Construction waste recycling and separating process

Abstract

The invention provides a construction waste recycling and separating process, and belongs to the technical field of solid waste reutilization, the construction waste recycling and separating process comprises the following steps: step S1, crushing and screening construction mixed waste, separating and preparing to obtain recycled fine aggregate, recycled concrete powder and recycled brick powder; s2, placing the regenerated fine aggregate in a fluidized bed reactor, introducing gas containing carbon dioxide, and carrying out pre-carbonization treatment to obtain pre-carbonized regenerated fine aggregate; s3, providing slag powder, mixing the recycled concrete powder, the recycled brick powder and the slag powder according to a preset proportion, and performing mechanical grinding to obtain gelling powder; s4, uniformly mixing the pre-carbonized regenerated fine aggregate, the gelling powder, water and an additive to obtain a mixture, and carrying out compression molding on the mixture to obtain a green body; and S5, putting the green body into a closed container, and curing in a carbon dioxide atmosphere to prepare the all-solid waste concrete. According to the process, the mechanical property of the solid waste concrete material is improved.

Description

Technical Field

[0001] This invention belongs to the field of solid waste recycling technology, specifically relating to a separation process for the recycling of construction waste. Background Technology

[0002] Construction waste recycling technology, particularly the conversion of it into recycled concrete aggregate, is widely regarded as a key pathway to achieving green and circular development in the construction industry due to its enormous potential in solid waste resource utilization and reducing carbon emissions in the building materials sector. However, traditional recycled aggregates are highly susceptible to performance degradation during concrete preparation and service due to the microstructure of the hardened cement mortar (i.e., old mortar) adhering to their surface. For example, the loose and porous nature of old mortar results in a significantly higher water absorption rate than natural stone, causing it to aggressively absorb moisture from the mortar during the initial mixing stage, leading to a sharp drop in workability. Simultaneously, the lower strength of the old mortar itself and the presence of microcracks within it make it a weak point in the stress transmission process, significantly reducing the load-bearing capacity and service life of the recycled concrete.

[0003] To obtain usable recycled aggregates, the industry currently employs simple mechanical crushing and screening processes, attempting to separate waste concrete and bricks through physical pulverization. However, this traditional physical processing technique has significant inherent drawbacks: due to the substantial differences in hardness and crushing characteristics between concrete and clay bricks, conventional crushing methods struggle to achieve high-purity separation of components and cannot completely remove the tightly bonded old mortar layer from the aggregate surface. During the hardening process of recycled concrete, this heterogeneous structure easily leads to complex interfacial transition zone defects, namely, the formation of multiple and interconnected pore networks between the new paste, old mortar, and original aggregates, resulting in poor material impermeability and an inability to provide long-term, stable mechanical properties.

[0004] In existing technologies, the crushing and shaping process of construction waste inevitably generates a large amount of extremely fine recycled powder (less than 0.15 mm). However, these powders are currently mostly disposed of through direct landfill or as low-activity fillers. These recycled powders are mainly composed of hydrated cement products and fine brick powder, exhibiting chemical inertness and highly irregular particle morphology. In conventional cement-based systems, these powders not only fail to exert their cementitious activity but also increase water demand due to their large specific surface area, easily leading to paste shrinkage and cracking. This not only results in a significant waste of potential cementitious resources but also forces the production of recycled concrete to still heavily rely on high-carbon-emission Portland cement to compensate for insufficient strength, failing to truly achieve low-carbon manufacturing of materials. Summary of the Invention

[0005] In view of the above situation and to overcome the defects of the prior art, the purpose of the present invention is to provide a construction waste recycling and separation process to at least partially solve the problems mentioned in the background art.

[0006] The technical solution adopted in this invention is as follows: This invention proposes a separation process for the recycling of construction waste, comprising the following steps: Step S1: Crush and screen the mixed construction waste to separate and prepare recycled fine aggregate, recycled concrete powder and recycled brick powder; Step S2: Place the recycled fine aggregate in a fluidized bed reactor and introduce a gas containing carbon dioxide for pre-carbonization treatment to obtain pre-carbonized recycled fine aggregate; Step S3: Provide slag powder, mix the recycled concrete powder, recycled brick powder and the slag powder in a predetermined ratio and mechanically grind them to obtain cementitious powder; Step S4: Mix the pre-carbonized recycled fine aggregate, cementitious powder, water and additives evenly to obtain a mixture, and press the mixture into a green body; Step S5: Place the billet in a sealed container and cure it under a carbon dioxide atmosphere to obtain solid waste concrete.

