Anti-crack concrete slab and preparation method thereof

Abstract

This invention discloses a crack-resistant concrete slab and its preparation method, relating to the field of concrete technology. In preparing the crack-resistant concrete slab, the invention first reacts isophorone diisocyanate with polytetrahydrofuran ether diol, 2,2-dimethylolbutyric acid, 1,4-butanediol, castor oil, pentaerythritol triacrylate, and triethylamine, then adds water to obtain a double-bond modified polyurethane emulsion. Ula grass straw is then treated to obtain Ula grass fiber. Ula grass fiber is grafted with glycidyl methacrylate to obtain modified hollow fiber. Fine aggregate, coarse aggregate, fly ash, cement, water-reducing agent, water, double-bond modified polyurethane emulsion, aluminum acrylate, modified hollow fiber, and initiator are mixed and stirred evenly, poured into a mold, vibrated, and cured to obtain the crack-resistant concrete slab. The crack-resistant concrete slab prepared by this invention has the advantages of good crack resistance, high flexural strength, and high compressive strength.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a crack-resistant concrete slab and its preparation method. Background Technology

[0002] Cement concrete is a widely used and important structural material, extensively applied in major engineering projects such as roads, bridges, and dams. However, the volume shrinkage of cement concrete due to chemical shrinkage caused by cement hydration and drying shrinkage caused by water evaporation is an inherent property. Concrete may shrink and crack under the influence of various factors such as temperature, humidity, and hydration. However, in actual use, due to constraints of the maintenance environment and regulations, concrete foundations are prone to drying shrinkage, which is one of the main reasons for the volumetric instability and cracking of concrete.

[0003] In practical applications, concrete structures are often in a constrained state, closely contacting reinforcing steel, foundations, or adjacent components. This makes them highly susceptible to damage from significant concrete shrinkage. The volume shrinkage of the confined concrete generates shrinkage stress. Furthermore, in engineering applications, curing large volumes of concrete or in challenging environments such as seawater, chemical corrosion, high temperatures, or extreme cold presents significant challenges. After pouring, moisture in the concrete matrix easily evaporates, creating pores within the matrix. These pores generate negative pressure, creating drying shrinkage stress—the driving force for cracking. When this drying shrinkage stress exceeds the tensile strength of the matrix (cracking resistance), cracks will form. Cracks severely impact concrete structures, significantly reducing their load-bearing capacity and exacerbating leakage. When water or other corrosive media penetrate the concrete through these cracks, it can lead to steel corrosion and accelerate the deterioration of the concrete structure. According to relevant statistics, more than 80% of concrete cracks are caused by shrinkage deformation. Concrete cracks seriously affect the service safety, reliability and service life of concrete structures. Therefore, reducing the shrinkage stress of concrete, i.e. reducing the driving force of concrete cracking, and increasing the tensile strength of concrete, i.e. increasing the resistance to cracking, are the keys to improving the crack resistance of the concrete matrix. This is of great significance for improving the crack resistance of concrete. Summary of the Invention

[0004] The purpose of this invention is to provide a crack-resistant concrete slab and its preparation method to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A crack-resistant concrete slab is made by mixing fine aggregate, coarse aggregate, fly ash, cement, water-reducing agent, water, double bond modified polyurethane emulsion, aluminum acrylate, modified hollow fiber, and initiator evenly, pouring the mixture into a mold, vibrating it, and curing it to obtain the crack-resistant concrete slab.

[0007] The double bond modified polyurethane emulsion is prepared by reacting isophorone diisocyanate with polytetrahydrofuran ether diol, 2,2-dimethylolbutyric acid, 1,4-butanediol, castor oil, pentaerythritol triacrylate, and triethylamine, followed by adding water.

[0008] The modified hollow fiber is obtained by grafting glycidyl methacrylate onto Ula grass fiber.

[0009] The Ula grass fiber is obtained by combining the processing of Ula grass straw.

[0010] As an optimization, the combined treatment involves sequentially treating the Ula grass straw in a pretreatment solution, an enzyme treatment solution, a degumming treatment solution, and an alkaline treatment solution.

[0011] A method for preparing crack-resistant concrete slabs includes the following preparation steps:

[0012] (1) Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol are mixed at a molar ratio of isocyanate group to hydroxyl group of 1:(0.5~0.6). Dibutyltin dilaurate is added at a mass of 0.02~0.03 times that of isophorone diisocyanate. The mixture is stirred at 80~85℃ and 300~400rpm for 2~2.5h. 2,2-Dimethylolbutyric acid is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:(0.3~0.4). The mixture is stirred at 75~80℃ and 300~400rpm for 2~2.5h. 1,4-Butanediol is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:(0.5~0.6). The mixture is stirred at 75~80℃ and 350~450rpm for 2.5~3h. The mixture is stirred at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:(0.5~0.6). Add castor oil (6-0.7%), then add acetone in an amount of 2-2.5 times the mass of isophorone diisocyanate. Stir and react at 75-80℃ and 400-500 rpm for 1.5-2 hours. Add pentaerythritol triacrylate at a molar ratio of 1:(1-1.1) of the remaining isocyanate groups and hydroxyl groups. Stir and react at 75-80℃ and 400-500 rpm for 1.5-2 hours. Cool to 30-40℃. Add triethylamine at a molar ratio of 1:(1-1.02) of 2,2-dimethylolbutyric acid and triethylamine. Stir and react at 30-40℃ and 400-500 rpm for 30-40 minutes. Add deionized water. Stir at 1200-1300 rpm for 30-40 minutes at room temperature. Remove acetone by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 30%-35%.

[0013] (2) After washing and drying the Ula grass straw, add it to the pretreatment solution at a bath ratio of 1:(40~50)g / ml. Stir at 90~95℃ and 30~40rpm for 30~40min. Remove and wash with deionized water until neutral. Add it to the enzyme treatment solution at a bath ratio of 1:(40~50)g / ml. Stir at 45~50℃ and pH 4.5~5 and 40~50rpm for 3~4h. Remove and transfer to deionized water. Stir at 80~90℃ and 80~90rpm for 20~3 hours. 0 min, take out and wash with deionized water until neutral, add to degumming treatment solution at a bath ratio of 1:(40~50)g / ml, stir at 90~95℃ and 30~40rpm for 1.5~2h, take out and wash with deionized water until neutral, add to alkali treatment solution at a bath ratio of 1:(40~50)g / ml, stir at 75~80℃ and 30~40rpm for 30~40min, take out and wash with deionized water until neutral, air dry, cut into lengths of 3~5mm to obtain Ula grass fiber;

[0014] (3) Under a nitrogen atmosphere, 2-3 parts of Ula grass fiber, 0.12-0.18 parts of glycidyl methacrylate, 0.01-0.012 parts of sodium bicarbonate, 0.0001-0.00015 parts of p-hydroxyanisole, 15-18 parts of acetone and 35-40 parts of deionized water are mixed evenly by mass. The mixture is stirred at 60-65℃ and 100-150 rpm for 1.5-2 hours. After filtration and washing, the mixture is vacuum dried at 60-70℃ for 10-12 hours to obtain modified hollow fiber.

