Self-repairing capsules for low-calcium concrete and method for their preparation

Abstract

The application discloses a self-repairing capsule for low-calcium concrete and a preparation method thereof. The self-repairing capsule for low-calcium concrete comprises a capsule core and a capsule wall wrapped on the surface of the capsule core. The capsule core raw material comprises, by weight fraction, 60-100 parts of metakaolin, 20-40 parts of sodium carbonate, 10-20 parts of solid sodium silicate, 4-8 parts of water-absorbing resin and 1-3 parts of glucose. The capsule wall raw material is composed of paraffin, polyethylene wax and ethanol. The self-repairing capsule provided by the application has a fast reaction rate, a high repair efficiency, and a strength recovery rate of 104-106% after 7d repair, and is firmly bonded with low-calcium concrete after repair.

Description

Technical Field

[0001] The invention belongs to the technical field of mortar, concrete or similar building materials, and particularly relates to a self-repairing capsule for low-calcium concrete and a preparation method thereof. Background Art

[0002] In today's climate of energy conservation and emission reduction, research on using carbon dioxide to cure cement concrete products is growing. However, ordinary Portland cement concrete, with C3S as its primary mineral component, has a low carbonation reaction and limited carbon sequestration capacity. To achieve this goal of CO2-curing cement concrete products, it is necessary to rely on low-calcium silicate minerals with strong carbon sequestration capabilities, such as C3S2, CS, and γ-C2S. Consequently, low-calcium clinker, with C3S2, CS, and γ-C2S as its primary components, has emerged. Low-calcium concrete prepared using this low-calcium clinker, after rapid CO2 curing, can achieve excellent mechanical properties in a short period of time, significantly shortening the production cycle. Furthermore, the carbon sequestration properties of low-calcium clinker are utilized to solidify CO2 within concrete products, significantly reducing the cement industry's carbon footprint.

[0003] After the low-calcium clinker reacts with carbon dioxide to form carbonation, carbon dioxide reaction channels will be left inside the concrete, forming interconnected holes. Harmful media from the outside enter the concrete through these channels, destroying the internal structure and causing cracks inside the concrete. Currently, there are few reports on self-repairing capsules specifically for low-calcium concrete. Commonly used self-repairing capsules can be roughly divided into two categories: 1. Microbial repair capsules, which use microorganisms to induce the formation of calcium carbonate precipitation, filling concrete cracks to achieve the purpose of repairing concrete. However, microbial capsules are limited by the survival rate of microorganisms. In some extreme environments, microorganisms have difficulty surviving, resulting in a significant reduction in repair efficiency. For example, patent CN11108192B discloses a microbial self-repairing capsule for marine concrete. It uses coral reef calcareous sand as a carrier for microorganisms and forms stable calcite to achieve the purpose of repairing concrete cracks. However, this patent does not consider the impact of the marine environment on microbial survival rate, resulting in a significant reduction in repair efficiency. 2. Healing agent capsules, which achieve the purpose of repair by adding microcapsules containing a liquid healing agent to the concrete. When the concrete cracks, the microcapsules are destroyed, and the healing agent inside flows out and penetrates the cracks through capillary action. After the healing agent solidifies, it bonds the fractured surfaces together. Currently, most healing agent capsules are not early-strengthening materials, so the repair time is long. In addition, the healing agent and the concrete substrate are prone to poor adhesion. For example, patent CN106747653A provides a self-repairing capsule, but the repair efficiency is relatively low, and it takes more than 3 days to fully repair. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the existing technology and provide a self-repairing capsule for low-calcium concrete and a preparation method thereof, so as to solve the problem that the efficiency of repairing cracks in low-calcium concrete is slow and the repair agent is not firmly bonded to the concrete substrate after filling the cracks, resulting in the appearance of new cracks.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is:

[0006] A self-repairing capsule for low-calcium concrete comprises a capsule core and a capsule wall wrapped around the surface of the capsule core. The raw materials of the capsule core include, by weight, 60-100 parts of metakaolin, 20-40 parts of sodium carbonate, 10-20 parts of solid sodium silicate, 4-8 parts of water-absorbing resin (SAP), and 1-3 parts of glucose; the raw materials of the capsule wall are composed of paraffin, polyethylene wax, and ethanol.

