Method for producing hydraulically hardened cement and cement composition for carbonation curing

Abstract

To provide a manufacturing method of a hydraulic hardened body and a cement composition for carbonation curing, having excellent workability, less carbon dioxide gas discharge on manufacturing, having carbon dioxide gas fixation function, and exhibiting good strength.SOLUTION: A manufacturing method of a hydraulic hardened body of the present invention is a manufacturing method of a hydraulic hardened body, including manufacturing a hydraulic hardened body by hardening and carbonation curing a cement composition including water, a cement, calcium hydroxide, and a setting retarder, wherein the cement composition includes 5 pts.mass or over and 80 pts.mass or under of the calcium hydroxide to 100 pts.mass of a total amount of the cement and the calcium hydroxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a hydraulically hardened product and a cement composition for carbonation curing. [Background technology]

[0002] The cement used in concrete emits a large amount of carbon dioxide (CO2) during production due to the decarbonation of raw materials and the fuel used during firing. In response to growing interest in curbing climate change in recent years, there is a demand for a significant reduction in carbon dioxide emissions during concrete production.

[0003] For example, Patent Document 1 discloses precast concrete obtained by hardening a concrete mixture made by adding γ-C2S (γ-2CaO SiO2; also known as γ-belite) to powdered steelmaking slag and Portland cement, and then carbonation curing the concrete after demolding. In the precast concrete of Patent Document 1, carbonation curing progresses on the surface of the concrete due to the absorption of carbon dioxide gas, improving the strength of the concrete surface. However, carbonation may not progress easily inside the concrete.

[0004] Another method for reducing carbon dioxide emissions is to use a mixed cement in which granulated blast furnace slag (hereinafter also referred to as ground granulated blast furnace slag) is mixed with cement in a cement composition. However, increasing the amount of ground granulated blast furnace slag slows down the hardening of the cement composition, lengthening the time it takes to demold the hydraulically hardened body, and requiring prolonged wet curing of the cement composition to obtain sufficient strength for the hydraulically hardened body, resulting in poor workability in producing the hydraulically hardened body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3658568 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for producing a hydraulically hardened product and a cement composition for carbonation curing which have excellent workability, little carbon dioxide gas emission during production, a carbon dioxide gas fixation function, and good strength. [Means for solving the problem]

[0007] [1] A method for producing a hydraulically hardened body, comprising hardening and carbonation curing a cement composition containing water, cement, calcium hydroxide, and a set retarder, wherein the cement composition contains 5 to 80 parts by mass of calcium hydroxide per 100 parts by mass of the total amount of the cement and the calcium hydroxide. [2] The cement composition contains the cement and the calcium hydroxide in a total amount of 270 kg / m 3 More than 600kg / m 3 The method for producing a hydraulic hardened body according to the above-mentioned [1], wherein the cement composition contains 20 parts by mass or more and 65 parts by mass or less of water per 100 parts by mass of the total amount of the cement and the calcium hydroxide. [3] The method for producing a hydraulic hardened body according to [1] or [2] above, wherein the cement composition contains the set retarder in an amount of 0.010 parts by mass or more and 1,000 parts by mass or less per 100 parts by mass of the total amount of the cement and the calcium hydroxide. [4] The cement composition contains the set retarder in an amount of 0.05 kg / m 3 More than 2.00kg / m 3 A method for producing a hydraulically hardened product according to any one of the above [1] to [3], which comprises: [5] The cement composition has a viscosity of 0 kg / m 3 Super 50kg / m 3 The method for producing a hydraulically hardened body according to any one of the above [1] to [4], further comprising the following ground granulated blast furnace slag: [6] The cement composition contains one or more selected from the group consisting of fly ash, γ-CS, wollastonite, and mervinite in an amount of 0 kg / m 3 Super 50kg / m 3 A method for producing a hydraulically hardened product according to any one of the above [1] to [5], comprising: [7] The method for producing a hydraulic hardened product according to any one of the above [1] to [6], wherein the slump loss (|S1-S2|×100 / S1), which is the ratio of the difference between the slump (S1) of the cement composition immediately after mixing and the slump (S2) after 60 minutes has elapsed to the slump (S1) of the cement composition immediately after mixing, is 30.0% or less as measured in accordance with JIS A 1101:2005. [8] A cement composition for carbonation curing containing water, cement, calcium hydroxide, and a set retarder, wherein the calcium hydroxide is contained in an amount of 5 to 80 parts by mass per 100 parts by mass of the total amount of the cement and the calcium hydroxide. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a hydraulically hardened product and a cement composition for carbonation curing which are excellent in workability, emit little carbon dioxide gas during production, have a carbon dioxide gas fixation function, and have good strength. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a detailed description will be given based on an embodiment.

