High-strength recycled concrete based on construction waste and preparation method of high-strength recycled concrete

Abstract

The invention discloses high-strength recycled concrete based on construction waste and a preparation method thereof.The recycled concrete is prepared from composite modified recycled aggregate, fly ash, composite glass bead powder, Portland cement, composite reinforced fibers, water, carboxymethylcellulose and a water reducer, and the preparation method of the recycled concrete comprises the steps that S1, the composite modified recycled aggregate is prepared; the waste silicate concrete is used as a main raw material to prepare the recycled aggregate, and meanwhile, the recycled aggregate is matched with the fly ash and the composite glass bead powder with different particle sizes, so that a particle accumulation structure in the recycled concrete is further optimized, internal defects are reduced, and the overall strength is improved; and through dipping in the barium salt-hydroxyphospholime mixed solution and subsequent precipitant treatment, micro-cracks and pores in the recycled aggregate are effectively filled, and the compactness and mechanical properties of the recycled aggregate are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and particularly relates to a high-strength recycled concrete based on construction waste and a preparation method thereof. Background Art

[0002] Recycled concrete is produced by crushing, screening, washing and grading waste concrete blocks in construction waste, and then mixing them in a certain proportion and gradation to form recycled aggregates, which partially or completely replace natural sand and gravel aggregates. Due to the differences in physical and chemical properties between recycled aggregates and natural aggregates, such as large porosity, high water absorption, and small bulk density, etc., recycled concrete performs poorly in terms of strength, workability, durability, etc., which limits its wide application.

[0003] Based on the above situation, in the prior art, a patent with the patent number CN202010821970.3 discloses a recycled concrete and a preparation method thereof. The recycled concrete includes construction waste recycled coarse aggregates, stones, cement, mineral admixtures, activators, water reducers, fibers and water; the fibers include modified polypropylene fibers and plant fibers; the modification process of the modified polypropylene fibers includes adding polypropylene fibers into an oxidant, mixing, soaking, and then washing to obtain a first intermediate product, adding the first intermediate product into a coating material and mixing evenly to obtain modified polypropylene fibers. When preparing the recycled concrete, the mineral admixtures, cement and activator are mixed evenly, and 1 / 3 - 1 / 2 of the total weight of water is added and mixed evenly to obtain a first intermediate product; then the construction waste recycled coarse aggregates, modified polypropylene fibers and plant fibers are mixed evenly to obtain a second intermediate product; the water reducer, the first intermediate product, the second intermediate product, stones and the remaining water are mixed evenly to obtain the recycled concrete. Compared with ordinary concrete, the above concrete has the characteristics of high strength, good crack resistance and long service life.

[0004] Although the above recycled concrete has obtained good properties such as improved crack resistance, improved fiber dispersion and enhanced cross-linking between recycled coarse aggregates and other components of the concrete by adopting modified polypropylene fibers and plant fibers, and optimizing the ratio and preparation process of each component, there are still deficiencies in its actual application. Specifically, although the recycled coarse aggregates and fibers are mixed, a fiber layer can be coated on the surface of the recycled coarse aggregates, thereby enhancing the strength of the recycled coarse aggregates and improving the adhesion performance between the fibers and the recycled coarse aggregates, but the voids inside the recycled coarse aggregates are still not effectively filled, resulting in a decrease in the overall strength of the concrete. Especially under the action of heavy loads or long-term loads, the existence of voids inside the recycled coarse aggregates will accelerate the destruction process of the concrete, making the above recycled concrete have the problem of insufficient strength. Summary of the Invention

[0005] In view of the technical defects existing in the background art, the present invention provides a high-strength recycled concrete based on construction waste and its preparation method, which solves the above technical problems and meets the actual needs. The specific technical solutions are as follows: A high-strength recycled concrete based on construction waste, by weight, comprises the following raw materials: 80-120 parts of composite modified recycled aggregate, 10-20 parts of fly ash, 10-20 parts of composite glass bead powder, 30-50 parts of portland cement, 20-50 parts of composite reinforcing fiber, 15-25 parts of water, 1-5 parts of carboxymethyl cellulose, and 1-5 parts of water reducer; The composite modified recycled aggregate includes a first modified recycled aggregate with a particle size of 15-25 mm, a second modified recycled aggregate with a particle size of 10-20 mm, and a third modified recycled aggregate with a particle size of 5-15 mm. The mass ratio of the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate is 1:(1-5):(1-2.5). The composite glass bead powder includes a first glass bead powder with a particle size of 200-500 μm, a second glass bead powder with a particle size of 150-250 μm, and a third glass bead powder with a particle size of 100-150 μm. The mass ratio of the first glass bead powder, the second glass bead powder, and the third glass bead powder is (1-2):(3-5):(3-5); The fly ash has a particle size of 30-40 μm, a density of 2.7-3.5 g / m 3 and a strength activity index ≥ 90% and a water demand ratio ≤ 95%.

[0006] As a further technical solution of the present invention, the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate are obtained by impregnating and modifying the crushed waste portland concrete particles with a barium salt-hydroxyapatite mixed solution.

