JP4358645B2 - Polyolefin short fiber for cement reinforcement and cement-based molded body using the same - Google Patents

Description

  The present invention relates to a polyolefin reinforcing short fiber for cement reinforcement and a cement-based molded body using the same. More specifically, the present invention relates to a cement-based molded body for civil engineering and construction work, and more particularly to a cement-reinforced molded short fiber suitable for preventing cracking of concrete and a cement-based molded body using the same.

Cement-based molded products such as mortar, concrete, and cement / fiber molded products are generally resistant to compressive stress but weak to tensile stress and bending stress. Therefore, they are reinforced with reinforcing bars and other tendons. . However, since the cement-based molded body is highly brittle, it is currently impossible to sufficiently cope with cracks with reinforcing materials such as reinforcing bars, and the building outer wall and tunnel inner wall have fallen off. In recent years, the demand for higher strength in cement-based molded bodies has accelerated, and brittleness tends to become even greater, and improvements are required in terms of long-term stability.
The cause of exfoliation of the outer wall and the like is due to cracks occurring in the cement-based molded body and their expansion. Therefore, as a countermeasure, it is known to add and mix short fibers obtained by cutting a fibrous material such as steel fiber or vinylon fiber into a predetermined length (see, for example, Patent Documents 1 and 2).
However, steel fibers have drawbacks such as being heavy and rusting, and there are safety issues such as risk of injury due to stepping. Vinylon fibers have problems in terms of long-term stability, such as being easily hydrolyzed when the temperature rises under cement alkaline conditions.

On the other hand, polyolefin short fibers have excellent alkali durability and are inexpensive, but have poor hydrophilicity, and therefore, surfactants and the like are added to improve adhesion to cement. However, since polyolefin fibers basically do not adhere to cement, the surfactant treatment alone is insufficient. Therefore, as a measure against unplugging of fibers from the cement-based molded body, polyolefin fibers have been proposed in which the fiber surface is hot-pressed with a concavo-convex marking roller and the fiber surface is subjected to concavo-convex processing (see, for example, Patent Documents 3 and 4). ).
It is effective to give the fiber surface unevenness in terms of increasing the fiber pull-out resistance, but the pressed part of the fiber is flattened due to the processing technology called hot pressing, so the cracking of the cement-based molded body However, the compressive strength and bending strength of the cement-based molded body are reduced. Further, in order to impart practical crack resistance, it is necessary to blend a large amount of fibers, and a fiber-reinforced cement-based molded body that is practically satisfactory has not been obtained.

JP-A-5-262544 JP-A-8-218220 JP-A-11-116297 Japanese Unexamined Patent Publication No. 2000-64116

  The present invention has been made to solve the above problems, and has a sufficient strength as a cement-based molded article for civil engineering and construction work, and a cement-reinforced polypropylene short fiber capable of preventing the occurrence of cracks and the like. It aims at providing the cement-type molded object using this.

The inventors of the present invention focused on the contact area between the cement reinforcing fiber and the cement, and intensively studied a shape that can increase the surface area of the fiber and remarkably increase the physical bond. As a result, it has been found that the above problem can be solved by using polyolefin short fibers having specific protrusions.
That is, the present invention
(1) A drawn fiber having a polypropylene resin as a main component, wherein the cross-sectional shape of the fiber is a substantially polygonal shape having 3 to 6 protrusions, and at the tip of the protrusions, Cement-reinforcing polypropylene short fibers, wherein concave or convex portions with an arrangement interval of 0.5 to 5 mm are formed along the longitudinal direction, and the fiber length is 5 to 60 mm ,
(2) The polypropylene short fiber for cement reinforcement according to (1), wherein the shape of the cross section of the fiber is a substantially polygonal shape having four protrusions,
(3) At least one surfactant selected from polyethylene glycol alkyl ester nonionic surfactant, alkyl phosphate anionic surfactant, and polyhydric alcohol type amide nonionic surfactant is 0.05 to 2% by weight of the cement-reinforced polypropylene short fiber according to (1) or (2),
( 4 ) Cement-based molded article, characterized in that 0.05 to 1 % by volume of the cement-reinforced polypropylene short fiber according to any one of (1) to (3) is blended,
Is to provide.

