Preparation method of ultrahigh-strength fully-recycled coarse aggregate concrete

Abstract

The invention relates to a preparation method of ultrahigh-strength fully-recycled coarse aggregate concrete, which comprises the following steps: firstly, carrying out pyrolysis treatment on a waste polymer waterproof coiled material in an inert atmosphere to obtain a pyrolysis product containing carbon nanotubes; mixing the pyrolysis product, a silane coupling agent and water to obtain a carbon nanotube dispersion liquid; spraying the carbon nanotube dispersion liquid on the surface of the mixture of the recycled coarse aggregate and the sand, and drying to obtain reinforced aggregate; mixing the pyrolysis product with cement to obtain modified cement; and mixing the reinforced aggregate, the modified cement, a mineral admixture and water to obtain the fully-recycled coarse aggregate concrete. Compared with the prior art, the high-value utilization of the waste polymer waterproof coiled material is realized, the interface bonding strength of the recycled coarse aggregate and the cement matrix is remarkably improved, and the 28-day compressive strength of the concrete reaches 80-95 MPa and the elastic modulus is improved by 20-30% by utilizing the filling effect and bridging effect of the carbon nanotubes. Meanwhile, excellent deformation resistance, impermeability and durability are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building waste resource utilization and high-performance concrete preparation, and relates to a preparation method of super-high-strength full-recycled coarse aggregate concrete. BACKGROUND

[0002] In recent years, carbon reduction in the construction industry has received high attention from the global academic community. Preparing recycled aggregate from waste concrete and replacing natural aggregate to prepare recycled aggregate concrete is an important path for energy saving and carbon reduction in the construction industry, and has become a research hotspot in the current construction field. However, the mixing ratio of recycled aggregate in previous research and engineering is usually about 30%, which limits the carbon reduction potential of recycled aggregate concrete. Full-recycled coarse aggregate concrete is a recycled concrete with a mixing ratio of recycled coarse aggregate reaching 100%. It not only maximizes the high-value utilization of waste concrete, but also saves more natural sand and stone, and has more significant environmental benefits.

[0003] However, due to the attachment of old mortar on the surface of recycled aggregate and the inevitable production of micro-cracks in the production process, the crushing index of recycled aggregate is lower than that of the same type of natural aggregate, and the porosity and water absorption are higher than those of the same type of natural aggregate. Therefore, the strength and elastic modulus of recycled aggregate concrete are often lower than those of natural aggregate concrete with the same mixing ratio, thereby limiting the application of recycled aggregate concrete. The compressive strength and modulus of full-recycled coarse aggregate concrete are further reduced due to the use of 100% recycled coarse aggregate, so the mechanical property improvement path must be studied. The mechanical properties of recycled aggregate concrete used in current engineering are usually C30 and C40, and some research reports the preparation method of recycled aggregate concrete above C40, such as the preparation method of full-recycled coarse aggregate concrete with 28-day compressive strength above 50MPa proposed by Professor Cao Wanlin of Beijing University of Technology (CN102887679B). However, full-recycled coarse aggregate concrete with compressive strength above C60 is still rare.

[0004] Carbon nanotubes have ultra-high specific surface area and chemical stability, and can play key roles such as mechanical enhancement and pore filling in concrete, and have great potential in enhancing the mechanical properties of full-recycled coarse aggregate concrete. However, carbon nanotubes have poor dispersibility in concrete and are prone to aggregation, which weakens the enhancement effect; at the same time, carbon nanotube materials are expensive, which will significantly increase the cost of concrete. Therefore, the application not only needs to solve the problem of dispersibility of carbon nanotubes, but also needs to solve the problem of source of carbon nanotubes. SUMMARY

[0005] The purpose of this invention is to provide a method for preparing ultra-high strength fully recycled coarse aggregate concrete. This method utilizes waste polymer waterproof membrane to prepare carbon nanomaterials, and then pre-treats these carbon nanotubes to enhance the fully recycled coarse aggregate concrete. This invention not only enables the fully recycled coarse aggregate concrete to achieve a compressive strength exceeding C80 and an elastic modulus exceeding 40 GPa, but also solves the problem of carbon nanotube dispersion while reducing its cost, and provides a feasible high-value resource utilization path for waste waterproof materials.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing ultra-high strength fully recycled coarse aggregate concrete includes the following steps: 1) Waste polymer waterproof membrane was pyrolyzed in an inert atmosphere to obtain a pyrolysis product containing carbon nanotubes; The pyrolysis product, silane coupling agent, and water were mixed to obtain a carbon nanotube dispersion. Carbon nanotube dispersion was sprayed onto the surface of a mixture of recycled coarse aggregate and sand, and then dried to obtain reinforced aggregate; Pyrolysis products are mixed with cement to obtain modified cement; 2) Mix reinforced aggregate, modified cement, mineral admixtures and water to obtain fully recycled coarse aggregate concrete.

