A green, low-carbon concrete based on recycled aggregate and its preparation method

Abstract

This application relates to the field of building materials technology, specifically disclosing a green low-carbon concrete based on recycled aggregate and its preparation method. A green low-carbon concrete based on recycled aggregate comprises the following raw materials in parts by weight: 5-7 parts red mud, 10-15 parts slag, 6-10 parts fly ash, 30-40 parts cement, 10-15 parts alkali activator, 20-25 parts modified recycled aggregate, 3-5 parts zeolite powder, 2-4 parts cellulose ether, and 40-45 parts water. The preparation method is as follows: weigh each raw material component, add red mud, slag, alkali activator, and half of the water and mix, obtaining a primary mixture; add fly ash, cement, modified recycled aggregate, zeolite powder, cellulose ether, and the remaining water to the primary mixture and stir, obtaining the concrete. The composition of this application can be used in foundation engineering construction, and it has the advantages of high compressive strength and good crack resistance.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and more specifically, it relates to a green low-carbon concrete based on recycled aggregate and a method for preparing the same. Background Technology

[0002] With the acceleration of global urbanization, the construction industry's demand for building materials is increasing daily. At the same time, the construction industry is also one of the major sources of carbon emissions. The traditional production process of concrete not only consumes large amounts of natural resources, such as cement and sand, but also generates significant greenhouse gas emissions, severely impacting the environment. Furthermore, the accumulation of construction waste, including discarded concrete, also causes serious environmental problems.

[0003] To address these issues, recycled aggregate concrete and geopolymer concrete have gained increasing attention in recent years as new environmentally friendly building materials. Geopolymer concrete is a type of concrete made from inorganic aluminosilicate materials through a chemical reaction at high temperatures, resulting in a novel inorganic cementitious material. It boasts advantages such as high strength, high durability, low shrinkage, and good environmental friendliness.

[0004] Recycled aggregate concrete uses construction waste such as waste concrete as aggregate, reducing the consumption of natural resources and realizing the reuse of waste. However, the performance of recycled aggregate concrete is often affected by the high water absorption rate of recycled aggregate, resulting in low strength.

[0005] Therefore, how to combine the advantages of recycled aggregates and geopolymers to prepare a high-strength concrete material is a problem that needs to be solved. Summary of the Invention

[0006] To improve the compressive strength of recycled aggregate concrete, this application provides a green low-carbon concrete based on recycled aggregate and its preparation method.

[0007] Firstly, this application provides a green, low-carbon concrete based on recycled aggregates, employing the following technical solution:

[0008] A green, low-carbon concrete based on recycled aggregates comprises the following raw materials in parts by weight:

[0009] Red mud 5-7 parts, slag 10-15 parts, fly ash 6-10 parts, cement 30-40 parts, alkali activator 10-15 parts, modified recycled aggregate 20-25 parts, zeolite powder 3-5 parts, cellulose ether 2-4 parts, water 40-45 parts.

[0010] By adopting the above technical solution, industrial wastes such as red mud, slag, and fly ash are fully utilized as raw materials. This not only achieves resource reuse but also significantly reduces dependence on new raw materials and lowers carbon emissions during the production process. Specifically, red mud and slag, under the action of an alkali activator, can undergo a chemical reaction to form geopolymers. These polymers possess excellent mechanical properties and durability, providing a solid foundation for concrete. The addition of fly ash further reduces the amount of cement used in concrete, lowering costs, and also improves the workability and performance of concrete due to its microsphere effect. Simultaneously, the active components in fly ash can participate in the reaction during cement hydration, generating more hydration products and enhancing the strength of the concrete. In this solution, cement, alkali activator, red mud, slag, and other components work synergistically to form a denser and more stable structure, improving the overall performance of the concrete.

[0011] By further modifying recycled aggregates, the defects of easy water absorption and low strength of recycled aggregates are improved, and the bonding force between recycled aggregates and other raw materials in concrete is improved, thereby obtaining concrete with high strength and good durability.

[0012] In summary, this green, low-carbon recycled aggregate low-carbon carbon-fixing geopolymer concrete achieves the goals of resource reuse and low-carbon environmental protection through a scientifically and rationally proportioned raw material mix. At the same time, its excellent mechanical properties provide strong assurance for the quality and safety of construction projects.