[0007] In some embodiments of the present invention, in step S1, the crushing and screening steps specifically include: using an impact crusher to crush mixed construction waste by impact, controlling the rotor linear speed of the crusher to be 25m / s to 30m / s; screening the crushed material through a 10mm aperture screen to separate the material into oversize and undersize materials.

[0008] In some embodiments of the present invention, the steps of separating and preparing recycled fine aggregate, recycled concrete powder and recycled brick powder specifically include: collecting the oversize material and performing impact shaping and grading, selecting particles with a particle size of 0.15 mm to 2.0 mm as the recycled fine aggregate, selecting powder with a particle size of less than 0.15 mm as the recycled concrete powder, and returning particles with a particle size of more than 2.0 mm to the impact shaping equipment for further crushing; collecting the undersize material and performing grinding and powder selection, selecting powder with a particle size of less than 0.15 mm as the recycled brick powder.

[0009] In some embodiments of the present invention, in step S2, the volume concentration of carbon dioxide in the carbon dioxide-containing gas is 20% to 30%; the flow rate of the gas in the fluidized bed reactor is 1.5 to 2.0 times the critical fluidization velocity of the recycled fine aggregate.

[0010] In some embodiments of the present invention, the temperature of the pre-carbonization treatment is 25°C to 35°C, the relative humidity is 55% to 65%, and the treatment time is 10 minutes to 20 minutes.

[0011] In some embodiments of the present invention, in step S3, the mass percentage of each component in the cementitious powder is: 30% to 40% recycled concrete powder, 30% to 40% recycled brick powder, and 20% to 30% slag powder, and the sum of the mass percentages of the above components is 100%; the particle size of the recycled concrete powder and the recycled brick powder is less than 0.15 mm.

[0012] In some embodiments of the present invention, in step S3, the mechanical grinding is performed using a planetary ball mill with a ball-to-material ratio of 10:1, a rotation speed of 400 rpm, and a grinding time of 30 to 60 minutes.

[0013] In some embodiments of the present invention, in step S4, the admixture includes an alkali activator and a polycarboxylate superplasticizer; the alkali activator is water glass with a modulus of 1.2 to 1.5, and its dosage is 3% to 5% of the mass of the cementitious powder; the dosage of the polycarboxylate superplasticizer is 0.5% to 2.0% of the mass of the cementitious powder; the mass ratio of pre-carbonized recycled fine aggregate to cementitious powder in the mixture is 1.0:1 to 1.5:1; the mass ratio of water to cementitious powder in the mixture is 0.16:1 to 0.20:1.

[0014] In some embodiments of the present invention, in step S4, the pressure of the compression molding is 15 MPa to 20 MPa.

[0015] In some embodiments of the present invention, in step S5, the specific process conditions for curing are as follows: the pressure of carbon dioxide gas is 0.2 MPa to 0.5 MPa, the purity of carbon dioxide gas is greater than or equal to 95%, the curing time is 24 hours to 48 hours, and the relative humidity is less than 60%.

[0016] The beneficial effects achieved by this invention are as follows: This invention constructs a preparation process integrating raw material mechanochemical activation, aggregate fluidized bed gas-solid pre-carbonization, and matrix high-pressure molding-in-situ curing. This technical solution effectively removes the inert layer on the particle surface through high-energy ball milling to activate the gelling activity of the entire solid waste system; utilizes the volume expansion effect of the carbonization reaction to achieve dense filling of aggregate pores and pre-position crystal growth sites; and combines high-pressure pressing with crystal epitaxial growth mechanisms to overcome macroscopic pore and interface transition zone defects. This invention significantly improves the microstructure density and mechanical properties of solid waste concrete materials and achieves effective carbon dioxide mineralization without the need for Portland cement. Attached Figure Description

[0017] Figure 1 This is a flowchart of the construction waste recycling and separation process according to an embodiment of the present invention.

