Self-healing cement-based composite material and preparation method thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to a self-healing cement-based composite material and a preparation method thereof. The self-healing cement-based composite material is prepared from the following components in parts by weight: 380 to 420 parts of cement, 310 to 330 parts of fly ash, 65 to 75 parts of silica fume, 230 to 250 parts of sand, 10 to 12 parts of fiber and an encapsulated capillary crystalline material, the encapsulated capillary crystalline material comprises a porous skeleton and a capillary crystalline material loaded on the porous skeleton, and the mass of the encapsulated capillary crystalline material is 5% of the total mass of the cement, the fly ash and the silica fume. The self-healing cement-based composite material disclosed by the invention is beneficial to improving the mechanical property and the self-healing property of a cement structure.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a self-healing cement-based composite material and its preparation method. Background Technology

[0002] With the increasing construction of cross-sea bridges, underwater tunnels, and port terminals, cement-based materials have become the main materials for hydraulic infrastructure construction. However, concrete structures in water-related environments are prone to cracking and failure under complex mechanical conditions and extreme environments, seriously affecting their service life. For example, the lining structure of a submarine tunnel is prone to developing micro-cracks in the early stages under high water pressure and salt corrosion. These cracks are difficult to detect and can continue to extend and expand, eventually causing water leakage or even collapse. Therefore, designing high-strength and tough cement-based materials with self-healing capabilities is crucial to ensuring the long-term service life of water-related infrastructure.

[0003] Currently, many materials can enhance the self-healing ability of cement-based materials, such as nanomaterials, microorganisms, shape memory alloys, superabsorbent resins, microcapsules, and penetrating crystallizing materials. However, their performance and effects require further development. For example, nanomaterials react rapidly in the early stages of cement hydration, contributing little to the later self-healing effect. Similarly, microorganisms have high requirements for the microenvironment and nutrient solution, resulting in a low survival rate in cement-based materials. Among these, penetrating crystallizing materials, as fillers primarily composed of chemical materials, are widely used due to their high healing effect, lack of negative impact on mechanical properties, and controllable composition. However, due to their high activity, penetrating crystallizing materials are easily consumed during cement hydration, making it difficult to achieve self-healing effects under long-term service conditions.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a self-healing cement-based composite material and its preparation method, so as to help solve or improve the problem that the self-healing ability of cement-based materials in the prior art needs to be improved.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a self-healing cement-based composite material, comprising the following components: 380-420 parts cement, 310-330 parts fly ash, 65-75 parts silica fume, 230-250 parts sand, 10-12 parts fiber, and an encapsulated permeable crystalline material; the encapsulated permeable crystalline material comprises a porous skeleton and a permeable crystalline material loaded on the porous skeleton, wherein the mass of the encapsulated permeable crystalline material is 5% of the total mass of cement, fly ash, and silica fume.

[0007] Preferably, the encapsulated permeable crystallizing material is prepared by a method comprising the following steps: A1, mixing a porous framework with a permeable crystallizing material solution, vacuum impregnating, followed by solid-liquid separation and drying to obtain the encapsulated permeable crystallizing material; the permeable crystallizing material is calcium chloride and / or sodium silicate.

[0008] Preferably, the concentration of the permeation crystallization material solution is 10wt%-20wt%; the pressure during vacuum impregnation is -0.07~-0.09MPa, and the vacuum impregnation time is 15-25min; the porous framework is biochar.

[0009] Preferably, the encapsulated permeation crystallization material further includes a slow-release membrane; after step A1, the method further includes: A2, immersing the encapsulated permeation crystallization material in a slow-release membrane solution, separating the solid and liquid, and drying it to obtain the encapsulated permeation crystallization material wrapped by the slow-release membrane.

[0010] Preferably, the sustained-release membrane solution is a polyvinylpyrrolidone solution; in the sustained-release membrane solution, the mass ratio of polyvinylpyrrolidone to water is 1:(8-12); in step A2, the encapsulated permeation crystallizing material is immersed in the sustained-release membrane solution for 0.8-1.2 hours.

[0011] Preferably, the self-healing cement-based composite material further comprises fibers and / or water-reducing agents; the fibers are polyethylene fibers; the water-reducing agent is a polycarboxylate water-reducing agent, and the amount of the water-reducing agent is 5.3-5.8 parts; the sand is quartz sand with a particle size of 120-180 μm.

