Recycled coarse aggregate, method for producing the same, concrete composition, and concrete

Abstract

To provide a method for producing a recycled coarse aggregate, capable of reducing an environmental impact to produce the recycled coarse aggregate having excellent quality.SOLUTION: A method for producing a recycled coarse aggregate using crushed matter of a concrete block includes a carbonation step of absorbing carbon dioxide in the crushed matter of the concrete block in a carbon dioxide-containing atmosphere at a temperature of 0°C or more and less than 80°C and at relative humidity of 0 to 75%, wherein the recycled coarse aggregate is obtained which contains an aggregate component and a cement paste component, and has a ratio of the cement paste component of 5 to 30 mass%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to recycled coarse aggregates, a method for producing the same, a concrete composition, and concrete.

Background Art

[0002] At demolition sites, waste concrete is generated as industrial waste. In Patent Document 1, a technique for recycling aggregates from waste concrete has been proposed. In Patent Document 2, attempts have been made to subject powdery and granular materials of cementitious hardened bodies generated from waste materials of building materials, etc. to heat treatment by contacting them with a carbon dioxide-containing gas in a temperature atmosphere of 100°C to immobilize carbon dioxide. In this case, it has been reported that the carbonation rate of the cementitious hardened body can be adjusted by adjusting the relative humidity of the carbon dioxide-containing gas.

[0003] For quality assurance of structural concrete, it is known to evaluate the unit cement content. In Non-Patent Document 1, various methods have been studied as methods for measuring the unit cement content.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] At present, recycled coarse aggregates obtained by peeling off the mortar contained in waste concrete are not fully utilized as aggregates for concrete. The present disclosure provides a method for manufacturing recycled coarse aggregates capable of producing recycled coarse aggregates with reduced environmental impact and excellent quality. Further, recycled coarse aggregates capable of reducing environmental impact are provided. Further, by including such recycled coarse aggregates, a concrete composition and concrete capable of reducing environmental impact are provided.

Means for Solving the Problems

[0007] One aspect of the present disclosure is a method for manufacturing recycled coarse aggregates using crushed concrete blocks, the method having a carbonation step of absorbing carbon dioxide into the crushed concrete blocks in a carbon dioxide-containing atmosphere at 0°C or higher and less than 80°C and a relative humidity of 0 to 75%, and obtaining recycled coarse aggregates containing an aggregate component and a cement paste component, wherein the ratio of the cement paste component is 5 to 30% by mass.

[0008] The carbonation step in the above manufacturing method performs carbonation under relatively mild conditions of 0°C or higher and less than 80°C and a relative humidity of 0 to 75%. Since this manufacturing method carbonates under conditions where the temperature is not so high, the amount of fuel used and the amount of exhaust gas generated can be reduced, thereby reducing the environmental impact. Further, the recycled coarse aggregates obtained by carbonation under such conditions have a high absolute dry density and a low water absorption rate, and thus are excellent in quality. Therefore, the recycled coarse aggregates obtained by this manufacturing method can be utilized for coarse aggregates and various other applications.

[0009] One aspect of the present disclosure provides recycled coarse aggregates containing an aggregate component and a cement paste component, wherein the ratio of the cement paste component is 5 to 30% by mass, and the amount of CO2 immobilized by carbonation in terms of CaCO3 is 10 kg / ton or more.

[0010] The recycled coarse aggregate has a cement paste component ratio of 5 to 30% by mass, and the amount of CO2 fixed by carbonation in terms of CaCO3 is 10 kg / ton or more. Since such recycled coarse aggregate sufficiently fixes carbon dioxide, the environmental load can be reduced.

[0011] One aspect of the present disclosure provides a concrete composition including cement, water, and the recycled coarse aggregate. Since this concrete composition includes the recycled coarse aggregate, the environmental load can be reduced as compared with the case of using conventional recycled coarse aggregate. Further, since the recycled coarse aggregate has excellent quality, this concrete composition also has excellent quality.

[0012] One aspect of the present disclosure provides concrete including a cement hardened product and the recycled coarse aggregate. Since this concrete includes the recycled coarse aggregate, the environmental load can be reduced as compared with the case of using conventional recycled coarse aggregate. Further, since the recycled coarse aggregate has excellent quality, this concrete also has excellent quality.

Advantages of the Invention

[0013] In the present disclosure, it is possible to provide a method for manufacturing recycled coarse aggregate capable of manufacturing recycled coarse aggregate that reduces the environmental load and has excellent quality. Further, it is possible to provide recycled coarse aggregate capable of reducing the environmental load. Further, by including such recycled coarse aggregate, it is possible to provide a concrete composition and concrete capable of reducing the environmental load.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0015] Embodiments of the present disclosure will be described below. However, the following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant descriptions may be omitted as appropriate. Also, the positional relationships such as up, down, left, and right are based on the positional relationships based on the directions of the reference numerals shown in the drawings unless otherwise specified. The dimensional ratios of the respective elements are not limited to the ratios shown in the drawings. The numerical range exemplified by "a to b" is a numerical range with the lower limit a and the upper limit b, including a and b. Those obtained by replacing the upper limit or the lower limit of each numerical range with the numerical value of any embodiment are also included in the present disclosure. When a plurality of materials are exemplified, one of them may be used alone or a plurality of them may be used in combination.

