A method for preparing sintered bricks using recycled fine aggregate from construction waste.

Abstract

This invention belongs to the technical field of solid waste resource utilization and novel wall materials, and discloses a method for preparing sintered bricks using recycled fine aggregate from construction waste. The invention involves removing impurities, crushing, and screening construction waste to separate recycled fine aggregate components with different material properties. Each component undergoes adaptive modification treatment based on its material properties. The modified multi-component aggregates are then mixed to obtain composite recycled fine aggregate, which is then combined with flux and binder to prepare the slurry. The finished sintered bricks are obtained through aging, pressing, gradient drying, and sintering cooling processes. This invention effectively solves the problems of insufficient raw material compatibility, poor batch performance stability, and difficulty in balancing performance and environmental emissions under high-content recycled aggregate conditions in existing technologies. It improves the resource utilization rate of all components of construction waste, has strong industrial adaptability, and possesses good environmental benefits and application promotion value.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and new wall materials technology, specifically relating to a method for preparing sintered bricks using recycled fine aggregates from construction waste. Background Technology

[0002] During my country's urbanization process, the annual generation of urban construction waste remains high, with inorganic non-metallic components such as waste ceramics, waste mortar, waste concrete, and waste gypsum accounting for over 80%. Currently, landfill is still the main disposal method for construction waste, which not only occupies a large amount of land resources but also easily causes environmental problems such as soil and groundwater pollution. The harmless, high-value, and resource-based utilization of construction waste has become a core requirement for industry development and a key guiding direction for solid waste reduction policies.

[0003] Currently, the industry has carried out a series of studies and applications on the preparation of sintered bricks from recycled fine aggregates of construction waste. The recycled fine aggregates from sorted and crushed construction waste can be used as core raw materials to prepare sintered wall materials, realizing partial resource utilization of construction waste. At the same time, it can replace traditional sintering raw materials such as clay and shale, which reduces the dependence of wall material production on non-renewable natural mineral resources to a certain extent.

[0004] Existing technologies generally do not differentiate and adapt to the material properties of different components in recycled fine aggregates, resulting in insufficient adaptability to fluctuations in raw material composition and poor batch-to-batch stability of product performance. At the same time, there is a lack of stable and effective control methods for the high-temperature decomposition of gypsum components in construction waste. Under high-volume recycled aggregate conditions, it is difficult to simultaneously consider the mechanical properties, volume stability, and environmental emission requirements of sintered bricks, and the adaptability for industrial continuous production remains limited. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a method for preparing sintered bricks using recycled fine aggregates from construction waste, which solves the problems of insufficient compatibility of recycled fine aggregate components, poor batch stability of products, and difficulty in balancing product performance and environmental emissions under high admixture conditions in the prior art.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] A method for preparing sintered bricks using recycled fine aggregate from construction waste includes the following steps:

[0008] S1. After sorting and removing metallic and harmful non-metallic impurities from the construction waste, it is first coarsely crushed using a jaw crusher with a discharge particle size ≤50mm. Then, it is finely crushed using an impact crusher. After fine crushing, it is screened through a 5mm standard sieve to obtain recycled fine aggregate. The recycled fine aggregate is then separated into ceramic fine aggregate, mortar concrete fine aggregate, and gypsum fine aggregate by gravity separation using a shaking table.

[0009] S2. Calcium-aluminum modifier and mixing water are added to gypsum fine aggregate for mixing and modification treatment. After mixing, the aggregate is sealed and allowed to stand for pre-hydration. Mortar and concrete fine aggregate is mechanically activated using a planetary ball mill. After activation, an alkali activator aqueous solution is added for alkali activation modification treatment. After mixing evenly, the aggregate is sealed and allowed to stand. Ceramic fine aggregate is crushed, shaped, and physically modified using a vertical shaft impact crusher to obtain modified gypsum fine aggregate, modified mortar and concrete fine aggregate, and modified ceramic fine aggregate, respectively.

