A corrosion-resistant coating material for concrete pipes and its preparation method

Abstract

This invention belongs to the field of concrete technology, specifically disclosing an anti-corrosion coating material for concrete pipelines. It is made from the following raw materials in weight percentages: water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, and silicate cement 75.0%~77.5%. This invention also discloses a method for preparing the anti-corrosion coating material for concrete pipelines, including the following steps: (1) weighing each raw material according to the weight ratio; (2) mixing the dry calcium nitrite and silicate cement evenly; (3) slowly pouring in the aqueous solution and stirring slowly, then stirring rapidly for 1 minute after even mixing to obtain the pipeline anti-corrosion coating material. This invention has economic and environmental advantages, and the coating also possesses outstanding anti-corrosion performance, solving the problem of concrete durability degradation caused by internal chemical corrosion and microbial corrosion in municipal sewage pipelines, and effectively extending the service life of pipelines.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to an anti-corrosion coating material and its preparation method for concrete pipes. Background Technology

[0002] In complex wastewater environments, concrete drainage pipes face the dual challenges of chemical ion erosion and microbial corrosion. Microbial corrosion, in particular, is highly insidious, develops rapidly, and is extremely destructive, making it a primary cause of premature pipe failure. It often results in pipes designed for a 75-100 year lifespan serving less than 20 years, leading to water pollution, road collapses, and exorbitant maintenance costs. The inner wall of concrete pipes, as the corrosion frontier, is constantly subjected to alternating wet and dry conditions coupled with high humidity and oxygen levels. The porous and highly alkaline interface further exacerbates the penetration and dissolution processes of corrosive media. Therefore, research into long-term prevention and control technologies for microbial corrosion in concrete pipes is a crucial and pressing practical issue in the field of municipal infrastructure. Summary of the Invention

[0003] Technical problems to be solved The purpose of this invention is to address the shortcomings of existing concrete pipeline corrosion protection technologies in inhibiting microbial erosion in enclosed and humid environments, by providing an anti-corrosion coating material and its preparation method. This method aims to effectively curb the chain reaction of deterioration caused by microbial growth, such as mortar layer peeling off the inner wall of the pipeline, structural cracking, and steel reinforcement corrosion, thereby significantly extending the service life of pipelines in harsh wastewater environments and bridging the significant gap between actual service life and design reference period.

[0004] However, existing research on pipeline corrosion prevention mainly focuses on enhancing the performance of single materials or improving their antibacterial effects, and has not yet conducted systematic research on the organic synergy between material modification and antibacterial effects. Nitrites have material-strengthening properties, nitrites possess extremely strong antibacterial activity, and nitrites can combine with H+ under acidic conditions. + Nitric acid is generated. Based on this, it can be inferred that calcium nitrite concrete coatings possess both material strengthening and antibacterial potential in acidic environments with wastewater corrosion. The raw materials for calcium nitrite preparation, calcium chloride and sodium nitrite, can be obtained from the recovery of waste liquid from soda ash plants and as byproducts of nitric acid tail gas treatment, respectively. These sources are widely available, the process is simple, and the production process generates no waste, thus possessing both environmental and economic advantages related to resource reuse. Therefore, replacing part of silicate cement with calcium nitrite can be considered to improve the corrosion resistance of the material.

[0005] This invention uses calcium nitrite as a partial substitute component for silicate cement to prepare composite coating materials. This technical solution, while ensuring the coating's service performance, not only significantly extends the effective service life of the coating through a synergistic mechanism of material strengthening and antibacterial effects, but also reduces carbon emissions and resource consumption by decreasing the amount of cement clinker used. Furthermore, leveraging the cost advantages of widely available nitrite and simple processing, it comprehensively considers improved durability, environmental benefits, and engineering economics.

