Green low-carbon concrete and preparation method thereof

Abstract

The invention relates to the field of building materials, and particularly discloses green low-carbon concrete and a preparation method thereof, and the green low-carbon concrete comprises the following raw materials: cement, modified recycled aggregate, a composite admixture, a water reducing agent, a strength-promoting shrinkage-reducing agent, reinforced fibers and water; wherein the composite admixture is a mixture of fly ash and steel slag powder and / or volcanic ash; the modified recycled aggregate is prepared by sequentially crushing, cleaning, modifying and grading building waste; the preparation method comprises the following steps: dry-mixing the cement and the composite admixture, and then mixing with the modified recycled aggregate and the reinforced fiber to prepare a dry mixture; mixing the strength-promoting shrinkage-reducing agent, the water reducing agent and water to obtain a mixture, mixing the mixture with the dry mixture, and stirring to obtain the green low-carbon concrete. The method has the characteristics that the cement consumption is reduced, the industrial solid waste utilization rate is increased, and meanwhile, the concrete strength and the impermeability are improved.

Description

Technical Field

[0001] This application relates to the field of building materials, and more specifically, to a green, low-carbon concrete and its preparation method. Background Technology

[0002] In the field of building materials, concrete, as a fundamental material widely used in various building structures, has always been a focus of industry attention regarding its performance and environmental friendliness. The traditional concrete production process heavily relies on energy-intensive cement as the main binder, leading not only to enormous energy consumption but also to substantial carbon emissions, causing serious environmental impacts. Furthermore, the aggregates required for traditional concrete production typically come from the mining of natural minerals, a process that further damages the ecological environment and exacerbates resource depletion.

[0003] With increasing environmental awareness and the growing acceptance of sustainable development concepts, the research and application of green concrete has gradually become a hot topic in the industry. Existing green concrete technologies attempt to reduce cement usage by using alternative materials such as industrial waste, aiming to achieve energy conservation and emission reduction. However, while these attempts have achieved environmental goals, they have also exposed a series of technical problems.

[0004] Current green concrete often uses single industrial waste materials (such as fly ash and slag) to replace part of the cement. However, this substitution method often leads to poorer impermeability, insufficient early strength, and the failure to fully optimize the synergistic effect between admixtures. These problems limit the widespread application of green concrete in practical engineering, especially in situations where high concrete performance is required.

[0005] Therefore, developing a new type of green concrete and its preparation method that can significantly reduce cement usage, improve the utilization rate of industrial solid waste, and maintain or even improve concrete performance has become a pressing technical challenge in the field of building materials. Summary of the Invention

[0006] In order to reduce cement usage, increase the utilization rate of industrial solid waste, and improve the strength and impermeability of concrete, this application provides a green low-carbon concrete and its preparation method.

[0007] Firstly, this application provides a green, low-carbon concrete, employing the following technical solution: A green, low-carbon concrete comprises the following raw materials in parts by weight: 200-300 parts cement, 800-1000 parts modified recycled aggregate, 80-120 parts composite admixture, 1.2-1.8 parts water-reducing agent, 0.5-1.5 parts strength-promoting and shrinkage-reducing agent, 20-30 parts reinforcing fiber, and 120-160 parts water; Among them, the composite admixture is a mixture of fly ash and steel slag powder and / or pozzolanic; Modified recycled aggregate is obtained by sequentially crushing, washing, modifying and grading construction waste. The modification process involves first impregnating the recycled aggregate in a water glass solution and then drying it. Next, it is impregnated in an ethanol solution of aminosilane coupling agent and vinyltriethoxysilane. After filtration, it is treated in a modification solution containing ethylene carbonate, an initiator and amino silicone oil.

[0008] By adopting the above technical solution, this application uses composite admixture industrial solid waste to replace part of the cement, reducing cement usage and thus lowering carbon emissions. Furthermore, it uses recycled aggregate as aggregate, which not only reduces landfill pollution from construction waste but also achieves resource recycling, thereby realizing the preparation of green and low-carbon concrete. However, because recycled aggregate is subjected to external forces during the crushing process, microcracks and pores are generated inside. This not only leads to low strength of the recycled aggregate, affecting the strength and mechanical properties of the concrete, but also results in high water absorption due to the high microcracks and porosity, thus causing poor impermeability of the concrete.

[0009] Therefore, this application modifies the recycled aggregate. Specifically, it first impregnates the recycled aggregate in a water glass solution to initially fill and bind the pores, improving the pore structure and reducing its porosity and water absorption, thereby increasing its strength and impermeability. Then, it impregnates the aggregate again in an ethanol solution of an aminosilane coupling agent and vinyltriethoxysilane to introduce amino and vinyl functional groups. Following this, it is treated in a modifying liquid where, under the action of an initiator, ethylene carbonate polymerizes with the vinyl groups introduced onto the surface of the recycled aggregate to form polymer chains, significantly reducing the water absorption of the recycled aggregate and thus improving the low strength and impermeability caused by its high water absorption. The addition of amino silicone oil further improves its hydrophobic properties and reduces water absorption. Ultimately, this application achieves the reuse of solid waste and recycled aggregate while further improving the mechanical properties and impermeability of concrete, thereby enhancing its performance and durability.

