Putty for external wall thermal insulation and preparation method thereof

Abstract

The invention belongs to the technical field of building thermal insulation materials, and particularly relates to putty for external wall thermal insulation and a preparation method thereof. The method comprises the following steps: 1) preparing materials; (2) premixing the nano aerogel, the ceramic fiber, the calcium sulfate whisker, the basalt fiber and the calcium stearate according to a proportion after material preparation is completed, so as to prepare composite powder; 3) uniformly dry-mixing a cement-based cementing material, cellulose ether and a water reducing agent, and mixing with the composite powder to prepare a base material; 4) slowly adding water into the base material, and continuously stirring to prepare a precursor; and 5) performing dynamic pre-aging on the precursor, and crushing and grinding the precursor into the putty powder after dynamic pre-aging. Cracking is reduced through a curing agent-free design, and the construction safety is improved; the pre-aging process widens the adaptability of the construction environment, and the requirements on humidity and temperature are obviously reduced; the microstructure is uniform, the heat conductivity coefficient is low and the mechanical property is stable; the cost is controllable and the method is suitable for large-scale popularization and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building thermal insulation materials, and particularly relates to a putty for external wall thermal insulation and a preparation method thereof. BACKGROUND

[0002] Under the trend of global climate extreme, building external wall thermal insulation materials are facing more severe environmental tests.

[0003] In the prior art, ordinary external wall thermal insulation putty generally has problems such as rapid attenuation of thermal insulation performance, decrease of mechanical strength, cracking and falling off under the environment of extreme temperature (below-30 ℃ or above 70 ℃), high humidity and salt spray erosion. For example, the traditional cement-based putty will be damaged due to ice crystal expansion below-20 ℃, and the strength loss rate is more than 40% after 50 freeze-thaw cycles; the organic modified putty is prone to high molecular chain rupture under long-term ultraviolet radiation, and the thermal conductivity coefficient rises by more than 20% after 2000 h of aging. These problems lead to high maintenance cost of external wall thermal insulation putty.

[0004] Although the existing patent technology such as CN114933822A improves the water resistance and mildew resistance, it does not involve the design of adaptability to extreme temperature; although the aerogel composite putty has excellent thermal insulation, it loses workability below-15 ℃. Therefore, it is a technical problem to be solved to develop an external wall thermal insulation putty which can work stably in a wide temperature range of-50~80 ℃ and resist the erosion of salt spray, high humidity and other extreme environments. SUMMARY

[0005] The technical scheme of the present application provides a putty for external wall thermal insulation and a preparation method thereof, aiming at the problems of existing external wall thermal insulation putty such as serious performance attenuation under extreme temperature, salt spray, ultraviolet radiation and other environments, and poor construction adaptability.

[0006] The main purpose of the present application is to: I. provide an external wall thermal insulation putty which still has excellent thermal insulation and mechanical stability in a wide temperature range of-50~80 ℃; II. improve the durability of the putty under extreme environments such as salt spray, high humidity and ultraviolet radiation through component optimization and process innovation; III. realize the workability and rapid curing of the putty in low temperature environment, and break through the limitation of winter construction.

[0007] To achieve the above purpose, the present application adopts the following technical scheme.

[0008] A preparation method of a putty for external wall thermal insulation, The method comprises: 1) batching in the following mass percentages: cementitious material 45-55 wt%, nanometer aerogel 5-10 wt%, ceramic fiber 3-5 wt%, calcium sulfate whisker 2-4 wt%, basalt fiber 1-3 wt%, calcium stearate 0.5-1.0 wt%, cellulose ether 0.3-0.5 wt%, water reducing agent 0.5-1.0 wt%, and the balance being water.

[0009] 2) After batching is completed, the nanometer aerogel, ceramic fiber, calcium sulfate whisker, basalt fiber and calcium stearate are premixed in proportion to form a composite powder.

[0010] 3) After the cementitious material, cellulose ether and water reducing agent are dry mixed uniformly, the composite powder is mixed to form a base material.

[0011] 4) Slowly add water to the base material and continue to stir to form a precursor.

[0012] 5) Dynamic pre-aging is performed on the precursor, and the precursor is broken and ground into putty powder after dynamic pre-aging.

[0013] Preferably, In step 1), the nanometer aerogel is a silica aerogel modified by secondary grafting of methyltrimethoxysilane; In step 1), the ceramic fiber has a length of 3-6 mm and an aspect ratio of 30-50; In step 1), the calcium sulfate whisker has a length of 50-100 μm and an aspect ratio of 20-30; In step 1), the basalt fiber has a length of 3-6 mm.

[0014] Preferably, In step 1), the nanometer aerogel is prepared by the following method: Silica aerogel and methyltrimethoxysilane are mixed in a mass ratio of (8-12):1, dispersed in anhydrous ethanol, and reacted at a temperature of 60-70 ℃ and a pH of 4-5 for 4-6 h, and then washed and dried to obtain a specific surface area ≥600 m 2 / g.

[0015] Preferably, In step 2), the premixing is ultrasonically treated at a temperature of 20-30 ℃, a fluctuation frequency of 40-50 kHz and a power of 600-700 W for 20-40 min.

[0016] Preferably, Step 1) the cement-based cementitious material is a sulphoaluminate cement and Portland cement compound system, the sulphoaluminate cement and Portland cement are mixed in a mass ratio of (3-4):6, and nano-silicon dioxide is added in an amount of 1-2 wt% of the mass of the Portland cement.

[0017] As preferred, Step 3) the prepared substrate is stirred at a temperature of 15-25 DEG C and a rotation speed of 30-70 rpm for 5-10 min.

[0018] As preferred, Step 4) the stirring is carried out at a temperature of 15-25 DEG C and a rotation speed of 300-500 rpm for 10-20 min.

[0019] As preferred, Step 5) the dynamic pre-aging is gradient aging, the first section is aged in an environment at a temperature of -5-5 DEG C for 2-3 h, and the second section is aged in an environment at a temperature of 20-25 DEG C for 4-5 h. Step 4) the crushing and grinding are carried out so that the product has a mesh size of 240-300 mesh.

[0020] An external wall insulation putty.

[0021] In the technical scheme of the present application, the core is to realize the comprehensive improvement of the external wall insulation putty in the aspects of thermal insulation performance, mechanical strength, construction adaptability and environmental durability by constructing a synergistic platform of methyltrimethoxysilane modified aerogel compatible intermediate system, nano-modified compound cementitious material, ultrasonic premixing dynamic aging process and controllable fiber breaking technology.

