JP2009102183A - Fiber-reinforced concrete, and method for producing fiber-reinforced concrete member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide fiber-reinforced concrete which has more excellent dynamic performance, endurance performance and execution property by reducing shrinkage deformation during curing, and to provide a method for producing a fiber-reinforced concrete member. <P>SOLUTION: The fiber-reinforced concrete is obtained by: a cutting stage S1 where a fiber material composed of a polyvinyl alcohol fiber is cut in such a manner that an aspect ratio is controlled to 20 to 200 so as to be a short fiber; a shrinking stage S1 where the cut short fiber is subjected to heat shrinking treatment; and a kneading stage S3 where the heat-treated short fiber is mixed into concrete so as to be the range of 0.5 to 6.0% by volume ratio. A method for producing a fiber-reinforced concrete member comprises: a placing stage S4 where the fiber-reinforced concrete is placed into a prescribed part; and a curing stage S5 where the placed fiber-reinforced concrete is cured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fiber reinforced concrete reinforced by mixing fibers and a method for manufacturing a fiber reinforced concrete member.

  In recent years, in the field of civil engineering and architecture, ultra-high-strength fiber reinforced concrete has been applied to various concrete structures for the purpose of reducing the thickness and weight of members, improving the degree of freedom of design, and improving durability.

Conventionally, such fiber reinforced concrete includes a mixture of short steel fibers and a mixture of organic short fibers such as polyvinyl alcohol short fibers (hereinafter sometimes simply referred to as “PVA short fibers”). is there.
Among these, PVA short fibers are non-magnetic materials, so that they can meet the demands of non-magnetic material structures such as hospital facilities and do not need to be subjected to rust prevention. The demand for reinforced concrete is increasing.

For example, Patent Document 1 discloses an invention in which a composition having an increased tensile strength is produced by mixing PVA short fibers in cement mortar or concrete.
Patent Document 2 discloses a hardened fiber-reinforced cement obtained by mixing two or more types of PVA short fibers having different aspect ratios as cement fibers into cement concrete.
Furthermore, Patent Document 3 discloses a high-strength cement-based matrix obtained by mixing a large amount of organic short fibers such as polyvinyl alcohol, polyacrylonitrile, polyethylene, polyamide, polypropylene, aramid, and carbon fiber. Organic fiber reinforced concrete is disclosed.
JP 59-8664 A JP-A-62-241852 JP-T-2002-514567

  Conventionally, fiber reinforced concrete in which organic short fibers are mixed in a high-strength cementitious matrix is obtained by mixing PVA short fibers in a high-strength cement-based matrix in a volume ratio of 2 to 6%, and has a compressive strength. Generally, the tensile strength obtained by 150 to 180 MPa, the split tensile test is 7 to 10 MPa, and the bending tensile strength in the bending test is about 20 to 23 MPa (bending test using a 4 cm × 4 cm × 16 cm specimen).

  However, the conventional fiber reinforced concrete is a stage from the start of setting to the initial strength development (compressive strength of about 1 to 5 MPa), and the strength development (in terms of compressive strength) that can be demolded by increasing the strength. Large shrinkage deformation occurs in the stage up to about 50 to 70 MPa) (hereinafter, the stage from the start of condensation until the strength at which demolding can be developed may be referred to as “primary curing”). It was necessary to take various measures such as dimensional adjustment and restraint measures for embedded hardware.

  In addition, since conventional fiber reinforced concrete materials are subjected to thermal curing at 90 ° C. for 48 hours after demolding (hereinafter sometimes simply referred to as “secondary curing”), large shrinkage deformation may occur. However, there is a problem that applicable structures are limited.

Note that the amount of shrinkage and deformation generated during the primary curing of the fiber reinforced concrete increases when the temperature of the primary curing is high, and the increase amount is sensitively influenced by the temperature of the primary curing.
And if the member has a three-dimensionally complicated shape, even if the primary curing atmosphere temperature is controlled to be spatially uniform, the heat due to the temperature rise due to the hydration reaction depends on the shape of the member. In order to generate | occur | produce, it is difficult to make uniform the spatial temperature distribution of a member. For example, when the thickness of the member is large, after the temperature rises due to heat of hydration reaction, it takes time for heat radiation and the temperature becomes higher than that of the thin member. Therefore, at the time of primary curing, the temperature distribution with spatial variation of the members made of the conventional fiber reinforced concrete material gives a contraction amount distribution with spatial variation. When shrinkage with spatial variation occurs, when the mold is removed after primary curing, the deformation of the shrinkage with spatial variation remains in the member, so the member is deformed such as “bend” or “sledge”. Will occur. Therefore, when manufacturing a member to which a conventional fiber reinforced concrete material is applied, it has been difficult to form the member shape according to the shape of the mold.

  Furthermore, since the amount of shrinkage and deformation of the fiber reinforced concrete material is large during the primary curing and the secondary curing, cracks may occur due to constraints due to the formwork or constraints due to embedded metal such as inserts.

