Concrete additive and concrete thereof

Abstract

The concrete additive is prepared from the following raw materials in parts by weight: modified red mud, wheat orange ash, nano silicon carbide, graphite, composite fibers, a super plasticizer, dipropylene glycol, waterborne polyurethane, a high-efficiency water reducing agent, a high-efficiency retarder and a fiber dispersant. The composite fiber is a mixture of towel gourd fiber, palm fiber and carbon fiber; the red mud is doped into concrete to prepare the high-ground-temperature tunnel lining concrete, all the raw materials are matched with one another, the red mud is matched with the nanometer silicon carbide and the graphite to achieve the micro-filling and macro-reinforcing effects, and the mechanical property and durability of the concrete are improved through cooperation of the three materials; a fiber network formed through interaction among the composite fibers can block a heat transfer path and reduce the heat conduction performance of the concrete, and the composite fibers complement each other in physical properties and mechanical properties through microcrack blocking, bridging effect and rigidity complementation, so that the crack resistance, toughness and impact resistance of the concrete are improved.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to a concrete additive and concrete thereof. Background Technology

[0002] When tunnels traverse areas with high geothermal anomalies, the initial temperature of the surrounding rock is high, reaching up to approximately 100℃. The lining structure is situated in this high-temperature environment, where the heat of hydration in the concrete during curing is difficult to dissipate, hindering normal concrete setting and easily leading to a decrease in the mechanical properties of the lining structure, rendering it ineffective in its support and load-bearing function. Furthermore, the large temperature difference between the inside and outside of the lining structure in this high-temperature environment easily causes cracks and fissures, reducing its load-bearing capacity and affecting its durability, preventing the tunnel structure from meeting its 100-year service life requirement. As the part of the tunnel structure in direct contact with the surrounding rock, the bonding performance of shotcrete with the rock is crucial to the effective functioning of the support structure. With tunnel construction increasingly focusing on length and depth, the problem of high geothermal heat hazards is becoming increasingly prominent. Under dry or humid conditions, the bonding performance between shotcrete and rock may be severely compromised. Particularly under dry conditions, the large drying shrinkage of shotcrete can lead to debonding and cracking, resulting in the loss of its support function. Current research mainly addresses the adverse effects of high geothermal temperatures by focusing on heat insulation in high-temperature tunnels, material degradation, and construction techniques. Regarding material degradation, the addition of mineral admixtures is typically used to improve concrete performance. While this can increase concrete strength to some extent, it doesn't solve the problem of rapid moisture evaporation in the early stages of high-temperature, low-humidity environments, resulting in low hydration levels. Furthermore, patent CN110510954B discloses a high-strength shotcrete for high-temperature tunnels and its preparation method, which reduces thermal conductivity by introducing modified rubber powder and vitrified microspheres to achieve heat insulation, but it doesn't consider the impact of high-volume lightweight aggregates on concrete strength.

[0003] Therefore, it is necessary to address the issues of heat resistance stability, interfacial bonding strength, and crack resistance of concrete under high geothermal conditions, while ensuring the strength of the concrete. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a concrete additive for high-temperature tunnel lining, which can improve the various properties of concrete under high-temperature environment, and has excellent heat resistance, interfacial adhesion and crack resistance.

[0005] The concrete additive for high-temperature tunnel lining of the present invention comprises the following components by weight: 100-150 parts modified red mud, 40-60 parts wheat ash, 25-55 parts nano-silicon carbide, 20-30 parts graphite, 40-60 parts composite fiber, 5-12 parts superplasticizer, 5-10 parts dipropylene glycol, 10-16 parts waterborne polyurethane, 2-6 parts high-efficiency water-reducing agent, 5-10 parts high-efficiency retarder, and 4-10 parts fiber dispersant; wherein the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber.

[0006] Furthermore, the raw materials include the following components by weight: 120 parts modified red mud, 50 parts wheat ash, 40 parts nano silicon carbide, 25 parts graphite, 50 parts composite fiber, 8 parts superplasticizer, 7 parts dipropylene glycol, 12 parts waterborne polyurethane, 4 parts high-efficiency water-reducing agent, 7 parts high-efficiency retarder, and 7 parts fiber dispersant.

