A recycled aggregate low-carbon concrete and a preparation method thereof

Abstract

The application discloses a kind of recycled mixture low-carbon concrete and preparation method thereof, belong to green building material and building waste resource utilization technical field.The application is aimed at the industry pain point that existing recycled aggregate concrete raw material source is single, solid waste utilization rate is low, cannot realize the full amount of multi-class housing construction waste collaborative utilization, with reinforced concrete structure house demolition waste, brick-concrete structure house demolition waste, house decoration waste three kinds of building solid waste as raw material, respectively prepare recycled coarse mixture, recycled medium-coarse mixture, recycled fine mixture and recycled micro-powder as composite main material, compound ordinary portland cement, solid waste-based cementitious material, alkali-activated cementitious material to form composite activation system, and the total mass content of solid waste is greater than or equal to 70%.The application sets up a differentiated formula system according to the characteristics of different building waste materials, and prepares gradient functional concrete of high-strength load-bearing type, light structure type and thermal insulation integrated type respectively;Optimize the preparation process, which can be directly adapted to the existing mixing station for rapid technical transformation and mass production.

Description

Technical Field

[0001] This invention belongs to the technical fields of green building materials, resource recycling of construction waste and low-carbon concrete preparation. Specifically, it relates to a multi-gradient functional recycled low-carbon concrete and its preparation process that is suitable for the full and high-value utilization of three types of building waste: reinforced concrete structure, brick-concrete structure and decoration waste. Background Technology

[0002] For more than a decade, the utilization of construction waste resources in China has been continuously promoted. However, due to limitations in industry standards, technical routes, on-site management and product performance, the development of traditional recycled aggregates and recycled aggregate concrete has been slow, and large-scale application has not been achieved, making it difficult to complete the task of supply-side structural low-carbon reform in the concrete industry.

[0003] The current "Technical Standard for Recycled Concrete Structures" (JGJ / T443-2018) stipulates that recycled coarse aggregate for concrete can only be processed from pure concrete, mortar, and stone materials from building waste. It restricts the use of demolition and renovation waste containing clay sintered bricks, fly ash bricks, and blocks as compliant recycled coarse aggregate, and the aggregate replacement rate for structural recycled coarse aggregate concrete must not exceed 30%. Under this standard, recycled aggregate concrete can only utilize the stone components of waste concrete. A large amount of brick and concrete materials, waste mortar, and construction waste powder are directly discarded. Building waste is mostly a mixture of raw sand and gravel, cement stone, clay sintered bricks, and brick slab composite clinker. This single-source purification of aggregates not only results in a limited source of raw materials and extremely low resource utilization, but also generates a large amount of secondary solid waste, exacerbating environmental pollution and land occupation.

[0004] Meanwhile, traditional recycled aggregate concrete suffers from the practical problem of uncontrollable admixture types and proportions. Recycled aggregate concrete falls under the category of structural concrete, which has strict requirements on aggregate types and substitution ratios. However, construction sites lack effective testing and monitoring methods, and project supervisors cannot verify the types of recycled aggregates and actual admixture ratios in real time. Due to structural safety control requirements, most construction sites comprehensively restrict or refuse to use recycled aggregate concrete, severely hindering the promotion of recycled aggregate concrete technology.

[0005] In terms of building structural safety, modern natural sand and gravel-based load-bearing reinforced concrete continues to upgrade towards high strength, high durability, and high workability, and generally uses high-quality refined sand and gravel raw materials; while traditional recycled coarse aggregates have old mortar coatings on the surface, high internal porosity, and large material strength dispersion. When used directly in core load-bearing components such as beams, floor slabs, and columns, they are prone to problems such as insufficient strength, shrinkage cracking, and durability reduction, posing significant building structural safety hazards.

[0006] Under the guidance of the national dual-carbon target policy, documents such as the "Action Plan for Carbon Peaking before 2030", the "Implementation Plan for Carbon Peaking in the Industrial Sector", and the "Implementation Plan for Carbon Peaking in the Urban and Rural Construction Sector" have been successively issued. These documents clearly require strengthening the research and application of low-carbon building materials such as new cementitious materials and low-carbon concrete, supporting the large-scale, high-value utilization of solid waste, accelerating the promotion of all-solid-waste cementitious materials and all-solid-waste green concrete technologies, promoting centralized treatment and graded utilization of construction waste, guiding the building materials industry towards lightweight, intensive, and prefabricated low-carbon transformation, and specifying a mandatory target that the national construction waste resource utilization rate must reach 50% by 2027.