[0007] As a further technical solution of the present invention, the composite reinforcing fiber is obtained by modifying glass fiber and basalt fiber with an amino silane coupling agent and then crosslinking with glutaraldehyde.

[0008] As a further technical solution of the present invention, the water reducer is compounded by a naphthalene-based high-range water reducer and a polycarboxylate superplasticizer, and the mass ratio of the polycarboxylate superplasticizer to the naphthalene-based high-range water reducer is 1:(1-1.5).

[0009] A method for preparing a high-strength recycled concrete based on construction waste, comprising the following steps: S1. Prepare the composite modified recycled aggregate; S11. Put calcium hydroxyphosphate into a planetary ball mill for crushing, and then screen it to obtain calcium hydroxyphosphate powder with a particle size of 10 μm. Put 10 g of calcium hydroxyphosphate powder into 1 L of 0.5 mol / L water-soluble barium salt solution and mix evenly to obtain a barium salt-calcium hydroxyapatite mixture; S12. Crush the waste silicate concrete, perform magnetic separation, impurity removal, and screening treatments. Screen out the first recycled aggregate with a particle size of 15 - 25 mm, the second recycled aggregate with a particle size of 10 - 20 mm, and the third recycled aggregate with a particle size of 5 - 15 mm. Place the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate into corresponding containers respectively, then evacuate, and then add the corresponding amount of barium salt-calcium hydroxyapatite mixture into the corresponding containers, and apply a pressure of 5 - 10 MPa and maintain the pressure application state for 8 - 10 h, so that barium ions and micron-sized calcium hydroxyapatite in the barium salt-calcium hydroxyapatite mixture can penetrate into the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate respectively. Then filter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate, wash them with 5 times the volume of deionized water, and then dry them at 100 °C for 8 - 10 h; S13. Place the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate impregnated with the barium salt-calcium hydroxyapatite mixture in step S12 into corresponding containers respectively, then evacuate, and then add a precipitant solution that can form a precipitate with barium ions into the corresponding containers. The concentration of the precipitant solution is 1.0 mol / L, and apply a pressure of 5 - 10 MPa and maintain the pressure application state for 8 - 10 h, so that the precipitant in the precipitant solution can enter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate and form a barium salt precipitate with barium ions. Then filter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate, wash them with 5 times the volume of deionized water, and then dry them at 120 °C for 5 - 6 h to obtain the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate. Compound the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate according to a mass ratio of 1:(1 - 5):(1 - 2.5) to obtain the prepared composite modified recycled aggregate.

[0010] S2. Prepare composite reinforcing fibers; S21. Add 0.5 - 0.1 part of deionized water and 0.8 - 1 part of amino silane coupling agent to 80 - 100 parts of absolute ethanol in two containers and mix evenly. Then add 4 - 5 parts of glass fiber to one container and 4 - 5 parts of basalt fiber to the other container, and then stir and mix for 6 h, filter, take the precipitate, wash it with absolute ethanol, and finally vacuum dry it at 50 - 60 °C until constant weight to obtain modified glass fiber and modified basalt fiber respectively; S22. Add 8 - 10 parts of modified glass fiber, 1 - 2 parts of modified basalt fiber, and 0.1 - 1 part of glutaraldehyde to 80 - 90 parts of deionized water, then stir and mix at 60 - 70 °C for 24 h, filter, take the precipitate, wash it with deionized water, and finally vacuum dry at 50 - 60 °C until constant weight to obtain composite reinforcing fibers; S3. Prepare recycled concrete; Mix 80 parts of composite modified recycled aggregate, 10 parts of fly ash, 10 parts of composite glass bead powder, 50 parts of portland cement, 20 parts of composite reinforcing fibers, 1 part of carboxymethyl cellulose, and 1 part of water - reducing agent evenly in a mixer, and then add 25 parts of water and stir evenly again to obtain high - strength recycled concrete.

[0011] As a further technical solution of the present invention, in step S11, the barium salt in the water - soluble barium salt solution is any one of barium chloride and barium nitrate.

[0012] As a further technical solution of the present invention, in step S12, the mass ratio of the barium salt - hydroxyapatite mixture to the first recycled aggregate is (10 - 15):1, the mass ratio to the second recycled aggregate is (10 - 15):1, and the mass ratio to the third recycled aggregate is (10 - 15):1.

[0013] As a further technical solution of the present invention, in step S13, the precipitant in the precipitant solution is any one of sodium carbonate and sodium sulfate, and the concentration of the precipitant solution is 1.0 mol / L.

[0014] As a further technical solution of the present invention, in step S13, the mass ratio of the precipitant solution to the first recycled aggregate is (15 - 20):1, the mass ratio to the second recycled aggregate is (15 - 20):1, and the mass ratio to the third recycled aggregate is (15 - 20):1.

