Reinforcing process and application of recycled concrete fine aggregate

Abstract

The invention discloses a reinforcing process and application of recycled concrete fine aggregate, and belongs to the technical field of building materials. The strengthening process comprises the following steps: S1, mixing the high-strength grouting material with nano TiO2 to obtain a large-flow substrate dilute solution, and then adding a strengthening functional aid to obtain a strengthening dilute solution. S2, the waste concrete is crushed and processed into recycled aggregate, screening is conducted, and recycled fine aggregate with the particle size smaller than or equal to 5.0 mm is prepared; and S3, infiltrating the recycled fine aggregate in the step S2 into the strengthening dilute solution prepared in the step S1, uniformly stirring and sufficiently strengthening to obtain the modified recycled aggregate. The strengthening functional auxiliary agent is a mixture of a carbon nano tube or nano Al2O3 and Al2 (SO4) 3. The strengthening treatment process is simple to operate, low in economic cost and good in strengthening effect, can also have special functions such as photocatalysis when being applied to mortar, and has important significance on actual application landing of recycled aggregate, optimization of a construction waste treatment process and reduction of total carbon emission in the construction 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 the bacteria, so that the calcium carbonate CaCO3 precipitated by the 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 amount of graphene oxide added exceeds a certain range, the water absorption and agglomeration of graphene oxide may cause the frost resistance and other durability indicators of the concrete to decrease. 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: In a first aspect, the present application provides a strengthening process for recycled concrete fine aggregate, comprising the following steps: S1, mixing high-strength grouting material and nano-TiO2 to obtain a large-flow base dilute solution, and then adding a strengthening functional additive to obtain a strengthening dilute solution; S2, the waste concrete is crushed and processed into recycled aggregate, screened, and a recycled fine aggregate with a particle size of ≤5.0 mm is prepared; S3, the recycled fine aggregate in S2 is soaked in the reinforced dilute solution prepared in S1, stirred uniformly and sufficiently reinforced, and a modified recycled aggregate is obtained; The reinforcing functional additive is a mixture of carbon nanotubes or nano-Al2O3 and Al2(SO4)3. The carbon nanotubes are also subjected to modification treatment to obtain modified carbon nanotubes, and the specific preparation method is as follows: A1, the carbon nanotubes are added to deionized water, ultrasonically dispersed for 10-20 min, a Tris-HCl buffer solution with pH=8.5 is added, then hydrochloric acid dopamine is added, stirred for 6-8 h, centrifuged, washed, and dried to obtain PDA@carbon nanotubes; A2, the PDA@carbon nanotubes are added to anhydrous ethanol, ultrasonically dispersed for 60-80 min, then aminosilica cage is added, reacted at 50-60°C for 18-24 h, washed, and dried to obtain modified carbon nanotubes.

[0006] Further, in step S1, the water-binder ratio in the high-strength grouting material is (0.35-2):1. The functional components in the high-strength grouting material include the following raw materials in weight parts: SAC 42.5 sulphoaluminate cement 65 parts, anhydrous gypsum 8 parts, silica fume 10 parts, 200-mesh quartz powder 40 parts, polycarboxylic acid-based 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.

[0007] Further, in step S1, the mass of nano-TiO2 accounts for 1-5% of the mass of the high-fluidity base dilute solution. When the reinforcing functional additive is carbon nanotubes, the mass of the carbon nanotubes accounts for 0.05%-2% of the mass of the reinforcing dilute solution. 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 reinforcing dilute solution, and the mass of nano-Al2(SO4)3 accounts for 1% of the mass of the reinforcing dilute solution.

[0008] Further, in step A1, the use amount ratio of the carbon nanotubes, deionized water, hydrochloric acid dopamine, and Tris-HCl buffer solution is 3g:300mL:0.1-0.2g:50-70mL.

[0009] Further, in step A2, the mass ratio of the PDA@carbon nanotube to the aminated cage-type silsesquioxane is 8:(0.5-1.5); the amount of anhydrous ethanol is 10-13 times the mass of the PDA@carbon nanotube.

