A Synergistic Modified Bamboo Fiber Concrete and Its Preparation Method

Abstract

A synergistically modified bamboo fiber concrete is composed of the following components in parts by weight: 250-280 parts of P.O42.5 ordinary Portland cement, 680-720 parts of river sand, 992-1115 parts of crushed stone with a particle size of 4.5-9mm, 58-66 parts of fly ash, 60-72 parts of mineral powder, 2.13-3.25 parts of calcium lignosulfonate, 0.9-1.2 parts of aluminum powder paste conforming to the current JC / T407 standard, 3.4-6.2 parts of modified bamboo fiber, and 127-140 parts of water. A method for preparing the synergistically modified bamboo fiber concrete is also provided. This invention achieves a dual enhancement of interfacial bonding strength and interlocking force in concrete, significantly improving crack resistance and mechanical stability, extending the service life of engineering projects, and effectively expanding its application range in special engineering scenarios such as underground and marine environments.

Description

Technical Field

[0001] This invention belongs to the field of concrete modification and application in the technology of building materials. Specifically, it relates to a synergistically modified bamboo fiber concrete and its preparation method, which is particularly suitable for special engineering scenarios such as underground integrated pipe corridors, marine docks, and airport runways that have high humidity, high alkali erosion and impact resistance requirements. It can meet the core performance requirements of high impermeability and high durability of concrete in such scenarios. Background Technology

[0002] Concrete, as the most widely used and extensive basic material in engineering construction, supports the development of numerous fields such as construction, transportation, and water conservancy due to its advantages including abundant raw material sources, low production costs, mature production processes, excellent compressive strength, and good long-term durability. However, the inherent material properties of concrete, such as its tensile strength being only 1 / 8 to 1 / 15 of its compressive strength, significant brittleness, poor impact and wear resistance, and susceptibility to early cracking due to plastic shrinkage, increasingly limit its application in scenarios with stringent requirements for crack resistance and durability, such as underground engineering and marine engineering. When the width of concrete cracks exceeds the limit of 0.2 mm, external corrosive media such as moisture, chloride ions, and sulfates can quickly penetrate into the material through the cracks, accelerating the aging of cement paste and the corrosion of reinforcing steel, leading to a decrease in structural load-bearing capacity, a shortened service life, and in severe cases, even endangering the safe operation of the project. Therefore, developing modification technologies that can effectively inhibit concrete cracking, control crack propagation, and improve overall durability has become a key direction that the industry urgently needs to address.

[0003] Fiber reinforcement is an important technical approach for modifying concrete performance. Among them, plant fiber concrete has become a research hotspot in recent years because it aligns with the development concepts of green circular economy and energy conservation and emission reduction under the dual carbon goals. As a major bamboo resource country, my country has an annual output of over 10 million tons of natural bamboo fiber. It not only has the advantages of sustainable regeneration, low cost, and environmental friendliness, but its internal porous structure also endows it with excellent toughness and tensile strength. When used as a reinforcing phase in concrete, it can inhibit crack initiation and propagation through the bridging effect of fibers, thereby improving the tensile and compressive synergistic performance of concrete. However, the direct application of natural bamboo fiber to concrete presents three major drawbacks: First, the non-crystalline components of bamboo fiber, such as hemicellulose and lignin, easily absorb water and swell, resulting in low fiber durability and high hygroscopicity. When exposed to the highly alkaline environment of concrete (pH 12-13) for extended periods, they are prone to hydrolytic degradation and loss of reinforcing properties. Second, the surface of natural bamboo fiber is often covered with impurities such as wax and pectin, and the active hydroxyl groups are insufficiently exposed. The fiber's bond with the cement matrix relies solely on physical interlocking, resulting in weak interfacial adhesion and susceptibility to fiber pull-out failure under stress. Third, variations in fiber hygroscopicity lead to uneven moisture distribution within the concrete, creating micropores that affect overall density and impermeability. These combined defects make it difficult for natural bamboo fiber concrete to meet engineering requirements in terms of mechanical performance stability and service life.

[0004] Existing technologies for modifying plant fibers still have significant limitations. For example, patent CN114620973A only uses a simple two-step process of acid-alkali treatment + water-retaining agent / antioxidant to modify sisal and jute mixed plant fibers, without constructing a multi-step, multi-mechanism synergistic modification system. On the one hand, it lacks a specific design for strengthening interfacial bonding and does not improve the bonding force between the fiber and the cement matrix through chemical coupling or other methods. On the other hand, it does not design a protective structure for the alkali resistance of the fibers, only vaguely mentioning improving crack resistance, without disclosing key performance indicators such as crack resistance grade, impermeability grade, and alkali resistance strength retention rate. Based on publicly available data and industry test results of similar single modification processes, the concrete prepared by this technology typically retains only about 65% of its strength after soaking in 5% NaOH solution for 180 days, with a fiber-matrix interfacial shear strength of less than 1.5 MPa and no clear impermeability grade, making it difficult to adapt to high-standard engineering scenarios such as underground and marine applications.

[0005] For example, patent CN119822722A uses only silane coupling agent to modify bamboo fiber: no alkali activation pretreatment is performed, the non-crystalline components on the fiber surface are not removed, and the active sites are insufficiently exposed, resulting in inadequate grafting of coupling agent molecules. Furthermore, it lacks an inorganic coating protection step, making the fiber prone to degradation in a high-alkali environment over a long period. The disclosed interfacial shear strength is only increased by 28%, and based on its basic properties, the increased interfacial shear strength is estimated to be approximately 2.0 MPa. Simultaneously, it does not optimize the interfacial compatibility between recycled aggregate and bamboo fiber, easily leading to interconnected pores within the concrete. The disclosed impermeability grade is only P8, and the crack resistance grade is not clearly defined, making it difficult to withstand the long-term effects of harsh engineering environments such as high underground humidity and high marine permeability.