  The present invention was made to solve such problems, and by reducing the amount of shrinkage deformation during curing, a fiber reinforced concrete having better mechanical performance, durability performance and workability, and It aims at providing the manufacturing method of a fiber reinforced concrete member.

  In order to solve the above problems, the fiber reinforced concrete of the present invention is a fiber reinforced concrete obtained by mixing short fibers with a volume ratio of 0.5% to 6.0%, and the short fibers are preliminarily obtained. While being subjected to heat treatment, it is provided with a shrinkage strain and includes organic short fibers cut so as to have an aspect ratio of 20 to 200.

According to such fiber reinforced concrete, it becomes possible to significantly reduce shrinkage deformation caused by depending on the temperature at the time of curing, so a material with better mechanical performance, durability performance and workability is generated. Therefore, it is preferable.
In addition, since the amount of shrinkage deformation becomes small, the risk of cracking is reduced by restraining the formwork or restraining the embedded hardware. In addition, the risk of occurrence of variation in shrinkage, etc., is reduced in the member manufactured from the fiber reinforced concrete, and a member with high dimensional accuracy can be manufactured.

Furthermore, by mixing short fibers in a volume ratio within the range of 0.5% to 6.0%, it exhibits a high flow and a fresh property of self-filling performance, and obtains a high tensile reinforcement effect after curing. This is preferable.
The short fibers may contain other fiber materials such as steel fibers in addition to the organic short fibers.

The fiber reinforced concrete includes cement, silica fume, a pozzolanic reactant, an aggregate having a maximum particle size of 2.5 mm or less, at least one dispersant, and water. If it is present, it is preferable because it is possible to produce a material having high fluidity, excellent self-filling performance, and excellent durability after hardening by a dense structure.
As the pozzolanic reactant, for example, precipitated silica, fly ash, blast furnace slag, volcanic ash, silica sol, stone powder and the like can be suitably used.

  Moreover, if the organic short fiber which concerns on the said fiber reinforced concrete is a polyvinyl alcohol fiber which has the shape stability whose shrinkage rate is 8% or less in boiling water of 100 degreeC, a higher tensile reinforcement effect can be acquired. This is preferable because it is possible. In particular, when mixed in a high-strength cementitious matrix, it is suitable because it has the strength and elastic modulus expected for short fibers.

  Moreover, the manufacturing method of the 1st fiber reinforced concrete member of this invention cut | disconnects the fiber material which consists of polyvinyl alcohol fibers so that an aspect-ratio may be 20-200, The cutting process which produces a short fiber, The said short fiber And a kneading step for producing a fiber reinforced concrete in which the short fibers subjected to the heat shrink treatment are mixed so that the volume ratio is within a range of 0.5% to 6.0%. And a placing step for placing the fiber reinforced concrete at a predetermined location, and a curing step for curing the placed fiber reinforced concrete.

  Further, in the second method for producing a fiber-reinforced concrete member of the present invention, an aspect ratio of a fiber material made of polyvinyl alcohol fiber is subjected to a heat shrinkage treatment, and the fiber material subjected to the heat shrinkage treatment has an aspect ratio. A cutting step of cutting short fibers to form 20 to 200, and mixing the short fibers with concrete so that the volume ratio is within a range of 0.5% to 6.0%, thereby reinforcing the fibers. The method includes a kneading step for producing concrete, a placing step for placing the fiber-reinforced concrete at a predetermined location, and a curing step for curing the placed fiber-reinforced concrete.

  According to such a method for manufacturing a fiber reinforced concrete member, it is possible to significantly reduce shrinkage deformation caused by depending on the temperature during curing, so that it has better mechanical performance, durability performance and workability. Therefore, it is preferable.

  Further, in the shrinking step in the method for producing a fiber reinforced concrete member, the fiber material is heated in a hot water of 40 ° C. to 90 ° C. or in the air of 40 ° C. to 90 ° C. for 24 hours to 72 hours, thereby producing the fiber material. If the moisture on the surface or inside of the fiber material is evaporated so that the moisture content is at most 5% or less, the shrinkage deformation at the time of curing is given It is effective to reduce.

  According to this invention, it becomes possible to produce | generate the fiber reinforced concrete and fiber reinforced concrete member which had the more excellent mechanical performance, durability performance, and workability by reducing the amount of shrinkage deformation during curing.

Hereinafter, preferred embodiments of the present invention will be described.
The fiber-reinforced concrete according to the present embodiment is obtained by mixing cement, silica fume, pozzolanic reactant, aggregate having a maximum particle size of 5 mm or less, at least one dispersant, and water. It is configured by mixing short fibers made of PVA fibers (hereinafter simply referred to as “PVA short fibers”) into the cement matrix.

  Hereinafter, the detail of each material used for the fiber reinforced concrete of this invention is demonstrated.

