Anti-cracking calcium silicate board and preparation method thereof

Abstract

The invention discloses an anti-cracking calcium silicate board and a preparation method thereof, and relates to the technical field of light building materials. The method comprises the following steps: carrying out ball milling, acid pickling and silane coupling agent surface modification on quartz sand to obtain alkylated quartz sand; and carrying out dry mixing on the mixture, metakaolin, silica fume and cement. The linen fiber is subjected to alkali treatment and hydroxyethyl acrylate graft modification, and the PVA fiber is subjected to silane coupling agent and nano silicon dioxide coating treatment. Dispersing graphene oxide, carboxylated styrene-butadiene emulsion and other assistants in water, adding the dry mixture, uniformly stirring, and then adding the two modified fibers to prepare mixed slurry; and finally, carrying out pressure forming, pre-curing, high-pressure steam curing and drying to obtain a finished product. Through substrate silanization, fiber grafting / nanocrystalline seed modification and synergistic introduction of graphene oxide and elastic emulsion, the interface bonding strength and toughness are remarkably enhanced, crack initiation and propagation are effectively inhibited, and the plate has excellent cracking resistance.

Description

Technical Field

[0001] This invention relates to the field of lightweight building materials technology, specifically to a crack-resistant calcium silicate board and its preparation method. Background Technology

[0002] Calcium silicate boards are high-performance inorganic non-metallic materials made primarily from siliceous and calcareous materials through processes such as batching, molding, and autoclaving. Due to their excellent comprehensive properties, they are highly favored in various fields. Specifically, their fire resistance limit can reach 1-4 hours, effectively preventing the spread of flames and meeting the fire protection design requirements of various buildings; they have a low thermal conductivity, providing significant heat insulation and reducing building energy consumption; they also possess good resistance to insects, mold, and aging, allowing for long-term stable service even in harsh environments such as dampness and darkness, with a service life of over 20 years. Based on these advantages, calcium silicate boards are widely used in ceilings, interior partitions, exterior wall linings, and floor subfloors in civil and industrial buildings; in thermal insulation and protective linings for boilers and kilns in industrial fields; and in special working conditions such as the decoration and protection of rail transit platforms and tunnel interiors, ship cabin partitions, and offshore platform enclosures. In recent years, with the development of modern construction industry towards green, high-end, and intelligent directions, building structures have become increasingly complex, and engineering service environments have become increasingly harsh. Whether it is the high-altitude wind pressure environment of high-rise buildings, the high-humidity and high-salt corrosion environment of underground engineering, the vibration load and temperature alternation environment of rail transit, or the high-temperature radiation environment around industrial kilns, all have placed higher demands on the performance of calcium silicate boards. Among them, crack resistance, as a core indicator to ensure the structural integrity and safety of the board, has become a major bottleneck restricting the further expansion of calcium silicate boards into high-end building fields and special industrial scenarios, as well as improving the long-term service stability and extending the service life of the boards. Once the board cracks, it will not only destroy its core functions such as heat insulation, sound insulation, and fire resistance, but may also trigger a chain of problems such as a decrease in structural load-bearing capacity and water vapor penetration leading to substrate weathering, which may even affect the overall safety of the project in severe cases. Summary of the Invention

[0003] The purpose of this invention is to provide a crack-resistant calcium silicate board and its preparation method, so as to solve the technical problem of poor mechanical strength of calcium silicate boards mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a crack-resistant calcium silicate board includes the following steps: (1) High-purity quartz sand is ball-milled, then soaked in hydrochloric acid solution, washed and dried to obtain pretreated quartz sand; Pretreated quartz sand was mixed with an ethanol / water solution of silane coupling agent, the pH was adjusted to acidic with glacial acetic acid, and the mixture was stirred at a constant temperature, then filtered and dried to obtain alkyl quartz sand. (2) Alkyl silica sand is dry-mixed with metakaolin, silica fume and silicate cement to obtain dry mix; (3) The flax fiber was treated with sodium hydroxide solution, then washed and dried to obtain pretreated flax fiber; Pretreated flax fibers were grafted with hydroxyethyl acrylate under nitrogen protection in the presence of ammonium persulfate as an initiator, and then dried to obtain modified flax fibers. (4) Place the PVA fiber in anhydrous ethanol for ultrasonic cleaning and then dry it to obtain pretreated PVA fiber; Pretreated polyvinyl alcohol fibers were mixed with silane coupling agent KH-560 and nano-silica to obtain modified polyvinyl alcohol fibers. (5) Disperse graphene oxide, carboxylated styrene-butadiene emulsion, water-reducing agent and retarder in deionized water, then add dry mix, stir and mix, then add modified flax fiber and modified polyvinyl alcohol fiber, stir and mix to obtain mixed slurry; (6) The mixed slurry is pressurized to form a blank, and then the blank is pre-cured, high-pressure steam cured, depressurized and dried in sequence to obtain crack-resistant calcium silicate board.