[0012] Preferably, the water-cement ratio of the self-healing cementitious composite material is 0.2.

[0013] The present invention also provides a method for preparing a self-healing cement-based composite material, which adopts the following technical solution: The method for preparing the self-healing cement-based composite material as described above includes the following steps: (1) mixing the cement, fly ash, silica fume, sand and encapsulating penetrating crystallizing material evenly to obtain a dry mixture; (2) mixing the water-reducing agent and water evenly to obtain a water-reducing agent solution; (3) mixing the dry mixture with the water-reducing agent solution, adding fiber, mixing evenly to obtain the self-healing cement-based composite material.

[0014] Beneficial effects: The self-healing cement-based composite material of the present invention helps to improve the mechanical properties and self-healing properties of cement-based composite materials.

[0015] The self-healing cement-based composite material of the present invention can achieve a crack healing rate of over 60%, and even over 85%. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 The tensile curve test results are shown for the self-healing cement-based composite materials of Examples 1-4 and the cement-based materials of Comparative Examples 1 and 5. Figure 2 The images show the test results of the self-healing of cracks in the self-healing cement-based composite materials of Examples 1-4 and the cement-based materials of Comparative Examples 1 and 5; where (a) is the image of Comparative Example 1 before self-healing, (b) is the image of Comparative Example 1 after self-healing, (c) is the image of Comparative Example 5 before self-healing, (d) is the image of Comparative Example 5 after self-healing, (e) is the image of Example 1 before self-healing, (f) is the image of Example 1 after self-healing, (g) is the image of Example 2 before self-healing, (h) is the image of Example 2 after self-healing, (i) is the image of Example 3 before self-healing, (j) is the image of Example 3 after self-healing, (k) is the image of Example 4 before self-healing, and (l) is the image of Example 4 after self-healing. Figure 3 To Figure 2 The image after binarization. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0018] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0019] This invention addresses the problem that the self-healing ability of existing cement-based materials needs to be improved, and provides a self-healing cement-based composite material.

[0020] The self-healing cement-based composite material of this invention comprises, by weight, the following components: 380-420 parts cement (e.g., 380, 390, 400, 410, or 420 parts), 310-330 parts fly ash (e.g., 310, 320, or 330 parts), 65-75 parts silica fume (e.g., 65, 68, 70, 72, or 75 parts), 230-250 parts sand (e.g., 230, 240, or 250 parts), 10-12 parts fiber (e.g., 10, 11, or 12 parts), and an encapsulated penetrating crystalline material. The encapsulated penetrating crystalline material comprises a porous skeleton and a penetrating crystalline material loaded on the porous skeleton. To ensure that the cement-based composite material possesses both excellent mechanical properties and good self-healing properties, the mass of the encapsulated penetrating crystalline material is preferably 5% of the total mass of cement, fly ash, and silica fume. If the amount of encapsulated penetrating crystallizing material used is too large, the fluidity of the composite slurry will be severely reduced due to its excessive water absorption, making it difficult to cast and form. If the amount of encapsulated penetrating crystallizing material used is too small, the amount of adsorbed penetrating crystallizing material will be too small, resulting in poor self-healing performance of the cement-based composite material.

[0021] In a preferred embodiment of the self-healing cement-based composite material of the present invention, the encapsulated permeable crystalline material is prepared by a method comprising the following steps: A1. Mixing a porous framework with a permeable crystalline material solution, vacuum impregnating, followed by solid-liquid separation and drying, to obtain the encapsulated permeable crystalline material; the permeable crystalline material is calcium chloride and / or sodium silicate. Vacuum impregnation helps the permeable crystalline material solution enter the pores of the porous framework, allowing the porous framework to fully absorb the permeable crystalline material.

[0022] Preferably, in step A1, the mass ratio of the porous framework to the permeation crystallization material solution is 1:(1.5-2.5) (e.g., 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5).

