Environment-friendly concrete prepared from construction waste and preparation method of environment-friendly concrete

Abstract

The invention relates to the technical field of building materials, and discloses an environment-friendly concrete using construction waste and a preparation method thereof, and the concrete is composed of composite modified recycled aggregate, cement, industrial solid waste composite powder, water, a polycarboxylate superplasticizer, nano calcium carbonate and cardanol modified carbon nanotubes according to a specific proportion. The composite modified recycled aggregate is derived from construction waste and is modified by calcium hydroxide soaking and carbon dioxide curing; the industrial solid waste composite powder is prepared by mixing and grinding phosphorus slag, fly ash and mineral powder; the cardanol modified carbon nanotubes are obtained by acylating chlorination of carboxylated carbon nanotubes, preparation of hyperbranched polyglycerol from cardanol and glycidol, and reaction modification. All the components are stirred and mixed according to a process to prepare a finished product. The construction waste and industrial solid waste are recycled, the process is simple, and the obtained concrete is excellent in mechanical property and durability and low in cost and conforms to the green and low-carbon concept.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to an environmentally friendly concrete using construction waste and its preparation method. Background Technology

[0002] With the acceleration of urbanization and the advancement of urban renewal, a large amount of construction waste has been generated, such as discarded concrete blocks, bricks, and mortar. Currently, the main method of construction waste disposal is landfill, which not only occupies a large amount of land resources but also easily causes ecological and environmental problems such as soil and groundwater pollution. At the same time, the preparation of traditional concrete requires the consumption of large amounts of non-renewable resources such as natural sand and gravel. With the increasing depletion of natural sand and gravel resources, the construction industry faces a severe challenge of resource shortage.

[0003] To achieve the resource utilization of construction waste and alleviate the shortage of natural resources, existing technologies have included research on using crushed construction waste as recycled aggregate to prepare concrete. However, existing technologies for preparing recycled concrete from construction waste generally suffer from the following drawbacks: First, the recycled aggregate has a high content of cement mortar and impurities on its surface, resulting in high water absorption, low apparent density, and high crushing rate, which in turn affects the mechanical properties and durability of the concrete. Second, the mix design of recycled concrete is often unreasonable, making it difficult to balance the flowability, strength, and environmental friendliness of the concrete. Third, the preparation process is complex and has low production efficiency, hindering large-scale application. For example, some existing recycled aggregate pretreatment processes only use a single washing or soaking method, resulting in poor modification effects and limited performance improvement of the recycled aggregate. Some preparation methods also suffer from uneven mixing and harsh curing conditions, leading to unstable quality of the finished concrete.

[0004] Therefore, developing an environmentally friendly concrete made from construction waste that can effectively improve the performance of recycled aggregates, has a scientific and reasonable mix proportion, a simple and efficient preparation process, and excellent mechanical properties and durability, as well as its preparation method, has important practical significance and application value. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an environmentally friendly concrete utilizing construction waste and its preparation method, which improves the mechanical properties and durability of the concrete. At the same time, the preparation process is simple and efficient, realizing the high-value utilization of construction waste, reducing the production cost of concrete, and conforming to the concept of green and low-carbon development.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: an environmentally friendly concrete utilizing construction waste, comprising the following weight components: 800-900 parts of composite modified recycled aggregate, 300-350 parts of cement, 80-120 parts of industrial solid waste composite powder, 150-180 parts of water, 3-5 parts of polycarboxylate-based high-efficiency water-reducing agent, 4-6 parts of nano-calcium carbonate, and 3-4 parts of cashew nut shell modified carbon nanotubes; The composite modified recycled aggregate is obtained from construction waste through crushing, screening, and composite modification treatment. The composite modification treatment includes the following steps: first, soak the screened recycled aggregate in calcium hydroxide solution for 12-24 hours, take it out and dry it, and then place it in a carbon dioxide atmosphere for 8-12 hours. The industrial solid waste composite powder is made by mixing and grinding phosphorus slag, fly ash and mineral powder in a mass ratio of 3:2:1, and its specific surface area is 400-500 m² / kg. Construction waste consists of waste concrete blocks, waste bricks, and waste mortar in a 6:3:1 mass ratio. This ratio balances aggregate strength and the availability of diverse sources, avoiding performance fluctuations caused by a single type of waste material.

