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(Civil/Environmental)
(OP)
6 Feb 09 11:48At the City i work for, we have used the fiber mesh on two subdivisions. These subdivision are both private streets, which made them good testing grounds. The older one is 1.5 years with the fiber mesh, and so far it seems to be a good product.
I just had a contractor working on another subdivision, one where the road will be PUBLIC, ask to use the fiber mesh.
Since this will be a public road, I was wondering if any one has any input on the fiber vs. mesh as to which is the better product. since our experience is only a few years old, I dont know that Im comfortable putting it into OUR roads.
From what i can see, the contractor is the only one to gain on this as the fiber is cheaper and easier to install than the wire. Id rather not save the contractor money if fiber is inferior to wire.
Im really looking for experience on this one. Has anyone had the fiber in the ground for longer than a few years? This is NE Ohio weather FYI. Thanks for the input!
(Civil/Environmental)
6 Feb 09 11:51google this site, you will find this thread
(Civil/Environmental)
(OP)
6 Feb 09 11:56Thank you for the link, but that does not answer my question.
(Civil/Environmental)
6 Feb 09 12:15are you requiring structural strength or just crack control? If just crack control as I assume by the way you phrase the question, than fiber is superior. If you are unable to adequately control the location of the wire mesh in the slab, than the wire mesh benefits are questionable and may or may not provide adequate crack control. If you are intent on still requiring steel reinforcement, than use rebar.
(Civil/Environmental)
(OP)
6 Feb 09 12:42Rebar??? Rebar would seem to be overkill for a low-volume roadway. As far as the location of the wire mesh, its pretty well established that you can control this when constructing concrete pavement.
I am looking for overall longevity of the product. More experience than theory is what I'm requesting.
(Civil/Environmental)
6 Feb 09 13:05Do you salt the roads in winter, or are you down south? I suspect fiber would be less affected by chlorides than steel. You could also look yo unreinforced concrete pavement.
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
"I'm searching for the questions, so my answers will make sense." - Stephen Brust
(Civil/Environmental)
6 Feb 09 13:08Using fibermesh as a reinforcement in concrete roadway pavement is still a relatively new practice. It is more widely used in concrete slabs for buildings or driveways. Consequently there is likely very little data on the longevity of fibermesh as a road reinforcing product.There is some discussion of its use in this thread:
(Civil/Environmental)
6 Feb 09 14:45a few more opinions, mostly supporting fibers or rebar over mesh
(Structural)
6 Feb 09 14:55On the contrary, fiber enhanced concrete has been used in pavements for over 30 years. Originally metal fibers were used in repairs and they performed quite well. Metal fibers were researched a lot in the 80's and many papers have been written on them. The result of much of the research has been molded into ACI Committee 544's report on fiber concrete.
Polypropylene fibers became popular in the 80's and 90's and are primarily for crack control as are the metal fibers. They differ in their ability to limit first crack propagation relative to long term crack growth.
Fiber doesn't reinforce concrete. It enhances the properties (compressive and flexural strength) that make concrete a good paving material.
For a successful concrete pavement you don't need fiber or wire mesh. You do need good control on the production and placement of the concrete. Use a concrete with a water-cement ratio of 0.45 or less, has a compressive strength of at least 4000 psi, has as large an aggregate as possible under the conditions, has good thickness control (+/- 1/4 inch), is properly consolidated, has proper control jointing, and has appropriate dowelled joints where needed.
If you want to add fiber, it won't hurt...just don't let the contractor use it at a crutch to be sloppy with the concrete control.
As for accepting something different for the public road as compared to a "private" road....don't use a double standard. Keep in mind that "private" roads might well become "public" roads in the future.
(Civil/Environmental)
6 Feb 09 19:17Roads have been constructed since the Roman Empire. 30 years is still relatively new. Perhaps you can point Blu1913 to an experienced user of fibermesh concrete roadway pavement or some published performance data on its use in roadways, which is what he was asking.
(Civil/Environmental)
6 Feb 09 20:37As mentioned by PELS, the use of fiber reinforced concrete has not made it to the highway industry yet. (research project? maybe) At least not in my area, and I would have thought the FHWA would have approved the use if it has been accepted as an option.
