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Understanding of the application of polypropylene fiber concrete

Abstract: The application of polypropylene fiber reinforced concrete, in recent years, the engineering construction industry in China has made great progress. Polypropylene fiber in construction of the promotion and application, involving a class of work and increasingly broad range of applications. In this paper, polypropylene fiber with a large number of various projects in the application of practice, the role of the real from the fiber and fiber play a role in conditions of adequate fiber content, considered indicators of fiber reinforced concrete and fiber concrete will easily prepared and other aspects on the current practice of polypropylene fiber reinforced concrete in the prevailing understanding of issues open to question, raised in the polypropylene fiber reinforced concrete on the promotion and application of some of the issues to be resolved.

The role of a real fiber

1.1 The promotion of wider use of polypropylene fiber concrete proof of the unique role of synthetic fibers.

After a number of polypropylene fiber manufacturer to promote and polypropylene fibers in various engineering crack to get a full range of applications. Mainly used in roads, bridges, airports, subways, industrial and civil construction, water conservancy and prefabricated units, insulation materials, dry mortar and other aspects. Since 1999, polypropylene fiber waterproof experts will write "Shenzhen Atlas Waterproof Construction", the Guangzhou, Beijing and other places a lot of engineering practice based on data and experts, in the light panel wall construction, insulation works the polypropylene fiber included the use of local technical regulations. Several large projects in the domestic fiber manufacturers, and many other brands under the lead engineering promotion and application of a large number of fibers, synthetic fibers for the concrete development of a good momentum of development.

Works with the synthetic nature of the role of what is in the end? How to look at the role of synthetic fibers? With the current project presents many brands start with fierce competition from synthetic fibers, but this issue raises many questions.

Promote the role of some manufacturers, when there is one-sided fiber, it seems as long as the concrete / mortar mixing in a fiber, cracks ceased to exist, contrary to the fibers play a role in the mechanism and the neglect of the specific conditions of individual projects. Synthetic solution is the main target of early native of concrete cracks, unlimited exaggerate the inhibitory effect of synthetic fibers on the crack is not right. In fact, the concrete / mortar mixing fibers, can only be for non-structural cracks crack resistance effect, can not completely eliminate cracks.

1.2 The effect of polypropylene fibers and the combined effect of the real

Micro-fiber adding in the concrete / mortar to crack resistance effect of the crack as the main characterization, in fact, adding the low elastic modulus of the fiber at a relatively high elastic modulus of concrete, the effect may be reduced in real terms is the largest concrete brittle, thus solving some of the concrete caused by congenital lack of problems --- caused by brittle cracking easily, to improve the concrete / mortar to play an important role in the internal structure. This role is different from the reinforced steel bars, but a fundamental of concrete / mortar to improve its own defects. Including the effective increase in the toughness of concrete; reduce cracks and improve the impermeability; reduce fractures, delaying steel corrosion; reduce the chemical erosion by concrete structures; enhance the anti-freeze and reduce damage to concrete structures; to reduce the bleeding of concrete, so that to improve the quality of the concrete surface; reduce fractures and improve the wear resistance and impact resistance and so on. The role of indicators can not reflect the strength of a few, but a comprehensive reflection of various indicators, particularly the durability of concrete. Synthetic fiber reinforced concrete became the theorists of the true meaning of passion, it really reveals is how to measure the nature of the role of fiber reinforced concrete.

Concrete is the most amount of engineering materials, is the main structural material, reinforced concrete structure has become the world's most widely used structure. Our world is currently engaged in an unprecedented large-scale infrastructure, but there are many concrete structures, including bridges, roads, tunnels, ports, dams, buildings, etc., under construction or completed during the period not long after visible cracks affect the appearance affect the operating environment in the erosion durability of the structure, but also to make use of some structural features are affected, revealed more serious durability, life expectancy is lower than the standard design life. Only seriously address the durability of various concrete structures, so that resources can be fully utilized. To extend the life of all types of buildings as far as possible, delaying the passage of time brought the threat in terms of structural safety and ensure its normal use, can save as much as possible the reconstruction and repair costs. A large number of concrete structures in the promotion of universal synthetic fiber reinforced concrete can not only solve the current due to high buildings, large, complex development of some of the problems, should also be part of the solution structure of an important means of durability.

