A kind of high strength recycled concrete and preparation method thereof

Abstract

The invention discloses a high-strength recycled concrete and a preparation method thereof, and relates to the technical field of recycled concrete. The preparation method comprises the following steps: the steps include: adding amphoteric monomers, polyether monomers, acrylic acid, and n-propanol to a reaction vessel, ultrasonically dispersing, adding chalcone-based RAFT reagents, vinyl nano-silica, and azobisisobutyronitrile under a nitrogen atmosphere, heating to 60-65°C for reaction for 12-48h, cooling to room temperature, and obtaining a nano-silica-doped water reducer; soaking recycled coarse and fine aggregates in the nano-silica-doped water reducer for 1-2d, taking them out, placing them in an oven for drying, curing, and carbonizing to obtain recycled aggregates; adding recycled aggregates, cement, fly ash, mineral powder, sand and gravel, water, and nano-silica-doped water reducers to a mixer, stirring evenly, pouring, and curing to obtain high-strength recycled concrete.

Description

Technical Field

[0001] The invention relates to the technical field of recycled concrete, in particular to high-strength recycled concrete and a preparation method thereof. Background Art

[0002] In the modern construction industry, concrete is a widely used building material. It has become the main material for civil engineering and construction due to its high strength, durability and convenient molding. However, with the continuous advancement of urbanization and the demolition of a large number of old buildings, a large amount of construction waste has been generated. Among them, recycled concrete aggregate (RCA) as one of the main components of construction waste has been widely studied and applied.

[0003] Traditional recycled concrete faces several significant problems during its application. First, since the quality of recycled aggregates is inferior to that of virgin aggregates, there are problems such as high water absorption, high porosity, and low strength, which makes it difficult for the strength and durability of recycled concrete to meet the high requirements of engineering applications. Secondly, the interface transition zone (ITZ) of recycled concrete is relatively weak, which easily leads to the generation and development of cracks, thereby affecting the overall performance of the structure. Therefore, how to improve the strength and durability of recycled concrete and achieve efficient recycling of construction waste has become an urgent problem to be solved.

[0004] In recent years, various modification methods, such as adding admixtures, nanomaterials, polymer modifiers, etc., have been used to improve the performance of recycled concrete. Among them, the preparation technology of high-strength recycled concrete has gradually become a research hotspot. By adding a certain proportion of high-performance admixtures to concrete or adopting a specific mix design, the compressive strength, tensile strength and durability of recycled concrete can be greatly improved, and the interface bonding between recycled aggregate and cement paste can be significantly improved.

[0005] Therefore, inventing a high-strength recycled concrete and a preparation method thereof can not only achieve the effective reuse of construction waste and reduce resource pressure, but also meet the engineering needs of high-performance concrete, and has important economic value and social significance. Summary of the invention

[0006] The object of the present invention is to provide a high-strength recycled concrete and a preparation method thereof, so as to solve the problems raised in the prior art.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing high-strength recycled concrete comprises the following steps: S1: adding isophorone diisocyanate to polyethylene glycol, stirring evenly, adding dibutyltin dilaurate, heating to 70-75°C for heat preservation, adding terminal hydroxyl polysilane, acrylamide, and chalcone capping agent in sequence, and heat-retaining reaction until the isocyanate group reaches the theoretical value to obtain a polyurethane prepolymer;

[0009] Furthermore, in the preparation method of the polyurethane prepolymer, the proportions of the components are calculated by weight, including 10-20 parts of polyethylene glycol, 5.5-8 parts of isophorone diisocyanate, 0.2-0.3 parts of dibutyltin dilaurate, 9-13.5 parts of terminal hydroxyl polysilane, 5-7 parts of acrylamide, and 3-5 parts of chalcone capping agent;

[0010] Furthermore, the heat preservation reaction is carried out until the isocyanate groups reach the theoretical value, and the mass percentage of the favorable isocyanate groups in the reaction system is 14-16%;

[0011] S2: Add polyurethane prepolymer and hydroquinone to acetone, stir evenly, heat to 50-55°C, add 1,3-propane sultone acetone solution, keep warm for 20-22 hours, cool to room temperature, filter, wash the precipitate with a mixed solution of acetone and ether, and vacuum dry to obtain amphoteric monomer;