[0007] Existing experimental and engineering studies have shown that different types of construction waste have differentiated functional utilization values: recycled aggregate from demolition waste of old brick-concrete structures has the characteristics of lightweight expanded clay aggregate and can be used as high-quality lightweight aggregate. The apparent density of the concrete prepared is less than 1950 kg / m³, which falls into the category of lightweight aggregate concrete. Cement stone powder and brick powder from demolition waste and decoration waste can be recycled into micro powder after ultrafine grinding and activation. This powder can be used to formulate thermal insulation foam concrete and integrated structural insulation building materials. The density can cover the range of thermal insulation concrete below 800 kg / m³ and structural insulation composite functional concrete between 800 and 1400 kg / m³.

[0008] Urban construction waste in my country is mainly classified into three categories: demolition waste from mid-to-high-rise reinforced concrete structures, demolition waste from low-rise and multi-story brick-concrete structures, and renovation waste. This constitutes the largest category of solid waste generated in cities, generally characterized by mixed components, high proportion of lightweight materials, and high moisture content. Particularly in the southeastern coastal regions of my country, where prolonged rainy weather exacerbates the problem, demolition waste contains hydrophilic components such as clay bricks and aerated concrete blocks, resulting in severe material sticking due to moisture. Traditional crushing and screening processes are inefficient, requiring a drying process to ensure screening effectiveness, leading to high energy consumption, high disposal costs, easy screen clogging, and significant maintenance pressure. Currently, the industry lacks a complete low-carbon concrete technology that can fully cover all three types of construction waste, requires no deep drying, features continuous gradation, high solid waste content, and controllable multi-performance gradients. This technology cannot simultaneously meet the multiple demands of full solid waste disposal, low-cost production, structural safety, and building energy conservation. Summary of the Invention

[0009] Purpose of the invention

[0010] The purpose of this invention is to overcome the shortcomings of existing recycled aggregates and recycled aggregate concrete, such as single raw material sources, low utilization rate of solid waste components, difficulty in admixture control, poor structural application safety, complex production processes, high energy consumption and cost of disposal, and single product function. It addresses the industry pain points of high processing difficulty, low sorting efficiency, and high mass production cost associated with using traditional recycled aggregate technologies for demolition and renovation waste, and provides a recycled aggregate low-carbon concrete, its preparation method, and its preparation process. This invention breaks through the limitations of traditional recycled aggregate raw material definitions, achieving full coverage and full component resource utilization of three types of construction solid waste: reinforced concrete demolition waste, brick-concrete structure demolition waste, and building renovation waste. It simplifies the production process, eliminates forced drying pretreatment, and reduces equipment investment and production energy consumption. Through raw material classification and matching and synergistic control of formulation processes, it prepares multi-gradient functional concrete products, taking into account the integrated needs of structural load-bearing, lightweight earthquake resistance, and building insulation. Relying on an alkali-activated composite cementitious system, it significantly reduces cement usage, achieving low-carbon and carbon-reducing production, and promoting the high-value, low-carbon, standardized, and industrialized application of construction solid waste.

[0011] Technical solution

[0012] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a recycled low-carbon concrete, comprising recycled coarse aggregate, recycled medium-coarse aggregate, recycled fine aggregate and recycled micro powder prepared from classified building waste as composite filler main materials, and an activator as a cementing material; wherein the total mass content of the recycled coarse aggregate, recycled medium-coarse aggregate, recycled fine aggregate and recycled micro powder is ≥70%; wherein the activator is one or any combination of ordinary silicate cement, solid waste-based cementing materials and alkali-activated cementing materials.

[0013] Furthermore, the recycled coarse aggregate is a natural continuous gradation aggregate with a particle size ≤20mm suitable for the production of demolition waste for reinforced concrete structures. It consists of 5-20mm recycled coarse aggregate and 0-5mm recycled fine aggregate. The total mass content of lightweight combustibles and organic impurities in the recycled coarse aggregate is ≤1%, and metallic impurities are completely stripped.

