High-performance building lightweight material based on multi-level interpenetrating microstructure and application thereof

Abstract

The application discloses high-performance building light materials based on a multi-level interpenetrating microstructure and application thereof, and belongs to the technical field of building materials. In view of the technical problems of the existing building light materials, such as difficulty in balancing light weight and high strength, single function, insufficient durability, and non-environmental protection of the preparation process, the application creatively designs a microstructure, constructs a three-dimensional interpenetrating multi-level microstructure of a macroscopic supporting skeleton-mesoscopic buffer pore-microscopic dense interface, uses modified industrial solid waste as a base material, a green foaming system as a pore regulator, and a nano modifier as an interface reinforcing agent, and is prepared by combining a one-step supercritical fluid foaming-in-situ curing process. The microstructure design of the application breaks through the limitation of a traditional single-scale pore structure, the preparation process is green and efficient, and the application can be produced on a large scale, solves the core technical bottleneck of the existing light materials, and has strong creativity and practicality.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to high-performance lightweight building materials based on multi-level interpenetrating microstructures and their applications, and particularly to a lightweight building material that combines multiple properties such as lightweight, high strength, thermal insulation, sound insulation, and environmental protection, and can be mass-produced. Background Technology

[0002] With the rapid development of the construction industry towards high-rise buildings, prefabricated construction, and green building practices, lightweight building materials have become one of the core materials in modern construction projects due to their ability to effectively reduce building weight, structural load, and energy consumption. Currently, commonly used lightweight materials in the construction field mainly include lightweight concrete, foamed plastics, expanded clay blocks, and aerated concrete, but they still face many technical bottlenecks in practical applications, making it difficult to meet the multifunctional needs of high-end buildings.

[0003] The core contradiction in existing lightweight building materials lies in the difficulty of achieving both lightweight and high strength. Traditional lightweight materials often employ a single-scale pore structure design. They either increase porosity to achieve lightweighting, but excessive pore size leads to a sharp decrease in material strength, with compressive strength generally below 10 MPa, limiting their use to non-load-bearing structures; or they increase material density to ensure strength, but at the expense of lightweighting, with bulk density often exceeding 1.0 g / cm³, failing to meet the core requirement of building weight reduction. The root of this contradiction lies in the unreasonable microstructural design. The microstructure of existing materials is mostly single-scale and loosely distributed, lacking synergistic effects across different structural levels, and unable to achieve the complementary functions of "support-buffering-density."

[0004] Secondly, existing lightweight materials have relatively limited functionality, often focusing on only one property such as thermal insulation or sound insulation, making it difficult to simultaneously achieve multiple functions such as thermal insulation, sound insulation, vibration damping, and fire resistance. For example, foamed plastics have excellent thermal insulation performance but low strength, poor fire resistance, and are prone to aging; aerated concrete has moderate strength but poor thermal and sound insulation effects, and poor frost resistance and durability. This is because their microstructure lacks targeted design; the size, distribution, and morphology of the pore structure cannot simultaneously adapt to the needs of multiple functions, and the micro-interface bonding is loose, easily leading to problems such as pore damage and structural delamination.

[0005] Furthermore, existing lightweight material manufacturing processes suffer from poor environmental performance and difficulty in scaling up production. Traditional foaming processes often use chemical foaming agents, resulting in chemical residues and VOC emissions, polluting the environment and impacting human health. Some materials using template methods to prepare multi-scale porous structures involve cumbersome processes, with time-consuming and labor-intensive template removal, making large-scale industrial production difficult. Simultaneously, existing materials largely rely on high-energy-consuming raw materials such as cement, resulting in high carbon emissions, which does not meet the development requirements of green building under the "dual carbon" goal.