[0010] S3. Modified gypsum fine aggregate, modified mortar concrete fine aggregate, and modified ceramic fine aggregate are mixed to obtain composite recycled fine aggregate. Then, flux and binder are added, water is added, and the mixture is kneaded for 15-30 minutes to obtain uniform mud with a wet basis moisture content of 12%-18%.

[0011] S4. The uniform clay is aged, and after aging, it is pressed into shape to obtain brick blanks;

[0012] S5. The brick blanks are sent into a hot air circulating drying kiln and dried using gradient temperature control to obtain dried brick blanks;

[0013] S6. The dried brick blanks are sintered, and after sintering, they are cooled to room temperature to obtain sintered bricks.

[0014] Furthermore, in step S1, ceramic fine aggregate is sieved through a 3mm standard sieve; mortar concrete fine aggregate is sieved through a 3mm standard sieve; and gypsum fine aggregate is sieved through a 1mm standard sieve. The ceramic and mortar concrete fine aggregates are controlled to be below 3mm to meet the feeding requirements of subsequent mechanical activation, crushing, and shaping equipment, thereby improving the efficiency of the modification process. The gypsum fine aggregates are controlled to be below 1mm to increase the specific surface area of ​​the particles, improve the hydration reaction with the calcium-aluminum modifier, and avoid incomplete modification of large-particle gypsum.

[0015] Further, in step S2, the calcium-aluminum modifier is aluminate cement, with 8-15 parts by weight. The mixing water content is 20%-30% of the mass of the gypsum-based fine aggregate. The mixing time is 5-15 minutes, the temperature is 20℃-60℃, and the sealed, static pre-hydration time is 12-24 hours. It is clear that the calcium-aluminum modifier is aluminate cement, whose core mineral, monocalcium aluminate, can hydrate with gypsum at room temperature to form ettringite, and at high temperatures, it transforms into thermally stable anhydrous calcium sulfoaluminate, avoiding the high-temperature decomposition of calcium sulfate and the release of SO3. The 8-15 parts by weight dosage matches the stoichiometric ratio for gypsum curing, with the lower limit meeting the minimum requirements for complete gypsum curing and the upper limit preventing the system's alkali content from exceeding the standard. 20%-30% of the mixing water provides the necessary medium for the hydration reaction. Mixing for 5-15 minutes achieves uniform coating of the gypsum particles by the modifier. The temperature range of 20℃-60℃ is matched to the suitable temperature range for the hydration reaction. Sealing and standing for 12-24 hours ensures that the hydration reaction is complete.

[0016] Furthermore, in the mechanical activation treatment of fine aggregate in mortar concrete in step S2, the ball-to-material ratio is 4:1-6:1, the rotation speed is 300r / min-500r / min, and the time is 30min-90min. Subsequently, the material is sieved through a 0.075mm standard sieve, and the specific surface area is 300m² / kg-450m² / kg. In the alkali activation modification treatment, the alkali activator is a sodium hydroxide aqueous solution with a mass concentration of 10%-20%, and the alkali activator is 2-6 parts by weight. The standing treatment time is 12h-24h. In the mechanical activation parameters, the ball-to-powder ratio is 4:1-6:1, the rotation speed is 300-500 r / min, and the time is 30-90 min. This controls the impact grinding intensity of the steel balls on the aggregate, breaking down the dense glassy structure on the aggregate surface and releasing active silica-alumina components. Sieving using a 0.075 mm standard sieve and controlling the specific surface area to 300-450 m² / kg ensures the aggregate fineness meets standards and provides sufficient active sites. The alkali activator is limited to a 10%-20% sodium hydroxide aqueous solution, matching the optimal parameter range for activating the activity of mortar aggregates. A dosage of 2-6 parts by weight fully activates the sintering activity of the aggregates, avoiding excessive addition that could lead to blooming in the finished product. Sealing and standing for 12-24 hours completes the pre-hydration reaction, enhancing the plasticity and sintering reaction activity of the clay.