[0015] The beneficial effects of the present invention are as follows: The present invention uses waste silicate concrete as the main raw material to prepare recycled aggregate, and at the same time cooperates with fly ash and composite glass bead powder of different particle sizes to further optimize the particle packing structure inside the recycled concrete, reduce internal defects, and improve the overall strength. Through impregnation with the barium salt - hydroxyapatite mixture and subsequent treatment with the precipitant, the micro - cracks and pores inside the recycled aggregate are effectively filled, improving the density and mechanical properties of the recycled aggregate. The composite reinforcing fibers are modified and cross - linked by coupling agents, enabling the recycled concrete to effectively inhibit crack propagation when bearing loads, and enhancing its crack resistance, impact resistance, and toughness. Detailed implementation methods

[0016] The embodiments of the present invention will be described below in conjunction with related embodiments. The embodiments of the present invention are not limited to the following embodiments, and the present invention relates to relevant necessary components in the technical field, which should be regarded as well-known technologies in the technical field and can be known and mastered by those skilled in the technical field.

[0017] A high-strength recycled concrete based on construction waste, in parts by weight, comprises the following raw materials: 80-120 parts of compound modified recycled aggregate, 10-20 parts of fly ash, 10-20 parts of compound glass bead powder, 30-50 parts of portland cement, 20-50 parts of compound reinforcing fiber, 15-25 parts of water, 1-5 parts of carboxymethyl cellulose, and 1-5 parts of water reducing agent; The compound modified recycled aggregate includes a first modified recycled aggregate with a particle size of 15-25 mm, a second modified recycled aggregate with a particle size of 10-20 mm, and a third modified recycled aggregate with a particle size of 5-15 mm. The mass ratio of the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate is 1:(1-5):(1-2.5). The compound glass bead powder includes a first glass bead powder with a particle size of 200-500 μm, a second glass bead powder with a particle size of 150-250 μm, and a third glass bead powder with a particle size of 100-150 μm. The mass ratio of the first glass bead powder, the second glass bead powder, and the third glass bead powder is (1-2):(3-5):(3-5); The fly ash has a particle size of 30-40 μm, a density of 2.7-3.5 g / m 3 and a strength activity index ≥ 90% and a water demand ratio ≤ 95%.

[0018] In terms of raw material composition, the present invention uses waste silicate concrete particles as raw materials, impregnates them with a barium salt-hydroxyapatite mixed solution and treats them with a precipitating agent, so that barium ions and micron-sized hydroxyapatite enter the interior of the aggregate, filling voids or cracks to form barium salt precipitation, effectively enhancing the structural strength of the recycled aggregate, overcoming the defects of low strength and high water absorption of traditional recycled aggregates, and realizing the resource utilization of construction waste. The compound modified recycled aggregate is composed of a first modified recycled aggregate, a second modified recycled aggregate, and a third modified recycled aggregate with different particle sizes. The compound glass bead powder composed of different particle sizes can further optimize the particle packing structure of the concrete, reduce internal defects, and improve the overall strength.

[0019] The composite reinforcing fiber is obtained by modifying glass fiber and basalt fiber with an amino-silane coupling agent and then crosslinking with glutaraldehyde, which can improve the interfacial bonding force between the composite reinforcing fiber and the matrix, inhibit the crack propagation when the concrete bears load, effectively enhance the crack resistance, impact resistance and toughness. The water reducer is compounded by a naphthalene-based superplasticizer and a polycarboxylate superplasticizer, which can reduce the water consumption, ensure the workability of the concrete, improve the strength and durability, and reduce the cost. Carboxymethyl cellulose can improve the water retention and workability of the slurry, ensuring the homogeneity and long-term durability of the concrete.

[0020] As one of the preferred embodiments of the present invention, the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate are obtained by impregnating and modifying the crushed waste silicate concrete particles with a barium salt-hydroxyapatite mixed solution.

[0021] Specifically, barium ions and micron-sized hydroxyapatite in the barium salt-hydroxyapatite mixed solution enter the interior of the recycled aggregate through a negative pressure - positive pressure method, and then an impregnating precipitating agent solution that forms a barium salt precipitate with barium ions is used to fill and repair the voids or cracks inside the recycled aggregate, thereby increasing the structural strength of the recycled aggregate and overcoming the defect of low strength of traditional recycled aggregates.

[0022] Specifically, the composite recycled aggregate selects modified recycled aggregates with multi-level particle sizes, namely the first modified recycled aggregate with a particle size of 25 mm, the second modified recycled aggregate with a particle size of 20 mm, and the third modified recycled aggregate with a particle size of 15 mm, and they are proportioned according to a specific mass ratio of 1:2.5:2.5. At the same time, in combination with the grading scheme of the composite glass beads powder, the first glass beads powder with a particle size of 200 μm, the second glass beads powder with a particle size of 150 μm, and the third glass beads powder with a particle size of 100 μm are compounded according to a mass ratio of 2:5:5, thereby further optimizing the particle packing structure of the recycled concrete, effectively reducing the defects inside the concrete, and thus improving the overall strength of the recycled concrete.

[0023] As one of the preferred embodiments of the present invention, the composite reinforcing fiber is obtained by modifying glass fiber and basalt fiber with an amino-silane coupling agent and then crosslinking with glutaraldehyde.