[0006] The patent with publication number CN110759685A only improves the corrosion resistance of bamboo fiber through composite modification of silane coupling agent and epoxy resin. However, due to the lack of a low-temperature plasma pretreatment step, impurities such as wax and pectin adhering to the fiber surface cannot be completely removed, affecting the bonding strength of the modified coating. Furthermore, the lack of an inorganic dense coating process makes the organic modified coating prone to peeling off during the exothermic process of cement hydration. The 28-day flexural strength disclosed in this patent is only 5.2 MPa, and the strength retention rate after soaking in 5% NaOH solution is only 83%. The crack resistance grade and impermeability grade are not clearly defined. In addition, the mixing process parameters are not optimized, and the bamboo fiber is prone to agglomeration in concrete, resulting in poor performance uniformity. It is only suitable for ordinary civil building scenarios with lower performance requirements.

[0007] A review of existing bamboo fiber modification technologies reveals core limitations stemming from the lack of synergy and singularity in modification methods: First, while alkali treatment alone can improve fiber surface roughness through etching, it fails to construct a long-lasting alkali-resistant protective layer, making the fiber susceptible to degradation in the high-alkali environment of concrete over extended periods. Second, silane treatment alone suffers from insufficient active sites on the fiber surface, hindering the grafting of coupling agent molecules and resulting in limited improvement in interfacial adhesion, thus failing to meet high load-bearing requirements. Third, some two-step modification schemes, while attempting to combine alkali and silane treatments, fail to address the agglomeration problem during nano-stone powder coating, leading to interconnected pores within the concrete and hindering the achievement of impermeability standards. Furthermore, existing modified bamboo fiber concrete formulations and process parameters are largely developed based on general building scenarios, lacking specific optimization for underground and marine engineering projects, thus failing to meet the stringent requirements for impermeability, corrosion resistance, and crack resistance in these applications. In summary, there is an urgent need to develop a modification technology that combines the synergistic effects of "interface strengthening, fiber protection, and matrix compaction" to simultaneously address the three core problems of bamboo fiber concrete: weak interfacial bonding, easy fiber degradation, and poor concrete impermeability, in order to meet the performance requirements of special engineering scenarios. Summary of the Invention

[0008] To overcome the shortcomings of existing bamboo fiber concrete, such as weak interfacial bonding, easy fiber degradation, and poor impermeability, this invention provides a synergistically modified bamboo fiber concrete and its preparation method. This invention innovatively constructs a three-step synergistic modification mechanism: alkali activation removes amorphous components from the bamboo fiber surface and activates hydroxyl sites; coupling crosslinking builds a chemical bridge between the fiber and the cement matrix; and inorganic dense coating forms a long-lasting protective layer. These three steps synergistically improve the mechanical properties, durability, and impermeability of the concrete. Simultaneously, graphene oxide (GO) is introduced to construct a KH-560 / TEPA / GO ternary composite modification liquid. GO's high specific surface area and strong adsorption properties promote uniform grafting of the coupling agent, enhancing the interfacial bonding effect. Furthermore, a combination of nano-granite powder and a polycarboxylate dispersant is used to solve the problem of powder agglomeration during coating, forming a dense protective layer to block moisture and alkaline ion erosion. This invention ultimately achieves a dual enhancement of the bonding force and interlocking force at the concrete interface, significantly improving crack resistance and mechanical stability, extending the service life of engineering projects, and effectively expanding its application scope in special engineering scenarios such as underground and marine environments.

[0009] The technical solution adopted by this invention to solve its technical problem is: A synergistic modified bamboo fiber concrete is composed of the following components in parts by weight: 250-280 parts of P.O42.5 ordinary Portland cement, 680-720 parts of river sand, 992-1115 parts of crushed stone with a particle size of 4.5-9mm, 58-66 parts of fly ash, 60-72 parts of mineral powder, 2.13-3.25 parts of calcium lignosulfonate, 0.9-1.2 parts of aluminum powder paste conforming to the current standard JC / T407, 3.4-6.2 parts of modified bamboo fiber, and 127-140 parts of water.

