Hardening accelerators, cementitious components, and hardeners for hydraulic materials

Abstract

This invention relates to a hardening accelerator for hydraulic materials, comprising: 20.0-80.0% by mass of calcium formate, 15.0-70.0% by mass of inorganic calcium compound, and 0.5-30.0% by mass of inorganic sulfate excluding calcium sulfate.

Description

Hardening accelerator for hydraulic materials, cement composition, and hardened body The present invention relates to a hardening accelerator for hydraulic materials, a cement composition containing the same, and a hardened body. Hydraulic materials such as cement used in the civil engineering and construction fields generally harden by being mixed with water and left standing for a predetermined time. Although the hardening speed of hydraulic materials may also be affected by the ratio of the material to water, the surrounding environmental temperature, and the aging method, by using a mixing and kneading material that promotes hardening, that is, a hardening accelerator, the time until the hydraulic material hardens can be shortened. Shortening the time until the hydraulic material hardens is closely related to improving the productivity at the work site. For example, in the case of a hardened body of concrete used in a precast method such as a reinforced concrete building, generally, after pouring the cement composition into a mold frame and leaving it standing for a predetermined time, it is further aged by steam aging or the like to obtain a hardened body. However, by using a hardening accelerator, the time to reach the initial strength at which demolding is possible can be shortened, so the hardened body can be produced efficiently. Also, usually after pouring the cement composition, in order to make the cement composition uniformly distributed in the mold frame, a vibrator or the like is used to perform "compaction". However, if the fluidity of the cement composition immediately after pouring decreases, the labor and time required for performing compaction will be consumed, and the productivity will decrease. 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 mixing and kneading material 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 formates, acetates, and lactates. [Prior art documents] [Patent documents] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-19618 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-235399 [Problems to be solved by the invention] However, in the case of a hydraulic material using a hardening accelerator as described above, the fluidity is immediately lost after being kneaded with water, and labor and time are required for compaction after pouring, so there is a concern about a decrease in productivity. In summary, an object of the present invention is to provide a hardening accelerator for hydraulic materials that can exhibit good fluidity retention, setting property, and initial strength exhibition property of hydraulic materials. [Means for solving the problems] As a result of intensive studies by the inventors of the present invention to solve the above problems, it has been found that the above problems can be solved and the present invention can be completed by using a hardening accelerator for hydraulic materials containing calcium formate, an inorganic calcium compound, and an inorganic sulfate excluding calcium sulfate in a predetermined ratio. That is, the present invention is as described below. [1]A hardening accelerator for hydraulic materials, comprising: 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 hardening accelerator for hydraulic materials according to the above [1], wherein the inorganic calcium compound is at least one selected from the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide. [3]The hardening accelerator for hydraulic materials according to the above [1] or [2], wherein the inorganic sulfate is at least one selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and metabisulfite. [4]The hardening accelerator for hydraulic materials according to any one of the above [1] to [3] further contains 4.5 to 65.0% by mass of calcium sulfoaluminate. [5]A cement composition, comprising: the hardening accelerator for hydraulic materials according to any one of the above [1] to [4], and cement. [6]The cement composition according to the above [5], wherein the content of the hardening accelerator for hydraulic materials is 0.5 to 10% by mass. [7]A hardened body obtained by hardening the cement composition according to the above [5] or [6]. [8]A method for manufacturing a hardened body, which hardens a cement composition containing the hardening