A precast wall panel based on recycled aggregate from construction waste and its preparation method

Abstract

This invention belongs to the technical field of construction waste resource utilization and prefabricated wall technology for prefabricated buildings. Specifically, it relates to a prefabricated wall panel based on recycled aggregate from construction waste and its preparation method. The prefabricated wall panel is prepared from recycled coarse aggregate, recycled fine aggregate, recycled micro powder, P.O42.5 cement, slag micro powder, silicon, mixing water, polycarboxylate superplasticizer, nano-silicon activator, composite fiber, and physical foaming agent. Among them, the recycled coarse aggregate is pure waste concrete crushed material, which adopts a weakly acidic water vapor erosion interface reconstruction process; the recycled fine aggregate is recycled sand from waste red brick ceramic, which adopts a room temperature alkali-activated microporous recrystallization process; and the composite fiber adopts a nano-silicon graft copolymerization modification process. This invention can realize the full utilization of coarse, fine, and micro powders from construction waste to prepare a low-carbon, lightweight, crack-resistant, sound-insulating, and heat-insulating prefabricated wall.

Description

Technical Field

[0001] This invention belongs to the field of construction waste resource utilization and prefabricated wall technology for prefabricated buildings, specifically relating to a prefabricated wall panel based on recycled aggregate from construction waste and its preparation method. Background Technology

[0002] Currently, precast walls made from recycled construction waste generally suffer from three major technical defects: First, the aggregates are mixed and disordered, with waste concrete aggregates and red brick aggregates being directly mixed and added. The two types of aggregates have significant differences in pH and pore structure, resulting in poor matrix compatibility and a tendency to generate internal stress, causing cracking. Second, the recycled aggregates themselves have obvious defects. The surface of the crushed construction waste aggregates is covered with old mortar, and there are micro-cracks inside. They have high water absorption and low strength. Conventional modification only performs surface waterproofing treatment and cannot repair the internal defects of the aggregates. Third, the wall structure is simple. Ordinary recycled walls have a dense structure with poor thermal and sound insulation performance, while foamed lightweight walls suffer from severe strength loss, making it difficult to achieve multiple performances such as load-bearing, lightweight, and thermal insulation. Fourth, the utilization rate of solid waste is low. Most formulas only utilize coarse aggregates, and the crushing tailings are directly discarded, resulting in a resource utilization rate of less than 50%. Summary of the Invention

[0003] This invention aims to provide a precast wall panel based on recycled aggregate from construction waste and its preparation method, solving the technical problems of existing recycled precast wall panels, such as mixed aggregates, poor compatibility, drying shrinkage cracking, low solid waste utilization rate, and inability to simultaneously achieve strength and thermal insulation performance. It realizes the full utilization of coarse, fine, and micro powders from construction waste, and prepares a low-carbon, lightweight, crack-resistant, sound-insulating, and thermally insulating prefabricated wall panel.

[0004] To achieve the above objectives, the technical solution specifically adopted by the present invention is as follows: A precast wall panel based on recycled aggregate from construction waste is prepared from the following raw materials in parts by weight: 450-480 parts recycled coarse aggregate, 440-475 parts recycled fine aggregate, 135-155 parts recycled micro powder, 200-225 parts P.O42.5 cement, 125-145 parts slag micro powder, 20-25 parts silica fume, 115-125 parts mixing water, 3.5-4.2 parts polycarboxylate superplasticizer, 6.8-7.5 parts nano-silicon activator, 3.0-3.5 parts composite fiber, and 1.8-2.3 parts physical foaming agent; The recycled coarse aggregate is pure waste concrete crushed material, processed using a weakly acidic water vapor erosion interface reconstruction process. This process utilizes the gentle corrosion of old, loose mortar by weakly acidic water vapor without damaging the original hard structure of the aggregate, achieving damage-free interface peeling. The recycled fine aggregate is recycled clay sand from waste red bricks, processed using a room-temperature alkali-activated microporous recrystallization process. This process utilizes an alkaline solution to react with the active silica inside the red bricks, generating stable crystals within the pores, optimizing the pore structure and improving thermal insulation and sound absorption capabilities. The composite fiber is modified using a nano-silicon graft copolymerization process. The material consists of 6mm basalt fiber and 3mm polypropylene fiber, with surface grafting using nano-silica sol. The coating thickness is 20-40nm, and it is cured at a constant temperature for 18 hours to grow a rigid nano-silica coating on the fiber surface, forming a rigid nano-transition layer. This solves the problem of hydrophobic and difficult bonding of polypropylene fiber and compensates for the brittleness of basalt fiber. The long and short fibers are arranged in an interlaced manner to form a spatial network crack-resistant structure. Combined with nano-silica activator and trace foaming agent, it precisely repairs the internal cracks of the aggregate and generates closed micropores, taking into account both strength and thermal insulation and sound insulation performance.