[0023] In a preferred embodiment of the self-healing cement-based composite material of the present invention, the concentration of the penetrating crystallizing material solution is preferably 12wt%-18wt% (e.g., 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt% or 18wt%); the pressure during vacuum impregnation is -0.07 to -0.09 MPa (e.g., -0.07 MPa, -0.08 MPa or -0.09 MPa), and the vacuum impregnation time is 15-25 min (e.g., 15 min, 17 min, 20 min, 22 min or 25 min); the porous framework is biochar. If the concentration of the penetrating crystallizing material solution is too high, the adsorption capacity of the porous framework is limited and cannot be further increased. Furthermore, if the concentration of the penetrating crystallizing material adsorbed by the porous framework is too high, it will cause the material to be released too quickly and prematurely in localized areas of the cement-based composite material, leading to the formation of a dense outer shell on the surface of the porous framework and hindering further release of the material from the pores. If the concentration of the penetrating crystallizing material solution is too low, the content of the adsorbed material in the porous framework will be too low, limiting the improvement in the self-healing performance of the cement-based composite material. If the vacuum impregnation time is too short, the porous framework may not fully absorb the solution; if the vacuum impregnation time is too long, it will not allow the porous framework to fully absorb the solution and further increase its absorption capacity.

[0024] In a preferred embodiment of the self-healing cement-based composite material of the present invention, the encapsulated permeable crystalline material further includes a slow-release membrane; after step A1, the method further includes: A2, immersing the encapsulated permeable crystalline material in a slow-release membrane solution, separating the solid and liquid, and drying to obtain the encapsulated permeable crystalline material wrapped by the slow-release membrane. The present invention, by first immersing the porous skeleton in a permeable crystalline material solution, drying to obtain the encapsulated permeable crystalline material, and then immersing it in a slow-release membrane solution, allows the permeable crystalline material to be adsorbed into the pores of the porous skeleton first, and then the slow-release membrane (polyvinylpyrrolidone) to coat the surface of the porous skeleton. If the porous skeleton is immersed in a solution containing both permeable crystalline material and polyvinylpyrrolidone, it may result in the pores of the porous skeleton simultaneously adsorbing both the permeable crystalline material and polyvinylpyrrolidone.

[0025] In a preferred embodiment of the self-healing cement-based composite material of the present invention, the slow-release membrane solution is a polyvinylpyrrolidone solution; in the slow-release membrane solution, the mass ratio of polyvinylpyrrolidone to water is 1:(8-12) (e.g., 1:8, 1:9, 1:10, 1:11 or 1:12; to help form a dense and uniform film on the surface of the encapsulating material); in step A2, the encapsulated permeable crystalline material is immersed in the slow-release membrane solution for 0.8-1.2 hours (e.g., 0.8 hours, 0.9 hours, 1 hour, 1.1 hours or 1.2 hours). If the concentration of the slow-release membrane solution is too high, the membrane will be too thick, making it difficult to release the internal permeable crystalline material; if the concentration of the slow-release membrane solution is too low, the membrane encapsulated by the porous skeleton will be too thin or incomplete, leading to premature leakage of the internal permeable crystalline material. If the encapsulated permeation crystallizing material is immersed in the slow-release membrane solution for too short a time, the film will be too thin and uneven, and the skeleton will not be completely wrapped, which will cause the internal permeation crystallizing material to leak prematurely. If the encapsulated permeation crystallizing material is immersed in the slow-release membrane solution for too long, it will cause the wrapped membrane to be too thick or to swell again, resulting in the leakage of the internally adsorbed permeation crystallizing material.

[0026] In a preferred embodiment of the self-healing cement-based composite material of the present invention, the components of the self-healing cement-based composite material further include fibers and / or water-reducing agents; the fibers are polyethylene fibers; the water-reducing agent is a polycarboxylate water-reducing agent, and in order to ensure that the cement-based composite material has good workability, the amount of water-reducing agent is selected to be 5.3-5.8 parts (e.g., 5.3 parts, 5.4 parts, 5.5 parts, 5.6 parts, 5.7 parts or 5.8 parts); the sand is quartz sand with a particle size of 120-180 μm.

[0027] In a preferred embodiment of the self-healing cement-based composite material of the present invention, the water-cement ratio of the self-healing cement-based composite material is 0.20.

[0028] The self-healing cement-based composite material of the present invention will be described in detail below through specific embodiments.

