Reservoir composite plant fiber concrete and preparation method thereof

Abstract

The invention discloses composite plant fiber concrete for a water storage reservoir and a preparation method, and relates to the technical field of building materials, the composite plant fiber concrete comprises the following raw materials by mass: 350-400 parts of cement, 50-110 parts of a mineral admixture, 700-750 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 150-170 parts of water, 3.2-7.65 parts of a water reducer, 0.8-2.0 parts of modified jute fiber and 1.6-3.0 parts of modified straw fiber; wherein both the modified jute fibers and the modified straw fibers are composed of plant fiber bodies and composite coatings wrapping the plant fiber bodies. According to the invention, a double-layer composite coating of epoxy resin / nano clay and polydimethylsiloxane / wollastonite powder is constructed to carry out targeted modification on jute fibers and straw fibers, and an optimized fiber mixing amount and a mixing process are combined, so that the plant fiber concrete special for the water storage reservoir with excellent mechanical properties and long-term durability is prepared; the industrial problem that a single coating modification technology cannot give consideration to alkali resistance and hydrophobicity of fibers and strong interface bonding with a cement matrix is solved.

Description

A composite plant fiber concrete for reservoirs and its preparation method Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a composite plant fiber concrete for water storage reservoirs and its preparation method. Background Technology

[0002] As a green building material, the development of plant fiber concrete is constrained by two major problems: the susceptibility of fibers to corrosion from the alkaline environment inside concrete, and the interface deterioration caused by the inherent hydrophilicity of the fibers. In existing technologies, coating the surface of the fibers with a single polymer emulsion (such as epoxy resin or styrene-acrylic emulsion) is a common improvement method. Forming an isolation film to delay alkaline erosion and, to some extent, improve the initial bond between the fibers and the cement matrix provides a foundation for the application of plant fibers.

[0003] Single-coating solutions have inherent limitations. While they primarily provide a physical barrier function, they struggle to systematically address the deeper issues arising from the porous structure of plant fibers: the coating's ability to fill the internal pores of the fibers is limited, failing to fundamentally eliminate their potential as moisture storage points; furthermore, the resulting dense, smooth film may weaken the mechanical interlocking between the fiber surface and the cementitious matrix, thus hindering the long-term maintenance of interfacial strength. This makes this technology inadequate for meeting the high durability requirements of materials in harsh environments such as reservoirs. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a composite plant fiber concrete for reservoirs and a preparation method to solve the technical problem that single polymer coating does not adequately modify plant fibers and cannot simultaneously ensure durability and interfacial bonding strength.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a composite plant fiber concrete for reservoirs, comprising, by weight, the following raw materials:

[0008] The ingredients are: 350-400 parts cement, 50-110 parts mineral admixtures, 700-750 parts fine aggregate, 1000-1100 parts coarse aggregate, 150-170 parts water, 3.2-7.65 parts water-reducing agent, 0.8-2.0 parts modified jute fiber, and 1.6-3.0 parts modified rice straw fiber.

[0009] The modified jute fiber and modified straw fiber are both composed of a plant fiber body and a composite coating covering the plant fiber body.

[0010] As a preferred embodiment of the composite plant fiber concrete for reservoirs according to the present invention, the composite coating includes a first composite coating and a second composite coating sequentially covering the plant fiber body.

[0011] The first composite coating is composed of an epoxy resin emulsion and nano-clay dispersed therein;

[0012] The second composite coating is composed of a polydimethylsiloxane emulsion and wollastonite powder dispersed therein.

[0013] In a preferred embodiment of the composite plant fiber concrete for reservoirs described in this invention, the mass of the nano-clay is 15%-25% of the solid mass of the epoxy resin emulsion.

[0014] The mass of the wollastonite powder is 15%-25% of the mass of the polydimethylsiloxane emulsion solids.

[0015] Secondly, the present invention provides a method for preparing composite plant fiber concrete for reservoirs, comprising:

[0016] S1. After pretreating jute fiber and rice straw fiber, a first composite coating and a second composite coating are sequentially constructed on their surfaces to obtain modified jute fiber and modified rice straw fiber.

