Recycled concrete based on iron tailings and preparation method thereof

Abstract

The invention discloses recycled concrete based on iron tailings and a preparation method thereof, and belongs to the field of recycled concrete. Comprising the following steps: step 1, preparing raw materials: preparing the following raw materials in parts by weight: 100-120 parts of a cementing material, 150-200 parts of fine aggregate, 300-400 parts of coarse aggregate, 35-40 parts of water, 0.5-1.5 parts of a high-efficiency water reducing agent and 1-2 parts of a composite additive; step 2, dry mixing: putting the cementing material, the fine aggregate, the coarse aggregate and the composite additive into a mixer, and carrying out dry mixing for 3-5 minutes to obtain a mixture; and step 3, wet mixing: firstly adding water into the mixture obtained in the step 2, then adding an efficient water reducing agent, and continuously stirring for 2-4 minutes until a homogeneous concrete mixture is obtained. The added composite additive effectively improves the strength and comprehensive performance of the recycled concrete through a unique chemical structure.

Description

Technical Field

[0001] This invention belongs to the field of recycled concrete technology, specifically, it relates to a recycled concrete based on iron tailings and its preparation method. Background Technology

[0002] With the continuous development of infrastructure construction and increasing emphasis on environmental protection, utilizing construction waste to prepare recycled aggregate concrete and disposing of the large amounts of iron ore tailings generated during mining have become key research directions for the building materials industry to achieve sustainable development. Using iron ore tailings powder as an auxiliary cementitious material and iron ore tailings sand as fine aggregate to partially replace natural sand in recycled concrete can not only effectively consume industrial solid waste and reduce the extraction of natural resources, but also reduce environmental pollution, resulting in significant economic and environmental benefits.

[0003] However, the practical application of this type of recycled concrete based on solid waste still faces a series of technical bottlenecks. First, the activity of iron ore tailings powder is generally lower than that of ordinary Portland cement, and its large-scale incorporation may lead to slow early strength development in the concrete, and difficulty in achieving the required strength for high-performance concrete in the later stages. Second, recycled aggregates themselves have lower strength, higher porosity, and higher water absorption, and the old mortar adhering to their surface forms a relatively weak secondary interface transition zone with the new cement paste. These factors collectively result in the mechanical properties of recycled concrete, especially its flexural strength, often being lower than that of ordinary concrete with the same mix proportions.

[0004] More significantly, the aforementioned internal defects often result in unsatisfactory durability of recycled concrete, particularly its resistance to chloride ion attack. The loose and porous interface transition zone and the abundant microcracks within the matrix provide pathways for the rapid migration of corrosive media such as chloride ions and moisture, leading to premature deterioration of reinforced concrete structures in saline environments and severely limiting their application in projects with high durability requirements.

[0005] In existing technologies, although adding fibers or nanomaterials is often used to improve concrete performance, the interfacial bonding force between ordinary fibers and the matrix is ​​limited, while nanomaterials such as unmodified graphene oxide tend to agglomerate in the cement matrix, making it difficult to fully utilize their nano-effects. The improvement effect is often limited to a single property (such as only improving strength or only improving toughness), and the effect on improving long-term durability is limited, especially in that it cannot systematically strengthen the interfacial transition zone to fundamentally block the erosion path. Therefore, it is particularly urgent to develop a new technology that can simultaneously improve the mechanical properties and long-term durability of recycled concrete, especially significantly enhance its resistance to salt erosion. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a recycled concrete based on iron tailings and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing recycled concrete based on iron tailings includes the following steps: Step 1: Raw material preparation: Prepare the following raw materials by weight: 100-120 parts cementitious material, 150-200 parts fine aggregate, 300-400 parts coarse aggregate, 35-40 parts water, 0.5-1.5 parts high-efficiency water-reducing agent, and 1-2 parts composite additive. Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 3-5 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 2-4 minutes until a homogeneous concrete mixture is obtained.

[0008] More optimally, the cementitious material is composed of ordinary silicate cement and iron ore tailings powder, wherein the amount of iron ore tailings powder accounts for 15% of the total weight of the cementitious material.

[0009] More optimally, the fine aggregate is composed of recycled sand and iron ore tailings, wherein the amount of iron ore tailings accounts for 20% of the total weight of the fine aggregate.

