A self-healing concrete admixture and its preparation method

Abstract

This invention relates to the field of concrete technology, specifically disclosing a self-healing concrete admixture and its preparation method. By weight, the self-healing concrete admixture comprises the following raw materials: 5-20 parts of an expanding agent and 3-15 parts of a slow-release curing agent. The slow-release curing agent releases curing agent in response to external loads through cracking or deformation. Upon contact with air, the released curing agent undergoes self-oxidation for repair. Furthermore, the addition of a mixed expanding agent addresses the problem of the capsule wall failing to rupture in time under certain circumstances, facilitating the flow of curing agent to exert its effect while also helping to fill the pores after the slow-release curing agent is consumed. Moreover, the unruptured slow-release curing agent can also exert its effect through slow release, improving the utilization rate and repair time of the self-healing admixture.

Description

Technical Field

[0001] This invention belongs to the field of concrete, specifically relating to a self-healing concrete admixture and its preparation method. Background Technology

[0002] Concrete, as a multi-component composite material, inevitably develops cracks due to differences in the physical and chemical properties of its components. Changes in external environment (temperature, humidity, ion concentration, etc.) and load conditions (dynamic and static loads) are common. These cracks reduce structural load-bearing capacity and safety, affecting waterproofing, durability, and service life. Traditional repair methods, primarily surface treatment, grouting, and structural reinforcement, are costly. Concrete self-healing technology, however, can repair damaged concrete before micro-cracks develop into macro-cracks, eliminating the need for manual inspection. This significantly reduces structural maintenance costs and is simple to implement.

[0003] Based on the self-healing mechanism, the Japan Concrete Institute (JCI) categorized self-healing mechanisms into three types in 2009: natural healing, auto-healing, and self-repair. Natural healing primarily relies on the inherent potential of the material itself; that is, unhydrated cement in the concrete reacts with water that seeps into the concrete through cracks to generate hydration products that repair the cracks. Auto-healing can be considered an enhancement and acceleration of auto-healing. For this type of self-healing, domestic and international research mainly focuses on three directions: mineral additives primarily composed of fly ash, silica fume, and slag; mineral additives combining expansive agents and chemical substances; and mineral additives primarily composed of limestone and limestone. Self-repairing methods mainly include microcapsules, microbial self-healing, hollow fiber repair, and shape memory alloy repair.

[0004] Currently, relevant technical personnel have made certain achievements in the research of concrete self-healing. For example, patent CN114835428B provides a concrete crack self-healing admixture containing water-absorbing resin, complexing agent, and hydration inhibitor. The complexing agent transports calcium ions to the gel formed by the water-absorbing resin, where they react with unhydrated silicate ions in the concrete to form water-insoluble calcium silicate crystals, thus blocking concrete cracks and achieving self-healing. However, the resulting hydrogel has low strength, which may affect the compressive strength of the concrete. Another example is patent CN 114180875 B, which discloses a penetrating crystalline high-performance anti-crack and anti-seepage agent for concrete and its preparation method. The complexing agent, as a penetrating crystalline component, forms a complex with calcium ions when the concrete matrix cracks and leaks water. This complex diffuses into the accumulated water in the concrete pores and cracks, continuously undergoing a complexation and precipitation reaction to repair the pores and cracks of the concrete. However, this method requires a certain amount of time to precipitate and generate crystals that block cracks, and the calcium ions in the concrete used will be depleted, resulting in poor overall anti-seepage performance. Therefore, there is an urgent need in the market for a concrete self-healing admixture that has minimal impact on concrete strength, short self-healing time, and long-lasting effect. Summary of the Invention

[0005] To address the aforementioned issues, this invention employs a slow-release curing agent, which utilizes the self-oxidation process between the ruptured capsule wall and air to repair microcracks. The oxidation products exhibit high hardness, minimal impact on concrete strength, and a short curing time. Furthermore, by combining this agent with a mixed expansion agent, a self-healing concrete admixture is obtained that minimizes the impact on concrete strength, has a short self-healing time, and a long effective period.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a self-healing concrete admixture, comprising, by weight, the following raw materials: 5-20 parts of an expanding agent and 3-15 parts of a slow-release curing agent, wherein the preparation steps of the slow-release curing agent are as follows:

[0008] S1. Add emulsifier and curing agent to a 1-5 wt% gelatin solution, and shear at 5000-9000 rpm for 0.1-1.0 h at 20-40°C to obtain a cured solution;

[0009] S2. Dissolve the film-forming agent in dichloromethane to obtain the capsule wall fluid;

[0010] S3. Pour the capsule wall liquid into the curing liquid at a rate of 1g / 1~5s, stir at 500~900rpm at 20~40℃ for 1~5h, raise the temperature to 40~48℃ and keep it at that temperature for 0.5~3h, then sieve, rotary evaporate, wash and dry to obtain the slow-release curing agent.

