Ceramic-polymer composite material for reinforcing V-grade surrounding rock culvert and preparation method of ceramic-polymer composite material

Abstract

The invention discloses a ceramic-polymer composite material for reinforcing a V-grade surrounding rock culvert and a preparation method of the ceramic-polymer composite material, and belongs to the technical field of civil engineering materials. The problems that an existing reinforcing material is difficult to have self-sensing and self-healing functions and functional components are prone to being damaged in the preparation process are solved. The method is characterized by comprising the following steps: dry-mixing fly ash, slag and fibers; preparing an alkali activator; shearing and dispersing the acidized multi-walled carbon nanotubes, a water reducing agent and water to form a carbon nanotube suspension; sequentially adding the carbon nanotube suspension, water and a defoaming agent into the dry powder mixture, and stirring at a low speed for wetting; adding styrene-butadiene latex, stirring and dispersing, adding an alkali activator, and stirring at a medium speed to form slurry; and finally, adding the self-healing microcapsules, and stirring at a low speed until uniform distribution. The prepared material is mainly used for reinforcing a V-grade surrounding rock culvert, and can sense damage in real time and automatically repair cracks.

Description

Technical Field

[0001] This invention relates to the field of civil engineering materials and composite materials technology. More specifically, this invention relates to a ceramic-polymer composite material for reinforcing Class V surrounding rock culverts and its preparation method. Background Technology

[0002] With the rapid development of infrastructure construction such as transportation and water conservancy, a large number of tunnel and culvert projects inevitably need to traverse areas with extremely poor geological conditions and weak surrounding rock. Class V surrounding rock, as one of the least stable rock types, has a series of unfavorable characteristics, including low strength, large deformation, extremely short self-stabilization time, and easy softening and mudding upon contact with water. Culvert construction and support in this type of surrounding rock places almost stringent performance requirements on reinforcement materials: not only do they need extremely high early and final strength to quickly provide support force and resist surrounding rock pressure, but they also need excellent toughness to adapt to large deformations of the surrounding rock and avoid brittle failure. Simultaneously, they must possess excellent durability and impermeability to resist groundwater erosion and performance degradation under long-term environmental effects. Currently, the reinforcement of Class V surrounding rock culverts in engineering mainly relies on the following traditional materials and technologies: Ordinary concrete or shotcrete is the most traditional reinforcement method. However, the inherent brittleness of concrete makes it prone to microcracks under load. These microcracks not only become weak points in the structure's strength but also become vulnerable to moisture and corrosive ions (such as Cl-). - SO4 2- This provides a rapid intrusion channel, leading to a series of durability problems such as internal steel corrosion and material neutralization, ultimately jeopardizing the safety and long-term service life of the structure. Ordinary concrete is insufficiently adaptable to Class V surrounding rock, which requires high deformation capacity.

[0003] Fiber-reinforced concrete, by incorporating steel fibers, polypropylene fibers, and other materials into concrete, can effectively bridge cracks and improve the material's toughness and crack resistance. This technology improves the brittleness of traditional concrete to some extent. However, it remains a passive reinforcement method. While the addition of fibers can inhibit crack propagation, it cannot automatically repair existing cracks, nor can it prevent the penetration of media along microcracks. More importantly, this type of material has a limited function and lacks the ability to monitor and provide early warning of internal structural damage.

[0004] Chemical grouting technology is mainly used for sealing cracks and waterproofing, but the overall strength of the solidified body it forms is usually not high, making it difficult to use as a primary structural support material. Its effects are often localized and temporary, and it cannot achieve holistic and permanent reinforcement of the surrounding rock.

[0005] In recent years, the concept of self-healing concrete has emerged to improve the durability of materials. Among them, microencapsulation technology has become a research hotspot due to its high repair efficiency and strong controllability. This technology involves pre-embedding microcapsules containing repair agents into concrete, which rupture when cracks propagate to release the repair agent and bond the cracks. However, simply transplanting microencapsulation technology to traditional silicate cement systems for Class V surrounding rock culverts faces severe challenges: First, the high alkalinity environment generated by traditional cement hydration can easily erode the wall material of some microcapsules, leading to poor storage stability or failure before service; second, in the shotcrete construction process commonly used for culvert reinforcement, the high-speed impact of aggregates and the high-pressure shear force during pumping can easily cause a large number of microcapsules to break during the construction stage, making them unable to heal as needed later; finally, the introduction of microcapsules may have an adverse effect on the mechanical properties of the material, especially its strength.

