Concrete composition, hardened body, and method for manufacturing the hardened body

Abstract

The objective is to provide a concrete composition with good fluidity retention, setting properties, and initial strength development. [Solution] A concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the binder content is 300 kg / m 3 The above conditions apply, with a water-binder ratio of 55% or less, and an amount of the water-hardening material hardening accelerator added of 1 to 50 kg / m³. 3 A concrete composition wherein 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 concrete compositions, hardened bodies, and methods for producing the same. [Background technology]

[0002] Hydraulic materials such as cement used in civil engineering and construction typically harden when mixed with water and left to stand for a specified time. The hardening rate of hydraulic materials can be affected by the ratio of material to water, the ambient temperature, and the curing method, but the time it takes for hydraulic materials to harden can be shortened by using admixtures that accelerate hardening, i.e., hardening accelerators.

[0003] Reducing the time it takes for hydraulic materials to harden leads to improved productivity at the worksite. For example, in precast construction methods used for reinforced concrete buildings, hardened concrete bodies are generally obtained by pouring the cement composition into the formwork, letting it stand for a predetermined time, and then curing it further by steam curing, etc. However, by using a hardening accelerator, the time it takes to reach the initial strength required for demolding can be shortened, allowing for the efficient production of hardened bodies.

[0004] Furthermore, after the cement composition is poured, compaction is usually performed using a vibrator or similar device to ensure uniform distribution within the formwork. However, if the fluidity of the cement composition is low immediately after pouring, the labor and time required for compaction will increase, leading to decreased productivity.

[0005] Regarding hardening accelerators, for example, Patent Document 1 describes a hardening accelerator for hydraulic materials containing predetermined amounts of inorganic sulfate, calcium sulfoaluminate, and inorganic hydroxide. Patent Document 2 describes a Blaine specific surface area value of 4000 cm². 2 The present invention refers to a cement admixture containing calcium sulfoaluminate in amounts of 1 / g or more, and one or more substances selected from the group consisting of formate, acetate, and lactate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-19618 [Patent Document 2] Japanese Patent Publication No. 2010-235399 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, hydraulic materials using the hardening accelerators described above lose their fluidity immediately after mixing with water, and require considerable effort and time for compaction after placement, raising concerns about reduced productivity.

[0008] Based on the above, the present invention aims to provide a concrete composition with good fluidity retention, setting properties, and initial strength development properties. [Means for solving the problem]

[0009] The present inventors conducted intensive research to solve the above-mentioned problems and found that the problems can be solved by a concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the amount of binder, the water-binder ratio, and the amount of hardening accelerator for hydraulic materials added are within a predetermined range, and the hardening accelerator for hydraulic materials has a specific composition. This led to the present invention. In other words, the present invention is as follows.

[0010] [1] A concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, wherein the binder content is 300 kg / m³ 3 The above conditions apply, with a water-binder ratio of 55% or less, and an amount of the water-hardening material hardening accelerator added of 1 to 50 kg / m³. 3 A concrete composition wherein 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. [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, comprising curing the concrete composition according to any one of [1] to [4] above 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-to-binder ratio is 55% or less, and the addition amount of the hardening accelerator for hydraulic materials is 1 to 50 kg / m 3The hydraulic material hardening accelerator 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 of the present invention has good fluidity retention, setting properties, and initial strength development, and is suitable for the manufacture of precast concrete and the like. Furthermore, in the case of precast concrete, for example, it can be sufficiently hardened without the use of steam curing, which is advantageous in terms of energy consumption and CO2 emissions.

[0014] In this invention, "binder" refers to a general term for substances that react with water to produce materials that contribute to the strength development of concrete. Examples include cement, calcium aluminate, calcium sulfoaluminate, fly ash, blast furnace slag, silica fume, limestone powder, metakaolin, allophane, etc. The amount of binder in the binder blending ratio and the water-binder ratio refers to the total amount of these. Furthermore, the "hardening accelerator for hydraulic materials" of this invention not only accelerates the hardening of the hydraulic material in the binder when it is mixed with water and hardens, but the hardening accelerator for hydraulic materials itself may also harden while accelerating the hardening process.

