Method for producing recycled concrete fine powder

Abstract

To provide a manufacturing method of a recycled concrete fine powder capable of manufacturing, at a low energy consumption, a recycled concrete fine powder useful for carbon dioxide gas adsorption with reduced aggregate-derived components from a concrete mass.SOLUTION: A manufacturing method of a recycled concrete fine powder includes: a first step of classifying a crushed matter with a particle diameter 40 mm or less obtained by crushing or milling a concrete mass into a recycled coarse aggregate and a recycled fine aggregate; and a second step of collecting the recycled fine aggregate classified in the first step, shot-blasting the recycled coarse aggregate by the collected recycled fine aggregate, repeating the shot-blasting in plural times, and obtaining a recycled fine aggregate having a water absorption over 3.5% and a recycled concrete fine powder with a central diameter 100 μm or less generated by the shot-blasting.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for producing recycled concrete fine powder.

Background Art

[0002] Concrete blocks obtained by demolishing concrete of buildings and the like are waste materials that are difficult to process. Currently, most of the recycling is used as roadbed materials. Therefore, a recycling method for concrete blocks with higher added value has become an issue. Currently, attempts have been made to crush concrete blocks to obtain recycled aggregates. However, there are problems such as the need for a large amount of energy in the production of recycled aggregates and the limited uses of the demolished concrete fine powder separated from the recycled aggregates. As described above, most of the concrete blocks are only used as roadbed materials. In the recycling of concrete blocks, a technology for recovering recycled coarse aggregates has been established. However, since the uses of the demolished concrete fine powder obtained from concrete blocks are limited, the recycling of the demolished concrete fine powder has not progressed. Consequently, the recycling of the entire concrete block has not progressed at present. Therefore, if the uses of the fine powder after obtaining recycled coarse aggregates and recycled fine aggregates are expanded, it is expected that the recycling of concrete blocks will also progress.

[0003] A method for recovering waste concrete fine powder has been proposed, in which waste concrete blocks are coarsely crushed, screened, the remaining fraction after screening is crushed, milled, and classified, and recycled coarse aggregates, recycled fine aggregates, and uncarbonated waste concrete fine powder are separated and recovered. The fraction passing through the sieve is further crushed, milled, and classified, and separated and recovered into recycled fine aggregates and waste concrete fine powder with advanced carbonation (see Patent Document 1). According to the method described in Patent Document 1, waste concrete fine powder with different degrees of carbonation is obtained, and it is described that separation of fine powder suitable for uses is possible. Furthermore, if the amount of cement-derived components adhering to recycled aggregate is high, the water absorption rate of the recycled aggregate increases, which leads to a problem where the compressive strength of the resulting hardened concrete decreases when recycled aggregate is used in the manufacture of hardened concrete. As a method to reduce the cement-derived components in recycled aggregate, a method has been proposed in which coarse aggregate raw material derived from concrete waste is heated to over 100°C, stirred in a dry stirring device, and the surface is abraded (see Patent Document 2). On the other hand, as a method for modifying recycled aggregate separated from fine powder, a method has been proposed for producing recycled aggregate that improves the water absorption rate caused by cement-derived components by carbonizing recycled aggregate obtained by crushing and sieving concrete waste (see Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-17227 [Patent Document 2] Japanese Patent Application Publication No. 8-109052 [Patent Document 3] Japanese Patent Application Publication No. 5-238792 [Overview of the project] [Problems that the invention aims to solve]

[0005] Conventionally, in manufacturing methods for obtaining recycled aggregate and waste concrete fine powder from waste concrete blocks, such as the method described in Patent Document 1, which involves repeated crushing, sieving, and crushing, it is stated that heat treatment after crushing is also preferable. The method described in Patent Document 2 also requires heating to 100°C or higher. Thus, in order to reduce the amount of cement-derived components and obtain high-quality recycled aggregate, methods that remove cement-derived components by heating at high temperatures or by strong stress increase the manufacturing energy of the recycled aggregate and waste concrete fine powder. Furthermore, according to the inventors' studies, in the above methods, phenomena such as the recycled aggregate becoming brittle due to heat and the surface of the aggregate being scraped off by strong abrasive force occur, resulting in a large amount of aggregate-derived components being contained in the fine powder separated from the recycled aggregate, and a relatively low amount of cement-derived components. This makes it difficult to obtain the expected performance when used, for example, as a carbon dioxide adsorbent or alkali stimulant. Furthermore, Patent Document 3 concerns a technology for modifying aggregate obtained from concrete waste, and does not focus on the physical properties of the separated fine powder.

