JP2013166353A - Method for manufacturing concrete formed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a concrete formed body of high strength, with a small water/cement ratio, and containing very little amount of bubbles, in a shorter time than ever.SOLUTION: Uncured concrete is manufactured, then placed into a form, an atmosphere where the concrete is present is left in a decompressed state for a given time and a water/cement ratio is lowered, to obtain a concrete formed body of high strength.

Description

  The present invention relates to a method for producing a concrete molded body.

Conventionally, several methods aimed at obtaining a high-strength concrete molded body have been proposed.
For example, in Patent Document 1, a frame is composed of a mold frame in which a dewatering / degassing sheet is affixed to the surface of a barrier plate, and concrete is placed in the frame of the mold with the dehydration / degasification sheet affixing surface inside. A concrete pouring method is described in which a depressurized state is formed inside the dewatering / degassing sheet after being driven.

  Further, for example, in Patent Document 2, prior to producing a lightweight aerated concrete by high-pressure steam curing of a mortar foam, the mortar foam is put in a sealed container and the moisture is reduced to a saturated steam pressure below the foam temperature. In the vacuum deaeration processing method of the lightweight cellular concrete to be evaporated, the vacuum deaeration processing method of the lightweight cellular concrete is characterized in that the end point of the vacuum deaeration processing is set by using the amount of water evaporated from the foam as an index. Has been.

JP-A-4-309663 JP-A-5-105545

  However, the present inventor has found that the conventional method as described in Patent Documents 1 and 2 promotes hardening of the surface of the concrete molded body, but it is difficult to obtain a sufficiently strong concrete molded body in a short time. .

  The objective of this invention is providing the manufacturing method which can obtain the concrete molded object whose intensity | strength is higher than before in a short time compared with the past. Moreover, it is providing the manufacturing apparatus which can implement such a manufacturing method.

As described above, the present inventor diligently studied the cause of difficulty in obtaining a concrete molded body having a sufficiently high strength in a short time by the conventional method, and completed the present invention.
The present invention includes the following (1) to (7).
(1) Producing uncured concrete, then placing it in a mold, reducing the amount of water contained in the concrete by reducing the amount of water contained in the concrete by reducing the atmosphere in which the concrete exists for a predetermined time. A method for producing a concrete molded body that obtains a high-strength concrete molded body by lowering the cement ratio.
(2) The method for producing a concrete molded body according to the above (1), wherein the concrete placed is vibrated during the reduced pressure state.
(3) The method for producing a concrete molded body according to (2), wherein the vibration is performed using a vibration generator.
(4) The method for producing a concrete molded body according to (2) above, wherein the vibration is performed using an ultrasonic vibrator.
(5) The method for producing a concrete molded body according to any one of the above (1) to (4), wherein the concrete is concrete that does not use a water reducing agent.
(6) A concrete molded body produced by the method for producing a concrete molded body according to any one of (1) to (5) above.
(7) A concrete molded body manufacturing apparatus,
A formwork for placing uncured concrete,
A sealed container that can contain a formwork inside;
A decompressor for reducing the pressure inside the sealed container;
A concrete molded body production apparatus, characterized in that the method for producing a concrete molded body according to any one of (1) to (5) can be performed.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method which can obtain a high-strength concrete molded object with a small water-cement ratio and few bubbles is easier than before. Moreover, the manufacturing apparatus which can implement such a manufacturing method can be provided.

It is the schematic of the apparatus used in the Example of this invention. It is a flowchart which shows the operation procedure in an Example.

The present invention will be described.
The present invention produces uncured concrete, and then casts it into a formwork, reduces the amount of water contained in the concrete by reducing the amount of water contained in the concrete by reducing the atmosphere in which the concrete exists for a predetermined time. This is a method for producing a concrete molded body that obtains a high-strength concrete molded body by reducing the water-cement ratio.

<Concrete>
In the present invention, concrete is defined as a mixture containing at least cement and water. Therefore, in the present invention, concrete includes mortar and cement paste.

  In the present invention, the concrete contains cement and water, and may contain aggregate and admixture.

  Here, the cement is not particularly limited, and conventionally known ones can be used, for example, Portland cement can be used. Specifically, for example, ordinary Portland cement, early-strength Portland cement, blast furnace cement, low heat Portland cement, intermediate heat Portland cement, and the like can be used.

  Also, water is not particularly limited, and for example, tap water, ion exchange water, pure water, or the like can be used.