[0024] The modification treatment with aminosilane coupling agent can change the surface properties of glass fiber and basalt fiber, making their surface have better compatibility and chemical bonding ability with the concrete matrix. After modification, the active groups on the fiber surface can chemically react or physically adsorb with the components in the concrete matrix, thereby enhancing the interfacial bonding force between the fiber and the matrix. Glutaraldehyde cross-linking connects the glass fiber and basalt fiber to form a composite reinforcing fiber with better performance, which can absorb and disperse a large amount of energy when the concrete is subjected to impact load. At the same time, the toughening effect of the composite reinforcing fiber makes the recycled concrete show better deformation ability during the stress process, improves the toughness of the concrete, and makes it safer when subjected to dynamic loads or accidental impacts.

[0025] When recycled concrete is under load, stress concentration will occur inside, causing microcracks. Composite reinforcing fibers have high strength and toughness due to modification and cross-linking treatment, and can play a bridging role in the early stages of crack generation and development. The fibers span across the two ends of the crack, transfer and disperse the stress, and prevent further expansion of the crack. This effective ability to inhibit crack expansion can effectively improve the crack resistance of recycled concrete, reduce the damage to concrete caused by crack expansion, and extend the service life of concrete structures.

[0026] As one of the preferred embodiments of the present invention, the water reducer is compounded by a naphthalene-based high-efficiency water reducer and a polycarboxylic acid high-performance water reducer, and the mass ratio of the polycarboxylic acid high-performance water reducer to the naphthalene-based high-efficiency water reducer is 1: (1-1.5).

[0027] Specifically, the mass ratio of the polycarboxylic acid high-performance water-reducing agent and the naphthalene-based high-efficiency water-reducing agent is 1:1. The polycarboxylic acid high-performance water-reducing agent and the naphthalene-based high-efficiency water-reducing agent have different molecular structures and action mechanisms. The polycarboxylic acid high-performance water-reducing agent can form a three-dimensional adsorption layer on the surface of cement particles, and effectively disperse the cement particles through steric hindrance, while the naphthalene-based high-efficiency water-reducing agent mainly disperses the cement particles through electrostatic repulsion. When the two are compounded, they can play a synergistic role, optimize the water-reducing effect of the water-reducing agent, more effectively reduce the water consumption of the concrete mixture, and improve the strength and durability of the concrete.

[0028] A method for preparing high-strength recycled concrete based on construction waste, comprising the following steps: S1. preparing composite modified recycled aggregate; S11, crushing calcium hydroxyphosphate in a planetary ball mill, and then sieving to obtain calcium hydroxyphosphate powder with a particle size of 10-30 μm, and adding 10 g of calcium hydroxyphosphate powder into 1 L of 0.5 mol / L water-soluble barium salt solution and mixing well to obtain a barium salt-hydroxyapatite lime mixed solution; S12. Crush the waste silicate concrete, perform magnetic separation treatment, impurity removal, and sieving treatment to screen out the first recycled aggregate with a particle size of 15 - 25 mm, the second recycled aggregate with a particle size of 10 - 20 mm, and the third recycled aggregate with a particle size of 5 - 15 mm. Place the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate into corresponding containers respectively, then evacuate the air, and then add the corresponding amount of barium salt-hydroxyapatite mixed solution into the corresponding containers, apply a pressure of 5 - 10 MPa, and maintain the pressure application state for 8 - 10 h, so that barium ions and micron-sized hydroxyapatite in the barium salt-hydroxyapatite mixed solution can penetrate into the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate respectively. Then filter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate, wash with 5 times the volume of deionized water, and then dry at 100 °C for 8 - 10 h; S13. Place the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate impregnated with the barium salt-hydroxyapatite mixed solution in step S12 into corresponding containers respectively, then evacuate the air, and then add a precipitant solution that can form a precipitate with barium ions into the corresponding containers. The concentration of the precipitant solution is 1.0 mol / L, apply a pressure of 5 - 10 MPa, and maintain the pressure application state for 8 - 10 h, so that the precipitant in the precipitant solution can enter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate and form barium salt precipitation with barium ions. Then filter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate, wash with 5 times the volume of deionized water, and then dry at 120 °C for 5 - 6 h to obtain the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate. Mix the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate according to a mass ratio of 1:(1 - 5):(1 - 2.5) to obtain the prepared composite modified recycled aggregate.

[0029] S2. Prepare composite reinforcing fibers; S21. Add 0.5 - 0.1 part of deionized water and 0.8 - 1 part of amino silane coupling agent to 80 - 100 parts of absolute ethanol in two containers respectively and mix evenly. Then add 4 - 5 parts of glass fiber to one container and 4 - 5 parts of basalt fiber to the other container, and then stir and mix for 6 h, filter, take the precipitate, wash with absolute ethanol, and finally vacuum dry at 50 - 60 °C until constant weight to obtain modified glass fiber and modified basalt fiber respectively; S22. Add 8 - 10 parts of modified glass fiber, 1 - 2 parts of modified basalt fiber, and 0.1 - 1 part of glutaraldehyde to 80 - 90 parts of deionized water, and then stir and mix at 60 - 70 °C for 24 h, filter, take the precipitate, wash with deionized water, and finally vacuum dry at 50 - 60 °C until constant weight to obtain composite reinforcing fibers; S3. Prepare recycled concrete; Mix 80 parts of the composite modified recycled aggregate, 10 parts of fly ash, 10 parts of composite glass bead powder, 50 parts of portland cement, 20 parts of composite reinforcing fiber, 1 part of carboxymethyl cellulose, and 1 part of water reducer evenly in a mixer, and then add 25 parts of water and mix evenly again to obtain high-strength recycled concrete.