[0010] Optionally, the modified recycled aggregate is prepared by the following method: 1) The construction waste is crushed and cleaned to form a waste matrix; 2) The waste matrix is ​​immersed in a water glass solution with a mass concentration of 3-5 wt% for 2-3 hours at an immersion temperature of 25-35℃, and then dried to obtain pretreated waste. 3) Dissolve γ-aminopropyltriethoxysilane and vinyltriethoxysilane in an aqueous ethanol solution to prepare a preliminary modified solution, adjust the pH value to 4-5, and then add the pretreated waste obtained in step 2), impregnate for 60-90 minutes at an impregnation temperature of 50-60℃, filter, and obtain the preliminary modified waste. 4) Mix ethylene tert-carbonate with amino silicone oil, add N,N-dimethylformamide, stir and mix, then add the initial modified waste material from step 3), heat to 60-70℃, then add initiator and react for 1-2 hours, filter, dry, and obtain modified recycled aggregate.

[0011] By adopting the above technical solution, the construction waste is first crushed and cleaned to remove impurities such as mud. Then, it is impregnated in a water glass solution. The water glass reacts with the calcium hydroxide, a cement hydration product on the surface of the recycled aggregate, to generate calcium silicate colloid, which initially fills and bonds the pores of the recycled aggregate, improving its pore structure. Then, it is impregnated in an ethanol solution of aminosilane coupling agent and vinyltriethoxysilane to introduce amino and vinyl functional groups onto the surface of the recycled aggregate. Then, a modifying liquid is added, and under the action of an initiator, ethylene tert-carbonate polymerizes with the vinyl groups introduced on the surface of the recycled aggregate to form polymer chains, introducing tert-carbonate groups and forming a large steric hindrance, thereby introducing hydrophobic functional groups and significantly reducing the water absorption rate of the recycled aggregate, thus improving the problem of low strength and impermeability caused by its high water absorption rate.

[0012] On the other hand, the addition of amino silicone oil to the modified liquid utilizes the hydrogen bonding between its amino groups and oxygen-containing functional groups on the surface of recycled aggregates to form a protective film. This allows the amino silicone oil to oriented and form a protective film on the surface of the recycled aggregates. This reduces the friction coefficient of the aggregate particles, improves their fluidity, and alleviates the problem of strength reduction caused by the need to add water due to the low water absorption rate of recycled aggregates. Furthermore, the amino groups in the amino silicone oil can also form CSH gel hydration products with calcium ions in the cementitious matrix, improving the interfacial transition zone performance between recycled aggregates and fresh cement paste, enhancing interfacial bonding strength, and thus increasing compressive strength. At the same time, the formation of its protective film can block the entry of powder and water, reduce the water absorption rate of recycled aggregates, and improve their impermeability. More importantly, the addition of amino silicone oil introduces siloxane chains, which are flexible and can rotate freely within a certain range, thereby helping to improve the interfacial transition zone performance between recycled aggregates and other raw materials, thus improving the strength and impermeability of concrete.

[0013] Optionally, in the preparation of modified recycled aggregate, in step 3), the mass concentration of γ-aminopropyltriethoxysilane in the initial modified solution is 8-15 wt%, and the mass concentration of vinyltriethoxysilane is 20-30 wt%. In step 4), the amount of ethylene tert-carbonate added is 5-10 wt% of the initial modified waste, the amount of amino silicone oil added is 3-8 wt% of the initial modified waste, the amount of N,N-dimethylformamide added is 3-4 times the mass of ethylene tert-carbonate added, and the amount of initiator added is 1-3 wt% of the initial modified waste.

[0014] Optionally, in the preparation of modified recycled aggregate, after adding the initiator and reacting for 1-2 hours in step 4), polyurethane prepolymer is added, and after stirring and mixing for 30-40 minutes, water is added, stirred for 10-20 minutes, and then allowed to stand for 1-2 hours. After filtration, the modified recycled aggregate is dried to obtain the modified recycled aggregate.

[0015] By adopting the above technical solution, the initial modified waste is treated in the modification liquid and then polyurethane prepolymer is added. The amino groups in the amino silicone oil can form a chemical cross-linking structure with the polyurethane prepolymer. At the same time, the polyurethane prepolymer can also form a chemical cross-linking structure with the amino and other functional groups introduced in the modification liquid and the active groups in the raw materials. This makes the recycled aggregate and other raw materials form a whole, enhances the cohesion and interfacial bonding strength of the overall material, and can effectively prevent the penetration of water and harmful substances. This helps to improve the strength of concrete and its impermeability.

[0016] Optionally, the mass ratio of polyurethane prepolymer to amino silicone oil is 1:(0.5-0.7), and the amount of water added is 10-20 wt% of the polyurethane prepolymer.

[0017] By adopting the above technical solution, water is added after the polyurethane prepolymer reacts in this application, and the unreacted polyurethane prepolymer is formed into a polyurethane macromolecular structure. This structure forms a physical entanglement with the hydrophobic polymer generated by the polymerization of ethylene carbonate on the surface of recycled aggregate and the amino silicone oil, ultimately forming a macromolecular network structure. This not only significantly improves its compressive strength but also significantly enhances its impermeability.

[0018] Optionally, in the preparation of modified recycled aggregate, after the construction waste is crushed and cleaned in step 1), it is stirred and soaked in a sodium hydroxide solution with a mass concentration of 3-5 wt%, and then cleaned to obtain the waste matrix. The soaking temperature is 35-45℃, and the stirring and soaking time is 30-40 min.

