High-crack-resistance premixed concrete and preparation method thereof

Abstract

The invention relates to the technical field of concrete, in particular to high-crack-resistance premixed concrete and a preparation method thereof. The invention discloses high-crack-resistance premixed concrete. Comprising the following raw materials in parts by weight: 160-180 parts of cement, 120-140 parts of gravel, 90-110 parts of fine aggregate, 30-50 parts of fly ash, 40-50 parts of slag powder, 25-30 parts of silica fume, 8-12 parts of modified rice hull ash, 6-8 parts of modified diatomite, 6-8 parts of steel fiber, 1.5-2.5 parts of polypropylene fiber, 1-2 parts of silicon dioxide, 3-5 parts of calcium carbonate, 2.5-3.5 parts of a polycarboxylate superplasticizer, 0.3-0.5 part of organic bentonite, 0.1-0.3 part of a defoaming agent and 85-95 parts of water. According to the high-crack-resistance premixed concrete provided by the invention, the crack resistance of the premixed concrete is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and in particular to a highly crack-resistant ready-mixed concrete and a preparation method thereof. Background Art

[0002] In modern construction, concrete is a crucial building material, and its performance directly impacts the quality, safety, and durability of buildings. Ready-mixed concrete, an advanced form of concrete production, boasts numerous advantages, including high production efficiency, stable quality, and convenient construction, making it widely used in various construction projects. However, with the increasing complexity and scale of building structures, coupled with rising environmental requirements, conventional ready-mixed concrete is increasingly lacking in crack resistance, failing to meet the demands of modern engineering for high-performance concrete materials.

[0003] High-crack-resistant ready-mix concrete is a new type of ready-mix concrete that significantly improves its resistance to crack formation and expansion by optimizing raw material selection, mix design, and the addition of special admixtures. Cracks are a common defect in concrete structures. They not only affect the building's appearance but also, more importantly, reduce the structure's load-bearing capacity, durability, and waterproofing, potentially leading to serious safety accidents. The emergence of high-crack-resistant ready-mix concrete provides an effective technical solution to the problem of concrete cracks.

[0004] Mix design is a core step in the preparation of highly crack-resistant ready-mixed concrete. However, some current mix design methods still have certain limitations, often focusing only on concrete strength indicators while ignoring the requirements for crack resistance. In actual design, there is a lack of comprehensive consideration of factors such as raw material properties, construction technology, and the operating environment, resulting in concrete crack resistance failing to achieve the desired effect. Based on this, the present invention proposes a highly crack-resistant ready-mixed concrete and a preparation method thereof. Summary of the Invention

[0005] The present invention provides a highly crack-resistant ready-mixed concrete and a preparation method thereof, which improve the crack resistance and mechanical properties of the ready-mixed concrete.

[0006] The technical solutions of the present invention are as follows: In a first aspect, the present invention provides a highly crack-resistant ready-mixed concrete, comprising the following raw materials in parts by weight: 160-180 parts of cement, 120-140 parts of crushed stone, 90-110 parts of fine aggregate, 30-50 parts of fly ash, 40-50 parts of slag powder, 25-30 parts of silica fume, 8-12 parts of modified rice husk ash, 6-8 parts of modified diatomaceous earth, 6-8 parts of steel fiber, 1.5-2.5 parts of polypropylene fiber, 1-2 parts of silicon dioxide, 3-5 parts of calcium carbonate, 2.5-3.5 parts of polycarboxylic acid water reducer, 0.3-0.5 parts of organic bentonite, 0.1-0.3 parts of defoaming agent, and 85-95 parts of water.

[0007] Nano-silica and nano-calcium carbonate enhance concrete strength through the synergistic effect of nano-scale filling and nucleation induction. Nano-silica has a high specific surface area and can fill the capillary pores in cement paste, forming chemical bonds with cement hydration products and strengthening the interfacial transition zone; nano-calcium carbonate acts as a nucleation inducer, promoting the directional growth of the cement hydration product CSH gel and refining the size of the hydration products. When the two work together, nano-silica preferentially fills the pores, and nano-calcium carbonate then induces the formation of a dense layer of hydration products on its surface, forming a "filling-induction" dual-effect strengthening mechanism. In addition, the introduction of nano-calcium carbonate can adjust the pH value of the concrete pore solution, promote the pozzolanic reaction of mineral admixtures such as fly ash and slag powder, and further enhance the later strength.

