How does this rubbish happen? Concrete Bob Mc Alpine would turn in his grave . The Glenfinnan Viaduct still stands to this day!
RAAC Reinforced Autoclaved Aerated Concrete
- Thread starter Dustydog
- Start date
So does the Colosseum and probably in better shape than some schools or hospitals.
What happened to the three year old modular school that is now closed as being unsafe.
RAAC was first used in Sweden in 1929 and has been commonly used throughout Europe since the 1950s - how come it's an issue in the UK - apparently it's been an issue since 1995 so successive governments of all colours have failed to tackle the problem.
So if it’s been around for so long and widely used in Europe do they suffer collapse?
Probably, I suspect the difference is that their governments didn't ignore it/cancel the programs that were in place and would have replaced it.
In 1995 someone decided the lifespan of the RAAC (which I guess you do need to wait around for) was 30 years. So back in 1995 some buildings were affected. Maybe they got replaced. Whatever the deal back then Labour introduced a policy to rebuild all secondaries over a certain age, as well as many primaries, and had that have run its course the problem would likely be far more minor now if at all.
Where the wheels really come off the excuse bus is that in 2019 it was recommended all public buildings with RAAC in them should be replaced. Apparently they decided instead to spend 4 years surveying buildings and grading them instead of doing the work. Only to have that all thrown out the window over the summer when it was found that the grading system used was not fit for purpose.
In France private houses were constructed using RAAC but I’ve not come across any reported problems in Europe. Cannot believe it’s only a UK problem unless our construction developers did not understand how to use it, as per Grenfell Tower.
What makes you think that?
In the past, the same as today if a building product failed it would either fall down or be taken down, and either erased, or rebuilt slightly differently. Failures were rarely left standing. Sites with failures have been found, and very often they have been rifled and the stones or other materials used in new buildings.
Architect's who produce poor designs either change their designs or loose business. But if you look at most canal and rail structures that have only survived only becasue of continual maintenance, repairs or modification over time.
This explains a lot. Nearly 40 years on Westminster hasn’t grasped the nettle.
https://www.theguardian.com/uk-news...who-knew-what-when-crumbling-concrete-england
https://www.theguardian.com/uk-news...who-knew-what-when-crumbling-concrete-england
Sarcasm. Sarcasm makes me think that.
Were they raac or aac though? Here we still use aircrete and other thermal blocks which are similar enough. The issue only happens when some clever bod thought they could add some rebar and make 'planks' from it to provide support beams for roofs.
So far as I am aware, raac is not used in what we mostly consider structural concrete. It only has to support itself, and is used in flat roof construction. My only experience was in Germany. We built a single garage, a lorry with a Hiab lifted the planks onto the walls and they were spread out by hand. Sized at around 3 metres x 500 x 150. 2 people could easily move them. Walking on them made them deflct and bounce. But after the joints were grouted they became solid.
I understand that it is water penetration and rust of the reinforcement that is the big problem. Which often can be attributed to poor maintenance. After all, flat roof coverings are always failing.
The pictures shown on the TV looks to have insufficient grouting. A spokesman from Loghbourer said poor dimensional accuracy, installation and seating can often be to blame. He said some can be fixed by using brackets to reduce the span. A big issue is that they are always hidden within the construction.
John
I understand that it is water penetration and rust of the reinforcement that is the big problem. Which often can be attributed to poor maintenance. After all, flat roof coverings are always failing.
The pictures shown on the TV looks to have insufficient grouting. A spokesman from Loghbourer said poor dimensional accuracy, installation and seating can often be to blame. He said some can be fixed by using brackets to reduce the span. A big issue is that they are always hidden within the construction.
John
The website said RAAC. Our son has a three storey house in Wales set into a slope and it has concrete “ planks” that support the floors between ground and first and first and second. He’s going to check what the materials are. It was an architect designed self build circa 1980 and in an area not renowned for aridity.
And they wont be Raac beams if it is. You may have aac blocks between said beams though but thats fine. As above RAAC can't be used in flooring AFAIK, its not strong enough.
HSE report that it has been found in flooring, and I read one website where the surveyor found RAAC flooring and it was visibly deflecting when he walked on it. I would not be surprised if there are yet to be discovered instances where it has been used incorrectly.
https://www.hse.gov.uk/education/raac.htm
Without wishing to diminish the risks associated with the use of RAAC and the real need to have the condition of RAAC in buildings assessed, Whilst there are several reports of where RAAC has been found in poor condition, and should be replaced, thankfully there has only been one reported incident of complete failure back in 2018.
There are understandable concerns about constructions that use RAAC, there are also a number of installations where the design or application of the material has been called into question. So how many installations are failing becasue of poor design, or construction techniques or even possibly the RAAC its self was mixed incorrectly. We have no way of instinctively knowing or telling which if any of these issues are concerned, but it may not be the RAAC itself that's to blame.
