Fireproof mortar, preparation method and application thereof

Abstract

The present application relates to the technical field of building engineering materials, and particularly relates to a fireproof mortar, a preparation method and application, so as to solve the problem that the existing fireproof mortar is difficult to consider fireproof performance, mechanical performance and durability. The fireproof mortar comprises natural fine aggregate, ordinary Portland cement, fly ash, silica aerogel, silane coupling agent, polycarboxylic acid superplasticizer and water. The present application constructs a low-thermal-conductivity porous heat-insulating structure through the silica aerogel, so as to reduce the thermal conductivity of the mortar. The pore structure of the mortar is optimized through the pozzolanic reaction and micro-filling effect of the fly ash, so as to improve the compactness and chloride ion penetration resistance of the mortar. The interface of the aerogel is modified through the silane coupling agent, so as to enhance the interface bonding capacity between the aerogel and the cement matrix, and reduce the strength loss caused by the high content of the aerogel. The present application is mainly used in the engineering fields with high requirements for fireproofing, heat insulation and durability, such as marine engineering, underground engineering, tunnel lining and steel structure fireproofing protection.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a fireproof mortar, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of marine engineering, underground space, and large public buildings, building structures not only need to meet load-bearing requirements but also need to possess excellent fire resistance and long-term durability. Ordinary cement mortar has a high thermal conductivity, and under fire conditions, heat transfer is rapid, easily leading to a rapid increase in the internal temperature of the concrete. This, in turn, causes a decrease in the load-bearing capacity of the reinforcing steel and a significant reduction in the fire resistance of the structure. At the same time, in marine and chloride-rich environments, chloride ions can easily penetrate into the structure through the mortar pores, causing corrosion of the reinforcing steel and deterioration of durability, seriously affecting the service life of the project.

[0003] Silica aerogel, with its ultra-high porosity, extremely low thermal conductivity, and excellent high-temperature resistance, is one of the most widely used inorganic thermal insulation materials. Incorporating it into cement-based materials can effectively reduce thermal conductivity and improve the material's fire resistance and insulation performance. However, aerogel has low density, a loose particle surface, and weak interfacial bonding with cement paste. High admixture levels can easily lead to increased porosity within the paste and a loose interfacial transition zone, resulting in a decline in the mechanical properties of the mortar and limiting its engineering applications.

[0004] Fly ash has pozzolanic activity and micro-filling effect, which can improve the pore structure of cement paste and increase the density and durability of the material. Silane coupling agents can improve the interfacial bonding performance between inorganic particles and cement matrix, enhance the density of the interfacial transition zone, and improve the interfacial adhesion between aerogel and paste, which is expected to compensate for the mechanical property degradation caused by high aerogel content.

[0005] Currently, research on silica aerogel fireproof mortar mainly focuses on improving its thermal insulation performance. However, research on the combined effect of fly ash and silane coupling agents to systematically enhance the fire resistance, chloride ion penetration resistance, and mechanical properties of fireproof mortar remains relatively scarce. In particular, the mix design and preparation method that balances fire resistance, durability, and mechanical properties is still lacking. Therefore, there is an urgent need to develop a new type of fireproof mortar and its preparation method that combines excellent fireproof and thermal insulation performance, chloride ion corrosion resistance, and good mechanical properties to meet the pressing need for long-term safe service of engineering structures in complex service environments. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0007] Therefore, this invention proposes a fireproof mortar, its preparation method, and its application. Through ternary modification of silica aerogel, fly ash, and silane coupling agent, it ensures excellent thermal insulation performance while also taking into account good mechanical properties and resistance to chloride ion erosion.

[0008] A fireproof mortar according to an embodiment of the present invention comprises the following components by weight: 641-804 parts of natural fine aggregate; 478-508 parts of ordinary silicate cement; 83-113 parts of fly ash; 32-41 parts of silica aerogel; 1.9-2.1 parts of silane coupling agent; 5.3-5.6 parts of polycarboxylate superplasticizer; and 245-255 parts of water.

[0009] In this invention, the silica aerogel undergoes interfacial modification using a silane coupling agent. This silane coupling agent improves the interfacial bonding between the silica aerogel and the cement paste, enhances the density of the interfacial transition zone, and reduces the strength loss caused by high silica aerogel content. The cement paste in this invention is composed of ordinary Portland cement, fly ash, water, and a polycarboxylate superplasticizer.

