Multi-layer core-shell structure lightweight aggregate and preparation method thereof

Abstract

The embodiment of the invention provides a lightweight aggregate with a multi-layer core-shell structure and a preparation method thereof, the lightweight aggregate with the multi-layer core-shell structure comprises: an inner core, the preparation raw materials of the inner core comprise water-storage lightweight particles and a functional ion solution; the inner shell covers the inner core, and the preparation raw materials of the inner shell comprise cement, a volcanic ash material, solid waste, lime, a water reducing agent and water; the inner shell is coated with the outer shell, and preparation raw materials of the outer shell comprise cement, a volcanic ash material, a water reducing agent, nanofibers and water. According to the lightweight aggregate with the multi-layer core-shell structure and the preparation method of the lightweight aggregate, through internal curing of the inner core, pozzolanic reaction in the inner shell and the toughening effect of the nanofibers in the outer shell, the mechanical property of the lightweight aggregate with the multi-layer core-shell structure is improved, and the filling and bridging effects of the nanofibers are fully exerted; the mechanical property of an interface transition area is improved, and the lightweight aggregate with the multi-layer core-shell structure, which is low in density, high in strength and high in elastic modulus, is obtained.

Description

Multilayer core-shell structured lightweight aggregate and its preparation method Technical Field

[0001] This application belongs to the field of building materials technology, and in particular relates to a multi-layer core-shell structure lightweight aggregate and its preparation method. Background Technology

[0002] In recent years, with the development of high-rise buildings, long-span bridges, and floating structures at sea, lightweight concrete, with its advantages of being lightweight, heat-insulating, sound-absorbing, and energy-saving, has gradually become one of the main alternatives to ordinary concrete. Lightweight concrete is often used to manufacture precast components, which are easy to construct and mold, greatly reducing costs and time. However, achieving lightweighting comes with a loss of mechanical properties, especially a significant reduction in compressive strength and modulus of elasticity, which restricts the wider application of lightweight concrete. Therefore, designing lightweight concrete with higher mechanical properties is urgently needed.

[0003] As a major component of lightweight concrete, the low strength and low modulus of elasticity of lightweight aggregates are the main factors leading to the low mechanical properties of lightweight concrete. Cold-bonded lightweight aggregates are spherical artificial aggregates made by mixing, granulating, and cold-bonding particles. Although the mechanical properties of cold-bonded lightweight aggregates are slightly lower than those of sintered lightweight aggregates, they have become a preferred alternative to sintered aggregates due to their advantages such as low energy consumption, low cost, and low environmental pollution. Among them, core-shell lightweight aggregates have become one of the most widely studied forms due to the requirements of low density and versatility. However, although some studies have slightly improved the strength of core-shell lightweight aggregates by introducing different cores or optimizing the shell, the density and strength of core-shell lightweight aggregates are still not well balanced. In addition, the performance of most lightweight aggregates is measured by compressive strength, with little attention paid to its impact on the modulus of elasticity of lightweight concrete. Therefore, it is necessary to develop a lightweight aggregate that simultaneously possesses low density, high strength, and high modulus of elasticity to broaden the application range of lightweight concrete. Summary of the Invention

[0004] In view of this, embodiments of this application provide a multi-layer core-shell structure lightweight aggregate and its preparation method to solve the technical problem that the elastic modulus of existing lightweight aggregates is not high enough.

[0005] In a first aspect, embodiments of this application provide a multi-layer core-shell structured lightweight aggregate, comprising:

[0006] The core, the raw materials for its preparation include water-storing lightweight particles and functional ionic solutions;

[0007] An inner shell, which encloses the core, is prepared from raw materials including cement, volcanic ash, solid waste, lime, water-reducing agents, and water; and

[0008] The outer shell covers the inner shell, and the raw materials for preparing the outer shell include cement, volcanic ash, water-reducing agent, nanofiber and water.

[0009] In some embodiments, the inner shell comprises the following raw materials prepared by weight method:

[0010] 26-39 parts cement;

[0011] 34-51 parts fly ash;

[0012] 10-40 portions of solid waste;

[0013] 2-3 parts lime;

[0014] 2-3 parts of polycarboxylate superplasticizer;

[0015] 20-25 parts water.

[0016] In some embodiments, the outer shell comprises the following raw materials prepared by weight method:

[0017] 70-80 parts cement;

[0018] 20-30 parts silica fume;

[0019] Nanofibers, 0.1–0.3 parts;

[0020] 2-3 parts of polycarboxylate superplasticizer;

[0021] 20-25 parts water.

[0022] In some embodiments, the water-storing lightweight particles include one of hydrogel, zeolite, expanded vermiculite, biochar, fly ash ceramsite, diatomite, and perlite.

[0023] In some embodiments, the functional ionic solution includes one of pure water, calcium hydroxide solution, sodium sulfate solution, shrinkage reducing agent, polymer solution, etc.

[0024] In some embodiments, the average particle size of the solid waste is less than 10 μm.

[0025] In some embodiments, the solid waste includes at least one of glass powder, coal gangue, silica fume, red mud, lithium slag, nickel slag, mineral slag, and steel slag.

[0026] In some embodiments, the nanofibers include at least one of carbon nanotubes, carbon nanofibers, and nanocellulose.

[0027] In some embodiments, the diameter of the core is 3 to 10 mm, the thickness of the inner shell is 1 to 3 mm, and the thickness of the outer shell is 1 to 3.5 mm.

