Concrete class XC

Carbonization-induced corrosion

Carbonization is a chemical reaction that occurs in concrete exposed to weather conditions. The emitted Са(OH)₂ from the cement reacts with СО₂ from the atmosphere and forms СаСО₃.

Ca(OH)₂ + CO₂ → CaCO₃+ H₂O

Carbonization on hardened concrete does not damage the concrete matrix but significantly reduces the concrete's pH value to 8. At a pH above 10, a passive coating is formed on the reinforcement surface, which permanently protects it from corrosion. If the pH value drops below 9, the reinforcement corrodes and, over time, begins to increase its volume to 2-3 times.

The water-cement ratio, the type and amount of cement, as well as variable wetting and drying, are the dominant factors for the speed and depth of carbonization.


Environment: Dry or permanently under water.
Example: Concrete inside buildings with low air humidity. Concrete immersed in water.
Attention: Concrete XC1 is not suitable for outdoor application!


Environment: Under water, rarely dry.
Example: Concrete surfaces subject to continuous contact with water. In many cases it is applicable for fundamentals.
Additional classes covered: XC1


Environment: Moderate humidity.
Example: Concrete inside buildings with moderate or high air humidity. Outdoor concrete protected from rain.
Additional classes covered: XC1, XC2


Environment: Cyclical wetting and drying.
Example: Concrete surfaces in contact with water, but not in class XC2 for impact.
Additional classes covered: XC1, XC2, XC3, XF1, XA1, XM1