[0017] S2. After dry mixing cement, mineral admixtures, fine aggregates and coarse aggregates evenly, add the modified jute fiber and modified rice straw fiber obtained in step S1 and continue dry mixing. Add water containing water-reducing agent for wet mixing to obtain the reservoir composite plant fiber concrete.

[0018] This invention provides a method for preparing composite plant fiber concrete for reservoirs, wherein, in step S1, the pretreatment includes: cutting jute fibers to a length of 40-50 mm and straw fibers to a length of 5-10 mm, and then drying them.

[0019] This invention provides a method for preparing composite plant fiber concrete for reservoirs, including, in step S1, the method for constructing the first composite coating includes: adding nano-clay to an epoxy resin emulsion, stirring and ultrasonically dispersing it to prepare a first spraying liquid, and uniformly spraying it onto the pretreated fiber surface, and pre-curing it at 60±5℃ for 1-2 hours.

[0020] This invention provides a method for preparing composite plant fiber concrete for reservoirs, wherein the stirring speed is 500 rpm and the time is 15 minutes; the ultrasonic dispersion power is 300W and the time is 30 minutes.

[0021] This invention provides a method for preparing composite plant fiber concrete for reservoirs, wherein the method for constructing the second composite coating includes: adding wollastonite powder to polydimethylsiloxane emulsion, stirring to prepare a second spraying liquid, uniformly spraying it onto the fiber surface where the first composite coating has been constructed, and completely curing it at 70±5℃ for 24-48 hours.

[0022] This invention provides a method for preparing composite plant fiber concrete for reservoirs, wherein the stirring speed is 400 rpm and the stirring time is 20-30 minutes.

[0023] This invention provides a method for preparing composite plant fiber concrete for reservoirs, wherein in step S2, the dry mixing time is 60 seconds; the dry mixing time after adding fibers is 90 seconds; and the wet mixing time is 180 seconds.

[0024] The beneficial effects of this invention are as follows: By constructing a double-layer composite coating of epoxy resin / nanoclay and polydimethylsiloxane / wollastonite powder to target the modification of jute fiber and straw fiber, and combined with optimized fiber adsorption and mixing process, a special plant fiber concrete for reservoirs with excellent mechanical properties and long-term durability is prepared, which solves the industry problem that single coating modification technology cannot take into account the fiber's alkali resistance, water repellency and strong interfacial adhesion with cement matrix. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 is a schematic diagram of a method for preparing composite plant fiber concrete for water storage reservoirs.

[0027] Figure 2 is a schematic diagram of the compressive strength of modified jute fiber concrete.

[0028] Figure 3 is a schematic diagram of the flexural strength of modified jute fiber concrete.

[0029] Figure 4 is a schematic diagram of the mass loss rate of modified jute fiber concrete.

[0030] Figure 5 is a schematic diagram of the compressive strength retention rate of modified jute fiber concrete after sulfate wet-dry cycles.

[0031] Figure 6 is a schematic diagram of the retention rate of flexural strength of modified jute fiber concrete after sulfate wet-dry cycles.

[0032] Figure 7 is a schematic diagram of the compressive strength of modified composite fiber concrete.

[0033] Figure 8 is a schematic diagram of the flexural strength of modified composite fiber concrete.

[0034] Figure 9 is a schematic diagram of the mass loss rate of modified composite fiber concrete.

[0035] Figure 10 is a schematic diagram of the compressive strength retention rate of modified composite fiber concrete after sulfate wet-dry cycles.

[0036] Figure 11 is a schematic diagram of the retention rate of flexural strength of modified composite fiber concrete after sulfate wet-dry cycles. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0040] Example 1

[0041] Referring to Figures 1-11, this is the first embodiment of the present invention, which provides a composite plant fiber concrete for a reservoir, comprising:

[0042] The ingredients are: 350-400 parts cement, 50-110 parts mineral admixtures, 700-750 parts fine aggregate, 1000-1100 parts coarse aggregate, 150-170 parts water, 3.2-7.65 parts water-reducing agent, 0.8-2.0 parts modified jute fiber, and 1.6-3.0 parts modified rice straw fiber.

