Method for evaluating co2 fixation amount and method for evaluating cement amount

Abstract

To provide a new method for evaluating the CO2 fixation amount of a material containing a cement solidified substance and a new method for evaluating the amount of cement.SOLUTION: The method for evaluating a CO2 fixation amount and the method for evaluating the amount of cement include calculating the cement amount (mass%) of the target material by dividing the sulfur content (mass%) of the target material by the sulfur content (mass%) of the cement that was used as the raw material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating a fixed amount of CO2 and a method for evaluating a cement amount. [Background technology]

[0002] Methods for evaluating the amount of CO2 fixed in concrete have been under study for a long time. For example, Non-Patent Document 1 reports a case in which the amount of CO2 fixed was estimated from the results of inorganic carbon analysis. Non-Patent Document 2 reports a case in which the amount of CO2 fixed was estimated from the results of differential thermogravimetric analysis. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Tsuyoshi Torimachi, Kosuke Yokozeki, Ichiro Yoshioka, and Minoru Morioka, "Study on evaluation methods for CO2 fixation amount and changes in physical properties in carbonated cement-based materials," Journal of the Japan Society of Civil Engineers, Vol. 77, No. 2, pp. 37-54, 2021 [Non-patent document 2] Yosuke Nagahama, "Understanding the CO2 absorption effect of concrete structures," SAT Technology Showcase 2015, General Poster Presentation P-72, 2015 Summary of the Invention [Problem to be solved by the invention]

[0004] The main reaction in CO2 fixation in concrete is the reaction of calcium hydroxide in the concrete with carbon dioxide to produce calcium carbonate (Ca(OH)2 + CO2 → CaCO3 + H2O). One of the reasons why it is difficult to accurately evaluate the amount of CO2 fixed in concrete is that CaCO3-containing materials (e.g., limestone aggregate, limestone fine powder, and precipitated calcium carbonate fine powder) may be used as raw materials in concrete production. The CaCO3 introduced into the concrete by the CaCO3-containing raw materials is detected during CO2 fixation analysis, resulting in an overestimation of the amount of CO2 fixed.

[0005] It is against this background that the present disclosure has been made. An objective of the present disclosure is to provide a new method for evaluating the amount of CO2 fixed in materials containing cement solidified materials. [Means for solving the problem]

[0006] The disclosed method for evaluating CO2 fixation focuses on the small amount of sulfur contained in cement. The disclosed method for evaluating CO2 fixation assumes that all of the sulfur contained in the target material originates from the cement used as a raw material. Under this assumption, the disclosed method for evaluating CO2 fixation includes a step of calculating the cement content (mass%) of the target material from the sulfur content (mass%) of the target material and the sulfur content (mass%) of the cement used as a raw material. This step is step (5).

[0007] The method for evaluating the amount of CO2 fixation disclosed herein includes a step of calculating the amount of CaCO3 introduced into the target material by the raw material of the target material. This step is step (10). The CO2 fixation amount evaluation method disclosed herein calculates the amount of CaCO3 brought into concrete by the CaCO3-containing raw material, thereby improving the accuracy of the evaluation of the CO2 fixation amount.

