The kinetic competition between transport and oxidation of ferrous ions governs precipitation of corrosion products in carbonated concrete

Abstract

Corrosion products, originating from steel corrosion in carbonated concrete and precipitating in the concrete pore system, can lead to cracking and spalling of the concrete cover. To avoid this common form of structural deterioration and thus ensure durable structures, reliable quantitative models are needed. 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 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 reaches the saturation level, which permits the diffusion of corrosion products up to millimetres away from the steel without necessarily leading to expansive stresses. Under accelerated corrosion conditions, however, in a chloride‐free environment, precipitation is accelerated immediately at the steel surface. This changes the corrosion products precipitation distribution and suggests careful evaluation of accelerated tests and related models.