Early strength agent, its preparation method and application

Abstract

This invention relates to an early-strength agent, its preparation method, and its application, and relates to the field of building materials technology. It solves the problems of low early-stage strength, slow setting and hardening, insufficient later-stage strength, and the inability to simultaneously achieve early-stage strength, later-stage mechanical properties, and CO2 adsorption and conversion in traditional solid waste cementitious materials. The preparation steps of the early-strength agent provided by this invention include: dissolving a high-calcium component in water and stirring the mixture, centrifuging, and collecting the supernatant; adding desulfurized gypsum, triethanolamine, silica fume, and aluminate cement to the supernatant, stirring, and adjusting the pH; subjecting the mixture to a first hydrothermal reaction to form a high-calcium silica-alumina silica composite precursor phase; ultrasonically dispersing, filtering, and drying the filter residue; mixing the filter residue with the CO2 capturing component uniformly, performing a first grinding treatment, subjecting the mixed particles to a second hydrothermal reaction, drying, sieving, performing a second grinding treatment, and centrifuging the mixed particles to obtain the early-strength agent, which can be applied to concrete structures and green building materials.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to an early strength agent, its preparation method, and its application. Background Technology

[0002] Currently, solid waste cementitious materials are receiving increasing attention in research and engineering applications as an important approach to green building materials and the resource utilization of industrial waste. These materials primarily use industrial byproducts such as granulated blast furnace slag, fly ash, steel slag, stainless steel slag, and desulfurization gypsum as raw materials. Through hydration reactions, they form C–S–H (calcium silicate hydrate) or C–A–S–H (calcium aluminum silicate hydrate) gels, offering advantages such as low carbon footprint, energy saving, and resource recycling, significantly reducing cement clinker usage and carbon emissions. However, due to the slow dissolution rate of active Ca, Si, and Al components and the high stability of the glassy structure in solid waste raw materials, solid waste cementitious materials generally suffer from problems such as low early strength, slow setting and hardening, and insufficient later-stage strength. Especially when compared with P·O42.5 silicate cement, its initial setting time usually exceeds 20 hours, and its 3-day compressive strength is only 7-12 MPa, which is far below the requirements for engineering construction. This leads to a longer construction period and insufficient early load-bearing capacity of the structure, which seriously restricts its promotion and application in the fields of road base, mine filling and building structure.

[0003] To address the aforementioned issues, researchers attempted to introduce early-strength agents to accelerate the hydration process of solid waste cementitious systems. Early-strength agents, as important additives promoting the early reaction of cementitious materials, are widely used in traditional cement systems. Common early-strength agents include inorganic salts and organic amines. Inorganic salt early-strength agents (such as calcium chloride, calcium nitrate, and calcium nitrite) can rapidly release soluble calcium ions, accelerating the hydration of C3S and C2S minerals and significantly shortening the initial and final setting times, exhibiting good early-strength effects in ordinary Portland cement systems. Organic amine early-strength agents (such as triethanolamine and diisopropanolamine) work by reacting with Ca... 2+These early-strength agents form complexes and regulate the charge distribution at the hydration interface, promoting the directional deposition of hydration products and thus improving early mechanical properties. The effectiveness of these early-strength agent systems is primarily based on the high reactivity of C3S and C2S in silicate clinker systems. However, the main active components in solid waste raw materials are primarily glassy or inert minerals, especially Ca, Si, and Al, whose reactivity is far lower than that of clinker minerals. Hydration reactions are limited by surface dissolution and ion diffusion, preventing traditional early-strength agents from effectively triggering the dissolution and polymerization of potential active phases in the solid waste cementitious system. Furthermore, the chemical environment of the solid waste system is characterized by high alkalinity, high sulfate concentration, and high aluminum ion concentration. These complex ionic environments alter the chemical equilibrium behavior of early-strength agents. Even though existing technologies propose improving the dosage of early-strength agents or adjusting the water-cement ratio to shorten the initial setting time of solid waste cementitious materials to some extent, this often comes at the cost of sacrificing later strength and volume stability. It is difficult to simultaneously achieve early strength, later mechanical properties, and long-term structural stability, and it lacks the ability to regulate the micro- and nano-structure of the solid waste system and continuously release active ions. Furthermore, existing early-strength agents primarily focus on increasing the hydration reaction rate, neglecting the regulation of the system's carbon cycle and CO2 adsorption and conversion behavior. This is especially true for commonly used inorganic salt-based early-strength agents (such as chlorides and nitrates), which rapidly release Ca2+. 2+ It can promote hydration, but it will disrupt the formation equilibrium of the carbonate phase in the system, which will greatly reduce the number of active sites in the hydration products that can react with CO2.