[0006] (II) Technical Solution The anti-corrosion coating material for concrete pipes provided by this invention significantly extends the service life of municipal sewage pipes while effectively reducing the operation, maintenance and replacement costs throughout the pipe's life cycle, thus achieving cost reduction and efficiency improvement in sewage pipe network management.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A corrosion-resistant coating material for concrete pipes is characterized by being made from the following raw materials in weight percentages: water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, and silicate cement 75.0%~77.5%. The corrosion-resistant coating material contains Ca3Si2O. 10 H6, Ca3SiAlO9H7, Ca4Al2(NO2)2O 10 H 12 Highly polymerized CSH and CASH gels.

[0008] Furthermore, the preferred weight percentages of each raw material are: water 22.5%, calcium nitrite 1.0%, and silicate cement 76.5%.

[0009] Furthermore, the water is tap water, the calcium nitrite is commercially available grade, and the silicate cement is commercially available grade.

[0010] Furthermore, the silicate cement grade was 425, and the main diffraction peaks detected in the cement particles were calcium sulfate dihydrate, tricalcium silicate, and dicalcium silicate.

[0011] Furthermore, the calcium nitrite is of analytical grade, with a purity of not less than 92%.

[0012] Another aspect of the present invention is to provide a method for preparing an anti-corrosion coating material for concrete pipes, characterized by comprising the following steps: S1. Weigh each raw material according to the following weight ratio. Water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, silicate cement 75.0%~77.5% S2. Mix the calcium nitrite powder and silicate cement dry materials evenly; S3. Slowly pour the aqueous solution into the mixture synthesized in step S2 and stir slowly for one minute. After stirring evenly, stir quickly for one minute to obtain the anti-corrosion coating material for the pipeline.

[0013] The hydration process of the anti-corrosion coating is as follows: calcium nitrite dissolves in the mixing water and then dissociates to release Ca. 2+ With NO2 - NO2 - Complexing the active sites on the mineral surface of cement clinker breaks the passivation film and induces the activation of cement particles, promoting the dissolution of active SiO2 and Al2O3 components in the clinker; the dissolved active SiO2 and Al2O3 react with free Ca... 2+ The water molecules undergo a hydration reaction to generate CSH, CAH, and CASH gel phases. As the gel phases accumulate, their degree of polymerization increases, forming a dense and hardened matrix, which improves the density and corrosion resistance of concrete. The hydration reaction process during the preparation of the coating material is shown in Equations 1-4.

[0014] (III) Beneficial Effects (1) By incorporating an appropriate amount of calcium nitrite, this invention can precisely control the hydration process of cementitious materials, promote the full hydration reaction of silicate minerals, and drive the orderly and abundant generation of stable hydration products such as calcium hydroxide and hydrated calcium silicate gel, significantly improving the density of the microstructure and the interfacial bonding strength of the coating matrix. This dense structure can effectively block the penetration of external corrosive media into the concrete interior, reduce the intrusion and migration of corrosive ions, and thus greatly enhance the coating's resistance to microbial erosion. This coating can significantly extend the service life of concrete pipelines in sewage environments, greatly reduce the frequency of maintenance and replacement throughout the pipeline's life cycle, thereby reducing the resource waste and environmental impact caused by road excavation, traffic disruption, and reconstruction construction due to pipeline failure.

[0015] (2) This invention utilizes the antibacterial activity of calcium nitrite to significantly improve the inactivation efficiency of the coating against corrosion-related microorganisms, and reshapes the microbial community structure of the sewage environment by targeting and regulating the metabolic pathways and population proportions of erosive bacteria such as sulfate-reducing bacteria and methanogenic archaea, so that it evolves in a direction unfavorable to concrete corrosion.

[0016] (3) The present invention replaces part of the cement with calcium nitrite to prepare coating material without introducing heavy metal ions, which will not affect the subsequent sewage treatment process and has virtually no pollution to the environment.

[0017] (4) The present invention uses calcium nitrite to partially replace silicate cement to prepare coating materials, which effectively reduces the amount of cement clinker used, thereby reducing energy consumption and carbon dioxide emissions in the material production process, which is in line with the concept of green and low-carbon development and has significant environmental benefits.

