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Are the fiber strands that you can add to ready-mix cement worth it. I’ve heard conflicting stories about whether they do very much, and also stroies about how much of a pain it is to finish off the cement. Up here in Canada they’re charging about $15Cdn/yd and I’m wondering if it is worth it.
Thanks
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Replies
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Hi Steve,
Unless there is no alternatives, whatever that may be, the answer is no.
Gabe
*Well the first time I had any personal experience with fibre additive was last year. Two small projects on jobs next to mine. After the 7 month winter one of them was cracked and one wasn't. Both fibre additive but installed by two different contractors. In my opinion the one that cracked would not have done so if conventional rebar had been used.
*I use the fiber almost all the time. I just want to do all I can to protect a slab. I'm nervous about slabs. I use the fiber to help prevent small cracks and spalling and still use re-wire to prevent shifting and big cracks.The fiber, as I understand it, is not a substitute for rebar or wire. BTW, here fiber is an extra $7.00
*I agree it's no substitute for steel. I've noticed fewer microcracks with fiber and steel than with steel only. But fiber only, if it cracks, can have bigger cracks than steel only. I tried fiber only on a 1.5 " pour on top of a nice, crack-free slab. The new 1.5" pour developed wide and long cracks (same contractor, same mix plant, smaller aggregate, slightly richer mix) In retrospect, I'd have put 6"x6" #10 mesh in. All these additives to prevent cracks, cure faster, etc are helpful for special situations but how about just keeping the concrete warm and wet for a week like you're supposed to? It does make a big difference in final strength and therefore results in fewer cracks, longer wearing harder surfaces, and less freeze spauling. In dams and bridges they keep the concrete wet for 28 days. -David
*Here, in NC, fiber is 5$ extra per cubic yard. About 85% of residential concrete gets fiber (excluding footers). For a medium sized pour - say 50 yards - that comes out to $250. By the time you pay for the prep, concrete and labor you've spent upwards to 7K so, as Ryan said, fiber is cheap insurance.As far as it being harder to finish - never heard or experienced that, but I do know that if you screw around when you are brooming it out, the fibers come up and get a little messy. If it was much trouble there'd be an up-charge on the labor - which there isn't.
*Matt, Fiber reinforced concrete is harder to finish in that you simply can't get the quality of surface that you can with regular rich concrete, but most of the projects are driveways , walks etc. The big plus when installing it is that you can get on it much faster, so you save on labor time.
*Steve,There are other important things to consider when planning a concrete pour.* Fibers are not structural reinforcement and should not be used as such.* A well proportioned mix design with soft porous coarse aggregate will still spall after a few freeze-thaw cycles.* Air entrainment is critical in areas where there will be numerous freeze-thaw cycles. Air entrained concrete will not "bleed" water like non-air entrained. with non-air entrained concrete the bleed water must be allowed to rise and evaporate before closing up the surface. If the surface is troweled before the bleed water is out, it will be trapped and form water pockets below the surface. Concrete finished this way can spall in weeks, not months.* Use of a high-range water reducer is critical to getting a workable mix with a low water/cement ratio.* Poor finishing trumps all the above. If your finishers show up with buckets and "baptismal brushes" start to worry. Wetting the surface blows the water/cement ratio at the surface where it is most critical to longevity. I usually trip over the buckets (accidentally), dumping them. Eric
*right on eric... but y r u repeating yurself ?
*mikenever have good luck with that edit feature . . .sometimes double posts. now i deleted the earliest one and see that the later one was the original. sometimes yer just better off going to bed early!!
*G.LaLonde:So, you are saying that fiber is not appropriate for, say, a concrete countertop where a perfect finish is essential but it's OK for sidewalks & driveways?
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Eric,
can you explain what "air entrainment" is? I'm going to have a large walk way and steps poured shortly and want to mention this to the cement contractor. I will be experiencing a lot of freeze thaw here in Chicago. thanks
Ed
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Hi Ed,
The easiest way of explaining this is taking a bottle of detergent soap and adding it to the concrete and making air bubbles in the mix as it's turning in the drum.(this is an over simplification)
The additive is either put in at the plant or can be added at site.
All concrete that is exposed to freeze thaw cycles should have air added to the mix.
Gabe
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Gabe,
thanks very much for the explanation. I'll make sure that I mention this to the contractor. Is there a specific amount that you should add? I wonder if the plant would automatically take this into account in cold weather areas?
Ed
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Hi Ed,
5 to 8% is the standard we use.
Gabe
*Ed W.You're in the Chicago area, I can make this really simple for you. have your contractor order an IDOT approved mix. If 3500 psi meets your requirements order a Class SI mix. This will assure that you get a workable mix, with good aggregate and air entrainment. If you need a 4000 psi mix Prairie Materials has an I0Y08 structural concrete mix. (Mix numbers will vary depending on which yard it comes from). I believe Al Cygan is still in charge of QC at Prairie. They can help you further. If your contractor uses Meyer Materials I can suggest mix number 9375. (5.2 bag w/ flyash, 0.40 water/cement ratio)or mix 9312, both 4000 psi mixes.Tell your contractor he may not add more than 1 gallon of water per yard of concrete to adjust slump on site. If he needs to add water, do so to a full load, not when he's half-way poured out. And no buckets and brushes for the finishers!Email me if I can be of further assistance.Eric
*Matt, I can think of no reason to use fiber in a countertop. Use a rich mix and wire mesh, possibly with rebar if required. Fiber is mainly used in outdoor pours.
*
Eric,
Can you suggest a good book on the basics of concrete?
*
I had that fiber put in my garage floor in '94, and haven't seen a crack yet. Maybe I'm just lucky?
They poured the floor on a windy day in late September. Leaves kept blowing off the trees and getting trowelled into the concrete. The concrete finisher said that was his "fall pattern" and he charged extra for it.
*"Construction Manual: Concrete and Formwork" by craftsman books. It's like a concrete book for dummies but written in tech speak so dummies won't understand it. It's published in 73 so some of it might be outdated but I think It's got good information.
*As far as books, I hear that the Portland Cement Association is supposed to have some good books but to tell ya the truth, I havn't bought any myself.
*
Thanks, Ryan.
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Are the fiber strands that you can add to ready-mix cement worth it. I've heard conflicting stories about whether they do very much, and also stroies about how much of a pain it is to finish off the cement. Up here in Canada they're charging about $15Cdn/yd and I'm wondering if it is worth it.
Thanks
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Ron,
In your library's reference section look for the American Concrete Institute (ACI) manuals. Kind of dry reading, but a lot of good information on masonry of all types. PCA, as previously stated, is also a good source. Also check out Aberdeen's Construction Supernetwork site for concrete and masonry info.
Happy reading.
Eric