JP7748664B2 - Method for mixing concrete composition and method for producing concrete composition - Google Patents

Description

The present invention relates to a method for mixing a concrete composition and a method for producing a concrete composition.

One known method for producing high-strength concrete is to reduce the water-binder ratio of the concrete composition. For example, when producing high-strength concrete with a compressive strength exceeding 150 N/ ^mm2 , the water-binder ratio is set to 25% or less. However, reducing 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 predetermined amounts _of 2CaO.SiO2 and _3CaO.Al2O3 , silica fume, and _gypsum .

JP 2011-68546 A

However, because silica fume is an ultrafine particle, it is prone to secondary aggregation. Therefore, long mixing times are required to disperse silica fume in the concrete composition.

The present invention was made in consideration of these circumstances, and aims 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, as well as a method for manufacturing a concrete composition.

The method for kneading a concrete composition according to the present invention is a method for kneading a concrete composition including 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, the method comprising: a first kneading step of kneading the first cement C1, the first silica fume SF1, the fine aggregate S, and the coarse aggregate G to obtain a first kneaded product; a second kneading step of kneading a cement C1, water W, and a chemical admixture SP to obtain a second kneaded product; and a third kneading step of kneading the second kneaded product, a second cement C2, and a second silica fume SF2 to obtain a third kneaded product, wherein the water-binder ratio (W/(C+SF)) is 25 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 (kg/m ³ ) of each component.)

This configuration of the concrete composition mixing method allows for a reduction in the mixing time for concrete compositions that have a low water-to-binder ratio and contain silica fume.

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

With this configuration, the concrete composition mixing method allows the concrete composition to be mixed using a general-purpose mixer.

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 (kg/m ³ ) of each component.)

This configuration of the concrete composition mixing method can further shorten the mixing time for concrete compositions that have a low water-to-binder ratio and contain silica fume.

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 (kg/m ³ ) of each component.)

This configuration of the concrete composition mixing method can further shorten the mixing time for concrete compositions that have a low water-to-binder ratio and contain silica fume.

The method for producing a concrete composition according to the present invention includes the method for mixing a concrete composition described above.

This configuration of the concrete composition manufacturing method shortens the mixing time for concrete compositions that have a low water-binder ratio and contain silica fume, allowing for efficient production of concrete compositions.

The present invention provides 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 containing silica fume, and a method for manufacturing a concrete composition.

1 is a graph showing the load current applied to the mixer when mixing the concrete composition of Example 2-3.

The method for mixing the concrete composition and the method for manufacturing the concrete composition according to this embodiment are described below.

<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 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, 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, water W, and 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.

Below, we will explain each material used in the concrete composition mixing method according to this embodiment, and then explain the concrete composition mixing method.

Cement C consists of first cement C1 and second cement C2. First cement C1 is the cement contained in the first kneaded mixture, which will be described later, and second cement C2 is the cement contained in the third kneaded mixture, which will be described later. 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, such as Portland cement mixed with fly ash or blast furnace slag, can also be used. First cement C1 and second cement C2 may be composed of one of the above cements alone, or two or more of them may be used in combination. First cement C1 and second cement C2 may be the same type of cement or different types of cement.

Silica fume SF consists of first silica fume SF1 and second silica fume SF2. First silica fume SF1 is the silica fume contained in the first mixture, and second silica fume SF2 is the silica fume contained in the third mixture. Examples of first silica fume SF1 and second silica fume SF2 include powdered silica fume, granular silica fume, and silica fume slurry as specified in JIS A 6207:2016. Among these, first silica fume SF1 and 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 first silica fume SF1 and 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, first silica fume SF1 and second silica fume SF2 may be the same type of silica fume or different types of silica fumes.

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 indicates the content (kg/m ³ ) of each component.

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 types.

The coarse aggregate G is not particularly limited, and examples 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. These coarse aggregates may be used alone or in combination of two or more types.