As the cement, a low heat Portland cement or a medium heat Portland cement having an average particle diameter of 4 to 18 μm and a brain value of 2000 to 4000 cm ² / g is used. In addition, the kind of cement is not limited, For example, normal Portland cement, early-strength Portland cement, sulfate Portland cement, etc. can also be used.

Silica fume having an average particle diameter of 0.15 to 3.00 μm and a brain value of 150,000 to 300,000 cm ² / g is used. In place of silica fume, a compound selected from kaolin derivatives, precipitated silica, classified fly ash, or the like may be used.

As the pozzolanic reaction particles, those having an average particle diameter of 4 to 10 μm and a brain value of 3,000 to 7,500 cm ² / g are used. As such a material, precipitated silica, fly ash, blast furnace slag, volcanic ash, silica sol, stone powder and the like can be suitably used.

  Here, the silica fume and pozzolanic reaction particles contribute to the improvement of durability and the compression / tensile strength by densifying the cement matrix by the micro filler effect and the cement dispersion effect of fine particles containing cement. The pozzolanic reaction is a reaction in which a pozzolanic substance reacts with an alkali substance produced by a cement hydration reaction and gradually becomes a hardened body, and contributes to long-term and stable strength development.

Aggregate shall be fine sand with a maximum particle size D _max of 2.5 mm or less and an average particle size of 0.1 mm to 0.8 mm, which is hard and has a small water absorption rate, and does not contain coarse aggregate. To do.

  Dispersants include water-soluble vinyl copolymers having phenoxyl groups and carbonyl groups, acrylates, methallyl sulfonates, lignosulfonates, alkali metal purinaphthalene sulfonates, alkali metal polycarboxylates A so-called plasticizer such as salt is used. Moreover, only one type or several types of dispersants may be used.

  Water is added so that the weight ratio of water to cement is 22% to 30%.

The PVA short fibers are mixed so that the volume ratio is 0.5% to 6.0%.
This PVA short fiber gives a shrinkage strain by applying heat treatment to a fiber material made of polyvinyl alcohol fiber having shape stability with a shrinkage rate of 8% or less in boiling water at 100 ° C., and an aspect ratio of 20 to It was cut to 200.

  Polyvinyl alcohol (PVA) is a synthetic resin obtained by saponifying polyvinyl acetate, and is a water-soluble polymer having strong hydrophilicity due to the presence of many hydroxy groups (—OH) in the molecule. . The PVA fiber according to the present embodiment ensures morphological stability by performing high stretching, high heat treatment, and crosslinking treatment so that PVA becomes insoluble in water at the time of production.

  Moreover, the PVA fiber used in the present embodiment has a mechanical performance having a tensile strength of 500 MPa or more and an elastic modulus of 13 GPa or more. Even when immersed in a saturated aqueous solution of calcium hydroxide at 90 ° C. for 48 hours, the decrease in tensile strength and elastic modulus is 10% or less. In addition, it has shape stability with a shrinkage rate of 8% or less in boiling water at 100 ° C.

  The shape of the PVA fiber is not limited, and it is possible to use a deformed cross-sectional shape in addition to a deformed cross section such as a circular cross section, a rectangular cross section, or a polygon cross section. For example, for the purpose of improving the adhesion between the fiber and the cementitious matrix, the fiber has a deformed cross-section that is twisted, is deformed into a corrugated shape, has a hook or hook at the end. The thing and the edge part may be crushed and what is called a dog horn shape may be sufficient. Moreover, you may use what changed the roughness of the fiber in the length direction of the fiber, or changed the cross-sectional area of the fiber. Further, the fibers may be formed by knitting several fibers into a cable shape, braided knitting, or integrating by twisting.

Next, the manufacturing method of the fiber reinforced concrete member of this embodiment is demonstrated.
In this embodiment, as shown to Fig.1 (a), a fiber reinforced concrete member is manufactured by cutting process S1, shrinkage | contraction process S2, kneading | mixing process S3, placing process S4, and curing process S5.

  The cutting step S1 is a step of creating a PVA short fiber by cutting the fiber material so that the aspect ratio is 20 to 200.

The shrinking step S2 is a step of subjecting the PVA short fibers created in the cutting step S1 to a heat shrinking process, and the PVA short fibers are heated at 40 ° C. to 90 ° C. or in the air at 40 ° C. to 90 ° C. for 24 hours. Perform by heating for ~ 72 hours.
The shrinkage of about 1% to 6% is applied to the PVA short fiber by heat shrink treatment to shorten the length of the PVA short fiber, and the PVA short fiber has a moisture content of 5% or less. Moisture on the surface and inside evaporates.

  In the kneading step S3, a cement-based matrix made of cement, silica fume, a pozzolanic reactant, an aggregate having a maximum particle size of 5 mm or less, at least one dispersant, and water is used. By kneading.