[0022] The core of the methyltrimethoxysilane modified silica aerogel in this scheme is to construct a bifunctional surface chemical environment to realize the molecular level bridging of the organic-inorganic interface. The methyltrimethoxysilane molecule structure contains both hydrophobic methyl and hydrolysable methoxy groups, which makes it an ideal surface modifier. During the modification process, methyltrimethoxysilane forms covalent bonds with the surface silanol groups of the aerogel through hydrolysis-polycondensation reaction. The hydrolysis reaction is first carried out under acidic or basic catalytic conditions, and the methoxy group reacts with water molecules to form a silanol group and methanol. Subsequently, the newly generated silanol group undergoes polycondensation reaction with the surface silanol group of the aerogel, and a stable Si-O-Si covalent bond is formed by the release of water molecules. This chemical bonding not only ensures the stability of the modified layer, but also constructs a high-density functional group distribution on the surface of the aerogel. The modified aerogel surface presents a gradient chemical environment: the outer layer is rich in methyl groups, providing hydrophobicity and compatibility with organic components; the inner layer retains part of the silanol groups, maintaining the affinity with inorganic components. This gradient surface chemistry provides a molecular basis for the compatibility of multi-component systems, enabling the aerogel to form effective interfacial bonding with both fiber fillers and inorganic cementitious materials. The bifunctional groups on the surface of the aerogel achieve directional molecular bridging effect, the methyl groups interact with the hydrophobic surface of the fiber filler through van der Waals force, forming a physical adsorption layer. Although the individual bond energy is low, the total binding force is considerable due to the large specific surface area of the aerogel. The silanol group forms hydrogen bonds and chemical bonds with the hydration products of calcium silicate gel and calcium hydroxide in inorganic cementitious materials. As a hydrogen bond donor, the silanol group forms a hydrogen bond network with the oxygen atoms in the hydration products; at the same time, in an alkaline environment, the silanol group may undergo deprotonation and form ionic or coordination bonds with calcium ions. This multiple interaction ensures the firm bonding of the aerogel with the cementitious matrix. The key to directional bridging is the control of molecular orientation. By adjusting the modification conditions and the dispersion state of the aerogel, the functional groups can be arranged in an orderly manner at the interface, maximizing the efficiency of interfacial interaction. This molecular level interface engineering significantly improves the compatibility and stability of the multi-phase system.

[0023] Another important function of the aerogel compatibility intermedium is to promote the uniform distribution of each component at the microscale. The porous network structure of the aerogel provides a dispersion carrier for other components, the fiber filler can be partially embedded in the large pores of the aerogel, and the fine particles of the cementitious material can fill the medium and small pores. This multi-scale spatial distribution avoids macroscopic separation and aggregation of components. The realization of synergistic distribution also depends on the adjustment of the surface chemistry of the aerogel, which has differential affinity for different components and can selectively adsorb and disperse specific components, forming an ordered microstructure. This selective dispersion mechanism not only improves the uniformity of dispersion, but also optimizes the spatial configuration of each component, enabling them to fully exert their respective functional characteristics. The formation of the fiber network, the hydration of the cementitious material, and the thermal insulation effect of the aerogel are organically integrated at the microscale.

[0024] In the present application, the compounded cementitious material adopts the synergistic proportioning of sulphoaluminate cement and Portland cement, making full use of the complementary characteristics of the two cementitious materials. Sulphoaluminate cement has the characteristics of fast hardening and early strength, its main mineral phase reacts rapidly in the early stage of hydration to generate ettringite and aluminum hydroxide gel, providing early strength for the system. Portland cement provides long-term strength development, and the hydration of its tricalcium sulfate and dicalcium sulfate mineral phases produces calcium silicate gel to form a dense cementitious structure. The synergistic hydration of the two cements follows a time-sequential reaction mechanism. In the early stage of hydration, sulphoaluminate cement dominates, rapidly consuming water and sulfate ions in the system, forming an initial structural framework; as the reaction proceeds, Portland cement gradually participates in the hydration, and the generation of C-S-H gel fills and strengthens the initial structure, achieving a smooth transition from early strength to long-term strength. The optimization of the compounded ratio is based on the hydration kinetics and strength development law. By adjusting the mass ratio of sulphoaluminate to Portland cement (usually 3:7 to 4:6), the best balance of hydration rate and strength development can be achieved. Too high sulphoaluminate content will lead to rapid hydration, affecting the construction performance; too low will not provide enough early strength. The introduction of nano-silica micro-powder is based on its unique micro-filling effect and pozzolanic activity. Nano-silica particles can fill the small voids between cementitious material particles, improving the packing density and compactness of the system. This micro-filling effect not only reduces porosity, but also optimizes the pore size distribution, converting harmful macropores into harmless gel pores. The pozzolanic activity of nano-silica is manifested in its secondary reaction with the hydration product calcium hydroxide. In an alkaline environment, the silicon-oxygen bonds on the surface of nano-silica break, releasing silicate ions which combine with calcium ions to form additional C-S-H gel. This secondary hydration reaction not only consumes calcium hydroxide which can lead to carbonation, but also increases the total amount of cementitious products, improving the strength and durability of the matrix. At the same time, the improvement of aerogel encapsulation by nano-silica is due to its surface chemical properties. The abundant silicon hydroxyl groups on the surface of nano-silica have good chemical compatibility with the silicon hydroxyl groups on the surface of aerogel, forming a hydrogen bond network that enhances the encapsulation and protection of the cementitious matrix to the aerogel. This encapsulation effect prevents the damage of aerogel during construction and use, maintaining the long-term stability of its thermal insulation performance.

[0025] The nano-modified composite cementitious material can maintain good hydration activity under low temperature conditions, which is mainly due to the nano effect and the synergistic effect of the composite. The high specific surface area and surface energy of nano-silicon dioxide provide additional nucleation sites for hydration reaction, and reduce the activation energy of hydration reaction. Under low temperature conditions, these nucleation sites can promote the formation and crystallization of hydration products, and maintain the progress of hydration reaction. The low temperature adaptability of the composite system is also reflected in the reasonable distribution of hydration heat. The rapid hydration of sulphoaluminate cement releases heat, which provides temperature compensation for the subsequent hydration of portland cement, forming a self-heating effect. This endogenous heat helps to maintain the system temperature and prevent the hydration reaction from stagnating under low temperature conditions. The improvement of low temperature hydration performance is of great significance to the construction adaptability. Under winter construction conditions, the modified cementitious material can still maintain good fluidity and workability, and can achieve the design strength requirement after solidification, expanding the temperature window for construction.

[0026] In addition, in the present application, the ultrasonic premixing technology utilizes the cavitation effect and mechanical vibration of ultrasonic waves to achieve efficient dispersion and mixing of components. When ultrasonic waves propagate in a liquid medium, they produce alternating compression and rarefaction waves. When the negative pressure of the rarefaction wave exceeds the cavitation threshold of the liquid, a large number of microbubbles are generated. These bubbles collapse rapidly under the action of compression waves, generating local high temperature and pressure and strong micro-jets, which have a strong dispersing effect on particle agglomerates. For aerogels and other lightweight porous materials, low-frequency ultrasonic waves can effectively break up the agglomerates without damaging their internal structure. For dense particles such as nano-silicon dioxide, higher ultrasonic intensity is required to overcome the van der Waals forces and electrostatic forces between particles. The mechanical action of ultrasonic waves enhances the wetting of the liquid on the surface of the solid, reduces the interfacial tension, and is beneficial to the formation and stability of the interface between components. This wetting enhancement effect is particularly important for improving the compatibility of hydrophobic aerogels and water-based cementitious systems.

