High-cracking-resistance concrete and preparation method thereof

Abstract

The invention relates to the field of concrete, and provides high-cracking-resistance concrete and a preparation method thereof.The concrete comprises a surface modified rubber fiber composition, surface modified end-hooked steel fibers, Portland cement, fly ash, silica fume, a superplasticizer, mineral powder, coarse aggregate, fine aggregate and water. The surface modified rubber fiber composition is composed of millimeter-sized and micron-sized rubber fibers, and is subjected to alkali treatment, oxidative sulfonation and amination modification, so that the cement compatibility and interface bonding force of the fibers are improved; the surface modified end-hooked steel fiber is subjected to dopamine hydrochloride auto-polymerization deposition and drying curing treatment, and the reinforcing effect is improved. The preparation method comprises the steps of fiber pretreatment, admixture mixing, aggregate dry mixing, slurry preparation, fiber uniform dispersion and concrete forming maintenance, and material uniformity and performance stability are ensured. By optimizing fiber modification and component proportion, the cracking resistance and durability of the concrete are improved, and the concrete is suitable for high-performance building structures and engineering application.

Description

Technical Field

[0001] The present invention relates to the field of concrete, and specifically relates to a concrete with high crack resistance performance and a preparation method thereof. Background Art

[0002] In the fields of modern construction engineering, transportation infrastructure, and water conservancy projects, etc., as one of the most important structural materials, the durability and structural integrity of concrete directly affect the service life and safety of the project. However, during long-term service, concrete is easily affected by factors such as dry shrinkage, temperature changes, load effects, and environmental erosion, resulting in the generation of microcracks on the surface or inside, thereby reducing the overall mechanical properties and providing penetration channels for erosion media such as moisture, chloride ions, and sulfates, accelerating steel corrosion and material deterioration. Therefore, improving the crack resistance performance and anti-permeability ability of concrete is of great significance for enhancing structural durability, reducing maintenance costs, and extending the service life. High crack resistance performance concrete needs to have good toughness and deformation ability to effectively resist stress concentration caused by external loads or environmental factors. At the same time, its internal pore structure should be optimized to reduce permeability and reduce the intrusion of harmful media. In recent years, with the development of engineering construction towards high-rise, large-span, and extreme environment adaptability, higher requirements have been put forward for the crack resistance and anti-seepage performance of concrete. Especially in bridges, highways, marine structures, and underground projects, it is urgent to develop high-performance concrete with excellent crack resistance and anti-seepage performance to ensure the long-term stability and safety of the structure.

[0003] Currently, the research on improving the crack resistance performance and anti-permeability ability of concrete is relatively extensive, mainly focusing on aspects such as optimizing the aggregate gradation, modifying the cement matrix, and doping reinforcing materials, etc., but there are still many deficiencies. For example, the Chinese patent with the publication number CN104386959A discloses a technical solution for crack-resistant and anti-seepage concrete. However, this method mainly relies on the filling effects of polypropylene fibers, polypropylene fibers, and glass fibers, etc., which can effectively improve the toughness of the concrete. However, since the scale of the fibers is mainly in the micron scale and is relatively single, it is still easy to generate microcracks under temperature changes and load effects. Another patent research uses fiber reinforcement technology. For example, the Chinese patent with the publication number CN118344078A discloses a polypropylene fiber concrete. However, due to the weak interfacial bonding force between the polypropylene fibers and the cement matrix, it is difficult to effectively inhibit the expansion of microcracks, and the fiber dispersion is poor, affecting the overall crack resistance effect. In addition, some research attempts to improve the microscopic structure of concrete by introducing mineral admixtures. Although the anti-seepage performance is improved to a certain extent, due to the lack of an effective toughening mechanism, it is still difficult to meet the crack resistance requirements under high-stress environments. Therefore, there is still room for improvement in the existing technology in terms of improving the crack resistance and anti-seepage performance of concrete. It is urgent to develop a new type of concrete material with high toughness, low permeability, and good interfacial bonding performance to meet the long-term service requirements in complex engineering environments. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The object of the present invention is to provide a concrete with high crack resistance and its preparation method, so as to solve the problems of insufficient crack resistance and impermeability of current concrete.

[0006] (2) Technical solution

[0007] In order to achieve the above object, the present invention provides the following technical solution:

[0008] A concrete with high crack resistance, comprising the following raw materials in parts by weight: 5.0 - 12.0 parts of surface-modified rubber fiber composition, 20.0 - 35.0 parts of surface-modified end-hook steel fiber, 300 - 400 parts of Portland cement P.O 52.5, 50.0 - 80.0 parts of fly ash, 8.0 - 13.0 parts of silica fume, 1.5 - 3.0 parts of high-range water reducer, 50 - 100 parts of mineral powder, 900 - 1100 parts of coarse aggregate, 600 - 750 parts of fine aggregate, and 140 - 180 parts of water.

[0009] The surface-modified rubber fiber composition is obtained by subjecting the rubber fiber composition to alkali treatment, oxidative sulfonation and amination modification processes;

[0010] The rubber fiber composition is composed of millimeter-scale rubber fibers and micron-scale rubber fibers;

[0011] The rubber fiber composition is obtained from waste rubber tires through liquid nitrogen cryogenic embrittlement, mechanical crushing, multi-stage ultrasonic vibration screening and eddy current separation;

[0012] The surface-modified end-hook steel fiber is obtained by subjecting the end-hook steel fiber to surface modification by self-polymerization deposition of dopamine hydrochloride and drying and curing;

[0013] Further, the preparation method of the surface-modified rubber fiber composition is as follows: Immerse the rubber fiber composition in an aqueous sodium hydroxide solution with a mass concentration of 8 - 12%, control the solid-liquid ratio of 1:(5 - 8), stir and treat at 25 - 35°C at 50 - 100 rpm for 20 - 28 h, after the reaction is completed, filter and separate, retain the solid component and wash it with deionized water until the conductivity of the filtrate ≤ 50 μS / cm, and then in a vacuum drying oven at 40 - 60°C at 10 - 15m 3Treat with a gas flow rate of 10-14 h to obtain an alkali-treated intermediate; put the obtained intermediate into an aqueous potassium permanganate solution with a mass concentration of 4-6%, add a sulfuric acid solution with a mass concentration of 15-25% to adjust the pH of the system to 1.5-2.5, heat to 55-65 °C at a rate of 2-5 °C / min and maintain for 1.5-2.5 h to complete the oxidation modification. After centrifugal separation, carry out sulfonation treatment with a sodium bisulfite solution with a mass concentration of 5-8% at 60-70 °C for 0.8-1.2 h, and control the stirring rate at 150-250 rpm; then filter to retain the solid powder, dry it to obtain the sulfonated modified product. Subsequently, mix the sulfonated modified product with an aqueous urea solution with a mass concentration of 8-12% according to a mass ratio of 1:(3-5), adjust the pH to 7.5-8.5 with ammonia water, heat to 85-95 °C at a rate of 3-5 °C / min for amination reaction for 1.5-2.5 h. After the reaction system is dehydrated by a plate and frame filter press under a pressure of 0.3-0.5 MPa, carry out hot air circulation treatment at 70-80 °C in a fluidized bed dryer for 4-6 h to finally obtain the surface-modified rubber fiber composition.

[0014] Furthermore, the mass ratio of the millimeter-scale rubber fibers to the micron-scale rubber fibers is (60-75):(25-40).

[0015] Furthermore, the average length of the millimeter-scale rubber fibers is 15.0-20.0 mm; the average diameter is 2.0-5.0 mm.

[0016] Furthermore, the average length of the micron-scale rubber fibers is 500-900 μm; the average diameter is 50-120 μm.

[0017] Furthermore, the preparation method of the millimeter-scale rubber fibers is as follows: using waste rubber as the raw material, put the waste rubber tire in a liquid nitrogen environment at -132 to -138 °C for embrittlement treatment, then carry out coarse crushing with a crusher with a tooth disc gap of 2.0-5.0 mm at a rotation speed of 3500-4800 rpm, screen through a multi-stage ultrasonic vibration screening system with a frequency of 12-15 kHz, and then remove metal impurities through an eddy current separation device with a magnetic field strength of 0.8-1.2 T to finally obtain the millimeter-scale rubber fibers.

