Method for carbonating hardened cementitious material, method for manufacturing cement mixture, and apparatus for carbonating hardened cementitious material

Abstract

To provide a method for carbonating cementitious hardened materials that allows for the easy estimation of the reaction progress and improves work efficiency. [Solution] A method for carbonating cementitious material is provided, comprising: step A, which involves supplying a gas containing carbon dioxide into a container containing a mixture of cementitious material and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas; and step B, which involves changing the reaction conditions based on the temperature inside the container.

Description

Technical Field

[0001] The present disclosure relates to a carbonation method for a cementitious hardened body, a method for producing a cement admixture, and a carbonation apparatus for a cementitious hardened body.

Background Art

[0002] In recent years, demands for measures against global warming have increased, and reduction of CO₂ emissions in cement production is required. As a method for reducing CO₂ emissions, a method of immobilizing carbon dioxide as calcium carbonate (CaCO₃) in calcium-containing materials such as cementitious hardened bodies for carbonation has been studied. For example, Patent Document 1 proposes a method of bringing a carbon dioxide-containing gas having a water content of 1.5% or more and a temperature of 75 to 175°C into contact with a cementitious hardened body to immobilize carbon dioxide. Patent Document 2 proposes a method of bringing a CO₂-containing gas into contact with an aggregate of solid particles containing CaO and / or Ca(OH)₂ to immobilize CO₂ in exhaust gas onto the solid particles. Further, Patent Document 3 proposes a method of grinding waste concrete to separate aggregate and cement paste to obtain cement paste. Patent Document 4 describes a method of accumulating a material obtained by crushing waste concrete, supplying water thereto, stirring the mixture, and repeating alternating wetting and drying steps to immobilize CO₂.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent documents 1 to 4 do not include any consideration of how to understand the progress of the carbonation reaction. As a result, the reaction may be stopped before it has fully progressed, or after it has progressed sufficiently and some time has passed, which is problematic in terms of work efficiency.

[0005] In one aspect, this disclosure aims to provide a method for carbonating cementitious hardened material and an apparatus for carbonating cementitious hardened material that can easily estimate the progress of the reaction and improve work efficiency. In another aspect, this disclosure aims to provide a method for producing a cement mixture obtained by efficiently carbonating cementitious hardened material. [Means for solving the problem]

[0006] The inventors of the present invention have found that when a cementitious hardened material is carbonated, the temperature inside the reaction vessel rises and the carbonation proceeds efficiently in the initial stages of the reaction when the carbonation reaction is active, while in the later stages of the reaction, when the reaction has progressed to a certain extent, the temperature inside the reaction vessel decreases and the efficiency of the carbonation reaction also decreases. Next, based on this finding, the inventors investigated a method that can easily estimate the progress of the reaction and found the following method.

[0007] One aspect of this disclosure provides a method for carbonating a cementitious hardened body, comprising: step A, supplying a gas containing carbon dioxide into a container containing a mixture of cementitious hardened body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas; and step B, changing the reaction conditions for carbonation based on the temperature inside the container.

[0008] In step A above, for example, if the temperature inside the container is rising, it is presumed that the carbonation of the cementitious hardened material is in progress. In such cases, the reaction can be continued by maintaining the carbonation reaction conditions. On the other hand, in step B above, if the temperature inside the container is not rising, the carbonation reaction conditions can be changed in step B to promote the reaction. Also, if the temperature inside the container rises once and then falls, it means that the carbonation of the cementitious hardened material has progressed sufficiently, so the carbonation reaction conditions can be changed in step B to stop the reaction. Thus, by using the above method, the progress of the carbonation reaction of the cementitious hardened material can be estimated using the temperature inside the container as a simple indicator, and work efficiency can be improved.

[0009] Another aspect of this disclosure provides a method for producing a cement mixture obtained by carbonating a cementitious hardened body, comprising: step A, supplying a gas containing carbon dioxide into a container containing a mixture of cementitious hardened body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas; and step B, changing the reaction conditions for carbonation based on the temperature inside the container. According to the above method, a cementitious hardened body can be carbonized efficiently to produce a cement mixture.

[0010] Another aspect of this disclosure provides a carbonation apparatus for cementitious hardened bodies, comprising: a container configured to contain a mixture; a temperature detector for detecting the temperature inside the container; a gas supply unit for supplying a gas containing carbon dioxide into the container; and a control unit for adjusting the amount of gas supplied from the gas supply unit based on measurement data from the temperature detector.

