Anti-permeability and anti-freezing environment-friendly recycled concrete and preparation method thereof

Abstract

The application discloses an anti-permeation and anti-freezing environment-friendly recycled concrete and a preparation method thereof, and the concrete comprises the following components in parts by weight: cement 35-45 parts, composite recycled aggregate 100-120 parts, mineral admixture 15-25 parts, composite anti-permeation and anti-freezing additive 2-4 parts, water 18-22 parts, environment-friendly interface regulator 1-2 parts and modified reinforcing agent 0.5-1.5 parts. The composite recycled aggregate and the composite anti-permeation and anti-freezing additive are used in cooperation. After the composite recycled aggregate is modified by a silane coupling agent and a calcium hydroxide-sodium sulfate solution, the surface pores are effectively filled, the micro cracks are reduced, the interface activity is improved, and the combination with the cementing material is more compact. In the composite anti-permeation and anti-freezing additive, the polycarboxylate superplasticizer can reduce the water-binder ratio and reduce the internal pores of the concrete, the air entraining agent introduces uniform and small closed air bubbles, blocks the water permeation channel, buffers the expansion stress generated by the freeze-thaw cycle, the organic silicon waterproof agent forms a hydrophobic layer, and the anti-permeation performance is further improved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a water-resistant, freeze-resistant, environmentally friendly recycled concrete and its preparation method. Background Technology

[0002] With the acceleration of urbanization and the continuous advancement of infrastructure construction, the amount of waste concrete generated from the demolition of large-scale construction projects is increasing year by year. This waste concrete pollutes soil and water bodies due to weathering, leaching, and other processes, becoming a significant bottleneck restricting the green and sustainable development of the construction industry. Recycled concrete, as an effective way to solve the resource utilization of construction waste, obtains recycled aggregates by crushing and screening waste concrete, which can then replace natural aggregates in concrete formulation. This reduces the mining of natural sand and gravel, protects the ecological environment, and alleviates the pressure of construction waste disposal, resulting in significant economic, environmental, and social benefits.

[0003] In the prior art, the invention patent with publication number CN114380562B discloses a method for preparing antifreeze recycled concrete, including the following steps: after crushing and screening waste concrete, pre-formed coarse aggregate particles are obtained; the pre-formed coarse aggregate particles are fully soaked in graphene oxide dispersion, then taken out and dried until the surface is dry to obtain recycled coarse aggregate; by weight, 270290 parts of cement, 830850 parts of recycled coarse aggregate, 830850 parts of fine aggregate, 110130 parts of admixture, 4050 parts of waste foamed rubber powder, 170180 parts of water, 68 parts of antifreeze water-reducing agent and 510 parts of expansion crack-resistant agent are taken, and stirred evenly to obtain antifreeze recycled concrete.

[0004] Concrete prepared using the method provided in the aforementioned patent exhibits good frost resistance; however, it falls short in terms of impermeability, severely limiting its large-scale application in harsh environments such as cold and humid regions, underground engineering, and water conservancy projects. Recycled aggregates, due to the large amount of old cement paste adhering to their surface and the numerous micro-cracks generated during crushing, suffer from high porosity, high water absorption, and a weak interfacial transition zone. This results in an unreasonable internal pore structure in the prepared recycled concrete, with numerous interconnected pores, significantly reducing its impermeability. It becomes susceptible to penetration by external moisture, chloride ions, and other corrosive media, leading to problems such as concrete carbonation and steel corrosion, thus shortening the service life of the project.

[0005] Furthermore, the aforementioned patents do not incorporate diverse solid wastes such as waste ceramics, resulting in low utilization rates of recycled aggregates. The admixture system also lacks environmentally friendly components, posing certain environmental risks. Existing preparation processes also exhibit low utilization rates of recycled aggregates, failing to fully realize the resource recycling of construction waste. Therefore, there is an urgent need for a recycled concrete that can balance impermeability, frost resistance, and environmental friendliness, while also possessing a simple preparation process and controllable costs. Addressing the shortcomings of existing technologies and promoting the application of recycled concrete in demanding environmental engineering projects has become a current research hotspot and pressing need in the field of building materials. Summary of the Invention

[0006] The purpose of this invention is to provide an impermeable, frost-resistant, environmentally friendly recycled concrete and its preparation method, aiming to improve the problems of poor impermeability and frost resistance, insufficient environmental protection, and low utilization rate of recycled aggregates in the existing technology of recycled concrete.

[0007] This invention is implemented as follows: To achieve the above objectives, according to one aspect of the present invention, the present invention provides: 1. A type of impermeable, frost-resistant, environmentally friendly recycled concrete, comprising, by weight, the following raw material components: 35-45 parts cement, 100-120 parts composite recycled aggregate, 15-25 parts mineral admixture, 2-4 parts composite impermeable and frost-resistant admixture, 18-22 parts water, 1-2 parts environmentally friendly interface modifier, and 0.5-1.5 parts modified reinforcing agent.