[0010] According to one embodiment of the present invention, the fly ash accounts for 12% to 18% of the total mass of the cementitious material, preferably 15%; the fly ash is Class II fly ash, whose active SiO2 and Al2O3 can undergo a pozzolanic reaction with Ca(OH)2 produced by cement hydration to generate more CSH gel, so as to give full play to the pozzolanic reaction and micro-filling effect, improve the pore structure of the slurry, and improve the density and chloride ion penetration resistance of the mortar; the cementitious material is composed of ordinary silicate cement and fly ash.

[0011] According to one embodiment of the present invention, the silane coupling agent is γ-aminopropyltriethoxysilane (KH550), and its dosage is 0.35% to 0.45% of the total mass of the cementitious material, preferably 0.40%, in order to obtain better interfacial bonding performance and comprehensive mechanical properties.

[0012] According to one embodiment of the present invention, the water-cement ratio of the fireproof mortar is 0.42 to 0.46, preferably 0.44, so as to take into account the workability, mechanical properties and fireproof properties of the mortar; the mass ratio of the natural fine aggregate to the cementitious material is 2.80 to 2.90, preferably 2.85.

[0013] According to one embodiment of the present invention, the silica aerogel is a granular inorganic porous material with a particle size of 0.6 to 1.5 mm, a specific surface area of ​​400 to 700 m² / g, and a thermal conductivity of 0.017 to 0.023 W / (m·K), which can effectively reduce the thermal conductivity of mortar and improve the fire resistance and heat insulation performance of the material.

[0014] According to one embodiment of the present invention, the natural fine aggregate meets the requirements of Class II or above natural sand in GB / T 14684-2022, with a particle size of 0.075-4.75 mm, a fineness modulus of 2.3-3.0, a mud content of no more than 2.5%, and a chloride ion content of no more than 0.015%; the ordinary Portland cement has a strength grade of no less than 42.5; and the polycarboxylate superplasticizer has a water reduction rate of no less than 20%, which can reduce water consumption while ensuring that the mortar has good fluidity and workability.

[0015] According to one embodiment of the present invention, the volume of the silica aerogel accounts for 40% to 70% of the total volume of the natural fine aggregate and the silica aerogel.

[0016] This invention utilizes silica aerogel to construct a low thermal conductivity porous insulation structure, and leverages the pozzolanic reaction and micro-filling effect of fly ash to optimize the pore structure of the slurry, improving the mortar's density and resistance to chloride ion penetration. Simultaneously, a silane coupling agent is used to modify the aerogel interface, enhancing the interfacial bonding between aerogel particles and the cement matrix, improving the structure of the interfacial transition zone, and reducing the strength loss caused by high aerogel content. While ensuring excellent fireproof and thermal insulation performance, this invention improves the mortar's compressive strength, flexural strength, and durability, achieving a 28-day compressive strength exceeding 15 MPa, while also exhibiting a low chloride ion migration coefficient and good fire resistance and thermal insulation properties. This invention, through the combined action of fly ash and silane coupling agent, effectively solves the problem that aerogel easily weakens the mechanical properties and interfacial bonding ability of cement-based materials while ensuring the excellent thermal insulation performance of high-content silica aerogel. It achieves simultaneous improvement in fire resistance, mechanical properties and durability, and can be widely used in engineering fields with high requirements for fire resistance, thermal insulation and durability, such as marine engineering, underground engineering, tunnel lining, prefabricated buildings and steel structure fire protection.

