Preparation method of environment-friendly mineral powder blended cement

Abstract

The invention discloses a preparation method of environment-friendly mineral powder blended cement, and relates to the technical field of building materials. Abundant carbonation active sites are generated on the surface of mineral powder through the synergistic effect of CO2 partial pressure reaction grinding and gradient thermal activation, the crystal structure of the mineral powder is changed, a sufficient reaction basis is provided for a subsequent hydration reaction, and the mineral powder blended cement is prepared. The temperature-sensitive phase change microcapsules in the composite activator release Ca < 2 + > when cement is hydrated and heated to 45 DEG C, the Ca < 2 + >, the nano geopolymer precursor and the basic magnesium sulfate whiskers act together to induce to generate hydration products of carbonated datolite and magnesium silicate gel, and the products are interwoven to form a compact network structure, so that the temperature-sensitive phase change microcapsules in the composite activator can be used for preparing the composite activator. The internal binding force of the set cement is enhanced, and the pore structure is optimized, so that the cement has excellent mechanical property and durability.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of building materials, in particular to a preparation method of an environment-friendly mineral powder mixed cement. BACKGROUND

[0002] Traditional Portland cement is facing severe challenges due to high energy consumption, high carbon emission and resource dependency. The potential activity of mineral powder as industrial solid waste has not been fully stimulated, resulting in low early strength and slow hydration rate of the mineral powder mixed cement, which is difficult to meet the rapid construction demand. In addition, the existing activators have the problems of single composition and extensive action mechanism, which cannot accurately control the hydration process of the mineral powder and easily cause the deterioration of the later volume stability.

[0003] In the existing technology, the use of traditional alkaline activators only accelerates hydration by increasing pH value, but easily leads to concentrated early hydration heat release, causing microcracks. Although the sulfate activator can promote the generation of ettringite, it cannot dynamically control the Ca 2+ Concentration, resulting in the later strength reduction, and the existing activators cannot accurately release active ions according to the temperature change in the cement hydration process, resulting in insufficient utilization of the activity of the mineral powder and ignoring the synergistic optimization of the toughness and durability of the cement-based material.

[0004] In summary, there is an urgent need for an environment-friendly mineral powder mixed cement that can simultaneously solve the problems of efficient activation of mineral powder and accurate control of the hydration process, and realize the dual goals of efficient resource utilization and product performance optimization. SUMMARY

[0005] The purpose of the present application is to make up for the shortcomings of the prior art, and provide a preparation method of an environment-friendly mineral powder mixed cement. The method can generate abundant carbonation active sites on the surface of the mineral powder and change its crystal structure through the synergistic effect of CO2 partial pressure reaction grinding and gradient heat activation, thereby providing sufficient reaction basis for the subsequent hydration reaction. The temperature-sensitive phase change microcapsules in the composite activator release Ca 2+ , which together with the nano-geopolymer precursor and basic magnesium sulfate whiskers, induces the generation of carbonated tobermorite and magnesium silicate gel hydration products. These products interweave to form a dense network structure, which not only enhances the internal bonding force of the cement stone, but also optimizes the pore structure, so that the cement has excellent mechanical properties and durability.

[0006] The present application provides the following technical solution to solve the above technical problems: a preparation method of an environment-friendly mineral powder mixed cement, the specific steps of which are as follows: S100, multi-source synergistic pretreatment of mineral powder: mix blast furnace slag, calcined coal gangue and iron-containing tailings in a mass ratio of 4:3.5:2.5, and place them in a CO2 partial pressure reaction grinding machine to form a multi-source synergistic pretreated mineral powder; S200, gradient thermal activation: the obtained mineral powder is treated in a variable temperature fluidized bed in stages to form a gradient thermal activated mineral powder; S300, intelligent activator synthesis: a composite activator is prepared, and the two are dispersed in a modified lignin solution by an ultrasonic field; S400, dynamic gradient compounding: 40%-50% of low calcium silicate clinker, 2.5% of phosphogypsum, and 45-55% of gradient thermal activated mineral powder are jointly fed into a vortex resonance mixer, and the composite activator is sprayed in four stages to form a dynamic gradient compounded mixture; S500, post-activation treatment: the dynamic gradient compounded mixture is aged while an alternating magnetic field of 0.5T is applied, with a magnetic field frequency of 10 kHz, to induce directional growth of hydrated crystal nuclei, thereby obtaining an environmentally friendly mineral powder blended cement product.

