Low-thermal-conductivity high-pressure-resistant phase change microcapsule foam concrete and preparation method thereof

Abstract

The application discloses a kind of low thermal conductivity high compression phase change microcapsule foam concrete and its composite dispersion-interface anchoring preparation method.The method prepares composite dispersion solution with non-ionic surfactant and silane coupling agent, carries out pre-adsorption coating treatment to phase change microcapsule, so that wet dispersion layer and interface anchoring layer are formed on its surface;Then, the treated phase change microcapsule is mixed with cement and prefabricated foam, and foam concrete is prepared by pouring, hardening and curing.The application can improve the dispersion stability of phase change microcapsule in cement paste, enhance the interface combination of phase change microcapsule and cement hydration product, reduce the thermal conductivity of the material and increase the compressive strength, and is suitable for building energy saving and temperature regulation type cement-based material.

Description

Technical Field

[0001] This invention relates to the field of concrete materials, specifically to a low thermal conductivity, high compressive strength phase change microcapsule foam concrete and its preparation method. Background Technology

[0002] Foamed concrete is a lightweight porous material formed by introducing a large number of closed or semi-closed pores into the interior of cement-based materials through physical or chemical foaming. Due to its low density, low thermal conductivity, good workability, and ability to reduce building weight, foamed concrete has been widely used in building energy conservation, lightweight partitions, roof insulation, ground backfilling, and urban infrastructure. Compared with ordinary dense cement-based materials, foamed concrete effectively reduces heat conduction through its internal porous structure, thus exhibiting better thermal insulation performance. However, traditional foamed concrete mainly relies on static insulation to reduce heat transfer. When there are diurnal temperature variations, seasonal temperature fluctuations, or dynamic heat loads, it lacks the ability to actively absorb, store, and release heat, making it difficult to effectively buffer and regulate temperature fluctuations.

[0003] To further enhance the thermal regulation capabilities of foamed concrete, existing technologies propose introducing phase change materials (PCMs) into the foamed concrete system. PCMs can absorb or release latent heat during solid-liquid phase transitions, thereby achieving thermal energy storage and temperature regulation. Compared to directly incorporating PCMs such as paraffin wax and fatty acids, preparing PCMs into microcapsules before introducing them into cement-based systems can, to some extent, prevent leakage of the PCM core material and improve the morphological stability, thermal cycling stability, and environmental adaptability of the PCMs. Therefore, PCM microcapsules are considered a suitable functional component for cement-based materials such as foamed concrete. Incorporating PCM microcapsules into foamed concrete is expected to endow it with heat storage, heat release, and temperature regulation functions while maintaining the material's lightweight and insulating properties, thus achieving the integration of structural load-bearing and thermal functions.

[0004] However, foamed concrete systems are typical multiphase, multi-interface, high-alkalinity, and high-ionic-strength systems, making the stable dispersion and interfacial bonding of phase change microcapsules within them quite challenging. Phase change microcapsules typically consist of an organic phase change core material and an inorganic, organic, or organic-inorganic composite shell. Because phase change core materials are often hydrophobic, and organic components may remain or trace amounts of core material may seep out during microcapsule preparation, the surface of phase change microcapsules often exhibits certain hydrophobic properties, making it difficult to fully wet and disperse in hydrophilic cement paste. In the initial mixing stage, phase change microcapsules are prone to initial agglomeration, leading to uneven distribution within the paste.

[0005] In addition, cement paste contains a large amount of Plasma, with its high ionic strength and strong alkalinity, compresses the electrical double layer on the surface of phase change microcapsule particles, weakening the electrostatic repulsion between particles. This leads to secondary aggregation of the microcapsules during stirring, flow, shearing, and early hydration. The aggregated microcapsules form unevenly sized and spatially distributed clusters within the foamed concrete, disrupting its homogeneity and creating stress concentration points under load, thus reducing the material's compressive strength and durability.

[0006] On the other hand, existing phase change microcapsule shells typically lack active groups capable of forming stable chemical bonds with cement hydration products. The bonding between phase change microcapsules and cement hydration products such as hydrated calcium silicate gel, calcium hydroxide, and ettringite relies primarily on physical embedding, van der Waals forces, or weak interfacial interactions, resulting in insufficient interfacial bonding strength. During the hardening and service life of foamed concrete, phase change microcapsules may experience interfacial debonding, slippage, or even localized rupture, leading to problems such as pore structure deterioration, cell wall damage, or an increase in locally interconnected pores. These defects not only affect the mechanical properties of the material but also reduce the proportion of phase change microcapsules effectively participating in phase changes, making it difficult for latent heat to be uniformly absorbed and released within the material, thereby weakening the overall thermal buffering and temperature regulation capabilities of foamed concrete.

