Artificial aggregate prepared on basis of waste concrete and PEI (polyetherimide) as well as preparation method and application of artificial aggregate

Abstract

The invention belongs to the technical field of building materials, and particularly relates to an artificial aggregate prepared based on waste concrete and PEI, a preparation method and application. The preparation method comprises the following steps: crushing waste concrete to obtain regenerated micro powder, mixing the regenerated micro powder with cement dry powder to obtain mixed powder, then jointly granulating sand grains, the mixed powder and a PEI aqueous solution to obtain artificial aggregate particles, and finally carbonizing and curing the artificial aggregate particles to obtain the required artificial aggregate. The PEI is introduced in the granulation process of the waste concrete, CO2 and active components in the waste concrete are fully reacted to generate calcium carbonate sediment by utilizing the efficient carbon capture performance of the PEI, pores of the aggregate are effectively filled, the strength, compactness and durability of the recycled aggregate are remarkably improved, and the prepared artificial aggregate has a very good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and in particular relates to an artificial aggregate prepared based on waste concrete and PEI, a preparation method and application thereof. Background Art

[0002] Using waste concrete to prepare recycled aggregate is an effective way to solve the high pollution problem of waste concrete. The prepared recycled aggregate can not only replace part of natural aggregate for the production of building materials, but also reduce the dependence on natural resources to a certain extent. However, the quality of recycled aggregate from waste concrete is generally poor, mainly manifested in the problems of rough surface, porosity, many microcracks, high water absorption, etc. These defects lead to poor interface bonding performance between recycled aggregate and cement matrix, and its mechanical properties are often lower than those of natural aggregate, which limits the promotion and application of recycled aggregate.

[0003] In recent years, in order to improve the performance of recycled aggregates, carbonization curing technology has gradually attracted attention. Carbonization curing can partially fill the pores in the aggregates by reacting recycled aggregates with CO2 to generate calcium carbonate, which increases the density and mechanical properties of the aggregates. At the same time, the formation process of calcium carbonate can also form a protective film on the surface of the aggregates, thereby improving the anti-carbonization and anti-aging properties of the aggregates.

[0004] However, the current carbonization process usually has problems such as low efficiency, uneven CO2 penetration and insufficient reaction. For example, patent CN110790541A discloses a method for preparing artificial aggregate using recycled micropowder, and patent CN118771811A discloses a method for preparing carbon mineralized recycled micropowder, a solid waste-based low-carbon concrete and preparation method based on it with carbon mineralization enhancement. Both of them react CO2 with active components in waste concrete to generate calcium carbonate to improve material properties, but rely on complex process flows and chemical additives, and have problems such as low carbonization efficiency, uneven CO2 distribution and insufficient internal density, resulting in uneven carbonization effect, especially it is difficult to achieve complete carbonization inside the particles, and it is difficult to achieve complete densification of the internal structure, resulting in poor carbonization effect. In addition, some existing carbonization processes have high requirements for temperature and humidity, complex operations and high equipment costs, which are not conducive to large-scale applications.

[0005] Polyethyleneimine (PEI) is a multifunctional organic polymer compound that has attracted widespread attention due to its highly active amino (-NH2) group that can react quickly with CO2 under mild conditions. Studies have shown that PEI can be used as an efficient CO2 capture agent to promote the generation rate of calcium carbonate and improve the uniformity of distribution in the carbonization process. However, existing research mainly focuses on the use of PEI for gas capture and carbon sequestration. Patent CN113929524A discloses a fertilizer coating slow-release agent. PEI is one of the coating components. It reacts in a CO2 environment to generate carbamate and calcium carbonate, which not only enhances the slow-release effect of the fertilizer, but also improves the carbon fixation capacity of the fertilizer; Patent CN115520888A discloses the application of a carbon dioxide adduct of polyethyleneimine to prepare calcium carbonate. This material is mainly used in the biomedical field.

