Refractory concrete and preparation method thereof

Abstract

The invention belongs to the technical field of concrete, and particularly relates to refractory concrete and a preparation method thereof. The refractory concrete is prepared from the following raw materials in parts by weight: 300 to 350 parts of sulphoaluminate cement, 50 to 80 parts of silane modified nano metakaolin, 900 to 1000 parts of aluminum oxide plated steel slag aggregate, 100 to 150 parts of nano SiO2 modified expanded perlite, 8 to 12 parts of silane modified silicon carbide fiber, 5 to 8 parts of zinc borate flame retardant, 3 to 5 parts of polycarboxylate superplasticizer, 0.5 to 1 part of hydroxypropyl methyl cellulose and 150 to 180 parts of water. According to the prepared refractory concrete, the compressive strength is kept, meanwhile, the high strength retention rate at the temperature of 1200 DEG C is achieved, and meanwhile the protection requirements of heavy-load and high-temperature environments are met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of concrete, and particularly relates to a fire-resistant concrete and a preparation method thereof. BACKGROUND

[0002] Traditional fire-resistant concrete, in terms of heavy load, generally has a 28-day compressive strength lower than 40 MPa due to the use of lightweight aggregate as raw material, which cannot meet the mechanical requirements of heavy-load bridges (requiring > 60 MPa) or industrial plants (requiring > 50 MPa), and the deformation of lightweight aggregate concrete under repeated action of heavy-load vehicles is obvious, which seriously affects the safety in use; in terms of high temperature, the strength attenuation at 600℃ exceeds 50%, and due to the lack of effective thermal stress compensation mechanism, the concrete is prone to burst in the temperature range of 300-600℃. Especially when subjected to dynamic load, the interface deterioration at high temperature is accelerated, and the residual bearing capacity drops to less than 30% of that at room temperature.

[0003] Some existing technologies attempt to improve the performance of fire-resistant concrete to some extent, but new problems also exist, for example: the existing technologies either have a high risk of high-temperature burst or have insufficient elastic modulus, and the deformation exceeds the standard under heavy load. For example, the fire-resistant high-strength concrete disclosed in Chinese Patent Application Publication No. CN104045272A has the advantages of strong impact resistance, good durability, high compressive strength, etc. due to the addition of periclase powder, ultra-fine mineral powder and montmorillonite, etc. However, the cost of this patent is high, and the periclase powder expands in a humid environment, which increases the internal volume of the concrete and generates internal stress. In a high-temperature environment, the stress generated by the thermal expansion and contraction of the concrete itself and the internal stress caused by the hydration expansion of the periclase powder are superimposed, which easily causes high-temperature burst, so it cannot be applied to bridge and other "high-temperature-heavy load" coupling scenarios.

[0004] In summary, the existing fire-resistant concrete technology faces many bottlenecks, and a new type of concrete material that can withstand heavy-load traffic and high temperature is urgently needed to meet the demand of modern engineering structures for "high strength-high fire resistance-high durability" integration. SUMMARY

[0005] To solve the problem that the existing fire-resistant concrete cannot simultaneously meet the performance requirements in heavy-load and high-temperature environments, the present application provides a fire-resistant concrete and a preparation method thereof. The fire-resistant concrete prepared by the present application has a high retention rate of strength at 1200℃ while maintaining the compressive strength, and can meet the protection requirements in heavy-load and high-temperature environments.

[0006] To solve the above problems, the technical scheme of the present application is as follows:

[0007] In a first aspect, the present invention provides a refractory concrete. The raw materials of the refractory concrete include, by weight, 300-350 parts of sulphoaluminate cement, 50-80 parts of silane-modified nano-metakaolin, 900-1000 parts of alumina-coated steel slag aggregate, 100-150 parts of nano-SiO2-modified expanded perlite, 8-12 parts of silane-modified silicon carbide fiber, 5-8 parts of zinc borate flame retardant, 3-5 parts of polycarboxylate water reducer, 0.5-1 part of hydroxypropyl methylcellulose, and 150-180 parts of water.

[0008] This refractory concrete uses alumina-coated steel slag aggregate as its structural framework, a multi-scale reinforcement network composed of silane-modified silicon carbide fibers and silane-modified nanometakaolin, nano-SiO2-modified expanded perlite as a thermal stress compensation material, and is supplemented with a zinc borate flame retardant and a polycarboxylate superplasticizer. This concrete combines ultra-high mechanical properties with excellent high-temperature stability, overcoming the technical shortcomings of conventional refractory concrete, such as insufficient strength and high-temperature failure of polymer fibers.

