Method for manufacturing concrete, and method for curing concrete compositions

Abstract

To provide a method for producing concrete capable of suppressing deterioration in compressive strength and improving freeze-thaw resistance, and a method for curing a concrete composition.SOLUTION: A method for producing concrete comprises: a kneading step in which cement, granular silica fume, a fine aggregate, a coarse aggregate and water are kneaded to obtain a concrete composition; and a stream curing step in which the concrete composition is cured at 60°C or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing concrete and a method for curing concrete compositions. [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, which belongs to the granular silica fume category, has a larger particle size compared to powdered silica fume, and was therefore 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, and for example, Patent Document 1 discloses a cement composition containing powdered silica fume, limestone powder, and gypsum. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-211956 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, in regions where temperatures drop below freezing, damage to concrete due to freeze-thaw cycles is a problem. Freeze-thaw cycles are caused by the freezing and expansion of water content in concrete. As described in Patent Document 1, concrete containing powdered silica fume and subjected to steam curing may experience reduced freeze-thaw resistance. Therefore, a method is desired to improve freeze-thaw resistance while maintaining high compressive strength.

[0006] This invention has been made in view of these circumstances, and aims to provide a method for producing concrete that suppresses a decrease in compressive strength and improves freeze-thaw resistance, as well as a method for curing a concrete composition. [Means for solving the problem]

[0007] The concrete manufacturing method according to the present invention includes a mixing step of mixing cement, granular silica fume, fine aggregate, coarse aggregate, and water to obtain a concrete composition, and a steam curing step of curing the concrete composition at a temperature of 60°C or higher.

[0008] The aforementioned concrete manufacturing method, with this configuration, can suppress the decrease in the compressive strength of the concrete and improve its freeze-thaw resistance.

[0009] In the concrete manufacturing method according to the present invention, the concrete composition may be held at a temperature of 60°C or higher for 6 hours or more and 36 hours or less during the steam curing step.

[0010] The aforementioned concrete manufacturing method, with this configuration, can further suppress the decrease in the compressive strength of the concrete and further improve its freeze-thaw resistance.

[0011] The concrete manufacturing method according to the present invention may further include a pre-curing step in which the concrete composition is held at a temperature of 5°C to 35°C for 6 hours to 36 hours prior to the steam curing step.

[0012] The aforementioned concrete manufacturing method, with this configuration, can further suppress the decrease in the compressive strength of the concrete and further improve its freeze-thaw resistance.

[0013] The concrete manufacturing method according to the present invention is characterized in that the bulk density of the granular silica fume is 0.55 g / cm³. 3 More than 0.70g / cm3 It may be as follows.

[0014] With such a configuration, the method for producing concrete can further suppress a decrease in the compressive strength of the concrete and further improve the freeze-thaw resistance.

[0015] The method for producing concrete according to the present invention may have a water-binder ratio (W / B) of 16% by mass or more and 24% by mass or less.

[0016] With such a configuration, the method for producing concrete can further suppress a decrease in the compressive strength of the concrete and further improve the freeze-thaw resistance.

[0017] The method for curing a concrete composition according to the present invention is to steam-cure a concrete composition containing cement, granular silica fume, fine aggregate, coarse aggregate, and water at a temperature of 60°C or higher.

[0018] With such a configuration, the method for curing the concrete composition can suppress a decrease in the compressive strength of the concrete and improve the freeze-thaw resistance.

[0019] The method for curing a concrete composition according to the present invention may hold the concrete composition at a temperature of 60°C or higher for 6 hours or more and 36 hours or less.

[0020] With such a configuration, the method for curing the concrete composition can further suppress a decrease in the compressive strength of the concrete and further improve the freeze-thaw resistance. [Effect of the Invention]

[0021] According to the present invention, it is possible to provide a method for producing concrete that suppresses a decrease in compressive strength and improves freeze-thaw resistance, and a method for curing a concrete composition. [Mode for Carrying Out the Invention]

[0022] The following describes a method for manufacturing concrete according to this embodiment, and a method for curing the concrete composition.

[0023] <Concrete manufacturing method> The concrete manufacturing method according to this embodiment includes a mixing step of mixing cement, granular silica fume, fine aggregate, coarse aggregate, and water to obtain a concrete composition, and a steam curing step of curing the concrete composition at a temperature of 60°C or higher.

[0024] The following describes the materials used in the concrete manufacturing method according to this embodiment, followed by a description of the concrete manufacturing method.

[0025] Examples of cement (C) include Portland cements such as ordinary Portland cement, rapid-hardening Portland cement, ultra-rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, and white Portland cement as specified in JIS R 5210, as well as ultrafast-setting cement and alumina cement. Various mixed cements obtained by mixing fly ash, blast furnace slag, etc., with the Portland cement can also be used. Among these, moderate-heat Portland cement or low-heat Portland cement is preferred from the viewpoint of increasing compressive strength. One type of cement may be used alone, or two or more types may be used in combination.