  Also, the aggregate is not particularly limited, and conventionally known ones can be used, for example, fine aggregates and coarse aggregates can be used. Here, as the fine aggregate, land sand, river sand, crushed sand, sea sand, dredged sand, slag fine aggregate, lightweight fine aggregate, heavy fine aggregate, recycled fine aggregate, or a mixed fine aggregate thereof can be used. Further, as the coarse aggregate, river gravel, mountain gravel, sea gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, heavy coarse aggregate, recycled coarse aggregate, or a mixed coarse aggregate thereof can be used.

  Also, the admixture is not particularly limited, and conventionally known materials can be used, for example, blast furnace slag fine powder, fly ash, silica fume, limestone fine powder, early-strength expansion material, high-performance water reducing agent, etc. Can be used. In addition, air entraining agents, antifoaming agents, antifoaming agents, foaming agents, thickeners, rust preventives, pigments, etc. may be used as admixtures as long as the strength and workability are not impaired. Further, fibers such as metals may be mixed.

Concrete can be obtained by mixing such cement and water, and if necessary, aggregates and admixtures at a conventionally known mixing ratio.
For example, concrete can be obtained by mixing water and cement so that the water-cement ratio is 40% or less, preferably 20% or less, more preferably 17% or less. In addition, when using cement for ultra high strength concrete, such as silica fume cement (SFC) using low heat system Portland cement, it can also be made into 15% or less.
Here, the water-cement ratio means a percentage (water / cement × 100) of the mass ratio of water and cement.

  The amount of aggregate is a volume ratio ((coarse aggregate + fine aggregate) / total volume), which is 0% for cement paste, about 40% for mortar, and about 70% for concrete. In the case of concrete, the mass ratio to cement ((cement / (coarse aggregate + fine aggregate)) can be about 15%.

  Further, the amount of the admixture can be from about 0.1% by mass ratio (admixture / total mass) to about 10% when the reinforcing fiber is used.

  Moreover, when placing concrete in a formwork, a water reducing agent can be used in order to reduce a moisture content, ensuring fluidity | liquidity. When the water reducing agent is not used, the water cement ratio is about 40%. However, by using the water reducing agent, concrete having a water cement ratio of 20% or less or 17% or less in advance can be used. In addition, when not using a water reducing agent, the water-cement ratio of concrete can also be made into 20% or less or 17% or less after casting to a formwork by extending the holding time of the pressure reduction state mentioned later. In addition, when using the above-mentioned cement for ultra high strength concrete, it can also be made into 15% or less.

<Decompression>
After placing the concrete as described above into a desired formwork, the atmosphere in which the concrete exists is brought into a reduced pressure state. For example, the formwork in which uncured concrete is cast is put into a sealed container, and the inside of the sealed container is decompressed using a decompression machine (such as a decompression pump), so that the decompressed state can be achieved. The decompressed state is maintained for a predetermined time. The predetermined time can be, for example, 3 minutes to 20 minutes, and is preferably 5 minutes to 10 minutes. By setting the reduced pressure state, the boiling point of water is lowered, and the water in the concrete is easily converted to water vapor. As a result, the water-cement ratio of the concrete can be lowered after placement. That is, the strength of the placed concrete can be increased.
The degree of decompression is not particularly limited, but the pressure of the atmosphere in which the formwork on which uncured concrete has been placed is preferably 5 to 60 Torr, more preferably 5 to 40 Torr, and 5 to 30 Torr. More preferably it is.

In a reduced pressure atmosphere, moisture is released from the surface of the uncured concrete. Further, bubbles containing moisture are released from the inside of the concrete to the outside. As a result, moisture in the concrete is reduced.
Here, since the surface portion of the concrete is easily hardened before the inside, the hardened portion may obstruct the release of bubbles.
In order to prevent the hardening of the concrete surface portion, a vibration exciter can be installed in the sealed container, and vibration can be applied to the formwork on which the uncured concrete is placed. That is, the vibration is also applied to the surface portion of the concrete, so that the hardening is inhibited and the release of bubbles is not hindered. Moreover, the discharge | release of the bubble from concrete inside is accelerated | stimulated. Here, as the vibrator, the mold may be vibrated using a vibration generator, or the mold may be vibrated using an ultrasonic vibrator.