[0012] Furthermore, in the preparation of the amphoteric monomer, the molar ratio of polyurethane prepolymer:1,3-propane sultone is 1:1;

[0013] Furthermore, in the mixed solution of acetone and ether, the volume ratio of acetone to ether is 1:1;

[0014] S3: Add tetrabutylammonium bromide and dodecanethiol to acetone, stir evenly, add sodium hydroxide solution, carbon disulfide acetone solution, and 2-bromopropionic acid in sequence under nitrogen atmosphere and ice bath conditions, react at room temperature for 12-14 hours, filter, wash, and recrystallize using petroleum ether to obtain a RAFT reagent;

[0015] Furthermore, in the preparation process of the RAFT agent, the mass ratio of tetrabutylammonium bromide: dodecanethiol: 2-bromopropionic acid is (0.966-1.1592): (7.5-8.925): (3.4-4.08);

[0016] S4: Add the RAFT reagent to tetrahydrofuran, stir evenly, add dicyclohexylcarbodiimide, 4-dimethylaminopyridine, and hydroxydimethylaminochalcone in sequence, react at room temperature for 24 hours, filter, concentrate the filtrate, and recrystallize using a mixed solution of ethanol and dichloromethane to obtain a diaminochalcone-based RAFT reagent;

[0017] Further, in the diaminochalcone-based RAFT agent, the molar ratio of RAFT agent: dicyclohexylcarbodiimide: 4-dimethylaminopyridine: hydroxydimethylaminochalcone is 1:1:0.1:1;

[0018] Furthermore, in the mixed solution of ethanol and dichloromethane, the volume ratio of ethanol to dichloromethane is 4:1;

[0019] S5: Add diaminochalcone-based RAFT reagent and hydroquinone to acetone, stir evenly, heat to 50-55°C, add 1,3-propane sultone acetone solution, keep warm for 20-22 hours, cool to room temperature, filter, wash the precipitate with a mixed solution of acetone and ether, and vacuum dry to obtain a chalcone-based RAFT reagent;

[0020] Further, in the preparation of the chalcone-based RAFT agent, the molar ratio of diaminochalcone-based RAFT agent: 1,3-propane sultone is 1:1;

[0021] Furthermore, in the mixed solution of acetone and ether, the volume ratio of acetone to ether is 1:1.

[0022] S6: Add vinyl triethoxysilane to deionized water, add sodium dodecylbenzene sulfonate, react at 25-30°C for 2.5-3h, add ammonia water, keep warm and react for 6h to obtain vinyl nano-silica;

[0023] Furthermore, in the preparation process of the vinyl nano-silica, the volume ratio of vinyl triethoxysilane: ammonia water is 2:1;

[0024] Furthermore, the dripping rate of the ammonia water is 0.8-1.0 mL / min; the critical micelle concentration of the sodium dodecylbenzene sulfonate is 1.2 mmol / L;

[0025] S7: adding amphoteric monomers, polyether monomers, acrylic acid, and n-propanol into a reaction container, performing ultrasonic dispersion, adding chalcone-based RAFT reagents, vinyl nano-silica, and azobisisobutyronitrile under a nitrogen atmosphere, heating to 60-65° C. for reaction for 12-48 hours, and cooling to room temperature to obtain a nano-silica-doped water reducer;

[0026] Furthermore, in the preparation process of the nano-silica doped water reducer, the proportion of each component, by molar proportion, includes 0.5-1.5 parts of amphoteric monomer, 0.5-1.5 parts of polyether monomer, 6-12 parts of acrylic acid, 57.5-60 parts of n-propanol, 0.1-0.2 parts of chalcone-based RAFT agent, 0.1-0.5 parts of vinyl nano-silica, and 0.05-0.06 parts of azobisisobutyronitrile;

[0027] Furthermore, the polyether monomer includes any one of IPEG, EPEG, and HPEG.

[0028] S8: Soak the recycled coarse and fine aggregates in nano-silica-doped water-reducing agent for 1-2 days, take them out, put them in an oven for drying, curing, and carbonization to obtain recycled aggregates; add the recycled aggregates, cement, fly ash, mineral powder, sand and gravel, water, and nano-silica-doped water-reducing agent into a mixer, mix them evenly, pour, and cure to obtain high-strength recycled concrete.