Since the polyolefin short fiber for cement reinforcement of the present invention has an irregular cross section having 3 to 6 protrusions, the contact area with the cement is large. Furthermore, since the concave portion or the convex portion is formed only at the tip of the protruding portion, the physical bond with the cement is remarkably high, and the decrease in the tensile property of the fiber due to the uneven shape is small. As a result, it is possible to prevent the fiber from coming off after the cement has been cured, so that an extremely excellent reinforcing effect is exhibited. Therefore, when applied to a cement-based molded body (such as mortar, concrete and cement / fiber molded body), the bending toughness and tensile strength can be remarkably improved and cracking can be effectively prevented.
Moreover, since the specific gravity of a polypropylene short fiber is light, it is excellent in carrying work and workability when blended with concrete.

The fiber raw material in the present invention is required to be a polyolefin resin from the viewpoint of requiring cement alkali resistance. As the polyolefin resin, polypropylene resin, polyethylene resin, poly-4-methylpentene-1 resin and the like can be used, and polypropylene resin is particularly preferable.
As the polypropylene resin, a propylene homopolymer, a propylene copolymer such as a block copolymer or a random copolymer of an α-olefin and propylene such as ethylene, or a mixture thereof can be used. Among these, a propylene homopolymer or an ethylene-propylene block copolymer is preferable. Since it is desirable that the tensile Young's modulus of the fiber is greater than the adhesion strength to cement, it is most preferable to select and use a polypropylene resin having an isotactic pentad fraction of 0.95 or more. Here, the isotactic pentad fraction is an isotactic fraction in a pentad unit in a polypropylene molecule, measured by ¹³ C NMR, published by Macromolecules 6 925 (1973) by A. Zambelli et al. Means.
Moreover, the melt flow rate (MFR) of polypropylene resin is 0.1-30 g / 10min from the point of continuous stable productivity, Preferably it is 0.3-20 g / 10min, More preferably, it is 0.5- It is preferable to select in the range of 10 g / 10 minutes.

In the polypropylene resin, before the spinning and / or in the process, other polyolefins can be blended as necessary. Other polyolefins to be blended here include polyethylene resins such as high density polyethylene, linear low density polyethylene, low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-alkyl acrylate copolymer, polybutene-1 Etc.
In addition, the polyolefin resin has an antioxidant, a light stabilizer, an ultraviolet absorber, a neutralizer, a nucleating agent, an epoxy stabilizer, a lubricant, an antibacterial agent, a flame retardant, as long as the effects of the present invention are not hindered. In addition, additives such as an antistatic agent, an inorganic filler, an organic filler, a pigment, and a plasticizer can be appropriately added.

The polyolefin short fiber in the present invention is a drawn fiber mainly composed of a polyolefin resin, and the fiber has a substantially polygonal shape having 3 to 6 protrusions in cross section, and the tip of the protrusions. Only, it is the feature that the recessed part or the convex part is formed along the longitudinal direction of this fiber. As the substantially polygonal cross section, a shape having 3 or 4 apexes is more preferable. By forming the shape of the fiber in this way, the secondary moment of bending at the time of cement blending is improved as compared with a fiber having a conventional round cross section or flat round cross section. For this reason, even short fibers with a relatively small tensile Young's modulus, bending of the short fibers due to collision with coarse aggregates, fine aggregates, etc. when cement is mixed is suppressed, and the dispersibility and large concrete property improvement effect are reduced. Demonstrate.
Moreover, the recessed part or convex part of the polyolefin short fiber in this invention is formed only in the front-end | tip of a projection part. This is to make the fixing property to the cement and the drawing resistance effective, and to suppress the decrease in the tensile strength and Young's modulus of the fiber.