Here, in order to finely manage the moisture content of the concrete, the surface of the concrete is released in a depressurized state while keeping the moisture on the surface of the concrete to be above a certain value, so that the surface of the concrete releases air bubbles from the inside. It is also possible to efficiently remove the moisture inside the concrete so as not to hinder.
Further, the moisture concentration of the surface portion of the concrete is controlled to be 15% by mass or more, more preferably 14% by mass or more, more preferably 13% by mass or more, and 12% by mass. % Or more is more preferable. This is because the moisture inside the concrete can be efficiently removed.

  For example, by measuring the surface resistance value of the concrete, it can be managed so that the moisture concentration on the surface of the concrete becomes a certain value or more. Specifically, by controlling the concrete surface resistance value to be 40 kΩ / □ or less, the moisture concentration on the concrete surface can be controlled to a certain value or more. The surface resistance value is preferably 35 kΩ / □ or less, more preferably 30 kΩ / □ or less, more preferably 25 kΩ / □ or less, and further preferably 20 kΩ / □ or less.

As described above, the moisture concentration of the portion is managed by measuring the resistance value of the concrete surface, and when the moisture concentration is smaller than a predetermined value, the surface portion of the concrete is stirred. When agitated, the water concentration increases because it mixes with the inner part of the concrete.
When the moisture concentration is smaller than a predetermined value, moisture may be added to the surface portion of the concrete using a spray bottle or the like.

  Such a method for producing a concrete molded body according to the present invention includes a mold for placing uncured concrete, a sealed container that can contain the mold, and a reduced pressure in which the inside of the sealed container is decompressed. And a concrete molded body manufacturing apparatus including the machine. Such a concrete molded body manufacturing apparatus may be of the form shown in FIG. 1 used in the examples described later. With such an apparatus, the concrete molded body of the present invention can be produced.

<Example 1>
The apparatus shown in FIG. 1 was prepared. The apparatus 10 shown in FIG. 1 includes a sealed container 12, a decompression pump 20, and a vibration exciter 26. The sealed container 12 is provided with a vacuum gauge 22 and an air valve 24. Here, a mold 14 in which the concrete 1 is cast can be installed in the sealed container 12.

  The sealed container 12 only needs to be able to maintain a reduced pressure state of about 5 to 15 Torr (that is, a reduced pressure state having a lower degree of vacuum than 30 Torr, 40 Torr, and 60 Torr (that is, a reduced pressure state close to atmospheric pressure). ), Metals such as stainless steel, and containers such as glass can be used. Moreover, the formwork 14 into which the concrete 1 was poured can be installed inside the sealed container 12. The hermetic container 12 is provided with an opening capable of maintaining an airtight state after the mold 14 is installed. Further, a vacuum pump 20, a vacuum gauge 22, and an air valve 24 are connected to the sealed container 12, and airtightness is maintained. In addition, when using metal containers, such as stainless steel, for the airtight container 12, it is desirable to provide an observation window so that the state of the internal concrete 1 can be observed.

  As long as the formwork 14 can cast the concrete 1 therein, a steel formwork, a wooden formwork, or the like can be used. When producing a precast product in a factory, a steel formwork is desirable from the viewpoint of cost.

  The decompression pump 20 is a decompressor and decompresses the inside of the sealed container 12. As the decompression pump 20, a type that operates from atmospheric pressure, such as a diaphragm pump and a rotary pump, can be used. Moreover, if it is a pressure reduction machine which can be decompressed to about 5-15 Torr, it will not be restricted to said pump, You may use various pressure reduction machines.

  The vacuum gauge 22 measures the pressure in the sealed container 12. The vacuum gauge 22 may be a mechanical pressure gauge such as a Bourdon tube gauge or a diaphragm gauge. As long as the vacuum gauge 22 can measure a pressure of about 5 to 15 Torr from atmospheric pressure, another type may be used.

  The air valve 24 is a so-called vacuum valve, is closed when the inside of the sealed container 12 is brought into a reduced pressure state, and is released when the pressure in the sealed container 12 is returned to atmospheric pressure.

  The vibration exciter 26 is installed at the bottom of the sealed container 12 and applies vibration to the mold 14 installed on the vibration exciter 26. Various kinds of vibration generators can be used for the shaker 26. For example, an electrodynamic shaker, a piezoelectric shaker, a hydraulic shaker, or the like can be used. Further, an ultrasonic vibrator may be used.

  In addition, the apparatus 10 is provided with a mixing rod (not shown) that can stir the surface portion of the concrete 1 poured into the mold 14, and this mixing rod is operated from the outside of the sealed container 12. The surface portion of the concrete 1 poured into the mold 14 can be agitated. Further, a sprayer that sprays water on the surface of the concrete 1 may be provided.