[0007] Particle size classification: 5-20mm coarse aggregate accounts for 60-70%, and 0.16-5mm fine aggregate accounts for 30-40%, which conforms to the principle of concrete aggregate gradation optimization, can reduce porosity and improve density.

[0008] Modification process: Soaking in 5-8% calcium hydroxide solution for 12-24 hours (chemical pretreatment) → Curing in 80-90% carbon dioxide atmosphere at 25-35℃ for 8-12 hours (air-hardening reaction). Calcium hydroxide solution can dissolve loose cement mortar and impurities adhering to the aggregate surface, while simultaneously forming an alkaline protective film on the aggregate surface. During carbon dioxide curing, it reacts with the calcium hydroxide inside and on the surface of the aggregate to generate calcium carbonate (Ca(OH)2+CO2=CaCO3+H2O). Calcium carbonate crystals fill the aggregate pores, reducing water absorption, increasing apparent density and strength, thus addressing the performance shortcomings of recycled aggregates from the source.

[0009] Preferably, the construction waste includes waste concrete blocks, waste bricks, and waste mortar, with a mass ratio of 6:3:1.

[0010] Preferably, the particle size classification of the composite modified recycled aggregate is as follows: 60-70% of the recycled coarse aggregate is 5-20mm, and 30-40% of the recycled fine aggregate is 0.16-5mm; the mass concentration of the calcium hydroxide solution is 5-8%; the concentration of the carbon dioxide atmosphere is 80-90%; and the curing temperature is 25-35℃.

[0011] Preferably, the modified carbon nanotubes are prepared by: Step (1): After uniformly dispersing N,N-dimethylformamide solvent, carboxylated carbon nanotubes and thionyl chloride by ultrasonication, the mixture is heated to reflux and reacted at 125-135℃ for 18-24h. After the reaction is completed, the mixture is rotary evaporated, washed with tetrahydrofuran, and dried to obtain acyl chloride carbon nanotubes. Step (2): Add cashew phenol and glycidol to the reaction flask, blow nitrogen into the mixture and stir evenly for 16-20 min to remove air, react at 75-80℃ for 1-2 h; then raise the temperature to 95-100℃ at 8-10℃ / min and react for 2-4 h; finally raise the temperature to 110-120℃ at 8-10℃ / min and react for 1.5-2 h, then cool the mixture to room temperature to obtain hyperbranched cashew phenol polyglycerol; Step (3): Add hyperbranched cashew phenol polyglycerol to 70-80 mL of N,N-dimethylformamide solvent, stir and mix, then add acyl chloride carbon nanotubes and pyridine catalyst, react at 30-40℃ for 5-8 h, after which distill under reduced pressure, filter, wash, and obtain cashew phenol modified carbon nanotubes.

[0012] Acyl chloride reaction: N,N-dimethylformamide (solvent), carboxylated carbon nanotubes, and thionyl chloride are mixed in a specific ratio and refluxed. The core function is to convert carboxyl groups (-COOH) into acyl chloride groups (-COCl), thereby enhancing the reactivity of carbon nanotubes and laying the foundation for subsequent grafting (acyl chloride groups have a much higher reactivity with hydroxyl groups than carboxyl groups).

[0013] Preparation of hyperbranched cashew phenol polyglycerol: Cashew phenol and glycidol are reacted in a stepwise manner according to a specific ratio, followed by a pre-reaction at 75-80℃, followed by a reaction at 8-10℃ / min to 95-100℃, and then a further reaction at 110-120℃. The hyperbranched structure provides a large number of hydroxyl groups (-OH), while the long-chain alkyl groups improve the dispersibility of carbon nanotubes in concrete and prevent agglomeration.

