RAAC Planks
RAAC Planks and Survey Services
Reinforced autoclaved aerated concrete (RAAC) planks were often used as roof decks and sometimes as vertical wall cladding.
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RAAC Roofing Planks have, in some cases been found to have deflected excessively, leading to ponding on roofs, failure of roof membranes and sometimes collapse.
Deflection is sometime evident by a series of transverse cracks on the soffits of the planks. The material is usually light grey in colour and easily broken or damaged.
In cross section, the cellular nature of the product is easily seen. The basic material is in all respects similar to lightweight insulating blockwork.
RAAC Roofing planks are rectangular in section with chamfered edges to form a vee groove appearance when installed. Typically, planks vary in width from 300mm-750mm and spans up to 6m are not unknown. A thickness of around 100-250mm would be typical.
Steel reinforcement in concrete is normally protected from corrosion by the highly alkaline nature of concrete, but in the case of RAAC, the porous nature of the material does not provide this protection.
Possible defects to look out for include:
- slippage of the reinforcement under load. (Because the material is soft and easily crushed, it does not secure the reinforcement as solidly as with conventional concrete.) Slippage could lead to deflection;
- crushing of bearing ends;
- corrosion of light steel reinforcement;
- transverse cracking on the soffit.
RS carry out surveys to identify RAAC planks and establish their condition.
Surveys are discreet and not unduly disruptive.
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RS provides a professional, innovative, reliable and competetive service drawing on many years experience in the investigation, inspection and remediation of buildings and structures.