[0004] Therefore, developing an early-strength agent that provides high early and late-stage strength and rapid setting for solid waste cementitious materials is essential to improve the early and long-term strength of solid waste cementitious materials, expand their engineering application scope, and meet the development needs of green and low-carbon building materials. Summary of the Invention

[0005] To address the problems of low early strength, slow setting and hardening, and insufficient later strength in traditional solid waste gelling materials, as well as the inability of early-strength agents to simultaneously achieve early strength, later mechanical properties, carbon cycling, and CO2 adsorption and conversion in solid waste gelling materials, this invention proposes an early-strength agent, its preparation method, and its application. The technical solution of this invention is as follows: An early strength agent, comprising the following components by mass parts: 40-60 parts high-calcium component, 10-20 parts silica fume, 15-25 parts aluminate cement, 5-10 parts desulfurized gypsum, 0.5-2 parts triethanolamine, and 5-20 parts CO2 capturing component; The high-calcium component includes 25-35 parts quicklime and 15-25 parts carbide slag; the CO2 capturing component includes 3-12 parts nano-calcium carbonate and 2-8 parts magnesium carbonate.

[0006] A method for preparing the above-mentioned early strength agent includes the following preparation steps: The high-calcium component is dissolved in water and stirred to react. After centrifugation, the supernatant is collected. Desulfurized gypsum, triethanolamine, silica fume, and aluminate cement are added to the supernatant, stirred, and the pH is adjusted. The mixture undergoes a first hydrothermal reaction to form a high-calcium silicon-aluminum-silicon composite precursor phase. The mixture is then ultrasonically dispersed, filtered, and the filter residue is dried. The filter residue is mixed evenly with the CO2 capturing component and subjected to a first grinding treatment. The mixed particles undergo a second hydrothermal reaction, are dried, sieved, and subjected to a second grinding treatment. The mixed particles are then graded and centrifuged to obtain the early-strength agent.

[0007] Furthermore, the stirring time is 15-30 min, and the stirring speed is 1500-1800 rpm; the centrifugation speed is 3000-5000 rpm, and the centrifugation time is 10-15 min; the pH adjustment is performed using 1.0 mol·L⁻¹. -1 The pH is adjusted to 13.5-14.5 using an aqueous sodium hydroxide solution.

[0008] Furthermore, the temperature of the first hydrothermal reaction is 120~160℃, and the hydrothermal reaction time is 3~5 h.

[0009] Furthermore, the ultrasonic dispersion time is 10-20 min; the drying temperature is 60-80℃; and the drying time is 1-3 h.

[0010] Furthermore, the first grinding process involves mixed ball milling using grinding media balls with diameters of 10 mm and 3 mm. The 10 mm diameter grinding media balls comprise 50%–70% of the total ball weight, and the 3 mm diameter grinding media balls comprise 30%–50% of the total ball weight. This ensures that the 10 mm grinding media balls provide low-frequency impact, while the 3 mm grinding media balls provide high-frequency friction to form particles of different sizes. The mass ratio of grinding media balls to material is 6:1–8:1. The ball milling speed is 300–600 rpm. The first grinding time is 30–120 min, followed by uniform mixing and further grinding for another 30–120 min. The particle size of the particles in the first grinding process is a mixture of 10–20 μm and 3–10 μm.

