The four types of concrete corrosion

The term concrete corrosion refers to the internal decomposition and aging of the concrete by chemical reactions. This includes both internal pure concrete damage and the introduction of corrosion by steel reinforcements. Experts describe four defined chemical and physical causes as concrete corrosion.

Four exposure classes

The four so-called exposure classes describe the respective types of damage that lead to concrete corrosion. Frost effect with or without de-icing salt triggers it just as much as chemical agents that act on the environment and usually lead to carbonation. Mechanical exposure is the effect of heavy traffic that leads to physical damage. Chemically, the alkali-silica reaction.

In most cases, several causes mix and accelerate the concrete corrosion. Similar to a disease, early detection and "treating" is important to prevent chain reactions. If concrete corrosion has been detected, a thorough renovation of the concrete floor or concrete wall is essential.

Metal corrosion and chain reactions

The cost of a concrete rehabilitation can increase rapidly, since in the damage analysis and causal research exposing the damaged areas is rarely to be avoided. This also applies in particular to reinforced concrete, the reinforcing steel of which has to be exposed so far that no corroded parts are left.

The corrosion of the reinforcement initiates a chemical chain reaction, which leads to further reaction patterns. Steel is particularly vulnerable when it partially comes into contact with the surface. This can be done mainly by heavy mechanical stress. Outbreaks on sides of concrete works often expose the ends of reinforcing steel. The reaction of the steel with oxygen allows the rust to eat into the concrete.

Lengthy concrete cancer

A special, dreaded and not yet completely explored type of concrete corrosion is the concrete cancer. The concrete structure decomposes as a result of the encounter between the alkaline environment of the cement and reactive silicic acid from some rock types, the alkali-silica reaction (AKR). The porosity changes and "bloat" occurs, causing the concrete to crack and burst. Often other exposures accelerate this process.

Concrete cancer develops undetected for many years and is usually not discovered until it has become visible in the concrete after it has broken off or burst. In some cases, this type of concrete corrosion can not be rehabilitated. An alkali guideline lists the rocks and mining regions known for their concrete corrosion.

Fast and slow carbonation

The process of carbonation seems paradoxical because this type of concrete corrosion water-filled pores hinder the uptake of water. While the effect is less pronounced in the case of severe weather conditions with direct rainfall, corrosion accelerates in weather-protected concrete. The moisture in the air can be less effective as a precipitate against the water-repellent effect.

Tips & Tricks

If you are worried about concrete corrosion in your building, you can use some test methods to perform measurements without exposing the potentially damaged areas. Especially for metal corrosion, there are electrically effective remediation and avoidance techniques.

Video Board: Corrosion in Reinforced Concrete