[0043] The modified jute fiber and the modified straw fiber are both composed of a plant fiber body and a composite coating covering the plant fiber body.

[0044] Furthermore, the composite coating includes a first composite coating and a second composite coating that sequentially coat the plant fiber body.

[0045] The first composite coating is composed of an epoxy resin emulsion and nano-clay dispersed therein;

[0046] The second composite coating consists of a polydimethylsiloxane emulsion and wollastonite powder dispersed therein;

[0047] The mass of the nano-clay is 15%-25% of the solid mass of the epoxy resin emulsion;

[0048] The mass of the wollastonite powder is 15%-25% of the mass of the polydimethylsiloxane emulsion solids.

[0049] This embodiment also provides a method for preparing composite plant fiber concrete for reservoirs, including:

[0050] S1. After pretreating jute fiber and rice straw fiber, a first composite coating and a second composite coating are sequentially constructed on their surfaces to obtain modified jute fiber and modified rice straw fiber.

[0051] S2. After dry mixing cement, mineral admixtures, fine aggregates and coarse aggregates evenly, add the modified jute fiber and modified rice straw fiber obtained in step S1 and continue dry mixing. Add water containing water-reducing agent for wet mixing to obtain the reservoir composite plant fiber concrete.

[0052] Concrete was prepared according to the above methods and the industry standard JGJ 55-2011 "Specification for Concrete Mix Design". Mechanical performance tests were conducted according to the national standard GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". Freeze-thaw cycle tests and sulfate wet-dry cycle tests were conducted according to the national standard GB / T50082-2009 "Test Methods for Long-term Performance and Durability of Ordinary Concrete".

[0053] The experiment is as follows:

[0054] 1. Optimization of modified jute fiber incorporation:

[0055] Adding 0% to 3% of 40 mm-50 mm modified jute fiber to concrete and testing the compressive strength and flexural strength of the concrete are shown in Figures 2 and 3.

[0056] Adding 0% to 3% of 50 mm modified jute fiber to concrete and conducting freeze-thaw cycle tests yielded the mass loss rate of the modified jute fiber concrete, as shown in Figure 4. The mass loss rate represents the percentage reduction in mass after freeze-thaw cycles. Sulfate wet-dry cycle tests were conducted to obtain the compressive strength retention rate and flexural strength retention rate of the modified jute fiber concrete after sulfate wet-dry cycles, as shown in Figures 5 and 6. The strength retention rate is calculated as (strength after cycles / cyclic strength) * 100%.

[0057] Based on the above data, an in-depth analysis was conducted from three dimensions: load-bearing capacity, toughness, and durability balance. The optimal content of modified jute fiber was determined to be 1.5%, as demonstrated below:

[0058] Compressive strength: Data shows that the compressive strength reaches a peak of 45.0 MPa at a dosage of 1.5%. Above this dosage, the strength decreases. This indicates that 1.5% is the critical point where the fiber can exert its "micro-reinforcing" effect without compromising the matrix's density. Beyond this point, fiber agglomeration and the introduction of weak interfaces increase, and its "splitting effect" on the matrix begins to dominate, leading to a decrease in macroscopic load-bearing capacity. 1.5% is the optimal dosage for maintaining the highest compressive strength.

[0059] Flexural strength and durability: Under standard curing conditions, the flexural strength peaked at 2.0% (6.5 MPa). However, after sulfate attack, the 1.5% admixture group showed a higher compressive strength retention rate (89.5%) than the 2.0% group (85.3%), and the lowest mass loss rate (0.71%). This indicates that the 1.5% admixture resulted in the most stable matrix density and fiber-matrix interface in the corrosive environment. Although the 2.0% admixture group showed a slightly higher flexural strength retention rate after cycles (86.8%) than the 1.5% group (85.2%), the difference was only 1.6 percentage points. In contrast, the 1.5% admixture group outperformed the 2.0% group by 4.2 percentage points in the more critical overall corrosion resistance (compressive strength retention rate) and exhibited less physical damage (mass loss). This demonstrates that the 1.5% admixture achieved a better balance between long-term toughness retention and overall corrosion resistance. While higher dosage (2.0%) can provide slightly better toughness retention, it comes at the cost of sacrificing the integrity of the matrix and higher mass loss, which is detrimental to hydraulic structures that are exposed to corrosive environments for a long time.

