Chitosan-polyacrylic acid-Fe 3+ Hydrogel cement-based composites and methods of making

Abstract

The application is a chitosan-polyacrylic acid-Fe 3+ Aqueous gel cement-based composite material and preparation method. Including the following steps: (1) using directional ice template method to construct layered cement skeleton with unidirectional pores; (2) configuring chitosan-polyacrylic acid-Fe 3+ Aqueous gel solution; (3) using vacuum negative pressure immersion method to fill chitosan-polyacrylic acid-Fe 3+ Aqueous gel into the unidirectional pores of the layered cement skeleton; (4) using 'freezing-thawing' multiple cycle method to obtain high toughness self-repairing cement-based-chitosan-polyacrylic acid-Fe 3+ Aqueous gel shell-like composite material. The application cements the aqueous gel and the cement-based material together through 'freezing-thawing' cycle to prepare shell-like structure, which enhances the toughness, strength, impact resistance and structural reliability of the concrete, and has self-repairing effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of concrete composite materials, and particularly relates to a chitosan-polyacrylic acid-Fe 3+ Hydrogel cement-based composite material and preparation method. BACKGROUND

[0002] Cement-based materials are one of the most widely used building materials in the world, but they have low toughness and are prone to micro-cracks under the action of environmental erosion, non-load deformation and external load, resulting in reduced strength and durability. Some people use hydrogels to self-repair cement-based materials by loading phosphates into the hydrogels and adding them into the cement-based materials to repair cracks with dense hydroxyapatite. Although this material has super repair function, its strength and toughness are still not high. SUMMARY

[0003] The present application aims to provide a chitosan-polyacrylic acid-Fe 3+ Hydrogel cement-based composite material and preparation method.

[0004] The technical solution for achieving the purpose of the present application is: a chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material comprises the following steps:

[0005] Step (1): using a directional ice template method to construct a layered cement skeleton with unidirectional pores;

[0006] Step (2): configuring a chitosan-polyacrylic acid-Fe 3+ Hydrogel solution;

[0007] Step (3): using vacuum negative pressure impregnation to fill the chitosan-polyacrylic acid-Fe 3+ Hydrogel into the unidirectional pores of the layered cement skeleton;

[0008] Step (4): using a "freeze-thaw" multiple cycle method to obtain a high-toughness self-repairing cement-based-chitosan-polyacrylic acid-Fe 3+ Hydrogel shell-like composite material.

[0009] Further, the specific steps of step (1) are as follows:

[0010] Step (11): configuring cement mortar: mixing cement, fly ash and deionized water in a ratio of 1:0.29:0.7 in a blender, stirring uniformly, and placing on a vibration table to perform vibration to remove air bubbles;

[0011] Step (12): Prepare a cement skeleton using an ice template method: Use a mold made of polytetrafluoroethylene material on all sides and a brass bottom, pour the cement mortar prepared in step (11) into the mold, place the lower part of the mold in a constant -70-80°C liquid cold source for 2-2.5 hours, and wait for the water in the cement mortar to completely crystallize from bottom to top to form a frozen cement mortar with a layered structure;

[0012] Step (13): refrigerate the frozen cement mortar at 2-5°C for 48-54 hours, move it to a room temperature environment after thawing for 24-32 hours, and after demoulding, place it in an environment with a temperature of 20°C ± 2°C and a relative humidity of 95% RH for curing for 5-7 days;

[0013] Step (14): After the curing is completed, the porous cement matrix is ​​placed in a vacuum oven and dried at 65-70°C for 2-3 days, and then dried again with anhydrous silica gel for 18-24 hours to form a layered cement skeleton with unidirectional pores.

[0014] Furthermore, the cement in step (11) is ordinary Portland cement P.I 52.5, and the deionized water is 80-100°C hot water, which is added to the mixer in two batches and stirred for 30-60 minutes each time.

[0015] Furthermore, the mold used in step (12) is a triple mold, and the triple mold has three identical inner grooves, each of which is in the shape of a cube;

[0016] The liquid cooling source in step (12) is analytical grade anhydrous ethanol.

