Anti-crack self-repairing concrete and preparation method thereof

Abstract

This invention relates to the field of self-healing concrete technology, and more particularly to a crack-resistant self-healing concrete and its preparation method. The invention comprises the following components: 280-350 parts cement, 60-100 parts fly ash, 40-80 parts mineral powder, 15-30 parts silica fume, 700-850 parts fine aggregate, 1000-1200 parts coarse aggregate, 140-170 parts water, 4-8 parts water-reducing agent, 20-40 parts expansion agent, 8-20 parts self-healing microcapsules, 5-12 parts nano-silica, 1-3 parts polypropylene fiber, and 15-30 parts steel fiber. This invention uses melamine-formaldehyde resin as the wall material and epoxy resin as the core material. The resulting microcapsules have good mechanical strength and chemical stability, and a high core material coverage rate. When the width of concrete cracks reaches 0.1-0.3 mm, the microcapsules can effectively rupture and release the repair agent, achieving self-repair of the cracks. Furthermore, the synergistic effect of multiple functional components such as expansion agents, nano-silica, polypropylene fibers, and steel fibers forms a multi-level crack-resistant system, significantly improving the crack resistance of concrete and effectively extending the service life of concrete structures.

Description

Technical Field

[0001] This invention relates to the field of self-healing concrete technology, and in particular to a crack-resistant self-healing concrete and its preparation method. Background Technology

[0002] Concrete, as the most widely used building material in the world, is extensively used in various civil engineering structures. However, the inherent brittleness of concrete makes it prone to cracking during the hardening process and service life. Cracks not only affect the aesthetics of the structure but, more importantly, allow harmful substances to penetrate, accelerate steel corrosion, and reduce the structure's durability and service life.

[0003] Traditional methods for repairing concrete cracks mainly include surface sealing, pressure grouting, and localized repair. While these methods can repair cracks to some extent, they suffer from drawbacks such as complex construction, high costs, and difficulty in detecting and treating internal micro-cracks. More importantly, traditional repair methods are reactive measures and cannot repair cracks in their early stages.

[0004] Self-healing concrete technology is an effective way to solve the above problems. Currently, self-healing concrete technologies mainly include: cement hydration-based self-healing, mineral admixture-based self-healing, crystallization precipitation-based self-healing, and microcapsule-based self-healing. Among them, microcapsule self-healing technology involves incorporating microcapsules into concrete. When cracks propagate and cause the microcapsules to rupture, a repair agent is released to fill the cracks, achieving self-repair.

[0005] However, existing microcapsule self-healing concrete technology still has some shortcomings: (1) the compatibility between microcapsules and concrete matrix is ​​poor, affecting the mechanical properties of concrete; (2) the core material release efficiency of microcapsules is not high, and the repair effect is limited; (3) the crack resistance of concrete still needs to be improved, and the frequency of crack formation is relatively high; (4) there is a lack of systematic preparation process parameters, making it difficult to achieve industrial production. Therefore, developing a concrete material with both excellent crack resistance and efficient self-healing function is of great significance for improving the durability of concrete structures and extending their service life. To this end, we propose a crack-resistant self-healing concrete and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a crack-resistant self-healing concrete and its preparation method to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A crack-resistant self-healing concrete comprises the following components: 280-350 parts cement, 60-100 parts fly ash, 40-80 parts mineral powder, 15-30 parts silica fume, 700-850 parts fine aggregate, 1000-1200 parts coarse aggregate, 140-170 parts water, 4-8 parts water-reducing agent, 20-40 parts expansion agent, 8-20 parts self-healing microcapsules, 5-12 parts nano silica, 1-3 parts polypropylene fiber, and 15-30 parts steel fiber.

[0009] The self-healing microcapsules use epoxy resin as the core material and melamine-formaldehyde resin as the wall material. The microcapsule particle size is 50-150μm, and the core-to-wall mass ratio is 1.5:1-2.5:1.

[0010] Preferably, in preparing the self-healing microcapsules, epoxy resin and curing agent are first mixed at a mass ratio of 10:1, heated to 60-70°C, and stirred to disperse evenly to form a core material emulsion; then melamine and formaldehyde are mixed at a molar ratio of 1:3, the pH is adjusted to 8.5-9.0, and prepolymerized at 70-80°C for 30-60 minutes to obtain a wall material prepolymer; next, the core material emulsion is added to the wall material prepolymer, along with emulsifiers and dispersants, and in-situ polymerization is carried out at 60-70°C and 800-1200 rpm for 2-4 hours; finally, after the reaction is completed, the mixture is cooled to room temperature, filtered, washed, and dried to obtain the self-healing microcapsules.