[0006] On the other hand, advancements in structural health monitoring technology have created a demand for intelligent materials. While some studies have attempted to incorporate conductive materials such as carbon nanotubes into cement matrices to prepare self-sensing materials, achieving high content, uniformity, and stable dispersion of carbon nanotubes in the high-viscosity, high-flowability jet slurry required for Class V surrounding rock reinforcement to form a continuous and reliable three-dimensional conductive network remains a significant technical bottleneck. The tendency of carbon nanotubes to easily aggregate leads to insensitive and unstable signals, rendering the self-sensing function ineffective. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0008] To achieve these objectives and other advantages according to the present invention, a method for preparing a ceramic-polymer composite material for reinforcing Class V surrounding rock culverts is provided, comprising the following steps: S1. Raw material pretreatment, which includes: Fly ash, granulated blast furnace slag, and polypropylene fiber are mixed evenly in a dry powder state to obtain a dry powder mixture. The amount of fly ash added is 100 parts, the amount of granulated blast furnace slag added is 40-60 parts, and the amount of polypropylene fiber added is 1-2 parts. Sodium hydroxide is dissolved in the first part of the mixing water, cooled, and then water glass solution is added. The mixture is stirred evenly and allowed to stand for aging to obtain an alkali activator. The amount of water glass solution added is 80-100 parts, its solid content is 35-45%, its modulus is 1.5-1.8, the amount of sodium hydroxide added is 10-15 parts, and the amount of the first part of the mixing water added is 10-20 parts. Acid-treated multi-walled carbon nanotubes are sheared and dispersed with polycarboxylate superplasticizer and a second part of mixing water to form a carbon nanotube suspension. The amount of multi-walled carbon nanotubes added is 0.5%-1.0% of the total mass of dry powder of fly ash and granulated blast furnace slag, and the amount of the second part of mixing water added is 10-20 parts. S2. Preparation of slurry, including: First, add the carbon nanotube suspension, the third part of the mixing water, and the defoamer to the dry powder mixture, stirring to fully wet all the powders. Then, add styrene-butadiene latex, stirring to evenly disperse the latex in the slurry. The amount of styrene-butadiene latex added is 15-25 parts, the amount of polycarboxylate superplasticizer added is 0.5-1.5 parts, and the amount of defoamer added is 0.1-0.3 parts. The amount of the third part of the mixing water is the remaining amount after deducting the first and second parts of the mixing water from the total amount of mixing water. The amount of mixing water is 50-80 parts; then add the alkali activator and stir until a slurry is formed; then add the self-healing microcapsules and stir until the self-healing microcapsules are evenly distributed, wherein the amount of self-healing microcapsules added is 3%-5% of the total mass of dry powder of fly ash and granulated blast furnace slag; the core of the self-healing microcapsules is a compound of epoxy resin and ketimine latent curing agent, and the capsule wall is a urea-formaldehyde resin or gelatin-gum arabic composite cohesive wall material with a particle size of 50-150μm.

[0009] Preferably, the acidification treatment of multi-walled carbon nanotubes includes: placing the multi-walled carbon nanotubes in a mixed solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:2 to 1:3, ultrasonically treating them at 50-70°C for 2-4 hours, then repeatedly washing them with deionized water until the washing solution is neutral, and finally vacuum drying them at 70-90°C.

[0010] Preferably, it also includes: S3, Maintenance, which includes initial maintenance and long-term maintenance; Initial curing involves covering the slurry with plastic film after pouring or spraying it, and curing it for 24-48 hours at a temperature of 15℃-25℃ and a relative humidity greater than 90%. Long-term maintenance includes curing for 7-28 days at a temperature of 15℃-25℃ and a relative humidity of not less than 80% after removing the plastic film; the methods for maintaining humidity include, but are not limited to: covering with a damp cloth, using an automatic spray system to keep moist, or placing directly in a fog chamber, to ensure that the surface of the component remains moist throughout the curing period.

[0011] Preferably, the modulus of the water glass solution is adjusted to 1.5 to 1.8 using sodium hydroxide.

[0012] Preferably, in the preparation of the carbon nanotube suspension, a dispersant accounting for 50%-150% of the mass of the multi-walled carbon nanotubes is added, and the dispersant is polyvinylpyrrolidone or sodium dodecyl sulfate. After shear dispersion, the carbon nanotube suspension is further processed using a probe-type ultrasonic disperser with an ultrasonic power of 200-400W and a processing time of 5-15 minutes.

[0013] Preferably, during the slurry preparation stage, after adding self-healing microcapsules and stirring, the working pressure of the spray gun nozzle during wet spraying is controlled to be 0.3-0.5 MPa.

[0014] Preferably, during the slurry preparation stage, the styrene-butadiene latex is premixed with a stabilizer, which is sodium lignosulfonate or polyethylene glycol, and the amount added is 0.5%-2.0% of the mass of the styrene-butadiene latex.

[0015] Preferably, during the slurry preparation stage, while adding the self-healing microcapsules, a suspension stabilizer accounting for 0.1%-0.5% of the total slurry volume is added, and the suspension stabilizer is bentonite.

[0016] Preferably, during the slurry preparation stage, after adding the alkali activator, a segmented variable speed stirring method is adopted: first stirring at a speed of 100-200 rpm for 1-2 minutes, and then stirring at a speed of 400-600 rpm for 2-4 minutes.