[0060] Performance Matrix Evaluation: The performance of each dosing level was compared with the baseline group to construct a three-dimensional evaluation of "strength improvement," "toughness improvement," and "durability retention." The 1.5% dosing group showed the best performance in compressive strength improvement (peak value) and erosion resistance (peak value retention rate + minimum mass loss), while its flexural strength (6.3 MPa) reached 96.9% of the peak strength, and its toughness was improved. The 2.0% dosing group only had a slight advantage in the flexural strength under non-erosion conditions, but the erosion resistance of the core load-bearing capacity and the matrix integrity index were significantly deteriorated.

[0061] Failure Mode and Long-Term Performance: Under sulfate attack, low-dosage fiber crack-blocking networks are insufficient, while high-dosage introduces too many erosion channels. A dosing of 1.5% is just right for the fibers to effectively block cracking, while the interface protected by the modified coating is the most stable, allowing the structure to maintain its integrity under long-term erosion and avoiding cascading damage caused by local interface failure. This is crucial for reservoir structures requiring a 100-year service life.

[0062] The impact of modified jute fiber incorporation on concrete performance involves multiple trade-offs. Experimental data shows that at a dosage of 1.5%, the concrete achieves the highest compressive strength and the best erosion resistance (highest compressive strength retention rate and lowest mass loss), while its flexural strength also reaches a very high level (close to peak value). When the dosage is increased to 2.0%, although the non-eroded flexural strength increases slightly, it leads to a decline in compressive strength, durability, and matrix integrity—indicators more critical to hydraulic structures. Considering maximizing the comprehensive performance (high strength, high durability, and good toughness) required for the long-term safe operation of reservoir concrete structures under harsh erosive environments, 1.5% is the optimal dosage of modified jute fiber. This conclusion reflects that in engineering designs prioritizing durability, it is necessary to seek the optimal balance among multiple performance aspects, rather than pursuing the local optimum of a single indicator.

[0063] 2. Optimization of modified composite fiber incorporation amount:

[0064] 1.5% of 40-50 mm modified jute fiber and 0% to 3% of 5-10 mm modified rice straw fiber were added to the concrete. The compressive strength and flexural strength of the modified composite fiber concrete were obtained by the test, as shown in Figures 7 and 8.

[0065] 1.5% of 40-50 mm modified jute fiber and 0% to 3% of 5-10 mm modified straw fiber were added to the concrete. The mass loss rate of the modified composite fiber concrete was obtained through freeze-thaw cycle tests, as shown in Figure 9. The mass loss rate is the percentage reduction in mass after freeze-thaw cycles. Sulfate wet-dry cycle tests were conducted to obtain the compressive strength retention rate and flexural strength retention rate of the modified composite fiber concrete after sulfate wet-dry cycles, as shown in Figures 10 and 11. The strength retention rate = (strength after cycles / cyclic strength) * 100%.

[0066] Adding modified rice straw fiber to concrete already containing 1.5% modified jute fiber primarily serves to further refine the concrete and inhibit cracking; however, excessive addition can also have negative effects. Analysis suggests that 2.0% is the optimal dosage of modified rice straw fiber, as demonstrated below:

[0067] Compressive strength: With increasing modified rice straw fiber content, the compressive strength initially increased and then decreased, reaching a peak of 47.0 MPa at a content of 2.0%. Short-chopped rice straw fibers effectively fill micropores and prevent the initiation and propagation of microcracks, forming a multi-scale crack-resistant system with jute fibers, thus improving matrix density and integrity. However, strength begins to decrease after exceeding 2.0%, falling below the baseline at 3.0%. This is because excessive short fibers increase the consistency of the mixture, potentially introducing more air bubbles or weak interfaces even with water-reducing agents, thereby weakening the matrix.