[0011] Furthermore, the temperature of the second hydrothermal reaction is 120~150℃; the time of the second hydrothermal reaction is 4~12 h.

[0012] Furthermore, the sieve aperture size of the sieve is 10 μm, retaining particles with a diameter of 10~20 μm, and the particles with a diameter <10 μm are subjected to a second grinding process; The second grinding process involves ball milling with grinding media balls of 1 mm and 0.3 mm diameters, wherein the 1 mm diameter grinding media balls account for 70%–80% of the total ball mass, and the 0.3 mm diameter grinding media balls account for 20%–30% of the total ball mass; the mass ratio of grinding media balls to material is 10:1–15:1; the second grinding process takes 30–120 min; the rotational speed is 60–100 rpm; and the particle size in the second grinding process is 0.5–10 μm. The centrifugation speed is 2000~4000 rpm, and particle size stratification is achieved by the difference in the sedimentation rate of particles in the centrifugal field. After centrifugation, particles with a particle size of 0.5~2 μm are used as early rapid reaction components, particles with a particle size of 3~10 μm are used as mid-term structurally stable components, and particles with a particle size of 10~20 μm retained in the sieving step are used as late-term strength retention components, forming a three-order particle size distribution structure.

[0013] One application of the aforementioned early-strength agent is in the fields of concrete structures and green building materials.

[0014] Furthermore, it can be applied to the preparation of solid waste cementitious materials.

[0015] Compared with existing technologies, this invention solves the problems of low early strength, slow setting and hardening, insufficient later strength, and the inability of early strength agents to simultaneously address the early strength, later mechanical properties, carbon cycling, and CO2 adsorption and conversion of solid waste gel materials. Specific beneficial effects include: 1. This invention employs a two-step ball milling and graded centrifugation process to form a three-tiered particle size distribution structure of 0.5~2 μm, 3~10 μm, and 10~20 μm for the early-strength agent. This allows the early-strength agent to participate in the hydration reaction simultaneously at different scales within the solid waste cementitious material system. Small particles (0.5~10 μm) rapidly dissolve in the early stages of hydration, generating C–S–H gel, C–A–H gel, and AFm crystals, quickly forming a cross-linked crystal network and a three-dimensional network-like initial gel network. Larger particles (10~20 μm) provide structural support as the later-stage strength framework, achieving rapid early strength improvement while maintaining long-term mechanical property stability. The Ca of the solid waste cementitious material with added early-strength agent... 2+ SiO4 4- and AlO4 5-The ion dissolution rate is significantly accelerated. The early strength agent stimulates the depolymerization ability of solid waste masterbatch through particle size classification and microstructure optimization, significantly shortening the setting and hardening time (4.0~4.5h), effectively increasing the 3-day compressive strength (reaching 22~26 MPa), while maintaining the 28-day compressive strength to the maximum extent (46~50MPa). The early strength agent provided by this invention meets the requirements of rapid demolding and early construction.

[0016] 2. The early-strength agent provided by this invention introduces nano-calcium carbonate and magnesium carbonate as CO2 capturing components, providing nucleation sites during hydration. Through the adsorption of water and ions in the porous microstructure system, it promotes the carbonation reaction and the production of Ca. 2+ This combination enhances CO2 adsorption and fixation capacity, effectively increasing the specific surface area of ​​solid waste cementitious materials (70~75 m²). 2 The early-strength agent exhibits a uniform pore structure, effectively accelerating ion migration and reaction rates within the system, significantly improving the carbon recycling efficiency of solid waste cementitious materials, and providing technical support for green building materials and carbon neutrality applications.

