Solid waste composite admixture for concrete and preparation method thereof

Abstract

This invention discloses a solid waste composite admixture for concrete and its preparation method. The solid waste composite admixture for concrete is prepared from the following materials: 30-50 parts steel slag powder, 20-40 parts blast furnace slag powder, 10-25 parts phosphorus slag powder, 5-15 parts nickel slag powder, 0.5-3 parts high-molecular low-carbon stabilizer, and also includes 5-10 parts modified phosphogypsum. The phosphogypsum is calcined at 600℃ to remove impurities and then mixed with sodium citrate at a ratio of 9:1, resulting in a specific surface area ≥350 m². 2 / kg; the steel slag powder is steelmaking solid waste that has been ground to a specific surface area ≥400m². 2 / kg; the slag powder is blast furnace slag ground to a specific surface area ≥420m². 2 / kg; the fineness of the phosphorus slag powder and nickel slag powder meets the requirement of ≤15% residue on a 45μm sieve; the high-molecular low-carbon stabilizer is composed of silane coupling agent and polycarboxylic acid copolymer; the porosity of the composite admixture is controlled at 12%-16%, with an average pore size ≤420nm, and is used to replace 20%-50% of cement in concrete; this invention uses slag alkali activation to replace high-energy-consuming steam curing, and reduces peak energy consumption by 40% through a dynamic thermal control system.

Description

Technical Field

[0001] This invention belongs to the field of lightweight building materials, and more specifically, relates to a solid waste composite admixture for concrete. Furthermore, this invention also relates to a method for preparing the solid waste composite admixture for concrete. Background Technology

[0002] Lightweight building materials, as key materials for reducing structural loads and improving thermal and sound insulation performance, mainly include categories such as expanded clay concrete, foamed concrete, and aerated concrete blocks. Their core performance indicator requires a bulk density ≤ 1.5 g / cm³. 3 Under these conditions, it has both a compressive strength of ≥20MPa and a thermal conductivity of ≤0.08W / (m·K). Currently, the industry generally uses air-entraining agents to create pores or adds expanded perlite / vitrified microspheres to achieve lightweighting.

[0003] Existing lightweight building materials have low solid waste utilization rates, only accepting ≤15% fly ash / slag, and cannot handle difficult-to-treat solid wastes such as steel slag. Although steel slag has potential cementitious activity, due to the f-CaO hydration expansion effect, a dosage >10% will cause deterioration of volume stability. Currently, f-CaO is forcibly decomposed through autoclaving, but this leads to a surge in production energy consumption, and the autoclaving process conflicts with the ambient temperature curing system of lightweight building materials, but its effect is not ideal. Therefore, we propose a solid waste composite admixture for concrete and its preparation method to achieve safe utilization of high dosage of steel slag under autoclaving-free and strong acid-free conditions, and simultaneously achieve precise control of the pore structure of lightweight building materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and proposes a solid waste composite admixture for concrete and its preparation method. Through three innovative modules—safe activation of steel slag, precise control of pores, and synergistic treatment of industrial solid waste—a new generation of lightweight building materials with ultra-low density, ultra-high strength, and excellent durability can be successfully prepared.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A solid waste composite admixture for concrete, wherein the solid waste composite admixture for concrete is prepared from the following materials:

[0007] 30-50 parts steel slag powder, 20-40 parts slag powder, 10-25 parts phosphorus slag powder, 5-15 parts nickel slag powder, and 0.5-3 parts high-molecular low-carbon stabilizer;

[0008] The steel slag powder is steelmaking solid waste that has been ground to a specific surface area ≥ 400 m². 2 / kg; the slag powder is blast furnace slag ground to a specific surface area ≥420m². 2 / kg; the fineness of the phosphorus slag powder and nickel slag powder meets the requirement of ≤15% residue on a 45μm sieve; the high-molecular low-carbon stabilizer is composed of silane coupling agent and polycarboxylic acid copolymer; the porosity of the composite admixture is controlled at 12%-16%, with an average pore size ≤420nm, and is used to replace 20%-50% of cement in concrete.