[0007] Plastics can be chemically reacted (pyrolysis carbonization, chemical vapor deposition, etc.) to prepare carbon nanotubes and graphene, providing a feasible path to reduce the cost of carbon nanotubes. Waste waterproofing materials contain a large amount of polymers, such as TPO and PVC. Using these as raw materials for preparing carbon nanomaterials can not only solve the problem of high-quality resource utilization of my country's waste waterproofing materials, which have reserves of hundreds of billions of square meters, but also enhance the mechanical properties of fully recycled coarse aggregate concrete. Regarding the dispersion problem of carbon nanotubes, they can be separately coated onto the surface of recycled aggregates and sand, and then uniformly mixed with cement to reduce the aggregation problem. Based on the above ideas, this invention proposes a method for preparing ultra-high strength fully recycled coarse aggregate concrete, successfully producing fully recycled coarse aggregate concrete with a 28-day compressive strength exceeding C80, while maintaining good durability and workability.

[0008] This invention mixes carbon nanotubes with recycled aggregate, sand, and cement, allowing the carbon nanotubes to be uniformly distributed in the interfacial transition zone and within the mortar of fully recycled coarse aggregate concrete. The carbon nanotubes located in the interfacial transition zone not only reduce the porosity and water absorption of the recycled aggregate, improving the mechanical properties of the transition zone, but also enhance the bond strength between the recycled aggregate and the mortar through a bridging effect. Meanwhile, the carbon nanotubes dispersed within the mortar form a network, significantly enhancing the mechanical properties of the mortar.

[0009] In some specific implementations, in step 1), the waste polymer waterproof membrane includes thermoplastic polyolefin (TPO) waterproof membrane or polyvinyl chloride (PVC) waterproof membrane.

[0010] In some specific embodiments, the waste polymer waterproof membrane is further subjected to rinsing with clean water, ultrasonic cleaning, drying, and grinding before use; During the water rinsing process, the rinsing time is 5-10 minutes. In the ultrasonic cleaning process, the ultrasonic temperature is 50-60℃, the ultrasonic frequency is 40-50kHz, and the ultrasonic time is 30-60min. The drying process involves natural air drying, which takes 2-3 hours. After grinding, the particle size is ≤1mm.

[0011] In some specific embodiments, in step 1), the pyrolysis treatment is carried out at a temperature of 900-1000℃, with a preferred heating rate of 5-6℃ / min and a treatment time of 2-3 h; the catalyst used is nickel nitrate, and the mass ratio of nickel nitrate to waste polymer waterproof membrane is 3-4:10. The inert atmosphere includes inert gas and / or nitrogen.

[0012] In some specific embodiments, in step 1), the silane coupling agent includes KH550 silane coupling agent or KH560 silane coupling agent. In the preparation of the carbon nanotube dispersion, the mass ratio of pyrolysis product, silane coupling agent, and water is 1:0.1:100.

[0013] In some specific embodiments, in step 1), the preparation process of the carbon nanotube dispersion includes stirring, ultrasonic treatment, and centrifugation in sequence; During the stirring process, the stirring frequency is 20-40kHz and the stirring time is 10-20 min. In the ultrasonic treatment, the ultrasonic frequency is 20-40kHz and the ultrasonic time is 30-60 min. During the centrifugation, the centrifugation speed is 2000-3000 rpm and the centrifugation time is 20-60 min; The solid content of the carbon nanotube dispersion is 0.5-2 wt%.

[0014] In some specific embodiments, in step 1), the water absorption rate of the recycled coarse aggregate does not exceed 3%, the crushing index does not exceed 15%, and the particle size distribution is 5-25mm; the particle size distribution of the sand is 0.15-4.75mm. During the preparation of the reinforced aggregate, the spraying pressure is 0.25-0.3 MPa; the spraying time is 25-30 s / kg per kilogram of the mixture; the drying is carried out by static drying at room temperature for 24-48 h.

