An anti-seepage coating for drainage pipes and its preparation method

Abstract

This invention discloses an anti-seepage coating for drainage pipes and its preparation method, relating to the technical field of drainage pipe protection and repair materials. The anti-seepage coating comprises a polymer base, a cementitious substrate, hierarchical microcapsules, nano-reinforcing fillers, and a silane coupling agent. The polymer base includes shape memory polyurethane, and the hierarchical microcapsules have a double-shell structure with an inner and outer shell. The preparation process involves first preparing and modifying the hierarchical microcapsules, then preparing liquid and powder components separately and mixing them for application. The resulting coating is suitable for application on damp substrates and can achieve active crack closure, controlled release of healing agents, and enhanced interface stability under crack conditions, thereby improving the anti-seepage repair capability and long-term protective performance of drainage pipes.

Description

Technical Field

[0001] This invention relates to the field of drainage pipeline protection and repair materials, specifically to an anti-seepage coating for drainage pipelines and its preparation method. Background Technology

[0002] As urban drainage systems develop towards deeper burial, networking, and longer service life, the service environment of drainage pipelines is becoming increasingly complex. The inner and outer walls of the pipelines are subjected to the coupled effects of multiple factors such as sewage media, groundwater infiltration, temperature and humidity fluctuations, acid and alkali alternation, chloride and sulfate corrosion, micro-vibration induced by vehicle loads, and local uneven settlement. This can easily lead to problems such as pore expansion, interface debonding, and crack penetration, which in turn can cause leakage, reduced structural durability, and damage to the surrounding soil.

[0003] Existing anti-seepage materials and repair technologies for drainage pipes still have significant limitations. Traditional cement-based or ordinary polymer-based anti-seepage coatings mostly focus on initial sealing and static waterproofing. When faced with common issues in drainage pipes such as damp substrate construction, dynamic water pressure circulation, micro-vibration disturbance, and alternating pH and ion environments, they are prone to problems such as interface adhesion attenuation, brittle cracking, local peeling, and long-term decrease in anti-seepage capacity. Summary of the Invention

[0004] To address the shortcomings of traditional technologies, this invention provides an anti-seepage coating for drainage pipes and its preparation method, thus solving the problems mentioned in the background art.

[0005] An anti-seepage coating for drainage pipes, characterized in that it comprises a polymer base, a cementitious substrate, graded microcapsules, nano-reinforcing fillers, and a silane coupling agent;

[0006] The polymer base material includes shape memory polyurethane, and the glass transition temperature of the shape memory polyurethane is 10-40°C.

[0007] The hierarchical microcontainer is a double-shell structure with an inner shell and an outer shell. The inner shell is a pH and ion-responsive layer, and the outer shell is a humidity and vibration-responsive layer. The outer shell contains silane-modified shape memory polyurethane.

[0008] The surface of the hierarchical microcontainer is modified by the silane coupling agent and forms an interfacial chemical bond with the shape memory polyurethane network. The hierarchical microcontainer is encapsulated with a composite healing agent.

[0009] After the anti-permeability coating is cured into a film, under the stress, humidity changes or vibration induced by crack expansion, the outer shell of the hierarchical micro-container ruptures or its permeability increases to release the composite healing agent, which, combined with the shape recovery effect of the shape memory polyurethane, closes and repairs the crack.

[0010] Preferably, the inner shell material is selected from one or both of layered double hydroxides and polyelectrolytes.

[0011] Preferably, the composite healing agent comprises epoxy resin monomer, silicate penetrating crystallizing activator, and benzothiazole corrosion inhibitor.

[0012] Preferably, the particle size of the graded microcapsules is 80–150 μm, and the core material loading rate is 75–85%.

[0013] Preferably, the anti-permeability coating comprises, by weight, parts of:

[0014] The mixture contains 35-45 parts polymer base material, 25-35 parts cement base material, 6-12 parts graded microcapsules, 1.5-3.5 parts nano-reinforced filler, 0.8-1.5 parts silane coupling agent, and appropriate amount of additives.

[0015] Preferably, the impermeable coating is suitable for the inner or outer wall of concrete or clay drainage pipes and is suitable for application on damp substrates.

[0016] Preferably, the coating formed by the anti-permeability coating, under the condition of 0.2-0.5mm cracks, after being circulated for 168 hours under simulated sewage pH 4-9 alternating, micro-vibration frequency 5-10Hz and dynamic water pressure of 0.5MPa, has a self-healing rate of not less than 98% after 7 days, and the anti-permeability pressure after removing the coating is not less than 1.8MPa.

[0017] A method for preparing an anti-seepage coating for drainage pipes, characterized by comprising the following steps:

[0018] A double-shell hierarchical microcontainer with an inner shell and an outer shell is prepared. A composite healing agent is encapsulated inside the hierarchical microcontainer, and the surface of the hierarchical microcontainer is modified using a silane coupling agent.

[0019] A polymer base containing shape memory polyurethane is mixed with nano-reinforced fillers to obtain a liquid material;

[0020] The cementitious base material is dry-mixed with the auxiliary active components to obtain a powder.

[0021] The surface-modified hierarchical microcapsules are added to the liquid and dispersed and mixed.

[0022] The liquid and powder are mixed at a mass ratio of 1:1.0 to 1.2 to obtain an anti-seepage coating.

[0023] Preferably, the surface-modified hierarchical microcapsules and the shape memory polyurethane network in the liquid form interfacial chemical bonds during the curing process.

[0024] This invention provides an anti-seepage coating for drainage pipes and its preparation method, which has the following beneficial effects:

[0025] 1. This invention constructs an anti-seepage coating comprising shape memory polyurethane, double-shell hierarchical micro-containers, composite healing agent, nano-reinforced filler, and silane coupling interface modification system. The resulting coating not only has good initial film-forming properties and anti-seepage sealing ability, but is also suitable for construction under damp substrate conditions, thereby improving the construction adaptability of on-site repair of drainage pipes.

[0026] 2. By utilizing the shape recovery property of shape memory polyurethane, active closure can be initiated on both sides of the crack after it is formed. Through the response of the double-shell hierarchical micro-container to pH, ions, humidity and vibration, the composite healing agent can be released in the crack area in a controlled manner, thereby improving the crack repair efficiency and the adequacy of the repair.

[0027] 3. The hierarchical microcapsules modified with silane coupling agents can form relatively stable interfacial chemical bonds with polymer base materials and inorganic substrates, which is beneficial to enhance the interfacial bonding stability of microcapsules in polymer / cement composite matrix, reduce the risk of debonding and failure under dynamic water pressure cycle, micro-vibration and repeated crack opening and closing conditions. The epoxy resin monomer, silicate penetrating crystallizing activator and benzothiazole corrosion inhibitor in the composite healing agent can synergistically achieve organic sealing, inorganic densification and interfacial protection, thereby improving the long-term impermeability stability and durability of the coating in complex drainage environment. Attached Figure Description

[0028] Figure 1 This is a structural diagram of the anti-seepage coating;

[0029] Figure 2 A schematic diagram illustrating the response and repair mechanism of cracks in drainage pipes;

[0030] Figure 3 A flowchart of the collaborative repair mechanism;

[0031] Figure 4 This is a flowchart of the process for preparing anti-seepage coatings. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] Reference Figures 1 to 3 This invention provides an anti-seepage coating for drainage pipes:

[0035] Including polymer base materials, cement-based materials, graded microcapsules, nano-reinforced fillers, and silane coupling agents;

[0036] The polymer matrix includes shape memory polyurethane, which has a glass transition temperature of 10–40°C, so that the resulting coating has crack closure response capability under the common service temperature conditions of drainage pipes.

