JP2000102912A - Method for decreasing air bubble on surface of high flow concrete molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease air bubbles generated on the surface of a molding by directly giving internal vibration to concrete which is placed into a formwork and has high fluidity. SOLUTION: Air bubbles generated on the surface of a molding are decreased by using a rodlike or beltlike internal vibrator and giving internal vibration to concrete having 400-700 mm slump flow and high fluidity. Concrete is aged and cured. The internal vibrator is inserted between a formwork and a reinforcing bar or between the reinforcing bars for concrete. In concrete having high fluidity, cement is 400-600 kg/m3, volume ratio Vw/Vp of water and powder is 0.90-1.20, volume ratio Vs/Vm of fine aggregate is 0.40-0.50 and substitution rate of an admixture such as blast furnace slag fine powder is 10-50 wt.% of total powder amount. Further, the addition rate of an admixture consisting of a polycarboxylic acid-based water reducing agent for powder is 0.5-2.0 wt.%. Number of vibration due to the internal vibrator is 12,000-14,000 vpm and time giving vibration is short time of several ten seconds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing surface air bubbles of a high-fluidity concrete molded product, and to directly apply internal vibration to a high-fluidity concrete cast in a form by a rod-shaped or band-shaped internal vibrator. By reducing bubbles generated on the surface of the molded article while suppressing the generation of noise, the quality and product value of the molded article are increased, for example, side grooves, U-shaped grooves,
It is most suitable for molding molded products such as box culverts, catchment basins, rainwater basins, L-shaped retaining walls, sidewalk flats, and curb blocks.

[0002]

2. Description of the Related Art Conventionally, cast concrete (slump 5 to 12 cm) and mortar molded products formed using a mold, such as gutters, U-shaped grooves, box culverts,
When forming a catchment basin, rainwater basin, L-shaped retaining wall, sidewalk flat plate, curb block, etc., the formwork is vibrated by an external vibrator to vibrate concrete and mortar to compact the concrete. The compaction method by vibration is performed. When vibration due to external vibration is insufficient,
Internal vibration, in which a vibration source is inserted into a mold to give vibration to concrete, etc., was rarely supplemented using external vibration together, but this was only a complementary role of external vibration. Did not. As described above, the compaction method using external vibration that applies vibration to the mold itself from the outside involves setting the frequency and amplitude for each mold having various shapes and dimensions depending on the molded product and applying vibration to the mold from outside. Has been done by

[0003]

In the case of molding a molded article made of concrete or mortar, the above-mentioned conventional external vibration, which mainly applies external vibration to a formwork in which concrete or mortar is cast by a vibrator. According to the compaction method, not only does it cause noise to the surroundings, but also the formwork is severely damaged, its service life is shortened, and large vibrations are transmitted to the formwork to compact concrete etc., so kneading was performed. In concrete and mortar, cement paste and aggregates can be easily separated, which causes bleeding water on the concrete surface and reduces the strength and quality of molded products. If the bubbles inside are vibrating the formwork itself, it moves toward the formwork as a vibration source, so after concrete etc. hardens Remains after the form is a number of the surface of the molded article are bubbles, it was not possible to mold the appearance poor reliability moldings in appearance. The present invention
The present invention solves the above-mentioned conventional problems, and the inventor inserts a rod-shaped or band-shaped internal vibrator into a high-fluidity concrete poured into a mold without using any external vibration, thereby achieving high fluidity. When the internal vibration is given to the concrete for a short time, bubbles generated on the surface of the molded article are drawn from the surface to the vicinity of the internal vibrator and reduced,
Utilizing this positively extended to the present invention. The present invention uses high-fluidity concrete, and is formed by giving internal vibration for a short time to improve productivity, and is cast into a mold when molding a molded product using high-fluidity concrete. Excellent workability without segregation or settling of cement paste on aggregates of high-fluidity concrete and reinforcing steel arranged inside, and quickly and reliably reduce bubbles generated on the surface of molded products. Since the concrete filling property is good, the reinforcing steel bar arranged inside is protected, the strength and quality of the molded product are improved, the appearance is good, the noise around is small, and the formwork is also An object of the present invention is to provide a method for reducing surface bubbles of a high-fluidity concrete molded product, which has a long service life due to less damage to the concrete, and has a small facility itself and can be manufactured at low cost.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a first aspect of the present invention is to cast concrete having high fluidity into a formwork and use a rod-shaped or band-shaped internal vibrator. Means is adopted in which internal vibration is applied to the high-fluidity concrete to reduce bubbles generated on the surface of the molded article, and then the concrete is cured and hardened.

