ABOUT RAAC
WHAT IS RAAC?
Reinforced Autoclaved Aerated Concrete (RAAC) is typically found in buildings constructed between 1950s and 1980s and was used as a construction material, mainly for the formation of lightweight masonry blocks and structural units such as roof planks, wall and floor units.
RAAC is relatively weak due to the materials used within the mixing process and is more susceptible to the affects of water ingress or humidity than standard concrete, which can be an issue when used in particular applications, for example roof planks. This can cause rusting of embedded steel reinforcement, cracking of the RAAC and excessive deflection of structural members.
Typical life expectancy is around 30 years, as such, much of the RAAC now in situ within buildings is beyond this.
WHAT ARE THE RISKS?
RAAC can collapse without warning, which when used within a structural capacity, can pose a danger to the occupiers of the building. The material also deflects more than traditional concrete, is more vulnerable to corrosion of steel reinforcements and has a lower compressive strength than reinforced concrete which can lead to the depletion of their integrity over a period of time. This is often compounded by a lack of maintenance of a building.
IDENTIFIED RAAC
HOW CAN RAAC BE IDENTIFIED?
Firstly, the date of construction of the buildings should be identified as RAAC was typically used from 1950s to 1980s. Ensure that extensions and alterations to buildings are also considered.
If construction drawings are available, these can be really useful in identifying how the building was built and the materials that were used. Previous condition surveys may also provide information on construction and whether RAAC is present.
If a building is identified as being constructed within that time frame, a visual inspection should be undertaken. This may involve high-level access (ladder or scaffolding) and opening up works to reveal the building structure. It should be noted that buildings constructed in the relevant timeframe are also likely to contain asbestos and the asbestos register should be reviewed, or a survey undertaken if no information is available on the area in question.
RAAC is typically found in the form of planks, around 450mm to 600mm wide and around 2.4m to 3m long, with a chamfered edge detail. The concrete has an aerated, ‘bubbly’ texture and is softer than typical concrete, which may be able to be indented with a sharp tool such as a screwdriver. Typical defects include mass hairline cracking and deflection of the planks between the structural supports.
If you believe that RAAC may be in situ, further investigation is required in the form of sampling for lab analysis and the appointment of a structural engineer. It would also be prudent to consider the potential impact of reduced maintenance regimes on the condition of your property portfolio; in particular where RAAC is used, given the susceptibility of the material to water ingress.
