JP6445400B2 - Polyvinyl alcohol fiber for reinforcing mortar concrete, and mortar concrete containing the same - Google Patents

Description

  The present invention relates to a polyvinyl alcohol fiber for reinforcing mortar concrete, which is excellent in dispersibility and has high reinforcing performance for mortar concrete.

  Mortar concrete is widely used around the world as a building material because of its excellent durability and fire resistance, high moldability, and excellent compressive strength. However, mortar concrete has drawbacks such as being brittle and having poor folding resistance and tensile resistance. In addition, because the strain is small, cracks are likely to occur, and it may lead to destruction later, and the impact resistance is poor.Further, cracking occurs due to repeated expansion and contraction of the matrix, causing the structure to break down, It also has safety disadvantages such as water leakage and appearance damage due to lack of peeling.

  In order to make up for such drawbacks, methods for reinforcing mortar concrete using various reinforcing fibers have been developed. Examples of such reinforcing fibers include various fibers such as steel fibers, polyvinyl alcohol fibers, nylon, polyolefins, and acrylic fibers. These reinforcing fibers may be deformed in whole or in part to further enhance their reinforcing performance. For example, in patent document 1, the mechanical strength of concrete is raised by making the terminal part of a fiber into a waveform.

JP 2000-119052 A

  However, when the fibers are deformed, the fibers may be entangled with each other in the hydraulic composition to generate a fiber lump (fiber ball). Reinforcing fibers are inherently dispersed uniformly in the hydraulic composition and exhibit reinforcing performance. However, when the reinforcing fibers generate fiber balls, defects occur in the resulting mortar concrete, and the structure Problems can result that result in reduced strength.

  Accordingly, the present invention provides a fiber for reinforcing mortar concrete that has excellent dispersibility because fiber balls are hardly generated when dispersed in a hydraulic composition, and at the same time, mortar concrete excellent in mechanical strength. It is an issue to provide.

  In order to solve the above-mentioned problems, the present inventor has arrived at the present invention as a result of detailed studies on fibers for reinforcing mortar concrete.

That is, the present invention includes the following preferred embodiments.
[1] Polyvinyl alcohol fiber for reinforcing mortar concrete having an elastic modulus of 100 cN / dtex or more and a fiber end portion damage degree of 5% or less.
[2] The polyvinyl alcohol fiber for reinforcing mortar concrete according to [1], wherein the fiber length is 6 to 60 mm.
[3] The polyvinyl alcohol fiber for reinforcing mortar concrete according to [1] or [2], wherein the aspect ratio is 20 to 200.
[4] The polyvinyl alcohol fiber for reinforcing mortar concrete according to any one of [1] to [3], wherein the average fiber strength is 4.0 cN / dtex or more.
[5] Mortar concrete containing a cement component, aggregate, and polyvinyl alcohol fiber for reinforcing mortar concrete according to any one of [1] to [4].

  According to the present invention, fiber balls are less likely to be generated when dispersed in a hydraulic composition and have excellent dispersibility, and at the same time, mortar concrete reinforcing fibers having high reinforcing performance against mortar concrete, and mortar concrete having excellent mechanical strength Can be provided.

  The mortar concrete reinforcing fiber of the present invention is a polyvinyl alcohol fiber having an elastic modulus of 100 cN / dtex or more and a fiber end portion damage degree of 5% or less.

  The elastic modulus of the polyvinyl alcohol fiber of the present invention is 100 cN / dtex or more, preferably 120 cN / dtex or more, more preferably 140 cN / dtex or more. When the elastic modulus of the polyvinyl alcohol fiber is equal to or more than the above lower limit value, it is possible to produce mortar concrete that is excellent in reinforcement performance with respect to mortar concrete and has high mechanical strength. When the elastic modulus of the polyvinyl alcohol fiber is less than 100 cN / dtex, the fiber end portion damage degree tends to be low, but the reinforcement performance with respect to the mortar concrete is lowered. Although the upper limit of the elastic modulus of the polyvinyl alcohol fiber of the present invention is not particularly limited, it is, for example, 300 cN / dtex or less. The elastic modulus can be measured by the method in the following examples.

