High-toughness and strong-anti-crack pva fiber modified high-strength machine-made sand concrete

Abstract

The application relates to high-toughness strong-anti-crack PVA fiber modified high-strength machine-made sand concrete and belongs to the technical field of concrete. The application is prepared by self-preparing a grafting modifier, modifying PVA fibers by the grafting modifier to obtain modified PVA fibers and preparing concrete. The phosphoric acid monoester group and the sulfonic acid group of the grafting modifier can form a coordination bond and an ionic bond with calcium ions of a cement matrix, an amide bond can form a hydrogen bond with cement hydration products, a strong bonding interface is constructed, the strong hydrophilic group can improve the hydrophilicity of the PVA fibers, improve dispersibility, optimize the wrapping effect of cement on the fibers, and further significantly enhance the mechanical properties of the concrete. The bridging effect of the modified fibers can inhibit early and later cracks of the concrete. The siloxane film formed by the silane group, the calcium salt interface and the stable effect of the sulfonic acid group improve the alkali resistance and corrosion resistance of the fibers, reduce fiber degradation, prolong the service life of the concrete structure, and improve the compactness and impermeability of the concrete structure.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically, it relates to a high-toughness, high-crack-resistant PVA fiber-modified high-strength manufactured sand concrete. Background Technology

[0002] As building construction projects become more high-rise and heavy-duty, more stringent requirements are being placed on the strength grade, crack resistance, and durability of concrete materials.

[0003] To improve the brittleness and crack resistance of high-strength concrete, fiber reinforcement technology has been widely used. Among them, PVA fiber has become a preferred reinforcing fiber due to its high specific strength, moderate elastic modulus, good compatibility with cement matrix, and ability to delay crack propagation through bridging. However, PVA fiber still has significant limitations in practical applications, restricting its reinforcing effectiveness in manufactured sand high-strength concrete. PVA fiber and cement matrix rely only on physical adsorption and weak hydrogen bonding, resulting in insufficient interfacial bond strength, low stress transfer efficiency, and susceptibility to fiber debonding and pull-out failures, failing to fully utilize the reinforcing toughness effect of the fiber. PVA fiber has a high surface energy, making it prone to agglomeration in cement paste, with poor dispersion uniformity, which can easily lead to increased local stress concentration and may even become a crack initiation point. PVA fiber has poor stability in the strongly alkaline environment formed by cement hydration, and long-term service can lead to swelling and degradation, with surface grooves and delamination, resulting in a significant decline in mechanical properties and affecting the long-term reliability of concrete structures. To address the pain points in the application of PVA fiber, existing modification methods mainly include acid-base etching and polymer coating. While acid and alkali etching can increase the roughness of the fiber surface and strengthen the physical interlocking force, it will destroy the integrity of the fiber structure and lead to a decline in the mechanical properties of the fiber itself. Polymer coating can reduce the surface energy of the fiber and improve the initial dispersibility, but the bonding stability between the coating and the fiber and cement matrix is ​​poor, and it is easy to fall off and fail during the hydration process, so it cannot achieve the synergy of long-term dispersion and interface strengthening.

[0004] Based on this, the present invention will provide a high-toughness, crack-resistant PVA fiber modified high-strength manufactured sand concrete. Summary of the Invention

[0005] The purpose of this invention is to provide a high-toughness, high-crack-resistant PVA fiber-modified high-strength manufactured sand concrete to solve the problems mentioned in the background art.

[0006] The objective of this invention can be achieved through the following technical solutions: A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete comprises the following raw materials in parts by weight: 350-370 parts cement, 900-1100 parts crushed stone, 700-800 parts manufactured sand, 6-10 parts modified PVA fiber, 5-10 parts water-reducing agent, 0.8-1 part air-entraining agent, and 143.5-151.5 parts water; Furthermore, concrete is made by the following steps: Cement, crushed stone, manufactured sand and water are added to a mixer and mixed for 3 to 5 minutes. Then, water-reducing agent and air-entraining agent are added and the mixture is mixed for another 3 to 5 minutes. Finally, modified PVA fiber is added and the mixture is mixed for another 3 to 5 minutes to obtain concrete.

[0007] Furthermore, the water-reducing agent is at least one of polycarboxylate-based water-reducing agents and slow-release polycarboxylate-based water-reducing agents.