[0017] In this invention, silica aerogel, fly ash, and a silane coupling agent form a combined reinforcing system. Silica aerogel possesses ultra-high porosity, ultra-low thermal conductivity, and a nanoscale three-dimensional porous network structure, which can form a continuous insulating layer within the mortar, effectively reducing the heat transfer rate and improving the mortar's fire resistance and heat insulation performance. Its internal closed pores can extend the heat transfer path and slow down the diffusion of heat into the material under high-temperature conditions. The active SiO2 and Al2O3 in fly ash can undergo a pozzolanic reaction with Ca(OH)2 produced during cement hydration, generating more CSH gel and improving the density of the slurry. Simultaneously, the fly ash particles have a micro-filling effect, further optimizing the mortar's pore structure, reducing pore connectivity, and decreasing the transport channels for chloride ions and other corrosive media, thereby improving the fire-resistant mortar's resistance to chloride ion penetration and its long-term durability. The silane coupling agent molecules contain siloxane groups that can undergo condensation reactions with hydroxyl groups on the aerogel surface, while the other active group can form stable bonds with cement hydration products. This improves the interfacial adhesion between aerogel particles and the slurry, reduces the strength loss caused by interfacial defects in high-dosage aerogels, and allows the aerogel to maintain excellent thermal insulation performance while also possessing good mechanical properties. The combined effect of these three factors ensures the mortar's excellent fireproof and thermal insulation performance while simultaneously improving mechanical properties, chloride ion penetration resistance, and long-term durability.

[0018] This invention also provides a method for preparing fireproof mortar, comprising the following steps: S1, weighing natural fine aggregate, ordinary silicate cement, fly ash, silica aerogel, silane coupling agent, polycarboxylate superplasticizer, and water according to the formula; S2, adding the natural fine aggregate, ordinary silicate cement, and fly ash to a mortar mixer, dry mixing at 40-140 r / min for 10-60 s until uniformly mixed; S3, mixing water, polycarboxylate superplasticizer, and silane coupling agent at 30%-70% of their respective total amounts to prepare a first mixture, and then mixing it with silica aerogel before adding it to the mixer. Stir at 40–140 r / min for 40–120 s to fully wet and modify the surface of the silica aerogel particles with the silane coupling agent; S4, continue to add the remaining water, polycarboxylate superplasticizer and silane coupling agent, and continue stirring at 40–140 r / min for 40–120 s to ensure the slurry is fully and uniformly mixed; S5, pour the obtained mortar into a mold or 3D printing equipment for molding; when molding with a mold, vibrate on a vibrating table for 5–30 s to remove air bubbles, let it stand at room temperature for 12–48 h before demolding, and cure under standard curing conditions to the specified age to obtain fireproof mortar.

[0019] According to one embodiment of the present invention, in step S2, natural fine aggregate, ordinary silicate cement, and fly ash are added to a mortar mixer and dry-mixed at 90 r / min for 30 seconds until uniformly mixed; in step S3, water, polycarboxylate superplasticizer, and silane coupling agent are mixed at 50% of their respective total amounts to prepare a first mixture, which is then mixed with silica aerogel and added to the mixer. The inner wall of the mixing tank is cleaned with a scraper to ensure uniform dispersion of the aerogel and reduce material loss, and the mixture is stirred at 90 r / min for 80 seconds. In step S4, the remaining water, polycarboxylate superplasticizer, and silane coupling agent are added, and the mixture is stirred at 90 r / min for 80 s to ensure thorough and uniform mixing. In step S5, the resulting mortar is poured into a mold or 3D printing equipment for molding. When molding with a mold, the mortar is vibrated on a vibrating table for 10 s to remove air bubbles, allowed to stand at room temperature for 24 h, then demolded and cured under standard curing conditions to the specified age to obtain fireproof mortar.

[0020] According to one embodiment of the present invention, the standard maintenance conditions are a temperature of 20±5℃ and a relative humidity of 90±5%.

[0021] This invention also provides an application of fire-resistant mortar in marine engineering, underground engineering, tunnel lining, prefabricated buildings, or fire protection of steel structures.

[0022] The beneficial effects of this invention are as follows: This invention uses silica aerogel, fly ash, and silane coupling agent to construct a joint reinforcement system, achieving simultaneous improvement in fire resistance, mechanical properties, and durability. Silica aerogel has an ultra-low thermal conductivity and a nanoporous structure, which can significantly reduce the thermal conductivity of mortar and delay heat transfer to the interior of the component. The active SiO2 and Al2O3 in fly ash can react with Ca(OH)2 to generate more CSH gel, optimize the pore structure, reduce the chloride ion migration coefficient, and simultaneously promote the formation of stable ceramic phases such as mullite under high-temperature conditions. The silane coupling agent can improve the interfacial bonding between the aerogel and cement paste, increase the density of the interfacial transition zone, and reduce interfacial defects caused by high-dosage aerogel. The combined effect of silica aerogel, fly ash, and silane coupling agent enables the mortar to form a uniform and stable multi-scale porous structure, increasing pore tortuosity and reducing heat and chloride ion transport efficiency. The relevant mechanisms have been verified by SEM-EDS, TGA, and MIP tests. Attached Figure Description