[0015] In some specific embodiments, in step 1), the cement is Portland 42.5 cement; the mass ratio of the cement to the pyrolysis product is 1-2:50, the mixing method is stirring, the stirring speed is 500 rpm, and the stirring time is 30-60 min.

[0016] In some specific embodiments, in step 2), the mineral admixture includes slag powder and fly ash in a mass ratio of 2-3:1; The slag powder is S95 grade slag powder; the fly ash is Grade I fly ash.

[0017] In some specific implementations, in step 2), the mass ratio of the recycled coarse aggregate, cement, mineral admixture, sand, and water is 100-110:40-46:21-28:75-85:16-18. The mixing process includes stirring for 10-15 minutes, followed by standing for 15-20 minutes.

[0018] In some specific embodiments, in step 2), a water-reducing agent is also added during the mixing process of the reinforcing aggregate, modified cement, and mineral admixture; the mass ratio of the recycled coarse aggregate to the water-reducing agent is 1000-1100:5.4-8.4.

[0019] This invention utilizes a pyrolysis carbonization method to prepare carbon nanotubes from waste polymer waterproof membranes. These nanotubes are then used for surface modification of recycled coarse aggregates and optimization of the sand and cementitious system. By adjusting the mix proportions, ultra-high compressive strength fully recycled coarse aggregate concrete is obtained. The specific steps include: 1) Select waste TPO-based or PVC-based polymer waterproof membranes, perform pretreatment such as cleaning, drying, and cutting, and use pyrolysis carbonization to prepare carbon nanotubes from the treated waste polymer waterproof membranes. 2) The obtained carbon nanotubes are loaded onto the surface of recycled coarse aggregate to form a reinforced coating by ultrasonic dispersion. 3) The sand and carbon nanotubes are mixed evenly to obtain reinforced coarse aggregate and reinforced sand; 4) Cement and carbon nanotubes are mixed evenly to obtain reinforced cement; 5) By uniformly mixing reinforced coarse aggregate, reinforced sand, reinforced cement, water, mineral admixtures and high-efficiency water-reducing agent in a certain proportion, ultra-high strength fully recycled coarse aggregate concrete can be prepared.

[0020] This invention not only realizes the high-value utilization of waste polymer waterproof membrane, but also significantly improves the interfacial bonding strength between recycled coarse aggregate and cement matrix. By utilizing the filling and bridging effects of carbon nanotubes, the 28-day compressive strength of concrete reaches 80-95 MPa, the elastic modulus is increased by 20%-30%, and it also has excellent resistance to deformation, impermeability and durability.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1) Co-utilization of waste resources: Pyrolysis and carbonization of waterproof membrane into carbon nanotubes reduces the cost of nano-reinforcing agents; 2) Dual-path interface enhancement: Carbon nanotubes both coat the aggregate surface to improve interfacial bonding and disperse in the cement matrix to fill pores; 3) Significantly improved performance: The 28-day compressive strength of the all-recycled coarse aggregate concrete developed in this invention exceeds 80 MPa, the elastic modulus is greater than 40 GPa, and the chloride ion permeability coefficient is less than 1.5 × 10⁻⁶. -12 m 2 / s; 4) Great potential for engineering applications: Except for carbon nanotube pyrolysis carbonization, there are no special requirements for raw materials, making it more widely applicable. Moreover, its mechanical properties are excellent, which can significantly expand the application scenarios of recycled aggregate concrete.

[0022] In summary, this invention can produce fully recycled coarse aggregate concrete with a 28-day compressive strength exceeding 80 MPa and good resistance to chloride ion penetration. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments.

[0024] A method for preparing ultra-high strength fully recycled coarse aggregate concrete includes the following steps: (1) Carbon nanotubes were prepared from waste polymer waterproofing materials. Select waste polymer waterproof membranes with thermoplastic polyolefin (TPO) or polyvinyl chloride (PVC) as the main components. First, rinse with clean water for 5-10 minutes to remove impurities such as dust, sand, and nails from the surface. Then, ultrasonically clean at 50-60℃ for 30-60 minutes to remove oil stains and surface additives from the waste polymer waterproof membranes. After cleaning, let the waste polymer waterproof membranes air dry naturally for 2-3 hours to remove moisture. Next, use a crusher and grinder to crush and grind the waste polymer waterproof membranes into powder with a particle size of less than 1mm.