[0007] Furthermore, in the composite fiber, the mass ratio of palm fiber: loofah fiber: carbon fiber is 6-8:3-5:1;

[0008] Furthermore, in the composite fiber, the mass ratio of palm fiber: loofah fiber: carbon fiber is 6:4:1;

[0009] Furthermore, the palm fiber is modified by soaking it in a 2-5% sodium hydroxide solution for 1-2 hours and controlling the solution temperature at 40-60°C. Then, the fiber is immersed in a silane coupling agent solution for grafting reaction, the pH is adjusted to weakly acidic, and the fiber is dried after the reaction is completed.

[0010] Furthermore, the silane coupling agent is a 1-5% vinyltriethoxysilane solution;

[0011] Furthermore, the palm fiber is 20-30mm long, the loofah fiber is 10-20mm long, and the carbon fiber is 30-40mm long;

[0012] Furthermore, the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0013] Furthermore, the preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0014] The present invention also discloses a type of concrete, wherein the concrete raw materials include ordinary silicate cement, coarse aggregate and the concrete additives described above.

[0015] The beneficial effects of this invention are as follows: The concrete additive of this invention, when incorporated into concrete to prepare high-temperature tunnel lining concrete, utilizes the synergistic effects of various raw materials. Red mud, combined with nano-silicon carbide and graphite, provides both microscopic filling and macroscopic reinforcement. Red mud provides cementitious activity and an alkali-activated environment, while nano-silicon carbide serves as a high-strength physical framework. The lamellar structure of graphite disperses stress and absorbs energy, reducing crack formation. These three elements work together to improve the mechanical properties and durability of concrete. Furthermore, the combination of red mud and wheat straw ash enhances the compressive strength, tensile strength, and flexural strength of concrete, while also providing a certain degree of toughness. The micro-expansion generated by red mud helps compensate for the volume shrinkage of graphite and silicon carbide fibers during long-term use, maintaining structural stability. The fiber network formed by the interaction between composite fibers blocks heat transfer paths, reducing the thermal conductivity of concrete. The composite fibers also complement each other in physical and mechanical properties through micro-crack blocking, bridging effects, and stiffness complementarity, improving the crack resistance, toughness, and impact resistance of concrete. The prepared concrete has the characteristics of low thermal conductivity, good heat resistance, and high interfacial bond strength. It also has good toughness, ductile failure characteristics, and high residual strength, which can inhibit the propagation of microcracks. Detailed Implementation

[0016] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0017] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0018] The concrete additive in this embodiment comprises the following components by weight: 100-150 parts modified red mud, 40-60 parts wheat ash, 25-55 parts nano-silicon carbide, 20-30 parts graphite, 40-60 parts composite fiber, 5-12 parts superplasticizer, 5-10 parts dipropylene glycol, 10-16 parts waterborne polyurethane, 2-6 parts high-efficiency water-reducing agent, 5-10 parts high-efficiency retarder, and 4-10 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; red mud replaces part of the cement, and ordinary silicate cement is used. The red mud needs to be modified to activate its activity and improve its high-temperature resistance; dipropylene glycol (C6H) is used to replace it. 14O3) improves high-temperature resistance, reduces cracks caused by temperature changes, and enhances the fluidity of the slurry. Simultaneously, red mud, in combination with nano-silicon carbide and graphite, acts as a micro-filler and macro-reinforcer: red mud provides cementitious activity and an alkali-activated environment, while nano-silicon carbide serves as a high-strength physical framework. The lamellar structure of graphite disperses stress and absorbs energy, reducing crack formation. These three elements synergistically improve the mechanical properties and durability of concrete. Under high-temperature conditions, red mud and silicon carbide synergistically promote the formation of calcium silicate (C6S6H), increasing compressive strength and allowing concrete to maintain good residual strength at high temperatures. It also reduces internal porosity and densifies the concrete, thereby reducing moisture evaporation channels and preventing drying shrinkage cracks caused by rapid water loss. Furthermore, nano-silicon carbide improves the interfacial bonding between aggregates and cement paste, preventing aggregate detachment and peeling under high-temperature conditions. The combination of red mud and wheat straw ash enhances the compressive, tensile, and flexural strength of concrete while also providing a degree of toughness. The micro-expansion generated by red mud helps compensate for the volume shrinkage of graphite and silicon carbide fibers during long-term use, maintaining structural stability. Wheat straw ash requires ultrafine grinding, with a particle size less than 45µm, to ensure sufficient reaction. Wheat straw ash primarily functions as a binder and filler. It can be combined with composite fibers such as palm fiber and loofah fiber. Wheat straw ash provides chemical reinforcement through its binding and filling properties, while palm fiber and loofah fiber provide physical reinforcement through their skeletal and crack-resistant properties.

