Reinforced autoclaved aerated concrete – better known as RAAC – has been in the news recently following the discovery it has been declared unsafe in many schools and other buildings. People are understandably worried and are being cautious around concrete products while solutions are found.
We have put together this guide to RAAC to explain what it is, why it could be dangerous and to address any concerns people have regarding Specwall’s A1-rated panels which are an aerated concrete product.
What is RAAC?
RAAC is a concrete material that is aerated or “bubbly” to make it a lighter alternative to regular concrete. It was used extensively in the 1950s and 1960s for flat roofing, floors and walls. It is quicker and cheaper to produce, making it a desirable material at the time for rapid programmes of public building, including schools, hospitals and more.
The concrete is made from cement, lime, water and an aeration agent which are mixed together and poured into a mould. They are then put under high heat and pressure – a procedure known as autoclaving – which creates a lightweight, porous material.
Why is RAAC dangerous?
The structure of RAAC described above makes it significantly different from traditional reinforced concrete to the point where a report from the Institution for Structural Engineers said: “It is perhaps unfortunate that the term concrete has been retained for these aerated product.”
The main point of weakness is that its production opens it up to structural failure over time when exposed to water. The bubbles can allow water to enter the material and this can decay, rust or otherwise weaken any rebar included in the material. RAAC was often coated with other materials such as bitumen to help combat this, but this material can also degrade. Overall, it is estimated that RAAC has an ideal lifespan of just 30 years, making it a major risk in buildings today.
It is estimated that short-term exposure to moisture reduced the strength of RAAC by 13%, while long-term exposure to "polluted air" reduced it by 40%. This is a big difference when compared to traditional concrete.
How are Specwall A1 panels different?
Specwall’s A1-panel is an aerated concrete product but it differs from RAAC in major ways which make it a completely different – and completely safe – prospect.
Whereas RAAC differs so much from traditional concrete panels that experts consider it to be a completely separate product, our A1 panel follows the same manufacturing process as our A2 panel.
The concrete is assembled in panel moulds before being moved to the pouring/filling area. Admixtures and additives are then introduced into the concrete and water mix. The only difference between this and the A2 concrete panel is that polystyrene EPS beads are not added.
Next, the mix is poured into pre-prepared moulds and allowed to set. Crucially, the moulds are not subjected to intense heat and pressure as RAAC is. Once the concrete is set, usually after a few hours, it is de-moulded and transferred to the curing area where it is watered daily for the next seven days before proceeding to finishing and packing. At this stage it is ready for shipping and then installation.
This gives the A1 panel all the strengths of the A2 panel as well as other advantages such as hugely increased fire performance of at least 3.5 hours. You can find out more about the A1 panel and its excellent performance and advantages by clicking here.
RAAC is in the news for good reason and it will have to be replaced in many buildings over the coming years. However, Specwall’s A1-rated panel undergoes a superior production process and does not share the weaknesses of RAAC.
Want to learn more about Specwall and how it can benefit your development? Get in touch with the team today by clicking here.