Method for producing recycled fine aggregate for concrete, and method for producing ready-mixed concrete

Abstract

To provide a production method of a recovered fine aggregate for concrete capable of producing high-quality recovered fine aggregate for concrete.SOLUTION: A production method of a recovered fine aggregate for concrete comprises the steps of: adding a first treating agent having microbubble water and iron oxide to a derivative of returned ready-mixed concrete or residual concrete; and adding a second treating agent having a cationic surfactant to the derivative to which the first treating agent has been added.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled fine aggregate for concrete and a method for producing ready-mixed concrete. [Background technology]

[0002] Ready-mixed concrete produced at a ready-mixed concrete factory (ready-mixed concrete factory) is delivered to a construction site by agitator truck. However, if any remains at the construction site, the agitator truck is returned to the ready-mixed concrete factory. Such unused ready-mixed concrete is called returned ready-mixed concrete or residual ready-mixed concrete, and fine aggregate is sometimes recovered from the unused ready-mixed concrete. Such recovered fine aggregate is called recovered fine aggregate or recovered sand, but it may not be of sufficient quality to be used in the production of ready-mixed concrete. In such cases, the fine aggregate recovered from the returned ready-mixed concrete or residual ready-mixed concrete is sometimes discarded. Alternatively, the returned ready-mixed concrete or residual ready-mixed concrete may be discarded as is. However, for the purposes of effective resource reuse and waste volume reduction, a method for producing recovered fine aggregate from the returned ready-mixed concrete or residual ready-mixed concrete that can be suitably used as fine aggregate for concrete is desired.

[0003] An example of a method for producing recycled fine aggregate for concrete is the method described in Patent Document 1. Patent Document 1 describes a method for producing aggregate from returned concrete, including the steps of: charging returned concrete into a high-intensity mixer; adding an organic or inorganic coagulant mixture, either alone or in combination; mixing the returned concrete for 20 seconds to 5 minutes until the returned concrete has set and is substantially dry, does not contain cement paste, and is divided into a larger particle size fraction consisting primarily of the original natural aggregate contained in the returned concrete, and a smaller particle size fraction consisting primarily of agglomerates containing water, a coagulant mixture, fresh cement, and the fine fraction of the mixture (sand and silt); and separating the mixture by vibrating, rotating, or passing it through a cyclone sieve to separate it into at least two particle size classes: one larger particle size fraction consisting primarily of the original natural aggregate contained in the returned concrete, which is substantially dry, does not contain cement paste, and is the smaller particle size fraction consisting primarily of agglomerates containing water, a coagulant mixture, fresh cement, and the fine fraction of the mixture (sand and silt). Patent document 1 discloses that aggregates can be produced from concrete residues that are not used for construction purposes, or more generally from cement mixtures that are not used for any reason and are returned to the production facility in the mixer truck. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2020-528858 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, fine aggregate (recovered fine aggregate) recovered from returned ready-mix concrete or residual ready-mix concrete may not be of sufficiently high quality to be used in the production of ready-mix concrete. Specifically, such recovered fine aggregate tends to have higher water absorption properties than ordinary aggregate, which may result in a lower quality fine aggregate for concrete. Furthermore, when such fine aggregate for concrete is stored in a silo or the like, it tends to caking easily. This affects the operating conditions, etc., when the recovered fine aggregate for concrete is used to produce ready-mix concrete. Furthermore, recovered fine aggregate tends to be more susceptible to quality degradation than recovered coarse aggregate.

[0006] For these reasons, there are fine aggregates recovered from returned or leftover ready concrete, such as recovered aggregates specified in JIS A 5308:2019, and recycled aggregates, but there are also recovered fine aggregates of higher quality than, for example, recycled aggregate for concrete H and recycled aggregate for concrete M. Recycled aggregate for concrete H is specified in JIS A 5021:2018 and is a recycled aggregate for concrete produced by subjecting concrete blocks generated by the demolition of structures to advanced processing, such as crushing, grinding, and classification. Recycled aggregate for concrete M is specified in JIS A 5022:2018 and can be handled in much the same way as ordinary aggregate, making it a high-quality aggregate that can be used regardless of the part of a building.

[0007] There is a demand for fine aggregate recovered from returned ready concrete or residual concrete to be of the H or M level. However, no method has been established for obtaining sufficiently high-quality recovered fine aggregate for concrete from returned ready concrete or residual concrete. Specifically, even with the method described in Patent Document 1, for example, there are cases where the problem of residual cement (cement paste) contained in the returned concrete remaining in the aggregate (recovered aggregate) obtained from returned concrete has not been fully resolved. Among recovered aggregates, in particular, it is more difficult to remove the cement from recovered fine aggregate than when producing recovered coarse aggregate, making it more difficult to obtain high-quality recovered fine aggregate. Therefore, there is a demand for a production method for obtaining high-quality recovered fine aggregate for concrete.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for producing recycled fine aggregate for concrete, which can produce high-quality recycled fine aggregate for concrete. Another aim of the present invention is to provide a method for producing ready-mixed concrete, which can produce high-quality ready-mixed concrete. [Means for solving the problem]

[0009] As a result of various investigations, the present inventors have found that the above object can be achieved by the present invention described below.

[0010] A first aspect of the present invention provides a method for producing recycled fine aggregate for concrete, which includes the steps of: adding a first treatment agent containing microbubble water and iron oxide to a material derived from returned ready-mixed concrete or residual ready-mixed concrete; and adding a second treatment agent containing a cationic surfactant to the material to which the first treatment agent has been added.

[0011] According to this configuration, it is possible to provide a method for producing recycled fine aggregate for concrete, which can produce high-quality recycled fine aggregate for concrete.

[0012] In conventional methods for producing recycled fine aggregate, the recycled fine aggregate itself tends to have high water absorption, making it difficult to sufficiently improve the quality of the recycled fine aggregate for concrete. This is thought to be because, when fine aggregate is recovered from returned fresh concrete and residual concrete, the cement (cement paste) derived from the returned fresh concrete and residual concrete is not sufficiently removed from the fine aggregate, resulting in the cement remaining in the fine aggregate. In contrast, the method for producing recycled fine aggregate for concrete according to the first aspect of the present invention can produce high-quality recycled fine aggregate for concrete. In the method for producing recycled fine aggregate for concrete according to the first aspect of the present invention, a first treating agent containing microbubble water and iron oxide is added to a product derived from returned fresh concrete or residual concrete, followed by a second treating agent containing a cationic surfactant. This is thought to effectively remove the cement from the fine aggregate contained in the product. Therefore, it is thought that high-quality recycled fine aggregate for concrete can be produced. Specifically, it is believed that the cement component attached to the fine aggregate contained in the derived product (e.g., cement component of cement paste derived from returned fresh concrete and residual fresh concrete) is easily swollen by the first treatment agent. Even when returned fresh concrete and residual fresh concrete themselves are used as the derived product, it is believed that the cement component attached to the fine aggregate contained in the returned fresh concrete and residual fresh concrete is easily swollen. It is believed that the swelling of the cement component makes it easier for the cement component to peel off from the fine aggregate contained in the derived product that will become the fine aggregate for concrete. It is believed that the cement component in this easily peelable state is then suitably peeled off and removed from the fine aggregate contained in the derived product that will become the fine aggregate for concrete by the second treatment agent. Therefore, it is believed that the method for producing recycled fine aggregate for concrete according to the first aspect of the present invention can produce high-quality recycled fine aggregate for concrete from which the cement component has been suitably removed.

[0013] A second aspect of the present invention is a method for producing recycled fine aggregate for concrete, which is the same as the first aspect of the present invention, except that it further comprises a step of adding a third treatment agent containing percarbonate to the derived product to which the second treatment agent has been added.