[0017] Preferably, in the raw material pretreatment of step S1, the self-healing microcapsules are subjected to surface pretreatment: the self-healing microcapsules are mixed with 0.1%-0.5% by weight of nano-silica powder in a tumbling container for 5-15 minutes.

[0018] A ceramic-polymer composite material for reinforcing Class V surrounding rock culverts is provided, prepared by the above-described method.

[0019] The present invention has at least the following beneficial effects: First, it has excellent mechanical properties. Through the combination of geopolymer and styrene-butadiene latex, the material has both high strength and high toughness, and can effectively resist the large deformation of Class V surrounding rock.

[0020] Secondly, intelligent self-sensing: by constructing a uniformly dispersed three-dimensional conductive network of carbon nanotubes, the material itself becomes a sensor. Its resistivity is sensitive to stress and crack propagation, enabling real-time online monitoring and early warning of structural health.

[0021] Third, intelligent self-healing: the self-healing microcapsules with ketimine as a latent curing agent embedded inside can activate the repair agent when the crack is exposed to water, effectively healing the microcracks, restoring the material's impermeability and mechanical properties, and significantly extending the service life of the structure.

[0022] Fourth, it has excellent construction performance. Through optimized step-by-step feeding and segmented mixing processes, as well as the introduction of suspension stabilizers, it ensures the uniform distribution and integrity of each component (especially microcapsules) in the high-viscosity slurry, giving the material good fluidity and sprayability, making it suitable for complex tunnel construction environments.

[0023] Fifth, it boasts outstanding environmental and economic advantages, using industrial solid waste such as fly ash and slag as its main raw materials, aligning with the development direction of green building materials. Its long lifespan and low maintenance requirements offer significant advantages in terms of total life-cycle cost.

[0024] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of one of the preparation methods of the present invention. Detailed Implementation

[0026] like Figure 1 As shown, to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention. Process parameters in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0027] <Example 1> A ceramic-polymer composite material for reinforcing Class V surrounding rock culverts, comprising: 1. Raw materials and proportions (by weight) Ceramic phase matrix: 100 parts fly ash (F grade) and 50 parts granulated blast furnace slag (S95 grade); Alkali activator: 90 parts water glass solution (modulus 2.2, solid content 40%), 12 parts sodium hydroxide (caustic soda flakes), and 15 parts mixing water (for dissolving NaOH). Polymer phase and additives: 20 parts styrene-butadiene latex (48% solids content), 1.0 part polycarboxylate superplasticizer, 0.2 parts defoamer (silicone type); the solids content of the styrene-butadiene latex is limited to 45%-50%. This is because too low a solids content will introduce too much free water, changing the water-cement ratio and affecting the slurry properties and final strength; too high a solids content will make the latex viscosity too high, making it difficult to disperse uniformly in the slurry. This solids content range ensures the accuracy and stability of the added polymer phase in the system, which is an important guarantee for achieving the expected toughening effect.

[0028] Functional components: 0.8 parts of multi-walled carbon nanotubes (acid-treated) (0.53% of the total mass of fly ash and slag dry powder), 4.5 parts of self-healing microcapsules (urea-formaldehyde resin wall material, epoxy resin and ketimine latent curing agent compound core, with a mass ratio of 2.5:1 and a particle size of 80-120μm) (3.0% of the total mass of fly ash and slag dry powder), and 1.5 parts of polypropylene fiber (12mm in length); In the core, the mass ratio of epoxy resin (preferably bisphenol A type epoxy resin with an epoxy value of 0.48-0.54) to a ketimine-based latent curing agent is 2:1 to 3:1. This curing agent is chemically stable under alkaline and dry conditions, decomposing only upon contact with water to generate active amines, thereby initiating the curing of the epoxy resin and ensuring the long-term stability of the microcapsules before construction.

[0029] Among them, multi-walled carbon nanotubes have an outer diameter of 10-30 nm, a length of 10-30 μm, and a specific surface area of ​​200-400 m². 2 / g; Other auxiliary components: 0.018 parts of nano-silica (for microcapsule pretreatment) (0.4% of the microcapsule mass), and 0.8 parts of bentonite (as a suspension stabilizer) (this addition amount is based on an estimated slurry density of 2.2 g / cm³). 3 The first part is 0.3% of the total volume of the slurry, the second part is 15 parts of mixing water (used to prepare carbon nanotube suspension), and the third part is 30 parts of mixing water (total mixing water is controlled at 60 parts).

[0030] 2. Preparation method S1. Raw material pretreatment: S1a) Dry-mix fly ash, slag and polypropylene fiber in a mixer for 5 minutes to obtain a uniform dry powder mixture.