[0023] Figure 1 This is a flowchart of the fireproof mortar preparation method of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The raw materials used in the following embodiments and comparative examples are as follows: The natural fine aggregate is natural river sand, which meets the requirements of GB / T 14684-2022 Class II sand, with a particle size of 0.075~2.36mm, a fineness modulus of 2.5, an apparent density of 2590.4 kg / m³, and a water absorption rate of 5.6%. Ordinary Portland cement is ordinary Portland cement P·O 42.5 with a strength grade of 42.5; The fly ash is Class II dry-discharged fly ash; The silica aerogel is a hydrophobic commercial aerogel particle purchased from Suzhou Kangmai New Material Co., Ltd., with a particle size of 0.6-1.5 mm, a pore size of 20-100 nm, a specific surface area of ​​400-700 m² / g, a thermal conductivity of 0.017-0.023 W / (m·K), a porosity greater than 90%, and a contact angle greater than 145°. The silane coupling agent was γ-aminopropyltriethoxysilane KH550, purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a purity of 100%, a boiling point of 217 ℃, and a density of 0.942 g / cm³. 3 ; The polycarboxylate superplasticizer was purchased from Sichuan Dongfang Tongren Concrete New Materials Co., Ltd., model DFTR-PCE standard type, with a water reduction rate of approximately 25%.

[0026] It should be noted that the proportion of silica aerogel in the total volume of natural fine aggregate and silica aerogel in this invention is calculated based on the apparent density of natural river sand (2590.4 kg / m³) and the measured bulk density of silica aerogel (approximately 110–120 kg / m³), taking the average of 115 kg / m³. Taking Example 1 (642.70 parts natural sand and 40.56 parts aerogel) as an example, the volume occupied by sand = 642.70 / 2590.4 ≈ 0.248 m³; the volume occupied by aerogel = 40.56 / 115 ≈ 0.353 m³. The ratio of aerogel volume to the total aggregate volume is approximately 0.353 / (0.248+0.353) ≈ 58.7%, close to 60% volume. The proportions in other examples and comparative examples are adjusted according to this density conversion relationship, and will not be repeated below.

[0027] The fireproof mortar specimens prepared in Examples 1-4 and Comparative Examples 1-4 were all cured in a standard curing room at 20±5℃ and 90±5% relative humidity for 28 days.

[0028] Example 1: See Figure 1 This embodiment provides a fireproof mortar, in which aerogel accounts for 60% of the total volume of natural fine aggregate and aerogel, and fly ash accounts for 15% of the total mass of cementitious materials. Its preparation method includes the following steps: S1. Weigh the raw materials according to the following formula: 642.70 parts of natural fine aggregate, 507.20 parts of ordinary silicate cement, 84.53 parts of fly ash, 40.56 parts of silica aerogel, 2.03 parts of silane coupling agent, 5.50 parts of polycarboxylate superplasticizer, and 250 parts of water.

[0029] S2. Dry material premixing: Add natural fine aggregate, ordinary silicate cement and fly ash to the mortar mixer and dry mix at 90 r / min for 30 s until uniform.

[0030] S3. Slurry preparation: Water, polycarboxylate superplasticizer and silane coupling agent are mixed at 50% of their respective total amounts to prepare the first mixture, and then mixed with silica aerogel and added to a mixer. The mixture is stirred at 90 r / min for 80 s to fully wet and modify the surface of silica aerogel particles with the silane coupling agent.

[0031] S4. Secondary stirring: Continue to add the remaining 50% of water, polycarboxylate superplasticizer and silane coupling agent, and continue stirring at 90 r / min for 80 s to ensure that the slurry is fully and uniformly mixed.