[0008] As a further technical solution, the preparation method of the modified rice husk ash includes: soaking fresh rice husks with a moisture content of ≤15wt% and a SiO2 content of ≥18wt% in dilute hydrochloric acid with a mass concentration of 5%-10%, soaking at room temperature for 20-24 hours, washing with water to neutrality after acid soaking, and drying to constant weight; controlling the heating rate to 4-6℃ / min to heat to 550-650℃ and calcining for 2-3 hours, adding a silane coupling agent and ball milling to obtain the product.

[0009] As a further technical solution, the mass ratio of the fresh rice husk to the dilute hydrochloric acid is 1:4-5.

[0010] As a further technical solution, the ball mill uses zirconia grinding balls, the ball-to-material ratio is 4-6:1, ethanol is used as the dispersion medium, the solid content is controlled at 25%-35%, and the ball milling is carried out at a rotation speed of 250-350 rpm for 4-5 hours.

[0011] As a further technical solution, the amount of the silane coupling agent added is 0.5%-1% by weight relative to the weight of the calcined product.

[0012] As a further technical solution, the preparation method of the modified diatomite includes: heating the diatomite to 500-600°C at a controlled heating rate of 4-6°C / min and calcining for 2-3 hours to obtain the calcined diatomite; then adding the diatomite to a suspension of nano-calcium carbonate; calcining the diatomite in a constant temperature water bath at 55-65°C and 250-350W with the assistance of ultrasound for 5-7 hours; drying the diatomite at 100-110°C to a constant weight; and grinding the diatomite to pass through a 400 mesh sieve.

[0013] As a further technical solution, the suspension of nano-calcium carbonate is obtained by dispersing 20 g of calcium carbonate with an average particle size of 20-50 nm in 800-900 mL of water.

[0014] As a further technical solution, the solid-liquid ratio of the diatomaceous earth and the suspension is 1g:9-11mL.

[0015] In a second aspect, the present invention provides a method for preparing highly crack-resistant ready-mixed concrete, comprising the following steps: (1) Add cement, crushed stone, fine aggregate, fly ash, slag powder, silica fume, modified rice husk ash, and modified diatomaceous earth into the mixer in sequence and dry mix for 1-2 minutes to fully mix the raw materials; (2) Add steel fiber, polypropylene fiber, silica, and calcium carbonate into a blender and continue stirring for 2-3 minutes to evenly disperse the fiber and nanomaterials in the mixture; (3) Mix water, polycarboxylic acid water reducer, organic bentonite and defoamer evenly, then slowly add them into the mixer and stir for 5-10 minutes; (4) Pour the freshly mixed concrete into a mold and allow it to solidify and cure.

[0016] As a further technical solution, the curing step includes: curing for 22-24 hours at a relative humidity ≥ 95% and a temperature of 20±2°C, then demolding, and then curing for at least 14 days at a relative humidity ≥ 95% and a temperature of 20±2°C.

[0017] The working principle and beneficial effects of the present invention are: The modified rice husk ash in the present invention is subjected to an acid leaching-calcination-coupling agent modification process, which significantly improves its volcanic ash activity. The acid leaching process removes impurities and exposes active SiO2, high-temperature calcination promotes SiO2 crystal transformation, and the silane coupling agent strengthens its interface bonding with the cement matrix through surface grafting. The modified diatomaceous earth is filled and strengthened with microscopic pores through calcination-nano calcium carbonate ultrasonic loading technology. Nano calcium carbonate is evenly dispersed in the diatomaceous earth pores to form a nanoscale reinforcing phase. When the two act synergistically, the active SiO2 in the modified rice husk ash undergoes a secondary hydration reaction with the cement hydration product Ca(OH)2 to generate CSH gel, which fills the microcracks in the cement stone-aggregate interface transition zone; the nanoscale pore structure of the modified diatomaceous earth further refines the pore size distribution of the concrete, reduces the total porosity, and forms a "micro-nano" multi-scale pore optimization system, which significantly improves the impermeability and density of the concrete.

