Anti-crack concrete and preparation method thereof

Abstract

The invention discloses anti-crack concrete and a preparation method thereof, and belongs to the technical field of concrete materials. The anti-crack concrete is prepared from the following raw materials in parts by weight: 300 to 500 parts of cement, 900 to 1200 parts of coarse aggregate, 600 to 800 parts of fine aggregate, 15 to 40 parts of admixture, 3 to 10 parts of water reducing agent, 20 to 50 parts of composite fiber reinforcing agent, 10 to 20 parts of filler, 1 to 3 parts of internal curing agent and 140 to 180 parts of water. The composite fiber reinforcing agent is formed by compounding basalt fibers and modified cotton stalk fibers according to the mass ratio of 1: (4-6). Through the triple effects of synergistic toughening of the composite fibers, microstructure compactness of the functional filler and continuous moisturizing of the internal curing agent, the obtained concrete has excellent crack resistance and excellent durability while maintaining good construction workability, and comprehensive improvement of the crack resistance is achieved.

Description

Technical Field

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

[0002] Concrete, as the most widely used and consumed man-made building material in the world today, is an indispensable structural and functional carrier for all kinds of construction projects. However, since its inception, cracking has been a persistent problem, becoming a major obstacle in the engineering field. Cracks not only damage the integrity and aesthetics of a structure, but more importantly, they provide convenient pathways for moisture, corrosive ions (such as chloride and sulfate ions), and oxygen, significantly accelerating the corrosion of internal steel reinforcement, carbonation and freeze-thaw damage of concrete, severely weakening the structure's load-bearing capacity, durability, and service life, and may even lead to catastrophic safety accidents, causing huge economic losses and resource waste.

[0003] Cracking of concrete is a complex physicochemical process, rooted in the inherent brittleness of the material and the combined effects of external environment and loads. Internally, chemical shrinkage during cement hydration, thermal expansion and contraction due to temperature changes, drying shrinkage caused by moisture evaporation, and settlement shrinkage during the plastic stage all generate tensile stress within the concrete. When these tensile stresses exceed the concrete's tensile strength at that time, cracks inevitably form. Externally, the design load on the structure, secondary stresses (such as uneven settlement and constrained deformation), early disturbances during construction (such as formwork deformation and improper curing), and long-term environmental effects (such as wet-dry cycles and freeze-thaw cycles) are all key external forces that induce and propagate cracks.

[0004] To suppress and control concrete cracking, long-term and in-depth research has been conducted in the fields of engineering technology and materials science, resulting in the development of various traditional technical routes. However, all of these have certain limitations: 1) Optimizing mix proportions and material selection: By reducing the water-cement ratio, selecting low-heat or micro-expansion cement, adding high-quality mineral admixtures (such as fly ash and slag powder), and optimizing aggregate gradation, shrinkage can be reduced to some extent, heat of hydration can be lowered, and density and tensile strength can be improved. However, this method has limited effect on improving cracking, especially for cracking caused by strong external constraints or drastic temperature and humidity changes, which is often difficult to completely avoid and may adversely affect workability or early strength. 2) Fiber reinforcement technology: Incorporating short-cut fibers (such as steel fibers, synthetic fibers, glass fibers, and natural fibers) into concrete is a widely used crack-resistant method. Fibers can bridge microcracks and hinder their propagation, thereby improving the toughness, crack resistance, and impact resistance of concrete. However, this technology has significant drawbacks: the effect is insignificant when the fiber content is too low; excessive content can lead to a sharp decrease in the fluidity of the mixture and fiber clumping, severely affecting construction performance and material uniformity. Some fibers (such as steel fibers) also pose a risk of corrosion, are costly, and may affect surface treatment. In addition, fibers mainly control micro and fine cracks, and have limited ability to suppress macroscopic structural cracks. 3) Chemical admixture approach: mainly including expanding agents and shrinkage reducing agents. Expanding agents compensate for some shrinkage by generating moderate volume expansion in the early stage of concrete hardening, but their expansion efficiency is greatly affected by curing conditions (especially moisture supply), and improper curing may lead to insufficient expansion or unfavorable delayed expansion in the later stage. Shrinkage reducing agents reduce capillary stress by reducing the surface tension of the pore solution, thereby reducing drying shrinkage, but their long-term effectiveness, adaptability to different cementitious material systems, and possible subtle effects on strength development still need attention. Using chemical admixtures alone is often insufficient to cope with complex, multi-factor coupled shrinkage stresses. 4) Design and construction measures: These include the reasonable setting of expansion joints and post-pouring strips, strengthening of structural reinforcement (such as using small-diameter, closely spaced steel mesh), and implementation of strict moisture-retaining and heat-preserving curing systems. While these measures are effective, they increase the complexity and time of construction, are sometimes constrained by structural form and site conditions, and cannot fundamentally improve the crack resistance of the concrete material itself.

