Fiber-reinforced anti-crack concrete and preparation method thereof

Abstract

The invention discloses fiber-reinforced anti-crack concrete and a preparation method thereof, and relates to the technical field of building materials, the fiber-reinforced anti-crack concrete comprises the following raw material components: 310-450 parts of cement, 150-190 parts of water, 930-1200 parts of coarse aggregate, 630-800 parts of fine aggregate, 80-180 parts of mineral active admixture, 1.2-18 parts of multi-element composite fiber, 1.8-4.5 parts of polycarboxylic acid water reducer, and 20-35 parts of anti-crack synergistic system. Through a quaternary fiber system, a three-dimensional interlocking net-shaped crack-resistant framework is formed in concrete slurry, the problems that the single fiber reinforcement effect is limited, and the interface bonding force with a concrete matrix is insufficient are solved, and the crack resistance and the mechanical property of the concrete are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, in particular to a fiber-reinforced crack-resistant concrete and a preparation method thereof. Background Art

[0002] As a core material in civil engineering, concrete's crack resistance directly impacts the durability, safety, and service life of structures. However, due to its inherent brittleness, traditional concrete is prone to cracking during the setting and hardening process due to temperature fluctuations, shrinkage stress, or loads. This can lead to problems such as water infiltration and steel corrosion, severely shortening the structure's service life.

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

[0004] The above patent improves the crack resistance of asphalt concrete by modifying sepiolite, but relies on the water absorption and expansion of sepiolite to form a physical water barrier layer, which has no inhibitory effect on the chemical shrinkage of cement-based concrete. At the same time, there is still the problem of unoptimized fiber-matrix interface.

[0005] To this end, the present application proposes a fiber-reinforced crack-resistant concrete and a preparation method thereof, which can optimize the interface structure through multiple crack-resistance mechanisms and improve the crack resistance throughout the entire life cycle. Summary of the Invention

[0006] The purpose of the present invention is to provide a fiber-reinforced crack-resistant concrete and a preparation method thereof, so as to solve the technical problem raised in the above-mentioned background technology that concrete, due to its own brittle characteristics, is prone to cracks due to temperature changes, shrinkage stress or load during the coagulation and hardening process, leading to moisture penetration and steel corrosion.

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

[0008] The coarse aggregate is graded crushed stone with a particle size of 4-25 mm, the fine aggregate is machine-made 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 of ​​≥450 m² / kg, and the mass ratio of the fly ash to the slag powder is 5-8:1-4.

[0009] Preferably, the multi-component composite fiber is composed of a four-component fiber system, which includes a main reinforcing fiber, a rigidity reinforcing fiber and a function 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 20-28 mm;

[0012] Function-adjusting fibers are chopped carbon fibers with a length of 8-10 mm, accounting for 8%-15% of the total mass of the composite fibers.

[0013] The quaternary fiber system forms a rough interface after surface treatment. The surface of the polyethylene / polypropylene fiber forms a micro-groove structure of Ra4.0-6.0μm through oxidation etching. The surface of the basalt / carbon fiber is grafted with silane coupling agent KH550 to form a reactive interface transition layer.

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

[0015] Preferably, the anti-cracking synergistic system is a dual-mechanism anti-cracking component, which includes a crack-blocking component and an expansion component. The crack-blocking 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 in a mass ratio of 7:1.5:2;

[0016] The expansion component includes a calcium sulfoaluminate-based expansion agent, the magnesium oxide content of the calcium sulfoaluminate-based expansion agent is ≤4%, and the expansion component continuously generates micro-expansive crystals in the middle and late stages of cement hydration, directionally filling the capillary pore-aggregate interface area;

[0017] The crack-resistance component forms a three-dimensional micro-support skeleton in the slurry through the sepiolite fibrous structure, the cellulose ether regulates the water migration path, and the powder water reducer synergistically reduces the interfacial tension of the capillary pore wall;

[0018] The amount of the anti-cracking enhancement system is 8-11% of the total mass of the cementitious material, and the water-binder 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-silicon dioxide with a specific surface area of ​​200-280m² / g and a particle size of 20-40nm, which is modified by a silane coupling agent KH560.