There are no particular limitations on the size of the concave portion or convex portion of the protrusion and the arrangement thereof, but it is preferable that the protrusion is arranged at an appropriate interval of 0.5 to 5 mm as much as possible along the longitudinal direction of the fiber on the surface of the protrusion. However, irregular spacing may be used as long as it is disposed over a length of approximately 70% or more of the length of the short fiber after fiber cutting. The protrusions do not need to be on the same line with respect to the longitudinal direction of the fiber, and may be arranged in a spiral shape or irregularly arranged. Moreover, although it is preferable that the recessed part or convex part of the front-end | tip of a projection part is formed in the front-end | tip of all the projection parts, what is necessary is just to be formed in the projection part of 2 or more rows.
In addition, the polyolefin fiber of this invention can use not only a single layer fiber but the composite fiber which uses a polyolefin high melting point component as a core layer, and uses a polyolefin low melting point component as a sheath layer. The manufacturing method of such a composite fiber is well-known.

  The manufacturing method of the polyolefin short fiber of this invention is not specifically limited, A various method is employable. Usually, first, the above-mentioned polyolefin resin is used to melt and extrude from a nozzle having a shape corresponding to a desired protrusion shape, and after cooling and stretching, a single layer having fin-like protrusions continuous in the longitudinal direction of the fiber A fiber or a composite fiber is formed. Next, the fin-like protrusions can be produced by transforming the protrusions having the recesses or protrusions of the present invention, applying a surface-active agent adhesion treatment, and finally cutting to a desired length. . Below, the manufacturing method of polyolefin short fiber is demonstrated in detail.

The method for forming a single fiber having fin-like protrusions continuous in the longitudinal direction of the fiber is not particularly limited, and the cross-section provided with the protrusions has approximately 3 to 6 protrusions. Any method can be used as long as it can be manufactured so as to form a square, for example, a substantially triangular shape, a substantially star polygon shape, a substantially complex polygon shape, or the like. For example, a polyolefin resin can be obtained by melt-extruding a polyolefin resin from a die using a cross-shaped, Y-shaped, triangular, X-shaped, quadrangular, star-shaped or a continuous yarn-shaped nozzle and cooling and solidifying it. .

Next, the polyolefin fiber obtained as described above is subjected to heat stretching and, if necessary, heat relaxation treatment. By this heat treatment, the rigidity of the fiber can be increased, and a fiber suitable for cement reinforcement having a small elongation can be obtained. The thermal stretching is performed at a temperature below the melting point of the polyolefin resin and above the softening point, and usually the stretching temperature is in the range of 70 to 150 ° C.
As the thermal stretching method, a heating method such as a hot roll method, a hot plate method, an infrared irradiation method, a hot air oven method, a hot water method, a water vapor method and the like can be adopted. The stretching operation may be one-stage stretching, two-stage stretching, or multi-stage stretching. The draw ratio may be as long as it is 2 times or more and does not break, and is usually 3 to 12 times, preferably 6 to 9 times. Here, the draw ratio is represented by the ratio between the supply roll speed and the take-up roll speed.

There is no particular limitation on the method for forming the recesses or protrusions only on the tips of the polyolefin fiber protrusions. For example, it is possible to adopt a method in which the strand is engraved only on the tip of the projection with a heat application roller. In addition, while passing a fiber having fins continuous in the longitudinal direction of the fiber in a heating furnace in a short time, only fins having a low melting latent heat are melted, cooled, and partially agglomerated so as to protrude only at the tip of the protrusion. A method of forming the part can also be employed.
The heating method for forming the convex portion only at the tip of the protruding portion is not particularly limited as long as the method can raise the temperature to a temperature at which the resin can be melted in a short time. For example, even in a short-time contact in a hot air atmosphere heated to 180 ° C. or higher, the tip of the protrusion has a lower latent heat of fusion than the core of the fiber, so only the tip of the protrusion is melted and aggregated, A convex shape can be formed.

  The polyolefin fiber has a single yarn fineness of 100 to 10,000 dtex, preferably 1000 to 9000 dtex. If the single yarn fineness is less than 100 dtex, the fibers are too thin, the dispersion during mixing with the cement is not uniform, and the fiber ball tends to be formed, which is not preferable in terms of workability and reinforcement. On the other hand, when the single yarn fineness exceeds 10,000 dtex, the contact area of the fiber with the cement mixture decreases, and the adjustment effect is inferior in adjusting the blended fiber amount (volume%).