[0014] Grafting reaction: Hyperbranched cashew phenol polyglycerol, acyl chloride carbon nanotubes, and pyridine catalyst are reacted in the specified proportions. Pyridine acts as an acid-binding agent to neutralize the HCl generated in the reaction, preventing it from corroding equipment or affecting the reaction process. The reaction temperature of 30-40℃ is mild, ensuring reaction efficiency while avoiding molecular structure damage caused by high temperatures, ultimately achieving stable grafting of cashew phenol polyglycerol and carbon nanotubes. Carbon nanotubes themselves have excellent reinforcing and toughening properties, but they have problems such as "easy agglomeration and poor compatibility with concrete matrix". Cashew phenol has an aromatic ring structure and long-chain alkyl, and has both lipophilicity and reactivity. By chemically modifying it and grafting it onto the surface of carbon nanotubes, both dispersibility and compatibility are improved.

[0015] Preferably, in step (1), the ratio of N,N-dimethylformamide, carboxylated carbon nanotubes, and thionyl chloride is 65-75 mL: 2.5-3 g: 22-26 g.

[0016] Preferably, in step (2), the ratio of cashew phenol to glycidol is 4.51-4.6g: 3.3-3.5g. Preferably, in step (3), the ratio of hyperbranched cashew polyglycerol, acyl chloride carbon nanotubes, and pyridine catalyst is 0.8-1 mmol: 1.2-1.5 mmol: 0.01 g-0.015 g.

[0017] Preferably, the process includes the following steps: adding modified recycled aggregate, cement, industrial solid waste composite powder, water, polycarboxylate-based high-efficiency water-reducing agent, nano-calcium carbonate, and cashew phenol-modified carbon nanotubes into a mixer and stirring for 2-3 minutes. The stirring speed of the mixer is 300-400 r / min, and finally, environmentally friendly concrete utilizing construction waste is obtained; phosphorus slag, fly ash, and mineral powder are mixed and ground in a mass ratio of 3:2:1, and the specific surface area is controlled at 400-500 m² / kg. This formulation fully utilizes the complementarity of three types of industrial solid waste: phosphorus slag has high hydration activity, fly ash can improve concrete fluidity, and mineral powder can enhance later-stage strength. The high specific surface area design enhances its pozzolanic activity, reacting with cement hydration products to generate hydrated calcium silicate (CSH) gel, filling the voids inside the concrete and replacing part of the cement, thus reducing costs. Composite modified recycled aggregate (macroscopic skeleton), industrial solid waste composite powder (mesoscopic filler), nano-calcium carbonate (microscopic filler), and cashew phenol modified carbon nanotubes (microscopic reinforcement) form a multi-level structural optimization of "macro-meso-micro", comprehensively improving concrete performance.

[0018] Beneficial technical effects: This invention uses construction waste as raw material to prepare composite modified recycled aggregate, achieving the reduction and resource utilization of construction waste, effectively solving the problems of land occupation and environmental pollution caused by construction waste landfill. Simultaneously, it introduces industrial solid waste composite powder to replace part of the cement, further utilizing industrial waste such as phosphorus slag and fly ash, reducing dependence on natural resources, and meeting the requirements of green development. Through a composite modification process of "calcium hydroxide soaking + carbon dioxide curing" on the recycled aggregate, impurities attached to the aggregate surface are effectively removed, aggregate pores are filled, and the apparent density and strength of the aggregate are improved. At the same time, the addition of cashew phenol-modified carbon nanotubes, utilizing their excellent mechanical properties and dispersibility, forms a three-dimensional overlapping network inside the concrete, significantly enhancing the compressive and flexural strength of the concrete.

