Method for mixing concrete composition and method for producing concrete composition

Abstract

To provide a concrete composition kneading method capable of reducing the kneading time of a concrete composition having a low water-binding material ratio and comprising silica fume, and a concrete composition production method.SOLUTION: A concrete composition kneading method comprises: a first kneading step where first cement C1, first silica fume SF1, a fine aggregate and a coarse aggregate are kneaded to obtain a first kneaded material; a second kneading step where the first kneaded material, water and an additive are kneaded to obtain a second kneaded material; and a third kneading step where the second kneaded material, second cement C2 and second silica fume SF2 are kneaded to obtain a third kneaded material. A water-kneading material ratio (W / (C+SF)) is 25 mass% or less, and the mass ratio of the total content of the first cement and the first silica fume satisfies the following inequality (1): 0.40≤(C1+SF1) / (C+SF)≤0.60(1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for mixing a concrete composition and a method for producing a concrete composition. [Background technology]

[0002] One method for producing high-strength concrete is to reduce the water-binder ratio of the concrete composition. 2 When producing high-strength concrete exceeding this limit, the water-binder ratio is set to 25% or less. However, lowering the water-binder ratio increases the viscosity of the concrete composition, making it difficult to mix. Therefore, silica fume is sometimes added to reduce the viscosity of the concrete composition. For example, Patent Document 1 discloses a high-strength cement composition containing Portland cement containing specified amounts of 2CaO·SiO2 and 3CaO·Al2O3, silica fume, and gypsum. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-68546 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because silica fume is an ultrafine particle, it is prone to secondary aggregation, and therefore requires long mixing times to disperse silica fume in concrete compositions.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for mixing a concrete composition that has a low water-binder ratio and that can shorten the mixing time for a concrete composition that contains silica fume, and a method for producing a concrete composition. [Means for solving the problem]

[0006] The method for mixing a concrete composition according to the present invention is a method for mixing a concrete composition containing cement C consisting of a first cement C1 and a second cement C2, silica fume SF consisting of a first silica fume SF1 and a second silica fume SF2, fine aggregate S, coarse aggregate G, water W, and admixture SP, the method comprising: a first mixing step of mixing the first cement C1, the first silica fume SF1, the fine aggregate S, and the coarse aggregate G to obtain a first mixture; a second mixing step of mixing the first mixture, water W, and the admixture SP to obtain a second mixture; and a third mixing step of mixing the second mixture, the second cement C2, and the second silica fume SF2 to obtain a third mixture, wherein the water-to-binder ratio (W / (C+SF)) is 25% by mass or less, and the mass ratio of the total content of the first cement C1 and the first silica fume SF1 to the total content of the cement C and the silica fume SF satisfies the following formula (1): 0.40≦(C1+SF1) / (C+SF)≦0.60 (1) (In the formula, each symbol represents the content of each component (kg / m 3 ) indicates.

[0007] With this configuration, the method for mixing a concrete composition can shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume.

[0008] In the method for kneading a concrete composition according to the present invention, the water-binder ratio (W / (C+SF)) may be 14 mass % or more.

[0009] With this configuration, the method for mixing a concrete composition can mix the concrete composition using a general-purpose mixer.

[0010] In the method for kneading a concrete composition according to the present invention, the mass ratio of the content of the silica fume SF to the total content of the cement C and the silica fume SF may satisfy the following formula (2). 0.08≦SF / (C+SF)≦0.20 (2) (In the formula, each symbol represents the content of each component (kg / m 3 ) indicates.

[0011] With this configuration, the method for mixing a concrete composition can further shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume.

[0012] In the method for kneading a concrete composition according to the present invention, the mass ratio of the first silica fume SF1 to the total content of the first cement C1 and the first silica fume SF1 may satisfy the following formula (3). 0.05≦SF1 / (C1+SF1)≦0.40 (3) (In the formula, each symbol represents the content of each component (kg / m 3 ) indicates.

[0013] With this configuration, the method for mixing a concrete composition can further shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume.

[0014] The method for producing a concrete composition according to the present invention includes the method for kneading a concrete composition described above.

[0015] With this configuration, the method for producing a concrete composition can shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume, thereby enabling the concrete composition to be produced efficiently. [Effects of the Invention]

[0016] According to the present invention, a method for mixing a concrete composition and a method for producing a concrete composition can be provided that can shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume. [Brief explanation of the drawings]

[0017] [Figure 1] 10 is a graph showing the load current applied to the mixer when mixing the concrete composition of Example 2-3. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the method for kneading a concrete composition and the method for producing a concrete composition according to this embodiment will be described.