[0017] Furthermore, in the physical modification treatment of ceramic fine aggregate in step S2, the rotor linear speed of the crusher is 50m / s-70m / s, the processing time is 10min-30min, and the particle size of the processed material is 0.075mm-2mm. The rotor linear speed of 50m / s-70m / s matches the shaping working range of the vertical shaft impact crusher. Through inter-particle collision and grinding, needle-like and flaky particles are trimmed into near-spherical particles. The processing time of 10min-30min controls the degree of shaping to avoid inadequate shaping or over-crushing. The particle size range of 0.075mm-2mm is controlled to form a continuous particle size distribution, reduce the particle packing porosity, improve the density of brick forming, and reduce volume shrinkage during sintering.

[0018] Further, in step S3, by weight, there are 3-5 parts of modified gypsum-based fine aggregate, 35-57 parts of modified mortar-concrete fine aggregate, and 40-60 parts of modified ceramic-based fine aggregate. The 40-60 parts of modified ceramic-based fine aggregate serve as a structural component of the brick body, improving the compressive strength and volume stability of the finished product. The 35-57 parts of modified mortar-concrete fine aggregate provide the active silica-alumina-calcium components required for sintering, regulating the amount of liquid phase generated during sintering and improving the density of the brick body. The 3-5 parts of modified gypsum-based fine aggregate serve as an auxiliary fluxing component to lower the sintering temperature, while controlling the upper limit of the admixture dosage to avoid volume stability problems caused by incomplete modification.

[0019] Further, in step S3, by weight, the composite recycled fine aggregate comprises 75-90 parts, the flux is sodium-calcium-silicon waste glass powder at a dosage of 3-8 parts, and the binder is sodium-based bentonite at a dosage of 7-22 parts. The 75-90 parts of composite recycled fine aggregate achieves a high dosage of recycled fine aggregate, completely replacing natural mineral resources such as clay and shale; the flux is limited to sodium-calcium-silicon waste glass powder, and a dosage of 3-8 parts can lower the sintering temperature of the system, promote the formation of a eutectic liquid phase, and fill the gaps between particles; the binder is limited to sodium-based bentonite, and a dosage of 7-22 parts can improve the plasticity and adhesion of the clay, compensate for the insufficient plasticity of high-dosage recycled aggregate, improve the qualified rate of brick forming, and avoid drying cracking.

[0020] Furthermore, in step S4, the aging time is 24-72 hours, the molding pressure is 15-30 MPa, and the holding time is 5-20 seconds. The aging time of 24-72 hours allows for uniform diffusion of moisture in the clay, ensuring full hydration of the bentonite, improving the plasticity and uniformity of the clay, and reducing the risk of cracking during molding and drying. The molding pressure of 15-30 MPa controls the density of the brick blank, avoiding insufficient strength due to too low pressure or delamination and rebound cracking due to too high pressure. The holding time of 5-20 seconds removes air bubbles trapped within the brick blank, ensuring uniform density and preventing honeycomb and pore defects in the finished product.

[0021] Furthermore, in step S5, the drying process involves first holding the brick at 80℃-100℃ for 6-12 hours, and then at 120℃-150℃ for 6-12 hours. After drying, the wet base moisture content of the brick blank is ≤3%. A two-stage gradient temperature-controlled drying method is employed. The first stage, holding at 80℃-100℃ for 6-12 hours, slowly removes water from the brick blank, preventing rapid surface crusting and bulging / cracking caused by the inability to expel internal moisture. The second stage, holding at 120℃-150℃ for 6-12 hours, removes any remaining water from the brick blank, ensuring uniform drying. After drying, the moisture content of the brick blank is ≤3%, preventing the brick blank from cracking due to rapid vaporization of moisture during sintering.