[0006] The object of one aspect of this disclosure is to provide a method for producing recycled concrete powder, which is useful for carbon dioxide adsorption and has reduced aggregate-derived components from concrete blocks, with low energy consumption. [Means for solving the problem]

[0007] The means for solving the above problem include the following embodiments. <1> A method for producing recycled concrete fine powder, comprising: a first step of classifying crushed material obtained by crushing or grinding concrete blocks into recycled coarse aggregate and recycled fine aggregate with a particle size of 40 mm or less; and a second step of recovering the recycled fine aggregate classified in the first step, shot blasting the recycled coarse aggregate with the recovered recycled fine aggregate, and performing the shot blasting multiple times to obtain recycled fine aggregate with a water absorption rate of more than 3.5%, and recycled concrete fine powder with a central diameter of 100 μm or less generated by the shot blasting.

[0008] <2> The apparatus used comprises a cylindrical body that can rotate around a horizontal axis, a classification screen with openings inside the cylindrical body that are the size of fine aggregate to be collected, a rotary classifier that classifies crushed concrete lumber fed into the cylindrical body into recycled coarse aggregate on the upper side of the classification screen and recycled fine aggregate on the lower side of the classification screen, a dust collector that collects and recovers recycled concrete fine powder with a central diameter of 100 μm or less generated inside the cylindrical body, and a blast shot machine that recovers the recycled fine aggregate on the lower side of the classification screen and shot blasts it onto the recycled coarse aggregate on the upper side of the classification screen. <1> A method for producing recycled concrete fine powder as described above.

[0009] <3> The recycled concrete fine powder has a recovery rate of 10% to 45% by mass relative to the concrete mass, and the cement-derived components contained in the recycled concrete fine powder are 25% or more by mass of the total mass of the fine powder. <1> or <2> A method for producing recycled concrete fine powder as described above. [Effects of the Invention]

[0010] According to one aspect of this disclosure, a method for producing recycled concrete powder, which is useful for carbon dioxide adsorption and in which aggregate-derived components are reduced from concrete blocks, can be provided with low energy consumption. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing a rotatable cylindrical portion of one embodiment of a crushing device that can be used in the method for producing recycled concrete fine powder according to the present disclosure. [Figure 2] This graph shows the relationship between the amount of electricity required to recover 1 ton of cement components in the manufacturing methods of Examples 1 to 3, Comparative Example 1, and Comparative Example 2, and the water absorption rate of the recycled fine aggregate. [Modes for carrying out the invention]

[0012] The method for producing recycled concrete powder according to this disclosure will be described in detail below with specific examples. The following description may be based on a typical embodiment of this disclosure, but the following description is illustrative and the disclosure is not limited to the following description. In this disclosure, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the lower and upper limits, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the term "process" includes not only independent processes but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved. In this disclosure, "demolition concrete fine powder" refers to untreated concrete fine powder obtained by crushing concrete blocks, and "recycled concrete fine powder" refers to concrete fine powder that has undergone the necessary processing to obtain fine powder from concrete blocks, thereby improving its carbon dioxide adsorption properties. In this disclosure, unless otherwise specified, room temperature refers to the ambient temperature without any particular temperature control, and more specifically, it is used to mean a temperature range of 20°C to 30°C.

[0013] <Method for producing recycled concrete fine powder> The method for manufacturing recycled concrete fine powder of the present disclosure (hereinafter sometimes referred to as "the manufacturing method of the present disclosure") includes a first step of classifying crushed materials with a particle size of 40 mm or less, obtained by crushing or grinding concrete blocks, into recycled coarse aggregate and recycled fine aggregate, and a second step of collecting the recycled fine aggregate classified in the first step, shot blasting the recycled coarse aggregate with the collected recycled fine aggregate, performing the shot blasting a plurality of times, and obtaining recycled fine aggregate with a water absorption rate exceeding 3.5% and recycled concrete fine powder with a median diameter of 100 μm or less generated by the shot blasting.

[0014] (First step) The first step is a step of classifying crushed materials with a particle size of 40 mm or less, obtained by crushing or grinding concrete blocks, into recycled coarse aggregate and recycled fine aggregate. In the first step, prior to classification, first, the concrete blocks are crushed or ground to obtain crushed materials with a particle size of 40 mm or less. The step of obtaining the crushed materials may be referred to as a preparation step. The first step includes a preparation step of crushing or grinding concrete blocks to obtain crushed materials with a particle size of 40 mm or less and a step of classifying the crushed materials. The concrete blocks used in the present disclosure are块状解体コンクリート obtained by disassembling buildings, structures, etc. containing concrete. Due to the influence of the composition of the original concrete, the environment where the building, structure, etc. was placed, the elapsed time, etc., the concrete blocks have various compositions. According to the manufacturing method of the present disclosure, regardless of the composition of the concrete blocks, recycled concrete fine powder suitable for reuse can be obtained with low energy.