[0011] Preferably, the expanding agent is a magnesium oxide-based expanding agent or an ettringite-based expanding agent, with an expansion rate of 0.02%-0.05%.

[0012] Preferably, the specific surface area of ​​the nano-silica is 200-400 m² / g, and the particle size is 15-30 nm.

[0013] Preferably, the polypropylene fiber has a length of 12-19 mm, a diameter of 20-40 μm, and a tensile strength ≥400 MPa.

[0014] Preferably, the steel fiber is a hook-shaped steel fiber with a length of 30-60 mm, a diameter of 0.5-1.0 mm, and an aspect ratio of 40-80.

[0015] A method for preparing crack-resistant self-healing concrete, applicable to a type of crack-resistant self-healing concrete, includes the following steps:

[0016] S1: Weigh the raw materials of each component according to the proportion;

[0017] S2: Add cement, fly ash, mineral powder, silica fume, nano silica and expansion agent into the mixer and dry mix for 60-90 seconds;

[0018] S3: Add fine and coarse aggregates and continue dry mixing for 30-60 seconds;

[0019] S4: Add 80% of the total water and water-reducing agent, and stir for 120-180 seconds;

[0020] S5: Add self-healing microcapsules and stir for 30-60 seconds;

[0021] S6: Pour the mixture into a mold and cure for 28 days to obtain the crack-resistant self-healing concrete.

[0022] Preferably, after the stirring in step S5 is completed, polypropylene fiber and steel fiber, along with the remaining 20% ​​water, are added, and the mixture is stirred for 90-120 seconds until homogeneous.

[0023] Preferably, when adding the self-healing microcapsules in step S5, the stirring speed is controlled at 20-40 rpm to avoid microcapsule rupture.

[0024] It is clear without a doubt that the technical solution described above in this application can solve the technical problem that this application aims to address.

[0025] Meanwhile, through the above technical solutions, the present invention has at least the following beneficial effects:

[0026] 1. This invention optimizes the preparation process of self-healing microcapsules, using melamine-formaldehyde resin as the wall material and epoxy resin as the core material. The resulting microcapsules exhibit good mechanical strength and chemical stability, high core material coverage, and significant repair effect. When the width of a concrete crack reaches 0.1-0.3 mm, the microcapsules can effectively rupture and release the repair agent, achieving self-repair of the crack.

[0027] 2. This invention utilizes the synergistic effect of multiple functional components, including an expanding agent, nano-silica, polypropylene fiber, and steel fiber, to form a multi-level crack-resistant system. The expanding agent compensates for shrinkage, nano-silica fills pores, polypropylene fiber inhibits microcracks, and steel fiber prevents the propagation of macro-cracks. The components work together to significantly improve the crack resistance of concrete and effectively extend the service life of concrete structures. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the microcapsule structure of the present invention;

[0030] Figure 2 This is a flowchart of the microcapsule preparation process of the present invention;

[0031] Figure 3 This is a schematic diagram of the multi-stage crack-prevention system of the present invention;

[0032] Figure 4 This is a schematic diagram of the self-healing mechanism of the present invention;

[0033] Figure 5 This is a flowchart of the preparation process of the present invention.

[0034] Figure 6 This is a performance comparison chart of the embodiments and comparative examples of the present invention;

[0035] Figure 7 This is a performance comparison chart of Embodiments 1-3 of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] A crack-resistant self-healing concrete, the components of which are expressed in parts by weight as follows:

[0038] The present invention comprises the following components by weight: 280-350 parts cement, 60-100 parts fly ash, 40-80 parts mineral powder, 15-30 parts silica fume, 700-850 parts fine aggregate, 1000-1200 parts coarse aggregate, 140-170 parts water, 4-8 parts water-reducing agent, 20-40 parts expansion agent, 8-20 parts self-healing microcapsules, 5-12 parts nano silica, 1-3 parts polypropylene fiber, and 15-30 parts steel fiber.

