Photocatalytic self-healing capsules for cement-based materials and methods of preparation

Abstract

This invention relates to a photocatalytic self-healing capsule for cement-based materials and its preparation method. The method for preparing the self-healing capsule includes the following steps: Step 1, mixing sodium bicarbonate, calcium hydroxide, citric acid, and water to obtain a slurry; Step 2, injecting the slurry into a mold and solidifying it to form a capsule core sphere; Step 3, coating the capsule core sphere with a capsule shell, the capsule shell comprising polyethylene material and a photocatalyst to promote polyethylene degradation. This invention, by adding a polyethylene shell made with a photocatalyst, ensures that after concrete cracks appear, the photocatalyst promotes the degradation and breakage of the polyethylene shell under light, thus ensuring that the self-healing material inside the capsule shell can be released and function, solving the problem of existing capsule shells potentially failing to break. After the capsule core sphere is released, it reacts with rainwater to generate a calcium solid substance, filling the concrete cracks and achieving self-healing repair of the concrete cracks.

Description

Technical Field

[0001] This invention relates to the field of building materials, specifically to a photocatalytic self-healing capsule for cement-based materials and its preparation method. Background Technology

[0002] Due to factors such as deformation, creep, fatigue, drying shrinkage, and freeze-thaw cycles, concrete structures inevitably develop cracks. These cracks reduce the strength and durability of the concrete structure, thereby shortening the service life and safety of the building.

[0003] Currently, there are methods for repairing concrete cracks using capsules. These capsules are equipped with repair materials to enhance their crack-healing ability. When a crack forms, the capsule ruptures, releasing the repair material to heal the crack. These repair materials are primarily composed of cyanoacrylate, polyurethane, epoxy resin, silicone, and hydrogel. However, capsules do not always rupture with the appearance of cracks, and current rupture mechanisms rely mainly on instantaneous external forces. Capsule rupture occurs only when subjected to significant impact, meaning that slowly forming cracks, such as those caused by long-term creep in concrete, cannot be healed by capsules. Existing technology, such as the invention patent with publication number CN106220014A, discloses a self-healing microcapsule for concrete, its preparation method, and a microcapsule self-healing coating. When the concrete surface cracks, the microcapsules within the coating rupture. Ultraviolet light or sunlight irradiates the healing agent sealed within the microcapsules through the crack, stimulating an active polymerization reaction in the coating, thereby repairing the concrete surface cracks. The rupture of the microcapsules also relies on the external force generated by the concrete cracking.

[0004] To address the issue of capsule rupture, current research typically employs thinner and more brittle materials to prepare the capsule shell. However, the ease with which these materials break makes construction difficult. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a photocatalytic self-healing capsule for cement-based materials and its preparation method. When concrete cracks, photocatalysis is used to rupture the capsule after light exposure, thereby releasing the repair material inside the capsule. This ensures that the capsule can rupture when concrete cracks, thus ensuring the self-healing repair of the concrete.

[0006] The technical objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a photocatalytic self-healing capsule for cement-based materials, the method comprising:

[0008] Step 1: Mix sodium bicarbonate, calcium hydroxide, citric acid and water until homogeneous to obtain a slurry;

[0009] Step 2: Inject the slurry into the mold and allow it to solidify to form the capsule core sphere;

[0010] Step 3: Cover the capsule core sphere with a capsule shell, which includes polyethylene material and a photocatalyst to promote the degradation of polyethylene.

[0011] Further, in step 1, sodium bicarbonate, calcium hydroxide, citric acid, and water are prepared in the following mass ratios: 2-3 parts sodium bicarbonate, 0.8-1 parts calcium hydroxide, 5-6 parts citric acid, and 0.02-0.03 parts water.

[0012] Furthermore, in step 1, sodium bicarbonate, calcium hydroxide, and citric acid are all solid powders.

[0013] Furthermore, in step 2, the slurry is cured and solidified in a mold at 25°C and 90% RH to form capsule core spheres, with a curing time of not less than 72 hours.

[0014] Furthermore, in step 3, after melting the polyethylene particles, the capsule core spheres and photocatalyst are added to the melted polyethylene and stirred so that the surface of the capsule core spheres is uniformly coated with polyethylene and photocatalyst.