[0022] Further, in step S6, the sintering process involves raising the temperature to 1050℃-1180℃ at a rate of 3℃ / min-8℃ / min, with a holding time of 2h-4h. After holding, the brick is cooled to room temperature in the furnace. The heating rate of 3℃ / min-8℃ / min controls the temperature difference between the inside and outside of the brick blank, preventing thermal stress cracking caused by excessive heating. The sintering temperature of 1050℃-1180℃ matches the sintering characteristics of the modified raw material system, ensuring sufficient effective liquid phase formation for brick densification at the lower limit and avoiding excessive liquid phase leading to softening and deformation of the brick at the upper limit. The holding time of 2h-4h ensures complete phase reaction and uniform diffusion of the liquid phase, stabilizing the performance of the finished product. Cooling to room temperature in the furnace controls the cooling rate to avoid stress concentration and cracking caused by rapid cooling, ensuring the volume stability of the finished product.

[0023] This invention addresses the differences in material properties among different components of recycled fine aggregate from construction waste by employing a design logic that combines precise component sorting with single-component adaptive modification. This logic is matched to the entire process of sintered brick preparation, thus solving the problems of insufficient compatibility and large fluctuations in product performance caused by the mixed use of recycled fine aggregate.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) The present invention realizes the precise sorting and modification of the components of recycled fine aggregate from construction waste, reduces the impact of raw material component fluctuations on product performance, and improves batch stability in industrial production;

[0026] (2) This invention achieves the harmless and stable treatment of gypsum components in decoration waste, avoids the release of sulfur oxides during sintering, and improves the resource utilization rate of all components of decoration waste;

[0027] (3) This invention enhances the sintering activity of recycled fine aggregates, enabling the high proportion of recycled fine aggregates to be added, replacing non-renewable natural mineral resources such as clay and shale used in the production of sintered bricks;

[0028] (4) This invention broadens the temperature adaptation window of the sintering process, reduces the production control difficulty of industrial kilns, and improves the adaptability of the process to continuous industrial production.

[0029] (5) The mechanical properties, volume stability and environmental emission indicators of the sintered bricks of the present invention meet the requirements of industry standards and there is no risk of secondary pollution. Attached Figure Description

[0030] Figure 1 This is a comparison chart of the amount of recycled fine aggregate in various cases of this invention;

[0031] Figure 2 This is a comparison chart of the average compressive strength of various cases in this invention. Detailed Implementation

[0032] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0035] Example 1

[0036] A method for preparing sintered bricks using recycled fine aggregate from construction waste according to the present invention includes the following steps:

[0037] S1. After sorting and removing metallic and harmful non-metallic impurities from the construction waste, it is first coarsely crushed using a jaw crusher with a discharge particle size ≤50mm. Then, it is finely crushed using an impact crusher. After fine crushing, it is screened through a 5mm standard sieve to obtain recycled fine aggregate. The recycled fine aggregate is then gravity-separated into ceramic fine aggregate, mortar concrete fine aggregate, and gypsum fine aggregate using a shaking table. The ceramic fine aggregate is screened through a 3mm standard sieve, the mortar concrete fine aggregate is screened through a 3mm standard sieve, and the gypsum fine aggregate is screened through a 1mm standard sieve.

[0038] S2. Add 15 parts of aluminate cement and mixing water to the gypsum-based fine aggregate. The mixing water content is 30% of the mass of the gypsum-based fine aggregate. Perform mixing modification treatment at 60℃ for 5 minutes. After mixing, seal and let stand for pre-hydration for 12 hours. Perform mechanical activation treatment on the mortar concrete fine aggregate using a planetary ball mill. The ball-to-material ratio is 6:1, the speed is 500 r / min, and the time is 30 minutes. Then, the material is sieved through a 0.075 mm standard sieve, and the specific surface area is 450. m² / kg, after activation, 6 parts of 20% sodium hydroxide aqueous solution were added for alkali activation modification treatment, mixed evenly and sealed and left to stand for 12 hours; ceramic fine aggregate was subjected to crushing and shaping physical modification treatment using a vertical shaft impact crusher. The rotor linear speed of the crusher was 70m / s, the processing time was 10min, and the particle size of the material after treatment was 0.075mm, respectively obtaining modified gypsum fine aggregate, modified mortar concrete fine aggregate and modified ceramic fine aggregate;