[0010] More optimally, the composite additive is composed of aminated carbon fiber and modified graphene oxide, wherein the mass ratio of aminated carbon fiber to modified graphene oxide is (1-2):(1-2).

[0011] In a more optimized manner, the preparation process of the modified graphene oxide is as follows: S1: Mix 4-formylphenol, dibromohexane, potassium carbonate, and acetonitrile, stir until homogeneous, then raise the temperature to 70°C and reflux for 6-7 hours. After the reaction is complete, add 3-amino-1,2,4-triazole and acetic acid to the filtrate, raise the temperature to 70°C, and reflux for 10-12 hours. After the reaction is complete, filter, wash, and dry to obtain product A. S2: Diethanolamine and paraformaldehyde are mixed, the temperature is raised to 65°C, and the reaction is carried out for 2-3 hours. Then eugenol is added, the temperature is raised to 95°C, and the reaction is continued for 6-8 hours. After the reaction is completed, post-processing is performed to obtain product B. S3: Mix product A, product B, and N,N-dimethylformamide, stir evenly, raise the temperature to 70-80℃, react for 4-5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, mercapto-modified graphene oxide is added to ethanol and ultrasonically dispersed for 30-40 min. Then, a modifier and azobisisobutyronitrile are added, the temperature is raised to 90-95℃, and the reaction is carried out for 3-4 h. After cooling to room temperature, the mixture is filtered, washed, and dried to obtain modified graphene oxide.

[0012] In the scheme, firstly, 4-formylphenol and dibromohexane undergo a Williamson etherification reaction to generate an intermediate containing an aldehyde group and an active bromine terminus. This intermediate then reacts with 3-amino-1,2,4-triazole via a condensation reaction to form a Schiff base structure, yielding product A with a triazole ring and a chlorine atom at the end. Simultaneously, diethanolamine condenses with paraformaldehyde to generate a nitrogen-containing five-membered ring intermediate, deprotonating the phenolic hydroxyl group of eugenol. The resulting phenoxy anion attacks the imine cation generated from the ring-opening of the five-membered ring, undergoing ortho-electrophilic substitution to obtain a product containing... Product B is formed from a tertiary amine and an alkene bond. Subsequently, the chlorine atom at the end of product A undergoes a quaternization reaction with the tertiary amine group of product B, synthesizing a multifunctional modifier that simultaneously possesses a triazole structure, a long-chain alkyl group, a quaternary ammonium salt cation, and a reactive alkene bond. Finally, in the presence of a free radical initiator, this modifier undergoes an efficient "thiol-alkene" click chemical reaction with the thiol group on the thiolized graphene oxide through its alkene bond, thereby covalently grafting the above functional groups onto the surface of graphene oxide, resulting in a structurally stable modified graphene oxide with excellent interfacial compatibility.

[0013] The structure of the modifier is shown below: In a more optimized manner, the raw materials for preparing product A include the following components: by weight, 12-13 parts of 4-formylphenol, 22-23 parts of dibromohexane, 20-22 parts of potassium carbonate, 120-130 parts of acetonitrile, 8-9 parts of 3-amino-1,2,4-triazole, and 5-6 parts of acetic acid.

[0014] In a more optimized manner, the raw materials for preparing product B include the following components: 3-4 parts by weight of diethanolamine, 2-3 parts by weight of paraformaldehyde, and 4-5 parts by weight of eugenol.

[0015] In a more optimized manner, the raw materials for preparing the modifier include the following components: by weight, 20-22 parts of product A, 15-18 parts of product B, and 80-100 parts of N,N-dimethylformamide.

[0016] In a more optimized manner, the raw materials for preparing the modified graphene oxide include the following components: by weight, 5-6 parts of mercapto-modified graphene oxide, 120-130 parts of ethanol, 10-12 parts of modifier, and 0.5-0.8 parts of azobisisobutyronitrile.

