Preparation method of freeze-thaw resistant protective coating for all-steel bridge

Abstract

The invention relates to a preparation method of a protective coating, in particular to a preparation method of a freeze-thaw-resistant protective coating for an all-steel bridge. The invention aims to solve the technical problem that the performance of the existing bridge protective paint is reduced under the freezing and thawing cycle condition in an extremely cold region. The method comprises the following steps: preparing a nano silica sol-polyurethane prepolymer, preparing a mixed slurry, adding the dispersed carbon nanotubes, uniformly dispersing, and adding the pH regulator and the polyurethane thickener. The freeze-thaw resistance, weather resistance and mechanical strength of the coating are remarkably improved. The coating prepared by the invention is used for protecting bridges in extreme climate.

Description

Technical Field

[0001] The present invention relates to a preparation method of a protective coating, and particularly to a preparation method of an anti-freeze-thaw protective coating for all-steel bridges, belonging to the technical field of materials science and engineering. Background Art

[0002] At present, the bridge protective coating system mainly constructs a multi-layer protection system based on materials such as epoxy resin, polyurethane, acrylic acid and inorganic zinc-rich. Epoxy resin coatings occupy an important position in the field of conventional anti-corrosion due to their excellent chemical bonding ability (such as the zinc powder content of epoxy zinc-rich primer ≥ 80%, and the cathodic protection efficiency is significant) and low permeability characteristics. Polyurethane coatings are often used as intermediate coats and topcoats due to their adjustable rigidity and flexibility, two-component reaction curing characteristics and good weather resistance. Acrylic coatings are gradually replacing chlorinated rubber coatings in the field of concrete protection due to their convenient construction and environmental protection advantages. The prior art improves the protection performance through nano-modification (such as SiO2 nanoparticles increasing the salt spray resistance by 3 times), functional fillers (such as mica iron oxide forming a maze shielding structure) and multi-layer coating systems (primer - intermediate coat - topcoat), but there are the following technical bottlenecks:

[0003] 1) Insufficient anti-freeze-thaw performance: Existing coatings are prone to frost heave damage caused by water penetration in extremely cold regions. Epoxy resin has significant low-temperature brittleness, and although polyurethane has elasticity, it lacks an interpenetrating network structure and is difficult to relieve the stress concentration generated by freeze-thaw cycles. Traditional fillers such as talcum powder and mica powder can improve the mechanical strength, but cannot achieve self-healing of microcracks through photothermal effects.

[0004] 2) Weak interfacial bonding force: Epoxy resin and the metal matrix rely on physical adsorption and chemical bonding, but the adhesion is likely to decrease due to insufficient hydroxyl reaction on a wet base surface. The interfacial compatibility between polyurethane prepolymer and inorganic fillers is poor, and the dopamine biomimetic adhesion mechanism has not been effectively applied.

[0005] 3) Limitations in weather resistance: Although fluorocarbon topcoats have a weather resistance of more than 20 years, they are costly and lack photocatalytic self-cleaning function. Although graphene-modified coatings improve the thermal conductivity, the two-dimensional sheet structure is prone to defect sites, and the physical barrier effect against corrosive media is not perfect.

[0006] Therefore, it is urgent to develop a new type of protective coating with a three-dimensional interpenetrating network structure, biomimetic interface enhancement, photothermal self-healing and nano-synergistic enhancement to break through the bottlenecks of anti-freeze-thaw, weather resistance and mechanical strength in extreme environments. Summary of the Invention

[0007] The present invention provides a preparation method of an anti-freeze-thaw protective coating for all-steel bridges to solve the technical problem of performance degradation of existing bridge protective coatings under freeze-thaw cycle conditions in extremely cold regions.

[0008] A preparation method of an anti-freezing and thawing protection coating for all-steel bridges is carried out according to the following steps:

[0009] I. Add nano-silica sol into a reaction kettle, then add a silane coupling agent, control the temperature at 60 - 65 °C, stir evenly, and then carry out vacuum defoaming to obtain activated silica sol;

[0010] II. Mix polyether polyol, isocyanate and a catalyst, and carry out a reaction under the protection of nitrogen, controlling the temperature at 80 - 85 °C to obtain a polyurethane prepolymer;

[0011] III. Inject the polyurethane prepolymer into the activated silica sol, control the temperature at 60 - 70 °C and stir, while adding dopamine-functionalized alumina nanoparticles to carry out an emulsification reaction, and then add ethylenediamine for reaction to obtain a nano-silica sol - polyurethane prepolymer;

[0012] IV. Disperse carboxyl-modified carbon nanotubes in absolute ethanol, add deionized water, then add aluminum isopropoxide, adjust the pH to 3 - 4, stir at a temperature of 60 - 80 °C for 6 - 12 h, then carry out centrifugal washing, dry and then calcine. The calcination temperature is 200 - 300 °C and the calcination time is 2 h to obtain Al2O3@CNTs;

[0013] Disperse Al2O3@CNTs in an ethanol solution, add tetraethyl orthosilicate, adjust the pH to 9 - 10 with ammonia water, stir at a temperature of 40 - 45 °C for 24 h, then carry out centrifugal washing and drying to obtain double-shell carbon nanotubes;