[0019] By adopting the above technical solution, this application further treats the crushed and cleaned construction waste with alkali, significantly increasing the hydroxyl content. This facilitates subsequent treatment with silane coupling agents and modifying liquids, improving the interfacial properties between recycled aggregates and the matrix, and ultimately enhancing concrete performance. Furthermore, the dense structure of the construction waste surface, such as the oxide coating, hinders the contact and reaction between water glass and the modifying liquid with the waste matrix, impeding the filling and action on the pores within the construction waste. Therefore, this application performs alkali treatment before water glass treatment, increasing the specific surface area of ​​the waste matrix. This allows water glass and subsequent modifying liquids to penetrate deeper into the waste matrix, reacting with more components, filling micro-cracks within the waste matrix, and forming stronger chemical bonds. This improves the modification effect on recycled aggregates, ultimately resulting in concrete with better overall performance.

[0020] Optionally, the reinforcing fiber is selected from one or more of carbon fiber, polypropylene fiber, glass fiber and steel fiber, with glass fiber being more preferred.

[0021] By adopting the above technical solutions, the addition of reinforcing fibers helps to improve strength, especially the addition of glass fibers. The surface of glass fibers contains hydroxyl active functional groups, which can form chemical bonds with modified recycled aggregates, thereby further improving the performance of the interface transition zone between aggregates, cement matrix and reinforcing fibers, forming a tighter connection structure, reducing stress concentration, and improving the strength and durability of concrete.

[0022] Optionally, the modified recycled aggregate includes 60-70% modified recycled fine aggregate and 30-40% modified recycled coarse aggregate by mass, wherein the particle size of the modified recycled fine aggregate is 0.08-5 mm and the particle size of the modified recycled coarse aggregate is 5-10 mm.

[0023] Optionally, the reinforcing fiber is a modified glass fiber, which is prepared by the following method: immersing the glass fiber in a sodium hydroxide solution with a mass concentration of 5-8 wt% for 20-30 minutes, washing, and drying to obtain activated glass fiber; Carboxymethyl chitosan and γ-aminopropyltriethoxysilane were dissolved in an ethanol solution to prepare an impregnation solution. Then, activated glass fibers were added, and the solution was impregnated at 55-65℃ for 1-2 hours and then dried to obtain modified glass fibers.

[0024] By adopting the above technical solution, the glass fiber is first impregnated in an alkaline solution to increase the active sites of the glass fiber. Then, it is impregnated in an impregnation solution containing carboxymethyl chitosan and an aminosilane coupling agent. The amino groups are introduced by the interaction with the silanol groups on the surface of the glass fiber. At the same time, the amino or carboxyl groups on the carboxymethyl chitosan react with the silanol groups on the surface of the glass fiber or with the amino groups of the silane coupling agent, thereby further introducing carboxyl and amino functional groups. Finally, modified glass fiber containing amino and carboxyl functional groups is obtained. It can form chemical bonds with the cement matrix and also form certain chemical bonds with modified recycled aggregates, improving the interfacial bonding performance between the fiber and the matrix and aggregates, and further improving the strength of concrete.

[0025] Optionally, during the preparation of modified glass fibers, the mass ratio of carboxymethyl chitosan to γ-aminopropyltriethoxysilane is 1:(1.5-1.8), and the mass ratio of γ-aminopropyltriethoxysilane to ethanol solution is 1:(4-6). The amount of impregnation solution added is 6-8 times the mass of the activated glass fibers.

[0026] Optionally, the composite admixture may be selected from volcanic ash, steel slag powder and fly ash in a mass ratio of 1:(1.8-2.2):(2.8-3.2).

[0027] Secondly, this application provides a method for preparing green low-carbon concrete, which adopts the following technical solution: A method for preparing green low-carbon concrete includes the following steps: The cement and composite admixtures are first activated by applying air pressure of 0.5-0.6 MPa simultaneously during dry mixing, and then the pressure is released before mixing with modified recycled aggregates and reinforcing fibers to obtain dry mix. A strength-enhancing and shrinkage-reducing agent, a water-reducing agent, and water are mixed to prepare a mixture. The mixture is then mixed with dry mix and stirred to produce green low-carbon concrete.

[0028] By adopting the above technical solution, the cement and composite admixture are first subjected to air pressure activation treatment, which helps to promote the pseudo-surface reaction between the cement and composite admixture, form a tighter particle bond, improve the overall performance of the mixture, and finally produce concrete with better mechanical properties and impermeability.