[0017] The beneficial effects of this invention are: The composite additive used in this invention, through its unique chemical structure, effectively improves the strength and overall performance of recycled concrete. Specifically: Firstly, in the initial stage of cement hydration, the quaternary ammonium cations in the modified graphene oxide preferentially adsorb onto the surfaces of negatively charged cement particles (such as C3S and C2S) and early hydration products through strong electrostatic interactions, acting as an "electrostatic anchor." This not only improves its own dispersion stability but also optimizes the packing state between particles. Simultaneously, the graphene oxide nanosheets and their grafted triazole ring structures provide a wealth of nucleation sites for hydration products, guiding the formation of high-density, low-porosity CSH gel and inhibiting the crystallization and orientation growth of the weak phase, calcium hydroxide. This synergistic effect of "anchoring" and "nucleation" fundamentally densifies the fiber-matrix and aggregate-matrix interface transition zones, transforming them from weak points in the material into reinforced areas. This not only significantly improves the early and later strength of concrete but also greatly enhances its resistance to the penetration of harmful ions (such as chloride ions) by reducing the overall porosity of the matrix, thus ensuring the long-term durability of concrete in salt-corrosion environments.

[0018] Secondly, a stable interfacial bond is formed between aminated carbon fibers and modified graphene oxide through multiple intermolecular forces. On one hand, a broad network of multiple hydrogen bonds forms between the amino groups on the carbon fiber surface and the various oxygen-containing functional groups on the graphene oxide surface. This multidimensional hydrogen bonding provides a reliable interfacial anchorage between the fiber and the nanosheet. On the other hand, the sp... 2 Hybrid conjugated structure and sp of graphene oxide 2 Strong π-π conjugated interactions occur between carbon domains, further enhancing the stability of the interfacial bonding. The synergistic effect of these two intermolecular forces enables one-dimensional fibers and two-dimensional nanosheets to form a stable three-dimensional reinforcing network in the cement matrix. This effectively promotes stress transfer and inhibits microcrack propagation, improves toughness, and can also deflect and block the penetration paths of external corrosive media (especially chloride ions), thus synergistically endowing concrete with excellent resistance to salt ion attack. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Pre-preparation: The preparation process of aminated carbon fiber is as follows: (1) Add 1g of carbon fiber to 20mL of concentrated nitric acid and stir magnetically at 80℃ for 4-5h. After the reaction is complete, cool to room temperature and wash repeatedly with deionized water until the pH of the filtrate is ≈7. Then wash with anhydrous ethanol 2-3 times to remove residual acid and dry to obtain acid-oxidized carbon fiber. (2) Mix 95 mL of anhydrous ethanol and 5 mL of deionized water in a three-necked flask; adjust the pH to 4.0-4.5 with glacial acetic acid, slowly add 4 vol% APTES (based on the total volume of ethanol), stir for 30 min, then add the acid-oxidized carbon fiber to the above silane solution, react at 70 °C for 6 h under a nitrogen atmosphere, and then perform post-treatment to obtain aminated carbon fiber.

[0021] Preparation process of thiolized graphene oxide: 4g of graphene oxide was placed in a round-bottom flask, and 150mL of a mixed solution of ethanol and mercaptopropyltrimethoxysilane with a volume ratio of 95:5 was added. The pH of the solution was adjusted to 4 with acetic acid, and then the reaction was carried out in an oil bath at 80℃ for 8h. After the reaction was completed, the product was washed 4 times with a mixed solution of ethanol and deionized water, and then dried in a vacuum drying oven at 100℃ for 24h to obtain thiolized graphene oxide.