[0032] S5. Molding and curing: The obtained mortar is filled into 40 mm × 40 mm × 160 mm test molds and bond strength test molds, vibrated on a vibrating table for 10 s to remove internal air bubbles, left to stand at room temperature for 24 h, demolded, and cured under standard curing conditions to the specified age to obtain fireproof mortar.

[0033] Example 2: This embodiment provides a fireproof mortar, in which aerogel accounts for 50% of the total volume of natural fine aggregate and aerogel, and fly ash accounts for 15% of the total mass of cementitious materials. The preparation method includes the following steps: Weigh the raw materials according to the following formula: 803.38 parts natural fine aggregate, 507.20 parts ordinary silicate cement, 84.53 parts fly ash, 33.80 parts silica aerogel, 2.03 parts silane coupling agent, 5.50 parts polycarboxylate superplasticizer, and 250 parts water. The remaining operating steps are the same as in Embodiment 1.

[0034] Example 3: This embodiment provides a fireproof mortar, in which aerogel accounts for 40% of the total volume of natural fine aggregate and aerogel, and fly ash accounts for 15% of the total mass of cementitious materials. The preparation method includes the following steps: Weigh the raw materials according to the following formula: 946.05 parts natural fine aggregate, 507.20 parts ordinary Portland cement, 84.53 parts fly ash, 27.04 parts silica aerogel, 2.03 parts silane coupling agent, 5.50 parts polycarboxylate superplasticizer, and 250 parts water. The remaining operating steps are the same as in Embodiment 1.

[0035] Example 4: This embodiment provides a fireproof mortar, in which aerogel accounts for 70% of the total volume of natural fine aggregate and aerogel, and fly ash accounts for 15% of the total mass of cementitious materials. The preparation method includes the following steps: Weigh the raw materials according to the following formula: 482.03 parts natural fine aggregate, 507.20 parts ordinary silicate cement, 84.53 parts fly ash, 47.32 parts silica aerogel, 2.03 parts silane coupling agent, 5.50 parts polycarboxylate superplasticizer, and 250 parts water. The remaining operating steps are the same as in Embodiment 1.

[0036] Comparative Example 1: This comparative example provides a method for preparing fireproof mortar, which differs from Example 1 in that: no fly ash is added, and an equal mass of cement is used to replace fly ash; the aerogel accounts for 60% of the total volume of natural fine aggregate and aerogel, and fly ash accounts for 0% of the total mass of cementitious materials. The raw materials are weighed according to the following formula: 642.70 parts of natural fine aggregate, 591.73 parts of ordinary Portland cement, 0 parts of fly ash, 40.56 parts of silica aerogel, 2.03 parts of silane coupling agent, 5.50 parts of polycarboxylate superplasticizer, and 250 parts of water. The remaining operating steps are the same as in Example 1.

[0037] Comparative Example 2: This comparative example provides a method for preparing fireproof mortar, which differs from Example 1 in that: no silane coupling agent is added, aerogel accounts for 60% of the total volume of natural fine aggregate and aerogel, and fly ash accounts for 15% of the total mass of cementitious materials. The raw materials are weighed according to the following formula: 642.70 parts natural fine aggregate, 507.20 parts ordinary Portland cement, 84.53 parts fly ash, 40.56 parts silica aerogel, 0 parts silane coupling agent, 5.50 parts polycarboxylate superplasticizer, and 250 parts water. The remaining operating steps are the same as in Example 1.

[0038] Comparative Example 3: This comparative example provides a method for preparing fireproof mortar, which differs from Example 1 in that: fly ash accounts for 20% of the total mass of the cementitious materials, and aerogel accounts for 60% of the total volume of natural fine aggregate and aerogel. The raw materials are weighed according to the following formula: 642.70 parts of natural fine aggregate, 479.03 parts of ordinary Portland cement, 112.71 parts of fly ash, 40.56 parts of silica aerogel, 2.03 parts of silane coupling agent, 5.50 parts of polycarboxylate superplasticizer, and 250 parts of water. The remaining operating steps are the same as in Example 1.