[0009] It also includes 5-10 parts of modified phosphogypsum, which is calcined at 600℃ to remove impurities and then mixed with sodium citrate at a ratio of 9:1, resulting in a specific surface area ≥350m². 2 / kg.

[0010] Preferably, the steel slag powder is derived from converter steel slag, with FeO content ≤8%, f-CaO content ≤3.5%, and residual metallic iron content ≤1.5% after magnetic separation; the slag powder is S95 grade granulated blast furnace slag powder, with CaO / SiO2 molar ratio controlled at 0.9-1.2 and 7d activity index ≥75%.

[0011] Preferably, the polymeric low-carbon stabilizer is a compound of silane coupling agent KH-550 and polycarboxylic acid copolymer at a mass ratio of 1:0.8-1.2, and the amount added is 0.5-1.5 parts of the total admixture, used to reduce the porosity to below 14%.

[0012] A method for preparing a solid waste composite admixture for concrete, the method being used to prepare the aforementioned solid waste composite admixture for concrete, characterized by comprising the following steps:

[0013] S1. Grind steel slag, mineral slag, phosphorus slag, and nickel slag to the target fineness, wherein the specific surface area of ​​steel slag powder is ≥400m². 2 / kg, slag powder with a specific surface area ≥420m² 2 / kg, the residue of phosphorus slag powder and nickel slag powder on a 45μm sieve is ≤15%;

[0014] S2. Test the FeO content and f-CaO content of steel slag powder to ensure that they are ≤8% and ≤3.5% respectively, and test the CaO / SiO2 molar ratio and activity index of slag powder.

[0015] S3. Calculate the amount of each component to be fed based on the mass fractions;

[0016] S4. Add the metered components into the mixer, control the temperature ≤50℃ and humidity ≤30%, and dry mix at 60-80rpm for 15-20min.

[0017] S5. Monitor the state of the mixed materials in real time, and adjust the mixing time to reduce the porosity to 12%-16% and the average pore size to ≤420nm.

[0018] Preferably, in step S1, the converter steel slag is magnetically separated to remove metallic iron until the residual amount is ≤1.5%, and then subjected to gradient drying. First, it is dried at 105±5℃ for 1 hour, then heated to 200±10℃ for 30 minutes to decompose f-CaO, and finally ground to a specific surface area ≥420m². 2 / kg and ≤5% residue on 45μm sieve;

[0019] The process involves co-grinding slag powder and phosphorus slag powder at a mass ratio of 1:0.5-0.8, followed by simultaneous grinding. During grinding, 0.1%-0.3% (by weight of the slag) of triethanolamine grinding aid is added to control the final mixed powder to have a specific surface area ≥430 m². 2 / kg.

[0020] Preferably, after detecting the CaO / SiO2 molar ratio of the slag powder in step S2, the slag exceeding the standard is subjected to alkaline activation pretreatment by spraying a sodium hydroxide solution with a concentration of 1 mol / L, the amount of which is 2%-4% of the slag mass, and aging for 24 hours to improve the activity index to ≥80%.

[0021] Preferably, the dry mixing process in step S4 adopts a segmented time control strategy: the first stage is premixing at a low speed of 20-40 rpm for 5 min; the second stage is high-speed mixing at 100-120 rpm for 8-10 min; and the third stage is disintegration and agglomeration at 40-60 rpm for 3-5 min; nitrogen gas with a dew point ≤-20℃ is introduced throughout the process to maintain humidity ≤25%.

[0022] The segmented timing control is carried out in a vibrating mixer, with the vibration frequency set to 15-25Hz and the amplitude to 0.5-1.0mm. The inner wall of the mixer is lined with a polytetrafluoroethylene wear-resistant lining.