[0005] In this invention, the crack resistance of calcium silicate boards is improved synergistically from the following aspects: Firstly, cracking is suppressed at its source through a dual approach of interfacial bonding strengthening and matrix structure densification. Specifically, after hydrolysis, the silane coupling agent KH550 undergoes a dehydration condensation reaction with the hydroxyl groups on the surface of quartz sand to form stable Si-O-Si covalent bonds. At the same time, the exposed amino functional groups can have a chemical affinity with cement hydration products (such as calcium hydroxide and hydrated calcium silicate), which completely solves the problem of poor interfacial compatibility between traditional quartz sand and cement matrix, and easy separation due to drying shrinkage or stress, thus eliminating the core hidden danger of interfacial crack initiation. Furthermore, metakaolin and silica fume in the composite system, as highly active admixtures, utilize their ultra-fine particle size characteristics to fill the gaps inside the matrix in the early stage of cement hydration, reducing porosity, improving the density of the matrix structure, and preventing stress concentration at the pores. In addition, they participate in the hydrothermal reaction during subsequent curing, synergistically generating more stable hydration product phases with cement hydration products, optimizing the internal crystal structure of the matrix, and simultaneously regulating the cement hydration rate, reducing the peak hydration heat, and reducing thermal stress caused by internal and external temperature differences. From the two dimensions of interface bonding and densification of the matrix structure, they block the initial induction of cracking, providing a foundation for the crack resistance of the board.

[0006] On the other hand, for flax fibers, the grafting polymerization of hydroxyethyl acrylate monomers initiated by ammonium persulfate introduces flexible polymer segments onto the fiber surface, significantly improving the fiber's elastic bridging ability. When the board is subjected to external loads or internal stress, the flexible segments can absorb energy through deformation, buffering local stress and preventing the initiation of microcracks caused by stress concentration. At the same time, the increased surface roughness of the grafted fibers enhances the mechanical interlocking force with the cement matrix, further improving the interfacial bonding stability. For PVA fibers, the silane coupling agent KH560, after hydrolysis, opens its ring and binds to the hydroxyl groups on the fiber surface, firmly anchoring nano-silica to form nano-seeds. These seed crystals can guide the directional growth of cement hydration products, eliminating the weak layer in the interfacial transition zone between the fiber and the matrix (the traditional fiber-matrix interface is prone to voids due to weak bonding, becoming the initiation point of cracks), achieving a tight fusion between the fiber and the matrix. Furthermore, the two modified fibers form a continuous cross-linked network in the matrix, intertwining with the tobermorite crystals generated by subsequent high-pressure steam curing. When microcracks appear in the board, the fiber network can prevent crack propagation through bridging. At the same time, the directional hydration products induced by nanocrystal seeds further enhance the structural stability at the crack, forming a dual protection of crack initiation inhibition and crack propagation blocking. This significantly improves the board's ability to resist stress. From the perspectives of stress buffering and crack inhibition, it makes up for the shortcomings of simple matrix modification in dynamic stress response, forming a synergistic effect with the first aspect, thereby endowing calcium silicate boards with excellent crack resistance.

[0007] This invention discovered in experiments that during high-pressure steam curing, the interfacial chemical bonding between the modified fibers (i.e., HEA-grafted flax fibers and nano-SiO2-coated PVA fibers) and the rigid matrix with a tobermorite crystal framework is too strong and rigid, lacking an effective stress buffer layer. This leads to huge internal stress between the rigid matrix and the tough fibers due to the mismatch in thermal shrinkage coefficients, causing brittle micro-peeling at the interface or fiber fracture, severely limiting the upper limit of the crack resistance of the board under high strain conditions. To further solve this technical problem, graphene oxide and carboxylated styrene-butadiene emulsion are introduced into the mixed slurry. Through the synergistic effect of graphene oxide and carboxylated styrene-butadiene emulsion, a multi-scale interfacial transition layer that combines rigidity and flexibility is constructed: graphene oxide acts as a nanoscale high-strength constraint point, forming a three-dimensional anchoring network with the modified substrate and fibers, providing basic interfacial strength and sliding friction resistance; while the carboxylated styrene-butadiene emulsion forms a micron-scale elastic film in situ at the interface, acting as a stress buffer and shock-absorbing pad between the rigid tobermorite and the tough fibers. The two work together to guide the directional growth of hydrothermal crystals and fill interface defects, thus avoiding stress concentration at the source. On the other hand, under load or thermal deformation, controlled elastic slip of fibers is allowed, converting destructive energy into frictional energy and elastic deformation energy. This transforms the interface bonding method from "hard locking" to "elastic constraint slip," making the interface change from "strong and brittle" to "strong and tough." This achieves a simultaneous improvement in the flexural strength and fracture toughness of the board, ultimately giving it excellent resistance to environmental temperature difference cracking.

