Modified recycled fine aggregate, method for producing the same, and concrete

Abstract

The application relates to the technical field of building materials, in particular to modified recycled fine aggregate, a preparation method thereof and concrete. The method comprises the following steps: sequentially performing dry grinding treatment and wet grinding treatment on recycled fine aggregate by using composite grinding beads to obtain modified recycled fine aggregate. The composite grinding beads comprise first beads, second beads and third beads, the particle diameters of the three kinds of beads are sequentially reduced, and the three kinds of beads have specific density ranges; a composite reagent is added in the wet grinding treatment, and the composite reagent contains a silane coupling agent and a polymer emulsion. The three kinds of composite grinding beads are cooperated, the functions of crushing, polishing and trimming and filling and polishing are sequentially played, the particle gradation is closer to that of natural river sand, the mechanical properties are improved, and the density is improved. The surface of the recycled fine aggregate is modified by the method of first dry grinding and then wet grinding, a dense coated organic-inorganic composite film layer is formed, the bonding strength and the compatibility with the cement paste are improved, and the recycled fine aggregate can replace the natural river sand.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and in particular to modified recycled fine aggregates and their preparation methods, and concrete. Background Technology

[0002] Recycled fine aggregates made from construction waste can serve as a substitute for natural river sand in building materials such as concrete, achieving resource utilization. However, due to their complex origins and crude preparation processes, raw recycled fine aggregates suffer from numerous performance defects, severely limiting their large-scale application in concrete. On one hand, the particle size distribution is unreasonable: limited by crushing technology, the proportion of coarse particles (>2.36mm) in recycled fine aggregates is too high, while the proportion of fine particles (<0.15mm) is insufficient, resulting in poor workability and high bleeding rates in concrete mixtures during practical applications. On the other hand, their mechanical properties are weak: old mortar adheres to the particle surface, resulting in high internal porosity and generally high crushing values ​​across all particle sizes, directly affecting the compressive and flexural strength of concrete. On the other hand, the physical properties are poor: due to the presence of a large amount of low-density construction waste such as aerated concrete blocks in the fine aggregate, the apparent density and bulk density of the original recycled fine aggregate are much lower than those of natural fine aggregate, resulting in insufficient concrete density and reduced durability. On the other hand, the interface bonding is poor: the old mortar on the surface of the recycled fine aggregate has poor compatibility with the newly generated cement hydration products, forming a weak interface transition zone, which is prone to micro-cracks and reduces the long-term stability of the concrete structure. At the same time, dust, organic matter and other impurities attached to the surface further weaken its bonding performance with cement paste.

[0003] To address these issues, existing technologies have proposed several physical and chemical modification methods to improve the performance of recycled fine aggregates, but the results have been less than ideal. Physical modification alone often employs a single steel ball mill, which only improves particle size distribution but fails to remove surface impurities or optimize interfacial properties. Furthermore, it can easily lead to excessive particle breakage, increasing fine powder content and reducing concrete strength. Chemical modification alone often involves adding agents such as silane coupling agents and polymer emulsions through soaking or spraying, but this suffers from uneven agent distribution, incomplete reactions, limited modification effects, and high agent loss rates. Combining physical and chemical modification is difficult due to the lack of synergistic coupling in existing technologies. The lack of matching design between milling parameters and agent application timing makes it challenging to simultaneously optimize the particle morphology, physical properties, mechanical properties, and interfacial properties of recycled fine aggregates. Summary of the Invention

[0004] The purpose of this application is to provide modified recycled fine aggregate and its preparation method, as well as concrete, in order to solve the problem that the performance of modified recycled fine aggregate made from construction waste does not meet the requirements and the concrete prepared from it has poor performance.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a method for preparing modified recycled fine aggregate, comprising: Modified recycled fine aggregates were obtained by sequentially dry grinding and wet grinding of the recycled fine aggregates with composite grinding beads.

[0006] The composite grinding beads consist of a first bead, a second bead, and a third bead. The first bead has a larger particle size than the second bead, and the second bead has a larger particle size than the third bead. The density of the first bead is 7.5 g / cm³. 3 ~9.0g / cm 3 The density of the second bead is 3.7 g / cm³. 3 ~4.1g / cm 3 The density of the third bead is 5.0 g / cm³. 3 ~6.1g / cm 3 The wet milling process involves adding a composite agent containing a silane coupling agent and a polymer emulsion.

[0007] The original recycled fine aggregate often has a high proportion of coarse particles, insufficient fine particles and sharp edges, with a lot of surface dust and high porosity. Therefore, the preparation method of this application uses composite grinding beads to perform dry grinding and wet grinding in sequence. (1) On the one hand, the three-stage grinding beads work together to form a composite grinding bead. The first bead has the largest size and the highest density, and has a high impact energy during ball milling, which can break the coarse particles in the recycled fine aggregate; the second bead has a moderate size and the lowest density, which is conducive to the finer requirements after the first bead coarse crushing during ball milling, grinding and trimming the edges of the particles, and significantly reducing the proportion of needle-like and flaky particles in the particles; the third bead has the smallest size and moderate density, which is conducive to penetrating into the micropores of the recycled fine aggregate, further polishing the particle surface, improving chemical stability, reducing the dissolution of impurities, and generating a large number of active reaction sites. Therefore, the three-stage grinding beads can play a synergistic role, significantly optimizing the particle size distribution and surface morphology. This not only helps to reduce the proportion of coarse particles and increase the proportion of fine particles, making the particle size distribution closer to natural river sand, but also helps to improve mechanical properties, reduce crushing value, and further improve apparent density and bulk density. All of these are beneficial to improving the processing performance and mechanical properties after curing of the modified recycled fine aggregate for concrete. (2) On the other hand, dry grinding followed by wet grinding with composite agent can not only improve the dust removal rate and reduce the phenomenon of dust and agent forming sticky lumps during dry grinding by the synergistic crushing, grinding and polishing of the three grinding beads, thus reducing the impact on the ball milling effect, but also allows wet grinding to take over dry grinding in time. This is conducive to the timely reaction of newly formed active reaction sites with composite agent, so as to avoid the decay of the number of active sites. Moreover, during wet grinding, the composite grinding balls continuously act on the recycled fine aggregate, which is conducive to the continuous dynamic rolling of the recycled fine aggregate particles and the full reaction with the composite agent. (3) Furthermore, during wet grinding, the composite agent can synergistically enhance the aforementioned characteristics of the composite grinding balls, which is beneficial for fully and uniformly coating the recycled fine aggregate particles and for continuous penetration into the particle pores, promoting the reaction between the composite agent and the recycled fine aggregate particles, and facilitating the formation of a densely coated organic-inorganic composite film. The silane coupling agent helps improve the interfacial bonding strength between the modified recycled fine aggregate and cement, while the polymer emulsion helps improve film-forming properties and subsequent compatibility with cement. Therefore, the modified recycled fine aggregate after wet grinding is beneficial for improving the bond strength with cement hydration products, reducing the thickness of the interfacial transition zone, and improving long-term stability when used in concrete. In summary, the modified recycled fine aggregate prepared by this method can partially replace natural river sand, and its use in concrete promotes a strong bond with cement-based materials and exhibits good compatibility.

[0008] Secondly, this application provides a modified recycled fine aggregate, which is prepared by the method described above for preparing modified recycled fine aggregate.

[0009] Compared to the original recycled fine aggregate, the modified recycled fine aggregate of this application exhibits improved particle size distribution, with a gradation curve closely resembling that of natural river sand, meeting the Class II standard. This improves workability in concrete. Simultaneously, the crushing value of each particle size is significantly reduced, resulting in higher mechanical properties that meet the national standard requirements for "Recycled Fine Aggregates for Concrete and Mortar." Furthermore, the apparent density of the particles is increased, meeting the Class II standard, with some indicators approaching or reaching the Class I standard. The bulk density is also increased, meeting the Class II recycled fine aggregate standard. Finally, the modified recycled fine aggregate is coated with a dense organic-inorganic composite film, improving its bond strength with cement paste and reducing the thickness of the interfacial transition zone, thus significantly enhancing the performance of the prepared concrete.

[0010] Thirdly, this application provides a concrete comprising the modified recycled fine aggregate prepared by the method described above.

[0011] Concrete containing the aforementioned modified recycled fine aggregates is beneficial for improving the concrete's impermeability and frost resistance, reducing carbonation depth, and can partially replace natural river sand, thus reusing waste resources and achieving high environmental and economic benefits. Detailed Implementation

[0012] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0013] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0014] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions mean any combination of these items, including any combination of single or multiple items.

[0015] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0016] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, a first feature may also be referred to as a second feature, and similarly, a second feature may also be referred to as a first feature. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0017] In the embodiments of this application, the "density" of the first bead, the second bead, the third bead, and the composite grinding bead refers to the apparent density, and each grinding bead is considered to be homogeneous; for grinding beads that are composed of different materials, or have a non-homogeneous material distribution, or have a hollow structure, the equivalent density is calculated.

[0018] The performance of the modified recycled fine aggregate prepared in this application embodiment can be referenced to the following standards: Particle size distribution level can refer to the Class II standard, or even the Class I standard, in GB / T 25176-2010 "Recycled Fine Aggregates for Concrete and Mortar". Mechanical strength can refer to the reuse requirements in GB / T 25176-2010 "Recycled Fine Aggregates for Concrete and Mortar". Apparent density can refer to the evaluation value of Class II recycled fine aggregate (>2350 kg / m³). 3 ), and even a class of standards (>2450kg / m 3 The bulk density can be referenced from the evaluation value of Class II recycled fine aggregate (>1300 kg / m³). 3 ).

[0019] The first aspect of this application provides a method for preparing modified recycled fine aggregate, comprising: Modified recycled fine aggregate is obtained by sequentially dry grinding (i.e., dry ball milling) and wet grinding (i.e., wet ball milling) of the recycled fine aggregate using composite grinding beads.