[0019] This invention utilizes cashew phenol-modified carbon nanotubes. While the nanotubes themselves possess extremely high tensile strength, unmodified carbon nanotubes are prone to agglomeration due to van der Waals forces, hindering their superior performance. This invention addresses this by modifying the carbon nanotubes with hyperbranched polyglycerol using cashew phenol. The steric hindrance effect of the hyperbranched structure breaks the agglomeration of the carbon nanotubes, allowing them to disperse uniformly within the concrete matrix, forming a three-dimensional network of nanoscale support framework. This framework effectively bears external forces, transmits stress, and inhibits the generation and propagation of microcracks within the concrete. When the concrete is subjected to compressive or tensile loads, the dispersed modified carbon nanotubes can "bridge" the ends of the cracks, preventing further extension and significantly improving the compressive strength, tensile strength, and fracture toughness of the concrete. Combined with the micro-filling effect of nano-calcium carbonate in the concrete mix, the modified carbon nanotubes and nano-calcium carbonate form a "reinforcement-filling" synergy, further optimizing the density of the concrete microstructure and enhancing its mechanical properties.

[0020] Traditional concrete (including recycled concrete) generally suffers from high brittleness and poor impact resistance. Cashew phenol-modified carbon nanotubes achieve toughening in two ways: the long-chain alkyl groups in the cashew phenol molecule have flexible characteristics. After being grafted onto the surface of carbon nanotubes, they can form "flexible connection points" inside the concrete. When the concrete is subjected to external impact, the long-chain alkyl groups can absorb energy through their own deformation, thus relieving impact stress. The high aspect ratio of carbon nanotubes allows them to form a "fibrous dispersed phase" in the concrete matrix, similar to the role of steel bars in concrete. This improves the flexural strength of the concrete, reduces the risk of brittle fracture, and makes the concrete less prone to sudden failure under load.

[0021] Unmodified carbon nanotubes have a strong inert surface and weak interfacial bonding with cement hydration products (such as CSH gel), easily forming voids at the interface and becoming a weakness in concrete performance. Cashew nut shell modified carbon nanotubes optimize compatibility through a combination of chemical and physical processes. The hyperbranched cashew nut shell polyglycerol molecules contain a large number of hydroxyl groups (-OH), which can undergo hydrogen bonding or chemical reactions with hydroxyl and carboxyl groups in cement hydration products, forming a stable chemical bond that allows the carbon nanotubes to adhere tightly to the cement matrix. The aromatic ring structure and long-chain alkyl groups of cashew nut shell enhance the oleophilicity and interfacial adsorption capacity of carbon nanotubes, improving their dispersion stability in concrete mixtures, preventing interfacial defects caused by agglomeration, and improving the quality of interfacial bonding.

[0022] The preparation process of this invention does not require complex equipment or harsh curing conditions. The mixing process is simple and efficient, and it is highly feasible for large-scale production. At the same time, the raw materials are scientifically and rationally matched, and the synergistic effect of each component is stable, which ensures the consistency of the quality of the finished concrete and is conducive to industrial promotion and application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the specifications and specific embodiments.

[0025] The preparation of carboxylated carbon nanotubes was described in the reference "Carboxyl Functionalization of Carbon Nanotubes and Its Influence on Cement Stone". A small amount of carbon nanotubes was placed in a beaker, moistened with 10 mL of ethanol, and then thoroughly mixed with 10 mL of dilute sulfuric acid solution. The solution was heated at 80°C and slowly stirred for 6 hours. After the mixture was allowed to cool to room temperature, 1 mL of nitric acid was added dropwise under slow stirring. After stirring for 24 hours, the mixture was washed with water until the pH reached 7.

[0026] The cement is P·O425 grade ordinary Portland cement.

