JPS641424B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to cement mortar, fibers with excellent reinforcing properties for concrete, and cement mortar and concrete molded products reinforced with the fibers. Hardened cement products, typified by Portland cement, are used in large quantities in the fields of architecture, civil engineering, etc. because of their excellent properties such as compressive strength, durability, and nonflammability, as well as their low cost. However, since it is a brittle material, it has extremely low bending resistance, easily breaks or cracks when tensile or bending stress is applied, and has weak impact resistance. In order to compensate for these drawbacks, methods are known: (1) combining with reinforcing bars or steel frames, and (2) mixing fibrous substances with inorganic fibers, organic fibers, etc. The present invention relates to (2). Methods for reinforcing cement brittle matrices with fibrous materials can be roughly divided into the following two methods. (A) By mixing a matrix mainly composed of cement and fibers as a dilute slurry (approximately 50 to 200 g/water/cement ratio is very high), forming it into a round net or fourdrinier, and pressing it. , a method of curing after removing excess moisture (hereinafter referred to as the mixed molding method). A typical example is asbestos slate, and this method is mainly used to manufacture boards. (B) A method in which a cement-based matrix, fibers, and the minimum amount of water are added, and the mixture is poured directly into a formwork or molded using various molding machines (hereinafter referred to as dry molding method), in which water is intentionally added. It becomes the hardening water of the matrix without being removed. The strength of hardened cement is greatly influenced by the ratio of water to cement during hardening (hereinafter abbreviated as W/C), and it is common knowledge that the smaller the W/C, that is, the smaller the amount of water added, the better. . Therefore, compared to method (A), since water is not removed before curing, the amount of water must be reduced from the beginning, and the minimum amount necessary for molding is used.
Therefore, W/C is very small, about 0.3 to 0.8. Mortar and concrete fall under this category. In method (A), since the step of mixing various materials is a dilute slurry as described above, it is relatively easy to uniformly disperse the fibrous material, and various studies have been conducted. For example, asbestos slate is typically reinforced with asbestos, a fibrous material. However, in recent years, its harmfulness has been pointed out, and alternative fibers are desperately being investigated. Polyvinyl alcohol (PVA)-based fibers are one of the alternative fibers, and the possibility of this alternative has been studied and is beginning to be used in some products. Other polypropylene,
Nylon and the like are used to improve impact resistance. One of the reasons why thin and long fibers with a large reinforcing effect can be used in this wet molding method is because the slurry concentration is low and branching is possible. On the other hand, as mentioned above, the dry molding method uses a small amount of water, so it has poor fluidity, and the fibers are thin and long, that is, they have a large aspect ratio (the ratio l/d of the fiber diameter d and length l is called the aspect ratio). It is very difficult to mix fibers such as these, and although studies have been conducted, sufficient effects have not yet been achieved. Although the reinforcement mechanism of brittle materials by fibrous materials is not simple, it can be considered as a model as follows. In other words, the reinforcement mechanism is a matter of stress burden by fibers and reinforcement efficiency. Regarding the former, when an external stress such as tension is applied to a composite reinforced with short fibers, the stress acting on the entire composite is ideally the stress borne by the reinforcing material + the stress borne by the matrix. Stress is expressed as composite stress, and even after minute cracks occur in the brittle matrix, the first term on the left side acts effectively, improving the strength of the composite as a whole (Hannant). In other words, the fiber length of the short fiber is l,
When the critical fiber length is lc, the fiber breaking strength is σfu, and the added amount is expressed as a volume fraction V _f , the fiber reinforcement effect regarding tension is _{σ R =} ησ _fu (1−lc/2l) V _f …… ...(1) However, η is the fiber orientation coefficient. On the other hand, the interfacial bonding force between the fiber and matrix is τ
Assuming that the fiber is cylindrical and its diameter is d, the critical fiber length l _C has the relationship l _C = σ _fu・d/2τ ……………(2), and equation (1) is σ It can be rewritten as _R = ησ _fu (1−σ _fu /4l/dτ)V _f (3). In other words, the effect of reinforcing fibers is expected to be greater as the fiber strength is stronger and the interfacial bonding force with the matrix is higher.In terms of morphology, fibers with a large aspect ratio l/d, that is, thin and long fibers, are effective for reinforcement. Shown to be valid. On the other hand, in addition to the stress burden caused by the fibers mentioned above, there is a problem in reinforcing efficiency. The above theory assumes that fibers or fibrous materials as reinforcing materials are homogeneously distributed in the matrix, and it is difficult to manufacture composites on a commercial scale using actual hydraulic materials as a matrix. In this case, uniform dispersion of fibrous materials is a very important problem and a difficult technique. In other words, if an attempt is made to increase the aspect ratio or increase the reinforcing material addition rate in an attempt to improve reinforcing properties, the dispersion