[0020] The composite grinding beads consist of a first bead, a second bead, and a third bead. The first bead has a larger particle size than the second bead, and the second bead has a larger particle size than the third bead. The density of the first bead is 7.5 g / cm³. 3 ~9.0g / cm 3 The density of the second bead is 3.7 g / cm³. 3 ~4.1g / cm 3 The density of the third bead is 5.0 g / cm³. 3 ~6.1g / cm 3 The wet milling process involves adding a composite agent containing a silane coupling agent and a polymer emulsion.

[0021] The original recycled fine aggregate often has a high proportion of coarse particles, insufficient fine particles and sharp edges, and a lot of surface dust and high porosity. Therefore, the preparation method of this application uses composite grinding beads to perform dry grinding and wet grinding in sequence. (1) On the one hand, the three-stage grinding beads work together to form a composite grinding bead. The first bead has the largest size and the highest density, and has a high impact energy during ball milling, which can break the coarse particles in the recycled fine aggregate; the second bead has a moderate size and the lowest density, which is conducive to the finer requirements after the first bead coarse crushing during ball milling, grinding and trimming the edges of the particles, and significantly reducing the proportion of needle-like and flaky particles in the particles; the third bead has the smallest size and moderate density, which is conducive to penetrating into the micropores of the recycled fine aggregate, further polishing the particle surface, improving chemical stability, reducing the dissolution of impurities, and generating a large number of active reaction sites. Therefore, the three-stage grinding beads can play a synergistic role, significantly optimizing the particle size distribution and surface morphology. This not only helps to reduce the proportion of coarse particles and increase the proportion of fine particles, making the particle size distribution closer to natural river sand, but also helps to improve mechanical properties, reduce crushing value, and further improve apparent density and bulk density. All of these are beneficial to improving the processing performance and mechanical properties after curing of the modified recycled fine aggregate for concrete. (2) On the other hand, dry grinding followed by wet grinding with composite agent can not only improve the dust removal rate and reduce the phenomenon of dust and agent forming sticky lumps during dry grinding by the synergistic crushing, grinding and polishing of the three grinding beads, thus reducing the impact on the ball milling effect, but also allows wet grinding to take over dry grinding in time. This is conducive to the timely reaction of newly formed active reaction sites with composite agent, so as to avoid the decay of the number of active sites. Moreover, during wet grinding, the composite grinding balls continuously act on the recycled fine aggregate, which is conducive to the continuous dynamic rolling of the recycled fine aggregate particles and the full reaction with the composite agent. (3) Furthermore, during wet grinding, the composite agent can synergistically enhance the aforementioned characteristics of the composite grinding balls, which is beneficial for fully and uniformly coating the recycled fine aggregate particles and for continuous penetration into the particle pores, promoting the reaction between the composite agent and the recycled fine aggregate particles, and facilitating the formation of a densely coated organic-inorganic composite film. The silane coupling agent helps improve the interfacial bonding strength between the modified recycled fine aggregate and cement, while the polymer emulsion helps improve film-forming properties and subsequent compatibility with cement. Therefore, the modified recycled fine aggregate after wet grinding, when used in concrete, helps improve the bonding strength with cement hydration products, reduces the thickness of the interfacial transition zone, and enhances long-term stability. In summary, the modified recycled fine aggregate prepared by this method can partially replace natural river sand, and its use in concrete promotes a strong bonding interface with cement-based materials, exhibiting good compatibility.

[0022] In the composite grinding beads, the first bead has the highest density, at 7.5 g / cm³. 3 ~9.0g / cm 3 This can include, but is not limited to, 7.5 g / cm³. 3 8.0g / cm 38.5g / cm 3 9.0g / cm 3 Or a value within the range formed by any two of the above values. The first bead is also the largest in size; in some embodiments, the particle size of the first bead can be 8mm to 12mm, including but not limited to 8mm, 9mm, 10mm, 11mm, 12mm, or a value within the range formed by any two of the above values. In some embodiments, the first bead is a steel ball. These first beads of density, size, or material are advantageous in providing higher impact energy to crush coarse particles of recycled fine aggregate; they are also advantageous in exposing dust on the surface of recycled fine aggregate.

[0023] The second bead has the lowest density, at 3.7 g / cm³. 3 ~4.1g / cm 3 It may include, but is not limited to, 3.7 g / cm³. 3 3.8g / cm 3 3.9g / cm 3 4.0g / cm 3 4.1g / cm 3 Or a value within the range formed by any two of the above values. The second bead is of medium size; in some embodiments, the particle size of the second bead can be 4mm to 8mm, including but not limited to 4mm, 5mm, 6mm, 7mm, 8mm, or a value within the range formed by any two of the above values. In some embodiments, the second bead is a corundum bead (alumina bead). These second beads of density, size, or material are beneficial for grinding and trimming the particles after coarse crushing of the first bead, reducing sharp edges and needle-like shapes; they are also beneficial for removing dust from the recycled fine aggregate through friction.

[0024] The third bead has a medium density of 5.0 g / cm³. 3 ~6.1g / cm 3 This can include, but is not limited to, 5.0 g / cm³. 3 5.3g / cm 3 5.5g / cm 3 5.8g / cm 3 6.1g / cm 3Or a value within the range formed by any two of the above values. The third bead is the smallest; in some embodiments, the particle size of the third bead can be 2mm to 4mm, including but not limited to 2mm, 2.5mm, 3mm, 3.5mm, 4mm, or a value within the range formed by any two of the above values. In some embodiments, the third bead is a zirconium bead (zirconia bead). These third beads, with their density, size, or material, are advantageous for penetrating deep into the micropores of the recycled fine aggregate, further polishing the particle surface, improving chemical stability, reducing impurity leaching, and generating a large number of active reaction sites, such as hydroxyl sites; they are also advantageous for reducing dust adhesion through polishing.

[0025] Through the aforementioned three-stage grinding bead synergistic system, the composite grinding beads, based on the principles of impact energy gradient distribution and stepwise improvement of grinding precision, achieve a synergistic effect of coarse crushing and fine grinding, directly promoting the gradation optimization of recycled fine aggregates and making the gradation curve approach the continuous gradation of natural river sand. This is beneficial for reducing the porosity between aggregate particles, increasing bulk density, and significantly improving fluidity, laying the foundation for subsequent uniform mixing with cement materials to prepare concrete; at the same time, the blunting of edges and corners reduces the frictional resistance between particles, reducing energy consumption during concrete mixing.

[0026] In some embodiments, the mass ratio of the first, second, and third beads is (44~55):(30~40):(15~25), which may include, but is not limited to, (44 or 48 or 52 or 55):(30 or 33 or 36 or 40):(15 or 18 or 21 or 25) or any two of the above ratios. These mass ratios, combined with the aforementioned particle size and density distribution, facilitate the synergistic effect of the three types of abrasive beads in the composite abrasive beads. The first bead concentrates impact energy and avoids excessive breakage; the second bead refines and polishes the edges of the particles, reducing the content of needle-like particles to below 12% in the example; and the third bead penetrates deep into micropores to fill and polish the surface.

[0027] In the example, the composite grinding beads can be prepared in a mass ratio of 50:35:15 for steel beads (10mm diameter): corundum beads (6mm diameter): zirconium beads (3mm diameter), resulting in a bulk density of 5.2 g / cm³. 3 The grinding process using these composite grinding beads significantly optimizes the particle size distribution of recycled fine aggregates, reducing the proportion of coarse particles, increasing the proportion of fine particles, improving bulk density, decreasing the content of needle-like and flaky particles, increasing pore filling rate, and improving apparent density. When the aggregate with optimized gradation is applied to concrete, it significantly improves the workability of the concrete mixture, i.e., the slump loss rate is significantly reduced compared to the original aggregate, the spread is improved, and bleeding and segregation are effectively reduced; at the same time, the dense particle packing reduces the internal porosity of the concrete, providing a physical basis for increased strength.

[0028] In some embodiments, the process includes impurity removal treatment of the recycled fine aggregate before dry grinding. This impurity removal treatment removes impurities such as fine dust, soluble calcium salts, and soluble magnesium salts adhering to the surface of the original recycled fine aggregate, resulting in a clean surface and exposing more hydroxyl active sites, which is beneficial for chemical reaction with the silane coupling agent during subsequent wet grinding. Specifically, this can be achieved by washing with water, mixing and stirring the recycled fine aggregate with water, and then filtering and drying it.

[0029] In some embodiments, the ball-to-material ratio of the composite grinding beads to the recycled fine aggregate is (8~12):1, which may include, but is not limited to, 8:1, 9:1, 10:1, 11:1, 12:1, or any combination of the above ratios. This ball-to-material ratio ensures that the composite grinding beads have sufficient impact energy on the recycled fine aggregate; for example, an impact energy density of 8.5 J / cm³ can be achieved with a ball-to-material ratio of 10:1. 3 This process ensures that the first grinding bead fully breaks down coarse particles ranging from 2.36mm to 4.75mm, while avoiding over-grinding by the second and third grinding beads to produce fine powder ≤0.075mm, thus preventing dust formation. After effective crushing of the coarse particles, the gradation remains continuous, resulting in a significantly reduced bleeding rate in concrete mixing compared to the original recycled fine aggregate, and a significant improvement in workability. This ball-to-material ratio also promotes dynamic tumbling of the recycled fine aggregate and the creation of numerous new active reaction sites, which is beneficial for the uniform adhesion of composite agents during wet grinding.

[0030] The ball milling method in this embodiment involves dry milling followed by wet milling with added chemicals. Dry milling utilizes the physical action of composite grinding beads to efficiently remove impurities, shape, and polish particles, improve particle size distribution, reduce dust, and prevent dust from mixing with chemicals to form sticky clumps. Wet milling uses composite chemicals to reduce the particle friction coefficient and allows the composite chemicals to adhere and react evenly as the particles tumble, easily penetrating into the pores.