[0014] Then dissolve aniline monomer in a hydrochloric acid solution, control the pH to 1 - 2, then add ammonium persulfate, control the temperature at 0 - 5 °C for a polymerization reaction, then add the double-shell carbon nanotubes, and then add APS for reaction for 6 - 24 h to obtain polyaniline-coated double-shell carbon nanotubes;

[0015] Mix the polyaniline-coated double-shell carbon nanotubes with absolute ethanol, add sodium dodecylbenzenesulfonate, carry out ultrasonic treatment, then transfer to a three-roll grinder for grinding, and then add polyether-modified silicone for dispersion treatment to obtain a polyaniline-coated double-shell carbon nanotube dispersion;

[0016] V. Put titanium dioxide, nano-titanium dioxide / graphene oxide composite powder, alumina, calcium carbonate, rare earth silicate, mica powder and talc powder into a dispersion tank in sequence, disperse evenly, then transfer to a high-speed vibration grinder for grinding, and then export to the dispersion tank, add the nano-silica sol - polyurethane prepolymer obtained in step III for dispersion to obtain a mixed slurry;

[0017] VI. Transfer the mixed slurry obtained in Step V to a high-shear disperser, add the polyaniline-coated double-shell carbon nanotube dispersion obtained in Step IV, continue to disperse evenly, then add a pH regulator and mix, and then add a polyurethane thickener and stir evenly to obtain the all-steel bridge freeze-thaw resistant protective coating.

[0018] Advantages of the present invention:

[0019] 1. Significantly improved freeze-thaw resistance

[0020] In the present invention, nano-silica sol is activated by a silane coupling agent to form a three-dimensional network structure. At the same time, the catechol and amino functional groups of dopamine form covalent bonds and hydrogen bonds with the isocyanate groups in the polyurethane prepolymer and the hydroxyl groups of nano-silica sol, forming a biomimetic interface enhancement structure, improving the interfacial bonding force and cohesion of the coating, enhancing the denseness of the coating, reducing water penetration, and reducing the damage caused by ice crystal formation during freeze-thaw cycles. And the prepared polyurethane prepolymer and activated silica sol form an interpenetrating network structure (IPN) after emulsification, endowing the coating with high elasticity and low-temperature toughness, alleviating the crack propagation caused by temperature stress. In addition, the adhesion characteristics of dopamine can also improve the adhesion of the coating on a wet substrate.

[0021] In the present invention, the carbon nanotubes have a high aspect ratio (>1000). Coating the carbon nanotubes with a double shell can not only inhibit the aggregation of carbon nanotubes through a ceramic network, but also enhance the corrosion resistance and freeze-thaw resistance of the coating through the acid and alkali resistance of Al2O3 and the hydrophobicity of SiO2; and further coat with a polyaniline polymer, and utilize the photothermal effect of polyaniline to achieve the photo-thermal synergistic self-healing of microcracks in the coating; in addition, the electrostatic repulsion and steric hindrance of sodium dodecylbenzenesulfonate effectively prevent the aggregation of carbon nanotubes, and after surface carboxyl modification, it binds tightly to the substrate, inhibiting the propagation of microcracks through bridging action and improving the crack resistance of the coating.

[0022] 2. Enhanced weather resistance and corrosion resistance

[0023] The present invention adds a nano-titanium dioxide / graphene oxide composite powder. The two-dimensional sheet structure of graphene oxide forms a physical barrier to hinder the diffusion of water, oxygen and corrosive media; nano-titanium dioxide provides a photocatalytic self-cleaning function to reduce the accumulation of surface pollutants. In addition, the doping of rare earth silicates (such as yttrium zirconium silicate) can refine the coating grains, improve the acid and alkali resistance, and delay corrosion through an ion exchange mechanism.

[0024] 3. Excellent mechanical strength and adhesion

[0025] In the present invention, polyether-modified siloxane is used as a dispersant to improve the uniform distribution of carbon nanotubes in the matrix and enhance the interfacial bonding force of the composite material. At the same time, the use of flaky fillers such as mica powder and talc powder arranged in parallel in the coating forms a "labyrinth effect", enhancing the mechanical strength and impact resistance.

[0026] In summary, through the synergistic effects of nanocomposite, interface optimization, and functional fillers, this technology significantly improves the freeze-thaw resistance, weather resistance, and mechanical strength of the coating.

