JP2012166968A - Explosion-proof hydraulic hardened body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber for high fluidity concrete that prevents a concrete molding from explosion by volume expansion of water vapor internally rapidly generated by high temperature at the time of fire and has low decrease in fluidity and compression strength; and high fluidity concrete.SOLUTION: An explosion-proof hydraulic hardened body is provided whose component is an ethylene-vinyl alcohol copolymer whose content of ethylene is at least 25-70 mol% and which contains a fiber whose cross-section is hollow shape.

Description

  The present invention relates to a concrete member having high fluidity at the time of construction, and further relates to a hydraulic hardened body excellent in explosion resistance in a fire.

  Cement, water, sand, hydraulic hardened body mainly composed of gravel, especially concrete is known as a material with excellent fire resistance, and in recent years, its strength has been increasing with the building of super high-rise buildings. . However, since high-strength concrete is designed to be denser than normal concrete, a phenomenon called “explosion” occurs in which concrete on the surface layer is peeled off due to the expansion of water vapor generated inside the concrete during a fire. Sometimes. Therefore, for such high-strength concrete, in order to suppress the explosion phenomenon, by mixing organic fibers such as polypropylene and polyvinyl alcohol in the concrete, before the concrete in the event of a fire, A method of controlling explosion by forming a fine tunnel serving as an escape route has been studied (see, for example, Patent Documents 1 and 2).

  However, even when polypropylene fibers or polyvinyl alcohol fibers are used, the explosion prevention effect is not always sufficient, and in the method as described in Patent Document 2, when the thickness of the member is small or When the cover is thin, it is not always effective, and a large amount of fiber must be added. Moreover, in the high-strength concrete as described in Patent Document 1, since the structure is dense, there is a tendency that a large amount of fiber reinforcing material is mixed therein, and thus there is a problem that fluidity is deteriorated. And when this high-strength concrete is used for casting, there are problems that it becomes difficult to place due to poor fluidity and that compressive strength is lowered.

  In order to solve these problems, an ethylene-vinyl alcohol copolymer fiber (hereinafter referred to as EVA) having excellent miscibility with base concrete, little influence on fluidity, and a melting point of 160 ° C. to 190 ° C. When used in a fire, the mixed EVA-based fiber melts and becomes a passage for water vapor generated inside, and suppresses explosion. It has been reported that this can be achieved (for example, see Patent Document 3).

  However, even when the above fibers are used, the melting temperature is 160 ° C. or higher, and it takes time from the start of melting to the formation of voids. On the other hand, when the water heated to 100 ° C. becomes water vapor, its volume increases by 1700 times, so that the explosion phenomenon occurs before the fiber exhibits its performance with respect to explosion suppression in the early stage of fire occurrence. There is a risk of occurring.

  On the other hand, inorganic building materials in which hollow polypropylene fibers are mixed in concrete have been reported (for example, see Patent Document 4). However, Patent Document 4 is intended to form voids in heating during heat curing, and has a dense hardened structure obtained by performing high-fluidity concrete under low temperature and wet curing for a long time. In order to use it as the explosion-suppressing fiber for high-strength concrete, there are problems such as poor dispersibility in high-fluidity concrete, poor workability derived therefrom, and reduced compressive strength.

Japanese Patent No. 2620910 JP 2000-143322 A Japanese Patent No. 4090762 JP 59-128245

  Accordingly, an object of the present invention is to mix EVA fiber having a hollow fiber cross section in the concrete in order to suppress explosion due to rapid volume expansion of water vapor in the concrete in the early stage of the concrete fire occurrence. An object of the present invention is to provide a fiber for an explosion-resistant hydraulic cured body and an explosion-resistant hydraulic cured body for the purpose of securing a water vapor escape path in the initial stage of fire occurrence.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have at least an ethylene-vinyl alcohol copolymer having an ethylene content of 25 to 70 mol% as a component, and have a specific range of fineness and fiber length. In addition, it has been found that by including a specific range of fibers having a hollow cross section, it is possible to obtain an explosion-resistant hydraulic hardened body excellent in explosion suppression performance in the initial stage of fire occurrence of concrete, and the present invention is completed. I let you.

