Structural Concrete Defects and Damage – The Causes
We’ve been involved in the maintenance and repair of reinforced concrete for 18 years and we have seen a sizeable increase in recent years in the amount of replacement and repair work now needing to be done.
This may simply reflect the fact that a large number of reinforced concrete structures are now ‘coming-of-age’ and need repair or replacement work through natural usage, but there have also been some changes in materials used over the last twenty years or so which might point to something else at work…
Discovery of Alkali Reactive Aggregates
In the early seventies it was believed that there were no deposits of alkali reactive aggregates in the UK and yet within a few years, alkali aggregate reaction became a subject of major interest as increasingly more cases came to light.
This upsurge in alkali silica reaction problems may be traceable to an increase in cement alkali content in the preceding years. In the light of this detail, it became clear that concrete should be regarded as a complex mixture of materials and each component may, in itself, vary, or be affected by environmental factors.
Furthermore, increases in the early age strength of cement may have meant that specified minimum strengths were being achieved with less cement than had previously been used. This reduction in the amount of cement used would in turn have a corresponding effect on subsequent durability.
From our experience, around 90 % of the problems that we experience in concrete repair will involve steel reinforcement corrosion as a primary problem.
For the most part this will have been caused entirely by simple concrete carbonation and/or the presence of chloride salts either from calcium chloride used as an accelerator, or in some cases, even de-icing salt.
Other Possible Causes of Concrete Damage
However, there may be a whole variety of other possibilities causing damage such as
- shrinkable aggregate
- frost attack
- sulphate attack
- structural cracks
It must be taken into consideration that many of these problems may reveal themselves first of all in areas of low cover and carbonated concrete; this will be because ‘micro’ cracking from one or other of these causes has permitted carbonation to advance more rapidly in the concrete than would have otherwise been the case.
In such cases, it is all too easy to look at the symptoms of the problem, (eg steel corrosion) and mistakenly identify them as the cause.
Attempting to repair concrete affected by such problems, instead of curing the underlying cause may simply mean that the problem recurs in a relatively short space of time.
This is why we recommend and provide a comprehensive range of concrete tests and inspections, to determine exactly what is needed for your particular defective concrete problem.
Please look at our range of concrete tests available or simply contact us if you’d like further advice.