A method for preparing a pore-enhanced artificial aggregate and a method for preparing a concrete material using the same

Abstract

A method for preparing porous reinforced artificial aggregate and a method for preparing concrete materials using it are disclosed. This invention addresses the technical problem that directly adding biochar particles to concrete yields poor results in improving the water absorption and retention capacity of the material. The method for preparing the porous reinforced artificial aggregate involves: uniformly mixing biochar particles, slag powder, steel slag powder, desulfurized gypsum, and phosphogypsum to obtain a mixed dry material; firstly, adding water to a portion of the mixed dry material and preparing an aggregate core in a disc granulator; then, intermittently spraying water into the disc granulator and adding the remaining mixed dry material, forming a covering layer on the outer surface of the aggregate core to obtain an aggregate blank; after curing, the porous reinforced artificial aggregate is obtained. Using porous reinforced artificial aggregate to replace part of the natural aggregate in the preparation of concrete materials increases the capillary water absorption coefficient by 77% to 205% compared to ordinary concrete materials, making it suitable for use in the construction industry.

Description

Technical Field

[0001] This invention relates to methods for preparing artificial aggregates and concrete materials, and belongs to the field of road engineering materials technology. Background Technology

[0002] With the rapid increase in urbanization in my country, urban flooding has become increasingly frequent in recent years, causing not only huge economic losses but also seriously affecting people's lives and even threatening their safety. Flood control has become a major challenge for many regions during the flood season. The root causes of urban flooding lie in two aspects: firstly, the existing stormwater drainage network design standards are too low and its drainage capacity is insufficient; secondly, the extensive use of impermeable pavement materials leads to a decrease in surface infiltration and water storage capacity. Building sponge cities through technologies such as water absorption, storage, infiltration, purification, and slow-release can give cities sufficient "elasticity" to cope with weather changes, mitigate the urban heat island effect, and conserve water resources.

[0003] From an engineering practice perspective, permeable modification of road pavement is one of the main ways to achieve urban sponge city status. Unfortunately, the permeable concrete materials widely used in current road reconstruction projects only have good water permeability, but almost no water absorption, storage, or purification functions; therefore, their effects in slowing water flow, suppressing flood peaks, and reducing pipeline pressure are not ideal, limiting the "elasticity" of sponge cities. Adding biochar to concrete materials can improve their water absorption and retention capacity. For example, the Chinese patent application number CN202211477168.2, "Carbon-fixed Concrete Material for Sponge Cities Based on Pore Gradient and Its Preparation Method", discloses a concrete material made by mixing biochar particles with slag powder, steel slag powder, desulfurized gypsum, phosphogypsum, silica, coarse aggregate, fine aggregate and chemical admixtures. It utilizes the introduced micron and nano-sized pores to improve the water absorption and retention capacity of the concrete material. However, the improvement in the water absorption and retention capacity of the material is limited because most of the water permeability is achieved through interconnected macropores larger than millimeters, while the water absorption and retention functions of micron and nano-sized pores are relatively small. Summary of the Invention

[0004] The present invention aims to solve the technical problem that the existing method of directly adding biochar particles to concrete has poor effect on improving the water absorption and water retention capacity of the material, and provides a method for preparing porous reinforced artificial aggregate and a method for preparing concrete materials using it.

[0005] The method for preparing the porosity-reinforced artificial aggregate of the present invention is carried out according to the following steps:

[0006] I. Preparation of biochar granules:

[0007] 2. Weigh 100-800 parts of biochar granules, 600-1000 parts of slag powder, 200-500 parts of steel slag powder, 100-250 parts of desulfurized gypsum and 0-100 parts of phosphogypsum according to the mass ratio and add them to a dry mixer and mix evenly to obtain a mixed dry material.