[0025] 100mg of waste polymer waterproof membrane powder was placed in a horizontal tube furnace, with inert argon as the protective gas and nickel nitrate as the catalyst. The temperature was gradually increased to about 900-1000℃ at a rate of 5℃ / min. The powder was then allowed to fully pyrolyze and carbonize for 2-3 hours. After cooling and fine grinding (D50≤5μm), carbon nanotubes with a purity of 30%-35% were obtained.

[0026] (2) Modification of recycled aggregates, sand and cement using carbon nanotubes First, carbon nanotubes, silane coupling agent (KH550 or KH560), and water are mixed in a mass ratio of 1:0.1:100 and stirred at a frequency of 20-40 kHz for 10-20 min. Then, the mixture is treated with an ultrasonic disruptor for 30-60 min. To remove undispersed agglomerates, the mixture is centrifuged at 2000-3000 rpm for 30-60 min to obtain a uniform carbon nanotube dispersion with a solid content of 0.5-2 wt%.

[0027] Recycled aggregate (5-25mm) that has undergone two crushing and screening pretreatments, with a water absorption rate controlled below 3% and a crushing index ≤15%, is selected. The sand selected meets the requirements of the national standard GB / T 14684-2022 for construction sand. The carbon nanotube dispersion with uniform dispersion is sprayed onto the surface of the recycled aggregate and construction sand using ultrasonic atomization spraying equipment to form a reinforced coating. Then, it is left to stand for more than 24 hours until the moisture evaporates completely.

[0028] For cement modification, cement and carbon nanotubes are placed in a mixer at a mass ratio of 1:50 and stirred at 500 rpm for 30-60 minutes to ensure uniform mixing.

[0029] The mineral admixture was prepared by mixing S95 grade slag powder and Grade I fly ash at a mass ratio of 2:1.

[0030] (3) Obtain ultra-high strength fully recycled coarse aggregate concrete samples After obtaining the above-mentioned reinforced coarse aggregate, reinforced sand, and reinforced cement, they are mixed with water, mineral admixtures, and high-efficiency water-reducing agent according to the absolute volume method in a certain mix proportion. The water-cement ratio is controlled between 0.30 and 0.45, the dosage of high-efficiency water-reducing agent is between 0.05% and 0.30%, and the dosage of fly ash is between 10% and 25%. The mixture is stirred according to the mixing parameters of conventional concrete until the concrete is formed, thus obtaining high-strength fully recycled coarse aggregate concrete.

[0031] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0032] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0033] Based on the above method, three groups of ultra-high strength recycled aggregate concrete samples were prepared in Examples 1-3, and their compressive strength, elastic modulus, and chloride ion permeability coefficient were tested. The test results showed that the 28-day compressive strength of the fully recycled coarse aggregate concrete was between 80-95 MPa, the elastic modulus was between 40-52 GPa, and the chloride ion permeability coefficient was 1.0-1.5 × 10⁻⁶. -12 m 2 The range of / s indicates that the present invention can significantly improve the mechanical properties and durability of fully recycled coarse aggregate concrete.

[0034] Example 1 A method for preparing ultra-high strength fully recycled coarse aggregate concrete includes the following steps: S1: Select 100g of waste polymer waterproof membrane with TPO as the main component. This waste polymer waterproof membrane comes from a waste resource utilization center in Shanghai. First, rinse with clean water for 5 minutes to remove surface impurities, and then ultrasonically clean at 50℃ for 30 minutes (frequency 40kHz, power 300W) to remove oil and surface additives. After cleaning, air dry for 2 hours. Subsequently, use a crusher and grinder to grind the waste polymer waterproof membrane to a particle size ≤1mm to obtain waste polymer waterproof membrane powder.

[0035] S2: Place approximately 100 mg of waste polymer waterproof membrane powder in a horizontal tube furnace. Use inert argon gas as a protective gas (flow rate 200 mL / min) and 30 mg of nickel nitrate as a catalyst. Mix the waste polymer waterproof membrane powder with the catalyst, then gradually increase the temperature to 900°C at a rate of 5°C / min and maintain the temperature for 2 hours. After cooling, finely grind the product to obtain a carbon nanotube product with a purity of approximately 30%. Repeat this process multiple times until the obtained carbon nanotube product is sufficient for subsequent sample preparation.