[0026] The amount of cement used in the concrete composition is not particularly limited; for example, if the mass ratio of cement to the unit volume of the concrete composition is 500 kg / m³ 3 More than 1100kg / 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.

[0027] Silica fume (SF) is fine particles mainly composed of silicon dioxide (specifically, amorphous spherical fine particles). Silica fume can be collected from exhaust gas generated when producing metallic silicon or ferrosilicon in an arc furnace. The silica fume according to this embodiment is granular silica fume.

[0028] 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 granular silica fume according to this embodiment means silica fume with a bulk density of 0.50 g / cm 3 or more and 0.80 g / cm 3 or less. Note that powdered silica fume refers to powdered silica fume defined in JIS A 6207:2016. The bulk density of powdered silica fume is, for example, 0.25 g / cm 3 or more and 0.40 g / cm 3 or less. The bulk density is the density when powder is filled in a container of a certain volume and the inner volume is taken as the volume, and it is measured according to the Japan Society of Powder Technology Standard SAP01-79.

[0029] The bulk density of the granular silica fume is, for example, preferably 0.55 g / cm 3 or more and 0.70 g / cm 3 or less, and more preferably 0.57 g / cm 3 or more and 0.70 g / cm 3 or less. Further, 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.

[0030] The blending amount of the granular silica fume is, for example, preferably 5% by mass or more and 20% by mass or less, and more preferably 8% by mass or more and 15% by mass or less, based on the total blending amount of cement and granular silica fume, from the viewpoint of improving the fluidity of the concrete composition and shortening the mixing time.

[0031] Examples of fine aggregate (S) include naturally derived sands such as mountain sand, river sand, land sand, sea sand, crushed sand, and crushed limestone sand as specified in JIS A 5308 Annex A, Aggregates for Ready-Mixed Concrete; 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 individually or in combination of two or more types.

[0032] The amount of fine aggregate used is not particularly limited; for example, the mass ratio of the fine aggregate to the unit volume of the concrete composition is 350 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.

[0033] 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.

[0034] The amount of coarse aggregate used is not particularly limited; for example, if the mass ratio of the coarse aggregate to the unit volume of the concrete composition is 650 kg / m³ 3 More than 1000kg / 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.

[0035] 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:

[0036] The water-to-binder ratio (W / B) is preferably 16% to 24% by mass, and more preferably 16% to 20% by mass, from the viewpoint of increasing the compressive strength of the concrete. In this embodiment, the binder (B) is cement and silica fume.

[0037] The concrete composition according to this embodiment may further contain admixtures. Examples of admixtures include air-entraining agents, air-entraining water-reducing agents, high-performance water-reducing agents, fluidizers, 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, defoaming agents, etc. One type of admixture may be used alone, or two or more types may be used in combination.

[0038] The concrete composition according to this embodiment may further contain admixtures. Examples of admixtures include inorganic powders such as fly ash, cement kiln dust, blast furnace fume, 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 balloon, 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.

[0039] The mixing process involves mixing cement, granular silica fume, fine aggregate, coarse aggregate, and water to obtain a concrete composition. The method of mixing each material is not particularly limited, and for example, it can be mixed using a mixing machine such as a twin-shaft forced-mix mixer in a conventionally known manner.

[0040] The steam curing process involves curing the concrete composition at a temperature of 60°C or higher. The curing method may be atmospheric pressure steam curing as specified in JIS A 0203:2014, or high-pressure steam curing at a pressure higher than atmospheric pressure. The curing temperature in the steam curing process is 60°C or higher, preferably 70°C or higher, and more preferably 90°C or higher. Furthermore, the curing temperature in the steam curing process is preferably 100°C or lower, and more preferably 95°C or lower.

[0041] The steam curing process preferably involves holding the concrete composition at a temperature of 60°C or higher for 6 to 36 hours, and more preferably for 12 to 24 hours.

[0042] The curing means in the steam curing process is not particularly limited and can be appropriately selected depending on the construction state of the concrete composition. For example, the concrete composition may be cured while contained in the mold, or it may be cured after being removed from the mold. When curing while contained in the mold, for example, a heating device such as a heater may be attached to the mold to heat the mold and the concrete composition may be cured inside the mold by the heat of the mold, or hot air or high-temperature steam may be supplied to the inside of the mold itself to heat the mold and the concrete composition may be cured inside the mold by the heat of the mold.