[0018] The synergistic effect between the steel fibers and polypropylene fibers of the present invention improves the toughness of concrete. Steel fibers inhibit crack expansion through a bridging effect on a macro scale, and their high elastic modulus can effectively transfer stress and delay stress concentration at the crack tip; polypropylene fibers, on a micro scale, prevent the initiation and expansion of microcracks through a "microfiber" bridging effect. When the two work together, the steel fibers bear the main tensile stress, and the polypropylene fibers fill the microcracks between the steel fibers, forming a "macro-micro" two-level crack control network. In addition, polypropylene fibers have a low melting point and can partially melt to form pore channels during the early hydration heat release process of concrete, thereby improving the internal moisture distribution of concrete, reducing autogenous shrinkage stress, and further inhibiting early cracking.

[0019] This technical solution achieves comprehensive improvements in concrete performance through a three-dimensional "activity-pore-fiber" synergistic reinforcement model. Modified rice husk ash and modified diatomaceous earth provide pozzolanic activity, filling pores and refining pore size distribution. Steel fibers and polypropylene fibers inhibit crack propagation through cross-scale bridging. Nanosilica and nanocalcium carbonate strengthen the interfacial transition zone through nanoscale filling and nucleation induction. Organobentonite and polycarboxylate superplasticizer optimize workability and pore structure through rheological manipulation. These components work synergistically across five dimensions: activity activation, pore optimization, fiber toughening, nanoreinforcement, and rheological manipulation. This creates a multi-scale "micro-nano-macro" reinforcement system, significantly improving concrete's crack resistance, strength, and durability. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0021] The cement model in the present invention is Conch brand ordinary silicate PO42.5 cement; the crushed stone particle size is 10-20 mm; the fine aggregate is purchased from Shouyang Yongxing Stone Factory; the fly ash is Class II fly ash; the slag powder is purchased from Dezhou Hualian High-tech Co., Ltd.; the silica fume is purchased from Beijing Zhongjian Special Cement Co., Ltd.; the diatomaceous earth is purchased from Yixing Junlian Diatomaceous Earth Co., Ltd.; the steel fiber is 0.2-0.5 mm and 10-30 mm in length; the polypropylene fiber is 18-48 μm in diameter and 6-12 mm in length; and the polycarboxylate water reducer is purchased from Shanghai Kaiyin Chemical, with the brand name RHEOPLUS412.

[0022] Example 1 This embodiment provides a highly crack-resistant ready-mixed concrete, comprising the following raw materials in parts by weight: 170 parts of cement, 130 parts of crushed stone, 100 parts of fine aggregate, 40 parts of fly ash, 45 parts of slag powder, 27 parts of silica fume, 10 parts of modified rice husk ash, 7 parts of modified diatomaceous earth, 7 parts of steel fiber, 2 parts of polypropylene fiber, 1.5 parts of silicon dioxide, 4 parts of calcium carbonate, 3 parts of polycarboxylate water reducer, 0.4 parts of organic bentonite, 0.2 parts of defoaming agent, and 90 parts of water; The preparation method of modified rice husk ash includes: immersing 10g of fresh rice husk with a moisture content of 15wt% and a SiO2 content of 18wt% in 45g of dilute hydrochloric acid with a mass concentration of 7% at room temperature for 22h, washing with water to neutrality after acid immersion, and drying to constant weight; controlling the heating rate to 5℃ / min to heat to 600℃ and calcining for 2.5h, adding 0.7 parts by weight of silane coupling agent KH560 relative to the weight of the calcined product, ball milling, using zirconium oxide grinding balls, a ball-to-material ratio of 5:1, ethanol as the dispersion medium, and controlling the solid content to 30%, and ball milling at a speed of 300rpm for 4.5h to obtain the product; The preparation method of the modified diatomite includes: dispersing 20 g of calcium carbonate with an average particle size of 20 nm in 800 mL of water to obtain a suspension of nano-calcium carbonate; heating the diatomite to 500 ° C at a controlled heating rate of 4 ° C / min and calcining for 2 hours to obtain calcined diatomite, and then adding the diatomite to the suspension of nano-calcium carbonate at a solid-liquid ratio of 1 g:9 mL; keeping the mixture in a constant temperature water bath at 55 ° C and 250 W under ultrasonic assistance for 5 hours, drying at 100 ° C to constant weight, and grinding the mixture to pass through a 400 sieve to obtain the modified diatomite; A method for preparing highly crack-resistant ready-mixed concrete comprises the following steps: (1) Add cement, crushed stone, fine aggregate, fly ash, slag powder, silica fume, modified rice husk ash, and modified diatomaceous earth into the mixer in sequence, and dry mix at 600 rpm for 1 min to ensure that the raw materials are fully mixed; (2) Add steel fiber, polypropylene fiber, silica, and calcium carbonate into a blender and continue stirring at 600 rpm for 2 min to evenly disperse the fiber and nanomaterials in the mixture; (3) After mixing water, polycarboxylic acid water reducer, organic bentonite and defoamer evenly, slowly add them into the mixer and stir at 1000 rpm for 7 minutes; (4) The fresh concrete was poured into a mold for curing, and then cured at a relative humidity of 95% and a temperature of 20°C for 23 hours before demoulding. The concrete was then cured at a relative humidity of 95% and a temperature of 20°C for 14 days.