[0005] In recent years, with the development of infrastructure towards ultra-long, ultra-large, and complex structures, and the unprecedented increase in requirements for building durability and sustainability, higher standards have been set for the crack resistance of concrete materials. Especially for projects involving large-volume concrete, thin-walled structures, prestressed structures, ultra-high-strength concrete, and projects in harsh environments, crack control has become one of the key technical bottlenecks determining the success or failure of a project. Therefore, developing a new type of crack-resistant concrete and its preparation method to improve the crack resistance and comprehensive mechanical properties of concrete is particularly urgent and important. Summary of the Invention

[0006] The purpose of this invention is to provide a crack-resistant concrete with comprehensive crack resistance and good construction adaptability, as well as a method for its preparation.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: A crack-resistant concrete is made from the following raw materials in parts by weight: 300-500 parts cement, 900-1200 parts coarse aggregate, 600-800 parts fine aggregate, 15-40 parts admixture, 3-10 parts water-reducing agent, 20-50 parts composite fiber reinforcing agent, 10-20 parts filler, 1-3 parts internal curing agent, and 140-180 parts water; wherein the composite fiber reinforcing agent is composed of basalt fiber and modified cotton stalk fiber in a mass ratio of 1:(4-6).

[0008] Preferably, the modified cotton stalk fiber is prepared by the following method: (1) After washing the cotton stalks, dry them and break them into small pieces of 1-3cm. Then, put them into a high-speed pulverizer to crush them, sieve them, and collect the fibers that pass through the 20-mesh sieve but are retained in the 60-mesh sieve for later use. (2) Dissolve Ca(OH)2 in deionized water and stir evenly to prepare a Ca(OH)2 solution of constant concentration. Then add the cotton stalk fiber obtained in step (1) into it according to the solid-liquid ratio and stir at 500-600 r / min at room temperature for 1-2 hours. (3) Transfer the alkali-treated cotton stalk fiber mixture to a high-pressure reactor, seal the reactor and introduce carbon dioxide gas to reach a fixed pressure, adjust the stirring rate, maintain this pressure at room temperature for 4-5 hours until the pH of the reaction system reaches 6.5-7.0, the reaction ends, take out the slurry, and wash the slurry with deionized water by centrifugation multiple times until the supernatant is clear. Vacuum dry the washed solid product to obtain modified cotton stalk fiber.

[0009] Preferably, the concentration of the Ca(OH)2 solution in step (2) is 0.8 wt%.

[0010] Preferably, in step (2), the solid-liquid ratio of cotton stalk fiber to Ca(OH)2 solution is 1 g: 20 mL.

[0011] Preferably, in step (3), the fixed pressure is 1.2 MPa and the stirring rate is 400-500 r / min.

[0012] Preferably, the admixture is at least one of fly ash, slag powder, and silica fume.

[0013] Preferably, the filler is composed of nano-silica and mica powder in a mass ratio of 2:1.

[0014] Preferably, the water-reducing agent is a high-efficiency polycarboxylate water-reducing agent.

[0015] Preferably, the internal protective agent is composed of sodium polyacrylate and vermiculite in a mass ratio of 2:1.

[0016] The present invention also provides a method for preparing the above-mentioned crack-resistant concrete, comprising the following steps: Step 1: Modified cotton stalk fiber is prepared using the above method, and it is mixed evenly with basalt fiber in a dry state in a certain proportion to obtain a composite fiber reinforcing agent for later use. Step 2: Mix sodium polyacrylate and vermiculite at a mass ratio of 2:1 to form an internal curing agent; add the internal curing agent to 40-60 times its total mass of mixing water, let it stand for 20-40 minutes to allow it to fully absorb water and become pre-saturated, forming a gel-like mixture. Step 3: Put the cement, admixture, fine aggregate, coarse aggregate, filler and the composite fiber reinforcing agent prepared in step 1 into the mixer and dry mix at a speed of 30-50 r / min for 60-120 seconds until the materials are evenly mixed and the fibers are dispersed without clumping. Step 4: Add the pre-saturated gel-like internal curing agent prepared in Step 2 into the mixer and stir at a speed of 40-60 r / min for 60-90 seconds to evenly disperse it in the concrete mix. Step 5: Discharge the final mixture, pour it into a container, compact it with mechanical vibration, and then cure it.

