High-durability recycled concrete and preparation method thereof

Abstract

The present application relates to the field of concrete technology, and specifically discloses a high-durability recycled concrete and a preparation method thereof. The high-durability recycled concrete is obtained by curing a concrete mixture into a mold, and the concrete mixture includes the following components by weight: 260-280 parts of silicate cement, 30-50 parts of fly ash, 1100-1200 parts of recycled coarse aggregate, 850-870 parts of modified recycled fine aggregate, 162-166 parts of water, and 2.9-3.3 parts of polycarboxylate water reducer, wherein the modified recycled fine aggregate is obtained by copolymerizing recycled fine aggregate grafted with vinyl on the surface with polyvinyl maleate. In the recycled concrete of the present application, the penetration of chloride ions is blocked, and the drying shrinkage of the recycled concrete is reduced, so the durability of the recycled concrete is improved.

Description

Technical Field

[0001] The present application relates to the technical field of concrete, and more specifically, to a high-durability recycled concrete and a preparation method thereof. Background Art

[0002] Recycled concrete usually refers to concrete produced using recycled aggregates. Recycled aggregates are usually the crushed products of abandoned concrete structures. Therefore, the production of recycled concrete is an important means of reusing construction waste.

[0003] There is a kind of recycled concrete in the related technology, which is obtained by curing a concrete mixture into a mold. The concrete mixture includes the following components in parts by weight: 260-280 parts of silicate cement, 30-50 parts of fly ash, 1100-1200 parts of recycled coarse aggregate, 850-870 parts of recycled fine aggregate, 162-166 parts of water, and 2.9-3.3 parts of polycarboxylate water reducer; the recycled fine aggregate and the recycled coarse aggregate are both crushed products of waste concrete.

[0004] With respect to the above-mentioned related technologies, the inventors believe that although recycled concrete is prepared in the related technologies, the mortar layers on the surface of the recycled coarse aggregate and the recycled fine aggregate contain a certain number of structural defects such as pores and cracks. When the recycled concrete is used together with steel bars in a humid environment rich in chloride ions, the structural defects on the surface of the recycled aggregate will reduce the difficulty of chloride ion penetration, and the water absorption of the recycled aggregate will also lead to increased drying shrinkage, which will affect the durability of the recycled concrete. Summary of the invention

[0005] In the related art, when recycled concrete is used together with steel bars in an environment where chloride ion penetration exists, the structural defects of the recycled aggregate will reduce the difficulty of chloride ion penetration, and the water absorption of the recycled aggregate will also lead to increased drying shrinkage, which will affect the durability of the recycled concrete. In order to improve this defect, the present application provides a high-durability recycled concrete and a preparation method thereof.

[0006] In the first aspect, the present application provides a highly durable recycled concrete, which adopts the following technical solution:

[0007] A high-durability recycled concrete, wherein the high-durability recycled concrete is obtained by subjecting a concrete mixture to mold curing, wherein the concrete mixture comprises the following components in parts by weight: 260-280 parts of silicate cement, 30-50 parts of fly ash, 1100-1200 parts of recycled coarse aggregate, 850-870 parts of modified recycled fine aggregate, 162-166 parts of water, and 2.9-3.3 parts of a polycarboxylate water reducer, wherein the modified recycled fine aggregate is obtained by copolymerizing recycled fine aggregate with vinyl grafted on its surface with vinyl and polyvinyl maleate.