[0039] Comparative Example 4: This comparative example provides a method for preparing fireproof mortar, which differs from Example 1 in that: fly ash accounts for 25% of the total mass of the cementitious materials, and aerogel accounts for 60% of the total volume of natural fine aggregate and aerogel. The raw materials are weighed according to the following formula: 642.70 parts of natural fine aggregate, 450.85 parts of ordinary Portland cement, 140.89 parts of fly ash, 40.56 parts of silica aerogel, 2.03 parts of silane coupling agent, 5.50 parts of polycarboxylate superplasticizer, and 250 parts of water. The remaining operating steps are the same as in Example 1.

[0040] The fire-resistant mortars prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests: 28-day compressive strength and flexural strength were tested according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar"; chloride ion migration coefficient was tested according to the rapid chloride ion migration method in GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete"; thermal conductivity was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method"; fire resistance tests were conducted according to the temperature rise curve of ISO 834 standard, and the temperature changes at different depths of 25 mm, 50 mm, and 75 mm of the test specimens were monitored, and the high-temperature mass loss rate and residual compressive strength were measured; bond strength was also tested. Samples were taken from specimens cured for 28 days and specimens after high-temperature treatment. SEM-EDS, Mapping, TG-DTG and MIP tests were used to analyze their micromorphology, changes in hydration products and pore structure characteristics, in order to reveal the mechanism of fireproof mortar performance improvement.

[0041] The component contents of the examples and comparative examples are shown in Table 1, and the test results of the corresponding fireproof mortars are shown in Table 2.

[0042] Table 1. Content (parts by mass) of each component in the Examples and Comparative Examples

[0043] Table 2 Test Results of Fireproof Mortar Performance

[0044] Table 2 shows that the fireproof mortar prepared in Example 1 has the best overall performance. When silica aerogel accounts for 60% of the total volume of natural fine aggregate and aerogel, fly ash accounts for 15% of the total mass of cementitious materials, and a silane coupling agent is added, the mortar has a 28-day compressive strength of 15.46 MPa, a flexural strength of 4.62 MPa, a thermal conductivity of only 0.2553 W / (m·K), and a chloride ion migration coefficient of 1.90 × 10⁻⁶. - The heat transfer rate was 12 m² / s, and the high-temperature mass loss rate was 13.32%. In the ISO 834 standard fire resistance test, after 2 hours of exposure to fire, the temperatures at distances of 25 mm, 50 mm, and 75 mm from the exposed surface were only 367℃, 305℃, and 134℃, respectively, all significantly lower than other groups, indicating that the fireproof mortar of this invention has excellent thermal insulation, chloride ion penetration resistance, and fire resistance. SEM observation results showed that the silica aerogel in Example 1 could be uniformly dispersed in the cement matrix, with a complete internal nanoporous structure forming a continuous and stable thermal insulation network; MIP test results further showed that an appropriate amount of fly ash could refine the pore size distribution, reduce the proportion of harmful pores, and improve the density of the slurry, thereby effectively blocking the transmission channels of heat and chloride ions. The above microstructure analysis results are consistent with the thermal conductivity, chloride ion migration coefficient, and fire resistance test results, indicating that there is a significant synergistic reinforcing effect between silica aerogel, fly ash, and silane coupling agent.

[0045] Examples 1, 2, 3, and 4 are used together to illustrate the effect of silica aerogel content on the performance of fireproof mortar. As the proportion of aerogel in the total aggregate volume increases from 40% to 50% and then to 60%, the thermal conductivity decreases from 0.3122 W / (m·K) to 0.2717 W / (m·K) and 0.2553 W / (m·K), respectively, while the chloride ion migration coefficient increases from 3.70 × 10⁻⁶ W / (m·K) to 0.2717 W / (m·K) and 0.2553 W / (m·K). - ¹² m² / s decreased to 3.10 × 10 - ¹² m² / s and 1.90 × 10 -The high-temperature mass loss rate decreased from 15.63% to 14.69% and 13.32% with an aerogel content of ¹² m² / s, and the temperature at a depth of 75 mm decreased from 210℃ to 165℃ and 134℃, indicating that with the increase of aerogel content, a continuous and uniform nanoporous thermal insulation network gradually forms inside the mortar, which can significantly reduce the heat transfer rate and improve the resistance to chloride ion penetration. When the aerogel content is further increased to 70%, i.e., Example 4, the thermal conductivity increases to 0.4305 W / (m·K), the high-temperature mass loss rate increases to 15.68%, the temperature at a depth of 75 mm increases to 218℃, and the compressive strength decreases to 12.92 MPa, indicating that excessive aerogel content will lead to particle agglomeration, increased interface defects, and damage to the continuity of the pore structure, weakening the thermal insulation and mechanical properties. Therefore, when the aerogel accounts for 60% of the total aggregate volume, it can balance thermal insulation, mechanical properties, and durability, which is the preferred solution of this invention.

