Composite coating applied to corrosion prevention of sewage pipeline and preparation method

Abstract

The invention belongs to the technical field of concrete, and particularly discloses an anti-corrosion composite coating material applied to a sewage concrete pipeline. The invention relates to a water-aluminum-sludge-ash-containing cement mortar, which is prepared from the following raw materials in percentage by weight: 11.3 to 12 percent of water, 0.12 to 0.5 percent of nano SiO2, 0.5 to 0.6 percent of water-aluminum-sludge ash and 83 to 83.5 percent of Portland cement. The invention also discloses a preparation method of the concrete pipeline anticorrosive coating material. The preparation method comprises the following steps: (1) weighing the raw materials according to the weight ratio; (2) uniformly mixing the water supply sludge ash and nano SiO2, and dissolving in water; and (3) pouring the cement and the sand into the prepared mixed solution, slowly stirring for 1 minute, and quickly stirring for 1-2 minutes after uniformly stirring, so as to obtain the pipeline anti-corrosion coating material. And (4) coating a common concrete test block with the prepared anti-corrosion coating material for the sewage pipeline, wherein the thickness is 4mm. The invention has the advantages of energy conservation, environmental protection and excellent corrosion resistance, can effectively solve the problem of service life shortening caused by chemical corrosion and microbial corrosion of the municipal sewage pipeline, obviously prolongs the service life of the pipeline, and has important practical application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a composite coating material for anti-corrosion of sewage concrete pipes and a preparation method thereof. Background Art

[0002] Urban underground sewage pipes are crucial for public health. With the growth of the population and the advancement of urbanization, their scale is constantly expanding. Concrete has become the main material for pipe construction due to its low cost and long service life. However, concrete is vulnerable to the erosion of harmful substances such as chloride ions, moisture, carbon dioxide, and sulfates in a sewage environment, resulting in the peeling off of the surface mortar of the pipe, pipe cracking, and steel bar corrosion, shortening the service life and even causing environmental and safety problems. Therefore, it is of great significance to develop high-performance anti-corrosion coating materials to extend the pipe life and ensure safe operation. Summary of the Invention

[0003] (1) Technical Problems to be Solved

[0004] Aiming at the deficiencies of the prior art, the present invention provides an anti-corrosion coating material and a preparation method for sewage concrete pipes, which solve the problems that sewage concrete pipes are vulnerable to the erosion of harmful substances such as chloride ions, moisture, carbon dioxide, and sulfates in a closed and humid environment, resulting in the peeling off of the surface mortar of the pipe, pipe cracking, and steel bar corrosion, and shortening the service life.

[0005] Research shows that aluminum elements exhibit significant anti-biological sulfuric acid corrosion performance in concrete modification, and this characteristic has been verified in the application of aluminate cement as an anti-corrosion material. Its anti-corrosion mechanism mainly stems from the aluminum hydroxide colloid (Al(OH)3) generated during the hydration process of aluminate, which can effectively inhibit the proliferation of microorganisms and has excellent resistance to sewage chemical corrosion. Therefore, aluminate cement anti-corrosion mortar is regarded as an effective technical solution to alleviate corrosion problems in sewage pipe networks. However, its large-scale application is restricted by the difficulty in controlling preparation process parameters and high production costs, which restricts the engineering promotion of this technology.

[0006] DWTS (drinking water treatment sludge) is a high-aluminum material. During the drinking water treatment process, to meet water quality standards, water plants usually add coagulants such as Al2(SO4) and polyaluminum chloride to destroy the colloidal stability, promote the interaction between particles to form aggregates, and then remove suspended solids and colloidal substances in raw water through precipitation and filtration processes. During this process, the coagulant combines with suspended solids, colloids, organic matter, and microorganisms in raw water to form DWTS with a high aluminum content. Its main components are alumina and silica, similar to clay components, and it can be classified as N-type natural pozzolan. Therefore, it can be considered to use solid waste materials to replace part of the Portland cement to improve the anti-corrosion performance of the material.

