RAAC Concrete - Any rail infrastructure affected?

[Merle Haggard]

Just to point out that this is an example of a building with a structure in concrete and brick and with a single width brick 'wall' outside to make it look better. The brick wall only has to support its own weight and resist changes internal air pressure caused by wind.

There was a similar collapse with detailed pictures that showed, after a part collapse, that the brickwork had been tied (???) to the structure by sparingly applied No 6 (3.5 m.m.) screws screwed into plastic plugs in the concrete blocks of the structure. Perhaps unsurprisingly (but evidently not to the person that signed it off) the outwardforce, as a result of pressure caused by a moderate wind, was greater than the restraining one.

Many modern station buildings seem to use the principle (hopefully, executed better) and the give away is the perfect mortar joints - perhaps they are prefabricated with narrow bricks. From memory, Leicester platform buildings would be an example.

Abandoned brick built warehouses and factories, sometimes dating back to the 19th century, seem to be capable of resisting collapse even when roof-less and window-less and clearly long abandoned - you can see a few from the Stour Valley line.

They have indeed.

It's worth reading Professor John Coles report concerning the 17 PPP Edinburgh schools, that had significant structural defects.

 

[HSTEd]

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.

Whilst the environment inside the concrete foaming is likely to be initially reducing due to the hydrogen foaming agent used in the concrete, in order for it to get wet enough to suffer serious corrosive attack large amounts of water has to be penetrating the foam to the reinforcing bar.

At which point the hydrogen will be repeatedly displaced and replaced with atmospheric air and the environment inside the beam will shift to oxidising, won't it? This is especially true as one of the major identified flaws in RAAC panels is that the voids in the vicinity of the bars are joined when this was not originally expected. That makes it easier for water and thus air to penetrate into the plank.

It is true that many common stainless steels perform poorly in strongly reducing environments, but a RAAC plank is most certainly not a strongly reducing environment, at least in anything beyond the immediate short term.

 

[jfowkes]

Abandoned brick built warehouses and factories, sometimes dating back to the 19th century, seem to be capable of resisting collapse even when roof-less and window-less and clearly long abandoned - you can see a few from the Stour Valley line.

These buildings tend to fail when someone paints over the brickwork to make it look "nicer" as part of conversion into flats or something. Then the brick loses its moisture permeability, soaks up all the water it can find, turns into putty and falls apart.

 

[Prime586]

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.

RAAC is still commonly used in the rest of the world, but it has to be manufactured properly and used in the appropriate situation. In Australia, for example, it is commonly used as the floor for the first floor of wooden-framed houses as it has better soundproofing, fireproofing and insualtion properties than wood or chipboard with only a slight increase in weight. It is used in block form (about 1m x 05m) and screwed onto conventional wooden joists. They generally don't use it to form flat roofs where it will be exposed to water, or in long unsupported spans. In China, however, they are using RAAC in much the same ways we did, but the Chinese construction industry is not exactly known for it's commitment to quality and safety.

Part of the problem with the British use of RAAC between the 1960s to early 1980s is that it's light weight was exploited to allow very long roof/floor spans to be used with no intermediate supporting beams or joists. It was used this way in hospitals and schools to provide large open plan floor areas that could be easily reconfigured by changing the layout of non-load bearing dividing walls. It was issues with this approach (and with related manufacturing defects in the placement of the reinforcement in these long panels) that led to the first wave of building modifications in the early 1980s.

In the case of the 'Best Buy' hospitals programme, it was the Ministry of Health and the NHS's own architectural departments that selected and mandated the use of RAAC to keep costs down, not the contractors who built them. I expect there will be a similar situation with council architects and/or the groups they formed between councils (as mentioned im my previous post) selecting the material and devising modular building systems for it to be used in to keep costs down.

In the case of the Large Panel industrialised building systems used to build the disastrous blocks of flats in the 1960s and 70s it was for the most part 'Design and Build' package deals that the construction companies were presenting to the councils as a way of keeping costs down (Liverpool being an notable exception to that, as the council licenced the Camus system themselves and then handed it to their tame contractor to make it work).

