High-strength low-shrinkage castable and preparation method thereof

Abstract

The invention discloses a high-strength low-shrinkage castable and a preparation method thereof, and relates to the technical field of refractory materials, the high-strength low-shrinkage castable is prepared by adopting special-grade high bauxite aggregate with special particle size distribution, matching with spinel fine powder, nano silicon dioxide, calcium aluminate cement, and additives such as a water reducing agent, a retarder, organic fibers and an expanding agent. The concrete is prepared through specific dry mixing, wet mixing and curing processes. Experiments show that after the castable is maintained for 28 days, the compressive strength reaches 95 MPa to the maximum, the breaking strength reaches 14 MPa, compared with a traditional product, the compressive strength is remarkably improved, and high-temperature medium scouring and high-load pressure can be effectively borne. Meanwhile, the linear shrinkage rate is only 0.4%, the shrinkage crack risk is greatly reduced, and the structural stability and the heat insulation performance are guaranteed. The lining is suitable for high-temperature equipment linings in industries of metallurgy, building materials and the like, and can prolong the service life of equipment and reduce maintenance cost and potential safety hazards.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a high-strength, low-shrinkage castable and its preparation method. Background Technology

[0002] Currently, there are some problems with commonly available castable refractory materials that urgently need to be solved during use, as follows:

[0003] In terms of strength, traditional castables are unable to meet the high strength requirements of materials under high temperature and high load conditions. For example, in equipment such as steelmaking converters and ironmaking blast furnaces in the metallurgical industry, the lining castables need to withstand the scouring of high-temperature molten steel and iron as well as frequent temperature changes. Ordinary castables are prone to wear and spalling due to insufficient strength, which leads to a shortened service life of the equipment lining and increases the maintenance cost and downtime of the equipment.

[0004] Regarding shrinkage, existing castables undergo significant shrinkage during curing and use due to factors such as moisture evaporation and chemical reactions, leading to internal cracks. These cracks not only reduce the overall strength and thermal insulation performance of the castable but can also become channels for high-temperature media penetration, affecting the safety and stability of the equipment. For example, in cement rotary kilns in the building materials industry, shrinkage cracks in the castable can increase heat loss within the kiln, reducing production efficiency, while the leakage of high-temperature gases also poses a safety hazard. Summary of the Invention

[0005] To address the technical problems existing in the background art, this invention proposes a high-strength, low-shrinkage castable and its preparation method.

[0006] The present invention proposes a high-strength, low-shrinkage castable, which, by weight, comprises the following components: 40-60 parts of high-alumina bauxite aggregate, 10-20 parts of spinel powder, 5-10 parts of nano-silica, 5-10 parts of calcium aluminate cement, 0.5-1 parts of water-reducing agent, 0.1-0.5 parts of retarder, 0.1-0.3 parts of organic fiber, and 1-3 parts of expansion agent.

[0007] Furthermore, the particle size distribution of the premium high-alumina bauxite aggregate is as follows: 30-40% of the aggregate is 5-10mm, 20-30% is 3-5mm, 15-25% is 1-3mm, and 15-25% is less than 1mm.

[0008] Furthermore, the average particle size of the spinel powder is less than 5 μm;

[0009] The average particle size of nano-silica is 20-50 nm.

[0010] Furthermore, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0011] Furthermore, the retarder is tartaric acid.

[0012] Furthermore, the organic fiber is polypropylene fiber.

[0013] Furthermore, the expanding agent is an ettringite-based expanding agent.

[0014] The preparation method of the above-mentioned high-strength, low-shrinkage castable includes the following steps:

[0015] S1. Add the high-alumina bauxite aggregate, spinel powder, nano silica, calcium aluminate cement, and expansion agent to the mixer and dry mix for 5-10 minutes.

[0016] S2. Add water-reducing agent, retarder and water accounting for 60-70% of the total water volume to the dry-mixed material, and wet mix for 8-12 minutes.

[0017] S3. Add organic fiber and the remaining water to the preliminary mixture and continue wet mixing for 3-5 minutes;

[0018] S4. Place the castable into a sealed container and cure it for 24-48 hours at a temperature of 20-25℃ and a humidity of 60-80% to obtain a high-strength, low-shrinkage castable.

[0019] Furthermore, the dry mixing time is 8 minutes;

[0020] The wet mixing time is 10 minutes in S2 and 4 minutes in S3;

[0021] The curing time is 36 hours.

