Crumbling concrete sparks international debate on peculiarly British problem

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As the UK reeled from revelations of unsafe bubbly concrete in schools this month, construction experts who had gathered in Prague to celebrate the material were frantically gleaning details of the scandal engulfing Britain.

“I got mobbed and I’ve never been mobbed,” said Chris Goodier, a professor who has shot to prominence as one of the few British experts with in-depth knowledge of the concrete. “It’s exploded as an issue in the UK and it hasn’t in other countries.”

The UK government’s closure of more than 100 school sites at risk of collapse just days before the start of the academic year has caused a political firestorm, and sparked a hunt across government departments to find other public and private buildings containing reinforced autoclaved aerated concrete — or RAAC.

The government has defended its record by arguing that awareness of the UK’s troubles stem from Britain’s “world-leading” monitoring systems.

But the furore has sparked a debate over whether the UK has lagged behind peer countries on construction standards, with some experts telling the Financial Times the UK’s Raac problems were caused by shortcomings in the design, construction and maintenance of Britain’s public estate.

“It’s very, very strange because AAC has been a very well-known and respected product for many years,” said Fouad H. Fouad, who heads the civil engineering department at the University of Alabama at Birmingham. He helped bring the lightweight material to the US in the 1980s.

He added that he had studied photographs of some of the British buildings where there had been failures and found there were “specific issues in the UK . . . with design, production and construction”.

In some cases, he said panels of concrete appeared to be cut at the wrong place, including at critical reinforcement points. In others, he noted that reinforcement was missing or not sealed properly to keep out water.

Raac was a popular building material across Europe and North America in the postwar period, most notably in Germany. It was also used for construction in Australia, New Zealand and Mexico.

News of serious concerns about the integrity of buildings constructed in the UK using the material between the 1960s and 1990s, including several reported incidents of collapse, has shocked experts overseas.

Four international experts on the material told the Financial Times that they had not heard of any issues with severe corrosion or collapse associated with Raac outside of Britain. The UK government was unable to point to known examples overseas, or studies suggesting it was an international problem.

The government said that it had “acted decisively to tackle this issue and has taken a proportionate approach informed by experts”.

“Professional advice from experts on Raac has evolved over time, from advice in the 1990s that Raac did not pose a safety hazard to more recent advice on identifying and assessing structural adequacy,” it said.

Raac was commonly used in the UK during the postwar drive to build a large number of schools and hospitals at the lowest cost possible. More recently, maintenance of the public estate has suffered during the past decade of Conservative government.

The Institute for Government think-tank estimates that the overall capital budget for school repairs fell by more than a third between 2007-08 and 2020-21, from £7.9bn to £5.1bn in real terms.

Karl-Christian Thienel, chair of the European standard-setting body on autoclaved aerated concrete, said the problem of fragile public buildings with Raac stemmed in part from the UK’s cost-cutting approach.

“Poor maintenance led to water ingress and . . . opened the chance for [reinforcement] corrosion,” he said. “In addition the old slabs often had a rather small support.”

Others have said that it just a matter of time before other countries discover similar issues. Patrick Hayes, technical director of the Institute of Structural Engineers, said he thought cases had only been identified in Britain thus far because the UK has a robust system in place that allows confidential reporting of structural problems with buildings.

He and Goodier, professor of construction engineering and materials at Loughborough University, were confident that failures would be found internationally at some point.

But Goodier added that some Raac had been found in the UK built with supports that were too small and reinforcements in the wrong place, “both of which can have structural implications”.

He said that in countries such as Germany the construction industry tends to have “much better training and construction practices”. “They have higher-quality [material] than us and they have good engineers.”

Jiří Kolísko, a professor at the technical university in Prague, said Raac had been used for decades in the Czech Republic, predominantly for walls and building facades. In the UK, he said it was predominantly used to construct long flat roofs, where it is more exposed to rainfall that can erode the concrete if it is not properly sealed.

Professor Manfred Curbach, director of the Institute of Concrete Structures at the Dresden University, said he was not aware of Raac causing any problems in Germany. When asked why, he said: “Because when we use Raac we use plastic-covered rebar [reinforcement bars]. [It is] very expensive but it works.”