Janus phase change recycled aggregate for 3D printing, concrete and method for preparing the same

Abstract

The present application relates to a kind of Janus phase change recycled aggregate for 3D printing, concrete and its preparation method, Janus phase change recycled aggregate includes porous recycled aggregate matrix, the porous recycled aggregate matrix inside is loaded with phase change material;The surface of the porous recycled aggregate matrix has asymmetric surface structure, wherein one side is coated with heat-conducting coating to form heat-conducting shielding surface, the other side remains original porous structure as phase change energy storage surface.Janus phase change recycled aggregate concrete includes the Janus phase change recycled aggregate, also includes cement matrix, the Janus phase change recycled aggregate is arranged in the cement matrix at preset angle of inclination orientation, so that the concrete has different thermal conductivity in parallel with its arrangement direction and perpendicular to its arrangement direction.Compared with prior art, the present application has the advantages of constructing asymmetric heat passage in concrete, thereby regulating heat flow direction as needed, improving the thermal management efficiency and energy saving effect of building envelope and the like.

Description

Technical Field

[0001] This invention relates to the field of building materials and 3D printing technology, and in particular to a Janus phase change recycled aggregate, concrete and its preparation method for 3D printing. Background Technology

[0002] With the acceleration of global urbanization, the amount of construction waste generated is increasing year by year. Crushing and screening waste concrete to produce recycled aggregate concrete has become a core approach to achieving the recycling of building resources and reducing carbon emissions from engineering projects. However, recycled aggregates possess natural properties such as high porosity and numerous microcracks due to residual old mortar on their surface. While this gives them superior thermal performance compared to natural aggregate concrete, it also results in generally lower mechanical strength. Therefore, how to fully utilize their excellent thermal performance and effectively improve their mechanical properties has become a bottleneck limiting their widespread application in high-standard energy-efficient buildings.

[0003] In the field of building thermal management, traditional energy-saving methods mainly rely on external insulation materials such as polystyrene boards or mineral wool. This approach has significant technical bottlenecks. Its thermal conductivity is isotropic, with a constant thermal conductivity coefficient and no directional selectivity. As a result, while the walls can block heat from entering the room during the day in summer, they also hinder heat dissipation at night. In winter, they cannot dynamically adjust thermal resistance according to sunlight and temperature differences. This "static insulation" mode lacks the ability to adaptively regulate changes in ambient temperature. Furthermore, the separation of the insulation layer from the load-bearing structure not only increases construction complexity but also poses safety hazards such as detachment, fire, and aging. It is also difficult to adapt to the customized production needs of modern complex building geometries.

[0004] Thermal rectification technology, as a cutting-edge solution for achieving unidirectional heat conduction, has been preliminarily studied in the field of microelectronic thermal management. However, constructing microscopic asymmetric structures and achieving macroscopic directional arrangement in large-scale, non-homogeneous concrete materials remains a significant technical challenge. Traditional mixing and casting processes, due to the random distribution of aggregates in the matrix, cause the thermal properties of microscopic functional units to cancel each other out on a macroscopic scale, failing to induce an effective thermal rectification effect.

[0005] In recent years, the rise of 3D printed concrete technology has provided an opportunity for precise control of material spatial distribution. However, current research focuses primarily on the printability of the slurry, improvement of mechanical strength, and breakthroughs in the morphology of complex components, with limited in-depth research on functional properties. In particular, how to fully leverage the advantages of recycled aggregates in thermal properties such as low thermal conductivity and high thermal resistance, while simultaneously improving overall mechanical properties, remains a critical issue that urgently needs to be addressed. By controlling the flow field and stress field during additive manufacturing, functional units can be oriented in a controlled manner, potentially endowing concrete components with adaptive thermal management capabilities such as "heat ingress prevention in summer and heat dissipation prevention in winter." However, mature technical solutions and systematic research are currently lacking.

[0006] CN120172668A discloses a phase change recycled aggregate, its preparation method, and an antifreeze water-stabilized material. The method utilizes the phase change material to impregnate and fill the pores on the surface of aerated concrete aggregate, followed by encapsulation with cement slurry, thereby reinforcing the recycled aggregate, reducing its water absorption, and encapsulating the phase change material within the aggregate to minimize detachment loss. The high-temperature heat absorption and low-temperature heat release properties of the organic phase change material mitigate the stress damage to its internal structure caused by temperature shocks, extending the insulation period during winter construction and prolonging the effective hydration time of cement. However, achieving macroscopic directional arrangement of this phase change recycled aggregate remains challenging. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem in the prior art where the macroscopic directional arrangement of phase change recycled aggregates is difficult to achieve, resulting in insufficient mechanical strength of recycled aggregate concrete. This invention proposes a Janus phase change recycled aggregate concrete for 3D printing and its preparation method. By fully utilizing its low thermal conductivity and high thermal resistance characteristics, and constructing an asymmetric thermal pathway to achieve controllable adjustment of heat flow, this invention ensures that while improving structural strength, it also significantly enhances the thermal management and energy-saving performance of the building envelope.

[0008] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a Janus phase change recycled aggregate for 3D printing. The Janus phase change recycled aggregate includes a porous recycled aggregate matrix, wherein the porous recycled aggregate matrix is ​​loaded with a phase change material. The porous recycled aggregate matrix has an asymmetrical surface structure, with one side coated with a thermally conductive coating to form a thermally conductive shielding surface, and the other side retaining the original porous structure to serve as a phase change energy storage surface.

[0009] Furthermore, the porous recycled aggregate matrix has a particle size of 5-20 mm and an apparent density of 2300-2600 kg / m³. 3 It has a water absorption rate of 5%~10%, a porosity of 3%~10%, and a specific surface area of ​​0.4~0.5 m². 2 / g; moisture content is 2%~5%; The phase change material is a liquid organic phase change material with a melting point between 18 and 30°C, selected from one or more of alkanes, paraffins, fatty acids, alcohols, or esters; The thermally conductive coating uses a thermally conductive material with a thermal conductivity of not less than 100 W / (m·K), and the thermally conductive material includes one or more of graphite, graphene, carbon nanotubes or boron nitride. The thickness of the thermally conductive coating is 50~80 μm.

[0010] Furthermore, the phase change material includes one or more of n-eicosane, paraffin, fatty acids, lauric acid, myristic acid, and glycerol.

[0011] Furthermore, the latent heat of phase change of the phase change material is 150–260 J / g.

[0012] Furthermore, the thermally conductive coating also includes 1wt% to 20wt% of functional fillers; The functional filler includes magnetic filler and / or non-magnetic filler, wherein the magnetic filler includes nickel powder and / or ferrite; and the non-magnetic filler includes one or more of aluminum powder, copper powder, silver powder, zinc oxide, titanium dioxide, aluminum nitride, or silicon carbide. The average particle size of the functional filler is 1~50μm, and it is uniformly and discretely distributed or continuously overlapped in the thermally conductive coating.

[0013] Furthermore, the phase change material fills the pores of the porous recycled aggregate matrix.

[0014] Furthermore, the thermally conductive shielding surface and the phase change energy storage surface are distributed in a hemispherical asymmetric shape with reference to the geometric center of the porous recycled aggregate matrix; There is a clear physical boundary between the thermally conductive shielding surface and the phase change energy storage surface, and this boundary forms a closed loop on the surface of the porous recycled aggregate matrix. The thermally conductive shielding surface continuously covers the surface of the porous recycled aggregate matrix, and its geometric center line is consistent with the direction of the minor axis or major axis of the porous recycled aggregate matrix. The surface area of ​​the thermally conductive shielding surface accounts for 40% to 60% of the total surface area of ​​the porous recycled aggregate matrix, preferably 45% to 55%, and more preferably 50%.

[0015] The second technical solution of the present invention provides a method for preparing Janus phase change recycled aggregate for 3D printing, comprising the following steps: A1. The phase change material is loaded into the porous recycled aggregate matrix using a vacuum impregnation method; A2. A porous recycled aggregate matrix loaded with phase change material is masked, and a thermally conductive material is deposited on one side of the carrier gas to form a thermally conductive coating, resulting in a thermally conductive shielding surface. The other side of the shielding surface is then the phase change energy storage surface.

[0016] Further, in step A1, the vacuum impregnation method is as follows: the porous recycled aggregate matrix is ​​evacuated to remove the internal air, the evacuated porous recycled aggregate matrix is ​​impregnated in a phase change material, and pressure is applied to load the phase change material inside the porous recycled aggregate matrix.

[0017] Furthermore, the pressure after pressurization is 0.2~1MPa, the immersion time is 20~240min, and the solid-liquid ratio during immersion is 1:1.5~4.

[0018] Furthermore, the thermally conductive coating is applied to the surface of the porous recycled aggregate matrix using directional spraying, roller coating, or magnetron sputtering techniques.

[0019] The third technical solution of the present invention is to provide Janus phase change recycled aggregate concrete for 3D printing, including the Janus phase change recycled aggregate and a cement matrix. The Janus phase change recycled aggregate is oriented at a preset tilt angle in the cement matrix, so that the concrete has different thermal conductivity coefficients in the direction parallel to its arrangement and in the direction perpendicular to its arrangement.