[0014] According to this configuration, a higher quality recycled fine aggregate for concrete can be obtained, which is believed to be because the third treating agent more effectively removes the cement components from the fine aggregate contained in the derived material to be used as fine aggregate for concrete.

[0015] A third aspect of the present invention is a method for producing recycled fine aggregate for concrete, which is the method for producing recycled fine aggregate for concrete according to the first aspect of the present invention, further comprising the step of spraying microbubble water onto the derived material to which the second treatment agent has been added, or the step of immersing the derived material to which the second treatment agent has been added in microbubble water.

[0016] According to this configuration, a higher quality recycled fine aggregate for concrete can be obtained. This is thought to be because, by spraying or immersing the microbubble water, the cement components are more effectively removed from the fine aggregate contained in the derived material to be used as the fine aggregate for concrete, and the cationic surfactant that may remain in the fine aggregate is also more effectively removed.

[0017] A fourth aspect of the present invention is a method for producing recycled fine aggregate for concrete, which is the method for producing recycled fine aggregate for concrete according to the second aspect of the present invention, further comprising the step of spraying microbubble water onto the derived material to which the third treatment agent has been added, or the step of immersing the derived material to which the third treatment agent has been added in microbubble water.

[0018] According to this configuration, a higher quality recovered fine aggregate for concrete can be obtained. This is thought to be because, by spraying or immersing the microbubble water, the cement component is more effectively removed from the fine aggregate contained in the derived material to be used as fine aggregate for concrete, and the cationic surfactant and percarbonate that may remain in the fine aggregate are also more effectively removed.

[0019] A method for producing ready-mixed concrete according to a fifth aspect of the present invention is a method for producing ready-mixed concrete, comprising a step of mixing cement, aggregate, and water, and using as the aggregate an aggregate containing recycled fine aggregate for concrete produced by the method for producing recycled fine aggregate for concrete according to any one of the first to fourth aspects of the present invention.

[0020] According to this configuration, it is possible to provide a method for producing ready-mixed concrete that can produce high-quality ready-mixed concrete. Specifically, by using as aggregate an aggregate containing recycled fine aggregate for concrete produced by the method for producing recycled fine aggregate for concrete according to any one of the first to fourth aspects of the present invention, it is possible to produce high-quality ready-mixed concrete. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a method for producing recycled fine aggregate for concrete, which can produce high-quality recycled fine aggregate for concrete. Also, according to the present invention, it is possible to provide a method for producing ready-mixed concrete, which can produce high-quality ready-mixed concrete. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these.

[0023] A method for producing recycled fine aggregate for concrete according to one embodiment of the present invention includes a step of adding a first treatment agent containing microbubble water and iron oxide to a material derived from returned ready-mixed concrete or residual ready-mixed concrete (first addition step), and a step of adding a second treatment agent containing a cationic surfactant to the material to which the first treatment agent has been added (second addition step).

[0024] The derived material is not particularly limited as long as it is derived from returned ready-mixed concrete or from leftover ready-mixed concrete. The returned ready-mixed concrete and leftover ready-mixed concrete are ready-mixed concrete produced at a ready-mixed concrete plant or the like that is transported to a construction site by an agitator truck or the like, but is returned to the ready-mixed concrete plant. Among these, the returned ready-mixed concrete is ready-mixed concrete that is not used at a construction site or the like, but is returned as is to the ready-mixed concrete plant. The leftover ready-mixed concrete is ready-mixed concrete that remains in an agitator truck or the like that has returned from a construction site or the like.

[0025] The derived material may be, for example, the returned fresh concrete or the remaining fresh concrete. That is, in this case, the production method is a method for producing recycled fine aggregate for concrete, comprising the steps of adding a first treating agent containing microbubble water and iron oxide to the returned fresh concrete or the remaining fresh concrete, and adding a second treating agent containing a cationic surfactant to the returned fresh concrete or the remaining fresh concrete to which the first treating agent has been added. Whether the derived material is the returned fresh concrete or the remaining fresh concrete, the production method can produce high-quality recycled aggregate for concrete. Examples of the derived material include the returned fresh concrete diluted with water such as microbubble water, the remaining fresh concrete diluted with water such as microbubble water, fine aggregate extracted from the returned fresh concrete, and fine aggregate extracted from the remaining fresh concrete. Specifically, the fine aggregate may be obtained by adding water such as microbubble water to the returned ready-mixed concrete and extracting the fine aggregate from the water-added returned ready-mixed concrete, or by adding water such as microbubble water to the remaining ready-mixed concrete and extracting the fine aggregate from the water-added remaining ready-mixed concrete. When microbubble water is used to produce fine aggregate from returned ready-mixed concrete or remaining ready-mixed concrete, the production method includes the steps of adding microbubble water to the returned ready-mixed concrete or remaining ready-mixed concrete, extracting fine aggregate from the returned ready-mixed concrete or remaining ready-mixed concrete to which the microbubble water has been added, adding a first treating agent containing microbubble water and iron oxide to the fine aggregate, and adding a second treating agent containing a cationic surfactant to the fine aggregate to which the first treating agent has been added. Whether the derived product is aggregate extracted from returned ready-mixed concrete or fine aggregate extracted from remaining ready-mixed concrete, the production method can produce high-quality recovered aggregate for concrete.

[0026] In the first addition step, a first treatment agent containing microbubble water and iron oxide is added to the derived material.

[0027] The first treatment agent is not particularly limited as long as it contains microbubble water and iron oxide, and examples thereof include a treatment agent (dispersion liquid) in which iron oxide is dispersed in microbubble water. Examples of the first treatment agent include a liquid obtained by immersing an iron-containing object (iron-containing material) in microbubble water. By immersing the iron-containing material in microbubble water, the iron present near the surface of the iron-containing material is oxidized, and the iron oxide is released from the iron-containing material, resulting in a treatment agent in which iron oxide is dispersed in microbubble water. The iron-containing material is not particularly limited as long as iron is present near its surface, and may be made of iron, for example. Examples of the iron-containing material that is the raw material for the iron oxide include iron nails and iron from disposable hand warmers. Examples of the iron from disposable hand warmers include iron-containing material from used disposable hand warmers. The conditions for preparing the first treatment agent are not particularly limited as long as the first treatment agent is obtained. For example, the time for immersing the iron-containing object in the microbubble water is preferably 5 minutes to 60 hours, more preferably 30 minutes to 60 hours. The temperature of the microbubble water in which the iron-containing object is immersed is not particularly limited. For example, it is preferably 5 to 50°C, more preferably 5 to 40°C, even more preferably 10 to 40°C, and particularly preferably 10 to 35°C, and examples include room temperature. The amount of microbubble water added is preferably 10 to 10,000 parts by mass, more preferably 50 to 1,000 parts by mass, per 100 parts by mass of the iron-containing object. While the iron-containing object is immersed in the microbubble water, the microbubble water may be subjected to a bubbling treatment. The first treatment agent may be, for example, a liquid or semi-solid. Examples of the liquid include a paste. The semi-solid state is classified as a state of 30 Pa·s or more in the JAS standard, and examples thereof include a state of 30 Pa·s or more.

[0028] The microbubble water is water containing microbubbles, and examples thereof include microbubble water as defined in ISO 20480-1:2017. The average particle size of the microbubbles is preferably 0.1 to 100 μm, and more preferably 0.1 to 50 μm. Examples of the average particle size of the microbubbles include the volume-equivalent spherical diameter, which is the diameter calculated based on the volume of a bubble assuming a spherical shape.