[0023] Preferably, in step S5, the porosity control includes: synchronously monitoring the mixing temperature and material rheological properties; when the temperature exceeds 45°C, starting the cooling system to ensure that the temperature difference fluctuation is ≤3°C; and extending the mixing time of the third stage by 2-3 minutes when the rheological viscosity exceeds 5000 cP.

[0024] Preferably, the amount V of sodium hydroxide solution added satisfies:

[0025] ,in, The mass of the slag exceeding the standard, where ρ is the solution density. To measure the CaO / SiO2 molar ratio, The target molar ratio threshold, It is a natural constant.

[0026] Preferably, the relationship between the rheological viscosity η and the cooling time is as follows:

[0027] Where η is the real-time rheological viscosity, and regulation is triggered when η > 5000 cP. The cooling system startup time is represented by ΔT, where ΔT is the temperature overshoot. It is the linear speed of the mixing machine. The constant resistance coefficient of the material is given by the above formula, which establishes a coupled control mechanism of temperature, velocity, and viscosity, thereby increasing the porosity convergence rate.

[0028] The technical effects and advantages of this invention are as follows: Compared with traditional solid products, the solid waste composite admixture for concrete and its preparation method provided by this invention replace high-energy-consuming steam curing with slag alkali activation, and reduce peak energy consumption by 40% through a dynamic thermal control system; it also realizes the synergistic utilization of steel plant solid waste and phosphoric acid chemical waste, with a single production line consuming more than 100,000 tons of solid waste annually, completely changing the high-carbon production mode of traditional lightweight building materials that relies on natural aggregates;

[0029] In the preparation method, a gradient drying and mechanical activation synergistic process is used to completely decompose the free calcium oxide (f-CaO) in the steel slag under normal pressure, fundamentally eliminating the volume expansion and cracking problem in lightweight building materials caused by the incorporation of steel slag. Simultaneously, it avoids the chloride ion corrosion risk introduced by acid pickling, providing a safe path for the large-scale application of steel slag.

[0030] By employing multi-stage segmented mixing and interface strengthening technologies, a closed pore structure with controllable size and independent distribution is constructed inside the material, significantly reducing the pore connectivity rate. Attached Figure Description

[0031] Figure 1 This is a flowchart of the preparation method of the solid waste composite admixture for concrete according to the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0033] This invention provides a solid waste composite admixture for concrete and its preparation method, pioneering a core technology chain for the large-scale application of solid waste in lightweight building materials: through three innovative modules—safe activation of steel slag, precise control of pore size, and co-processing of industrial solid waste—a new generation of lightweight building materials with ultra-low density, ultra-high strength, and excellent durability has been successfully prepared. This not only completely solves the engineering failure problem caused by steel slag expansion, but also completely replaces natural aggregates with recyclable solid waste resources, promoting the strategic transformation of the construction industry from resource-consuming to environmentally restorative, resulting in significant economic and social benefits.

[0034] Specifically, the solid waste composite admixture for concrete is prepared by mixing the following materials: steel slag powder, slag powder, phosphorus slag powder, nickel slag powder, high-molecular low-carbon stabilizer, and modified phosphogypsum.

[0035] Among them, steel slag powder is steelmaking solid waste that has been ground to a specific surface area ≥400 m². 2 / kg; blast furnace slag powder is blast furnace slag ground to a specific surface area ≥420m². 2 / kg; the fineness of phosphorus slag powder and nickel slag powder meets the requirement of ≤15% residue on 45μm sieve; the high molecular weight low carbon stabilizer is composed of silane coupling agent and polycarboxylic acid copolymer; the porosity of the composite admixture is controlled at 12% to 16%, with an average pore size of ≤420nm, and is used to replace 20% to 50% of cement in concrete, and is suitable for the field of lightweight building materials.

[0036] It should be noted that the steel slag powder is derived from converter steel slag, with an FeO content ≤8%, f-CaO content ≤3.5%, and residual metallic iron content ≤1.5% after magnetic separation; the slag powder is S95 grade granulated blast furnace slag powder, with a CaO / SiO2 molar ratio controlled between 0.9 and 1.2, and a 7-day activity index ≥75%.

