Temperature-controlled concrete and preparation method based on magnetic field regulation of phase-change lightweight aggregate distribution

Abstract

The present invention relates to a temperature-controlled concrete and a preparation method thereof based on magnetic field regulation of phase-change lightweight aggregate distribution. The components of the concrete are arranged in a mass ratio of (kg / m 3 : 730-870g magnetic phase-change lightweight aggregate; 240-380g shale sand; 450-550g cement; 40-60g silica fume; 0-30g fly ash; 5-7g water reducer; 0-61.4g daptom beads; 0-15g nano-SiO2; 50-80g water; 1.5-7.5g carbon fiber. Preparation method: 1. Design a magnetic field device to cover the entire concrete pouring area; 2. Mix the six magnetic phase-change aggregates; 3. Pre-wet the shale sand until saturated and dry; 4. Mix the silica fume, cement, fly ash, daptom beads, and nano-SiO2 uniformly; 5. Add the remaining components in two batches; 6. After mixing the concrete, pour it into a mold and activate the magnetic field device simultaneously; 8. After the concrete has initially set, turn off the magnetic field device and allow it to cure.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and in particular relates to temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution and a preparation method thereof. Background Art

[0002] Traditional temperature-regulated concrete mostly relies on adding specific additives or adopting complex structural designs, but these methods often have problems such as limited adjustment range, high cost or difficult construction.

[0003] Phase change aggregates effectively regulate concrete temperature by undergoing a phase change within the concrete, absorbing or releasing heat. However, existing technologies for preparing phase change aggregates have numerous limitations. For one thing, the bond between the phase change material and the aggregate is not strong enough, making it prone to leakage during use, affecting the durability and temperature regulation of the concrete. Furthermore, the distribution of the phase change aggregate is difficult to control, often leading to uneven temperature distribution within the concrete and preventing effective temperature regulation of specific areas.

[0004] To improve the bonding between phase-change aggregates and concrete, some studies have attempted to chemically immobilize phase-change materials on the aggregate surface or within its pores. However, these methods often present challenges such as complex processes, high costs, and environmental impacts. Furthermore, during the preparation process, existing phase-change aggregate concrete often struggles to precisely control the distribution of the phase-change aggregate within the concrete, limiting its temperature-regulating properties.

[0005] Magnetic field manipulation technology, as a non-contact control method, has extensive applications in materials science. However, its application in the preparation of phase-change aggregate concrete to achieve directional distribution of phase-change aggregate within the concrete is still rare. Existing magnetic field manipulation technologies are mostly used to manipulate microscopic particles or adjust the magnetic properties of materials, while their application in macroscopic building materials remains underexplored.

[0006] Therefore, how to provide a temperature-controlled concrete and a preparation method based on magnetic field regulation of phase-change lightweight aggregate distribution is a technical problem that technical personnel in this field urgently need to solve. Summary of the Invention

[0007] In response to the problems existing in the prior art, such as the difficulty in controlling the distribution of phase change aggregates in concrete, the insufficient durability of phase change materials, and the uneven temperature control effect, the present invention proposes a method for preparing temperature-controlled concrete based on magnetic field regulation of the distribution of phase change aggregates. The purpose of the present invention is to solve the defects of traditional concrete materials in temperature control accuracy, phase change material stability and durability, and at the same time provide a novel, efficient and controllable temperature-controlled building material. By preparing magnetic phase change aggregates with different magnetic strengths and using an adjustable magnetic field device to achieve a stepped arrangement of aggregates in concrete, a phase change concrete material with precise temperature control performance, good durability and stability is prepared to meet the demand for intelligent temperature regulation of concrete structures and promote the development of intelligent and functional building materials.

[0008] In order to solve the above technical problems, the present invention includes the following technical solutions:

[0009] A temperature-controlled concrete based on magnetic field regulation of phase change lightweight aggregate distribution, wherein the components of the concrete are in a mass ratio of (kg / m 3 ):

[0010] Magnetic phase change lightweight aggregate 730~870; shale ceramic sand 240~380; cement 450~550; silica fume 40~60; fly ash 0~30; water reducer 5~7; floating beads 0~61.4; nano-SiO2 0~15; water 50~80; carbon fiber: 1.5~7.5 parts.