[0008] Preferably, in step (1), the mass concentration of the hydrochloric acid solution is 2-5%.

[0009] Preferably, in step (1), the silane coupling agent is silane coupling agent KH-550; The mass ratio of the pretreated quartz sand to the silane coupling agent KH-550 is 55:(0.3~0.8).

[0010] Preferably, in step (2), the mass ratio of alkyl silica sand, metakaolin, silica fume, and silicate cement is 55:(3-5):(1-3):(30-35).

[0011] Preferably, in step (3), the mass ratio of pretreated flax fiber to hydroxyethyl acrylate is 5:(1-3).

[0012] Preferably, in step (4), the mass ratio of pretreated polyvinyl alcohol fiber to silane coupling agent KH-560 is 3:(0.2-0.6).

[0013] Preferably, in step (4), the mass ratio of pretreated polyvinyl alcohol fiber to nano silica is 3:(1-2).

[0014] Preferably, in step (5), the mass ratio of graphene oxide to carboxylated styrene-butadiene emulsion is 0.3:(12-16).

[0015] Preferably, in step (5), the mass ratio of modified flax fiber to modified polyvinyl alcohol fiber is 4.5:(2-4).

[0016] A crack-resistant calcium silicate board is prepared by the method described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. By using silane coupling agents to achieve strong chemical bonding between quartz sand and cement matrix, the potential for separation caused by poor compatibility at traditional interfaces is eliminated; at the same time, active admixtures fill pores and optimize hydration products, significantly improving matrix density and blocking the initial cause of cracking from both interfacial bonding and structural dimensions. 2. The modified fibers form a continuous cross-linked network in the matrix. The flexible segments on the surface can buffer stress, while the nanocrystals strengthen the interfacial transition zone. When microcracks appear, the fiber network can effectively bridge and prevent crack propagation, thus achieving active dissipation and blocking of dynamic stress. 3. A synergistic system of graphene oxide and carboxylated styrene-butadiene emulsion is introduced to construct a multi-scale transition layer at the interface, characterized by nano-anchoring and micron-elasticity. This structure ensures high-strength bonding while buffering thermal stress through an elastic film, enabling controlled slippage at the interface and converting destructive energy into dissipative energy, thereby significantly improving the crack resistance of the board under temperature variations. Attached Figure Description

[0018] Figure 1 This is a SEM image of the cross-section of the calcium silicate plate prepared in Example 1 of the present invention; Figure 2 The image shows the XPS spectrum of the calcium silicate board prepared in Example 1 of this invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1

[0020] A method for preparing a crack-resistant calcium silicate board includes the following steps: Step 1: Take 55 parts of high-purity quartz sand, ball mill it to 325 mesh (pass rate ≥95%), soak it in 4% hydrochloric acid solution for 2 hours, wash it with deionized water until pH 7, and dry it at 105℃ to obtain pretreated quartz sand.

[0021] 55 parts of pretreated quartz sand were added to an ethanol / water solution (volume ratio 95:5) containing 0.7 parts of silane coupling agent KH-550. The pH of the system was adjusted to 4.5-5.0 using glacial acetic acid. After being magnetically stirred at 55°C for 2 hours, the mixture was filtered. The filter residue was then placed in an oven at 105°C for drying and heat treatment for 1.5 hours to obtain alkylated quartz sand.

[0022] Step 2: Add 55 parts of alkyl silica sand, 4.5 parts of metakaolin, 2.5 parts of silica fume, and 34 parts of ordinary silicate cement (PO 42.5) to a V-type mixer for dry mixing. Set the speed to 60 r / min and the dry mixing time to 30 min to ensure that the inorganic micro-nano components are highly uniformly distributed in powder form, thus obtaining the dry mix.

[0023] Step 3: Cut flax fibers to a length of 4 mm, immerse them in a 5% sodium hydroxide solution, and treat them at 60°C for 1 hour to remove surface pectin and lignin. Wash and dry to obtain pretreated flax fibers.