[0031] S1b) Dissolve 12 parts of sodium hydroxide in 15 parts of the first batch of mixed water, stir until completely dissolved, cool to room temperature, add 90 parts of water glass solution, stir evenly, seal and let stand for 24 hours to obtain the alkali activator.

[0032] S1c) 0.8 parts of acid-treated multi-walled carbon nanotubes, 1.0 part of polycarboxylate superplasticizer, and 15 parts of the second mixing water were added to a container. The mixture was sheared and dispersed using a high-speed shear mill at 4000 rpm for 30 minutes to obtain a stable carbon nanotube suspension. The specific method of acid treatment was as follows: the multi-walled carbon nanotubes were placed in a mixed solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio 1:3), ultrasonically treated at 60℃ for 4 hours, then repeatedly washed with deionized water until neutral, and finally dried in a vacuum drying oven at 80℃ for later use. This treatment can introduce functional groups such as carboxyl groups on the surface, improving its dispersibility in aqueous systems.

[0033] S1d) 4.5 parts of self-healing microcapsules and 0.018 parts of nano silica powder were placed together in a laboratory tumbling coating machine and tumbled and mixed at low speed for 10 minutes to make the nano silica uniformly adhere to the surface of the microcapsules and form a physical protective layer.

[0034] S2. Preparation of slurry (using a forced mixer): S2a) Pour the dry powder mixture from step S1a) into the mixing pot.

[0035] S2b) Add the carbon nanotube suspension prepared in step S1c), 30 parts of the third mixing water, and 0.2 parts of defoamer to the mixing vessel in sequence.

[0036] S2c), stir at low speed (100 rpm) for 2 minutes to fully wet all powder particles with liquid.

[0037] Add 20 parts of styrene-butadiene latex (S2d) and continue stirring at a low speed of 100 rpm for 1.5 minutes to evenly disperse the styrene-butadiene latex.

[0038] S2e) The alkali activator prepared in step S1b) is added rapidly and uniformly.

[0039] Use segmented variable speed mixing: first mix at 150 rpm for 2 minutes, then increase to 500 rpm for 3 minutes, until the slurry is uniform, fine, and glossy.

[0040] S2f), and finally, add the self-healing microcapsules pretreated in step S1d) and 0.3% by volume of bentonite, and stir at a low speed of 80 rpm for 1.5 minutes to ensure that the microcapsules are evenly distributed in the slurry without damage.

[0041] S3, Maintenance: Inject the slurry into the mold or apply it by spraying, controlling the working pressure of the spray gun nozzle at 0.3-0.5 MPa during wet spraying. Immediately cover the surface with plastic film and cure for 48 hours in a standard curing room with a temperature of (20±2)℃ and a relative humidity >95% (initial curing). For on-site construction, if continuous high humidity cannot be guaranteed, alternative solutions can be adopted: uniformly spray a layer of film-forming curing agent (such as acrylic copolymer emulsion) onto the slurry surface to form a water-retaining film, or add 0.5% of the total mass of fly ash and slag pre-absorbent SAP particles during the internal mixing stage to ensure sufficient hydration and reaction of the cementitious system through internal water retention.

[0042] After demolding, continue curing in a humid environment at (20±2)℃ (keeping the surface moist by regularly spraying water) for 28 days (long-term curing).

[0043] 3. Performance Testing The performance of the composite material specimens prepared according to Example 1 was tested, and the results are as follows: Mechanical properties: 28-day compressive strength: 68.5 MPa; 28-day flexural strength: 9.2 MPa; fracture energy: approximately 450% higher than ordinary C30 concrete.

[0044] Self-sensing function: Resistivity is measured using a four-electrode method. When the specimen is subjected to pressure and experiences a micro-strain of 0.5%, the resistivity change rate reaches 35%; when a visible micro-crack (approximately 50 μm wide) appears in the specimen, the resistivity change rate exceeds 200%, demonstrating a highly sensitive response. The four-electrode method is used to eliminate the influence of contact resistance during the self-sensing function test. Specifically, four parallel stainless steel mesh electrodes are pre-embedded during specimen molding, with an electrode spacing of 20 mm. During testing, a constant, small alternating current is applied to the two outer electrodes using a precision digital bridge (or source meter), and the voltage drop between the two inner electrodes is measured. The resistivity is then calculated. Strain is simultaneously measured using resistance strain gauges attached to the specimen.

[0045] Self-healing function: After curing pre-cracked specimens (crack width 100μm) under standard conditions for 28 days, microscopic observation showed that the cracks were essentially filled and healed. After healing, the permeability pressure of the specimens recovered to 88% of that of the uncracked specimens, and the flexural strength recovery rate reached 82%. The permeability pressure recovery was conducted according to the water permeability test method in GB / T 50082-2009 Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete. The flexural strength recovery rate was calculated by comparing the flexural strength of the pre-cracked and self-healed specimens with that of intact specimens. Pre-cracking can be achieved by loading the specimen with a specified crack width (e.g., 100μm) using the three-point bending method.