[0007] Further, the CO2 partial pressure reaction grinder in S100 is built-in carbonation catalyst, and the grinding is carried out under a CO2 atmosphere of 0.15-0.3 MPa to a specific surface area of ≥600 m² / kg, thereby realizing carbonation and mechanical activation simultaneously.

[0008] Further, the staged treatment process in S200 is as follows: Raising the temperature to 180°C at a rate of 10°C / min and keeping it for 10 min to remove water and small molecular impurities in the mineral powder; Raising the temperature to 260°C at a rate of 5°C / min and keeping it for 15 min to activate the mineral powder.

[0009] Further, the composite activator includes inorganic components and organic components, wherein: The inorganic components are composed of nano-geopolymer precursors and basic magnesium sulfate whiskers, the nano-geopolymer precursors are fly ash-based geopolymer precursors with a SiO2 / Al2O3 molar ratio of 3.2, accounting for 1.2% of the total mass of the composite activator, and the basic magnesium sulfate whiskers account for 0.8% of the total mass of the composite activator. The organic component is temperature-sensitive phase change microcapsules loaded with Ca2+, accounting for 2.5% of the total mass of the composite activator.

[0010] Further, the low calcium silicate clinker in S400 has a mineral composition of: 40%-50% of C2S, 25%-35% of C3S, 4%-6% of C3A, and 10%-15% of C4AF.

[0011] Further, the composite activator in S400 is sprayed in four stages, and the specific timing control is as follows: Stage 1: low-speed mixing at 300 rpm within 0 to 120 seconds after the start of mixing, and simultaneously spraying 40% of the total amount of the activator to form an initial dispersion system; Stage 2: During 120-240 seconds, the rotation speed is increased to 500 rpm, 30% of the total amount of activator is sprayed to strengthen the shear dispersion and preliminary hydration of the material; Stage 3: During 240-360 seconds, the rotation speed is reduced to 300 rpm, 20% of the total amount of activator is sprayed to promote the interface reaction between the activator and the mineral particles; Stage 4: During 360-480 seconds, the low-speed stirring of 150 rpm is maintained, and the remaining 10% of the activator is sprayed to complete the construction of the gradient concentration field.

[0012] Further, the S500 is aged at 50℃, 85%RH for 24h.

[0013] Further, the mineral composition of the environmentally friendly mineral powder blended cement in the S500 comprises: C2S 20%-30%, C3S 15%-25%, carbonated calcium silicate 8%-12%, and magnesium silicate gel 15%-20%.

[0014] Compared with the prior art, the preparation method of the environmentally friendly mineral powder blended cement has the following beneficial effects: I. The present application generates abundant carbonated active sites on the surface of the mineral powder and changes its crystal structure through the synergistic effect of CO2 partial pressure reaction, grinding and gradient thermal activation, providing sufficient reaction basis for subsequent hydration reaction. The temperature-sensitive phase change microcapsules in the composite activator release Ca 2+ , nanogeopolymer precursor and basic magnesium sulfate whisker, inducing the generation of carbonated calcium silicate and magnesium silicate gel hydration products, which interweave to form a dense network structure, not only enhancing the internal bonding force of the cement stone, but also optimizing the pore structure, making the cement have excellent mechanical properties and durability.

[0015] II. The present application can real-time perceive the change of raw material composition, dynamically adjust the mineral powder content and activator ratio, ensure the stability of the production process, and the vortex resonance mixing machine cooperates with the four-stage gradient spraying of the activator to make the activator play a specific role in different stages, from initial dispersion to deep reaction, realizing precise control of the cement hydration process. At the same time, the alternating magnetic field is applied in the post-activation treatment stage to guide the directional growth of the hydration crystal nucleus, further optimizing the microstructure of the cement. This intelligent and dynamic regulation method effectively improves the uniformity of the cement quality, improves the production efficiency, and makes the preparation process more scientific and efficient.

[0016] Additional advantages, objects, and features of the application will be apparent to those skilled in the art upon examination of the following detailed description, it being understood that each of the foregoing general statements are true of the particular embodiments of the application yet the particular embodiments thereof are demonstrative in nature and are not to be taken in a limiting sense. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings required to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0018] Figure 1 A preparation flow chart of a preparation method of an environment-friendly mineral powder mixed cement. DETAILED DESCRIPTION

[0019] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined application purposes, the specific embodiments, structures, features and effects according to the present application will be described in detail below in combination with the drawings and preferred embodiments.