[0015] Furthermore, the particle size of the polyethylene particles does not exceed 2 mm.

[0016] Furthermore, the polyethylene particles are melted in an oil bath at a temperature of 110℃-130℃. Heating in an oil bath increases stability during heating and avoids the boiling and evaporation problems associated with water bath heating.

[0017] Furthermore, the photocatalyst is nano-titanium dioxide powder with a purity of ≥99%.

[0018] The present invention also provides a photocatalytic self-healing capsule for cement-based materials, comprising a capsule core sphere and a capsule shell covering the outside of the capsule core sphere, wherein the capsule shell covers the outside of the capsule core sphere according to the method described above.

[0019] Furthermore, the particle size of the capsule core spheres is 1.5mm-2mm.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention uses a polyethylene shell made with a photocatalyst to ensure that the photocatalyst promotes the degradation and cracking of the polyethylene shell under light after cracks appear in the concrete, so as to ensure that the self-healing material inside the capsule shell can be released to play its role, thus solving the problem that existing capsule shells may not be able to break.

[0022] 2. The capsule shell of the present invention is made of polyethylene material, which can be sourced from waste polyethylene plastic, such as common plastic bottles and packaging boxes, thereby realizing the reuse of waste, which is green and environmentally friendly and has a low cost.

[0023] 3. After the capsule core spheres in this invention are released, sodium bicarbonate, calcium hydroxide, and water react to form calcium carbonate. The water mainly comes from natural rainwater. Citric acid reacts with calcium ions in calcium hydroxide to form calcium citrate solid. In addition, citric acid reacts with sodium bicarbonate to generate carbon dioxide gas, which escapes and forms bubbles, promoting the reaction of sodium bicarbonate, calcium hydroxide, and water. This promotes the calcium solid formed by the combination of calcium carbonate and calcium citrate to fully fill the gaps, achieving self-healing repair of concrete cracks. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments:

[0025] Example 1

[0026] A method for preparing a photocatalytic self-healing capsule for cement-based materials, the method comprising:

[0027] Step 1: Take 2 parts sodium bicarbonate, 0.8 parts calcium hydroxide, 5 parts citric acid and 0.02 parts water by mass ratio, mix and stir for 2 minutes to make the mixture uniform. Sodium bicarbonate, calcium hydroxide and citric acid are all solid powders.

[0028] Step 2: The slurry is injected into a spherical mold and cured at 25°C and 90% RH for 72 hours. The mold is then removed to obtain spherical capsule core spheres. Preferably, the particle size of the capsule core spheres is 1mm-2mm.

[0029] Step 3: The capsule shell is coated around the capsule core sphere. The capsule shell includes polyethylene material and a photocatalyst to promote polyethylene degradation. The polyethylene material can be waste polyethylene plastic bottles, packaging boxes, etc. The polyethylene material is crushed into small particles with a diameter not exceeding 2mm, then heated and melted. After the polyethylene particles melt, the capsule core sphere and photocatalyst are added to the melted polyethylene and stirred for 1 minute to ensure the surface of the capsule core sphere is uniformly coated with polyethylene and the photocatalyst. In this embodiment, the polyethylene particles are added to a beaker and heated and melted in an oil bath at a temperature of 110℃-130℃, preferably 120℃.

[0030] The main function of the photocatalyst is to promote the degradation and cracking of polyethylene materials. In this embodiment, the photocatalyst is nano carbon dioxide powder, which is a white powder with a purity of ≥99%.

[0031] The photocatalytic self-healing capsule for cement-based materials obtained in this embodiment was used for the self-healing of concrete cracks. Cement mortar test strips of 40mm*40mm*160mm were prepared according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar" and cured for 28 days. A non-penetrating crack with an average width of approximately 2mm was created in the middle of the test strip using a three-point bending test, and the capsule was placed in the crack. The test strips were placed outdoors for 30 days, subjected to sunlight and rain, ensuring at least 150 hours of sunlight exposure and at least two rainfalls. After 30 days, the cracks in the cement mortar test strips were observed. A milky white solid substance was observed forming and filling the cracks. The crack width was measured with calipers, and the average crack width was less than 1mm.

