A nano-composite modified high-strength durable concrete composition, and a preparation method and application thereof

Abstract

The application discloses a kind of nano-composite modified high-strength durable concrete compositions and its preparation method and application.The concrete includes cementitious material, fine aggregate, coarse aggregate, nano-composite additive, water reducing agent, air entraining agent and water by weight parts.The nano-composite additive used includes nanometer silicon dioxide, nanometer titanium dioxide, carbon nanotube, hydrotalcite and polyvinylpyrrolidone component, and is made by ultrasonic dispersion process.The additive system realizes the high uniform dispersion and synergistic effect of nanoparticles in cement matrix, so that the obtained concrete has ultrahigh strength, excellent freeze-thaw resistance, chloride ion penetration resistance, acid erosion resistance and excellent long-term volume stability, and is especially suitable for tunnel, bridge and other engineering construction fields with extremely high durability requirements.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a nanocomposite modified high-strength and durable concrete composition, its preparation method, and its applications. It is especially suitable for tunnel and bridge construction under harsh environmental conditions. Background Technology

[0002] Traditional concrete, as a primary material in infrastructure construction, possesses good strength and durability, but it still faces numerous technical challenges in specialized engineering environments such as tunnels and bridges. In tunnel engineering, due to the long-term high humidity and lack of sunlight, the interfacial transition zone strength of ordinary concrete is insufficient, resulting in poor freeze-thaw resistance. Recycled aggregate concrete experiences strength losses as high as 28% after freeze-thaw cycles. In bridge engineering, especially in marine environments, chloride ion penetration often leads to steel corrosion, causing carbonization and spalling of the concrete cover. After 30 years of service, the rate of rust-induced cracking reaches 12%. Furthermore, the application of concrete in bridge and tunnel engineering also faces technical bottlenecks such as large creep deformation and poor crack resistance; the creep degree of recycled aggregate concrete is 7.4%-13.4% higher than that of ordinary concrete.

[0003] In recent years, the rapid development of nanotechnology in materials science has opened up new avenues for the research and development of high-performance concrete. Studies have shown that introducing nanomaterials into cement-based materials can regulate the cement hydration process and microstructure at the nanoscale, thereby significantly improving their macroscopic properties. For example, nano-silica, due to its extremely high pozzolanic activity and nano-filling effect, can effectively promote cement hydration, fill micropores, and optimize the interfacial transition zone (ITZ), thus improving the density and strength of concrete. Nano-alumina, through its nucleation effect, can accelerate the formation of CSH gel and fill the gel pores, similarly contributing to improved material density and mechanical properties.

[0004] However, existing technologies still face many challenges in applying nanomaterials to modify concrete: First, the problem of dispersion: due to their huge specific surface area and surface energy, nanoparticles are prone to agglomeration, making it difficult to achieve uniform dispersion in the concrete matrix. Agglomerated nanoparticles not only fail to exert their intended modifying effect but also become new sources of defects, leading to a decline in concrete performance instead of an improvement. Second, the limitations of single-material modification: most studies focus on the modifying effect of single nanomaterials, while different nanomaterials have their own advantages in modification mechanisms. For example, nano-SiO2 has a stronger promoting effect on pozzolanic reaction, while nano-Al2O3 has a more significant nucleation effect. How to utilize the advantages of different nanomaterials to achieve a synergistic enhancement effect is the key to current technological development.

[0005] Therefore, developing a nanocomposite modified concrete that can solve the above problems, possesses ultra-high strength, excellent durability and long-term stability, and is suitable for tunnel and bridge engineering is of great theoretical significance and engineering application value for ensuring engineering safety and extending structural life. Summary of the Invention

[0006] The purpose of this invention is to provide a nanocomposite modified high-strength and durable concrete composition and its preparation method. This concrete significantly improves the mechanical properties, durability and long-term stability of concrete through the synergistic effect of nanomaterials, and is particularly suitable for tunnel and bridge engineering.

[0007] This invention provides a nanocomposite modified high-strength and durable concrete composition, which, by weight, comprises: 100 parts of cementitious material, 50-115 parts of fine aggregate, 40-100 parts of coarse aggregate, 20-43 parts of water, 8-15 parts of nanocomposite additive, 1.2-2.0 parts of water-reducing agent, and 0.01-0.05 parts of air-entraining agent.