of the fiber material will become poorer in proportion to that, and not only will the expected effect not be achieved, but the product will be uneven. This not only causes a decline in performance, but also reduces the aesthetic value of the appearance and causes a loss of commercial value. As mentioned above, when reinforcing brittle materials such as cement with fibers or fibrous materials, it is essential that the material has excellent adhesion to the matrix and mechanical properties such as tensile strength of the fibers. However, in order to increase the reinforcing effect, it is a prerequisite that the fiber material be uniformly dispersed in the matrix. As mentioned above, in the dry molding method, the amount of water added is small and fluidity is poor, making it very difficult to uniformly disperse the fibrous material. Therefore, the aspect ratio has to be reduced,
As a result, a sufficient reinforcing effect is not obtained. For example, copper fiber is the reinforcing fiber that has been the most researched and has been put into practical use in dry molding methods. There are various shapes of steel fibers, but approximately 0.5 with a round cross section.
mm diameter equivalent, length 20~30mm (aspect ratio approx. 40~
60) are used. As seen in the known literature, when looking at the fracture surface of concrete reinforced with steel fibers after a bending fracture or tensile fracture test, the steel fibers are definitely pulled out and the fibers themselves are not fractured at all. In other words, the aspect ratio is small and the adhesion to the cement matrix is not very good, which means that the strength of the steel fibers (approximately 70 kg/mm ² ) is not fully utilized, and the reinforcing effect is not as good as the left. I can't wait. In addition, alkali-resistant glass fibers have been studied and used as bundled yarns, but the purpose of this bundled yarn is completely different from that of the present invention. The bundled yarn of the present invention is in a temporary form to improve dispersion, and after being uniformly dispersed, it is fibrillated into single fibers in order to improve the reinforcing effect. On the other hand, in the case of glass fiber, the glass itself is a brittle substance and is extremely brittle and easily damaged.
Therefore, as a preventive measure, bundled yarns are used, and binding agents are especially selected to prevent fibrillation into single fibers. However, such a bundled fiber state is not sufficient, and in mortar and concrete with little water, the shear force is large when mixing, resulting in breakage, or in extreme cases, shattering.
No reinforcing effect can be expected. In addition, even though it is an alkali-resistant glass fiber, there are concerns about its alkali resistance, and durability remains a problem. Organic fibers have also been considered, but as mentioned above they are used in wet molding, but in dry molding they are difficult to disperse and do not have a reinforcing effect. It is known that PVA-based fibers are essentially the most suitable fibers for reinforcing cement matrices. In other words, it not only has high strength (more than 90 kg/mm ² , higher than steel fiber), but also has excellent adhesive strength with the cement matrix. In addition, it is stable against alkalinity and has excellent durability. The reason for its excellent adhesion is that PVA has many hydroxyl groups in its molecular chain that have a strong affinity for cement, and because it is wet or dry spun and highly stretched, it has numerous hydroxyl groups on the side of the fiber. This is because it has folds. Kevlar, polyester,
Although nylon and the like have high strength, they have poor adhesion to cement due to their hydrophobicity, and cannot improve the bending and tensile properties of cement molded products. In addition, polyester has no alkali resistance, and there are concerns about durability. Although PVA fibers have basically excellent properties for reinforcing cement matrices, they are not used in dry molding processes because they are difficult to disperse into the matrix. The present inventors have arrived at the present invention as a result of intensive research on how to disperse thin and long PVA fibers, that is, with a large aspect ratio, in a cement matrix. The present invention relates to fibers for reinforcing concrete, mortar, and concrete molded products using the fibers. That is, the fibers with a large aspect ratio are hardened and thickened with a sizing agent to substantially reduce the aspect ratio and facilitate dispersion, and once the sizing fibers are uniformly dispersed during the mortar and concrete forming process, The purpose is to increase the average aspect ratio and the reinforcing effect by splitting the fibers into single fibers by 20% or more using the shearing force generated by swelling, dissolving and stirring the sizing agent. More specifically, 200 to 200 monofilaments of 0.5 to 25 dr.
The fibers are bundled to 5,000 denier, hardened with hydrophilic resin, and then cut so that the aspect ratio of each single fiber unit is 100 to 700 (the aspect ratio of each cut bundled yarn unit is very small, ranging from 5 to 145). . Then, either (a) mix it in a dry state with a matrix mainly composed of cement and aggregates, then add water and stir, or (b) add the fibers to a paste of cement, aggregates, and water and stir. It is post-molded. The present invention will be further explained in detail below. The important factors constituting the present invention are the strength of the PVA fiber, the thickness of the single fiber denier, its aspect ratio, the thickness of the bundled yarn (total denier number), and the binding agent. If the above factors are made appropriate, the bending, tensile properties and cracking resistance of mortar and concrete will be significantly improved, and the effect of improving impact resistance and toughness will also be significant. In mortar and concrete products, bundled threads are