[0008] Furthermore, the air-entraining agent is at least one of rosin resin-based air-entraining agents, alkyl sulfonate-based air-entraining agents, saponin-based air-entraining agents, and polyether-based air-entraining agents.

[0009] Furthermore, the modified PVA fibers are made by the following steps: Sodium hydroxide aqueous solution and PVA fiber particles were added to a reaction vessel and reacted at room temperature for 1–3 hours. After the reaction was completed, the PVA fiber particles were filtered out and washed sequentially with deionized water and anhydrous ethanol. Then, the fiber particles, grafting modifier, anhydrous ethanol and deionized water were added to the reaction vessel and reacted at room temperature for 1–2 hours. After the reaction was completed, the modified fiber material was filtered out and placed in an electric heating oven and dried at 40–60°C for 2–4 hours to obtain modified PVA fibers.

[0010] Furthermore, the mass fraction of the sodium hydroxide aqueous solution is 1-5%.

[0011] Furthermore, the mass ratio of sodium hydroxide aqueous solution, PVA fiber particles, grafting modifier, anhydrous ethanol and deionized water is 30-48: 5.8-9.8: 7-11: 100-180: 40-60.

[0012] Furthermore, the grafting modifier is prepared by the following steps: S1. Add 4-chloro-3-hydroxybutyric acid, anhydrous sodium sulfite and distilled water to a reaction vessel and react at 90-110℃ for 6-8 hours. After the reaction is completed and cooled to room temperature, add concentrated hydrochloric acid dropwise to the reaction solution to adjust the pH to 1-2. Then, remove part of the solvent by rotary evaporation. After cooling to room temperature, add anhydrous ethanol to dissolve the solvent. After cooling and precipitating the solid, filter and retain the filtrate. Then, dry the filtrate by rotary evaporation to obtain the hydrophilic agent. S2. Add hydrophilic agent, phosphorus oxychloride, aluminum chloride and acetonitrile to the reaction vessel, react at 55-65℃ for 2-3 hours, add deionized water and continue the reaction at a constant temperature for 1-2 hours, after cooling to room temperature, filter and discard the filter residue, and the remaining filtrate is dried by rotary evaporation to obtain the binder. S3. Add silane coupling agent, Carter condensing agent and tetrahydrofuran to the reaction vessel and mix evenly. After reacting at room temperature for 1-2 hours, add binder and continue to react at room temperature for 2-6 hours. After the reaction is completed, pour the product into methyl tert-butyl ether, filter the precipitated solid and retain the solid, and then dry the solid to obtain the grafting modifier.

[0013] Furthermore, the mass fraction of concentrated hydrochloric acid is 31-34%.

[0014] Furthermore, in step S1, the mass ratio of 4-chloro-3-hydroxybutyric acid, anhydrous sodium sulfite, and distilled water is 16.3–19.3: 15.6–17.6: 120–160.

[0015] Furthermore, in step S2, the mass ratio of the hydrophilic agent, phosphorus oxychloride, aluminum chloride, acetonitrile, and distilled water is 12–16:10–14:0.4–0.6:150–190:80–120.

[0016] Furthermore, the silane coupling agent in step S3 is one of silane coupling agent KH-550 and silane coupling agent KH-540.

[0017] Furthermore, in step S3, the mass ratio of silane coupling agent, Caterpillar condensing agent, binder, and tetrahydrofuran is 6.4–8.4: 4.4–5.2: 8–8.8: 100–140.

[0018] Furthermore, the Carter condensing agent is benzotriazole-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate.

[0019] The beneficial effects of this invention are: 1. The phosphate monoester groups and sulfonic acid groups on the graft modifier of this invention can form coordination bonds and ionic bonds with calcium ions in the cement matrix, respectively; at the same time, the amide bonds of the modifier can form hydrogen bonds with the hydroxyl groups on the surface of cement hydration products, thus constructing a strong bonding interface from the three levels of fiber-modifier-cement matrix, which greatly improves stress transfer efficiency. The sulfonic acid groups and phosphate groups introduced by the graft modifier are strong hydrophilic groups, which can significantly improve the surface hydrophilicity of PVA fibers, reduce fiber agglomeration, and make the fibers uniformly dispersed in concrete. At the same time, it can effectively alleviate the effect of cement becoming viscous due to the water-reducing agent, which affects the wrapping of PVA fibers. The improvement of interfacial bonding and the uniform dispersion of fibers can more effectively transfer stress and significantly improve the compressive strength and crack resistance of concrete.