[0018] (5) The calcium nitrite component used in this invention can be obtained from industrial by-products. It is widely available and inexpensive. The alternative process is simple and easy to implement. There is no need to add complex production equipment. It effectively controls the raw material cost of coating materials and shows good engineering economy. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the components of the present invention.

[0020] Figure 2 This is a schematic diagram illustrating the coating application effect of the present invention.

[0021] Figure 3 These are XRD diffraction images of the coating material of the present invention after 7 days and 28 days of curing.

[0022] Figure 4 This is the TG / DTG curve of the coating material of the present invention after 28 days of curing.

[0023] Figure 5 This is a graph showing the pH change on the surface of the coating during the microbial corrosion process of the present invention.

[0024] Figure 6 This is a graph showing the change in calcium ion concentration in the acid solution during the chemical corrosion process of the coating of this invention.

[0025] Figure 7 These are the adhesion strength diagrams of the coating material of the present invention after 7 days and 28 days of curing.

[0026] In the diagram: 1-Silicate cement; 2-Calcium nitrite; a-Coating material; b-Sewage concrete pipe. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Please see Figure 1-7 A corrosion-resistant coating material for concrete pipes is made from the following raw materials in weight percentages: water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, and silicate cement 75.0%~77.5%.

[0029] In this invention, the water is tap water, which is readily available and inexpensive. Tap water can also adjust the workability and stability of the mixture.

[0030] The silicate cement 1 used in this invention is a commercially available 42.5 grade ordinary silicate cement. It is a hydraulic cementitious material made by calcining limestone and clay at high temperatures to obtain silicate cement clinker, then adding an appropriate amount of gypsum and 0%~5% of admixtures and grinding them together. Its main mineral composition is tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. Its 28-day standard curing compressive strength is not less than 42.5 MPa. The specific chemical composition of this cement is detailed in Table 1.

[0031] Table 1 Chemical composition of cement Components (%) CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[TiO2]]> MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> <![CDATA[P2O5]]> <![CDATA[SO3]]> Burn vector cement 57.02 19.67 9.78 5.76 0.52 1.68 1.97 1.22 0.34 0.32 0.26 The calcium nitrite 2 used in this invention is a white crystalline powder, easily soluble in water, and chemically stable, provided by Shanghai Aladdin Biochemical Technology Co., Ltd. This material has high purity, good dispersibility, and excellent compatibility with cementitious materials such as silicate cement, and can be directly incorporated into concrete mixing systems. Specific technical indicators are shown in Table 2.

[0032] Table 2 Technical Specifications of Calcium Nitrite Technical indicators <![CDATA[Calcium nitrite (Ca(NO2)2) content]]> 92% <![CDATA[Calcium nitrate (Ca(NO3)2) content]]> 5.5% <![CDATA[Water (H2O)]]> 0.8% Water-insoluble content 0.1% pH value (1% aqueous solution) 8.0~12.0 Density (20℃, liquid) 1.26~1.32 g / cm3 Appearance White to slightly yellow crystalline powder chloride 0.01% sulfates 0.01% Heavy metals (as Pb) 0.001% CAS number 13780-06-8 UN number 2627 The present invention will be described in detail below through examples.

[0033] Example The weight percentages of each component in the anti-corrosion coating material for concrete pipes in Examples 1 and 2 are shown in Table 3.

[0034] Table 3 Weight percentage of each component in the anti-corrosion coating material for concrete pipes Tap water (%) Calcium nitrite (%) Silicate cement (%) Example 1 23 0.5 76.5 Example 2 23 1 76 The preparation method of the anti-corrosion coating material for concrete pipes described in Examples 1 and 2 includes the following steps: (1) Weigh out tap water, calcium nitrite and silicate cement according to the above weight ratios and set aside; (2) Place the dry materials of calcium nitrite and silicate cement into the mixing site for dry mixing. The mixing can be assisted by manual labor to ensure that the dry materials are mixed evenly. (3) Slowly pour in the aqueous solution and stir slowly for one minute. After stirring evenly, stir quickly for one minute to obtain the anti-corrosion coating material for the pipeline.