[0017] Furthermore, step (2) specifically includes the following steps:

[0018] Step (21): 250 ml of deionized water, 15 g of chitosan CS, and 150 ml of acrylic acid AA were added to a 1000 ml beaker and stirred with a magnetic stirrer for 20-30 min to form a CS-AA mixed solution;

[0019] Step (22): Add another 25 ml, 0.25 mol.L -1 The ferric chloride solution was stirred continuously and finally 25 ml of 0.2 mol.L -1 The potassium persulfate KPS solution was stirred again to obtain a CS-AA-KPS mixed solution;

[0020] Step (23): The reaction system is subjected to a "heating-cooling" cycle 8-9 times to cause a polymerization reaction, thereby obtaining chitosan-polyacrylic acid-Fe 3+ Hydrogel solution.

[0021] Further, the chitosan in step (21) is analytical pure, the deacetylation degree is 96%, the acrylic acid is analytical pure, and the potassium persulfate is analytical pure;

[0022] In step (22), the ferric chloride solution should be added first and stirred for 5-8 min, and then the potassium persulfate solution is added and stirred for 5-8 min.

[0023] Further, in step (23), the “heating-cooling” is specifically that the hydrogel solution is placed in a microwave oven and heated for 20-30 s, stopped for 20-30 s, and then placed in a refrigerator and cooled for 2-4 min after each two microwave heating operations, and the operation is repeated for 8-9 times until a small amount of gel film appears on the surface, so that the chitosan-polyacrylic acid-Fe 3+ hydrogel solution is obtained.

[0024] Further, in step (3), the chitosan-polyacrylic acid-Fe 3+ hydrogel solution is continuously pressed into the unidirectional pore layered cement skeleton under vacuum negative pressure until no obvious bubbles appear in the cement skeleton, and at this time, the vacuum meter count value is 0.08-0.09.

[0025] Further, step (4) is specifically as follows: after the chitosan-polyacrylic acid-Fe 3+ hydrogel solution is stably present, the filled cement test piece is placed in an environment of-30±2℃ for 8-12 h, and then thawed at room temperature for 2-4 h, and then the “heating-cooling” cycle is performed for 8-9 times to complete the first freeze-thaw cycle; the “heating-cooling” cycle is the same as that of the hydrogel solution.

[0026] After the above operation is repeated for 2-3 times of freeze-thaw cycles, a high-toughness self-repairing shellfish structure cement-based composite material filled with chitosan-polyacrylic acid-Fe 3+ hydrogel is obtained.

[0027] A chitosan-polyacrylic acid-Fe 3+ hydrogel cement-based composite material is prepared by the above method.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] The purpose of the present application is to provide a chitosan-polyacrylic acid-Fe 3+ hydrogel cement-based composite material and a preparation method, and the cement-hydrogel composite material has high toughness, self-repairing, high strength and other excellent properties, and the chitosan-polyacrylic acid-Fe 3+The hydrogel enhances the adsorption force by constructing two-layer cross-linking network interacting with the cement-based material, and bears tensile strain to enhance the toughness of the composite material. Based on the water storage function of the hydrogel material, when the humidity inside the cement-based material decreases, the stored water can be released to repair micro-cracks and improve the service life of the cement-based material.

[0030] (1) The present application realizes the directional growth of the single-direction "imitated shell" cement-based layered cement skeleton structure by controlling the temperature gradient, introducing the ice template method, and pouring by using a special mold; meanwhile, the hydrogel solution is introduced to fill the pores of the cement-based layered cement skeleton, and the mechanical connection between the cement-based "layers" is strengthened, so that the bending strength of the cement-based material is increased while the super-high toughness is obtained;

[0031] (2) The chitosan-polyacrylic acid-Fe 3+ The hydrogel constructs two physical cross-linking networks, has the characteristics of high stretchability, high strength, self-repairing and the like;

[0032] (3) The chitosan-polyacrylic acid-Fe 3+ When the material is stretched, the network structure of the hydrogel in the interlayer is continuously stretched, the chitosan-polyacrylic acid-Fe 3+ Molecular chains are gradually separated from each other, bear tensile strain, and prevent the composite material from being broken. The high flexibility of the hydrogel and the high interfacial affinity between C-S-H and the hydrogel jointly determine the great ductility and toughness of the composite material. Meanwhile, the water storage capacity and slow release capacity of the hydrogel are strong, which helps the subsequent hydration reaction to proceed, repairs the cracks of the cement-based material, and improves the durability of the cement-based material;