[0016] A method for manufacturing recycled coarse aggregate according to an embodiment includes a carbonation step of absorbing carbon dioxide into the crushed material of a concrete block in a carbon dioxide-containing atmosphere at 0°C or higher and lower than 80°C and with a relative humidity of 0 to 75%, to obtain recycled coarse aggregate containing an aggregate component and a cement paste component, and having a cement paste component ratio of 5 to 30% by mass. The "carbon dioxide-containing atmosphere" in the present disclosure refers to an atmosphere having a higher CO2 concentration than the atmosphere. Examples of the concrete block include concrete scraps discharged during construction sites or demolition work of civil engineering and building structures. The concrete block includes an aggregate component and a cement paste component. The aggregate component contained in the concrete block is derived from the aggregate (also referred to as "original aggregate") used when manufacturing the concrete block. The original aggregate may be, for example, those listed in Appendix A, "Aggregates for Ready-Mixed Concrete," of JIS A 5308, "Ready-Mixed Concrete," or may be an aggregate not listed in Appendix A of the same standard.

[0017] By performing at least one pretreatment selected from the group consisting of pulverization, crushing, and grinding on the concrete block, crushed materials of the concrete block can be obtained. The pretreatment may include a sorting step of sorting according to the size of the crushed materials, such as classification and / or screening.

[0018] As an example of the pretreatment, a crushing step, a heating step, and a grinding step may be performed to obtain crushed materials of the concrete block. The crushing step may be performed using a crusher. Examples of crushers include a jaw crusher that crushes by sandwiching the concrete block between a fixed tooth and a movable tooth, a hammer crusher that crushes the concrete block using the impact force of a rapidly rotating hammer, and a centrifugal crusher that breaks the concrete block by causing it to fly at high speed by centrifugal force and colliding it with the concrete blocks and concrete crushed materials already present in the surroundings, and crushing the concrete block with the impact force at that time. Crushing may be performed using one of these devices, or two or more devices may be combined for crushing. The particle size of the crushed materials of the concrete block obtained by the crushing step (hereinafter sometimes simply referred to as "crushed materials") may be 40 mm or less.

[0019] In the heating step, the crushed materials may be heated to 80°C or higher, 90°C or higher, or 100°C or higher. The upper limit of the heating temperature may be 350°C. Examples of the heating device used in the heating step include a rotary kiln. As the heat source used for the heating device, exhaust gas discharged from at least one of a cement factory and a waste disposal site may be used. Thereby, fuel consumption in the heating device can be reduced, and the environmental load can be further reduced. The heating time may be 0.1 to 5 hours, 0.2 to 3 hours, or 0.3 to 1 hour. By performing such a heating step, the cement paste component contained in the crushed materials can be embrittled by a dehydration reaction, and the cement paste component can be easily peeled off from the crushed materials.

[0020] The crushing process may be carried out using a device that crushes or pulverizes a substance mainly by the force of friction with a shearing action applied. Examples of such devices include, for example, stone mortars, kneading machines, edge runners, roller mill type mills, planetary crushers, stirring tank type mills, etc. Specifically, it may be carried out using a Marmal (trade name) manufactured by Kurimoto Iron Works. In the crushing process, while suppressing the crushing of the aggregate components contained in the crushed material, the concrete paste component can be peeled off from the crushed material. Thereby, the ratio of the cement paste component in the crushed material can be further reduced. In the crushing process, the crushing of the crushed material may be carried out using a plurality of crushers (for example, a primary crusher and a secondary crusher). The respective ratios of the aggregate component and the cement paste component in the crushed material can be adjusted by changing the output (rotation speed) of the crusher.

[0021] In the carbonation process, carbon dioxide is absorbed into the crushed material. Thereby, calcium oxide contained in the crushed material reacts with carbon dioxide to generate calcium carbonate and carbonated cement hydrates. Thereby, carbon dioxide can be immobilized. The carbonation process is carried out in a carbon dioxide-containing atmosphere at 0°C or higher and less than 80°C, and with a relative humidity of 0 to 75%. Since carbonation is carried out under such mild conditions, the environmental load can be reduced.

[0022] The temperature in the carbonation process may be 10°C or higher, 15°C or higher, 20°C or higher, 30°C or higher, or 40°C or higher from the viewpoint of obtaining recycled coarse aggregate with a sufficiently high absolute dry density and a sufficiently low water absorption rate. The temperature in the carbonation process may be 90°C or lower, 80°C or lower, or 70°C or lower from the viewpoint of obtaining recycled coarse aggregate with a sufficiently high absolute dry density and a sufficiently low water absorption rate. The relative humidity in the carbonation process may be 10% or higher, 15% or higher, or 20% or higher from the viewpoint of obtaining recycled coarse aggregate with a sufficiently high absolute dry density and a sufficiently low water absorption rate. The relative humidity in the carbonation process may be 70% or lower, 60% or lower, 50% or lower, or 40% or lower from the viewpoint of obtaining recycled coarse aggregate with a sufficiently high absolute dry density and a sufficiently low water absorption rate.

