JPH08294912A - Manufacture of fiber-reinforced concrete - Google Patents

Abstract

PURPOSE: To eliminate the dispersion failure of reinforcing fiber, to suppress the generation of a fiber ball and to reduce the irregularity of the strength by giving vibration when the fiber is mixed with a cement component. CONSTITUTION: When carbon fiber which particularly tends to become dispersion failure as reinforcing fiber and is easily broken is mixed with a cement component, vibration is given. The frequency of the vibration at this time is different depending upon the content of the reinforcing fiber and the viscosity of the mixture, and normally 3000rpm or more. A method for giving the vibration is, for example, vibrating an agitating shaft, mounting a vibrator at an agitating blade, providing a barlike vibrator rotated synchronously with an agitator, or mounting the vibrator like a box state at the outer wall of the mixing tank of the mixer. In order to use the energy of the vibrator without waste, the vibrator is installed at the side and/or the bottom of the tank of the mixer. When the vibration is uniformly given in the tank or in the case of a large-sized mixer for kneading a large quantity at once, a plurality of the vibrators are installed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fiber reinforced concrete, and more particularly to the production of short carbon fiber reinforced concrete having excellent strength and durability used in the field of civil engineering and construction.

[0002]

2. Description of the Related Art As the fibers used in fiber reinforced concrete, steel fibers, glass fibers, organic fibers and the like are generally used in order to increase the strength and toughness thereof. However, when steel fibers are used, there is a problem that the rate of increase in bending strength with respect to unreinforced is low, about 50%, and the load at the time of initial cracking is low. Furthermore, durability problems such as rust may occur, and particularly when used for road paving, steel fibers may protrude in the ruts, causing problems such as flat tires in automobiles.

When glass fibers and organic fibers are used, their reinforcing effect is extremely low due to the influence of the alkali resistance of the fibers and the properties such as the tensile strength and elastic modulus of the fibers. Absent. On the other hand, when carbon fiber is used, durability such as deterioration prevention of the fiber is improved. However, in carbon fiber reinforced concrete, it was carried out only with long fibers such as rods and meshes, and those with short fibers were only mortar without coarse aggregate and spray repair materials. Although it was limited to such applications, when carbon fibers were mixed with short fibers, in the presence of coarse aggregate, cutting and
This is because the damage was severe and the fiber reinforcing effect on the molded body was small. Even when it was used intentionally, it was only about the extent to which crack propagation that had already occurred was suppressed. Attempts have been made to increase the strength by curing carbon fiber with epoxy to make it rod-shaped and shortened into fibers, but when a bending load is applied, the fibers drop out between the matrix and the fibers, and the reinforcing effect is insufficient. Met.

When various fibers are added for the purpose of increasing the strength of concrete and preventing cracks, almost no exception is caused by the water content in the matrix being taken up on the fiber surface during kneading, resulting in a decrease in fluidity as compared to when no fiber is added. Occurs and the workability deteriorates. Not only that, there was a high possibility of causing problems such as dispersion of products due to poor dispersion of fibers during kneading, and difficulty in manufacturing large-sized products due to easy formation of weak portions due to poor dispersion.
Further, if the kneading is carried out for a long time in order to carry out a sufficient kneading in order to suppress the variation, the fibers themselves will be broken or powdered, so that it is impossible to obtain a fiber-reinforced concrete having high strength.

[0005]

DISCLOSURE OF THE INVENTION As a result of various investigations to solve the above-mentioned problems, the inventors of the present invention suppressed the dispersion of fibers and the formation of fiber balls by applying vibration during kneading, and It was found that a fiber reinforced concrete with less variation of the above is produced, and the present invention has been completed.

[0006]

That is, the present invention resides in a method for producing fiber reinforced concrete characterized by applying vibration when mixing reinforcing fibers and cement components. Hereinafter, the present invention will be described in detail. First, as the cement component used in the present invention, a known cement component can be used, for example, ordinary Portland cement, early-strength Portland cement, blast furnace cement, alumina cement and low shrinkage cement may be any, preferably low shrinkage cement. And early strength Portland cement.

The reinforcing fiber used in the present invention may be any fiber such as steel fiber, carbon fiber, synthetic fiber, glass fiber or the like, and is particularly suitable for carbon fiber which is likely to cause poor dispersion and is easily broken. is there. For example, as the carbon fiber, one having a tensile strength of 300 kg / mm ² or more, preferably 300 kgf / cm ² , and an elongation of 1% or more is particularly preferable. For example, coal tar pitch, petroleum pitch, coal liquefaction, polyacrylonitrile. Carbon fibers made of cellulose, cellulose, or the like can be used. The elongation here is a value obtained by dividing the tensile strength of carbon fiber by its tensile elastic modulus.

