Concrete composition, and method for manufacturing the concrete composition

Abstract

To provide a concrete composition that can be formed by using a granular silica fume and can reduce its self-shrinkage when it hardens to become concrete, and to provide a method for producing the concrete composition.SOLUTION: A concrete composition contains cement, silica fume, fine aggregate, coarse aggregate and water, wherein the silica fume contains granular silica fume, and a ratio (W / C) of the cement to the water is 16 mass% or more and 24 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Silica fume is sometimes used as a concrete material to increase the strength and reduce the viscosity of concrete. Silica fume for concrete is classified into three types depending on the product form: powdered silica fume, granular silica fume, and silica fume slurry (JIS A 6207:2016).

[0003] Granular silica fume, such as granular silica fume, has a larger particle size compared to powdered silica fume, and has therefore been considered inferior to powdered silica fume in terms of concrete fluidity and strength characteristics. For this reason, powdered silica fume is often used when manufacturing high-strength concrete. For example, Patent Document 1 discloses a high-strength cementitious hardened body using powdered silica fume (powdered silica fume) obtained by crushing granular silica fume. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-189621 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, when storing powdered materials such as powdered silica fume separately from other materials, the powdered material located at the bottom of the storage container can be compressed by the pressure from the weight of the powdered material located above it, causing it to solidify near the discharge port at the bottom of the storage container. When the powdered material solidifies near the discharge port in this way, it becomes difficult to discharge the powdered material from the port. Therefore, measures are taken to break up the solidified powdered material by installing vibrators or aerators near the discharge port of the storage container using vibration or air pressure.

[0006] However, because powdered silica fume consists of extremely small particles, vibration alone cannot adequately break up the clumps. Furthermore, attempting to break up the clumps by pneumatic transport generates a large amount of dust, worsening the working environment. Thus, powdered silica fume is difficult to handle, and there is a desire to utilize granular silica fume, which is easier to handle, as a concrete material for high-strength concrete.

[0007] Furthermore, as described in Patent Document 1, if powdered silica fume is used as a concrete material, there is a risk that the self-shrinkage of the concrete will increase when the concrete material hardens and becomes concrete.

[0008] This invention has been made in view of these circumstances, and aims to provide a concrete composition that can be formed using granular silica fume and that can reduce the self-shrinkage of the concrete when it hardens into concrete, and a method for producing the concrete composition. [Means for solving the problem]

[0009] The concrete composition according to the present invention is a concrete composition comprising cement, silica fume, fine aggregate, coarse aggregate, and water, wherein the silica fume comprises granular silica fume, and the water-cement ratio (W / C) of the cement to water is 16% by mass or more and 24% by mass or less.

[0010] When the concrete composition contains fumed silica in the form of granular fumed silica, the autogenous shrinkage of the concrete can be reduced when the concrete composition hardens into concrete. In addition, the fluidity of the concrete composition can be improved and the mixing time can be shortened. Furthermore, when the water-cement ratio (W / C) of the concrete composition is within the above range, the strength reduction of the concrete can be suppressed.

[0011] The bulk density of the fumed silica in the concrete composition according to the present invention may be 0.55 g / cm 3 or more and 0.70 g / cm 3 or less.

[0012] With such a configuration, the autogenous shrinkage of the concrete can be reduced when the concrete composition hardens into concrete. In addition, the fluidity of the concrete composition can be improved and the mixing time can be shortened. Furthermore, when the bulk density of the fumed silica is within the above range, even when the fumed silica is subjected to compression and vibration during storage, a significant decrease in bulk volume is less likely to occur. As a result, the lumps generated by the pressure during storage of the fumed silica can be crushed by vibration or pneumatic conveying.

[0013] The content of the fumed silica in the concrete composition according to the present invention may be 5% by mass or more and 20% by mass or less based on the cement.

[0014] With such a configuration, the autogenous shrinkage of the concrete can be reduced when the concrete composition hardens into concrete. In addition, the fluidity of the concrete composition can be improved and the mixing time can be shortened.