[0029] Furthermore, during the preparation of the recycled aggregate, the curing step includes: curing in a curing room at a temperature of 20° C. and a humidity of 70% for 24 hours; the carbonization step includes: carbonizing in a carbonization tank at a pressure of 0.3 MPa for 24 hours;

[0030] Furthermore, in the preparation process of high-strength recycled concrete, the proportion of each component, by mass, includes 1076-1124 parts of recycled aggregate, 270-300 parts of cement, 100-110 parts of fly ash, 60-65 parts of mineral powder, 718-746 parts of sand and gravel, 160-165 parts of water, and 9.7-10.2 parts of nano-silica doped water reducer.

[0031] Furthermore, the recycled coarse and fine aggregates are prepared by continuous grading of the particle size distribution of 5-20 mm from discarded C40 and C50 concrete through two stages of cone crusher and impact crusher.

[0032] Furthermore, the preparation method of hydroxydimethylaminochalcone comprises the following steps: adding 4-hydroxyacetophenone to ethanol, stirring evenly, adding sodium hydroxide solution and 4-dimethylaminobenzaldehyde ethanol solution in turn under ice bath condition, reacting at room temperature for 24 hours, pouring the product into an aqueous solution of glacial acetic acid for precipitation, filtering, washing, recrystallizing with ethanol, and vacuum drying to obtain hydroxydimethylaminochalcone;

[0033] Furthermore, in the preparation process of hydroxydimethylaminochalcone, the molar ratio of 4-hydroxyacetophenone:4-dimethylaminobenzaldehyde is 1:1;

[0034] Furthermore, the preparation method of the chalcone end-capping agent comprises the following steps: adding hydroxydimethylaminochalcone, bromoethanol, potassium carbonate, and N,N-dimethylformamide to a reaction container in sequence, heating to 90-95° C. under a nitrogen atmosphere for reaction for 48 hours, cooling to room temperature, pouring the product into deionized water for precipitation, filtering, vacuum drying, and recrystallizing using a mixed solution of ethanol and dichloromethane to obtain a chalcone end-capping agent;

[0035] Furthermore, in the preparation process of the chalcone capping agent, the molar ratio of hydroxydimethylaminochalcone: bromoethanol: potassium carbonate is (0.3-0.45): (0.36-0.54): (0.45-0.60);

[0036] Furthermore, in the mixed solution of ethanol and dichloromethane, the volume ratio of ethanol:dichloromethane is 4:1.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention uses homemade hydroxydimethylaminochalcone as a raw material to prepare a chalcone capping agent, then uses isophorone diisocyanate, terminal hydroxyl polysilane, acrylamide and the chalcone capping agent as raw materials to prepare a polyurethane prepolymer having an acryl and diaminochalcone structure, and finally reacts with 1,3-propane sultone to prepare an amphoteric monomer. The present invention further uses homemade hydroxydimethylaminochalcone as a raw material, and successively reacts with a RAFT agent and 1,3-propane sultone to prepare a chalcone-based RAFT agent also having a zwitterionic structure. The invention uses amphoteric monomers, vinyl nano-silicon dioxide, chalcone-based RAFT agents and other substances as raw materials to prepare a nano-silicon dioxide-doped water reducer; the recycled coarse and fine aggregates are immersed in the water reducer, and the nano-silicon dioxide has the characteristics of strong permeability and micro-filling effect, so that the water reducer is loaded on the surface and micro-pores of the recycled coarse and fine aggregates in advance; on the one hand, the water reducer can penetrate into the pores of the recycled aggregates, micro-fill the micro-pores of the recycled aggregates, and compact the microstructure; on the other hand, it is helpful to further reduce water absorption in the subsequent concrete preparation process, thereby improving the workability of the concrete, improving the fluidity, making the concrete mixture easier to construct, further enhancing the compactness of the concrete, and possibly improving the compressive strength of the concrete.