[0008] Preferably, the cement is P·O42.5 grade ordinary Portland cement with a specific surface area of ​​300-350 m². 2 / kg, initial setting time ≥45min, final setting time ≤600min; the water is drinking water that meets the standards, with a pH value of 6.5-8.5, free of impurities and odors, to avoid harmful components in the water affecting the properties of the concrete.

[0009] Preferably, the composite recycled aggregate is obtained by mixing waste concrete recycled coarse aggregate, waste concrete recycled fine aggregate, and waste ceramic recycled aggregate in a mass ratio of 6-8:3-4:1, followed by composite modification treatment; the composite anti-seepage and anti-freeze admixture is prepared by mixing polycarboxylate-based high-efficiency water-reducing agent, air-entraining agent, organosilicon waterproofing agent, and nano-silica in a mass ratio of 5-7:2-3:1-2:0.5-1; the air-entraining agent is a rosin thermal polymer air-entraining agent with an air content controlled at 3-5%; the organosilicon waterproofing agent is sodium methylsilicate waterproofing agent with a purity ≥98%; the nano-silica has a particle size of 50-100nm and a purity ≥99%; the polycarboxylate-based high-efficiency water-reducing agent is a retarded polycarboxylate water-reducing agent with a water reduction rate ≥25%, a solid content of 40-50%, and is free of harmful components such as chlorides and sulfates, which can reduce the water-cement ratio and avoid corrosion of steel bars.

[0010] Preferably, the mineral admixture is prepared by mixing fly ash, slag powder and silica fume in a mass ratio of 4-5:3-4:1; the environmentally friendly interface modifier is a compound of chitosan and polyacrylamide in a mass ratio of 1:2-3; and the modified reinforcing agent is a compound of nano-calcium carbonate and sodium lignosulfonate in a mass ratio of 3-4:1.

[0011] Preferably, the fly ash is Class II fly ash with a loss on ignition ≤8% and a water requirement ratio ≤105%; the slag powder is S95 grade slag powder with a specific surface area ≥400 m². 2 / kg; the specific surface area of ​​the silica fume is ≥18000m² 2 / kg, with a silica content of ≥90%, all three are recycled industrial waste residues, further enhancing environmental friendliness while increasing the density of concrete.

[0012] Preferably, the composite modification process of the composite recycled aggregate is as follows: S100. The waste concrete is crushed and screened to obtain recycled coarse aggregate with a particle size of 5-20mm and recycled fine aggregate with a particle size of 0.15-5mm; the waste ceramics are crushed and screened to obtain recycled ceramic aggregate with a particle size of 0.5-2mm; the three aggregates are washed clean and dried to constant weight at 105±5℃. S200, prepare a 1.5-2.5% (w / w) aqueous solution of silane coupling agent KH-550, mix the three aggregates evenly in proportion and immerse them in the solution for 2-3 hours, stirring once every 30 minutes during the soaking period, then take them out and let them air dry naturally. S300. After drying, the aggregate is ground in a vertical impact crusher for 1-2 minutes, and then soaked in a modifier solution for 1-1.5 hours. The modifier solution is prepared by calcium hydroxide, sodium sulfate and water in a mass ratio of 1:0.5:100. After soaking, the aggregate is taken out and dried at 80±5℃ for 30-40 minutes to obtain composite recycled aggregate.

[0013] Preferably, the drying time in step S100 is 2-3 hours; In step S200, during the preparation of the aqueous solution of silane coupling agent KH-550, a nonionic surfactant of 0.1-0.2% by mass of the aqueous solution is added. The nonionic surfactant is polyoxyethylene octylphenyl ether (OP-10), which is used to improve the uniformity of the coupling agent's adhesion on the aggregate surface, enhance the modification effect, and reduce the porosity of the aggregate surface. In step S300, the grinding speed of the vertical impact crusher is 1200-1500 r / min, the soaking temperature of the modifier solution is 25±3℃, and the mixture is stirred once every 20 minutes during the soaking process; the dried composite recycled aggregate has a moisture content ≤0.5%, a crushing value ≤18%, and a needle-like and flaky particle content ≤8%, ensuring the mechanical properties of the composite recycled aggregate and improving the overall strength of the concrete.

[0014] Preferably, it also includes 0.3-0.8 parts of an environmentally friendly rust inhibitor, which is a compound of phytic acid and zinc dihydrogen phosphate in a mass ratio of 2:1. It is free of heavy metal pollution and is used to improve the rust protection performance of concrete for internal steel bars, delay steel bar corrosion, and extend the service life of the project.

