Concrete self-repairing admixture and preparation method thereof

Abstract

The invention relates to the technical field of concrete, and particularly discloses a concrete self-repairing admixture and a preparation method thereof.The concrete self-repairing admixture is prepared from, by weight, 5-20 parts of expanding agent and 3-15 parts of slow-release curing agent, and the slow-release curing agent can respond to external load through cracking or deformation to release the curing agent. The released curing agent can be self-oxidized for repairing after being in contact with air, on the basis, the problem that the capsule wall cannot be broken in time under some conditions is solved by matching with the mixed expanding agent, the curing agent can conveniently flow out to exert the effect, and meanwhile pores formed after the slow-release curing agent is consumed can be filled; and the unbroken slow-release curing agent can play a role through slow release, so that the utilization rate of the self-repairing admixture is increased, and the repairing time is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of concrete, and particularly relates to a concrete self-repairing admixture and a preparation method thereof. Background Art

[0002] As a multi-component composite material, concrete will inevitably produce cracks when the external environment (temperature, humidity, ion concentration, etc.) and load conditions (dynamic and static loads) change due to the differences in the physical and chemical properties of each component. The occurrence of concrete cracks will reduce the structural bearing capacity and safety of use, and affect the waterproof performance, durability and service life of the structure. Traditional repair methods mainly include surface treatment, grouting treatment and structural reinforcement, which have high technical costs. Concrete self-repair technology can achieve timely repair of the damaged part of concrete before microcracks develop into macrocracks without the need for manual inspection, saving a lot of costs on structural maintenance, and is simple to operate.

[0003] Based on the self-repair mechanism, in 2009, the Japanese Concrete Institute (JCI) divided the self-repair mechanism into three categories: natural healing, automatic healing and autonomous repair. Natural healing mainly relies on the potential of the material itself, that is, the unhydrated cement in the concrete reacts with the water that penetrates into the concrete through the cracks to generate hydration products to fill the cracks. Automatic healing can be regarded as the enhancement and acceleration of automatic healing. For this kind of self-repair, domestic and foreign research mainly focuses on three directions: mineral additives based on fly ash, silica fume, and slag; mineral additives based on expansion agent composite chemical substances; mineral additives based on limestone and limestone. The main methods of autonomous repair include microcapsules, microbial self-repair, hollow fiber repair, shape memory alloy repair, etc.

[0004] At present, relevant technical personnel have achieved certain results in the self-repair research of concrete. For example, patent CN114835428B provides a concrete crack self-healing admixture containing a water-absorbing resin, a complexing agent and a hydration inhibitor. The calcium ions are transported to the gel formed by the water-absorbing resin through the complex, and react with the unhydrated silicate ions in the concrete to form water-insoluble calcium silicate crystals, which block the concrete cracks and achieve self-repair. However, the strength of the formed hydrogel is low, which may affect the compressive strength of the concrete. For example, patent CN 114180875 B discloses a permeable crystallization type high-performance concrete crack-proof and anti-seepage agent and its preparation method, wherein the complexing agent is a permeable crystallization component. When the concrete matrix cracks and seeps water, the water in the environment will form a complex with the calcium ions, diffuse into the accumulated water in the concrete pores and cracks, and continuously undergo a complex precipitation reaction to achieve the effect of repairing the pores and cracks of the concrete. However, this method requires a certain amount of time to precipitate and generate crystals that block the cracks, and the calcium ions in the concrete used will be consumed, resulting in poor comprehensive anti-seepage performance. Therefore, there is an urgent need on the market for a concrete self-repairing admixture that has little impact on concrete strength, short self-repairing time and long effectiveness. Summary of the invention

[0005] In order to solve the above problems, the present invention adopts a slow-release curing agent, which uses the self-oxidation of the capsule wall with air to repair microcracks after it ruptures. The oxidation product has a high hardness, has little effect on the strength of concrete, and has a short curing time. On this basis, a mixed expansive agent is used to obtain a concrete self-repairing admixture that has little effect on the strength of concrete, takes a short self-repairing time, and has a long effectiveness.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] On one hand, the present invention provides a concrete self-repairing admixture, which comprises the following raw materials in parts by weight: 5 to 20 parts of an expansion agent and 3 to 15 parts of a slow-release curing agent, wherein the preparation steps of the slow-release curing agent are as follows:

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

[0009] S2, dissolving the film-forming agent in dichloromethane to obtain a capsule wall liquid;

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

[0011] The slow-release curing agent provided by the present invention can be evenly distributed inside the cement-based material structure, and can achieve better repair of damaged parts. When microcracks appear in the concrete, the slow-release curing agent located there can release the curing agent by cracking or deforming in response to external loads, and it can undergo self-oxidation after contact with air, and can repair the microcracks without a catalyst. However, since the capsule wall has a certain hardness and toughness, the stress changes caused by the cracks sometimes cannot destroy the capsule wall in time to allow the curing agent to flow out.