[0011] In the above apparatus, a mixture of cementitious hardened material and water is placed in a container, and a gas containing carbon dioxide is supplied into the container from a gas supply unit to carry out the carbonation reaction of the cementitious hardened material. During the carbonation reaction, the temperature inside the container is detected by a temperature detector, and the progress of the reaction can be easily estimated from the temperature measurement data inside the container. Furthermore, the amount of gas supplied into the container from the gas supply unit can be adjusted based on the estimation result. In this way, the above apparatus can improve the work efficiency when carbonating cementitious hardened material. [Effects of the Invention]

[0012] In one aspect, this disclosure provides a method and apparatus for carbonating cementitious hardened materials that can easily estimate the progress of the reaction and improve work efficiency. In another aspect, this disclosure provides a method for producing a cement mixture obtained by efficiently carbonating cementitious hardened materials. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram showing one embodiment of a carbonation apparatus for cementitious hardened materials. [Figure 2] Figure 2 is a graph showing the measurement results for Example 1. [Figure 3] Figure 3 is a graph showing the measurement results for Example 2. [Figure 4] Figure 4 is a graph showing the measurement results for Example 3. [Modes for carrying out the invention]

[0014] The embodiments for implementing this disclosure (hereinafter referred to as "this embodiment") will be described in detail below, with reference to the drawings as appropriate. The dimensional ratios of each element in the drawings are not limited to those shown. This disclosure is not limited to the following embodiments.

[0015] In the present specification, a numerical range indicated by the term "to" includes the numerical values stated before and after "to" as the minimum value and the maximum value, respectively. In addition, in the numerical ranges described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another stepwise described numerical range. Further, in the numerical ranges described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the Examples.

[0016] [Method for carbonation of hardened cementitious body] A method for carbonating a hardened cementitious body according to one embodiment comprises Step A of supplying a gas containing carbon dioxide into a container accommodating a mixture containing the hardened cementitious body and water, and measuring the temperature inside the container while bringing the mixture and the gas into contact with each other, and Step B of changing the carbonation reaction conditions based on the temperature inside the container. According to such a method, in the method of carbonating a hardened cementitious body, the progress of the reaction can be estimated by a simple method, and the working efficiency can be improved.

[0017] In Step A, first, a mixture containing a hardened cementitious body and water is accommodated in a container. Then, a gas containing carbon dioxide is supplied into the container, and the temperature inside the container is measured while bringing the mixture and the gas into contact with each other. As the container, a container that allows gas to be introduced thereinto and allows gas to be discharged therefrom can be used. Further, in order to reduce the influence of outside air and the like on the measured value of the temperature inside the container, it is preferable that the container has a structure that can be hermetically sealed at portions other than the paths for supplying and discharging gas such as pipes during the carbonation reaction of the hardened cementitious body.

[0018] In Step A, the mixture may be stirred while being in contact with the gas containing carbon dioxide inside the container. By stirring the mixture, the unreacted hardened cementitious body and carbon dioxide are easily brought into contact with each other, and the carbonation reaction of the hardened cementitious body can be promoted. The stirring of the mixture may be performed by, for example, a conventional stirrer.

[0019] The filling ratio of the mixture in the container may be 20 to 40% or 30 to 40%. In this case, the efficiency of the carbonation reaction of the hardened cementitious body can be improved. The term "filling ratio" as used in the present specification refers to the ratio of the volume of the accommodated mixture to the internal volume of the container (unit: %).

[0020] The container in which the mixture containing the hardened cementitious body and water is accommodated may be prepared by accommodating a previously prepared mixture containing the hardened cementitious body and water into the container, or may be prepared by mixing the hardened cementitious body and water inside the container.

[0021] The hardened cementitious body is a hardened body obtained by hardening a composition containing cement and water. The hardened cementitious body may be any of a hardened cement paste body, a hardened mortar body, and a hardened concrete body. Examples of the cement include various cements such as Portland cement, blended cement, and eco-cement. Further, the hardened cementitious body may be, for example, waste material of building materials made of concrete or mortar, waste material of hardened cement paste body, or waste such as sludge generated from ready-mixed concrete. The hardened cementitious body may be obtained by crushing concrete lumps. Effective utilization of resources can be achieved by using such waste. The shape and size of the hardened cementitious body are not particularly limited.