The polyolefin fibers can be subjected to various treatments before or after cutting to make short fibers. For example, the surface of the fiber may be treated with a surfactant, a dispersant, a coupling agent, or the like, or may be subjected to treatment such as surface activation or crosslinking by corona discharge treatment, ultraviolet irradiation, electron beam irradiation, or the like. Good. In particular, it is preferable to perform a surface hydrophilization treatment with a surfactant or the like from the viewpoint of enhancing dispersibility when blended in a cement-based molded body.
As the surfactant, a hydrophilic surfactant is preferably used in order to improve the affinity between the hydrophobic polyolefin fiber and the cement. Dispersibility is improved by imparting hydrophilicity to the polyolefin fiber, and fiber reinforcing effect is improved by uniformly mixing the fiber and cement.
As the hydrophilic surfactant, it can be used without any particular limitation. Among them, a polyethylene glycol alkyl ester nonionic surfactant, an alkyl phosphate anionic surfactant, a polyhydric alcohol type amide nonionic surfactant Etc. can be preferably used.

As the polyethylene glycol alkyl ester, those in which the long-chain aliphatic alkyl group constituting the polyethylene glycol alkyl ester has 6 to 18, preferably 8 to 16 carbon atoms are preferable from the viewpoint of the stability of the aqueous dispersion and the fiber adhesion. Specific examples of preferable polyethylene glycol alkyl esters include polyethylene glycol laurate, polyethylene glycol oleate, and polyethylene glycol stearate.
The alkyl phosphate is a phosphate having an average carbon number of 18 or less, preferably 6 to 16, more preferably 8 to 14 alkyl groups in one molecule, preferably 1 and an alkali metal salt as a salt. , Alkaline earth metal salts, ammonium salts, and amine salts. Specific examples of preferred alkyl phosphates include salts of higher alcohol phosphates such as octyl phosphate, lauryl phosphate, stearyl phosphate, such as sodium, potassium, magnesium, calcium, and amine salts. The neutralization is preferably 50% or more of the free hydroxyl group, particularly a completely neutralized product.
As the polyhydric alcohol type amido nonion, an addition reaction product of an alkylamine having 4 to 18 carbon atoms and polyglycerin having 3 to 13 hydroxyl groups is used, preferably an alkylamine having 11 to 17 carbon atoms and 3 Addition reactants with polyglycerin having ˜6 hydroxyl groups are used.

  Other preferable surfactants include polyoxyalkylene alkylphenyl ether phosphate esters and polyoxyalkylene fatty acid esters. Specific examples of the polyoxyalkylene alkyl phenyl ether phosphate ester include polyoxyethylene nonyl phenyl ether phosphate ester, polyoxyethylene dodecyl phenyl ether phosphate ester, and specific examples of the polyoxyalkylene fatty acid ester include Examples thereof include polyoxyethylene oleate and polyoxyethylene stearate. These surfactants can be used singly or in combination of two or more.

  The amount of the surfactant attached to the fiber is not particularly limited, but is generally used in the range of 0.05 to 2% by weight with respect to the total fiber from the viewpoint of suppressing the generation of foam when blending cement. If the adhesion amount to the fiber is less than 0.05% by weight based on the total fiber, the polyolefin fiber may not be sufficiently hydrophilic, and if it exceeds 2% by weight, the hydrophilicity will reach its peak, and the fiber kneading will be performed. It is not preferable because air bubbles are generated in the cement fresh at the time, and the physical properties such as compressive strength and bending strength of the cement-based molded body may be lowered. In order to suppress the generation of bubbles, an antifoaming agent can be used in combination with the surfactant treatment on the fiber.

  The method for attaching the surface treatment agent to the polyolefin fiber is not particularly limited, and any of a dipping method, a spray method, and a coating method can be employed. After the surface treatment agent is applied to the fiber, it can be penetrated into the fiber assembly using a squeeze roll or the like, if necessary.