[0008] Specific means for solving the above problems include the following aspects. <1> A method for evaluating the amount of CO2 fixed in a target material including a cement-solidified material, comprising: The method includes the following steps (1) to (11): CO2 fixation evaluation method. Step (1): The hydrochloric acid soluble content (mass %) of the target material is measured. Step (2): The ignition loss (mass%) of the target material is measured. Step (3): The carbon content (mass %) and sulfur content (mass %) of the target material are measured. Step (4): Obtain information on the carbon content (mass%) and sulfur content (mass%) of the cement that was the raw material for the target material. Step (5): The amount of sulfur (mass%) in the target material obtained in step (3) is divided by the amount of sulfur (mass%) in the cement obtained in step (4) to calculate the amount of cement (mass%) in the target material. Step (6): The carbon content (mass%) of the target material obtained in step (3) is converted to the CO content (mass%), and the CO content (mass%) is subtracted from the ignition loss (mass%) of the target material obtained in step (2) to calculate the bound water content (mass%) of the target material. Step (7): The remaining hydrochloric acid soluble fraction (mass%) of the target material obtained in step (1) is calculated by subtracting the amount of cement (mass%) of the target material obtained in step (5) and the amount of bound water (mass%) of the target material obtained in step (6) from the hydrochloric acid soluble fraction (mass%) of the target material obtained in step (1). Step (8): The carbon content (mass%) of the cement in the target material is calculated from the cement content (mass%) of the target material obtained in step (5) and the carbon content (mass%) of the cement obtained in step (4), and the carbon content (mass%) of the cement is converted to the CO content (mass%) of the cement. Step (9): The carbon content (% by mass) of the target material obtained in step (3) is converted to the CO content (% by mass), and the CO content (% by mass) of the cement obtained in step (8) is subtracted from the converted CO content (% by mass) to calculate the remaining CO content (% by mass). Step (10): The amount of CaO (mass%) in the raw material-derived CaCO3 is calculated by subtracting the amount of residual CO2 (mass%) obtained in step (9) from the amount (mass%) of the hydrochloric acid soluble matter obtained in step (7), and the amount of CaO (mass%) is converted to the amount of CaCO3 (mass%) derived from the raw material. Step (11): The amount of CaCO3 (mass%) derived from the raw material obtained in step (10) is subtracted from the remaining amount (mass%) of the hydrochloric acid soluble matter obtained in step (7) to calculate the amount of CO2 fixed (mass%) of the target material. <2> A method for evaluating the amount of CO2 fixed in a target material including a cement-solidified material, comprising: The target material does not contain CaCO3-containing materials as raw materials during manufacturing, The method includes the following steps (3), (4), (5), (8) and (9): CO2 fixation evaluation method. Step (3): The carbon content (mass %) and sulfur content (mass %) of the target material are measured. Step (4): Obtain information on the carbon content (mass%) and sulfur content (mass%) of the cement that was the raw material for the target material. Step (5): The amount of sulfur (mass%) in the target material obtained in step (3) is divided by the amount of sulfur (mass%) in the cement obtained in step (4) to calculate the amount of cement (mass%) in the target material. Step (8): The carbon content (mass%) of the cement in the target material is calculated from the cement content (mass%) of the target material obtained in step (5) and the carbon content (mass%) of the cement obtained in step (4), and the carbon content (mass%) of the cement is converted to the CO content (mass%) of the cement. Step (9): The carbon content (% by mass) of the target material obtained in step (3) is converted to the CO content (% by mass), and the CO content (% by mass) of the cement obtained in step (8) is subtracted from the converted CO content (% by mass) to calculate the remaining CO content (% by mass), i.e., the CO fixation amount (% by mass) of the target material. <3> The target material is a recycled material derived from concrete waste, concrete waste, or in-service concrete, <1> or <2> The method for evaluating the amount of CO2 fixation described in <4> A method for evaluating the cement content of a target material containing cement-solidified material, comprising: The method includes the following steps (3-S), (4-S) and (5): Cement quantity evaluation method. Step (3-S): The sulfur content (mass%) of the target material is measured. Step (4-S): Obtain information on the sulfur content (mass%) of the cement that was the raw material for the target material. Step (5): The amount of sulfur (mass%) of the target material obtained in step (3-S) is divided by the amount of sulfur (mass%) of cement obtained in step (4-S) to calculate the amount of cement (mass%) of the target material. <5> The target material is a recycled material derived from concrete waste, concrete waste, or in-service concrete, <4> The cement amount evaluation method described in . [Effects of the Invention]

[0009] According to the present disclosure, a new method for evaluating the CO2 fixation amount of materials including cement solidified materials is provided. According to the present disclosure, a new method for assessing the cement content of a cement-containing material is provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a wet carbonation device used to carbonate recycled fine powder. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0012] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit value of the numerical range may be replaced with the value shown in the examples.

[0013] In the present disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" means that it may be only A, only B, or a combination of A and B.

