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Old 12-06-2009, 03:03 PM   #1
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Fiber in concrete?


What is the purpose of using fiber in concrete, whether it be a slab, or driveway

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Old 12-06-2009, 03:27 PM   #2
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Fiber in concrete?


Steel or polyester fibers improve the resistance of the concrete to cracking. They are not designed to increase the compressive strength of the concrete, and in most cases do not improve the tensile strength either.

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Old 12-06-2009, 04:19 PM   #3
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Fiber in concrete?


The main purpose of fibers is to decrease the micro cracking, but they may also help with some other cracking (especially shrinkage cracking), but no supplier will ever claim that. - Contractors may claim that mesh is the savior, but they may not be really familiar or be around when there is a problem.

There is no substitute for proper concrete and wire mesh if it is a driveway and sawing deep enough control joints as soon as possible (definitely within 24 hours or less), depending on the temperature.

I had a couple of driveway slabs poured and used 4500 psi air entrained (5-7%) with a maximum slump of 3" that had fibers plus I use welded wired mesh since it is such cheap insurance if you have concerns with frost, salt and durability.

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Old 12-07-2009, 04:17 AM   #4
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Fiber in concrete?


just my opinion BUT fiber was market'd as the answer to thorough reinforcement in conc to increase resistance to crking,,, there was dissatisfaction by many as to the location of welded wire mesh,,, as i recall, for mesh to be effective, its had to be placed exactly mid-point vertically +/- 5% according to aci,,, as we all know, when the jabonies finish walking thru fresh conc, stamping down the mesh, then pulling it back into place w/hooks, ' exact location ' takes a beating,,, mesh/steel adds greatly to the conc's ability to resist the forces of tension which threaten the ability of conc to resist random crking during the ' green ' stage when conc's neither hard OR liquid/plastic,,, after curing, mesh just holds broken pieces together .

reinforcing steel adds no compressive strength,,, it does, however, add greatly to flexural strength - that's why its used in bdge decks, driveway throats, tunnels, etc - adding addl strength to resist ' loading moments ' thrust upon the conc.

we're currently seeing a decrease in the amt of conc spec'd to receive fiber compared to 5yrs ago.
when i replaced my home's d/w ( 4,000psi - 4" slump - no air { atlanta } ), no steel or mesh - just proper jnt pattern AND timing jnt sawing + jnt depth - sawed same day as placing = no crks


dick's in a different region subject to salt & freezing temps - we're not,,, then again, steel's not impervious to salt attack,,, we see problems w/steel in structures along the shore due to salt air - spalling due to steel corrosion & expansion

bear in mind my experience was 1st conc repair so i got to see conc 20-50yrs AFTER it'd been plac'd,,, was only 20yrs ago i start'd paving/flatwork/vertical/tunnel therefore my frame of reference's different than 2 previous licens'd posters,,, yet we're all 3 on the same chapter if not the same page
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Old 12-07-2009, 01:40 PM   #5
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Fiber in concrete?


I tend to agree with the "marketing" opinion of fibers. IMO, there mostly a gimmick that the Manufacturer, ready-mix suppliers, & contractors have used to lower the material & labor cost to install concrete re-inforcement.

I often use my experiences tearing out concrete to form an opinion on what works best. I've torn out plenty of concrete w/ fiber without knowing it until it was on the truck.
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Old 12-07-2009, 02:13 PM   #6
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Fiber in concrete?


When I poured the driveway that I used both fibers and mesh on, I could not use wire mesh on the apron to the street or sidewalk (future utility access) that was on city property, so I got to be able to use the same concrete on all areas and just eliminate the mesh in some areas. The extra cost of the fibers was minimal in the big picture, even though a friend did the work and the finishing and placement was still the same. - Cheap insurance and easy.

I am not a "penny pincher" when it comes to materials if they do not effect the labor cost, which is many times greater.

Where I now am located we do not have the easy weather conditions and you would be hard pressed to even get concrete below 4000 psi, 3" maximum slump, air entrained delivered for use in a driveway. The extra cost of the mesh is minimal because the and the dispensing and mixing cycle is automated. Fibers is never a substitute for wire or rebar, but they offer a benefit if properly batched and mixed. Under mixing or over mixing is a real problem.

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Old 12-07-2009, 02:26 PM   #7
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Fiber in concrete?


I can agree with that as well Dick. I should have noted that I do use Fibers fairly often, because, as you said, it's cheap insurance. We often use them exclusively in the street "right of way" as well, as no steel re-inforcement is allowed in most muni's around here. But, as you stated, we use it in addition to steel re-inforcement.

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