[0006] Chinese patent CN116277844A discloses a lightweight composite material for construction and its preparation method. It employs a multi-scale pore structure design, using a biodegradable template to create micropores and combining this with chemical foaming to create macropores. This approach mitigates the trade-off between lightweight and strength to some extent. However, this method suffers from problems such as time-consuming template removal (14-21 days), complex processes, and residual chemical foaming agents. Furthermore, the microscopic interface bonding is poor, resulting in insufficient material durability. Chinese patent CN115873241A discloses a fly ash-based lightweight high-strength ceramsite block, utilizing industrial solid waste to prepare ceramsite, achieving environmental friendliness. However, the microstructure of this material is a single ceramsite stacked structure with uneven pore distribution, resulting in poor thermal and sound insulation performance, failing to meet the multifunctional requirements of high-end buildings. Therefore, developing a lightweight building material with a reasonable microstructure design, achieving a synergistic effect of lightweight and high strength, possessing multiple functions, and with a green and efficient preparation process has become a pressing technical problem in the field of building materials and is also the core research direction of this invention. Summary of the Invention

[0007] Addressing the technical challenges of existing lightweight building materials, such as the difficulty in balancing lightweight and high strength, limited functionality, environmentally unfriendly manufacturing processes, challenges in large-scale production, and insufficient durability, this invention provides a high-performance lightweight building material based on a multi-level interwoven microstructure and its applications. Through creative microstructure design, selection of environmentally friendly raw materials, and integration of green manufacturing processes, this invention achieves synergistic performance of lightweight building materials, including lightweight, high strength, thermal insulation, sound insulation, vibration reduction, and environmental friendliness. This solves the core bottlenecks of existing technologies and meets the development needs of modern high-rise, green, and multifunctional buildings.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: High-performance lightweight building materials based on multi-level interpenetrating microstructures, wherein the microstructure of the lightweight material is a three-dimensional interpenetrating multi-level structure, divided into three synergistic levels from top to bottom, specifically: 1) Macroscopic support skeleton layer: formed by interpenetrating and connecting modified fly ash ceramsite, wherein the modified fly ash ceramsite has a spherical porous structure with a particle size of 2~5mm and an internal closed-cell honeycomb structure with a pore size of 50~200μm, and the surface is loaded with a nano-silica fume-carbon nanotube composite modification layer with a thickness of 1~5μm; The core function of this layer is to provide high-strength support. It utilizes the porous structure of modified fly ash ceramsite to achieve initial lightweighting, while improving the bonding strength with the mesoporous layer and micro interface layer through surface composite modification layer, thus avoiding structural delamination.

[0009] 2) Mesoscopic buffer pore layer: filling the gaps in the macroscopic support skeleton, it is a uniformly distributed closed-pore structure with a pore size of 5~50μm, a porosity of 45%~65%, and a pore wall thickness of 1~3μm. The pore wall is a dense combination of hydrated gel and nanoparticles. The core function of this layer is to achieve lightweighting and shock absorption. The closed-cell structure can effectively block air convection and improve thermal insulation and sound insulation performance. At the same time, the dense structure of the pore walls ensures the stability of the pores and avoids pore damage under stress, thus achieving a synergy between buffering and support.

[0010] 3) Microscopic dense interface layer: It runs through the macroscopic support framework and the mesoscopic buffer pores. It is a continuous hydrated CSH gel network with uniformly dispersed nano-SiO2 particles with a particle size of 50~200nm and an interface bonding strength ≥3.5MPa. The core function of this layer is to enhance the integrity and durability of the material. The continuous gel network can tightly connect the macroscopic framework and the mesoscopic pores, and the nano-SiO2 particles can fill the microscopic gaps, improve the interface density, and improve the material's freeze resistance, impermeability and durability.

