Underwater non-dispersible thermal-insulation fire-retardant low-carbon magnesium phosphate cement-based repairing material and preparation method thereof

Abstract

The application discloses an underwater non-dispersive heat-preservation flame-retardant low-carbon magnesium phosphate cement-based repairing material and a preparation method thereof. The repairing material comprises the following raw materials in parts by weight: brucite 42-48 parts, potassium dihydrogen phosphate 18-22 parts, warm rubber 0.03-0.06 parts, chitosan nanocrystals 0.1-0.2 parts, surface hydrophobic modified alumina hollow microspheres 5-10 parts, boric acid 1.5-2 parts and water 14-18 parts; wherein the weight ratio of the warm rubber to the chitosan nanocrystals is 1:2-1:5. The application replaces heavy-burning magnesium oxide with natural brucite to realize low carbon from the source, realizes underwater non-dispersivity in a strong ion and easy flash condensation system of magnesium phosphate cement by compounding the warm rubber and the chitosan nanocrystals, and gives the surface hydrophobic modified alumina hollow microspheres to impart heat preservation and heat insulation and assist in achieving A1-grade non-combustion, so that the low carbon, underwater non-dispersivity, heat preservation and flame retardation are integrated on the basis of retaining the fast hardening, early strength and high bonding advantages of the magnesium phosphate cement, and the application is suitable for repairing and reinforcing engineering in underwater, low-temperature and fireproof environment.

Description

Technical Field

[0001] This invention relates to the field of building materials and repair and reinforcement engineering technology, and in particular to an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material suitable for underwater, low-temperature and fire-resistant environments, and its preparation method. Background Technology

[0002] Magnesium phosphate cement (MPC), as a novel cementitious material with rapid hardening, early strength, and excellent bonding properties, has shown great potential in the field of rapid repair of concrete structures. Compared with traditional silicate cement, it has concentrated heat release during hydration and rapid early strength development, reaching the target strength within minutes to hours. It is particularly suitable for emergency repair projects such as roads, bridge decks, and airport runways that require rapid restoration of traffic.

[0003] However, existing magnesium phosphate cement-based repair materials still face a series of bottlenecks when facing more complex and demanding application scenarios: First, conventional magnesium phosphate cement uses recalcined magnesium oxide as the main magnesium source, which requires high-temperature calcination of magnesite and other materials, resulting in high energy consumption and large carbon dioxide emissions, contradicting the green and low-carbon development trend of the building materials industry; Second, existing materials lack anti-dispersion design specifically for underwater construction. When used directly for underwater repairs, the freshly mixed slurry is easily washed away and segregated by water flow, leading to the loss of solid particles, non-dense repairs, and failure to bond with the substrate, as well as water pollution; Third, for special environments such as hydraulic structures in cold northern regions, offshore platforms, and ship cabins, repair materials not only need to be water-resistant and durable, but also often need to have certain thermal insulation and fire-retardant properties to cope with temperature stress, icing damage, and fire risks. Currently, there is no magnesium phosphate cement-based repair material that integrates multiple functions such as low carbon, underwater non-dispersion, thermal insulation, and fire retardancy.

[0004] Furthermore, the pore solution of magnesium phosphate cement is a system containing strong ions such as potassium, magnesium, and phosphate, which rapidly transitions from slightly acidic to alkaline and sets quickly. Conventional underwater anti-dispersion components often fail to stabilize and function effectively in this system due to salting out, ion shielding, or flash setting before they can form a network. Conventional lightweight insulating aggregates also easily absorb water and are corroded in this water-containing, strongly ionic slurry, thus losing their insulating function. Therefore, how to simultaneously achieve low carbonization, underwater anti-dispersion, insulation, and flame retardancy while retaining the core advantages of magnesium phosphate cement, such as rapid hardening, early strength, and high bonding, is a technical problem that urgently needs to be solved in this field.

[0005] The background description is provided for the purpose of understanding the relevant technologies in this field and is not intended as an admission of prior art. Summary of the Invention

[0006] Therefore, the present invention aims to provide an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material and its preparation method, so as to simultaneously achieve low carbonization of the preparation process and the underwater anti-dispersibility, heat insulation and flame retardancy of the material while retaining the advantages of rapid hardening, early strength and high adhesion of magnesium phosphate cement, so as to meet the engineering repair needs in complex and harsh environments.

[0007] In a first aspect, embodiments of the present invention provide an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material, which may include the following raw materials in parts by weight: 42-48 parts of brucite, 18-22 parts of potassium dihydrogen phosphate, 0.03-0.06 parts of styrene colloid, 0.1-0.2 parts of chitosan nanocrystals, 5-10 parts of surface-hydrophobically modified alumina hollow microspheres, 1.5-2 parts of boric acid, and 14-18 parts of water; wherein the weight ratio of the styrene colloid to the chitosan nanocrystals is 1:2 to 1:5.

[0008] Optionally, the chitosan nanocrystals have a particle size of 10-50 nm and a purity greater than or equal to 95%; the weight ratio of the warming agent to the chitosan nanocrystals is preferably 1:3 to 1:4.

[0009] Optionally, the surface-hydrophobic modified alumina hollow microspheres have a particle size of 0.1~0.5mm, a thermal conductivity of less than or equal to 0.10W / (m·K), a closed-cell ratio of greater than or equal to 85%, and a cylinder compressive strength of greater than or equal to 8MPa.

[0010] Optionally, the amount of the warm wheel adhesive is 0.05 to 0.06 parts by weight, and the amount of the chitosan nanocrystals is 0.15 to 0.2 parts by weight.

[0011] Optionally, the surface-hydrophobic modified alumina hollow microspheres are 8 to 10 parts by weight.

[0012] Optionally, the brucite has a particle size of 200-325 mesh and a magnesium hydroxide content of 75% or more, and the weight ratio of the brucite to the potassium dihydrogen phosphate is 1.9:1 to 2.7:1.

[0013] Optionally, the raw materials further include 15-18 parts of blast furnace slag and 5-8 parts of fly ash; and / or, the raw materials further include 0.1-0.5 parts of aramid pulp; and / or, the raw materials further include 1-2 parts of nano-silica.

[0014] In a second aspect, embodiments of the present invention also provide a method for preparing an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material according to any of the above embodiments of the present invention, comprising the following steps:

[0015] S1. Measure each raw material according to the stated weight parts;

[0016] S2. Dissolve the warm wheel adhesive in the formula water to obtain a thickening solution. Dry mix the powdered raw materials of magnesium hydroxide, potassium dihydrogen phosphate and boric acid to obtain a dry powder mixture. Add the dry powder mixture to the thickening solution and stir. Then add chitosan nanocrystals and stir. Then add surface hydrophobic modified alumina hollow microspheres and add the remaining water. Stir to obtain a repair slurry.

[0017] S3. The repair slurry is poured and cured underwater to obtain the underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material.

[0018] Optionally, in S2, the warm wheel adhesive is dissolved in 60% to 70% of the total amount of water in the formulation and allowed to stand until dissolved to obtain the thickening solution; the dry powder mixture is added to the thickening solution and stirred for 2 to 3 minutes, chitosan nanocrystals are added and stirred for 2 minutes, surface-hydrophobic modified alumina hollow microspheres are added and the remaining 30% to 40% of water is added and stirred for 1 to 2 minutes; the fluidity of the repair slurry is 220 to 260 mm.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] Using natural mineral brucite as a magnesium source, it completely replaces the recalcined magnesium oxide that requires high-temperature calcination, significantly reducing energy consumption and carbon dioxide emissions in the preparation process from the source. While achieving low carbonization, it can still maintain or even optimize the mechanical properties of the material and reduce its density.

