Concrete corrosion occurs wherever the surface of concrete or reinforcement is exposed to the effects of various kinds of destructive factors. Very roughly speaking, it is assumed that there are three types of concrete corrosion: physical, biological and chemical corrosion.
Physical corrosion is caused primarily by processes related to concrete cavitation, abrasion and erosion, as well as water freezing in its pores. It is relatively easy to detect since it can be observed right after the emergence of destructive factors. Biological corrosion is much more difficult to detect. It is related to the growth of algae, fungi and bacteria strains on the concrete surface. In itself, the presence of the above mentioned organisms is not something particularly dangerous. Unfortunately, the additional presence of certain sulphur, nitrogen or carbon compounds can cause the bacteria to start producing various kinds of damaging acids and other substances promoting chemical corrosion.
Of course, chemical corrosion does not consist only of the adverse effects of acids (e.g. sulphuric or nitric acid) on the composite surface, and particularly on the calcium hydroxide contained therein. It can also be caused by the presence of too soft water (the so-called lyeing corrosion) and also certain sulphates generating salts causing the concrete structure to burst. Furthermore, reinforcement can be damaged as well, especially steel reinforcement, which is particularly sensitive to the presence of chloride ions.
Of course, different types concrete corrosion pose a much more complicated issue, if only due to carbonisation. Very roughly speaking, it is a process that, during its initial stage, increases the compressive strength and hardness of composite, but the longer it lasts and the deeper it reaches inside its structure, the higher the risk of damage to the concrete and reinforcement structure.
Effective concrete corrosion prevention is, contrary to appearances, a relatively difficult task, since it encompasses many interlinked activities. Mainly, the mixture porosity should be decreased by laying and compacting it efficiently or with the choice of components enhanced with proper admixtures and additives. Aside of that, special protective chemical coatings are used, preventing water, acidic ions or other damaging factors from penetrating and also guaranteeing that water can freely evaporate from the concrete. It should be kept in mind that this is a still developing domain of the construction industry, where new and increasingly better solutions are constantly emerging, significantly increasing the life and other physicochemical properties of composite.