  The fiber end portion damage degree of the polyvinyl alcohol fiber of the present invention is 5% or less, preferably 4% or less, more preferably 3% or less, and further preferably 1% or less. When the fiber end portion damage degree of the polyvinyl alcohol fiber is not more than the above upper limit value, the dispersibility of the fiber is improved when the hydraulic composition containing the cement component and water and the polyvinyl alcohol fiber are mixed, and the reinforcement to the mortar concrete Performance can be improved. Further, when the fiber end portion damage degree of the polyvinyl alcohol fiber is equal to or less than the above upper limit value, it is difficult to become resistance when the hydraulic composition and the fiber are mixed, and the reduction in fluidity due to the addition of the fiber is effectively suppressed. Furthermore, even if the addition speed of the fiber to the hydraulic composition is increased, the fibers are hardly entangled with each other and workability is improved. When the fiber end portion damage degree of the polyvinyl alcohol fiber exceeds 5%, a fiber ball is likely to be generated depending on the fiber addition method. For example, if the fiber addition rate is too high, fiber balls are likely to be generated, the mechanical strength of the mortar concrete is lowered, and the fluidity of the hydraulic composition may be lowered. In addition, the fiber terminal part damage degree of the polyvinyl alcohol fiber of this invention is 0% or more normally.

  The fiber end portion damage degree can be measured by the following method. For 100 arbitrarily selected fibers, when both ends are observed using a video microscope or the like, and there is a crack of 1 mm or more in the fiber length direction at one or both ends of the fiber, Alternatively, if there is a crack having a spread of 20% or more in the horizontal direction with respect to the fiber diameter, it is determined that the fiber is damaged, and the ratio of the damaged fiber in 100 fibers is the fiber end portion damage degree. Can be expressed as

  The fiber length of the polyvinyl alcohol fiber of the present invention is preferably 6 mm or more, more preferably 8 mm or more, further preferably 10 mm or more, preferably 60 mm or less, more preferably 50 mm or less, and further preferably 40 mm or less. When the fiber length of the polyvinyl alcohol fiber is not more than the above upper limit, the entanglement of the fibers is further suppressed, the dispersibility in the mortar concrete is further increased, and the fiber followability to the expansion and contraction of the mortar concrete is excellent. Further, the reinforcing performance for mortar concrete is further improved. When the fiber length of the polyvinyl alcohol fiber is not less than the above lower limit value, the adherence of the fiber to the mortar concrete is increased, and the reinforcement performance to the mortar concrete is further improved.

  The aspect ratio of the polyvinyl alcohol fiber of the present invention is preferably 20 to 200, more preferably 25 to 150, and still more preferably 30 to 120. When the aspect ratio of the polyvinyl alcohol fiber is within the above range, the entanglement between the fibers is suppressed and the dispersibility in the mortar concrete is further increased, so that the reinforcing performance with respect to the mortar concrete can be enhanced. In the present invention, the aspect ratio means the ratio (L / D) between the fiber length (L) and the fiber diameter (D). As for the aspect ratio, the fiber length can be calculated in accordance with JIS L1015 “Chemical Fiber Staple Test Method (8.5.1)”, and the aspect ratio of the fiber can be calculated based on the ratio to the fiber diameter.

  The average fiber strength of the polyvinyl alcohol fiber of the present invention is preferably 4.0 cN / dtex or more, more preferably 4.5 cN / dtex or more, and further preferably 5.0 cN / dtex or more. The reinforcement performance with respect to mortar concrete can be improved as the average fiber strength of a polyvinyl alcohol fiber is more than the said lower limit. The upper limit value of the average fiber strength of the polyvinyl alcohol fiber of the present invention is appropriately set according to the type of fiber, and is, for example, 20 cN / dtex or less. In addition, average fiber strength shows the value measured by the method described in the Example mentioned later.

