Concrete composition, hardened body, and method for producing hardened body

Abstract

An object of the present invention is to provide a concrete composition having good fluidity retention, cohesiveness, and early strength development property. 【Solution means】A concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the binder content is 300 kg / m 3 or more, the water-binder ratio is 55% or less, and the addition amount of the hardening accelerator for hydraulic materials is 1 to 50 kg / m 3 and the hardening accelerator for hydraulic materials contains 20.0 to 80.0% by mass of calcium formate, 15.0 to 70.0% by mass of an inorganic calcium compound, and 0.5 to 30.0% by mass of an inorganic sulfate excluding calcium sulfate.

Description

Technical Field

[0001] The present invention relates to a concrete composition, a hardened body, and a method for producing the same.

Background Art

[0002] Hydraulic materials such as cement used in the civil engineering and construction fields usually harden by mixing with water and standing for a predetermined time. The hardening speed of the hydraulic material can be affected by the ratio of the material to water, the ambient temperature, and the curing method, but by using an admixture that accelerates hardening, that is, a hardening accelerator, the time until the hydraulic material hardens can be shortened.

[0003] Shortening the time until the hydraulic material hardens leads to an improvement in productivity at the work site. For example, a precast concrete hardened body used in a precast method for use in a reinforced concrete building or the like can generally be obtained by placing a cement composition in a formwork, standing for a predetermined time, and then further curing by steam curing or the like, but by using a hardening accelerator, the time until the initial strength at which demolding is possible can be shortened, so that the hardened body can be produced efficiently.

[0004] Also, usually, after placing the cement composition, in order to evenly distribute the cement composition in the formwork, "compaction" is performed using a vibrator or the like, but if the fluidity of the cement composition immediately after placement is reduced, it takes labor and time to perform compaction, and productivity decreases.

[0005] Regarding hardening accelerators, for example, Patent Document 1 discloses a hardening accelerator for hydraulic materials containing a predetermined amount of inorganic sulfate, calcium sulfoaluminate, and inorganic hydroxide. Patent Document 2 discloses a cement admixture containing calcium sulfoaluminate having a Blaine specific surface area value of 4000 cm 2 / g or more and one or more selected from the group consisting of formate, acetate, and lactate.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 2014-19618 Patent Document 2 Japanese Patent Application Laid-Open No. 2010-235399 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, in the hydraulic material using the above-mentioned hardening accelerator, the fluidity is lost immediately after kneading with water, and labor and time are required for tamping after placing, so there is a concern that the productivity may decrease.

[0008] From the above, an object of the present invention is to provide a concrete composition having good fluidity retention, setting property, and initial strength development property. MEANS FOR SOLVING THE PROBLEM

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that a concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the blending amount of the binder, the water-binder ratio, and the addition amount of the hardening accelerator for hydraulic materials are within a predetermined range, and the hardening accelerator for hydraulic materials has a specific composition can solve the problem, and the present invention has been achieved. That is, the present invention is as follows.

[0010] [1] A concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the blending amount of the binder is 300 kg / m 3 or more, the water-binder ratio is 55% or less, the addition amount of the hardening accelerator for hydraulic materials is 1 to 50 kg / m 3 , and the hardening accelerator for hydraulic materials contains 20.0 to 80.0% by mass of calcium formate, 15.0 to 70.0% by mass of an inorganic calcium compound, and 0.5 to 30.0% by mass of an inorganic sulfate excluding calcium sulfate, the concrete composition. [2] The inorganic calcium compound in the concrete composition according to [1] above is one or more selected from the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide. [3] The inorganic sulfate in the concrete composition according to [1] or [2] above is one or more selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and pyrobisulfite. [4] The binder in the concrete composition according to any one of [1] to [3] above contains 1 to 15% by mass of calcium sulfoaluminate. [5] A cured body obtained by curing the concrete composition according to any one of [1] to [4] above. [6] A method for producing a cured body, wherein the concrete composition according to any one of [1] to [4] above is cured by curing under conditions of a temperature of 40°C or lower. [Advantages of the Invention]

[0011] According to the present invention, a concrete composition having good fluidity retention, setting property, and initial strength development property can be provided. [Modes for Carrying Out the Invention]

[0012] Hereinafter, an embodiment (this embodiment) of the present invention will be described in detail, but the present invention is not limited to the embodiment. In the present specification, “%” and “parts” are based on mass unless otherwise specified.