[0027] The dynamic pre-aging process controls the temperature, humidity and time parameters to complete the partial hydration reaction and preliminary reorganization of the microstructure of the cementitious material before formal construction. The key to this pre-treatment process is to accurately control the hydration degree, both to achieve the pre-organization of the structure and to maintain sufficient construction performance. During the pre-aging process, hydration reactions begin to occur on the surface of the cementitious material particles, generating a thin layer of hydration products. These initial hydration products act as "cementing agents" to preliminarily connect the components into a network structure, improving the cohesion and stability of the system. At the same time, the aerogel particles are gradually wrapped in this process, forming a protective layer to prevent damage during subsequent processing. The "dynamic" feature of dynamic aging is reflected in the periodic changes of temperature and humidity. By simulating the temperature and humidity fluctuations of the actual use environment, the material is adapted to environmental changes during the pre-treatment stage, improving its stability in actual application. This environmental adaptability training significantly improves the crack resistance and long-term durability of the material.

[0028] The synergistic effect of ultrasonic premixing and dynamic aging realizes the rapid curing of 4-6 min initial setting and 4-6 h reaching the strength of the next process, and the rapid curing mechanism is based on the time optimization of hydration reaction and the acceleration of structure development. The uniform dispersion system formed in the premixing process provides ideal conditions for rapid hydration, the high dispersion of each component increases the reaction interface and shortens the ion diffusion distance, and the initial structure formed in the pre-aging process provides skeleton support for the subsequent rapid strength development. The rapid curing also benefits from the fast hardening characteristics of sulphoaluminate cement and the nucleation promotion effect of nano-silica. Under the optimized ratio and process conditions, these factors work together to achieve the best match of hydration rate and strength development, ensuring construction performance and meeting the construction period requirements.

[0029] In the present application, the controllable fiber breaking technology breaks long fibers into short fibers with high aspect ratio by controlled mechanical treatment during the crushing and grinding process. This treatment method has unique advantages compared to directly using short fibers or nanofibers: maintaining the basic mechanical properties of the fibers, avoiding performance loss caused by excessive crushing, and effectively controlling the cost. The control of fiber breaking is based on the precise matching of mechanical force and fiber characteristics. Different types of fibers have different breaking characteristics and critical stress. By adjusting the grinding parameters, the length and aspect ratio of the broken fibers can be accurately controlled. Too low aspect ratio will reduce the reinforcing effect, and too high aspect ratio may affect the dispersibility and construction performance. The controllable breaking technology realizes the optimization of fiber length distribution through multi-stage grinding and screening, and obtains the best performance of the fiber reinforced system.

[0030] The short fibers treated by controllable fracture form a three-dimensional network structure in the putty matrix. The formation of this network follows the percolation theory and the fiber orientation distribution law. When the fiber content exceeds the percolation threshold, the fibers begin to contact and overlap each other, forming a continuous network structure. This network not only provides mechanical reinforcement, but also effectively prevents crack propagation. The reinforcement mechanism of the fiber network includes three aspects: load transfer, crack bridging, and energy dissipation. Load transfer is achieved through the shear action of the fiber-matrix interface, which disperses concentrated stress to a larger area. Crack bridging prevents crack propagation by fibers spanning the crack surface. Energy dissipation consumes the energy of destruction through fiber extraction and fracture. The short fiber network has better isotropy and uniformity than the long fiber. Long fibers tend to entangle into clusters during stirring, forming an oriented distribution and leading to anisotropy of performance. Short fibers can be more uniformly distributed in the matrix, forming an isotropic reinforcing network and improving the overall performance stability of the material. At the same time, the improvement of the fiber network on the cohesion of the putty is mainly achieved by increasing the toughness and ductility of the matrix. The presence of fibers changes the failure mode of the material from brittle fracture to ductile fracture. Under external force, fibers first undergo elastic deformation and absorb part of the strain energy. When the stress exceeds the fiber-matrix interface strength, interface debonding occurs, further consuming energy. Finally, the fibers are pulled out or broken, achieving the final energy dissipation. The improvement of crack resistance not only lies in preventing crack initiation, but more importantly, in controlling crack propagation. The fiber network decomposes large cracks into multiple micro-cracks, reducing the degree of stress concentration. The bridging effect of fibers keeps the crack surface with a certain binding force, preventing rapid crack propagation. This synergistic reinforcement effect enables the putty to maintain good integrity under drying shrinkage, temperature changes, and external forces, significantly improving its reliability and durability in practical applications.

[0031] The performance stability of the material in a wide temperature range of-50 to 80℃ in the present application is derived from the synergistic effect of the multiphase composite structure. The ultra-low thermal conductivity of aerogel provides excellent thermal insulation performance for the material, reducing the influence of temperature gradient on the internal structure. The presence of fiber network prevents cracking caused by temperature stress through stress dispersion and crack arrest mechanism. Under low temperature conditions, the main challenge is the increase in brittleness of the material. The present application optimizes the matrix formulation and fiber content to improve toughness while maintaining strength. The micro-filling effect of nano-silica reduces defects in the matrix, reducing stress concentration; the porous structure of aerogel provides space for thermal stress release; the fiber network absorbs stress energy through deformation. Under high temperature conditions, the material faces the risk of thermal decomposition and performance degradation. The high temperature stability of inorganic components provides a basic guarantee for the material, and the selection of organic components considers their thermal stability and decomposition temperature to ensure stability within the use temperature range. Under high humidity conditions, the material faces the challenges of moisture absorption and strength loss, and the hydrophobic modification of aerogel significantly reduces its water absorption, maintaining the stability of thermal insulation performance. The densification of the gelled matrix and the micro-filling effect of nano-silica reduce the penetration path of water, improving the impermeability. In the salt spray environment, the corrosion of chloride ions is the main threat, and the presence of sulphoaluminate in the compounded cementitious material can combine with chloride ions to form Friedel salt, solidifying chloride ions and reducing their corrosion of metal components such as steel bars, and the pozzolanic reaction of nano-silica consumes calcium hydroxide which is susceptible to carbonation, improving the carbonation resistance of the matrix.

[0032] The low-temperature construction adaptability of the present application is realized by optimizing the low-temperature hydration performance and rheological properties of the cementitious material. The modified compounded cementitious material still maintains sufficient hydration activity at low temperature, ensuring strength development; the use of thixotropic modifier improves the drawdown performance at low temperature, reducing the construction difficulty. The rapid curing ability enables the material to adapt to the tight construction schedule requirements, improving the construction efficiency. The stability of construction performance is also reflected in the adaptability to environmental changes. The material can maintain consistent construction performance under different temperature and humidity conditions, reducing the quality fluctuations caused by environmental changes and improving the controllability and reliability of construction.

[0033] The advantages of the present application are: the solidifying agent-free design of the present application reduces cracking and improves construction safety; the pre-aging process broadens the construction environmental adaptability, significantly reducing the requirements for humidity and temperature; the uniform microstructure, low thermal conductivity and stable mechanical properties; the controllable cost is suitable for large-scale popularization and application. DETAILED DESCRIPTION

[0034] The present application will be further described in greater detail by way of specific embodiments. Those skilled in the art will be able to implement the present application based on the foregoing description. In addition, the embodiments of the present application involved in the following description are generally only a part of the embodiments of the present application, not all the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative labor shall fall within the scope of protection of the present application.

[0035] Unless otherwise specified, the raw materials used in the embodiments of the present application are commercially available or available to those skilled in the art. Unless otherwise specified, the methods used in the embodiments of the present application are methods mastered by those skilled in the art.

