Suitability of several current used concrete durability indices on evaluating the corrosion hazard for carbonated concrete

In this paper, the suitability of several current used concrete durability indices on evaluating the corrosion hazard for a carbonated concrete is examined. The experiment results reveal that the phenolphthalein solution (suggested by the RILEM CPC 18) may underestimate the corrosion risk. The X-ray diffraction analysis shows that there exists the carbonation product, CaCO3, before the carbonation front reaches there. In addition, the electrochemical measurements indicate the rebar encounters corrosion danger before the carbonation front reaches the rebar. Another two durability indices, namely the apparent resistance and the total charge accumulated in the chloride penetration test (RCPT), have been examined as well. These two methods may mislead our judgments to believe the reinforced concrete is in a sound condition once the concrete is carbonated. The densification of microstructure due to CaCO3 will reduce the apparent resistance and total accumulated charge in RCPT such that one may make a wrong judgment. The water absorption rate and sorptivity test also indicate that a carbonated concrete has a denser microstructure. Based on our experiments, it is suggested that the current used concrete durability indices may not be suitable on evaluating the corrosion hazard for a carbonated concrete. A more reliable pH indicator than the phenolphthalein solution is necessary in detecting the carbonation hazard.