[0009] Furthermore, the silane-modified nanometakaolin has a particle size of 50-500 nm. The silane-modified nanometakaolin is prepared by wet ball milling the metakaolin to nanoparticles, followed by surface modification with a silane coupling agent. The specific preparation steps are: wet ball milling the metakaolin to nanopowders, then mixing the nanopowders with a silane solution at 60±2°C and drying. Furthermore, the silane is KH-550.

[0010] Furthermore, the alumina-coated steel slag aggregate is obtained by forming an alumina coating on the surface of steel slag using a sol-gel method using steel slag and aluminum nitrate as raw materials. The steel slag has a particle size of 5-15 mm. The specific preparation steps are: after cleaning the steel slag aggregate, immersing it in an aluminum nitrate solution, drying it, and then calcining it in stages. The first stage is a reaction at 300°C for 1 hour; the second stage is a reaction at 500°C for 2 hours. This produces the steel slag aggregate with an alumina protective layer, namely the alumina-coated steel slag aggregate.

[0011] Furthermore, the nano-SiO2-modified expanded perlite is obtained by modifying expanded perlite with a nano-SiO2 sol (silica sol). The expanded perlite has a particle size of 1-3 mm. The specific preparation steps are: vacuum impregnating the expanded perlite in the nano-SiO2 sol, returning the pressure to normal, soaking it, drying it, and heat treating it at 350°C for 1 hour to obtain the nano-SiO2-modified expanded perlite. The nano-SiO2 sol has a solid content of 20%. The nano-SiO2-modified perlite exhibits controllable expansion characteristics at 300-600°C.

[0012] Further, the silane-modified silicon carbide fiber has a diameter of 15±2 μm. The silane-modified silicon carbide fiber is obtained by surface modification of silicon carbide fiber with silane coupling agent. The specific preparation steps are as follows: after ultrasonic treatment of the silicon carbide fiber in a silane solution, drying is performed to obtain the silane-modified silicon carbide fiber. The tensile strength of the single filament of the silane-modified silicon carbide fiber is significantly improved. Further, the silane is KH-550.

[0013] Further, the zinc borate flame retardant has a particle size of about 800 nm. The zinc borate is a high-purity flame retardant with a Zn3(BO3)2 content of ≥99%. At high temperatures, the zinc borate can decompose to form a ceramic protective layer.

[0014] Further, the polycarboxylic acid water reducing agent can be prepared by copolymerization of methyl allyl polyoxyethylene ether and acrylic acid, and the water reducing rate can be more than 30%.

[0015] In the second aspect of the present application, a preparation method of the refractory concrete is provided, which comprises the following steps:

[0016] Step 1: The polycarboxylic acid water reducing agent and hydroxypropyl methyl cellulose are dissolved in warm water at 60±2 ℃, and stirring is performed until complete dissolution to obtain an additive solution. The proportion of the warm water accounts for 30% of the water;

[0017] Step 2: The silane-modified silicon carbide fiber is premixed with the silane-modified nano metakaolin to ensure that the surface of the silane-modified silicon carbide fiber is uniformly wrapped with the silane-modified nano metakaolin particles, thereby obtaining a fiber composite.

[0018] Step 3: The fiber composite and the sulphoaluminate cement are mixed, and then the zinc borate flame retardant is added and mixed. Finally, the alumina-coated steel slag and the nano-SiO2 modified expanded perlite are added and uniformly mixed.

[0019] Step 4: The remaining 70% of water (cold water) below 10 ℃ is added and stirred, and then the additive solution is injected and stirred until the slump reaches 650±20 mm. After the alumina-coated steel slag and the nano-SiO2 modified perlite are added, the stirring and mixing are performed in two steps. The stirring speed in the first step is greater than that in the second step. Specifically, the stirring speed in the first step is 55±5 rpm, and the stirring speed in the second step is 35±5 rpm.

[0020] Step 5: Pumping and pouring, and then layering and vibrating are performed to obtain the refractory concrete.