The polyvinyl alcohol fiber of the present invention is a fiber rich in hydrophilicity due to its molecular structure, and since OH in the polyvinyl alcohol fiber and Ca in the cement component are bonded to each other, the affinity to the cement component is high, and polypropylene. Compared with other fibers, etc., the chemical adhesive force is extremely large. Therefore, even if the whole or part of the fiber is not deformed, high adhesion to the cement component can be exhibited and high reinforcement performance to the mortar concrete can be exhibited.
Polyvinyl alcohol has a high crystallinity because it can form a strong intermolecular hydrogen bond due to the OH group in the molecular structure. Therefore, it becomes a high-strength fiber, so it is very useful as a fiber for reinforcing mortar concrete. is there. In this invention, from these characteristics, it is excellent in the reinforcement performance with respect to mortar concrete, and the expansion of the crack width over the long term of mortar concrete can be suppressed effectively.

  The polyvinyl alcohol fiber of the present invention is a fiber containing a vinyl alcohol polymer, and the content of the vinyl alcohol polymer in the fiber is preferably from the viewpoint of mechanical strength, adhesion to mortar concrete, alkali resistance, and the like. Is 30% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. The polyvinyl alcohol fiber of the present invention may be a composite fiber with other polymer or a sea island fiber. The vinyl alcohol polymer is composed of polyvinyl alcohol, and may be a copolymer with other monomers other than polyvinyl alcohol as long as the effects of the present invention are not impaired. From the viewpoint of the mechanical strength and alkali resistance of the fiber, the ratio of the modified unit in the vinyl alcohol polymer is preferably 30 mol% or less, more preferably 10 mol% or less. Further, from the viewpoint of the mechanical strength and alkali resistance of the fiber, the average degree of polymerization obtained by the viscosity method with an aqueous solution at 30 ° C. is preferably 1000 or more, more preferably 1500 or more, from the viewpoint of production cost, etc. Preferably it is 10,000 or less, More preferably, it is 5000 or less, More preferably, it is 3000 or less. Further, from the viewpoint of heat resistance, durability and dimensional stability, the saponification degree is preferably 99 mol% or more, more preferably 99.8 mol% or more.

  The polyvinyl alcohol fiber of the present invention can be produced, for example, by the following method. The polyvinyl alcohol-based polymer is formed into a hydrous chip having a concentration of 40 to 60% by mass, heated and melted with an extruder, and defoamed. And a crosslinking agent is added to this polyvinyl alcohol-type polymer aqueous solution. Examples of the cross-linking agent include ammonium sulfate, sulfuric acid, ammonium phosphate, phosphoric acid, hydrochloric acid, nitric acid, acetic acid and oxalic acid. From the viewpoint of not corroding the pipe, causing bad odor, and not foaming the fiber, ammonium sulfate. Is preferred. As addition amount of a crosslinking agent, 0.5-10 mass% is preferable with respect to the mass of a polyvinyl alcohol-type polymer. The temperature of the spinning dope is preferably 90 to 140 ° C. The spinning stock solution to which such a crosslinking agent is added is pressurized and discharged into the air from the nozzle holes to dry-spin. The nozzle hole may be circular, or may have a different shape other than a circle, such as a flat shape, a cross shape, a T shape, a Y shape, an L shape, a triangular shape, a square shape, or a star shape. Note that the spinning method may be any of wet, dry wet, and dry methods.

  Next, the polyvinyl alcohol fiber obtained by spinning is dried. The drying temperature is usually 100 ° C. or lower, and it is preferable that the drying is completely performed under a temperature condition of 100 ° C. or higher when the drying is performed to some extent.