[0008] 3. Take 70% to 80% of the dry mixture from step 2, add water and stir evenly to obtain a wet mixture; the amount of water added is 23% to 28% of the mass of the dry mixture; pour the wet mixture into a disc granulator, start the granulator, and rotate and roll it for 8 to 12 minutes under the conditions of disc tilt angle of 30 to 45° and rotation speed of 18 to 30 rpm to obtain the aggregate core;

[0009] 4. Spray water intermittently into the disc granulator while simultaneously spraying the remaining mixed dry material from step 2, forming a covering layer on the outer surface of the aggregate core to obtain aggregate blanks; wherein the amount of water sprayed is 30%~35% of the mass of the remaining mixed dry material;

[0010] 5. Transfer the aggregate blanks to a carbonization curing chamber and cure them for 2-5 days under conditions of 20% carbon dioxide concentration and atmospheric pressure; then transfer them to a standard curing chamber and cure them for 7-28 days to obtain porosity-reinforced artificial aggregates.

[0011] Furthermore, the method for preparing biochar particles described in step one is carried out according to the following steps:

[0012] (1) Dry the biomass waste in an oven at 50℃~80℃ for 24 hours, then crush it to a particle size of 5~8 mm, then pyrolyze it under anaerobic conditions at 300℃~500℃ for 2~5 hours, then take it out and cool it in air to obtain biochar particles with a porous structure.

[0013] (2) Place the biochar particles in a container and add the dilute hydrochloric acid solution at a mass ratio of 1:(5~25) to the biochar particles. Mix the solution at a speed of 250 rpm to 400 rpm for 5 to 20 minutes using magnetic stirring. Then seal the container and evacuate it to a vacuum level of -0.05 MPa to -0.1 MPa for 2 to 10 minutes. Filter out the biochar particles and dry them to obtain porous biochar particles.

[0014] The biomass waste mentioned in step (1) is one or more of fallen leaves, sawdust, wood blocks, rice husks and straw.

[0015] Furthermore, the slag powder mentioned in step one is composed of 40%~48% CaO, 24%~28% SiO2, 11%~13% Al2O3, 3%~8% MgO, and the balance being impurities by mass percentage; its specific surface area is 150~650 m². 2 / kg.

[0016] Furthermore, the steel slag powder mentioned in step one is composed of 32%~38% CaO, 10%~19% SiO2, 1%~5% Al2O3, and the balance being impurities by mass percentage; its specific surface area is 400 m². 2 / kg~650m 2 / kg.

[0017] Furthermore, the main component of the desulfurized gypsum mentioned in step one is dihydrate gypsum, with a specific surface area of ​​200~500 mm². 2 / kg.

[0018] Furthermore, the phosphogypsum mentioned in step one is dihydrate gypsum with a specific surface area of ​​200~500 m². 2 / kg.

[0019] The method for preparing concrete materials using the above-mentioned porous reinforced artificial aggregate is carried out according to the following steps:

[0020] The porous reinforced artificial aggregate was screened, and the porous reinforced artificial aggregate particles with an average diameter d of 2 mm ≤ d < 5 mm were selected as fine aggregate, and the porous reinforced artificial aggregate particles with an average diameter d of 5 mm ≤ d < 10 mm were selected as coarse aggregate.

[0021] 2. Select the following components by weight: 100-180 parts fine aggregate, 1200-1600 parts coarse aggregate, 1600-2400 parts natural aggregate particles with an average diameter of 5-10 mm, 600-1000 parts slag powder, 100-300 parts standard silicate cement, 20-100 parts silica, 360-420 parts water, and 0-20 parts chemical admixtures.

[0022] 3. Mix fine aggregate, coarse aggregate and natural aggregate particles evenly, soak in water for 20-24 hours and air dry, ensuring the surface is moist but without excess moisture, to obtain mixed aggregate;

[0023] 4. Add slag powder, standard silicate cement, and silica to a dry mixer and mix thoroughly to obtain a mixed powder; the silica has a particle size of 300-600 nanometers and a specific surface area of ​​80-300 m². 2 / g;

[0024] 5. Add the chemical additive to water and stir until homogeneous to obtain a chemical additive solution;

[0025] 6. Place the mixed aggregate obtained in step 3 into a mixer, add 25%~30% water and mix at a mixing speed of 10~15 rpm for 1~2 minutes to fully wet the surface of the aggregate; then add 30%~35% mixed powder and mix at a mixing speed of 10~15 rpm for 1~2 minutes to ensure that the mixed powder fully coats the mixed aggregate; finally add the remaining mixed powder and water and mix at a mixing speed of 18~25 rpm for 3~5 minutes to obtain the mixture.