[0020] 2. The modified PVA fibers of this invention exhibit a strong bridging effect that effectively inhibits the generation and propagation of early-stage plastic cracks and later-stage drying shrinkage cracks in concrete, reducing the penetration channels for harmful media. The silane groups of the graft modifier can form a dense siloxane film on the fiber surface, and the phosphate groups combine with calcium ions to form calcium phosphate, providing dual protection. This improves the fiber's corrosion resistance in alkaline cement environments, reduces fiber degradation, thereby extending the service life of concrete structures and improving the overall density and impermeability of concrete.

[0021] 3. The concrete of this invention is prone to cracking due to shrinkage-expansion stress caused by rapid evaporation and absorption of moisture during wet-dry cycles. The sulfonic acid groups on the modified PVA fibers have high water absorption and can store moisture, which is slowly released in a dry environment, alleviating matrix cracking. At the same time, the phosphate groups have strong water retention capacity, which can reduce the rapid loss of moisture and effectively maintain the stability of interface humidity. Thus, they synergistically inhibit the shrinkage-expansion stress and microcracks caused by wet-dry cycles, significantly improving the durability of concrete. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application.

[0023] The raw materials used in this invention are not particularly restricted in terms of their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0024] The parts mentioned in the following examples and comparative examples are by weight. Example 1

[0025] A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete comprises the following raw materials in parts by weight: 350 parts cement, 900 parts crushed stone, 700 parts manufactured sand, 6 parts modified PVA fiber, 5 parts water-reducing agent, 0.8 parts air-entraining agent, and 143.5 parts water. Manufactured sand concrete is made by the following steps: Add 350 parts cement, 900 parts crushed stone, 700 parts manufactured sand and 143.5 parts water to a mixer and mix for 3 minutes. Then add 5 parts polycarboxylate superplasticizer and 0.8 parts rosin resin air-entraining agent and continue mixing for 3 minutes. Then add 6 parts modified PVA fiber and mix for 3 minutes to obtain concrete paste. Then, install the paste, vibrate it, shape it and steam it to obtain manufactured sand concrete. Modified PVA fibers are made by the following steps: 48 parts of a 1% sodium hydroxide aqueous solution and 5.8 parts of PVA fiber particles were added to a reaction vessel and reacted at room temperature for 1 hour. After the reaction was completed, the PVA fiber particles were filtered out and washed with deionized water and anhydrous ethanol in sequence. Then, the fiber particles, 7 parts of grafting modifier, 100 parts of anhydrous ethanol and 40 parts of deionized water were added to the reaction vessel and reacted at room temperature for 1 hour. After the reaction was completed, the modified fiber material was filtered out and placed in an electric heating oven and dried at 40°C for 4 hours to obtain modified PVA fiber. The grafting modifier is prepared by the following steps: S1. Add 16.3 parts of 4-chloro-3-hydroxybutyric acid, 15.6 parts of anhydrous sodium sulfite and 120 parts of distilled water to a reaction vessel and react at 90°C for 8 hours. After the reaction is completed and cooled to room temperature, add 31% concentrated hydrochloric acid dropwise to the reaction solution to adjust the pH to 2. Then, remove part of the solvent by rotary evaporation. After cooling to room temperature, add anhydrous ethanol to dissolve the solvent. After cooling and precipitating the solid, filter and retain the filtrate. Then, evaporate the filtrate to dryness to obtain the hydrophilic agent. S2. Add 12 parts of hydrophilic agent, 10 parts of phosphorus oxychloride, 0.4 parts of aluminum chloride and 150 parts of acetonitrile to a reaction vessel. After reacting at 55°C for 3 hours, add 80 parts of deionized water and continue the reaction at a constant temperature for 1 hour. After cooling to room temperature, filter and discard the filter residue. The remaining filtrate is dried by rotary evaporation to obtain the binder. S3. Add 6.4 parts of silane coupling agent KH-550, 4.4 parts of Caterpillar condensing agent and 100 parts of tetrahydrofuran to a reaction vessel and mix well. After reacting at room temperature for 1 hour, add 8 parts of binder and continue to react at room temperature for 2 hours. After the reaction is completed, pour the product into methyl tert-butyl ether, filter the precipitated solid and retain the solid, and then dry the solid to obtain the graft modifier. Example 2