[0028] Secondly, embodiments of this application provide a method for preparing a multi-layer core-shell structured lightweight aggregate, comprising the following steps:

[0029] Provide raw materials for the preparation of the core, the inner shell, and the outer shell as described in the first aspect;

[0030] The water-saturated lightweight particles are subjected to water saturation treatment to obtain the core.

[0031] The raw materials for preparing the core and the inner shell are mixed and granulated to obtain an intermediate.

[0032] The nanofibers, the water-reducing agent, and the water are mixed and dispersed to obtain a suspension.

[0033] The suspension is mixed with the remaining raw materials for preparing the outer shell to obtain a slurry;

[0034] The slurry is coated onto the intermediate and cured to obtain the multi-layer core-shell structured lightweight aggregate.

[0035] In some embodiments, the step of saturating the water-retaining lightweight particles to obtain the core includes:

[0036] The water-retaining lightweight particles include a hydrogel, and the water saturation treatment includes immersing the hydrogel in water for at least 4 hours.

[0037] In some embodiments, the maintenance treatment includes:

[0038] The slurry is coated onto the intermediate and then cured in a sealed environment;

[0039] Then, perform curing using at least one of the following methods: steam curing, standard curing, or carbon dioxide curing.

[0040] The conditions for maintenance treatment include:

[0041] The temperature for steam curing is 60–90℃, and the relative humidity is 100%.

[0042] The standard maintenance temperature is controlled at 23±2℃, and the relative humidity is greater than 95%;

[0043] Carbon dioxide curing can be either gas flow curing or sealed pressure curing, with a carbon dioxide volume concentration of 10-100% and a relative humidity of 20-80%.

[0044] The multi-layered core-shell lightweight aggregate provided in this application embodiment utilizes a multi-layered design that incorporates the stress characteristics of a multi-layered core-shell structure within a concrete matrix. Through internal curing of the core, pozzolanic reaction of the inner shell, and nanofiber toughening of the outer shell, the physicochemical reactions between materials are fully utilized from the inside out, thereby enhancing the synergy between the lightweight aggregate and the concrete matrix in terms of stress distribution. The physical effects include: the addition of nanofibers optimizes the Coulomb forces between hydrated particles, promoting dense particle packing; and the three-dimensional network structure formed in the concrete matrix effectively bridges and fills the gaps, improving the strength of the outer shell while densifying the interface transition zone between the outer shell, inner shell, and concrete matrix. Furthermore, the core releases an ionic solution to internally cure the inner shell, improving its density and addressing the stress concentration problem caused by the hollow structure. The chemical effects include: pozzolanic materials such as fly ash and silica fume in the inner shell react with the hydration products of cement, enhancing the bond between the inner and outer shells, thus improving the mechanical properties of the lightweight aggregate. The multi-layer core-shell lightweight aggregate provided in this application has high strength, high elastic modulus and low density, which solves the problem of low strength of cold-bonded aggregates. In addition, it is the first time that the focus is on the elastic modulus of core-shell lightweight aggregates, which is of great significance for promoting the development of high-performance lightweight concrete.

[0045] The method for preparing multi-layer core-shell lightweight aggregate provided in this application is simple in procedure and does not require surface modification of the core material; it also has high production efficiency, using disc granulation instead of traditional hemispherical die extrusion molding, which is beneficial for large-scale production. The multi-layer core-shell lightweight aggregate provided in this application is environmentally friendly and has low energy consumption, using cold bonding technology instead of sintering, which greatly reduces the energy consumption required for high-temperature processing; and it utilizes a variety of solid wastes, giving full play to their added value. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 is a schematic diagram of the preparation method of multi-layer core-shell structured lightweight aggregate provided in the embodiments of this application. Detailed Implementation

[0048] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the embodiments of this application with unnecessary detail.

[0049] It should also be understood that the term "and / or" as used in the specification of embodiments of this application and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0050] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0051] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0052] Furthermore, in the description of the embodiments and the appended claims of this application, the terms "first," "second," "third," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0053] In this specification, references to "one embodiment" or "some embodiments" mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in still other embodiments" appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized. "A plurality" refers to two or more.

[0054] The first aspect of this application provides a multi-layered core-shell structured lightweight aggregate, including a core, an inner shell, and an outer shell, wherein the inner shell covers the core, and the outer shell covers the inner shell.

[0055] The raw materials for preparing the core include water-storing lightweight particles and functional ionic solutions;

[0056] The raw materials for preparing the inner shell include cement, pozzolanic materials, solid waste, lime, water-reducing agents, and water;

[0057] The raw materials for preparing the outer shell include cement, volcanic ash, water-reducing agents, nanofibers, and water.

[0058] The multi-layered core-shell lightweight aggregate provided in this application embodiment utilizes a multi-layered design that incorporates the stress characteristics of a multi-layered core-shell structure within a concrete matrix. Through internal curing of the core, pozzolanic reaction of the inner shell, and nanofiber toughening of the outer shell, the physicochemical reactions between materials are fully utilized from the inside out, thereby enhancing the synergy between the lightweight aggregate and the concrete matrix in terms of stress distribution. The physical effects include: the addition of nanofibers optimizes the Coulomb forces between hydrated particles, promoting dense particle packing; and the three-dimensional network structure formed in the concrete matrix effectively bridges and fills the gaps, improving the strength of the outer shell while densifying the interface transition zone between the outer shell, inner shell, and concrete matrix. Furthermore, the core releases an ionic solution to internally cure the inner shell, improving its density and addressing the stress concentration problem caused by the hollow structure. The chemical effects include: pozzolanic materials such as fly ash and silica fume in the inner shell react with the hydration products of cement, enhancing the bond between the inner and outer shells, thus improving the mechanical properties of the lightweight aggregate. The multi-layer core-shell lightweight aggregate provided in this application has high strength, high elastic modulus and low density, which solves the problem of low strength of cold-bonded aggregates. In addition, it is the first time that the focus is on the elastic modulus of core-shell lightweight aggregates, which is of great significance for promoting the development of high-performance lightweight concrete.