[0037] The hierarchical microcontainer is a double-shell structure with an inner shell and an outer shell. The inner shell is a pH and ion-responsive layer, and the outer shell is a humidity and vibration-responsive layer. The outer shell contains silane-modified shape memory polyurethane.

[0038] The surface of the hierarchical microcontainer is modified with a silane coupling agent and then forms an interfacial chemical bond with a shape memory polyurethane network. The hierarchical microcontainer is encapsulated with a composite healing agent.

[0039] After the anti-permeability coating is cured into a film, under the stress, humidity changes or vibration induced by crack expansion, the outer shell of the graded micro-container will rupture or its permeability will increase to release the composite healing agent, and the shape memory polyurethane will close and repair the crack in combination with the shape recovery effect.

[0040] The inner shell material is selected from one or both of layered double hydroxides and polyelectrolytes;

[0041] The composite healing agent includes epoxy resin monomers, silicate penetrating crystallizing agents, and benzothiazole corrosion inhibitors;

[0042] The particle size of the hierarchical microcapsules is 80–150 μm, and the core material loading rate is 75–85%.

[0043] By weight, the above-mentioned anti-seepage coating comprises:

[0044] The mixture contains 35-45 parts polymer base material, 25-35 parts cement base material, 6-12 parts graded microcapsules, 1.5-3.5 parts nano-reinforced filler, 0.8-1.5 parts silane coupling agent, and appropriate amount of additives.

[0045] Anti-seepage coatings are suitable for the inner or outer walls of concrete or terracotta drainage pipes and can be applied to damp substrates.

[0046] Preferably, in this embodiment, the following proportions are used: 40 parts polymer base material, 30 parts cement base material, 9 parts graded microcapsules, 2.5 parts nano-reinforcing filler, 1.2 parts silane coupling agent, and the additives are a combination of dispersant, defoamer, water-retaining agent and rheology modifier. The amount added is based on meeting the requirements of construction fluidity, coating properties and film uniformity.

[0047] The above ratio can take into account the film-forming continuity of the coating, construction adaptability, micro-container dispersion stability, and impermeability after crack repair.

[0048] In this embodiment, shape memory polyurethane can be prepared by reacting polyether polyol, diisocyanate and chain extender.

[0049] By adjusting the ratio of soft segments to hard segments and the degree of chain extension, the glass transition temperature of the obtained shape memory polyurethane is preferably controlled at around 25°C. This temperature range enables the material to maintain good shape memory response characteristics under conditions of humid drainage pipes, normal temperature and temperature fluctuations in the underground environment. This allows the material to form a recovery pulling effect on both sides of the crack after the crack is generated, reducing the crack width and creating conditions for the subsequent healing agent to enter the crack and complete the repair.

[0050] In addition to shape memory polyurethane, polymer base materials can also be used in combination with a small amount of film-forming auxiliary components according to construction needs, but this does not change their main role as continuous polymer phase and shape recovery functional phase;

[0051] In this embodiment, the hierarchical microcontainer is prepared by a double-shell hierarchical construction method. The core material of the microcontainer is a composite healing agent. The epoxy resin monomer in the composite healing agent is used to form an organic sealing phase in the crack area. The silicate penetrating crystallizing activator is used to promote the inorganic densification filling of the crack and pore areas. The benzothiazole corrosion inhibitor is used to improve the corrosion resistance stability of the crack repair area and the surrounding interface.

[0052] By combining and encapsulating the above three types of components, the microcapsule can have a comprehensive effect of organic curing repair, inorganic infiltration crystallization and interface durability enhancement after being released in the crack area, rather than relying on a single repair material to achieve short-term sealing.

[0053] In this embodiment, the inner shell material is selected from one or two of layered double hydroxides and polyelectrolytes, preferably using layered double hydroxides and polyelectrolytes to synergistically form the inner shell layer;

[0054] Layered double hydroxides have ion exchange properties, and polyelectrolytes have sensitive response properties to local acid and alkaline environments and changes in ion concentration. When the two are combined, the inner shell can regulate the permeability under conditions of pH fluctuations and ion intrusion in the drainage medium, thereby achieving further control over the core material release process.

[0055] The outer shell uses a responsive layer containing silane-modified shape memory polyurethane, which can undergo moderate moisture absorption and softening in humid environments. Under the local stress concentration and micro-vibration accompanying crack propagation, it can undergo local rupture or increased permeability, allowing the composite healing agent to be preferentially released to the crack damage area.

[0056] Through the division of labor between the inner and outer shells, the microcontainer possesses both environmental screening response and damage-triggered release capabilities.

[0057] In this embodiment, the particle size of the graded microcapsules is controlled within the range of 80–150 μm, and the core material loading rate is controlled within the range of 75–85%, preferably with a particle size of about 110 μm and a core material loading rate of about 80%.

[0058] Using the above particle size range is beneficial in two ways: firstly, it helps the microcapacitors to be uniformly dispersed in the composite system composed of polymer matrix and cement matrix, avoiding local stress concentration or weakening of coating density caused by excessively large particle size; secondly, it can avoid insufficient effective loading or excessively thin shell due to excessively small particle size, which would affect the subsequent triggering and release effect.

[0059] By adopting the above-mentioned load rate range, it is possible to increase the effective healing agent reserve while ensuring the stability of the shell structure, thereby balancing storage stability and repair efficiency.

[0060] To improve the interfacial bonding performance between the hierarchical microcapsules and the polymer matrix, the hierarchical microcapsules are surface-modified with a silane coupling agent in this embodiment.

[0061] Specifically, the prepared double-shell hierarchical microcapsules can be added to an alcohol-water system containing a silane coupling agent for surface treatment, allowing the active groups in the silane coupling agent to be grafted or deposited onto the surface of the microcapsules. After surface modification, when the hierarchical microcapsules are subsequently mixed with a polymer base containing shape memory polyurethane and cured into a film, they can form a stable interfacial connection with the polyurethane network and the surface of the inorganic phase. This reduces the migration, debonding, and interfacial void generation of the microcapsules during the coating's service life, and improves the retention stability of the microcapsules under crack opening and closing and dynamic water pressure alternation environments. This interfacial chemical bonding achieved through coupling modification is one of the important structural features that distinguishes the anti-permeability coating of this embodiment from ordinary microcapsule-doped coatings.

[0062] In this embodiment, the nano-reinforcing filler can be selected from one or two of nano-silica, nano-layered silicate, and graphene oxide, preferably a combination of nano-silica and nano-layered silicate.

[0063] The main functions of the nano-reinforcing filler in this embodiment include: improving the initial compactness of the polymer / cement composite matrix, reducing capillary pores and defect channels, improving the structure of the interface transition zone between the polymer phase and the cement phase, improving the dispersion stability of the hierarchical microcapsules in the system, and providing a microscale reinforcing skeleton for the organic repair phase and the inorganic crystalline phase after subsequent crack repair, thereby improving the overall stability and impermeability of the repaired area.

