Durable modified epoxy resin composite coating and preparation method thereof

Abstract

The invention discloses a durable modified epoxy resin composite coating and a preparation method thereof. The durable modified epoxy resin composite coating comprises a component A and a component B, the component A comprises the following components in parts by mass: 100 parts of epoxy resin, 15 parts of mica, 20 parts of glass flakes, 10 parts of mica iron oxide, 5 parts of zinc phosphate, 3 parts of a penetrant and 10 parts of a solvent; the component B is prepared from the following components in parts by mass: 20 parts of doped polyaniline, 100 parts of N-methyl pyrrolidone and 30 parts of a modified amine curing agent. The prepared durable modified epoxy resin composite coating provides more durable surface protection for concrete structures of expressways and bridges, the salt freezing resistance and chloride ion corrosion resistance of the concrete structures subjected to modified epoxy resin surface treatment can be remarkably improved, and the durability of the concrete structures is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of epoxy resin coatings, and in particular relates to a durable modified epoxy resin composite coating and a preparation method thereof. Background Art

[0002] For concrete structures of highways and bridges, surface protection can extend their service life and reduce maintenance costs during use. Surface coating protection is the most common maintenance method. Among them, epoxy coatings with epoxy resin as the main component have been widely developed and applied. The principle is to form a dense physical protective layer on the concrete surface to prevent corrosive media from penetrating into the concrete and enhance the durability of concrete.

[0003] Combined with the engineering applications in northern China, it is found that for economic reasons, the main component of highway and bridge deicing salt is chloride salt, while Cl - Solution erosion is one of the main destructive effects on highways and bridges. - The damage of ions to concrete structures of highways and bridges is mainly reflected in two aspects. On the one hand, it is reflected in the salt crystallization of chloride ions in cement concrete, which expands in volume and causes the cement concrete to crack. Specifically, chloride ions replace calcium hydroxide in cement. The presence of chloride ions makes the solubility of CaCl2 generated by it higher than Ca(OH)2. Due to the osmotic pressure of the salt solution, the water inside the concrete migrates to the outer surface, causing the concrete to expand and crack, and the corrosion process is accelerated. When the concentration of CaCl2 in the concrete is high (>15%), it can form extremely small needle-shaped crystals with CaO in the liquid phase. When this substance accumulates more, it will cause expansion and corrosion of the concrete. In addition, microscopic studies have shown that Cl - It can penetrate into the concrete and destroy the internal structure of the gel. The presence of high concentrations of chloride salts will make the shrinkage and swelling of concrete more obvious. On the other hand, the use of deicing agents and deicing salts leads to the Cl - As the concentration increases, Cl - With a small radius and high activity, it is easy to penetrate the concrete passivation film and cause steel corrosion. When the chloride content in the solution is high, or there are repeated dry-wet cycles, more salt will be brought into the concrete. As a result, the crystalline salt produces very high crystallization pressure in the concrete pores, causing the concrete surface to peel or crack and break, resulting in the actual service life of the concrete structure often being lower than the design requirements.

[0004] The freeze-thaw durability of epoxy resin protective coatings in highway and bridge concrete structures is insufficient. - and Cl -Under the erosion of corrosive media such as solutions, corrosive ions will slowly penetrate the coating and react with the concrete, causing the physical protective layer to gradually fail. Within 2-3 years of using the epoxy resin coating, the structure will quickly suffer from surface peeling and reduced structural strength due to the freeze-thaw action of chloride salts, which greatly shortens the maintenance cycle of the concrete structure and significantly increases the workload, resulting in additional manpower and material costs. Chloride salt erosion of concrete is a more harmful type of corrosive medium damage and one of the important factors affecting the durability of concrete, causing a large amount of economic losses every year.

[0005] Therefore, it is necessary to improve epoxy resin coatings to make the protective effect of its covering layer more durable, especially for the problem of erosion and damage to highway concrete structures caused by the spraying of deicing agents in rainy and snowy weather in seasonally frozen areas. Improving epoxy resin coatings can reduce the physical and chemical erosion damage to concrete structures caused by deicing agents and deicing salts, so as to prevent the premature deterioration of concrete structures due to insufficient durability.

[0006] Since epoxy resin cured products have large internal stress, poor toughness, easy degradation at high temperature, and poor moisture resistance, these are objective conditions that limit their durability. In response to these defects, a variety of anti-corrosion coatings have been studied, including solvent-based epoxy anti-corrosion coatings and solvent-free epoxy anti-corrosion coatings, and some success has been achieved in the research field of modifying epoxy resins using rubber, silicone and nanoparticles. However, the above methods still have some defects, such as the cost of nanoparticles and silicone modification, and the weather resistance of rubber modified epoxy resins. Summary of the invention

[0007] The purpose of the present invention is to provide a durable modified epoxy resin composite coating and a preparation method thereof, which can provide longer-lasting surface protection for concrete structures of highways and bridges, reduce chloride salt corrosion of concrete, and enhance the durability of concrete structures.