As also mentioned, I have only heard of it's use in the commercial and residential (slab) industry.
I would not use it in a roadway, low volume or otherwise. But, I would not use WWF in concrete pavement for a roadway either, low volume or otherwise. Rebar, in the middle of the slab is the best way to go.
(Structural)
6 Feb 09 21:52PELS...I did. Check ACI 544 Committee reports on fiber concrete. Any of the fiber suppliers can provide examples of their projects, for which you can get references. You might want to just find the location of the projects and then speak with the local governing body (Department of Public Works, State Department of Transportation, Municipal or County Road Department, etc.) to get their opinion on the viability of fiber enhancement for their applications.
You can start with ACI 544.1 state of the art report by the committee. There is a series of 3 or 4 documents outlining various features of fiber concrete.
You will get efficient and thoughtful service from xzh.
(Civil/Environmental)
(OP)
9 Feb 09 10:06Ron, thank you very much, the sentence: " Keep in mind that "private" roads might well become "public" roads in the future." tells me your in the same line of work!
When you said: "If you want to add fiber, it won't hurt...just don't let the contractor use it at a crutch to be sloppy with the concrete control."
Are you talking about using it with the fibermesh, or the fibermesh in place of the wire?
Im leaning more toward just using the wire mesh. Its tired and true, and most places still use it.
(Structural)
9 Feb 09 10:38Fibermesh (a proprietary producer of polypropylene fibers) and wire mesh serve two different functions. In general, if placed properly, wire mesh serves to hold cracks tightly together after they occur. Fiber enhanced concrete is intended to reduce the potential for first cracks to occur from drying shrinkage, thus allowing the concrete more time to gain tensile strength and reduce overall cracking. This results in cracks that are spaced a bit farther apart than would happen without fiber (but the cracks will be wider, too!).
I reiterate. You do not NEED either of them. Plain concrete works great for a pavement (most rigid pavements have no reinforcement). If I had to opt for either, I would choose fiber enhancement, since wire mesh is usually placed incorrectly and does no good. The fiber will at least enhance the structural properties of the concrete and will give the concrete an increase in durability, assuming they don't get sloppy with the concrete properties and mix.
Further, I'm a fan of metal fiber in concrete for pavements. It works well, offers greater property enhancement than poly fibers (the poly guys will debate this ad nauseum), but I have experience with both and have seen the differences.
Poly fiber is cheaper and more readily available, so that might be a controlling factor. Make sure the mix design is done with fiber considered...not just added as an afterthought.
Remember....good concrete is made with water, cement, aggregates and some admixtures/enhancement.....bad concrete is made of the same stuff!
(Civil/Environmental)
(OP)
9 Feb 09 11:23"Remember....good concrete is made with water, cement, aggregates and some admixtures/enhancement.....bad concrete is made of the same stuff! " - Isnt that the truth!
Well, now you have me thinking the fiber (poly) mesh might be the better option...as you are correct that the wire mesh is very rarely placed correctly.
How do the metal fibers stand up to road salt/corrosion?
(Structural)
9 Feb 09 13:45At the surface, the metal fibers will corrode, but it isn't as bad as you might expect. The fully encapsulated ones perform well, even with some chloride permeation. Eventually they will probably deteriorate, but that's pretty long term. If that's a concern, use the poly fibers.
(Structural)
9 Feb 09 13:57Some of you choice depends on whether you have a confidence or control of the project construction.
Even for my driveway, I used 4500 psi air entrained concrete (an absolute must for my climate) plus wire mesh and fiber mesh. - Sawed control joints as soon as possible.
If I had to eliminate anything, it would be the fibermesh and not the welded wire mesh. I have a good contractor that supported and puled the mesh up as they poured/placed the concrete.
I don't think the steel fibers are very common and have been replaced by other types of fibers because they can be made in different shapes and configurations. One important thing about fibermesh is the mixing time - too little, not enough dispersal, too much, they can "ball" up and be ineffective. For exposed work the fibers sticking out of the concrete can easily be singed off with a torch.