[0030] In the preparation method of the present invention, through impregnation with a barium salt-hydroxyapatite mixed solution and subsequent treatment with a precipitating agent, the microcracks and pores inside the recycled aggregate are effectively filled. Barium ions and micron-sized hydroxyapatite enter the inside of the recycled aggregate through a negative pressure - pressure method, and the precipitating agent in the precipitating agent solution reacts with barium ions to form a barium salt precipitate, thereby effectively improving the density and mechanical properties of the aggregate and overcoming the defect of low strength of traditional recycled aggregates.

[0031] After the above treatment, the voids or cracks inside the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate are filled and repaired, increasing the structural strength of the recycled aggregate. By using an optimized ratio of multi-level particle size aggregates and combining with the grading design of composite glass bead powder, the particle packing structure of the concrete is further optimized. Aggregates with different particle sizes are matched with each other, reducing the internal defects of the concrete and improving the overall strength.

[0032] The composite reinforcing fiber is modified and cross-linked through a coupling agent, improving the interfacial bonding force between the fiber and the matrix. When the concrete bears load, the fiber can effectively inhibit crack propagation, effectively improving the crack resistance, impact resistance, and toughness of the concrete. The introduction of fly ash and composite glass bead powder optimizes the hydration reaction of the cementitious system, reduces the porosity of the concrete, and improves the impermeability. The addition of carboxymethyl cellulose further improves the water retention and workability of the paste, ensuring the homogeneity and long-term durability of the concrete.

[0033] As one of the preferred embodiments of the present invention, in step S11, the barium salt in the water-soluble barium salt solution is any one of barium chloride and barium nitrate. In step S13, the precipitating agent in the precipitating agent solution is any one of sodium carbonate and sodium sulfate.

[0034] Specifically, in the preparation method of the composite modified recycled aggregate, the barium salt in the water-soluble barium salt solution is barium nitrate, and the precipitating agent in the precipitating agent solution is sodium sulfate.

[0035] Barium chloride and barium nitrate are both barium salts soluble in water and can ionize barium ions in water. When preparing the barium salt-hydroxyapatite mixed solution, the barium ions formed by the dissolution of the barium salt coexist with micron-scale hydroxyapatite in the mixed solution. Through the negative pressure - positive pressure method, barium ions can penetrate into the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate. When a precipitant solution is added subsequently, the barium ions react with the precipitant to form barium salt precipitates, thereby filling the voids or cracks inside the aggregate and increasing the structural strength of the recycled aggregate. Barium chloride and barium nitrate have good solubility and stability, which can ensure a sufficient and stable barium ion concentration when preparing the barium salt-hydroxyapatite mixed solution, helping to ensure that barium ions can fully penetrate into the recycled aggregate during the impregnation process and improving the consistency and reliability of the modification effect.

[0036] The carbonate ions of sodium carbonate and the sulfate ions of sodium sulfate can chemically react with the barium ions that have penetrated into the recycled aggregate in step S11 to form barium carbonate or barium sulfate precipitates respectively. These precipitates can fill the voids or cracks inside the recycled aggregate together with the micron-scale hydroxyapatite particles. At the same time, the formation of barium carbonate or barium sulfate precipitates can fix the position of the micron-scale hydroxyapatite particles in the voids or cracks inside the recycled aggregate, thereby effectively improving the density and mechanical properties of the aggregate. By impregnating the precipitant solution into the recycled aggregate again through the negative pressure - positive pressure method, the precipitant can fully contact and react with the barium ions. This deep repair method can ensure that the microcracks and pores inside the aggregate are effectively filled, overcoming the defects of low strength and high water absorption of traditional recycled aggregates.

[0037] As one of the preferred embodiments of the present invention, in step S12, the mass ratio of the barium salt-hydroxyapatite mixed solution to the first recycled aggregate is (10 - 15):1, the mass ratio to the second recycled aggregate is (10 - 15):1, and the mass ratio to the third recycled aggregate is (10 - 15):1.

[0038] Specifically, the mass ratio of the barium salt-hydroxyapatite mixed solution to the first recycled aggregate is 15:1, the mass ratio to the second recycled aggregate is 10:1, and the mass ratio to the third recycled aggregate is 10:1.

[0039] Recycled aggregates with different particle sizes have different internal structures and pore distributions. The first recycled aggregate has a particle size of 15 - 25 mm, which is relatively large, and there may be more macroscopic pores and cracks inside it; while the second recycled aggregate (10 - 20 mm) and the third recycled aggregate (5 - 15 mm) have smaller particle sizes, and the pore structure is relatively more delicate. By setting different mass ratios, it is possible to better adapt to the characteristics of recycled aggregates with different particle sizes, enabling the barium salt-hydroxyapatite mixed solution to penetrate more effectively into the aggregate.