[0026] 7. Pour the mixture into the mold in several batches, each layer being 30-50mm thick. Hold each batch under a pressure of 50-80kN for 20-30 seconds, then demold to obtain concrete blanks.

[0027] 8. The concrete blanks are cured for 28 days at a temperature of 25~45℃ and a relative humidity of 92%~95% to obtain concrete material.

[0028] Furthermore, the chemical additives mentioned in step two are one or both of polycarboxylate-based high-efficiency water-reducing agents and fatty acid-based high-efficiency water-reducing agents.

[0029] Furthermore, the polycarboxylate-based high-efficiency water-reducing agent is a liquid substance with a solid mass percentage of 40% obtained by free radical polymerization of allyl polyoxyethylene ether and maleic anhydride copolymer.

[0030] Furthermore, the fatty acid-based high-efficiency water-reducing agent is a sulfonated acetone-formaldehyde condensate with a solid mass percentage of 30%.

[0031] Furthermore, the silica mentioned in step two is prepared by a gas-phase method. It is a nanoscale amorphous aggregate generated by the high-temperature hydrolysis of silicon tetrachloride in an oxyhydrogen flame. Its surface contains a large number of silanol groups that are linked together by hydrogen bonds, thus exhibiting high pozzolanic cementing activity.

[0032] Furthermore, the concrete material mentioned in step eight is permeable brick or permeable board.

[0033] This invention improves the preparation process of traditional concrete materials (permeable bricks, permeable panels). Traditional concrete materials use a direct mixing method of biochar, aggregate, and binder, which makes it difficult to ensure sufficient contact between the binder and aggregate, leading to uneven coating and slurry settling in the later stages. Biochar is also not easily distributed evenly, affecting the pore connectivity and strength of the permeable brick. This invention utilizes biochar to prepare core-shell structured artificial aggregate, employing a pre-mixing method for wet materials, quantifying the water addition for granulation, and using a two-step granulation method. This promotes the formation of a relatively dense protective shell with a high calcium carbonate content on the outer layer of the artificial aggregate, forming a self-compacting shell on the surface of the artificial aggregate, improving its strength and stability. Simultaneously, the addition of biochar to the artificial aggregate fills and divides the large pores, resulting in a reduction in the average pore size. These two factors work synergistically to improve the strength of the artificial aggregate. The preparation of the artificial aggregate ensures the uniform distribution of biochar, further enhancing the water absorption and retention capacity of the concrete material. Compared to ordinary concrete materials, the capillary water absorption coefficient of concrete materials with the artificial aggregate of this invention is increased by 77% to 205%.

[0034] Meanwhile, the core-shell structure of the artificial aggregate of the present invention is prepared by using dry powder and relatively high moisture conditions. Under high strength, no obvious aggregate-cement interface transition zone is generated during the bonding process with the slurry. When using this artificial aggregate to prepare concrete materials (permeable bricks), it can promote the bonding between the mixed powder and the aggregate to a greater extent. The compatibility between artificial aggregate and cement and other binders is better. During the curing and molding process, due to the strong connection between artificial aggregate and binder, aggregate settlement is not easy to occur. The pores in the concrete material are not easily blocked. The uniform coating of powder is conducive to the formation of a relatively uniform three-dimensional pore structure, thereby improving the permeability of the concrete material.

[0035] This invention prepares a porous-reinforced artificial aggregate by using biochar particles and cementing materials within a certain particle size range, and then mixes and molds it with a low-carbon binder to produce a sponge city pavement concrete material with long-lasting carbon sequestration function. Due to the uniform distribution of pores inside the material and the abundance of active functional groups in the biochar particles, the material's water absorption, water storage, and water purification functions are significantly enhanced. It can provide an "urban microclimate," alleviate the urban heat island effect, and effectively adsorb organic matter and heavy metals in road surface water, thus realizing the water purification function of a sponge city and reducing carbon emissions. Attached Figure Description

[0036] Figure 1 This is a pore distribution diagram of the pore-reinforced artificial aggregate obtained in Example 1;

[0037] Figure 2 These are capillary water absorption rate diagrams for the permeable concrete bricks prepared in Examples 5-8;

[0038] Figure 3 These are curves showing the relationship between the percentage of the dried area of ​​the permeable concrete bricks prepared in Examples 5-8 and time.