[0007] How to enable phase change microcapsules to simultaneously achieve good initial wettability, dispersion stability, and interfacial bonding stability in a high-alkali, high-ionic-strength foamed concrete system, and thus prepare phase change microcapsule foamed concrete with low thermal conductivity, high compressive strength, and thermal regulation capability, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address one of the aforementioned technical problems, this patent provides a low thermal conductivity, high compressive strength phase change microcapsule foam concrete and its preparation method.

[0009] According to a first aspect of the present invention, a phase change microcapsule foamed concrete with low thermal conductivity and high compressive strength is provided, comprising a cement matrix, phase change microcapsules dispersed in the cement matrix, and a pore structure; the surface of the phase change microcapsules has a composite interface functional layer, the composite interface functional layer comprising a wetting and dispersing layer formed by a nonionic surfactant and an interface anchoring layer formed by a silane coupling agent; the wetting and dispersing layer is used to improve the wettability of the phase change microcapsules in cement paste and inhibit the agglomeration of the phase change microcapsules, and the interface anchoring layer is used to form an interfacial bond between the phase change microcapsules and cement hydration products.

[0010] Preferably, the amount of phase change microcapsules is 5 wt.% to 15 wt.% of the cement mass.

[0011] Preferably, the nonionic surfactant is one or both of polyoxyethylene surfactant and polyvinylpyrrolidone.

[0012] Preferably, the nonionic surfactant is polyvinylpyrrolidone K30.

[0013] Preferably, the silane coupling agent is an organosilicon compound that can be hydrolyzed in an alkaline environment and undergo a condensation reaction with cement hydration products.

[0014] Preferably, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0015] Preferably, the phase change microcapsule is a core-shell structured microparticle, which includes a phase change core material and a shell layer covering the phase change core material.

[0016] Preferably, the phase change core material includes one or more of paraffin wax and fatty acids; and / or, the shell layer includes a silica shell layer, a polymer shell layer, or an organic-inorganic composite shell layer.

[0017] Preferably, the phase change microcapsule is a silica shell phase change microcapsule, and the silane coupling agent forms a Si-O-Si bond by condensation reaction with the silica shell through hydrolysis of the silanol group.

[0018] Preferably, the cement hydration product includes hydrated calcium silicate gel, and the silane coupling agent forms a chemically bridged structure with the hydrated calcium silicate gel.

[0019] Preferably, the cell structure is introduced by pre-formed foam, which is formed by foaming with an anionic foaming agent.

[0020] Preferably, the phase change microcapsule foam concrete has a dry density of 500 kg / m³ to 700 kg / m³, a thermal conductivity of not more than 0.20 W / (m·K), and a 28-day compressive strength of not less than 2.0 MPa.

[0021] According to another aspect of the present invention, a method for preparing phase change microcapsule foam concrete with low thermal conductivity and high compressive strength is provided, comprising the following steps: S1, preparing a composite dispersion solution: adding a nonionic surfactant and a silane coupling agent to water and dispersing them to obtain a composite dispersion solution; S2, preparing a phase change microcapsule composite dispersion liquid: adding phase change microcapsules to the composite dispersion solution for pre-adsorption and coating treatment, so that the nonionic surfactant and the silane coupling agent are adsorbed or grafted onto the surface of the phase change microcapsules to obtain a phase change microcapsule composite dispersion liquid; S3, preparing pre-foam: adding a foaming agent to... A foaming liquid is prepared in water and foamed to obtain pre-made foam; S4, a cement slurry containing phase change microcapsules is prepared by mixing and stirring cement with the phase change microcapsule composite dispersion to obtain a cement slurry containing phase change microcapsules; S5, a phase change microcapsule foamed concrete slurry is prepared by adding the pre-made foam to the cement slurry containing phase change microcapsules and mixing evenly to obtain a phase change microcapsule foamed concrete slurry; S6, molding and curing: the phase change microcapsule foamed concrete slurry is poured into a mold, hardened, demolded, and then cured to obtain the low thermal conductivity and high compressive strength phase change microcapsule foamed concrete.

