Anti-cracking hollow brick for high temperature and high humidity environment and preparation method thereof

Abstract

The application belongs to the technical field of building materials, and particularly relates to a kind of anti-cracking hollow brick for high temperature and high humidity environment and a preparation method thereof.The hollow brick comprises a brick body and a through hole, and the brick body raw material comprises cement, fly ash, ceramic sand, modified polypropylene fiber, composite expansion agent, paraffin microcapsule, layered double metal hydroxide, microsilica, metakaolin and water by weight parts, and the outer surface of the brick body is coated with a waterproof coating.During preparation, the fiber and the microcapsule are premixed, then mixed with other dry materials, water is added and stirred, and then molding, static standing, stepwise temperature increasing steam curing, airing and coating of the waterproof coating are performed to obtain the product.The application effectively reduces temperature and humidity coupling stress through multi-component synergistic effect, and the brick body has high compactness, small dry shrinkage and good impermeability, and is suitable for high temperature and high humidity environment wall.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a crack-resistant hollow brick for high temperature and high humidity environments and its preparation method. Background Technology

[0002] Hollow bricks, due to their advantages such as light weight, heat insulation, and material saving, have become one of the dominant materials for building walls. However, the problem of cracking in hollow brick walls has long existed, especially in the hot and humid regions of southern my country and in environments with frequent alternations of heat and humidity, where the cracking problem is more prominent. Drastic changes in temperature and humidity are the main causes of cracking. The pore walls and rib walls of ordinary hollow bricks are relatively thin. In high-temperature environments, the cement hydration reaction accelerates, and the heat of hydration is released in a concentrated manner, forming a large temperature gradient inside the brick. In high-humidity environments, the brick absorbs moisture and undergoes significant expansion and contraction deformation. When high temperature and high humidity coexist, the coupled effect of temperature and humidity makes the stress state inside the brick far more complex than that of a single factor. Cracks easily initiate at the weak points of the pore walls, and these micro-cracks will further expand during subsequent service, seriously weakening the load-bearing capacity and durability of the wall.

[0003] To address the crack resistance problem of hollow bricks, some studies have attempted to improve it by adding fibers, improving the pore shape, or optimizing the curing process. For example, one study used small concrete hollow blocks to construct frame infill walls and tested the drying shrinkage deformation of individual blocks and the infill wall under constant temperature and humidity conditions. The study found that drying shrinkage is a significant contributing factor to cracks in the block walls (Influence of Settlement Shrinkage on Cracks in Small Concrete Hollow Block Infill Walls, New Building Materials, 2010, No. 4). However, most of these studies are based on conventional environmental conditions for design and verification, and do not adequately consider the crack resistance requirements in special high-temperature and high-humidity environments. Existing crack resistance methods often target only a single factor, such as simply reducing the drying shrinkage rate or simply increasing the flexural strength, which is insufficient to cope with the complex stress changes under the coupled effects of temperature and humidity. More importantly, during the high-temperature and high-humidity curing or use of existing hollow bricks, microcracks are prone to appear on the pore walls and rib walls inside the brick. Once these microcracks appear, they will further aggravate the uneven distribution of temperature and humidity inside the brick, forming a positive feedback mechanism for crack propagation. Current products lack a systematic solution to this problem from the perspective of synergistic material composition and manufacturing process.

[0004] Therefore, developing a hollow brick that can be used for a long time in high temperature and high humidity environments without cracking has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a crack-resistant hollow brick for high temperature and high humidity environments and its preparation method, aiming to solve the technical problem that existing hollow bricks are prone to cracking of the pore wall and accelerated microcrack propagation due to temperature and humidity coupling stress under high temperature and high humidity conditions, so that the hollow brick has long-lasting and stable crack resistance and good durability in humid and hot environments.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a crack-resistant hollow brick for use in high-temperature and high-humidity environments. The hollow brick includes a brick body and a plurality of through holes formed on the brick body. The raw materials for preparing the brick body include, by weight, 100 parts cement, 30-50 parts fly ash, 40-60 parts ceramic sand, 0.5-2 parts modified polypropylene fiber, 5-10 parts composite expansion agent, 3-8 parts paraffin microcapsules, 3-5 parts layered bimetallic hydroxide, 5-10 parts silica fume, 5-15 parts metakaolin, and 30-45 parts water. The outer surface of the brick body is coated with a waterproof coating.

