Reinforced process for recycled concrete fine aggregate and application thereof

Abstract

The application discloses a reinforcing process of recycled concrete fine aggregate and application thereof, and belongs to the technical field of building materials. The reinforcing process comprises the following steps: S1, mixing high-strength grouting material and nano-TiO2 to obtain a large-flow base dilute solution, and then adding a reinforcing functional additive to obtain a reinforcing dilute solution; S2, crushing waste concrete into recycled aggregate, and screening to prepare recycled fine aggregate with a particle size of less than or equal to 5.0 mm; and S3, soaking the recycled fine aggregate in the reinforcing dilute solution prepared in S1, uniformly stirring and sufficiently reinforcing to obtain modified recycled aggregate. The reinforcing functional additive is a mixture of carbon nanotubes or nano-Al2O3 and Al2(SO4)3. The reinforcing process has the advantages of simple operation, low economic cost, good reinforcing effect, special functions such as photocatalysis when applied to mortar, and important significance for actual application of recycled aggregate, optimization of building waste treatment process, and reduction of total carbon emission of the building industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a reinforcing process of recycled concrete fine aggregate and application thereof. BACKGROUND

[0002] The recycled aggregate produced from waste concrete is divided into recycled coarse aggregate and recycled fine aggregate. In the recycled fine aggregate, the content of broken fine cement blocks is large, and the surface of part of the broken sandstone is attached with old cement mortar, which leads to large water absorption rate, rough surface, many corners, and a large number of holes and micro-cracks generated in the secondary crushing process. In addition, there is a weak interface area between the cement mortar attached to the surface of the recycled fine aggregate. Therefore, there is a large gap in performance between the recycled fine aggregate and the natural fine aggregate. The untreated recycled fine aggregate is difficult to apply, thereby generating a large amount of industrial waste and causing waste of social resources.

[0003] At present, the strengthening means of recycled aggregate is mostly for recycled coarse aggregate, and there are few methods specially for fine aggregate. The patent with publication number CN105174766B provides a method for strengthening recycled concrete fine aggregate by using carbon dioxide. The advantage of this method is that when the calcium hydroxide solution or calcium salt solution treatment increases the carbonizable substance content in the recycled aggregate, after carbonization treatment, the formed calcium carbonate effectively fills the microcracks and effectively reduces the porosity of the recycled aggregate, thereby reducing the aggregate crushing value and reducing the water absorption of the aggregate. However, the sealed carbonization box is usually batch operation, and the capacity is limited, which is difficult to meet the processing needs of "large-scale and continuous" of construction waste recycled fine aggregate. The patent with publication number CN112047654B provides a method for strengthening recycled fine aggregate by using bacillus pasteurii DSM33. The advantage of this method is that it fully utilizes the components in the culture medium and the urease produced by bacteria, so that the calcium carbonate CaCO3 precipitated by bacteria induction is fully deposited on the recycled aggregate defects and old mortar layer, thereby achieving the purpose of strengthening the recycled fine aggregate old mortar and repairing microcracks, reducing the water absorption of the recycled aggregate and improving the quality of the recycled aggregate. However, this method needs to configure the proliferation culture medium, sterilization, inoculation and culture, and the whole process is relatively complicated. From the configuration of the culture medium to the recycled fine aggregate after one-time strengthening, it needs to go through multiple culture and standing processes, which consumes a lot of time and is not conducive to large-scale and rapid production. The patent with publication number CN107129235B provides a method for strengthening recycled concrete by using graphene oxide. This patent is simple to operate, and the abundant sheet structure of graphene oxide has a large number of oxygen-containing active groups to provide growth points for the hydration products of cement; it plays a template effect for the hydration of concrete, and improves the mechanical properties and durability of recycled concrete. However, when the graphene oxide content exceeds a certain range, it may cause the frost resistance and other durability indicators of concrete to decrease due to its water absorption and agglomeration phenomenon. Therefore, it is urgent to develop a strengthening process and application technology for recycled concrete fine aggregate to solve the problems of long processing cycle, unstable strengthening effect and difficulty in meeting the engineering performance requirements of recycled fine aggregate in the prior art. SUMMARY

[0004] The present application provides a strengthening process and application of recycled concrete fine aggregate, aiming to solve the problems of long processing cycle, unstable strengthening effect and difficulty in meeting the engineering performance requirements of recycled fine aggregate in the prior art.