[0007] According to the above solution, the average particle size of the metakaolin is 12.0 to 14.0 μm.

[0008] According to the above solution, the modulus of the solid sodium silicate is 1.0 to 1.5.

[0009] According to the above solution, the water-absorbing resin is a polyacrylic acid salt water-absorbing resin.

[0010] According to the above solution, the particle size of the capsule core is 1 to 10 mm, and the thickness of the capsule wall is 0.2 to 0.4 mm.

[0011] According to the above scheme, the mass ratio of the paraffin wax, polyethylene wax and ethanol is 1:0.1-0.2:5-5.5.

[0012] The present invention also includes a method for preparing the self-repairing capsule for low-calcium concrete, which comprises the following steps:

[0013] 1) Weigh the raw materials in proportion and set aside;

[0014] 2) uniformly mixing metakaolin, sodium carbonate, solid sodium silicate, a water-absorbing resin, and glucose, pre-pressing the mixture to obtain a repair agent powder, granulating the obtained repair agent powder using a granulator, and sieving the mixture to obtain capsule core particles;

[0015] 3) Paraffin wax, polyethylene wax, and ethanol are mixed, heated and stirred to obtain a suspension, and then the obtained suspension is quickly sprayed on the surface of the rolling capsule core particles, followed by drying and curing at room temperature to obtain self-healing capsules for low-calcium concrete.

[0016] According to the above scheme, the pre-pressing pressure in step 2) is 1-5 MPa, and the pre-pressing time is 10-20 s.

[0017] According to the above scheme, the heating and stirring temperature in step 3) is 60-65°C.

[0018] The present invention also provides a self-repairing low-calcium concrete, which comprises low-calcium clinker and the self-repairing capsule. The amount of the self-repairing capsule added is 1-5% of the mass of the low-calcium clinker.

[0019] Preferably, the raw materials and mass proportions of the self-repairing low-calcium concrete are as follows: low-calcium clinker 220-400 kg / m 3 , machine-made sand 800~1000kg / m 3 , 5-16mm crushed stone 400-600kg / m 3 , 16~31.5mm crushed stone 500~800kg / m 3 , water 110~200kg / m 3 , polycarboxylate water reducer 2.0~5.0kg / m 3 , self-repairing capsules account for 1 to 5% of the mass of low-calcium clinker.

[0020] Low-calcium concrete is different from ordinary concrete. It has weak hydration ability, and its hydration products such as calcium hydroxide are much less than those of ordinary concrete. Therefore, some repair agents for ordinary concrete are not suitable for low-calcium concrete. The self-repairing capsules provided by the present invention are added to low-calcium concrete for use. When cracks appear in the low-calcium concrete, the self-repairing capsule wall also breaks and enters the cracks. When external moisture enters the cracks, the absorbent resin absorbs water and expands, becoming liquid, carrying the remaining core components of the repair agent out and filling the gaps. The Al2O3·2SiO2 in the kaolin and the uncarbonized CaO·SiO2 in the low-calcium concrete react with alkaline activators such as solid sodium silicate and sodium carbonate, as well as water, to generate NASH gel and calcium carbonate. The reaction products begin to grow from the crack surface of the low-calcium concrete and gradually fill the entire gap. In this way, the bonding effect is stronger and the reaction is very rapid.

[0021] The repair efficiency is higher and the purpose of quickly repairing concrete can be achieved.

[0022] Furthermore, the glucose used in the present invention acts as a binder, providing a certain degree of cohesion during the capsule core preparation process, allowing the capsule core to cohere during the pressing process, thus preventing it from falling apart upon pressing. Glucose also acts as a calcium carbonate crystal phase-shifting agent, inducing the calcium carbonate crystal phase to transform into a needle-rod-like structure of aragonite during the reaction to form calcium carbonate. The interweaving of the needle-rod-like structure of aragonite further enhances the repair strength.