[0017] The crack-resistant concrete of this invention utilizes a composite of basalt fiber and modified cotton stalk fiber, which complement each other in terms of dimensionality, modulus, and surface properties. Basalt fiber possesses high strength, high elastic modulus, and excellent dispersibility, effectively inhibiting early-stage plastic shrinkage cracks and the propagation of macroscopic cracks after hardening. Modified cotton stalk fiber, after alkali-carbonation treatment, exhibits significantly improved surface roughness and activity, enhanced adhesion to the cement matrix, and its flexibility and water absorption / release properties can bridge fine cracks and alleviate localized stress concentrations at the microscopic level. The synergistic effect of both achieves multi-scale crack resistance throughout the entire process, from microscopic to macroscopic levels and from early to long-term effects.

[0018] This invention utilizes admixtures and specific fillers (a blend of nano-silica and mica powder) to leverage the micro-aggregate filling effect and pozzolanic activity effect. Nano-silica, with its high activity, reacts rapidly with cement hydration products, refining the pore structure; the flake-like structure of mica powder can be layered, blocking moisture and harmful ion channels. The synergistic effect of these two materials further densifies the microstructure of concrete, improving not only its mechanical properties but also its impermeability and erosion resistance, thereby comprehensively enhancing the long-term durability of concrete.

[0019] The internal curing agent used is a composite of highly absorbent sodium polyacrylate and porous, slow-release vermiculite in a specific ratio. Pre-water absorption treatment is performed before mixing to create distributed micro-reservoirs within the concrete. During cement hydration, as internal humidity decreases, the internal curing agent continuously releases moisture, effectively promoting the later-stage hydration of the cementitious materials. This significantly reduces internal tensile stress caused by self-drying and drying shrinkage, thereby lowering the risk of shrinkage cracks and improving the volume stability of the concrete.

[0020] Compared with existing technologies, the beneficial effects of this invention are as follows: By using a specific composite fiber reinforcing agent, this invention ensures uniform dispersion of fibers in concrete, avoids fiber clumping, and guarantees the homogeneity of the mixture. The internal curing agent is added in the form of a pre-saturated gel, which not only avoids the adverse competition for mixing water caused by directly adding dry powder, but also has a certain thickening and water-retaining effect, which is beneficial to improving the cohesiveness of concrete and reducing bleeding and segregation. Combined with the use of a high-efficiency polycarboxylate superplasticizer, the concrete achieves high crack resistance while maintaining good fluidity and pumpability, resulting in strong construction adaptability. Furthermore, the modified cotton stalk fiber is derived from agricultural waste cotton stalks. Through the modification treatment of this invention, its compatibility with cement is improved, while realizing the recycling of waste resources, reducing production costs, and reducing the environmental pollution that may be caused by traditional chemical modification, which is in line with the development direction of green building materials. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments, but is not limited thereto. The cement used in the present invention is ordinary Portland cement, grade 42.5R, and all raw materials are commercially available products unless otherwise specified.

[0022] Example 1 A crack-resistant concrete is made from the following raw materials in parts by weight: 300 kg of cement, 900 kg of coarse aggregate, 600 kg of fine aggregate, 15 kg of admixture, 3 kg of high-efficiency polycarboxylate superplasticizer, 20 kg of composite fiber reinforcing agent, 10 kg of filler, 1 kg of internal curing agent, and 140 kg of water; wherein the composite fiber reinforcing agent is composed of basalt fiber and modified cotton stalk fiber in a mass ratio of 1:4.