[0024] Five parts of pretreated flax fiber were placed in a reaction vessel, and 2.5 parts of hydroxyethyl acrylate (HEA) and 0.04 parts of ammonium persulfate initiator were added. After nitrogen gas was introduced to purge air, the mixture was stirred at 70°C for 2.5 hours. After the reaction was completed, the flax fiber was washed and dried to obtain the modified flax fiber.

[0025] Step 4: Cut polyvinyl alcohol (PVA) fibers to a length of 3 mm, place them in anhydrous ethanol and ultrasonically clean for 8 minutes to remove surface oil, and dry to obtain pretreated PVA fibers.

[0026] Three parts of pretreated PVA fiber were added to a mixed solution containing 0.5 parts of silane coupling agent KH-560 and 1.8 parts of nano silica (particle size 30nm), the pH value was adjusted to 4.5, ultrasonically dispersed and treated at 60℃ for 30min, filtered and dried to obtain modified polyvinyl alcohol fiber with surface-coated nanocrystal seeds.

[0027] Step 5: Disperse 0.03 parts graphene oxide, 1.5 parts carboxylated styrene-butadiene emulsion (XSBRL), 0.4 parts polycarboxylate superplasticizer, and 0.05 parts sodium gluconate retarder in 40 parts deionized water and perform ultrasonic pre-dispersion for 15 minutes. Then add the dry mix and stir at 300 rpm for 3 minutes; then add modified flax fiber (4.5 parts) and modified polyvinyl alcohol fiber (3.5 parts), adjust the speed to 600 rpm and continue stirring for 5 minutes to ensure that the fibers do not agglomerate and the slurry is uniform, thus obtaining a mixed slurry.

[0028] Step 6: The mixed slurry is fed into a mold and pressed and dehydrated under a pressure of 20 MPa on a press for 20 minutes to obtain a 12 mm thick board blank. The blank is placed in a pre-curing chamber at 35℃ and 95% relative humidity for 15 hours for pre-curing; then it is transferred to a high-pressure steam curing kettle and cured under high pressure at 1.2 MPa and 190℃ saturated steam for 12 hours. After the reaction is complete, the depressurization rate is controlled at 0.08-0.1 MPa / h, and after reducing to atmospheric pressure, it is taken out and dried at a constant temperature of 60℃ to constant weight to obtain crack-resistant calcium silicate board. Example 2

[0029] A method for preparing a crack-resistant calcium silicate board includes the following steps: Step 1: Take 55 parts of high-purity quartz sand, ball mill it to 325 mesh (pass rate ≥95%), soak it in 3% hydrochloric acid solution for 2 hours, wash it with deionized water until pH 7, and dry it at 105℃ to obtain pretreated quartz sand.

[0030] 55 parts of pretreated quartz sand were added to an ethanol / water solution (volume ratio 95:5) containing 0.4 parts of silane coupling agent KH-550. The pH of the system was adjusted to 4.5-5.0 using glacial acetic acid. After being magnetically stirred at 55°C for 2 hours, the mixture was filtered. The filter residue was then placed in an oven at 105°C for drying and heat treatment for 1.5 hours to obtain alkylated quartz sand.

[0031] Step 2: Add 55 parts of alkyl silica sand, 3.5 parts of metakaolin, 1.5 parts of silica fume, and 32 parts of ordinary silicate cement (PO 42.5) to a V-type mixer for dry mixing. Set the speed to 60 r / min and the dry mixing time to 30 min to ensure that the inorganic micro-nano components are highly uniformly distributed in powder form, thus obtaining the dry mix.

[0032] Step 3: Cut flax fibers to a length of 4 mm, immerse them in a 5% sodium hydroxide solution, and treat them at 60°C for 1 hour to remove surface pectin and lignin. Wash and dry to obtain pretreated flax fibers.

[0033] Five parts of pretreated flax fiber were placed in a reaction vessel, and 1.5 parts of hydroxyethyl acrylate (HEA) and 0.04 parts of initiator ammonium persulfate were added. After purging with nitrogen to remove air, the mixture was stirred at 70°C for 2.5 hours. After the reaction was completed, the flax fiber was washed and dried to obtain modified flax fiber.

[0034] Step 4: Cut polyvinyl alcohol (PVA) fibers to a length of 3 mm, place them in anhydrous ethanol and ultrasonically clean for 8 minutes to remove surface oil, and dry to obtain pretreated PVA fibers.

[0035] Three parts of pretreated PVA fiber were added to a mixed solution containing 0.3 parts of silane coupling agent KH-560 and 1.2 parts of nano silica (particle size 30 nm), the pH value was adjusted to 4.5, ultrasonically dispersed and treated at 60 °C for 30 min, filtered and dried to obtain modified polyvinyl alcohol fiber with surface-coated nanocrystal seeds.