[0068] Flexural strength: The flexural strength also reaches a peak of 7.5 MPa at a 2.0% admixture content. The addition of straw fiber enhances the toughness of concrete, forming a synergistic effect with long fibers (jute) to improve the material's resistance to deformation and fracture. Beyond 2.0%, the flexural strength begins to decrease, but the rate of decrease is slightly slower than that of the compressive strength, indicating that the fiber contributes a wider window to toughness. However, excessive admixture leading to deterioration in workability and increased defects will ultimately weaken its reinforcing effect.

[0069] After sulfate wet-dry cycling, the 2.0% dosage group exhibited the best overall durability performance, with the highest retention rates of compressive and flexural strength (92.0%, 90.5%) and the lowest mass loss rate (0.52%). This indicates that at this dosage, the composite network formed by straw and jute fibers can most effectively refine cracks and block the migration paths of corrosive ions, thereby maximizing the protection of the matrix and fiber-matrix interface.

[0070] When the doping concentration exceeds 2.0%, all durability indicators deteriorate. For example, the compressive strength retention rate (90.5%) and mass loss rate (0.68%) of the 2.5% doping group are significantly worse than those of the 2.0% group. This indicates that 2.0% is the critical threshold for maintaining optimal durability. Beyond this value, the interface introduced by excessive fibers becomes a sensitive area for sulfate crystallization and damage, and fiber agglomeration may lead to localized failure of the protective coating, thus accelerating corrosion.

[0071] Performance matrix trade-offs: The 2.0% dosage is at the optimal or near-optimal level in compressive strength (peak), flexural strength (peak), and durability (peak or near-peak), achieving simultaneous high-level synergy in all key performance indicators. Although the performance of the 1.5% dosage group is very close to that of the 2.0% group (the difference is mostly within 2%), the 2.0% group has a more obvious advantage in flexural strength and durability.

[0072] Failure Mode and Long-Life Design: For reservoir structures, microcrack control and impermeability are core to durability. A 2.0% modified straw fiber content allows the short fibers to reach an ideal "critical density" in the concrete, maximizing stress dispersion and crack prevention without compromising the homogeneity and density of the matrix. From the perspective of long-term performance retention, composite fiber-reinforced concrete with this content exhibits the highest reliability.

[0073] Marginal benefit analysis: Increasing from 1.5% to 2.0% still results in a slight improvement in all performance aspects; however, from 2.0% to 2.5%, the main performance aspects begin to decline. Therefore, 2.0% is the inflection point for performance growth, offering the best cost-effectiveness and performance stability.

[0074] Based on a fixed 1.5% modified jute fiber, the addition of modified rice straw fiber can further optimize the overall performance of concrete. Experimental data shows that when the modified rice straw fiber content is 2.0%, the compressive strength and flexural strength of the concrete both reach their peak values. Simultaneously, it exhibits the highest strength retention rate and the lowest mass loss rate in harsh sulfate wet-dry cycles, indicating optimal overall durability. Below this content, the reinforcing and crack-resistant potential of the fiber is not fully realized; above this content, excessive interface defects and construction problems lead to a decline in both mechanical properties and durability. Therefore, aiming to maximize the synergistic effect of the material in terms of load-bearing capacity, toughness, and long-term durability, 2.0% was determined to be the optimal content of modified rice straw fiber.

[0075] Based on previous research, the recommended mix proportion of the composite plant fiber concrete for reservoirs in this invention is: 1.5% modified jute fiber + 2.0% modified rice straw fiber.

[0076] Example 2 is a second embodiment of the present invention, which provides a high-toughness, low-shrinkage composite fiber-reinforced concrete mix proportion, comprising:

[0077] Cement (P·O 42.5 grade): 380 parts, mineral admixture (Grade I fly ash): 80 parts, fine aggregate (medium sand, fineness modulus 2.6): 720 parts, coarse aggregate (5-25mm continuously graded crushed stone): 1050 parts, water: 160 parts, polycarboxylate superplasticizer: 5.5 parts, modified jute fiber: 1.5 parts (corresponding to 1.5% of the total mass of cementitious materials), modified straw fiber: 2.0 parts (corresponding to 2.0% of the total mass of cementitious materials).

