JP7628149B2 - Hardening accelerators for hydraulic materials, cement compositions, and hardened products - Google Patents

Description

The present invention relates to a hardening accelerator for hydraulic materials, and a cement composition and hardened body containing the material.

Hydraulic materials such as cement used in civil engineering and construction fields usually harden by mixing with water and leaving to stand for a certain period of time. The hardening speed of hydraulic materials can be affected by the ratio of the material to water, the surrounding environmental 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.

Reducing the time it takes for hydraulic materials to harden leads to improved productivity at work sites. For example, the hardened concrete used in precast construction methods used in reinforced concrete buildings and the like is generally obtained by pouring a cement composition into a formwork, leaving it to stand for a specified period of time, and then curing it further by steam curing or the like. However, by using a hardening accelerator, the time it takes for the concrete to reach an initial strength that allows it to be removed from the form can be reduced, allowing the hardened concrete to be produced more efficiently.

In addition, after pouring the cement composition, it is usually "compacted" using a vibrator or the like to distribute the cement composition evenly within the formwork. However, if the fluidity of the cement composition has decreased immediately after pouring, the compaction process requires time and effort, resulting in reduced productivity.

Regarding hardening accelerators, for example, Patent Document 1 discloses a hardening accelerator for hydraulic materials that contains predetermined amounts of inorganic sulfate, calcium sulfoaluminate, and inorganic hydroxide, while Patent Document 2 discloses a cement admixture that contains calcium sulfoaluminate having a Blaine specific surface area value of 4000 ^cm2 /g or more and one or more salts selected from the group consisting of formate, acetate, and lactate.

JP 2014-19618 A JP 2010-235399 A

However, hydraulic materials that use hardening accelerators such as those mentioned above lose their fluidity immediately after mixing with water, and compaction after pouring requires time and effort, which raises concerns about reduced productivity.

Based on the above, the present invention aims to provide a hardening accelerator for hydraulic materials that can improve the fluidity retention, setting properties, and early strength development of hydraulic materials.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that the problems could be solved by a hardening accelerator for hydraulic materials that contains calcium formate, an inorganic calcium compound, and an inorganic sulfate other than calcium sulfate in a specified ratio, and thus arrived at the present invention. That is, the present invention is as follows.

[1] A hardening accelerator for hydraulic materials, comprising 20.0 to 80.0 mass% calcium formate, 15.0 to 70.0 mass% inorganic calcium compound, and 0.5 to 30.0 mass% inorganic sulfate other than 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 pyrobisulfite.
[4] The hardening accelerator for hydraulic materials according to any one of the above [1] to [3], further comprising 4.5 to 65.0 mass% calcium sulfoaluminate.
[5] A cement composition comprising the hardening accelerator for hydraulic materials according to any one of [1] to [4] above and cement.
[6] The content of the hydraulic material hardening accelerator is 0.5 to 10 mass %. The cement composition according to [5].
[7] A hardened body obtained by hardening the cement composition according to [5] or [6] above.
[8] A method for producing a hardened body, comprising: hardening a cement composition containing the hardening accelerator for hydraulic materials according to any one of [1] to [4] above, cement, and water by steam curing at a maximum temperature of 40 to 80°C for 2 to 8 hours.

The present invention provides a hardening accelerator for hydraulic materials that can improve the fluidity retention, setting properties, and early strength development of hydraulic materials.

One embodiment of the present invention (present embodiment) will be described in detail below, but the present invention is not limited to this embodiment. In this invention, "hydraulic material" refers to a material that hardens when kneaded with water, and "hardened body" refers to hardened cement paste, mortar, concrete, etc. In this specification, "%" and "parts" are based on mass unless otherwise specified.

[Curing accelerator for hydraulic materials]
The hydraulic material hardening accelerator according to this embodiment contains 20.0 to 80.0 mass% calcium formate, 15.0 to 70.0 mass% inorganic calcium compound, and 0.5 to 30.0 mass% inorganic sulfates other than calcium sulfate. The hydraulic material hardening accelerator not only accelerates the hardening of the hydraulic material when the hydraulic material is kneaded with water and hardens, but also may harden itself while accelerating the hardening.

