Preparation method of recycled concrete based on building solid waste garbage

Abstract

The invention discloses a preparation method of recycled concrete based on building solid waste garbage, which comprises the following steps: S1, preparing modified recycled aggregate, S2, preparing reinforced fiber, S3, uniformly mixing Portland cement, fine aggregate, modified recycled aggregate, mineral admixture, water reducing agent, reinforced fiber, carboxymethyl cellulose, water reducing agent and water to obtain the recycled concrete, tetraethyl orthosilicate is hydrolyzed to generate nano silicon dioxide particles to fill gaps of the recycled concrete aggregate, and silicon carbide is coated on the surface of a recycled aggregate intermediate by using a vinyl coupling agent, so that the compactness and the strength of the aggregate are effectively improved; the titanium dioxide sol and the glass fiber are mixed to form mixed sol, the mixed sol is coated on the surface of the steel fiber, the tensile strength and the toughness of the concrete are effectively improved by the obtained reinforced fiber, and the regenerated concrete has better mechanical properties and working performance through the synergistic effect of the modified regenerated aggregate, the reinforced fiber and other raw materials.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and particularly relates to a preparation method of recycled concrete based on construction waste. Background Art

[0002] As an effective way to recycle construction waste resources, the technology of recycled concrete, which breaks construction waste into recycled aggregates to replace natural aggregates, has important practical significance. On the one hand, the traditional production of concrete consumes a large amount of natural aggregates (sand and stone), resulting in over-exploitation of natural aggregates and serious damage to the ecological environment. For example, excessive sand mining in river channels causes the riverbed to drop and the river ecosystem to be damaged. By using construction waste to prepare recycled concrete, these waste materials can be transformed into reusable resources, reducing the extraction amount of natural aggregates and the damage to the natural environment. On the other hand, the production of recycled concrete can reduce the accumulation of construction waste, relieve the pressure of waste treatment, and contribute to the sustainable development of the construction industry.

[0003] However, there are many deficiencies in the existing recycled concrete technology. Due to the attachment of old mortar, recycled aggregates have problems such as high porosity, strong water absorption, and weak bonding at the interface with the matrix, which directly affect the mechanical properties and durability of recycled concrete. To improve the performance of recycled aggregates, existing technologies mostly use methods such as pickling, polymer impregnation, or mechanical grinding for modification, but these methods have obvious defects. The pickling method has a high cost and may cause corrosion to the environment and equipment; the polymer impregnation process is complex and difficult to operate; mechanical grinding may lead to uneven modification and is difficult to ensure the overall improvement of the performance of recycled aggregates. Therefore, the existing modification methods are difficult to balance the requirements of performance improvement and large-scale application.

[0004] In addition, ordinary recycled concrete has the disadvantages of high brittleness and poor crack resistance, and usually fibers are incorporated to enhance its toughness. However, the insufficient bonding at the interface between the fiber and the matrix easily causes stress concentration, affecting the reinforcement effect. At the same time, the performance of the recycled concrete aggregate itself is relatively poor, and there are many micro-cracks and pores inside, resulting in low strength and durability. Summary of the Invention

[0005] Aiming at the technical defects in the background art, the present invention proposes a preparation method of recycled concrete based on construction waste, which solves the above technical problems and meets the actual needs. The specific technical solutions are as follows: A preparation method of recycled concrete based on construction waste, comprising the following steps: S1. Prepare modified recycled aggregates; S11. Put recycled concrete aggregates and an ethanol solution of tetraethyl orthosilicate into a reaction flask, then use 1M NaOH to adjust the solution pH to 7.5 - 9.0. Then evacuate the reaction flask and react for a period of time under stirring to obtain recycled aggregate intermediates; S12. Respectively use vinyl silane coupling agents to modify the recycled aggregate intermediates and silicon carbide. Then put the recycled aggregate intermediates treated with vinyl silane coupling agents, silicon carbide, and absolute ethanol into a container, then add a certain amount of photoinitiator. Irradiate the solution under an ultraviolet lamp and stir and react for 30 - 60 min, filter, wash, and dry to obtain modified recycled aggregates; S2. Prepare reinforcing fibers; Drop tetrabutyl titanate into absolute ethanol, stir vigorously at room temperature, and drop a mixed solution of absolute ethanol, concentrated hydrochloric acid, and deionized water under vigorous stirring. After dropping, continue to stir for 50 min to obtain titanium dioxide sol. Add glass fibers to the titanium dioxide sol and mix evenly to obtain a mixed sol. Coat the mixed sol on the surface of steel fibers and dry and cure the mixed sol to obtain reinforcing fibers; S3. Mix 30 - 35 parts of portland cement, 55 - 60 parts of fine aggregate, 90 - 115 parts of modified recycled aggregates, 5 - 10 parts of mineral admixture, 4 - 8 parts of reinforcing fibers, 1 - 5 parts of carboxymethyl cellulose, 1 - 5 parts of water - reducing agent, and 30 - 36 parts of water evenly to obtain recycled concrete.