[0007] The present invention prepares a nano-SiO₂ modified cement-based composite coating material by partially replacing portland cement with pretreated water supply aluminum sludge and nano-SiO₂. This technology not only realizes the resource utilization of water supply aluminum sludge but also reduces the consumption of portland cement, thereby reducing carbon emissions. In addition, this composite coating material can significantly improve the corrosion resistance of municipal sewage pipes and thus extend their service life. On the basis of ensuring that the content of water supply aluminum sludge ash is at least required to produce an anti-corrosion effect, the present invention introduces nano-SiO₂ into the aluminum sludge ash modified concrete coating material to further improve the anti-corrosion performance of the composite coating of aluminum sludge ash and portland cement. Therefore, it is necessary to scientifically and reasonably calculate the ratio of water supply aluminum sludge ash, nano-SiO₂, and portland cement to achieve the best economic benefits.

[0008] (II) Technical Solution

[0009] The present invention provides an anti-corrosion composite coating material for concrete sewage pipes, aiming to realize the resource utilization of sludge, significantly extend the service life of municipal sewage pipes, and have both environmental benefits and practical value.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is:

[0011] An anti-corrosion composite coating material for concrete pipes, characterized in that it is made of the following raw materials by weight percentage: water 11.3% - 12%, nano-SiO₂ 0.12% - 0.5%, water supply aluminum sludge ash 0.5 - 0.6%, portland cement 83% - 83.5%. The anti-corrosion coating material is a nano-SiO₂-modified aluminum sludge ash composite coating material, containing highly polymerized C-A-H and C-A-S-H gels of Ca 24 Al 22.79 O 96 H 76.8 、CaAl₂Si₂O₈·H₂O, Mg₆Al₂(OH) 16 CO₃·4H₂O.

[0012] Further, the preferred weight percentages of each raw material are: water 11.3%, nano-SiO₂ 0.37%, water supply aluminum sludge ash 5.0%, portland cement 83%.

[0013] Further, the water is tap water, the water supply aluminum sludge ash is obtained by mechanical dehydration and pretreatment of the chemical flocculation sludge in the sedimentation tank of the municipal water supply company, the average particle size of the nano-SiO₂ is 10 nm, and the portland cement is of commercial grade.

[0014] Further, the pretreatment process of the feedwater sludge ash includes drying at 105°C for 24 hours, crushing with a crusher, screening through a 200-mesh sieve, and calcining at 800°C. The main crystal phases in the aluminum-containing sludge after drying at 105°C are quartz, albite, microcline, muscovite, and kaolinite. After calcination activation at 800°C, muscovite dehydrates and dehydroxylates at 800°C, decomposes into Al2O3 and SiO2, and the diffraction peaks disappear; the diffraction peaks of quartz crystals shift, indicating that there is a large amount of amorphous silica in the sludge particles, and the six-coordinate (Al VI ) transforms into the four-coordinate (Al IV ) state. The crystal structure in the sludge is destroyed and transformed into γ-Al2O3 and amorphous SiO2 (Q4). High-temperature calcination greatly reduces the influence of organic matter on the cement hydration process and already has better reactivity of aluminum-phase substances. Coupled with the pozzolanic effect and small-size effect of nano-SiO2, the performance of the aluminum sludge ash coating material can be better improved.

[0015] Further, the grade of the Portland cement is 425.

[0016] Further, the average particle size of the nano-SiO2 is 10 nm.

[0017] Further, the thickness of the anti-corrosion coating is 4 mm.

[0018] Another aspect of the present invention is to provide a preparation method of a composite coating applied to the anti-corrosion of sewage pipes, which is characterized by including the following steps:

[0019] S1. Weigh each raw material according to the following weight ratio,

[0020] Water 11.3% - 12%, nano-SiO2 0.12% - 0.5%, feedwater aluminum sludge ash 0.5 - 0.6%, Portland cement 83% - 83.5%.

[0021] S2. Mix the feedwater sludge ash and nano-SiO2 evenly and dissolve them in water;

[0022] S3. Pour the cement and sand into the mixture synthesized in step S3, and stir slowly for one minute. After stirring evenly, stir quickly for 1 - 2 minutes to obtain the sewage pipe anti-corrosion composite coating material through hydration;

[0023] S4. Coat the prepared sewage pipe anti-corrosion composite coating material on ordinary concrete test blocks with a thickness of 4 mm.