[0010] 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 the dry recycled aggregate by using the first mode or the second mode. 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 in full contact. The second mode comprises: under normal temperature and pressure, spraying the strengthening dilute solution on the dry recycled aggregate while stirring, stirring for 2-5 min to ensure that the dry recycled aggregate is fully infiltrated and strengthened; after the strengthening, air-drying the modified recycled aggregate for 1 h-24 h for standby or directly putting into use; and the mass ratio of the dry recycled aggregate to the strengthening dilute solution is 3:2.

[0011] In a second aspect, the application provides application of the modified recycled aggregate obtained by the strengthening process described in any one of the above aspects to a raw material for concrete.

[0012] The application has at least the following beneficial effects: 1. The application provides a strengthening process for recycled concrete fine aggregate, and the water absorption of the recycled aggregate is significantly reduced after the strengthening, and the mechanical properties of the recycled fine aggregate cement mortar with the recycled aggregate as a raw material are improved, and the specific improvements are as follows: first, the method uses high-strength grouting material and nano-TiO2 as a base to ensure the fluidity and basic strength of the solution, adds a strengthening functional additive, and uses 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, the waste concrete is crushed and sieved, and the particle size is accurately controlled to be less than or equal to 5.0 mm, which realizes resource utilization of solid waste, ensures uniform grading of the fine aggregate, and avoids the influence of uneven particle size on subsequent infiltration and the final performance of the concrete. Finally, the fine aggregate is infiltrated in the strengthening dilute solution and stirred, so that the solution fully penetrates the pores of the aggregate, and the nano components and additives in the solution repair the defects of the aggregate and improve the interfacial bonding strength, so that the modified aggregate with improved performance is obtained, and the overall strength and water absorption of the recycled concrete and other properties are improved.

[0013] 2, The application creatively mixes high-strength grouting material and nano-TiO2 to obtain a large-flow base dilute solution, and then adds a reinforcing functional additive to obtain a reinforced dilute solution, the reinforcing functional additive being a mixture of carbon nanotubes or nano-Al2O3 and Al2(SO4)3. The nano-TiO2 can increase the C-S-H gel content, fill the micropores and cracks in the recycled fine aggregate, improve the compressive performance of the cement mortar, reduce the water absorption rate, and expose clean sites on the surface of the recycled fine aggregate, thereby improving the anchoring efficiency of the subsequent nano-materials and further improving the comprehensive performance of the cement mortar. The high-strength grouting material contains water-reducing and compacting components, and cooperates with the nano-dispersion liquid to form a high-flow and compatible system, which is beneficial to penetration; the carbon nanotubes optimize the C-S-H structure by adjusting the distribution of calcium ions to enhance the mechanical properties; and the nano-Al2O3 and Al2(SO4)3 synergistically play the roles of physical filling and chemical gel generation to realize gradient reinforcement, avoid excessive expansion, and comprehensively improve the strength, interface bonding and durability of the recycled aggregate.

[0014] 3, The application also modifies the carbon nanotubes on the basis of the carbon nanotubes, and the modified carbon nanotubes have strong bonding force with raw materials and recycled fine aggregate, which can improve the compressive performance of the cement mortar. The modified carbon nanotubes of the application have cage-type silsesquioxane, which can further improve the compressive performance of the cement mortar and reduce the water absorption rate.

[0015] 4, The strengthening process of the recycled concrete fine aggregate can effectively convert construction waste into construction raw materials that meet certain construction requirements. The strengthening process is simple, environmentally friendly and low in economic cost. The recycled aggregate can add different concentrations of nano-TiO2 in the strengthening base solution according to the functional requirements of the mortar, so that the prepared mortar can have special functionality, such as the ability of TiO2 to adsorb and decompose volatile organic pollutants such as formaldehyde, thereby improving indoor air quality. BRIEF DESCRIPTION OF DRAWINGS

[0016] The application will be further described below with reference to the drawings.

[0017] Figure 1 is a scanning electron microscope image of the modified recycled aggregate obtained in Example 1 of the application; Figure 2 is a scanning electron microscope image of the recycled fine aggregate of the application. DETAILED DESCRIPTION

[0018] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below.