Since it is fibrillated to 20% or more, the physical properties of the single fibers have a significant impact on the physical properties of the product. First, the conditions to be met by the single fiber in the present invention will be described. As mentioned above, when reinforcing a brittle cement matrix with fibers, the important requirements are that the fibers have excellent tensile strength, excellent adhesion to the matrix, and a large aspect ratio. In order to increase the reinforcing efficiency, it is important to uniformly disperse it in the matrix. As a means of uniformly dispersing the fibers in the matrix, the single fibers are hardened with a hydrophilic resin and dispersed uniformly in the molded product manufacturing process as bundled yarns with a small aspect ratio, and then 20% or more are made into single fibers again to create a uniform fiber. The aim is to increase the aspect ratio through dispersion and increase the reinforcing effect. If an appropriate single fiber denier and aspect ratio are not selected in the process of defibrating the bundled yarn into single fibers, the defibrated single fibers will become entangled and become fiber balls, worsening the dispersion state. Efforts to improve dispersion end up being in vain. A smaller aspect ratio is better from the viewpoint of dispersibility, but a larger one is better from the viewpoint of reinforcing properties, which are contradictory, so it is important to select an appropriate aspect ratio that satisfies both. The aspect ratio of the fibers used for mortar and concrete is suitably 100-2000, more preferably 400-1500. If it is less than 100, there will be no poor dispersion due to entanglement of bundled yarns during the defibration process, but reinforcing properties will be poor. Moreover, if it is 2000 or more, although the reinforcing property is excellent, tangles occur during the defibration process and fiber balls are formed, which is not preferable. Single fiber denier does not affect dispersibility and reinforcing properties as much as aspect ratio, but based on the results of various experiments, 0.5
~25 dr is suitable. If the aspect ratio is less than 0.5 denier, poor dispersion will occur due to entanglement in the fibrillation process of the bundled yarn even if the aspect ratio is limited to 100 to 2000, and if it is more than 25 denier, the reinforcing property will be slightly reduced. Furthermore, the strength of the single fiber must be 90 kg/mm ² or more; if it is less than that, the reinforcing effect will be small even if the dispersion and adhesion are good. The above are the conditions that a single fiber should have, and are the first requirements constituting the present invention. The present invention uses bundled yarn as a means for uniformly dispersing the single fibers in a matrix. It is essential that the bundled yarn be uniformly dispersed in the matrix and that it be defibrated into 20% or more single fibers. The inventors of the present invention have discovered that the object can be achieved by selecting the total denier of the sizing yarn and the type and amount of sizing agent applied. Mortar with low W/C, that is, low fluidity, should be uniformly dispersed in concrete, and should be equipped with bundled threads to disperse 20% or more into single fibers without causing poor dispersion due to entanglement. One of the important requirements is the thickness, that is, the total denier number, which is suitably between 200 and 5,000 deniers, more preferably between 500 and 2,000 deniers. If the fiber is less than 200 denier, the aspect ratio is too large, and it is not preferable that the fiber ball remains undefibrated into single fibers when mixed with the matrix, or becomes entangled and forms fiber balls even after being defibrated only slightly. In addition, if it is 5,000 denier or more, the number of bundled yarns will be small and their dispersion will be good, but even if they are defibrated into single fibers, the single fibers will be scattered locally, and even during the defibration process, the bundled yarns will be dispersed. It is easy to make fiber balls in units, which is not desirable. It is important to defibrate the bundled yarn into 20% or more single fibers during the forming process, but if it is less than 20%, the average aspect ratio is too small and the reinforcing effect is small. In order to defibrate to 20% or more, it is important to select the sizing agent and its adhesion amount. The sizing agent used must maintain its sizing power at the early stage of mixing with the matrix and reduce the aspect ratio to improve dispersion, and at the later stages the sizing agent must reduce its sizing power and defibrate 20% or more into single fibers. A sizing agent that produces such an effect must be water-soluble and have a film-forming ability, and the following are effective. Natural products and their derivatives include starches, cellulose derivatives (eg, methylcellulose, ethylcellulose, hydroxymethylcellulose, carboxymethylcellulose, etc.), and sodium alginate. As a synthetic sizing agent, unsaponified polyvinyl acetate emulsion as a polyvinyl alcohol type,
There are cationized polyvinyl acetate emulsions, partially saponified PVA, and completely saponified PVA. Modified PVA includes itaconic acid-modified, phthalic acid-modified, and acrylic acid-modified PVA. Ethylene-vinyl acetate copolymer emulsion, which is a copolymerization of vinyl acetate and ethylene, and emulsions of saponified products of this, vinyl acetate/maleic acid copolymer, vinyl acetate/crotonic acid copolymer, vinyl acetate, and acrylic acid copolymer. is used. Monomers for modifying polyvinyl alcohol include:

【formula】

Cation-modified PVA is used by copolymerizing [Formula] with vinyl acetate monomer and saponifying it with alkali. degeneration
As PVAC, in polymer

It is possible to use an emulsion in which a vinyl polymer containing a polymerizable quaternary ammonium salt represented by the formula as one component is made of a water-soluble polymer such as PVA as a protective colloid. Other ethylene and vinylacetate monomers and

A cationic ethylene acetate emulsion copolymerized with [Formula] can also be used. In particular, the polymers shown here are cationic and are particularly effective sizing agents for improving adhesion to cement. Next, examples of acrylic polymers include sodium polyacrylate, partially saponified products of polyacrylic esters, partially saponified products of polyacrylic ester copolymers, polymethacrylates, polyacrylamide, especially 2-aminoethyl Acrylate, 2-
Cationic substances such as aminoethyl methacrylate are effective as sizing agents because of their adhesive properties with cement. The above water-soluble polymers and emulsions can be used alone or in combination. If the amount of the sizing agent attached to the fiber is less than 2% by weight based on the fiber, the sizing property after cutting will deteriorate. Moreover, if it exceeds 20% by weight, many manufacturing troubles occur and bundled yarn cannot be easily produced.
Preferably it is 4 to 9% by weight. The adhered sizing agent is dried and heat-treated to harden it onto the fibers, and the long fibers are bundled and set by heat. At a low temperature of 100°C or less, not only is heat setting impossible, but the processing speed must be reduced, which is disadvantageous. Furthermore, if the temperature is higher than 270°C, a part of the water-soluble polymer may decompose and harden, so higher temperature conditions cannot be maintained. The conditions that PVA fibers must meet for highly reinforcing mortar and concrete are: a single fiber denier of 0.5 to 25, a denier strength of 90 kg/mm2 or ^more , a water-soluble sizing agent of 2 to 20% by weight, and a total denier of 2 to 20% by weight.
It is gathered and consolidated to have a denier of 200 to 5000, and the aspect ratio of each single fiber is 100 to 5000.
2000 in length, and the degree of fibrillation of single fibers in the molded product is 20% or more. Such PVA-based fibers are manufactured by the following method. The PVA fiber used for the bundled yarn may be manufactured by any method as long as it has a denier of 0.5 to 25 and a strength of 90 kg/mm ² or more. A known general production method uses water as a solvent.
Spinning is performed using a solution containing dissolved PVA as a stock solution, and the method is a dry spinning method in which water is blown away with hot air from a spinneret to form a thread, and it is dehydrated and gelled in a bath of mirabilite, caustic soda, or a mixture of both. There is a wet spinning method. Alternatively, a special method may be used in which boric acid is added to the stock solution using a wet method and an alkaline salt is used as a coagulation bath. Only fibers with a single fiber strength of 90 Kg/mm ² or higher may be used. The fibers thus obtained are wound into long fibers. In order to make the total denier of the bundled yarns 200 to 5000 deniers, one or more of the long fiber bundles may be hardened by using a binding agent. More preferably 1
The long fiber bundles of books are manufactured to have a denier of 200 to 5,000 deniers and are then hardened with a sizing agent. These long fibers are continuously fed from a beam creel, and either immersed in a tank containing a sizing agent, or attached to the long fibers using a roller touch method, and then squeezed with a subsequent squeezing roll to a uniform consistency. The adhesion amount shall be . As the sizing agent used at this time, a sizing agent suitable for the degree of defibration of the sizing yarn is selected, and the one described above is used. It is desirable that the concentration of the water-soluble polymer used be 100 g/min or less, or the viscosity of the glue should be 50 poise or below, preferably 10 poise or below, to ensure good adhesion and ease of handling, and good processability. The drying temperature is preferably low, around 80 to 200 degrees Celsius.