[0029] In summary, this application has the following beneficial effects: 1. This application uses composite admixture industrial solid waste to replace part of the cement, reducing cement usage and thus reducing carbon emissions. Furthermore, it uses recycled aggregate as aggregate, which not only reduces landfill pollution from construction waste but also achieves resource recycling, thereby realizing the preparation of green and low-carbon concrete. On this basis, the recycled aggregate is modified to improve the strength loss and poor impermeability caused by its high porosity and high water absorption. Ultimately, this application achieves the reuse of solid waste and recycled aggregate while further improving the mechanical properties and impermeability of concrete to enhance its performance and durability. 2. In this application, the recycled aggregate is first impregnated in a water glass solution to preliminarily fill and bond the pores, improving the pore structure and thus reducing its porosity and water absorption, thereby increasing its strength and impermeability. Then, it is impregnated again in an ethanol solution of aminosilane coupling agent and vinyltriethoxysilane to introduce amino and vinyl functional groups. Next, it is treated in a modifying solution where, under the action of an initiator, ethylene carbonate polymerizes with the vinyl groups introduced on the surface of the recycled aggregate to form polymer chains, significantly reducing the water absorption of the recycled aggregate and thus improving the problem of low strength and impermeability caused by its high water absorption. The addition of amino silicone oil further improves its hydrophobic properties and reduces water absorption. Detailed Implementation

[0030] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0031] In the following examples, polycarboxylate superplasticizer is selected as the water-reducing agent, and more specifically, polycarboxylate superplasticizer from Jinan Qingtian Chemical Technology Co., Ltd. is selected. The model is industrial grade, the brand is Qingtianyu QTYU, and the category is high-performance water-reducing agent. The cement used is P.O42.5 ordinary Portland cement; The strength-promoting and shrinkage-reducing agent selected is BJX concrete strength-promoting and shrinkage-reducing agent from Tangshan Arctic Bear Building Materials Co., Ltd.

[0032] Carboxymethyl chitosan was selected from Guangdong Mingtong Biotechnology Co., Ltd. In the following preparation examples, the polyurethane prepolymer used is the polyurethane prepolymer from Hubei Xinghengye Technology Co., Ltd. The amino silicone oil selected is SL-206 from Laiyang Shengbang Organosilicon Technology Co., Ltd., with an amino value of 0.3-0.6.

[0033] The following preparation examples illustrate the preparation of modified recycled aggregates. Preparation Example 1 A method for preparing modified recycled aggregate includes the following steps: 1) The construction waste is crushed and cleaned, then stirred and soaked in a 4wt% sodium hydroxide solution (sodium hydroxide and water are mixed), and then washed to obtain the waste matrix. The soaking temperature is 40℃ and the stirring and soaking time is 35min. The amount of sodium hydroxide solution added is 9 times the mass of the construction waste. 2) The waste matrix was immersed in a 4 wt% water glass solution (prepared by mixing water as solvent and sodium silicate as solute, and the mass concentration of sodium silicate in the water glass solution was 4%) for 2.5 h at an immersion temperature of 30 °C, and then dried to obtain pretreated waste. The mass ratio of waste matrix to water glass solution was 1:5. 3) Dissolve γ-aminopropyltriethoxysilane and vinyltriethoxysilane in an aqueous ethanol solution to prepare a preliminary modified solution, adjust the pH value to 4.5, then add the pretreated waste obtained in step 2), impregnate for 70 min at an impregnation temperature of 55℃, filter, and obtain the preliminary modified waste. The ethanol-water solution was prepared by mixing ethanol and water in a mass ratio of 1:1.3, and the mass concentration of γ-aminopropyltriethoxysilane in the modified solution was 12wt%, the mass concentration of vinyltriethoxysilane was 25wt%, and the mass ratio of pretreated waste to initial modified solution was 1:7. 4) Mix ethylene tert-carbonate with amino silicone oil, add N,N-dimethylformamide, stir and mix, then add the initial modified waste material from step 3), heat to 65℃, then add initiator and react for 1.5h, filter, dry, and obtain modified recycled aggregate; In step 4), the amount of ethylene tert-carbonate added is 8 wt% of the initial modified waste, the amount of amino silicone oil added is 5 wt% of the initial modified waste, the amount of N,N-dimethylformamide added is 3.5 times the mass of ethylene tert-carbonate, and benzoyl peroxide is selected as the initiator, with the amount of initiator added being 2 wt% of the initial modified waste.

[0034] Preparation Example 2 A method for preparing modified recycled aggregate includes the following steps: 1) The construction waste is crushed and cleaned, then stirred and soaked in a 3wt% sodium hydroxide solution (prepared by mixing sodium hydroxide and water), and then cleaned to obtain the waste matrix. The soaking temperature is 45℃ and the stirring and soaking time is 30min. The amount of sodium hydroxide solution added is 8 times the mass of the construction waste. 2) The waste matrix is ​​immersed in a 3 wt% water glass solution (prepared by mixing water as solvent and sodium silicate as solute, and the mass concentration of sodium silicate in the water glass solution is 3%) for 2 hours at a immersion temperature of 35°C, and then dried to obtain pretreated waste. The mass ratio of waste matrix to water glass solution is 1:4. 3) Dissolve γ-aminopropyltriethoxysilane and vinyltriethoxysilane in an aqueous ethanol solution to prepare a preliminary modified solution, adjust the pH value to 4, and then add the pretreated waste obtained in step 2), impregnate for 60 min at an impregnation temperature of 60℃, filter, and obtain the preliminary modified waste. The ethanol-water solution was prepared by mixing ethanol and water at a mass ratio of 1:1.2, and the mass concentration of γ-aminopropyltriethoxysilane in the modified solution was 8 wt%, the mass concentration of vinyltriethoxysilane was 20 wt%, and the mass ratio of pretreated waste to initial modified solution was 1:6. 4) Mix ethylene tert-carbonate with amino silicone oil, add N,N-dimethylformamide, stir and mix, then add the initial modified waste material from step 3), heat to 60℃, then add initiator and react for 2 hours, filter, dry, and obtain modified recycled aggregate. In step 4), the amount of ethylene tert-carbonate added is 5 wt% of the initial modified waste, the amount of amino silicone oil added is 3 wt% of the initial modified waste, the amount of N,N-dimethylformamide added is 3 times the mass of ethylene tert-carbonate, and benzoyl peroxide is selected as the initiator, with the amount of initiator added being 1 wt% of the initial modified waste.

