Manufacturing method of fresh concrete

Abstract

To improve cost-effectiveness and quality stability of fresh concrete production by preventing a material loss due to scattering of powdered admixture when producing fresh concrete by a method charging and stirring easily scattered powdered admixture such as the hollow microsphere into a mixing drum of an agitator vehicle.SOLUTION: A manufacturing method for fresh concrete includes: a powder charging step of charging a powdered mixture into a mixing drum 3 from a hopper opening 21 of an agitator vehicle 10; a hopper sealing step in which a hopper opening 21 is sealed by covering the hopper with a hopper cover 1 having a dome-shaped resin or cloth cover and an adjuster 12 having a function of increasing or decreasing a peripheral length of a cover bottom side opening 113 and provided on an outer edge of the cover bottom side opening 113; and an agitating step of agitating a fresh concrete material and the powdered admixture in the mixing drum 3.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing fresh concrete. More specifically, the present invention relates to a method for producing fresh concrete by adding a powdered admixture such as hollow microspheres to fresh concrete material in a mixing drum of an agitator vehicle. [Background technology]

[0002] It is widely known that concrete with excellent freeze-thaw resistance (referred to as "frost-resistant microcellular concrete" in this specification) can be obtained by forming fine bubbles with an appropriate diameter within an appropriate range of air content in concrete. In order to obtain such concrete, development of a manufacturing method for fresh concrete in which hollow resin microspheres are mixed into fresh concrete material is underway as one of the means for appropriately forming fine bubbles in concrete (see Patent Documents 1 and 2).

[0003] On the other hand, when producing fresh concrete with enhanced functionality by adding various kinds of admixtures to fresh concrete materials of a general mix, it is common to produce fresh concrete for pouring by adding specific admixtures to the fresh concrete materials that have been mixed in advance to a general prescribed mix at a ready-mix concrete plant and transported on an agitator truck at the concrete pouring site (see Patent Document 3).

[0004] The above-mentioned "frost-resistant microcellular concrete" is often produced by adding hollow microspheres to the mixing drum of an agitator truck at the concrete pouring site and mixing the hollow microspheres at high speed together with fresh concrete materials in the mixing drum.

[0005] However, the above hollow microspheres have a density of 0.13 g / cm 3Because the hollow microspheres are so light, when they are produced using the above-mentioned method, some of the hollow microspheres tend to scatter during the initial stage of high-speed mixing using a mixing drum, resulting in material loss and quality variations.

[0006] In order to cope with this problem, the amount of hollow microspheres added is currently increased based on past experimental data and past estimates of the losses. However, this is not economical and there is room for improvement in terms of quality stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2016-47790 A [Patent Document 2] JP 2017-105655 A [Patent Document 3] JP 2006-117466 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been developed in view of the above circumstances, and has an object to prevent loss of material due to scattering of powdered admixture, such as hollow microspheres, which are prone to scattering, when producing fresh concrete by feeding the powdered admixture, such as hollow microspheres, into the mixing drum of an agitator vehicle and stirring the mixture, thereby improving economy and quality stability in the production of fresh concrete. [Means for solving the problem]

[0009] The inventors have found that when producing fresh concrete by adding and stirring powdery admixture that is prone to scattering, the above-mentioned problems can be solved by using a hopper cover whose shape and function are optimized to match the shape of a hopper for adding materials to a mixing drum that has an inverted truncated cone shape and a circular or nearly circular opening, and have completed the present invention. Specifically, the present invention provides the following production methods, etc.

[0010] (1) A method for producing fresh concrete carried out in a mixing drum of an agitator vehicle, comprising the steps of: a powder feeding process in which powdered admixture is fed into the mixing drum from a hopper opening of the agitator vehicle on which fresh concrete material containing cement material, aggregate, and water is loaded; a hopper sealing process in which the hopper opening is sealed by covering it with a hopper cover which is a dome-shaped cover made of resin or cloth and has an adjuster attached to the outer edge of the bottom opening having a function of increasing or decreasing the circumference of the bottom opening of the cover; and a mixing process in which the fresh concrete material and the powdered admixture are mixed in the mixing drum.

[0011] According to the method for producing fresh concrete described in (1), when fresh concrete is produced by feeding powdered admixture that is easily scattered, such as hollow microspheres, into the mixing drum of an agitator vehicle and stirring the mixture, loss of material due to scattering of the powdered admixture can be prevented, thereby improving the cost-effectiveness and quality stability of the production of fresh concrete.

