A modified coral microcrystal composite fiber-based concrete material and a preparation method thereof

Abstract

The present application relates to the technical field of building materials, and in particular to a concrete material based on modified coral microcrystalline composite fiber and a preparation method thereof. The concrete material based on modified coral microcrystalline composite fiber comprises cementitious materials, coarse aggregate, fine aggregate, modified coral microcrystalline composite fiber, water reducing agent and mixing water. The modified coral microcrystalline composite fiber is prepared by wet spinning with modified coral microcrystalline and polyvinyl alcohol as raw materials. The modified coral microcrystalline is aragonite type calcium carbonate microcrystalline modified by a silane coupling agent. By adding the modified coral microcrystalline composite fiber to the concrete base material, the industry pain point of traditional fibers that are not toughened and not enhanced in compressive resistance is solved. The 28d splitting tensile strength, bending toughness and compressive strength of the prepared concrete material are simultaneously improved, and a comprehensive breakthrough in the mechanical properties of concrete is achieved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a concrete material based on modified coral microcrystalline composite fibers and its preparation method. Background Technology

[0002] Concrete, as the most widely used and important basic material in the construction industry, has many advantages such as high strength, simple construction, and low cost. However, the hydration reaction of concrete generates a certain amount of heat, which can easily cause internal cracking. These internal cracks not only allow water to easily penetrate the concrete but also reduce its crack resistance, directly affecting its service life.

[0003] Currently, the mainstream technology for crack-resistant and toughening modification of concrete materials is fiber reinforcement modification. Commonly used reinforcing fibers are mainly divided into steel fibers, synthetic organic fibers, and plant fibers. However, existing fiber modification technologies still have unavoidable core defects in practical engineering applications: although steel fibers have higher strength, they are too expensive, and steel fibers are prone to corrosion in concrete, leading to reduced or failed interfacial strength; although synthetic organic fibers have better toughness, they have poor compatibility with the concrete matrix interface, insufficient interfacial adhesion, requiring additional complex surface modification, and the raw materials rely on the petrochemical industry chain, resulting in high carbon emissions during the preparation process, and high transportation costs when used in remote marine engineering; although natural plant fibers are widely available and inexpensive, they are prone to cellulose degradation in the highly alkaline pore fluid of concrete, and the reinforcing effect continues to decline after long-term service. Moreover, the fiber and concrete matrix are only mechanically bonded, and the interfacial transition zone is loose and weak, making it easy for the fiber to detach and pull out. At the same time, the introduction of fibers generally leads to a 3% to 8% decrease in the compressive strength of concrete, making it impossible to achieve "simultaneous improvement of toughness and reinforcement". Summary of the Invention

[0004] To overcome the above problems, the present invention provides a concrete material based on modified coral microcrystalline composite fiber and its preparation method.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a concrete material based on modified coral microcrystalline composite fibers, wherein the raw materials comprise, by weight: 300-450 parts of cementitious material, 900-1200 parts of coarse aggregate, 600-800 parts of fine aggregate, 3-15 parts of modified coral microcrystalline composite fiber, 3-8 parts of water-reducing agent and 120-180 parts of mixing water; The cementitious material includes cement and mineral admixtures; The modified coral microcrystalline composite fiber is prepared by wet spinning of modified coral microcrystalline and polyvinyl alcohol (PVA) as raw materials; the modified coral microcrystalline accounts for 5% to 21% of the total mass of the modified coral microcrystalline and polyvinyl alcohol; the polyvinyl alcohol accounts for 79% to 95% of the total mass of the modified coral microcrystalline and polyvinyl alcohol. The modified coral microcrystals are aragonite-type calcium carbonate microcrystals modified with silane coupling agents.

[0006] A second aspect of the present invention provides a method for preparing the concrete material based on modified coral microcrystalline composite fibers as described in the first aspect, comprising the following steps: After the cementitious material, coarse aggregate and fine aggregate are mixed evenly, modified coral microcrystalline composite fiber is added, and the mixture is mixed evenly again to obtain dry mixed material. The water-reducing agent is dissolved in the mixing water to obtain a mixture; A mixture is added to the dry-mixed material and mixed evenly to obtain a concrete material based on modified coral microcrystalline composite fiber.

[0007] The beneficial effects of this invention are as follows: (1) This invention solves the industry pain point of traditional fibers “toughening without enhancing compressive strength” by adding modified coral microcrystalline composite fibers to concrete substrate. The concrete material based on modified coral microcrystalline composite fibers prepared has a 28-day splitting tensile strength that is 35%~70% higher than that of the benchmark concrete, a flexural strength that is 35%~75% higher, a bending toughness that is 110%~200% higher, and a compressive strength that is 6%~34% higher, thus achieving a comprehensive breakthrough in the mechanical properties of concrete materials.