[0006] As a further technical solution of the present invention, in step S11, crush construction waste into recycled aggregate particles with a continuous gradation having a particle size of 10 - 25 mm. After magnetic separation and flotation, dry in the air to obtain recycled concrete aggregates. Configure tetraethyl orthosilicate and ethanol into an ethanol solution of tetraethyl orthosilicate according to a molar ratio of 1:1. The volume ratio of the recycled concrete aggregates and the ethanol solution of tetraethyl orthosilicate in the reaction flask is 1:(2 - 4).

[0007] As a further technical solution of the present invention, in step S11, put recycled concrete aggregates and an ethanol solution of tetraethyl orthosilicate into a reaction flask, then use 1M NaOH to adjust the solution pH to 8.5. Then evacuate the reaction flask and place it in a constant - temperature water bath, maintain a water bath temperature of 60 °C, and react for 6 - 12 h under stirring.

[0008] As a further technical solution of the present invention, in step S11, the vinyl silane coupling agent is selected from any one of vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltris(2 - methoxyethoxy)silane.

[0009] As a further technical solution of the present invention, in step S12, the recycled aggregate intermediate and silicon carbide are respectively placed in two containers. An coupling agent solution is prepared by mixing absolute ethanol, vinyl silane coupling agent and deionized water according to a mass ratio of 25: (1-2): 2 and added to the above two containers. The reaction is carried out for 6 h under stirring conditions. After the reaction is completed, filtration and washing are carried out, and the product is dried in a vacuum drying oven at 80 °C for 8 h to obtain the recycled aggregate intermediate treated with vinyl silane coupling agent and silicon carbide treated with vinyl silane coupling agent respectively. The mass ratio of the recycled aggregate intermediate to the coupling agent solution in the container is (1-5): 100, and the mass ratio of the silicon carbide to the coupling agent solution in the container is (1-2): 100.

[0010] As a further technical solution of the present invention, in step S12, the recycled aggregate intermediate treated with vinyl silane coupling agent, the silicon carbide treated with vinyl silane coupling agent and absolute ethanol are added to the container according to a mass ratio of 5: (1-2): 20. Then a certain amount of benzoin dimethyl ether is added as a photoinitiator. The solution is irradiated under an ultraviolet lamp and stirred for reaction for 30-60 min, followed by filtration, washing and drying to obtain the modified recycled aggregate. The mass ratio of the silicon carbide treated with vinyl silane coupling agent to benzoin dimethyl ether is 1: (0.01-0.025), and the particle size of the silicon carbide is 20-50 nm.

[0011] As a further technical solution of the present invention, in step S2, the diameter of the steel fiber is 200-500 μm and the length is 1-2 cm, and the length of the glass fiber is 10-50 μm and the diameter is 2-6 μm.

[0012] As a further technical solution of the present invention, in step S2, tetrabutyl titanate is dropped into 7.5 times the volume of absolute ethanol, and vigorously stirred at room temperature. After dropping, continue to stir to obtain a transparent and uniform light yellow solution. Under vigorous stirring, a mixed solution mixed with absolute ethanol, concentrated hydrochloric acid and water in a volume ratio of (1-2): 1: 1 is dropped. The volume ratio of tetrabutyl titanate to the mixed solution is 1: 1. After dropping, continue to stir for 50-60 min to obtain a uniform and transparent titanium dioxide sol. The titanium dioxide sol and the glass fiber are mixed at a mass ratio of 100: 1 to obtain a mixed sol. The mixed sol is coated on the surface of the steel fiber, and the coating thickness is 0.01-0.05 mm, and then dried and cured at 80 °C for 24-48 h to obtain the reinforced fiber.

[0013] As a further technical solution of the present invention, in step S3, the fine aggregate is continuously graded machine-made sand with a particle size of 1-3 mm; the mineral admixture is any one or more of fly ash, silica fume and blast furnace slag.