[0059] In applications, water-retaining lightweight particles include one of the following: hydrogel, zeolite, expanded vermiculite, biochar, fly ash ceramsite, diatomaceous earth, and perlite. Water-retaining lightweight particles have multiple functions in concrete and lightweight aggregates, mainly reflected in the following aspects: 1. Internal curing effect: Water storage and slow release. Water-retaining lightweight particles can absorb a large amount of water during concrete mixing and slowly release this water during concrete hardening, providing a continuous water supply for cement hydration. Reduced drying shrinkage: Through internal curing, the drying shrinkage of concrete can be significantly reduced, thereby reducing the risk of cracking and improving concrete durability. 2. Improved concrete performance: Increasing density. The internal curing effect of water-retaining lightweight particles can promote the full hydration of cement, reduce internal porosity, and increase the density of concrete. Enhanced strength: By increasing the density of concrete, the compressive and flexural strength of concrete can be enhanced. Improved durability: Reducing internal porosity and cracks can improve the impermeability and freeze-thaw resistance of concrete, extending its service life. 3. Lightweight and density reduction: Water-retaining lightweight particles typically have low density, significantly reducing the overall density of concrete and achieving lightweighting. Reduced structural weight: Lightweight concrete reduces the building's self-weight, decreasing foundation requirements and lowering construction costs. 4. Environmental friendliness and sustainability: Utilizing industrial waste, many water-retaining lightweight particles (such as fly ash ceramsite and diatomaceous earth) can be prepared from industrial waste, achieving resource recycling and reducing environmental pollution. Some water-retaining lightweight particles (such as biochar) have good eco-friendliness, contributing to improved sustainability of building materials.

[0060] Specifically, hydrogels possess high water absorption, capable of absorbing hundreds of times their own weight in water and slowly releasing it, providing continuous internal curing. Zeolite's porous structure, with its high specific surface area and adsorption capacity, can absorb and release moisture, improving the density and durability of concrete. Expanded vermiculite, lightweight and porous, can absorb moisture and slowly release it within the concrete, reducing drying shrinkage. Biochar's porous structure, with good water absorption and adsorption capacity, can improve the pore structure of concrete, increasing density and durability. Fly ash ceramsite, lightweight and porous, can absorb moisture and slowly release it within the concrete, providing internal curing. Diatomaceous earth, with its thermal porous structure, high specific surface area and adsorption capacity, can absorb and release moisture, improving the density and durability of concrete. Perlite, lightweight and porous, can absorb moisture and slowly release it within the concrete, reducing drying shrinkage.

[0061] Water-retaining lightweight aggregates offer significant advantages for concrete and lightweight aggregate applications through internal curing, improved concrete performance, lightweighting, and enhanced environmental sustainability. Selecting the appropriate water-retaining lightweight aggregates can be optimized based on specific engineering needs and environmental conditions to achieve optimal performance.

[0062] In applications, functional ionic solutions include one of the following: pure water, calcium hydroxide solution, sodium sulfate solution, shrinkage reducing agents, and polymer solutions. Pure water serves as the most basic solvent, used to dissolve other functional substances and provide necessary moisture. In the preparation of lightweight aggregates, pure water is used to adjust the fluidity of the mixture and ensure uniform distribution of each component. Its advantages include being non-toxic, harmless, and inexpensive. Calcium hydroxide solution is used to increase the alkalinity of the mixture, promoting the hydration reaction of cement. An alkaline environment facilitates the formation of early cement hydration products, improving the early strength of concrete. Calcium hydroxide solution can also provide additional moisture, reducing the drying shrinkage of concrete. Sodium sulfate solution has a setting-accelerating effect, speeding up the hydration reaction of cement and shortening the initial and final setting times. Appropriate amounts of sodium sulfate can improve the fluidity of concrete and reduce the amount of mixing water. Sodium sulfate solution can also provide additional moisture, reducing the drying shrinkage of concrete. In the preparation of lightweight aggregates, sodium sulfate solution can be used to adjust the setting time and fluidity of the core and shell. Shrinkage reducing agents, as the name suggests, are used to reduce shrinkage: they can significantly reduce the drying shrinkage of concrete, lowering the risk of cracking. By reducing shrinkage, the density of concrete can be increased, enhancing its durability. Reducing shrinkage cracks can improve the impermeability of concrete and extend its service life. In the preparation of the inner and outer shells of lightweight aggregates, shrinkage reducing agents can be used to improve the overall performance of lightweight aggregates. Polymer solutions improve adhesion; they can enhance the bond between lightweight aggregates and the concrete matrix, improving overall performance. Polymer solutions can improve the fluidity of concrete, making it easier to work with. Polymer solutions can form a thin film, reducing moisture evaporation and providing internal curing. Polymer solutions can improve the impermeability, freeze-thaw resistance, and chemical corrosion resistance of concrete. In the preparation of the inner and outer shells of lightweight aggregates, polymer solutions can be used to improve the strength and durability of lightweight aggregates.

