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As other's have said there may be some in some of the stations built in the 1960s however stations in many ways have been better maintained than schools as if you think about many stations have been refurbished over and over again since they were built. Schools on the other hand haven't.
As other's have said there may be some in some of the stations built in the 1960s however stations in many ways have been better maintained than schools as if you think about many stations have been refurbished over and over again since they were built. Schools on the other hand haven't.
A lot will depend on whether this type of concrete was ever in vogue amongst BR architects. They seemed to use a lot of standard building methods at various times.
From what little I know about the BR Civil Engineering Department, they were traditionalists. Structures were normally built out of wood, brick or normal concrete. But privatisation took a wreaking ball to it, as they lost work to private contractors.
But the railway may be lucky in that RAAC looks to have fallen out of favour by the 1990s.
That doesn’t mean that the BR Civil Engineering Department didn’t get things right. Far too many flat roofs were used. Fine if they are properly maintained… Otherwise they spring leaks.
And that’s one of the biggest problems, be it wood or RAAC, water damage over a period of time weakens structural parts. Eventually they will fail.
This is true, but the specific issue of RAAC is that that failure is invisible. Rotting wood is visible, as is normal "concrete cancer" as the expansion of the rusting rebar causes bits to fall off long before it totally fails. With RAAC, the rebar just expands into the air holes in the concrete, crushing it from inside, and the failure isn't visible until it falls on someone's head.
On the other hand, I'm not sure the railway cares that much about such things. Anyone who's seen the state of many footbridges, or say Kirkdale station's ticket office on a bridge thing (which is rusting to bits), wouldn't trust their management of structures as far as they could throw it...
The Victorians had the right idea building everything with bricks! I've yet to find a case where they've not lasted as long as the ever-popular rusty-reinforced concrete now.. Nothing to stop you building tall structures with it either - just look at Battersea Power Station!
Unfortunately, as other things take priority, with less money being spent on maintenance, even obviously damaged items are left to deteriorate even further. So if there is no visible damage, even if a proper inspection may find otherwise, it’s likely to be left as is…
Which as we now know, with RAAC, this can lead to the structure being unsafe and liable to collapse without warning.
The Victorians had the right idea building everything with bricks! I've yet to find a case where they've not lasted as long as the ever-popular rusty-reinforced concrete now.. Nothing to stop you building tall structures with it either - just look at Battersea Power Station!
Now all you need is an unlimited supply of Irish peasants who you can pay almost nothing to do back breaking labour all day! Building in brick today costs an absolute fortune.
And lots of brick buildings have fallen down, looking at today's buildings gives a serious problem with survivorship bias.
RAAC built with stainless steel rebar would have none of the known issues, just as stainless steel reinforced concrete is largely immune to the rust based failure modes plaguing buildings from the 1950s.
(EDIT: In addition Battersea Power Station is steel framed with brick cladding, it is not a true structural brick building. The chimneys are made of concrete)
A lot will depend on whether this type of concrete was ever in vogue amongst BR architects. They seemed to use a lot of standard building methods at various times.
"in vogue": The current affected school lists (which will grow) highlights how key being "in vogue" with local architect /engineers teams doing local authority work was for RAAC being used. e.g. Essex is very very badly affected (37.4%) with other significant concentrations of affect schools in County Durham (and close by), some Greater Manchester boroughs, Lea valley corridor for NE London boroughs.
Then there are other smaller low density clusters e.g. SE London /NW Kent, Suffolk (adjacent to Essex so a continuation of the Essex concentration???), Birmingham.
Then a number of 1 per county type distributions (e.g. Oxfordshire) and quite few completely unaffected counties/boroughs.
"in vogue": The current affected school lists (which will grow) highlights how key being "in vogue" with local architect /engineers teams doing local authority work was for RAAC being used. e.g. Essex is very very badly affected (37.4%) with other significant concentrations of affect schools in County Durham (and close by), some Greater Manchester boroughs, Lea valley corridor for NE London boroughs.
Then there are other smaller low density clusters e.g. SE London /NW Kent, Suffolk (adjacent to Essex so a continuation of the Essex concentration???), Birmingham.
Then a number of 1 per county type distributions (e.g. Oxfordshire) and quite few completely unaffected counties/boroughs.
Most of the affected GM schools are post war Grammar schools reflecting the period in which they were built, so the predominantly Victorian/Edwardian/20's primary schools and 70/80's Comprehensive high schools aren't really affected.