[0005] Furthermore, the weakly acidic water vapor erosion interface reconstruction process involves: crushing the original waste concrete blocks using a jaw crusher at a speed of 280–320 r / min; controlling the initial particle size after crushing to 8–25 mm; and then introducing aggregates of this size into a spray modification process. A weakly acidic mist of water vapor with a pH of 5.2–5.6 is used for spraying, and the mixture is kept in a constant-temperature, sealed environment for 14–18 hours to gently remove the loose old mortar from the aggregate surface while retaining the dense aggregate core. After modification, the aggregates are screened a second time to ultimately control the finished product particle size to 5–20 mm.

[0006] Furthermore, the room-temperature alkali-activated microporous recrystallization process involves: crushing waste red bricks using an impact crusher at a speed of 240–280 r / min, with the initial particle size controlled at 0.15–5 mm; during the soaking modification stage, a saturated calcium hydroxide dilute solution is used, with a solid-liquid ratio of 1:2.5–1:3, a soaking water temperature of 20–25°C, and soaking for 40–50 minutes at room temperature and pressure, generating hydrated calcium carbonate crystals inside the pores of the red bricks, which penetrate and modify the microporous structure; after modification, the bricks are naturally air-dried to remove free alkali solution from the surface.

[0007] Furthermore, the recycled micro powder is tailings from the crushing and screening of construction waste, which has undergone low-temperature grinding and activation treatment, resulting in a particle size of less than 0.075 mm and possessing potential gelling activity. Specifically, a planetary ball mill is used for grinding, with a grinding speed of 360–400 r / min and a grinding time of 25–35 min. The temperature during the grinding process is controlled to not exceed 55°C to avoid the degradation of powder activity due to high temperature. After grinding, the sieved particle size is less than 0.075 mm, which breaks down the dense inert film on the surface of the tailings powder, exposing active silicon-aluminum oxides and giving it potential gelling activity.

[0008] Furthermore, the nano-silicon activator is an organosilicon-modified nano-silica solution: silica particle size 15-20 nm, solid content 12%-15%, pH value 8.5-9.0; the molecular chain of this modified activator has hydrophobic methyl functional groups, which have both penetrating repair and hydrophobic sealing capabilities. When used for pretreatment of recycled aggregates, it can penetrate and repair internal cracks in the aggregates, seal surface pores in the aggregates, and inhibit water absorption and efflorescence in the recycled aggregates.

[0009] Furthermore, the water-cement ratio of the precast wall mix is ​​controlled at 0.28, the sand ratio is controlled at 46%, and the dry density of the finished product is controlled at 1720-1800 kg / m³.

[0010] Furthermore, the proportions can be optimized according to the usage scenario. For ultra-high sound insulation scenarios, the amount of recycled red brick sand can be increased and the upper limit of foaming agent can be adjusted to 2.3kg; for high-strength load-bearing scenarios, foaming agent can be eliminated and the amount of recycled coarse aggregate and cement can be increased; for low-cost temporary fencing scenarios, silica fume and nano-silicon activator can be eliminated.