[0040] As one of the preferred embodiments of the present invention, in step S13, the mass ratio of the precipitant solution to the first recycled aggregate is (15 - 20):1, the mass ratio to the second recycled aggregate is (15 - 20):1, and the mass ratio to the third recycled aggregate is (15 - 20):1; specifically, the mass ratio of the precipitant solution to the first recycled aggregate is 20:1, the mass ratio to the second recycled aggregate is 15:1, and the mass ratio to the third recycled aggregate is 15:1.

[0041] Aggregates of different particle sizes play slightly different roles in recycled concrete. The larger first recycled aggregate plays a role of skeleton support in the concrete. Through a mass ratio of 20:1, more barium salt precipitates are formed inside the first recycled aggregate, improving its density and structural strength. While the second and third recycled aggregates play a role in filling voids and enhancing the overall performance of the concrete, and a mass ratio of 15:1 can specifically improve their performance, enabling them to work better in coordination with other aggregates.

[0042] For the first recycled aggregate, with a mass ratio of 20:1, more precipitant solution can ensure sufficient contact between barium ions and the precipitant, improving the sufficiency of the precipitation reaction, and enabling more barium salt to precipitate inside the aggregate, thereby better repairing its internal defects. For the second and third recycled aggregates, a mass ratio of 15:1 can ensure the effectiveness of the precipitation reaction while avoiding waste and inconvenience in subsequent treatment that may be caused by excessive precipitant solution.

[0043] As one of the preferred embodiments of the present invention, in step S21, the diameter of the glass fiber is 100 - 200 μm, the length is 6 - 12 mm, the tensile strength is 1700 MPa, the tensile elastic modulus is 85 GPa, the diameter of the basalt fiber is 10 - 25 μm, the length is 0.1 - 0.5 mm, the tensile strength is 3200 MPa, the elastic modulus is 96 GPa, and the amino silane coupling agent is selected from at least one of γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

[0044] The amino silane coupling agent can introduce amino groups on the surfaces of the glass fiber and the basalt fiber. The aldehyde groups of glutaraldehyde react with the amino groups introduced on the surfaces of the glass fiber and the basalt fiber respectively. Through the cross-linking action of glutaraldehyde, the basalt fiber can be coated on the surface of the glass fiber to form a composite reinforcing fiber. The composite reinforcing fiber combines the advantages of the glass fiber and the basalt fiber, thereby enabling the formation of a more stable and effective reinforcing network, improving the mechanical properties of the concrete. Through the cross-linked composite reinforcing fiber, the glass fiber and the basalt fiber can work better in coordination. When the concrete bears the load, the two fibers can complement each other and share the stress together, improving the crack resistance, impact resistance, and toughness of the concrete. At the same time, the structure of the composite fiber also helps to reduce the interfacial defects between the fiber and the matrix, improving the reinforcing effect of the fiber.

[0045] Example 1 S1. Preparation of composite modified recycled aggregate Crush the waste silicate concrete and remove impurities by magnetic separation, and screen it into 25 mm (the first recycled aggregate), 20 mm (the second recycled aggregate), and 15 mm (the third recycled aggregate); disperse 10 g of 10 - 30 μm hydroxyapatite powder in 1 L of 0.5 mol / L barium nitrate solution; impregnate the three - stage aggregates respectively according to the mass ratio of 15:1 (mixed liquid / aggregate), treat under vacuum - pressure (8 MPa) conditions for 9 hours, then wash with water and dry; then use 1.0 mol / L sodium sulfate solution to impregnate and treat for the second time according to the mass ratio of 20:1 (solution / aggregate), and pressurize (8 MPa) for 9 hours; after washing with water and drying, obtain the three - stage modified recycled aggregate, and mix and reserve according to the mass ratio of 1:2.5:2.5.

[0046] S2. Preparation of composite reinforcing fiber Modify glass fiber (diameter 150 μm, length 10 mm) and basalt fiber (diameter 20 μm, length 0.3 mm) respectively with γ - aminopropyltrimethoxysilane; add 10 parts of modified glass fiber, 1 part of modified basalt fiber, and 0.5 part of glutaraldehyde to 80 parts of deionized water, then stir and mix at 60 °C for 24 h, filter, wash with deionized water, and finally vacuum - dry at 50 - 60 °C until constant weight to obtain the composite reinforcing fiber; S3. Concrete preparation Raw material ratio (by weight): 100 parts of composite modified recycled aggregate, 15 parts of fly ash (35 μm, water demand ratio 93%), 15 parts of composite glass bead powder (compound the first glass bead powder with a particle size of 200 μm, the second glass bead powder with a particle size of 150 μm, and the third glass bead powder with a particle size of 100 μm according to the mass ratio of 2:5:5), 40 parts of portland cement, 35 parts of composite reinforcing fiber, 8 parts of naphthalene - type + polycarboxylate water - reducing agent (1:1), 3 parts of carboxymethyl cellulose, 20 parts of water. Mix uniformly according to the above raw material ratio to obtain recycled concrete.

[0047] Comparative Example 1 Difference from Example 1: Use unmodified recycled aggregate (without barium salt - hydroxyapatite impregnation and precipitation treatment), and the rest is the same as Example 1.

[0048] Comparative Example 2 Difference from Example 1: Replace the composite reinforcing fiber with an equal amount of unmodified glass fiber (without coupling agent treatment and cross - linking), and the rest is the same as Example 1.