[0027] Example 1 An environmentally friendly concrete utilizing construction waste is characterized by comprising the following weight components: 850 parts of composite modified recycled aggregate, 320 parts of cement, 100 parts of industrial solid waste composite powder, 165 parts of water, 4 parts of polycarboxylate-based high-efficiency water-reducing agent, 5 parts of nano-calcium carbonate, and 3.5 parts of cashew phenol-modified carbon nanotubes. The construction waste includes waste concrete blocks, waste bricks, and waste mortar, with a mass ratio of 6:3:1. The particle size classification of the composite modified recycled aggregate is as follows: 65% of the recycled coarse aggregate is 10mm, and 35% of the recycled fine aggregate is 0.2mm. The composite modification treatment steps are as follows: the screened recycled aggregate is soaked in a 6% calcium hydroxide solution for 18 hours, taken out and dried, and then cured in a carbon dioxide atmosphere with a concentration of 85% and a temperature of 30℃ for 10 hours. The industrial solid waste composite powder is made by mixing and grinding phosphorus slag, fly ash and mineral powder in a mass ratio of 3:2:1, and its specific surface area is 450m² / kg. The preparation method of modified carbon nanotubes is as follows: Step (1): 70 mL of N,N-dimethylformamide solvent, 2.8 g of carboxylated carbon nanotubes and 24 g of thionyl chloride were ultrasonically dispersed evenly, heated to reflux, and reacted at 130 °C for 20 h. After the reaction was completed, the mixture was rotary evaporated, washed with tetrahydrofuran, and dried to obtain acyl chloride carbon nanotubes. Step (2): Add 4.55g of cashew phenol and 3.4g of glycidol to the reaction flask, blow nitrogen into the mixture and stir evenly for 18min to remove air, react at 78℃ for 1.5h; then increase the temperature to 98℃ at 9℃ / min and react for 3h; finally increase the temperature to 115℃ at 9℃ / min and react for 1.8h, then cool the mixture to room temperature to obtain hyperbranched cashew phenol polyglycerol; Step (3): Add 0.9 mmol of hyperbranched cashew phenol polyglycerol to 75 mL of N,N-dimethylformamide solvent, stir and mix, then add 1.3 mmol of acyl chloride carbon nanotubes and 0.01 g of pyridine catalyst, react at 35 °C for 7 h, after which distill under reduced pressure, filter, wash, and obtain cashew phenol modified carbon nanotubes.

[0028] The preparation of environmentally friendly concrete includes the following steps: adding composite modified recycled aggregate, cement, industrial solid waste composite powder, water, polycarboxylate-based high-efficiency water-reducing agent, nano calcium carbonate, and cashew phenol modified carbon nanotubes into a mixer and mixing for 2.5 minutes. The mixing speed of the mixer is 350 r / min, and finally environmentally friendly concrete made from construction waste is obtained.

[0029] Example 2 An environmentally friendly concrete utilizing construction waste is characterized by comprising the following weight components: 800 parts of composite modified recycled aggregate, 300 parts of cement, 80 parts of industrial solid waste composite powder, 150 parts of water, 3 parts of polycarboxylate-based high-efficiency water-reducing agent, 4 parts of nano-calcium carbonate, and 3 parts of cashew phenol-modified carbon nanotubes. The construction waste includes waste concrete blocks, waste bricks, and waste mortar, with a mass ratio of 6:3:1. The particle size classification of the composite modified recycled aggregate is as follows: 60% of the recycled coarse aggregate is 5mm, and 40% of the recycled fine aggregate is 0.16mm. The composite modification treatment steps are as follows: the screened recycled aggregate is soaked in a 5% calcium hydroxide solution for 12 hours, then taken out and dried, and then cured in a carbon dioxide atmosphere with a concentration of 80% and a temperature of 25℃ for 8 hours. The industrial solid waste composite powder is made by mixing and grinding phosphorus slag, fly ash and mineral powder in a mass ratio of 3:2:1, and its specific surface area is 400m² / kg. The preparation method of modified carbon nanotubes is as follows: Step (1): 65 mL of N,N-dimethylformamide solvent, 2.5 g of carboxylated carbon nanotubes and 22 g of thionyl chloride were ultrasonically dispersed evenly, heated to reflux, and reacted at 125 °C for 18 h. After the reaction was completed, the mixture was rotary evaporated, washed with tetrahydrofuran, and dried to obtain acyl chloride carbon nanotubes. Step (2): Add 4.51g of cashew phenol and 3.3g of glycidol to the reaction flask, blow nitrogen into the mixture and stir evenly for 16min to remove air, react at 75℃ for 1h; then increase the temperature to 95℃ at 8℃ / min and react for 2h; finally increase the temperature to 110℃ at 8℃ / min and react for 1.5h, then cool the mixture to room temperature to obtain hyperbranched cashew phenol polyglycerol; Step (3): Add 0.8 mmol of hyperbranched cashew phenol polyglycerol to 70 mL of N,N-dimethylformamide solvent, stir and mix, then add 1.2 mmol of acyl chloride carbon nanotubes and 0.01 g of pyridine catalyst, react at 30 °C for 5 h, after which vacuum distillation, filtration, and washing are performed to obtain cashew phenol modified carbon nanotubes.