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

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

The concrete composition may further contain an admixture. Examples of admixtures include fly ash, cement kiln dust, blast furnace fume, ground granulated blast furnace slag, ground uncooled blast furnace slag, ground converter slag, gypsum hemihydrate, expansive additives, fine inorganic powders such as limestone powder, quicklime powder, and dolomite 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.

The first mixing step is a step in which first cement C1, first silica fume SF1, fine aggregate S, and coarse aggregate G are mixed to obtain a first mixture. The method for mixing the materials is not particularly limited, and for example, mixing can be performed using 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.

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 indicates the content (kg/m ³ ) of each component.

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 (kg/m ³ ) of each component.

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 indicates the content (kg/m ³ ) of each component.

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 they can be mixed 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.

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 by a conventional 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.

The content of second cement C2 and second silica fume SF2 is the total content of cement C and silica fume SF in the concrete composition minus the total content of first cement C1 and first silica fume SF1. Second cement C2 and second silica fume SF2 may be premixed and then mixed with the second mixture.

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 will be 0.

The method for mixing a concrete composition 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 indicates the content (kg/m ³ ) of each component.

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

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), so that the water-binder ratio of a concrete composition containing silica fume is low and the mixing time can be further shortened.
0.08≦SF/(C+SF)≦0.20 (2)
In formula (2), each symbol indicates the content (kg/m ³ ) of each component.

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 of a concrete composition containing silica fume can be reduced and the mixing time can be further shortened.
0.05≦SF1/(C1+SF1)≦0.40 (3)
In formula (3), each symbol indicates the content (kg/m ³ ) of each component.

<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 method for mixing a concrete composition described above.

The concrete composition manufacturing method according to this embodiment includes the concrete composition mixing method described above, which shortens the mixing time for a concrete composition that has a low water-to-binder ratio and contains silica fume, enabling the concrete composition to be manufactured efficiently.

The following describes examples of the present invention, but the present invention is not limited to these examples.

<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.

Specifically, first cement C1, first silica fume SF1, fine aggregate S, and coarse aggregate G were first mixed in a twin-screw forced mixer (Super Double Mixer SD55, manufactured by Pacific Machinery Works) 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, in accordance with the mixing time measurement method described below. Next, 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.

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 the cement C and silica fume SF contained in the concrete composition together with the other materials that make up 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 two-axis 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.

Details of each component shown in Table 1 are given below.
Water (W): Tap water Cement (C): Low-heat Portland cement (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.)

<Measurement of mixing time>
The mixing times of the dry kneading (first kneading), second kneading, and third kneading 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 kneading time for the dry kneading was measured simultaneously with the start of kneading by operating the mixer, and was terminated when uniform mixing was visually confirmed. The kneading times for the second and third kneading were determined based on the load current during mixer operation. Specifically, as shown in FIG. 1 , when the mixer was operated and each kneading step was initiated, the load current rose sharply, peaked, and then began to decline. The measurement of the kneading time was initiated immediately before the load current rose sharply, and the point at which the load current, which had begun to decline, was estimated to have transitioned to a steady state was determined to be the point at which each kneading step was completed, and the measurement of the kneading 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)I ₀ (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.

The mixing times for dry kneading and main kneading were measured for 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 for measuring the mixing time for dry kneading in each Example. The mixing time for main kneading was measured using the same method as for measuring the mixing time 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 mixing times are shown in Table 1.

<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.

As can be seen from the results in Table 1, the concrete composition mixing method 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 concrete composition mixing method of each comparative example that has the same water-binder ratio. Therefore, the concrete composition mixing method of each example that satisfies all of the constituent requirements of the present invention can shorten the mixing time for concrete compositions that have a low water-binder ratio and contain silica fume.

Claims (5)

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 (kg/m ³ ) of each component.) 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. 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 (kg/m ³ ) of each component.) 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 (kg/m ³ ) of each component.) A method for producing a concrete composition, comprising the method for mixing a concrete composition according to any one of claims 1 to 4.