[0013] Optionally, the modified recycled aggregate is obtained by modification with a catalyst, acrylic resin, and benzoxazine.

[0014] By adopting the above technical solution, the ester bonds and carboxyl groups in the acrylic resin molecules react chemically with the hydroxyl groups and silicate groups on the surface of the recycled aggregate to form chemical bonds, which adhere tightly to the surface of the recycled aggregate. At the same time, the unsaturated acids in the resin can further promote the ring-opening reaction of benzoxazine, generate OH groups, form hydrogen bonds, and form a network structure on the surface of the recycled aggregate, thereby modifying the recycled aggregate and improving the problems of high water absorption and poor strength of the recycled aggregate.

[0015] Meanwhile, the modification of benzoxazine gives the recycled aggregate better toughness and lower porosity, and reduces the shrinkage of the resin material during curing, further improving the strength of the recycled aggregate.

[0016] Optionally, the preparation of the modified recycled aggregate includes the following steps:

[0017] (1) After crushing and pre-treatment, recycled aggregates with a particle size of 4.75-22.5 mm are obtained;

[0018] (2) Mix benzoxazine, catalyst and ethanol and stir and disperse at 90-100℃ for 20-30 min to obtain a uniform mixture. Then add acrylic resin and continue to mix and stir at a constant temperature for 4-6 h to obtain a modifier solution.

[0019] (3) The prepared modifier solution is mixed evenly with the crushed recycled aggregate, and the temperature is gradually increased to 200℃ at a rate of 20℃ / h to solidify. Then, the temperature is reduced to room temperature to obtain the modified recycled aggregate.

[0020] By employing the above-mentioned technical solution, benzoxazine undergoes a ring-opening polymerization reaction at high temperature to form a polymer network structure with excellent mechanical properties, endowing recycled aggregate with higher strength and toughness. Simultaneously, the functional groups in the acrylic resin can undergo a cross-linking reaction with the polymerization product of benzoxazine, forming strong chemical bonds. This not only enhances the bonding force between the modifier solution and the recycled aggregate but also allows the modifier to more effectively penetrate into the internal pores of the recycled aggregate, filling these pores and further improving the overall strength and density of the recycled aggregate.

[0021] Simultaneously, by utilizing the low water absorption property of benzoxazine, the modified recycled aggregate does not readily absorb water. Therefore, when used as concrete aggregate for curing, its shrinkage rate is significantly reduced, decreasing internal stress and the generation of microcracks. This not only improves the compressive strength of concrete but also extends its service life.

[0022] Optionally, the weight ratio of recycled aggregate, benzoxazine, and acrylic resin in the preparation step is 25:2-4:1.5-2.

[0023] By employing the above technical solution, benzoxazine serves as the core modifier. Through ring-opening polymerization, a polymer network structure is formed. The acrylic resin and the polymerization product of benzoxazine undergo a cross-linking reaction, enhancing the adhesion between recycled aggregate and substrates such as concrete, and filling the pores within the recycled aggregate, thereby improving its density and strength. By controlling the weight ratio of each modifying raw material within this range, the advantages of each raw material can be fully utilized to form a synergistic effect, resulting in modified recycled aggregate with high mechanical strength. This recycled aggregate not only possesses excellent physical and chemical properties but also exerts good bonding and reinforcing effects in substrates such as concrete, thus significantly improving the compressive strength of concrete.

[0024] Optionally, the acrylic resin is an epoxy acrylate resin.

[0025] By adopting the above technical solution, epoxy acrylic resin containing epoxy groups is selected. The epoxy groups can undergo cross-linking reactions with other functional groups through ring-opening addition reactions, further densifying the network structure on the surface of recycled aggregates, thereby further improving the compressive strength of concrete.

[0026] Optionally, the alkaline activator is a sodium silicate solution.

[0027] By adopting the above technical solution, the sodium silicate solution can fully activate the activity of the geopolymer cementitious materials red mud and slag, generating more geopolymers. These geopolymers play a skeletal supporting role in concrete, which can significantly improve the compressive strength of concrete.