[0037] The polymeric low-carbon stabilizer is a compound of silane coupling agent KH-550 and polycarboxylic acid copolymer at a mass ratio of 1:0.8-1.2, and the amount added is 0.5-1.5 parts of the total admixture, used to reduce porosity.

[0038] This invention also relates to a method for preparing a solid waste composite admixture for concrete. The method for preparing the above-mentioned solid waste composite admixture for concrete includes the following steps:

[0039] S1. Grind steel slag, mineral slag, phosphorus slag, and nickel slag to the target fineness, wherein the specific surface area of ​​steel slag powder is ≥400m². 2 / kg, slag powder with a specific surface area ≥420m² 2 / kg, the residue of phosphorus slag powder and nickel slag powder on a 45μm sieve is ≤15%; in step S1, the converter steel slag is magnetically separated to remove metallic iron until the residue is ≤1.5%, and then subjected to gradient drying, first drying at 105±5℃ for 1h, then heating to 200±10℃ for 30min to decompose f-CaO, and finally grinding to a specific surface area ≥420m². 2 / kg and ≤5% residue on 45μm sieve;

[0040] The process involves co-grinding slag powder and phosphorus slag powder at a mass ratio of 1:0.5-0.8, followed by simultaneous grinding. During grinding, 0.1%-0.3% (by weight of the slag) of triethanolamine grinding aid is added to control the final mixed powder to have a specific surface area ≥430 m². 2 / kg.

[0041] S2. Test the FeO content and f-CaO content of steel slag powder to ensure that they are ≤8% and ≤3.5% respectively, and test the CaO / SiO2 molar ratio and activity index of slag powder.

[0042] After detecting the CaO / SiO2 molar ratio of the slag powder in step S2, the slag exceeding the standard was subjected to alkaline activation pretreatment by spraying a 1 mol / L sodium hydroxide solution at an addition amount of 2%-4% of the slag mass, and aging for 24 hours to improve the activity index to ≥80%.

[0043] The amount of sodium hydroxide solution added, V, satisfies the following:

[0044] ,in, The mass of the slag exceeding the standard, where ρ is the solution density. To measure the CaO / SiO2 molar ratio, The target molar ratio threshold, It is a natural constant.

[0045] S3. Calculate the feed amount of each component based on the mass fractions; this step is the core control point to ensure the balance between performance and cost of solid waste admixtures, and the calculation must be performed based on a four-dimensional dynamic model. The specific implementation process is as follows:

[0046] Input the target parameters, receive the production task instructions, and extract key performance indicators: target value of cement substitution rate (range of 20%~50%); strength threshold and thermal conductivity limit corresponding to concrete application scenarios (road / block / precast components); measured data of steel slag f-CaO residue (feedback value of step S2).

[0047] The raw material database is dynamically matched, and real-time inventory data from the raw material warehouse is called. Available batches are locked according to priority rules: Steel slag powder: Pre-treated batches with FeO≤6% and f-CaO≤2.8% are preferred (such as the pre-stored batch number ZD2024-08); Slag micro powder: The activity compensation mechanism is activated, and when CaO / SiO2>1.15, the amount of alkali activator added is automatically increased to the upper limit of 4%; Polymer stabilizer: Based on the target porosity value, if the required porosity is ≤13%, the KH550 / PC compound ratio is set to 1:1.2 (the copolymer ratio is increased to enhance the interfacial sealing).

[0048] S4. Add the metered components to the mixer, controlling the temperature to ≤50℃ and humidity to ≤30%, and dry mix at 60-80 rpm for 15-20 minutes. In step S4, the dry mixing process adopts a segmented time control strategy: the first stage is premixing at a low speed of 20-40 rpm for 5 minutes, the second stage is high-speed mixing at 100-120 rpm for 8-10 minutes, and the third stage is disintegration and agglomeration at 40-60 rpm for 3-5 minutes. Nitrogen gas with a dew point ≤-20℃ is introduced throughout the process to maintain humidity ≤25%.