[0021] By combining warming colloid and chitosan nanocrystals, the warming colloid provides a continuous thickening phase, while the chitosan nanocrystals construct a nano-overlapping network. The two work together to form a stable three-dimensional network structure that locks in both free water and solid particles. In particular, the salt and ion resistance of the warming colloid and the compatibility of the chitosan nanocrystals with protonation and positive charge in a slightly acidic environment enable this compound system to establish and maintain an anti-dispersion network before flash-setting in the strong ionic and easily flash-setting system of magnesium phosphate cement. This significantly improves the scouring and segregation resistance of the freshly mixed slurry in water, achieving underwater non-dispersion—an effect that is difficult to achieve by warming colloid or chitosan nanocrystals alone.

[0022] By introducing surface-hydrophobic modified alumina hollow microspheres as lightweight thermal insulation aggregate, their closed pores endow the material with low density and low thermal conductivity thermal insulation performance. After hydrophobic modification, the microspheres can maintain the integrity of the closed-cell structure in the water-containing strong ionic slurry of magnesium phosphate cement, thereby stably playing a thermal insulation role. Due to their ceramic, high temperature resistance and non-combustible properties, the auxiliary material achieves A1 grade non-combustible.

[0023] This invention retains the advantages of magnesium phosphate cement, such as rapid hardening, early strength, and high adhesion, while integrating low carbon content, underwater non-dispersion, heat insulation, and flame retardancy. It is suitable for repair and reinforcement projects in complex and harsh environments such as underwater, low temperature, and fire-resistant environments.

[0024] Other optional features and technical effects of the embodiments of the present invention are partly described below and partly apparent from reading this document. Attached Figure Description

[0025] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0026] Figure 1 This is a photograph of a sample of underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material obtained according to an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0028] This invention provides an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material. It uses natural mineral brucite as the main magnesium cementitious material and potassium dihydrogen phosphate as the phosphorus source. The two react with an acid-base mixture to generate potassium magnesium phosphate hydration products, forming a magnesium phosphate cement matrix. Within this matrix, a composite of thermoplasticizer and chitosan nanocrystals is used to construct an underwater anti-dispersion system. Furthermore, surface-modified hydrophobic alumina hollow microspheres are introduced as lightweight, heat-insulating, and flame-retardant aggregates, and boric acid is used as a retarding component. Thus, while retaining the core advantages of magnesium phosphate cement—rapid hardening, early strength, and high adhesion—it simultaneously achieves underwater non-dispersion, heat insulation, flame retardancy, and low carbon emissions in underwater, low-temperature, and fire-resistant environments. The following details the components, parameters, and mechanisms of action.

[0029] In some embodiments, the brucite is a natural magnesium mineral whose main component is magnesium hydroxide. The content of magnesium hydroxide, by weight, is greater than or equal to 75%, for example, 75%, 80%, 85%, or 90%. In some embodiments, the particle size of the brucite is 200-325 mesh, for example, 200 mesh, 250 mesh, 300 mesh, or 325 mesh.

[0030] Traditional magnesium phosphate cement uses recalcined magnesium oxide as the magnesium source, which requires high-temperature calcination (usually above 1000℃) of magnesite and other materials, resulting in high energy consumption and large carbon dioxide emissions. This invention uses finely ground natural brucite as the direct magnesium source, eliminating the need for high-temperature calcination of recalcined magnesium oxide. This reduces energy consumption and carbon emissions at the source, achieving low-carbon materials. Furthermore, brucite ground to 200-325 mesh possesses suitable reactivity, reacting with potassium dihydrogen phosphate to provide cementation. Natural brucite does not require high-temperature calcination, and compared to systems using recalcined magnesium oxide, it also improves the mechanical strength of the repair and reduces its dry density while achieving low carbon emissions.

[0031] In some embodiments, the potassium dihydrogen phosphate is analytically pure, with a purity greater than or equal to 99.0%, for example, 99.0%, 99.5%, or 99.9%; and its solubility in water at 20°C is not less than 33 g / 100 ml. As an acidic phosphate, the potassium dihydrogen phosphate provides phosphate ions and is slightly acidic during mixing. It reacts with the magnesium components provided by brucite to generate a hydration product mainly composed of potassium magnesium phosphate. This hydration product hardens rapidly and provides early strength and high bond strength to the old concrete substrate.

[0032] In some embodiments, the weight ratio of the brucite to the potassium dihydrogen phosphate is 1.9:1 to 2.7:1, for example, 1.9:1, 2.0:1, 2.25:1, 2.5:1, or 2.7:1. Controlling this weight ratio ensures an appropriate degree of reaction between the magnesium component and the phosphate ions, guaranteeing sufficient formation of hydration products and good strength development, while avoiding excessive unreacted components or overly rapid reactions.

[0033] In some embodiments, the boric acid is industrial grade with a purity greater than or equal to 99.5%. Magnesium phosphate cement exhibits concentrated exothermic hydration and rapid setting; without proper regulation, it is prone to premature setting (flash setting) during mixing and pouring, making it difficult to meet the working time requirements for underwater pouring. The boric acid, by inhibiting the early dissolution of magnesium components and regulating the release and complexation of magnesium ions, prolongs the workable time of the slurry and inhibits flash setting, ensuring the slurry maintains suitable fluidity before underwater pouring and self-leveling filling / repairing areas.

[0034] In some embodiments, the sorbent is industrial grade, and its effective ingredient content is greater than or equal to 99%. In some embodiments, the chitosan nanocrystals have a particle size of 10-50 nm and a purity greater than or equal to 95%, for example, particle sizes of 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm. In some embodiments, the weight ratio of the sorbent to the chitosan nanocrystals is 1:2 to 1:5, for example, 1:2, 1:3, 1:4, or 1:5.

[0035] When freshly mixed magnesium phosphate cement slurry is used directly for underwater pouring, it is easily eroded and segregated by water flow, leading to the loss of solid particles, loose repairs, and failure to bond with the substrate. The Wenlun adhesive, a microbial polysaccharide thickener, has intertwined molecular chains and thixotropic properties, which can significantly increase the viscosity of the slurry and form a continuous thickening phase. The chitosan nanocrystals are rigid rod-shaped crystals at the nanoscale with a large specific surface area, which can overlap and bridge solid particles in the slurry, constructing a nano-network. The combination of these two materials, with the Wenlun adhesive providing a continuous thickening phase and the chitosan nanocrystals providing a nano-overlapping network, complements each other to form a stable three-dimensional network structure in the slurry, locking in free water and solid particles. This significantly improves the erosion and segregation resistance of the freshly mixed slurry in water, achieving underwater non-dispersion.

[0036] It should be noted that the pore solution of magnesium phosphate cement is a system containing strong ions such as potassium, magnesium, and phosphate, which rapidly transitions from slightly acidic to alkaline and solidifies quickly. Conventional underwater anti-dispersion agents often fail in this system due to salting out, ion shielding, or flash solidification before they can form a network. The linalool used in this invention has excellent salt resistance and resistance to ion interference, maintaining thickening and thixotropy in this strong ionic system. Chitosan nanocrystals are protonated and positively charged in the early slightly acidic environment of magnesium phosphate cement, making them compatible with the system and enabling rapid network formation. The combination of the two works synergistically in magnesium phosphate cement, a system not favorable to conventional anti-dispersion methods, rapidly building and maintaining a stable anti-dispersion network before flash solidification occurs. This anti-dispersion effect is difficult to achieve by linalool or chitosan nanocrystals alone.

[0037] In some embodiments, the surface-modified hydrophobic alumina hollow microspheres have a particle size of 0.1~0.5mm, a thermal conductivity less than or equal to 0.10W / (m·K), a closed-cell ratio greater than or equal to 85%, and a cylinder compressive strength greater than or equal to 8MPa. The alumina hollow microspheres have closed cavities inside, with low gas thermal conductivity. When incorporated as lightweight aggregate, they can significantly reduce the material's density and thermal conductivity, imparting thermal insulation properties. Furthermore, the alumina hollow microspheres are ceramic, high-temperature resistant, and non-combustible, contributing to the material's non-combustible rating and imparting flame-retardant properties.