[0027] The coating prepared by the present invention is used for the protection of bridges in extreme climates. Specific Embodiments

[0028] Specific Embodiment 1: A method for preparing an anti-freeze-thaw protective coating for all-steel bridges in this embodiment is carried out according to the following steps:

[0029] I. Add nano-silica sol to the reaction kettle, then add silane coupling agent, control the temperature at 60 - 65 °C, stir evenly, and then perform vacuum defoaming to obtain activated silica sol;

[0030] II. Mix polyether polyol, isocyanate, and catalyst, and carry out a reaction under nitrogen protection at a temperature of 80 - 85 °C to obtain a polyurethane prepolymer;

[0031] III. Inject the polyurethane prepolymer into the activated silica sol, control the temperature at 60 - 70 °C and stir, while adding dopamine-functionalized alumina nanoparticles to carry out an emulsification reaction, and then add ethylenediamine for reaction to obtain nano-silica sol - polyurethane prepolymer;

[0032] IV. Disperse carboxyl-modified carbon nanotubes in absolute ethanol, add deionized water, then add aluminum isopropoxide, adjust the pH to 3 - 4, stir at a temperature of 60 - 80 °C for 6 - 12 h, then centrifuge and wash, dry and then calcine at a calcination temperature of 200 - 300 °C for 2 h to obtain Al2O3@CNTs;

[0033] Disperse Al2O3@CNTs in an ethanol solution, add tetraethyl orthosilicate, adjust the pH to 9 - 10 with ammonia water, stir at a temperature of 40 - 45 °C for 24 h, then centrifuge, wash and dry to obtain double-shell carbon nanotubes;

[0034] Then dissolve aniline monomer in hydrochloric acid solution, control the pH to 1 - 2, then add ammonium persulfate, control the temperature at 0 - 5 °C for polymerization reaction, then add double-shell carbon nanotubes, and then add APS for reaction for 6 - 24 h to obtain polyaniline-coated double-shell carbon nanotubes;

[0035] Mix polyaniline-coated double-shell carbon nanotubes with absolute ethanol, add sodium dodecylbenzenesulfonate, perform ultrasonic treatment, then transfer to a three-roll grinder for grinding, and then add polyether-modified silicone for dispersion treatment to obtain a polyaniline-coated double-shell carbon nanotube dispersion;

[0036] V. Put titanium dioxide, nano-titanium dioxide / graphene oxide composite powder, alumina, calcium carbonate, rare earth silicate, mica powder and talc powder into the dispersion tank in sequence, disperse them evenly, then transfer them to a high-speed vibration grinder for grinding, and then export them to the dispersion tank. Add the nano-silica sol-polyurethane prepolymer obtained in Step III for dispersion to obtain a mixed slurry;

[0037] VI. Transfer the mixed slurry obtained in Step V to a high-shear disperser, add the polyaniline-coated double-shell carbon nanotube dispersion liquid obtained in Step IV, continue to disperse evenly, then add a pH regulator and mix, and then add a polyurethane thickener and stir evenly to obtain the all-steel bridge anti-freezing and thawing protective coating.

[0038] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the mass ratio of the nano-silica sol to the silane coupling agent in Step I is 100:5. Others are the same as Specific Embodiment 1.

[0039] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the mass ratio of the polyether polyol to the isocyanate in Step II is 40:(10-20). Others are the same as Specific Embodiment 1 or 2.

[0040] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the mass ratio of the polyurethane prepolymer to the activated silica sol in Step III is 1:(2-2.5);

[0041] The particle size of the dopamine-functionalized alumina nanoparticles is 20-50 nm, and the addition amount is 3-5% of the total mass of the polyurethane prepolymer and the activated silica sol. The dopamine-functionalized alumina nanoparticles are prepared by coating a dopamine layer on the surface of the alumina nanoparticles by the sol-gel method. Others are the same as any one of Specific Embodiments 1 to 3.

[0042] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the mass ratio of the carboxyl-modified carbon nanotubes to sodium dodecylbenzenesulfonate in Step IV is 2:(0.5-0.8), and the aspect ratio of the carboxyl-modified carbon nanotubes > 1000. Others are the same as any one of Specific Embodiments 1 to 4.

[0043] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that by weight, the nano-silica sol-polyurethane prepolymer is 80-100 parts, titanium dioxide is 10-15 parts, nano-titanium dioxide / graphene oxide composite powder is 5-10 parts, alumina is 5-10 parts, calcium carbonate is 5-10 parts, rare earth silicate is 5-10 parts, mica powder is 5-10 parts, talc powder is 5-10 parts, and deionized water is 10-20 parts. Others are the same as any one of Specific Embodiments 1 to 5.

[0044] Specific Embodiment Seven: The difference between this embodiment and any one of Embodiments One to Six is that the mass ratio of titanium dioxide nanoparticles to graphene oxide in the titanium dioxide / graphene oxide composite powder described in Step Five is 2:1, and the particle size is 10 - 50 nanometers. Others are the same as any one of Embodiments One to Six.

[0045] Specific Embodiment Eight: The difference between this embodiment and any one of Embodiments One to Seven is that the rare earth silicate described in Step Five is one or more of yttrium zirconium silicate, yttrium lanthanum silicate, yttrium cerium silicate, zirconium lanthanum silicate, yttrium silicate, ytterbium silicate, cerium silicate, gadolinium silicate, samarium silicate, erbium silicate, holmium silicate. Others are the same as any one of Embodiments One to Seven.

[0046] Specific Embodiment Nine: The difference between this embodiment and any one of Embodiments One to Eight is that the ratio of the mixed slurry to the polyaniline-coated double-shell carbon nanotube dispersion in Step Six is 100:(2 - 3). Others are the same as any one of Embodiments One to Eight.

