The presence of Reinforced autoclaved aerated concrete (RAAC) in a building is a cause for concern, requiring immediate attention. As a leading independent construction materials consultancy, Sandberg can provide guidance and carry out inspections for RAAC.
Concerns about RAAC
Concerns about Reinforced autoclaved aerated concrete (RAAC were raised as early as the 1990s by the Building Research Establishment and the Standing Committee on Structural Safety (SCOSS). Poor in-service performance, with cracking, excessive displacements and durability, was identified.
In May 2019, SCOSS raised a further alert about the potential risks of RAAC construction. This was after a failure within an operational school in 2018 and the deterioration of planks at retail premises following water ingress reported in early 2019.
Since then, there have been further sudden collapses of RAAC panels in roofs that appeared to be in good condition.
It is, therefore, essential that all responsible bodies undertake work to identify any RAAC they have in their estate following the stages set out in this guidance. 1
What is RAAC?
Reinforced autoclaved aerated concrete (RAAC) is a reinforced version of autoclaved aerated concrete commonly used in flat roofing but also in floors and walls between the 1950s and 1990s. Its advantages were its lighter weight and lower cost compared to traditional concrete and its good insulation and fire resistance properties.
It is very different from ordinary concrete due to its aerated, bubbly appearance and porous properties. The porous nature of this concrete means that reinforcing steel within is less protected. The concrete is also more prone to moisture ingress, meaning that reinforcement corrosion is more likely, with a potential loss of structural integrity.
Although RAAC is currently in the news because of its presence in schools and hospitals, it may be found in a variety of other types of buildings, such as retail, offices, recreational buildings and more. The same risks of collapse exist in these buildings. Therefore, it is important that the use of the product is identified and recorded.
Identification of RAAC
Identification of RAAC can be relatively straightforward. The panels are light grey or white in appearance. The outside face is smooth, but internally, the concrete contains bubbles, similar to an Aero chocolate bar. There is no visible aggregate in the concrete.
RAAC panels were most commonly used in flat roofs, although they may also be found in pitched roofs, floors and walls. The panels are typically 600 mm wide and up to 6 m long. They are soft and can easily be marked with a screwdriver. Identification of the panels is easiest if they are exposed. However, they are often obscured by suspended or false ceilings or other finishes. In these situations, care must be taken of the risk of asbestos exposure. Asbestos was extensively used during the same period.
A useful guide and further information can be found here.
RAAC Surveys and Testing
The presence of RAAC in a building is a cause for concern, requiring immediate attention. If it is identified, a structural and durability assessment should be undertaken by a suitably qualified structural engineer.
As a leading independent construction materials consultancy, Sandberg can provide guidance and carry out inspections for RAAC, including:
- RAAC site identification surveys
- Condition assessments
- Laboratory testing
- Structural monitoring
For more information contact our in-house experts:
- Department for Education (August 2023) Retrieved from Reinforced Autoclaved Aerated Concrete (RAAC): Identification Guidance ↩︎