In light of recent UK government investigations into the safety of buildings constructed with Reinforced Autoclaved Aerated Concrete (RAAC), public concern has risen. This comprehensive Q&A guide aims to provide a detailed understanding of RAAC, exploring its history, benefits, drawbacks, and current status.

What Exactly is RAAC?

Answer: RAAC, or Reinforced Autoclaved Aerated Concrete, is a type of lightweight concrete that contains a large number of small air bubbles. It is formed by mixing sand, lime, and cement with aluminum powder, which reacts to produce the bubbles. The concrete is then autoclaved (exposed to high-pressure steam) to strengthen it. The end result is a material that is lightweight yet strong, with good thermal insulation properties.

Historical Context: When Was RAAC Introduced?

Answer: RAAC was developed and introduced in the mid-20th century, initially gaining traction in the 1960s and 1970s. The material was considered revolutionary for its time because it offered a lightweight yet durable alternative to traditional concrete, reducing costs and construction time.

The Timeline: What Years Was RAAC Concrete Used?

Answer: RAAC was mainly used from the late 1950s through to the 1980s. It was a popular choice for public buildings, schools, and large residential blocks, particularly in the United Kingdom.

When and Why Did RAAC Use Decline?

Answer: Use of RAAC started to decline in the late 1980s. This was largely due to growing concerns over its long-term structural integrity. Instances of cracking and degradation were reported, leading to investigations that questioned its suitability for long-term use, especially in load-bearing structures.

Is RAAC Used in Modern Construction?

Answer: As of today, RAAC is seldom used in new constructions. Contemporary building codes and practices have generally moved away from RAAC in favor of materials that offer longer-term durability and safety.

The Risks: Why is RAAC Considered Unsafe?

Answer: The primary risk associated with RAAC lies in its susceptibility to degradation over time. Factors such as moisture ingress, freeze-thaw cycles, and general aging can cause the material to lose its structural integrity. This is particularly concerning in buildings where RAAC has been used in load-bearing components or large panel systems, as it could lead to catastrophic structural failures.

How Does RAAC Differ from Regular Concrete?

Answer: While both RAAC and regular concrete consist of similar basic ingredients (sand, lime, and cement), the addition of aluminum powder and the autoclaving process in RAAC make it significantly different. It’s lighter, has better thermal properties but can be less durable than traditional concrete.

What Should You Do if Your Building Contains RAAC?

Answer: If you own or reside in a building constructed with RAAC, it’s crucial to have a structural assessment performed by qualified engineers. They can check for signs of degradation, such as cracking or bowing, and recommend either remedial measures or, in extreme cases, replacement of the material.

UK Specific: What Steps is the Government Taking?

Answer: The UK government is actively investigating older buildings that were constructed using RAAC. These structures are being assessed for safety, and owners may be required to take remedial action if any risks are identified.


As the UK government takes steps to assess the safety of buildings constructed with RAAC, it’s essential for building owners and occupants to understand this material. Though innovative for its time, RAAC has shown limitations that make it less desirable for modern construction, especially concerning long-term structural integrity.

Note: This article serves as a general guide and should not replace professional advice.

By equipping yourself with this information, you’ll be better prepared to address any RAAC-related issues with your property or community buildings.

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