[0039] S3. Mix 5 parts of modified gypsum fine aggregate, 35 parts of modified mortar concrete fine aggregate, and 60 parts of modified ceramic fine aggregate to obtain composite recycled fine aggregate. By weight, there are 90 parts of composite recycled fine aggregate, 3 parts of sodium calcium silicon waste glass powder, and 7 parts of sodium-based bentonite. After adding water and mixing, knead for 30 minutes to obtain uniform mud with a wet basis moisture content of 18%.

[0040] S4. The uniform clay is aged for 72 hours. After aging, it is pressed into shape with a molding pressure of 30 MPa and a holding time of 5 seconds to obtain a brick blank.

[0041] S5. The brick blanks are sent into a hot air circulating drying kiln and dried using gradient temperature control. First, they are kept at 100℃ for 6 hours, and then at 150℃ for 6 hours. After drying, the wet basis moisture content of the brick blanks is ≤3%, and the dried brick blanks are obtained.

[0042] S6. The dried brick blanks are sintered by heating them to a sintering temperature of 1180℃ at a heating rate of 8℃ / min and holding them for 2 hours. After the holding time is completed, the bricks are cooled to room temperature in the furnace to obtain sintered bricks.

[0043] Example 2

[0044] A method for preparing sintered bricks using recycled fine aggregate from construction waste according to the present invention includes the following steps:

[0045] S1. After sorting and removing metallic and harmful non-metallic impurities from the construction waste, it is first coarsely crushed using a jaw crusher with a discharge particle size ≤50mm. Then, it is finely crushed using an impact crusher. After fine crushing, it is screened through a 5mm standard sieve to obtain recycled fine aggregate. The recycled fine aggregate is then gravity-separated into ceramic fine aggregate, mortar concrete fine aggregate, and gypsum fine aggregate using a shaking table. The ceramic fine aggregate is screened through a 3mm standard sieve, the mortar concrete fine aggregate is screened through a 3mm standard sieve, and the gypsum fine aggregate is screened through a 1mm standard sieve.

[0046] S2. 11 parts of aluminate cement and mixing water were added to gypsum-based fine aggregate, with the mixing water content being 25% of the mass of the gypsum-based fine aggregate. The mixture was mixed and modified at 40℃ for 10 minutes, and then sealed and allowed to stand for 18 hours for pre-hydration. Mortar-concrete-based fine aggregate was mechanically activated using a planetary ball mill at a ball-to-material ratio of 5:1, a rotation speed of 400 r / min, and a time of 60 minutes. The material was then sieved through a 0.075 mm standard sieve, with a specific surface area of ​​375 m² / kg. After activation, 4 parts of a 15% sodium hydroxide aqueous solution were added for alkali-activated modification. After mixing evenly, the mixture was sealed and allowed to stand for 18 hours. Ceramic-based fine aggregate was physically modified using a vertical shaft impact crusher at a rotor linear speed of 60 m / s and a processing time of 20 minutes. The particle size of the processed material was 1 mm, resulting in modified gypsum-based fine aggregate, modified mortar-concrete-based fine aggregate, and modified ceramic-based fine aggregate.

[0047] S3. Mix 4 parts of modified gypsum fine aggregate, 46 parts of modified mortar concrete fine aggregate, and 50 parts of modified ceramic fine aggregate to obtain composite recycled fine aggregate. By weight, there are 82 parts of composite recycled fine aggregate, 5 parts of sodium calcium silicon waste glass powder, and 13 parts of sodium-based bentonite. After adding water and mixing, knead for 22 minutes to obtain uniform mud with a wet basis moisture content of 15%.

[0048] S4. The uniform clay is aged for 48 hours. After aging, it is pressed into shape with a molding pressure of 22 MPa and a holding time of 12 seconds to obtain a brick blank.