[0028] Optionally, the raw material may also include 2-4 parts of basalt fiber.

[0029] By adopting the above technical solution, basalt fiber can bridge the micro-cracks in recycled aggregates and inhibit the propagation of cracks through its excellent mechanical properties, thus providing an additional layer of protection for improving the compressive strength of concrete. Its excellent mechanical properties can further improve the strength of concrete.

[0030] Secondly, this application provides a method for preparing green low-carbon concrete based on recycled aggregates, employing the following technical solution:

[0031] A method for preparing green, low-carbon concrete based on recycled aggregates includes the following steps:

[0032] (1) Weigh each raw material component, add red mud, slag, alkali activator and half of the water and mix to obtain a one-time mixture;

[0033] (2) Add fly ash, cement, modified recycled aggregate, zeolite powder, cellulose ether and the remaining water to the above-mentioned primary mixture and stir to obtain the green low-carbon recycled aggregate low-carbon carbon-fixing geological polymer concrete.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. This application fully utilizes industrial waste such as red mud, slag, and fly ash as raw materials, which not only achieves resource reuse and reduces dependence on new raw materials, but also significantly reduces carbon emissions during the production process. This green and low-carbon raw material selection not only conforms to the concept of sustainable development, but also helps to alleviate pressure on natural resources and reduce environmental pollution. Through a scientific and reasonable raw material ratio, this concrete maximizes resource efficiency and environmental benefits while ensuring performance.

[0036] 2. In this application, benzoxazine and acrylic resin are preferably used to modify recycled aggregates. Through chemical reaction, a network structure is formed on the surface of the recycled aggregates, which significantly improves the water absorption of the recycled aggregates and reduces the internal shrinkage stress during the curing process of concrete. At the same time, the modified recycled aggregates have higher strength and toughness, which can further improve the compressive strength of concrete. Detailed Implementation

[0037] The present application will be further described in detail below with reference to the embodiments.

[0038] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0039] Acrylic resin was purchased from Guangzhou Wenjia Chemical Co., Ltd., grade: GA-1700; epoxy acrylate resin was purchased from Langfang Xiangteng Chemical Co., Ltd., model: XH051908; the cement was silicate cement purchased from Lingshou County Qianfu Mineral Products Processing Plant, strength grade 42.5; zeolite powder was purchased from Lingshou County Yongshun Mineral Products Processing Plant, SiO2 content 62.5%, 325 mesh; sodium silicate solution was purchased from Zhengzhou Longfan Chemical Co., Ltd., modulus 3.3; basalt fiber was purchased from Hebei Sanliujiu New Material Technology Co., Ltd., diameter 7-25μm, length 6-12mm.

[0040] Preparation examples of raw materials and / or intermediates

[0041] Preparation Example 1

[0042] A modified recycled aggregate, prepared by the following steps:

[0043] (1) Take recycled aggregate and put it into a crusher for crushing and screening to obtain recycled aggregate with a particle size of 4.75-22.5mm for later use;

[0044] (2) Take 3 kg of benzoxazine, 0.5 kg of 4-dimethylaminopyridine (catalyst) and 30 kg of ethanol, mix them and stir at 90 °C for 20 min to obtain a uniform mixture, then add 1.5 kg of acrylic resin and continue mixing and stirring at a constant temperature for 4 h to obtain a modifier solution.

[0045] (3) Take 25 kg of crushed recycled aggregate and mix it evenly with the prepared modifier solution. Gradually heat the mixture to 200℃ at a rate of 20℃ / h to solidify it, and then cool it to room temperature to obtain the modified recycled aggregate.

[0046] Preparation Example 2

[0047] A modified recycled aggregate, prepared by the following steps:

[0048] (1) Take recycled aggregate and put it into a crusher for crushing and screening to obtain recycled aggregate with a particle size of 4.75-22.5mm for later use;

[0049] (2) Take 2 kg of benzoxazine, 0.5 kg of 4-dimethylaminopyridine (catalyst) and 30 kg of ethanol, mix them and stir at 100 °C for 30 min to obtain a uniform mixture, then add 2 kg of acrylic resin and continue mixing and stirring at a constant temperature for 5 h to obtain a modifier solution.