[0036] Embodiment 1: A putty for external wall thermal insulation, comprising the following components:

[0037] The preparation method of the putty comprises: 1) mixing silica aerogel and methyltrimethoxysilane uniformly according to a mass ratio of 8:1, dispersing in anhydrous ethanol, reacting at a temperature of 60 ℃ and a pH of 4 for 6 h, and washing and drying to obtain a nano-aerogel with a specific surface area ≥600 m 2 / g.

[0038] 2) Pre-mixing the nano-aerogel, ceramic fiber, calcium sulfate whisker, basalt fiber and calcium stearate according to the above table proportion, and ultrasonic treating at a temperature of 20 ℃, a fluctuation frequency of 40 kHz and a power of 600 W for 40 min to prepare a composite powder.

[0039] 3) Dry mixing the cement-based binding material, cellulose ether and water reducing agent uniformly according to the above table proportion, and mixing with the composite powder, stirring at a temperature of 15 ℃ and a rotation speed of 30 rpm for 10 min to prepare a base material, wherein the cement-based binding material is a mixture of sulfoaluminate cement and portland cement according to a mass ratio of 3:6, and nano-silicon dioxide is added to the portland cement at a proportion of 1 wt%.

[0040] 4) Slowly adding water to the base material according to the above table proportion, and stirring at a temperature of 15 ℃ and a rotation speed of 300 rpm for 20 min to prepare a precursor.

[0041] 5) Dynamic aging of the precursor, first segment aging at a temperature of -5 ℃ for 3 h, second segment aging at a temperature of 20 ℃ for 5 h, and then crushing and grinding the product to a mesh size of 240 mesh to prepare a putty powder.

[0042] The material prepared in the example was subjected to performance testing, and before the performance testing, the putty powder prepared in the example was mixed with deionized water in a ratio of 100:28 to form a putty paste, and the specific characterization results are as follows.

[0043] Thermal insulation performance test: According to the standard GB / T 10294-2008 "Determination of Steady-state Thermal Resistance and Related Properties of Thermal Insulation Materials", the steady-state heat flow method was used to evaluate the thermal insulation performance of the material. The sample preparation was to inject the putty paste into a 300 mm×300 mm×30 mm standard mold and scrape it into shape, and after curing, it was dried to a constant weight state. The detection used DRPL-III type flat plate thermal conductivity tester to measure the thermal conductivity at 25 ℃ average temperature, and the dry density parameter was calculated by the ratio of dry mass to volume of the sample.

[0044] Mechanical property test: According to the strength test part of the dynamic anti-cracking test in the standard JG / T 157-2009 "Putty for Building Exterior Wall", the standard test block method was used to evaluate the compressive strength, flexural strength and compression ratio of the material. The sample preparation was to inject the putty paste into a 40 mm×40 mm×160 mm three-ply metal mold to standardize the molding, and the INSTRON 3365 type universal testing machine was used to test the mechanical properties at a constant loading rate of 2.0 mm / min. The compressive strength and flexural strength were calculated according to the corresponding standard method, and the compression ratio was obtained by the ratio of compressive strength to flexural strength.

[0045] Freeze-thaw cycle test: According to the standard GB / T 50082-2009 "Standard for Testing Methods of Long-term Performance and Durability of Ordinary Concrete", the rapid freeze-thaw method was used to evaluate the durability of the material in a temperature alternating environment. The same standard test block as the mechanical property test was used, and after curing for 28 d, it was soaked in water for 48 h to reach saturation, and then placed in a TDR-1 type freeze-thaw test box for cycle test. Each freeze-thaw cycle includes 4 h of freezing at -20±2 ℃ and 4 h of melting in water at 20±2 ℃, and after 100 cycles, the test block was taken out and the surface water was wiped off to measure the compressive strength. The strength retention rate was calculated as (compressive strength after freeze-thaw / compressive strength before freeze-thaw)×100 %.

[0046] Salt fog resistance test: According to GB / T 1771-2007 "Determination of Resistance to Neutral Salt Spray of Paints and Varnishes", the neutral salt spray corrosion method was used to evaluate the corrosion resistance of the material in the marine environment. The putty paste was scraped onto the 70 mm x 150 mm x 4 mm asbestos cement board substrate, and after curing and molding, the remaining surfaces except the test surface were sealed with epoxy resin to prevent edge effects. The test was placed in a YWX-750 type salt spray test chamber, and a 5% NaCl solution was continuously sprayed at a constant temperature of 35±2 ℃ for 500 h to simulate the marine atmospheric corrosion environment. After the test, the sample surface was rinsed with deionized water and dried to constant weight, and the weight loss rate was calculated as [(pre-test mass - post-test mass) / pre-test mass] x 100%.

[0047] Anti-ultraviolet test: According to GB / T 1865-2009 "Artificial Weathering and Artificial Radiation Exposure of Paints and Varnishes", the xenon lamp artificial accelerated aging method was used to evaluate the durability of the material in the ultraviolet radiation environment. The same size sample as the salt fog resistance test was used for the test, and was placed in a xenon lamp aging test chamber for accelerated aging test. The test conditions were set as irradiance 0.51 W / m 2 @340 nm, blackboard temperature 65±3 ℃, chamber temperature 38±3 ℃, relative humidity 50±5 %, and a cycle mode of spraying water every 120 min for 18 min was used to simulate natural rainfall. After 2000 h of continuous aging, the thermal conductivity of the sample was measured, and the change rate of thermal conductivity was calculated as [(thermal conductivity after aging - thermal conductivity before aging) / thermal conductivity before aging] x 100%.

[0048]

[0049] Based on the above characterization results, the present application achieves a balance between thermal insulation, mechanical strength and environmental durability through component optimization and process innovation, meeting the long-term use requirements of external wall insulation materials in complex climate conditions.

[0050] The performance test results of Example 1 show that the prepared putty material exhibits excellent comprehensive performance. In terms of thermal insulation performance, the dry density is 285.5 kg / m 3, the thermal conductivity is as low as 0.037 W / (m·K), which is mainly due to the high thermal insulation properties of nano-aerogel and the uniform dispersion structure of composite powder, which is significantly better than the thermal conductivity of traditional external wall insulation materials. In the mechanical property test, the compressive strength is 12.8 MPa, the bending strength is 4.9 MPa, and the compression-bending ratio is as low as 2.61, which meets the requirement of JG / T 157-2009 standard that the compression-bending ratio of flexible putty is ≤3.0. The mechanical properties are due to the three-dimensional network structure formed by the controllable broken fibers: the synergistic effect of ceramic fibers, calcium sulfate whiskers and basalt fibers effectively transfers the load and bridges micro-cracks, while calcium stearate and cellulose ether optimize the interfacial bonding strength.

[0051] The durability test results are outstanding: the strength retention rate is as high as 93.3 % after 100 freeze-thaw cycles, indicating that the dynamic aging process significantly improves the structural stability of the material in a temperature alternating environment. The weight loss rate of salt spray resistance test is only 1.1 %, verifying the synergistic corrosion prevention mechanism of sulfaluminate cement solidification of chloride ions (generation of fried salt) and nano-silica filling effect. After 2000 h of ultraviolet accelerated aging, the change rate of thermal conductivity is only +3.2 %, indicating that the hydrophobically modified nano-aerogel and fiber network effectively inhibit the material degradation induced by ultraviolet light.