[0011] This invention also provides a method for preparing precast wall panels based on recycled aggregates from construction waste, characterized by comprising the following preparation steps: Step 1: Pre-processing of key raw materials: ①Recycled coarse aggregate: Select crushed concrete aggregate, spray with weakly acidic water mist with citric acid (pH=5.2~5.6), keep it at a constant temperature and sealed for 14~18h, remove dust with high pressure air jet, and screen to obtain dense aggregate of 5~20mm. ② Recycled fine aggregate: Red brick recycled sand is soaked in saturated calcium hydroxide solution at room temperature for 40-50 minutes to complete the pore recrystallization modification, and then taken out and air-dried; ③ Composite fiber: 6mm basalt fiber and 3mm polypropylene fiber were grafted and modified with 8% solid content nano silica sol. The coating thickness was 20-40nm, and the film was cured at a constant temperature for 18h. After modification, the film was sealed and stored for later use. In the pre-processing stage of raw materials, three types of key raw materials are chemically modified: coarse aggregate is eroded by weak acid water vapor to remove old slurry, red brick fine aggregate is alkali-activated recrystallized, and composite fiber nano-silicon grafting is applied. The feeding sequence is strictly controlled during the stirring process to avoid problems such as composite fiber clumping and uneven distribution of foaming agent, forming a gradient composite structure of hard aggregate + dense mortar + micropores.

[0012] Step 2: Raw Material Weighing and Activation: Accurately weigh each raw material according to the unit weight ratio of the mix: 450-480 parts recycled coarse aggregate, 440-475 parts recycled fine aggregate, 135-155 parts recycled micro powder, 200-225 parts P.O42.5 cement, 125-145 parts slag micro powder, 20-25 parts silica fume, 115-125 parts mixing water, 3.5-4.2 parts polycarboxylate superplasticizer, and nano-silicon activator. 6.8–7.5 parts, composite fiber 3.0–3.5 parts, physical foaming agent 1.8–2.3 parts; the weighed recycled coarse aggregate and recycled fine aggregate are screened and washed, and then sprayed with a nano-silicon activator aqueous solution; among them, because the alkali-modified red brick fine aggregate has well-developed pores and a fast adsorption rate, the soaking and standing time of the red brick fine aggregate is extended by 15–20 minutes, while the coarse aggregate is kept at the conventional soaking time, to complete the differentiated secondary activation pretreatment; Step 3, Layered Gradient Mixing: The activated recycled coarse aggregate and recycled fine aggregate are put into the mixing equipment for pre-mixing. Then, cement, slag powder and silica fume are added for coating and mixing with cementitious materials. Next, the modified composite fiber is added and dispersed and mixed. Finally, mixing water, polycarboxylate superplasticizer and physical foaming agent are added and mixed evenly to obtain the mixture. Step 4: Low-frequency vibration molding: Inject the mixture into the precast wall mold and use 35Hz low-frequency directional vibration to expel large air bubbles and retain closed micropores inside the matrix. Step 5: Constant Temperature Gradual Curing: After molding, allow the material to stand still for 4 hours, then cover it with a film and cure it at a constant temperature of 22℃ for 7 days. Finally, allow it to undergo natural carbonization curing for 28 days to obtain the finished precast wall. This invention has the following characteristics and beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. High innovation in modification process: This invention abandons the industry's conventional crude treatment methods such as physical grinding, high temperature roasting, and simple coupling. Instead, it adopts three types of microscopic chemical reaction modification methods: weak acid water vapor erosion, alkali-activated microporous recrystallization, and nano-silicon grafting coating. This optimizes the performance of raw materials from the level of mineral microstructure, resulting in a deeper level of modification and stronger stability of the modification effect. 2. Excellent comprehensive performance of aggregate: The secondary impregnation pretreatment with methyl-modified nano-silicon activator transforms the traditional single-surface waterproofing into crack penetration repair, effectively closing micro-defects inside the aggregate, realizing the strength regeneration of recycled aggregate, and significantly reducing the water absorption rate of aggregate. 3. Improve the interfacial compatibility of mixed aggregates: Use slag powder to finely adjust the matrix alkalinity, neutralize the weak alkalinity of red brick ceramic aggregate, coordinate the interfacial properties between concrete aggregate and red brick aggregate, and avoid matrix cracking and deformation problems caused by poor compatibility of mixed aggregates. 4. Balanced and controllable structural performance: This invention adopts a gradient composite structure design of hard aggregate dense skeleton + cement mortar transition layer + closed micropores, which optimizes thermal insulation and sound insulation performance while ensuring the mechanical strength of the wall. It overcomes the technical pain point of traditional recycled walls that are difficult to balance lightweight and high strength. The finished product has a 28-day compressive strength ≥24MPa and a dry density ≤1800kg / m³. 5. Excellent durability and crack resistance: The long and short composite fibers are arranged in an interlaced pattern to form a spatial network crack-resistant system. Combined with a constant temperature gradual curing system, it effectively inhibits the shrinkage and deformation of the matrix. The finished product has a drying shrinkage rate of ≤0.035%, and its ability to resist drying cracks is significantly better than that of conventional recycled construction waste wall panels. 6. Wide range of engineering applications: This invention sets up differentiated formulation schemes for multiple scenarios, and the dosage of components can be flexibly adjusted according to different engineering needs such as sound insulation, load-bearing capacity, and low cost. It is suitable for various application scenarios such as interior walls of civil buildings, low-rise building enclosure walls, and temporary municipal fences. Detailed Implementation