[0008] Preferably, the cementitious material comprises the following raw materials in parts by weight: 70-90 parts silicate cement, 5-20 parts fly ash, and 2-10 parts silica fume.

[0009] Preferably, the fly ash is Class I fly ash with a specific surface area ≥350 m². 2 / kg; the mass content of SiO2 in the silicon micropowder is ≥95%, the 28-day activity index is ≥120%, and the loss on ignition is ≤5%.

[0010] Preferably, the fine aggregate is river sand or manufactured sand with a particle size of 0.2-1.0 mm and a mud content of ≤3%.

[0011] Preferably, the coarse aggregate is crushed stone with a particle size of 5-20 mm.

[0012] Preferably, the water-reducing agent is at least one of polycarboxylate water-reducing agent and naphthalene-based water-reducing agent.

[0013] Preferably, the air-entraining agent is at least one of rosin-based air-entraining agents, alkylbenzene sulfonate-based air-entraining agents, and fatty alcohol sulfonate-based air-entraining agents.

[0014] Preferably, the nanocomposite additive comprises the following components based on 100% of the total mass of the additive: 50%-82% water, 3.0%-12.0% nanoparticles, 8.0%-22.0% hydrotalcite, and 0.4%-2.5% polyvinylpyrrolidone; preferably, the nanoparticles are composed of nano-silica, nano-titanium dioxide, and carbon nanotubes in a mass ratio of 3-5:1-2:0.5-1.

[0015] Preferably, the nanocomposite additive may further contain 0.1%-1.2% of a dispersant; the dispersant is selected from sodium dodecylbenzenesulfonate, sodium polyacrylate, trisodium citrate, sodium polycarboxylate, and fatty alcohol polyoxyethylene ether.

[0016] Preferably, the nano-silica has a particle size of 15-20 nm and a specific surface area of ​​200-300 m². 2 / g.

[0017] Preferably, the carbon nanotubes are multi-walled carbon nanotubes with a length of 1-5 μm and a diameter of 10-30 nm.

[0018] Preferably, the nano-titanium dioxide is rutile type, with a particle size of 20-30 nm and a specific surface area of ​​160-200 m². 2 / g.

[0019] Preferably, the hydrotalcite is at least one of magnesium aluminum hydrotalcite, calcium aluminum hydrotalcite, and magnesium iron hydrotalcite.

[0020] Preferably, the preparation method of the nanocomposite additive includes the following steps: S1. Weigh out nano-silica, nano-titanium dioxide, hydrotalcite and carbon nanotubes according to mass percentage and dry them in a vacuum drying oven for later use. S2. Add polyvinylpyrrolidone to water and stir to obtain a dispersant solution. Add the nano-silica, nano-titanium dioxide, hydrotalcite, and carbon nanotubes from step S1 to the dispersant solution, and then ultrasonically disperse to obtain a uniform nanocomposite additive. Specific stirring temperature, stirring speed, and stirring time are not required; only dispersion needs to be achieved.

[0021] Preferably, step S2 may further include 0.1%-1.2% of a dispersant, wherein the dispersant is selected from sodium dodecylbenzenesulfonate, sodium polyacrylate, trisodium citrate, sodium polycarboxylate, and fatty alcohol polyoxyethylene ether, and the dispersant is added to water together with polyvinylpyrrolidone.

[0022] Preferably, the drying in step S1 is performed by drying in a vacuum drying oven at 80-95°C for 8-12 hours.

[0023] Preferably, the ultrasonic dispersion in step S2 is performed for 10-30 minutes at a power of 300-360W and a frequency of 10-30kHz.

[0024] This invention also provides a method for preparing a nanocomposite modified high-strength and durable concrete composition, comprising the following steps: Mix the cementitious materials, fine aggregates, and coarse aggregates evenly, add water-reducing agent, air-entraining agent, nanocomposite additives, and water, and continue stirring until nanocomposite modified high-strength and durable concrete is obtained.

[0025] This invention also provides an application of a nanocomposite modified high-strength and durable concrete composition in tunnel or bridge engineering.