[0014] As a further technical solution of the present invention, in step S3, the water reducing agent is composed of a naphthalene-based water reducing agent and a polycarboxylate water reducing agent, and the mass ratio of the polycarboxylate water reducing agent to the naphthalene-based water reducing agent is 1:(1 - 3).

[0015] The beneficial effects of the present invention are as follows: By hydrolyzing tetraethyl orthosilicate under alkaline catalysis to generate nano-silica particles to fill the gaps of recycled concrete aggregates, the density and strength of the aggregates are effectively improved. The recycled aggregate intermediate and silicon carbide are modified with vinyl silane coupling agent, and vinyl is introduced. Under the action of a photoinitiator, addition crosslinking occurs, so that silicon carbide is coated on the surface of the recycled aggregate intermediate, significantly enhancing the interfacial properties and durability of the aggregates. The prepared titanium dioxide sol is mixed with glass fiber to form a mixed sol, which is coated on the surface of steel fiber and dried and cured, and the obtained reinforcing fiber effectively improves the tensile strength and toughness of the concrete. Through the synergistic effect of modified recycled aggregates, reinforcing fibers and other raw materials, the recycled concrete has better mechanical properties. Specific embodiments

[0016] The following combines relevant embodiments to illustrate the implementation manners of the present invention. The implementation manners of the present invention are not limited to the following embodiments, and the relevant necessary components involved in the present invention should be regarded as well-known technologies in the technical field, which can be known and mastered by those skilled in the technical field.

[0017] A preparation method of recycled concrete based on construction waste, comprising the following steps: S1. Prepare modified recycled aggregates; S11. Put recycled concrete aggregates and an ethanol solution of tetraethyl orthosilicate into a reaction flask, then use 1M NaOH to adjust the solution pH = 7.5 - 9.0, then evacuate the reaction flask and react for a period of time under stirring to obtain a recycled aggregate intermediate; S12. Respectively use vinyl silane coupling agent to modify the recycled aggregate intermediate and silicon carbide, then put the recycled aggregate intermediate treated with vinyl silane coupling agent, silicon carbide and absolute ethanol into a container, then add a certain amount of photoinitiator, irradiate the solution under ultraviolet light, and stir and react for 30 - 60 min, filter, wash, and dry to obtain modified recycled aggregates; S2. Prepare reinforcing fibers; Drop tetrabutyl titanate into absolute ethanol, stir vigorously at room temperature, and drop a mixed solution of absolute ethanol, concentrated hydrochloric acid and deionized water under vigorous stirring. After dropping, continue to stir for 50 min to obtain titanium dioxide sol. Add glass fiber to the titanium dioxide sol and mix evenly to obtain a mixed sol. Coat the mixed sol on the surface of steel fiber and dry and cure the mixed sol to obtain reinforcing fibers; S3. Mix 30 - 35 parts of portland cement, 55 - 60 parts of fine aggregate, 90 - 115 parts of modified recycled aggregate, 5 - 10 parts of mineral admixture, 4 - 8 parts of reinforcing fiber, 1 - 5 parts of carboxymethyl cellulose, 1 - 5 parts of water - reducing agent, and 30 - 36 parts of water evenly to obtain recycled concrete.

[0018] In the preparation method of the recycled concrete of the present invention, tetraethyl orthosilicate is hydrolyzed under the catalysis of alkali to generate nano - silica particles, and these particles can fill the gaps in the recycled concrete aggregate. This helps to improve the density of the recycled aggregate, reduce internal defects, and further enhance the strength and durability of the recycled concrete.

[0019] The recycled aggregate intermediate and silicon carbide are respectively modified with vinyl silane coupling agent to introduce vinyl groups. Under the action of a photo - initiator, the vinyl groups undergo addition cross - linking reaction, so that the silicon carbide treated with vinyl silane coupling agent is coated on the surface of the recycled aggregate intermediate. On the one hand, this coating structure can further protect the recycled aggregate and improve its corrosion resistance; on the other hand, silicon carbide has good mechanical properties and chemical stability, which can enhance the overall performance of the recycled aggregate, thereby improving the comprehensive performance of the recycled concrete.

[0020] In the preparation method of the recycled concrete of the present invention, titanium dioxide sol is mixed with glass fiber to obtain a mixed sol, and the mixed sol is coated on the surface of steel fiber. After drying and curing, reinforcing fiber is obtained. This composite fiber structure combines the high strength of steel fiber and the characteristics of glass fiber and titanium dioxide sol. The addition of glass fiber can increase the bonding force between the fiber and the concrete matrix, improve the dispersion and force - transfer effect of the fiber in the concrete; titanium dioxide sol may endow the fiber with certain functional characteristics, such as photocatalytic performance, etc. At the same time, the synergistic effect between different fibers can more effectively enhance the toughness and crack - resistance of the concrete.