[0007] Furthermore, the modified polypropylene fiber is prepared by the following method: the polypropylene fiber is immersed in a 2-5% silane coupling agent ethanol solution for 30-60 minutes, then removed and dried to obtain the modified polypropylene fiber.

[0008] Furthermore, the composite expanding agent is composed of calcium sulfoaluminate expanding agent, calcium oxide expanding agent and periclase-type magnesium oxide expanding agent mixed in a mass ratio of 1:0.5-1:0.1-0.5.

[0009] Calcium sulfoaluminate expansive agent reacts with water to form ettringite, resulting in early expansion. It primarily functions in the early stages of cement hydration, compensating for chemical shrinkage and early drying shrinkage. Calcium oxide expansive agent reacts with water to form calcium hydroxide; the expansion reaction is rapid but short-lived, mainly compensating for plastic shrinkage and early drying shrinkage. Pernicotinic magnesium oxide expansive agent hydrates to form magnesium hydroxide; the expansion reaction is slower but can last for weeks or even months, compensating for later temperature-induced shrinkage and autogenous shrinkage. When these three components are blended in a specific ratio, the expansion process covers the entire shrinkage process from the plastic stage to the long-term shrinkage after hardening. In high-temperature and high-humidity environments, the hydration reaction accelerates, and a single expansive agent often runs out prematurely or provides insufficient expansion. The three-component blend allows for the gradual release of expansion energy, ensuring that the brick maintains compensating stress that matches shrinkage at different ages, preventing cracking of the pore walls due to concentrated shrinkage stress.

[0010] Furthermore, the paraffin microcapsules are composed of a core material and a wall material, wherein the core material is paraffin with a phase change temperature of 38-45℃, and the wall material is urea-formaldehyde resin.

[0011] Furthermore, the paraffin microcapsules have a particle size of 50-200 μm and a wall thickness of 5-20 μm.

[0012] Paraffin wax undergoes a solid-liquid phase transition within the 38-45℃ range, absorbing a large amount of latent heat. In high-temperature environments, the internal temperature of hollow bricks rises rapidly, creating a temperature gradient. The melting paraffin wax within the microcapsules absorbs heat, reducing the peak internal temperature of the brick and decreasing the temperature difference between the inside and outside, thereby reducing thermal stress. Urea-formaldehyde resin wall materials encapsulate liquid paraffin within the capsules, preventing paraffin wax from seeping out and contaminating the matrix or affecting cement hydration.

[0013] Furthermore, the layered bimetallic hydroxide is a magnesium-aluminum type layered bimetallic hydroxide with a magnesium-aluminum molar ratio of 2:1 to 4:1 and a particle size of 50-150 nm.

[0014] Further, the layered bimetallic hydroxide is prepared by the following method: magnesium salt and aluminum salt are dissolved in deionized water at a magnesium-aluminum molar ratio of 2:1 to 4:1, urea is added, and the total molar ratio of urea to magnesium and aluminum metal ions is 2:1 to 4:1. The mixture is reacted at 90-100℃ for 12-24 hours, centrifuged, washed and dried to obtain magnesium-aluminum type layered bimetallic hydroxide.

[0015] Magnesium-aluminum layered bimetallic hydroxides (LDHs) possess a layered structure and interlayer anion exchange capacity. In the highly alkaline environment of cement hydration, carbonate ions between LDH layers can exchange with chloride and sulfate ions in the environment, fixing the corrosive anions within the layers and reducing their erosion and damage to ettringite and CSH gel in the cement paste. In high-humidity environments, where salt damage accelerates penetration, LDHs can effectively delay ion migration. Simultaneously, the LDH nanosheets can fill the capillaries in the cement matrix, increasing density and reducing water absorption, thereby minimizing the extent of wet expansion and dry shrinkage.

[0016] Furthermore, the waterproof coating is made of the following components in parts by weight: 40-60 parts cement, 30-50 parts quartz sand, 5-10 parts additives, and 20-30 parts water; wherein the additives are sodium silicate, sodium carbonate, and sodium gluconate mixed in a mass ratio of 5:(1-1.5):(0.4-0.8); the coating thickness is 0.2-0.5 mm.

