The alkaline reaction of the concrete protects the reinforcing steel against corrosion. Where does this alkaline reaction come from??
During the hydraulic hardening of cement, which is a binder in concrete, a significant amount of calcium hydroxide is formed (lime lye). It is calcium hydroxide that is the source of the alkaline reaction of concrete.

What value should the alkaline reaction of the concrete have to protect the reinforcing steel against corrosion??
Freshly manufactured concrete has a pH value of approx. 12,5. If, due to acidic additives, the pH value drops below 9,5, corrosion of reinforcing steel begins.

Acidifying substances, which neutralize the concrete
1. Dwutlenek węgla, whose content in the air is 0,04%. It forms carbonic acid in combination with moisture.
2. Dwutlenek siarki, formed during fuel combustion in domestic and local boiler houses. The sulfur dioxide is oxidized to trioxide, forming sulfuric acid with water.
3. Chlorki, penetrating into concrete together with salt used for sprinkling icy roads.
4. Siarczki, affecting concrete, especially in sewage treatment plants.

Factors influencing the intensity of corrosion of reinforcing steel in concrete
The corrosion intensity of reinforcing steel in concrete depends on the following factors:

1) odległość zbrojenia od powierzchni betonu (cover thickness);

2) warunki środowiskowe (the degree of air pollution);

3) skład betonu (type of cement, water-cement index);

4) obecność wad. in concrete (Lynx, cracks, crayfish);

5) treatment of concrete after it has set (impregnation, protective coatings);

6) wiek betonu.