  After drying, the fiber is stretched. Stretching is usually performed at a stretching temperature of 200 to 250 ° C, preferably 220 to 240 ° C. The draw ratio is usually 5 times or more, preferably 6 times or more. At the time of drawing, the cross-linking agent added to the spinning dope reacts with the OH group of polyvinyl alcohol to cause cross-linking. Stretching is performed in a hot air stretching furnace over a period of about 20 seconds to 3 minutes. The fiber thus stretched is subjected to heat treatment in order to achieve constant length or shrinkage as necessary. If necessary, the fibers thus obtained may be crimped or an oil agent may be applied.

  Thereafter, the polyvinyl alcohol fiber is cut into a fiber length in the above range. The cutting method is not particularly limited as long as the fiber end portion is not easily damaged, and examples thereof include a side cut method, a water jet method, a laser cut method, a disk blade cut method, an ultrasonic cut method, and a scissor cut method. It is done. Especially, since it is hard to produce damage especially in a fiber terminal part, a side cut system, a laser cut system, and a water jet system are preferable, and a side cut system is more preferable. In order to reduce the fiber end portion damage degree, for example, a thin blade that minimizes the contact area between the blade and the fiber is used. However, in the case of the side cut method, the blade used is thin, and the blade and the fiber are used. Can be minimized, and at the same time, the impact and shearing force applied to the blade can be suppressed, so that damage at the fiber end can be suppressed. In the case of the laser cut method and the water jet method, since no blade is used, damage at the fiber end portion can be suppressed. Further, in order to lower the damage degree of the fiber end part, the fiber end part may be cut while dissolving the fiber end part using heat or a solvent, or the fiber end part is dissolved using heat and / or a solvent after cutting. End damage may be improved.

  In this invention, the mortar concrete containing a cement component, an aggregate, and the said polyvinyl alcohol fiber is also provided. Since the mortar concrete has a low number of fiber balls and high mechanical strength, it is useful as various building materials such as wall materials and roof materials.

  Examples of the cement component in the present invention include ordinary Portland cement, early-strength Portland cement, ultra-high-strength Portland cement, and moderately hot Portland cement, such as Portland cement, alumina cement, blast furnace cement, silica cement, and fly ash cement. It is done. These cements may be used alone or in combination of two or more.

  As the aggregate in the present invention, various aggregates can be used as necessary. Examples of such aggregates include fine aggregates, lightweight aggregates, and coarse aggregates. These aggregates may be used alone or in combination of two or more.

  The fine aggregate may be a fine aggregate having a particle size of 5 mm or less, such as sands having a particle size of 5 mm or less; silica stone, fly ash, blast furnace slag, volcanic ash-based shirasu, various sludges, rock minerals, etc. Fine aggregate obtained by pulverizing or granulating the inorganic material. These fine aggregates may be used alone or in combination of two or more. Examples of sands include sands such as river sand, mountain sand, sea sand, crushed sand, quartz sand, slag, glass sand, iron sand, ash sand, calcium carbonate, and artificial sand. These fine aggregates may be used alone or in combination of two or more.

  The coarse aggregate is an aggregate containing 85% by mass or more of particles having a particle size of 5 mm or more. The coarse aggregate may be composed of particles having a particle size of more than 5 mm. Examples of the coarse aggregate include various types of gravel, artificial aggregate (eg, blast furnace slag), recycled aggregate (eg, recycled aggregate of building waste), and the like. These coarse aggregates may be used alone or in combination of two or more.

  Examples of lightweight aggregates include natural lightweight aggregates such as volcanic gravel, expanded slag and charcoal, and artificial lightweight bones such as foamed pearlite, foamed perlite, foamed black stone, vermiculite, shirasu balloons and fly ash microballoons. Materials. These lightweight aggregates may be used alone or in combination of two or more.

