The crumbly concrete problem

[not done it yetParticipant @notdoneityet]

Posted by John MC on 03/09/2023 07:20:03:

Is RAAC failure the same as "concrete cancer"? My understanding of the current problems of with RAAC is water ingress leading to corrosion of the steel reinforcement.

Concrete cancer is a chemical reaction within the concrete, alkali vs silica(?). This causes spalling of the surface of the structure that, in turn, eventually exposes the reinforcement which then corrodes.

The media seemed to have latched on to the term concrete cancer when it is, in fact, another mode of failure.

Agreed, John,

Alkali aggregate reaction was my take, on the original use of that term. Recognised from about the early’70’s as I recall – particularly with cement manufactured by the ‘dry’ process (as opposed to the ‘wet’ process where the raw materials were fed to the kilns as a slurry). The dry process involves heat transfer within cyclones as the kiln exhaust gases exit the system and the powder feed descends the cyclone tower before entering the kin at near to (or even above) calcining temperature – depending on whether extra fuel is injected at the flue gas exit to the kiln. Alkali metal salts (mainly as chlorides and sulphates), sulphates were a result sulphur content in the coal and gypsum in the raw materials These mostly evaporate in the kiln burning zone and recirculate by condensation within the cyclone tower. This led to build-up, and possible blockage, in the final cyclone feed pipe – from the hottest cyclone to the kiln.

The alkali metals either eventually passed through to the cement clinker or, in some cases some exhaust gases were bled away, via a bypass system, where the high alkali metal salts were collected (along with a fraction of what was the kiln feed) and dumped back to the quarry. In the much less energy efficient wet process, the alkalis were generally lower, even though far more coal was consumed in the process (approx twice the amount!). They were collected in the dust collectors and dumped in the quarry.

As a addition to the discussion of RAAC, it may be noted that the ‘norm’ for removing frost protection from curing concrete/mortar was around the ‘5N’ level – 10N levels were typical for one-day strengths under standard condition, so less in cold weather – so any RAAC which might absorb water could suffer from frost damage. Not a good idea for flat roof structures – so just yet another risk with older buildings – and particularly roofs over (heated) swimming pools!

[Tony Pratt 1Participant @tonypratt1]

I read some where that this 'stuff' has a design life of 30 years, trying not to swear but who in the hell constructs a building which will need replacing in 30 odd years??? And what idiots would think it's a good idea?

Tony

[Ady1Participant @ady1]

If I was king for a day I would buy all the spare stainless rebar from China, negotiate a government quantity package please while their economy is struggling

[peak4Participant @peak4]

Posted by Tony Pratt 1 on 03/09/2023 10:35:29:

I read some where that this 'stuff' has a design life of 30 years, trying not to swear but who in the hell constructs a building which will need replacing in 30 odd years??? And what idiots would think it's a good idea?

Tony

Hmmmm. a friend of mine is a civil engineer, with an involvement in newbuild housing estates.
Design life came up in one of our conversations a couple of months ago; he reckoned that most new builds he's involved with have a design life of 40 years; 50 if you're lucky and going for a more expensive option.

Other stuff I'd read suggested that 60 years was the normal design life for UK housing stock.

I've just looked around for an article to back up his comments, and dropped on this one about timber frame construction
http://www.brand-newhomes.co.uk/timber-frame-new-homes.htm

"In 2010, one in four new homes is being constructed using timber frame or, to be more accurate timber panel, construction."

And then this one;
http://www.brand-newhomes.co.uk/considerations-when-buying-a-timber-frame-new-home.htm

"The timber frame itself is normally "guaranteed" by the manufacturer for various periods ranging from 10 to 40 years. It is a commonly perceived opinion within the industry that 25 –30 years is a reasonably expected life span for a softwood timber framed building."

I've no idea about the veracity of either of those links; not my field of expertise.
I wonder if there is another problem looming.

Bill

[Tony Pratt 1Participant @tonypratt1]

Posted by peak4 on 03/09/2023 11:43:21:

Posted by Tony Pratt 1 on 03/09/2023 10:35:29:

I read some where that this 'stuff' has a design life of 30 years, trying not to swear but who in the hell constructs a building which will need replacing in 30 odd years??? And what idiots would think it's a good idea?

Tony

Hmmmm. a friend of mine is a civil engineer, with an involvement in newbuild housing estates.
Design life came up in one of our conversations a couple of months ago; he reckoned that most new builds he's involved with have a design life of 40 years; 50 if you're lucky and going for a more expensive option.