[0035] Preparation Example 3 A method for preparing modified recycled aggregate includes the following steps: 1) The construction waste is crushed and cleaned, then stirred and soaked in a 5wt% sodium hydroxide solution (made by mixing sodium hydroxide and water), and then cleaned to obtain the waste matrix. The soaking temperature is 35℃ and the stirring and soaking time is 40min. The amount of sodium hydroxide solution added is 10 times the mass of the construction waste. 2) The waste matrix is ​​immersed in a 5 wt% water glass solution (prepared by mixing water as solvent and sodium silicate as solute, and the mass concentration of sodium silicate in the water glass solution is 5%) for 3 hours at an immersion temperature of 25°C, and then dried to obtain pretreated waste. The mass ratio of waste matrix to water glass solution is 1:6. 3) Dissolve γ-aminopropyltriethoxysilane and vinyltriethoxysilane in an aqueous ethanol solution to prepare a preliminary modified solution, adjust the pH value to 5, and then add the pretreated waste obtained in step 2), impregnate for 90 min at an impregnation temperature of 50°C, filter, and obtain the preliminary modified waste. The ethanol-water solution is prepared by mixing ethanol and water at a mass ratio of 1:1.5, and the mass concentration of γ-aminopropyltriethoxysilane in the modified solution is 15wt%, the mass concentration of vinyltriethoxysilane is 30wt%, and the mass ratio of pretreated waste to initial modified solution is 1:8. 4) Mix ethylene tert-carbonate with amino silicone oil, add N,N-dimethylformamide, stir and mix, then add the initial modified waste material from step 3), heat to 70°C, then add initiator and react for 1 hour, filter, dry, and obtain modified recycled aggregate. In step 4), the amount of ethylene tert-carbonate added is 10 wt% of the initial modified waste, the amount of amino silicone oil added is 8 wt% of the initial modified waste, the amount of N,N-dimethylformamide added is 4 times the mass of ethylene tert-carbonate, and benzoyl peroxide is selected as the initiator, with the amount of initiator added being 3 wt% of the initial modified waste.

[0036] Preparation Example 4 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that in step 4), after adding the initiator and reacting for 1.5 h, polyurethane prepolymer is added, and the mass ratio of prepolymer to amino silicone oil is 1:0.6. After stirring and mixing for 35 min, water is added, and the amount of water added is 15 wt% of the polyurethane prepolymer. After stirring for 15 min, it is allowed to stand for 1.5 h, and then filtered and dried to obtain modified recycled aggregate.

[0037] Preparation Example 5 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that in step 4), after adding the initiator and reacting for 1.5 hours, polyurethane prepolymer is added, and the mass ratio of prepolymer to amino silicone oil is 1:0.5. After stirring and mixing for 30 minutes, water is added, and the amount of water added is 10 wt% of the polyurethane prepolymer. After stirring for 10 minutes, it is allowed to stand for 1 hour, and then filtered and dried to obtain modified recycled aggregate.

[0038] Preparation Example 6 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that in step 4), after adding the initiator and reacting for 1.5 hours, polyurethane prepolymer is added, and the mass ratio of prepolymer to amino silicone oil is 1:0.7. After stirring and mixing for 40 minutes, water is added, and the amount of water added is 20 wt% of the polyurethane prepolymer. After stirring for 20 minutes, it is allowed to stand for 2 hours, and then filtered and dried to obtain modified recycled aggregate.

[0039] Comparative Preparation Example 1 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that step 2) is not performed, and step 3) is performed directly after step 1).

[0040] Comparative Preparation Example 2 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that steps 3) and 4) are not performed, and the pretreated waste obtained in step 2) is used as modified recycled aggregate.

[0041] Comparative preparation example 3 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that step 4) is not performed, and the primary modified waste obtained in step 3) is directly used as modified recycled aggregate.

[0042] Comparative preparation example 4 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that vinyltriethoxysilane is not added in step 3).

[0043] Comparative preparation example 5 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that in step 4), ethylene tert-carbonate is replaced by an equal amount of acrylic acid.

[0044] Comparative preparation example 6 A method for preparing modified recycled aggregate is carried out according to the method in Preparation Example 1, except that amino silicone oil is not added in step 4).

[0045] Example 1 A method for preparing green, low-carbon concrete includes the following steps: 250 kg of cement and 90 kg of composite admixture were first dry-mixed in a planetary mixer. During the dry mixing, 0.5 MPa air pressure was applied simultaneously for activation. After depressurization, it was mixed with 900 kg of modified recycled aggregate and 25 kg of reinforcing fiber to obtain dry mix. Mix 1 kg of strength-promoting and shrinkage-reducing agent, 1.5 kg of water-reducing agent, and 140 kg of water to prepare a mixture. Then, mix the mixture with dry mix and stir to obtain green low-carbon concrete.