[0047] Specific Embodiment Ten: The difference between this embodiment and any one of Embodiments One to Nine is that a pH regulator is added in Step Six to adjust the pH to 8.5 - 9.5. Others are the same as any one of Embodiments One to Nine.

[0048] The content of the present invention is not limited to the content of the above embodiments. The combination of one or several specific embodiments can also achieve the purpose of the invention.

[0049] Example 1:

[0050] The preparation method of a full-steel bridge anti-freeze and thaw protection coating in this example is specifically carried out according to the following steps:

[0051] I. Add 10 kg of nano-silica sol to the reaction kettle, then add 0.5 kg of silane coupling agent KH-570, control the temperature at 60 °C, stir at a speed of 300 r / min for 30 min, and then perform vacuum defoaming to obtain activated silica sol;

[0052] II. Mix 40 kg of polyether polyol (Mn = 2000), 10 kg of isocyanate and 0.1 kg of catalyst DBTDL, and under the condition of nitrogen protection, control the temperature at 80 °C and react for 3 h to obtain a polyurethane prepolymer with an NCO content of 6.5%;

[0053] III. Inject 10 kg of polyurethane prepolymer into 20 kg of activated silica sol, control the flow rate at 0.4 kg / min, control the temperature at 65 °C, stir at a rotation speed of 800 r / min for 60 min, and simultaneously add 1 kg of dopamine-functionalized alumina nanoparticles to carry out an emulsification reaction, and then add 1 kg of ethylenediamine for reaction to obtain nano-silica sol-polyurethane prepolymer;

[0054] Among them, the particle size of the dopamine-functionalized alumina nanoparticles is 20 - 50 nm, and they are prepared by coating a dopamine layer on the surface of alumina nanoparticles by the sol-gel method;

[0055] IV. Disperse 2 kg of carboxyl-modified carbon nanotubes in absolute ethanol, add a small amount of deionized water, and then add aluminum isopropoxide. The molar ratio of carboxyl-modified carbon nanotubes to aluminum isopropoxide is 1:5. Adjust the pH to 3 - 4, stir at a temperature of 60 °C for 10 h, then centrifuge and wash, dry and then calcine. The calcination temperature is 200 °C and the calcination time is 2 h to obtain Al2O3@CNTs;

[0056] Disperse 1 kg of Al2O3@CNTs in an ethanol solution with a volume concentration of 80%, add 2 kg of tetraethyl orthosilicate, adjust the pH to 9 - 10 with ammonia water, stir at a temperature of 45 °C for 24 h, then centrifuge, wash and dry to obtain double-shell carbon nanotubes;

[0057] Then dissolve aniline monomer in a hydrochloric acid solution with a concentration of 1 mol / L, the concentration of aniline monomer is 0.2 mol / L, adjust the pH to 1 - 2, then add ammonium persulfate, the molar ratio of aniline monomer to ammonium persulfate is 1:1, control the temperature at 5 °C for polymerization reaction, then add double-shell carbon nanotubes, and then add APS for reaction for 12 h to obtain polyaniline-coated double-shell carbon nanotubes;

[0058] Mix 2 kg of polyaniline-coated double-shell carbon nanotubes with 20 kg of absolute ethanol, add 0.5 kg of sodium dodecylbenzenesulfonate, carry out ultrasonic treatment for 30 min, the ultrasonic power is 1000 W, the frequency is 20 kHz, then transfer to a three-roll grinder and grind until the agglomerate particle size is less than 500 nm, and then add 1 kg of polyether-modified silicone oil BYK-349 for dispersion treatment at a rate of 2000 r / min for 60 min to obtain a polyaniline-coated double-shell carbon nanotube dispersion;

[0059] V. Put 15 kg of titanium dioxide, 5 kg of nano titanium dioxide / graphene oxide composite powder, 5 kg of alumina, 5 kg of calcium carbonate, 5 kg of yttrium silicate, 5 kg of mica powder and 5 kg of talc powder into the dispersion tank in sequence, disperse them evenly at 1000 r / min for 30 - 60 min, then transfer them to a high-speed vibration grinding machine, grind them at a speed of 4000 r / min for 60 min, and then export them to the dispersion tank. Add 100 kg of the nano silica sol-polyurethane prepolymer obtained in Step III, and continue to disperse them at 1000 r / min for 60 min to obtain a mixed slurry;

[0060] VI. Transfer the mixed slurry obtained in Step V to a high-shear dispersing machine, add 3 kg of the polyaniline-coated double-shell carbon nanotube dispersion liquid obtained in Step IV, continue to disperse them evenly, then add the pH regulator AMP-95 and mix them, and then add a polyurethane thickener and stir evenly to obtain the all-steel bridge anti-freezing and thawing protective coating.