[0063] In applications, polymer solutions include, but are not limited to, polyacrylamide, polyvinyl alcohol, polyacrylates, polyurethane, polyvinylpyrrolidone, polyethylene oxide, sodium polyacrylate, and polyvinyl formal. Polyacrylamide is a high-molecular-weight linear polymer with good water solubility and thickening properties. It can improve the fluidity and stability of concrete, reduce water evaporation, and enhance the crack resistance and durability of concrete. Polyvinyl alcohol is a water-soluble polymer with good film-forming and adhesive properties. It can improve the adhesion and impermeability of concrete, reduce water evaporation, and prevent cracking. Polyacrylates are a class of polymeric compounds polymerized from acrylate monomers, with good water solubility and emulsifying properties. They can improve the fluidity and stability of concrete, reduce water evaporation, and enhance the crack resistance and durability of concrete. Polyurethane is a polymer produced by the reaction of isocyanates and polyols, possessing excellent adhesion and waterproofing properties. It can improve the adhesion and waterproofing of concrete, reduce water evaporation, and prevent cracking. Polyvinylpyrrolidone is a water-soluble polymer with good thickening and dispersing properties. These additives can improve the fluidity and stability of concrete, reduce moisture evaporation, and enhance its crack resistance and durability. Polyethylene oxide is a high-molecular-weight, water-soluble polymer with excellent thickening and lubricating properties. It can also improve the fluidity and stability of concrete, reduce moisture evaporation, and enhance its crack resistance and durability. Sodium polyacrylate is a highly absorbent polymer capable of absorbing hundreds of times its own weight in water. It can improve the internal curing ability of concrete, reduce moisture evaporation, and enhance its crack resistance and durability. Polyvinyl alcohol formal is a high-molecular-weight polymer produced by the reaction of polyvinyl alcohol and formaldehyde, possessing good adhesion and water resistance. It can improve the adhesion and water resistance of concrete, reduce moisture evaporation, and prevent cracking.

[0064] In summary, these polymer solutions offer different functions and advantages in the preparation of concrete and lightweight aggregates, and the appropriate polymer solution can be selected based on specific engineering needs. They can not only improve the fluidity, bond strength, and durability of concrete, but also reduce moisture evaporation, prevent cracking, and enhance the overall performance of concrete.

[0065] In some embodiments, based on 100 parts by weight of the entire core, the core contains 70-80 parts of water-retaining lightweight particles and 20-30 parts of functional ionic solution. These particles can store moisture, providing the necessary internal curing conditions for the lightweight aggregate while maintaining its lightweight properties. These solutions can provide the necessary chemical activity, promoting good bonding between core materials and potentially improving the stability of the core.

[0066] In some embodiments, the inner shell comprises the following raw materials prepared by weight method:

[0067] 26-39 parts cement;

[0068] 34-51 parts fly ash;

[0069] 10-40 portions of solid waste;

[0070] 2-3 parts lime;

[0071] 2-3 parts of polycarboxylate superplasticizer;

[0072] 20-25 parts water.

[0073] In application, the inner shell obtained through the above proportions exhibits high strength: the appropriate ratio of cement and fly ash ensures sufficient strength. High density: the use of fly ash and water-reducing agents improves the density of the inner shell and reduces porosity. Low shrinkage: fly ash and water-reducing agents reduce the drying shrinkage of the inner shell, lowering the risk of cracking. High durability: the hydrated calcium silicate (CSH) gel generated by the volcanic ash reaction and the alkaline environment of lime improve the durability of the inner shell. Environmental friendliness: utilizing industrial waste reduces environmental pollution and achieves resource recycling. Economic efficiency: utilizing industrial waste and water-reducing agents significantly reduces raw material costs and improves economic benefits. In a preferred embodiment, the inner shell consists of 30 parts cement, 40 parts fly ash, 25 parts solid waste, 3 parts lime, 3 parts polycarboxylate superplasticizer, and 25 parts water.

[0074] In some embodiments, the average particle size of the solid waste is less than 10 μm. The advantages of an average particle size of less than 10 μm include increased activity; the smaller particles have a larger specific surface area, allowing for better reaction with cement hydration products, generating more calcium silicate hydrate (CSH) gel, thus improving the strength and density of the inner shell. It also improves flowability; the smaller particles enhance the flowability of concrete, making it easier to mix and mold. Furthermore, it reduces porosity; the smaller particles fill the tiny pores in the concrete, reducing porosity and improving the density and durability of the inner shell. Finally, it improves uniformity; the smaller particles disperse better in the concrete, enhancing the uniformity and stability of the inner shell.