[0018] Furthermore, the preparation method of the rubber fibers at the micron scale is as follows: using waste rubber as raw material, putting the coarsely pulverized rubber particles into an ultrafine pulverizer cooled by liquid nitrogen, pulverizing for 90 - 150 minutes under the conditions of a rotation speed of 16500 - 18500 rpm and a liquid nitrogen injection flow rate of 0.5 - 1.2 L / min. During the pulverizing process, the particle size distribution is monitored in real time by a laser diffractometer and the rotation speed is dynamically adjusted to control the average diameter of the fibers to be 50 - 120 μm; the pulverized product is introduced into a two-stage turbine classification system, and the main classification wheel separates the fibers with an average length of 300 - 800 μm at a rotation speed of 4500 - 6500 rpm. Subsequently, a high-voltage electrostatic dispersion system of 10 - 15 kV is used to treat for 30 - 60 minutes to eliminate fiber agglomeration, and finally, rubber fibers at the micron scale are obtained.

[0019] The design of the surface-modified rubber fiber composition in the present invention is mainly used to enhance the anti-cracking performance and anti-permeability performance of concrete. By reasonably controlling the mass ratio of millimeter-scale and micron-scale rubber fibers and performing alkali treatment, oxidative sulfonation, and amination modification on their surfaces, stronger interfacial bonding is formed between the fibers in the concrete matrix, improving the dispersibility and strengthening effect of the fibers. The millimeter-scale rubber fibers mainly provide a framework support function, can effectively bridge cracks, delay crack propagation, and disperse stress under external loads, improving the tensile strength and toughness of concrete; the micron-scale rubber fibers fill the matrix pores, optimize the internal pore structure, help reduce permeability, and reduce the intrusion of moisture and harmful ions, thereby improving the durability of concrete. During the preparation process, the liquid nitrogen cryogenic embrittlement and mechanical pulverization processes are used to ensure the integrity of the fiber morphology, and impurities are removed through multi-stage ultrasonic vibration screening and eddy current separation to obtain fiber materials with uniform sizes. In terms of surface modification, first, sodium hydroxide solution is used to remove impurities and hydrophobic groups on the rubber surface, improving hydrophilicity and interfacial bonding ability; then, potassium permanganate oxidation and sodium bisulfite sulfonation treatments are carried out to introduce polar groups on the fiber surface, further enhancing its compatibility with the cement matrix; finally, through urea amination reaction, the fiber surface is rich in active functional groups, enhancing the microscopic strengthening effect and long-term stability of the fibers. This surface modification strategy not only improves the hydrophilicity of the fibers but also enhances the anchoring effect of the fibers in the concrete matrix, ensuring that the fibers are evenly distributed and not easily agglomerated, thus forming a uniform strengthening network inside the concrete and further enhancing the anti-cracking and anti-seepage performance. In addition, the optimized solid-liquid ratio and temperature control conditions ensure the stability and repeatability of the surface modification process, enabling the obtained modified fibers to maintain excellent mechanical properties and durability in different environments. Generally speaking, through the gradient design of fiber size, optimization of the modification process, and enhancement of interfacial interaction, the present invention realizes high anti-cracking and low permeability of concrete in complex stress environments, providing a new technical route for the development of high-performance concrete materials.

[0020] Further, the preparation method of the surface-modified hooked steel fiber is as follows: Prepare a tris(hydroxymethyl)aminomethane buffer solution with a mass concentration of 0.008 - 0.015 mol / L and a pH value of 7.5 - 8.0. Subsequently, add dopamine hydrochloride to this buffer solution, control the addition amount of dopamine hydrochloride to be 0.1 - 1.0 wt% of the solution mass, and stir evenly to prepare a uniform dopamine hydrochloride solution. Immerse the hooked steel fiber in the dopamine hydrochloride solution at a solid-liquid mass ratio of 0.4 - 0.6, control the immersion time to be 12 - 24 h. After the reaction is completed, take out the hooked steel fiber and rinse it 3 times with deionized water to remove the residual dopamine hydrochloride on the surface. Then place it in a constant temperature environment at 55 - 65 °C and dry it for 2 - 4 h. During the drying process, weigh the sample every 2 h. When the mass change rate between two adjacent weighing results is less than 0.01%, the drying process is completed, and finally the surface-modified hooked steel fiber is obtained.

[0021] Further, the average length of the hooked steel fiber is 30 - 50 mm; the average diameter is 0.5 - 1.2 mm.

[0022] The design of the present invention using surface-modified hooked steel fibers is mainly used to enhance the anti-cracking performance and anti-permeability performance of concrete. By introducing a dopamine hydrochloride coating on the surface of the hooked steel fiber, its dispersibility and interfacial bonding force in the concrete matrix are effectively improved, thereby enhancing the overall anti-cracking ability and durability. During the preparation process, first, prepare a tris(hydroxymethyl)aminomethane buffer solution to ensure that dopamine hydrochloride dissolves evenly and remains stable under suitable pH conditions. Subsequently, immerse the hooked steel fiber in it, enabling the self-polymerization deposition of dopamine hydrochloride on its surface to form a uniform and stable functionalized coating. This coating can enhance the adhesion between the steel fiber and the cement matrix, improve the interfacial anchoring effect of the fiber, and effectively reduce the agglomeration phenomenon of the fiber during the concrete mixing process, thereby ensuring the uniformity of the strengthening effect. After immersion, rinse with deionized water to remove the unreacted dopamine hydrochloride, and then dry it in a constant temperature environment. By controlling the weighing change rate during the drying process, the stable curing and thickness uniformity of the coating are ensured. The optimized coating structure not only enhances the durability of the hooked steel fiber but also improves its distribution uniformity in the concrete, enabling it to effectively bridge cracks, inhibit crack propagation, and further reduce the permeability inside the concrete under the stressed state. In addition, reasonably control the length and diameter of the hooked steel fiber so that while enhancing the anti-cracking performance of the concrete, it does not affect the overall construction performance and working performance. Through this modification method, the hooked steel fiber forms a stable strengthening network in the concrete matrix, synergistically acts with other components, effectively improves the mechanical properties and durability of the concrete, and provides a reliable technical support for the application of high-performance concrete materials.

[0023] The present invention also discloses a preparation method of high anti-cracking performance concrete, comprising the following steps:

[0024] S1. Place the surface-modified rubber fiber composition and the surface-modified end-hooked steel fiber in an environment of 50-60 °C for drying for 2-4 h respectively to remove the residual moisture on the surface. Meanwhile, add fly ash, silica fume and mineral powder into a high-speed mixer according to the ratio, and premix at a low speed of 100-300 rpm for 2-5 min, then increase the stirring speed to 800-1200 rpm and continue to mix for 3-7 min to ensure the uniform distribution of the fine admixtures. Then, add Portland cement P.O 52.5 into the mixer, and gradually add the premixed fine admixtures, and stir at a speed of 300-500 rpm for 3-5 min. Then, slowly add water and simultaneously add a high-range water reducer to completely dissolve it within 2-4 min, and continue to stir for 5-8 min to form a uniform cement paste;

[0025] S2. Subsequently, add the coarse aggregate and the fine aggregate into the mixer in sequence, and dry mix at a low speed of 50-100 rpm for 1-3 min to ensure the preliminary uniformity of the aggregates;

[0026] S3. On the basis of the uniform dry mixing of the aggregates, gradually add the prepared cement paste, and at the same time increase the stirring speed to 200-400 rpm and continuously stir for 3-5 min until a uniform matrix mixture is formed. While maintaining the stirring state, gradually add the surface-modified rubber fiber composition and the surface-modified end-hooked steel fiber, and simultaneously increase the stirring speed to 200-300 rpm and continuously stir for 5-10 min to ensure the uniform dispersion of the fibers in the concrete matrix and avoid fiber agglomeration or local enrichment;

[0027] S4. Pour the evenly mixed concrete mixture into a mold, and vibrate it on a vibrating table at 50-80 Hz for 30-60 s to remove the air bubbles inside the concrete and improve the density. The formed concrete specimens are initially cured in an environment of room temperature and relative humidity ≥ 95% for 24-36 h. After reaching the demolding strength, demold them and transfer them to a standard curing environment of room temperature and relative humidity ≥ 95% for 24-28 d of standard curing.