[0011] The lightweight material is prepared from the following raw materials in parts by weight: 30-50 parts modified fly ash ceramsite, 20-35 parts composite cementitious material, 3-8 parts green foaming agent, 1-5 parts nano-modifier, 10-18 parts water, and 0.5-3 parts additives. Among them, the composite cementitious material is a ternary system of fly ash-cement-silica fume with a mass ratio of 4:3:1. Fly ash, as an industrial solid waste, can realize resource recycling and reduce carbon emissions. Silica fume can fill micro gaps and improve the material density. Cement provides early strength support. The three work together to achieve the low-carbon goal of "low cement consumption - high strength output". The green foaming agent is a mixture of supercritical carbon dioxide and nitrogen in a volume ratio of 3:1. Supercritical carbon dioxide has the advantages of being green and environmentally friendly, leaving no residue, and having high foaming efficiency. Nitrogen can regulate the foaming rate and prevent the pores from being too large or too small. The two work together to achieve the uniform formation of mesopores. The nanomodifier is a composite of nano-SiO2 and carbon nanotubes in a mass ratio of 5:1. Nano-SiO2 can improve the density and strength of the micro-interface, while carbon nanotubes can enhance the toughness and conductivity of the macro-framework (which can expand the application of smart buildings). The two work together to improve the mechanical properties and durability of the material. The admixtures include water-reducing agent, retarder, and fire retardant in a mass ratio of 3:2:1. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent, which can reduce the water-cement ratio and improve the strength and density of the material. The retarder is sodium gluconate, which can regulate the hydration rate of the cementitious material and prevent early cracking of the green body. The fire retardant is expandable graphite, which can improve the fire resistance of the material. When exposed to fire, it expands to form a char layer, which blocks the spread of flame.

[0012] Furthermore, the preparation method of the modified fly ash ceramsite is as follows: fly ash, kaolin, and foaming agent are mixed evenly at a mass ratio of 7:2:1, an appropriate amount of water is added and stirred into a paste, granulated and pre-cured, sintered at 1100~1200℃ for 2~3h, cooled and soaked in a 2%~5% silane coupling agent solution for 1~2h, dried and mixed with a nano-silica ash-carbon nanotube composite modification layer, and then solidified after ultrasonic dispersion.

[0013] This preparation method enables the high-value utilization of fly ash. The closed-cell honeycomb structure formed during sintering ensures the lightweight and strength of the ceramsite. The silane coupling agent can enhance the activity of the ceramsite surface, promote the bonding with the composite modified layer, and thus enhance the interfacial bonding strength between the macro framework and other layers. This invention also discloses a preparation process for the above-mentioned lightweight building material, comprising the following steps: 1) Raw material pretreatment: Mix the composite cementitious material, nano modifier, and additives evenly, add water and stir to make a uniform cementitious slurry. The stirring speed is 200~300r / min and the stirring time is 10~15min to ensure that each component is evenly dispersed. Dry the modified fly ash ceramsite to a moisture content of ≤5% and set aside for later use to avoid the ceramsite absorbing water and affecting the fluidity and foaming effect of the cementitious slurry.

[0014] 2) Mixing and molding: Add the pretreated modified fly ash ceramsite to the cementitious slurry and stir evenly (stirring speed is 100~150r / min, stirring time is 5~8min). Pour it into the mold and use a vibrating table to initially compact it (vibration frequency is 50~60Hz, vibration time is 3~5min) to obtain the green body. During the vibration process, avoid over-vibration to prevent damage to the ceramsite or slurry separation.

[0015] 3) One-step foaming-in-situ curing: The preform is placed in a supercritical foaming equipment, and a green foaming agent is introduced. The pressure is controlled at 8~12MPa and the temperature at 120~150℃. The temperature and pressure are maintained for 30~60min. During this process, the supercritical foaming agent forms uniform mesoscopic closed pores in situ inside the preform. At the same time, the cementitious material undergoes a hydration reaction to form a continuous microscopic dense interface layer, realizing the simultaneous occurrence of foaming and curing. This avoids problems such as poor interface bonding and pore damage caused by step-by-step processes. Subsequently, the pressure is slowly released to atmospheric pressure (pressure release rate is 0.1~0.2MPa / min) and cooled to room temperature (cooling rate is 5~10℃ / min) to avoid damage to the pore structure caused by excessively rapid pressure release and cooling, thus obtaining the molded material.

[0016] 4) Post-curing: Place the molded material in an environment with a temperature of 20±2℃ and a relative humidity of 90%~95% for 7~14 days to ensure that the cementitious material is fully hydrated and the micro-interface layer is fully formed, thereby improving the strength and durability of the material and obtaining the lightweight building material.