 

[Mikey C]

The theatre in my home town (Dartford) has been closed with immediate effect due to RAAC, and that opened in 1983, so right at the end of the period when it was used...

 

[WatcherZero]

It is true that many common stainless steels perform poorly in strongly reducing environments, but a RAAC plank is most certainly not a strongly reducing environment, at least in anything beyond the immediate short term.

Indeed why it was assessed as still having a 30 year life remaining in the 90's.

 

[Zinger]

Seems to be coming up everywhere, check out https://onlineplaces.wixsite.com/raac

 

[Mag_seven]

Just a reminder that this thread is specifically about RAAC concrete affecting Rail Infrastructure.

thanks

 

[TAS]

Greater Anglia have confirmed that they are checking stations following concrete falling off the multistorey car park at Colchester station, though initial checks suggest this doesn't contain RAAC. This morning the upper storey and the parking spaces underneath were taped off, though access through the structure was still being allowed for vehicles and pedestrians and the secure cycle park underneath was also still open.

BBC:

Greater Anglia checking 134 rail stations for unsafe concrete​

A rail operator said it was inspecting all 134 stations it owned for any unsafe lightweight concrete.

Greater Anglia said it did not expect to find Raac (reinforced autoclaved aerated concrete) in its buildings but would carry out the review as a precaution.

A section of Colchester Railway Station car park was closed off after a small piece of concrete fell off, it said.

Schools in Essex have been worst affected by the recent concrete crisis.

"Because of things going on elsewhere we are undergoing checks of all our stations just to make sure," said Jonathan Denby, Greater Anglia's head of corporate affairs, speaking to BBC Essex.

"We don't think, from the inspections we've already had, that Raac is an issue [at Colchester], but we are going to have a wider check as well."

Mr Denby said a member of staff reported that a "very, very small" piece of concrete had fallen from a section of the two-storey car park at Colchester.

The single-storey sections of the car park were still usable, he added.

Greater Anglia operates the majority of the rail network in the east of England.

 

[N0G83]

Just to point out that this is an example of a building with a structure in concrete and brick and with a single width brick 'wall' outside to make it look better. The brick wall only has to support its own weight and resist changes internal air pressure caused by wind.

There was a similar collapse with detailed pictures that showed, after a part collapse, that the brickwork had been tied (???) to the structure by sparingly applied No 6 (3.5 m.m.) screws screwed into plastic plugs in the concrete blocks of the structure. Perhaps unsurprisingly (but evidently not to the person that signed it off) the outwardforce, as a result of pressure caused by a moderate wind, was greater than the restraining one.

Many modern station buildings seem to use the principle (hopefully, executed better) and the give away is the perfect mortar joints - perhaps they are prefabricated with narrow bricks. From memory, Leicester platform buildings would be an example.

Abandoned brick built warehouses and factories, sometimes dating back to the 19th century, seem to be capable of resisting collapse even when roof-less and window-less and clearly long abandoned - you can see a few from the Stour Valley line.

But would the brick wall be tied into the block work with internal piers along with an expansion joint?

 

[Annetts key]

It appears that Network Rail have identified that some railway property does contain RAAC. Controls are in place. No further details have been provided.

 

[Merle Haggard]

But would the brick wall be tied into the block work with internal piers along with an expansion joint?

Sorry for not responding earlier. My recollection of the photo. was it showed the outer brick remaining from ground level about a quarter of the original height (and obviously a mound of bricks) exposing above a completely plain breezeblock wall.
I'm just a bit doubtful of some of the practices that presumably are acceptable nowadays; for instance, my garage (built 1982) has single course walls with what look like internal reinforcing piers. However, the piers are only tied into the main wall but a few '8' shaped wire loops, the pier is just built up separately with no stretchers. The same principle seems to apply to new work across the road from Wellingborough station. A high wall (12' ??) was built to retain the higher ground level when the road was built and what looks like piers are placed at intervals. It's clear that these piers cannot be tied into the wall in the traditional way (stretchers into the main wall would result in half width bricjks in courses, all the bricks are longways). Ominously, a vehicle has struck one of these and it's moved away from the main wall it's supporting...

note I'm saying 'stretcher to mean bricks that are laid ay right angles to connect two parallel courses.