[0015] In the preparation step, first, the concrete blocks are crushed or ground to obtain crushed materials with a particle size of 40 mm or less. In the following, in the present disclosure, "crushing or grinding" may sometimes be collectively referred to as "crushing etc.". There is no particular limitation on the method of crushing or grinding the concrete blocks, and known crushing devices or grinding devices can be used. The concrete blocks may be first coarsely crushed, and the obtained coarsely crushed materials may be further crushed or ground, and multi-stage crushing etc. may be performed. It should be noted that there seems to be an incorrect expression "块状解体コンクリート" in the original text. It might be a typo. The correct term should probably be "块状解体混凝土" (block-shaped disassembled concrete). But I translated it as it was presented in the original for the purpose of following the rules. For coarse crushing of concrete blocks, known crushers such as jaw crushers and impeller breakers can be used. If further crushing is to be performed on the coarsely crushed material, for example, a shot blast crushing device, an impact crusher, or a grinding device such as a mechanical grinding method that does not involve heating can be used.

[0016] The coarsely crushed concrete obtained by crushing or grinding concrete blocks is classified in the first step into recycled aggregate raw materials with a particle size of 40 mm or less. There are no particular restrictions on the classification method, and known methods, such as a sieving method using a mesh with an opening of 40 mm or less, can be applied.

[0017] Furthermore, when crushing concrete blocks during the preparation process, fine powder may be generated as a result of the crushing. Since large shear forces are not easily applied to the aggregate contained within the concrete blocks during the preparation process, the fine powder generated during the preparation process is likely to have a high proportion of cement-derived components. Therefore, the fine powder generated during the preparation process may be collected at the preparation stage using a dust collector or the like.

[0018] The first step, as described above, includes a preparation step of crushing or grinding concrete blocks to obtain crushed material with a particle size of 40 mm or less, and a step of further classifying the obtained crushed material with a particle size of 40 mm or less into recycled coarse aggregate and recycled fine aggregate. The classification can be carried out by applying the known classification method described above, taking into consideration the particle size of the recycled fine aggregate to be extracted.

[0019] (2nd process) The second step involves recovering the recycled fine aggregate from the recycled aggregate raw materials with a particle size of 40 mm or less obtained in the first step, shot blasting the recycled coarse aggregate with the recovered recycled fine aggregate, and performing the shot blasting multiple times to obtain recycled fine aggregate with a water absorption rate of more than 3.5%, and recycled concrete fine powder with a median diameter of 100 μm or less generated by the shot blasting.

[0020] In recycled aggregate, a preferred method for separating recycled fine aggregate from recycled coarse aggregate and recovering the recycled fine aggregate is to use a classification screen. By adjusting the size of the openings in the classification screen, it is possible to recover the desired recycled fine aggregate for shot blasting. By setting the size of the openings in the classification screen to a size equivalent to the fine aggregate to be collected, it is possible to recover recycled fine aggregate of the desired size for shot blasting.

[0021] In the second step, the recycled coarse aggregate is shot-blasted with the recovered recycled fine aggregate. Compared to shot-blasting with hard blasting materials such as metal, this method reduces damage to the recycled coarse aggregate, and as a result, only the cement-derived components present near the surface of the aggregate can be effectively separated and recovered from the recycled coarse aggregate. Furthermore, it has the advantage of not requiring a step to separate and recover the blasting material from the recycled fine aggregate after processing. In the second step, the recycled fine aggregate that is shot-blasted is also subjected to damage to the aggregate components of the recycled fine aggregate because the solid object it collides with during shot blasting is recycled coarse aggregate.

[0022] In the second step, the recovered recycled fine aggregate is subjected to multiple shot blasts onto the recycled coarse aggregate to obtain recycled fine aggregate with a water absorption rate exceeding 3.5%, and recycled concrete fine powder with a central diameter of 100 μm or less generated by the shot blasting. The number of shot blasting cycles can be selected based on the physical properties of the concrete block to which the manufacturing method of this disclosure is applied. Methods for determining the number of shot blasting cycles include, for example, conducting a preliminary test on a concrete block sample to measure the water absorption rate of the recycled aggregate obtained after each blast, or performing a predetermined number of shot blasts, stopping the device, collecting the recycled aggregate, and determining the timing of the end of the shot blasting cycle. However, there are no particular limitations on the method.

[0023] By ending the shot blasting process when the water absorption rate of the recycled fine aggregate exceeds 3.5%, the excessive shear force applied to the recycled fine aggregate is suppressed, preventing the aggregate components from being included in the recovered recycled concrete powder. As a result, the resulting recycled concrete powder has a high content of cement-derived components and excellent carbon dioxide adsorption properties, making it suitable for various applications.