[0023] The modified cotton stalk fiber was prepared using the following method: (1) After washing the cotton stalks, dry them and break them into small pieces of 1-3cm. Then, put them into a high-speed pulverizer to crush them, sieve them, and collect the fibers that pass through the 20-mesh sieve but are retained in the 60-mesh sieve for later use. (2) Dissolve Ca(OH)2 in deionized water and stir evenly to prepare a Ca(OH)2 solution with a concentration of 0.8 wt%. Then add the cotton stalk fiber obtained in step (1) into it at a solid-liquid ratio of 1 g: 20 mL and stir at 500 r / min for 2 h at room temperature. (3) Transfer the alkali-treated cotton stalk fiber mixture to a high-pressure reactor, seal the reactor and introduce carbon dioxide gas to reach 1.2 MPa, adjust the stirring speed to 400 r / min, maintain this pressure at room temperature for 4 hours until the pH of the reaction system reaches 6.5, the reaction ends, take out the slurry, and wash the slurry with deionized water by centrifugation multiple times until the supernatant is clear. Vacuum dry the washed solid product to obtain modified cotton stalk fiber.

[0024] The admixture is fly ash; the filler is composed of nano-silica and mica powder in a mass ratio of 2:1; the internal curing agent is composed of sodium polyacrylate and vermiculite in a mass ratio of 2:1.

[0025] The above-mentioned method for preparing crack-resistant concrete includes the following steps: Step 1: Modified cotton stalk fiber is prepared using the above method, and it is mixed evenly with basalt fiber in a dry state in a certain proportion to obtain a composite fiber reinforcing agent for later use. Step 2: Mix sodium polyacrylate and vermiculite at a mass ratio of 2:1 to form an internal curing agent; add the internal curing agent to 40 times its total mass of mixing water, let it stand for 20 minutes to allow it to fully absorb water and become pre-saturated, forming a gel-like mixture. Step 3: Put the cement, admixture, fine aggregate, coarse aggregate, filler and the composite fiber reinforcing agent prepared in step 1 into the mixer and dry mix at a speed of 30 r / min for 120 seconds until the materials are evenly mixed and the fibers are dispersed without clumping. Step 4: Add the pre-saturated gel-like internal curing agent prepared in Step 2 into the mixer and stir at 40 r / min for 90 seconds to evenly disperse it in the concrete mix. Step 5: Discharge the final mixture, pour it into a container, compact it with mechanical vibration, and then cure it.

[0026] Example 2 A type of crack-resistant concrete is made from the following raw materials in parts by weight: 500 kg of cement, 1200 kg of coarse aggregate, 800 kg of fine aggregate, 40 kg of admixture, 10 kg of high-efficiency polycarboxylate superplasticizer, 50 kg of composite fiber reinforcing agent, 20 kg of filler, 3 kg of internal curing agent, and 180 kg of water; wherein the composite fiber reinforcing agent is composed of basalt fiber and modified cotton stalk fiber in a mass ratio of 1:6.

[0027] The modified cotton stalk fiber was prepared using the following method: (1) After washing the cotton stalks, dry them and break them into small pieces of 1-3cm. Then, put them into a high-speed pulverizer to crush them, sieve them, and collect the fibers that pass through the 20-mesh sieve but are retained in the 60-mesh sieve for later use. (2) Dissolve Ca(OH)2 in deionized water and stir evenly to prepare a Ca(OH)2 solution with a concentration of 0.8 wt%. Then add the cotton stalk fiber obtained in step (1) into it at a solid-liquid ratio of 1 g: 20 mL and stir at 600 r / min for 1 h at room temperature. (3) Transfer the alkali-treated cotton stalk fiber mixture to a high-pressure reactor, seal the reactor and introduce carbon dioxide gas to reach 1.2 MPa, adjust the stirring speed to 500 r / min, maintain this pressure at room temperature for 5 hours until the pH of the reaction system reaches 7.0, the reaction ends, take out the slurry, and wash the slurry with deionized water by centrifugation multiple times until the supernatant is clear. Vacuum dry the washed solid product to obtain modified cotton stalk fiber.

[0028] The admixture is slag powder; the filler is composed of nano-silica and mica powder in a mass ratio of 2:1; the internal curing agent is composed of sodium polyacrylate and vermiculite in a mass ratio of 2:1.