[0020] Furthermore, the tilt angle of the Janus phase change recycled aggregate in the concrete, measured by the angle between the axis of symmetry of its asymmetric surface structure and the thickness direction of the concrete, is 30° to 60°.

[0021] Furthermore, it comprises the following components by weight: 500-600 parts cement; 40-80 parts silica fume; 600-1000 parts of recycled fine sand; Janus phase change recycled aggregate 200~600 parts; 1-20 parts of admixture; 100-200 parts water.

[0022] Furthermore, the admixture includes a water-reducing agent and cellulose, with a mass ratio of 5 to 15:1.

[0023] Furthermore, the water-reducing agent includes one or more of polycarboxylate water-reducing agents, naphthalene-based water-reducing agents, aliphatic water-reducing agents, or aminosulfonate water-reducing agents; The cellulose includes one or more of hydroxypropyl methylcellulose, methylcellulose, hydroxyethylcellulose, or carboxymethylcellulose.

[0024] Furthermore, the cement also contains 0.1% to 2% fiber, including one or more of chopped basalt fiber, glass fiber, polypropylene fiber, or carbon fiber.

[0025] Furthermore, the cement is silicate cement.

[0026] Furthermore, the silica fume contains at least 85% SiO2 by mass and has a specific surface area of ​​15-30 m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%.

[0027] Furthermore, the fineness modulus of the recycled fine sand is 1 to 5.

[0028] The fourth technical solution of the present invention provides a method for preparing Janus phase change recycled aggregate concrete for 3D printing, comprising the following steps: B1. Janus phase change recycled aggregate is mixed with other raw materials of the concrete to make a printable cement-based slurry; B2. The cement-based slurry is extruded and printed through a 3D printing nozzle, and the layers are stacked to obtain the formed concrete. The cement-based slurry is subjected to shear force during the extrusion process, which causes the Janus phase change recycled aggregate to be oriented at a preset tilt angle. B3. Curing the formed concrete.

[0029] Furthermore, in step B2, the shear force is generated by a venturi tube structure disposed within the 3D printing nozzle, or by setting the axial direction of the 3D printing nozzle to form a preset angle with the printing plane.

[0030] Furthermore, the Venturi tube structure includes a shrinkage section with an internal shrinkage angle of 10°~25°. By utilizing the drag coupling effect between the extrusion shear flow field and the printed layer, the Janus phase change recycled aggregate is oriented at 30°~60° in the cement matrix.

[0031] Furthermore, the ratio of the moving speed of the 3D printing nozzle to the slurry extrusion speed is 0.8~1.5:1.

[0032] Furthermore, in step B2, the cement-based slurry is also subjected to a directional electric field or a directional magnetic field during the extrusion process.

[0033] Furthermore, the directional electric field is generated by setting parallel electrode plates on both sides of the 3D printing nozzle outlet, with an electric field strength of 500~2000 V / m. Polarization orientation is achieved by utilizing the difference in dielectric constant between the thermally conductive coating on the surface of the porous recycled aggregate matrix and the porous recycled aggregate matrix.

[0034] Furthermore, the directional magnetic field is generated by arranging electromagnetic coils outside the printing path, with a magnetic induction intensity of 0.1~0.5 T. The magnetic torque experienced by the magnetic filler doped in the thermally conductive coating helps to achieve a 30°~60° directional arrangement of the Janus phase change recycled aggregate within the cement matrix. Compared with the prior art, this invention has the following advantages: (1) This invention utilizes the asymmetric structure of Janus phase change recycled aggregate to integrate active energy storage and passive heat insulation into a single particle. Compared with traditional phase change recycled aggregate, it can not only reduce environmental fluctuation load through the latent heat of phase change, but also break the linear law of heat conduction through the asymmetric interface, providing a microscopic physical property basis for the macroscopic thermal rectification effect.

[0035] (2) This invention realizes the leap from "disordered pile" to "ordered array" of aggregates, transforming concrete from an isotropic material to a thermally anisotropic material, and achieving controllable guidance of heat flow. The Janus phase change recycled aggregate is subjected to the fluid shear torque generated by the non-uniform flow field in the Venturi tube, and its long axis tends to be streamlined. At the moment of extrusion, the aggregate is dragged by the interlayer slurry and embedded into the matrix along the inclined direction, thereby forming an directional angle of 30°~60°.

[0036] (3) This invention breaks the isotropic nature of heat conduction in traditional building materials by combining the asymmetric design of the microscopic Janus structure with the macroscopic directional arrangement of 3D printing. Under high-temperature conditions in summer, the outer phase change surface absorbs latent heat and, together with the high thermal conductivity surface, generates thermal resistance mismatch to prevent heat from entering the room. Under low-temperature conditions in winter, when heat is conducted to the obliquely arranged aggregate, the impact of the low thermal conductivity core and the solid phase change material generates heat flow refraction and interface scattering, effectively cutting off the thermal bridge path. This invention not only realizes the added value enhancement of waste resources, but also endows the building components with an integrated adaptive thermal management function.

[0037] (4) In this invention, the thermally conductive coating constructs a "highway" for phonon transmission through micro-sheets such as highly thermally conductive graphene, forming local channels with extremely low thermal resistance on the aggregate surface. This allows the Janus phase change recycled aggregate to conduct heat rapidly in a specific direction, thereby generating a huge thermal gradient (i.e., a huge difference in thermal conductivity) with the original porous structure on the other side. This is the physical prerequisite for realizing the thermal rectification effect (unidirectional conduction). Furthermore, the non-magnetic functional filler (such as aluminum powder) has extremely low infrared emissivity. On the one hand, it assists in heat transfer through its high thermal conductivity, and on the other hand, it plays a reflective shielding role in the process of thermal radiation penetration, further blocking thermal radiation in a specific direction and improving the coating's ability to intercept radiative heat flow.

[0038] (5) In this invention, the cement-based slurry (containing silica fume, recycled fine sand, etc.) not only serves as the structural load-bearing matrix, but also provides good encapsulation and support for Janus phase change recycled aggregate through precisely controlled rheological properties. The micro-filling effect of silica fume significantly optimizes the interface transition zone between aggregate and matrix, ensuring the continuity of heat flow when penetrating the interface and preventing unexpected thermal resistance. Fibers (such as chopped basalt fibers or polypropylene fibers) construct a three-dimensional randomized support network in the slurry. During the 3D printing process, the fibers not only suppress gravity collapse and drying shrinkage cracks after extrusion, but also play a "micro-anchoring" role, helping to lock the 30°~60° tilt angle formed by Janus phase change recycled aggregate under directional shear force, preventing angular deflection during subsequent stacking.

[0039] (6) The purpose of setting up a directional electric field or magnetic field in this invention is to provide non-contact auxiliary strain torque. The electric field is used to generate a polarization torque in a non-uniform electric field by utilizing the anisotropy of the conductivity / dielectric constant of the two sides of the Janus phase change recycled aggregate, which induces the aggregate to be precisely aligned at the moment of slurry extrusion. The directional magnetic field is used to generate a strong magnetic torque when magnetic fillers are doped in the thermally conductive coating, which overcomes the initial yield stress of the slurry and realizes remote, non-invasive, and precise control of the spatial orientation of the aggregate. The introduction of these two physical fields greatly improves the fault tolerance and automation accuracy of the 3D printing orientation process and ensures the consistency of the thermal rectification performance of large-scale printed components. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the microstructure of Janus phase change recycled aggregate in this invention; Figure 2 This is a schematic diagram of the force and flow field distribution that induces the aggregate to be oriented at 45° during the extrusion process of the 3D printing nozzle in this invention. Figure 3 This is a schematic diagram of the heat-insulating mechanism of the present invention under summer operating conditions (high outdoor temperature); Figure 4This is a schematic diagram illustrating the heat dissipation prevention mechanism of the present invention under winter operating conditions (indoor insulation); Figure 5 This is a schematic diagram of the internal distribution of Janus phase change recycled aggregate in Example 1(a) and Comparative Example 1(b).

[0041] Explanation of markings in the diagram: 1-Janus phase change recycled aggregate, 11-Porous recycled aggregate matrix, 12-Phase change material, 13-Thermal conductive shielding surface, 14-Phase change energy storage surface; 2-Cement matrix; 3-3D printing nozzle, 31-Venturi tube structure, 311-Contraction section; 4-Outdoor side; 5-Indoor side; 6-Heat flow path. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0043] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0044] In the following embodiments, the recycled coarse aggregate is purchased from a local construction waste recycling plant, and is processed by crushing, screening, washing and drying, with performance indicators conforming to GB / T 25177-2010. Standard n-eicosane liquid, CAS No. 112-95-8, purity ≥ 99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. The bisphenol A type epoxy resin, model E-51 (epoxy value 0.51), was purchased from Jiangsu Sanmu Group Co., Ltd. The modified graphene microplates, model SE1232, were purchased from Changzhou Sixth Element Materials Technology Co., Ltd.