[0050] (3) Take 25 kg of crushed recycled aggregate and mix it evenly with the prepared modifier solution. Gradually heat the mixture to 200℃ at a rate of 20℃ / h to solidify it, and then cool it to room temperature to obtain the modified recycled aggregate.

[0051] Preparation Example 3

[0052] A modified recycled aggregate, prepared by the following steps:

[0053] (1) Take recycled aggregate and put it into a crusher for crushing and screening to obtain recycled aggregate with a particle size of 4.75-22.5mm for later use;

[0054] (2) Take 4 kg of benzoxazine, 0.5 kg of 4-dimethylaminopyridine (catalyst) and 30 kg of ethanol, mix them and stir and disperse them at 95°C for 30 min to obtain a uniform mixture. Then add 1.75 kg of acrylic resin and continue to mix and stir at a constant temperature for 4 h to obtain a modifier solution.

[0055] (3) Take 25 kg of crushed recycled aggregate and mix it evenly with the prepared modifier solution. Gradually heat the mixture to 200℃ at a rate of 20℃ / h to solidify it, and then cool it to room temperature to obtain the modified recycled aggregate.

[0056] Preparation Example 4

[0057] A modified recycled aggregate differs from Preparation Example 1 in that the weight ratio of recycled aggregate, benzoxazine, and acrylic resin in this preparation example is 25:5:3, that is, 25 kg of recycled aggregate, 5 kg of benzoxazine, and 3 kg of acrylic resin were added.

[0058] Preparation Example 5

[0059] A modified recycled aggregate differs from Preparation Example 1 in that the weight ratio of recycled aggregate, benzoxazine, and acrylic resin in this preparation example is 25:1:1, that is, 25 kg of recycled aggregate, 1 kg of benzoxazine, and 1 kg of acrylic resin were added.

[0060] Preparation Example 6

[0061] A modified recycled aggregate, which differs from Preparation Example 1 in that the acrylic resin used in this preparation example is an epoxy acrylate resin.

[0062] Comparative Preparation Example 1

[0063] A modified recycled aggregate, differing from Preparation Example 1 in that the preparation of the modified recycled aggregate used in this preparation example includes the following steps:

[0064] (1) Take recycled aggregate and put it into a crusher for crushing and screening to obtain recycled aggregate with a particle size of 4.75-22.5mm for later use;

[0065] (2) Take 1.5 kg of acrylic resin and 30 kg of ethanol, mix and stir at 90°C for 4 h to obtain a modifier solution; (3) Take 25 kg of crushed recycled aggregate and mix it with the prepared modifier solution. Gradually raise the temperature to 200°C at a rate of 20°C / h to solidify, and then lower it to room temperature to obtain the modified recycled aggregate.

[0066] Comparative Preparation Example 2

[0067] A modified recycled aggregate, differing from Preparation Example 1 in that the preparation of the modified recycled aggregate used in this preparation example includes the following steps:

[0068] (1) Take recycled aggregate and put it into a crusher for crushing and screening to obtain recycled aggregate with a particle size of 4.75-22.5mm for later use;

[0069] (2) Take 3 kg of benzoxazine, 0.5 kg of 4-dimethylaminopyridine (catalyst) and 30 kg of ethanol, mix them and stir and disperse at 90 °C for 20 min to obtain a modifier solution;

[0070] (3) Take 25 kg of crushed recycled aggregate and mix it evenly with the prepared modifier solution. Gradually heat the mixture to 200℃ at a rate of 20℃ / h to solidify it, and then cool it to room temperature to obtain the modified recycled aggregate.

[0071] Example

[0072] Example 1

[0073] A green, low-carbon concrete based on recycled aggregates is prepared by the following steps:

[0074] (1) Weigh each raw material component, add red mud, slag, alkali activator and half of the water and mix to obtain a one-time mixture;

[0075] (2) Add fly ash, cement, modified recycled aggregate, zeolite powder, cellulose ether, and the remaining water to the above-mentioned primary mixture and stir to obtain the concrete. In this embodiment, the modified recycled aggregate prepared in Preparation Example 1 is used, and the alkali activator is sodium silicate solution.