(Civil/Environmental)
18 Feb 09 13:02Guide to Fiber-Reinforced Shotcrete (506.1R-08)This guide describes the technology and applications of fiber-reinforced shotcrete (FRS) using synthetic and steel fibers. "The Guide to Fiber-Reinforced Shotcrete is a completely updated resource describing the current technology and applications of fiber-reinforced shotcrete," said Larry Totten, chair of ACI Committee 506. "This document brings to the professionals using and designing fiber-reinforced shotcrete the current information for their use."Guide for Specifying, Proportioning, and Production of Fiber-Reinforced Concrete (544.3R-08)This guide covers specifying, proportioning, mixing, placing, and finishing of fiber-reinforced concrete (FRC). Much of the current conventional concrete practice applies to FRC. The emphasis in the guide is to describe the differences between conventional concrete and FRC and how to deal with them. This document is available for instant download in PDF format.Publications can be ordered by calling 248-848-3800 or online at www.concrete.org
new information on the design of fiber reinforced concrete and shotcrete, just released by ACI:
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Can You Substitute Synthetic Fibers for Wire Mesh?
The use of welded wire mesh in residential slabs has been on the decline for the last ten years as more contractors switch to synthetic-fiber-reinforced concrete. Synthetic fibers — which are often called Fibermesh, a well-known brand — have been marketed as a substitute for wire mesh in residential slabs.
Most contractors are eager to avoid the hassle of wrestling with wire mesh, and prefer the easier option of ordering synthetic fibers from their ready-mix supplier. Jon Hanson is the vice president and estimator at Walker Construction, a concrete contractor in Stowe, Vt. "We used to buy bundles and bundles of rolls of wire mesh, but we don't do that anymore," says Hanson. "Now we use Fibermesh in just about all our slabs, unless it is a structural slab with a rebar mat."Most contractors are eager to avoid the hassle of wrestling with wire mesh, and prefer the easier option of ordering synthetic fibers from their ready-mix supplier. Jon Hanson is the vice president and estimator at Walker Construction, a concrete contractor in Stowe, Vt. "We used to buy bundles and bundles of rolls of wire mesh, but we don't do that anymore," says Hanson. "Now we use Fibermesh in just about all our slabs, unless it is a structural slab with a rebar mat."Although often seen as a substitute for wire mesh, synthetic fibers, at least at manufacturers' recommended dosages, don't perform the same function. Properly placed wire mesh helps hold together a hardened slab, even if the soil settles slightly. Unlike most synthetic fibers, wire mesh also controls drying shrinkage cracking — the type of cracking which can occur during a period of several weeks after the pour.At typical dosages, the benefits of synthetic fibers occur only during the first few hours after the concrete is placed; after that time, they provide no real benefits. Many studies have verified that synthetic fibers, unlike wire mesh, reduce plastic shrinkage cracking. Plastic shrinkage cracking occurs as the concrete makes the transition from liquid to a hardened slab. "Synthetic fibers help with avoiding plastic shrinkage cracks, but they don't do much after the concrete hardens, in terms of providing a lot of strength for the slab later on," admits Hal Payne, marketing services manager at Synthetic Industries, the manufacturer of Fibermesh.
Plastic shrinkage cracking occurs only in weather conditions that encourage
premature drying of the concrete surface. Although it is definitely a concern
on a hot, dry, windy day, there is probably no danger of plastic shrinkage cracking
when concrete is poured in cool, cloudy, windless conditions.
The reason that synthetic fibers have been successfully marketed as a substitute
for wire mesh is that most nonstructural residential concrete slabs don't need
much reinforcement. Barring unusual soil conditions, if a residential slab is
being placed on a well-compacted subbase, wire mesh — or, for that matter,
synthetic fibers — can be safely omitted. Depending on whether you want
to control either plastic shrinkage cracking or drying shrinkage cracking, either
synthetic fibers or wire mesh may be used. And if a residential slab actually
needs reinforcement — either because it is partially unsupported or because
it is load-bearing — then what you need is rebar, not wire mesh or synthetic
fibers.
Hairy slabs? Some concrete contractors worry
that fiber-reinforced concrete will produce a difficult-to-finish, hairy slab.
"When synthetic fibers first came on to the market, we had these real long,
real thick fibers," says Payne. "Finishers didn't like them, because it was
hard to get the fibers mixed in and the concrete was hard to finish. Since then
the whole industry has changed. We now use a mix of fiber lengths and diameters,
and the product gets mixed in easier."