Other stuff I'd read suggested that 60 years was the normal design life for UK housing stock.

I've just looked around for an article to back up his comments, and dropped on this one about timber frame construction
http://www.brand-newhomes.co.uk/timber-frame-new-homes.htm

"The timber frame itself is normally "guaranteed" by the manufacturer for various periods ranging from 10 to 40 years. It is a commonly perceived opinion within the industry that 25 –30 years is a reasonably expected life span for a softwood timber framed building."

I've no idea about the veracity of either of those links; not my field of expertise.
I wonder if there is another problem looming.

Bill

Has everything in our society got to be a throw away item? Last time I looked a house isn't quite the same as white goods which last a short time and are then launched into some recycling scheme.

Latest update. 'Hunt to spend what it takes' to make schools safe.

Tony

Edited By Tony Pratt 1 on 03/09/2023 12:52:06

[Ady1Participant @ady1]

It appears that a "home" only has to last the period it takes to pay off the mortgage

[duncan webster 1Participant @duncanwebster1]

Financially it can make sense to build something more cheaply with a lower design life than to build the expensive long life solution. On 30 years time it might be obsolete. However this means you have to firstly do the required maintainance, and secondly you have to make financial provision for replacement when the time comes. Neither of these are particularly good at getting votes. Lots of the road gullies around me are blocked, some of them even have grass growing. Consequence, when it rains the roads flood. They did find the money to replace all the footpath finger posts, because that's visible, basic stuff isn't. You can always put off maintainance, until something breaks

[Dave HalfordParticipant @davehalford22513]

Posted by Graham Meek on 02/09/2023 17:23:55:

What really gets me is that they have no records of where the stuff was used.

Nothing more than a "grade A" farce as regards how this has been handled.

Regards

Gray,

It reminds me of a recent contributor on here 'Drawings are for dum people and toymakers'

Buildings are built using drawings, do they burn / shred them in case they may be held liable later?

[Michael GilliganParticipant @michaelgilligan61133]

It never rains but it pours, they say:

[quote] Experts warn that the presence of RAAC also increases the danger of exposure to asbestos, which kills 5,000 people a year in the UK. Asbestos is safe while stable but if it is disturbed — for example, if a classroom roof made from crumbling concrete suddenly collapses — it could release fibres which can cause mesothelioma, asbestosis and lung cancer. Even removing or assessing RAAC panels could disturb asbestos, engineers said.[/quote]

From the Sunday Times

MichaelG.

[duncan webster 1Participant @duncanwebster1]

In a sensible contract, drawings and specifications etc would be passed to the customer. Then sometime later an accountant will decide that the cost of storing them is a saving that can be made, so when you come to needing them, they've gone. Been there, done that. It is not usually the builder's job to store this information.

[Dave HalfordParticipant @davehalford22513]

Posted by vic newey on 02/09/2023 20:24:05:

Exactly the same happened with Spaghetti junction flyovers which involve 559 concrete columns being replaced, also large overhead sections of the M5 at Oldbury near West Bromwich caused long delays for many months

Wasn't that Hi Alumina Cement High Alumina Cement – Manufacturing, Pros & Cons (civiconcepts.com) the link imples this stuff is still great even though roof beams in a school collapsed back in 74.

[Dave HalfordParticipant @davehalford22513]

Posted by Mark Rand on 02/09/2023 20:49:54:

I might be getting to a certain age, but I'm getting increasingly irritated by the likes of the BBC dumbing down engineering stories and getting them hopelessly wrong in the process.

What do you expect, some BBC morning news presenters don't what what a Blue Tit is so they dumb it down to the level they they understand.

[BazParticipant @baz89810]

Posted by Ady1 on 03/09/2023 10:43:02:

If I was king for a day I would buy all the spare stainless rebar from China, negotiate a government quantity package please while their economy is struggling

If you are buying it from China I would recommend you check every single piece with a magnet, their certificates of conformity aren’t worth the paper they are written on.

[DiogenesIIParticipant @diogenesii]

Posted by Baz on 03/09/2023 18:55:46:

Posted by Ady1 on 03/09/2023 10:43:02:

If I was king for a day I would buy all the spare stainless rebar from China, negotiate a government quantity package please while their economy is struggling

If you are buying it from China I would recommend you check every single piece with a magnet, their certificates of conformity aren’t worth the paper they are written on.

..yes, we're so lucky that those kind of sharp business practices never happen in western democracies..

