Corrosion rates in carbonated low clinker cements: are the new binders really sustainable?

Lowering the clinker content of concrete using SCMs can contribute significantly to reduce the en-ergy consumption and the CO2 emissions of building materials. Substitution of clinker up to 65% is now possible according to European and Swiss standards. Uncertainty about durability, especially carbonation induced corrosion, is the main factor limiting the practical use of these blended ce-ments: containing less CaO they have less capacity to neutralize CO2 and thus higher carbonation rate, which may lead to premature corrosion of steel reinforcement. Results in literature on the corrosion rate in carbonated concrete are rare and refer to ordinary Port-land cement only. For service life prediction of concrete structures with new, blended cements, cor-rosion rate data are urgently needed because the so-called “corrosion propagation stage” might be a significant part of the total service life of the structure. To be able to collect data of corrosion propagation rates in a reasonable time a new experimental set up has been designed. Parameters that can be measured are electrical resistivity of the sample, cor-rosion potential and corrosion rate of the steel, oxygen diffusion and consumption rate; their evalua-tion should allow to investigate the protective nature of the low clinker material for steel in concrete and the mechanism, particularly the kinetics, of carbonation induced corrosion. The first results show that in certain environments blended cements could be more susceptible to corrosion.