[0010] The present inventors focused on the fact that calcium hydroxide (slaked lime) reacts with carbon dioxide during the hardening process of hydraulically hardened bodies formed by the reaction of cement with water, commonly known as concrete. They investigated incorporating a large amount of calcium hydroxide into a cement composition and fixing carbon dioxide in the hydraulically hardened body through carbonation curing. However, they found that adding a large amount of calcium hydroxide to a cement composition accelerates the setting of the hydraulically hardened body of the cement composition, making it difficult to fix carbon dioxide throughout the hydraulically hardened body even through carbonation curing, which is a workability issue. To address this issue, they found that adding a set retarder to the cement composition can slow the setting of the hydraulically hardened body due to calcium hydroxide, and therefore carbon dioxide can be fixed throughout the hydraulically hardened body through carbonation curing, even when a large amount of calcium hydroxide is added to the cement composition. The present invention was completed based on this finding.

[0011] First, the method for producing the hydraulically hardened product of the present invention will be described.

[0012] The method for producing a hydraulic hardened body of the present invention comprises hardening and carbonation curing a cement composition containing water (W), cement (OPS), calcium hydroxide (CH), and a set retarder to produce a hydraulic hardened body, wherein the cement composition contains 5 to 80 parts by mass of calcium hydroxide per 100 parts by mass of the total amount of cement and calcium hydroxide. More specifically, in the method for producing a hydraulically hardened product of the present invention, a product obtained by mixing water, cement, calcium hydroxide, and a setting retarder hardens over time, and is then subjected to carbonation curing for a predetermined period of time, mainly during and after hardening.

[0013] The cement composition in the method for producing a hydraulically hardened body contains water, cement, calcium hydroxide, and a set retarder. The cement composition may also contain aggregate (fine aggregate, coarse aggregate) depending on the desired properties of the cement composition and the hydraulically hardened body.

[0014] The cement constituting the cement composition is preferably Portland cement. Portland cement includes ordinary Portland cement (OPC), as well as types such as high-early-strength, ultra-high-early-strength, moderate-heat, low-heat, and sulfate-resistant, which are specified in JIS R 5210:2019. The cement composition can contain one or more of these various Portland cements. Among these, it is preferable to use one or two of ordinary Portland cement and high-early-strength Portland cement.

[0015] The calcium hydroxide that constitutes the cement composition reacts with carbon dioxide, thereby serving as a carbon dioxide immobilizing agent that can immobilize carbon dioxide in the hydraulically hardened body. To increase the amount of carbon dioxide immobilized in the hydraulically hardened body, the present invention incorporates, for example, a larger amount of calcium hydroxide into the cement composition than in the case of conventionally used hardening accelerators. Because the cement composition contains a larger amount of calcium hydroxide than conventionally used, it can absorb more carbon dioxide even when carbonation curing is performed immediately after production. Furthermore, because calcium hydroxide reacts with carbon dioxide during carbonation curing to form calcium carbonate, calcium carbonate is generated throughout the hydraulically hardened body, resulting in a uniform and high strength of the hydraulically hardened body.

[0016] Calcium hydroxide has the advantage of being relatively inexpensive and easily available. For example, quicklime, a by-product of the acetylene gas production process, may be used as calcium hydroxide. This allows for effective use of waste materials. It is also preferable to use calcium hydroxide in the form of powder.

