Concrete Damage and Problems

Concrete damage, defects and problems can be caused for many different reasons, or as a result of a combination of several root causes. These causes are normally referred to and classified as:

Concrete Damage

Damage that is caused by Mechanical, Physical or Chemical exposure, i.e.

Mechanical impact, blast or abrasion damage.
Physical attack from Freeze-Thaw action, or from Expansive Alkali Aggregate Reaction (AAR), - which is also known as Alkali Silica Reaction (ASR).
Chemical Attack by aggressive soft water leaching, acidic liquid or gaseous attack, or other adverse chemical exposure.

Concrete Damage Due to Steel Reinforcement Corrosion

Concrete damage that is caused by the corrosion of the embedded steel reinforcement, i.e.

Cracking and spalling concrete over the reinforcement due to expansive steel corrosion caused by carbonation of the concrete and loss of the protective alkalinity.
Cracking and spalling over the reinforcement due to accelerated and expansive steel corrosion caused by chloride presence.
Electro-potential differences with other metal elements or stray electric currents from elsewhere can also cause steel corrosion.

A summary and examples of Concrete Defects and Damage, plus Concrete Damage due to Reinforcement Corrosion is given in the following Two Tables:

Mechanical	Chemical	Physical
Concrete Defects and Damage
Impact. Overloading. Movement (settlement). Vibration. Earthquake. Explosion.	Alkali aggregate reaction. Aggressive chemical agents exposure i.e. sulphates, nitrates and other salts, soft water (acidic/low pH). Bacterial or other biological action. Efflorescence/leaching.	Freeze/thaw action. Thermal movement. Salt crystal expansion. Shrinkage. Erosion. Abrasion and wear.
Example: Cracking caused by incorrect handling or fixing of precast panels.	Example: Chemical attack from aggressive gases (and subsequent reinforcement corrosion) on the top of chimneys or the soffits of a factory roof.	Example: Freeze/thaw effects with progressive scaling on the soffits of a parking structure.

Carbonation	Stray / Electrical Current	Corrosive Contaminants e.g. Chlorides
Concrete Damage due to Reinforcement Corrosion
Carbon dioxide (CO₂) in the atmosphere reacting with calcium hydroxide in the concrete pore liquid. CO₂ + Ca(OH)₂ CaCO₃ + H₂O Soluble and strongly alkaline pH 12-13 almost insoluble and much less alkaline pH 9. Steel passivated steel unprotected.	Metals of different electro potential are connected to each other in the concrete and corrosion occurs. Corrosion can also be due to stray electrical currents from power supply and transmission networks.	Chlorides accelerate the corrosion process however it was originally caused. At above 0.2-0.4% concentration in the concrete they can break down the passive oxide protective layer on the steel surface. Chlorides are typically from marine/salt water exposure or the use of de-icing salts.
Example: Reinforcement corrosion following reduction of the passivating concrete alkalinity, by natural atmospheric carbonation.	Example: Reinforcement corrosion evident as rust staining from cracks, after galvanised steel supports for parapet railings were fixed in direct contact with the embedded steel reinforcement.	Example: Steel corrosion accelerated by chloride ingress from de-icing salts used on a bridge and penetrating, particularly through the joints over the support piers.

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