[0046] The composite admixture is selected from volcanic ash, steel slag powder and fly ash in a mass ratio of 1:2:3; the reinforcing fiber is glass fiber; the modified recycled aggregate includes 65% modified recycled fine aggregate and 35% modified recycled coarse aggregate by mass, and the modified recycled fine aggregate and modified recycled coarse aggregate are obtained by grading the modified recycled aggregate prepared in Example 1. The particle size of the modified recycled fine aggregate is 0.08-5mm and the particle size of the modified recycled coarse aggregate is 5-10mm.

[0047] Example 2 A method for preparing green, low-carbon concrete includes the following steps: 200 kg of cement and 80 kg of composite admixture were first dry-mixed in a planetary mixer. During the dry mixing, 0.5 MPa air pressure was applied simultaneously for activation. After depressurization, it was mixed with 800 kg of modified recycled aggregate and 20 kg of reinforcing fiber to obtain dry mix. Mix 0.5 kg of strength-promoting and shrinkage-reducing agent, 1.2 kg of water-reducing agent, and 120 kg of water to prepare a mixture. Then, mix the mixture with dry mix and stir to obtain green low-carbon concrete.

[0048] The composite admixture is selected from volcanic ash, steel slag powder and fly ash in a mass ratio of 1:1.8:2.8; the reinforcing fiber is steel fiber; the modified recycled aggregate includes 60% modified recycled fine aggregate and 40% modified recycled coarse aggregate by mass, and the modified recycled fine aggregate and modified recycled coarse aggregate are obtained by grading the modified recycled aggregate prepared in Example 2. The particle size of the modified recycled fine aggregate is 0.08-5mm and the particle size of the modified recycled coarse aggregate is 5-10mm.

[0049] Example 3 A method for preparing green, low-carbon concrete includes the following steps: 300 kg of cement and 120 kg of composite admixture were first dry-mixed in a planetary mixer. During dry mixing, a pressure of 0.6 MPa was applied simultaneously for activation. After depressurization, the admixture was mixed with 1000 kg of modified recycled aggregate and 30 kg of reinforcing fiber to obtain a dry mix. 1.5 kg of strength-promoting and shrinkage-reducing agent, 1.8 kg of water-reducing agent, and 160 kg of water were mixed to obtain a composite material. The composite material was then mixed with the dry mix and stirred to obtain green low-carbon concrete.

[0050] The composite admixture is selected from volcanic ash, steel slag powder and fly ash in a mass ratio of 1:2.2:3.2; the reinforcing fiber is carbon fiber; the modified recycled aggregate includes 70% modified recycled fine aggregate and 30% modified recycled coarse aggregate by mass, and the modified recycled fine aggregate and modified recycled coarse aggregate are obtained by grading the modified recycled aggregate prepared in Example 3. The particle size of the modified recycled fine aggregate is 0.08-5mm and the particle size of the modified recycled coarse aggregate is 5-10mm.

[0051] Examples 4-6 A method for preparing green low-carbon concrete is carried out according to the method in Example 1, except that the modified recycled fine aggregate and modified recycled coarse aggregate are obtained by grading the modified recycled aggregates prepared in Examples 4-6, respectively.

[0052] Example 7 A method for preparing green, low-carbon concrete is carried out according to the method in Example 1, except that modified glass fiber is used as the reinforcing filler. The modified glass fiber is prepared by the following method: Glass fibers were immersed in a 6 wt% sodium hydroxide solution for 25 min, washed, and the amount of sodium hydroxide solution added was 4.5 times the mass of the glass fibers. The fibers were then dried to obtain activated glass fibers. Carboxymethyl chitosan and γ-aminopropyltriethoxysilane were dissolved in an ethanol solution to prepare an impregnation solution. The pH of the impregnation solution was adjusted to 4.5, and then activated glass fibers were added. After impregnation at 60°C for 1.5 hours, the solution was dried to obtain modified glass fibers.

[0053] The mass ratio of carboxymethyl chitosan to γ-aminopropyltriethoxysilane is 1:1.6, and the mass ratio of γ-aminopropyltriethoxysilane to ethanol solution is 1:5. The ethanol solution is made by mixing ethanol and water at a mass ratio of 1:1.2. The amount of impregnation solution added is 7 times the mass of the activated glass fiber.

[0054] Example 8 A method for preparing green, low-carbon concrete is carried out according to the method in Example 1, except that modified glass fiber is used as the reinforcing filler. The modified glass fiber is prepared by the following method: Glass fibers were immersed in a 5 wt% sodium hydroxide solution for 30 min, washed, and the amount of sodium hydroxide solution added was 4 times the mass of the glass fibers. The activated glass fibers were then dried. Carboxymethyl chitosan and γ-aminopropyltriethoxysilane were dissolved in an ethanol solution to prepare an impregnation solution. The pH of the impregnation solution was adjusted to 4, and then activated glass fibers were added. After impregnation at 55°C for 2 hours, the glass fibers were dried to obtain modified glass fibers.

[0055] The mass ratio of carboxymethyl chitosan to γ-aminopropyltriethoxysilane is 1:1.5, and the mass ratio of γ-aminopropyltriethoxysilane to ethanol solution is 1:4. The ethanol solution is made by mixing ethanol and water at a mass ratio of 1:1.2. The amount of impregnation solution added is 6 times the mass of the activated glass fiber.