[0020] Embodiment one The present embodiment provides a preparation method of an environment-friendly mineral powder mixed cement, as shown in Figure 1 The method realizes efficient utilization of industrial solid waste and optimization of cement performance by the steps of multi-source collaborative pretreatment, gradient thermal activation, intelligent activator synthesis, dynamic gradient compounding and post-activation treatment, etc. The method realizes the activation of mineral powder by the cooperation of CO2 partial pressure reaction grinding and gradient thermal activation, and accurately controls the hydration process by combining temperature-sensitive phase change microcapsules and four-stage gradient compounding process. The finally prepared cement has excellent mechanical properties and durability, and is suitable for various engineering scenes.

[0021] Firstly, enter the multi-source collaborative pretreatment stage of mineral powder (S100), select blast furnace slag, calcined coal gangue and iron-containing tailings as raw materials, accurately weigh them according to the mass ratio of 4:3.5:2.5, the blast furnace slag needs to meet the requirements of silicon dioxide content ≥32% and aluminum oxide content ≥14%, the calcined coal gangue needs to be calcined at 800°C to remove the crystal water, and the iron content of the iron-containing tailings needs to be controlled at 10%-15% to ensure the activity, and then put the three kinds of raw materials into the CO2 partial pressure reaction grinder, the main body of the equipment is a closed grinding cavity, and a supported ZnO-TiO2 carbonization catalyst (loading amount 6wt%) is built-in, which has a CO2 partial pressure control system and a grinding medium automatic compensation device. After starting the equipment, first introduce CO2 gas with a purity of ≥99%, and make the pressure in the cavity stable at 0.2MPa. In the grinding process, CO2 reacts with calcium and magnesium oxides on the surface of the mineral powder under the action of the catalyst to form active sites such as calcium carbonate, and mechanical grinding refines the mineral powder particles. When the specific surface area of the mineral powder reaches 650m² / kg, stop grinding, and prepare the multi-source collaborative pretreated mineral powder. In this stage, the CO2 partial pressure reaction grinder realizes the mechanical activation of the mineral powder through the synergy of mechanical force and chemical action, and also completes the fixation of CO2, and the utilization rate of CO2 reaches 88% through detection, which lays a foundation for the subsequent reaction.

[0022] Secondly, enter the gradient thermal activation stage (S200), and transport the multi-source collaborative pretreated mineral powder prepared in S100 to a variable-temperature fluidized bed equipment, which is composed of a preheating section, a constant-temperature section and a cooling section, and uses nitrogen as the fluidizing medium, and the gas flow rate is controlled at 1.5m / s to ensure uniform suspension of the mineral powder. After starting the equipment, increase the bed temperature to 180°C at a rate of 10°C / min, and keep it for 10min. The main purpose of this stage is to remove the residual moisture in the mineral powder (moisture content reduced to below 0.5%) and the adsorbed small molecular impurities, so as to avoid their adverse effects on the subsequent hydration reaction. After the heat preservation is completed, adjust the heating rate to 5°C / min, continue to heat to 260°C and keep it for 15min, and stimulate the activity of the mineral powder. Under the condition of 260°C, the crystal structure of the mineral powder will change, so that the active ingredients in the mineral powder can be released, thereby improving the reaction activity of the mineral powder. The gradient thermal activation process avoids the sintering of the mineral powder surface caused by direct high temperature through segmented temperature control, ensures the effective stimulation of the activity, and provides a more active material basis for the subsequent reaction with the activator.

[0023] Then, enter the intelligent activator synthesis stage (S300), and prepare a composite activator, which is composed of inorganic components and organic components. The inorganic components include nano-geopolymer precursor and basic magnesium sulfate whisker, wherein the nano-geopolymer precursor is a fly ash-based geopolymer precursor with a SiO2 / Al2O3 molar ratio of 3.2, accounting for 1.2% of the total mass of the composite activator, and the basic magnesium sulfate whisker accounts for 0.8% of the total mass. The organic component is Ca2+ The temperature-sensitive phase change microcapsules of the application have a total mass of 2.5%, and such components are selected to achieve precise regulation of the hydration process of the mineral powder. The nanogeopolymer precursor has good activity and can provide silicon, aluminum and other elements during the hydration process to participate in the formation of hydration products. The basic magnesium sulfate whisker can enhance and toughen the cement and improve the mechanical properties of the cement. The temperature-sensitive phase change microcapsules of the application can dynamically release Ca 2+ 2+ When the cement hydration is heated to 45℃, the microcapsules undergo phase change and release Ca 2+ , thereby regulating the Ca 2+ concentration in the hydration environment and promoting the hydration reaction. The composite activator is dispersed in the modified lignin solution by the ultrasonic field. The ultrasonic field uniformly disperses the activator particles and avoids agglomeration, thereby better playing the role of the activator. The modified lignin solution not only uniformly disperses the activator but also has a positive impact on the performance of the cement, thereby laying a foundation for precise regulation of the hydration process.