[0017] This coating is a cement-based penetrating crystallization system. Sodium silicate hydrolyzes to produce silicate ions, sodium carbonate provides carbonate ions, and sodium gluconate acts as a retarder. These three react with calcium hydroxide, a cement hydration product, to form insoluble crystalline calcium silicate hydrate and calcium carbonate, which block the surface and shallow capillary channels of the brick. When the brick absorbs water again in a high-humidity environment, the unreacted active components can continue to form crystals, giving the coating self-healing capabilities. Even if micro-cracks appear on the surface, they can be partially repaired upon contact with moisture. This coating reduces the saturated water absorption rate of the brick, thereby reducing the magnitude of expansion and contraction due to moisture, and isolates external moisture from entering the brick's interior, reducing the severity of temperature and humidity coupling.

[0018] The second aspect of this invention provides a method for preparing the above-mentioned crack-resistant hollow brick for high temperature and high humidity environments, comprising the following steps: (1) Mix the modified polypropylene fiber with paraffin microcapsules to obtain a premix; put cement, fly ash, ceramsite sand, silica fume, metakaolin, layered bimetallic hydroxide and composite expansion agent into a mixer and dry mix, then add the premix and continue to dry mix, and finally add water and stir to obtain a mixture. (2) The mixture is fed into the hollow brick forming machine and vibrated and pressed to form a hollow brick wet blank; (3) First, the hollow brick wet blanks are statically cured for 8-12 hours at a temperature of 20-30℃ and a relative humidity of 90%-95%, and then steam cured for 12-24 hours at a temperature of 50-70℃ and a relative humidity of 85%-95%. After that, they are naturally air-dried for 24-48 hours. (4) Apply a waterproof coating to the outer surface of the brick body after drying in step (3), and cure for 20-40 hours after coating to obtain crack-resistant hollow bricks for use in high temperature and high humidity environments.

[0019] Furthermore, the steam curing in step (3) adopts a stepped heating method: first, the temperature is raised from room temperature to 50-60℃ at a rate of 10-15℃ / h and kept constant for 6-12h; then, the temperature is raised to 65-70℃ at a rate of 5-10℃ / h and kept constant for 6-12h.

[0020] This invention employs a stepped heating method. First, the temperature is increased to 50-60℃ at a rate of 10-15℃ / h, ensuring a uniform temperature rise in the brick body. The paraffin microcapsules gradually adapt to the temperature changes without leakage. During the 6-12 hour constant-temperature period, the cement hydration reaction proceeds smoothly, the expanding agent slowly releases its expansion energy, and the fiber and LDH structures remain stable. Then, the temperature is increased even more slowly at a rate of 5-10℃ / h to 65-70℃, further promoting the formation of hydrated calcium silicate and ettringite, increasing strength, while simultaneously controlling the rate of moisture evaporation. Ultimately, the brick body has fewer internal defects and lower porosity, enabling it to more effectively resist temperature and humidity coupled stresses in subsequent high-temperature and high-humidity service environments.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention systematically solves the problem of cracking in hollow bricks caused by temperature and humidity coupling stress in high-temperature and high-humidity environments through the synergistic effect of multiple components, including a composite expanding agent, paraffin microcapsules, layered bimetallic hydroxide, modified polypropylene fiber, microsilica powder, metakaolin, and a surface waterproof coating. Specifically, the three-component composite expanding agent achieves graded shrinkage compensation from early to late stages; paraffin microcapsules reduce the temperature peak and temperature gradient inside the brick; the layered bimetallic hydroxide simultaneously exerts ion adsorption and nano-filling effects to improve density; the modified polypropylene fiber enhances the crack resistance of the matrix; and the surface waterproof coating effectively reduces external moisture intrusion. The drying shrinkage value of the hollow bricks produced by this invention can be controlled below 0.32 mm / m, the water absorption rate is less than 8%, and the impermeability grade reaches P6. They are not prone to cracking during long-term use in high-temperature and high-humidity environments and exhibit good volume stability and durability. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0023] Unless otherwise specified, all raw materials used in the embodiments are commercially available products. The following sources are illustrative examples.