(Calcium Formate)
The hardening accelerator for hydraulic materials contains calcium formate at 20.0 to 80.0 mass%, preferably 30.0 to 70.0 mass%, and more preferably 40.0 to 65.0 mass%. If the calcium formate content is less than 20.0 mass%, there is a risk that the fluidity retention, setting property, and early strength development of the hydraulic material cannot be improved, and if it exceeds 80.0 mass%, there is a risk that the fluidity retention, setting property, and early strength development cannot be improved.

(Inorganic calcium compounds)
The hardening accelerator for hydraulic materials contains an inorganic calcium compound in an amount of 15.0 to 70.0% by mass, preferably 18.0 to 60.0% by mass, and more preferably 20.0 to 40.0% by mass. If the content of the inorganic calcium compound is less than 15.0% by mass, there is a risk that the fluidity retention, setting property, and early strength development of the hydraulic material may not be improved, and if it exceeds 70.0% by mass, there is a risk that the fluidity retention, setting property, and early strength development of the hydraulic material may not be improved.

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 content of the inorganic calcium compounds is the sum of the respective content ratios. In this embodiment, from the viewpoint of early strength development, 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 preferable that it is anhydrous.

(Inorganic sulfates)
The hardening accelerator for hydraulic materials contains 0.5 to 30.0 mass %, preferably 1.0 to 25.0 mass %, and more preferably 3.0 to 15.0 mass % of inorganic sulfates other than calcium sulfate. If the content of inorganic sulfates other than calcium sulfate is outside the range of 0.5 to 30.0 mass %, there is a risk that the fluidity retention, setting property, and early strength development of the hydraulic material cannot be improved.

In this embodiment, the inorganic sulfate is preferably one or more selected from the group consisting of sulfate, thiosulfate, sulfite, bisulfite, pyrosulfate, and pyrobisulfite. When two or more inorganic sulfates are used, the total of the respective content ratios is the content ratio of the inorganic sulfate. As inorganic substances that form salts, alkali metals and alkaline earth metals are preferred. In this embodiment, from the viewpoint of early strength development, it is preferable to use sulfate and/or thiosulfate, and sodium sulfate, aluminum sulfate, sodium thiosulfate, and potassium alum are more preferred, and sodium sulfate and aluminum sulfate are even more preferred from the viewpoint of early strength development, and among them, sodium sulfate is even more preferred from the viewpoint of improving fluidity retention. When sodium sulfate is used, it is more preferable that it is anhydrous.

The hardening accelerator for hydraulic materials according to the present embodiment further contains calcium sulfoaluminate in an amount of preferably 4.5 to 65.0 mass%, more preferably 15.0 to 60.0 mass%, and even more preferably 30.0 to 50.0 mass%. When the content of calcium sulfoaluminate is within the above range, the hydraulic material can have better fluidity retention and early strength development.
Calcium sulfoaluminate is a general term for hydraulic substances and hydrated salts represented by the chemical formula _{xCaO.yAl2O3.zCaSO4.mH2O} ( _x , y, and z are non- _zero positive real numbers, and _m is ₀ or a positive real number) _, and examples thereof include auyne ( _{3CaO.3Al2O3.CaSO4} ), AFt _phase represented by ettringite ( _{3CaO.Al2O3.3CaSO4.32H2O} ), _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 replaced with a small amount of _Fe2O3 or _{SiO2 , etc.} , and a part of _CaSO4 may be replaced _with Ca(OH) ₂ or _CaCO3 , _etc. In the present invention, z cannot be set to ₀ in the above chemical formula _{xCaO.yAl2O3.zCaSO4.mH2O} , since the hydraulic material would not be able to maintain its fluidity and the strength during hardening would be reduced due to phase transition.