[0023] The CO₂ concentration in the carbon dioxide-containing atmosphere of the carbonation process may be 0.1% by volume or more, 1% by volume or more, 3% by volume or more, or 5% by volume or more from the viewpoint of obtaining recycled coarse aggregate with a sufficiently high absolute dry density and a sufficiently low water absorption rate. The CO₂ concentration in the carbon dioxide-containing atmosphere of the carbonation process may be 50% by volume or less, 30% by volume, or 25% by volume or less from the viewpoint of sufficiently enhancing the safety of the working environment.

[0024] The period of the carbonation process for carbonating the crushed material may be 0.2 days or more, 0.5 days or more, 0.8 days or more, or 1 day or more from the viewpoint of obtaining recycled coarse aggregate with a sufficiently high absolute dry density and a sufficiently low water absorption rate. The period of the carbonation process for carbonating the crushed material may be 20 days or less, 15 days or less, or 10 days or less from the viewpoint of efficiency. When the carbonation process is carried out in multiple stages, the total carbonation period may be within the above range.

[0025] The carbonation process may be carried out in a closed container such as a thermo-hygrostat or an oven, or in an open container. The recycled coarse aggregate obtained through such a carbonation process is of excellent quality because it has a high absolute dry density and a low water absorption rate. Therefore, it can be used for coarse aggregate and various other applications. The composition and properties of the recycled coarse aggregate may be as described in the embodiments of the recycled coarse aggregate.

[0026] The moisture content of the crushed material before the carbonation process may be 3% by mass or more, 4% by mass or more, or 5% by mass or more. By subjecting such crushed material to a carbonation treatment, recycled coarse aggregate having a sufficiently high absolute dry density can be obtained. The moisture content of the crushed material (recycled coarse aggregate before carbonation treatment) in this specification is measured in accordance with JIS A 1125:2015 "Test Method for Moisture Content of Aggregates and Test Method for Surface Moisture Ratio Based on Moisture Content".

[0027] In a modified example of the above manufacturing method, the heating step may not be performed. In yet another modified example, at least one of the crushing step, the heating step, and the grinding step may be performed simultaneously with the carbonation step. For example, if the temperature, humidity, and CO2 concentration of the heating device are adjusted within the range of the above carbonation step, the heating step and the carbonation step can be performed simultaneously. For example, by performing carbonation while stirring the crushed material in a rotary kiln, the carbonation can proceed sufficiently. Also, for example, if the temperature, humidity, and CO2 concentration in the atmosphere inside the grinder are adjusted within the range of the above carbonation step, the grinding step and the carbonation step can be performed simultaneously. Thereby, the time required for a series of steps can be shortened.

[0028] In yet another modified example of the above manufacturing method, the carbonation step may be performed while transporting the crushed material of the concrete block. For example, by performing carbonation using the carbon dioxide in the exhaust gas discharged from the transportation equipment that transports the crushed material or recycled coarse aggregate, it is possible to further contribute to reducing the environmental load. Also, in yet another modified example, the carbonation step may be performed while storing the crushed material in a silo or the like, or it may be performed in a manner of spraying carbon dioxide gas derived from the exhaust gas while storing the crushed material outdoors.

[0029] In yet another modified example of the above manufacturing method, the carbonation step may be performed by kneading the crushed material of the concrete block before carbonation with cement or the like to prepare concrete containing the crushed material, placing the concrete in a formwork, and performing carbonation curing. Thereby, a carbonation hardened body excellent in strength can be produced.

[0030] In yet another modified example of the above manufacturing method, it may include a mixing step of mixing the crushed material of the concrete block before carbonation with another aggregate (coarse aggregate) capable of carbonation, such as electric furnace oxidation slag and electric furnace reduction slag. By performing the above carbonation step after the mixing step of mixing the crushed material with another aggregate (coarse aggregate) capable of carbonation, carbon dioxide can be sufficiently immobilized and the yield of recycled coarse aggregate can be increased. Note that embodiments combining the above-described modified examples are also included in the present embodiment.

[0031] A screening step of screening the crushed materials according to their sizes may be performed during or before and after each process. The screening step may be performed using a classifier or an electric sieve. By performing the screening step, the size of the recycled coarse aggregate can be adjusted.

[0032] The recycled coarse aggregate according to one embodiment contains a coarse aggregate component and a cement paste component. The recycled coarse aggregate may be manufactured by the above-described manufacturing method. However, the manufacturing method is not limited to the above-described manufacturing method. The ratio of the cement paste component in the recycled coarse aggregate is 5 to 30% by mass. From the viewpoint of sufficiently increasing the amount of carbon dioxide fixation, the ratio of the cement paste component in the recycled coarse aggregate may be 7% by mass or more, 9% by mass or more, or 10% by mass or more. From the same viewpoint, the ratio of the aggregate component in the recycled coarse aggregate may be 93% by mass or less, 91% by mass or less, or 90% by mass or less.