[0019] A strengthening process of recycled concrete fine aggregate, comprising 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 reinforced dilute solution; S2, crushing waste concrete to prepare recycled aggregate, and screening to prepare recycled fine aggregate with a particle size of less than or equal to 5.0 mm; S3, soaking the recycled fine aggregate in S2 in the reinforced dilute solution prepared in S1, stirring uniformly and reinforcing sufficiently to obtain modified recycled aggregate; The reinforcing functional additive is a mixture of carbon nanotubes or nano-Al2O3 and Al2(SO4)3; The carbon nanotubes are further modified to obtain modified carbon nanotubes, and the specific preparation method is as follows: 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; By using the above technical scheme, the mechanical properties of the recycled aggregate can be improved by adding carbon nanotubes. However, the specific surface area of carbon nanotubes is large and they are easy to agglomerate, so the dispersibility in the reinforced dilute solution is not good, which is not conducive to the enhancement effect. Therefore, the carbon nanotubes are modified based on the addition of carbon nanotubes. After PDA (polydopamine) is wrapped on the surface of the carbon nanotubes, the agglomeration of the carbon nanotubes can be reduced by the steric hindrance effect, which is conducive to the enhancement effect of the carbon nanotubes. And PDA has strong adhesion, which can enhance the bonding force of the modified carbon nanotubes with nano-TiO2, high-strength grouting material and other raw materials, and the bonding force with the recycled fine aggregate, forming a bonding network, thereby comprehensively improving the mechanical properties of the cement mortar.

[0020] A2, adding PDA@carbon nanotubes to anhydrous ethanol, ultrasonic dispersion for 60-80 min, then adding aminated cage-type silsesquioxane, and reacting at 50-60 DEG C for 18-24 h, washing, and drying to obtain modified carbon nanotubes.

[0021] In order to further improve the performance of PDA@carbon nanotubes, the catechol groups on the polydopamine layer are used as secondary reaction sites to react with the amino groups of aminated cage-type silsesquioxane to obtain modified carbon nanotubes. Cage-type silsesquioxane is a kind of inorganic-organic hybrid material with nano structure, which can fill the micropores and cracks in the recycled fine aggregate together with nano-TiO2 and other components to improve the mechanical properties of the aggregate. Through experiments, it can be confirmed that the cage-type silsesquioxane can reduce the water absorption of the cement mortar prepared finally.

[0022] The recycled fine aggregate is mainly the block of original cement paste in waste concrete or the broken sandstone with old cement mortar adhered on the surface, and the main components are cement hydration products such as C-S-H, Ca(OH)2, AFt and unreacted cement particles. The high-strength grouting material is used as the base of the reinforced dilute solution, and nano-level chemical ions are introduced into the base to fully penetrate into the cement paste containing pores or cracks, and chemical reactions occur to generate precipitates that can fill the voids of the aggregate. The high-strength grouting material contains water-reducing components, dense components, expansion components, ultra-fine powder and other nano dispersions, which can be prepared into a uniform dispersion liquid with water-like fluidity and fully compatible cement mortar. In addition, nano TiO2 can penetrate into the recycled fine aggregate with the water solution, promote the cement hydration reaction, increase the C-S-H gel content, and at the same time, the TiO2 nanoparticles fill the micropores and cracks in the recycled fine aggregate. Nano TiO2 also has photocatalytic properties. Under light irradiation, the oxide species generated on the surface will react with organic pollutants to degrade organic pollutants. By adding nano TiO2, the organic pollutants adhered to the surface of the aggregate can be oxidized to expose clean sites on the surface of the recycled fine aggregate, improving the anchoring efficiency of the subsequent nano materials. Carbon nanotubes have the ability to regulate the distribution of calcium ions, optimize the stacking of C-S-H and reduce the slip, and enhance the cohesion of C-S-H, which can improve the mechanical properties of recycled aggregate. Nano Al2O3 particles have small particle size and can fill the microcracks and pores on the surface of recycled aggregate, reducing the water absorption rate, but the strengthening effect is weak. Al2(SO4)3 can participate in the cement hydration reaction to generate AFt and C-A-S-H gel to fill the microcracks on the surface and the internal pores of the recycled fine aggregate, but excessive use will cause the expansion damage of the recycled fine aggregate cement mortar. By using a mixture of nano Al2O3 dispersion and Al2(SO4)3, the synergistic effect of physical densification and chemical expansion is realized, and the gradient strengthening of "first densification and then expansion" is realized at the micro level, which significantly improves the strength, interface adhesion and durability of the recycled aggregate.