[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 includes various types of Portland cement such as ordinary, rapid-hardening, ultra-rapid-hardening, low-heat, and moderate-heat cements, environmentally friendly cement (eco-cement) manufactured from municipal solid waste incineration ash and sewage sludge incineration ash, commercially available fine-particle cement, white cement, etc. It is also possible to use various types of cement after they have been finely powdered. Furthermore, cements that have been adjusted by increasing or decreasing the amount of components commonly used in cement (e.g., gypsum) can also be used. In addition, combinations of two or more of these can also be used. From the viewpoint of improving initial strength development, it is preferable to select ordinary Portland cement or rapid-hardening Portland cement.

[0016] The cement used in this invention has a Blaine specific surface area value (hereinafter also simply referred to as "Blaine value") of 2,500 to 7,000 cm², from the viewpoint of manufacturing cost and strength development. 2 It is preferable that the amount is / g, and the range is 2,750 to 6,000 cm³. 2 It is more preferable that the amount is / g, and the range is 3,000 to 4,500 cm 2 It is even more preferable that the value is / g. In this 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, per 100 parts by mass of 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 improved.

[0018] The concrete composition of the present invention may contain calcium sulfoaluminate as a binder. Calcium sulfoaluminate is a general term for hydraulic substances and hydrated salts represented by the chemical formula xCaO·yAl2O3·zCaSO4·mH2O (where x, y, and z are non-zero positive real numbers, and m is 0 or a positive real number). Examples include hauyne (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 both the AFt and AFm phases coexist. Calcium sulfoaluminate may be amorphous. Furthermore, some of the Al2O3 may be substituted with trace amounts of Fe2O3 or SiO2, and some of the CaSO4 may be substituted with Ca(OH)2 or CaCO3. In this invention, z cannot be set to 0 in the above chemical formula xCaO·yAl2O3·zCaSO4·mH2O because it would be impossible to maintain the fluidity of the hydraulic material, and there is a risk that the strength during hardening will decrease due to the phase transition.

[0019] Calcium sulfoaluminate is produced by using raw materials such as calcia raw materials like lime, sulfate raw materials like gypsum, and alumina raw materials like bauxite (aluminum hydroxide), etc. For example, the raw materials are blended at a predetermined ratio such as a ratio of 3:3:1 in terms of the molar ratio of CaO:CaSO4:Al2O3, and fired at about 1,500 °C using a kiln or the like, and then 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 the 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 2The silica fume is in the range of / g, with a BET specific surface area of ​​20,000 to 300,000 cm². 2 It is preferable that the range is within / g.

[0024] The content of silica fine powder is preferably 5 to 60 parts by mass, more preferably 10 to 50 parts by mass, and even more preferably 20 to 40 parts by mass, per 100 parts by mass of binder in the concrete composition. A silica fine powder content above the lower limit tends to improve fluidity retention and initial strength development. Furthermore, a silica fine powder blending ratio below the upper limit tends to further improve fluidity retention.

[0025] The amount of binder in the concrete composition of the present invention is 300 kg / m³. 3 That's all. The binder content is 300 kg / m³. 3 If the amount is less than 320 kg / m³, there is a risk of poor initial strength development. Furthermore, the binder content should be 320 kg / m³. 3 The above is preferable, and 350 kg / m 3 The above is more preferable, 380 kg / m 3 The above is even more preferable. Also, 550 kg / m 3 Preferably, it is 580 kg / m 3 It is more preferable that the following conditions are met: 600 kg / m 3 The following is even more preferable: By having the binder content within the above range, the initial strength development can be improved.

[0026] The water-to-binder ratio in the concrete composition of the present invention is 55% or less. The water-to-binder ratio (W / B) is the ratio of the amount of water to the amount of binder, but if the water-to-binder ratio exceeds 55%, the setting performance may be poor. Furthermore, the water-to-binder ratio is preferably 55% or less, more preferably 48% or less, and even more preferably 45% or less. There is no particular lower limit, but it is preferably 20% or more. By keeping the water-to-binder ratio within the above range, the setting performance can be improved.