[0033] From the viewpoint of sufficiently increasing the absolute dry density and sufficiently decreasing the absorption rate, the ratio of the cement paste component in the recycled coarse aggregate may be 25% by mass or less, 20% by mass or less, or 15% by mass or less. From the same viewpoint, the ratio of the aggregate component in the recycled coarse aggregate may be 75% by mass or more, 80% by mass or more, or 85% by mass or more. The ratios of the cement paste component and the aggregate component in the recycled coarse aggregate can be adjusted according to the heating conditions in the heating step, the operating conditions of the grinder in the grinding step, and the like.

[0034] The ratio of the cement paste component in the recycled coarse aggregate can be obtained by measuring the insoluble residue of the recycled coarse aggregate and subtracting the ratio of the insoluble residue from the recycled coarse aggregate. When the original aggregate contained in the crushed material used for manufacturing the recycled coarse aggregate contains limestone aggregate, the limestone aggregate also dissolves when measuring the insoluble residue of the recycled coarse aggregate. Therefore, when the original aggregate contains limestone aggregate, the ratio of the cement paste component in the recycled coarse aggregate can be obtained by the following formula.

[0035] Ratio of cement paste component [mass%] = 100 - (insoluble residue [%] of recycled coarse aggregate / insoluble residue [%] of original aggregate)

[0036] When the original aggregate contains limestone aggregate, or when it is difficult to measure the insoluble residue of the original aggregate, etc., the ratio of the cement paste component may be determined by a measurement method different from the above. Examples of such measurement methods include the "hydrofluoric acid treatment method" and the "ICP method" described in Table-1 of Non-Patent Document 1.

[0037] The absolute dry density of the recycled coarse aggregate is 2.39 g / cm 3 or more, 2.40 g / cm 3 or more, or.41 g / cm 3 or more. The water absorption rate of the recycled coarse aggregate may be 4.40% or less, 4.20% or less, 4.00% or less, or 3.90% or less. When the original aggregate contains limestone aggregate, the insoluble residue of the recycled coarse aggregate may be 85% or less, 80% or less, or 75% or less. Thereby, the amount of carbon dioxide immobilization can be made sufficiently large. When the original aggregate contains limestone aggregate, the insoluble residue of the recycled coarse aggregate may be 60% or more, 65% or more, or 70% or more. Thereby, the quality of the recycled coarse aggregate can be made sufficiently high. The insoluble residue of the original aggregate may be 60% or more, 70 - 95%, or 80 - 90%.

[0038] The absolute dry density and water absorption rate in this specification are values measured in accordance with JIS A 1110:2020 "Test Method for Density and Water Absorption Rate of Coarse Aggregate". The insoluble residue of the recycled coarse aggregate and the original aggregate is a value (mass ratio) measured in accordance with JIS R 5202:2010 "Cement Chemical Analysis Method".

[0039] The recycled coarse aggregate has a CaCO3-equivalent amount of CO2 immobilized by carbonation of 10 kg-CaCO3 / ton or more, preferably 20 kg-CaCO3 / ton or more, more preferably 30 kg-CaCO3 / ton or more, still more preferably 35 kg-CaCO3 / ton or more, and particularly preferably 40 kg-CaCO3 / ton or more. By this, carbon dioxide can be sufficiently immobilized to further reduce the environmental load. The recycled coarse aggregate may have a CaCO3-equivalent amount of CO2 immobilized by carbonation of, for example, less than 70 kg-CaCO3 / ton. The CaCO3-equivalent amount of CO2 immobilized by carbonation of the recycled coarse aggregate can be measured by the method described in the examples.

[0040] The carbonation rate of the recycled coarse aggregate may be 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, or 50% or more. By this, carbon dioxide can be sufficiently immobilized to further reduce the environmental load. The carbonation rate of the recycled coarse aggregate can be measured by the method described in the examples. The particle size of the recycled coarse aggregate may be 40 mm or less, and may be 5 - 20 mm. The particle size can be adjusted, for example, by changing the mesh of an electric sieve.

[0041] The manufacturing apparatus for the recycled coarse aggregate according to one embodiment includes a rotary kiln that heats the crushed material of the concrete block, and a grinder that grinds the crushed material heated by the rotary kiln. In this manufacturing apparatus, the grinding by the grinder is performed in a carbon dioxide-containing atmosphere at 0°C or more and less than 80°C, and with a relative humidity of 0 - 75% to cause the crushed material to absorb carbon dioxide, and a recycled coarse aggregate containing an aggregate component and a cement paste component, and having a ratio of the cement paste component of 5 - 30 mass% is manufactured.

[0042] The above manufacturing apparatus performs carbonation while grinding under relatively mild conditions of 0°C or higher and less than 80°C, and a relative humidity of 0 to 75%. Since this manufacturing apparatus performs carbonation under conditions where the temperature is not so high, it is possible to reduce the amount of fuel used and the amount of exhaust gas generated, thereby reducing the environmental load. In addition, the recycled coarse aggregate obtained by carbonation under such conditions has a high absolute dry density and a low water absorption rate, and thus is of excellent quality. Therefore, the recycled coarse aggregate manufactured by this manufacturing apparatus can be utilized for coarse aggregate and various other applications.

