Concrete degradation can have several causes. Concrete can be damaged by fire, aggregate expansion, seawater effects, bacterial corrosion, calcium leaching, physical damage and chemical damage (by carbonation, chlorides, sulfates, and non-distilled water). Concrete deterioration can cause major headaches for building owners. It is important to correctly identify these defects in time and plan appropriate repair strategies.
Concrete deterioration can occur through fouling, disintegration, erosion, reinforcement corrosion, delamination, chipping, alkaline aggregate reactions and concrete cracking. Water is the most common cause of concrete deterioration. Because concrete is porous, water can seep into the concrete and reach the structure below. This exposure to water can oxidize steel particles in concrete and oxidize reinforcing bars in reinforced concrete.
Rusty rebar can expand up to four times their normal size, causing concrete to break. If you've noticed red streaks on your concrete structure, you likely have rust underneath. Believe it or not, carbon dioxide in the air we breathe can cause the deterioration of calcium hydroxide in the concrete mix, it is responsible for the required alkalinity, but is compromised when carbon dioxide is allowed to react with it. The reaction is capable of lowering the pH to an undesirable level, exposing the steel to corrosion.
For horizontal surfaces, where stagnant water is allowed to accumulate, freezing and thawing will make the concrete more permeable, further exposing the reinforcement to carbon dioxide, chlorides and water. When water enters small holes and then freezes, the expansion damages the surrounding concrete and widens the holes over time. Chemical attack is one of the most common causes of concrete deterioration in today's industry. Animal fats, natural and artificial oils, acids, alkalis and various industrial salts are harmful to concrete.
Chemical attack occurs due to pollution products and after discharge activity on the surface of the insulator. Examination of aged insulators in the field has found the formation of thin and uniform contaminant layers on the surface. A chemical attack involves the dissolution of substances or chemical reactions between substances and components of concrete. Reaction products can cause problems, due to dissolution or expansion.
Freeze-thaw damage is a potentially serious deterioration process that occurs in concrete structures in cold climates. In the worst case, the formation of thaumasite can cause concrete to decay into a mush form, losing its strength. Concrete can deteriorate for a variety of reasons, and damage to concrete is often the result of a combination of factors. Concrete can also leak water through the suction of the subbase or, depending on the type of material used in its manufacture, the formwork.
This means that structural concrete may no longer live up to the job it was built for once deterioration begins. As the outer concrete paste wears, the fine and coarse aggregate are exposed and abrasion and impact will cause further degradation related to the strength of the aggregate to paste bond and the hardness of the aggregate. Figg308 and Eglinton give good summaries of the sulfate attack; 309 more extensive treatments can be found in Swenson310 and in a publication of the American Concrete Institute. Rapid moisture loss from newly laid concrete can also lead to plastic shrinkage cracks, which are random shallow cracks on the concrete surface.
The total contribution of the aggregate to the carbonate content of a concrete was resolved in three ranges (A higher, B and C lowest), depending on the calcium carbonate content of the total aggregate and the proportion of that total that was present in the fine aggregate fraction. Sulfate attack is one of the most harmful causes of concrete deterioration, as it causes softening and decay of the concrete matrix (the type of attack of “acidic” sulfate) or expansive cracking and other disturbances associated with the formation of ettringite (calcium sulfoaluminate hydrate) and other product reactions inside hardened concrete. Samarai,313, in experiments in Iraq with powdered gypsum in mortar bars, produced unacceptably high expansions with Portland cement mixtures containing a total sulphate content of more than 5 per cent by weight of cement. Computer modeling of the expansive behavior of rectangular or inverted T-shaped sections to replicate the level of cracking of the concrete surface would have been a complex effort involving non-linear material behavior.
Premature damage to concrete slabs during freezing and thawing cycles represents a major challenge to pavement durability and resilience. The influence of thermal neutrons on concrete is low and decreases with distance from the inner face; this has a negligible effect on the properties of concrete (Brandt %26 Jóźwiak-Niedźwiedzka, 201. .