[0008] (2) The core reinforcing phase of the modified coral microcrystalline composite fiber of the present invention is aragonite-type calcium carbonate microcrystals, which are chemically homologous with cement hydration products. This can induce the hydration products to grow in situ on the fiber surface, achieving a dual bonding of "chemical bonding + mechanical binding". At the same time, the fiber has no cellulose component, which completely solves the problem of degradation of plant fibers in a high-alkali environment. The strength continues to increase steadily at 90 days without performance degradation.

[0009] (3) The components in this invention work together to significantly improve the early crack resistance and long-term structural stability of concrete materials, which can meet the long-term service requirements of various harsh engineering environments. At the same time, the concrete mixing, pouring and curing process is completely consistent with that of ordinary concrete, without the need for any additional construction equipment. The fiber has good dispersion and no problem of clumping and pump blockage, making it easy to implement on a large scale.

[0010] (4) This invention uses waste coral reef debris from waterway dredging as raw material to prepare highly active coral microcrystals and synthesize modified coral microcrystal composite fibers, which solves the ecological problem of long-term accumulation of marine solid waste and realizes the high-value and functional utilization of solid waste. Detailed Implementation

[0011] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0012] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0013] Currently, the mainstream technology for crack-resistant and toughening modification of concrete materials is fiber reinforcement modification. Commonly used reinforcing fibers are mainly divided into steel fibers, synthetic organic fibers, and plant fibers. However, existing fiber modification technologies still have unavoidable core defects in practical engineering applications: although steel fibers have higher strength, they are too expensive, and steel fibers are prone to corrosion in concrete, leading to reduced or failed interfacial strength; although synthetic organic fibers have better toughness, they have poor compatibility with the concrete matrix interface, insufficient interfacial adhesion, requiring additional complex surface modification, and the raw materials rely on the petrochemical industry chain, resulting in high carbon emissions during the preparation process, and high transportation costs when used in remote marine engineering; although natural plant fibers are widely available and inexpensive, they are prone to cellulose degradation in the highly alkaline pore fluid of concrete, and the reinforcing effect continues to decline after long-term service. Moreover, the fiber and concrete matrix are only mechanically bonded, and the interfacial transition zone is loose and weak, making it easy for the fiber to detach and pull out. At the same time, the introduction of fibers generally leads to a 3% to 8% decrease in the compressive strength of concrete, making it impossible to achieve "simultaneous improvement of toughness and reinforcement".

[0014] To overcome the above problems, the present invention provides a concrete material based on modified coral microcrystalline composite fiber and its preparation method.

[0015] This invention addresses the industry pain point of traditional fibers "increasing toughness but not compressive strength" by adding modified coral microcrystalline composite fibers to concrete substrates. The concrete material prepared based on modified coral microcrystalline composite fibers has a 28-day splitting tensile strength that is 35%~70% higher than that of the benchmark concrete, a flexural strength that is 35%~75% higher, a flexural toughness that is 110%~200% higher, and a compressive strength that is 6%~34% higher, achieving a comprehensive breakthrough in the mechanical properties of concrete materials.

[0016] The specific reasons are as follows: Modified coral microcrystalline composite fibers have the effect of "microscopic nucleus reinforcement - mesoscopic interface strengthening - macroscopic crack resistance and toughening"; the highly active aragonite-type calcium carbonate microcrystals exposed on the surface of modified coral microcrystalline composite fibers can serve as heterogeneous nuclei for cement hydration, inducing CSH gel to grow in situ on the fiber surface, realizing the chemical bonding between hydration products and fibers, and fundamentally solving the problem of fiber debonding failure; the core reinforcing phase of modified coral microcrystalline composite fibers is aragonite-type calcium carbonate, which is chemically homologous with cement hydration products, avoiding the interface mismatch problem between traditional fibers and matrix, greatly optimizing the structure of the interface transition zone, and reducing interface porosity; modified coral microcrystalline composite fibers can cross the micro-cracks and macro-cracks that initiate in concrete materials, directly bear tensile stress, prevent crack propagation, and consume a large amount of energy through fiber pull-out and fracture processes, greatly improving the toughness and deformation resistance of concrete.

