Fiber reinforced anti-cracking concrete and method for preparing the same

Abstract

The application discloses a fiber-reinforced anti-cracking concrete and a preparation method thereof, and relates to the technical field of building materials, and comprises the following raw material components: cement 310-450 parts, water 150-190 parts, coarse aggregate 930-1200 parts, fine aggregate 630-800 parts, mineral active admixture 80-180 parts, multi-component composite fiber 1.2-18 parts, polycarboxylate superplasticizer 1.8-4.5 parts, and anti-cracking synergistic system 20-35 parts. The four-component fiber system is used to form a three-dimensional interlocking net-shaped anti-cracking framework in the concrete slurry, so that the problems of limited single-fiber reinforcing effect and insufficient interface bonding force between the fiber and the concrete matrix are solved, and the anti-cracking performance and the mechanical properties of the concrete are improved.

Description

Technical Field

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

[0002] Concrete, as a core material in civil engineering, directly affects the durability, safety, and service life of a structure due to its crack resistance. However, due to its inherent brittleness, traditional concrete is prone to cracking during the setting and hardening process due to temperature changes, shrinkage stress, or loads, leading to problems such as moisture penetration and steel corrosion, which severely shortens the service life of the structure.

[0003] Patent CN118580031B discloses a fiber-reinforced crack-resistant asphalt concrete and its preparation method. The patent reduces the excessive deformation of asphalt concrete caused by the decrease in strength under wet conditions. At the same time, the sepiolite layer absorbs water and expands to form a water-blocking layer, which fixes the absorbed water and reduces the strong dynamic water pressure generated by rutting in the asphalt concrete by the infiltrated water. This reduces the erosion of the asphalt concrete pores by water, so that the asphalt and aggregate maintain a stable bonding strength and reduce the generation of cracks.

[0004] The aforementioned patent improves the crack resistance of asphalt concrete through sepiolite modification, but it relies on sepiolite to absorb water and expand to form a physical water-blocking layer, which does not inhibit the chemical shrinkage of cement-based concrete. At the same time, the fiber-matrix interface is still not optimized.

[0005] Therefore, this application proposes a fiber-reinforced crack-resistant concrete and its preparation method that can optimize the interface structure through multiple crack-resistant mechanisms to improve the crack resistance performance throughout the entire life cycle. Summary of the Invention

[0006] The purpose of this invention is to provide a fiber-reinforced crack-resistant concrete and its preparation method, in order to solve the technical problem mentioned in the background art that concrete, due to its inherent brittleness, is prone to cracking during the setting and hardening process due to temperature changes, shrinkage stress, or load, leading to water penetration and steel corrosion.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a fiber-reinforced crack-resistant concrete, comprising the following raw material components: 310-450 parts cement, 150-190 parts water, 930-1200 parts coarse aggregate, 630-800 parts fine aggregate, 80-180 parts mineral active admixture, 1.2-18 parts multi-component composite fiber, 1.8-4.5 parts polycarboxylate superplasticizer, and 20-35 parts crack-resistant enhancement system;

[0008] The coarse aggregate is graded crushed stone with a particle size of 4-25mm, the fine aggregate is manufactured sand with a fineness modulus of 1.8-2.8, and the mineral active admixture includes fly ash and slag powder with a specific surface area ≥450m² / kg, and the mass ratio of fly ash to slag powder is 5-8:1-4.

[0009] Preferably, the multi-component composite fiber is composed of a quaternary fiber system, which includes a main reinforcing fiber, a rigid reinforcing fiber, and a functional regulating fiber.

[0010] The main reinforcing fibers are polyethylene fibers with a length of 16-20 mm and polypropylene fibers with a length of 13-24 mm, with a mass ratio of 1.5-3.5:1;

[0011] The rigid reinforcing fiber is basalt fiber with a length of 20-28mm;

[0012] The functional regulating fiber is a short carbon fiber filament with a length of 8-10mm, accounting for 8%-15% of the total mass of the composite fiber;

[0013] After surface treatment, the quaternary fiber system forms a rough interface. The surface of polyethylene / polypropylene fiber is oxidized and etched to form a micro-groove structure with Ra 4.0-6.0μm. The surface of basalt / carbon fiber is grafted with silane coupling agent KH550 to form a reactive interface transition layer.

[0014] Preferably, the fly ash can also be Class F, Grade I, with a loss on ignition ≤5%.

[0015] Preferably, the crack-resistant enhancement system is a dual-mechanism crack-resistant component, which includes a crack-inhibiting component and an expansion component. The crack-inhibiting component consists of sepiolite powder with a particle size of 0.02-0.08 mm, hydroxypropyl methylcellulose ether, and a water-reducing agent with a fineness ≤75 μm in a mass ratio of 7:1.5:2.

[0016] The expansion component includes a calcium sulfoaluminate-based expansion agent with a magnesium oxide content of ≤4%. The expansion component continuously generates micro-expansive crystals in the middle and late stages of cement hydration, which directionally fill the capillary-aggregate interface region.