[0015] According to a second aspect of the present invention, the present invention provides a method for preparing impermeable, freeze-resistant, environmentally friendly recycled concrete, the method comprising the following steps: T100. Weigh each raw material component according to the weight parts and set aside; among them, the composite recycled aggregate shall be subjected to composite modification treatment in advance, and the composite anti-permeability and antifreeze admixture shall be mixed evenly in advance. T200: Place the composite recycled aggregate into a mixer, add an environmentally friendly interface modifier, and mix for 3-5 minutes. T300: Add cement, mineral admixtures and modifiers to the mixer, and continue mixing for 5-8 minutes to form a dry powder mixture; T400: Divide the water into two parts. The first part, which accounts for 60-70% of the total water, is added to the dry powder mixture and stirred for 8-10 minutes to form a semi-wet mixture. T500: Add composite anti-permeability and anti-freeze admixture and the remaining water to the semi-wet mixture, and continue stirring for 10-15 minutes to obtain anti-permeability and anti-freeze environmentally friendly recycled concrete. T600: The prepared recycled concrete is poured into shape, vibrated to compact it, and then cured at room temperature for 24 hours. It is then transferred to a standard curing room and cured for 28 days at a temperature of 20±2℃ and a relative humidity of ≥95% to obtain the finished product.

[0016] Preferably, the stirring speed of the mixer in step T200 is 600-800 r / min, and the stirring speed in step T300 is 800-1000 r / min; The stirring speed in step T400 is 700-900 r / min; the stirring speed in step T500 is 1000-1200 r / min; In step T600, the concrete is poured and compacted using an immersion vibrator for 20-30 seconds per point, until no air bubbles appear on the concrete surface and cement slurry rises to the surface. The ambient temperature for curing is 20±5℃, and the relative humidity is ≥70%. During the curing process in the standard curing room, the concrete test blocks are sprayed with water every 7 days to maintain moisture, and the relative humidity of the curing room is maintained at ≥95% after watering. After 28 days of curing, the concrete test blocks have a permeability grade ≥P12, a frost resistance grade ≥F200, and a 28-day compressive strength ≥40MPa. The performance indicators of the finished product are clearly defined to ensure that they meet the requirements for use in the project.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes the synergistic effect of composite recycled aggregate and composite anti-permeability and anti-freeze admixture. After the composite recycled aggregate is modified by a silane coupling agent and a calcium hydroxide-sodium sulfate solution, the surface pores are effectively filled, microcracks are reduced, interfacial activity is improved, and the bond with cementitious materials is tighter. In the composite anti-permeability and anti-freeze admixture, the polycarboxylate superplasticizer can reduce the water-cement ratio and reduce the internal pores of the concrete. The air-entraining agent introduces uniform and fine closed air bubbles to block water penetration channels and buffer the expansion stress generated by freeze-thaw cycles. The organosilicon waterproofing agent forms a hydrophobic layer to further improve the anti-permeability performance. Nano-silica fills the micropores and enhances the density of the concrete. The synergistic effect of these three components makes the anti-permeability and anti-freeze grade of the recycled concrete significantly better than that of existing recycled concrete.

[0018] 2. This invention uses waste concrete and waste ceramics as raw materials to prepare composite recycled aggregates, which greatly improves the utilization rate of construction waste and reduces environmental pollution caused by the mining of natural sand and gravel and the dumping of waste. The admixtures and interface modifiers used are all environmentally friendly materials with no harmful components and will not cause secondary pollution to the environment. The mineral admixtures are made from industrial waste residue, realizing the resource utilization of industrial waste and reducing carbon emissions in the concrete production process, which is in line with the concept of green and low-carbon development.

[0019] 3. By optimizing the raw material ratio and adding modifiers and environmentally friendly interface modifiers, this invention effectively improves the performance of the interface transition zone between recycled aggregates and cementitious materials, enhances the bond strength and overall mechanical properties of concrete, and significantly increases the compressive strength of finished concrete, which can meet the strength requirements of most projects. At the same time, the preparation process is simple, requires no complex equipment, and has a lower production cost than existing high-performance recycled concrete, making it easy for large-scale industrial production and application.

[0020] 4. This invention uses physical and chemical composite modification to treat recycled aggregates, and combines the addition of waste ceramic aggregates to improve the performance of the aggregates themselves; at the same time, it designs a composite anti-permeability and anti-freeze admixture to achieve synergistic effect of multiple components, which solves the technical problem that existing recycled concrete is difficult to balance anti-permeability and anti-freeze performance and is not environmentally friendly, and has significant creativity and novelty.