2 conditions play a role in fiber

2.1 fibers play a role in the external and internal conditions

2.1.1 External conditions:
From the fiber in the concrete / mortar in which the morphology and the fiber aggregate to understand two aspects of the relationship.

Fiber in the concrete / mortar to the uniform distribution could mess is related to the fiber could play a role in the key. Fibers, no matter how the mechanism to explain the role, must ensure that fiber in the concrete / mortar was uniform, random distribution of the conditions to be play a role. Micro-cracks in the development process, met with the fiber block, consumption of energy, making it difficult to further development in order to block the stress reaches the cracking effect. As the fiber surface in the production process for its compatibility with different active agent for processing, the fibers dispersed water, plus a variety of external and concrete aggregate mix the fiber with a variety of further aggregate bond. General, in a transparent glass of clean water stirred into a small amount of fiber, we can find an intuitive three-dimensional high-quality polypropylene fibers are suspended like to spread chaos, and the extended period of time will not bring much change; and some similar product may be distributed by the agitated, but long after it will go up as a flocculent layer. According to the latter reflects the situation where there are fibers in the concrete / mortar in the actual preparation process more difficult to evenly disperse. This observation was put forward approach and "fiber-storey stable rate" means much the same. Polypropylene fiber density less than water as well as the role of fiber surface active agent, dispersed in water by the buoyancy and surface fibers of the activation energy will gradually show more clearly the state of stratification and segregation, will be placed on different brands of short fiber After standing in the measuring cup and stir in different time periods to measure the suspension means to compare like-storey way to determine the stability of the fiber dispersion.

Fiber aggregate bond status, whether it works is another key. Fiber to bond as much as possible the aggregate, to avoid being pulled out by force. Different standards of different fibers, can be seen under the electron microscope show different bond aggregate situation. If, after the addition of fiber does not damage the concrete slump, the fiber dispersion is not a bad bond strength is poor, the role of fiber out of the question.

2.1.2 Internal conditions:

Fiber can work, but also because the mechanical properties of the fiber itself. Such as tensile strength, tensile limit, fiber uniformity, resistance to acid corrosion and ultraviolet aging ability. According to experts explain the fiber, the tensile strength and tensile limit as some inverse relationship. This relationship should be appropriate, is not particularly high tensile strength fibers can produce a high crack resistance effect. Fiber in place by the tension in the tensile deformation process, if the ratio of inappropriate, the tensile strength can not meet the requirements. Of course, as made of material constraints, the data can only try to meet the requirements. Polypropylene fiber tensile strength is too large, may result in increased brittleness. Stretch limit is too large, concrete / mortar in the deformation of fiber in force beyond the control of the process they may crack. Modification of the fiber but also in this regard. Indicators is to measure the ultimate tensile crack can really achieve the effect of fiber as a target.

2.1.3 Combined Effects of material to make fiber may play a role in the largest

To truly understand the characteristics of each material and the advantages and disadvantages, emphasizing the exclusion of another material of a material approach is not feasible. Material is constant change, we must continue to understand and use new materials. Only the full effect of composite materials, integrated solutions to engineering problems encountered.

For example, steel with high elastic modulus and low elastic modulus polypropylene fiber mix, the process could damage the concrete, respectively, play different roles. Because of its large number of polypropylene fibers and performance characteristics of early primary key constraint of concrete cracks and micro cracks under tensile stress in the lower works; steel small number of fibers but with obvious enhancement of macro-cracks can play a significant crack resistance effect. Two fibers from different stages of expansion of concrete cracks and constraints play a role in enhancing the concrete tensile strength and flexural strength, elastic modulus can be integrated in two different fibers absorb the energy of the advantages of the concrete house defects synergy can effectively enhance the toughness they can.

In another example, the application of the hydraulic concrete mixed with fly ash or silica fume to increase the strength and crack resistance abrasion resistance. According to the authority of the ratio of experimental center experiment done in adding 20% fly ash and high-quality polypropylene fibers 0.6/0.9/1.2kg / m3 the case of content, impact strength increased by 6-18% wear. Experimental proof of the Nanjing IWHR, polypropylene fibers and silica fume were mixed, can more effectively improve the abrasion resistance of concrete 33-58%.

