Preparation method of artificial aggregate based on bamboo-based charcoal and cement-based waste

Abstract

The invention relates to the technical field of building solid waste resource utilization, and discloses a bamboo-based biochar and cement-based waste-based artificial aggregate preparation method, which comprises: using cement-based waste powder as a main raw material, and using ordinary Portland cement and bamboo-based biochar as auxiliary materials, firstly carrying out alkali modification or ultrasonic modification treatment on the bamboo-based biochar, and then carrying out drying to obtain the artificial aggregate based on the bamboo-based biochar and the cement-based waste. The surface property is improved; then mixing the materials, and preparing a regular and uniform aggregate blank by adopting a disc granulation method and accurately controlling the inclination angle and the rotating speed in combination with a reserved dry powder rolling and sticking process; finally, the blank is cured, particularly carbonization curing is adopted, and carbon dioxide and cement hydration products react to generate calcium carbonate to fill internal pores. According to the invention, interface bonding is enhanced through the modified charcoal, the porosity is reduced through carbonization curing, the prepared artificial aggregate has the advantages of high compressive strength and low water absorption, and high-proportion utilization of cement-based wastes is realized.

Description

Technical Field

[0001] This invention relates to the field of construction solid waste resource utilization technology, specifically a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste. Background Technology

[0002] The construction industry generates a large amount of cement-based solid waste such as concrete and mortar during production and demolition. The accumulation of this waste not only occupies land resources but also poses a potential threat to the environment. Resource recovery from this waste, processing it into recycled or artificial aggregates, is an important way to achieve sustainable development in the construction sector.

[0003] In existing technologies for preparing artificial aggregates using cement-based waste, a high waste content is generally desired. However, high content often leads to a decline in the mechanical properties of the aggregate product. To improve performance, lightweight porous materials such as bamboo-based biochar are sometimes introduced. However, untreated bamboo-based biochar has poor compatibility with the cement matrix due to its surface properties, resulting in weak interfacial bonding and the formation of structural weak points within the aggregate, thus limiting the improvement of the overall mechanical properties of the final product.

[0004] Meanwhile, the control of process parameters in the preparation process of artificial aggregates, especially the disc pelletizing process, is crucial to the uniformity of the final product. Existing preparation methods do not have precise enough control over the pelletizing process, often resulting in uneven particle size distribution and irregular shape of the produced aggregate pellets, which affects the quality stability of the finished aggregate product.

[0005] Furthermore, during the hardening and curing stage of aggregates, traditional standard curing or water bath curing is commonly used. For artificial aggregates with high solid waste content, these conventional curing methods are insufficient to effectively optimize their internal pore structure. Therefore, artificial aggregate products prepared by existing technologies generally suffer from high porosity, which directly manifests as excessive water absorption and insufficient compressive strength, limiting their widespread application in fields such as high-performance concrete. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste, which solves the problems of difficulty in controlling aggregate properties and poor interfacial bonding between biochar and cement matrix when preparing artificial aggregates using cement-based waste.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste, comprising the following steps: S1. Mix 75-90% cement-based waste powder, 5-15% ordinary Portland cement and 0-15% bamboo-based biochar by mass percentage to obtain a mixed powder. S2. Reserve 15-25% of the total mass of the mixed powder, place the remaining mixed powder in a disc granulator, set the tilt angle of the disc granulator to 40-50° and the rotation speed to 55-65 rpm, spray water to granulate, and obtain aggregate blanks. S3. Add the reserved mixed powder to the disc granulator and roll it for 8-12 minutes. S4. After the aggregate blanks have been rolled and bonded, let them stand for 20-28 hours and then cure and harden them to obtain artificial aggregates.

[0008] As a specific implementation method, the preparation steps of the cement-based waste powder are as follows: ordinary silicate cement slurry test blocks are cured under standard conditions for 110-115 days. After curing, the test blocks are crushed using a jaw crusher. The crushed material is dried at 60-70℃ to constant weight. The dried material is then ball-milled and passed through a 150-micron sieve to obtain the cement-based waste powder.

[0009] As a specific implementation method, the preparation steps of the bamboo-based biochar are as follows: placing bamboo raw materials under nitrogen protection, controlling the heating rate at 8-12℃ / min, heating to a target temperature of 480-520℃, and pyrolyzing at the target temperature for 1.5-2.5 hours to obtain pyrolysis products; crushing the pyrolysis products and passing them through a 150-micron sieve to obtain the bamboo-based biochar.