[0021] Through the above technical solution, the present application has the following beneficial effects:

[0022] (1) The present invention uses alumina-coated steel slag aggregate as a high-strength skeleton, combined with a silane-modified silicon carbide fiber-silane-modified nano-metakaolin multi-scale reinforcement system and nano-SiO2-modified expanded perlite, so that the prepared heavy-duty refractory concrete has both excellent mechanical properties and high-temperature stability. This refractory concrete not only solves the technical bottleneck of insufficient bearing capacity of lightweight aggregate concrete, but also overcomes the problems of poor fire resistance and high-temperature cracking of traditional high-strength concrete. It is particularly suitable for special engineering environments where heavy traffic and fire risks coexist, providing a revolutionary fire protection solution for modern building structures.

[0023] (2) The present invention achieves strength retention at 1200°C while maintaining high compressive strength through the synergistic effect of alumina-coated steel slag aggregate and silane-modified silicon carbide fibers. The alumina coating on the steel slag surface generates calcite at high temperatures, while the silane-modified silicon carbide fibers form a three-dimensional reinforcement network, resolving the technical contradictions of traditional refractory concrete, which results in insufficient strength due to lightweighting, or high-strength concrete, which suffers from poor fire resistance. The invention also significantly reduces material costs through the high-value utilization of industrial solid waste.

[0024] (3) The present invention realizes the dual protection of precise compensation of thermal stress and release of steam pressure by the gradient temperature expansion characteristics of nano-SiO2 modified expanded perlite and micropore regulation of silane modified nano-metakaolin. The gradient temperature expansion characteristics refer to: under the condition of 25-300℃, the perlite matrix is ​​stable and has no reaction with nano-SiO2; under the condition of 300-450℃, the surface SiO2 reacts with CaCl2. 2+ The reaction generates calcite silica (CSH), with a surface expansion rate of 1.0-1.2%. At 450-600℃, the core SiO2 and Al 3+ The overall expansion rate of the generated mullite (3Al2O3·2SiO2) increases to 1.5-1.8%. In other words, the surface of the perlite expands in advance to offset the shrinkage stress of the matrix, while the core expands later to prevent structural cracking.

[0025] (4) The present invention effectively suppresses the risk of bursting in the temperature range of 300-600°C by modifying the gradient expansion characteristics of expanded perlite through nano-SiO2.

[0026] (5) The concrete slump of the present invention is greater than 650mm, and the pumping flow rate reaches 25m 3 / h, shortening the steam curing cycle by 50%. Using industrial steel slag instead of natural aggregate reduces material costs by 30-40%. CO2 emissions over the entire lifecycle are reduced by 33%, meeting green building standards. The preparation process of this invention utilizes sol-gel coating and graded mixing technology, resulting in a simple and efficient process and excellent product pumping performance, meeting the comprehensive requirements of high strength, fire resistance, and durability in modern engineering.

[0027] (6) The present invention can achieve a 28-day compressive strength of >60 MPa while maintaining a strength retention rate of >60% at a high temperature of 1200°C through the synergistic effect of alumina-coated steel slag aggregate and silane-modified silicon carbide fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 1 is a schematic diagram of the process for preparing refractory concrete according to Example 1 of the present invention. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] The present invention is described in detail below with reference to specific examples. In the following examples, if no specific conditions are specified, the experiments were carried out according to conventional conditions or those recommended by the manufacturer. Raw materials and reagents used, if the manufacturer is not specified, are all commercially available conventional products.

[0031] Preparation of silane-modified nanometakaolin: Kaolin was calcined at 600°C for 2 hours to obtain highly active metakaolin. The highly active metakaolin was then mixed with ethanol and water (water:ethanol ratio of 1:1 by volume) to form a slurry with a solid content of 30%, and 0.6% sodium polyacrylate was added as a dispersant. The slurry was ball milled in a planetary ball mill using zirconia balls at 420±10 rpm for 3 hours. The slurry temperature was controlled at ≤40°C and the pH was controlled at 8.0-8.5. The slurry was then centrifuged (3000 rpm, 5 minutes) to remove coarse particles and spray-dried to obtain a nanopowder. The nanopowder was placed in a high-speed mixer, preheated to 60±2°C, and a 2% KH-550 silane solution (silane:ethanol:water = 2:93:5, pH = 4.5-5.0) was sprayed in at a rate of 2.5 mL / min·kg and mixed for 30 minutes. The silane-modified nano-metakaolin was dried at 100° C. for 1 hour and then passed through a 325-mesh sieve to obtain the silane-modified nano-metakaolin with a particle size of 50-500 nm.