[0014] Furthermore, the recycled medium-coarse mixture is a natural continuous gradation mixture with a particle size ≤10mm, suitable for producing waste from demolished brick-concrete structures. It consists of 5-10mm recycled coarse aggregate and 0-5mm recycled fine aggregate, and the total mass content of lightweight combustibles and organic impurities in the recycled medium-coarse mixture is ≤1%.

[0015] Furthermore, the recycled fine aggregate is a natural continuous gradation aggregate suitable for producing construction waste with a particle size ≤5mm, consisting of 0-5mm recycled fine aggregate and 0-0.15mm recycled micro aggregate.

[0016] Furthermore, the recycled micro powder conforms to the industry standard "Recycled Micro Powder for Concrete and Mortar" (JG / T573-2020), with a particle size ≤0.15mm and an activity index ≥75%.

[0017] Furthermore, the solid waste-based cementitious material is one or a mixture of two of S95 grade slag powder and Grade I fly ash; the alkali-activated cementitious material is prepared by compounding industrial water glass, slag powder and fly ash with a modulus of 2.2 to 2.6, and the preferred compounding mass ratio is: water glass with a modulus of 2.4: slag powder: fly ash = 1:2:1.

[0018] Furthermore, the recycled low-carbon concrete uses differentiated and precise mass proportions based on the type of raw materials: 1. High-strength concrete based on waste concrete: 45-65 parts recycled coarse mixture, 15-35 parts recycled micro powder, 15-30 parts activator, and 10-12 parts mixing water; 2. Lightweight structural concrete based on brick-concrete demolition waste: 55-65 parts recycled medium-coarse mixture, 15-35 parts recycled micro powder, 10-30 parts activator, and 10-11 parts mixing water; 3. Insulation integrated concrete based on decoration waste: 10-60 parts recycled fine mixture, 10-60 parts recycled micro powder, 10-30 parts activator, and 9-10 parts mixing water.

[0019] Furthermore, the low-carbon concrete made from recycled fine-mixed building waste contains functional additives, including 0.1 to 0.3 parts of foaming agent and 0.2 to 0.4 parts of modified polypropylene short-cut fiber, to improve the crack resistance and thermal insulation performance of the concrete.

[0020] This invention also provides the following technical solutions:

[0021] A method for preparing low-carbon concrete using recycled aggregate includes the following steps: S1, dry mixing: adding recycled aggregate, recycled micro powder, solid activator, and modified fiber into a mixing device and dry mixing for 150-270 seconds to achieve uniform mixing of powder and aggregate; S2, wet mixing modification: adding mixing water, liquid alkali activator, and foaming agent, and continuously wet mixing for 120-180 seconds to form a homogeneous cementitious aggregate; S3, molding and curing: according to product requirements, using natural pouring and vibration molding or 10-15 MPa pressure molding, standard curing at room temperature for 28 days, or moisture-sealed curing for 14 days to obtain finished concrete.

[0022] Beneficial effects

[0023] Compared with existing technologies, this invention has the following significant technological innovations and advantages in industrial application: First, the process is extremely simple and efficient, significantly reducing industrial production costs. This invention abandons the traditional single-particle-size sorting and classification mode of recycled materials. Based on the different physicochemical properties of construction waste, it configures three types of continuously graded raw materials: recycled coarse mixture, recycled medium-coarse mixture, and recycled fine mixture. It avoids multi-stage screening processes and adopts a natural continuous gradation integrated mixture design, shortening the overall production process by more than 40%, and reducing equipment operating energy consumption, labor maintenance, and equipment wear and tear costs by more than 40%. It completely solves the industry problems of screen clogging and low sorting efficiency of damp construction waste. It does not require raw material drying pretreatment and can be quickly upgraded directly based on existing commercial mixing plants and solid waste disposal production lines. It has strong mass production adaptability, short production cycle, and is suitable for continuous and stable industrial production.