[0008] The technical solution of the present invention is as follows: The invention discloses a durable modified epoxy resin composite coating, comprising component A and component B; The component A comprises the following components in parts by mass: 100 parts of epoxy resin, 15 parts of mica, 20 parts of glass flakes, 10 parts of mica iron oxide, 5 parts of zinc phosphate, 3 parts of penetrant, and 10 parts of solvent; The component B comprises the following components in parts by mass: 20 parts of doped polyaniline, 100 parts of N-methylpyrrolidone, and 30 parts of modified amine curing agent.

[0009] Preferably, the modified curing agent is diethyltoluenediamine with an effective ingredient content greater than 90%.

[0010] Preferably, the penetrant is nonylphenol polyoxyethylene (12) ether phosphate monoester.

[0011] Preferably, the solvent is dimethyl carbonate solvent. Dimethyl carbonate mainly acts as a diluent in epoxy resin, which can effectively reduce the viscosity of epoxy resin, facilitate processing and use, and improve the ductility and fluidity of epoxy resin, while having little effect on the performance of epoxy resin and having good stability.

[0012] Preferably, the measured viscosity of the epoxy resin at 25° C. should be between 11000 and 13000 mPa·s.

[0013] Furthermore, the present invention also discloses a method for preparing the modified epoxy resin composite coating, comprising the following steps: The raw materials in the component A are mixed uniformly at 20-50° C. to obtain agent A; Mix the raw materials in component B to obtain agent B; The agent A is mixed with the agent B to obtain the durable modified epoxy resin composite coating.

[0014] Furthermore, the mass ratio of the agent A to the agent B is 2.5-3.5:1.

[0015] The durable modified epoxy resin composite coating is used as a concrete surface protective agent.

[0016] Furthermore, the composite coating can be applied to concrete structures of highways and bridges.

[0017] Preferably, the composite coating is applied at a temperature of 25±5°C and a relative humidity of 65±10%. This prevents the modified epoxy resin from precipitation, poor fluidity, poor surface adhesion, premature hardening, etc. on the surface of the concrete structure after the mixture of agent A and agent B.

[0018] The present invention proposes a durable modified epoxy resin composite coating and a preparation method thereof, improves the epoxy resin protective agent, provides longer surface protection for concrete structures of highways and bridges, and the concrete structures treated with the durable modified epoxy resin surface can significantly improve the salt and frost resistance, corrosion resistance, and frost resistance durability, thereby enhancing the durability of the concrete structure. Based on the advantages of dimethyl carbonate being environmentally friendly and safe, the present invention uses dimethyl carbonate as a solvent, and polyurethane has the characteristics of excellent weather resistance and chemical resistance, high gloss, and wear resistance, and selects a modified amine and a polyaniline composite curing agent to react with the epoxy resin to form a film.

[0019] When the surface of concrete is covered with a durable modified epoxy resin composite coating, the water repellency, impermeability and salt erosion resistance of the concrete surface are significantly improved, and the total amount of chloride ions in the environmental liquid can be effectively reduced. According to the theory of porous medium mechanics, when the durable modified epoxy resin coating is covered on the surface of concrete, the surface of the concrete is in a saturated state, and the water absorption rate in the saturated liquid environment is reduced, and the degree of damage accumulation is reduced during repeated freeze-thaw cycles; in addition, the internal porosity of the mortar layer on the surface of the concrete is reduced, the average pore size is reduced, and the freezing point and ice formation rate in the surface pore solution are reduced, which will reduce the microscopic damage inside the surface of the concrete, and can effectively improve the ability of the concrete surface to resist salt freezing damage, which is ultimately manifested as the improvement of salt freezing and thawing damage resistance. Under the condition of meeting the same damage standard, the present invention can experience a longer freeze-thaw effect, and obtain a smaller mass loss and dynamic modulus loss inside the structure under the freeze-thaw cycle involving deicing salt, showing more excellent durability.

[0020] The present invention proposes a durable modified epoxy resin composite coating and a preparation method thereof based on epoxy resin materials, which conforms to the concept of low-carbon and sustainable green development of road traffic, and has the advantages of increasing the maintenance cycle and reducing the maintenance cost, and significantly improves the durability of concrete structures, and has great potential in improving the frost resistance and corrosion resistance of concrete pavements. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Surface morphology of each group of samples after freeze-thaw experiment in 3.5% NaCl solution.

[0022] Figure 2 The changing trend of mass loss of each group of samples with the number of freeze-thaw cycles.

[0023] Figure 3 Variation trend of relative dynamic elastic modulus of each group of samples with the number of freeze-thaw cycles.