[0024] In the manufacturing method of the present disclosure, it is preferable to use a crushing apparatus comprising: a cylindrical body that can rotate around a horizontal axis; a classification screen inside the cylindrical body having an opening of a size equivalent to fine aggregate for collection; a rotary classifier that classifies crushed concrete lumber fed into the cylindrical body into recycled coarse aggregate on the upper side of the classification screen and recycled fine aggregate on the lower side of the classification screen; a dust collector that collects and recovers recycled concrete fine powder with a central diameter of 100 μm or less generated inside the cylindrical body; and a blast shot machine that recovers the recycled fine aggregate on the lower side of the classification screen and shot blasts it onto the recycled coarse aggregate on the upper side of the classification screen.

[0025] The aforementioned device will hereinafter be referred to as the "specific crushing device." Figure 1 is a schematic cross-sectional view showing a rotatable cylindrical portion of one embodiment of a crushing device (specific crushing device) that can be used in the method for producing recycled concrete fine powder according to this disclosure. The specific crushing device includes a cylindrical body 10 that can rotate around a horizontal axis, and a classification screen 12 inside the cylindrical body 10 with openings of a size equivalent to fine aggregate intended for collection. The device also includes a rotary classifier that classifies the crushed concrete blocks fed into the cylindrical body 10 into recycled coarse aggregate 14 on the upper side of the classification screen 12 and recycled fine aggregate 16 on the lower side of the classification screen. By placing crushed concrete blocks inside the cylindrical body 10 and rotating the cylindrical body 10, the crushing of the concrete blocks progresses as they collide with each other due to the rotation, and as the crushed concrete blocks that have risen due to the rotation fall due to their own weight, they collide with the crushed concrete blocks below them. The crushed concrete lumps, which have been reduced to a size that can pass through the openings of the classification screen 12, are separated as recycled fine aggregate 16 and classified as recycled coarse aggregate 14 on the upper side of the classification screen and recycled fine aggregate 16 on the lower side of the classification screen.

[0026] By setting the opening of the classification screen in a specific crushing device to a size equivalent to the fine aggregate intended for collection, it is possible to classify recycled fine aggregate of the desired size. Although the maximum size of fine aggregate is specified as 5 mm, in reality, fine aggregate is a mixture of crushed sand of various sizes, and even if there are fine aggregate particles with a maximum diameter exceeding 5 mm but not exceeding 10 mm, it is acceptable as long as the content is 10% by mass or less. The size of the opening in the classification screen can be determined in accordance with the above criteria and taking into consideration the maximum size equivalent to the fine aggregate to be collected. According to the above criteria, the opening in the classification screen can have a predetermined width relative to the target maximum size, but since the inclusion of particles larger than 10 mm is not permitted, the size of the opening in the classification screen is 10 mm or less. In the above-described specific crushing apparatus, the purpose is to classify the recycled fine aggregate that is shot-blasted against the recycled coarse aggregate. Therefore, the size of the opening is appropriately selected within a range that does not exceed 10 mm. The lower limit of the opening size can be determined by considering the particle size of the target fine aggregate (e.g., 2 mm to 5 mm). For example, when the purpose is to shot-blast recycled coarse aggregate, a larger maximum size results in a higher blasting effect, and from this perspective, the opening size of the classification screen may exceed 5 mm. If the size of the opening exceeds 5 mm, after the shot blasting is complete, the recycled fine aggregate can be sorted and recovered using a sieve, if necessary.

[0027] The specific crushing device is equipped with a dust collector (not shown) that collects and recovers recycled concrete fine powder (not shown) with a central diameter of 100 μm or less that is generated inside the cylindrical body 10. The recycled concrete fine powder (not shown) with a central diameter of 100 μm or less that is generated when the concrete mass is crushed by the rotation of the cylindrical body 10 is recovered by the dust collector. The rotation of the cylindrical body 10 of the specific crushing device and the separation by the classification screen 12 allow the recycled fine aggregate 16 collected on the lower side of the classification screen to be recovered and transported to the blast shot machine 18, where it is shot blasted onto the recycled coarse aggregate 14 located on the upper side of the classification screen 12.

[0028] The median diameter of the recycled concrete powder used in this disclosure is the value measured by the following method. Approximately 0.05 g of recycled concrete fine powder was ultrasonically dispersed for 180 seconds using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII: manufactured by Microtrac-Bell Co., Ltd.) with ethanol as the solvent, and the 50% particle size measured at room temperature (25°C) was used as the median diameter value of the recycled concrete fine powder in this disclosure. That is, "median diameter" in this disclosure means the 50% particle size measured with a particle size distribution analyzer as exemplified above.