[0023] The beneficial effects of the present invention are as follows: 1. The self-repairing capsules provided by the present invention have a fast reaction rate and high repair efficiency, with a maximum strength recovery rate of 104-106% after 7 days of repair, and strong adhesion to low-calcium concrete after repair. 2. The preparation method of the present invention has simple steps, low raw material costs, and is easy to implement industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a surface SEM image of the capsule core prepared in Example 1 of the present invention after simulating concrete repair reaction;

[0025] Figure 2 This is a surface SEM image of the capsule core prepared in Example 1 after simulating concrete repair reaction. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be fully and clearly described below in conjunction with embodiments, but the described embodiments are only some embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] A self-repairing capsule for low-calcium concrete comprises a capsule core and a capsule wall wrapped around the surface of the capsule core. The preparation method comprises the following steps:

[0029] Preparation of capsule core: 60 parts of metakaolin (average particle size 12.0-14.0 μm), 20 parts of sodium carbonate, 10 parts of solid sodium silicate (modulus 1.0), 4 parts of water-absorbing resin (polyacrylate water-absorbing resin, purchased from Shandong Linchuan Water Technology Co., Ltd.), and 1 part of glucose were mixed uniformly, placed in a press, and pre-pressed at 5 MPa for 10 seconds to form micro-spherical particles to obtain a certain strength. These micro-spherical particles were then granulated in a disc granulator and sieved to obtain spherical capsule core particles with a particle size of less than 10 mm.

[0030] Preparation of self-healing capsule wall: paraffin wax, polyethylene wax and ethanol are weighed in a mass ratio of 1:0.1:5, stirred evenly at 60°C to obtain a suspension, and the suspension is quickly and evenly sprayed on the rolling capsule core particles using a high-pressure spray gun until a thin film with a thickness of 0.3±0.1mm is formed on the surface of the capsule core. Then, the spraying is stopped and the capsule core is kept rolling. After 5 minutes, the rolling is stopped, the suspension is collected, dried and solidified to obtain a self-healing capsule.

[0031] Self-repairing low-calcium concrete was prepared based on the self-repairing capsules prepared in this embodiment. The components and their contents are as follows: low-calcium clinker (provided by Huaxin Cement Factory, the mineral composition and mass percentage of the low-calcium clinker are: CS: 12-18%, C3S2: 30-48%, C2S: 18-25%, the remainder is impurities, 45μm sieve residue is less than 15%, and the specific surface area is 500-550m 3 / kg)380kg / m 3 , machine-made sand 900kg / m 3, 5-16mm crushed stone 400kg / m 3 , 16~31.5mm crushed stone 600kg / m 3 , water 160kg / m 3 , polycarboxylate water reducer 3.8kg / m 3 The self-repairing capsules prepared in this embodiment are 0, 3.8, 11.4, and 19 kg / m 3 (i.e., low-calcium clinker content of 0, 1%, 3%, and 5%), with a manufactured sand fineness modulus of 2.5. Four sets of 100mm×100mm×100mm concrete test blocks were prepared using this mix ratio, with three concrete blocks per set. After three days of standard curing, the blocks were placed in a carbonization chamber and carbonized for 20 hours at 30°C, 100% CO2 concentration, and 0.3MPa pressure, yielding four sets of low-calcium concrete test blocks.

[0032] Comparison of self-repair capsule repair efficiency: Each group of low-calcium concrete specimens was further divided into two groups. One group was directly compressed to the limit, and the second group was compressed to 80% of the limit pressure value of the first group. After being moved to a standard curing room and cured for 7 days, the strength test was conducted again to analyze and compare the repair rate of low-calcium concrete. The repair results are shown in Table 1:

[0033] Table 1

[0034]

[0035] Result analysis: It can be seen from Table 1 that the strength recovery rate of low-calcium concrete added with self-repairing capsules is higher than that of the group without self-repairing capsules, and with the increase of the self-repairing capsule dosage, the strength recovery rate also gradually increases, and even exceeds the original strength when the dosage is 5%.

[0036] Take 10 capsule cores prepared in this example, the low calcium concrete test block prepared in this example (the amount of self-repairing capsules is 3% of the mass of low calcium clinker), and the powder ground from the cementitious material (specific surface area of ​​about 350m 2 / g, simulating the reaction that occurs when repairing in concrete) 50 parts and 30 parts of water, after mixing evenly, stir at a speed of 60r / min for 3 minutes, pour into a mold for molding, and measure its surface SEM image after curing at room temperature for 7 days. Figure 1 and Figure 2 As shown, it can be seen that the self-repairing reaction product includes needle-rod-shaped aragonite, which is intertwined with other reaction products to form a compact structure, making the repair effect better.