[0046] Workability: The initial fluidity of the slurry is 220 mm, and it remains greater than 180 mm after standing for 30 minutes, which meets the requirements for pumping and wet spraying.

[0047] Long-term stability verification: To evaluate the long-term stability of carbon nanotubes in an alkaline matrix, the specimen from Example 1 was accelerated-cured for 90 days at 50°C in a 1 mol / L NaOH solution. After curing, its resistivity was measured and compared with that of a specimen cured for 28 days under standard conditions. The results showed that its baseline resistivity increase was less than 15%, and it still exhibited a significant electrical response under load (resistivity change rate under microcracks >180%). This demonstrates that after acidification and sufficient dispersion, the carbon nanotube network has good long-term stability in this composite material system. To further improve durability, graphene nanosheets and multi-walled carbon nanotubes can be preferably used in a mass ratio of 1:2 to 1:4. The two-dimensional layered structure of graphene provides better coating and protection for the carbon nanotubes, jointly constructing a more stable three-dimensional conductive network.

[0048] The core of the self-healing microcapsule of this invention is a compound of epoxy resin and a ketimine-based latent curing agent. Its stability and triggering mechanism are as follows: The ketimine-based latent curing agent is chemically stable in dry and alkaline environments and can coexist with epoxy resin for a long time without reacting, thus ensuring the stability of the microcapsule during material storage and construction. When cracks form in the material, stress concentration at the crack tip causes brittle fracture of the microcapsule wall. The core repair agent (a mixture of epoxy resin and latent curing agent) is drawn into the crack fissure by capillary action. Subsequently, moisture in the environment (such as groundwater or humidity) seeps into the crack, causing the ketimine to decompose and generate active amines, which then trigger the cross-linking and curing reaction of the epoxy resin, effectively bonding the crack interface and restoring the material's mechanical properties and impermeability.

[0049] <Example 2> The slag content was changed: the only difference between this embodiment and Example 1 is that the amount of granulated blast furnace slag added was adjusted to 40 parts, and the total mixing water was adjusted to 58 parts to maintain similar fluidity. The amount of self-healing microcapsules added was adjusted to 4.2 parts (accounting for 3.0% of the total mass of fly ash and slag dry powder). The remaining raw materials and preparation steps were exactly the same. The second part of the mixing water was 15 parts, and the third part of the mixing water was 28 parts (the total mixing water was controlled at 58 parts, calculated as: 15 parts of the first part + 15 parts of the second part + 28 parts of the third part).

[0050] Performance test results: 28-day compressive strength: 60.1 MPa; 28-day flexural strength: 8.1 MPa.

[0051] The self-sensing and self-healing functions remain effective, resistivity changes are sensitive, and the self-healing efficiency (anti-permeability recovery) reaches 85%.

[0052] <Example 3> The difference between this embodiment and Example 1 lies only in the amount of styrene-butadiene latex added, which is adjusted to 25 parts. All other raw materials and preparation steps remain identical. The total mixing water remains 60 parts (15 parts for Part 1 + 15 parts for Part 2 + 30 parts for Part 3).

[0053] Performance test results: 28-day compressive strength: 62.8 MPa; 28-day flexural strength: 10.5 MPa, with further improved fracture energy.

[0054] The toughness is significantly enhanced, but the self-sensing sensitivity (resistivity change rate) is slightly lower than that of Example 1, but it still has a significant response (resistivity change at the crack >150%). The self-healing function remains good.

[0055] <Example 4> Change of self-healing microcapsule wall material: The only difference between this embodiment and Example 1 is that the capsule wall of the self-healing microcapsule is replaced with gelatin-gum arabic prepared by composite coagulation method. The capsule core (a compound of epoxy resin and ketimine latent curing agent) and all other raw materials, proportions (including a total mixing water of 60 parts) and preparation steps are the same as in Example 1.

[0056] Performance test results: 28-day compressive strength: 66.8 MPa; 28-day flexural strength: 8.9 MPa.

[0057] Self-sensing function: The resistivity change response is sensitive, comparable to Example 1.

[0058] Self-healing function: After curing the pre-cracked specimen for 28 days, the impermeability pressure recovered to 85% of that of the uncracked specimen, and the flexural strength recovery rate reached 80%.

[0059] Microcapsules using gelatin-gum arabic composite coagulation wall material can also work effectively in this system, proving that the present invention has a wide range of applicability in the selection of microcapsule wall materials.

[0060] <Comparative Example 1> No polymers or functional components: This comparative example differs from Example 1 in that it does not contain styrene-butadiene latex, multi-walled carbon nanotubes, self-healing microcapsules, or polypropylene fibers. Pure geopolymer materials were prepared using only fly ash (100 parts) and slag (50 parts). The total mixing water was adjusted to 45 parts.