[0017] Calcium hydroxide accelerates the hydration reaction of cement and accelerates the setting of the hydraulically hardened body. Therefore, the product of mixing water, cement, and calcium hydroxide has reduced workability, such as the ability to pour concrete into forms after mixing, compared to a mixture of water and cement. To address this workability issue, a set retarder is added to the cement composition. This is a chemical admixture for hydraulically hardened bodies that is highly effective in improving the quality of the hydraulically hardened body and is used to delay the setting and initial hardening of the hydraulically hardened body. By including a set retarder in the cement composition, the mixed product can maintain good workability for a longer period of time after mixing.

[0018] Examples of set retarders include those primarily composed of silicon fluorides, which have a retarding effect, and those primarily composed of hydroxycarboxylates, which are designed to delay set longer than conventional methods. Lignin sulfonates and hydroxycarboxylates adsorb to the surface of cement particles, temporarily blocking contact between the cement and water and thereby delaying the initial hydration reaction. Set retarders can be selected from a variety of agents that delay the setting reaction of cement. Specific examples of set retarders include those primarily composed of sodium gluconate, gluconates, hydroxycarboxylates, ultrafine acrylic polymer emulsions, hydroxycarboxylic acid compounds, polyhydroxycarboxylic acids, lignin sulfonates, and complexes containing these components (e.g., complexes of modified lignin sulfonates and hydroxycarboxylic acid compounds).

[0019] The set retarder is adopted as an admixture based on the following test and is included in the cement composition.

[0020] The set retarder to be selected is preferably an admixture that complies with JIS A 6204:2011 "Chemical admixtures for concrete" and that has the property that the difference in cement setting time according to JIS A 1147:2019 "Testing method for setting time of concrete" is greater than +15 minutes at the initial setting time or greater than +0 minutes at the final setting time. Furthermore, it is preferable to select a set retarder that has the property that the difference in the setting time is greater than +30 minutes at the initial setting time and greater than +0 minutes at the final setting time.

[0021] Furthermore, it is preferable to select a retarder that has a better effect in retarding the setting of cement, etc., such as a retarder that produces a difference in the setting time of cement according to JIS A 1147:2019 "Testing method for setting time of concrete" of +60 to +210 minutes at the initial setting time and +0 to +210 minutes at the final setting time.

[0022] Generally, the amount of setting retarder (chemical admixture for hydraulic hardened body) added, which is expressed as a ratio to the unit amount of cement, is determined as a specific addition weight (kg / m) in the following procedure in this embodiment. 3 It is preferable to determine the amount of addition as follows. The following procedure is an example, and the procedure for determining the amount of addition is not limited to this.

[0023] First, a mortar specified in JIS R 5201:2015 "Physical Tests of Cement" with a mass mix of cement (ordinary Portland cement):standard sand:water = 1:3:0.5 is added with a set retarder at a specified test weight ratio (X%) relative to the unit cement content. Then, a test specified in JIS A 1147:2019 "Test Method for Setting Time of Concrete" is conducted.

[0024] In this setting time test, a setting retarder is selected that results in a difference in setting time of +60 minutes to +210 minutes at the start time and +0 minutes to +210 minutes at the end time. The amount of retarder added is determined by the ratio (Y%) to the total parts by mass of cement (OPS) and calcium hydroxide (CH). In other words, the amount of set retarder to be added (Y%) is set based on the ratio (CH / (OPS+CH)) of parts by mass of calcium hydroxide (CH). The larger the ratio (CH / (OPS+CH)) of parts by mass of calcium hydroxide (CH), the larger the amount of set retarder to be added (Y%). The smaller the ratio (CH / (OPS+CH)) of parts by mass of calcium hydroxide (CH), the smaller the amount of set retarder to be added (Y%). The amount of the setting retarder contained in the cement composition in this embodiment may be set as a multiple of the test weight ratio (X%) based on the test weight ratio (X%) used in the setting time test. The preferred range (lower limit, upper limit) of the amount of setting retarder added (Y%) is as follows: CH / (OPS+CH): 6~20% Addition amount (Y%): 0.05 times or more, 0.75 times or less CH / (OPS+CH): 20~40% Addition amount (Y%): 0.75 times or more, 1.50 times or less CH / (OPS+CH): 40~60% Addition amount (Y%): 1.25 times or more, 2.00 times or less CH / (OPS+CH): 60~80% Addition amount (Y%): 2.25 times or more, 3.00 times or less A more preferable range (lower limit, upper limit) of the amount of setting retarder added (Y%) is as follows: CH / (OPS+CH): 6~20% Addition amount (Y%): 0.25 times or more, 0.50 times or less CH / (OPS+CH): 20~40% Addition amount (Y%): 1.00 times or more, 1.25 times or less CH / (OPS+CH): 40~60% Addition amount (Y%): 1.50 times or more, 1.75 times or less CH / (OPS+CH): 60~80% Addition amount (Y%): 2.50 times or more, 2.75 times or less