[0026] A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete comprises the following raw materials in parts by weight: 355 parts cement, 950 parts crushed stone, 725 parts manufactured sand, 7 parts modified PVA fiber, 6.5 parts water-reducing agent, 0.85 parts air-entraining agent, and 145.5 parts water. Manufactured sand concrete is made by the following steps: Add 355 parts cement, 950 parts crushed stone, 725 parts manufactured sand and 145.5 parts water to a mixer and mix for 3.5 minutes. Then add 6.5 parts slow-release polycarboxylate superplasticizer and 0.85 parts alkyl sulfonate air-entraining agent and continue mixing for 3.5 minutes. Then add 7 parts modified PVA fiber and mix for 3.5 minutes to obtain concrete paste. Then, mold, vibrate, shape and steam cure to obtain manufactured sand concrete. Modified PVA fibers are made by the following steps: 42 parts by mass of 2% sodium hydroxide aqueous solution and 6.8 parts by mass of PVA fiber particles were added to a reaction vessel and reacted at room temperature for 1.5 h. After the reaction was completed, the PVA fiber particles were filtered out and washed with deionized water and anhydrous ethanol in sequence. Then, the fiber particles, 8 parts by mass of grafting modifier, 120 parts by mass of anhydrous ethanol and 45 parts by mass of deionized water were added to the reaction vessel and reacted at room temperature for 1.2 h. After the reaction was completed, the modified fiber material was filtered out and placed in an electric heating oven and dried at 45°C for 3.5 h to obtain modified PVA fiber. The grafting modifier is prepared by the following steps: S1. Add 17.1 parts of 4-chloro-3-hydroxybutyric acid, 16.1 parts of anhydrous sodium sulfite and 130 parts of distilled water to a reaction vessel and react at 95°C for 7.5 h. After the reaction is completed and cooled to room temperature, add concentrated hydrochloric acid (32% by mass) dropwise to the reaction solution to adjust the pH to 1.8. Then, remove part of the solvent by rotary evaporation. After cooling to room temperature, add anhydrous ethanol to dissolve the solvent. After cooling and precipitating the solid, filter and retain the filtrate. Then, evaporate the filtrate to dryness to obtain the hydrophilic agent. S2. Add 13 parts of hydrophilic agent, 11 parts of phosphorus oxychloride, 0.45 parts of aluminum chloride and 160 parts of acetonitrile to a reaction vessel. After reacting at 57.5℃ for 2.5h, add 90 parts of deionized water and continue the reaction at a constant temperature for 1.2h. After cooling to room temperature, filter and discard the filter residue. The remaining filtrate is dried by rotary evaporation to obtain the binder. S3. Add 6.9 parts of silane coupling agent KH-550, 4.6 parts of Caterpillar condensing agent and 110 parts of tetrahydrofuran to a reaction vessel and mix well. After reacting at room temperature for 1.2 hours, add 8.2 parts of binder and continue to react at room temperature for 3 hours. After the reaction is completed, pour the product into methyl tert-butyl ether, filter the precipitated solid and retain the solid. Then dry the solid to obtain the graft modifier. Example 3

