carbonation of concrete
Carbonation of concrete is one of the causes of corrosion of reinforcement. It is a process by which carbon dioxide from the air enters the concrete and reacts with calcium hydroxide to form calcium carbonate.
CO. percentage of2 The current wind varies from place to place. In case of rural areas CO. concentration of2 Air can be about 0.03% by volume, while it can vary from 0.3% to 1.0% in urban areas. this co2In the presence of moisture, the dilute turns into carbonic acid and attacks the concrete and reduces the alkalinity of the concrete.
Due to the decrease in the alkalinity of concrete, the pH value of pore water in hardened cement paste is reduced from 13 to 9.0. When all Ca(OH)2 has been carbonated, the pH value decreases again to about 8.3. And at this low pH value, the protective layer is destroyed and the steel is exposed to corrosion.
Factors affecting the rate of carbonation
The rate of carbonation depends on the following factors.
- presence of pore water
- grade of concrete
- permeability of concrete
- protected or unprotected concrete
- depth of cover
If the pores in the concrete are dry then CO2 remains gaseous from and does not react with hydrated lime and carbonation cannot occur.
The higher the grade of concrete, the slower the rate of carbonation
In case of less permeable concrete the rate of carbonation is slower and vice versa.
Preserved concrete, of course, is less prone to carbonation.