The polyolefin fiber thus obtained is cut into a predetermined length and used as a short fiber for cement reinforcement. From the viewpoint of improving the cracking resistance (toughness) of the cement-based molded body, the short fiber has a smaller thickness (fiber diameter D) and a longer length (fiber length L), that is, an aspect of the short fiber. The higher the ratio (L / D), the better, but the polyolefin short fiber of the present invention has a smaller aspect ratio than the conventional product, that is, even if the fiber length is short as long as the short fiber diameter is the same. It is characterized by a large reinforcing effect.
The polyolefin short fiber of the present invention has a short fiber length (apparent length) of 5 to 80 mm, preferably 5 to 60 mm, and more preferably 5 to 50 mm. If the fiber length is less than 5 mm, it is easy for the cement to come off, and if it exceeds 70 mm, the dispersibility may be poor.

  Next, the polyolefin short fiber of the present invention is compounded as a reinforcing fiber material in cement, fine aggregate, coarse aggregate, water and an appropriate amount of concrete admixture, or cement, fine aggregate, water and an appropriate amount of mortar admixture. It can be used as a cement-based molded body such as concrete and mortar. Here, as the cement, it is possible to use ordinary portland cement, blast furnace cement, silica cement, fly ash cement, white portland cement, hydraulic cement such as alumina cement or cement such as plaster, lime and other pneumatic cement. it can. Examples of fine aggregates include river sand, sea sand, mountain sand, quartz sand, glass sand, iron sand, ash sand, and other artificial sand. Coarse aggregates include reki, gravel, crushed stone, slag, and various artificial light weights. Examples include aggregates. As the admixture, an air entraining agent (AE agent), a fluidizing agent, a water reducing agent, a thickening agent, a water retention agent, a water repellent, a swelling agent and the like can be mixed and used.

  The blending amount of the polyolefin short fibers with respect to the cement is usually 0.05 to 2% by volume with respect to the volume of the cement-based molded body. From the viewpoint of uniform dispersibility of fibers at the time of cement blending, fluidity of blended cement, workability, and improvement in physical properties of cement-based molded article, the blending amount of polyolefin fiber with respect to cement is preferably 0.3 to 2% by volume, More preferably, it is the range of 0.5-1 volume%.

As a method for producing a cement-based molded body, polyolefin short fibers are dispersed in a cement-based powder, cement-based flash or slurry to form a cement-based mixture, which is predetermined by a wet papermaking molding method, extrusion molding or cast molding method. After molding into a shape, various cement-based molded bodies can be produced by natural curing, steam curing, autoclave curing, and the like.
More specifically, it is preferable to use a concrete mixture made of cement, fine aggregate, coarse aggregate, water and the like as base concrete, and after kneading the base concrete, polyolefin fiber is subsequently added and kneaded. Although the kneading time varies depending on the amount of mixing per one time, generally, the base concrete is kneaded for 45 to 90 seconds, and the polyolefin fiber is kneaded for 45 to 90 seconds.

The cement-based molded body thus obtained is particularly suitable as a concrete molded body for civil engineering and construction work. For example, in the concrete road pavement field, it is possible to reduce the amount of reinforcing bars to improve the bending strength by fiber reinforcement, and to reduce the thickness of the concrete plate, which is effective for shortening the construction period and saving raw materials. In addition, when used in the tunnel inner wall spraying method, the fibers are flexible and elastic, hydrophilic and light, so there is little flaking of aggregates and fibers during spraying, less falling of concrete, and yield safety. It is effective in terms.
As a concrete product, it can also be used for sheet piles formed by molding, concrete pulp, piles, poles, etc. of hollow cylindrical products. As road concrete, it can be used for sidewalk concrete flat plates, reinforced concrete U-shaped, concrete guardrails and the like. In addition, it can also be used for plastering mortars, exterior materials and roofing materials as building-related members, and wall materials, reliefs, flooring materials, ceiling materials as interior materials.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

