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When are fibres in concrete not structural?


epsilonGreedy

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My local go-to concrete outfit could not deliver on my preferred day and so I phoned a brandname concrete supplier.

 

The pro sales team expended 10 times the veribiage just to agree with my suggestion of the nearest outlet. Then we got onto what mix I needed:

  • Me "how much extra for fibres in the mix".
  • Supplier "Oh no you won't need fibres for a garage floor because its not structural".
  • Me "well how much anyway"
  • Supplier "Will you want ordinary fibres or structural fibres?"

 

At this point I started wondering if the cheaper ordinary fibres are not structural what purpose do they serve?

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7 minutes ago, Crofter said:

I thought fibres were primarily for prevention of shrinkage cracks?

 

 

In another thread a couple of Buildhub veterans indicated that for a garage floor fibres were a reasonable substitute for rebar.

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2 hours ago, Ian said:

@epsilonGreedy

I suspect they are asking if you want steel fibres or plastic ones

 

 

Having read some turgid scientific reports on fibre reinforced concrete this evening I think you are correct.

 

I cannot find the original BuildHub thread, @PeterWmust have been referring to steel fibres when he mentioned fibres were an alternative to rebar.

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9 hours ago, Ian said:

@epsilonGreedy

the main advantage of the plastic fibres over the steel variety is that you can easily burn off the excess fibre ends that stick up from the surface of the slab once it is cured.

 

 

Since starting this thread I now question whether steel fibres are suitable for a garage slab floor if there is a tendency for some to migrate to the surface.

 

If plastic fibres do not contribute to longterm tensile strength should they be considered a substitute for rebar? Think I am coming around to my original hunch of 2 months ago that rebar is right for me after all.

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1 hour ago, PeterW said:

Steel tend to be used where they are not seen

 

 

Ok that makes sense.

 

1 hour ago, PeterW said:

 poly or fibre where it can be floated or finished. 

 

A few months ago when you suggested fibres as an alternative to rebar in a garage floor were you thinking of a specialist non metal fibre like carbon fibre? 

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23 minutes ago, PeterW said:

Nope just good old glass fibres

 

 

Oh. My local concrete suppliers offer metal or poly fibres. Glass fibres (GFRC) seems to be used in specialist concrete panel products manufactured offsite in a factory.

 

If metal or poly are the mainstream options for wagon delivered concrete and if metal is out for a slab floor then there does not appear to be a realistic fibre substitute for rebar.  

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Poly is fine - my supplier uses glass as they do it as standard. They are not a full structural solution like metal fibres (usually called needles) but for what you are doing I wouldn’t worry. 

 

As @Mr Punter says you could put a sheet of A142 in the slab, just break up a council 50mm slab to use as chairs and job done but tbh this is overkill on a garage slab. 

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