[0039] The self-healing microcapsules use epoxy resin as the core material and melamine-formaldehyde resin as the wall material. The microcapsule particle size is controlled within the range of 50-150 μm, and the core-to-wall mass ratio is 1.5:1-2.5:1. These microcapsules possess good mechanical strength and chemical stability, allowing them to remain intact during concrete mixing and pouring. When cracks appear in the concrete, stress concentration at the crack tip causes the microcapsules to rupture, releasing the epoxy resin repair agent. Under the action of a curing agent, this forms a solid filler, achieving self-healing of the cracks.

[0040] The expanding agent used is either a magnesium oxide-based or ettringite-based expanding agent, with an expansion rate of 0.02%-0.05%. During the concrete hardening process, the expanding agent produces micro-expansion, compensating for concrete shrinkage and reducing the formation of shrinkage cracks.

[0041] Nano-silica has a specific surface area of ​​200-400 m² / g and a particle size of 15-30 nm. It exhibits extremely high pozzolanic activity, reacting with calcium hydroxide, a cement hydration product, to form hydrated calcium silicate gel. This gel fills the pores within concrete, improving its density and strength. Simultaneously, nano-silica also promotes cement hydration and improves the structure of the interfacial transition zone.

[0042] The polypropylene fibers are 12-19 mm in length, 20-40 μm in diameter, and have a tensile strength ≥400 MPa. The polypropylene fibers are uniformly dispersed in the concrete matrix, which can inhibit the formation of plastic shrinkage cracks and early drying shrinkage cracks, thus improving the crack resistance of the concrete.

[0043] The steel fibers are hook-shaped, with a length of 30-60 mm, a diameter of 0.5-1.0 mm, and an aspect ratio of 40-80. Steel fibers can significantly improve the tensile strength, flexural strength, and toughness of concrete, and inhibit the propagation of macroscopic cracks.

[0044] This invention utilizes a hybrid approach of polypropylene fibers and steel fibers to create a multi-stage crack-resistant system: polypropylene fibers primarily inhibit the formation of microcracks, while steel fibers primarily prevent the propagation of macrocracks. The synergistic effect of both significantly improves the crack resistance of concrete.

[0045] Example 1

[0046] Reference Figure 1-7 This embodiment provides a crack-resistant self-healing concrete, the components of which are as follows by weight: 300 parts cement, 80 parts fly ash, 60 parts mineral powder, 20 parts silica fume, 780 parts fine aggregate, 1100 parts coarse aggregate, 155 parts water, 6 parts water-reducing agent, 30 parts expansion agent, 12 parts self-healing microcapsules, 8 parts nano silica, 2 parts polypropylene fiber, and 20 parts steel fiber.

[0047] The preparation method of self-healing microcapsules is as follows:

[0048] (1) Mix epoxy resin and curing agent at a mass ratio of 10:1, heat to 65°C, and disperse evenly at a stirring speed of 500 rpm to form a core material emulsion;

[0049] (2) Melamine and formaldehyde were mixed in a molar ratio of 1:3, and the pH was adjusted to 8.8 with triethanolamine. The mixture was prepolymerized at 75°C for 45 minutes to obtain the wall material prepolymer.

[0050] (3) Add the core material emulsion to the wall material prepolymer, add 2% emulsifier and 1% dispersant of the total mass of the system, and carry out in-situ polymerization reaction for 3 hours under stirring conditions of 65℃ and 1000rpm.

[0051] (4) After the reaction was completed, the mixture was cooled to room temperature, filtered, washed three times with deionized water, and dried under vacuum at 50°C to obtain self-healing microcapsules. The obtained microcapsules had a particle size of 80-120 μm and a core-to-wall mass ratio of 2:1.

[0052] The preparation method of crack-resistant self-healing concrete is as follows:

[0053] (1) Weigh each component raw material according to the proportion;

[0054] (2) Put cement, fly ash, mineral powder, silica fume, nano silica and expansion agent into a forced mixer and dry mix for 75 seconds;

[0055] (3) Add fine and coarse aggregates and continue to dry mix for 45 seconds;

[0056] (4) Add 80% of the total water and water-reducing agent, and stir for 150 seconds;

[0057] (5) Add the self-healing microcapsules and stir at 30 rpm for 45 seconds;

[0058] (6) Add polypropylene fiber and steel fiber, and the remaining 20% ​​water, and stir for 100 seconds until uniform;

[0059] (7) The mixture is poured into a mold and cured for 28 days to obtain crack-resistant self-healing concrete.