[0012] (2) The method for producing fresh concrete according to (1), wherein the powdered admixture is hollow microspheres.

[0013] According to the method for producing fresh concrete of (2), in the production of "frost-resistant micro-cellular concrete", the above-mentioned effects of the method for producing fresh concrete of (1) can be enjoyed, and by preventing the generation of dust and scattering of hollow microspheres, which are expensive materials, it is possible to significantly improve the economy and quality stability in the production of "frost-resistant micro-cellular concrete".

[0014] (3) A method for producing fresh concrete described in (1) or (2), in which the hopper cover is a transparent cover.

[0015] According to the method for producing fresh concrete of (3), when carrying out the method for producing fresh concrete described in (1) or (2), the condition inside the mixing drum and the adhesion of fresh concrete materials and admixtures to the inner surface of the hopper cover can be visually checked at all times while keeping the opening of the mixing drum sealed, so that a good mixing state can be maintained more reliably.

[0016] (4) A method for producing fresh concrete described in (1) or (2), in which, in the powder-feeding step, the powdered admixture is sealed in a water-soluble bag and fed into the mixing drum through the hopper opening.

[0017] According to the method for producing fresh concrete of (4), when carrying out the method for producing fresh concrete described in (1) or (2), scattering of powdery admixture that occurs when pouring into a mixing drum can be prevented, so that the cost efficiency and quality stability in the production of fresh concrete can be improved to an even more preferable level.

[0018] (5) A method for producing fresh concrete as described in (1) or (2), in which the hopper cover has an opening for inserting a supply pipe on its top surface, and the adjuster is also installed on the outer edge of the opening for inserting the supply pipe, the powder feeding process is performed by inserting a powder supply pipe into the mixing drum through the opening for inserting the supply pipe with the hopper cover installed on the hopper opening, and in the hopper sealing process, the adjuster installed on the outer edge of the opening for inserting the supply pipe is used to reduce the inner diameter of the opening for inserting the supply pipe to close the opening for inserting the supply pipe, thereby sealing the hopper opening.

[0019] According to the method for producing fresh concrete of (5), when carrying out the method for producing fresh concrete described in (1) or (2), scattering of powdery admixture that occurs when pouring into a mixing drum can be prevented, so that the cost efficiency and quality stability in the production of fresh concrete can be improved to a more preferable level.

[0020] (6) A sealing structure for a hopper for producing fresh concrete in the mixing drum of an agitator vehicle, comprising: a hopper having an inverted truncated cone shape; and a hopper cover having a dome-shaped cover made of resin or cloth, the hopper cover having an adjuster on the outer edge of the bottom opening having the function of increasing or decreasing the circumference of the bottom opening of the cover, the hopper cover being installed to cover the hopper opening, and the hopper opening being sealed by the function of the adjuster causing the outer edge of the cover bottom opening to be in close contact with the outer surface of the hopper near the hopper opening.

[0021] According to the sealed structure of the hopper of the agitator vehicle (6), when fresh concrete is produced by feeding powdered admixture that is prone to scattering, such as hollow microspheres, into the mixing drum of the agitator vehicle and stirring it, by using a hopper cover whose shape and function are optimized to match the shape of the hopper for feeding materials into the mixing drum, which has an inverted truncated cone shape with a circular or nearly circular opening, it is possible to prevent loss of material due to scattering of the powdered admixture and improve the cost-effectiveness and quality stability in the production of fresh concrete. Effect of the Invention

[0022] According to the present invention, when fresh concrete is produced by a method of adding a powdered admixture that is prone to scattering, such as hollow microspheres, into the mixing drum of an agitator vehicle and stirring the mixture, it is possible to prevent loss of material due to the scattering of the powdered admixture, thereby improving the cost-effectiveness and quality stability in the production of fresh concrete. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is an overall explanatory diagram of an example of an embodiment of a method for producing fresh concrete of the present invention. [Diagram 2] FIG. 2 is an overall explanatory diagram of another embodiment of the method for producing fresh concrete of the present invention. [Diagram 3] FIG. 2 is an explanatory diagram of an embodiment of a powder charging step and a hopper sealing step of the fresh concrete manufacturing method of the present invention. [Figure 4] 1A and 1B are a plan view and a side view of a hopper cover used in the fresh concrete manufacturing method of the present invention. [Diagram 5] 3A and 3B are a plan view and a side view of a hopper cover (another embodiment) used in the method for producing fresh concrete of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] <Manufacturing method of fresh concrete> The "manufacturing method for fresh concrete" of the present invention (hereinafter, simply referred to as "manufacturing method for fresh concrete") is a process for producing various kinds of fresh concrete that can be obtained by adding powdery admixtures such as hollow microspheres, etc., such as "frost-resistant microcellular concrete" containing hollow microspheres, by stirring the powdery admixtures with fresh concrete materials in the mixing drum of an agitator vehicle. According to the "manufacturing method for fresh concrete", concrete for casting having the performance required at each casting site can be produced by adding specific admixtures at the casting site, so that the above-mentioned various kinds of concrete for casting can be efficiently produced at or near the casting site without reducing the productivity of ready-mixed concrete at the ready-mixed concrete plant.