[0027] (Curing 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 calcium formate content is less than 20.0% by mass, it may not be possible to improve the fluidity retention, setting properties, and initial strength development of the concrete composition. If it exceeds 80.0% by mass, it may not be possible to improve the fluidity retention, setting properties, and initial strength development of the concrete composition. If the inorganic calcium compound content is less than 15.0% by mass, it may not be possible to improve the fluidity retention, setting properties, and initial strength development of the concrete composition. If it exceeds 70.0% by mass, it may not be possible to improve the fluidity retention, setting properties, and initial strength development of the concrete composition. If the content of inorganic sulfates excluding calcium sulfate is less than 0.5% by mass, it may not be possible to achieve good fluidity retention, setting properties, and initial strength development of the concrete composition. If it exceeds 30.0% by mass, it may not be possible to achieve good fluidity retention, setting properties, and initial strength development of the concrete composition.

[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 40.0 to 65.0% by mass. When the calcium formate content is within the above range, the fluidity retention, setting properties, and initial strength development properties of the concrete composition can be improved.

[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 20.0 to 40.0% by mass. When the content of the inorganic calcium compound is within the above range, the fluidity retention, setting properties, and initial strength development properties of the concrete composition can be improved.

[0030] In this embodiment, the inorganic calcium compound is preferably one or more 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 their respective content percentages is considered the total content of the inorganic calcium compound. In this embodiment, from the viewpoint of initial strength development, it is preferable to use calcium sulfate, calcium hydroxide, and / or calcium oxide, with calcium sulfate being more preferable. When calcium sulfate is used, it is even more preferable that it be anhydrous.

[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 sulfates excluding calcium sulfate, and more preferably 3.0 to 15.0% by mass. When the content of inorganic sulfates excluding calcium sulfate is within the above range, the fluidity retention, setting properties, and initial strength development properties of the concrete composition can be improved.

[0032] In this embodiment, the inorganic sulfate is preferably one or more selected from the group consisting of sulfates, thiosulfates, sulfites, bisulfites, pyrosulfates, and pyrobisulfites. When two or more inorganic sulfates are used, the sum of their respective content percentages is considered the inorganic sulfate content percentage. Alkali metals and alkaline earth metals are preferred as the inorganic substances that form the salt. In this embodiment, from the viewpoint of initial strength development, sulfates and / or thiosulfates are preferred, with sodium sulfate, aluminum sulfate, sodium thiosulfate, and potassium alum being more preferred, and sodium sulfate and aluminum sulfate being even more preferred from the viewpoint of improving fluidity retention. When sodium sulfate is used, it is even more preferable that it be anhydrous.

[0033] The amount of hardening accelerator for hydraulic materials added to the concrete composition of the present invention is 1 to 50 kg / m². 3 The amount of hardening accelerator added to the hydraulic material is 1 kg / m³. 3If the value is less than 50 kg / m², there is a risk of poor initial strength development. 3 If the amount exceeds this, poor fluidity retention may occur. The amount of hardening accelerator added to hydraulic materials should be 5 to 48 kg / m³. 3 Preferably, it is 10-45 kg / m 3 It is more preferable that the load is 13-43 kg / m³. 3 It is even more preferable that the amount of hardening accelerator for hydraulic materials added is within the above range, which can further improve the fluidity retention, setting properties, and initial strength development of the concrete composition.

[0034] The concrete composition of the present invention substantially contains aggregate, but the aggregate used can be the same fine aggregate or coarse aggregate used in ordinary concrete. Specifically, 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 can be used, and these can also be combined.

[0035] The aggregate mixing ratio 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, per 100 parts by mass of cement in the concrete composition. By having the aggregate mixing ratio within the above range, the fluidity retention and initial strength development of the concrete composition can be improved.

[0036] Concrete compositions can contain alkali metal carbonates. The inclusion of alkali metal carbonates in concrete compositions tends to improve fluidity retention and initial strength development. Examples of alkali metal carbonates include sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate, and combinations of these are also possible.

[0037] The mixing ratio of alkali metal carbonate is preferably 1 to 6 parts by mass, and more preferably 2 to 5 parts by mass, in terms of solid content, per 100 parts by mass of cement in the concrete composition. Having the alkali metal carbonate content within this range makes it easier to achieve good fluidity retention and initial strength development.

[0038] Concrete compositions may also contain defoaming agents, provided that they do not adversely affect performance. The purpose of defoaming agents is to suppress the amount of air incorporated during mixing. The type of defoaming agent is not particularly limited, as long as it does not significantly adversely affect the strength characteristics of the hardened concrete; both liquid and powder forms can be used. Examples include polyether-based defoaming agents, polyhydric alcohol-based defoaming agents such as esterified polyhydric alcohols and alkyl ethers, alkyl phosphate-based defoaming agents, and silicone-based defoaming agents.