[0006] At present, there is still relatively little research on the application of PEI in the carbonization of waste concrete-based recycled aggregates. How to effectively utilize PEI in the carbonization treatment of waste concrete-based recycled aggregates is a powerful development direction for improving the mechanical properties and density of recycled aggregates. Summary of the invention

[0007] In order to solve the above problems, one of the objectives of the present invention is to provide a method for preparing artificial aggregate based on waste concrete and PEI.

[0008] The present invention adopts the following technical solutions: A method for preparing artificial aggregate based on waste concrete and PEI, wherein the PEI is polyethyleneimine, comprises the following steps: S1. crushing the waste concrete to a particle size of less than 0.16 mm to obtain recycled micro powder; S2. The recycled micropowder and cement powder are uniformly mixed according to a set mass ratio to obtain a recycled micropowder-cement mixture; S3. Using sand, recycled micropowder - cement mixture and PEI aqueous solution to co-granulate to obtain artificial aggregate particles with sand as the core, recycled micropowder - cement mixture and PEI wrapped around the sand; S4. Carbonization-curing the prepared artificial aggregate particles to obtain the desired artificial aggregate.

[0009] Preferably, the cement dry powder is ordinary Portland cement, the median particle size D50 is 15-25 μm, and the set mass ratio of the regenerated micropowder to the cement dry powder is (9-8): (1-2).

[0010] Preferably, the particle size of the sand is 2-5 mm, the particle size of the artificial aggregate particles is 8-20 mm, and the usage ratio of the sand to the recycled micropowder-cement mixture and the PEI aqueous solution is 1:42:10.

[0011] In the present application, the sand particles may be any component of relatively dense sand, such as machine-made sand with a particle size of 2.36 to 4.75 mm.

[0012] Preferably, in the PEI aqueous solution, the PEI solid content is 1-16 wt%.

[0013] Preferably, in the PEI aqueous solution, the PEI solid content is 4-12 wt %, more preferably, the PEI solid content is 8 wt %.

[0014] Preferably, the specific method of granulation is to place sand in a granulator, divide the recycled micropowder-cement mixture into 50 equal parts, and add it 50 times during the granulation process, spray 0.2-0.3 parts of PEI aqueous solution between two adjacent additions, and the interval time for adding the recycled micropowder-cement mixture and the PEI aqueous solution is 12-24 s to form the desired artificial aggregate particles.

[0015] Preferably, the rotation speed of the granulator is 20-40 rpm, the total mass of a single feed is in the range of 0.5-3 kg, and the granulation time is 10-20 min.

[0016] Preferably, the carbonization curing conditions are curing for at least 3 days in an environment with a CO2 concentration of 5-20%, a temperature of 20-40°C, and a humidity of 50-70%.

[0017] In this method, the regenerated micropowder has good fineness and is suitable as a granulation substrate, while the sand has high strength and controllable particle size, which helps to improve the final performance of artificial aggregate. PEI, as an active chemical reagent, contains rich amino groups (-NH2), which can react with CO2 in the subsequent carbonization process, provide an excellent chemical environment for the formation of calcium carbonate, and provide good carbonization conditions for the regenerated micropowder. In step S3, the PEI solution is evenly sprayed on the regenerated micropowder-cement mixture to form an active coating, which provides sufficient contact area for granulation and carbonization reactions. Through multiple spraying and rolling operations, the PEI solution is evenly distributed and gradually pressed into the pores of the particles to form stable core-shell structure particles. Controlling the granulation rate is conducive to controlling the size growth rate of the particles, which can ensure that the particle surface is dense and the shape is stable, thereby improving the overall mechanical properties of the particles. In this process, PEI reacts with CO2 to form carbamate and bicarbonate, and these intermediates further react with Ca in the aggregate. 2+The reaction generates calcium carbonate. The deposition of calcium carbonate not only fills the pores of the aggregate, but also forms a stable protective layer on the surface of the particles, significantly improving the density, mechanical properties and durability of the aggregate. During the carbonization curing process, PEI reacts with CO2 in the presence of water to first generate carbamate, which is further converted into bicarbonate and further reacts with Ca in the particles. 2+ A reaction to generate calcium carbonate occurs. The deposition of calcium carbonate not only fills the pores of the aggregate, but also forms a stable calcium carbonate protective layer on the surface of the particles (the protective layer is mainly calcium carbonate, combined with a small amount of incompletely reacted cementitious materials and recycled micro-powder active ingredients). This protective layer enhances the density and durability of the aggregate, effectively improving the mechanical properties of artificial aggregates. The generated calcium carbonate can also significantly improve the interface bonding between the aggregate and the cement matrix, thereby effectively improving the mechanical properties and anti-aging properties of the aggregate.