[0024] Subsequently, the dynamic gradient compounding stage (S400) is entered, in which 40%-50% of low-calcium silicate clinker, 2.5% of phosphogypsum and 45-55% of gradient thermal activated mineral powder are jointly fed into a vortex resonance mixer. The mineral composition of the low-calcium silicate clinker is 40%-50% of C2S, 25%-35% of C3S, 4%-6% of C3A and 10%-15% of C4AF, which can provide the basic strength and other properties of the cement. The phosphogypsum can adjust the setting time of the cement and participate in the hydration reaction. The vortex resonance mixer can produce strong vortex and resonance during the mixing process, thereby realizing uniform mixing and sufficient contact of the materials. The mixer adopts a double-frequency vibration superposition technology (main frequency 25 kHz and auxiliary frequency 18 kHz) with a vibration power density of 0.9 W / cm². The mixer is started and pre-mixed at a speed of 300 rpm for 60 seconds to preliminarily disperse the materials. Then, the four-stage dynamic injection of the composite activator is entered: Stage 1: Within 0-120 seconds after the start of mixing, the speed is maintained at 300 rpm, and 40% of the total amount of the activator is synchronously injected by a metering pump. At this time, the low-speed mixing cooperates with the initial injection of the activator to uniformly wrap the activator around the material particles to form an initial dispersion system. Stage 2: Within 120-240 seconds, the speed is increased to 500 rpm, and 30% of the total amount of the activator is injected. The strong shear force generated by the high speed makes the activator fully contact with the materials and promotes the preliminary hydration reaction of the nanogeopolymer precursor and the surface of the mineral powder to form an early hydration induction layer. ​Stage 3: During 240-360 seconds, the speed is reduced to 300 rpm, and 20% of the total amount of activator is sprayed. At this time, the speed is reduced, and the residence time of the material in the mixer is increased, which is beneficial to the deep interface reaction between the activator and the mineral particles. The basic magnesium sulfate whisker starts to play a crystal nucleus induction role, promoting the ordered growth of the hydration product. Stage 4: During 360-480 seconds, the low-speed stirring of 150 rpm is maintained, and the remaining 10% of the activator is sprayed. Under low-speed stirring, the activator forms a gradient concentration field in the mixture, and the temperature-sensitive phase change microcapsules are uniformly distributed in the system, preparing for the release of Ca²⁺ when the temperature rises during subsequent hydration. During the entire compounding process, the dual-frequency vibration of the vortex resonance mixer effectively breaks the material agglomeration, ensuring micron-level dispersion. Through this four-stage dynamic spraying of activator, the amount and effect of the activator can be precisely controlled according to different stages of mixing and reaction, achieving dynamic regulation of the cement hydration process.

[0025] Finally, enter the post-activation processing stage (S500), and transfer the dynamic gradient compounding mixture prepared in S400 to the aging device. Set the aging environment to 50°C, 85% RH, and apply an alternating magnetic field of 0.5T and frequency of 10kHz. During the aging process, the temperature of 50°C promotes the temperature-sensitive phase change microcapsules to reach the phase change point, causing volume phase change and releasing Ca(NO3)2・4H2O. The release rate of Ca²⁺ is 0.3mmol / (g・min), providing additional calcium source for the hydration reaction. The humidity of 85% ensures the water needed for cement hydration, promoting the continuous hydration reaction. The application of alternating magnetic field produces directional induction effect on the crystal growth of cement hydration products, affecting ion migration and crystal orientation through Lorentz force, making the hydration nucleus grow in the direction of the magnetic field. After 24h of aging, the cement product is detected, and the content of carbonated calcium silicate in the hydration product reaches 10%, and the content of magnesium silicate gel reaches 18%. Scanning electron microscopy shows that the hydration product forms a dense network structure that interweaves with each other, with a porosity reduction of 20% and an average pore size of less than 20nm. Through post-activation processing, the final environmentally friendly mineral powder blended cement product is obtained, which contains 20%-30% C2S, 15%-25% C3S, 8%-12% carbonated calcium silicate, and 15%-20% magnesium silicate gel. These mineral compositions together determine the excellent performance of the cement.

