The combined effect of carbonation and chloride-contamination of concrete on the intelligence of Mg alloy sacrificial anode for reinforcing steel

Reinforced concrete infrastructure may be simultaneously exposed to concentrated sodium chloride and carbon dioxides in some cases, and the reinforcing steel may suffer severe corrosion due to the combined effect of carbonation and chloride (Cl-) contamination of the concrete. To better understand the combined effect of carbonation and Cl- contamination, the cathodic protection performance of AZ91 Mg alloy was compared with that of the widely used conventional Al and Zn sacrificial anodes for the steel in simulated concrete pore solutions (SCPSs) in this work. The results showed that the Al and Zn were not sensitive to the corrosivity variation of the SCPS caused by the Cl- contamination and carbonation, and the Zn could not sufficiently protect the steel in Cl--contaminated SCPSs. However, the AZ91 Mg alloy could sensitively respond to the corrosivity change of the SCPS, be activated automatically by the Cl- contamination and carbonation, give out a sufficient cathodic current density to protect the steel according to the corrosivity of the SCPS, and act as an intelligent sacrificial anode for reinforced concrete in some environments with concentrated CO2 and Cl-. Based on the different anodic behaviors, the dissolution mechanisms of the Al, Zn and AZ91 Mg alloy were analyzed and the combined effect of the carbonation and Cl- contamination on the cathodic protection performance of these anodes were investigated.