[0025] In the test specified in JIS A 1147:2019 "Testing method for setting time of concrete," when the test weight ratio (X%) to the unit cement amount is 0.2%, the preferred range (lower limit, upper limit) of the amount of retarder to be added (Y%) is as follows: CH / (OPS+CH): 6~20% Addition amount (Y%): 0.01% or more, 0.15% or less CH / (OPS+CH):20~40% Addition amount (Y%): 0.15% or more, 0.30% or less CH / (OPS+CH): 40~60% Addition amount (Y%): 0.25% or more, 0.40% or less CH / (OPS+CH): 60~80% Addition amount (Y%): 0.45% or more, 0.60% or less A more preferable range (lower limit, upper limit) of the amount of setting retarder added (Y%) is as follows: CH / (OPS+CH): 6~20% Addition amount (Y%): 0.05% or more, 0.10% or less CH / (OPS+CH):20~40% Addition amount (Y%): 0.20% or more, 0.25% or less CH / (OPS+CH): 40~60% Addition amount (Y%): 0.30% or more, 0.35% or less CH / (OPS+CH): 60~80% Addition amount (Y%): 0.50% or more, 0.55% or less As an example of this embodiment, the amount of the setting retarder added is set within the above range relative to the total mass parts of cement and calcium hydroxide. Note that even if the test weight ratio (X%) is unknown, it can be set within a similar range.

[0026] On the other hand, it is also possible to select a retarder (admixture) that shows a relatively small difference in setting time in the above-mentioned setting time test, for example, +30 to +90 minutes at the start time and +0 to 90 minutes at the end time. Similarly, the amount of set retarder to be added is set as a ratio (Y%) to the total parts by mass of cement (OPS) and calcium hydroxide (CH). In other words, the amount of set retarder to be added (Y%) is set based on the ratio (CH / (OPS+CH)) of parts by mass of calcium hydroxide (CH). The larger the ratio (CH / (OPS+CH)) of parts by mass of calcium hydroxide (CH), the larger the amount of set retarder to be added (Y%). The smaller the ratio (CH / (OPS+CH)) of parts by mass of calcium hydroxide (CH), the smaller the amount of set retarder to be added (Y%).

[0027] Thus, the set retarder added to the cement composition may be any chemical admixture that has been confirmed to cause a certain degree of delay in the setting time measured by the test specified in JIS A 1147:2019 "Testing Method for the Setting Time of Concrete." Furthermore, the amount (Y%) added per 100 parts by mass of the total cement and calcium hydroxide in the cement composition may be changed depending on the degree of delay in the setting time confirmed. For example, the upper limit of the weight ratio (%) added may be lower for set retarders that cause a longer delay in setting time and higher for set retarders that cause a shorter delay in setting time. Thus, when using a set retarder that causes a relatively long delay in setting time, reducing the amount of set retarder added to the cement composition can suppress increases in construction costs for structures.

[0028] Furthermore, the fine aggregate contained in the cement composition is an aggregate defined in JIS A 5308, JIS A 5005, JIS A 5002, and JIS A 5011. Examples of fine aggregate include crushed sand, sand, river sand, sea sand, crushed lime sand, recycled aggregate, lightweight aggregate, and heavy aggregate.