[0049] S5. The brick blanks are sent into a hot air circulating drying kiln and dried using gradient temperature control. First, they are kept at 90℃ for 9 hours, and then at 135℃ for 9 hours. After drying, the wet basis moisture content of the brick blanks is ≤3%, and the dried brick blanks are obtained.

[0050] S6. The dried brick blanks are sintered by heating them to a sintering temperature of 1115℃ at a heating rate of 5℃ / min and holding them for 3 hours. After the holding time is completed, the bricks are cooled to room temperature in the furnace to obtain sintered bricks.

[0051] Example 3

[0052] A method for preparing sintered bricks using recycled fine aggregate from construction waste according to the present invention includes the following steps:

[0053] S1. After sorting and removing metallic and harmful non-metallic impurities from the construction waste, it is first coarsely crushed using a jaw crusher with a discharge particle size ≤50mm. Then, it is finely crushed using an impact crusher. After fine crushing, it is screened through a 5mm standard sieve to obtain recycled fine aggregate. The recycled fine aggregate is then gravity-separated into ceramic fine aggregate, mortar concrete fine aggregate, and gypsum fine aggregate using a shaking table. The ceramic fine aggregate is screened through a 3mm standard sieve, the mortar concrete fine aggregate is screened through a 3mm standard sieve, and the gypsum fine aggregate is screened through a 1mm standard sieve.

[0054] S2. Add 8 parts of aluminate cement and mixing water to gypsum-based fine aggregate, with the mixing water content being 20% ​​of the mass of gypsum-based fine aggregate. Mix and modify the aggregate at 20℃ for 15 minutes, and then seal and let it stand for 24 hours for pre-hydration. Mechanically activate mortar-concrete fine aggregate using a planetary ball mill with a ball-to-material ratio of 4:1, a rotation speed of 300 r / min, and a time of 90 minutes. Then, sieve the material through a 0.075 mm standard sieve, with a specific surface area of ​​300 m² / kg. After activation, add 2 parts of 10% sodium hydroxide aqueous solution for alkali activation modification. Mix evenly and then seal and let stand for 24 hours. Physically modify ceramic fine aggregate using a vertical shaft impact crusher with a rotor linear speed of 50 m / s and a processing time of 30 minutes. The particle size of the processed material is 2 mm, resulting in modified gypsum-based fine aggregate, modified mortar-concrete fine aggregate, and modified ceramic fine aggregate.

[0055] S3. Mix 3 parts of modified gypsum fine aggregate, 57 parts of modified mortar concrete fine aggregate, and 40 parts of modified ceramic fine aggregate to obtain composite recycled fine aggregate. By weight, the composite recycled fine aggregate contains 75 parts, sodium-calcium-silicon waste glass powder 8 parts, and sodium-based bentonite 17 parts. After adding water and mixing, knead for 15 minutes to obtain a uniform mud with a wet basis moisture content of 12%.

[0056] S4. The uniform clay is aged for 72 hours. After aging, it is pressed into shape with a molding pressure of 15 MPa and a holding time of 20 seconds to obtain a brick blank.

[0057] S5. The brick blanks are sent into a hot air circulating drying kiln and dried using gradient temperature control. First, they are kept at 80℃ for 12 hours, and then at 120℃ for 12 hours. After drying, the wet basis moisture content of the brick blanks is ≤3%, and the dried brick blanks are obtained.

[0058] S6. The dried brick blanks are sintered by heating them to a sintering temperature of 1050℃ at a heating rate of 3℃ / min and holding them for 4 hours. After the holding time is completed, the bricks are cooled to room temperature in the furnace to obtain sintered bricks.

[0059] Comparative Example

[0060] The comparative method for preparing sintered bricks includes the following steps:

[0061] S1. After sorting and removing metallic and harmful non-metallic impurities from the construction waste, it is first coarsely crushed using a jaw crusher with a discharge particle size ≤50mm, and then finely crushed using an impact crusher. After fine crushing, it is screened through a 5mm standard sieve to obtain recycled fine aggregate.