That is, the present invention is an explosion-resistant hydraulic cured body comprising at least an ethylene-vinyl alcohol copolymer having an ethylene content of 25 to 70 mol% and containing a fiber having a hollow cross section. Preferably, the hollow fiber is the above explosion-resistant hydraulic hardened body satisfying the following (1) to (4).
(1) The fiber fineness is 0.1 to 100 dtex,
(2) The hollowness is 0.1 to 50%,
(3) The fiber length is 1 to 30 mm,
(4) 0.05 to 0.5% by volume is contained with respect to 100% by volume of the hydraulic cured body.

  According to the present invention, by dispersing the EVA fibers having a hollow cross section in the concrete, it is possible to provide a water vapor escape path against the rapid volume expansion of water in the early stage of the fire occurrence, When exposed to a temperature of 160 ° C or higher in the subsequent temperature rising process, the EVA fiber dissolves to increase the void size and secure a space for further relaxing the expansion pressure generated in the concrete. It is possible to provide an explosion-resistant hydraulic hardened body that can exhibit an explosion-inhibiting effect from the initial stage at the time of occurrence to all stages after the temperature increase.

  Hereinafter, the present invention will be described in detail. The fiber of the present invention can be produced by melt spinning an ethylene-vinyl alcohol copolymer. Various conditions such as spinning temperature, take-up speed, drawing temperature, draw ratio, heat treatment temperature, etc. can be appropriately selected and set according to the physical properties of the raw cotton such as the desired fineness, hollowness, shrinkage, etc. For example, it can be produced by melting an ethylene-vinyl alcohol copolymer with an extruder and spinning the melt with a spinning device using a spinning pack equipped with a die for forming a hollow section. A spinning temperature in the range of 200 to 300 ° C. is employed. About the process after spinning, it may be stretched as necessary after spinning, and various conditions such as stretching temperature, stretching ratio, heat treatment temperature, etc. are set according to the desired fineness, strength, elongation characteristics, etc. It is desirable to set appropriately.

  The EVA fiber of the present invention is a fiber containing a saponified copolymer of ethylene and vinyl acetate as a component, and an EVA fiber having a melting point of 200 ° C. or less can be produced by controlling the ethylene content. Is possible. In the EVA fiber of the present invention, the amount of ethylene contained in the copolymer is 25 to 70 mol%. When the ethylene content is lower than 25 mol%, the fiber has a property of being easily dissolved in water, so that there is a problem that the fiber is easily dissolved before being cured by water in the hydraulic material. On the other hand, when the ethylene content is higher than 70 mol%, the melting point is a fiber having a low melting point of 120 ° C. or less, and therefore the fiber is easily melted by heat of hydration before curing in the hydraulic material. There is a point. Preferably it is 30-50 mol%.

  The average fineness of the EVA fiber of the present invention is preferably in the range of 0.1 to 100 dtex. If the fineness is less than 0.1 dtex, dispersion becomes difficult, and if it exceeds 100 dtex, the void size after heating and melting becomes too large, so that the compressive strength after heating decreases, which is not preferable. More preferably, it is 0.5-80 dtex.

The EVA fiber of the present invention preferably has a hollowness of 0.1 to 50% represented by the following formula (1). If the hollowness is less than 0.1% or the explosion-inhibiting effect at the initial stage of re-generation is not sufficiently exhibited, and if it exceeds 50%, the hollow is crushed and clogged during concrete mixing, which is not preferable. More preferably, it is 1-40%, More preferably, it is 5-30%.
Hollow ratio (%) = <A/(A+B)> × 100 (1)
However, A: Area of a hollow part, B: Area of a non-hollow part

  The fiber length of the EVA fiber of the present invention is preferably in the range of 1 to 30 mm, and more preferably in the range of 5 to 25 mm. When the fiber length is less than 1 mm, the space into which water vapor generated before the fiber dissolves is small, which is not preferable because the explosion suppressing effect in the initial stage of the fire is reduced. In addition, when the fiber length exceeds 30 mm, the fibers are entangled during kneading into concrete, which is not preferable because of adverse effects such as poor dispersibility and poor fluidity.

