start once the protective passive film on the rebar surface breaks
down (depassivation) due to the carbonation processes [3,4]. In
general, cement paste contains 25–50 wt.% calcium hydroxide,
which means that the pH of fresh cement paste is usually at least
12.5. The pH of a fully carbonated paste however is about 7.
When the pH value of concrete pore solution drops to about 8.5–
9.0, the passive film will be completely damaged and the protection
to the rebar will be destroyed and the durability of RC structure
will be significantly affected [5,6].
Carbon dioxide concentration is increasing due to fossil energy
consumption and the damage of RC structures due to carbonation
is reported to increase due to increasing CO2 concentration.
Concrete carbonation should be carefully considered in the durability
design of RC structures especially those in metropolitan cities
where the rise in CO2 concentration is accelerating. The straight
cause of carbonation is the presence of CO2 in the surrounding