[0005] The object of the present application can be achieved by the following technical solutions:

[0006] In a first aspect, the present application provides a strengthening process for recycled concrete fine aggregate, comprising the following steps:

[0007] S1, mixing high-strength grouting material and nano-TiO2 to obtain a large flow base dilute solution, then adding a reinforcing functional additive to obtain a reinforced dilute solution;

[0008] S2, crushing and processing waste concrete into recycled aggregate, screening, and preparing recycled fine aggregate with a particle size of ≤5.0 mm;

[0009] S3, soaking the recycled fine aggregate in S2 in the reinforced dilute solution prepared in S1, stirring uniformly and sufficiently reinforcing to obtain modified recycled aggregate;

[0010] The reinforcing functional additive is a mixture of carbon nanotubes or nano-Al2O3 and Al2(SO4)3;

[0011] The carbon nanotubes are also subjected to modification treatment to obtain modified carbon nanotubes, and the specific preparation method is as follows:

[0012] A1, adding carbon nanotubes to deionized water, ultrasonic dispersion for 10-20 min, adding Tris-HCl buffer solution with pH=8.5, then adding hydrochloric acid dopamine, stirring for 6-8 h, centrifugation, washing, and drying to obtain PDA@carbon nanotubes;

[0013] A2, adding PDA@carbon nanotubes to anhydrous ethanol, ultrasonic dispersion for 60-80 min, then adding aminosilica cage, reacting at 50-60°C for 18-24 h, washing, and drying to obtain modified carbon nanotubes.

[0014] Further, in step S1, the water-binder ratio in the high-strength grouting material is (0.35-2):1;

[0015] The functional components in the high-strength grouting material include the following raw materials by weight: SAC 42.5 sulphoaluminate cement 65 parts, anhydrous gypsum 8 parts, silica fume 10 parts, 200 mesh quartz powder 40 parts, polycarboxylic acid type water reducer 2 parts, polyether modified polysiloxane powder defoamer 0.5 parts, retarding agent tartaric acid 0.1 parts, vinyl acetate-ethylene copolymer 4.5 parts.

[0016] Further, in step S1, the mass of nano-TiO2 accounts for 1-5% of the mass of the large flow base dilute solution;

[0017] When the reinforcing functional additive is carbon nanotubes, the mass of the carbon nanotubes accounts for 0.05%-2% of the mass of the reinforced dilute solution;

[0018] When the reinforcing functional additive is a mixture of nano-Al2O3 and Al2(SO4)3, the mass of nano-Al2O3 in the mixture of nano-Al2O3 and Al2(SO4)3 accounts for 2% of the mass of the reinforced dilute solution, and the mass of nano-Al2(SO4)3 accounts for 1% of the mass of the reinforced dilute solution.

[0019] Further, in step A1, the use amount ratio of the carbon nanotube, deionized water, dopamine hydrochloride and Tris-HCl buffer solution is 3g: 300mL: 0.1-0.2g: 50-70mL.

[0020] Further, in step A2, the mass ratio of the PDA@carbon nanotube and the aminated cage-type silsesquioxane is 8: (0.5-1.5); the use amount of the anhydrous ethanol is 10-13 times of the mass of the PDA@carbon nanotube.

[0021] Further, the specific step of step S3 is: air-drying the recycled fine aggregate, and controlling the water content to be less than or equal to 10%, to obtain dry recycled aggregate; and strengthening by using the first mode or the second mode.

[0022] The first mode comprises: placing the dry recycled aggregate in a sealed environment with a vacuum degree less than or equal to 0.01 MPa, directly adding the strengthening dilute solution, and synchronously stirring until the two are fully contacted.

[0023] The second mode comprises: under normal temperature and pressure, spraying the strengthening dilute solution on the dry recycled aggregate while stirring, and stirring for 2-5 min to ensure that the dry recycled aggregate is fully infiltrated and strengthened; after the strengthening, the modified recycled aggregate is air-dried for 1-24 h for standby or directly put into use; and the mass ratio of the dry recycled aggregate and the strengthening dilute solution is 3:2.

[0024] In a second aspect, the application provides application of the modified recycled aggregate obtained by the strengthening process according to any one of the above-mentioned contents to a raw material of concrete.

[0025] The application has at least the following beneficial effects:

[0026] 1. The application provides a strengthening process for recycled concrete fine aggregate, and after the strengthening, the water absorption rate of the recycled aggregate is significantly reduced, and the mechanical properties of the recycled fine aggregate cement mortar are improved, and the specific steps are as follows: firstly, taking high-strength grouting material and nano-TiO2 as a base to ensure the fluidity and basic strength of the solution, adding a strengthening functional additive, and selecting a carbon nanotube or a mixed system of nano-Al2O3 and Al2(SO4)3 to give the solution excellent interfacial bonding and strengthening capacity, thereby laying a functional foundation for subsequent aggregate modification; then, crushing and screening the waste concrete, and accurately controlling the particle size to be less than or equal to 5.0 mm, so as to realize the resource utilization of solid waste, ensure the uniformity of the fine aggregate grading, and avoid the influence of uneven particle size on subsequent infiltration and the final performance of the concrete; finally, infiltrating the fine aggregate in the strengthening dilute solution and stirring to make the solution fully penetrate the pores of the aggregate, and repairing the defects of the aggregate and improving the interfacial bonding force by means of the action of the nano components and the additive in the solution, so as to finally obtain the modified aggregate with improved performance, and improve the overall strength and water absorption rate of the recycled concrete.