Calcium sulfoaluminate can be produced by blending raw materials such as lime or other calcia raw materials, gypsum or other sulfate raw materials, and bauxite (aluminum hydroxide) or other alumina raw materials in a predetermined ratio, for example, a molar ratio of CaO: _CaSO4 : _Al2O3 of 3:3:1, firing the mixture at about 1,500° _C in a kiln or the like, and pulverizing it. Alternatively, the mixture may be heat-treated by adding silicon dioxide or the like to the fired mixture, and then pulverized.

The Blaine specific surface area value (hereinafter simply referred to as "Blaine value") of calcium sulfoaluminate is preferably 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 the present invention, the Blaine specific surface area value is measured in accordance with the specific surface area test described in JIS R 5201:2015 "Physical testing methods for cement".

[Cement composition]
The cement composition according to the present embodiment contains a hardening accelerator for hydraulic materials and cement.

The cement is not particularly limited, and examples thereof include various Portland cements such as ordinary, early strength, super early strength, low heat and medium heat, various mixed cements in which Portland cement is mixed with blast furnace slag, fly ash, silica fume, etc., environmentally friendly cements (eco-cement) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials, commercially available fine particle cements, white cements, etc., and various cements can be used in a fine powder form. In addition, cements adjusted by increasing or decreasing the amount of components (e.g., gypsum, etc.) normally used in cements can also be used. Furthermore, combinations of two or more of these can also be used. From the viewpoint of increasing the early strength development, it is preferable to select ordinary Portland cement or early strength Portland cement, but early demolding is also possible even if blast furnace cement or fly ash cement, which has low early strength development, is used.

From the viewpoints of production costs and strength development, the cement used in the present invention preferably has a Blaine specific surface area value of 2,500 cm ² /g to 7,000 cm ² /g, more preferably 2,750 cm ² /g to 6,000 cm ² /g, and even more preferably 3,000 cm ² /g to 4,500 cm ² /g.

The content of the hydraulic material hardening accelerator in the cement composition is preferably 0.5 to 10 mass%, more preferably 1.0 to 9.0 mass%, and even more preferably 2.5 to 8.0 mass%. When the content of the hydraulic material hardening accelerator in the cement composition is within the above range, the hydraulic material can have better fluidity retention, setting properties, and early strength development.

The flow value of the cement composition before pouring is preferably 160 to 230, more preferably 170 to 220, and even more preferably 190 to 200. When the flow value of the cement composition is within the above range, pouring and compaction are easily performed, and workability is improved. Furthermore, the rate of change in the flow value (flow change rate) one hour after kneading the cement composition is preferably less than 20%, more preferably less than 15%, and even more preferably less than 10%. When the flow change rate of the cement composition is within the above range, pouring and compaction are easily performed, and workability is improved, even if pouring is performed one hour after kneading the cement composition.
In the present invention, the flow value can be measured in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement". The flow rate can be calculated by subtracting the value calculated by (flow value after 1 hour of mixing)/(flow value immediately after mixing)×100(%) from 100%.

The cement composition preferably contains aggregate. The aggregate to be used may be the same fine aggregate or coarse aggregate as that used in ordinary cement mortar or concrete. 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, heavy aggregate, etc. may be used, and these may also be combined.

The aggregate content 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, relative to 100 parts by mass of cement in the cement composition. By having the aggregate content within the above range, the hydraulic material can have better fluidity retention and early strength development.

The cement composition may contain an alkali metal carbonate. When the cement composition contains an alkali metal carbonate, it is easier to improve fluidity retention and early strength development. Examples of alkali metal carbonates include sodium carbonate, potassium carbonate, lithium carbonate, sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate, and these may be used in combination.

The content of the 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 cement composition. By having the content of the alkali metal carbonate within the above range, it is easy to improve the fluidity retention and early strength development.