[0064] In this embodiment, the anti-permeability coating can be prepared as follows: First, a polymer base material containing shape memory polyurethane is added to a stirring device, and then nano-reinforced filler is added under stirring conditions for pre-dispersion, so that the nano-reinforced filler is uniformly introduced into the polymer phase to obtain a liquid material.

[0065] Then, the graded microcapacitors modified with silane coupling agent are added to the liquid and mixed using a low-shear method to ensure that the graded microcapacitors are evenly dispersed in the liquid while avoiding a large number of breakages during the mixing process.

[0066] The cementitious base material is dry-mixed with the auxiliary active powder to obtain a powder. Before construction, the liquid material and the powder are mixed at a mass ratio of 1:1.0 to 1.2, preferably 1:1.1. After stirring evenly, a workable anti-seepage coating slurry is obtained.

[0067] The anti-seepage coating obtained in this embodiment can be applied to the inner or outer wall of concrete drainage pipes or clay drainage pipes, and is suitable for application on damp substrates. Before application, the substrate can be cleaned in a conventional manner to remove floating dust, oil stains and loose layers, and the substrate should be kept moist but without standing water. The coating can be applied by brushing, rolling or spraying to form a continuous and dense anti-seepage protective layer.

[0068] Because this embodiment uses a composite system constructed by polymer base material, cement substrate and graded micro-containers, the resulting coating has both adaptability to damp substrate and good substrate adhesion and subsequent impermeability stability.

[0069] To verify the applicability of the anti-seepage coating of this embodiment under the service conditions of drainage pipelines, this embodiment selects a section of buried concrete drainage pipeline as the object. The pipeline has a nominal inner diameter of 600 mm and an operating life of 6 years. During maintenance, the inner surface of the pipe wall has a damp base, local carbonization, slight leakage, and micro-cracks in the range of 0.2 to 0.5 mm. Considering that this type of drainage pipeline is in an environment of alternating humidity and heat, fluctuation of sewage acid and alkali, ion intrusion, micro-vibration, and dynamic water pressure fluctuation during operation, this embodiment simultaneously introduces temperature fluctuation, pH alternation, ion disturbance, low-frequency micro-vibration, and dynamic water pressure circulation to examine the film-forming adaptability, crack response release ability, and subsequent anti-seepage recovery ability of the anti-seepage coating of this embodiment under near-real working conditions.

[0070] In this embodiment, the substrate is a concrete specimen that is similar to the condition of the inner wall of the drainage pipe on site. After routine cleaning, the surface of the specimen is kept moist but without standing water. The anti-seepage coating obtained in this embodiment is mixed with the powder at a mass ratio of 1:1.1 and applied to the surface of the specimen to form a coating with an average thickness of about 1.15 mm to 1.32 mm. After the coating is cured, surface cracks of different widths are prefabricated on the surface of the specimen to show the early crack propagation caused by foundation settlement, vehicle disturbance and temperature and humidity changes during the operation of the drainage pipe. The working parameters are shown in Table 1.

[0071] Table 1 Operating parameters for service scenarios

[0072] project condition Substrate type Concrete specimens for C40 drainage pipes Base surface condition The substrate is damp, without standing water, and has a surface moisture content of approximately 7.8% to 9.6%. Average coating thickness 1.15~1.32 mm Precast crack width 0.21~0.48 mm Ambient temperature fluctuations 16.8～29.4 ℃ Wastewater pH Alternating cycles of 4.6 to 8.7 Main ionic environment <![CDATA[Cl - 420~690 mg / L,SO4 2- 180~340 mg / L]]> Micro-vibration frequency 5.8–8.6 Hz Dynamic water pressure 0.26~0.47 MPa circulation Loop duration 168 h Subsequent resting and self-healing period 7 d

[0073] In the above scenario, six parallel samples were tracked and recorded. The initial crack width, coating thickness, apparent seepage state at the end of the cycle, crack closure rate after 7 days, change in seepage after self-healing, and recovery of anti-seepage pressure after coating removal were measured respectively. The exemplary verification data obtained are shown in Table 2.

[0074] Table 2. Exemplary verification data under drainage pipeline operating conditions in this embodiment.

[0075] Sample number Initial crack width / mm Coating thickness / mm <![CDATA[Water seepage volume at the end of 168h cycle / mL·h -1 > 7d crack closure rate / % <![CDATA[Water seepage volume after 7 days / mL·h -1 > Water permeability pressure after coating removal / MPa S1 0.23 1.18 5.7 98.4 0.22 1.86 S2 0.31 1.21 7.9 98.9 0.31 1.93 S3 0.27 1.15 6.4 98.1 0.28 1.88 S4 0.42 1.32 11.6 98.3 0.47 1.91 S5 0.48 1.27 13.1 98.0 0.55 1.84 S6 0.36 1.24 8.8 98.7 0.34 1.96

[0076] As shown in Table 2, under the conditions of initial crack width of 0.21-0.48 mm and simultaneous exposure to acid-base alternation, ion disturbance, micro-vibration, and dynamic water pressure circulation, the coating formed by the anti-seepage coating in this embodiment exhibited varying degrees of instantaneous seepage after 168 hours of circulation. However, during the subsequent 7-day self-healing process, the crack closure rate of each sample reached over 98.0%, and the seepage volume significantly decreased and stabilized at a low level. Samples S4 and S5, with relatively larger crack widths, had higher seepage volume during the circulation stage than other samples, but still showed a high crack closure rate and low residual seepage volume. This indicates that the solution in this embodiment is not only applicable to extremely narrow cracks, but also has good repair adaptability in the crack range of 0.2-0.5 mm.

[0077] Further analysis suggests that the good anti-seepage restoration effect achieved by this embodiment in the above-mentioned drainage pipeline service scenarios is mainly related to the following structural synergy: the shape memory polyurethane can generate a recovery and attraction effect on both sides of the crack within the ambient temperature range, so that the crack width is physically converged in the early stage of self-healing; the shell of the hierarchical microcontainer undergoes local rupture or increased permeability under the action of humidity changes, vibration and stress concentration at the crack tip, so that the composite healing agent can be preferentially released along the crack; the pH and ion response layer in the inner shell further regulates the release process of the healing agent in the alternating acid and alkali environment of sewage and ion environment, so that the epoxy resin monomer, silicate penetrating crystallizing activator and benzothiazole corrosion inhibitor play a composite role of organic sealing, inorganic densification and interface stability enhancement in the crack area; the hierarchical microcontainer modified with silane coupling agent forms a relatively stable interface chemical bond with the shape memory polyurethane network, so that the microcontainer is not easy to detach from the composite matrix under cyclic vibration and dynamic water pressure conditions, thereby ensuring that there are still enough effective repair units near the crack;

[0078] As can be seen from the "Impermeability Pressure After Coating Removal" data in Table 2, the impermeability pressure of the substrate remained between 1.84 and 1.96 MPa after the surface coating was removed. This indicates that the repair effect of the solution in this embodiment is not limited to surface sealing, but can also cause a certain degree of internal densification and impermeability restoration in the crack area and adjacent pore structure. This is related to the migration of silicate penetrating crystallizing active agent in the composite healing agent into the crack and the formation of an inorganic dense phase. It also shows that the solution in this embodiment is suitable for on-site construction and subsequent operation protection of drainage pipes under wet substrate conditions, and has good engineering feasibility.