[0024] The following materials were purchased: cement (PO 42.5 ordinary Portland cement) from Huaxin Cement Co., Ltd.; fly ash (Class F, Grade II fly ash) from Anhui Conch Cement Co., Ltd.; ceramic sand (average particle size 3mm) from Shantou Chenxin Building Materials Co., Ltd.; microsilica powder (average particle size 0.3μm) from Luoyang Minshi Silicon Products Co., Ltd.; metakaolin (average particle size 1.2μm) from BASF (China) Co., Ltd.; calcium sulfoaluminate expansion agent from Tangshan Polar Bear Building Materials Co., Ltd.; calcium oxide expansion agent from Changsha Lidong Building Materials Co., Ltd.; periclase-type magnesium oxide expansion agent from Wuhan Sanyuan Special Building Materials Co., Ltd.; and strong base styrene-based anion exchange resin (201×7 type I strong base styrene-based anion exchange resin) from Anhui Wanshu Chemical Co., Ltd.

[0025] Example 1 This embodiment provides a crack-resistant hollow brick for use in high temperature and high humidity environments, and its preparation method includes the following steps: (1) Mix 1.2 kg of modified polypropylene fiber with 6 kg of paraffin microcapsules evenly to obtain a premix. Add 100 kg of cement, 40 kg of fly ash, 50 kg of ceramic sand, 8 kg of silica fume, 10 kg of metakaolin, 4 kg of layered bimetallic hydroxide, and 8 kg of composite expansion agent into a mixer and dry mix for 4 min; then add the premix and continue to dry mix for 2 min; finally add 38 kg of water and wet mix for 6 min to obtain a mixture.

[0026] The preparation method of modified polypropylene fiber is as follows: the polypropylene fiber is immersed in an ethanol solution of silane coupling agent KH550 with a mass concentration of 3% for 45 minutes, and then dried at 70°C for 3 hours.

[0027] The composite expanding agent is composed of calcium sulfoaluminate expanding agent, calcium oxide expanding agent and periclase-type magnesium oxide expanding agent mixed in a mass ratio of 1:0.8:0.3.

[0028] The core material of the paraffin microcapsules is paraffin with a phase change temperature of 42℃, and the wall material is urea-formaldehyde resin. The average particle size is 120μm and the wall thickness is 12μm.

[0029] The preparation method of layered bimetallic hydroxide is as follows: 0.4 mol of magnesium chloride hexahydrate and 0.15 mol of aluminum chloride hexahydrate are dissolved in 2L of deionized water, 1.1 mol of urea is added, and the mixture is reacted at 95℃ for 18h. After centrifugation, washing and drying, magnesium-aluminum type layered bimetallic hydroxide is obtained with a magnesium-aluminum molar ratio of 2.67:1.

[0030] (2) The mixture obtained in step (1) is fed into a hollow brick forming machine and vibrated and pressed under a pressure of 2.2 MPa to obtain a hollow brick wet blank. The forming mold is 390mm×190mm×190mm, with three rows of circular holes, a hole diameter of 25mm, and a hole spacing of 40mm.

[0031] (3) The hollow brick wet blanks are first statically cured for 10 hours at a temperature of 25℃ and a relative humidity of 92%, and sprayed every 2 hours to keep the surface moist. Then they are transferred to the steam curing room and the temperature is raised in a stepwise manner: from room temperature to 55℃ at a rate of 12℃ / h, and kept at a constant temperature for 8 hours, and then raised to 68℃ at a rate of 8℃ / h, and kept at a constant temperature for 10 hours, while maintaining a relative humidity of 90%. After curing, they are taken out and air-dried under natural conditions for 36 hours.

[0032] (4) Apply a waterproof coating to the outer surface of the brick body after drying in step (3). The waterproof coating is prepared as follows: Take 50 kg of cement, 40 kg of quartz sand, 7 kg of additives (sodium silicate, sodium carbonate, and sodium gluconate are mixed in a mass ratio of 5:1.2:0.6), and 25 kg of water, and stir them into a uniform slurry. Apply the slurry evenly to the surface of the brick body with a coating thickness of 0.3 mm. After coating, cover with a damp cloth and cure for 24 hours at a temperature of 22℃ and a relative humidity of 95%. This yields crack-resistant hollow bricks suitable for high temperature and high humidity environments.