[0045] The polyamide curing agent, model 650, was purchased from Jinling DSM Resins Co., Ltd. The silicate cement was grade P.II 52.5 cement, purchased from Conch Cement Co., Ltd. The aluminum powder, grade FLP-12, with a median particle size of 12μm, was purchased from Zibo Metal Powder Factory in Shandong. The chopped basalt fibers were 6±1mm in length and 13±2mm in diameter, and were purchased from Jiangsu Tianlong Basalt Continuous Fiber Co., Ltd. The polycarboxylate superplasticizer, model Sika Viscocrete-225P, was purchased from Jiangsu Subote New Material Co., Ltd. Hydroxypropyl methylcellulose, model RT-200000, was purchased from Shandong Ruitaigude New Material Co., Ltd. The recycled fine sand is made from construction waste concrete after crushing and screening, and the fineness modulus of the recycled fine sand is 2.6. The silica fume, model 920D, was purchased from Shanghai Elken International Trading Co., Ltd., with an average particle size of 0.1~0.15 μm and a SiO2 content of >85%.

[0046] Janus phase change recycled aggregate for 3D printing. Janus phase change recycled aggregate 1 includes a porous recycled aggregate matrix 11, wherein a phase change material 12 is loaded inside the porous recycled aggregate matrix 11. The porous recycled aggregate matrix 11 has an asymmetrical surface structure, with one side coated with a thermally conductive coating to form a thermally conductive shielding surface 13, and the other side retaining the original porous structure to serve as a phase change energy storage surface 14.

[0047] In some specific embodiments, the porous recycled aggregate matrix 11 has a particle size of 5-20 mm and an apparent density of 2300-2600 kg / m³. 3 It has a water absorption rate of 5%~10%, a porosity of 1.3%~2.9%, a pore size of 200~400 μm, and a specific surface area of ​​4.19~5.98 cm². 2 / g; The phase change material 12 is a liquid organic phase change material with a melting point between 18 and 30°C, selected from one or more of alkanes, paraffins, fatty acids, alcohols, or esters; The thermally conductive coating uses a thermally conductive material with a thermal conductivity of not less than 100 W / (m·K), and the thermally conductive material includes one or more of graphite, graphene, carbon nanotubes or boron nitride. The thickness of the thermally conductive coating is 50~80 μm.

[0048] In some specific embodiments, the phase change material 12 includes one or more of n-eicosane, paraffin, fatty acids, lauric acid, myristic acid, and glycerol.

[0049] In some specific embodiments, the latent heat of phase change of the phase change material 12 is 150–260 J / g.

[0050] In some specific embodiments, the thermally conductive coating further includes 1wt% to 20wt% of functional fillers; The functional filler includes magnetic filler and / or non-magnetic filler, wherein the magnetic filler includes nickel powder and / or ferrite; and the non-magnetic filler includes one or more of aluminum powder, copper powder, silver powder, zinc oxide, titanium dioxide, aluminum nitride, or silicon carbide. The average particle size of the functional filler is 1~50μm, and it is uniformly and discretely distributed or continuously overlapped in the thermally conductive coating.

[0051] In some specific embodiments, the phase change material 12 fills the pores of the porous recycled aggregate matrix 11.

[0052] In some specific embodiments, the thermally conductive shielding surface 13 and the phase change energy storage surface 14 are distributed in a hemispherical asymmetric shape with reference to the geometric center of the porous recycled aggregate matrix 11; There is a clear physical boundary between the thermally conductive shielding surface 13 and the phase change energy storage surface 14, and this boundary forms a closed loop on the surface of the porous recycled aggregate matrix 11. The thermally conductive shielding surface 13 continuously covers the surface of the porous recycled aggregate matrix 11, and its geometric center line is consistent with the direction of the minor axis or major axis of the porous recycled aggregate matrix 11. The surface area of ​​the thermally conductive shielding surface 13 accounts for 40% to 60% of the total surface area of ​​the porous recycled aggregate matrix 11, preferably 45% to 55%, and more preferably 50%.

[0053] A method for preparing Janus phase change recycled aggregate for 3D printing includes the following steps: A1. The phase change material 12 is loaded into the porous recycled aggregate matrix 11 by vacuum impregnation. A2. A porous recycled aggregate matrix 11 loaded with phase change material 12 is masked, and a thermally conductive material is deposited on one side of the carrier gas to form a thermally conductive coating, resulting in a thermally conductive shielding surface 13. The other side of the shielding surface is a phase change energy storage surface 14.

[0054] In some specific embodiments, in step A1, the vacuum impregnation method is as follows: the porous recycled aggregate matrix 11 is evacuated to remove the internal air, the evacuated porous recycled aggregate matrix 11 is impregnated in the phase change material 12, and pressure is applied to load the phase change material 12 inside the porous recycled aggregate matrix 11.

[0055] In some specific embodiments, the pressure after pressurization is 0.2~1MPa, the impregnation time is 20~240min, and the solid-liquid ratio of impregnation is 1:1.5~4.

[0056] Furthermore, the thermally conductive coating is applied to the surface of the porous recycled aggregate matrix 11 by directional spraying, roller coating, or magnetron sputtering technology.

[0057] A Janus phase change recycled aggregate concrete for 3D printing includes the Janus phase change recycled aggregate and a cement matrix 2. The Janus phase change recycled aggregate is oriented at a predetermined tilt angle in the cement matrix 2, such that the concrete has different thermal conductivity coefficients in the direction parallel to its arrangement and in the direction perpendicular to its arrangement.

[0058] In some specific embodiments, the tilt angle of the Janus phase change recycled aggregate 1 in the concrete, measured by the angle between the axis of symmetry of its asymmetrical surface structure and the thickness direction of the concrete, is 30° to 60°.

[0059] In some specific embodiments, the composition includes the following components by weight: 500-600 parts cement; 40-80 parts silica fume; 600-1000 parts of recycled fine sand; Janus phase change recycled aggregate 200~600 parts; 1-20 parts of admixture; 100-200 parts water.

[0060] In some specific embodiments, the admixture includes a water-reducing agent and cellulose, with a mass ratio of 5 to 15:1.

[0061] In some specific embodiments, the water-reducing agent includes one or more of polycarboxylate water-reducing agents, naphthalene-based water-reducing agents, aliphatic water-reducing agents, or aminosulfonate water-reducing agents; The cellulose includes one or more of hydroxypropyl methylcellulose, methylcellulose, hydroxyethylcellulose, or carboxymethylcellulose.

[0062] In some specific embodiments, the cement also contains 0.1% to 2% fiber, including one or more of chopped basalt fiber, glass fiber, polypropylene fiber, or carbon fiber.

[0063] In some specific embodiments, the cement is silicate cement.

[0064] In some specific embodiments, the silica fume contains a SiO2 mass fraction of not less than 85% and a specific surface area of ​​15~30m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%.

[0065] In some specific embodiments, the fineness modulus of the recycled fine sand is 1 to 5.

[0066] A method for preparing Janus phase change recycled aggregate concrete for 3D printing includes the following steps: B1. Janus phase change recycled aggregate is mixed with other raw materials of the concrete to make a printable cement-based slurry; B2. The cement-based slurry is extruded and printed through a 3D printing nozzle 3, and the layers are stacked to obtain the formed concrete. The cement-based slurry is subjected to shear force during the extrusion process, which causes the Janus phase change recycled aggregate to be oriented at a preset tilt angle. B3. Curing the formed concrete.

[0067] In some specific embodiments, in step B2, the shear force is generated by the venturi tube structure 31 disposed in the 3D printing nozzle, or by setting the axial direction of the 3D printing nozzle 3 to form a preset angle with the printing plane.

[0068] In some specific embodiments, the Venturi tube structure 31 includes a shrinkage section 311 with an internal shrinkage angle of 10° to 25°. By utilizing the drag coupling effect between the extrusion shear flow field and the printing layer, the Janus phase change recycled aggregate is oriented at 30° to 60° in the cement matrix 2.

[0069] In some specific embodiments, the ratio of the moving speed of the 3D printing nozzle to the slurry extrusion speed is 0.8 to 1.5:1.

[0070] In some specific embodiments, in step B2, the cement-based slurry is also subjected to a directional electric field or a directional magnetic field during the extrusion process.

[0071] In some specific embodiments, the directional electric field is generated by setting parallel electrode plates on both sides of the 3D printing nozzle outlet, with an electric field strength of 500~2000 V / m. Polarization orientation is achieved by utilizing the difference in dielectric constant between the thermally conductive coating on the surface of the porous recycled aggregate matrix 11 and the porous recycled aggregate matrix 11.

[0072] In some specific embodiments, the directional magnetic field is generated by arranging electromagnetic coils outside the printing path, with a magnetic induction intensity of 0.1~0.5 T. The magnetic torque experienced by the magnetic filler doped in the thermally conductive coating helps to achieve a 30°~60° directional arrangement of the Janus phase change recycled aggregate in the cement matrix 2. Compared with the prior art, the present invention has the following advantages: Each of the above embodiments can be implemented individually or in any combination of two or more.