[0008] By adopting the above technical scheme, the present application modifies the recycled fine aggregate, grafts vinyl on the surface of the recycled fine aggregate, and grafts maleic acid polyvinyl alcohol ester to the surface of the recycled fine aggregate through copolymerization. The surface state of the recycled fine aggregate is changed by the copolymer, and the surface defects of the recycled fine aggregate are reduced. In the concrete mixture, a part of the ester group introduced by maleic acid polyvinyl alcohol ester is hydrolyzed under the action of alkali to produce carboxylate ions and polyvinyl alcohol. Polyvinyl alcohol can fill the surface of the recycled coarse aggregate and reduce the defects on the surface of the recycled coarse aggregate. Since the defects distributed on the surface of the recycled coarse aggregate and the modified recycled fine aggregate are reduced, it helps to hinder the penetration of chloride ions. After the ester group is hydrolyzed, the carboxylate ions remaining on the surface of the modified recycled fine aggregate have an electrostatic repulsion effect on the polycarboxylate water reducer, which reduces the adsorption of the recycled fine aggregate on the polycarboxylate water reducer, thereby increasing the free water content in the concrete mixture and reducing the drying shrinkage of the recycled concrete. Therefore, in the final concrete, on the one hand, the penetration of chloride ions is blocked, and on the other hand, the drying shrinkage of the recycled concrete is reduced, thereby improving the durability of the recycled concrete.

[0009] Preferably, the concrete mixture comprises the following components in parts by weight: 265-275 parts of Portland cement, 35-45 parts of fly ash, 1125-1175 parts of recycled coarse aggregate, 855-865 parts of modified recycled fine aggregate, and 3.0-3.2 parts of polycarboxylate water reducer.

[0010] By adopting the above technical solution, the proportion of concrete mixture is optimized, which helps to improve the durability of recycled concrete.

[0011] Preferably, the recycled coarse aggregate and modified recycled fine aggregate are prepared according to the following method:

[0012] (1) crushing the waste concrete and soaking it in a washing liquid for 24 hours, washing it with water, drying it and sieving it after soaking to obtain recycled coarse aggregate and recycled fine aggregate; mixing water, ethanol and vinyl triethoxysilane to obtain a first modified liquid with a silane mass fraction of 10%; mixing polyvinyl maleate, water and an azo initiator in a weight ratio of 4:10:0.1 to obtain a second modified liquid;

[0013] (2) adding the recycled fine aggregate into the first modified liquid and soaking for 18-24 hours, then filtering and recovering the solid in the first modified liquid, and obtaining the silanized recycled fine aggregate after drying;

[0014] (3) The silanized recycled aggregate and the second modified liquid are mixed, and the mixture is heated at 65-75° C. for 2-3 hours, and then the solid in the second modified liquid is recovered by filtration, and the modified recycled fine aggregate is obtained after drying.

[0015] By adopting the above technical scheme, the present application first prepares recycled coarse aggregate and recycled fine aggregate, then introduces vinyl to the surface of the recycled fine aggregate through the coupling effect of vinyltriethoxysilane, then copolymerizes the newly introduced vinyl with polyvinyl maleate under the action of an azo initiator, and then obtains the modified recycled fine aggregate through filtration and drying.

[0016] Preferably, the polyvinyl maleate is prepared according to the following method:

[0017] (1) polyvinyl alcohol and DMSO are mixed, and then stirred and dissolved at 80° C. to obtain liquid A; maleic anhydride is mixed with DMSO to obtain liquid B;

[0018] (2) Add solution B dropwise to solution A at 60° C., continue to keep warm for 2 hours after the addition is completed, then purify and wash with acetone, and dry the obtained solid to obtain maleic anhydride polyvinyl alcohol ester.

[0019] By adopting the above technical solution, the present application uses DMSO as a solvent and obtains maleic anhydride polyvinyl alcohol ester through an esterification reaction between maleic anhydride and polyvinyl alcohol.

[0020] Preferably, the mass fraction of chloride ions in the waste concrete is 0.4-0.5%. In the step (1) of preparing the modified recycled aggregate, the components of the washing liquid include sodium sulfate and water. In the washing liquid, the mass fraction of sodium sulfate is 5%.