[0032] Preparation of alumina-coated steel slag aggregate: First, the steel slag aggregate is pretreated, and the 5-15mm steel slag aggregate is pickled and washed with water in sequence; then, the treated steel slag aggregate is immersed in 1mol / L aluminum nitrate solution (the ratio of steel slag aggregate to aluminum nitrate solution is 1.5L of 1mol / L aluminum nitrate solution for every 1kg of steel slag aggregate), and the soaking time is 24 hours. During this period, ultrasonic oscillation is performed every 2 hours, and each ultrasonic oscillation lasts for 10 minutes; after the soaking is completed, the steel slag aggregate is taken out and pre-dried at 80°C for 2 hours; then, the pre-dried steel slag aggregate is gradient calcined, first at 300°C for 1 hour, and then heated to 500°C for 2 hours; after the above series of treatments, a uniform 10-20μm thick alumina coating will be formed on the surface of the steel slag aggregate, thereby obtaining alumina-coated steel slag aggregate.

[0033] Preparation of nano-SiO2 modified expanded perlite: 1-3 mm expanded perlite is vacuum impregnated in nano-SiO2 sol (0.5 L of nano-SiO2 sol is required for impregnation for every 100 g of expanded perlite, and the solid content of the SiO2 sol is 20%) for 30 minutes, and then the impregnation is continued for 2 hours after returning to normal pressure; first, the expanded perlite is dried at 80°C for 12 hours; then, the expanded perlite pretreated by nano-SiO2 impregnation is calcined and heat-treated at 350°C for 1 hour to form a stable network structure of nano-SiO2 in the pores to obtain nano-SiO2 modified expanded perlite.

[0034] Preparation of Silane-Modified Silicon Carbide Fibers: Silicon carbide fibers were ultrasonically treated in a 2% mass concentration KH-550 silane solution for 30 minutes (5 L of KH-550 solution was required for every 100 g of silicon carbide fiber), followed by drying at 120°C for 1 hour. The diameter of the silane-modified silicon carbide fibers was 15 ± 2 μm.

[0035] The sulphoaluminate cement used in the following examples was purchased from Tangshan Polar Bear Building Materials Co., Ltd., and the purchase specifications were as follows: Specific surface area 400±10m 2 / kg; zinc borate flame retardant was purchased from Jinan Taixing Fine Chemical Co., Ltd. with the following specifications: high-purity flame retardant with a Zn3(BO3)2 content ≥99% and a particle size of approximately 800nm; polycarboxylate water reducer was purchased from Jiangsu Subote New Materials Co., Ltd. with the following specifications: water reduction rate ≥30% and compatibility with sulphoaluminate cement; hydroxypropyl methylcellulose was purchased from Dow Chemical Company of the United States with the following specifications: viscosity 4000-6000mPa·s and ash content ≤5%.

[0036] Example 1

[0037] A refractory concrete is composed of the following raw materials in the following proportions by weight: 320 parts of sulphoaluminate cement, 60 parts of silane-modified nano-metakaolin, 950 parts of alumina-coated steel slag aggregate, 120 parts of nano-SiO2-modified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 6 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0038] Prepare refractory concrete according to the above weight ratio of raw materials, such as Figure 1 As shown, the following steps are included:

[0039] Step 1: Pre-dissolve the polycarboxylate water reducer and hydroxypropyl methylcellulose in 60°C warm water, and stir until completely dissolved to obtain an additive solution; the proportion of warm water accounts for 30% of the water.

[0040] Step 2: premix the silane-modified silicon carbide fiber and the silane-modified nano-metakaolin for 15 minutes to ensure that the silane-modified nano-metakaolin particles are evenly coated on the surface of the silane-modified silicon carbide fiber to obtain a fiber composite.

[0041] Step 3: Mix the fiber composite and sulphoaluminate cement at 45 rpm for 60 seconds, then add the zinc borate flame retardant and continue mixing at 45 rpm for 30 seconds, then add the alumina-coated steel slag and nano-SiO2 modified expanded perlite, increase the rpm to 55 rpm and continue mixing for 90 seconds, then reduce the rpm to 35 rpm and mix until uniform.

