Abstract
Corrosion products, originating from steel corrosion and precipitating in the concrete pore system, can lead to concrete cracking and to spalling of the concrete cover. Related premature structural repair causes high costs. Thus, reliable quantitative models are needed, which currently do not exist. Here, we present a new conceptual model to describe the fate of ferrous ions that are released at the steel surface during the corrosion process. The key novelty of our approach can be found in explicitly considering the kinetics of oxidation and transport of Fe2+ in the pore solution. These two processes constantly dilute the Fe2+ concentration and are in competition with the supply of Fe2+ from the anodic iron dissolution reaction. We use a numerical model to elucidate which of the described processes is the fastest. The results find good agreement with experimental data and reveal that under natural corrosion conditions, Fe2+ hardly reach the saturation level, which permits the diffusion of corrosion products up to millimeters away from the steel without necessarily leading to expansive stresses. Under accelerated corrosion conditions, however, precipitation is forced immediately at the steel surface. This fundamentally changes the cracking mechanism and questions the relevance of such tests and related models.
Highlights
Reinforced concrete structures undergo a variety of degradation processes, among which corrosion‐induced damages are the most common cause of deterioration [1, 2]
That is why the process is generally accelerated by impressed current methods, which enhances the corrosion rate of steel embedded in concrete [5‐10], and enhances the formation of corrosion products
Modeling studies typically considered corrosion induced cracking as a consequence of a uniform volume expansion of the steel rebar, which arises from the uniform formation of corrosion products on the steel surface, building up pressure against the concrete surrounding the steel [3, 5, 7, 12‐16]
Summary
Reinforced concrete structures undergo a variety of degradation processes, among which corrosion‐induced damages are the most common cause of deterioration [1, 2]. A common model approach is to introduce a so‐called “corrosion accommodation region” [5, 12] which is thought to be a porous cement paste layer around the steel bar, into which corrosion products can be pushed and no pressure is assumed to be exerted to the concrete until this porous zone is filled [7, 13, 16]. Modeling approaches consider instantaneous precipitation of corrosion products quantified by Faraday’s law [3] This assumption of simple “expansion” of the steel bars, due to the positive volumetric difference between corrosion products and iron in metallic state (factor 2 to 6) [1, 17], is based on assuming immediate precipitation of the iron oxides directly at the steel surface. It is suggested that the ferrous ions have the possibility to diffuse into the cementitious matrix before further oxidation and precipitation occurs
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