[0027] 2. This invention creatively mixes high-strength grouting material and nano-TiO2 to obtain a highly fluid dilute solution, then adds a reinforcing functional additive to obtain a reinforced dilute solution. The reinforcing functional additive is carbon nanotubes or a mixture of nano-Al2O3 and Al2(SO4)3. Nano-TiO2 can increase the CSH gel content, and the TiO2 nanoparticles fill the micropores and cracks in the recycled fine aggregate, improving the compressive strength of cement mortar, reducing its water absorption rate, and exposing clean sites on the surface of the recycled fine aggregate, thus improving the anchoring efficiency of subsequent nanomaterials and further enhancing the overall performance of cement mortar. The high-strength grouting material contains water-reducing and densifying components, which, combined with the nano-dispersion, form a highly fluid and compatible system, facilitating penetration. Carbon nanotubes optimize the CSH structure by adjusting the calcium ion distribution, enhancing mechanical properties. Nano-Al2O3 and Al2(SO4)3 synergistically play the roles of physical filling and chemical gel generation, achieving gradient reinforcement, avoiding excessive expansion, and comprehensively improving the strength, interfacial bonding, and durability of the recycled aggregate.

[0028] 3. Based on carbon nanotubes, this invention further modifies the carbon nanotubes. The modified carbon nanotubes exhibit strong bonding with raw materials and recycled fine aggregates, thereby improving the compressive strength of cement mortar. Furthermore, the modified carbon nanotubes of this invention contain cage-like silsesquioxanes, which can further enhance the compressive strength of cement mortar and reduce its water absorption rate.

[0029] 4. The strengthening process of recycled concrete fine aggregate described in this invention can effectively transform construction waste into building materials that meet certain construction requirements. The strengthening process is simple and easy to implement, environmentally friendly, and economically cost-effective. Furthermore, the recycled aggregate described in this invention can have different concentrations of nano-TiO2 added to the strengthening base liquid according to the functional requirements of the mortar, enabling the prepared mortar to possess special functionalities. For example, TiO2 can adsorb and decompose volatile organic pollutants such as formaldehyde, thereby improving indoor air quality. Attached Figure Description

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] Figure 1 This is a scanning electron microscope image of the modified recycled aggregate obtained in Example 1 of the present invention;

[0032] Figure 2 This is a scanning electron microscope image of the recycled fine aggregate of the present invention. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0034] A process for strengthening fine aggregates in recycled concrete includes the following steps:

[0035] S1. Mix high-strength grouting material and nano-TiO2 to obtain a high-flow-rate substrate dilute solution, and then add a reinforcing functional additive to obtain a reinforcing dilute solution;

[0036] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0037] S3. The recycled fine aggregate in S2 is immersed in the strengthening dilute solution prepared in S1, stirred evenly and fully strengthened to obtain modified recycled aggregate.

[0038] The enhanced functional additive is carbon nanotubes or a mixture of nano-Al2O3 and Al2(SO4)3;

[0039] The carbon nanotubes are further modified to obtain modified carbon nanotubes, and the specific preparation method is as follows:

[0040] A1. Add carbon nanotubes to deionized water, sonicate for 10-20 min, add Tris-HCl buffer solution with pH=8.5, then add dopamine hydrochloride, stir for 6-8 h, centrifuge, wash, and dry to obtain PDA@carbon nanotubes.

[0041] By employing the above-mentioned technical solution, the addition of carbon nanotubes can improve the mechanical properties of recycled aggregates. However, carbon nanotubes have a large specific surface area and are prone to agglomeration. Direct addition to a dilute reinforcing solution results in poor dispersibility, hindering their reinforcing effect. Therefore, this invention modifies the carbon nanotubes in addition to their addition. By coating the surface of the carbon nanotubes with PDA (polydopamine), the steric hindrance effect can reduce the agglomeration of the carbon nanotubes, thus facilitating their reinforcing effect. Furthermore, PDA has strong adhesive properties, which can enhance the bonding force between the modified carbon nanotubes and raw materials such as nano-TiO2 and high-strength grouting materials, as well as their bonding force with recycled fine aggregates, forming an adhesive network and thereby comprehensively improving the mechanical properties of cement mortar.