[0017] The crack-inhibiting component forms a three-dimensional micro-support framework in the slurry through the sepiolite fibrous structure, the cellulose ether regulates the water migration path, and the powder water-reducing agent synergistically reduces the interfacial tension of the capillary walls.

[0018] The crack-resistant enhancement system accounts for 8-11% of the total mass of the cementitious material, and the water-cement ratio of the cementitious material is 0.32-0.38.

[0019] Preferably, the coarse aggregate gradation follows the principle of close packing;

[0020] The raw material components also include 15-25 parts of nano-silica with a specific surface area of ​​200-280m² / g and a particle size of 20-40nm, modified by silane coupling agent KH560.

[0021] Preferably, the volumetric content of the multi-component composite fiber is 0.15-0.35%, and a three-dimensional interlocking network crack-resistant architecture is formed by the fiber end hook structure and the micro-rough surface.

[0022] Preferably, the cement is P・II52.5R rapid-hardening silicate cement, with a tricalcium aluminate content ≤7% and an alkali content ≤0.7%;

[0023] The water is purified water with a chloride ion content ≤150mg / L;

[0024] The fine aggregate contains ≤6.5% stone powder, ≤0.8% sulfide and sulfate, and has an average particle size of 0.20-0.30 mm.

[0025] Preferably, the crack-resistant component forms a micro-support framework through the sepiolite fibrous structure, the cellulose ether delays water evaporation, and the powder water-reducing agent reduces interfacial tension.

[0026] During the hardening stage, the expanded component forms needle-like ettringite crystals with an aspect ratio of 1.5-2.5, a crystal length of 2-4 μm, and the crystal orientation is parallel to the crack propagation path.

[0027] Preferably, the preparation method includes the following steps:

[0028] S1. Dry the coarse and fine aggregates at 110-120℃ to constant weight, cool them, and then mix them according to the gradation requirements, controlling the moisture content to ≤0.5%;

[0029] S2. After premixing polyethylene fiber and polypropylene fiber, the mixture is passed through a vibrating sieve with a sieve aperture of 0.8 mm. Basalt fiber and carbon fiber short filaments are soaked in a 2-3% silane coupling agent solution for 5-8 minutes and then dried for later use.

[0030] S3. Add cement, mineral active admixtures, crack-resistant and synergistic system, and nano-silica into a planetary mixer and mix at a low speed of 80-150 r / min for 4-7 minutes to form a homogeneous composite cementitious powder without agglomeration.

[0031] S4. Add coarse and fine aggregates and stir at a medium speed of 100-180r / min for 3-5 minutes to form a pre-hydrated coating layer on the surface of the aggregates.

[0032] S5. Mix the polycarboxylate superplasticizer with water in a certain proportion to prepare an 8-10% concentration solution, control the solution temperature at 22-28℃, and add 0.1-0.3% defoamer;

[0033] S6. Add the water-reducing agent solution to the mixer in two batches. Add 60% of the solution for the first time and stir at 120-160 r / min for 3-4 minutes until the slump reaches 150-180 mm.

[0034] Add the remaining solution and multi-component composite fibers, and stir at a high speed of 200-250 r / min for 5-8 minutes. Monitor the fiber dispersion state in real time using an image recognition device.

[0035] S7. Immediately after pouring the mixture, cover it with a polyethylene film and let it stand for 2-3 hours at a temperature of 20±2℃ and a humidity of ≥95%. Before the initial solidification, use a pressure trowel to smooth the surface a second time. After 24 hours, remove the mold and transfer it to a curing room at a temperature of 20±1℃ and a humidity of ≥98% for 28 days. During the curing period, spray regularly to keep the surface water film continuous.

[0036] Preferably, the preparation method further includes the following steps:

[0037] S11. Surface oxidation treatment of polyethylene and polypropylene fibers: First, treat in a 6-9% sodium hydroxide solution at 50-55℃ for 1.0-1.2 hours, then wash with deionized water until pH=7, and after drying, the density of hydroxyl groups on the fiber surface is ≥5×10⁻⁶. 14 pcs / cm²;

[0038] S61. Fibers are added using a screw feeder at a uniform speed of 30-40g / s. During the mixing process, the temperature inside the mixer is controlled to be ≤32℃ and the ambient humidity is ≤60%.

[0039] When the dispersion uniformity coefficient determined by laser diffraction is <88%, the system automatically triggers the addition of 0.1-0.3 parts of sodium polycarboxylate dispersant and extends the stirring time by 2 minutes.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] 1. This invention achieves the formation of a three-dimensional interlocking network crack-resistant structure in concrete slurry through a quaternary fiber system, which solves the problems of limited reinforcement effect of single fiber and insufficient bonding force with the concrete matrix interface, thereby improving the crack resistance and mechanical properties of concrete.

