Carbonation induced corrosion of steel in concrete based on low pH binders
Résumé
Nowadays, with an increase of awareness of society and industry on the environmental footprints, there is an increasing need in innovative concrete binders, usually secondary resources and by-products, utilised as partial or full substitution of ordinary Portland cement. Most of these materials have beneficial particle size distribution and/or chemical composition, leading to concrete with lower permeability and higher electrical resistivity. At the same time, their different chemistry leads to changes in pH values of pore solution and in concrete microstructure, which could consequently lead to changes in corrosion properties of steel embedded in these types of concrete. These changes in corrosion properties are especially highlighted when concrete is exposed to long-term carbonation process.The aim of this paper is to research the difference in corrosion behaviour of steel in carbonated concrete based on different types of low pH binders. In the paper results on four concrete mixes are presented, all having different type of binder reference mix with ordinary Portland cement, mix with high volume of fly ash and silica fume, mix with blast furnace slag cement with the addition of nanosilica and mix with high volume of metakaolin and lime. After curing reinforced concrete samples were carbonated at 3% CO2 to ensure representativeness with natural carbonation. During early ages and after carbonation changes of corrosion potential, corrosion rate and electrical impedance parameters are monitored and discussed in the paper. Corrosion behaviour was connected to the changes in microstructure of these different types of concrete during carbonation.