[0017] Furthermore, this invention achieves chemical bonding between hydration products and fibers through the nucleation effect of modified coral microcrystals, transforming the loose interfacial transition zone into a dense structure and significantly improving matrix density and interfacial bond strength. Simultaneously, the multi-level crack-resistant effect of the fibers effectively inhibits the initiation and propagation of microcracks in concrete during hydration hardening and service. Combined with the pore-refining effect of mineral admixtures, this further enhances the volume stability and crack resistance of concrete, enabling the material to meet the long-term safe service requirements of various engineering structures.

[0018] Cementitious materials provide the basic strength of concrete materials. Ordinary Portland cement is the core cementitious component, which generates hydration products through hydration reaction to build the concrete matrix skeleton. Mineral admixtures can optimize the matrix pore structure, reduce the heat of hydration, reduce the initiation of temperature cracks, and at the same time, work synergistically with coral microcrystals to improve the matrix density and improve the long-term durability of concrete.

[0019] Coarse and fine aggregates provide skeletal support for concrete. Using crushed stone or coral gravel, river sand or coral sand, it can meet the local material needs of different engineering scenarios inland and marine islands. Continuously graded aggregates can optimize the workability of concrete, reduce the amount of cementitious materials, and reduce the risk of shrinkage cracking.

[0020] Polycarboxylate superplasticizers can be used to reduce the water-cement ratio of concrete, further improve the density and mechanical properties of the matrix, while ensuring the workability of fresh concrete, offsetting the loss of fluidity caused by fiber introduction, and meeting the construction requirements of pumping, pouring and other engineering projects.

[0021] The components in this invention work synergistically to significantly improve the early crack resistance and long-term structural stability of concrete materials, which can meet the long-term service requirements of various harsh engineering environments. At the same time, the concrete mixing, pouring and curing processes are completely consistent with ordinary concrete, requiring no additional construction equipment. The fiber has good dispersibility, no clumping or pump blockage problems, and is easy to implement on a large scale.

[0022] A first typical embodiment of the present invention provides a concrete material based on modified coral microcrystalline composite fibers, the raw materials of which comprise, by weight: 300-450 parts of cementitious material, 900-1200 parts of coarse aggregate, 600-800 parts of fine aggregate, 3-15 parts of modified coral microcrystalline composite fiber, 3-8 parts of water-reducing agent and 120-180 parts of mixing water; The cementitious material includes cement and mineral admixtures; The modified coral microcrystalline composite fiber is prepared by wet spinning of modified coral microcrystalline and polyvinyl alcohol (PVA) as raw materials; the modified coral microcrystalline accounts for 5% to 21% of the total mass of the modified coral microcrystalline and polyvinyl alcohol; the polyvinyl alcohol accounts for 79% to 95% of the total mass of the modified coral microcrystalline and polyvinyl alcohol. The modified coral microcrystals are aragonite-type calcium carbonate microcrystals modified with silane coupling agents.

[0023] In one or more embodiments, the mass ratio of cement to mineral admixtures in the cementitious material is (20~35):(5~15); Preferably, the cement is P·O42.5 grade or higher silicate cement; Preferably, the mineral admixture is S95 grade or higher slag powder, Class I F fly ash, or has a specific surface area ≥15000 m². 2 One or more of the silica fume per kg.

[0024] In one or more embodiments, the coarse aggregate is 5-25 mm continuously graded crushed stone or coral crushed stone, with a crushing index ≤10%.

[0025] In one or more embodiments, the fine aggregate is river sand or coral sand with a fineness modulus of 2.3 to 3.0 and a mud content (by mass) of ≤1%.

[0026] In one or more embodiments, the modified coral microcrystalline composite fiber has a fiber diameter of 10~50 μm, a length of 6~15 mm, a tensile strength of 400~700 MPa, and an elastic modulus of 15~25 GPa.

[0027] In one or more embodiments, the method for preparing the modified coral microcrystalline composite fiber includes the following steps: Coral reef fragments are ground and sieved to obtain coarse coral powder; Coral microcrystals are obtained by ball milling and grading coarse coral powder. Modified coral microcrystals were obtained by surface modification of coral microcrystals with a silane coupling agent; Modified coral microcrystals, polyvinyl alcohol, auxiliaries, and deionized water are mixed evenly to obtain a spinning solution; the spinning solution is then wet-spun to obtain modified coral microcrystal composite fibers.