Production Example 1
Using a single-screw melt extruder equipped with a nozzle with 30 holes and a Y-shaped hole, extrusion temperature of 250 ° C. for isotactic polypropylene (Made by Idemitsu Petrochemical Co., Ltd., Y-400GP) with MFR 4 g / 10 min. And melt extruded. After the extruded resin was put into a cooling water tank and solidified, it was stretched 4.6 times in a steam heating chamber at 110 ° C. between two stretching Nelson rollers, and the section was substantially triangular. A strand having a single yarn fineness of 7,100 dtex was obtained.
Next, a parallel pattern uneven roller (φ220 mm, projection tip radius 0.5 mm, depth 0.9 mm, projection pitch 4.4 mm) perpendicular to the pair of upper and lower strands heated with a heating medium of 180 ° C. The clearance was adjusted to 0.9 mm, the roller surface speed was rotated forward at the same speed as the strand, and a concave shape was formed only at the tip portion of the cross section. Thereafter, a polyhydric alcohol type amide nonionic surfactant (manufactured by Takemoto Yushi Co., Ltd.) diluted with water is attached to the strand so as to be equivalent to 0.4% by weight by spraying, and is heated at 90 ° C. with a hot air dryer. Then, after removing the moisture, it was cut to a constant length of 30 mm with a fan-type cutter to obtain a polypropylene short fiber 1 shown in FIG.
The tensile properties of the short polypropylene fiber 1 were a strength of 3.3 cN / dtex, an elongation at break of 18%, and a Young's modulus of 3.9 kN / mm ² .

Production Example 2
The nozzle hole shape is X-type, the draw ratio is 6 times, a stretched strand with a cross shape of approximately cruciform and a single yarn fineness of 6,900 dtex is formed, and an alkyl phosphate amine salt type activator as a surfactant is 0.13% by weight A polypropylene short fiber 2 shown in FIG. 2 was obtained in the same manner as in Production Example 1 except that the material was considerably adhered. The tensile properties of the short polypropylene fiber 2 were a strength of 3.6 cN / dtex, a breaking elongation of 14%, and a Young's modulus of 4.4 kN / mm ² .

Production Example 3
The shape of the nozzle hole is X, the draw ratio is 6 times, the stretched strand is molded with a cross shape of approximately 6600 dtex, and a parallel pattern uneven roller (φ220 mm, protrusion tip radius 0.5 mm, depth 0.9 mm) 2 in the same manner as in Production Example 1 except that 0.11% by weight of an alkyl phosphate amine salt-based activator is attached as a surfactant. Short fiber 3 was obtained. The tensile properties of the short polypropylene fiber 3 were a strength of 3.7 cN / dtex, a breaking elongation of 16%, and a Young's modulus of 5.8 kN / mm ² .

Production Example 4
A single yarn with a △ cross section in the same manner as in the first stage of Production Example 1 except that a single screw melt extruder equipped with a nozzle having 30 nozzle holes and a △ shape nozzle was used and the draw ratio was 5 times. A drawn strand having a fineness of 7,930 dtex was obtained.
Next, this strand is passed through a propane gas flame burner for an extremely short time within 0.3 seconds, and only the tip portion of the cross-section Δ shape is melted and rapidly cooled with air in an aggregated state, with an average interval of 0.5 mm. A thorn-shaped molten mass was shaped. After that, 0.5 wt% of alkyl phosphate potassium salt surfactant diluted with water was attached, and after removing moisture at 90 ° C. with a hot air dryer, it was cut to a constant length of 30 mm with a fan type cutter. The polypropylene short fiber 4 having a substantially triangular cross section shown in FIG. 3 was obtained.
The tensile physical properties of this polypropylene short fiber 4 were strength 3 cN / dtex, breaking elongation 22%, Young's modulus 1.65 kN / mm ² .

Production Example 5
Except for changing the nozzle hole shape to X and changing the draw ratio to 6 times, a drawn strand having a substantially cross-shaped cross section and a single yarn fineness of 7,100 dtex was obtained in the same manner as in the previous stage of Production Example 1.
Next, this strand was treated in the same manner as in the latter stage of Production Example 4 to obtain polypropylene short fibers 5 shown in FIG. The tensile physical properties of this short polypropylene fiber 5 were strength 2.3 cN / dtex, breaking elongation 12%, and Young's modulus 4.40 kN / mm ² .