The temperature is preferably 120°C to 180°C. Furthermore, in order to fix the attached polymer to the long fiber surface by heat treatment and to control water solubility, it is desirable to perform the treatment at 100 to 270°C. Preferably it is 150-240°C. The drying process mainly involves drying the surface of the sizing agent, and in order to improve process passability and prevent gum from building up on the machine base, there are two methods: hot air and heated rollers. If using a heated roller type, dry at 80 to 130°C. In addition, in the heat treatment process, a hot roller contact type is used to improve heat transfer efficiency and heat treatment effect, and in the case of a 100 to 180℃ hot air type
Heat treatment is performed at 180-270℃. The bundled yarn thus obtained is formed into several bundles and wound to prevent soft fibers. This bundled tow-like material can be cut into a predetermined length using a cutting machine to obtain a target bundled thread. The adhesion rate of the sizing agent is calculated from the amount of polymer carried by the yarn, and the concentration or viscosity is controlled so that a predetermined amount of adhesion is achieved, and the amount of adhesion is further controlled from the amount of squeezing with a squeezing roll. Of course, it is also possible to produce a bundled yarn by directly connecting the long fibers after spinning without winding them up. In order to judge the fibrillation properties of the cut bundled fibers, we used a mixing machine specified in JISR5201 (Physical Test Methods for Cement), with a sand/cement ratio of 1/1 and a water/solids content of 0.40. Knead for a minute. The fiber-containing mortar was washed out using a 50-mesh wire mesh according to JISA1103 (aggregate washing test method) to prepare a standard sample for the degree of defibration. Sample Defibration degree A 0 ~ 20 B 20 ~ 40 C 40 ~ 60 D 60 ~ 80 E 80 ~ 100 Here, 0 ~ 20% defibration means that the bundled yarn is completely undefibrated or a part of it is This is a state in which the single fibers are slightly defibrated and mixed with the bundled yarn. Defibration of 20 to 80% means that the number of single fibers increases and the total denier of the bundled yarns decreases considerably. 80 to 100% defibration means that most of the bundled yarns are defibrated and dispersed into single fibers, and theoretically this is where the most reinforcing effect can be expected. As a result of various experiments, the reason is not clear, but
Regarding the reinforcing effect of PVA fibers, it was found that the degree of defibration of the sizing agent differed depending on the type of cement molded product. In other words, B and C are suitable for concrete in which fibers are randomly oriented three-dimensionally in a molded product or in which coarse aggregate is used, and E is suitable for mortar in which fibers are mainly quadraticly oriented. is suitable. However, even if B and C are preferable for other than A, D and E still have a reinforcing effect, and even if E is preferable, B,
C and D are also effective and are within the scope of the present invention. One of the important constituent requirements of the present invention is to increase the degree of fibrillation of the bundled yarn into single fibers to 20% or more.
The purpose can be achieved primarily by selecting the type of sizing agent and, secondarily, by selecting the amount of the sizing agent. When manufacturing mortar and concrete on an industrial scale, there are various mixers used in the manufacturing process, and the usage conditions vary widely, but as long as you select a sizing agent for each mixer, the mixing conditions can be adjusted to a certain level. It is possible to obtain approximately the desired degree of defibration of the bundled yarn into single fibers by simply changing the . For example, typical examples of the relationship between defibration degree and sizing agent include the case of a pan mixer, which is commonly used for mixing mortar and concrete, and the case of an omni mixer, which is a special mixer and is said to be suitable for dispersing fibers. It is shown as follows.