[0015] (4) By mass, add 650-700 parts of fine aggregate and 1000-1100 parts of coarse aggregate to the mixer and mix at 5-7 rpm for 3-4 minutes. Add 60-70 parts of fly ash and 350-400 parts of cement and mix for 1-2 minutes. Add 100-120 parts of water and 4-5 parts of water-reducing agent and mix for 3-4 minutes. Add 40-50 parts of double bond modified polyurethane emulsion and 5-8 parts of aluminum acrylate and mix for 1-2 minutes. Add 15-20 parts of modified hollow fiber in 5 equal portions, once every 20 seconds, while keeping the mixture stirred. After adding the fiber, continue stirring for 1 minute. Add 0.8-0.9 parts of initiator and stir for 2-3 minutes. Pour the mixture into the mold, vibrate for 1 minute, fill the mold, continue vibrating for 1 minute, let stand for 3-4 minutes, smooth the surface, cure at room temperature for 24 hours, remove the mold, and cure naturally for 28 days to obtain crack-resistant concrete slabs.

[0016] As an optimization, the pretreatment solution in step (2) contains 6~8 g / L sodium hydroxide and 0.4~0.5 g / L urea.

[0017] As an optimization, the enzyme treatment solution in step (2) contains 0.8~1g / L pectinase and 0.4~0.5g / L penetrant.

[0018] As an optimization, the degumming solution in step (2) contains 7~9 g / L sodium hydroxide and 4~5 g / L hydrogen peroxide.

[0019] As an optimization, the alkaline treatment solution in step (2) contains 10~20g / L sodium hydroxide.

[0020] As an optimization, the curing conditions described in step (4) are 20℃±5℃ and 55%~65% relative humidity before demolding, and 20℃±2℃ and 95%~99% relative humidity after demolding.

[0021] As an optimization, the initiator in step (4) is a redox initiator, including sodium persulfate and sodium sulfite, and the molar ratio of sodium persulfate to sodium sulfite is 2:1.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0023] In preparing crack-resistant concrete slabs, this invention first reacts isophorone diisocyanate with polytetrahydrofuran ether diol, 2,2-dimethylolbutyric acid, 1,4-butanediol, castor oil, and pentaerythritol triacrylate, then adds water to obtain a double-bond modified polyurethane emulsion. Ula grass straw is then treated sequentially in a pretreatment solution, an enzyme treatment solution, a degumming treatment solution, and an alkali treatment solution to obtain Ula grass fiber. Ula grass fiber is grafted with glycidyl methacrylate to obtain modified hollow fiber. Fine aggregate, coarse aggregate, fly ash, cement, water-reducing agent, water, double-bond modified polyurethane emulsion, aluminum acrylate, modified hollow fiber, and initiator are mixed and stirred evenly, then poured into a mold and vibrated. After curing, crack-resistant concrete slabs are obtained.

[0024] First, a double-bond modified polyurethane emulsion was prepared by reacting isophorone diisocyanate with polytetrahydrofuran ether diol, 2,2-dimethylolbutyric acid, 1,4-butanediol, castor oil, pentaerythritol triacrylate, and triethylamine, followed by the addition of water. Anionic hydrophilic monomer 2,2-dimethylolbutyric acid was added to the double-bond modified polyurethane emulsion. After neutralization with triethylamine, it became an effective hydrophilic group, stabilizing the emulsion. Simultaneously, castor oil, containing multifunctional groups with double bonds, was added as a crosslinking agent. This introduced double bonds into the polyurethane segments, allowing for a small amount of crosslinking and forming a loose crosslinked network. Since the double bonds are present at the nodes of the crosslinked network, subsequent polymerization can form a more three-dimensional polymer network and play a bridging role, improving the crack resistance of concrete. Finally, pentaerythritol triacrylate was used for end-capping, introducing more double bonds at the ends of the polyurethane segments and enhancing the polymerization ability of the polyurethane segments.

[0025] Secondly, Ula grass straw is sequentially treated in a pretreatment solution, an enzyme treatment solution, a degumming treatment solution, and an alkaline treatment solution to obtain Ula grass fiber. In the pretreatment solution, the first layer of pectin, lignin, and hemicellulose is removed under the action of alkali and urea. Furthermore, urea decomposes in a high-temperature alkaline environment to produce ammonia and carbon dioxide. The release of these gases helps to break down the structure of the Ula grass straw, making it looser and allowing the active ingredients in subsequent treatment solutions to penetrate deep into the straw and exert their effects, thus improving the treatment efficiency. Subsequently, a combination of biological and chemical methods is used to remove most of the lignin, pectin, and hemicellulose from the Ula grass straw, while preserving as much of the Ula grass fiber structure as possible to improve its strength. Finally, in the final alkaline treatment step, the last trace of lignin, pectin, and hemicellulose is removed again, further improving the strength of the Ula grass fiber and reducing the number of alkaline erosion sites, resulting in a more robust Ula grass fiber. In alkaline concrete environments, fibers can better exert their reinforcing effect and avoid failure caused by alkali erosion. Subsequently, modified hollow fibers are prepared by grafting glycidyl methacrylate onto Ula grass fibers. The epoxy groups on glycidyl methacrylate react with the hydroxyl groups on Ula grass fibers, thereby grafting onto the Ula grass fibers and introducing double bonds into the Ula grass fibers, allowing the Ula grass fibers to participate in the formation of copolymer networks. At the same time, the hollow structure of Ula grass itself is preserved in each treatment. The hollow structure of Ula grass fibers, while possessing high strength, can effectively relieve internal stress and prevent crack propagation when incorporated into concrete. Furthermore, a three-dimensional interpenetrating network structure of "fiber-polymer network-inorganic matrix" is formed during copolymerization. After participating in the construction of the copolymer network, the fiber interface pull-out effect is also improved, which can more effectively improve crack resistance, flexural strength, and compressive strength.