As for the govt response to the issue. They have followed the advice from the specialists. the majority of warnings were accompanied with advice to have sites assessed, not closed down. How much ire would have been directed at Govt if they had disregarded the inspection advice and gone straight to closure?
As far as I can see, the govt line has been to followed the advice of the experts, and the decision to close affected buildings was only issued when the experts changed their advice.
Of course it would have been sensible to announce closures before the summer break, but the experts had not identified the change in the risk level at that point, So why should they close buildings without the evidenced justification?
The Govt will be dammed if they did or didn't issue an earlier closure notices.
And I stress the same situation would have arisen regardless of the political colour of the government.
There are understandable concerns about constructions that use RAAC, there are also a number of installations where the design or application of the material has been called into question. So how many installations are failing becasue of poor design, or construction techniques or even possibly the RAAC its self was mixed incorrectly. We have no way of instinctively knowing or telling which if any of these issues are concerned, but it may not be the RAAC itself that's to blame.
As for the govt response to the issue. They have followed the advice from the specialists. the majority of warnings were accompanied with advice to have sites assessed, not closed down. How much ire would have been directed at Govt if they had disregarded the inspection advice and gone straight to closure?
As far as I can see, the govt line has been to followed the advice of the experts, and the decision to close affected buildings was only issued when the experts changed their advice.
Of course it would have been sensible to announce closures before the summer break, but the experts had not identified the change in the risk level at that point, So why should they close buildings without the evidenced justification?
The Govt will be dammed if they did or didn't issue an earlier closure notices.
And I stress the same situation would have arisen regardless of the political colour of the government.
There’s a meeting of Bristol City Council this afternoon to discuss the deterioration of the Cumberland Basin bridge which is reported to be susceptible to sudden and catastrophic failure. The repair bill is an estimated £50m. The bridge is conventional concrete and steel and is a main artery into and out of the city. Interesting to hear what action will be taken to address the “sudden and catastrophic “ aspect.
Similarly but previously the Spaghetti Junction and M5 & M6 fly overs. Grenfel tower cladding, etc.....
Quality control in buildings has, imho, deteriated over the past 30 years of so with the dimise of local authortiy building control by privatisation. And the limited use of clerks of works on larger works.
Also the skimping of building managers in allowing for budgeted planned maintenance.
At least major contracts are handed over with drawings and schedules and a maintenance plan/manual. It seems that these are often discarded after a few years.
I think government have had some years of notice of the impending problems. It may not be them that are directly responsible for the buildings, but they could have been more forceful in insisting that authorities and academies returned questionairs and reports. Hospitals seem to be more on top of the issue.
The reporting of the raac failures has been very poor. One news reported that 3 schools had collapsed. In reality, they had cracked ceilings, and in one case a beam had fallen. Not quite the same.
I may well be wrong, but I believe the raac concrete mix does not lend itself to on-site mixing and casting. But the beams are factory manufactured. Standards are easier to maintain, but there can be many insalation problems.
Raac is made from PFA, (Pulverised Fuel Ash). As are Celcon or Thermolite blocks. It is a fantasic material in the right place and makes full use of a waste product. I wonder what the supply of PVA is like now with the closure of coal fired power stations.
John
Thanks for the post, and I’d agree your comments. RAAC is made in factories so quality and dimensional control are reported as good. The underlying problem with it seems to be its porosity and the affinity for moisture ingress. Bit like caravans 😂
Did he have an independent structural survey before purchase? The full building spec would have been reviewed and passed by the LA Building Surveyor. Maybe they still have everything on file?
My limited experience of fitting these beams is that the edge profile is closed at the bottom and open at the top with a keyway in the middle. In this way, the grouting will bind each plank together. So if one fails, it is hard to see how it would collapse without warning, IF the grouting was done correctly.
But evidently, the seating or end bearing is also a problem. Which is why one of the fixes is installing brackets.
John
He did have an independent survey and he’s contacting the council planning department for records. He’s looked at the ceiling above the ground floor garage and the workshop. Both are unpainted. His view is that the “planks” are conventional concrete and before the new first floor flooring is laid he’s going to lift areas of the pine boards to access the structural members below. Also in his favour is the house was constructed about the time RAAC was going out of favour, and being a private one off build for the previous owner probably low likelihood of RAAC. So he’s just gathering information.
It's probable likely the RAAC products would be manufactured correctly being made in the relatively controlled conditions of a factory, but stranger things have happened.
But I do wonder if we will ever get to know the real causes of the specific failures, and what proportion are down to just material age failure and what other causes are responsible such as incorrect application, poor construction techniques, poor maintenance etc.
The link in my post #22. The Loughborough professor has examined many and has data from NHS installations with clear causes of failure.
The fact that it only had a 30 year life expectancy would assume proper installation. The concrete itself will go on. It is the reinforcement that fails. Excabated if the fitting is poor.
I am not sure if you mean ‘we’ as in the general public. Or those surveying the sites, who will not get to know. Either way, there will be accurate reports which will be made public. But the results will be smothered by politicians and poor news reporting.
John
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