[0013] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0014] This invention, based on a defined mixing ratio range, sets up three differentiated gradient examples. All raw materials are weighed according to the single-unit mixture mass ratio, with the unit uniformly expressed as kg / m³. The raw material modification processes and preparation steps are completely identical across the three examples, with only the raw material dosage adjusted. The molding and curing conditions are uniform, and the testing standards are consistent. Four core indicators are uniformly tested: 28-day compressive strength, dry density, drying shrinkage rate, and solid waste comprehensive utilization rate. Some groups also include auxiliary indicators such as thermal insulation and sound insulation to form a horizontal performance comparison. Specifically, all performance test indicators of this invention comply with current national building materials testing standards. The test environment temperature is 20±2℃, and the relative humidity is ≥50%. All specimens are uniformly sized as 100mm×100mm×100mm cubic blocks, and the curing conditions are consistent across batches. The specific testing methods for each indicator are as follows: (1) 28-day compressive strength test According to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", an electro-hydraulic servo pressure testing machine was used, with the loading rate controlled at 0.5 MPa / s. Six parallel specimens were prepared for each group, and the arithmetic mean was taken as the final compressive strength after removing the maximum and minimum values.

[0015] (2) Dry density test According to GB / T34018-2017 "Lightweight Partition Boards for Civil Buildings", the specimens cured for 28 days were dried to constant weight. The mass of the specimens was weighed using an electronic analytical balance, and the apparent volume was accurately measured using vernier calipers. The dry density was calculated as dry density = dried mass / solid volume.

[0016] (3) Drying shrinkage rate test According to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", the initial gauge length and 28-day gauge length of the specimens were measured using a vertical shrinkage meter. The specimens were observed under static conditions with constant temperature and humidity. The formula for calculating the drying shrinkage rate is: (initial length - curing length) / initial length × 100%.

[0017] (4) Calculation of comprehensive utilization rate of solid waste According to the general accounting formula for the utilization rate of solid waste in building materials: Comprehensive utilization rate of solid waste = (mass of recycled coarse aggregate + mass of recycled fine aggregate + mass of recycled micro powder) / total mass of mixture × 100%; where the mixing water is not included in the solid phase mass statistics, to ensure the industry's general calculation caliber.

[0018] (5) Auxiliary thermal conductivity testing According to GB / T10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method", a flat plate thermal conductivity meter was used to test the thermal conductivity of the sample at room temperature to determine its thermal insulation performance. Example 1: General Standard Mix Proportion (Balanced Precast Wall Panels) (1) Raw material consumption per unit volume (kg / m³) 465 kg of recycled coarse aggregate, 455 kg of recycled fine aggregate, 145 kg of recycled micro powder, 210 kg of P.O42.5 cement, 135 kg of slag micro powder, 22 kg of silica fume, 120 kg of mixing water, 3.8 kg of polycarboxylate superplasticizer, 7.2 kg of nano-silicon activator, 3.3 kg of composite fiber, and 2.1 kg of physical foaming agent (animal protein physical foaming agent).