[0013] [Concrete Composition] The concrete composition according to this embodiment is a concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the amount of the binder is 300 kg / m 3 or more, the water-binder ratio is 55% or less, and the addition amount of the hardening accelerator for hydraulic materials is 1 to 50 kg / m 3and the hardening accelerator for the hydraulic material contains 20.0 to 80.0% by mass of calcium formate, 15.0 to 70.0% by mass of inorganic calcium compound, and 0.5 to 30.0% by mass of inorganic sulfate excluding calcium sulfate. The concrete composition of the present invention has good fluidity retention, setting property, and initial strength development property, and is suitable for the production of precast concrete and the like. Also, for example, in the case of precast concrete, it can be sufficiently hardened without using steam curing, which is advantageous in terms of energy consumption and CO2 emissions.

[0014] The "binder" in the present invention refers to a general term for substances that react with water to produce substances contributing to the strength development of concrete, and examples include cement, calcium aluminate, calcium sulfoaluminate, fly ash, blast furnace slag, fly ash, silica fume, fine limestone powder, metakaolin, allophane, etc. The amount of binder in the binder content and the water-binder ratio refers to the total amount of these. Also, the "hardening accelerator for hydraulic material" of the present invention not only accelerates the hardening of the hydraulic material when the hydraulic material in the binder is kneaded with water and hardened, but may also harden itself while accelerating the hardening.

[0015] The concrete composition of the present invention preferably contains at least cement as a binder. The type of cement is not particularly limited, and examples include various Portland cements such as ordinary, early-strength, ultra-early-strength, low-heat, and medium-heat Portland cements, environment-friendly cements (eco-cements) manufactured using municipal waste incineration ash or sewage sludge incineration ash as raw materials, commercially available fine particle cements, white cements, etc. It is also possible to use various cements in a micronized form. Also, those adjusted by increasing or decreasing the amount of components (for example, gypsum, etc.) usually used in cement can be used. Furthermore, those obtained by combining two or more of these can also be used. From the viewpoint of enhancing the initial strength development property, it is preferable to select ordinary Portland cement or early-strength Portland cement.

[0016] The cement used in the present invention preferably has a Blaine specific surface area value (hereinafter, also simply referred to as "Blaine value") of 2,500 to 7,000 cm 2 / g, more preferably 2,750 to 6,000 cm 2 / g, and even more preferably 3,000 to 4,500 cm 2 / g. In the present invention, the Blaine specific surface area value is measured in accordance with the specific surface area test specified in JIS R 5201:2015 "Physical Testing Methods for Cement".

[0017] The cement content is preferably 20.0 parts by mass or more, more preferably 50.0 parts by mass or more, and even more preferably 60.0 parts by mass or more with respect to 100 parts by mass of the binder in the concrete composition. When the cement content is within the above range, the fluidity retention and initial strength development of the concrete composition can be made better.

[0018] The concrete composition of the present invention can contain calcium sulfoaluminate as a binder. Calcium sulfoaluminate is a general term for hydraulic substances and hydrates represented by the chemical formula xCaO·yAl2O3·zCaSO4·mH2O (x, y, and z are positive real numbers other than 0, and m is 0 or a positive real number). Examples include, in addition to awin (3CaO·3Al2O3·CaSO4), the AFt phase represented by ettringite (3CaO·Al2O3·3CaSO4·32H2O), the AFm phase represented by monosulfate (3CaO·Al2O3·CaSO4·12H2O), and those in which the AFt phase and the AFm phase coexist. Calcium sulfoaluminate may be amorphous. Also, a part of Al2O3 may be substituted with a small amount of Fe2O3 or SiO2, etc., and a part of CaSO4 may be substituted with Ca(OH)2 or CaCO3, etc. In the present invention, in the above chemical formula xCaO·yAl2O3·zCaSO4·mH2O, z cannot be set to 0 because the fluidity of the hydraulic material cannot be maintained and the strength during hardening may decrease due to phase transition.