The cement composition may contain a siliceous fine powder. The cement composition containing the siliceous fine powder is likely to improve the fluidity retention and early strength development. Examples of the siliceous fine powder include latent hydraulic substances such as granulated blast furnace slag powder, fly ash, and pozzolanic substances such as silica fume, among which silica fume is preferred. The type of silica fume is not limited, but from the viewpoint of fluidity, it is more preferred to use silica fume containing 10% or less of _ZrO2 as an impurity or acidic silica fume. The acidic silica fume refers to a silica fume that exhibits an acidity of pH 5.0 or less when 1 g of silica fume is added to 100 cc of pure water and stirred.

The fineness of the siliceous powder is not particularly limited, but typically, the Blaine value of ground granulated blast furnace slag and fly ash is in the range of 3,000 ^cm2 /g to 9,000 ^cm2 /g, and the BET specific surface area of silica fume is in the range of 20,000 ^cm2 /g to 300,000 ^cm2 /g.

The content of the siliceous fine powder is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and even more preferably 3 to 12 parts by mass, per 100 parts by mass of cement in the cement composition. When the content of the siliceous fine powder is equal to or greater than the above lower limit, it is easy to improve the fluidity retention and early strength development. Furthermore, when the content of the siliceous fine powder is equal to or less than the above upper limit, it is easy to improve the fluidity retention.

The cement composition may contain an antifoaming agent to the extent that it does not adversely affect performance. Antifoaming agents are used to suppress the amount of air entrained during mixing. There are no particular limitations on the type of antifoaming agent, as long as it does not significantly adversely affect the strength properties of the hardened mortar, and either liquid or powdered antifoaming agents can be used. Examples include polyether-based antifoaming agents, polyhydric alcohol-based antifoaming agents such as esters of polyhydric alcohols and alkyl ethers, alkyl phosphate-based antifoaming agents, and silicone-based antifoaming agents.

The content 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 cement composition. When the content of the defoaming agent is equal to or greater than the lower limit, the defoaming effect can be fully exerted, and when the content of the defoaming agent is equal to or less than the upper limit, the fluidity retention can be easily improved.

In addition, the cement composition may contain one or more of the following additives, provided that they do not adversely affect performance: gas foaming substances, water reducing agents, air entraining agents, rust inhibitors, water repellents, antibacterial agents, colorants, antifreeze agents, limestone fine powder, slowly cooled blast furnace slag fine powder, sewage sludge incineration ash and its molten slag, municipal waste incineration ash and its molten slag, and pulp sludge incineration ash; thickeners, shrinkage reducing agents, polymers, clay minerals such as bentonite and sepiolite, and anion exchangers such as hydrotalcite.

[Hardened body]
The hardened body according to the present embodiment is obtained by hardening a cement composition. The hardened body is usually formed by kneading the cement composition with water, which causes a hydration reaction of the hydraulic material cement and hardens it. The amount of water used for mixing is not particularly limited, but 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, relative to 100 parts by mass of the cement composition. When the amount of water used for mixing is within the above range, it is easy to improve the initial strength development of the hydraulic material.

The hardened body is obtained by mixing the cement composition with water and then leaving it to harden, but it can also be obtained more efficiently by filling (casting) the mixture into a formwork and curing it, or by pouring it directly into the construction area, or by spraying or painting it.

The compressive strength of the hardened body depends on the type of cement used, but 6 hours after casting, it is preferably 10.5 to 15.0 N/ ^mm2 , more preferably 11.0 to 14.0 N/ ^mm2 , and even more preferably 12.0 to 13.0 N/ ^mm2 . Also, at 7 days, it is preferably 40.0 to 50.0 N/ ^mm2 , more preferably 41.0 to 48.0 N/ ^mm2 , and even more preferably 42.0 to 46.0 N/ ^mm2 .
In the present invention, the compressive strength can be measured in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement".