[0019] <Method of mixing concrete composition> The method for mixing a concrete composition according to this embodiment is a method for mixing a concrete composition containing cement C consisting of first cement C1 and second cement C2, silica fume SF consisting of first silica fume SF1 and second silica fume SF2, fine aggregate S, coarse aggregate G, water W, and admixture SP, and includes a first mixing step of mixing the first cement C1, the first silica fume SF1, the fine aggregate S, and the coarse aggregate G to obtain a first mixture, a second mixing step of mixing the first mixture with water W and the admixture SP to obtain a second mixture, and a third mixing step of mixing the second mixture with second cement C2 and the second silica fume SF2 to obtain a third mixture.

[0020] Hereinafter, each material used in the method for kneading a concrete composition according to this embodiment will be described, followed by a description of the method for kneading a concrete composition.

[0021] Cement C consists of first cement C1 and second cement C2. First cement C1 is the cement contained in the first kneaded mixture described below, and second cement C2 is the cement contained in the third kneaded mixture described below. The first cement C1 and second cement C2 are not particularly limited, and examples include Portland cements such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, and white Portland cement, as specified in JIS R 5210, ultra-rapid-hardening cement, and alumina cement. Various blended cements obtained by mixing the Portland cement with fly ash, blast furnace slag, etc. can also be used. The first cement C1 and second cement C2 may be composed of one of the above cements alone or two or more of them in combination. Furthermore, the first cement C1 and the second cement C2 may be the same type of cement or different types of cement.

[0022] The silica fume SF consists of a first silica fume SF1 and a second silica fume SF2. The first silica fume SF1 is the silica fume contained in the first kneaded mixture, and the second silica fume SF2 is the silica fume contained in the third kneaded mixture. Examples of the first silica fume SF1 and the second silica fume SF2 include powdered silica fume, granular silica fume, and silica fume slurry as specified in JIS A 6207:2016. Among these, the first silica fume SF1 and the second silica fume SF2 are preferably powdered silica fume or granular silica fume from the viewpoint of shortening the mixing time of the concrete composition. Note that the first silica fume SF1 and the second silica fume SF2 may be one of the above-mentioned various silica fumes, or two or more of them may be used in combination. Furthermore, the first silica fume SF1 and the second silica fume SF2 may be the same type of silica fume or different types of silica fumes.

[0023] The mass ratio of the content of silica fume SF to the total content of cement C and silica fume SF in the concrete composition may satisfy the following formula (2). 0.08≦SF / (C+SF)≦0.20 (2) In formula (2), each symbol represents the content of each component (kg / m 3 ) is shown.

[0024] Examples of fine aggregate S include naturally occurring sand such as mountain sand, river sand, land sand, sea sand, crushed sand, and crushed limestone sand, as specified in JIS A 5308 Appendix A Aggregates for Ready-Mixed Concrete, sand derived from slag such as blast furnace slag, electric furnace oxidized slag, and ferronickel slag, recycled aggregate, artificial lightweight aggregate, and recovered aggregate. These fine aggregates may be used alone or in combination of two or more.

[0025] The coarse aggregate G is not particularly limited, and examples thereof include natural aggregates such as river gravel, mountain gravel, and sea gravel, artificial aggregates such as crushed stone such as sandstone, hard sandstone, hard limestone, basalt, and andesite, and recycled aggregates, etc. These coarse aggregates may be used alone or in combination of two or more types.

[0026] The water W is not particularly limited, and examples thereof include tap water, industrial water, recycled water, groundwater, river water, rainwater, etc. The water-to-binder ratio (W / (C+SF)) is preferably 25% by mass or less, and 14% by mass or more.

[0027] Examples of the admixture SP include air-entraining agents, air-entraining water-reducing agents, high-performance water-reducing agents, superplasticizers, separation-reducing agents, setting retarders (e.g., tartaric acid, etc.), setting accelerators (e.g., aluminum sulfate, etc.), quick-setting admixtures, shrinkage-reducing agents, foaming agents, foaming agents, waterproofing agents, antifoaming agents, etc. These admixtures may be used alone or in combination of two or more.