[0029] The method for producing the microbubble water is not particularly limited, and examples thereof include the ejector method, cavitation method, swirl flow method, and pressure dissolution method. Examples of the ejector method include a method in which pressurized liquid is fed into an ejector and the gas self-absorbed by countless separation flows generated inside the ejector is atomized to generate bubbles. Examples of the cavitation method include a method in which pressurized liquid is fed into a generator with a cavitation structure and the cavitation phenomenon (cavitation phenomenon) generated in the structure is utilized to precipitate dissolved gas contained in the liquid and generate bubbles. Examples of the swirl flow method include a method in which pressurized liquid is fed from an eccentric direction into a cylindrical generator, air is self-absorbed by an air column formed in the center of the cylinder, and bubbles are generated by the shear force generated by the velocity difference during discharge. Examples of the pressure dissolution method include a method in which gas is forcibly dissolved under pressure and then the bubbles are precipitated by decompression (opening to the atmosphere). A swirl-type microbubble generator is desirable as it is less affected by water quality. Specifically, a microbubble generator using a YJ nozzle manufactured by Bay Clean Co., Ltd. is preferred. The microbubble water is preferably microbubble water produced by a microbubble generator using a YJ nozzle manufactured by Bay Clean Co., Ltd.

[0030] The iron oxide is not particularly limited, but examples thereof include iron oxide generated by immersing an iron-containing material in microbubble water (iron oxide formed by oxidizing the iron in the iron-containing material), as described above.

[0031] The concentration of the iron oxide in the first treating agent is preferably 0.01 to 50% by mass, more preferably 0.1 to 20% by mass, and even more preferably 0.1 to 10% by mass, relative to the first treating agent. If the iron oxide concentration is too low, the quality of the final recycled fine aggregate for concrete tends to be insufficient. This is thought to be because the cement components attached to the fine aggregate are not sufficiently swollen by the first treating agent, making it difficult to effectively remove the cement components from the fine aggregate even when the second treating agent is added. Furthermore, if the iron oxide concentration is too high, not only will the effect of improving the quality of the final recycled fine aggregate for concrete saturate, but the impact of the iron oxide on the quality of the final recycled fine aggregate for concrete may become significant. Therefore, if the iron oxide concentration is within the above range, high-quality recycled fine aggregate for concrete can be effectively obtained.

[0032] In the second addition step, a second treatment agent containing a cationic surfactant is added to the derived material to which the first treatment agent has been added.

[0033] The second treatment agent is not particularly limited as long as it contains a cationic surfactant, and examples thereof include an aqueous solution in which a cationic surfactant is dissolved in water. Furthermore, when the second treatment agent contains water, for example, when the second treatment agent is an aqueous solution in which a cationic surfactant is dissolved in water, the water may be ordinary water such as tap water or industrial water, or microbubble water. Furthermore, as long as the second treatment agent contains a cationic surfactant, it may also contain components other than the cationic surfactant.

[0034] The cationic surfactant is not particularly limited, and examples thereof include quaternary ammonium surfactants and amine surfactants. More specific examples thereof include amine salts (alkylamine salts, amide-bonded amine salts, ester-bonded amine salts, etc.), quaternary ammonium salts (alkylammonium salts, amide-bonded ammonium salts, ester-bonded ammonium salts, ether-bonded ammonium salts, etc.), and pyridinium salts (alkylpyridinium salts, amide-bonded pyridinium salts, ether-bonded pyridinium salts, ester-bonded pyridinium salts, etc.).

[0035] Examples of the quaternary ammonium surfactants include tetraalkylammonium hydroxide, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, tetraalkylammonium chloride, and alkylbenzyldimethylammonium chloride. Examples of the tetraalkylammonium hydroxides include tetraethylammonium hydroxide (TEAH) and tetrabutylammonium hydroxide (TBAH). Examples of the alkyltrimethylammonium chlorides include lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, and cetyltrimethylammonium chloride. Examples of the dialkyldimethylammonium chlorides include dilauryldimethylammonium chloride and distearyldimethylammonium chloride. Examples of the tetraalkylammonium chlorides include tetraethylammonium chloride and tetrabutylammonium chloride.

[0036] Examples of the amine surfactant include ethylamine chloride, diethylamine chloride, triethylamine chloride, butylamine chloride, dibutylamine chloride, tributylamine chloride, octylamine chloride, dioctylamine chloride, trioctylamine chloride, dodecylamine chloride, didodecylamine chloride, tridodecylamine chloride, stearylamine chloride, and distearylamine chloride.

[0037] The cationic surfactants may be used alone or in combination of two or more.

[0038] The concentration of the cationic surfactant in the second treating agent is preferably 0.01 to 20% by mass, more preferably 0.1 to 15% by mass, and even more preferably 0.1 to 10% by mass, relative to the second treating agent. If the concentration of the cationic surfactant is too low, the quality of the final recycled fine aggregate for concrete tends to be insufficient. This is thought to be because the addition of the second treating agent makes it difficult to adequately remove the cement from the fine aggregate. Furthermore, if the concentration of the cationic surfactant is too high, not only will the effect of improving the quality of the final recycled fine aggregate for concrete saturate, but the cationic surfactant may remain in the final recycled fine aggregate for concrete, significantly increasing the impact of the cationic surfactant on the quality of the final recycled fine aggregate for concrete. Therefore, when the concentration of the cationic surfactant is within the above range, high-quality recycled fine aggregate for concrete can be obtained.

[0039] The manufacturing method may include a step (third adding step) of adding a third treating agent containing percarbonate to the derived material to which the second treating agent has been added. By including the third adding step, the manufacturing method can obtain a higher quality recycled fine aggregate for concrete. This is thought to be because the third treating agent more effectively removes the cement from the fine aggregate contained in the derived material to be used as fine aggregate for concrete. The third adding step is not particularly limited as long as it is a step of adding the third treating agent to the derived material to which the second treating agent has been added.

[0040] The third treatment agent is not particularly limited as long as it contains percarbonate, and examples thereof include an aqueous solution in which percarbonate is dissolved in water. Furthermore, when the third treatment agent contains water, for example, when the third treatment agent is an aqueous solution in which percarbonate is dissolved in water, the water may be ordinary water such as tap water or industrial water, or may be microbubble water. Furthermore, as long as the third treatment agent contains percarbonate, it may also contain components other than percarbonate. Examples of components other than percarbonate contained in the third treatment agent include a pH adjuster.

[0041] The percarbonate is not particularly limited, but examples thereof include sodium percarbonate, potassium percarbonate, calcium percarbonate, magnesium percarbonate, and ammonium percarbonate. Among these, sodium percarbonate is preferred. The percarbonate may be used alone or in combination of two or more.

[0042] The concentration of the percarbonate in the third treating agent is preferably 0.01 to 20% by mass, more preferably 0.1 to 15% by mass, and even more preferably 0.1 to 10% by mass, relative to the third treating agent. If the percarbonate concentration is too low, the effect of adding the third treating agent, such as the effect of removing cement from the fine aggregate contained in the derived material to be used as fine aggregate for concrete, tends to be insufficient. Therefore, even if the third treating agent is added, the quality of the final recycled fine aggregate for concrete tends not to be sufficiently improved. Furthermore, if the percarbonate concentration is too high, not only will the effect of improving the quality of the final recycled fine aggregate for concrete be saturated, but the percarbonate may remain in the final recycled fine aggregate for concrete, potentially significantly affecting the quality of the final recycled fine aggregate for concrete. Therefore, if the percarbonate concentration is within the above range, a higher quality recycled fine aggregate for concrete can be obtained.