[0029] The main raw materials used in the following examples are sourced as follows: The cement is PO42.5 cement, produced by Pingtang Cement Co., Ltd., with oxide composition mainly including 59% CaO and 19% SiO2, and a median particle size of 15.8 μm; the fly ash is grade F, with a density of 2.37 g / cm³. 3 The silica fume is a gray powder with a median particle size of 12.1 μm; the sand is quartz sand with a particle size mainly of 120-180 μm; the fiber is polyethylene (PE) fiber, 18 mm in length and 15.6 μm in diameter, with a density and elastic modulus of 0.97 g / cm³. 3The water-reducing agent was a liquid polycarboxylate-type high-efficiency water-reducing agent, purchased from Shaanxi Qinfen Building Materials Co., Ltd., with an effective solid content of 40% and a water reduction rate of 30%. The penetrating crystallization material consisted of calcium chloride (CaCl2) and sodium silicate (Na2SiO3). The calcium chloride was anhydrous calcium chloride, which was white granules. The sodium silicate was sodium silicate pentahydrate, which was white powder. The encapsulation material mainly consisted of a porous skeleton and a slow-release film. The porous skeleton was made of wood-based biochar, which was a black porous powder with a water absorption rate of 1.0 g / g. The slow-release film was formed from polyvinylpyrrolidone (PVP), which was a slightly yellow powder and of analytical grade. The water was tap water from the laboratory.

[0030] Example 1 The self-healing cement-based composite material of this embodiment includes: 400 parts cement, 320 parts fly ash, 72 parts silica fume, 240 parts sand, 4.21 parts water-reducing agent, 11.64 parts fiber, 160 parts water, 5.53 parts water-reducing agent, and 39.6 parts encapsulating penetrating crystallizing material; The encapsulated permeation crystallization material is prepared by the following steps: A1. The porous framework and calcium chloride solution (15wt%) are mixed at a mass ratio of 1:2. The mixture is stirred at 1000r / min for 10min, then immersed in a vacuum chamber under negative pressure (-0.08MPa) for 20min. After restoring to normal pressure, the mixture is filtered, and the resulting solid is dried at 80℃ to constant weight to obtain the encapsulated permeation crystallization material. (The amount of calcium chloride contained in the encapsulated permeation crystallization material can be calculated based on the mass change of the calcium chloride solution before and after filtration and the concentration of the calcium chloride solution.)

[0031] The preparation method of the self-healing cement-based composite material in this embodiment includes the following steps: (1) A CAJ-30 mortar mixer with a mixing pot capacity of 30L and a voltage of 380V was used. The entire mixing process was carried out at room temperature (20℃). Except for the high-efficiency water-reducing agent, all solid materials were first mixed at speed 1 for 2 minutes in the mixer.

[0032] (2) Mix the high-efficiency water-reducing agent and water, stir mechanically until uniform, add to the mixer, continue stirring at low speed for 1 minute, and then stir at high speed for 2 minutes.

[0033] (3) After mixing evenly, slowly add the fiber and mix at low speed for 5 minutes; finally, mix at high speed for 3 minutes.

[0034] (4) Pour the fresh self-healing cement-based composite material mixture into the mold, cure at room temperature (20℃) for 1 day and then demold; place it under standard curing conditions of 20±2℃ and 95% relative humidity for 28 days.

[0035] Example 2 The self-healing cement-based composite material of this embodiment includes: 400 parts cement, 320 parts fly ash, 72 parts silica fume, 240 parts sand, 4.21 parts water-reducing agent, 11.64 parts fiber, 160 parts water, 5.70 parts water-reducing agent, and 39.6 parts encapsulating penetrating crystallizing material; The encapsulated permeation crystallization material is prepared by the following steps: A1. The porous framework and sodium silicate solution (15wt%) are mixed at a mass ratio of 1:2. The mixture is stirred at 1000r / min for 10min, then immersed in a vacuum chamber under negative pressure (-0.08MPa) for 20min. After restoring to normal pressure, the mixture is filtered, and the resulting solid is dried at 80℃ to constant weight to obtain the encapsulated permeation crystallization material. (The amount of sodium silicate contained in the encapsulated permeation crystallization material can be calculated based on the mass change of the sodium silicate solution before and after filtration and the concentration of the sodium silicate solution.)

[0036] The preparation method of the self-healing cement-based composite material in this embodiment includes the following steps: (1) A CAJ-30 mortar mixer with a mixing pot capacity of 30L and a voltage of 380V was used. The entire mixing process was carried out at room temperature (20℃). Except for the high-efficiency water-reducing agent, all solid materials were first mixed at speed 1 for 2 minutes in the mixer.