[0049] Comparative Example 3 Difference from Example 1: The composite glass bead powder adopts a single - grading (all 200 μm), and the rest is the same as Example 1.

[0050] Comparative Example 4 Difference from Example 1: Only naphthalene-based water reducer (8 parts) was used, and the rest was the same as in Example 1.

[0051] Comparative Example 5 Difference from Example 1: The aggregate particle size ratio was changed to 1:1:1 (grading optimization was cancelled), and the rest was the same as in Example 1.

[0052] The above Examples 1 and Comparative Examples 1-5 were tested for 28-day compressive strength, 28-day flexural strength, slump, and drying shrinkage rate, and the test results are shown below:

[0053] In the above test data, in Example 1, composite modified recycled aggregates treated by barium salt-hydroxyapatite impregnation and precipitation were used, with a 28-day compressive strength of 68.5 MPa and a 28-day flexural strength of 8.2 MPa; while in Comparative Example 1, unmodified recycled aggregates were used, with a 28-day compressive strength of only 42.3 MPa and a 28-day flexural strength of 5.1 MPa. This shows that the composite modified recycled aggregates can effectively improve the strength and flexural performance of recycled concrete, because the barium salt-hydroxyapatite impregnation and precipitation treatment can fill the voids or cracks inside the recycled aggregates, increase the structural strength of the aggregates, and thus improve the overall mechanical properties of the concrete. In terms of drying shrinkage rate, the drying shrinkage rate of Example 1 was 0.028, while that of Comparative Example 1 was 0.042. It shows that the composite modified recycled aggregates help to reduce the drying shrinkage rate of recycled concrete, reduce the cracks generated by shrinkage of the concrete, and improve the durability of the concrete.

[0054] In the above test data, in Example 1, composite reinforced fibers modified by coupling agent and cross-linked treatment were used, with a 28-day compressive strength of 68.5 MPa and a 28-day flexural strength of 8.2 MPa; in Comparative Example 2, the same amount of unmodified glass fibers was used, with a 28-day compressive strength of 55.1 MPa and a 28-day flexural strength of 6.7 MPa. This shows that through the coupling agent modification and cross-linked treatment of the composite reinforced fibers, the interfacial bonding force between the fibers and the matrix is improved, enabling the concrete to effectively inhibit crack propagation when under load, and effectively enhancing the strength and flexural performance of the concrete.

[0055] In the above test data, in Example 1, a composite glass bead powder (200μm:150μm:100μm = 2:5:5) grading was adopted, with a 28-day compressive strength of 68.5 MPa; in Comparative Example 3, a single grading (all 200μm) composite glass bead powder was adopted, with a 28-day compressive strength of 60.2 MPa. This shows that a reasonable composite glass bead powder grading can optimize the particle packing structure of the concrete, reduce internal defects, and improve the strength of the concrete.

[0056] In the above test data, in Example 1, a naphthalene-based + polycarboxylate water reducer (1:1) was used, and the slump was 180 mm; in Comparative Example 4, only the naphthalene-based water reducer was used, and the slump was 155 mm, indicating that the compounding of water reducers can improve the slump of concrete, improve the workability of concrete, and make the concrete easier to construct.

[0057] In the above test data, in Example 1, an optimized aggregate particle size ratio (1:2.5:2.5) was adopted, and the 28-day compressive strength was 68.5 MPa; in Comparative Example 5, the aggregate particle size ratio was changed to 1:1:1 (canceling the gradation optimization), and the 28-day compressive strength was 58.7 MPa, indicating that a reasonable aggregate particle size ratio can give full play to the advantages of aggregates with different particle sizes and improve the density and strength of concrete.

[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 of this technology, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A high-strength recycled concrete based on construction waste, characterized in that, By weight parts, it includes the following raw materials: 80 - 120 parts of compound modified recycled aggregate, 10 - 20 parts of fly ash, 10 - 20 parts of compound glass bead powder, 30 - 50 parts of portland cement, 20 - 50 parts of compound reinforcing fiber, 15 - 25 parts of water, 1 - 5 parts of carboxymethyl cellulose, and 1 - 5 parts of water reducing agent; The compound modified recycled aggregate includes a first modified recycled aggregate with a particle size of 15 - 25 mm, a second modified recycled aggregate with a particle size of 10 - 20 mm, and a third modified recycled aggregate with a particle size of 5 - 15 mm. The mass ratio of the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate is 1:(1 - 5):(1 - 2.5). The compound glass bead powder includes a first glass bead powder with a particle size of 200 - 500 μm, a second glass bead powder with a particle size of 150 - 250 μm, and a third glass bead powder with a particle size of 100 - 150 μm. The mass ratio of the first glass bead powder, the second glass bead powder, and the third glass bead powder is (1 - 2):(3 - 5):(3 - 5); The particle size of the fly ash is 30 - 40 μm, the density is 2.7 - 3.5 g / m 3 , the strength activity index is ≥ 90%, and the water demand ratio is ≤ 95%.

2. The high-strength recycled concrete based on construction waste according to claim 1, characterized in that, The first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate are obtained by impregnating and modifying the crushed waste portland cement concrete particles with a barium salt - hydroxyapatite mixed solution.