[0031] In some embodiments, the total time for dry grinding and wet grinding is 30 to 90 minutes, including but not limited to 30 minutes, 50 minutes, 70 minutes, 90 minutes, or any two of the above values. This total time is beneficial for thoroughly grinding the recycled fine aggregate, improving the gradation improvement effect, more effectively removing dust, and facilitating the adhesion of composite agents. In some embodiments, the dry grinding time can be 10 to 30 minutes, including but not limited to 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or any two of the above values. This time is beneficial for removing loose mortar and dust from the surface of the recycled fine aggregate, increasing the surface hydroxyl exposure rate, providing active sites for subsequent composite agent reactions, and also avoiding excessive surface wear. The wet grinding time can be 20 to 60 minutes, including but not limited to 20 minutes, 30 minutes, 40 minutes, 45 minutes, 50 minutes, 60 minutes, or any two of the above values. In the demonstration example, the dry grinding process can be set to 15 minutes. Based on the quantitative results of the air-classified dust removal rate, the first bead in the first 5 minutes mainly exposes the surface dust through impact, the second bead in the middle 5 minutes mainly removes the dust through friction, and the third bead in the last 5 minutes mainly reduces dust adhesion through polishing, ultimately improving the dust removal rate and reducing the phenomenon of composite agent and dust gelling in the subsequent wet grinding process. In the demonstration example, the wet grinding process can be set to 45 minutes, which is beneficial for a high degree of matching with the reaction cycle of the composite agent. In the first 20 minutes, the composite agent penetrates into the deep pores of the particles, and in the last 25 minutes, the silane coupling agent fully reacts with the hydroxyl groups on the particle surface, improving the reaction rate. The above wet grinding duration also reduces the risk of the formed polymer emulsion film being worn away by the composite grinding beads. The wet grinding process allows the composite agent to react fully, which is beneficial for enhancing the bond strength between the modified recycled fine aggregate and the cement paste interface when preparing concrete, thereby improving the compressive strength of the concrete.

[0032] In some embodiments, the ball mill cylinder volume for both dry and wet grinding processes can be 100L~500L, and can be lined with wear-resistant ceramic with a thickness of 10mm~15mm. This volume is suitable for industrial production and can process 5kg~25kg of recycled fine aggregate in a single batch, avoiding the problems of low efficiency in small volumes and uneven movement of composite grinding balls in large volumes. The Al2O3 mass ratio in the wear-resistant ceramic lining is ≥92%, and the hardness can be HRA85-88, which helps to reduce the wear rate, impurity content, and noise of the ball mill.

[0033] In some embodiments, the container volume and rotation speed of the dry grinding and wet grinding processes are designed to allow the first grinding ball to drop, while the second and third grinding balls roll with the container. This parameter design facilitates the effective functioning of the three types of grinding balls in the composite grinding system, meeting the requirements of synergistic impact grinding, crushing and shaping of recycled fine aggregates, and adhesion reaction efficiency of the composite agent in wet grinding. Specifically, the above effects can be achieved by selecting a suitable container and setting an appropriate rotation speed, combined with the different sizes and densities of the three grinding balls. In some embodiments, the container volume for dry grinding and wet grinding is 100L~500L, and the rotation speed is 250r / min~350r / min, which may include, but is not limited to, 250r / min, 275r / min, 300r / min, 325r / min, 350r / min, or any value within the range of any two of the above values. At this volume and rotation speed, on the one hand, because the first bead is the largest and heaviest, it is thrown up and then falls, and its falling motion has high impact energy, which can break up the coarse particles in the recycled fine aggregate. The second and third beads roll with the container wall and have a certain linear velocity, which can continuously grind and polish the recycled fine aggregate. On the other hand, the recycled fine aggregate can also continuously tumble dynamically, which, together with the composite grinding beads, can optimize the particle size distribution. In wet grinding, it can easily come into full contact with the composite agent and react to form a dense organic-inorganic composite film layer, which is beneficial for improving the interfacial bonding strength and compatibility with cement when used in concrete. Furthermore, the parameter settings in this range can avoid the problem of insufficient impact energy of the first bead leading to an excessively high proportion of coarse particles, and can also avoid the problem of reduced grinding efficiency and easy agglomeration caused by the synchronous rotation of the recycled fine aggregate and the composite grinding balls. In the demonstration example, for a 100L ball mill cylinder, a rotation speed of 300r / min can be set. The first ball can drop to a height of 28cm and an impact speed of 1.4m / s, which can effectively crush coarse particles without damaging the already shaped particles. At the same time, the second and third balls can generate a linear velocity of 0.8m / s as the cylinder rolls, which can precisely grind the edges of the particles. After the edges of the particles are blunted, the internal friction angle during concrete mixing is reduced, the slump is improved, and the spread is significantly increased.

[0034] Meanwhile, the loading amount of composite grinding beads in the grinding container also affects the movement mode and grinding effect of the three types of grinding beads. In some embodiments, the loading amount of composite grinding beads is the volume of the reaction vessel cylinder × the bulk density of the composite grinding beads × the filling coefficient. In the example, the filling coefficient can be 0.5~0.7, and can be selected as 0.6. This range of filling coefficients allows the composite grinding beads to have a movement space of 10mm~15mm, avoiding the problems of insufficient impact frequency due to too large a movement space caused by too low a filling coefficient and reduced grinding efficiency due to obstructed movement caused by too high a filling coefficient.

[0035] In some embodiments, wet milling includes spraying the composite agent. Spraying facilitates uniform contact and reaction between the composite agent and the recycled fine aggregate, saving on the amount of composite agent required. It also ensures that the composite agent forms a film primarily on the surface of the (recycled fine aggregate) particles, thereby reducing localized particle agglomeration. In contrast, adding the composite agent directly to the container after dry milling for wet milling can lead to problems. Adding too little agent can cause localized particle agglomeration, while other particles may struggle to react. Adding too much agent can result in a near-slurry-like consistency, wasting agent and requiring subsequent drying and impurity removal, further affecting the uniformity of the film formation on the particle surface. Spraying, with its smaller dosage, ensures uniform contact and reaction with the recycled fine aggregate, reducing localized particle agglomeration. In some embodiments, the mass ratio of the composite agent to the recycled fine aggregate is (0.05~0.1):1, which may include, but is not limited to, 0.05:1, 0.07:1, 0.09:1, 0.1:1 or any two of the above ratios. These mass ratios are conducive to the full contact and reaction between the composite agent and the recycled fine aggregate, forming a uniform film layer on the particle surface.

[0036] In the example, for a 100L ball mill cylinder, an annular atomizing nozzle can be installed. Made of 304 stainless steel, with a diameter of 20mm-30mm, it is installed at 1 / 3 of the height from the bottom of the cylinder, with 8-12 nozzles evenly distributed. This installation height matches the trajectory of the first bead in the composite grinding beads (the lowest point is 1 / 4 of the height from the bottom), facilitating full contact between the composite agent and the recycled fine aggregate particles and composite grinding beads. The 8-12 nozzles correspond to the circumference of the cylinder, with each nozzle covering a 30°-45° range, achieving no spray dead zones.

[0037] In the example, the atomizing nozzle for spray treatment can employ a pressure atomization design. In some embodiments, the droplet size for spray treatment is 50 μm to 100 μm, including but not limited to 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any two of the above values. This spray droplet size not only ensures that the composite agent is fully and uniformly bonded to the surface of the recycled fine aggregate, especially penetrating deep into the pores, to form a coated organic-inorganic composite film layer through reaction; but also avoids the problems of easy volatilization of the composite agent when the particle size is too small, and uneven bonding between the composite agent and the recycled fine aggregate when the particle size is too large. The spray pressure can be 0.3 MPa to 0.5 MPa, which is beneficial for improving the atomization effect and avoiding the problems of insufficient atomization when the pressure is too low, and accelerated nozzle wear when the pressure is too high.

[0038] In the demonstration, the spray treatment can be started simultaneously with the rotation of the wet grinding treatment, or it can be started after a delay of 5 to 10 minutes. This is beneficial for the composite agent to continuously penetrate into the pores of the recycled fine aggregate during the grinding process. At the same time, the grinding action promotes the chemical reaction between the composite agent and the surface of the recycled fine aggregate, avoiding the problem of uneven agent distribution in the traditional soaking method.

[0039] In some embodiments, the spray flow rate is 3 mL / min to 8 mL / min, and may include, but is not limited to, 3 mL / min, 4 mL / min, 6 mL / min, 8 mL / min, or any value within the range of any two of the above. This spray flow rate is beneficial for the composite agent to fully coat and modify the recycled fine aggregate.

[0040] In some embodiments, the spray flow rate is reduced during the wet milling process. This reduced flow rate design can be matched with a process that involves dry milling followed by wet milling. Specifically, the flow rate is higher in the early stage of the spraying process, which can match the greater number of active sites on the surface of the recycled fine aggregate particles after dry milling. The higher flow rate allows for rapid spraying of the composite agent, improving the agent coverage rate in the early stage of the wet milling process and achieving uniform coverage. The flow rate is lower in the later stage of the spraying process because a preliminary film layer has already formed on the particle surface. Slow replenishment of the composite agent is beneficial to improving the completeness of the chemical reaction between the composite agent and the recycled fine aggregate. In addition, the design of the reduced spray flow rate helps to avoid the problems of agent waste due to high speed throughout the process or insufficient reaction due to low speed throughout the process. In the example, the spray flow rate can be set in a gradient. The wet process lasts for 45 minutes. The flow rate can be 5 mL / min to 8 mL / min in the first 30 minutes of the wet milling process, and 3 mL / min to 5 mL / min in the last 15 minutes of the wet milling process. This ensures that the composite agent reacts fully with the recycled fine aggregate, and the residual rate of the composite agent after the wet milling process is less than 2%.