[0022] The beneficial effects of this invention are:

[0023] 1. By employing premium high-alumina bauxite aggregate with a special particle size distribution, combined with spinel powder, nano-silica, and calcium aluminate cement, a tightly packed and interwoven microstructure is formed within the castable. The premium high-alumina bauxite aggregate provides the basic skeleton, while spinel powder and nano-silica fill the pores and enhance density. The calcium aluminate cement is fully hydrated under the action of a water-reducing agent. The synergistic effect of these materials significantly improves the compressive and flexural strength of the castable. Compared to traditional castables, the castable of this invention achieves a compressive strength of up to 95 MPa and a flexural strength of 14 MPa after 28 days of curing. It can effectively withstand the scouring of high-temperature media, high load pressure, and frequent temperature changes in industrial high-temperature equipment, greatly reducing wear and spalling, extending the service life of equipment linings, reducing equipment maintenance costs and downtime for repairs, and providing strong support for the continuity and stability of industrial production.

[0024] 2. The key roles of ettringite-based expanding agents and nano-silica are crucial. The ettringite-based expanding agent undergoes moderate expansion during hydration, precisely compensating for the shrinkage caused by water evaporation and chemical reactions. Nano-silica, with its high specific surface area and activity, participates in the hydration reaction, refining the pore structure of the cement stone and reducing pore shrinkage due to water loss. The synergistic effect of these two agents significantly reduces the linear shrinkage rate of the castable, reaching only 0.4% after 28 days of curing. This low shrinkage effectively prevents internal cracks, ensuring the overall integrity and structural stability of the castable, reducing the risk of high-temperature media penetration, and improving the thermal insulation performance and safety of equipment. It is particularly suitable for high-temperature equipment with extremely high requirements for dimensional stability, such as cement rotary kilns and steelmaking converters, reducing heat loss, improving production efficiency, and lowering safety hazards. Detailed Implementation

[0025] Example 1

[0026] The present invention proposes a high-strength, low-shrinkage castable and its preparation method, which is implemented by the following technical solution:

[0027] I. Raw material ratio of high-strength, low-shrinkage castable:

[0028] By weight, 40 parts of premium high-alumina bauxite aggregate were selected, of which 30% were 5-10mm aggregate, 20% were 3-5mm aggregate, 25% were 1-3mm aggregate, and 25% were less than 1mm aggregate; 10 parts of spinel fine powder with an average particle size of less than 5μm; 5 parts of nano-silica with an average particle size of 20nm; 5 parts of calcium aluminate cement; 0.5 parts of polycarboxylate-based high-efficiency water-reducing agent; 0.1 parts of tartaric acid; 0.1 parts of polypropylene fiber; and 1 part of ettringite-based expanding agent.

[0029] II. High-strength, low-shrinkage castables and their preparation methods:

[0030] The above-mentioned high-alumina bauxite aggregate, spinel powder, nano silica, calcium aluminate cement, and expansion agent are added to a mixer and dry-mixed for 5 minutes. Then, water-reducing agent, retarder, and water accounting for 60% of the total water volume are added to the dry-mixed material and wet-mixed for 8 minutes to obtain a preliminary mixture. Next, organic fiber and the remaining water are added to the preliminary mixture and wet-mixed for another 3 minutes to obtain a uniform castable. Finally, the castable is placed in a sealed container and cured for 24 hours at a temperature of 20°C and a humidity of 60% to obtain the finished high-strength, low-shrinkage castable.

[0031] Example 2

[0032] The present invention proposes a high-strength, low-shrinkage castable and its preparation method, which is implemented by the following technical solution:

[0033] I. Raw material ratio of high-strength, low-shrinkage castable:

[0034] By weight, 50 parts of premium high-alumina bauxite aggregate were selected, of which 35% were 5-10mm aggregate, 25% were 3-5mm aggregate, 20% were 1-3mm aggregate, and 20% were less than 1mm aggregate; 15 parts of spinel fine powder with an average particle size of less than 5μm; 8 parts of nano-silica with an average particle size of 35nm; 8 parts of calcium aluminate cement; 0.8 parts of polycarboxylate-based high-efficiency water-reducing agent; 0.3 parts of tartaric acid; 0.2 parts of polypropylene fiber; and 2 parts of ettringite-based expanding agent.