[0039] Figure 4 The graphs show the relationship between the temperature of the upper and lower surfaces of the permeable concrete bricks prepared in Examples 5-8 and time under simulated solar radiation; (a) in dry state (b) in wet state. Detailed Implementation

[0040] The beneficial effects of the present invention will be verified using the following examples.

[0041] Example 1: The preparation method of the porosity-reinforced artificial aggregate in this example is carried out according to the following steps:

[0042] Preparation of biochar particles:

[0043] (1) Dry the rice husks in an oven at 60°C for 24 hours, then crush them to a particle size of 5 mm, then pyrolyze them at 500°C under anaerobic conditions for 5 hours, then take them out and cool them in the air to obtain biochar particles with a porous structure.

[0044] (2) Place the biochar particles in a container and add the dilute hydrochloric acid solution with a concentration of 1 mol / L to the container at a mass ratio of 1:5. Mix the solution at a speed of 250 rpm for 5 minutes using magnetic stirring. Then seal the container and evacuate it to a vacuum level of -0.09 MPa for 5 minutes. Filter out the biochar particles and dry them in an oven at 60°C for 24 hours to obtain porous biochar particles.

[0045] 2. Weigh 600 parts of biochar granules, 800 parts of slag powder, 300 parts of steel slag powder, 200 parts of desulfurized gypsum, and 50 parts of phosphogypsum according to the mass ratio, mix them, and add them to a dry mixer to mix evenly to obtain a mixed dry material with a mass of 1950 parts.

[0046] 3. Take 70% of the dry mixture from step 2, i.e., 1365 parts, add water to it and stir evenly to obtain a wet mixture; the amount of water added is 28% of the mass of the dry mixture, i.e., 382.2 parts; pour the wet mixture into a disc granulator, start the granulator, and rotate and roll it for 12 minutes under the condition that the disc tilt angle is 45° and the rotation speed is 30 rpm to obtain the aggregate core;

[0047] 4. Spray water intermittently into the disc granulator while simultaneously spraying the remaining mixed dry material from step 2, i.e., 585 parts, to form a covering layer on the outer surface of the aggregate core, thereby obtaining an aggregate blank; wherein the amount of water sprayed is 35% of the mass of the remaining mixed dry material, i.e., 204.8 parts.

[0048] 5. Transfer the aggregate blanks to a carbonization curing chamber and cure them for 4 days under conditions of 20% carbon dioxide concentration and atmospheric pressure; then transfer them to a standard curing chamber and cure them for 7 days to obtain porosity-reinforced artificial aggregate, which is denoted as porosity-reinforced artificial aggregate a.

[0049] Example 2: The difference between this example and Example 1 is that the amount of biochar particles weighed in step two is 200 parts. The other steps and parameters are the same as in Example 1. The resulting pore-reinforced artificial aggregate is denoted as pore-reinforced artificial aggregate b.

[0050] Example 3: The difference between this example and Example 1 is that the biochar particles weighed in step two are 100 parts. The other steps and parameters are the same as in Example 1. The resulting pore-reinforced artificial aggregate is denoted as pore-reinforced artificial aggregate c.

[0051] Example 4: The difference between this example and Example 1 is that the amount of biochar particles weighed in step two is 0 parts. The other steps and parameters are the same as in Example 1. The resulting carbon-free artificial aggregate is denoted as artificial aggregate d.