[0052] In addition, the construction performance test is carried out under the environmental conditions of low temperature construction. The actual working condition is simulated by self-defined method to evaluate the construction adaptability and early strength of the material in low temperature environment. The construction test is carried out in an environmental chamber with a temperature of-15±1 ℃ and a relative humidity of less than 85 %. 500 g of putty paste is placed on the squeegee to observe the working performance change within 5 min. The paste is soft, easy to squeegee, and no edge curling phenomenon is considered as good construction performance. The bad construction phenomena such as skinning and hardening are excluded. The low temperature curing strength test is carried out in the same low temperature environment. The putty is injected into a standard mold with a size of 40 mm×40 mm×160 mm. After leveling, it is placed for 24 h and demolded immediately. The bending strength is measured immediately using a universal testing machine. The curing strength achievement rate is obtained by calculating the ratio of the low temperature 24 h curing strength to the bending strength of the standard curing 28 d test block. The specific characterization results are as follows:

[0053] Example 2: A putty for external wall insulation, comprising the following components:

[0054] The preparation method of the putty comprises: 1) mixing silica aerogel and methyltrimethoxysilane uniformly according to a mass ratio of 10:1, dispersing in anhydrous ethanol, reacting at a temperature of 65 ℃ and a pH of 4.5 for 5 h, and washing and drying to obtain a nano-aerogel with a specific surface area of ≥600 m 2 / g.

[0055] 2) Nanometer aerogel, ceramic fiber, calcium sulfate whisker, basalt fiber, calcium stearate were premixed according to the above table, and were treated by ultrasonic at a temperature of 25 ℃, a fluctuation frequency of 45 kHz and a power of 650 W for 30 min to prepare a composite powder.

[0056] 3) The cement-based binding material, cellulose ether and water reducing agent were uniformly dry mixed according to the above table, and were mixed with the composite powder, and were stirred at a temperature of 20 ℃ and a rotation speed of 50 rpm for 7 min to prepare a base material, wherein the cement-based binding material was a mixture of sulfoaluminate cement and portland cement at a mass ratio of 3.5:6, and 1.5 wt% of nanometer silicon dioxide was added to the portland cement.

[0057] 4) Water was slowly added to the base material according to the above table, and was stirred at a temperature of 20 ℃ and a rotation speed of 400 rpm for 15 min to prepare a precursor.

[0058] 5) The precursor was dynamically aged, the first segment was aged at a temperature of 0 ℃ for 2.5 h, and the second segment was aged at a temperature of 23 ℃ for 4.5 h, and after dynamic pre-aging, the product was broken and ground to have a mesh number of 270 to prepare a putty powder.

[0059] The material prepared in the example was subjected to performance detection, and the specific characterization results were as follows.

[0060] Thermal insulation performance detection: according to the standard GB / T 10294-2008 "Determination of Steady Thermal Resistance and Related Properties of Thermal Insulation Materials", the steady heat flow method was used to evaluate the thermal insulation performance of the material. The sample preparation was that the putty paste was injected into a 300 mm×300 mm×30 mm standard mold and was scraped to form a shape, and after curing, it was dried to a constant weight state. The detection used a DRPL-III type flat plate thermal conductivity tester to measure the thermal conductivity at an average temperature of 25 ℃, and the dry density parameter was calculated by the ratio of the dry mass to the volume of the sample.

[0061] Mechanical performance detection: according to the strength test part of the dynamic anti-cracking test in the standard JG / T 157-2009 "Putty for Building Exterior Wall", the standard test block method was used to evaluate the compressive strength, flexural strength and compression-bending ratio of the material. The sample preparation was that the putty paste was injected into a 40 mm×40 mm×160 mm three-ply metal mold to form a standard shape, and the mechanical performance test was carried out using an INSTRON 3365 type universal testing machine at a constant loading rate of 2.0 mm / min. The compressive strength and flexural strength were calculated according to the corresponding standard method, and the compression-bending ratio was obtained by the ratio of the compressive strength to the flexural strength.

[0062] Freeze-thaw cycle test: According to GB / T 50082-2009 "Standard for testing long-term properties and durability of ordinary concrete", the durability of the material in the temperature alternating environment was evaluated by the rapid freeze-thaw method. The same size standard test blocks as the mechanical properties were used for the test, and after curing for 28 d, they were immersed in water for 48 h to reach saturation, and then placed in a TDR-1 type freeze-thaw test box for cycle test. Each freeze-thaw cycle included -20±2 ℃ freezing for 4 h and 20±2 ℃ thawing in water for 4 h, and after 100 cycles, the test blocks were taken out and the surface water was wiped off to determine the compressive strength. The strength retention rate was calculated as (compressive strength after freeze-thaw / compressive strength before freeze-thaw) x 100%.

[0063] Salt spray resistance test: According to GB / T 1771-2007 "Determination of resistance to neutral salt spray of paint and varnish", the corrosion resistance of the material in the marine environment was evaluated by the neutral salt spray corrosion method. The putty paste was coated on the 70 mm x 150 mm x 4 mm asbestos cement board substrate, and after curing and molding, the remaining surfaces except the test surface were sealed with epoxy resin to prevent edge effects. The test sample was placed in a YWX-750 type salt spray test chamber, and a 5% NaCl solution was continuously sprayed at a constant temperature of 35±2 ℃ for 500 h to simulate the marine atmospheric corrosion environment. After the test, the sample surface was rinsed with deionized water and dried to constant weight, and the weight loss rate was calculated as [(mass before test - mass after test) / mass before test] x 100%.

[0064] UV resistance test: According to GB / T 1865-2009 "Artificial weathering and artificial radiation exposure of paint and varnish", the durability of the material in the ultraviolet radiation environment was evaluated by the xenon lamp artificial accelerated aging method. The same size test samples as the salt spray resistance were used for the test, and were placed in a xenon lamp aging test chamber for accelerated aging test. The test conditions were set as irradiance 0.51 W / m 2 @340 nm, blackboard temperature 65±3 ℃, chamber temperature 38±3 ℃, relative humidity 50±5%, and a cycle mode of spraying water every 120 min for 18 min was used to simulate natural rainfall. After 2000 h of continuous aging, the thermal conductivity of the sample was measured, and the thermal conductivity change rate was calculated as [(thermal conductivity after aging - thermal conductivity before aging) / thermal conductivity before aging] x 100%.

[0065]

[0066] Based on the above characterization results, the present scheme further improves the mechanical strength and environmental durability on the basis of maintaining excellent thermal insulation performance through component ratio adjustment and process optimization. In terms of thermal insulation performance, the dry density is 288.9 kg / m 3The thermal conductivity of 0.035 W / (m·K) indicates that the material maintains low heat conduction characteristics, which is due to the more complete closed pore structure formed by methyltrimethoxysilane modified nano-aerogel, which has a specific surface area of ≥600 m 2 / g significantly blocks the transfer of thermal radiation. In the mechanical property test, the compressive strength of 13.5 MPa and the flexural strength of 5.2 MPa are increased by 5.5% and 6.1% respectively compared with Example 1, and the ratio of compression to folding is reduced to 2.60, which is due to the ultrasonic treatment process making the fiber-powder interface combination more closely, effectively improving the load transfer efficiency.