[0036] Step 5: Disperse 0.03 parts graphene oxide, 1.3 parts carboxylated styrene-butadiene emulsion (XSBRL), 0.4 parts polycarboxylate superplasticizer, and 0.05 parts sodium gluconate retarder in 40 parts deionized water and perform ultrasonic pre-dispersion for 15 minutes. Then add the dry mix and stir at 300 rpm for 3 minutes; then add modified flax fiber (4.5 parts) and modified polyvinyl alcohol fiber (2.5 parts), adjust the speed to 600 rpm and continue stirring for 5 minutes to ensure that the fibers do not agglomerate and the slurry is uniform, thus obtaining a mixed slurry.

[0037] Step 6: The mixed slurry is fed into a mold and pressed and dehydrated under a pressure of 20 MPa on a press for 20 minutes to obtain a 12 mm thick board blank. The blank is placed in a pre-curing chamber at 35℃ and 95% relative humidity for 15 hours for pre-curing; then it is transferred to a high-pressure steam curing kettle and cured under high pressure at 1.2 MPa and 190℃ saturated steam for 12 hours. After the reaction is complete, the depressurization rate is controlled at 0.08-0.1 MPa / h, and after reducing to atmospheric pressure, it is taken out and dried at a constant temperature of 60℃ to constant weight to obtain crack-resistant calcium silicate board. Example 3

[0038] A method for preparing a crack-resistant calcium silicate board includes the following steps: Step 1: Take 55 parts of high-purity quartz sand, ball mill it to 325 mesh (pass rate ≥95%), soak it in 3.5% hydrochloric acid solution for 2 hours, wash it with deionized water until pH 7, and dry it at 105℃ to obtain pretreated quartz sand.

[0039] 55 parts of pretreated quartz sand were added to an ethanol / water solution (volume ratio 95:5) containing 0.6 parts of silane coupling agent KH-550. The pH of the system was adjusted to 4.5-5.0 using glacial acetic acid. After being magnetically stirred at 55°C for 2 hours, the mixture was filtered. The filter residue was then dried and heat-treated in an oven at 105°C for 1.5 hours to obtain alkylated quartz sand.

[0040] Step 2: Add 55 parts of alkyl silica sand, 4 parts of metakaolin, 2 parts of silica fume, and 33 parts of ordinary silicate cement (P.O42.5) to a V-type mixer for dry mixing. Set the speed to 60 r / min and the dry mixing time to 30 min to ensure that the inorganic micro-nano components are highly uniformly distributed in powder form, thus obtaining the dry mix.

[0041] Step 3: Cut flax fibers to a length of 4 mm, immerse them in a 5% sodium hydroxide solution, and treat them at 60°C for 1 hour to remove surface pectin and lignin. Wash and dry to obtain pretreated flax fibers.

[0042] Five parts of pretreated flax fiber were placed in a reaction vessel, and two parts of hydroxyethyl acrylate (HEA) and 0.04 parts of initiator ammonium persulfate were added. After purging with nitrogen to remove air, the mixture was stirred at 70°C for 2.5 hours. After the reaction was completed, the flax fiber was washed and dried to obtain the modified flax fiber.

[0043] Step 4: Cut polyvinyl alcohol (PVA) fibers to a length of 3 mm, place them in anhydrous ethanol and ultrasonically clean for 8 minutes to remove surface oil, and dry to obtain pretreated PVA fibers.

[0044] Three parts of pretreated PVA fiber were added to a mixed solution containing 0.4 parts of silane coupling agent KH-560 and 1.5 parts of nano silica (particle size 30 nm), the pH value was adjusted to 4.5, ultrasonically dispersed and treated at 60 °C for 30 min, filtered and dried to obtain modified polyvinyl alcohol fiber with surface-coated nanocrystal seeds.

[0045] Step 5: Disperse 0.03 parts graphene oxide, 1.4 parts carboxylated styrene-butadiene emulsion (XSBRL), 0.4 parts polycarboxylate superplasticizer, and 0.05 parts sodium gluconate retarder in 40 parts deionized water and perform ultrasonic pre-dispersion for 15 minutes. Then add the dry mix and stir at 300 rpm for 3 minutes; then add modified flax fiber (4.5 parts) and modified polyvinyl alcohol fiber (3 parts), adjust the speed to 600 rpm and continue stirring for 5 minutes to ensure that the fibers do not agglomerate and the slurry is uniform, thus obtaining a mixed slurry.