[0061] Example 2:

[0062] The preparation method of an all-steel bridge anti-freezing and thawing protective coating in this example is specifically carried out according to the following steps:

[0063] I. Add 10 kg of nano silica sol to the reaction kettle, then add 0.5 kg of silane coupling agent KH-570, control the temperature at 60 °C, stir at a stirring speed of 300 r / min for 30 min, and then carry out vacuum defoaming to obtain activated silica sol;

[0064] II. Mix 40 kg of polyether polyol (Mn = 2000), 15 kg of isocyanate and 0.1 kg of catalyst DBTDL, and under the condition of nitrogen protection, control the temperature at 80 °C and react for 3 h to obtain a polyurethane prepolymer with an NCO content of 6.5%;

[0065] III. Inject 10 kg of polyurethane prepolymer into 20 kg of activated silica sol, control the flow rate at 0.4 kg / min, control the temperature at 65 °C, stir at a rotation speed of 800 r / min for 60 min, and at the same time add 1 kg of dopamine-functionalized alumina nanoparticles for emulsification reaction, and then add 1 kg of ethylenediamine for reaction to obtain nano silica sol-polyurethane prepolymer;

[0066] The particle size of the dopamine-functionalized alumina nanoparticles is 20 - 50 nm, and they are prepared by coating a dopamine layer on the surface of the alumina nanoparticles by the sol-gel method;

[0067] IV. Disperse 2 kg of carboxyl-modified carbon nanotubes into absolute ethanol, add a small amount of deionized water, and then add aluminum isopropoxide. The molar ratio of carboxyl-modified carbon nanotubes to aluminum isopropoxide is 1:5. Adjust the pH to 3 - 4, stir at 60 °C for 10 h, then centrifuge, wash, dry, and calcine. The calcination temperature is 200 °C and the calcination time is 2 h to obtain Al2O3@CNTs;

[0068] Disperse 1 kg of Al2O3@CNTs into an ethanol solution with a volume concentration of 80%, add 2 kg of tetraethyl orthosilicate, adjust the pH to 9 - 10 with ammonia water, stir at 45 °C for 24 h, then centrifuge, wash, and dry to obtain double-shell carbon nanotubes;

[0069] Then dissolve aniline monomer in a hydrochloric acid solution with a concentration of 1 mol / L, the concentration of aniline monomer is 0.2 mol / L, adjust the pH to 1 - 2, then add ammonium persulfate. The molar ratio of aniline monomer to ammonium persulfate is 1:1. Control the temperature at 5 °C for the polymerization reaction, then add double-shell carbon nanotubes, and then add APS and react for 12 h to obtain polyaniline-coated double-shell carbon nanotubes;

[0070] Mix 2 kg of polyaniline-coated double-shell carbon nanotubes with 20 kg of absolute ethanol, add 0.5 kg of sodium dodecylbenzenesulfonate, perform ultrasonic treatment for 30 min, the ultrasonic power is 1000 W, and the frequency is 20 kHz. Then transfer to a three-roll grinder and grind until the agglomerate particle size is less than 500 nm. Then add 1 kg of polyether-modified silicone BYK-349 for dispersion treatment at a rate of 2000 r / min for 60 min to obtain a polyaniline-coated double-shell carbon nanotube dispersion;

[0071] V. Put 15 kg of titanium dioxide, 5 kg of nano-titanium dioxide / graphene oxide composite powder, 5 kg of alumina, 5 kg of calcium carbonate, 5 kg of yttrium silicate, 5 kg of mica powder, and 5 kg of talc powder into the dispersion tank in sequence, disperse at a constant speed of 1000 r / min for 30 - 60 min, then transfer to a high-speed vibration grinder and grind at a speed of 4000 r / min for 60 min, and then export to the dispersion tank. Add 100 kg of the nano-silica sol-polyurethane prepolymer obtained in step III and continue to disperse at 1000 r / min for 60 min to obtain a mixed slurry;

[0072] VI. Transfer the mixed slurry obtained in step V to a high-shear disperser, add 3 kg of the polyaniline-coated double-shell carbon nanotube dispersion obtained in step IV, continue to disperse evenly, then add the pH regulator AMP-95 and mix, and then add a polyurethane thickener and stir evenly to obtain the all-steel bridge anti-freeze and thaw protection coating.

[0073] Comparative Example 1:

[0074] The preparation method of the coating in this comparative example is specifically carried out according to the following steps:

[0075] I. Put 15 kg of titanium dioxide, 5 kg of nano-titanium dioxide / graphene oxide composite powder, 5 kg of alumina, 5 kg of calcium carbonate, 5 kg of yttrium silicate, 5 kg of mica powder and 5 kg of talc powder into the dispersion tank in sequence, disperse uniformly at 1000 r / min for 30 - 60 min, then transfer to a high-speed vibration grinding machine, grind at a speed of 4000 r / min for 60 min, and then export to the dispersion tank, add 100 kg of nano-silica sol, and continue to disperse at 1000 r / min for 60 min to obtain a mixed slurry;

[0076] II. Transfer the mixed slurry obtained in step I to a high-shear disperser, disperse evenly, then add the pH regulator AMP-95 and mix, and then add a polyurethane thickener and stir evenly to obtain the coating.

