A report on the synthetic fiber reinforced conccrete

Plastic fiber reinforced concrete

Consequently, the structure is sized so that, in service, these crack opening limits are never exceeded. The notion of ductility in the interior of cracks is nonsensical and demonstrates a lack of basic understanding of physics and mechanics. He suggests that the difference in capacity to absorb energy in the interior of cracks that exists between synthetic fibers and metal fibers to the advantage of the synthetic fibers increases because of three problems: fragilization, corrosion, and creep. This is most common in industrial flooring but also in some other precasting applications. This is not a difficulty specific to steel fiber-reinforced concrete. This is not the case for metal fibers, which respond to cracking much more quickly. Perhaps, however, with hindsight, we can consider ourselves lucky that a colleague has illustrated that there remains confusion and misunderstanding about the benefits and special requirements for the design and application of fiber-reinforced concretes. In certain specific circumstances, steel fiber or macro synthetic fibers can entirely replace traditional steel reinforcement bar " rebar " in reinforced concrete. Moreover, I assert that the steel fibers usually used in shotcrete, having a length of around 30mm, can be used in a matrix for which compressive strength can reach 90MPa with only a small percentage of them breaking. From this first considered statement, all further points in the paper are intended to confirm that synthetic macro-fibers are superior to metal fibers in treating each concern. In the WTC conference paper entitled The use of macro-synthetic fiber-reinforced shotcrete FRS for safe underground hard rock support, the author summarizes the benefits of using macro-synthetic fiber-reinforced shotcrete for underground works carried out in rocky ground. As for synthetic fibers, the fact that they are capable of resisting more force than steel fibers across very open cracks, which occur when the real stress is greater than the design stress, does not provide any greater safety if it is not within the framework of a mechanical hyperstatic system. The problem raised by the author is, in fact, quite different.

In the WTC conference paper entitled The use of macro-synthetic fiber-reinforced shotcrete FRS for safe underground hard rock support, the author summarizes the benefits of using macro-synthetic fiber-reinforced shotcrete for underground works carried out in rocky ground.

Corrosion of isolated steel fiber at an intersection with a crack Finally, we note that the author forgets to mention that the creep of synthetic fibers when the cracked underground support is truly subjected to creep stress between the lips of the cracks leads to a significant increase in the opening of the cracks, and therefore the underground support can no longer ensure its sealing function.

fiber reinforced concrete pdf

Care should be taken to ensure that local design code requirements are also met, which may impose minimum quantities of steel reinforcement within the concrete. What the author says on this subject is confusing, at the very least. Reduction of ductility with age Steel fiber in a concrete mix Steel fiber across a concrete crack The author returns to the notion of ductility, but does not seem to have mastered the concept.

Fiber reinforced concrete research paper

Reduce crack widths and control the crack widths tightly, thus improving durability Improve impact— and abrasion—resistance Improve freeze-thaw resistance Blends of both steel and polymeric fibers are often used in construction projects in order to combine the benefits of both products; structural improvements provided by steel fibers and the resistance to explosive spalling and plastic shrinkage improvements provided by polymeric fibers. This is not a difficulty specific to steel fiber-reinforced concrete. Consequently, the structure is sized so that, in service, these crack opening limits are never exceeded. He suggests that the difference in capacity to absorb energy in the interior of cracks that exists between synthetic fibers and metal fibers to the advantage of the synthetic fibers increases because of three problems: fragilization, corrosion, and creep. It is evident that, in a case where poor design, calculation, or production of an underground support is implemented, and consequently the crack openings are abnormally large, the fibers inside of the cracks can corrode and thus lose their mechanical efficiency. How can that be affirmed? Consequently, we are confronted with the classic problem connected with the difficulty of defining dimensioning or design stresses, which is a problem that is generally resolved by using a safety factor. In this situation, the redistribution of forces is even more important because the fibers respond rapidly and effectively to cracks as they are created i. What the author says on this subject is confusing, at the very least. Other ideas are emerging to use recycled materials as fibers: recycled Polyethylene terephthalate PET fiber, for example. With respect to the rupture of the underground support related to overloading, the author suggests that "fiber-reinforced shotcrete can have great ductility in the interior of cracks when they are very open," which can be used to facilitate the redistribution of forces and therefore to warn of an imminent unstable rupture of the structure.

In fact, the problem cited by the author concerns the following situation: the service stress that the retaining wall support of the paper's case study example must overcome is poorly understood because this stress develops slowly over time.

Typically, these are corroborated with laboratory testing to confirm that performance requirements are met. Polyfiber being dosed into the concrete mix Long-term safety According to the author, there are two main causes of long-term ruptures in underground supports: under design of the structure because of changes over time in the stress levels to the underground support wall or lining and corrosion of the metal reinforcements.

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Critique of synthetic