[0028] The concrete composition may further contain an admixture. Examples of admixtures include inorganic fine powders such as fly ash, cement kiln dust, blast furnace fume, ground granulated blast furnace slag, ground granulated blast furnace slag, ground granulated converter slag, gypsum hemihydrate, expansive additives, limestone fine powder, quicklime fine powder, and dolomite fine powder, as well as inorganic fillers such as sodium bentonite, calcium bentonite, attapulgite, sepiolite, activated clay, acid clay, allophane, imogolite, shirasu (volcanic ash), shirasu balloons, kaolinite, metakaolin (calcined clay), synthetic zeolite, artificial zeolite, mordenite, and clinoptilolite. These admixtures may be used alone or in combination of two or more.

[0029] The first mixing step is a step of mixing the first cement C1, the first silica fume SF1, the fine aggregate S, and the coarse aggregate G to obtain a first mixture. The method for mixing the materials is not particularly limited, and for example, the materials can be mixed by a conventionally known method using a mixer such as a twin-screw forced mixer. The mixing time can be, for example, 10 to 30 seconds, which is enough time for the mixture to be visually confirmed as uniform.

[0030] The first cement C1 and the first silica fume SF1 are mixed so that the mass ratio of the total content of the first cement C1 and the first silica fume SF1 to the total content of the cement C and the silica fume SF satisfies the following formula (1). 0.40≦(C1+SF1) / (C+SF)≦0.60 (1) In formula (1), each symbol represents the content of each component (kg / m 3 ) is shown.

[0031] Furthermore, from the viewpoint of further shortening the mixing time of the concrete composition, the first cement C1 and the first silica fume SF1 may be mixed so that the mass ratio of the total content of the first cement C1 and the first silica fume SF1 to the total content of the cement C and the silica fume SF satisfies the following formula (1'): 0.45≦(C1+SF1) / (C+SF)≦0.55 (1') In formula (1'), each symbol represents the content of each component (kg / m 3 ) is shown.

[0032] The first silica fume SF1 may be mixed so that the mass ratio of the first silica fume SF1 to the total content of the first cement C1 and the first silica fume SF1 satisfies the following formula (3). 0.05≦SF1 / (C1+SF1)≦0.40 (3) In formula (3), each symbol represents the content of each component (kg / m 3 ) is shown.

[0033] The second mixing step is a step in which the first mixture, water W, and admixture SP are mixed to obtain a second mixture. The water W is mixed in an amount such that the water-binder ratio (W / (C+SF)) is 25% by mass or less. The method for mixing the materials is not particularly limited, and mixing can be performed by a conventional method using a mixer such as a twin-screw forced mixer. Mixing in the second mixing step is preferably performed so that the difference in the unit volume mass of mortar in the concrete tested in accordance with JIS A 1119:2014 is 0.8% or less, and the difference in the unit volume of coarse aggregate in the concrete is 5% or less. Completion of mixing in the second mixing step can be determined based on the load current during mixer operation.

[0034] The third mixing step is a step in which the second mixture, second cement C2, and second silica fume SF2 are mixed to obtain a third mixture. The method for mixing the materials is not particularly limited, and mixing can be performed, for example, by a conventionally known method using a mixer such as a twin-screw forced mixer. Mixing in the third mixing step is preferably performed so that the difference in the unit volume mass of mortar in the concrete tested in accordance with JIS A 1119:2014 is 0.8% or less, and the difference in the unit volume of coarse aggregate in the concrete is 5% or less. Completion of mixing in the third mixing step can be determined based on the load current during mixer operation, as in the second mixing step.

[0035] The contents of the second cement C2 and the second silica fume SF2 are calculated by subtracting the total contents of the first cement C1 and the first silica fume SF1 from the total contents of the cement C and the silica fume SF in the concrete composition. The second cement C2 and the second silica fume SF2 may be mixed in advance and then mixed with the second mixture.

[0036] The content of second silica fume SF2 is the content of silica fume SF minus the content of first silica fume SF1. If the content of silica fume SF and the content of first silica fume SF1 are equal, the content of second silica fume SF2 is 0.

[0037] The concrete composition mixing method according to this embodiment includes a first mixing step of mixing a first cement C1, a first silica fume SF1, a fine aggregate S, and a coarse aggregate G to obtain a first mixture, a second mixing step of mixing the first mixture with water W and a chemical admixture SP to obtain a second mixture, and a third mixing step of mixing the second mixture with a second cement C2 and a second silica fume SF2 to obtain a third mixture, wherein the water-to-binder ratio (W / (C+SF)) is 25% by mass or less, and the mass ratio of the total content of the first cement C1 and the first silica fume SF1 to the total content of the cement C and the silica fume SF satisfies the following formula (1): This enables the mixing time of a concrete composition having a low water-to-binder ratio and containing silica fume to be shortened. 0.40≦(C1+SF1) / (C+SF)≦0.60 (1) In formula (1), each symbol represents the content of each component (kg / m 3 ) is shown.