[0038] The alumina hollow microspheres are surface-modified with hydrophobic properties. Magnesium phosphate cement slurry contains water and is a strong ionic system. Unmodified hollow microspheres easily absorb water and are susceptible to erosion in wet mixing and alkaline environments, leading to pore wall damage and pore collapse, thus losing their low-density and low-thermal-conductivity insulation effects. After surface hydrophobic modification, the alumina hollow microspheres can resist the intrusion of water and ions in the slurry, maintaining the integrity of the closed-cell structure during mixing, casting, and hydration, thereby stably playing a role in thermal insulation and auxiliary flame retardancy within the magnesium phosphate cement matrix.

[0039] In some embodiments, the raw material further includes aramid pulp. In some embodiments, the aramid pulp has a length of 50-200 μm, a diameter of 1-5 μm, an aspect ratio greater than or equal to 50, and a specific surface area greater than or equal to 8 m². 2 / g, with a purity greater than or equal to 98%. The aramid pulp is a high-strength, high-modulus organic fiber. Its pulp morphology has a large number of branches and a high specific surface area, which can anchor and bridge microcracks in the matrix, improve the mechanical strength and fracture toughness of the repair, and make it suitable for use in harsh environments.

[0040] In some embodiments, the raw materials further include blast furnace slag and / or fly ash as admixtures. In some embodiments, the Blaine specific surface area of ​​the blast furnace slag is greater than or equal to 400 m². 2 / kg; the fly ash is Class II fly ash, with a sieve residue of less than or equal to 25% on a 45μm square mesh sieve and a loss on ignition of less than or equal to 8%. The blast furnace slag and fly ash are industrial solid wastes. Their addition can improve the workability of the slurry, regulate the reaction process, reduce costs, and increase the utilization rate of solid waste, further enhancing the low-carbon and economical properties of the material. It should be understood that the blast furnace slag and fly ash are optional admixtures and are not essential for achieving the cementing and the above-mentioned functions of this invention. In embodiments without the addition of the blast furnace slag and fly ash, a magnesium phosphate cement matrix composed of brucite, potassium dihydrogen phosphate, boric acid, and water can also be established and achieve the underwater non-dispersibility, heat insulation, flame retardancy, and low-carbon properties of this invention.

[0041] In some embodiments, the raw material further includes nano-silica. In some embodiments, the nano-silica has a particle size of 10-30 nm and a specific surface area greater than or equal to 200 m². 2 / g. The nano-silica can fill the micropores of the matrix, improve the matrix density, and help enhance mechanical properties.

[0042] In some embodiments, the underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material comprises the following raw materials in parts by weight: 42-48 parts of brucite, 18-22 parts of potassium dihydrogen phosphate, 0.03-0.06 parts of styrene, 0.1-0.2 parts of chitosan nanocrystals, 5-10 parts of surface-hydrophobic modified alumina hollow microspheres, 1.5-2 parts of boric acid, and 14-18 parts of water; in some embodiments, the raw materials further include at least one of 15-18 parts of blast furnace slag, 5-8 parts of fly ash, 0.1-0.5 parts of aramid pulp, and 1-2 parts of nano-silica.

[0043] This invention, through the combination of the above components, enables the material to possess multiple functions simultaneously: using natural brucite instead of calcined magnesium oxide as the magnesium source, achieving low carbon emissions from the outset; the reaction of brucite with potassium dihydrogen phosphate to generate potassium magnesium phosphate hydration products provides rapid hardening, early strength, and high adhesion, while boric acid slows the setting to ensure the workability required for underwater casting; the combination of thermal colloid and chitosan nanocrystals synergistically constructs and maintains a stable anti-dispersion network in the strong ionic, easily flash-setting system of magnesium phosphate cement, achieving underwater non-dispersion; the surface-modified hydrophobic alumina hollow microspheres maintain closed-cell integrity in this system, providing thermal insulation and assisting in achieving a non-combustible rating; and aramid pulp can be used for reinforcement and toughening. Therefore, this invention, while retaining the rapid hardening, early strength, and high adhesion advantages of magnesium phosphate cement, integrates low carbon emissions, underwater non-dispersion, thermal insulation, and flame retardancy, making it suitable for repair and reinforcement projects in complex and harsh environments such as underwater, low temperatures, and those requiring fire protection.

[0044] In this invention, the dosage of each component and the numerical range of each parameter recorded above include not only the listed endpoint values ​​and specific values, but also any intermediate value within the range and any sub-range formed by any two of the stated values; the listed specific values ​​are merely examples and do not constitute a limitation on the scope of protection of this invention.

[0045] In some embodiments, the underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material comprises the following raw materials in parts by weight: 42-48 parts of brucite, 18-22 parts of potassium dihydrogen phosphate, 0.03-0.06 parts of styrene colloid, 0.1-0.2 parts of chitosan nanocrystals, 5-10 parts of surface-hydrophobic modified alumina hollow microspheres, 1.5-2 parts of boric acid, and 14-18 parts of water; wherein the weight ratio of styrene colloid to chitosan nanocrystals is 1:2-1:5.

[0046] In some embodiments, the brucite is 42-48 parts, preferably 44-46 parts; for example, 42, 44, 45, 46, or 48 parts. In some embodiments, the potassium dihydrogen phosphate is 18-22 parts, preferably 19-21 parts; for example, 18, 20, 21, or 22 parts. In some embodiments, the boric acid is 1.5-2 parts; for example, 1.5, 1.8, or 2 parts. In some embodiments, the water is 14-18 parts; for example, 14, 16, or 18 parts.

[0047] In some embodiments, the raw materials further include at least one of the following: 15-18 parts (e.g., 15, 16, or 18 parts) of blast furnace slag, 5-8 parts (e.g., 5, 6, or 8 parts) of fly ash, 0.1-0.5 parts (e.g., 0.1, 0.3, or 0.5 parts) of aramid pulp, and 1-2 parts (e.g., 1 part, 1.5, or 2 parts) of nano-silica.

[0048] In some embodiments, the warming agent is 0.03 to 0.06 parts, preferably 0.05 to 0.06 parts; for example, 0.03 parts, 0.04 parts, 0.05 parts, or 0.06 parts. In some embodiments, the chitosan nanocrystals are 0.1 to 0.2 parts, preferably 0.15 to 0.2 parts; for example, 0.1 parts, 0.12 parts, 0.15 parts, 0.18 parts, or 0.2 parts.

[0049] In some embodiments, the weight ratio of the humectant to the chitosan nanocrystals is 1:2 to 1:5, preferably 1:3 to 1:4; for example, 1:2, 1:3, 1:3.3, 1:4, or 1:5. Within this compounding ratio range, the continuous thickening phase provided by the humectant matches the nano-overlapping network provided by the chitosan nanocrystals, and the two synergistically construct and maintain a stable three-dimensional anti-dispersion network. If the humectant is relatively too small, the thickening phase will be discontinuous, and if the chitosan nanocrystals are relatively too small, the nano-network support will be insufficient, both of which are not conducive to achieving and maintaining underwater non-dispersion in magnesium phosphate cement, a strong ionic and easily flash-setting system. Under the preferred ratio of 1:3 to 1:4, the synergistic anti-dispersion effect of the humectant and chitosan nanocrystals is optimal.

[0050] In some embodiments, the chitosan nanocrystals are industrial grade, with an effective component content greater than or equal to 99%. In some embodiments, the particle size of the chitosan nanocrystals is 10-50 nm, preferably 10-30 nm; for example, 10 nm, 20 nm, 30 nm, 40 nm or 50 nm; the purity is greater than or equal to 95%, preferably greater than or equal to 98%.