[0079] In this embodiment, after the anti-permeability coating is cured into a film, during the service of the drainage pipe, when microcracks appear on the surface of the coating or substrate, the stress concentration at the crack tip, changes in the humid environment, and vibration can cause the shell of the graded microcontainer to rupture locally or increase permeability. This causes the composite healing agent encapsulated inside the microcontainer to be preferentially released into the crack area. The shape memory polyurethane recovers its shape under ambient temperature conditions, causing the two sides of the crack to have a mutual recovery effect, thus reducing the crack width.

[0080] The released epoxy resin monomers form an organic sealing phase in the crack area, while silicate-based penetrating crystallizing agents migrate into the cracks and pores and promote inorganic crystallization and densification. Benzothiazol-based corrosion inhibitors improve the stability of the crack repair area and its adjacent interface. Due to the relatively stable interfacial chemical bond formed between the hierarchical microcapsules and the shape memory polyurethane network, the microcapsules are not easily detached from the matrix during the repair process. The repair area can still maintain good integrity under subsequent vibration and water pressure cycling conditions. Thus, this anti-seepage coating has the comprehensive effects of active crack closure, controlled release of healing agent, and interface strengthening repair.

[0081] This embodiment employs the aforementioned raw material composition, structural design, and preparation method, enabling the obtained anti-seepage coating to be suitable for complex working conditions such as dampness, vibration, changes in sewage pH, and dynamic water pressure in drainage pipes without sacrificing workability. This embodiment uses the optimal combination within the range of parameters, which not only fully reflects the technical concept of the present invention, but also reserves reasonable space for subsequent comparative design and performance difference verification around the interface coupling structure, double-shell hierarchical structure, shape memory polyurethane setting, and micro-container triggered release behavior.

[0082] Example 2

[0083] Reference Figure 4 This embodiment provides a method for preparing a drainage pipe, including the following steps:

[0084] A double-shell hierarchical microcontainer with an inner shell and an outer shell was prepared. A composite healing agent was encapsulated inside the hierarchical microcontainer, and the surface of the hierarchical microcontainer was modified using a silane coupling agent.

[0085] A polymer base containing shape memory polyurethane is mixed with nano-reinforced fillers to obtain a liquid material;

[0086] The cementitious base material is dry-mixed with the auxiliary active components to obtain a powder.

[0087] The surface-modified hierarchical microcapsules were added to the liquid and dispersed and mixed.

[0088] The liquid and powder are mixed at a mass ratio of 1:1.0 to 1.2 to obtain an anti-seepage coating, which is then applied to the base surface of the drainage pipe.

[0089] The surface-modified hierarchical microcapsules and the shape memory polyurethane network in the liquid material form interfacial chemical bonds during the curing process;

[0090] This embodiment provides a method for preparing an anti-seepage coating for drainage pipes. Unless otherwise specified, the raw material system used in this embodiment can be the raw material system of Example 1 and its preferred ratio. The preparation method includes the steps of preparing and surface modifying a double-shell graded micro-container, preparing liquid material, preparing powder material, mixing liquid material and powder material, and construction curing to form a film.

[0091] In this embodiment, a double-shell hierarchical microcontainer is first prepared. The double-shell hierarchical microcontainer is encapsulated with a composite healing agent. The composite healing agent includes an epoxy resin monomer, a silicate penetrating crystallizing agent, and a benzothiazole corrosion inhibitor. The epoxy resin monomer is used to form an organic sealing phase in the crack area. The silicate penetrating crystallizing agent is used to migrate into the crack and pores and promote inorganic densification filling. The benzothiazole corrosion inhibitor is used to improve the durability and stability of the crack repair area and adjacent interfaces.

[0092] By combining the above components to form a core material, the subsequently released repair material can have the functions of organic sealing, inorganic densification and interface protection.

[0093] After the core material droplet is formed, an inner shell is first constructed on its outer surface. The inner shell is a pH and ion response layer. The inner shell material is selected from one or two of layered double hydroxides and polyelectrolytes.

[0094] In this embodiment, it is preferred to use a composite of layered double hydroxide and polyelectrolyte to construct the inner shell. Specifically, the layered double hydroxide can be dispersed in the aqueous phase, and a polyelectrolyte with opposite charge can be introduced to adsorb and coat the core material droplets layer by layer, forming an inner shell layer that responds to changes in acid and alkali and changes in ionic environment. The resulting inner shell can regulate the release behavior of the core material under the action of drainage medium while ensuring the stability of the core material packaging.

[0095] After the inner shell is formed, an outer shell is further constructed on the outer surface of the inner shell. The outer shell is a humidity and vibration response layer and contains silane-modified shape memory polyurethane.

[0096] In this embodiment, the shape memory polyurethane prepolymer can be grafted with a modified component containing hydrolyzable silane groups to obtain silane-modified shape memory polyurethane, which is then coated on the outer surface of the inner shell to form an outer shell layer. The resulting outer shell layer has certain moisture absorption, softening and permeability regulation characteristics in a humid environment, and will undergo local rupture or increased permeability under the local stress concentration caused by crack expansion and the vibration of the drainage pipe operation, thereby allowing the composite healing agent to be preferentially released along the crack area.

[0097] In this embodiment, the particle size of the obtained double-shell graded microcapsules is controlled to be 80–150 μm, preferably 105–120 μm, and the core material loading rate is 75–85%, preferably 78–82%. Using the above particle size range is beneficial for the double-shell graded microcapsules to maintain good dispersibility in subsequent liquid materials, and reduces the risk of increased local defects in the coating due to excessively large particle size or insufficient effective loading due to excessively small particle size.

[0098] Using the above-mentioned core material load rate range is beneficial to balancing the stability of the shell structure and the effective reserve of repair materials.

[0099] After the fabrication of the double-shell hierarchical microcontainer was completed, its surface coupling modification was performed.

[0100] Specifically, a double-shell hierarchical microcontainer is added to a mixed medium composed of alcohol and water. A silane coupling agent is added under weakly acidic conditions and hydrolyzed to allow the active groups in the silane coupling agent to be grafted or deposited on the surface of the microcontainer. The modified microcontainer is then filtered, washed, and dried at low temperature to obtain a surface-modified hierarchical microcontainer.

[0101] After the above surface modification, an interface layer with good compatibility and reactivity with the subsequent polymer base and inorganic phase can be introduced into the surface of the microcontainer, thereby providing conditions for the formation of interfacial chemical bonds during the subsequent curing process.

[0102] After completing the surface modification of the hierarchical microcapsules, a liquid material was prepared, which consisted of a polymer base containing shape memory polyurethane and nano-reinforced fillers.

[0103] In this embodiment, the polymer base material is first added to the stirring device, and then the nano-reinforced filler is added under stirring conditions for pre-dispersion to obtain a liquid. The nano-reinforced filler can be nano-silica, nano-layered silicate or a combination thereof. The addition of the nano-reinforced filler is beneficial to improving the initial density of the matrix and the strength of the micro-skeleton, and is beneficial to improving the dispersion stability of the hierarchical micro-containers in the liquid.

[0104] The powder is prepared by dry mixing of cement base material and auxiliary active components. The cement base material can be silicate cement, special repair cement or a combination thereof, and the auxiliary active components can be fine silica fume, mineral admixtures or setting regulators. By dry mixing the powder components, they can be evenly distributed, thus providing conditions for the formation of a stable slurry when the liquid material is mixed with the powder.