[0052] The porosity-reinforced artificial aggregates prepared in Examples 1-4 were subjected to mercury intrusion porosimetry, and the pore size distribution maps obtained are shown below. Figure 1 As shown, from Figure 1 It can be seen that the pore distribution of the pore-reinforced artificial aggregate prepared in Example 1 is uniform. As the biochar content decreases, the average pore size of the pores in the artificial aggregate increases significantly. The artificial aggregate obtained by pore-reinforced artificial aggregate a has the best pore distribution, which proves that porous biochar particles can effectively optimize the pore distribution of artificial aggregate, enhance the performance of artificial aggregate, and achieve effective and stable carbon sequestration.

[0053] Example 5: A method for preparing permeable concrete bricks using the porous reinforced artificial aggregate prepared in Example 1, comprising the following steps:

[0054] 1. The porous reinforced artificial aggregate prepared in Example 1 is screened, and porous reinforced artificial aggregate particles with an average diameter d of 2mm≤d<5mm are selected as fine aggregate, and porous reinforced artificial aggregate particles with an average diameter d of 5mm≤d<10mm are selected as coarse aggregate.

[0055] The following components were selected by weight ratio: 150 parts fine aggregate, 1450 parts coarse aggregate, 1600 parts natural aggregate particles with an average diameter of 8 mm, 800 parts slag powder, 200 parts standard silicate cement, 20 parts silica, 380 parts water, and 5 parts polycarboxylate-based high-efficiency water-reducing agent; the silica had an average particle size of 400 nanometers and a specific surface area of ​​200 m². 2 / g; the polycarboxylate-based high-efficiency water-reducing agent is a copolymer of allyl polyoxyethylene ether and maleic anhydride, which is a liquid substance with a solid mass percentage of 40% obtained by free radical polymerization reaction; the silica is prepared by gas phase method, which is a nano-scale amorphous aggregate generated by high-temperature hydrolysis of silicon tetrachloride in oxyhydrogen flame, and its surface contains a large number of silanol groups that are linked together by hydrogen bonds, thus having high pozzolanic cementitious activity;

[0056] 3. Mix fine aggregate, coarse aggregate and natural aggregate particles evenly, soak in water for 24 hours and air dry, ensuring that the surface is moist but without excess moisture, to obtain mixed aggregate;

[0057] 4. Add slag powder, standard silicate cement and silica to a dry mixer and mix evenly to obtain a mixed powder with a volume of 1020 parts;

[0058] 5. Add the polycarboxylate-based high-efficiency water-reducing agent to water and stir evenly to obtain a chemical admixture solution;

[0059] 6. Place the mixed aggregate obtained in step 3 into a mixer, add 25% water (i.e., 95 parts), and mix at a mixing speed of 10 rpm for 2 minutes to fully wet the surface of the aggregate; then add 30% mixed powder (i.e., 306 parts), and mix at a mixing speed of 10 rpm for 2 minutes to ensure that the mixed powder fully coats the mixed aggregate; finally, add the remaining mixed powder (i.e., 714 parts) and water (i.e., 285 parts), and mix at a mixing speed of 20 rpm for 5 minutes to obtain the mixture;

[0060] 7. Pour the mixture into the permeable brick mold in three batches, each layer being 40mm thick. Hold the mixture under a pressure of 60kN for 30 seconds each time, then demold to obtain the permeable brick blank.

[0061] 8. Concrete blanks are cured for 28 days at a temperature of 30℃ and a relative humidity of 92% to obtain permeable concrete bricks. These permeable concrete bricks are denoted as 50AG.

[0062] Example 6: This example differs from Example 5 in that step two uses 70 parts fine aggregate, 800 parts coarse aggregate, 2030 parts natural aggregate particles with an average diameter of 8mm, 800 parts slag powder, 200 parts standard silicate cement, 20 parts silica, 385 parts water, and 5 parts chemical admixtures. Other steps and parameters are the same as in Example 5. The resulting permeable concrete brick is denoted as 30AG.

[0063] Example 7: This example differs from Example 5 in that step two uses 50 parts fine aggregate, 355 parts coarse aggregate, 2295 parts natural aggregate particles with an average diameter of 8mm, 800 parts slag powder, 200 parts standard silicate cement, 20 parts silica, 5 parts chemical admixture, and 390 parts water. Other steps and parameters are the same as in Example 5. The resulting permeable concrete brick is denoted as 15AG.