[0038] In the method for mixing a concrete composition according to this embodiment, the water-binder ratio (W / (C+SF)) is 14 mass % or more, so that the concrete composition can be mixed with a general-purpose mixer.

[0039] In the method for mixing a concrete composition according to this embodiment, the mass ratio of the content of silica fume SF to the total content of cement C and silica fume SF satisfies the following formula (2), thereby enabling the mixing time of a concrete composition having a low water-binder ratio and containing silica fume to be further shortened. 0.08≦SF / (C+SF)≦0.20 (2) In formula (2), each symbol represents the content of each component (kg / m 3 ) is shown.

[0040] In the method for mixing a concrete composition according to this embodiment, the mass ratio of the first silica fume SF1 to the total content of the first cement C1 and the first silica fume SF1 satisfies the following formula (3), so that the water-binder ratio is low and the mixing time of a concrete composition containing silica fume can be further shortened. 0.05≦SF1 / (C1+SF1)≦0.40 (3) In formula (3), each symbol represents the content of each component (kg / m 3 ) is shown.

[0041] <Method of manufacturing concrete composition> The method for producing a concrete composition according to this embodiment is a method for producing a concrete composition containing cement C consisting of first cement C1 and second cement C2, silica fume SF consisting of first silica fume SF1 and second silica fume SF2, fine aggregate S, coarse aggregate G, water W, and admixture SP, and includes the above-described method for mixing a concrete composition.

[0042] The method for producing a concrete composition according to this embodiment includes the above-described method for mixing a concrete composition, and therefore can shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume, thereby enabling the concrete composition to be produced efficiently. [Example]

[0043] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0044] <Preparation of concrete composition> The concrete compositions of each Example and Comparative Examples 1-2, 1-3, 1-6, 2-2, 2-3, 2-5, 3-2, 3-3, 3-5, and 4-2 were prepared by dividing cement C and silica fume SF into first cement C1 and first silica fume SF1, and second cement C2 and second silica fume SF2 in the proportions shown in Table 1, and mixing these with the other materials that make up the concrete composition. However, Comparative Examples 1-6, 2-5, and 3-5 did not contain silica fume SF.

[0045] Specifically, first cement C1, first silica fume SF1, fine aggregate S, and coarse aggregate G were mixed in a twin-screw forced mixer (Super Double Mixer SD55, manufactured by Pacific Machinery Works, Ltd.) for 15 seconds (first mixing) to obtain a substantially uniformly mixed first mixture. Next, water W and admixture SP were added to the first mixture, and the mixture was mixed (second mixing) to obtain a second mixture. The completion of mixing in the second mixing step was determined based on the load current during mixer operation, according to the method for measuring mixing time described below. Then, second cement C2 and second silica fume SF2 were added to the second mixture, and the mixture was mixed (third mixing) to obtain a third mixture (concrete composition). The completion of mixing in the third mixing step was determined based on the load current during mixer operation, as in the second mixing step. Note that in Examples 1-5 and 1-6, the content of second silica fume SF2 was set to 0.

[0046] The concrete compositions of Comparative Examples 1-1, 1-4, 1-5, 2-1, 2-4, 3-1, 3-4, and 4-1 were prepared by mixing cement C and silica fume SF together with the other materials constituting the concrete composition without dividing them. Specifically, cement C, silica fume SF, fine aggregate S, and coarse aggregate G were first dry-mixed for 15 seconds in a biaxial forced mixer (Pacific Machinery Works, Super Double Mixer SD55). Water W and admixture SP were then added, and the mixture was mixed (main mixing) to obtain a concrete composition. Completion of the main mixing was determined based on the load current during mixer operation, as in the second and third mixing steps of each Example. Comparative Examples 1-5, 2-4, and 3-4 did not contain silica fume SF.

[0047] Details of each component shown in Table 1 are given below. Water (W): Tap water Cement (C): Low-heat Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.) Daiichi Cement (C1): Low-heat Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.) Silica fume (SF): SF-RD (Tomoe Engineering Co., Ltd.) Daiichi Silica Fume (SF1): SF-RD (Tomoe Engineering Co., Ltd.)