[0027] A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete comprises the following raw materials in parts by weight: 360 parts cement, 1000 parts crushed stone, 750 parts manufactured sand, 8 parts modified PVA fiber, 8 parts water-reducing agent, 0.9 parts air-entraining agent, and 147.5 parts water; Manufactured sand concrete is made by the following steps: Add 360 parts cement, 1000 parts crushed stone, 750 parts manufactured sand and 147.5 parts water to a mixer and mix for 4 minutes. Then add 8 parts slow-release polycarboxylate superplasticizer and 0.9 parts saponin air-entraining agent and continue mixing for 4 minutes. Then add 8 parts modified PVA fiber and mix for 4 minutes to obtain concrete paste. Then, install the paste, vibrate it, shape it and steam it to obtain manufactured sand concrete. Modified PVA fibers are made by the following steps: 39 parts by mass of 3% sodium hydroxide aqueous solution and 7.8 parts by mass of PVA fiber particles were added to a reaction vessel and reacted at room temperature for 2 hours. After the reaction was completed, the PVA fiber particles were filtered out and washed with deionized water and anhydrous ethanol in sequence. Then, the fiber particles, 9 parts by mass of grafting modifier, 140 parts by mass of anhydrous ethanol and 50 parts by mass of deionized water were added to the reaction vessel and reacted at room temperature for 1.5 hours. After the reaction was completed, the modified fiber material was filtered out and placed in an electric heating oven and dried at 50°C for 3 hours to obtain modified PVA fiber. The grafting modifier is prepared by the following steps: S1. 17.8 parts of 4-chloro-3-hydroxybutyric acid, 16.6 parts of anhydrous sodium sulfite and 140 parts of distilled water were added to a reaction vessel and reacted at 100°C for 7 hours. After the reaction was completed and cooled to room temperature, concentrated hydrochloric acid with a mass fraction of 32.5% was added dropwise to adjust the pH to 1.5. The reaction solution was then rotary evaporated to remove part of the solvent. After cooling to room temperature, anhydrous ethanol was added to dissolve the solvent. After cooling and precipitating the solid, the solution was filtered and the filtrate was retained. The filtrate was then evaporated to dryness to obtain the hydrophilic agent. S2. Add 14 parts of hydrophilic agent, 12 parts of phosphorus oxychloride, 0.5 parts of aluminum chloride and 170 parts of acetonitrile to a reaction vessel. After reacting at 60°C for 2 hours, add 100 parts of deionized water and continue the reaction at a constant temperature for 1.5 hours. After cooling to room temperature, filter and discard the filter residue. The remaining filtrate is dried by rotary evaporation to obtain the binder. S3. Add 7.4 parts of silane coupling agent KH-540, 4.8 parts of Caterpillar condensing agent and 120 parts of tetrahydrofuran to a reaction vessel and mix well. After reacting at room temperature for 1.5 h, add 8.4 parts of binder and continue to react at room temperature for 4 h. After the reaction is completed, pour the product into methyl tert-butyl ether, filter the precipitated solid and retain the solid, and then dry the solid to obtain the graft modifier. Example 4

[0028] A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete comprises the following raw materials in parts by weight: 365 parts cement, 1050 parts crushed stone, 775 parts manufactured sand, 9 parts modified PVA fiber, 9 parts water-reducing agent, 0.95 parts air-entraining agent, and 149.5 parts water. Manufactured sand concrete is made by the following steps: Add 365 parts cement, 1050 parts crushed stone, 775 parts manufactured sand and 149.5 parts water to a mixer and mix for 4.5 minutes. Then add 9 parts slow-release polycarboxylate superplasticizer and 0.95 parts polyether air-entraining agent and continue mixing for 4.5 minutes. Then add 9 parts modified PVA fiber and mix for 4.5 minutes to obtain concrete paste. Then, fill the mold, vibrate, shape and steam cure to obtain manufactured sand concrete. Modified PVA fibers are made by the following steps: 36 parts of a 4% sodium hydroxide aqueous solution and 8.8 parts of PVA fiber particles were added to a reaction vessel and reacted at room temperature for 2.5 hours. After the reaction, the PVA fiber particles were filtered out and washed with deionized water and anhydrous ethanol in sequence. Then, the fiber particles, 10 parts of grafting modifier, 160 parts of anhydrous ethanol and 55 parts of deionized water were added to the reaction vessel and reacted at room temperature for 1.8 hours. After the reaction, the modified fiber material was filtered out and placed in an electric heating oven and dried at 55°C for 2.5 hours to obtain modified PVA fiber. The grafting modifier is prepared by the following steps: S1. Add 18.5 parts of 4-chloro-3-hydroxybutyric acid, 17.1 parts of anhydrous sodium sulfite and 150 parts of distilled water to a reaction vessel and react at 105℃ for 6.5 h. After the reaction is completed and cooled to room temperature, add concentrated hydrochloric acid (33% by mass) dropwise to the reaction solution to adjust the pH to 1.2. Then, remove part of the solvent by rotary evaporation. After cooling to room temperature, add anhydrous ethanol to dissolve the solvent. After cooling and precipitating the solid, filter and retain the filtrate. Then, evaporate the filtrate to dryness to obtain the hydrophilic agent. S2. Add 15 parts of hydrophilic agent, 13 parts of phosphorus oxychloride, 0.55 parts of aluminum chloride and 180 parts of acetonitrile to a reaction vessel. After reacting at 62.5℃ for 2.2h, add 110 parts of deionized water and continue the reaction at a constant temperature for 1.8h. After cooling to room temperature, filter and discard the filter residue. The remaining filtrate is dried by rotary evaporation to obtain the binder. S3. Add 7.9 parts of silane coupling agent KH-540, 5.0 parts of Caterpillar condensing agent and 130 parts of tetrahydrofuran to a reaction vessel and mix well. After reacting at room temperature for 1.8 h, add 8.6 parts of binder and continue to react at room temperature for 5 h. After the reaction is completed, pour the product into methyl tert-butyl ether, filter the precipitated solid and retain the solid, and then dry the solid to obtain the graft modifier. Example 5