[0043] The concrete manufacturing method according to this embodiment may include a pre-curing step before the steam curing step. The pre-curing step preferably involves holding the concrete composition at a temperature of 5°C to 35°C, and more preferably at a temperature of 15°C to 25°C. Furthermore, the pre-curing step preferably involves holding the concrete composition at a temperature of 6 hours to 36 hours, and more preferably at a temperature of 12 hours to 24 hours. The pre-curing step refers to the period from the mixing of the concrete composition to the start of the temperature rise in the steam curing step.

[0044] The aforementioned pre-curing step preferably involves holding the concrete composition at a temperature of 5°C to 35°C for 6 hours to 36 hours, and more preferably at a temperature of 15°C to 25°C for 12 hours to 24 hours.

[0045] The concrete manufacturing method according to this embodiment includes a mixing step of mixing cement, granular silica fume, fine aggregate, coarse aggregate, and water to obtain a concrete composition, and a steam curing step of curing the concrete composition at a temperature of 60°C or higher. This method suppresses a decrease in the compressive strength of the concrete and improves its freeze-thaw resistance.

[0046] In the concrete manufacturing method according to this embodiment, by holding the concrete composition at a temperature of 60°C or higher for 6 to 36 hours during the steam curing step, the decrease in the compressive strength of the concrete can be further suppressed, and the freeze-thaw resistance can be further improved.

[0047] The concrete manufacturing method according to this embodiment includes a pre-curing step in which the concrete composition is held at a temperature of 5°C to 35°C for 6 to 36 hours before the steam curing step, thereby further suppressing the decrease in the compressive strength of the concrete and further improving its freeze-thaw resistance.

[0048] The concrete manufacturing method according to this embodiment is provided when the bulk density of the granular silica fume is 0.55 g / cm³. 3 More than 0.70g / cm 3 The following factors can further suppress the decrease in the compressive strength of concrete and improve its resistance to freeze-thaw cycles.

[0049] In the concrete manufacturing method according to this embodiment, the water-to-binder ratio (W / B) is 16% by mass or more and 24% by mass or less, which further suppresses the decrease in the compressive strength of the concrete and further improves its freeze-thaw resistance.

[0050] <Curing Method for Concrete Compositions> The curing method for the concrete composition according to this embodiment involves steam curing the concrete composition, which contains cement, granular silica fume, fine aggregate, coarse aggregate, and water, at a temperature of 60°C or higher. The curing temperature is 60°C or higher, preferably 70°C or higher, and more preferably 90°C or higher. Furthermore, the curing temperature is preferably 100°C or lower, and more preferably 95°C or lower.

[0051] In the curing method for the concrete composition according to this embodiment, it is preferable to hold the concrete composition at a temperature of 60°C or higher for 6 hours or more and 36 hours or less, and more preferably for 12 hours or more and 24 hours or less. [Examples]

[0052] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0053] <Materials for concrete compositions> Water (W): Tap water Cement (C): Ordinary Portland cement (NC, manufactured by Sumitomo Osaka Cement Co., Ltd.) High-early-strength Portland cement (HC, manufactured by Sumitomo Osaka Cement Co., Ltd.) Moderate-heat Portland cement (MC, manufactured by Sumitomo Osaka Cement Co., Ltd.) Low-heat Portland cement (LC, manufactured by Sumitomo Osaka Cement Co., Ltd.) Silica fume (SF): Granular silica fume, SF-RD (bulk density: 0.70g) / cm 3 (Manufactured by Tomoe Industrial Co., Ltd.) Powdered silica fume, 940U (bulk density: 0.35 g / cm³) m 3 (Manufactured by Elchem ​​Japan Co., Ltd.) Fine aggregate (S): Mountain sand Coarse aggregate (G): Hard sandstone Admixture (high-performance water-reducing agent): SSP-104H (manufactured by Takemoto Oil Co., Ltd.) Admixture (antifoaming agent): AFK-2 (manufactured by Takemoto Oil Co., Ltd.)

[0054] [Table 1]

[0055] <Concrete preparation> Each of the above materials was mixed according to the proportions shown in Table 1 and then mixed in a twin-screw forced mixer to prepare each concrete composition. Specifically, first, cement, silica fume, fine aggregate, and coarse aggregate were dry-mixed in the mixer for 15 seconds, then water was added and mixed for 10 minutes to obtain the concrete compositions for each example, comparative example, and reference example. Subsequently, each concrete composition was placed in a curing tank at 20°C for a predetermined time (0 to 72 hours) for pre-curing. Granular silica fume was used in each example and comparative example, while powdered silica fume was used in each reference example.