[0046] Step 6: The mixed slurry is fed into a mold and pressed and dehydrated under a pressure of 20 MPa on a press for 20 minutes to obtain a 12 mm thick board blank. The blank is placed in a pre-curing chamber at 35℃ and 95% relative humidity for 15 hours for pre-curing; then it is transferred to a high-pressure steam curing kettle and cured under high pressure at 1.2 MPa and 190℃ saturated steam for 12 hours. After the reaction is complete, the depressurization rate is controlled at 0.08-0.1 MPa / h, and after reducing to atmospheric pressure, it is taken out and dried at a constant temperature of 60℃ to constant weight to obtain crack-resistant calcium silicate board. Example 4

[0047] A method for preparing a crack-resistant calcium silicate board includes the following steps: Step 1: Take 55 parts of high-purity quartz sand, ball mill it to 325 mesh (pass rate ≥95%), soak it in 5% hydrochloric acid solution for 2 hours, wash it with deionized water until pH 7, and dry it at 105℃ to obtain pretreated quartz sand.

[0048] 55 parts of pretreated quartz sand were added to an ethanol / water solution (volume ratio 95:5) containing 0.8 parts of silane coupling agent KH-550. The pH of the system was adjusted to 4.5-5.0 using glacial acetic acid. After being magnetically stirred at 55°C for 2 hours, the mixture was filtered. The filter residue was then dried and heat-treated in an oven at 105°C for 1.5 hours to obtain alkylated quartz sand.

[0049] Step 2: Add 55 parts of alkyl silica sand, 5 parts of metakaolin, 3 parts of silica fume, and 35 parts of ordinary silicate cement (P.O42.5) to a V-type mixer for dry mixing. Set the speed to 60 r / min and the dry mixing time to 30 min to ensure that the inorganic micro-nano components are highly uniformly distributed in powder form, thus obtaining the dry mix.

[0050] Step 3: Cut flax fibers to a length of 4 mm, immerse them in a 5% sodium hydroxide solution, and treat them at 60°C for 1 hour to remove surface pectin and lignin. Wash and dry to obtain pretreated flax fibers.

[0051] Five parts of pretreated flax fiber were placed in a reaction vessel, and three parts of hydroxyethyl acrylate (HEA) and 0.04 parts of initiator ammonium persulfate were added. After purging with nitrogen to remove air, the mixture was stirred at 70°C for 2.5 hours. After the reaction was completed, the flax fiber was washed and dried to obtain the modified flax fiber.

[0052] Step 4: Cut polyvinyl alcohol (PVA) fibers to a length of 3 mm, place them in anhydrous ethanol and ultrasonically clean for 8 minutes to remove surface oil, and dry to obtain pretreated PVA fibers.

[0053] Three parts of pretreated PVA fiber were added to a mixed solution containing 0.6 parts of silane coupling agent KH-560 and 2 parts of nano silica (particle size 30nm), the pH value was adjusted to 4.5, ultrasonically dispersed and treated at 60℃ for 30min, filtered and dried to obtain modified polyvinyl alcohol fiber with surface-coated nanocrystal seeds.

[0054] Step 5: Disperse 0.03 parts graphene oxide, 1.6 parts carboxylated styrene-butadiene emulsion (XSBRL), 0.4 parts polycarboxylate superplasticizer, and 0.05 parts sodium gluconate retarder in 40 parts deionized water and perform ultrasonic pre-dispersion for 15 minutes. Then add the dry mix and stir at 300 rpm for 3 minutes; then add modified flax fiber (4.5 parts) and modified polyvinyl alcohol fiber (4 parts), adjust the speed to 600 rpm and continue stirring for 5 minutes to ensure that the fibers do not agglomerate and the slurry is uniform, thus obtaining a mixed slurry.

[0055] Step 6: The mixed slurry is fed into a mold and pressed and dehydrated under a pressure of 20 MPa on a press for 20 minutes to obtain a 12 mm thick board blank. The blank is placed in a pre-curing chamber at 35℃ and 95% relative humidity for 15 hours for pre-curing; then it is transferred to a high-pressure steam curing kettle and cured under high pressure at 1.2 MPa and 190℃ saturated steam for 12 hours. After the reaction is complete, the depressurization rate is controlled at 0.08-0.1 MPa / h, and after reducing to atmospheric pressure, it is taken out and dried at a constant temperature of 60℃ to constant weight to obtain crack-resistant calcium silicate board. Example 5

[0056] A method for preparing a crack-resistant calcium silicate board includes the following steps: Step 1: Take 55 parts of high-purity quartz sand, ball mill it to 325 mesh (pass rate ≥95%), soak it in 2% hydrochloric acid solution for 2 hours, wash it with deionized water until pH 7, and dry it at 105℃ to obtain pretreated quartz sand.