[0033] (4) The freeze-thaw cycle is adopted, the molecular chains in contact can interact and entangle when frozen, new microzones are formed when defrosted, and the excess water is removed by heating, so that the hydrogel and the cement-based body are cross-linked together, the cement-based material is assisted to be shaped, the adhesion of the hydrogel network is enhanced, and the strength of the cement-based material is indirectly enhanced;

[0034] (5) The "cement-hydrogel" composite gradient material has stronger functionality, has high toughness, high strength, self-repairing, impact resistance and structural reliability, and improves the tensile performance of the concrete material;

[0035] (6) The cement-based composite material has reasonable economy and environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is the chitosan-polyacrylic acid-Fe 3+ A schematic diagram of the formation process of the hydrogel;

[0037] Figure 2 It is a schematic diagram of preparing a porous cement-based triple mold by the ice template method of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to the accompanying drawings.

[0039] Example 1:

[0040] Chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material comprises the following steps:

[0041] Step 1: Use the directional ice template method to construct a layered cement skeleton with unidirectional porosity;

[0042] Step 2: Using chitosan-polyacrylic acid-Fe 3+ Hydrogel as filler and chitosan-polyacrylic acid-Fe 3+ hydrogel solution;

[0043] Step 3: Use vacuum negative pressure impregnation to 3+ The hydrogel is filled into the unidirectional pores;

[0044] Step 4: The high toughness self-repairing cement-chitosan-polyacrylic acid-Fe is obtained by multiple cycles of "freeze-thaw". 3+ Hydrogel imitation shell.

[0045] A chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material specifically includes:

[0046] (1.1) Mix ordinary Portland cement P.I 52.5, fly ash, and deionized water in a blender at a ratio of 1:0.29:0.7. Add 80°C hot water to the blender in two batches, stirring for 30 minutes each time. Oscillate the mixture on an oscillating table to remove any air bubbles.

[0047] (1.2) Preparation of porous cement skeleton by ice template method: Pour the cement mortar prepared in step (1.1) into a mold that has been frozen in a -80°C refrigerator in advance. Then place the mold in a constant -70°C ethanol solution for 2 hours to wait for the water in the cement mortar to completely crystallize from bottom to top, forming a frozen cement mortar with a layered structure.

[0048] (1.3) Refrigerate the frozen cement mortar at 2°C for 48 hours, allow it to slowly thaw, and then move it to room temperature for 24 hours. After demolding, place it in an environment with a temperature of 20°C and a relative humidity of 95% and cure it for 5 days.

[0049] (1.4) After curing, the porous cement matrix was placed in a vacuum oven and dried at 65°C for 2 days, and then dried again with anhydrous silica gel for 18 hours to form a layered cement skeleton with unidirectional pores.

[0050] A chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material specifically includes:

[0051] (2.1) Add 250 ml of deionized water, 15 g of chitosan (CS), and 150 ml of acrylic acid (AA) to a 1000 ml beaker and stir with a magnetic stirrer for 20 min to form a CS / AA mixed solution.

[0052] (2.2) Add 25 ml, 0.25 mol.L -1 The ferric chloride solution was stirred for 5 min and finally 25 ml of 0.2 mol.L -1 The potassium persulfate (KPS) solution was stirred for 5 min and then stirred again to obtain a CS / AA / KPS mixed solution;

[0053] (2.3) The mixture was heated in a microwave oven for 20 seconds, then stopped for 20 seconds. After each two microwave heating steps, the mixture was placed in a refrigerator and cooled for 2 minutes. This operation was repeated 8 times to allow polymerization to occur until a small amount of gel film appeared on the surface. Chitosan-polyacrylic acid-Fe 3+ Hydrogel solution.

[0054] In step 3, the chitosan-polyacrylic acid-Fe 3+ The hydrogel solution is continuously pressed into the layered cement skeleton with unidirectional pores until no obvious bubbles appear in the cement skeleton, at which point the vacuum count value is 0.08.

[0055] Step 4 is specifically: chitosan-polyacrylic acid-Fe 3+ After the hydrogel solution stabilized, the filled cement specimen was placed in a -30°C environment for 8 hours, then thawed at room temperature for 2 hours, and then subjected to a "heating-cooling" cycle 8 times to complete the first freeze-thaw cycle. Repeat the above operation, and after 2 freeze-thaw cycles, the inner pore filled chitosan-polyacrylic acid-Fe 3+ Highly tough self-healing shell-like structure cement-based composites with hydrogel.