[0042] 2. This invention achieves a three-dimensional micro-support skeleton through a dual-mechanism crack-resistant system, which solves the problem of cracking caused by shrinkage and stress concentration in concrete during the hardening process and enhances the durability of concrete structures;

[0043] 3. This invention optimizes the aggregate particle packing structure by modifying nano-silica, solving the problems of high porosity and insufficient density caused by unreasonable aggregate gradation in traditional concrete, and improving the overall strength and impermeability of concrete.

[0044] 4. This invention increases the number of active groups on the surface of multi-component composite fibers by performing surface oxidation treatment, which solves the problem that fibers are prone to agglomeration and uneven dispersion in concrete mixtures and thus cannot fully exert their reinforcing effect. This allows the fibers to better bond with the concrete matrix and fully exert the fiber reinforcement and crack resistance effect. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0046] Figure 2 This is a schematic diagram of the surface treatment process for multi-component composite fibers according to the present invention;

[0047] Figure 3 This is a schematic diagram of the gel preparation process of the present invention;

[0048] Figure 4 This is a schematic diagram of the working process of the crack-resistant and enhancing system of the present invention. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Please see Figure 1 , Figure 2 , Figure 3 and Figure 4 The present invention provides an embodiment of a fiber-reinforced crack-resistant concrete, the preparation method of which includes the following steps:

[0051] S1. Dry the coarse and fine aggregates at 110-120℃ to constant weight, cool them, and then mix them according to the gradation requirements, controlling the moisture content to ≤0.5%;

[0052] S2. After premixing polyethylene fiber and polypropylene fiber, the mixture is passed through a vibrating sieve with a sieve aperture of 0.8 mm. Basalt fiber and carbon fiber short filaments are soaked in a 2-3% silane coupling agent solution for 5-8 minutes and then dried for later use.

[0053] S3. Add cement, mineral active admixtures, crack-resistant and synergistic system, and nano-silica into a planetary mixer and mix at a low speed of 80-150 r / min for 4-7 minutes to form a homogeneous composite cementitious powder without agglomeration.

[0054] S4. Add coarse and fine aggregates and stir at a medium speed of 100-180r / min for 3-5 minutes to form a pre-hydrated coating layer on the surface of the aggregates.

[0055] S5. Mix the polycarboxylate superplasticizer with water in a certain proportion to prepare an 8-10% concentration solution, control the solution temperature at 22-28℃, and add 0.1-0.3% defoamer;

[0056] S6. Add the water-reducing agent solution to the mixer in two batches. Add 60% of the solution for the first time and stir at 120-160 r / min for 3-4 minutes until the slump reaches 150-180 mm.

[0057] Add the remaining solution and multi-component composite fibers, and stir at a high speed of 200-250 r / min for 5-8 minutes. Monitor the fiber dispersion state in real time using an image recognition device.

[0058] S7. Immediately after the mixture is poured, cover it with polyethylene film and let it stand for 2-3 hours in an environment with a temperature of 20±2℃ and a humidity of ≥95%. Before the initial solidification, use a pressure trowel to smooth the surface twice. After 24 hours, remove the mold and transfer it to a curing room with a temperature of 20±1℃ and a humidity of ≥98% for 28 days. During the curing period, spray regularly to keep the surface water film continuous.

[0059] The preparation method further includes the following steps:

[0060] S11. Surface oxidation treatment of polyethylene and polypropylene fibers: First, treat in a 6-9% sodium hydroxide solution at 50-55℃ for 1.0-1.2 hours, then wash with deionized water until pH=7, and after drying, the density of hydroxyl groups on the fiber surface is ≥5×10⁻⁶. 14 pcs / cm²;

[0061] S61. Fibers are added using a screw feeder at a uniform speed of 30-40g / s. During the mixing process, the temperature inside the mixer is controlled to be ≤32℃ and the ambient humidity is ≤60%.

[0062] When the dispersion uniformity coefficient determined by laser diffraction is <88%, the system automatically triggers the addition of 0.1-0.3 parts of sodium polycarboxylate dispersant and extends the stirring time by 2 minutes.

[0063] Furthermore, firstly, the surfaces of polyethylene and polypropylene fibers were oxidized using a constant-temperature water bath stirred autoclave. The fibers were immersed in a 6% sodium hydroxide solution at 50℃ with a solid-liquid ratio of 1:8 and treated with a stirring rate of 150 r / min for 1.2 hours. The surface paraffin layer was removed through a saponification reaction, and micron-level grooves were etched. The Ra value was observed to reach 5.2 μm by scanning electron microscopy. Subsequently, the fibers were transferred to a three-legged centrifuge at 2000 r / min and washed three times with deionized water until the pH of the washing solution was measured to be 7 by pH test paper. Finally, the fibers were dried in a forced-air drying oven at 60℃ until the moisture content was ≤0.3%. The density of hydroxyl groups was measured to be 6.8 × 10⁻⁶ by X-ray photoelectron spectroscopy. 14 pcs / cm²;

[0064] Then, a variable frequency screw feeder is used to add fibers, with a feeding speed of 35g / s. An ultrasonic static eliminator is used to eliminate static electricity in the fibers. During the mixing process, the temperature of the mixer cavity is monitored in real time by a temperature sensor. When the temperature exceeds 30℃, the jacket water circulation cooling system is activated to reduce the water temperature to 18℃. At the same time, the dehumidifier is turned on to maintain the ambient humidity at 55±5%RH.