[0105] After the liquid material is prepared, the surface-modified hierarchical microcontainers are added to the liquid material for dispersion and mixing. It is preferred to use a low-shear method for dispersion to reduce the possibility of large-area damage to the hierarchical microcontainers during addition and dispersion. After the surface-modified hierarchical microcontainers are added to the liquid material, they can form a relatively uniform suspended dispersion in the polymer base. They can also undergo interfacial adsorption and pre-reaction bonding with the shape memory polyurethane segments in the liquid material through their surface coupling layer. The liquid material and powder are mixed at a mass ratio of 1:1.0 to 1.2, preferably 1:1.1. After stirring evenly, the anti-permeability coating slurry is obtained.

[0106] The anti-seepage coating slurry obtained in this embodiment can be applied to the base surface of drainage pipes, preferably to the inner or outer wall of concrete or clay drainage pipes that are damp but without standing water. The application method can be brushing, rolling or spraying. After the slurry is applied, during the curing and film formation process, the surface-modified graded microcapsules and the shape memory polyurethane network in the liquid gradually form interfacial chemical bonds.

[0107] Specifically, the coupling active groups on the surface of the microcapsule can chemically react with or form stable connections with the active groups in the polyurethane network, while enhancing the interfacial transition between the microcapsule and the cement-based inorganic phase. The hierarchical microcapsule can be embedded in the polymer / cement composite matrix in an interfacial coupling state, thereby reducing its risk of debonding, migration and failure under crack opening and closing, vibration and dynamic water pressure cycling conditions.

[0108] To facilitate the explanation of the process control conditions of this embodiment, the preferred process parameters of this embodiment are shown in Table 3;

[0109] Table 3 Preferred process control parameters for Example 2

[0110] Process Control Project Preferred conditions Preparation of bi-shell hierarchical microcapsules Particle size 105~120μm Preparation of bi-shell hierarchical microcapsules Core material load rate 78～82% Inner shell formation Inner shell material Layered double hydroxide + polyelectrolyte Shell formation Shell material Response layer of silane-modified shape memory polyurethane Surface coupling modification Medium system alcohol / water mixture Surface coupling modification pH 4.5～5.5 Surface coupling modification Processing temperature 25～35℃ Surface coupling modification Processing time 1.5～3h Liquid preparation Nano-reinforced filler pre-dispersion time 20–40 min Microcontainer addition of liquid Distributed method Low shear dispersion for 10–20 min Powder preparation Just passing the time 5–15 min Liquid and powder mixing mass ratio 1:1.0 to 1.2, preferably 1:1.1 Construction base surface Base surface condition Damp but without visible water Curing into film Curing conditions room temperature maintenance

[0111] The anti-permeability coating prepared by the above method, after being applied and cured into a film, allows the hierarchical microcapsules to be stably embedded in the polymer / cement composite matrix. When the drainage pipe coating is subjected to crack expansion, humidity changes or vibration during service, the outer shell of the hierarchical microcapsules will experience local rupture or increased permeability, causing the composite healing agent encapsulated inside to be released along the crack area. The shape memory polyurethane will produce a shape recovery effect on both sides of the crack, thereby working in synergy with the release behavior of the healing agent to achieve crack closure and repair.

[0112] Because the interface chemical bonding between the hierarchical microcapacitors and the shape memory polyurethane network is achieved through surface coupling modification during the preparation process in this embodiment, the resulting coating not only has crack response repair capability, but also has good interface stability and dynamic service adaptability.

[0113] The preparation method in this embodiment, through the stepwise construction of double-shell hierarchical microcapsules, the sequential setting of surface coupling modification, the stepwise preparation of liquid and powder materials, and the formation of interfacial chemical bonds during the curing process, enables the obtained anti-permeability coating to take into account construction adaptability, microcapsule dispersion stability, crack response repair ability, and anti-permeability durability.

[0114] Example 3

[0115] This embodiment provides an anti-seepage coating for drainage pipes and a method for preparing the same, including:

[0116] The anti-seepage coating formed under 0.2-0.5mm crack conditions, after being circulated for 168 hours under alternating sewage pH 4-9, micro-vibration frequency 5-10Hz, and dynamic water pressure of 0.5MPa, has a self-healing rate of not less than 98% after 7 days, and the anti-seepage pressure after removing the coating is not less than 1.8MPa.

[0117] This embodiment is used to verify the self-healing performance and anti-seepage recovery ability of the anti-seepage coating of the present invention under crack conditions. Unless otherwise specified, the anti-seepage coating used in this embodiment can be prepared by the composition and preferred ratio of the anti-seepage coating in Example 1 and by the preparation method in Example 2.

[0118] In this embodiment, concrete drainage pipe specimens and clay drainage pipe specimens in service status of municipal drainage branch pipes are selected as application objects. The concrete drainage pipe specimens are prepared using C40 concrete, and the clay drainage pipe specimens are prepared by cutting sintered clay pipe segments.

[0119] To closely simulate the on-site maintenance conditions of drainage pipelines, only routine cleaning of the specimen surface was performed before construction to remove floating dust, loose layers and attached contaminants. The base surface was kept moist but without standing water. The anti-seepage coating was then applied to the inner wall surface of the specimen to form a continuous anti-seepage protective layer.

[0120] The above construction method can be applied by brushing, roller coating or spraying. In this embodiment, a combination of brushing and roller coating is preferred to control the thickness of the resulting coating within the range of 1.10 to 1.35 mm.

[0121] After the anti-seepage coating has cured and formed a film, cracks are pre-made on the surface of the specimen to simulate the micro-crack state formed by the drainage pipe under the influence of foundation settlement, traffic load disturbance, temperature and humidity alternation and local scouring. The width of the pre-made cracks is controlled within the range of 0.2 to 0.5 mm. After the cracks are prepared, the specimens are placed in the service environment of the drainage pipe for composite cycle action.

[0122] The composite circulation conditions include: the pH of the wastewater environment alternates within the range of 4 to 9, the micro-vibration frequency is controlled within the range of 5 to 10 Hz, and a dynamic water pressure of 0.5 MPa is applied for circulation, which is carried out continuously for 168 hours. The environment also takes into account the ion intrusion, humidity changes and periodic hydraulic disturbances in the drainage medium, so as to closely approximate the actual operating conditions of the drainage pipeline.

[0123] In this embodiment, after the composite cycle is completed, the specimen is placed in a room temperature static environment for another 7 days to evaluate the self-healing effect of the anti-seepage coating on the crack. The crack self-healing rate is calculated according to the change between the initial crack width and the residual crack width after 7 days. The anti-seepage pressure after removing the coating is obtained by conducting an anti-seepage test on the specimen after crack repair to evaluate whether the repair effect is only limited to surface sealing or whether it has formed internal densification and restoration of the crack area and adjacent pore structure.

[0124] To illustrate the verification conditions of this embodiment, the service condition parameters of this embodiment are shown in Table 4.