[0014] In the present disclosure, the term "step" includes not only an independent step but also a step whose purpose can be achieved even if it cannot be clearly distinguished from other steps.

[0015] When referring to the amount of each component in a composition in the present disclosure, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the multiple substances present in the composition.

[0016] <CO2 Fixation Amount Evaluation Method> The CO2 fixation amount evaluation method of the present disclosure targets materials including cement-solidified materials. Examples of the target materials include recycled materials derived from concrete waste, concrete waste, in-service concrete, recycled materials derived from mortar waste, mortar waste, and in-service mortar. When the target material is in-service concrete or in-service mortar, the CO2 fixation amount calculated by the CO2 fixation amount evaluation method of the present disclosure can be used as an index for the neutralization of in-service concrete or in-service mortar.

[0017] The CO2 fixation amount evaluation method of the present disclosure includes steps (1) to (11) and calculates the CO2 fixation amount of the target material. The key points of steps (1) to (11) are shown in Table 1.

[0018]

Table 1

[0019] Steps (1) to (4) are measurement steps. However, step (4) may or may not be an actual measurement step, as long as information on the carbon amount and sulfur amount can be obtained. Details will be described later. Steps (5) to (11) are calculation steps, and calculations are performed using the measurement values obtained in steps (1) to (4). Details of each step will be described below.

[0020] [Preparation of Samples for Steps (1) to (3)] If the target material is a fine powder, prepare the sample in accordance with JIS R5202:2010 "Methods for chemical analysis of cement" "4. Preparation of cement samples." If the target material is a lump or has a large particle size, crush it and then prepare a sample according to the above standards.

[0021] Prepare samples quickly to minimize exposure to ambient air. Ideally, prepare samples in an inert gas environment. Store prepared samples in airtight containers.

[0022] Each measurement in steps (1) to (3) is carried out quickly to minimize the time the sample is exposed to the ambient air. It is preferable to carry out steps (1) to (3) on the same day to prevent changes in the degree of carbonation of the sample.

[0023] [Process (1)] Step (1) is a step of measuring the hydrochloric acid soluble content (mass %) of a target material. Quantify the insoluble residue (mass%) in accordance with JIS R5202:2010 "Methods for chemical analysis of cement" "6. Method for determining insoluble residue by hydrochloric acid-sodium carbonate method," and subtract this insoluble residue (mass%) from 100 to obtain the hydrochloric acid soluble content (mass%).

[0024] The CO2 fixation amount evaluation method disclosed herein assumes that the hydrochloric acid soluble portion of the target material is the sum of cement, bound water, CaCO3 brought into the target material by the raw materials used during production (referred to as "raw material-derived CaCO3"), and CO2 fixed by carbonation of the target material (referred to as "fixed CO2"), and performs the calculation process based on this assumption.

[0025] CaCO3-containing materials used in the production of concrete or mortar, i.e., materials that introduce raw material-derived CaCO3 into the target material, include limestone aggregate, limestone fine powder, and precipitated calcium carbonate fine powder.

[0026] [Process (2)] Step (2) is a step of measuring the ignition loss (mass %) of the target material. The loss on ignition is measured in accordance with JIS R5202:2010 "Methods for chemical analysis of cement" "5. Methods for determining loss on ignition" or by thermogravimetric analysis. Thermogravimetric analysis is performed using 10 mg to 20 mg of sample, with a heating rate of 10°C / min to 20°C / min, a final temperature of 1000°C, and a nitrogen flow of 50 ml / min to 200 ml / min, and the average value of three measurements is calculated.

[0027] The CO2 fixation amount evaluation method disclosed herein assumes that the ignition loss of the target material is the sum of bound water and CO2 released by oxidation of carbon, and performs the calculation process under this assumption.

[0028] [Process (3)] Step (3) is a step of measuring the carbon content (mass%) and sulfur content (mass%) of the target material. The carbon content and sulfur content may be measured simultaneously or separately. From the viewpoints of simplicity and accuracy, the preferred measurement method is the combustion-infrared absorption method, in which a sample is burned in an oxygen stream, and carbon and sulfur in the sample are extracted as oxides and quantified.