Example 1
(1) 60L using pan rotary mixer, cement 360 kg / m ^3, fine aggregates 1,065kg / m ^3, coarse aggregate 691kg / m ^3, were premixed for 60 seconds at a mixing ratio of water 165 kg / m ³ . Next, polypropylene short fibers 1 having a substantially triangular cross section are added at a ratio of 11 kg / m ³ , and a total amount of 35 L and a further 60 are added so that the fiber amount is 1.2 vol% and the water / cement ratio is 46 wt%. Mix for 2 seconds to obtain ready-mixed concrete.
Using this ready-mixed concrete, physical property test concrete was produced according to the production of the concrete test specimen of the following (2), and each test was performed according to the concrete properties test method of the following (3). The results are shown in Table 1.

(2) Manufacture of concrete test specimens Concrete test specimens were manufactured in accordance with JSCE F552 (Japan Society of Civil Engineers / How to make steel fiber reinforced concrete strength and toughness test specimens) using the following materials. . Note that the concrete was cured at room temperature for 24 hours, then released, and cured in water for 6 days. Then, what was cured at room temperature in the atmosphere until the age of 28 days was used as a specimen.
・ Cement: Ordinary Portland cement (specific gravity: 3.16)
-Coarse aggregate: surface dry specific gravity 2.65, maximum particle size 25mm
-Fine aggregate: surface dry specific gravity 2.59, maximum particle size 5mm
・ Water: City water ・ AE agent: Polycarboxylic acid-based high-performance AE water reducing agent

(3) Concrete physical property test method / compressive strength: According to JSCE G551 (Japan Society of Civil Engineers / Compressive strength test method for steel fiber reinforced concrete).
-Bending strength and bending toughness: Follow JSCE G552 (Japan Society of Civil Engineers / Bending strength and bending toughness test method of steel fiber reinforced concrete).
-Slump: According to JIS A1101 (Concrete slump test method).
-Air amount: According to JIS A1128 (Test method using pressure of air amount of concrete that has not yet solidified).

Comparative Example 1
Using the 60L pan rotary mixer, cement 360 kg / m ^3, fine aggregates 1065kg / m ^3, coarse aggregate 691kg / m ^3, pre 60 seconds mixing ratio of water 165 kg / m ^3, water / cement ratio of 46 The mixture was mixed in a total amount of 35 L so as to obtain a blending ratio by weight to obtain ready-mixed concrete.
Using this ready-mixed concrete, each test was performed in the same manner as in Example 1 (2) and (3). The results are shown in Table 1.

Example 2
Using 100L pan rotary mixer, cement 455 kg / m ^3, fine aggregates 1,021kg / m ^3, coarse aggregate 638kg / m ^3, were premixed for 60 seconds at a mixing ratio of water 200 kg / m ^3, the mixture The AE agent was added to the cement weight ratio of 0.8%, and the antifoaming agent was added to the cement weight ratio of 0.8%. Next, polypropylene short fibers 2 having a substantially cross-shaped cross section are added at a ratio of 9.1 kg / m ³ , and the total amount is adjusted so that the amount of short fibers is 1.0% by volume and the water / cement ratio is 44% by weight. The mixture was further mixed at 50 L for 60 seconds to obtain ready-mixed concrete.
Using this ready-mixed concrete, each test was performed in the same manner as in Example 1 (2) and (3). The results are shown in Table 1.

Example 3
Each test was performed in the same manner as in Example 2 except that the addition ratio of the short polypropylene fiber 2 was 4.55 kg / m ³ and the short fiber amount was 0.5% by volume.

Example 4
Except for using the polypropylene short fiber 4, ready-mixed concrete was prepared in the same manner as in Example 2, and a concrete property test was performed in the same manner as in Examples 1 (2) and (3).

Comparative Example 2
Using 100L pan rotary mixer, cement 455 kg / m ^3, fine aggregates 1021kg / m ^3, coarse aggregate 638kg / m ^3, pre 60 seconds mixing ratio of water 200 kg / m ^3, water / cement ratio of 44 The mixture was mixed in a total amount of 50 L so as to obtain a weight percent blend. During this mixing, an AE agent was added at a cement weight ratio of 0.8%, and an antifoaming agent was added at a cement weight ratio of 0.8%. Furthermore, mixing was continued as it was for 60 seconds to obtain ready-mixed concrete.
Using this ready-mixed concrete, each test was performed in the same manner as in Example 1 (2) and (3). The results are shown in Table 1.