3. A high-strength recycled concrete based on construction waste according to claim 1, characterized in that, The compound reinforcing fiber is obtained by modifying glass fiber and basalt fiber with an amino - silane coupling agent and then cross - linking with glutaraldehyde.

4. A high-strength recycled concrete based on construction waste according to claim 1, characterized in that, The water reducing agent is compounded by a naphthalene - based high - range water reducing agent and a polycarboxylate superplasticizer. The mass ratio of the polycarboxylate superplasticizer to the naphthalene - based high - range water reducing agent is 1:(1 - 1.5).

5. A method for preparing high-strength recycled concrete based on construction waste according to any one of claims 1-4, characterized in that, It includes the following steps: S1. Prepare the compound modified recycled aggregate; S11. Put calcium hydroxyphosphate into a planetary ball mill for crushing, and then screen it to obtain calcium hydroxyphosphate powder with a particle size of 10 - 30 μm. Put 10 g of calcium hydroxyphosphate powder into 1 L of 0.5 mol / L water - soluble barium salt solution and mix evenly to obtain a barium salt - hydroxyapatite mixed solution; S12. Crush the waste portland cement concrete, perform magnetic separation treatment, impurity removal, and screening treatment. Screen out the first recycled aggregate with a particle size of 15 - 25 mm, the second recycled aggregate with a particle size of 10 - 20 mm, and the third recycled aggregate with a particle size of 5 - 15 mm. Put the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate into corresponding containers respectively, then evacuate, and then add the corresponding amount of barium salt - hydroxyapatite mixed solution into the corresponding containers, and apply a pressure of 5 - 10 MPa and maintain the pressurized state for 8 - 10 h, so that barium ions and micron - scale hydroxyapatite in the barium salt - hydroxyapatite mixed solution can penetrate into the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate respectively. Then filter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate, wash them with 5 times the volume of deionized water, and then dry them at 100 °C for 8 - 10 h; S13. Place the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate impregnated with the barium salt-hydroxyapatite mixed solution in step S12 into corresponding containers respectively, then evacuate, and then add a precipitant solution capable of forming a precipitate with barium ions into the corresponding containers. The concentration of the precipitant solution is 1.0 mol / L, apply a pressure of 5 - 10 MPa, and maintain the pressurized state for 8 - 10 h, so that the precipitant in the precipitant solution can enter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate and form barium salt precipitates with barium ions. Then filter the first recycled aggregate, the second recycled aggregate, and the third recycled aggregate, wash with 5 times the volume of deionized water, and then dry at 120 °C for 5 - 6 h to obtain the first modified recycled aggregate, the second modified recycled aggregate, and the third modified recycled aggregate; S2. Prepare composite reinforcing fibers; S21. Add 0.5 - 0.1 part of deionized water and 0.8 - 1 part of amino silane coupling agent to 80 - 100 parts of absolute ethanol in two containers respectively and mix evenly. Then add 4 - 5 parts of glass fibers to one container and 4 - 5 parts of basalt fibers to the other container, and then stir and mix for 6 h, filter, take the precipitate, wash with absolute ethanol, and finally vacuum dry at 50 - 60 °C until constant weight to obtain modified glass fibers and modified basalt fibers respectively; S22. Add 8 - 10 parts of modified glass fibers, 1 - 2 parts of modified basalt fibers, and 0.1 - 1 part of glutaraldehyde to 80 - 90 parts of deionized water, and then stir and mix at 60 - 70 °C for 24 h, filter, take the precipitate, wash with deionized water, and finally vacuum dry at 50 - 60 °C until constant weight to obtain composite reinforcing fibers; S3. Prepare recycled concrete; Mix 80 parts of the composite modified recycled aggregate, 10 parts of fly ash, 10 parts of composite glass bead powder, 50 parts of portland cement, 20 parts of composite reinforcing fibers, 1 part of carboxymethyl cellulose, and 1 part of water reducing agent evenly in a mixer, and then add 25 parts of water and stir evenly again to obtain high-strength recycled concrete.

6. A method for preparing high-strength recycled concrete based on construction waste according to claim 5, characterized in that, In step S11, the barium salt in the water-soluble barium salt solution is any one of barium chloride and barium nitrate.

7. A method for preparing high-strength recycled concrete based on construction waste according to claim 5, characterized in that, In step S12, the mass ratio of the barium salt-hydroxyapatite mixed solution to the first recycled aggregate is (10 - 15):1, the mass ratio to the second recycled aggregate is (10 - 15):1, and the mass ratio to the third recycled aggregate is (10 - 15):

1.

8. A method for preparing high-strength recycled concrete based on construction waste according to claim 5, characterized in that, In step S13, the precipitant in the precipitant solution is any one of sodium carbonate and sodium sulfate, and the concentration of the precipitant solution is 1.0 mol / L.

9. A method for preparing high-strength recycled concrete based on construction waste according to claim 5, characterized in that, In step S13, the mass ratio of the precipitant solution to the first recycled aggregate is (15 - 20):1, the mass ratio to the second recycled aggregate is (15 - 20):1, and the mass ratio to the third recycled aggregate is (15 - 20):1.

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