[0073] The following description uses specific examples to illustrate the point.

[0074] Example 1 This embodiment relates to a method for preparing Janus phase change recycled aggregate concrete for 3D printing, including the following steps: (1) Preparation of Janus phase change recycled aggregate Select particles with a diameter of 5-20 mm and an apparent density of 2420 kg / m³. 3 It has a water absorption rate of 6.5%, a porosity of 1.8%, a pore size of 300 μm, and a specific surface area of ​​4.51 cm². 2 / g of recycled coarse aggregate was used as the porous recycled aggregate matrix 11. It was placed in a vacuum pressure vessel, evacuated to -0.095MPa and maintained for 45 minutes to completely remove air from the internal interconnected micropores. Then, a phase change material 12 was added, immersing the porous recycled aggregate matrix 11 in the phase change material 12. The phase change material 12 was n-eicosane liquid with a melting point of 26℃ and a latent heat of phase change of 185J / g. The solid-liquid ratio during immersion was 1:1.8. The pressure was increased to 0.6MPa and maintained for 1 hour, allowing the phase change material 12 to fill the internal pores of the porous recycled aggregate matrix 11.

[0075] A porous recycled aggregate matrix 11 loaded with phase change material 12 is subjected to surface masking treatment, which is achieved by physical masking: the aggregate loaded with phase change material 12 is densely laid in a fixed mold, so that the upper half of the aggregate is exposed and the lower half is embedded in an elastic silicone mask layer; the mask depth is controlled at 1 / 2 of the equivalent diameter of the aggregate, ensuring that the exposed spraying area accounts for 50%±5% of the total area of ​​the aggregate; after the spraying is completed and the coating is cured, the aggregate is separated from the mask layer by vibration demolding, thereby obtaining recycled aggregate with a clear Janus interface.

[0076] A thermally conductive slurry is directionally sprayed onto a semi-surface, so that one side of the porous recycled aggregate matrix 11 is coated with a thermally conductive coating with a thickness of 60 μm to form a thermally conductive shielding surface 13; the other side of the porous recycled aggregate matrix 11 retains its original porous structure to serve as a phase change energy storage surface 14. The thermally conductive slurry comprises the following components by mass percentage: 100 parts bisphenol A type epoxy resin, 8 parts modified graphene microsheets, and 15 parts polyamide curing agent.

[0077] like Figure 1As shown, the Janus phase change recycled aggregate includes a porous recycled aggregate matrix 11, and a phase change material 12 is loaded inside the porous recycled aggregate matrix 11. The surface of the porous recycled aggregate matrix 11 has an asymmetrical surface structure, one side of which is covered with a thermally conductive coating to form a thermally conductive shielding surface 13, and the other side retains the original porous structure to serve as a phase change energy storage surface 14. The thermally conductive shielding surface 13 and the phase change energy storage surface 14 are asymmetrically distributed in a hemispherical shape with the geometric center of the porous recycled aggregate matrix 11 as the reference. There is a clear physical boundary line between the thermally conductive shielding surface 13 and the phase change energy storage surface 14, which forms a closed loop on the surface of the porous recycled aggregate matrix 11. The thermally conductive shielding surface 13 continuously covers the surface of the porous recycled aggregate matrix 11, and its geometric center line is consistent with the direction of the minor axis or major axis of the porous recycled aggregate matrix 11. The surface area of ​​the thermally conductive shielding surface 13 accounts for 50% ± 5% of the total surface area of ​​the porous recycled aggregate matrix 11.

[0078] (2) Preparation of cement-based slurry Weigh the following parts by weight of raw materials. 550 parts cement; 65 parts silica fume; 800 parts of recycled fine sand; Janus Phase Change Regenerated Aggregate 400 parts; 5.5 parts of polycarboxylate superplasticizer; 0.6 parts of hydroxypropyl methylcellulose; 165 portions of water.

[0079] In this embodiment, the cement used is ordinary Portland cement; The silica fume contains no less than 85% SiO2 by mass and has a specific surface area of ​​15-30 m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%; The fineness modulus of the recycled fine sand is 2.6.

[0080] Mix the above raw materials to prepare a printable cement-based slurry. A dry-then-wet mixing process is used: first, dry mix cement, silica fume, and recycled fine sand for 2.5 minutes until homogeneous; then, add premixed polycarboxylate superplasticizer, hydroxypropyl methylcellulose, and water, and continue mixing for 4 minutes; finally, add Janus phase change recycled aggregate and slowly mix for 1.5 minutes to prevent the aggregate surface coating from peeling off due to mechanical impact. The dry mixing speed is controlled at 80 rpm; the high-intensity mixing speed after adding the liquid is 200 rpm; and the mixing speed after adding Janus aggregate is controlled at 40 rpm.

[0081] (3) Preparation of Janus phase change recycled aggregate concrete The cement-based slurry is extruded and printed layer by layer through a 3D printing nozzle 3 with a Venturi tube structure 31 to obtain shaped concrete. The extrusion pump speed is set to 47.5 rpm, and the height of the print head along the Z-axis is set to 10 mm after each layer is printed. During extrusion, the cement-based slurry is subjected to shear force, causing the Janus phase change recycled aggregate to be oriented at a preset tilt angle of 45°±3° (measured by the angle between the axis of symmetry of its asymmetric surface structure and the thickness direction of the concrete), ensuring that the phase change energy storage surface uniformly faces the outdoor side 4 and the thermally conductive shielding surface 13 uniformly faces the indoor side 5. The Venturi tube structure 31 includes a contraction section 311 with an internal contraction angle of 12°. The 3D printing nozzle 3 is set to move at a speed of 120 mm / s and the extrusion pressure is 0.8 MPa.

[0082] like Figure 2 As shown, the Janus phase change recycled aggregate concrete includes a cement matrix 2, in which the Janus phase change recycled aggregate is oriented at a preset tilt angle of 45°±3°, so that the concrete has different thermal conductivity coefficients in the direction parallel to its arrangement and in the direction perpendicular to its arrangement.

[0083] (4) Curing of Janus phase change recycled aggregate concrete The molded concrete was then cured. The 3D-printed concrete was allowed to stand at room temperature (20±5℃) for 24 hours to allow initial setting, and then demolded after 48 hours. It was then transferred to a standard curing chamber and cured for 28 days at a temperature of 20±2℃ and a relative humidity of over 95%. During curing, a thin film was covered or water mist was sprayed onto the concrete surface to prevent rapid moisture loss, thus fully utilizing the secondary pozzolanic reaction of silica fume to strengthen the interfacial bond between the Janus phase change recycled aggregate 1 and the porous recycled aggregate matrix 11.

[0084] (5) Performance testing of Janus phase change recycled aggregate concrete The compressive strength and thermal rectification coefficient of the Janus phase change recycled aggregate concrete were tested.

[0085] The compressive strength test was conducted according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The specific steps were as follows: Concrete cured for 28 days was cut / processed into 100 × 100 × 100 mm cube specimens; the specimens were placed under a compression testing machine and continuously and uniformly loaded at a loading rate of 0.5~0.8 MPa / s until the specimen failed; the failure load was recorded, and the 28-day compressive strength was calculated. Actual measurements showed that, due to the directional arrangement of Janus phase change recycled aggregate 1 and the interface strengthening effect of silica fume, its 28-day compressive strength reached 51.2 MPa.

[0086] The test procedure for the thermal rectification coefficient is as follows: the equivalent thermal resistance of the component under forward and reverse temperature differences is determined using a dual-sample steady-state thermal method. The specific steps are as follows: Forward heat transfer (simulating summer, Figure 3): 3D-printed Janus concrete was placed between heat and cold control chambers as a wall specimen (300×300×30mm), so that the outdoor side 4 was in a high-temperature environment (T). h = 40°C), the indoor side 5 is in a constant temperature environment (T c = 25°C). Data acquisition: After the heat flow stabilizes, the unit heat flow Q1 penetrating the specimen is measured using a heat flow sensor, and the equivalent thermal conductivity λ under summer conditions is calculated. summer At this point, heat transfer is inhibited due to the obstruction of the heat-conducting shielding surface of Janus phase change recycled aggregate 1 and the heat absorption effect of phase change.

[0087] Reverse heat transfer (simulating winter), Figure 4 ( ) Reverse the temperature field direction so that the temperature on the indoor side 5 is higher than that on the outdoor side 4, simulating the condition of heat loss from indoor heating. Data acquisition: Measure the heat flow Q2 at this time and calculate the equivalent thermal conductivity λ under winter conditions. winter Due to the asymmetric structure of Janus phase change recycled aggregate, it exhibits different refractive and conductive properties under reverse heat flow, resulting in varying heat transfer efficiencies.