[0030] The preparation of environmentally friendly concrete includes the following steps: adding composite modified recycled aggregate, cement, industrial solid waste composite powder, water, polycarboxylate-based high-efficiency water-reducing agent, nano calcium carbonate, and cashew phenol modified carbon nanotubes into a mixer and stirring for 2 minutes. The stirring speed of the mixer is 300 r / min, and finally environmentally friendly concrete made from construction waste is obtained.

[0031] Example 3 An environmentally friendly concrete utilizing construction waste is characterized by comprising the following weight components: 900 parts of composite modified recycled aggregate, 350 parts of cement, 120 parts of industrial solid waste composite powder, 180 parts of water, 5 parts of polycarboxylate-based high-efficiency water-reducing agent, 6 parts of nano-calcium carbonate, and 4 parts of cashew phenol-modified carbon nanotubes. The construction waste includes waste concrete blocks, waste bricks, and waste mortar, with a mass ratio of 6:3:1. The particle size classification of the composite modified recycled aggregate is as follows: 70% of the recycled coarse aggregate is 20mm, and 30% of the recycled fine aggregate is 4mm. The composite modification treatment steps are as follows: the screened recycled aggregate is soaked in an 8% calcium hydroxide solution for 24 hours, then taken out and dried, and then cured in a 90% carbon dioxide atmosphere at 35℃ for 12 hours. The industrial solid waste composite powder is made by mixing and grinding phosphorus slag, fly ash and mineral powder in a mass ratio of 3:2:1, and its specific surface area is 500m² / kg. The preparation method of modified carbon nanotubes is as follows: Step (1): 75 mL of N,N-dimethylformamide solvent, 3 g of carboxylated carbon nanotubes and 26 g of thionyl chloride were ultrasonically dispersed evenly, heated to reflux, and reacted at 135 °C for 24 h. After the reaction was completed, the mixture was rotary evaporated, washed with tetrahydrofuran, and dried to obtain acyl chloride carbon nanotubes. Step (2): Add 4.6g of cashew nut powder and 3.5g of glycidol to the reaction flask, blow nitrogen into the mixture and stir evenly for 20min to remove air, react at 80℃ for 2h; then increase the temperature to 100℃ at 10℃ / min and react for 4h; finally increase the temperature to 120℃ at 10℃ / min and react for 2h, then cool the mixture to room temperature to obtain hyperbranched cashew nut powder polyglycerol; Step (3): Add 1 mmol of hyperbranched cashew phenol polyglycerol to 80 mL of N,N-dimethylformamide solvent, stir and mix, then add 1.5 mmol of acyl chloride carbon nanotubes and 0.015 g of pyridine catalyst, react at 40 °C for 8 h, after which distill under reduced pressure, filter, wash, and obtain cashew phenol modified carbon nanotubes.

[0032] The preparation of environmentally friendly concrete includes the following steps: adding composite modified recycled aggregate, cement, industrial solid waste composite powder, water, polycarboxylate-based high-efficiency water-reducing agent, nano calcium carbonate, and cashew phenol modified carbon nanotubes into a mixer and stirring for 3 minutes at a stirring speed of 400 r / min, ultimately obtaining environmentally friendly concrete made from construction waste.