[0049] The segmented timing control is carried out in a vibrating mixer, with the vibration frequency set at 15-25Hz and the amplitude at 0.5-1.0mm. The inner wall of the mixer is lined with a wear-resistant polytetrafluoroethylene lining.

[0050] S5. Monitor the state of the mixture in real time, and adjust the mixing time to reduce the porosity to 12%-16% and the average pore size to ≤420nm. In step S5, porosity control includes: simultaneously monitoring the mixing temperature and material rheological properties; activating the cooling system when the temperature exceeds 45℃ to ensure temperature fluctuations are ≤3℃; extending the third-stage mixing time by 2-3 minutes when the rheological viscosity exceeds 5000cP; the relationship between rheological viscosity η and cooling time is:

[0051] Where η is the real-time rheological viscosity, and regulation is triggered when η > 5000 cP. The cooling system startup time is represented by ΔT, where ΔT is the temperature overshoot. It is the linear speed of the mixing machine. The constant resistance coefficient of the material is given by the above formula, which establishes a coupled control mechanism of temperature, velocity, and viscosity, thereby increasing the porosity convergence rate.

[0052] The preparation process also includes a finished product verification step, which uses X-CT technology to create a 3D model and detect the pore distribution. If the porosity is >15%, the mixture is returned for 1-2 minutes for remixing. After confirming that the bulk density is qualified, the product is sealed in a vacuum aluminum foil bag with a residual oxygen content ≤0.5%. The residual oxygen threshold O2 of the vacuum aluminum foil bag meets the following requirements:

[0053] , where P i The initial porosity, Bulk density, For ambient relative humidity, For the warehousing cycle, This represents the interface enhancement coefficient.

[0054] Based on the above, the following embodiments are possible:

[0055] Example 1

[0056]

[0057] Example 2

[0058]

[0059] Example 3

[0060]

[0061] Example description:

[0062] Scenario differentiation: Example 1 focuses on high-strength road concrete (strictly controlling steel slag content and f-CaO); Example 2 pursues ultra-lightweight blocks (enhancing pore sealing); Example 3 is adapted to precast components (balancing expansion rate and early strength requirements).

[0063] Feasibility of process parameters: The amount of slag alkali-activated spraying (2-4%) is directly related to the VVV formula calculation results; the gradient drying time strictly matches the t-function model of claim 10; Table function: It includes mandatory test indicators such as density / strength / expansion rate, and compares with industry standards to prove the technical advantages;

[0064] According to the above embodiments, the following parameters are available:

[0065]

[0066] In summary:

[0067] Example 1 is high-performance lightweight concrete for roads:

[0068] In response to the requirements for lightweight roads (density <1500kg / m³) 3 ), using medium to high steel slag content (28 parts);

[0069] Steel slag activation, 200℃ gradient drying extended to 30 minutes (industry standard 15 minutes), combined with 425m 2 High specific surface area grinding reduces f-CaO residue to 2.7%;

[0070] The strength contradiction was resolved by strengthening the interfacial bonding with KH550 / PC copolymer (1.2 parts), achieving a compressive strength of 24.8 MPa (65% higher than the national standard) even with a porosity of 14.2%.

[0071] The essence of pore control is achieved by using a three-stage vibration mixing process (22Hz amplitude). During the high-speed mixing stage, a forced dispersion of 110rpm is maintained to ensure that the micropores are independently sealed (average pore size 360nm).

[0072] Application results: When used in the load reduction layer of urban elevated bridges, it reduces the structural load by 30%, and the 180-day expansion rate is only 0.03% (compared to 0.15% for traditional steel slag concrete), completely eliminating road surface heave defects.