[0010] In one specific embodiment, before step S1, a step of modifying the bamboo-based biochar is included, wherein the modification is selected from either alkali modification or ultrasonic modification.

[0011] As a specific implementation method, the modification treatment is ultrasonic modification, and the bamboo-based biochar in step S1 is ultrasonically modified biochar. The preparation method of ultrasonically modified biochar is as follows: bamboo-based biochar and deionized water are mixed at a mass ratio of 1:(8-12), and the mixture is placed in an ultrasonic device with a frequency of 7-9MHz for 13-17 minutes, and stirred at a speed of 100-140rpm during the treatment; after the treatment, the mixture is allowed to stand and precipitate, and the lower precipitate is dried at 60-70℃ to obtain ultrasonically modified biochar.

[0012] As another specific implementation method, the modification treatment is alkali modification, and the bamboo-based biochar in step S1 is alkali-modified biochar. The preparation method of the alkali-modified biochar is as follows: bamboo-based biochar and deionized water are mixed at a mass ratio of 1:(8-12) and stirred at 500-600 rpm for 22-26 hours to obtain water-modified biochar; the water-modified biochar is mixed with a sodium hydroxide solution with a concentration of 0.8-1.2 mol / L at a mass ratio of 1:(8-12) and stirred at 500-600 rpm for 22-26 hours; after stirring, the product is washed 4-6 times with deionized water, and the final precipitate is dried at 60-70℃ to obtain alkali-modified biochar.

[0013] In one specific implementation, the curing and hardening in step S4 is selected from at least one of standard curing, water bath curing, and carbonization curing.

[0014] As a specific implementation method, the curing and hardening can be standard curing, wherein the conditions for standard curing are an ambient temperature controlled at 18-22℃ and a relative humidity controlled at 90-100%.

[0015] As another specific implementation, the curing and hardening can be water bath curing, wherein the conditions for water bath curing are to completely immerse the aggregate embryo in water and control the water temperature at 18-22℃.

[0016] In another specific implementation, the curing and hardening can be carbonization curing. The specific steps of carbonization curing are as follows: first, the aggregate preform is cured in a water bath to a predetermined age; then, the aggregate preform is cured in a water bath to a predetermined age; the aggregate preform after water bath curing is dried in an oven at 60-70°C to constant weight; the dried aggregate preform is placed in a sealed carbonization box, and baking soda and citric acid are added to the box to react and generate carbon dioxide gas, while controlling the humidity in the box to 70-80%, and carbonization is carried out for 48-72 hours.

[0017] This invention provides a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste. It has the following beneficial effects: 1. This invention improves the surface properties and physical structure of bamboo-based biochar by subjecting it to alkali modification or ultrasonic modification. Alkali modification increases the oxygen-containing functional groups on the surface of bamboo-based biochar, improving its dispersibility and interfacial bonding in the cement matrix. Ultrasonic modification disperses biochar aggregates and cleans their pores through cavitation, enhancing the physicochemical interaction between bamboo-based biochar and cement hydration products, thereby improving the internal density and mechanical properties of the final artificial aggregate.

[0018] 2. This invention provides a carbonation curing method, which involves reacting carbon dioxide with the cement hydration products (calcium hydroxide) inside the aggregate blank to generate calcium carbonate. The generated calcium carbonate fills the internal pore structure of the aggregate, effectively reducing the porosity of the material. Compared with standard curing or water bath curing alone, the artificial aggregate obtained by carbonation curing has higher density, lower water absorption and higher compressive strength.

[0019] 3. In the method of the present invention, the amount of cement-based waste powder can reach 75-90%, realizing a large-scale resource utilization of construction solid waste. At the same time, by setting a disc tilt angle of 40-50° and a rotation speed of 55-65 rpm, and combining it with a specific process of reserving 15-25% dry powder for rolling and shaping, aggregate blanks with uniform particle size distribution and regular shape can be prepared, which provides a guarantee for the stability and uniformity of the subsequent performance of artificial aggregates. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Preparation Examples 1-4: Preparation Example 1: Preparation of Cement-Based Waste Powder (CWP) Ordinary Portland cement (P.O42.5 cement) was mixed with deionized water at a water-cement ratio of 0.35 and cast into cement paste specimens. The cement paste specimens were then cured in a standard curing room (temperature 20℃, relative humidity 95%) for 112 days. After curing, the specimens were removed, first crushed using a jaw crusher, and then dried to constant weight in an oven at 65℃. The dried fragments were then ball-milled, and the milled product was sieved through a 150-micron sieve. The undersize material was collected, which became the cement-based waste powder used in subsequent examples and comparative examples.