[0028] The present invention adopts an optimized preparation method, which is mainly used to enhance the uniformity and enhancement effect of high crack-resistant concrete. By strictly controlling the pretreatment, mixing sequence and stirring conditions of each component, efficient dispersion and stable combination of materials are achieved. During the preparation process, first, the surface-modified rubber fiber composition and the surface-modified end-hook steel fiber are dried to remove residual surface moisture, ensuring good dispersibility and interfacial bonding performance of the fibers in the subsequent stirring stage. At the same time, fly ash, silica fume and mineral powder are pre-mixed according to the ratio, and through staged stirring at different speeds, the fine admixtures are evenly distributed, providing a good foundation for the stable formation of the subsequent cement matrix. During the preparation of the cement paste, the Portland cement P.O 52.5 is added step by step, and the pre-mixed fine admixtures, water and high-range water reducer are added in turn while controlling the stirring speed to ensure the uniformity of the paste, improve the compatibility and workability of each component. In the stage of adding coarse and fine aggregates, the method of low-speed dry mixing is adopted to initially evenly distribute the aggregates and avoid local accumulation or segregation. At the same time, during the mixing process of the paste, by gradually increasing the stirring speed, it is ensured that the cement paste can fully wrap the aggregates and improve the overall homogeneity of the concrete. In the fiber dispersion stage, the method of adding step by step and synchronously increasing the stirring speed is adopted to evenly distribute the surface-modified rubber fiber composition and the surface-modified end-hook steel fiber in the concrete matrix, avoiding fiber agglomeration or local enrichment, so as to maximize the enhancement effect. In the forming stage, the vibration exhaust process is used to further improve the density of the concrete, reduce internal defects and improve durability. Finally, through the standardized curing process, the performance of the concrete develops stably, ensuring high crack resistance and low permeability of the material in the long-term service environment. Under the optimized control of the preparation method of the present invention, each component acts synergistically, making the concrete perform excellently in terms of mechanical properties, durability and construction adaptability, providing a reliable technical support for the popularization and application of high-performance concrete materials.

[0029] (3) Beneficial technical effects

[0030] 1. Through the gradient design and interface optimization of the surface-modified rubber fiber composition, the present invention has achieved a significant improvement in the crack resistance and anti-permeability performance of concrete. Compared with the prior art, it not only enhances the bonding force between the fiber and the cement matrix, improves the fiber dispersibility, but also effectively inhibits crack propagation, reduces the penetration channels and improves the durability. The millimeter-scale fibers provide skeleton support, and the micron-scale fibers fill the pores. The two act synergistically to optimize the mechanical properties and anti-seepage ability. Combining the liquid nitrogen cryogenic embrittlement, mechanical crushing and chemical modification processes, it ensures the integrity of the fiber morphology and enhanced interfacial affinity, and has broad application prospects in fields such as bridges, high-rise buildings and marine structures.

[0031] 2. By introducing a polydopamine hydrochloride coating on the surface of hooked-end steel fibers, the present invention improves the dispersibility and interfacial bonding force of the fibers in concrete. Compared with the prior art, the anti-cracking and strengthening effect is optimized and the permeability is reduced. The uniform stability of the coating ensures the anchoring effect of the fibers in concrete, effectively inhibits crack propagation, improves durability, and at the same time maintains construction adaptability. In the fields of bridges, high-rise buildings, and hydraulic structures, etc., the present invention can significantly enhance the structural integrity and long-term service performance of concrete, providing more reliable technical support for engineering construction.

[0032] 3. In the present invention, the surface-modified waste rubber fibers and the surface-modified hooked-end steel fibers act synergistically. The former optimizes the microscopic pore structure to improve impermeability, and the latter enhances the interfacial bonding force to improve anti-cracking performance. The two together improve the mechanical properties and durability of concrete and are applicable to high-stress and complex environment projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the morphology diagram of millimeter-scale rubber fibers prepared in Example 1 of the present invention.

[0034] Figure 2 It is the morphology diagram of micron-scale rubber fibers prepared in Example 1 of the present invention.

[0035] Figure 3 It is the morphology diagram of the hooked-end steel fibers used in Example 1 of the present invention.

[0036] Figure 4 It is the interfacial morphology between the surface-modified hooked-end steel fibers prepared in Example 1 of the present invention and the concrete matrix.

[0037] Figure 5 It is the interfacial morphology between the un-surface-modified hooked-end steel fibers prepared in Comparative Example 5 of the present invention and the concrete matrix DETAILED DESCRIPTION OF THE INVENTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] Example 1

[0040] A concrete with high anti-cracking performance comprises the following raw materials in parts by weight: 5.0 parts of surface-modified rubber fiber composition, 20.0 parts of surface-modified hooked-end steel fibers, 300 parts of Portland cement P.O 52.5, 50.0 parts of fly ash, 8.0 parts of silica fume, 1.5 parts of high-range water reducer, 50 parts of blast furnace slag powder, 900 parts of coarse aggregate, 600 parts of fine aggregate, and 140 parts of water.

[0041] The surface-modified rubber fiber composition is obtained by subjecting the rubber fiber composition to alkali treatment, oxidative sulfonation, and amination modification processes; the rubber fiber composition consists of rubber fibers at the millimeter scale and rubber fibers at the micron scale; the rubber fiber composition is obtained from waste rubber tires through liquid nitrogen cryogenic embrittlement, mechanical pulverization, multi-stage ultrasonic vibration screening, and eddy current separation; the surface-modified end-hooked steel fiber is obtained by subjecting the end-hooked steel fiber to surface modification by self-polymerization deposition of dopamine hydrochloride and drying and curing.

[0042] The preparation method of the surface-modified rubber fiber composition in this example is as follows: Immerse the rubber fiber composition in an aqueous sodium hydroxide solution with a mass concentration of 8%, control the solid-liquid ratio at 1:5, stir and treat at 25°C at 50 rpm for 20 h. After the reaction, filter and separate, retain the solid component and wash it with deionized water until the conductivity of the filtrate ≤ 50 μS / cm. Subsequently, treat it in a vacuum drying oven at 40°C at an air flow rate of 10 m3 / h for 10 h to obtain an alkali-treated intermediate; Put the obtained intermediate into an aqueous potassium permanganate solution with a mass concentration of 4%, add a sulfuric acid solution with a mass concentration of 15% to adjust the pH of the system to 1.5, heat it to 55°C at 2°C / min and maintain for 1.5 h to complete the oxidation modification. After centrifugal separation, carry out sulfonation treatment at 60°C for 0.8 h with an aqueous sodium bisulfite solution with a mass concentration of 5%, and control the stirring rate at 150 rpm; Then filter to retain the solid powder, dry it to obtain a sulfonated modified product. Subsequently, mix the sulfonated modified product with an aqueous urea solution with a mass concentration of 8% at a mass ratio of 1:3, adjust the pH to 7.5 with ammonia water, heat it to 85°C at 3°C / min for amination reaction for 1.5 h. After the reaction system is dehydrated by a plate and frame filter press at a pressure of 0.3 MPa, treat it in a fluidized bed dryer with hot air circulation at 70°C for 4 h to finally obtain the surface-modified rubber fiber composition.

[0043] In this example, the mass ratio of the rubber fibers at the millimeter scale to the rubber fibers at the micron scale is 60:40. The average length of the rubber fibers at the millimeter scale is 15.0 mm; the average diameter is 2.0 mm. The average length of the rubber fibers at the micron scale is 500 μm; the average diameter is 50 μm.

[0044] The preparation method of the rubber fibers at the millimeter scale in this example is as follows: Using waste rubber as the raw material, place the waste rubber tire in a liquid nitrogen environment at -138°C for embrittlement treatment. Subsequently, use a crusher with a tooth disc gap of 2.0 mm to carry out rough pulverization at a rotation speed of 3500 rpm, sieve it through a multi-stage ultrasonic vibration screening system with a frequency of 12 kHz, and then remove metal impurities through an eddy current separation device with a magnetic field intensity of 0.8 T to finally obtain the rubber fibers at the millimeter scale.

[0045] The preparation method of the rubber fibers at the micron scale in this embodiment is as follows: Using waste rubber as the raw material, putting the coarsely crushed rubber particles into an ultra-fine pulverizer cooled by liquid nitrogen, pulverizing for 90 min under the conditions of a rotation speed of 16500 rpm and a liquid nitrogen injection flow rate of 0.5 L / min. During the pulverization process, the particle size distribution is monitored in real time by a laser diffractometer and the rotation speed is dynamically adjusted to control the average diameter of the fibers to be 50 μm. The pulverized product is introduced into a two-stage turbine classification system. The main classification wheel separates the fibers with an average length of 300 μm at a rotation speed of 4500 rpm. Subsequently, a 10 kV high-voltage electrostatic dispersion system is used to treat for 30 min to eliminate fiber agglomeration, and finally, rubber fibers at the micron scale are obtained.