[0024] Figure 4 The relationship between water absorption rate and immersion time of each group of samples.

[0025] Figure 5 Pore ​​structure distribution of MIP mercury injection test for each group of samples: (a) pore volume corresponding to pore size, (b) cumulative mercury injection volume; pore size evaluation indicators are: harmless (<20nm), less-harmless (20-50nm), harmful (50-200nm), more-harmful (>200nm).

[0026] Figure 6 Internal porosity images of CT tomography of each group of samples.

[0027] In the figure: NS-blank control group, EC-epoxy resin coating group, SC-silane coating group, MECC-durable modified epoxy resin composite coating group. DETAILED DESCRIPTION

[0028] The following embodiments and comparative examples are used to further describe the technical scheme of the present invention, so that those skilled in the art can understand and utilize the present invention well, but they are not intended to limit the scope of protection of the present invention.

[0029] The names and abbreviations of the experimental methods, production processes, instruments and equipment involved in the embodiments and comparative examples of the present invention are conventional names in the field and are very clear and unambiguous in the relevant application fields. Technicians in the field can understand the conventional process steps and apply the corresponding equipment based on the names and implement them according to conventional conditions or conditions recommended by the manufacturer.

[0030] The various raw materials or reagents used in the examples and comparative examples of the present invention are not particularly limited in their sources, and are all conventional products that can be purchased commercially. Example 1 Preparation of durable modified epoxy resin composite coating

[0031] Preparation method of durable modified epoxy resin composite coating: S1. Prepare, by mass, 100 parts of epoxy resin, 15 parts of mica, 20 parts of glass flakes, 10 parts of mica iron oxide, 5 parts of zinc phosphate, 3 parts of nonylphenol polyoxyethylene (12) ether phosphate monoester penetrant, and 10 parts of dimethyl carbonate solvent.

[0032] Heat the epoxy resin in a water bath until its viscosity decreases. The measured viscosity of the epoxy resin at 25°C should be 11000-13000 mPa·s. Put the prepared epoxy resin into a reactor, add dimethyl carbonate solvent to further reduce the viscosity of the resin, control the temperature of the reactor between 20-50°C, and stir at a speed of 150-200 r / min.

[0033] After stirring evenly, add mica, glass flakes, mica iron oxide, and zinc phosphate from the feed port. The pigment-to-base ratio is controlled at about 1:8. Start the reactor and stir and disperse at high speed for 20 minutes at a speed of 1200r / min. Add nonylphenol polyoxyethylene (12) ether phosphate monoester penetrant. Finally, adjust the viscosity to about 600mpa·s, grind the paint, and filter it. Put the filtered paint into the colloid mill in batches and continue to grind and mix evenly. Set the fineness to 50μm to pass, and then obtain Agent A, which is sealed in a storage barrel.

[0034] S2. Prepare, by mass, 20 parts of doped polyaniline, 100 parts of N-methylpyrrolidone (NMP), and 30 parts of modified amine curing agent; the modified amine curing agent is specifically diethyltoluenediamine with an active ingredient greater than 90%.

[0035] The doped polyaniline is ground and passed through a 200-mesh sieve, then dissolved in N-methylpyrrolidone (NMP), and electromagnetically stirred until the polyaniline is evenly dispersed in the NMP. The dispersion is then mixed with the modified amine curing agent and electromagnetically stirred evenly to obtain component B, which is then sealed and stored in a storage barrel.

[0036] S3. Mix the mixture A and the mixture B in a mass ratio of 2.5:1 and stir them evenly to obtain the durable modified epoxy resin composite coating. Example 2 Preparation of durable modified epoxy resin composite coating

[0037] Preparation method of durable modified epoxy resin composite coating: S1. Prepare, by mass, 100 parts of epoxy resin, 15 parts of mica, 20 parts of glass flakes, 10 parts of mica iron oxide, 5 parts of zinc phosphate, 3 parts of nonylphenol polyoxyethylene (12) ether phosphate monoester penetrant, and 10 parts of dimethyl carbonate solvent.

[0038] Heat the epoxy resin in a water bath until its viscosity decreases. The measured viscosity of the epoxy resin at 25°C should be 11000-13000 mPa·s. Put the prepared epoxy resin into a reactor, add dimethyl carbonate solvent to further reduce the viscosity of the resin, control the temperature of the reactor between 20-50°C, and stir at a speed of 150-200 r / min.

[0039] After mixing evenly, add mica, glass flakes, mica iron oxide, and zinc phosphate from the feed port. The pigment-to-base ratio is controlled at about 1:8. Start the reactor and stir and disperse at high speed for 20 minutes at a speed of 1200r / min. Add nonylphenol polyoxyethylene (12) ether phosphate monoester penetrant. Finally, adjust the viscosity to about 600mpa·s, grind the paint, and filter it. Put the filtered paint into the colloid mill in batches and continue to grind and mix evenly. Set the fineness to 50μm to pass, and then obtain Agent A, which is sealed in a storage barrel.