[0021] By adopting the above technical scheme, when the waste concrete is a concrete building from a coastal area, the waste concrete usually contains more chloride ions. For waste concrete with a mass fraction of chloride ions of 0.4-0.5%, if it is directly crushed and used as aggregate in concrete production, the initial content of chloride ions in the concrete will be significantly increased, which is not conducive to improving the effect of concrete resisting chloride ion penetration. Therefore, the present application preferably selects the components of the washing liquid, and sodium sulfate is added to the washing liquid. There is a competitive adsorption relationship between sulfate ions and chloride ions, so immersion in the washing liquid can reduce the chloride ion content in the waste concrete, which helps to improve the effect of recycled concrete resisting chloride ion penetration.

[0022] Preferably, in the step (1) of preparing the modified recycled aggregate, when the crushed product of the waste concrete is soaked, the pH of the washing liquid is adjusted to 6.5.

[0023] By adopting the above technical scheme, the present application adjusts the pH of the washing liquid to make the washing liquid weakly acidic, thereby consuming some soluble alkali on the surface of the waste concrete crushing product, thereby reducing the possibility of premature hydrolysis of maleic anhydride polyvinyl alcohol ester on the surface of recycled fine aggregate, which is beneficial to reducing the premature release of polyvinyl alcohol in the process of preparing modified recycled fine aggregate, and enhancing the filling effect of polyvinyl alcohol on the surface defects of recycled coarse aggregate.

[0024] Preferably, in the step (1) of preparing the modified recycled aggregate, aminopolysaccharide is added to the washing liquid when the crushed product of the waste concrete is soaked.

[0025] By adopting the above technical solution, the amino groups in amino polysaccharides are protonated in an acidic environment, and have a certain adsorption effect on chloride ions. The adsorption of chloride ions by amino polysaccharides reduces the chloride ion concentration in the washing liquid, increases the driving force for the diffusion of chloride ions into the washing liquid, promotes the dissolution of chloride ions, helps to reduce the chloride ion content in the waste concrete crushing products, and improves the performance of recycled concrete in resisting chloride ion penetration.

[0026] Preferably, the amino polysaccharide is chitosan, and the amount of the amino polysaccharide used is 3% of the weight of the waste concrete crushed product in the washing liquid.

[0027] By adopting the above technical scheme, chitosan is selected as the amino polysaccharide, and the dosage of chitosan is selected, which helps to reduce the chloride ion content in the waste concrete crushing product and improves the performance of the recycled concrete in resisting chloride ion penetration.

[0028] Preferably, the deacetylation degree of the chitosan is 85-95%.

[0029] By adopting the above technical solution, the deacetylation degree of chitosan is optimized, which helps to fully reduce the chloride ion content in the waste concrete crushing product and helps to improve the performance of recycled concrete in resisting chloride ion penetration.

[0030] In a second aspect, the present application provides a method for preparing highly durable recycled concrete, using the following technical solution.

[0031] A method for preparing highly durable recycled concrete comprises the following steps:

[0032] (1) mixing a polycarboxylate water reducer and water to obtain a water reducer solution; mixing silicate cement, fly ash, recycled coarse aggregate and modified recycled fine aggregate to obtain a dry material;

[0033] (2) The dry material and the water reducing agent solution are mixed and stirred to obtain a concrete mixture, and the concrete mixture is molded and cured to obtain a highly durable recycled concrete.

[0034] By adopting the above technical scheme, the method of the present application prepares a water reducing agent solution and a dry material respectively, and then uses the water reducing agent solution and the dry material to mix a concrete mixture, and obtains a highly durable recycled concrete after curing.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. The present application modifies the recycled fine aggregate and reduces the surface defects of the recycled fine aggregate. Moreover, in the concrete mixture, the ester group introduced by polyvinyl maleate is hydrolyzed under the action of alkali, and the generated polyvinyl alcohol fills the defects on the surface of the recycled coarse aggregate, hindering the penetration of chloride ions. The carboxylate ions reduce the adsorption of the recycled fine aggregate to the polycarboxylate water reducer, increase the free water content in the concrete mixture, and reduce the drying shrinkage of the recycled concrete. Since the penetration of chloride ions is blocked and the drying shrinkage of the recycled concrete is reduced, the durability of the recycled concrete is improved.