[0025] As the agitator vehicle, any agitator vehicle that has been widely used in the past for transporting fresh concrete from a ready-mix concrete factory that produces fresh concrete materials to a concrete pouring site can be used without any particular limitations. An agitator vehicle is a freight vehicle equipped with a mixing drum in the loading platform that can transport ready-mix concrete while stirring it. There are maximum load capacity vehicles of 2 to 11 ton class, and they are used according to the purpose.

[0026] The "method of manufacturing fresh concrete" is a process that includes a "powder adding process," a "hopper sealing process" in which the hopper opening of the mixing drum is sealed using a hopper cover, and a "mixing process" in which powdered admixture and fresh concrete materials are mixed in the mixing drum with the hopper opening sealed.

[0027] The "Fresh Concrete Manufacturing Method", in which the above-mentioned processes are carried out, is characterized primarily by the use of a proprietary hopper cover for the mixing drum (hopper cover 1 (see Figures 4 and 5)) in the "hopper sealing process", which prevents powdered admixtures from scattering from the mixing drum during the "mixing process".

[0028] The powdered admixture that can be used in the "manufacturing method for fresh concrete" is not limited to a specific admixture. However, in the following, unless otherwise specified, the details of the "manufacturing method for fresh concrete" in which the powdered admixture added to the fresh concrete material is "hollow microspheres" for producing "frost-resistant fine-celled concrete" will be described as a specific example of a preferred embodiment of the present invention.

[0029] [Powder feeding process] The "powder injection process" in the "method for producing fresh concrete" is a process in which powdered admixture is injected into a mixing drum from the hopper opening of an agitator vehicle which is loaded with fresh concrete material containing cement material, aggregate, and water.

[0030] In this "powder charging step", hollow microspheres (powder admixture) are charged into the mixing drum through a hopper opening, which is an opening on the top side of an inverted truncated cone hopper. The charging means and charging method are not particularly limited, but as an example, hollow microspheres 6 can be charged into the mixing drum 3 in the embodiment shown in Figure 1. In the embodiment shown in Figure 1, hollow microspheres 6 sealed in a water-soluble bag 4 are charged into the mixing drum 3 through a hopper opening 21 of an agitator car 10. The water-soluble bag 4 for encapsulating the hollow microspheres 6 is not limited to a specific bag as long as it is made of a material that dissolves in water during stirring in a mixing drum. For example, as disclosed in Japanese Patent No. 6664998, a bag made of water-soluble paper made from raw materials such as wood pulp, polysaccharides, cellulose, polyvinyl alcohol (poval), carboxymethyl cellulose, and starch, in which the wood pulp content in the raw materials is about 75% to 95%, can be preferably used.

[0031] Alternatively, the introduction of hollow microspheres (powder-like admixture) into the mixing drum in the "powder introduction step" can be performed in the embodiment shown in Fig. 2 as another example. In the embodiment shown in Fig. 2, the hollow microspheres 6 are sucked out of a bag 51 (see Fig. 2) made of resin or the like in which the hollow microspheres 6 are sealed, and are transported through a powder supply pipe 52 without contacting with the outside air until they are discharged outside the device, and are introduced into the mixing drum 3 from a hopper opening 21 of an agitator car 10. The overall configuration of the hollow microsphere introduction device 5 is not limited to a device having a specific configuration as long as it can introduce the hollow microspheres 6 into the mixing drum 3 through the powder supply pipe 52. For example, the "hollow microsphere introduction device" disclosed in Japanese Patent Publication No. 7241006 can be preferably used as the hollow microsphere introduction device 5 for carrying out the "powder introduction step" of the present invention.