[0018] The second object of the present invention is to provide an artificial aggregate, which is prepared by the method as described above, and comprises a sand core and a shell that wraps the sand core, wherein the shell is composed of a product of a reaction between a recycled micropowder-cement mixture and CO2 and residual recycled micropowder-cement mixture, and the apparent porosity of the artificial aggregate is less than 25%, and the average pore size is less than 30 nm; the diameter of the sand core is 2-5 mm, and the particle size of the artificial aggregate is 8-20 mm.

[0019] A third object of the present invention is to provide the use of the artificial aggregate as described above as a roadbed filling material and / or a building material.

[0020] A fourth object of the present invention is to provide a roadbed filling material or a building material, to which the artificial aggregate as described above is added.

[0021] The beneficial effects of the present invention are: 1) This application innovatively introduces polyethyleneimine (PEI) into the waste concrete granulation process, and utilizes its efficient carbon capture performance to introduce the reaction of PEI and CO2 into the preparation process of waste concrete recycled aggregate. PEI allows CO2 to fully react with the active components in the waste concrete to generate dense calcium carbonate deposits on the surface and inside of the particles, effectively filling the pores of the aggregate, and significantly improving the strength, density and durability of the recycled aggregate. Compared with traditional aggregates, the artificial aggregate of the present invention performs better in strength and stability, and is suitable for high-strength building materials.

[0022] 2) This method abandons the complex high-temperature carbonization equipment and chemical additives, realizes the efficient carbonization process under normal temperature conditions, simplifies the process flow, and reduces production energy consumption and costs. It not only overcomes the problems of low efficiency and high complexity of traditional technologies, but also realizes the effective capture and solidification of carbon dioxide. In this method, CO2 is converted into stable calcium carbonate deposited inside and outside the aggregate, effectively combining carbon fixation with resource utilization, and providing an efficient and low-carbon solution for the development of green building materials.

[0023] 3) The artificial aggregate prepared in this application has uniform particle size, rough surface and regular particle shape. When applied to materials such as cement, it can enhance the strength, density and interfacial bonding force of the aggregate with the cement matrix, and significantly improve the mechanical properties of the artificial aggregate.

[0024] 4) The protective layer formed by calcium carbonate on the surface of aggregate particles can effectively prevent the penetration of external gas and moisture, which can improve the anti-carbonization performance of aggregate during use and extend the service life of the material. At the same time, this protective layer increases the density of aggregate, making it more stable in complex environments.

[0025] Compared with the prior art, this application solves the following technical problems: 1) Improve the performance of recycled aggregates: Existing recycled aggregates generally have problems such as rough surface, porosity, and high water absorption (apparent porosity can reach 30%, and the average pore size is 50 nm), resulting in insufficient mechanical properties. This application generates a dense calcium carbonate protective layer through the reaction of PEI and CO2, making the surface structure of the aggregate more dense, and significantly reducing the water absorption and porosity of the aggregate, significantly improving the strength, durability and anti-aging properties of the aggregate. At the same time, the lower water absorption capacity helps to slow down the migration of water in the interface area and avoid abnormal local water-cement ratio, thereby improving the interface bonding performance between the cement matrix and the aggregate.

[0026] 2) Improve carbonization efficiency and uniformity: Compared with the traditional CO2 curing or carbon mineralization process disclosed in patents CN110790541A and CN118771811A, this application utilizes the high activity amino group of PEI to react quickly with CO2, solves the problems of uneven CO2 distribution and low carbonization rate, and realizes the synchronous carbonization of the inside and surface of the particles.