[0088] TR calculation: Thermal rectification coefficient TR = λ winter / λ summer As shown in Table 1, the TR value of the component of this invention is 1.38, indicating that it has significant unidirectional thermal conductivity regulation capability. Figure 3 and 4 As shown, Figure 3When the external environment is high, heat is transferred from the outdoor side 4 to the indoor side 5 along the heat flow path 6. Due to the directional and inclined arrangement of Janus phase change recycled aggregate 1, the heat flow first comes into contact with the phase change energy storage surface 14 on the outer side, and the phase change material melts and absorbs a large amount of latent heat; at the same time, the inner thermally conductive shielding surface 13 constructs a high thermal resistance barrier, forcibly changing the direction of the heat flow line, causing it to refract and attenuate significantly, effectively blocking external heat from entering the room. Figure 4 When indoor heating heat attempts to escape through the walls, the heat flow path 6 reverses direction. At this time, due to the long-axis orientation and asymmetric interface distribution of the Janus phase change recycled aggregate 1, the scattering effect of the heat flow is weakened when passing through the directional array, exhibiting thermal resistance characteristics different from those in summer. Through this asymmetric arrangement, the component achieves both active and passive energy-saving regulation of indoor and outdoor heat exchange. Compared to conventional recycled concrete, the Janus phase change recycled concrete prepared by this invention, while maintaining a mechanical strength increase of over 25%, endows the component with significant thermal rectification characteristics (TR=1.38). Under summer conditions, its indoor insulation effect is improved by approximately 30%, and the peak temperature delay time is increased by more than 2 hours, effectively breaking through the technical limitations of traditional recycled concrete's single thermal resistance and passive regulation, resulting in excellent energy-saving and emission-reduction benefits.

[0089] Example 2 This embodiment relates to a method for preparing Janus phase change recycled aggregate concrete for 3D printing, including the following steps: (1) Preparation of Janus phase change recycled aggregate Select particles with a diameter of 5-15 mm and an apparent density of 2420 kg / m³. 3 It has a water absorption rate of 6.5%, a porosity of 2.0%, a pore size of 350 μm, and a specific surface area of ​​4.85 cm². 2 / g of recycled coarse aggregate was used as the porous recycled aggregate matrix 11. It was placed in a vacuum pressure vessel, evacuated to -0.095MPa and maintained for 45 minutes to completely remove air from the internal interconnected micropores. Then, a phase change material 12 was added, immersing the porous recycled aggregate matrix 11 in the phase change material 12. The phase change material 12 was n-eicosane liquid with a melting point of 18℃ and a latent heat of phase change of 230J / g. The solid-liquid ratio during immersion was 1:2.2. The pressure was increased to 0.6MPa and maintained for 1 hour, allowing the phase change material 12 to fill the internal pores of the porous recycled aggregate matrix 11.

[0090] A porous recycled aggregate substrate 11 loaded with phase change material 12 undergoes surface masking treatment, which is achieved through a physical masking method: the aggregate loaded with phase change material 12 is densely laid in a fixed mold, exposing the upper half of the aggregate and embedding the lower half of the aggregate in an elastic silicone mask layer; the mask depth is controlled at 1 / 2 of the equivalent diameter of the aggregate, ensuring that the exposed sprayed area accounts for 50% ± 5% of the total area of ​​the aggregate; after spraying, the coating is allowed to cure, and the aggregate is separated from the mask layer by vibration demolding, thereby obtaining recycled aggregate with a clear Janus interface. A thermally conductive slurry is directionally sprayed onto the half-surface, so that one side of the porous recycled aggregate substrate 11 is covered with a thermally conductive coating with a thickness of 100 μm to form a thermally conductive shielding surface 13; the other side of the porous recycled aggregate substrate 11 retains the original porous structure to serve as a phase change energy storage surface 14. The thermally conductive slurry comprises the following components by weight: 100 parts bisphenol A epoxy resin, 8 parts modified graphene microsheets, 15 parts polyamide curing agent, and 6.5 parts aluminum powder. Aluminum powder is added to the thermally conductive shielding layer slurry to improve infrared reflectivity.

[0091] (2) Preparation of cement-based slurry Weigh the following parts by weight of raw materials. 550 parts cement; 65 parts silica fume; 800 parts of recycled fine sand; Janus Phase Change Regenerated Aggregate 400 parts; 5.5 parts of polycarboxylate superplasticizer; 0.6 parts of hydroxypropyl methylcellulose; 165 portions of water.

[0092] In this embodiment, the cement used is ordinary Portland cement; The silica fume contains no less than 85% SiO2 by mass and has a specific surface area of ​​15-30 m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%; The fineness modulus of the recycled fine sand is 2.6.

[0093] Mix the above raw materials to prepare a printable cement-based slurry. A dry-then-wet mixing process is used: first, dry mix cement, silica fume, and recycled fine sand for 2.5 minutes until homogeneous; then, add premixed polycarboxylate superplasticizer, hydroxypropyl methylcellulose, and water, and continue mixing for 4 minutes; finally, add Janus phase change recycled aggregate and slowly mix for 1.5 minutes to prevent the aggregate surface coating from peeling off due to mechanical impact. The dry mixing speed is controlled at 80 rpm; the high-intensity mixing speed after adding the liquid is 200 rpm; and the mixing speed after adding Janus aggregate is controlled at 40 rpm.

[0094] (3) Preparation of Janus phase change recycled aggregate concrete The cement-based slurry is extruded and printed layer by layer through a 3D printing nozzle 3 with a Venturi tube structure 31 to obtain shaped concrete. The extrusion pump speed is set to 55 rpm, and the height of the print head along the Z-axis is set to 11 mm after each layer is printed. During extrusion, the cement-based slurry is subjected to shear force, causing the Janus phase change recycled aggregate to be oriented at a preset tilt angle of 50°±3°, ensuring that the phase change energy storage surface uniformly faces the outdoor side 4 and the thermally conductive shielding surface 13 uniformly faces the indoor side 5. The Venturi tube structure 31 includes a contraction section 311 with an internal contraction angle of 15°. The 3D printing nozzle 3 is set to a moving speed of 130 mm / s and an extrusion pressure of 1.0 MPa.

[0095] (4) Curing of Janus phase change recycled aggregate concrete The molded concrete was then cured. The 3D-printed concrete was allowed to set for 24 hours at room temperature (20±5℃), and demolded after 48 hours. It was then transferred to a standard curing chamber and cured for 28 days at a temperature of 20±2℃ and a relative humidity of over 95%. During curing, moisture was prevented from escaping rapidly by covering the surface of the component with a thin film or spraying water mist, thus fully utilizing the secondary pozzolanic reaction of silica fume to strengthen the interfacial bond between the Janus phase change recycled aggregate 1 and the porous recycled aggregate matrix 11.

[0096] (5) Performance testing of Janus phase change recycled aggregate concrete As shown in Table 1, the Janus phase change recycled aggregate concrete, tested using a dual-plate thermal conductivity meter, exhibited an equivalent thermal conductivity of 0.62 W / (m·K) under simulated summer conditions (heat flow direction from outside to inside), resulting in a thermal rectification ratio of 1.49 compared to conventional recycled concrete. In a comparative experiment simulating winter conditions, under the same heating conditions, the rate of indoor temperature loss from the concrete was reduced by 32% compared to conventional recycled concrete.

[0097] Example 3 This embodiment relates to a method for preparing Janus phase change recycled aggregate concrete for 3D printing, including the following steps: (1) Preparation of Janus phase change recycled aggregate Select particles with a diameter of 5-20 mm and an apparent density of 2560 kg / m³. 3 It has a water absorption rate of 2.5%, a porosity of 1.5%, a pore size of 400 μm, and a specific surface area of ​​5.20 cm². 2 / g of recycled coarse aggregate was used as the porous recycled aggregate matrix 11. It was placed in a vacuum pressure vessel, evacuated to -0.095MPa and maintained for 45 minutes to completely remove air from the internal interconnected micropores. Then, a phase change material 12 was added, immersing the porous recycled aggregate matrix 11 in the phase change material 12. The phase change material 12 was n-eicosane liquid with a melting point of 26℃ and a latent heat of phase change of 185J / g. The solid-liquid ratio during immersion was 1:3.0. The pressure was increased to 0.6MPa and maintained for 1 hour, allowing the phase change material 12 to fill the internal pores of the porous recycled aggregate matrix 11.

[0098] A porous recycled aggregate substrate 11 loaded with phase change material 12 undergoes surface masking treatment, which is achieved through a physical masking method: the aggregate loaded with phase change material 12 is densely laid in a fixed mold, exposing the upper half of the aggregate and embedding the lower half of the aggregate in an elastic silicone mask layer; the mask depth is controlled at 1 / 2 of the equivalent diameter of the aggregate, ensuring that the exposed sprayed area accounts for 50% ± 5% of the total area of ​​the aggregate; after spraying, the coating is allowed to cure, and the aggregate is separated from the mask layer by vibration demolding, thereby obtaining recycled aggregate with a clear Janus interface. A thermally conductive slurry is directionally sprayed onto the half-surface, so that one side of the porous recycled aggregate substrate 11 is covered with a thermally conductive coating with a thickness of 60 μm to form a thermally conductive shielding surface 13; the other side of the porous recycled aggregate substrate 11 retains the original porous structure to serve as a phase change energy storage surface 14. The thermally conductive slurry comprises the following components by mass percentage: 100 parts of bisphenol A epoxy resin, 8 parts of modified graphene microsheets, and 15 parts of polyamide curing agent.