[0028] Preferably, the coral microcrystals have a D50 of 500 nm to 2 μm and an aragonite-type calcium carbonate content of ≥95%; Preferably, the method for obtaining modified coral microcrystals by surface modification with a silane coupling agent includes: Coral microcrystals were dispersed in anhydrous ethanol, a silane coupling agent was added, and the mixture was stirred in a water bath at 50-60°C for 2-3 hours. After the reaction was completed, the mixture was filtered and dried to obtain modified coral microcrystals. More preferably, the mass ratio of coral microcrystals to silane coupling agent is 1:(0.01~0.03). More preferably, the mass fraction of coral microcrystals in anhydrous ethanol is 10%~15%; More preferably, the silane coupling agent is one of KH550, KH560 or KH570; Preferably, the polyvinyl alcohol is type 1788, with a degree of polymerization of 1700 and a degree of alcoholysis of 88%. Preferably, the adjuvant includes glycerin and an antioxidant; The mass ratio of glycerol to antioxidant is (2.5~4):1.

[0029] Preferably, the mass ratio of modified coral microcrystals, polyvinyl alcohol, additives and deionized water is (5~20):(80~95):(1~3):(400~600).

[0030] Preferably, the method for obtaining modified coral microcrystalline composite fibers by wet spinning of the spinning solution includes: Modified coral microcrystalline composite fibers are obtained by degassing, filtering, wet spinning, multi-stage stretching and orientation, heat setting and cutting of the spinning solution.

[0031] More preferably, during the multi-stage stretching orientation process, the total stretching ratio is 6 to 10 times; More preferably, the heat setting temperature is 120~160℃.

[0032] In one or more embodiments, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a water reduction rate ≥25% and a solid content of 40%±2%.

[0033] A second typical embodiment of the present invention provides a method for preparing the concrete material based on modified coral microcrystalline composite fibers as described in the first aspect, comprising the following steps: After the cementitious material, coarse aggregate and fine aggregate are mixed evenly, modified coral microcrystalline composite fiber is added, and the mixture is mixed evenly again to obtain dry mixed material. The water-reducing agent is dissolved in the mixing water to obtain a mixture; A mixture is added to the dry-mixed material and mixed evenly to obtain a concrete material based on modified coral microcrystalline composite fiber.

[0034] In one or more embodiments, a method for obtaining a dry-mixed material by uniformly mixing cementitious materials, coarse aggregates, and fine aggregates, then adding modified coral microcrystalline composite fibers, and mixing again until uniformly mixed includes: Coarse and fine aggregates are put into a twin-shaft forced mixer and dry-mixed for 30-60 seconds. Then, cementitious materials are added and dry-mixed for 60-90 seconds. Finally, coral microcrystalline composite fibers are added and dry-mixed for 90-120 seconds.

[0035] In one or more embodiments, a mixing liquid is added to the dry mixture and the mixture is stirred to achieve uniform mixing; the stirring rate is 100~120 r / min and the stirring time is 120~180 s.

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0037] Example 1 A concrete material based on modified coral microcrystalline composite fiber, the raw materials of which include, by weight: 300 parts of cementitious material, 1200 parts of coarse aggregate, 800 parts of fine aggregate, 3 parts of modified coral microcrystalline composite fiber, 3 parts of water-reducing agent and 180 parts of mixing water; The cementitious material consists of 200 parts of P·O42.5 cement, 50 parts of S95 slag powder and 50 parts of Grade I fly ash; The coarse aggregate consists of 5-25 mm continuously graded coral gravel; The fine aggregate is coral sand with a fineness modulus of 2.3 to 3.0 and a mud content of ≤1%. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent; The preparation method of modified coral microcrystalline composite fibers is as follows: Marine waste coral reef fragments were placed in a forced-air drying oven and dried at 105℃ to constant weight. The dried coral reef fragments were then placed in a ball mill and ground at 300 rpm for 30 min. The powder was passed through a 100-mesh standard sieve to obtain coarse coral powder. After wet ball milling (with anhydrous ethanol as an additive) for 2 h, coral microcrystals with a D50 of 2 μm and an aragonite-type calcium carbonate content of 95.3% were obtained. The coral microcrystals were dispersed in anhydrous ethanol to prepare a 10% (w / w) suspension. 1% (w / w) of KH560 silane coupling agent was added to the suspension, and the mixture was stirred in a water bath at 50℃ for 3 h. After filtration and drying, modified coral microcrystals were obtained.

[0038] Five parts by weight of modified coral microcrystals, 93.7 parts by weight of PVA resin, 1.0 part by weight of glycerin, and 0.3 parts by weight of antioxidant 1010 were added to 567 parts by weight of deionized water. The mixture was stirred at 90°C for 6 hours to prepare a spinning solution. After vacuum degassing and filtration through a 200-mesh filter, the solution was extruded using a wet spinning process, solidified in a sodium sulfate coagulation bath, stretched 6 times, heat-set at 120°C, dried, and then cut to obtain modified coral microcrystal composite fibers. The modified coral microcrystal composite fibers have a fiber length of 6 mm, a diameter of 40-50 μm, a tensile strength of 480 MPa, and an elastic modulus of 16 GPa.