[0022] Example 1: A method for preparing recycled concrete based on iron tailings, characterized by comprising the following steps: Step 1: Raw material preparation: Prepare the following raw materials by weight: 100 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, wherein the amount of iron ore tailings powder accounts for 15% of the total weight of cementitious material), 150 parts fine aggregate (composed of recycled sand and iron ore tailings, wherein the amount of iron ore tailings accounts for 20% of the total weight of fine aggregate), 300 parts coarse aggregate (5mm continuously graded natural limestone crushed stone), 35 parts water, 0.5 parts high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 1 part composite additive (ammoniated carbon fiber and modified graphene oxide in a mass ratio of 1:1). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 3 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 2 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 12 parts of 4-formylphenol, 22 parts of dibromohexane, and 20 parts of potassium carbonate were added to 120 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 8 parts of 3-amino-1,2,4-triazole and 5 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 10 hours. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 3 parts diethanolamine and 2 parts paraformaldehyde, raise the temperature to 65°C, react for 2 hours, then add 4 parts eugenol, raise the temperature to 95°C, and continue the reaction for 6 hours. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 20 parts of product A, 15 parts of product B, and 80 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 70℃, react for 4 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 5 parts of mercapto-modified graphene oxide were added to 120 parts of ethanol and ultrasonically dispersed for 30 min. Then, 10 parts of modifier and 0.5 parts of azobisisobutyronitrile were added, the temperature was raised to 90℃, and the reaction was carried out for 3 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0023] Example 2: A method for preparing recycled concrete based on iron tailings, characterized by comprising the following steps: Step 1: Raw material preparation: Prepare the following raw materials by weight: 120 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, of which the iron ore tailings powder accounts for 15% of the total weight of the cementitious material), 200 parts fine aggregate (composed of recycled sand and iron ore tailings, of which the iron ore tailings accounts for 20% of the total weight of the fine aggregate), 400 parts coarse aggregate (20mm continuously graded natural limestone crushed stone), 40 parts water, 1.5 parts high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 2 parts composite additive (ammoniated carbon fiber and modified graphene oxide in a mass ratio of 1:2). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 5 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 4 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 13 parts of 4-formylphenol, 23 parts of dibromohexane, and 22 parts of potassium carbonate were added to 130 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 7 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 9 parts of 3-amino-1,2,4-triazole and 6 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 12 hours. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 4 parts of diethanolamine and 3 parts of paraformaldehyde, raise the temperature to 65°C, react for 3 hours, then add 5 parts of eugenol, raise the temperature to 95°C, and continue the reaction for 8 hours. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 22 parts of product A, 18 parts of product B, and 100 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 80℃, react for 5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 6 parts of mercapto-modified graphene oxide were added to 130 parts of ethanol and ultrasonically dispersed for 40 min. Then, 12 parts of modifier and 0.8 parts of azobisisobutyronitrile were added, the temperature was raised to 95℃, and the reaction was carried out for 4 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0024] Example 3: A method for preparing recycled concrete based on iron tailings, characterized by comprising the following steps: Step 1: Raw material preparation: Prepare the following raw materials by weight: 110 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, wherein the amount of iron ore tailings powder accounts for 15% of the total weight of cementitious material), 175 parts fine aggregate (composed of recycled sand and iron ore tailings, wherein the amount of iron ore tailings accounts for 20% of the total weight of fine aggregate), 350 parts coarse aggregate (12.5mm continuously graded natural limestone crushed stone), 37.5 parts water, 1.0 part high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 1.5 parts composite additive (ammoniated carbon fiber and modified graphene oxide in a mass ratio of 1:1.5). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 4 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 3 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 12.5 parts of 4-formylphenol, 22.5 parts of dibromohexane, and 21 parts of potassium carbonate were added to 125 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 6.5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 8.5 parts of 3-amino-1,2,4-triazole and 5.5 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 11 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 3.5 parts of diethanolamine and 2.5 parts of paraformaldehyde, raise the temperature to 65°C, and react for 2.5 h. Then add 4.5 parts of eugenol, raise the temperature to 95°C, and continue to react for 7 h. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 21 parts of product A, 16.5 parts of product B, and 90 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 75°C, react for 4.5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 5.5 parts of mercapto-modified graphene oxide were added to 125 parts of ethanol and ultrasonically dispersed for 35 min. Then, 11 parts of modifier and 0.65 parts of azobisisobutyronitrile were added, the temperature was raised to 92.5℃, and the reaction was carried out for 3.5 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0025] Comparative Example 1: No compound additives were added, as follows: Step 1: Raw material preparation: Prepare the following raw materials by weight: 110 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, wherein the amount of iron ore tailings powder accounts for 15% of the total weight of cementitious material), 175 parts fine aggregate (composed of recycled sand and iron ore tailings, wherein the amount of iron ore tailings accounts for 20% of the total weight of fine aggregate), 350 parts coarse aggregate (12.5mm continuously graded natural limestone crushed stone), 37.5 parts water, and 1.0 part high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 4 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 3 minutes until a homogeneous concrete mixture is obtained.