[0062] S2. Based on a total dry weight of 100 parts, take 55 parts of recycled fine aggregate, add 25 parts of clay, 12 parts of shale, 3 parts of potassium feldspar, and 5 parts of sodium bentonite, add water and mix for 20 minutes to obtain a uniform mud with a wet moisture content of 15%.

[0063] S3. The uniform clay is aged for 48 hours. After aging, it is pressed into shape with a molding pressure of 20 MPa and a holding time of 10 seconds to obtain a brick blank.

[0064] S4. The brick blanks are sent into a hot air circulating drying kiln and dried at a constant temperature of 120℃ for 18 hours. After drying, the wet basis moisture content of the brick blanks is ≤3%, and the dried brick blanks are obtained.

[0065] S5. The dried brick blanks are sintered by heating them to a sintering temperature of 1100℃ at a heating rate of 5℃ / min and holding them for 3 hours. After the holding time is completed, the bricks are cooled to room temperature in the furnace to obtain sintered bricks.

[0066] The testing method is as follows:

[0067] Average compressive strength: According to GB / T 2542-2012 "Test Methods for Masonry Bricks", the compressive strength of standard-sized specimens was tested using a universal testing machine, and the arithmetic mean of the compressive strength of 10 parallel specimens was taken.

[0068] Water absorption rate: According to GB / T 2542-2012 "Test Methods for Masonry Bricks", the water absorption mass of the sample after boiling for 5 hours and the dry sample mass after drying at 105℃ to constant weight are tested by boiling method, and the percentage of water absorption mass to dry sample mass is calculated.

[0069] Freeze-thaw resistance rating: According to GB / T 2542-2012 "Test Methods for Masonry Bricks", the slow freezing method is used to repeatedly freeze the sample at -15℃ and thaw it at 20℃. The freeze-thaw resistance rating is determined by the maximum number of freeze-thaw cycles with a strength loss rate of no more than 25% and a mass loss rate of no more than 5%.

[0070] SO3 emission concentration during sintering process: According to GB / T 16157-1996 "Determination of particulate matter and sampling method of gaseous pollutants in exhaust gas from stationary sources", the constant potential electrolysis method was used to continuously sample and detect the flue gas at the outlet of the sintering kiln exhaust stack, and the hourly average emission concentration during the stable sintering and heat preservation stage was taken.

[0071] Batch variation coefficient of compressive strength: Calculated using mathematical statistics methods, taking the compressive strength test data of 3 independent production batches, 10 parallel samples in each batch, and calculating the ratio of the standard deviation of the data to the arithmetic mean, expressed as a percentage.

[0072] Table 1: Experimental Results of Examples 1-3 and Comparative Examples

[0073]

[0074] In summary, refer to Table 1 and Figure 1-2 Examples 1-3 of this invention achieve a comprehensive improvement in the performance of sintered bricks with high recycled aggregate content through precise sorting and modification of the components of recycled fine aggregate from construction waste. The recycled fine aggregate content in these examples is 75 to 90 parts, significantly higher than the 55 parts in the comparative example. Simultaneously, the compressive strength reaches a maximum of 28.4 MPa, the water absorption rate is significantly lower, the frost resistance grade reaches a maximum of F100, the batch variation coefficient of compressive strength is consistently controlled within 5%, and the SO3 emission concentration during sintering is as low as 22 mg / m³. Example 2 exhibits the best compatibility between modification and sintering processes, resulting in the best overall performance. The comparative example, without component sorting and modification, not only has limited aggregate content but also suffers from large performance fluctuations and high harmful emissions, fully verifying the advanced nature and stability of the process in this invention.