accelerator for hydraulic materials according to any one of the above [1] to [4], cement, and water by steam curing at a maximum temperature of 40 to 80°C for 2 to 8 hours. According to the present invention, a hardening accelerator for hydraulic materials capable of maintaining good fluidity retention, setting property, and initial strength development property of hydraulic materials can be provided. Hereinafter, an embodiment of the present invention (this embodiment) will be described in detail, but the present invention is not limited to this embodiment. In the present invention, "hydraulic material" refers to a material that hardens by kneading with water, and "hardened body" refers to a hardened product such as cement paste, mortar, and concrete. In addition, in this specification, "%" and "parts" are based on mass unless otherwise specified. [Hardening accelerator for hydraulic materials] The hardening accelerator for hydraulic materials of this embodiment 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. This hardening accelerator for hydraulic materials not only promotes the hardening of the hydraulic material when the hydraulic material and water are kneaded and hardened, but also includes the case where the hardening accelerator for hydraulic materials itself is hardened simultaneously while promoting the hardening. (Calcium formate) The hardening accelerator for hydraulic materials contains 20.0 to 80.0% by mass of calcium formate, preferably contains 30.0 to 70.0% by mass, and more preferably contains 40.0 to 65.0% by mass. If the content ratio of calcium formate is less than 20.0% by mass, there is a concern that the fluidity retention, setting property, and initial strength exhibition property of the hydraulic material may not be good. If it exceeds 80.0% by mass, there is a concern that the fluidity retention, setting property, and initial strength exhibition property may not be good. (Inorganic calcium compound) The hardening accelerator for hydraulic materials contains 15.0 to 70.0% by mass of inorganic calcium compound, preferably contains 18.0 to 60.0% by mass, and more preferably contains 20.0 to 40.0% by mass. If the content ratio of the inorganic calcium compound is less than 15.0% by mass, there is a concern that the fluidity retention, setting property, and initial strength exhibition property of the hydraulic material may not be good. If it exceeds 70.0% by mass, there is a concern that the fluidity retention, setting property, and initial strength exhibition property of the hydraulic material may not be good. 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 using two or more inorganic calcium compounds, 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 initial strength exhibition property, it is preferable to use calcium sulfate, calcium hydroxide, and / or calcium oxide, and calcium sulfate is more preferable. When using calcium sulfate, anhydrous calcium sulfate is more preferable. (Inorganic sulfate) The hardening accelerator for hydraulic materials contains 0.5 to 30.0% by mass of inorganic sulfate excluding calcium sulfate, preferably contains 1.0 to 25.0% by mass, and more preferably contains 3.0 to 15.0% by mass. If the content ratio of the inorganic sulfate excluding calcium sulfate is outside the range of 0.5 to 30.0% by mass, there is a concern that the fluidity retention, setting property, and initial strength exhibition property of the hydraulic material may not be good. In this embodiment, the inorganic sulfate is preferably at least one selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and metabisulfite. When using two or more inorganic sulfates, the total of the respective content ratios is defined as the content ratio of the inorganic sulfate. As for the inorganic substance forming the salt, alkali metals and alkaline earth metals are preferable. In this embodiment, from the viewpoint of initial strength exhibition, sulfate and / or thiosulfate is preferably used, more preferably sodium sulfate, aluminum sulfate, sodium thiosulfate, and potassium alum, still more preferably sodium sulfate and aluminum sulfate from the viewpoint of initial strength exhibition, and still more preferably sodium sulfate from the viewpoint of good fluidity retention. When using sodium sulfate, anhydrous sodium sulfate is more preferable. The hardening accelerator for hydraulic materials of this embodiment preferably further contains 4.5 to 65.0% by mass of calcium sulfoaluminate, more preferably 15.0 to 60.0% by mass, and still more preferably 30.0 to 50.0% by mass. If the content ratio of calcium sulfoaluminate falls within the above range, the