[0019] Calcium sulfoaluminate is produced using raw materials such as calcia raw materials like lime, sulfate raw materials like gypsum, and alumina raw materials like bauxite (aluminum hydroxide). For example, the raw materials are blended in a predetermined ratio such as a ratio of 3:3:1 in terms of the molar ratio of CaO:CaSO4:Al2O3, and then fired at about 1,500 °C using a kiln or the like, and pulverized. Also, silicon dioxide or the like may be added to the once-fired product for heat treatment and then pulverized.

[0020] The Blaine specific surface area value of calcium sulfoaluminate is preferably 1,000 - 6,000 cm 2 / g, more preferably 2,000 - 4,000 cm 2 / g, and even more preferably 2,200 - 3,800 cm 2 / g.

[0021] The content of calcium sulfoaluminate is preferably 1 - 15% by mass, more preferably 1 - 8% by mass, and even more preferably 2 - 5% by mass based on the binder. When the content of calcium sulfoaluminate is within the above range, the fluidity retention and early strength development of the concrete composition can be made better.

[0022] The concrete composition of the present invention can contain siliceous fine powder as a binder. When the concrete composition contains siliceous fine powder, it is easy to improve the fluidity retention and early strength development. Examples of siliceous fine powder include latent hydraulic substances such as blast furnace slag fine powder, pozzolanic substances such as fly ash, silica fume, metakaolin, and allophane. Among them, blast furnace slag fine powder, fly ash, and metakaolin are preferred.

[0023] The fineness of the siliceous fine powder is not particularly limited. Usually, blast furnace slag fine powder and fly ash have a Blaine value of 3,000 - 9,000 cm 2in the range of / g, and the silica fume preferably has a BET specific surface area in the range of 20,000 to 300,000 cm 2 / g.

[0024] The content of the silica fine powder is preferably 5 to 60 parts by mass, more preferably 10 to 50 parts by mass, and still more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the binder in the concrete composition. When the content of the silica fine powder is at least the above lower limit value, it is easy to improve the fluidity retention and the initial strength development property. Furthermore, when the blending ratio of the silica fine powder is at most the above upper limit value, it is easy to further improve the fluidity retention.

[0025] The blending amount of the binder in the concrete composition of the present invention is 300 kg / m 3 or more. If the blending amount of the binder is less than 300 kg / m 3 , there is a risk that the initial strength development property becomes poor. Also, the blending amount of the binder is preferably 320 kg / m 3 or more, more preferably 350 kg / m 3 or more, and still more preferably 380 kg / m 3 or more. Also, it is preferably 550 kg / m 3 or less, more preferably 580 kg / m 3 or less, and still more preferably 600 kg / m 3 or less. By the blending amount of the binder being within the above range, the initial strength development property can be made better.

[0026] The water-binder ratio in the concrete composition of the present invention is 55% or less. The water-binder ratio (W / B) is the ratio of the blending amount of water to the blending amount of the binder. However, if the water-binder ratio exceeds 55%, there is a risk that the setting property becomes poor. Also, the water-binder ratio is preferably 55% or less, more preferably 48% or less, and still more preferably 45% or less. Also, the lower limit is not particularly limited, but it is preferably 20% or more. By the water-binder ratio being within the above range, the setting property can be made better.