[0015] The manufacturing method of the concrete composition according to the present invention has a kneading step of kneading cement, silica fume, fine aggregate, coarse aggregate, and water, wherein the silica fume includes granular silica fume, and in the kneading step, the water-cement ratio (W / C) of the cement and water is kneaded so as to be 16% by mass or more and 24% by mass or less.

[0016] In the manufacturing method of the concrete composition, since the silica fume includes granular silica fume, when the concrete composition hardens into concrete, the autogenous shrinkage of the concrete can be reduced. Also, the fluidity of the concrete composition can be improved and the kneading time can be shortened. Furthermore, in the manufacturing method of the concrete composition, since the water-cement ratio (W / C) is within the above range, the strength reduction of the concrete can be suppressed.

Effects of the Invention

[0017] According to the present invention, it is possible to provide a concrete composition that can be formed using granular silica fume and can reduce the autogenous shrinkage of the concrete when it hardens into concrete, and a manufacturing method of the concrete composition.

Brief Description of the Drawings

[0018] [Figure 1] It is a graph showing the change in the measured values of the autogenous shrinkage strain of Example 2, Example 5, and Comparative Example 2.

Modes for Carrying Out the Invention

[0019] Hereinafter, the concrete composition according to the present embodiment and the manufacturing method of the concrete composition will be described.

[0020] <Concrete Composition> The concrete composition according to the present embodiment includes cement, silica fume, fine aggregate, coarse aggregate, and water.

[0021] The cement (C) is not particularly limited and can include, for example, ordinary Portland cement, rapid-hardening Portland cement, ultra-rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, white Portland cement, and other Portland cements specified in JIS R 5210, as well as ultrafast-setting cement and alumina cement. Various mixed cements obtained by mixing the Portland cement with fly ash, blast furnace slag, etc., can also be used. One type of cement may be used alone, or two or more types may be used in combination.

[0022] The amount of cement used in the mix is ​​not particularly limited; for example, the mass ratio of cement to the unit volume of the concrete composition is 500 kg / m³. 3 More than 1050kg / m 3 The following may apply: If two or more types of cement are included, the aforementioned blending amount is the total blending amount of cement.

[0023] Silica fume (SF) is a fine particle (specifically, amorphous spherical fine particle) whose main component is silicon dioxide. Silica fume can also be collected from exhaust gases generated during the production of metallic silicon or ferrosilicon in an arc electric furnace. The bulk density of silica fume is not particularly limited; for example, from the viewpoint of reducing the auto-shrinkage of concrete, 0.55 g / cm³ is considered. 3 More than 0.70g / cm 3 Preferably, it is 0.57 g / cm³. 3 More than 0.70g / cm 3 The following is more preferable. Note that bulk density refers to the density when powder is filled into a container of a certain volume and its internal volume is used as the volume.

[0024] The amount of silica fume added is not particularly limited, but from the viewpoint of improving the fluidity of the concrete composition and shortening the mixing time, it is preferably 5% to 20% by mass relative to the cement, and more preferably 8% to 15% by mass.

[0025] The silica fume contains granular silica fume. The granular silica fume can be obtained by aggregating silica fume ultrafine particles with a BET specific surface area of 1 m 2 / g or more. The bulk density of the granular silica fume is preferably, for example, 0.55 g / cm 3 or more and 0.70 g / cm 3 or less, more preferably 0.57 g / cm 3 or more and 0.70 g / cm 3 or less. Also, the content of the granular silica fume is not particularly limited, and can be, for example, 75% by mass or more and 100% by mass or less based on the total silica fume.

[0026] The granular silica fume may contain, for example, 85% by mass or more and 98% by mass or less of silicon dioxide and 0.6% by mass or more and 2.0% by mass or less of magnesium oxide.

[0027] The silica fume may contain powdered silica fume in addition to the granular silica fume. In this embodiment, the silica fume in which the granular silica fume and the powdered silica fume are mixed is called semi-granular silica fume. The powdered silica fume refers to the powdered silica fume defined in JIS A 6207:2016. The bulk density of the powdered silica fume is not particularly limited, and is preferably, for example, 0.25 g / cm 3 or more and 0.40 g / cm 3 or less. The content of the powdered silica fume is not particularly limited, and can be, for example, 0% by mass or more and 25% by mass or less based on the total silica fume.