[0046] The preparation method of the surface-modified hooked steel fibers in this embodiment is as follows: Prepare a tris(hydroxymethyl)aminomethane buffer solution with a mass concentration of 0.008 mol / L and a pH value of 7.5. Subsequently, add dopamine hydrochloride to the buffer solution, control the addition amount of dopamine hydrochloride to be 0.1 wt% of the solution mass, and stir evenly to prepare a uniform dopamine hydrochloride solution. Immerse the hooked steel fibers in the dopamine hydrochloride solution at a solid-liquid mass ratio of 0.4, control the immersion time to be 12 h. After the reaction is completed, take out the hooked steel fibers and rinse them 3 times with deionized water to remove the residual dopamine hydrochloride on the surface. Subsequently, place them in a constant temperature environment at 55 °C and dry for 2 h. During the drying process, weigh the samples every 2 h. When the mass change rate between two adjacent weighing results is less than 0.01%, the drying process is completed, and finally, surface-modified hooked steel fibers are obtained.

[0047] The average length of the hooked steel fibers in this embodiment is 30 mm; the average diameter is 0.5 mm.

[0048] The preparation method of a kind of high crack resistance performance concrete in this embodiment includes the following steps:

[0049] S1. Place the surface-modified rubber fiber composition and the surface-modified hooked steel fibers in an environment at 50 °C and dry for 2 h to remove the residual moisture on the surface. At the same time, add fly ash, silica fume, and mineral powder to a high-speed mixer according to the ratio, premix at a low speed of 100 rpm for 2 min, and then increase the stirring speed to 800 rpm and continue to mix for 3 min to ensure the uniform distribution of the fine admixtures. Then, add Portland cement P.O52.5 to the mixer, and gradually add the premixed fine admixtures, stir at a speed of 300 rpm for 3 min, then slowly add water, and simultaneously add a high-range water reducer to completely dissolve it within 2 min, and continue to stir for 5 min to form a uniform cement paste;

[0050] S2. Subsequently, add the coarse aggregate and the fine aggregate to the mixer in sequence and dry-mix at a low speed of 50 rpm for 1 min to ensure the preliminary uniformity of the aggregates;

[0051] S3. On the basis of uniformly dry-mixing the aggregates, gradually add the prepared cement paste while increasing the stirring speed to 200 rpm, and continuously stir for 3 min until a uniform matrix mixture is formed. While maintaining the stirring state, gradually add the surface-modified rubber fiber composition and the surface-modified end-hooked steel fibers, and simultaneously increase the stirring speed to 200 rpm and continuously stir for 5 min to ensure the uniform dispersion of the fibers in the concrete matrix and avoid fiber agglomeration or local enrichment;

[0052] S4. Pour the uniformly mixed concrete mixture into a mold and vibrate it on a vibrating table at 50 Hz for 30 s to remove the internal air bubbles in the concrete and improve the density. The formed concrete specimens are initially cured for 24 h in an environment at room temperature and a relative humidity ≥ 95%. After reaching the demolding strength, demold them and transfer them to a standard curing environment at room temperature and a relative humidity ≥ 95% for 24 d of standard curing.

[0053] It can be seen through Figure 1 and Figure 2 that the rubber fibers prepared by the present invention at the millimeter scale and the micron scale have complete morphology and uniform sizes, indicating that the liquid nitrogen cryogenic embrittlement, mechanical crushing and multi-stage sorting processes can effectively ensure the integrity and size control of the fibers. Figure 3 shows the end-hooked steel fibers used in the present invention, and its end hook-shaped structure is clear and the morphology is intact, providing a good mechanical anchoring effect for enhancing the crack resistance of concrete. Figure 4 shows the interfacial morphology between the surface-modified end-hooked steel fibers and the concrete matrix. It can be clearly seen that the fibers are tightly combined with the matrix and there is no obvious debonding phenomenon, indicating that the dopamine hydrochloride coating can effectively improve the interfacial bonding force of the fibers. Therefore, combined with the modification process of the present invention, the interfacial bonding performance of the end-hooked steel fibers can be significantly improved, thereby improving the crack resistance and durability of the concrete, proving the effectiveness of the surface modification technology adopted by the present invention.

[0054] Example 2

[0055] A high crack-resistant concrete, comprising the following raw materials in parts by weight: 7.0 parts of surface-modified rubber fiber composition, 25.0 parts of surface-modified end-hooked steel fibers, 330 parts of Portland cement P.O 52.5, 59.0 parts of fly ash, 9.0 parts of silica fume, 2.0 parts of high-range water reducer, 65 parts of mineral powder, 960 parts of coarse aggregate, 645 parts of fine aggregate, and 152 parts of water.

[0056] The surface-modified rubber fiber composition is obtained from the rubber fiber composition through alkali treatment, oxidative sulfonation, and amination modification processes; the rubber fiber composition consists of rubber fibers at the millimeter scale and rubber fibers at the micron scale; the rubber fiber composition is obtained from waste rubber tires through liquid nitrogen cryogenic embrittlement, mechanical crushing, multi-stage ultrasonic vibration screening, and eddy current separation; the surface-modified end-hook steel fiber is obtained by self-polymerization deposition of dopamine hydrochloride and drying and curing the surface modification of the end-hook steel fiber;

[0057] The preparation method of the surface-modified rubber fiber composition in this example is as follows: Immerse the rubber fiber composition in an aqueous sodium hydroxide solution with a mass concentration of 9%, control the solid-liquid ratio of 1:6, stir at 65 rpm at 28 °C for 22 h, filter and separate after the reaction, retain the solid component and wash it with deionized water until the conductivity of the filtrate ≤ 50 μS / cm, and then treat it in a vacuum drying oven at 46 °C with an air flow rate of 12 m3 / h for 11 h to obtain an alkali-treated intermediate; Put the obtained intermediate into an aqueous potassium permanganate solution with a mass concentration of 5%, add a sulfuric acid solution with a mass concentration of 18% to adjust the pH of the system to 1.8, heat up to 58 °C at a rate of 3 °C / min and maintain for 1.8 h to complete the oxidation modification, after centrifugal separation, carry out sulfonation treatment at 63 °C with an aqueous sodium bisulfite solution with a mass concentration of 6% for 0.9 h, and control the stirring rate at 180 rpm; Then filter and retain the solid powder, dry it to obtain a sulfonated modified product, and then mix the sulfonated modified product with an aqueous urea solution with a mass concentration of 9% at a mass ratio of 1:4, adjust the pH to 7.8 with ammonia water, heat up to 88 °C at a rate of 4 °C / min for amination reaction for 1.8 h, after the reaction system is dehydrated by a plate and frame filter press under a pressure of 0.4 MPa, it is treated in a fluidized bed dryer with hot air circulation at 73 °C for 5 h to finally obtain the surface-modified rubber fiber composition.

[0058] In this example, the mass ratio of the rubber fibers at the millimeter scale to the rubber fibers at the micron scale is 65:35. The average length of the rubber fibers at the millimeter scale is 16.5 mm; the average diameter is 2.9 mm. The average length of the rubber fibers at the micron scale is 620 μm; the average diameter is 71 μm.

[0059] The preparation method of the rubber fibers at the millimeter scale in this example is as follows: Using waste rubber as the raw material, place the waste rubber tire in a liquid nitrogen environment at -136 °C for embrittlement treatment, then carry out coarse crushing with a crusher with a tooth disc gap of 2.9 mm at a rotational speed of 3890 rpm, screen it through a multi-stage ultrasonic vibration screening system with a frequency of 13 kHz, and then remove metal impurities through an eddy current separation device with a magnetic field strength of 0.9 T to finally obtain the rubber fibers at the millimeter scale.

[0060] The preparation method of the micron-scale rubber fibers in this embodiment is as follows: Using waste rubber as raw material, putting the coarsely crushed rubber particles into an ultra-fine pulverizer cooled by liquid nitrogen, pulverizing for 108 min under the conditions of a rotation speed of 17100 rpm and a liquid nitrogen injection flow rate of 0.7 L / min. During the pulverization process, the particle size distribution is monitored in real time by a laser diffractometer and the rotation speed is dynamically adjusted to control the average fiber diameter to be 71 μm. Then, the pulverized product is introduced into a two-stage turbine classification system. The main classification wheel separates fibers with an average length of 450 μm at a rotation speed of 5100 rpm. Subsequently, a 12 kV high-voltage electrostatic dispersion system is used to treat for 39 min to eliminate fiber agglomeration. Finally, micron-scale rubber fibers are obtained.