[0029] Coarse aggregate contained in cement compositions is aggregate defined in JIS A 5308, JIS A 5005, JIS A 5002, and JIS A 5011, and is distinguished from the above-mentioned fine aggregate by particle size, and is classified by whether or not it passes through a 5mm sieve. In practice, fine aggregate is defined as aggregate that passes entirely through a 10mm sieve and 85% or more by weight passes through a 5mm sieve, and coarse aggregate is defined as aggregate that is retained by 85% or more by weight on a 5mm sieve.

[0030] The calcium hydroxide contained in the cement composition is 5 parts by mass or more, preferably 15 parts by mass or more, and more preferably 20 parts by mass or more, per 100 parts by mass of the total amount of cement and calcium hydroxide. When the calcium hydroxide is 5 parts by mass or more per 100 parts by mass of the total amount of cement and calcium hydroxide, carbon dioxide can be taken in from the early stage of carbonation curing, and carbon dioxide can be sufficiently fixed in the hydraulic hardened body.

[0031] The amount of calcium hydroxide contained in the cement composition is 80 parts by mass or less, preferably 60 parts by mass or less, and more preferably 40 parts by mass or less, per 100 parts by mass of the total amount of cement and calcium hydroxide. When the amount of calcium hydroxide is 80 parts by mass or less, per 100 parts by mass of the total amount of cement and calcium hydroxide, the composition can fully function as a hydraulic hardened body.

[0032] The cement composition contains cement and calcium hydroxide in a total amount of 270 kg / m 3 More than 600kg / m 3 Preferably, the cement composition contains 20 to 65 parts by mass of water per 100 parts by mass of the total amount of cement and calcium hydroxide. 3 More than 400kg / m 3 It is more preferable that the amount of water contained is 40 parts by mass or more and 55 parts by mass or less per 100 parts by mass of the total amount of cement and calcium hydroxide.

[0033] When the ratio of the parts by mass of water to the total of cement and calcium hydroxide and the parts by mass of the total amount of cement and calcium hydroxide is within the above range, the concrete can be distributed generally as ordinary concrete and can have performance equivalent to that of ready-mix concrete specified by the JIS.

[0034] When the amount of water is 40 parts by mass or more and 65 parts by mass or less per 100 parts by mass of the total amount of cement and calcium hydroxide, a mixture with excellent workability can be obtained.

[0035] The amount of the set retarder contained in the cement composition is preferably 0.010 parts by mass or more, more preferably 0.050 parts by mass or more, and even more preferably 0.100 parts by mass or more, per 100 parts by mass of the total amount of cement and calcium hydroxide. When the amount of the set retarder is 0.010 parts by mass or more, per 100 parts by mass of the total amount of cement and calcium hydroxide, the decrease in workability caused by calcium hydroxide can be sufficiently improved.

[0036] The amount of the set retarder contained in the cement composition is preferably 1.000 parts by mass or less, more preferably 0.500 parts by mass or less, and even more preferably 0.400 parts by mass or less, per 100 parts by mass of the total amount of cement and calcium hydroxide. When the amount of the set retarder is 1.000 parts by mass or less, per 100 parts by mass of the total amount of cement and calcium hydroxide, excessive delay in the setting completion time of the hydraulic hardened body can be suppressed, and workability can be improved.

[0037] The set retarder contained in the cement composition is 0.05 kg / m 3 It is preferable that the content is 0.10 kg / m or more. 3 More preferably, it is 0.30 kg / m or more. 3 It is more preferable that the set retarder contained in the cement composition is 0.05 kg / m or more. 3 In this case, the setting of the hydraulic hardened body can be sufficiently delayed, and carbon dioxide gas can be sufficiently fixed throughout the hydraulic hardened body by carbonation curing, thereby further improving workability.

[0038] The set retarder contained in the cement composition is 2.00 kg / m 3 Preferably, it is 1.80 kg / m or less. 3 More preferably, it is 1.50 kg / m or less. 3 It is more preferable that the content of the set retarder contained in the cement composition is 2.00 kg / m or less. 3 When the temperature is equal to or less than this, excessive delay in the setting completion time of the hydraulic hardened body can be suppressed, and workability can be improved.