[0032] Example 2

[0033] A method for preparing a photocatalytic self-healing capsule for cement-based materials, the method comprising:

[0034] Step 1: Take 3 parts sodium bicarbonate, 1 part calcium hydroxide, 6 parts citric acid and 0.03 parts water according to the mass ratio, mix and stir for 3 minutes to make the mixture uniform. Sodium bicarbonate, calcium hydroxide and citric acid are all solid powders.

[0035] Step 2: The slurry is injected into a spherical mold and cured at 25°C and 90% RH for 72 hours. The mold is then removed to obtain spherical capsule core spheres. Preferably, the particle size of the capsule core spheres is 2 mm.

[0036] Step 3: The capsule shell is coated around the capsule core sphere. The capsule shell includes polyethylene material and a photocatalyst to promote polyethylene degradation. The polyethylene material can be waste polyethylene plastic bottles, packaging boxes, etc. The polyethylene material is crushed into small particles with a diameter not exceeding 2mm, then heated and melted. After the polyethylene particles melt, the capsule core sphere and photocatalyst are added to the melted polyethylene and stirred for 1 minute to ensure the surface of the capsule core sphere is uniformly coated with polyethylene and the photocatalyst. In this embodiment, the polyethylene particles are added to a beaker and heated and melted in an oil bath at a temperature of 110℃-130℃, preferably 120℃.

[0037] The main function of the photocatalyst is to promote the degradation and cracking of polyethylene materials. In this embodiment, the photocatalyst is nano carbon dioxide powder, which is a white powder with a purity of ≥99%.

[0038] The photocatalytic self-healing capsule for cement-based materials obtained in this embodiment was used for the self-healing of concrete cracks. Cement mortar test strips of 40mm*40mm*160mm were prepared according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar" and cured for 28 days. A non-penetrating crack with an average width of approximately 2mm was created in the middle of the test strip using a three-point bending test, and the capsule was placed in the crack. The test strips were placed outdoors for 30 days, subjected to sunlight and rain, ensuring at least 150 hours of sunlight exposure and at least two rainfalls. After 30 days, the cracks in the cement mortar test strips were observed. A milky white solid substance was observed forming and filling the cracks. The crack width was measured with calipers, and the average crack width was less than 1mm.

[0039] This embodiment is merely a further explanation of the present invention and is not intended to limit the present invention. Those skilled in the art can make non-inventive modifications to this embodiment as needed after reading this specification, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing a photocatalytic self-healing capsule for cement-based materials, characterized in that, The method includes: Step 1: Mix sodium bicarbonate, calcium hydroxide, citric acid and water until homogeneous to obtain a slurry; Step 2: The slurry is injected into the mold and solidified to form the capsule core sphere; Step 3: Cover the capsule core sphere with a capsule shell, the capsule shell comprising polyethylene material and a photocatalyst to promote the degradation of polyethylene; In step 1, the sodium bicarbonate, calcium hydroxide, citric acid, and water are prepared in the following proportions by mass: 2-3 parts sodium bicarbonate, 0.8-1 parts calcium hydroxide, 5-6 parts citric acid, and 0.02-0.03 parts water. In step 2, the slurry is cured and solidified in a mold at 25°C and 90%RH to form a capsule core sphere, and the curing time is not less than 72 hours. In step 3, polyethylene particles are melted, and capsule core spheres and photocatalyst are added to the melted polyethylene and stirred so that the surface of the capsule core spheres is uniformly coated with polyethylene and photocatalyst. The polyethylene particles are melted in an oil bath at a temperature of 110°C-130°C. The photocatalyst is nano-titanium dioxide powder with a purity of ≥99%.

2. The method for preparing a photocatalytic self-healing capsule for cement-based materials according to claim 1, characterized in that, In step 1, sodium bicarbonate, calcium hydroxide, and citric acid are all solid powders.

3. The method for preparing a photocatalytic self-healing capsule for cement-based materials according to claim 1, characterized in that, The diameter of the polyethylene particles does not exceed 2 mm.

4. A photocatalytic self-healing capsule for cement-based materials, characterized in that, The self-healing capsule is prepared according to the method described in any one of claims 1-3.

5. A photocatalytic self-healing capsule for cement-based materials according to claim 4, characterized in that, The particle size of the capsule's core spheres is 1.5mm-2mm.