[0026] Preferably, the concrete mixture is poured at a temperature of 5-40℃, and the mixture is kept moist for at least 14 days after pouring to ensure that the mechanical properties and durability of the concrete meet the standards.

[0027] This invention constructs a multi-scale synergistic reinforcement system in cement-based concrete using three types of nanoparticles, achieving a comprehensive leap in the mechanical properties and durability of concrete. Nano-silica, with its high pozzolanic activity and micro-filling effect, reacts with cement hydration products to generate a large amount of CSH gel, refining the pore structure and constructing a dense microstructure, providing support for the other two types of particles to function. Nano-titanium dioxide exerts a nucleation-inducing effect, promoting the directional and dense growth of CSH gel and optimizing the gel network structure. Simultaneously, it forms a dual micro-filling effect with nano-silica, and its UV resistance also enhances macroscopic environmental durability, slows down the aging of concrete in open-air environments, and improves the serviceability of concrete in high-altitude, high-UV environments. Carbon nanotubes form a three-dimensional interwoven nanoskeleton, achieving stress bridging and toughness reinforcement, compensating for the brittleness defects of concrete. At the same time, relying on its high thermal conductivity to disperse the heat of hydration and reduce the risk of temperature cracking, it forms a multi-level filling system with the first two types of nanoparticles, further densifying the cement paste structure. The three components synergistically achieve simultaneous improvement in the compressive and flexural strength, impermeability, UV resistance, and crack resistance of concrete, adapting to the complex service requirements of tunnels and bridges.

[0028] This invention achieves stable and uniform dispersion of nanoparticles through the synergistic dispersion mechanism of hydrotalcite and polyvinylpyrrolidone (PVP). The layered structure of hydrotalcite, acting as an inorganic dispersion carrier, stabilizes the three types of nanoparticles within its interlayers and on the surface of its layers through physical adsorption and intercalation, achieving macroscopic spatial separation of the nanoparticles and fundamentally preventing particle aggregation due to van der Waals forces. Simultaneously, the uniform dispersion of hydrotalcite in cement-based slurries promotes the synchronous and uniform distribution of nanoparticles, and its interlayer anion exchange capacity can also simultaneously adsorb Cl-. -The PVP (Polydimethyl hydroxyl) dispersant effectively removes harmful ions, achieving a dual benefit of dispersion and resistance to chloride ion corrosion. As a high-molecular-weight organic dispersant, PVP tightly coats the surfaces of nanoparticles and hydrotalcite through physical adsorption of its molecular chains, forming a high-molecular-weight adsorption film. This film utilizes steric hindrance to microscopically inhibit secondary aggregation of nanoparticles. Simultaneously, its hydrophilic groups enhance the interfacial compatibility between nanoparticles and cementitious slurries, reducing interfacial porosity and strengthening the bond between nanoparticles and cement hydration products. The two mutually promote each other: hydrotalcite provides PVP with more surface-active adsorption sites, while PVP improves the dispersion stability of hydrotalcite, preventing its layers from stacking due to van der Waals forces. Ultimately, this achieves nanoscale uniform dispersion of the three types of nanoparticles in the cement-based system, ensuring the full realization of the multi-scale enhancement effect of each nanoparticle.

[0029] Furthermore, to more effectively improve the dispersion stability of nanoparticles in concrete paste, this invention introduces a dispersant based on polyvinylpyrrolidone (PVP), preferably trisodium citrate. The polycarboxylic acid anions generated by the ionization of trisodium citrate selectively adsorb onto the surface of the nanoparticles, significantly enhancing their surface negative charge density and effectively inhibiting particle aggregation through electrostatic repulsion. Simultaneously, trisodium citrate, by regulating the pH and interfacial tension of the dispersion medium, promotes the adsorption of PVP molecular chains onto the nanoparticle surface in a more extended configuration. This synergistic dispersion system ensures that the nanoparticles remain highly dispersed in the complex cement-based environment, thereby significantly improving the mechanical properties and long-term durability of concrete.