[0042] A2. PDA@carbon nanotubes were added to anhydrous ethanol and ultrasonically dispersed for 60-80 min. Then, amino-modified cage-type silsesquioxane was added and reacted at 50-60℃ for 18-24 h. After washing and drying, modified carbon nanotubes were obtained.

[0043] To further improve the performance of PDA@carbon nanotubes, this invention utilizes the catechol groups on the polydopamine layer as secondary reaction sites to react with the amino groups of aminated cage-like silsesquioxanes, thereby obtaining modified carbon nanotubes. Cage-like silsesquioxanes are inorganic-organic hybrid materials with nanostructures that can synergistically fill the micropores and cracks in raw fine aggregates with components such as nano-TiO2, improving the mechanical properties of the aggregates. Experiments also demonstrate that cage-like silsesquioxanes can reduce the water absorption rate of the final cement mortar.

[0044] Recycled fine aggregate mainly consists of blocks of original cement paste from waste concrete or crushed sand and gravel with old cement mortar adhering to their surface. Its main components are cement hydration products such as CSH, Ca(OH)2, and AFt, as well as incompletely reacted cement particles. The enhanced dilute solution uses high-strength grout as a matrix, introducing nano-sized chemical ions to fully penetrate the pores or cracks in the cement paste, causing a chemical reaction that generates precipitates that fill the aggregate voids. The high-strength grout contains water-reducing components, densifying components, expanding components, and ultrafine powders. Combined with other nano-dispersions, a uniform dispersion with fluidity close to water and full compatibility with cement mortar can be prepared. Furthermore, nano-TiO2 can penetrate into the interior of the recycled fine aggregate with the aqueous solution, promoting cement hydration reaction, increasing CSH gel content, and simultaneously filling the micropores and cracks in the recycled fine aggregate. Nano-TiO2 also possesses photocatalytic properties; under light irradiation, the oxide species generated on its surface react with organic pollutants, degrading them. By adding nano-TiO2, organic contaminants adhering to the surface of oxidized aggregates are removed, exposing clean sites on the surface of recycled fine aggregates and improving the anchoring efficiency of subsequent nanomaterials. Carbon nanotubes have the ability to regulate calcium ion distribution; by optimizing CSH stacking and reducing slip, they enhance CSH cohesion and improve the mechanical properties of recycled aggregates. Nano-Al2O3 particles have a small particle size and can fill microcracks and pores on the surface of recycled aggregates, reducing water absorption, but their strengthening effect is relatively weak. Al2(SO4)3 can participate in cement hydration reactions, generating AFt and CASH gels to fill microcracks and internal pores on the surface of recycled fine aggregates, but excessive use can lead to expansion and damage of the recycled fine aggregate cement mortar. By using a mixture of nano-Al2O3 dispersion and Al2(SO4)3, a synergistic effect of physical compaction and chemical expansion is achieved, realizing a gradient strengthening of "first compaction, then expansion" at the microscopic level, significantly improving the strength, interfacial adhesion, and durability of recycled aggregates.

[0045] In some embodiments, the water-cement ratio in the high-strength grout is (0.35-2):1;

[0046] The functional components of the high-strength grout include the following raw materials in parts by weight: 65 parts SAC 42.5 sulfoaluminate cement, 8 parts anhydrous gypsum, 10 parts silica fume, 40 parts 200-mesh quartz powder, 2 parts polycarboxylate superplasticizer, 0.5 parts polyether-modified polysiloxane powder defoamer, 0.1 parts tartaric acid retarder, and 4.5 parts vinyl acetate-ethylene copolymer. This water-cement ratio can be adapted to different scenarios, balancing strength, flowability, and cost to meet diverse grouting needs.

[0047] In some embodiments, the mass of the nano-TiO2 accounts for 1 to 5% of the mass of the dilute solution in the high-flow substrate. This proportion ensures that the nano-TiO2 can fully penetrate the micropores of the recycled fine aggregate, repairing the microcracks in the aggregate through physical filling and reducing water absorption. At the same time, its surface-active groups can oxidize organic pollutants on the aggregate surface, exposing clean bonding sites and improving the interfacial bonding force with high-strength grouting materials and reinforcing functional additives, laying the foundation for overall strength improvement.

[0048] When the reinforcing functional additive is carbon nanotubes, the mass of the carbon nanotubes accounts for 0.05% to 2% of the mass of the reinforcing dilute solution; an addition of as low as 0.05% can utilize the high aspect ratio of carbon nanotubes to construct a "three-dimensional mechanical support network" and improve the flexural strength and crack resistance of recycled aggregates; the upper limit of 2% can avoid the problem of uneven dispersion caused by carbon nanotube agglomeration, achieving a balance between "cost control" and "mechanical enhancement effect".