[0039] 2. The present invention is centered on developing a new high-efficiency water reducer by combining amphoteric polycarboxylates (for hydration control) and RAFT polymerization (for molecular structure accuracy) to meet the high strength requirements of recycled concrete. The anionic groups in the amphoteric monomers interact with the positively charged calcium ions in the cement mixture, delaying the early hydration reaction. As the cement hydration proceeds, the cationic groups in the polycarboxylates can interact with the negatively charged surface of the hydrated cement particles to promote the later hydration reaction. The controlled hydration process balances the workability and setting time, and improves the quality and strength of the concrete without affecting the curing time.

[0040] RAFT polymerization allows the design of comb-like molecular structures in polycarboxylate superplasticizers, where a central backbone has many side chains. These side chains (polyethylene glycol and related compounds) provide steric hindrance, preventing cement particles from clumping. The result is a more stable dispersion of cement particles in the mix, resulting in a uniform cement paste with better workability and flowability. By controlling the molecular weight and structure of the polymer, RAFT polymerization ensures that the superplasticizer is optimally adsorbed onto the cement particles. This uniform adsorption enhances the dispersing power of the superplasticizer, ensuring uniform separation of cement particles for better hydration and ultimate strength. Higher dispersion efficiency, resulting in reduced dosage requirements, and more consistent performance across a variety of cement types. Enhanced control over the molecular structure results in superior adsorption and dispersion properties, making the concrete mix easier to handle and stronger after setting.

[0041] The dual-stage hydration mechanism is ensured by the amphoteric nature of the polycarboxylate, while the molecular weight precision provided by RAFT polymerization ensures that the high-range water reducer is effectively adsorbed onto the cement particles. This results in both lasting fluidity and faster strength development, thereby improving the strength and durability of the concrete and maintaining workability over time. RAFT polymerization can create complex polymer structures that can improve the interaction with cement hydration products. The polymer is adjusted to minimize the dosage while maximizing the performance, further enhancing the strength of the recycled concrete. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] In the following examples, EPEG has 66 polyethylene glycol repeating units, Mn=3000, purchased from Zibo Huawei Yinkai Building Materials Technology Co., Ltd.; polyethylene glycol Mn=1000; the brand of hydroxyl-terminated polysilane is COSiL ® , purchased from Jiangsu Kexing New Materials Co., Ltd.; cement is Tongchuan Shengwei P·O42.5 cement; fly ash is Class II fly ash from Weihe Power Plant; mineral powder is S95 grade mineral powder from Shaanxi Delong Powder Engineering Co., Ltd.; polycarboxylate water reducer is purchased from China Construction Western Construction North Co., Ltd.; the remaining raw materials are commercially available,

[0044] The preparation method of vinyl nano-silica comprises the following steps: adding 10 mL of vinyl triethoxysilane into 50 mL of deionized water, adding 1.2 mmol / L of sodium dodecylbenzene sulfonate, reacting at 30°C for 2.5 hours, controlling the ammonia water drop rate to be 0.8 mL / min, adding 5 mL of ammonia water, and keeping the temperature for reaction for 6 hours to obtain vinyl nano-silica.

[0045] The preparation method of hydroxydimethylaminochalcone comprises the following steps: adding 4-hydroxyacetophenone into ethanol, stirring evenly, adding sodium hydroxide solution and 4-dimethylaminobenzaldehyde ethanol solution in sequence under ice bath condition, reacting at room temperature for 24 hours, pouring the product into an aqueous solution of glacial acetic acid for precipitation, filtering, washing, recrystallizing with ethanol, and vacuum drying to obtain hydroxydimethylaminochalcone.

[0046] The preparation method of a chalcone end-capping agent comprises the following steps: hydroxydimethylaminochalcone, bromoethanol, potassium carbonate and N,N-dimethylformamide are sequentially added into a reaction container, heated to 90-95°C for reaction for 48 hours under a nitrogen atmosphere, cooled to room temperature, poured the product into deionized water for precipitation, filtered, vacuum dried, and recrystallized using a mixed solution of ethanol and dichloromethane to obtain a chalcone end-capping agent.

[0047] The preparation method of a RAFT agent comprises the following steps: adding 0.996 g of tetrabutylammonium bromide and 7.5 g of dodecanethiol to acetone, stirring evenly, adding 1.5 g of a 50 wt% sodium hydroxide solution, an acetone solution containing 2.25 mL of carbon disulfide, and 3.4 g of 2-bromopropionic acid in sequence under a nitrogen atmosphere and an ice bath, reacting at room temperature for 12 hours, filtering, washing, and recrystallizing using petroleum ether to obtain a RAFT agent.