I was told by a civil engineer of my acquaintance that prestressed concrete can also fail suddenly. Rather than normal rebar it has "tendons" which are in tension, putting the concrete in compression where it is strongest. If the tendons fail then the concrete itself, now unreinforced, is taking loads in tension, something it isn't intended to do. This was in the context of why the previous platform canopies in Derby suddenly gained a heavy Meccano-like supporting structure that was in place for some years until the present ones replaced them.
I was told by a civil engineer of my acquaintance that prestressed concrete can also fail suddenly. Rather than normal rebar it has "tendons" which are in tension, putting the concrete in compression where it is strongest. If the tendons fail then the concrete itself, now unreinforced, is taking loads in tension, something it isn't intended to do. This was in the context of why the previous platform canopies in Derby suddenly gained a heavy Meccano-like supporting structure that was in place for some years until the present ones replaced them.
Prestressed concrete structures contain a normal steel reinforcement cage as well as the stressing tendons. However it's correct that if the tendons fail, the stress distribution changes and the structure is likely to fail in tension as a result of overstressing the remaining reinforcement. When tendon failure does occur it's usually a result of incomplete grouting of the ducts which they're contained in, allowing corrosion to occur.
Normal reinforced concrete is designed so that if it's overloaded, the steel reinforcement should fail in tension before the concrete fails in compression. This is because the former is progressive and deflects visibly before ultimate failure, whereas the latter may occur suddenly with little or no prior warning.
RAAC built with stainless steel rebar would have none of the known issues, just as stainless steel reinforced concrete is largely immune to the rust based failure modes plaguing buildings from the 1950s.
There was some film on the BBC News ( 18.00 bulletin, Wednesday 6th September if anyone wants to hunt for a recording of it ) from the university which triggered the warnings. This showed that the RAAC when wet soaks up water like a sponge and this corrodes the rebar inside it; they discovered that in many cases the rebar itself has failed completely through corrosion and this is why the risk of sudden failure.
From what little I know about the BR Civil Engineering Department, they were traditionalists. Structures were normally built out of wood, brick or normal concrete. But privatisation took a wreaking ball to it, as they lost work to private contractors.
Long before privatisation, the Southern Region of BR used the CLASP prefabricated frame and panel system to build a number of stations and signalboxes in the 1960s and 1970s. It was replaced with the 'D70' steel and glass modular building system, which was als oused by the Eastern Region. The London Midland Region developed it's own prefabricated modular building system in 1959 called Mod-X to replace stations that needed to be rebuilt as part of the WCML electrification. Even in BR days, tradition went out of the window when savings needed to be made.
RAAC built with stainless steel rebar would have none of the known issues, just as stainless steel reinforced concrete is largely immune to the rust based failure modes plaguing buildings from the 1950s.
Stainless steel reinforcement is very expensive, and the low cost of RAAC was one of the reasons it was widely adopted. The original method for corrosion protection was to dip the steelwork in a cement-latex slurry prior to being placed in the mould. Unfortunately the latex has degraded over time, or the corrosion protection step was omitted completely. For RAAC nowadays it's more likely to be a bituminius coating, hot-dip galvanised or epoxy coated.
Due to the extra cost involved, stainless steel reinforcement is only used for concrete that will be exposed to a marine environment, or to road salt. The Highways Agency have adopted it for road bridges, for instance, as a result of the lessons learned from the corrosion of the rebar used on 60s and 70s motorway bridges (such as the M6 elevated section in Birmingham).
"in vogue": The current affected school lists (which will grow) highlights how key being "in vogue" with local architect /engineers teams doing local authority work was for RAAC being used. e.g. Essex is very very badly affected (37.4%) with other significant concentrations of affect schools in County Durham (and close by), some Greater Manchester boroughs, Lea valley corridor for NE London boroughs.
Then there are other smaller low density clusters e.g. SE London /NW Kent, Suffolk (adjacent to Essex so a continuation of the Essex concentration???), Birmingham.
Then a number of 1 per county type distributions (e.g. Oxfordshire) and quite few completely unaffected counties/boroughs.
In the NHS, the use of RAAC came along with the government's 'Best Buy' hospital building plan between the late 1960s and 80s, where hospitals were built all over the country to the same design using standardised components as a cost-saving measure.
