In early 2019, the standing committee on structural safety issued an alert following the near-miss in a school, alerting all affected building managers to be aware of the RAAC problem. The panels typically have a chamfer along their edge, meaning there is a distinctive V-shaped groove every 600mm in the surface of the roof, floor or wall. RAAC panels are typically 600mm (approximately 2ft) wide and are typically up to six metres in length. An example of RAAC failure occurred in 2018 where the roof at a school fell in without warning, triggering an investigation by the Government. The cost-effective material has a functional lifespan of around 30 years, beyond which its strength can deteriorate. Water ingress is a problem for buildings with flat roofs, but other problems have been identified specific to poor installation, such as inadequate reinforcement and bearings that are too small.
The material can appear fine and then suddenly fail catastrophically without warning. Air inside the material makes it vulnerable to moisture, which leads to corrosion and jeopordises the material’s tensile strength, posing a risk of collapse. However, the material has small air pockets throughout, which poses long-term durability concerns. These blocks and planks can then be used in buildings. It can grow to five times its original size following completion of the reaction. This makes the slush swell in size as the gas is generated. This slurry is poured into a mould and the chemical reaction between the aluminium and other reagents creates hydrogen gas. The raw materials are cement, blast furnace slag and pulverised fuel ash or silica flour, and these are mixed with water and aluminium powder. The material consists of lightweight concrete planks reinforced with steel rods. It was a common building material in public buildings between the 60s and 80s, and was used for roofs and walls in many schools and hospitals. RAAC, or reinforced autoclaved aerated concrete, is a type of concrete widely used in buildings during the second half of the 20th century.
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