[0077] Comparative Example 2:

[0078] The preparation method of the coating in this comparative example is specifically carried out according to the following steps:

[0079] I. Put 15 kg of titanium dioxide, 5 kg of nano-titanium dioxide / graphene oxide composite powder, 5 kg of alumina, 5 kg of calcium carbonate, 5 kg of yttrium silicate, 5 kg of mica powder and 5 kg of talc powder into the dispersion tank in sequence, disperse uniformly at 1000 r / min for 30 - 60 min, then transfer to a high-speed vibration grinding machine, grind at a speed of 4000 r / min for 60 min, and then export to the dispersion tank, add 100 kg of polyurethane, and continue to disperse at 1000 r / min for 60 min to obtain a mixed slurry;

[0080] II. Transfer the mixed slurry obtained in step I to a high-shear disperser, disperse evenly, then add the pH regulator AMP-95 and mix, and then add a polyurethane thickener and stir evenly to obtain the coating.

[0081] Comparative Example 3:

[0082] The preparation method of the coating in this comparative example is specifically carried out according to the following steps:

[0083] I. Add 10 kg of nano-silica sol to the reaction kettle, then add 0.5 kg of silane coupling agent KH-570, control the temperature at 60 °C, stir at a speed of 300 r / min for 30 min, and then carry out vacuum degassing to obtain activated silica sol;

[0084] II. Mix 40 kg of polyether polyol (Mn = 2000), 10 kg of isocyanate, and 0.1 kg of catalyst DBTDL. Under nitrogen protection, control the temperature at 80 °C and react for 3 h to obtain a polyurethane prepolymer with an NCO content of 6.5%.

[0085] III. Inject 10 kg of the polyurethane prepolymer into 20 kg of activated silica sol. Control the flow rate at 0.4 kg / min, the temperature at 65 °C, and the rotation speed at 800 r / min, and stir for 60 min to carry out an emulsification reaction. Then add 1 kg of ethylenediamine for reaction to obtain a nano-silica sol - polyurethane prepolymer.

[0086] IV. Add 15 kg of titanium dioxide, 5 kg of nano-titanium dioxide / graphene oxide composite powder, 5 kg of alumina, 5 kg of calcium carbonate, 5 kg of yttrium silicate, 5 kg of mica powder, and 5 kg of talc powder into the dispersion tank in sequence. Disperse uniformly at 1000 r / min for 30 - 60 min, then transfer to a high-speed vibration mill and grind at 4000 r / min for 60 min. Then export to the dispersion tank, add 100 kg of the nano-silica sol - polyurethane prepolymer obtained in step III, and continue to disperse at 1000 r / min for 60 min to obtain a mixed slurry.

[0087] V. Transfer the mixed slurry obtained in step IV to a high-shear disperser to continue dispersing evenly. Then add the pH regulator AMP-95 and mix, and then add a polyurethane thickener and stir evenly to obtain a coating.

[0088] For the coatings prepared in the above examples and comparative examples, coat them on the simulated bridge concrete surface (coating thickness 300 - 500 μm) and test their performance.

[0089] 1. Frost resistance and thawing cycle performance experiment

[0090] 1.1 Experimental standards and conditions

[0091] Refer to the rapid freezing method in GB / T 50082-2009 "Test Methods for Long-Term Performance and Durability of Ordinary Concrete" and ASTM D6944 (coating freeze-thaw cycle test). The temperature in the freezing stage is -18 °C ± 2 °C, and the temperature in the thawing stage is 5 °C ± 2 °C; set 50 times, 100 times, 150 times, 300 times, 320 times, etc. (adjust according to the durability requirements of the material). The coating specimen needs to be coated on the surface of a standard steel plate (such as Q235 steel), with a dry film thickness of 80 - 120 μm, and cured for 7 days; the concrete specimen is a 100 mm × 100 mm × 100 mm cube and cured for 28 days.

[0092] 1.2 Experimental method

[0093] ① Specimen pretreatment:

[0094] Coating specimen: Vacuum-saturated water treatment for 15 minutes and atmospheric-pressure immersion for 30 minutes.

[0095] Concrete specimen: Immersed for 4 days, then dried and weighed.

[0096] ② Freeze-thaw cycle:

[0097] Freezing stage: The specimen is placed in a freeze-thaw box for 2.5 hours, and the central temperature drops to -18°C. Melting stage: Transferred to a 20°C water bath for 1 hour to ensure complete thawing.

[0098] ③ Intermediate inspection: Measure the mass loss rate ( where m0 is the initial mass, and m n is the mass at the nth time) and the dynamic elastic modulus (transverse fundamental vibration frequency method) every 25 cycles.

[0099] ④ Termination condition:

[0100] Mass loss ≥ 5%, relative dynamic elastic modulus ≤ 60% or reach the preset number of cycles.