[0061] The preparation method of the surface-modified hooked steel fibers in this embodiment is as follows: Prepare a tris(hydroxymethyl)aminomethane buffer solution with a mass concentration of 0.010 mol / L and a pH value of 7.7. Then, add dopamine hydrochloride to this buffer solution, control the addition amount of dopamine hydrochloride to be 0.4 wt% of the solution mass, and stir evenly to prepare a uniform dopamine hydrochloride solution. Immerse the hooked steel fibers in the dopamine hydrochloride solution at a solid-liquid mass ratio of 0.5, control the immersion time to be 16 h. After the reaction is completed, take out the hooked steel fibers, rinse them 3 times with deionized water to remove the residual dopamine hydrochloride on the surface. Then, place them in a constant-temperature environment at 58 °C and dry for 3 h. During the drying process, weigh the samples every 2 h. When the mass change rate between two adjacent weighing results is less than 0.01%, the drying process is completed. Finally, surface-modified hooked steel fibers are obtained.

[0062] The average length of the hooked steel fibers in this embodiment is 36 mm; the average diameter is 0.7 mm.

[0063] The preparation method of a high crack-resistant performance concrete in this embodiment includes the following steps:

[0064] S1. Place the surface-modified rubber fiber composition and the surface-modified hooked steel fibers in an environment at 53 °C and dry for 3 h to remove the residual moisture on the surface. At the same time, add fly ash, silica fume, and mineral powder to a high-speed mixer according to the ratio, premix at a low speed of 160 rpm for 3 min, then increase the stirring speed to 920 rpm and continue to mix for 4 min to ensure the uniform distribution of the fine admixtures. Then, add Portland cement P.O52.5 to the mixer, and gradually add the premixed fine admixtures, stir at a speed of 360 rpm for 4 min, then slowly add water, and simultaneously add a high-range water reducer to completely dissolve it within 3 min, and continue to stir for 6 min to form a uniform cement paste.

[0065] S2. Subsequently, add the coarse aggregate and the fine aggregate to the mixer in sequence and dry-mix at a low speed of 65 rpm for 2 min to ensure the preliminary uniformity of the aggregates.

[0066] S3. On the basis of uniformly dry-mixing the aggregates, gradually add the prepared cement paste while increasing the stirring speed to 260 rpm and continuously stir for 4 min until a uniform matrix mixture is formed. While maintaining the stirring state, gradually add the surface-modified rubber fiber composition and the surface-modified end-hooked steel fibers, and simultaneously increase the stirring speed to 230 rpm and continuously stir for 7 min to ensure uniform dispersion of the fibers in the concrete matrix and avoid fiber agglomeration or local enrichment.

[0067] S4. Pour the uniformly mixed concrete mixture into a mold and vibrate it on a vibrating table at 59 Hz for 39 s to remove the internal air bubbles in the concrete and improve the density. The formed concrete specimens are initially cured for 28 h in an environment at room temperature and a relative humidity ≥ 95%. After reaching the demolding strength, demold them and transfer them to a standard curing environment at room temperature and a relative humidity ≥ 95% for 25 d of standard curing.

[0068] Example 3

[0069] A concrete with high crack resistance performance comprises the following raw materials in parts by weight: 12.0 parts of surface-modified rubber fiber composition, 35.0 parts of surface-modified end-hooked steel fibers, 400 parts of Portland cement P.O 52.5, 80.0 parts of fly ash, 13.0 parts of silica fume, 3.0 parts of high-range water reducer, 100 parts of blast furnace slag powder, 1100 parts of coarse aggregate, 750 parts of fine aggregate, and 180 parts of water.

[0070] The surface-modified rubber fiber composition is obtained by subjecting the rubber fiber composition to alkali treatment, oxidative sulfonation, and amination modification processes; the rubber fiber composition is composed of millimeter-scale rubber fibers and micron-scale rubber fibers; the rubber fiber composition is obtained from waste rubber tires through liquid nitrogen cryogenic embrittlement, mechanical crushing, multi-stage ultrasonic vibration screening, and eddy current separation; the surface-modified end-hooked steel fibers are obtained by subjecting the end-hooked steel fibers to surface modification by dopamine hydrochloride self-polymerization deposition and drying and curing.

[0071] The preparation method of the surface-modified rubber fiber composition in this example is as follows: Immerse the rubber fiber composition in an aqueous sodium hydroxide solution with a mass concentration of 12%, control the solid-liquid ratio at 1:8, stir at 100 rpm for 28 h at 35°C. After the reaction, filter and separate, retain the solid component and wash it with deionized water until the conductivity of the filtrate ≤ 50 μS / cm. Subsequently, treat it in a vacuum drying oven at 60°C with an air flow rate of 15 m³ / h for 14 h to obtain an alkali-treated intermediate; Put the obtained intermediate into an aqueous potassium permanganate solution with a mass concentration of 6%, add a sulfuric acid solution with a mass concentration of 25% to adjust the pH of the system to 2.5, heat it to 65°C at a rate of 5°C / min and maintain for 2.5 h to complete the oxidation modification. After centrifugal separation, carry out sulfonation treatment at 70°C for 1.2 h with a sodium bisulfite solution with a mass concentration of 8%, and control the stirring rate at 250 rpm; Then filter and retain the solid powder, dry it to obtain the sulfonated modified product. Subsequently, mix the sulfonated modified product with an aqueous urea solution with a mass concentration of 12% at a mass ratio of 1:5, adjust the pH to 8.5 with ammonia water, heat it to 95°C at a rate of 5°C / min for amination reaction for 2.5 h. After the reaction system is dehydrated by a plate and frame filter press under a pressure of 0.5 MPa, treat it in a fluidized bed dryer with hot air circulation at 80°C for 6 h to finally obtain the surface-modified rubber fiber composition.

[0072] In this example, the mass ratio of millimeter-scale rubber fibers to micron-scale rubber fibers is 75:25. The average length of the millimeter-scale rubber fibers is 20.0 mm; the average diameter is 5.0 mm. The average length of the micron-scale rubber fibers is 900 μm; the average diameter is 120 μm.

[0073] The preparation method of the millimeter-scale rubber fibers in this example is as follows: Using waste rubber as raw material, place the waste rubber tire in a liquid nitrogen environment at -132°C for embrittlement treatment, then carry out coarse crushing with a crusher with a tooth disc gap of 5.0 mm at a rotational speed of 4800 rpm, sieve it through a multi-stage ultrasonic vibration screening system with a frequency of 15 kHz, and remove metal impurities through an eddy current separation device with a magnetic field intensity of 1.2 T to finally obtain millimeter-scale rubber fibers.

[0074] The preparation method of the micron-scale rubber fibers in this example is as follows: Using waste rubber as raw material, put the coarsely crushed rubber particles into an ultra-fine crusher cooled by liquid nitrogen, crush for 150 min at a rotational speed of 18500 rpm and a liquid nitrogen injection flow rate of 1.2 L / min. During the crushing process, monitor the particle size distribution in real time through a laser diffractometer and dynamically adjust the rotational speed to control the average diameter of the fibers at 120 μm; Import the crushed product into a two-stage turbine classification system, and the main classification wheel separates fibers with an average length of 800 μm at a rotational speed of 6500 rpm. Subsequently, treat it with a 15 kV high-voltage electrostatic dispersion system for 60 min to eliminate fiber agglomeration, and finally obtain micron-scale rubber fibers.

[0075] The preparation method of the surface-modified hooked steel fiber in this embodiment is as follows: Prepare a tris(hydroxymethyl)aminomethane buffer solution with a mass concentration of 0.015 mol / L and a pH value of 8.0. Subsequently, add dopamine hydrochloride to the buffer solution, control the addition amount of dopamine hydrochloride to be 1.0 wt% of the solution mass, and stir evenly to prepare a uniform dopamine hydrochloride solution. Immerse the hooked steel fiber in the dopamine hydrochloride solution at a solid-liquid mass ratio of 0.6, control the soaking time to be 24 h, take out the hooked steel fiber after the reaction is completed, rinse it 3 times with deionized water to remove the residual dopamine hydrochloride on the surface, and then place it in a constant temperature environment at 65 °C for drying for 4 h. During the drying process, weigh the sample every 2 h. When the mass change rate between two adjacent weighing results is less than 0.01%, the drying process is completed, and finally, the surface-modified hooked steel fiber is obtained.

[0076] The average length of the hooked steel fiber in this embodiment is 50 mm; the average diameter is 1.2 mm.