[0017] 3. This invention utilizes the synergistic effect of early-strength agents and solid waste masterbatches to reduce the content of CaO, SiO2, Al2O3, and Na in the solid waste masterbatches. + Key elements dissolve rapidly in the early stages of hydration, and the coordination number of AlO4 tetrahedra gradually rearranges to enter the gel backbone, forming a high-density cross-linked structure. Na... + Alkali metal ions further promote the dissolution and repolymerization of the Si–O–Al framework. This mechanism accelerates the formation and polymerization rate of C–S–H and C–A–H gel networks, significantly improving the early strength development speed of solid waste cementitious materials, while ensuring long-term strength stability for 28 days. This overcomes the technical bottleneck in existing technologies where early strength agents cannot simultaneously achieve rapid early hardening, long-term mechanical properties, and carbon fixation capacity.

[0018] 4. The preparation process of this invention is simple and energy-efficient. The material's structure and performance can be controlled and constructed using only conventional wet mixing, ball milling dispersion, graded centrifugation, and standard wet curing. It has low equipment requirements, strong process compatibility, and meets the requirements of large-scale industrial production. Furthermore, the raw materials used in this invention (slag, fly ash, steel slag, desulfurized gypsum, and nano-carbonates) are all industrial solid waste or byproducts, sourced environmentally friendly and cost-controllable. This further enhances the added value of the material based on existing solid waste utilization, enabling the efficient conversion of CaO, SiO2, and Al2O3 in the solid waste, truly achieving the synergistic utilization of "waste-to-solid waste". In addition, the byproduct emissions from the preparation process of this invention are extremely low, generating no additional industrial wastewater, waste residue, or volatile organic gases, achieving clean production. This provides a scalable, replicable, and long-term applicable process route and industrialization foundation for the resource utilization of solid waste, the development of green building materials, and the implementation of carbon-neutral industries. Attached Figure Description

[0019] Figure 1 A photograph of the actual product of the early-strength agent; Figure 2 These are scanning electron microscope images of the early-strength agent at different magnifications; among them... Figure 2 (a) is a scanning electron microscope image of the early-strength agent at a magnification of 50 μm; Figure 2 (b) is a scanning electron microscope image of the early-strength agent at a magnification of 10 μm; Figure 2 (c) is a scanning electron microscope image of the early strength agent at a magnification of 2 μm; Figure 2 (d) is a scanning electron microscope image of the early strength agent at a magnification of 1 μm; Figure 3 The X-ray diffraction pattern of the early-strength agent is shown; among them, Figure 3 (a) is the X-ray diffraction spectrum of large-particle (10~20 μm) early strength agent; Figure 3 (b) is the X-ray diffraction spectrum of small-particle (0.5~10 μm) early strength agent; Figure 4 Scanning electron microscope images of solid waste cementitious materials incorporating early-strength agents at different hydration reaction times; among them... Figure 4 (a) A scanning electron microscope image of solid waste cementitious material hydrated for 3 h with early strength agent added; Figure 4 (b) is a scanning electron microscope image of solid waste cementitious material hydrated for 24 h with early strength agent added; Figure 4 (c) is a scanning electron microscope image of solid waste cementitious material hydrated for 72 h with early strength agent added. Detailed Implementation

[0020] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0021] Example 1. S1: Dissolve 30 g of quicklime and 20 g of carbide slag in 150 mL of deionized water, and stir at 1600 rpm for 20 min to fully dissolve the quicklime and carbide slag to generate Ca(OH)2 and some Ca. 2+ SiO3 2- Ionic solution. Then centrifuge at 4000 rpm for 10 min, and collect the supernatant; add 8 g desulfurized gypsum, 1 g triethanolamine, 15 g silica fume, and 20 g aluminate cement to the supernatant sequentially, and use 1.0 mol·L⁻¹ solution. -1 The pH was adjusted to 14 with NaOH aqueous solution, and a hydrothermal reaction was carried out at this pH and 140℃ for 4 h to obtain a calcium-silicon-aluminum-silicon composite precursor phase. The precursor phase was separated and precipitated by vacuum filtration, and the filtrate was sampled and stored for ICP determination of the changes in the concentrations of dissolved Ca, Si, Al, and Na ions to establish a dissolution kinetic curve.