[0043] The manufacturing method may include a step of spraying microbubble water onto the derived material to which the second treating agent has been added, a step of spraying microbubble water onto the derived material to which the third treating agent has been added, a step of immersing the derived material to which the second treating agent has been added in microbubble water, or a step of immersing the derived material to which the third treating agent has been added in microbubble water (a microbubble water treatment step). By including the microbubble water treatment step, the manufacturing method can obtain a higher quality recycled fine aggregate for concrete. This is believed to be due to the following: By spraying or immersing the derived material in microbubble water, the cement component can be more effectively removed from the fine aggregate contained in the derived material to be used as fine aggregate for concrete. The cationic surfactant contained in the second treating agent may remain in the fine aggregate. Furthermore, when the third treating agent is added, the percarbonate contained in the third treating agent may remain. It is believed that spraying or immersing the fine aggregate in the microbubble water can more effectively remove the cationic surfactant and percarbonate that may remain in the fine aggregate, thereby producing a higher quality recycled fine aggregate for concrete.

[0044] In this production method, the addition of the first treatment agent, the second treatment agent, the third treatment agent, and the microbubble water in the microbubble water treatment step to the derived material and the derived material to which any of the treatment agents has been added is not particularly limited, as long as the added treatment agents come into contact with the derived material. Examples of the method of adding the treatment agents to the derived material include pouring, immersion, and pouring. Examples of the pouring method include spraying and scattering.

[0045] After the addition, the derived material may be stirred. The stirring time is not particularly limited as long as the derived material is thoroughly mixed. For example, it is preferably 30 seconds to 24 hours, and more preferably 5 minutes to 15 hours. The amounts of the first treating agent, the second treating agent, the third treating agent, and the microbubble water in the microbubble water treatment step added are not particularly limited as long as they are in sufficient contact with the derived material. In this case, the amounts added are preferably 0.1 to 1,000 parts by mass, more preferably 1 to 500 parts by mass, per 100 parts by mass of the derived material. If the amount added is too small, the quality of the finally obtained recycled fine aggregate for concrete tends to be insufficient. This is thought to be because the cement component attached to the fine aggregate is not sufficiently swollen, making it difficult to adequately remove the cement component from the fine aggregate. Furthermore, if the amount added is too large, not only will the effect of improving the quality of the finally obtained recycled fine aggregate for concrete be saturated, but the effect of subsequently removing the cement component may be insufficient. Therefore, when the amount added is within the above range, a high-quality recycled fine aggregate for concrete can be suitably obtained.

[0046] In the case of immersion, the immersion time is not particularly limited as long as sufficient contact with the derived product is ensured, and is, for example, preferably 30 seconds to 24 hours, more preferably 5 minutes to 15 hours. The temperature of the treatment agent in which the derived product is immersed is also not particularly limited, and is, for example, preferably 0 to 50°C, more preferably 5 to 35°C, and may be, for example, room temperature.

[0047] When spraying the treatment agent onto the derived material, the spraying time is not particularly limited as long as it allows sufficient contact with the derived material, and is preferably, for example, 30 seconds to 24 hours, and more preferably, 5 minutes to 2 hours. Furthermore, when sprinkling (spraying) the treatment agent onto the derived material, the number of sprays is not particularly limited as long as it allows sufficient contact of the treatment agent with the derived material, and is preferably, for example, two or more times, more preferably, two to five times, and even more preferably, two to four times. The spraying may be carried out using, for example, a spiral water washer, a spiral washer, or a spiral classifier. When such a treatment agent is sprayed onto the derived material, the temperature of the treatment agent is not particularly limited, and is preferably, for example, 0 to 50°C, more preferably, 5 to 35°C, and may be, for example, room temperature.

[0048] The amount of the treatment agent added in the addition step is not particularly limited in the case of the immersion and spraying, as long as the treatment agent can be sufficiently brought into contact with the derived material. The amount of the treatment agent added is, for example, preferably 0.05 to 30% by volume, more preferably 1 to 20% by volume, and even more preferably 3 to 10% by volume, relative to the derived material. The amount is particularly suitable when the addition step is carried out on a batch scale, such as by immersing the derived material in the treatment agent. Furthermore, the amount of the treatment agent added is, for example, 0.05 to 30% by volume, more preferably 1 to 20% by volume, and even more preferably 3 to 10% by volume, relative to the derived material. 3The amount is preferably 1 to 300 kg, and more preferably 5 to 100 kg, relative to the amount of the recovered fine aggregate. This amount is particularly suitable when the addition step is performed continuously, such as by applying a treatment agent to the derived material. If the amount is too small, the quality of the finally obtained recycled fine aggregate for concrete tends to be insufficiently improved. This is thought to be because the cement components attached to the fine aggregate are not sufficiently swollen by the treatment agent, making it difficult to effectively remove the cement components from the derived material even when the treatment agent is added. Furthermore, if the amount is too large, not only will the effect of improving the quality of the finally obtained recycled fine aggregate for concrete saturate, but the effect of the subsequently added treatment agent in removing the cement components may also be insufficient. Therefore, when the amount is within the above range, a high-quality recycled fine aggregate for concrete can be obtained.

[0049] When the derived material is returned ready-mixed concrete or remaining ready-mixed concrete, the manufacturing method may include a step (extraction step) of extracting fine aggregate (solids of a size suitable for use as fine aggregate) from the derived material. Examples of the extraction step include allowing solids to settle in the returned ready-mixed concrete or remaining ready-mixed concrete to which the first and second treatment agents have been added, and sieving the solids obtained by this settling to separate the fine aggregate (solids of a size suitable for use as fine aggregate). Furthermore, the first, second, and third treatment agents may be removed from the extracted fine aggregate using a spiral water washer, a spiral washer, a spiral screw sand reclaimer, a spiral classifier, or the like. The extracted fine aggregate is obtained as recovered fine aggregate for concrete. Furthermore, in the manufacturing method, when the derived material is fine aggregate extracted from the returned ready-mixed concrete or the residual ready-mixed concrete, water such as microbubble water may be added to the returned ready-mixed concrete, and the extracted concrete to which the water has been added may be subjected to the extraction step. By doing so, the fine aggregate extracted from the returned ready-mixed concrete or the residual ready-mixed concrete can be used as the derived material.

[0050] The manufacturing method may include a step of removing magnetic material components from the obtained recovered fine aggregate for concrete by magnetic force (removal step). In the removal step, for example, magnetic material components such as iron oxide contained in the first treatment agent are removed from the fine aggregate for concrete by magnetic force. The removal can be performed using a magnetic separator or the like, without any particular limitation. Examples of the magnetic separator include a drum-type magnetic separator using a permanent magnet, a belt-type magnetic separator using a permanent magnet, a drum-type magnetic separator using an electromagnet, and a belt-type magnetic separator using an electromagnet. Examples of the magnetic separator include a hanging electromagnet for iron removal. The magnetic material components removed in the removal step are not particularly limited, as long as they are components that should not be contained in the recovered fine aggregate for concrete, and examples thereof include iron oxide contained in the first treatment agent.

[0051] As described above, the method for producing recycled fine aggregate for concrete can produce high-quality recycled fine aggregate for concrete. The method for producing recycled fine aggregate for concrete can produce fine aggregate for concrete of higher quality than recycled aggregate specified in JIS A 5308:2019, for example. Furthermore, the method can produce recycled fine aggregate for concrete of higher quality than recycled aggregate for concrete H specified in JIS A 5021:2018 and recycled aggregate for concrete M specified in JIS A 5022:2018, for example.

[0052] The recycled fine aggregate for concrete obtained by the method for producing recycled fine aggregate for concrete has, for example, an oven-dry density of 1.5 g / cm 3 The recycled fine aggregate for concrete has a water absorption rate of 7% or less, and when the color tone is expressed by the Lab system, the a value is 0 to 3 and the b value is 5 to 15. Such recycled fine aggregate for concrete is a high-quality recycled fine aggregate for concrete. In addition, fine aggregate other than recycled fine aggregate (ordinary fine aggregate) has an oven-dry density of 1.5 g / cm 3 It is possible to obtain fine aggregate having a water absorption rate of 7% or less and a color tone expressed in the Lab system with an a value of 0 to 3 and a b value of 5 to 15. However, it has not been possible to produce such recycled fine aggregate for concrete from recycled fine aggregate in the past. The method for producing recycled fine aggregate for concrete according to this embodiment allows the production of the recycled fine aggregate for concrete.