[0026] In summary, the strength test of the prepared environment-friendly mineral powder blended cement is carried out, the 3-day compressive strength reaches 28 MPa, the 28-day compressive strength reaches 65 MPa, the hydration heat is determined by the adiabatic calorimetry method, the 28-day hydration heat is 210 kJ / kg, the fluidity is tested, the initial fluidity is 240 mm, the fluidity retention value after 30 minutes is 220 mm, at the same time, the chloride ion penetration resistance is determined, the chloride ion binding capacity is 1.6 mmol / g, the pore structure is determined by the mercury intrusion method, the total porosity is 18%, the harmless pore (<20 nm) accounts for 60%, and the hydration heat is low, the chloride ion penetration resistance is strong, and it is suitable for harsh environments such as mass concrete engineering.

[0027] Example two The embodiment provides a preparation method of an environment-friendly mineral powder blended cement, which aims to verify the adaptability of the technical scheme under the raw material ratio fine tuning and specific engineering requirements, and to prepare a cement product suitable for marine concrete structure.

[0028] S100, multi-source synergistic pretreatment of mineral powder: blast furnace slag, calcined coal gangue and iron-containing tailings are mixed in a mass ratio of 3.5:4:2.5, wherein the silica content of the blast furnace slag is ≥33%, the alumina content is ≥15%, the calcined coal gangue is treated by calcination at 850°C, and the iron content of the iron-containing tailings is controlled to be 12%-14%. The raw materials are put into a CO2 partial pressure reaction grinder, a built-in supported ZnO-TiO2 carbonization catalyst (loading amount 7wt%) is arranged inside, CO2 is introduced to stabilize the pressure in the cavity at 0.25 MPa, and grinding is performed until the specific surface area of the mineral powder reaches 680 m² / kg, and the CO2 utilization rate reaches 89%, thereby preparing a multi-source synergistic pretreated mineral powder.

[0029] S200, gradient thermal activation: the pretreated mineral powder is conveyed to a variable temperature fluidized bed, nitrogen is used as the fluidizing medium, and the gas flow rate is 1.5 m / s. First, the temperature is raised to 185°C at a rate of 10°C / min and kept for 12 min, and then the temperature is raised to 270°C at a rate of 5°C / min and kept for 13 min, thereby removing impurities and exciting the activity of the mineral powder, and completing the gradient thermal activation.

[0030] S300, synthesis of intelligent activator: a composite activator is prepared, the nano geopolymer precursor (SiO2 / Al2O3=3.2) accounts for 1.3% in the inorganic component, the basic magnesium sulfate whisker accounts for 0.7%, the temperature-sensitive phase change microcapsule loaded with Ca²⁺ accounts for 2.4% in the organic component, and is dispersed in the modified lignin solution by ultrasonic field.

[0031] S400, dynamic gradient compounding: 42% low-calcium silicate clinker (C2S 42%, C3S 30%, C3A 5%, C4AF 13%), 2.5% phosphogypsum, 50% gradient thermal activated slag are put into a vortex resonance mixer (main frequency 26 kHz, auxiliary frequency 19 kHz, vibration power density 0.95 W / cm²). After pre-mixing at 300 rpm for 60 seconds, the activator is sprayed in four stages: 0-120 seconds, 40% is sprayed; 120-240 seconds, 30% is sprayed (the speed is increased to 500 rpm); 240-360 seconds, 20% is sprayed (the speed is reduced to 300 rpm); 360-480 seconds, the remaining 10% is sprayed (the speed is maintained at 150 rpm), to achieve uniform mixing of the materials and gradient effect of the activator.

[0032] S500, post-activation treatment: the mixed material is placed in an environment of 52°C and 86% RH, and is aged for 24 hours under an alternating magnetic field of 0.5T and 10 kHz. The content of carbonated calcium silicate in the hydration product of the finished cement reaches 11%, and the content of magnesium silicate gel reaches 19%.