[0048] The preparation method of a diaminochalcone-based RAFT agent comprises the following steps: adding 1 mmol of a RAFT agent into tetrahydrofuran, stirring evenly, sequentially adding 1 mmol of dicyclohexylcarbodiimide, 0.1 mmol of 4-dimethylaminopyridine, and 1 mmol of hydroxydimethylaminochalcone, reacting at room temperature for 24 hours, filtering, concentrating the filtrate, and recrystallizing using a mixed solution of ethanol and dichloromethane to obtain a diaminochalcone-based RAFT agent.

[0049] The preparation method of a chalcone-based RAFT agent comprises the following steps: adding 1 mmol of a diaminochalcone-based RAFT agent and hydroquinone into acetone, stirring evenly, heating to 50-55° C. for heat preservation, adding 1 mmol of an acetone solution of 1,3-propane sultone, heat preservation for reaction for 20 hours, cooling to room temperature, filtering, washing a precipitate with a mixed solution of acetone and ether, and vacuum drying to obtain a chalcone-based RAFT agent.

[0050] Embodiment 1: A method for preparing high-strength recycled concrete: comprising the following steps: S1: adding 5.5 parts of isophorone diisocyanate to 10 parts of polyethylene glycol, stirring evenly, adding 0.2 parts of dibutyltin dilaurate, heating to 70°C for insulation, adding 9 parts of terminal hydroxyl polysilane, 7 parts of acrylamide, and 3 parts of chalcone capping agent in sequence, and reacting at the temperature until the isocyanate group reaches the theoretical value to obtain a polyurethane prepolymer;

[0051] S2: Add 1 mmol of polyurethane prepolymer and hydroquinone to acetone, stir evenly, heat to 50°C, add 1 mmol of 1,3-propane sultone acetone solution, keep warm for 20 hours, cool to room temperature, filter, wash the precipitate with a mixed solution of acetone and ether, and vacuum dry to obtain amphoteric monomers;

[0052] S3: 0.5 parts of amphoteric monomer, 0.5 parts of polyether monomer, 6 parts of acrylic acid, and 57.5 parts of n-propanol were added to a reaction container, ultrasonically dispersed, and under a nitrogen atmosphere, 0.1 parts of chalcone-based RAFT agent, 0.1 parts of vinyl nano-silica, and 0.05 parts of azobisisobutyronitrile were added, heated to 60°C for reaction for 12 hours, and cooled to room temperature to obtain a nano-silica doped water reducer;

[0053] S4: Soak the recycled coarse and fine aggregates in nano-silica-doped water-reducing agent for 1 day, take them out, put them in an oven for drying, curing, and carbonization to obtain recycled aggregate; add 1076 parts of recycled aggregate, 270 parts of cement, 100 parts of fly ash, 60 parts of mineral powder, 718 parts of sand and gravel, 160 parts of water, and 9.7 parts of nano-silica-doped water-reducing agent into a mixer, mix well, pour, and cure to obtain high-strength recycled concrete.

[0054] Example 2: A method for preparing high-strength recycled concrete: comprising the following steps: S1: adding 5.5 parts of isophorone diisocyanate to 10 parts of polyethylene glycol, stirring evenly, adding 0.2 parts of dibutyltin dilaurate, heating to 70°C for insulation, adding 9 parts of terminal hydroxyl polysilane, 5 parts of acrylamide, and 5 parts of chalcone capping agent in sequence, and reacting at the temperature until the isocyanate group reaches the theoretical value to obtain a polyurethane prepolymer;

[0055] The remaining steps are the same as those in Example 1.

[0056] Example 3: A method for preparing high-strength recycled concrete: comprising the following steps: S3: adding 0.5 parts of amphoteric monomers, 1.5 parts of polyether monomers, 12 parts of acrylic acid, and 57.5 parts of n-propanol into a reaction container, ultrasonically dispersing, adding 0.1 parts of chalcone-based RAFT agent, 0.1 parts of vinyl nano-silica, and 0.05 parts of azobisisobutyronitrile under a nitrogen atmosphere, heating to 60°C for reaction for 12 hours, and cooling to room temperature to obtain a nano-silica-doped water reducer;

[0057] The remaining steps are the same as those in Example 2.