[0039] Preparation of concrete materials based on modified coral microcrystalline composite fibers: Coral gravel and coral sand were added to a twin-shaft forced mixer according to the specified ratio and dry-mixed for 30 seconds. P·O42.5 cement, slag powder, and fly ash were added and dry-mixed for another 60 seconds. Modified coral microcrystalline composite fibers were then added and dry-mixed for another 90 seconds to obtain a uniformly dispersed dry-mixed material. Mixing water containing polycarboxylate superplasticizer was added to the dry-mixed material and stirred at 100 r / min for 120 seconds to obtain concrete material based on modified coral microcrystalline composite fibers with a slump of 180 mm. After pouring, vibration, and demolding, the finished product was obtained after 28 days of standard curing.

[0040] Example 2 A concrete material based on modified coral microcrystalline composite fiber, the raw materials of which include, by weight: The mixture consists of 370 parts cementitious material, 1100 parts coarse aggregate, 720 parts fine aggregate, 9 parts modified coral microcrystalline composite fiber, 5.2 parts water-reducing agent, and 150 parts mixing water. The cementitious material consists of 265 parts of P·O42.5 cement, 60 parts of S95 slag powder and 45 parts of Grade I fly ash; The coarse aggregate is 5~25 mm continuously graded crushed stone; The fine aggregate is river sand with a fineness modulus of 2.3 to 3.0 and a mud content of ≤1%. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent; The preparation method of modified coral microcrystalline composite fibers is as follows: Marine waste coral reef fragments were placed in a forced-air drying oven and dried at 108℃ to constant weight. The dried coral reef fragments were then placed in a ball mill and ground at 350 rpm for 38 min. The powder was passed through a 100-mesh standard sieve to obtain coarse coral powder. After wet ball milling (with anhydrous ethanol as an additive) for 3 h, coral microcrystals with a D50 of 1 μm and an aragonite-type calcium carbonate content of 96.2% were obtained. The coral microcrystals were dispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 12%. 2% KH560 silane coupling agent by mass of the coral microcrystals was added, and the mixture was stirred in a water bath at 55℃ for 2.5 h. After filtration and drying, modified coral microcrystals were obtained.

[0041] 10 parts by weight of modified coral microcrystals, 88 parts by weight of PVA resin, 1.5 parts by weight of glycerol, and 0.5 parts by weight of antioxidant 1010 were added to 456 parts by weight of deionized water. The mixture was stirred at 90℃ for 6 hours to prepare a spinning solution. After vacuum degassing and filtration through a 200-mesh filter, the solution was extruded through a spinneret using a wet spinning process. The solution was then coagulated in a sodium sulfate coagulation bath, stretched 8 times, heat-set at 120℃, dried, and cut to obtain modified coral microcrystal composite fibers. The modified coral microcrystal composite fibers have a fiber length of 12 mm, a diameter of 20-30 μm, a tensile strength of 620 MPa, and an elastic modulus of 22 GPa.

[0042] Preparation method of concrete material based on modified coral microcrystalline composite fiber: According to the mixing ratio, crushed stone and river sand are put into a twin-shaft forced mixer and dry-mixed for 45 seconds. Cement, slag powder and fly ash are added and dry-mixed for another 75 seconds. Then, the prepared coral microcrystalline composite fiber is added and dry-mixed for 100 seconds to obtain a uniformly dispersed dry-mixed material. Mixing water containing polycarboxylate superplasticizer is added to the dry-mixed material and stirred at 110 r / min for 150 seconds to obtain concrete material based on modified coral microcrystalline composite fiber with a slump of 160 mm. After pouring, vibration and demolding, the finished product is obtained after standard curing for 28 days.