[0075] In some embodiments, solid waste includes at least one of glass powder, coal gangue, silica fume, red mud, lithium slag, nickel slag, ore slag, and steel slag. Glass powder is a fine glass particle, typically obtained by crushing and grinding waste glass. Its function is to increase density, improve fluidity, and provide strength. Fine glass powder can fill pores in concrete, increasing the density of the inner shell. It can also improve the fluidity of concrete, making it easier to mix and mold. Furthermore, glass powder can provide additional active ingredients, enhancing the strength and durability of the inner shell. Coal gangue is a waste product generated during coal mining and washing, typically black or gray. Its function is to increase activity. Coal gangue contains certain active ingredients that can react with cement hydration products to form calcium silicate hydrate (CSH) gel, increasing the strength of the inner shell. Coal gangue can absorb excess moisture, reducing the drying shrinkage of the inner shell and lowering the risk of cracking. Utilizing coal gangue can significantly reduce raw material costs. Silica fume is a fine dust generated during the production of ferrosilicon alloys and possesses extremely high activity. Silica fume can significantly improve the early and late strength of the inner shell. It can fill the tiny pores in concrete, increasing the density of the inner shell. Silica fume can also improve the impermeability of the inner shell, extending its service life. Red mud is a red waste product generated during the alumina refining process from bauxite. Red mud contains a large amount of active alumina and silica, which can react with cement hydration products to form calcium silicate hydrate (CSH) gel, increasing the strength of the inner shell. Red mud can also improve the durability and corrosion resistance of the inner shell. Lithium slag is a waste product generated during lithium mining and processing. Lithium slag contains certain active ingredients that can react with cement hydration products to form calcium silicate hydrate (CSH) gel, increasing the strength of the inner shell. Lithium slag can also improve the durability and corrosion resistance of the inner shell. Nickel slag is a waste product generated during nickel smelting. Nickel slag contains certain active ingredients that can react with cement hydration products to form calcium silicate hydrate (CSH) gel, increasing the strength of the inner shell. Nickel slag can improve the durability and corrosion resistance of the inner shell. Slag is a waste product generated during steel production, typically gray or black. It contains a large amount of active silica and calcium oxide, which can react with cement hydration products to form calcium silicate hydrate (CSH) gel, increasing the strength of the inner shell. Steel slag is also a waste product generated during steel production, typically black or gray. It contains a large amount of active silica and calcium oxide, which can react with cement hydration products to form calcium silicate hydrate (CSH) gel, increasing the strength of the inner shell. Steel slag can improve the durability and corrosion resistance of the inner shell.

[0076] Solid waste and volcanic ash materials, through a volcanic ash reaction, generate more hydrated calcium silicate (CSH) gel, increasing the strength of the inner shell. Fine particles can fill the pores in the concrete, improving the density of the inner shell. Solid waste can absorb excess moisture, reducing the drying shrinkage of the inner shell and lowering the risk of cracking. Solid waste can improve the durability and corrosion resistance of the inner shell, extending its service life. Utilizing industrial waste can reduce environmental pollution and achieve resource recycling. Utilizing industrial waste can significantly reduce raw material costs and improve economic efficiency.

[0077] In some embodiments, the shell comprises the following raw materials prepared by weight method:

[0078] 70-80 parts cement;

[0079] 20-30 parts silica fume;

[0080] Nanofibers, 0.1–0.3 parts;

[0081] 2-3 parts of polycarboxylate superplasticizer;

[0082] 20-25 parts water.

[0083] In application, high cement and silica fume content can significantly improve the strength of the outer shell, ensuring sufficient load-bearing capacity of the lightweight aggregate. The addition of silica fume and nanofibers can improve the density and impermeability of the outer shell, extending its service life. Polycarboxylate superplasticizer can improve the fluidity of concrete, making it easier to construct, while reducing water consumption and increasing density. Nanofibers can significantly improve the toughness and crack resistance of the outer shell, reducing the generation and propagation of microcracks. By optimizing the proportions of each component, unnecessary material waste can be reduced, improving economic efficiency. In a preferred embodiment, the outer shell consists of 75 parts cement, 25 parts silica fume, 0.2 parts nanofibers, 3 parts polycarboxylate superplasticizer, and 25 parts water.

[0084] In some embodiments, assuming a total mass of 100 parts of lightweight aggregate, the weight proportions of the core, inner shell, and outer shell are as follows: core 40-50 parts: inner shell 30-40 parts: outer shell 20-30 parts. The core comprises 40-50% of the total mass of the lightweight aggregate, providing lightweight properties and internal curing function. A higher core proportion ensures the lightweight aggregate's water retention capacity. The inner shell comprises 30-40% of the total mass of the lightweight aggregate, providing structural support and reinforcing the bond between the core and shell. A moderate inner shell proportion balances the strength and lightweight requirements of the lightweight aggregate. The outer shell comprises 20-30% of the total mass of the lightweight aggregate, providing high strength and durability. A lower outer shell proportion ensures the overall lightweight of the lightweight aggregate while providing necessary protection and reinforcement.

[0085] In applications, nanofibers include at least one of carbon nanotubes, carbon nanofibers, and nanocellulose. Carbon nanotubes, carbon nanofibers, and nanocellulose can all significantly improve the strength and toughness of concrete, reduce the generation and propagation of microcracks, and improve the overall performance of the material. These nanofibers can enhance the mechanical properties of the interfacial transition zone between lightweight aggregates and the concrete matrix, improving overall bond strength. Nanocellulose can improve the fluidity of concrete, making it easier to construct, while reducing water consumption and increasing density. Nanofibers can improve the density and impermeability of concrete, extending its service life. As a renewable biomass material, nanocellulose has good biodegradability and environmental friendliness, meeting the requirements of sustainable development.