[0019] (2) Preparation process Step 1: Pre-processing of key raw materials: Original waste concrete blocks are selected and crushed using a 290r / min jaw crusher. Initially selected aggregates with a particle size of 8-25mm are screened. The aggregates are then sprayed with a weakly acidic water mist (pH=5.4 citric acid), kept at a constant temperature and sealed for 16 hours to complete the reconstruction of the weakly acidic water vapor erosion interface. After high-pressure air jet dust removal, the aggregates are screened to obtain dense recycled coarse aggregates of 5-20mm. Waste red bricks are selected and crushed using a 260r / min impact crusher. Initially selected aggregates with a particle size of 0.15-5mm are screened. The bricks are immersed in a saturated calcium hydroxide solution at room temperature for 45 minutes at a solid-liquid ratio of 1:2.8. Microporous recrystallization is completed at room temperature and pressure. The bricks are then removed and air-dried to remove free alkali from the surface. 6mm basalt fibers and 3mm polypropylene fibers are selected and grafted with 8% solids nano-silica sol for modification. The coating thickness is 30nm, and the mixture is cured at a constant temperature for 18 hours. After modification, the modified material is sealed and stored for later use. Step 2, Raw Material Weighing and Activation: Weigh all raw materials precisely according to the single-component ratio in this embodiment. Screen and wash the modified recycled coarse aggregate and recycled fine aggregate, and then spray them with a methyl-modified hydrophilic nano silica activator aqueous solution. Considering the well-developed pores of the alkali-modified red brick fine aggregate, extend the soaking and standing time by 18 minutes, while the coarse aggregate is kept at the conventional soaking time to complete the differentiated secondary activation pretreatment. Step 3, Layered Gradient Mixing: During the mixing stage, the layered mixing time is strictly controlled. First, the two types of activated aggregates are put into the mixing equipment for pre-mixing for 90 seconds. Then, cement, slag powder, and silica fume are added for coating and mixing for 120 seconds. Next, modified composite fibers are added and dispersed and mixed for 60 seconds. Finally, mixing water, polycarboxylate superplasticizer, and physical foaming agent are added and mixed for 150 seconds until the mixture is uniform, thus obtaining the mixture. Step 4, Low-frequency vibration molding: Inject the mixture into a special mold for precast walls, and use 35Hz low-frequency directional vibration for 45s to expel large air bubbles and retain closed micropores inside the matrix. Step 5, constant temperature gradual curing: After molding, let it stand for 4 hours, then cover and seal it with a film, keep it at a constant temperature of 22℃ for 7 days, and then let it undergo natural carbonization curing for 28 days to obtain the finished precast wall panel.

[0020] (3) Key performance test results Core test indicators: 28-day compressive strength 25.7 MPa, dry density 1765 kg / m³, drying shrinkage rate 0.031%, solid waste comprehensive utilization rate 73.2%; auxiliary test indicators: thermal conductivity 0.55 W / (m·K). This embodiment exhibits balanced strength, thermal insulation, and shrinkage performance, making it suitable for non-load-bearing interior partition walls in ordinary buildings.

[0021] Example 2: High-strength load-bearing ratio (high-mechanical-performance precast wall panels) (1) Raw material consumption per unit volume (kg / m³) 480kg recycled coarse aggregate, 440kg recycled fine aggregate, 135kg recycled micro powder, 225kg P.O42.5 cement, 125kg slag micro powder, 25kg silica fume, 115kg mixing water, 4.2kg polycarboxylate superplasticizer, 7.5kg nano-silicon activator, 3.5kg composite fiber, 0kg physical foaming agent (foaming agent omitted).