[0078] Preparation method:

[0079] Pretreatment: Jute fibers are cut to a length of 45 mm and straw fibers are cut to a length of 8 mm, and dried at 105°C to constant weight.

[0080] First composite coating: Weigh epoxy resin emulsion (50% solid content) and add nano-clay equivalent to 20% of its solid mass. First, mechanically stir at 500 rpm for 15 minutes, then ultrasonically disperse at 300W for 30 minutes to obtain the first spray coating liquid.

[0081] First layer spraying and pre-curing: The pretreated fiber single layer is laid flat, and the first spray liquid is sprayed evenly with a spray gun at a pressure of 0.4MPa until it is completely wetted. Then it is placed in a 60℃ oven for pre-curing for 1.5 hours.

[0082] Second composite coating: Weigh out polydimethylsiloxane emulsion (40% solid content) and add 20% wollastonite powder of its solid mass. Stir at 400 rpm for 25 minutes to obtain the second spray coating liquid.

[0083] Second layer spraying and complete curing: The pre-cured fiber single layer is laid flat, and the second spraying liquid is sprayed evenly under a pressure of 0.4MPa until it is completely wetted. Then it is placed in a 70℃ oven for complete curing for 36 hours to obtain modified jute fiber and modified straw fiber, which are then sealed for later use.

[0084] Concrete mixing and preparation:

[0085] Weigh out the cement, fly ash, sand, and crushed stone according to the proportions, put them into a forced mixer, and dry mix for 60 seconds.

[0086] Add the modified jute fiber and modified rice straw fiber prepared above, and continue to dry mix for 90 seconds.

[0087] The water-reducing agent is completely dissolved in the mixing water, and then the solution is poured into the mixer and wet-mixed for 180 seconds. The material is then discharged to obtain the composite plant fiber concrete for the reservoir.

[0088] Example 3 is the third embodiment of the present invention, which provides a high-strength, high-durability composite fiber-reinforced concrete mix proportion, comprising:

[0089] The difference between this embodiment and Embodiment 2 is that the mineral admixture is silica fume, with a dosage of 60 parts; the cement dosage is adjusted accordingly to 400 parts; the modified jute fiber dosage is 1.2 parts (approximately 1.2%), and the modified rice straw fiber dosage is 2.4 parts (approximately 2.4%). The preparation process parameters are the same as in Embodiment 1.

[0090] Example 4 is the fourth embodiment of the present invention. This embodiment provides a composite fiber-reinforced concrete mix proportion that balances workability and early strength, comprising:

[0091] The difference between this embodiment and Embodiment 2 is that the mineral admixture is a mixture of fly ash and silica fume (fly ash: silica fume = 3:1), with a total dosage of 100 parts; the cement dosage is adjusted accordingly to 360 parts; the dosage of modified jute fiber is 1.8 parts (approximately 1.8%), and the dosage of modified rice straw fiber is 1.8 parts (approximately 1.8%). The preparation process parameters are the same as in Embodiment 2.

[0092] Comparative Example 1 (unmodified fibers)

[0093] The difference between this comparative example and Example 2 is that it uses unmodified ordinary jute fiber (45 mm) and ordinary rice straw fiber (8 mm), with the same dosage as in Example 2. The fiber modification step is omitted in the preparation method; the ordinary fiber is added directly during mixing. The remaining raw material ratios and mixing process are exactly the same as in Example 1.

[0094] Comparative Example 2 (Single-coated modified fiber)

[0095] The difference between this comparative example and Example 2 lies in the fiber modification method. Only a single coating treatment is applied to the fibers. This coating liquid is prepared from epoxy resin emulsion and nano-clay (in the same proportions as in Example 2). It is sprayed and cured only once, forming only one layer equivalent to the first composite coating of this invention; the second composite coating is not applied. The fiber content and the proportions and processes of the remaining concrete components are the same as in Example 2.

