What is the most common cause of concrete deterioration?

Corrosion of reinforcing steel and other embedded metals is the main cause of concrete deterioration. When steel corrodes, the resulting rust occupies a larger volume than steel. This expansion creates tensile stresses in the concrete, which can eventually cause cracking, delamination and chipping (Figs. This expansion creates tensile stresses in the concrete, which can eventually lead to cracking, delamination and chipping.

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. The freeze/thaw cycle also affects the soil.

The soil settles differently in the warm months than when it is frozen. This fit can crack and break concrete foundations. Climate damage most often occurs in the form of cracks and potholes. Adding new levels to a building, placing heavy machinery, or building with heavy materials can place too much stress on concrete and cause serious damage.

Stress can manifest itself in many ways, chipping, peeling and cracking. 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. One of the most common defects in concrete is cracking. Cracking can be caused by improper preparation of the substrate or subbase, a high water-cement ratio, improper curing methods, poor concrete consolidation, the timing of the installation of the control joint and many other factors of placement. Cracking can also be caused by design-related issues such as improper reinforcement or insufficient joint spacing.

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. 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).

This process negatively affects concrete exposed to these harmful stimuli. This change in volume results in expansive pressures, resulting in gradual scaling, cracking and eventually chipping of the concrete. Water can also cause deterioration of concrete with its expansive and contractive properties related to freezing and thawing. If concrete is heavily reinforced, it may first cause some prestressing effect before cracking and damaging the structure.

Early removal of formwork or storage of heavy materials or operation of equipment in and around the structure can lead to overloading of certain concrete members. Concrete has enjoyed a reputation as a “place it and forget it” building material since it became popular in the mid-20th century. 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. If the concrete is not fully consolidated around the reinforcing steel, design capability may not be achieved and cracks may occur.

The repair of localized areas of concrete deterioration has proven to be an effective means of increasing the life expectancy of a structural element. In very old concrete where calcium hydroxide has leached from the leachate filtration path, the chemistry may again be similar to the chemistry of speleothems in the limestone cave. Carbon dioxide (CO) from the atmosphere diffuses easily into the leachate and causes a chemical reaction that precipitates (deposits) calcium carbonate (CaCO) outside the concrete structure. Paramagnetic defects and optical centers are easily formed, but very high fluxes are needed to displace a sufficiently high number of atoms in the crystal lattice of minerals present in concrete before significant mechanical damage is observed.

Most concrete deterioration resulting from environmental exposure occurs through water, either by the expansion of water in the freeze-thaw cycle, by contaminants carried in the water to the limb, or the combination of both effects. This form of thaumasite sulfate (“TSA”) attack seemed more likely to occur under consistently humid and cold conditions and, in the worst case, was found to cause concrete to break down into a porridge-like form, losing its strength and integrity. Documented cases around the world272—275 reported that a particular form of sulfate attack had occurred in particular that was designed to resist sulfates. 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.

Analytical methods for determining the sulfate content of concrete cannot distinguish between the two different forms of attack, ettringite and thaumasite. . .

Chloe Robinson
Chloe Robinson

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