[0029] The above-mentioned method for preparing crack-resistant concrete includes the following steps: Step 1: Modified cotton stalk fiber is prepared using the above method, and it is mixed evenly with basalt fiber in a dry state in a certain proportion to obtain a composite fiber reinforcing agent for later use. Step 2: Mix sodium polyacrylate and vermiculite at a mass ratio of 2:1 to form an internal curing agent; add the internal curing agent to 60 times its total mass of mixing water, let it stand for 40 minutes to allow it to fully absorb water and become pre-saturated, forming a gel-like mixture. Step 3: Put the cement, admixture, fine aggregate, coarse aggregate, filler and the composite fiber reinforcing agent prepared in step 1 into the mixer and dry mix at a speed of 50 r / min for 60 seconds until the materials are evenly mixed and the fibers are dispersed without clumping. Step 4: Add the pre-saturated gel-like internal curing agent prepared in Step 2 into the mixer and stir at 60 r / min for 60 seconds to evenly disperse it in the concrete mix. Step 5: Discharge the final mixture, pour it into a container, compact it with mechanical vibration, and then cure it.

[0030] Example 3 A type of crack-resistant concrete is made from the following raw materials in parts by weight: 400 kg of cement, 1000 kg of coarse aggregate, 700 kg of fine aggregate, 30 kg of admixture, 6 kg of high-efficiency polycarboxylate superplasticizer, 40 kg of composite fiber reinforcing agent, 15 kg of filler, 2 kg of internal curing agent, and 160 kg of water; wherein the composite fiber reinforcing agent is composed of basalt fiber and modified cotton stalk fiber in a mass ratio of 1:5.

[0031] The modified cotton stalk fiber was prepared using the following method: (1) After washing the cotton stalks, dry them and break them into small pieces of 1-3cm. Then, put them into a high-speed pulverizer to crush them, sieve them, and collect the fibers that pass through the 20-mesh sieve but are retained in the 60-mesh sieve for later use. (2) Dissolve Ca(OH)2 in deionized water and stir evenly to prepare a Ca(OH)2 solution with a concentration of 0.8 wt%. Then add the cotton stalk fiber obtained in step (1) into it at a solid-liquid ratio of 1 g: 20 mL and stir at 550 r / min for 2 h at room temperature. (3) Transfer the alkali-treated cotton stalk fiber mixture to a high-pressure reactor, seal the reactor and introduce carbon dioxide gas to reach 1.2 MPa, adjust the stirring speed to 450 r / min, maintain this pressure at room temperature for 4.5 h until the pH of the reaction system reaches 6.8, the reaction ends, take out the slurry, and wash the slurry with deionized water by centrifugation multiple times until the supernatant is clear. Vacuum dry the washed solid product to obtain modified cotton stalk fiber.

[0032] The admixture is silica fume; the filler is composed of nano-silica and mica powder in a mass ratio of 2:1; the internal curing agent is composed of sodium polyacrylate and vermiculite in a mass ratio of 2:1.

[0033] The above-mentioned method for preparing crack-resistant concrete includes the following steps: Step 1: Modified cotton stalk fiber is prepared using the above method, and it is mixed evenly with basalt fiber in a dry state in a certain proportion to obtain a composite fiber reinforcing agent for later use. Step 2: Mix sodium polyacrylate and vermiculite at a mass ratio of 2:1 to form an internal curing agent; add the internal curing agent to 50 times its total mass of mixing water, let it stand for 30 minutes to allow it to fully absorb water and become pre-saturated, forming a gel-like mixture. Step 3: Add cement, admixture, fine aggregate, coarse aggregate, filler and composite fiber reinforcing agent prepared in step 1 into a mixer and dry mix at 40 r / min for 100 seconds until the materials are evenly mixed and the fibers are dispersed without clumping. Step 4: Add the pre-saturated gel-like internal curing agent prepared in Step 2 into the mixer and stir at 50 r / min for 80 seconds to evenly disperse it in the concrete mix. Step 5: Discharge the final mixture, pour it into a container, compact it with mechanical vibration, and then cure it.

[0034] Comparative Example 1 A crack-resistant concrete, the raw material ratio is the same as in Example 1 except that it does not contain composite fiber reinforcing agent.

[0035] Comparative Example 2 A crack-resistant concrete, wherein the composite fiber reinforcing agent in the raw material ratio is replaced with an equal amount of basalt fiber, and the rest is the same as in Example 1.