  In the kneading step S3 according to the present embodiment, as shown in FIG. 1B, a liquid is applied to the dry kneading step S31 in which the powder portion of the cement matrix is kneaded and the powder portion kneaded in the dry kneading step S31. It includes a wet kneading step S32 in which parts are added and kneaded, and a fiber kneading step S33 in which PVA short fibers are introduced into the cement matrix kneaded in the wet kneading step S32.

  In the dry kneading step S31, cement, silica fume, pozzolanic reaction particles, and aggregate, which are powder portions of the cement matrix, are kneaded in a dry state. The mixing method and means of each material in the dry kneading step S31 are not limited, and may be appropriately selected from known methods and means.

  In the wet-kneading step S32, after the mixing of the powder portion of the cement-based matrix is completed, water, a dispersant, and the like, which are liquid portions of the cement-based matrix, are added and mixed, and the predetermined fluidity is added to the cement-based matrix. To express. The kneading method and means in the wet kneading step S32 are not limited, and may be appropriately selected from known methods and means.

In the fiber kneading step S33, the PVA short fibers are mixed and further kneaded into the cement matrix in which the predetermined fluidity is obtained in the wet kneading step S32. The kneading method and means in the fiber kneading step S33 are not limited, and may be appropriately selected from known methods and means.
In the fiber kneading step S33, the PVA short fibers are added so that the volume ratio with respect to the entire fiber reinforced concrete (the total of the cement matrix and the PVA short fibers) is in the range of 0.5% to 6.0%. To do.

  Here, it is desirable to use the PVA short fibers as soon as possible after the heat treatment. It is desirable to manage so as to avoid moisture absorption of the PVA short fibers during the storage period after the heat treatment of the PVA short fibers until use. In general, it is known that the elastic modulus and tensile strength of the PVA fiber decrease as the water content increases. It is also known that the hydrophilic capacity originally possessed by PVA decreases when the water content increases. Therefore, when using PVA fibers, quality control is required so that the water content is not more than a predetermined level.

  In the placing step S4, a cement-based matrix (fiber reinforced concrete) containing the fibers kneaded in the kneading step S3 is placed at a predetermined location by a known means.

  In the curing step S5, first, after concrete placement, primary curing is performed in a temperature environment of 20 ° C. to 45 ° C. for 18 hours to 48 hours. After the primary curing, when a predetermined strength is developed, the mold is removed and secondary curing is performed. As the secondary curing, thermal curing is performed for 48 hours to 72 hours in a temperature environment of 60 ° C to 95 ° C. The secondary curing is not limited to the thermal curing described above, and air curing at room temperature or underwater curing performed with conventional concrete may be employed. Moreover, the curing method of the fiber reinforced concrete is not limited to the above method.

  As described above, according to the fiber-reinforced concrete and the method for manufacturing fiber-reinforced concrete according to the present embodiment, the PVA short fibers that have been subjected to the shrinking process in advance are used in the shrinking step S1, and therefore, it occurs during curing after placing. The shrinkage can be greatly reduced, and various measures such as the dimension adjustment of the mold and the restraint measures for the embedded hardware, which have been conventionally required, can be omitted.

  In addition, since the temperature dependence of the primary curing is eliminated and the amount of shrinkage deformation is greatly reduced, the occurrence of “sledge” and “bend” deformation of a concrete member made of fiber-reinforced concrete is prevented.

  Moreover, since the amount of shrinkage deformation of the fiber reinforced concrete is smaller than the conventional one, the risk of cracking due to the restraint of the formwork or the embedded hardware is greatly reduced, and the quality of the member production can be improved. .

  The fresh property such as fluidity of the fiber reinforced concrete according to the present embodiment is equivalent to the conventional fiber reinforced concrete in which the PVA short fibers are not heat-treated, and thus has high fluidity and excellent self-filling performance.

  Moreover, the compressive strength of the concrete member by the fiber reinforced concrete according to the present embodiment is equivalent or increased by about 5% compared to the conventional fiber reinforced concrete in which the PVA short fibers are not subjected to heat treatment. However, when the heat treatment of the fiber material is performed in water and the PVA short fibers are used in a wet state (moisture content is 7% to 12%), the compressive strength is reduced by about 10%. It is desirable that the water content is at most 5% at least.

  Further, the bending strength of the concrete member made of fiber reinforced concrete according to the present embodiment is equal to or increased by about 2% to 3% compared with the concrete member made of fiber reinforced concrete. However, when the PVA short fibers are used in a wet state with a moisture content of 7% to 12%, the bending strength decreases by about 5% to 7%. Therefore, after the heat treatment, the dry state, that is, the moisture content is at most 5% or less. Is desirable.