[0041] In some embodiments, the spraying treatment is intermittent spraying, which involves spraying for a period of time, stopping for a period of time, and then spraying again for a period of time, continuously. The stopping period provides a time window for the composite agent to fully penetrate into the micropores of the recycled fine aggregate, alleviating the problems of agent surface aggregation and flow loss caused by continuous spraying, and can significantly improve agent utilization. It also allows the composite agent to fully and uniformly react with the surface of the recycled fine aggregate to form a coating film. However, the stopping period may also be accompanied by the loss and attenuation of active reaction sites.

[0042] The silane coupling agent in the composite agent can chemically react with the active sites on the surface of recycled fine aggregate, such as undergoing a hydrolysis-condensation reaction with hydroxyl sites, modifying the surface of the recycled fine aggregate and forming abundant Al-O-Si bonds, which is beneficial for improving the interfacial bonding strength with cement during subsequent concrete preparation. In some embodiments, the silane coupling agent can be KH-550, KH-560, KH-570, etc., wherein KH-550 contains an amino group, KH-560 contains an epoxy group, and KH-570 contains a methacryloyloxy group. These silane coupling agents can undergo hydrolysis-condensation reactions with active sites such as hydroxyl groups on the surface of recycled fine aggregate, thereby modifying it. In some embodiments, the silane coupling agent contains an amino group, and the amino value is greater than or equal to 1.2 mmol / g. Silane coupling agents containing an amino group and having this amino value have high reactivity and readily react with hydroxyl groups.

[0043] Polymer emulsions can form a film on the surface of recycled fine aggregates, improving the compatibility of modified recycled fine aggregates with cement and filling micropores. In some embodiments, polymer emulsions may include styrene-butadiene rubber emulsions, polyurethane emulsions, polyacrylate emulsions, etc. These types of emulsions have good film-forming properties and excellent compatibility with cement paste when preparing concrete. In particular, oil-in-water polyacrylate emulsions with a solid content of 38% to 42% and a glass transition temperature of 5°C to 10°C are preferred, exhibiting ideal film-forming properties and compatibility with cement paste.

[0044] In some embodiments, the compound agent comprises the following components in parts by weight: 0.5 to 2.0 parts of silane coupling agent; 5 to 10 parts polymer emulsion; 88-94.5 parts deionized water; 0.1 to 0.3 parts of excipients; The auxiliary agent includes ethylene glycol.

[0045] The silane coupling agent in the above-mentioned mass fraction can fully react with the active reaction sites on the surface of recycled fine aggregate, improving the interfacial bond strength with cement-based materials. This avoids the phenomenon that insufficient dosage leads to incomplete reaction, while excessive dosage causes bridging and agglomeration, thus reducing bond strength. In the example, 1.2 parts can be selected.

[0046] The polymer emulsion of the above-mentioned mass fraction has good film-forming properties, high pore filling rate, and low water absorption rate, which reduces the impact on cement hydration and avoids the phenomenon that too little dosage leads to low pore filling rate and high water absorption rate of recycled fine aggregate particles, and that too much dosage results in an emulsion film layer that is too thick and affects cement hydration. In the example, 7.5 parts can be selected.

[0047] Deionized water can participate in the hydrolysis reaction of silane coupling agents and can also wet the surface of recycled fine aggregates. The above-mentioned mass fraction of deionized water ensures that the curing amount of the composite agent is within a suitable range, providing both sufficient concentration of effective ingredients for chemical reaction and suitable viscosity for atomization and uniform coating. In the example, 91.3 parts of deionized water can be selected.

[0048] Ethylene glycol, as an auxiliary agent, can lower the freezing point of the composite agent and prevent it from freezing easily in low-temperature environments. At the same time, the above-mentioned mass fraction of ethylene glycol is also beneficial to improving the stability of the polymer emulsion. In the example, 0.3 parts of ethylene glycol can be selected.

[0049] After wet grinding, further steps include discharge, drying, screening, and quality inspection. Discharge is achieved through a 4.75mm screen at the ball mill outlet. Drying can be done in a forced-air drying oven at 100℃~110℃ for 2~3 hours. This temperature is the standard drying temperature for aggregates, ensuring the integrity of the surface film on the particles and maintaining a moisture content of less than or equal to 5%, meeting the moisture content requirements for concrete aggregates. Screening uses a 4.75mm vibrating screen for secondary screening to remove excessively crushed fine powder, ensuring that the dust content of particles smaller than 0.075mm is less than or equal to 5%, guaranteeing stable particle size distribution. Quality inspection focuses on core indicators such as particle size distribution, crushing value, and density to ensure the modified recycled fine aggregate meets standards.

[0050] The second aspect of this application provides a modified recycled fine aggregate, which is prepared by the method for preparing modified recycled fine aggregate described in the above-described embodiments of this application.

[0051] Compared to the original recycled fine aggregate, the modified recycled fine aggregate in this application exhibits improved particle size distribution, with a gradation curve closely resembling that of natural river sand, meeting the Class II standard. This improves workability in concrete. Simultaneously, the crushing value of each particle size is significantly reduced, resulting in higher mechanical properties that meet the national standard requirements for recycled fine aggregates for concrete and mortar. Furthermore, the apparent density of the particles is increased, meeting the Class II standard, with some indicators approaching or reaching the Class I standard. The bulk density is also increased, meeting the Class II recycled fine aggregate standard. Finally, the modified recycled fine aggregate is coated with a dense organic-inorganic composite film, improving its bond strength with cement paste and reducing the thickness of the interfacial transition zone, thus significantly enhancing the performance of the prepared concrete.

[0052] A third aspect of this application provides a concrete comprising the modified recycled fine aggregate prepared by the preparation method described in the embodiments of this application.

[0053] Concrete containing the above-mentioned modified recycled fine aggregates is beneficial to improving the concrete's impermeability and frost resistance, reducing the carbonation depth, and can partially replace natural river sand, thus reusing waste resources and having high environmental and economic benefits.

[0054] The raw materials for this concrete may include cement and other auxiliary cementitious materials, natural river sand, modified recycled fine aggregate partially replacing natural river sand, coarse sand, water, water-reducing agents, etc. The mass percentage of modified recycled fine aggregate replacing natural river sand can range from 1% to 90%. In the example, it can be 20% to 70%, meaning that where 100 parts by mass of river sand were originally required for concrete preparation, 1 to 90 parts can now be completely replaced by modified recycled fine aggregate; further, 20 to 70 parts can be completely replaced by modified recycled fine aggregate.

[0055] The following description is based on specific embodiments.

[0056] Example 1 Construction waste is first crushed using a jaw crusher to obtain raw recycled fine aggregate. The performance parameters of the raw recycled fine aggregate are shown in Table 1 below.

[0057] The original recycled fine aggregate was first dry-milled using composite grinding beads, then wet-milled with a composite agent to obtain modified recycled fine aggregate. The modification effect of the modified recycled fine aggregate compared to the original recycled fine aggregate was evaluated. Finally, the modified recycled fine aggregate was used to prepare concrete. The specific process is as follows: 1. Setting modification parameters Composite grinding beads: comprised of steel beads, corundum beads, and zirconium beads in a mass ratio of 50:35:15. The steel beads are made of GCr15 bearing steel with a hardness of HRC60-62, a particle size of 10 mm, and a density of 7.85 g / cm³. 3 The corundum beads are made of white corundum, with a hardness of HRA90-92, a particle size of 6mm, and a density of 3.95g / cm³. 3 The zirconium beads are made of zirconium oxide, with a hardness of HRA 93-95, a particle size of 3 mm, and a density of 6.0 g / cm³. 3 The total mass of the composite grinding beads is 50 kg. First, load the composite grinding beads into a 100 L ball mill cylinder.

[0058] The original recycled fine aggregate was fed into the ball mill cylinder in an amount of 5 kg, so the ball-to-material ratio was 10:1.

[0059] The ball milling parameters were set at a rotation speed of 300 r / min and a total time of 60 min, including 15 min of dry milling and 45 min of wet milling.

[0060] A ring-shaped atomizing nozzle, 25 mm in diameter, is installed in the ball mill cylinder at 1 / 3 of its height from the bottom, with 10 evenly distributed nozzle holes. The atomizing nozzle sprays a composite agent, producing droplets of 75 μm at a spray pressure of 0.4 MPa. The composite agent is prepared by mixing 1.2% KH-550 silane coupling agent, 7.5% (poly)acrylate emulsion, 0.2% ethylene glycol, and 91.1% deionized water by mass, with a total dosage of 0.3 kg. The silane coupling agent KH-550 is industrial grade with a purity ≥98%, and the acrylate emulsion has a solid content of 40%.

[0061] The spraying parameters were set up to start the wet grinding process and the spraying of the compound agent simultaneously. During the 45-minute wet grinding process, the first 30 minutes were the initial stage with a spraying flow rate of 6 mL / min. During the second 45 minutes, the spraying flow rate was 4 mL / min. After the wet grinding was completed, the modified recycled fine aggregate was obtained.

[0062] 2. The modification effect is shown in Table 2 after testing:

[0063] 3. Concrete Application Effects C40 concrete was prepared by replacing 30% of natural river sand with modified recycled fine aggregate. The specific mix proportions of the concrete were as follows: cement: modified recycled fine aggregate: natural river sand: crushed stone: water: water-reducing agent = 420:320:747:1120:168:2.1. The cement was PO42.5R, the crushed stone had a particle size of 5mm~25mm, and the water-reducing agent was a polycarboxylate-based high-efficiency water-reducing agent with a water reduction rate ≥25%. The workability and mechanical properties of the concrete after curing are shown in Table 3.