[0019] When composite fibers are used in combination with superplasticizers and fiber dispersants, the fiber network formed by the interaction between the composite fibers can block the heat transfer path and reduce the thermal conductivity of concrete. Palm fibers act as a skeleton and are dispersed by fiber dispersants. They complement each other in terms of physical and mechanical properties, thereby improving the crack resistance, toughness and impact resistance of concrete. Palm fiber acts as a tough skeleton, primarily providing crack resistance and ductility, effectively inhibiting the propagation of early microcracks and preventing brittle failure. Loofah fiber acts as a toughening agent, its mesh structure acting like "anchors" to lock the matrix in place. Carbon fiber compensates for the shortcomings of natural fibers, primarily bearing tensile stress and increasing the elastic modulus of concrete. In the early stages of concrete stress, loofah and palm fibers are distributed in the concrete matrix like a "fishing net." When microcracks appear in the matrix, the fibers hinder crack propagation, forcing cracks to bypass the fibers and continue developing, thus consuming more fracture energy and acting as a microcrack blocking agent. When cracks propagate, palm fibers can pull the concrete blocks at both ends of the crack together through interfacial bonding, acting as a bridge and significantly improving tensile strength, making the material exhibit "ductile failure" characteristics. Carbon fiber, with its extremely high stiffness and strength, can effectively limit concrete deformation, providing complementary stiffness. Furthermore, loofah and palm fibers can form better mechanical bonding with cement hydrates, while the high surface energy of carbon fiber helps form a dense ITZ, reducing permeability and improving durability. The added waterborne polyurethane utilizes polymer segment adsorption to rapidly disrupt the vapor film, inhibiting thermal shock-induced cracking and improving the residual strength of concrete. Waterborne polyurethane requires modification to improve high-temperature resistance; typically, butyl acrylate and silane coupling agents are introduced for modification to increase crosslinking density and bond strength under high-temperature conditions, reducing cracking in concrete due to thermal deformation. Polyurethane modification methods are existing technologies and will not be elaborated upon here. Furthermore, the loofah fibers and nano-silicon carbide in the composite fiber complement each other in mechanical properties, enhancing interfacial bonding strength. The combination of loofah fibers and nano-silicon carbide can also effectively block crack propagation paths.

[0020] The preferred embodiment is: 120 parts modified red mud, 50 parts wheat ash, 40 parts nano silicon carbide, 25 parts graphite, 50 parts composite fiber, 8 parts superplasticizer, 7 parts dipropylene glycol, 12 parts waterborne polyurethane, 4 parts high-efficiency water-reducing agent, 7 parts high-efficiency retarder, and 7 parts fiber dispersant.

[0021] In this embodiment, the composite fibers are in a mass ratio of palm fiber:loofah fiber:carbon fiber = 6-8:3-5:1; preferably, the mass ratio is 6:4:1. The proportions of palm fiber, loofah fiber, and carbon fiber are determined based on their respective functions, and the fiber lengths are optimized. Fibers of different sizes and properties are used to form a multi-level reinforcement system in concrete. This combination is not a simple physical superposition, but rather achieves mechanical synergy through microcrack blocking, bridging effect, and interfacial bonding. To ensure uniform three-dimensional dispersion and avoid stress concentration leading to early failure, the palm fiber length is 20-30 mm; too long and it tends to agglomerate, too short and it cannot form a "bridging effect." The loofah fiber length is 10-20 mm, and the carbon fiber length is 30-40 mm. A superplasticizer is also used to enhance fiber dispersion.