[0051] In some embodiments, the hydrophobic modified alumina hollow microspheres are 5-10 parts, preferably 8-10 parts; for example, 5 parts, 6 parts, 8 parts, or 10 parts. In some embodiments, the particle size of the hydrophobic modified alumina hollow microspheres is 0.1-0.5 mm (e.g., 0.1 mm, 0.3 mm, or 0.5 mm), the thermal conductivity is less than or equal to 0.10 W / (m·K) (e.g., 0.06, 0.08, or 0.10 W / (m·K)), the closed-cell rate is greater than or equal to 85%, preferably greater than or equal to 90% (e.g., 85%, 88%, 90%, or 92%), and the cylinder compressive strength is greater than or equal to 8 MPa (e.g., 8 MPa, 10 MPa, or 12 MPa). When the hydrophobic modified alumina hollow microspheres are incorporated at a higher dosage of 8-10 parts, the material can be stably made to achieve A1 grade non-combustible, and the dry density and thermal conductivity of the material can be significantly reduced.

[0052] In some embodiments, the particle size of the brucite is 200-325 mesh, preferably 250-300 mesh; for example, 200 mesh, 250 mesh, 300 mesh, or 325 mesh. The magnesium hydroxide content, based on the weight of the brucite, is greater than or equal to 75%, preferably greater than or equal to 80%; for example, 75%, 80%, 85%, or 90%. In some embodiments, the potassium dihydrogen phosphate is analytical grade, with a purity greater than or equal to 99.0%. In some embodiments, the boric acid is industrial grade, with a purity greater than or equal to 99.5%.

[0053] In some embodiments, the weight ratio of the brucite to the potassium dihydrogen phosphate is 1.9:1 to 2.7:1, preferably 2.0:1 to 2.4:1; for example, 1.9:1, 2.0:1, 2.25:1, 2.5:1 or 2.7:1.

[0054] In some embodiments, the Blaine specific surface area of ​​the blast furnace slag is greater than or equal to 400 m². 2 / kg, its main components include CaO, SiO2, Al2O3 and MgO. In some embodiments, the fly ash is Grade II fly ash, with a 45μm square hole sieve residue of less than or equal to 25% and a loss on ignition of less than or equal to 8%. In some embodiments, the aramid pulp has a length of 50~200μm, a diameter of 1~5μm, an aspect ratio of greater than or equal to 50, and a specific surface area of ​​greater than or equal to 8m². 2 / g, with a purity greater than or equal to 98%. In some embodiments, the nano-silica has a particle size of 10~30nm and a specific surface area greater than or equal to 200m². 2 / g, with a SiO2 mass percentage content greater than or equal to 99.8%. The blast furnace slag and fly ash, as admixtures, can improve workability, regulate the reaction process, and reduce costs; the aramid pulp can enhance and toughen the material; and the nano-silica can improve the matrix density. It should be understood that the above-mentioned admixtures and additives are optional components. In embodiments without admixtures, a magnesium phosphate cement matrix composed of brucite, potassium dihydrogen phosphate, boric acid, and water can also be formed and achieve the underwater non-dispersibility, heat insulation, flame retardancy, and low carbon content of the present invention.

[0055] In some embodiments, the repair material satisfies at least one of the following conditions: 3-day compressive strength greater than or equal to 34 MPa, preferably greater than or equal to 38 MPa; 28-day compressive strength greater than or equal to 56 MPa, preferably greater than or equal to 60 MPa; 28-day bond strength with the old concrete substrate greater than or equal to 2.7 MPa, preferably greater than or equal to 3.0 MPa; and dry density less than or equal to 1400 kg / m³. 3 Preferably less than or equal to 1300 kg / m 3The thermal conductivity is less than or equal to 0.10 W / (m·K), preferably less than or equal to 0.08 W / (m·K); the underwater suspended solids content of the freshly mixed slurry is less than or equal to 80 mg / L, preferably less than or equal to 55 mg / L; the underwater spread loss rate is less than or equal to 8%, preferably less than or equal to 5.5%; the combustion performance rating is A1, with a furnace temperature rise of less than or equal to 30℃, a mass loss rate of less than or equal to 10%, and a continuous combustion time of 0 s.

[0056] In some embodiments, the present invention also provides an underwater non-dispersible magnesium phosphate cement-based material, comprising a magnesium phosphate cement cementitious component and an underwater anti-dispersion component; the magnesium phosphate cement cementitious component comprises magnesium materials and phosphates, and the underwater anti-dispersion component comprises styrene colloid and chitosan nanocrystals, wherein the weight ratio of styrene colloid to chitosan nanocrystals is 1:2 to 1:5.

[0057] In some embodiments, the magnesium material includes at least one of brucite and calcined magnesium oxide; in some embodiments, the magnesium material is brucite to achieve low carbon emissions while achieving non-dispersion underwater.

[0058] In some embodiments, the phosphate is potassium dihydrogen phosphate; in some embodiments, the weight ratio of the magnesium material to the potassium dihydrogen phosphate is 1.9:1 to 2.7:1.

[0059] In some embodiments, the particle size of the chitosan nanocrystals is 10-50 nm; in some embodiments, the weight ratio of the sorbate to the chitosan nanocrystals is 1:3 to 1:4.

[0060] In some embodiments, the underwater non-dispersible magnesium phosphate cement-based material further includes surface-hydrophobically modified alumina hollow microspheres to further impart thermal insulation and flame retardant properties to the material.

[0061] In some embodiments, the underwater non-dispersible magnesium phosphate cementitious material further includes boric acid and water; in some embodiments, it further includes at least one of blast furnace slag, fly ash, aramid pulp, and nano-silica. In some embodiments, the flowability of the freshly mixed slurry of the underwater non-dispersible magnesium phosphate cementitious material is 220-260 mm.

[0062] In some embodiments, the present invention provides a method for preparing any of the repair materials described above, comprising the following steps:

[0063] S1. Measure each raw material according to the stated weight parts, and prepare the solid raw materials separately as gelling powder, functional additives and lightweight aggregates; in some embodiments, the gelling powder includes brucite and potassium dihydrogen phosphate and optionally blast furnace slag and fly ash, the functional additives include hummus, chitosan nanocrystals, boric acid and optionally nano silica, and the lightweight aggregates include surface hydrophobically modified alumina hollow microspheres and optionally aramid pulp.

[0064] S2. Dissolve the warm wheel adhesive in 60%~70% of the total water in the formula and let it stand until dissolved (e.g., stand for 15 minutes) to obtain a thickening solution; dry mix the powdered raw materials such as brucite, potassium dihydrogen phosphate, and boric acid (e.g., 3~5 minutes) to obtain a dry powder mixture; add the dry powder mixture to the thickening solution and stir (e.g., high-speed stirring for 2~3 minutes); then add chitosan nanocrystals and stir (e.g., medium-speed stirring for 2 minutes); then add surface-hydrophobic modified alumina hollow microspheres and add the remaining 30%~40% water and stir (e.g., low-speed stirring for 1~2 minutes) to obtain a repair slurry with a flowability of 220~260 mm.

[0065] S3. The repair grout is poured underwater through a conduit or a special container and leveled by its own weight to fill the repair area. It is then kept in still water for 7 days and then cured for 28 days at a temperature of (23±2)℃ and a relative humidity of (90±5)%.

[0066] In some embodiments, the feeding sequence is as follows: first, pre-dissolve the gluten gel to form a thickening phase, then disperse the gelling powder, then add chitosan nanocrystals to construct a nano-network in the thickening phase, and finally add lightweight aggregates and add water. This sequence is beneficial for forming a stable and uniform anti-dispersion network before the slurry flashes and avoids the hollow microspheres from breaking due to high-speed stirring.