[0056] Example 2:

[0057] Chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material comprises the following steps:

[0058] Step 1: Use the directional ice template method to construct a layered cement skeleton with unidirectional porosity;

[0059] Step 2: Using chitosan-polyacrylic acid-Fe 3+ Hydrogel as filler and chitosan-polyacrylic acid-Fe 3+ hydrogel solution;

[0060] Step 3: Use vacuum negative pressure impregnation to 3+ The hydrogel is filled into the unidirectional pores;

[0061] Step 4: The high toughness self-repairing cement-chitosan-polyacrylic acid-Fe is obtained by multiple cycles of "freeze-thaw". 3+ Hydrogel imitation shell.

[0062] A chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material specifically includes:

[0063] (1.1) Mix ordinary Portland cement P.I 52.5, fly ash, and deionized water in a blender at a ratio of 1:0.29:0.7. Add 95°C hot water to the blender in two batches, stirring for 60 minutes each time. Oscillate the mixture on a shaker to remove any bubbles.

[0064] (1.2) Preparation of porous cement skeleton by ice template method: Pour the cement mortar prepared in step (1.1) into a mold that has been frozen in a -80°C refrigerator in advance. Then, place the mold in a constant -70°C ethanol solution for 2.5 hours to allow the water in the cement mortar to completely crystallize from bottom to top, forming a frozen cement mortar with a layered structure.

[0065] (1.3) The frozen cement mortar was refrigerated at 2°C for 54 hours, allowed to slowly thaw, and then moved to room temperature for 32 hours. After demolding, it was placed in an environment with a temperature of 20°C and a relative humidity of 95% and cured for 7 days.

[0066] (1.4) After curing, the porous cement matrix was placed in a vacuum oven and dried at 70°C for 3 days, and then dried again with anhydrous silica gel for 24 hours to form a layered cement skeleton with unidirectional pores.

[0067] A chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material specifically includes:

[0068] (2.1) Add 250 ml of deionized water, 15 g of chitosan (CS), and 150 ml of acrylic acid (AA) to a 1000 ml beaker and stir with a magnetic stirrer for 30 min to form a CS / AA mixed solution.

[0069] (2.2) Add 25 ml, 0.25 mol.L -1 The ferric chloride solution was stirred for 8 minutes and then 25 ml of 0.2 mol.L was added. -1 The potassium persulfate (KPS) solution was stirred for 8 min and then stirred again to obtain a CS / AA / KPS mixed solution;

[0070] (2.3) The mixture was heated in a microwave oven for 30 seconds, then stopped for 30 seconds. After each two microwave heating steps, the mixture was placed in a refrigerator and cooled for 4 minutes. This operation was repeated 8 times to allow polymerization to occur until a small amount of gel film appeared on the surface. Chitosan-polyacrylic acid-Fe 3+ Hydrogel solution.

[0071] In step 3, the chitosan-polyacrylic acid-Fe 3+ The hydrogel solution was continuously pressed into the layered cement skeleton with unidirectional pores until no obvious bubbles appeared in the cement skeleton, at which point the vacuum count value was 0.09.

[0072] Step 4 is specifically: chitosan-polyacrylic acid-Fe 3+ After the hydrogel solution stabilized, the filled cement specimen was placed in a -30°C environment for 12 hours, then thawed at room temperature for 4 hours, and then subjected to a "heating-cooling" cycle 8 times to complete the first freeze-thaw cycle. The above operation was repeated for 3 freeze-thaw cycles to obtain the inner pore filled chitosan-polyacrylic acid-Fe 3+ Highly tough self-healing shell-like structure cement-based composites with hydrogel.

[0073] Example 3:

[0074] Chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material comprises the following steps:

[0075] Step 1: Use the directional ice template method to construct a layered cement skeleton with unidirectional porosity;

[0076] Step 2: Using chitosan-polyacrylic acid-Fe 3+ Hydrogel as filler and chitosan-polyacrylic acid-Fe 3+ hydrogel solution;

[0077] Step 3: Use vacuum negative pressure impregnation to 3+ The hydrogel is filled into the unidirectional pores;

[0078] Step 4: The high toughness self-repairing cement-chitosan-polyacrylic acid-Fe is obtained by multiple cycles of "freeze-thaw". 3+Hydrogel imitation shell.