[0022] Preferably, in step S1, the nonionic surfactant is polyvinylpyrrolidone K30, and the silane coupling agent is γ-aminopropyltriethoxysilane.

[0023] Preferably, in step S1, the total amount of the nonionic surfactant and the silane coupling agent is 20 wt.% to 40 wt.% of the mass of the phase change microcapsules.

[0024] Preferably, in step S1, the dispersion treatment is ultrasonic treatment, with an ultrasonic power of 100 W to 160 W and an ultrasonic time of 10 min to 20 min.

[0025] Preferably, the ultrasonic power is 130 W and the ultrasonic time is 15 min.

[0026] Preferably, in step S2, the amount of phase change microcapsules used is 5 wt.% to 15 wt.% of the cement mass.

[0027] Preferably, in step S2, the pre-adsorption coating treatment includes stirring at a speed of 600 rpm to 1000 rpm for 20 min to 40 min.

[0028] Preferably, the pre-adsorption coating treatment includes stirring at 800 rpm for 30 min.

[0029] Preferably, in step S3, the foaming agent is an anionic foaming agent, and the liquid-to-solid ratio of the foaming liquid is 1:250 to 1:350.

[0030] Preferably, the liquid-to-solid ratio of the foaming liquid is 1:310.

[0031] Preferably, in step S3, the density of the pre-made foam is 50 kg / m³ to 70 kg / m³.

[0032] Preferably, the density of the pre-made foam is 60 kg / m³.

[0033] Preferably, in step S4, when the cement and the phase change microcapsule composite dispersion are mixed, the mixture is first slowly stirred for 0.5 min to 2 min, and then quickly stirred for 0.5 min to 2 min.

[0034] Preferably, in step S5, the pre-made foam is added to the cement slurry containing phase change microcapsules in multiple batches.

[0035] Preferably, the pre-made foam is added to the cement slurry containing phase change microcapsules in three separate additions.

[0036] Preferably, in step S6, the phase change microcapsule foam concrete slurry is added to the mold in two batches, vibrated for 20 to 60 seconds, leveled, covered with a film, and hardened at 18 to 25 degrees Celsius for 36 to 60 hours before demolding and continued curing for 28 days.

[0037] Preferably, in step S6, the oscillation time is 30 s, and the hardening condition is hardening at 20±2 ℃ for 48 h.

[0038] Preferably, the water-to-gel ratio of the composite dispersion solution is 0.4 to 0.6.

[0039] Preferably, the water-to-gel ratio of the composite dispersion solution is 0.5.

[0040] According to another aspect of the present invention, an application of a composite dispersion-interface anchoring system in the preparation of phase change microcapsule foamed concrete is provided, the composite dispersion-interface anchoring system comprising a nonionic surfactant and a silane coupling agent; the nonionic surfactant is used to form a wetting and dispersion layer on the surface of the phase change microcapsules to improve the dispersion stability of the phase change microcapsules in cement paste; the silane coupling agent is used to form an interfacial anchoring structure between the phase change microcapsules and cement hydration products to improve the compressive strength of the phase change microcapsule foamed concrete and reduce its thermal conductivity.

[0041] Preferably, the nonionic surfactant is polyvinylpyrrolidone K30, and the silane coupling agent is γ-aminopropyltriethoxysilane.

[0042] Preferably, the composite dispersion-interface anchoring system is used for pre-adsorption and coating of silica shell phase change microcapsules.

[0043] Preferably, the phase change microcapsule foam concrete is used as a building energy-saving material, lightweight partition wall material, thermal insulation material, or temperature-regulating cement-based material.

[0044] This invention utilizes a composite dispersion-interface anchoring system formed by combining a nonionic surfactant and a silane coupling agent. Pre-adsorption and coating treatment is applied to the phase change microcapsules before they enter the cement slurry, resulting in a pre-formed wetting and dispersion layer and an interface anchoring layer on the surface of the microcapsules. The nonionic surfactant improves the wettability of the microcapsules in the cement slurry and inhibits initial agglomeration and secondary flocculation of the microcapsules in a high-alkali, high-ionic-strength environment through steric hindrance. The silane coupling agent forms condensation, coordination, or bridging interactions with the microcapsule shell and cement hydration products, enhancing the interfacial bonding between the microcapsules and the cement matrix. Therefore, this invention simultaneously solves the problems of uneven microcapsule dispersion and weak interfacial bonding in existing phase change microcapsule foamed concrete, reducing agglomerates, interfacial debonding, and local structural defects.