[0024] The hydration process of the anticorrosive composite coating material is as follows: First, the incorporation of 20% aluminum sludge ash provides nucleation sites for the precipitation of early cement hydration products, promoting early hydration and facilitating the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) gels. In addition, the incorporation of nano-SiO2 provides free silicon phase, promoting the consumption of C3S and C2S throughout the hydration process, increasing the Si / Ca ratio, further promoting the formation of C-S-H gels with low Ca / Si ratio and more C-A-S-H, making the average chain length of C-S-H longer and the crystallinity higher, which is beneficial to improving the densification and corrosion resistance of the material. Moreover, the addition of nano-SiO2 gradually reduces the pore size of the cement paste, refines the pore size of the cement-based composite material, and improves the physical filling effect.

[0025] The hydration reaction process during the preparation of the coating material is shown in Equations 1-5.

[0026] C3S + OH - → C-S-H + Ca(OH)2 Equation 1

[0027] DWTS + OH - → [AlO4] 5- + [SiO4] 4- Equation 2

[0028] nSiO2 + H2O → H2SiO4 2- Equation 3

[0029] [AlO4] 5- + [SiO4] 4- + Ca 2+ → C-A-S-H Equation 4

[0030] [AlO4] 5- + Ca 2+ + H2O → C-A-H Equation 5

[0031] (III) Beneficial effects

[0032] (1) The microstructure of the coating material of the present invention is more compact, mainly because a certain amount of nano-SiO2 and water supply aluminum sludge ash are added during the preparation process. The incorporation of nano-SiO2 promotes the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) gel with a low Ca / Si ratio, and due to its small size effect, it fills the capillary pores, effectively blocking the further penetration of the acid solution, so that the surface of the coating maintains a high pH and inhibits the growth and reproduction of acidophilic sulfur oxidizing bacteria. As time goes by, a dense gypsum corrosion layer is formed on the surface of the coating, which effectively blocks the further penetration of the acid solution and reduces the generation of corrosion products. In addition, by using water supply aluminum sludge ash as a supplementary gelling material, more aluminum phase substances are introduced. When the dense gypsum corrosion layer barrier fails, these aluminum ions will be released and penetrate into the surface biofilm. Over time, these aluminum ions accumulate and have the ability to inhibit the acid production of sulfur oxidizing bacteria. Therefore, this coating material not only prolongs the formation time of the biofilm inside the sewage pipe, but also inhibits the growth of bacteria with corrosive effects, thereby significantly extending the service life of the pipe.

[0033] (2) The present invention prepares the coating material by replacing part of the cement with aluminum sludge from water supply and nano-SiO2, without introducing heavy metal ions, which will not affect the subsequent sewage treatment process, is basically pollution-free to the environment, and has significant environmental advantages.

[0034] (3) The present invention uses water supply aluminum sludge as raw material, which not only reduces the pressure of sludge treatment on the water supply plant, but also realizes the resource utilization of sludge.

[0035] (4) The raw materials of the present invention are widely available and can be obtained locally; the preparation process is simple and suitable for industrial production; at the same time, it has excellent stability and corrosion resistance, broad market prospects, and significant application and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of each component of the present invention;

[0037] Figure 2 It is a schematic diagram of the coating application effect of the present invention.

[0038] Figure 3 1 and 2 are XRD diffraction images of the coating material of the present invention after curing for 7 days and 28 days.

[0039] Figure 4 This is a thermogravimetric curve of the coating material of the present invention after curing for 28 days.

[0040] Figure 5 This is a pore size distribution diagram of the coating material of the present invention after 28 days of curing.

[0041] Figure 6It is the surface pH change diagram during the acid corrosion process of the coating of the present invention.

[0042] Figure 7 It is the mass loss diagram during the acid corrosion process of the coating of the present invention.

[0043] Figure 8 It is the corrosion depth diagram during the acid corrosion process of the coating of the present invention.

[0044] Figure 9 It is the change diagram of calcium ion concentration in the acid solution during the acid corrosion process of the coating of the present invention.

[0045] In the figure: 1 - Feed water sludge ash; 2 - Portland cement; 3 - Nano-SiO₂; a - Sewage concrete pipe; b - Coating material. Detailed implementation manners

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0047] Please refer to Figures 1-9 , an anti-corrosion composite coating material applied to concrete pipes, is made of raw materials with the following weight percentages: water 11.3% - 12%, nano-SiO₂ 0.12% - 0.5%, feed water aluminum sludge ash 0.5 - 0.6%, Portland cement 83% - 83.5%.