[0042] Step 4: Then add 70% cold water (water below 10°C) and stir for 30 seconds, then slowly inject the additive solution and continue stirring for 150 seconds until the slump reaches 650±20mm.

[0043] Step 5: Pump and pour, then vibrate layer by layer. Cover with a water-retaining film after pouring. After removing the formwork, spray with a curing agent. Steam cure at 60°C for 12 hours, then naturally cure for 28 days to obtain refractory concrete. Water three times daily for the first seven days to maintain moisture.

[0044] This embodiment uses alumina-coated steel slag aggregate as a high-strength skeleton, combined with a silane-modified silicon carbide fiber-silane-modified nano-metakaolin multi-scale reinforcement system and nano-SiO2-modified expanded perlite, to produce a heavy-duty refractory concrete with both excellent mechanical properties and high-temperature stability. The high-value utilization of industrial solid waste also significantly reduces material costs. The preparation process of the present invention utilizes sol-gel coating and graded mixing technology, resulting in a simple and efficient process and excellent product pumping performance, meeting the comprehensive requirements of high strength, fire resistance, and durability in modern engineering.

[0045] Example 2

[0046] The refractory concrete of Example 2 differs from that of Example 1 in that the weight portion of the silane-modified nano-metakaolin is 68 parts.

[0047] The refractory concrete of Example 2 is composed of the following raw materials in the following weight proportions: 320 parts of sulphoaluminate cement, 68 parts of silane-modified nano-metakaolin, 950 parts of alumina-coated steel slag aggregate, 120 parts of nano-SiO2-modified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 6 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0048] The preparation method of the refractory concrete of Example 2 is the same as that of Example 1.

[0049] Compared with Example 1, Example 2 has higher compressive strength, but its fire resistance is not as good as Example 1. This example is suitable for environments such as nuclear power facilities that have higher requirements for strength at room temperature.

[0050] Example 3

[0051] The refractory concrete of Example 3 differs from that of Example 1 in that the weight portion of the zinc borate flame retardant is 8 parts.

[0052] The refractory concrete of Example 3 is composed of the following raw materials in the following proportions by weight: 320 parts of sulphoaluminate cement, 60 parts of silane-modified nano-metakaolin, 950 parts of alumina-coated steel slag aggregate, 120 parts of nano-SiO2-modified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 8 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0053] The preparation method of the refractory concrete of Example 3 is the same as that of Example 1.

[0054] Compared with Example 1, this embodiment has better fire resistance, but its pressure resistance is not as good as that of Example 1. Therefore, Example 1 is the optimal ratio. This embodiment is suitable for ultra-high temperature environments such as industrial kiln linings.

[0055] Comparative Example 1

[0056] The refractory concrete of Comparative Example 1 differs from that of Example 1 in that ordinary steel slag aggregate is used instead of alumina-coated steel slag aggregate in Comparative Example 1. Pretreatment of ordinary steel slag aggregate: 5-15 mm steel slag aggregate is subjected to acid washing and water washing.

[0057] The refractory concrete of Comparative Example 1 is composed of the following raw materials in the following weight proportions: 320 parts of sulphoaluminate cement, 60 parts of silane-modified nano-metakaolin, 950 parts of ordinary steel slag aggregate, 120 parts of nano-SiO2 modified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 6 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0058] The preparation method of the refractory concrete of Comparative Example 1 is the same as that of Example 1.

[0059] The high-temperature stability of Comparative Example 1 is far inferior to that of Example 1. This is because the steel slag aggregate in Comparative Example 1 is not plated with alumina, and the Al2O3 coating effectively isolates the high-temperature reduction reaction of iron oxide (Fe2O3) in the steel slag. The alumina coating can significantly inhibit the high-temperature expansion of the steel slag.

[0060] Comparative Example 2

[0061] The refractory concrete of Comparative Example 2 differs from that of Example 1 in that silica fume is used in place of silane-modified nano-metakaolin.

[0062] The refractory concrete of Comparative Example 2 is composed of the following raw materials in the following weight proportions: 320 parts of sulphoaluminate cement, 60 parts of silica fume, 950 parts of alumina-coated steel slag aggregate, 120 parts of nano-SiO2 modified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 6 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0063] The preparation method of the refractory concrete of Comparative Example 2 is the same as that of Example 1.