[0086] In some embodiments, the diameter of the core is 3–10 mm. Optionally, the diameter of the core can be any value within the range of 3 mm to 10 mm, such as 3 mm, 3.5 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm. The thickness of the inner shell is 1–3 mm. Optionally, the thickness of the inner shell can be any value within the range of 1 mm to 3 mm, such as 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.4 mm, 2.8 mm, or 3 mm. The thickness of the outer shell is 1–3.5 mm. Optionally, the thickness of the outer shell can be any value within the range of 1 mm to 3.5 mm, such as 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.4 mm, 2.8 mm, 3 mm, 3.2 mm, or 3.5 mm.

[0087] In applications, a smaller core diameter helps reduce the overall weight of lightweight aggregates, making it suitable for projects requiring lightweight properties, such as high-rise buildings and bridges. A larger core diameter can provide greater water storage capacity, improve internal curing effects, and reduce concrete drying shrinkage. In the embodiments of this application, using a core diameter within the above range ensures the uniform distribution of lightweight aggregates in concrete, avoiding problems of localized over-density or under-density. An inner shell thickness in the range of 1–3 mm provides sufficient structural support, enhances the stability of the core, and prevents the core from cracking during mixing and pouring. An appropriate inner shell thickness can improve the interface transition zone between the core and shell, increase the bonding force between the two, and enhance overall performance. A moderate inner shell thickness can balance the strength and lightweight requirements of lightweight aggregates, ensuring good performance of lightweight aggregates in concrete. An outer shell thickness in the range of 1–3.5 mm provides effective protection, preventing external environmental erosion of the core and inner shell, and improving the durability of lightweight aggregates. An appropriate outer shell thickness can significantly improve the surface strength and abrasion resistance of lightweight aggregates, enhancing their role in concrete. A moderate outer shell thickness can optimize the interfacial properties between lightweight aggregates and the concrete matrix, thereby improving overall adhesion and mechanical properties.

[0088] In summary, the multi-layered core-shell lightweight aggregate provided in this application ensures both lightweight requirements and water retention capacity, improving internal curing effectiveness and reducing concrete drying shrinkage. The inner shell, with its moderate thickness, provides sufficient structural support to prevent core cracking and improve the interface transition zone. The outer shell, also with moderate thickness, provides effective protection, enhancing the durability and surface strength of the lightweight aggregate. The optimized core, inner shell, and outer shell dimensions balance the strength and lightweight requirements of the lightweight aggregate, ensuring its excellent performance in concrete.

[0089] In practical applications, this multi-layered core-shell lightweight aggregate can be used in high-modulus lightweight concrete, and is particularly suitable for projects requiring high strength, high durability, and lightweight properties, such as high-rise buildings, bridges, and tunnels. By rationally selecting and controlling the dimensions and thickness of the core, inner shell, and outer shell, the lightweight aggregate can be ensured to perform excellently under various complex working conditions, meeting engineering requirements.

[0090] This application also provides a method for preparing a multi-layer core-shell structured lightweight aggregate, as shown in Figure 1, including the following steps:

[0091] S10, providing raw materials for the preparation of the core, inner shell, and outer shell in the first aspect;

[0092] S20. The water-saturated lightweight particles are treated with water to obtain the core.

[0093] S30. Mix the raw materials for preparing the core and the inner shell, granulate them, and obtain an intermediate.

[0094] S40. Nanofibers, water-reducing agent and water are mixed and dispersed to obtain a suspension;

[0095] S50. Mix the suspension with the remaining raw materials for preparing the shell to obtain a slurry;

[0096] S60. The slurry is coated onto the intermediate body and cured to obtain a multi-layer core-shell structure lightweight aggregate.

[0097] The method for preparing multi-layer core-shell lightweight aggregate provided in this application is simple in procedure and does not require surface modification of the core material; it also has high production efficiency, using disc granulation instead of traditional hemispherical die extrusion molding, which is beneficial for large-scale production. The multi-layer core-shell lightweight aggregate provided in this application is environmentally friendly and has low energy consumption, using cold bonding technology instead of sintering, which greatly reduces the energy consumption required for high-temperature processing; and it utilizes a variety of solid wastes, giving full play to their added value.

[0098] In step S10, raw materials for preparing the core, inner shell, and outer shell of the first aspect are provided. The raw materials for preparing the core include water-storing lightweight particles and functional ionic solutions. The water-storing lightweight particles include, but are not limited to, hydrogels, zeolites, expanded vermiculite, biochar, fly ash ceramsite, diatomaceous earth, and perlite. The functional ionic solutions include, but are not limited to, pure water, calcium hydroxide solution, sodium sulfate solution, shrinkage reducing agents, and polymer solutions. The raw materials for preparing the inner shell include cement, volcanic ash materials, solid waste, lime, water-reducing agents, and water. The volcanic ash materials include, but are not limited to, fly ash, silica fume, and volcanic ash. The solid waste includes, but is not limited to, glass powder, coal gangue, silica fume, red mud, lithium slag, nickel slag, ore slag, and steel slag. The raw materials for preparing the outer shell include cement, volcanic ash materials, water-reducing agents, nanofibers, and water. The nanofibers include, but are not limited to, carbon nanotubes, nanocellulose, and carbon nanofibers. The water-reducing agent includes polycarboxylate superplasticizers.

[0099] In step S20, the water-retaining lightweight particles are saturated with water to obtain the core. In one specific embodiment, the hydrogel core is placed in water for at least 4 hours to allow it to fully absorb water and reach saturation. The fully water-absorbed hydrogel core can store more moisture, providing sufficient hydration for subsequent internal curing. The saturated hydrogel core can slowly release moisture inside the concrete, reducing drying shrinkage and improving the density and strength of the concrete.