[0046] Example 1 and Comparative Example 1 are used together to illustrate the important role of fly ash in the performance of fireproof mortar. Comparative Example 1 omits fly ash and replaces it with an equal mass of cement. Test results show that although the 28-day compressive strength of Comparative Example 1 increased to 39.25 MPa and the flexural strength increased to 9.66 MPa, the thermal conductivity increased to 0.5460 W / (m·K), approximately 2.14 times that of Example 1; the chloride ion migration coefficient increased to 7.10 × 10⁻⁶. - The density of fly ash increased by 12 m² / s, and the high-temperature mass loss rate increased to 16.76%. After 2 hours of firing, the temperatures at 25 mm, 50 mm, and 75 mm reached 597℃, 551℃, and 461℃, respectively, all significantly higher than in Example 1. This indicates that fly ash not only generates more CSH gel through pozzolanic reaction, refining the pore structure and reducing pore connectivity, but also promotes the formation of a stable refractory phase under high-temperature conditions, improving the high-temperature stability of the material. Therefore, fly ash plays an irreplaceable role in reducing thermal conductivity, improving resistance to chloride ion penetration, and enhancing refractory performance.

[0047] Example 1 and Comparative Example 2 are used together to illustrate the crucial role of silane coupling agents in the performance of fireproof mortar. Comparative Example 2, without the addition of silane coupling agent KH550, showed a 28-day compressive strength decreasing to 14.56 MPa, a thermal conductivity recovering to 0.2902 W / (m·K), and a significant increase in temperature at a depth of 75 mm after 2 hours of exposure to fire, from 134℃ in Example 1 to 165℃. This indicates that without the addition of silane coupling agents, the abundant hydroxyl groups on the surface of silica aerogel particles cannot form chemical bonds with the cement matrix. Physical encapsulation alone is insufficient to resist interfacial debonding during mixing and curing. Numerous aerogel-slurry interfaces become weak channels for heat and stress conduction, leading to disruption of the insulation network continuity and a decline in mechanical properties. The introduction of KH550, through the condensation of the siloxy groups in its molecules with the hydroxyl groups on the surface of the aerogel and the bonding of the amino groups at the other end with the cement hydration product CSH, forms a stable molecular bridge, which significantly improves the density of the interfacial transition zone and ensures the structural integrity and joint reinforcement effect of the mortar under high aerogel content conditions.

[0048] Example 1, along with Comparative Examples 3 and 4, are used to illustrate the effect of changes in fly ash content on the performance of fireproof mortar. When the proportion of fly ash in the total mass of cementitious materials increases from 15% to 20% and 25%, the thermal conductivity is 0.2831 W / (m·K) and 0.3000 W / (m·K), respectively, both higher than that of Example 1; the chloride ion migration coefficient increases to 2.00 × 10⁻⁶. - ¹² m² / s and 2.10 × 10 - ¹² m² / s; at a depth of 75 mm, temperatures increased to 158℃ and 176℃, respectively, and compressive strength decreased to 15.02 MPa and 14.25 MPa, respectively. This indicates that when the fly ash content is too high, some fly ash cannot fully participate in the pozzolanic reaction, leading to a decrease in the density of the slurry and hindering the improvement of overall performance. Therefore, there is an optimal value for the fly ash content, with 15% of the total mass of the cementitious material resulting in the best overall performance.