[0035] II. High-strength, low-shrinkage castables and their preparation methods:

[0036] High-alumina bauxite aggregate, spinel powder, nano-silica, calcium aluminate cement, and expansion agent are added to a mixer and dry-mixed for 8 minutes. Then, water-reducing agent, retarder, and water accounting for 65% of the total water volume are added to the dry mixture and wet-mixed for 10 minutes to obtain a preliminary mixture. Organic fiber and the remaining water are then added to the preliminary mixture and wet-mixed for another 4 minutes to obtain a uniform castable. The castable is then placed in a sealed container and cured for 36 hours at a temperature of 23°C and a humidity of 70% to obtain a finished high-strength, low-shrinkage castable.

[0037] Example 3

[0038] The present invention proposes a high-strength, low-shrinkage castable and its preparation method, which is implemented by the following technical solution:

[0039] I. Raw material ratio of high-strength, low-shrinkage castable:

[0040] By weight, the composition includes 60 parts of premium high-alumina bauxite aggregate, of which 40% is 5-10mm aggregate, 30% is 3-5mm aggregate, 15% is 1-3mm aggregate, and 15% is less than 1mm aggregate; 20 parts of spinel fine powder with an average particle size of less than 5μm; 10 parts of nano-silica with an average particle size of 50nm; 10 parts of calcium aluminate cement; 1 part of polycarboxylate-based high-efficiency water-reducing agent; 0.5 parts of tartaric acid; 0.3 parts of polypropylene fiber; and 3 parts of ettringite-based expanding agent.

[0041] II. High-strength, low-shrinkage castables and their preparation methods:

[0042] High-alumina bauxite aggregate, spinel powder, nano-silica, calcium aluminate cement, and expansion agent are placed into a mixer and dry-mixed for 10 minutes. Water-reducing agent, retarder, and water accounting for 70% of the total water volume are added to the dry-mixed material and wet-mixed for 12 minutes to obtain a preliminary mixture. Organic fiber and the remaining water are added to the preliminary mixture and wet-mixed for another 5 minutes to obtain a uniform castable. The castable is placed in a sealed container and cured for 48 hours at a temperature of 25°C and a humidity of 80% to obtain a finished high-strength, low-shrinkage castable.

[0043] Experimental Section

[0044] 1. Experimental Materials

[0045] I. Experimental Group: High-strength, low-shrinkage castables prepared in Examples 1, 2, and 3;

[0046] II. Control Group:

[0047] Two common high-strength castables (control group 1 and control group 2) were purchased from the market. Both were products of a well-known refractory materials company and are mainly used for the construction of industrial kiln linings.

[0048] 2. Performance Testing Indicators and Methods

[0049] I. Compressive strength: According to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the castable is made into test blocks with a size of 40mm×40mm×160mm. Under standard curing conditions, the test blocks are cured for 3 days, 7 days and 28 days respectively, and then the compressive strength is tested using a pressure testing machine.

[0050] II. Flexural strength: The flexural strength of the above test blocks was tested in accordance with GB / T 50081-2019 standard, and the test time was the same as that for compressive strength.

[0051] III. Linear shrinkage rate: According to GB / T 5988-2007 "Test method for permanent linear change of refractory materials under heating", the castable is made into a test block with a size of 25mm×25mm×150mm. After drying at 110℃ for 24 hours, it is then treated at 1000℃ for 3 hours. After cooling to room temperature, the length change is measured and the linear shrinkage rate is calculated.

[0052] 3. Experimental Data Comparison Table

[0053]

[0054] 4. Data Analysis

[0055] I. Regarding compressive strength, all three experimental examples were significantly superior to the control group. Data from 3 days of curing showed that Example 1 had a compressive strength of 45 MPa, Example 2 50 MPa, and Example 3 55 MPa, while Control Groups 1 and 2 only achieved 35 MPa and 38 MPa, respectively. This difference widened further as the curing time increased to 7 days and 28 days. After 28 days of curing, the compressive strength of Example 1 increased to 85 MPa, Example 2 to 90 MPa, and Example 3 reached a high of 95 MPa. In contrast, Control Groups 1 and 2 only achieved compressive strengths of 65 MPa and 68 MPa, respectively, after 28 days.

[0056] II. The flexural strength data also showed the superiority of the experimental group. After 3 days of curing, the flexural strengths of Examples 1, 2, and 3 were 8 MPa, 9 MPa, and 10 MPa, respectively, while those of Control Groups 1 and 2 were 6 MPa and 7 MPa. By the 28-day curing period, the flexural strengths of Examples 1-3 reached 12 MPa, 13 MPa, and 14 MPa, respectively, while those of Control Groups 1 and 2 were only 10 MPa and 11 MPa.