[0027] (Hardening accelerator for hydraulic materials) The hardening accelerator for hydraulic materials in the present invention contains 20.0 to 80.0% by mass of calcium formate, 15.0 to 70.0% by mass of an inorganic calcium compound, and 0.5 to 30.0% by mass of an inorganic sulfate excluding calcium sulfate. If the content ratio of calcium formate is less than 20.0% by mass, there is a possibility that the fluidity retention, setting property, and initial strength development property of the concrete composition cannot be improved. If it exceeds 80.0% by mass, there is a possibility that the fluidity retention, setting property, and initial strength development property of the concrete composition cannot be improved. If the content ratio of the inorganic calcium compound is less than 15.0% by mass, there is a possibility that the fluidity retention, setting property, and initial strength development property of the concrete composition cannot be improved. If it exceeds 70.0% by mass, there is a possibility that the fluidity retention, setting property, and initial strength development property of the concrete composition cannot be improved. If the content ratio of the inorganic sulfate excluding calcium sulfate is less than 0.5% by mass, there is a possibility that the fluidity retention, setting property, and initial strength development property of the concrete composition cannot be improved. If it exceeds 30.0% by mass, there is a possibility that the fluidity retention, setting property, and initial strength development property of the concrete composition cannot be improved.

[0028] The hardening accelerator for hydraulic materials in the concrete composition of the present invention preferably contains 30.0 to 70.0% by mass of calcium formate, and more preferably contains 40.0 to 65.0% by mass. When the content ratio of calcium formate is within the above range, the fluidity retention, setting property, and initial strength development property of the concrete composition can be improved more favorably.

[0029] The hardening accelerator for hydraulic materials in the concrete composition of the present invention preferably contains 18.0 to 60.0% by mass of an inorganic calcium compound, and more preferably contains 20.0 to 40.0% by mass. When the content ratio of the inorganic calcium compound is within the above range, the fluidity retention, setting property, and initial strength development property of the concrete composition can be improved more favorably.

[0030] In this embodiment, the inorganic calcium compound is preferably at least one selected from the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide. When two or more inorganic calcium compounds are used, the sum of the respective content ratios is defined as the content ratio of the inorganic calcium compound. In this embodiment, from the viewpoint of early strength development property, it is preferable to use calcium sulfate, calcium hydroxide and / or calcium oxide, and calcium sulfate is more preferable. When calcium sulfate is used, it is more preferably an anhydride.

[0031] The hardening accelerator for hydraulic materials in the concrete composition of the present invention preferably contains 1.0 to 25.0% by mass of inorganic sulfate excluding calcium sulfate, and more preferably contains 3.0 to 15.0% by mass. When the content ratio of the inorganic sulfate excluding calcium sulfate is within the above range, the fluidity retention, setting property, and early strength development property of the concrete composition can be made better.

[0032] In this embodiment, the inorganic sulfate is preferably at least one selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and pyrobisulfite. When two or more inorganic sulfates are used, the sum of the respective content ratios is defined as the content ratio of the inorganic sulfate. As the inorganic substance forming the salt, an alkali metal and an alkaline earth metal are preferable. In this embodiment, from the viewpoint of early strength development property, it is preferable to use sulfate and / or thiosulfate, more preferably sodium sulfate, aluminum sulfate, sodium thiosulfate, and potassium alum, even more preferably sodium sulfate and aluminum sulfate from the viewpoint of early strength development property, and among them, sodium sulfate is even more preferably from the viewpoint of improving fluidity retention. When sodium sulfate is used, it is more preferably an anhydride.

[0033] The addition amount of the hardening accelerator for hydraulic materials in the concrete composition of the present invention is 1 to 50 kg / m 3 is. When the addition amount of the hardening accelerator for hydraulic materials is 1 kg / m 3If it is less than that, the initial strength development property may be poor, and if it exceeds 50 kg / m 3 there is a risk that the fluidity retention property will be poor. The addition amount of the hardening accelerator for hydraulic materials is preferably 5 to 48 kg / m 3 more preferably 10 to 45 kg / m 3 even more preferably 13 to 43 kg / m 3 When the addition amount of the hardening accelerator for hydraulic materials is within the above range, the fluidity retention property, setting property, and initial strength development property of the concrete composition can be made better.

