Plastic Fibre Reinforcing

[StructuralDzine]

I found the following on a web site. What do other engineers think of fibre reinforcing. Does it do what it claims? Is it worth using and in what applications?
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Benefits of fiber reinforcement to Engineers:
       
Reduces plastic cracking: Synthetic fiber reinforcement inhibits the formation of plastic shrinkage and plastic settlement cracks, contributing to the long-term durability of concrete structures.  Conventional reinforcement does not function in concrete until the concrete cracks.  By the time this occurs, microcracking can lead to larger macrocracks, which can affect the long-term functionality of the concrete.
       
Minimizes plastic settlement cracking: Plastic settlement cracks occur when fluid concrete settles around rebar and embedments.  Fiber reinforcement provides a support mechanism that helps resist the migration of bleed water to the surface and the gravitation settlement of aggregates and cement.  The support mechanism provided by the fibers also reduces the tendency for concrete to crack directly over traditional reinforcement and other embedments.
       
Provides fire resistance: Synthetic fiber reinforcement, particularly in high strength, structural concrete, dramatically improves fire resistance.  In concrete, synthetic fibers reduce in volume under high temperatures forming millions of pressure relief voids in the concrete.  These voids accommodate the stress created when water vapor turns to steam in the concrete.

 

[phuduhudu]

Interesting what it says about fire resistance. Does this not mean that the reinforcement loses it's strength in fire? Carl Bauer

http://www.bauerconsultbotswana.com

 

[StructuralDzine]

Carl, I guess it means that the plastic fibres are performing no structural purpose in the hardened concrete.

 

[WIM32]

Carl,
The plastic indeed has no measurable effect on the strength of the concrete. The best way to have strength as well as the benefits of the plastic fibers, is to use a mix of plastic and steel fibers. This way high strength (120Mpa compressive, 12Mpa tensile) concrete is possible.
regards
Wim

 

[StructuralDzine]

Wim, won't you achieve those benefits by using steel fibers alone?

 

[WIM32]

StructuralDzine,

Many of the benefits (plastic cracking) are indeed achieved using only steel fibers. Fire resistance on the other hand is not as strongly benefitted by steel fibers as it is by using plastic. Also using a mixture of both fibermaterials seems in practice better processable.

 

[Riz]

Try checking with

http://www.fibermesh.com

They have pertinent details.

Additionally, I would be worried with any claim that supports its fire resistance capability.

Of interest would also be a 4 year study was carried out on the "effects of Polypropylene fibers in reducing corrosion of rebars in concrete" by Landau and Webster.
This report was presented at the ACI conference in Hong Kong (Dec. 5th 1991) and has been included in ACI publication SP-128.

Wim, please is it possible to substantiate in terms of research or publication the following:
"Also using a mixture of both fibermaterials seems in practice better processable".

 

[WIM32]

Riz,

In terms of research: I have been doing some research using different compositions of fibers, i.e. only steel fibers, only plastic fibers, and a combination of both. I have been testing the processability in a B65 concrete. The mixture, using both fibers gave the best results in terms of thin-walled structure casting (this research cannot be seen as acadamically valid!!)

In terms of publications: I have read about the processability of different fiber types in "Challenges for Concrete in the Next Millennium" Volume I or II by Stoelhorst and den Boer. Unfortunately I haven't written the exact name of the piece...

So summarizing I would say that some research on this is still needed.

regards
Wim 32