[0057] Flexural strength reflects a material's ability to resist bending failure, and the addition of organic fibers (polypropylene fibers) in the castable of this invention plays a crucial role. The polypropylene fibers form a three-dimensional randomly distributed network structure within the castable. When the material is subjected to bending stress, the fibers can effectively disperse the stress, preventing the generation and propagation of cracks. Simultaneously, the synergistic effect of the various raw materials ensures the integrity of the matrix, thereby improving the flexural strength.

[0058] III. Linear shrinkage rate is an important indicator for evaluating the performance of castables. A low linear shrinkage rate means better dimensional stability of the material during use. Experimental data show that the linear shrinkage rates of control groups 1 and 2 after 28 days of curing were as high as 1.2% and 1.1%, respectively, while the linear shrinkage rates of Examples 1-3 were only 0.5%, 0.45%, and 0.4%.

[0059] The low linear shrinkage rate of the castable in this invention is attributed to the use of an expanding agent (ettringite-based expanding agent) and nano-silica. The ettringite-based expanding agent produces moderate expansion during hydration, compensating for the shrinkage caused by water evaporation and chemical reactions. Nano-silica has an extremely high specific surface area and activity, enabling it to participate in the hydration reaction, refine the pore structure of the cement paste, and reduce shrinkage caused by water loss from the pores. The combined effect of these two agents significantly reduces the linear shrinkage rate of the castable.

[0060] 5. Conclusion

[0061] This high-strength, low-shrinkage castable outperforms existing commercially available castables in both mechanical properties and dimensional stability. Its high strength allows it to withstand greater loads and stresses, making it suitable for applications requiring high strength, such as industrial kilns and high-temperature equipment linings. The low shrinkage rate ensures structural integrity and stability, reduces cracks caused by shrinkage, extends equipment lifespan, and lowers maintenance costs. These performance advantages demonstrate the innovation and advancement of this invention in raw material selection, formulation design, and preparation process, resulting in significant technological advantages and broad application prospects.

[0062] 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 high-strength, low-shrinkage castable, characterized in that, By weight, it includes the following components: 40-60 parts of high-alumina bauxite aggregate, 10-20 parts of spinel fine powder, 5-10 parts of nano silica, 5-10 parts of calcium aluminate cement, 0.5-1 part of water-reducing agent, 0.1-0.5 parts of retarder, 0.1-0.3 parts of organic fiber, and 1-3 parts of expansion agent.

2. The high-strength, low-shrinkage castable according to claim 1, characterized in that, The particle size distribution of the premium high-alumina bauxite aggregate is as follows: 30-40% of the aggregate is 5-10mm, 20-30% is 3-5mm, 15-25% is 1-3mm, and 15-25% is less than 1mm.

3. The high-strength, low-shrinkage castable according to claim 1, characterized in that, The average particle size of the spinel powder is less than 5 μm; The average particle size of nano-silica is 20-50 nm.

4. The high-strength, low-shrinkage castable according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

5. The high-strength, low-shrinkage castable according to claim 1, characterized in that, The retarder is tartaric acid.

6. The high-strength, low-shrinkage castable according to claim 1, characterized in that, The organic fiber is polypropylene fiber.

7. The high-strength, low-shrinkage castable according to claim 1, characterized in that, The expanding agent is an ettringite-based expanding agent.

8. A method for preparing a high-strength, low-shrinkage castable as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Add the high-alumina bauxite aggregate, spinel powder, nano silica, calcium aluminate cement, and expansion agent to the mixer and dry mix for 5-10 minutes. S2. Add water-reducing agent, retarder and water accounting for 60-70% of the total water volume to the dry-mixed material, and wet mix for 8-12 minutes. S3. Add organic fiber and the remaining water to the preliminary mixture and continue wet mixing for 3-5 minutes; S4. Place the castable into a sealed container and cure it for 24-48 hours at a temperature of 20-25℃ and a humidity of 60-80% to obtain a high-strength, low-shrinkage castable.

9. The method for preparing the high-strength, low-shrinkage castable according to claim 8, characterized in that, The dry mixing time is 8 minutes; The wet mixing time is 10 minutes in S2 and 4 minutes in S3; The curing time is 36 hours.

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