[0022] In this embodiment, the palm fiber undergoes modification treatment: the palm fiber is soaked in a 2-5% sodium hydroxide solution for 1-2 hours, with the solution temperature controlled at 40-60℃. This process dissolves and removes pectin, wax, and hemicellulose from the fiber surface, exposing the internal cellulose crystalline regions and significantly reducing the fiber's water absorption rate. The fiber is then immersed in a silane coupling agent solution for a grafting reaction, adjusting the pH to weakly acidic. After the reaction, the fiber is dried. The silane coupling agent is a 1-5% vinyltriethoxysilane solution. Silane hydrolyzes to generate silanol, which forms covalent bonds with the hydroxyl groups on the fiber surface, simultaneously forming a hydrophobic film on the fiber surface to prevent moisture erosion. Natural palm fiber has strong surface hydrophilicity and weak interfacial bonding with the cement matrix. Direct use often leads to decreased concrete strength or interfacial debonding. Therefore, palm fiber modification is necessary to enhance the "interlocking force" between the fiber and cement by removing impurities and introducing functional groups.

[0023] In this embodiment, the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0024] In this embodiment, the preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling to remove some alkaline substances and reduce the risk of corrosion to steel bars, and then carrying out pile fermentation to regulate the pore structure and improve water absorption and adhesion through the action of microorganisms.

[0025] Example 1

[0026] The concrete additive of this embodiment comprises the following components by weight: 100 parts modified red mud, 40 parts wheat ash, 25 parts nano silicon carbide, 20 parts graphite, 40 parts composite fiber, 5 parts superplasticizer, 5 parts dipropylene glycol, 10 parts waterborne polyurethane, 2 parts high-efficiency water-reducing agent, 5 parts high-efficiency retarder, and 4 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; in the composite fiber, the mass ratio of palm fiber:loofah fiber:carbon fiber = 6:3:1;

[0027] The palm fiber was modified by soaking it in a 5% sodium hydroxide solution for 1 hour and controlling the solution temperature at 40°C. Then, the fiber was immersed in a silane coupling agent solution for grafting reaction, the pH was adjusted to 4, and the fiber was dried after the reaction was completed.

[0028] The silane coupling agent is a 1% vinyltriethoxysilane solution; the palm fiber is 20 mm long, the loofah fiber is 10 mm long, and the carbon fiber is 30 mm long; the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0029] The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0030] Example 2

[0031] The concrete additive of this embodiment comprises the following components by weight: 150 parts modified red mud, 60 parts wheat ash, 55 parts nano silicon carbide, 30 parts graphite, 60 parts composite fiber, 12 parts superplasticizer, 10 parts dipropylene glycol, 16 parts waterborne polyurethane, 6 parts high-efficiency water-reducing agent, 10 parts high-efficiency retarder, and 10 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; in the composite fiber, the mass ratio of palm fiber:loofah fiber:carbon fiber = 8:5:1;

[0032] The palm fiber was modified by soaking it in a 10% sodium hydroxide solution for 1 hour and controlling the solution temperature at 60°C. Then, the fiber was immersed in a silane coupling agent solution for grafting reaction, the pH was adjusted to 5, and the fiber was dried after the reaction was completed.