[0033] Example 2 This embodiment provides a crack-resistant hollow brick for use in high temperature and high humidity environments, and its preparation method includes the following steps: (1) Mix 0.8 kg of modified polypropylene fiber with 4 kg of paraffin microcapsules evenly to obtain a premix. Put 100 kg of cement, 30 kg of fly ash, 60 kg of ceramic sand, 6 kg of silica fume, 8 kg of metakaolin, 5 kg of layered bimetallic hydroxide, and 10 kg of composite expansion agent into a mixer and dry mix for 2 min; then add the premix and continue to dry mix for 1 min; finally add 32 kg of water and wet mix for 8 min to obtain a mixture.

[0034] The preparation method of modified polypropylene fiber is as follows: the polypropylene fiber is immersed in an ethanol solution of 2% silane coupling agent KH550 for 60 min, and then dried at 60℃ for 4 h.

[0035] The composite expanding agent is composed of calcium sulfoaluminate expanding agent, calcium oxide expanding agent and periclase-type magnesium oxide expanding agent mixed in a mass ratio of 1:0.5:0.1.

[0036] The core material of the paraffin microcapsules is paraffin with a phase change temperature of 38℃, and the wall material is urea-formaldehyde resin with an average particle size of 50μm and a wall thickness of 5μm.

[0037] The preparation method of layered bimetallic hydroxide is as follows: 0.4 mol of magnesium chloride hexahydrate and 0.2 mol of aluminum chloride hexahydrate (magnesium-aluminum molar ratio 2:1) are dissolved in 2L of deionized water, 1.2 mol of urea (urea to total metal ion molar ratio 2:1) are added, and the mixture is reacted at 90℃ for 24h. After centrifugation, washing and drying, magnesium-aluminum type layered bimetallic hydroxide is obtained.

[0038] (2) The mixture obtained in step (1) is fed into a hollow brick forming machine and vibrated and pressed under a pressure of 1.5 MPa to obtain a hollow brick wet blank. The forming mold is 390 mm × 190 mm × 190 mm, and the holes are three rows of circular holes with a diameter of 25 mm and a hole spacing of 40 mm.

[0039] (3) The hollow brick wet blanks are first statically cured for 12 hours at a temperature of 20℃ and a relative humidity of 90%, and sprayed every 2 hours to keep the surface moist. Then they are transferred to the steam curing room and the temperature is raised in a stepwise manner: the temperature is raised from room temperature to 50℃ at a rate of 10℃ / h and kept constant for 12 hours, and then raised to 65℃ at a rate of 5℃ / h and kept constant for 12 hours, while maintaining a relative humidity of 85%. After curing, they are taken out and air-dried under natural conditions for 24 hours.

[0040] (4) Apply a waterproof coating to the outer surface of the brick body after drying in step (3). The waterproof coating is prepared as follows: Take 40 kg of cement, 30 kg of quartz sand, 5 kg of additives (sodium silicate, sodium carbonate, and sodium gluconate are mixed in a mass ratio of 5:1:0.4), and 20 kg of water, and stir them into a uniform slurry. Apply the slurry evenly to the surface of the brick body with a coating thickness of 0.2 mm. After coating, cover with a damp cloth and cure for 20 hours at a temperature of 20℃ and a relative humidity of 90%. This yields crack-resistant hollow bricks suitable for high temperature and high humidity environments.

[0041] Example 3 This embodiment provides a crack-resistant hollow brick for use in high temperature and high humidity environments, and its preparation method includes the following steps: (1) Mix 1.8 kg of modified polypropylene fiber with 7 kg of paraffin microcapsules evenly to obtain a premix. Put 100 kg of cement, 50 kg of fly ash, 40 kg of ceramic sand, 9 kg of silica fume, 14 kg of metakaolin, 3.5 kg of layered bimetallic hydroxide, and 6 kg of composite expansion agent into a mixer and dry mix for 5 min; then add the premix and continue to dry mix for 3 min; finally add 42 kg of water and wet mix for 3 min to obtain a mixture.

[0042] The preparation method of modified polypropylene fiber is as follows: the polypropylene fiber is immersed in an ethanol solution of 5% silane coupling agent KH550 for 30 minutes, and then dried at 80℃ for 2 hours.