fluidity retention and initial strength exhibition of the hydraulic material can be made better. Calcium sulfoaluminate is the general term for hydraulic substances and hydrates represented by the chemical formula xCaO･yAl 2 O 3 ･zCaSO 4 ･mH 2 O (x, y, and z are non-zero positive real numbers, and m is 0 or a positive real number), and examples thereof include lazurite (3CaO･3Al 2 O 3 ･CaSO 4 ), and in addition, examples include AFt phases represented by ettringite (3CaO･Al 2 O 3 ･3CaSO 4 ･32H 2 O), AFm phases represented by monosulfate (3CaO･Al 2 O 3 ･CaSO 4 ･12H 2 O), and those in which the AFt phase and the AFm phase coexist, etc. Calcium sulfoaluminate can also be amorphous. Also, Al 2 O 3 A part of it can also be replaced with a trace amount of Fe 2 O 3 or SiO 2 etc., and a part of CaSO 4 can also be replaced with Ca(OH) 2 or CaCO 3 etc. In addition, in the present invention, in the above chemical formula xCaO･yAl 2 O 3 ･zCaSO 4 ･mH 2 O, since there is a concern that the fluidity of the hydraulic material cannot be maintained and the strength during hardening is reduced due to phase transition, z cannot be 0. Calcium sulfoaluminate can use calcium oxide raw materials such as lime, sulfate raw materials such as gypsum, and alumina raw materials such as bauxite (aluminum hydroxide) as raw materials, and for example, use a molar ratio of CaO:CaSO 4 :Al 2 O 3 of 3:3:1 and other predetermined ratios to blend the raw materials, use a kiln, etc. to calcine at about 1,500 °C, and pulverize to manufacture. Also, silica, etc. can be added to the once-calcined product, followed by heat treatment and pulverization. The Blaine specific surface area value of calcium sulfoaluminate (hereinafter also simply referred to as "Blaine's value") should be 1,000 to 6,000 cm 2 / g, more preferably 2,000 to 4,000 cm 2 / g, and even more preferably 2,200 to 3,800 cm 2 / g. In addition, in the present invention, the Blaine specific surface area value is measured according to the specific surface area test described in JIS R 5201:2015 "Physical Test Methods for Cement". [Cement Composition] The cement composition of this embodiment contains a hardening accelerator for hydraulic materials and cement. The cement is not particularly limited, and examples include various Portland cements such as ordinary, early strength, ultra-early strength, low heat, and medium heat, various blended cements obtained by mixing blast furnace slag, fly ash, silica fume, etc. into these Portland cements, environmentally friendly cements (eco-cements) manufactured using municipal waste incineration ash, sewage sludge incineration ash as raw materials, commercially available fine cement, white cement, etc. Also, various cements can be used in a finely powdered form. Moreover, those obtained by adjusting the amount of components (such as gypsum, etc.) usually used in ordinary cement can also be used. In addition, those obtained by combining two or more of them can also be used. From the viewpoint of improving the initial strength exhibition property, it is advisable to select ordinary Portland cement or early strength Portland cement. However, even if blast furnace cement or fly ash cement with low initial strength exhibition property is used, early demolding is still possible. Regarding the cement used in the present invention, from the viewpoints of manufacturing cost and strength exhibition property, the Blaine specific surface area value of the cement is preferably 2,500 cm 2 / g to 7,000 cm 2 / g, more preferably 2,750 cm 2 / g to 6,000 cm 2 / g, still more preferably 3,000 cm 2 / g to 4,500 cm 2 / g. The content of the hardening accelerator for hydraulic materials in the cement composition is preferably 0.5 to 10% by mass, more preferably 1.0 to 9.0% by mass, and still more preferably 2.5 to 8.0% by mass. If the content of the hardening accelerator for hydraulic materials in the cement composition falls within the above range, the fluidity retention, setting property, and initial strength exhibition property of the hydraulic materials can be made better. The fluidity value of the cement composition before pouring should be 160 to 230, more preferably 170 to 220, and even more preferably 190 to 200. If the fluidity value of the cement composition falls within the above range, pouring and compaction are easily carried out, and the workability is improved. Also, the change rate of the fluidity value (fluidity change rate) after kneading the cement composition for 1 hour should preferably be less than 20%, more preferably less than 15%, and even more preferably less than 10%. If the fluidity change rate of the cement composition