[0099] (2) Preparation of cement-based slurry Weigh the following parts by weight of raw materials. 550 parts cement; 65 parts silica fume; 800 parts of recycled fine sand; Janus Phase Change Regenerated Aggregate 400 parts; 5.5 parts of polycarboxylate superplasticizer; 0.6 parts of hydroxypropyl methylcellulose; 165 portions of water.

[0100] In this embodiment, the cement used is P.II52.5 grade cement, and 0.6% of short-cut basalt fibers (12mm in length) are added to it to improve interlayer toughness; The silica fume contains no less than 85% SiO2 by mass and has a specific surface area of ​​15-30 m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%; The fineness modulus of the recycled fine sand is 2.6.

[0101] Mix the above raw materials to prepare a printable cement-based slurry. A dry-then-wet mixing process is used: first, dry mix cement, silica fume, and recycled fine sand for 2.5 minutes until homogeneous; then, add premixed polycarboxylate superplasticizer, hydroxypropyl methylcellulose, and water, and continue mixing for 4 minutes; finally, add Janus phase change recycled aggregate and slowly mix for 1.5 minutes to prevent the aggregate surface coating from peeling off due to mechanical impact. The dry mixing speed is controlled at 80 rpm; the high-intensity mixing speed after adding the liquid is 200 rpm; and the mixing speed after adding Janus aggregate is controlled at 40 rpm.

[0102] (3) Preparation of Janus phase change recycled aggregate concrete The cement-based slurry is extruded and printed layer by layer through a 3D printing nozzle 3 with a Venturi tube structure 31 to obtain shaped concrete. The extrusion pump speed is set to 65 rpm, and the height of the print head along the Z-axis is set to 9 mm after each layer is printed. During extrusion, the cement-based slurry is subjected to shear force, causing the Janus phase change recycled aggregate to be oriented at a preset tilt angle of 45°±3°, ensuring that the phase change energy storage surface uniformly faces the outdoor side 4 and the thermally conductive shielding surface 13 uniformly faces the indoor side 5. The Venturi tube structure 31 includes a contraction section 311 with an internal contraction angle of 12°. The 3D printing nozzle 3 is set to a moving speed of 110 mm / s and an extrusion pressure of 1.1 MPa.

[0103] (4) Curing of Janus phase change recycled aggregate concrete The molded concrete was then cured. The 3D-printed concrete was allowed to set for 24 hours at room temperature (20±5℃), and demolded after 48 hours. It was then transferred to a standard curing chamber and cured for 28 days at a temperature of 20±2℃ and a relative humidity of over 95%. During curing, a thin film was covered or water mist was sprayed onto the surface of the component to prevent rapid moisture loss, thus maximizing the secondary pozzolanic reaction of the silica fume and strengthening the interfacial bond between the Janus aggregate and the matrix.

[0104] (5) Performance testing of Janus phase change recycled aggregate concrete As shown in Table 1, after 28 days of standard curing, the compressive strength of the concrete reached 55.6 MPa, meeting the structural strength requirements of the exterior wall of high-rise buildings. While bearing this load, its thermal conductivity (TR) remained stable at 1.3, achieving synergy between structural load-bearing capacity and directional heat management. Compared with conventionally randomly arranged recycled concrete, this invention slowed the indoor temperature rise rate by more than 30% under summer conditions, and reduced the peak temperature by 5.2℃, achieving synergistic optimization of structural load-bearing capacity and directional heat management.

[0105] Example 4 This embodiment relates to a method for preparing Janus phase change recycled aggregate concrete for 3D printing using directional electric field-assisted arrangement. The specific steps are as follows: (1) Preparation of Janus phase change recycled aggregate Select particles with a diameter of 5-20 mm and an apparent density of 2520 kg / m³. 3 It has a water absorption rate of 2.8%, a porosity of 2%, a pore size of 260 μm, and a specific surface area of ​​4.90 cm². 2 / g of recycled coarse aggregate was used as the porous recycled aggregate matrix 11. It was placed in a vacuum pressure vessel, evacuated to -0.095MPa and maintained for 45 minutes to completely remove air from the internal interconnected micropores. Then, a phase change material 12 was added, immersing the porous recycled aggregate matrix 11 in the phase change material 12. The phase change material 12 was n-eicosane liquid with a melting point of 26℃ and a latent heat of phase change of 185J / g. The solid-liquid ratio during immersion was 1:2.5. The pressure was increased to 0.6MPa and maintained for 1 hour, allowing the phase change material 12 to fill the internal pores of the porous recycled aggregate matrix 11.

[0106] A porous recycled aggregate substrate 11 loaded with phase change material 12 undergoes surface masking treatment, which is achieved through a physical masking method: the aggregate loaded with phase change material 12 is densely laid in a fixed mold, exposing the upper half of the aggregate and embedding the lower half of the aggregate in an elastic silicone mask layer; the mask depth is controlled at 1 / 2 of the equivalent diameter of the aggregate, ensuring that the exposed sprayed area accounts for 50% ± 5% of the total area of ​​the aggregate; after spraying, the coating is allowed to cure, and the aggregate is separated from the mask layer by vibration demolding, thereby obtaining recycled aggregate with a clear Janus interface. A thermally conductive slurry is directionally sprayed onto the half-surface, so that one side of the porous recycled aggregate substrate 11 is covered with a thermally conductive coating with a thickness of 60 μm to form a thermally conductive shielding surface 13; the other side of the porous recycled aggregate substrate 11 retains the original porous structure to serve as a phase change energy storage surface 14. The thermally conductive slurry comprises the following components by mass percentage: 100 parts of bisphenol A epoxy resin, 8 parts of modified graphene microsheets, 15 parts of polyamide curing agent, and 6.5 parts of aluminum powder.

[0107] (2) Preparation of cement-based slurry Weigh the following parts by weight of raw materials. 550 parts cement; 65 parts silica fume; 800 parts of recycled fine sand; Janus Phase Change Regenerated Aggregate 400 parts; 5.5 parts of polycarboxylate superplasticizer; 0.6 parts of hydroxypropyl methylcellulose; 165 portions of water.

[0108] In this embodiment, the cement used is P.II52.5 grade cement, and 0.6% of short-cut basalt fibers (12mm in length) are added to it to improve interlayer toughness; The silica fume contains no less than 85% SiO2 by mass and has a specific surface area of ​​15-30 m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%; The fineness modulus of the recycled fine sand is 2.6.

[0109] Mix the above raw materials to make a printable cement-based slurry. The mixing process of dry mixing followed by wet mixing is adopted: first, dry mix cement, silica fume and recycled fine sand for 2.5 min until uniform; then add polycarboxylate superplasticizer, hydroxypropyl methylcellulose and water after premixing, and continue mixing for 4 min; finally add Janus phase change recycled aggregate and mix slowly for 1.5 min to prevent the coating on the surface of the aggregate from peeling off due to mechanical impact. The dry mixing speed is controlled at 80 rpm; the strong mixing speed after adding liquid is 200 rpm; the mixing speed after adding Janus aggregate is controlled at 40 rpm. (3) Preparation of Janus phase change recycled aggregate concrete A 3D printing nozzle with a Venturi tube structure 31 is used. A pair of insulated electrode plates are installed parallel to each other at the nozzle exit and connected to a DC high-voltage power supply to generate a directional electric field. The extrusion pump speed is set to 65 rpm, and the print head lift height along the Z-axis is set to 9 mm after each layer is printed. The print head moving speed is set to 120 mm / s, the extrusion pressure is 1.0 MPa, and a uniform directional electric field with an intensity of 1200 V / m is applied. Janus phase change recycled aggregate 1 undergoes initial rotation due to the shear force of the flow field when passing through the Venturi tube; at the moment of exiting the nozzle, the difference in polarization stress on both sides of the aggregate (the thermally conductive coating side and the original aggregate side) in the 1200 V / m electric field generates an electric torque, which helps the aggregate to be precisely locked at an inclined position of 45±2° with respect to the horizontal direction.

[0110] (4) Curing of Janus phase change recycled aggregate concrete The molded concrete was then cured. The 3D-printed concrete was allowed to stand at room temperature (20±5℃) for 24 hours for initial setting, and then demolded after 48 hours. It was then transferred to a standard curing chamber and cured for 28 days at a temperature of 20±2℃ and a relative humidity of over 95%. During curing, a thin film was covered or water mist was sprayed onto the surface of the component to prevent rapid moisture loss, thus fully utilizing the secondary pozzolanic reaction of silica fume to strengthen the interfacial bond between the Janus phase change recycled aggregate 1 and the porous recycled aggregate matrix 11.

