ChatterBank1 min ago
Raac-Hi Prone To Unexpected Collapse
The problems with RAAC-hi seem to be getting worse. They have been known about for some time but there is widespread concern about his unpredictable and catastrophic crumbling. Obviously RAAC-hi would be difficult to replace but work is going on behind the scenes looking for alternatives. Use of the Truss-method proved highly unsatisfactory and while RAAC-hi initially looked attractive, he is now considered only a short-term option. The Men in Grey Suits are believed to be considering something that is less brittle, with more substance.
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PP poncily pronounces ( = asks)
anyone out there - builder? - know about Brittleness, what it is, and where it comes from?
It is not about weight bearing ( he poncily proceeds) but failure wivvart warning - OK, OK, OK, - splat!
Brittle what it den?
any answers?
comes up a bit - as a POW miner 1943 - my daddy commented ( tv prog the wooden horse 1958 (*)) - wood tells you it is going to give in a tunnel by creaking, metal joists based just break....
Cge interview 1968 ( moi) - examiner dipped a flower petal into liquid ox
and got pliers and shattered the petal
and turned to me ( horrified wide eyed) and asked
why does that happen?
I still dont know the answer
(*) one two buckle my shoe, three four open the door. I will let you mull on what means
anyone out there - builder? - know about Brittleness, what it is, and where it comes from?
It is not about weight bearing ( he poncily proceeds) but failure wivvart warning - OK, OK, OK, - splat!
Brittle what it den?
any answers?
comes up a bit - as a POW miner 1943 - my daddy commented ( tv prog the wooden horse 1958 (*)) - wood tells you it is going to give in a tunnel by creaking, metal joists based just break....
Cge interview 1968 ( moi) - examiner dipped a flower petal into liquid ox
and got pliers and shattered the petal
and turned to me ( horrified wide eyed) and asked
why does that happen?
I still dont know the answer
(*) one two buckle my shoe, three four open the door. I will let you mull on what means
RAAC was cheaper and lighter than its regular equivalent so ideal for cash strapped politicos to use to throw up cheap schools, etc. that it has a finite life didn't matter to said cash strapped politicos because by the time the problems arise they're long gone and it's someone else's problem.
from what I've read though, the root problem isn't the material itself but poor or inadequate maintenance allowing water ingress to rot it from the inside. so every subsequent generation of cash strapped politicos must share their proportion of blame for slashing maintenance budgets.
while the present administration now owns the immediate problem as it's now become a matter of safety, every previous administration has left their fingerprints all over it.
BTW, I'm pleased to announce that without training in architecture, building or health & safety, I have set up a school roof repair business in my shed, and just await multi-million pound government contracts and my inevitable knighthood.
from what I've read though, the root problem isn't the material itself but poor or inadequate maintenance allowing water ingress to rot it from the inside. so every subsequent generation of cash strapped politicos must share their proportion of blame for slashing maintenance budgets.
while the present administration now owns the immediate problem as it's now become a matter of safety, every previous administration has left their fingerprints all over it.
BTW, I'm pleased to announce that without training in architecture, building or health & safety, I have set up a school roof repair business in my shed, and just await multi-million pound government contracts and my inevitable knighthood.
Mushroom25 ^^ has it.
Aerated concrete has been around for decades. It's lightweight as it's full of air bubbles (also provides good insulating properties.)
Used all the time today (Thermalite/Celcon/Durox concrete blocks.)
The problems are with RAAC. The'R' is for 'reinforced, using steel bar.
The problems are not usually with walls. Aerated Concrete has good compression strength without reinforcement.
It has though, very little tensile or shear strength (if you pull it, it fractures. If you try to bend it, the same thing happens.)
Hence the steel reinforcement.
Most of today's RAAC crisis comes from 'planks' that are used to give a ready-insulated material for concrete roofs.
It's essential that they're kept completely waterproof (usually felt or poured asphalt.)
If you neglect maintenance and ignore cracks in the roof covering, water gets in, starts a chemical reaction with the steel, and the concrete crumbles.
Continuing cost-cutting lack of maintenance adds up.
The product is wrongly blamed. For instance, timber is a perfectly good construction material, but will soon deteriorate if neglected.
For 'saggy' roof panels, one remedy is to fit an internal steel frame to reduce roof spans help prevent panels from coming crashing down.
It's the old story. Everything's fine until you neglect it.
Aerated concrete has been around for decades. It's lightweight as it's full of air bubbles (also provides good insulating properties.)
Used all the time today (Thermalite/Celcon/Durox concrete blocks.)
The problems are with RAAC. The'R' is for 'reinforced, using steel bar.
The problems are not usually with walls. Aerated Concrete has good compression strength without reinforcement.
It has though, very little tensile or shear strength (if you pull it, it fractures. If you try to bend it, the same thing happens.)
Hence the steel reinforcement.
Most of today's RAAC crisis comes from 'planks' that are used to give a ready-insulated material for concrete roofs.
It's essential that they're kept completely waterproof (usually felt or poured asphalt.)
If you neglect maintenance and ignore cracks in the roof covering, water gets in, starts a chemical reaction with the steel, and the concrete crumbles.
Continuing cost-cutting lack of maintenance adds up.
The product is wrongly blamed. For instance, timber is a perfectly good construction material, but will soon deteriorate if neglected.
For 'saggy' roof panels, one remedy is to fit an internal steel frame to reduce roof spans help prevent panels from coming crashing down.
It's the old story. Everything's fine until you neglect it.
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