[0067] Durability performance is particularly outstanding: freeze-thaw cycle strength retention rate reaches 95.4%, proving that the two-stage dynamic aging process significantly enhances the material's resistance to freeze-thaw by regulating the crystalline morphology of hydration products; salt spray resistance rate is only 0.9%, reflecting the dual corrosion prevention mechanism of sulfaluminate cement solidifying chloride ions and nano-silica filling capillary pores; the change rate of thermal conductivity after UV aging is +2.9%, which is the best in the series, confirming that the hydrophobically modified aerogel still maintains a stable pore structure under xenon lamp radiation, and its mass fraction of 7% forms an effective UV barrier. Therefore, this formula ensures ultra-low thermal conductivity while meeting the requirements of external wall insulation engineering in harsh climate regions in terms of comprehensive performance indicators.

[0068] In addition, the construction performance is tested under low-temperature construction environmental conditions, and a self-defined method is used to simulate actual working conditions to evaluate the material's construction adaptability and early strength in low-temperature environments. The construction test is conducted in an environmental chamber with a temperature of -15±1 ℃ and a relative humidity of less than 85%. 500 g of putty paste is placed on a squeegee to observe the working performance changes within 5 min. The paste is considered to have good construction performance if it is soft, easy to squeegee, and has no edge curling. Unfavorable construction phenomena such as skinning and hardening are excluded. The low-temperature curing strength test is conducted in the same low-temperature environment. The putty is injected into a 40 mm×40 mm×160 mm standard mold, leveled off, and then left to stand for 24 h before demolding. Immediately after demolding, the universal testing machine is used to measure the flexural strength. The curing strength achievement rate is obtained by calculating the ratio of the low-temperature 24 h curing strength to the standard curing 28 d test block flexural strength. The specific representation results are as follows:

[0069] Example 3: A putty for external wall insulation, comprising the following components:

[0070] The preparation method of the putty comprises: 1) mixing silica aerogel and methyltrimethoxysilane in a mass ratio of 12:1 uniformly, dispersing in anhydrous ethanol, reacting at a temperature of 70 ℃ and a pH of 5 for 4 h, and then washing and drying to obtain a specific surface area of ≥600 m 2 / g, to prepare nano-aerogels.

[0071] 2) Premix nano-aerogel, ceramic fiber, calcium sulfate whiskers, basalt fiber and calcium stearate according to the proportions in the table above, and sonicate them for 20 min at a temperature of 30 ℃, a fluctuation frequency of 50 kHz and a power of 700 W to prepare composite powder.

[0072] 3) After dry mixing the cement-based cementitious material, cellulose ether, and water-reducing agent according to the proportions in the table above, mix them with the composite powder and stir for 5 minutes at a temperature of 25 ℃ and a speed of 70 rpm to form a base material. The cement-based cementitious material is a mixture of sulfoaluminate cement and silicate cement in a mass ratio of 4:6, with 2 wt% nano silica added to the silicate cement.

[0073] 4) Slowly add water to the substrate according to the proportions in the table above, and stir for 10 minutes at a temperature of 25 ℃ and a speed of 500 rpm to prepare the precursor.

[0074] 5) The precursor is dynamically aged. The first stage is aged at 5 ℃ for 2 h, and the second stage is aged at 25 ℃ for 4 h. After dynamic pre-aging, it is crushed and ground to make the product with a mesh size of 300 mesh, and putty powder is made.

[0075] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0076] Thermal insulation performance testing: Referring to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials", the steady-state heat flow method was used to evaluate the thermal insulation performance of the materials. Sample preparation: Putty paste was poured into a 300 mm × 300 mm × 30 mm standard mold, smoothed, and cured before drying to constant weight. Testing: The thermal conductivity was measured using a DRPL-III type flat plate thermal conductivity meter at an average temperature of 25 ℃. Simultaneously, the dry density parameter was calculated using the ratio of the dry mass to the volume of the sample.

[0077] Mechanical property testing: Referring to the strength test section of the dynamic crack resistance test in JG / T 157-2009 "Putty for Building Exterior Walls" standard, the compressive strength, flexural strength, and compressive-flexural ratio of the material were evaluated using the standard specimen method. Specimen preparation: Putty paste was injected into a 40 mm × 40 mm × 160 mm triple metal mold for standard forming. Mechanical property testing was conducted using an INSTRON 3365 universal testing machine at a constant loading rate of 2.0 mm / min. Compressive strength and flexural strength were calculated separately according to the corresponding standard methods, and the compressive-flexural ratio was obtained by the ratio of compressive strength to flexural strength.

[0078] Freeze-thaw cycle test: According to GB / T 50082-2009 "Standard for testing long-term properties and durability of ordinary concrete", the durability of the material in the temperature alternating environment was evaluated by the rapid freeze-thaw method. The same size standard test blocks as the mechanical properties were used for the test, and after curing for 28 d, they were immersed in water for 48 h to reach saturation, and then placed in a TDR-1 type freeze-thaw test box for cycle test. Each freeze-thaw cycle included -20±2 ℃ freezing for 4 h and 20±2 ℃ thawing in water for 4 h, and after 100 cycles, the test blocks were taken out and the surface water was wiped off to determine the compressive strength. The strength retention rate was calculated as (compressive strength after freeze-thaw / compressive strength before freeze-thaw) x 100%.

[0079] Salt spray resistance test: According to GB / T 1771-2007 "Determination of resistance to neutral salt spray of paint and varnish", the corrosion resistance of the material in the marine environment was evaluated by the neutral salt spray corrosion method. The putty paste was coated on the 70 mm x 150 mm x 4 mm asbestos cement board substrate, and after curing and molding, the remaining surfaces except the test surface were sealed with epoxy resin to prevent edge effects. The test sample was placed in a YWX-750 type salt spray test chamber, and a 5% NaCl solution was continuously sprayed at a constant temperature of 35±2 ℃ for 500 h to simulate the marine atmospheric corrosion environment. After the test, the sample surface was rinsed with deionized water and dried to constant weight, and the weight loss rate was calculated as [(mass before test - mass after test) / mass before test] x 100%.

[0080] UV resistance test: According to GB / T 1865-2009 "Artificial weathering and artificial radiation exposure of paint and varnish", the durability of the material in the ultraviolet radiation environment was evaluated by the xenon lamp artificial accelerated aging method. The same size test samples as the salt spray resistance were used for the test, and were placed in a xenon lamp aging test chamber for accelerated aging test. The test conditions were set as irradiance 0.51 W / m 2 @340 nm, blackboard temperature 65±3 ℃, chamber temperature 38±3 ℃, relative humidity 50±5%, and a cycle mode of spraying water every 120 min for 18 min was used to simulate natural rainfall. After 2000 h of continuous aging, the thermal conductivity of the sample was measured, and the thermal conductivity change rate was calculated as [(thermal conductivity after aging - thermal conductivity before aging) / thermal conductivity before aging] x 100%.