[0100] In step S30, the raw materials for preparing the core and inner shell are mixed and granulated to obtain an intermediate. The granulation process includes powder spraying and water spraying at a speed of 40 rpm and an angle of 45° for approximately 20 minutes. This allows the inner shell to encapsulate the hydrogel core, resulting in the intermediate. The powder spraying and water spraying method ensures uniform mixing of the raw materials for the inner shell, forming particles with a specific size. Low-speed powder spraying and water spraying ensures uniform mixing of the inner shell raw materials and avoids agglomeration. By adjusting the powder spraying speed and angle, the size of the inner shell particles can be controlled, ensuring a uniform inner shell structure. Uniform inner shell particles provide better structural support and enhance the overall stability of the lightweight aggregate.

[0101] In step S40, nanofibers, a water-reducing agent, and water are mixed and dispersed to obtain a suspension. The nanofibers, polycarboxylate superplasticizer, and water are mixed and then ultrasonically dispersed for 1 hour. Ultrasonic dispersion ensures uniform dispersion of the nanofibers in water, preventing agglomeration. Ultrasonic dispersion ensures uniform dispersion of the nanofibers in water, improving their dispersibility and stability in the slurry. Uniformly dispersed nanofibers can better exert their reinforcing and toughening effects, improving the mechanical properties and durability of the slurry.

[0102] In step S50, the suspension is mixed with the remaining raw materials for preparing the outer shell to obtain a slurry. High-speed mixing ensures that the raw materials for preparing the outer shell are thoroughly mixed with the nanofiber suspension, forming a homogeneous slurry. High-speed mixing ensures uniform mixing of all raw materials, avoiding localized unevenness. The homogeneous slurry better coats the inner shell, improving the overall performance of the lightweight aggregate, including strength, toughness, and durability.

[0103] In step S60, the slurry is coated onto the intermediate body, and after curing, a multi-layered core-shell lightweight aggregate is obtained. Through coating and curing, the outer shell slurry solidifies, forming a complete multi-layered core-shell lightweight aggregate. Complete coating: The outer shell slurry can uniformly coat the inner shell, forming a complete multi-layered structure. The curing of the outer shell can significantly improve the surface strength and abrasion resistance of the lightweight aggregate, enhancing its role in concrete. Appropriate curing conditions can ensure sufficient curing of the outer shell, improving the overall performance of the lightweight aggregate, including strength, toughness, and durability.

[0104] In the preparation method of the multi-layer core-shell structured lightweight aggregate provided in this application embodiment, the hydrogel core can fully absorb water to provide sufficient internal curing moisture, reducing drying shrinkage. During the preparation of the inner and outer shells, powdering, water spraying, and high-speed stirring ensure uniform mixing of raw materials and avoid agglomeration. Uniform inner shell particles and outer shell slurry provide better structural support and enhance the overall stability of the lightweight aggregate. Uniform dispersion of nanofibers and full curing of the outer shell can significantly improve the mechanical properties and durability of the lightweight aggregate. Appropriate curing conditions can ensure full curing of the outer shell and improve the overall performance of the lightweight aggregate.

[0105] In some embodiments, the curing conditions in step S60 include coating the intermediate with the slurry and then curing it in a sealed environment.

[0106] Then, perform curing using at least one of the following methods: steam curing, standard curing, or carbon dioxide curing.

[0107] The conditions for maintenance treatment include:

[0108] The temperature for steam curing is 60–90℃, and the relative humidity is 100%.

[0109] The standard maintenance temperature is controlled at 23±2℃, and the relative humidity is greater than 95%;

[0110] Carbon dioxide curing can be either gas flow curing or sealed pressure curing, with a carbon dioxide volume concentration of 10-100% and a relative humidity of 20-80%.

[0111] In application, initial curing in a sealed environment ensures the initial formation of a stable structure for the core and shell of the lightweight aggregate. This prevents moisture loss; the sealed environment prevents excessively rapid evaporation, ensuring the smooth progress of the initial curing process for the core and shell. Furthermore, initial curing provides a stable base for subsequent curing steps, improving the initial strength of the lightweight aggregate.

[0112] In application, steam curing is used at a temperature of 60–90℃ and a relative humidity of 100%. This high-temperature, high-humidity environment accelerates the hydration reaction of cement, improving the early strength of lightweight aggregates. This environment significantly accelerates cement hydration, increasing the early strength and density of lightweight aggregates. It also reduces drying shrinkage and lowers the risk of cracking. Compared to standard curing, steam curing significantly shortens curing time and improves production efficiency. Standard curing is used at a temperature of 23±2℃ and a relative humidity greater than 95%. Long-term curing under standard conditions ensures sufficient hydration and stable performance of lightweight aggregates. Standard curing conditions ensure uniform cement hydration, improving the overall performance of lightweight aggregates. Standard curing improves the durability of lightweight aggregates and extends their service life. Standard curing conditions meet the standard requirements of most building materials, facilitating quality control and testing. Carbon dioxide curing is also used, employing either gas flow curing or sealed pressure curing, with a carbon dioxide volume concentration of 10–100% and a relative humidity of 20–80%. Carbon dioxide carbonation improves the early strength and durability of lightweight aggregates. It significantly increases early strength and reduces early cracking. It also enhances durability by improving impermeability and corrosion resistance, extending service life. Finally, carbon dioxide carbonation reduces drying shrinkage and increases density.