[0125] Table 4 Service condition parameters of Example 3

[0126] project condition Base surface condition Damp but without visible water Coating thickness 1.10~1.35mm Precast crack width 0.20~0.50mm simulated wastewater pH Alternating cycles of 4 to 9 Micro-vibration frequency 5~10Hz Dynamic water pressure 0.5MPa cycle Loop duration 168h Subsequent settling time 7d Evaluation indicators Self-healing rate, impermeability pressure after coating removal

[0127] Based on the analysis of the material structure and preparation process of Examples 1 and 2, it is believed that the effect in this example mainly comes from the following synergistic effect:

[0128] Shape memory polyurethane can restore the shape of both sides of a crack under service temperature conditions, thereby reducing the crack width.

[0129] The outer shell of the double-shell graded microcontainer may experience localized rupture or increased permeability under the influence of humidity changes, vibration, and stress concentration at the crack tip, causing the composite healing agent to be preferentially released along the crack area.

[0130] The pH and ion-responsive layer in the inner shell further regulates the release process of the healing agent in the wastewater environment, enabling epoxy resin monomers, silicate penetrating crystallizing agents and benzothiazole corrosion inhibitors to exert a comprehensive effect of organic plugging, inorganic densification and interface stabilization enhancement in the crack area.

[0131] The hierarchical microcapsules modified with silane coupling agent form interfacial chemical bonds with the shape memory polyurethane network during the curing process. This makes the microcapsules less likely to detach from the polymer / cement composite matrix under dynamic water pressure and micro-vibration cycling conditions, thus helping to maintain continuous repair capabilities and long-term impermeability stability.

[0132] Comparative Example 1

[0133] This comparative example provides an anti-seepage coating for drainage pipes. Unless otherwise specified, the composition of raw materials, proportioning range, hierarchical microcapsule structure, composition of composite healing agent, polymer base, cement base material, nano-reinforcing filler, types of additives and construction methods are basically the same as those in Examples 1 and 2. The difference is that in this comparative example, after the double-shell hierarchical microcapsules are prepared, silane coupling agents are no longer used to modify their surface. The hierarchical microcapsules are directly added to the liquid for dispersion and mixing, so that they are distributed in the anti-seepage coating system by ordinary physical mixing.

[0134] In this comparative example, the anti-permeability coating still includes a polymer base, a cementitious substrate, hierarchical microcapsules, nano-reinforcing fillers, and additives. The polymer base still contains shape memory polyurethane, and the hierarchical microcapsules still adopt the same double-shell structure as in Example 1. The double-shell structure includes an inner shell that responds to pH and ions and an outer shell that responds to humidity and vibration. The hierarchical microcapsules are still encapsulated with a composite healing agent, which includes epoxy resin monomers, silicate penetrating crystallizing activators, and benzothiazole corrosion inhibitors. The particle size and core material loading rate of the hierarchical microcapsules are also controlled within the same range as in Example 1 to ensure that the only difference between this comparative example and the example is in the surface coupling modification and the resulting interfacial bonding mode.

[0135] In this comparative example, the double-shell hierarchical microcontainer can be prepared using the same method as in Example 2, with epoxy resin monomer, silicate penetrating crystallizing surfactant and benzothiazole corrosion inhibitor forming a composite healing agent core material; pH and ion-responsive inner shell and humidity and vibration-responsive outer shell are sequentially constructed on the outer surface of the core material to obtain the double-shell hierarchical microcontainer. The difference is that after the double-shell hierarchical microcontainer is prepared, no silane coupling agent surface modification treatment is performed, and no active interface layer that can undergo interfacial chemical reaction with the shape memory polyurethane network in the polymer matrix is ​​introduced on the surface of the microcontainer.

[0136] In this comparative example, the liquid material is still prepared by pre-dispersing a polymer base containing shape memory polyurethane and nano-reinforced fillers, and the powder material is still prepared by dry mixing a cement base material and auxiliary active components. Unmodified graded micro-containers are added to the liquid material for dispersion and mixing. Then, the liquid material and powder material are mixed at the same mass ratio as in Example 2 to obtain an anti-seepage coating slurry. After the obtained slurry is applied to the base surface of a damp but dry concrete drainage pipe or clay drainage pipe, it is cured at room temperature to form an anti-seepage coating.

[0137] Since the hierarchical microcapsules were not modified with silane coupling agents in this comparative example, they were mainly dispersed in the polymer / cement composite matrix in a physical blending state during the curing and film formation process. It was difficult for them to form stable interfacial chemical bonds with the shape memory polyurethane network in the liquid material. During the service of the coating, the interfacial bonding between the microcapsules and the surrounding matrix mainly relied on physical interlocking and local interfacial adsorption, resulting in relatively weak interfacial stability.

[0138] In this comparative example, the same verification conditions as in Example 3 were used for performance evaluation. That is, after the coating was formed, 0.2-0.5 mm cracks were pre-made on the surface of the specimen, and the specimen was subjected to a composite working condition of alternating sewage pH 4-9, micro-vibration frequency 5-10 Hz, and dynamic water pressure circulation of 0.5 MPa for 168 h. After that, the specimen was left to stand for 7 days and the crack repair and the anti-seepage recovery after the coating was removed were evaluated.

[0139] The results show that, under the above-mentioned composite conditions, although the double-shell hierarchical microcapsules in this comparative example can still release the composite healing agent in the crack area, and the shape memory polyurethane can still produce a certain recovery effect on both sides of the crack, due to the lack of stable interfacial chemical bonding between the hierarchical microcapsules and the polymer matrix, the microcapsules are more prone to local migration, interfacial debonding, or the formation of peripheral voids under vibration, water pressure cycling, and repeated opening and closing of the crack, thereby affecting the effective utilization rate of the repair agent in the crack area and the subsequent stability of the repair area.

[0140] Furthermore, since the hierarchical microcontainers do not form a relatively stable interface coupling structure with the shape memory polyurethane network, after the crack area undergoes composite cycle action, the repair area is more prone to local discontinuities in bonding or secondary seepage channels, resulting in a decrease in the anti-seepage retention capacity after crack closure. This is especially true when the crack width is close to the upper limit, where the above-mentioned interface instability is more obvious. This manifests as an increase in moisture traces, local edge instability, and a decrease in anti-seepage recovery capacity after the surface coating is removed under subsequent dynamic working conditions.

[0141] This comparative example shows that, under the condition that the double-shell hierarchical microcapsules, shape memory polyurethane, and composite healing agent system remain basically unchanged, simply removing the silane coupling modification on the surface of the hierarchical microcapsules will weaken the interfacial bonding stability between the microcapsules and the polymer / cement composite matrix, thereby affecting the long-term impermeability and dynamic service adaptability after crack repair. It can be seen that the interfacial chemical bonding achieved by surface modification of silane coupling agent in the examples plays an important role in improving the interfacial stability, repair effectiveness, and impermeability durability of hierarchical microcapsules in impermeable coatings.

[0142] Comparative Example 2

[0143] This comparative example provides an anti-seepage coating for drainage pipes. Unless otherwise specified, the composition of raw materials, proportioning range, polymer base, cement base, nano-reinforcing filler, silane coupling agent, type of additives, construction method and verification conditions are basically the same as those in Examples 1 to 3. The difference is that in this comparative example, ordinary single-shell microcapsules are used instead of the double-shell hierarchical microcapsules in the examples. That is, the inner shell with pH and ion response functions and the outer shell with humidity and vibration response functions are no longer provided. Instead, only a single shell layer is used to encapsulate the composite healing agent.