[0029] [Process (4)] Step (4) is a step of obtaining information on the carbon content (mass %) and sulfur content (mass %) of the cement that was the raw material of the target material (referred to as "raw cement"). Examples of embodiments of step (4) include obtaining a recipe for the target material at the time of production, learning the manufacturer and product number of the raw cement from the recipe, obtaining a cement test report for that product number at the time of production of the target material, and learning the carbon and sulfur contents from the cement test report; measuring and recording the carbon and sulfur contents of raw cement as a sample at the time of production of the target material; and measuring the carbon and sulfur contents of raw cement that has been stored in an inert gas environment or in an airtight container as a sample.

[0030] When measuring the carbon and sulfur contents of raw cement, the sample to be used for the measurement should be prepared in accordance with JIS R5202:2010 "Methods for Chemical Analysis of Cement" "4. Preparation of Cement Samples." From the viewpoints of simplicity and accuracy, the combustion-infrared absorption method is preferred as the measurement method.

[0031] The measurement methods performed in steps (1) to (4) are widely used in the technical fields related to cement and concrete, and are relatively simple. The method for evaluating the amount of CO2 fixation disclosed herein does not require the construction of a new special measurement device.

[0032] [Process (5)] Step (5) is a step of calculating the cement content (mass%) of the target material by dividing the sulfur content (mass%) of the target material obtained in step (3) by the sulfur content (mass%) of the cement obtained in step (4). The calculation formula is as follows:

[0033] Amount of cement in target material (mass%) = Amount of sulfur in target material (mass%) ÷ Amount of sulfur in raw cement (mass%) × 100

[0034] In the method for evaluating the amount of CO2 fixation disclosed herein, all sulfur contained in the target material is assumed to originate from the raw cement, and step (5) is carried out under this assumption.

[0035] [Process (6)] Step (6) is a step of converting the carbon content (mass%) of the target material obtained in step (3) into the CO content (mass%), and subtracting the CO content (mass%) from the ignition loss (mass%) of the target material obtained in step (2) to calculate the bound water content (mass%) of the target material.

[0036] Since the atomic weight of carbon is 12 and the molar mass of CO2 is 44, the formula for converting the amount of carbon in a material to the amount of CO2 is as follows:

[0037] CO2 amount (mass%) = carbon amount of target material (mass%) ÷ 12 × 44

[0038] The ignition loss of the target material obtained in step (2) is the sum of bound water and CO2 released by oxidation of carbon. The amount of carbon in the target material converted to CO2 is subtracted from the ignition loss of the target material, and the resulting value is used as the amount of bound water.

[0039] [Process (7)] Step (7) is a step of calculating the remaining hydrochloric acid soluble content (mass%) of the target material obtained in step (1) by subtracting the cement content (mass%) of the target material obtained in step (5) and the bound water content (mass%) of the target material obtained in step (6) from the hydrochloric acid soluble content (mass%) of the target material obtained in step (1).

[0040] The hydrochloric acid soluble content of the target material obtained in step (1) is the sum of cement, bound water, CaCO3 derived from the raw materials, and fixed CO2. The cement and bound water are subtracted from the hydrochloric acid soluble content, and the resulting value is taken as the remaining hydrochloric acid soluble content. In other words, the remaining hydrochloric acid soluble content is the sum of CaCO3 derived from the raw materials and fixed CO2.

[0041] [Process (8)] Step (8) is a step of calculating the carbon content (mass%) of the cement in the target material from the cement content (mass%) of the target material obtained in step (5) and the carbon content (mass%) of the cement obtained in step (4), and converting the carbon content (mass%) of the cement content into the CO content (mass%) of the cement.