[0043] The composite expanding agent is composed of calcium sulfoaluminate expanding agent, calcium oxide expanding agent and periclase-type magnesium oxide expanding agent mixed in a mass ratio of 1:1:0.5.

[0044] The core material of the paraffin microcapsules is paraffin with a phase change temperature of 45℃, and the wall material is urea-formaldehyde resin. The average particle size is 200μm and the wall thickness is 20μm.

[0045] The preparation method of layered bimetallic hydroxide is as follows: 0.4 mol of magnesium chloride hexahydrate and 0.1 mol of aluminum chloride hexahydrate (magnesium-aluminum molar ratio 4:1) are dissolved in 2L of deionized water, 2.0 mol of urea (urea to total metal ion molar ratio 4:1) are added, and the mixture is reacted at 100℃ for 12h. After centrifugation, washing and drying, magnesium-aluminum type layered bimetallic hydroxide is obtained.

[0046] (2) The mixture obtained in step (1) is fed into a hollow brick forming machine and vibrated and pressed under a pressure of 3.0 MPa to obtain a hollow brick wet blank. The forming mold is 390mm×190mm×190mm, and the holes are three rows of circular holes with a diameter of 25mm and a hole spacing of 40mm.

[0047] (3) The hollow brick wet blanks are first statically cured at a temperature of 30℃ and a relative humidity of 95% for 8 hours, and sprayed every 2 hours to keep the surface moist. Then they are transferred to the steam curing room and the temperature is raised in a stepwise manner: from room temperature to 60℃ at a rate of 15℃ / h, and kept constant for 6 hours, and then raised to 70℃ at a rate of 10℃ / h, and kept constant for 6 hours, while maintaining a relative humidity of 95%. After curing, they are taken out and air-dried under natural conditions for 48 hours.

[0048] (4) Apply a waterproof coating to the outer surface of the brick body after drying in step (3). The waterproof coating is prepared as follows: Take 60 kg of cement, 50 kg of quartz sand, 10 kg of additives (sodium silicate, sodium carbonate, and sodium gluconate are mixed in a mass ratio of 5:1.5:0.8), and 30 kg of water, and stir into a uniform slurry. Apply the slurry evenly to the surface of the brick body with a coating thickness of 0.5 mm. After coating, cover with a damp cloth and cure for 40 hours at a temperature of 25℃ and a relative humidity of 95% to obtain crack-resistant hollow bricks suitable for high temperature and high humidity environments.

[0049] Comparative Example 1 The difference between this comparative example and Example 1 is that the composite expanding agent is composed of calcium sulfoaluminate expanding agent and calcium oxide expanding agent mixed in a mass ratio of 1:0.8, and does not contain periclase-type magnesium oxide expanding agent. All other aspects are the same as in Example 1.

[0050] Comparative Example 2 The difference between this comparative example and Example 1 is that the wall material of the paraffin microcapsules is silica, and the core material is paraffin with a phase transition temperature of 42°C. The preparation method of the paraffin microcapsules is as follows: 100g of paraffin and 10g of emulsifier (Span-80) are added to 500mL of deionized water and emulsified at high speed at 70°C for 30min to form a paraffin emulsion. Separately, 50mL of tetraethyl orthosilicate is mixed with 100mL of ethanol and slowly added dropwise to the paraffin emulsion. The pH is adjusted to 9-10 with ammonia, and the reaction is carried out at 50°C for 4h, allowing the tetraethyl orthosilicate to hydrolyze and condense on the surface of the paraffin droplets to form a silica shell layer. After the reaction, the mixture is centrifuged, washed with ethanol and deionized water, and dried at 60°C for 12h to obtain silica-walled paraffin microcapsules. All other steps are the same as in Example 1.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that the layered bimetallic hydroxide is replaced with a strongly basic styrene-based anion exchange resin. Everything else is the same as in Example 1.

[0052] Comparative Example 4 The difference between this comparative example and Example 1 is that the additive for the waterproof coating is a mixture of sodium silicate, sodium carbonate, and lithium silicate in a mass ratio of 5:1.2:0.6, that is, sodium gluconate in Example 1 is replaced with lithium silicate. Everything else is the same as in Example 1.