falls within the above range, even if pouring is carried out 1 hour after kneading the cement composition, pouring and compaction can still be easily carried out, and the workability is improved. In addition, in the present invention, the fluidity value can be measured according to the method specified in JIS R 5201:2015 "Physical Test Methods for Cement". The fluidity change rate can be obtained by subtracting the value calculated by (fluidity value after kneading for 1 hour) / (fluidity value just after kneading)×100(%) from 100%. The cement composition preferably contains aggregates. As the aggregates used, the same fine aggregates and coarse aggregates as those used in ordinary cement mortar and concrete can be used. That is, river sand, river sand gravel, mountain sand, mountain sand gravel, crushed stone, crushed sand, limestone aggregate, lime sand, silica sand, colored sand, artificial aggregate, blast furnace slag aggregate, sea sand, sea sand gravel, artificial lightweight aggregate, and heavy aggregate, etc. can be used, and they can also be combined. The content ratio of the aggregate is preferably 40 parts by mass or more and 250 parts by mass or less, more preferably 50 parts by mass or more and 230 parts by mass or less, and even more preferably 60 parts by mass or more and 200 parts by mass or less, based on 100 parts by mass of the cement in the cement composition. By the content ratio of the aggregate falling within the above range, the fluidity retention and initial strength exhibition of the hydraulic material can be made better. The cement composition may contain alkali metal carbonates. By the cement composition containing alkali metal carbonates, it is easy to make the fluidity retention and initial strength exhibition good. Examples of the alkali metal carbonates include: sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, lithium bicarbonate, etc., and they can also be combined. The content ratio of the alkali metal carbonate is preferably 1 to 6 parts by mass, more preferably 2 to 5 parts by mass, based on 100 parts by mass of the cement in the cement composition, in terms of the solid component amount. By the content ratio of the alkali metal carbonate falling within the above range, it is easy to make the fluidity retention and initial strength exhibition good. The cement composition may contain silica fine powder. By the cement composition containing silica fine powder, it is easy to make the fluidity retention and initial strength exhibition good. Examples of the silica fine powder include: latent hydraulic substances such as blast furnace granulated slag fine powder, fly ash, silica fume and other pozzolanic substances, among which silica fume is preferred. The type of silica fume is not limited. From the viewpoint of fluidity, use containing 10% or less of ZrO 2Silica fume and acidic silica fume as impurities are more preferable. Acidic silica fume refers to the one whose supernatant liquid shows an acidity with a pH of 5.0 or less when 1 g of silica fume is put into 100 cc of pure water and stirred. The fineness of the silica-based fine powder is not particularly limited. Generally, blast furnace granulated slag fine powder and fly ash, in terms of Blaine’s value, fall within the range of 3,000 cm 2 / g or more and 9,000 cm 2 / g or less, and silica fume, in terms of BET specific surface area, falls within the range of 20,000 cm 2 / g or more and 300,000 cm 2 / g or less. The content ratio of the silica-based fine powder is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and still more preferably 3 to 12 parts by mass relative to 100 parts by mass of the cement in the cement composition. By the content ratio of the silica-based fine powder falling above the above lower limit value, it is easy to exhibit good fluidity retention and initial strength development. In addition, by the content ratio of the silica-based fine powder falling below the above upper limit value, it is easy to make the fluidity retention better. In the cement composition, within the range that does not adversely affect its performance, an antifoaming agent may also be contained. The antifoaming agent is used to suppress the amount of air involved during kneading. As long as the type of the antifoaming agent does not have a significant adverse effect on the strength characteristics of the hardened mortar, there is no particular limitation, and both liquid and powder forms can be used. For example, polyether-based antifoaming agents, esterified products of polyhydric alcohols, polyhydric alcohol-based antifoaming agents such as alkyl ethers, alkyl phosphate-based antifoaming