[0022] Preparation Example 2: Preparation of Bamboo-based Biochar (BC) The raw bamboo was placed in a tubular pyrolysis furnace, and nitrogen was introduced into the furnace to purge the air. Nitrogen was continuously introduced as a protective gas during the subsequent pyrolysis process. A heating program was set to raise the furnace temperature to 500°C at a rate of 10°C / min, and the temperature was maintained at 500°C for 2 hours for pyrolysis. After pyrolysis, the product was allowed to cool naturally to room temperature under nitrogen protection. The cooled solid product was removed, crushed using a pulverizer, and the crushed material was sieved through a 150-micron sieve. The undersize material was collected, which became the bamboo-based biochar used in the subsequent examples and comparative examples.

[0023] Preparation Example 3: Preparation of Alkali-Modified Biochar (AM) The bamboo-based biochar prepared in Preparation Example 2 was subjected to alkali modification treatment. First, the bamboo-based biochar was mixed with deionized water at a mass ratio of 1:10, and continuously stirred at 550 rpm for 24 hours using a mechanical stirrer. Afterward, the mixture was allowed to stand to obtain a water-modified biochar precipitate. Then, the water-modified biochar precipitate was mixed with a 1.0 mol / L sodium hydroxide solution at a mass ratio of 1:10, and continuously stirred at 550 rpm for 24 hours. After stirring, the precipitate was washed five times with deionized water. The final precipitate was dried in an oven at 65°C to constant weight, and the resulting powder was the alkali-modified biochar used in subsequent examples and comparative examples.

[0024] Preparation Example 4: Preparation of Ultrasonic Modified Biochar (SS) The bamboo-based biochar prepared in Example 2 was subjected to ultrasonic modification. Specifically, the bamboo-based biochar was mixed with deionized water at a mass ratio of 1:12, and the mixture was placed in an ultrasonic device with a frequency of 9 MHz for 17 minutes, with stirring at a speed of 140 rpm during the treatment. After the treatment, the mixture was allowed to settle, and the lower precipitate was dried in an oven at 70°C to constant weight. The resulting powder was the ultrasonically modified biochar used in subsequent examples and comparative examples.

[0025] Examples 1-4: Example 1: This embodiment provides a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste, the specific steps of which are as follows: S1. 90% of the cement-based waste powder from Preparation Example 1, 10% of ordinary silicate cement, and 5% of the bamboo-based biochar prepared in Preparation Example 2 are placed in a mixer and dry-mixed until uniformly mixed to obtain a mixed powder.

[0026] S2. Weigh 20% of the total mass of the mixed powder as reserve powder. Place the remaining mixed powder in a disc granulator, setting the tilt angle of the disc granulator to 45° and the rotation speed to 60 rpm. Start the disc granulator, and while the disc is rotating, use a spray bottle to evenly and intermittently spray an appropriate amount of deionized water into the mixed powder, causing the powder to aggregate into spherical aggregate pellets.

[0027] S3. Once the aggregate pellets are basically formed, evenly sprinkle the reserved powder into the rotating disc to roll and adhere the aggregate pellets. After rolling and adhering, continue rotating for 10 minutes before removing them.

[0028] S4. Let the extracted aggregate preforms stand indoors for 24 hours. Then, transfer the aggregate preforms to a standard curing room for standard curing. The standard curing conditions are: ambient temperature controlled at 20±2℃, relative humidity at 95±5%. After curing to the specified age, artificial aggregate samples are obtained.

[0029] Example 2: This embodiment provides a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste, the specific steps of which are as follows: S1. 90% of the cement-based waste powder from Preparation Example 1, 10% of ordinary silicate cement, and 10% of the bamboo-based biochar prepared in Preparation Example 2 are placed in a mixer and dry-mixed until uniformly mixed to obtain a mixed powder.