[0021] 5. This invention adds an environmentally friendly rust inhibitor component, which can effectively improve the concrete's ability to protect the internal steel bars, delay steel bar corrosion, and further extend the service life of the project. At the same time, it refines the performance parameters of each raw material, optimizes the modification and preparation process details, making the technical solution more operable and stable, ensuring that the performance of the finished concrete meets the standards, and improving the comprehensiveness of patent protection. Attached Figure Description

[0022] Figure 1 This is a flowchart of the preparation method of the present invention; Figure 2 This is a flowchart of the composite modification process of the composite recycled aggregate of the present invention. Detailed Implementation

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] The following detailed explanation, in conjunction with specific embodiments, further illustrates the following: Example 1

[0025] This invention provides an impermeable, freeze-resistant, environmentally friendly recycled concrete, which, by weight, comprises the following raw material components: 35 parts cement, 100 parts composite recycled aggregate, 15 parts mineral admixture, 2 parts composite impermeable and freeze-resistant admixture, 18 parts water, 1 part environmentally friendly interface modifier, 0.5 parts modified reinforcing agent, and 0.3 parts environmentally friendly rust inhibitor.

[0026] The cement used is P·O42.5 grade ordinary Portland cement with a specific surface area of ​​300 m². 2 / kg, initial setting time ≥45min, final setting time ≤600min; the water is drinking water that meets the standards, with a pH value of 6.5, free of impurities and odors, to avoid harmful components in the water affecting the properties of the concrete.

[0027] The composite recycled aggregate is obtained by mixing waste concrete recycled coarse aggregate, waste concrete recycled fine aggregate and waste ceramic recycled aggregate in a mass ratio of 6:3:1 and then undergoing composite modification treatment.

[0028] The composite anti-seepage and anti-freeze admixture is made by mixing polycarboxylate-based high-efficiency water-reducing agent, rosin thermal polymer air-entraining agent, sodium methylsilicate waterproofing agent, and nano-silica in a mass ratio of 5:2:1:0.5. The polycarboxylate-based high-efficiency water-reducing agent is a retarded polycarboxylate water-reducing agent with a water reduction rate of ≥25%, a solid content of 40%, and no harmful components such as chlorides and sulfates. It can reduce the water-cement ratio and avoid corrosion of steel bars.

[0029] The mineral admixture is made by mixing fly ash, slag powder, and silica fume in a mass ratio of 4:3:1. The fly ash is Class II fly ash with a loss on ignition ≤8% and a water requirement ≤105%; the slag powder is S95 grade slag powder with a specific surface area ≥400 m². 2 / kg; Specific surface area of ​​silica fume ≥18000m² 2 / kg, with a silica content of ≥90%, all three are recycled industrial waste, further enhancing environmental friendliness while improving the density of concrete. The environmentally friendly interface modifier is a compound of chitosan and polyacrylamide in a mass ratio of 1:2.

[0030] The modifier is a compound of nano-calcium carbonate and sodium lignosulfonate, with a mass ratio of 3:1.

[0031] The environmentally friendly rust inhibitor is a compound of phytic acid and zinc dihydrogen phosphate in a mass ratio of 2:1. It is free of heavy metal pollution and is used to improve the rust protection performance of concrete against internal steel bars, delay steel bar corrosion, and extend the service life of the project.

[0032] The method for preparing this impermeable, freeze-resistant, environmentally friendly recycled concrete is as follows: Step 1: First, the composite recycled aggregate undergoes composite improvement treatment. The specific treatment process is as follows: (1) Waste concrete is crushed and screened to obtain recycled coarse aggregate with a particle size of 5-20 mm and recycled fine aggregate with a particle size of 0.15-5 mm. Waste ceramics are crushed and screened to obtain recycled ceramic aggregate with a particle size of 0.5-2 mm. The three are washed clean and dried at 105℃ to constant weight. (2) Mix the three aggregates in proportion and soak them in a 1.5% aqueous solution of silane coupling agent KH-550 for 2 hours. Stir once every 30 minutes and take them out to air dry. During the preparation of the aqueous solution of silane coupling agent KH-550, add 0.1% of nonionic surfactant by mass of the aqueous solution. The nonionic surfactant is polyoxyethylene octylphenyl ether (OP-10) to improve the uniformity of the coupling agent on the surface of the aggregate, enhance the modification effect, and reduce the porosity of the aggregate surface.

[0033] (3) Then it is put into a vertical impact crusher for grinding for 1 minute, and then soaked in a modifier solution prepared by calcium hydroxide, sodium sulfate and water in a mass ratio of 1:0.5:100 for 1 hour. After taking it out, it is dried at 80°C for 30 minutes to obtain composite recycled aggregate; the composite impermeable and antifreeze admixture is mixed evenly in advance. Step 2: Weigh each raw material component according to the specified weight and set aside; Step 3: Put the composite recycled aggregate into the mixer, add the environmentally friendly interface modifier, and mix for 3 minutes; Step 4: Add cement, mineral admixtures and modifiers, and continue stirring for 5 minutes to form a dry powder mixture; Step 5: Take 60% of the total water volume and add it to the dry powder mixture. Stir for 8 minutes to form a semi-wet mixture. Step 6: Add the composite anti-seepage and anti-freeze admixture and the remaining water, stir for 10 minutes to obtain recycled concrete; Step 7: Cast the mold, vibrate to compact it, and cure at room temperature for 24 hours. Then, transfer it to a standard curing room (20±2℃, relative humidity ≥95%) for 28 days to obtain the finished product.