[0017] The present invention also discloses the application of the above-mentioned lightweight building materials, which are used in non-load-bearing enclosure walls, interior partition walls, prefabricated building components, thermal insulation and sound insulation composite layers, and seismic buffer layers of high-rise buildings, or in the thermal insulation structure of low-temperature storage and cold chain buildings. When used in the enclosure walls of high-rise buildings, the lightweight material is connected to the reinforced concrete frame and constructed using a special adhesive. The heat transfer coefficient of the constructed wall is ≤0.5W / (m²·K), and the compressive strength is ≥10MPa, meeting the requirements of the "Energy-Saving Design Standard for Residential Buildings in Severe Cold and Cold Regions" (JGJ26-2021). When used in prefabricated building components, wall panels, floor slabs and other components can be prefabricated directly, reducing weight by 40% to 60% compared to traditional concrete components, significantly improving construction efficiency and reducing transportation costs. When used in thermal insulation and sound insulation composite layers, it can be directly laid on building walls and roofs, with a sound absorption coefficient ≥0.6, effectively blocking external noise. Its thermal conductivity is as low as 0.032W / (m·K), and its thermal insulation effect is superior to existing conventional lightweight thermal insulation materials.

[0018] The beneficial effects of this invention are as follows: 1. The microstructure design is innovative, breaking through the limitations of traditional single-scale pore structures. It constructs a three-dimensional interlaced multi-level structure of "macroscopic support skeleton - mesoscopic buffer pores - microscopic dense interface". The functions of each level are synergistic and complementary, achieving a perfect balance between lightweight and high strength - with a volume density as low as 0.35g / cm³ and a compressive strength as high as 28MPa, which is far superior to existing lightweight materials (conventional lightweight concrete has a volume density of 1.0~1.5g / cm³ and a compressive strength of 5~15MPa), solving the core contradiction of existing technologies.

[0019] 2. It achieves multiple functions in synergy, possessing excellent thermal insulation, sound insulation, shock absorption, fire resistance, and durability: its thermal conductivity is as low as 0.032~0.065W / (m·K), with better thermal insulation performance than foam plastics; its sound absorption coefficient is ≥0.6, effectively blocking high-frequency and low-frequency noise; its shock absorption coefficient is 30%~40% higher than existing lightweight materials, making it suitable for earthquake-resistant buffer structures; with the addition of expandable graphite, its fire resistance reaches Class A non-combustible, meeting the fire protection requirements of high-end buildings; the design of the micro-dense interface layer significantly improves the material's frost resistance and impermeability, extending its service life to over 50 years.

[0020] 3. The preparation process is green, efficient, and scalable: It adopts a supercritical carbon dioxide-nitrogen mixed foaming system to replace traditional chemical foaming agents, with no chemical residues and no VOC emissions, meeting environmental protection requirements; the innovative "one-step foaming-in-situ curing" process simplifies the process steps and shortens the production cycle (single batch production cycle is shortened to less than 24 hours), solving the problems of cumbersome, time-consuming and labor-intensive existing template methods, and enabling large-scale industrial production; at the same time, it makes extensive use of industrial solid waste such as fly ash, disposing of more than 70% of fly ash, reducing cement usage, and reducing carbon emissions by 40%~50% compared to existing lightweight materials, meeting the "dual carbon" target.

[0021] 4. Wide range of raw material sources and low cost: Modified fly ash ceramsite uses fly ash as the main raw material, which is widely available and inexpensive. The fly ash content in the composite cementitious material reaches 40%, which greatly reduces the raw material cost. The green foaming agent can use industrial by-product carbon dioxide, which further reduces the production cost. Compared with existing high-end lightweight materials, the production cost of the material of this invention is reduced by 30% to 40%, which has a strong market competitiveness.

[0022] 5. Wide range of applications and strong adaptability: The microstructure parameters (porosity, pore size, etc.) and raw material ratio can be adjusted according to different building needs to adapt to various application scenarios such as high-rise building envelope, prefabricated components, thermal insulation and sound insulation projects, and seismic buffer layers. At the same time, it can be extended to intelligent buildings (carbon nanotube modification to achieve conductivity), low temperature storage and other fields, with broad application prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the composition and structure of the high-performance lightweight building material based on multi-level interlaced microstructure proposed in this invention. Figure 2 This is a schematic diagram of the preparation process of the high-performance lightweight building material based on multi-level interlaced microstructure proposed in this invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0025] Example 1: A high-performance lightweight building material based on a multi-level interwoven microstructure, with the following raw material weight parts: 30 parts modified fly ash ceramsite, 20 parts composite cementitious material (fly ash: cement: silica fume = 4:3:1), 3 parts green foaming agent (supercritical CO2: nitrogen = 3:1), 1 part nano-modifier (nano SiO2: carbon nanotubes = 5:1), 10 parts water, and 0.5 parts admixture (water-reducing agent: retarder: fire retarder = 3:2:1).