[0011] Furthermore, the magnetic phase change lightweight aggregate preparation process includes:

[0012] The first step is to soak the ceramsite in 5wt% NaOH solution, ultrasonically treat at 60℃ for 30 minutes, rinse with deionized water until neutral, and dry at 80℃ for later use;

[0013] The second step is to immerse the pre-treated cloud concrete stone ceramsite into The mixed solution was added with ammonia water until pH = 10, stirred at 60℃ for 2 hours, and Fe3O4 nanoparticles were deposited in the pores and surface of the cloud concrete ceramsite; magnetic separation and recovery were carried out, and vacuum drying was carried out at 60℃ to obtain a magnetic lightweight aggregate matrix. By adjusting the concentration of the mixed solution or the reaction time, the deposition amount of Fe3O4 nanoparticles on the surface of the ceramsite is controlled to be 8-12wt%, thereby preparing a magnetic lightweight aggregate matrix with different magnetic strengths. The prepared magnetic lightweight aggregate matrix is ​​divided into several groups, each with a different Fe3O4 loading, corresponding to different magnetic strengths.

[0014] The third step is to put the phase change material into a beaker, and then put it into an oven and heat it to 60°C to ensure that the phase change material is in a completely molten state. 1wt% expanded graphite is added and stirred to improve thermal conductivity.

[0015] The fourth step is to place the vacuum barrel in a constant temperature water bath. After the temperature in the vacuum barrel reaches 60°C, the magnetic lightweight aggregate matrix is ​​placed in the vacuum impregnation tank, and the vacuum is pumped to -0.1MPa and maintained for 30 minutes.

[0016] The fifth step is to inject the molten phase change material and pressurize it to -0.5MPa for 2 hours to fully fill the pores of the ceramsite and the gaps of Fe3O4 to form magnetic phase change lightweight aggregate; the magnetic phase change lightweight aggregate is grouped from low to high according to the phase change temperature;

[0017] Step 6: After depressurization, centrifuge to remove residual phase change material on the surface, then place in cold water for condensation, wait for cooling and solidification, and dry;

[0018] Step 7: Prepare a cement-based material with a water-binder ratio of 0.25. Add 0.5-1.5wt% carbon fiber and 0.2wt% carboxymethyl cellulose to a cementitious system of Portland cement and silica fume in a mass ratio of 7:3, and stir until the slurry viscosity reaches 2000-3000 cP.

[0019] In the eighth step, the magnetic phase change lightweight aggregate adsorbing the phase change material is immersed in the slurry for 10 seconds, slowly pulled to form a uniform wet film, placed in a 90% humidity and 25°C environment for pre-curing for 24 hours, and then transferred to a 60°C steam curing box for curing for 48 hours to form a dense cement-based shell;

[0020] The ninth step is to spray 0.5wt% silane hydrophobic agent on the surface of the coated magnetic phase change lightweight aggregate, and heat treat it at 120°C for 1 hour to improve the waterproofness and durability, thereby preparing the magnetic phase change lightweight aggregate.

[0021] Furthermore, when the phase change materials are hexadecane, dodecanol, decanoic acid, lauric acid, tetradecanoic acid, and palmitic acid, the corresponding loading amounts are 8 wt%, 8.8 wt%, 9.6 wt%, 10.4 wt%, 11.2 wt%, and 12 wt%, respectively.

[0022] Furthermore, the phase transition temperature of hexadecane is 18.2°C, the latent heat of phase change is 200 J / g, and the density is 0.834 g / cm 3 , boiling point is 286.8℃; dodecanol phase transition temperature is 25.8℃, phase transition latent heat is 216J / g, density is 0.831g / cm 3 , boiling point is 258.0℃; the phase transition temperature of decanoic acid is 31.4℃, the phase transition latent heat is 167J / g, and the density is 0.893g / cm 3, boiling point is 269.6℃; lauric acid phase transition temperature is 43.4℃, phase transition latent heat is 212J / g, density is 0.867g / cm 3 , boiling point is 299.0℃; the phase transition temperature of tetradecanoic acid is 53.7℃, the phase transition latent heat is 187J / g, and the density is 0.862g / cm 3 , boiling point is 250.5℃; palmitic acid phase transition temperature is 62.4℃, phase transition latent heat is 241J / g, density is 0.852g / cm 3 .