[0033] Comparative Example 1 (without composite modification of recycled aggregate) Key differences: The recycled aggregate was only crushed and screened, and did not undergo the composite modification process of "soaking in 8% calcium hydroxide solution for 24 hours and curing in 90% carbon dioxide atmosphere at 35°C for 12 hours". The preparation standards of the other raw materials were the same as in Example 3.

[0034] Comparative Example 2 (without added industrial solid waste composite powder) Key differences: No industrial solid waste composite powder (a finely ground mixture of phosphorus slag, fly ash, and mineral powder in a 3:2:1 ratio) was used; the volume difference was compensated by increasing the amount of cement. Raw material composition: The industrial solid waste composite powder was removed, and the amount of cement was adjusted to 470 parts (to make up for the original volume ratio of the industrial solid waste composite powder and ensure the density of the concrete system). The remaining raw materials (900 parts of composite modified recycled aggregate, 180 parts of water, 5 parts of polycarboxylate-based high-efficiency water-reducing agent, 6 parts of nano-calcium carbonate, and 4 parts of cashew nut shell modified carbon nanotubes) and preparation standards are completely consistent with Example 3.

[0035] Comparative Example 3 (using cashew nut shell extract instead of cashew nut shell extract to modify carbon nanotubes) The difference between this comparative example and Example 3 is that cashew phenol is used instead of cashew phenol to modify carbon nanotubes.

[0036] Performance testing The impermeability grade and carbonation depth were tested according to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete"; the compressive strength and flexural strength were tested according to GB / T50107-2010 "Standard for Evaluation of Concrete Strength". Table 1: Performance Tests.

[0037]

[0038] As shown in Table 1, the 28-day flexural strength of Examples 1-3 reached 7.6-8.1 MPa, higher than that of the comparative examples (5.1-6.2 MPa), demonstrating the core toughening effect of cashew phenol-modified carbon nanotubes: the high aspect ratio of the modified carbon nanotubes forms a "fibrous dispersed phase," bridging microcracks and inhibiting their propagation; the flexible characteristics of the long-chain alkyl groups of cashew phenol absorb impact energy, improving the brittleness of concrete and thus increasing flexural strength. The 28-day flexural strength of Comparative Example 3 (cashew phenol replacing cashew phenol-modified carbon nanotubes) was only 5.1 MPa, proving that cashew phenol alone cannot replace the "reinforcing-toughening" synergistic effect of modified carbon nanotubes, further verifying the necessity of the carbon nanotube modification process. The impermeability grades of Examples 1-2 reached P12, and Example 3 reached P11, both superior to Comparative Example 1 (P8) and Comparative Examples 2-3 (P10). The low water absorption of the composite modified recycled aggregate reduced capillary pore channels, the multi-level filling of industrial solid waste composite powder and nano-calcium carbonate reduced internal interconnected pores, and the cashew phenol modified carbon nanotubes optimized the interface bonding, jointly constructing a dense impermeable structure. Comparative Example 1, due to the high porosity of the unmodified aggregate, only achieved an impermeability grade of P8, which could not meet the requirements for medium to high impermeability. The carbonation depth of Examples 1-3 was 2.9-3.2 mm, far lower than that of Comparative Example 1 (5.1 mm) and Comparative Example 3 (4.0 mm): the calcium carbonate protective film on the surface of the composite modified recycled aggregate and the alkaline environment inside the concrete delayed carbon dioxide erosion; the dense microstructure reduced the penetration path of carbon dioxide, while Comparative Example 1, due to its high aggregate porosity, and Comparative Example 3, due to the lack of interface reinforcement from modified carbon nanotubes, showed a significantly increased carbonation depth and accelerated durability degradation.