[0064] In this embodiment, the largest steel beads (50%) efficiently impact and crush coarse particles, the medium-sized corundum beads (35%) are finely ground to remove sharp edges, and the smallest zirconium beads (15%) precisely fill the micropores, creating a gradient effect that makes the gradation of the modified recycled fine aggregate approximate that of natural river sand. A ball-to-particle ratio of 10:1 provides 8.5 J / cm³. 3 Impact energy and a rotation speed of 300 r / min ensure that the composite grinding beads achieve synergistic grinding and crushing, effectively avoiding over-crushing or under-grinding. 1.2% KH-550 condenses with the hydroxyl groups of the particles to form Si-O-Al bonds, and 7.5% acrylate emulsion uniformly fills the micropores and forms a film on the surface of the recycled fine aggregate. The composite film significantly improves the interfacial adhesion between the composite film and the cement paste in the later stage. The spraying process is also well-suited: initially, 6 mL / min is used to rapidly cover the active sites, and later, 4 mL / min is used to replenish the reaction in a timely manner, greatly improving the uniformity of agent coverage and significantly enhancing the sufficiency of the reaction.

[0065] Combining Tables 1, 2, and 3, the following performance improvements can be observed: 1. Significantly optimized particle size distribution The proportion of coarse particles in the modified recycled fine aggregate is significantly reduced, while the proportion of fine particles is reasonably increased. The particle size distribution curve is closer to that of natural river sand, meeting the Class II standard of GB / T 25176-2010 "Recycled Fine Aggregates for Concrete and Mortar". The workability of concrete mixtures is improved.

[0066] 2. Significantly improved mechanical properties The crushing values ​​of each particle size decreased significantly, and the mechanical strength of the modified recycled fine aggregate met the reuse requirements of GB / T 25176-2010 "Recycled Fine Aggregates for Concrete and Mortar".

[0067] 3. Overall improvement in physical properties Apparent density increased to 2389 kg / m³ 3 Exceeding the evaluation value for Class II recycled fine aggregate (>2350kg / m³) 3 Some parameters can reach Class I standards (>2450kg / m³). 3 ); Bulk density from 1184 kg / m³ 3 Increased to 1388kg / m 3 Exceeding the evaluation value for Class II recycled fine aggregate (>1300 kg / m³) 3 ); 4. Interface performance and durability optimization The composite agent reacts fully with the particle surface to form a dense organic-inorganic composite film. The bond strength between recycled fine aggregate and cement paste is improved, and the thickness of the interfacial transition zone is reduced. Concrete prepared using modified recycled fine aggregates exhibits improved impermeability, improved frost resistance, and reduced carbonation depth.

[0068] 5. Outstanding technical, economic, and environmental benefits. The modification process has low energy consumption (unit product energy consumption ≤50kWh / t), reagent loss rate <5%, and modification cost increases by only 50~80 yuan / t, which is far lower than the purchase cost of natural river sand (150-300 yuan / t). Using 1 ton of modified recycled fine aggregate can reduce the land occupied by construction waste by 0.8 m². 2 This saves 1.2 tons of natural river sand and reduces CO2 emissions by 0.3 tons, meeting the "dual carbon" target requirements. The modification process is simple and can be adapted from existing ball milling equipment, making it easy to promote industrialization.

[0069] Example 2 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the particle size of the three types of grinding beads is adjusted; all other aspects are the same. Specifically, the particle size of the steel beads is changed from 10mm to 12mm, the particle size of the corundum beads is changed from 6mm to 8mm, and the particle size of the zirconium beads is changed from 3mm to 4mm.

[0070] 2. The modification effect was tested and is shown in Table 4:

[0071] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 5.

[0072] In Example 2, the particle size of the composite grinding beads is increased, resulting in a slight imbalance between the particle size and the original recycled fine aggregate. The particle size of these composite grinding beads is more suitable for coarse particles >4.75mm. However, since the original recycled fine aggregate is generally ≤4.75mm, the fine particles in the 0.15mm~2.36mm range are not sufficiently refined, leading to a coarser overall gradation curve. Furthermore, compared to the 3mm zirconium beads used in Example 1, the 4mm zirconium beads, due to their larger size, have limited penetration into micropores, resulting in increased pore filling rate and decreased particle density. In addition, the impact energy of the large-diameter steel beads is excessively concentrated in the coarse particles, simultaneously reducing the grinding efficiency of the corundum beads on the edges and corners, increasing inter-particle frictional resistance, and ultimately leading to reduced concrete spread and decreased performance. Overall, the performance of this example meets the standards, but is slightly lower than that of Example 1.

[0073] Example 3 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the particle size of the three types of grinding beads is adjusted; all other aspects are the same. Specifically, the particle size of the steel beads is changed from 10mm to 8mm, the particle size of the corundum beads is changed from 6mm to 4mm, and the particle size of the zirconium beads is changed from 3mm to 2mm.

[0074] 2. The modification effect was tested and is shown in Table 6:

[0075] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 7.

[0076] In this embodiment, the composite grinding beads have a generally smaller particle size. The impact energy of a single 8mm steel bead is significantly lower than that of a 10mm steel bead. Although it cannot completely crush coarse particles ranging from 2.36mm to 4.75mm, resulting in the 4.75mm sieve residue not meeting the Class I standard, it still achieves a significant reduction in the proportion of coarse particles compared to the original recycled fine aggregate. The 4mm corundum beads and 2mm zirconium beads achieve particle edge grinding and micropore filling, and the crushing value, apparent density, and bulk density of each particle size are significantly improved compared to the original recycled fine aggregate. The workability and strength of the concrete are also significantly better than those of the original recycled fine aggregate. However, due to the imbalance in particle size gradient, the movement trajectory of such small-diameter 8mm grinding beads is closer to the cylinder wall, which cannot form an effective impact, resulting in insufficient crushing of coarse particles. The overall modification effect is not as good as the optimal solution in Example 1. Overall, the performance of this embodiment meets the standard, but is slightly lower than that of Example 1.

[0077] Example 4 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the mass ratio of steel balls, corundum balls, and zirconium balls is changed from 50:35:15 to 60:25:15; all other aspects are the same.

[0078] 2. The modification effect was tested and is shown in Table 8:

[0079] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 9.

[0080] In this embodiment, the steel ball mass ratio increased to 60%, resulting in excess impact energy and efficient crushing of coarse particles. The gradation curve was significantly optimized compared to the original recycled fine aggregate, and the fine aggregate gradation met the Class I recycled fine aggregate standard. The crushing value and density of each particle size were significantly improved compared to the original recycled fine aggregate, and the concrete performance was also significantly better than that of the original recycled fine aggregate. However, compared to Example 1, due to the decrease in the proportion of corundum beads, the particle edge grinding ability was insufficient, the content of needle-like and flaky particles increased, and the fine powder content exceeded the standard, leading to accelerated slump loss and decreased mechanical properties. Overall, the performance of this embodiment met the standard, but was slightly lower than that of Example 1.

[0081] Example 5 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the mass ratio of steel balls, corundum balls, and zirconium balls is changed from 50:35:15 to 40:40:20; all other aspects are the same.

[0082] 2. The modification effect is shown in Table 10 after testing:

[0083] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 11.

[0084] In this embodiment, the steel ball mass ratio was reduced to 40%, resulting in insufficient overall impact energy density and a coarse particle crushing effect that was not as optimal as the optimal solution. The 4.75mm sieve residue did not meet the Class I standard, but it still achieved significant optimization of the gradation compared to the original recycled fine aggregate. The increased proportion of corundum and zirconium beads enhanced the particle edge grinding and micropore filling effects, and the crushing value and density of each particle size were significantly improved compared to the original recycled fine aggregate. The workability and strength of the concrete were also significantly better than those of the original recycled fine aggregate. However, due to the insufficient steel ball proportion, the dynamic tumbling effect of the recycled fine aggregate particles was weakened, and the uniform coverage of the reagent decreased, ultimately leading to a significant decrease in the mechanical properties of the concrete specimens. Overall, the performance of this embodiment met the standards, but was lower than that of Example 1.

[0085] Example 6 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the total mass of the composite grinding beads is changed from 50kg to 40kg, which changes the ball-to-material ratio from 10:1 to 8:1. Everything else is the same.

[0086] 2. The modification effect was tested and is shown in Table 12:

[0087] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 13.

[0088] In this embodiment, the ball-to-material ratio is reduced to 8:1, resulting in insufficient impact energy density, low coarse particle crushing efficiency, increased porosity, and an excessively thick layer of recycled fine aggregate, leading to a decrease in grinding frequency. The effects of corundum and zirconium beads are also difficult to fully realize, increasing the content of needle-like and flaky particles and increasing the internal friction angle. Furthermore, incomplete surface cleaning easily leaves dust residue, adsorbing water-reducing agents and hindering coupling agent reactions. An excessively thick layer affects uniform tumbling, resulting in uneven coverage of composite agents and reduced interfacial bond strength. Ultimately, this leads to a decrease in the slump and compressive strength of C40 concrete, significantly reducing its workability and mechanical properties. Overall, the performance of this embodiment meets the standards, but is slightly lower than that of Example 1.

[0089] Example 7 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the silane coupling agent is replaced with KH-560; all other aspects are the same.

[0090] 2. The modification effect was tested and is shown in Table 14:

[0091] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 15.

[0092] In this embodiment, the composite milling beads, process parameters, and acrylate emulsion content remained unchanged, ensuring no significant difference in particle size distribution and physical properties, and consistent concrete workability. However, the type of silane coupling agent was adjusted compared to Example 1, resulting in differences in interfacial chemical properties. Specifically, the reactivity of the epoxy groups in KH-560 with the hydroxyl groups on the particle surface was significantly lower than that of the amino groups in KH-550, leading to a relative decrease in the efficiency of chemical bond formation at the interface. More importantly, the Si-O-Al bond energy formed by KH-550 was higher than that formed by the Si-OC bond energy in KH-560. This difference directly led to a decrease in the interfacial bond strength between the modified recycled fine aggregate and the cement paste, which is also the main reason for the decrease in the mechanical properties of the concrete specimens. Overall, the performance of this embodiment met the standards, and the parameters of the modified recycled fine aggregate and the concrete workability were similar to those of Example 1, but the concrete strength was slightly lower than that of Example 1.