[0043] Figure 1 shows an example of a manufacturing apparatus for recycled coarse aggregate. The manufacturing apparatus 100 in Figure 1 includes, along the flow direction of the crushed material of the concrete block, a heavy machine, a jaw crusher, a first electric sieve, a rotary kiln, a primary grinder, a secondary grinder, and a second electric sieve from the upstream side. The heavy machine can be used without limitation as long as it can crush the concrete block. As the primary grinder and the secondary grinder, those exemplified in the above grinding process can be used. In the manufacturing apparatus 100, as equipment for crushing the concrete block and its crushed material, it includes a heavy machine, a jaw crusher, and an impact crusher, but is not limited thereto, and various crushers and grinders can be used. For example, it may be provided with a hammer crusher, a centrifugal crusher, etc.

[0044] In the rotary kiln, the crushed material may be heated under the heating conditions of the above heating process. Since the cement paste component of the crushed material heated in the rotary kiln is embrittled by the dehydration reaction, it is possible to easily peel off the cement paste component from the crushed material by the primary grinder and the secondary grinder. As the heat source of the rotary kiln, exhaust gas discharged from at least one of a cement factory and a waste disposal site may be used. Thereby, fuel consumption in the rotary kiln can be reduced, and the environmental load can be further reduced.

[0045] In the manufacturing apparatus 100, carbonation of the crushed material is performed in the primary crusher and / or the secondary crusher. The temperature, humidity, and CO2 concentration in the atmosphere inside the primary crusher and / or the secondary crusher are adjusted within the range of the above-described carbonation process to perform carbonation of the crushed material. In this way, recycled coarse aggregate can be efficiently manufactured. Also, for example, in a rotary kiln, carbonation of the crushed material may be performed by adjusting the temperature, humidity, and CO2 concentration in the atmosphere inside the rotary kiln within the range of the above-described carbonation process.

[0046] The crushed material crushed by the primary crusher and the secondary crusher is screened by a second electric sieve. After screening, recycled coarse aggregate is obtained below the sieve. The composition and properties of the recycled coarse aggregate are as described above. The components on the sieve may be returned to the upstream side (for example, jaw crusher, impact crusher, primary crusher, or secondary crusher) to repeat crushing and grinding again. Thereby, the yield of the recycled coarse aggregate can be increased.

[0047] The exhaust gas generated in the rotary kiln, primary crusher, and secondary crusher may be introduced into a dust collector to recover fine powder. This fine powder contains a cement paste component. If carbonation of the crushed material is performed in the rotary kiln, primary crusher, and secondary crusher, the properties of the fine powder can be sufficiently stabilized. Since carbon dioxide is also immobilized in the fine powder, the environmental load can be further reduced.

[0048] The manufacturing apparatus of this embodiment is not limited to that of FIG. 1. For example, a carbonation device for carbonating the crushed material may be provided between the rotary kiln and the primary crusher, between the primary crusher and the secondary crusher, or downstream of the second electric sieve. The carbonation device is not particularly limited as long as it can carbonize the pulverized material in a carbon dioxide-containing atmosphere at 0°C or higher and lower than 80°C and with a relative humidity of 0 to 75%. The carbonation device may include, for example, a main body portion that has a tank or a container and performs carbonation, and a supply portion that supplies carbon dioxide gas to the main body portion.

[0049] A concrete composition according to an embodiment includes cement, water, and recycled coarse aggregate. This concrete composition can be prepared by kneading cement, water, recycled coarse aggregate, and components blended as necessary. Since this concrete composition includes the above-described recycled coarse aggregate in which carbon dioxide is immobilized, the environmental load can be reduced. Also, since this recycled coarse aggregate has excellent quality, this concrete composition also has excellent quality. This concrete composition may contain components of cement, water, and recycled coarse aggregate. Such components include various admixtures and aggregates different from the recycled coarse aggregate.

[0050] Concrete according to an embodiment provides concrete including a cement hardened product and the above-described recycled coarse aggregate. This concrete can be obtained by hardening the above-described concrete composition. Since this concrete includes a recycled coarse aggregate in which carbon dioxide is immobilized, the environmental load can be reduced. Also, since this recycled coarse aggregate has excellent quality, this concrete also has excellent quality. This concrete may contain components other than the cement hardened product and the recycled coarse aggregate. Such components include aggregates other than the recycled coarse aggregate.

[0051] As described above, the embodiments of the present disclosure have been described, but the present disclosure is not limited to the above embodiments at all. The present disclosure includes the following embodiments [1] to

[13] .