[0077] The preparation method of a high crack resistance performance concrete in this embodiment includes the following steps:

[0078] S1. Place the surface-modified rubber fiber composition and the surface-modified hooked steel fiber in an environment at 56 °C for drying for 3 h to remove the residual moisture on the surface. At the same time, add fly ash, silica fume, and mineral powder to a high-speed mixer according to the ratio, premix at a low speed of 220 rpm for 4 min, then increase the stirring speed to 1040 rpm, and continue to mix for 5 min to ensure that the fine admixtures are evenly distributed. Then, add Portland cement P.O 52.5 to the mixer, and gradually add the premixed fine admixtures, stir at a speed of 420 rpm for 4 min, then slowly add water, and simultaneously add a high-range water reducer to completely dissolve it within 3 min, and continue to stir for 7 min to form a uniform cement paste;

[0079] S2. Subsequently, add the coarse aggregate and the fine aggregate to the mixer in sequence, and dry mix at a low speed of 80 rpm for 2 min to ensure that the aggregates are initially uniform;

[0080] S3. On the basis of the uniform dry mixing of the aggregates, gradually add the prepared cement paste, and at the same time increase the stirring speed to 320 rpm, and continuously stir for 4 min until a uniform matrix mixture is formed. While maintaining the stirring state, gradually add the surface-modified rubber fiber composition and the surface-modified hooked steel fiber, and simultaneously increase the stirring speed to 260 rpm, and continuously stir for 8 min to ensure that the fibers are evenly dispersed in the concrete matrix and avoid fiber agglomeration or local enrichment;

[0081] S4. Pour the evenly mixed concrete mixture into the mold and vibrate it on a vibrating table at 68 Hz for 48 s to remove the air bubbles inside the concrete and improve the density. The formed concrete specimens are initially cured for 31 h in an environment at room temperature and a relative humidity ≥ 95%, and after reaching the demolding strength, they are demolded and transferred to a standard curing environment at room temperature and a relative humidity ≥ 95% for 26 d of standard curing.

[0082] Example 4

[0083] A concrete with high crack resistance performance, comprising the following raw materials in parts by weight: 9.0 parts of surface-modified rubber fiber composition, 29.0 parts of surface-modified end-hooked steel fiber, 360 parts of portland cement P.O 52.5, 68.0 parts of fly ash, 11.0 parts of silica fume, 2.4 parts of high-range water reducer, 80 parts of mineral powder, 1020 parts of coarse aggregate, 690 parts of fine aggregate, and 164 parts of water.

[0084] The surface-modified rubber fiber composition is obtained by subjecting the rubber fiber composition to alkali treatment, oxidative sulfonation, and amination modification processes; the rubber fiber composition is composed of millimeter-scale rubber fibers and micron-scale rubber fibers; the rubber fiber composition is obtained from waste rubber tires through liquid nitrogen cryogenic embrittlement, mechanical crushing, multi-stage ultrasonic vibration screening, and eddy current separation; the surface-modified end-hooked steel fiber is obtained by subjecting the end-hooked steel fiber to surface modification by dopamine hydrochloride self-polymerization deposition and drying and curing.

[0085] The preparation method of the surface-modified rubber fiber composition in this example is as follows: Immerse the rubber fiber composition in a 10% sodium hydroxide aqueous solution, control the solid-liquid ratio of 1:7, stir at 80 rpm at 31 °C for 25 h, after the reaction, filter and separate, retain the solid component and wash it with deionized water until the conductivity of the filtrate ≤ 50 μS / cm, and then treat it in a vacuum drying oven at 52 °C at an air flow rate of 13 m3 / h for 12 h to obtain an alkali treatment intermediate; put the obtained intermediate into a 5% potassium permanganate aqueous solution, add a 21% sulfuric acid solution to adjust the pH of the system to 2.1, heat it to 61 °C at 4 °C / min and maintain it for 2.1 h to complete the oxidation modification, after centrifugal separation, carry out sulfonation treatment at 66 °C for 1.0 h with a 7% sodium bisulfite solution, control the stirring rate at 210 rpm; then filter to retain the solid powder, dry it to obtain the sulfonated modification product, and then mix the sulfonated modification product with a 10% urea aqueous solution according to a mass ratio of 1:4, adjust the pH to 8.1 with ammonia water, heat it to 91 °C at 4 °C / min for amination reaction for 2.1 h, after the reaction system is dehydrated by a plate and frame filter press under a pressure of 0.4 MPa, treat it in a fluidized bed dryer with hot air circulation at 76 °C for 5 h to finally obtain the surface-modified rubber fiber composition.

[0086] In this embodiment, the mass ratio of millimeter-scale rubber fibers to micron-scale rubber fibers is 69:31. The average length of the millimeter-scale rubber fibers is 18.0 mm; the average diameter is 3.8 mm. The average length of the micron-scale rubber fibers is 740 μm; the average diameter is 92 μm.

[0087] The preparation method of the millimeter-scale rubber fibers in this embodiment is as follows: Using waste rubber as the raw material, placing waste rubber tires in a liquid nitrogen environment at -134°C for embrittlement treatment, then performing coarse crushing with a crusher having a disk gap of 3.8 mm at a rotational speed of 4280 rpm, screening through a multi-stage ultrasonic vibration screening system with a frequency of 14 kHz, and removing metal impurities through an eddy current separation device with a magnetic field strength of 1.0 T, finally obtaining millimeter-scale rubber fibers.

[0088] The preparation method of the micron-scale rubber fibers in this embodiment is as follows: Using waste rubber as the raw material, putting the coarsely crushed rubber particles into an ultra-fine crusher cooled by liquid nitrogen, crushing for 126 min under the conditions of a rotational speed of 17700 rpm and a liquid nitrogen injection flow rate of 0.9 L / min. During the crushing process, the particle size distribution is monitored in real time by a laser diffractometer and the rotational speed is dynamically adjusted to control the average diameter of the fibers to be 92 μm; the crushed product is introduced into a two-stage turbine classification system, and the main classification wheel separates fibers with an average length of 600 μm at a rotational speed of 5700 rpm. Subsequently, it is treated with a 13 kV high-voltage electrostatic dispersion system for 48 min to eliminate fiber agglomeration, and finally micron-scale rubber fibers are obtained.

[0089] The preparation method of the surface-modified hooked steel fibers in this embodiment is as follows: Prepare a tris(hydroxymethyl)aminomethane buffer solution with a mass concentration of 0.012 mol / L and a pH value of 7.8. Subsequently, add dopamine hydrochloride to this buffer solution, control the addition amount of dopamine hydrochloride to be 0.6 wt% of the solution mass, and stir evenly to prepare a uniform dopamine hydrochloride solution. Immerse the hooked steel fibers in the dopamine hydrochloride solution at a solid-liquid mass ratio of 0.5, control the immersion time to be 19 h. After the reaction is completed, take out the hooked steel fibers, rinse them 3 times with deionized water to remove the residual dopamine hydrochloride on the surface, and then place them in a constant-temperature environment at 61°C for drying for 3 h. During the drying process, weigh the samples every 2 h. When the mass change rate between two adjacent weighing results is less than 0.01%, the drying process is completed, and finally surface-modified hooked steel fibers are obtained.

[0090] The average length of the hooked steel fibers in this embodiment is 42 mm; the average diameter is 0.9 mm.

[0091] The preparation method of a high crack resistance performance concrete in this embodiment includes the following steps:

[0092] S1. Place the surface-modified rubber fiber composition and the surface-modified end-hook steel fiber in an environment of 60 °C and dry for 4 h to remove residual surface moisture. Meanwhile, add fly ash, silica fume, and mineral powder to a high-speed mixer according to the ratio, and premix at a low speed of 300 rpm for 5 min. Then increase the stirring speed to 1200 rpm and continue mixing for 7 min to ensure the uniform distribution of the fine admixtures. Then, add Portland cement P.O52.5 to the mixer and gradually add the premixed fine admixtures, and stir at a speed of 500 rpm for 5 min. Then slowly add water and simultaneously add a high-range water reducer to completely dissolve it within 4 min, and continue stirring for 8 min to form a uniform cement paste;

[0093] S2. Subsequently, add the coarse aggregate and the fine aggregate to the mixer in sequence and dry mix at a low speed of 100 rpm for 3 min to ensure the preliminary uniformity of the aggregates;

[0094] S3. On the basis of the uniform dry mixing of the aggregates, gradually add the prepared cement paste, and at the same time increase the stirring speed to 400 rpm and continuously stir for 5 min until a uniform matrix mixture is formed. While maintaining the stirring state, gradually add the surface-modified rubber fiber composition and the surface-modified end-hook steel fiber, and simultaneously increase the stirring speed to 300 rpm and continuously stir for 10 min to ensure the uniform dispersion of the fibers in the concrete matrix and avoid fiber agglomeration or local enrichment;

[0095] S4. Pour the uniformly mixed concrete mixture into a mold and vibrate it on a vibrating table at 80 Hz for 60 s to remove the internal air bubbles in the concrete and improve the density. The formed concrete specimens are initially cured for 36 h in an environment of room temperature and relative humidity ≥ 95%. After reaching the demolding strength, demold them and transfer them to a standard curing environment of room temperature and relative humidity ≥ 95% for 28 d of standard curing.