[0033] The silane coupling agent is a 5% vinyltriethoxysilane solution; the palm fiber is 30 mm long, the loofah fiber is 20 mm long, and the carbon fiber is 40 mm long; the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0034] The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0035] Example 3

[0036] The concrete additive of this embodiment comprises the following components by weight: 100 parts modified red mud, 60 parts wheat ash, 25 parts nano silicon carbide, 30 parts graphite, 40 parts composite fiber, 12 parts superplasticizer, 5 parts dipropylene glycol, 16 parts waterborne polyurethane, 2 parts high-efficiency water-reducing agent, 10 parts high-efficiency retarder, and 4 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; in the composite fiber, the mass ratio of palm fiber:loofah fiber:carbon fiber = 7:4:1;

[0037] The palm fiber was modified by soaking it in a 5-10% sodium hydroxide solution for 1.2 hours and controlling the solution temperature at 55°C. Then, the fiber was immersed in a silane coupling agent solution for grafting reaction, the pH was adjusted to 6, and the fiber was dried after the reaction was completed.

[0038] The silane coupling agent is a 2% vinyltriethoxysilane solution; the palm fiber is 22 mm long, the loofah fiber is 12 mm long, and the carbon fiber is 30 mm long; the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0039] The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0040] Example 4

[0041] The concrete additive of this embodiment comprises the following components by weight: 150 parts modified red mud, 40 parts wheat ash, 55 parts nano silicon carbide, 20 parts graphite, 60 parts composite fiber, 5 parts superplasticizer, 10 parts dipropylene glycol, 10 parts waterborne polyurethane, 6 parts high-efficiency water-reducing agent, 5 parts high-efficiency retarder, and 10 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; in the composite fiber, the mass ratio of palm fiber:loofah fiber:carbon fiber = 6:4:1;

[0042] The palm fiber was modified by soaking it in a 7% sodium hydroxide solution for 1.8 hours and controlling the solution temperature at 50°C. Then, the fiber was immersed in a silane coupling agent solution for grafting reaction, the pH was adjusted to 5, and the fiber was dried after the reaction was completed.

[0043] The silane coupling agent is a 3% vinyltriethoxysilane solution; the palm fiber is 25mm long, the loofah fiber is 15mm long, and the carbon fiber is 35mm long; the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0044] The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0045] Example 5

[0046] The concrete additive of this embodiment comprises the following components by weight: 110 parts modified red mud, 55 parts wheat ash, 40 parts nano silicon carbide, 22 parts graphite, 50 parts composite fiber, 7 parts superplasticizer, 8 parts dipropylene glycol, 10 parts waterborne polyurethane, 4 parts high-efficiency water-reducing agent, 6 parts high-efficiency retarder, and 7 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; in the composite fiber, the mass ratio of palm fiber:loofah fiber:carbon fiber = 7:5:1;

[0047] The palm fiber is modified by soaking it in a 5-10% sodium hydroxide solution for 1-2 hours and controlling the solution temperature at 40-60°C. Then, the fiber is immersed in a silane coupling agent solution for grafting reaction, the pH is adjusted to 6, and the fiber is dried after the reaction is completed.

[0048] The silane coupling agent is a 4% vinyltriethoxysilane solution; the palm fiber is 30 mm long, the loofah fiber is 20 mm long, and the carbon fiber is 30 mm long; the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0049] The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0050] Example 6

[0051] The concrete additive of this embodiment comprises the following components by weight: 120 parts modified red mud, 50 parts wheat ash, 40 parts nano silicon carbide, 25 parts graphite, 50 parts composite fiber, 8 parts superplasticizer, 7 parts dipropylene glycol, 12 parts waterborne polyurethane, 4 parts high-efficiency water-reducing agent, 7 parts high-efficiency retarder, and 7 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber; in the composite fiber, the mass ratio of palm fiber:loofah fiber:carbon fiber = 6:4:1;

[0052] The palm fiber was modified by soaking it in a 7% sodium hydroxide solution for 1.5 hours and controlling the solution temperature at 50°C. Then, the fiber was immersed in a silane coupling agent solution for grafting reaction, the pH was adjusted to 5, and the fiber was dried after the reaction was completed.