[0022] (2) Preparation process The basic preparation process, all raw material pre-modification parameters, and process logic of this embodiment are completely identical to those of Example 1. It strictly follows the complete process of the claims, maintaining uniform mixing and stratification time and low-frequency vibration time, with only a single variable adjusted. Specific differentiated modifications are as follows: In the raw material weighing stage, the physical foaming agent is removed, and the content of recycled coarse aggregate, cement, and silica fume is increased, while the amount of mixing water is reduced to improve matrix density. In the infiltration and activation stage, the differentiated infiltration time of the red brick fine aggregate is shortened to 15 minutes to reduce pore water saturation and further decrease internal porosity. All process parameters and operating steps, including pre-crushing modification, stratified gradient mixing time, 35Hz low-frequency vibration for 45 seconds, and 22℃ constant temperature curing, remain completely consistent with Example 1, strictly adhering to the single-variable testing principle to ensure effective performance data comparison.

[0023] (3) Key performance test results Core test indicators: 28-day compressive strength 32.4 MPa, dry density 1795 kg / m³, drying shrinkage rate 0.028%, solid waste comprehensive utilization rate 70.5%; no auxiliary test indicators. This embodiment has high density and excellent mechanical properties, and is suitable for load-bearing partition walls and enclosure walls of low-rise buildings.

[0024] Example 3: Sound insulation and heat preservation ratio (lightweight sound insulation prefabricated wall panel) (1) Raw material consumption per unit volume (kg / m³) 450kg recycled coarse aggregate, 475kg recycled fine aggregate, 155kg recycled micro powder, 200kg P.O42.5 cement, 145kg slag micro powder, 20kg silica fume, 125kg mixing water, 3.5kg polycarboxylate superplasticizer, 6.8kg nano-silicon activator, 3.0kg composite fiber, and 2.3kg physical foaming agent (animal protein physical foaming agent).

[0025] (2) Preparation process The basic preparation process, all raw material pre-modification parameters, and process logic of this embodiment are completely identical to those of Embodiment 1, strictly following the patented complete preparation process. The stirring and stratification time and low-frequency vibration time are kept constant, with only a single variable adjusted. The specific differentiated modifications are as follows: In the raw material weighing stage, the dosage of porous red brick fine aggregate, recycled micro powder, and physical foaming agent is increased, while the dosage of cement and recycled coarse aggregate is reduced; in the infiltration and activation stage, to adapt to the penetration requirements of high-porosity red brick aggregate, the differentiated infiltration and standing time of red brick fine aggregate is extended to 20 minutes, allowing the nano-silicon activator to fully penetrate the internal micropores; all basic processes such as crushing modification, stratified gradient stirring sequence, 35Hz low-frequency vibration for 45s, and constant temperature curing remain unchanged to ensure that the experimental variable is unique and the experimental data is reliable. (3) Key performance test results Core test indicators: 28-day compressive strength 21.3 MPa, dry density 1725 kg / m³, drying shrinkage rate 0.034%, solid waste comprehensive utilization rate 75.1%; auxiliary test indicators: thermal conductivity 0.49 W / (m·K), sound insulation performance improved by 16% compared to the standard group. This embodiment is lightweight, has excellent thermal insulation and sound insulation performance, and is suitable for soundproof partitions in hotels and apartments.

[0026] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A precast wall panel based on recycled aggregate from construction waste, characterized in that, Prepared from the following parts by weight of raw materials: 450-480 parts recycled coarse aggregate, 440-475 parts recycled fine aggregate, 135-155 parts recycled micro powder, 200-225 parts P.O42.5 cement, 125-145 parts slag micro powder, 20-25 parts silica fume, 115-125 parts mixing water, 3.5-4.2 parts polycarboxylate superplasticizer, 6.8-7.5 parts nano-silicon activator, 3.0-3.5 parts composite fiber, and 1.8-2.3 parts physical foaming agent; The recycled coarse aggregate is pure waste concrete crushed material, and a weakly acidic water vapor erosion interface reconstruction process is adopted; the recycled fine aggregate is waste red brick ceramic recycled sand, and a room temperature alkali-activated microporous recrystallization process is adopted; the composite fiber adopts a nano-silicon graft copolymerization modification process: basalt fiber 6mm, polypropylene fiber 3mm, surface grafting is carried out using nano-silica sol, the coating thickness is 20-40nm, and constant temperature curing is carried out for 18h.