[0023] Example 2 This embodiment provides a highly crack-resistant ready-mixed concrete, comprising the following raw materials in parts by weight: 160 parts of cement, 120 parts of crushed stone, 90 parts of fine aggregate, 30 parts of fly ash, 40 parts of slag powder, 25 parts of silica fume, 8 parts of modified rice husk ash, 6 parts of modified diatomaceous earth, 6 parts of steel fiber, 1.5 parts of polypropylene fiber, 1 part of silicon dioxide, 3 parts of calcium carbonate, 2.5 parts of polycarboxylate water reducer, 0.3 parts of organic bentonite, 0.1 parts of defoaming agent, and 85 parts of water; The preparation method of modified rice husk ash includes: immersing 10g of fresh rice husk with a moisture content of 15wt% and a SiO2 content of 18wt% in 40g of dilute hydrochloric acid with a mass concentration of 5% at room temperature for 20h, washing with water to neutrality after acid immersion, and drying to constant weight; heating to 550°C at a controlled heating rate of 4°C / min and calcining for 2h, adding 0.5% of a silane coupling agent KH560 relative to the weight of the calcined product, and ball milling, using zirconium oxide grinding balls with a ball-to-material ratio of 4:1, ethanol as the dispersion medium, and controlling the solid content to be 25%, and ball milling at a speed of 250rpm for 4h to obtain the product; The preparation method of the modified diatomite includes: dispersing 20 g of calcium carbonate with an average particle size of 20 nm in 800 mL of water to obtain a suspension of nano-calcium carbonate; heating the diatomite to 500 ° C at a controlled heating rate of 4 ° C / min and calcining for 2 hours to obtain calcined diatomite, and then adding the diatomite to the suspension of nano-calcium carbonate at a solid-liquid ratio of 1 g:9 mL; keeping the mixture in a constant temperature water bath at 55 ° C and 250 W under ultrasonic assistance for 5 hours, drying at 100 ° C to constant weight, and grinding the mixture to pass through a 400 sieve to obtain the modified diatomite; A method for preparing highly crack-resistant ready-mixed concrete comprises the following steps: (1) Add cement, crushed stone, fine aggregate, fly ash, slag powder, silica fume, modified rice husk ash, and modified diatomaceous earth into the mixer in sequence, and dry mix at 600 rpm for 1 min to ensure that the raw materials are fully mixed; (2) Add steel fiber, polypropylene fiber, silica, and calcium carbonate into a blender and continue stirring at 600 rpm for 2 min to evenly disperse the fiber and nanomaterials in the mixture; (3) After mixing water, polycarboxylic acid water reducer, organic bentonite and defoamer evenly, slowly add them into the mixer and stir at 1000 rpm for 5 minutes; (4) The fresh concrete was poured into a mold for curing, and then cured at a relative humidity of 95% and a temperature of 20°C for 22 hours before demoulding. The concrete was then cured at a relative humidity of 95% and a temperature of 20°C for 14 days.