[0023] Furthermore, the thickness of the cement-based shell is 200-300 μm.

[0024] The present invention also provides a method for preparing temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution, comprising the following steps:

[0025] Step S1: Before concrete pouring, an adjustable magnetic field device is designed. The magnetic field device covers the entire concrete pouring area and adopts a radial gradient magnetic field. The magnetic field intensity gradually decreases from the center to the outside.

[0026] Step S2: mixing magnetic phase change aggregates prepared respectively from hexadecane, dodecanol, capric acid, lauric acid, myristic acid, and palmitic acid in a mass ratio of 1:1:2:2:3:3 to obtain a composite phase change aggregate;

[0027] Step S3: pre-wetting the shale sand to make it reach a saturated surface dry state;

[0028] Step S4: dry-mix silica fume, cement, fly ash, floating beads, and nano-SiO2 in a concrete mixer for 1.0 min and mix evenly to obtain a primary dry mix;

[0029] Step S5: adding composite phase change aggregate, 50% water, 50% water reducer, and 50% carbon fiber to the primary mixed dry material obtained in S4, and stirring for 1 minute to form a medium mixed material;

[0030] Step S6: adding shale sand, 50% water, 50% water reducer, and 50% carbon fiber to the primary mixed material obtained in S5, and stirring for 1 minute to obtain magnetic phase change lightweight aggregate concrete;

[0031] Step S7: After mixing the concrete, pour it into the mold and activate the magnetic field device at the same time. Due to the different magnetic strengths of the magnetic phase-change aggregates, under the action of the magnetic field, the aggregates with lower phase-change temperatures will be attracted to the outer area with weaker magnetic field, while the aggregates with higher phase-change temperatures will be attracted to the central area, thereby achieving a stepped arrangement of the aggregates in the concrete.

[0032] S8: After the concrete has initially set, turn off the magnetic field device and continue curing until final setting.

[0033] Furthermore, in step S1, the magnetic field uses an electromagnetic coil or a permanent magnet array, and by adjusting the current or the arrangement of the magnets, a magnetic field distribution with a strong center and a weak periphery is formed.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The temperature-controlled concrete provided by the present invention, which uses a magnetic field to regulate the distribution of phase-change lightweight aggregate, has four advantages:

[0036] 1) Precisely Controlled Aggregate Distribution: A designed radial gradient magnetic field device enables a stepped arrangement of magnetic phase-change aggregate within the concrete. This arrangement allows aggregates with different phase-change temperatures to be distributed according to a preset temperature gradient, thereby optimizing the concrete's thermal management and improving the precision and efficiency of temperature control.

[0037] 2) Improved thermal performance of concrete: Since the magnetic phase change aggregate forms an orderly temperature gradient distribution in the concrete, the concrete can more effectively absorb or release heat when subjected to external temperature changes, balancing the temperature fluctuations inside the concrete and improving its thermal stability and thermal comfort.

[0038] 3) Enhanced phase change material utilization: By adjusting By adjusting the concentration of the mixed solution or the reaction time, the amount of Fe₃O₄ nanoparticles deposited on the surface of the ceramsite can be controlled, thereby producing a magnetic lightweight aggregate matrix with varying magnetic strengths. This allows for the selection of different phase change materials based on actual needs, enabling flexible control of the phase change temperature.

[0039] 4) Multi-gradient thermal response control capability: Through the precise matching of magnetic field gradient and Fe3O4 loading, aggregates with phase change temperatures from low to high are arranged in six layers within the concrete, forming a wide-temperature adaptive heat storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of a method for preparing temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to the present invention;

[0041] Figure 2 This is a magnetic field arrangement diagram of a temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to the present invention;

[0042] Figure 3 Schematic cross-sectional view of the magnetic field in a temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to the present invention;

[0043] Figure 4This is a distribution diagram of magnetic phase-change lightweight aggregate in section 1-1 of a method for preparing temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to the present invention;

[0044] Figure 5 This is a distribution diagram of magnetic phase-change lightweight aggregate in section 2-2 in a method for preparing temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to the present invention. DETAILED DESCRIPTION

[0045] The following is a detailed description of a temperature-controlled concrete and a preparation method thereof based on magnetic field regulation of phase-change lightweight aggregate distribution provided by the present invention, in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description.