[0023] In some embodiments, the water-binder ratio in the high-strength grouting material is (0.35-2):1; 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 reducing agent 2 parts, polyether modified polysiloxane powder defoamer 0.5 parts, retarder tartaric acid 0.1 parts, vinyl acetate-ethylene copolymer 4.5 parts. The water-binder ratio can be adapted to different scenarios to balance strength, fluidity and cost, and meet the diversified grouting needs.

[0024] In some embodiments, the mass of the nano-TiO2 accounts for 1-5% of the mass of the dilute solution of the bulk flow substrate; the proportion can ensure that the nano-TiO2 fully penetrates the micro-pores of the recycled fine aggregate, repairs the micro-cracks of the aggregate by physical filling, and reduces the water absorption; at the same time, the surface active groups of the nano-TiO2 can oxidize the organic pollutants on the surface of the aggregate, expose clean bonding sites, and improve the interfacial bonding strength with the high-strength grouting material and the strengthening functional additive in the subsequent process, thereby laying a foundation for the overall strength improvement.

[0025] When the strengthening functional additive is carbon nanotubes, the mass of the carbon nanotubes accounts for 0.05%-2% of the mass of the strengthening dilute solution; an addition amount as low as 0.05% can construct a “three-dimensional mechanical support network” by using the high aspect ratio of the carbon nanotubes, thereby improving the breaking strength and crack resistance of the recycled aggregate; the upper limit of 2% can avoid the problem of uneven dispersion caused by the agglomeration of the carbon nanotubes, and achieve a balance between “cost control” and “mechanical enhancement effect”.

[0026] When the strengthening functional additive is a mixture of nano-Al2O3 and Al2(SO4)3, the mass of the nano-Al2O3 in the mixture of nano-Al2O3 and Al2(SO4)3 accounts for 2% of the mass of the strengthening dilute solution, and the mass of the nano-Al2(SO4)3 accounts for 1% of the mass of the strengthening dilute solution. The 2% nano-Al2O3 can physically fill the fine pores of the aggregate that are not covered by the nano-TiO2, thereby further improving the density; the 1% Al2(SO4)3 can react with Ca(OH)2 in the high-strength grouting material to generate C-A-S-H gel, thereby chemically cementing the aggregate interface and solving the problem of weak interface transition zone between the recycled aggregate and the cementitious material; the mass ratio of 2:1 of the two can achieve gradient strengthening of “first physical filling and then chemical cementing”, thereby avoiding the defects of limited strengthening effect of single nano-Al2O3 and expansion caused by single Al2(SO4)3, and significantly improving the compressive strength and durability of the aggregate.

[0027] In some embodiments, in step A1, the use amount ratio of the carbon nanotubes, deionized water, hydrochloric acid dopamine, and Tris-HCl buffer is 3g:300mL:0.1-0.2g:50-70mL. By precisely controlling the ratio of hydrochloric acid dopamine and 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 with pH=8.5, and the 300mL deionized water guarantees the ultrasonic dispersion effect, thereby finally realizing the efficient introduction of active groups on the surface of the carbon nanotubes and laying a foundation for the subsequent grafting modification.

[0028] In some embodiments, in step A2, the mass ratio of the PDA@carbon nanotube to the aminated cage-type silsesquioxane is 8:(0.5-1.5); the amount of anhydrous ethanol is 10-13 times the mass of the PDA@carbon nanotube. By precisely controlling the amount of aminated cage-type silsesquioxane, a cage structure can be moderately grafted on the surface of the PDA coating, thereby avoiding agglomeration caused by excessive amount or affecting the modification effect caused by insufficient amount.