[0029] According to the specific crushing device, recycled fine aggregate, acting as abrasive particles, can be uniformly impacted onto the entire crushed material located above the classification screen within the cylindrical body, enabling efficient crushing. By controlling the number of times recycled fine aggregate is shot-blasted onto recycled coarse aggregate, recycled fine aggregate with a target water absorption rate exceeding 3.5% can be obtained. Furthermore, the separated and recovered recycled concrete fine powder contains a large amount of cement-derived components from the crushed concrete blocks and very little aggregate-derived components, making it suitable for carbon dioxide adsorption applications. For example, Patent Document 1 states that recycled concrete fine powder obtained by separating coarse aggregate has not undergone significant carbonation and can be used as a raw material for decarbonated cement, but that fine powder obtained by separating fine aggregate has undergone significant carbonation and can be used as an admixture or ground improvement material. However, according to the manufacturing method of the present disclosure, recycled coarse aggregate can be shot-blasted multiple times with the recovered recycled fine aggregate to simultaneously recover recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder. Therefore, concerns about the ongoing carbonation of recycled concrete fine powder after the recovery of recycled fine aggregate, as described in Patent Document 1, are reduced, and recycled concrete fine powder with carbon dioxide adsorption capacity can be recovered more efficiently.

[0030] In processing using a specific crushing device, the number of shot blasting cycles is selected considering the point at which the water absorption rate of the recovered recycled fine aggregate exceeds 3.5%. The method for determining the number of shot blasts is as previously described, but we will now explain in more detail the case when using the specific crushing device mentioned above. In a specific crushing device, the physical properties of the recovered recycled fine aggregate can be controlled by controlling the number of shot blast cycles and the airflow rate of the dust collector. For example, the raw material size of the crushed concrete blocks to be processed (in this disclosure, greater than 0 mm and less than or equal to 40 mm) is determined, and in the initial stage, basic data is collected by applying several patterns of operating conditions (number of shot blasts and airflow in the dust collector). Based on the obtained basic data, the operating conditions are input into the program, and thereafter, the system can be operated automatically according to the program. By managing the operating records of the specific crushing equipment as data, it becomes possible to indirectly manage the water absorption rate of the recycled fine aggregate and the quality of the recovered recycled concrete powder using the obtained data.

[0031] For example, considering the results of the examples described later, when processing concrete blocks obtained from building waste, the number of blasting cycles can typically be 2 to 30. In particular, from the viewpoint of suppressing energy consumption when obtaining recycled concrete fine powder, it is preferable to blast 2 to 10 times; from the viewpoint of easily obtaining recycled concrete fine powder with a high cement content, it is preferable to blast 5 to 20 times; and from the viewpoint of further lowering the water absorption rate of recycled aggregate and improving the amount of recycled concrete fine powder recovered, it is preferable to blast 10 to 30 times.

[0032] In this disclosure, the water absorption rate of recycled fine aggregate is the value measured in accordance with JIS A1109 (2020), and the water absorption rate of recycled coarse aggregate is the value measured in accordance with JIS A1110 (2020).

[0033] As described above, the specific crushing device can be any device that includes a cylindrical body that can rotate around a horizontal axis, a rotary classifier equipped with a classification screen, a dust collector, and a blast shot machine, and is capable of blasting the classified recycled fine aggregate. A preferred example of a specific crushing device is, for example, the granular material crushing device described in Japanese Patent Publication No. 6161586.

[0034] One of the features of the manufacturing method disclosed herein is that the classified recycled fine aggregate is shot-blasted and ground against the recycled coarse aggregate, and the recycled concrete fine powder is collected. Conventionally, when obtaining recycled fine aggregate from crushed concrete blocks, attempts have been made to minimize the amount of cement-derived components adhering to the recycled fine aggregate. According to JIS A5021 (2018), which defines the performance of recycled fine aggregate, recycled fine aggregate with a water absorption rate of 3.5% or less is defined as high-quality Class H. Conventionally, in order to obtain high-quality recycled fine aggregate, i.e., Class H level recycled fine aggregate, the goal has been to reduce the water absorption rate of the recycled fine aggregate to 3.5% or less. Attempts have been made to remove as much cement-derived component as possible from the surface of the aggregate by heating to 100°C or higher or by applying high shear force. However, both heating and applying high shear force consume a large amount of energy, and there is a problem that the aggregate component content increases in the recycled concrete fine powder obtained by separating it from the recycled fine aggregate, while the proportion of cement-derived component in the fine powder decreases. According to the manufacturing method of this disclosure, by ending the crushing and classification process when the water absorption rate of the recycled fine aggregate exceeds 3.5%, energy consumption is kept low, damage to the recycled fine aggregate is suppressed, and recycled concrete fine powder with good carbon dioxide adsorption capacity can be produced.

[0035] Preferably, the recycled concrete fine powder obtained by the manufacturing method of this disclosure has a recovery rate of 10% to 45% by mass relative to the concrete mass used as a raw material, and the cement-derived components contained in the recycled concrete fine powder are 25% by mass or more of the total mass of the fine powder.