[0079] A chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material specifically includes:

[0080] (1.1) Mix ordinary Portland cement P.I 52.5, fly ash, and deionized water in a blender at a ratio of 1:0.29:0.7. Add 90°C hot water to the blender in two batches, stirring for 40 minutes each time. Oscillate the mixture on an oscillating table to remove any air bubbles.

[0081] (1.2) Preparation of porous cement skeleton by ice template method: Pour the cement mortar prepared in step (1.1) into a mold that has been frozen in a -80°C refrigerator in advance. Then, place the mold in a constant -70°C ethanol solution for 2 hours, and then place it in a -80°C refrigerator for 30 minutes. Wait for the water in the cement mortar to completely crystallize from bottom to top, forming a frozen cement mortar with a layered structure.

[0082] (1.3) Refrigerate the frozen cement mortar at 4°C for 50 hours, allow it to slowly thaw, and then move it to room temperature for 24 hours. After demolding, place it in an environment with a temperature of 20°C and a relative humidity of 95% and cure it for 7 days.

[0083] (1.4) After curing, the porous cement matrix was placed in a vacuum oven and dried at 67°C for 2 days, and then dried again with anhydrous silica gel for 24 hours to form a layered cement skeleton with unidirectional pores.

[0084] A chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material specifically includes:

[0085] (2.1) Add 250 ml of deionized water, 15 g of chitosan (CS), and 150 ml of acrylic acid (AA) to a 1000 ml beaker and stir with a magnetic stirrer for 25 min to form a CS / AA mixed solution.

[0086] (2.2) Add 25 ml, 0.25 mol.L -1 The ferric chloride solution was stirred for 6 minutes and then 25 ml of 0.2 mol.L -1 The potassium persulfate (KPS) solution was stirred for 6 min and then stirred again to obtain a CS / AA / KPS mixed solution;

[0087] (2.3) The mixture was heated in a microwave oven for 30 seconds, then stopped for 30 seconds. After each two microwave heating steps, the mixture was placed in a refrigerator to cool for 3 minutes. This operation was repeated 9 times to allow polymerization to occur until a small amount of gel film appeared on the surface. Chitosan-polyacrylic acid-Fe3+ Hydrogel solution.

[0088] In step 3, the chitosan-polyacrylic acid-Fe 3+ The hydrogel solution is continuously pressed into the layered cement skeleton with unidirectional pores until no obvious bubbles appear in the cement skeleton, at which point the vacuum count value is 0.08.

[0089] Step 4 is specifically: chitosan-polyacrylic acid-Fe 3+ After the hydrogel solution stabilized, the filled cement specimen was placed in a -30°C environment for 10 hours, then thawed at room temperature for 3 hours, and then subjected to a "heating-cooling" cycle 9 times to complete the first freeze-thaw cycle. Repeat the above operation, and after 3 freeze-thaw cycles, the inner pore filled chitosan-polyacrylic acid-Fe 3+ Highly tough self-healing shell-like structure cement-based composites with hydrogel.

[0090] The present invention adopts chitosan-polyacrylic acid-Fe 3+ The hydrogel forms Ca-O coordination bonds and a large hydrogen bond network between the hydrogel and the cement, achieving strong adsorption of the hydrogel and cement-based materials; while improving high toughness, it also performs self-repair. When subjected to force, the hydrogel can bear tensile strain and prevent the composite material from breaking to achieve high toughness; in addition, when the internal humidity decreases, the hydrogel will release excess water and react with the unhydrated cement material to repair the microcracks in the cement material; to achieve this composite material, a porous cement base is prepared by the ice template method, which provides space for adding hydrogel soft fillers, and then prepares a soft and hard combined shell-like layered structure, which greatly improves the strength of the material; at the same time, based on the prepared chitosan-polyacrylic acid-Fe 3+ The two-layer cross-linked network of hydrogel greatly improves the toughness of the material, providing a new idea for the construction industry to prepare building materials with self-healing function, high toughness and high mechanical properties.