[0043] Example 3 A concrete material based on modified coral microcrystalline composite fiber, the raw materials of which include, by weight: 420 parts of cementitious material, 1000 parts of coarse aggregate, 650 parts of fine aggregate, 15 parts of modified coral microcrystalline composite fiber, 7.2 parts of water-reducing agent and 135 parts of mixing water; The cementitious material consists of 350 parts of P·O42.5 cement, 40 parts of S95 slag powder and 30 parts of silica fume. The coarse aggregate is 5~25 mm continuously graded crushed stone; The fine aggregate is river sand with a fineness modulus of 2.3 to 3.0 and a mud content of ≤1%. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent; The preparation method of modified coral microcrystalline composite fibers is as follows: Marine waste coral reef fragments were placed in a forced-air drying oven and dried at 110℃ to constant weight. The dried coral reef fragments were then placed in a ball mill and ground at 400 rpm for 45 min. The powder was passed through a 100-mesh standard sieve to obtain coarse coral powder. After wet ball milling (with anhydrous ethanol as an additive) for 4 h, coral microcrystals with a D50 of 800 nm and an aragonite-type calcium carbonate content of 95.8% were obtained. The coral microcrystals were dispersed in anhydrous ethanol to prepare a suspension with a mass fraction of approximately 15%. 3% KH560 silane coupling agent by mass of the coral microcrystals was added, and the mixture was stirred in a water bath at 60℃ for 2 h. After filtration and drying, modified coral microcrystals were obtained.

[0044] 20 parts by weight of modified coral microcrystals, 78.5 parts by weight of PVA resin, 1.2 parts by weight of glycerol, and 0.3 parts by weight of antioxidant 1010 were added to 400 parts by weight of deionized water. The mixture was stirred at 90℃ for 6 hours to prepare a spinning solution. After vacuum degassing and filtration through a 200-mesh filter, the solution was extruded through a spinneret using a wet spinning process. The solution was then coagulated in a sodium sulfate coagulation bath, stretched 10 times, heat-set at 160℃, dried, and cut to obtain modified coral microcrystal composite fibers. The modified coral microcrystal composite fibers have a fiber length of 15 mm, a diameter of 10–20 μm, a tensile strength of 680 MPa, and an elastic modulus of 24 GPa.

[0045] Preparation of concrete materials based on modified coral microcrystalline composite fibers: According to the mixing ratio, crushed stone and river sand are put into a twin-shaft forced mixer and dry-mixed for 60 s. P·O42.5 cement, slag powder and fly ash are added and dry-mixed for another 90 s. Modified coral microcrystalline composite fiber is then added and dry-mixed for 120 s to obtain a uniformly dispersed dry-mixed material. Mixing water containing polycarboxylate superplasticizer is added to the dry-mixed material and stirred at 120 r / min for 180 s to obtain concrete material based on modified coral microcrystalline composite fiber with a slump of 120 mm. After pouring, vibration and demolding, the finished product is obtained after standard curing for 28 days.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is that the coral microcrystals were not modified with silane coupling agent, while the other components and preparation methods are the same as in Example 1.

[0047] Comparative Example 2 The difference between this comparative example and Example 1 is that the coral coarse powder was not subjected to ultrafine wet ball milling, and the composite fiber was prepared directly from the coral coarse powder. The other components and preparation methods are the same as in Example 1.

[0048] Comparative Example 3 The difference between this comparative example and Example 1 is that no coral microcrystalline composite fiber was added, while the other components and preparation methods are the same as in Example 1.

[0049] Comparative Example 4 The difference between this comparative example and Example 1 is that the amount of coral microcrystalline composite fiber added is 1 part, while the other components and preparation methods are the same as in Example 1.

[0050] Comparative Example 5 The difference between this comparative example and Example 1 is that the amount of coral microcrystalline composite fiber added is 20 parts, while the other components and preparation methods are the same as in Example 1.

[0051] Comparative Example 6 The difference between this comparative example and Example 1 is that the modified coral microcrystals account for 3% of the total mass of the modified coral microcrystals and polyvinyl alcohol, and the mass ratio of modified coral microcrystals, polyvinyl alcohol, additives and deionized water is 3:97:2:455.5. The other components and preparation methods are the same as in Example 1.

[0052] Comparative Example 7 The difference between this comparative example and Example 1 is that the modified coral microcrystals account for 25% of the total mass of the modified coral microcrystals and polyvinyl alcohol, and the mass ratio of modified coral microcrystals, polyvinyl alcohol, additives and deionized water is 25:75:2:464.7. The other components and preparation methods are the same as in Example 1.

[0053] Comparative Example 8 The difference between this comparative example and Example 1 is that the coral microcrystalline composite fiber is replaced with an equal mass of ordinary PVA fiber, while the other components and preparation methods are the same as in Example 1.

[0054] Comparative Example 9 The difference between this comparative example and Example 1 is that the coral microcrystalline composite fiber is replaced with an equal mass of engineering bamboo fiber, while the other components and preparation methods are the same as in Example 1.