[0012] In this regard, the slow-release curing agent can repair microcracks by slowly releasing the curing agent, wherein the slow-release effect is achieved due to 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 holes 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] The present invention specifically selects tung oil as a curing agent, which not only cures quickly but also has low reactivity to free radicals, and can retain more monomers before the slow-release curing agent is released, thereby extending the service life.

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

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

[0018] The invention uses sodium dodecylbenzene sulfonate and PVA as compound emulsifiers. Sodium dodecylbenzene sulfonate makes the slow-release curing agent present in a regular spherical shape without mutual adhesion, but with a wide particle size distribution. PVA has both a hydrophilic group and a lipophilic group, and can reduce surface tension when adsorbed on the surface of emulsion droplets, maintain the stability of emulsion droplets, provide a uniform particle size, and thus improve 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:(0.001-0.006).

[0020] The present invention controls the mass ratio of the curing agent to the emulsifier so that the water-insoluble curing agent can be stably present in the composite emulsifier system in the form of fine droplets 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 dibutyl lauroyl glutamine.

[0022] Preferably, the film former is dibutyl lauroyl glutamide.

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

[0024] In some embodiments, the expansion 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 the present invention can timely fill the pores generated inside, among which calcium sulfoaluminate has good durability and stable expansion performance, and can continuously improve the strength of concrete; calcium oxide can generate calcium hydroxide through hydration reaction, and the combination of the two is suitable for a wider range of environmental conditions.

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

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

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

[0030] The present invention provides a concrete self-repairing admixture, which comprises an expansion agent and a slow-release curing agent. When microcracks appear in concrete, it can be repaired relatively quickly. The slow-release curing agent used in the present invention can release the curing agent by cracking or deforming in response to an external load. The released curing agent can undergo self-oxidation and repair after contacting with air. The oxidation product has a high hardness and has little effect on the strength of concrete. On this basis, the problem that the capsule wall cannot be ruptured in time in some cases is solved by complexing the mixed expansion agent with the capsule wall, which facilitates the outflow of the curing agent to exert its effect while helping to fill the pores after the slow-release curing agent is consumed; and the unruptured slow-release curing agent can also exert its effect through slow release, thereby improving the utilization rate of the self-repairing admixture and the repair time. DETAILED DESCRIPTION

[0031] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0032] In order to facilitate those skilled in the art to implement the present invention, some of the raw materials of the embodiments and comparative examples are described as follows:

[0033] The PVA model is 17-92.

[0034] Preparation Example 1

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

[0036] S1. Add 1.0 g of sodium dodecylbenzene sulfonate, 0.2 g of PVA and 300 g of tung oil to 3 kg of 2 wt% gelatin solution, and shear at 7000 rpm for 0.5 h at 30° C. to obtain a solidified liquid;

[0037] S2, dissolving 150 g of dibutyl lauroyl glutamine in 2.5 L of dichloromethane to obtain a capsule wall liquid;

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

[0039] Preparation Example 2

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

[0041] S1. Add 1.2 g of sodium dodecylbenzene sulfonate and 300 g of tung oil to 3 kg of 2 wt% gelatin solution, and shear at 7000 rpm at 30° C. for 0.5 h to obtain a solidified liquid.

[0042] Preparation Example 3

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

[0044] S2. Dissolve 25 g of dibutyl lauroyl glutamide in 416 mL of dichloromethane to obtain a capsule wall liquid.

[0045] Preparation Example 4

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

[0047] S2. Dissolve 300 g of dibutyl lauroyl glutamide in 5 L of dichloromethane to obtain a capsule wall liquid.

[0048] The particle size distribution test was performed on the sustained-release curing agents A to D. PDI is a dimensionless value reflecting 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 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 concrete self-repairing admixture comprises the following raw materials, measured by weight: 13 parts of an expansion agent and 8 parts of a slow-release curing agent A, wherein the expansion agent comprises 10 parts of calcium sulfoaluminate and 3 parts of calcium oxide.

[0053] The method for preparing the concrete self-repairing admixture in this embodiment comprises the following steps: the expansion agent and the slow-release curing agent A are mixed evenly.

[0054] Example 2

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

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

[0057] Example 3

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

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

[0060] Example 4

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

[0062] Example 5

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

[0064] Example 6

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

[0066] Example 7

[0067] This embodiment provides a concrete self-repairing admixture and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that calcium sulfoaluminate is replaced by an equal portion of calcium oxide.