[0053] The bone dry density of the recycled fine aggregate for concrete is 1.5 g / cm as described above. 3 or more, and 2 g / cm 3 It is preferable that the concentration is 2.5 g / cm or more. 3 It is more preferable that the bone dry density of the recycled fine aggregate for concrete is 4.5 g / cm or more. 3 It is preferable that the bone dry density is less than 1000 g / cm. If the bone dry density is within the above range, it is found that there are few voids, and from this, it is considered that the cement content in the derived material is sufficiently removed.3 ) is the mass (g) of a substance in a dry state, expressed as the volume (cm 3 ) divided by the mass of the sample. The bone-dry state is when a sample is left in a hot air dryer at 110°C, and the mass of the sample is measured at 15-minute intervals, with the difference between the mass before and after being within 0.1% of the mass after. The bone-dry state mass is the mass of the sample when it has reached a bone-dry state. The bone-dry state volume is the volume of the sample when it has reached a bone-dry state.

[0054] As described above, the water absorption of the recycled fine aggregate for concrete is 7% or less, preferably 5% or less, more preferably 4.5% or less, even more preferably 4% or less, particularly preferably 3.5% or less, and particularly preferably 3% or less. Furthermore, while a lower water absorption rate is preferable for the recycled fine aggregate for concrete, in practice, the limit is often around 0.5%, and the lower limit of the water absorption rate range for the recycled fine aggregate for concrete is, for example, 0.5%. If the water absorption rate is within the above range, it is considered that the cement content in the derived material has been sufficiently removed, resulting in a high-quality recycled fine aggregate for concrete. The water absorption rate is the percentage of the total amount of water contained in the aggregate in a surface-dry, water-saturated state relative to the mass of the aggregate in an absolute dry state. In other words, it is a numerical value that represents the amount of water that the aggregate can contain, expressed as a percentage. The surface-dry, water-saturated state (surface-dry state) refers to a state in which there is no surface water on the aggregate and all voids within the aggregate grains are filled with water. The total amount of water contained in surface-dry, water-saturated aggregate is the difference between the mass of the surface-dry aggregate and the mass of the bone-dry aggregate.

[0055] When the color tone of the recycled fine aggregate for concrete is expressed by the Lab system, the a-value is 0 to 3, preferably 0.5 to 3, and more preferably 0.5 to 2.5. The b-value is 5 to 15, preferably 7 to 15, and more preferably 7 to 12. While conventional fine aggregate for concrete (fine aggregate that is not recycled fine aggregate) may have a-values ​​and b-values ​​within the above ranges, it has been difficult to achieve a-values ​​and b-values ​​within the above ranges for recycled fine aggregate for concrete.

[0056] The angle of repose of the recycled fine aggregate for concrete is preferably 45° or less, more preferably 42° or less, even more preferably 40° or less, and particularly preferably 38° or less. Although a smaller angle of repose of the fine aggregate is preferable, in practice, the limit is often around 10°, and the lower limit of the range of the angle of repose of the recycled fine aggregate for concrete is, for example, 10°. If the angle of repose is within the above range, the cement paste has been removed, reducing the adhesion between the fine aggregates. This reduces adhesion between the fine aggregates, improving storage stability.

[0057] The fine powder content of the recycled fine aggregate for concrete is preferably 7% or less, more preferably 5% or less, and even more preferably 3% or less. The fine powder content is the ratio of fine powder contained in the aggregate that passes through a 75 μm (0.075 mm) mesh sieve to the total mass of the aggregate. If the fine powder content is within the above range, the cement paste has been removed, reducing the adhesion between the fine aggregates. This reduces adhesion between the fine aggregates and improves storage stability.

[0058] The Ca content in the entire recovered fine aggregate for concrete is preferably 25% by mass or less, and more preferably 5 to 20% by mass. The Si content in the entire recovered fine aggregate for concrete is preferably 70% by mass or more, and more preferably 70 to 95% by mass. Furthermore, the ratio of the Ca content to the Si content in the entire recovered fine aggregate for concrete (Ca content / Si content) is preferably 0 to 0.5, and more preferably 0 to 0.4. The Si content and Ca content in the entire recovered fine aggregate for concrete can be measured, for example, by fluorescent X-ray analysis. Furthermore, the ratio of the Ca content to the Si content in the entire recovered fine aggregate for concrete (Ca content / Si content) can be calculated from these Si content and Ca content.

[0059] The amount of Ca on the surface of the recycled fine aggregate for concrete is preferably 9% by mass or less, and more preferably 0.5 to 7% by mass. The amount of Si on the surface of the recycled fine aggregate for concrete is preferably 12 to 40% by mass, and more preferably 15 to 30% by mass. The ratio of the amount of Ca to the amount of Si on the surface of the recycled fine aggregate for concrete (Ca amount / Si amount) is preferably 0.22 or less, and more preferably 0.05 to 0.2. The amounts of Si and Ca on the surface of the recycled fine aggregate for concrete can be measured, for example, by X-ray analysis, and more specifically, by an energy dispersive X-ray analyzer (EDS) equipped in a scanning electron microscope. The ratio of the amount of Ca to the amount of Si in the entire recycled fine aggregate for concrete (Ca amount / Si amount) can be calculated from these amounts of Si and Ca.

[0060] [Ready-mix concrete manufacturing method] A method for producing ready-mixed concrete according to another embodiment of the present invention includes a step (mixing step) of mixing cement, aggregate, and water, and uses aggregate containing the recycled fine aggregate for concrete (recycled fine aggregate for concrete produced by the method for producing recycled fine aggregate for concrete) as the aggregate. Specific examples of the method for producing ready-mixed concrete include a method similar to a general method for producing ready-mixed concrete, except that the recycled fine aggregate for concrete is used as the aggregate. By using the recycled fine aggregate for concrete as the aggregate, excellent ready-mixed concrete can be produced. By including the recycled fine aggregate for concrete in the ready-mixed concrete, excellent ready-mixed concrete can be obtained. Furthermore, the ready-mixed concrete may contain only the recycled fine aggregate for concrete as a fine aggregate, or may contain the recycled fine aggregate for concrete and other fine aggregates. Furthermore, the ready-mixed concrete may contain coarse aggregate. In the mixing step in the ready-mixed concrete production method, other components, such as those mentioned above, may be mixed as needed in addition to cement, aggregate, and water. The mixing step is a step of mixing cement, aggregate, water, and, as necessary, the other components, etc. The mixing step is not particularly limited except that the recycled aggregate for concrete is used as the aggregate, and examples thereof include a mixing step in a general method for producing ready-mixed concrete.

[0061] The cement is not particularly limited as long as it is a cement used in producing ready-mixed concrete. Specific examples include Portland cement, such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and white Portland cement, as well as blast-furnace cement, alumina cement, silica cement, and silica fume cement. Among these, Portland cement is preferred, and ordinary Portland cement is more preferred. Examples of ordinary Portland cement include those described in JIS R 5210:2009. The use of such cement is believed to facilitate the hydration reaction and porazon reaction of the cement. Therefore, the use of such cement can produce ready-mixed concrete that can provide a concrete structure with higher strength and stability. The content of the cement is preferably 8.84 to 18.13 volume % relative to the ready-mixed concrete. If the amount of cement is too small, the resulting concrete structure tends to have insufficient strength. If the amount of cement is too large, the resulting concrete structure tends to have insufficient stability. This is thought to be because if the amount of cement is too large, the amount of coal ash becomes relatively small, making it difficult for the pozzolanic reaction to proceed properly, and the effect of improving stability due to the pozzolanic reaction becomes insufficient.