[0029] A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete comprises the following raw materials in parts by weight: 370 parts cement, 1100 parts crushed stone, 800 parts manufactured sand, 10 parts modified PVA fiber, 10 parts water-reducing agent, 1 part air-entraining agent, and 151.5 parts water. Manufactured sand concrete is made by the following steps: Add 370 parts cement, 1100 parts crushed stone, 800 parts manufactured sand and 151.5 parts water to a mixer and mix for 5 minutes. Then add 10 parts slow-release polycarboxylate superplasticizer and 1 part rosin resin air-entraining agent and continue mixing for 5 minutes. Then add 10 parts modified PVA fiber and mix for 5 minutes to obtain concrete paste. Then, install the paste, vibrate it, shape it and steam it to obtain manufactured sand concrete. Modified PVA fibers are made by the following steps: 33 parts by mass of 5% sodium hydroxide aqueous solution and 9.8 parts by mass of PVA fiber particles were added to a reaction vessel and reacted at room temperature for 3 hours. After the reaction was completed, the PVA fiber particles were filtered out and washed with deionized water and anhydrous ethanol in sequence. Then, the fiber particles, 11 parts by mass of grafting modifier, 180 parts by mass of anhydrous ethanol and 60 parts by mass of deionized water were added to the reaction vessel and reacted at room temperature for 2 hours. After the reaction was completed, the modified fiber material was filtered out and placed in an electric heating oven and dried at 60°C for 2 hours to obtain modified PVA fiber. The grafting modifier is prepared by the following steps: S1. Add 19.3 parts of 4-chloro-3-hydroxybutyric acid, 17.6 parts of anhydrous sodium sulfite and 160 parts of distilled water to a reaction vessel and react at 110℃ for 6 hours. After the reaction is completed and cooled to room temperature, add concentrated hydrochloric acid (34% by mass) dropwise to adjust the pH to 1. Then, remove part of the solvent by rotary evaporation. After cooling to room temperature, add anhydrous ethanol to dissolve the solvent. After cooling and precipitating the solid, filter and retain the filtrate. Then, evaporate the filtrate to dryness to obtain the hydrophilic agent. S2. Add 16 parts of hydrophilic agent, 14 parts of phosphorus oxychloride, 0.6 parts of aluminum chloride and 190 parts of acetonitrile to a reaction vessel. After reacting at 65°C for 2.7 hours, add 120 parts of deionized water and continue the reaction at a constant temperature for 2 hours. After cooling to room temperature, filter and discard the filter residue. The remaining filtrate is dried by rotary evaporation to obtain the binder. S3. Add 8.4 parts of silane coupling agent KH-550, 5.2 parts of Caterpillar condensing agent and 140 parts of tetrahydrofuran to a reaction vessel and mix well. After reacting at room temperature for 2 hours, add 8.8 parts of binder and continue to react at room temperature for 6 hours. After the reaction is completed, pour the product into methyl tert-butyl ether, filter the precipitated solid and retain the solid. Then dry the solid to obtain the graft modifier.

[0030] Comparative Example 1 Add 370 parts cement, 1100 parts crushed stone, 800 parts manufactured sand and 151.5 parts water to a mixer and mix for 5 minutes. Then add 10 parts slow-release polycarboxylate superplasticizer and 1 part rosin resin air-entraining agent and continue mixing for 5 minutes. Then add 10 parts PVA fiber and mix for 5 minutes to obtain concrete paste. Then, mold, vibrate, shape and steam cure to obtain concrete paste. Finally, mold, vibrate, shape and steam cure to obtain manufactured sand concrete.