[0010] Furthermore, the modified bamboo fiber is prepared by a three-step synergistic method of alkali activation-coupling crosslinking-inorganic dense coating, as follows: Step 1: Take the middle fiber of the bamboo stalk, with an average length of 2.0~2.5mm and a diameter of 120~180μm. After pretreatment with low-temperature plasma for 3~5min, soak it in deionized water for 1.5~2.5h, stirring 2~3 times during the period, with each stirring lasting 5~8min, to remove loose impurities on the fiber surface. Step 2: Place the bamboo fiber pretreated in Step 1 into a 3% to 5% sodium hydroxide or potassium hydroxide aqueous solution at a temperature of 40 to 60°C. After soaking for 5 to 6 hours, filter the solution and rinse it repeatedly with water until the pH of the filtrate is 7 to 8. Then, vacuum dry the solution at 55 to 65°C for 7.5 to 8.5 hours to obtain alkali-activated bamboo fiber. Step 3: Prepare a composite modification solution. The composite modification solution is prepared by mixing γ-glycidyl etheroxypropyltrimethoxysilane (KH-560), triethylenetetramine (TEPA), and graphene oxide (GO) in a mass ratio of 1:(1.2~1.8):(0.05~0.1). Add the alkali-activated bamboo fiber obtained in Step 2 to the composite modification solution in a ratio of 1g:19.5mL to 1g:20.5mL based on the fiber mass and the volume of the modification solution. Stir for 2~3 hours under constant temperature water bath conditions at 45~55℃. After filtration, wash 2~3 times with anhydrous ethanol, then wash 1~2 times with deionized water. Finally, vacuum dry at 55~65℃ to constant weight to obtain coupled cross-linked bamboo fiber. Step 4: Using the coupled cross-linked bamboo fiber obtained in Step 3 as a reference, take 0.3-0.5 parts by mass of polycarboxylic acid dispersant and add it to a suspension of nano-granite powder with a mass fraction of 4-6%. The solid-liquid ratio of the suspension is 1:15-1:16, which is calculated as 1g:15mL-1g:16mL by mass of nano-granite powder and volume of water. After ultrasonic dispersion for 10-15 minutes, add the coupled cross-linked bamboo fiber obtained in Step 3, stir for 30-40 minutes, filter, and then dry at 55-65℃ to obtain modified bamboo fiber.

[0011] Preferably, the particle size of the nano-granite powder is 50~100nm, and the particle size test meets the technical requirements of GB / T19077-2016 "Particle Size Analysis by Laser Diffraction"; the mass ratio of KH-560, TEPA and GO in the composite modified liquid is preferably 1:1.5:0.08; the polycarboxylate dispersant is a polycarboxylate high-efficiency water-reducing agent, which meets the technical requirements of high-efficiency water-reducing agents in GB8076-2008 "Concrete Admixtures", and has a solid content ≥40% to ensure the dispersion effect of the stone powder.

[0012] A method for preparing synergistically modified bamboo fiber concrete includes the following steps: (1) Weigh each raw material according to the following mass parts: 250-280 parts of P.O42.5 ordinary Portland cement, 680-720 parts of river sand, 992-1115 parts of crushed stone with a particle size of 4.5-9mm, 58-66 parts of fly ash, 60-72 parts of mineral powder, 2.13-3.25 parts of calcium lignosulfonate, 0.9-1.2 parts of aluminum powder paste conforming to the current standard of JC / T407, 3.4-6.2 parts of modified bamboo fiber, and 127-140 parts of water; all raw materials must meet the following requirements: moisture content ≤0.5% to avoid affecting the water-cement ratio of concrete, impurity content ≤0.1% to prevent the introduction of harmful components, and conform to the current national standards of the corresponding raw materials (e.g., cement conforms to GB175-2007 "General Portland Cement"); (2) Add the modified bamboo fiber to water at a temperature of 48~52℃ and stir at a stirring speed of 1000~1400r / min for 8~15min until no obvious agglomerates are visible to the naked eye, ensuring that the fiber is evenly dispersed. (3) Take P.O42.5 ordinary silicate cement, river sand, crushed stone, fly ash, mineral powder, calcium lignosulfonate and aluminum powder paste as dry materials, put them into a mixer and premix them for 3 to 4 minutes at a mixing speed of 600~1000r / min until there is no obvious color difference in the dry materials, and ensure that the mixture is uniform. (4) Slowly pour the pre-mixed dry material into water containing dispersed modified bamboo fiber, and mix at a stirring speed of 800~1200r / min for 3~5 minutes until the slurry has a uniform color, no particle clumping and no local fiber accumulation, to obtain concrete mixture.

[0013] Furthermore, the preparation method further includes the following steps: (5) Pour the concrete mixture into a standard mold and vibrate it for 20 to 40 seconds with a vibrating table with a frequency of 50±5Hz and an amplitude of 0.6~1.0mm until there are no obvious air bubbles overflowing from the surface. Smooth the surface of the mold with a trowel. (6) After the concrete is poured, cover the concrete surface with a sealing plastic film to prevent moisture evaporation. After standing at room temperature of 20±5℃ for 24 hours, remove the formwork to obtain concrete specimens. (7) After demolding, the concrete specimens were placed in a standard curing environment with a temperature of 20±2℃ and a relative humidity of 95% or higher for 28 days to obtain synergistic modified bamboo fiber concrete.

[0014] In step (2), the stirring speed is 1200 r / min and the stirring time is 10 min; in step (3), the stirring speed is 800 r / min to avoid dust from dry materials and ensure thorough mixing; in step (4), the stirring speed is 1000 r / min to ensure uniform slurry and prevent fiber agglomeration.