[0144] In this comparative example, the anti-seepage coating still includes a polymer base, a cementitious substrate, microcapsules, nano-reinforcing fillers, a silane coupling agent, and additives. The polymer base still contains shape memory polyurethane, and the glass transition temperature of the shape memory polyurethane is still controlled within the same range as in Example 1 to ensure consistency between this comparative example and the example in terms of active crack closure. The microcapsules still encapsulate a composite healing agent, which still includes epoxy resin monomers, silicate penetrating crystallizing activators, and benzothiazole corrosion inhibitors. The particle size and core material loading rate of the microcapsules are also controlled within the same range as in Example 1, so that the main difference between this comparative example and the example is focused on the shell structure and its response mode.

[0145] In this comparative example, ordinary single-shell microcapsules can be prepared using conventional encapsulation methods. The core material of the composite healing agent is formed by epoxy resin monomers, silicate penetrating crystallizing surfactants, and benzothiazole corrosion inhibitors. A single shell layer is formed on the outer surface of the core material to encapsulate the composite healing agent. The single shell layer can be made of an organic shell material similar to that of the shell in the example. After preparation, a silane coupling agent can still be used for surface modification to give the surface good interfacial compatibility with the polymer base and inorganic phases. This comparative example still retains the surface coupling modification and interfacial coupling ability, but no longer has the hierarchical response release structure formed by the division of labor and cooperation between the inner shell and the outer shell in the example.

[0146] In this comparative example, the liquid material is still prepared by pre-dispersing a polymer base containing shape memory polyurethane and nano-reinforced fillers, and the powder material is still prepared by dry mixing a cement base material and auxiliary active components. Ordinary single-shell microcapsules with surface modification are added to the liquid material for dispersion and mixing. Then, the liquid material and powder material are mixed at the same mass ratio as in Example 2 to obtain an anti-seepage coating slurry. After the obtained slurry is applied to the base surface of a damp but dry concrete drainage pipe or clay drainage pipe, it is cured at room temperature to form an anti-seepage coating.

[0147] Since this comparative example uses ordinary single-shell microcapsules, although they can still encapsulate the composite healing agent and release some repair substances when cracks form, their shells only have single encapsulation and triggering characteristics, lacking the environmental response regulation and damage-triggered release functions undertaken by the inner and outer shells respectively in the embodiments.

[0148] Specifically, the single-shell microcapsules in this comparative example cannot simultaneously respond in a stratified manner to acid-base fluctuations, ion intrusion, humidity changes, and micro-vibration effects in the drainage medium. Therefore, their release behavior under complex service conditions is mainly manifested as local rupture or permeability changes of a single shell, and the stratification and targeting of the remediation agent release process are relatively insufficient.

[0149] In this comparative example, the same verification conditions as in Example 3 were used for performance evaluation. That is, after the coating was formed, 0.2-0.5 mm cracks were pre-made on the surface of the specimen, and the specimen was subjected to a composite working condition of alternating sewage pH 4-9, micro-vibration frequency 5-10 Hz and dynamic water pressure circulation of 0.5 MPa for 168 h. After that, the specimen was left to stand for 7 days and the crack repair and the anti-seepage recovery after the coating was removed were evaluated.

[0150] The results show that, under the above-mentioned combined working conditions, although the ordinary single-shell microcapsules in this comparative example can still release the composite healing agent in the crack area, and the shape memory polyurethane can still produce a certain recovery effect on both sides of the crack, the microcapsules are relatively weak in adapting to complex environmental factors due to the lack of a graded response mechanism in the single-shell structure, making it more difficult to maintain a stable release rhythm and release position of the repair agent in the crack area.

[0151] Furthermore, under the combined effects of alternating acid and alkali conditions, ion intrusion, micro-vibration, and dynamic water pressure in the drainage medium, the ordinary single-shell microcapsules in this comparative example are more prone to the following situations: First, the shell layer may rupture prematurely under local conditions, causing some of the repair agent to be released prematurely in non-target areas, reducing the effective utilization rate; second, the release process after crack expansion lacks synergistic regulation between the inner and outer layers, resulting in insufficient continuous supply of the repair agent to the deeper parts of the crack and adjacent pore areas; third, under the condition of larger cracks, the response release of single-shell microcapsules is more likely to be a one-time release, making it difficult to maintain the continuous effect in the subsequent repair stages. After experiencing the combined cycle, the crack repair area is more likely to experience insufficient repair, large local residual openings, or insufficient internal densification.

[0152] This comparative example demonstrates that, while maintaining the shape memory polyurethane system, composite healing agent composition, surface coupling modification method, and construction verification conditions essentially unchanged, simply replacing the double-shell graded microcapsules in the examples with ordinary single-shell microcapsules weakens the coating's response regulation capability and the controlled release capability of the repair agent in complex drainage environments. This, in turn, affects the adequacy of crack repair, impermeability recovery capability, and long-term service stability. The double-shell graded response structure formed by the graded setting of the inner and outer shells in the examples plays an important role in improving the release targeting, repair continuity, and impermeability durability of the repair agent under complex working conditions.

[0153] Comparative Example 3

[0154] This comparative example provides an anti-seepage coating for drainage pipes. Unless otherwise specified, the composition of raw materials, proportioning range, hierarchical micro-container structure, composite healing agent composition, nano-reinforcing filler, silane coupling agent, type of additives, construction method, and verification conditions are basically the same as those in Examples 1 to 3. The difference is that in this comparative example, the polymer base material no longer uses a system containing shape memory polyurethane, but instead uses a common polymer base material that does not have shape recovery function. The common polymer base material can be a common polyurethane emulsion, acrylic emulsion, or other conventional film-forming polymer system, so that the resulting anti-seepage coating still has basic film-forming properties and adhesion to inorganic substrates, but does not have the function of the shape memory polyurethane in the examples to actively recover and pull together the two sides of the crack.

[0155] In this comparative example, the anti-permeability coating still includes a polymer base, a cementitious substrate, hierarchical microcapsules, nano-reinforcing fillers, silane coupling agents, and additives. The hierarchical microcapsules still adopt the same double-shell structure as in Example 1, which includes an inner shell that responds to pH and ions and an outer shell that responds to humidity and vibration. The hierarchical microcapsules are still encapsulated with a composite healing agent, which still includes epoxy resin monomers, silicate penetrating crystallizing activators, and benzothiazole corrosion inhibitors. The particle size and core material loading rate of the hierarchical microcapsules are still controlled within the same or substantially the same range as in Example 1, and the surface is still modified with a silane coupling agent to ensure that the main difference between this comparative example and the example is whether the polymer base has shape memory recovery function.

[0156] In this comparative example, the double-shell hierarchical microcontainer can be prepared using the same method as in Example 2. A composite healing agent core material is formed using epoxy resin monomer, silicate penetrating crystallizing surfactant, and benzothiazole corrosion inhibitor. A pH- and ion-responsive inner shell and a humidity- and vibration-responsive outer shell are constructed sequentially to obtain the double-shell hierarchical microcontainer. After the double-shell hierarchical microcontainer is prepared, it is still surface modified using a silane coupling agent to ensure that its surface has an active interface layer that can form a good interface bond with the polymer base material and the cement-based inorganic phase.