[0034] The concrete composition of the present invention substantially contains aggregates, and as the aggregates to be used, fine aggregates and coarse aggregates similar to those used in ordinary concrete can be used. That is, river sand, river gravel, mountain sand, mountain gravel, crushed stone, crushed sand, limestone aggregate, lime sand, silica sand, colored sand, artificial aggregate, blast furnace slag aggregate, sea sand, sea gravel, artificial lightweight aggregate, and heavy aggregate, etc. can be used, and these can also be combined.

[0035] The blending ratio of the aggregates is preferably 40 to 250 parts by mass, more preferably 50 to 230 parts by mass, and even more preferably 60 to 200 parts by mass with respect to 100 parts by mass of cement in the concrete composition. When the blending ratio of the aggregates is within the above range, the fluidity retention property and initial strength development property of the concrete composition can be made better.

[0036] The concrete composition can contain an alkali metal carbonate. When the concrete composition contains an alkali metal carbonate, it is easy to improve the fluidity retention property and initial strength development property. Examples of the alkali metal carbonate include sodium carbonate, potassium carbonate, lithium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium hydrogen carbonate, etc., and these can also be combined.

[0037] The blending ratio of the alkali metal carbonate is preferably 1 to 6 parts by mass in terms of solid content with respect to 100 parts by mass of cement in the concrete composition, and more preferably 2 to 5 parts by mass. By the content ratio of the alkali metal carbonate being within the above range, it is easy to improve the fluidity retention and the initial strength development property.

[0038] The concrete composition can also be blended with an antifoaming agent within a range that does not adversely affect the performance. The antifoaming agent is used for the purpose of suppressing the amount of air entrained during mixing. The type of the antifoaming agent is not particularly limited as long as it does not significantly adversely affect the strength characteristics of the hardened body, and either a liquid form or a powder form can be used. For example, polyether-based antifoaming agents, polyhydric alcohol-based antifoaming agents such as esterified products of polyhydric alcohols and alkyl ethers, alkyl phosphate-based antifoaming agents, silicone-based antifoaming agents, etc. can be mentioned.

[0039] The blending ratio of the antifoaming agent is preferably 0.002 to 0.5 parts by mass with respect to 100 parts by mass of cement in the concrete composition, more preferably 0.005 to 0.45 parts by mass, and even more preferably 0.01 to 0.4 parts by mass. By the blending ratio of the antifoaming agent being not less than the above lower limit value, the antifoaming effect can be sufficiently exhibited, and by the blending ratio of the antifoaming agent being not more than the above upper limit value, it is easy to improve the fluidity retention.

[0040] Further, the concrete composition can use one or more of gas foaming substances, water reducing agents, AE agents, rust preventives, water repellents, antibacterial agents, coloring agents, antifreezing agents, fine limestone powder, fine blast furnace slag powder, incineration ash of sewage sludge and its molten slag, incineration ash of municipal waste and its molten slag, and incineration ash of pulp sludge, etc., thickeners, and shrinkage reducing agents, polymers, clay minerals such as bentonite and sepiolite, and anion exchangers such as hydrotalcite within a range that does not substantially inhibit the object of the present invention.

[0041] As the fresh properties of the concrete composition before placing, appropriate slump values and slump flow values according to the product to be manufactured make it easy to place and compact, improve workability, and suppress the occurrence of material separation. The amount of change in slump (slump change amount) after kneading the concrete composition for 1 hour is preferably less than 10%, more preferably less than 7.5%, and even more preferably less than 5%. When the slump change amount of the concrete composition is within the above range, even if placing is carried out 1 hour after kneading the cement composition, it is easy to place and compact, and the workability is improved. In addition, the amount of change in slump flow (slump flow change amount) after kneading the concrete composition for 1 hour is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. In the present invention, the slump can be measured in accordance with the method specified in JIS A 1101:2020 "Method for Slump Test of Concrete", and the slump flow can be measured in accordance with the method specified in JIS A 1150:2020 "Method for Slump Flow Test of Concrete". Further, the slump change amount can be obtained by subtracting from 100% the value calculated by (slump after kneading for 1 hour) / (slump immediately after kneading)×100(%), and the slump flow change amount can be obtained by subtracting from 100% the value calculated by (slump flow after kneading for 1 hour) / (slump flow immediately after kneading)×100(%).