[0039] In addition, the cement composition is 0 kg / m 3 Super 50kg / m 3 The following ground granulated blast furnace slag (BFS) may further be contained.

[0040] Ground granulated blast furnace slag is a fine powder specified in JIS A 6206:2013 "Ground granulated blast furnace slag for concrete." Granulated blast furnace slag is produced in a blast furnace by rapidly cooling molten blast furnace slag, which is produced at the same time as shear iron, with water or air, and has a basicity of 1.60 or higher. Ground granulated blast furnace slag is produced by drying and pulverizing this granulated blast furnace slag, or by adding gypsum to it. By replacing part of the Portland cement with ground granulated blast furnace slag, it is possible to reduce carbon dioxide emissions during the cement manufacturing process.

[0041] The types of ground granulated blast furnace slag are classified by specific surface area (cm 2 There are four types depending on the molecular weight (g), and any of them may be used in the present invention. a) Blast furnace slag powder 3000: specific surface area is 2750 or more and less than 3500 b) Blast furnace slag powder 4000: specific surface area is 3500 or more and less than 5000 c) Blast furnace slag powder 6000: specific surface area is 5000 or more and less than 7000 d) Blast furnace slag powder 8000: specific surface area is 7000 or more but less than 10000

[0042] The cement composition contains at least one selected from the group consisting of fly ash, γ-CS, wollastonite and mervinite in an amount of 0 kg / m 3 Super 50kg / m 3 The following may be contained: When the cement composition contains at least one of the above compounds within the above range, the amount of carbon dioxide gas fixed in the hydraulic hardened body during carbonation curing can be further increased.

[0043] The cement composition may further contain other additives within the range in which the effects of the present invention are achieved, such as coal ash, limestone fine powder, carbonate compounds such as light calcium carbonate that fixes atmospheric carbon dioxide, water-reducing agents, and fluidizing agents.

[0044] The slump (cm) of the mixed cement composition is measured according to JIS A 1101:2005, "Test Method for Slump of Concrete." The slump of the mixed cement composition is preferably 8.0 cm or more and 21.0 cm or less, more preferably 10.0 cm or more and 18.0 cm or less. Generally, the slump of the mixed cement composition decreases over time, resulting in a decrease in workability and fluidity. In particular, since the cement contains a relatively large amount of calcium hydroxide, the slump loss after mixing is significant. The slump loss (|S1-S2|×100 / S1), which is the ratio of the difference between the slump (S1) of the mixed cement composition immediately after mixing and the slump (S2) after 60 minutes, to the slump (S1) of the mixed cement composition, is preferably 30.0% or less. The slump loss is controlled by the setting retarder contained in the cement composition. If the slump loss is 30.0% or less, good workability can be maintained for a certain period of time, improving practicality and allowing an increase in the amount of carbon dioxide fixed in the hydraulic hardened body during carbonation curing.Furthermore, if the slump loss is 20.0% or less, good workability can be maintained for a longer period of time, and an increase in the amount of carbon dioxide fixed in the hydraulic hardened body during carbonation curing can be achieved.

[0045] The above cement composition is hardened and carbonation cured to produce a hydraulically hardened body. For example, the cement composition is filled into a formwork, hardened to a predetermined shape, and then carbonation cured. The cement composition does not need to be completely hardened before carbonation curing; it may be semi-hardened to a degree that makes it self-standing (to the extent that it can maintain a predetermined shape even when removed from the formwork). The cement composition can be cast in place as well as precast concrete.

[0046] Carbonation curing can be carried out, for example, by exposing the semi-hardened body to a carbon dioxide-containing gas. The carbon dioxide content in the carbon dioxide-containing gas is higher than the atmospheric concentration of about 0.03%, preferably 1% or more, and more preferably 10% or more. This allows carbonation curing to be carried out quickly. Furthermore, combustion exhaust gas emitted from factories or facilities can be used as a source of carbon dioxide gas used in carbonation curing. The combustion exhaust gas may be sent directly into the carbonation curing chamber, or the combustion exhaust gas may be mixed with other gases and sent into the chamber as a mixed gas.