[0021] Preferably, the multi-component composite fiber has a volume content of 0.15-0.35%, and forms a three-dimensional interlocking network crack-resistant structure through the fiber end hook structure and the micro-rough surface.

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

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

[0024] The fine aggregate stone powder content is ≤6.5%, the sulfide and sulfate content is ≤0.8%, and the average particle size is 0.20-0.30mm.

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

[0026] During the hardening stage, the expansion component generates needle-shaped ettringite crystals with an aspect ratio of 1.5-2.5, a crystal length of 2-4 μm, and a crystal orientation parallel to the crack development path.

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

[0028] S1. Dry the coarse aggregate and fine aggregate at 110-120℃ to constant weight, cool them down and mix them according to grading requirements, and control the moisture content to ≤0.5%;

[0029] S2. The polyethylene fiber and the polypropylene fiber are pre-mixed and passed through a vibrating screening device with a mesh size of 0.8 mm. The basalt fiber and the carbon fiber chopped strands are impregnated with a 2-3% silane coupling agent solution for 5-8 minutes and dried for later use.

[0030] S3. Place cement, mineral active admixtures, anti-cracking synergistic system, and nano-silica into a planetary mixer and stir at a low speed of 80-150 r / min for 4-7 minutes to form a homogeneous composite gelled 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 allow the powder to form a pre-hydrated coating on the surface of the aggregate;

[0032] S5. Mix the polycarboxylic acid water reducer with water in proportion to prepare a solution with a concentration of 8-10%. Control the solution temperature at 22-28°C and add 0.1-0.3% defoaming agent.

[0033] S6. Add the water-reducing agent solution into 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, stir at a high speed of 200-250 r / min for 5-8 minutes, and monitor the fiber dispersion state in real time using an image recognition device;

[0035] S7. Cover the mixture with polyethylene film immediately after pouring, and let it stand for 2-3 hours in an environment with a temperature of 20±2℃ and a humidity of ≥95%. Use a pressure trowel to smooth the surface for the second time before the initial solidification. Remove the mold after 24 hours, and transfer it to a curing room with a temperature of 20±1℃ and a humidity of ≥98% for curing for up to 28 days. During the curing period, spray regularly to keep the surface water film continuous.

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

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

[0038] S61. Fiber is added by a screw feeder at a constant speed of 30-40g / s. During the mixing process, the temperature inside the mixer is controlled to be ≤32°C and the ambient humidity is ≤60%;

[0039] When the dispersion uniformity coefficient measured by laser diffraction method is less than 88%, it is automatically triggered to add 0.1-0.3 parts of polycarboxylate sodium salt dispersant and extend the stirring for 2 minutes.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. This invention uses a quaternary fiber system to form a three-dimensional interlocking network of crack-resistant structures in the concrete paste, solving the problems of limited reinforcement effect of single fibers and insufficient interfacial bonding with the concrete matrix, thereby improving the crack resistance and mechanical properties of concrete.

[0042] 2. This invention uses a dual-mechanism anti-cracking system to achieve a three-dimensional micro-support skeleton, solving the problem of concrete cracking caused by shrinkage and stress concentration during the hardening process, thereby enhancing the durability of the concrete structure.

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

[0044] 4. The present invention increases the active groups on the fiber surface by performing surface oxidation treatment on the multi-component composite fiber, thereby solving the problem that the fiber is easily agglomerated and unevenly dispersed in the concrete mixture and cannot fully exert its reinforcing effect, so that the fiber is better combined with the concrete matrix and the fiber reinforcement and anti-cracking effect is fully exerted. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It 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 of the multi-component composite fiber of 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 anti-cracking synergistic system of the present invention. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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 creative efforts are within the scope of protection of the present invention.