[0026] Comparative Example 2: Only modified graphene oxide was added, as detailed below: Step 1: Raw material preparation: Prepare the following raw materials by weight: 110 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, of which the amount of iron ore tailings powder accounts for 15% of the total weight of cementitious material), 175 parts fine aggregate (composed of recycled sand and iron ore tailings, of which the amount of iron ore tailings accounts for 20% of the total weight of fine aggregate), 350 parts coarse aggregate (12.5mm continuously graded natural limestone crushed stone), 37.5 parts water, 1.0 part high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 1.5 parts composite additive modified graphene oxide. Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 4 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 3 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 12.5 parts of 4-formylphenol, 22.5 parts of dibromohexane, and 21 parts of potassium carbonate were added to 125 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 6.5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 8.5 parts of 3-amino-1,2,4-triazole and 5.5 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 11 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 3.5 parts of diethanolamine and 2.5 parts of paraformaldehyde, raise the temperature to 65°C, and react for 2.5 h. Then add 4.5 parts of eugenol, raise the temperature to 95°C, and continue to react for 7 h. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 21 parts of product A, 16.5 parts of product B, and 90 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 75°C, react for 4.5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 5.5 parts of mercapto-modified graphene oxide were added to 125 parts of ethanol and ultrasonically dispersed for 35 min. Then, 11 parts of modifier and 0.65 parts of azobisisobutyronitrile were added, the temperature was raised to 92.5℃, and the reaction was carried out for 3.5 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0027] Comparative Example 3: An excessive amount of modified graphene oxide was added, as detailed below: Step 1: Raw material preparation: Prepare the following raw materials by weight: 110 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, wherein the amount of iron ore tailings powder accounts for 15% of the total weight of cementitious material), 175 parts fine aggregate (composed of recycled sand and iron ore tailings, wherein the amount of iron ore tailings accounts for 20% of the total weight of fine aggregate), 350 parts coarse aggregate (12.5mm continuously graded natural limestone crushed stone), 37.5 parts water, 1.0 part high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 1.5 parts composite additive (ammoniated carbon fiber and modified graphene oxide in a mass ratio of 1:5). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 4 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 3 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 12.5 parts of 4-formylphenol, 22.5 parts of dibromohexane, and 21 parts of potassium carbonate were added to 125 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 6.5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 8.5 parts of 3-amino-1,2,4-triazole and 5.5 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 11 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 3.5 parts of diethanolamine and 2.5 parts of paraformaldehyde, raise the temperature to 65°C, and react for 2.5 h. Then add 4.5 parts of eugenol, raise the temperature to 95°C, and continue to react for 7 h. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 21 parts of product A, 16.5 parts of product B, and 90 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 75°C, react for 4.5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 5.5 parts of mercapto-modified graphene oxide were added to 125 parts of ethanol and ultrasonically dispersed for 35 min. Then, 11 parts of modifier and 0.65 parts of azobisisobutyronitrile were added, the temperature was raised to 92.5℃, and the reaction was carried out for 3.5 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0028] Comparative Example 4: No iron ore tailings were added, as follows: Step 1: Raw material preparation: Prepare the following raw materials by weight: 110 parts cementitious material (composed of ordinary Portland cement (P.O42.5) and iron ore tailings powder, of which the iron ore tailings powder accounts for 15% of the total weight of cementitious material), 175 parts fine aggregate (recycled sand), 350 parts coarse aggregate (12.5mm continuously graded natural limestone crushed stone), 37.5 parts water, 1.0 part high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 1.5 parts composite additive (ammoniated carbon fiber and modified graphene oxide in a mass ratio of 1:1.5). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 4 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 3 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 12.5 parts of 4-formylphenol, 22.5 parts of dibromohexane, and 21 parts of potassium carbonate were added to 125 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 6.5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 8.5 parts of 3-amino-1,2,4-triazole and 5.5 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 11 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 3.5 parts of diethanolamine and 2.5 parts of paraformaldehyde, raise the temperature to 65°C, and react for 2.5 h. Then add 4.5 parts of eugenol, raise the temperature to 95°C, and continue to react for 7 h. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 21 parts of product A, 16.5 parts of product B, and 90 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 75°C, react for 4.5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 5.5 parts of mercapto-modified graphene oxide were added to 125 parts of ethanol and ultrasonically dispersed for 35 min. Then, 11 parts of modifier and 0.65 parts of azobisisobutyronitrile were added, the temperature was raised to 92.5℃, and the reaction was carried out for 3.5 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0029] Comparative Example 5: No iron ore tailings powder was added, as follows: Step 1: Raw material preparation: Prepare the following raw materials by weight: 110 parts cementitious material (ordinary silicate cement (P.O42.5)), 175 parts fine aggregate (composed of recycled sand and iron ore tailings, of which the amount of iron ore tailings accounts for 20% of the total weight of fine aggregate), 350 parts coarse aggregate (12.5mm continuously graded natural limestone crushed stone), 37.5 parts water, 1.0 part high-efficiency water-reducing agent (polycarboxylate-based high-performance water-reducing agent), and 1.5 parts composite additive (ammoniated carbon fiber and modified graphene oxide in a mass ratio of 1:1.5). Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 4 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 3 minutes until a homogeneous concrete mixture is obtained. The preparation process of modified graphene oxide is as follows: S1: 12.5 parts of 4-formylphenol, 22.5 parts of dibromohexane, and 21 parts of potassium carbonate were added to 125 parts of acetonitrile and stirred until homogeneous. The temperature was then raised to 70°C and refluxed for 6.5 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and 8.5 parts of 3-amino-1,2,4-triazole and 5.5 parts of acetic acid were added to the filtrate. The temperature was raised to 70°C and refluxed for 11 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain product A. S2: Mix 3.5 parts of diethanolamine and 2.5 parts of paraformaldehyde, raise the temperature to 65°C, and react for 2.5 h. Then add 4.5 parts of eugenol, raise the temperature to 95°C, and continue to react for 7 h. After the reaction is completed, perform post-processing to obtain product B. S3: Mix 21 parts of product A, 16.5 parts of product B, and 90 parts of N,N-dimethylformamide, stir evenly, raise the temperature to 75°C, react for 4.5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, 5.5 parts of mercapto-modified graphene oxide were added to 125 parts of ethanol and ultrasonically dispersed for 35 min. Then, 11 parts of modifier and 0.65 parts of azobisisobutyronitrile were added, the temperature was raised to 92.5℃, and the reaction was carried out for 3.5 h. After cooling to room temperature, the mixture was filtered, washed, and dried to obtain modified graphene oxide.