  The conventional fiber reinforced concrete has verified the long-term durability of the material on the assumption that secondary curing is performed at 90 ° C. The fiber reinforced concrete according to the present embodiment has a temperature of 90 ° C. or less even if the temperature of the heat treatment of the polyvinyl alcohol fiber is high, and does not exceed the design temperature by secondary curing. However, it is considered that the long-term material durability is not affected.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and it goes without saying that the above-described constituent elements can be appropriately changed in design without departing from the spirit of the present invention.
For example, in the said embodiment, as a manufacturing method of a fiber reinforced concrete member, although it shall carry out in order of cutting process S1, shrinkage | contraction process S2, kneading | mixing process S3, placing process S4, and curing process S5, as shown in FIG. Alternatively, the shrinking step S1 ′, the cutting step S2 ′, the kneading step S3, the placing step S4, and the curing step S5 may be performed in this order.
That is, after the fiber material is shrunk in the shrinking step S1 ′, it may be cut in the cutting step S2 ′ so that the aspect ratio becomes 20 to 200.

In the above embodiment, high-strength fiber reinforced concrete is produced by mixing PVA short fibers into a cement-based matrix. However, fiber reinforced concrete can be obtained by mixing PVA short fibers into general concrete. It may be configured. Further, the composition and dimensions of each material constituting the cement-based matrix are not limited to the contents described above.
What is necessary is just to adjust the mixing amount of a PVA short fiber within the range of 0.5 to 6.0% with respect to the volume of the whole fiber reinforced concrete according to the other material which comprises fiber reinforced concrete. For example, when mixed in a cement-based matrix, 2.0 to 6.0%, and when mixed in general concrete, 0.5 to 1.5% is mixed to maintain high fluidity. It is good also as a structure.

  Further, in the above-described embodiment, as the kneading step of the cement-based matrix, a method of kneading the short fiber after kneading only the powder material, adding the liquid material, and further kneading to develop a predetermined fluidity However, the order in which the materials are charged in the kneading step is not limited, and may be set as appropriate.

Moreover, although the said embodiment demonstrated the case where a PVA short fiber was used as a short fiber, the organic type short fiber which can be used as a short fiber is not limited to a PVA short fiber, For example, a polypropylene fiber Alternatively, other organic short fibers such as polyethylene fibers may be used.
Moreover, although the said embodiment demonstrated the case where only a PVA short fiber was used as a short fiber, other fibers other than PVA short fiber, such as adding a steel short fiber other than a PVA short fiber, are mixed. It may be. In addition, when mixing steel short fiber, it is suitable if steel short fiber mixes about 1-2% by volume ratio, and PVA short fiber mixes about 3-4% by volume ratio.

  Needless to say, the weight ratio of cement, pozzolanic reaction particles, aggregate, and the like is not limited and may be set as appropriate.

  Hereinafter, the result of the demonstration experiment performed on the effect of reducing the shrinkage deformation of the fiber reinforced concrete according to the present invention will be described.

  In this demonstration experiment, in addition to the fiber reinforced concrete mixed with the PVA short fibers previously subjected to the heat shrink treatment according to the present invention, as a comparative example, the fiber reinforced concrete mixed with the steel fibers and the heat shrink treatment are performed. The shrinkage deformation of a conventional fiber reinforced concrete mixed with untreated PVA short fibers was also measured.

  In this demonstration experiment, as shown in FIG. 3, the shrinkage deformation of the fiber reinforced concrete 2 generated during curing is measured using a steel mold 1 of 10 cm × 10 cm × 40 cm. A Teflon (registered trademark) is provided on the inner side of the steel mold 1 to reduce the friction between the cement-based matrix material (fiber reinforced concrete 2) and the wall surface of the steel mold 1 so as not to constrain the shrinkage deformation of the material. ) Sheet 3 was installed. Further, a mold type strain gauge 4 capable of guaranteeing the temperature against a high temperature (upper limit temperature: 100 ° C.) is set in the center of the steel mold 1. In the experiment, the temperature data, shrinkage deformation, in a state where the material to be tested (fiber reinforced concrete 2) is placed in the steel mold 1 and placed in a thermo-hygrostat capable of controlling the necessary curing temperature. Get quantity data in chronological order. In the drawings, reference numeral 5 denotes a lead wire connected to the strain gauge 4.

Each demonstration experiment was conducted according to the following procedure.
First, fiber reinforced concrete is placed on the steel mold 1 to start primary curing and measurement. After raising the temperature at 15 ° C./hour, primary curing is performed for 48 hours within a curing temperature range of 20 ° C. to 50 ° C.
Next, the temperature of the primary curing is lowered at 15 ° C./hour, and demolding is performed at a temperature of 20 ° C.
Further, after demolding, secondary curing is performed at 90 ° C. for 48 hours. At this time, the temperature is raised and lowered at 15 ° C./hour.
Note that the strain obtained from the gauge embedded in the specimen is measured including the amount of deformation caused by thermal expansion of the specimen. Accordingly, the strain amount shown in FIGS. 4 to 7 is a result of correcting the deformation amount expanded and deformed due to the thermal change of the specimen with the material thermal expansion coefficient as 13 μ / ° C. with reference to the temperature at the time of placing the material. .