[0067] In some embodiments, the present invention also provides the application of any of the above-described repair materials in the repair and reinforcement of concrete structures in underwater, low-temperature and / or fire-resistant environments.

[0068] In some embodiments, the present invention also provides a repair and reinforcement structure comprising a concrete substrate to be repaired and a repair body formed by curing any of the repair materials described above and bonded to the substrate.

[0069] In some embodiments, the present invention also provides an underwater repair and reinforcement construction method, which includes underwater pouring of the slurry of any of the above-mentioned repair materials through a conduit or a special container, leveling and filling the repair area by its own weight, and then curing under constant temperature and humidity conditions after maintaining static water curing to obtain a repaired and reinforced body.

[0070] In some embodiments, the present invention also provides an underwater non-dispersible magnesium phosphate cement-based material, comprising the following raw materials in parts by weight: 42-48 parts of brucite, 18-22 parts of potassium dihydrogen phosphate, 0.03-0.06 parts of styrene, 0.1-0.2 parts of chitosan nanocrystals, 1.5-2 parts of boric acid, and 14-18 parts of water, wherein the weight ratio of styrene to chitosan nanocrystals is 1:2-1:5; the material achieves underwater non-dispersibility through the compounding of styrene and chitosan nanocrystals, and optionally further comprises surface-hydrophobically modified alumina hollow microspheres to also possess thermal insulation and flame retardant properties.

[0071] In some embodiments, the present invention also provides an underwater anti-dispersion agent for magnesium phosphate cement-based materials, comprising styrene colloid and chitosan nanocrystals, wherein the weight ratio of styrene colloid to chitosan nanocrystals is 1:2 to 1:5.

[0072] To better illustrate the present invention, Examples 1-3 and Comparative Examples 1-7 are described below by changing the presence and dosage of magnesium source, functional additives, and heat-insulating and flame-retardant aggregates, as well as the morphology of chitosan and alumina hollow microspheres (whether they are nanocrystalline or have undergone surface hydrophobic modification). The proportions of each example and comparative example are shown in Table 1 (by weight).

[0073] Example 1

[0074] This embodiment provides a basic formulation of an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material and its preparation method.

[0075] The repair material, by weight, comprises the following raw materials: 42 parts brucite, 18 parts potassium dihydrogen phosphate, 15 parts blast furnace slag, 5 parts fly ash, 0.03 parts thermal slag, 0.1 parts chitosan nanocrystals, 5 parts surface-hydrophobically modified alumina hollow microspheres, 0.1 parts aramid pulp, 1.5 parts boric acid, 1 part nano-silica, and 14 parts water. The brucite has a particle size of 200-325 mesh and a magnesium hydroxide content greater than or equal to 75%; the chitosan nanocrystals have a particle size of 10-50 nm and a purity greater than or equal to 95%; and the surface-hydrophobically modified alumina hollow microspheres have a particle size of 0.1-0.5 mm, a closed-cell rate greater than or equal to 85%, and a compressive strength greater than or equal to 8 MPa.

[0076] The preparation steps are as follows:

[0077] S1. Raw material measurement and classification: Accurately measure each raw material according to the above weight proportions, and divide the solid raw materials into three categories: cementitious powder (brucite, potassium dihydrogen phosphate, blast furnace slag, fly ash), functional additives (warm wheel adhesive, chitosan nanocrystals, boric acid, nano silica), and lightweight aggregates (surface hydrophobically modified alumina hollow microspheres, aramid pulp), and store them separately for later use.

[0078] S2. Preparation of Repair Slurry: First, dissolve the warm wheel adhesive in 60%~70% of the total water in the formula, and let it stand for 15 minutes to fully dissolve it and form a thickening solution; stir the brucite, potassium dihydrogen phosphate, blast furnace slag, fly ash, boric acid and nano silica in dry powder state for 3~5 minutes until uniform to obtain a dry powder mixture; add the dry powder mixture to the thickening solution while stirring, and stir at high speed for 2~3 minutes to form a uniform slurry; then add chitosan nanocrystals and stir at medium speed for 2 minutes to disperse them evenly; then add aramid pulp and surface hydrophobic modified alumina hollow microspheres, and then add the remaining 30%~40% water, and stir gently at low speed for 1~2 minutes to obtain the repair slurry, controlling its fluidity to be 220~260 mm;

[0079] S3. Construction and curing: The repair slurry is poured underwater through a conduit or a special container, and the repair area is filled by its own weight; it is kept in static water for 7 days, and then moved into a constant temperature and humidity environment with a temperature of (23±2)℃ and a relative humidity of (90±5)% for 28 days to obtain the underwater non-dispersible thermal insulation flame retardant low-carbon magnesium phosphate cement-based repair material.

[0080] Example 2

[0081] This embodiment provides an optimized formulation of an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material and its preparation method. Compared with Example 1, the dosage of each functional component is appropriately increased. By weight: 45 parts brucite, 20 parts potassium dihydrogen phosphate, 16 parts blast furnace slag, 6 parts fly ash, 0.05 parts thermal slag, 0.15 parts chitosan nanocrystals, 8 parts surface-hydrophobic modified alumina hollow microspheres, 0.3 parts aramid pulp, 1.8 parts boric acid, 1.5 parts nano-silica, and 16 parts water. The preparation steps are the same as in Example 1.

[0082] Example 3

[0083] This embodiment provides a high-performance underwater non-dispersible thermal insulation and flame-retardant low-carbon magnesium phosphate cement-based repair material and its preparation method. Compared with Examples 1 and 2, higher dosages of each component are used. By weight: 48 parts brucite, 22 parts potassium dihydrogen phosphate, 18 parts blast furnace slag, 8 parts fly ash, 0.06 parts thermal slag, 0.2 parts chitosan nanocrystals, 10 parts surface-hydrophobic modified alumina hollow microspheres, 0.5 parts aramid pulp, 2 parts boric acid, 2 parts nano-silica, and 18 parts water. The preparation steps are the same as in Example 1.

[0084] Comparative Example 1

[0085] This comparative example provides a magnesium phosphate cement-based repair material using conventionally recalcined magnesium oxide and its preparation method. The formulation is similar to that of Example 2, but brucite is completely omitted; instead, an equal weight portion of recalcined magnesium oxide is used as the magnesium source (i.e., 45 parts of recalcined magnesium oxide replace 45 parts of brucite). The remaining components and dosages are the same as in Example 2. The preparation steps are the same as in Example 1.

[0086] Comparative Example 2

[0087] This comparative example provides a magnesium phosphate cement-based repair material lacking thermal insulation and flame retardant aggregate and its preparation method. Compared with Example 2, no surface-modified hydrophobic alumina hollow microspheres are added. The missing mass is balanced by fly ash (i.e., fly ash increases from 6 parts to 14 parts, and surface-modified hydrophobic alumina hollow microspheres are 0 parts). The remaining components and dosages are the same as in Example 2. The preparation steps are the same as in Example 1.

[0088] Comparative Example 3

[0089] This comparative example provides a magnesium phosphate cement-based repair material lacking an underwater anti-dispersion system and its preparation method. Compared with Example 2, it does not incorporate warming sizing agent and chitosan nanocrystals (i.e., warming sizing agent is 0 parts, chitosan nanocrystals are 0 parts), while the remaining components and dosages are the same as in Example 2. The preparation steps are the same as in Example 1.

[0090] Comparative Example 4

[0091] This comparative example only added styrax without adding chitosan nanocrystals; the other components and dosages were exactly the same as in Example 1. It was used to verify the underwater anti-dispersion effect of styrax alone.

