Reinforced autoclave aerated concrete (RAAC) planks are concrete planks that were commonly used in construction between 1960 and 1995. Essentially, these are planks that incorporate bubbles of air within them to make the planks more lightweight - meaning that they are easier and cheaper to transport and handle.
Many public sector buildings across the UK are likely to have used RAAC planks in their construction. A recent BBC article highlights the extent of the issue in Scotland: Faulty concrete fears at 250 NHS Scotland sites - BBC News (opens in new tab)