[0053] Comparative Example 5 The difference between this comparative example and Example 1 is that the amounts of each raw material in the formula are as follows: cement 100kg, fly ash 60kg, ceramic sand 35kg, modified polypropylene fiber 0.3kg, composite expansion agent 12kg, paraffin microcapsules 9kg, layered bimetallic hydroxide 2kg, microsilica powder 12kg, metakaolin 3kg, and water 50kg. The formula for the waterproof coating and the preparation method for the hollow bricks are the same as in Example 1.

[0054] Performance testing To verify the crack resistance of the hollow bricks of the present invention under high temperature and high humidity conditions, the hollow bricks prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to the following performance tests: 1. Compressive strength: Determined according to GB / T 4111-2013 "Test Methods for Concrete Blocks and Bricks", reflecting the basic mechanical properties of the brick.

[0055] 2. Flexural strength: Measured according to GB / T 4111-2013, it reflects the brick's resistance to bending and is closely related to its crack resistance.

[0056] 3. Water absorption rate: Measured according to GB / T 4111-2013, it reflects the brick's ability to absorb water. The lower the water absorption rate, the denser the brick and the smaller the expansion and contraction due to moisture.

[0057] 4. Drying shrinkage value: Measured according to GB / T 4111-2013, it reflects the degree of volume shrinkage of the brick during the drying process and is a key indicator for evaluating the risk of wall cracking. The drying shrinkage value in this scheme is measured under accelerated testing conditions (40℃, 40% relative humidity) after high temperature and high humidity treatment to simulate extreme service environments.

[0058] 5. Permeability Resistance: Tested according to GB / T 4111-2013, using a permeability testing device to apply the specified water pressure and maintain it for 2 hours, then splitting the specimen to measure the penetration height; the result is indicated by P, referring to the concrete permeability resistance grade (e.g., P6 indicates that it can resist 0.6MPa water pressure without leakage). The higher the permeability resistance grade, the denser the brick body, and the more difficult it is for moisture and corrosive media to penetrate, effectively reducing the risk of cracking under the combined effects of temperature and humidity.

[0059] Hollow brick samples prepared in Examples 1-3 and Comparative Examples 1-5 were selected, with 10 samples taken from each group. After curing under standard curing conditions for 28 days, performance tests were conducted according to the above test methods, and the average value of the results was taken.

[0060] The test results are shown in Table 1.

[0061] Table 1 Performance Test Results

[0062] As can be seen from the above performance test results, all the properties of Examples 1-3 are excellent, the compressive strength reaches MU10 or above, the water absorption rate is controlled at a low level of 7.1%~7.9%, the drying shrinkage value is far below the standard limit, and the impermeability grade reaches P6.

[0063] Comparative Example 1 changed the expansion agent from a three-component to a two-component one, resulting in insufficient compensation for later shrinkage, significantly increased drying shrinkage, and a decrease in the impermeability grade, indicating that tiered compensation is crucial for long-term crack resistance. Comparative Example 2 replaced the paraffin microcapsule urea-formaldehyde resin wall material with a silica shell. During steam curing, the silica shell may crack or its sealing performance may decrease, leading to leakage of phase change paraffin, weakened temperature control, increased internal temperature gradient of the brick, worsened water absorption and shrinkage, and a lower impermeability grade. Comparative Example 3 replaced the layered bimetallic hydroxide with a strongly basic anion exchange resin. Although some anion exchange capacity was retained, the nanoscale physical filling effect was lost, capillary pores could not be effectively refined, water absorption and drying shrinkage significantly increased, and the impermeability grade dropped to P4. Comparative Example 4, by removing sodium gluconate from the waterproof coating, lacked a retarding component, resulting in faster setting of the coating slurry, insufficient penetration and crystallization depth, and inadequate blockage of the internal pores of the brick. This led to an increase in water absorption and drying shrinkage compared to Example 1. Although the impermeability grade remained P6, it was measurable at the edges, indicating that the retarding effect of sodium gluconate makes a practical contribution to achieving deep penetration and long-term durability of the coating. Comparative Example 5 adjusted the dosage of each raw material, disrupting the balance between the components in the formula. This resulted in a loose brick skeleton, poor bonding, and a significant overall deterioration of all performance indicators. This fully demonstrates that the component dosage range defined in this invention has a significant synergistic optimization effect, and deviations from the formula dosage range will seriously impair the crack resistance of hollow bricks in high-temperature and high-humidity environments.