[0057] 55 parts of pretreated quartz sand were added to an ethanol / water solution (volume ratio 95:5) containing 0.3 parts of silane coupling agent KH-550. The pH of the system was adjusted to 4.5-5.0 using glacial acetic acid. After being magnetically stirred at 55°C for 2 hours, the mixture was filtered. The filter residue was then dried and heat-treated in an oven at 105°C for 1.5 hours to obtain alkylated quartz sand.

[0058] Step 2: Add 55 parts of alkyl silica sand, 3 parts of metakaolin, 1 part of silica fume, and 30 parts of ordinary silicate cement (P.O42.5) to a V-type mixer for dry mixing. Set the speed to 60 r / min and the dry mixing time to 30 min to ensure that the inorganic micro-nano components are highly uniformly distributed in powder form, thus obtaining the dry mix.

[0059] Step 3: Cut flax fibers to a length of 4 mm, immerse them in a 5% sodium hydroxide solution, and treat them at 60°C for 1 hour to remove surface pectin and lignin. Wash and dry to obtain pretreated flax fibers.

[0060] Five parts of pretreated flax fiber were placed in a reaction vessel, and one part of hydroxyethyl acrylate (HEA) and 0.04 parts of initiator ammonium persulfate were added. After purging with nitrogen to remove air, the mixture was stirred at 70°C for 2.5 hours. After the reaction was completed, the flax fiber was washed and dried to obtain the modified flax fiber.

[0061] Step 4: Cut polyvinyl alcohol (PVA) fibers to a length of 3 mm, place them in anhydrous ethanol and ultrasonically clean for 8 minutes to remove surface oil, and dry to obtain pretreated PVA fibers.

[0062] Three parts of pretreated PVA fiber were added to a mixed solution containing 0.2 parts of silane coupling agent KH-560 and 1 part of nano silica (particle size 30nm), the pH value was adjusted to 4.5, ultrasonically dispersed and treated at 60℃ for 30min, filtered and dried to obtain modified polyvinyl alcohol fiber with surface-coated nanocrystal seeds.

[0063] Step 5: Disperse 0.03 parts graphene oxide, 1.2 parts carboxylated styrene-butadiene emulsion (XSBRL), 0.4 parts polycarboxylate superplasticizer, and 0.05 parts sodium gluconate retarder in 40 parts deionized water and perform ultrasonic pre-dispersion for 15 minutes. Then add the dry mix and stir at 300 rpm for 3 minutes; then add modified flax fiber (4.5 parts) and modified polyvinyl alcohol fiber (2 parts), adjust the speed to 600 rpm and continue stirring for 5 minutes to ensure that the fibers do not agglomerate and the slurry is uniform, thus obtaining a mixed slurry.

[0064] Step 6: The mixed slurry is fed into a mold and pressed and dehydrated under a pressure of 20 MPa on a press for 20 minutes to obtain a 12 mm thick board blank. The blank is placed in a pre-curing chamber at 35℃ and 95% relative humidity for 15 hours for pre-curing; then it is transferred to a high-pressure steam curing kettle and cured under high pressure at 1.2 MPa and 190℃ saturated steam for 12 hours. After the reaction is complete, the depressurization rate is controlled at 0.08-0.1 MPa / h, and after reducing to atmospheric pressure, it is taken out and dried at a constant temperature of 60℃ to constant weight to obtain crack-resistant calcium silicate board.

[0065] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that step 1 is omitted and alkyl silica sand in step 2 is replaced with ordinary silica sand.

[0066] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that steps 3 and 4 are omitted, and the modified flax fiber and modified polyvinyl alcohol fiber in step 5 are replaced with ordinary flax fiber and polyvinyl alcohol fiber.

[0067] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that no graphene oxide and carboxylated styrene-butadiene emulsion are added to the mixed slurry in step 4.

[0068] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that graphene oxide is not added to the mixed slurry in step 4.

[0069] Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that no carboxylated styrene-butadiene emulsion is added to the mixed slurry in step 4.

[0070] Performance testing: 1. Flexural Strength Test: The test was conducted according to the national standard GB / T 7019-2014 "Test Methods for Fiber Cement Products". Standard specimens (300mm × 300mm × 12mm) were cut from the cured and dried sample boards of the examples and comparative examples. The three-point bending method was used on a universal testing machine. The support span was set to 200mm, and the loading speed was 5mm / min. The maximum load at specimen fracture was recorded, and the flexural strength (MPa) was calculated using the formula. This index reflects the basic mechanical bearing capacity of the board matrix and reinforcing fibers under combined stress. The test results are shown in Table 1.