[0049] When the reinforcing functional additive is a mixture of nano-Al2O3 and Al2(SO4)3, the mass of nano-Al2O3 in the mixture accounts for 2% of the mass of the reinforcing dilute solution, and the mass of nano-Al2(SO4)3 accounts for 1% of the mass of the reinforcing dilute solution. 2% nano-Al2O3 can physically fill the fine pores in the aggregate that are not covered by nano-TiO2, further improving density; 1% Al2(SO4)3 can react with Ca(OH)2 in the high-strength grout to generate CASH gel, chemically binding the aggregate interface and solving the problem of weak transition zone between recycled aggregate and cementitious material; the 2:1 mass ratio of the two achieves a gradient reinforcement of "physical filling first, then chemical binding," avoiding the defects of limited reinforcing effect of single nano-Al2O3 and easy expansion caused by single Al2(SO4)3, significantly improving the compressive strength and durability of the aggregate.

[0050] In some embodiments, in step A1, the ratio of carbon nanotubes, deionized water, dopamine hydrochloride, and Tris-HCl buffer is 3g:300mL:0.1-0.2g:50-70mL. By precisely controlling the ratio of dopamine hydrochloride to carbon nanotubes, a uniform and moderately thick PDA coating can be formed on the surface of the carbon nanotubes. The Tris-HCl buffer (50-70mL) maintains the optimal dopamine self-polymerization environment at pH=8.5, and 300mL of deionized water ensures effective ultrasonic dispersion, ultimately achieving efficient introduction of active groups onto the surface of the carbon nanotubes, laying the foundation for subsequent grafting modification.

[0051] In some embodiments, in step A2, the mass ratio of PDA@carbon nanotubes to aminated cage-like silsesquioxane is 8:(0.5-1.5); the amount of anhydrous ethanol used is 10-13 times the mass of PDA@carbon nanotubes. By precisely controlling the amount of aminated cage-like silsesquioxane, cage-like structures can be appropriately grafted onto the surface of the PDA coating, avoiding excessive amounts that lead to agglomeration or insufficient amounts that affect the modification effect.

[0052] In some embodiments, step S3 specifically involves: air-drying the recycled fine aggregate, controlling the moisture content to ≤10%, to obtain dried recycled aggregate; and strengthening it using either the first or second method.

[0053] The first method includes: placing the dried recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, directly adding the strengthening dilute solution, and simultaneously stirring until the two are fully in contact;

[0054] The second method includes: spraying a strengthening dilute solution onto the dried recycled aggregate while stirring for 2-5 minutes at room temperature and pressure to ensure it is fully impregnated and strengthened; after strengthening, air-drying the modified recycled aggregate for 1-24 hours for later use, or putting it directly into use; the mass ratio of the dried recycled aggregate to the strengthening dilute solution is 3:2. By controlling the moisture content of the recycled fine aggregate to ≤10%, moisture is avoided from interfering with the strengthening effect. Matching the aggregate and strengthening liquid at a mass ratio of 3:2 ensures sufficient strengthening; a vacuum environment (≤0.01MPa) can promote the penetration of the strengthening liquid into the pores of the aggregate, and spraying and stirring at room temperature (2-5 minutes) ensures uniform impregnation. Both methods allow the strengthening liquid (containing nano-components, modified carbon nanotubes, etc.) to fully act on the aggregate. Subsequent air drying (1-24 hours) or direct use takes into account operational flexibility, ultimately effectively improving the activity, density, and bonding force with the matrix of the recycled aggregate.

[0055] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0056] The specific information of the raw materials used in the embodiments and comparative examples of this invention is as follows:

[0057] The high-strength grout in this invention is a full-powder high-strength grout with a particle size of <80um, a 28-day compressive strength of ≥60MPa at a water-cement ratio of 0.25±0.05, a neat grout flowability of ≥400mm, and no segregation;

[0058] The average particle size of nano-TiO2 is 20 nm;

[0059] The carbon nanotubes are single-walled carbon nanotubes with a diameter of 1 nm;

[0060] The nano-Al2O3 has an α-phase crystal form, an average particle size of 30 nm, and an Al2(SO4)3 purity of AR≥99.0%.

[0061] Preparation Example 1

[0062] In this preparation example, the carbon nanotubes underwent modification treatment. The specific preparation method is as follows:

[0063] A1. Add 3g of carbon nanotubes to 300mL of deionized water, sonicate for 10min, add 60mL of Tris-HCl buffer solution with pH=8.5, add 0.1g of dopamine hydrochloride, stir for 6h, centrifuge, wash, and dry to obtain PDA@carbon nanotubes.