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

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

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] Reference Figure 1 To address the problems raised in the background art, this invention provides a construction waste recycling and separation process, comprising the following steps: Step S1: Crush and screen the mixed construction waste to separate and prepare recycled fine aggregate, recycled concrete powder and recycled brick powder; Step S2: Place the recycled fine aggregate in a fluidized bed reactor and introduce a gas containing carbon dioxide for pre-carbonization treatment to obtain pre-carbonized recycled fine aggregate; Step S3: Provide slag powder, mix recycled concrete powder, recycled brick powder and slag powder in a predetermined ratio and mechanically grind them to obtain cementitious powder; Step S4: Mix the pre-carbonized recycled fine aggregate, cementitious powder, water and additives evenly to obtain a mixture, and press the mixture into a green body; Step S5: Place the billet in a sealed container and cure it under a carbon dioxide atmosphere to obtain solid waste concrete.

[0023] First, this invention employs a pretreatment process combining multi-stage physical separation and mechanical grinding, overcoming the technical shortcomings of construction waste's complex composition and difficulty in direct utilization. By utilizing the physical differences in hardness between concrete and clay bricks for differentiated crushing, effective separation of high-strength aggregates and low-strength brick powder is achieved. Furthermore, a planetary ball mill is used to mechanically activate the separated micro-powder. This not only ensures uniform mixing of the raw materials but, more importantly, removes the inert hydration layer from the powder surface through mechanical friction, exposing the fresh, active components inside. This treatment method transforms the originally low-activity construction waste micro-powder into a recycled material with cementing potential, providing a material basis for the preparation of all-solid-waste concrete.

[0024] Secondly, this invention utilizes a fluidized bed reactor for gas-solid pre-carbonization modification of recycled aggregates. Addressing the technical challenge of loose old mortar adhering to the surface of recycled aggregates and their high water absorption, the fluidized bed reactor leverages the thorough contact between gas and particles to promote a mineralization reaction between carbon dioxide and the calcium components in the old mortar. Based on the "volume expansion effect" of the carbonation reaction, newly generated calcium carbonate crystals can densely fill the capillaries and microcracks on the aggregate surface in situ. This modification process significantly reduces the porosity and water absorption of the aggregates, preventing excessive adsorption of free water from the mixture during stirring. Simultaneously, it pre-establishes nucleation sites for crystal growth on the aggregate surface, promoting chemical bonding between the aggregate and the matrix interface.

[0025] Furthermore, the synergistic effect of high-pressure molding and in-situ carbonation curing technologies improved the problems of internal porosity and weak interfaces in recycled concrete. High-pressure molding forces particle rearrangement and expels air, eliminating macroscopic pores; subsequent carbon dioxide atmosphere curing induces the in-situ growth of a large number of crystals within the matrix. Due to the pre-formed carbonization layer on the aggregate surface, the newly formed crystals can grow epitaxially across the interface region using the aggregate as a base point, forming a "crystal bridging" structure. This mechanism enhances the connection strength between the aggregate and the matrix through chemical bonding, repairs the interface transition zone, and thus improves the mechanical properties and impermeability durability of the material.

[0026] Finally, this invention achieves the full-component resource utilization of construction waste and the chemical sequestration of carbon dioxide. This process eliminates the need for Portland cement, reducing carbon emissions at the source; simultaneously, it utilizes carbon dioxide mineralization technology to stably fix carbon dioxide in the concrete matrix in the form of carbonate crystals. This technological approach, while replacing cement, achieves high-value utilization of solid waste resources and effective sequestration of greenhouse gases.

[0027] In summary, this invention constructs a preparation process integrating raw material mechanochemical activation, aggregate fluidized bed gas-solid pre-carbonization, and matrix high-pressure molding-in-situ curing. This technical solution effectively removes the inert layer on the particle surface through high-energy ball milling to activate the gelling activity of the entire solid waste system; utilizes the volume expansion effect of the carbonization reaction to achieve dense filling of aggregate pores and pre-position crystal growth sites; and combines high-pressure pressing with crystal epitaxial growth mechanisms to overcome macroscopic pore and interface transition zone defects. This invention significantly improves the microstructure density and mechanical properties of the material and achieves effective carbon dioxide mineralization without the need for Portland cement.