[0021] Through the synergistic effect of modified recycled aggregate, reinforcing fiber and other raw materials, the recycled concrete of the present invention has better mechanical properties, durability and workability. The modified recycled aggregate improves the strength and stability of the concrete, the reinforcing fiber enhances the toughness and crack - resistance of the concrete, and mineral admixture and water - reducing agent, etc. improve the workability and durability of the concrete.

[0022] As a further technical solution of the present invention, in step S11, the construction waste is crushed into recycled aggregate particles with a continuous gradation of particle size of 10 - 25 mm. After magnetic separation and flotation, it is dried to obtain recycled concrete aggregate. Tetraethyl orthosilicate and ethanol are configured into an ethanol solution of tetraethyl orthosilicate according to a molar ratio of 1:1, and the volume ratio of the recycled concrete aggregate in the reaction flask to the ethanol solution of tetraethyl orthosilicate is 1:(2 - 4).

[0023] Further, in step S11, recycled concrete aggregate and an ethanol solution of tetraethyl orthosilicate are put into a reaction flask, and then the pH of the solution is adjusted to 8.5 using 1M NaOH. Then, the reaction flask is evacuated and placed in a constant temperature water bath, maintaining a water bath temperature of 60°C, and reacting for 6 - 12 h under stirring conditions.

[0024] Further, in step S11, the vinyl silane coupling agent is selected from any one of vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltris(2 - methoxyethoxy)silane.

[0025] Specifically, in step S11, the volume ratio of the recycled concrete aggregate to the ethanol solution of tetraethyl orthosilicate is 1:4, and the vinyl silane coupling agent is selected as vinyltriethoxysilane.

[0026] In step S11, through the hydrolysis reaction of tetraethyl orthosilicate under alkaline conditions, nano - silica particles are formed on the surface of the recycled concrete aggregate, thereby filling the gaps in the aggregate and improving the properties of the aggregate.

[0027] Tetraethyl orthosilicate (TEOS) undergoes a hydrolysis reaction under alkaline conditions. In the hydrolysis reaction, the ethoxy groups in the TEOS molecule are replaced by hydroxyl groups, generating silicic acid molecules and ethanol. The silicic acid molecules generated by hydrolysis further condense under alkaline conditions to form silicon - oxygen chains (Si - O - Si), and finally nano - silica (SiO2) particles are formed. The nano - silica particles have a smaller particle size and a larger specific surface area, and can effectively fill the gaps in the recycled concrete aggregate, improving the density and strength of the aggregate.

[0028] As one of the preferred embodiments of the present invention, in step S12, the recycled aggregate intermediate and silicon carbide are respectively placed in two containers. An anhydrous ethanol, vinyl silane coupling agent, and deionized water are configured into a coupling agent solution according to a mass ratio of 25:(1 - 2):2 and added to the above two containers. Reacting for 6 h under stirring conditions, after the reaction is completed, filtering and washing are carried out, and the products are placed in a vacuum drying oven at 80°C for drying for 8 h to respectively obtain the recycled aggregate intermediate treated with the vinyl silane coupling agent and the silicon carbide treated with the vinyl silane coupling agent. The mass ratio of the recycled aggregate intermediate to the coupling agent solution in the container is (1 - 5):100, and the mass ratio of the silicon carbide to the coupling agent solution in the container is (1 - 2):100.

[0029] Specifically, in step S12, an anhydrous ethanol, vinyl silane coupling agent, and deionized water are configured into a coupling agent according to a mass ratio of 25:2:2. The mass ratio of the recycled aggregate intermediate to the coupling agent solution in the container is 5:100, and the mass ratio of the silicon carbide to the coupling agent solution in the container is 2:100.

[0030] Place the recycled aggregate intermediate into a container, and add the prepared coupling agent solution. Under stirring conditions, hydrolyzable groups such as ethoxy or methoxy in the vinyl silane coupling agent molecule will hydrolyze to form silanol groups. These silanol groups can undergo a condensation reaction with the hydroxyl groups on the surface of the recycled aggregate intermediate to form stable Si-O-Si bonds. As a result, the vinyl silane coupling agent molecules are firmly grafted onto the surface of the recycled aggregate intermediate, thereby introducing vinyl functional groups. Similarly, place silicon carbide into another container, and add the coupling agent solution. The vinyl silane coupling agent undergoes a condensation reaction with the silanol groups on the surface of silicon carbide to introduce vinyl functional groups onto the surface of silicon carbide.