[0024] Secondly, it achieves full coverage of various types of solid waste, realizing complete resource utilization with zero waste. This invention establishes differentiated classification and quality control standards based on the differences in impurity content, moisture content, and particle size distribution of three main types of construction waste: reinforced concrete demolition waste, brick-concrete structure demolition waste, and renovation waste. Through graded screening at 20mm, 10mm, and 5mm, it adapts to the preparation needs of medium- and high-strength load-bearing concrete, lightweight structural concrete, and integrated insulation concrete, respectively. This achieves 100% full-component building material utilization of construction waste, with no secondary waste emissions. The maximum solid waste content can reach 90% or more, filling the technological gap in the collaborative, full-volume, high-value utilization of mixed construction waste.

[0025] Third, the gradient performance is precise and controllable, comprehensively covering various engineering application scenarios. This invention forms three types of functionally graded products: medium-high strength recycled coarse mixture low-carbon concrete with a stable density in the range of 2300-2500 kg / m³, a 28-day compressive strength ≥32 MPa, high density, and excellent impermeability and durability, which can be widely used in municipal load-bearing components, building structural bases, and prefabricated building materials; medium-low strength brick-concrete-based lightweight concrete with a density of 1600-1950 kg / m³, reducing the overall building weight by 20%-30%, with outstanding seismic and settlement resistance, suitable for low-rise and multi-story building walls, slope retaining walls, and lightweight renovation and reinforcement projects of old residential areas; and integrated insulation concrete based on construction waste, which can be used to prepare lightweight insulation concrete with a density below 800 kg / m³ and 800-1400 kg / m³. The structural insulation composite concrete has a thermal conductivity of ≤0.22W / (m・K), achieving integrated structural enclosure and thermal insulation, eliminating the need for additional external wall insulation layers, and meeting the construction requirements of ultra-low energy consumption and near-zero energy consumption buildings.

[0026] Fourth, it boasts outstanding carbon reduction benefits, aligning perfectly with the dual-carbon development policy requirements. This invention employs a recycled micro-powder activated composite cementitious and alkali-activated technology system, achieving a cement replacement rate of 15% to 100%. Among these, the insulation concrete based on construction waste can be prepared entirely without silicate cement. Compared to ordinary commercial concrete, overall carbon emissions are reduced by 35% to 65%, effectively cutting the high carbon emissions from cement clinker calcination. Simultaneously, it completely replaces natural sand and gravel aggregates, reducing ecological damage and energy consumption from mining and stone processing. It possesses multiple values, including solid waste disposal, energy conservation and carbon reduction, and ecological protection, perfectly aligning with the carbon peaking and circular economy development policy orientation of the building materials industry.

[0027] Fifth, it enhances the overall performance of buildings and strengthens energy conservation and durability. The lightweight product of this invention can effectively reduce the vertical load on building foundations and improve the overall earthquake resistance, deformation resistance, and settlement resistance of buildings; the virgin trace inorganic fibers from construction waste, combined with modified polypropylene short-cut fibers, synergistically improve the crack resistance, flexibility, and volume stability of the concrete matrix, and improve the defects of traditional recycled concrete such as easy shrinkage and cracking; the porous lightweight matrix combined with the foaming system significantly optimizes the thermal insulation, heat insulation, and noise reduction performance, and comprehensively improves the building's energy-saving indicators.

[0028] Sixth, the technology boasts strong adaptability to the industrial chain, resulting in significant synergistic benefits. This invention offers broad technological compatibility, enabling the rapid construction of an integrated closed-loop industrial chain encompassing "solid waste collection and storage - classification and grading disposal - low-carbon building materials production - multi-scenario engineering applications." It supports the green and low-carbon transformation and upgrading of cement enterprises and commercial mixing plants nationwide, fostering new green and low-carbon productivity in the building materials industry. Once implemented, the technology can simultaneously reduce solid waste disposal costs, conserve natural mineral resources, and decrease carbon emissions and environmental pollution, achieving a high degree of unity between economic, ecological, and social benefits, with broad prospects for industrialization and promotion. Detailed Implementation