[0048] In the present invention, the water is tap water, which is convenient to obtain and has low cost. Tap water can adjust the workability and stability of the mixture.

[0049] The feed water aluminum sludge is taken from Qujiang Water Plant in Xi'an and is the surplus sludge generated after the coagulation treatment in the water plant. After pretreatment steps such as centrifugal dehydration, drying at 105 °C, crushing, sieving through 200 meshes, calcination at 800 °C, and grinding by a ball mill, the feed water aluminum sludge ash (DWTS) with certain pozzolanic activity is finally obtained.

[0050] The main components of the feed water sludge ash are SiO₂ and Al₂O₃, which have certain pozzolanic activity and can be used as supplementary cementitious materials for Portland cement. The main components are shown in Table 1.

[0051] Table 1 XRF composition table of feed water aluminum sludge ash

[0052]

[0053] The nano-Silica dioxide is produced by Jinan Zhongye New Materials Co., Ltd. The nano-Silica dioxide is an amorphous white powder with an average particle size of 10 nm.

[0054] The present invention will be described in detail below through examples.

[0055] Example

[0056] The weight percentages of the components of the anticorrosive composite coating material for concrete pipes in Examples 1 and 2 are shown in Table 2.

[0057] Table 2 Weight percentages of the components of the anticorrosive composite coating material for concrete pipes

[0058]

[0059]

[0060] The preparation method of the anticorrosive composite coating material for concrete pipes described in Examples 1 and 2 includes the following steps:

[0061] (1) Weigh tap water, nano-Silica dioxide, water supply aluminum sludge ash, and Portland cement according to the weight ratios of the above components and set aside.

[0062] (2) Put the water supply aluminum sludge ash and nano-Silica dioxide into a mixing bucket for dry mixing. Manual assistance can be added during mixing to ensure uniform mixing of the dry materials.

[0063] (3) Dissolve the water supply sludge ash and nano-Silica dioxide in water. Ultrasonic assistance can be used for dissolution and dispersion to ensure complete dissolution.

[0064] (4) Pour the cement and sand into the prepared mixed solution and stir slowly for one minute. After stirring evenly, stir quickly for 1 - 2 minutes to obtain the pipeline anticorrosive coating material.

[0065] (5) Coat the prepared sewage pipeline anticorrosive coating material on ordinary concrete test blocks with a thickness of 4 mm.

[0066] Cover the coating materials prepared in Examples 1 and 2 on the surface of sewage concrete pipe a, put it into a curing box and keep it at T = 20°C ± 5°C, RH ≥ 95% for 28 days to obtain the anticorrosive coating b.

[0067] Put the cured coating material into a sulfuric acid solution for soaking. Use concentrated sulfuric acid with a mass fraction of 98% and add sulfuric acid at 1% of the solvent mass (that is, add 1 g of concentrated sulfuric acid to 100 g of water) to prepare the acid corrosion solution. The ratio of the solution volume to the test block volume is 10:1 for the soaking experiment. Simultaneously soak the test blocks of the coating with only 20% aluminum sludge ash and the coating with the compound addition of nano-Silica dioxide for 90 days, and the measured mass loss rates are shown in Table 3.

[0068] Table 3 Mass loss rate (%) of concrete pipes and coating materials after 90 days of corrosion

[0069]

[0070] As can be seen from Table 3, Figure 7 it can be seen that the mass loss rate of Coating Material Example 2 at 90 days is lower than that of Example 1 without added nano-SiO2, and the difference in mass loss rate is significant (up to 1.82%). This indicates that this coating material can significantly improve the chemical corrosion resistance of the coating.

[0071] Figure 3 and Figure 4 and Figure 5 it can be seen that in the coating material of Coating Material Example 2 doped with nano-SiO2, the hydration products increase, the diffraction peak of Ca(OH)2 is observed to decrease, and the diffraction peak of gypsum in the hydration products disappears, indicating that the generated Ca(OH)2 re-participates in the dissolution of aluminum sludge ash and the hydration reaction of nano-SiO2 and aluminum sludge ash, resulting in more calcium ions reacting to form more C-S-H and C-A-S-H existing in the coating material. Moreover, the addition of nano-SiO2 in Example 2 gradually reduces the pore size of the cement paste, refines the pore size of the cement-based composite material, and improves the physical filling effect.

