England’s concrete crisis could extend to hospitals and courts, experts say (www.theguardian.com)

submitted 2 years ago by thehatfox@lemmy.world to c/unitedkingdom@feddit.uk

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[-] collegefurtrader@discuss.tchncs.de 38 points 2 years ago

TLDR you limey bastards built school roofs out of a material that was advertised as with a 30 year life span, and here we are 40 years later and its surprised pikachu faces all around.

[-] tal@kbin.social 20 points 2 years ago* (last edited 2 years ago)

advertised as with a 30 year life span,

It's not clear to me from the article whether it was expected to only last 30 years at the time, or whether it was subsequently revised down in some way.

I mean, my guess is that many building materials may only guarantee some number of years, but it may be the norm for them to last longer. I assume that businesses selling stone do not rate, say, masonry for hundreds of years, though it clearly can last that long.

The article has:

Raac, a lightweight building material, was commonly used in panel-form in public building construction from the 1950s to mid-1990s. It is estimated to have a lifespan of 30 years, and many structures have now passed that age.

EDIT: Yeah. From another article, it sounds like at the time it was built, it was not realized that the material would last only 30 years:

https://news.sky.com/story/the-once-wonder-material-reinforced-aerated-autoclaved-concrete-will-cause-chaotic-start-to-academic-year-12951727

During the post-war building boom of the 1950s, 60s and 70s, reinforced aerated autoclaved concrete (RAAC) was something of a wonder material.

In the 1990s, when the material was still being used, structural engineers discovered that the strength of RAAC wasn't standing the test of time.

The porous, sponge-like concrete - especially when used on roofs - could easily absorb moisture, weakening the material and also corroding steel reinforcement within.

As it weakened, it sagged, leading to water pooling on roofs, exacerbating the problem.

RAAC made in the 1950s was at risk of failure by the 1980s, the report concluded.

About 30 years ago, it became known that the lifespan of RAAC in many public buildings, including hospitals and schools was no greater than 30 years.

[-] collegefurtrader@discuss.tchncs.de 1 points 2 years ago

Oh, bummer.

[-] tal@kbin.social 2 points 2 years ago* (last edited 2 years ago)

I do kind of wonder whether it would have been cheaper to, back then, go through and seal all of this stuff against moisture, if that is possible. It sounds like what kills it is exposure to moisture.

If they're already starting to collapse and inspections are finding a lot of instances of degraded concrete, though, I assume that it's too late for that.

EDIT: It also sounds like the stuff has been widely used in mainland Europe, not just the UK. I don't know whether the UK being particularly rainy might be a factor, but if the UK is seeing serious problems now, then it might be worth taking a look at usage in mainland Europe as well.

https://en.wikipedia.org/wiki/Reinforced_autoclaved_aerated_concrete

RAAC was used in roof, floor and wall construction due to its lighter weight and lower cost compared to regular concrete,[1] and has good fire resistance properties; it does not require plastering to achieve good fire resistance and fire does not cause spalls.[2] RAAC was used predominantly in public-sector construction in Europe, in buildings constructed since the mid-1950s.[3][4] RAAC elements have also been used in Japan as walling units owing to their good behaviour in seismic conditions.[5]

Reading some other articles, it sounds like we in the US and the Canucks do have some as well, but not much, mostly because apparently wood is cheaply available and dominates as a material, and the American construction industry isn't very familiar with use of AAC. There is only one small (13 person) US factory that produces the stuff, in Haines City, Florida.

https://www.resilientdesign.org/aac-an-ideal-material-for-resilient-buildings/

It’s no secret that autoclaved aerated concrete (AAC) has struggled to gain a foothold in North America. AAC is in widespread use in Europe, Mexico, and much of the world, but it has had trouble competing against wood-frame building here in the United States and Canada.

I couldn't find reference to specifically the reinforced form (RAAC) in the US, but looking at the factory's webpage, they list reinforced AAC roof panels as one variant that they can provide, so I assume that they must have sold some.

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this post was submitted on 02 Sep 2023

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