Carbonation-induced corrosion of steel in sodium carbonate alkali-activated slag

The carbonation-induced corrosion of steel reinforcement embedded in sodium carbonate alkali-activated slag (AAS) and a CEM III/B reference binder were investigated. The primary objective of this study was to evaluate the influence of both natural and accelerated carbonation (1% CO₂) on reinforcement corrosion. Reinforced cylindrical mortars specimens with a low cover (8.5 mm) were cast and subjected to exposure under natural and accelerated carbonation conditions. The initial weights of the rebar were recorded with high precision prior to casting. Throughout one year of exposure, the corrosion potential and linear polarization resistance of the rebars were systematically monitored. Upon completion of the exposure period, the specimens were split to enable visual inspection of corrosion and to determine corrosion-induced mass loss. The applicability of the Stern-Geary equation to carbonated AAS systems was confirmed by comparing the corrosion current densities estimated from this equation (using a B-value of 26 mV) with the values calculated from the actual mass loss of the reinforcement, as determined by Faraday’s law. Although accelerated carbonation at 1% CO₂ induces differences in pH stabilization and carbonation product formation compared to natural carbonation, it was found to be representative method for quantifying reinforcement corrosion in AAS systems. Overall, AAS exhibited superior resistance to steel reinforcement corrosion compared to CEM III/B reference binder, which was attributed to the more stable and higher pH environment maintained within the AAS matrix.