agents, polysiloxane-based antifoaming agents, etc. can be cited. The content ratio of the antifoaming agent is preferably 0.002 to 0.5 parts by mass, more preferably 0.005 to 0.45 parts by mass, and still more preferably 0.01 to 0.4 parts by mass relative to 100 parts by mass of the cement in the cement composition. By the content ratio of the antifoaming agent falling above the above lower limit value, the antifoaming effect can be fully exhibited, and by the content ratio of the antifoaming agent falling below the above upper limit value, it is easy to make the fluidity retention good. Furthermore, within the range that does not adversely affect the performance, the cement composition can also contain one or more of the following materials: gas foaming agents, water reducing agents, AE agents, rust inhibitors, water repellents, antibacterial agents, coloring agents, antifreezing agents, fine limestone powder, fine powder of slowly cooled blast furnace slag, incineration ash of sewage sludge or its molten slag, incineration ash of municipal waste or its molten slag, and incineration ash of pulp sludge, etc., as well as thickening agents, shrinkage reducing agents, polymers, clay minerals such as bentonite and sepiolite, and anion exchangers such as hydrotalcite, etc., and can be used within the range that does not substantially impede the object of the present invention. [Hardened body] The hardened body of this embodiment is formed by hardening the cement composition. Usually, the hardened body is obtained by kneading the cement composition with water, causing the cement, which is a hydraulic material, to undergo a hydration reaction and harden. The amount of kneaded water is not particularly limited, and relative to 100 parts by mass of the cement composition, it is preferably 10 to 70 parts by mass, more preferably 14 to 65 parts by mass, and even more preferably 16 to 60 parts by mass. If the amount of kneaded water falls within the above range, it is easy to exhibit good initial strength of the hydraulic material. The hardened body is obtained by kneading the cement composition with water and then allowing it to stand and harden. After kneading, it can also be more efficiently obtained by filling (pouring) it into a mold frame and aging, or directly flowing it into the construction location, or spraying or coating. The compressive strength of the hardened body depends on the type of cement used. It is preferably 10.5 to 15.0 N / mm 2 6 hours after pouring, more preferably 11.0 to 14.0 N / mm 2 even more preferably 12.0 to 13.0 N / mm 2 Calculated based on the age of 7 days, it is preferably 40.0 to 50.0 N / mm 2 more preferably 41.0 to 48.0 N / mm 2 even more preferably 42.0 to 46.0 N / mm 2 even more preferably. In addition, in the present invention, the compressive strength can be measured according to the method specified in JIS R 5201:2015 "Physical Test Methods for Cement". [Method for manufacturing hardened body] The method for manufacturing the hardened body of the present embodiment is a method of hardening a cement composition containing a hardening accelerator for hydraulic materials, cement, and water by steam aging at a maximum temperature of 40 to 80°C for 2 to 8 hours. The method for manufacturing the hardened body preferably includes, in order: a kneading step of kneading the hardening accelerator for hydraulic materials, cement, and water, a pouring step of filling the kneaded cement composition into a mold frame, and an aging step of aging the cement composition filled in the mold frame. The kneading method in the kneading step is not particularly limited, and the respective materials may be mixed during construction, or a part or all of them may be mixed in advance. As the mixing device, all existing devices can be used. For example, an inclined mixer, an omnidirectional mixer, a Henschel mixer, a V-type mixer, a Proshare mixer, a Nauta mixer, etc. can be used. The pouring method in the pouring step can be implemented using a known method. The temperature of the cement composition during pouring is preferably 0 to 50°C, more preferably 10 to 40°C. If the temperature of the cement composition during pouring falls within the above range, it is easy to demold the hardened body at an early stage. The method for manufacturing the hardened body preferably further includes a compaction step after the pouring step. As the compaction method, a known method can be used. From the viewpoint of workability, a vibrator is preferably used. Since the cement composition containing the hardening accelerator for hydraulic materials of the present invention maintains good fluidity