[0022] The hardened cementitious body may be a crushed material. It may be classified using a test sieve specified in JIS Z 8801-1:2019 for the hardened cementitious body, or may have an average particle diameter (such as d50 on a volume basis or a number basis) measured by a laser particle size distribution analyzer. The particle size may be 40 mm or less, may be 10 mm or less, and may be 1 mm or less.

[0023] The bulk density of the hardened cementitious body may be 0.5 to 1.2 kg / L, 0.6 to 1.1 kg / L, or 0.7 to 1.0 kg / L. Thereby, the efficiency of the carbonation reaction of the hardened cementitious body can be further improved.

[0024] The age of the cementitious body is not particularly limited; for example, it may be 1 day or older, 7 days or older, 14 days or older, or 1 year or older.

[0025] The cementitious body may contain moisture. The moisture content in the cementitious body may be, for example, 15% by mass or more, or 20% by mass or more. The moisture content in the cementitious body may be, for example, 70% by mass or less, or 60% by mass or less.

[0026] The water content in a mixture containing cementitious hardened material and water may be 10 to 50 parts by mass, 15 to 40 parts by mass, or 15 to 30 parts by mass per 100 parts by mass of cementitious hardened material. In this case, the carbonation reaction of the cementitious hardened material tends to proceed more easily.

[0027] The gas containing carbon dioxide is not particularly limited and may be, for example, exhaust gas, such as exhaust gas from a factory, an incinerator, or exhaust gas emitted from equipment such as an electrostatic precipitator. The gas supply rate may be, for example, 0.5 to 50 L / min, 1 to 30 L / min, 5 to 30 L / min, or 10 to 30 L / min if the carbonation container is small. If the carbonation apparatus is large, the gas supply rate may be, for example, 50 to 1000 L / min, 100 to 900 L / min, or 200 to 800 L / min. The gas temperature may be 10°C or higher, and may be 20 to 150°C, 30 to 120°C, or 30 to 70°C. If the reaction is carried out in a container, the gas temperature may be the temperature at the inlet of the container.

[0028] The carbon dioxide content in the gas may be 1% or more by volume, 5% or more by volume, or 10% or more by volume, and may be 100% or less by volume, 70% or less by volume, or 50% or less by volume, or 1 to 100% by volume, 5 to 70% by volume, or 10 to 50% by volume. The gas may contain nitrogen, oxygen, volatile organic compounds, water (water vapor), etc., in addition to carbon dioxide.

[0029] The temperature inside the container may be measured, for example, by a temperature measuring device such as a thermocouple placed inside the reactor. The temperature measuring device is not limited to a thermocouple; any device capable of measuring the temperature inside the reactor is acceptable.

[0030] Step A may include a step of stirring or agitating the mixture. By stirring or agitating the mixture, the unreacted cementitious material can come into contact with carbon dioxide, thereby promoting the carbonation reaction of the cementitious material. Methods for stirring or agitating the mixture include stirring the mixture using a mixer housed in a container, and agitating the contents of the container by shaking the container itself.

[0031] In step B, the reaction conditions for the carbonation reaction of the cementitious hardened material are changed based on the temperature inside the container measured in step A. In step B, the progress of the carbonation reaction of the cementitious hardened material is determined based on the measured temperature inside the container, and the reaction conditions for carbonation are changed to complete the reaction efficiently. The reaction conditions may be changed by changing at least one of the gas supply amount and the proportion of carbon dioxide in the gas. For example, if the temperature inside the container measured in step A has not risen since the start of the reaction, the reaction is considered not to have progressed sufficiently, and the reaction conditions are changed to accelerate the reaction. If the temperature inside the container measured in step A tends to rise and then fall, the reaction is considered to have progressed sufficiently, and the reaction conditions are changed to stop the reaction.

[0032] Modifications to the reaction conditions that promote the reaction include, for example, increasing the supply of carbon dioxide to the container, stirring the mixture, and agitating the container. These operations may be performed individually or in combination. The method of increasing the supply of carbon dioxide may be by increasing the supply of gas, or by increasing the proportion of carbon dioxide in the supplied gas. These operations may be performed individually or in combination.