[0028] In some embodiments, step S1, the crushing and screening steps specifically include: using an impact crusher to crush the mixed construction waste, controlling the rotor linear velocity of the crusher to be 25 m / s to 30 m / s. Under this specific impact kinetic energy, the low-strength, brittle clay bricks mainly undergo through-crushing, being pulverized into fine particles with a particle size of less than 10 mm; while the high-strength concrete blocks mainly undergo edge wear or dissociation along grain boundaries, with the main particle size remaining above 10 mm. The crushed material is then screened through a 10 mm aperture screen to separate the material into oversize and undersize. Combined with the 10 mm aperture screening step, this process can efficiently physically separate the high-hardness component rich in concrete (oversize) from the low-strength component rich in crushed brick powder (undersize).

[0029] In some embodiments, the steps of separating and preparing recycled fine aggregate, recycled concrete powder, and recycled brick powder specifically include: collecting the oversize material and performing impact shaping and grading, selecting particles with a particle size of 0.15 mm to 2.0 mm as recycled fine aggregate, selecting powder with a particle size of less than 0.15 mm as recycled concrete powder, and returning particles with a particle size of more than 2.0 mm to the impact shaping equipment for further crushing; collecting the undersize material and performing grinding and powder selection, selecting powder with a particle size of less than 0.15 mm as recycled brick powder.

[0030] For the oversize material (high-hardness concrete component), the "stone-on-stone" principle of vertical shaft impact crushing effectively removes the aged mortar layer adhering to the aggregate surface. This process not only improves the particle shape of the recycled fine aggregate with a particle size of 0.15mm to 2.0mm, making it more spherical to enhance fluidity, but also transforms the old mortar rich in hydrated calcium silicate and calcium hydroxide into recycled concrete powder with a particle size of less than 0.15mm. This treatment transforms the old mortar, which was originally an aggregate defect, into a cementitious component with high calcium activity. For the undersize material (component rich in broken bricks), recycled brick powder (particle size less than 0.15mm) prepared through grinding and powder selection processes is rich in silica-alumina components and has a porous structure, which can serve as a silica-alumina source for geopolymer reactions and an internal curing material for concrete. This fine classification strategy transforms the originally unusable mixed powder into independent components (calcium source and silica-alumina source) with specific chemical functions, overcoming the defects of large fluctuations in the composition and low utilization rate of recycled micro powder in traditional processes, and improving the stability of subsequent reactions in the all-solid waste cementitious system.

[0031] In some embodiments, in step S2, the volume concentration of carbon dioxide in the carbon dioxide-containing gas is 20% to 30%; the gas flow rate in the fluidized bed reactor is 1.5 to 2.0 times the critical fluidization velocity of the recycled fine aggregate. Controlling the carbon dioxide volume concentration at 20% to 30% effectively balances the relationship between the surface reaction rate and the internal gas diffusion resistance, providing sufficient reaction driving force while avoiding the formation of a dense shielding layer due to instantaneous carbonization of the outermost layer of the aggregate caused by excessive concentration, thus preventing premature blockage of the channels for carbon dioxide diffusion into the deep pores of the old mortar. Simultaneously, setting the gas flow rate to 1.5 to 2.0 times the critical fluidization velocity places the aggregate particles in a typical "bubbling fluidization" state within the reactor. Under this hydrodynamic state, the particles undergo vigorous tumbling and mixing within the bed, maximizing the contact area and mass transfer efficiency between the gas and solid phases. This combination of process parameters enables the old mortar adhering to the aggregate surface to undergo a rapid and uniform mineralization reaction, overcoming the technical defects of airflow short-circuiting and uneven reaction commonly found in traditional fixed-bed carbonization processes, and significantly improving the strengthening effect of aggregates.