[0093] Example 8 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the spraying parameters of the compound agent are changed to intermittent spraying: the spraying of the compound agent and wet grinding are started simultaneously, and the intermittent spraying is carried out in the manner of spraying for 5 minutes, then stopping for 2 minutes and then continuing to spray, with a total spraying time of 45 minutes and an average flow rate of 5 mL / min.

[0094] 2. The modification effect was tested and is shown in Table 16:

[0095] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 17.

[0096] The intermittent spraying in this embodiment provides a time window for the agent to fully penetrate the micropores of the recycled fine aggregate during the stop spraying phase. This avoids the problems of agent accumulation and flow loss on the surface during continuous spraying, improving agent utilization. It also allows the silane coupling agent to fully complete the hydrolysis and condensation with the hydroxyl groups on the aggregate surface, forming stable Si-O-Al bonds. The acrylate emulsion can uniformly form a film to seal the pores and reduce water absorption, significantly improving the interfacial compatibility between the aggregate and the cement paste. Therefore, the workability and strength at all ages of the concrete remain at a high level, significantly better than traditional soaking and single physical modification schemes. However, compared with the gradient continuous spraying in Example 1 that matches the exposure pattern of active sites in the aggregate, intermittent spraying cannot accurately match the agent application and the interfacial reaction process. Insufficient coverage of active sites in the early stage and inaccurate agent replenishment in the later stage result in slightly lower agent reaction coverage and interfacial bond strength. In addition, there is uneven film formation in some areas and slight dispersion in the interfacial transition zone. Ultimately, the workability and strength at all ages of the concrete are slightly lower than the optimal scheme. Overall, the performance of this embodiment meets the requirements. The parameters of the modified recycled fine aggregate and the concrete processing performance are similar to those of Example 1, but the concrete strength is slightly lower than that of Example 1.

[0097] Example 9 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the raw materials are pretreated: the recycled fine aggregate is washed with water, mixed with water at a mass ratio of 1:3, stirred for 10 minutes, filtered and dried. Everything else is the same.

[0098] 2. The modification effect was tested and is shown in Table 18:

[0099] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 19.

[0100] This embodiment effectively removes soluble salts (such as Ca²⁺) adhering to the surface of recycled fine aggregates through a water washing pretreatment process. + Mg² +The removal of fine dust significantly reduces impurity content. Due to the prior removal of fine dust, the physical parameters of the modified recycled fine aggregate after dry and wet grinding are significantly improved compared to Example 1. The water washing pretreatment process not only cleans the aggregate surface but also increases the exposure rate of hydroxyl (-OH) active sites on its surface, thereby improving the reaction coverage of the subsequent silane coupling agent on its surface and resulting in a stronger interfacial bond. Ultimately, thanks to the effective removal of soluble impurities, the salting-out reaction inside the concrete is suppressed, pore connectivity is reduced, and the carbonation depth is further reduced. The slump, spread, and early strength of the concrete are all higher than in Example 1, with only the final setting strength being slightly lower. Overall, this example meets the performance standards and is slightly better than Example 1.

[0101] Example 10 The only difference between this embodiment and Embodiment 1 is that 70% of the natural river sand is replaced with modified recycled fine aggregate in the C40 concrete mix. The specific mix proportions are as follows: cement: modified recycled fine aggregate: natural river sand: crushed stone: water: water-reducing agent = 450:1067:457:1150:175:2.6. The workability and mechanical properties of the concrete after curing are shown in Table 20.

[0102] This embodiment, at a high substitution rate of 70%, effectively counteracts performance degradation and achieves concrete performance standards by precisely increasing the mixing water volume and simultaneously optimizing the polycarboxylate superplasticizer dosage. The increased water volume replenishes the moisture adsorbed by the micropores of the modified aggregate, stabilizing the effective water-cement ratio. It also replenishes the lubricating paste, reduces internal particle frictional resistance, and addresses the workability degradation problem under high substitution rates. The added superplasticizer disperses cement particles through steric hindrance, enhancing plasticization and water retention, avoiding the risk of bleeding and segregation caused by increased water content. Furthermore, it synergistically works with the aggregate interface modification effect to strengthen interfacial bonding, compensate for interfacial structural defects under high substitution rates, and ensure sufficient cement hydration and stable strength. The two work together to ensure the concrete specimens meet mechanical performance standards. The early strength of the concrete is slightly higher than in Example 1, while the final setting strength is slightly lower. Overall, this embodiment meets performance standards and is close to that of Example 1, indicating that modified recycled fine aggregate can replace a large proportion of natural river sand, possessing high environmental and economic value.

[0103] Example 11 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is the composite grinding beads: all three types of grinding beads are made hollow, and their density is adjusted, with the steel beads having a density of 7.85 g / cm³. 3 Reduced to 7.5 g / cm³ 3 The density of corundum beads is 3.95 g / cm³. 3 Reduced to 3.7 g / cm³3 The density of zirconium beads is 6.0 g / cm³. 3 Reduced to 5.3 g / cm³ 3 Everything else is the same.

[0104] 2. The modification effect was tested and is shown in Table 21:

[0105] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 22.

[0106] In this embodiment, all three types of grinding beads adopt a hollow structure design. While maintaining the particle size, mass ratio, and other process parameters unchanged, the apparent density of the grinding beads is simultaneously reduced by controlling the hollowness ratio: the steel beads are reduced from 7.85 g / cm³. 3 Reduced to 7.5 g / cm³ 3 The corundum beads are made of 3.95 g / cm³. 3 The concentration of zirconium beads decreased to 3.7 g / cm³, while the concentration of zirconium beads decreased from 6.0 g / cm³. 3 Reduced to 5.3 g / cm³ 3 .

[0107] The results showed that although the density of the grinding beads decreased, the three-level gradient synergistic mechanism was still effective: the hollow steel beads still had sufficient impact energy to crush the coarse particles, and the cumulative sieve residue of 4.75mm was 10.2%, which basically met the Class II standard; the grinding effect of the hollow corundum beads on the edges of the particles was slightly weakened, and the content of needle-like and flaky particles increased slightly; the micropore filling and surface polishing ability of the hollow zirconium beads decreased, resulting in a decrease in the apparent density (2358kg / m³) and bulk density (1342kg / m³) of the aggregate compared with Example 1, but still met the Class II recycled fine aggregate standard.

[0108] In concrete applications, due to the decrease in the overall kinetic energy of the grinding beads, the reduction in the exposure of active sites on the particle surface, the slight decrease in the silane coupling agent reaction coverage, and the slight decrease in interfacial bond strength, the 28-day compressive strength of C40 concrete is 46.3 MPa, which is lower than that of Example 1, but still meets the design requirements of C40 concrete.

[0109] Overall, this embodiment verifies that within the density range defined in this application, even with hollow grinding beads and a density close to the lower limit, effective modification of recycled fine aggregates can still be achieved, indicating that the density parameter range of this application has a wide applicability and process tolerance.

[0110] Example 12 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is the composite grinding beads: the materials of the three types of grinding beads are adjusted, and all are made hollow. The density is also adjusted; specifically, the steel beads are replaced with tungsten carbide steel beads, and the density is changed from 7.85 g / cm³. 3 Increased to 8.8 g / cm³ 3 The corundum beads were replaced with high-density sintered beads, with a density of 3.95 g / cm³. 3 Increased to 4.05 g / cm³ 3 The zirconium beads (zirconia beads) were replaced with cerium-stabilized zirconium oxide beads, and the density was reduced from 6.0 g / cm³. 3 Increased to 6.05 g / cm³ 3 Everything else is the same.

[0111] 2. The modification effect was tested and is shown in Table 23:

[0112] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 24.

[0113] In this embodiment, all three types of grinding beads are made of high-density materials and supplemented with hollow structure control. While maintaining particle size, mass ratio, and other process parameters unchanged, the apparent density of the grinding beads is simultaneously increased to near the upper limit of the claims: tungsten carbide steel hollow beads have an apparent density of 7.85 g / cm³. 3 Increased to 8.8 g / cm³ 3 High-density sintered corundum beads with a density of 3.95 g / cm³ 3 Increased to 4.05 g / cm³ 3 Cerium-stabilized zirconia beads are made of 6.0 g / cm³. 3 Increased to 6.05 g / cm³ 3 .

[0114] The results showed that high-density grinding beads provided higher impact energy, further improving the crushing effect of coarse particles. The cumulative residue on the 4.75mm sieve decreased to 7.9%, and the particle size distribution still met the standards for Class II recycled fine aggregates. The crushing values ​​of each particle size remained at a low level, and the mechanical properties were excellent. The apparent density increased to 2392 kg / m³. 3 The bulk density is 1390 kg / m³. 3 Its physical properties are close to those of a Class I standard.

[0115] However, due to the grinding bead density being close to the upper limit, the impact energy was too high, resulting in a slight increase in the fine powder content. The exposure of active sites on the particle surface was slightly lower than the optimal mix ratio, and the uniformity of the interfacial reaction decreased. As a result, the workability and mechanical properties of the concrete were slightly lower than those of Example 1: the slump was 178 mm and the 28-day compressive strength was 48.7 MPa. However, it was still significantly better than Comparative Example 4 (density far exceeding the upper limit) and fully met the design requirements of C40 concrete.