[0058] Example 4: A method for preparing high-strength recycled concrete: comprising the following steps: S3: adding 1 part of amphoteric monomer, 1 part of polyether monomer, 12 parts of acrylic acid, and 57.5 parts of n-propanol into a reaction container, ultrasonically dispersing, adding 0.1 part of chalcone-based RAFT agent, 0.1 part of vinyl nano-silica, and 0.05 part of azobisisobutyronitrile under a nitrogen atmosphere, heating to 60°C for reaction for 12 hours, and cooling to room temperature to obtain a nano-silica-doped water reducer;

[0059] The remaining steps are the same as those in Example 2.

[0060] Example 5: A method for preparing high-strength recycled concrete: comprising the following steps: S3: adding 1 part of amphoteric monomer, 1 part of polyether monomer, 12 parts of acrylic acid, and 57.5 parts of n-propanol into a reaction container, ultrasonically dispersing, adding 0.2 parts of chalcone-based RAFT agent, 0.5 parts of vinyl nano-silica, and 0.05 parts of azobisisobutyronitrile under a nitrogen atmosphere, heating to 60°C for reaction for 12 hours, and cooling to room temperature to obtain a nano-silica-doped water reducer;

[0061] The remaining steps are the same as those in Example 2.

[0062] Comparative Example 1: A method for preparing high-strength recycled concrete: comprising the following steps: S1: adding 5.5 parts of isophorone diisocyanate to 10 parts of polyethylene glycol, stirring evenly, adding 0.2 parts of dibutyltin dilaurate, heating to 70°C for insulation, adding 9 parts of terminal hydroxyl polysilane, 7 parts of acrylamide, and 3 parts of ethylenediamine in sequence, and reacting at the same temperature until the isocyanate group reaches the theoretical value to obtain a polyurethane prepolymer;

[0063] The remaining steps are the same as those in Example 1.

[0064] Comparative Example 2: A method for preparing high-strength recycled concrete: comprising the following steps: S3: adding 0.5 parts of amphoteric monomers, 0.5 parts of polyether monomers, 6 parts of acrylic acid, and 57.5 parts of n-propanol into a reaction container, ultrasonically dispersing, adding 0.1 parts of chalcone-based RAFT reagents and 0.05 parts of azobisisobutyronitrile under a nitrogen atmosphere, heating to 60° C. for reaction for 12 hours, and cooling to room temperature to obtain a nano-silica doped water reducer;

[0065] The remaining steps are the same as those in Example 1.

[0066] Comparative Example 3: A method for preparing high-strength recycled concrete: comprising the following steps: S3: adding 0.5 parts of amphoteric monomers, 0.5 parts of polyether monomers, 6 parts of acrylic acid, and 57.5 parts of n-propanol into a reaction container, ultrasonically dispersing, adding 0.1 parts of vinyl nano-silica and 0.05 parts of azobisisobutyronitrile under a nitrogen atmosphere, heating to 60°C for reaction for 12 hours, and cooling to room temperature to obtain a nano-silica doped water reducer;

[0067] The remaining steps are the same as those in Example 1.

[0068] Test: According to GB / T 50081-2019, the cube compressive strength, splitting tensile strength and flexural strength of high-strength recycled concrete were tested. Each group of test blocks consisted of 3 specimens, and the results were taken as the average of the three.

[0069] Cube compressive strength test: Place the test block cured for 28 days on the pressure plate of the servo hydraulic testing machine, and the test loading rate is 0.5MPa / s. This test uses a non-standard specimen size of 100mm×100mm×100mm, so the concrete compressive strength is multiplied by the size conversion factor of 0.95.

[0070] Split tensile strength test: Draw parallel straight lines in the middle of the top and bottom surfaces of the test block that has been cured for 28 days to determine the position of the splitting surface. Place it in the splitting mold and set it at the center of the pressure plate of the servo hydraulic testing machine. Load evenly during the test, with a loading rate of 0.05MPa / s, and record the load-displacement curve of the entire test process. This test uses a non-standard specimen size of 100mm×100mm×100mm, so the concrete splitting tensile strength is multiplied by the size conversion factor of 0.85.