[0027] 3) Simplify the process and reduce energy consumption: In the prior art, such as CN118771811A, a complex high temperature and high humidity environment and chemical additives are relied on to improve the carbonization effect. The present application completes the carbonization curing under normal temperature conditions, without the need for additional high energy consumption equipment or complex additives, significantly reducing the complexity of the process.

[0028] 4) Increased carbon fixation and environmental benefits: PEI in this application efficiently captures CO2, which not only improves the compactness of aggregates, but also significantly increases carbon fixation. Compared with the synthesis of nano calcium carbonate for biomedicine in CN115520888A, this application combines PEI with the preparation of recycled aggregates, which reflects higher economic benefits and environmental value in large-scale building material applications.

[0029] The artificial aggregate preparation method provided in this application shows great potential in the field of green building material development, and provides a low-cost and high-efficiency technical solution for the resource utilization of construction waste and the realization of carbon emission reduction goals, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the XRD diagram of the recycled micro powder raw material.

[0031] Figure 2 The XRD diagrams of the hydration products of Examples 1-3 and Comparative Examples 1-2 are shown.

[0032] Figure 3 The porosity distribution of the hydration products of Example 2 and Comparative Examples 1-2.

[0033] Figure 4 Carbonization test and carbonization depth test of aggregate examples 1-3 and comparative examples 1-2.

[0034] Figure 5 It is the weight loss graph of the hydration product of aggregate Examples 1-3 and Comparative Examples 1-2 at different temperatures. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described in more detail below in conjunction with the embodiments.

[0036] Unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. The cement powder used in the examples is commercially available P·O 42.5 ordinary Portland cement, which meets the standard requirements of "General Portland Cement" (GB175-2007). The construction waste was provided by a construction waste site in Anhui.

[0037] Example 1 A method for preparing artificial aggregate based on the carbon capture performance of waste concrete and PEI comprises the following steps: S1. The waste construction concrete is subjected to multi-stage crushing, screening and sorting to obtain recycled micro powder with a particle size of less than 0.16 mm; S2. Take 80 parts of recycled micropowder and 20 parts of cement powder and mix them evenly to obtain a recycled micropowder-cement mixture; S3. Put the machine-made sand with a particle size of 2.36-4.75 mm into the disc granulator, control the granulator speed to 31 rpm, and granulate. During the granulation process, the recycled micro powder-cement dry powder mixture is divided into 500 portions, added at intervals of 50 times, and 0.2-0.3 portions of PEI aqueous solution with a molecular weight of 10,000 and a solid content of 4% are sprayed between each two adjacent additions. The interval between each powdering and water spraying is 12-24 s, so that PEI is evenly covered on the surface and inside of the particles to form artificial aggregate particles with a stable core-shell structure.

[0038] S4. Place the prepared artificial aggregate particles in a carbonization curing device, adjust the CO2 concentration to 10%, control the temperature at 20°C, maintain the humidity at 70%, and carbonize and cure for 14 days to obtain the desired artificial aggregate.

[0039] Example 2 A method for preparing artificial aggregate based on the carbon capture performance of waste concrete and PEI comprises the following steps: S1. The waste construction concrete is subjected to multi-stage crushing, screening and sorting to obtain recycled micro powder with a particle size of less than 0.16 mm; S2. Take 80 parts of recycled micropowder and 20 parts of cement powder and mix them evenly to obtain a recycled micropowder-cement mixture; S3. Put the machine-made sand with a particle size of 2.36-4.75 mm into the disc granulator, control the granulator speed to 31 rpm, and granulate. During the granulation process, the recycled micro powder-cement dry powder mixture is divided into 500 portions, added at intervals of 50 times, and 0.2-0.3 portions of PEI aqueous solution with a molecular weight of 10,000 and a solid content of 8% are sprayed between each two adjacent additions. The interval between each powdering and water spraying is 12-24 s, so that PEI is evenly covered on the surface and inside of the particles to form artificial aggregate particles with a stable core-shell structure.