[0064] Example 8: This example differs from Example 5 in that step two contains 0 parts fine aggregate, 0 parts coarse aggregate, 2400 parts natural aggregate particles with an average diameter of 8mm, 800 parts slag powder, 200 parts standard silicate cement, 20 parts silica, 5 parts chemical admixtures, and 400 parts water. The other steps and parameters are the same as in Example 5. The resulting permeable concrete brick is denoted as 0AG.

[0065] Comparative Example 1: This comparative example uses the biochar particles from Example 1 and the carbon-free artificial aggregate prepared in Example 4 to directly mix into the mixture to prepare permeable bricks. The specific method is as follows:

[0066] Biochar particles were prepared according to step one of Example 1;

[0067] 2. Weigh out the following components according to the following mass ratios: 600 parts biochar granules, 1600 parts carbon-free artificial aggregate prepared in Example 4, 1600 parts natural aggregate granules with an average diameter of 8 mm, 400 parts slag powder, 200 parts standard silicate cement, 20 parts silica, 380 parts water, and 5 parts polycarboxylate-based high-efficiency water-reducing agent; the silica has an average particle size of 400 nm and a specific surface area of ​​200 m². 2 / g;

[0068] 3. Mix the carbon-free artificial aggregate and natural aggregate particles evenly, soak them in water for 24 hours and air dry them, ensuring that the surface is moist but without excess moisture, to obtain the mixed aggregate;

[0069] 4. Add biochar granules, slag powder, standard silicate cement and silica to a dry mixer and mix evenly to obtain a mixed powder.

[0070] 5. Add the polycarboxylate-based high-efficiency water-reducing agent to water and stir evenly to obtain a chemical admixture solution;

[0071] 6. Place the mixed aggregates into a mixer, add 25% water and mix at a mixing speed of 10 rpm for 2 minutes to fully wet the surface of the aggregates; then add 30% of the mixed powder and mix at a mixing speed of 10 rpm for 2 minutes to ensure that the mixed powder fully coats the mixed aggregates; finally, add the remaining mixed powder and water and mix at a mixing speed of 20 rpm for 5 minutes to obtain the mixture.

[0072] 7. Pour the mixture into the permeable brick mold in three batches, each layer being 40mm thick. Hold the mixture under a pressure of 60kN for 30 seconds each time, then demold to obtain the permeable brick blank.

[0073] 8. Concrete blanks were cured for 28 days at a temperature of 30℃ and a relative humidity of 92% to obtain permeable concrete bricks for comparison.

[0074] The water absorption and water retention capacity of the permeable concrete bricks prepared in Examples 5-8 and the comparative example were tested. The specific steps are as follows:

[0075] (1) Select a sample of permeable concrete bricks and weigh and test it to determine the initial mass m0;

[0076] (2) Place the permeable concrete brick sample into the water tank, set up support points on the base to keep the sample away from the bottom of the water tank, and keep the water level in the tank 5 mm higher than the bottom of the sample and keep it constant during the test; start timing when the sample is immersed in the water, take out the sample after 5 minutes, wipe the surface moisture with a wet sponge, and weigh the sample. Repeat the process of soaking, taking out, wiping the surface and weighing for 24 hours, and record the weight each time;

[0077] The capillary water absorption rate of the permeable concrete bricks prepared in Examples 5-8 was obtained in this experiment as follows: Figure 2 As shown. 0AG represents no artificial aggregate used, 15AG represents 15% artificial aggregate by volume, 30AG represents 30% artificial aggregate by volume, and 50AG represents 50% artificial aggregate by volume. From Figure 2 As can be seen, compared to 0AG, the capillary water absorption coefficients of 15AG, 30AG, and 5AG increased by 77.47%, 147.53%, and 204.40%, respectively. With the increase in the proportion of artificial aggregate, the water absorption per unit area significantly increased, and the water absorption window period was effectively extended, proving that pore-reinforced artificial aggregate can effectively improve the water absorption and retention capacity of carbon-fixed concrete materials. In contrast, the biochar particles in permeable concrete bricks are not added to the artificial aggregate but are directly mixed into the mixture. This not only leads to a decrease in the adhesive bonding ability, but also to a decrease in the strength of the permeable bricks. Furthermore, the adhesive is mainly used to bond the aggregate particles, resulting in a low average thickness and tight bonding with the aggregate, which reduces the total water-absorbing surface area and volume of the biochar particles. Consequently, its water absorption and retention capacity is worse than that of 15AG, 30AG, and 50AG permeable concrete bricks.