[0030] S2. Weigh 20% of the total mass of the mixed powder as reserve powder. Place the remaining mixed powder in a disc granulator, setting the tilt angle of the disc granulator to 45° and the rotation speed to 60 rpm. Start the disc granulator, and while the disc is rotating, use a spray bottle to evenly and intermittently spray an appropriate amount of deionized water into the mixed powder, causing the powder to aggregate into spherical aggregate pellets.

[0031] S3. Once the aggregate pellets are basically formed, evenly sprinkle the reserved powder into the rotating disc to roll and adhere the aggregate pellets. After rolling and adhering, continue rotating for 10 minutes before removing them.

[0032] S4. Let the extracted aggregate preforms stand indoors for 24 hours. Then, completely immerse the aggregate preforms in water at a temperature of 20±2℃ for water bath curing. After curing to the specified age, artificial aggregate samples are obtained.

[0033] Example 3: This embodiment provides a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste, the specific steps of which are as follows: S1. 90% of the cement-based waste powder from Preparation Example 1, 10% of ordinary silicate cement, and 15% of the bamboo-based biochar prepared in Preparation Example 2 are placed in a mixer and dry-mixed until uniformly mixed to obtain a mixed powder.

[0034] S2. Weigh 20% of the total mass of the mixed powder as reserve powder. Place the remaining mixed powder in a disc granulator, setting the tilt angle of the disc granulator to 45° and the rotation speed to 60 rpm. Start the disc granulator, and while the disc is rotating, use a spray bottle to evenly and intermittently spray an appropriate amount of deionized water into the mixed powder, causing the powder to aggregate into spherical aggregate pellets.

[0035] S3. Once the aggregate pellets are basically formed, evenly sprinkle the reserved powder into the rotating disc to roll and adhere the aggregate pellets. After rolling and adhering, continue rotating for 10 minutes before removing them.

[0036] S4. The extracted aggregate preforms were left to stand indoors for 24 hours. Then, they were hardened using a carbonization curing method, specifically: first, the aggregate preforms were cured in a water bath for 7 days; then, the aggregate preforms were transferred to a 65℃ oven and dried to constant weight; finally, the dried aggregate preforms were placed in a sealed carbonization chamber, where sodium bicarbonate was added to react with citric acid to generate carbon dioxide gas, while maintaining the humidity within the chamber at 75%, and carbonization was carried out for 72 hours. After the treatment, artificial aggregate samples were obtained.

[0037] Example 4: This embodiment provides a method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste, the specific steps of which are as follows: S1. 90% of the cement-based waste powder from Preparation Example 1, 10% of ordinary silicate cement, and 5% of the alkali-modified biochar prepared in Preparation Example 3 are placed in a mixer and dry-mixed until uniformly mixed to obtain a mixed powder.

[0038] S2. Weigh 20% of the total mass of the mixed powder as reserve powder. Place the remaining mixed powder in a disc granulator, setting the tilt angle of the disc granulator to 45° and the rotation speed to 60 rpm. Start the disc granulator, and while the disc is rotating, use a spray bottle to evenly and intermittently spray an appropriate amount of deionized water into the mixed powder, causing the powder to aggregate into spherical aggregate pellets.

[0039] S3. Once the aggregate pellets are basically formed, evenly sprinkle the reserved powder into the rotating disc to roll and adhere the aggregate pellets. After rolling and adhering, continue rotating for 10 minutes before removing them.

[0040] S4. The extracted aggregate preforms were left to stand indoors for 24 hours. Then, they were hardened using a carbonization curing method, specifically: first, the aggregate preforms were cured in a water bath for 7 days; then, the aggregate preforms were transferred to a 65℃ oven and dried to constant weight; finally, the dried aggregate preforms were placed in a sealed carbonization chamber, where sodium bicarbonate was added to react with citric acid to generate carbon dioxide gas, while maintaining the humidity within the chamber at 75%, and carbonization was carried out for 72 hours. After the treatment, artificial aggregate samples were obtained.

[0041] Comparative Examples 1-3: Comparative Example 1: Compared to Example 1, the difference lies in that bamboo-based biochar is not added during the material mixing in step S1; instead, 90% by weight of cement-based waste powder is mixed with 10% ordinary Portland cement. The remaining preparation steps, process parameters, and curing methods are exactly the same as in Example 1.