[0040] S4. Place the prepared artificial aggregate particles in a carbonization curing device, adjust the CO2 concentration to 10%, control the temperature at 20°C, maintain the humidity at 60%, and carbonize and cure for 14 days to obtain the desired artificial aggregate.

[0041] Example 3 A method for preparing artificial aggregate based on the carbon capture performance of waste concrete and PEI comprises the following steps: S1. The waste construction concrete is subjected to multi-stage crushing, screening and sorting to obtain recycled micro powder with a particle size of less than 0.16 mm; S2. Take 80 parts of recycled micropowder and 20 parts of cement powder and mix them evenly to obtain a recycled micropowder-cement mixture; S3. Put the machine-made sand with a particle size of 2.36-4.75 mm into the disc granulator, control the granulator speed to 31 rpm, and granulate. Divide the recycled micro powder-cement dry powder mixture into 500 equal parts, add it at intervals of 50 times, and spray 0.2-0.3 parts of PEI aqueous solution with a molecular weight of 10,000 and a solid content of 12% between each two adjacent additions. The interval between each powdering and water spraying is 12-24 s, so that PEI is evenly covered on the surface and inside of the particles to form artificial aggregate particles with a stable core-shell structure.

[0042] S4. Place the prepared artificial aggregate particles in a carbonization curing device, adjust the CO2 concentration to 10%, control the temperature at 20°C, maintain the humidity at 70%, and carbonize and cure for 14 days to obtain the desired artificial aggregate.

[0043] Comparative Example 1 Prepare artificial aggregates as follows: S1. The waste construction concrete is subjected to multi-stage crushing, screening and sorting to obtain recycled micro powder with a particle size of less than 0.16 mm; S2. Take 80 parts of recycled micropowder and 20 parts of cement powder and mix them evenly to obtain a recycled micropowder-cement mixture; S3. Put the machine-made sand with a particle size of 2.36~4.75mm into the disc granulator, control the granulator speed to 31rpm, and granulate. During the granulation process, divide the recycled micro powder-cement dry powder mixture into 500 equal parts, add it at intervals of 50 times, and spray water as a granulation medium between each two adjacent additions to make the particles uniformly formed.

[0044] S4. Place the prepared artificial aggregate particles in a curing device, control the temperature at 20° C., maintain the humidity at 70%, and cure for 14 days to obtain the desired artificial aggregate.

[0045] Comparative Example 2 Prepare artificial aggregates as follows: S1. The waste construction concrete is subjected to multi-stage crushing, screening and sorting to obtain recycled micro powder with a particle size of less than 0.16 mm; S2. Take 80 parts of recycled micropowder and 20 parts of cement powder and mix them evenly to obtain a recycled micropowder-cement mixture; S3. Put the machine-made sand with a particle size of 2.36~4.75mm into the disc granulator, control the granulator speed to 31rpm, and granulate. During the granulation process, divide the recycled micro powder-cement dry powder mixture into 500 equal parts, add it at intervals of 50 times, and spray water as a granulation medium between each two adjacent additions to make the particles uniformly formed.

[0046] S4. Place the prepared artificial aggregate particles in a carbonization curing device, adjust the CO2 concentration to 10%, control the temperature at 20°C, maintain the humidity at 70%, and carbonize and cure for 14 days to obtain the desired artificial aggregate.

[0047] result For the XRD patterns of the regenerated micropowder used in Examples 1-3 and Comparative Examples 1-2, see Figure 1 .

[0048] The artificial aggregates obtained in Examples 1-3 and Comparative Examples 1-2 were tested on the 1st, 3rd, 7th and 14th days of curing, respectively, wherein the depth of calcium carbonate was tested using phenolphthalein reagent, and the amount of calcium carbonate generated was quantitatively analyzed using TG.

[0049] Table 1 shows the components and their mass fractions in Examples 1-3 and Comparative Examples 1-2, and Table 2 shows the performance test and microscopic test results of artificial aggregates prepared by the physical-chemical method for improving the activity of recycled micropowder obtained in Examples 1-3 and Comparative Examples 1-3. Figure 2 The XRD diagrams of the hydration products of Examples 1-3 and Comparative Examples 1-2 are shown.