[0037] (2) Mix the high-efficiency water-reducing agent and water, stir mechanically until uniform, add to the mixer, continue stirring at low speed for 1 minute, and then stir at high speed for 2 minutes.

[0038] (3) After mixing evenly, slowly add the fiber and mix at low speed for 5 minutes; finally, mix at high speed for 3 minutes.

[0039] (4) Pour the fresh self-healing cement-based composite material mixture into the mold, cure at room temperature (20℃) for 1 day and then demold; place it under standard curing conditions of 20±2℃ and 95% relative humidity for 28 days.

[0040] Example 3 The self-healing cement-based composite material of this embodiment includes: 400 parts cement, 320 parts fly ash, silica fume, 240 parts sand, 4.21 parts water-reducing agent, 11.64 parts fiber, 160 parts water, 5.35 parts water-reducing agent, and 39.6 parts encapsulating and penetrating crystallizing material wrapped in a slow-release membrane; The encapsulated permeation crystallization material is prepared by the following steps: A1. The porous framework and calcium chloride solution (15wt%) are mixed at a mass ratio of 1:2. The mixture is stirred at 1000r / min for 10min, then immersed in a vacuum chamber under negative pressure (-0.08MPa) for 20min. After restoring to normal pressure, the mixture is filtered and the resulting solid is dried at 80℃ to constant weight to obtain the encapsulated permeation crystallization material. A2. Immerse the encapsulated permeation crystallization material in a slow-release membrane solution (PVP and water are mixed at a mass ratio of 1:10, stirred at 80℃ for 1 hour, and then cooled naturally to form a slow-release membrane solution) for 1 hour. The mass ratio of the encapsulated permeation crystallization material to the slow-release membrane solution is 1:3. After filtration, place it in an oven at 60℃ for 2 hours to dry, and the encapsulated permeation crystallization material wrapped in the slow-release membrane is obtained.

[0041] The preparation method of the self-healing cement-based composite material in this embodiment includes the following steps: (1) A CAJ-30 mortar mixer with a mixing pot capacity of 30L and a voltage of 380V was used. The entire mixing process was carried out at room temperature (20℃). Except for the high-efficiency water-reducing agent, all solid materials were first mixed at speed 1 for 2 minutes in the mixer.

[0042] (2) Mix the high-efficiency water-reducing agent and water, stir mechanically until uniform, add to the mixer, continue stirring at low speed for 1 minute, and then stir at high speed for 2 minutes.

[0043] (3) After mixing evenly, slowly add the fiber and mix at low speed for 5 minutes; finally, mix at high speed for 3 minutes.

[0044] (4) Pour the fresh self-healing cement-based composite material mixture into the mold, cure at room temperature (20℃) for 1 day and then demold; place it under standard curing conditions of 20±2℃ and 95% relative humidity for 28 days.

[0045] Example 4 The self-healing cement-based composite material of this embodiment includes: 400 parts cement, 320 parts fly ash, 72 parts silica fume, 240 parts sand, 4.21 parts water-reducing agent, 11.64 parts fiber, 160 parts water, 5.48 parts water-reducing agent, and 39.6 parts encapsulating and penetrating crystallizing material wrapped in a slow-release membrane; The encapsulated permeation crystallization material is prepared by the following steps: A1. The porous framework and sodium silicate solution are mixed at a mass ratio of 1:2 (15wt%). The mixture is stirred at 1000r / min for 10min, then immersed in a vacuum chamber under negative pressure (-0.08MPa) for 20min. The pressure is then restored to normal, filtered, and the resulting solid is dried at 80℃ to constant weight to obtain the encapsulated permeation crystallization material. A2. Immerse the encapsulated permeation crystallization material in a slow-release membrane solution (PVP and water are mixed at a mass ratio of 1:10, stirred at 80℃ for 1 hour, and then cooled naturally to form a slow-release membrane solution) for 1 hour. The mass ratio of the encapsulated permeation crystallization material to the slow-release membrane solution is 1:3. After filtration, place it in an oven at 60℃ for 2 hours to dry, and the encapsulated permeation crystallization material wrapped in the slow-release membrane is obtained.