[0052] [1] A method for producing recycled coarse aggregate using crushed concrete blocks, having a carbonation step of absorbing carbon dioxide into the crushed concrete blocks in a carbon dioxide-containing atmosphere at 0°C or higher and lower than 80°C and with a relative humidity of 0 to 75%, A method for producing recycled coarse aggregate, which obtains recycled coarse aggregate containing an aggregate component and a cement paste component and having a ratio of the cement paste component of 5 to 30% by mass. [2] The method for producing recycled coarse aggregate according to [1], wherein the insoluble residue of the recycled coarse aggregate is 60 to 95%. [3] The manufacturing method of the recycled coarse aggregate according to [1] or [2], wherein the carbon dioxide concentration in the carbon dioxide-containing atmosphere in the carbonation step is 5 to 30% by volume. [4] The manufacturing method of the recycled coarse aggregate according to any one of [1] to [3], wherein the carbonation rate of the recycled coarse aggregate is 20% or more. [5] The manufacturing method of the recycled coarse aggregate according to any one of [1] to [4], having a grinding step of grinding the crushed material at least on one side before and after the carbonation step. [6] The manufacturing method of the recycled coarse aggregate according to any one of [1] to [5], having a heating step of heating the crushed material to 80°C or higher before the carbonation step. [7] The manufacturing method of the recycled coarse aggregate according to [6], wherein the heating step is performed in a rotary kiln using exhaust gas discharged from at least one of a cement factory and a waste disposal site as a heat source. [8] Containing a coarse aggregate component and a cement paste component, wherein the ratio of the cement paste component is 5 to 30% by mass, A recycled coarse aggregate, wherein the amount of CO2 absorbed by carbonation in terms of CaCO3 is 10 kg / ton or more. [9] The recycled coarse aggregate according to [8], having an absolute dry density of 2.39 g / cm 3 or more and a water absorption rate of 4.40% or less.

[10] A concrete composition containing cement, water, and the recycled coarse aggregate according to [8] or [9].

[11] Concrete containing a cement hardened product and the recycled coarse aggregate according to [8] or [9].

Examples

[0053] The content of the present disclosure will be described in more detail with reference to Examples and Comparative Examples, but the present disclosure is not limited to the following Examples.

[0054] (Example 1) [Manufacture of Concrete Blocks] Fine aggregates A, B, C, and coarse aggregates shown in Table 1 were prepared.

Table 1

[0055] The following commercially available products were prepared as cement and admixtures. Cement: manufactured by UBE Mitsubishi Cement Corporation, density: 3.16 g / cm 3 , Na2O eq : 0.56% Admixture (AE water reducing agent retarder type I): manufactured by Pozolith Solutions Co., Ltd., Master Polyhead 15SR (trade name), Na2O eq : 1.3%

[0056] The above cement, admixture, aggregate, and water were mixed in the proportions shown in Table 2 to produce concrete blocks. The specifications and properties of the ready-mixed concrete were as shown in Table 3. "N" in Table 3 means ordinary Portland cement.

[0057]

Table 2

[0058]

Table 3

[0059] [Manufacture of recycled coarse aggregate] A processing device having a device configuration as shown in FIG. 2 was prepared. This processing device was equipped with a crusher (heavy machinery), a jaw crusher, a first electric sieve, a rotary kiln, a grinder, and a second electric sieve from the upstream side. Also, the oversize components of the first electric sieve were crushed by an impact crusher and supplied to the first electric sieve again, and only the undersize components of the first electric sieve were supplied to the rotary kiln. In the rotary kiln, heating was not performed and it was only allowed to pass through. As the grinder, a Marmal (trade name) manufactured by Kurimoto Iron Works was used. The output of the grinder was 80% and the rotational speed was 345 rpm. The crushed material (ground material) obtained by the grinder was supplied to an electric sieve, and the oversize was recovered as recycled coarse aggregate (before carbonation treatment). The properties of the recovered recycled coarse aggregate (before carbonation treatment) were as shown in Table 4. Note that the recycled coarse aggregate (before carbonation treatment) is a type of crushed material of concrete blocks.

[0060]

Table 4

[0061] The absolute dry density and water absorption of the crushed material before carbonation treatment are also values measured in accordance with JIS A 1110:2020 "Test Method for Density and Water Absorption of Coarse Aggregate". The insoluble residue of the crushed material before carbonation treatment is also a value measured in accordance with JIS R 5202:2010 "Cement Chemical Analysis Method". The actual ratio of particle size determination is a value measured by the method described in JIS A 5021:2018 "Recycled Aggregate H for Concrete". The fine particle content is a value measured by the method described in JIS A 1103:2014 "Test Method for Fine Particle Content of Aggregate". The FM frost damage index is a value measured by the method described in Appendix D of JIS A 5022:2018 "Test Method for Freezing and Thawing of Recycled Aggregate M".

[0062] From the following formula (1), the ratio of the cement paste component of the recycled coarse aggregate (before carbonation treatment) was calculated. The insoluble residue of the original aggregate in formula (1) is the aggregate used in the production of concrete blocks, that is, the insoluble residue of the aggregate contained at the ratio of the unit amounts of fine aggregates A, B, C and coarse aggregate shown in Table 1 in Table 2. This insoluble residue was also measured by the method described in JIS R 5202:2010 "Chemical Analysis Method of Cement".

[0063] Ratio of cement paste component [mass%] = 100 - (insoluble residue of recycled coarse aggregate [%] / insoluble residue of original aggregate [%]) × 100 ··· (1)

[0064] The ratio of the cement paste component of the recycled coarse aggregate (before carbonation treatment) calculated by the above formula (1) was 10 mass%. Also, the insoluble residue of the original aggregate was 84.4%.