(1) Shrinkage Deformation of Steel Fiber Reinforced Concrete First, as Comparative Experiment A, the results of measuring shrinkage deformation during curing for steel fiber reinforced concrete are shown.

In comparative experiment A, using steel fiber reinforced concrete containing steel short fibers as a test material, test A1 performed at a primary curing temperature of 20 ° C., test A2 performed at a primary curing temperature of 40 ° C., and Using a test material consisting only of a cement-based matrix, three tests of test A3 performed at a primary curing temperature of 40 ° C. were measured.
As the steel fiber reinforced concrete, a steel fiber having a diameter of 0.2 mm and a length of 15 mm mixed with 2% by volume in a cement matrix was used.

FIG. 4 shows the behavior of shrinkage deformation of each test material in Comparative Experiment A. In FIG. 4, the horizontal axis represents the elapsed time since the fiber reinforced concrete was placed on the mold, and the vertical axis represents the shrinkage strain. The minus of the strain value indicates shrinkage deformation, and the strain is indicated by micro (μ: × 10 ⁻⁶ ).

  The end time of the primary curing is about 60 hours in elapsed time. As a result of the comparative experiment A, as shown in FIG. 4, the case where the temperature of the primary curing is 20 ° C. (test A1) and the case of 40 ° C. (test A2) show similar shrinkage behavior, and the steel fiber reinforcement In the case of concrete, it can be seen that there is little effect on the amount of shrinkage deformation due to differences in the temperature of primary curing. In the case of steel fiber reinforced concrete (tests A1 and A2), the shrinkage after the primary curing was 300 to 350 μm regardless of the temperature of the primary curing. In addition, the steel fiber reinforced concrete (tests A1 and A2) showed a shrinkage behavior similar to the shrinkage behavior (test A3) of the test material containing only the cementitious matrix not containing steel fibers.

  As described above, from the comparison results of the three types of shrinkage behaviors (tests A1, A2, and A3), the shrinkage during the primary curing and the secondary curing of these specimens is a deformation behavior due to self-shrinkage of the cementitious matrix itself. Presumed. That is, it is estimated that the deformation behavior is due to self-shrinkage due to the large amount of unit cement and the absence of coarse aggregate. The thermal expansion coefficient of the steel fiber itself is 10 μ / ° C., which is not significantly different from the thermal expansion coefficient of the cementitious matrix (13 μ / ° C.), and the effect on the ultra high strength fiber reinforced concrete due to the thermal expansion of the steel fiber. Are considered to be few.

(2) Shrinkage deformation of conventional fiber reinforced concrete Next, as a comparative experiment B, the results of measurement of shrinkage deformation during curing of conventional fiber reinforced concrete using PVA short fibers not subjected to shrinkage treatment in advance are shown. Show.

In comparative experiment B, fiber reinforced concrete containing PVA short fibers not subjected to shrink heat treatment in advance as a test material was used, and test B1 was performed at a primary curing temperature of 20 ° C, and the primary curing temperature was performed at 40 ° C. The test B2, the test B3 conducted at a primary curing temperature of 50 ° C., and the test B4 conducted at a primary curing temperature of 40 ° C. using a test material consisting only of a cement-based matrix were measured.
As the conventional fiber reinforced concrete, a PVA short fiber having a diameter of 0.3 mm and a length of 15 mm mixed with 3% by volume in a cement matrix was used.

FIG. 5 shows the behavior of shrinkage deformation of each test material in Comparative Experiment B. In FIG. 5, the horizontal axis represents the elapsed time since the fiber reinforced concrete was placed on the mold, and the vertical axis represents the shrinkage strain. The minus of the strain value indicates shrinkage deformation, and the strain is indicated by micro (μ: × 10 ⁻⁶ ).

  As shown in FIG. 5, in the conventional fiber reinforced concrete, the difference in shrinkage deformation appears remarkably in the results of each test (tests B1, B2, B3) performed by changing the temperature of the primary curing, The influence of the temperature (20 ° C. to 50 ° C.) on the amount of shrinkage deformation is large, and it has been demonstrated that the amount of shrinkage deformation after primary curing increases as the primary curing temperature increases.

  Moreover, in each test (test B1, B2, B3), even if the conditions for secondary curing (after demolding, 48 hours at 90 ° C.) are the same, the amount of contraction deformation after primary and secondary curing is The higher the curing temperature, the greater the amount of shrinkage deformation.