[0032] [Hopper sealing process] The "hopper sealing process" is a process for sealing the hopper opening after the hollow microspheres (powder admixture) are introduced into the mixing drum in the "powder introduction process." The hopper opening is an inverted truncated cone shape with a circular or nearly circular opening, and the hopper cover is optimized in shape and function to fit the shape of the hopper.

[0033] The hopper opening can be sealed in the "hopper sealing step" by using a hopper cover 1 shown in Fig. 4, as an example, in the embodiment shown in Fig. 3. Specifically, as an example, in the case where the hollow microspheres 6 sealed in the water-soluble bag 4 are fed into the mixing drum 3 through the hopper opening 21 of the agitator car 10 as described above, the hopper opening 21 is sealed by covering it with the hopper cover 1 (see Fig. 4) as shown in Fig. 3. If the hopper 2 has a hopper lid 22, the hopper lid 22 can be closed after sealing with the hopper cover 1. The hollow microspheres 6 are scattered during agitation by the mixing drum 3 through the gap of the hopper lid 22 provided on the hopper 2 of the agitator car 10, and it has been confirmed that scattering of the hollow microspheres 6 cannot be effectively prevented by simply closing the hopper lid 22.

[0034] The hopper cover 1, which is installed at the hopper opening 21 to form a "sealed structure of the hopper", is a dome-shaped cover made of resin or cloth as shown in Fig. 4. The hopper cover 1 is provided with an adjuster 12 along the outer edge of the cover bottom opening 113, which has the function of increasing or decreasing the perimeter of the cover bottom opening 113 (the circumference if the opening shape is circular).

[0035] The adjuster 12 is provided so as to be slidable along the circumference of the cover bottom side opening 113, and so may be a string having an appropriate length that can arbitrarily increase or decrease the effective length of the circumference between a length that can cover the hopper opening 21 and a length that can bring the cover side surface 112 into close contact with the outer periphery of the outer surface immediately below the vicinity of the hopper opening 21. However, it is more preferable that the string constituting the adjuster 12 is a rubber string having an appropriate length and elasticity that acts as described above.

[0036] Here, the hopper 2 is necessarily in an inverted truncated cone shape to ensure its functionality, and the shape of its opening (hopper opening 21) is circular or approximately circular. Therefore, by providing the hopper cover 1 with the adjuster 12 having the above configuration and capable of performing the above function, the cover side surface 112 of the hopper cover 1 can be tightly fitted and engaged with the outer periphery of the outer surface of the hopper 2 immediately below the vicinity of the hopper opening 21 while covering the hopper opening 21, even with a simple configuration.

[0037] As described above as another example of the embodiment of the "powder charging step", when the hollow microspheres 6 are charged into the mixing drum 3 through the powder supply pipe 52 as shown in FIG. 2, the "manufacturing method of fresh concrete" can be carried out by using a hopper cover 1A shown in FIG. 5 instead of the hopper cover 1.

[0038] 5, the hopper cover 1A is made of the same material, shape, and structure as the hopper cover 1, and has a supply tube insertion opening 114 on the cover top surface 111 of the cover body 11, and an adjuster 13 having the same function as the adjuster 12 described above is provided on the outer edge of the supply tube insertion opening 114. The adjuster 13 only needs to be configured so that the inner edge of the supply tube insertion opening 114 can be brought into close contact with the outer edge of the powder supply tube 52, and more preferably, the adjuster 13 is configured so that the inner diameter of the supply tube insertion opening 114 can be further reduced to completely close the supply tube insertion opening 114 after the powder supply tube 52 is removed.

[0039] When the hollow microspheres are introduced into the mixing drum through the powder supply pipe 52 as shown in FIG. 2, the "powder introduction step" can be performed by inserting the powder supply pipe 52 into the mixing drum 3 through the opening 114 of the hopper cover 1A shown in FIG. 5, with the hopper cover 1A installed at the hopper opening 21. In this case, it is preferable to introduce the hollow microspheres 6 in a state where the inner edge of the opening 114 of the hopper cover 1A is brought into close contact with the outer edge of the powder supply pipe 52 by the function of the adjuster 13. In this case, by maintaining the inner edge of the opening 114 of the hopper cover 1A in close contact with the outer edge of the powder supply pipe 52 even after the hollow microspheres 6 are introduced, a sealed structure for preventing the hollow microspheres 6 from scattering at the hopper opening 21 can be formed. Alternatively, the same sealed structure as above can be formed by closing the opening 114 of the hopper cover 1A by the function of the adjuster 13 after the powder supply pipe 52 is removed. Alternatively, the above-mentioned sealed structure can be formed using the hopper cover 1 after removing the powder supply pipe 52. In any of these embodiments, as long as the sealed structure at the hopper opening 21 is formed by the hopper cover 1 or hopper cover 1A having an adjuster, this is regarded as the "hopper sealing step" of the present invention being performed.