[0039] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0041] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. An environmentally friendly concrete utilizing construction waste, characterized in that, It includes the following components by weight: 800-900 parts of composite modified recycled aggregate, 300-350 parts of cement, 80-120 parts of industrial solid waste composite powder, 150-180 parts of water, 3-5 parts of polycarboxylate-based high-efficiency water-reducing agent, 4-6 parts of nano calcium carbonate, and 3-4 parts of cashew phenol modified carbon nanotubes. The composite modified recycled aggregate is obtained from construction waste through crushing, screening, and composite modification treatment. The composite modification treatment includes the following steps: first, soak the screened recycled aggregate in calcium hydroxide solution for 12-24 hours, take it out and dry it, and then place it in a carbon dioxide atmosphere for 8-12 hours. The industrial solid waste composite powder is made by mixing and grinding phosphorus slag, fly ash and mineral powder in a mass ratio of 3:2:1, and its specific surface area is 400-500m² / kg.

2. The environmentally friendly concrete utilizing construction waste according to claim 1, characterized in that, The construction waste includes waste concrete blocks, waste bricks, and waste mortar, with a mass ratio of 6:3:

1.

3. The environmentally friendly concrete utilizing construction waste according to claim 1, characterized in that, The particle size classification of the composite modified recycled aggregate is as follows: 60-70% of the recycled coarse aggregate is 5-20mm, and 30-40% of the recycled fine aggregate is 0.16-5mm; the mass concentration of the calcium hydroxide solution is 5-8%; the concentration of the carbon dioxide atmosphere is 80-90%, and the curing temperature is 25-35℃.

4. The environmentally friendly concrete utilizing construction waste according to claim 1, characterized in that, The method for preparing the modified carbon nanotubes is as follows: Step (1): After uniformly dispersing N,N-dimethylformamide solvent, carboxylated carbon nanotubes and thionyl chloride by ultrasonication, the mixture is heated to reflux and reacted at 125-135℃ for 18-24h. After the reaction is completed, the mixture is rotary evaporated, washed with tetrahydrofuran, and dried to obtain acyl chloride carbon nanotubes. Step (2): Add cashew phenol and glycidol to the reaction flask, blow nitrogen into the mixture and stir evenly for 16-20 min to remove air, react at 75-80℃ for 1-2 h; then raise the temperature to 95-100℃ at 8-10℃ / min and react for 2-4 h; finally raise the temperature to 110-120℃ at 8-10℃ / min and react for 1.5-2 h, then cool the mixture to room temperature to obtain hyperbranched cashew phenol polyglycerol; Step (3): Add hyperbranched cashew phenol polyglycerol to 70-80 mL of N,N-dimethylformamide solvent, stir and mix, then add acyl chloride carbon nanotubes and pyridine catalyst, react at 30-40℃ for 5-8 h, after which distill under reduced pressure, filter, wash, and obtain cashew phenol modified carbon nanotubes.

5. The environmentally friendly concrete utilizing construction waste according to claim 4, characterized in that, In step (1), the ratio of N,N-dimethylformamide, carboxylated carbon nanotubes, and thionyl chloride is 65-75 mL: 2.5-3 g: 22-26 g.

6. The environmentally friendly concrete utilizing construction waste according to claim 4, characterized in that, In step (2), the ratio of cashew phenol to glycidol is 4.51-4.6g: 3.3-3.5g.

7. The environmentally friendly concrete utilizing construction waste according to claim 4, characterized in that, In step (3), the ratio of hyperbranched cashew polyglycerol, acyl chloride carbon nanotubes, and pyridine catalyst is 0.8-1 mmol: 1.2-1.5 mmol: 0.01 g-0.015 g.

8. A method for preparing environmentally friendly concrete using construction waste as described in any one of claims 1-7, characterized in that, The process includes the following steps: adding modified recycled aggregate, cement, industrial solid waste composite powder, water, polycarboxylate-based high-efficiency water-reducing agent, nano-calcium carbonate, and cashew phenol-modified carbon nanotubes into a mixer and mixing for 2-3 minutes at a speed of 300-400 r / min, ultimately obtaining environmentally friendly concrete made from construction waste.

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