[0030] The advantages or beneficial effects of the nanocomposite modified high-strength and durable concrete composition of the present invention include at least the following: By employing a synergistic reinforcement system of nano-silica, nano-titanium dioxide, and carbon nanotubes, combined with a synergistic dispersion mechanism of hydrotalcite and polyvinylpyrrolidone, the industry-wide challenge of nanoparticle agglomeration is solved, achieving the dual benefits of dispersion and resistance to harmful ion erosion. Simultaneously, the complementary functions of each nanoparticle significantly enhance the mechanical properties of concrete, achieving a 28-day compressive strength exceeding 75 MPa and a flexural strength exceeding 8 MPa, exhibiting both high strength and good toughness. The concrete exhibits significantly enhanced durability, with a strength retention rate exceeding 90% after 100 freeze-thaw cycles, a chloride ion flux below 55°C, and a strength retention rate of nearly 90% after 60 days of acid immersion. It can withstand harsh environments such as high humidity tunnels and marine bridges. Furthermore, it demonstrates excellent long-term stability, with a 28-day volume shrinkage rate ≤0.14% and a 180-day creep ≤261×10⁻⁶. -6 It can effectively reduce the risk of cracking. In addition, its raw materials are readily available and its preparation process is simple, making it particularly suitable for critical projects such as tunnels and bridges. It can significantly improve the safety and service life of the project, combining practicality and economy. Detailed Implementation

[0031] To more clearly illustrate the purpose, technical solution, and advantages of this invention, the technical solution of this invention will be described in detail below through specific embodiments. It should be noted that these embodiments are only for illustrating this invention and not for limiting its scope of protection; the actual scope of protection of this invention should be determined by the claims.

[0032] Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available. Unless otherwise specified, the amount of each component in the following examples is 1 g per part by weight.

[0033] The raw materials used in the following embodiments: Cement: PO 52.5 grade Portland cement.

[0034] Fly ash: Grade I fly ash.

[0035] Silica powder: SiO2 content 96%, 28-day activity index 120%, loss on ignition 4%.

[0036] Nano-silica: average particle size 20 nm, specific surface area 200 m² 2 / g.

[0037] Nano-titanium dioxide: average particle size 30 nm, specific surface area 180 m² 2 / g.

[0038] Carbon nanotubes: Multi-walled carbon nanotubes, with a length of 1-5 μm and a diameter of 20 nm.

[0039] Hydrotalcite: Magnesium aluminum hydrotalcite.

[0040] Fine aggregate: River sand from Zone II, fineness modulus 2.8.

[0041] Coarse aggregate: 5~20 mm continuously graded basalt crushed stone.

[0042] Water-reducing agent: Polycarboxylate-based water-reducing agent.

[0043] Air-entraining agent: Rosin resin-based air-entraining agent.

[0044] Water: Tap water in the laboratory.

[0045] Polyvinylpyrrolidone, trisodium citrate: commercially available.

[0046] I. Examples of Preparation of Nanocomposite Additives Example A1 S1. Weigh out 5.33 parts of nano-silica, 1.78 parts of nano-titanium dioxide, 0.89 parts of carbon nanotubes, and 16.0 parts of hydrotalcite according to the mass percentage of the total mass of the nanocomposite additives. Place them in a vacuum drying oven at 85℃ and dry for 10 hours. After drying, set aside for later use. The mass ratio of the three nanoparticles is 3:1:0.5.

[0047] S2. According to the mass percentage of the total mass of the nanocomposite additive, add 1.0 part of polyvinylpyrrolidone to 75.0 parts of water and stir until completely dissolved to obtain a dispersant solution; add the dried nano-silica, nano-titanium dioxide, carbon nanotubes and hydrotalcite from step S1 to the dispersant solution, place it in an ultrasonic dispersion device, and ultrasonically disperse for 20 minutes at a power of 330W and a frequency of 20kHz to obtain a uniform and stable nanocomposite additive A1.

[0048] Example A2 S1. Weigh out 7.62 parts of nano-silica, 2.86 parts of nano-titanium dioxide, 1.52 parts of carbon nanotubes, and 18.0 parts of hydrotalcite according to the mass percentage of the total mass of the nanocomposite additives. Place them in a vacuum drying oven at 90℃ and dry for 12 hours. After drying, set aside for later use. The mass ratio of the three nanoparticles is 4:1.5:0.8.