[0045] Because phase change microcapsules are more uniformly distributed and have more stable interfacial bonding in foamed concrete, this invention can reduce the adverse effects on the mechanical properties of foamed concrete while introducing phase change heat storage function and improve the effective utilization rate of latent heat of phase change. Specifically, compared with the control group without composite dispersion solution treatment, the composite dispersion group obtained by this invention has lower dry density, higher porosity, lower thermal conductivity, and higher 28-day compressive strength, achieving synergistic optimization of low thermal conductivity and high compressive strength. Therefore, the material obtained by this invention combines lightweight insulation, phase change heat storage, temperature regulation, and high load-bearing capacity, making it suitable for applications such as building energy conservation, thermal insulation, lightweight partition walls, and temperature-regulating cement-based materials. Attached Figure Description

[0046] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a flowchart of a method for preparing phase change microcapsule foam concrete according to an embodiment of the present invention. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. Without departing from the inventive concept of the present invention, those skilled in the art can make appropriate adjustments to the types and amounts of raw materials, stirring conditions, foaming conditions, curing conditions, etc., and such adjustments should all fall within the scope of protection of the present invention.

[0048] The phase change microcapsules of this invention are core-shell structured microparticles, comprising a phase change core material and a shell layer covering the core material. The phase change core material can be paraffin, fatty acid, or other solid-liquid phase change materials, preferably paraffin (n-octadecane, phase change temperature 28.18℃); the shell layer can be a silica shell, a polymer shell, or an organic-inorganic composite shell, preferably a silica shell. The average particle size D50 of the phase change microcapsules is preferably 15 μm, and the particle size distribution range is preferably 2 μm to 50 μm; the phase change temperature is preferably 25℃ to 33℃; and the phase change enthalpy is preferably 100 J / g to 150 J / g.

[0049] The nonionic surfactant used in this invention is preferably polyvinylpyrrolidone, polyoxyethylene ether surfactants, or a combination thereof, and more preferably polyvinylpyrrolidone K30. Polyvinylpyrrolidone K30 can form a nonionic polymer adsorption layer on the surface of phase change microcapsules, improving the wettability and steric stability of phase change microcapsules in high-alkali, high-ionic-strength cement pore solutions, thereby reducing initial agglomeration and secondary flocculation.

[0050] The silane coupling agent of this invention is preferably an organosilicon compound capable of hydrolysis to generate silanol groups and undergoing condensation reactions with the shell of phase change microcapsules and cement hydration products, more preferably γ-aminopropyltriethoxysilane, i.e., KH-550. For silica-shell phase change microcapsules, the silanol groups formed after hydrolysis of KH-550 can undergo dehydration condensation with the silanol groups on the surface of the silica shell to form Si—O—Si bonds; simultaneously, the amino groups in KH-550 can react with those generated during cement hydration. Through coordination, the unreacted silanol groups can further undergo condensation reactions with hydration products such as hydrated calcium silicate gel, thereby forming an interfacial anchoring structure between the phase change microcapsules and the cement matrix.

[0051] The composite dispersion-interface anchoring system described in this invention does not simply improve the short-term dispersibility of phase change microcapsules, but rather achieves wetting and dispersion, anti-agglomeration, and interfacial anchoring of phase change microcapsules simultaneously through the synergistic effect of nonionic surfactants and silane coupling agents. Specifically, the nonionic surfactant primarily functions as a wetting agent and provides steric hindrance dispersion in the initial stage of slurry mixing; the silane coupling agent mainly forms chemical bridges or coordination bonds between the microcapsule surface and cement hydration products. The two complement each other in time and function, enabling the phase change microcapsules to form a pre-prepared functional layer before being added to the slurry, inhibiting agglomeration at its source and forming a stable interfacial structure during the hardening process.

[0052] Example 1: Preparation of low thermal conductivity, high compressive strength phase change microcapsule foam concrete This embodiment provides a method for preparing low thermal conductivity, high compressive strength phase change microcapsule foam concrete, such as... Figure 1As shown. Unless otherwise stated, the dosage of each component is calculated based on the mass of cement or the mass of phase change microcapsules.

[0053] I. Raw Materials The cement used is the standard cement (strength grade 52.5R).