[0015] The beneficial effects of this invention are mainly reflected in: 1. A three-step synergistic modification mechanism addresses all pain points: Alkali activation can strip away non-crystalline components and activated hydroxyl groups, laying the foundation for interfacial bonding; Coupling crosslinking (KH-560 / TEPA / GO) constructs chemical bridges, strengthening the fiber-matrix bond; and the inorganic dense coating of nano-stone powder layers blocks corrosive media. These three aspects work synergistically to solve the three core problems of weak interfacial bonding, easy fiber degradation, and high concrete porosity. Compared with existing single / two-step modification technologies, the overall mechanical properties, durability, and impermeability of concrete are improved by more than 40%. 2. GO-enhanced interface strengthening: GO's high specific surface area and strong adsorption can uniformly load coupling agent molecules, upgrading the bonding form between fibers and cement matrix from physical interlocking to chemical bridging and physical interlocking. The interfacial shear strength is increased by more than 50% compared with single silane modification technology, reaching 3.0~3.3 MPa. 3. Long-lasting alkali-resistant protection: The nano stone powder coating has a density of over 92%, forming a double protection with the silane coating, effectively blocking the contact between moisture, alkaline ions and fibers. After being soaked in 5% NaOH solution for 180 days, the strength retention rate is ≥95%, and the service life can be extended to more than 30 years in harsh environments such as underground and marine environments. 4. Excellent crack resistance and impermeability: The concrete has an impermeability grade of P12 and a crack resistance grade of L-Ⅰ. The incidence of early plastic shrinkage cracks is reduced by more than 80%, which can effectively inhibit the initiation and propagation of cracks during the service life of concrete and meet the crack control requirements of high durability projects. 5. Strong industrial adaptability: The concrete has excellent workability, with a slump loss rate of ≤15% within 1 hour. It is easy to mix, pour and vibrate, and can be mass-produced without special equipment. Moreover, its performance is suitable for special scenarios such as underground integrated pipe corridors, marine docks, and airport runways, combining green environmental protection with engineering practicality. Attached Figure Description

[0016] Figure 1 This is a flow chart of the preparation process of the synergistically modified bamboo fiber concrete of the present invention. Detailed Implementation

[0017] The present invention will now be further described with reference to the accompanying drawings.

[0018] Reference Figure 1 A synergistic modified bamboo fiber concrete is composed of the following components in parts by weight: 250-280 parts of P.O42.5 ordinary Portland cement, 680-720 parts of river sand, 992-1115 parts of crushed stone with a particle size of 4.5-9mm, 58-66 parts of fly ash, 60-72 parts of mineral powder, 2.13-3.25 parts of calcium lignosulfonate, 0.9-1.2 parts of aluminum powder paste conforming to the current standard JC / T407, 3.4-6.2 parts of modified bamboo fiber, and 127-140 parts of water.

[0019] In this embodiment, the composition by weight parts can be: 250 parts of P.O42.5 ordinary silicate cement, 680 parts of river sand, 992 parts of crushed stone with a particle size of 4.5-9mm, 586 parts of fly ash, 60 parts of mineral powder, 2.13 parts of calcium lignosulfonate, 0.9 parts of aluminum powder paste conforming to the current standard JC / T407, 3.4 parts of modified bamboo fiber, and 127 parts of water.

[0020] Alternatively: 270 parts of P.O42.5 ordinary silicate cement, 700 parts of river sand, 1000 parts of crushed stone with a particle size of 4.5-9mm, 60 parts of fly ash, 68 parts of mineral powder, 3 parts of calcium lignosulfonate, 1 part of aluminum powder paste conforming to the current standard JC / T407, 5 parts of modified bamboo fiber, and 130 parts of water.

[0021] Alternatively: 280 parts of P.O42.5 ordinary silicate cement, 720 parts of river sand, 1115 parts of crushed stone with a particle size of 4.5-9mm, 66 parts of fly ash, 72 parts of mineral powder, 3.25 parts of calcium lignosulfonate, 1.2 parts of aluminum powder paste conforming to the current standard JC / T407, 6.2 parts of modified bamboo fiber, and 140 parts of water.

[0022] Furthermore, the modified bamboo fiber is prepared by a three-step synergistic method of alkali activation-coupling crosslinking-inorganic dense coating, as follows: Step 1: Take the middle fiber of the bamboo stalk, with an average length of 2.0~2.5mm and a diameter of 120~180μm. After pretreatment with low-temperature plasma for 3~5min, soak it in deionized water for 1.5~2.5h, stirring 2~3 times during the period, with each stirring lasting 5~8min, to remove loose impurities on the fiber surface. Step 2: Place the bamboo fiber pretreated in Step 1 into a 3% to 5% sodium hydroxide or potassium hydroxide aqueous solution at a temperature of 40 to 60°C. After soaking for 5 to 6 hours, filter the solution and rinse it repeatedly with water until the pH of the filtrate is 7 to 8. Then, vacuum dry the solution at 55 to 65°C for 7.5 to 8.5 hours to obtain alkali-activated bamboo fiber. Step 3: Prepare a composite modification solution. The composite modification solution is prepared by mixing γ-glycidyl etheroxypropyltrimethoxysilane (KH-560), triethylenetetramine (TEPA), and graphene oxide (GO) in a mass ratio of 1:(1.2~1.8):(0.05~0.1). Add the alkali-activated bamboo fiber obtained in Step 2 to the composite modification solution in a ratio of 1g:19.5mL to 1g:20.5mL based on the fiber mass and the volume of the modification solution. Stir for 2~3 hours under constant temperature water bath conditions at 45~55℃. After filtration, wash 2~3 times with anhydrous ethanol, then wash 1~2 times with deionized water. Finally, vacuum dry at 55~65℃ to constant weight to obtain coupled cross-linked bamboo fiber. Step 4: Using the coupled cross-linked bamboo fiber obtained in Step 3 as a reference, take 0.3-0.5 parts by mass of polycarboxylic acid dispersant and add it to a suspension of nano-granite powder with a mass fraction of 4-6%. The solid-liquid ratio of the suspension is 1:15-1:16, which is calculated as 1g:15mL-1g:16mL by mass of nano-granite powder and volume of water. After ultrasonic dispersion for 10-15 minutes, add the coupled cross-linked bamboo fiber obtained in Step 3, stir for 30-40 minutes, filter, and then dry at 55-65℃ to obtain modified bamboo fiber.