[0042] The formula for calculating the carbon content of the cement in the target material from the cement content of the target material and the carbon content of the raw cement is as follows:

[0043] Carbon content of cement in target material (mass%) = Cement content of target material (mass%) × Carbon content of raw cement (mass%) ÷ 100

[0044] Since the atomic weight of carbon is 12 and the molar mass of CO2 is 44, the formula for converting the amount of carbon in cement to the amount of CO2 in cement is as follows:

[0045] Amount of CO2 in cement (mass%) = Amount of carbon in cement (mass%) ÷ 12 × 44

[0046] [Process (9)] Step (9) is a step of converting the carbon content (mass%) of the target material obtained in step (3) into a CO content (mass%), subtracting the CO content (mass%) of the cement portion obtained in step (8) from the converted CO content (mass%), and calculating the remaining CO content (mass%).

[0047] Since the atomic weight of carbon is 12 and the molar mass of CO2 is 44, the formula for converting the amount of carbon in a material to the amount of CO2 is as follows:

[0048] CO2 amount (mass%) = carbon amount of target material (mass%) ÷ 12 × 44

[0049] The amount of CO2 for cement is subtracted from the value obtained by converting the amount of carbon in the target material into the amount of CO2, and the resulting value is regarded as the remaining amount of CO2. In the CO2 fixation amount evaluation method of the present disclosure, the remaining CO2 amount is assumed to be the sum of the CO2 content of the CaCO3 derived from the raw material and the fixed CO2, and the subsequent calculation steps are performed under this assumption.

[0050] [Process (10)] Step (10) is a step of calculating the amount of CaO (mass%) in the raw material-derived CaCO by subtracting the amount of residual CO (mass%) obtained in step (9) from the amount (mass%) of the hydrochloric acid-soluble matter obtained in step (7), and converting the amount of CaO (mass%) to the amount of CaCO (mass%) derived from the raw material.

[0051] The value obtained by subtracting the remaining CO amount (i.e., the sum of the CO content of the CaCO3 derived from the raw materials and the fixed CO2) from the remainder of the hydrochloric acid soluble matter (i.e., the sum of the CaCO3 derived from the raw materials and the fixed CO2) is the CaO content of the CaCO3 derived from the raw materials.

[0052] Since the molar mass of CaO is 56 and the molar mass of CaCO3 is 100, the formula for converting CaO to CaCO3 is as follows:

[0053] Amount of CaCO3 derived from raw materials = Amount of CaO ÷ 56 x 100

[0054] [Process (11)] Step (11) is a step of calculating the amount of CO2 fixation (mass%) of the target material by subtracting the amount of CaCO3 derived from the raw material (mass%) obtained in step (10) from the remaining amount (mass%) of the hydrochloric acid soluble matter obtained in step (7).

[0055] The value obtained by subtracting the amount of CaCO3 derived from the raw materials from the remainder of the hydrochloric acid soluble matter (i.e., the total of CaCO3 derived from the raw materials and fixed CO2) is the amount of CO2 fixed in the target material.

[0056] Step (11) may be a step of calculating the amount of fixed CO2 (% by mass) of the target material by subtracting the amount of cement (% by mass) obtained in step (5), the amount of bound water (% by mass) obtained in step (6), and the amount of CaCO3 derived from the raw materials obtained in step (10) from the hydrochloric acid soluble matter (% by mass) of the target material obtained in step (1). Subtracting the amount of CaCO3 derived from the raw materials from the remainder of the hydrochloric acid soluble matter is synonymous with subtracting the amount of cement, the amount of bound water, and the amount of CaCO3 derived from the raw materials from the hydrochloric acid soluble matter.

[0057] In the method for evaluating the amount of CO2 fixation disclosed herein, if it is known in advance that no CaCO3-containing material is used as a raw material in the production of the target material, steps (10) and (11) and steps (1), (2), (6), and (7) required to reach step (10) do not need to be performed. This is because the amount of CaCO3 (mass%) derived from the raw materials obtained in step (10) is theoretically zero, and therefore does not need to be derived by calculation.

[0058] That is, when the target material does not contain a CaCO3-containing material as a raw material during production, the CO2 fixation amount evaluation method of the present disclosure only requires performing steps (3), (4), (5), (8), and (9). In this case, the remaining CO2 amount (% by mass) obtained in step (9) is the CO2 fixation amount (% by mass) of the target material.