  When the EVA fiber of the present invention is added to the hydraulic cured body, it is preferably contained in an amount of 0.05 to 0.5% by volume with respect to 100% by volume of the hydraulic cured body. When the content is less than 0.05% by volume, the effect of suppressing explosion is reduced. Conversely, when the content exceeds 0.5% by volume, the kneadability is deteriorated. Preferably it is 0.08-0.25 volume%.

  The hydraulic cured body of the present invention includes conventional additives such as AE agent, water reducing agent, setting / curing modifier, rust inhibitor, foaming agent / foaming agent, polymer admixture, blast furnace slag, fly ash, natural Alternatively, it may contain an artificial siliceous mixed material, a cement admixture such as an expanding material, or synthetic fibers or steel fibers. These additives can be used alone or in combination of two or more.

  The conventional polyvinyl alcohol fiber (hereinafter referred to as vinylon fiber) added for explosion prevention when preparing a hydraulic composition such as concrete and mortar starts to decompose while melting at a high temperature of 200 ° C. or higher. On the other hand, the EVA fiber of the present invention has a melting point lower than 200 ° C. by controlling the ethylene content as described above. Therefore, when the hydraulic hardened body to which the EVA fiber is added is heated by a fire or the like, the EVA fiber is rapidly melted and decomposed as compared with the hydraulic hardened body to which the vinylon fiber is added, thereby providing an escape route for water vapor. Since a fine tunnel is formed, the hydraulic hardened body to which EVA fiber is added is superior in explosion prevention property to the hydraulic hardened body to which vinylon fiber is added.

  In addition, since the EVA fiber of the present invention is a fiber that is rich in hydrophilicity when the fiber is added to the fresh mix of the hydraulic hardened body, the flowability is improved when the fiber is added to the fresh mix of the hydraulic hardened body. On the other hand, EVA fibers are more hydrophobic than vinylon fibers, and thus have the advantage of superior fluidity than vinylon fibers.

  On the other hand, in comparison with polypropylene fiber, polypropylene fiber has a specific gravity of 0.9. Therefore, when polypropylene fiber is added to a fresh mix of a hydraulic cured body, the fiber floats on the surface, and the fiber is added to the fresh mix. While it is difficult to mix uniformly, the EVA fiber has a specific gravity of about 1.1 to 1.2. Therefore, the EVA fiber has an advantage that uniform mixing is easy in a fresh mix. . Uniform mixing of the fiber into the fresh mix is an important factor in obtaining excellent explosion-proof performance.

  Furthermore, in this invention, it is an important factor which should also consider about the adhesiveness of a fiber and a hydraulic hardening body. When the hydraulic hardened body is heated with a sudden rise in temperature such as a fire, the moisture present in the voids vaporizes and the vapor pressure increases, so the surrounding matrix has a stress that tries to destroy it. Be loaded. If the fiber is not present in the hydraulic hardened body, the matrix is easily destroyed, resulting in an explosion. In the presence of fibers, cross-links are formed in the matrix that tends to break, and attempts to prevent matrix destruction. Thereafter, when the temperature is further increased, the fiber melts and decomposes to form a fine tunnel serving as a water vapor escape path, thereby preventing explosion.

  Conventionally, it is known that the vinylon fiber is excellent in adhesiveness with the hydraulic cured body, whereas the polypropylene fiber is known to have low adhesiveness with the hydraulic cured body. When a hydraulic hardened body to which vinylon fiber is added is heated with a rapid temperature rise such as a fire, vinylon fiber has high adhesiveness to the matrix, so the presence of vinylon fiber causes water vaporization during heating. It tries to prevent the destruction of the matrix against the increase in vapor pressure, but once the matrix breaks down before the fiber melts or decomposes due to further temperature and vapor pressure increase, the fibers are firmly fixed to the matrix. This may lead to a large explosion. Polypropylene fibers, on the other hand, have low adhesion to the matrix and weak crosslinks formed by the fibers before they melt, so they cannot resist the increase in vapor pressure due to moisture vaporization during heating and easily explode. There is a case.