[0096] Comparative Example 1

[0097] It is basically the same as Example 1, except that the rubber fiber composition is not surface-modified, resulting in reduced dispersion of the fibers in the concrete matrix, weaker interfacial bonding force, decreased crack resistance effect, and easy fiber agglomeration, affecting the strengthening effect.

[0098] Comparative Example 2

[0099] It is basically the same as Example 1, except that the mass ratio of millimeter-scale rubber fibers to micron-scale rubber fibers is adjusted to 30:70, resulting in weakened skeleton support effect, decreased crack bridging ability, reduced crack resistance performance, and at the same time, excessive filling of micron-scale fibers leads to poor workability of the concrete.

[0100] Comparative Example 3

[0101] Basically the same as Example 1, except that cryogenic embrittlement treatment of waste rubber fibers with liquid nitrogen was not adopted, resulting in incomplete fiber morphology, serious fiber damage during the crushing process, uneven particle size distribution, and thus affecting the fiber reinforcement effect and the crack resistance of concrete.

[0102] Comparative Example 4

[0103] Basically the same as Example 1, except that potassium permanganate oxidation was not adopted during the oxidation modification process, and only sulfonation modification was carried out, resulting in fewer polar groups on the fiber surface, decreased compatibility with the cement matrix, weaker interfacial bonding force, and reduced fiber reinforcement effect.

[0104] Comparative Example 5

[0105] Basically the same as Example 1, except that the hooked-end steel fibers with surface modification were not treated with dopamine hydrochloride coating, resulting in a decrease in the interfacial bonding force between the fibers and the cement matrix, a weakened crack resistance effect, and the fibers being prone to agglomeration during the mixing process, with poor dispersibility. Figure 5 Shows the interfacial morphology of unmodified hooked-end steel fibers in the concrete matrix, with obvious interfacial debonding phenomenon, indicating that the interfacial bonding force between the unmodified fibers and the matrix is weak, which easily affects the reinforcement effect.

[0106] Comparative Example 6

[0107] Basically the same as Example 1, except that the pH value of the dopamine hydrochloride solution was adjusted to 5.0, resulting in an unstable self-polymerization deposition process, uneven coating thickness, a decrease in the surface modification effect of the fibers, and affecting the interfacial bonding force and reinforcement effect.

[0108] Comparative Example 7

[0109] Basically the same as Example 1, except that the immersion time of the hooked-end steel fibers in the dopamine hydrochloride solution was shortened to 4 h, resulting in incomplete coating deposition, insufficient interfacial bonding force, a decrease in the fiber reinforcement effect, and the crack resistance performance not reaching the optimal level.

[0110] Comparative Example 8

[0111] Basically the same as Example 1, except that the drying temperature of the hooked-end steel fibers with surface modification was increased to 90 °C, resulting in uneven coating curing, peeling of the coating in some areas, a decrease in the interfacial bonding force, and affecting the overall crack resistance performance of the concrete.

[0112] Comparative Example 9

[0113] Basically the same as Example 1, except that the length of the rubber fibers at the millimeter scale was adjusted to 5 mm, resulting in a decrease in the crack bridging ability, a decrease in the fiber reinforcement effect, the crack resistance performance not reaching the optimal level, and affecting the durability of the concrete.

[0114] Comparative Example 10

[0115] It is basically the same as Example 1, except that the diameter of the micron-sized rubber fibers is adjusted to 200 μm, resulting in a weakened filling effect, a decreased pore optimization ability, a reduced anti-permeation performance, and insufficient interfacial bonding force, which affects the fiber reinforcement effect.

[0116] Performance test:

[0117] Anti-cracking performance test (four-point bending test): Referring to the ASTM C1609 standard, a four-point bending test is carried out on concrete specimens incorporated with surface-modified rubber fiber compositions and surface-modified end-hooked steel fibers. Prismatic specimens of 100×100×400 mm are used for the test, and the flexural strength and crack propagation behavior of the concrete are measured at a constant loading rate. By comparing the ultimate deflections and crack widths at different fiber dosages, the anti-cracking performance of fiber-reinforced concrete is evaluated, and the bridging effect of the fibers during the crack propagation process is analyzed.

[0118] Anti-permeation performance test (RCM rapid chloride migration test): According to the NT Build 492 standard, the rapid chloride migration (RCM) test is used to evaluate the anti-permeation performance of concrete. After curing the cylindrical specimens for 28 days, they are placed in a 10% NaCl solution, and a DC voltage of 30 V is applied at both ends for 6 hours. The chloride ion penetration depth is measured, and the diffusion coefficient is calculated to evaluate the anti-permeation performance.

[0119] Interfacial bonding performance test (single fiber pull-out test): Referring to the Pull-Out Test method, specimens with a single surface-modified end-hooked steel fiber embedded in the cement matrix are prepared, and a single fiber pull-out test is carried out using an electronic universal testing machine. The fiber pull-out load-displacement curve is recorded, and the interfacial shear strength between the fiber and the cement matrix is calculated. By comparing the pull-out loads of unmodified and modified fibers, the influence of the interfacial bonding force between the fiber and the matrix is analyzed.

[0120] Durability test (freeze-thaw cycle test): According to the ASTM C666 standard, a rapid freeze-thaw cycle test is carried out. Concrete specimens of 100×100×400 mm are placed in a freeze-thaw cycle environment of -20°C to 20°C, and after 300 cycles, the mass loss, relative dynamic elastic modulus, and crack propagation are measured.

[0121] Mechanical property test (compressive and splitting tensile strength): The compressive strength and splitting tensile strength tests are carried out in accordance with ASTM C39 and ASTM C496. Standard-sized concrete cubes (150×150×150 mm) and cylinders are prepared and mechanical tests are carried out after 28 days of curing. By comparing the strengths of specimens with different fiber dosages, the influence of fiber reinforcement on the overall mechanical properties of concrete is studied.

[0122] The properties of concretes of Examples 1 to 4 and Comparative Examples 1 to 10 are summarized in Table 1. It can be seen from the table that the failure to modify the surface of the waste rubber fibers leads to a decrease in interfacial bonding strength, fiber agglomeration affects the reinforcement effect, and reduces crack resistance and interfacial shear strength; the improper ratio of millimeter-level to micron-level fibers weakens the skeleton support, reduces the crack bridging ability, and at the same time, too many micron fibers affect the working performance and reduce the anti-penetration ability; the failure to use liquid nitrogen low-temperature embrittlement treatment makes the fiber morphology incomplete, the particle size distribution is uneven, the reinforcement effect is reduced, and the crack resistance and durability are reduced; the lack of potassium permanganate oxidation leads to a decrease in polar groups on the fiber surface, a decrease in compatibility with the cement matrix, a weakened interfacial bonding strength, and a decrease in crack resistance; the end hook steel fibers are not modified with dopamine hydrochloride coating, which makes the interface bonding The combined force is greatly reduced, the dispersion of the fiber in the concrete becomes worse, and the reinforcement effect is weakened; the pH value of the dopamine hydrochloride solution is too low, resulting in uneven coating, reduced interface bonding, and affecting the crack resistance; insufficient immersion time leads to incomplete coating deposition, insufficient interface bonding, and reduced crack resistance; excessive drying temperature leads to uneven coating curing, peeling in some areas, and reduced interface bonding, affecting the overall crack resistance of the concrete; the millimeter-level fiber length is too short, which weakens the crack bridging ability, affects the reinforcement effect, and reduces the overall durability; the micron-level fiber diameter is too large, resulting in reduced filling effect, weakened pore optimization ability, reduced anti-permeability performance, and insufficient interface bonding, affecting the fiber reinforcement effect. In general, a reasonable fiber modification process, optimized size and proportion are crucial to improving the crack resistance, anti-permeability and durability of concrete. Single parameter optimization is not enough to guarantee the overall performance, and coordinated optimization of various process parameters is required to achieve the best reinforcement effect.