[0050] See also Figure 1 、 Figure 2 、 Figure 3 and Figure 4 The present invention provides an embodiment of a fiber-reinforced crack-resistant concrete, wherein the preparation method comprises the following steps:

[0051] S1. Dry the coarse aggregate and fine aggregate at 110-120℃ to constant weight, cool them down and mix them according to grading requirements, and control the moisture content to ≤0.5%;

[0052] S2. The polyethylene fiber and the polypropylene fiber are pre-mixed and passed through a vibrating screening device with a mesh size of 0.8 mm. The basalt fiber and the carbon fiber chopped strands are impregnated with a 2-3% silane coupling agent solution for 5-8 minutes and dried for later use.

[0053] S3. Place cement, mineral active admixtures, anti-cracking synergistic system, and nano-silica into a planetary mixer and stir at a low speed of 80-150 r / min for 4-7 minutes to form a homogeneous composite gelled 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 allow the powder to form a pre-hydrated coating on the surface of the aggregate;

[0055] S5. Mix the polycarboxylic acid water reducer with water in proportion to prepare a solution with a concentration of 8-10%. Control the solution temperature at 22-28°C and add 0.1-0.3% defoaming agent.

[0056] S6. Add the water-reducing agent solution into 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, stir at a high speed of 200-250 r / min for 5-8 minutes, and monitor the fiber dispersion state in real time using an image recognition device;

[0058] S7. Immediately after pouring the mixture, cover it with polyethylene film and place it in an environment with a temperature of 20±2℃ and a humidity of ≥95% for 2-3 hours. Use a pressure trowel to smooth the surface for a second time before the initial solidification. Remove the formwork after 24 hours and transfer it to a curing room with a temperature of 20±1℃ and a humidity of ≥98% for curing for up to 28 days. During the curing period, spray regularly to maintain a continuous water film on the surface.

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

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

[0061] S61. Fiber is added by a screw feeder at a constant speed of 30-40g / s. During the mixing process, the temperature inside the mixer is controlled to be ≤32°C and the ambient humidity is ≤60%;

[0062] When the dispersion uniformity coefficient measured by laser diffraction method is less than 88%, it will automatically trigger the addition of 0.1-0.3 parts of polycarboxylate sodium salt dispersant and extend the stirring for 2 minutes;

[0063] Furthermore, first, the surfaces of polyethylene fibers and polypropylene fibers were oxidized in a constant temperature water bath stirred tank. The fibers were immersed in a 6% sodium hydroxide solution at 50°C at a solid-liquid ratio of 1:8 and treated at a stirring rate of 150 r / min for 1.2 hours. The surface paraffin layer was removed by saponification reaction and micron-scale grooves were etched. The Ra value reached 5.2 μm by scanning electron microscopy. The fibers were then washed three times with deionized water in a three-legged centrifuge at a speed of 2000 r / min until the pH value of the washing solution was 7 as detected by pH test paper. Finally, the fibers were dried in a blast drying oven at a temperature of 60°C to a moisture content of ≤0.3%. The hydroxyl group density was 6.8×10 14 pieces / cm²;

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

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

[0066] See also Figure 1 、 Figure 3 and Figure 4 The present invention provides an embodiment of a fiber-reinforced crack-resistant concrete, comprising the following raw material components: 310-450 parts of cement, 150-190 parts of water, 930-1200 parts of coarse aggregate, 630-800 parts of fine aggregate, 80-180 parts of mineral active admixture, 1.2-18 parts of multi-component composite fiber, 1.8-4.5 parts of polycarboxylic acid-based water reducer, and 20-35 parts of an anti-cracking synergistic system; the coarse aggregate is graded crushed stone with a particle size of 4-25 mm, the fine aggregate is machine-made sand with a fineness modulus of 1.8-2.8, and the mineral active admixture comprises fly ash and slag powder with a specific surface area of ​​≥450 m² / kg, wherein the mass ratio of the fly ash to the slag powder is 5-8:1-4;

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

[0068] Furthermore, the cementitious material used was Conch P・II52.5R cement, which contains 6.8% tricalcium aluminate and 0.65% alkali. It was mixed with Grade I fly ash (with a loss on ignition of 4.2% and a specific surface area of ​​520 m² / kg) and S95 slag powder (with a specific surface area of ​​480 m² / kg), in a mass ratio of 6:1. A laser particle size analyzer was used to measure the cementitious particle distribution. The fly ash and slag powder ratio was adjusted to achieve a cumulative sieve residue of ≤12%, forming a tightly packed system with a D50 of 18 μm. The peak hydration exotherm was 15°C lower than that of the cement alone.