[0040] S2. Prepare, by mass, 20 parts of heteropolyaniline, 100 parts of N-methylpyrrolidone (NMP), and 30 parts of modified amine curing agent; the modified amine curing agent is specifically diethyltoluenediamine with an active ingredient greater than 90%.

[0041] The doped polyaniline is ground and passed through a 200-mesh sieve, then dissolved in N-methylpyrrolidone (NMP), and electromagnetically stirred until the polyaniline is evenly dispersed in the NMP. The dispersion is then mixed with the modified amine curing agent and electromagnetically stirred evenly to obtain component B, which is then sealed and stored in a storage barrel.

[0042] S3. Mix the mixture A and the mixture B in a mass ratio of 3:1 and stir them evenly to obtain the durable modified epoxy resin composite coating. Example 3 Preparation of durable modified epoxy resin composite coating

[0043] Preparation method of durable modified epoxy resin composite coating: S1. Prepare, by mass, 100 parts of epoxy resin, 15 parts of mica, 20 parts of glass flakes, 10 parts of mica iron oxide, 5 parts of zinc phosphate, 3 parts of nonylphenol polyoxyethylene (12) ether phosphate monoester penetrant, and 10 parts of dimethyl carbonate solvent.

[0044] Heat the epoxy resin in a water bath until its viscosity decreases. The measured viscosity of the epoxy resin at 25°C should be 11000-13000 mPa·s. Put the prepared epoxy resin into a reactor, add dimethyl carbonate solvent to further reduce the viscosity of the resin, control the temperature of the reactor between 20-50°C, and stir at a speed of 150-200 r / min.

[0045] After mixing evenly, add mica, glass flakes, mica iron oxide, and zinc phosphate from the feed port. The pigment-to-base ratio is controlled at about 1:8. Start the reactor and stir and disperse at high speed for 20 minutes at a speed of 1200r / min. Add nonylphenol polyoxyethylene (12) ether phosphate monoester penetrant. Finally, adjust the viscosity to about 600mpa·s, grind the paint, and filter. Put the filtered paint into the colloid mill in batches and continue to grind and mix evenly. Set the fineness to 50μm to pass, and then obtain Agent A, which is sealed in a storage barrel.

[0046] S2. Prepare, by mass, 20 parts of heteropolyaniline, 100 parts of N-methylpyrrolidone (NMP), and 30 parts of modified amine curing agent; the modified amine curing agent is specifically diethyltoluenediamine with an active ingredient greater than 90%.

[0047] The doped polyaniline is ground and passed through a 200-mesh sieve, then dissolved in N-methylpyrrolidone (NMP), and electromagnetically stirred until the polyaniline is evenly dispersed in the NMP. The dispersion is then mixed with the modified amine curing agent and electromagnetically stirred evenly to obtain component B, which is then sealed and stored in a storage barrel.

[0048] S3. Mix the mixture A and the mixture B in a mass ratio of 3.5:1 and stir them evenly to obtain the durable modified epoxy resin composite coating. Comparative Example

[0049] In this experiment, four experimental groups were set up to test concrete specimens, one of which was a blank control group (NS), and the other three groups were concrete specimens treated with three types of coatings, namely, epoxy resin coating group (EC): transparent emulsion, film-forming type, effective content of 81.0%, coating thickness of 2.8-4.0mm; silane coating group (SC): special silane impregnation coating for roads and bridges, penetrating type, the main material is high-purity isobutyl silane, silane content of 98.9%; and the durable modified epoxy resin composite coating group (MECC) proposed in the present invention.

[0050] The cement concrete surface was treated by the recommended treatment methods of each coating. The NS group was the control group, and the sample surface was not coated. The EC group samples were coated with ordinary epoxy resin coating. The treatment method was to first clean the concrete surface and use a plastic brush for the first treatment. It should be noted that the ordinary epoxy resin should be applied repeatedly to make it even, and the second treatment was carried out after an interval of 5 minutes. The amount of ordinary epoxy resin was 0.40L / m 2 The coating of the SC group samples is silane coating. After cleaning the concrete surface, a plastic brush is used to apply it three times continuously. The interval between each treatment is 1-2 minutes. The amount of silane coating is 0.40L / m 2 The coating of the MECC group samples is a modified epoxy resin composite coating. After cleaning the concrete surface, a plastic brush is used to apply it three times continuously. The interval between each treatment is 1-2 minutes. The amount of modified epoxy resin coating is 0.35L / m 2 After each group of samples was processed, they were cured for 24 hours at a temperature of about 25°C and a relative humidity of 65%.