  Moreover, the mortar concrete of this invention may contain a functional aggregate in addition to the said aggregate. Here, functional aggregates include colored aggregates, hard aggregates, aggregates having elasticity, aggregates having a specific shape, and the like. Specifically, layered silicates (for example, , Mica, talc, kaolin), alumina, silica and the like. The ratio of the functional aggregate to the aggregate can be appropriately set according to each type. For example, the mass ratio of the aggregate to the functional aggregate (aggregate / functional aggregate) is 99/1 to 70/30, preferably 98/2 to 75/25, more preferably 97/3 to 80/20. These functional aggregates may be used alone or in combination of two or more.

  The mass ratio of aggregate total amount (S) to cement component (C) (aggregate (S) / cement component (C)) is preferably 1/10 to 5/1, more preferably 1/8 to 4 /. 1, more preferably 1/6 to 3/1.

The content of the polyvinyl alcohol fiber in the mortar concrete of the present invention can be appropriately set according to the type of fiber, fiber length, aspect ratio, etc. When using fibers having an average fiber diameter of 660 μm or more, the entire mortar concrete based on the volume, preferably 1~70kg / ^{m 3,} more preferably 2~40kg / ^{m 3,} more preferably from 3 to 30 kg / ^{m 3,} when the average fiber diameter of fibers are used in less than 660Myuemu, mortar It is preferably 1 to 70 kg / m ³ , more preferably 2 to 40 kg / m ³ , and further preferably 2 to 30 kg / m ^{3 based} on the volume of the entire concrete. When the fiber content is within the above range, the reinforcement effect by the polyvinyl alcohol fiber is further enhanced, and the entanglement of fibers based on the excessive fiber content can be suppressed, and the reinforcement effect by the polyvinyl alcohol fiber is further improved. Can do.

  The mortar concrete of the present invention may contain various admixtures as necessary. Examples of the admixture include AE agent, fluidizing agent, water reducing agent, high performance water reducing agent, AE water reducing agent, high performance AE water reducing agent, thickener, water retention agent, water repellent, swelling agent, curing accelerator, Examples thereof include a setting retarder, a polymer emulsion [acrylic emulsion, ethylene-vinyl acetate emulsion, and SBR (styrene butadiene rubber) emulsion]. The admixture may be contained alone or in combination of two or more. The polymer emulsion not only strengthens the brittleness of the mortar concrete but also can strengthen the adhesive force between the components in the mortar concrete. Furthermore, by combining the polymer emulsion, not only can the water permeability of the mortar concrete be improved, but also excessive drying can be suppressed.

  The mortar concrete of the present invention may contain a water-soluble polymer substance as necessary. Examples of the water-soluble polymer substance include cellulose ethers such as methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and hydroxypropyl methyl cellulose, polyvinyl alcohol, polyacrylic acid, and lignin sulfonate. These water-soluble polymer substances may be used alone or in combination of two or more.

  The number of fiber balls contained in the mortar concrete of the present invention is preferably 0 to 5, more preferably 0 to 1. When the number of fiber balls in the mortar concrete is within the above range, the mechanical strength of the mortar concrete becomes higher, and the bending strength and the compressive strength are excellent. The fiber ball is generated due to poor mixing of the fiber and the cement component in the hydraulic composition and is formed by entanglement of the fibers and has a ball shape. The number of fiber balls can be measured by the method described in Examples described later.

  The slump loss of the mortar concrete of the present invention is preferably 6 cm or less, more preferably 4 cm or less, and further preferably 2 cm or less. When the slump loss is less than or equal to the above upper limit, workability is improved because the miscibility between the polyvinyl alcohol fiber and the cement component is high. The lower limit of the slump loss is not particularly limited, but is usually 1 cm or more. The slump loss can be measured by performing a slump test in accordance with a concrete slump test method according to JIS A1101.

  The mortar concrete of the present invention is prepared by mixing water, a cement component, an aggregate, and, if necessary, a hydraulic composition containing various admixtures within a range not impairing the effects of the present invention, with the polyvinyl alcohol fiber. Can be obtained.