  EVA fiber has fewer hydroxyl groups than vinylon fiber, so its adhesion to hydraulic cured body is lower than that of vinylon fiber. On the other hand, it has higher adhesion than polypropylene fiber, that is, moderate to prevent matrix destruction. Have good adhesion. The hydraulic hardened body to which EVA fiber is added is heated before the EVA fiber melts the matrix to be divided by the increase of vapor pressure due to vaporization of water during heating when heating with rapid temperature increase such as fire. By being further heated, it is melted and decomposed rapidly at a temperature of 200 ° C. or less, and a fine tunnel serving as an escape route for water vapor is formed. Therefore, the EVA fiber has a cross-link formation in the matrix to prevent explosion before the fiber melts when the vapor pressure rises due to heating, and the generation of fine tunnels by melting and decomposing the fiber due to further temperature rise. However, since it proceeds more smoothly than vinylon fiber or polypropylene fiber, it has superior explosion-proof performance compared to vinylon fiber or polypropylene fiber.

  Furthermore, the adhesion between the fiber and the matrix is small in a matrix with a large amount of cement (less sand), such as high-strength concrete or high-strength mortar, and a matrix with a small amount of cement (a lot in sand), such as ordinary concrete or ordinary mortar. It is generally said that it is large. Therefore, vinylon fibers excellent in adhesiveness with the matrix are suitable for obtaining an appropriate adhesiveness in a matrix with a large amount of cement. On the other hand, if an appropriate adhesiveness is obtained with a matrix with a small amount of cement, Polypropylene fibers with low adhesion to the matrix are preferred. As described above, EVA-based fibers have lower adhesion to the matrix than vinylon fibers, but higher than polypropylene fibers, and the adhesiveness can be adjusted by controlling the ethylene content in the copolymer. It is suitable for the use of concrete and mortar with a wide range of physical properties from concrete and ordinary mortar to high-strength concrete and high-strength mortar. Here, high strength concrete and high strength mortar are concrete and mortar having a compressive strength of 60 MPa or more, and ordinary concrete and normal mortar are concrete and mortar of 20 MPa or more and less than 60 MPa.

  The hydraulic hardened body containing EVA fiber of the present invention has a wider range of compression from ordinary concrete, ordinary mortar, etc. to high-strength concrete, high-strength mortar, etc. A strong hydraulic hardened body is excellent in explosion prevention performance, and can be used as a concrete member constituting a floor, wall, column, beam, etc. of a building. In addition, because thin-walled members such as handrails tend to explode due to a rapid increase in temperature because of their large surface area, in the case of using conventional vinylon fibers or polypropylene fibers, it is not easy to impart explosion resistance, If the EVA fiber of the present invention is used, explosion resistance can be imparted even to a thin-walled member.

  Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples. In addition, the physical property of each fiber in this invention and the physical property of the obtained hydraulic hardening body and evaluation of explosion resistance mean what was measured with the following method.

[Fiber fineness dtex]
Evaluation was made according to JIS L1015 “Testing method for chemical fiber staples (8.5.1)”.

[Fiber length mm]
Evaluation was made according to JIS L1015 “Testing method for chemical fiber staples (8.4.1)”.

[Preparation of concrete for fire test specimens]
Pozoris SP-8N was used as ordinary Portland cement (manufactured by Taiheiyo Cement), fine aggregate (river sand), coarse aggregate (maximum particle size 20 mm), and high-performance AE water reducing agent (SP). Using a 100 liter twin screw mixer, first mix the cement and sand for 1 minute, then add water and knead for 2 minutes. The fibers were then added and kneaded for 1 minute, scraped off once and kneaded again for 1 minute. Next, it was discharged and turned over, and kneaded again for 2 minutes to prepare.

[Concrete slump value mm]
In accordance with the concrete slump test method according to JIS A1101, fill the cone (upper side diameter 10 cm, lower side diameter 20 cm, height 30 cm) with fresh concrete according to the prescribed procedure, pull up the cone and lower the collapsed fresh concrete on the upper side. Was measured.