[0026] Finally, fine aggregate, coarse aggregate, fly ash, cement, water-reducing agent, water, double-bond modified polyurethane emulsion, aluminum acrylate, modified hollow fiber, and initiator are mixed evenly and poured into a mold for vibration. After curing, crack-resistant concrete slabs are obtained. The double-bond modified polyurethane emulsion contains a micro-crosslinked polymer network and polymerizable double bonds. These bonds, along with modified hollow fiber and aluminum acrylate, polymerize under the action of a redox initiator, forming a three-dimensional polymer-fiber crosslinked network. The backbone of this crosslinked network contains hydroxyl and carboxyl groups, which can adhere to and interweave with the concrete through hydrogen bonds and metal coordination bonds. Within the inorganic matrix, aluminum acrylate effectively improves crack resistance, flexural strength, and compressive strength. It also contains aluminum ions, which are released during cement hydration and react with calcium hydroxide, a cement hydration product, to form a small amount of fibrous expanded ettringite. This reacts with the CSH gel formed during cement hydration to form a three-dimensional continuous skeleton, filling concrete pores while providing micro-expansion. This refines the early-stage microstructure of concrete and reduces drying shrinkage in the later stages of hardening, thus improving crack resistance, compressive strength, and flexural strength. During the reaction, the aluminum ions also consume a portion of the calcium hydroxide. This invention slightly inhibits early hydration and reduces the calcium hydroxide content, avoiding alkaline erosion of the modified hollow fibers by high-concentration calcium hydroxide, thus protecting the modified hollow fibers. Simultaneously, the invention copolymerizes the polymer network during concrete hydration. Under the action of a redox initiator, the polyurethane segments, modified hollow fibers, and aluminum acrylate in the double-bond modified polyurethane emulsion can complete the formation of the polymer network within 1-2 hours, adsorbing, entangled, and coating the cement particles. This hinders the contact between water and minerals such as tricalcium silicate and dicalcium silicate, significantly prolonging the induction period and reducing the early exothermic rate. Furthermore, the formation of the polymer network improves... The water retention of the cement matrix is ​​improved, reducing water evaporation and thus inhibiting the formation of plastic shrinkage cracks, thereby improving crack resistance. At the same time, this inhibition only delays the peak hydration without reducing the final degree of hydration. Due to the support of the three-dimensional continuous skeleton formed by aluminum ions and CSH gel, as well as the presence of fiber-polymer network, the early strength of cement concrete will not decrease too much. The crack-resistant concrete slabs prepared in the end have excellent crack resistance under the support of the three-dimensional continuous skeleton and the three-dimensional interpenetrating network structure of "fiber-polymer network-inorganic matrix". The compressive strength and flexural strength are also improved. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] The raw material information used in all the following examples and comparative examples is as follows:

[0029] Polytetrahydrofuran ether diol: weight average molecular weight of 2000, purchased from Guangzhou Haoyi New Material Technology Co., Ltd.

[0030] Castor oil: purchased from Nantong Runfeng Petrochemical Co., Ltd.;

[0031] Ula grass straw: purchased from Jilin Beiguo Ula Grass Products Co., Ltd.;

[0032] Fine aggregate: natural river sand, conforming to the gradation requirements of Zone 2 sand in GB / T 14684-2022;

[0033] Coarse aggregate: graded crushed stone, apparent density 2759 kg / m³ 3 Bulk density 1512.66 kg / m³ 3 Particle size 10~20mm, purchased from Shandong Luqiao Building Materials Co., Ltd.;

[0034] Fly ash: Grade 1 ash, purchased from Jining Hengzhi New Building Materials Co., Ltd.;

[0035] Cement: P·Ⅱ 52.5R Portland cement, purchased from Anhui Conch Cement Co., Ltd.;

[0036] Water-reducing agent: Polycarboxylate superplasticizer, purchased from Shandong Yuncheng Huihuang New Building Materials Technology Co., Ltd.;

[0037] Initiator: Redox initiator, including sodium persulfate and sodium sulfite, with a molar ratio of sodium persulfate to sodium sulfite of 2:1;

[0038] Pretreatment solution: contains 7 g / L sodium hydroxide and 0.45 g / L urea;

[0039] Enzyme treatment solution: contains 0.9 g / L pectinase and 0.45 g / L penetrant;

[0040] Degumming solution: contains 8 g / L sodium hydroxide and 4.5 g / L hydrogen peroxide;

[0041] Alkali treatment solution: contains 15 g / L sodium hydroxide;

[0042] Penetrant: JFC-1 penetrant, purchased from Anyi Chemical (Jiangsu) Co., Ltd.;

[0043] Pectinase: Model FDY-2212, enzyme activity 60000u, purchased from Xiasheng (Beijing) Biotechnology Development Co., Ltd.

[0044] Unless otherwise specified in the test requirements, all the following examples and comparative examples were maintained under the following conditions: 20°C and 60% relative humidity before demolding, and 20°C and 95% relative humidity after demolding.

[0045] Example 1:

[0046] A method for preparing crack-resistant concrete slabs, the method comprising the following preparation steps:

[0047] (1) Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol were mixed at a molar ratio of isocyanate groups to hydroxyl groups of 1:0.5. Dibutyltin dilaurate was added at 0.02 times the mass of isophorone diisocyanate. The mixture was stirred at 80°C and 300 rpm for 2.5 h. 2,2-dimethylolbutyric acid was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.3. The mixture was stirred at 75°C and 300 rpm for 2.5 h. 1,4-butanediol was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.5. The mixture was stirred at 75°C and 350 rpm for 3 h. The mixture was then stirred at the remaining isocyanate groups to hydroxyl groups for 3 h. Castor oil was added at a molar ratio of 1:0.6, followed by acetone at twice the mass of isophorone diisocyanate. The mixture was stirred at 75°C and 400 rpm for 2 hours. Pentaerythritol triacrylate was added at a molar ratio of 1:1 for the remaining isocyanate groups and hydroxyl groups. The mixture was stirred at 75°C and 400 rpm for 2 hours. After cooling to 30°C, triethylamine was added at a molar ratio of 1:1 for 2,2-dimethylolbutyric acid and triethylamine. The mixture was stirred at 30°C and 400 rpm for 40 minutes. Deionized water was added, and the mixture was stirred at 1200 rpm for 40 minutes at room temperature. Acetone was removed by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 30%.