[0073] Example 2 is a building exterior wall insulation block:

[0074] Focusing on the core requirements of ultra-lightweight thermal insulation (density target ≤1300kg / m³) 3 Key to solid waste co-processing: Co-grinding slag and phosphorus slag at a ratio of 1:0.65 (containing triethanolamine grinding aid) to form a porous core-shell structure (specific surface area 438 m²). 2 / kg), significantly improving heat retention;

[0075] The highlights of the process adjustment are: controlling the mixing temperature to ≤42℃ (nitrogen dew point -22℃), and adjusting the cooling time according to the trigger formula η=5200cP to obtain an optimal porosity of 15.1%.

[0076] Breakthrough in durability: the residual oxygen content of vacuum aluminum foil packaging is 0.42%, and with the calcium sulfoaluminate formation effect of modified phosphogypsum, the mass loss after 100 freeze-thaw cycles is only 2.1% (national standard requires ≤5%).

[0077] Application results: The thermal conductivity of the blocks is 0.069 W / (m·K), meeting the 75% energy-saving standard in extremely cold regions; the weight of a single block is reduced by 45% (1260 kg / m²). 3 This increases masonry efficiency by 40%.

[0078] Example 3 is a prefabricated panel for assembled buildings:

[0079] Balancing structural safety with industrial production requirements, deep activation of steel slag was achieved: treatment at 200℃ was extended by 5 minutes to 35 minutes (with steel slag content reaching 33 parts), and f-CaO decomposed from the initial 4.1% to 2.9%.

[0080] Early strength technology breakthrough: Sodium hydroxide (3.5% addition) is used to activate slag activity to 85%, and the strength reaches 90% of the design value in 14 days (the traditional process requires 28 days).

[0081] Storage life design, based on vacuum equation calculations (O2=0.38, O2=0.38%), combined with phosphogypsum passivation of metal ions, ensures a 180-day strength shrinkage rate of <3%.

[0082] Application results show that the lifting strength of the panels is 6.3 MPa (26% higher than the industry standard); the chloride ion content is as low as 0.02%, completely solving the problem of steel corrosion in coastal prefabricated buildings and achieving a 50-year design life.

[0083] The above three sets of embodiments, through differentiated compounding ratios (15-33 parts steel slag) and process combinations (gradient drying / co-grinding / alkali activation), verified the universality of the present invention in three major scenarios: road load-bearing, building insulation, and prefabrication. All embodiments achieved the core advantages of solid waste content ≥90%, expansion rate ≤0.04%, and strength exceeding national standards by 20-65%.

[0084] In summary, compared with traditional solid products, this invention replaces high-energy-consuming steam curing with slag alkaline activation, and reduces peak energy consumption by 40% through a dynamic thermal control system; it simultaneously realizes the synergistic utilization of steel plant solid waste and phosphoric acid chemical waste, with a single production line consuming more than 100,000 tons of solid waste annually, completely changing the traditional high-carbon production mode of lightweight building materials that relies on natural aggregates.

[0085] In the preparation method, a gradient drying and mechanical activation synergistic process is used to completely decompose the free calcium oxide (f-CaO) in the steel slag under normal pressure, fundamentally eliminating the volume expansion and cracking problem in lightweight building materials caused by the incorporation of steel slag. Simultaneously, it avoids the chloride ion corrosion risk introduced by acid pickling, providing a safe path for the large-scale application of steel slag.

[0086] By employing multi-stage segmented mixing and interface strengthening technologies, a closed pore structure with controllable size and independent distribution is constructed inside the material, significantly reducing the pore connectivity rate.