[0011] The slow-release curing agent provided by this invention can be uniformly distributed within the structure of cement-based materials, achieving good repair of damaged areas. When microcracks appear in concrete, the slow-release curing agent located there can release the curing agent in response to external loads through cracking or deformation. Upon contact with air, it can undergo self-oxidation, repairing microcracks without the need for a catalyst. However, due to the certain hardness and toughness of the capsule wall, the stress changes caused by the cracks sometimes cannot break down the capsule wall in time to allow the curing agent to flow out.

[0012] In response, this slow-release curing agent can repair microcracks by slowly releasing the curing agent. The slow-release effect is achieved by the volatilization of dichloromethane. The rapid formation of the capsule wall hinders the volatilization of dichloromethane inside the capsule wall. As the curing temperature increases, the concentration of dichloromethane inside the capsule wall increases and passes through the capsule wall, thereby forming pores with a slow-release effect in the capsule wall.

[0013] In some embodiments, in step S1, the curing agent is any one of siloxane, urea-formaldehyde resin, and tung oil.

[0014] Preferably, the curing agent is tung oil.

[0015] This invention specifically selects tung oil as a curing agent, which not only cures quickly but also has low reactivity to free radicals, allowing it to retain more monomers before the slow-release curing agent is released, thus extending its service life.

[0016] In some embodiments, in step S1, the emulsifier comprises sodium dodecylbenzenesulfonate and PVA.

[0017] In some embodiments, the mass ratio of sodium dodecylbenzenesulfonate to PVA is (5-12):1.

[0018] This invention uses sodium dodecylbenzenesulfonate and PVA as compound emulsifiers. Sodium dodecylbenzenesulfonate makes the slow-release curing agent into regular spherical shape without mutual adhesion, but with a wide particle size distribution. PVA has both hydrophilic and lipophilic groups, which can reduce surface tension and maintain droplet stability when adsorbed on the surface of the emulsion droplets, providing a uniform particle size, thereby improving the mixing uniformity of the slow-release curing agent in concrete.

[0019] In some embodiments, in step S1, the mass ratio of the curing agent to the emulsifier is 1:(0.001 to 0.006).

[0020] This invention controls the mass ratio of curing agent to emulsifier, so that the water-insoluble curing agent exists stably in the form of fine droplets in the composite emulsifier system after high-speed shearing.

[0021] In some embodiments, in step S2, the film-forming agent is any one of sodium carboxymethyl cellulose, gum arabic, chitosan, and butyllauroyl glutamine.

[0022] Preferably, the film-forming agent is butyllauroyl glutamine.

[0023] In some embodiments, in step S2, the mass ratio of the film-forming agent to the curing agent in step S1 is (0.1 to 0.9):1.

[0024] In some embodiments, the expanding agent comprises calcium sulfoaluminate and calcium oxide.

[0025] In some embodiments, the mass ratio of calcium sulfoaluminate to calcium oxide is (1-5):1.

[0026] The expansion agent used in this invention can fill the pores generated inside in a timely manner. Among them, calcium sulfoaluminate has good durability and stable expansion performance, which can continuously improve the strength of concrete; calcium oxide can generate calcium hydroxide through hydration reaction. The combination of the two is suitable for a wider range of environmental conditions.

[0027] In addition, this mixed expansion agent also increases the rupture degree of the slow-release curing agent, which to some extent solves the problem of the capsule wall not being able to rupture in time. The possible reason is that calcium ions form a complex with dibutyllauroyl glutamine, which then changes the structure of dibutyllauroyl glutamine, making it easier for the curing agent to flow out. Furthermore, this flocculent precipitate complex also helps to replenish the pores after the slow-release curing agent is consumed.