At present, the application of the domestic construction sector and promotion of many brands of synthetic fibers, imported, and also made in China, which varies greatly, a big difference. As the project is the production of chemical fiber industry, the user for the construction sector. Users of chemical fiber production is unfamiliar, you can not intuitively determine the merits of the fiber, but are generally concerned about the question whether dispersed. Dispersion of the surface, intuitive, but from the fiber tensile strength, stretching the limit, bond strength and other inherent quality of view, not directly by observation to draw conclusions.

Of course, the polypropylene fibers in the role, after all is a supporting role. We are often called secondary ribs. Normal maintenance requirements of the construction of concrete, of course, can not believe that there will be no cracks in the fibers added to the neglect of normal maintenance. This is, needless to repeat them.

3 fiber content appropriate

3.1 The fiber content should be adjusted for different purposes

The fiber content for what value? Made of synthetic fiber materials from the point of view, because of its acid and alkali, and the toughening and strengthening physical, broadly speaking on the concrete is useful. But in the end what content is appropriate, the views of theorists and engineers are different. From synthetic fibers in concrete terms the substance of the role, just add synthetic fibers, is bound to varying degrees, to solve concrete congenital defects --- brittle, so no matter how Canadian are not wrong, it seems the fuzzy theory to solve a range of change for the better. But from the perspective of design and construction must be considered in quantitative indicators. From the concrete work of the other considerations, the construction had to meet to consider the relevant requirements.

Fiber content should be determined depending on the purpose of use, taking into account the specific ratio of concrete, aggregates and other additives in specific circumstances. At present, most manufacturers recommend a dosage data come from the theorists of the fiber volume content of 0.05% and 0.1% of the studies conclude that data. Fibers made of materials of different weight because of its varied content in accordance with the volume calculation, converted into the weight of the fiber content, of course not the same. For different requirements, experienced per cubic meter of concrete / mortar mixing 0.5,0.67,0.7,0.8,0.9,1.0,1.3, 1.36,1.5 kg, ranging from the situation, are a low dosage, got the good engineering results , when the content in 0.7--0.9kg/m3 have been able to meet the general requirements for the design. In general, cracking, permeability, wear-resistant parts that require high, relatively high dosage; on the use of ultra-fine sand content areas relatively high; have special requirements of the project site and use the ratio to be a special . In addition to the high content of special uses, in general engineering applications do not necessarily apply.

3.2 The poor quality of the fiber will not only not on concrete reinforced, toughened, but have a negative impact. Some people think that poor quality products can be effective by increasing the dosage to make up for poor quality products to increase volume, but also due to end groups, cellular, hollow cause serious problems, there can not be used. At present, there had been mixed with fiber quality due to poor quality of concrete construction have caused serious problems had to be determined to blow up the lesson. The development of synthetic fiber reinforced concrete is to address the new conditions so that the project be the best, to ensure a permanent solution. Especially for irrigation, hydropower also has a special significance of such works. Appropriate adjustments to fiber content, to pay attention to theory, should also pay attention to experience. Empirical data and theoretical data to combine parts of different projects, adjusting and selecting the appropriate dosage, is the scientific attitude.

3.3 should be fully collect and provide engineering data and laboratory data, as soon as the preparation of national technical specifications for engineering design and application. As we all know, a standard formulation is not easy, requires a lot of time, money, data validation and engineering practice. Synthetic fiber reinforced concrete is a new technology, but in many projects have proved successful application is, empirical data is also a promotion in the current sense. The key now is not what value the data, but rather whether the recognition of this technology is needed to solve engineering problems. If not resolved, no matter how good the technology nor the application and promotion of the necessary, are called to "the right medicine."

