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The exposure conditions for car parks in countries where de-icing chemicals are frequently used are much more severe than those for conventional buildings. The form of the construction will have a significant influence on the severity of conditions that lead to deterioration of vulnerable details. Some elements are in conditions of exposure similar to those in normal buildings for which BS 8500 or similar exposure classifications are suitable. Evaluation of car parks where premature deterioration has occurred has shown that surfaces or details exposed to de-icing salt carried into car parks on vehicles or used for de-icing in the car park need greater protection and/or higher standards than for concrete elsewhere.
The major corrosion mechanisms that affect the durability of car park structures are corrosion of steel reinforcement, caused by the ingress of chlorides from de-icing salts and coastal environments, and carbonation of the concrete surface leading to loss of alkalinity and hence reduced protection against corrosion.
Sufficient water and oxygen, the two other components required for corrosion, are almost always present in car parks in the UK.
Car parks, as with all buildings, can also be at risk from freeze-thaw attack, alkali-silica reaction and sulfate attack (see separate entries). Codes now include requirements that should address some historic problems in older structures, such as HAC conversion, corrosion from the use of calcium chloride as an accelerator or the use of aggregates containing significant chlorides.
Acknowledgement: The Institution of Structural Engineers
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