[0047] The temperature during carbonation curing is not particularly limited, but is preferably 15° C. or higher, and more preferably 50° C. or higher. The temperature during carbonation curing is preferably, for example, 70° C. or lower.

[0048] The curing period for carbonation curing may be appropriately set depending on the shape of the object to be cured, the curing conditions, etc. For example, the curing period may be about 1 to 28 days. In the carbonation curing step, the curing reaction of the uncured components may proceed simultaneously.

[0049] The hydraulically hardened body produced by the above-mentioned method for producing a hydraulically hardened body may be used as it is for purposes such as remaining formwork, or may be used for specific purposes after being shaped, processed, etc. as needed. The hydraulically hardened body can be used for purposes such as cast-in-place reinforced concrete, slump concrete, zero-slump concrete, prestressed concrete, etc.

[0050] Next, the carbonation curing cement composition of the present invention will be described.

[0051] The carbonation curing cement composition of the present invention contains water, cement, calcium hydroxide, and a set retarder, and contains 5 to 80 parts by mass of calcium hydroxide per 100 parts by mass of the total of cement and calcium hydroxide. The lower limit of the parts by mass of calcium hydroxide per 100 parts by mass of the total of cement and calcium hydroxide is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and the upper limit is preferably 60 parts by mass or less, more preferably 40 parts by mass or less.

[0052] The carbonation curing cement composition is suitably used as the cement composition in the above-mentioned method for producing a hydraulic hardened product. From this viewpoint, the components and composition of the carbonation curing cement composition of the present invention are preferably the same as the components and composition of the cement composition in the above-mentioned method for producing a hydraulic hardened product.

[0053] Although the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept and scope of the claims of the present disclosure, and can be modified in various ways within the scope of the present disclosure. [Example]

[0054] Next, examples and comparative examples will be described, but the present invention is not limited to these examples.

[0055] Examples 1 to 9 Cement compositions were prepared with the compositions shown in Table 1. The cement compositions were then poured into cylindrical forms with a diameter of 10 cm and a height of 20 cm, and pre-cured at 20°C for two days. Each solidified body was then subjected to carbonation curing. The carbonation curing conditions were a temperature of 20°C, humidity of 50% RH, and an atmospheric pressure environment with a carbon dioxide concentration of 80%. The carbonation curing was completed after 28 days. In this way, hydraulically hardened bodies with immobilized carbon dioxide were obtained.

[0056] (Comparative Examples 1 to 12) Comparative Examples 1 to 12 were carried out in the same manner as in the above-mentioned Examples, except that the cement compositions shown in Table 1 were changed to cement compositions shown in Table 2.

[0057] In Tables 1 and 2, W is water, OPC is ordinary Portland cement, CH is calcium hydroxide, retarder is an oxycarboxylate-based retarder, S is fine aggregate, G is coarse aggregate, BFS is ground granulated blast furnace slag, and F is fly ash. The units for W, OPC(N), CH(C), retarder, S, G, BFS(B), F, and N+C are kg / m 3 Furthermore, C / (N+C) is the mass part of calcium hydroxide per 100 mass parts of the total amount of cement and calcium hydroxide. W / (N+C) is the mass part of water per 100 mass parts of the total amount of cement and calcium hydroxide. Retarder / (N+C) is the mass part of set retarder per 100 mass parts of the total amount of cement and calcium hydroxide. C / N is the mass part of calcium hydroxide per 100 mass parts of cement. The properties of each material are as follows:

[0058] OPC: Density 3.16g / cm 3 CH: Density 2.21g / cm 3 Set retarder: Density 1.19g / cm 3 S: Density 2.64g / cm 3 G: Density 2.65g / cm 3 BFS: Density 2.91g / cm 3 F: Density 2.20g / cm 3

[0059] [Table 1]

[0060] [Table 2]

[0061] The hydraulically hardened bodies obtained from the cement compositions of the above Examples and Comparative Examples were subjected to the following measurements and evaluations. The results are shown in Tables 3 and 4.