[0065] Finally, the dispersion uniformity was tested using a Malvern laser particle size analyzer with a detection wavelength of 633 nm. When the dispersion uniformity coefficient was <88%, 0.2 parts of 5% sodium polycarboxylate dispersant were automatically added via a peristaltic pump, and the high-speed stirring at 220 r / min was extended for 2.5 minutes. According to the image analysis software, the average fiber spacing was ≤1.2 mm, the orientation distribution index was 0.89, and the number of early plastic cracks in the concrete was reduced by 82%.

[0066] Please see Figure 1 , Figure 3 and Figure 4 This invention provides an embodiment of a fiber-reinforced crack-resistant concrete, comprising the following raw material components: 310-450 parts cement, 150-190 parts water, 930-1200 parts coarse aggregate, 630-800 parts fine aggregate, 80-180 parts mineral active admixture, 1.2-18 parts multi-component composite fiber, 1.8-4.5 parts polycarboxylate superplasticizer, and 20-35 parts crack-resistant enhancement system; wherein the coarse aggregate is graded crushed stone with a particle size of 4-25mm, the fine aggregate is manufactured sand with a fineness modulus of 1.8-2.8, and the mineral active admixture includes fly ash and slag powder with a specific surface area ≥450m² / kg, wherein the mass ratio of fly ash to slag powder is 5-8:1-4;

[0067] The multi-component composite fiber is composed of a quaternary fiber system, which includes a main reinforcing fiber, a rigid reinforcing fiber, and a functional regulating fiber. The main reinforcing fiber consists of polyethylene fiber with a length of 16-20 mm and polypropylene fiber with a length of 13-24 mm, in a mass ratio of 1.5-3.5:1. The rigid reinforcing fiber is basalt fiber with a length of 20-28 mm. The functional regulating fiber is chopped carbon fiber filaments with a length of 8-10 mm, accounting for 8%-15% of the total mass of the composite fiber. After surface treatment, the quaternary fiber system forms a rough interface. The surface of the polyethylene / polypropylene fiber is etched with oxidation to form a micro-groove structure with a thickness of Ra 4.0-6.0 μm. The surface of the basalt / carbon fiber is grafted with silane coupling agent KH550 to form a reactive interface transition layer.

[0068] Furthermore, firstly, Conch P・II52.5R cement was selected as the cementitious material. Conch P・II52.5R cement contains 6.8% tricalcium aluminate and 0.65% alkali content. It was combined with Grade I fly ash (4.2% loss on ignition, 520 m² / kg specific surface area) and S95 slag powder (480 m² / kg specific surface area) at a mass ratio of 6:1. The distribution of cementitious particles was detected using a laser particle size analyzer. The ratio of fly ash to slag powder was adjusted to ensure a cumulative sieve residue ≤12%, forming a densely packed system with D50=18μm. The peak hydration exothermic temperature was reduced by 15℃ compared to using cement alone.

[0069] Then, the coarse aggregate is continuously graded crushed stone with a crushing value of 8% and a needle-like and flaky particle content of <5% and a fine aggregate is Jiangxi manufactured sand with a fineness modulus of 2.3 and a stone powder content of 5.8%. The particle distribution parameter n=0.45 is calculated based on the Andreasen equation. The gradation is adjusted by sieving to make the porosity of the mixed aggregate 34.2%. 18 parts of KH560 modified nano-SiO2 with a particle size of 30nm are introduced into the cementitious material and premixed for 5 minutes to form a composite powder with a dispersion of ≥95%.

[0070] The amount of silane coupling agent used in the modified nano-SiO2 was 3% of the powder mass. It was hydrolyzed in an ethanol / water mixture of 9:1 for 30 minutes, ultrasonically dispersed for 1 hour, and then stirred in a planetary mixer with the stirring paddle speed set at 120 r / min.

[0071] Finally, the molded specimens were tested using an RMT-150C rock mechanics testing machine, and the compressive strength after 28 days reached 68.5 MPa. For the permeability test: Φ175mm×185mm×150mm frustum-shaped specimens were prepared, cured under standard conditions for 28 days, and then placed in a permeability tester. Pressure was increased from 0.1 MPa, increasing by 0.1 MPa every 8 hours, until 1.2 MPa was reached without water penetration. X-ray diffraction analysis showed that the Ca(OH)2 crystal orientation factor in the interface transition zone decreased from 0.72 to 0.41, indicating a 23% increase in density.