[0062] As described above, the aggregate is not particularly limited as long as it contains the recycled fine aggregate for concrete, and may contain aggregates other than the recycled fine aggregate for concrete. Examples of the aggregate include fine aggregate and coarse aggregate. As described above, the ready-mixed concrete may contain the recycled fine aggregate for concrete alone as the fine aggregate, or the recycled fine aggregate for concrete in combination with other fine aggregates. Even when the recycled fine aggregate for concrete is used alone as the fine aggregate, the ready-mixed concrete may contain an aggregate other than the recycled fine aggregate for concrete as the coarse aggregate. The aggregate other than the recycled fine aggregate for concrete is not particularly limited as long as it is an aggregate commonly used in producing ready-mixed concrete. The fine aggregate other than the recycled fine aggregate for concrete is not particularly limited as long as it is a fine aggregate to be contained in ready-mixed concrete. Examples of such fine aggregate include natural sand such as silica sand, and crushed stone powder. Examples of fine aggregates other than the recycled fine aggregate for concrete include sand and the like specified in JIS A 5005:2020. The coarse aggregate is not particularly limited as long as it is a fine aggregate to be contained in ready-mixed concrete. Examples of the coarse aggregate include crushed stone and the like. Examples of the coarse aggregate include Coarse Aggregate 1505 and Coarse Aggregate 2010 specified in JIS A 5005:2020, as well as mixtures thereof. Examples of aggregates other than the recycled fine aggregate for concrete include, for example, mountain sand, which is a sandy soil collected as a construction material from alluvial deposits in land areas such as mountains, hills, and plateaus. The content of the aggregate is preferably 66.80 to 90.33% by volume relative to the ready-mixed concrete. Among the aggregates, the content of the recycled fine aggregate for concrete is preferably 31.31 to 43.10% by volume relative to the ready-mixed concrete.

[0063] The water is not particularly limited as long as it is water that is commonly used when producing ready-mixed concrete. Examples of water include common water such as tap water and industrial water. The content of the water is preferably 6.84 to 8.85% by volume of the ready-mixed concrete.

[0064] The ready-mixed concrete may contain, in addition to the cement, aggregate, and water, other components that are generally added to ready-mixed concrete, such as coal ash, slag powder, surfactants such as air entraining agents (AE agents), and admixtures such as AE water-reducing agents.

[0065] The coal ash is not particularly limited as long as it is ash generated when coal is burned. Examples of the coal ash include fly ash and clinker ash, and fly ash is preferably used.

[0066] The slag powder is not particularly limited, and examples thereof include blast furnace slag powder, copper slag powder, etc. That is, the slag powder is preferably blast furnace slag powder, copper slag powder, or a mixture of blast furnace slag powder and copper slag powder.

[0067] The admixture is not particularly limited as long as it is an admixture to be contained in ready-mixed concrete. Examples of the admixture include surfactants such as air-entraining agents and air-entraining water-reducing agents, and specifically include water-reducing agents specified in JIS A 6204:2011 (high-performance air-entraining water-reducing agents).

[0068] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. [Example]

[0069] First, the treating agents used in this example will be described.

[0070] [First treatment agent] (First treatment agent A) One kilogram of iron nails was immersed in 10 kg of microbubble water produced using a swirl-type microbubble water generator (a microbubble water generator using a YJ nozzle manufactured by Bay Clean Co., Ltd.). The microbubble water containing the iron nails was then bubbled for 12 hours using the microbubble generator. This process caused the microbubble water to turn blackish-brown. A blackish-brown component was dispersed in the microbubble water, which was analyzed using microscopic Raman spectroscopy and identified as iron oxide (magnetite: Fe3O4). This confirmed that the liquid was microbubble water containing dispersed iron oxide produced by the oxidation of the iron nails. This microbubble water containing dispersed iron oxide produced by the oxidation of the iron nails was used as a first treatment agent A containing microbubble water and iron oxide. The concentration of iron oxide in this first treatment agent A was 3% by mass relative to the first treatment agent A.

[0071] (First treatment agent B) 1 kg of iron from a used disposable hand warmer was immersed in 10 kg of microbubble water produced using a swirl-type microbubble water generator (a microbubble water generator using a YJ nozzle manufactured by By-Clean Co., Ltd.). The microbubble water containing the iron-containing material from the used disposable hand warmer was then bubbled for 12 hours using the microbubble generator. This process caused the microbubble water to turn blackish-brown. A blackish-brown component was dispersed in the microbubble water, which was analyzed using microscopic Raman spectroscopy and identified as iron oxide (magnetite: Fe3O4). This liquid was determined to be microbubble water containing dispersed iron oxide, which was generated by the oxidation of iron from the iron-containing material in the used disposable hand warmer. This microbubble water containing dispersed iron oxide, which was generated by the oxidation of iron from the iron-containing material in the used disposable hand warmer, was used as the first treatment agent B, containing microbubble water and iron oxide. The concentration of iron oxide in this first treatment agent B was 4 mass % relative to the first treatment agent B.

[0072] [Second treatment agent] A 1% by mass aqueous solution of a cationic surfactant (quaternary ammonium salt type cationic surfactant) (lauryltrimethylammonium chloride, Kohtamin 24P manufactured by Kao Corporation) was used as the second treatment agent containing a cationic surfactant.

[0073] [Third treatment agent] A solution of sodium percarbonate (manufactured by Hayashi Pure Chemical Industries, Ltd.) dissolved in the microbubble water (microbubble water produced using a swirl-type microbubble water generator) was used as a third treatment agent containing percarbonate. The concentration of sodium percarbonate (percarbonate) in this third treatment agent was 10% by mass relative to the third treatment agent.

[0074] [Example 1] To 1 kg of returned ready-mixed concrete, 1 kg of the first treating agent A (a first treating agent derived from iron nails) was added and stirred for 10 hours. Then, 0.1 kg of the second treating agent was added to the returned ready-mixed concrete to which the first treating agent A had been added, and the mixture was stirred for 5 hours. The solids in the returned ready-mixed concrete to which the first treating agent A and the second treating agent had been added were then allowed to settle, and the solids obtained by this settling were sieved to separate the fine aggregate from the solids. The separated fine aggregate was washed with water using a spiral screw sand recovery machine (manufactured by Kitagawa Iron Works Co., Ltd.), dried, and then stored. The fine aggregate thus obtained was used as the recovered fine aggregate for concrete according to Example 1.

[0075] [Example 2] 10 kg of the microbubble water (microbubble water produced using a swirl-type microbubble water generator) was added to 1 kg of returned ready-mixed concrete and stirred. The solids in the returned ready-mixed concrete to which the microbubble water had been added were allowed to settle, and the solids obtained by this settling were sieved to separate fine aggregate from the solids. The separated fine aggregate was dispersed in the microbubble water and washed. 1 kg of the first treatment agent B (a first treatment agent derived from a used disposable hand warmer) was added to the fine aggregate and stirred for 10 hours. 0.5 kg of the second treatment agent was then added to the fine aggregate to which the first treatment agent B had been added, and the mixture was stirred for 8 hours. 1 kg of the third treatment agent was then added to the fine aggregate to which the first treatment agent B and the second treatment agent had been added. The fine aggregate to which the third treatment agent had been added was stirred for 1 hour, and the fine aggregate was then separated using the spiral water washer. The separated fine aggregate was washed with water using the spiral water washer, dried, and then stored. The fine aggregate thus obtained was obtained as the recycled fine aggregate for concrete according to Example 2.