[0056] Example 9 A method for preparing green, low-carbon concrete is carried out according to the method in Example 1, except that modified glass fiber is used as the reinforcing filler. The modified glass fiber is prepared by the following method: Glass fibers were immersed in an 8 wt% sodium hydroxide solution for 20 minutes, washed, and the amount of sodium hydroxide solution added was 5 times the mass of the glass fibers. The activated glass fibers were then dried. Carboxymethyl chitosan and γ-aminopropyltriethoxysilane were dissolved in an ethanol solution to prepare an impregnation solution. The pH of the impregnation solution was adjusted to 5, and then activated glass fibers were added. After impregnation at 65°C for 1 hour, the modified glass fibers were obtained by drying.

[0057] The mass ratio of carboxymethyl chitosan to γ-aminopropyltriethoxysilane is 1:1.8, and the mass ratio of γ-aminopropyltriethoxysilane to ethanol solution is 1:6. The ethanol solution is made by mixing ethanol and water at a mass ratio of 1:1.3. The amount of impregnation solution added is 8 times the mass of the activated glass fiber.

[0058] Example 10 A method for preparing green low-carbon concrete is carried out according to the method in Example 7, except that when preparing modified glass fiber, carboxymethyl chitosan is replaced by an equal amount of γ-aminopropyltriethoxysilane.

[0059] Comparative Examples 1-6 A method for preparing green low-carbon concrete is carried out according to the method in Example 1, except that the modified recycled fine aggregate and the modified recycled coarse aggregate are obtained by grading the modified recycled aggregate prepared in Comparative Preparation Examples 1-6.

[0060] Comparative Example 7 A method for preparing green low-carbon concrete is carried out according to the method in Example 1, except that the modified recycled fine aggregate is selected from pretreated recycled fine aggregate, and the modified recycled coarse aggregate is selected from pretreated recycled coarse aggregate. The particle size of the pretreated recycled fine aggregate is 0.08-5mm, and the particle size of the pretreated recycled coarse aggregate is 5-10mm. The pretreated recycled fine aggregate and the pretreated recycled coarse aggregate are obtained by crushing and washing construction waste, spraying it with a KH-550 solution with a mass concentration of 5%, and then classifying it. The amount of KH-550 solution added is 5wt% of the construction waste.

[0061] Performance testing The concrete prepared in the above examples and comparative examples was tested for 7-day and 28-day compressive strength according to GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". The impermeability was tested with reference to GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". The seepage pressure was 4 MPa and the pressurization time was 48 h. The smaller the seepage height, the better the impermeability. The test results are shown in Table 1 below.

[0062] Table 1: Referring to the test results in Table 1 above, the green low-carbon concrete made from recycled aggregate in this application has excellent compressive strength, especially good early compressive strength and impermeability. Combining the test results of Examples 1 and 4-6, when modifying recycled aggregate, polyurethane prepolymer and water are added after polymerization of ethylene tert-carbonate, which can form chemical bonds with recycled aggregate and amino silicone oil, further modifying the recycled aggregate and combining it with the physical entanglement of macromolecular structures, ultimately improving the mechanical properties and impermeability of the concrete. Combining the test results of Examples 7-9, when modified glass fiber is used as the reinforcing fiber, its mechanical properties are further significantly improved. Combining the test results of Example 10, when glass fiber is modified without the addition of carboxymethyl chitosan and only modified with silane coupling agent, its mechanical properties are reduced compared to Example 7. The addition of carboxymethyl chitosan further improves the interfacial bonding performance between modified glass fiber, cement matrix and recycled aggregate, further improving its mechanical properties.

[0063] Combining the test results of Example 1 and Comparative Example 1, when the recycled aggregate was modified without water glass impregnation modification, its mechanical properties and impermeability were reduced. Water glass impregnation modification initially filled the microcracks and pores inside the recycled aggregate, which helped improve its mechanical properties and impermeability. Combining the test results of Comparative Example 2, when the recycled aggregate was modified only by water glass impregnation modification, its mechanical properties and impermeability were significantly reduced compared to Example 1, indicating that the effect of water glass impregnation modification was limited. The synergistic effect of water glass impregnation modification and modified liquid treatment on the recycled aggregate significantly improved its mechanical properties and impermeability. Furthermore, combining the test results of Comparative Example 2... The test results of Example 3 show that the mechanical properties and impermeability of the recycled aggregate after water glass impregnation modification and silane coupling agent modification are significantly reduced compared to Example 1. After modification with silane coupling agent and subsequent polymerization to introduce tertiary carbonate groups and siloxane groups, the impermeability of the recycled aggregate is significantly improved, while water absorption and strength are also improved. Combining the test results of Comparative Examples 4-6, the amino silicone oil and the introduction of tertiary carbonate groups during the modification of recycled aggregate have a significant impact on its performance. Combining the test results of Comparative Example 7, the mechanical properties and impermeability of the recycled aggregate after only silane coupling agent spraying treatment are poor.