[0037] Example 2

[0038] A self-repairing capsule for low-calcium concrete comprises a capsule core and a capsule wall wrapped around the surface of the capsule core. The preparation method comprises the following steps:

[0039] Preparation of capsule core: 60 parts of metakaolin (average particle size 12.0-14.0 μm), 20 parts of sodium carbonate, 10 parts of solid sodium silicate (modulus 1.0), 4 parts of water-absorbing resin (polyacrylate water-absorbing resin), and 1 part of glucose are mixed uniformly, placed in a press, and pre-pressed at 5 MPa for 10 seconds to form micro-spherical particles. These micro-spherical particles are then granulated in a disc granulator and sieved to obtain spherical capsule core particles with a particle size of less than 10 mm.

[0040] Preparation of self-healing capsule wall: paraffin wax, polyethylene wax and ethanol are weighed in a mass ratio of 1:0.1:5, stirred evenly at 60°C to obtain a suspension, and the suspension is quickly and evenly sprayed on the rolling capsule core particles using a high-pressure spray gun until a thin film with a thickness of 0.6±0.1 mm is formed on the surface of the capsule core. Then, the spraying is stopped and the capsule core is kept rolling. After 5 minutes, the rolling is stopped, the suspension is collected, dried and solidified to obtain a self-healing capsule.

[0041] Self-repairing low-calcium concrete was prepared based on the self-repairing capsules prepared in this example. Four groups of low-calcium concrete test blocks were prepared using the same method as in Example 1.

[0042] The repair rate of the prepared low-calcium concrete was tested using the same method as in Example 1. The repair results are shown in Table 2:

[0043] Table 2

[0044]

[0045] Results Analysis: Table 2 shows that the strength recovery rate of low-calcium concrete incorporating the self-repairing capsules prepared in this example is higher than that of the concrete without self-repairing capsules. The strength recovery rate also increases with increasing self-repairing capsule dosage. Increasing the wall thickness of the self-repairing capsules prepared in this example to 0.6±0.1mm results in a lower repair efficiency than that of 0.3±0.1mm. This may be because the increased wall thickness makes it more difficult to rupture, reducing the repair efficiency.

[0046] Example 3

[0047] A self-repairing capsule for low-calcium concrete comprises a capsule core and a capsule wall wrapped around the surface of the capsule core. The preparation method comprises the following steps:

[0048] Preparation of capsule core: 60 parts of metakaolin (average particle size 12.0-14.0 μm), 20 parts of sodium carbonate, 10 parts of solid sodium silicate (modulus 1.0), 4 parts of water-absorbing resin (polyacrylate water-absorbing resin), and 1 part of glucose are mixed uniformly, placed in a press, and pre-pressed at 5 MPa for 10 seconds to form micro-spherical particles. These micro-spherical particles are then granulated in a disc granulator and sieved to obtain spherical capsule core particles with a particle size of less than 10 mm.

[0049] Preparation of self-healing capsule wall: paraffin wax, polyethylene wax and ethanol are weighed in a mass ratio of 1:0.2:5.5, stirred evenly at 60°C to obtain a suspension, and the suspension is quickly and evenly sprayed on the rolling capsule core particles using a high-pressure spray gun until a thin film with a thickness of 0.3±0.1mm is formed on the surface of the capsule core. Then, the spraying is stopped and the capsule core is kept rolling. After 5 minutes, the rolling is stopped, the suspension is collected, dried and solidified to obtain a self-healing capsule.

[0050] Self-repairing low-calcium concrete was prepared based on the self-repairing capsules prepared in this example. Four groups of low-calcium concrete test blocks were prepared using the same method as in Example 1.

[0051] The repair rate of the prepared low-calcium concrete was tested using the same method as in Example 1. The repair results are shown in Table 3:

[0052] Table 3

[0053]

[0054] Results Analysis: Table 3 shows that the strength recovery rate of low-calcium concrete incorporating the self-repairing capsules prepared in this example is higher than that of the concrete without self-repairing capsules. Furthermore, the strength recovery rate increases with increasing self-repairing capsule dosage, exceeding the original strength at a 5% dosage. Adjusting the capsule wall ratio has no significant negative impact on strength recovery.