[0023] The nano-granite powder has a particle size of 50~100nm, and the particle size test meets the technical requirements of GB / T19077-2016 "Particle Size Analysis by Laser Diffraction"; the preferred mass ratio of KH-560, TEPA and GO in the composite modified liquid is 1:1.5:0.08; the polycarboxylate dispersant is a polycarboxylate high-efficiency water-reducing agent, which meets the technical requirements of high-efficiency water-reducing agents in GB8076-2008 "Concrete Admixtures", and has a solid content ≥40% to ensure the dispersion effect of the stone powder.

[0024] The core raw material parameters used in this embodiment and comparative example are as follows: The bamboo fiber is extracted from the middle part of natural bamboo stalks, with an average length of 2.0~2.5mm, a diameter of 120~180μm, and a moisture content of ≤8%. The graphene oxide has a purity of ≥98%, a sheet thickness of 0.8~1.2nm, and a lateral dimension of 1~5μm; The nano-granite powder has a particle size of 50~100nm and a SiO2 content of ≥65%, which meets the testing requirements of GB / T19077-2016 "Particle Size Analysis by Laser Diffraction". The polycarboxylate dispersant, model PCA-R, has a solid content ≥40% and a water reduction rate ≥25%, conforming to GB8076-2008 "Concrete Admixtures"; The γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) has a purity ≥97% and a density of 0.970~0.980 g / cm³. 3 ; The triethylenetetramine (TEPA) has a purity of ≥98% and a boiling range of 260~265℃. Other raw materials: PO 42.5 ordinary Portland cement (compliant with GB175-2007), river sand (medium sand, fineness modulus 2.3~3.0), 4.5-9mm crushed stone (crushing value ≤10%), fly ash (Grade II, compliant with GB / T1596-2017), mineral powder (Grade S95, compliant with GB / T18046-2017), calcium lignosulfonate (water reduction rate ≥8%), aluminum powder paste (compliant with the current standard JC / T407).

[0025] This embodiment is a standard preparation scheme for synergistically modified bamboo fiber concrete, which uses the optimal combination of raw materials and parameters.

[0026] Modified bamboo fiber was prepared by a three-step synergistic method of alkali activation, coupling crosslinking, and inorganic dense coating, as follows: Step 1: Pretreatment: Take 4.8 kg of dried bamboo fiber with an average length of 2.0~2.5 mm and a diameter of 120~180 μm, and pretreat it for 3 min in an argon atmosphere using a TP-1200 low-temperature plasma treatment instrument at a power of 300W. Then soak it in deionized water for 2 h, stirring once every 40 min for 5 min each time at a stirring speed of 500 r / min to remove loose impurities such as surface wax and pectin. After filtration, the pretreated bamboo fiber is obtained. Step 2, Alkali Activation: Prepare 48L of 4% sodium hydroxide aqueous solution, heat to 50℃ and keep warm. Immerse the pretreated bamboo fiber in the solution for 5.5h, stirring once every 1h for 3min each time. After soaking, filter and rinse the fiber repeatedly with deionized water until the pH of the filtrate is 7.5. Place it in a DZF-6000 vacuum drying oven and vacuum dry at 60℃ for 8h to obtain 4.2kg of alkali-activated bamboo fiber. Step 3, Coupling and Crosslinking: Weigh 0.9 kg of KH-560, 1.35 kg of TEPA, and 0.072 kg of GO according to the mass ratio of KH-560:TEPA:GO = 1:1.5:0.08. Add deionized water to a total volume of 84 L and stir for 15 min until homogeneous to prepare a ternary composite modified solution. Add alkali-activated bamboo fiber to the modified solution and place it in a 50℃ constant temperature water bath. Stir at 600 r / min for 2 h. After the reaction is complete, filter the solution. Wash twice with anhydrous ethanol, 5 L each time, to remove ungrafted coupling agent. Wash once with deionized water, 8 L each time. Finally, vacuum dry at 60℃ to constant weight. Weigh the solution at 1 h intervals. The difference between the two weighings should be ≤0.1% to obtain 4.0 kg of coupled and crosslinked bamboo fiber. Step 4, Inorganic Dense Coating: Weigh 2.0 kg of nano-granite powder with a particle size of 70-90 nm, add 30 L of deionized water, and then add 0.06 kg of polycarboxylate dispersant. Use a 20 kHz ultrasonic disperser to ultrasonically disperse for 10 min to break up the stone powder agglomeration. Add the coupled cross-linked bamboo fiber to the above suspension and stir at 800 r / min for 30 min to ensure that the stone powder is uniformly coated on the fiber surface. After filtration, place it in a 60℃ forced-air drying oven to dry for 4 h. After cooling to room temperature, weigh to obtain 4.8 kg of modified bamboo fiber.