[0049] S2. According to the mass percentage of the total mass of the nanocomposite additives, add 1.8 parts of polyvinylpyrrolidone to 68.2 parts of water and stir until completely dissolved to obtain a dispersant solution; add the dried nano-silica, nano-titanium dioxide, carbon nanotubes and hydrotalcite from step S1 to the dispersant solution, place it in an ultrasonic dispersion device, and ultrasonically disperse for 25 minutes at a power of 360W and a frequency of 25kHz to obtain a uniform and stable nanocomposite additive A2.

[0050] Example A3 S1. Weigh out 1.88 parts of nano-silica, 0.75 parts of nano-titanium dioxide, 0.38 parts of carbon nanotubes, and 14.0 parts of hydrotalcite according to the mass percentage of the total mass of the nanocomposite additives. Place them in a vacuum drying oven at 80℃ and dry for 8 hours. After drying, set aside for later use. The mass ratio of the three nanoparticles is 5:2:1.

[0051] S2. According to the mass percentage of the total mass of the nanocomposite additives, add 1.0 part of polyvinylpyrrolidone to 82.0 parts of water and stir until completely dissolved to obtain a dispersant solution; add the dried nano-silica, nano-titanium dioxide, carbon nanotubes and hydrotalcite from step S1 to the dispersant solution, place it in an ultrasonic dispersion device, and ultrasonically disperse it for 15 minutes at a power of 300W and a frequency of 15kHz to obtain a uniform and stable nanocomposite additive A3.

[0052] Example A4 S1. Weigh out 6.60 parts of nano-silica, 2.26 parts of nano-titanium dioxide, 1.13 parts of carbon nanotubes, and 22.0 parts of hydrotalcite according to the mass percentage of the total mass of the nanocomposite additives. Place them in a vacuum drying oven at 95℃ and dry for 11 hours. After drying, set aside for later use. The mass ratio of the three nanoparticles is 3.5:1.2:0.6.

[0053] S2. According to the mass percentage of the total mass of the nanocomposite additive, add 2.5 parts of polyvinylpyrrolidone to 65.5 parts of water and stir until completely dissolved to obtain a dispersant solution; add the dried nano-silica, nano-titanium dioxide, carbon nanotubes and hydrotalcite from step S1 to the dispersant solution, place it in an ultrasonic dispersion device, and ultrasonically disperse for 30 minutes at a power of 340W and a frequency of 30kHz to obtain a uniform and stable nanocomposite additive A4.

[0054] Example A5 S1. Weigh out 5.63 parts of nano-silica, 2.25 parts of nano-titanium dioxide, 1.13 parts of carbon nanotubes, and 22.0 parts of hydrotalcite according to the mass percentage of the total mass of the nanocomposite additives. Place them in a vacuum drying oven at 88℃ and dry for 9 hours. After drying, set aside for later use. The mass ratio of the three nanoparticles is 4.5:1.8:0.9.

[0055] S2. According to the mass percentage of the total mass of the nanocomposite additive, add 0.7 parts of polyvinylpyrrolidone to 68.2 parts of water and stir until completely dissolved to obtain a dispersant solution; add the dried nano-silica, nano-titanium dioxide, carbon nanotubes and hydrotalcite from step S1 to the dispersant solution, place it in an ultrasonic dispersion device, and ultrasonically disperse for 10 minutes at a power of 320W and a frequency of 10kHz to obtain a uniform and stable nanocomposite additive A5.

[0056] Example A6 The difference from Example A1 is that 0.2 parts of trisodium citrate were added, the mass percentage of polyvinylpyrrolidone was 0.8 parts, and other conditions were the same as in Example A1, resulting in a uniform and stable nanocomposite additive A6.

[0057] Example A7 The difference from Example A1 is that an equal amount of water was used instead of hydrotalcite, while other conditions were the same as in Example A1, resulting in a uniform and stable nanocomposite additive A7.

[0058] Example A8 The difference from Example A1 is that an equal amount of nano-silica is used to replace carbon nanotubes, while other conditions are the same as in Example A1, resulting in a uniform and stable nanocomposite additive A8.

[0059] Example A9 The difference from Example A1 is that an equal amount of nano-silica was used instead of nano-titanium dioxide, while other conditions were the same as in Example A1, resulting in a uniform and stable nanocomposite additive A9.