[0051] The mix ratio of cement concrete is shown in Table 1. The water-cement ratio of concrete is 0.46, and the 28d compressive strength is 46.0Mpa. The cement is PO42.5 ordinary Portland cement produced by Hangzhou Sea Lion Cement Co., Ltd. (specific area 300m 2 / kg, consistency 22.5%), its chemical composition is shown in Table 2. The fine aggregate is natural river sand (fineness modulus 2.7, bulk density 2710kg / m 3 ). The coarse aggregate is selected in two grades of continuous grading: 5-10mm and 10-20mm. The water reducer is a high-efficiency polycarboxylic acid type water reducer. The test water is tap water.

[0052] Table 1 Cement concrete mix ratio (kg / m 3 ) Table 2 Chemical composition of cement (%)

[0053] Salt and frost resistance test of durable modified epoxy resin composite coating:

[0054] Based on the reference of "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009), the cement concrete specimens were tested by first erosion and then freeze-thaw. The specimens with a size of 100mm×100mm×400mm were treated with surface coating, and then subjected to long-term erosion for 120 days. The chloride salt solution used to prepare the environmental solution was prepared with sodium chloride powder (AR, 99%). The erosion liquid was NaCl solution; after taking out, the fundamental frequency of the specimen was calibrated, the initial value of the ultrasonic velocity was tested, and then 200 rapid freeze-thaw tests were carried out. According to the main types of snow melting agents in highway engineering, 3.5wt% NaCl solution was selected as the freeze-thaw medium. The maximum and minimum temperatures set in the rapid freeze-thaw test were 5℃±2℃ and -18℃±2℃, respectively. The freeze-thaw cycle time was about 4h each time. The mass loss of the specimen was tested after every 25 cycles; the relative dynamic elastic modulus of the specimen was tested by ultrasonic testing after every 40 cycles, and the solution of the freeze-thaw test tank was replaced at the same time. After all freeze-thaw cycles were completed, the residual compressive strength of all specimens was measured.

[0055] In order to study the effect of durable modified epoxy resin composite coating on the salt-freezing resistance of concrete, the antifreeze performance of concrete was analyzed based on three indicators: loss mass, relative dynamic elastic modulus, and residual compressive strength. After 200 rapid freeze-thaw tests, the surface morphology of the specimens after the freeze-thaw test was shown in Figure 2. Figure 1 The trend of mass loss with the number of freeze-thaw cycles is shown in Figure 2 The variation trend of relative dynamic elastic modulus with the number of freeze-thaw cycles is shown in Figure 3 The residual compressive strength of the specimens is shown in Table 3.

[0056] like Figure 1 As shown in the figure, from the appearance morphology, the surface damage of the NS group specimens is the most serious, and the internal coarse aggregate at the corners is completely exposed; followed by the SC group and the EC group, with more holes on the surface. The number of holes in the EC group is observed to be less overall. The surfaces of the SC group and the EC group are accompanied by slight slag falling, but there is no aggregate peeling and damage; the surface morphology of the MECC group is well maintained, the surface color is relatively uniform, there is little pore exposure, and no aggregate peeling occurs.

[0057] like Figure 2As shown in the figure, the three evaluation indicators of the concrete specimens in the NS group performed the worst, and the average mass loss of the specimens was 256g, the largest among all groups. The specimens in the other three groups that had been surface coated did not experience aggregate peeling, and the SC and EC groups only had surface damage, while the surface morphology of the MECC group specimens remained good. The average mass loss of the surface coating specimens was 99g (SC), 71g (EC), and 49g (MECC), respectively, which was only 38.67% (SC), 27.73% (EC), and 19.14% (MECC) of the control group. During the entire freeze-thaw process, the surface damage of the NS group specimens intensified after 50 freeze-thaw cycles, and the mass loss began to be obvious; while the mass loss rate of the surface coating specimens was relatively slow due to the protective effect of the surface coating. The mass loss of the SC and EC group specimens increased significantly after 150 cycles, while the mass loss rate of the MECC group remained almost unchanged during the entire freeze-thaw process, indicating the reliability of the surface protection effect of MECC.