[0054] Phase change microcapsules utilize a silica shell, with a paraffin core and a shell made of silica. The shell has an average particle size D50 of 14.46 μm, a phase transition temperature of 21.5–32 °C, and a phase transition enthalpy of 122.50 J / g. In this embodiment, the dosage of phase change microcapsules is 15 wt.% of the cement mass.

[0055] The nonionic surfactant used is polyvinylpyrrolidone K30, abbreviated as PVP K30, and the amount of PVP K30 used is 10 wt. of the phase change microcapsule mass.

[0056] The silane coupling agent used is γ-aminopropyltriethoxysilane, abbreviated as KH-550, and the amount of KH-550 used is 20 wt.% of the phase change microcapsule mass.

[0057] The foaming agent used is an anionic foaming agent, preferably a commercial foaming agent (named nano foaming agent, model LC-01B). The ratio of foaming agent to water is 1:310 (this ratio is by mass).

[0058] The mixing water can be deionized water or tap water, with deionized water being preferred.

[0059] II. Preparation of Composite Dispersion Solutions Under room temperature conditions of 20℃~25℃, PVP K30 and KH-550 were weighed according to the formula and added to deionized water to obtain the mixture to be dispersed. The mixture to be dispersed was placed in an ultrasonic device and ultrasonically treated at 130 W power for 15 min to obtain a composite dispersion solution.

[0060] In this embodiment, based on 1000 g of cement, the amount of phase change microcapsules is 150 g, the amount of PVP K30 is 15 g, the amount of KH-550 is 30 g, and the total amount of mixing water is 500 g based on a water-cement ratio of 0.50. Of this, 500 g is used to prepare the composite dispersion solution.

[0061] III. Preparation of Phase Change Microcapsule Composite Dispersion The weighed phase change microcapsules were slowly added to the above composite dispersion solution while stirring to avoid instantaneous accumulation of the phase change microcapsules. After all the phase change microcapsules were added, the mixture was stirred at 800 rpm for 30 min at room temperature using a magnetic stirrer or mechanical stirrer to allow PVP K30 and KH-550 to be fully adsorbed or grafted onto the surface of the phase change microcapsules, thus obtaining the phase change microcapsule composite dispersion.

[0062] In this process, the carbonyl groups of PVP K30 can form hydrogen bonds with the silanol groups on the surface of the silica shell or with the hydrolyzed KH-550, thereby forming a flexible polymer protective layer on the surface of the phase change microcapsules. The silanol groups generated from the hydrolysis of KH-550 can undergo a condensation reaction with the silanol groups on the surface of the silica shell to form Si—O—Si bonds. This composite pretreatment enables the phase change microcapsules to obtain a wetting and dispersing layer and an interfacial anchoring layer before entering the highly alkaline cement slurry.

[0063] IV. Preparation of Pre-formed Foam An anionic foaming agent was added to water at room temperature (20℃~25℃) and stirred until completely dissolved to obtain a foaming liquid. The ratio of the foaming agent to water was 1:310 (mass ratio). The pre-made foam was then foamed using a foaming machine, controlling the density to be 60 kg / m³.

[0064] The density of pre-made foam can be determined by the graduated cylinder weighing method, which involves taking a certain volume of fresh foam, weighing its mass, and calculating the foam density by mass / volume. If the foam density deviates from 60 kg / m³, it can be corrected by adjusting the gas-liquid ratio of the foaming machine, the foaming time, or the concentration of the foaming agent.

[0065] V. Preparation of cement slurry containing phase change microcapsules Add cement to a mixing pot, then add the phase change microcapsule composite dispersion obtained in step three. Use a cement mortar mixer or other suitable mixing equipment to mix, first slowly for 1 minute, then quickly for 1 minute, to obtain cement paste containing phase change microcapsules.

[0066] The slow mixing speed is 950 rpm, and the fast mixing speed is 1350 rpm. If a standard cement mortar mixer is used, the corresponding equipment speed for the slow and fast speeds can be specified.

[0067] VI. Preparation of Phase Change Microcapsule Foamed Concrete Slurry The amount of precast foam to be added is calculated based on the target wet density. In this embodiment, the target wet density is approximately 800 kg / m³. The precast foam obtained in step four is added to the cement paste containing phase change microcapsules in three batches, with low-speed stirring after each addition to ensure uniform mixing of the precast foam and the paste, thus obtaining phase change microcapsule foamed concrete paste.

[0068] The stirring time after each addition of pre-made foam is 300 s to 3000 s, and the stirring speed is 40 rpm. The stirring time should not be too long to avoid rupture of the foam cells; the stirring intensity should not be too high to avoid damage to the shell of the phase change microcapsules and defoaming of the pre-made foam.