[0029] In some embodiments, the specific step of step S3 is: air-drying the recycled fine aggregate to control the water content to be less than or equal to 10%, to obtain dry recycled aggregate; and using the first method or the second method for strengthening; The first method comprises: placing the dry recycled aggregate in a sealed environment with a vacuum degree less than or equal to 0.01 MPa, directly adding a strengthening dilute solution, and synchronously stirring until the two are in full contact. The second method comprises: under normal temperature and pressure, spraying the strengthening dilute solution to 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; the mass ratio of the dry recycled aggregate to the strengthening dilute solution is 3:2. By controlling the water content of the recycled fine aggregate to be less than or equal to 10%, the water interference with the strengthening effect is avoided, and the recycled aggregate and the strengthening solution are matched in a mass ratio of 3:2 to ensure that the strengthening is sufficient; the vacuum environment (less than or equal to 0.01 MPa) can promote the infiltration of the strengthening solution into the pores of the aggregate, and the normal temperature spraying and stirring (2-5 min) can ensure uniform infiltration, so that the strengthening solution (containing nano components, modified carbon nanotubes, etc.) can fully act on the aggregate, and the subsequent air-drying (1-24 h) or direct use can take into account the operation flexibility, thereby effectively improving the activity, compactness and bonding force of the recycled aggregate to the matrix.

[0030] The specific embodiments of the present application are described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments.

[0031] The specific information of the raw materials used in the examples and comparative examples of the present application is as follows: The high-strength grouting material in the present application is a full-powder high-strength grouting material with a particle size of <80 um, a water-binder ratio of 0.25±0.05, a 28d compressive strength of ≥60 MPa, and a neat paste fluidity of ≥400 mm without segregation; The average particle size of the nano TiO2 is 20 nm; The carbon nanotube is a single-walled carbon nanotube with a diameter of 1 nm; The crystal form of the nano Al2O3 is alpha phase, the average particle size is 30 nm, and the purity of Al2(SO4)3 is AR≥99.0%.

[0032] Preparation Example 1

[0033] In the preparation example, the carbon nanotubes are modified, and the specific preparation method is as follows: A1, 3g of carbon nanotubes were added to 300mL of deionized water, ultrasonic dispersion for 10min, then 60mL of Tris-HCl buffer solution with pH=8.5 was added, 0.1g of dopamine hydrochloride was added, and then stirred for 6h, centrifuged, washed, and dried to obtain PDA@carbon nanotubes; A2, 8g of PDA@carbon nanotubes were added to 80mL of anhydrous ethanol, ultrasonic dispersion for 60min, then 0.5g of aminosilica cage was added, and reacted at 50℃ for 18h, washed, and dried to obtain modified carbon nanotubes.

[0034] Preparation Example 2

[0035] In the preparation example, the carbon nanotubes are modified, and the specific preparation method is as follows: A1, 3g of carbon nanotubes were added to 300mL of deionized water, ultrasonic dispersion for 20min, then 60mL of Tris-HCl buffer solution with pH=8.5 was added, 0.2g of dopamine hydrochloride was added, and then stirred for 8h, centrifuged, washed, and dried to obtain PDA@carbon nanotubes; A2, 8g of PDA@carbon nanotubes were added to 80mL of anhydrous ethanol, ultrasonic dispersion for 80min, then 1.5g of aminosilica cage was added, and reacted at 60℃ for 24h, washed, and dried to obtain modified carbon nanotubes.

[0036] Comparative Example 1

[0037] The difference between this comparative example and Preparation Example 1 is only that the amount of aminosilica cage is adjusted from "0.5g" to "0.4g".

[0038] Comparative Example 2

[0039] The difference between this comparative example and Preparation Example 2 is only that the amount of aminosilica cage is adjusted from "1.5g" to "1.6g".