The shape of the fiber is preferably at least 1 time, preferably at least 1.5 times the maximum size of the coarse aggregate used, and in terms of the actual length, it is at least 20 mm.
It is preferably 30 mm or more. Fiber length is 20m
If it is m or less, the reinforcing effect is small because the critical fiber length of the composite material has not been reached. Thread diameter is 5 to 3
Those having a thickness of 0 μm, preferably 6 to 18 μm are suitably used.

[0009] It is preferable to use a fiber strand obtained by using such a fiber with a sizing agent. The smaller the number of one fiber strand, the more remarkable the reinforcing effect. This is because the number of fiber strands to bear during loading simply increases. The amount of the fiber added is 0.1 vol% or more, preferably 0.5 vol% or more.

The fiber sizing agent is not particularly limited, and when it is poured into concrete containing coarse aggregate, the sizing agent is such that the chopped strand-shaped carbon fibers start to separate without breaking, for example, a hardening agent. Unadded epoxy emulsion and polyvinyl alcohol-based include unsaponified polyvinyl acetate, partially saponified polyvinyl alcohol, and fully saponified polyvinyl alcohol. Further, cellulose derivatives such as methyl cellulose, ethyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose and starch derivatives such as soluble starch are also used.
An epoxy emulsion without a curing agent is preferably used. As the epoxy emulsion used in the present invention, the following epoxy compounds emulsified with a surfactant can be used. Examples of epoxy compounds include bisphenol-type, novolak-type, alicyclic-type, resol-type, amino-type, and other epoxy compound monomers and low-polymerization products. Among them, bisphenol A-type and molecular weight 470 or less, or novolac Type has a molecular weight of 60
An epoxy compound of 0 or less is preferable. For example, Shell Chemical Co. "Epicote" 815, 827, 828 and 8
34, "Araldite" ECN-1235 manufactured by CIBA-GEIGY.

Surfactants for emulsifying these include polyoxymethylene castor oil ether, nonylphenyl ether, polyoxyethylene alkyl ethers such as styrenated phenyl ether, polyoxyethylene alkyl allyl ether and polyvinyl alcohol. At least one surfactant selected from

The amount of the fiber sizing agent impregnated is preferably as small as possible in terms of the kneading condition and strength of the concrete, and the handleability of the fiber is not a problem, the quality of the fiber is not deteriorated, and the environmental hygiene is adversely affected. It is enough to add the amount that does not reach. Although the exact amount varies depending on the type of the sizing agent, for example, in the case of Matsumoto Yushi's epoxy emulsion, the weight% relative to the fiber is 5 wt% or less, preferably 2 wt% or less.

The concrete of the present invention may further contain known materials as concrete components, for example: coarse aggregate, fine aggregate, water reducing agent and the like. The type and diameter of the coarse aggregate (gravel) are not particularly limited, and crushed stone,
Any of artificial lightweight coarse aggregate and iron oxide ore may be used. Crushed stone having a diameter of 50 mm or less is preferable. There is no particular problem with the addition amount as long as it is a usual formulation used for civil engineering and construction, and preferably 1500 kg / m ³ or less.

As fine aggregate (sand), sand, silica stone, gravel,
Examples include shirasu balloon fly ash and silica fume. There is no particular problem with the addition amount as long as it is a usual formulation used for civil engineering and construction, and preferably 150
0 kg / m ³ or less is preferable. The fine aggregate ratio (sand ratio) is not particularly problematic as long as it is a usual formulation used for civil engineering and construction, and preferably 30 to 60%.

As the water-reducing agent, a special surfactant containing a triazine ring-based highly condensate salt as a main component, a special polymer having a special sulfone group and a carboxyl group, an anionic special polymer surfactant, a naphthalenesulfonic acid condensate ligninsulfonic acid derivative , Oxycarboxylic acid, ligninsulfonic acid and the like. The addition amount is 1 to 5 parts with respect to 100 parts of cement.