[0034] Step 8: Test the poured concrete to ensure that its impermeability grade is P12, its freeze-thaw resistance grade is F200, and its 28-day compressive strength is 40.2 MPa, which meet the design requirements.

[0035] Example 2

[0036] This invention provides an impermeable, frost-resistant, environmentally friendly recycled concrete, which, by weight, comprises the following raw material components: 40 parts cement, 110 parts composite recycled aggregate, 20 parts mineral admixture, 3 parts composite impermeable and frost-resistant admixture, 20 parts water, 1.5 parts environmentally friendly interface modifier, 1.0 part modified reinforcing agent, and 0.55 parts environmentally friendly rust inhibitor.

[0037] The cement used is P·O42.5 grade ordinary Portland cement with a specific surface area of ​​325 m². 2 / kg, initial setting time ≥45min, final setting time ≤600min; the water is drinking water that meets the standards, with a pH value of 7.5, free of impurities and odors, to avoid harmful components in the water affecting the properties of the concrete.

[0038] The composite recycled aggregate is obtained by mixing waste concrete recycled coarse aggregate, waste concrete recycled fine aggregate and waste ceramic recycled aggregate in a mass ratio of 7:3.5:1 and then undergoing composite modification treatment.

[0039] The composite anti-seepage and anti-freeze admixture is made by mixing polycarboxylate-based high-efficiency water-reducing agent, rosin thermal polymer air-entraining agent, sodium methylsilicate waterproofing agent, and nano-silica in a mass ratio of 6:2.5:1.5:0.8. The polycarboxylate-based high-efficiency water-reducing agent is a retarded polycarboxylate water-reducing agent with a water reduction rate of ≥25% and a solid content of 45%. It does not contain harmful components such as chlorides and sulfates, which can reduce the water-cement ratio and avoid corrosion of steel bars.

[0040] The mineral admixture is prepared by mixing fly ash, slag powder, and silica fume in a mass ratio of 4.5:3.5:1. The fly ash is Grade II fly ash with a loss on ignition ≤8% and a water requirement ≤105%; the slag powder is Grade S95 slag powder with a specific surface area ≥400 m². 2 / kg; Specific surface area of ​​silica fume ≥18000m² 2 / kg, with a silica content of ≥90%, all three are recycled industrial waste residues, further enhancing environmental friendliness while increasing the density of concrete.

[0041] The environmentally friendly interface modifier is a compound of chitosan and polyacrylamide, with a mass ratio of 1:2.5.

[0042] The modifier is a compound of nano-calcium carbonate and sodium lignosulfonate, with a mass ratio of 3.5:1.

[0043] The environmentally friendly rust inhibitor is a compound of phytic acid and zinc dihydrogen phosphate in a mass ratio of 2:1. It is free of heavy metal pollution and is used to improve the rust protection performance of concrete against internal steel bars, delay steel bar corrosion, and extend the service life of the project.

[0044] The method for preparing this impermeable, freeze-resistant, environmentally friendly recycled concrete is as follows: Step 1: First, the composite recycled aggregate undergoes composite improvement treatment. The specific treatment process is as follows: (1) Waste concrete is crushed and screened to obtain recycled coarse aggregate with a particle size of 5-20 mm and recycled fine aggregate with a particle size of 0.15-5 mm. Waste ceramics are crushed and screened to obtain recycled ceramic aggregate with a particle size of 0.5-2 mm. The three are washed clean and dried at 105℃ to constant weight. (2) Mix the three types of aggregates in proportion and immerse them in a 2% aqueous solution of silane coupling agent KH-550 for 2.5 hours, stirring once every 30 minutes. Remove and air dry naturally. During the preparation of the aqueous solution of silane coupling agent KH-550, add 0.15% of a nonionic surfactant, which is polyoxyethylene octylphenyl ether (OP-10), to improve the uniformity of the coupling agent on the surface of the aggregates, enhance the modification effect, and reduce the porosity of the aggregate surface. (3) Then it is put into a vertical impact crusher for grinding for 1.5 min, and then soaked in a modifier solution prepared by calcium hydroxide, sodium sulfate and water in a mass ratio of 1:0.5:100 for 1.2 h. After taking it out, it is dried at 80℃ for 35 min to obtain composite recycled aggregate; the composite impermeable and antifreeze admixture is mixed evenly in advance. Step 2: Weigh each raw material component according to the specified weight and set aside; Step 3: Put the composite recycled aggregate into the mixer, add the environmentally friendly interface modifier, and mix for 4 minutes; Step 4: Add cement, mineral admixtures and modifiers, and continue stirring for 6.5 minutes to form a dry powder mixture; Step 5: Take 65% of the total water volume and add it to the dry powder mixture. Stir for 9 minutes to form a semi-wet mixture. Step 6: Add the composite anti-seepage and anti-freeze admixture and the remaining water, stir for 12 minutes to obtain recycled concrete; Step 7: Cast the mold, vibrate to compact it, and cure at room temperature for 24 hours. Then, transfer it to a standard curing room (20±2℃, relative humidity ≥95%) for 28 days to obtain the finished product.