[0029] Example 1 Preparation of Recycled Mixture Raw Materials

[0030] This production line is equipped with a three-stage crushing and three-screening system for recycled building materials from construction waste. The core equipment includes a toothed roller crusher, a vertical shaft impact mill (VSM) for fine crushing, and grinding equipment, all fitted with grading screens of 50mm, 20mm, 10mm, and 5mm. The first stage uses a toothed roller crusher to coarsely crush demolition and renovation waste. After screening through a 50mm screen, materials larger than 50mm are returned for further crushing, while materials smaller than 50mm enter the fine grading process. The second stage uses a VSM for fine crushing and modification. The appropriate screen is changed according to the type of waste being processed: for reinforced concrete construction waste, a 20mm screen is used to produce a coarse recycled mixture; for brick-concrete construction waste, a 10mm screen is used to produce a medium-coarse recycled mixture; and for renovation waste, a 5mm screen is used to produce a fine recycled mixture. For dry recycled mixtures with a moisture content below 3%, a second screening is performed using a 5mm screen. The undersized fines are then fed into an ultrafine grinding mill to produce standard recycled micro-powder. This complete set of equipment is simple to configure and has low modification costs. It can be directly adapted to the technical transformation of municipal and county-level mixing plants. The raw materials produced can be used to stably prepare full-gradient, all-solid-waste low-carbon concrete and its products.

[0031] Example 2: Low-carbon concrete made from recycled aggregate for reinforced concrete structures

[0032] By weight proportions: 55 parts recycled coarse aggregate, 25 parts recycled micro powder, 20 parts composite activator (8 parts ordinary Portland cement + 12 parts alkali-activated cementitious material), and 12 parts mixing water. Preparation process: Dry mix the recycled coarse aggregate, recycled micro powder, and solid activator in a mixer for 150 seconds. After thorough mixing, add the mixing water and liquid alkali activator, and continue wet mixing for 120 seconds. Pour and vibrate to compact, then cure at room temperature for 28 days. Core performance indicators: Total solid waste content 80%, cement replacement rate 60%; 28-day compressive strength 32.5 MPa, apparent density 2420 kg / m³; carbon emissions reduced by 35% compared to ordinary concrete, production energy consumption reduced by 41%; high matrix density, excellent impermeability, frost resistance, and durability, suitable for precast products such as municipal load-bearing components, building structural base layers, curbs, and manholes.

[0033] Example 3: Low-carbon concrete made from recycled materials for brick-concrete structures

[0034] By weight proportions: 60 parts recycled medium-coarse mixture, 22 parts recycled micro powder, 18 parts composite activator (5 parts ordinary silicate cement + 13 parts alkali-activated cementitious material), and 11 parts mixing water. Preparation process: All solid raw materials are dry-mixed in a mixing device for 210 seconds, then wet-mixed with water for 150 seconds. The mixture is then pressed into shape under 15 MPa pressure and cured at room temperature for 28 days. Core performance indicators: Total solid waste content 82%, cement replacement rate 72%; 28-day compressive strength 28.6 MPa, apparent density 1850 kg / m³, building self-weight reduced by 26%; carbon emissions reduced by 48%, production energy consumption reduced by 42%; lightweight and high-strength, excellent toughness, and outstanding seismic performance, suitable for low-rise and multi-story building wall materials, slope protection retaining walls, and lightweight reinforcement projects for old residential areas.

[0035] Example 4: Low-carbon concrete with integrated insulation from recycled construction waste mixture

[0036] By weight proportions: 45 parts recycled fine aggregate, 35 parts recycled micro powder, 20 parts alkali-activated cementitious material, 10 parts mixing water, 0.3 parts modified polypropylene fiber, and 0.2 parts foaming agent. Preparation process: The solid waste fine aggregate, recycled micro powder, and modified fiber are dry-mixed together for 270 seconds to ensure uniform fiber dispersion without agglomeration; then, mixing water, liquid activator, and foaming agent are added and wet-mixed for 180 seconds. The mixture is then pressed into shape under 10 MPa pressure and cured in a moist and sealed environment for 14 days. Core performance indicators: The entire process is silicate-free cement preparation, with a total solid waste content of 90%; 28-day compressive strength of 15.2 MPa, apparent density of 1200 kg / m³; thermal conductivity of 0.22 W / (m·K), exhibiting excellent thermal insulation, crack resistance, and noise reduction performance; carbon emissions are reduced by 65% ​​compared to ordinary concrete, making it suitable for self-insulating walls, roof insulation layers, and prefabricated insulated panels in ultra-low energy consumption buildings.