[0064] This comparative example does not use silane-modified nanometakaolin. Instead, silica fume is used instead. Example 1 demonstrates advantages over this comparative example in terms of multi-scale reinforcement and interface optimization. This is because the silane-modified nanometakaolin can plug the pores of the cement matrix through its nanoparticles, accelerate the hydration reaction to form a denser CSH gel, and enhance the bonding strength between the silicon carbide fibers and the matrix.

[0065] Comparative Example 3

[0066] The refractory concrete of Comparative Example 3 differs from that of Example 1 in that 3 parts of silane-modified silicon carbide fibers + 7 parts of polypropylene fibers are used instead of 10 parts of silane-modified silicon carbide fibers.

[0067] The refractory concrete of Comparative Example 3 is composed of the following raw materials in the following weight proportions: 320 parts of sulphoaluminate cement, 60 parts of silane-modified nano-metakaolin, 950 parts of alumina-coated steel slag aggregate, 120 parts of nano-SiO2 modified expanded perlite, 3 parts of silane-modified silicon carbide fiber + 7 parts of polypropylene fiber, 6 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0068] The preparation method of the refractory concrete of Comparative Example 3 is the same as that of Example 1.

[0069] In this comparative example, 7 of the 10 parts of silane-modified silicon carbide fiber in Example 1 were replaced with polypropylene fiber. This resulted in microcracks in the refractory concrete of this comparative example. Compared to this comparative example, Example 1 demonstrated superior high-temperature reinforcement and burst resistance, primarily because silicon carbide fiber can prevent crack development at high temperatures, while this comparative example contained insufficient silicon carbide fiber.

[0070] Comparative Example 4:

[0071] The refractory concrete of Comparative Example 4 differs from that of Example 1 in that: unmodified expanded perlite is used instead of nano-SiO2 modified expanded perlite;

[0072] The refractory concrete of Comparative Example 4 is composed of the following raw materials in the following proportions by weight: 320 parts of sulphoaluminate cement, 60 parts of silane-modified nano-metakaolin, 950 parts of alumina-coated steel slag aggregate, 120 parts of unmodified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 6 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0073] The preparation method of the refractory concrete of Comparative Example 4 is the same as that of Example 1.

[0074] The expanded perlite in this comparative example was not modified with nano-SiO2, resulting in a significantly increased burst rate. This demonstrates the advantages of Example 1 in thermal stress gradient compensation compared to this comparative example. This is because the nano-SiO2-modified expanded perlite reduces internal vapor pressure; SiO2 softens at high temperatures, buffering the differential expansion between aggregate and cement matrix; and the gradient expansion properties of the nano-SiO2-modified expanded perlite effectively suppress the risk of bursting in the 300-600°C temperature range.

[0075] Comparative Example 5:

[0076] The refractory concrete of Comparative Example 5 differs from that of Example 1 in that the weight portion of zinc borate is 2 parts.

[0077] The refractory concrete of Comparative Example 5 is composed of the following raw materials in the following weight proportions: 320 parts of sulphoaluminate cement, 60 parts of silane-modified nano-metakaolin, 950 parts of alumina-coated steel slag aggregate, 120 parts of nano-SiO2-modified expanded perlite, 10 parts of silane-modified silicon carbide fiber, 2 parts of zinc borate flame retardant, 4 parts of polycarboxylate water reducer, 0.8 parts of hydroxypropyl methylcellulose, and 165 parts of water.

[0078] The preparation method of the refractory concrete of Comparative Example 5 is the same as that of Example 1.

[0079] This comparative example reduces the amount of zinc borate flame retardant, resulting in a lower fire resistance and higher smoke production. Compared to this comparative example, Example 1 demonstrates both flame retardancy and fire resistance advantages. This is primarily due to the dual action of zinc borate at high temperatures: on the one hand, it consumes a large amount of heat through endothermic decomposition; on the other hand, it promotes the formation of a dense ceramic protective layer, reducing the release of high-temperature toxic gases.

[0080] Test conditions for the refractory concrete prepared in Examples 1-3 and Comparative Examples 1-5:

[0081] The performance tests of the examples and comparative examples were carried out in strict accordance with the standards such as GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the test results are shown in Table 1.