[0031] Experimental Example 1 The performance of the manufactured sand concrete in Examples 1-5 and Comparative Example 1 was tested. The impermeability grade and chloride ion diffusion coefficient of each group of manufactured sand concrete were tested according to GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Concrete". The slump of each group of manufactured sand concrete was tested according to GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The compressive strength of the concrete was tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" after curing for 28 days. The concrete was applied to a 160mm×120×5mm cement fiberboard with a thickness of 10mm and placed in an oven heated to 70℃ with hot air internal circulation for 4 hours. The cracking was observed. The test results are shown in Table 1.

[0032] Table 1 project impermeability grade <![CDATA[Chloride ion diffusion coefficient (10 -12 m 2 / s)]]> Slump (mm) 28-day compressive strength / MPa Crack resistance Example 1 P12 2.98 215 53.5 No cracks Example 2 P12 2.88 218 54.3 No cracks Example 3 P12 2.82 220 54.8 No cracks Example 4 P12 2.76 222 55.6 No cracks Example 5 P12 2.65 225 56.0 No cracks Comparative Example 1 P10 3.38 165 45.8 cracking As can be seen from Table 1, Examples 1-5 have higher impermeability grades, slump and 28-day compressive strength, smaller chloride ion diffusion coefficient and superior crack resistance. This indicates that the impermeability, corrosion resistance, concrete fluidity, compressive strength and crack resistance of Examples 1-3 are all better than those of Comparative Example 1. Combined with Table 1, it can be seen that using the graft modifier of the present invention to modify PVA fibers can better improve the overall impermeability, corrosion resistance, concrete fluidity, compressive strength and crack resistance of concrete.

[0033] The descriptions of the above embodiments are merely illustrative of the methods and core ideas of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete, characterized in that, The raw materials include: cement, crushed stone, manufactured sand, modified PVA fiber, water-reducing agent, air-entraining agent, and water; The modified PVA fiber is prepared by the following steps: Modified PVA fibers were obtained by grafting a grafting modifier onto PVA fiber particles that had been treated with sodium hydroxide aqueous solution.

2. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 1, characterized in that, The mass ratio of cement, crushed stone, manufactured sand, modified PVA fiber, water-reducing agent, air-entraining agent, and water is 350-370: 900-1100: 700-800: 6-10: 5-10: 0.8-1: 143.5-151.

5.

3. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 1, characterized in that, The water-reducing agent is at least one of polycarboxylate-based water-reducing agents and slow-release polycarboxylate-based water-reducing agents.

4. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 1, characterized in that, The air-entraining agent is at least one of rosin resin-based air-entraining agents, alkyl sulfonate-based air-entraining agents, saponin-based air-entraining agents, and polyether-based air-entraining agents.

5. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 1, characterized in that, The mass fraction of the sodium hydroxide aqueous solution is 1-5%.

6. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 1, characterized in that, The mass ratio of sodium hydroxide aqueous solution, PVA fiber particles, and graft modifier is 30–48: 5.8–9.8: 7–11.

7. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 1, characterized in that, The grafting modifier is prepared by the following steps: S1. A hydrophilic agent is obtained by nucleophilic substitution reaction of 4-chloro-3-hydroxybutyric acid and anhydrous sodium sulfite. S2. Phosphorylation reaction of hydrophilic agent and phosphorus oxychloride to obtain binder; S3. The silane coupling agent, Carter's condensing agent, and binder are subjected to an amidation reaction to obtain a graft modifier.

8. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 7, characterized in that, The silane coupling agent is one of silane coupling agent KH-550 or silane coupling agent KH-540.

9. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 7, characterized in that, The mass ratio of 4-chloro-3-hydroxybutyric acid to anhydrous sodium sulfite is 16.3–19.3:15.6–17.

6.

10. The high-toughness, crack-resistant PVA fiber-modified high-strength manufactured sand concrete according to claim 7, characterized in that, The mass ratio of hydrophilic agent and phosphorus oxychloride is 12-16:10-14, and the mass ratio of silane coupling agent, Caterpillar condensing agent and binder is 6.4-8.4:4.4-5.2:8-8.8.