  The hydraulic composition is kneaded by kneading means such as a known or conventional mixer. Further, the kneading order of the constituent materials can be carried out without any particular limitation, but in order to minimize the physical impact on the polyvinyl alcohol fiber, the constitution of the hydraulic composition, the water / cement component ratio ( W / C) and the like are adjusted as appropriate.

  The water / cement component ratio (W / C) in the hydraulic composition is appropriately adjusted according to the configuration of the hydraulic composition, etc., but is preferably 20 to 50% by mass, more preferably 25 to 45% by mass, More preferably, it is 30-40 mass%.

  When adding polyvinyl alcohol fiber to the hydraulic composition, for example, in order to improve the dispersibility of the polyvinyl alcohol fiber, (i) polyvinyl alcohol fiber may be supplied in a fixed amount, and (ii) polyvinyl in an undissolved state Alcohol fibers may be added, and (iii) a mixer or kneader with high stirring performance may be used when mixing polyvinyl alcohol fibers. You may perform these (i)-(iii) methods individually or in combination of 2 or more types.

  When the polyvinyl alcohol fiber is quantitatively supplied, it is not particularly limited as long as the fiber can be continuously fed within a predetermined range. For example, various quantitative supply devices (for example, a vibration feeder, a screw feeder, a belt feeder, etc.) can be used as a device for supplying fibers while controlling the input amount and / or the input speed of the fibers.

  When the fiber is added and dispersed in the hydraulic composition, the polyvinyl alcohol fiber of the present invention is less likely to generate fiber balls and has high dispersibility. Therefore, it can be added at a relatively high addition rate. For example, the addition rate of the polyvinyl alcohol fiber is preferably 0.05 to 0.5 kg / second, more preferably 0.07 to 0.4 kg / second, and still more preferably 0.000 per 1 t of the solid content of the hydraulic composition. 1 to 0.3 kg / sec. When the fiber is added to the mixture at an addition rate within the above range, the fiber can be efficiently added. Therefore, the workability is excellent, and at the same time, the fiber hardly generates a fiber ball.

  When unraveling the polyvinyl alcohol fiber, for example, the fiber aggregate can be unwound to a smaller fiber aggregate unit by a predetermined dissociation means or the like to such an extent that the fiber ball can be prevented from being formed in the hydraulic composition. . In addition, when a fiber aggregate is unraveled, it is preferable to carry out within a range in which fiber fibrillation and fiber pulverization do not occur from the viewpoint of maintaining fiber strength.

  The fiber aggregate can be usually solved by various methods in a dry process. For example, fiber agglomerates (fiber veil, coarse fiber fiber defibrated material, shortcut fiber bundles, etc.) may be unwound by hooking the fibers on a roll having protrusions and passed between opposing rotating gears. It may be solved by a shearing force of a rotating disk having a groove, or by an air blow collision force. You may perform these methods individually or in combination of 2 or more types. For example, the fiber aggregates (such as a short-cut fiber lump cut to a predetermined length) may be unraveled in a dry manner to separate the fibers, thereby unraveling the fiber aggregates.

  As for the dispersion method of the polyvinyl alcohol fiber, it is possible to disperse the fiber by various methods as long as the fiber can be dispersed in a state where the fiber is not substantially present as a fiber aggregate. For example, when using a mixer or kneader with high stirring performance, examples of the mixer and kneader with high stirring performance include, for example, a double-arm kneader, a pressure kneader, an Eirich mixer, a super mixer, a planetary mixer, a Banbury mixer, and a continuous mixer. A mixer or a continuous kneader can be used.

  Thereafter, the hydraulic composition containing the polyvinyl alcohol fiber is put into the mold, but may be vibrated as necessary. The vibration is usually performed by vibrating the formwork. By applying vibration, the hydraulic composition can be more evenly distributed inside the mold.

  The frequency when vibrating is preferably 10 to 1000 Hz, more preferably 20 to 900 Hz, and still more preferably 30 to 800 Hz. The amplitude is preferably 0.1 to 20 μm, more preferably 0.5 to 18 μm, and still more preferably 1 to 15 μm.