[0072] Figure 6 Figure shows the change curve of the surface pH of the specimens of the coating with only 20% aluminum sludge ash and the coating with nano-SiO2 doped repeatedly after being soaked for 90 days. When the pH drops to 7, the environment on the surface of the specimen is suitable for the survival of mesophilic bacteria. At this time, the corrosion of the specimen also changes from chemical sulfur oxidation to biological sulfur oxidation, which dominates and further enhances the corrosion effect of the specimen. It can be seen from the figure that the surface pH of Example 2 is higher than that of Example 1, and it can still remain at about 4 after 90 days of corrosion, while the surface pH of Example 1 is about 3.8. The specimens of the coating with nano-SiO2 doped repeatedly can effectively slow down the microbial corrosion situation.

[0073] Figure 9The calcium ion concentration changes in the corrosion solution after 90 days of corrosion are shown respectively. It can be seen from the figure that for the ordinary concrete sewage pipe specimens, as the corrosion time prolongs, the sulfuric acid solution continuously erodes the C-S-H gel and AFt crystals on the surface of the specimens, and the calcium ion concentration continuously increases. However, during the corrosion process of the specimens coated with Example 2, the overall precipitation amount of calcium ions is less than that of the specimens coated only with 20% aluminum sludge ash. The calcium ion concentration remains at about 411.65 mg / L at 45 days. The main reason is that nano-SiO2 fills the tiny pores in the cement matrix, reducing the porosity and permeability of the coating, decreasing the penetration of the acid solution into the coating interior, and delaying the dissolution of calcium ions. Meanwhile, the dense gypsum corrosion layer formed on the coating surface during the corrosion process further blocks the penetration of the acid solution, reducing the contact between the acid and the internal calcium hydroxide (Ca(OH)2), and slowing down the dissolution rate of calcium ions.

[0074] The present invention mainly has the following characteristics in terms of service performance: (1) Improving the corrosion resistance and service life of concrete pipes in municipal sewage pipe networks. The microstructure of this anti-corrosion coating material is denser. The synergistic effect of nano-SiO2 and aluminum sludge promotes the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) gels with a low Ca / Si ratio, filling the capillary pores, making the microstructure of the cement-based coating denser, reducing the leaching of calcium ions and the intrusion of sulfuric acid, and being able to maintain a relatively high pH value to inhibit the growth and reproduction of acidophilic sulfur-oxidizing bacteria, thus slowing down the corrosion process of concrete pipes and extending the service life of sewage pipes. (2) Realizing the resource utilization of water supply sludge. This anti-corrosion coating material innovatively uses the surplus sludge from municipal water treatment plants as a supplementary cementitious material, not only solving the problems of large output, high water content, and high treatment cost of water supply sludge (DWTS), but also avoiding the harm to the environment caused by improper disposal, realizing the resource utilization of sludge, and effectively reducing the treatment pressure of water treatment plants. (3) Having no toxic effects. This material is non-toxic. The main components of water supply sludge are alumina and silica, without heavy metal ions, and no toxic and harmful substances will be precipitated after corrosion, having no impact on the subsequent sewage treatment process and being environmentally friendly. Nano-silica is also non-toxic and will not have a negative impact on sewage treatment. (4) Not being restricted by region. With the advancement of urbanization, large water treatment plants are generally set up in each prefecture-level city, and most of them use PAC as a coagulant, making the sludge raw material sources extensive and the output sufficient, which can be obtained locally, and the market prospect is broad.

[0075] The present invention uses water supply sludge ash and nano-SiO2 as supplementary cementitious materials. Compared with traditional concrete materials, it has the advantages of being green and environmentally friendly, having low cost, and significantly improved stability and corrosion resistance. At the same time, its raw material components are simple, the process is simple, and it is convenient for construction, having a wide application prospect.

[0076] The present invention is not restricted by regions, has a broad market prospect and is suitable for large-scale production. Besides being used in municipal sewage pipes, it can also be applied to the concrete structures of sewage treatment plants and other acid-resistant corrosion sites, significantly prolonging the service life of materials or equipment and having extensive application potential.

[0077] Certainly, the above description is not a limitation to the present invention, and the present invention is not limited to the above examples either. Changes, modifications, additions or substitutions made by those skilled in the art within the essence of the present invention shall also fall within the protection scope of the present invention.