[0058] Further analysis of the relative dynamic elastic modulus is carried out, such as Figure 3 As shown in the figure, after 200 freeze-thaw cycles, the relative dynamic elastic modulus of the four groups of specimens were 67.89% (NS), 85.24% (SC), 87.06% (EC) and 89.51% (MECC), respectively, which increased by 17.35%, 19.17% and 21.62%, respectively. The loss of relative dynamic elastic modulus in the NS group was also the largest among all groups, followed by the SC group, the EC group and the MECC group, which was consistent with the law of mass loss. Silane coating treatment can improve the salt-freezing resistance of concrete, but in this experiment, the SC group performed worse than the EC group and the MECC group in the second half of the freeze-thaw cycle. The surface damage of the EC group was similar to that of the SC group, and the loss of relative dynamic elastic modulus was further reduced. The EC and SC groups showed obvious uneven color distribution on the surface. It is speculated that this is because the surface coatings treated by the SC and EC groups are unevenly distributed on the concrete base. Therefore, the protective layer disappears in some areas under the action of freeze-thaw cycles, resulting in premature damage to the concrete surface in this area, even if these damaged areas are not distributed in the corner areas, resulting in local damage after erosion of these areas. After 200 rapid freeze-thaw cycles, the loss of relative dynamic elastic modulus in the MECC group with added modifier components was reduced by 21.62% (NS), 4.27% (SC), and 2.45% (EC) compared with the other three groups. The decay period of the relative dynamic elastic modulus of the MECC group was longer. According to the antifreeze performance evaluation standards specified in the specifications, this means that under the same damage conditions, the MECC group experienced more freeze-thaw cycles, that is, better antifreeze durability.

[0059] The residual compressive strength is also an important indicator for evaluating the degree of internal damage of concrete specimens. As shown in Table 3, the residual compressive strength of the NS group specimens is 29.03 MPa, which is about 63.10% of the initial strength; while the residual compressive strengths of the SC group, EC group, and MECC group are 32.86 MPa, 34.79 MPa, and 36.08 MPa, respectively, which are 13.21%, 19.85%, and 24.28% higher than those of the NS group.

[0060] Table 3 Residual compressive strength of each group of specimens

[0061] A comprehensive comparison of the three indicators shows that the durable modified epoxy resin composite coating can improve the salt-freeze resistance of concrete structures, and compared with ordinary epoxy resin coatings and silane coatings, it can further improve its salt-freeze resistance durability. After experiencing the same number of freeze-thaw cycles, the MECC group specimens have the lowest mass loss and relative dynamic elastic modulus loss, the largest residual compressive strength, and the lowest freeze-thaw damage.

[0062] Permeability test of durable modified epoxy resin composite coating: The impermeability is correlated with the resistance to environmental erosion. The water absorption rate of cement concrete specimens (150mm×150mm×150mm) was tested according to the reference standard (GB-T50081-2019). The four groups of test specimens were completely immersed in water, and the top surface of the water was kept 5.0±0.5mm higher than the top surface of the mortar specimen. The surface dry mass of the specimen was first measured as m s The immersion can be stopped only when the mass change of two consecutive 24h intervals is less than 0.2% of the larger value. The total immersion time of the specimen must be greater than 48h. After the measurement, the specimen is dried in a drying oven at 105±5℃. The mass of the dried specimen is measured as m d The drying time shall not be less than 48 hours, and the drying shall be stopped until the mass change between two consecutive 24-hour intervals is less than 0.2% of the smaller value.

[0063] The water absorption rate of concrete is W r Calculate according to the following formula:

[0064] As a physical barrier to protect cement concrete, one of the functions of the surface coating is to reduce the amount of water that enters the concrete, thereby reducing the freezing pressure inside the concrete and further reducing freeze-thaw damage under repeated freeze-thaw cycles. The water absorption test is to test the effect of different surface coatings on preventing water from entering the concrete. The water absorption test results are shown in Figure 4 .

[0065] like Figure 4As shown in Figure 2, when the sample is immersed in water, the W of the uncoated sample r It increases sharply in the first 48 hours, then increases slowly as the soaking time further prolongs, and reaches a saturated state. r In contrast, the water absorption of concrete with surface coating is significantly reduced, which is consistent with the expected results. r The water absorption rates of the MECC group were 1.32% (SC), 1.13% (EC), and 0.93% (MECC), respectively. The water absorption rate of the MECC group was the lowest, which was 56.94% lower than that of the control group. The growth trends of the EC and MECC group samples were basically the same. r It slowly increased in the first 36 hours, and once the immersion time exceeded 48 hours, the specimen was close to reaching saturation. It is worth noting that the water absorption rate of the SC group was still increasing after 72 hours, which is consistent with existing research, which believes that silane cannot prevent the invasion of external solutions under supersaturated conditions. In addition, because the environmental solution is the transmission medium for corrosive ions such as chloride ions to enter the internal structure of concrete, low water absorption can also reduce the total amount of chloride ion intrusion and reduce freeze-thaw damage caused by chloride salts.

[0066] Chloride ion penetration resistance test of durable modified epoxy resin composite coating: The penetration of chloride ions in the surface coating specimens was tested by the coulometric method (RCPT), and the surface morphology of the concrete specimens that had been immersed in the chloride solution for 120 days was observed. The specimen size of the RCPT was φ100mmÍ50mm, and the immersion solution was NaCl solution. The YC-RCM concrete chloride ion diffusion coefficient tester was used. During the power-on process, the solutions in the containers at both ends were 0.3mol / L NaOH (positive electrode) and 3.0wt% NaCl (negative electrode), respectively. Under an external electric field of 60V, the current value passing through the specimen was measured every 30 minutes, and the test lasted for 6 hours.