[0072] Please see Figure 1 , Figure 2 and Figure 3 One embodiment of the present invention is a fiber-reinforced crack-resistant concrete, wherein the fly ash can also be Class F, Grade I, with a loss on ignition ≤5%;

[0073] The cement is P・II52.5R rapid-hardening silicate cement, with a tricalcium aluminate content ≤7% and an alkali content ≤0.7%; the water is purified water with a chloride ion content ≤150mg / L; the fine aggregate has a stone powder content ≤6.5%, a sulfide and sulfate content ≤0.8%, and an average particle size of 0.20-0.30mm;

[0074] Furthermore, firstly, the crack-inhibiting components were premixed at a mass ratio of 0.05 mm sepiolite powder: hydroxypropyl methylcellulose ether: naphthalene-based powder water-reducing agent = 7:1.5:2, and mixed for 8 minutes in a V-type mixer at a speed of 25 r / min. The fibrous structure of sepiolite with an aspect ratio of 15-20 formed a micro-support network with a spacing of 0.3-0.5 mm in the slurry. The plastic viscosity of the slurry was increased to 800 mPa·s by measuring the hydroxypropyl methylcellulose ether using a Brookfield viscometer, and the water evaporation rate was slowed down by 58%. The surface tension of the capillary solution was reduced from 72 mN / m to 50 mN / m by the pendant drop method.

[0075] Then, CSA90 type calcium sulfoaluminate expansive agent was selected as the expansion component. Thermogravimetric analysis at a heating rate of 10℃ / min determined that the peak amount of ettringite formation was reached after 7 days of cement hydration, and the expansion stress was measured to be 0.035MPa using a dial gauge. The ettringite crystals were observed to be needle-shaped by scanning electron microscopy, with an aspect ratio of 2.1, a length of 3.1μm, and an orientation degree of 82% along the capillary axis.

[0076] Finally, when the total mass of the cementitious material was 500 kg, the dosage of the crack-resistant enhancement system was 45 kg, the water-cement ratio was 0.35, and the molded specimens were tested using a non-contact shrinkage meter. Monitoring continued for 28 days, starting 24 hours after molding. The 28-day drying shrinkage rate was 185 × 10⁻⁻⁻⁶. 6 This represents a 42.2% reduction compared to the benchmark concrete.

[0077] Crack resistance test: A crack observation instrument was set up on the cracking test platform. The surface of the specimen was exposed to a dry environment with a wind speed of 3 m / s, an ambient temperature of 25±2℃, and a relative humidity of 40±5%. The time from specimen molding to the appearance of the first visible crack with a width ≥0.02 mm was recorded. Within 24 hours after molding, the maximum crack width was measured every 30 minutes and the average value was taken. The cracking time was extended from the baseline of 4.5 hours to 12.8 hours, and the maximum crack width was 0.09 mm.

[0078] Please see Figure 1 , Figure 3 and Figure 4 The present invention provides an embodiment of a fiber-reinforced crack-resistant concrete, wherein the coarse aggregate gradation follows the principle of close packing; the raw material components also include 15-25 parts of nano silica with a specific surface area of ​​200-280m² / g and a particle size of 20-40nm, modified by silane coupling agent KH560.

[0079] The multi-component composite fiber has a volume content of 0.15-0.35%, and forms a three-dimensional interlocking network crack-resistant architecture with the fiber end hook structure and the micro-rough surface.

[0080] Furthermore, firstly, the principle of close packing:

[0081] When the granite crushed stone is 4-18mm, 4-8mm accounts for 35-40%, 8-15mm accounts for 45-50%, and 15-18mm accounts for 10-15%, with a water absorption rate of ≤1.2% and a loss of soundness of ≤10%.

[0082] When the crushed stone is continuously graded in the range of 5-25mm, the ratio of 5-10mm:10-20mm:20-25mm is 3.5:4.5:2, the content of needle-like and flaky particles is ≤12%, and the crushing value is ≤10%.

[0083] The main reinforcing fibers are 18mm polyethylene fibers from a Shanghai factory and 24mm polypropylene fibers from Yanshan Petrochemical, blended at a mass ratio of 2:1. The polyethylene fibers have an elastic modulus of 700MPa and an elongation at break of 15%, while the polypropylene fibers have an elastic modulus of 1400MPa and an elongation at break of 8%. Monofilament pull-out tests showed that the bond strength between the PE fibers and the cement matrix was 1.2MPa, and that of the PP fibers reached 1.8MPa. The two fibers form a gradient crack-resistant structure of "flexible energy dissipation - rigid load bearing." In the flexural test on a universal testing machine, the slope of the load-displacement curve in the early stage of crack propagation was 25% lower than that of a single fiber, while the slope increased by 18% in the later stage.