[0101] 1.3 Experimental results

[0102] Table 1 Comparison of freeze-thaw cycle resistance performance

[0103]

[0104]

[0105] As can be seen from Table 1, Examples 1-2 adopt a nano-silica sol-polyurethane interpenetrating network (IPN) structure, which significantly improves the elasticity and low-temperature toughness of the coating (glass transition temperature Tg ≤ -40°C). The dopamine-functionalized alumina nanoparticles enhance the interfacial bonding force through the synergistic action of hydrogen bonds and covalent bonds, effectively inhibiting the crack propagation caused by freeze-thaw stress. In Comparative Example 1, due to the lack of elastic buffer of polyurethane, the coating is highly brittle and fails rapidly after freeze-thaw. In Comparative Example 2, because the IPN structure is not formed, the freeze-thaw resistance performance is only better than that of the traditional epoxy system, but still cannot meet the requirements of extreme environments. Comparative Example 3 adopts a nano-silica sol-polyurethane prepolymer matrix, and its freeze-thaw resistance performance is better than that of Comparative Example 1 and Comparative Example 2. However, due to the lack of biomimetic interface enhancement of dopamine-functionalized alumina nanoparticles and the crack resistance of polyaniline-coated carbon nanotubes, the interfacial bonding force decreases after freeze-thaw.

[0106] 2. Adhesion and mechanical strength experiments

[0107] 2.1 Adhesion test (ASTM D4541)

[0108] An aluminum ingot with a diameter of 20 mm is bonded to the coating surface with epoxy glue and cured for 24 hours. Hydraulic loading is applied until the coating peels off, and the maximum tensile force (MPa) is recorded.

[0109] 2.2 Impact resistance test (GB / T 1732)

[0110] The specimen is fixed horizontally, and the falling hammer freely falls from a height of 50 cm to impact the surface of the coating. Observe whether cracks or peeling occur, and record the maximum impact resistance energy (kg·cm).

[0111] 2.3 Compressive and flexural strength (GB / T 9966)

[0112] The universal testing machine is used for testing according to the standard.

[0113] 2.4 Results

[0114] Table 2 Adhesion and mechanical strength

[0115]

[0116]

[0117] As can be seen from Table 2, in Examples 1-2, through the bridging effect of the double-shell carbon nanotubes and the polyaniline coating layer, the cohesion and impact resistance of the coating are enhanced. At the same time, the polyether-modified silicone optimizes the dispersion of the nano-fillers and avoids stress concentration. In Comparative Examples 1-2, due to the lack of functionalized carbon nanotubes and the biomimetic interface enhancement structure, the fillers are unevenly dispersed, resulting in a significant decrease in adhesion and mechanical strength. The adhesion of Comparative Example 3 is only 63% of that of Example 1, because of the lack of the biomimetic adhesion effect of dopamine-functionalized alumina (the interfacial bonding force decreases), and the microcracks are not bridged by the double-shell carbon nanotubes.

[0118] 3. Weather resistance and self-healing ability experiments

[0119] 3.1 Salt spray test (ASTM B117)

[0120] Test conditions: 5% NaCl solution, temperature 35°C ± 2°C, spray rate 1-2 mL / (h·80 cm 2 ).

[0121] The specimen is placed at an inclination of 15°, and continuous spraying is carried out until the preset time. Observe the corrosion area and the blistering grade (ISO 4628 standard).

[0122] 3.2 UV aging test (ASTM G154)

[0123] Test conditions: QUV UV aging chamber (UVA-340 lamp tube), cycle period: 8 h UV (60°C) + 4 h condensation (50°C). Evaluate the ΔE color difference according to the ASTM G154 method.

[0124] 3.3 Photothermal self-healing ability test

[0125] Artificially create coating microcracks (width ≤ 50 μm). Simulate sunlight (1 kW / m 2 ) to irradiate the crack area and record the temperature change. Observe the crack closure situation and calculate the self-healing efficiency. The formula is:

[0126] 3.4 Results

[0127] Table 3 Weather resistance and self-healing ability

[0128]

[0129]

[0130] As can be seen from Table 3, in Examples 1-2, the nano-titanium dioxide / graphene oxide composite powder forms a dense physical barrier to block the diffusion of corrosive media; rare earth silicate (yttrium silicate) refines the coating grains through ion exchange to delay the corrosion process. The polyaniline-coated carbon nanotubes generate local temperature rise under light irradiation, promoting the rearrangement of polymer segments at the microcracks to achieve self-healing, and the healing efficiency reaches more than 85%. Comparative Examples 1-2 lack photothermal response materials and synergistic protection mechanisms, and their weather resistance only depends on traditional fillers, and the performance is far lower than that of the examples. In Comparative Example 3, due to the absence of polyaniline-coated double-shell carbon nanotubes, the microcracks cannot be repaired by the photothermal effect.

[0131] In summary, the anti-freeze and thaw performance of the present invention is significantly improved: through the combination of a three-dimensional interpenetrating network (IPN) structure and bionic interface enhancement, the freeze-thaw stress is effectively relieved, and the mass loss rate is reduced by 90% compared with traditional coatings. The photothermal self-healing mechanism (efficiency ≥ 85%) significantly extends the coating life and reduces the maintenance cost. The weather resistance is significantly improved: the nano-titanium dioxide / graphene oxide composite powder provides dual protection of "physical shielding + photocatalytic self-cleaning", and the salt spray resistance time reaches more than 3000 h. The mechanical strength is improved: the shell carbon nanotubes inhibit agglomeration through the ceramic network, and the surface polyaniline coating enhances the compatibility with the matrix, and the impact resistance is improved.