[0040] The material for the hopper covers 1 and 1A may be any material that is airtight and flexible, but it is preferable that the material be a transparent resin such as various polyethylene-based resins.

[0041] [Stirring process] The "mixing process" is a process of mixing and mixing the hollow microspheres (powder admixture) introduced into the mixing drum in the "powder introduction process" with the fresh concrete material in the mixing drum. As described above, the "mixing process" can be carried out by using, without any particular limitation, an agitator vehicle that has been widely used in the past for transporting fresh concrete material from a ready-mix concrete factory where the fresh concrete material is produced to a concrete pouring site, and by utilizing a given mixing and mixing function.

[0042] [Fresh concrete] "Frost-resistant microcellular concrete", which is a representative fresh concrete obtainable by the "manufacturing method for fresh concrete" of the present invention, is preferably one in which the amount of air bubbles having a diameter of 0.01 mm to 0.3 mm is 0.5 volume % to 4.0 volume % after hardening. The volume ratio of air bubbles and the air bubble spacing coefficient in the hardened concrete can be measured by, for example, the well-known method "ASTM C457 Method for measuring air bubble parameters of hardened concrete by microscope".

[0043] [Hollow microsphere] In addition, the "hollow microspheres" in this specification are particles having cavities contained therein, and include organic and inorganic ones. Inorganic ones include fly ash balloons, shirasu balloons, borosilicate glass balloons, perlite, recycled glass, etc., and organic ones include acrylonitrile, acrylic acid esters, methacrylic acid esters, phenol, polymethyl methacrylate, methacrylonitrile, polystyrene, vinylidene chloride, vinyl acetate, and polyphenols, etc. In the "method for producing fresh concrete" of the present invention, any of the above "hollow microspheres" can be used without any particular limitation, but it is particularly effective when inorganic hollow microspheres, which have a very small bulk density of 0.60 g / cc at the maximum and are particularly prone to scattering during mixing, are used. The bulk density (g / cc) of the main inorganic "hollow microspheres" is as shown in Table 1 below.

[0044] [Table 1]

[0045] [Other powder admixtures] In the "manufacturing method for fresh concrete" of the present invention, the admixture that can be used as the "powdered admixture" is not limited to the above-mentioned "hollow microspheres". The "manufacturing method for fresh concrete" of the present invention can be applied to the manufacture of various fresh concretes by adding various powdered admixtures or admixtures to the fresh concrete material loaded in the agitator vehicle. In addition, the "admixture" in the present invention also includes agents generally called "admixtures" (AE agents, high-performance water reducing agents, high-performance AE water reducing agents, etc.).

[0046] More specifically, in the "production method for fresh concrete" of the present invention, various "powder admixtures" having a bulk density of 1.0 g / cc or less, preferably 0.6 or less, can be used without any particular restrictions, not limited to "hollow microspheres". By feeding various "powder admixtures" having a low bulk density into the mixing drum of an agitator vehicle and kneading and stirring them, the "production method for fresh concrete" of the present invention can produce fresh concrete having various functions while maintaining high economic efficiency and quality stability, as in the embodiment using "hollow microspheres" described above, while preventing the powder from scattering.

[0047] An example of the "other powdery admixture" suitable for the "manufacturing method for fresh concrete" of the present invention is a "powdered high-performance air-entraining water-reducing agent whose main component is polycarboxylic acid" having a bulk density of approximately 0.5 to 0.6. EXAMPLES

[0048] The "method for producing fresh concrete" of the present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below.

[0049] In order to confirm the excellent effect of the manufacturing method of the present invention, a manufacturing test of concrete hardened bodies was carried out using each material described below. In the examples, fresh concrete was manufactured by the "manufacturing method of fresh concrete (embodiment shown in FIG. 1)" of the present invention described in detail above, using a "hopper cover" made of polyethylene resin having the shape and configuration shown in FIG. 4, and the fresh concrete thus obtained was hardened in a test formwork (diameter 10 cm x height 20 cm) to manufacture a concrete hardened body. The amount of air (volume) present in each hardened body of concrete after hardening was measured in accordance with ASTM-C457. The "amount of air in hardened concrete (%) per 1 volume% of hollow microspheres added" calculated from the measurement results and the "loss rate of hollow microspheres (%)" which is presumed to be due to scattering during the manufacturing process are shown in Table 2.