[0060] Example A10 The difference from Example A1 is that in step S2, an equal amount of water is used instead of polyvinylpyrrolidone, while other conditions are the same as in Example A1, resulting in a uniform and stable nanocomposite additive A10.

[0061] II. Application Examples and Comparative Application Examples of Nanocomposite Modified High-Strength and Durable Concrete The preparation method of nanocomposite modified high-strength and durable concrete involved in the application examples and comparative application examples includes the following steps: Add the cementitious materials, fine aggregates, and coarse aggregates as shown in Table 1-2 into the mixing equipment and mix at low speed for 15 minutes until the mixture is uniform. Then add the water-reducing agent, air-entraining agent, corresponding numbered nanocomposite additives, and water, and mix at high speed for 10 minutes until a uniform, lump-free concrete mixture is obtained, which is the nanocomposite modified high-strength and durable concrete.

[0062] Table 1: The mass fractions (g) of each component in application examples B1-B9 are as follows.

[0063]

[0064] Table 2: The mass fractions (g) of each component in the comparative application examples are as follows.

[0065]

[0066] III. Performance Testing 1. Mechanical property testing (1) Specimen preparation Compressive strength: 3 cube specimens of 150mm×150mm×150mm were used in each group; Flexural strength: 3 prism specimens of 100mm×100mm×400mm were used in each group.

[0067] (2) Maintenance conditions After pouring, the concrete was left to stand for 24 hours at 20±5℃ and relative humidity ≥90%. After demolding, it was placed in a standard curing chamber (temperature 20±2℃, relative humidity ≥95%) and cured for the specified age (3 days, 28 days). Tests were performed according to GB / T 50081-2019 "Standard for Test Methods of Mechanical Properties of Concrete".

[0068] 2. Freeze-thaw resistance test (1) Specimen preparation Three 100mm×100mm×100mm cubic specimens were used in each group and tested after 28 days of standard curing.

[0069] (2) Test method Freeze-thaw medium: distilled water (simulating the high humidity environment of a tunnel); Temperature cycling: Freezing stage temperature -18±2℃, held for 4 hours; thawing stage temperature 5±2℃, held for 4 hours; total duration of each cycle 8 hours, 100 cycles. Tested according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete".

[0070] Strength retention rate calculation: the ratio of compressive strength 28 days after freeze-thaw to compressive strength 28 days before freeze-thaw × 100%.

[0071] 3. Chloride ion penetration resistance test A cylindrical specimen with a diameter of 100 mm and a diameter of 50 mm was used. After standard curing for 28 days, the sides of the specimen were sealed. A DC voltage of 60 V was applied at a temperature of 20 ± 2 °C and the test was conducted continuously for 6 hours. The cumulative current flux was calculated according to ASTM C1202 standard. The smaller the current flux, the stronger the resistance to chloride ion penetration.

[0072] 4. Resistance to acid corrosion test (1) Specimen preparation Immersion tests were conducted using 150mm×150mm×150mm cubic specimens after standard curing for 28 days.

[0073] (2) Test medium and conditions Immersion medium: 0.5 mol / L H2SO4 solution, simulating the acidic erosion environment of tunnel drainage and the acid rain erosion environment of bridges; Immersion conditions: temperature 20±2℃, liquid level 20mm above the top surface of the specimen, immersion for 60 days, solution changed every 7 days. Tests were conducted according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete".

[0074] Strength retention rate calculation: the ratio of compressive strength after immersion to compressive strength 28 days before immersion × 100%.

[0075] 5. Long-term stability test (1) Volume shrinkage rate Specimen preparation: Three 100mm×100mm×500mm prism shrinkage specimens were used in each group; Test conditions: After standard curing for 3 days, the samples were moved into a constant temperature and humidity chamber (temperature 20±2℃, relative humidity 60±5%). Test method: The length change at different ages was measured using a contact extensometer, and the 28-day volume shrinkage rate was calculated according to the formula in GB / T50082-2009.