[0092] By weight: 42 parts brucite, 18 parts potassium dihydrogen phosphate, 15 parts blast furnace slag, 5 parts fly ash, 0.03 parts pyrite, 0 parts chitosan nanocrystals, 5 parts surface-hydrophobically modified alumina hollow microspheres, 0.1 parts aramid pulp, 1.5 parts boric acid, 1 part nano-silica, and 14 parts water. The preparation steps are the same as in Example 1.

[0093] Comparative Example 5

[0094] This comparative example only added chitosan nanocrystals and did not add warming agent. The other components and dosages were completely the same as in Example 1. It was used to verify the underwater anti-dispersion effect of single chitosan nanocrystals.

[0095] By weight: 42 parts brucite, 18 parts potassium dihydrogen phosphate, 15 parts blast furnace slag, 5 parts fly ash, 0 parts thermal slag, 0.1 parts chitosan nanocrystals, 5 parts surface-hydrophobically modified alumina hollow microspheres, 0.1 parts aramid pulp, 1.5 parts boric acid, 1 part nano-silica, and 14 parts water. The preparation steps are the same as in Example 1.

[0096] Comparative Example 6

[0097] In this comparative example, the chitosan nanocrystals in Example 1 were replaced with an equal weight of ordinary chitosan, while all other raw material types and dosages were completely consistent with those in Example 1. This was used to verify the effect of nanoscale chitosan crystals on improving underwater anti-dispersion performance compared to ordinary chitosan.

[0098] By weight: 42 parts brucite, 18 parts potassium dihydrogen phosphate, 15 parts blast furnace slag, 5 parts fly ash, 0.03 parts fumed silica, 0.1 parts ordinary chitosan, 5 parts surface-hydrophobically modified alumina hollow microspheres, 0.1 parts aramid pulp, 1.5 parts boric acid, 1 part nano-silica, and 14 parts water. The preparation steps are the same as in Example 1.

[0099] Comparative Example 7

[0100] In this comparative example, the surface hydrophobic modified alumina hollow microspheres in Example 1 were replaced with an equal weight of ordinary alumina hollow microspheres without hydrophobic modification. All other raw material types and dosages were completely consistent with those in Example 1. This was used to verify the protective effect of the surface hydrophobic modification layer on the thermal insulation performance and closed-cell integrity of the aggregate.

[0101] By weight: 42 parts brucite, 18 parts potassium dihydrogen phosphate, 15 parts blast furnace slag, 5 parts fly ash, 0.03 parts ferruginous acid, 0.1 parts chitosan nanocrystals, 5 parts unmodified hydrophobic alumina hollow microspheres, 0.1 parts aramid pulp, 1.5 parts boric acid, 1 part nano-silica, and 14 parts water. The preparation steps are the same as in Example 1.

[0102] Table 1. Combination ratios of the examples and comparative examples (parts by weight)

[0103] Example 1 42 0 18 15 5 0.03 0.1 5 0.1 1.5 1 14 Example 2 45 0 20 16 6 0.05 0.15 8 0.3 1.8 1.5 16 Example 3 48 0 22 18 8 0.06 0.2 10 0.5 2 2 18 Comparative Example 1 0 45 20 16 6 0.05 0.15 8 0.3 1.8 1.5 16 Comparative Example 2 45 0 20 16 14 0.05 0.15 0 0.3 1.8 1.5 16 Comparative Example 3 45 0 20 16 6 0 0 8 0.3 1.8 1.5 16 Comparative Example 4 42 0 18 15 5 0.03 0 5 0.1 1.5 1 14 Comparative Example 5 42 0 18 15 5 0 0.1 5 0.1 1.5 1 14 Comparative Example 6 42 0 18 15 5 0.03 0.1g of regular chitosan 5 0.1 1.5 1 14 Comparative Example 7 42 0 18 15 5 0.03 0.1 Unhydrophobic modified hollow alumina microspheres 5 0.1 1.5 1 14

[0104] To evaluate the performance of the materials prepared in Examples 1-3 and Comparative Examples 1-7 of the present invention, mechanical, thermal insulation, flame retardancy, underwater anti-dispersion and low carbon (carbon emission) performance tests were conducted on each group of samples according to the following methods.

[0105] (1) Compressive strength and bond strength: The 3-day and 28-day compressive strength were tested in accordance with GB / T50448-2015 "Technical Specification for Application of Cement-based Grouting Materials". The fresh grout was poured into a 40mm×40mm×160mm prism mold and tested at a loading rate of 2.4kN / s after standard curing to the specified age. The 28-day bond strength with the old concrete substrate was tested using the figure-eight tensile clamp method in accordance with DL / T5126-2001 "Test Procedure for Polymer Modified Cement Mortar".

[0106] (2) Dry density: The dry density was determined according to GB / T5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products". The dry density was calculated after the specimen was dried to constant weight at (105±5)℃.

[0107] (3) Thermal conductivity: The thermal conductivity was determined according to GB / T10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials by protective hot plate method", with an average temperature of 23℃.

[0108] (4) Flame retardant (combustion) performance: The furnace temperature rise ΔT, mass loss rate Δm and continuous combustion time tf were determined in accordance with GB / T8624-2012 "Classification of Combustion Performance of Building Materials and Products" and GB / T5464-2010 "Test Method for Non-combustibility of Building Materials". The specimen was a cylinder with a diameter of about 45 mm and a height of about 50 mm. After drying to constant weight at (60±5)℃, it was placed in a heating furnace preheated to (750±5)℃ for 30 min.

[0109] (5) Underwater anti-dispersion performance: Refer to DL / T5117-2000 "Test Procedure for Underwater Non-dispersion Concrete", and evaluate it by the content of suspended solids in the water after the slurry falls freely underwater (pH value change method) and the underwater spread loss rate.

[0110] (6) Low-carbon emission performance: Referring to GB / T44716-2024 "Low-carbon assessment method for building materials", only the carbon emission difference of magnesium source (natural brucite / high-temperature re-fired magnesium oxide) is distinguished, and the emissions of other auxiliary materials and processing procedures are uniformly offset in each group; the functional unit is 1m 3 Hardened repair material, unit: t CO2 / m 3 .

[0111] The test results of mechanical, thermal insulation and underwater anti-dispersion properties of each group of samples are shown in Table 2, the test results of flame retardant properties are shown in Table 3, and the test results of low carbon (carbon emission) properties are shown in Table 4.

[0112] Table 2 Mechanical, thermal insulation and underwater anti-dispersion properties of the examples and comparative examples

[0113] Example 1 34.6 56.4 2.7 1380 0.095 76 7.6 Example 2 41.3 62.8 3.4 1290 0.078 52 5.2 Example 3 38.5 68.5 3.0 1210 0.069 38 3.8 Comparative Example 1 37.1 51.2 2.9 1470 0.082 61 6.1 Comparative Example 2 39.7 59.6 3.2 1660 0.165 55 5.5 Comparative Example 3 40.2 55.3 2.0 1300 0.079 276 27.6 Comparative Example 4 35.1 55.8 2.6 1385 0.096 182 18.3 Comparative Example 5 34.2 56.1 2.5 1378 0.094 205 21.1 Comparative Example 6 34.5 56.0 2.6 1382 0.095 156 16.5 Comparative Example 7 34.4 55.9 2.6 1435 0.142 78 7.8

[0114] Table 3 Flame retardant (combustion) performance of the examples and comparative examples

[0115] Example 1 27 8.6 0 A1 Example 2 22 6.3 0 A1 Example 3 18 4.9 0 A1 Comparative Example 1 29 9.2 0 A1 Comparative Example 2 36 18.7 15 A2 Comparative Example 3 28 8.8 0 A1 Comparative Example 4 27 8.5 0 A1 Comparative Example 5 28 8.7 0 A1 Comparative Example 6 27 8.6 0 A1 Comparative Example 7 32 12.1 0 A2

[0116] Table 4. Comparison of carbon emissions per unit volume of materials between the examples and comparative examples.