Claims

1. A method for preparing an anti-freeze-thaw protective coating for an all-steel bridge, characterized in that The method is specifically carried out in the following steps:

1. Add nano silica sol into the reaction kettle, then add silane coupling agent, control the temperature to 60-65°C, stir evenly, and then vacuum degas to obtain activated silica sol; 2. Mixing polyether polyol, isocyanate and catalyst, and reacting at a temperature of 80-85° C. under nitrogen protection to obtain a polyurethane prepolymer; 3. Inject the polyurethane prepolymer into the activated silica sol, control the temperature to 60-70°C and stir, add dopamine functionalized alumina nanoparticles while stirring, carry out emulsification reaction, then add ethylenediamine to react, and obtain nano silica sol-polyurethane prepolymer; Fourth, the carboxyl modified carbon nanotubes are dispersed in anhydrous ethanol, deionized water is added, and aluminum isopropoxide is added, the pH is adjusted to 3-4, and stirred at a temperature of 60-80°C for 6-12 hours, and then centrifuged and washed, and calcined after drying, the calcination temperature is 200-300°C, and the calcination time is 2 hours to obtain Al2O3@CNTs; Al2O3@CNTs were dispersed in an ethanol solution, tetraethyl orthosilicate was added, the pH was adjusted to 9-10 with aqueous ammonia, the solution was stirred at 40-45°C for 24 hours, and then centrifuged, washed and dried to obtain double-shell carbon nanotubes; Then, the aniline monomer is dissolved in a hydrochloric acid solution, the pH value is controlled to be 1-2, and then ammonium persulfate is added, and the temperature is controlled to be 0-5°C for polymerization reaction, and then double-shell carbon nanotubes are added, and then APS is added to react for 6-24 hours to obtain polyaniline-coated double-shell carbon nanotubes; The polyaniline-coated double-shell carbon nanotubes are mixed with anhydrous ethanol, sodium dodecylbenzene sulfonate is added, ultrasonic treatment is performed, and then the mixture is transferred to a three-roll mill for grinding, and polyether-modified siloxane is added for dispersion treatment to obtain a polyaniline-coated double-shell carbon nanotube dispersion; 5. Put titanium dioxide, nano titanium dioxide / graphene oxide composite powder, aluminum oxide, calcium carbonate, rare earth silicate, mica powder and talc into a dispersion tank in sequence, disperse them at a uniform speed, then transfer them to a high-speed oscillating grinder for grinding, and then export them to a dispersion tank, add the nano silica sol-polyurethane prepolymer obtained in step 3 for dispersion, and obtain a mixed slurry; 6. Transfer the mixed slurry obtained in step 5 to a high shear disperser, add the polyaniline-coated double-shell carbon nanotube dispersion obtained in step 4, continue to disperse evenly, then add a pH adjuster and mix, then add a polyurethane thickener and stir evenly to obtain the anti-freeze-thaw protective coating for the all-steel bridge.

2. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that The mass ratio of the nano silica sol to the silane coupling agent in step 1 is 100:

5.

3. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that In step 2, the mass ratio of the polyether polyol to the isocyanate is 40:(10-20).

4. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that The mass ratio of the polyurethane prepolymer to the activated silica sol in step 3 is 1:(2-2.5); The dopamine functionalized aluminum oxide nanoparticles have a particle size of 20 to 50 nm and are added in an amount of 3 to 5% of the total mass of the polyurethane prepolymer and the activated silica sol. The dopamine functionalized aluminum oxide nanoparticles are prepared by coating a dopamine layer on the surface of the aluminum oxide nanoparticles using a sol-gel method.

5. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that In step 4, the mass ratio of the carboxyl-modified carbon nanotubes to sodium dodecylbenzene sulfonate is 2:(0.5-0.8), and the aspect ratio of the carboxyl-modified carbon nanotubes is >1000.

6. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that Step 5: by weight, 80-100 parts of nano silica sol-polyurethane prepolymer, 10-15 parts of titanium dioxide, 5-10 parts of nano titanium dioxide / graphene oxide composite powder, 5-10 parts of aluminum oxide, 5-10 parts of calcium carbonate, 5-10 parts of rare earth silicate, 5-10 parts of mica powder, 5-10 parts of talc and 10-20 parts of deionized water.

7. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that In step 5, the mass ratio of nano-titanium dioxide to graphene oxide in the nano-titanium dioxide / graphene oxide composite powder is 2:1, and the particle size is 10 to 50 nanometers.

8. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that In step 5, the rare earth silicate is one or more of zirconium yttrium silicate, lanthanum yttrium silicate, yttrium cerium silicate, zirconium lanthanum silicate, yttrium silicate, ytterbium silicate, cerium silicate, gadolinium silicate, samarium silicate, erbium silicate, and holmium silicate.

9. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that In step 6, the mass ratio of the mixed slurry to the polyaniline-coated double-shell carbon nanotube dispersion is 100:(2-3).

10. The method for preparing the anti-freeze-thaw protective coating for all-steel bridges according to claim 1, characterized in that Step 6: Add a pH adjuster to adjust the pH to 8.5-9.5.

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