[0053] The silane coupling agent is a 3% vinyltriethoxysilane solution; the palm fiber is 25mm long, the loofah fiber is 25mm long, and the carbon fiber is 35mm long; the superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

[0054] The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

[0055] Using the concrete additives described above to prepare concrete includes the following steps:

[0056] Ordinary silicate cement and modified red mud are mixed evenly. Then, wheat ash, nano-silicon carbide, graphite, coarse aggregate, and composite fibers are added and mixed evenly. Finally, superplasticizer, dipropylene glycol, waterborne polyurethane, high-efficiency water-reducing agent, high-efficiency retarder, fiber dispersant, and water are added and mixed evenly to obtain a concrete mixture. The mixture is then sprayed using a wet spraying machine. Since red mud replaces part of the cement, the red mud content is 10%, ordinary silicate cement is 90%, and the water-cement ratio is controlled to not exceed 4%. The amount of coarse aggregate added usually accounts for about 55% of the total mass of concrete. The coarse aggregate is generally selected from basalt, andesite, and diorite.

[0057] Concrete additives from Examples 1-6 were used to prepare concrete according to the above method, resulting in high-temperature concrete test examples 1-6 corresponding to Examples 1-6. Performance tests were then conducted on these samples. The thermal conductivity of the concrete was tested using the transient flat plate heat source method according to ISO 22007-2:2015. The compressive strength and flexural strength of the concrete were tested using a multi-purpose testing machine according to GB / T50081-2019. The permeability grade of the concrete was tested using a permeability testing machine according to GB / T50082-2009. The test results are shown in the table below:

[0058]

[0059] The concrete samples from Examples 1-6 were cured at 80°C for 28 days to test their performance. The results are shown in the table below:

[0060]

[0061] Finally, 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 concrete additive, characterized in that: The raw materials include the following components by weight: 100-150 parts modified red mud, 40-60 parts wheat ash, 25-55 parts nano silicon carbide, 20-30 parts graphite, 40-60 parts composite fiber, 5-12 parts superplasticizer, 5-10 parts dipropylene glycol, 10-16 parts waterborne polyurethane, 2-6 parts high-efficiency water-reducing agent, 5-10 parts high-efficiency retarder, and 4-10 parts fiber dispersant; the composite fiber is a mixture of loofah fiber, palm fiber, and carbon fiber.

2. The concrete additive according to claim 1, characterized in that: The raw materials include the following components by weight: 120 parts modified red mud, 50 parts wheat ash, 40 parts nano silicon carbide, 25 parts graphite, 50 parts composite fiber, 8 parts superplasticizer, 7 parts dipropylene glycol, 12 parts waterborne polyurethane, 4 parts high-efficiency water-reducing agent, 7 parts high-efficiency retarder, and 7 parts fiber dispersant.

3. The concrete additive according to claim 1, characterized in that: In the composite fiber, the mass ratio of palm fiber: loofah fiber: carbon fiber is 6-8:3-5:

1.

4. The concrete additive according to claim 3, characterized in that: In the composite fiber, the mass ratio of palm fiber: loofah fiber: carbon fiber is 6:4:

1.

5. The concrete additive according to claim 4, characterized in that: The palm fiber is modified by soaking it in a 2-5% sodium hydroxide solution for 1-2 hours and controlling the solution temperature at 40-60°C. Then, the fiber is immersed in a silane coupling agent solution for grafting reaction, the pH is adjusted to weakly acidic, and the fiber is dried after the reaction is completed.

6. The concrete additive according to claim 5, characterized in that: The silane coupling agent is a 1-5% vinyltriethoxysilane solution.

7. The concrete additive according to claim 1, characterized in that: The palm fiber is 20-30mm long, the loofah fiber is 10-20mm long, and the carbon fiber is 30-40mm long.

8. The concrete additive according to claim 1, characterized in that: The superplasticizer is a polycarboxylate superplasticizer; the high-efficiency retarder is sodium gluconate; and the fiber dispersant is polyoxyethylene octylphenol.

9. The concrete additive according to claim 1, characterized in that: The preparation of the modified red mud includes the following steps: crushing and screening the red mud, adding sodium oxalate for ball milling, and then carrying out pile fermentation.

10. A type of concrete, characterized in that: The concrete raw materials include ordinary silicate cement, coarse aggregate, and concrete additives as described in any one of claims 1-9.

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