[0033] Modifications to the reaction conditions that suppress or stop the reaction include, for example, stopping the supply of carbon dioxide to the container, stopping the stirring of the mixture, and stopping the shaking of the container. These operations may be performed individually or in combination.

[0034] [Method for manufacturing cement mixtures] A method for producing a cement mixture obtained by carbonating a cementitious body according to one embodiment comprises: step A, which involves supplying a gas containing carbon dioxide into a container containing a mixture of cementitious body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas; and step B, which involves changing the reaction conditions based on the temperature inside the container. In other words, the cement mixture produced by the production method according to one embodiment may be produced by the carbonation method of cementitious body according to the above embodiment. According to the above production method, a cementitious body can be carbonized efficiently to obtain a cement mixture.

[0035] There are no particular restrictions on the use of cement mixtures; as long as they are used in combination with cement, there are no specific limitations. However, they can also be used as solidifying agents, such as soil conditioners.

[0036] [Carbonation device for hardened cementum] Figure 1 shows a schematic diagram of a cementitious carbonation apparatus according to one embodiment. The cementitious carbonation apparatus 10 according to one embodiment comprises a container 1 configured to contain a mixture, a temperature detector 2 for detecting the temperature inside the container, a gas supply unit 3 for supplying gas containing carbon dioxide into the container 1, and adjustment units 4A and 4B for adjusting the amount of gas supplied from the gas supply unit 3 based on the measurement data of the temperature detector 2. One embodiment of the above-described method for carbonating cementitious carbonation and the method for producing a cementitious mixture obtained by carbonating cementitious carbonation can be carried out, for example, by using the cementitious carbonation apparatus 10 described above.

[0037] The shape of container 1 is not particularly limited as long as it can contain the mixture. To reduce the influence of outside air and other factors on the temperature measurement inside the container, it is preferable that container 1 be airtight in all parts except for the gas supply path such as piping.

[0038] Container 1 may be equipped with a stirrer. By stirring the mixture inside the container using the stirrer, the carbonation reaction of the cementitious hardened material can be accelerated.

[0039] Container 1 may be configured to be rotatable or oscillating in order to promote the carbonation reaction of the cementitious hardened body. Container 1 may be rotated or oscillated by a drive unit provided within Container 1, or by equipment other than Container 1, such as an oscillating platform.

[0040] The gas supply unit 3 is connected to the container 1, and the gas supply unit 3 can introduce gas containing carbon dioxide into the container 1. The gas supply unit 3 may supply gases other than carbon dioxide. Examples of gases other than carbon dioxide include nitrogen, air, and atmospheric gas. The gas supply unit 3 may have cylinders such as a carbon dioxide (CO2) cylinder and a nitrogen (N2) cylinder. In Figure 1, the gas supply unit 3 has a carbon dioxide cylinder 3A and a nitrogen cylinder 3B, but the gas supply unit of the cementitious body carbonization apparatus according to this embodiment does not need to have a carbon dioxide cylinder 3A and a nitrogen cylinder 3B; it is sufficient if it can supply gas containing carbon dioxide.

[0041] The gas supply adjustment units 4A and 4B are installed in the piping connecting the gas supply unit 3 and the container 1. The signals from the temperature detector 2 are input to each of the gas supply adjustment units 4A and 4B. These gas supply adjustment units 4A and 4B adjust the amount of gas supplied from the gas supply unit 3 to the container 1 based on the measurement data from the temperature detector 2. Although Figure 1 shows two adjustment units 4A and 4B, the number of adjustment units is not limited to this and may be changed depending on, for example, the number of types of gas used.

[0042] The apparatus 10 shown in Figure 1 includes a thermocouple 5 attached to a container 1. The thermocouple 5 is connected to a temperature detector 2, and the temperature inside the container 1 can be measured by the thermocouple 5. Note that the temperature measuring unit for measuring the temperature inside the container 1 is not limited to a thermocouple; the temperature inside the container 1 may be measured by a temperature measuring unit other than a thermocouple.

[0043] The apparatus 10 shown in Figure 1 includes a rocking platform 6. The rocking platform 6 allows the container 1 to be rocked. The means for rocking the container 1 are not limited to the rocking platform; the container 1 may be rocked by means other than the rocking platform. In a modified example, the apparatus 10 may also include a drive unit for rotating the container 1.