2. The precast wall panel based on recycled aggregate from construction waste according to claim 1, characterized in that: The weakly acidic water vapor erosion interface reconstruction process uses weakly acidic mist water vapor spray with pH=5.2~5.6, and is left to stand in a constant temperature and sealed environment for 14~18h to gently erode the loose old mortar on the surface of the aggregate, and the particle size after screening is 5~20mm.

3. The precast wall panel based on recycled aggregate from construction waste according to claim 1, characterized in that: The room-temperature alkaline-activated microporous recrystallization process involves soaking recycled red brick sand in a saturated calcium hydroxide solution for 40–50 minutes. Under normal temperature and pressure, hydrated calcium carbonate crystals are generated inside the pores of the red brick, which penetrate and modify the microporous structure.

4. The precast wall panel based on recycled aggregate from construction waste according to claim 1, characterized in that: The recycled micro powder is the tailings powder from crushing and screening of construction waste, which has undergone low-temperature grinding and activation treatment, and has a particle size of less than 0.075 mm.

5. The precast wall panel based on recycled aggregate from construction waste according to claim 1, characterized in that: The nano-silicon activator is an organosilicon-modified nano-silica solution.

6. The precast wall panel based on recycled aggregate from construction waste according to claim 1, characterized in that: The water-cement ratio of the precast wall mix is ​​controlled at 0.28, the sand ratio is controlled at 46%, and the dry density of the finished product is controlled at 1720-1800 kg / m³.

7. A method for preparing precast wall panels based on recycled aggregates from construction waste, characterized in that, The preparation process includes the following steps: Step 1: Pre-processing of key raw materials: ①Recycled coarse aggregate: Select crushed concrete aggregate, spray with weakly acidic water mist with citric acid (pH=5.2~5.6), keep it at a constant temperature and sealed for 14~18h, remove dust with high pressure air jet, and screen to obtain dense aggregate of 5~20mm. ② Recycled fine aggregate: Red brick recycled sand is soaked in saturated calcium hydroxide solution at room temperature for 40-50 minutes to complete the pore recrystallization modification, and then taken out and air-dried; ③ Composite fiber: 6mm basalt fiber and 3mm polypropylene fiber were grafted and modified with 8% solid content nano silica sol, with a coating thickness of 20-40nm, and cured at constant temperature for 18h. After modification, the fiber was sealed and stored for later use. Step 2: Raw Material Weighing and Activation: Accurately weigh each raw material according to the mass ratio of the single-unit mixture: 450-480 parts recycled coarse aggregate, 440-475 parts recycled fine aggregate, 135-155 parts recycled micro powder, 200-225 parts P.O42.5 cement, 125-145 parts slag micro powder, 20-25 parts silica fume, 115-125 parts mixing water, 3.5-4.2 parts polycarboxylate superplasticizer, 6.8-7.5 parts nano-silicon activator, 3.0-3.5 parts composite fiber, and 1.8-2.3 parts physical foaming agent; sieve and wash the weighed recycled coarse and fine aggregates, and then spray them uniformly with an aqueous solution of nano-silicon activator; Step 3, Layered Gradient Mixing: The activated recycled coarse aggregate and recycled fine aggregate are put into the mixing equipment for pre-mixing. Then, cement, slag powder and silica fume are added for coating and mixing with cementitious materials. Next, the modified composite fiber is added and dispersed and mixed. Finally, mixing water, polycarboxylate superplasticizer and physical foaming agent are added and mixed evenly to obtain the mixture. Step 4: Low-frequency vibration molding: Inject the mixture into the precast wall mold and use 35Hz low-frequency directional vibration to expel large air bubbles and retain closed micropores inside the matrix. Step 5, constant temperature gradual curing: After molding, let it stand for 4 hours and then cover it with a film. Keep it at a constant temperature of 22℃ for 7 days and then let it undergo natural carbonization curing for 28 days to obtain the finished precast wall.

8. The method for preparing precast wall panels based on recycled aggregates from construction waste as described in claim 7, characterized in that, For fine aggregates of red bricks, extend the soaking and standing time by 15-20 minutes separately, while maintaining the normal soaking time for coarse aggregates.