Consider synthetic indicators of the role of 4

The mechanical properties of fiber reinforced concrete greatest change, not to increase its compressive strength, flexural strength index, etc., but greatly increases the extent of the fracture energy of concrete, ductility. Generally follow the concrete compressive strength, tensile strength and other performance indicators to measure synthetic fiber concrete, fiber reinforced concrete is not fully reflect the fundamental performance improvement. As mentioned above, synthetic fibers in concrete / mortar is a comprehensive role, in low dosage (about 0.1% volume content) conditions, with enhanced dual-toughening effect. Especially for high-strength concrete is mixed with synthetic fibers, especially the use of its toughening effect. From a large number of laboratory test data and engineering data, with the compressive strength indicators have improved, there are also reduced. But from the change in amplitude and in absolute terms, are not sufficient to affect the concrete's original design requirements. The reason why sometimes some of the indicators show improved strength, but also to solve some of the cracks and the added effect.

Currently, the synthetic fiber concrete research and application in our short history, plus the people are accustomed to the specimen to measure the compressive or flexural strength of the material level of performance indicators to consider for enhancing more than can really reflect on the role of the target fiber such as flexural toughness, fatigue strength, fatigue life and other indicators to consider toughening less. Synthetic fibers in concrete on the consideration of the role of indicators still remain if the original basis of knowledge, will be not conducive to the promotion of synthetic fiber reinforced concrete. Toughness should be quantified, the early development of a unified technical conditions for a point of order, to make synthetic fiber reinforced concrete used in large scale real. Fortunately, theorists have begun research in this area. Some experts and scholars have started from the flexural toughness indices and residual bending strength to study and consider the toughening effect of synthetic fibers in concrete. Recently, the National Commission on fiber reinforced concrete academic experts have been by direct tensile test of polypropylene fiber concrete stress - strain curve.

5 will easily prepared synthetic fiber of concrete

Practice has proved that a large number of projects, preparation of polypropylene fiber reinforced concrete is a simple, easy to row.

(1) simple physical reinforcement, and preparation of a variety of concrete aggregate, admixtures and cement will not be any conflict. Ratio without changing the original design;

(2) requires no special mixing equipment, easy to commodity concrete mixing station or on-site operation;

(3) The construction process does not have special requirements, no special training, workers easy to grasp.

No matter how good a product, if the actual number of complicated operation, it certainly is not easy to promote. Good quality fibers, not only in its function to ensure the realization, there are also simple to use and adapt large-scale construction. Can a polypropylene fiber brand has spread rapidly, and its concrete preparation simple and convenient but also has a relationship. Some fiber manufacturers for the degradation of paper bags, easy to disperse in the medium, large mixer mixing, you can not rip directly into the mixing bag, small mixer can follow the content into a centralized, without manual shaking into the mixer. Where the preparation of polypropylene fibers had concrete / mortar engineering staff has deep experience of this. If adding fiber needs dedicated staff a little bit of thrown into the mixer, how to meet the requirements of large-scale construction. Some quality time in the fiber to prevent uneven or difficult to stir mixing scattered to avoid the naked eye directly observed floc agglomerate in the process of actually preparing the concrete to reduce the fiber content is free. It should be said that from a functional implementation and concrete / mortar, two aspects of the preparation are not allowed. Doped fiber mixture slump will be losses, but the content in the volume rate of 0.05 - 0.1% or so of the concrete work can still be easily satisfied the requirements of pumping and irrigation, concrete should be no special preparation requirements.
China's current construction of the construction industry in general is not high quality of personnel, construction management is still relatively extensive. For large-scale construction of synthetic fiber reinforced concrete, it must require the preparation of its easy to have, or will affect the subjective problems caused by the preparation and the use of synthetic fiber concrete results, will in turn affect a large area to promote this technology.

Synthetic fiber reinforced concrete has been developed in foreign countries more than 20 years, our country in the last century began to develop after the mid 90s and gradually accepted by the general engineering. China is the production and use of cement concrete with a great country, the application of synthetic fiber reinforced concrete is also only in the initial stage. The real popularity of synthetic fibers and development of concrete, and ultimately rely on low-cost home-made fibers. The use of synthetic products of various projects to improve the level of the real, must be built on the basis of technological progress, any quick success, and even fraud, can affect synthetic fiber reinforced concrete as a healthy development of new technologies.



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