Concrete Defects Flashcards
How much cover of concrete is required to steel reinforcement?
Minimum of 20-70mm of cover, depending on it’s function. If insufficient cover, steel reinforcement can corrode
What are available remedial actions for Alkali Silica Reaction?
Remedial actions are limited. It is important to monitor the reaction, and recommended to take core samples to test for silica gel. Minimising the ability to absorb water will stop the gel from expanding further. Badly effected areas will require strengthening or replacement.
What is Concrete Carbonation?
Concrete Carbonation is the reaction of carbon dioxide in the atmosphere, water and cement to form a carbonic acid. This acid then reduces the alkaline nature of the concrete, breaks down the passive layer surrounding the steel reinforcement, and causes corrosion.
What is Chloride Attack in concrete?
Chloride attack in concrete is when chloride ions affect the natural passive protective film to steel reinforcement and cause corrosion.
Calcium chloride additive in concrete have been banned since 1977. Can be introduced from de-icing salts or from sea spray.
What are the available remedial actions for Concrete Carbonation?
Firstly, remove the water source. As carbonation can only occur in a solution, removing the water will not only prevent the corrosion of the steel work but also the carbonation.
To treat the effects, wish brush corroded areas and apply a corrosion inhibitor. It may be beneficial to coat the finished concrete to prevent further carbonation.
What is Alkali Silica Reaction?
Alkali Silica Reaction is when alkalines in cement react with silica in aggregates to form a silica gel which expands with contact with water, causing cracking
What is Honeycombing to concrete?
Honeycombing is where there are small voids within the concrete. This can be cause by number of things, including insufficient vibration when poured, and poor formwork, including the use of wood wool slabs as formwork.
Why is Honeycombing to concrete an issue?
If concrete is honeycombed it becomes more vulnerable to corrosion to the steel reinforcement, to fire, and to the effects of the freeze-thaw cycle due to all of the voids.
What remedial actions are available for treating chloride attack in concrete?
Cut out the affected areas, wire brush corroded reinforcement, apply a corrosion inhibitor and reinstate the concrete. Monitoring over time will be required
What advice would you give a client if you identified Concrete Carbonation within their property?
If I suspected that Concrete Carbonation was present I would like to confirm that definitely, therefore I would recommend that my client engage concrete specialist to carry out testing to confirm my diagnosis.
Following that I would recommend that the water source be reduced as much as possible. Thereafter I would recommend treatment including wire brushing the areas, applying a corrosion inhibitor and possible coating the area to prevent further carbonation.
What advice would you give a client if you identified Alkali Silica Reaction within their property?
If I suspected Alkali Silica Reaction within a property or structure, I would advice the client to engage with a concrete specialist to confirm the diagnosis. Sample of the concrete can be taken, and examination/pH test carried out to identify the silica gel or the level of alkaline content in the aggregate. If possible, I would advise the client to carry out works that reduced the water ingress to the area. Depending on the severity of the issue, it may be necessary to recommend some are of replacement of the concrete.
What are the indicators of chloride attack in concrete?
The location may be an indicator, such as a car park where the use of de-icing salts are used, or by the sea.
Corrosion of the steel reinforcement, and additionally the concrete will show signs of cracking and crazing.
Chloride attack reduces structural strength over time, and is displayed by spalling and pitting of concrete.
What are the indicators for Concrete Carbonation?
Corrosion of the steel reinforcement, which expands and causes cracking and damage to concrete surrounding.
ACTUAL INDICATOR - Phenolphthalein indicator can be used to assess if the concrete is acidic, and therefore carbonated. It will turn pick if no acidic content, and will remain colourless if carbonation is present.
What are the indicators for Alkali Silica Reaction?
Alkali Silica Reaction is uncommon in the UK. It is most easily identified by map like cracking across the surface of the concrete. In some extreme case the silica gel can be seen on the surface of the concrete
What is the treatment for Honeycombing of concrete?
Affected areas of concrete should be broken out and replaced
