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

• Applicant: Professor Dr.-Ing. Christoph Gehlen
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 388850785

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. 

• DFG Programme: Research Grants