Long-term reinforcement corrosion in low carbon concrete with a high volume of SCMs exposed to NaCl solutions and field marine environment

Chloride-induced corrosion in low carbon concrete with a high volume of SCMs exposed to (i) accelerated corrosion by impressed current, (ii) 9-year NaCl-simulated tidal condition and (iii) 5-year field marine tidal condition was compared in this study. The effectiveness of different exposure conditions and indicators in distinguishing the parameters affecting the corrosion resistance of concrete was investigated. The results showed that at a high w/b ratio of 0.6, the accelerated corrosion test provided inconsistent ranking for the corrosion resistance of binders when continuous and intermittent impressed voltage were applied. At a w/b ratio of 0.4, the electrochemical measurements from both accelerated corrosion and laboratory-simulated tidal exposure confirmed the advantage of 30 % FA blended cement concrete in protecting reinforcement, whereas results from two exposure conditions denoted opposite ranking for the corrosion resistance of GP cement and 50 % slag blended cement concrete. The statistical analysis of the 674 independent data points (Ecorr, Rp) suggested that using -465 mVSCE as the upper limit for indicating a higher than 90 % corrosion probability was more reliable than the -350 mVSCE from ASTM C876. Compared to field marine tidal exposure, long-term wet/dry cycles in 3 % NaCl induced faster corrosion initiation and propagation, thereby higher weight loss of reinforcement. The chloride contents permitting corrosion initiation were higher for concrete with more binder due to a higher alkalinity. The complex interaction between chloride, alkalis and reinforcement corrosion leads to difficulty in discriminating the corrosion resistance of various binders, especially in long-term exposure.