[0032] In some embodiments, the pre-carbonization treatment temperature is 25°C to 35°C, the relative humidity is 55% to 65%, and the treatment time is 10 to 20 minutes. Precisely controlling the relative humidity between 55% and 65% effectively balances the gas-phase diffusion and liquid-phase dissolution of carbon dioxide gas. Capillary condensation maintains a suitable liquid film thickness within the aggregate pores, avoiding both insufficient carbon dioxide dissolution and ionization due to excessively low humidity (<55%) and excessively high humidity (>65%) which would saturate the pores and block the gas diffusion channels. Furthermore, the combination of a room temperature environment of 25°C to 35°C and a treatment time of 10 to 20 minutes fully utilizes the advantage of the large gas-solid contact area of ​​the fluidized bed reactor.

[0033] In some embodiments, in step S3, the mass percentage of each component in the cementitious powder is: 30% to 40% recycled concrete powder, 30% to 40% recycled brick powder, and 20% to 30% slag powder, and the sum of the mass percentages of the above components is 100%; the particle size of both recycled concrete powder and recycled brick powder is less than 0.15 mm. The synergistic effect of each component overcomes the technical defects of low activity and difficult utilization of single recycled micro-powder. By configuring 30% to 40% recycled concrete powder, its rich calcium hydroxide and hydrated calcium silicate serve as the main calcium source, providing a sufficient reactant basis for subsequent carbonization and mineralization reactions. Introducing 30% to 40% recycled brick powder as a silica-alumina component to participate in the geopolymer reaction, and utilizing its unique porous water-absorbing properties to perform an "internal curing" function, slowly releasing moisture in the later stages of hardening, effectively inhibits the autogenous shrinkage cracking phenomenon common in high-performance concrete. In addition, 20% to 30% of slag powder is added to the system, and its highly active glassy structure makes up for the shortcomings of insufficient early hydration activity of the recycled micro powder, which significantly improves the early strength of the material.

[0034] In some embodiments, in step S3, the mechanical grinding employs a planetary ball mill with a ball-to-powder ratio of 10:1, a rotation speed of 400 rpm, and a grinding time of 30 to 60 minutes. By setting a high ball-to-powder ratio of 10:1 and a rotation speed of 400 rpm, this process generates intense mechanical impact and shearing within the grinding jar. This high energy input not only achieves physical mixing but, more importantly, causes severe lattice distortion and dislocations within the powder particles, increasing the internal energy and chemical reactivity of the material.

[0035] In some embodiments, in step S4, the admixtures include an alkali activator and a polycarboxylate superplasticizer; the alkali activator is water glass with a modulus of 1.2 to 1.5, and its dosage is 3% to 5% of the mass of the cementitious powder; the dosage of the polycarboxylate superplasticizer is 0.5% to 2.0% of the mass of the cementitious powder; the mass ratio of pre-carbonized recycled fine aggregate to cementitious powder in the mixture is 1.0:1 to 1.5:1; the mass ratio of water to cementitious powder in the mixture is 0.16:1 to 0.20:1. By limiting the mass ratio of water to cementitious powder in the mixture (i.e., the water-cement ratio) to the range of 0.16:1 to 0.20:1, the mixture can exhibit a non-flowing wetted state, effectively reducing capillary pores left due to water evaporation during matrix hardening and improving the density of the material. Meanwhile, controlling the mass ratio of pre-carbonized recycled fine aggregate to cementitious powder at 1.0:1 to 1.5:1 allows the fine cementitious powder to accurately fill the voids in the aggregate structure. In addition, it can be combined with the venting effect during high-pressure molding to further improve the density of the material.

[0036] In some embodiments, in step S4, the pressing pressure is between 15 MPa and 20 MPa. This specific pressure range provides sufficient mechanical energy to overcome the frictional resistance between particles, allowing the solid particles to rearrange and compact.

[0037] In some embodiments, the specific process conditions for curing in step S5 are as follows: the pressure of carbon dioxide gas is 0.2 MPa to 0.5 MPa, the purity of carbon dioxide gas is greater than or equal to 95%, the curing time is 24 hours to 48 hours, and the relative humidity is less than 60%. By maintaining a positive pressure environment of carbon dioxide of 0.2 MPa to 0.5 MPa and a gas purity of greater than or equal to 95%, carbon dioxide gas can overcome the high density diffusion resistance of the high-pressure molded matrix and effectively penetrate into the depth of the material.

[0038] The present invention will be further described below by way of specific embodiments.