  You may press the hydraulic composition thrown into the mold with a press using a top surface shaping | molding die, a roll, etc. The pressure at the time of pressing can be appropriately set depending on the state of the kneaded hydraulic composition, the form of the formwork, etc., preferably 10 to 150 MPa, more preferably 20 to 140 MPa, and still more preferably 30 to 130 MPa. . When the pressure is 10 MPa or more, the integration of the respective materials is sufficient, and when the pressure is 150 MPa or less, the fiber is hardly damaged by pressing from the aggregate, and the decrease in fiber strength and the durability of the formwork are avoided. be able to.

  The pressing may be performed while heating as necessary. As heating temperature, Preferably it is 40-90 degreeC, More preferably, it is 45-85 degreeC, More preferably, it is 50-80 degreeC.

  After molding into a predetermined shape, the mortar concrete of the present invention can be obtained by curing the hydraulic composition by curing in an atmosphere of 100 ° C. or lower.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these Examples.

[Fiber length, average fiber diameter and aspect ratio]
The fiber length was calculated according to JIS L1015 “Testing method for chemical fiber staples (8.5.1)”, and the aspect ratio of the fiber was evaluated based on the ratio to the average fiber diameter. In addition, about the average fiber diameter, 100 fibers were taken out at random, the fiber diameter in the center part of the length direction of each fiber was measured with the optical microscope, and the average value was made into the average fiber diameter.

[Elastic modulus and average fiber strength]
In accordance with JIS L1015 “Chemical Fiber Staple Test Method (8.5.1)”, the fiber was left to stand for 5 days in an atmosphere at a temperature of 20 ° C. and a relative humidity of 65%. Fiber strength was measured by FAFEGRAPH M [manufactured by Texttechno] at a thickness of 60 mm and a tensile speed of 60 mm / min, and the strength was calculated by dividing this strength by the fiber diameter. Fiber strength was measured for 10 or more randomly selected fibers, and the average value was taken as the average fiber strength.

[Fiber end damage]
For 100 polyvinyl alcohol fibers arbitrarily selected in the same lot, both ends thereof are observed using a video microscope or the like, and one or both ends of the fibers have a length of 1 mm or more in the fiber length direction. If there was a crack, or if there was a crack having a spread of 20% or more in the horizontal direction with respect to the fiber diameter, the fiber was judged to be damaged. The ratio of fibers having damage in 100 polyvinyl alcohol fibers was defined as the fiber end portion damage degree.

[Number of fiber balls]
50 L of fiber reinforced concrete kneaded with a forced biaxial mixer was discharged into a container, and the entire amount was checked with a tentacle for the presence of fiber balls. A fiber ball of about 3 cm or more that cannot be easily removed was taken out, and the number thereof was defined as the number of fiber balls.

[Slump loss]
A slump test is performed in accordance with JIS A1101 “Method for testing slump of concrete”, and fresh concrete is filled into a cone (upper side diameter 10 cm, lower side diameter 20 cm, height 30 cm) according to a predetermined procedure, the cone is pulled up, and collapsed. Was measured as the slump loss.

[Maximum yield strength (MOR) and bending toughness coefficient]
In accordance with JIS A1106 “Concrete Bending Strength Test Method”, the mortar kneaded by the mixer was poured into a 15 cm × 15 cm × 53 cm prismatic mold, and then cured in a 20 ° C. room for 28 days. A strength test was performed. The bending strength test was performed with a universal testing machine having a maximum capacity of 2000 kN, and the maximum proof stress (MOR: Modulus of Rupture) and the bending toughness coefficient were measured.