[0036] S3: Mix carbon nanotube product, KH550 silane coupling agent and water at a mass ratio of 1:0.1:100 and stir at 1500 rpm / min for 20 min. Then, treat with an ultrasonic disruptor for 40 min (ultrasonic frequency 30 kHz, power 500 W, duty cycle 50%). Finally, centrifuge at 2000 rpm for 60 min to obtain a uniform carbon nanotube dispersion with a solid content of 1 wt%.

[0037] S4: Select recycled coarse aggregate (particle size distribution 5-25mm, average particle size 10mm) with a water absorption rate controlled at 3% and a crushing index of 15%, and construction sand that meets the requirements of national standard GB / T 14684-2022 (recycled coarse aggregate and construction sand are from Shaoxing Lvcheng New Material Manufacturing Co., Ltd., the same below), and crush and screen them twice. Use ultrasonic atomization spraying equipment to spray the uniformly dispersed carbon nanotube dispersion onto the surface of recycled coarse aggregate and construction sand to form a reinforced coating. The spraying pressure is 0.3MPa, the spraying rate is 0.67 mL (dispersion) / s, and the spraying time is 30 seconds / kg of aggregate (recycled coarse aggregate + construction sand), and then let it stand for 48 hours.

[0038] For cement modification, Portland 42.5 cement (Guangdong Jinyang Building Materials Co., Ltd., the same below) and carbon nanotube products were placed in a mixer at a mass ratio of 1:50 and stirred at 500 rpm for 40 minutes to mix the cement and carbon nanotubes evenly.

[0039] The mineral admixture was prepared by mixing S95 grade slag powder (Lingshou County Anda Mineral Powder Factory, the same below) and Grade I fly ash at a mass ratio of 2:1.

[0040] S5: Prepare the all-recycled coarse aggregate concrete sample according to the mix proportions shown in Table 1. Mix the sample in a mixer for about 10 minutes to ensure it is homogeneous. Observe the fluidity and water retention of the sample. If the fluidity is poor (slump less than 50 mm, the same below), a small amount of high-efficiency water-reducing agent (Shandong Wanshan Group Co., Ltd., the same below) can be added. Let the mixture stand for about 15 minutes and conduct a simple slump test. If the slump meets the requirements (slump greater than 60 mm, the same below), then compact the sample.

[0041] Table 1. Mix proportions of all recycled coarse aggregate concrete in Example 1 (water-cement ratio 0.35) Note: The amount of raw materials used refers to the amount of raw materials after modification by the corresponding method.

[0042] Example 2 A method for preparing ultra-high strength fully recycled coarse aggregate concrete includes the following steps: S1: Select 100g of PVC-based waste waterproof membrane. First, rinse with clean water for 5 minutes to remove surface impurities. Then, ultrasonically clean at 55℃ for 40 minutes (frequency 40kHz, power 300W) to remove oil and surface additives. After cleaning, air dry naturally for 2 hours. Subsequently, use a crusher and grinder to grind the waste polymer waterproof membrane to a particle size ≤1mm to obtain waste polymer waterproof membrane powder.

[0043] S2: Place approximately 100 mg of waste polymer waterproof membrane powder in a horizontal tube furnace. Use inert argon gas as a protective gas (flow rate 200 mL / min) and 30 mg of nickel nitrate as a catalyst. Mix the waste polymer waterproof membrane powder with the catalyst, then gradually increase the temperature to 1000℃ at a rate of 5℃ / min and maintain the temperature for 2.5 hours. Afterward, allow the product to cool naturally to room temperature and finely grind it until D50 ≤ 5 μm to obtain a carbon nanotube product with a purity of approximately 32%. Repeat this process multiple times until the obtained carbon nanotube product is sufficient for subsequent sample preparation.

[0044] S3: Mix carbon nanotube product, KH550 silane coupling agent and water at a mass ratio of 1:0.1:100 and stir at 20kHz for 15min. Then, treat with an ultrasonic disruptor for 45min (ultrasonic frequency 35kHz, power 500W, duty cycle 50%). Finally, centrifuge at 3000rpm for 20min to obtain a uniform carbon nanotube dispersion with a solid content of 1.2wt%.