[0036] The recovery rate of recycled concrete powder can be calculated, for example, by measuring the mass of the concrete blocks initially fed into the specific crushing device and the mass of the recovered recycled concrete powder, and using these values ​​as a basis. The recovery rate of recycled concrete fine powder from concrete blocks is preferably 10% to 45% by mass, more preferably 15% to 40% by mass, and even more preferably 15% to 30% by mass. A recovery rate of recycled concrete powder in the range of 10% to 45% by mass makes the recovery of recycled concrete powder from waste concrete more efficient, resulting in a decrease in aggregate-derived components and an increase in cement-derived component content in the recycled concrete powder.

[0037] Furthermore, the cement-derived components contained in the recovered recycled concrete fine powder are preferably 25% by mass or more, more preferably 35% by mass or more, and even more preferably 45% by mass or more, based on the total amount of recovered recycled concrete fine powder. There is no particular upper limit on the content of cement-derived components in recycled concrete fine powder, but considering the recovery rate of recycled concrete fine powder in the manufacturing method of this disclosure, it can be set to 70% by mass or less.

[0038] The cement-derived components contained in the fine powder exhibit carbon dioxide adsorption properties. Therefore, the higher the cement-derived component content in recycled concrete fine powder, the better the carbon dioxide adsorption performance of the recycled concrete fine powder. It can also be used as an alkali stimulant in concrete compositions as needed.

[0039] The content of cement-derived components in recycled concrete fine powder can be measured by the following method.

[0040] (Method for measuring the content of cement-derived components) Reagent-grade hydrochloric acid (concentration approximately 35% by mass) is mixed with pure water in a volume ratio of 1:100 to obtain an aqueous HCl(1+100) hydrochloric acid solution. The hydrochloric acid solution is prepared at room temperature. At room temperature, weigh 1 g of recycled concrete powder and add it to 250 ml of the hydrochloric acid solution prepared above, stirring for 20 minutes. After stirring, the solution is filtered to separate the solids. The filtered material is thoroughly washed on filter paper with warm water at 80°C to 90°C, placed in a crucible to ash the filter paper, and then strongly heated at 950°C for 30 minutes. The intensely heated sample is allowed to cool to room temperature, and the mass of the remaining material is measured. Compared to the initially weighed sample, the amount of remaining solids is considered the insoluble portion, and the amount of the reduced mass is considered the soluble portion. As the above measurement method determines that the soluble matter dissolved in the hydrochloric acid aqueous solution is almost entirely cement-derived components in the fine powder, in this disclosure, the soluble matter obtained by the above measurement method is defined as the amount of cement-derived components in the fine powder.

[0041] In the manufacturing method disclosed herein, recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder are separated by rotating a cylindrical body without high-temperature heating or the application of high shear force, using a device such as the specified crushing device described above. By controlling the number of times the recovered recycled fine aggregate is blasted against the recycled coarse aggregate, recycled concrete fine powder with good carbon dioxide adsorption capacity can be produced. The energy required for manufacturing is extremely low compared to processes involving heating. For example, the power consumption required to process 1 ton of crushed concrete material under 40 mm can be 30 kWh or less, and in a preferred embodiment, it can be 20 kWh or less. For example, if the method described in Patent Document 2 is applied, and in the separation of fine aggregate, heating to 100°C is performed in addition to crushing and classification, then considering the power consumption required to raise 1 ton of crushed material to 100°C, it can be said that the power consumption required to produce recycled concrete fine powder with good carbon dioxide adsorption capacity can be significantly reduced.

[0042] The resulting recycled concrete powder is fine, and if left exposed to air, it may react with carbon dioxide in the air, potentially reducing its carbon dioxide adsorption capacity. For this reason, the recovered recycled concrete powder may be stored, for example, under an inert gas atmosphere or in water.

[0043] The recycled concrete fine powder obtained by the manufacturing method of this disclosure has a high content of cement-derived components, and therefore has good carbon dioxide adsorption capacity. It can be suitably used, for example, for the fixation of carbon dioxide emitted from power plants, factories, etc., and for the adsorption of carbon dioxide in exhaust gas from power machinery, etc. Furthermore, due to its high cement-derived component content, it can also be used as an alkali stimulant for concrete compositions. [Examples]

[0044] The manufacturing method of this disclosure will be described in detail below with reference to specific examples, but these examples are merely examples, and various modifications can be made in accordance with the spirit of this disclosure.

[0045] [Preliminary test of specific crushing equipment] In the following example, the raw material size of the crushed concrete blocks to be processed was determined to be 40 mm or less, and in the initial stage, basic data was collected by applying several patterns of operating conditions (number of shot blasts and airflow rate in the dust collector). According to the obtained basic data, the number of shot blasts was set to 2 to 30 times, and the airflow rate of the dust collector was set to 100 m³. 3 / min~250m 3 By setting the rate to / min, it was estimated that recycled fine aggregate with a target water absorption rate exceeding 3.5% could be obtained. Therefore, the operating conditions were entered into the program, and the specific crushing device was automatically operated according to the program. The number of shot blasts was set to the number of times specified in Examples 1 to 3 below, and the operation of the specific crushing device was stopped to ensure that the water absorption rate of the recycled fine aggregate and the cement components contained in the recycled concrete fine powder were within the target range. The water absorption rate of the obtained recycled fine aggregate and the quality of the recovered recycled concrete fine powder were then evaluated.