[0065] A sieving test of the recycled coarse aggregate (before carbonation treatment) was conducted. The passing rate of each sieve size was as shown in Figure 3. In Figure 3, for reference, the standard values of recycled aggregate M2005 described in JIS A 5022:2018 "Recycled Aggregate Concrete M" were also shown together.

[0066] Chemical analysis of the recycled coarse aggregate (before carbonation treatment) was carried out with reference to JIS R 5204:2019 "Fluorescent X-ray Analysis Method of Cement". The calibration curve used was that of cement. The results were as shown in Table 5.

[0067]

Table 5

[0068] The carbonation treatment of the recycled coarse aggregate (before carbonation treatment) having the above-mentioned properties was carried out according to the following procedure. The water content of the recycled coarse aggregate (before carbonation treatment) stored for several days in an atmospheric environment with a temperature of 20°C and a relative humidity of 60% was 3.75% by mass. The water content was measured in accordance with JIS A 1125:2015 "Test Method for Water Content of Aggregates and Test Method for Surface Water Content Based on Water Content". Approximately 5 kg of this recycled coarse aggregate (before carbonation treatment) was placed in a vat and left to stand in a thermo-hygrostat or oven in which the CO2 concentration, temperature, and relative humidity were controlled to the values shown in Table 6 for carbonation. A thermo-hygrostat was used when the temperature was 100°C or lower, and an oven was used when the temperature exceeded 100°C. The standing time was shown in Table 6 as the carbonation period. The absolute dry density and water absorption of the recycled coarse aggregate obtained by carbonation were measured. The results were as shown in Table 6.

[0069] (Example 2) Recycled coarse aggregate (before carbonation treatment) with a water content different from that in Example 1 was prepared. This recycled coarse aggregate (before carbonation treatment) was in a surface-dry state, and its water content was 5.63% by mass. Using this recycled coarse aggregate (before carbonation treatment), the same carbonation treatment as in Example 1 was carried out. The CO2 concentration, temperature, relative humidity, and standing time during the carbonation treatment were as shown in Table 6. The absolute dry density and water absorption of the recycled coarse aggregate obtained by carbonation were measured. The results were as shown in Table 6.

[0070] (Example 3) Recycled coarse aggregate (before carbonation treatment) with a water content different from that in Example 1 was prepared. This recycled coarse aggregate (before carbonation treatment) was in a wet state, and its water content was 7.56% by mass. Using this recycled coarse aggregate (before carbonation treatment), the same carbonation treatment as in Example 1 was carried out. The CO2 concentration, temperature, relative humidity, and standing time during the carbonation treatment were as shown in Table 6. The absolute dry density and water absorption of the recycled coarse aggregate obtained by carbonation were measured. The results were as shown in Table 6.

[0071]

Table 6

[0072] As shown in Table 6, the recycled coarse aggregates after carbonation treatment in each example all had an absolute dry density of 2.39 g / cm 3 or more and a water absorption rate of 4.40% or less. On the other hand, in Comparative Examples 1-1 and 1-2 where the temperature during carbonation treatment was 100°C or higher, the absolute dry density was lower than that of the examples, and the water absorption rate was higher than that of the examples. This is presumably because when the temperature is high, the moisture contained in the recycled aggregates evaporates, making it difficult for the carbonation reaction in the liquid phase to proceed, and the cement paste component is not sufficiently carbonated. From the comparison of Examples 1-4, Example 2, and Example 3, it was confirmed that the higher the water content of the recycled coarse aggregates (before carbonation treatment), the lower the water absorption rate of the recycled coarse aggregates after carbonation treatment can be.

[0073] With reference to "Report of the Concrete Special Committee F-18 Method for Estimating the Mix Proportion of Hardened Concrete", the CaO content of the recycled coarse aggregates (after carbonation treatment) of Examples 1-1, 1-5, and 1-7 was measured. Specifically, up to the "Method for Determination of Insoluble Residue", "Report of the Concrete Special Committee F-18 Method for Estimating the Mix Proportion of Hardened Concrete" was referred to, and for the method of determining calcium oxide, the method of determining calcium oxide in JIS R5202:2010 "Chemical Analysis Method of Cement" was used. The measurement results were as shown in Table 7.

[0074]

Table 7

[0075] The insoluble residue of the recycled coarse aggregates (after carbonation treatment) of Examples 1-1, 1-5, and 1-7 was measured. The results were as shown in Table 8. Table 8 also shows the insoluble residue of the original aggregates.

[0076] The recycled coarse aggregates (after carbonation treatment) of Examples 1-1, 1-5, and 1-7 were each pulverized, and thermogravimetric analysis was performed using a thermogravimetric differential thermal analyzer. Specifically, about 2 kg of the recycled coarse aggregates (after carbonation treatment) of each example were weighed and crushed using a hammer crusher. After being crushed to a certain extent, they were pulverized using a disk mill until the particle size became 90 μm or less. Thermogravimetric analysis of the pulverized samples was performed. In the same manner, thermogravimetric analysis of the original aggregates (a mixture of fine aggregates A, B, C and coarse aggregates in Table 1) was performed.