High-strength concrete was manufactured using the apparatus 10 described above. Hereinafter, description will be made with reference to the flowchart shown in FIG.
First, the concrete 1 was cast into the inside of the mold 14, that is, poured into the mold 14, and the mold 14 into which the concrete 1 was poured was placed on the vibration exciter 26 in the sealed container 12 (step S 10).

Here, the concrete 1 is a mixture (so-called mortar) in which the following cement, silica fume, silica sand, water reducing agent, and water are sufficiently mixed.
Portland cement (model number: normal Portland cement, manufactured by Taiheiyo Cement): 1200 g
Silica fume (model number: silica fume, manufactured by BASF Pozzolith): 120 g
・ Silica sand (fine aggregate): 330 g of cinnabar 3, 330 g of cinnabar 5
Water reducing agent (model number: Leobilt SP-8HU, manufactured by BASF Pozzolith): 26.4 g
・ Water (purified water): 237.6 g
・ Water cement ratio: 20%
The above concrete was mixed to prepare three 450 g cylindrical specimens.

Next, after the air valve 24 is closed, the decompression pump 20 starts decompressing the inside of the sealed container 12, and the inside of the sealed container 12 is decompressed to about 20 Torr while confirming the pressure with the vacuum gauge 22 (step S12). ).
Here, after the pressure was reduced to a predetermined pressure, the vibrator 26 was operated in order to vibrate for a predetermined time (for example, about 10 minutes). Thereby, the air entrained at the time of concrete production can be aerated, and the generated water vapor can be discharged from the concrete. Thereafter, the shaker 26 was stopped, the air valve 24 was opened, and the inside of the sealed container 12 was returned to atmospheric pressure (step S14).

  Subsequently, the concrete 1 and the mold 14 were taken out from the sealed container 12 and left at room temperature for 1 day (step S16). Then, underwater curing was performed for 19 days (step S18), and a specimen having a material age of 21 days was obtained.

  Next, the compression strength of the obtained specimen was measured using a concrete automatic compression tester CONCRETO 2000 (manufactured by Shimadzu Corporation). As a result, the compressive strength was 151.6 MPa (average value of three specimens).

<Comparative Example 1>
Next, as Comparative Example 1, the same concrete as in Example 1 was poured into the mold 14 and allowed to cure under water after standing at room temperature to obtain a specimen having a material age of 21 days. Then, when the compressive strength was measured by the same method as in Example 1, the compressive strength was 114.6 MPa (average value of three specimens).

  From the results of Example 1 and Comparative Example 1 above, it was confirmed that when the production method according to the present invention was applied, a concrete molded body with a remarkably high compressive strength could be obtained in a short time.

  As mentioned above, although the manufacturing method of the concrete molded object which concerns on this invention, and the manufacturing apparatus of a concrete molded object were demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it is various. Of course, improvements and changes may be made.

DESCRIPTION OF SYMBOLS 1 Concrete 10 Apparatus 12 Sealed container 14 Formwork 20 Depressurization pump 22 Vacuum gauge 24 Air valve 26 Exciter

Claims (7)

  An uncured concrete is prepared, and then placed in a mold, and the atmosphere in which the concrete exists is reduced in pressure for a predetermined time, the amount of water contained in the concrete is reduced, and the water-cement ratio of the concrete is increased. A method for producing a concrete molded body that obtains a high-strength concrete molded body by lowering.   2. The method for producing a concrete compact according to claim 1, wherein, in the reduced pressure state, the concrete placed is vibrated.   The method for producing a concrete molded body according to claim 2, wherein the vibration is performed using a vibration generator.   The method for producing a concrete molded body according to claim 2, wherein the vibration is performed using an ultrasonic vibrator.   The said concrete is a concrete which does not use a water reducing agent, The manufacturing method of the concrete molded object in any one of Claims 1-4 characterized by the above-mentioned.   The concrete molded object manufactured by the manufacturing method of the concrete molded object in any one of Claims 1-5. An apparatus for producing a concrete molded body,
A formwork for placing uncured concrete,
A sealed container that can contain a formwork inside;
A decompressor for reducing the pressure inside the sealed container;
An apparatus for producing a concrete molded body, characterized in that the method for producing a concrete molded body according to any one of claims 1 to 5 can be performed.

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