[Method of manufacturing the cured product]
The method for producing a hardened body according to this embodiment is a method for hardening a cement composition containing a hardening accelerator for hydraulic materials, cement, and water by steam curing for 2 to 8 hours at a maximum temperature of 40 to 80° C. The method for producing a hardened body preferably includes, in this order, a kneading step of kneading the hardening accelerator for hydraulic materials, cement, and water, a casting step of filling a formwork with the mixed cement composition, and a curing step of curing the cement composition filled in the formwork.

The mixing method in the mixing process is not particularly limited, and each material may be mixed at the time of construction, or some or all of the materials may be mixed in advance. As a mixing device, any existing device such as a tilting mixer, omni mixer, Henschel mixer, V-type mixer, Plosser mixer, and Nauta mixer can be used.

The casting method in the casting step can be performed by a known method. The temperature of the cement composition during casting is preferably 0 to 50°C, and more preferably 10 to 40°C. If the temperature of the cement composition during casting is within the above range, it becomes easier to quickly remove the hardened body from the mold.

The method for producing the hardened body preferably further includes a compaction step after the casting step. Any known method can be used for the compaction method, but from the viewpoint of workability, it is preferable to use a vibrator. The cement composition containing the hardening accelerator for hydraulic materials of the present invention maintains good fluidity immediately before casting, so compaction can be easily performed, the cement composition can be distributed uniformly within the formwork, and air bubbles that are mixed in during casting can be removed.

As a curing method used in the curing step, from the viewpoint of improving productivity, it is preferable to use steam curing using a curing chamber or a heating sheet. Steam curing is usually performed by raising the temperature of the atmosphere around the target and maintaining a constant temperature while maintaining an appropriate humidity. The conditions for steam curing are preferably a maximum temperature of 40 to 80°C and a curing time of 2 to 8 hours, more preferably a maximum temperature of 40 to 75°C and a curing time of 2.5 to 7.5 hours, and even more preferably a maximum temperature of 45 to 60°C and a curing time of 3 to 7 hours. If the maximum temperature of the atmosphere around the cement composition during steam curing is set within the above range and the curing time is set within the above range, it becomes easier to enable early demolding of the hardened body.

The relative humidity around the cement composition during steam curing is preferably 50% RH or higher, more preferably 75% RH or higher, and even more preferably 90% RH or higher. There is no upper limit, but it may be 100% RH. When the relative humidity around the cement composition during steam curing is within the above range, it becomes easier to quickly demold the hardened body.

It is preferable that the curing process includes a pre-curing process. The pre-curing conditions are preferably a temperature of 10 to 50°C, which is kept constant for about 1 to 3 hours. By including the pre-curing process in the curing process, the temperature inside the poured cement composition can be made uniform, making it easier to prevent thermal cracks caused by temperature differences between the inside and outside.

The curing step preferably includes a heating step. A known method can be used as the heating method, and heating is preferably performed at a heating rate of 10 to 30°C/hour, more preferably at a heating rate of 12 to 28°C/hour, and even more preferably at a heating rate of 15 to 25°C. When the heating rate in the heating step is within the above range, hardening can be further promoted while preventing thermal cracking due to a sudden increase in temperature of the cement composition.

The curing step preferably includes a temperature holding step. Known methods can be used as the temperature holding method, and a constant temperature is preferably held in the range of 40 to 80°C for 1 to 8 hours, more preferably in the range of 40 to 75°C for 1 to 6 hours, and even more preferably in the range of 45 to 65°C for 2.5 to 5 hours. By holding a constant temperature within the above numerical range in the temperature holding step, the poured cement composition can be hardened uniformly, making it easier to remove from the mold quickly.

The method for producing a hardened body preferably includes a natural cooling step after the curing step. In the natural cooling step, the hardened body obtained in the curing step is naturally cooled in a room temperature atmosphere. The cooling time is not particularly limited, but it is sufficient that the hardened body is cooled to a temperature at which it can be easily demolded, and may be about 0.5 to 2 hours. By including the natural cooling step after the curing step, it is possible to prevent thermal cracking of the hardened body.