[0022] S2: The precursor phase was ultrasonically dispersed for 15 min, filtered, and dried at 70℃ for 2 h to obtain filter residue. 8 g of nano-calcium carbonate and 2 g of magnesium carbonate were added to the filter residue, and the mixture was ball-milled at 400 rpm for 60 min, stirred, and then ball-milled for another 60 min to obtain a mixture of 10-20 μm and 3-10 μm particles. The ball milling was performed using grinding media balls with diameters of 10 mm and 3 mm, with 10 mm diameter grinding media balls accounting for 60% of the total ball weight and 3 mm diameter grinding media balls accounting for 40% of the total ball weight. The mass ratio of grinding media balls to material was 6:1. S3: The mixture was hydrothermally reacted at 130℃ for 6 h to allow the CO2 trapping component to combine with calcium and silicon to form a CaCO3-derived core and a CASH coating layer. After the reaction, it was dried at 70℃ for 2 h. Particles with a diameter of 10-20 μm were retained by sieving. Particles with a diameter <10 μm were ball-milled at 80 rpm for 60 min and then mixed. The ball milling was performed using grinding media balls with diameters of 1 mm and 0.3 mm. The grinding media balls with a diameter of 1 mm accounted for 75% of the total weight of the balls, and the grinding media balls with a diameter of 0.3 mm accounted for 25% of the total weight of the balls. The mass ratio of grinding media balls to material was 12:1. Subsequently, the mixture was centrifuged at 3000 rpm to classify the particles by the difference in the settling rate of the particles in the centrifugal field. After centrifugation, particles with a diameter of 0.5-2 μm were used as the early fast-reaction component, and particles with a diameter of 3-10 μm were used as the intermediate structurally stable component. The 10-20 μm particles retained in the sieving step were... μm particles serve as the component that retains strength in the later stages, forming a three-dimensional particle size distribution structure, such as... Figure 1 The early-strength agent shown.

[0023] Example 2. The difference between this embodiment and Example 1 is that the raw material amounts in S1 are 28 g of quicklime, 17 g of carbide slag, 18 g of aluminate cement, and 7 g of desulfurized gypsum; the amounts in S2 are 11 g of nano-calcium carbonate and 3 g of magnesium carbonate; the hydrothermal reaction temperature in S1 is 150℃ and the hydrothermal reaction time is 5 h; the hydrothermal reaction temperature in S3 is 140℃ and the hydrothermal reaction time is 8 h. The remaining preparation steps and conditions are the same as in Example 1, and an early strength agent is obtained.

[0024] Example 3. The difference between this embodiment and Example 1 is that in S2, ball milling is performed at 500 rpm for 90 min, followed by stirring and ball milling for another 90 min; grinding media balls with a diameter of 10 mm account for 50% of the total ball weight, and grinding media balls with a diameter of 3 mm account for 50% of the total ball mass, with a mass ratio of grinding media balls to material of 7:1; the remaining preparation steps and conditions are the same as in Example 1, resulting in an early strength agent; in S3, the ball milling speed is 70 rpm, the ball milling time is 90 min, and the remaining preparation steps and conditions are the same as in Example 1, resulting in an early strength agent.

[0025] Example 4. The difference between this embodiment and Example 1 is that the hydrothermal reaction temperature in S3 is 150°C, and the hydrothermal reaction time is 12 h; the remaining preparation steps and conditions are the same as in Example 1, resulting in an early-strength agent.

[0026] like Figure 2(ad) shows scanning electron microscope images of the early-strength agent prepared in Example 4 at different magnifications. Figure 2 As can be seen in (a) (50 μm), the early strength agent exhibits a distinct three-dimensional structure with a mixture of large and small particles. The large particles are mainly maintained in the size range of 10–20 μm, exhibiting a relatively regular blocky morphology and well-defined crystal boundaries; while the small particles are mainly concentrated between 0.5–10 μm, with a loose surface structure and a higher proportion of gel phase. Figure 2 (b) (10 μm) Figure 2 (c) (2 μm) and Figure 2 In (d) (1 μm), small particles can be observed to adhere to the surface of large particles, forming a microstructure with complementary and synergistic particle-level structure. This structure not only significantly improves the packing density, pore distribution and ion channel uniformity of the early strength agent material, but also realizes the hierarchical deposition and dynamic migration of calcium, silicon and aluminum ions, laying the foundation for the early strength improvement, mid-term dissolution equilibrium and long-term structural retention of the early strength agent.