[0036] Comparative Example 3 A crack-resistant concrete, wherein the composite fiber reinforcing agent in the raw material ratio is replaced with an equal amount of modified cotton stalk fiber, and the rest is the same as in Example 1.

[0037] Comparative Example 4 A crack-resistant concrete, wherein the modified cotton stalk fiber in the composite fiber reinforcing agent of the raw material mix is ​​replaced with an equal amount of unmodified cotton stalk fiber, and the rest is the same as in Example 1. The specific preparation method of the unmodified cotton stalk fiber is as follows: The washed cotton stalks are dried and broken into small segments of 1-3 cm. The segments are then crushed in a high-speed pulverizer and sieved, with fibers that pass through a 20-mesh sieve but are retained in a 60-mesh sieve being collected. The collected sieved cotton stalk fibers are then vacuum dried to obtain unmodified cotton stalk fibers.

[0038] Comparative Example 5 A crack-resistant concrete, the raw material ratio does not contain fillers, and the rest is the same as in Example 1.

[0039] Comparative Example 6 A crack-resistant concrete, wherein the raw material ratio is the same as in Example 1 except that the filler is replaced with an equal amount of ordinary quartz powder.

[0040] Performance testing To further verify the performance of the crack-resistant concrete of the present invention, a series of standard performance tests were conducted on the concrete prepared in Examples 1-3 and Comparative Examples 1-6. The specific test methods are as follows: Slump and flowability: Tested in accordance with GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; Compressive strength and flexural strength: tested in accordance with GB / T50107-2010 "Standard for Testing and Evaluation of Concrete Strength"; Splitting tensile strength: Tested according to JTG 3420-2020 "Test Procedures for Cement and Cement Concrete in Highway Engineering"; Drying shrinkage and chloride ion permeability were tested according to GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete".

[0041] The specific test results are shown in Tables 1-2.

[0042] Table 1 Performance Test Results Table 2 Performance Test Results As can be seen from the data results in Tables 1-2 above, the concrete slump of Examples 1-3 of the present invention remained above 200 mm and the spread was greater than 500 mm, indicating that it had good fluidity and workability. Comparative Example 3 had the worst workability, indicating that single plant fiber had an adverse effect on fluidity, while the combination with basalt fiber effectively improved this problem, demonstrating the synergistic advantage of composite fibers in ensuring workability. In terms of compressive and flexural strength, Examples 1-3 of the present invention were significantly better than all comparative examples. Compared with Comparative Example 1, the 28-day compressive and flexural strengths of Example 1 increased by 18.7% and 51.9%, respectively. Compared with Comparative Examples 2 and 3, the flexural strength of Example 1 was 14.5% and 33.9% higher, respectively, indicating that the synergistic effect of the composite of basalt fiber and modified cotton stalk fiber, with both complementing each other in terms of load-bearing and crack resistance, was evident. The mechanical properties of Comparative Example 4 were all lower than those of Example 1, indicating that the modification treatment significantly improved the interfacial bonding between the fiber and the cement matrix, thus more effectively exerting its reinforcing effect. The strength of Comparative Examples 5 and 6 was lower than that of Examples 1-3, indicating that the specific functional filler of the present invention has a positive effect on improving the density and mechanical properties of concrete. Replacing or changing the amount and proportion of any of the raw materials will cause the corresponding effect to disappear or weaken.

[0043] Splitting tensile strength is a key direct mechanical indicator characterizing concrete's resistance to internal tensile stress and reflecting its crack resistance potential. The splitting tensile strength of Examples 1-3 of this invention is significantly higher than that of Comparative Examples 1-6. This higher splitting tensile strength indicates that the concrete of this invention has a higher safety threshold to resist internal tensile stress caused by shrinkage, temperature, etc., thus exhibiting excellent crack resistance. Chloride ion migration coefficient is a core indicator for evaluating concrete durability. The examples of this invention demonstrate excellent impermeability, with chloride ion migration coefficients far lower than those of the comparative examples. This also indicates that the concrete of this invention has excellent reinforcement protection and long-term durability potential. In particular, the comparison with Comparative Example 6 shows that the composite filler system of nano-silica and mica powder, through interaction with hydration products and physical barrier, can more effectively refine the pore structure and block permeation channels, thereby achieving excellent concrete durability. The concrete of this invention achieves a significant improvement in mechanical strength, a substantial reduction in drying shrinkage, and a significant improvement in chloride ion penetration resistance while ensuring good workability. The above data results indicate that: 1) the composite of the two fibers has a significant synergistic reinforcing effect; 2) the chemical modification of the cotton stalk fiber is crucial to its performance; and 3) the functional filler and internal curing agent system is indispensable for improving the volume stability and durability of concrete. The technical solution provided by this invention effectively solves the problems of easy cracking and insufficient durability in traditional concrete, and has broad application prospects.