until pouring, compaction can be easily implemented, the cement composition can be evenly distributed in the mold frame, and air bubbles mixed in during pouring etc. can be removed. Regarding the aging method used in the aging step, from the viewpoint of improving productivity, steam aging using an aging chamber, heating sheets, etc. is preferably used. Steam aging generally heats the environment around the object and ages while maintaining an appropriate humidity and a certain temperature. The conditions for steam aging are preferably a maximum temperature of 40 to 80°C and an aging time of 2 to 8 hours, more preferably a maximum temperature of 40 to 75°C and an aging time of 2.5 to 7.5 hours, and even more preferably a maximum temperature of 45 to 60°C and an aging time of 3 to 7 hours. If the maximum temperature of the environment around the cement composition during steam aging is set within the above range and the aging time is set within the above range to perform steam aging, it is easy to demold the hardened body at an early stage. The relative humidity around the cement composition during steam aging is preferably 50%RH or more, more preferably 75%RH or more, and even more preferably 90%RH or more. The upper limit is not limited and can also be 100%RH. If the relative humidity around the cement composition during steam aging falls within the above range, it is easy to demold the hardened body at an early stage. The curing step preferably includes a pre-curing step. The conditions for pre-curing should maintain a constant temperature at 10 - 50°C for about 1 - 3 hours. By including the pre-curing step in the curing step, the temperature inside the cast cement composition can be made uniform, and it is easy to prevent temperature crack damage caused by the temperature difference between the inside and the outside. The curing step preferably includes a heating step. Known methods can be used for the heating method. It is preferably heated at a temperature increase rate of 10 - 30°C / hour, more preferably at a temperature increase rate of 12 - 28°C / hour, and even more preferably at a temperature increase rate of 15 - 25°C / hour. If the temperature increase rate in the heating step falls within the above range, temperature crack damage caused by a sharp temperature increase of the cement composition can be prevented, and hardening can be promoted more effectively. The curing step preferably includes a temperature holding step. Known methods can be used for the temperature holding method. It is preferably held at a constant temperature in the range of 40 - 80°C for 1 - 8 hours, more preferably held at a constant temperature in the range of 40 - 75°C for 1 - 6 hours, and even more preferably held at a constant temperature in the range of 45 - 65°C for 2.5 - 5 hours. In the temperature holding step, by maintaining a constant temperature within the above numerical range, the cast cement composition can be hardened uniformly, and it is easy to demold it early. The method for manufacturing a hardened body preferably includes a natural cooling step after the curing step. The natural cooling step is to naturally cool the hardened body obtained in the curing step in a normal temperature environment. The cooling time is not particularly limited as long as it can cool to a temperature at which the hardened body can be easily demolded, and about 0.5 - 2 hours is sufficient. By including a natural cooling step after the curing step, temperature crack damage of the hardened body can be prevented. [Examples] Hereinafter, the present invention will be further described based on experimental examples, but the present invention is not limited thereto. <Example 1> Using the following materials, a mortar with a water / cement ratio of 45% and a ratio of cement to aggregate of 1:2.5 (mass ratio) was prepared. A water reducing agent was added to the obtained mortar in the proportion described in Table 1, and the amount of the hardening accelerator for the hydraulic material with the composition shown in Table 1 was kneaded so as to be in the proportion shown in Table 1 to obtain a cement composition. The flow value of the obtained cement composition was measured, and the flow change rate was calculated. Also, the initial setting time was measured. All are shown in Table 1 together. Further, the obtained cement composition was filled into a mold frame with dimensions of 4×4×16 cm, and then steam curing was carried out to obtain a hardened body. The steam curing conditions were set as pre-curing at 20°C for 1 hour, heating at a rate of 20°C / hour for 1.5 hours, holding at a temperature of 50°C for 