[0048] (2) After washing and drying the Ula grass straw, add it to the pretreatment solution at a bath ratio of 1:40 g / ml. Stir at 90℃ and 30 rpm for 40 min. Take it out and wash it with deionized water until neutral. Add it to the enzyme treatment solution at a bath ratio of 1:40 g / ml. Stir at 45℃ and pH 4.5 at 40 rpm for 4 h. Take it out and transfer it to deionized water. Stir at 80℃ and 80 rpm for 30 min. Take it out and wash it with deionized water until neutral. Add it to the degumming treatment solution at a bath ratio of 1:40 g / ml. Stir at 90℃ and 30 rpm for 2 h. Take it out and wash it with deionized water until neutral. Add it to the alkali treatment solution at a bath ratio of 1:40 g / ml. Stir at 75℃ and 30 rpm for 40 min. Take it out and wash it with deionized water until neutral. Dry it and cut it into lengths of 3 mm to obtain Ula grass fiber.

[0049] (3) Under a nitrogen atmosphere, 2 parts of Ula grass fiber, 0.12 parts of glycidyl methacrylate, 0.01 parts of sodium bicarbonate, 0.0001 parts of p-hydroxyanisole, 15 parts of acetone and 35 parts of deionized water were mixed evenly by mass. The mixture was stirred at 60°C and 100 rpm for 2 hours, filtered, washed and vacuum dried at 60°C for 12 hours to obtain modified hollow fiber.

[0050] (4) By mass, add 650 parts of fine aggregate and 1000 parts of coarse aggregate to the mixer, mix at 5 rpm for 4 min, add 70 parts of fly ash and 350 parts of cement, mix for 1 min, add 100 parts of water and 4 parts of water-reducing agent, mix for 3 min, add 50 parts of double bond modified polyurethane emulsion and 5 parts of aluminum acrylate, mix for 1 min, add 15 parts of modified hollow fiber evenly in 5 portions, add once every 20 s, keep stirring during the process, continue stirring for 1 min after adding, add 0.8 parts of initiator, mix for 2 min, pour into the mold, vibrate for 1 min, fill the mold, continue vibrating for 1 min, let stand for 3 min, smooth, cure at room temperature for 24 h, remove the mold, and cure naturally for 28 days to obtain crack-resistant concrete slabs.

[0051] Example 2:

[0052] A method for preparing crack-resistant concrete slabs, the method comprising the following preparation steps:

[0053] (1) Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol were mixed at a molar ratio of isocyanate groups to hydroxyl groups of 1:0.55. Dibutyltin dilaurate was added at 0.025 times the mass of isophorone diisocyanate. The mixture was stirred at 80°C and 350 rpm for 2 h. 2,2-Dimethylolbutyric acid was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.35. The mixture was stirred at 80°C and 350 rpm for 2 h. 1,4-Butanediol was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.55. The mixture was stirred at 75°C and 400 rpm for 2.5 h. The mixture was then stirred at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.35. Add 0.65g of castor oil, then add acetone in an amount twice the mass of isophorone diisocyanate, and stir at 75°C and 450rpm for 1.5h. Add pentaerythritol triacrylate in a molar ratio of 1:1.05 of the remaining isocyanate groups and hydroxyl groups, and stir at 75°C and 450rpm for 1.5h. Cool to 35°C, add triethylamine in a molar ratio of 1:1.01 of 2,2-dimethylolbutyric acid and triethylamine, and stir at 35°C and 450rpm for 35min. Add deionized water, stir at 1250rpm for 35min at room temperature, and remove acetone by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 32%.

[0054] (2) After washing and drying the Ula grass straw, add it to the pretreatment solution at a bath ratio of 1:45 g / ml. Stir at 90℃ and 35 rpm for 35 min. Take it out and wash it with deionized water until neutral. Add it to the enzyme treatment solution at a bath ratio of 1:45 g / ml. Stir at 45℃ and pH 5 for 3.5 h. Take it out and transfer it to deionized water. Stir at 85℃ and 85 rpm for 25 min. Take it out and wash it with deionized water until neutral. Add it to the degumming treatment solution at a bath ratio of 1:45 g / ml. Stir at 90℃ and 35 rpm for 1.5 h. Take it out and wash it with deionized water until neutral. Add it to the alkali treatment solution at a bath ratio of 1:45 g / ml. Stir at 75℃ and 35 rpm for 35 min. Take it out and wash it with deionized water until neutral. Dry it and cut it into lengths of 4 mm to obtain Ula grass fiber.

[0055] (3) Under a nitrogen atmosphere, 2.5 parts of Ula grass fiber, 0.15 parts of glycidyl methacrylate, 0.011 parts of sodium bicarbonate, 0.00012 parts of p-hydroxyanisole, 16.5 parts of acetone and 37.5 parts of deionized water were mixed evenly by mass, stirred at 125 rpm for 1.5 h at 60 °C, filtered, washed and vacuum dried at 65 °C for 11 h to obtain modified hollow fiber;

[0056] (4) By mass, add 675 parts fine aggregate and 1050 parts coarse aggregate to the mixer and mix at 6 rpm for 3.5 min. Add 65 parts fly ash and 375 parts cement and mix for 1.5 min. Add 110 parts water and 4.5 parts water-reducing agent and mix for 3.5 min. Add 45 parts double bond modified polyurethane emulsion and 6.5 parts aluminum acrylate and mix for 1.5 min. Add 17.5 parts modified hollow fiber evenly in 5 portions, one portion every 20 s, while keeping the mixture stirred. After adding the fiber, continue stirring for 1 min. Add 0.85 parts initiator and stir for 2.5 min. Pour the mixture into the mold, vibrate for 1 min, fill the mold, continue vibrating for 1 min, let stand for 3.5 min, smooth the surface, cure at room temperature for 24 h, remove the mold, and cure naturally for 28 days to obtain crack-resistant concrete slabs.

[0057] Example 3:

[0058] A method for preparing crack-resistant concrete slabs, the method comprising the following preparation steps:

[0059] (1) Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol were mixed at a molar ratio of isocyanate groups to hydroxyl groups of 1:0.6. Dibutyltin dilaurate was added at 0.03 times the mass of isophorone diisocyanate. The mixture was stirred at 85°C and 400 rpm for 2 h. 2,2-Dimethylolbutyric acid was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.4. The mixture was stirred at 80°C and 400 rpm for 2 h. 1,4-Butanediol was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0.6. The mixture was stirred at 80°C and 450 rpm for 2.5 h. The mixture was then stirred at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:0. 7. Castor oil was added, followed by acetone in an amount 2.5 times the mass of isophorone diisocyanate. The mixture was stirred at 80°C and 500 rpm for 1.5 h. Pentaerythritol triacrylate was added at a molar ratio of 1:1.1 for the remaining isocyanate groups and hydroxyl groups. The mixture was stirred at 80°C and 500 rpm for 1.5 h. The mixture was cooled to 40°C. Triethylamine was added at a molar ratio of 1:1.02 for 2,2-dimethylolbutyric acid and triethylamine. The mixture was stirred at 40°C and 500 rpm for 30 min. Deionized water was added, and the mixture was stirred at 1300 rpm for 30 min at room temperature. Acetone was removed by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 35%.