[0116] Overall, this embodiment verifies that within the density range defined in this application, even with high-density materials and densities close to the upper limit, effective modification of recycled fine aggregates can still be achieved. This demonstrates that the density parameter range of this application has a wide applicability and process tolerance, and can provide guidance for the selection of grinding beads of different materials and structures.

[0117] Example 13 1. Setting modification parameters The only difference between this embodiment and Embodiment 1 is that the ball milling speed for both dry and wet grinding exceeds the critical speed, increasing from 300 r / min to 380 r / min; all other aspects are the same.

[0118] 2. The modification effect was tested and is shown in Table 25:

[0119] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 26.

[0120] In this embodiment, a systemic failure occurred due to an excessively high rotation speed: when the rotation speed reached the critical value of 380 r / min, the composite grinding beads rotated synchronously with the cylinder instead of being thrown, reducing the impact energy conversion efficiency and resulting in insufficient crushing of coarse particles. Simultaneously, the excessively high rotation speed caused violent collisions between particles and the composite grinding beads, leading to electrostatic adsorption and mechanical bonding, forming secondary agglomerates and causing disordered particle size distribution. This series of problems directly resulted in increased internal frictional resistance in the concrete, and a decrease in slump and spread compared to Example 1. Ultimately, because the agglomerated particles could not be uniformly coated by the cement paste, structural voids existed at the interface, significantly reducing the compressive strength of the concrete compared to Example 1, although it still met the requirements for C40 concrete. Overall, the performance of this embodiment met the standards, but was significantly lower than that of Example 1.

[0121] Comparative Example 1 1. Setting modification parameters The only difference between this comparative example and Example 1 is that composite grinding beads are not used; only steel beads from Example 1 are used, totaling 50 kg. No corundum beads or zirconium beads are used. Everything else is the same.

[0122] 2. The modification effect was tested and is shown in Table 27:

[0123] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 28.

[0124] In this comparative example, only a single steel ball was used as the grinding ball, completely lacking the edge-grinding effect of corundum balls and the micropore-filling and surface-polishing effect of zirconium balls. It could only achieve impact crushing of coarse particles and could not complete the gradient synergistic modification of "crushing-refining-polishing". With a single steel ball as the grinding ball, the content of needle-like and flaky particles increased significantly compared to Example 1, and the frictional resistance between particles increased significantly, directly leading to serious deterioration of concrete workability. At the same time, the micropores on the particle surface could not be effectively filled, and the porosity increased significantly compared to Example 1. The apparent density and bulk density did not meet the Class II standard. Furthermore, it could not remove surface impurities or optimize interface properties. It also easily led to excessive particle crushing, increased fine powder content, and insufficient exposure of surface active sites, resulting in a significant decrease in the coverage of the reagent reaction compared to Example 1. Ultimately, this caused a significant decrease in concrete strength, fully demonstrating that a single steel ball cannot achieve comprehensive modification of recycled fine aggregates.

[0125] Comparative Example 2 1. Setting modification parameters The only difference between this comparative example and Example 1 is that composite grinding beads are not used; only the corundum beads from Example 1 are used, totaling 50 kg. Steel beads and zirconium beads are not used. Everything else is the same.

[0126] 2. The modification effect was tested and is shown in Table 29:

[0127] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 30.

[0128] This comparative example uses only a single corundum bead as the grinding ball, completely lacking the impact crushing effect of steel balls and the micropore filling effect of zirconium beads. The density of the corundum bead is only 3.95 g / cm³. 3The process fails to generate effective impact energy, making it difficult to break coarse particles larger than 2.36 mm. This results in a coarse particle ratio that is almost identical to the original recycled fine aggregate, and the gradation of the modified recycled fine aggregate does not meet the Class I recycled fine aggregate standard. Furthermore, single corundum beads cannot penetrate deep into the micropores of the particles for filling and polishing, leading to an increase in particle porosity compared to Example 1, excessive crushing values, and severe deterioration of mechanical properties. The excessively high proportion of coarse particles causes a significant increase in particle packing voids, requiring a large amount of cement paste to fill the voids during concrete mixing. This not only wastes cement but also causes severe bleeding and segregation problems. Numerous primary defects exist in the interface transition zone, ultimately preventing the concrete from achieving the C40 design strength at 28 days. This fully demonstrates that single corundum beads, as grinding beads, are completely incapable of meeting the modification requirements of recycled fine aggregate.

[0129] Comparative Example 3 1. Setting modification parameters The only difference between this comparative example and Example 1 is the adjustment of the material type and density of the three grinding beads. Specifically, the steel beads are replaced with ordinary carbon steel beads, and the density is changed from 7.85 g / cm³. 3 Reduced to 7.2 g / cm³ 3 The corundum beads were changed to brown corundum beads, and the density was reduced from 3.95 g / cm³. 3 Reduced to 3.6 g / cm³ 3 Zirconium beads (zirconia beads) were replaced with zirconium silicate beads, and the density was changed from 6.0 g / cm³. 3 Reduced to 4.0 g / cm³ 3 Everything else is the same.

[0130] 2. The modification effect was tested and is shown in Table 31:

[0131] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 32.

[0132] This comparative example altered the density of the composite grinding beads. Because the overall density of the composite grinding beads was lower, even lower than in Example 11, it directly led to a systematic deterioration of the modification effect. Under the same particle size and mass ratio, the lower the density of the composite grinding beads, the smaller the mass of each particle, and the lower the effective energy of impact grinding: 7.2 g / cm³. 3 The single-particle impact energy of the carbon steel ball is slightly lower than that of the reference steel ball in Example 1, at 3.6 g / cm³. 3 The grinding kinetic energy of brown corundum beads is only 90% of that of the reference corundum beads, 4.0 g / cm³. 3The micropore-filling polishing kinetic energy of zirconium silicate beads is only 65% ​​of that of the benchmark zirconium beads, failing to achieve the gradient synergistic effect of "coarse crushing-refining-polishing". This ultimately leads to insufficient crushing of coarse particles, with the cumulative sieve residues of 4.75mm and 2.36mm exceeding the Class I standard limit. The improvement in crushing values ​​of each particle size is insufficient, and the apparent density and bulk density do not meet the Class II standard. At the same time, the insufficient kinetic energy of the composite ball mill beads results in insufficient exposure of active sites on the particle surface, a significant decrease in the agent reaction coverage compared to Example 1, a substantial decrease in interfacial bond strength, and extremely limited improvement in concrete workability and strength compared to the original recycled fine aggregate.

[0133] Comparative Example 4 1. Setting modification parameters The only difference between this comparative example and Example 1 is the composite grinding beads: the material type and density of the three grinding beads were adjusted, with the steel beads replaced by tungsten carbide steel beads, and the density changed from 7.85 g / cm³. 3 Increased to 14.5 g / cm³ 3 The corundum beads were replaced with high-density sintered beads, with a density of 3.95 g / cm³. 3 Increased to 4.2 g / cm³ 3 The zirconium beads (zirconia beads) were replaced with cerium-stabilized zirconium oxide beads, and the density was reduced from 6.0 g / cm³. 3 Increased to 6.2 g / cm³ 3 Everything else is the same.

[0134] 2. The modification effect was tested and is shown in Table 33:

[0135] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 34.

[0136] In this comparative example, the excessively high density of the steel balls (even higher than in Example 12) and the imbalance in the density gradient of the composite ball milling beads led to a significant deterioration in the modification effect and concrete performance. The impact energy of a single tungsten steel ball was greater than that of the reference steel ball in Example 1, resulting in a severe excess of impact energy. Although this achieved efficient crushing of coarse particles and significantly improved the gradation, crushing value, and density compared to the original recycled fine aggregate, it directly led to over-grinding of particles, with the content of fine powder with a particle size <0.075mm increasing to 7.2%, far exceeding the 3.2% in Example 1. Meanwhile, the density gradient difference between steel balls and corundum and zirconium balls is too large, the movement trajectory of the composite ball milling beads is seriously unbalanced, the drop height of steel balls exceeds the design range, and it cannot form a synergistic effect with the refinement of corundum balls and the polishing of zirconium balls, resulting in insufficient grinding of needle-like particles; excessive fine powder will adsorb a large amount of cement hydration products and water-reducing agents, leading to accelerated slump loss of concrete, decreased workability stability, and a large number of fine powder agglomerations causing original defects in the interface transition zone. Ultimately, the 28-day compressive strength of concrete decreased by 7.7 MPa compared with Example 1.

[0137] Comparative Example 5 1. Setting modification parameters The only difference between this comparative example and Example 1 is that the composite reagent is not used, and an equal amount of deionized water is used instead of the composite reagent in the wet milling stage; all other aspects are the same.

[0138] 2. The modification effect was tested and is shown in Table 35:

[0139] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 36.

[0140] No composite agents were added in this comparative example, and only an equal amount of deionized water was used in the wet grinding stage, resulting in obvious defects in the overall performance of the recycled fine aggregate.

[0141] On the one hand, the hydroxyl groups (-OH) on the particle surface were not effectively activated, and the bonding with the cement paste relied solely on physical adsorption, resulting in low interfacial bond strength. Compared with Comparative Example 6 (with the addition of a silane coupling agent), the interfacial chemical bonding was absent, leading to a significant decrease in the strength of the concrete at all ages. On the other hand, due to the lack of a polymer emulsion to seal the micropores, the water absorption rate of the particles increased, causing uneven moisture distribution within the concrete and a decrease in workability. Furthermore, the lack of lubrication from the reagents during wet grinding resulted in greater frictional resistance between particles, slightly reducing grinding efficiency and causing physical properties such as particle size distribution and crushing value to be slightly inferior to Comparative Example 6.

[0142] Although the ball milling process of the three-stage composite grinding beads still has a certain optimization effect on particle morphology, it cannot fundamentally solve key issues such as interfacial compatibility and bonding strength due to the complete lack of interfacial chemical modification. The overall performance improvement is relatively limited, significantly worse than Comparative Example 6 with added silane coupling agent, and even worse than Example 1. This fully demonstrates the key role of silane coupling agent in improving interfacial performance in composite agents.