[0062] [1] Slump Measurements were performed in accordance with JIS A 1101:2005 "Test Method for Slump of Concrete." Measurements were performed immediately after mixing of the cement composition (S1), 30 minutes after mixing, and 60 minutes after mixing (S2), and the results were used to determine the slump at each timing. The ratio of the difference between slump (S1) and slump (S2) to the slump (S1) was calculated as slump loss (|S1-S2| x 100 / S1), and the change over time from immediately after mixing of the cement composition was evaluated. Slump was evaluated as follows: ◯ if the slump loss was 20.0% or less; △ if the slump loss was greater than 20.0% but less than 30.0%; and × (fail) if the slump loss was greater than 30.0% or was unmeasurable.

[0063] [2] Pouring ability (workability) The pourability was evaluated as follows: When the mixed cement composition could be sampled into a formwork even 60 minutes after mixing, it was evaluated as ○, and when it was impossible to sample into a formwork 60 minutes after mixing, it was evaluated as × (fail).

[0064] [3] Whether or not the product has hardened within 24 hours The mixed cement composition was poured into a formwork and left to stand for 24 hours. If the composition had hardened enough to remove the formwork after 24 hours, it was marked as ○; if it had not hardened, it was marked as × (fail); and if it was impossible to collect the composition into the formwork, it was marked as “impossible to measure” (fail).

[0065] [4] Carbon dioxide absorption per hydraulic hardening body For the hydraulically hardened bodies obtained in the above Examples and Comparative Examples, the amount of carbon dioxide gas absorbed was measured within the carbonation range measured according to JIS A 1152:2018 "Method for measuring carbonation depth of concrete."

[0066] [5] Compressive strength Using the cement compositions of the above examples and comparative examples, compressive strength was measured at a predetermined age in accordance with JIS A 1108:2018 "Test method for compressive strength of concrete."

[0067] [Table 3]

[0068] [Table 4]

[0069] As described above, in the above examples, the cement composition contained water, cement, calcium hydroxide, and a setting retarder, and contained 5 to 80 parts by mass of calcium hydroxide per 100 parts by mass of the total amount of cement and calcium hydroxide. Therefore, the amount of carbon dioxide emitted during production was low, the cement composition had excellent carbon dioxide immobilization function, and the workability when the cement composition was hardened and carbonation cured was excellent. Furthermore, the hydraulically hardened body obtained by hardening and carbonation curing the cement composition immobilized a large amount of carbon dioxide and had excellent strength.

Claims

1. A method for producing a hydraulically hardened body, comprising hardening and carbonation curing a cement composition containing water, cement, calcium hydroxide, and a set retarder, to produce a hydraulically hardened body, The cement composition contains 15 parts by mass or more and 80 parts by mass or less of the calcium hydroxide per 100 parts by mass of the total amount of the cement and the calcium hydroxide.

2. The cement composition contains the cement and the calcium hydroxide in a total amount of 270 kg / m ３ More than 600kg / m ３ Contains:

2. The method for producing a hydraulic hardened body according to claim 1, wherein the cement composition contains 20 parts by mass or more and 65 parts by mass or less of the water per 100 parts by mass of the total amount of the cement and the calcium hydroxide.

3. 3. The method for producing a hydraulic hardened body according to claim 1, wherein the cement composition contains the set retarder in an amount of 0.010 parts by mass or more and 1.000 parts by mass or less per 100 parts by mass of the total amount of the cement and the calcium hydroxide.

4. The cement composition contains the set retarder in an amount of 0.05 kg / m ３ 2.00kg / m or more ３ The method for producing a hydraulically hardened product according to any one of claims 1 to 3, comprising:

5. The method for producing a hydraulic hardened product according to any one of claims 1 to 4, wherein a slump loss (|S1-S2| x 100 / S1), which is a ratio of a difference between a slump (S1) of the cement composition immediately after mixing and a slump (S2) after 60 minutes has elapsed to a slump (S1) of the cement composition immediately after mixing, is 30.0% or less as measured in accordance with JIS A 1101:2005.

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