Carbonation is a process in which carbon dioxide from the atmosphere diffuses through the porous
Cover concrete and may reduce the pH to 8 or 9, at which the passivating /oxide film is no longer
stable. Carbonation process involves the following two stages: First, the atmospheric carbon
dioxide (CO2) reacts with water in the concrete pores to form carbonic acid (H2CO3).
This is followed by reaction of the carbonic acid with calcium hydroxide [Ca(OH)2] to form calcium
Carbonate (CaCO3). This process leads to cause a reduction in the pH value of the pore solution
from 12.5 to 13.5 to around 8 to 9, which causes depassivation of protective layer of the reinforcement bars and initiates their corrosion.
Carbonation of concrete is one of the main reasons for corrosion of reinforcement. Oxygen and
moisture are the other components required for corrosion of embedded steel. In this test, the
depth of carbonation is determined. The rate of carbonation depends on the grade of concrete,
permeability of concrete, whether the concrete is protected or not, depth of cover, time, etc.
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