[0039] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods already existing in the art; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0040] Example 1: S1: Construction waste is fed into an impact crusher with a rotor linear velocity set to 28 m / s. The crushed material is screened through a 10 mm aperture screen, separating it into oversize and undersize particles. The oversize particles are collected and subjected to impact shaping and grading. Particles with a diameter of 0.15 mm to 2.0 mm are selected as recycled fine aggregate, and powder with a diameter less than 0.15 mm is selected as recycled concrete powder. Coarse particles larger than 2.0 mm are returned to the crusher for reshaping. The undersize particles are collected and subjected to grinding and powder selection. Powder with a diameter less than 0.15 mm is selected as recycled brick powder.

[0041] S2: Place the recycled fine aggregate in a fluidized bed reactor, introduce CO2 gas with a volume concentration of 25% at a flow rate of 1.8 times the critical fluidization rate, and process for 15 minutes at a temperature of 30℃ and a relative humidity of 60%.

[0042] S3: Mix 35% recycled concrete powder, 35% recycled brick powder, and 30% slag powder. Use a planetary ball mill with a ball-to-powder ratio of 10:1, a rotation speed of 400 rpm, and grind for 45 minutes to obtain a highly active cementitious powder.

[0043] S4: Mix pre-carbonized aggregate and cementitious powder at a mass ratio of 1.2:1. Add water glass (4% dosage) with a modulus of 1.4 and polycarboxylate superplasticizer (1.0% dosage), controlling the water-cement ratio to be 0.18:1. After mixing evenly, press into shape under a pressure of 18 MPa.

[0044] S5: Place the billet in a high-pressure autoclave, introduce CO2 with a purity of 99%, pressure of 0.3 MPa, relative humidity of 55%, and cure for 36 hours to obtain solid waste concrete.

[0045] Example 2: The only difference between this embodiment and Embodiment 1 is the value of the process parameters, which are adjusted as follows: In step S1, the rotor linear velocity of the impact crusher is controlled to be 25 m / s.

[0046] In step S2, the volume concentration of carbon dioxide gas is 20%, and the pre-carbonization treatment time is 10 minutes.

[0047] In step S3, the mass percentages of each component in the cementitious powder are adjusted as follows: 40% recycled concrete powder, 40% recycled brick powder, and 20% slag powder; the ball milling time is 30 minutes.

[0048] In step S4, the water-to-glue ratio is controlled at 0.16, and the pressing pressure is 15 MPa.

[0049] In step S5, the pressure of carbon dioxide gas is 0.2 MPa, and the curing time is 24 hours.

[0050] Example 3: The only difference between this embodiment and Embodiment 1 is the value of the process parameters, which are adjusted as follows: In step S1, the rotor linear velocity of the impact crusher is controlled to be 30 m / s.

[0051] In step S2, the volume concentration of carbon dioxide gas is 30%, and the pre-carbonization treatment time is 20 minutes.

[0052] In step S3, the mass percentages of each component in the cementitious powder are adjusted as follows: 30% recycled concrete powder, 40% recycled brick powder, and 30% slag powder; the ball milling time is 60 minutes.

[0053] In step S4, the water-to-glue ratio is controlled at 0.20, and the pressing pressure is 20 MPa.

[0054] In step S5, the pressure of carbon dioxide gas is 0.5 MPa, and the curing time is 48 hours.

[0055] Example 4: The only difference between this embodiment and Example 1 is the ratio of the cementitious material and the parameters of the admixtures. The specific adjustments are as follows: In step S3, the mass percentage of each component in the cementitious powder is adjusted to: 40% recycled concrete powder, 30% recycled brick powder, and 30% slag powder.

[0056] In step S4, the modulus of the alkali activator (water glass) is adjusted to 1.2 and the dosage is adjusted to 3%; the dosage of the polycarboxylate superplasticizer is adjusted to 0.5%.

[0057] Example 5: The only difference between this embodiment and Embodiment 1 is the mixing ratio and the pre-carbonization environment. The specific adjustments are as follows: In step S2, the temperature of the pre-carbonization treatment is adjusted to 25°C and the relative humidity is adjusted to 55%.

[0058] In step S4, the mass ratio of pre-carbonized recycled fine aggregate to cementitious powder in the mixture is adjusted to 1.0:1.