[0060] The crack-resistant self-healing concrete prepared in this embodiment has the following properties after testing: 28-day compressive strength of 62.5 MPa, flexural strength of 9.8 MPa, splitting tensile strength of 5.2 MPa, impermeability grade of P12, self-healing efficiency of 78% when the initial crack width is 0.2 mm, and impermeability recovery rate of 85% after repair.

[0061] Example 2

[0062] Reference Figure 1-7 This embodiment provides a crack-resistant self-healing concrete, the components of which are as follows by weight: 320 parts cement, 70 parts fly ash, 50 parts mineral powder, 25 parts silica fume, 800 parts fine aggregate, 1150 parts coarse aggregate, 160 parts water, 7 parts water-reducing agent, 25 parts expansion agent, 15 parts self-healing microcapsules, 10 parts nano silica, 1.5 parts polypropylene fiber, and 25 parts steel fiber.

[0063] The self-healing microcapsules were prepared using the same method as in Example 1, and the resulting microcapsules had a particle size of 60-100 μm and a core-to-wall mass ratio of 2.2:1.

[0064] The preparation method of crack-resistant self-healing concrete is the same as in Example 1.

[0065] The crack-resistant self-healing concrete prepared in this embodiment has the following properties after testing: 28-day compressive strength of 68.3 MPa, flexural strength of 10.5 MPa, splitting tensile strength of 5.8 MPa, impermeability grade of P12, self-healing efficiency of 82% when the initial crack width is 0.2 mm, and impermeability recovery rate of 88% after repair.

[0066] Example 3

[0067] Reference Figure 1-7 This embodiment provides a crack-resistant self-healing concrete, the components of which are as follows by weight: 280 parts cement, 90 parts fly ash, 70 parts mineral powder, 18 parts silica fume, 750 parts fine aggregate, 1050 parts coarse aggregate, 150 parts water, 5 parts water-reducing agent, 35 parts expansion agent, 10 parts self-healing microcapsules, 6 parts nano silica, 2.5 parts polypropylene fiber, and 18 parts steel fiber.

[0068] The self-healing microcapsules were prepared using the same method as in Example 1, and the resulting microcapsules had a particle size of 100-150 μm and a core-to-wall mass ratio of 1.8:1.

[0069] The preparation method of crack-resistant self-healing concrete is the same as in Example 1.

[0070] The crack-resistant self-healing concrete prepared in this embodiment has the following properties after testing: 28-day compressive strength of 58.6 MPa, flexural strength of 8.9 MPa, splitting tensile strength of 4.8 MPa, impermeability grade of P10, self-healing efficiency of 75% when the initial crack width is 0.2 mm, and impermeability recovery rate of 82% after repair.

[0071] Comparative Example 1

[0072] Reference Figure 6 The difference between this comparative example and Example 1 is that no self-healing microcapsules were added. Other components and preparation methods are the same as in Example 1.

[0073] Tests showed that the concrete prepared in this comparative example had a 28-day compressive strength of 64.2 MPa and a flexural strength of 10.1 MPa, but it could not repair itself after cracks appeared.

[0074] Comparative Example 2

[0075] Reference Figure 6 The difference between this comparative example and Example 1 is that no polypropylene fibers and steel fibers are added. Other components and preparation methods are the same as in Example 1.

[0076] Tests showed that the concrete prepared in this comparative example had a 28-day compressive strength of 60.5 MPa and a flexural strength of 7.2 MPa, with a significant increase in early shrinkage cracks.

[0077] As can be seen from the above embodiments and comparative examples, the crack-resistant self-healing concrete prepared by the present invention, through the synergistic effect of multiple functional components, has excellent mechanical properties, crack resistance and self-healing ability, and can effectively extend the service life of concrete structures.

[0078] In summary:

[0079] This invention addresses the following technical problems: poor compatibility between microcapsules and concrete matrix, affecting the mechanical properties of concrete; low core material release efficiency of microcapsules, resulting in limited repair effects; the crack resistance of concrete still needs improvement, with a high frequency of crack formation; and the lack of systematic preparation process parameters, making industrial production difficult. By employing the technical solutions of the above embodiments and through the aforementioned settings, this application can certainly solve the above technical problems and simultaneously achieve the following technical effects:

[0080] 1. This invention optimizes the preparation process of self-healing microcapsules, using melamine-formaldehyde resin as the wall material and epoxy resin as the core material. The resulting microcapsules exhibit good mechanical strength and chemical stability, high core material coverage, and significant repair effect. When the width of a concrete crack reaches 0.1-0.3 mm, the microcapsules can effectively rupture and release the repair agent, achieving self-repair of the crack.