[0055] Comparative Example 10 The difference between this comparative example and Example 1 is that no mineral admixtures were added, while the other components and preparation methods are the same as in Example 1.

[0056] Comparative Example 11 The difference between this comparative example and Example 1 is that no polycarboxylate superplasticizer was added, while the other components and preparation methods are the same as in Example 1.

[0057] Comparative Example 12 The difference between this comparative example and Example 1 is that multi-stage stretching and orientation were not performed during the preparation of the composite fiber, while the other components and preparation methods are the same as in Example 1.

[0058] Experimental Example 1 The performance of the concrete materials prepared in Examples 1-3 and Comparative Examples 1-12 was tested.

[0059] The 28-day cubic compressive strength, 28-day splitting tensile strength, and 28-day flexural strength were all tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete"; the 28-day flexural toughness was tested according to CECS 13:2009 "Standard for Test Methods of Fiber Reinforced Concrete" for its energy absorption value; the 90-day compressive strength growth rate was calculated based on the measured values ​​of the 90-day and 28-day compressive strengths; the results are shown in Table 1.

[0060] Table 1 Performance test results of each embodiment and comparative example

[0061] Analysis of the data in Table 1 shows that: Comparative Example 1 did not undergo surface modification with a silane coupling agent on the coral microcrystals, resulting in a significant decrease in interfacial adhesion. Its 28-day compressive strength was 4.6% lower than that of Example 1, and its flexural toughness was 16.8% lower. Comparative Example 2 did not undergo ultrafine wet ball milling of the coral coarse powder, preventing the coarse microcrystals from exerting a nucleation reinforcement effect. Its 28-day compressive strength was 5.6% lower than that of Example 1, and its flexural toughness was 19.6% lower. Comparative Example 12 did not undergo multi-stage stretching and orientation, resulting in insufficient fiber strength and orientation. Its 28-day compressive strength was 6.9% lower than that of Example 1, and its flexural toughness was 26.2% lower.

[0062] In Comparative Example 4, the fiber content was only 1 part, far below the minimum effective content of 3 parts in this invention. The fibers could not form an effective bridging and crack-resistant network, resulting in extremely weak reinforcement. The 28-day compressive strength was only 0.2% higher than the blank reference Comparative Example 3, while the flexural toughness was 32.0% higher. In Comparative Example 5, the fiber content was as high as 20 parts, exceeding the maximum saturated content of 15 parts in this invention. The fibers severely agglomerated during stirring, introducing numerous internal defects, resulting in a 28-day compressive strength that was actually 1.7% lower than the blank reference, and a flexural toughness that was only 18.0% higher.

[0063] In Comparative Example 6, the modified coral microcrystals accounted for only 3%, and the insufficient reinforcing phase resulted in a 6.7% lower 28-day compressive strength and a 26.2% lower flexural toughness compared to Example 1. In Comparative Example 7, the modified coral microcrystals accounted for as much as 25%, and severe agglomeration of the microcrystals introduced a large number of internal defects. The 28-day compressive strength was 7.6% lower than that of Example 1, and the flexural toughness was 31.8% lower. It is worth noting that the deterioration effect of excessive microcrystal agglomeration is slightly greater than that of insufficient microcrystals. This is because agglomerated microcrystals not only fail to play a reinforcing role, but also become stress concentration sources, accelerating the initiation and propagation of cracks.

[0064] Compared with Comparative Example 8 (ordinary PVA fiber) and Comparative Example 9 (bamboo fiber), the 28-day compressive strength of the concrete material prepared in Example 1 of the present invention is 8.0% and 8.5% higher, respectively, and the flexural toughness is 62.1% and 78.3% higher, respectively. In particular, compared with Comparative Example 9, its 90-day strength growth rate is only 5.2%, which is much lower than that of the embodiments of the present invention (>10%).