[0069] Then, the coarse aggregate used was continuously graded crushed stone with a crushing value of 8% for 4-25 mm and a needle-like particle content of less than 5%. The fine aggregate used was Jiangxi machine-made sand with a fineness modulus of 2.3 and a stone powder content of 5.8%. The particle distribution parameter n = 0.45 was calculated based on the Andreasen equation. The gradation was adjusted by screening to a void ratio of 34.2% for the mixed aggregate. 18 parts of KH560 modified nano-SiO2 with a particle size of 30 nm was 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 to modify nano-SiO2 is 3% of the powder mass. It is hydrolyzed in a mixture of ethanol and water = 9:1 for 30 minutes, ultrasonically dispersed for 1 hour, and then stirred in a planetary mixer with the stirring blade speed set at 120 r / min.

[0071] Finally, the formed specimens were tested by the RMT-150C rock mechanics testing machine, and the compressive strength reached 68.5Mpa after 28 days; impermeability test: Φ175mm×185mm×150mm frustum-shaped specimens were prepared and cured for 28 days according to the standard. The specimens were placed in the impermeability tester, and the pressure was increased from 0.1MPa, and increased by 0.1MPa every 8 hours. When the pressure was increased to 1.2MPa, no water permeability was observed; the X-ray diffractometer detected that the Ca(OH)2 crystal orientation factor in the interface transition zone dropped from 0.72 to 0.41, and the density was increased by 23%.

[0072] See also Figure 1 、 Figure 2 and Figure 3 , an embodiment provided by the present invention: a fiber-reinforced crack-resistant concrete, wherein the fly ash may also be selected from Class F, Grade I, with a loss on ignition ≤5%;

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

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

[0075] Then, a CSA90 calcium sulfoaluminate expansion agent was selected as the expansion component. Thermogravimetric analysis at a heating rate of 10°C / min determined that the amount of ettringite generated reached its peak after 7 days of cement hydration. The micrometer method measured an expansion stress of 0.035 MPa. Scanning electron microscopy revealed that the ettringite crystals were needle-shaped, with an aspect ratio of 2.1, a length of 3.1 μm, and an axial orientation degree of 82% along the capillary pores.

[0076] Finally, when the total mass of the cementitious material is 500 kg, the amount of the anti-cracking enhancement system is 45 kg, the water-cement ratio is 0.35, and the molded specimens are tested by a non-contact shrinkage instrument. Starting from 24 hours after molding, the observation is continuously carried out for 28 days. The drying shrinkage rate after 28 days is 185×10⁻ 6 , which is 42.2% lower than that of the benchmark concrete;

[0077] Crack resistance test: A crack observation instrument was set up on the crack 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°C, 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. It was found that the cracking time was extended from the baseline 4.5 hours to 12.8 hours, and the maximum crack width was 0.09 mm.

[0078] See also 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 close packing principle; the raw material components also include 15-25 parts of nano-silicon dioxide with a specific surface area of ​​200-280m² / g and a particle size of 20-40nm, modified by a 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 structure through the fiber end hook structure and the micro-rough surface;

[0080] Further, first, the close packing principle:

[0081] When it comes to 4-18mm granite crushed stones, 4-8mm accounts for 35-40%, 8-15mm accounts for 45-50%, 15-18mm accounts for 10-15%, water absorption rate ≤1.2%, and solidity quality loss ≤10%;

[0082] When it is 5-25mm continuous graded gravel, 5-10mm:10-20mm:20-25mm=3.5:4.5:2, the content of needle-like 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, compounded in 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%. Single-filament pullout tests showed the bond strength between the PE fibers and the cement matrix to be 1.2MPa, while that of the PP fibers reached 1.8MPa. The two fibers form a gradient crack resistance mechanism characterized by "flexible energy dissipation and rigid load bearing." In flexural tests using a universal testing machine, the slope of the load-displacement curve at the initial stage of crack expansion was 25% lower than that of a single fiber, and the slope increased by 18% in the later stages.

