Abstract
Corrosion in carbonated concrete is an example of corrosion in dense porous media of tremendous socio-economic and scientific relevance. The widespread research endeavors to develop novel, environmentally friendly cements raise questions regarding their ability to protect the embedded steel from corrosion. Here, we propose a fundamentally new approach to explain the scientific mechanism of corrosion kinetics in dense porous media. The main strength of our model lies in its simplicity and in combining the capillary condensation theory with electrochemistry. This reveals that capillary condensation in the pore structure defines the electrochemically active steel surface, whose variability upon changes in exposure relative humidity is accountable for the wide variability in measured corrosion rates. We performed experiments that quantify this effect and find good agreement with the theory. Our findings are essential to devise predictive models for the corrosion performance, needed to guarantee the safety and sustainability of traditional and future cements.
Highlights
Corrosion of metals in porous media is a phenomenon that occurs in a variety of conditions, including metals in contact with soils[1], in transportation and storage of granular materials[2,3], or in timber[4,5]
A number of different hypotheses have been suggested including kinetic control related to the electrical resistivity of the concrete or the limited availability of oxygen at the steel surface – that both correlate with the moisture state of the concrete pore system
The result is a nonlinear increase of the water filled porosity, which determines an increase of the steel surface area being in contact with liquid water (Fig. 4).We suggest the following proportional relationship between area fraction φ and relative humidity (RH): φ = Aactive ∝ − 1
Summary
Corrosion of metals in porous media is a phenomenon that occurs in a variety of conditions, including metals in contact with soils[1], in transportation and storage of granular materials[2,3], or in timber[4,5] Another example of particular scientific and practical relevance is corrosion of reinforcing steel in concrete. The question of corrosion rates in carbonated concrete is, after having been addressed for over half a century, currently receiving more and more attention This is because of the increasing market share and promotion of blended cements as alternatives for the traditional Portland cement[15,16,17]. The continuously increasing diversity in physical and chemical properties of modern cement types imposes an urgent need for a mechanistic model for the prediction of corrosion rates in carbonated concrete[21]
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