[0065] Comparative Example 10, without the addition of mineral admixtures and using only pure cement as the cementitious material, showed a slight improvement in early strength at 28 days. However, the lack of pore structure refinement from mineral admixtures resulted in decreased long-term durability and a significantly increased heat of hydration, making it prone to temperature cracking. Overall performance was still far inferior to the embodiments of this invention. Comparative Example 11, without the addition of polycarboxylate-based high-efficiency water-reducing agent, exhibited extremely poor workability and could not be properly vibrated to achieve compaction.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A concrete material based on modified coral microcrystalline composite fibers, characterized in that, Its raw materials, by weight, include: 300-450 parts of cementitious material, 900-1200 parts of coarse aggregate, 600-800 parts of fine aggregate, 3-15 parts of modified coral microcrystalline composite fiber, 3-8 parts of water-reducing agent and 120-180 parts of mixing water; The cementitious material includes cement and mineral admixtures; The modified coral microcrystalline composite fiber is prepared by wet spinning using modified coral microcrystalline and polyvinyl alcohol as raw materials; the modified coral microcrystalline accounts for 5% to 21% of the total mass of the modified coral microcrystalline and polyvinyl alcohol; and the polyvinyl alcohol accounts for 79% to 95% of the total mass of the modified coral microcrystalline and polyvinyl alcohol. The modified coral microcrystals are aragonite-type calcium carbonate microcrystals modified with silane coupling agent; the mass ratio of coral microcrystals to silane coupling agent is 1:(0.01~0.03); the silane coupling agent is one of KH550, KH560 or KH570; The preparation method of the modified coral microcrystalline composite fiber includes the following steps: Coral reef fragments are ground and sieved to obtain coarse coral powder; the coarse coral powder is ball-milled and graded to obtain coral microcrystals; the coral microcrystals are surface-modified with a silane coupling agent to obtain modified coral microcrystals; the modified coral microcrystals, polyvinyl alcohol, auxiliaries and deionized water are mixed evenly to obtain a spinning solution; the spinning solution is wet-spun to obtain modified coral microcrystal composite fibers. Coral microcrystals have a D50 of 500 nm to 2 μm and an aragonite-type calcium carbonate content of ≥95%. The exposed aragonite-type calcium carbonate microcrystals on the surface of the modified coral microcrystalline composite fiber serve as heterogeneous nuclei for cement hydration, inducing the in-situ directional growth of CSH gel on the fiber surface.

2. The concrete material as described in claim 1, characterized in that, In cementitious materials, the mass ratio of cement to mineral admixtures is (20~35):(5~15); The cement is P·O42.5 grade or higher silicate cement; The mineral admixture is S95 grade or higher slag powder, Class I F fly ash, or a material with a specific surface area ≥15000 m². 2 One or more of the silica fume per kg.

3. The concrete material as described in claim 1, characterized in that, The coarse aggregate is 5~25mm continuously graded crushed stone or coral crushed stone, with a crushing index ≤10%; The fine aggregate is river sand or coral sand with a fineness modulus of 2.3 to 3.0 and a mud content of ≤1%. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a water reduction rate of ≥25% and a solid content of 40%±2%.

4. The concrete material as described in claim 1, characterized in that, The modified coral microcrystalline composite fiber has a fiber diameter of 10~50 μm, a length of 6~15 mm, a tensile strength of 400~700 MPa, and an elastic modulus of 15~25 GPa.

5. The concrete material as described in claim 1, characterized in that, Polyvinyl alcohol of type 1788 with a degree of polymerization of 1700 and a degree of alcoholysis of 88% is selected; the additives include glycerol and antioxidants; the mass ratio of glycerol to antioxidant is (2.5~4):1; The mass ratio of modified coral microcrystals, polyvinyl alcohol, additives and deionized water is (5~20):(80~95):(1~3):(400~600). Methods for obtaining modified coral microcrystalline composite fibers by wet spinning of spinning solution include: Modified coral microcrystalline composite fibers are obtained by degassing, filtering, wet spinning, multi-stage stretching and orientation, heat setting and cutting of the spinning solution. During the multi-stage stretching orientation process, the total stretching ratio is 6 to 10 times; The heat setting temperature is 120~160℃.

6. The method for preparing the concrete material according to any one of claims 1 to 5, characterized in that, Includes the following steps: After the cementitious material, coarse aggregate and fine aggregate are mixed evenly, modified coral microcrystalline composite fiber is added, and the mixture is mixed evenly again to obtain dry mixed material. The water-reducing agent is dissolved in the mixing water to obtain a mixture; A mixture is added to the dry-mixed material and mixed evenly to obtain a concrete material based on modified coral microcrystalline composite fiber.

7. The preparation method according to claim 6, characterized in that, Methods for obtaining dry-mixed materials by uniformly mixing cementitious materials, coarse aggregates, and fine aggregates, then adding modified coral microcrystalline composite fibers, and mixing again until uniform, include: Coarse and fine aggregates are put into a twin-shaft forced mixer and dry-mixed for 30-60 seconds. Then, cementitious materials are added and dry-mixed for 60-90 seconds. Finally, coral microcrystalline composite fibers are added and dry-mixed for 90-120 seconds. Add the mixing liquid to the dry mixture and mix it evenly by stirring; the stirring rate is 100~120 r / min and the stirring time is 120~180 s.

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