The present invention will be further explained below based on experimental examples, but the present invention is not limited to these.

<Experimental Example 1>
Using the following materials, mortar was prepared with a water/cement ratio of 45% and a cement to aggregate ratio of 1:2.5 (mass ratio). A water reducer was added to the obtained mortar in the ratio shown in Table 1, and the hydraulic material hardening accelerator with the composition shown in Table 1 was mixed in the amount shown in Table 1 to obtain a cement composition. The flow value of the obtained cement composition was measured, and the flow rate of change was calculated. The initial time was also measured. Both are shown in Table 1.
The prepared cement composition was filled into a form measuring 4 x 4 x 16 cm, and then steam cured to obtain a hardened body. The steam curing conditions were 1 hour pre-curing at 20°C, 1.5 hours of temperature increase at a rate of 20°C/hour, 3 hours of temperature retention at 50°C, and 0.5 hours of natural cooling. The compressive strength of the hardened body was measured. The results are shown in Table 1.

(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: River sand from the Himekawa River system in Niigata Prefecture Water reducing agent: Polycarboxylic acid-based high-performance water reducing agent (commercially available)
Calcium formate: Reagent Calcium sulfate (inorganic calcium compound): Reagent Sodium sulfate (inorganic sulfate): Anhydrous, Reagent

(Measurement items)
Flow change rate: The flow values of the cement composition were measured immediately after mixing and 1 hour after mixing according to the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement". All flow values immediately after mixing were about 200. Using each measured flow value, the flow change rate was calculated as (flow change rate) = 1 - (flow value 1 hour after mixing) / (immediately after mixing) x 100.
Initial setting time: In accordance with the method specified in JIS A 1147:2019 "Test method for setting time of concrete", the initial setting time was the time at which the penetration resistance value reached 3.5 N/ ^mm2 .
Compressive strength: In accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement," the compressive strength of the hardened body 6 hours after steam curing (immediately after demolding) and 7 days after the completion of steam curing was measured.

The results shown in Table 1 confirm that the use of a hydraulic material hardening accelerator containing calcium formate, inorganic calcium compounds, and inorganic sulfates other than calcium sulfate in a specified ratio can improve the fluidity retention, setting properties, and early strength development of the cement composition.

<Experimental Example 2>
Mortar, cement composition, and hardened body were prepared and the flow rate, initial time, and compressive strength were measured in the same manner as in Experimental Example 1, except that calcium hydroxide, calcium carbonate, and calcium oxide were used as the inorganic calcium compounds contained in the hardening accelerator for hydraulic materials in the ratios shown in Table 2 in addition to calcium sulfate. The results are shown in Table 2.

(Inorganic calcium compounds)
Calcium hydroxide: Reagent Calcium carbonate: Reagent Calcium oxide: Reagent

From the results shown in Table 2, it was confirmed that by using calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide as the inorganic calcium compounds contained in the hardening accelerator for hydraulic materials, the fluidity retention, setting property, and early strength development of the cement composition can be improved. In particular, it was confirmed that when calcium sulfate is contained, the early strength development of the cement composition can be particularly improved.

<Experimental Example 3>
Mortar, cement composition, and hardened body were prepared and the flow rate, initial time, and compressive strength were measured in the same manner as in Experimental Example 1, except that aluminum sulfate, potassium alum, and sodium thiosulfate were used as inorganic sulfates in the hardening accelerator for hydraulic materials in the ratios shown in Table 3. The results are shown in Table 3.

(Inorganic sulfates)
Aluminum sulfate: Reagent Potassium alum: Reagent Sodium thiosulfate: Reagent

From the results shown in Table 3, it was confirmed that the use of sodium sulfate, aluminum sulfate, potassium alum, and sodium thiosulfate as inorganic sulfates contained in the hardening accelerator for hydraulic materials can improve the fluidity retention, setting properties, and early strength development of the cement composition. In particular, it was confirmed that when sodium sulfate and aluminum sulfate are contained, the early strength development can be further improved, and in particular, when sodium sulfate is contained, the fluidity retention can be further improved.