[0050] Table 1 Mass of components and curing conditions of artificial aggregates prepared in Examples 1-3 and Comparative Examples 1-2 ; Table 2 Test results of physical properties of artificial aggregates obtained in Examples 1-3 and Comparative Examples 1-2 ; From Table 2 and Figure 2 It can be seen that the carbonization and PEI treatment have a significant effect on the apparent density, strength and water absorption. The calcium carbonate generated during the carbonization process fills the pores of the aggregate, significantly increases the apparent density and improves the strength of the aggregate; at the same time, due to the generation of calcium carbonate, the water absorption of the aggregate is significantly reduced. In addition, the addition of PEI can further promote the formation of calcium carbonate and contribute to its uniform distribution in the aggregate, thereby further improving the microstructure and comprehensive properties of the aggregate. The XRD analysis results show that the carbonization process consumes more calcium oxide and generates more calcium carbonate; the generated calcium carbonate not only enhances the mechanical properties of the aggregate, but also effectively fills the pores of the aggregate. The deposition and uniform distribution of calcium carbonate work together to significantly improve the strength and resistance to water absorption of the aggregate.

[0051] Figure 3 Table 3 is the porosity distribution of the hydration products of Example 2 and Comparative Examples 1-2, and Table 4 is the test results of the total porosity and average pore size of Example 2 and Comparative Examples 1-2.

[0052] Table 3 Test results of total porosity and average pore size of Example 2 and Comparative Examples 1-2 ; like Figure 3 As shown in Table 3, the artificial aggregate prepared by Example 2 shows significantly better performance than Comparative Examples 1 and 2 in terms of pore structure. The porosity distribution of Example 2 is obviously concentrated in the low-porosity direction, the number of high-porosity sections is significantly reduced, and its total porosity and average pore size are lower than those of the comparative sample, indicating that the overall structure of the sample is more compact and the pore distribution is more uniform. In comparison, because Comparative Example 1 has not undergone carbonization treatment, the aggregate structure is loose, the porosity is high, and the high-porosity interval accounts for a large proportion; although Comparative Example 2 has been carbonized, there are still many open pores in the shell structure because PEI is not introduced, and the density and stability are not ideal. The above results show that the introduction of an appropriate amount of PEI combined with carbonization treatment can not only improve the uniformity of the coating of the slurry on the aggregate surface, but also promote the deposition and densification of calcium carbonate on the aggregate surface and inside the pores during the carbonization process, thereby forming a more continuous and dense shell structure, effectively closing the open pores, reducing the porosity, and enhancing the structural stability and mechanical properties of the aggregate. This structural optimization effect is of great significance for improving the interfacial bonding performance between artificial aggregate and cement matrix and its long-term service durability.

[0053] Figure 4 It shows that the carbonization depth of aggregates under different curing methods continues to increase with time. Comparative Example 1 cured at room temperature has the slowest carbonization and the lowest carbonization depth; the carbonization speed of Comparative Example 2 without PEI has increased, but it is still lower than that of the various embodiments with PEI added. Examples 1 to 3 are samples with different amounts of PEI added, and the carbonization reaction is significantly accelerated, especially Examples 2 and 3, which can be completely carbonized within 48 hours, indicating that an appropriate amount of PEI helps promote the carbonization process. Accelerated carbonization not only increases the amount of calcium carbonate generated, but also allows it to preferentially deposit on the surface of the aggregate, forming a dense protective layer, effectively closing the pores, reducing gas and moisture penetration, and improving the durability and structural stability of the aggregate. Especially with the assistance of PEI, the calcium carbonate distribution is more even and the shell layer is more complete, which is beneficial to the performance of the aggregate in subsequent use.