[0069] VII. Molding and Curing The prepared phase change microcapsule foamed concrete slurry was poured into the mold in two batches, with slight vibration or compaction after each filling. In this embodiment, after filling the mold, the slurry was vibrated for 10 seconds, the surface was smoothed, and the mold was covered with plastic wrap. The specimens were demolded after being allowed to harden at 20±2℃ for 48 hours, and then cured for another 28 days at a temperature of 20±2℃ and a relative humidity of ≥95%.

[0070] The mold size is 40 mm × 40 mm × 40 mm / other sizes. Different test items can use different sized specimens. For example, the compressive strength specimen size is 40 mm × 40 mm × 40 mm, the thermal conductivity specimen size is 100 mm × 50 mm × 30 mm, and the dry density and porosity test specimen sizes are 40 mm × 40 mm × 40 mm, respectively. The specimens are cylinders with a diameter of 2 mm and a height of 2 mm.

[0071] VIII. Performance Testing The specimens cured for 28 days were tested for dry density, porosity, thermal conductivity and compressive strength.

[0072] The dry density test method is as follows: the specimen is dried at 50℃ to constant weight, the mass and volume of the specimen are measured, and the dry density is calculated by mass / volume. The test standard used is GB / T 43487-2023.

[0073] The porosity testing method is mercury porosimetry.

[0074] The thermal conductivity test method is as follows: a KEM QTM-700 thermal conductivity meter is used, the transient hot wire method is employed, the test temperature is 20℃, and the standard is GB / T 10297-2015.

[0075] The 28-day compressive strength test method is as follows: a ZQ-970A pressure testing machine is used, the loading rate is 0.2 mm / min, the specimen size is 40 mm × 40 mm × 40 mm, and the test standard is GB / T 5486-2022.

[0076] IX. Test Results The dry density, porosity, thermal conductivity, and 28-day compressive strength of the composite dispersion specimens obtained in this embodiment are as follows: Dry density 548.87 kg / m³ Porosity 58.01% thermal conductivity 0.1471 W / (m·K) 28-day compressive strength 2.10 MPa The above results indicate that, with a phase change microcapsule content of 15 wt.% of cement mass, phase change microcapsule foamed concrete can simultaneously achieve low thermal conductivity and high compressive strength after pre-adsorption coating treatment with PVP K30 and KH-550.

[0077] Comparative Example 1: Phase change microcapsule foam concrete without composite dispersion solution This comparative example is basically the same as Example 1, except that PVP K30 and KH-550 are not added. Instead, the phase change microcapsules are added to water and ultrasonically dispersed before being directly mixed with cement. The amount of phase change microcapsules is still 15 wt.% of the cement mass, and the wet density of the specimen is approximately 800 kg / m³. Other preparation, molding, and curing conditions are the same as in Example 1.

[0078] The test results of the specimens obtained in this comparative example are as follows: Dry density 678.07 kg / m³ Porosity 45.00% thermal conductivity 0.2461 W / (m·K) 28-day compressive strength 1.82 MPa Compared with Comparative Example 1, Example 1 showed a 19.05% decrease in dry density, a 28.91% increase in porosity, a 40.23% decrease in thermal conductivity, and a 15.38% increase in 28-day compressive strength. These results indicate that the composite dispersion-interfacial anchoring treatment using PVP K30 and KH-550 can improve the dispersion and interfacial bonding of phase change microcapsules in foamed concrete, thereby increasing compressive strength while reducing thermal conductivity.

[0079] Comparative Example 2: Phase Change Microencapsulated Foam Concrete Treated with PVP K30 Only This comparative example is basically the same as Example 1, except that only PVP K30 is added to the composite dispersion solution, and KH-550 is not added. The amount of PVP K30 is 10 wt.% of the mass of the phase change microcapsules. The amount of phase change microcapsules is 15 wt.% of the mass of cement. The water-cement ratio, pre-made foam density, target wet density, stirring conditions, molding conditions, and curing conditions are all the same as in Example 1.

[0080] This comparative example was used to verify the effect of nonionic surfactants alone on the initial wetting and dispersion of phase change microcapsules. Since KH-550 was not added, the phase change microcapsules in this comparative example primarily relied on physical intercalation and weak interfacial interactions with the cement hydration products, making it difficult to form a stable chemical anchoring structure.