[0064] A2. Add 8g of PDA@carbon nanotubes to 80mL of anhydrous ethanol and sonicate for 60min. Then add 0.5g of amino-modified cage-type silsesquioxane and react at 50℃ for 18h. Wash and dry to obtain modified carbon nanotubes.

[0065] Preparation Example 2

[0066] In the preparation example, the carbon nanotubes underwent modification treatment. The specific preparation method is as follows:

[0067] A1. Add 3g of carbon nanotubes to 300mL of deionized water, sonicate for 20min, add 60mL of Tris-HCl buffer solution with pH=8.5, add 0.2g of dopamine hydrochloride, stir for 8h, centrifuge, wash, and dry to obtain PDA@carbon nanotubes.

[0068] A2. Add 8g of PDA@carbon nanotubes to 80mL of anhydrous ethanol and sonicate for 80min. Then add 1.5g of amino-modified cage-type silsesquioxane and react at 60℃ for 24h. Wash and dry to obtain modified carbon nanotubes.

[0069] Compare with Example 1

[0070] The only difference between this comparative example and preparation example 1 is that the amount of amino-encapsulated silsesquioxane was adjusted from "0.5g" to "0.4g".

[0071] Compare with Example 2

[0072] The only difference between this comparative example and preparation example 2 is that the amount of amino-encapsulated silsesquioxane was adjusted from "1.5g" to "1.6g".

[0073] Compare with Example 3

[0074] The only difference between this comparative example and preparation example 1 is that the aminated cage-type silsesquioxane is omitted. The specific steps are as follows:

[0075] Add 3g of carbon nanotubes to 300mL of deionized water, sonicate for 10min, then add 60mL of Tris-HCl buffer solution (pH=8.5), add 0.1g of dopamine hydrochloride, stir for 6h, centrifuge, wash, and dry to obtain modified carbon nanotubes.

[0076] Example 1

[0077] This embodiment provides a process for strengthening fine aggregates in recycled concrete, including the following steps:

[0078] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer. Add nano-TiO2 and mix for 2 minutes to obtain a highly fluid base dilute solution. The mass of nano-TiO2 accounts for 5% of the mass of the highly fluid base dilute solution. Then, add carbon nanotubes to prepare a reinforced dilute solution. The mass of carbon nanotubes accounts for 0.05% of the mass of the reinforced dilute solution.

[0079] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0080] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0081] Example 2

[0082] This embodiment provides a process for strengthening fine aggregates in recycled concrete, including the following steps:

[0083] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer. Add nano-TiO2 and mix for 2 minutes to obtain a highly fluid substrate dilute solution. The mass of nano-TiO2 accounts for 5% of the mass of the highly fluid substrate dilute solution. Then, add carbon nanotubes to prepare a reinforced dilute solution. The mass of carbon nanotubes accounts for 2% of the mass of the reinforced dilute solution.

[0084] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0085] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0086] Example 3

[0087] This embodiment provides a process for strengthening fine aggregates in recycled concrete, including the following steps:

[0088] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer to obtain a highly fluid base dilute solution. The mass of nano-TiO2 accounts for 5% of the mass of the highly fluid base dilute solution. Then, a mixture of nano-Al2O3 and Al2(SO4)3 is added to prepare a reinforced dilute solution. The mass of nano-Al2O3 in the mixture of nano-Al2O3 and Al2(SO4)3 accounts for 2% of the mass of the reinforced dilute solution, and the mass of nano-Al2(SO4)3 accounts for 1% of the mass of the reinforced dilute solution.

[0089] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0090] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0091] Example 4

[0092] The only difference between this embodiment and Example 2 is that the modified carbon nanotubes obtained in Example 1 are used to replace the carbon nanotubes in Example 2.

[0093] Example 5

[0094] The only difference between this embodiment and Example 2 is that the modified carbon nanotubes obtained in Example 2 are used to replace the carbon nanotubes in Example 2 in an equal amount.

[0095] Comparative Example 1

[0096] The only difference between this comparative example and Example 4 is that the "carbon nanotubes obtained in Preparation Example 1" in Example 4 are replaced with an equal amount of "modified carbon nanotubes obtained in Comparative Example 1".

[0097] Comparative Example 2

[0098] The only difference between this comparative example and Example 5 is that the carbon nanotubes obtained in Example 2 of Example 5 were replaced with an equal amount of the modified carbon nanotubes obtained in Comparative Example 2.