[0078] It should be noted that in this text, terms such as "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without more limitations, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0079] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An anti-corrosion composite coating material applied to sewage concrete pipes, characterized in that, It is made from raw materials with the following weight percentages: water 11.3% - 12%, nano-SiO₂ 0.12% - 0.5%, feedwater aluminum sludge ash 0.5 - 0.6%, portland cement 83% - 83.5%.

2. The anti-corrosion composite coating material applied to sewage concrete pipes according to claim 1, characterized in that: The anti-corrosion coating material described contains Ca 24 Al 22.79 O 96 H 76.8 , CaAl2Si2O8·H2O, Mg6Al2(OH) 16 CO3·4H2O high-polymerization-degree C-A-H and C-A-S-H gels.

3. The anti-corrosion composite coating material applied to concrete pipes according to claim 1 or 2, characterized in that It is made from raw materials with the following weight percentages: water 11.3% - 12%, nano-SiO₂ 0.12% - 0.5%, feedwater aluminum sludge ash 0.5 - 0.6%, portland cement 83% - 83.5%.

4. The anti-corrosion composite coating material applied to concrete pipes according to claim 3, characterized in that: The water is tap water. The feedwater aluminum sludge ash is obtained by mechanically dewatering, drying and pre-treating the chemical flocculation sludge in the sedimentation tank of the municipal tap water company. The nano-SiO₂ is amorphous white powder with an average particle size of 10 nm.

5. The anticorrosive coating material applied to concrete pipes according to claim 4, characterized in that: The pre-treatment procedure of the feedwater sludge ash includes drying at 105 °C for 24 hours, crushing with a crusher, passing through a 200-mesh sieve, and calcining at 800 °C to obtain the aluminum sludge ash.

6. The anti-corrosion composite coating material applied to concrete pipes according to claim 5, characterized in that: The grade of the portland cement is 425.

7. The anticorrosive composite coating material applied to concrete pipes according to claim 6, characterized in that: The thickness of the anti-corrosion composite coating material is 4 mm.

8. A composite coating material for sewage pipeline anti-corrosion, comprising the following steps: S1. Weigh each raw material according to the following weight ratio, water 11.3% - 12%, nano-SiO₂ 0.12% - 0.5%, feedwater aluminum sludge ash 0.5 - 0.6%, portland cement 83% - 83.5%; S2. Mix the feedwater sludge ash and nano-SiO₂ evenly and dissolve them in water; S3. Pour the cement and sand into the mixture synthesized in step S3, and stir slowly for one minute. After stirring evenly, stir quickly for 1 - 2 minutes to hydrate and obtain the pipeline anti-corrosion coating material. S4. Coat the prepared sewage pipeline anti-corrosion coating material on a common concrete test block with a thickness of 4 mm.

9. The preparation method of a composite coating material applied to the anti-corrosion of sewage pipelines according to claim 8, characterized in that, The hydration process is as follows: First, the incorporation of the aluminum sludge ash provides nucleation sites for the precipitation of early cement hydration products, which promotes the early hydration and the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) gels. In addition, the incorporation of nano-SiO₂ provides free silicon phase, promotes the consumption of C3S and C2S in the whole hydration process, increases the Si / Ca ratio, promotes the formation of C-S-H gels with low Ca / Si ratio and more C-A-S-H. The decrease of the Ca / Si ratio and Al / Si ratio of the material promotes the increase of the average chain length of C-S-H and the improvement of crystallinity, which is beneficial to the improvement of the material's compactness and corrosion resistance. And the addition of nano-SiO₂ gradually reduces the pore size of the cement paste, refines the pore size of the cement-based composite material, and improves the physical filling effect.

10. The preparation method of a composite coating material applied to the anti-corrosion of sewage pipelines according to claim 9, characterized in that, The chemical equation of the hydration reaction process during the preparation of the coating material is: C3S + OH - → C-S-H + Ca(OH)2 Equation 1; DWTS+OH - →[AlO4] 5- +[SiO4] 4- Formula 2; nSiO2 + H2O → H2SiO4 2- Formula 3; [AlO4] 5- + [SiO4] 4- + Ca 2+ → C-A-S-H type 4; [AlO4] 5- +Ca 2+ +H2O → C-A-H Equation 5.

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