[0046] [Example 1] 1. Preparation of recycled concrete powder We obtained crushed concrete blocks, generated during the demolition of a building, by crushing them to a size of 40 mm or less. (Preparation process) The resulting crushed material, which was less than 40 mm in size, was separated into recycled coarse aggregate, recycled fine aggregate, and recycled concrete powder using a specific crushing device equipped with a rotatable cylindrical body as shown in Figure 1. The openings in the classification screen placed inside the cylindrical body were set to 5 mm, taking into consideration the size of the recycled fine aggregate intended for recovery.

[0047] 298 kg of crushed material less than 40 mm in size obtained from concrete blocks was placed into the cylindrical body, the rotation of the cylindrical body was started, and shot blasting of the crushed, classified, and recovered recycled fine aggregate onto the recycled coarse aggregate was started inside the cylindrical body. After six shot blasting cycles, the operation of the specific crushing device was stopped, and recycled coarse aggregate, recycled fine aggregate, and recycled concrete powder were recovered from the device. The recovery rates for recycled coarse aggregate, recycled fine aggregate, and recycled concrete powder were 52.1% by mass, 33.0% by mass, and 14.9% by mass, respectively.

[0048] 2. Evaluation of recovered materials 2-1. Water absorption rate of recycled coarse aggregate and recycled fine aggregate The water absorption rate of recycled coarse aggregate was measured in accordance with JIS A1110 (2020), and the water absorption rate of recycled fine aggregate was measured in accordance with JIS A1109 (2020). The results are shown in Table 1 below. As shown in Table 1, the water absorption rate of the recycled fine aggregate was 7.55%, which was higher than 3.5%.

[0049] 2-2. Measurement of cement components contained in recycled concrete fine powder A reagent-grade hydrochloric acid (concentration approximately 35% by mass) was mixed with pure water in a volume ratio of 1:100 to obtain an aqueous HCl (1+100) hydrochloric acid solution. The hydrochloric acid solution was prepared at room temperature (25°C). At room temperature, 1 g of the recovered recycled concrete powder was weighed and added to 250 ml of the hydrochloric acid aqueous solution prepared above, and stirred for 2 minutes. After stirring, the solution was filtered to separate the solids. The filtered material was thoroughly washed on filter paper with warm water at 80°C to 90°C, placed in a crucible to ash the filter paper, and then strongly heated at 950°C for 30 minutes. The strongly heated sample was allowed to cool to room temperature, and the mass of the remaining material was measured. For 1 g of weighed sample, the amount of remaining solids was calculated as insoluble matter, and the amount of reduced mass as soluble matter. The soluble matter was found to be 49.5% by mass. Since the soluble matter consists almost entirely of cement-derived components, the cement-derived component content in the recycled concrete fine powder obtained by the method of Example 1 was estimated to be 49.5% by mass. Taking into account the amount of recovered fine powder, the total amount of cement-derived components contained in the recovered recycled concrete fine powder per ton of crushed concrete blocks under 40 mm was calculated to be 0.074 t.

[0050] 2-3. Measurement of 50% particle size of recycled concrete fine powder Approximately 0.05 g of recovered recycled concrete fine powder was ultrasonically dispersed for 180 seconds using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII: manufactured by Microtrac-Bell Co., Ltd.) with ethanol as the solvent, and then the 50% particle size was measured at room temperature (25°C). As a result, the 50% particle size was found to be 25.9 μm, confirming that the particles are fine enough to be used in a variety of applications.

[0051] 2-4. Power consumption required for the recovery of recycled concrete powder The power consumption required to operate the specific crushing equipment to process the above 1-ton concrete block and separate it into recycled coarse aggregate, recycled fine aggregate, and recycled concrete powder was measured to be 10.0 kWh. Based on the measurement results of the cement-derived component content in the recycled concrete powder mentioned above, the power consumption required to recover the cement-derived components was calculated to be 135.6 kWh.

[0052] [Examples 2-3] In Example 1, 1 ton of concrete was processed in the same manner as in Example 1, except that the number of shot blasts was changed to the number shown in Table 1 below. The recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder were separated and recovered, and evaluated in the same manner as in Example 1.