[0045] Step 8: Test the poured concrete to ensure that its impermeability grade is P14, its freeze-thaw resistance grade is F250, and its 28-day compressive strength is 45.6 MPa, which meets the design requirements.

[0046] Example 3

[0047] This invention provides an impermeable, freeze-resistant, environmentally friendly recycled concrete, which, by weight, comprises the following raw material components: 45 parts cement, 120 parts composite recycled aggregate, 25 parts mineral admixture, 4 parts composite impermeable and freeze-resistant admixture, 22 parts water, 2 parts environmentally friendly interface modifier, 1.5 parts modified reinforcing agent, and 0.8 parts environmentally friendly rust inhibitor.

[0048] The cement used is P·O42.5 grade ordinary Portland cement with a specific surface area of ​​350 m². 2 / kg, initial setting time ≥45min, final setting time ≤600min; the water is drinking water that meets the standards, with a pH value of 8.5, free of impurities and odors, to avoid harmful components in the water affecting the properties of the concrete.

[0049] The composite recycled aggregate is obtained by mixing waste concrete recycled coarse aggregate, waste concrete recycled fine aggregate and waste ceramic recycled aggregate in a mass ratio of 8:4:1 and then undergoing composite modification treatment.

[0050] The composite anti-seepage and anti-freeze admixture is made by mixing polycarboxylate-based high-efficiency water-reducing agent, rosin thermal polymer air-entraining agent, sodium methylsilicate waterproofing agent, and nano-silica in a mass ratio of 7:3:2:1. The polycarboxylate-based high-efficiency water-reducing agent is a retarded polycarboxylate water-reducing agent with a water reduction rate of ≥25%, a solid content of 50%, and no harmful components such as chlorides and sulfates. It can reduce the water-cement ratio and avoid corrosion of steel bars.

[0051] The mineral admixture is made by mixing fly ash, slag powder, and silica fume in a mass ratio of 5:4:1. The fly ash is Class II fly ash with a loss on ignition ≤8% and a water requirement ≤105%; the slag powder is S95 grade slag powder with a specific surface area ≥400 m². 2 / kg; Specific surface area of ​​silica fume ≥18000m² 2 / kg, with a silica content of ≥90%, all three are recycled industrial waste residues, further enhancing environmental friendliness while increasing the density of concrete.

[0052] The environmentally friendly interface modifier is a compound of chitosan and polyacrylamide, with a mass ratio of 1:3.

[0053] The modifier is a compound of nano-calcium carbonate and sodium lignosulfonate, with a mass ratio of 4:1.

[0054] The environmentally friendly rust inhibitor is a compound of phytic acid and zinc dihydrogen phosphate in a mass ratio of 2:1. It is free of heavy metal pollution and is used to improve the rust protection performance of concrete against internal steel bars, delay steel bar corrosion, and extend the service life of the project.

[0055] The method for preparing this impermeable, freeze-resistant, environmentally friendly recycled concrete is as follows: Step 1: First, the composite recycled aggregate undergoes composite improvement treatment. The specific treatment process is as follows: (1) Waste concrete is crushed and screened to obtain recycled coarse aggregate with a particle size of 5-20 mm and recycled fine aggregate with a particle size of 0.15-5 mm. Waste ceramics are crushed and screened to obtain recycled ceramic aggregate with a particle size of 0.5-2 mm. The three are washed clean and dried at 105℃ to constant weight. (2) Mix the three aggregates in proportion and soak them in a 2.5% aqueous solution of silane coupling agent KH-550 for 3 hours. Stir once every 30 minutes and take them out to air dry. During the preparation of the aqueous solution of silane coupling agent KH-550, add 0.2% of nonionic surfactant by mass of the aqueous solution. The nonionic surfactant is polyoxyethylene octylphenyl ether (OP-10) to improve the uniformity of the coupling agent on the surface of the aggregate, enhance the modification effect, and reduce the porosity of the aggregate surface.