[0084] The rigid reinforcement fiber used was 25mm basalt fiber from Sichuan Aerospace, with an elastic modulus of 85GPa and a diameter of 13μm. After being impregnated with silane coupling agent KH550 for 5 minutes and then dried, the surface grafting rate was determined to be 92% by infrared spectroscopy of the Si-OC characteristic peak intensity. In the concrete crack propagation energy test, a three-point bending beam with prefabricated 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 the Gf from the baseline 75J / m² to 112J / m², and the stress concentration factor at the crack tip was reduced by 34%.

[0085] Finally, the function-adjusting fiber uses 9mm carbon fiber chopped strands from Japan’s Toray, with a resistivity of 1.7×10⁻ 5 Ω・m, accounting for 12% of the total mass of the composite fiber. The surface was electrochemically oxidized at a voltage of 5V for 10 minutes to form an oxide layer, and the hydrophilic contact angle dropped from 89° to 42°. A four-electrode monitoring system was constructed. When microcracks with a width of ≥0.02mm appeared in the concrete, the resistivity change rate was greater than 5%, realizing damage warning. The four-component fiber system with a volume content of 0.25% made the concrete flexural strength reach 12.3MPa, compared with the baseline flexural strength of 8.5MPa, and the impact toughness was improved by 210%.

[0086] See also Figure 1 、 Figure 2 、 Figure 3 and Figure 4, the present invention provides an embodiment: a fiber-reinforced crack-resistant concrete, the crack-resistant synergistic system is a dual-mechanism crack-resistant component, the dual-mechanism crack-resistant component includes a crack-blocking component and an expansive component, the crack-blocking 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, in a mass ratio of 7:1.5:2; the expansive component includes a calcium sulfoaluminate-based expansive agent, the magnesium oxide content of the calcium sulfoaluminate-based expansive agent is ≤4%, the expansive component continuously generates micro-expandable crystals in the middle and late stages of cement hydration, and directionally fills the capillary pore-aggregate interface area; the crack-resistant component forms a three-dimensional micro-support skeleton 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 pore wall; the amount of the anti-cracking synergistic 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-resistance component forms a micro-support skeleton through the fibrous structure of sepiolite, the cellulose ether delays water evaporation, and the powder water-reducing agent reduces interfacial tension; the expansion component generates needle-shaped 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 development path;

[0088] Furthermore, first, a twin-shaft forced mixer was used in the premixing stage of the cementitious material. The impeller speed was set at 100 r / min. Cement, fly ash, slag powder, nano-SiO2 and anti-cracking synergistic system were first added and stirred at low speed for 6 minutes. The powder particle size distribution was monitored in real time by an online laser particle size analyzer to ensure that D90 was ≤ 60 μm and the agglomerate content was < 1.5%. After the coarse and fine aggregates were added, the mixture was stirred at medium speed for 4 minutes. The stirring power change was monitored by a torque sensor. When the power fluctuation was < 5%, it was determined that the prehydration coating was formed.

[0089] Next, a water-reducing agent solution was prepared by mixing a polycarboxylate water-reducing agent with a solid content of 40% and deionized water with a chloride ion content of 120 mg / L in a ratio of 1:4.5. 0.2% silicone defoamer was added, and the solution temperature was controlled at 25±1°C using a digital thermostatic water bath. An electromagnetic metering pump was used to dispense the solution. After the initial injection of 60% of the solution, stirring was performed at 140 rpm for 3.5 minutes, resulting in a measured slump of 165 mm. The remaining solution and fibers were then added simultaneously, with high-speed stirring at 230 rpm. The fiber dispersion was analyzed in real time using an industrial camera coupled with a visual algorithm. When the dispersion index was <0.85, stirring was automatically extended for 3 minutes.