[0059] Whether or not the target material contains a CaCO3-containing material as a raw material at the time of manufacturing can be known from the recipe of the target material at the time of manufacturing.

[0060] When the target material contains a CaCO3-containing material as a raw material during production, but the amount of the CaCO3-containing material mixed is small compared to the amount of cement mixed, or when the CaCO3 content is low based on the breakdown of the components of the CaCO3-containing material, the amount of fixed CO2 (mass%) may be calculated by performing only steps (3), (4), (5), (8), and (9), just as when the target material does not contain a CaCO3-containing material as a raw material during production.

[0061] The target material may contain chemical admixtures (materials containing carbon) as raw materials during manufacturing. Generally, the amount of chemical admixtures mixed is small compared to the amount of cement and aggregate mixed, so the CO2 fixation amount evaluation method disclosed herein evaluates the amount of CO2 fixation while ignoring the amount of chemical admixtures mixed.

[0062] The target material may contain organic fibers and / or carbon fibers (collectively referred to as "fibers") as raw materials during production. When the fiber material and blending amount are known from the recipe for the target material during production, the CO2 fixation amount evaluation method of the present disclosure may include the following fiber-related correction step.

[0063] [Correction process for fibers] Since fibers are insoluble in dilute hydrochloric acid, the hydrochloric acid-soluble portion of the target material determined in step (1) does not include fibers. On the other hand, the ignition loss of the target material determined in step (2) includes CO2 released by oxidation of carbon from the fibers, the carbon content of the target material determined in step (3) includes carbon from the fibers, and the remaining CO2 content of the fibers is included in the amount of CO2 determined in step (9). Under the above provisions, the following fiber correction process is carried out between step (9) and step (10). Fiber-related correction process: The fiber material and amount are identified from the formulation table at the time of manufacturing the target material, the carbon content (mass%) of the fiber contained in the target material is calculated, the carbon content of the fiber is converted to the CO2 content (mass%) of the fiber, and the CO2 content of the fiber is subtracted from the residual CO2 content obtained in step (9) to calculate the corrected residual CO2 content. Then, the corrected remaining CO2 amount is used in the calculation in step (10).

[0064] The fiber correction step is an optional step. When the target material contains fibers as raw materials during manufacturing but the amount of fibers mixed is small compared to the amounts of cement and aggregate mixed, the CO2 fixation amount evaluation method disclosed herein may evaluate the CO2 fixation amount while ignoring the fiber mixture.

[0065] <Cement amount evaluation method> The present disclosure also provides a new method for evaluating the cement content of target materials containing cement-solidified products. Target materials for the cement content evaluation method of the present disclosure include recycled materials derived from waste concrete, waste concrete, in-service concrete, recycled materials derived from waste mortar, waste mortar, and in-service mortar.

[0066] The cement content evaluation method disclosed herein assumes that all sulfur contained in the target material originates from raw cement, and under this assumption, calculates the cement content (mass%) of the target material from the sulfur content (mass%) of the target material and the sulfur content (mass%) of the raw cement.

[0067] The cement amount evaluation method of the present disclosure includes the following steps (3-S), (4-S), and (5).

[0068] Step (3-S): The sulfur content (mass%) of the target material is measured. Step (4-S): Obtain information on the sulfur content (mass%) of the cement that was the raw material for the target material. Step (5): The amount of sulfur (mass%) of the target material obtained in step (3-S) is divided by the amount of sulfur (mass%) of cement obtained in step (4-S) to calculate the amount of cement (mass%) of the target material.

[0069] Step (3-S) is substantially the same as step (3), and step (4-S) is substantially the same as step (4). However, to calculate the cement content of the target material, it is sufficient to know the sulfur content of the target material and the sulfur content of the raw cement. Therefore, the cement content evaluation method does not require measuring the carbon content of the target material or obtaining information on the carbon content of the raw cement.