[0056] (3) Then it is put into a vertical impact crusher for grinding for 1.5 min, and then soaked in a modifier solution prepared by calcium hydroxide, sodium sulfate and water in a mass ratio of 1:0.5:100 for 1.5 h. After taking it out, it is dried at 80℃ for 40 min to obtain composite recycled aggregate; the composite impermeable and antifreeze admixture is mixed evenly in advance; Step 2: Weigh each raw material component according to the specified weight and set aside; Step 3: Put the composite recycled aggregate into the mixer, add the environmentally friendly interface modifier, and mix for 4 minutes; Step 4: Add cement, mineral admixtures and modifiers, and continue stirring for 8 minutes to form a dry powder mixture; Step 5: Take 70% of the total water volume and add it to the dry powder mixture. Stir for 10 minutes to form a semi-wet mixture. Step 6: Add the composite anti-seepage and anti-freeze admixture and the remaining water, stir for 15 minutes to obtain recycled concrete; Step 7: Cast the mold, vibrate to compact it, and cure at room temperature for 24 hours. Then, transfer it to a standard curing room (20±2℃, relative humidity ≥95%) for 28 days to obtain the finished product.

[0057] Step 8: Test the poured concrete to ensure that its impermeability grade is P16, its freeze-thaw resistance grade is F300, and its 28-day compressive strength is 48.9 MPa, which meets the design requirements.

[0058] Comparative test The performance of conventional recycled concrete (control group) and recycled concrete prepared in Example 2 of this invention (experimental group) was compared. The control group used ordinary recycled aggregate without composite modification, and the admixture was a single polycarboxylate superplasticizer. The remaining raw materials and proportions were the same as in Example 2, and the preparation process was the same. The performance was tested after 28 days of curing, and the results are shown in the table below: control group P6 F100 32.5 75 experimental group P14 F250 45.6 90 The comparative test results show that the impermeable and frost-resistant environmentally friendly recycled concrete prepared by this invention has significantly better impermeability, frost resistance and compressive strength than existing conventional recycled concrete, and the utilization rate of recycled aggregate is greatly improved, which fully demonstrates the superiority and inventiveness of this technical solution.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of impermeable, freeze-thaw resistant, environmentally friendly recycled concrete, characterized in that, By weight, it includes the following raw material components: 35-45 parts cement, 100-120 parts composite recycled aggregate, 15-25 parts mineral admixture, 2-4 parts composite anti-seepage and anti-freeze admixture, 18-22 parts water, 1-2 parts environmentally friendly interface modifier, and 0.5-1.5 parts modified reinforcing agent.

2. The impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 1, characterized in that, The cement is P·O42.5 grade ordinary Portland cement with a specific surface area of ​​300-350 m². 2 / kg, initial setting time ≥45min, final setting time ≤600min; the pH value of the water is 6.5-8.

5.

3. The impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 1, characterized in that, The composite recycled aggregate is obtained by mixing waste concrete recycled coarse aggregate, waste concrete recycled fine aggregate, and waste ceramic recycled aggregate in a mass ratio of 6-8:3-4:1, followed by composite modification treatment. The composite anti-seepage and anti-freeze admixture is prepared by mixing polycarboxylate-based high-efficiency water-reducing agent, air-entraining agent, organosilicon waterproofing agent, and nano-silica in a mass ratio of 5-7:2-3:1-2:0.5-1. The air-entraining agent is a rosin thermal polymer air-entraining agent with an air content controlled at 3-5%. The organosilicon waterproofing agent is a sodium methylsilicate waterproofing agent with a purity ≥98%. The nano-silica has a particle size of 50-100nm and a purity ≥99%. The polycarboxylate-based high-efficiency water-reducing agent is a retarded polycarboxylate water-reducing agent with a water reduction rate ≥25% and a solid content of 40-50%. It does not contain harmful components such as chlorides and sulfates, which can reduce the water-cement ratio and avoid corrosion of steel bars.

4. The impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 1, characterized in that, The mineral admixture is made by mixing fly ash, slag powder and silica fume in a mass ratio of 4-5:3-4:1; the environmentally friendly interface modifier is a compound of chitosan and polyacrylamide in a mass ratio of 1:2-3; the modified reinforcing agent is a compound of nano-calcium carbonate and sodium lignosulfonate in a mass ratio of 3-4:

1.

5. The impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 4, characterized in that, The fly ash is Class II fly ash, with a loss on ignition ≤8% and a water requirement ratio ≤105%; the slag powder is S95 grade slag powder with a specific surface area ≥400 m². 2 / kg; the specific surface area of ​​the silica fume is ≥18000m² 2 / kg, with a silica content of ≥90%, all three are recycled industrial waste residues, which further enhances environmental protection while increasing the density of concrete.