[0055] Comparative Example 1

[0056] Concrete test blocks were prepared according to the mix ratio of the self-repairing low-calcium concrete in Example 1, except that the self-repairing capsules prepared in Example 1 were replaced with microbial self-repairing capsules of equal mass (prepared according to CN202110400525.4). The self-repairing capsules were tested for repair efficiency using the method of Example 1. The test results are shown in Table 4.

[0057] Table 4

[0058]

[0059] Result analysis: Comparing Tables 1-4, it can be seen that the concrete repair efficiency of the microbial self-repair capsules used in the comparative example is significantly lower than the repair efficiency of the self-repair capsules prepared in the embodiment of the present invention.

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art who, within the technical scope disclosed by the present invention, makes equivalent substitutions or changes based on the technical solutions and improved concepts of the present invention shall be covered by the scope of protection of the present invention.

Claims

1. A self-repairing capsule for low-calcium concrete, characterized in that: The capsule comprises a capsule core and a capsule wall wrapped around the surface of the capsule core. The raw materials of the capsule core comprise, by weight, 60 to 100 parts of metakaolin, 20 to 40 parts of sodium carbonate, 10 to 20 parts of solid sodium silicate, 4 to 8 parts of water-absorbing resin, and 1 to 3 parts of glucose; the raw materials of the capsule wall are composed of paraffin, polyethylene wax, and ethanol.

2. The self-repairing capsule for low-calcium concrete according to claim 1, characterized in that: The average particle size of the metakaolin is 12.0 to 14.0 μm; and the modulus of the solid sodium silicate is 1.0 to 1.

5.

3. The self-repairing capsule for low-calcium concrete according to claim 1, characterized in that: The water-absorbing resin is a polyacrylic acid salt water-absorbing resin.

4. The self-repairing capsule for low-calcium concrete according to claim 1, characterized in that: The particle size of the capsule core is 1 to 10 mm, and the thickness of the capsule wall is 0.2 to 0.4 mm.

5. The self-repairing capsule for low-calcium concrete according to claim 1, characterized in that: The mass ratio of the paraffin wax, polyethylene wax and ethanol is 1:0.1-0.2:5-5.

5.

6. A method for preparing a self-repairing capsule for low-calcium concrete according to any one of claims 1 to 5, characterized in that: The specific steps are as follows: 1) Weigh the raw materials in proportion and set aside; 2) uniformly mixing metakaolin, sodium carbonate, solid sodium silicate, a water-absorbing resin, and glucose, pre-pressing the mixture to obtain a repair agent powder, granulating the obtained repair agent powder using a granulator, and sieving the mixture to obtain capsule core particles; 3) Paraffin wax, polyethylene wax, and ethanol are mixed, heated and stirred to obtain a suspension, and then the obtained suspension is quickly sprayed on the surface of the rolling capsule core particles, followed by drying and curing at room temperature to obtain self-healing capsules for low-calcium concrete.

7. The method for preparing the self-repairing capsule for low-calcium concrete according to claim 6, characterized in that: The pre-pressing pressure in step 2) is 1-5 MPa, and the pre-pressing time is 10-20 s.

8. The method for preparing the self-repairing capsule for low-calcium concrete according to claim 6, characterized in that: Step 3) heating and stirring at a temperature of 60-65°C.

9. A self-repairing low-calcium concrete, characterized in that: The method comprises low-calcium clinker and the self-repairing capsule according to any one of claims 1 to 5, wherein the amount of the self-repairing capsule added is 1 to 5% of the mass of the low-calcium clinker.

10. The self-repairing low-calcium concrete according to claim 9, characterized in that: The raw materials and mass proportions of the self-repairing low-calcium concrete are as follows: low-calcium clinker 220-400 kg / m 3 , machine-made sand 800~1000kg / m 3 , 5-16mm crushed stone 400-600kg / m 3 , 16~31.5mm crushed stone 500~800kg / m 3 , water 110~200kg / m 3 , polycarboxylate water reducer 2.0~5.0kg / m 3 , self-repairing capsules account for 1 to 5% of the mass of low-calcium clinker.

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