[0099] Comparative Example 3

[0100] Compared with Example 4, this comparative example uses "modified carbon nanotubes obtained in Comparative Example 3" instead of "carbon nanotubes obtained in Preparation Example 1" in Example 4.

[0101] Comparative Example 4

[0102] The only difference between this comparative example and Example 1 is that carbon nanotubes are omitted. The specific steps are as follows:

[0103] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer. Add nano-TiO2 and mix for 2 minutes to obtain a reinforced dilute solution. The mass of nano-TiO2 accounts for 5% of the mass of the reinforced dilute solution.

[0104] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0105] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0106] Comparative Example 5

[0107] The only difference between this comparative example and Example 1 is that nano-TiO2 is omitted. The specific steps are as follows:

[0108] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer. Then, carbon nanotubes are added to prepare a reinforced dilute solution. The mass of carbon nanotubes accounts for 0.05% of the mass of the reinforced dilute solution.

[0109] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0110] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0111] Comparative Example 6

[0112] The only difference between this comparative example and Example 3 is that nano-TiO2 is omitted. The specific steps are as follows:

[0113] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer. Then, add a mixture of nano-Al2O3 and Al2(SO4)3 to prepare a reinforced dilute solution. The mass of nano-Al2O3 in the mixture of nano-Al2O3 and Al2(SO4)3 accounts for 2% of the mass of the reinforced dilute solution, and the mass of nano-Al2(SO4)3 accounts for 1% of the mass of the reinforced dilute solution.

[0114] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0115] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0116] Comparative Example 7

[0117] This comparative example and a process for strengthening fine aggregates in recycled concrete include the following steps:

[0118] S1. Mix high-strength grout with water at a water-cement ratio of 2:1 and stir for 3 minutes. The functional components of the high-strength grout include the following raw materials by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer, to prepare a reinforced dilute solution.

[0119] S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared.

[0120] S3. Air-dry the recycled fine aggregate until the moisture content is less than 10% to obtain dry recycled aggregate; place the dry recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, add the strengthening dilute solution directly, stir for 5 minutes and use directly to obtain modified recycled aggregate. The mass ratio of dry recycled aggregate to strengthening dilute solution is 3:2.

[0121] The modified recycled aggregates prepared in Examples 1-5 and Comparative Examples 1-7 were used to replace standard sand at a mass substitution rate of 50% as aggregate components in cement mortar. A blank control group was also set up, in which no modified recycled aggregates were added and the mass substitution rate of standard sand was 0%.

[0122] Based on the design strength grade of cement mortar, and in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar", P·Ⅱ52.5 silicate cement and ISO standard sand were used to prepare standard cement mortar samples with a water-cement ratio of 0.5 and a mortar-sand ratio of 1:3. A set of three 40×40×160mm samples was produced. 3 Cement mortar specimens were prepared. After standard curing for 1 day, the specimens were demolded and placed in water at 20±2℃ for standard curing for 28 days. The compressive strength, flexural strength, crushing index, and saturated surface-dry water absorption rate were tested according to standard methods, referring to GB / T 14684-2022.

[0123] Table 1

[0124]

[0125] Note: In Table 1, " / " indicates that no reinforcement dilute solution was added.

[0126] As can be seen from Table 1, the cement mortars obtained in Examples 1-5 have excellent overall performance.

[0127] Data from Examples 1 and 2, and Examples 4 and 5 show that further modification of carbon nanotubes can improve the mechanical properties of cement mortar and reduce its saturated surface-dry water absorption rate. This indicates that the modified carbon nanotubes have a strong bonding force with the raw materials and recycled fine aggregates, thus improving the compressive strength of the cement mortar. Furthermore, the modified carbon nanotubes of this invention have a POSS structure, which can further improve the compressive strength of the cement mortar and reduce its water absorption rate.

[0128] Based on the test results of Comparative Examples 1 and 2, and Examples 4 and 5, it can be seen that too little or too much aminocage-type silsesquioxane will affect the overall performance of the final sample, indicating that the amount of aminocage-type silsesquioxane added in this invention is the optimal amount.

[0129] The test results of Comparative Example 3 and Example 4 show that cage-type silsesquioxane is an inorganic-organic hybrid material with a nanostructure. It can work with components such as nano-TiO2 to fill the micropores and cracks in raw fine aggregates, thereby improving the mechanical properties of the aggregates. Experiments also confirm that cage-type silsesquioxane can reduce the water absorption rate of the final cement mortar.

[0130] The test results of Comparative Examples 4-7 show that omitting any one or more of the strengthening dilute solutions will affect the overall performance of the sample and reduce its overall performance.

