Underpinning - mesh fibres in concrete

[rocky_robin]

Hi all.

My architect has called up for mesh fibre concrete to be used to underpin one of my gable walls (building an extension alongside it).

I've never used this product before, nor can get hold of it locally from the usual building merchants (Jewsons, Travis Perkins, etc).

Has anyone got any experience in using this additive? I would assume that it could bulk out the cement and will have to add gallons of plasticiser to make it workable?

The building inspector has simply said that as long as the structural guy is happy then he is. The structural guy was a waste of time and non committal!!!
I was trying to find out the type of fibre required. (steel, polymers, etc)

Any assistance would be great.

Robin

 

[hammerswinger]

Just Google "Concrete Fibers"

Also take a look on the Paving Expert site as they have some info on the subject.

http://www.pavingexpert.com/reinfrc1.htm


Cheers.

 

[^woody^]

A total waste of time, with no purpose at all. Whoever specified this is a clueless idiot

 

[Norcon]

We do a lot of flooring and yarding with fibers added.
Less chance of cracking.

Also should reduce the chances of frost spalling.

Spend a day on a breaker where fibers are holding the stuff together and you won't be saying it has no purpose.
You need extra joules to rip it up!

 

[^woody^]

Foundations are not floors though

 

[Norcon]

Foundations are not floors though

Can you give a reasoned technical explanation as to why you think they are useless in a foundation?

Some of the foundations we do are finished floors!

 

[^woody^]

Because foundation concrete for underpinning does not get affected by shrinkage cracks, does not get affected by frost, does not get affected by tension, does not need a finished face and does not need any sort of controlled set.

Plus we've been concreting without fibres and without problems for a few hundred years now

 

[Norcon]

What about compressive forces? Shear forces? Ground movement forces?
Fibered concrete will with stand much higher compressive forces before failing!

There is no evidence to suggest fibers are useless in an underpinned foundation.

Pre cast concrete beam deflection where fibers are added is increased so what does that tell you?

 

[^woody^]

A beam is not a foundation and acts differently

There is no evidence to suggest that bananas are useless in a foundation either

A lump of concrete deals with the forces and loads of a foundation without the need for any extra help. To specify something when it is not required, shows a lack of understanding by the designer

 

[pred]

I think you supply the fibres and when the truck turns up you ask him to chuck them in. Don't quote me on this, it's something I have never got involved with, just what one of my labourers was discussing.

 

[^woody^]

Yes, that will surely mess the mix up and invalidate any suppliers guarantee of concrete grade. Get a better labourer

 

[stuart45]

He did say don't quote him on this woody
If you want fibres in the crete tell the company and they put them in for you, to save the driver throwing a few handfulls into the mix.
I've never worked on any underpinning job, or foundations that had them added though.

 

[Norcon]

A beam is not a foundation and acts differently

Ground beams are foundations are they not?

What happens when you add cement to a concrete mix?
It increases the strength!

Also without adding any cement you can increase the strength just by using a crushed stone as opposed to a round (non crushed) stone.
So whats going to happen when you add fibers?

If you crush a fibered test cube and a non fibered test cube in a test rig which one will sustain the highest force?

 

[^woody^]

We are discussing the OPs thread which is fibres in underpinning foundation, and the benefit of this in this situation

If you want to discuss the comparison of beams, ground beams, edge beams, cantilever beams, pads, strips, steps, piles etc then lets start a new thread.

Meanwhile what actual benefit would these fibres have to an underpinning strip foundation, that makes them a necessary or even desirable addition?

 

[stuart45]

Here's one report.
http://www.concreteconstruction.net/images/Polypropylene Fibers in Concrete_tcm45-347135.pdf