[0046] The preparation method of the self-healing cement-based composite material in this embodiment includes the following steps: (1) A CAJ-30 mortar mixer with a mixing pot capacity of 30L and a voltage of 380V was used. The entire mixing process was carried out at room temperature (20℃). Except for the high-efficiency water-reducing agent, all solid materials were first mixed at speed 1 for 2 minutes in the mixer.

[0047] (2) Mix the high-efficiency water-reducing agent and water, stir mechanically until uniform, add to the mixer, continue stirring at low speed for 1 minute, and then stir at high speed for 2 minutes.

[0048] (3) After mixing evenly, slowly add the fiber and mix at low speed for 5 minutes; finally, mix at high speed for 3 minutes.

[0049] (4) Pour the fresh self-healing cement-based composite material mixture into the mold, cure at room temperature (20℃) for 1 day and then demold; place it under standard curing conditions of 20±2℃ and 95% relative humidity for 28 days.

[0050] Comparative Example 1 The only difference between this comparative example and Example 1 is that the encapsulating penetrating crystallizing material is omitted, and the amount of water-reducing agent is adjusted to 4.21 parts; all other aspects are the same as in Example 1.

[0051] Comparative Example 2 The only difference between this comparative example and Example 1 is that the encapsulation penetrating crystallizing material is omitted, and calcium chloride is added. The amount of calcium chloride added is the same as the amount of calcium chloride contained in the encapsulation penetrating crystallizing material in Example 1. The amount of water-reducing agent is adjusted to 5.98 parts. All other aspects are the same as in Example 1.

[0052] Comparative Example 3 The only difference between this comparative example and Example 1 is that the encapsulation penetrating crystallization material is omitted, and sodium silicate is added. The amount of sodium silicate added is the same as the amount of sodium silicate contained in the encapsulation penetrating crystallization material in Example 2. The amount of water-reducing agent is adjusted to 5.79 parts. All other aspects are the same as in Example 1.

[0053] Comparative Example 4 The only difference between this comparative example and Example 1 is that an equal amount of porous skeleton is used instead of the encapsulation permeation crystallization material in Example 1, the amount of water is adjusted to 396 parts, and the steps of adding fiber and water-reducing agent are omitted. All other aspects are consistent with Example 1.

[0054] Comparative Example 5 The only difference between this comparative example and Example 1 is that an equal amount of porous skeleton is used instead of the encapsulation and permeation crystallization material in Example 1, and the amount of water-reducing agent is adjusted to 5.02 parts; all other aspects are the same as in Example 1.

[0055] Comparative Example 6 The only difference between this comparative example and Example 1 is that the amount of water is adjusted to 396 parts, and the steps of adding fiber, porous skeleton and water-reducing agent are omitted; all other aspects are the same as in Example 1.

[0056] Comparative Example 7 The only difference between this comparative example and Example 1 is that the step of encapsulating the penetrating crystallizing material is omitted, and a porous framework and calcium chloride are added respectively. The amount of porous framework and calcium chloride added is the same as the amount of porous framework and calcium chloride contained in the encapsulated penetrating crystallizing material in Example 1. The amount of water-reducing agent is adjusted to 6.12 parts; all other aspects are the same as in Example 1.

[0057] Comparative Example 8 The only difference between this comparative example and Example 2 is that the step of encapsulating the penetrating crystallizing material is omitted, and a porous framework and sodium silicate are added respectively. The amount of porous framework and sodium silicate added is the same as that of the porous framework and sodium silicate contained in the encapsulating penetrating crystallizing material in Example 2. The amount of water-reducing agent is adjusted to 6.03 parts; the rest are the same as in Example 1.

[0058] Experimental Example 1. Compressive strength test: A 40×40×40mm cubic specimen was used for the compressive strength test, with a loading rate of 2.4kN / s.

[0059] 2. Tensile strength test: A uniaxial tensile test was conducted on a 100kN microcomputer-controlled electronic universal testing machine at a speed of 0.5mm / min, and the stress-strain curves were recorded. The specimen was dumbbell-shaped, with a total length of 320mm, a width of 60mm at both ends, a length of 40mm at the variable cross-section, a length of 80mm and a width of 30mm in the middle, and a thickness of 13mm.