[0046] Please refer to Figures 1 to 5 , the temperature-controlled concrete based on magnetic field regulation of phase change lightweight aggregate distribution of the present invention is described below.

[0047] Example 1

[0048] A magnetic phase-change lightweight aggregate concrete material and a preparation method thereof are disclosed in Example 1 of the present application, including magnetic phase-change lightweight aggregate; shale ceramic sand; cement; silica fume; fly ash; water reducing agent; floating beads; nano-SiO2; water; and carbon fiber.

[0049] In addition, the magnetic phase-change lightweight aggregate used is 5mm dome-shaped concrete ceramsite obtained by adsorption of magnetic materials and phase-change materials and encapsulation modification. The prepared magnetic phase-change lightweight aggregates are hexadecane magnetic phase-change lightweight aggregate, dodecanol magnetic phase-change lightweight aggregate, capric acid magnetic phase-change lightweight aggregate, lauric acid magnetic phase-change lightweight aggregate, tetradecanoic acid magnetic phase-change lightweight aggregate and palmitic acid magnetic phase-change lightweight aggregate, and their cylinder compressive strength is 22~24MPa; shale ceramic sand adopts continuous grading, and its particle size is 0~5mm; the floating beads used have an apparent density of 0.7~0.9×10 3 kg / m 3 The fly ash spherical floating beads; the apparent density of the silica fume used is 2200kg / m 3 The particle size range is 0.1~0.3µm; the cement grade used is PII52.5, the 28d compressive strength is 60.6MPa, and the flexural strength is 9.1MPa; the fly ash density used is 2.24g / cm 3 The nano-SiO2 particle size used is 20nm and the specific surface area is 640m 2 / g, loose density 0.1g / cm 3 ; The solid content of the water reducer used is 20%, and its water reduction rate is greater than 30%.

[0050] Preparation of magnetic phase change lightweight aggregate:

[0051] The first step is to soak the ceramsite in 5wt% NaOH solution, ultrasonically treat at 60℃ for 30 minutes, rinse with deionized water until neutral, and dry at 80℃ for later use;

[0052] The second step is to immerse the pre-treated cloud concrete stone ceramsite into The mixed solution was added with ammonia water until pH = 10, stirred at 60℃ for 2 hours, and Fe3O4 nanoparticles were deposited in the pores and surface of the cloud concrete ceramsite; magnetic separation and recovery were carried out, and vacuum drying was carried out at 60℃ to obtain a magnetic lightweight aggregate matrix. By adjusting the concentration of the mixed solution or the reaction time, the deposition amount of Fe3O4 nanoparticles on the surface of the ceramsite is controlled to be 8-12wt%, thereby preparing a magnetic lightweight aggregate matrix with different magnetic strengths. The prepared magnetic lightweight aggregate matrix is ​​divided into several groups, each with a different Fe3O4 loading, corresponding to different magnetic strengths.

[0053] The third step is to put the phase change material into a beaker, and then put it into an oven and heat it to 60°C to ensure that the phase change material is in a completely molten state. 1wt% expanded graphite is added and stirred to improve thermal conductivity.

[0054] The fourth step is to place the vacuum barrel in a constant temperature water bath. After the temperature in the vacuum barrel reaches 60°C, the magnetic lightweight aggregate matrix is ​​placed in the vacuum impregnation tank, and the vacuum is pumped to -0.1MPa and maintained for 30 minutes.

[0055] The fifth step is to inject the molten phase change material and pressurize it to -0.5MPa for 2 hours to fully fill the pores of the ceramsite and the gaps of Fe3O4 to form magnetic phase change lightweight aggregate; the magnetic phase change lightweight aggregate is grouped from low to high according to the phase change temperature;

[0056] Step 6: After depressurization, centrifuge to remove residual phase change material on the surface, then place in cold water for condensation, wait for cooling and solidification, and dry;

[0057] Step 7: Prepare a cement-based material with a water-binder ratio of 0.25. Add 0.5-1.5wt% carbon fiber and 0.2wt% carboxymethyl cellulose to a cementitious system of Portland cement and silica fume in a mass ratio of 7:3, and stir until the slurry viscosity reaches 2000-3000 cP.