[0040] Comparative Example 3

[0041] The difference between this comparative example and Preparation Example 1 is only that the aminosilica cage is omitted, and the specific steps are as follows: 3g of carbon nanotubes were added to 300mL of deionized water, ultrasonic dispersion for 10min, then 60mL of Tris-HCl buffer solution with pH=8.5 was added, 0.1g of dopamine hydrochloride was added, and then stirred for 6h, centrifuged, washed, and dried to obtain modified carbon nanotubes.

[0042] Example 1

[0043] The embodiment provides a reinforcing process of recycled concrete fine aggregate, and comprises the following steps: S1, high-strength grouting material and water are mixed and stirred according to a water-binder ratio of 2:1 for 3 min, functional components in the high-strength grouting material include the following raw materials in parts 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 water reducer 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarder tartaric acid 0.1 part, vinyl acetate-ethylene copolymer 4.5 parts, nano-TiO2 is added, mixed and stirred for 2 min to obtain a large-flow base dilute solution, the mass of nano-TiO2 accounts for 5% of the mass of the large-flow base dilute solution, then carbon nanotubes are added to prepare a reinforced dilute solution, and the mass of the carbon nanotubes accounts for 0.05% of the mass of the reinforced dilute solution; S2, waste concrete is crushed and processed into recycled aggregate, and is sieved to prepare recycled fine aggregate with a particle size of less than or equal to 5.0 mm; S3, the recycled fine aggregate is air-dried to have a water content of less than 10% to obtain dry recycled aggregate; the dry recycled aggregate is placed in a sealed environment with a vacuum degree of less than or equal to 0.01 MPa, the reinforced dilute solution is directly added, and the mixture is stirred for 5 min to obtain modified recycled aggregate, and the mass ratio of the dry recycled aggregate to the reinforced dilute solution is 3:2.

[0044] Embodiment 2

[0045] The embodiment provides a reinforcing process of recycled concrete fine aggregate, and comprises the following steps: S1, high-strength grouting material and water are mixed and stirred according to a water-binder ratio of 2:1 for 3 min, functional components in the high-strength grouting material include the following raw materials in parts 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 water reducer 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarder tartaric acid 0.1 part, vinyl acetate-ethylene copolymer 4.5 parts, nano-TiO2 is added, mixed and stirred for 2 min to obtain a large-flow base dilute solution, the mass of nano-TiO2 accounts for 5% of the mass of the large-flow base dilute solution, then carbon nanotubes are added to prepare a reinforced dilute solution, and the mass of the carbon nanotubes accounts for 0.05% of the mass of the reinforced dilute solution; S2, waste concrete is crushed and processed into recycled aggregate, and is sieved to prepare recycled fine aggregate with a particle size of less than or equal to 5.0 mm; S3, the recycled fine aggregate is air-dried to have a water content of less than 10% to obtain dry recycled aggregate; the dry recycled aggregate is placed in a sealed environment with a vacuum degree of less than or equal to 0.01 MPa, the reinforced dilute solution is directly added, and the mixture is stirred for 5 min to obtain modified recycled aggregate, and the mass ratio of the dry recycled aggregate to the reinforced dilute solution is 3:2.

[0046] Embodiment 3

[0047] The embodiment provides a reinforcing process of recycled concrete fine aggregate, and comprises the following steps: S1, high-strength grouting material is mixed with water at a water-binder ratio of 2:1 for 3 min, functional components in the high-strength grouting material include the following raw materials in parts 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 water reducer 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarding agent tartaric acid 0.1 part, vinyl acetate-ethylene copolymer 4.5 parts, to obtain a large-flow base dilute solution, the mass of nano-TiO2 accounts for 5% of the mass of the large-flow base dilute solution, then a nano-Al2O3 and Al2(SO4)3 mixture is added, to prepare a reinforced dilute solution, the mass of nano-Al2O3 in the nano-Al2O3 and Al2(SO4)3 mixture 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; S2, the waste concrete is crushed into recycled aggregate, and is screened to prepare recycled fine aggregate with a particle size of 5.0 mm or less; S3, the recycled fine aggregate is air-dried to a water content of less than 10%, to obtain dry recycled aggregate; the dry recycled aggregate is placed in a sealed environment with a vacuum degree of 0.01 MPa, the reinforced dilute solution is directly added, stirred for 5 min, and then directly used, to obtain modified recycled aggregate, and the mass ratio of the dry recycled aggregate to the reinforced dilute solution is 3:2.