[0076] (2) 180d creep Specimen preparation: 100mm×100mm×400mm prism specimens were used and cured under standard conditions for 28 days; Loading conditions: Apply constant compressive stress (40% of the specimen's 28-day compressive strength) and load it under axial compression. Test environment: Temperature 20±2℃, relative humidity ≥95%; Creep calculation: The ratio of creep deformation to applied stress at 180 days, reflecting the long-term deformation capacity of concrete.

[0077] Table 3 shows the performance of application examples B1-B9 as follows:

[0078] Table 4 compares the performance of application examples C1-C5 as follows:

[0079] According to the test results in Table 3-4, the concrete compositions of Application Examples B1-B9 exhibit outstanding characteristics of high strength, high durability, and high stability: 28-day compressive strength reaches 76.9-88.7 MPa, and flexural strength reaches 8.2-9.8 MPa; after 100 freeze-thaw cycles, the strength retention rate is still above 90%, the chloride ion flux is below 521 C, and the acid erosion resistance is excellent; at the same time, its 28-day volume shrinkage rate is as low as 0.08%-0.14%, and the 180-day creep is relatively small. The main reasons are: firstly, nano-SiO2, TiO2, and carbon nanotubes constitute a multi-scale synergistic reinforcing network, which respectively play the roles of micro-filling, nucleation induction, and toughness bridging, simultaneously improving mechanical and crack resistance properties; secondly, hydrotalcite and polyvinylpyrrolidone form a unique "inorganic carrier-organic dispersion" synergistic dispersion mechanism, fundamentally solving the problem of nanoparticle aggregation and ensuring their uniform distribution and stable function; the two work together to improve the comprehensive performance of concrete.

[0080] Based on the comparison between application examples B1 and B9, trisodium citrate effectively inhibits nanoparticle aggregation and regulates the properties of the dispersion medium, promoting better adsorption of PVP on the particle surface. Both enhance the dispersibility of nanoparticles in the cement system, making application example B9 superior to application example B1 in terms of chlorine resistance, acid resistance, and long-term stability.

[0081] Compared to Application Example C1, the nano-silica that was physically incorporated only agglomerated due to the lack of hydrotalcite carrier and PVP dispersant, thus failing to exert the nano-reinforcing effect. Furthermore, it lacked the nucleation effect of nano-titanium dioxide and the toughening effect of carbon nanotubes, resulting in limited improvement in its mechanical properties and durability. Its 28-day compressive strength and resistance to chloride ion penetration were lower than those of Application Example B1.

[0082] Compared with comparative application example C2, application example B1 lacks the hydrotalcite component. On the one hand, the nanoparticles lose the spatial barrier effect of the inorganic carrier, resulting in a decrease in dispersion uniformity. On the other hand, it loses the unique function of anion exchange and chloride ion adsorption between hydrotalcite layers. Therefore, its anti-permeability and freeze-thaw related durability are significantly deteriorated.

[0083] In contrast application example C3, the absence of carbon nanotubes resulted in the loss of the three-dimensional nanofiber bridging network and thermal conductivity pathways constructed by carbon nanotubes within the concrete, thereby weakening the material's crack resistance, toughness, and ability to control hydration heat and long-term creep. In contrast application example C4, the lack of nano-titanium dioxide prevented the effective nucleation-inducing effect of titanium dioxide, affecting the densification process of CSH gel in the early stages of cement hydration and leading to slower early strength development. Simultaneously, the protective effect of nano-TiO2 against UV-induced aging was also lost, indirectly impacting long-term durability under complex environments such as acid rain.

[0084] In contrast, application example C5 lacks polyvinylpyrrolidone dispersant, which leads to severe agglomeration of nanoparticles and hydrotalcite sheets in the cement paste, causing the entire synergistic enhancement and stabilization dispersion system of the present invention to fail and its performance to degrade significantly.

[0085] 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 the scope of protection of the present invention. Based on the basic principles and core design concepts disclosed in the present invention, those skilled in the art can make appropriate modifications, adjustments, or equivalent substitutions. Any modifications and improvements made based on the same or similar concepts as the present technical solutions should be considered to fall within the scope of protection defined by the claims of the present invention.