[0037] 2. In the step (1) of preparing the modified recycled aggregate, the crushed products of the waste concrete are soaked in a washing liquid containing sodium sulfate, and the competitive adsorption between sulfate ions and chloride ions is utilized to reduce the chloride ion content in the crushed products of the waste concrete, thereby improving the quality of the recycled aggregate and enhancing the ability of the recycled concrete to resist chloride ion penetration. DETAILED DESCRIPTION

[0038] The present application is further described in detail below in conjunction with embodiments, preparation examples and comparative examples. The raw materials involved in the present application can all be obtained commercially.

[0039] Preparation example of modified recycled fine aggregate and recycled coarse aggregate

[0040] The following is an explanation using Preparation Example 1.

[0041] Preparation Example 1

[0042] The waste concrete used in this preparation example has a chloride ion content of 0.47% and is taken from a concrete building with an original design strength grade of C40.

[0043] The polyvinyl maleate used in this preparation example was prepared according to the following method:

[0044] (1) polyvinyl alcohol 1750 and DMSO were mixed, and then stirred and dissolved at 80° C. to obtain a liquid A with a polyvinyl alcohol mass fraction of 5%; maleic anhydride was mixed with DMSO to obtain a liquid B with a maleic anhydride mass fraction of 2%;

[0045] (2) adding solution B to solution A at a weight ratio of 1:1 at 60° C., and continuing to keep warm for 2 hours after all solution B is added. Then, the solution is purified and washed with acetone, and the obtained solid is dried to obtain maleic anhydride polyvinyl alcohol ester.

[0046] In this preparation example, modified recycled fine aggregate and recycled coarse aggregate were prepared according to the following method:

[0047] (1) crushing the waste concrete and soaking it in a washing liquid for 24 hours, washing it with water, drying it and sieving it after soaking to obtain recycled coarse aggregate and recycled fine aggregate; mixing water, ethanol and vinyl triethoxysilane to obtain a first modified liquid with a silane mass fraction of 10%; mixing polyvinyl maleate, water and azobisisobutylamidine hydrochloride in a weight ratio of 4:10:0.1 to obtain a second modified liquid; in this step, the washing liquid is domestic water with a chloride ion content that meets the quality standard for concrete water;

[0048] (2) adding the recycled fine aggregate into the first modified liquid and soaking for 20 hours, then filtering and recovering the solid in the first modified liquid, and obtaining the silanized recycled fine aggregate after drying;

[0049] (3) The silanized recycled aggregate and the second modified liquid are mixed, and the mixture is heated at 70° C. for 2.5 hours. The solid in the second modified liquid is then filtered and recovered, and the modified recycled fine aggregate is obtained after drying.

[0050] Preparation Example 2

[0051] The difference between this preparation example and preparation example 1 is that the washing liquid is prepared from domestic water whose chloride ion content meets the quality standard for concrete water and sodium sulfate, and the mass fraction of sodium sulfate is 5%.

[0052] Preparation Example 3

[0053] The difference between this preparation example and preparation example 2 is that in step (1) of preparing the modified recycled aggregate, when the crushed product of the waste concrete is soaked, the pH of the washing liquid is adjusted to 6.5.

[0054] Preparation Example 4

[0055] The difference between this preparation example and preparation example 3 is that in step (1) of preparing the modified recycled aggregate, when soaking the crushed products of the waste concrete, amino polysaccharide is added to the washing liquid, the amino polysaccharide is chitosan oligosaccharide with a deacetylation degree of 80%, and the amount of chitosan oligosaccharide is 3% of the weight of the crushed products of the waste concrete in the washing liquid.

[0056] Preparation Example 5

[0057] The difference between this preparation example and preparation example 4 is that the amino polysaccharide is chitosan, the amount of chitosan used is 3% of the weight of the waste concrete crushed product in the washing liquid, and the deacetylation degree of chitosan is 80%.