[0048] Example 4

[0049] Compared with example 2, the only difference of the embodiment is that the modified carbon nanotube obtained in preparation example 1 is used to replace the carbon nanotube in example 2.

[0050] Example 5

[0051] Compared with example 2, the only difference of the embodiment is that the modified carbon nanotube obtained in preparation example 2 is used to replace the carbon nanotube in example 2.

[0052] Comparative example 1

[0053] Compared with example 4, the only difference of the comparative example is that the modified carbon nanotube obtained in comparative example 1 is used to replace the carbon nanotube obtained in preparation example 1 in example 4.

[0054] Comparative example 2

[0055] Compared with example 5, the only difference of the comparative example is that the modified carbon nanotube obtained in comparative example 2 is used to replace the carbon nanotube obtained in preparation example 2 in example 5.

[0056] Comparative example 3

[0057] The comparative example is compared with Example 4, and the only difference is that the modified carbon nanotubes obtained in Comparative Example 3 are used to replace the carbon nanotubes obtained in Preparation Example 1 in Example 4.

[0058] Comparative Example 4

[0059] The comparative example is compared with Example 1, and the only difference is that the carbon nanotubes are omitted, and the specific steps are as follows: S1, the high-strength grouting material and water are mixed and stirred at a water-binder ratio of 2:1 for 3 min, the functional components in the high-strength grouting material include the following raw materials in parts 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-based water reducing agent 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarder tartaric acid 0.1 parts, vinyl acetate-ethylene copolymer 4.5 parts, then nano-TiO2 is added and mixed and stirred for 2 min to obtain a strengthened dilute solution, the mass of nano-TiO2 accounts for 5% of the mass of the strengthened dilute solution; S2, the waste concrete is crushed and processed into recycled aggregate, and sieved to prepare recycled fine aggregate with a particle size of ≤5.0 mm; S3, the recycled fine aggregate is air-dried to a water content of less than 10% to obtain dry recycled aggregate; the dry recycled aggregate is placed in a sealed environment with a vacuum degree of ≤0.01 MPa, and the strengthened dilute solution is directly added, stirred for 5 min, and then directly used to obtain modified recycled aggregate, and the mass ratio of the dry recycled aggregate to the strengthened dilute solution is 3:2.

[0060] Comparative Example 5

[0061] The comparative example is compared with Example 1, and the only difference is that the nano-TiO2 is omitted, and the specific steps are as follows: S1, the high-strength grouting material and water are mixed and stirred at a water-binder ratio of 2:1 for 3 min, the functional components in the high-strength grouting material include the following raw materials in parts 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-based water reducing agent 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarder tartaric acid 0.1 parts, vinyl acetate-ethylene copolymer 4.5 parts, then carbon nanotubes are added to prepare a strengthened dilute solution, and the mass of the carbon nanotubes accounts for 0.05% of the mass of the strengthened dilute solution; S2, the waste concrete is crushed and processed into recycled aggregate, and sieved to prepare recycled fine aggregate with a particle size of ≤5.0 mm; S3, air-drying the recycled fine aggregate to a water content of less than 10% to obtain dry recycled aggregate; placing the dry recycled aggregate in a sealed environment with a vacuum degree of less than or equal to 0.01 MPa, directly adding the reinforced dilute solution, stirring for 5 min, and then directly using to obtain the modified recycled aggregate, wherein the mass ratio of the dry recycled aggregate to the reinforced dilute solution is 3:2.