[0053] [Comparative Example 1] In Example 1, 1 ton of crushed material under 40 mm obtained from concrete blocks was processed in the same manner, except that the number of shot blasts was changed to 45, which exceeded the predetermined range. Recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder were separated and recovered, and the water absorption rate of the obtained recycled fine aggregate was measured to be 3.21%, which was outside the range of water absorption rates specified in the manufacturing method of this disclosure. Other items were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0054] [Comparative Example 2] In Example 1, 1 ton of concrete was processed in the same manner as in Example 1, except that shot blasting was performed only once instead of multiple times. Recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder were separated and recovered, and the water absorption rate of the obtained recycled fine aggregate was measured. The water absorption rate was 9.63%, which exceeded the 3.5% water absorption rate specified in the manufacturing method of this disclosure. However, the median diameter of the recycled concrete fine powder generated by blasting was 117.6 μm, which was outside the range specified in this disclosure. Furthermore, the recovery rate of recycled concrete fine powder was only 6.6% by mass. Other items were evaluated in the same manner as in Example 1.

[0055] The evaluation results are shown in Table 1 below. Furthermore, Figure 2 shows a graph illustrating the relationship between the amount of electricity required to recover 1 ton of cement components contained in recycled concrete fine powder in the manufacturing methods of Examples 1 to 3, Comparative Example 1, and Comparative Example 2, and the water absorption rate of the recycled fine aggregate.

[0056] [Table 1]

[0057] As shown in Table 1, the recycled concrete fine powder manufacturing methods of Examples 1 to 3 resulted in recycled concrete fine powder containing a large amount of cement components, low power consumption for separating recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder, and low power consumption for recovering cement-derived components. Therefore, it can be seen that the manufacturing methods of Examples 1 to 3 allow for the efficient production of recycled concrete fine powder with a high content of cement-derived components suitable for carbon dioxide adsorption and a fine particle size, using low energy.

[0058] On the other hand, in the manufacturing method of Comparative Example 1, recycled fine aggregate with low water absorption was obtained, and the recovery of recycled concrete fine powder was also good. However, the power consumption required to separate the recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder, as well as the power consumption required to recover cement-derived components, were higher compared to the example. In the manufacturing method of Comparative Example 2, the power consumption for separating the recycled coarse aggregate, recycled fine aggregate, and recycled concrete fine powder was low. However, because the resulting recycled concrete fine powder had a large particle size and contained a low amount of cement-derived components, the power consumption required to recover the cement-derived components was higher than in each of the examples.

[0059] As shown in Figure 2, the relationship between the amount of electricity used to recover recycled concrete fine powder in the manufacturing methods of Examples 1 to 3 and the water absorption rate of the recycled fine aggregate indicates that by obtaining recycled fine aggregate having a water absorption rate within the range specified in the manufacturing method of this disclosure, the amount of electricity required to recover cement components can be kept low.

[0060] Thus, according to the method for producing recycled concrete fine powder of this disclosure, recycled concrete fine powder containing a large amount of cement-derived components with good carbon dioxide adsorption capacity can be produced using concrete waste materials with low energy consumption. Therefore, it has been confirmed that the method for producing recycled concrete fine powder of this disclosure is useful for recycling concrete blocks and has the advantage of efficiently producing recycled concrete fine powder that is effective for carbon dioxide adsorption treatment while suppressing carbon dioxide emissions. [Explanation of symbols]

[0061] 10. A cylindrical body that can rotate around a horizontal axis (cylindrical body) 12-minute screen 14. Recycled coarse aggregate 16 Recycled fine aggregate 18 Blast Shot Machine

Claims

1. The first step involves classifying crushed material with a particle size of 40 mm or less, obtained by crushing or grinding concrete blocks, into recycled coarse aggregate and recycled fine aggregate. A second step involves recovering the recycled fine aggregate classified in the first step, shot blasting the recycled coarse aggregate with the recovered recycled fine aggregate, and performing the shot blasting multiple times to obtain recycled fine aggregate with a water absorption rate exceeding 3.5%, and recycled concrete fine powder with a central diameter of 100 μm or less generated by the shot blasting. A method for producing recycled concrete fine powder containing [the specified ingredient].

2. A cylindrical body that can rotate around a horizontal axis, The cylindrical body is equipped with a classification screen having openings equivalent to the size of fine aggregate intended for collection, and a rotary classifier is provided to classify the crushed concrete lumber fed into the cylindrical body into recycled coarse aggregate on the upper side of the classification screen and recycled fine aggregate on the lower side of the classification screen. A dust collector for collecting and recovering recycled concrete fine powder with a central diameter of 100 μm or less generated inside the cylindrical body, A blast shot machine that collects the recycled fine aggregate located below the classification screen and shot blasts it onto the recycled coarse aggregate located above the classification screen, A method for producing recycled concrete fine powder according to claim 1, using an apparatus equipped with the following:

3. The method for producing recycled concrete fine powder according to claim 1 or claim 2, wherein the recycled concrete fine powder has a recovery rate of 10% to 45% by mass relative to the concrete mass, and the cement-derived components contained in the recycled concrete fine powder are 25% by mass or more of the total mass of the fine powder.

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