RAAC autoclaved concrete, what about mannock blocks?

[CalvinHobbes]

So have a row of mannock blocks along the bottom and at the top of our new build. Now reading about schools and hospitals etc having used aerated concrete in the 50's right up to the 80's and it should be regarded as bad as asbestos. Tell me not to worry! 

[Jenki]

Don't worry 😜

[ProDave]

It's a different risk to asbestos, it won't kill you by poisoning you.

 

The problem with raac, used for example for ceilings, is it's strength seems to decline and it might collapse without warning.  I don't see that risk with your blocks.

[FuerteStu]

From what I've seen, most of the buildings affected area public ones built fast and cheap.. 

 

Yet another example of signing off poor working practices in the name of cost cutting. 

 

They knew threse buildings were crumbling years ago, but kicked the cost of repairing them down the road until the next election.. 

[Kelvin]

Isn’t one of the issues that the concrete has steel reinforcing bars that rust due to leaky roofs (as it was commonly used to span wide flat roofs) and over time  this has failed? 
 

I have Mannok foundation blocks too. I doubt I’ll see another 30 years so it will be someone else’s problem 😂 

[TonyT]

Yep and as the rebar rusts it expands and cracks the concrete…..

[FuerteStu]

35 minutes ago, Kelvin said:

Isn’t one of the issues that the concrete has steel reinforcing bars that rust due to leaky roofs (as it was commonly used to span wide flat roofs) and over time  this has failed? 
 

I have Mannok foundation blocks too. I doubt I’ll see another 30 years so it will be someone else’s problem 😂 

In part yes, but it's more a case that they were cheaply made with many imperfections. 

 

Most steal reenforced concrete has 'cover', a thickness of concrete before the steel that's supposed to stop moisture causing the steel to oxidise (oxidation expands causing the concrete to crack) 

 

The problem with this type is that the aerated concrete was supposed to be small bubbles, but in reality, they were large and allowed water in too easily

[Gus Potter]

1 hour ago, CalvinHobbes said:

So have a row of mannock blocks along the bottom and at the top of our new build. Now reading about schools and hospitals etc having used aerated concrete in the 50's right up to the 80's and it should be regarded as bad as asbestos. Tell me not to worry! 

If your blocks are designed as a normal unreinforced masonry domestic wall then they are a different animal from the problems you see in the press.

 

The problems you see published are when aerated concrete is used in combination with steel reinforcement so they act as beams.

 

Have attached some info from the IStructE for some bedtime reading.. so you can hopefully sleep ok.

 

 

RAACs-v3.pdf

[SteamyTea]

What is needed is a public enquiry.

That should delay any decision for 20 years.