[0027] The stratified particles prepared in Example 4 after centrifugation and fractionation were collected and subjected to X-ray diffraction tests, such as... Figure 3 Figures (a) and (b) show the X-ray diffraction spectra of the large-particle (10~20 μm) and small-particle (0.5~10 μm) accelerators prepared in Example 4, respectively. Figure 3 (a) It can be seen that the large-particle early strength agent has obvious high crystallinity characteristics, and its main diffraction peaks correspond to calcite-type CaCO3, Ca(OH)2 and a small amount of C–S–H phase with a high calcium-silicon ratio, respectively. Figure 3 The strong and sharp diffraction peaks shown in (a) prove that the large particles achieved recrystallization and grain growth during the secondary hydrothermal reaction, forming a dense and regular crystal structure. Figure 3 (b) shows that the overall diffraction intensity of the small-particle early-strength agent is low, the peak shape of each crystal phase is significantly broadened, the peak height is reduced, and a typical broad arc-shaped diffuse peak appears in the 2θ=20°~35° region, indicating that this particle size contains a large number of amorphous or quasi-amorphous silica-alumina gel (CASH) structures. Although Figure 3 (b) The diffraction peaks of CaCO3 and Ca(OH)2 are still present, but the peak shapes are more blunt, proving that the small particles are easily dissolved in the hydrothermal stage and redeposited on the surface of the large particles to form an outer porous gel film, thus the proportion of amorphous phase is the highest. This proves that the early strength agent prepared in Example 4 forms a typical gradient structure of mixed distribution of large and small particles in the hydrothermal-deposition-recrystallization process. The large particle component maintains a high content of crystalline phase, while the small particle component is mainly composed of amorphous silica-alumina gel and nano-scale CSH gel, realizing the composite reinforcement effect of synergistic crystal nucleus-gel of the early strength agent.

[0028] The early-strength agents prepared in Examples 1-4 were mixed uniformly with solid waste cementitious masterbatch at a mass ratio of 3:17. The solid waste cementitious masterbatch consisted of granulated blast furnace slag (50%), fly ash (25%), steel slag (15%), and desulfurized gypsum (10%) by mass. Solid waste cementitious masterbatch without early-strength agents was used as a control. During the mixing process, water was added to the system and stirred to carry out the hydration reaction until the slurry had good fluidity and no dry powder lumps. The mixed slurry was then poured into a 40×40×160 mm mold and vibrated on a vibrating table for 2-3 minutes to eliminate pores, making the slurry dense and the surface smooth. After casting, the samples were allowed to stand for 24 hours before demolding and cured at 18-22℃ and relative humidity ≥95%. The final setting time and early strength test were carried out at 4.0-4.5 hours, and 3 days, 7 days, and 28 days were used as early, mid-term, and long-term strength measurement points, respectively.

[0029] like Figure 4 (ac) are scanning electron microscope images of the hydration products of solid waste cementitious materials with added early-strength agents after 3 h, 24 h, and 72 h of hydration, respectively; from Figure 4 As can be seen in (a), when the solid waste coagulation system is hydrated for 3 hours, it is still in the initial stage of reaction. The particles are mainly blocky agglomerates with rough surfaces. The amount of hydration products generated is small, there are many pores, and the overall structure is loose. Figure 4 (b) After 24 hours of hydration, a large number of fine hydration products began to precipitate and accumulate on the particle surface, and a bridging effect gradually formed between the particles, which improved the density of the cementitious material, but some porosity still existed. Figure 4 (c) As shown, after 72 hours of hydration, the cementitious material exhibits a large amount of hydration products that interweave and fill the pores, forming a continuous and dense spatial network. The overall structure tends to be uniform and dense, with a significant reduction in porosity. This demonstrates that the addition of the early-strength agent effectively accelerates the hydration process of the solid waste cementitious material, increases the nucleation rate of early hydration products, and enables a large amount of hydration products to form and rapidly construct a stable and dense structure in a shorter time, thereby significantly improving the early structural strength and overall performance.