[0037] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-carbon concrete using recycled aggregate, characterized in that, The material is prepared by mixing recycled coarse aggregate, recycled medium-coarse aggregate, recycled fine aggregate, and recycled micro powder as composite filler main materials, and using an activator as a cementing material; the total mass content of the recycled coarse aggregate, recycled medium-coarse aggregate, recycled fine aggregate, and recycled micro powder is ≥70%; the activator is one or any combination of ordinary silicate cement, solid waste-based cementing materials, and alkali-activated cementing materials.

2. The recycled aggregate low-carbon concrete according to claim 1, characterized in that, The recycled coarse aggregate is a natural continuous gradation aggregate suitable for the production of demolition waste with a particle size ≤20mm for reinforced concrete structures. It consists of 5-20mm recycled coarse aggregate and 0-5mm recycled fine aggregate. The total mass content of lightweight combustibles and organic impurities in the recycled coarse aggregate is ≤1%, and metallic impurities are completely stripped.

3. The recycled aggregate low-carbon concrete according to claim 1, characterized in that, The recycled medium-coarse mixture is a natural continuous gradation mixture suitable for producing brick-concrete structure demolition waste with a particle size ≤10mm, consisting of 5-10mm recycled coarse aggregate and 0-5mm recycled fine aggregate; the total mass content of lightweight combustibles and organic impurities in the recycled medium-coarse mixture is ≤1%.

4. The recycled aggregate low-carbon concrete according to claim 1, characterized in that, The recycled fine aggregate is a natural continuous gradation aggregate suitable for producing building renovation waste with a particle size ≤5mm, consisting of 0-5mm recycled fine aggregate and 0-0.15mm recycled micro aggregate.

5. The recycled low-carbon concrete according to claim 1, characterized in that, The recycled micro powder conforms to the standard "Recycled Micro Powder for Concrete and Mortar" (JG / T573-2020), with a particle size ≤0.15mm and an activity index ≥75%.

6. The recycled aggregate low-carbon concrete according to claim 1, characterized in that, The solid waste-based cementitious material is one or a mixture of two of S95 grade slag powder and Grade I fly ash; the alkali-activated cementitious material is prepared by compounding industrial water glass, slag powder and fly ash with a modulus of 2.2 to 2.6, and the preferred compounding mass ratio is: water glass with a modulus of 2.4: slag powder: fly ash = 1:2:

1.

7. The recycled aggregate low-carbon concrete according to claim 1, characterized in that, The recycled low-carbon concrete uses a differentiated and precise mix proportion by weight: High-strength concrete based on waste concrete: 45-65 parts recycled coarse mix, 15-35 parts recycled micro powder, 15-30 parts activator, and 10-12 parts mixing water; Lightweight structural concrete based on brick-concrete demolition waste: 55-65 parts recycled medium-coarse mix, 15-35 parts recycled micro powder, 10-30 parts activator, and 10-11 parts mixing water; Integrated insulation concrete based on decoration waste: 10-60 parts recycled fine mix, 10-60 parts recycled micro powder, 10-30 parts activator, and 9-10 parts mixing water.

8. The recycled aggregate low-carbon concrete according to claim 7, characterized in that, The functional additives are added to the integrated thermal insulation concrete based on construction waste. The functional additives include 0.1 to 0.3 parts of foaming agent and 0.2 to 0.4 parts of modified polypropylene short-cut fiber.

9. A method for preparing low-carbon concrete using recycled aggregates, characterized in that, The process includes the following steps: S1, Dry mixing: Add the recycled mixture, recycled micro powder, solid activator, and modified fiber to the mixing equipment and dry mix for 150-270 seconds; S2, Wet mixing modification: Add mixing water, liquid alkali activator, and foaming agent, and continue wet mixing for 120-180 seconds to form a homogeneous cementitious mixture; S3, Molding and curing: Use natural pouring and vibration molding or 10-15 MPa pressure pressing molding, and cure at room temperature for 28 days or with moisture and sealing for 14 days to obtain the finished concrete.