AirCrete blocks

[wanabechippie]

Hey.

Was watching Grand Designs last night on C4. Couple were making a house out of AirCrete blocks. Seems like a good idea - recycled fly ash + air bubbles for insulation.

Was wondering: How to these aircrete blocks stack up against standard concrete blocks as regards cost per and strength? Are they suitable for use where ever concrete blocks are or do they have limitations due to their reduced density/porosity?

Cheers.

 

[^woody^]

Thermalite and Celcon (and others) have been around for years, and generall do anything a concrete block can.

In fact, check out the Celcon Ra House system - walls, floor, and roof all from aerated panels. Mega-efficient

 

[noseall]

we use airated celcon or thermalite blocks as a standard because they are easy to cut, easy to handle and easy to lay. yes, they are more expensive to buy but are cheaper to lay.

i'm not entirely convinced they are the strongest though, but adequate for the job. if i wanted a block with a good key for wet plastering, i would have to go for a cinderblock or concrete type and not a celcon or thermalite.

tarmac make a 'durox' block which is a long airated block, but these snap like biscuits.

 

[blasted]

I cant see how the compressive strength can be any where near that of a concrete block. Where it is a larger structure with more than one floor and a large roof, a structural engineer surely would be needed to do the calculations to ensure theat the overall weight pushing down on the blocks doesnt cause them to fail.

 

[^woody^]

Standard aerated are about 3 to 3.5 N - which is more or less the same as lightweigh concrete.

There are also 7N and higher blocks which is the same as your heavy concrete ball breakers.

I remember using Durox blocks on site (I remember as it was when Iraq invaded Kuwait - a hot summer and the subbie had a bright idea of us starting at 4AM and finishing at 12 midday to avoid the heat )

Anyway, I would lay the bed for one block, turn around to pick the block up and a joint, by which time the bluudy compo bed had gone off. We were not allowed to soak the blocks due to the Architects fear of excessive shrinkage cracking.

I thought we had it bad, but the plasterers could not earn a bean. lol

And to top it all, all the walls in the roof space were heavy concrete blocks. We had a suspicion that the site manager had the plans upside down. lol. We got through some hoddies on that job.

 

[Emeraude119]

Hi all.
With regard to strength, a 3.6 N/mm2 (or any strength block) would be that strength, regardless of what it was made from, e.g aircrete, medium dense or dense aggregate. Arguably an aircrete 3.6 N/mm2 block is going to be stronger than a 3.6 N/mm2 aggregate block, because less of its strength is used up in carrying its own dead weight.
To match the insulation power of a aircrete block at say 115mm wide, an aggregate block would have to be nearly 1.100 metres wide.
Any block can be used for any structure provided it is of the strength and type specified by the designer or structural engineer.
Under the latest regulations buildings with low thermal mass `seem' to fair better, therefore aircrete or timber frame buildings comply easier than heavier materials, but higher thermal mass does help to stabilize internal temperatures far better than in lightweight buildings. It is I guess a matter of balance.
Most building materials such as bricks, blocks, timber, renders plasters etcexpand the wetter they are, and shrink the drier they are, so keeping materials as dry as possible both during site storage, and when being built in. goes a long way towards avoiding issues associated with the drying out period of a new building.
As for aircrete. if someone came up with a material which is light enough to pick up with one hand, but can carry at a minimum 29 tons, is water resistant to the extent they float when placed on water, provides a better conductivity value than timber, but does not rot, catch fire, or support insects or fungal growth (they are even used for beehives) and is sustainable people would think it a remarkable product but this is exactly what aircrete can do.

 

[jeds]

However, if you are organising a 'break a concrete block over your head' competition. I'd go for the lightweight blocks. Because they will break a LOT easier than the dense aggregate ones.

 

[Emeraude119]

The tensile strength of a block is not its most important characteristic, since blocks are normally intended to be loaded in compression.
The tensile strength of any block is only 20% of its compressive strength so I don't believe that the way a block breaks over someones head, has any bearing on whether a particular block type is better / worse than another.
There is however a misconception, that if a block (or anything for that matter) is heavy it must be strong, and if it is light it must be weak.
If a block is heavy, it just means that it is heavy.
If a way could be found to make a 3.6 N/mm2 block out of duck feathers, it would STILL be a 3.6 N/mm2 compressive strength block, just a very light one!
The only time tensile strength becomes an issue, is when blocks undergo tensile stressing, e.g. during the drying out period of a new building. or when they are used as infill blocks for beam and block floors, and as noted above the tensile strength of a block is a function of its compressive strength rather than what it is made of.
Therefore a 3.6 N/mm2 aggregate block will break at the same tensile load point as a 3.6 N/mm2 aircrete block.

 

[jeds]

Is it always this much fun in the office of the aircrete block marketing board.

 

[Emeraude119]

John I deal with all block types not just aircrete, but I do know what blocks are best suited for different situations, including the requirements of the latest Building Regulations.
There are a lot of myths and misconceptions about blocks of `all' types so just doing my best to spread the truth about blocks generally.
Not a member of any marketing board, but yes i do believe aircrete blocks to be a modern superior technical product. they just have to be used in the right way.

 

[jeds]

When you say deal with them, I take it you mean deal with the paperwork.

 

[Emeraude119]

Hi John - Yes. now very much dealing with the paperwork but was on the tools for 20 years and taught brick block work at a tech college for another 13 years.

 

[Aircrete]

Any advice on MAKING aircrete... or FOAM GENERATORs...?

 

[John D v2.0]

You can even prop lintels on lightweight blocks if you want. Our SE just specified padstones big enough to spread the load to keep it below 3.6n. In the end the builder refused to do it and used 7n around the bearing, but there was no need.

 

[tomfe]

Very hard to make proper aircrete, they add aluminum to the concrete mix to make it expand and then they autoclave it to dry them out. It's not a diy thing.
Foam concrete is different and is quite easy to make, you need a correct non phosphate foaming agent (one for concrete) and mix this with your gauging water. You'll have to do lots of tests however to get this right.