[0071] 2. Drying shrinkage rate test: The specimen was immersed in water at (20±2)℃ for 24 hours until saturation, and its initial length L1 was measured. Then, the specimen was placed in an oven at (60±3)℃ and (30±5)% relative humidity to dry to constant weight, and after cooling to room temperature, its dried length L2 was measured. The ratio of shrinkage to original length was calculated. The drying shrinkage rate is a key indicator for evaluating the crack resistance of the board; the smaller the value, the better the volume stability of the board under dehydration conditions. The test results are shown in Table 1.

[0072] 3. Fracture toughness test: A pendulum impact testing machine was used to verify the energy absorption effect of the "flexible bridging and stress regulation" system of this invention. The specimen size was 100mm × 10mm × 12mm, without notches. The energy consumed by the pendulum to break the specimen (kJ / m²) was recorded. 2 Higher fracture toughness means that when the plate is subjected to impact or sudden changes in internal stress, it can dissipate energy through fiber slippage and elastic membrane deformation, and is less prone to brittle cracking. The test results are shown in Table 1.

[0073] 4. Temperature Difference Cracking Resistance Cyclic Test: Simulating a harsh service environment, the sheet material was placed in a high and low temperature cycling test chamber. Each cycle consisted of baking at (80±2)℃ for 6 hours, followed by rapid transfer to freezing at (-20±2)℃ for 6 hours. After 50 consecutive cycles, the surface of the sheet material was observed using a high-magnification magnifying glass to check for microcracks, and the width and number of cracks were recorded. If no obvious cracks were found, the test was deemed "crack-free." This test directly reflects the upper limit of the sheet material's crack resistance under conditions of mismatched thermal shrinkage coefficients. The test results are shown in Table 1.

[0074] Table 1:

[0075] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing crack-resistant calcium silicate board, characterized in that, Includes the following steps: (1) High-purity quartz sand is ball-milled, then soaked in hydrochloric acid solution, washed and dried to obtain pretreated quartz sand; Pretreated quartz sand was mixed with an ethanol / water solution of silane coupling agent, the pH was adjusted to acidic with glacial acetic acid, and the mixture was stirred at a constant temperature, then filtered and dried to obtain alkyl quartz sand. (2) Alkyl silica sand is dry-mixed with metakaolin, silica fume and silicate cement to obtain dry mix; (3) The flax fiber was treated with sodium hydroxide solution, then washed and dried to obtain pretreated flax fiber; Pretreated flax fibers were grafted with hydroxyethyl acrylate under nitrogen protection in the presence of ammonium persulfate as an initiator, and then dried to obtain modified flax fibers. (4) Place the PVA fiber in anhydrous ethanol for ultrasonic cleaning and then dry it to obtain pretreated PVA fiber; Pretreated polyvinyl alcohol fibers were mixed with silane coupling agent KH-560 and nano-silica to obtain modified polyvinyl alcohol fibers. (5) Disperse graphene oxide, carboxylated styrene-butadiene emulsion, water-reducing agent and retarder in deionized water, then add dry mix, stir and mix, then add modified flax fiber and modified polyvinyl alcohol fiber, stir and mix to obtain mixed slurry; (6) The mixed slurry is pressurized to form a blank, and then the blank is pre-cured, high-pressure steam cured, depressurized and dried in sequence to obtain crack-resistant calcium silicate board.

2. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (1), the mass concentration of the hydrochloric acid solution is 2-5%.

3. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (1), the silane coupling agent is silane coupling agent KH-550; The mass ratio of the pretreated quartz sand to the silane coupling agent KH-550 is 55:(0.3~0.8).

4. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (2), the mass ratio of alkyl silica sand, metakaolin, silica fume, and silicate cement is 55:(3-5):(1-3):(30-35).

5. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (3), the mass ratio of pretreated flax fiber to hydroxyethyl acrylate is 5:(1-3).

6. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (4), the mass ratio of pretreated polyvinyl alcohol fiber to silane coupling agent KH-560 is 3:(0.2~0.6).

7. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (4), the mass ratio of pretreated polyvinyl alcohol fiber to nano silica is 3:(1-2).

8. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (5), the mass ratio of graphene oxide to carboxylated styrene-butadiene emulsion is 0.3:(12-16).

9. The method for preparing a crack-resistant calcium silicate board according to claim 1, characterized in that, In step (5), the mass ratio of modified flax fiber to modified polyvinyl alcohol fiber is 4.5:(2-4).

10. A crack-resistant calcium silicate board, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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