[0024] Example 3 This embodiment provides a highly crack-resistant ready-mixed concrete, comprising the following raw materials in parts by weight: 180 parts of cement, 140 parts of crushed stone, 110 parts of fine aggregate, 50 parts of fly ash, 50 parts of slag powder, 30 parts of silica fume, 12 parts of modified rice husk ash, 8 parts of modified diatomaceous earth, 8 parts of steel fiber, 2.5 parts of polypropylene fiber, 2 parts of silicon dioxide, 5 parts of calcium carbonate, 3.5 parts of polycarboxylate water reducer, 0.5 parts of organic bentonite, 0.3 parts of defoaming agent, and 95 parts of water; The preparation method of modified rice husk ash includes: immersing 10g of fresh rice husk with a moisture content of 15wt% and a SiO2 content of 18wt% in 50g of dilute hydrochloric acid with a mass concentration of 10% at room temperature for 24h, washing with water to neutrality after acid immersion, and drying to constant weight; heating to 650°C at a controlled heating rate of 6°C / min and calcining for 3h, adding 1% of a silane coupling agent KH560 relative to the weight of the calcined product, and ball milling, using zirconium oxide grinding balls with a ball-to-material ratio of 6:1, ethanol as the dispersion medium, and controlling the solid content to 35%, and ball milling at a rotation speed of 350rpm for 5h to obtain the product; The preparation method of the modified diatomite includes: dispersing 20g of calcium carbonate with an average particle size of 50nm in 900mL of water to obtain a suspension of nano-calcium carbonate; heating the diatomite to 600℃ at a controlled heating rate of 6℃ / min and calcining for 3h to obtain calcined diatomite, which is then added to the suspension of nano-calcium carbonate at a solid-liquid ratio of 1g:11mL; keeping the mixture in a constant temperature water bath at 65℃ and 350W ultrasonic assistance for 7h; drying at 110℃ to constant weight; and grinding the mixture to pass through a 400 sieve. The method for preparing the highly crack-resistant ready-mixed concrete comprises the following steps: (1) Add cement, crushed stone, fine aggregate, fly ash, slag powder, silica fume, modified rice husk ash, and modified diatomaceous earth into the mixer in sequence, and dry mix at 600 rpm for 2 minutes to ensure that the raw materials are fully mixed; (2) Add steel fiber, polypropylene fiber, silica, and calcium carbonate into a blender and continue stirring at 600 rpm for 3 min to evenly disperse the fiber and nanomaterials in the mixture; (3) After mixing water, polycarboxylic acid water reducer, organic bentonite and defoamer evenly, slowly add them into the mixer and stir at 1000 rpm for 10 minutes; (4) The fresh concrete is poured into a mold for curing, and then cured at a relative humidity of 95% and a temperature of 20°C for 24 hours before demoulding. The concrete is then cured at a relative humidity of 95% and a temperature of 20°C for 14 days.

[0025] Comparative Example 1 Adjustments were made based on Example 1. The difference from Example 1 was that the modified rice husk ash in Comparative Example 1 was replaced with rice husk ash of equal mass.

[0026] Comparative Example 2 Adjustments were made based on Example 1. Unlike Example 1, no modified rice husk ash was added as a raw material in Comparative Example 2.

[0027] Comparative Example 3 Adjustments were made based on Example 1. The difference from Example 1 was that the modified diatomaceous earth in Comparative Example 3 was replaced with calcined diatomaceous earth of equal mass.

[0028] Comparative Example 4 Adjustments were made based on Example 1. The difference from Example 1 was that the modified diatomaceous earth in Comparative Example 4 was replaced with diatomaceous earth of equal mass.

[0029] Comparative Example 5 Adjustments were made based on Example 1. Unlike Example 1, no modified diatomaceous earth was added as a raw material in Comparative Example 5.