In the examples and comparative examples, the following components were used.
(fiber)
・ PVA: Polyvinyl alcohol fiber (circular cross section), manufactured by Kuraray Co., Ltd. ・ PP: Polypropylene fiber (circular cross section), Balchip MK manufactured by Sugawara Kogyo Co., Ltd.
(Cement component)
-Ordinary Portland cement, Taiheiyo Cement (aggregate)
・ Crumbled stone and crushed sand (admixture) from Kurashiki City, Okayama Prefecture
・ BASF Leo Build SP-8N

[Example 1]
First, PVA fibers having an average fiber diameter of 660 μm were cut by a side cut method to obtain a fiber length of 30 mm and an aspect ratio of 45. Using a biaxial forced-kneading mixer with a capacity of 50 L (manufacturer: Marui, product number: SD-55), the above cement component (320 parts by mass), crushed stone (910 parts by mass), crushed sand (770 parts by mass) and Admixture (0.4% by mass with respect to cement component) is dry blended for 1 minute, then water and admixture are added and mixed for another 1 minute, and the water / cement component ratio (W / C) is 50% by mass. A hydraulic composition was obtained. Thereafter, the fiber was added to the hydraulic composition and kneaded for 1 minute. In addition, the addition amount of the fiber was 6 kg / m ³ with respect to 1 m ^{3 of the} hydraulic composition. A slump test and a measurement test of the number of fiber balls were performed using the hydraulic composition containing the fiber thus obtained. The measurement results are shown in Table 1.
Next, the above hydraulic composition was poured into a 15 cm × 15 cm × 53 cm prismatic mold, then cured in a 20 ° C. room for 28 days, and a strength test was performed using the obtained mortar concrete. The measurement results are shown in Table 1.

[Examples 2-3 and Comparative Examples 1-4]
Various measurements were performed in the same manner as in Example 1 except that the fibers and fiber cutting methods shown in Table 1 were used. The measurement results are shown in Table 1. In addition, when the average fiber diameter is a fiber having an average fiber diameter of 660 μm or more (Example 2 and Comparative Examples 1, 2 and 4), the amount of fiber added is 6 kg / m ³ with respect to 1 m ^{3 of the} hydraulic composition. In the case of a fiber having a diameter of 200 μm (Example 3 and Comparative Example 3), the amount was 2 kg / m ³ with respect to 1 m ^{3 of the} hydraulic composition.

  As shown in Table 1, the mortar concrete obtained in Examples 1 to 3 having a fiber end portion damage degree of 5% or less has 0 fiber balls, and the occurrence of defects in the mortar concrete is suppressed. I understand that. Moreover, it turns out that the slump loss becomes a low numerical value and the polyvinyl alcohol fiber of the present invention has a high dispersibility, and hence brings about a high fluidity. Furthermore, when Example 1 and Comparative Example 1 having the same average fiber diameter, fiber length, and aspect ratio and different fiber end portion damage degrees, and Example 3 and Comparative Example 3 were compared, respectively, the mortar of the present invention was compared. Since all concrete has a high MOR (maximum yield strength) and bending toughness coefficient, it is clear that excellent reinforcement performance is exhibited when the polyvinyl alcohol fiber of the present invention is used.

  When the polyvinyl alcohol fiber of the present invention is dispersed in a hydraulic composition, fiber balls are less likely to be generated and have excellent dispersibility. At the same time, the mortar concrete using the mortar concrete is used in various constructions. It can be usefully used as a material.

Claims (5)

  Polyvinyl alcohol fiber for reinforcing mortar concrete having an elastic modulus of 100 cN / dtex or more and a fiber end portion damage degree of 5% or less.   The polyvinyl alcohol fiber for reinforcing mortar concrete according to claim 1, wherein the fiber length is 6 to 60 mm.   The polyvinyl alcohol fiber for reinforcing mortar concrete according to claim 1 or 2, wherein the aspect ratio is 20 to 200.   The polyvinyl alcohol fiber for reinforcing mortar concrete according to any one of claims 1 to 3, wherein the average fiber strength is 4.0 cN / dtex or more.   Mortar concrete containing a cement component, an aggregate, and the polyvinyl alcohol fiber for mortar concrete reinforcement in any one of Claims 1-4.