Fiber plays an increasingly important role in improving the performance of concrete. The development of concrete has been 100 years of history, high strength in a very long time is the goal, considered the feature of concrete quality. But concrete is a brittle material, poor toughness, anti fatigue ability is low, easy to crack, anti impact fragmentation is poor, this problem is not because of insufficient strength, but not enough durability.
Over the years, to study the improvement of engineering and technical personnel from raw materials, mix ratio, additive and manufacturing process, maintenance process and other aspects, although there has been some success but not ideal, therefore, high performance concrete is the key to solve the problem.
The compound is the main way of high performance cement-based composite materials, fiber reinforcement is the core. Since 70s, the development of fiber reinforced cement composite material, steel fiber, glass fiber has earlier applied to concrete, from the aspects of performance can improve the concrete. About steel fiber and glass fiber applications and usage has become clear, our country has promulgated the Standard Specification for design of steel fiber used in 1992. With the material processing technology, the successful development of polypropylene fiber for concrete, fiber concrete technology has entered a new stage.
fiber reinforced concrete
Fiber materials and fiber reinforced concrete is added in the concrete mixing process, to improve the performance of concrete by densely distributed fiber. In the folk, early put the straw chopped or cut hair mixed with mud, adobe building or retaining wall, obtain crack resistance effect. The mechanism of fiber reinforced concrete with a close, contribution of fiber reinforced concrete is inhibited from plastic cracking start. While the fiber on properties of concrete improve, must have the following conditions:
(2) and concrete bond is strong
(3) strong resistance to corrosion, alkali aggregate reaction materials
(4) the tensile strength of the material.
These four conditions each of which is important and essential. That is, the effect of fiber on concrete is not to improve the strength, but through the above conditions, to improve the concrete cracking resistance, anti broken, seepage, bending strength, impact resistance, anti fatigue performance. Steel fiber and synthetic fiber will increase the strength of concrete, due to different materials of steel fiber to improve the.
Steel fiber is first applied to the concrete, inspired by this natural source in reinforced concrete, with the development of fiber concrete technology, the research is focused on synthetic fiber, synthetic fiber and low cost, when the uniform distribution in concrete, can provide better toughness. Concrete is a hard material, synthetic fiber is soft material, soft steel combining this approach can improve the toughness of concrete. In synthetic fibre polypropylene is the best material, corrosion resistance, anti alkali reaction.
In early 70s, the west coast of the reinforcement project, the engineering staff of polypropylene fiber chopped into concrete, brick for dike. Many engineering and technical personnel in polypropylene fiber for concrete research. The test results were contradictory or not ideal, these results have been done based on Evaluation of polypropylene fiber. People always think that PP can not produce the effect of concrete, and these concerns still exist, this is very unfortunate. Because of those used in the test of polypropylene fiber, or is made of recycled polypropylene waste, either borrowed from the textile industry, and cut packing belt, the rope is replaced, these materials can not solve the four points of the fiber concrete, because of the fiber itself, in the mix in easy cluster in the concrete, so a polypropylene is available for concrete has been controversial.
In early 80s, US Army Engineer concrete expert to solve the concrete problems of military fortifications in the crushing by the fire after the attack, but also to solve the problem of durability of military engineering, they studied many kinds of test materials and methods. The final confirmation, the best effect of adding a certain amount of polypropylene fiber in concrete, fiber concrete and special expert with the largest chemical products enterprises -- Synthesis of industrial company experts jointly developed polypropylene material for concrete, and in 1984 successfully developed the polypropylene fiber reinforced concrete - "FIBERMESH", translated as "Chinese fiber net". This is the world's first successful for polypropylene fiber reinforced concrete.
Polypropylene fiber bundle fiber net a mesh structure, by the fiber net concrete companies and international agencies have patents. It solves the problems of polypropylene fiber concrete used from various angles:
(1) cluster shaped network structure in the concrete mixing when a bunch of large area distribution, mixing a small bunch of fibres per metaphase 5-8 in the beam separated by the aggregate shock after the expansion into the mesh, and mixing with the impact ripped into irregular monofilament, achieve the aim of uniformly distributed. The staple type called uniform distribution two distribution method "and can also be a uniform row of steel fiber is a principle. Completely solve the problem of uniform distribution.
(2) and concrete bond issues, steel fiber made of wavy or two bow to solve the bond issue, in synthetic fibers, a variety of monofilament fiber cross section into a round, smooth surface, can not achieve good grip of. Fiber net in mixing torn silk.
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