[0035] The coating materials prepared in Examples 1 and 2 were applied to the surface of the sewage concrete pipe b and placed in a curing chamber at T=20℃ and RH95% for 28 days to obtain the anti-corrosion coating a.

[0036] The chemical corrosion resistance immersion test shall be conducted according to the following steps: (1) Preparation of corrosion solution: Measure deionized water and slowly add concentrated sulfuric acid with a mass fraction of 98% at a ratio of 1% of the solvent mass. Stir well and cool before use. (2) Immersion test: The cured coated specimen and the uncoated blank specimen were immersed in the above corrosion solution at a solution volume to specimen volume ratio of 10:1 and placed on a magnetic stirrer for continuous stirring. The immersion period was 90 days, and the freshly prepared corrosion solution was replaced every 3 days during the period. (3) Performance characterization: After soaking, the specimens were taken out, the loose adhering substances on the surface were removed, and after drying, they were weighed and the mass loss rate was calculated. The results are shown in Table 4.

[0037] Table 4. Mass loss rate (%) of concrete pipes and coating materials after 90 days of chemical corrosion project Example 1 Example 2 Concrete pipes Quality loss rate (%) 15.33 12.23 18.89 Antimicrobial corrosion immersion test: The cured coated specimens and blank specimens were immersed in a continuous flow reactor containing artificially enhanced wastewater at a concentration ten times higher (liquid-to-solid volume ratio 10:1). Fresh enhanced wastewater was continuously injected using a peristaltic pump, while the old liquid was discharged at a constant rate. The hydraulic retention time was controlled at 24 hours, the reactor temperature was maintained at 252 °C, and continuous aeration was provided. After 90 days of continuous operation, the specimens were removed, and the mass loss rate was measured. The results are shown in Table 5.

[0038] Table 5. Mass loss rate (%) of concrete pipes and coating materials after 90 days of microbial corrosion. project Example 1 Example 2 Concrete pipes Quality loss rate (%) 4.69 2.89 7.67 As shown in Tables 4 and 5, compared with the blank test block of ordinary silicate cement, the mass loss rate of the test block protected by the coating is significantly reduced in acid corrosion and microbial corrosion environments, indicating that the coating material described in this invention can effectively improve the acid erosion resistance and microbial corrosion resistance of concrete pipes.

[0039] Table 6. Sterilization rate (%) of concrete pipes and coating materials under microbial corrosion project Example 1 Example 2 Concrete pipes Sterilization rate (%) 13.48 19.06 5.85 As shown in Table 6, compared with the blank test block of ordinary silicate cement, the sterilization rate of the test block protected by the coating is significantly increased in the microbial corrosion environment, indicating that the coating material described in this invention can effectively improve the antibacterial performance of concrete pipes.

[0040] Figure 3 and Figure 4 The figures show the X-ray diffraction patterns of the concrete pipe specimens and the thermogravimetric-differential thermogravimetric analysis curves at 28 days, respectively. As can be seen from the figures, compared to the ordinary concrete blank specimens, the diffraction peak intensities and thermogravimetric characteristics of calcium hydroxide, hydrated calcium silicate gel, and hydrated calcium aluminosilicate in Example 2 are significantly more pronounced, indicating a higher degree of hydration and a richer amount of hydration products, thereby effectively improving the microstructure density of the material matrix.