[0030] Comparative Example 6 Adjustments were made based on Example 1. Different from Example 1, no polypropylene fiber was added as raw material in Comparative Example 6.

[0031] Test Example 1: The highly crack-resistant ready-mixed concrete prepared in Examples 1-3 and Comparative Examples 1-6 was subjected to the following tests: Chloride ion penetration resistance: The chloride ion penetration depth of the standard test block is tested according to the rapid chloride ion migration coefficient method in GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete"; Flexural strength: Standard test blocks were prepared in accordance with GB / T50081-2016 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", and the flexural strength of the standard test blocks was measured after 7 days and 28 days of curing. Compressive strength: Standard test blocks were made in accordance with GB / T50081-2016 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", and the compressive strength of the standard test blocks was measured after 7 days and 28 days of curing; Crack resistance: Test the crack resistance of the specimens in accordance with the standards in 3.0.4 of JGJ / T 193-2009 "Concrete Durability Test and Evaluation Standard"; The results are shown in Table 1 below: Table 1

[0032] Combined with the above, all samples from Examples 1-3 exhibit excellent overall performance, including low chloride ion penetration depth, high strength, and crack resistance grade I. This is attributed to the treatment with modified rice husk ash and modified diatomaceous earth, which enhances volcanic ash activity and density while reducing porosity. The synergistic effect of steel fiber and polypropylene fiber enhances toughness and crack control. Silica and calcium carbonate fill micropores, improving strength and durability.

[0033] In Comparative Example 1, modified rice husk ash was replaced with rice husk ash. The results showed increased chloride ion penetration depth, decreased 28-day flexural strength, decreased 28-day compressive strength, and a decrease in crack resistance to II. Unmodified rice husk ash exhibits low activity and poor bonding with cement, resulting in increased porosity and a weak interface. This demonstrates that modification treatments (acid leaching, calcination, and KH560 coupling agent) are crucial for improving durability and strength.

[0034] In Comparative Example 2, which omitted modified rice husk ash, performance deteriorated further, with increased chloride ion penetration depth, decreased 28-day flexural strength, decreased 28-day compressive strength, and a crack resistance rating of II. The filling and activation effects of modified rice husk ash were completely absent, and concrete density was significantly reduced. This demonstrates that modified rice husk ash is a key component in improving impermeability and strength.

[0035] In Comparative Example 3, the modified diatomite was replaced with calcined diatomite. Performance decreased slightly, with increased chloride ion penetration depth, decreased 28-day flexural strength, and decreased 28-day compressive strength, while maintaining a crack resistance grade of 1. Calcined diatomite exhibits some activity, but lacks nano-calcium carbonate modification, resulting in insufficient microstructural strengthening. This demonstrates that the introduction of nano-calcium carbonate (ultrasound-assisted loading) is key to improving diatomite performance.

[0036] In Comparative Example 4, modified diatomite was replaced with diatomite. Performance declined moderately, with increased chloride ion penetration depth, decreased 28-day flexural strength, decreased 28-day compressive strength, and a lower crack resistance rating of II. The original diatomite was uncalcined, had high impurities, and lacked optimized porosity, resulting in lower activity. This highlights the necessity of calcination and nano-modification to improve interfacial bonding.

[0037] Comparative Example 5, which omitted modified diatomite, exhibited significantly lower performance, increased chloride ion penetration depth, decreased 28d flexural strength and 28d compressive strength, and achieved a crack resistance rating of II. The modified diatomite's micropore-filling and reinforcing properties were completely absent, resulting in a reduced overall density of the concrete. This demonstrates the irreplaceable contribution of modified diatomite to durability and strength.

[0038] Comparative Example 6, which omitted polypropylene fiber, exhibited a significant decrease in crack resistance (grade dropped from I to III), a slight increase in chloride ion penetration depth, and a decrease in both 28-day flexural strength and 28-day compressive strength. Removing polypropylene fiber weakened crack bridging, increasing the risk of premature cracking. Other properties were less affected, as the fiber primarily contributes to toughness rather than strength. This emphasizes the central role of polypropylene fiber in crack-resistant design.

