Early depassivation of reinforcing steel due to accelerated-carbonation in limestone calcined clay cement concretes

Abstract

The effect of carbonation on corrosion of reinforced steel was investigated in five limestone and calcined clay (LC3) concrete mixtures designed adjusting their cement SO₃ content. Accelerated carbonation tests were carried out according to BS EN 12390-12, while simultaneously the rebar corrosion activity was also monitored using electrochemical tests such as the linear polarization resistance (LPR). This paper reports on the methodology proposed to evaluate the reinforcement's response to corrosion while concrete carbonates. Results showed that LC3 concretes had a significant increase in the carbonation rate, and showed from a Carbonation Index (C_I), defined as the carbonation depth to the concrete cover ratio, that there is an early depassivation of the rebar. It means that steel corrosion processes begin before the carbonation front reaches the rebar, demonstrating that concrete using very high limestone and calcined clay replacement levels are much more vulnerable to accelerated carbonation.