Concrete Roadways - Fiber vs. Wire Mesh 1

[Blu1913]

At 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!

 

[cvg]

google this site, you will find this thread

http://www.eng-tips.com/viewthread.cfm?qid=126594

 

[Blu1913]

Thank you for the link, but that does not answer my question.

 

[cvg]

are 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.

 

[Blu1913]

Rebar??? 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.

 

[ACtrafficengr]

Do 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

 

[PELS]

Using 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:

http://www.eng-tips.com/viewthread.cfm?qid=699&page=1

 

[cvg]

a few more opinions, mostly supporting fibers or rebar over mesh

http://www.eng-tips.com/viewthread.cfm?qid=125492&page=1

http://www.eng-tips.com/viewthread.cfm?qid=191441&page=6

http://www.eng-tips.com/viewthread.cfm?qid=80294

 

[Ron]

On 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.

 

[PELS]

Roads 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.

 

[Drumchaser]

As 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.

 

[Ron]

PELS...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.

 

[Blu1913]

Ron, 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.

 

[Ron]

Fibermesh (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!

 

[Blu1913]

"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?

 

[Ron]

At 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.

 

[concretemasonry]

Some 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.

 

[cvg]

new information on the design of fiber reinforced concrete and shotcrete, just released by ACI:

[blue]Guide 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

http://www.concrete.org.

[/blue]