Polypropylene Vs. Nylon fibers 1

[ggone]

If someone could give me some insight on the advantages and disadvantages of polypropylene and nylon fibers, and give some opinions on what works best, I would really appreciate it. Thanx

 

[Ron]

The use of either depends upon your application. Polypropylene is the most commonly used fiber these days. Nylon is more expensive and has properties that are not as amenable to good performance for the intended purpose in concrete...I'm sure someone will disagree with that statement, but that's my opinion.

I am not a fan of "plastic" fiber in concrete. It has been sold as the panacea of concrete quality, intended to overcome all the ills of poorly controlled concrete processes including mixing, placement, and curing. Steel fibers work well and provide good property enhancement of good concrete.

My caution is to not use fiber as a substitute for good quality concrete from supply to finished product.

 

[ggone]

Thanks for your insight Ron. I really appreciate it. I have been talking to some other people about it. It sound like if you are going to use fiber that Nylon is worth the extra money. Because nylon wets out it actually forms a hydrogen bond with the matrix, where as polypropylene is inert and does nothing. I have even found a statement by the marketing manager of Fibermesh (polypropylene) that Fibermesh does nothing in hardened concrete. It is strictly for plastic shrinkage cracking. I have also found out that Nylon does work in hardened concrete and will replace wire mesh in non structural applications. Let me know if you have any information that does not support that. Thanks again.

 

[Prepakt1]

Nylon fibres are stronger than poly based on the same volume.I believe about 1.8 times as strong .They also are denser and do not float.

 

[jhardy1]

I for one am very sceptical about any claims of using plastic fibres as a substitute for steel reinforcement. The reason is that the elastic modulus of the plastic fibres is LOWER than that of hardened concrete, so when a crack starts to form, the fibres don't significantly restrain the crack or carry much load - they just stretch. From ggone's comments, it seems that Fibermesh has recognised this fact, and I think the same would apply for nylon fibres also.

Plastic fibres can however be effective in controlling early plastic cracking when the concrete has not yet cured. As Ron pointed out, this can be beneficial, but should not be taken as a substitute for good placement and quality control etc.

Steel fibres or bars have an elastic modulus higher than that of hardened concrete, so are able to carry tensile stresses in cracked concert.

 

[illeniumsd]

I used the Nylon Fibermesh in a recent project for the United States Dept. of Energy and the Border Patrol and I liked it. It was an 8000psi mix and it went above and beyond our expectations.

 

[sdz]

There are claims that plastic fibers will replace wire mesh in non structural applications.

That means you can use it to replace the mesh if you don't need mesh!

 

[abe456]

Speaking from bitter experience, I will never again substitute fibermesh for wire or reinf steel.
I do think fibermesh is great for crack control and "hardening" of the wearing surface.

 

[Ron]

It is not appropriate to directly substitute fiber, of any ilk, for structural reinforcement. The fiber is an enhancement to the concrete material, not the structure, except in the sense that it might improve the concrete quality, thus improving the structure quality.

The enhancement of fiber in concrete material will increase its properties if done properly. Since a strength increase would be realized, there is a probability that the total volume of reinforcement might be reduced as a result of the increase in strength.

 

[Ginger]

The primary purpose of adding fibres to the concrete mix is to improve the concrete's DURABILITY. It is deigned to be dispersed throughout the mix and to effectively "knit together" any cracks forming in the section by spanning across the crack itself.

Polypropylene fibres have been proven to be very successful in preventing explosive failure of concrete when exposed to a fire. The fibres melt in the heat thus producing air paths through which the air and free water in the concrete body can vent itself.

Fibres are not included in the mix to replace the structural rinforcement, although we in the UK do use fibres in the design of tunnel segments (without rebar) to take small bending moments generated by self weight under handling and tunnel erection loads.