[0077] The mass loss rate between 500 and 750 °C was considered to be due to the thermal decomposition of CaCO3 generated by fixing CO2 and carbonated cement hydrates, and the CO2 desorbed by this thermal decomposition. Since this CO2 can be considered to be the one fixed during the carbonation treatment, it can be considered that the recycled coarse aggregates (after carbonation treatment) with a large mass loss rate have fixed a large amount of carbon dioxide. The mass loss rates between 500 and 750 °C of the recycled coarse aggregates (after carbonation treatment) and the original aggregates were as shown in Table 8.

[0078]

Table 8

[0079] The values of each item described in Table 9 were obtained using each measured value of the analysis items described in Table 8. The calculation formulas for obtaining each value in Table 9 using the symbols shown in Table 8 are also shown in Table 9.

[0080]

Table 9

[0081] The carbonation rate calculation formula in Table 9 is as follows. In recycled coarse aggregate, all of the coarse aggregate components can be considered to be derived from the aggregate components contained in the original aggregate. Therefore, by dividing the insoluble residue of the recycled coarse aggregate by the insoluble residue of the original aggregate, the ratio of the original aggregate in the recycled coarse aggregate (= the ratio of the coarse aggregate components in the recycled coarse aggregate [d / e]) can be calculated. By multiplying this ratio by the mass loss rate of the original aggregate, the mass loss rate of the original aggregate is converted to the ratio in the recycled coarse aggregate.

[0082]

Number

[0083] (Examples 4, 5) Except for changing the output and rotation speed of the grinder (Marumaru (trade name) manufactured by Kurimoto Iron Works) in the processing apparatus shown in Fig. 2 as shown in Table 10, recycled coarse aggregate (before carbonation treatment) was produced in the same manner as in Example 1. Then, carbonation treatment was carried out under the same conditions as in Example 1-1 to produce recycled coarse aggregate (after carbonation treatment) of Examples 4 and 5. The absolute dry density, water absorption rate, insoluble residue, ratio of cement paste component, and CO2 content in terms of CaCO3 of the recycled coarse aggregate of Examples 4 and 5 obtained by carbonation were as shown in Table 10. For comparison, Example 1-1 was also shown in Table 10.

[0084]

Table 10

[0085] As shown in Table 10, it was confirmed that by adjusting the operating conditions of the grinder, the ratio of the cement paste component can be adjusted. Also, it was confirmed that by increasing the ratio of the cement paste component, the amount of carbon dioxide immobilization can be made sufficiently large. Since such recycled coarse aggregate is produced by carrying out carbonation treatment under mild conditions while immobilizing a sufficient amount of carbon dioxide, the environmental load can be reduced.

Industrial Applicability

[0086] According to the present disclosure, it is possible to provide a method and an apparatus for manufacturing recycled coarse aggregate capable of reducing environmental impact and producing recycled coarse aggregate having excellent quality. Further, it is possible to provide recycled coarse aggregate capable of reducing environmental impact. Further, by including such recycled coarse aggregate, it is possible to provide a concrete composition and concrete capable of reducing environmental impact.

Description of Reference Numerals

[0087] 100…Manufacturing apparatus.

Claims

1. A method for manufacturing recycled coarse aggregate using crushed concrete blocks, comprising: a carbonation step of absorbing carbon dioxide into the crushed concrete blocks in a carbon dioxide-containing atmosphere at 0°C or higher and lower than 80°C and with a relative humidity of 0 to 75%; A method for manufacturing recycled coarse aggregate, which contains an aggregate component and a cement paste component and obtains recycled coarse aggregate in which the ratio of the cement paste component is 5 to 30% by mass.

2. The method for manufacturing recycled coarse aggregate according to Claim 1, wherein the insoluble residue of the recycled coarse aggregate is 60 to 95%.

3. The method for manufacturing recycled coarse aggregate according to Claim 1 or 2, wherein the carbon dioxide concentration in the carbon dioxide-containing atmosphere in the carbonation step is 5 to 30% by volume.

4. The method for manufacturing recycled coarse aggregate according to Claim 1 or 2, wherein the carbonation rate of the recycled coarse aggregate is 20% or more.

5. The method for manufacturing recycled coarse aggregate according to Claim 1 or 2, having a grinding step of grinding the crushed material at least on one side before and after the carbonation step.

6. The method for manufacturing recycled coarse aggregate according to Claim 1 or 2, having a heating step of heating the crushed material to 80°C or higher before the carbonation step.

7. The method for manufacturing recycled coarse aggregate according to Claim 6, wherein the heating step is performed in a rotary kiln using exhaust gas discharged from at least one of a cement factory and a waste disposal site as a heat source.

8. Containing a coarse aggregate component and a cement paste component, wherein the ratio of the cement paste component is 5 to 30% by mass, CO immobilized by carbonation ２ CaCO ３ Recycled coarse aggregate with a conversion amount of 10 kg / ton or more.

9. The absolute dry density is 2.39 g / cm ３ or more, and the water absorption rate is 4.40% or less, the recycled coarse aggregate according to claim 8.

10. A concrete composition comprising cement, water, and the recycled coarse aggregate according to Claim 8 or 9.

11. Concrete comprising a cement hardened product and the recycled coarse aggregate according to Claim 8 or 9.

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