A similar drive happened in the building of schools in that period - the aforementioned CLASP system used my BR's Southern Region was orignally developed through a collaboration of a number of local authoirties to develop a standard buikling system for schools. This was followed on by the Second Consortium of Local Authorities (SCOLA), the Metropolitan Architectural Consortium for Education (MACE), the South-East Architects Collaboration (SEAC), the Consortium of Method Building (CMB), the Organisation of North-West Authorities for Nationalised Design (ONWAND), the Anglian Standing Conference (ASC) and the Con sortium of Local Authorities Wales (CLAW), who all devised standardised systems for municipal buildings. It's no surprise therefore that there are 'clusters' of affected schools in certain areas
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There was some film on the BBC News ( 18.00 bulletin, Wednesday 6th September if anyone wants to hunt for a recording of it ) from the university which triggered the warnings. This showed that the RAAC when wet soaks up water like a sponge and this corrodes the rebar inside it; they discovered that in many cases the rebar itself has failed completely through corrosion and this is why the risk of sudden failure.
The poster you replied to was advocating the use of stainless steel as reinforcement for RAAC, due to it being inpervious to corrrosion. If the reinforcement that was used at the time these buildings were built was stainless steel then no amount of water ingress into the aerated concrete matrix would cause the reinforcement to corrode (the effect of the extra weight loading on the reinforcement from the saturated concrete s another matter).
There was some film on the BBC News ( 18.00 bulletin, Wednesday 6th September if anyone wants to hunt for a recording of it ) from the university which triggered the warnings. This showed that the RAAC when wet soaks up water like a sponge and this corrodes the rebar inside it; they discovered that in many cases the rebar itself has failed completely through corrosion and this is why the risk of sudden failure.
Also affects RAAC which isnt reinforced, the water ingress gradually dissolves away the material making the air bubble cavities larger and larger and with less rigidity the material then sags which then amplifies the load into a smaller contact area.
Also affects RAAC which isnt reinforced, the water ingress gradually dissolves away the material making the air bubble cavities larger and larger and with less rigidity the material then sags which then amplifies the load into a smaller contact area.
There was some film on the BBC News ( 18.00 bulletin, Wednesday 6th September if anyone wants to hunt for a recording of it ) from the university which triggered the warnings. This showed that the RAAC when wet soaks up water like a sponge and this corrodes the rebar inside it; they discovered that in many cases the rebar itself has failed completely through corrosion and this is why the risk of sudden failure.
If the rebar was fabricated from stainless steel then being waterlogged wouldn't matter.
There is a reason stainless steel rebar is increasingly being used in civil infrastructure projects, it is essentially immune to this failure mechanism.
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Stainless steel reinforcement is very expensive, and the low cost of RAAC was one of the reasons it was widely adopted. The original method for corrosion protection was to dip the steelwork in a cement-latex slurry prior to being placed in the mould. Unfortunately the latex has degraded over time, or the corrosion protection step was omitted completely. For RAAC nowadays it's more likely to be a bituminius coating, hot-dip galvanised or epoxy coated.
Due to the extra cost involved, stainless steel reinforcement is only used for concrete that will be exposed to a marine environment, or to road salt. The Highways Agency have adopted it for road bridges, for instance, as a result of the lessons learned from the corrosion of the rebar used on 60s and 70s motorway bridges (such as the M6 elevated section in Birmingham).
Stainless steel rebar is spreading out from those applications as time goes by though.
Given the modern construction cost reality, spending the extra money for stainless rebar (especially more modern duplex grades) is increasingly being seen as a drop in the ocean compared to the potential lifetime advantages.
The primary saving from RAAC after all is not in the material itself, but in the reductions in supporting structure required on account of its very light weight.
RACC or other reinforced concrete reinforced with stainless steels are likely to have a service life measured in centuries.
In theory it has a two rectangular planes of longitudal smooth steel dowels in the bottom and top of the panel with a horizontal cross brace across the planes linking the longitudal dowels at either end (like the top and bottom of a cube which doesnt have vertical supports), but the Institute of Structural Engineers has flagged up that some had missing structural reinforcement as a production defect while in other cases builders cut down panels to size losing the end cross braces
Normal reinforced concrete is designed so that if it's overloaded, the steel reinforcement should fail in tension before the concrete fails in compression. This is because the former is progressive and deflects visibly before ultimate failure, whereas the latter may occur suddenly with little or no prior warning.
I was taught (early 1970s) that RC should tend to be slightly over-reinforced, so that failure would be by crushing of the concrete, which will be progressive and display signs of distress before failure, whereas reinforcement failure would be rapid and catastrophic.
I was taught (early 1970s) that RC should tend to be slightly over-reinforced, so that failure would be by crushing of the concrete, which will be progressive and display signs of distress before failure, whereas reinforcement failure would be rapid and catastrophic.