Claims

1. A nanocomposite modified high-strength and durable concrete composition, characterized in that, By weight, its raw material components include: 100 parts of cementitious material, 50-115 parts of fine aggregate, 40-100 parts of coarse aggregate, 20-43 parts of water, 8-15 parts of nano-composite additive, 1.2-2.0 parts of water-reducing agent, and 0.01-0.05 parts of air-entraining agent. The nano-composite additive comprises the following components, based on 100% of the nano-composite additive: water 50%-82%, nanoparticles 3.0%-12.0%, hydrotalcite 8.0%-22.0%, polyvinylpyrrolidone 0.4%-2.5%; the nanoparticles are composed of nano-silicon dioxide, nano-titanium dioxide and carbon nanotubes at a mass ratio of 3-5:1-2:0.5-1; the nano-titanium dioxide is of rutile type, has a particle size of 20-30 nm and a specific surface area of 160-200 m 2 / g. The nanocomposite additive also contains 0.1%-1.2% of a dispersant; the dispersant is selected from one of sodium dodecylbenzenesulfonate, sodium polyacrylate, trisodium citrate, sodium polycarboxylate, and fatty alcohol polyoxyethylene ether.

2. The nanocomposite modified high-strength and durable concrete composition as described in claim 1, characterized in that, The cementitious material comprises the following raw materials in parts by weight: 70-90 parts silicate cement, 5-20 parts fly ash, and 2-10 parts silica fume.

3. The nanocomposite modified high-strength and durable concrete composition as described in claim 2, characterized in that, The fly ash is grade I fly ash, and the specific surface area is greater than or equal to 350 m 2 / kg; and / or, the mass content of SiO2 in the silicon powder is greater than or equal to 95%, the 28d activity index is greater than or equal to 120%, and the loss on ignition is less than or equal to 5%; and / or, the fine aggregate is river sand or machine-made sand, the particle size is 0.2-1.0 mm, and the clay content is less than or equal to 3%; and / or, the coarse aggregate is gravel with a particle size of 5-20 mm.

4. The nanocomposite modified high-strength and durable concrete composition according to any one of claims 1-3, characterized in that, The water-reducing agent is at least one of polycarboxylate water-reducing agent and naphthalene-based water-reducing agent; and / or, the air-entraining agent is at least one of rosin-based air-entraining agent, alkylbenzene sulfonate-based air-entraining agent, and fatty alcohol sulfonate-based air-entraining agent.

5. The nanocomposite modified high-strength and durable concrete composition according to any one of claims 1-3, characterized in that, The nano-silica has a particle size of 15-20 nm and a specific surface area of ​​200-300 m². 2 / g; and / or, the carbon nanotubes are multi-walled carbon nanotubes with a length of 1-5 μm and a diameter of 10-30 nm; and / or, the hydrotalcite is at least one of magnesium aluminum hydrotalcite, calcium aluminum hydrotalcite and magnesium iron hydrotalcite.

6. The nanocomposite modified high-strength and durable concrete composition according to any one of claims 1-3, characterized in that, The preparation method of the nanocomposite additive includes the following steps: S1. Weigh out nano-silica, nano-titanium dioxide, hydrotalcite and carbon nanotubes according to mass percentage and dry them in a vacuum drying oven for later use. S2. Add polyvinylpyrrolidone and dispersant to water, stir, and obtain a dispersant solution; add nano-silica, nano-titanium dioxide, hydrotalcite and carbon nanotubes from step S1 to the dispersant solution, and then ultrasonically disperse to obtain a uniform nanocomposite additive.

7. The nanocomposite modified high-strength durable concrete composition as described in claim 6, characterized in that, The drying in step S1 is to dry in a vacuum drying oven at 80-95℃ for 8-12 hours; and / or, the ultrasonic dispersion in step S2 is to disperse for 10-30 minutes at a power of 300-360W and a frequency of 10-30kHz.

8. A method for preparing a nanocomposite modified high-strength and durable concrete composition as described in any one of claims 1-7, characterized in that, Includes the following steps: Mix the cementitious materials, fine aggregates, and coarse aggregates evenly, add water-reducing agent, air-entraining agent, nanocomposite additives, and water, and continue stirring until nanocomposite modified high-strength and durable concrete is obtained.

9. The application of a nanocomposite modified high-strength and durable concrete composition as described in any one of claims 1-7 in tunnel engineering or bridge engineering.

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