[0111] (5) Performance testing of Janus phase change recycled aggregate concrete As shown in Table 1, according to GB / T 50081 standard, with a loading rate of 0.6 MPa / s, the 28-day compressive strength reached 50.6 MPa, which is approximately 45.5% higher than that of conventional randomly distributed recycled concrete. The steady-state heat flow meter method with two specimens was used. The measured equivalent thermal conductivity (TR) of the specimens in summer (forward direction) was significantly lower than that in winter (reverse direction), with a TR of 1.32. In the simulated high-temperature summer experiment, compared with conventional recycled concrete, the peak indoor temperature of the concrete in this embodiment was reduced by 5.8°C, and the overall thermal insulation efficiency was improved by 30.2%, successfully achieving the integration of structural load-bearing and unidirectional thermal regulation.

[0112] Example 5 (1) Preparation of Janus phase change recycled aggregate Select particles with a diameter of 5-20 mm and an apparent density of 2460 kg / m³. 3 It has a water absorption rate of 2.2%, a porosity of 2.1%, a pore size of 250 μm, and a specific surface area of ​​5.85 cm². 2 / g of recycled coarse aggregate was used as the porous recycled aggregate matrix 11. It was placed in a vacuum pressure vessel, evacuated to -0.095MPa and maintained for 45 minutes to completely remove air from the internal interconnected micropores. Then, a phase change material 12 was added, immersing the porous recycled aggregate matrix 11 in the phase change material 12. The phase change material 12 was n-eicosane liquid with a melting point of 26℃ and a latent heat of phase change of 185J / g. The solid-liquid ratio during immersion was 1:2.9. The pressure was increased to 0.6MPa and maintained for 1 hour, allowing the phase change material 12 to fill the internal pores of the porous recycled aggregate matrix 11.

[0113] A porous recycled aggregate substrate 11 loaded with phase change material 12 undergoes surface masking treatment, which is achieved through a physical masking method: the aggregate loaded with phase change material 12 is densely laid in a fixed mold, exposing the upper half of the aggregate and embedding the lower half of the aggregate in an elastic silicone mask layer; the mask depth is controlled at 1 / 2 of the equivalent diameter of the aggregate, ensuring that the exposed sprayed area accounts for 50% ± 5% of the total area of ​​the aggregate; after spraying, the coating is allowed to cure, and the aggregate is separated from the mask layer by vibration demolding, thereby obtaining recycled aggregate with a clear Janus interface. A thermally conductive slurry is directionally sprayed onto the half-surface, so that one side of the porous recycled aggregate substrate 11 is covered with a thermally conductive coating with a thickness of 60 μm to form a thermally conductive shielding surface 13; the other side of the porous recycled aggregate substrate 11 retains the original porous structure to serve as a phase change energy storage surface 14. The thermally conductive slurry comprises the following components by weight: 100 parts bisphenol A epoxy resin, 8 parts doped modified graphene microsheets, 15 parts polyamide curing agent, and 6.5 parts aluminum powder. In the doped modified graphene microsheets, an additional 10 wt% of micron-sized nickel powder (average particle size 3 μm) is added. The addition of nickel powder imparts high magnetic permeability to the slurry, while the 6.5 parts of aluminum powder synergistically enhance its heat reflection performance.

[0114] (2) Preparation of cement-based slurry Weigh the following parts by weight of raw materials. 550 parts cement; 65 parts silica fume; 800 parts of recycled fine sand; Janus Phase Change Regenerated Aggregate 400 parts; 5.5 parts of polycarboxylate superplasticizer; 0.6 parts of hydroxypropyl methylcellulose; 165 portions of water.

[0115] In this embodiment, the cement used is P.II52.5 grade cement, and 0.6% of short-cut basalt fibers (12mm in length) are added to it to improve interlayer toughness; The silica fume contains no less than 85% SiO2 by mass and has a specific surface area of ​​15-30 m². 2 / g, with an average particle size of <1μm and a bulk density of 500~700 kg / m³. 3 Moisture content ≤ 3%, loss on ignition ≤ 4%; The fineness modulus of the recycled fine sand is 2.6.

[0116] Mix the above raw materials to make a printable cement-based slurry. The mixing process of dry mixing followed by wet mixing is adopted: first, dry mix cement, silica fume and recycled fine sand for 2.5 min until uniform; then add polycarboxylate superplasticizer, hydroxypropyl methylcellulose and water after premixing, and continue mixing for 4 min; finally add Janus phase change recycled aggregate and mix slowly for 1.5 min to prevent the coating on the surface of the aggregate from peeling off due to mechanical impact. The dry mixing speed is controlled at 80 rpm; the strong mixing speed after adding liquid is 200 rpm; the mixing speed after adding Janus aggregate is controlled at 40 rpm. (3) Preparation of Janus phase change recycled aggregate concrete A set of annular electromagnetic induction coils is installed around the venturi tube 31 at the exit of the 3D printing nozzle 3. The extrusion pump speed is set to 65 rpm, and the print head's Z-axis lift height is set to 9 mm after each layer is printed. The print head moving speed is set to 130 mm / s, and the extrusion pressure is 0.9 MPa. The coils are activated, generating a constant directional magnetic field of 0.3 T in the nozzle exit area, with the magnetic field lines forming a 45° angle with the printing direction. The aggregate undergoes initial rotation due to fluid shear force as it passes through the venturi tube's contraction section; subsequently, it enters the 0.3 T magnetic field region. Because the Janus phase change regenerated aggregate 1 contains a magnetic nickel powder coating on one side, it generates a significant magnetic torque in the magnetic field, forcibly correcting any residual misalignment and aligning the long axis of the Janus phase change regenerated aggregate 1 with the magnetic field lines.

[0117] (4) Curing of Janus phase change recycled aggregate concrete The molded concrete was then cured. The 3D-printed concrete was allowed to set for 24 hours at room temperature (20±5℃), and demolded after 48 hours. It was then transferred to a standard curing chamber and cured for 28 days at a temperature of 20±2℃ and a relative humidity of over 95%. During curing, a thin film was covered or water mist was sprayed onto the surface of the component to prevent rapid moisture loss, thus fully utilizing the secondary pozzolanic reaction of silica fume to strengthen the interfacial bond between the Janus phase change recycled aggregate 1 and the porous recycled aggregate matrix 11.

[0118] (5) Performance testing of Janus phase change recycled aggregate concrete As shown in Table 1, according to GB / T 50081 standard, with a loading rate of 0.6 MPa / s, the 28-day compressive strength reached 56.2 MPa. The introduction of nickel powder and graphene enhanced the coating stiffness, and the oriented arrangement formed an effective mechanical support structure. Due to the extremely regular arrangement, its TR increased to 1.42. In simulated summer conditions, compared with conventional randomly arranged recycled concrete, the indoor peak temperature decreased by 6.1℃, and the overall thermal insulation performance improved by 32.5%.

[0119] Comparative Example 1 Compared with Example 1, most of them are the same, except that in step (3) the molding method of Janus phase change recycled aggregate concrete is changed to traditional casting: the cement-based slurry is fully mixed and then directly poured into the mold, and vibrated on a vibrating table with a frequency of 50Hz for 40s.

[0120] Due to the lack of an internal directional shear flow field within the 3D printing nozzle 3, after the concrete curing period, a diamond cutter was used to longitudinally cut along the printing path to obtain cross-sectional samples. After rough grinding, fine grinding, and drying, the samples were placed under an industrial high-magnification scanner to obtain high-resolution images of the cross-section. ImageJ image analysis software was used to statistically analyze the long axis orientation of at least 100 Janus phase change recycled aggregates 1 within the cross-section. The results showed that in the control group without a directional shear flow field, the aggregate orientation was randomly distributed within the range of 0° to 180°. Figure 5 As shown; in Embodiment 1 of the present invention, the angle between the long axis of the aggregate and the horizontal plane is similar, thereby confirming the effectiveness of the flow field orientation from the microstructure perspective.

[0121] As shown in Table 1, the difference in thermal conductivity between the positive and negative directions was only 2.1%, with a TR of approximately 1.02. This is essentially consistent with the thermal rectification effect of conventional recycled concrete (TR≈1.0), indicating almost no unidirectional thermal conductivity. This demonstrates that simply adding Janus phase change recycled aggregate 11 without achieving directional arrangement cannot produce a thermal rectification effect. However, in terms of mechanical strength, since the comparative sample still contains silica fume and fibers, its compressive strength (approximately 41 MPa), while slightly higher than conventional recycled concrete, is far lower than the strength after directional arrangement in this invention (51.2 MPa). This result confirms that the shear flow field constructed through 3D printing directional extrusion is key to achieving a macroscopic thermal rectification effect.

[0122] Comparative analysis of Example 1 and Comparative Example 1 revealed that, under the premise of identical material formulation, the aggregate orientation deviation caused solely by the lack of a directional shear flow field (changing from 45°±3° in Example 1 to a random distribution of 0°~180° in Comparative Example 1) resulted in a sharp drop in the TR value from 1.38 to 1.02. This data comparison reveals that the dual-drive mechanism of microscopic Janus structure + macroscopic directional process proposed in this invention provides thermal rectification potential, and the 3D printing flow field orientation process is the only technical means to transform this potential into macroscopic energy-saving benefits.