[0062] Comparative Example 6

[0063] The present comparative example is compared with Example 3, the only difference being that the nano-TiO2 is omitted, and the specific steps are as follows: S1, mixing and stirring the high-strength grouting material with water at a water-binder ratio of 2:1 for 3 min, wherein 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-based water reducing agent 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarder tartaric acid 0.1 parts, vinyl acetate-ethylene copolymer 4.5 parts, and then adding a nano-Al2O3 and Al2(SO4)3 mixture, to prepare a reinforced dilute solution, wherein the mass of nano-Al2O3 in the nano-Al2O3 and Al2(SO4)3 mixture 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; S2, crushing and processing the waste concrete into recycled aggregate, and sieving to prepare recycled fine aggregate with a particle size of less than or equal to 5.0 mm; S3, air-drying the recycled fine aggregate to a water content of less than 10% to obtain dry recycled aggregate; placing the dry recycled aggregate in a sealed environment with a vacuum degree of less than or equal to 0.01 MPa, directly adding the reinforced dilute solution, stirring for 5 min, and then directly using to obtain the modified recycled aggregate, wherein the mass ratio of the dry recycled aggregate to the reinforced dilute solution is 3:2.

[0064] Comparative Example 7

[0065] The present comparative example is compared with Example 3, the only difference being that the nano-TiO2 is omitted, and the specific steps are as follows: S1, mixing and stirring the high-strength grouting material with water at a water-binder ratio of 2:1 for 3 min, wherein 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-based water reducing agent 2 parts, polyether modified polysiloxane powder defoaming agent 0.5 parts, retarder tartaric acid 0.1 parts, vinyl acetate-ethylene copolymer 4.5 parts, and then adding a nano-Al2O3 and Al2(SO4)3 mixture, to prepare a reinforced dilute solution, wherein the mass of nano-Al2O3 in the nano-Al2O3 and Al2(SO4)3 mixture 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; S2, crushing and processing the waste concrete into recycled aggregate, and sieving to prepare recycled fine aggregate with a particle size of less than or equal to 5.0 mm; S3, air-drying the recycled fine aggregate to a water content of less than 10% to obtain dry recycled aggregate; placing the dry recycled aggregate in a sealed environment with a vacuum degree of less than or equal to 0.01 MPa, directly adding the reinforced dilute solution, stirring for 5 minutes, and directly using to obtain modified recycled aggregate, and the mass ratio of the dry recycled aggregate to the reinforced dilute solution is 3:2.

[0066] The modified recycled aggregate prepared in Examples 1-5 and Comparative Examples 1-7 was used to replace standard sand at a mass substitution rate of 50% as the aggregate component of the cement mortar. A blank control group was also set up, in which no modified recycled aggregate was added, and the mass substitution rate of the standard sand was 0%.

[0067] According to the design strength grade of the cement mortar, P·II 52.5 Portland cement, national standard ISO standard sand, a water-binder ratio of 0.5, and a mortar ratio of 1:3 were used to prepare standard cement mortar samples according to GB / T 17671-2021 "Cement Mortar Strength Test Method", and three 40x40x160mm 3 cement mortar test pieces were prepared. After 1d of standard curing, the mold was removed and placed in water at a temperature of 20±2℃ for standard curing for 28 days. The compressive strength and flexural strength, crushing index, and saturated surface dry water absorption were tested according to the standard method, and the test was carried out according to GB / T 14684-2022.

[0068] Table 1

[0069] Note: " / " in Table 1 represents no addition of the reinforced dilute solution.

[0070] As can be seen from Table 1, the comprehensive performance of the cement mortar obtained in Examples 1-5 is excellent.

[0071] According to the data of Examples 1 and 2 and Examples 4 and 5, it can be seen that further modification of carbon nanotubes can improve the mechanical properties of the cement mortar and reduce the saturated surface dry water absorption, indicating that the modified carbon nanotubes have strong bonding force with the raw materials and the recycled fine aggregate, which can improve the compressive strength of the cement mortar. The modified carbon nanotubes of the present application have a POSS structure, which can further improve the compressive strength of the cement mortar and reduce the water absorption of the cement mortar.

[0072] According to the test results of Comparative Examples 1 and 2 and Examples 4 and 5, it can be seen that too little or too much aminated cage-type silsesquioxane will affect the comprehensive performance of the final sample, indicating that the addition amount of aminated cage-type silsesquioxane of the present application is the optimal amount.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

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