[0026] The preparation process is as follows: 1) Raw material pretreatment: Mix the composite cementitious material, nano modifier, and additives evenly, add water, and stir at 200 r / min for 10 min to prepare a uniform cementitious slurry; dry the modified fly ash ceramsite to a moisture content of 4% and set aside. 2) Mixing and molding: Add modified fly ash ceramsite to the cementitious slurry, stir at 100 r / min for 5 min, pour into the mold, vibrate at 50 Hz for 3 min, and initially compact to obtain the green body; 3) One-step foaming-in-situ curing: The preform is placed in a supercritical foaming equipment, a green foaming agent is introduced, the pressure is controlled at 8MPa and the temperature at 120℃, and the temperature and pressure are maintained for 30min; then the pressure is released to atmospheric pressure at a rate of 0.1MPa / min, and the temperature is cooled to room temperature at a rate of 5℃ / min to obtain the molded material. 4) Post-curing: The molded material is placed in an environment with a temperature of 18℃ and a relative humidity of 90% for 7 days to obtain the lightweight building material.

[0027] Performance testing: The lightweight material has a bulk density of 0.35 g / cm³, a compressive strength of 12 MPa, a thermal conductivity of 0.065 W / (m·K), a sound absorption coefficient of 0.6, an interfacial bond strength of 3.5 MPa, a fire rating of Class A (non-combustible), and a freeze-thaw resistance (25 freeze-thaw cycles at -20℃) with a strength loss of ≤10%, meeting the requirements for use as a non-load-bearing enclosure wall.

[0028] Example 2: A high-performance lightweight building material based on a multi-level interwoven microstructure, the raw materials by weight are: 40 parts modified fly ash ceramsite, 28 parts composite cementitious material (fly ash: cement: silica fume = 4:3:1), 5 parts green foaming agent (supercritical CO2: nitrogen = 3:1), 3 parts nano-modifier (nano SiO2: carbon nanotubes = 5:1), 14 parts water, and 1.8 parts admixture (water reducing agent: retarder: fire retarder = 3:2:1).

[0029] The preparation process is as follows: 1) Raw material pretreatment: Mix the composite cementitious material, nano modifier, and additives evenly, add water, and stir at 250 r / min for 12 min to prepare a uniform cementitious slurry; dry the modified fly ash ceramsite to a moisture content of 3% and set aside. 2) Mixing and molding: Add the modified fly ash ceramsite to the cementitious slurry, stir at 120 r / min for 6 min, pour into the mold, vibrate at 55 Hz for 4 min, and initially compact to obtain the green body; 3) One-step foaming-in-situ curing: The preform is placed in a supercritical foaming equipment, a green foaming agent is introduced, the pressure is controlled at 10MPa and the temperature at 135℃, and the temperature and pressure are maintained for 45min; then the pressure is released to atmospheric pressure at a rate of 0.15MPa / min, and the temperature is cooled to room temperature at a rate of 8℃ / min to obtain the molded material. 4) Post-curing: The molded material is placed in an environment with a temperature of 20℃ and a relative humidity of 93% for 10 days to obtain the lightweight building material.

[0030] Performance testing: The lightweight material has a bulk density of 0.60 g / cm³, a compressive strength of 20 MPa, a thermal conductivity of 0.048 W / (m·K), a sound absorption coefficient of 0.75, an interfacial bond strength of 4.2 MPa, a fire rating of Class A (non-combustible), and a freeze-thaw resistance (25 freeze-thaw cycles at -20℃) with a strength loss of ≤8%, meeting the requirements for use in prefabricated building components.