[0123] Comparative Example 2 Compared with Example 1, most of the steps are the same, except that in step (1), the porous recycled aggregate matrix 11 is only vacuum impregnated and no Janus asymmetric coating modification is performed on the surface. Specifically: Select particles with a diameter of 5-20 mm and an apparent density of 2420 kg / m³. 3 It has a water absorption rate of 6.5%, a porosity of 2.6%, a pore size of 260 μm, and a specific surface area of ​​5.22 cm². 2 / g of recycled coarse aggregate was used as the porous recycled aggregate matrix 11. It was placed in a vacuum pressure vessel, evacuated to -0.095MPa and maintained for 45 minutes to completely remove air from the internal interconnected micropores. Then, a phase change material 12 was added, immersing the porous recycled aggregate matrix 11 in the phase change material 12. The phase change material 12 was n-eicosane liquid with a melting point of 26℃ and a latent heat of phase change of 185J / g. The solid-liquid ratio during immersion was 1:2.2. The pressure was increased to 0.6MPa and maintained for 1 hour, allowing the phase change material 12 to fill the internal pores of the porous recycled aggregate matrix 11.

[0124] As shown in Table 1, tests were conducted using aggregates without asymmetric surface functionalization (i.e., whose surface thermophysical properties are isotropic) arranged in the same direction as in Example 1. Test results showed that the compressive strength at 28 days was 40 MPa, and the difference in thermal conductivity between the positive and negative directions was minimal, with a TR of only 1.06. This confirms that the Janus asymmetric structure of the aggregate itself is a necessary condition for the formation of a significant thermal rectification effect.

[0125] Comparative Example 3 Conventional recycled concrete was prepared according to the ordinary recycled concrete preparation process and used as a comparative example for evaluation of the basic properties of conventional recycled concrete. This set of data serves as a baseline to evaluate the comprehensive contribution of the Janus aggregate and directional process of this invention to the improvement of thermal rectification performance and strength. The difference compared to Example 1 is: Ordinary recycled coarse aggregate (particle size 5~20mm, apparent density 2420 kg / m³) without any modification treatment was used. 3 (Continuously graded), containing no phase change materials or Janus asymmetric coating. It was molded using conventional mixing and casting (same as Comparative Example 1), and vibrated on a 50Hz vibratory table for 40 seconds. The water-cement ratio remained consistent with Example 1. The specific preparation process is as follows: Cement, silica fume, recycled fine sand, and recycled coarse aggregate were added to a mixer and dry-mixed at 80 rpm for 2.5 minutes to ensure thorough and uniform mixing of the cementitious materials and aggregates. Premixed polycarboxylate superplasticizer, hydroxypropyl methylcellulose, and water were then added to the mixer, and the speed was increased to 200 rpm for vigorous mixing for 4 minutes to ensure the slurry achieved high fluidity and good rheological properties. To ensure consistency with the mixing process in the example, slow mixing was continued at 40 rpm for 1.5 minutes to eliminate large air bubbles and achieve final homogenization of the materials. After mixing, the slurry was poured into molds and cured for 28 days at a temperature of 20±2℃ and a relative humidity of over 95%.

[0126] As shown in Table 1, the test results indicate that its 28-day compressive strength is 35.5 MPa, the forward and reverse bidirectional thermal conductivity are basically the same, and the thermal rectification coefficient (TR) is approximately 1.00 (no thermal rectification effect). In summary, conventional recycled concrete, due to the randomness of the distribution of recycled coarse aggregate and the lack of asymmetric thermal path design, cannot achieve directional control of heat flow. This further proves that the present invention, through the combination of Janus asymmetric structural design and 3D printing directional arrangement technology, not only improves the mechanical strength of the material but also endows the concrete with a significant thermal rectification effect, which is key to achieving energy-saving temperature control in buildings.

[0127] Table 1. Comparison of key parameters and performance between the embodiments of the present invention and comparative examples. Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A Janus phase change recycled aggregate for 3D printing, characterized in that, The Janus phase change recycled aggregate (1) includes a porous recycled aggregate matrix (11) in which a phase change material (12) is loaded. The porous recycled aggregate matrix (11) has an asymmetrical surface structure, with one side covered with a thermally conductive coating to form a thermally conductive shielding surface (13), and the other side retaining the original porous structure to serve as a phase change energy storage surface (14).

2. The Janus phase change recycled aggregate for 3D printing according to claim 1, characterized in that, The porous recycled aggregate matrix (11) has a particle size of 5-20 mm and an apparent density of 2300-2600 kg / m³. 3 It has a water absorption rate of 5%~10%, a porosity of 3%~10%, and a specific surface area of ​​0.4~0.5 m². 2 / g; moisture content is 2%~5%; The phase change material (12) is a liquid organic phase change material with a melting point between 18 and 30°C, selected from one or more of alkanes, paraffins, fatty acids, alcohols or esters; The thermally conductive coating uses a thermally conductive material with a thermal conductivity of not less than 100 W / (m·K), and the thermally conductive material includes one or more of graphite, graphene, carbon nanotubes or boron nitride. The thickness of the thermally conductive coating is 50~80μm.

3. A Janus phase change recycled aggregate for 3D printing according to claim 1 or 2, characterized in that, The thermally conductive coating also includes 1wt% to 20wt% of functional fillers; The functional filler includes magnetic filler and / or non-magnetic filler, wherein the magnetic filler includes nickel powder and / or ferrite; and the non-magnetic filler includes one or more of aluminum powder, copper powder, silver powder, zinc oxide, titanium dioxide, aluminum nitride, or silicon carbide. The average particle size of the functional filler is 1~50μm, and it is uniformly and discretely distributed or continuously overlapped in the thermally conductive coating.

4. The Janus phase change recycled aggregate for 3D printing according to claim 1, characterized in that, The thermally conductive shielding surface (13) and the phase change energy storage surface (14) are distributed in a hemispherical asymmetric shape with reference to the geometric center of the porous recycled aggregate matrix (11); There is a clear physical boundary between the thermally conductive shielding surface (13) and the phase change energy storage surface (14), and this boundary forms a closed loop on the surface of the porous recycled aggregate matrix (11). The geometric center line of the thermally conductive shielding surface (13) is aligned with the direction of the short axis or long axis of the porous recycled aggregate matrix (11). The surface area of ​​the thermally conductive shielding surface (13) accounts for 40% to 60% of the total surface area of ​​the porous recycled aggregate matrix (11).

5. A method for preparing Janus phase change recycled aggregate for 3D printing as described in any one of claims 1 to 4, characterized in that, Includes the following steps: A1. The phase change material (12) is loaded into the porous recycled aggregate matrix (11) by vacuum impregnation. A2. A mask treatment is performed on the porous recycled aggregate matrix (11) loaded with phase change material (12). A thermally conductive material is deposited on the carrier gas side to form a thermally conductive coating, resulting in a thermally conductive shielding surface (13). The other side is the phase change energy storage surface (14).

6. A Janus phase change recycled aggregate concrete for 3D printing, characterized in that, The concrete includes Janus phase change recycled aggregate as described in any one of claims 1 to 4, and also includes a cement matrix (2), wherein the Janus phase change recycled aggregate is oriented in the cement matrix (2) at a predetermined tilt angle, such that the concrete has different thermal conductivity coefficients in the direction parallel to its arrangement and in the direction perpendicular to its arrangement. The tilt angle of the Janus phase change recycled aggregate in the concrete, measured by the angle between the axis of symmetry of its asymmetric surface structure and the thickness direction of the concrete, is 30° to 60°.

7. The Janus phase change recycled aggregate concrete for 3D printing according to claim 6, characterized in that, It comprises the following components by weight: 500-600 parts cement; 40-80 parts silica fume; 600-1000 parts of recycled fine sand; Janus phase change recycled aggregate 200~600 parts; 1-20 parts of admixture; 100-200 parts water.

8. A method for preparing Janus phase change recycled aggregate concrete for 3D printing according to claim 5, characterized in that, Includes the following steps: B1. Janus phase change recycled aggregate is mixed with other raw materials of the concrete to make a printable cement-based slurry; B2. The cement-based slurry is extruded and printed through a 3D printing nozzle (3), and the concrete is formed by layering. The cement-based slurry is subjected to shear force during the extrusion process, so that the Janus phase change recycled aggregate is oriented at a preset tilt angle. B3. Curing the formed concrete.

9. A method for preparing Janus phase change recycled aggregate concrete for 3D printing according to claim 8, characterized in that, In step B2, the shear force is generated by the venturi tube structure (31) set in the 3D printing nozzle, or by setting the axial direction of the 3D printing nozzle to form a preset angle with the printing plane.

10. A method for preparing Janus phase change recycled aggregate concrete for 3D printing according to claim 8, characterized in that, In step B2, the cement-based slurry is also subjected to a directional electric field or a directional magnetic field during the extrusion process.

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