[0070] Step (5) of the cement amount evaluation method is the same as step (5) of the CO2 fixation amount evaluation method. [Example]

[0071] The method for evaluating the amount of CO2 fixation and the method for evaluating the amount of cement according to the present disclosure will be specifically described below with reference to examples. However, the embodiments of the present disclosure are not limited to the following examples.

[0072] 1. Manufacturing recycled fine powder Concrete specimens were manufactured and dismantled, and recycled aggregate was produced. The recycled fine powder generated during the production of recycled aggregate was collected.

[0073] The materials of the concrete specimens are shown in Table 2, and the mix proportions are shown in Table 3. The concrete specimens were flat plates measuring 1000mm x 2500mm x 200mm. After demolding, they were steam-cured at 70°C for two weeks, then dried for one week before being dismantled. The dismantled debris was subjected to autogenous blasting to produce recycled aggregate, and the recycled fines generated during the autogenous blasting process were collected.

[0074] [Table 2]

[0075] [Table 3]

[0076] The carbon and sulfur contents of the cement and crushed limestone shown in Table 2 were measured using the combustion-infrared absorption method with an EMIA-Pro carbon-sulfur analyzer (high-frequency induction heating type, manufactured by Horiba, Ltd.). The sample preparation method used for this measurement was as described above.

[0077] The carbon content of the crushed limestone, 11.70 mass%, and sulfur content of 0.00 mass%, shown in Table 2, are very close to the theoretical values ​​(carbon content of 12 mass%, sulfur content of 0 mass%) calculated from the limestone composition formula CaCO3, confirming the accuracy of carbon-sulfur analysis using the combustion-infrared absorption method.

[0078] 2. Manufacturing of CO2 fixation materials The recycled fine powder was subjected to wet carbonation treatment to produce a CO2 fixation material.

[0079] The wet carbonation process of recycled fine powder was carried out using a bench-scale wet carbonation equipment (reaction tank capacity 2m 3 ) was used. Figure 1 shows an outline of the wet carbonation device. The wet carbonation process using this device is as follows. The recycled fine powder was added from the top of the reactor and mechanically stirred with a stirring blade while flowing in water for 1 hour. CO2 gas was then supplied from the bottom. After confirming that the pH in the reactor had reached 6.8, the contents were withdrawn from the bottom of the reactor in a solid-liquid mixture, and the carbonated recycled fine powder was recovered using a filter press. It took 30 minutes from the start of CO2 supply for the pH to reach 6.8.

[0080] 3.Evaluation of CO2 fixation amount The samples to be subjected to steps (1) to (3) were prepared as described above, and measurements were carried out in each step. The measured values ​​are shown in Table 4. The measurement of the ignition loss in step (2) was carried out in accordance with JIS R5202:2010 "Methods for chemical analysis of cement" and "5. Method for quantitative determination of ignition loss." The carbon and sulfur amounts in step (3) were measured using a carbon-sulfur analyzer EMIA-Pro (high-frequency induction heating type, manufactured by Horiba, Ltd.) based on the combustion-infrared absorption method.

[0081] Steps (5) to (11) were carried out based on the measured values ​​from steps (1) to (3) and the carbon and sulfur contents of the cement shown in Table 2. Table 4 shows the calculation results of the calculation steps.

[0082] [Table 4]

[0083] The amount of CO2 fixed by the recycled fine powder was 1.79% by mass, while the amount of CO2 fixed by the carbonation-treated recycled fine powder (CO2-fixing material) was 5.76% by mass. The fact that the amount of CO2 fixed was greater after carbonation supports the validity of the CO2 fixation amount evaluation method disclosed herein.