[0058] In the eighth step, the magnetic phase change lightweight aggregate adsorbing the phase change material is immersed in the slurry for 10 seconds, slowly pulled to form a uniform wet film, placed in a 90% humidity and 25°C environment for pre-curing for 24 hours, and then transferred to a 60°C steam curing box for curing for 48 hours to form a dense cement-based shell;

[0059] The ninth step is to spray 0.5wt% silane hydrophobic agent on the surface of the coated magnetic phase change lightweight aggregate, and heat treat it at 120°C for 1 hour to improve the waterproofness and durability, thereby preparing the magnetic phase change lightweight aggregate.

[0060] When the phase change materials are hexadecane, dodecanol, decanoic acid, lauric acid, myristic acid, and palmitic acid, the corresponding loading amounts are 8 wt%, 8.8 wt%, 9.6 wt%, 10.4 wt%, 11.2 wt%, and 12 wt%, respectively.

[0061] The performance test data of the prepared magnetic phase change lightweight aggregate are shown in Table 1.

[0062] Table 1 Magnetic phase change lightweight aggregate performance test data

[0063]

[0064] Please refer to Figure 1 The magnetic phase change lightweight aggregate concrete material and its preparation method include the following steps:

[0065] S1: Before pouring concrete, design an adjustable magnetic field device that covers the entire concrete pouring area and uses a radial gradient magnetic field. The magnetic field strength gradually decreases from the center to the outside. The magnetic field uses an electromagnetic coil or a permanent magnet array. By adjusting the current or the arrangement of the magnets, a magnetic field distribution with a strong center and a weak periphery is formed, such as Figure 2 shown.

[0066] S2: Magnetic phase change aggregates prepared from hexadecane, dodecanol, capric acid, lauric acid, myristic acid, and palmitic acid are mixed in a mass ratio of 1:1:2:2:3:3 to obtain a composite phase change aggregate;

[0067] S3: pre-wetting the shale sand to make it reach a saturated surface dry state;

[0068] S4: dry-mix silica fume, cement, fly ash, floating beads, and nano-SiO2 in a concrete mixer for 1.0 min and mix evenly to obtain a primary dry mix;

[0069] S5: Add composite phase change aggregate, 50% water, 50% water reducer, and 50% carbon fiber to the primary dry mix obtained in step S4, and stir for 1 minute to form a medium mix;

[0070] S6: adding shale sand, 50% water, 50% water reducer, and 50% carbon fiber to the primary mixed material obtained in step S5, and stirring for 1 minute to obtain magnetic phase change lightweight aggregate concrete;

[0071] S7: After mixing the concrete, pour it into the mold and start the magnetic field device at the same time. Due to the different magnetic strengths of the magnetic phase change aggregates, under the action of the magnetic field, the aggregates with lower phase change temperatures (Group A) will be attracted to the outer area with weaker magnetic field, while the aggregates with higher phase change temperatures (Group F) will be attracted to the central area, thereby achieving a stepped arrangement of aggregates in the concrete, that is, the central area of ​​the concrete is the Group F aggregate with the highest phase change temperature, and outwards are the Groups E, D, C, B, and A aggregates; among them, Group A (hexadecane, 18.2°C), Group B (dodecanol, 25.8°C), Group C (decanoic acid, 31.4°C), Group D (lauric acid, 43.4°C), Group E (tetradecanoic acid, 53.7°C), Group F (palmitic acid, 62.4°C), Figures 3 to 5 As shown;

[0072] S8: After the concrete has initially set, turn off the magnetic field device and continue curing until final setting.

[0073] Example 2 to Example 9

[0074] The difference between Examples 2 to 7 and Example 1 is that the magnetic phase-change lightweight aggregate components included are different. The difference between Example 8 and Example 1 is that no fiber is added. Example 9 adds ordinary lightweight aggregate with the same dosage as the magnetic phase-change lightweight aggregate, without adding fiber. Detailed values ​​are shown in Table 2.