[0060] (2) After washing and drying the Ula grass straw, add it to the pretreatment solution at a bath ratio of 1:50 g / ml. Stir at 95℃ and 40 rpm for 30 min. Take it out and wash it with deionized water until neutral. Add it to the enzyme treatment solution at a bath ratio of 1:50 g / ml. Stir at 50℃ and pH 5 for 3 h. Take it out and transfer it to deionized water. Stir at 90℃ and 90 rpm for 30 min. Take it out and wash it with deionized water until neutral. Add it to the degumming treatment solution at a bath ratio of 1:50 g / ml. Stir at 95℃ and 40 rpm for 1.5 h. Take it out and wash it with deionized water until neutral. Add it to the alkali treatment solution at a bath ratio of 1:50 g / ml. Stir at 80℃ and 40 rpm for 30 min. Take it out and wash it with deionized water until neutral. Dry it and cut it into 5 mm lengths to obtain Ula grass fiber.

[0061] (3) Under a nitrogen atmosphere, 3 parts of Ula grass fiber, 0.18 parts of glycidyl methacrylate, 0.012 parts of sodium bicarbonate, 0.00015 parts of p-hydroxyanisole, 18 parts of acetone and 40 parts of deionized water were mixed evenly by mass. The mixture was stirred at 65°C and 150 rpm for 1.5 h, filtered, washed and vacuum dried at 70°C for 10 h to obtain modified hollow fiber.

[0062] (4) By mass, add 700 parts fine aggregate and 1100 parts coarse aggregate to the mixer, mix at 7 rpm for 3 min, add 60 parts fly ash and 400 parts cement, mix for 2 min, add 120 parts water and 5 parts water-reducing agent, mix for 4 min, add 40 parts double bond modified polyurethane emulsion and 8 parts aluminum acrylate, mix for 2 min, add 20 parts modified hollow fiber evenly in 5 portions, add once every 20 s, keep stirring during the process, continue stirring for 1 min after adding, add 0.9 parts initiator, mix for 3 min, pour into the mold, vibrate for 1 min, fill the mold, continue vibrating for 1 min, let stand for 4 min, smooth, cure at room temperature for 24 h, remove the mold, and cure naturally for 28 days to obtain crack-resistant concrete slabs.

[0063] Comparative Example 1:

[0064] The difference between the preparation method of the crack-resistant concrete slab in Comparative Example 1 and Example 2 lies in the different step (1). Step (1) is modified as follows: Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol are mixed at a molar ratio of isocyanate group to hydroxyl group of 1:0.55. Dibutyltin dilaurate is added at 0.025 times the mass of isophorone diisocyanate. The mixture is stirred and reacted at 80°C and 350 rpm for 2 hours. 2,2-Dimethylolbutyric acid is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:0.35. The mixture is stirred and reacted at 80°C and 350 rpm for 2 hours. 2,2-Dimethylolbutyric acid is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:0.85. Add 1,4-butanediol and react with stirring at 75°C and 400 rpm for 2.5 h. Add acetone in an amount twice the mass of isophorone diisocyanate. Add pentaerythritol triacrylate at a molar ratio of 1:1.05 for the remaining isocyanate groups and hydroxyl groups. React with stirring at 75°C and 450 rpm for 1.5 h. Cool to 35°C. Add triethylamine at a molar ratio of 1:1.01 for 2,2-dimethylolbutyric acid and triethylamine. React with stirring at 35°C and 450 rpm for 35 min. Add deionized water and stir at 1250 rpm for 35 min at room temperature. Remove acetone by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 32%. The remaining steps are the same as in Example 2.

[0065] Comparative Example 2:

[0066] The difference between the preparation method of the crack-resistant concrete slab in Comparative Example 2 and that in Example 2 lies in the difference in step (1). Step (1) is modified as follows: Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol are mixed at a molar ratio of isocyanate group to hydroxyl group of 1:0.55. Dibutyltin dilaurate is added at 0.025 times the mass of isophorone diisocyanate. The mixture is stirred at 80°C and 350 rpm for 2 hours. 2,2-Dimethylolbutyric acid is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:0.35. The mixture is stirred at 80°C and 350 rpm for 2 hours. 1,4-Butanediol is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:0.55. The mixture is stirred at 75°C and 400 rpm. The reaction mixture was stirred for 2.5 h. Castor oil was added at a molar ratio of 1:0.65 for the remaining isocyanate groups to hydroxyl groups, followed by acetone at twice the mass of isophorone diisocyanate. The mixture was stirred at 75°C and 450 rpm for 1.5 h. Ethanol was added at a molar ratio of 1:1.05 for the remaining isocyanate groups to hydroxyl groups, and the mixture was stirred at 75°C and 450 rpm for 1.5 h. The mixture was then cooled to 35°C. Triethylamine was added at a molar ratio of 1:1.01 for 2,2-dimethylolbutyric acid to triethylamine, and the mixture was stirred at 35°C and 450 rpm for 35 min. Deionized water was added, and the mixture was stirred at 1250 rpm for 35 min at room temperature. Acetone was removed by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 32%. The remaining steps were the same as in Example 2.

[0067] Comparative Example 3:

[0068] The difference between the preparation method of the crack-resistant concrete slab in Comparative Example 3 and Example 2 lies in the different step (1). Step (1) is modified as follows: Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol are mixed at a molar ratio of isocyanate group to hydroxyl group of 1:0.55. Dibutyltin dilaurate is added at 0.025 times the mass of isophorone diisocyanate. The mixture is stirred and reacted at 80°C and 350 rpm for 2 hours. 2,2-Dimethylolbutyric acid is added at a molar ratio of the remaining isocyanate group to hydroxyl group of 1:0.35. The mixture is stirred and reacted at 80°C and 350 rpm for 2 hours. Add 1,4-butanediol to 85g of water and stir at 75°C and 400rpm for 2.5h. Then add acetone in an amount twice the mass of isophorone diisocyanate, and add ethanol at a molar ratio of 1:1.05 for the remaining isocyanate groups and hydroxyl groups. Stir at 75°C and 450rpm for 1.5h. Cool to 35°C, add triethylamine at a molar ratio of 1:1.01 for 2,2-dimethylolbutyric acid and triethylamine, and stir at 35°C and 450rpm for 35min. Add deionized water, and stir at 1250rpm for 35min at room temperature. Remove acetone by vacuum distillation to obtain a double-bond modified polyurethane emulsion with a solid content of 32%. The remaining steps are the same as in Example 2.