[0061] Performance test results: 28-day compressive strength: 55.2 MPa; 28-day flexural strength: 5.8 MPa. The material exhibits significant brittleness and low fracture energy.

[0062] It has no self-sensing function (its resistance hardly changes with strain).

[0063] It does not have self-healing function; the cracks in the pre-cracked specimens showed no signs of healing.

[0064] <Comparative Example 2> No microcapsule surface pretreatment or suspension stabilizer: The difference between this comparative example and Example 1 is that the self-healing microcapsules do not undergo nano-silica surface pretreatment, and no bentonite suspension stabilizer is added during slurry preparation. The remaining steps are exactly the same.

[0065] Performance test results: The mechanical strength is similar to that of Example 1.

[0066] However, during stirring and settling, signs of microcapsules floating were observed. The self-healing efficiency of the prepared specimens was significantly reduced, with a permeability recovery rate of only 45%. Microscopic observation revealed that the microcapsules were unevenly distributed in the slurry, and some capsules were already broken before construction.

[0067] <Comparative Example 3> Non-optimized stirring process: The difference between this comparative example and Example 1 is that after adding the alkali activator, segmented variable speed stirring is not used; instead, the stirring is carried out at a constant speed of 400 rpm for 5 minutes. The remaining steps are exactly the same.

[0068] Performance test results: Numerous air bubbles were visible inside the slurry, and the density of the specimen decreased after hardening.

[0069] The compressive strength decreased to 58.7 MPa after 28 days.

[0070] The self-sensing signal exhibits poor stability and large fluctuations in resistance values ​​between different specimens, which is presumably due to uneven dispersion of carbon nanotubes and the influence of air bubbles.

[0071] The observed breakage rate of microcapsules was relatively high.

[0072] <Comparative Example 4> Carbon nanotube-free dispersion optimization: The only difference between this comparative example and Example 1 is that, in preparing the carbon nanotube suspension, only high-speed shear dispersion was performed, without subsequent probe-type ultrasonic-assisted treatment. All other raw materials and preparation steps were exactly the same.

[0073] Performance test results: The mechanical strength is similar to that of Example 1.

[0074] Self-sensing function: The initial resistivity value is high and unstable. The resistivity changes slowly during loading. When obvious cracks appear, the resistivity change rate is less than 50%, which cannot achieve effective early warning.

[0075] Microscopic analysis: Scanning electron microscopy revealed obvious aggregates in the carbon nanotubes.

[0076] The results show that at high doping levels, without ultrasonic-assisted treatment, carbon nanotubes cannot fully deagglomerate to form a continuous conductive network, thus causing the self-sensing function to fail.

[0077] <Experimental Results and Data Analysis> 1. During the alkali activation process, fly ash and slag dissolve and rearrange to form a three-dimensional amorphous geopolymer network (ceramic phase) with -Si-O-Al-O- as the main chain. This dense network structure contributes to the material's high strength and stiffness. Simultaneously, the introduced styrene-butadiene latex (polymer phase) undergoes two key processes in the slurry: first, the latex particles are uniformly dispersed under stirring; second, during water evaporation and geopolymer condensation, the latex particles demulsify, aggregate, and form a film, creating a continuous and elastic polymer film. This film is not isolated but interwoven and penetrates the three-dimensional network of the geopolymer, forming an interpenetrating skeleton-ligament structure.

[0078] When the geopolymer network is subjected to load and is about to undergo brittle fracture, the interwoven polymer film effectively bridges, deflects, and inhibits the propagation of microcracks through its large deformation capacity. This process requires a large amount of energy, which macroscopically manifests as a significant increase in the material's fracture energy (approximately 450% in Example 1), thus achieving a balance between rigidity and toughness. Comparative Example 1, lacking a polymer phase, exhibits typical brittle fracture behavior, confirming the core role of this mechanism.

[0079] 2. The key to achieving stable self-sensing functionality lies in the formation of continuous and stable conductive pathways by carbon nanotubes within an insulating ceramic-polymer matrix. Strong van der Waals forces exist between carbon nanotubes, making them prone to agglomeration, especially at high doping levels. Simple shear dispersion primarily affects micron-scale mixing, and its shear force is insufficient to completely break up the tightly packed nanoscale carbon nanotube aggregates. These residual aggregates lead to discontinuous and unstable conductive networks (as shown in Comparative Example 4).

[0080] This application employs a three-stage dispersion strategy: pre-dispersion, ultrasonic-assisted dispersion, and shear mixing. Probe-type ultrasonic dispersion is the key step. Ultrasound generates a strong cavitation effect in the liquid, creating instantaneous high-temperature, high-pressure microjets and shock waves. This extremely localized energy is sufficient to penetrate and completely break down the van der Waals force bonds between carbon nanotubes, dissociating macroscopic aggregates into independent or small-group units. Subsequently, under optimized stirring, these fully de-agglomerated nanotubes are uniformly fixed in the slurry, solidifying to form a continuous and stable three-dimensional conductive network, thereby achieving a sensitive and reliable response to stress and cracks.