[0064] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A crack-resistant hollow brick for use in high-temperature and high-humidity environments, the hollow brick comprising a brick body and a plurality of through holes formed on the brick body, characterized in that, The raw materials for preparing the brick body include, by weight: 100 parts cement, 30-50 parts fly ash, 40-60 parts ceramic sand, 0.5-2 parts modified polypropylene fiber, 5-10 parts composite expansion agent, 3-8 parts paraffin microcapsules, 3-5 parts layered bimetallic hydroxide, 5-10 parts silica fume, 5-15 parts metakaolin, and 30-45 parts water; the outer surface of the brick body is coated with a waterproof coating.

2. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 1, characterized in that, The modified polypropylene fiber is prepared by the following method: the polypropylene fiber is immersed in a 2-5% silane coupling agent ethanol solution for 30-60 minutes, then removed and dried to obtain the modified polypropylene fiber.

3. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 1, characterized in that, The composite expanding agent is composed of calcium sulfoaluminate expanding agent, calcium oxide expanding agent and periclase-type magnesium oxide expanding agent mixed in a mass ratio of 1:0.5-1:0.1-0.

5.

4. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 1, characterized in that, The paraffin microcapsules consist of a core material and a wall material. The core material is paraffin with a phase change temperature of 38-45℃, and the wall material is urea-formaldehyde resin.

5. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 4, characterized in that, The paraffin microcapsules have a particle size of 50-200 μm and a wall thickness of 5-20 μm.

6. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 1, characterized in that, The layered bimetallic hydroxide is a magnesium-aluminum type layered bimetallic hydroxide with a magnesium-aluminum molar ratio of 2:1 to 4:1 and a particle size of 50-150 nm.

7. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 6, characterized in that, The layered bimetallic hydroxide is prepared by the following method: magnesium salt and aluminum salt are dissolved in deionized water at a magnesium-aluminum molar ratio of 2:1 to 4:1, urea is added, and the total molar ratio of urea to magnesium and aluminum metal ions is 2:1 to 4:

1. The mixture is reacted at 90-100℃ for 12-24 hours, centrifuged, washed and dried to obtain magnesium-aluminum type layered bimetallic hydroxide.

8. The crack-resistant hollow brick for high temperature and high humidity environments according to claim 1, characterized in that, The waterproof coating is made of the following components in parts by weight: 40-60 parts cement, 30-50 parts quartz sand, 5-10 parts additives, and 20-30 parts water; wherein the additives are sodium silicate, sodium carbonate, and sodium gluconate mixed in a mass ratio of 5:(1-1.5):(0.4-0.8); the coating thickness is 0.2-0.5 mm.

9. A method for preparing crack-resistant hollow bricks for high-temperature and high-humidity environments according to any one of claims 1-8, comprising the following steps: (1) Mix the modified polypropylene fiber with paraffin microcapsules to obtain a premix; put cement, fly ash, ceramsite sand, silica fume, metakaolin, layered bimetallic hydroxide and composite expansion agent into a mixer and dry mix, then add the premix and continue to dry mix, and finally add water and stir to obtain a mixture. (2) The mixture is fed into the hollow brick forming machine and vibrated and pressed to form a hollow brick wet blank; (3) First, the hollow brick wet blanks are statically cured for 8-12 hours at a temperature of 20-30℃ and a relative humidity of 90%-95%, and then steam cured for 12-24 hours at a temperature of 50-70℃ and a relative humidity of 85%-95%. After that, they are naturally air-dried for 24-48 hours. (4) Apply a waterproof coating to the outer surface of the brick body after drying in step (3), and cure for 20-40 hours after coating to obtain crack-resistant hollow bricks for use in high temperature and high humidity environments.

10. The preparation method according to claim 9, characterized in that, The steam curing in step (3) adopts a stepped heating method: first, the temperature is raised from room temperature to 50-60℃ at a rate of 10-15℃ / h and kept constant for 6-12h; then, the temperature is raised to 65-70℃ at a rate of 5-10℃ / h and kept constant for 6-12h.

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