[0157] In this comparative example, the liquid material was prepared by pre-dispersing ordinary polymer base material and nano-reinforced filler, while the powder material was prepared by dry mixing cement base material and auxiliary active components. The surface-modified double-shell graded microcontainers were added to the liquid material for dispersion and mixing. Then, the liquid material and powder material were mixed at the same mass ratio as in Example 2 to obtain an anti-seepage coating slurry. After the obtained slurry was applied to the base surface of a damp but dry concrete or clay drainage pipe, it was cured at room temperature to form an anti-seepage coating. Since the ordinary polymer base material in this comparative example still has basic film-forming ability, the obtained coating can still form a continuous protective layer on the surface of the base surface and, to a certain extent, support the graded microcontainers and the repair agent system.

[0158] Because the polymer base material in this comparative example does not have shape memory recovery function, after the crack is formed, the coating cannot actively pull the two sides of the crack together as in the example, and the crack width is difficult to shrink in time. Although the double-shell hierarchical microcontainer in this comparative example can still release composite healing agent under the action of humidity change, vibration and stress concentration at the crack tip, and the surface of the microcontainer can still form a relatively stable interface with the surrounding matrix after silane coupling modification, the crack area lacks an active crack shrinkage process, which causes the released repair agent to rely more on passive filling to enter the crack, and its effective filling degree in larger cracks or deep crack areas is limited.

[0159] In this comparative example, the same verification conditions as in Example 3 were used for performance evaluation. That is, after the coating was formed, 0.2-0.5 mm cracks were pre-made on the surface of the specimen, and the specimen was subjected to a composite working condition of alternating sewage pH 4-9, micro-vibration frequency 5-10 Hz, and dynamic water pressure circulation of 0.5 MPa for 168 h. After that, the specimen was left to stand for 7 days and the crack repair and the anti-seepage recovery after the coating was removed were evaluated.

[0160] The results show that, under the above-mentioned composite working conditions, although the double-shell hierarchical microcontainer in this comparative example can still release the composite healing agent and form a certain degree of sealing and densification repair in the crack area, the initial opening of the crack is difficult to effectively converge in the early stage of repair because the ordinary polymer matrix cannot provide shape recovery on both sides of the crack. As a result, the retention efficiency, filling continuity and bonding tightness of the repair agent in the crack are all affected.

[0161] Furthermore, the above effects become more pronounced when the crack width approaches its upper limit. For wider cracks, ordinary polymer-based materials can only provide conventional film-forming coating and local bridging effects, but are unable to actively narrow the crack opening. This makes it easier for the released repair agent to accumulate locally, fill discontinuously, or disperse into non-target areas. The repaired area is more likely to have large local openings or insufficiently densified pore channels. Under subsequent dynamic water pressure and micro-vibration cycles, it is more likely to experience residual seepage, local edge instability, and insufficient anti-seepage recovery after the surface coating is removed.

[0162] Because this comparative example lacks the active synergistic relationship between shape memory polyurethane and the double-shell hierarchical microcontainer, the crack repair process mainly relies on the release and curing of the repair agent. The overall repair speed and repair adequacy are lower than those of the example. Especially in the combined working conditions of drainage pipeline service environment, such as acid and alkali fluctuations, ion intrusion, humidity alternation and vibration disturbance, it is difficult to continuously ensure the effective closure of the crack area and long-term impermeability stability by relying solely on the passive release of the repair agent.

[0163] This comparative example shows that, while keeping the double-shell hierarchical micro-container structure, composite healing agent composition, surface coupling modification method, and construction verification conditions basically unchanged, simply replacing the shape memory polyurethane system in the examples with ordinary polymer base material will weaken the active closure effect in the early stage of crack repair, thereby affecting the effective filling degree of the repair agent in the crack area, the sufficiency of crack repair, and the anti-seepage recovery effect. The use of shape memory polyurethane in the examples and its shape recovery effect to achieve active crack shrinkage plays an important role in improving crack repair efficiency, repair integrity, and anti-seepage durability.

Claims

1. A waterproof coating for drainage pipes, characterized in that, Including polymer base materials, cement-based materials, graded microcapsules, nano-reinforced fillers, and silane coupling agents; The polymer base material includes shape memory polyurethane, and the glass transition temperature of the shape memory polyurethane is 10-40°C. The hierarchical microcontainer is a double-shell structure with an inner shell and an outer shell. The inner shell is a pH and ion-responsive layer, and the outer shell is a humidity and vibration-responsive layer. The outer shell contains silane-modified shape memory polyurethane. The surface of the hierarchical microcontainer is modified by the silane coupling agent and forms an interfacial chemical bond with the shape memory polyurethane network. The hierarchical microcontainer is encapsulated with a composite healing agent. After the anti-permeability coating is cured into a film, under the stress, humidity changes or vibration induced by crack expansion, the outer shell of the hierarchical micro-container ruptures or its permeability increases to release the composite healing agent, which, combined with the shape recovery effect of the shape memory polyurethane, closes and repairs the crack.

2. The anti-seepage coating according to claim 1, characterized in that, The inner shell material is selected from one or both of layered double hydroxides and polyelectrolytes.

3. The anti-seepage coating according to claim 1, characterized in that, The composite healing agent comprises epoxy resin monomers, silicate penetrating crystallizing activators, and benzothiazole corrosion inhibitors.

4. The anti-seepage coating according to any one of claims 1 to 3, characterized in that, The particle size of the graded microcapsules is 80–150 μm, and the core material loading rate is 75–85%.

5. The anti-seepage coating according to any one of claims 1 to 4, characterized in that, The anti-permeability coating comprises, by weight, parts of: The mixture contains 35-45 parts polymer base material, 25-35 parts cement base material, 6-12 parts graded microcapsules, 1.5-3.5 parts nano-reinforced filler, 0.8-1.5 parts silane coupling agent, and appropriate amount of additives.

6. The anti-seepage coating according to any one of claims 1 to 5, characterized in that, The anti-seepage coating is suitable for the inner or outer walls of concrete or clay drainage pipes and is suitable for application on damp substrates.

7. The anti-seepage coating according to any one of claims 1 to 6, characterized in that, The coating formed by the anti-seepage coating, under the condition of 0.2-0.5mm cracks, after being circulated for 168 hours with simulated sewage pH 4-9 alternating, micro-vibration frequency 5-10Hz and dynamic water pressure of 0.5MPa, has a self-healing rate of not less than 98% after 7 days, and the anti-seepage pressure after removing the coating is not less than 1.8MPa.

8. A method for preparing an anti-permeability coating as described in any one of claims 1 to 7, characterized in that, Includes the following steps: A double-shell hierarchical microcontainer with an inner shell and an outer shell is prepared. A composite healing agent is encapsulated inside the hierarchical microcontainer, and the surface of the hierarchical microcontainer is modified using a silane coupling agent. A polymer base containing shape memory polyurethane is mixed with nano-reinforced fillers to obtain a liquid material; The cementitious base material is dry-mixed with the auxiliary active components to obtain a powder. The surface-modified hierarchical microcapsules are added to the liquid and dispersed and mixed. The liquid and powder are mixed at a mass ratio of 1:1.0 to 1.2 to obtain an anti-seepage coating.

9. The method for preparing a drainage pipe according to claim 8, characterized in that, The surface-modified hierarchical microcapsules and the shape memory polyurethane network in the liquid material form interfacial chemical bonds during the curing process.

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