[0060] 3. Self-healing properties: At 28 days of age, the specimens were preloaded to 1% strain and then unloaded according to the tensile strength test procedure to form pre-cracked specimens, which were then subjected to self-healing curing. The curing regime adopted the common curing regime for self-healing tests: curing in water for 2 days, followed by curing in air for 2 days, with each cycle lasting 4 days. The curing temperature was maintained at 20±2℃ for a total of 28 days. Self-healing performance was evaluated by the crack healing rate, which is the ratio of the area difference before and after crack healing to the area before healing. A higher healing rate indicates better self-healing performance. The healing of cracks with a width of 80-100 μm before and after healing was photographed using a high-resolution electron digital microscope. The microscope magnification was set to 7000x, and ImageJ software was used to binarize the cracks and calculate the crack area.

[0061] The tensile curve of the cement-based composite material after 28 days was obtained by experiment as follows: Figure 1 As shown in Table 1, the test results of the mechanical properties are as follows. The crack healing situation in the 80-100μm width range measured by the experiment is as follows. Figure 2-3 As shown in Table 1 below.

[0062] Table 1. Test results of mechanical properties and self-healing properties

[0063] Compared to Comparative Example 5, Examples 1 and 2 incorporated a penetrating crystallizing material but lacked a slow-release membrane. Therefore, the leakage of the penetrating crystallizing material from the porous skeleton surface promoted the hydration degree of the slurry, thereby improving its mechanical properties. Example 1 supplemented with calcium ions, which readily generated calcium carbonate crystals to fill cracks, thus increasing the self-healing ability of the specimens. The sodium silicate supplemented in Example 2 further reacted with the calcium hydroxide generated during cement hydration, forming hydrated calcium silicate gel, which improved its mechanical properties and self-healing ability. The encapsulated permeable crystallizing materials in Examples 3 and 4, which were coated with slow-release membranes, showed a decrease in mechanical properties compared to the corresponding Examples 1 and 2. The main reasons are as follows: (1) due to the weak area caused by the PVP membrane at the interface with the cement matrix; (2) when coating with PVP membrane, the porous skeleton will be immersed in PVP solution, which will inevitably cause some permeable crystallizing material to fall off, resulting in a decrease in the total amount of permeable crystallizing material; (3) after the porous skeleton is coated with PVP film, there is a slow-release effect. In the early hydration process (before cracking), the permeable crystallizing material leaks very little, resulting in a decrease in the strength of the specimen before healing; but undoubtedly, due to its slow-release effect, the self-healing degree of the specimen is improved.

[0064] The 28-day compressive strength and tensile strength of Comparative Example 1 reached 72.6 MPa and 9.60 MPa, respectively. Compared with Comparative Example 1, the calcium chloride added in Comparative Example 2 accelerated the early hydration of cement, resulting in uneven distribution of cement hydration products. However, calcium chloride also activated the activity of fly ash, slightly increasing its 28-day compressive strength and tensile strength. The rehydration of unhydrated particles and the formation of calcium carbonate slightly increased the degree of self-healing. However, compared with Example 3, its crack healing rate was significantly reduced. This was mainly due to the rapid early reaction of the penetrating crystallizing material, which is an important defect caused by its lack of a slow-release effect.

[0065] Compared to Comparative Example 1, Comparative Example 3, with the addition of sodium silicate, accelerated the consumption of calcium ions generated during the early hydration of cement, forming calcium silicate gel that encapsulates cement particles, resulting in insufficient hydration in the later stages. However, sodium silicate also stimulates the activity of fly ash, slightly increasing its 28-day compressive and tensile strength. Due to the rehydration of unhydrated cement particles and the continuous geopolymerization reaction and calcium carbonate deposition of fly ash, the degree of self-healing is increased compared to Comparative Example 2, but it is still far lower than the self-healing performance of Example 4.

[0066] Compared to Comparative Example 1, Comparative Examples 4 and 6 showed an increased water-cement ratio and a higher degree of cement hydration at 28 days. However, the increased porosity of the hydration paste led to a significant decrease in their 28-day compressive and tensile strengths. In Comparative Example 4, the addition of biochar, without the addition of fibers, resulted in a significant decrease in strength compared to Comparative Example 1; however, compared to Comparative Example 6, its strength increased slightly. Regarding self-healing properties, both Comparative Examples 4 and 6 lacked the characteristic of multi-crack development. Although healing products were generated, they were insufficient to bind the specimens without fiber interweaving. After healing curing, the two ends remained non-continuous, making it impossible to quantitatively characterize the crack healing rate.