[0033] Performance test: 3-day compressive strength 29 MPa, 28-day compressive strength 68 MPa; 28-day hydration heat 205 kJ / kg; initial fluidity 245 mm, retention value after 30 minutes 225 mm; chloride ion binding capacity 1.7 mmol / g, total porosity 17%, harmless pore ratio 62%, suitable for marine concrete structures, resistant to chloride ion erosion.

[0034] Example Three This example focuses on improving the early strength of cement, and by optimizing the ratio of activator and process parameters, an environmentally friendly mineral powder blended cement suitable for rapid construction scenarios is prepared.

[0035] S100, multi-source synergistic pretreatment of mineral powder: blast furnace slag, calcined coal gangue, and iron-containing tailings are mixed in a mass ratio of 4.5:3:2.5, and the raw materials meet the corresponding quality requirements. In the CO2 partial pressure reaction grinder, the raw materials are ground to a specific surface area of 620 m² / kg under a CO2 pressure of 0.18 MPa, and the CO2 utilization rate is 87%, obtaining pretreated mineral powder.

[0036] S200, gradient thermal activation: a variable temperature fluidized bed is used to heat to 175°C at a rate of 10°C / min and maintain for 8 min, then heat to 250°C at a rate of 5°C / min and maintain for 16 min, to complete the gradient thermal activation of the mineral powder.

[0037] S300, intelligent activator synthesis: adjust the ratio of composite activator, nano-geopolymer precursor accounts for 1.4%, basic magnesium sulfate whisker accounts for 0.6%, and Ca²⁺ loaded temperature-sensitive phase change microcapsule accounts for 2.6%, which is dispersed in modified lignin solution by ultrasonic.

[0038] S400, dynamic gradient compounding: 38% low-calcium silicate clinker (C2S 43%, C3S 28%, C3A 6%, C4AF 13%), 2.5% phosphogypsum, 55% gradient thermal activated mineral powder are put into a vortex resonance mixer (main frequency 24 kHz, auxiliary frequency 18 kHz, vibration power density 0.85 W / cm²). After premixing, the activator is sprayed in four stages, and the speed change is controlled to realize the full reaction of the material.

[0039] S500, post-activation treatment: in a 50°C, 85% RH environment, apply a 0.5T, 10kHz alternating magnetic field for 24h. The content of carbonated calcium silicate in the hydration product of the finished cement is 9%, and the content of magnesium silicate gel is 17%.

[0040] Performance test: 3-day compressive strength 31MPa, 28-day compressive strength 63MPa; 28-day hydration heat 215kJ / kg; initial fluidity 235mm, 30min retention value 215mm; chloride ion binding capacity 1.5mmol / g, total porosity 19%, harmless pore ratio 58%, meeting the demand of rapid construction for early strength.

[0041] Comparative example The comparative example uses a traditional process to prepare mineral powder blended cement, which is used to verify the advantages of the technical scheme of the present application in improving the performance of cement and environmental benefits. The traditional process does not use the multi-source collaborative pretreatment, intelligent activator synthesis and dynamic gradient compounding technology of the present application. The specific steps are as follows: Raw material preparation: the same blast furnace slag, calcined coal gangue and iron-containing tailings as in Example 1 are selected and mixed in a mass ratio of 4:3.5:2.5, but only mechanical grinding is performed by a common ball mill without CO2 partial pressure treatment and gradient thermal activation. The specific surface area of the ground mineral powder is only 450m² / kg, which is much lower than 650m² / kg of Example 1. The selection standards of low-calcium silicate clinker and phosphogypsum are the same as those of Example 1.

[0042] Preparation of activator: single industrial-grade sodium sulfate is used as the activator instead of the composite intelligent activator of the present application, and the addition amount is 1.5% of the total mass of cement. The activator does not have temperature-sensitive regulation and multi-component synergistic activation capability.

[0043] Mixing process: the mineral powder (45%), low-calcium silicate clinker, phosphogypsum (2.5%) and sodium sulfate activator are directly put into a common double-shaft mixer for one-time mixing at 200rpm for 5 minutes, without using a vortex resonance mixer and a four-stage gradient compounding process, which is difficult to achieve micro-uniform dispersion of the material and precise action of the activator.

[0044] Post-processing: the mixture is cured for 24h at natural environment (25℃, 60%RH), without applying alternating magnetic field and precise temperature and humidity control, which cannot induce the directional growth of hydration crystal nucleus and regulate the structure of hydration products.