[0039] The mixing ratio of the defoaming agent is preferably 0.002 to 0.5 parts by mass, more preferably 0.005 to 0.45 parts by mass, and even more preferably 0.01 to 0.4 parts by mass, per 100 parts by mass of cement in the concrete composition. When the mixing ratio of the defoaming agent is above the lower limit, the defoaming effect can be sufficiently exhibited, and when the mixing ratio of the defoaming agent is below the upper limit, it is easier to maintain good fluidity.

[0040] Furthermore, the concrete composition may use one or more of the following, within limits that do not adversely affect its performance: gas foaming substances, water-reducing agents, air-entraining agents, rust inhibitors, water-repellent agents, antibacterial agents, colorants, antifreeze agents, admixtures such as limestone fine powder, blast furnace slow-cooling slag fine powder, sewage sludge incineration ash and its molten slag, municipal solid waste incineration ash and its molten slag, and pulp sludge incineration ash, as well as thickeners and shrinkage reducing agents, polymers, clay minerals such as bentonite and sepiolite, and anion exchangers such as hydrotalcite, within limits that do not substantially hinder the objectives of the present invention.

[0041] For concrete compositions, having appropriate slump and slump flow values ​​before placement, depending on the product being manufactured, facilitates placement and compaction, improves work efficiency, and suppresses material segregation. The change in slump of the concrete composition one hour after mixing is preferably less than 10%, more preferably less than 7.5%, and even more preferably less than 5%. When the change in slump of the concrete composition is within the above range, even if placement is carried out one hour after mixing the cement composition, placement and compaction are easier, improving work efficiency. Furthermore, the change in slump flow after 1 hour of mixing the concrete composition (slump flow change) is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. In this invention, slump can be measured in accordance with the method specified in JIS A 1101:2020 "Slump Test Method for Concrete", and slump flow can be measured in accordance with the method specified in JIS A 1150:2020 "Slump Flow Test Method for Concrete". Furthermore, the slump change can be calculated by subtracting the value obtained by (slump after 1 hour of mixing) / (slump immediately after mixing) × 100 (%) from 100%, and the slump flow change can be calculated by subtracting the value obtained by (slump flow after 1 hour of mixing) / (slump flow immediately after mixing) × 100 (%) from 100%.

[0042] The concrete composition may be prepared by mixing the materials at the time of construction, or some or all of the materials may be mixed in advance. Any existing mixing equipment can be used, such as a tilting drum mixer, omni mixer, Henschel mixer, V-type mixer, Proscher mixer, and Nauta mixer.

[0043] [Cured body] The hardened body according to this embodiment is obtained by hardening the concrete composition of the present invention. The hardened body is usually obtained when the concrete composition is mixed, causing a hydration reaction in the cement. It can be obtained by hardening the concrete composition after mixing and letting it stand, but it can be obtained more efficiently by filling (casting) it into a formwork and curing it, or by pouring, spraying, or coating it directly onto the construction site.

[0044] The compressive strength of the hardened material depends on the type of cement used, but it is 8.5 N / mm² 16 hours after placement. 2 Preferably, it is 10.0 N / mm² or higher. 2 It is more preferable that the value be greater than or equal to 11.0 N / mm². 2 It is even more preferable that the above conditions are met. In this 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] [Method for manufacturing a hardened body] The method for manufacturing a hardened body according to this embodiment is to cure the concrete composition of the present invention under conditions of a temperature of 40°C or lower. A hardened body can be obtained by pouring the concrete composition into a formwork and curing it under the above conditions.

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

[0047] In the method for producing the hardened body of the present invention, it is preferable to further compact the concrete composition after placement. While known methods can be used for compaction, it is preferable to use a vibrator from the viewpoint of workability. Since the concrete composition of the present invention maintains good fluidity immediately before placement, compaction can be easily performed, the concrete composition can be uniformly distributed within the formwork, and air bubbles mixed in during placement can be removed.