3 hours, and natural cooling for 0.5 hour. The compressive strength of the obtained hardened body was measured. The results are shown in Table 1 together. (Materials used) Cement: Ordinary Portland cement (commercial product), Blaine specific surface area 3,200 cm 2 / g, specific gravity 3.15 g / cm 3 Water: Tap water Aggregate: Kawagawa sand produced from the Himekawa River system in Niigata Prefecture Superplasticizer: Polycarboxylic acid-based high-performance superplasticizer (commercially available product) Calcium formate: Reagent Calcium sulfate (inorganic calcium compound): Reagent Sodium sulfate (inorganic sulfate): Anhydrous, reagent (Measurement items) Flow change rate: According to the method specified in JIS R 5201:2015 "Physical test methods for cement", measure the flow values of the cement composition immediately after mixing and 1 hour after mixing, respectively. The flow values immediately after mixing are all approximately 200. Using the measured flow values, calculate the flow change rate with (flow change rate) = 1 - (flow value 1 hour after mixing) / (immediately after mixing) × 100. Initial setting time: According to the method specified in JIS A 1147:2019 "Test method for setting time of concrete", the time when the penetration resistance reaches 3.5 N / mm 2 is defined as the initial setting time. Compressive strength: According to the method specified in JIS R 5201:2015 "Physical test methods for cement", measure the compressive strengths of the hardened bodies at 6 hours (just after demolding) and 7 days after steam curing, respectively. [Table 1] It was confirmed from the results shown in Table 1 that by using a hardening accelerator for hydraulic materials containing calcium formate, inorganic calcium compounds, and inorganic sulfates excluding calcium sulfate in a predetermined ratio, the fluidity retention, setting property, and initial strength exhibition property of the cement composition can be made good. <Example 2> In addition to calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide were used as inorganic calcium compounds contained in the hardening accelerator for hydraulic materials in the ratios shown in Table 2. Otherwise, the same procedures as in Example 1 were carried out to prepare mortar, cement composition, and hardened body, and the flow change rate, initial setting time, and compressive strength were measured. The results are shown in Table 2 together. (Inorganic calcium compounds) Calcium hydroxide: Reagent Calcium carbonate: Reagent Calcium oxide: Reagent [Table 2] It was confirmed from the results shown in Table 2 that by using calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide as inorganic calcium compounds contained in the hardening accelerator for hydraulic materials, the fluidity retention, setting property, and initial strength exhibition property of the cement composition can be made good. Among them, it was confirmed that when calcium sulfate is contained, the initial strength exhibition property of the cement composition is particularly good. <Experimental Example 3> In addition to sodium sulfate, aluminum sulfate, potassium alum, and sodium thiosulfate were used as the inorganic sulfates contained in the hardening accelerator for hydraulic materials in the proportions shown in Table 3. Other than that, the procedure was the same as in Experimental Example 1 to prepare mortar, cement composition, and hardened body, and the flow change rate, initial setting time, and compressive strength were measured. The results are shown together in Table 3. (Inorganic sulfate) Aluminum sulfate: reagent Potassium alum: reagent Sodium thiosulfate: reagent [Table 3] It was confirmed from the results shown in Table 3 that by using sodium sulfate, aluminum sulfate, potassium alum, and sodium thiosulfate as the inorganic sulfates contained in the hardening accelerator for hydraulic materials, the fluidity retention, setting property, and initial strength exhibition property of the cement composition were good. Among them, when sodium sulfate and aluminum sulfate were contained, the initial strength exhibition property was better, and especially when sodium sulfate was contained, the fluidity retention was also better. <Experimental Example 4> Calcium sulfoaluminate was further added to the hardening accelerator for hydraulic materials in the proportions shown in Table 4. Other than that, the procedure was the same as in Experimental Example 1 to prepare mortar, cement composition, and hardened body, and the flow change rate, initial setting time, and compressive strength were measured. The results are shown together in Table 