[brickyParticipant @bricky]

i live on a housing estate built by my onetime employer.That were built of block and clad with brick as was standard in the sixties .The estate was started in 64 and these houses will be standing for another 40plus years ,my house on the estate is 44 years old with no sign of any deteriation so, the only reason to go down the route of quick and cheap solutions is profit.I admire the modern rendering technique of housing but I don't think that it will out last as well as houses rendered in 1907 still with no spalling locally.If something works well why try to fix it.Building engineers used to work to a factor of ten so what whent wrong.Profit.

[Martin KyteParticipant @martinkyte99762]

Regarding the question of the appropriate design life for a building I would say that a lot depends on its function. Our last Laboratory was constructed in the late 1960’s and by the time we moved out into our new building it was definitely past its ‘sell by date’. Corridors were crammed with freezers, shakers and incubators. Infrastructure like chilled water supplies were often fed from chiller units ‘parked’ outside or on roof spaces. The Lab as built had no networking as desktop computers did not exist. Much of the science and instrumentation had changed beyond recognition so power supply needs and the way spaces needed to be configured was very different. I could go on but you get the gist. Really we pushed the building at least 10 to 20 years beyond its usefull life as a biosciences Lab.

The new lab is very different and taylored to fit the way we work today. To my mind it’s false economy to build something that will last decades longer than it’s usefull life.
regards Martin

[Ian PParticipant @ianp]

I think one of the facts I learnt (from the BBC I think) is that when rebar rusts in conventional concrete it causes visible spalling on the surface, whereas with RAAC, the expansion caused by the rust just compresses and crushes the aero surrounding it so is completely hidden externally.

Ian P

[Alan Waddington 2Participant @alanwaddington2]

Another ‘crisis’ pedalled by the media……just more smoke and mirrors.

[Michael GilliganParticipant @michaelgilligan61133]

You make a good point about ‘the media: Alan …

Jeremy Hunt gave a calm and measured performance when interviewed by Laura Kuenssberg yesterday morning, but then the reporting by the Independent last evening sensationalised it.

MichaelG.

[CirclipParticipant @circlip]

Geeee, wish someone had told me my house was/should have been demolished one hundred years before I bought it fifty years ago.

Regards Ian

[John Doe 2Participant @johndoe2]

Posted by Tony Pratt 1 on 03/09/2023 10:35:29:

I read some where that this 'stuff' has a design life of 30 years, trying not to swear but who in the hell constructs a building which will need replacing in 30 odd years??? And what idiots would think it's a good idea?

Tony

+1

Anybody approving construction with a design life of only 30 years should be strung up – unless the building was a farm building or temporary building. But something like a school or a hospital, where the colossal disruption and cost of rehousing all the inhabitants; pulling the old building down and constucting a new one in its place……

….it just beggars belief that anyone would think it was a good idea.

[noel shelleyParticipant @noelshelley55608]

There is a school that I know of – which when built won alsorts of awards. Modern construction methods and lots of glass ! To look pretty instead of I beam, channel was used and then on the top face angle was attached to allow a brick panel to be built, some 25' X 8' ! The bolt heads would spoil the look, so studs were welded in ( ground flat) and nuts on the inside. Time passed, about 25 years ! Corrosion took place between the angle and channel and the corrosive pressure pulled the welded studs out ! The brick panel fell 10' or more to the ground (with the angle iron) ! The steelwork for this particular panel was replaced and welded all round, but the rest of the school ? Noel.

Edited By noel shelley on 04/09/2023 14:45:14

[Terry BParticipant @terryb]

I always believed that the local councils were responsible for the siting, building, inspection and maintenance of schools and other public buildings. Not the government.

[duncan webster 1Participant @duncanwebster1]

I think the only person who has mentioned government is me, and I didn't specify local or Westminster. If the problem was brought to Westminster's attention and it wasn't their responsibility they should have made sure that local govt did something about it, and ensured that they did.

Edited By duncan webster on 04/09/2023 18:05:51

[BazyleParticipant @bazyle]

Anybody approving construction with a design life of only 30 years should be strung up –

Where I was working in about '85 the grade 2 listed Victorian house was demolished to be replaced with a modern block in fancy brick and concrete needing lots of 50ft piles into the clay. They left the two WW2 single storey 'temporary' hospital buildings. Two other big concrete panel factory buildings went up the next year, one custom built for housing a multimillion pound specialist test facility. Soon after I left in 2000 the company moved out and it was replaced with a housing estate. All that heavy duty concrete barely used for 15 years so why bother.

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