[0042] The concrete composition may mix each material during construction, or may mix part or all of them in advance. As the mixing device, any existing device, for example, a tilting drum mixer, an omnimixer, a Henschel mixer, a V-type mixer, a pro-shear mixer, and a Nauta mixer can be used.

[0043] [Hardened body] The hardened body according to this embodiment is obtained by hardening the concrete composition of the present invention. Usually, when the concrete composition is kneaded, the cement undergoes a hydration reaction and hardens. It is obtained by hardening after standing still after kneading the concrete composition. However, after kneading, it can be obtained more efficiently by filling (casting) it into a mold and curing it, or by directly pouring it, spraying it, or applying it to the construction site.

[0044] The compressive strength of the hardened body depends on the type of cement used, but it is preferably 8.5 N / mm 2 or more after 16 hours of casting, more preferably 10.0 N / mm 2 or more, and even more preferably 11.0 N / mm 2 or more. In the present invention, the compressive strength can be measured in accordance with the method specified in JIS A 1108:2018 "Test Method for Compressive Strength of Concrete".

[0045] [Manufacturing method of hardened body] The manufacturing method of the hardened body according to this embodiment is a method of curing and hardening the concrete composition of the present invention under the condition of a temperature of 40°C or lower. By casting the concrete composition into a mold and curing it under the above conditions, a hardened body can be obtained.

[0046] The temperature of the concrete composition at the time of casting is preferably 0 to 50°C, and more preferably 10 to 40°C. When the temperature of the concrete composition at the time of casting is within the above range, it becomes easier to demold the hardened body.

[0047] In the method for producing a cured body of the present invention, it is preferable to further compact the concrete composition after placing it. As the compaction method, known methods can be used, but from the viewpoint of workability, it is preferable to use a vibrator. Since the concrete composition of the present invention maintains good fluidity immediately before placing, compaction can be easily performed, the concrete composition can be evenly spread in the formwork, and bubbles mixed in during placing can be removed.

[0048] The curing conditions in the method for producing a cured body of the present invention are a temperature of 40°C or lower, preferably 35°C or lower. Also, the humidity is preferably 80%RH or lower, more preferably 70%RH or lower. The curing time is preferably 24 hours or shorter, more preferably 16 hours or shorter, and even more preferably 12 hours or shorter. Note that from the viewpoint of reducing CO2 emissions, it is preferable not to use steam curing in the present invention.

Examples

[0049] Hereinafter, the present invention will be further described based on experimental examples, but the present invention is not limited thereto.

[0050] <Experimental Example 1> Using the following materials, a hardening accelerator for hydraulic materials containing 60% by mass of calcium formate, 35% by mass of calcium sulfate, and 5% by mass of sodium sulfate was prepared, and the concrete compositions shown in Table 1 were prepared. The slump of the obtained concrete composition was measured, and the slump change amount was calculated. Also, the initial setting time was measured. All are shown together in Table 1. In addition, the prepared cement composition was filled into a mold having dimensions of φ10×20 cm, and then cured for 24 hours under the conditions of a temperature of 20°C and a humidity of 70%RH to obtain a cured body. The compressive strength of the obtained cured body was measured. The results are shown together in Table 1.

[0051] (Materials used) Cement: Ordinary Portland cement (commercial product), Blaine specific surface area 3,200 cm 2 / g, specific gravity 3.15 g / cm3 . Water: Tap water. Fine aggregate: River sand produced from the Hikawa River system in Niigata Prefecture. Coarse aggregate: River gravel produced from the Hikawa River system in Niigata Prefecture. Ground granulated blast furnace slag: Commercially available product. Fly ash: Commercially available product. Metakaolin: Commercially available product. Calcium sulfoaluminate: Using first-grade reagent calcium carbonate, calcium sulfate dihydrate, and aluminum hydroxide, mixed so that the molar ratio of CaO:CaSO4:Al2O3 is 4:3:1, fired at 1,400 °C for 2 hours, left to cool to room temperature, and ground until the Blaine specific surface area becomes 3,500 cm 2 / g. The resulting product is a trial product. Calcium formate: Reagent. Calcium sulfate (inorganic calcium compound): Reagent. Sodium sulfate (inorganic sulfate): Anhydrous, reagent.