[0059] In step S4, the modulus of the alkali activator (water glass) is adjusted to 1.5, and the dosage is adjusted to 5%.

[0060] Example 6: The only difference between this embodiment and Embodiment 1 is the fluidized bed parameters and the curing environment. The specific adjustments are as follows: In step S2, the gas flow rate in the fluidized bed reactor is adjusted to 1.5 times the critical fluidization velocity of the recycled fine aggregate.

[0061] In step S5, the relative humidity of the curing environment is controlled at 50%; the purity of carbon dioxide gas is 95%.

[0062] Comparative Example 1: Without fluidized bed pre-carbonization treatment, step S2 is omitted compared to Example 1. Specifically, the recycled fine aggregate without fluidized bed pre-carbonization treatment is directly mixed with cementitious powder, water, and additives. Due to the lack of pre-carbonization, the aggregate has a higher water absorption rate. To maintain the same workability of the mixture, the water-cement ratio is adjusted to 0.25. The remaining steps and parameters are the same as in Example 1.

[0063] Comparative Example 2: This method eliminates high-pressure molding and in-situ carbonization curing, modifying steps S4 and S5 compared to Example 1. Specifically, conventional mixing and vibration casting are used for molding. Standard curing (temperature 20±2℃, humidity ≥95%) is applied for 28 days, without CO2 atmosphere curing. The remaining raw material proportions and pretreatment steps are consistent with Example 1.

[0064] Test method: The specimens prepared in Examples 1-6 and Comparative Examples 1-2 were subjected to performance tests.

[0065] Compressive and flexural strength tests were conducted according to the national standards "Reactive Powder Concrete" (GB / T 31387-2015) and "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021). The mixtures from the examples and comparative examples were pressed into prism specimens with dimensions of 40mm × 40mm × 160mm, with three specimens prepared for each group. Testing was performed using a fully automatic electro-hydraulic servo universal testing machine. After curing, the specimens were removed, surface moisture was wiped off, and they were placed in a flexural clamp. A loading rate of 50 N / s was applied until fracture, and the flexural strength was recorded. The specimens were then placed in the center of a compressive clamp and uniformly loaded at a loading rate of 2.4 kN / s until failure, and the compressive strength was recorded. The final result was the average of the three specimens.

[0066] Water absorption test: Dry the specimen in a 105℃ drying oven to constant weight and weigh its dried mass m0. Immerse the specimen in water at 20℃, with the water level at least 20mm above the specimen, and soak for 48 hours. Remove the specimen, wipe off any excess water with a wrung-out damp cloth, and immediately weigh its saturated surface-dry mass m1. Calculate the water absorption rate W = (m1 - m0) / m0 × 100%.

[0067] Microhardness test of the interface transition zone: The specimen was cut to expose the fresh fracture surface, then inlaid with epoxy resin, and polished sequentially using coarse sandpaper and diamond polishing compound until the surface was mirror-like. Under a microscope, the interface area between the aggregate and the matrix was selected, and a test point was selected every 10 μm from the edge of the aggregate towards the matrix. A load of 0.49 N (50 gf) was applied, and the load was held for 10 seconds. The diagonal length of the indentation was measured and the Vickers hardness value (HV) was calculated.

[0068] Carbon sequestration calculation: Under a nitrogen atmosphere, the sample was heated from room temperature to 900℃ at a rate of 10℃ / min. Based on the mass loss caused by the decomposition of calcium carbonate in the 600℃-800℃ range, the mass of carbon dioxide fixed per unit volume of concrete was calculated.

[0069] Based on the above testing methods, the specific test data is shown in Table 1.

[0070] Table 1

[0071] As shown in Table 1, Comparative Example 2, which uses traditional casting technology and is not carbonized, has a compressive strength of only 32.6 MPa, falling within the category of ordinary strength concrete, and a water absorption rate as high as 8.4%. In contrast, the compressive strength of Example 1 of this invention is increased to 75.4 MPa, an increase of over 130%. Although Comparative Example 1 uses high-pressure molding and matrix carbonization curing, it omits the aggregate fluidized bed pre-carbonization (step S2), resulting in a compressive strength of 48.3 MPa, significantly lower than the 75.4 MPa of Example 1, and a higher water absorption rate (5.8%). Examples 2 to 6 adjusted the crushing speed, mix proportions, and curing parameters within the scope defined in the claims. The results show that the compressive strength of all examples is stable within the range of 60 MPa to 80 MPa, and the water absorption rate is controlled below 4.0%.