[0027] Example 1 A method for preparing synergistically modified bamboo fiber concrete, an example of which includes the following steps in a standard mix proportion: (1) Weighing of raw materials: Weigh the following raw materials according to the following mass percentages: 265 kg of PO 42.5 ordinary Portland cement, 700 kg of river sand, 1050 kg of 4.5-9 mm crushed stone, 62 kg of fly ash, 66 kg of mineral powder, 2.69 kg of calcium lignosulfonate, 1.05 kg of aluminum powder paste, 4.8 kg of the above modified bamboo fiber, and 132 kg of deionized water; All raw materials should be placed in an environment of 20±2℃ in advance to balance the temperature and ensure that the moisture content is ≤0.5%; (2) Fiber dispersion: Pour 132 kg of deionized water into the mixing tank of a JS750 mixer, heat it to 50±2℃, add 4.8 kg of modified bamboo fiber, stir at 1000~1400 r / min for 8~15 min, and confirm by visual observation that there are no obvious agglomerates of fiber to obtain fiber dispersion; (3) Dry material premixing: Take another 5-2000L high mixer, add cement, river sand, crushed stone, fly ash, mineral powder, calcium lignosulfonate and aluminum powder paste, premix at 600~1000r / min for 3min, and take samples after stopping the machine to ensure that the dry material has no obvious color difference and no lumps; (4) Mixing and stirring: Slowly pour the pre-mixed dry material into the mixing tank containing the fiber dispersion liquid. The pouring time is ≥2min to avoid fiber agglomeration. Stir at 800~1200r / min for 4min, stopping the machine twice for 10s each time. Use a scraper to clean the residual material on the tank wall to ensure that the slurry is uniform. After the mixing is completed, the concrete slump is measured to ensure that its workability meets the standard. (5) Molding: The concrete mixture is poured into 100mm×100mm×400mm bending test molds and 150mm×150mm×150mm compressive test molds respectively. Three sets of parallel specimens are poured into each test mold. The mixture is vibrated for 20~40s using a vibrating table with a frequency of 50±5Hz and an amplitude of 0.6~1.0mm. During the vibration process, the side of the test mold is observed until no obvious air bubbles are overflowing. After vibration, the surface of the test mold is smoothed with a trowel and excess mixture is removed. (6) Standing and demolding: Immediately after casting, cover the specimen with a sealed plastic film (to prevent moisture evaporation) and place it in an environment with a room temperature of 20±5℃ and a relative humidity of ≥60% for 24 hours; after standing, slowly demold to avoid damage to the edges and corners of the specimen, and check the surface of the specimen for defects such as honeycomb and pitting. (7) Standard curing: After demolding, the specimens were placed in a standard curing box and the curing conditions were set as follows: temperature 20±2℃, relative humidity ≥95%, and curing for 28 days. During the curing period, the water was changed once a week to ensure that the pH of the curing water was 7~8, and finally synergistic modified bamboo fiber concrete was obtained.

[0028] Example 2 The modified bamboo fiber preparation method of this embodiment includes the following steps: Step 1: Take 3.5 kg of dried bamboo stalk middle fiber, pre-treat it with low-temperature plasma for 3-5 minutes, and then soak it in deionized water for 2 hours, stirring 3 times during the process; Step 2: Prepare 35L of 3% sodium hydroxide aqueous solution, heat to 40℃, soak the fiber for 6 hours, filter and rinse until pH=7, vacuum dry at 60℃ for 8 hours to obtain alkali-activated fiber. Step 3: Prepare the composite modification solution: Weigh 0.7 kg of KH-560, 0.84 kg of TEPA, and 0.035 kg of GO according to the mass ratio of KH-560:TEPA:GO = 1:1.2:0.05, add deionized water to a total volume of 145 L, and stir evenly; add 2.9 kg of alkali-activated fiber to the composite modification solution, keep warm at 50℃ and stir for 2 hours, filter, rinse, and dry to constant weight; Step 4: Weigh 1.3 kg of 80-100 nm nano-granite powder, add 19.5 L of deionized water, add 0.039 kg of polycarboxylate dispersant, ultrasonically disperse for 10 min, add 2.6 kg of coupling crosslinked fiber to the suspension, stir for 30 min, filter and dry to obtain about 3.4 kg of modified bamboo fiber.

[0029] A method for preparing synergistically modified bamboo fiber concrete includes the following steps: (1) Weigh out the following raw materials by mass: 250 kg of cement, 680 kg of river sand, 992 kg of crushed stone, 58 kg of fly ash, 60 kg of mineral powder, 2.13 kg of calcium lignosulfonate, 0.9 kg of aluminum powder paste, 3.4 kg of modified bamboo fiber, and 127 kg of water. (2) The subsequent steps are consistent with the steps (2) fiber dispersion, (3) dry material premixing, (5) molding, (6) static demolding, and (7) standard curing in the preparation of synergistic modified bamboo fiber concrete in Example 1, except that the mixing time in step (4) is adjusted to 5 min.

[0030] Example 3 (Upper Limit Ratio) The modified bamboo fiber preparation method of this embodiment includes the following steps: Step 1: Take 6.5 kg of dried bamboo stalk middle fiber, pre-treat it with low-temperature plasma for 3 min, and then soak it in deionized water for 2 h, stirring 3 times during the process; Step 2: Prepare 65L of 5% potassium hydroxide aqueous solution, heat to 60℃, soak the fiber in it for 5h, filter and rinse until pH=8, vacuum dry at 60℃ for 8h to obtain 5.4kg of alkali-activated fiber. Step 3: Prepare the composite modification solution: Weigh 1.3 kg of KH-560, 2.34 kg of TEPA, and 0.13 kg of GO according to the mass ratio of KH-560:TEPA:GO = 1:1.8:0.1, add deionized water to a total volume of 270 L, and stir evenly; add 5.4 kg of alkali-activated fiber to the composite modification solution, keep warm at 50℃ and stir for 2 hours, filter, rinse, and dry to constant weight; Step 4: Weigh 2.6 kg of 50-80 nm nano-granite powder, add 39 L of deionized water, add 0.0735 kg of polycarboxylate dispersant, ultrasonically disperse for 10 min, add 4.9 kg of coupling crosslinked fiber to the suspension, stir for 30 min, filter and dry to obtain modified bamboo fiber.