[0056] For each example's concrete composition, after pre-curing, steam curing was performed at atmospheric pressure using a steam curing tank (manufactured by Hyuga Co., Ltd.). Specifically, after the pre-curing time shown in Tables 2 to 5 had elapsed, the temperature inside the curing tank was raised to the curing temperature (maximum temperature) shown in Tables 2 to 5 and maintained for a predetermined time (6 to 36 hours). After that, the temperature inside the curing tank was lowered to 20°C to obtain the concrete for each example. The concrete compositions for Comparative Examples 2, 4, 6, and 9, and Reference Examples 2 to 9, 11 to 18, 20 to 27, and 30 to 37 were also steam cured in the same manner as in each example to obtain their respective concretes.

[0057] The concrete compositions of Comparative Examples 1, 3, 5, 7, and 8, and Reference Examples 1, 10, 19, 28, and 29 were placed in a curing tank at 20°C for 72 hours. Subsequently, Comparative Examples 1, 3, 5, and 8, and Reference Examples 1, 10, 19, and 29 were cured underwater (at 20°C) until 28 days of age to obtain the respective concretes. Comparative Example 7 and Reference Example 28 were obtained without underwater curing.

[0058] <Evaluation of compressive strength> The compressive strength of each prepared concrete was measured in accordance with JIS A 1108:2018. The compressive strength was compared between the measured values ​​(reference values) of each reference example containing powdered silica fume and the measured values ​​of each example and comparative example containing granular silica fume, using the same curing method as the reference example. If the difference between the measured values ​​of each example and comparative example and the measured value of each reference example was 0 or greater, it was evaluated as "○ (Has compressive strength equivalent to or greater than concrete containing powdered silica fume)," and if it was less than 0, it was evaluated as "× (Lower compressive strength than concrete containing powdered silica fume)." The measured compressive strength values ​​and evaluation results are shown in Tables 2-5.

[0059] Furthermore, the increase in compressive strength was compared with the measured values ​​of each example, comparative example, and reference example that underwent steam curing, using the measured values ​​of Comparative Examples 1, 3, 5, and 8, and Reference Examples 1, 10, 19, and 29, which underwent only pre-curing, as a baseline. The value obtained by subtracting the measured values ​​of each comparative example and reference example that underwent only pre-curing from the measured values ​​of each example, comparative example, and reference example that underwent steam curing was 10 or more, was evaluated as "◎", a value between 0 and 10 was evaluated as "〇", and a value less than 0 was evaluated as "×". The evaluation results are shown in Tables 2 to 5.

[0060] <Evaluation of freeze-thaw resistance> For each concrete sample prepared, a freeze-thaw test was conducted in accordance with JIS A 1148:2010 to determine the relative dynamic modulus of elasticity. Freeze-thaw resistance was evaluated based on the Japan Society of Civil Engineers' Standard Specifications for Concrete. A relative dynamic modulus of 85% or higher after 600 freeze-thaw cycles was evaluated as "○", while a value below 85% was evaluated as "×". The measured values ​​and evaluation results for the relative dynamic modulus are shown in Tables 2-5.

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] [Table 5]

[0065] As can be seen from the results in Tables 2-5, the concrete from each example cured at a temperature of 60°C or higher has higher compressive strength compared to the concrete from each comparative example cured at a temperature of less than 60°C, and exhibits compressive strength equivalent to or greater than that of the concrete from each reference example using the same curing method. Furthermore, the concrete from each example containing granular silica fume exhibits superior freeze-thaw resistance compared to the concrete from each reference example containing powdered silica fume. In other words, the concrete manufacturing method that satisfies all the constituent requirements of the present invention can suppress the decrease in compressive strength of concrete and improve freeze-thaw resistance.

Claims

1. A mixing process to obtain a concrete composition by mixing cement, granular silica fume, fine aggregate, coarse aggregate, and water, A steam curing process in which the concrete composition is cured at a temperature of 90°C or higher, Includes, Furthermore, prior to the steam curing process, the concrete composition is held at a temperature of 5°C to 35°C for 6 hours to 36 hours. The bulk density of the granular silica fume is 0.55 g / cm³. ３ 0.70g / cm or more ３ The following: A method for producing concrete, comprising holding the concrete composition at a temperature of 90°C or higher for 6 hours or more and 36 hours or less in the steam curing step.

2. The method for producing concrete according to claim 1, wherein the water-to-binder ratio (W / B) is 16% by mass or more and 24% by mass or less.

3. A concrete composition containing cement, granular silica fume, fine aggregate, coarse aggregate, and water is steam-cured at a temperature of 90°C or higher. Furthermore, prior to the steam curing, the process includes a pre-curing step in which the concrete composition is held at a temperature of 5°C to 35°C for 6 to 36 hours. The bulk density of the granular silica fume is 0.55 g / cm³. ３ 0.70g / cm or more ３ The following: A method for curing a concrete composition, comprising holding the concrete composition at a temperature of 90°C or higher for 6 hours or more and 36 hours or less.

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