[0081] After curing, these randomly distributed carbon nanotubes interlock to form a continuous three-dimensional conductive network within the material. When the material is subjected to stress and deformation or develops microcracks, the distance between the carbon nanotubes changes, and some interlocking points even break, resulting in a significant change in the tunneling resistance of the entire network. As shown in Example 1, the 35% change rate under microstrain originates from the change in the spacing between the nanotubes, while the dramatic change of over 200% at the crack originates from the breakage of the conductive path. This response is macroscopic and sensitive. In Comparative Example 4, due to insufficient dispersion and a discontinuous conductive network, the self-sensing function is almost completely ineffective.

[0082] 3. This invention involves surface pretreatment of the microcapsules. The nano-silica particles attached to the capsule wall surface act as a physical barrier, effectively resisting friction and impact during stirring and pumping. Furthermore, their chemical inertness and stability to alkaline solutions delay the chemical erosion of the capsule wall material (especially gelatin-gum arabic) by the high-alkalinity environment. This, together with the suspension stabilizer, constitutes a comprehensive protection system for the microcapsules throughout the entire process.

[0083] When a crack propagates within a material, the stress at its tip is preferentially transferred to the microcapsule, causing brittle fracture of its wall. Subsequently, the epoxy resin and curing agent in the core are drawn into the crack gap by capillary action, and a cross-linking and curing reaction occurs upon contact, achieving a dual combination of mechanical interlocking and chemical bonding, thereby effectively sealing the crack.

[0084] In Comparative Example 2, due to a lack of protection, a large number of microcapsules were prematurely damaged during the construction phase, resulting in the absence of repair agents when needed, and the self-healing efficiency dropped significantly to 45%. In contrast, the high recovery rate of 88% in Example 1 was due to the intact microcapsules being triggered on demand at critical moments.

[0085] 4. Compatibility of Microcapsule Particle Size with Crack Healing. Cracks in Class V surrounding rock culvert structures typically originate and propagate from micron-sized microcracks. The 50-150 μm microcapsules selected in this invention are based on the following considerations: Firstly, microcapsules in this size range can be effectively contained within the slurry and maintain their integrity during wet spraying (working pressure 0.3-0.5 MPa) (as shown in Comparative Example 2, failure without protective measures would occur). Secondly, theoretical studies and experimental observations (such as microscopic observations in Example 1) show that when the crack width reaches 1 / 3 to 1 / 2 of the microcapsule particle size, the stress at the crack tip is sufficient to cause the microcapsule to rupture. Therefore, 50-150 μm microcapsules can effectively heal cracks with widths of approximately 15 μm to 75 μm, a range that completely covers the common microcrack scales (typically <100 μm) in Class V surrounding rock that affect durability and integrity. The successful healing of a 100 μm crack in Example 1 demonstrates that the microcapsules are effectively triggered during crack propagation, and the released repair agent is sufficient to fill and seal cracks that are slightly narrower than their own particle size.

[0086] Furthermore, the 50-150 μm range does not require all microcapsules to be of a single size, but rather refers to a range with a certain size distribution. Using a mixture of microcapsules with a specific size distribution helps to form a multi-scale repair system within the material: smaller microcapsules (e.g., 50-80 μm) are more easily triggered and used to repair microcracks in their initiation stage; larger microcapsules (e.g., 100-150 μm) can provide sufficient repair agent for wider cracks. This multi-scale synergy enhances the material's self-healing robustness against cracks of different sizes.

[0087] 5. Step-by-step feeding and segmented variable-speed mixing are key to optimizing the microstructure. First, mixing the dry powder and liquid at low speed ensures all powder particles are fully wetted, laying a uniform foundation for subsequent reactions. After adding the alkali activator, segmented mixing at low speed followed by high speed serves a dual purpose: the low-speed stage avoids excessive gas entrainment due to violent reactions; the high-speed stage provides sufficient shear force to break up initially formed powder agglomerates, promoting uniform geopolymerization, and also eliminates microbubbles, making the slurry more compact.

[0088] This process ensures a highly uniform distribution of functional components such as carbon nanotubes, polymer film precursors, and microcapsules in the final cured body, avoiding weak areas of strength caused by local defects (such as bubbles and agglomerates). Comparative Example 3, due to the use of single high-speed stirring, had a high gas content in the slurry, which ultimately led to a decrease in mechanical properties and a deterioration in functional stability, thus demonstrating the necessity of process optimization.

[0089] This invention enables the ceramic phase, polymer phase, carbon nanotubes, and self-healing microcapsules to form an ordered synergistic structure at the micro and meso scales, ultimately achieving a breakthrough in performance at the macro scale by integrating strength, toughness, self-sensing, and self-healing, providing a solution for the long-term safety of Class V surrounding rock culverts.