[0081] The performance test results for this comparative example are as follows: Dry density 678.97 kg / m³ Porosity 48.58% thermal conductivity 0.2178 W / (m·K) 28-day compressive strength 2.12 MPa Comparative Example 3: Phase change microcapsule foam concrete treated with KH-550 only This comparative example is basically the same as Example 1, except that only KH-550 is added to the composite dispersion solution, and PVP K30 is not added. The amount of KH-550 is 20 wt.% of the mass of the phase change microcapsules. The amount of phase change microcapsules is 15 wt.% of the mass of cement. The water-cement ratio, pre-made foam density, target wet density, stirring conditions, molding conditions, and curing conditions are all the same as in Example 1.

[0082] This comparative example is used to verify the effect of silane coupling agent alone on improving interfacial bonding. Because PVP K30 was not added, the phase change microcapsules in this comparative example lacked a non-ionic polymeric steric hindrance protective layer before entering the cement paste, resulting in weaker initial wetting and anti-agglomeration capabilities, and local aggregation was still possible.

[0083] The performance test results for this comparative example are as follows: Dry density 677.20 kg / m³ Porosity 58.72% thermal conductivity 0.2396 W / (m·K) 28-day compressive strength 2.83 MPa Example 2: Effect of different phase change microcapsule dosages on the performance of foamed concrete This embodiment illustrates that low thermal conductivity and high compressive strength phase change microcapsule foamed concrete can be prepared when the amount of phase change microcapsules is 5 wt.% to 15 wt.% of the cement mass.

[0084] Phase change microcapsule foamed concrete was prepared according to the method of Example 1, except that the dosage of phase change microcapsules was set to 5 wt.% and 15 wt.% of the cement mass, respectively. Other conditions were the same as those in Comparative Example 1.

[0085] The performance test results are as follows:

[0086] Example 3: Effect of different PVP K30 / KH-550 dosages on the performance of foamed concrete This example illustrates the effects of the dosage of PVP K30 and KH-550 on the dispersibility, pore structure stability, thermal conductivity, and compressive strength of phase change microcapsules.

[0087] Phase change microcapsule foamed concrete was prepared according to the method of Example 1, except that the mass percentages of PVP K30 and KH-550 relative to the phase change microcapsules were adjusted. The phase change microcapsule dosage was 15 wt.% of the cement mass, and other conditions were the same as in Example 1.

[0088]

[0089] Example 4: Effect of composite dispersion-interfacial anchoring treatment on interfacial bonding of phase change microcapsules This embodiment illustrates how KH-550 forms an interfacial anchoring structure between phase change microcapsules and cement hydration products.

[0090] Phase change microcapsules treated with PVP K30 and KH-550 in Example 1, as well as untreated phase change microcapsules, were subjected to X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and viscoelastic rheology tests, respectively.

[0091] FTIR testing can be used to observe changes in absorption peaks related to Si—O—Si, N—H, C=O, or other characteristic groups in the treated phase change microcapsules; XPS testing can be used to observe changes in the chemical environment of elements such as Si, N, and O; TGA testing can be used to evaluate the adsorption or grafting amount of PVP K30 and KH-550 on the surface of the microcapsules; and viscoelasticity testing can be used to evaluate the degree of formation of the composite network skeleton at the surface interface of cement / PCM particles under the synergistic effect of PVP K30 and KH-550.

[0092]

[0093] As shown in Example 1 and Comparative Example 1, under the conditions that the phase change microcapsule dosage is 15 wt.% of cement mass and the wet density of the specimen is approximately 800 kg / m³, the thermal conductivity of Comparative Example 1 without composite dispersion treatment is 0.2461 W / (m·K), and the 28-day compressive strength is 1.82 MPa. In Example 1, with composite dispersion-interface anchoring treatment using PVP K30 and KH-550, the thermal conductivity decreases to 0.1471 W / (m·K), and the 28-day compressive strength increases to 2.10 MPa. Therefore, this invention does not simply reduce thermal conductivity by increasing porosity, but rather achieves both low thermal conductivity and high compressive strength while improving the dispersion uniformity and interfacial bonding stability of the phase change microcapsules.