[Table] In the case of a pan mixer, stirring is mild and it is necessary to use a sizing agent with relatively high water solubility.
Furthermore, in a device having a relatively strong mixing ability such as an omnimixer, it is necessary to use a sizing agent with relatively low water solubility. In any case, a sizing agent suitable for the mixer to be used may be selected from among the water-soluble sizing agents described above. Although there is some influence on the amount of the sizing agent deposited, it is sufficient to select the sizing agent and adjust it within the range of 2 to 20% by weight as an auxiliary agent. The degree of defibration of the bundled yarn into single fibers can be determined as follows. Mix cement, aggregate, and other necessary additives with PVA-based bundled yarn, and after mixing, take out the unhardened composition just before or after molding, place it on a 50-mesh wire mesh, and carefully soak it with water to make cement. , fine aggregate, etc. can be identified and compared with a standard sample. In addition, if the state of fibrillation changes with the spray nozzle, such as with shotcrete, or if it solidifies immediately after spraying, or if it is unavoidable to judge based on the hardened product, bend or stretch the sample. The fracture is determined by applying stress and observing the fracture surface under a microscope. The mixing ratio of PVA fibers into mortar and concrete is preferably 0.5 to 6% by volume. If it is less than 0.5%, the reinforcing effect will be small, and if it is more than 6%, it will be difficult to disperse the fibers and the cost will be high, which is not preferable. As mentioned above, by using bundled PVA fibers, which have excellent reinforcing properties for mortar and concrete, they can be uniformly dispersed in molded products.
This invention is based on the invention that a remarkable reinforcing effect can be achieved by defibrating % or more of single fibers. In other words, the thin and long PVA fibers, which have high strength, high modulus of elasticity, and good adhesion to the cement matrix, are uniformly present in the cement matrix. It not only improves bending strength and shear strength, but also has a great crack prevention effect. It is said that the fibers present in the matrix prevent the spread of minute cracks that occur locally, thereby preventing the cracks from expanding, and as a result, cracks are prevented. Therefore, it can be said that the greater the number of fibers present in the matrix, that is, the smaller the fiber spacing, the greater the crack prevention effect. The fibers used in cement mortar and concrete have a small aspect ratio from the viewpoint of dispersibility, that is, they are thick and short, so the fiber spacing is large. Only in accordance with the invention can fibers with a high aspect ratio, ie thin and long, and therefore with small fiber spacings, be incorporated. Therefore, the crack prevention effect is one of the major features of the present invention. It also provides impact resistance and high toughness. Comparative examples of the excellent reinforcing properties of the present invention will be shown with steel fibers, which are partially used although unsatisfactory, and polyethylene fibers with protrusions on the fiber surface, which have recently been subject to considerable study. JIS R5201 sand, cement, and fibers were weighed so that the sand/cement ratio was 1/1 and the fibers were 2% by volume.
(Physical Test Methods for Cement) After mixing in a dry state using a mixer shown in
Water was added so that the concentration was 0.37, and mixing was performed for 3 minutes. The mortar was poured into a 4cm x 4cm x 16cm formwork, given some vibration to harden, and then left at room temperature for a day and night.The mortar was expanded and cured in water for 2 weeks, then air-dried for 2 weeks, and its bending strength was measured. did. Table 1 shows the physical properties and dispersion state of the fibers used at that time.