In addition to the dispersant and the water-reducing agent, an admixture such as an antifoaming agent and a foaming agent can be appropriately added. As the mixer for kneading the cement raw material and the carbon fiber, water, and other auxiliaries in the present invention, it is sufficient if vibration can be applied when the fibers are mixed, and all commonly used mixers can be used,
In the case of a mixer having a stirring blade of paddle type, propeller type, paddle type, turbine type, pan type, ribbon type, screw type, warner type, kneader type, etc., first add fiber and cement raw material without adding water. Mix and then add water and knead. Alternatively, raw materials other than fibers may be kneaded with water to produce ordinary concrete, and then carbon fibers may be added and kneaded again.

The gist of the present invention is to provide vibration when mixing the reinforcing fiber and the cement component. The frequency at this time varies depending on the content of the reinforcing fiber, the viscosity of the mixture, and the like, but it is usually preferably at least 3000 rpm. The method of applying vibration is not particularly limited, and can be arbitrarily set, for example, by vibrating the stirring shaft, attaching a vibrator to the stirring blade, or providing a rod-shaped vibrator that rotates in synchronization with the stirring blade. However, it is preferable to install a vibrating machine such as a box-shaped vibrating machine on the outer wall of the mixing tank of the mixing machine from the viewpoints of the simplicity of the mechanism, a small improvement of the existing apparatus, and the like. The position where the vibrator is installed is not particularly limited,
It suffices that vibration be uniformly applied in the mixing tank of the mixer. Also, in order to use the energy of the vibrator without waste,
A vibrator may be installed on the side surface and / or bottom surface of the mixing tank of the mixer, and in addition to uniformly vibrating the mixing tank, or when using a large mixer that performs a large amount of kneading at one time. It is preferable to install a plurality of vibrators. Specifically, for example, when two units are installed, they are preferably installed so as to face each other.
It may be installed at a position offset by 20 degrees. That is, since the stirring tank of a stirrer generally has a circular cross section, when three or more vibrators are installed, the vibrators may be installed at the apexes of polygons inscribed in the circle of this cross section.

The vibrator used in the present invention is not particularly limited, but it is preferable to use a vibrator having a built-in high frequency vibration motor having excellent vibration efficiency.

[0019]

The present invention will be described in more detail with reference to the following examples. Example Variable type high frequency vibrator (vibrator manufactured by Tokuden Denki Kogyo KK; type H)
V750B, vibrator 6000 to 7200 rpm, output 0.75 kw) was installed in a pan-type mixer with an internal volume of 70 liters.
00kg / m ³ , amount of crushed stone No. 6 (maximum particle size 15mm) is 900kg / m ³ , sandstone fine sand from Chichibu (sand ratio 50vol)
%) To 866 kg / m ³ and dry mixed for 30 seconds, and then 4 parts of water reducing agent “Palic SA” was added to water to make 204 parts by weight (W / C 50% by weight). The unit amount of water is 200 kg / m ³ ) and the mixture is wet mixed. Further, carbon fiber (12000 filaments) cut into 20 mm chopped strands is added by 1.0% in terms of the total volume fraction, and wet mixing is performed for 30 seconds while applying a vibration of 6000 rpm or more. The kneaded product is poured into a mold, and after 16 hours, the mold is removed. As an index for the fluidity of the obtained fiber reinforced concrete, JISA
The slump value was measured according to -1101, and the air amount was measured according to JISA-1128.

The strength test body is cured at 20 ° C. and 60 RT%, and after 4 weeks, a bending test is conducted according to JIS A110.
It carried out according to 6. The loading speed is 2 mm / min,
The test log was n = 12. Comparative Example A fiber reinforced concrete was obtained in the same manner as in Example 1 except that vibration was not applied during wet mixing, and a test was performed in the same manner as in Example 1.

[0021]

[Table 1]

[0022]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a hardened body produced by kneading concrete containing short carbon fibers preferably obtains carbon fiber reinforced concrete having high strength and little variation. It becomes possible.

Claims (5)

[Claims] 1. A method for producing a fiber-reinforced concrete, which comprises applying vibration when mixing the reinforcing fiber and the cement component. 2. The method for producing fiber reinforced concrete according to claim 1, wherein the vibration frequency is 3000 rpm or more. 3. A vibrating machine is installed on a side surface and / or a bottom surface of a mixing tank of a mixer used for mixing.
The method for producing a fiber-reinforced concrete according to item 1. 4. The method for producing fiber reinforced concrete according to claim 3, wherein a plurality of vibrators are installed. 5. The method for producing fiber reinforced concrete according to claim 1, wherein the reinforcing fiber is carbon fiber.