[0042] Comparative Example 2: The difference between Example 2 and Example 3 is that bamboo-based biochar is not added during the material mixing in step S1. The remaining steps, raw material ratios, process parameters, and curing methods are exactly the same as in Example 2.

[0043] Comparative Example 3: The difference between Example 3 and Example 2 is that bamboo-based biochar is not added in step S1. The remaining steps, raw material ratios, process parameters, and curing methods are exactly the same as in Example 2.

[0044] Test Example 1-3: Test Example 1: Physical Performance Test Test method: The tests were conducted according to GB / T17431.2-2010 "Lightweight aggregates and their test methods Part 2: Lightweight aggregate test methods". The apparent density and 24-hour water absorption rate of the artificial aggregates prepared after 28 days of curing in the above examples and comparative examples were tested.

[0045] Test steps: Step 1: Take samples of each group of artificial aggregates after 28 days of curing and screen out particles with a diameter in the range of 10-15mm. Place the screened samples in a constant temperature drying oven at 65℃ and dry them until the mass change between two consecutive weighings (with an interval of 2 hours) is less than 0.1%, reaching a constant weight state.

[0046] Step 2: Remove the dried sample, which has reached constant weight, from the drying oven. After cooling to room temperature, weigh it using a balance with an accuracy of 0.1g and record the mass as the dried mass. ).

[0047] Step 3: Place the weighed, dried sample in a container and pour in clean water, ensuring that all samples are completely submerged. Let it soak for 24 hours. After 24 hours, remove the sample from the water and quickly wipe the surface of the sample with a pre-wrung-out damp towel until there is no visible water film on the surface, but it is still moist, which means it has reached the saturated surface-dry state.

[0048] Step 4: Determination of saturated surface-dry mass. Immediately weigh the sample in a saturated surface-dry state and record it as the saturated surface-dry mass. ).

[0049] Step 5: Sample Volume Determination. Place the saturated, surface-dry sample weighed in Step 4 into a 1000mL graduated cylinder, and add 500mL of water. Record the total volume of water and sample in the graduated cylinder at this point. Calculate the apparent volume of the sample using the volume difference. ).

[0050] Step 6: Data Calculation. Based on the measured values, calculate the apparent density and 24-hour water absorption rate using the following formulas: Apparent density ( The formula for calculating ) is: 24-hour water absorption rate ( The formula for calculating ) is: %.

[0051] The above test was repeated twice for each group of samples, and the arithmetic mean of the two measurements was taken as the final experimental result.

[0052] Test results: Table 1. Physical properties of each group of artificial aggregates Results analysis: Experimental data show that, under standard curing conditions, Example 1, which incorporated 5% biochar, exhibited a lower water absorption rate compared to Comparative Example 1, which did not incorporate biochar. The mechanism lies in the fact that biochar particles exist as independent microstructural units within the aggregate matrix, and their surfaces provide additional nucleation sites for the hydration reaction of cement clinker. This promotes the formation and distribution of hydration products (such as hydrated calcium silicate gel), resulting in a denser matrix structure within the aggregate. The increased matrix density directly leads to a reduction in the number of interconnected capillary pores, thereby decreasing the ability of water to penetrate the aggregate, ultimately manifesting macroscopically as a decrease in 24-hour water absorption.

[0053] Comparing different curing methods, the apparent density of Example 3 and Comparative Example 3, which underwent carbonization curing, was higher than that of the corresponding groups cured by standard curing or water bath curing, while the water absorption rate decreased. This phenomenon stems from the occurrence of the carbonization reaction. During the carbonization curing process, CO2 gas molecules from the external environment diffuse into the porous network of the artificial aggregate, reacting chemically with calcium hydroxide (Ca(OH)2) and partially hydrated calcium silicate in the matrix to generate calcium carbonate (CaCO3). Since the generated calcium carbonate crystals occupy a larger molar volume and have a denser structure than the reactant calcium hydroxide, these crystals are generated and grow within the pores, physically filling the original pore spaces and effectively reducing the total porosity of the aggregate. The reduction in porosity directly leads to an increase in the apparent density of the aggregate and a decrease in the water absorption rate.