[0071] Flexural strength test: Wipe the surface of the test block that has been cured for 28 days, draw the loading line position on the side, load evenly during the test, take the loading rate of 0.05MPa / s, and record the load displacement curve of the entire test process. This test uses a non-standard specimen size of 100mm×100mm×400mm, so the concrete flexural strength is multiplied by the size conversion factor of 0.85.

[0072] The test data are shown in Table 1 below. In order to intuitively reflect the high strength performance of the recycled concrete of the present invention, a control blank group of recycled concrete is set, and its preparation method includes the following steps: 1076 parts of recycled aggregate, 270 parts of cement, 100 parts of fly ash, 60 parts of mineral powder, 718 parts of sand and gravel, 160 parts of water, and 9.7 parts of water reducer are added into a mixer, stirred evenly, poured, and cured to obtain recycled concrete.

[0073] Table 1 Recycled concrete performance test data

[0074]

[0075] Conclusion: The recycled concrete prepared by the present invention has excellent strength properties.

[0076] In Comparative Example 1, the diaminochalcone end-capping structure is not introduced into the polyurethane prepolymer, and the amphoteric monomer cannot be obtained subsequently, resulting in a decrease in the strength of the recycled concrete; in Comparative Example 2, the penetration and filling effect of the doped auxiliary water reducer of vinyl nano-silica is lacking, resulting in a decrease in the strength of the recycled concrete; in Comparative Example 3, the water reducer lacks a chalcone-based RAFT agent, which, on the one hand, leads to a reduction in anionic and cationic structures, and on the other hand, reduces the adsorption and dispersion properties, resulting in a decrease in the strength of the recycled concrete.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing high-strength recycled concrete, characterized in that: The following steps are involved: S1: Add amphoteric monomers, polyether monomers, acrylic acid, and n-propanol into a reaction container, perform ultrasonic dispersion, add chalcone-based RAFT reagents, vinyl nano-silica, and azobisisobutyronitrile under a nitrogen atmosphere, heat to 60-65°C for reaction for 12-48 hours, and cool to room temperature to obtain a nano-silica-doped water reducer; S2: Soak the recycled coarse and fine aggregates in the nano-silica-doped water reducer for 1-2 days, take them out, dry them in an oven, cure them, and carbonize them to obtain recycled aggregates; Add the recycled aggregates, cement, fly ash, mineral powder, sand and gravel, water, and nano-silica-doped water reducer into a mixer, mix them evenly, pour them, and cure them to obtain high-strength recycled concrete; The preparation method of the amphoteric monomer comprises the following steps: Step (1): adding isophorone diisocyanate to polyethylene glycol, stirring evenly, adding dibutyltin dilaurate, heating to 70-75° C. for heat preservation, adding terminal hydroxyl polysilane, acrylamide, and chalcone capping agent in sequence, and reacting at a heat preservation temperature until the isocyanate group reaches a theoretical value to obtain a polyurethane prepolymer; in the preparation method of the polyurethane prepolymer, the proportion of each component by mass includes 10-20 parts of polyethylene glycol, 5.5-8 parts of isophorone diisocyanate, 0.2-0.3 parts of dibutyltin dilaurate, 9-13.5 parts of terminal hydroxyl polysilane, 5-7 parts of acrylamide, and 3-5 parts of chalcone capping agent; Step (2): adding the polyurethane prepolymer and hydroquinone to acetone, stirring evenly, heating to 50-55°C and keeping warm, adding an acetone solution of 1,3-propane sultone, keeping warm for 20-22 hours, cooling to room temperature, filtering, washing the precipitate with a mixed solution of acetone and ether, and vacuum drying to obtain an amphoteric monomer; in the preparation process of the amphoteric monomer, the molar ratio of the polyurethane prepolymer to 1,3-propane sultone is 1:1; The preparation method of the chalcone end-capping agent comprises the following steps: adding hydroxydimethylaminochalcone, bromoethanol, potassium carbonate and N,N-dimethylformamide into a reaction container in sequence, heating to 90-95° C. for reaction for 48 hours under a nitrogen atmosphere, cooling to room temperature, pouring the product into deionized water for precipitation, filtering, vacuum drying, and recrystallizing with a mixed solution of ethanol and dichloromethane to obtain the chalcone end-capping agent; in the preparation process of the chalcone end-capping agent, the molar ratio of hydroxydimethylaminochalcone:bromoethanol:potassium carbonate is (0.3-0.45):(0.36-0.54):(0.45-0.60); The preparation method of hydroxydimethylaminochalcone comprises the following steps: adding 4-hydroxyacetophenone to ethanol, stirring evenly, adding sodium hydroxide solution and 4-dimethylaminobenzaldehyde ethanol solution in sequence under ice bath condition, reacting at room temperature for 24 hours, pouring the product into an aqueous solution of glacial acetic acid for precipitation, filtering, washing, recrystallizing with ethanol, and vacuum drying to obtain hydroxydimethylaminochalcone; in the preparation process of hydroxydimethylaminochalcone, the molar ratio of 4-hydroxyacetophenone:4-dimethylaminobenzaldehyde is 1:

1.

2. The method for preparing high-strength recycled concrete according to claim 1, characterized in that: The preparation method of the chalcone-based RAFT agent comprises the following steps: adding a diaminochalcone-based RAFT agent and hydroquinone into acetone, stirring evenly, heating to 50-55° C. for heat preservation, adding an acetone solution of 1,3-propane sultone, heat preservation for reaction for 20-22 hours, cooling to room temperature, filtering, washing a precipitate with a mixed solution of acetone and ether, and vacuum drying to obtain a chalcone-based RAFT agent; in the preparation process of the chalcone-based RAFT agent, the molar ratio of the diaminochalcone-based RAFT agent to the 1,3-propane sultone is 1:

1.

3. The method for preparing high-strength recycled concrete according to claim 2, characterized in that: The preparation method of the diaminochalcone-based RAFT agent comprises the following steps: adding a RAFT agent to tetrahydrofuran, stirring evenly, sequentially adding dicyclohexylcarbodiimide, 4-dimethylaminopyridine and hydroxydimethylaminochalcone, reacting at room temperature for 24 hours, filtering, concentrating the filtrate, and recrystallizing using a mixed solution of ethanol and dichloromethane to obtain a diaminochalcone-based RAFT agent; in the diaminochalcone-based RAFT agent, the molar ratio of RAFT agent: dicyclohexylcarbodiimide: 4-dimethylaminopyridine: hydroxydimethylaminochalcone is 1:1:0.1:

1.

4. The method for preparing high-strength recycled concrete according to claim 3, characterized in that: The preparation method of the RAFT agent comprises the following steps: adding tetrabutylammonium bromide and dodecanethiol into acetone, stirring evenly, adding sodium hydroxide solution, carbon disulfide acetone solution and 2-bromopropionic acid in sequence under nitrogen atmosphere and ice bath condition, reacting at room temperature for 12-14 hours, filtering, washing and recrystallizing with petroleum ether to obtain the RAFT agent; in the preparation process of the RAFT agent, the mass ratio of tetrabutylammonium bromide: dodecanethiol: 2-bromopropionic acid is (0.966-1.1592): (7.5-8.925): (3.4-4.08).

5. The method for preparing high-strength recycled concrete according to claim 1, characterized in that: In the preparation process of nano-silica doped water reducer, the proportion of each component is calculated by molar proportion, including 0.5-1.5 parts of amphoteric monomer, 0.5-1.5 parts of polyether monomer, 6-12 parts of acrylic acid, 57.5-60 parts of n-propanol, 0.1-0.2 parts of chalcone-based RAFT agent, 0.1-0.5 parts of vinyl nano-silica, and 0.05-0.06 parts of azobisisobutyronitrile.

6. The method for preparing high-strength recycled concrete according to claim 1, characterized in that: In the preparation process of high-strength recycled concrete, the proportion of each component by mass includes 1076-1124 parts of recycled aggregate, 270-300 parts of cement, 100-110 parts of fly ash, 60-65 parts of mineral powder, 718-746 parts of sand and gravel, 160-165 parts of water, and 9.7-10.2 parts of nano-silica doped water reducer.

7. The high-strength recycled concrete prepared according to the method for preparing high-strength recycled concrete according to any one of claims 1 to 6.

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