[0044] The above-described embodiment includes the following: [1] A method for carbonating a cementitious body, comprising: step A, supplying a gas containing carbon dioxide into a container containing a mixture of the cementitious body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas; and step B, changing the reaction conditions for carbonation based on the temperature inside the container. [2] The method according to [1], wherein the reaction conditions are modified by changing at least one of the amount of gas supplied and the proportion of carbon dioxide in the gas. [3] The method according to [1] or [2], wherein step A comprises a step of stirring or oscillating the mixture. [4] The method according to any one of [1] to [3], wherein the amount of water in the mixture relative to 100 parts by mass of the cementitious hardened body before supplying the gas containing carbon dioxide in step A is 10 to 50 parts by mass. [5] The method according to any one of [1] to [4], wherein the filling rate of the mixture in the container is 20 to 40%. [6] The method according to any one of [1] to [5], wherein the bulk density of the cementitious hardened body is 0.5 to 1.2 kg / L. [7] A method for producing a cement mixture obtained by carbonizing a cementitious hardened body, comprising: step A, supplying a gas containing carbon dioxide into a container containing a mixture of the cementitious hardened body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas; and step B, changing the reaction conditions for carbonation based on the temperature inside the container. [8] Carbonation apparatus for cementitious hardened bodies, comprising: a container configured to contain a mixture; a temperature detector for detecting the temperature inside the container; a gas supply unit for supplying a gas containing carbon dioxide into the container; and a control unit for adjusting the amount of gas supplied from the gas supply unit based on the measurement data of the temperature detector. [9] The apparatus according to [8], wherein the container is configured to be rotatable or swingable. [Examples]

[0045] The contents of this disclosure will be described in more detail below with reference to examples and comparative examples, but this disclosure is not limited to the following examples.

[0046] <Preparation of hardened cementum> Ordinary Portland cement was mixed with water to achieve a water-cement ratio (W / C) of 0.4, and then cured in the air for 28 days. After curing, the cementitious hardened material was pulverized in a ball mill until the particle size was 0.3 mm or less to obtain a cementitious hardened material. The particle size (average particle diameter) of the cementitious hardened material was measured using a laser particle size distribution analyzer. Table 1 shows the ignition loss and chemical composition of the cementitious hardened material. The ignition loss shown in Table 1 is the value measured in accordance with the method of JIS R 5202:2010 (unit: mass%), and the chemical composition is the value measured in accordance with the description of JIS R 5204:2019 "Method for X-ray fluorescence analysis of cement" (unit: mass%).

[0047] [Table 1]

[0048] The bulk density of the prepared cementitious hardened material was measured to be 0.8 kg / L. The bulk density was determined by filling a container of a predetermined volume with the cementitious hardened material, calculating the mass of the cementitious hardened material from the difference in mass of the container before and after filling, and then dividing this mass by the volume (= volume of the cementitious hardened material).

[0049] [Examples 1-3] Carbonation of cementitious hardened material was carried out in an apparatus having the configuration shown in Figure 1 using the following procedure. First, 12.5 kg of prepared cementitious hardened material and 2.5 kg of water were placed in the apparatus container (capacity: 30 L) and mixed by shaking the container. Carbon dioxide gas alone, or a mixture of carbon dioxide gas and nitrogen gas, was passed through the container at the flow rates shown in Tables 2 to 4 to carry out the carbonation reaction of the cementitious hardened material. During the carbonation reaction, the mixture was collected at regular intervals, and the collected mixture was heated using a thermogravimetric differential thermal analyzer (TG-DTA) under the following conditions, and the weight loss (unit: mass%) between 600°C and 800°C during heating was measured. Measurements were taken twice at each time interval, and the average value was taken as the ignition loss (unit: mass%). The results are shown in Tables 2 to 4. [Thermogravimetric differential thermal analysis conditions] The temperature was raised from room temperature to 1000°C at a rate of 10°C / min. After that, heating was stopped and the temperature was lowered to 40°C.