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

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

[0050] <Experimental Example 1> Using the materials listed below, a hardening accelerator for hydraulic materials was prepared containing 60% by mass of calcium formate, 35% by mass of calcium sulfate, and 5% by mass of sodium sulfate. The concrete compositions shown in Table 1 were then prepared. The slump of the obtained concrete compositions was measured, and the slump change was calculated. The start time was also measured. All of these results are shown in Table 1. Furthermore, the prepared cement composition was filled into a mold measuring φ10 × 20 cm, and then cured for 24 hours at a temperature of 20°C and a humidity of 70% RH to obtain a hardened body. The compressive strength of the obtained hardened body was measured. The results are shown in Table 1.

[0051] (Materials used) Cement: Ordinary Portland cement (commercially available), Blaine specific surface area 3,200 cm² 2 / g, specific gravity 3.15g / cm3 . Water: Tap water. Fine aggregate: River sand from the Himekawa River system in Niigata Prefecture. Coarse aggregate: River gravel from the Himekawa River system in Niigata Prefecture. Blast furnace slag fine powder: Commercially available product. Fly ash: A commercially available product. Metakaolin: A commercially available product. Calcium sulfoaluminate: Reagent grade calcium carbonate, calcium sulfate dihydrate, and aluminum hydroxide are mixed in a molar ratio of CaO:CaSO4:Al2O3 of 4:3:1, calcined at 1,400°C for 2 hours, and left to stand at room temperature until the Blaine specific surface area reaches 3,500 cm². 2 Prototype product ground down to / g. Calcium formate: Reagent. Calcium sulfate (inorganic calcium compound): Reagent. Sodium sulfate (inorganic sulfate): anhydrous, reagent.

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

[0053] First set time: In accordance with the method specified in JIS A 1147:2019 "Test method for concrete setting time", the penetration resistance value is 3.5 N / mm 2 The time at which this occurred was designated as the first departure time.

[0054] Compressive strength: The compressive strength was measured immediately after demolding in accordance with the method specified in JIS A 1108:2018 "Test method for compressive strength of concrete".

[0055] [Table 1]

[0056] <Experimental Example 2> Except for changing the composition of the hardening accelerator for hydraulic materials as shown in Table 2, the concrete composition was prepared in the same manner as in Experimental Example 1, No. 1-2, and the slump change, initial curing time, and compressive strength were measured. The results are also shown in Table 2.

[0057] [Table 2]

[0058] <Experimental Example 3> Except for using calcium hydroxide, calcium carbonate, and calcium oxide in proportions shown in Table 2 as inorganic calcium compounds in the hardening accelerator for hydraulic materials, concrete compositions were prepared in the same manner as in Experimental Example 1, No. 1-2, and the slump change, initial ignition time, and compressive strength were measured. The results are shown in Table 3.

[0059] (Inorganic calcium compounds) Calcium hydroxide: Reagent. Calcium carbonate: Reagent. Calcium oxide: Reagent.

[0060] [Table 3]

[0061] <Experimental Example 4> Except for using aluminum sulfate, potassium alum, and sodium thiosulfate in proportions shown in Table 4 as inorganic sulfates in the hardening accelerator for hydraulic materials, concrete compositions were prepared in the same manner as in Experimental Example 1, No. 1-2, and the slump change, initial ignition time, and compressive strength were measured. The results are shown in Table 4.

[0062] (Inorganic sulfates) Aluminum sulfate: Reagent. Potassium alum: Reagent. Sodium thiosulfate: Reagent.

[0063] [Table 4] [Industrial applicability]

[0064] The concrete composition of the present invention has good fluidity retention, setting properties, and initial strength development properties, making it widely applicable to civil engineering and construction fields, such as hardened concrete used in precast construction methods.

Claims

1. A concrete composition containing a binder, a hardening accelerator for hydraulic materials, and water, The binder content is 300 kg / m³. ３ The above conditions apply, with a water binder ratio of 55% or less, and an amount of the water-hardening material hardening accelerator added of 1 to 50 kg / m³. ３ And, A concrete composition wherein 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.

2. The concrete composition according to claim 1, wherein the inorganic calcium compound is one or more selected from the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide.

3. The concrete composition according to claim 1 or 2, wherein the inorganic sulfate is one or more selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and pyrobisulfite.

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

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

6. A method for producing a hardened body, comprising curing the concrete composition according to claim 1 or 2 at a temperature of 40°C or lower.

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