[0041] Figure 5 The figure shows the surface pH changes of uncoated specimens and coated specimens from each example during immersion in a microbial corrosion reactor for 30–90 days. As can be seen from the figure, the surface pH values ​​of the coated specimens from Examples 1 and 2 were significantly higher than those of the ordinary concrete blank specimens at all ages. In particular, the surface pH value of the specimen from Example 2 remained above 7.5 after 90 days of continuous corrosion immersion. This pH level is higher than the critical threshold for inhibiting the growth and reproduction of sulfur-oxidizing bacteria, indicating that the coating can effectively delay the neutralization process of the concrete surface and weaken the driving conditions for microbial acid-producing corrosion from the source.

[0042] Figure 6 The changes in the concentration of the corrosive solution over 60 days of chemical corrosion show that, with the extension of corrosion time, the sulfuric acid solution continuously erodes the CSH gel and AFt crystals on the surface of the concrete sewage pipe test block, leading to a continuous increase in calcium ion concentration. During the corrosion process, the cumulative calcium ion precipitation in the coated specimen of Example 2 was significantly lower than that in the ordinary concrete blank specimen. The mechanism is as follows: on the one hand, the coating material of Example 2 can promote the full formation of stable hydration products such as calcium hydroxide, CSH gel, and CASH, anchoring calcium ions in the solid phase structure through the chemical bonding and physical sealing effect of crystal or gel lattice, effectively reducing the relative proportion of free calcium ions; on the other hand, the above-mentioned hydration products intertwine and densely fill each other, significantly refining the microporous structure of the coating matrix, and hindering the dissolution and migration of calcium ions into the corrosive medium from the physical transport level.

[0043] Figure 7 The figure shows a comparison of the bond strength between the blank concrete pipe specimen and the coating materials of each embodiment. As can be seen from the figure, the bond strength of the coating material of Example 2 at 7 days and 28 days is significantly higher than that of the ordinary concrete blank specimen, indicating that the coating material of the present invention has superior interfacial bonding performance, which helps to enhance the bonding strength between the coating and the concrete substrate, thereby improving the overall protection effect of the pipeline in corrosive environments.

[0044] The present invention has the following main features in terms of performance: (1) It improves the corrosion resistance of concrete pipes in municipal sewage pipe networks and effectively extends their service life. The coating material itself is strongly alkaline and can continuously release alkaline substances during the corrosion process to neutralize the acidic corrosive medium and maintain a high pH environment on the coating surface, thereby inhibiting the growth and reproduction of acidophilic sulfur oxidizing bacteria; at the same time, the functional components contained in the coating have strong bactericidal activity and can effectively inactivate corrosion-related microorganisms. The above-mentioned alkaline buffering and bacteriostatic and bactericidal dual mechanisms work together to slow down the microbial corrosion process of concrete pipes from the two dimensions of chemical neutralization and biological inhibition, thereby extending the full service life of the pipes. (2) The coating material is prepared by partially replacing silicate cement with calcium nitrite, which effectively reduces the amount of cement clinker used while ensuring the service performance of the coating. The production process of cement clinker requires high-temperature calcination, which consumes a lot of energy and is accompanied by a large amount of carbon dioxide emissions. The present invention directly reduces the energy consumption and carbon footprint of the raw material production process by reducing the amount of cement clinker per cubic meter. In addition, the introduction of calcium nitrite does not require the addition of high-energy-consuming production equipment, which further reduces the overall energy consumption of material preparation. Therefore, the technical solution described in this invention is in line with the concept of green, low-carbon and sustainable development, and has significant environmental benefits while achieving pipeline anti-corrosion function. (3) Compared with functional additives that require complex synthesis processes or rely on high-purity chemical reagents, the calcium nitrite component used in this invention has obvious advantages in cost control. Its raw materials, calcium chloride and sodium nitrite, can be obtained by relying on the recovery of waste liquid from soda ash plants and the by-products of nitric acid tail gas treatment, turning waste into treasure. The raw material source is stable and the price is low. The calcium nitrite production process is mature and simple, with low equipment investment and low operating energy consumption. When it is introduced into the coating system, it can replace part of the cement, without the need to add a complex batching system. Therefore, this invention effectively controls material costs and has good engineering economics and industrialization prospects.