[Table] The PVA fiber used was a bundled yarn made by bundling 1000 single fibers of 1.8 denier and hardening them with PVA-217 (Poval manufactured by Kuraray). In addition, when the fractured surface at the time of bending fracture was observed under a microscope, the fibers of Kuraray Vinylon and Bonfix were broken, and the steel fibers were clearly pulled out. As is clear from Table 1, PVA fibers are uniformly dispersed using bundled yarns, and due to their high aspect ratio and excellent adhesive properties, their high tensile strength can be effectively utilized until they break. It is clear that the material has a high bending strength. Although steel fibers have a relatively high tensile strength, their aspect ratio is small and their adhesion to cement is not very good, causing pull-outs and the fibers not breaking, so their strength is not effectively utilized. Although polyethylene fibers have protrusions on their sides to prevent them from being pulled out of the mortar, the fibers themselves have low tensile strength and Young's modulus, so they do not contribute much to improving the bending strength and cracking strength of mortar. . As described above, the PVA fiber of the present invention has been studied in various fields for mortar and concrete, which use less water, and has shown a much better reinforcing effect than the steel fibers and polyethylene fibers used in some markets. became clear. PVA-based fibers having such excellent reinforcing effects can be used in a wide range of fields such as mortar and concrete products, and are not limited to those described below. First, by forming method, there are on-site forming methods such as pouring with fresh concrete, spray molding, and injection molding, and factory forming methods include vibration molding, centrifugal force forming, extrusion molding, and injection molding. It can also be applied to cement and mortar molded products formed by molding methods. In terms of usage, it can be applied to structural members or structures, such as improving the performance of unreinforced concrete structures such as pavements and tunnel linings, and as an alternative to reinforced concrete members, such as centrifugally formed concrete pipes. There is also a form of use in which it is used in combination with reinforced concrete to improve the performance of reinforced concrete members. Examples include shear reinforcement of shear walls, columns, and beam joints. As mentioned above, since it exhibits superior reinforcing properties to steel fibers, it can be used as a substitute in, for example, fields where steel fibers are used. First, a typical example of the application of steel fiber in the civil engineering field is pavement use. This includes road paving, airport runway paving, taxiway paving, yard paving used for transporting heavy goods within factories, and bridge surface paving. The first performance required for pavement use is high bending strength. The bending stress is a combination of the bending stress due to the wheel load and the warping stress caused by the temperature difference between the top and bottom surfaces. PVA fibers have a remarkable effect on improving bending strength, making it possible to significantly reduce the thickness of pavement. Second, it has a great effect on preventing cracks.
This is to prevent the cracks that occur on the bottom of the pavement surface from progressing due to traffic loads. As a result, the lifespan will be significantly extended. It is clear that PVA fibers are highly effective in preventing cracks. It can also be applied as an overlay to existing pavement with similar effects. The second example of application is shotcrete, typical examples of which are tunnel construction and slope protection construction. First of all, in the case of tunnel construction, there are three application forms. (1) Application to the primary lining of tunnels excavated through soft strata (2) Application to the secondary lining of areas where the behavior of the ground is difficult to stabilize due to faults, etc. (3) Application to the secondary lining of tunnels that are damaged due to disasters, etc. There are quick repairs, etc. The required performance in any application form is bending strength, shear strength, and crack resistance.
Reinforcement with PVA fibers shows remarkable effectiveness. In addition, it must be easy to implement and safe. PVA fibers are thinner and longer fibers than steel fibers, and have better adhesion to cement, so they are effective in preventing splashing and skin peeling.In addition, steel fibers cause problems because the fibers themselves tend to bounce back a lot. However, PVA fibers have a good affinity with cement, so they do not separate from the material, so there is no need to worry about this. The high bounce of the fibers means that fibers, which are more expensive than other materials, are wasted, which not only increases costs, but also reduces the amount of fibers in the sprayed area.
This is a very difficult problem as it does not exhibit the reinforcing properties as designed. A major feature of PVA fibers is that the fibers themselves do not bounce as much as the material itself. Next, in the case of slope protection work, reinforcing with PVA fiber has the advantage of being able to omit conventional reinforcing steel due to the properties mentioned above, and making it possible to reduce the spray thickness. It is also applied to the repair of aging structures. In addition, dams and hydraulic structures can be effectively repaired, and it can also be applied to road bridge decks. Furthermore, it is effective in reinforcing low-strength concrete such as lightweight concrete and aerated concrete. Examples of architectural applications include partition walls and precast external staircase plastering mortar. Although we have described only a few of the application examples above, it is applicable to all fields that use cement mortar and concrete that require bending strength, shear strength, crack resistance, and impact resistance.
Within the scope of the present invention. The invention will be explained in detail below with reference to Examples. Examples 1 to 5, Comparative Examples 1 to 2 Sand, cement, and fibers were weighed so that the sand/cement ratio was 1/1 and the fiber content was 2% by volume, according to JIS R-
After mixing in a dry state using a mixer shown in No. 5201, water was added so that the water-cement ratio was 0.4, and mixing was performed for 3 minutes. The PVA fiber used has a strength of 140-145Kg/mm ²
The single fiber denier is 0.8 (Example 1), 2.0 (Example 2), 5.0 (Example 3), 10.0 (Example 4), 20.0 (
Example 5), 0.2 (Comparative Example 1), and 40 (Comparative Example 2), the bundled yarns each have a total denier of 2000 denier.
After attaching 5% PVA-217 and hardening it, it was cut so that the aspect ratio of each single fiber was 1000. 4cm x mortar after mixing
After pouring into a 4cm x 16cm mold, shaking and hardening,
The mold was left overnight at room temperature, removed from the mold, and cured in water for 2 weeks and air-dried for 2 weeks. Fiber dispersion and degree of fibrillation were determined by placing the mortar on a 50-mesh wire mesh just before pouring it into the formwork, washing off cement, etc. with water, and comparing it with a standard sample of degree of fibrillation. The bending strength and measurement results are shown in Table 2.

【table】

[Table] Examples 6 to 8, Comparative Examples 3 to 4 The strength of the PVA fiber used was 151 Kg/mm ² , the single fiber denier was 2 denier, and the aspect ratio of the single fiber unit was 250 (Example 6), 400 (Example 7), 600 (Example 8), 80 (Comparative Example 3), and 2500 (Comparative Example 4), but in the same manner as Examples 1 to 5. Table 3 summarizes the results.

[Table] Examples 9 to 11, Comparative Example 5 The single fiber denier of the PVA fiber used is 2 denier, and the strength of the single fiber is 100 Kg/mm ² (Example 9),
120Kg/mm ² (Example 10), 150Kg/mm ² (Example 11),
70Kg/mm ² (Comparative Example 5) It was carried out in exactly the same manner as Examples 1 to 5 except for the respective changes. Table 4 summarizes the results.