[0068] Example 8

[0069] This embodiment provides a concrete self-repairing admixture and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that calcium oxide is replaced by an equal portion of calcium sulfoaluminate.

[0070] Performance Testing:

[0071] Self-repair experiment:

[0072] ① The concrete self-repairing admixtures provided in Examples 1 to 8 were respectively mixed with PO 42.5 type silicate cement at a dosage of 5 wt % to form cement slurry, cast and molded, demolded after 1 day, and placed in a standard curing box for curing to a standard age of 28 days to obtain a sample (100 mm×100 mm×400 mm);

[0073] ② Place the sample on a press and pressurize it at a loading speed 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 sample in still water and place it in a standard curing room for curing for 1d, 3d, and 7d, respectively. Take out the sample and measure the crack width again to obtain L0. n , n = 1, 3, 7, according to the formula L = [(L0-L n ) / L0]×100% to calculate the degree of crack repair. The results are shown in Table 2.

[0074] Table 2 Performance test results

[0075]

[0076] From the data in Table 2, it can be seen that the concretes of Examples 1 to 8 all completed self-repair on the 7th day, and the concretes of Examples 1 to 3 basically completed self-repair on the third day, and their self-repair speed is faster than that of the other examples. From Examples 1 and 4, it can be seen that when preparing the slow-release curing agent, the emulsifier needs to contain sodium dodecylbenzene sulfonate and PVA at the same time, otherwise the self-repair efficiency will be slowed down. Combined with the particle size distribution in Table 1, it can be seen that a single emulsifier will lead to an unconcentrated particle size distribution, that is, the slow-release curing agent particles are large and small, which affects its mixing uniformity in the cement paste, and then leads to limited release and a slow repair speed.

[0077] Compared with Example 1, Example 5 reduces the amount of film-forming agent, and the ratio of film-forming agent to curing agent changes, resulting in a decrease in the yield of the slow-release curing agent, and also affects the particle size distribution concentration of the slow-release curing agent. When the amount added remains unchanged, the self-repairing efficiency is partially reduced; Example 6 increases the amount of film-forming agent, and in addition to affecting the particle size distribution concentration, hollow capsules may appear, affecting the repair efficiency. Compared with Example 1, Examples 7-8 use a single swelling agent, which may affect its complexation with the film-forming agent dibutyl lauroyl glutamide, and then affect the outflow of the curing agent, resulting in a decrease in the repair efficiency.

[0078] The embodiments and comparative examples described above do not impose any form of limitation on the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A concrete self-repairing admixture, characterized in that: The invention comprises the following raw materials by weight: 5 to 20 parts of an expander and 3 to 15 parts of a slow-release curing agent, wherein the preparation steps of the slow-release curing agent are as follows: S1. Add an emulsifier and a curing agent to a 1-5 wt% gelatin solution, and shear at a rate of 5000-9000 rpm for 0.1-1.0 h at 20-40° C. to obtain a solidified liquid; S2, dissolving the film-forming agent in dichloromethane to obtain a capsule wall liquid; S3. Pour the capsule wall liquid into the curing liquid at a rate of 1 g / 1-5 s, stir at a rate of 500-900 rpm at 20-40° C. for 1-5 h, heat to 40-48° C. and keep warm for 0.5-3 h, then sieve, rotary evaporate, wash and dry to obtain a slow-release curing agent.

2. The concrete self-repairing admixture according to claim 1, characterized in that: In step S1, the curing agent is any one of siloxane, urea-formaldehyde resin, and tung oil.

3. The concrete self-repairing admixture according to claim 1, characterized in that: In step S1, the emulsifier comprises sodium dodecylbenzene sulfonate and PVA.

4. The concrete self-repairing admixture according to claim 3, characterized in that: The mass ratio of the sodium dodecylbenzene sulfonate to PVA is (5-12):

1.

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

6. The concrete self-repairing admixture according to claim 1, characterized in that: In step S2, the film-forming agent is any one of sodium carboxymethyl cellulose, gum arabic, chitosan, and dibutyl lauroyl glutamine.

7. The concrete self-repairing 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.

8. The concrete self-repairing admixture according to claim 1, characterized in that: The expansion agent comprises calcium sulphoaluminate and calcium oxide.

9. The concrete self-repairing admixture according to claim 8, characterized in that: The mass ratio of the calcium sulfoaluminate to calcium oxide is (1-5):

1.

10. A method for preparing the concrete self-repairing admixture according to any one of claims 1 to 9, characterized in that: The method specifically comprises the following steps: uniformly mixing the expansion agent and the slow-release curing agent.

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