[0117] Example 1 Brucite 352 0.0211 0.186 Example 2 Brucite 365 0.0219 0.192 Example 3 Brucite 378 0.0227 0.198 Comparative Example 1 Reburned magnesium oxide 365 0.2993 0.469 Comparative Example 2 Brucite 365 0.0219 0.195 Comparative Example 3 Brucite 365 0.0219 0.192 Comparative Example 4 Brucite 352 0.0211 0.185 Comparative Example 5 Brucite 352 0.0211 0.185 Comparative Example 6 Brucite 352 0.0211 0.186 Comparative Example 7 Brucite 352 0.0211 0.187

[0118] Results Analysis

[0119] Underwater anti-dispersion performance is an important property of the repair material of this invention. This invention achieves excellent effects in underwater anti-dispersion, heat preservation, and flame retardancy by combining a compound of acetone and chitosan nanocrystals with hydrophobically modified alumina hollow microspheres. As shown in Table 2, Examples 1-3, which simultaneously incorporate acetone and chitosan nanocrystals, have an underwater suspended solids content of only 38-76 mg / L and an underwater spread loss rate of only 3.8%-7.6% in their freshly mixed slurry. In contrast, Comparative Example 3, which has the same components and dosages as Example 2 except for the absence of acetone and chitosan nanocrystals, has an underwater suspended solids content as high as 276 mg / L and an underwater spread loss rate as high as 27.6%. That is, simply removing the acetone and chitosan nanocrystal compound system increases the underwater suspended solids content and underwater spread loss rate of the slurry by approximately 5.3 times.

[0120] The comparison shows that, without the aforementioned compound system, the freshly mixed magnesium phosphate cement slurry is immediately washed away by the water flow upon entering the water, resulting in a large loss of solid particles (hence the high suspended solids content). The slurry rapidly disperses and segregates in the water (hence the significant loss of spread), polluting the water and causing the repair to be loose and lose effective adhesion to the substrate—effectively making underwater pouring repair impossible. Test data shows that Comparative Example 4 has an underwater suspended solids content of 182 mg / L and an underwater spread loss rate of 18.3%, which are 2.40 times and 2.41 times that of Example 1, respectively. The underwater segregation and particle loss problems are severe, failing to meet the requirements for long-term underwater self-leveling construction. Comparative Example 5 has an underwater suspended solids content as high as 205 mg / L and an underwater spread loss rate of 21.1%, exhibiting even worse anti-dispersion performance than Comparative Example 4, which only contains warm wheel adhesive, and the slurry shows significant disintegration during underwater pouring. Example 1: Warm roller adhesive and chitosan nanocrystals were simultaneously incorporated. Warm roller adhesive formed a continuous, salt- and ion-resistant integral thickening matrix, encapsulating all solid particles and free water. Chitosan nanocrystals constructed a nano-rigid support network within the thickening phase, compensating for the insufficient erosion resistance of the flexible molecular chains of warm roller adhesive. The slurry remained essentially undispersed in water, and the solid particles and free water were effectively locked in, thus enabling underwater pouring through a conduit, self-weight leveling, and good bonding with the old concrete substrate, meeting the engineering requirements for underwater repair and reinforcement.

[0121] Comparative Example 6, using the same amount of ordinary chitosan instead of chitosan nanocrystals, showed an underwater suspended solids content of 156 mg / L and an underwater spread loss rate of 16.5%, significantly higher than the 76 mg / L and 7.6% of Example 1. Ordinary chitosan molecules have large sizes and low specific surface areas, making it unable to form a rigid nanoscale network; it can only bind particles through weak adsorption. Furthermore, ordinary chitosan exhibits low protonation and poor dispersibility in the slightly acidic, strongly ionic system of magnesium phosphate cement, making it difficult to form a nested three-dimensional water-locking network with the flexible thickening phase of the humectant. In contrast, chitosan nanocrystals with a scale of 10–50 nm have a significantly increased specific surface area. In the early slightly acidic environment, they are fully protonated and positively charged, uniformly dispersed within the humectant colloid, constructing a dense nano-support framework. This effectively locks in fine powder and free water, significantly reducing particle loss in water. This demonstrates that the nanocrystal morphology is an indispensable key to achieving excellent underwater anti-dispersion properties, an effect that ordinary chitosan cannot achieve.

[0122] Comparative Example 7 used unmodified alumina hollow microspheres instead of hydrophobic modified microspheres. Example 1 had a thermal conductivity of 0.095 W / (m·K) and a dry density of 1380 kg / m³. 3 Comparative Example 7 showed an increase in thermal conductivity to 0.142 W / (m·K) and dry density to 1435 kg / m³. 3 Unmodified hollow microspheres readily absorb water in magnesium phosphate cement slurry containing strong ions, and their internal closed pores are invaded by slurry ions. During mixing and hydration, the pore walls are corroded and damaged, the sealed cavities fail, the gaseous insulating medium is lost, and the aggregate density increases, while the thermal conductivity significantly improves. The hydrophobic modification layer can isolate the microspheres from moisture and ion erosion, completely preserving the closed pores inside the microspheres and stably maintaining their lightweight and low thermal conductivity characteristics.

[0123] It should be noted that the comparative examples of this invention are only used to illustrate the effect of the corresponding components or features on the material properties, and are not an admission of the prior art. The technical solution represented by Comparative Example 7 can also be used as an optional implementation of this invention. The protection scope of this invention and its subsequent improvements does not exclude this technical solution. Those skilled in the art can include comparative examples (such as Comparative Example 7) in subsequent applications based on the spirit of this invention, thereby obtaining a broad scope of protection.

[0124] As an explanation, and not a limitation, this significant effect stems from the synergistic effect of humulin and chitosan nanocrystals in the magnesium phosphate cement system: humulin is a microbial polysaccharide whose entangled molecular chains provide a continuous thickening phase, significantly increasing slurry viscosity and imparting thixotropy; chitosan nanocrystals are rigid crystals at the nanoscale with a large specific surface area, which overlap and bridge solid particles in the slurry to form a nano-network; when the two are combined, the continuous thickening phase of humulin and the nano-overlapping network of chitosan nanocrystals support each other to form a stable three-dimensional network structure, locking in free water and solid particles. This anti-dispersion effect is difficult to achieve by humulin or chitosan nanocrystals alone. It is particularly important to note that the pore solution of magnesium phosphate cement is a system containing strong ions such as potassium, magnesium, and phosphate, which rapidly transitions from slightly acidic to alkaline and solidifies quickly. This environment is not favorable for most conventional underwater anti-dispersion components—conventional components often fail due to salting out, ion shielding, or flash solidification before they can form a network. However, the linalool used in this invention has excellent salt resistance and resistance to ion interference, maintaining thickening and thixotropy in this strong ionic system. Chitosan nanocrystals, on the other hand, are protonated and positively charged in the early slightly acidic environment of magnesium phosphate cement, are compatible with the system, and can quickly form a network. Therefore, the combination of the two can establish and maintain a stable anti-dispersion network in this strong ionic, easily flash-solidified system before flash solidification occurs. Thus, Comparative Example 3 shows that removing the linalool and chitosan nanocrystal combination system essentially results in the loss of underwater anti-dispersion ability, indicating that the combination of linalool and chitosan nanocrystals can achieve underwater non-dispersion in the magnesium phosphate cement system, and its anti-dispersion effect is significant.