According to a second aspect of the present invention, in the first aspect, the internal vibrator is inserted from above into concrete having high fluidity between the formwork and the reinforcing bar or between the reinforcing bar and the reinforcing bar. In this case, the internal vibration is applied to the internal vibration.

A third aspect of the present invention employs a means according to any one of the first and second aspects, wherein the concrete having high fluidity has a slump flow of 400 mm to 700 mm.

According to a fourth aspect of the present invention, the concrete having high fluidity according to any one of the first, second and third aspects is characterized in that the cement comprises 400 to 600 (kg / m ³ ) Body volume ratio: Vw / Vp 0.90 to 1.20, fine aggregate volume ratio: Vs / Vm
Is 0.40 to 0.50, the replacement ratio of the admixture of the blast furnace slag fine powder is 10 to 50 (wt%) of the total powder amount, and the addition ratio of the polycarboxylic acid-based water reducing agent is 0.5 to 2.0 ( (wt%) was incorporated.

According to a fifth aspect of the present invention, the vibration frequency of the concrete having high fluidity according to any one of the first, second, third and fourth aspects is set to 12000 to 14000 vpm by an internal vibrator. A means characterized by the following is employed.

According to a sixth aspect of the present invention, the internal vibration of the concrete having high fluidity by the internal vibrator is set forth in any one of the first, second, third, fourth and fifth aspects. The productivity was improved by adopting a means in which the application time was as short as several tens of seconds.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the embodiments of the present invention will be described in detail. In the present invention, when molding a molded product using a mold, high-fluid concrete is used as a raw material, and the vibration given to the high-fluid concrete is not a vibration applied to the mold, but a high An internal vibrator is inserted into the fluidized concrete, and the internal vibrator directly vibrates the concrete itself by the internal vibrator (in this specification, the internal vibration means the above meaning).
The cement used here is not particularly limited, and is, for example, ordinary Portland cement, early-strength Portland cement, low-heat Portland cement (belite type), fly ash cement, blast furnace cement, silica cement or a mixture thereof.

[0011] These cements are used to form highly fluid concrete, but preferably the cement is 400 to 60
0 (kg / m ³ ), water powder volume ratio: Vw / Vp: 0.90 to 1.20, fine aggregate volume ratio: Vs / Vm: 0.40 to 0.50, replacement ratio of admixtures such as blast furnace slag fine powder is all powder 10 to 50 (wt%) of the amount, and the additive rate of the polycarboxylic acid-based water reducing agent is 0.5 to
2.0 (wt%) is preferably mixed. The amount of air contained in high-fluidity concrete is 2.0 ± 1.0
(%) Is preferable.

The slump flow is from 400 mm to 700 mm.
mm. If the slump flow is less than the lower limit given in the above range, the fluidity of the highly fluid concrete slurry is insufficient, and the workability at the time of casting into the formwork is poor. However, it is not possible to obtain a good molded article having substantially no air bubbles on the surface of concrete having high fluidity. On the other hand, if the slump flow value exceeds the upper limit given in the above range, material separation occurs between the cement slurry and the aggregate, and the quality of the hardened concrete molded product is greatly reduced.

The water reducing agent mixed into concrete having high fluidity is a commercially available water reducing agent, for example, a polycarboxylic acid-based water reducing agent. The use of a polycarboxylic acid-based water reducing agent increases the viscosity of concrete and increases the separation resistance of concrete, and the hydration of cement is not affected by curing conditions or heat of hydration during hardening. This is because the reaction is uniformly promoted, and after hardening, it is excellent in the performance of forming a high-quality concrete molded product without sudden shrinkage or cracking.

Further, blast furnace slag fine powder or the like is mixed as an admixture for highly fluid concrete. The reason why the blast furnace slag fine powder or the like is used as the admixture is to increase the separation resistance of the concrete and to increase the strength of the concrete.

The shape, size, and molding material of the mold are not particularly limited. When the high-fluidity concrete is poured into the formwork, the internal vibration is directly applied to the high-fluidity concrete by an internal vibrator to compact the concrete until the concrete is cured and hardened. .