[0031] As one of the preferred embodiments of the present invention, in step S12, the recycled aggregate intermediate treated with vinyl silane coupling agent, silicon carbide treated with vinyl silane coupling agent, and absolute ethanol are added into a container according to a mass ratio of 5:(1 - 2):20. Then, a certain amount of benzoin dimethyl ether is added as a photoinitiator. The solution is irradiated under an ultraviolet lamp and stirred for reaction for 30 - 60 min, filtered, washed, and dried to obtain the modified recycled aggregate. The mass ratio of the silicon carbide treated with vinyl silane coupling agent to benzoin dimethyl ether is 1:(0.01 - 0.025), and the particle size of the silicon carbide is 20 - 50 nm.

[0032] Specifically, the mass ratio of the recycled aggregate intermediate treated with vinyl silane coupling agent, silicon carbide treated with vinyl silane coupling agent, and absolute ethanol is 5:2:20, and the mass ratio of the silicon carbide treated with vinyl silane coupling agent to benzoin dimethyl ether is 1:0.01.

[0033] In step S12, the solution of the reaction system is placed under an ultraviolet lamp for irradiation. After benzoin dimethyl ether absorbs the ultraviolet light energy, a photolysis reaction occurs to generate free radicals, which can initiate the addition cross-linking reaction of the vinyl functional groups on the surface of the recycled aggregate intermediate treated with vinyl silane coupling agent and the silicon carbide treated with vinyl silane coupling agent. Under the initiation of free radicals, the vinyl functional groups on the surface of the recycled aggregate intermediate treated with vinyl silane coupling agent and the silicon carbide treated with vinyl silane coupling agent undergo an addition reaction, enabling the silicon carbide treated with vinyl silane coupling agent to closely coat the surface of the recycled aggregate intermediate treated with vinyl silane coupling agent.

[0034] As one of the preferred embodiments of the present invention, in step S2, tetrabutyl titanate is dropped into anhydrous ethanol with a volume 7.5 times that of tetrabutyl titanate, and stirred vigorously at room temperature. After the dropping is completed, stirring is continued to obtain a transparent, uniform, light yellow solution. Under vigorous stirring, a mixed solution of anhydrous ethanol, concentrated hydrochloric acid and water mixed in a volume ratio of (1 - 2):1:1 is added dropwise. The volume ratio of tetrabutyl titanate to the mixed solution is 1:1. After the dropping is completed, stirring is continued for 50 - 60 min to obtain a uniform and transparent titanium dioxide sol. The titanium dioxide sol and glass fibers are mixed in a mass ratio of 100:1 to obtain a mixed sol. The mixed sol is coated on the surface of steel fibers with a coating thickness of 0.01 - 0.05 mm, and then dried and cured at 80°C for 24 - 48 h to obtain reinforced fibers.

[0035] Further, in step S2, the steel fibers have a diameter of 200 - 500 μm and a length of 1 - 2 cm, and the glass fibers have a length of 10 - 50 μm and a diameter of 2 - 6 μm.

[0036] Specifically, the volume ratio of anhydrous ethanol, concentrated hydrochloric acid and water is 2:1:1, the coating thickness of the mixed sol on the surface of steel fibers is 0.01 mm, the steel fibers have a diameter of 200 μm and a length of 2 cm, and the glass fibers have a length of 10 μm and a diameter of 2 μm.

[0037] Tetrabutyl titanate is dropped into anhydrous ethanol with a volume 7.5 times that of tetrabutyl titanate, and stirred vigorously at room temperature. Tetrabutyl titanate begins to hydrolyze in anhydrous ethanol, and its alkoxy groups are replaced by hydroxyl groups to form titanium hydroxy compounds and butanol. Under vigorous stirring, a mixed solution of anhydrous ethanol, concentrated hydrochloric acid and water is added dropwise. Concentrated hydrochloric acid acts as a catalyst to promote the hydrolysis and condensation reactions of tetrabutyl titanate. After the dropping is completed, stirring is continued for 60 min to allow tetrabutyl titanate to fully hydrolyze and condense, forming a uniform and transparent titanium dioxide sol.

[0038] The titanium dioxide sol and glass fibers are mixed in a mass ratio of 100:1 to obtain a mixed sol. The addition of glass fibers helps to enhance the mechanical properties of the final product. The glass fibers have a length of 10 μm and a diameter of 2 μm. The small size enables the glass fibers to be evenly dispersed in the titanium dioxide sol, forming a uniform mixed sol.