[Table] Examples 12 to 15, Comparative Examples 6 to 7 The single fiber denier of the PVA fibers used was 2 denier, and the total denier of the bundled yarn was 300 (Example 12).
700 (Example 13), 1800 (Example 14), 4000 (Example
15), 100 (Comparative Example 6), and 8000 (Comparative Example 7), and the results were summarized in Table 5.

[Table] Examples 16 to 19, Comparative Examples 8 to 9 The single fiber denier of the PVA fiber used is 2 denier, and the fiber mixing rate is 0.8 in volume % (Example 16),
1.5 (Example 17), 3.0 (Example 18), 5.0 (Example 19)
,
It was carried out in exactly the same manner as in Examples 1 to 5, except that the values were changed to 0.2 (Comparative Example 8) and 8.0 (Comparative Example 9), and the results are summarized in Table 6.

【table】

[Table] Examples 20 to 23, Comparative Example 10 Sand, cement, and fibers were weighed so that the sand/cement ratio was 1/1 and the fibers were 2% by volume, according to JIS R-
After dry mixing using a mixer shown in No. 5201, water was added so that the water/cement ratio was 0.4, and mixing was performed for 3 minutes. After mixing, the mortar was poured into a 4 cm x 4 cm x 16 cm mold, hardened by shaking, and left at room temperature overnight. After that, it was removed from the mold and cured in water for 2 weeks and air-dried for 2 weeks. The PVA-based fibers used here had a single fiber denier of 2, a strength of 150 Kg/mm ² , a total bundled yarn denier of 2000, and bundled yarns were used in which the type of sizing agent was changed to a coating amount of 6%. The sizing agent is fully saponified PVA made by Kuraray.
PVA (Example 20), Kuraray PVA-217 (Example
21), PVA-105 manufactured by Kuraray, cationized polyvinyl acetate emulsion (Example 23), and urea-formalin resin (Comparative Example 10). The cutting length of the bundled yarn was such that the aspect ratio of each single fiber was 1000. The dispersibility and degree of fibrillation were the same as in Examples 1 to 5, and the bending strength was measured and summarized in Table 7.

【table】

[Table] Examples 24 to 27, Comparative Example 11 Amount of cement per ^1m3 : 490Kg, fine aggregate: 937Kg,
Coarse aggregate (15mm or less) 418Kg, PVA fiber 1.2Kg
(2% by volume) was mixed in a dry state for 2 minutes with a pan mixer, then 290 kg of water (W/C = 0.6) was added.
Mixing was continued for an additional 3 minutes. The concrete was poured into a 10 cm x 10 cm x 40 cm formwork, hardened by vibration, and then left at room temperature for one day and night, then removed from the mold, and after 2 weeks of water curing and 2 weeks of air drying, the bending strength was measured. Dispersion state and degree of fibrillation are Examples 1 to 5
I did the same thing. The PVA fiber used here has a monofilament denier of 2.
Assuming strength of 150Kg/mm ² and total bundled yarn denier of 2000,
A sizing yarn was used in which the type of sizing agent was changed to a coating amount of 6%. The sizing agent is PVA-217 manufactured by Kuraray (example)
24), Kuraray PVA-105 (Example 25), Kuraray
PVA-205 (Example 26), cationized polyvinyl acetate emulsion (Example 27), and urea-formalin resin (Comparative Example 11). The cutting length of the bundled yarn was such that the aspect ratio of each single fiber was 1000. The results are summarized in Table-8.

【table】

Claims (1)

[Claims] 1. 200 to 200 polyvinyl alcohol fibers with a single fiber denier of 0.5 to 25 deniers and a tensile strength of 90 Kg/mm ² or more, hardened with 2 to 20% by weight of a water-soluble sizing agent.
It is a bundled yarn of 5000 denier, and when it is opened into single fibers, the aspect ratio is 100 to 2000.
Fibers for reinforcing cement mortar and concrete, which are characterized by being defibrated to 20% or more single fibers in cement mortar and concrete molded products. 2 Single fibers with a denier of 0.5 to
It is a bundled yarn of 200 to 5000 denier made by hardening polyvinyl alcohol fibers with a tensile strength of 25 denier and a tensile strength of 90 Kg/mm ² or more with 2 to 20% by weight of a water-soluble sizing agent. aspect ratio
Cut into 100-2000, and cement mortar,
Cement mortar and concrete molded products reinforced with fibers, characterized in that 0.5 to 6% by volume of fibers that can be defibrated into single fibers are blended with 20% or more of the concrete molded products.