[0081]

[0082] Based on the above characterization results, the present scheme further improves the mechanical strength and environmental durability on the basis of maintaining excellent thermal insulation performance through component ratio adjustment and process optimization. In terms of thermal insulation performance, the dry density is 293.0 kg / m 3The thermal conductivity of 0.039 W / (m-K) indicates that the material maintains good low thermal conduction characteristics, which is mainly due to the closed pore structure formed by the nanometer aerogel effectively blocking heat transfer. In the mechanical property test, the compressive strength of 14.3 MPa and the flexural strength of 5.4 MPa are both improved compared to Example 2, and the compression and folding ratio is 2.65, indicating that the material exhibits good toughness balance when bearing load, which benefits from the ultrasonic treatment process optimizing the interfacial bonding strength between fibers and powders.

[0083] Durability: The freeze-thaw cycle strength retention rate reaches 91.7%, which proves that the two-stage dynamic aging process effectively enhances the stability of the internal structure of the material, so that it can still maintain a high strength under repeated freeze-thaw conditions; the salt spray resistance weight loss rate is 1.3%, which reflects the synergistic resistance of the sulphoaluminate cement matrix and the nanosilica filling to chloride ion corrosion; the thermal conductivity change rate after ultraviolet aging is +3.8%, which confirms that the hydrophobically modified aerogel has good structural stability under long-term ultraviolet irradiation environment, and effectively blocks the negative effects of ultraviolet radiation on the thermal insulation performance of the material.

[0084] In addition, the construction performance test is carried out under the environmental conditions of low temperature construction, and the actual working condition is simulated by using self-defined method to evaluate the construction adaptability and early strength of the material under low temperature environment. The construction test is carried out in an environment chamber with a temperature of-15±1 ℃ and a relative humidity of less than 85%. 500 g of putty paste is placed on the scraper to observe the working performance change within 5 min. The paste is soft, easy to scrape and coat, and has no edge curling phenomenon, which is the judgment standard of good construction performance. The skinning, hardening and other adverse construction phenomena are excluded. The low-temperature curing strength test is carried out under the same low-temperature environment. The putty is injected into a 40 mm×40 mm×160 mm standard mold, and after scraping, it is placed for 24 h and demolded immediately. The universal testing machine is used to measure the flexural strength. The curing strength achievement rate is obtained by calculating the ratio of the low-temperature 24 h curing strength to the flexural strength of the standard curing 28 d test block. The specific characterization results are as follows:

[0085] Comparative Example 1: Based on Example 2, only the preparation of nanometer aerogel is changed, and the other steps are the same as Example 2. The specific settings are as follows:

[0086] The performance test method of the product of the comparative example is completely consistent with Example 1, and part of the performance is characterized, and the characterization results are shown in the following table:

[0087] Based on the above characterization results, the thermal conductivity of D1-1 group using unmodified silica aerogel increases to 0.046 W / (m·K), the strength retention rate after freeze-thaw decreases, the interface bonding presents obvious gap and the aerogel appears agglomeration phenomenon. This is due to the high activity of unmodified aerogel surface hydroxyl group, which is easy to react with water during mixing and hydration, leading to self-aggregation between aerogel particles, destroying the integrity of closed pore structure, reducing the thermal insulation performance, and forming a weak interface between the fiber and the matrix, weakening the freeze-thaw resistance.

[0088] The thermal conductivity of D1-2 group using ordinary silane coupling agent modified aerogel is 0.041 W / (m·K), the strength retention rate after freeze-thaw is 85.2 %, and the interface bonding exists local poor area. This shows that although ordinary silane coupling agent can improve the dispersibility of aerogel to some extent, its hydrolytic stability and matching with the matrix are not as good as methyltrimethoxysilane. The modified layer is easy to partially fail in dynamic aging or hydration environment, resulting in slightly poor stability of closed pore structure and insufficient interface bonding strength. The thermal insulation and durability performance are inferior to Example 2.

[0089] The thermal conductivity of D1-3 group without using nano-aerogel is significantly deteriorated to 0.089 W / (m·K), the strength retention rate after freeze-thaw is greatly reduced, and the microstructure presents certain porous characteristics and the fiber is exposed. This fully proves that nano-aerogel is crucial for building efficient thermal insulation network in this system, and its absence leads to a sharp decrease in material thermal resistance. At the same time, the loss of aerogel's bridging effect on microcracks and pore structure optimization makes the material prone to structural damage due to water intrusion and ice crystal pressure during freeze-thaw cycles, resulting in serious damage to mechanical properties and durability.

[0090] Comparative Example 2: Based on Example 2, this example only modifies the preparation process of cement-based gel material, and the remaining steps are the same as Example 2. The specific settings are as follows:

[0091] The performance test method of the product of the comparative example is completely consistent with Example 1, and partial performance characterization is carried out, and the characterization results are shown in the following table:

[0092] Based on the above characterization results, the compressive strength of D2-1 group using ordinary Portland cement is significantly reduced to 10.2 MPa, the low-temperature curing strength achievement rate is only 58.2 %, the microstructure presents loose state and the aerogel wrapping is poor. This is mainly due to the fact that the early hydration rate of ordinary Portland cement is greatly slowed down in low temperature environment, resulting in insufficient hydration product generation, which cannot effectively wrap and fix nano-aerogel and other reinforcing components, making the overall structure of the material loose and the strength development slow, which seriously affects the early strength achievement and final mechanical properties after low-temperature construction.

[0093] D2-2 group only used sulphoaluminate cement, which had a compressive strength of 11.8 MPa, and the low-temperature curing strength achievement rate was 75.1%, but microstructure observation showed local microcracks. This shows that although sulphoaluminate cement has high early hydration activity, which helps to improve low-temperature curing performance, its single use leads to greater shrinkage of the system, which is prone to microcracks under the action of drying or stress, weakening the overall performance of the material.

[0094] D2-3 group used a composite system of sulphoaluminate cement and Portland cement, but did not add nano-silicon dioxide, which had a compressive strength of 12.1 MPa, and the low-temperature curing strength achievement rate was 70.6%, and the microstructure showed that the aerogel was not uniformly dispersed and had agglomeration. This confirms the key role of nano-silicon dioxide: as a nanoscale filler, it not only effectively fills the voids between cement particles, refines the pore structure to improve density, but also acts as a crystal nucleus to promote hydration reactions, especially significantly improving the dispersion stability of nano-aerogel in the matrix. The absence of nano-silicon dioxide leads to agglomeration of aerogel particles during mixing, which cannot form a uniformly distributed thermal insulation network, and reduces the wrapping and bonding strength of the matrix to the aerogel, thereby affecting the mechanical properties and low-temperature curing efficiency of the material.

[0095] The results of Comparative Example 2 fully verify the necessity of the cement-based gelling material formulation used in Example 2: this combination not only takes advantage of the early strength of sulphoaluminate cement and the late stability of Portland cement through the composite cement, but also optimizes the matrix density, hydration process, and dispersion and interfacial bonding of key functional components through the addition of nano-silicon dioxide, thereby synergistically ensuring excellent comprehensive performance of the material, especially the key low-temperature curing ability.

[0096] Comparative Example 3: Based on Example 2, this example only modifies the dynamic aging process, and the remaining steps are the same as Example 2. The specific settings are as follows:

[0097] The performance test method of the product of Comparative Example is completely consistent with Example 1, and partial performance characterization is carried out, and the characterization results are shown in the following table:

[0098] Analyzing the above characterization results, the D3-1 group cancels the pre-aging process and directly grinds, which significantly prolongs the construction curing time to >20 min, greatly reduces the low-temperature strength achievement rate, has poor surface flatness, and shortens the construction open time to 15 min. This is due to the lack of pre-aging stage, which destroys the uniformity of the internal hydration reaction of the material, making the microstructure loose and unable to form an effective support network, leading to delayed curing, insufficient strength development, and deterioration of workability.