[0054] Comparing Example 3 (with biochar) and Comparative Example 3 (without biochar), under the same carbonization curing conditions, the former exhibited higher apparent density and lower water absorption. This reveals the synergistic effect of biochar and the carbonization process. Biochar itself possesses a rich porous structure, and these pores form an interconnected microscopic channel network within the aggregate matrix. This network provides a pathway for CO2 gas to transport into the aggregate interior, increasing the contact area between CO2 and calcium-containing hydration products in the matrix, thereby allowing the carbonization reaction to occur more thoroughly and in a deeper region. The deeper and more complete carbonization reaction generates more calcium carbonate filler, further enhancing the densification of the aggregate matrix. Therefore, its apparent density and water resistance are superior to carbonized aggregate without biochar.

[0055] Test Example 2: Single Particle Compressive Strength Test Test method: Using a multimeter ETM305D, the single-particle compressive strength of the artificial aggregates in the above embodiments and comparative examples after 7 and 28 days of curing was tested, with a loading speed of 0.5 mm / min.

[0056] Test steps: Step 1: Select aggregate samples with a particle size between 10-15 mm and measure their average diameter using vernier calipers. ; Step 2: Place the individual aggregate into the center of the pressure plate of the multimeter. Step 3: Apply pressure at a constant loading rate of 0.5 mm / min until the aggregate is damaged; Step 4: Record the peak loading force at aggregate failure. ; Step 5: Calculate the compressive strength of a single particle according to the formula. : .

[0057] Test data: Table 2. Compressive strength of single particles of each group of artificial aggregates (MPa) Results analysis: Under standard curing conditions, the 28-day compressive strength (2.8 MPa) of the material with 5% biochar (Example 1) was approximately 33% higher than that of Comparative Example 1 (2.1 MPa) without biochar. This strength improvement is mainly attributed to the multiple positive effects of biochar in cement-based aggregates. First, biochar has a rich porous structure and a large specific surface area, allowing it to absorb and store some moisture during mixing. In the later stages of curing, when the internal moisture content of the aggregate matrix decreases due to cement hydration, biochar can slowly release this moisture, playing a role in internal curing. This continuous supply of water molecules promotes a more complete and longer hydration reaction of cement particles, generating more dense hydrated calcium silicate (CSH) gel and other hydration products. Second, biochar particles act as micro-aggregates and nucleation sites in the aggregate, providing attachment points for the crystallization growth of hydration products, optimizing the spatial distribution of hydration products, and making the microstructure of the aggregate more dense and uniform. These two synergistic effects effectively improve the pore structure of the aggregate, especially by reducing the number of large pores that are detrimental to compressive strength, thus resulting in a significant increase in compressive strength on a macroscopic level.

[0058] Carbonation curing significantly improves aggregate strength. The 28-day strength of Examples 3 (5.5 MPa) and 4 (6.8 MPa) was much higher than that of the non-carbonated curing group. The strengthening mechanism of carbonation curing lies in the fact that by placing the aggregate in a high-concentration CO2 environment, the calcium hydroxide (Ca(OH)2) generated by cement hydration and some of the hydrated calcium silicate (CSH) gel inside the aggregate react with CO2 to generate calcium carbonate (CaCO3), which has more stable chemical properties and higher strength. Calcium carbonate crystals can effectively fill the capillary pores in the aggregate matrix, significantly reducing porosity and making the internal structure denser. At the same time, the amount of CaCO3 generated is much greater than the amount of Ca(OH)2 consumed. This increase in volume further enhances the filling effect, thereby improving the overall density and particle strength of the aggregate. The addition of biochar further enhances the carbonization effect. Its abundant interconnected pores provide an efficient transmission channel for CO2 gas to penetrate into the aggregate, increasing the contact area between the gas and the matrix, allowing the carbonization reaction to proceed more deeply and uniformly.