[0094] The technical effects of this invention mainly stem from the following synergistic mechanisms: PVP K30, as a non-ionic polymeric dispersion component, can form a flexible adsorption layer and a steric hindrance protection layer on the surface of phase change microcapsules, improving the wettability and anti-agglomeration ability of phase change microcapsules in cement paste; KH-550, as a silane coupling agent, can undergo condensation, coordination, or bridging with the silica shell and cement hydration products, enhancing the interfacial bonding between phase change microcapsules and the cement matrix. The synergistic effect of these two mechanisms results in a more uniform and stable distribution of phase change microcapsules in foamed concrete, reducing agglomerates and weak interfacial defects, thereby lowering thermal conductivity and increasing compressive strength.

Claims

1. A low thermal conductivity and high compressive strength phase change microcapsule foam concrete, characterized in that, Includes a cement matrix, phase change microcapsules dispersed in the cement matrix, and a pore structure; The surface of the phase change microcapsule has a composite interface functional layer, which includes a wetting and dispersing layer formed by a nonionic surfactant and an interface anchoring layer formed by a silane coupling agent. The wetting and dispersing layer is used to improve the wettability of phase change microcapsules in cement slurry and inhibit the aggregation of phase change microcapsules, and the interface anchoring layer is used to form an interface bond between phase change microcapsules and cement hydration products.

2. The phase change microencapsulated foam concrete according to claim 1, characterized in that, The amount of phase change microcapsules is 5 wt.% to 15 wt.% of the cement mass.

3. The phase change microcapsule foam concrete according to claim 1, characterized in that, The nonionic surfactant is one or both of polyoxyethylene surfactant and polyvinylpyrrolidone.

4. The phase change microcapsule foam concrete according to any one of claims 1 to 3, characterized in that, The silane coupling agent is an organosilicon compound that can hydrolyze in an alkaline environment and undergo a condensation reaction with cement hydration products.

5. The phase change microcapsule foam concrete according to claim 4, characterized in that, The phase change microcapsule is a silica shell phase change microcapsule, and the silane coupling agent forms a Si-O-Si bond by condensation reaction with the silica shell through the hydrolysis of the silanol group.

6. The phase change microencapsulated foam concrete according to any one of claims 1 to 3, characterized in that, The cement hydration products include hydrated calcium silicate gel, and the silane coupling agent forms a chemically bridged structure with the hydrated calcium silicate gel.

7. A method for preparing phase change microcapsule foam concrete with low thermal conductivity and high compressive strength, characterized in that, Includes the following steps: S1, Preparation of composite dispersion solution: Add nonionic surfactant and silane coupling agent to water and disperse them to obtain composite dispersion solution; S2, Preparation of phase change microcapsule composite dispersion: Phase change microcapsules are added to the composite dispersion solution for pre-adsorption and coating treatment, so that the nonionic surfactant and the silane coupling agent are adsorbed or grafted onto the surface of the phase change microcapsules to obtain phase change microcapsule composite dispersion. S3, Preparing pre-made foam: Adding a foaming agent to water to prepare a foaming liquid, and foaming the foaming liquid to obtain pre-made foam; S4, Preparation of cement slurry containing phase change microcapsules: Cement is mixed and stirred with the phase change microcapsule composite dispersion to obtain cement slurry containing phase change microcapsules; S5, Preparation of phase change microcapsule foamed concrete slurry: The pre-made foam is added to the cement slurry containing phase change microcapsules and mixed evenly to obtain phase change microcapsule foamed concrete slurry. S6, Molding and Curing: The phase change microcapsule foam concrete slurry is poured into a mold, hardened, demolded, and then cured to obtain the low thermal conductivity and high compressive strength phase change microcapsule foam concrete.

8. The preparation method according to claim 7, characterized in that, In step S1, the nonionic surfactant is polyvinylpyrrolidone K30, and the silane coupling agent is γ-aminopropyltriethoxysilane.

9. The application of a composite dispersion-interface anchoring system in the preparation of phase change microcapsule foam concrete, characterized in that, The composite dispersion-interface anchoring system includes a nonionic surfactant and a silane coupling agent; The nonionic surfactant is used to form a wetting and dispersing layer on the surface of the phase change microcapsules to improve the dispersion stability of the phase change microcapsules in cement paste. The silane coupling agent is used to form an interfacial anchoring structure between the phase change microcapsules and cement hydration products, thereby improving the compressive strength of the phase change microcapsule foam concrete and reducing its thermal conductivity.

10. The application according to claim 9, characterized in that, The nonionic surfactant is polyvinylpyrrolidone K30, and the silane coupling agent is γ-aminopropyltriethoxysilane.

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