[0131] Depend on Figure 1 and Figure 2 It can be seen that the modified aggregate sample obtained in Example 1 has significantly smaller gaps compared to the recycled fine aggregate (which was not modified by a dilute strengthening solution, but was directly processed from waste concrete into recycled aggregate, screened, and prepared into recycled fine aggregate with a particle size ≤5.0mm), indicating that the gaps were filled.

[0132] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A process for strengthening fine aggregates in recycled concrete, characterized in that, Includes the following steps: S1. Mix high-strength grouting material and nano-TiO2 to obtain a high-flow-rate substrate dilute solution, and then add a reinforcing functional additive to obtain a reinforcing dilute solution; S2. The waste concrete is crushed and processed into recycled aggregate, screened, and recycled fine aggregate with a particle size ≤5.0mm is prepared. S3. The recycled fine aggregate in S2 is immersed in the strengthening dilute solution prepared in S1, stirred evenly and fully strengthened to obtain modified recycled aggregate. The enhanced functional additive is carbon nanotubes or a mixture of nano-Al2O3 and Al2(SO4)3; The carbon nanotubes are further modified to obtain modified carbon nanotubes. The specific preparation method is as follows: A1. Add carbon nanotubes to deionized water, ultrasonically disperse for 10-20 min, add Tris-HCl buffer solution with pH=8.5, then add dopamine hydrochloride, stir for 6-8 h, centrifuge, wash, and dry to obtain PDA@carbon nanotubes. A2. PDA@carbon nanotubes were added to anhydrous ethanol and ultrasonically dispersed for 60-80 min. Then, amino-modified cage-type silsesquioxane was added and reacted at 50-60℃ for 18-24 h. After washing and drying, modified carbon nanotubes were obtained.

2. The strengthening process of recycled concrete fine aggregate according to claim 1, characterized in that, In step S1, the water-cement ratio in the high-strength grout is (0.35~2):1; The functional components of the high-strength grout include the following raw materials in parts by weight: 65 parts of SAC 42.5 sulfoaluminate cement, 8 parts of anhydrous gypsum, 10 parts of silica fume, 40 parts of 200-mesh quartz powder, 2 parts of polycarboxylate superplasticizer, 0.5 parts of polyether-modified polysiloxane powder defoamer, 0.1 parts of tartaric acid retarder, and 4.5 parts of vinyl acetate-ethylene copolymer.

3. The strengthening process for recycled concrete fine aggregate according to claim 1, characterized in that, The mass of the nano-TiO2 accounts for 1 to 5% of the mass of the dilute solution in the high-flow substrate.

4. The strengthening process of recycled concrete fine aggregate according to claim 1, characterized in that, When the reinforcing functional additive is carbon nanotube, the mass of the carbon nanotube accounts for 0.05% to 2% of the mass of the reinforcing dilute solution.

5. The strengthening process for recycled concrete fine aggregate according to claim 1, characterized in that, When the enhancing functional additive is a mixture of nano-Al2O3 and Al2(SO4)3, the mass of nano-Al2O3 in the mixture of nano-Al2O3 and Al2(SO4)3 accounts for 2% of the mass of the enhancing dilute solution, and the mass of nano-Al2(SO4)3 accounts for 1% of the mass of the enhancing dilute solution.

6. The strengthening process for recycled concrete fine aggregate according to claim 1, characterized in that, In step A1, the ratio of carbon nanotubes, deionized water, dopamine hydrochloride, and Tris-HCl buffer is 3g:300mL:0.1-0.2g:50-70mL.

7. The strengthening process for recycled concrete fine aggregate according to claim 1, characterized in that, In step A2, the mass ratio of PDA@carbon nanotubes to aminated cage-type silsesquioxane is 8:(0.5-1.5); the amount of anhydrous ethanol used is 10-13 times the mass of PDA@carbon nanotubes.

8. The strengthening process for recycled concrete fine aggregate according to claim 1, characterized in that, The specific steps of step S3 are as follows: air-dry the recycled fine aggregate, control the moisture content to ≤10%, and obtain dried recycled aggregate; strengthen it using the first method or the second method. The first method includes: placing the dried recycled aggregate in a closed environment with a vacuum degree ≤0.01MPa, directly adding the strengthening dilute solution, and simultaneously stirring until the two are fully in contact; The second method includes: spraying a strengthening dilute solution onto the dry recycled aggregate while stirring at room temperature and pressure for 2 to 5 minutes to ensure that it is fully wetted and strengthened; after strengthening, air-drying the modified recycled aggregate for 1 to 24 hours for later use, or putting it directly into use; the mass ratio of the dry recycled aggregate to the strengthening dilute solution is 3:

2.

9. The use of modified recycled aggregate obtained by the strengthening process according to any one of claims 1 to 8 as a raw material for concrete.

Images