[0044] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A crack-resistant concrete, characterized in that, It is made from the following raw materials in parts by weight: 300-500 parts cement, 900-1200 parts coarse aggregate, 600-800 parts fine aggregate, 15-40 parts admixture, 3-10 parts water-reducing agent, 20-50 parts composite fiber reinforcing agent, 10-20 parts filler, 1-3 parts internal curing agent, and 140-180 parts water; the composite fiber reinforcing agent is composed of basalt fiber and modified cotton stalk fiber in a mass ratio of 1:(4-6).

2. The crack-resistant concrete according to claim 1, characterized in that, The modified cotton stalk fiber was prepared using the following method: (1) After washing the cotton stalks, dry them and break them into small pieces of 1-3cm. Then, put them into a high-speed pulverizer to crush them, sieve them, and collect the fibers that pass through the 20-mesh sieve but are retained in the 60-mesh sieve for later use. (2) Dissolve Ca(OH)2 in deionized water and stir evenly to prepare a Ca(OH)2 solution of constant concentration. Then add the cotton stalk fiber obtained in step (1) into it according to the solid-liquid ratio and stir at 500-600 r / min at room temperature for 1-2 hours. (3) Transfer the alkali-treated cotton stalk fiber mixture to a high-pressure reactor, seal the reactor and introduce carbon dioxide gas to reach a fixed pressure, adjust the stirring rate, maintain this pressure at room temperature for 4-5 hours until the pH of the reaction system reaches 6.5-7.0, the reaction ends, take out the slurry, and wash the slurry with deionized water by centrifugation multiple times until the supernatant is clear. Vacuum dry the washed solid product to obtain modified cotton stalk fiber.

3. The crack-resistant concrete according to claim 2, characterized in that, The concentration of the Ca(OH)2 solution in step (2) is 0.8 wt%.

4. The crack-resistant concrete according to claim 2, characterized in that, In step (2), the solid-liquid ratio of cotton stalk fiber to Ca(OH)2 solution is 1 g: 20 mL.

5. The crack-resistant concrete according to claim 2, characterized in that, In step (3), the pressure is fixed at 1.2 MPa and the stirring rate is 400-500 r / min.

6. The crack-resistant concrete according to claim 1, characterized in that, The admixture is at least one of fly ash, slag powder, and silica fume.

7. The crack-resistant concrete according to claim 1, characterized in that, The filler is composed of nano-silica and mica powder in a mass ratio of 2:

1.

8. The crack-resistant concrete according to claim 1, characterized in that, The water-reducing agent is a high-efficiency polycarboxylate water-reducing agent.

9. The crack-resistant concrete according to claim 1, characterized in that, The internal curing agent is composed of sodium polyacrylate and vermiculite in a mass ratio of 2:

1.

10. A method for preparing crack-resistant concrete according to any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Prepare modified cotton stalk fiber using the method described in claims 2-4, and mix it evenly with basalt fiber in a dry state in a certain proportion to obtain a composite fiber reinforcing agent for later use; Step 2: Mix sodium polyacrylate and vermiculite at a mass ratio of 2:1 to form an internal curing agent; add the internal curing agent to 40-60 times its total mass of mixing water, let it stand for 20-40 minutes to allow it to fully absorb water and become pre-saturated, forming a gel-like mixture. Step 3: Put the cement, admixture, fine aggregate, coarse aggregate, filler and the composite fiber reinforcing agent prepared in step 1 into the mixer and dry mix at a speed of 30-50 r / min for 60-120 seconds until the materials are evenly mixed and the fibers are dispersed without clumping. Step 4: Add the pre-saturated gel-like internal curing agent prepared in Step 2 into the mixer and stir at a speed of 40-60 r / min for 60-90 seconds to evenly disperse it in the concrete mix. Step 5: Discharge the final mixture, pour it into a container, compact it with mechanical vibration, and then cure it.

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