6. The impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 2, characterized in that, The composite modification process of the composite recycled aggregate is as follows: S100. The waste concrete is crushed and screened to obtain recycled coarse aggregate with a particle size of 5-20mm and recycled fine aggregate with a particle size of 0.15-5mm; the waste ceramics are crushed and screened to obtain recycled ceramic aggregate with a particle size of 0.5-2mm; the three aggregates are washed clean and dried to constant weight at 105±5℃. S200, prepare a 1.5-2.5% (w / w) aqueous solution of silane coupling agent KH-550, mix the three aggregates evenly in proportion and immerse them in the solution for 2-3 hours, stirring once every 30 minutes during the soaking period, then take them out and let them air dry naturally. S300. After drying, the aggregate is ground in a vertical impact crusher for 1-2 minutes, and then soaked in a modifier solution for 1-1.5 hours. The modifier solution is prepared by calcium hydroxide, sodium sulfate and water in a mass ratio of 1:0.5:

100. After soaking, the aggregate is taken out and dried at 80±5℃ for 30-40 minutes to obtain composite recycled aggregate.

7. The impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 4, characterized in that, The drying time in step S100 is 2-3 hours; In step S200, during the preparation of the aqueous solution of silane coupling agent KH-550, a nonionic surfactant of 0.1-0.2% by mass of the aqueous solution is added. The nonionic surfactant is polyoxyethylene octylphenyl ether (OP-10), which is used to improve the uniformity of the coupling agent's adhesion on the aggregate surface, enhance the modification effect, and reduce the porosity of the aggregate surface. In step S300, the grinding speed of the vertical impact crusher is 1200-1500 r / min, the soaking temperature of the modifier solution is 25±3℃, and the mixture is stirred once every 20 minutes during the soaking process; the dried composite recycled aggregate has a moisture content ≤0.5%, a crushing value ≤18%, and a needle-like and flaky particle content ≤8%, ensuring the mechanical properties of the composite recycled aggregate and improving the overall strength of the concrete.

8. The impermeable, frost-resistant, environmentally friendly recycled concrete according to any one of claims 1-7, characterized in that, It also includes 0.3-0.8 parts of an environmentally friendly rust inhibitor, which is a compound of phytic acid and zinc dihydrogen phosphate in a mass ratio of 2:

1. It is free of heavy metal pollution and is used to improve the rust protection performance of concrete for internal steel bars, delay steel bar corrosion, and extend the service life of the project.

9. A method for preparing impermeable, freeze-resistant, environmentally friendly recycled concrete, used to produce the impermeable, freeze-resistant, environmentally friendly recycled concrete according to any one of claims 1-8, characterized in that, The concrete preparation method includes the following steps: T100. Weigh each raw material component according to the weight parts and set aside; among them, the composite recycled aggregate shall be subjected to composite modification treatment in advance, and the composite anti-permeability and antifreeze admixture shall be mixed evenly in advance. T200: Place the composite recycled aggregate into a mixer, add an environmentally friendly interface modifier, and mix for 3-5 minutes. T300: Add cement, mineral admixtures and modifiers to the mixer, and continue mixing for 5-8 minutes to form a dry powder mixture; T400: Divide the water into two parts. The first part, which accounts for 60-70% of the total water, is added to the dry powder mixture and stirred for 8-10 minutes to form a semi-wet mixture. T500: Add composite anti-permeability and anti-freeze admixture and the remaining water to the semi-wet mixture, and continue stirring for 10-15 minutes to obtain anti-permeability and anti-freeze environmentally friendly recycled concrete. T600: The prepared recycled concrete is poured into shape, vibrated to compact it, and then cured at room temperature for 24 hours. It is then transferred to a standard curing room and cured for 28 days at a temperature of 20±2℃ and a relative humidity of ≥95% to obtain the finished product.

10. The method for preparing impermeable, frost-resistant, environmentally friendly recycled concrete according to claim 9, characterized in that, The stirring speed of the mixer in step T200 is 600-800 r / min, and the stirring speed in step T300 is 800-1000 r / min; The stirring speed in step T400 is 700-900 r / min; the stirring speed in step T500 is 1000-1200 r / min; In step T600, the concrete is poured and compacted using an immersion vibrator for 20-30 seconds per point, until no air bubbles appear on the concrete surface and cement slurry rises to the surface. The ambient temperature for curing is 20±5℃, and the relative humidity is ≥70%. During the curing process in the standard curing room, the concrete test blocks are sprayed with water every 7 days to maintain moisture, and the relative humidity of the curing room is maintained at ≥95% after watering. After 28 days of curing, the concrete test blocks have a permeability grade ≥P12, a frost resistance grade ≥F200, and a 28-day compressive strength ≥40MPa. The performance indicators of the finished product are clearly defined to ensure that they meet the requirements for use in the project.

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