[0082] Table 1. Performance comparison between examples and comparative examples

[0083]

[0084] The above table, comparing Comparative Examples 1-5 with Examples 1-3, demonstrates that the heavy-duty refractory concrete prepared by the present invention maintains a strength retention rate exceeding 61.7% at 1200°C, while maintaining a high compressive strength exceeding 65.2 MPa. Its critical burst temperature exceeds 850°C, significantly outperforming conventional solutions. The synergistic effect of the alumina-coated steel slag aggregate, silane-modified silicon carbide fibers, and nano-SiO2-modified expanded perlite in the present invention enables the concrete to possess both ultra-high mechanical properties and high-temperature stability, meeting the requirements for heavy-duty traffic and extreme fire protection.

[0085] The above examples are only used to clearly demonstrate the technical effects of the present invention and are not intended to be absolute limitations on the amounts of the components. In practical applications, the core technical innovations of the present invention can be achieved by adjusting the amounts of the concrete components and the process parameters within the scope of the claims.

Claims

1. A refractory concrete, characterized in that: The raw materials of the refractory concrete include, by weight, 300-350 parts of sulphoaluminate cement, 50-80 parts of silane-modified nano-metakaolin, 900-1000 parts of alumina-coated steel slag aggregate, 100-150 parts of nano-SiO2-modified expanded perlite, 8-12 parts of silane-modified silicon carbide fiber, 5-8 parts of zinc borate flame retardant, 3-5 parts of polycarboxylate water reducer, 0.5-1 part of hydroxypropyl methylcellulose, and 150-180 parts of water.

2. A refractory concrete according to claim 1, characterized in that: The particle size of the silane-modified nano-metakaolin is 50-500 nm. The silane-modified nano-metakaolin is obtained by subjecting metakaolin to a wet ball milling nano-process and then performing surface modification with a silane coupling agent.

3. A refractory concrete according to claim 2, characterized in that: The silane-modified nano-metakaolin is obtained by subjecting metakaolin to a wet ball-milling nano-process to obtain nano-powder, and then mixing the nano-powder with a silane solution at 60±2° C. and drying.

4. The refractory concrete according to claim 1, characterized in that: The alumina-coated steel slag aggregate is obtained by using steel slag and aluminum nitrate as raw materials and forming an alumina coating on the surface of the steel slag by a sol-gel method. The particle size of the steel slag is 5-15 mm.

5. The refractory concrete according to claim 4, characterized in that: The preparation method of alumina-coated steel slag aggregate is as follows: after cleaning the steel slag aggregate, immersing it in an aluminum nitrate solution, drying it, and then calcining it in stages. The first stage reacts at 300°C for 1 hour; the second stage reacts at 500°C for 2 hours to obtain alumina-coated steel slag aggregate.

6. The refractory concrete according to claim 1, characterized in that: The nano-SiO2 modified expanded perlite is obtained by modifying expanded perlite with nano-SiO2 sol, and the particle size of the expanded perlite is 1-3 mm.

7. The refractory concrete according to claim 6, characterized in that: The preparation method of nano-SiO2 modified expanded perlite is as follows: placing the expanded perlite in nano-SiO2 sol for vacuum impregnation, soaking after returning to normal pressure, drying, and heat treating at 350°C for 1 hour to obtain the nano-SiO2 modified expanded perlite.

8. The refractory concrete according to claim 1, characterized in that: The diameter of the silane-modified silicon carbide fiber is 15±2 μm, and the silane-modified silicon carbide fiber is obtained by surface-modifying silicon carbide fiber with a silane coupling agent.

9. The refractory concrete according to claim 1, characterized in that: The particle size of the zinc borate flame retardant is 800 nm, and the content of Zn3(BO3)2 in the zinc borate flame retardant is ≥99%.

10. The method for preparing refractory concrete according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Dissolve the polycarboxylate water reducer and hydroxypropyl methylcellulose in 60±2℃ warm water in advance, and stir until completely dissolved to obtain an additive solution; the proportion of warm water accounts for 30% of the water; Step 2: premixing the silane-modified silicon carbide fiber and the silane-modified nano-metakaolin to obtain a fiber composite; Step 3: Mix the fiber composite and sulphoaluminate cement, then add zinc borate flame retardant and mix well; finally, add alumina-coated steel slag and nano-SiO2 modified expanded perlite and mix well; Step 4: Add the remaining 70% of water below 10°C and stir, then inject the additive solution and stir until the slump reaches 650±20mm; Step 5: Pump and pour, then vibrate in layers to obtain refractory concrete.

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