[0075] Table 2 Schematic table of weight percentages of each component of magnetic phase change lightweight aggregate concrete

[0076]

[0077] Performance testing:

[0078] Compressive strength and splitting tensile strength tests were conducted on the concrete specimens prepared in each example. The concrete specimens were 100 mm × 100 mm × 100 mm cubes, with 6 specimens per group. The thermodynamic properties test used three concrete slabs with specimen dimensions of 300 mm × 300 mm × 35 mm. After molding, the specimens were cured according to standard methods (temperature 20°C ± 2°C, relative humidity 95% RH or above). The obtained performance results are shown in Table 3.

[0079] Table 3 Magnetic phase change lightweight aggregate concrete performance test data

[0080]

[0081] Result analysis:

[0082] The test data from Examples 8 and 9 indicate that the compressive strength and splitting tensile strength of magnetic phase-change lightweight aggregate concrete show a downward trend compared to concrete using ordinary lightweight aggregate. However, when carbon fiber is added, the compressive strength and splitting tensile strength of Example 1 show an upward trend compared to Example 8. Comparing Examples 2 to 7, the thermal conductivity and specific heat capacity show an upward trend, but are both lower than those of Example 1. This indicates that the magnetic phase-change aggregate prepared by mixing hexadecane, dodecanol, decanoic acid, lauric acid, myristic acid, and palmitic acid in a mass ratio of 1:1:2:2:3:3 forms a continuous heat absorption zone in the concrete, resulting in the optimal control performance of Example 1.

[0083] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. The above embodiments only express several embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several variations and improvements can be made, which all fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution, characterized in that: The mass ratio of the components of the concrete is (kg / m 3 ): Magnetic phase change lightweight aggregate 730-870; shale ceramic sand 240-380; cement 450-550; silica fume 40-60; fly ash 0-30; water reducer 5-7; floating beads 0-61.4; nano-SiO2 0-15; water 50-80; Carbon fiber: 1.5~7.5; The magnetic phase change lightweight aggregate preparation process comprises: The first step is to soak the ceramsite in 5wt% NaOH solution, ultrasonically treat at 60℃ for 30 minutes, rinse with deionized water until neutral, and dry at 80℃ for later use; In the second step, the pretreated ceramsite is immersed in a Fe²⁺ / Fe³⁺ mixed solution, ammonia water is added dropwise to a pH of 10, and the mixture is stirred at 60°C for 2 hours to deposit Fe3O4 nanoparticles in the pores and surface of the ceramsite. The ceramsite is then recovered by magnetic separation and vacuum dried at 60°C to obtain a magnetic lightweight aggregate matrix. Depending on the phase change material, the concentration of the Fe²⁺ / Fe³⁺ mixed solution or the reaction time are adjusted to control the deposition amount of Fe3O4 nanoparticles on the surface of the ceramsite to 8-12wt%, thereby preparing magnetic lightweight aggregate matrices with different magnetic strengths. The prepared magnetic lightweight aggregate matrices are divided into several groups, each with a different Fe3O4 loading, corresponding to different magnetic strengths. The third step is to put the phase change material into a beaker, and then put it into an oven and heat it to 60°C to ensure that the phase change material is in a completely molten state. 1wt% expanded graphite is added and stirred to improve thermal conductivity. The fourth step is to place the vacuum barrel in a constant temperature water bath. After the temperature in the vacuum barrel reaches 60°C, the magnetic lightweight aggregate matrix is ​​placed in the vacuum impregnation tank, and the vacuum is pumped to -0.1MPa and maintained for 30 minutes. The fifth step is to inject the molten phase change material and pressurize it to -0.5MPa for 2 hours to fully fill the pores of the ceramsite and the gaps of Fe3O4 to form magnetic phase change lightweight aggregate; the magnetic phase change lightweight aggregate is grouped from low to high according to the phase change temperature; Step 6: After depressurization, centrifuge to remove residual phase change material on the surface, then place in cold water for condensation, wait for cooling and solidification, and dry; Step 7: Prepare a cement-based material with a water-binder ratio of 0.

