Survey Finds Reinforced Autoclaved Aerated Concrete in Historic Palace; Restoration and Renewal Programme Ensures Safety.
A recent survey of the iconic Palace of Westminster, the historic meeting place of the UK Parliament, has unearthed the presence of reinforced autoclaved aerated concrete (Raac) in select areas of the building. Raac, a lightweight form of concrete popular in construction projects from the 1950s to the 1990s, has been identified as potentially prone to deterioration over time and sudden collapses.
This discovery comes as part of the ongoing Restoration and Renewal Programme, a multi-billion pound initiative aimed at refurbishing and modernizing the centuries-old palace, which traces its roots back to the 11th century. According to a spokesperson for the programme, Raac was identified in “a very small number of locations” within the palace, and they emphasized that it currently poses “no immediate risk to the safety of the building or its occupants.”
The spokesperson further stated that affected areas are under close monitoring, and remedial works will be carried out as part of the comprehensive Restoration and Renewal Programme. “The Restoration and Renewal Programme will ensure that the Palace of Westminster is fit for the future and preserves its rich heritage for generations to come,” they affirmed.
Raac has been a matter of concern for numerous public buildings in the UK, particularly schools and hospitals, where it was predominantly used in flat roofing but also in floors and walls. In August 2023, the Department for Education issued orders for schools to temporarily close buildings constructed with Raac until safety assessments and necessary repairs were completed, affecting thousands of students across England.
What sets Raac apart from standard concrete is its absence of coarse aggregate, such as gravel or crushed stones, which contributes to concrete’s strength. It is also aerated, giving it a lightweight quality. However, these characteristics make Raac less durable and more susceptible to water damage and corrosion. Experts assert that Raac typically has a life expectancy of just over 30 years, and buildings constructed with Raac between the 1950s and 1990s that have not undergone structural assessments are at risk of collapse.
The danger of Raac has been underscored by several incidents, including the roof collapse at Singlewell Primary School in Kent in 2018, which occurred suddenly, without prior warning, 24 hours after signs of structural stress first appeared.
The Institution of Structural Engineers has issued comprehensive guidance on how to identify and inspect Raac structures and has strongly advised building owners to arrange regular surveys conducted by qualified professionals. The guidance also recommends that any defective Raac structures should be replaced with more suitable materials as soon as possible.
The discovery of Raac within the Palace of Westminster serves as a reminder of the importance of diligent maintenance and preservation efforts for historic structures. While there is no immediate cause for alarm, it underscores the significance of ongoing restoration work to safeguard this iconic symbol of British democracy.
Resources:
2.https://en.wikipedia.org/wiki/Reinforced_autoclaved_aerated_concrete
3.https://www.istructe.org/get-involved/study-groups/reinforced-autoclaved-aerated-concrete-planks/
4.https://www.bbc.co.uk/news/education-66669239
5.https://www.itv.com/news/2023-08-31/what-is-raac-the-weak-concrete-thats-causing-schools-to-crumble
7.https://en.wikipedia.org/wiki/Palace_of_Westminster