4. (Calcium sulfoaluminate) Reagent-grade calcium carbonate, calcium sulfate dihydrate, and aluminum hydroxide were used and mixed in such a way that the molar ratio of CaO:CaSO 4 :Al 2 O 3 became 4:3:1, calcined at 1,400 °C for 2 hours, left to cool to room temperature, and pulverized to a Blaine specific surface area of 3,500 cm 2 / g of the test product. [Table 4] It was confirmed from the results shown in Table 4 that when the hardening accelerator for hydraulic materials further contained calcium sulfoaluminate, the initial strength exhibition property was better. <Experimental Example 5> The mixing amount of the hardening accelerator for hydraulic materials was set at the proportions shown in Table 5. Other than that, the procedure was the same as in Experimental Example 1 to prepare mortar, cement composition, and hardened body, and the flow change rate, initial setting time, and compressive strength were measured. The results are shown together in Table 5. [Table 5] It was confirmed from the results shown in Table 5 that by setting the mixing amount of the hardening accelerator for hydraulic materials within a predetermined range, the fluidity retention, setting property, and initial strength exhibition property of the cement composition were good. <Experimental Example 6> Using blast furnace cement and fly ash cement as the cement in the cement composition, and otherwise proceeding in the same manner as in Experimental Example 1, mortar, cement composition, and hardened body were prepared, and the flow change rate, initial setting time, and compressive strength were measured. The results are collectively shown in Table 6. (Cement) Blast furnace type B cement: commercially available product, Blaine specific surface area 3,200 cm 2 / g, specific gravity 3.15 g / cm 3 Blast furnace type C cement: commercially available product, Blaine specific surface area 3,500 cm 2 / g, specific gravity 3.15 g / cm 3 Fly ash cement type B: commercially available product, Blaine specific surface area 3,200 cm 2 / g, specific gravity 3.15 g / cm 3 [Table 6] It was confirmed from the results shown in Table 6 that even when blast furnace cement and fly ash cement are used as the cement in the cement composition, good fluidity retention, setting property, and initial strength exhibition property of the cement composition can still be exhibited. From the above results, it was confirmed that the hardening accelerator for hydraulic materials of the present invention can make the fluidity retention, setting property, and initial strength exhibition property of the cement composition good by containing calcium formate, inorganic calcium compound, and inorganic sulfate in a predetermined ratio. [Industrial Applicability] The hardening accelerator for hydraulic materials of the present invention can make the fluidity retention, setting property, and initial strength exhibition property of the hydraulic material good by containing calcium formate, inorganic calcium compound, and inorganic sulfate excluding calcium sulfate in a predetermined ratio. Therefore, it can be widely applied to civil engineering and construction fields such as hardened concrete used in precast construction methods.

Claims

1. A curing accelerator for hydraulic materials, comprising: 20.0-80.0% by mass of calcium formate, 15.0-70.0% by mass of inorganic calcium compound, and 0.5-20.0% by mass of inorganic sulfate excluding calcium sulfate.

2. As in claim 1, the hydraulic material uses a hardening accelerator, wherein, The inorganic calcium compound is selected from one or more of the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide.

3. For hydraulic materials as requested in item 1 or 2, a hardening accelerator may be used, wherein, The inorganic sulfate is selected from one or more of the group consisting of sulfates, thiosulfates, sulfites, bisulfites, pyrosulfites, and pyrobisulfites.

4. The hardening accelerator for hydraulic materials as requested in item 1 or 2 further contains 4.5 to 65.0% by weight of calcium sulfoaluminate.

5. A cement composition comprising: a hardening accelerator for hydraulic materials as claimed in claim 1 or 2, and cement.

6. As in claim 5, the cement composition, wherein, The content of hardening accelerator in this hydraulic material is 0.5-10% by mass.

7. A hardened body formed by hardening the cementitious composition as claimed in claim 5.

8. A method for manufacturing a hardened body, comprising hardening a cementitious composition containing the hydraulic material hardening accelerator as claimed in claim 1 and cement by steam curing at a maximum temperature of 40-80°C for 2-8 hours.