[0058] As shown in Table 1, the difference between Preparation Examples 5-9 is that the deacetylation degree of chitosan is different.

[0059] Table 1 Deacetylation degree of chitosan

[0060] sample Preparation Example 5 Preparation Example 6 Preparation Example 7 Preparation Example 8 Preparation Example 9 Deacetylation degree / % 80 85 90 95 98

[0061] Example

[0062] Examples 1-5

[0063] The following description is given by taking Example 1 as an example.

[0064] Example 1

[0065] In this embodiment, high-durability recycled concrete is prepared according to the following steps:

[0066] (1) 2.9 kg of polycarboxylate water reducer and 162 kg of water were mixed to obtain a water reducer solution; 260 kg of silicate cement of model P.O42.5, 30 kg of Class F Grade I fly ash, 1100 kg of recycled coarse aggregate of Preparation Example 1 and 850 kg of modified recycled fine aggregate of Preparation Example 1 were mixed to obtain a dry material;

[0067] (2) The dry material and the water reducing agent solution are mixed and stirred to obtain a concrete mixture, and the concrete mixture is molded and cured to obtain a highly durable recycled concrete.

[0068] As shown in Table 2, the differences between Examples 1-5 are mainly in the different raw material ratios.

[0069] Table 2

[0070] Embodiment 6-14

[0071] As shown in Table 3, the difference between Examples 6-13 and Example 3 is that the preparation examples of the recycled coarse aggregate and the modified recycled fine aggregate are different.

[0072] Table 3 Preparation examples of recycled coarse aggregate and modified recycled fine aggregate

[0073] sample Preparation Example sample Preparation Example Example 3 1 Example 10 6 Example 6 2 Embodiment 11 7 Example 7 3 Example 12 8 Example 8 4 Embodiment 13 9 Example 9 5 / /

[0074] Comparative Example

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 3 is that, according to the method of Preparation Example 1, the recycled fine aggregate obtained in step (1) of preparing recycled coarse aggregate and modified recycled fine aggregate is directly used as the fine aggregate in the concrete mixture.

[0077] Comparative Example 2

[0078] The difference between this comparative example and comparative example 1 is that the amount of the polycarboxylate water-reducing agent is increased to three times that of comparative example 1 (by weight).

[0079] Performance testing methods

[0080] The length reduction of the test specimens made of concrete in each embodiment and comparative example at the age of 90 days was calculated with reference to GB / T 29417-2012 Test method for drying shrinkage and cracking performance of cement mortar and concrete. The ratio between the length reduction measured in embodiments 1-5 and comparative examples 1-2 and the length reduction measured in comparative example 1 was calculated and recorded as the relative drying shrinkage rate. The results are shown in Table 4.

[0081] With reference to GB / T 50082-2009 Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete, the electric flux of the test pieces of each embodiment and comparative example was tested, and the ratio of the electric flux of each embodiment and comparative example to the electric flux of comparative example 1 was calculated, which was recorded as the relative electric flux. The results are shown in Table 5.

[0082] Table 4

[0083] sample Relative shrinkage / % Example 1 80.4 Example 2 80.6 Example 3 81.3 Example 4 82.1 Example 5 83.4 Comparative Example 1 100.0 Comparative Example 2 79.4

[0084] Table 5

[0085] sample Relative electric flux / % sample Relative electric flux / % Example 1 54.8 Example 9 39.2 Example 2 54.9 Example 10 38.5 Example 3 55.4 Embodiment 11 36.1 Example 4 55.8 Example 12 35.5 Example 5 56.2 Embodiment 13 35.4 Example 6 47.9 Comparative Example 1 100.0

[0086]