[0030] Testing and experimentation: The concrete obtained in the examples and comparative examples was cured according to standard for 49 days, and its compressive strength was tested. Then, it was cured in clean water and salt water (30% sodium chloride aqueous solution) for 180 days, and the flexural strength of the concrete was tested using a concrete pressure testing machine. Flexural strength was used to characterize its resistance to chloride ion attack. The data obtained are shown in the table below: Conclusion: Comparison data from the examples and comparative examples show that the recycled concrete based on iron tailings provided by this invention exhibits significant advantages in compressive strength, flexural strength, and resistance to chloride ion attack. The compressive strength of Examples 1 to 3 is all above 67 MPa, and the flexural strength remains at a high level in both clean water and salt water environments, especially maintaining above 9.2 MPa in salt water, indicating good durability. In contrast, the performance of Comparative Example 1 without the composite additive is significantly reduced, especially the flexural strength in salt water at only 5.3 MPa, indicating poor durability. Comparative Example 2 with only modified graphene oxide or Comparative Example 3 with excessive addition, while superior to Comparative Example 1, still falls short of the examples, demonstrating that the synergistic effect of aminated carbon fiber and modified graphene oxide in the composite additive is crucial for improving the overall performance of the concrete. In addition, Comparative Examples 4 and 5 removed iron ore tailings and iron ore tailings powder, respectively. Although Comparative Example 4 showed a slight improvement in strength and some properties, it deviated from the solid waste utilization purpose of this invention. Comparative Example 5 showed a decrease in performance without the use of iron ore tailings powder, further verifying that iron ore tailings have a certain reinforcing effect in the cementation system.

[0031] In summary, by introducing composite additives and making reasonable use of iron ore tailings, this invention significantly improves the salt erosion resistance of concrete while ensuring its mechanical properties, providing a feasible technical approach for realizing the resource utilization of industrial solid waste and the preparation of high-performance recycled concrete.