[0081] 2. This invention utilizes the synergistic effect of multiple functional components, including an expanding agent, nano-silica, polypropylene fiber, and steel fiber, to form a multi-level crack-resistant system. The expanding agent compensates for shrinkage, nano-silica fills pores, polypropylene fiber inhibits microcracks, and steel fiber prevents the propagation of macro-cracks. The components work together to significantly improve the crack resistance of concrete and effectively extend the service life of concrete structures.

[0082] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0083] Obviously, the embodiments described above are merely some embodiments of the present invention, not all embodiments. The accompanying drawings show preferred embodiments of the present invention, but do not limit the patent scope of the present invention. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A crack-resistant self-healing concrete, characterized in that, It includes the following components: 280-350 parts cement, 60-100 parts fly ash, 40-80 parts mineral powder, 15-30 parts silica fume, 700-850 parts fine aggregate, 1000-1200 parts coarse aggregate, 140-170 parts water, 4-8 parts water-reducing agent, 20-40 parts expansion agent, 8-20 parts self-healing microcapsules, 5-12 parts nano silica, 1-3 parts polypropylene fiber, and 15-30 parts steel fiber. The self-healing microcapsules use epoxy resin as the core material and melamine-formaldehyde resin as the wall material. The microcapsule particle size is 50-150μm, and the core-to-wall mass ratio is 1.5:1-2.5:

1.

2. The crack-resistant self-healing concrete according to claim 1, characterized in that, In preparing the self-healing microcapsules, epoxy resin and curing agent are first mixed at a mass ratio of 10:1, heated to 60-70℃, and stirred to disperse evenly to form a core material emulsion. Then, melamine and formaldehyde are mixed at a molar ratio of 1:3, the pH is adjusted to 8.5-9.0, and prepolymerized at 70-80℃ for 30-60 minutes to obtain a wall material prepolymer. Next, the core material emulsion is added to the wall material prepolymer, along with emulsifiers and dispersants, and in-situ polymerization is carried out at 60-70℃ and 800-1200 rpm for 2-4 hours. Finally, after the reaction is completed, the mixture is cooled to room temperature, filtered, washed, and dried to obtain the self-healing microcapsules.

3. The crack-resistant self-healing concrete according to claim 1, characterized in that, The expanding agent is a magnesium oxide-based expanding agent or an ettringite-based expanding agent, with an expansion rate of 0.02%-0.05%.

4. The crack-resistant self-healing concrete according to claim 1, characterized in that, The specific surface area of ​​the nano-silica is 200-400 m² / g, and the particle size is 15-30 nm.

5. The crack-resistant self-healing concrete according to claim 1, characterized in that, The polypropylene fiber has a length of 12-19 mm, a diameter of 20-40 μm, and a tensile strength ≥400 MPa.

6. The crack-resistant self-healing concrete according to claim 5, characterized in that, The steel fiber is a hook-shaped steel fiber with a length of 30-60mm, a diameter of 0.5-1.0mm, and an aspect ratio of 40-80.

7. A method for preparing crack-resistant self-healing concrete, applicable to the crack-resistant self-healing concrete described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Weigh the raw materials of each component according to the proportion; S2: Add cement, fly ash, mineral powder, silica fume, nano silica and expansion agent into the mixer and dry mix for 60-90 seconds; S3: Add fine and coarse aggregates and continue dry mixing for 30-60 seconds; S4: Add 80% of the total water and water-reducing agent, and stir for 120-180 seconds; S5: Add self-healing microcapsules and stir for 30-60 seconds; S6: Pour the mixture into a mold and cure for 28 days to obtain the crack-resistant self-healing concrete.

8. The method for preparing crack-resistant self-healing concrete according to claim 7, characterized in that, After the mixing in step S5 is completed, add polypropylene fiber and steel fiber, as well as the remaining 20% ​​water, and stir for 90-120 seconds until uniform.

9. The method for preparing crack-resistant self-healing concrete according to claim 8, characterized in that, When adding the self-healing microcapsules in step S5, the stirring speed should be controlled at 20-40 rpm to avoid microcapsule rupture.

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