Example 5
Using 100L pan rotary mixer, cement 455 kg / m ^3, fine aggregates 985kg / m ^3, coarse aggregate 615kg / m ^3, were premixed for 60 seconds at blending ratio of water 200 kg / m ^3, during the mixing An AE agent was added at a cement weight ratio of 0.6%, and an antifoaming agent was added at a cement weight ratio of 0.015%. Next, polypropylene short fiber 3 was added at a ratio of 4.55 kg / m ^{3, and} the mixture was further mixed for 60 seconds at a total amount of 50 L so that the fiber amount was 0.5% by volume and the water / cement ratio was 44% by weight. I got raw concrete. Furthermore, mixing was continued as it was for 60 seconds to obtain ready-mixed concrete.
Using this ready-mixed concrete, each test was performed in the same manner as in Example 1 (2) and (3). The results are shown in Table 1.

Example 6
A ready-mixed concrete was prepared in the same manner as in Example 5 except that polypropylene short fibers 3 were added at a ratio of 0.46 kg / m ^{3 and} the amount of fibers was 0.05% by volume. Example 1 (2), Concrete property tests were conducted in the same manner as (3).

Example 7
Except for using the polypropylene short fiber 5, a ready-mixed concrete was prepared in the same manner as in Example 5, and a concrete property test was performed in the same manner as in Examples 1 (2) and (3).

Example 8
A ready-mixed concrete was prepared in the same manner as in Example 5 except that polypropylene short fibers 5 were added at a ratio of 0.46 kg / m ^{3 and} the amount of fibers was 0.05% by volume, and Example 1 (2), Concrete property tests were conducted in the same manner as (3).

Comparative Example 3
Using 100L pan rotary mixer, cement 455 kg / m ^3, fine aggregates 985kg / m ^3, coarse aggregate 615kg / m ^3, pre 60 seconds mixing ratio of water 200 kg / m ^3, water / cement ratio of 44 The mixture was mixed in a total amount of 50 L so as to obtain a blending ratio by weight. During the mixing, 0.6% by weight of the AE agent and 0.015% by weight of the defoaming agent were added. Furthermore, mixing was continued as it was for 60 seconds to obtain ready-mixed concrete.
Using this ready-mixed concrete, each test was performed in the same manner as in Example 1 (2) and (3). The results are shown in Table 1.

第１表から明らかなとおり、実施例で用いたコンクリートの曲げ靭性は、何れも、対応する比較例（繊維無配合）の生コンクリートの曲げ靭性より優れていた。

As is clear from Table 1, the bending toughness of the concrete used in the examples was superior to the bending toughness of the ready-mixed concrete of the corresponding comparative example (containing no fiber).

1 is a schematic diagram of a polyolefin short fiber of the present invention obtained in Production Example 1. FIG. It is a schematic diagram of the polyolefin short fiber of the present invention obtained in Production Examples 2 and 3. 6 is a schematic diagram of a polyolefin short fiber of the present invention obtained in Production Example 4. FIG. 6 is a schematic view of a polyolefin short fiber of the present invention obtained in Production Example 5. FIG.

Claims (4)

A drawn fiber having a polypropylene resin as a main component, wherein the cross-sectional shape of the fiber is a substantially polygonal shape having 3 to 6 protrusions, and at the tip of the protrusions in the longitudinal direction of the fibers. along arrangement interval is formed concave or convex portions of 0.5 to 5 mm, cement reinforcing polypropylene staple fiber, wherein the fiber length of 5 to 60 mm. The polypropylene short fiber for cement reinforcement according to claim 1, wherein the cross-sectional shape of the fiber is a substantially polygonal shape having four protrusions. 0.05 to 2% by weight of at least one surfactant selected from a polyethylene glycol alkyl ester nonionic surfactant, an alkyl phosphate anionic surfactant, and a polyhydric alcohol amide nonionic surfactant The polypropylene short fiber for cement reinforcement according to claim 1 or 2, which is adhered. A cement-based molded body comprising 0.05 to 1 % by volume of the cement-reinforced polypropylene short fibers according to any one of claims 1 to 3 .

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