[0087] Combining Examples 1-5 and Comparative Example 1 and Tables 4-5, it can be seen that the relative shrinkage measured in Examples 1-5 is less than that in Comparative Example 1, indicating that the present application grafts maleic acid polyvinyl alcohol ester to the surface of recycled fine aggregate through copolymerization, reducing the surface defects of recycled fine aggregate, and the polyvinyl alcohol produced by the hydrolysis of maleic acid polyvinyl alcohol ester can fill the defects on the surface of recycled coarse aggregate, hindering the penetration of chloride ions and reducing the electrical flux of the concrete specimen. At the same time, the carboxylate ions produced by the hydrolysis of the ester group reduce the adsorption of the recycled fine aggregate to the polycarboxylate water-reducing agent, thereby increasing the free water content in the concrete mixture, reducing the drying shrinkage of the recycled concrete, and improving the durability of the recycled concrete.

[0088] In Examples 1-5, the water-cement ratio decreases successively, and the proportion of modified recycled fine aggregate also decreases gradually, so that the relative shrinkage rate gradually increases, and the relative electric flux also gradually increases. The data of Example 1 is close to that of Example 2, but the proportion of modified recycled fine aggregate in Example 1 is relatively large. After optimization. When recycled wontons are prepared according to the formula of Examples 2-4, modified recycled fine aggregate can be saved compared to Example 1, and the recycled concrete has relatively better durability than Example 5.

[0089] Combining Example 3 and Comparative Example 2 with Table 4, it can be seen that increasing the amount of water reducer can reduce drying shrinkage, but in the actual production process, the inventory capacity of water reducer is limited (often only 1% of the cement inventory capacity, taking a unit with a cement capacity of 500 tons as an example, the corresponding water reducer capacity is only 5 tons). Doubling the amount of water reducer means greatly increasing the frequency of water reducer replenishment, and during the replenishment period, concrete production needs to be temporarily stopped, delaying construction, so it is not suitable to adopt this method. However, the present application reduces the drying shrinkage of recycled concrete without adding the amount of water reducer by modifying the recycled fine aggregate, thereby improving the durability of recycled concrete.

[0090] Combining Example 3 and Example 6 with Table 5, it can be seen that in Preparation Example 2, after being soaked in the washing liquid, the ability of the waste concrete crushing product to bind chloride ions decreases, thereby reducing the initial content of chloride ions in the aggregate, which helps to improve the performance of the recycled concrete in resisting chloride ion penetration. Since sulfate ions replace a portion of chloride ions, and the sulfate ions that replace chloride ions during the soaking in the washing liquid exist in the concrete mainly in the form of insoluble matter (such as calcium sulfoaluminate), which is difficult to migrate, the relative electric flux of Example 6 is low.

[0091] Combining Example 7 with Example 6 and Table 5, it can be seen that by adjusting the pH of the washing liquid to 6.5, some soluble alkali on the surface of the waste concrete crushed product is consumed, reducing the possibility of premature hydrolysis of maleic anhydride polyvinyl alcohol ester on the surface of the waste concrete crushed product, which is conducive to preserving the polyvinyl alcohol chain segments in the maleic anhydride polyvinyl alcohol ester. Therefore, the modified recycled fine aggregate used in Example 7 can release more polyvinyl alcohol in the concrete mixture, improve the filling effect of polyvinyl alcohol on the surface defects of the recycled coarse aggregate, and hinder the penetration of chloride ions.

[0092] Combining Examples 8-9, Example 7 and Table 5, it can be seen that the amino groups of amino polysaccharides are protonated in a weakly acidic environment of pH 6.5, which has an adsorption effect on chloride ions, thereby increasing the difference in chloride ion concentration between the washing liquid and the waste concrete crushing product. The increase in the chloride ion concentration difference increases the driving force for the chloride ion to diffuse into the washing liquid, further reducing the chloride ion content in the waste concrete crushing product, and improving the performance of the recycled concrete in resisting chloride ion penetration.

[0093] Combining Examples 9-13 and Table 5, it can be seen that the relative electric flux measured in Example 9 is greater than that in Examples 10-12, while the relative electric flux measured in Example 13 is close to that in Example 12. Therefore, the selection of chitosan with a deacetylation degree of 85-95% can sufficiently reduce the chloride ion content in the waste concrete crushing product, which helps to improve the performance of recycled concrete in resisting chloride ion penetration.