[0039] The mixed sol is coated on the surface of steel fibers with a coating thickness of 0.01 mm. The steel fibers coated with the mixed sol are dried and cured at 80°C for 48 h. During this process, the titanium dioxide sol further cures to form a stable dry gel layer with a high degree of cross - linking in the network structure. At the same time, the glass fibers are tightly combined with the dry gel layer and adhere to the surface of the steel fibers to form reinforced fibers.

[0040] As one of the preferred embodiments of the present invention, in step S3, the fine aggregate is continuously graded manufactured sand with a particle size of 1 - 3 mm; the mineral admixture is any one or more of fly ash, silica fume, and blast furnace slag.

[0041] Specifically, fly ash, silica fume, and blast furnace slag are compounded in a mass ratio of 5:2:1 to obtain the mineral admixture.

[0042] Mineral admixtures such as fly ash, silica fume, and blast furnace slag have fine particle morphologies and can fill the microvoids in concrete, thereby improving the density and fluidity of the concrete. The compounded mineral admixture can more effectively optimize the particle gradation of the concrete, reduce the segregation and bleeding phenomena of the concrete mixture, and improve the workability of the concrete.

[0043] The active components in mineral admixtures such as fly ash, silica fume, and blast furnace slag can undergo a secondary reaction with the hydration products of cement to generate products with cementitious properties, thereby enhancing the strength and durability of the concrete. Through compounding, the advantages of various mineral admixtures can be fully utilized to form a complementary effect and further improve the mechanical properties of the concrete. For example, fly ash can improve the late strength of the concrete, silica fume can increase the early strength of the concrete, and blast furnace slag can enhance the impermeability and sulfate resistance of the concrete.

[0044] As one of the preferred embodiments of the present invention, in step S3, the water - reducing agent is compounded from a naphthalene - based water - reducing agent and a polycarboxylate water - reducing agent, and the mass ratio of the polycarboxylate water - reducing agent to the naphthalene - based water - reducing agent is 1:(1 - 3).

[0045] Specifically, the mass ratio of the polycarboxylate water - reducing agent to the naphthalene - based water - reducing agent is 1:2.

[0046] The polycarboxylate water - reducing agent has excellent dispersion performance and slump - retaining performance, enabling the concrete mixture to maintain good workability for a long time. The naphthalene - based water - reducing agent can improve the adhesiveness and water - retaining property of the concrete, reducing the segregation and bleeding phenomena of the concrete mixture. Through compounding, the advantages of the two water - reducing agents can be combined, making the concrete mixture have better workability and improving the construction efficiency.

[0047] Example 1 S1 Prepare modified recycled aggregate: S11: Mix the recycled aggregate (particle size 10 - 25 mm) with tetraethyl orthosilicate ethanol solution (volume ratio 1:4), adjust the pH to 8.5, react in a 60°C water bath for 12 h under stirring.

[0048] S12: The recycled aggregate intermediate and silicon carbide are respectively modified with vinyltriethoxysilane. The recycled aggregate intermediate treated with vinyl silane coupling agent, silicon carbide treated with vinyl silane coupling agent, and absolute ethanol are added into a container according to a mass ratio of 5:2:20. Then, benzoin dimethyl ether is added (silicon carbide: benzoin dimethyl ether = 1:0.01), and the reaction is carried out for 60 min under ultraviolet light irradiation.

[0049] S2 Preparation of reinforcing fibers: Tetrabutyl titanate is dropped into 7.5 times the volume of absolute ethanol, and a mixed solution (ethanol: concentrated hydrochloric acid: H2O = 2:1:1) is dropped under vigorous stirring. The volume ratio of tetrabutyl titanate to the mixed solution is 1:1 to prepare titanium dioxide sol. After mixing with glass fiber (mass ratio 100:1), it is coated on the surface of steel fiber (Φ200μm×2cm), and the coating thickness is 0.01 - 0.05 mm, and it is cured at 80°C for 48 h.

[0050] S3 Concrete preparation: 35 parts of Portland cement, 60 parts of fine aggregate (manufactured sand 1 - 3 mm), 115 parts of modified recycled aggregate, 10 parts of mineral admixture (fly ash: silica fume: slag = 5:2:1), 2.5 parts of water reducing agent (polycarboxylate water reducing agent: naphthalene-based water reducing agent = 1:2), 8 parts of reinforcing fiber, 5 parts of carboxymethyl cellulose, 36 parts of water.