[0032] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing recycled concrete based on iron tailings, characterized in that, Includes the following steps: Step 1: Raw material preparation: Prepare the following raw materials by weight: 100-120 parts cementitious material, 150-200 parts fine aggregate, 300-400 parts coarse aggregate, 35-40 parts water, 0.5-1.5 parts high-efficiency water-reducing agent, and 1-2 parts composite additive. Step 2: Dry mixing: Add the cementitious material, fine aggregate, coarse aggregate and composite additive into the mixer and dry mix for 3-5 minutes to obtain the mixture; Step 3: Wet mixing: Add water to the mixture obtained in Step 2, then add the high-efficiency water-reducing agent, and continue mixing for 2-4 minutes until a homogeneous concrete mixture is obtained.

2. The method for preparing recycled concrete based on iron tailings according to claim 1, characterized in that, The cementitious material is composed of ordinary silicate cement and iron ore tailings powder, wherein the amount of iron ore tailings powder accounts for 15% of the total weight of the cementitious material.

3. The method for preparing recycled concrete based on iron tailings according to claim 1, characterized in that, The fine aggregate consists of recycled sand and iron ore tailings, with the iron ore tailings accounting for 20% of the total weight of the fine aggregate.

4. The method for preparing recycled concrete based on iron tailings according to claim 1, characterized in that, The composite additive is composed of aminated carbon fiber and modified graphene oxide, wherein the mass ratio of aminated carbon fiber to modified graphene oxide is (1-2):(1-2).

5. The method for preparing recycled concrete based on iron tailings according to claim 4, characterized in that, The preparation process of the modified graphene oxide is as follows: S1: Mix 4-formylphenol, dibromohexane, potassium carbonate, and acetonitrile, stir until homogeneous, then raise the temperature to 70°C and reflux for 6-7 hours. After the reaction is complete, add 3-amino-1,2,4-triazole and acetic acid to the filtrate, raise the temperature to 70°C, and reflux for 10-12 hours. After the reaction is complete, filter, wash, and dry to obtain product A. S2: Diethanolamine and paraformaldehyde are mixed, the temperature is raised to 65°C, and the reaction is carried out for 2-3 hours. Then eugenol is added, the temperature is raised to 95°C, and the reaction is continued for 6-8 hours. After the reaction is completed, post-processing is performed to obtain product B. S3: Mix product A, product B, and N,N-dimethylformamide, stir evenly, raise the temperature to 70-80℃, react for 4-5 hours, after the reaction is completed, cool to room temperature, filter, wash, and dry to obtain the modifier. S4: Under a protective atmosphere, mercapto-modified graphene oxide is added to ethanol and ultrasonically dispersed for 30-40 min. Then, a modifier and azobisisobutyronitrile are added, the temperature is raised to 90-95℃, and the reaction is carried out for 3-4 h. After cooling to room temperature, the mixture is filtered, washed, and dried to obtain modified graphene oxide.

6. The method for preparing recycled concrete based on iron tailings according to claim 5, characterized in that, The raw materials for preparing product A include the following components: by weight, 12-13 parts of 4-formylphenol, 22-23 parts of dibromohexane, 20-22 parts of potassium carbonate, 120-130 parts of acetonitrile, 8-9 parts of 3-amino-1,2,4-triazole, and 5-6 parts of acetic acid.

7. A method for preparing recycled concrete based on iron tailings according to claim 5, characterized in that, The raw materials for preparing product B include the following components: by weight, 3-4 parts diethanolamine, 2-3 parts paraformaldehyde, and 4-5 parts eugenol.

8. A method for preparing recycled concrete based on iron tailings according to claim 5, characterized in that, The raw materials for preparing the modifier include the following components: by weight, 20-22 parts of product A, 15-18 parts of product B, and 80-100 parts of N,N-dimethylformamide.

9. A method for preparing recycled concrete based on iron tailings according to claim 5, characterized in that, The raw materials for preparing the modified graphene oxide include the following components: by weight, 5-6 parts of mercapto-modified graphene oxide, 120-130 parts of ethanol, 10-12 parts of modifier, and 0.5-0.8 parts of azobisisobutyronitrile.

10. The concrete mixture obtained by the method for preparing recycled concrete based on iron tailings according to any one of claims 1-9.

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