[0067] Compared to Comparative Example 1, Comparative Example 5 showed an increase of 4.7% in compressive strength and 4.2% in tensile strength at 28 days. This was attributed to the addition of a porous framework (biochar) component. The porous framework (biochar) provides internal curing during slurry hydration, increasing the degree of hydration and thus improving mechanical properties. Furthermore, the water absorption and release properties of the porous framework (biochar) enabled the specimen in Comparative Example 5 to absorb and release water during the self-healing process, thereby increasing the degree of self-healing.

[0068] Compared to Example 1, Comparative Example 7 showed a decrease in both compressive and tensile strength at 28 days. This was because, unlike the slow-release calcium chloride in Example 1, it consumed calcium chloride prematurely, leading to a reduction in mechanical properties and self-healing properties. However, compared to the single-component additions in Comparative Examples 2 and 5, its mechanical properties and self-healing properties were slightly improved.

[0069] Compared to Example 2, Comparative Example 8 consumed sodium silicate prematurely, leading to a decrease in its mechanical properties and self-healing properties, unlike the slow-release calcium chloride of Example 1. However, compared to the single-component additions of Comparative Examples 3 and 5, its mechanical properties and self-healing properties were slightly improved.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-healing cement-based composite material, characterized in that, It includes the following components: 380-420 parts cement, 310-330 parts fly ash, 65-75 parts silica fume, 230-250 parts sand, 10-12 parts fiber, and encapsulated penetrating crystallizing material; The encapsulated permeable crystallizing material comprises a porous framework and a permeable crystallizing material loaded on the porous framework, wherein the mass of the encapsulated permeable crystallizing material is 5% of the total mass of cement, fly ash, and silica fume.

2. The self-healing cement-based composite material as described in claim 1, characterized in that, The encapsulated permeable crystallizing material is prepared using a method comprising the following steps: A1. Mix the porous framework with the permeation crystallization material solution, vacuum impregnate, then separate the solid and liquid and dry to obtain the encapsulated permeation crystallization material; The permeation crystallization material is calcium chloride and / or sodium silicate.

3. The self-healing cement-based composite material as described in claim 2, characterized in that, The concentration of the permeation crystallization material solution is 10wt%-20wt%; The pressure during vacuum impregnation is -0.07 to -0.09 MPa, and the vacuum impregnation time is 15-25 minutes. The porous framework is biochar.

4. The self-healing cement-based composite material as described in claim 2, characterized in that, The components of the encapsulated permeable crystallizing material also include a slow-release membrane; Step A1 is followed by: A2. Immerse the encapsulated permeation crystallizing material in a slow-release membrane solution, separate the solid and liquid, and dry it to obtain the encapsulated permeation crystallizing material wrapped in a slow-release membrane.

5. The self-healing cement-based composite material as described in claim 4, characterized in that, The sustained-release membrane solution is a polyvinylpyrrolidone solution; in the sustained-release membrane solution, the mass ratio of polyvinylpyrrolidone to water is 1:(8-12); In step A2, the encapsulated permeation crystallizing material is immersed in the slow-release membrane solution for 0.8-1.2 hours.

6. The self-healing cement-based composite material according to any one of claims 1-5, characterized in that, The components of the self-healing cement-based composite material also include fibers and / or water-reducing agents; The fiber is polyethylene fiber; The water-reducing agent is a polycarboxylate water-reducing agent, and the dosage of the water-reducing agent is 5.3-5.8 parts; The sand is quartz sand with a particle size of 120-180μm.

7. The self-healing cement-based composite material according to any one of claims 1-5, characterized in that, The water-cement ratio of the self-healing cementitious composite material is 0.

2.

8. The method for preparing the self-healing cement-based composite material according to any one of claims 1-7, characterized in that, Includes the following steps: (1) The cement, fly ash, silica fume, sand and encapsulating penetrating crystallizing material are mixed evenly to obtain a dry mixture; (2) Mix the water-reducing agent and water evenly to obtain a water-reducing agent solution; (3) Mix the dry mix with the water-reducing agent solution, add the fiber, and mix evenly to obtain the self-healing cement-based composite material.

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