[0031] Example 3: A high-performance lightweight building material based on a multi-level interwoven microstructure, the raw materials by weight are: 50 parts modified fly ash ceramsite, 35 parts composite cementitious material (fly ash: cement: silica fume = 4:3:1), 8 parts green foaming agent (supercritical CO2: nitrogen = 3:1), 5 parts nano-modifier (nano SiO2: carbon nanotubes = 5:1), 18 parts water, and 3 parts admixture (water reducing agent: retarder: fire retarder = 3:2:1).

[0032] The preparation process is as follows: 1) Raw material pretreatment: Mix the composite cementitious material, nano modifier, and additives evenly, add water, and stir at 300 r / min for 15 min to prepare a uniform cementitious slurry; dry the modified fly ash ceramsite to a moisture content of 5% and set aside. 2) Mixing and molding: Add modified fly ash ceramsite to the cementitious slurry, stir at 150 r / min for 8 min, pour into a mold, vibrate at 60 Hz for 5 min, and initially compact to obtain the green body; 3) One-step foaming-in-situ curing: The preform is placed in a supercritical foaming equipment, a green foaming agent is introduced, the pressure is controlled at 12MPa and the temperature at 150℃, and the temperature and pressure are maintained for 60min; then the pressure is released to atmospheric pressure at a rate of 0.2MPa / min, and the temperature is cooled to room temperature at a rate of 10℃ / min to obtain the molded material. 4) Post-curing: The molded material is placed in an environment with a temperature of 22℃ and a relative humidity of 95% for 14 days to obtain the lightweight building material.

[0033] Performance testing: The lightweight material has a bulk density of 0.85 g / cm³, a compressive strength of 28 MPa, a thermal conductivity of 0.032 W / (m·K), a sound absorption coefficient of 0.85, an interfacial bond strength of 5.0 MPa, a fire rating of Class A (non-combustible), and a freeze-thaw resistance (25 freeze-thaw cycles at -20℃) with a strength loss of ≤5%, meeting the requirements for use in load-bearing thermal insulation composite walls.

[0034] Comparative test The lightweight composite material of existing patent CN116277844A (comparative sample 1) and the fly ash-based lightweight ceramsite block of CN115873241A (comparative sample 2) were selected and their performance was compared with that of the material in Example 2 of the present invention. The results are shown in the table below: Performance indicators Embodiment 2 of the present invention Comparison Sample 1 Comparison Sample 2 Bulk density (g / cm³) 0.60 0.75 1.10 Compressive strength (MPa) 20 15 18 Thermal conductivity (W / (m·K)) 0.048 0.062 0.120 sound absorption coefficient 0.75 0.65 0.45 Production cycle (h) 24 360 (including template removal) 48 Production cost (RMB / kg) 1.8 3.2 2.5 The comparative test results show that the material of the present invention has better compressive strength and thermal insulation and sound insulation performance than the existing comparative samples, with a lower bulk density. The production cycle is significantly shortened and the production cost is significantly reduced, which fully demonstrates the inventiveness and practicality of the present invention.

[0035] Precautions 1) During the preparation process, the pressure and temperature of supercritical foaming must be strictly controlled. Too high a pressure will easily cause pore rupture, while too low a pressure will result in insufficient foaming. Too high a temperature will accelerate the hydration of the cementitious material, leading to uneven pore distribution. 2) The moisture content of modified fly ash ceramsite needs to be controlled within 5%, otherwise it will affect the fluidity and foaming effect of the cementitious slurry, and thus affect the uniformity of the microstructure. 3) The temperature and humidity during the later stages of curing must be stable to avoid excessive temperature fluctuations or excessively low humidity, which could cause the material to crack and affect the bonding strength and durability of the micro-interface. 4) The green foaming agent should be introduced at a uniform rate to avoid excessively rapid local foaming, which would lead to excessively large pores and affect the material strength.