[0090] Finally, immediately after pouring, the specimens were covered with a 0.15mm thick polyethylene film. After standing for 2.5 hours, the surface was smoothed again with a gasoline trowel to eliminate surface slurry and microcracks. After 24 hours, the molds were removed and the specimens were transferred to a curing room where they were sprayed every two hours with an ultrasonic atomizing nozzle to maintain a continuous water film on the surface. After curing for 28 days, the specimens were split and phenolphthalein solution was sprayed onto the cross-section. After 30 seconds, the depth of the colorless area was measured. Ten measurements were taken at each cross-section and the average was calculated to the nearest 0.5mm. The resulting carbonization depth was 1.2mm, a 60% reduction compared to natural curing.

[0091] Wear resistance test: According to GB / T16925 "Test method for wear resistance of concrete", a 150mm×150mm×150mm cubic specimen was prepared and cured for 28 days. The upper surface was taken for testing. The specimen was fixed in a wear tester, a load of 200N was applied, the grinding head diameter was 50mm, the speed was 200r / min, and after 500 revolutions of wear, the mass difference before and after wear was weighed and found to be 38.9% lower than that of the single fiber-supported product without fiber support.

[0092] Working principle: First, the coarse and fine aggregates are graded according to the principle of close packing, and their moisture content is controlled and mixed to form a stable skeleton; the multi-component composite fibers are surface-treated separately, and the polyethylene / polypropylene fibers are oxidized and etched with sodium hydroxide solution to form a micro-grooved surface, thereby enhancing the mechanical bite with the cement matrix; the basalt / carbon fibers are impregnated with a silane coupling agent and grafted with a reactive interface layer to enhance the bonding strength. The anti-cracking and synergistic system consists of a crack-blocking component and an expansion component. The former forms a micro-support network, delays water evaporation and reduces capillary tension, while the latter generates needle-shaped calcium aluminate crystals in the middle and late stages of hydration to fill the interface pores. Cement, fly ash, slag powder and nano-silica are compounded to form a tightly packed powder, which reduces the hydration heat and refines the crystal structure;

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

[0094] Finally, after pouring, the concrete mixture is immediately covered with a film and allowed to stand at a specific temperature and humidity. A second finishing touch is applied before initial setting to eliminate surface laitance and microcracks. After demolding, the mixture is transferred to a high-humidity curing room for 28 days, with regular spraying to maintain a continuous surface water film, promote full hydration of the cementitious material, and improve interface density. The multi-component fibers then form a three-dimensional crack-resistant network, while the anti-crack enhancement system compensates for shrinkage stress. The cementitious material is optimized to reduce hydration heat and porosity. Ultimately, the concrete exhibits an 82% reduction in early plastic cracking, significantly reduces drying shrinkage, and significantly improves 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 embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A fiber-reinforced crack-resistant concrete, characterized by: The raw material components include: 310-450 parts of cement, 150-190 parts of water, 930-1200 parts of coarse aggregate, 630-800 parts of fine aggregate, 80-180 parts of mineral active admixture, 1.2-18 parts of multi-component composite fiber, 1.8-4.5 parts of polycarboxylic acid water reducer, and 20-35 parts of anti-cracking synergistic system. The coarse aggregate is graded crushed stone with a particle size of 4-25 mm, the fine aggregate is machine-made 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 of ​​≥450 m² / kg, and the mass ratio of the fly ash to the slag powder is 5-8:1-4.

2. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The multi-component composite fiber is composed of a four-component fiber system, which includes a main reinforcing fiber, a rigidity reinforcing fiber and a function 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 20-28 mm; Function-adjusting fibers are chopped carbon fibers with a length of 8-10 mm, accounting for 8%-15% of the total mass of the composite fibers; The quaternary fiber system forms a rough interface after surface treatment. The surface of the polyethylene / polypropylene fiber forms a micro-groove structure of Ra4.0-6.0μm through oxidation etching. The surface of the basalt / carbon fiber is grafted with silane coupling agent KH550 to form a reactive interface transition layer.

3. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The fly ash may also be of Class F, Grade I, with a loss on ignition of ≤5%.