[0039] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A highly crack-resistant ready-mixed concrete, characterized in that: The invention comprises the following raw materials in parts by weight: 160-180 parts of cement, 120-140 parts of crushed stone, 90-110 parts of fine aggregate, 30-50 parts of fly ash, 40-50 parts of slag powder, 25-30 parts of silica fume, 8-12 parts of modified rice husk ash, 6-8 parts of modified diatomaceous earth, 6-8 parts of steel fiber, 1.5-2.5 parts of polypropylene fiber, 1-2 parts of silicon dioxide, 3-5 parts of calcium carbonate, 2.5-3.5 parts of polycarboxylic acid water reducer, 0.3-0.5 parts of organic bentonite, 0.1-0.3 parts of defoaming agent and 85-95 parts of water.

2. A highly crack-resistant ready-mixed concrete according to claim 1, characterized in that: The preparation method of the modified rice husk ash includes: immersing fresh rice husks with a moisture content of ≤15wt% and a SiO2 content of ≥18wt% in dilute hydrochloric acid with a mass concentration of 5% to 10% at room temperature for 20-24 hours, washing with water to neutrality after acid immersion, and drying to constant weight; controlling the heating rate to 4-6°C / min to heat to 550-650°C, calcining for 2-3 hours, adding a silane coupling agent and performing ball milling to obtain the modified rice husk ash.

3. A highly crack-resistant ready-mixed concrete according to claim 2, characterized in that: The mass ratio of the fresh rice husk to the dilute hydrochloric acid is 1:4-5.

4. A highly crack-resistant ready-mixed concrete according to claim 2, characterized in that: The ball mill uses zirconia grinding balls, the ball-to-material ratio is 4-6:1, ethanol is used as the dispersion medium, the solid content is controlled at 25% to 35%, and the ball milling is carried out at a rotation speed of 250-350 rpm for 4-5 hours.

5. A highly crack-resistant ready-mixed concrete according to claim 2, characterized in that: The amount of the silane coupling agent added is 0.5%-1% by weight relative to the weight of the calcined product.

6. A highly crack-resistant ready-mixed concrete according to claim 1, characterized in that: The preparation method of the modified diatomite comprises: heating the diatomite to 500-600°C at a controlled heating rate of 4-6°C / min, calcining for 2-3 hours to obtain the calcined diatomite; then adding the calcined diatomite to a suspension of nano-calcium carbonate; simmering the diatomite in a constant temperature water bath at 55-65°C and 250-350W with ultrasonic assistance for 5-7 hours; drying the diatomite at 100-110°C to a constant weight; and grinding the diatomite to pass through a 400-grit sieve.

7. A highly crack-resistant ready-mixed concrete according to claim 6, characterized in that: The nano calcium carbonate suspension is obtained by dispersing 20 g of calcium carbonate with an average particle size of 20-50 nm in 800-900 mL of water.

8. The highly crack-resistant ready-mixed concrete according to claim 6, characterized in that: The solid-liquid ratio of the diatomaceous earth and the suspension is 1g:9-11mL.

9. A method for preparing highly crack-resistant ready-mixed concrete according to any one of claims 1 to 8, characterized in that the steps include: (1) Add cement, crushed stone, fine aggregate, fly ash, slag powder, silica fume, modified rice husk ash, and modified diatomaceous earth into the mixer in sequence and dry mix for 1-2 minutes to fully mix the raw materials; (2) Add steel fiber, polypropylene fiber, silica, and calcium carbonate into a blender and continue stirring for 2-3 minutes to evenly disperse the fiber and nanomaterials in the mixture; (3) Mix water, polycarboxylic acid water reducer, organic bentonite and defoamer evenly, then slowly add them into the mixer and stir for 5-10 minutes; (4) Pour the freshly mixed concrete into a mold and allow it to solidify and cure.

10. The method for preparing highly crack-resistant ready-mixed concrete according to claim 9, characterized in that: The curing step comprises: curing for 22-24 hours at a relative humidity of ≥95% and a temperature of 20±2°C, then demoulding, and then curing for at least 14 days at a relative humidity of ≥95% and a temperature of 20±2°C.

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