[0028] Examples of the fine aggregate (S) include natural-derived sands such as mountain sand, river sand, land sand, sea sand, crushed sand, and limestone crushed sand defined in the annex A of Ready-mixed concrete aggregates of JIS A 5308, slag-derived sands such as blast furnace slag, electric furnace oxidized slag, and ferronickel slag, recycled aggregates, artificial lightweight aggregates, and recovered aggregates. These fine aggregates may be used alone or in combination of two or more.

[0029] The amount of fine aggregate used is not particularly limited; for example, the mass ratio of the concrete composition to the unit volume is 400 kg / m³. 3 More than 900kg / m 3 The following may be applied: If two or more types of fine aggregate are included, the above-mentioned blending amount is the total blending amount of the fine aggregate.

[0030] The coarse aggregate (G) is not particularly limited and can include, for example, natural aggregates such as river gravel, mountain gravel, and sea gravel; artificial aggregates such as crushed sandstone, hard sandstone, hard limestone, basalt, andesite; and recycled aggregates. One type of coarse aggregate may be used alone, or two or more types may be used in combination.

[0031] The amount of coarse aggregate is not particularly limited; for example, the mass ratio of the concrete composition to the unit volume is 650 kg / m³. 3 More than 950kg / m 3 The following may be applied: If two or more types of coarse aggregate are included, the above-mentioned blending amount is the total blending amount of coarse aggregate.

[0032] The water (W) is not particularly limited, and can be tap water, industrial water, recycled water, groundwater, river water, rainwater, etc. The amount of water to be mixed is not particularly limited, for example, the mass ratio to the unit volume of the concrete composition is 150 kg / m³. 3 More than 180kg / m 3 The following is possible:

[0033] The water-cement ratio (W / C) should be 16% by mass or more, preferably 18% by mass or more, and more preferably 20% by mass or more, from the viewpoint of suppressing a decrease in concrete strength. Furthermore, the water-cement ratio should be 24% by mass or less, and may be less than 24% by mass.

[0034] The concrete composition may further contain admixtures. Examples of admixtures include inorganic powders such as fly ash, cement kiln dust, blast furnace fumes, blast furnace granulated slag powder, blast furnace decooked slag powder, converter slag powder, hemihydrate gypsum, expansive agents, limestone powder, quicklime powder, dolomite powder, sodium-type bentonite, calcium-type bentonite, attapulgite, sepiolite, activated clay, acid clay, allophane, imogolite, shirasu (volcanic ash), shirasu balloons, kaolinite, metakaolin (calcined clay), synthetic zeolite, artificial zeolite, mordenite, clinoptilolite, and other inorganic fillers. One type of admixture may be used alone, or two or more types may be used in combination.

[0035] The concrete material may further contain admixtures. Examples of admixtures include air-entraining agents, air-entraining water-reducing agents, high-performance water-reducing agents, superplasticizers, segregation-reducing agents, setting retarders (e.g., tartaric acid), setting accelerators (e.g., aluminum sulfate), rapid setting agents, shrinkage-reducing agents, foaming agents, foaming agents, waterproofing agents, and defoaming agents. One type of admixture may be used alone, or two or more types may be used in combination.

[0036] The concrete composition according to this embodiment is a concrete composition comprising cement, silica fume, fine aggregate, coarse aggregate, and water, wherein the silica fume includes granular silica fume, thereby reducing the self-shrinkage of the concrete when the concrete composition hardens into concrete. Furthermore, the fluidity of the concrete composition can be improved, and the mixing time can be shortened. In addition, the water-cement ratio (W / C) of the concrete composition is 16% by mass or more and 24% by mass or less, thereby suppressing a decrease in the strength of the concrete.