[0045] S4: Select recycled coarse aggregate (particle size distribution 5-25mm, average particle size 20mm) with a water absorption rate controlled at 2.8% and a crushing index of 12.5%, and construction sand that meets the requirements of national standard GB / T 14684-2022. The aggregate undergoes two crushing and screening processes. Using ultrasonic atomization spraying equipment, a uniformly dispersed carbon nanotube dispersion is sprayed onto the surface of the recycled coarse aggregate and construction sand to form a reinforced coating. The spraying pressure is 0.3MPa, the spraying rate is 1.77mL (dispersion) / s, and the spraying time is 30 seconds / kg of aggregate (recycled coarse aggregate + construction sand). The mixture is then allowed to stand for 48 hours.

[0046] For cement modification, Portland 42.5 cement and carbon nanotube products were placed in a mixer at a mass ratio of 1:50 and stirred at 500 rpm for 45 minutes to ensure uniform mixing. The resulting mixture had a specific surface area of ​​380 m². 2 / kg.

[0047] The mineral admixture was prepared by mixing S95 grade slag powder and Grade I fly ash at a mass ratio of 2:1.

[0048] S5: Prepare the all-recycled coarse aggregate concrete sample according to the mix proportions shown in Table 2. Mix the sample in a mixer for about 10 minutes to ensure it is homogeneous. Observe the fluidity and water retention of the sample. If the fluidity is poor, a small amount of high-efficiency water-reducing agent can be added. Let the mixture stand for about 15 minutes and conduct a simple slump test. If the slump meets the requirements, compact the sample.

[0049] Table 2. Mix proportions of fully recycled coarse aggregate concrete in Example 2 (water-cement ratio 0.40) Note: The amount of raw materials used refers to the amount of raw materials after modification by the corresponding method.

[0050] Example 3 A method for preparing ultra-high strength fully recycled coarse aggregate concrete includes the following steps: S1: Select 100g of waste PVC-based waterproof membrane. First, rinse with clean water for 8 minutes to remove surface impurities. Then, ultrasonically clean with water at 50℃ for 30 minutes (frequency 40kHz, power 250W) to remove oil and surface additives. After cleaning, air dry naturally for 2 hours. Subsequently, use a crusher and grinder to grind the waste polymer waterproof membrane to a particle size ≤1mm to obtain waste polymer waterproof membrane powder.

[0051] S2: Place approximately 100 mg of waste polymer waterproof membrane powder in a horizontal tube furnace. Use inert argon gas as a protective gas (flow rate 150 mL / min) and 30 mg of nickel nitrate as a catalyst. Mix the waste polymer waterproof membrane powder with the catalyst, then gradually increase the temperature to 1000℃ at a rate of 5℃ / min and maintain the temperature for 2 hours. Afterward, allow the product to cool naturally to room temperature and finely grind it until D50 ≤ 5 μm to obtain a carbon nanotube product with a purity of approximately 34%. Repeat this process multiple times until the obtained carbon nanotube product is sufficient for subsequent sample preparation.

[0052] S3: Mix carbon nanotube product, KH550 silane coupling agent and water at a mass ratio of 1:0.1:100 and stir at 20kHz for 10 min. Then, treat with an ultrasonic disruptor for 30 min (ultrasonic frequency 30kHz, power 400W, duty cycle 40%). Finally, centrifuge at 2500 rpm for 25 min to obtain a uniform carbon nanotube dispersion with a solid content of 0.8wt%.

[0053] S4: Select recycled coarse aggregate (particle size distribution 5-25mm, average particle size 15mm) with a water absorption rate controlled at 2.5% and a crushing index of 10.5%, and construction sand that meets the requirements of national standard GB / T 14684-2022. The aggregate undergoes two crushing and screening processes. Using ultrasonic atomization spraying equipment, a uniformly dispersed carbon nanotube dispersion is sprayed onto the surface of the recycled coarse aggregate and construction sand to form a reinforced coating. The spraying pressure is 0.25MPa, the spraying rate is 1.65mL (dispersion) / s, and the spraying time is 25 seconds / kg of aggregate (recycled coarse aggregate + construction sand). The mixture is then allowed to stand for 24 hours.

[0054] For cement modification, Portland 42.5 cement and carbon nanotube products were placed in a mixer at a mass ratio of 1:50 and stirred at 500 rpm for 30 minutes to ensure uniform mixing. The resulting mixture had a specific surface area of ​​360 m². 2 / kg.

[0055] The mineral admixture was prepared by mixing S95 grade slag powder and Grade I fly ash at a mass ratio of 2:1.