[0084] Then, the rigid reinforcing fiber was selected from Sichuan Aerospace 25mm basalt fiber, with an elastic modulus of 85GPa and a diameter of 13μm. After being impregnated with silane coupling agent KH550 for 5 minutes and dried, the surface grafting rate was determined to be 92% by infrared spectroscopy detection of the Si-OC characteristic peak intensity. In the concrete crack propagation energy test, a three-point bending beam with pre-fabricated cracks was prepared, and displacement-controlled loading was used at a rate of 0.05mm / min. The load-crack opening displacement curve was recorded. The addition of 0.8% basalt fiber increased Gf from the baseline 75J / m² to 112J / m², and reduced the stress concentration factor at the crack tip by 34%.

[0085] Finally, the functional conditioning fiber uses 9mm chopped carbon fiber filaments from Toray Industries, Japan, with a resistivity of 1.7×10⁻⁻. 5 The Ω·m, accounting for 12% of the total mass of the composite fiber, forms an oxide layer on the surface through an electrochemical oxidation method at 5V for 10 minutes, reducing the hydrophilic contact angle from 89° to 42°. A four-electrode monitoring system is constructed, and when microcracks with a width ≥0.02mm appear inside the concrete, the resistivity change rate is >5%, achieving damage early warning. The 0.25% quaternary fiber system by volume increases the flexural strength of the concrete to 12.3MPa, compared to the baseline flexural strength of 8.5MPa, and improves the impact toughness by 210%.

[0086] Please see Figure 1 , Figure 2 , Figure 3 and Figure 4This invention provides an embodiment of a fiber-reinforced crack-resistant concrete. The crack-resistant enhancement system is a dual-mechanism crack-resistant component, which includes a crack-inhibiting component and an expansion component. The crack-inhibiting component consists of sepiolite powder with a particle size of 0.02-0.08 mm, hydroxypropyl methylcellulose ether, and a powder water-reducing agent with a fineness ≤75 μm, in a mass ratio of 7:1.5:2. The expansion component includes a calcium sulfoaluminate-based expansion agent with a magnesium oxide content ≤4%. The expansion component continuously generates micro-expansive crystals in the later stages of cement hydration, directionally filling the capillary-aggregate interface region. The crack-inhibiting component forms a three-dimensional micro-support skeleton in the slurry through the fibrous structure of sepiolite, the cellulose ether regulates the water migration path, and the powder water-reducing agent synergistically reduces the interfacial tension of the capillary walls. The crack-resistant enhancement system accounts for 8-11% of the total mass of the cementitious material, and the water-cement ratio of the cementitious material is 0.32-0.38.

[0087] The crack-resistant component forms a micro-support framework through the sepiolite fibrous structure, the cellulose ether delays water evaporation, and the powder water-reducing agent reduces interfacial tension; the expansion component generates needle-like ettringite crystals with an aspect ratio of 1.5-2.5 and a crystal length of 2-4 μm during the hardening stage, and the crystal orientation is parallel to the crack propagation path.

[0088] Furthermore, firstly, in the premixing stage of the cementitious materials, a twin-shaft forced mixer is used with the mixing paddle speed set at 100 r / min. Cement, fly ash, slag powder, nano-SiO2 and crack-resistant enhancement system are added first and mixed at low speed for 6 minutes. The particle size distribution of the powder is monitored in real time by an online laser particle size analyzer to ensure that D90≤60μm and agglomerate content<1.5%. After adding coarse and fine aggregates, the mixture is mixed at medium speed for 4 minutes. The change in mixing power is monitored by a torque sensor. When the power fluctuation is <5%, the pre-hydrated coating layer is considered to have been formed.

[0089] Next, a water-reducing agent solution was prepared by mixing 40% solids polycarboxylate water-reducing agent with 120 mg / L chloride ion content deionized water at a ratio of 1:4.5, adding 0.2% silicone defoamer, and controlling the solution temperature at 25±1℃ using a digital display constant temperature water bath; the solution was dispensed using an electromagnetic metering pump, and after the first injection of 60% solution, it was stirred at 140 r / min for 3.5 minutes, with a measured slump of 165 mm. The remaining solution was added simultaneously with the fiber, and high-speed stirring at 230 r / min was started. The fiber dispersion was analyzed in real time using an industrial camera with a visual algorithm, and the stirring was automatically extended for 3 minutes when the dispersion index was <0.85.

[0090] Finally, immediately after pouring, a 0.15mm thick polyethylene film was applied, and after standing for 2.5 hours, a second troweling was used to remove surface laitance and micro-cracks. After 24 hours, the specimens were demolded and transferred to a curing chamber, where they were sprayed with an ultrasonic atomizing nozzle every 2 hours to maintain a continuous surface water film. After 28 days of curing, the specimens were split open, and phenolphthalein solution was sprayed onto the cross-section. The depth of the colorless area was measured after 30 seconds. Ten points were measured on each cross-section, and the average value was taken, accurate to 0.5mm. The carbonization depth was 1.2mm, which is 60% lower than that of natural curing.