[0054] Figure 5It is a weight loss diagram of the hydration product at different temperatures of aggregate Examples 1-3 and Comparative Examples 1-2. It can be seen from the figure that in the range of 600-800°C, each sample has obvious mass loss caused by the decomposition of calcium carbonate, among which the loss amplitude of Examples 1-3 is significantly greater than that of Comparative Example 1, indicating that more calcium carbonate is generated in the aggregate after adding PEI and accelerating carbonization treatment. In particular, Examples 2 and 3 have the largest decrease in the thermogravimetric curve (TG) and the strongest peak value of the differential thermogravimetric curve (DTG), indicating that the carbonization reaction is more sufficient. The deposition of a large amount of calcium carbonate not only enhances the compactness of the aggregate surface, but also effectively fills the original pores, improves the integrity and stability of the overall structure of the aggregate, thereby enhancing its mechanical properties, and provides a good mechanical basis for subsequent applications in cement-based composite materials.

[0055] The above implementation modes are only used to illustrate the technical solutions of the present invention, but not to limit the present invention. Although the present invention has been described in detail with reference to the above implementation modes, those skilled in the art should understand that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing artificial aggregate based on waste concrete and PEI, wherein the PEI is polyethyleneimine, characterized in that: The following steps are involved: S1. crushing the waste concrete to a particle size of less than 0.16 mm to obtain recycled micro powder; S2. The recycled micropowder and cement powder are uniformly mixed according to a set mass ratio to obtain a recycled micropowder-cement mixture; S3. Using sand, recycled micropowder - cement mixture and PEI aqueous solution to co-granulate to obtain artificial aggregate particles with sand as the core, recycled micropowder - cement mixture and PEI wrapped around the sand; S4. Carbonization-curing the prepared artificial aggregate particles to obtain the desired artificial aggregate.

2. The method for preparing artificial aggregate based on waste concrete and PEI according to claim 1, characterized in that: The cement dry powder is ordinary Portland cement, the median particle size D50 is 15-25 μm, and the set mass ratio of the regenerated micropowder to the cement dry powder is (9-8): (1-2).

3. The method for preparing artificial aggregate based on waste concrete and PEI according to claim 1, characterized in that: The particle size of the sand is 2-5 mm, the particle size of the artificial aggregate particles is 8-20 mm, and the usage ratio of the sand to the recycled micropowder-cement mixture and the PEI aqueous solution is 1:42:

10.

4. The method for preparing artificial aggregate based on waste concrete and PEI according to claim 3, characterized in that: In the PEI aqueous solution, the PEI solid content accounts for 1-16 wt%.

5. The method for preparing artificial aggregate based on waste concrete and PEI according to claim 3, characterized in that: The specific method of granulation is as follows: placing sand in a granulator, dividing the recycled micropowder-cement mixture into 50 equal parts, and adding it 50 times during the granulation process, spraying 0.2-0.3 parts of PEI aqueous solution between two adjacent additions, and the interval time for adding the recycled micropowder-cement mixture and the PEI aqueous solution is 12-24 seconds to form the required artificial aggregate particles.

6. The method for preparing artificial aggregate based on waste concrete and PEI as claimed in claim 5, characterized in that: The rotation speed of the granulator is 20-40 rpm, the total mass of a single feed is in the range of 0.5-3 kg, and the granulation time is 10-20 min.

7. The method for preparing artificial aggregate based on waste concrete and PEI according to claim 1, characterized in that: The carbonization curing conditions are: curing for at least 3 days in an environment with a CO2 concentration of 5-20%, a temperature of 20-40°C, and a humidity of 50-70%.

8. An artificial aggregate, characterized in that: The artificial aggregate is prepared by the method according to any one of claims 1 to 7, comprising a sand core and a shell wrapping the sand core, the shell being composed of a product of a reaction between a recycled micropowder-cement mixture and CO2 and residual recycled micropowder-cement mixture, the apparent porosity of the artificial aggregate being less than 25%, and the average pore size being less than 30 nm; the diameter of the sand core being 2 to 5 mm, and the particle size of the artificial aggregate being 8 to 20 mm.

9. Use of the artificial aggregate as claimed in claim 8 as roadbed filling material and / or building material.

10. A roadbed filling material or building material, characterized in that: The artificial aggregate as claimed in claim 8 is added.

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