[0045] This invention is not limited by geographical conditions; the availability of raw materials and the construction process are not significantly dependent on geographical location. It has strong market adaptability, broad application prospects, and excellent conditions for large-scale production and industrialization. In addition to being suitable for municipal sewage pipelines, the coating material can also be extended to concrete structures in sewage treatment plants, acid-resistant flooring in industrial plants, anti-corrosion linings in chemical workshops, marine engineering concrete facilities, and other industrial and civil building structures that require long-term resistance to acidic corrosion environments, effectively extending the structural service life and service cycle of the protected facilities.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims. Any equivalent transformations, modifications, additions or subtractions of elements or substitutions of materials made by those skilled in the art within the scope of the technical concept and essential spirit of the present invention should be understood as falling within the scope of protection of the present invention.

[0047] It should be noted that the terms "include," "contain," or any other variations thereof used herein are intended to cover non-exclusive inclusion relationships. Thus, a process, method, article, or apparatus described as comprising a list of elements covers not only the expressly listed elements but also other elements not expressly listed, or elements inherent to the process, method, article, or apparatus. Unless otherwise specified, including a qualified element in a statement does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, various equivalent changes, modifications, element substitutions, or technical variations can be made to the above embodiments without departing from the core principles and spirit of the present invention. The actual scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant coating material for concrete pipes, characterized in that, It is made from the following raw materials by weight percentage: water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, and silicate cement 75.0%~77.5%.

2. The anti-corrosion coating material for concrete pipes according to claim 1, characterized in that: The anti-corrosion coating material contains Ca3Si2O 10 H6, Ca3SiAlO9H7, Ca4Al2(NO2)2O 10 H 12 Highly polymerized CSH and CASH gels.

3. The anti-corrosion coating material for concrete pipes according to claim 1 or 2, characterized in that, It is made from the following raw materials by weight percentage: water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, and silicate cement 75.0%~77.5%.

4. The anti-corrosion coating material for concrete pipes according to claim 3, characterized in that: The water is tap water, the calcium nitrite is commercially available grade, and the silicate cement is commercially available grade.

5. The anti-corrosion coating material for concrete pipes according to claim 4, characterized in that: The grade of silicate cement is 425.

6. The anti-corrosion coating material for concrete pipes according to claim 5, characterized in that: Furthermore, the calcium nitrite is of analytical grade, with a purity of not less than 92%.

7. A method for preparing an anti-corrosion coating material for concrete pipes, characterized in that, Includes the following steps: S1. Weigh each raw material according to the following weight ratio. Water 22.5%~23.0%, calcium nitrite 0.5%~1.5%, silicate cement 75.0%~77.5% S2. Mix the calcium nitrite powder and silicate cement dry materials evenly; S3. Slowly pour the aqueous solution into the mixture synthesized in step S2 and stir slowly for one minute. After stirring evenly, stir quickly for one minute to obtain the anti-corrosion coating material for the pipeline.

8. The method for preparing an anti-corrosion coating material for concrete pipelines according to claim 7, characterized in that, The hydration process is as follows: calcium nitrite dissolves in the mixing water and then dissociates to release Ca. 2+ With NO2 - NO2 - Complexing the active sites on the mineral surface of cement clinker breaks the passivation film and induces the activation of cement particles, promoting the dissolution of active SiO2 and Al2O3 components in the clinker; the dissolved active SiO2 and Al2O3 react with free Ca... 2+ Water molecules undergo hydration reactions to generate CSH, CAH, and CASH gel phases. As the gel phases accumulate, the degree of polymerization of the gel phases increases, forming a dense and hardened matrix, which improves the density and corrosion resistance of concrete.

9. The method for preparing an anti-corrosion coating material for concrete pipelines according to claim 8, characterized in that, The equation for the hydration reaction process in the preparation of coating materials is as follows:

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