[0091] Abrasion resistance test: According to GB / T16925 "Test Method for Abrasion Resistance of Concrete", 150mm×150mm×150mm cubic specimens were prepared and cured for 28 days. The upper surface was taken for testing. The specimen was fixed in the abrasion testing machine, a 200N load was applied, the grinding head diameter was 50mm, the rotation speed was 200r / min, and after 500 revolutions of abrasion, the mass difference before and after abrasion was measured. Compared with products without fiber support or with single fiber support, the mass difference was reduced by 38.9%.

[0092] Working principle: First, coarse and fine aggregates are graded according to the principle of close packing, their moisture content is controlled and they are mixed to form a stable skeleton. Multi-component composite fibers undergo surface treatment; polyethylene / polypropylene fibers are oxidized and etched with sodium hydroxide solution to form a micro-grooved surface, enhancing mechanical bonding with the cement matrix; basalt / carbon fiber is impregnated with a silane coupling agent and grafted with a reactive interface layer to improve adhesion. The crack-resistant and enhancing system consists of crack-inhibiting components and expansion components. The former forms a micro-support network, delays moisture evaporation, and reduces capillary tension; the latter generates needle-like ettringite crystals in the later stages of hydration, filling interfacial pores. Cement, fly ash, slag powder, and nano-silica are compounded to form a close-packed powder, reducing the heat of hydration and refining the crystal structure.

[0093] Then, the cementitious material is first stirred at low speed into a homogeneous powder, and then coarse and fine aggregates are added and stirred at medium speed to form a pre-hydrated coating layer on the surface of the aggregates. The polycarboxylate superplasticizer is prepared into a solution of a specific concentration with water and added in two parts: 60% solution is added first to adjust the slump, and then the remaining solution and fibers are added. During high-speed stirring, the fibers are fed at a uniform speed by a screw feeder. At the same time, the fiber dispersion status is monitored in real time using image recognition equipment and laser diffraction technology. If the dispersion uniformity is insufficient, the dispersant is automatically added and the stirring is extended to ensure that the fibers are evenly distributed and the spacing is ≤1.2mm. Meanwhile, the stirring temperature and ambient humidity are controlled to avoid fiber electrostatic agglomeration or excessive temperature affecting performance.

[0094] Finally, the concrete mixture is immediately covered with a film after pouring and left to stand under specific temperature and humidity conditions. A second finishing process is performed before initial setting to eliminate surface laitance and micro-cracks. After demolding, it is transferred to a high-humidity curing chamber for 28 days, with regular spraying to maintain a continuous surface water film, promoting full hydration of the cementitious materials and improving interface density. Subsequently, a three-dimensional crack-resistant network is formed by multiple fibers, the crack-resistant enhancement system compensates for shrinkage stress, and the optimized cementitious materials reduce hydration heat and porosity. Ultimately, this results in an 82% reduction in early-stage plastic cracks in the concrete, a significant decrease in drying shrinkage, and a substantial improvement in impermeability and durability, achieving comprehensive enhancement of crack resistance.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A fiber-reinforced crack-resistant concrete, characterized in that: The raw material components include: 310-450 parts cement, 150-190 parts water, 930-1200 parts coarse aggregate, 630-800 parts fine aggregate, 80-180 parts mineral active admixture, 1.2-18 parts multi-component composite fiber, 1.8-4.5 parts polycarboxylate superplasticizer, and 20-35 parts crack-resistant and enhancing system; The coarse aggregate is graded crushed stone with a particle size of 4-25mm, the fine aggregate is manufactured sand with a fineness modulus of 1.8-2.8, and the mineral active admixture includes fly ash and slag powder with a specific surface area ≥450m² / kg, and the mass ratio of fly ash to slag powder is 5-8:1-4. The multi-component composite fiber is composed of a quaternary fiber system, which includes a main reinforcing fiber, a rigid reinforcing fiber, and a functional regulating fiber. The main reinforcing fibers are polyethylene fibers with a length of 16-20 mm and polypropylene fibers with a length of 13-24 mm, with a mass ratio of 1.5-3.5:1; The rigid reinforcing fiber is basalt fiber with a length of 20-28mm; The functional regulating fiber is a short carbon fiber filament with a length of 8-10mm, accounting for 8%-15% of the total mass of the composite fiber; After surface treatment, the quaternary fiber system forms a rough interface. The surfaces of polyethylene and polypropylene fibers are oxidized and etched to form a micro-groove structure with a diameter of Ra 4.0-6.0 μm. The surfaces of basalt and carbon fibers are grafted with silane coupling agent KH550 to form a reactive interface transition layer.

2. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The fly ash is selected as Class F, Grade I, with a loss on ignition ≤5%.

3. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The crack-resistant enhancement system is a dual-mechanism crack-resistant component, which includes a crack-inhibiting component and an expansion component. The crack-inhibiting component includes sepiolite powder with a particle size of 0.02-0.08 mm, hydroxypropyl methylcellulose ether, and a powder water-reducing agent with a fineness of ≤75 μm. The mass ratio of sepiolite powder, hydroxypropyl methylcellulose ether, and powder water-reducing agent with a fineness of ≤75 μm is 7:1.5:

2. The expansion component includes a calcium sulfoaluminate-based expansion agent with a magnesium oxide content of ≤4%. The expansion component continuously generates micro-expansive crystals in the middle and late stages of cement hydration, which directionally fill the capillary-aggregate interface region. The crack-inhibiting component forms a three-dimensional micro-support framework in the slurry through the sepiolite fibrous structure, the cellulose ether regulates the water migration path, and the powder water-reducing agent synergistically reduces the interfacial tension of the capillary walls. The crack-resistant enhancement system accounts for 8-11% of the total mass of the cementitious material, and the water-cement ratio of the cementitious material is 0.32-0.

38.

4. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The coarse aggregate gradation follows the principle of close packing. The raw material components also include 15-25 parts of nano-silica with a specific surface area of ​​200-280m² / g and a particle size of 20-40nm, modified by silane coupling agent KH560.

5. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The multi-component composite fiber has a volume content of 0.15-0.35%, and forms a three-dimensional interlocking network crack-resistant architecture with the fiber end hook structure and the micro-rough surface.

6. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The cement is P・II52.5R rapid-hardening silicate cement, with a tricalcium aluminate content ≤7% and an alkali content ≤0.7%; The water is purified water with a chloride ion content ≤150mg / L; The fine aggregate contains ≤6.5% stone powder, ≤0.8% sulfide and sulfate, and has an average particle size of 0.20-0.30 mm.

7. The fiber-reinforced crack-resistant concrete according to claim 3, characterized in that: The crack-resistant component forms a micro-support framework through the sepiolite fibrous structure, the cellulose ether delays water evaporation, and the powder water-reducing agent reduces interfacial tension. During the hardening stage, the expanded component forms needle-like ettringite crystals with an aspect ratio of 1.5-2.5, a crystal length of 2-4 μm, and the crystal orientation is parallel to the crack propagation path.

8. A method for preparing fiber-reinforced crack-resistant concrete, applicable to the fiber-reinforced crack-resistant concrete according to any one of claims 1-7, characterized in that: The preparation method includes the following steps: S1. Dry the coarse and fine aggregates at 110-120℃ to constant weight, cool them, and then mix them according to the gradation requirements, controlling the moisture content to ≤0.5%; S2. After premixing polyethylene fiber and polypropylene fiber, the mixture is passed through a vibrating sieve with a sieve aperture of 0.8 mm. Basalt fiber and carbon fiber short filaments are soaked in a 2-3% silane coupling agent solution for 5-8 minutes and then dried for later use. S3. Add cement, mineral active admixtures, crack-resistant and synergistic system, and nano-silica into a planetary mixer and mix at a low speed of 80-150 r / min for 4-7 minutes to form a homogeneous composite cementitious powder without agglomeration. S4. Add coarse and fine aggregates and stir at a medium speed of 100-180r / min for 3-5 minutes to form a pre-hydrated coating layer on the surface of the aggregates. S5. Mix the polycarboxylate superplasticizer with water in a certain proportion to prepare an 8-10% concentration solution, control the solution temperature at 22-28℃, and add 0.1-0.3% defoamer; S6. Add the water-reducing agent solution to the mixer in two batches. First, add 60% of the water-reducing agent solution and stir at 120-160 r / min for 3-4 minutes until the slump reaches 150-180 mm. Add the remaining solution and multi-component composite fibers, and stir at a high speed of 200-250 r / min for 5-8 minutes. Monitor the fiber dispersion state in real time using an image recognition device. S7. Immediately after pouring the mixture, cover it with a polyethylene film and let it stand for 2-3 hours at a temperature of 20±2℃ and a humidity of ≥95%. Before the initial solidification, use a pressure trowel to smooth the surface a second time. After 24 hours, remove the mold and transfer it to a curing room at a temperature of 20±1℃ and a humidity of ≥98% for 28 days. During the curing period, spray regularly to keep the surface water film continuous.

9. The method for preparing fiber-reinforced crack-resistant concrete according to claim 8, characterized in that: The preparation method further includes the following steps: S11. Surface oxidation treatment of polyethylene and polypropylene fibers: First, treat in a 6-9% sodium hydroxide solution at 50-55℃ for 1.0-1.2 hours, then wash with deionized water until pH=7, and after drying, the density of hydroxyl groups on the fiber surface is ≥5×10⁻⁶. 14 pcs / cm²; S61. Fibers are added using a screw feeder at a uniform speed of 30-40g / s. During the mixing process, the temperature inside the mixer is controlled to be ≤32℃ and the ambient humidity is ≤60%. When the dispersion uniformity coefficient determined by laser diffraction is <88%, the system automatically triggers the addition of 0.1-0.3 parts of sodium polycarboxylate dispersant and extends the stirring time by 2 minutes.

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