[0076] [Example 3] 10 kg of the microbubble water (microbubble water produced using a swirl-type microbubble water generator) was added to 1 kg of returned ready-mixed concrete and stirred. The solids in the returned ready-mixed concrete to which the microbubble water had been added were allowed to settle, and the solids obtained by this settling were sieved to separate fine aggregate from the solids. The separated fine aggregate was dispersed in the microbubble water and washed. 2 kg of the first treatment agent A (a first treatment agent derived from iron nails) was added to the fine aggregate to which the first treatment agent A had been added, and the mixture was stirred for 10 hours. 0.1 kg of the second treatment agent was added to the fine aggregate to which the first treatment agent A had been added, and the mixture was stirred for 5 hours. The fine aggregate to which the first treatment agent A and the second treatment agent had been added was then stirred for 10 hours, and the fine aggregate was then separated using the spiral water washer. The separated fine aggregate was washed with water using the spiral water washer, dried, and then stored. The fine aggregate thus obtained was used as the recovered fine aggregate for concrete according to Example 3.

[0077] [Comparative Example 1] 10 kg of the microbubble water (microbubble water produced using a swirl-type microbubble water generator) was added to 1 kg of returned ready-mixed concrete and stirred. The solids in the returned ready-mixed concrete to which the microbubble water had been added were allowed to settle, and the solids obtained by this settling were sieved to separate the fine aggregate from the solids. The separated fine aggregate was washed with water using the spiral water washer, dried, and then stored. The fine aggregate thus obtained was used as the recovered fine aggregate for concrete according to Comparative Example 1. Comparative Example 1 is an example in which the first treatment agent and the second treatment agent were not used.

[0078] Comparative Example 2 10 kg of the microbubble water (microbubble water produced using a swirl-type microbubble water generator) was added to 1 kg of returned ready-mixed concrete and stirred. The solids in the returned ready-mixed concrete to which the microbubble water had been added were allowed to settle, and the solids obtained by this settling were sieved to separate fine aggregate from the solids. The separated fine aggregate was dispersed in the microbubble water and washed. 1 kg of the first treatment agent A (a first treatment agent derived from iron nails) was added to the fine aggregate, and the mixture was stirred for 10 hours. The fine aggregate to which the microbubble water had been added was then stirred for 12 hours, and the fine aggregate was then separated using the spiral water washer. The separated fine aggregate was washed with water using the spiral water washer, dried, and then stored. The fine aggregate thus obtained was used as the recovered fine aggregate for concrete according to Comparative Example 2. Comparative Example 2 is an example in which the second treatment agent was not used.

[0079] Comparative Example 3 10 kg of the microbubble water (microbubble water produced using a swirl-type microbubble water generator) was added to 1 kg of returned ready-mixed concrete and stirred. The solids in the returned ready-mixed concrete to which the microbubble water had been added were allowed to settle, and the solids obtained by this settling were sieved to separate fine aggregate from the solids. The separated fine aggregate was dispersed in the microbubble water and washed. 1 kg of the second treatment agent was added to the fine aggregate, and the mixture was stirred for 5 hours. The fine aggregate to which the second treatment agent had been added was stirred for 12 hours, and then the fine aggregate was separated using the spiral water washer. The separated fine aggregate was washed with water using the spiral water washer, dried, and then stored. The fine aggregate thus obtained was used as the recovered fine aggregate for concrete according to Comparative Example 3. Comparative Example 3 is an example in which the first treatment agent was not used.

[0080] Comparative Example 4 2m 3 The returned fresh concrete was loaded into a double twin-shaft high-intensity mixer. After loading the returned fresh concrete into the mixer, 2 kg of an anionic polyacrylamide organic powder flocculant mixture was added and mixed for 1 minute and 30 seconds. After mixing was completed, the coarse material was discharged and separated in a vibrating sieve with 5 mm openings. The fine aggregate passed through the 5 mm sieve and collected at the bottom. The fine aggregate collected at the bottom was dried and then stored. The fine aggregate obtained in this way was used as the recovered fine aggregate for concrete according to Comparative Example 4.

[0081] The bone dry density, water absorption, angle of repose, and color values ​​(L value, a value, and b value) of the recycled fine aggregate for concrete produced as described above were measured by the following methods. The results are shown in Table 1 below.

[0082] (absolutely dry density) Each of the recovered fine aggregates for concrete obtained was left in a hot air dryer at a temperature of 110°C, and its mass was measured at 15-minute intervals. The mass was measured before and after the measurement and was left in the hot air dryer until the difference in mass before and after the measurement was within 0.1% of the mass after the measurement (absolutely dry state). The mass (g) and volume (cm) of the recovered fine aggregate for concrete in this absolute dry state were 3 ) and the mass (g) of the bone-dry recycled fine aggregate for concrete was measured, and the volume (cm) of the bone-dry recycled fine aggregate for concrete was calculated. 3 ) to obtain the bone dry density (g / cm 3 ) was calculated.

[0083] (Water absorption rate) The water absorption of each recovered concrete fine aggregate was measured using a method in accordance with JIS A 1109:2020. Specifically, the recovered concrete fine aggregate was first placed in a state where there was no surface water and all internal voids were filled with water (surface-dry, water-saturated state), and the mass (g) of this surface-dry, water-saturated recovered concrete fine aggregate was measured. The total amount of water (g) contained in the surface-dry, water-saturated recovered concrete fine aggregate was then calculated by calculating the difference between the mass (g) of the surface-dry, water-saturated recovered concrete fine aggregate and the mass (g) of the bone-dry recovered concrete fine aggregate. The water absorption (%) was then calculated by dividing the total amount of water (g) contained in the surface-dry, water-saturated recovered concrete fine aggregate by the mass (g) of the bone-dry recovered concrete fine aggregate. That is, the water absorption rate (%) was obtained by calculating [(mass (g) of surface-dry water-saturated recovered fine aggregate for concrete - mass (g) of bone-dry recovered fine aggregate for concrete) / mass (g) of bone-dry recovered fine aggregate for concrete × 100].

[0084] (Angle of repose) The angle of repose (°) of each of the obtained recycled fine aggregates for concrete was measured by a method in accordance with JIS R 9301-2-2:1999 Alumina powder - Part 2: Physical property measurement method - 2.

[0085] (L value, a value, and b value) Each of the obtained recycled fine aggregates for concrete was placed in a 3 cm Petri dish, and the L value, a value, and b value of the recycled fine aggregate for concrete in this state were measured using a spectrophotometer (CM-700 manufactured by Konica Minolta, Inc.).

[0086] (Si content, Ca content, and Ca content / Si content) The Si content (mass%) and Ca content (mass%) in the entire recovered fine aggregate for concrete were measured using an X-ray fluorescence analyzer (SEA6000VX HSFinder manufactured by Hitachi High-Tech Science Corporation). From the Si content and Ca content, the ratio of the Ca content to the Si content (Ca content / Si content) in the entire recovered fine aggregate for concrete was calculated.

[0087] Furthermore, the Si content (mass%) and Ca content (mass%) on the surface of the recycled fine aggregate for concrete were measured using a scanning electron microscope (TM3030Plus manufactured by Hitachi High-Technologies Corporation) with an energy dispersive X-ray analyzer (EDS) attached to the scanning electron microscope. From the obtained Si content and Ca content, the ratio of the Ca content to the Si content (Ca content / Si content) on the surface of the recycled fine aggregate for concrete was calculated.

[0088] [evaluation] The obtained recycled fine aggregate for concrete was evaluated by the following methods, and the results are shown in Table 1 below.