As the internal vibrator, for example, the rotation of a motor is converted into vibration using a mechanical member, or a fluid that can be transferred by a high-pressure pump and a valve that controls the flow path of the fluid are used. A commercially available one provided with a rod-shaped or band-shaped vibration generating portion of a type that generates vibration is used. And
The rod-shaped or band-shaped vibration generating part of the internal vibrator generates internal vibration by being inserted from above into concrete with high fluidity between the formwork and reinforcement, or between reinforcement. Need to give. At this time, the number of internal vibrators varies depending on dimensions such as the length, width, and height of the mold. For example, one vibrator is inserted at intervals of 20 cm to 50 cm. In addition, the rod-shaped or band-shaped vibration generator of the internal vibrator may touch the reinforcing bars indirectly,
Do not touch the formwork.

When the frequency of the high-fluidity concrete given by the internal vibrator exceeds 10,000 vpm, the bubbles generated on the surface and inside of the high-fluidity concrete gradually reduce the vibration from the internal vibrator. Receiving and being attracted to the vibration source. In particular, when the vibration frequency is 12000 to 14000 vpm, the effect of attracting air bubbles increases, and a molded article of high fluidity concrete having extremely few air bubbles on the concrete surface can be formed quickly and reliably. When the frequency is 12000 vpm or less in the above range, the effect of attracting bubbles to the vibration generating section of the internal vibrator is small because the transmission distance of the vibration is small, and when the frequency is 14000 vmp or more in the above range, the vibration Transmission distance is too large, bubbles are finely dispersed around the vibration generating part of the internal vibrator, it is difficult for bubbles to escape, and concrete near the vibration generating part separates, so the vicinity of the vibration generating part becomes mortar-rich and molding This is because it causes color unevenness on the product surface. The duration of internal vibration applied to high-fluidity concrete by an internal vibrator varies depending on the shape and dimensions of the formwork, the concrete composition and composition ratio, and the properties. It is a short time of several tens of seconds after inserting the machine.

After a predetermined vibration is applied to the high-fluidity concrete, the concrete is left for a predetermined time, for example, several hours, and is released after curing. Curing is not particularly limited, for example,
Either air curing or steam curing may be used.

[0019]

EXAMPLE In this example, a case where an L-shaped retaining wall is formed as a molded article of high-fluidity concrete will be described. As concrete having high fluidity, cement is more preferably 445 (kg / m ³ ) than the above range, natural crushed stone or gravel is 875 (kg / m ³ ) as coarse aggregate, and sand is 838 as fine aggregate. (kg/
m ^3), the water is 185 (kg / m ^3), blast furnace slag is 78 (kg / m ³ as admixture), also a polycarboxylic acid-based water-reducing agent as admixture 4.45 (kg / m ³ ) Mixed and air volume is 1.
A composition containing 4% was kneaded and used. Its slump flow was 660 × 630 mm. Further, the temperature as a fresh concrete was 29.0 ° C.

Immediately after the high-fluidity concrete of the above composition and slump flow was poured into the formwork, vibration was applied by inserting the rod-shaped or band-shaped vibration generating portion of the internal vibrator from above. At this time, the rod-shaped or band-shaped vibration generating portion of the internal vibrator is connected between the formwork and the reinforcement, or between the reinforcement and the reinforcement, of the reinforcement composed of the main reinforcement and the auxiliary reinforcement arranged in advance in the form. Concrete was inserted into the concrete having high fluidity at predetermined intervals from above, for example, at intervals of 20 cm to 50 cm. And the frequency of the internal vibrator
Vibration of 12000 to 14000 vpm was applied to each part for a short period of 15 seconds.

As a result, the air bubbles generated inside and on the surface of the concrete having high fluidity poured into the form are moved so as to be drawn toward the rod-shaped or band-shaped vibration generating portion of the internal vibrator. . Some are defoamed by vibrations while moving. In addition, bubbles generated on the surface of the high-fluidity concrete in contact with the formwork are also drawn inside from the surface side toward the vibration generating portion, and some of them are eliminated by being defoamed during the movement and are reduced. And between the formwork and reinforcement, or between reinforcement and reinforcement, for example 20
The surrounding air bubbles are attracted to each of the plurality of vibration generating portions inserted at intervals of cm to 50 cm, so that the surface air bubbles of the whole molded article are reduced efficiently and uniformly in a short time.