[0096] Comparative Example 3 (excessive fiber content)

[0097] The difference between this comparative example and Example 2 is that the amount of modified jute fiber is increased to 2.5 parts (approximately 2.5%), and the amount of modified rice straw fiber is increased to 3.5 parts (approximately 3.5%). The fiber modification process is the same as in Example 2. The proportions and processes for the remaining concrete components are the same as in Example 1.

[0098] In summary, this invention targets and modifies jute and straw fibers by constructing a two-layer composite coating of epoxy resin / nanoclay and polydimethylsiloxane / wollastonite powder. Combined with optimized fiber content and mixing process, it prepares a special plant fiber concrete for reservoirs that combines excellent mechanical properties and long-term durability. This solves the industry problem that single coating modification technology cannot simultaneously address the fiber's alkali resistance, water repellency, and strong interfacial adhesion to the cement matrix.

[0099] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A composite plant fiber concrete for water storage reservoirs, characterized in that: The raw materials it comprises, by mass parts, 350-400 parts of cement, 50-110 parts of mineral admixtures, 700-750 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 150-170 parts of water, 3.2-7.65 parts of water-reducing agent, 0.8-2.0 parts of modified jute fiber, and 1.6-3.0 parts of modified straw fiber; wherein the modified jute fiber and the modified straw fiber are both composed of plant fiber body and composite coating covering the plant fiber body.

2. The composite plant fiber concrete for reservoirs as described in claim 1, characterized in that: The composite coating comprises a first composite coating and a second composite coating sequentially coating the plant fiber body; the first composite coating is composed of an epoxy resin emulsion and nano-clay dispersed therein; the second composite coating is composed of a polydimethylsiloxane emulsion and wollastonite powder dispersed therein.

3. The composite plant fiber concrete for reservoirs as described in claim 2, characterized in that: The mass of the nano-clay is 15%-25% of the solid mass of the epoxy resin emulsion; the mass of the wollastonite powder is 15%-25% of the solid mass of the polydimethylsiloxane emulsion.

4. A method for preparing composite plant fiber concrete for reservoirs, based on the composite plant fiber concrete for reservoirs according to any one of claims 1 to 3, characterized in that: include: S1. After pretreating jute fiber and rice straw fiber, a first composite coating and a second composite coating are sequentially constructed on their surfaces to obtain modified jute fiber and modified rice straw fiber. S2. After dry mixing cement, mineral admixtures, fine aggregates and coarse aggregates evenly, add the modified jute fiber and modified rice straw fiber obtained in step S1 and continue dry mixing. Add water containing water-reducing agent for wet mixing to obtain the reservoir composite plant fiber concrete.

5. The method for preparing composite plant fiber concrete for reservoirs as described in claim 4, characterized in that: In step S1, the pretreatment includes: cutting jute fibers to a length of 40-50 mm and straw fibers to a length of 5-10 mm, and then drying them.

6. The method for preparing composite plant fiber concrete for reservoirs as described in claim 4, characterized in that: In step S1, the method for constructing the first composite coating includes: adding nano-clay to an epoxy resin emulsion, stirring and ultrasonically dispersing it to prepare a first spraying liquid, and uniformly spraying it onto the pretreated fiber surface, and pre-curing it at 60±5℃ for 1-2 hours.

7. The method for preparing composite plant fiber concrete for reservoirs as described in claim 6, characterized in that: The stirring speed is 500 rpm and the time is 15 minutes; the ultrasonic dispersion power is 300W and the time is 30 minutes.

8. The method for preparing composite plant fiber concrete for reservoirs as described in claim 4, characterized in that: The method for constructing the second composite coating includes: adding wollastonite powder to polydimethylsiloxane emulsion, stirring to prepare a second spraying liquid, uniformly spraying it onto the fiber surface where the first composite coating has been constructed, and completely curing it at 70±5℃ for 24-48 hours.

9. The method for preparing composite plant fiber concrete for reservoirs as described in claim 8, characterized in that: The stirring speed is 400 rpm, and the time is 20-30 minutes.

10. The method for preparing composite plant fiber concrete for reservoirs as described in claim 4, characterized in that: In step S2, the dry mixing time is 60 seconds; the dry mixing time after adding the fiber is 90 seconds; and the wet mixing time is 180 seconds.

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