25. Add 0.5-1.5wt% carbon fiber and 0.2wt% carboxymethyl cellulose to a cementitious system of Portland cement and silica fume in a mass ratio of 7:3, and stir until the slurry viscosity reaches 2000-3000 cP. In the eighth step, the magnetic phase change lightweight aggregate adsorbing the phase change material is immersed in the slurry for 10 seconds, slowly pulled to form a uniform wet film, placed in a 90% humidity and 25°C environment for pre-curing for 24 hours, and then transferred to a 60°C steam curing box for curing for 48 hours to form a dense cement-based shell; The ninth step is to spray 0.5wt% silane hydrophobic agent on the surface of the coated magnetic phase change lightweight aggregate, and heat treat it at 120°C for 1 hour to improve the waterproofness and durability, thereby preparing the magnetic phase change lightweight aggregate.

2. The temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to claim 1, characterized in that: When the phase change materials are hexadecane, dodecanol, decanoic acid, lauric acid, myristic acid, and palmitic acid, the corresponding loading amounts are 8 wt%, 8.8 wt%, 9.6 wt%, 10.4 wt%, 11.2 wt%, and 12 wt%, respectively.

3. The temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to claim 2, characterized in that: The phase transition temperature of hexadecane is 18.2°C, the latent heat of phase change is 200 J / g, and the density is 0.834 g / cm 3 , boiling point is 286.8℃; dodecanol phase transition temperature is 25.8℃, phase transition latent heat is 216J / g, density is 0.831g / cm 3 , boiling point is 258.0℃; the phase transition temperature of decanoic acid is 31.4℃, the phase transition latent heat is 167J / g, and the density is 0.893g / cm 3 , boiling point is 269.6℃; lauric acid phase transition temperature is 43.4℃, phase transition latent heat is 212J / g, density is 0.867g / cm 3 , boiling point is 299.0℃; the phase transition temperature of tetradecanoic acid is 53.7℃, the phase transition latent heat is 187J / g, and the density is 0.862g / cm 3 , boiling point is 250.5℃; palmitic acid phase transition temperature is 62.4℃, phase transition latent heat is 241J / g, density is 0.852g / cm 3 .

4. The temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to claim 2, characterized in that: The thickness of the cement-based shell is 200-300 μm.

5. The method for preparing temperature-controlled concrete based on magnetic field regulation of phase-change lightweight aggregate distribution according to any one of claims 1 to 4, characterized in that: The steps include: Step S1: Before concrete pouring, an adjustable magnetic field device is designed. The magnetic field device covers the entire concrete pouring area and adopts a radial gradient magnetic field. The magnetic field intensity gradually decreases from the center to the outside. Step S2: mixing magnetic phase change aggregates prepared respectively from hexadecane, dodecanol, capric acid, lauric acid, myristic acid, and palmitic acid in a mass ratio of 1:1:2:2:3:3 to obtain a composite phase change aggregate; Step S3: pre-wetting the shale sand to make it reach a saturated surface dry state; Step S4: dry-mix silica fume, cement, fly ash, floating beads, and nano-SiO2 in a concrete mixer for 1.0 min and mix evenly to obtain a primary dry mix; Step S5: adding magnetic phase change lightweight aggregate, 50% water, 50% water reducer, and 50% carbon fiber to the primary dry mix obtained in S4, and stirring for 1 minute to form a medium mix; Step S6: adding shale sand, 50% water, 50% water reducer, and 50% carbon fiber to the primary mixed material obtained in S5, and stirring for 1 minute to obtain magnetic phase change lightweight aggregate concrete; Step S7: After mixing the concrete, pour it into the mold and activate the magnetic field device at the same time. Due to the different magnetic strengths of the magnetic phase-change aggregates, under the action of the magnetic field, the aggregates with lower phase-change temperatures will be attracted to the outer area with weaker magnetic field, while the aggregates with higher phase-change temperatures will be attracted to the central area, thereby achieving a stepped arrangement of the aggregates in the concrete. S8: After the concrete has initially set, turn off the magnetic field device and continue curing until final setting.

6. The preparation method according to claim 5, characterized in that: In step S1, the magnetic field device uses an electromagnetic coil or a permanent magnet array, and forms a magnetic field distribution with a strong center and weak periphery by adjusting the current or the arrangement of the magnets.

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