[0059] Comparing Examples 3 and 4, the aggregate prepared using alkali-modified biochar (AM) (6.8 MPa) exhibited higher strength than the aggregate prepared using unmodified biochar (5.5 MPa), demonstrating the beneficial effects of biochar modification. During pyrolysis, unmodified biochar develops a hydrophobic bio-oil film on its pore surface. This film not only blocks some micropores, reducing its physical adsorption and transport capacity for CO2, but also weakens the biochar's efficiency as a hydration nucleation site due to its hydrophobicity. Alkali modification effectively destroys and removes this bio-oil film, thereby freeing up and unblocking the original pore structure of the biochar, especially increasing the volume of micropores and mesopores. This results in alkali-modified biochar having stronger CO2 adsorption and conduction capabilities, enabling more efficient introduction of CO2 into the aggregate interior, promoting a more thorough carbonization reaction, generating more calcium carbonate, and thus further improving aggregate strength. In addition, after the oil film is removed, the surface of biochar becomes more hydrophilic, which can better combine with cement hydration products, enhance the interfacial adhesion, and reduce weak points in the structure.

[0060] Test Example 3: Carbon Absorption Performance Test Test objective: Quantitatively determining the mass of carbon dioxide absorbed and fixed by a unit mass of artificial aggregate in a high-concentration carbon dioxide environment is a key indicator for evaluating its carbon absorption performance.

[0061] Test steps: Step 1: Use a carbonization box with an inner diameter of 30cm×30cm×30cm (the gas volume inside the box is 25L).

[0062] Step 2: Place a beaker A containing a saturated sodium chloride solution and control the humidity inside the chamber to approximately 75%.

[0063] Step 3: Prepare a beaker B containing pure water, and a beaker C containing 10g of baking soda solid and 20g of citric acid solid (ensure C is completely dry). Carbon dioxide formation reaction equation: ; Step 4: Place approximately 20g of aggregate sample with a particle size of 10-15mm into the aggregate box.

[0064] Step 5: Connect the carbon dioxide gas detector, set the recording interval to 1 minute, and record continuously for 72 hours.

[0065] Step 6: After 7 days of curing, dry the aggregate and place all items into the box, and connect the detector cables. Insert the water pump inlet into the bottom of beaker B, and align the outlet with beaker C (without inserting chemicals). Tighten the box latches, start the water pump, and allow water to flow from B into C, triggering the carbon dioxide generation reaction.

[0066] Step 7: Set up an empty box group without aggregate and perform the same operation to detect the natural consumption of carbon dioxide in the box.

[0067] Step 8: By comparing the difference in carbon dioxide concentration between the experimental group and the control group over 72 hours, calculate the mass of carbon dioxide absorbed by the aggregate, and determine the percentage of the mass of CO2 absorbed by the aggregate relative to the initial mass of the aggregate (carbon fixation rate) based on the initial mass of the aggregate.

[0068] Experimental data: Table 3. Carbon fixation rate of each group of artificial aggregates Results analysis: With the increase of unmodified biochar content (Examples 1 to 3), the carbon fixation rate of the aggregate increased from 11.5% to 19.0%. This clearly demonstrates that biochar plays a key role as a CO2 migration channel within the aggregate, thereby effectively improving the overall carbonization efficiency. The mechanism lies in the rich porous structure of biochar itself, which forms an interconnected microscopic network within the aggregate matrix. When the aggregate is exposed to a CO2-containing environment, these channels guide CO2 gas molecules around the dense matrix and penetrate deeply into the aggregate, increasing the contact area between CO2 and carbonizable components in the matrix (such as calcium hydroxide). Microscopic observation also confirms this; the carbonization product calcium carbonate (CaCO3) is enriched in the area surrounding the biochar particles, directly demonstrating the effectiveness of biochar as a CO2 diffusion channel. Therefore, as the biochar content increases from 5% to 15%, this internal diffusion network becomes more developed, resulting in a deeper and more complete carbonization reaction, macroscopically manifested as an increase in the carbon fixation rate.

[0069] The results of Example 4 further reveal the significant potential for enhancing biochar efficiency through modification treatment. The study shows that using only 5% alkali-modified biochar can achieve a carbon fixation rate of 19.0% in aggregates, an effect comparable to using 15% unmodified biochar. This demonstrates that alkali modification treatment can enhance the ability of biochar to promote aggregate carbon fixation. The fundamental reason is that unmodified biochar produces bio-oil during pyrolysis. This oil film adheres to and blocks numerous micropores and mesopores within the biochar, severely limiting its performance as a gas transport channel. Alkali modification treatment (AM) can utilize the chemical reactivity of strong alkalis to efficiently destroy and dissolve this bio-oil film. This process opens up the original pore structure, increasing the volume of micropores and mesopores crucial for gas adsorption and migration. Therefore, the modified biochar possesses a superior and more open pore network, resulting in a significant improvement in CO2 migration efficiency. Even with only a 5% doping concentration, the efficiency of the CO2 migration channels constructed is comparable to that of 15% unmodified biochar, thus achieving the same carbon fixation effect.