[0050] (Composition of fresh concrete materials) Cement: "ordinary Portland cement" (water / cement ratio: 0.48) Fine aggregate: (742kg / m 3 ) Coarse aggregate: (993kg / m 3 ) AE water reducing agent (No. 70, BASF Japan) (2.784 kg / m 3 ) AE auxiliary (Microair 202, BASF Japan) (24.4 g / m 3 ) (Powdered admixture) Hollow microspheres: acrylonitrile (1.95 kg / m 3 )

[0051] In the comparative example, the above-mentioned "hopper cover" was not used, the "hopper sealing process" was not performed, and the other manufacturing conditions were the same as those in the example, and a concrete hardened body was manufactured using the same materials and in the same manner.

[0052] [Table 2]

[0053] From the above test results, it was confirmed that the "method of producing fresh concrete" of the present invention can prevent the loss of materials due to scattering of powdered admixtures, such as hollow microspheres, when producing fresh concrete by adding the powdered admixtures, which are easily scattered, such as hollow microspheres, into the mixing drum of an agitator vehicle and stirring the mixture, thereby improving the economy and quality stability of the production of fresh concrete. Furthermore, it was confirmed that the hopper cover used to carry out the present invention is lightweight and can be easily installed and removed even by a single worker, and that the process is extremely easy to carry out and is excellent in terms of ease of operation. [Explanation of symbols]

[0054] 1, 1A Hopper cover 11 Cover body 111 Top of cover 112 Cover side 113 Cover bottom opening 114 Supply pipe insertion opening 12, 13 Adjuster 2 Hopper 21 Hopper opening 22 Hopper lid 3 Mixing drum 4 Water-soluble bag 5 Hollow microsphere mixing device 51 bags 52 Powder supply pipe 6. Hollow microspheres (powder admixture) 10 Agitator car

Claims

1. A method for producing fresh concrete in a mixing drum of an agitator vehicle, comprising: A powder injection process of injecting a powder admixture into the mixing drum from a hopper opening of the agitator car on which fresh concrete material containing cement material, aggregate, and water is loaded; a hopper sealing process for sealing the hopper opening by covering the hopper with a hopper cover having a dome-shaped resin or cloth cover, the hopper cover having an adjuster at the outer edge of the bottom opening of the cover that has a function of increasing or decreasing the perimeter of the bottom opening of the cover; A mixing step of mixing the fresh concrete material and the powdered admixture in the mixing drum; To carry out Method for producing fresh concrete.

2. The powder admixture is a hollow microsphere. A method for producing fresh concrete according to claim 1.

3. The hopper cover is a transparent cover. The method for producing fresh concrete according to claim 1 or 2.

4. In the powder charging step, the powder admixture is charged into the mixing drum from the hopper opening in a water-soluble bag. The method for producing fresh concrete according to claim 1 or 2.

5. The hopper cover has an opening for inserting a supply pipe on a top surface of the cover, and the adjuster is also provided on an outer edge of the opening for inserting the supply pipe, The powder introducing step is performed by inserting a powder supply pipe into the mixing drum through the supply pipe insertion opening with the hopper cover installed on the hopper opening, In the hopper sealing step, the adjuster provided on the outer edge of the supply pipe insertion opening reduces an inner diameter of the supply pipe insertion opening to close the supply pipe insertion opening, thereby sealing the hopper opening. The method for producing fresh concrete according to claim 1 or 2.

6. A sealing structure of a hopper for producing fresh concrete in a mixing drum of an agitator vehicle, A hopper having an inverted truncated cone shape; A hopper cover is a dome-shaped cover made of resin or cloth, and an adjuster having a function of increasing or decreasing the perimeter of the bottom opening of the cover is provided on the outer edge of the bottom opening of the cover; comprising The hopper cover is installed to cover the hopper opening, and the outer edge of the cover bottom side opening is in close contact with the outer surface of the hopper near the hopper opening due to the function of the adjuster, thereby sealing the hopper opening. Sealed structure of the hopper of the agitator vehicle.

Images