[0099] D3-2 group adopts single-stage aging, the construction curing time is 8 min, the low-temperature strength reaching rate is 65.6 %, the surface flatness is general, the construction open time is 30 min, and all are inferior to example 2. This shows that single-stage aging cannot simulate temperature gradient change, the hydration reaction is insufficient, the matrix density is reduced, the early strength development of the material and the construction stability are affected.

[0100] D3-3 group adjusts the grinding mesh to 180 meshes, the construction curing time is 6 min, the low-temperature strength reaching rate is 72.2 %, the surface flatness is general, and the construction open time is 35 min. Although it is improved compared with D3-1 and D3-2, it is still weaker than 5 min, 82.7 % and excellent flatness of example 2. This is mainly due to the decrease of the grinding mesh, which leads to the increase of the particle size, reduces the interface bonding efficiency of the fiber and the matrix, limits the strength reaching rate of the material in the low-temperature environment, and the rough surface microstructure affects the flatness performance.

[0101] D3-4 group adjusts the grinding mesh to 420 meshes, the construction curing time is 4 min, the low-temperature strength reaching rate is 68.9 %, the surface flatness is general, and the construction open time is 25 min. This is due to the excessive grinding, which leads to the non-uniformity of the distribution of the nano-aerogel and the fiber filler in the matrix in the microscale, the molecular bridging density of the methyltrimethoxysilane modified aerogel in the local area is too high, a “rich area” is formed, and the bridging point in the adjacent area is insufficient, which leads to the significant distribution gradient of the interface bonding energy. The discontinuity of this micro-component distribution weakens the overall synergistic enhancement effect of the material at low temperature, and the strength reaching rate is reduced.

[0102] The two-stage dynamic aging process adopted in the application significantly improves the low-temperature curing efficiency, the strength reaching rate and the construction flatness of the material by precisely controlling the hydration process and the particle refinement, and any simplification or adjustment weakens the comprehensive performance.

[0103] Comparative example 4: based on example 2, only the amount of water reducing agent is changed, and the other steps are the same as those of example 2. The specific settings are as follows:

[0104] The performance test method of the product of the comparative example is completely consistent with that of example 1, and part of the performance is characterized, and the characterization results are shown in the following table:

[0105] Based on the above characterization results, the water-reducing agent dosage in D4-1 group is insufficient, which leads to weakened dispersion and hydration inhibition effect on cement particles, premature hydration reaction, and advanced rapid hydration exothermic phase of sulphoaluminate cement, resulting in shortened temperature compensation window. As a result, the self-heating effect is not fully maintained, the early support strength structure is not sufficient at low temperature, and finally the low-temperature strength achievement rate and freeze-thaw stability are significantly reduced.

[0106] In D4-2 group, the excess water-reducing agent is excessively adsorbed on the surface of cement particles, significantly prolonging the hydration induction period and inhibiting the early exothermic reaction of sulphoaluminate cement. The self-heating effect is delayed and the strength is weakened, and the system cannot obtain sufficient heat compensation at the pre-hydration low temperature stage, resulting in too low hydration reaction rate and slow early structure formation. As a result, the low-temperature strength achievement rate is low, and the overall mechanical properties and freeze-thaw resistance are affected.

[0107] Based on the characterization data in this example, in the present application, the water-reducing agent not only adjusts the construction fluidity, but also precisely controls the hydration process and self-heating effect to affect the microstructure formation and low-temperature performance development. The dosage thereof needs to be strictly controlled within the range of 0.5-1.0 wt%, so as to achieve the balance between hydration inhibition and exothermic compensation, ensure the formation of uniform and dense microstructure in the pre-hydration stage, and finally obtain excellent construction performance, mechanical properties and durability.

Claims

1. A method for preparing a putty for external wall insulation, characterized in that, the method comprises: 1) proportioning according to the following mass percentages: cement-based binder 45-55 wt%, nano-aerogel 5-10 wt%, ceramic fiber 3-5 wt%, calcium sulfate whisker 2-4 wt%, basalt fiber 1-3 wt%, calcium stearate 0.5-1.0 wt%, cellulose ether 0.3-0.5 wt%, water reducing agent 0.5-1.0 wt%, and the balance being water; 2) after the proportioning is completed, the nano-aerogel, ceramic fiber, calcium sulfate whisker, basalt fiber and calcium stearate are premixed in proportion to form a composite powder; 3) the cement-based binder, cellulose ether and water reducing agent are dry-mixed uniformly, and then mixed with the composite powder to form a base material; 4) water is slowly added to the base material, and stirring is continued to form a precursor; and 5) the precursor is subjected to dynamic pre-aging, and then broken and ground into putty powder. 2.The method for preparing a putty for external wall insulation according to claim 1, characterized in that, in step 1), the nano-aerogel is silica aerogel modified by methyltrimethoxysilane twice; in step 1), the ceramic fiber has a length of 3-6 mm and an aspect ratio of 30-50; in step 1), the calcium sulfate whisker has a length of 50-100 μm and an aspect ratio of 20-30; and in step 1), the basalt fiber has a length of 3-6 mm. 3.The method for preparing a putty for external wall insulation according to claim 1 or 2, characterized in that, in step 1), the nano-aerogel is prepared by the following method: 4.The method for preparing a putty for external wall insulation according to claim 1, characterized in that, in step 2), the premixing is ultrasonically treated at a temperature of 20-30 ℃, a fluctuation frequency of 40-50 kHz and a power of 600-700 W for 20-40 min. 5.The method for preparing a putty for external wall insulation according to claim 1, characterized in that, in step 1), the cement-based binder is a composite system of sulfoaluminate cement and portland cement, the sulfoaluminate cement and the portland cement are mixed in a mass ratio of (3-4) : 6, and 1-2 wt% of nano-silicon dioxide is added to the portland cement. 6.The method for preparing a putty for external wall insulation according to claim 1, characterized in that, in step 3), the base material is stirred at a temperature of 15-25 ℃ and a rotation speed of 30-70 rpm for 5-10 min. 7.The method for preparing a putty for external wall insulation according to claim 1, characterized in that, in step 4), the stirring is carried out at a temperature of 15-25 ℃ and a rotation speed of 300-500 rpm for 10-20 min. 8.The method for preparing a putty for external wall insulation according to claim 1, characterized in that, in step 5), the dynamic pre-aging is gradient aging, the first section is aged in a temperature of -5-5 ℃ for 2-3 h, and the second section is aged in a temperature of 20-25 ℃ for 4-5 h. ​ ​ ​ ​ ​ ​ ​ Silica aerogel and methyltrimethoxysilane are mixed uniformly according to a mass ratio of (8-12):1, dispersed in anhydrous ethanol, and reacted at a temperature of 60-70 ℃ and a pH of 4-5 for 4-6 h, to obtain a product with a specific surface area of ≥600 m 2 / g after washing and drying. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Step 4) the crushing grinding makes the product mesh number 240-300 mesh.

9. A putty for external wall thermal insulation prepared by any of the methods of claims 1 to 8.

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