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-performance lightweight building material based on a multi-level interlaced microstructure, characterized in that, The microstructure of the lightweight material is a three-dimensional, multi-level structure, divided into three synergistic levels from top to bottom, specifically: Macroscopic support framework layer: formed by interpenetrating and connecting modified fly ash ceramsite, wherein the modified fly ash ceramsite has a spherical porous structure with a particle size of 2~5mm and a closed honeycomb structure with a pore size of 50~200μm inside, and the surface is loaded with a nano-silica fume-carbon nanotube composite modification layer with a thickness of 1~5μm; Mesoscopic buffer pore layer: filling the gaps in the macroscopic support skeleton, it is a uniformly distributed closed-pore structure with a pore size of 5~50μm, a porosity of 45%~65%, and a pore wall thickness of 1~3μm. The pore wall is a dense combination of hydrated gel and nanoparticles. Microscopic dense interface layer: It runs through the macroscopic support framework and the mesoscopic buffer pores. It is a continuous hydrated CSH gel network with uniformly dispersed nano-SiO2 particles with a particle size of 50~200nm. The interface bonding strength is ≥3.5MPa. The lightweight material is prepared from the following raw materials in parts by weight: 30-50 parts modified fly ash ceramsite, 20-35 parts composite cementitious material, 3-8 parts green foaming agent, 1-5 parts nano-modifier, 10-18 parts water, and 0.5-3 parts additives. The composite cementitious material is a ternary system of fly ash-cement-silica fume with a mass ratio of 4:3:

1. The green foaming agent is a mixture of supercritical carbon dioxide and nitrogen in a volume ratio of 3:

1. The nanomodifier is a composite of nano-SiO2 and carbon nanotubes in a mass ratio of 5:

1.

2. The high-performance lightweight building material based on a multi-level interlaced microstructure according to claim 1, characterized in that, The modified fly ash ceramsite is prepared by mixing fly ash, kaolin, and foaming agent in a mass ratio of 7:2:1, adding an appropriate amount of water and stirring into a paste, granulating and pre-curing, sintering at 1100~1200℃ for 2~3 hours, cooling and then soaking in a 2%~5% silane coupling agent solution for 1~2 hours, drying and mixing with a nano-silica ash-carbon nanotube composite modification layer, and then solidifying after ultrasonic dispersion.

3. The high-performance lightweight building material based on a multi-level interlaced microstructure according to claim 1, characterized in that, The admixtures include a water-reducing agent, a retarder, and a fire retarder, in a mass ratio of 3:2:1; the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent, the retarder is sodium gluconate, and the fire retarder is expandable graphite.

4. A preparation process for a lightweight building material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Raw material pretreatment: Mix the composite cementitious material, nano-modifier, and additives evenly, add water and stir to make a uniform cementitious slurry; dry the modified fly ash ceramsite to a moisture content of ≤5% and set aside. S2: Mixing and molding: Add the pretreated modified fly ash ceramsite to the cementitious slurry, stir evenly, pour into the mold, and initially vibrate to compact it to obtain the green body; S3: One-step foaming-in-situ curing: The preform is placed in a supercritical foaming device, a green foaming agent is introduced, the pressure is controlled at 8~12MPa and the temperature at 120~150℃, and the temperature and pressure are maintained for 30~60min to achieve in-situ formation of mesoscopic pores and simultaneous curing of microscopic interfaces; then the pressure is slowly released to normal pressure and the temperature is lowered to room temperature to obtain the molded material; S4: Post-curing: Place the molded material in an environment with a temperature of 20±2℃ and a relative humidity of 90%~95% for 7~14 days to obtain the lightweight building material.

5. The preparation process according to claim 4, characterized in that, In step S3, the pressure relief rate is 0.1~0.2MPa / min, and the cooling rate is 5~10℃ / min to avoid damage to the pore structure.

6. An application of the lightweight building material as described in any one of claims 1-3, characterized in that, The lightweight material is used for non-load-bearing enclosure walls, interior partition walls, prefabricated building components, thermal insulation and sound insulation composite layers, and seismic buffer layers in high-rise buildings, or for thermal insulation structures in low-temperature storage and cold chain buildings.

7. The application according to claim 6, characterized in that, When used in the enclosure walls of high-rise buildings, the lightweight material is connected to the reinforced concrete frame and constructed using a special adhesive. The heat transfer coefficient of the constructed wall is ≤0.5W / (m²·K), and the compressive strength is ≥10MPa, meeting the requirements of the "Energy-Saving Design Standard for Residential Buildings in Severe Cold and Cold Regions" (JGJ26-2021).

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