[0049] In summary, this invention utilizes a combination of silica aerogel, fly ash, and a silane coupling agent to modify and prepare fire-resistant mortar. Silica aerogel constructs a nanoporous insulating network, effectively reducing thermal conductivity; fly ash improves the density and high-temperature stability of the mortar through pozzolanic reaction and high-temperature ceramization; the silane coupling agent enhances the interfacial bonding between the aerogel and cement mortar, improving interfacial stability and overall material integrity. The combined effect of these three components gives the mortar excellent thermal insulation, chloride ion penetration resistance, fire resistance, and mechanical properties. This invention preferably uses a mortar with aerogel comprising 60% of the total volume of natural fine aggregate and aerogel, fly ash comprising 15% of the total mass of cementitious materials, and a silane coupling agent KH550 for modification. This proportion ensures a 28-day compressive strength of over 15 MPa while reducing the thermal conductivity to 0.2553 W / (m·K) and the chloride ion migration coefficient to 1.90 × 10⁻⁶. - ¹² m² / s, and significantly reduces the internal temperature of components under fire, resulting in the best overall performance. Among them, the mix proportion corresponding to Example 1 has the best overall performance and can meet the application requirements of fireproof mortar in engineering fields such as marine engineering, underground engineering, tunnel lining, and fire protection of steel structures.

[0050] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fireproof mortar, characterized in that, Includes the following components by mass: 641–804 parts of natural fine aggregate; 478-508 parts of ordinary Portland cement; 83-113 parts of fly ash; 32–41 parts of silica aerogel; 1.9–2.1 parts of silane coupling agent; 5.3–5.6 parts of polycarboxylate superplasticizer; 245-255 parts water.

2. The fireproof mortar according to claim 1, characterized in that, The fly ash accounts for 12% to 18% of the total mass of the cementitious material; the fly ash is Class II fly ash; the cementitious material is composed of ordinary silicate cement and fly ash.

3. The fireproof mortar according to claim 2, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane, and its dosage is 0.35% to 0.45% of the total mass of the cementitious material.

4. The fireproof mortar according to claim 2, characterized in that, The water-cement ratio of the mortar is 0.42 to 0.46; the mass ratio of the natural fine aggregate to the cementitious material is 2.80 to 2.

90.

5. The fireproof mortar according to claim 1, characterized in that, The silica aerogel is a granular material with a particle size of 0.6–1.5 mm, a specific surface area of ​​400–700 m² / g, and a thermal conductivity of 0.017–0.023 W / (m·K).

6. The fireproof mortar according to claim 1, characterized in that, The natural fine aggregate has a particle size of 0.075–4.75 mm and a fineness modulus of 2.3–3.0; the ordinary silicate cement is P·O 42.5 grade; and the polycarboxylate superplasticizer has a water reduction rate of not less than 20%.

7. The fireproof mortar according to claim 1, characterized in that, The volume of the silica aerogel accounts for 40% to 70% of the total volume of the natural fine aggregate and the silica aerogel.

8. A method for preparing fireproof mortar as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Weigh out the following ingredients according to the formula: natural fine aggregate, ordinary silicate cement, fly ash, silica aerogel, silane coupling agent, polycarboxylate superplasticizer, and water. S2. Add natural fine aggregate, ordinary silicate cement and fly ash to the mortar mixer and dry mix at 40-140 r / min for 10-60 seconds until evenly mixed. S3. Mix water, polycarboxylate superplasticizer and silane coupling agent at 30% to 70% of their respective total amounts to prepare a first mixture, and then mix it with silica aerogel and add it to a mixer. Stir at 40 to 140 r / min for 40 to 120 s to fully wet and modify the surface of silica aerogel particles with the silane coupling agent. S4. Continue to add the remaining water, polycarboxylate superplasticizer and silane coupling agent, and continue stirring at 40-140 r / min for 40-120 s to make the slurry fully and uniformly mixed. S5. The obtained mortar is poured into a test mold or 3D printing equipment for molding. When using a test mold, it is vibrated on a vibrating table for 5 to 30 seconds to remove air bubbles. After standing at room temperature for 12 to 48 hours, it is demolded and cured under standard curing conditions to the specified age to obtain fireproof mortar.

9. The preparation method according to claim 8, characterized in that, The standard curing conditions are a temperature of 20±5℃ and a relative humidity of 90±5%.

10. The application of the fireproof mortar according to any one of claims 1 to 7 or the fireproof mortar prepared by the preparation method according to any one of claims 8 or 9 in fire protection of marine engineering, underground engineering, tunnel lining, prefabricated buildings or steel structures.

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