[0113] This application provides a multi-layered core-shell structure lightweight aggregate that mimics the microstructure of a bamboo cross-section, utilizing its unique structural advantages to design a lightweight aggregate with excellent mechanical properties. This design effectively increases the strength and toughness of the material while reducing weight. Through specific technical means, a microenvironment conducive to improving the mechanical properties is formed within the lightweight aggregate. This helps improve the density and uniformity of the aggregate, further enhancing its physical properties. Utilizing reactive materials such as volcanic ash to chemically react with cement paste generates a denser structure, improving the bonding force between the lightweight aggregate and the concrete matrix. The addition of nanofibers significantly improves the tensile strength and fracture toughness of the material. These nanofibers act as fillers and bridges within the material, effectively dispersing external forces and reducing the possibility of crack propagation. Through the combined effect of the above methods, especially the presence of nanofibers, the performance of the interfacial transition zone between the lightweight aggregate and the concrete matrix can be greatly improved, promoting better bonding and synergistic work between the two, ultimately achieving the goal of improving the overall performance of the composite material.

[0114] The multi-layer core-shell lightweight aggregate design concept presented in this application is advanced, fully considering the multifunctionality and sustainable development of the material. By rationally combining different materials, especially utilizing industrial waste and nanomaterials, it not only improves the physical and mechanical properties of the lightweight aggregate but also promotes resource recycling, aligning with the development trend of green building. This lightweight aggregate is expected to be widely used in future construction projects, particularly in applications requiring high-elasticity lightweight concrete, such as high-rise buildings, bridges, and tunnels.

[0115] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0116] The above-described embodiments are only used to illustrate the technical solutions of the embodiments of this application, and are not intended to limit them. Although the embodiments of this application have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of the embodiments of this application.

Claims

1. A multi-layered core-shell structure lightweight aggregate, characterized in that, include: The core, the raw materials for its preparation include water-storing lightweight particles and functional ionic solutions; The inner shell covers the core, and the raw materials for preparing the inner shell include cement, volcanic ash materials, solid waste, lime, water-reducing agent, and water; and the outer shell covers the inner shell, and the raw materials for preparing the outer shell include cement, volcanic ash materials, water-reducing agent, nanofibers, and water.

2. The multi-layer core-shell structure lightweight aggregate as described in claim 1, characterized in that, The inner shell comprises the following raw materials prepared by weight method: 26-39 parts cement; 34-51 parts fly ash; 10-40 parts solid waste; 2-3 parts lime; 2-3 parts polycarboxylate superplasticizer; and 20-25 parts water.

3. The multi-layer core-shell structure lightweight aggregate as described in claim 1, characterized in that, The outer shell comprises the following raw materials prepared by weight method: 70-80 parts cement; 20-30 parts silica fume; 0.1-0.3 parts nanofibers; and 2-3 parts polycarboxylate superplasticizer. 20-25 parts water.

4. The multi-layer core-shell structure lightweight aggregate as described in claim 1, characterized in that, The water-storing lightweight particles include one of the following: hydrogel, zeolite, expanded vermiculite, biochar, fly ash ceramsite, diatomaceous earth, and perlite; and / or, the functional ionic solution includes one of the following: pure water, calcium hydroxide solution, sodium sulfate solution, shrinkage reducing agent, and polymer solution.

5. The multi-layer core-shell structure lightweight aggregate as described in claim 1, characterized in that, The average particle size of the solid waste is less than 10 μm; and / or the solid waste includes at least one of glass powder, coal gangue, silica fume, red mud, lithium slag, nickel slag, ore slag, and steel slag.

6. The multi-layer core-shell structure lightweight aggregate as described in claim 1, characterized in that, The nanofibers include at least one of carbon nanotubes, carbon nanofibers, and nanocellulose.

7. The multi-layer core-shell structure lightweight aggregate as described in claim 1, characterized in that, The core has a diameter of 3–10 mm, the inner shell has a thickness of 1–3 mm, and the outer shell has a thickness of 1–3.5 mm.

8. A method for preparing a multi-layered core-shell structured lightweight aggregate, characterized in that, Includes the following steps: The method provides raw materials for preparing the core, inner shell, and outer shell as described in any one of claims 1 to 7; saturating the water-retaining lightweight particles with water to obtain the core; mixing the core with the raw materials for preparing the inner shell and granulating them to obtain an intermediate; and mixing and dispersing the nanofibers, the water-reducing agent, and the water to obtain a suspension. The suspension is mixed with the remaining raw materials for the preparation of the outer shell to obtain a slurry; the slurry is coated onto the intermediate and cured to obtain the multi-layer core-shell structure lightweight aggregate.

9. The preparation method according to claim 8, characterized in that, The step of saturating the water-retaining lightweight particles to obtain the core includes: the water-retaining lightweight particles include a hydrogel, and the saturation process includes immersing the hydrogel in water for at least 4 hours.

10. The preparation method according to claim 8, characterized in that, The curing process includes: coating the intermediate with the slurry and then curing it in a sealed environment; followed by at least one of steam curing, standard curing, or carbon dioxide curing; wherein the curing conditions include: steam curing at a temperature of 60–90°C and a relative humidity of 100%; standard curing at a temperature of 23±2°C and a relative humidity greater than 95%; and carbon dioxide curing being either gas flow curing or sealed pressure curing, with a carbon dioxide volume concentration of 10–100% and a relative humidity of 20–80%.

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