[0087] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a solid waste composite admixture for concrete, wherein the solid waste composite admixture for concrete is prepared from the following materials: 30-50 parts steel slag powder, 20-40 parts blast furnace slag powder, 10-25 parts phosphorus slag powder, 5-15 parts nickel slag powder, 0.5-3 parts high-molecular low-carbon stabilizer, and 5-10 parts modified phosphogypsum, wherein the steel slag powder is derived from converter steel slag, characterized in that... Includes the following steps: S1. Grind steel slag, mineral slag, phosphorus slag, and nickel slag to the target fineness, wherein the specific surface area of ​​steel slag powder is ≥400m². 2 / kg, slag powder with a specific surface area ≥420m² 2 / kg, the residue of phosphorus slag powder and nickel slag powder on a 45μm sieve is ≤15%; in step S1, the converter steel slag is magnetically separated to remove metallic iron until the residue is ≤1.5%, and then subjected to gradient drying, first drying at 105±5℃ for 1h, then heating to 200±10℃ for 30min to decompose f-CaO, and finally grinding to a specific surface area ≥420m². 2 / kg and ≤5% residue on 45μm sieve; The process involves co-grinding slag powder and phosphorus slag powder at a mass ratio of 1:0.5-0.8, followed by simultaneous grinding. During grinding, 0.1%-0.3% (by weight of the slag) of triethanolamine grinding aid is added to control the final mixed powder to have a specific surface area ≥430 m². 2 / kg; S2. Test the FeO content and f-CaO content of steel slag powder to ensure that they are ≤8% and ≤3.5% respectively, and test the CaO / SiO2 molar ratio and activity index of slag powder. S3. Calculate the amount of each component to be fed based on the mass fractions; S4. Add the metered components to the mixer, controlling the temperature to ≤50℃ and humidity to ≤30%, and dry mix at 60-80 rpm for 15-20 minutes. In step S4, the dry mixing process adopts a segmented time control strategy: the first stage is premixing at a low speed of 20-40 rpm for 5 minutes, the second stage is high-speed mixing at 100-120 rpm for 8-10 minutes, and the third stage is disintegration and agglomeration at 40-60 rpm for 3-5 minutes. Nitrogen gas with a dew point ≤-20℃ is introduced throughout the process to maintain humidity ≤25%. S5. Monitor the state of the mixed materials in real time, and adjust the mixing time to reduce the porosity to 12%-16% and the average pore size to ≤420nm.

2. The method for preparing solid waste composite admixture for concrete according to claim 1, characterized in that, After detecting the CaO / SiO2 molar ratio of the slag powder in step S2, the slag exceeding the standard was subjected to alkaline activation pretreatment by spraying a sodium hydroxide solution with a concentration of 1 mol / L, with an addition amount of 2%-4% of the slag mass, and aging for 24 hours to improve the activity index to ≥80%.

3. The method for preparing solid waste composite admixture for concrete according to claim 1, characterized in that, In step S4, segmented timing is carried out in a vibrating mixer, with the vibration frequency set to 15-25Hz and the amplitude to 0.5-1.0mm. The inner wall of the mixer is lined with a wear-resistant polytetrafluoroethylene lining.

4. The method for preparing solid waste composite admixture for concrete according to claim 1, characterized in that, In step S5, porosity control includes: synchronously monitoring the mixing temperature and material rheological properties; when the temperature exceeds 45°C, starting the cooling system to ensure that the temperature difference fluctuation is ≤3°C; and extending the mixing time of the third stage by 2-3 minutes when the rheological viscosity exceeds 5000 cP.

5. The method for preparing solid waste composite admixture for concrete according to claim 2, characterized in that, The amount of sodium hydroxide solution added, V, satisfies the following: ,in, The mass of the slag exceeding the standard, where ρ is the solution density. To measure the CaO / SiO2 molar ratio, The target molar ratio threshold, It is a natural constant.

6. The method for preparing solid waste composite admixture for concrete according to claim 4, characterized in that, The relationship between the rheological viscosity η and the cooling time is as follows: Where η is the real-time rheological viscosity, and regulation is triggered when η > 5000 cP. The cooling system startup time is represented by ΔT, where ΔT is the temperature overshoot. It is the linear speed of the mixing machine. The constant resistance coefficient of the material is given by the above formula, which establishes a coupled control mechanism of temperature, velocity, and viscosity, thereby increasing the porosity convergence rate.

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