[0069] Comparative Example 4:

[0070] The difference between the preparation method of the crack-resistant concrete slab in Comparative Example 4 and Example 2 lies in step (2). Step (2) is modified as follows: After washing and drying the Ula grass straw, add it to the pretreatment solution at a bath ratio of 1:45 g / ml. Stir at 90℃ and 35 rpm for 35 min. Take it out and wash it with deionized water until neutral. Add it to the enzyme treatment solution at a bath ratio of 1:45 g / ml. Stir at 45℃ and pH 5 for 3.5 h. Take it out and transfer it to deionized water. Stir at 85℃ and 85 rpm for 25 min. Take it out and wash it with deionized water until neutral. Add it to the degumming treatment solution at a bath ratio of 1:45 g / ml. Stir at 90℃ and 35 rpm for 1.5 h. Take it out and wash it with deionized water until neutral. Dry it and cut it into 4 mm lengths to obtain Ula grass fibers. The remaining steps are the same as in Example 2.

[0071] Comparative Example 5:

[0072] The preparation method of the crack-resistant concrete slab in Comparative Example 5 differs from that in Example 2 in that step (3) is omitted, and step (4) is modified as follows: 675 parts fine aggregate and 1050 parts coarse aggregate are added to a mixer by mass, and mixed at 6 rpm for 3.5 min. 65 parts fly ash and 375 parts cement are added, and mixed for 1.5 min. 110 parts water and 4.5 parts water-reducing agent are added, and mixed for 3.5 min. 45 parts double-bond modified polyurethane emulsion and 6.5 parts aluminum acrylate are added, and mixed for 1.5 min. 17.5 parts Ula grass fiber are added evenly in 5 portions, one every 20 s, while maintaining mixing. After the addition is complete, mixing continues for 1 min. 0.85 parts initiator are added, and mixing continues for 2.5 min. The mixture is poured into a mold, vibrated for 1 min, and then the mold is filled. Vibration continues for 1 min. After standing for 3.5 min, the mixture is smoothed. It is cured at room temperature for 24 h, demolded, and naturally cured for 28 days to obtain the crack-resistant concrete slab. The remaining steps are the same as in Example 2.

[0073] Comparative Example 6:

[0074] The preparation method of the crack-resistant concrete slab in Comparative Example 6 differs from that in Example 2 in that step (1) is omitted, and step (4) is modified as follows: 675 parts fine aggregate and 1050 parts coarse aggregate are added to a mixer by mass, and mixed at 6 rpm for 3.5 min. 65 parts fly ash and 375 parts cement are added and mixed for 1.5 min. 150 parts water and 4.5 parts water-reducing agent are added and mixed for 3.5 min. 6.5 parts aluminum acrylate are added and mixed for 1.5 min. 17.5 parts modified hollow fiber are added evenly in 5 portions, one every 20 s, while maintaining mixing. After the addition is complete, mixing continues for 1 min. 0.85 parts initiator are added and mixed for 2.5 min. The mixture is poured into a mold, vibrated for 1 min, and then the mold is filled. Vibration continues for 1 min. After standing for 3.5 min, the mixture is smoothed and cured at room temperature for 24 h. The mold is then removed, and the mixture is naturally cured for 28 days to obtain the crack-resistant concrete slab. The remaining steps are the same as in Example 2.

[0075] Comparative Example 7:

[0076] The preparation method of the crack-resistant concrete slab in Comparative Example 7 differs from that in Example 2 in that steps (2) and (3) are omitted, and step (4) is modified as follows: 675 parts fine aggregate and 1050 parts coarse aggregate are added to a mixer by mass, and mixed at 6 rpm for 3.5 min. 65 parts fly ash and 375 parts cement are added, and mixed for 1.5 min. 110 parts water and 4.5 parts water-reducing agent are added, and mixed for 3.5 min. 45 parts double-bond modified polyurethane emulsion and 6.5 parts aluminum acrylate are added, and mixed for 1.5 min. 0.85 parts initiator are added, and mixed for 2.5 min. The mixture is poured into a mold, vibrated for 1 min, and then the mold is filled. Vibration continues for 1 min. After standing for 3.5 min, the mixture is smoothed, cured at room temperature for 24 h, demolded, and naturally cured for 28 days to obtain the crack-resistant concrete slab. The remaining steps are the same as in Example 2.

[0077] Comparative Example 8:

[0078] The difference between the preparation method of the crack-resistant concrete slab in Comparative Example 8 and Example 2 lies in step (4). Step (4) is modified as follows: 675 parts fine aggregate and 1050 parts coarse aggregate are added to a mixer by mass, and mixed at 6 rpm for 3.5 min. 65 parts fly ash and 375 parts cement are added and mixed for 1.5 min. 110 parts water and 4.5 parts water-reducing agent are added and mixed for 3.5 min. 45 parts double-bond modified polyurethane emulsion are added and mixed for 1.5 min. 17.5 parts modified hollow fiber are added evenly in 5 portions, one every 20 s, while maintaining stirring. After the addition is complete, stirring is continued for 1 min. 0.85 parts initiator are added and stirred for 2.5 min. The mixture is poured into a mold, vibrated for 1 min, and then the mold is filled. Vibration is continued for 1 min. After standing for 3.5 min, the mixture is smoothed. It is cured at room temperature for 24 h, demolded, and naturally cured for 28 days to obtain the crack-resistant concrete slab. The remaining steps are the same as in Example 2.

[0079] Comparative Example 9:

[0080] The difference between the preparation method of the crack-resistant concrete slab in Comparative Example 9 and Example 2 lies in step (4). Step (4) is modified as follows: 45 parts by mass of double-bond modified polyurethane emulsion, 6.5 parts of aluminum acrylate, 17.5 parts of modified hollow fiber, and 0.85 parts of initiator are mixed evenly and stirred at 50 rpm for 30 min to obtain a polymer emulsion. 675 parts of fine aggregate and 1050 parts of coarse aggregate are added to a mixer and mixed at 6 rpm for 3.5 min. 65 parts of fly ash and 375 parts of cement are added and stirred for 1.5 min. 110 parts of water and 4.5 parts of water-reducing agent are added and stirred for 3.5 min. The polymer emulsion is added and stirred for 2.5 min. The mixture is poured into a mold, vibrated for 1 min, and then the mold is filled. Vibration continues for 1 min. After standing for 3.5 min, the mixture is smoothed and cured at room temperature for 24 h. The mold is then removed, and the mixture is naturally cured for 28 days to obtain the crack-resistant concrete slab. The remaining steps are the same as in Example 2.