[0028] Another aspect of the present invention provides a method for preparing the above-mentioned self-healing concrete admixture, which specifically includes the following steps: mixing the expansion agent and the slow-release curing agent evenly.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention provides a self-healing concrete admixture comprising an expansive agent and a slow-release curing agent, enabling relatively rapid repair of microcracks in concrete. The slow-release curing agent used in this invention releases curing agent in response to external loads through cracking or deformation. Upon contact with air, the released curing agent undergoes self-oxidation for repair, producing oxidation products with high hardness and minimal impact on concrete strength. Furthermore, the complexation of the expansive agent with the capsule wall solves the problem of the capsule wall's inability to rupture in time under certain circumstances, facilitating the curing agent's outflow and effectiveness while also helping to fill pores after the slow-release curing agent is consumed. Moreover, the unruptured slow-release curing agent can still exert its effect through slow release, improving the utilization rate of the self-healing admixture and extending the repair time. Detailed Implementation

[0031] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0032] To facilitate implementation of the present invention by those skilled in the art, some of the raw materials used in the embodiments and comparative examples are described below:

[0033] The PVA model number is 17-92.

[0034] Preparation Example 1

[0035] The preparation steps of the slow-release curing agent A are as follows:

[0036] S1. Add 1.0g sodium dodecylbenzenesulfonate, 0.2g PVA and 300g tung oil to 3kg 2wt% gelatin solution, and shear at 7000rpm for 0.5h at 30℃ to obtain curing solution;

[0037] S2. Dissolve 150g of butyllauroyl glutamine in 2.5L of dichloromethane to obtain capsule wall fluid;

[0038] S3. Pour the capsule wall liquid into the curing liquid at a rate of 1g / 2s, stir at 700rpm for 3h at 30℃, raise the temperature to 45℃ and keep it at that temperature for 2h, then pass it through a 300-mesh sieve, rotary evaporate, wash with water, and dry at 50℃ to constant weight to obtain the slow-release curing agent A.

[0039] Preparation Example 2

[0040] The preparation steps of the slow-release curing agent B differ from those in Preparation Example 1 in that:

[0041] S1. Add 1.2g sodium dodecylbenzenesulfonate and 300g tung oil to 3kg of 2wt% gelatin solution, and shear at 7000rpm for 0.5h at 30℃ to obtain a cured solution.

[0042] Preparation Example 3

[0043] The preparation steps of the slow-release curing agent C differ from those in Preparation Example 1 in that:

[0044] S2. Dissolve 25g of butyllauroyl glutamine in 416mL of dichloromethane to obtain capsule wall fluid.

[0045] Preparation Example 4

[0046] The preparation steps of the slow-release curing agent D differ from those in Preparation Example 1 in that:

[0047] S2. Dissolve 300g of dibutyllauroyl glutamine in 5L of dichloromethane to obtain capsule wall fluid.

[0048] Particle size distribution tests were conducted on slow-release curing agents A to D. PDI is a dimensionless value that reflects the width of the particle size distribution, ranging from 0 to 1. The smaller the value, the more uniform the particle size and the more concentrated the particle size distribution. The results are shown in Table 1.

[0049] Table 1. Particle size distribution of the slow-release curing agent

[0050] Slow-release curing agent A B C D PDI 0.132 0.307 0.244 0.226

[0051] Example 1

[0052] A self-healing concrete admixture, by weight, comprises the following raw materials: 13 parts of an expansive agent and 8 parts of a slow-release curing agent A, wherein the expansive agent comprises 10 parts of calcium sulfoaluminate and 3 parts of calcium oxide.

[0053] The preparation method of the self-healing concrete admixture in this embodiment includes the following steps: mixing the expansion agent and the slow-release curing agent A evenly.

[0054] Example 2

[0055] A self-healing concrete admixture, by weight, comprises the following raw materials: 5 parts of an expansive agent and 3 parts of a slow-release curing agent A, wherein the expansive agent comprises 2.5 parts of calcium sulfoaluminate and 2.5 parts of calcium oxide.

[0056] The preparation method of the self-healing concrete admixture in this embodiment is the same as that in Embodiment 1.

[0057] Example 3

[0058] A self-healing concrete admixture, by weight, comprises the following raw materials: 20 parts of an expansive agent and 15 parts of a slow-release curing agent A, wherein the expansive agent comprises 16.5 parts of calcium sulfoaluminate and 3.5 parts of calcium oxide.

[0059] The preparation method of the self-healing concrete admixture in this embodiment is the same as that in Embodiment 1.

[0060] Example 4

[0061] This embodiment provides a self-healing concrete admixture and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the slow-release curing agent A is replaced by an equal amount of slow-release curing agent B.

[0062] Example 5

[0063] This embodiment provides a self-healing concrete admixture and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the slow-release curing agent A is replaced by an equal amount of slow-release curing agent C.

[0064] Example 6

[0065] This embodiment provides a self-healing concrete admixture and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the slow-release curing agent A is replaced by an equal amount of slow-release curing agent D.