  In contrast to the cement-based matrix alone (Test B4), the shrinkage strain after primary curing is about 350μ, whereas the conventional fiber reinforced concrete has a primary curing temperature of about 550μ when the primary curing temperature is 20 ° C (Test B1). When the temperature is 40 ° C. (Test B2), the temperature of the primary curing is 50 ° C. (Test B3) is about 1300 μ, and the conventional fiber reinforced concrete has a shrinkage deformation due to the temperature of the primary curing. It was proved that the influence of

  From these four types of test results (tests B1 to B4), the conventional fiber reinforced concrete is affected by the heat of the primary curing and the amount of shrinkage deformation becomes large. In other words, the self-shrinkage of the cementitious matrix itself and the effect of the PVA short fibers being shrunk and deformed by heat are added, and it is considered that a larger shrinkage deformation is generated as the fiber reinforced concrete. Generally, it is known that PVA has a property of shrinking when given high heat. In addition, even if the PVA short fiber is thermally contracted, the rigidity of the PVA short fiber itself is not so great, so it is generally considered that there is no influence, but at the stage of weak age from the start of setting of the cementitious matrix, When the PVA short fibers are subjected to heat shrinkage deformation, it is considered that the influence on the deformation behavior of the fiber reinforced concrete cannot be ignored.

  Moreover, when the primary curing temperature is 20 ° C. (test B1) and the cement matrix alone (test B4) is compared with the conventional fiber reinforced concrete, the amount of shrinkage deformation is larger in the fiber reinforced concrete. When the primary curing temperature is 20 ° C., there is no influence on the PVA short fibers due to the temperature, but this is because moisture in the fiber reinforced concrete is slightly even after the PVA short fibers are mixed in the cement matrix. It is thought that it was contracted and deformed by absorbing moisture. Generally, it is known that PVA has a property of contracting and deforming when it absorbs moisture.

(3) Shrinkage Deformation of Fiber Reinforced Concrete Next, as demonstration experiments C and D, the results of measurement of shrinkage deformation during curing of fiber reinforced concrete using PVA short fibers subjected to shrinkage treatment in advance are shown.

  In Demonstration Experiment C, as test material, test C1 was conducted by using a fiber reinforced concrete containing PVA short fibers preliminarily imparted with a shrinkage strain of 5.3% by heat treatment and a primary curing temperature of 40 ° C., and by heat treatment in advance. Measurement was performed for test C2 performed using a fiber reinforced concrete containing PVA short fibers given a shrinkage strain of 1.8% at a primary curing temperature of 40 ° C. In addition, as a comparative example, measurement was also performed on test C3 of a conventional fiber reinforced concrete not subjected to shrinkage treatment and test C4 using a test material composed only of a cementitious matrix. That is, in the demonstration experiment C, the primary curing temperature was all set to 40 ° C., and the difference in influence due to the curing temperature was excluded.

  The fiber reinforced concrete in the tests C1 and C2 is a fiber material made of PVA fibers having a diameter of 0.3 mm having a shape stability of 8% or less in boiling water at 100 ° C. and having a length of 15 mm. The PVA short fibers are cut to form a PVA short fiber, which is shrunk and deformed by heat treatment, and mixed into the cementitious matrix at a volume ratio of 3%.

FIG. 6 shows the behavior of shrinkage deformation of each test material in the demonstration experiment C. In FIG. 6, the horizontal axis represents the elapsed time since the fiber reinforced concrete was placed on the mold, and the vertical axis represents the shrinkage strain. The minus of the strain value indicates shrinkage deformation, and the strain is indicated by micro (μ: × 10 ⁻⁶ ).

  As shown in FIG. 6, the fiber reinforced concrete (tests C1 and C2) in which the PVA short fibers have been heat-treated in advance has a shrinkage deformation after the primary curing and the secondary curing as compared with the conventional fiber reinforced concrete (test C3). ) And proved less.

  Moreover, when the shrinkage strain is 5.3% (Test C1), the shrinkage deformation behavior is the same as that of the cement matrix only (Test C4), and the overall shrinkage is the self-shrinkage of the cement matrix. It was only. That is, the shrinkage strain of about 5.3% is given to the PVA short fibers in advance, so that the PVA short fibers are affected by the heat at the time of curing and affect the shrinkage deformation of the weak cement age matrix. Proving not to give.

  In Demonstration Experiment D, test D1 was conducted using a fiber reinforced concrete containing PVA short fibers preliminarily subjected to shrinkage strain by heat treatment as a test material at a primary curing temperature of 50 ° C., and by heat treatment in advance. Measurement was performed on test D2 in which the primary curing temperature was set to 50 ° C. using fiber reinforced concrete containing PVA short fibers given 5.0% shrinkage strain. Furthermore, as a comparative example, measurement was also performed for test D3 of a conventional fiber reinforced concrete that was not subjected to shrinkage treatment.

  In addition, the fiber reinforced concrete in tests D1 and D2 is a fiber material made of PVA fibers having a diameter of 0.3 mm having a shape stability of 8% or less in boiling water at 100 ° C. and having a length of 15 mm. The PVA short fibers are cut to form a PVA short fiber, which is shrunk and deformed by heat treatment, and mixed into the cementitious matrix at a volume ratio of 3%.

FIG. 7 shows the behavior of shrinkage deformation of each test material by the demonstration experiment D. In FIG. 7, the horizontal axis represents the elapsed time since the fiber reinforced concrete was placed on the mold, and the vertical axis represents the shrinkage strain. The minus of the strain value indicates contraction deformation, and the strain is indicated by micro (μ: × 10 ⁻⁶ ).