[0090] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. Other modifications can be easily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for preparing a ceramic-polymer composite material for reinforcing Class V surrounding rock culverts, characterized in that, Includes the following steps: S1. Raw material pretreatment, which includes: Fly ash, granulated blast furnace slag, and polypropylene fiber are mixed evenly in a dry powder state to obtain a dry powder mixture. The amount of fly ash added is 100 parts, the amount of granulated blast furnace slag added is 40-60 parts, and the amount of polypropylene fiber added is 1-2 parts. Sodium hydroxide is dissolved in the first part of the mixing water, cooled, and then water glass solution is added. The mixture is stirred evenly and allowed to stand for aging to obtain an alkali activator. The amount of water glass solution added is 80-100 parts, its solid content is 35-45%, its modulus is 1.5-1.8, the amount of sodium hydroxide added is 10-15 parts, and the amount of the first part of the mixing water added is 10-20 parts. Acid-treated multi-walled carbon nanotubes are sheared and dispersed with polycarboxylate superplasticizer and a second part of mixing water to form a carbon nanotube suspension. The amount of multi-walled carbon nanotubes added is 0.5%-1.0% of the total mass of dry powder of fly ash and granulated blast furnace slag, and the amount of the second part of mixing water added is 10-20 parts. S2. Preparation of slurry, including: First, add the carbon nanotube suspension, the third part of the mixing water, and the defoamer to the dry powder mixture, and stir to fully wet all the powders. Then, add styrene-butadiene latex and stir to evenly disperse the latex in the slurry. The amount of styrene-butadiene latex added is 15-25 parts, the solid content of the styrene-butadiene latex is 45%-50%, the amount of polycarboxylate superplasticizer added is 0.5-1.5 parts, and the amount of defoamer added is 0.1-0.3 parts. The amount of the third part of the mixing water is the total amount of mixing water minus the amount of the first part of the mixing water. The remaining water after the second batch of mixing water, with a total mixing water volume of 50-80 parts, is then added. The alkaline activator is stirred until a slurry is formed. Then, self-healing microcapsules are added and stirred until the self-healing microcapsules are evenly distributed. The amount of self-healing microcapsules added is 3%-5% of the total mass of dry powder of fly ash and granulated blast furnace slag. The core of the self-healing microcapsules is a compound of epoxy resin and ketimine latent curing agent, and the capsule wall is a urea-formaldehyde resin or gelatin-guar arabic composite cohesive wall material.

2. The method for preparing ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, Also includes: S3. Maintenance, which includes initial maintenance and long-term maintenance; Initial curing involves covering the slurry with plastic film after pouring or spraying it, and curing it for 24-48 hours at a temperature of 15℃-25℃ and a relative humidity greater than 90%. Long-term maintenance includes curing for 7-28 days at a temperature of 15℃-25℃ under wet curing conditions after removing the plastic film.

3. The method for preparing ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, The modulus of the water glass solution is adjusted to 1.5 to 1.8 using sodium hydroxide.

4. The method for preparing the ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, In the preparation of carbon nanotube suspension, a dispersant accounting for 50%-150% of the mass of multi-walled carbon nanotubes is added. The dispersant is polyvinylpyrrolidone or sodium dodecyl sulfate. After shear dispersion, the carbon nanotube suspension is further processed using a probe-type ultrasonic disperser with an ultrasonic power of 200-400W and a processing time of 5-15 minutes.

5. The method for preparing ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 2, characterized in that, During the slurry preparation stage, after adding self-healing microcapsules and stirring, the working pressure of the spray gun nozzle during wet spraying is controlled to be 0.3-0.5 MPa.

6. The method for preparing the ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, During the slurry preparation stage, styrene-butadiene latex is premixed with a stabilizer, which is sodium lignosulfonate or polyethylene glycol, and the amount added is 0.5%-2.0% of the mass of styrene-butadiene latex.

7. The method for preparing the ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, During the slurry preparation stage, while adding self-healing microcapsules, a suspension stabilizer of 0.1%-0.5% of the total slurry volume is added. The suspension stabilizer is bentonite.

8. The method for preparing the ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, During the slurry preparation stage, after adding the alkali activator, a segmented variable speed stirring method is adopted: first stir at a speed of 100-200 rpm for 1-2 minutes, and then stir at a speed of 400-600 rpm for 2-4 minutes.

9. The method for preparing the ceramic-polymer composite material for reinforcing Class V surrounding rock culverts as described in claim 1, characterized in that, In the raw material pretreatment in step S1, the self-healing microcapsules are subjected to surface pretreatment: the self-healing microcapsules are mixed with 0.1%-0.5% by weight of nano-silica powder in a tumbling container for 5-15 minutes.

10. The ceramic-polymer composite material for reinforcing Class V surrounding rock culverts prepared by the preparation method according to any one of claims 1 to 9.

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