[0066] Example 7

[0067] This embodiment provides a self-healing concrete admixture and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that calcium sulfoaluminate is replaced by an equal amount of calcium oxide.

[0068] Example 8

[0069] This embodiment provides a self-healing concrete admixture and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that calcium oxide is replaced by an equal amount of calcium sulfoaluminate.

[0070] Performance testing:

[0071] Self-repair experiment:

[0072] ①The self-healing concrete admixtures provided in Examples 1 to 8 were mixed with PO 42.5 type silicate cement at a dosage of 5wt% to form cement paste, which was then poured and molded. After 1 day, the paste was demolded and placed in a standard curing box for curing to the standard age of 28 days to obtain a sample (100mm×100mm×400mm).

[0073] ② Place the specimen on a press and apply pressure at a loading rate of 0.1 mm / s to create cracks. Select smaller longitudinal through cracks, mark them, and record the initial crack width L0. Then, place the cracked specimen in still water and cure it in a standard curing room for 1 day, 3 days, and 7 days respectively. Remove the specimen and measure the crack width again to obtain L. n n = 1, 3, 7, according to the formula L = [(L0 - L n The degree of crack repair was calculated by multiplying the crack size by 100% (L0) / 100%, and the results are shown in Table 2.

[0074] Table 2 Performance Test Results

[0075]

[0076] As shown in Table 2, the concrete in Examples 1-8 all completed self-healing by day 7. Specifically, the concrete in Examples 1-3 basically completed self-healing by day 3, showing a faster self-healing speed compared to the other examples. Examples 1 and 4 show that the emulsifier in preparing the slow-release curing agent needs to contain both sodium dodecylbenzenesulfonate and PVA; otherwise, the self-healing efficiency will be slower. Combined with the particle size distribution in Table 1, it can be seen that a single emulsifier leads to a non-concentrated particle size distribution, meaning the slow-release curing agent particles vary in size, affecting their mixing uniformity in the cement paste, thus limiting the release amount and slowing the repair speed.

[0077] Compared to Example 1, Example 5 reduced the amount of film-forming agent, changing its ratio with the curing agent. This resulted in a lower yield of the slow-release curing agent and also affected the particle size distribution concentration of the slow-release curing agent. With the amount added remaining constant, the self-healing efficiency was partially reduced. Example 6 increased the amount of film-forming agent, which, besides affecting the particle size distribution concentration, may also lead to the formation of hollow vesicles, impacting the repair efficiency. Compared to Example 1, Examples 7 and 8 used a single expanding agent, which may have affected its complexation with the film-forming agent dibutyllauroyl glutamine, thereby affecting the outflow of the curing agent and reducing the repair efficiency.

[0078] The embodiments and comparative examples described above do not limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A self-healing concrete admixture, characterized in that, By weight, it comprises the following raw materials: 5-20 parts of expanding agent and 3-15 parts of slow-release curing agent, wherein the preparation steps of the slow-release curing agent are as follows: S1. Add emulsifier and curing agent to a 1-5 wt% gelatin solution, and shear at 5000-9000 rpm for 0.1-1.0 h at 20-40°C to obtain a cured solution; S2. Dissolve the film-forming agent in dichloromethane to obtain the capsule wall fluid; S3. Pour the capsule wall liquid into the curing liquid at a rate of 1g / 1~5s, stir at 500~900rpm at 20~40℃ for 1~5h, raise the temperature to 40~48℃ and keep it at 0.5~3h, then sieve, rotary evaporate, wash and dry to obtain the slow-release curing agent. The curing agent is tung oil; The film-forming agent is butyllauroyl glutamine; The emulsifier comprises sodium dodecylbenzenesulfonate and PVA; The expanding agent comprises calcium sulfoaluminate and calcium oxide.

2. The self-healing concrete admixture according to claim 1, characterized in that, The mass ratio of sodium dodecylbenzenesulfonate to PVA is (5-12):

1.

3. The self-healing concrete admixture according to claim 1, characterized in that, In step S1, the mass ratio of the curing agent to the emulsifier is 1:(0.001 to 0.006).

4. The self-healing concrete admixture according to claim 1, characterized in that, In step S2, the mass ratio of the film-forming agent to the curing agent in step S1 is (0.1~0.9):

1.

5. The self-healing concrete admixture according to claim 1, characterized in that, The mass ratio of calcium sulfoaluminate to calcium oxide is (1-5):

1.

6. A method for preparing a self-healing concrete admixture according to any one of claims 1 to 5, characterized in that, Specifically, the steps include: mixing the expanding agent and the slow-release curing agent evenly.

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