[0089] (External observation) The appearance of the recycled fine aggregate for concrete was observed using a digital microscope manufactured by Sanwa Supply Co., Ltd. to observe the degree of adhesion of cement paste to the surface of the recycled fine aggregate for concrete. Specifically, from the image obtained by this observation, the area where cement paste was attached was visually determined and its area was calculated. The results were evaluated according to the following criteria.

[0090] When the presence of cement paste could not be confirmed visually (i.e., when the area ratio occupied by cement paste was 0%), it was evaluated as "1", when the area ratio occupied by cement paste was more than 0% but not more than 20%, it was evaluated as "2", when the area ratio occupied by cement paste was more than 20% but not more than 50%, it was evaluated as "3", when the area ratio occupied by cement paste was more than 50% but not more than 80%, it was evaluated as "4", and when the area ratio occupied by cement paste was more than 80%, it was evaluated as "5". The smaller the evaluation number, the more preferable the recovered fine aggregate for concrete obtained.

[0091] (Powder properties: cohesion) The recovered fine aggregate for concrete was stored at room temperature for one month. After this storage, the condition of the fine aggregate for concrete was visually observed. The results were evaluated according to the following criteria.

[0092] If no cohesion was observed, it was rated as "1," if slight cohesion was observed, it was rated as "2," if cohesion was observed relatively throughout, it was rated as "3," if cohesion was observed relatively throughout and further if strong cohesion was observed in some areas, it was rated as "4," and if cohesion was observed relatively throughout, it was rated as "5." The smaller the rating, the more suitable the recovered fine aggregate for concrete that was obtained.

[0093] Next, ready-mixed concrete was produced using each of the obtained recycled fine aggregates for concrete. Specifically, ready-mixed concrete was produced by mixing the following mixture compositions (mass %).

[0094] The mixture was mixed to a concentration of 12.91% by mass of cement, 42.97% by mass of coarse aggregate, 35.86% by mass of recycled fine aggregate for concrete (recycled fine aggregate for concrete according to Examples 1 to 3 and Comparative Examples 1 to 4), 8.13% by mass of industrial water, and 0.13% by mass of admixture (Flolic SV-10, an AE water-reducing agent manufactured by Flolic Co., Ltd.). Ready-mix concrete was thus obtained.

[0095] Then, using each of the resulting ready-mixed concretes, tests were conducted using a known method to achieve a nominal strength of 21 N and a target slump of 15 cm. The ready-mixed concrete with the above mix proportions is the standard mix for the above test. Specifically, the following evaluations were conducted. The results are shown in Table 1 below.

[0096] (Liquidity) The fluidity of the resulting ready-mixed concrete was visually confirmed. The fluidity of ready-mixed concrete is one of the indicators of workability on site, and if 9 to 10 workers on site judged it to have good fluidity, it was rated as "◎". If 6 to 8 workers on site judged it to have good fluidity, it was rated as "○". If 3 to 5 workers on site judged it to have good fluidity, it was rated as "△". If 0 to 2 workers on site judged it to have good fluidity, it was rated as "×".

[0097] (slump) The slump evaluation of the ready-mixed concrete was carried out in accordance with JIS A 1101:2020. Specifically, the height of the slump was measured immediately after the slump was formed as described above. In addition, the difference between the measured height and the target slump height of 15 cm (slump difference) was evaluated.

[0098] The evaluation of the slump height was carried out using ready-mixed concrete immediately after production and ready-mixed concrete 30 minutes after production.

[0099] (flow) The flow evaluation of the ready-mixed concrete was carried out in accordance with JIS A 1101:2020. Specifically, as described above, the spread of slump immediately after slump formation was evaluated as "standard," "large," or "small" according to the criteria in JIS A 1101:2020.

[0100] (air volume) The air content of the ready-mixed concrete was measured according to a method in accordance with JIS A 1101:2020. The air content was then evaluated as "standard," "large," or "small" in accordance with the standards of JIS A 1101:2020. Specifically, when the ratio of the volume of air mixed into the ready-mixed concrete to the volume of the ready-mixed concrete was 4 to 5% by volume, it was evaluated as "standard," when it exceeded 5% by volume it was evaluated as "large," and when it was less than 4% by volume it was evaluated as "small." In Comparative Example 1, the air content was 6.5% by volume.

[0101] (mixed state) The mixed state of the resulting ready-mixed concrete was evaluated based on the viscosity of the ready-mixed concrete. For example, a soft but sticky ready-mixed concrete is good ready-mixed concrete. If 9 to 10 out of 10 workers on-site judged the mixed state of the ready-mixed concrete to be good, it was rated as "◎". If 6 to 8 out of 10 workers on-site judged the mixed state to be good, it was rated as "○". If 3 to 5 out of 10 workers on-site judged the mixed state to be good, it was rated as "△". If 0 to 2 out of 10 workers on-site judged the mixed state to be good, it was rated as "×".

[0102] As mentioned above, good ready-mixed concrete is one that is soft but sticky. Therefore, the mixing state is more important than the fluidity in evaluating ready-mixed concrete.

[0103] (strength) The strength of the concrete obtained by solidifying the resulting ready-mixed concrete was measured according to a method in accordance with JIS A 1108:2018. The air content was then evaluated as "standard" or "poor" according to the criteria in JIS A 1108:2018.

[0104] (comprehensive evaluation) From the above evaluations, ready-mixed concrete that could be judged to be very good was rated as "○", that which was inferior but could still be used was rated as "△", and that which was judged to be difficult to use as ready-mixed concrete was rated as "×".

[0105] [Table 1]

[0106] It was found that when recycled fine aggregate for concrete (Example 1) was used, which was obtained by adding a first treatment agent containing microbubble water and iron oxide to returned ready-mix concrete or remaining ready-mix concrete, and then adding a second treatment agent containing a cationic surfactant, better ready-mix concrete could be obtained than when the first treatment agent and the second treatment agent were not added (Comparative Examples 1 and 4), when the second treatment agent was not added (Comparative Example 2), and when the first treatment agent was not added (Comparative Example 3). Furthermore, when a recycled fine aggregate for concrete (Example 2) obtained by adding not only the first and second treating agents but also a third treating agent containing percarbonate was used, microbubble water was added to returned ready-mixed concrete or remaining ready-mixed concrete, a first treating agent containing microbubble water and iron oxide was added to the fine aggregate extracted from the returned ready-mixed concrete or remaining ready-mixed concrete to which the microbubble water had been added, and then a second treating agent containing a cationic surfactant was added, the recycled fine aggregate for concrete (Example 3) was used, and it was found that a better ready-mixed concrete could be obtained than when the recycled fine aggregate for concrete of Example 1 was used and when the recycled fine aggregate for concrete of Comparative Examples 1 to 4 was used.

Claims

1. A step of adding a first treatment agent containing microbubble water and iron oxide to a material derived from returned ready-mixed concrete or residual ready-mixed concrete; and adding a second treating agent containing a cationic surfactant to the derived material to which the first treating agent has been added.

2. The method for producing recycled fine aggregate for concrete according to claim 1 , further comprising the step of adding a third treating agent containing percarbonate to the derived material to which the second treating agent has been added.

3. 2. The method for producing recycled fine aggregate for concrete according to claim 1, further comprising the step of spraying microbubble water onto the derived material to which the second treatment agent has been added, or the step of immersing the derived material to which the second treatment agent has been added in microbubble water.

4. 3. The method for producing recycled fine aggregate for concrete according to claim 2, further comprising the step of spraying microbubble water onto the derived material to which the third treatment agent has been added, or the step of immersing the derived material to which the third treatment agent has been added in microbubble water.

5. The method includes a step of mixing cement, aggregate, and water, A method for producing ready-mixed concrete using aggregate containing recycled fine aggregate for concrete produced by the method for producing recycled fine aggregate for concrete according to any one of claims 1 to 4 as the aggregate.

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