[0067] The total amount of electricity passing through the test piece is calculated according to the following formula:

[0068] Q s (C) is the amount of electricity passing through the φ95mmÍ50mm concrete specimen, Q x (C) is the amount of electricity passed through the φ100mmÍ50mm concrete specimen. The evaluation standard of chloride ion permeability by the electrical method is shown in Table 4. This section proves that the anti-chloride ion corrosion performance of the surface coating specimen is improved through full immersion appearance observation and RCPT test.

[0069]

[0070] The surface morphology of each group of specimens after 120 days of corrosion in 10.0wt% NaCl solution is as follows: Figure 6 As shown in the figure, the surface of the NS group specimens showed obvious cracks, especially at the corners of the concrete specimens, there was obvious peeling and aggregate leakage, while the surface of the surface coating group specimens did not show obvious peeling, but there was slight slag at the corners, and most of this slag was caused by the specimen molding process and repeated handling. When the concrete surface peels off and causes a large number of cracks, it will lead to an increase in the intrusion of environmental liquids and corrosive ions, further increasing the internal damage of concrete structures under freeze-thaw action.

[0071] The test results of RCPT are shown in Table 5. The average amount of electricity passed through the concrete specimens in the NS group was 2128, which was rated as "medium", while the amount of electricity passed through the surface coating group decreased significantly, and the ratings were all "very low", with average values ​​of 283 (EC), 367 (SC) and 157 (MEEC), which were 13.33%, 17.28% and 7.39% of the NS group, respectively. The concrete permeability increased by 2 levels, indicating that the three types of surface protective coatings played an effective protective role and improved the concrete's resistance to chloride ion corrosion. In addition, the test results were well consistent with the water absorption test, and it was believed that the transmission channels inside the concrete specimens in the MEEC group were more effectively blocked. Among the three coatings, the SC group performed the worst, and it was believed that under supersaturated conditions, the silane coating could not effectively prevent the intrusion of external moisture.

[0072]

[0073] Microstructure detection of durable modified epoxy resin composite coatings: Mercury intrusion porosimetry (MIP, Micromeritics AutoPore V 9620 analyzer) was used to analyze the pore distribution and porosity changes of surface samples, and the size of the concrete surface cube specimen was 10mmÍ10mmÍ10mm; CT scanning (Y.CT Precision high-precision computer tomography scanning system produced by YXLON International X-ray Co., Ltd. of Germany) was used to analyze the frost heave damage of the internal structure of concrete under the action of freeze-thaw, and the size of the concrete interior cube specimen was 40mmÍ40mmÍ40mm. All specimens were taken from samples with the same freeze-thaw damage using a cutting machine.

[0074] The pore structure distribution of the surface layer of the concrete specimens was tested by the MIP mercury injection test. After the freeze-thaw test, the specimens were taken out and cut to meet the test requirements. Combined with Table 6, the pore structure of concrete mainly includes harmless, low-harm, harmful and multi-harm pores, with pore size ranges of <20nm, 20~50nm, 50~200nm and >200nm, respectively.

[0075]

[0076] like Figure 5 As shown in the figure, the total porosity of the samples in the NS, SC, EC and MECC groups were 15.98%, 14.04%, 12.63% and 11.54%, respectively. The overall porosity of the surface coating group decreased, which was due to the physical barrier effect of the three protective agents. However, from the perspective of pore type, the MECC group improved the pore structure of cement concrete more significantly. There were two benign changes in the internal pore distribution of the MECC group specimens: First, the harmful pores with a pore size of more than 50nm and the proportion of pores occupied by harmful pores decreased. Compared with the NS group, EC group and SC group, the number of harmful pores (>50nm) in the MECC samples decreased by 31.69%, 34.47% and 48.02%, respectively. Second, the proportion of low-damage pores with a pore size of 20~50nm increased. Compared with the NS group, EC group and SC group, the number of harmful pores (<50nm) in the MECC group increased by 29.25%, 35.37% and 28.60%, respectively. This shows that under the same number of freeze-thaw cycles, the deterioration trend of the microstructure of the MECC group was significantly prevented, the overall porosity was lower, and there were more harmless and low-damage pores inside that were beneficial to the improvement of antifreeze performance, and the surface structure was less damaged. If the antifreeze test is continued, the freeze-thaw life of the MECC group concrete will be longer than that of the other three groups. In contrast, the proportion of pores with more damage pores (>200nm) in the EC and SC groups is lower than that in the NS group, and the distribution of the remaining pores is close to that of the NS group. It can be considered that after 200 freeze-thaw cycles, the surface physical barriers of the SC and EC groups are almost consumed, and their microstructures are degraded, so unevenly distributed pores and cracks have appeared on the surface. The internal structure of the specimens treated with MECC is more compact, and the protective layer does not completely disappear under the same freeze-thaw cycle. Therefore, from the appearance, the specimens of the MECC group are only partially damaged after being eroded in some areas, while other areas are not damaged.