[0123] Table 1 Performance summary of concrete of Examples 1 to 4 and Comparative Examples 1 to 10

[0124]

[0125]

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that all equivalent structural changes made under the concept of the present invention and using the contents of the present invention specification and drawings should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high crack resistance concrete, characterized in that: The invention comprises the following raw materials in parts by weight: 5.0-12.0 parts of surface modified rubber fiber composition, 20.0-35.0 parts of surface modified end hook steel fiber, 52.5300-400 parts of Portland cement PO, 50.0-80.0 parts of fly ash, 8.0-13.0 parts of silica fume, 1.5-3.0 parts of high-efficiency water reducing agent, 50-100 parts of mineral powder, 900-1100 parts of coarse aggregate, 600-750 parts of fine aggregate and 140-180 parts of water. The surface modified rubber fiber composition is obtained by subjecting the rubber fiber composition to alkali treatment, oxidation sulfonation and amination modification processes; The rubber fiber composition is composed of millimeter-scale rubber fibers and micrometer-scale rubber fibers; The rubber fiber compositions are obtained from waste rubber tires through liquid nitrogen low-temperature embrittlement, mechanical crushing, multi-stage ultrasonic vibration screening and eddy current sorting; The surface-modified end-hook steel fiber is obtained by subjecting the end-hook steel fiber to self-polymerization deposition of dopamine hydrochloride and surface modification by drying and solidification.

2. A high crack resistance concrete as claimed in claim 1, characterized in that: The preparation method of the surface modified rubber fiber composition is as follows: immersing the rubber fiber composition in an aqueous sodium hydroxide solution with a mass concentration of 8 to 12%, controlling the solid-liquid ratio to 1:(5 to 8), stirring at 50 to 100 rpm for 20 to 28 hours at 25 to 35°C, filtering and separating after the reaction, retaining the solid component and washing with deionized water until the filtrate conductivity is ≤50 μS / cm, and then treating in a vacuum drying oven at 40 to 60°C at an air flow rate of 10 to 15 m3 / h for 10 to 14 hours to obtain an alkali-treated intermediate; putting the obtained intermediate into an aqueous potassium permanganate solution with a mass concentration of 4 to 6%, adding a sulfuric acid solution with a mass concentration of 15 to 25% to adjust the system pH to 1.5 to 2.5, heating to 55 to 65°C at 2 to 5°C / min and maintaining The method comprises the following steps: the first step is to complete the oxidation modification for 1.5 to 2.5 hours, and after centrifugal separation, a sodium bisulfite solution with a mass concentration of 5 to 8% is used for sulfonation treatment at 60 to 70° C. for 0.8 to 1.2 hours, and a stirring rate of 150 to 250 rpm is controlled; the solid powder is then filtered and dried to obtain a sulfonated modified product, and then the sulfonated modified product is mixed with a urea aqueous solution with a mass concentration of 8 to 12% in a mass ratio of 1: (3 to 5), and the pH value is adjusted to 7.5 to 8.5 with ammonia water, and the temperature is raised to 85 to 95° C. at 3 to 5° C. / min for an amination reaction for 1.5 to 2.5 hours, and the reaction system is dehydrated at a pressure of 0.3 to 0.5 MPa by a plate and frame filter press, and then treated with hot air circulation at 70 to 80° C. in a fluidized bed dryer for 4 to 6 hours, and finally a surface-modified rubber fiber composition is obtained.

3. A high crack resistance concrete as claimed in claim 2, characterized in that: The mass ratio of the millimeter-scale rubber fiber to the micrometer-scale rubber fiber is (60-75):(25-40).

4. A high crack resistance concrete as claimed in claim 3, characterized in that: The average length of the millimeter-scale rubber fiber is 15.0-20.0 mm; the average diameter is 2.0-5.0 mm.

5. The high crack resistance concrete according to claim 3, characterized in that: The average length of the micrometer-scale rubber fiber is 500-900 μm, and the average diameter is 50-120 μm.

6. The high crack resistance concrete according to claim 4, characterized in that: The method for preparing the millimeter-scale rubber fiber is as follows: using waste rubber as raw material, placing the waste rubber tire in a liquid nitrogen environment at -132 to -138°C for embrittlement treatment, then using a grinder with a toothed disc gap of 2.0 to 5.0 mm to perform coarse crushing at a speed of 3500 to 4800 rpm, sieving through a multi-stage ultrasonic vibration screening system with a frequency of 12 to 15 kHz, and then removing metal impurities through an eddy current sorting device with a magnetic field strength of 0.8 to 1.2 T, and finally obtaining millimeter-scale rubber fibers.

7. The high crack resistance concrete according to claim 5, characterized in that: The preparation method of the micron-sized rubber fiber is as follows: using waste rubber as raw material, putting the coarsely crushed rubber particles into a liquid nitrogen-cooled ultrafine pulverizer, crushing for 90 to 150 minutes under the conditions of a rotation speed of 16500 to 18500 rpm and a liquid nitrogen injection flow rate of 0.5 to 1.2 L / min, monitoring the particle size distribution in real time through a laser diffractometer during the crushing process and dynamically adjusting the rotation speed to control the average fiber diameter to be 50 to 120 μm; introducing the crushed product into a two-stage turbine classification system, separating fibers with an average length of 300 to 800 μm at a main classification wheel at a rotation speed of 4500 to 6500 rpm, then using a 10 to 15 kV high-voltage electrostatic dispersion system for 30 to 60 minutes to eliminate fiber agglomeration, and finally obtaining the micron-sized rubber fiber.

8. The high crack resistance concrete according to claim 1, characterized in that: The preparation method of the surface modified end hook steel fiber is as follows: prepare a tris(hydroxymethyl)aminomethane buffer solution with a mass concentration of 0.008-0.015 mol / L and a pH value of 7.5-8.0, then add dopamine hydrochloride to the buffer solution, control the addition amount of dopamine hydrochloride to be 0.1-1.0wt% of the solution mass, and stir evenly to prepare a uniform dopamine hydrochloride solution, immerse the end hook steel fiber in the dopamine hydrochloride solution at a solid-liquid mass ratio of 0.4-0.6, control the immersion time to be 12-24 hours, take out the end hook steel fiber after the reaction is completed, rinse it with deionized water for 3 times to remove the residual dopamine hydrochloride on the surface, and then place it in a constant temperature environment with a temperature of 55-65°C for drying for 2-4 hours. During the drying process, weigh the sample every 2 hours. When the mass change rate of two adjacent weighing results is less than 0.01%, the drying process is completed, and finally the surface modified end hook steel fiber is obtained.

9. The high crack resistance concrete according to claim 1, characterized in that: The average length of the end hook steel fiber is 30-50 mm; the average diameter is 0.5-1.2 mm.

10. The method for preparing a high crack resistance concrete according to claim 1, characterized in that: The following steps are involved: S1. Dry the surface-modified rubber fiber composition and the surface-modified end-hook steel fiber at 50-60°C for 2-4 hours to remove residual surface moisture. At the same time, add fly ash, silica fume and mineral powder into a high-speed mixer according to the proportion, pre-mix at a low speed of 100-300rpm for 2-5min, then increase the stirring speed to 800-1200rpm, and continue mixing for 3-7min to ensure that the fine admixture is evenly distributed. Then, add silicate cement PO 52.5 into the mixer, and gradually add the pre-mixed fine admixture, stir at a speed of 300-500rpm for 3-5min, then slowly add water, and simultaneously add a high-efficiency water reducer to completely dissolve it within 2-4min, and continue stirring for 5-8min to form a uniform cement slurry; S2. Then, the coarse aggregate and the fine aggregate are added to the mixer in sequence, and dry mixed at a low speed of 50 to 100 rpm for 1 to 3 minutes to ensure that the aggregates are initially uniform; S3. On the basis of uniform dry mixing of aggregates, gradually add the prepared cement paste, while increasing the stirring speed to 200-400 rpm, and continue stirring for 3-5 minutes until a uniform matrix mixture is formed. While maintaining the stirring state, gradually add the surface-modified rubber fiber composition and the surface-modified end-hook steel fiber, and simultaneously increase the stirring speed to 200-300 rpm, and continue stirring for 5-10 minutes to ensure that the fibers are evenly dispersed in the concrete matrix and avoid fiber agglomeration or local enrichment; S4. Pour the uniformly mixed concrete mixture into the mold and vibrate it on a vibration table at 50 to 80 Hz for 30 to 60 seconds to remove the bubbles inside the concrete and improve the density. The molded concrete specimens are initially cured for 24 to 36 hours at room temperature and a relative humidity of ≥95%. After reaching the demoulding strength, the molds are removed and the specimens are transferred to a standard curing environment at room temperature and a relative humidity of ≥95% for standard curing for 24 to 28 days.

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