[0056] S5: Prepare the all-recycled coarse aggregate concrete sample according to the mix proportions shown in Table 3. Mix the sample in a mixer for about 10 minutes to ensure it is homogeneous. Observe the fluidity and water retention of the sample. If the fluidity is poor, a small amount of high-efficiency water-reducing agent can be added. Let the mixture stand for about 15 minutes and conduct a simple slump test. If the slump meets the requirements, compact the sample.

[0057] Table 3. Mix proportions of fully recycled coarse aggregate concrete in Example 3 (water-cement ratio 0.45) Table 4 shows the test results of compressive strength, elastic modulus, and chloride ion permeability coefficient of the fully recycled coarse aggregate concrete prepared in Examples 1-3 according to GB / T 50081-2019. Clearly, this invention can obtain fully recycled coarse aggregate concrete samples with a 28-day compressive strength between 80-95 MPa, an elastic modulus between 40-52 GPa, and a chloride ion permeability coefficient between 1.0-1.5 × 10⁻⁶. -12 m 2 Between / s.

[0058] Table 4 Performance test results of all recycled coarse aggregate concrete samples The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing ultra-high strength fully recycled coarse aggregate concrete, characterized in that, Includes the following steps: 1) Waste polymer waterproof membrane was pyrolyzed in an inert atmosphere to obtain a pyrolysis product containing carbon nanotubes; The pyrolysis product, silane coupling agent, and water were mixed to obtain a carbon nanotube dispersion. Carbon nanotube dispersion was sprayed onto the surface of a mixture of recycled coarse aggregate and sand, and then dried to obtain reinforced aggregate; Pyrolysis products are mixed with cement to obtain modified cement; 2) Mix reinforced aggregate, modified cement, mineral admixtures and water to obtain fully recycled coarse aggregate concrete.

2. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the waste polymer waterproof membrane includes thermoplastic polyolefin waterproof membrane or polyvinyl chloride waterproof membrane.

3. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the pyrolysis treatment is carried out at a temperature of 900-1000℃ for 2-3 hours; the catalyst used is nickel nitrate, and the mass ratio of nickel nitrate to waste polymer waterproof membrane is 3-4:

10. The inert atmosphere includes inert gas and / or nitrogen.

4. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the silane coupling agent includes KH550 silane coupling agent or KH560 silane coupling agent; In the preparation of the carbon nanotube dispersion, the mass ratio of pyrolysis product, silane coupling agent, and water is 1:0.1:

100.

5. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the preparation process of the carbon nanotube dispersion includes stirring, ultrasonic treatment, and centrifugation in sequence; During the stirring process, the stirring frequency is 20-40kHz and the stirring time is 10-20 min. In the ultrasonic treatment, the ultrasonic frequency is 20-40kHz and the ultrasonic time is 30-60 min. During the centrifugation, the centrifugation speed is 2000-3000 rpm and the centrifugation time is 20-60 min; The solid content of the carbon nanotube dispersion is 0.5-2 wt%.

6. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the water absorption rate of the recycled coarse aggregate does not exceed 3%, the crushing index does not exceed 15%, and the particle size distribution is 5-25mm; the particle size distribution of the sand is 0.15-4.75mm. During the preparation of the reinforced aggregate, the spraying pressure is 0.25-0.3 MPa; the spraying time is 25-30 s / kg per kilogram of the mixture; the drying is carried out by static drying at room temperature for 24-48 h.

7. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the cement is Portland 42.5 cement; the mass ratio of the cement to the pyrolysis product is 1-2:50, the mixing method is stirring, the stirring speed is 500 rpm, and the stirring time is 30-60 min.

8. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 2), the mineral admixture includes slag powder and fly ash in a mass ratio of 2-3:1; The slag powder is S95 grade slag powder; the fly ash is Grade I fly ash.

9. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 2), the mass ratio of the recycled coarse aggregate, cement, mineral admixture, sand, and water is 100-110:40-46:21-28:75-85:16-18; The mixing process includes stirring for 10-15 minutes, followed by standing for 15-20 minutes.

10. The method for preparing ultra-high strength fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 2), a water-reducing agent is added during the mixing process of the reinforcing aggregate, modified cement, and mineral admixture; the mass ratio of the recycled coarse aggregate to the water-reducing agent is 1000-1100:5.4-8.4.

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