[0051] Comparative example 1 The difference between comparative example 1 and example 1 is that step S1 is not carried out, and the recycled aggregate in step S12 is not modified and the crushed aggregate is directly used.

[0052] Comparative example 2 The difference between comparative example 2 and example 1 is that step S2 is not carried out, and in step S3, the reinforcing fiber is not coated with titanium dioxide / glass fiber and only ordinary steel fiber is used.

[0053] Comparative example 3 The difference between comparative example 3 and example 1 is that in S3, the mineral admixture is single fly ash (2.5 parts) Comparative example 4 The difference between comparative example 4 and example 1 is that in S3, only naphthalene-based water reducing agent (2.5 parts) is used as the water reducing agent. The 28-day compressive strength, 28-day flexural strength, slump, and drying shrinkage rate of the above example 1 and comparative examples 1 - 4 are detected, and the test results are as follows:

[0054] In the above test data, in Example 1, the modified recycled aggregate was prepared, with a 28-day compressive strength of 52.3 MPa and a 28-day flexural strength of 7.8 MPa; in Comparative Example 1, the recycled aggregate was not modified and the crushed aggregate was directly used, with a 28-day compressive strength of 38.6 MPa and a 28-day flexural strength of 5.2 MPa. This indicates that the modified recycled aggregate can significantly improve the compressive and flexural strengths of concrete because the modification treatment improves the density and strength of the recycled aggregate, thereby enhancing the overall performance of the concrete.

[0055] In the above test data, in Example 1, the reinforcing fiber coated with titanium dioxide / fiber glass was prepared, with a 28-day compressive strength of 52.3 MPa and a 28-day flexural strength of 7.8 MPa; in Comparative Example 2, the reinforcing fiber coated with titanium dioxide / fiber glass was not used and only ordinary steel fiber was used, with a 28-day compressive strength of 46.7 MPa and a 28-day flexural strength of 6.1 MPa. This shows that the reinforcing fiber coated with titanium dioxide / fiber glass can effectively enhance the toughness and crack resistance of concrete and improve the compressive and flexural strengths of concrete.

[0056] In the above test data, in Example 1, the compound mineral admixture (fly ash: silica fume: slag = 5:2:1) was used, with a 28-day compressive strength of 52.3 MPa, a slump of 195 mm, and a drying shrinkage rate of 380×10 -6 ; in Comparative Example 3, single fly ash was used as the mineral admixture, with a 28-day compressive strength of 44.5 MPa, a slump of 170 mm, and a drying shrinkage rate of 420×10 -6 . The compound mineral admixture can more effectively optimize the particle gradation of concrete, improve the compressive strength of concrete, improve the workability (slump) of concrete, and reduce the drying shrinkage rate.

[0057] In the above test data, in Example 1, the compound water reducer (polycarboxylic acid: naphthalene series = 1:2) was used, with a slump of 195 mm; in Comparative Example 4, only the naphthalene series water reducer was used, with a slump of 160 mm. The compound water reducer can keep the concrete mixture in good workability for a long time, increase the slump of concrete, and improve the construction efficiency.

[0058] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing recycled concrete based on construction solid waste, characterized in that: The following steps are involved: S1. preparing modified recycled aggregate; S11, adding recycled concrete aggregate and ethyl orthosilicate ethanol solution into a reaction bottle, and then using 1M NaOH to adjust the solution pH to 7.5-9.0, and then evacuating the reaction bottle and reacting for a period of time under stirring to obtain a recycled aggregate intermediate; S12, respectively modifying the recycled aggregate intermediate and silicon carbide using a vinyl silane coupling agent, then placing the recycled aggregate intermediate treated with the vinyl silane coupling agent, silicon carbide and anhydrous ethanol in a container, then adding a certain amount of photoinitiator, irradiating the solution under an ultraviolet lamp, stirring and reacting for 30-60 min, filtering, washing, and drying to obtain a modified recycled aggregate; S2, preparing reinforcing fibers; Tetrabutyl titanate is added dropwise to anhydrous ethanol, and the mixture is stirred vigorously at room temperature. A mixed solution of anhydrous ethanol, concentrated hydrochloric acid and deionized water is added dropwise under vigorous stirring. After the addition is completed, stirring is continued for 50 minutes to obtain a titanium dioxide sol. Glass fiber is added to the titanium dioxide sol and mixed uniformly to obtain a mixed sol. The mixed sol is coated on the surface of the steel fiber, and the mixed sol is dried and solidified to obtain a reinforcing fiber. S3. Evenly mix 30-35 parts of Portland cement, 55-60 parts of fine aggregate, 90-115 parts of modified recycled aggregate, 5-10 parts of mineral admixture, 4-8 parts of reinforcing fiber, 1-5 parts of carboxymethyl cellulose, 1-5 parts of water reducing agent and 30-36 parts of water to obtain recycled concrete.

2. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S11, the construction waste is crushed into continuously graded recycled aggregate particles with a particle size of 10-25 mm, and after magnetic separation and flotation, it is dried to obtain recycled concrete aggregate, and tetraethyl orthosilicate and ethanol are prepared into an ethanol solution of tetraethyl orthosilicate in a molar ratio of 1:

1. The volume ratio of the recycled concrete aggregate and the ethanol solution of tetraethyl orthosilicate in the reaction bottle is 1:(2-4).

3. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S11, recycled concrete aggregate and ethyl orthosilicate ethanol solution are added into a reaction bottle, and then 1M NaOH is used to adjust the solution pH to 8.

5. Then, the reaction bottle is evacuated and placed in a constant temperature water bath, the water bath temperature is maintained at 60° C., and the reaction is carried out for 6-12 hours under stirring.

4. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S11, the vinyl silane coupling agent is selected from any one of vinyl triethoxy silane, vinyl trimethoxy silane, and vinyl tri(2-methoxyethoxy) silane.

5. A method for preparing recycled concrete from construction solid waste according to claim 1 or 4, characterized in that: In step S12, the recycled aggregate intermediate and silicon carbide are placed in two containers respectively, anhydrous ethanol, vinyl silane coupling agent and deionized water are prepared into a coupling agent solution according to a mass ratio of 25: (1-2): 2 and added to the above two containers, and reacted for 6 hours under stirring conditions. After the reaction is completed, the product is filtered and washed, and placed in a vacuum drying oven at 80° C. for 8 hours to obtain a recycled aggregate intermediate treated with a vinyl silane coupling agent and silicon carbide treated with a vinyl silane coupling agent, respectively. The mass ratio of the recycled aggregate intermediate to the coupling agent solution in the container is (1-5): 100, and the mass ratio of the silicon carbide to the coupling agent solution in the container is (1-2):

100.

6. The method for preparing recycled concrete from construction solid waste according to claim 5, characterized in that: In step S12, a recycled aggregate intermediate treated with a vinyl silane coupling agent, silicon carbide treated with a vinyl silane coupling agent, and anhydrous ethanol are added into a container in a mass ratio of 5: (1-2): 20, and then a certain amount of benzoin dimethyl ether is added as a photoinitiator. The solution is irradiated under an ultraviolet lamp and stirred for reaction for 30-60 min, filtered, washed, and dried to obtain a modified recycled aggregate. The mass ratio of the silicon carbide treated with the vinyl silane coupling agent to the benzoin dimethyl ether is 1: (0.01-0.025), and the particle size of the silicon carbide is 20-50 nm.

7. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S2, the steel fiber has a diameter of 200-500 μm and a length of 1-2 cm, and the glass fiber has a length of 10-50 μm and a diameter of 2-6 μm.

8. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S2, tetrabutyl titanate is dripped into 7.5 times the volume of anhydrous ethanol, and the mixture is stirred vigorously at room temperature. After the dripping, stirring is continued to obtain a transparent and uniform light yellow solution. A mixed solution mixed with anhydrous ethanol, concentrated hydrochloric acid and water in a volume ratio of (1-2): 1:1 is dripped under vigorous stirring, wherein the volume ratio of tetrabutyl titanate to the mixed solution is 1:

1. After the dripping, stirring is continued for 50-60 minutes to obtain a uniform and transparent titanium dioxide sol. The titanium dioxide sol is mixed with glass fiber in a mass ratio of 100:1 to obtain a mixed sol. The mixed sol is coated on the surface of the steel fiber with a coating thickness of 0.01-0.05 mm, and then dried and cured at 80° C. for 24-48 hours to obtain a reinforcing fiber.

9. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S3, the fine aggregate is continuously graded machine-made sand with a particle size of 1-3 mm; the mineral admixture is any one or more of fly ash, silica fume, and blast furnace slag.

10. The method for preparing recycled concrete from construction solid waste according to claim 1, characterized in that: In step S3, the water reducer is compounded by a naphthalene-based water reducer and a polycarboxylic acid water reducer, and the mass ratio of the polycarboxylic acid water reducer to the naphthalene-based water reducer is 1:(1-3).

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