[Compressive strength of hydraulic cured body MPa]
A cylindrical body having a diameter of 10 cm and a height of 20 cm was formed as a sample, and a load was applied at an increasing rate of 0.25 MPa per second, and measurement was performed according to the JIS A1108-1993 test method.

[Evaluation of explosion resistance]
The residual rate of the specimen when it exploded was calculated by the following formula, and the explosion prevention property was evaluated.
<Main body weight after fire resistance test / Main body weight before fire resistance test> × 100

[Examples 1 and 2, Comparative Examples 1 to 5]
Table 1 shows the basic composition of concrete. Concrete in which various fibers were added to the concrete shown in Table 1 was prepared, and cast into a cylindrical specimen form having a diameter of 10 cm and a height of 20 cm, and four pieces were prepared for each level. The prepared cylindrical specimen was cured in air in a room at 20 ° C. and 65% RH for 24 hours, immediately demolded, placed in 20 ° C. water, and cured in water for 28 days. After that, 2 out of 4 per each level were taken out of the water and the compressive strength was measured after 5 hours. In addition, the remaining two for each level were dried for 7 days in a hot air dryer at 105 ° C. in order to perform the explosion test. The moisture content after drying was about 2%.

  The dried sample is 3m wide, 1m high, and 50cm deep, set in a fire brick heating machine with 9 LPG burner flame jets on the top and bottom, and heated to conduct a blast test did. The heating program of the refractory brick heater was implemented according to the ISO834 test method, and reached 700 ° C. 15 minutes after the start of heating and reached 830 ° C. 30 minutes after the heating. And after heating temperature reached 830 degreeC, gas supply was interrupted | blocked and it cooled until it became room temperature. After further natural cooling for about 4 hours, the explosion resistance of each cylindrical specimen after the explosion test was evaluated. The results are shown in Table 2.

  In the explosion evaluation program at the beginning of heating, the gas supply was cut off when the temperature reached 700 ° C. 15 minutes after the start of heating.

  For each specimen, a slump value indicating the degree of fluidity of fresh concrete was measured, and the measurement results are shown in Table 2 together with the explosion resistance (residual rate). When the slump value of the concrete with no fiber added is compared with the slump value of the concrete with the fiber added, the specimen slump value with the EVA fiber added does not add any fiber compared to the slump value of the specimen with the polypropylene fiber added. It was found that the decrease in the numerical value with respect to the slump value of concrete was small, that is, the test piece to which EVA fiber was added had a smaller influence on the slump value than the test piece to which polypropylene fiber was added.

  The hydraulic cured body containing EVA fibers having a hollow cross-section according to the present invention has a higher strength concrete than ordinary concrete, ordinary mortar, etc. It is excellent in explosion prevention performance in a hydraulic hardened body with a wide range of compressive strengths such as strength mortar, and can be used as a concrete member constituting a floor, wall, column, beam, etc. of a building. In addition, because thin-walled members such as handrails tend to explode due to a rapid increase in temperature because of their large surface area, in the case of using conventional vinylon fibers or polypropylene fibers, it is not easy to impart explosion resistance, If the EVA fiber of the present invention is used, explosion resistance can be imparted even to a thin-walled member.

The cross-sectional photograph (450 times magnification) which shows an example of the cross section of the EVA type fiber which the cross section of this invention has a hollow shape.

Claims (2)

  An explosion-resistant hydraulic hardened body comprising at least an ethylene-vinyl alcohol copolymer having an ethylene content of 25 to 70 mol% as a component and fibers having a hollow cross section. 2. Explosion-resistant hydraulic hardening according to claim 1, wherein the fiber comprising an ethylene-vinyl alcohol copolymer having an ethylene content of 25 to 70 mol% as a component satisfies the following (1) to (4): body.
(1) The fiber fineness is 0.1 to 100 dtex,
(2) The hollowness is 0.1 to 50%,
(3) The fiber length is 1 to 30 mm,
(4) 0.05 to 0.5% by volume is contained with respect to 100% by volume of the hydraulic cured body.

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