[0037] The concrete composition according to this embodiment has a silica fume bulk density of 0.55 g / cm³. 3 More than 0.70g / cm 3The following factors reduce the self-shrinkage of the concrete when the concrete composition hardens into concrete. Furthermore, it improves the fluidity of the concrete composition and shortens the mixing time. Additionally, the bulk density of silica fume is 0.55 g / cm³. 3 More than 0.70g / cm 3 As a result, even if silica fume is subjected to compression and vibration during storage, a significant reduction in bulk volume is unlikely. This allows the clumps that form due to the pressure during storage of silica fume to be broken up by vibration or pneumatic transport.

[0038] The concrete composition according to this embodiment has a silica fume content of 5% to 20% by mass relative to the cement, which reduces the self-shrinkage of the concrete when it hardens into concrete. Furthermore, it improves the fluidity of the concrete composition and shortens the mixing time.

[0039] <Method for manufacturing concrete compositions> The method for producing the concrete composition according to this embodiment includes a mixing step of mixing cement, silica fume, fine aggregate, coarse aggregate, and water. The silica fume includes granular silica fume.

[0040] In the mixing process, cement, silica fume, and fine aggregate are first mixed. Next, water is added and mixed, and then coarse aggregate is added and mixed. The means of mixing each material are not particularly limited, and conventionally known methods can be used. The mixing temperature is also not particularly limited, and can be, for example, between 5°C and 35°C.

[0041] In the mixing process, the mixture is kneaded so that the water-cement ratio (W / C) of cement to water is between 16% by mass and 24% by mass.

[0042] The method for producing the concrete composition according to this embodiment, by including granular silica fume, can reduce the self-shrinkage of the concrete when the concrete composition hardens into concrete. It can also improve the fluidity of the concrete composition and shorten the mixing time. The method for producing the concrete composition can suppress the decrease in concrete strength by having a water-cement ratio (W / C) of 16% by mass or more and 24% by mass or less. [Examples]

[0043] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0044] <Materials for concrete compositions> Water (W): Tap water Cement (LC): Low-heat Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.) Silica fume (SF): 945SD (manufactured by Elchem ​​Japan Co., Ltd.) SF-RD (manufactured by Tomoe Kogyo) 940U (manufactured by Elchem ​​Japan Co., Ltd.) Fine aggregate (S): Mountain sand Coarse aggregate (G): Hard sandstone Admixture (high-performance water-reducing agent): SSP-104 (manufactured by Takemoto Oil Co., Ltd.) Admixture (antifoaming agent): AFK-2 (manufactured by Takemoto Oil Co., Ltd.)

[0045] Table 1 shows the bulk density, dust volume, and P-funnel flow time of the silica fume described above. The bulk density was calculated by gently placing 100g of the sample into a dry 250mL graduated cylinder without compaction, carefully leveling the top surface of the sample without compaction, reading the loose bulk volume to the smallest division of 2mL, and dividing the sample mass by the loose bulk volume. The dust volume was measured using a digital dust meter (Dustmate LD-3K2, Shibata Scientific Co., Ltd.) at a height of 300mm when 500g of the sample was dropped from a height of 300mm. The P-funnel flow time was measured according to JSCE-F521.

[0046] [Table 1]

[0047] <Preparation of concrete compositions> Each of the above materials was mixed according to the proportions shown in Table 2 and then mixed in a twin-screw forced mixer to prepare each concrete composition. Specifically, first, cement, silica fume, and fine aggregate were dry-mixed in the mixer for 15 seconds, then water was added and mixed for 3 minutes. Next, coarse aggregate was added and mixed for 60 seconds, then left to stand for 5 minutes before being discharged. The concrete compositions were prepared with a target slump flow of 650 ± 100 mm and a target air content of 3%. Note that the units in Table 2 are kg / m 3 This indicates the mass ratio of the concrete composition to its unit volume.

[0048] [Table 2]

[0049] <Measurement of autologous contraction strain> For the concrete compositions of Example 2, Example 5, and Comparative Example 2, the autologous shrinkage strain was measured according to the Japan Concrete Institute's "Method for Testing Autologous Shrinkage of Superfluid Concrete." The measured values ​​are shown in Table 3. Figure 1 shows a graph illustrating the change in the measured autologous shrinkage strain.