[0076] Example 2-3

[0077] A green low-carbon concrete based on recycled aggregate differs from Example 1 in that its raw material components and their corresponding weight parts are shown in Table 1.

[0078] Table 1. Raw materials and their weights (kg) in Examples 1-3

[0079] Components Example 1 Example 2 Example 3 Red mud 6 7 5 slag 15 12.5 10 Alkali activator 6 8 10 fly ash 8 6 10 cement 40 30 35 Modified recycled aggregate 20 25 22.5 Zeolite powder 4 3 5 Cellulose ethers 2 3 4 water 45 40 42.5

[0080] Example 4

[0081] A green low-carbon concrete based on recycled aggregate differs from Example 1 in that the modified recycled aggregate prepared in Example 2 is used in this example.

[0082] Example 5

[0083] A green low-carbon concrete based on recycled aggregate is different from Example 1 in that the modified recycled aggregate prepared in Example 3 is used in this example.

[0084] Example 6

[0085] A green low-carbon concrete based on recycled aggregate is different from Example 1 in that the modified recycled aggregate prepared in Example 4 is used in this example.

[0086] Example 7

[0087] A green low-carbon concrete based on recycled aggregate differs from Example 1 in that the modified recycled aggregate prepared in Example 5 is used in this example.

[0088] Example 8

[0089] A green low-carbon concrete based on recycled aggregate differs from Example 1 in that the modified recycled aggregate prepared in Example 6 is used in this example.

[0090] Example 9

[0091] A green, low-carbon concrete based on recycled aggregate, differing from Example 1 in that it further includes 2 kg of basalt fiber, and its preparation comprises the following steps:

[0092] (1) Weigh each raw material component, add red mud, slag, alkali activator and half of the water and mix to obtain a one-time mixture;

[0093] (2) Fly ash, cement, modified recycled aggregate, basalt fiber, zeolite powder, cellulose ether, and the remaining water are added to the above-mentioned primary mixture and stirred to obtain the concrete. In this embodiment, the modified recycled aggregate prepared in Preparation Example 1 is used, and the alkali activator is sodium silicate solution.

[0094] Example 10

[0095] A green, low-carbon concrete based on recycled aggregates, which differs from Example 9 in that it includes 4 kg of basalt fiber.

[0096] Comparative Example

[0097] Comparative Example 1

[0098] A green low-carbon concrete based on recycled aggregates differs from Example 1 in that unmodified recycled aggregates are used in this comparative example.

[0099] Comparative Example 2

[0100] A green low-carbon concrete based on recycled aggregates differs from Example 1 in that the modified recycled aggregates in Comparative Preparation Example 1 are used in this comparative example.

[0101] Comparative Example 3

[0102] A green low-carbon concrete based on recycled aggregates differs from Example 1 in that the modified recycled aggregates in Comparative Preparation Example 2 are used in this comparative example.

[0103] Performance testing

[0104] Detection methods / test methods

[0105] Splitting tensile strength and compressive strength testing: The splitting tensile strength and compressive strength of concrete are determined according to the methods described in GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0106] Concrete porosity testing: The porosity of concrete prepared according to the formulations in the examples and comparative proportions was determined using the mercury intrusion porosimetry method.

[0107] Table 2 Test Results

[0108] Group 7d splitting tensile strength / MPa 7d compressive strength / MPa Porosity / % Example 1 8.59 50.32 3.63 Example 2 8.38 49.17 3.76 Example 3 8.29 49.05 3.98 Example 4 8.32 49.24 3.84 Example 5 8.18 48.94 3.81 Example 6 7.54 47.29 4.12 Example 7 7.62 47.51 4.27 Example 8 8.92 52.13 3.01 Example 9 9.11 53.27 3.14 Example 10 9.2 53.41 3.11 Comparative Example 1 7.23 38.27 7.95 Comparative Example 2 7.42 41.35 5.76 Comparative Example 3 7.38 41.13 5.63

[0109] Combining Examples 1-3 and Comparative Example 1 with Table 2, it can be seen that the test data of Examples 1-3 are all better than those of Comparative Example 1. This indicates that the modification treatment of recycled aggregate can improve the defect of easy water absorption of recycled aggregate, improve the bond strength of cement mortar transition zone, thereby enhancing the strength of recycled aggregate. At the same time, the modification fills the microcracks in the recycled aggregate, further enhancing the aggregate strength, thereby improving the compressive strength and crack resistance of concrete.