[0078] The surface temperature of the permeable concrete bricks prepared in Examples 5-8 and the comparative example was tested under solar radiation. A 600*400*400mm insulated and waterproof box was constructed, with an infrared lamp on top to simulate 600 W / m² solar radiation. The relative humidity was 60%, and the ambient temperature was 21℃. K-type thermocouples were used to measure the temperature changes on the upper and lower surfaces of the permeable concrete, with a measurement range of -40-360℃ and an accuracy of 0.5℃.

[0079] The permeable concrete surface was recorded every 10 minutes using a high-definition digital camera, showing changes in dry and saturated areas during evaporation. The images were then enhanced with grayscale to show the contrast between saturated and partially damp areas. Before testing, the samples should be soaked in water for 24 hours, and the surface moisture should be wiped dry before the test.

[0080] The curve showing the relationship between the percentage of the dry portion of permeable concrete bricks and time is as follows: Figure 3 As shown, by Figure 3 It can be seen that for carbon-fixed concrete materials prepared without artificial aggregates (0AG), the drying front exhibits a clear top-down moving trend, which is a typical one-dimensional unidirectional surface heat transfer. In the heat transfer direction, the samples can be considered isotropic. After adding artificial aggregates, the growth rate of the drying surface area decreased significantly, by approximately 38.09% of that of ordinary permeable concrete bricks. No obvious drying front was found in the 30AG and 50AG groups, indicating that artificial aggregates improved evaporation. Furthermore, due to their increased water retention, the transition period was longer and smoother. The drying performance of the permeable concrete bricks was comparable to that of the 0AG permeable bricks, demonstrating that the artificial aggregates containing biocarbon improved the water retention of the permeable concrete bricks and prolonged their evaporation time.

[0081] The curves showing the temperature variation of the upper and lower surfaces of permeable concrete bricks over time under simulated solar radiation are as follows: Figure 4 As shown, by Figure 4It can be seen that, under dry conditions, the permeable concrete bricks of Examples 5-8 all exhibited similar temperature change patterns. When the permeable concrete bricks were water-saturated, the evaporation of water delayed the rate of temperature rise on the surface of all samples. Corresponding to capillary suction, in the first evaporation stage, water was transported from the interior to the evaporation surface through capillary action, converting radiant heat into latent heat. Compared with the carbon-fixed concrete material 0AG without artificial aggregate, the surface temperature of carbon-fixed concrete materials with different artificial aggregates was significantly reduced. Among them, the highest surface temperatures of the 50AG group decreased by approximately 14°C and 3°C, respectively. This demonstrates that carbon-fixed concrete materials based on porous reinforced artificial aggregates can effectively regulate surface temperature and further mitigate local temperature changes under the heat island effect. Under strong solar irradiation, the surface temperature of the 0AG permeable concrete brick without artificial aggregate was approximately 68.7°C, while the surface temperature of the permeable concrete brick with added artificial aggregate was as low as approximately 56°C, demonstrating that the artificial aggregate prepared by biochar can effectively reduce the surface temperature of permeable concrete bricks under solar irradiation and regulate local temperature changes on the concrete surface. In contrast, the performance of the permeable concrete bricks was comparable to that of the permeable bricks 0AG.

Claims

1. A method for preparing concrete materials using porous reinforced artificial aggregate, characterized in that: The preparation method of porous reinforced artificial aggregate is carried out according to the following steps: I. Preparation of biochar granules; 2. Weigh 100-800 parts of biochar granules, 600-1000 parts of slag powder, 200-500 parts of steel slag powder, 100-250 parts of desulfurized gypsum and 0-100 parts of phosphogypsum according to the mass ratio and add them to a dry mixer and mix evenly to obtain a mixed dry material.