[0072] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A construction waste recycling and separation process, characterized in that, Includes the following steps: Step S1: Crush and screen the mixed construction waste to separate and prepare recycled fine aggregate, recycled concrete powder and recycled brick powder; Step S2: Place the recycled fine aggregate in a fluidized bed reactor and introduce a gas containing carbon dioxide for pre-carbonization treatment to obtain pre-carbonized recycled fine aggregate; Step S3: Provide slag powder, mix the recycled concrete powder, recycled brick powder and the slag powder in a predetermined ratio and mechanically grind them to obtain cementitious powder; Step S4: Mix the pre-carbonized recycled fine aggregate, cementitious powder, water and additives evenly to obtain a mixture, and press the mixture into a green body; Step S5: Place the billet in a sealed container and cure it under a carbon dioxide atmosphere to obtain solid waste concrete.

2. The process according to claim 1, characterized in that, In step S1, the crushing and screening steps specifically include: using an impact crusher to crush the mixed construction waste, controlling the rotor linear speed of the crusher to be 25m / s to 30m / s; screening the crushed material through a 10mm aperture screen to separate the material into oversize and undersize materials.

3. The process according to claim 2, characterized in that, The steps of separating and preparing recycled fine aggregate, recycled concrete powder, and recycled brick powder specifically include: collecting the oversize material and performing impact shaping and grading, selecting particles with a particle size of 0.15 mm to 2.0 mm as the recycled fine aggregate, selecting powder with a particle size of less than 0.15 mm as the recycled concrete powder, and returning particles with a particle size of more than 2.0 mm to the impact shaping equipment for further crushing; collecting the undersize material and performing grinding and powder selection, selecting powder with a particle size of less than 0.15 mm as the recycled brick powder.

4. The process according to claim 1, characterized in that, In step S2, the volume concentration of carbon dioxide in the carbon dioxide-containing gas is 20% to 30%; the flow rate of the gas in the fluidized bed reactor is 1.5 to 2.0 times the critical fluidization velocity of the recycled fine aggregate.

5. The process according to claim 4, characterized in that, The pre-carbonization treatment is carried out at a temperature of 25°C to 35°C, a relative humidity of 55% to 65%, and a treatment time of 10 to 20 minutes.

6. The process according to claim 1, characterized in that, In step S3, the mass percentage of each component in the cementitious powder is: 30% to 40% recycled concrete powder, 30% to 40% recycled brick powder, and 20% to 30% slag powder, and the sum of the mass percentages of the above components is 100%; the particle size of the recycled concrete powder and the recycled brick powder is less than 0.15 mm.

7. The process according to claim 1, characterized in that, In step S3, the mechanical grinding is performed using a planetary ball mill with a ball-to-material ratio of 10:1, a rotation speed of 400 rpm, and a grinding time of 30 to 60 minutes.

8. The process according to claim 1, characterized in that, In step S4, the admixtures include an alkali activator and a polycarboxylate superplasticizer; the alkali activator is water glass with a modulus of 1.2 to 1.5, and its dosage is 3% to 5% of the mass of the cementitious powder; the dosage of the polycarboxylate superplasticizer is 0.5% to 2.0% of the mass of the cementitious powder; the mass ratio of pre-carbonized recycled fine aggregate to cementitious powder in the mixture is 1.0:1 to 1.5:1; the mass ratio of water to cementitious powder in the mixture is 0.16:1 to 0.20:

1.

9. The process according to claim 1, characterized in that, In step S4, the pressure for pressing is 15 MPa to 20 MPa.

10. The process according to claim 1, characterized in that, In step S5, the specific process conditions for curing are as follows: the pressure of carbon dioxide gas is 0.2 MPa to 0.5 MPa, the purity of carbon dioxide gas is greater than or equal to 95%, the curing time is 24 hours to 48 hours, and the relative humidity is less than 60%.

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