Claims

1. A method for preparing sintered bricks using recycled fine aggregate from construction waste, characterized in that: Includes the following steps, S1. After sorting and removing metallic and harmful non-metallic impurities from the construction waste, it is first coarsely crushed using a jaw crusher with a discharge particle size ≤50mm. Then, it is finely crushed using an impact crusher. After fine crushing, it is screened through a 5mm standard sieve to obtain recycled fine aggregate. The recycled fine aggregate is then separated into ceramic fine aggregate, mortar concrete fine aggregate, and gypsum fine aggregate by gravity separation using a shaking table. S2. Calcium-aluminum modifier and mixing water are added to gypsum fine aggregate for mixing and modification treatment. After mixing, the aggregate is sealed and allowed to stand for pre-hydration. Mortar and concrete fine aggregate is mechanically activated using a planetary ball mill. After activation, an alkali activator aqueous solution is added for alkali activation modification treatment. After mixing evenly, the aggregate is sealed and allowed to stand. Ceramic fine aggregate is crushed, shaped, and physically modified using a vertical shaft impact crusher to obtain modified gypsum fine aggregate, modified mortar and concrete fine aggregate, and modified ceramic fine aggregate, respectively. S3. Modified gypsum fine aggregate, modified mortar concrete fine aggregate, and modified ceramic fine aggregate are mixed to obtain composite recycled fine aggregate. Then, flux and binder are added, water is added, and the mixture is kneaded for 15-30 minutes to obtain uniform mud with a wet basis moisture content of 12%-18%. S4. The uniform clay is aged, and after aging, it is pressed into shape to obtain brick blanks; S5. The brick blanks are sent into a hot air circulating drying kiln and dried using gradient temperature control to obtain dried brick blanks; S6. The dried brick blanks are sintered, and after sintering, they are cooled to room temperature to obtain sintered bricks.

2. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S1, ceramic fine aggregate is screened through a 3mm standard sieve; mortar concrete fine aggregate is screened through a 3mm standard sieve; and gypsum fine aggregate is screened through a 1mm standard sieve.

3. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S2, the calcium-aluminum modifier is aluminate cement, with 8-15 parts by weight. The mixing water content is 20%-30% of the mass of gypsum fine aggregate. The mixing time is 5-15 minutes, the temperature is 20℃-60℃, and the sealed standing pre-hydration time is 12-24 hours.

4. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S2, the mechanical activation treatment of fine aggregate in mortar concrete involves a ball-to-material ratio of 4:1 to 6:1, a rotation speed of 300 r / min to 500 r / min, and a time of 30 min to 90 min. Subsequently, the material is sieved through a 0.075 mm standard sieve, resulting in a specific surface area of ​​300 m² / kg to 450 m² / kg. In the alkali activation modification treatment, the alkali activator is a 10% to 20% sodium hydroxide aqueous solution, with 2 to 6 parts by weight, and the standing time is 12 to 24 hours.

5. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S2, during the physical modification treatment of ceramic fine aggregate through crushing and shaping, the rotor linear velocity of the crusher is 50m / s-70m / s, the processing time is 10min-30min, and the particle size of the processed material is 0.075mm-2mm.

6. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S3, by weight, there are 3-5 parts of modified gypsum fine aggregate, 35-57 parts of modified mortar concrete fine aggregate, and 40-60 parts of modified ceramic fine aggregate.

7. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S3, by weight, there are 75-90 parts of composite recycled fine aggregate, 3-8 parts of sodium-calcium-silicon waste glass powder as flux, and 7-22 parts of sodium-based bentonite as binder.

8. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S4, the aging time is 24h-72h, the molding pressure is 15MPa-30MPa, and the holding time is 5s-20s.

9. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S5, the drying process involves first maintaining the temperature at 80℃-100℃ for 6-12 hours, and then maintaining the temperature at 120℃-150℃ for 6-12 hours. After drying, the wet base moisture content of the brick blank is ≤3%.

10. The method for preparing sintered bricks using recycled fine aggregate from construction waste according to claim 1, characterized in that: In step S6, the sintering process is carried out at a heating rate of 3℃ / min-8℃ / min to reach the sintering temperature, which is 1050℃-1180℃. The holding time is 2h-4h. After the holding time is completed, the furnace is cooled to room temperature.

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