[0050] <Amount of carbon dioxide (CO2) reaction [mass%]> The ignition loss measured above was considered to represent the amount of carbon dioxide in the cementitious hardened material at the time of measurement, and the amount of carbon dioxide (CO2) reaction (unit: mass%) was calculated using the following formula (1). For example, the amount of carbon dioxide (CO2) reaction (unit: mass%) when the reaction time is 30 minutes is the value obtained by subtracting the ignition loss (unit: mass%) of the cementitious hardened material at the start of measurement (at 0 minutes) from the ignition loss (unit: mass%) of the sample collected after 30 minutes. The results are shown in Tables 2 to 4. Carbon dioxide (CO2) reaction amount [mass%] = Loss on ignition during this measurement [mass%] - Loss on ignition at the start of measurement [mass%] ... (1)

[0051] <Amount of carbon dioxide (CO2) reacted per 1 kg of hardened cementitious material [g]> The amount of carbon dioxide (CO2) reacted per 1 kg of cementitious hardened material (in g) was calculated from the obtained amount of carbon dioxide (CO2) reacted (in mass%) using the following formula (2). In formula (2), "reaction time" refers to the reaction time listed in Tables 2-4. The results are shown in Tables 2-4. Carbon dioxide (CO2) reaction amount per 1 kg of hardened cementitious material [g] ={(100 - Loss on ignition during reaction time [mass%]) - (100 - Loss on ignition at the start of measurement [mass%]) × Loss on ignition during reaction time [mass%] - Loss on ignition at the start of measurement [mass%]} × 1000 [g] ÷ 100 ... (2)

[0052] [Table 2]

[0053] [Table 3]

[0054] [Table 4]

[0055] Figures 2-4 are graphs showing the measurement results for Examples 1-3. For example, in the graph in Figure 2 showing the measurement results for Example 1, the amount of carbon dioxide reacted increased significantly until 20 minutes of reaction time, when the temperature inside the container showed an upward trend. However, after 20 minutes of reaction time, when the temperature inside the container showed a downward trend, the increase in the amount of carbon dioxide reacted slowed down. From these results, it can be said that the carbonation reaction of the cementitious hardened material in Example 1 proceeded efficiently until 20 minutes had elapsed from the start of the reaction, and then the reaction slowed down after 20 minutes had elapsed. Similarly, it can be said that the carbonation reaction of the cementitious hardened material in Examples 2 and 3 proceeded efficiently until 30 minutes had elapsed from the start of the reaction, and then the reaction slowed down after 30 minutes had elapsed. Thus, with the carbonation method for cementitious hardened material of this disclosure, the progress of the reaction can be estimated by the simple method of observing the temperature inside the container. Based on this estimation result, operations such as stopping the reaction can be performed, thereby improving work efficiency. [Explanation of Symbols]

[0056] 10...device, 1...container, 2...temperature detector, 3...gas supply unit, 3A...carbon dioxide cylinder, 3B...nitrogen cylinder, 4A,4B...adjustment unit, 5...thermocouple, 6...rocking platform.

Claims

1. A method for carbonizing a cementitious hardened body, Step A involves supplying a gas containing carbon dioxide into a container containing a mixture of the cementitious hardened body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas. A method comprising step B, which involves changing the reaction conditions for carbonation based on the temperature inside the container.

2. The method according to claim 1, wherein the reaction conditions are changed by changing at least one of the supply amount of the gas and the proportion of carbon dioxide in the gas.

3. The method according to claim 1, wherein step A includes a step of stirring or oscillating the mixture.

4. The method according to claim 1, wherein the water content in the mixture relative to 100 parts by mass of the cementitious hardened body is 10 to 50 parts by mass before supplying the gas containing carbon dioxide in step A.

5. The method according to claim 1, wherein the filling rate of the mixture in the container is 20 to 40%.

6. The method according to claim 1, wherein the bulk density of the cementitious hardened body is 0.5 to 1.2 kg / L.

7. A method for producing a cement mixture obtained by carbonizing a hardened cementitious body, Step A involves supplying a gas containing carbon dioxide into a container containing a mixture of the cementitious hardened body and water, and measuring the temperature inside the container while bringing the mixture into contact with the gas. A manufacturing method comprising step B, which involves changing the reaction conditions for carbonation based on the temperature inside the container.

8. A carbonation apparatus for cementitious hardened bodies, comprising: a container configured to contain a mixture; a temperature detector for detecting the temperature inside the container; a gas supply unit for supplying a gas containing carbon dioxide into the container; and a control unit for adjusting the amount of gas supplied from the gas supply unit based on the measurement data from the temperature detector.

9. The apparatus according to claim 8, wherein the container is configured to be rotatable or swingable.

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