Claims

1. CO of target materials including cement solidified materials ２ 1. A method for assessing a fixed amount, comprising: The method includes the following steps (1) to (11): CO ２ Fixed quantity evaluation method. Step (1): The hydrochloric acid soluble content (mass %) of the target material is measured. Step (2): The ignition loss (mass%) of the target material is measured. Step (3): The carbon content (mass%) and sulfur content (mass%) of the target material are measured. Step (4): Obtain information on the carbon content (mass%) and sulfur content (mass%) of the cement that was the raw material of the target material. Step (5): The amount of sulfur (% by mass) of the target material obtained in step (3) is divided by the amount of sulfur (% by mass) of cement obtained in step (4) to calculate the amount of cement (% by mass) of the target material. Step (6): The carbon content (mass%) of the target material obtained in step (3) is calculated by CO ２ The CO content is converted into a CO content (mass%) and then subtracted from the ignition loss (mass%) of the target material obtained in step (2). ２ The amount (mass%) of bound water in the target material is calculated by subtracting the amount (mass%) of bound water in the target material. Step (7): The amount of cement (% by mass) of the target material obtained in step (5) and the amount of bound water (% by mass) of the target material obtained in step (6) are subtracted from the hydrochloric acid soluble matter (% by mass) of the target material obtained in step (1) to calculate the remaining hydrochloric acid soluble matter (% by mass). Step (8): Calculate the carbon content (mass%) of the cement in the target material from the cement content (mass%) of the target material obtained in step (5) and the carbon content (mass%) of the cement obtained in step (4), and use the carbon content (mass%) of the cement as the CO content of the cement. ２ Convert to mass (%). Step (9): The carbon content (mass%) of the target material obtained in step (3) is calculated by CO ２ The CO ２ The amount (mass%) of the cement obtained in step (8) ２ The remaining CO ２ The amount (mass%) is calculated. Step (10): Removing the remaining CO obtained in step (9) from the remaining (mass%) of the hydrochloric acid soluble matter obtained in step (7). ２ The amount (mass%) of CaCO3 derived from the raw material was subtracted. ３ The CaO content (mass%) of the raw material-derived CaCO ３ Convert to mass (%). Step (11): The remaining (mass%) of the hydrochloric acid soluble matter obtained in step (7) is extracted with CaCO3 derived from the raw material obtained in step (10). ３ The CO content (mass%) of the target material is calculated by subtracting ２ The fixed amount (mass %) is calculated.

2. CO of target materials including cement solidified materials ２ 1. A method for assessing a fixed amount, comprising: The target material is made of CaCO ３ Contains no contained materials The method includes the following steps (3), (4), (5), (8) and (9): CO ２ Fixed quantity evaluation method. Step (3): The carbon content (mass%) and sulfur content (mass%) of the target material are measured. Step (4): Obtain information on the carbon content (mass%) and sulfur content (mass%) of the cement that was the raw material of the target material. Step (5): The amount of sulfur (% by mass) of the target material obtained in step (3) is divided by the amount of sulfur (% by mass) of cement obtained in step (4) to calculate the amount of cement (% by mass) of the target material. Step (8): Calculate the carbon content (mass%) of the cement in the target material from the cement content (mass%) of the target material obtained in step (5) and the carbon content (mass%) of the cement obtained in step (4), and use the carbon content (mass%) of the cement as the CO content of the cement. ２ Convert to mass (%). Step (9): The carbon content (mass%) of the target material obtained in step (3) is calculated by CO ２ The CO ２ The amount (mass%) of the cement obtained in step (8) ２ The remaining CO ２ Amount (mass%) of CO in the target material ２ The fixed amount (mass %) is calculated.

3. 3. The CO2 treatment method according to claim 1, wherein the target material is a recycled material derived from waste concrete, waste concrete, or in-service concrete. ２ Fixed quantity evaluation method.

4. A method for evaluating the cement content of a target material containing cement-solidified material, comprising: The method includes the following steps (3-S), (4-S), and (5): Cement quantity evaluation method. Step (3-S): The sulfur content (mass%) of the target material is measured. Step (4-S): Obtain information on the sulfur content (mass%) of the cement that was the raw material for the target material. Step (5): The amount of sulfur (% by mass) of the target material obtained in step (3-S) is divided by the amount of sulfur (% by mass) of cement obtained in step (4-S) to calculate the amount of cement (% by mass) of the target material.

5. The cement content evaluation method according to claim 4, wherein the target material is a recycled material derived from waste concrete, waste concrete, or in-service concrete.

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