后的研究表明，稳定腐蚀的缺乏并不依赖于原电池中电极表面的过程，而是分别来自复杂的裂纹特征和复杂的氯化物迁移。因此，关于间歇性污染裂缝钢筋混凝土腐蚀机制的最初问题仍然没有答案，但可以通过一种新的试件设计来回答，允许再现，均匀的裂缝：•在随后涂覆的钢筋混凝土试件中，大细胞腐蚀是如何发展的？•横向裂纹是否与弯曲裂纹中观察到的现象相同？•在随后涂层混凝土的钢筋腐蚀中，质量损失的哪个比例可追溯到微孔腐蚀？新的试样设计使弯曲裂纹和横向裂纹的起始一致。因此，作为衡量钢-混凝土界面大气状况的裂缝类型可以作为单一参数来研究。结合对电化学腐蚀参数的监测和电致质量损失的最终重量量化，对涂层混凝土中钢筋腐蚀机制的可重复性研究是可能的。结果表明，该修复方法的有效性得到了肯定，并能更可靠地预测出潜在的参数相关性。

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.