Mechanism of carbonation-induced corrosion of steel in blended cementitious materials
Responsible: Cristhiana Carine Albert
Funding: external pageGlobal Cement and Concrete Association (GCCA)
Background
The partial replacement of Portland cement by supplementary cementitious materials is increasingly welcomed due to environmental and technical benefits: reduced clinker consumption, lower CO2 emissions, lower cost, and improved concrete microstructure. However, these blended cementitious systems are usually more prone to carbonation, which causes a decrease in the pH of the pore solution and modifies the pore structure. Consequently, steel's passive film could break down, compromising the corrosion resistance of reinforced structures. Under certain conditions, this could lead to corrosion damage.
Furthermore, the moisture content and microstructure of concrete have major relevance for carbonated-induced corrosion. For example, the pore structure influences the moisture at the steel surface, defining the so-called active area of steel available for electrochemical corrosion reactions. In particular, reinforced concrete structures exposed to wetting-drying conditions are the most susceptible to severe corrosion damage by carbonation. The reason is that carbonation is faster in dry periods while corrosion rates increase in highly humid environments. Nonetheless, the combined effect of these factors – pore solution chemistry, pore structure, and moisture – on the corrosion kinetics is still not yet fully established in the literature, especially not for modern binders.
Aims and objectives
We aim to improve the fundamental scientific understanding of the corrosion mechanisms of steel in carbonated systems with various pore solution chemistry, pore structures, and moisture conditions. Ultimately, this knowledge is combined with other ongoing projects to develop a mechanism-based model for the corrosion rate of steel in different carbonated systems. The ultimate goal is to improve standardization and performance-based durability design.
Methodology
A multidisciplinary approach associating corrosion and concrete materials science is used. A systematic study is conducted on the corrosion kinetics of steel in different (i) pore solutions typical of carbonated blended systems, (ii) carbonated matrices in saturated conditions, (iii) carbonated matrices with diverse moisture states, and (iv) samples of real carbonated concretes. The individual and combined effects of pore solution chemistry, pore structure, and moisture condition is assessed. The contribution of these factors is incorporated in a complete mechanism-based model to predict corrosion rates of steel in carbonated blended cementitious materials.