After the surface bubbles have been reduced in this way, the semi-molded product is transferred to a steam curing room for each mold at a temperature of 25 ° C.
At the temperature of 20 ° C / hr.
Heat to 65 ° C and maintain for 2 hours. Then, the temperature was gradually lowered, and then the concrete was naturally cooled to cure and harden the concrete, and was demolded within several hours to obtain a retaining wall made of high-fluidity concrete. The surface cell area ratio of the retaining wall was measured in accordance with the method for evaluating surface cells of self-filling high-fluidity concrete of the Japan Society of Civil Engineers, and as a result, a value of 0.05% or less was obtained.

Furthermore, since the concrete is not separated near the vibration generating portion of the internal vibrator by applying the internal vibration, a mortar-rich layer is not formed near the vibration generating portion, so that the molded product does not have uneven color. I got

In the high-fluidity concrete, cement is 445 (kg / m ³ ), and natural crushed stone is 875 (kg / m ³ ) as coarse aggregate.
As the fine aggregate, sand is 838 (kg / m ³ ), water is 185 (kg / m ³ ), and polycarboxylic acid-based high-performance water reducing agent is mixed with 4.45 (kg / m ³ ). Or, it was hardly affected by temperature conditions such as winter season and heat of hydration at the time of hardening, the hydration reaction of cement was promoted uniformly, and no cracks were obtained, and a high strength and high quality retaining wall was obtained.

Further, since 78 (kg / m ³ ) of blast furnace slag fine powder is mixed into the highly fluid concrete as an admixture, the strength (compressive strength and bending strength) of the concrete is increased, and the salt permeability is increased. It is possible to mold a high-quality molded article excellent in preventing the occurrence of a molded article.

In the above embodiment, the case where the retaining wall is formed as a high-fluidity concrete molded product is described as a representative example. However, the present invention is not limited to this. It can also be applied to flat plates, curb blocks, etc.

[0027]

As described above, according to the present invention, it is only necessary to apply internal vibration for a short period of time to a highly fluid concrete poured into a formwork by using a rod-shaped or band-shaped internal vibrator to improve productivity. In addition to being connected, unlike the vibration by an external vibrator, the cement paste in the concrete and the aggregate do not separate, exhibiting high fluidity and excellent workability, and bubbles generated on the surface of the molded product Can be efficiently, quickly and reliably reduced. For this reason, a high-quality molded article having high durability can be obtained. Furthermore, since a mortar-rich layer is not formed near the vibration source, color unevenness does not occur on the surface of the molded product, so that a molded product with good appearance and high reliability can be molded. In addition, the generation of noise to the surroundings is small, and the formwork is less damaged, so that the service life of the formwork is increased and the equipment itself can be implemented on a small scale at low cost.

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Claims (6)

[Claims] 1. A high-flow concrete is poured into a mold, and internal vibration is applied to the high-flow concrete using a rod-shaped or band-shaped internal vibrator to generate air bubbles on the surface of the molded product. A method for reducing surface air bubbles in a high-fluidity concrete molded product, characterized by reducing the temperature and then curing and hardening the concrete. 2. The internal vibrator applies internal vibration by being inserted from above into concrete having high fluidity between the formwork and the reinforcing bar or between the reinforcing bar and the reinforcing bar. The method for reducing surface bubbles in a high-fluidity concrete molded product according to claim 1. 3. The method according to claim 1, wherein the concrete having high fluidity has a slump flow of 400 mm to 700 mm. 4. The concrete having high fluidity has a cement content of 400 to 600 (kg / m ³ ) and a water powder volume ratio: Vw / Vp of 0.90.
~ 1.20, fine aggregate volume ratio: Vs / Vm is 0.40 ~ 0.50, replacement ratio of admixtures such as blast furnace slag fine powder is 10 ~ 50 (wt%) of the total powder amount
4. The method according to claim 1, wherein the admixture of the polycarboxylic acid-based water reducing agent is added in an amount of 0.5 to 2.0 (wt%) with respect to the powder. The method for reducing surface bubbles of a high-fluidity concrete molded product according to the above aspect. 5. The vibrating frequency of concrete having high fluidity by an internal vibrator is 12000 to 14000 vpm.
A method for reducing surface bubbles in a high-fluidity concrete molded product according to claim 4. 6. The method according to claim 1, wherein the application time of the internal vibration to the concrete having a high fluidity by the internal vibrator is a short time of several tens of seconds. 4. The method for reducing surface bubbles of a high-fluidity concrete molded product according to claim 5.