  As shown in FIG. 7, the fiber reinforced concrete (tests D1 and D2) in which PVA short fibers have been heat-treated in advance has the amount of shrinkage deformation after the primary curing and the secondary curing, compared with the conventional fiber reinforced concrete (test D3). ) And proved less.

  In addition, when 5.0% shrinkage strain is applied by heat treatment (Test D2), the PVA short fibers are not affected by thermal shrinkage and hardly affect shrinkage deformation on weak-aged cementitious matrices. I understand that. Test D2 is primary because of the effect that the primary curing temperature is 50 ° C., which is 10 ° C. higher than the test C 1 shown in FIG. The amount of shrinkage during curing was slightly larger.

In addition, when the shrinkage strain is applied by 1.8% by heat treatment (Test D1), a significant effect of reducing the shrinkage deformation is seen as compared with the conventional fiber reinforced concrete (Test D3).
Furthermore, when the test D1 is compared with the test C2 shown in FIG. 6, the shrinkage strain after the primary curing is about 650 μm to 700 μm in both cases.

  That is, it was demonstrated that even if the shrinkage strain due to the prior heat treatment is about 1.8%, a shrinkage reduction effect that does not depend on the temperature of the primary curing can be expected. Therefore, it was proved that the deformation of the “sledge” and “bend” of the fiber-reinforced concrete member can be suppressed during the production of the member.

(A) And (b) is a flowchart figure which shows the manufacturing method of the fiber reinforced concrete member based on suitable embodiment of this invention. It is a flowchart figure which shows the modification of the manufacturing method of the fiber reinforced concrete member shown in FIG. It is a perspective view which shows the outline of the experimental apparatus in an Example. It is a graph which shows the behavior of the shrink deformation at the time of curing of steel fiber reinforced concrete. It is a graph which shows the behavior of the shrink deformation at the time of curing of the conventional fiber reinforced concrete. It is a graph which shows the behavior of the contraction deformation at the time of curing when the temperature of primary curing is 40 ° C about the fiber reinforced concrete concerning the present invention. It is a graph which shows the behavior of the contraction deformation at the time of curing when the temperature of primary curing is 50 ° C about the fiber reinforced concrete concerning the present invention.

Explanation of symbols

S1 Cutting process S2 Shrinking process S3 Kneading process S4 Placing process S5 Curing process

Claims (7)

A fiber-reinforced concrete obtained by mixing short fibers with a volume ratio of 0.5% to 6.0%,
The short fiber is subjected to a heat treatment in advance and is subjected to a shrinkage strain, and includes an organic short fiber cut to have an aspect ratio of 20 to 200. concrete.   The cement, silica fume, pozzolanic reactant, aggregate having a maximum particle size of 2.5 mm or less, at least one dispersant, and water. Fiber reinforced concrete.   The fiber reinforcement according to claim 1 or 2, wherein the organic short fibers are made of polyvinyl alcohol fibers having shape stability with a shrinkage rate of 8% or less in boiling water at 100 ° C. concrete. A cutting step in which a fiber material composed of polyvinyl alcohol fibers is cut to have an aspect ratio of 20 to 200 to form short fibers;
A shrinking step of applying heat shrinkage treatment to the short fibers;
A kneading step of mixing the short fibers subjected to heat treatment with concrete so that the volume ratio is within a range of 0.5% to 6.0% to produce fiber reinforced concrete;
A placing step of placing the fiber-reinforced concrete at a predetermined location;
A curing process for curing the fiber-reinforced concrete that has been laid, and a method for producing a fiber-reinforced concrete member. A shrinking process for applying a heat shrinkage treatment to a fiber material made of polyvinyl alcohol fiber;
A cutting step of cutting the fiber material subjected to the heat shrink treatment so as to have an aspect ratio of 20 to 200 to create a short fiber;
A kneading step of mixing the short fibers with concrete so that the volume ratio is within a range of 0.5% to 6.0% to produce fiber reinforced concrete;
A placing step of placing the fiber-reinforced concrete at a predetermined location;
A curing process for curing the fiber-reinforced concrete that has been laid, and a method for producing a fiber-reinforced concrete member.   In the shrinkage step, the fiber material is heated in warm water of 40 ° C. to 90 ° C. or in the air of 40 ° C. to 90 ° C. for 24 hours to 72 hours, thereby causing the fiber material to have a shrinkage strain of about 1% to 6%. The method for producing a fiber-reinforced concrete member according to claim 4, wherein the fiber-reinforced concrete member is provided.   The said shrinking process WHEREIN: The moisture content of this fiber material is made into 5% or less at least by evaporating the water | moisture content in the surface of the said fiber material to which the shrinkage | contraction strain was given, or an inside. The manufacturing method of the fiber reinforced concrete member of description.

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