[0110] Combining Examples 1-3 and Comparative Examples 2-3 with Table 2, it can be seen that the test data of Examples 1-3 are all better than those of Comparative Examples 2-3. This indicates that by modifying the recycled aggregate with benzoxazine and acrylic resin, a stronger and tougher polymer network structure can be formed on the surface of the recycled aggregate, giving the recycled aggregate higher strength and toughness, thereby greatly improving the compressive strength and crack resistance of the concrete prepared from it.

[0111] As can be seen from Examples 1-7 and Table 2, the test data of Examples 1-5 are all better than those of Examples 6-7. This indicates that the ratio of recycled aggregate to benzoxazine and acrylic resin affects the final modification effect when modifying recycled aggregate. A reasonable ratio can more effectively improve the performance of recycled aggregate, thereby improving the overall performance of concrete made from these aggregates.

[0112] Combining Examples 1 and 8 with Table 2, it can be seen that the test data of Example 8 are all better than those of Example 1. This indicates that the use of epoxy acrylic resin further allows the epoxy groups inside to participate in the formation of the network structure, enhancing the strength and stability of the surface modification layer of the recycled aggregate, thereby improving the overall performance of the recycled aggregate.

[0113] Combining Examples 1 and 9-10 with Table 2, it can be seen that the test data of Examples 9-10 are all better than those of Example 1, indicating that the addition of basalt fiber to the raw materials can inhibit the propagation of cracks in concrete when it is subjected to external forces and improve the crack resistance of concrete.

[0114] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A green, low-carbon concrete based on recycled aggregates, characterized in that, Including the following parts by weight of raw materials: The mixture comprises 5-7 parts red mud, 10-15 parts slag, 6-10 parts fly ash, 30-40 parts cement, 10-15 parts alkali activator, 20-25 parts modified recycled aggregate, 3-5 parts zeolite powder, 2-4 parts cellulose ether, and 40-45 parts water; wherein the modified recycled aggregate is obtained by modification with a catalyst, acrylic resin, and benzoxazine.

2. The green low-carbon concrete prepared based on recycled aggregate according to claim 1, characterized in that, The preparation of the modified recycled aggregate includes the following steps: (1) After crushing and pre-treatment, recycled aggregates with a particle size of 4.75-22.5 mm are obtained; (2) Mix benzoxazine, catalyst and ethanol and stir and disperse at 90-100℃ for 20-30 min to obtain a uniform mixture. Then add acrylic resin and continue to mix and stir at a constant temperature for 4-6 h to obtain a modifier solution. (3) The prepared modifier solution is mixed evenly with the crushed recycled aggregate, and the temperature is gradually increased to 200℃ at a rate of 20℃ / h to solidify. Then, the temperature is reduced to room temperature to obtain the modified recycled aggregate.

3. The green low-carbon concrete prepared based on recycled aggregate according to claim 2, characterized in that: In the preparation step, the weight ratio of recycled aggregate, benzoxazine, and acrylic resin is 25:2-4:1.5-2.

4. The green low-carbon concrete prepared based on recycled aggregate according to claim 3, characterized in that: The acrylic resin is an epoxy acrylate resin.

5. The green low-carbon concrete prepared based on recycled aggregate according to claim 1, characterized in that: The alkaline activator is a sodium silicate solution.

6. The green low-carbon concrete prepared based on recycled aggregate according to claim 1, characterized in that: The raw materials also include 2-4 parts of basalt fiber.

7. A method for preparing green low-carbon concrete based on recycled aggregate according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Weigh each raw material component, add red mud, slag, alkali activator and half of the water and mix and stir to obtain a one-time mixture; (2) Add fly ash, cement, modified recycled aggregate, zeolite powder, cellulose ether and the remaining water to the above-mentioned primary mixture and stir to obtain the green low-carbon concrete.