[0048] [Table 1]

[0049] <Measurement of mixing time> The mixing times for the dry mixing (first mixing), second mixing, and third mixing were measured for each Example and Comparative Examples 1-2, 1-3, 1-6, 2-2, 2-3, 2-5, 3-2, 3-3, 3-5, and 4-2. The dry mixing time was measured when the mixer was operated and mixing began, and the measurement was terminated when uniform mixing was visually confirmed. The mixing times for the second and third mixing were determined based on the load current during mixer operation. Specifically, as shown in FIG. 1 , when the mixer was operated and each mixing step began, the load current rose sharply, peaked, and then began to decline. The measurement of the mixing time was initiated immediately before the load current rose sharply, and the point at which the load current, which had begun to decline, was assumed to have transitioned to a steady state was determined as the completion of each mixing step, and the measurement of the mixing time was terminated. The steady state refers to a state in which the value of the fluctuating load current is stabilized and falls within the range of the following formula (i) relative to the initial value I0 of the load current in each kneading step. (1±0.25)I0(i) The total mixing time was the sum of the mixing time for dry kneading and the mixing times for the second and third kneading steps. The measured mixing times are shown in Table 1.

[0050] The mixing times for dry kneading and main kneading were measured in Comparative Examples 1-1, 1-4, 1-5, 2-1, 2-4, 3-1, 3-4, and 4-1. The mixing time for dry kneading was measured using the same method as that for dry kneading in each Example. The mixing time for main kneading was measured using the same method as that for second kneading and third kneading in each Example. The sum of the mixing time for dry kneading and the mixing time for main kneading was taken as the mixing time for the entire process. The measured values ​​of the mixing time are shown in Table 1.

[0051] <Slump flow measurement> The concrete compositions of each example and each comparative example were measured for slump flow in accordance with JIS A 1150: 2020. The measured values ​​are shown in Table 1.

[0052] As can be seen from the results in Table 1, the mixing method for the concrete composition of each Example that satisfies all of the constituent requirements of the present invention shortens the mixing time for the entire process compared to the mixing method for the concrete composition of each Comparative Example that has the same water-binder ratio. Therefore, the mixing method for the concrete composition of each Example that satisfies all of the constituent requirements of the present invention can shorten the mixing time for a concrete composition that has a low water-binder ratio and contains silica fume.

Claims

1. A method for mixing a concrete composition comprising cement C consisting of first cement C1 and second cement C2, silica fume SF consisting of first silica fume SF1 and second silica fume SF2, fine aggregate S, coarse aggregate G, water W, and admixture SP, a first mixing step of mixing a first cement C1, a first silica fume SF1, a fine aggregate S, and a coarse aggregate G to obtain a first mixed substance; A second kneading step of kneading the first kneaded mixture, water W, and an admixture SP to obtain a second kneaded mixture; a third kneading step of kneading the second kneaded material, a second cement C2, and a second silica fume SF2 to obtain a third kneaded material, The water-binder ratio (W / (C+SF)) is 25% by mass or less, A method for mixing a concrete composition, wherein the mass ratio of the total content of the first cement C1 and the first silica fume SF1 to the total content of the cement C and the silica fume SF satisfies the following formula (1): 0.40≦(C1+SF1) / (C+SF)≦0.60 (1) (In the formula, each symbol represents the content of each component (kg / m ３ ) indicates.

2. The method for mixing a concrete composition according to claim 1, wherein the water-binder ratio (W / (C+SF)) is 14% by mass or more.

3. 3. The method for kneading a concrete composition according to claim 1, wherein the mass ratio of the content of the silica fume SF to the total content of the cement C and the silica fume SF satisfies the following formula (2): 0.08≦SF / (C+SF)≦0.20 (2) (In the formula, each symbol represents the content of each component (kg / m ３ ) indicates.

4. The method for kneading a concrete composition according to any one of claims 1 to 3, wherein the mass ratio of the first silica fume SF1 to the total content of the first cement C1 and the first silica fume SF1 satisfies the following formula (3): 0.05≦SF1 / (C1+SF1)≦0.40 (3) (In the formula, each symbol represents the content of each component (kg / m ３ ) indicates.

5. A method for producing a concrete composition, comprising the method for kneading a concrete composition according to any one of claims 1 to 4.

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