[0094] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A highly durable recycled concrete, characterized in that: The high-durability recycled concrete is obtained by curing a concrete mixture into a mold, wherein the concrete mixture comprises the following components in parts by weight: 260-280 parts of silicate cement, 30-50 parts of fly ash, 1100-1200 parts of recycled coarse aggregate, 850-870 parts of modified recycled fine aggregate, 162-166 parts of water, and 2.9-3.3 parts of polycarboxylate water reducer; The recycled coarse aggregate and modified recycled fine aggregate are prepared according to the following method: (1) crushing the waste concrete and soaking it in a washing liquid for 24 hours, washing it with water, drying it and sieving it after soaking to obtain recycled coarse aggregate and recycled fine aggregate; mixing water, ethanol and vinyl triethoxysilane to obtain a first modified liquid with a silane mass fraction of 10%; mixing polyvinyl maleate, water and an azo initiator in a weight ratio of 4:10:0.1 to obtain a second modified liquid; (2) adding the recycled fine aggregate into the first modified liquid and soaking it for 18-24 hours, then filtering and recovering the solid in the first modified liquid, and obtaining the silanized recycled fine aggregate after drying; (3) mixing the silanized recycled fine aggregate and the second modified liquid, heating the mixture at 65-75° C. for 2-3 hours, then filtering and recovering the solid in the second modified liquid, and drying to obtain modified recycled fine aggregate; The polyvinyl maleate is prepared according to the following method: (1) Mix polyvinyl alcohol and DMSO, and then stir and dissolve at 80°C to obtain liquid A; mix maleic anhydride and DMSO to obtain liquid B; (2) Add solution B dropwise to solution A at 60°C. After the addition is completed, continue to keep the temperature to react for 2 hours. Then, purify and wash with acetone. After drying the obtained solid, obtain maleic anhydride polyvinyl alcohol ester.

2. The highly durable recycled concrete according to claim 1, characterized in that: The concrete mixture comprises the following components in parts by weight: 265-275 parts of silicate cement, 35-45 parts of fly ash, 1125-1175 parts of recycled coarse aggregate, 855-865 parts of modified recycled fine aggregate, and 3.0-3.2 parts of polycarboxylate water reducer.

3. The highly durable recycled concrete according to claim 1, characterized in that: The mass fraction of chloride ions in the waste concrete is 0.4-0.5%. In the step (1) of preparing the recycled coarse aggregate and the modified recycled fine aggregate, the components of the washing liquid include sodium sulfate and water. In the washing liquid, the mass fraction of sodium sulfate is 5%.

4. The highly durable recycled concrete according to claim 3, characterized in that: In the step (1) of preparing the recycled coarse aggregate and modified recycled fine aggregate, when the crushed product of the waste concrete is soaked, the pH of the washing liquid is adjusted to 6.

5.

5. The highly durable recycled concrete according to claim 4, characterized in that: In the step (1) of preparing the recycled coarse aggregate and modified recycled fine aggregate, when soaking the crushed product of the waste concrete, amino polysaccharide is added to the washing liquid; the amino polysaccharide is chitosan, and the amount of the amino polysaccharide is 3% of the weight of the crushed product of the waste concrete in the washing liquid.

6. The highly durable recycled concrete according to claim 5, characterized in that: The deacetylation degree of the chitosan is 85-95%.

7. The method for preparing highly durable recycled concrete according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Mixing a polycarboxylate water reducer and water to obtain a water reducer solution; mixing silicate cement, fly ash, recycled coarse aggregate and modified recycled fine aggregate to obtain a dry material; (2) The dry material and the water reducing agent solution are mixed and stirred to obtain a concrete mixture, and the concrete mixture is molded and cured to obtain a highly durable recycled concrete.

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