[0045] Compared with Example 1, the traditional process adopted in the comparative example has the problems of insufficient activation of mineral powder, single activator, and rough mixing process, resulting in low early strength of cement, high hydration heat, poor fluidity, and insufficient durability, which is specifically manifested as: 3-day compressive strength is 10MPa lower, 28-day hydration heat is 110kJ / kg higher, chloride ion binding capacity is decreased by 37.5%, and total porosity is increased by 55.6%. The comparison fully verifies that the technology of multi-source synergistic pretreatment, intelligent activator, and dynamic gradient compounding can significantly improve the comprehensive performance and environmental protection benefits of cement.

[0046] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present application. Any modification, equivalent change and modification of the above embodiments made in accordance with the technical essence of the present application still fall within the scope of the technical solution of the present application.

Claims

1. A method for preparing environmentally friendly mineral powder-blended cement, characterized in that: The specific steps of this method are: S100, multi-source synergistic pretreatment of mineral powder: blast furnace slag, calcined coal gangue, and iron-containing tailings are mixed in a mass ratio of 4:3.5:2.5, and placed in a CO2 partial pressure reaction grinder to form multi-source synergistic pretreated mineral powder; S200, gradient thermal activation: treating the obtained mineral powder in stages in a variable temperature fluidized bed to form gradient thermally activated mineral powder; S300, intelligent stimulant synthesis: preparing a composite stimulant, wherein the composite stimulant includes an inorganic component and an organic component, and dispersing the inorganic component and the organic component in a modified lignin solution through an ultrasonic field; S400, dynamic gradient compounding: 40%-50% low-calcium silicate clinker, 2.5% phosphogypsum and 45-55% gradient thermally activated mineral powder are put into a vortex resonance mixer, and the composite activator is sprayed in four stages to form a dynamic gradient compound mixture; S500, post-activation treatment: aging the dynamic gradient compound mixture, and applying a 0.5T alternating magnetic field with a magnetic field frequency of 10kHz to induce the directional growth of hydration nuclei, thereby obtaining an environmentally friendly mineral powder-blended cement product.

2. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: The CO2 partial pressure reaction grinder in S100 has a built-in carbonization catalyst and grinds the product to a specific surface area of ​​≥600 m² / kg in a CO2 atmosphere of 0.15-0.3 MPa.

3. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: The segmentation process in S200 is as follows: Raise the temperature to 180°C at a rate of 10°C / min and keep it at that temperature for 10 minutes to remove the residual moisture and small molecular impurities in the mineral powder; The temperature was raised to 260°C at 5°C / min and kept for 15 min to stimulate its activity.

4. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: The composite activator comprises an inorganic component and an organic component, wherein: The inorganic component consists of a nano geopolymer precursor and basic magnesium sulfate whiskers. The nano geopolymer precursor is a fly ash-based geopolymer precursor with a SiO2 / Al2O3 molar ratio of 3.2, accounting for 1.2% of the total mass of the composite activator, and the basic magnesium sulfate whiskers account for 0.8% of the total mass of the composite activator. The organic component is Ca-loaded 2+ The thermosensitive phase change microcapsules account for 2.5% of the total mass of the composite activator.

5. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: The mineral composition of the S400 low-calcium silicate clinker is: 40%-50% C2S, 25%-35% C3S, 4%-6% C3A, and 10%-15% C4AF.

6. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: The S400 dynamically injects the composite exciter in four stages, with the specific timing control being: Stage 1: From 0 to 120 seconds after the start of mixing, mix at a low speed of 300 rpm and simultaneously spray 40% of the total amount of activator to form an initial dispersion system; Phase 2: From 120 to 240 seconds, increase the speed to 500 rpm and inject 30% of the total activator; Stage 3: From 240 to 360 seconds, reduce the speed to 300 rpm and inject 20% of the total stimulant; Stage 4: From 360 seconds to 480 seconds, maintain low-speed stirring at 150 rpm and spray the remaining 10% of the stimulant to complete the construction of the gradient concentration field.

7. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: In the S500 , the dynamic gradient compounded mixture is aged for 24 hours at 50° C. and 85% RH.

8. The method for preparing an environmentally friendly mineral powder-blended cement according to claim 1, characterized in that: The mineral composition of the environmentally friendly mineral powder mixed with cement in the S500 includes: C2S 20%-30%, C3S 15%-25%, carbonated calcium silicate 8%-12%, and magnesium silicate gel 15%-20%.

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