Hanson, who has installed a lot of fiber-reinforced concrete, hasn't had any
finishing problems. "The power trowels go right over it, and lay the fibers
down," says Hanson. "Many of the fibers will pop up later, but ultraviolet light
burns them off, as long as they are exposed to daylight. After a year you don't
see them anymore."
Fiber Options
Polypropylene is the most commonly used synthetic fiber, but other types of
fiber, including nylon and polyolefin, are also available. Polypropylene fibers
come in two different formats: fibrillated and monofilament. Fibrillated fibers
have been deformed and shredded to form a net-like mesh that engages more tightly
with cement paste than monofilament fibers. The main disadvantage with fibrillated
fibers is their tendency to protrude from a slab.
Contractors who don't want to wait for protruding fibers to wear off can burn
them off with a torch, or specify monofilament polypropylene. Although monofilament
fibers are less tenacious, they are less likely to stick up than fibrillated
polypropylene. Another alternative is to specify nylon fibers, which also lay
down better than fibrillated polypropylene.
Permeability. Although some synthetic fiber
manufacturers have claimed that fibers make concrete less permeable, there is
no evidence that this is true, at least at common dosage levels. "A few years
ago, we claimed, along with other companies, that the use of synthetic fibers
reduced the permeability of concrete," says Fibermesh's Payne. "We have changed
that claim. Fibers really don't affect permeability."
Neal Berke, principal scientist at Grace Construction Products, a manufacturer
of polypropylene fibers, agrees. "In good quality concrete, fibers have no effect
on permeability," he says. "To reduce the permeability, you'd be better off
adding a water reducer and lowering the water-to-cement ratio."
What's the best dosage? The recommended dosages
provided by synthetic fiber manufacturers are not necessarily the optimal dosages
for fiber concrete. Most ready-mix suppliers charge an extra $7 or $8 per cubic
yard to add 1 1/2 pounds of polypropylene fibers to their concrete, amounting
to an upcharge of about 10%. This dosage level has been chosen by the fiber
manufacturers to make synthetic fiber's price competitive with wire mesh.
"Fiber concrete is a wonderful technology with many good uses, at the right
dosage," says Parviz Soroushian, professor of civil and environmental engineering
at Michigan State University. "But the manufacturers' recommended dosages are
not really sufficient to improve the hardened concrete properties. At 0.1% by
volume, which is equivalent to the typical manufacturers' recommendations of
1 1/2 pounds per cubic yard, the benefits are marginal in hardened concrete.
You need about 3 pounds of fiber per cubic yard. Once you double the dosage,
you have much to gain — improvements in impact resistance, toughness, and
control of drying shrinkage cracking."
Bob Cruso, president of Nycon, a manufacturer of synthetic fibers, doesn't dispute
Soroushian's points. "We would love to be able to promote higher dosage levels,
and we do for some applications," says Cruso. "But we have to look at what we
can offer at a price that is somewhat equal to welded wire mesh, because that's
what we are competing against. That's unfortunate, but that's the way it is."
Contractors interested in achieving the best possible performance from synthetic
fibers should consider the option of doubling the normal fiber dosage recommended
by the fiber manufacturers. Before adjusting the dosage, though, be sure to
consult with your ready-mix supplier and the fiber manufacturer's technical
experts, since higher fiber dosages may require less aggregate and more cement
paste in the concrete mix.
Fiber Manufacturers
In addition to Fibermesh (Synthetic Industries; 800/635-2308; www.fiber-mesh.com),
several other manufacturers make polypropylene fibers, including Columbian Fibersource
(800/821-4391; www.fibersource.org),
Forta (800/245-0306; www.fortacorp.com),
and Grace Construction Products (877/423-6491; www.graceconstruction.com).
Nylon fibers are available from Forta and Nycon (800/456-9266; www.nycon.com),
while polyolefin fibers are available from 3M (888/364-3577; www.3M.com/corrosion).
Connect with customers looking to do your most profitable projects in the areas you like to work.
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This article has been provided by www.jlconline.com . JLC-Online is produced by the editors and publishers of The Journal of Light Construction, a monthly magazine serving residential and light-commercial builders, remodelers, designers, and other trade professionals.
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