What is Reinforced Aerated Autoclaved Concrete (RAAC)?

About Reinforced Aerated Autoclaved Concrete (RAAC):

• It is a lightweight, bubbly form of concrete that was used in roofs, floors, and walls between the 1950s and 1990s.
• It looks like standard concrete, but compared with the “traditional” reinforced material, which is typically denser, Raac is weak and less durable.
• The material was favoured in construction projects because of its lightweight thermal properties.
• How is it made?
  • It is made from a combination of cement, lime, water, and an aeration agent. 
  • The mixture is poured into moulds and then subjected to high pressure and heat, known as autoclaving, to create a lightweight, strong, and porous material.
• Advantages over Standard concrete:
  • It is cheaper.
  • It is also quicker to produce and easier to install.
  • Insulation Properties: RAAC has excellent thermal insulation properties due to the air bubbles within the material.
  • It helps maintain a comfortable indoor temperature while reducing heating and cooling energy consumption.
• Why is it a risk?
  • The concrete is aerated and “bubbly”, contains no “coarse aggregate” and is less dense than traditional concrete, being around a third of the weight.
  • It could easily absorb moisture, weakening the material and also corroding steel reinforcement within.
  • This means it is more prone to collapse over time.

Q1) What is Concrete?

Concrete is a versatile and widely used construction material composed of a mixture of cement, water, aggregates (such as sand, gravel, or crushed stone), and often various chemical additives or admixtures. It is a fundamental building material known for its strength, durability, and versatility. Concrete is used in a wide range of construction applications, including buildings, bridges, roads, dams, and more.

Source: 100 schools across England ordered to close buildings as they are constructed using unsafe concrete