<Experimental Example 4>
Mortar, cement composition, and hardened body were prepared and the flow rate, initial time, and compressive strength were measured in the same manner as in Experimental Example 1, except that calcium sulfoaluminate was further added to the hardening accelerator for hydraulic materials in the proportions shown in Table 4. The results are shown in Table 4.

(Calcium Sulfoaluminate)
A prototype was prepared by mixing first-grade reagent calcium carbonate, calcium sulfate dihydrate, and aluminum hydroxide in a molar ratio of _CaO : _CaSO4 : _Al2O3 of 4:3:1, firing at 1,400°C for 2 hours, leaving to cool to room temperature, and pulverizing until the Blaine specific surface area reached 3,500 ^cm2 /g.

The results shown in Table 4 confirm that when the hardening accelerator for hydraulic materials further contains calcium sulfoaluminate, the early strength development can be improved.

<Experimental Example 5>
Mortar, cement composition, and hardened body were prepared and the flow rate, initial time, and compressive strength were measured in the same manner as in Experimental Example 1, except that the mixing amount of the hardening accelerator for hydraulic materials was set to the ratio shown in Table 5. The results are also shown in Table 5.

The results shown in Table 5 confirm that by mixing the amount of hydraulic material hardening accelerator within a specified range, the fluidity retention, setting properties, and early strength development of the cement composition can be improved.

<Experimental Example 6>
Except for using blast furnace cement and fly ash cement as the cement composition, mortar, cement composition, and hardened body were prepared in the same manner as in Experimental Example 1, and the flow rate, initial time, and compressive strength were measured. The results are shown in Table 6.

(cement)
Blast furnace type B cement: Commercial product, Blaine specific surface area 3,200 cm ² /g, specific gravity 3.15 g/cm ³
Blast furnace type C cement: Commercial 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

The results shown in Table 6 confirm that even when blast furnace cement or fly ash cement is used as the cement in the cement composition, the fluidity retention, setting properties, and early strength development of the cement composition can be improved.

The above results confirm that the hardening accelerator for hydraulic materials of the present invention, which contains calcium formate, an inorganic calcium compound, and an inorganic sulfate in a specified ratio, can improve the fluidity retention, setting property, and early strength development of the cement composition.

The hardening accelerator for hydraulic materials of the present invention contains calcium formate, inorganic calcium compounds, and inorganic sulfates other than calcium sulfate in a specified ratio, which makes it possible to improve the fluidity retention, setting properties, and early strength development of hydraulic materials. Therefore, it can be widely applied in the fields of civil engineering and construction, such as hardened concrete bodies used in precast construction methods.

Claims (5)

The composition contains 24.0 to 80.0 mass% of calcium formate, 15.0 to 70.0 mass% of an inorganic calcium compound, and 0.5 to 20.0 mass% of an inorganic sulfate other than calcium sulfate ,
The inorganic calcium compound is at least one selected from the group consisting of calcium sulfate, calcium hydroxide, calcium carbonate, and calcium oxide,
The hardening accelerator for hydraulic materials, wherein the inorganic sulfate is at least one selected from the group consisting of sulfates, thiosulfates, sulfites, bisulfites, pyrosulfates, and pyrobisulfites . The hardening accelerator for hydraulic materials according to claim 1 , further comprising 4.5 to 65.0 mass % of calcium sulfoaluminate. A method for producing a hydraulic material comprising the hardening accelerator according to claim 1 or 2 and cement ,
The content of the hydraulic material hardening accelerator is 0.5 to 10 mass % . A hardened body obtained by hardening the cement composition according to claim 3 . A method for producing a hardened body, comprising hardening a cement composition containing the hardening accelerator for hydraulic materials according to claim 1 and cement by steam curing at a maximum temperature of 40 to 80°C for 2 to 8 hours.