4. The fiber-reinforced crack-resistant concrete according to claim 1, characterized in that: The anti-cracking synergistic system is a dual-mechanism anti-cracking component, which includes a crack-blocking component and an expansion component. The crack-blocking 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 in a mass ratio of 7:1.5:

2. The expansion component includes a calcium sulfoaluminate-based expansion agent, the magnesium oxide content of the calcium sulfoaluminate-based expansion agent is ≤4%, and the expansion component continuously generates micro-expansive crystals in the middle and late stages of cement hydration, directionally filling the capillary pore-aggregate interface area; The crack-resistance 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 reducer synergistically reduces the interfacial tension of the capillary pore wall; The amount of the anti-cracking enhancement system is 8-11% of the total mass of the cementitious material, and the water-binder ratio of the cementitious material is 0.32-0.

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5. 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-silicon dioxide with a specific surface area of ​​200-280m² / g and a particle size of 20-40nm, which is modified by a silane coupling agent KH560.

6. 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 structure through the fiber end hook structure and the micro-rough surface.

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

8. The fiber-reinforced crack-resistant concrete according to claim 4, characterized in that: The crack-resistance component forms a micro-support skeleton through the fibrous structure of sepiolite, the cellulose ether delays water evaporation, and the powder water reducer reduces interfacial tension; During the hardening stage, the expansion component generates needle-shaped ettringite crystals with an aspect ratio of 1.5-2.5, a crystal length of 2-4 μm, and a crystal orientation parallel to the crack development path.

9. A method for preparing fiber-reinforced crack-resistant concrete, applicable to the fiber-reinforced crack-resistant concrete according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: S1. Dry the coarse aggregate and fine aggregate at 110-120℃ to constant weight, cool them down and mix them according to grading requirements, and control the moisture content to ≤0.5%; S2. The polyethylene fiber and the polypropylene fiber are pre-mixed and passed through a vibrating screening device with a mesh size of 0.8 mm. The basalt fiber and the carbon fiber chopped strands are impregnated with a 2-3% silane coupling agent solution for 5-8 minutes and dried for later use. S3. Place cement, mineral active admixtures, anti-cracking synergistic system, and nano-silica into a planetary mixer and stir at a low speed of 80-150 r / min for 4-7 minutes to form a homogeneous composite gelled powder without agglomeration; S4. Add coarse and fine aggregates and stir at a medium speed of 100-180r / min for 3-5 minutes to allow the powder to form a pre-hydrated coating on the surface of the aggregate; S5. Mix the polycarboxylic acid water reducer with water in proportion to prepare a solution with a concentration of 8-10%. Control the solution temperature at 22-28°C and add 0.1-0.3% defoaming agent. S6. Add the water-reducing agent solution into 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. Add the remaining solution and multi-component composite fibers, stir at a high speed of 200-250 r / min for 5-8 minutes, and monitor the fiber dispersion state in real time using an image recognition device; S7. Cover the mixture with polyethylene film immediately after pouring, and let it stand for 2-3 hours in an environment with a temperature of 20±2℃ and a humidity of ≥95%. Use a pressure trowel to smooth the surface for the second time before the initial solidification. Remove the mold after 24 hours, and transfer it to a curing room with a temperature of 20±1℃ and a humidity of ≥98% for curing for up to 28 days. During the curing period, spray regularly to keep the surface water film continuous.

10. The method for preparing fiber-reinforced crack-resistant concrete according to claim 9, characterized in that: The preparation method further comprises the following steps: S11. Surface oxidation treatment of polyethylene fiber and polypropylene fiber: first treat in 6-9% sodium hydroxide solution at 50-55℃ for 1.0-1.2 hours, then wash with deionized water to pH=7, and after drying, the density of hydroxyl groups on the fiber surface should be ≥5×10 14 pieces / cm²; S61. Fiber is added by a screw feeder at a constant speed of 30-40g / s. During the mixing process, the temperature inside the mixer is controlled to be ≤32°C and the ambient humidity is ≤60%; When the dispersion uniformity coefficient measured by laser diffraction method is less than 88%, it is automatically triggered to add 0.1-0.3 parts of polycarboxylate sodium salt dispersant and extend the stirring for 2 minutes.

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