[0031] A method for preparing synergistically modified bamboo fiber concrete includes the following steps: (1) Weigh the following raw materials by mass: 280 kg of cement, 720 kg of river sand, 1115 kg of crushed stone, 66 kg of fly ash, 72 kg of mineral powder, 3.25 kg of calcium lignosulfonate, 1.2 kg of aluminum powder paste, 6.2 kg of modified bamboo fiber, and 140 kg of water. (2) The subsequent steps are completely consistent with the steps in Example 1 for preparing synergistically modified bamboo fiber concrete: (2) fiber dispersion, (3) dry material premixing, (4) mixing, (5) molding, (6) static demolding, and (7) standard curing. No other parameters are adjusted.

[0032] Comparative Example 1 A method for preparing bamboo fiber concrete differs from Example 1 in that: unmodified bamboo fiber is used without any modification treatment, while the remaining components and preparation process are the same as in Example 1.

[0033] Comparative Example 2 A method for preparing modified bamboo fiber concrete differs from Example 1 in that: bamboo fiber is treated with a single alkali, without coupling crosslinking and nano-stone powder coating, while the remaining components and preparation process are the same as in Example 1.

[0034] Comparative Example 3 A method for preparing modified bamboo fiber concrete differs from Example 1 in that: bamboo fiber is treated with alkali and silane, without GO and nano stone powder coating, while the remaining components and preparation process are the same as in Example 1.

[0035] Comparative Example 4 A method for preparing modified bamboo fiber concrete differs from Example 1 in that the composite modifying liquid contains no GO, while the remaining components and preparation process are the same as in Example 1.

[0036] Comparative Example 5 A method for preparing modified bamboo fiber concrete differs from Example 1 in that: the nano-stone powder coating step is omitted, while the remaining components and preparation process are the same as in Example 1.

[0037] The concrete prepared in Examples 1-3 and Comparative Examples 1-5 was placed in a mold using a manual tamping method. The concrete was then tamped evenly with a tamping rod, followed by several tamping strokes with a trowel. After tamping, the mold was gently tapped with a rubber mallet until all voids disappeared. The mold was then cured under standard curing conditions for 28 days. The specimens were then removed from the mold for performance testing.

[0038] Crack resistance test: The plate method was used. The plate mold size was 600mm×400mm×100mm, and a bent corrugated iron plate was used for constraint. The cured specimens were placed in the plate mold and vibrated on a vibration table for about 1 minute. The surface was then smoothed and moved to the observation room. The temperature in the observation room was 24-26℃, and the relative humidity was 60-70%. After the specimens were placed, the surface was directly blown by an electric fan at a wind speed of 8m / s for 24 hours. During this period, the visible cracks were used as the standard, and their lengths were measured with a steel ruler. When the crack showed obvious bending, the sum of the lengths of the broken lines represented the crack length. The crack width was measured using a reading microscope with a graduation of 0.01mm. Three crack widths were measured along the crack length, and the maximum value was taken as the nominal maximum crack width. Referring to the evaluation method in the "Guidelines for Durability Design and Construction of Concrete Structures" of the Civil Engineering and Architecture Department of the Chinese Academy of Engineering, the crack resistance of fiber-reinforced concrete was comprehensively evaluated. The results are shown in Table 1. Table 1 shows the results of concrete cracking tests; Mechanical property testing: Compressive strength and flexural strength were tested according to GB / T50081-2019 standard; interfacial shear strength was tested according to GB / T14074-2017 standard; alkali resistance durability testing involved immersion in 5% NaOH solution for 180 days, followed by testing the retention rate of compressive strength. The results are shown in Table 2. Table 2 shows the test results of the mechanical properties and alkali resistance durability of concrete; As can be seen from the data in Tables 1 and 2, the synergistically modified bamboo fiber concrete prepared in Examples 1-3 all achieved crack resistance grades of L-I and impermeability grades of P10-P12, with significantly better mechanical properties and alkali resistance than the comparative examples. This indicates that the three-step synergistic modification mechanism of alkali activation-coupling crosslinking-inorganic dense coating, as well as the synergistic effect of GO and nano-stone powder, can effectively improve the comprehensive performance of concrete and overcome the shortcomings of existing technologies.

[0039] The embodiments described in this specification are merely examples of implementations of the inventive concept and are for illustrative purposes only. The scope of protection of this invention should not be considered limited to the specific forms described in these embodiments; rather, it extends to equivalent technical means conceived by those skilled in the art based on the inventive concept.

Claims

1. A synergistically modified bamboo fiber concrete, characterized in that, It is composed of the following components in parts by weight: 250-280 parts of P.O42.5 ordinary Portland cement, 680-720 parts of river sand, 992-1115 parts of crushed stone with a particle size of 4.5-9mm, 58-66 parts of fly ash, 60-72 parts of mineral powder, 2.13-3.25 parts of calcium lignosulfonate, 0.9-1.2 parts of aluminum powder paste conforming to the current standard JC / T407, 3.4-6.2 parts of modified bamboo fiber, and 127-140 parts of water.