[0064] 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, characterized in that, Including the following parts by weight of raw materials: 200-300 parts cement, 800-1000 parts modified recycled aggregate, 80-120 parts composite admixture, 1.2-1.8 parts water-reducing agent, 0.5-1.5 parts strength-promoting and shrinkage-reducing agent, 20-30 parts reinforcing fiber, and 120-160 parts water; Among them, the composite admixture is a mixture of fly ash and steel slag powder and / or pozzolanic; Modified recycled aggregate is obtained by sequentially crushing, washing, modifying and grading construction waste. The modification process involves first impregnating the recycled aggregate in a water glass solution and then drying it. Next, it is impregnated in an ethanol solution of aminosilane coupling agent and vinyltriethoxysilane. After filtration, it is treated in a modification solution containing ethylene carbonate, an initiator and amino silicone oil.

2. The green low-carbon concrete according to claim 1, characterized in that: The modified recycled aggregate is obtained by the following method: 1) The construction waste is crushed and cleaned to form a waste matrix; 2) The waste matrix is ​​immersed in a water glass solution with a mass concentration of 3-5 wt% for 2-3 hours at an immersion temperature of 25-35℃, and then dried to obtain pretreated waste. 3) Dissolve γ-aminopropyltriethoxysilane and vinyltriethoxysilane in an aqueous ethanol solution to prepare a preliminary modified solution, adjust the pH value to 4-5, and then add the pretreated waste obtained in step 2), impregnate for 60-90 minutes at an impregnation temperature of 50-60℃, filter, and obtain the preliminary modified waste. 4) Mix ethylene tert-carbonate with amino silicone oil, add N,N-dimethylformamide, stir and mix, then add the initial modified waste material from step 3), heat to 60-70℃, then add initiator and react for 1-2 hours, filter, dry, and obtain modified recycled aggregate.

3. The green low-carbon concrete according to claim 2, characterized in that: In the preparation of modified recycled aggregate, in step 3), the mass concentration of γ-aminopropyltriethoxysilane in the initial modification solution is 8-15 wt%, and the mass concentration of vinyltriethoxysilane is 20-30 wt%. Step 4) The amount of ethylene tert-carbonate added is 5-10 wt% of the initial modified waste, the amount of amino silicone oil added is 3-8 wt% of the initial modified waste, the amount of N,N-dimethylformamide added is 3-4 times the mass of ethylene tert-carbonate, and the amount of initiator added is 1-3 wt% of the initial modified waste.

4. The green low-carbon concrete according to claim 2, characterized in that: In the preparation of modified recycled aggregate, after adding an initiator and reacting for 1-2 hours in step 4), polyurethane prepolymer is added, and after stirring and mixing for 30-40 minutes, water is added, stirred for 10-20 minutes, and then allowed to stand for 1-2 hours. After filtration, the modified recycled aggregate is obtained by drying.

5. The green low-carbon concrete according to claim 4, characterized in that: The mass ratio of polyurethane prepolymer to amino silicone oil is 1:(0.5-0.7), and the amount of water added is 10-20wt% of the polyurethane prepolymer.

6. The green low-carbon concrete according to claim 2, characterized in that: In the preparation of modified recycled aggregate, in step 1), the construction waste is crushed and cleaned, then stirred and soaked in a sodium hydroxide solution with a mass concentration of 3-5 wt%, and then cleaned to obtain the waste matrix. The soaking temperature is 35-45℃, and the stirring and soaking time is 30-40 min.

7. The green low-carbon concrete according to claim 1, characterized in that: The reinforcing fiber is selected from one or more of carbon fiber, polypropylene fiber, glass fiber and steel fiber; And / or, the composite admixture is selected from volcanic ash, steel slag powder and fly ash in a mass ratio of 1:(1.8-2.2):(2.8-3.2); And / or, the modified recycled aggregate includes 60-70% modified recycled fine aggregate and 30-40% modified recycled coarse aggregate by mass, wherein the particle size of the modified recycled fine aggregate is 0.08-5 mm and the particle size of the modified recycled coarse aggregate is 5-10 mm.

8. The green low-carbon concrete according to claim 1, characterized in that: The reinforcing fiber is selected from modified glass fiber, which is prepared by the following method: Activated glass fibers are obtained by immersing glass fibers in a sodium hydroxide solution with a mass concentration of 5-8 wt% for 20-30 minutes, washing, and drying. Carboxymethyl chitosan and γ-aminopropyltriethoxysilane were dissolved in an ethanol solution to prepare an impregnation solution. Then, activated glass fibers were added, and the solution was impregnated at 55-65℃ for 1-2 hours and then dried to obtain modified glass fibers.

9. The green low-carbon concrete according to claim 8, characterized in that: When preparing modified glass fibers, the mass ratio of carboxymethyl chitosan to γ-aminopropyltriethoxysilane is 1:(1.5-1.8), and the mass ratio of γ-aminopropyltriethoxysilane to ethanol solution is 1:(4-6). The amount of impregnation solution added is 6-8 times the mass of the activated glass fibers.

10. The method for preparing green low-carbon concrete according to any one of claims 1-9, characterized in that: Includes the following steps: The cement and composite admixtures are first activated by applying air pressure of 0.5-0.6 MPa simultaneously during dry mixing, and then the pressure is released before mixing with modified recycled aggregates and reinforcing fibers to obtain dry mix. A strength-enhancing and shrinkage-reducing agent, a water-reducing agent, and water are mixed to prepare a mixture. The mixture is then mixed with dry mix and stirred to produce green low-carbon concrete.

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