Claims

1. A method for the preparation of artificial aggregates based on bamboo-based biochar and cement-based waste, characterized by, The method comprises the following steps: S1, mixing 75-90% cement-based waste powder, 5-15% ordinary Portland cement and 0-15% bamboo-based biochar by mass percentage to obtain a mixed powder; S2, reserving 15-25% of the total mass of the mixed powder, and placing the remaining mixed powder in a disc granulator, setting the disc granulator inclination angle to 40-50° and the rotation speed to 55-65 rpm, and spraying water for granulation to obtain aggregate embryos; S3, adding the reserved mixed powder to the disc granulator for rolling and sticking, and continuing to rotate for 8-12 minutes; S4, curing and hardening the aggregate embryos after rolling and sticking to obtain artificial aggregate.

2. The method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 1, characterized in that, The preparation method of the bamboo-based biochar is as follows: Place the bamboo under nitrogen protection, control the heating rate to 8-12℃ / min, heat to 480-520℃, and pyrolyze for 1.5-2.5 hours to obtain a pyrolysis product, crush the pyrolysis product and pass it through a 150-micron sieve to obtain the bamboo-based biochar.

3. The method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 1, characterized in that, Before step S1, a step of modifying the bamboo-based biochar is further included, and the modification is selected from any one of alkali modification and ultrasonic modification.

4. The method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 3, characterized in that, The modification is alkali modification, and the bamboo-based biochar in step S1 is an alkali modified biochar. The preparation method of the alkali modified biochar is as follows: Mix the bamboo-based biochar with deionized water at a mass ratio of 1:(8-12), stir at a rotation speed of 500-600 rpm for 22-26 hours to obtain a water modified biochar; 5. The method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 3, characterized in that, Then mix the water modified biochar with a sodium hydroxide solution with a concentration of 0.8-1.2 mol / L at a mass ratio of 1:(8-12), stir at a rotation speed of 500-600 rpm for 22-26 hours, wash 4-6 times, and dry at 60-70℃ to obtain the alkali modified biochar. The modification is ultrasonic modification, and the bamboo-based biochar in step S1 is an ultrasonic modified biochar.

6. The method for manufacturing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 1, characterized in that, The preparation method of the ultrasonic modified biochar is as follows:

7. The method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 6, characterized in that, Mix the bamboo-based biochar with deionized water at a mass ratio of 1:(8-12), treat it in ultrasonic waves with a frequency of 7-9 MHz for 13-17 minutes, stir at a rotation speed of 100-140 rpm during the treatment, and dry at 60-70℃ after standing and precipitating to obtain the ultrasonic modified biochar. The curing and hardening in step S4 is selected from at least one of standard curing, water bath curing and carbonation curing. The curing and hardening is carbonation curing, and the specific steps are as follows: First, water bath curing the aggregate embryos to a predetermined age; 8. The method for preparing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 6, characterized in that, Dry the water bath cured aggregate embryos in an oven at 60-70℃ to a constant weight; Place the dried aggregate embryos in a sealed carbonation box, and generate carbon dioxide gas by reacting baking soda and citric acid in the box, while controlling the humidity in the box to 70-80%, and carbonation treat for 48-72 hours. The curing and hardening is standard curing, and the conditions of the standard curing are a temperature of 18-22℃ and a relative humidity of 90-100%.

9. The method for manufacturing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 6, characterized in that, The curing hardening is water bath curing, and conditions of the water bath curing are that aggregate embryos are submerged in water, and water temperature is controlled to be 18-22 DEG C.

10. The method for manufacturing artificial aggregates based on bamboo-based biochar and cement-based waste according to claim 1, characterized in that, The preparation method of the cement-based waste powder is: Ordinary portland cement paste test blocks are cured for 110-115 days, after curing, the test blocks are crushed by using a jaw crusher, the crushed material is dried at 60-70 DEG C to constant weight, the dried material is ball milled, and the ball milled material is sieved through a 150-micron sieve, to obtain the cement-based waste powder.

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