[0143] Comparative Example 6 1. Setting modification parameters The only difference between this comparative example and Example 1 is that the polymer emulsion is not added to the composite agent, and the composite agent is prepared according to the mass ratio of 1.2% KH-550 silane coupling agent, 0.2% ethylene glycol and 98.6% deionized water. All other aspects are the same.

[0144] 2. The modification effect was tested and is shown in Table 37:

[0145] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 38.

[0146] In this comparative example, the absence of an acrylic emulsion prevented the formation of a coating layer, resulting in ineffective filling and closure of micropores inside and on the surface of the particles. The interconnected pores led to significantly insufficient density and a higher porosity compared to Example 1. Furthermore, while the single silane coupling agent improved interfacial compatibility, it failed to form an effective moisture barrier layer. Moisture penetration continued to damage the interfacial bonding structure, increasing the particle water absorption rate. This combination of interconnected pores and insufficient interfacial protection resulted in the formation of moisture transport channels within the concrete, significantly increasing the risk of leakage. Ultimately, due to the lack of synergy between the interfacial strengthening function of the silane coupling agent and the pore-filling effect of the polymer emulsion, relying solely on a single coupling agent could not achieve systematic optimization of material properties, resulting in significant shortcomings in overall performance.

[0147] Comparative Example 7 1. Setting modification parameters The only difference between this comparative example and Example 1 is that only steel balls are used as grinding balls, without corundum balls or zirconium balls, and there are no wet ball milling and synergistic spraying of agents. Instead, after dry milling, the balls are directly immersed in the agent of Example 1 for 30 minutes, and then taken out and dried. All other aspects are the same.

[0148] 2. The modification effect was tested and is shown in Table 39:

[0149] 3. The concrete mix proportions were the same as in Example 1. The workability and mechanical properties of the concrete after curing were tested and are shown in Table 40.

[0150] In this comparative example, on the one hand, dry grinding with only steel balls resulted in substandard particle size distribution and apparent density; on the other hand, the separation of physical and chemical modification steps led to systemic failure: the newly formed active sites on the particle surface after ball milling rapidly decayed within 30 minutes, preventing the reagent from fully contacting the effective active surfaces during subsequent soaking treatment, ultimately resulting in a low interfacial reaction rate. Simultaneously, the static soaking method caused severely uneven reagent distribution, with excessive agglomeration in some areas and insufficient coverage in others, leading to significant fluctuations in interfacial bonding strength. Furthermore, the single-ball milling process could not simultaneously achieve particle refinement and surface polishing, resulting in an overall coarser gradation curve, directly affecting the workability of concrete. More seriously, a large amount of reagent failed to be effectively adsorbed by the particles during soaking, resulting in a high loss rate and significantly increasing modification costs.

[0151] Orthogonal experiment verification Finally, this application underwent orthogonal experimental verification. Under the condition that the types, particle sizes, densities, and ratios of the three types of grinding beads in the composite grinding ball remained constant, and the volume of the grinding cylinder and the composite agent spraying treatment remained constant, the importance of other parameters was verified, including A: ball-to-material ratio, B: grinding speed, C: mass percentage of KH-550 in the composite agent, and D: mass percentage of (poly)acrylate emulsion in the composite agent. Design L9(3 4 Orthogonal experiments were conducted using composite grinding beads with the following particle sizes: 4.75mm cumulative sieve residue (%), 2.36mm cumulative sieve residue (%), 1.18mm cumulative sieve residue (%), 0.6mm cumulative sieve residue (%), 0.3mm cumulative sieve residue (%), 0.15mm cumulative sieve residue (%), crushing value of 2.36~4.75mm composite grinding beads (%), crushing value of 1.18~2.36mm composite grinding beads (%), crushing value of 0.6~1.18mm composite grinding beads (%), crushing value of 0.3~0.6mm composite grinding beads (%), and apparent density of composite grinding beads (kg / m³). 3 ), bulk density composite milling beads (kg / m 3 An evaluation system was constructed using multiple performance indicators, including those from various dimensions, to ensure the scientific and comprehensive nature of parameter optimization. The factor levels and results are as follows: 1. Factor Level Table 41

[0152] 2. Orthogonal experimental design 42

[0153] 3. Results and Analysis of Orthogonal Experiments (Table 43)

[0154] 4. Significance Analysis Optimal parameter combination: Considering both performance stability and economy, the core optimal combination remains A2B2C2D2 (ball-to-powder ratio 10:1, rotation speed 300 r / min, 1.2% KH-550, 7.5% acrylate emulsion). Under this combination: The particle size distribution fully meets the Class II recycled fine aggregate standard (8.9% residue on 4.75mm sieve and 22.7% residue on 2.36mm sieve). The crushing value of each particle size is ≤13.8%, indicating excellent mechanical properties; Apparent density 2389 kg / m³ 3 Bulk density 1388 kg / m³ 3 Its physical properties are close to those of a Class I standard; The 7-day compressive strength of C40 concrete is 34.8 MPa, which meets the requirements for early construction and strength of high-grade concrete.

[0155] The influence patterns of these four factors have been verified: The ball-to-particle ratio (A) remains the most critical influencing factor. A ratio of 10:1 can ensure the crushing effect of coarse particles while avoiding excessive fine powder production, thus laying the foundation for particle size distribution for early strength improvement. The content of silane coupling agent (C) is the second highest. At 1.2%, the interfacial adhesion and reaction efficiency reach a balance, which effectively improves the early bond strength of concrete. At a rotational speed (B) of 300 r / min, the composite ball milling beads exhibit the best synergistic effect of ball milling and grinding, with optimal particle morphology and density. The content of acrylic emulsion (D) has a relatively small impact. At 7.5%, the pore filling and cement hydration compatibility are optimal, avoiding obstruction of early strength development.

Claims

1. A method for preparing modified recycled fine aggregate, characterized in that, include: Modified recycled fine aggregate was obtained by sequentially dry grinding and wet grinding of the recycled fine aggregate with composite grinding beads. The composite grinding beads include a first bead, a second bead, and a third bead, wherein the particle size of the first bead is larger than that of the second bead, and the particle size of the second bead is larger than that of the third bead. The density of the first bead is 7.5 g / cm³. 3 ~9.0g / cm 3 The density of the second bead is 3.7 g / cm³. 3 ~4.1g / cm 3 The density of the third bead is 5.0 g / cm³. 3 ~6.1g / cm 3 ; The wet milling process involves the addition of a composite agent, which contains a silane coupling agent and a polymer emulsion.

2. The method for preparing modified recycled fine aggregate according to claim 1, characterized in that, The first bead has a particle size of 8mm~12mm; and / or, The second bead has a particle size of 4mm~8mm; and / or, The particle size of the third bead is 2mm to 4mm.

3. The method for preparing modified recycled fine aggregate according to claim 1 or 2, characterized in that, The mass ratio of the first bead, the second bead, and the third bead is (44~55):(30~40):(15~25); and / or, The ball-to-particle ratio of the composite grinding beads to the recycled fine aggregate is (8~12):1; and / or, The dry grinding process includes impurity removal treatment of the recycled fine aggregate.

4. The method for preparing modified recycled fine aggregate according to claim 1 or 2, characterized in that, The first bead is a steel bead, the second bead is a corundum bead, and the third bead is a zirconium oxide bead; and / or, The container volume and rotation speed of the dry grinding and wet grinding processes are such that the first bead undergoes a throwing motion, while the second and third beads roll with the container; and / or, The container volume for both the dry grinding and wet grinding processes is 100L~500L, and the rotation speed is 250r / min~350r / min.

5. The method for preparing modified recycled fine aggregate according to claim 1 or 2, characterized in that, The wet milling process includes spraying the composite agent, wherein the spraying process satisfies at least one of the following: (1) The droplet size of the spray treatment is 50μm~100μm, and the spray pressure is 0.3MPa~0.5MPa; (2) The flow rate of the spray treatment is 3 mL / min to 8 mL / min; (3) During the wet milling process, the flow rate of the spray treatment is reduced; (4) The spray treatment is intermittent spraying.

6. The method for preparing modified recycled fine aggregate according to claim 1 or 2, characterized in that, The silane coupling agent contains an amino group, and the amino group value is greater than or equal to 1.2 mmol / g; and / or, The polymer emulsion includes an oil-in-water polyacrylate emulsion with a solid content of 38% to 42% and a glass transition temperature of 5°C to 10°C.

7. The method for preparing modified recycled fine aggregate according to claim 1 or 2, characterized in that, The compound agent comprises the following components in parts by weight: The silane coupling agent is 0.5 to 2.0 parts; The polymer emulsion is 5 to 10 parts; 88-94.5 parts deionized water; 0.1 to 0.3 parts of excipients; The auxiliary agent includes ethylene glycol.

8. The method for preparing modified recycled fine aggregate according to claim 1 or 2, characterized in that, The total duration of the dry grinding and wet grinding processes is 30 min to 90 min; and / or, The dry grinding process lasts for 10 to 30 minutes, and the wet grinding process lasts for 20 to 60 minutes; and / or, The mass ratio of the composite agent to the recycled fine aggregate is (0.05~0.1):

1.

9. A modified recycled fine aggregate, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. A type of concrete, characterized in that, This includes modified recycled fine aggregates prepared by the preparation method described in any one of claims 1 to 8.

11. The concrete according to claim 10, characterized in that, Includes river sand and the modified recycled fine aggregate, wherein the modified recycled fine aggregate accounts for 20% to 70% of the total mass of the river sand and the modified recycled fine aggregate; and / or, The concrete comprises cementitious materials, river sand, the modified recycled fine aggregate, coarse sand, water, and a water-reducing agent.

Images