3. Take 70% to 80% of the dry mixture from step 2, add water and stir evenly to obtain a wet mixture; the amount of water added is 23% to 28% of the mass of the dry mixture; pour the wet mixture into a disc granulator, start the granulator, and rotate and roll it for 8 to 12 minutes under the conditions of disc tilt angle of 30 to 45° and rotation speed of 18 to 30 rpm to obtain the aggregate core; 4. Spray water intermittently into the disc granulator while simultaneously spraying the remaining mixed dry material from step 2, forming a covering layer on the outer surface of the aggregate core to obtain aggregate blanks; wherein the amount of water sprayed is 30%~35% of the mass of the remaining mixed dry material; 5. Transfer the aggregate blanks to a carbonization curing chamber and cure them for 2-5 days under conditions of 20% carbon dioxide concentration and atmospheric pressure; then transfer them to a standard curing chamber and cure them for 7-28 days to obtain porosity-reinforced artificial aggregates. The method for preparing concrete materials using porous reinforced artificial aggregates is carried out according to the following steps: The porous reinforced artificial aggregate was screened, and the porous reinforced artificial aggregate particles with an average diameter d of 2 mm ≤ d < 5 mm were selected as fine aggregate, and the porous reinforced artificial aggregate particles with an average diameter d of 5 mm ≤ d < 10 mm were selected as coarse aggregate.

2. Select the following components by weight: 100-180 parts fine aggregate, 1200-1600 parts coarse aggregate, 1600-2400 parts natural aggregate particles with an average diameter of 5-10 mm, 600-1000 parts slag powder, 100-300 parts standard silicate cement, 20-100 parts silica, 360-420 parts water, and 0-20 parts chemical admixtures.

3. Mix fine aggregate, coarse aggregate and natural aggregate particles evenly, soak in water for 20-24 hours and air dry, ensuring the surface is moist but without excess moisture, to obtain mixed aggregate; 4. Add slag powder, standard silicate cement, and silica to a dry mixer and mix thoroughly to obtain a mixed powder; the silica has a particle size of 300-600 nanometers and a specific surface area of ​​80-300 m². 2 / g; 5. Add the chemical additive to water and stir until homogeneous to obtain a chemical additive solution; 6. Place the mixed aggregate obtained in step 3 into a mixer, add 25%~30% water and mix at a mixing speed of 10~15 rpm for 1~2 minutes to fully wet the surface of the aggregate; then add 30%~35% mixed powder and mix at a mixing speed of 10~15 rpm for 1~2 minutes to ensure that the mixed powder fully coats the mixed aggregate; finally, add the remaining mixed powder and water and mix at a mixing speed of 18~25 rpm for 3~5 minutes to obtain the mixture.

7. Pour the mixture into the mold in several batches, each layer being 30-50mm thick. Hold each batch under a pressure of 50-80kN for 20-30 seconds, then demold to obtain concrete blanks.

8. The concrete blanks are cured for 28 days at a temperature of 25~45℃ and a relative humidity of 92%~95% to obtain concrete material.

2. The method for preparing concrete material using porous reinforced artificial aggregate according to claim 1, characterized in that... The chemical additives mentioned in step two are one or both of polycarboxylate-based high-efficiency water-reducing agents and fatty acid-based high-efficiency water-reducing agents.

3. The method for preparing concrete material using porous reinforced artificial aggregate according to claim 2, characterized in that, The polycarboxylate-based high-efficiency water-reducing agent is a liquid substance with a solid mass percentage of 40% obtained by free radical polymerization of allyl polyoxyethylene ether and maleic anhydride copolymer.

4. The method for preparing concrete material using porous reinforced artificial aggregate according to claim 2, characterized in that, The fatty acid-based high-efficiency water-reducing agent is a sulfonated acetone-formaldehyde condensate with a solid mass percentage of 30%.

5. The method for preparing concrete material using porous reinforced artificial aggregate according to claim 1, characterized in that, The concrete material mentioned in step eight is permeable brick or permeable board.

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