[0081] Test Example 1:

[0082] Mechanical properties and crack resistance testing: The compressive strength, flexural strength, and cracking index of the prepared crack-resistant concrete slabs are tested to characterize their mechanical strength and crack resistance. The specific test methods are as follows:

[0083] Compressive strength: The compressive strength of the prepared crack-resistant concrete slabs was tested according to the test method for compressive strength in GB / T 50081-2019. The specimen size was set to 150mm×150mm×150mm, the loading rate was 2mm / min, and the slabs were cured according to the standard requirements for 3 days and 28 days. The compressive strength of the crack-resistant concrete slabs for the two curing periods was tested. Five specimens were tested in parallel for each group, and the average value was recorded.

[0084] Flexural strength: The flexural strength of the prepared crack-resistant concrete slabs was tested according to the test method for flexural strength in GB / T 50081-2019. The specimen size was set to 150mm×150mm×150mm, the loading rate was 2mm / min, and the flexural strength was cured according to the standard requirements for 3 days and 28 days. The flexural strength of the crack-resistant concrete slabs for the two curing periods was tested. Five specimens were tested in parallel for each group, and the average value was recorded.

[0085] Cracking Index: The cracking index of the prepared crack-resistant concrete slabs was tested according to the test method in standard GB / T 29417-2012. First, the drying shrinkage stress and splitting tensile strength of the crack-resistant concrete slabs were tested. Then, the cracking index was calculated according to the formula in the standard. The specimen size for the drying shrinkage stress test was set to 100mm×100mm×550mm as required by the standard. The corresponding specimen size for the splitting tensile strength test was set to 100mm×100mm×100mm as required by the standard. The specimens were cured according to the standard requirements for 28 days. Five specimens were tested in parallel in each group, and the average value was recorded.

[0086] The results are shown in Table 1.

[0087] Table 1:

[0088] ;

[0089] A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-9 in Table 1 reveals that the crack-resistant concrete slabs prepared by the present invention have high compressive strength, flexural strength and good crack resistance.

[0090] By comparing the data in the table, the data from Comparative Examples 1 to 3 illustrate that the introduction of double bonds on the polyurethane segments in the double-bond modified polyurethane emulsion and the formation of the castor oil stereopolymer network make the polymer network formed by the polyurethane segments more three-dimensional and effective, effectively improving the compressive strength and flexural strength of the crack-resistant concrete slabs. Furthermore, due to the improved strength of the polymer network, the crack resistance is also significantly improved.

[0091] By comparing the data in the table, the data in Comparative Example 4 shows that the final alkali treatment of Ula grass fiber removes the last part of pectin, lignin and hemicellulose, and reduces the damage of alkali erosion to the strength of Ula grass fiber. This improves the strength contribution rate of modified hollow fiber in crack-resistant concrete slabs and increases compressive strength, flexural strength and cracking index.

[0092] By comparing the data in the table, the data in Comparative Example 5 shows that grafting glycidyl methacrylate onto the surface of Ula grass fiber introduces reactive double bonds, allowing Ula grass fiber to participate in the construction of interpenetrating networks. This enriches the interpenetrating network structure, enabling it to provide higher strength support and effectively improving the compressive strength, flexural strength, and crack resistance of crack-resistant concrete slabs.

[0093] By comparing the data in the table, the data in Comparative Examples 6 and 7 show that the addition of double-bond modified polyurethane emulsion and modified hollow fibers constructs a complex three-dimensional interpenetrating network structure of "fiber-polymer network-inorganic matrix". In addition to providing strength support, this interpenetrating network structure also effectively improves crack resistance, significantly reduces the cracking risk of crack-resistant concrete slabs, and effectively improves the compressive strength, flexural strength and crack resistance of crack-resistant concrete slabs.

[0094] By comparing the data in the table, the data in Comparative Example 8 shows that after the addition of aluminum acrylate, the aluminum ions contained therein can be released during the cement hydration process. They react with calcium hydroxide, a product of cement hydration, to form a small amount of fibrous expanded ettringite, which interweaves with the CSH gel formed by cement hydration to form a three-dimensional continuous skeleton. This skeleton fills the pores of the concrete while providing micro-expansion, refining the early microstructure of the concrete, and reducing the drying shrinkage of cement concrete in the later stages of hardening. This improves the crack resistance, compressive strength, and flexural strength. During the reaction, the aluminum ions also consume some calcium hydroxide, slightly inhibiting early hydration and reducing the calcium hydroxide content. This avoids the alkaline erosion of the modified hollow fibers by high concentrations of calcium hydroxide, thus protecting the modified hollow fibers and effectively improving the compressive strength, flexural strength, and crack resistance of the crack-resistant concrete slab.

[0095] By comparing the data in the table, the data in Comparative Example 9 shows that when the constituent units of the three-dimensional interpenetrating network structure are polymerized in advance and then added, the polymerized cross-linked network with a larger molecular weight is difficult to disperse and cannot fully contact and mix with the concrete material. As a result, the interpenetrating network structure obtained by synchronous polymerization cannot be formed, and the strength support and crack resistance provided are significantly reduced. It cannot effectively improve the compressive strength, flexural strength and crack resistance of concrete slabs.

[0096] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A crack-resistant concrete slab, characterized in that, The crack-resistant concrete slab is made by mixing fine aggregate, coarse aggregate, fly ash, cement, water-reducing agent, water, double bond modified polyurethane emulsion, aluminum acrylate, modified hollow fiber, and initiator evenly, pouring the mixture into a mold, vibrating it, and then curing it. The double bond modified polyurethane emulsion is prepared by reacting isophorone diisocyanate with polytetrahydrofuran ether diol, 2,2-dimethylolbutyric acid, 1,4-butanediol, castor oil, pentaerythritol triacrylate, and triethylamine, followed by adding water. The modified hollow fiber is obtained by grafting glycidyl methacrylate onto Ula grass fiber. The Ula grass fiber is obtained by combined processing of Ula grass straw; The combined treatment involves sequentially treating Ula grass straw in a pretreatment solution, an enzyme treatment solution, a degumming treatment solution, and an alkaline treatment solution. The pretreatment solution contains 6-8 g / L sodium hydroxide and 0.4-0.5 g / L urea; The enzyme treatment solution contains 0.8~1 g / L pectinase and 0.4~0.5 g / L penetrant; The degumming solution contains 7-9 g / L sodium hydroxide and 4-5 g / L hydrogen peroxide. The alkaline treatment solution contains 10-20 g / L sodium hydroxide.