That's the same era as me so I'm surprised at that, it's the opposite of my recollection.
Such RC design as I did (not all that much ) was to CP110 and BS8110, and I think that the design equations in those produce an ultimate steel failure moment that is smaller than the ultimate concrete failure moment. When I was still working I could have checked that in a few minutes, but being retired I no longer have easy access to them.
Plus I'm going off topic for RAAC, so maybe better to leave it at that
Also affects RAAC which isnt reinforced, the water ingress gradually dissolves away the material making the air bubble cavities larger and larger and with less rigidity the material then sags which then amplifies the load into a smaller contact area.
The problem with RAAC is that the progressive failure mode is invisible from the outside. Today it looks fine, tomorrow it falls on someone's head and kills them. It might be absolutely fine, but you can't know. Thus it basically all needs removing.
If the rebar was fabricated from stainless steel then being waterlogged wouldn't matter.
There is a reason stainless steel rebar is increasingly being used in civil infrastructure projects, it is essentially immune to this failure mechanism.
== Doublepost prevention - post automatically merged: ==
Stainless steel rebar is spreading out from those applications as time goes by though.
Given the modern construction cost reality, spending the extra money for stainless rebar (especially more modern duplex grades) is increasingly being seen as a drop in the ocean compared to the potential lifetime advantages.
The primary saving from RAAC after all is not in the material itself, but in the reductions in supporting structure required on account of its very light weight.
RACC or other reinforced concrete reinforced with stainless steels are likely to have a service life measured in centuries.
I have been thinking about this. Does this mean that the sensible rationale next step would be to replace the roof spans with RAAC done properly?
I have read elsewhere that another problem they are going to have is asbestos lurking in the same area.
It’s a mess and shows the near of not actual criminality of some forms of value engineering, bearing in mind the obvious danger to safety that will follow at some point.
There are other possible lightweight materials such as plastics which are also an option. Or some of the buildings are just old and should be pulled down and rebuilt entirely.
There are other possible lightweight materials such as plastics which are also an option. Or some of the buildings are just old and should be pulled down and rebuilt entirely.
I suppose the question I am really asking is would RAAC have been a good material if the reinforcement material had been correct, or would it likely have failed in other ways. It sounds like any water ingress might have caused failure of the concrete sections even if the reinforcement held, so you would have had smaller failures but still meaningful enough to require removal and replacement.
Feels like they might have got another 10 years out of it though as more scope to patch repair.
It sticks in the throat though doesn’t it. Somebody decides a form of value engineering is okay, profits from the subsequent contract and instantly dumps a massive bill on the future public purse.
Probably just short termism, the material was expected to last longer than a generation therefore there was no need to work out its precise lifetime and it was just expected if it became an issue in the future they would just deal with it then. TBH even if they had known it had a lifetime of two generations when they were using it in the post war period its doubtful they would have cared, they probably didnt foresee the requirement for their buildings lasting more than 60 years.
Probably just short termism, the material was expected to last longer than a generation therefore there was no need to work out its precise lifetime and it was just expected if it became an issue in the future they would just deal with it then
And that'd be fine were it not for the invisible failure mode that hadn't occurred to them. There's no particular issue with a temporary building designed to last 30 years as long as it's possible to actually see that it's deteriorating and in need of replacement. We do in the UK see buildings as permanent, but in other countries they don't - almost all houses in the US are wooden, for instance, it's the plot of land that has value, not the fancy shed on it.
The problem here is that failure mode - it can look absolutely fine then fall and kill someone, and you can't tell by looking at it that that's about to happen. If it was wood, you'd see all the rot.
There is a reason stainless steel rebar is increasingly being used in civil infrastructure projects, it is essentially immune to this failure mechanism.
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Stainless steel rebar is spreading out from those applications as time goes by though.
I wish people would remember (or learn) that stainless steel isn't the answer to every corrosion problem. Apart from the mentions above of a couple of specific stainless alloys to resist salt (sodium chloride) corrosion, you should be aware that the French name for stainlwess is "INOX." This is because it is inoxydable... put it in reducing conditions and it rapidly gets attacked. So wet foamed cement might be exactly what you would expect to attack generic "stainless" steel.
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) was to CP110 and BS8110, and I think that the design equations in those produce an ultimate steel failure moment that is smaller than the ultimate concrete failure moment. When I was still working I could have checked that in a few minutes, but being retired I no longer have easy access to them.