[0050] [Table 3]

[0051] <Measurement of freshness properties> For each pre-hardening concrete composition prepared, the time to reach a 500 mm flow was measured according to ISO 1920-2:2005. Slump flow and flow stop time were measured according to JIS A 1150:2014. Concrete temperature was measured according to JIS A 1156:2014. Air content was measured according to JIS A 1128:2019. The measured values ​​are shown in Table 4.

[0052] [Table 4]

[0053] <Measurement of compressive strength> For each concrete composition prepared, test specimens were prepared according to JIS A 1108:2018, and the compressive strength was measured. The compressive strength was measured using the design standard strength (80, 90, 100, 110 N / mm²). 2 Target strengths for each (96, 108, 120, 132 N / mm²) 2 A target strength was established, and samples with a measured compressive strength of 28 days or more were evaluated as "○" and samples with a measured compressive strength below the target strength were evaluated as "×". The measurement and evaluation results of the compressive strength are shown in Table 5. The target strength was calculated using formula (1).

[0054] F=(fc+S)+2σ (1) In the formula, fc represents the design strength, S represents the structural strength correction value, and σ represents the standard deviation (0.1 × (fc + S) if there is no manufacturing history).

[0055] [Table 5]

[0056] As can be seen from the results in Table 3, Examples 2 and 5 exhibit smaller autologous shrinkage strain compared to Comparative Example 2. This result is expected to be similar when comparing other examples with the same water-cement ratio to other comparative examples. In other words, a concrete composition that satisfies all the constituent elements of the present invention can reduce the autologous shrinkage of the concrete when it hardens into concrete.

[0057] As can be seen from the results in Table 4, the concrete compositions of Examples 1 to 6 showed shorter 500 mm flow time at each water-cement ratio compared to the concrete compositions of Comparative Examples 1 to 3. In other words, by satisfying all the constituent requirements of the present invention, the fluidity can be improved and the mixing time can be shortened. Furthermore, as can be seen from the results in Table 5, the concrete compositions of Examples 1 to 6, when hardened into concrete, have a design standard strength of 80 N / mm². 2 In all cases, the target strength is 96 N / mm². 2 It is confirmed that the above compressive strength is observed. In other words, by satisfying all the constituent requirements of the present invention, the decrease in the strength of the concrete can be suppressed.

Claims

1. A concrete composition comprising cement, silica fume, fine aggregate, coarse aggregate, and water, The silica fume has a bulk density of 0.55 g / cm³. ３ 0.70g / cm or more ３ The following granular silica fume has a bulk density of 0.25 g / cm³. ３ 0.40g / cm or more ３ The following powdered silica fume is included: The silica fume content is 5% by mass or more and 20% by mass or less relative to the cement. The content of the granular silica fume is 75% by mass or more and 100% by mass or less relative to the total silica fume. The water-cement ratio (W / C) of the cement and water is 16% by mass or more and less than 24% by mass. The cement is low-heat Portland cement or moderate-heat Portland cement. The aforementioned cement has a mass ratio of 638 kg / m³ to the unit volume of the concrete composition. ３ More than 1050kg / m ３ The following is: Concrete composition.

2. It has a mixing process in which cement, silica fume, fine aggregate, coarse aggregate, and water are mixed together. The silica fume has a bulk density of 0.55 g / cm ３ or more and 0.70 g / cm ３ or less of granular silica fume, and a bulk density of 0.25 g / cm ３ or more and 0.40 g / cm ３ or less of powdered silica fume, and The silica fume content is 5% by mass or more and 20% by mass or less relative to the cement. The content of the granular silica fume is 75% by mass or more and 100% by mass or less relative to the total silica fume. The cement is low-heat Portland cement or moderate-heat Portland cement. The aforementioned cement has a mass ratio of 638 kg / m³ to the unit volume of the concrete composition. ３ More than 1050kg / m ３ The following: In the aforementioned kneading process, A method for producing a concrete composition, comprising mixing the cement and water so that the water-cement ratio (W / C) is 16% by mass or more and less than 24% by mass.

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