Corrosion Rates from Reinforcing Steel Embedded in Carbonated Concrete

Concrete carbonation is the second cause of corrosion in reinforced concrete structures. Once concrete is carbonated, plain rebars are known to corrode actively. However, carbonation-induced corrosion tends to develop later, proceeds at slower rates than chloride-induced corrosion, and leads to uniform steel corrosion that would accelerate the crack formation and decrease the structure service life. In inland environments, carbonation-induced corrosion would be the main corrosion mechanism in reinforced concrete. The objective of this investigation was to study the effect of the water/cement ratio in the corrosion rates after complete carbonation of the reinforced concrete specimens. Four different water/cement ratios were used, and the corrosion behavior was monitored using a linear polarization resistance technique. The specimens were carbonated in an accelerated carbonation chamber at 4% CO₂ and 60% RH. After full carbonation, the RH was increased above 90% in order to increase corrosion. Results showed a direct correlation between the water/cement ratio and the corrosion rate. Corrosion rates were obtained using a potentiostat and a galvanostat with a guard-ring electrical confinement array, both commercially available. The good agreement of the results from both tests provided enough confidence for the use of the galvanostat on field applications.