[0125] Compared with Comparative Example 2, which is identical in all aspects except for the absence of surface-hydrophobic modified alumina hollow microspheres (the deficiency was balanced by fly ash), it can be seen that the thermal conductivity of Example 2 is only 0.078 W / (m·K) and the dry density is only 1290 kg / m³. 3 The thermal conductivity of Comparative Example 2 is as high as 0.165 W / (m·K), and its dry density is as high as 1660 kg / m³. 3The addition of hydrophobically modified alumina hollow microspheres reduces the thermal conductivity of the material by about 53% and the dry density by about 22%, significantly improving its thermal insulation performance. This is because the hollow microspheres have closed cavities inside and, after hydrophobic modification, can maintain the integrity of the closed-cell structure in the water-containing strong ionic slurry of magnesium phosphate cement, thus stably exerting a low-density, low-thermal-conductivity thermal insulation effect. Regarding flame retardant performance (Table 3), Examples 1-3 and Comparative Examples 1, 3-6 all had furnace temperature rise ΔT of 18-29°C, mass loss rate Δm of no more than 10%, and continuous combustion time tf of 0 s, meeting the A1 grade. However, Comparative Example 2, without the inclusion of the hollow microspheres, had a furnace temperature rise ΔT of 36°C, a mass loss rate Δm of 18.7%, and a continuous combustion time tf of 15 s, only reaching the A2 grade. Comparative Example 7 used unmodified alumina hollow microspheres, with a furnace temperature rise ΔT of 32°C and a mass loss rate Δm of 12.1%, both exceeding the A1 grade limit and only reaching the A2 grade. These results indicate that incorporating the hydrophobically modified alumina hollow microspheres helps the material achieve an overall A1 non-combustible grade.

[0126] Comparative Example 1 used an equal weight of reburned magnesium oxide as the magnesium source. The carbon emission from the magnesium source alone reached 0.2993 tCO2 / m³, and the total carbon emission was 0.469 tCO2 / m³. 3 Example 2 uses natural brucite, with magnesium source carbon emissions of only 0.0219 tCO2 / m³. 3 The overall total carbon emissions are only 0.192 tCO2 / m³. 3 Carbon emissions were reduced by 59.06%, demonstrating a significant low-carbon advantage. Examples 1, 2, and 3 all used brucite as a magnesium source; only a slight increase in brucite content resulted in a minor rise in carbon emissions, with overall carbon emissions remaining stable at 0.186~0.198 tCO2 / m³. 3 The carbon emission range is much lower than that of Comparative Example 1, which uses a reburned magnesium oxide system. Comparative Examples 2 and 3 use the same magnesium source as Example 2 (both are brucite), with only the amount of fly ash and anti-dispersion components adjusted. The total carbon emissions are basically the same as those of Example 2, proving that the insulating aggregate and underwater anti-dispersion components do not affect the low-carbon properties of the material, and the low-carbon performance is determined only by the type of magnesium source.

[0127] Comparing Example 2 with Comparative Example 1, which uses an equal amount of reburned magnesia instead of brucite and is otherwise identical, it can be seen that: the 28-day compressive strength (62.8 MPa) of Example 2 is higher than that of Comparative Example 1 (51.2 MPa), the bond strength (3.4 MPa) is higher than that of Comparative Example 1 (2.9 MPa), while the dry density (1290 kg / m³) is lower. 3 The value was significantly lower than that of control example 1 (1470 kg / m³). 3 This indicates that replacing high-energy-consuming recalcined magnesium oxide with natural brucite can reduce energy consumption and carbon emissions in the preparation process from the source, achieving low-carbonization, while still maintaining or even optimizing the mechanical properties of the material and reducing its density.

[0128] In summary, this invention achieves low carbon emissions at the source by replacing reburned magnesium oxide with natural brucite. Furthermore, the combination of thermal colloid and chitosan nanocrystals in magnesium phosphate cement, a strong ionic and easily flash-setting system, achieves excellent underwater non-dispersion (underwater suspended solids content as low as 38 mg / L, spread loss rate as low as 3.8%). Hydrophobically modified alumina hollow microspheres provide thermal insulation (thermal conductivity as low as 0.069 W / (m·K)) and help achieve A1 non-combustible rating. Meanwhile, Examples 1-3, containing the above components, retain the rapid hardening, early strength, and high adhesion of magnesium phosphate cement (3d compressive strength 34.6~41.3 MPa, 28d compressive strength 56.4~68.5 MPa, 28d adhesion 2.7~3.4 MPa), while integrating low carbon emissions, underwater non-dispersion, thermal insulation, flame retardancy, and high strength. This makes it suitable for repair and reinforcement projects in complex and harsh environments such as underwater, low temperatures, and those requiring fire protection.

[0129] This document describes several embodiments of the present invention; however, for the sake of brevity, the descriptions of the embodiments are not exhaustive, and identical or similar features or parts between the embodiments may be omitted. In this document, "one embodiment," "some embodiments," "example," "specific example," or "some examples" refers to embodiments applicable to at least one, but not all, of the present invention. The above terms do not necessarily refer to the same embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described herein, as well as the features of the different embodiments or examples.

[0130] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material, characterized in that, The raw materials include the following parts by weight: 42-48 parts of brucite, 18-22 parts of potassium dihydrogen phosphate, 0.03-0.06 parts of styrax, 0.1-0.2 parts of chitosan nanocrystals, 5-10 parts of surface-hydrophobically modified alumina hollow microspheres, 1.5-2 parts of boric acid, and 14-18 parts of water; wherein the weight ratio of styrax to chitosan nanocrystals is 1:2 to 1:

5.

2. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, The chitosan nanocrystals have a particle size of 10-50 nm and a purity greater than or equal to 95%.

3. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, The weight ratio of the warming gel to the chitosan nanocrystals is 1:3 to 1:

4.

4. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, The surface-hydrophobic modified alumina hollow microspheres have a particle size of 0.1~0.5mm, a thermal conductivity of less than or equal to 0.10W / (m·K), a closed-cell rate of greater than or equal to 85%, and a cylinder compressive strength of greater than or equal to 8MPa.

5. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, By weight, the warm wheel adhesive is 0.05~0.06 parts and the chitosan nanocrystals are 0.15~0.2 parts.

6. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, The amount of the surface-hydrophobic modified alumina hollow microspheres is 8-10 parts by weight.

7. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, The brucite has a particle size of 200-325 mesh, and the magnesium hydroxide content is greater than or equal to 75% based on the weight of the brucite. The weight ratio of the brucite to the potassium dihydrogen phosphate is 1.9:1 to 2.7:

1.

8. The underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material according to claim 1, characterized in that, The raw materials also include 15-18 parts of blast furnace slag and 5-8 parts of fly ash; and / or, the raw materials also include 0.1-0.5 parts of aramid pulp; and / or, the raw materials also include 1-2 parts of nano-silica.

9. A method for preparing an underwater non-dispersible, heat-insulating, flame-retardant, low-carbon magnesium phosphate cement-based repair material as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Measure each raw material according to the stated weight parts; S2. Dissolve the warm wheel adhesive in the formula water to obtain a thickening solution. Dry mix the powdered raw materials of magnesium hydroxide, potassium dihydrogen phosphate and boric acid to obtain a dry powder mixture. Add the dry powder mixture to the thickening solution and stir. Then add chitosan nanocrystals and stir. Then add surface hydrophobic modified alumina hollow microspheres and add the remaining water. Stir to obtain a repair slurry. S3. The repair slurry is poured and cured underwater to obtain the underwater non-dispersible thermal insulation and flame retardant low-carbon magnesium phosphate cement-based repair material.

10. The preparation method according to claim 9, characterized in that, In step S2, the warm wheel adhesive is dissolved in 60% to 70% of the total water in the formulation and allowed to stand until dissolved to obtain the thickening solution; the dry powder mixture is added to the thickening solution and stirred for 2 to 3 minutes, chitosan nanocrystals are added and stirred for 2 minutes, surface-hydrophobic modified alumina hollow microspheres are added and the remaining 30% to 40% of water is added and stirred for 1 to 2 minutes; the fluidity of the repair slurry is 220 to 260 mm.

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