2. A method for preparing crack-resistant concrete slabs according to claim 1, characterized in that, The preparation steps include the following: (1) Under a nitrogen atmosphere, isophorone diisocyanate and polytetrahydrofuran ether diol were mixed, dibutyltin dilaurate was added, and the mixture was stirred and reacted. 2,2-dihydroxymethylbutyric acid was added, and the mixture was stirred and reacted. 1,4-butanediol was added, and the mixture was stirred and reacted. Castor oil and acetone were added, and the mixture was stirred and reacted. Pentaerythritol triacrylate was added, and the mixture was stirred and reacted. Triethylamine was added, and the mixture was stirred and reacted. Deionized water was added, and the mixture was stirred at room temperature. Acetone was removed by vacuum distillation to obtain a double bond modified polyurethane emulsion. (2) After washing and drying the Ula grass straw, add it to the pretreatment solution, stir, take it out and wash it, add it to the enzyme treatment solution, stir, take it out and transfer it to deionized water, stir at 80~90℃, take it out and wash it, add it to the degumming treatment solution, stir, take it out and wash it, add it to the alkali treatment solution, stir, take it out and wash it, dry it, cut it to obtain Ula grass fiber. (3) Under a nitrogen atmosphere, Ula grass fiber, glycidyl methacrylate, sodium bicarbonate, p-hydroxyanisole, acetone and deionized water are mixed evenly, stirred and reacted, filtered, washed and dried to obtain modified hollow fiber. (4) Add fine aggregate and coarse aggregate to the mixer, mix and stir, add fly ash and cement, stir, add water and water-reducing agent, stir, add double bond modified polyurethane emulsion and aluminum acrylate, stir, add modified hollow fiber, stir, add initiator, stir, pour into mold, vibrate, smooth, cure, and obtain crack-resistant concrete slab.

3. The method for preparing a crack-resistant concrete slab according to claim 2, characterized in that, Step (1) involves mixing isophorone diisocyanate and polytetrahydrofuran ether diol under a nitrogen atmosphere at a molar ratio of isocyanate groups to hydroxyl groups of 1:(0.5~0.6), adding dibutyltin dilaurate at 0.02~0.03 times the mass of isophorone diisocyanate, and stirring at 80~85℃ for 2~2.5h. Then, 2,2-dimethylolbutyric acid is added at a remaining molar ratio of isocyanate groups to hydroxyl groups of 1:(0.3~0.4), and stirring at 75~80℃ for 2~2.5h. Finally, 1,4-butanediol is added at a remaining molar ratio of isocyanate groups to hydroxyl groups of 1:(0.5~0.6), and stirring at 75~80℃ for 2.5~3h. Castor oil was added at a molar ratio of isocyanate groups to hydroxyl groups of 1:(0.6~0.7), followed by acetone at a mass of 2~2.5 times that of isophorone diisocyanate. The mixture was stirred at 75~80℃ for 1.5~2h. Pentaerythritol triacrylate was added at a molar ratio of the remaining isocyanate groups to hydroxyl groups of 1:(1~1.1), and the mixture was stirred at 75~80℃ for 1.5~2h. The mixture was then cooled to 30~40℃, and triethylamine was added at a molar ratio of 2,2-dimethylolbutyric acid to triethylamine of 1:(1~1.02). The mixture was stirred at 30~40℃ for 30~40min, and deionized water was added. The mixture was stirred at 1200~1300rpm at room temperature for 30~40min, and acetone was removed by vacuum distillation to obtain the final product.

4. The method for preparing a crack-resistant concrete slab according to claim 2, characterized in that, The solid content of the double bond modified polyurethane emulsion in step (1) is 30%~35%.

5. The method for preparing a crack-resistant concrete slab according to claim 2, characterized in that, The Ula grass fiber described in step (2) is prepared by washing and drying Ula grass straw, adding it to a pretreatment solution at a bath ratio of 1:(40~50) g / ml, stirring at 90~95℃ for 30~40 min, removing it and washing it with deionized water until neutral, adding it to an enzyme treatment solution at a bath ratio of 1:(40~50) g / ml, stirring at 45~50℃ and pH 4.5~5 for 3~4 h, removing it and transferring it to deionized water, stirring at 80~90℃ for 20~30 min, removing it and washing it with deionized water until neutral, adding it to a degumming treatment solution at a bath ratio of 1:(40~50) g / ml, stirring at 90~95℃ for 1.5~2 h, removing it and washing it with deionized water until neutral, adding it to an alkali treatment solution at a bath ratio of 1:(40~50) g / ml, stirring at 75~80℃ for 30~40 min, removing it and washing it with deionized water until neutral, drying it, and cutting it into the final product.

6. The method for preparing a crack-resistant concrete slab according to claim 2, characterized in that, The modified hollow fiber described in step (3) is prepared by mixing 2-3 parts of Ula grass fiber, 0.12-0.18 parts of glycidyl methacrylate, 0.01-0.012 parts of sodium bicarbonate, 0.0001-0.00015 parts of p-hydroxyanisole, 15-18 parts of acetone, and 35-40 parts of deionized water under a nitrogen atmosphere. The mixture is stirred at 60-65°C and 100-150 rpm for 1.5-2 hours, filtered, washed, and vacuum dried at 60-70°C for 10-12 hours.

7. The method for preparing a crack-resistant concrete slab according to claim 2, characterized in that, The crack-resistant concrete slab described in step (4) is prepared by adding 650-700 parts of fine aggregate and 1000-1100 parts of coarse aggregate to a mixer by weight, mixing for 3-4 minutes, adding 60-70 parts of fly ash and 350-400 parts of cement, mixing for 1-2 minutes, adding 100-120 parts of water and 4-5 parts of water-reducing agent, mixing for 3-4 minutes, adding 40-50 parts of double-bond modified polyurethane emulsion and 5-8 parts of aluminum acrylate, mixing for 1-2 minutes, adding 15-20 parts of modified hollow fiber evenly in 5 portions every 20 seconds, while maintaining stirring, and continuing to stir for 1 minute after adding all the fiber, adding 0.8-0.9 parts of initiator, stirring for 2-3 minutes, pouring into a mold, vibrating for 1 minute, filling the mold, vibrating for another 1 minute, letting stand for 3-4 minutes, smoothing, curing at room temperature for 24 hours, removing the mold, and naturally curing for 28 days.

8. The method for preparing a crack-resistant concrete slab according to claim 2, characterized in that, The curing conditions described in step (4) are 20℃±5℃ and relative humidity of 55%~65% before demolding, and 20℃±2℃ and relative humidity of 95%~99% after demolding.