[0077] The internal damage of each specimen was further determined by CT tomography, and the pore structure characteristics are shown in Table 7. After 120 days of salt erosion and 200 freeze-thaw cycles, the overall porosity of the internal structure of the NS, SC, EC, and MECC specimens was 4.60%, 4.01%, 3.32%, and 3.00%, respectively, and the overall density of the internal structure was more intuitively presented in Figure 6 middle.

[0078]

[0079] The three-dimensional reconstructed images of the internal structure of each group of specimens are shown in Figure 2. Figure 6As shown in the figure, consistent with the MIP test results, the internal freeze-thaw damage of the surface coating group is smaller, and the treatment effect of the MECC group is the best. The data of the CT scan test were further divided into large pores (≥1.0mm 3 )、Medium hole(0.1-1.0mm 3 ) and small holes (<0.1mm 3 ). Among them, the proportion of small pores in the four groups of samples is close, which are 95.05%, 95.48%, 95.95%, and 95.5% respectively. The proportion of mesopores in the four groups of samples is too low, and the total number is small. Based on the simple calculation of pore volume = number of pores × average volume, it can be seen that the total volume of mesopores in the four groups of samples is not much different, which are 644.88mm 3 、492.564mm 3 、512.63mm 3 and 604.31mm 3 . Therefore, it is believed that mesopores and small pores are not the cause of the differences in density and porosity of the specimens. The greater the freeze-thaw damage inside the structure, the greater the number and proportion of macropores. The macropores in the structure were observed to have a ratio of 16.55%, 16.8%, 12.14%, and 10.05%, respectively, which is in good agreement with the overall porosity test results, and this is also the main reason for the difference in average pore volume. The proportion of macropores in the MECC group was 39.27%, 40.17%, and 17.21% lower than that in the other three groups, respectively. The total pore volume was approximately half of that in the NS group and the SC group, and 6.56% lower than that in the EC group. The data from MIP and CT scans reflect the degree of damage inside the four groups of samples to a certain extent. Combined with the data results of the salt freezing resistance test, it shows that the internal damage of the MECC group is the smallest and the freeze-thaw durability is improved.

[0080] The experiment tested the pore structure characteristic parameters of the samples in four control groups (NS, EC, SC, MECC) after freeze-thaw. The experimental results show that after the concrete was modified by MECC, the freeze-thaw damage degree of cement concrete was consistent with the reasoning, the pore distribution characteristics of its surface and internal structure were optimal, the proportion of harmless pores less than 50nm on the surface was the highest, and the porosity of the internal structure was only 56.18% of that in the control group. This shows that the MECC group specimens can experience longer freeze-thaw cycles under the condition of meeting the same damage standards, and obtain smaller mass loss and dynamic modulus loss inside the structure under the freeze-thaw cycle involving deicing salt, showing better durability.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A durable modified epoxy resin composite coating, characterized in that: Comprising component A and component B; The component A comprises the following components in parts by mass: 100 parts of epoxy resin, 15 parts of mica, 20 parts of glass flakes, 10 parts of mica iron oxide, 5 parts of zinc phosphate, 3 parts of penetrant, and 10 parts of solvent; The component B comprises the following components in parts by mass: 20 parts of doped polyaniline, 100 parts of N-methylpyrrolidone, and 30 parts of modified amine curing agent.

2. The durable modified epoxy resin composite coating according to claim 1, characterized in that: The modified curing agent is diethyltoluenediamine with an effective component content greater than 90%.

3. The durable modified epoxy resin composite coating according to claim 1, characterized in that: The penetrant is nonylphenol polyoxyethylene (12) ether phosphate monoester.

4. The durable modified epoxy resin composite coating according to claim 1, characterized in that: The solvent is dimethyl carbonate solvent.

5. The durable modified epoxy resin composite coating according to claim 1, characterized in that: The measured viscosity of the epoxy resin at 25° C. is 11000-13000 mPa·s.

6. A method for preparing a durable modified epoxy resin composite coating as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: The raw materials in the component A are mixed uniformly at 20-50° C. to obtain agent A; The raw materials in the component B are mixed evenly to obtain agent B; The agent A is mixed with the agent B to obtain the durable modified epoxy resin composite coating.

7. The preparation method according to claim 6, characterized in that: The mass ratio of the A agent to the B agent is 2.5-3.5:

1.

8. Use of the durable modified epoxy resin composite coating according to claim 1 as a concrete surface protective agent.

9. The use according to claim 8, characterized in that: The composite coating is applied under the conditions of a temperature of 25±5° C. and a relative humidity of 65±10%.

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