[0052] (Measurement items) Slump change: In accordance with the method specified in JIS A 1101:2020 "Test Method for Slump of Concrete", the slump of the concrete immediately after mixing and 1 hour after mixing was measured respectively. The slump immediately after mixing was about 12.0 cm for all. Using the measured slumps, the slump change was calculated as (slump change) = (slump immediately after mixing) / (slump 1 hour after mixing), and the fluidity retention was evaluated.

[0053] Initial setting time: In accordance with the method specified in JIS A 1147:2019 "Test Method for Setting Time of Concrete", the time when the penetration resistance value reaches 3.5 N / mm 2 was defined as the initial setting time.

[0054] Compressive strength: In accordance with the method specified in JIS A 1108:2018 "Test Method for Compressive Strength of Concrete", the compressive strength immediately after demolding was measured.

[0055] [Table 1]

[0056] <Experimental Example 2> A concrete composition was prepared in the same manner as No. 1-2 of Experimental Example 1, except that the hardening accelerator for the hydraulic material was changed to the composition shown in Table 2, and the slump change amount, initial setting time, and compressive strength were measured. The results are also shown in Table 2.

[0057]

Table 2

[0058] <Experimental Example 3> A concrete composition was prepared in the same manner as No. 1-2 of Experimental Example 1, except that in addition to calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide were used at the ratios shown in Table 2 as the inorganic calcium compounds contained in the hardening accelerator for the hydraulic material, and the slump change amount, initial setting time, and compressive strength were measured. The results are also shown in Table 3.

[0059] (Inorganic Calcium Compound) Calcium hydroxide: reagent. Calcium carbonate: reagent. Calcium oxide: reagent.

[0060]

Table 3

[0061] <Experimental Example 4> A concrete composition was prepared in the same manner as No. 1-2 of Experimental Example 1, except that in addition to sodium sulfate, aluminum sulfate, potassium alum, and sodium thiosulfate were used at the ratios shown in Table 4 as the inorganic sulfates contained in the hardening accelerator for the hydraulic material, and the slump change amount, initial setting time, and compressive strength were measured. The results are also shown in Table 4.

[0062] (Inorganic Sulfate) Aluminum sulfate: reagent. Potassium alum: reagent. Sodium thiosulfate: reagent.

[0063] [Table 4]

Industrial Applicability

[0064] Since the concrete composition of the present invention has good fluidity retention, setting property, and initial strength development property, it can be widely applied to civil engineering and construction fields such as concrete hardened bodies used in the precast method.

Claims

1. A concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, The binder content is 300 kg / m ３ or more, the water-binder ratio is 55% or less, and the addition amount of the hardening accelerator for the hydraulic material is 1 to 50 kg / m ３ and wherein the hardening accelerator for hydraulic materials contains 30.0 to 80.0% by mass of calcium formate, 15.0 to 65.0% by mass of an inorganic calcium compound, and 0.5 to 30.0% by mass of an inorganic sulfate excluding calcium sulfate, the inorganic calcium compound is one or more selected from the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide, and the inorganic sulfate is one or more selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and pyrobisulfite. The concrete composition.

2. The concrete composition according to claim 1, wherein the binder contains 1 to 15% by mass of calcium sulfoaluminate.

3. A hardened body obtained by hardening the concrete composition according to claim 1 or 2.

4. A method for producing a hardened body, wherein the concrete composition according to claim 1 or 2 is cured and hardened under conditions of a temperature of 40°C or lower.

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