2. The synergistically modified bamboo fiber concrete as described in claim 1, characterized in that, The modified bamboo fiber was prepared by a three-step synergistic method of alkali activation, coupling crosslinking, and inorganic dense coating, as follows: Step 1: Take the middle fiber of the bamboo stalk, with an average length of 2.0~2.5mm and a diameter of 120~180μm. After pretreatment with low-temperature plasma for 3~5min, soak it in deionized water for 1.5~2.5h, stirring 2~3 times during the period, with each stirring lasting 5~8min, to remove loose impurities on the fiber surface. Step 2: Place the bamboo fiber pretreated in Step 1 into a 3% to 5% sodium hydroxide or potassium hydroxide aqueous solution at a temperature of 40 to 60°C. After soaking for 5 to 6 hours, filter the solution and rinse it repeatedly with water until the pH of the filtrate is 7 to 8. Then, vacuum dry the solution at 55 to 65°C for 7.5 to 8.5 hours to obtain alkali-activated bamboo fiber. Step 3: Prepare a composite modification solution. The composite modification solution is prepared by mixing γ-glycidyl etheroxypropyltrimethoxysilane (KH-560), triethylenetetramine (TEPA), and graphene oxide (GO) in a mass ratio of 1:(1.2~1.8):(0.05~0.1). Add the alkali-activated bamboo fiber obtained in Step 2 to the composite modification solution in a ratio of 1g:19.5mL to 1g:20.5mL based on the fiber mass and the volume of the modification solution. Stir for 2~3 hours under constant temperature water bath conditions at 45~55℃. After filtration, wash 2~3 times with anhydrous ethanol, then wash 1~2 times with deionized water. Finally, vacuum dry at 55~65℃ to constant weight to obtain coupled cross-linked bamboo fiber. Step 4: Using the coupled cross-linked bamboo fiber obtained in Step 3 as a reference, take 0.3-0.5 parts by mass of polycarboxylic acid dispersant and add it to a suspension of nano-granite powder with a mass fraction of 4-6%. The solid-liquid ratio of the suspension is 1:15-1:16, which is calculated as 1g:15mL-1g:16mL by mass of nano-granite powder and volume of water. After ultrasonic dispersion for 10-15 minutes, add the coupled cross-linked bamboo fiber obtained in Step 3, stir for 30-40 minutes, filter, and then dry at 55-65℃ to obtain modified bamboo fiber.

3. The synergistically modified bamboo fiber concrete as described in claim 2, characterized in that, The nano-granite powder has a particle size of 50~100nm, and the particle size test meets the technical requirements of GB / T19077-2016 "Particle Size Analysis by Laser Diffraction".

4. The synergistically modified bamboo fiber concrete as described in claim 2, characterized in that, The mass ratio of KH-560, TEPA and GO in the composite modified liquid is 1:1.5:0.

08.

5. The synergistically modified bamboo fiber concrete as described in claim 2, characterized in that, The polycarboxylate dispersant is a polycarboxylate high-efficiency water-reducing agent, which meets the technical requirements for high-efficiency water-reducing agents in GB8076-2008 "Concrete Admixtures", and has a solid content of ≥40% to ensure the stone powder dispersion effect.

6. A method for preparing synergistically modified bamboo fiber concrete as described in claim 1, characterized in that, Includes the following steps: (1) Weigh each raw material according to the following mass parts: 250-280 parts of P.O42.5 ordinary Portland cement, 680-720 parts of river sand, 992-1115 parts of crushed stone with a particle size of 4.5-9mm, 58-66 parts of fly ash, 60-72 parts of mineral powder, 2.13-3.25 parts of calcium lignosulfonate, 0.9-1.2 parts of aluminum powder paste conforming to the current standard of JC / T407, 3.4-6.2 parts of modified bamboo fiber, and 127-140 parts of water; all raw materials must meet the following requirements: moisture content ≤0.5% to avoid affecting the water-cement ratio of concrete, impurity content ≤0.1% to prevent the introduction of harmful components, and conform to the current national standards of the corresponding raw materials (e.g., cement conforms to GB175-2007 "General Portland Cement"); (2) Add the modified bamboo fiber to water at a temperature of 48~52℃ and stir at a stirring speed of 1000~1400r / min for 8~15min until no obvious agglomerates are visible to the naked eye, ensuring that the fiber is evenly dispersed. (3) Take P.O42.5 ordinary silicate cement, river sand, crushed stone, fly ash, mineral powder, calcium lignosulfonate and aluminum powder paste as dry materials, put them into a mixer and premix them for 3 to 4 minutes at a mixing speed of 600~1000r / min until there is no obvious color difference in the dry materials, and ensure that the mixture is uniform. (4) Slowly pour the pre-mixed dry material into water containing dispersed modified bamboo fiber, and mix at a stirring speed of 800~1200r / min for 3~5 minutes until the slurry has a uniform color, no particle clumping and no local fiber accumulation, to obtain concrete mixture.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes the following steps: (5) Pour the concrete mixture into a standard mold and vibrate it for 20 to 40 seconds with a vibrating table with a frequency of 50±5Hz and an amplitude of 0.6~1.0mm until there are no obvious air bubbles overflowing from the surface. Smooth the surface of the mold with a trowel. (6) After the concrete is poured, cover the concrete surface with a sealing plastic film to prevent moisture evaporation. After standing at room temperature of 20±5℃ for 24 hours, remove the formwork to obtain concrete specimens. (7) After demolding, the concrete specimens were placed in a standard curing environment with a temperature of 20±2℃ and a relative humidity of 95% or higher for 28 days to obtain synergistic modified bamboo fiber concrete.

8. The preparation method according to claim 6 or 7, characterized in that, In step (2), the stirring speed is 1200 r / min and the stirring time is 10 min; in step (3), the stirring speed is 800 r / min to avoid dust from dry materials and ensure thorough mixing; in step (4), the stirring speed is 1000 r / min to ensure uniform slurry and prevent fiber agglomeration.

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