Claims

1. Chitosan-polyacrylic acid-Fe 3+ The preparation method of the hydrogel cement-based composite material is characterized in that: The steps include: Step (1): constructing a layered cement skeleton with unidirectional pores using a directional ice template method; Step (2): Preparation of chitosan-polyacrylic acid-Fe 3+ hydrogel solution; Step (3): Chitosan-polyacrylic acid-Fe 3+ The hydrogel is filled into the unidirectional pores of the layered cement skeleton; Step (4): The cement skeleton filled with hydrogel is subjected to multiple cycles of "freeze-thaw" to obtain a high toughness self-repairing cement-chitosan-polyacrylic acid-Fe 3+ hydrogel shell-like composites; Step (2) specifically includes the following steps: Step (21): 250 ml of deionized water, 15 g of chitosan CS, and 150 ml of acrylic acid AA were added to a 1000 ml beaker and stirred with a magnetic stirrer for 20-30 min to form a CS-AA mixed solution; Step (22): Add another 25 ml, 0.25 mol.L -1 The ferric chloride solution was stirred continuously and finally 25 ml of 0.2 mol.L -1 The potassium persulfate KPS solution was stirred again to obtain a CS-AA-KPS mixed solution; Step (23): The reaction system is subjected to a "heating-cooling" cycle 8-9 times to cause a polymerization reaction, thereby obtaining chitosan-polyacrylic acid-Fe 3+ hydrogel solution; The chitosan in step (21) was of analytical grade with a deacetylation degree of 96%, acrylic acid was of analytical grade, and potassium persulfate was of analytical grade; In step (22), the ferric chloride solution should be added first and stirred for 5-8 minutes, and then the potassium persulfate solution should be added and stirred for 5-8 minutes.

2. The method according to claim 1, characterized in that Step (1) The specific steps are as follows: Step (11): Prepare cement mortar: mix cement, fly ash and deionized water in a ratio of 1:0.29:0.7 in a blender, stir evenly, and place on an oscillating table for oscillation to remove air bubbles; Step (12): Prepare a cement skeleton using an ice template method: Use a mold made of polytetrafluoroethylene material on all sides and a brass bottom, pour the cement mortar prepared in step (11) into the mold, place the lower part of the mold in a constant -70-80°C liquid cold source for 2-2.5 hours, and wait for the water in the cement mortar to completely crystallize from bottom to top to form a frozen cement mortar with a layered structure; Step (13): refrigerate the frozen cement mortar at 2-5°C for 48-54 hours, move it to a room temperature environment after thawing for 24-32 hours, and after demoulding, place it in an environment with a temperature of 20°C ± 2°C and a relative humidity of 95% RH for curing for 5-7 days; Step (14): After the curing is completed, the porous cement matrix is ​​placed in a vacuum oven and dried at 65-70°C for 2-3 days, and then dried again with anhydrous silica gel for 18-24 hours to form a layered cement skeleton with unidirectional pores.

3. The method according to claim 2, characterized in that The cement in step (11) is ordinary Portland cement P.I 52.5, and the deionized water is 80-100°C hot water, which is added to the mixer in two batches and stirred for 30-60 minutes each time.

4. The method according to claim 3, characterized in that The mold used in step (12) is a triple mold, which has three identical inner grooves, each of which is in the shape of a cube; The liquid cooling source in step (12) is analytical grade anhydrous ethanol.

5. The method according to claim 4, characterized in that The "heating-cooling" step (23) specifically includes heating the hydrogel solution in a microwave oven for 20-30 seconds, stopping for 20-30 seconds, and cooling in a refrigerator for 2-4 minutes after each two microwave heatings. The operation is repeated 8-9 times until a small amount of gel film appears on the surface to obtain chitosan-polyacrylic acid-Fe 3+ Hydrogel solution.

6. The method according to claim 5, characterized in that Step (3) uses vacuum negative pressure to mix chitosan-polyacrylic acid-Fe 3+ The hydrogel solution is continuously pressed into the layered cement skeleton with unidirectional pores until no obvious bubbles appear in the cement skeleton, at which point the vacuum count value is 0.08-0.

09.

7. The method according to claim 6, characterized in that Step (4) is specifically: chitosan-polyacrylic acid-Fe 3+ After the hydrogel solution stabilizes, the filled cement specimen is placed in an environment of -30±2℃ for 8-12 hours, then thawed at room temperature for 2-4 hours, and then subjected to a "heating-cooling" cycle 8-9 times to complete the first freeze-thaw cycle; Repeat the above operation and after 2-3 freeze-thaw cycles, the inner pores are filled with chitosan-polyacrylic acid-Fe 3+ Highly tough self-healing shell-like structure cement-based composites with hydrogel.

8. A chitosan-polyacrylic acid-Fe 3+ The hydrogel cement-based composite material is characterized in that: The method according to any one of claims 1 to 7 is used for preparation.

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