Use of synthetic fiber reinforcing

[StructuralDzine]

What are the advantages of plastic fiber reinforcing?
In particular what are "micro fibres" and "stealth" fibers. How are these different to other varieties?

 

[JAE]

They are used only for plastic shrinkage crack control and do nothing in terms of structural strength. Stealth is a proprietary name used by the Fibermesh company.

See:

http://www.fibermesh.com

 

[rustbuster1]

ACI 506.1R-98 Committee Report on Fiber Reinforced Shotcrete reports that propylene fibers will afect the shotcrete properties in a manner similar to steel fibers but not to the same effect.

The report quotes from a reference that at normal addition rates of 1 to 2 kg/m3, "Synthetic fibers contribute to the stability of shotcrete material having excessively low mechanical properties by modifying rheological behaviour of the fresh concrete and of the concrete during hardening (improved cohesion and shearing resistance). Contirbutions to improve the hardened properties are negligible." It also says that "tests at higher addition rates show improved properties."

This obviously is about shotcrete, but similar work has been done on placed concrete and fibers can provide measurable improvement in flexural strength, ductility and toughness.

 

[Ron]

Micro-fibers and Stealth fibers are just proprietary gimmicks for the addition of polypropylene fibers to concrete. As JAE says, they have limited use for structural strength...their primary benefit is delayed "first crack" occurrence and growth. They provide moderate enhancement to Modulus of Rupture.

 

[dik]

I seem to recall reading some literature that the PPF affect the rate of bleed water leaving the mix and improving the concrete properties by improving the hydration process... will see if I can dig up the article...

 

[StructuralDzine]

Here's what I found. Does anyone have any comments.Note that the last benefit applies only to steel fibres but with a casual reading you m,ight miss that distinction.
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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.

Reduces drying and restrained shrinkage cracking: Drying shrinkage stress occurs in concrete many years after initial placement. As moisture slowly exits the concrete, a reduction in volume occurs. If concrete is free to move in all directions, the tensile stress will remain low and the concrete will not crack. If the concrete is restrained from movement, tensile stresses will develop and cracks will form to relieve stress. If steel fiber reinforcement is used and cracking occurs, the steel fibers that cross each crack will redistribute the stress to a crack-free segment of concrete. When fibers are used, cracks are held tighter and the serviceability of the concrete in severe environments is improved.

http://www.fibermesh.com/

 

[Togel]

I wouldn't recommend the use of fibre reinforcment for new constuction. The use is primarily for bridge deck repair or for mitigating the failure due to concrete cracking. It is largely the product of specialty contractors and therefore, is given great praise by those that would benefit to a wider spread use. The same is observed of epoxy pressure injection. All are good, but they do not substitute new construction both in reality or in theory.