[0030] In accordance with the requirements of GB / T 17671-2021 "Test Method for Strength of Cement Mortar" and GB / T 50080-2016 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", the compressive strength, flexural strength, and CO2 constant-pressure adsorption-desorption performance of each sample were tested, and the specific surface area and pore structure were characterized (BET and SEM analysis). The experimental results are shown in Table 1: Table 1

[0031] As can be seen from the table, the solid waste cementitious material prepared using the early-strength agent provided by this invention has a significantly shorter final setting time compared to the control group without the early-strength agent, reaching final setting in 4.0~4.5 h. This proves that the early-strength agent provided by this invention can significantly accelerate the setting of active Ca in the solid waste cementitious system. 2+ SiO4 4- and AlO4 5- The depolymerization and dissolution rates of the components promote the rapid formation of hydration nuclei; simultaneously, the synergistic effect of the high-calcium component and the nano-CO2 trapping component in the early-strength agent, with the high-calcium component providing a large amount of Ca... 2+ Ions accelerate the initial formation of C–S–H and AFt phases, while nano-calcium carbonate / magnesium carbonate, as reactive nuclei, not only provide nucleation sites but also adsorb moisture and ions through microporous structures, further enhancing the system's activity, shortening the setting time, and fulfilling the application requirements of early and rapid hardening. It is especially suitable for the production of green building materials that require rapid demolding or high early strength.

[0032] The early-strength agent provided by this invention significantly improves the 3-day and 28-day strength of solid waste cementitious materials. The 3-day compressive strength reaches 22-26 MPa, almost double that of the control group, while the 28-day strength remains at 46-50 MPa, indicating that the early-strength effect does not come at the expense of long-term strength. This performance improvement is mainly due to the synergistic effect of particle size classification and microstructure optimization achieved by the early-strength agent. This invention obtains a three-tiered particle size distribution of 0.5-2 μm, 3-10 μm, and 10-20 μm through two-step ball milling and graded centrifugation, allowing the hydration reaction to occur simultaneously at different scales. Small particles (0.5-10 μm) dissolve rapidly to form the initial gel, while large particles (10-20 μm) provide structural support for later stages, forming a dense three-dimensional skeletal network, thus achieving a balance between rapid early-strength improvement and long-term structural stability. The flexural strength is simultaneously increased to 5.9-6.5 MPa, proving that the early-strength agent provided by this invention can effectively improve the toughness of cementitious materials, which is beneficial for withstanding bending or localized stress in practical engineering applications.

[0033] Table 1 shows that the BET specific surface area and CO2 adsorption capacity of the solid waste cementitious material prepared using the early-strength agent of this invention are significantly higher than those of the control group, proving that the solid waste cementitious material system has a uniform pore structure, a reasonable micropore / mesopore ratio, and effectively increases the active interface of the solid waste material. This pore structure is due to the combined effect of the microstructure of the early-strength agent and the particle size distribution formed by graded ball milling, which allows the hydration reaction inside the slurry to proceed uniformly, while providing sufficient surface area and adsorption sites for CO2 fixation. In particular, Example 4 shows a typical three-dimensional structure with a mixed distribution of large and small particles. The small particles are attached to the surface of the large particles, which can control the hydration rate of the large particles and achieve the advantage of rapid initial strength generation while maintaining long-term strength. This not only improves the physical properties of the material, but also enhances its CO2 capture and solidification capabilities, providing a technical basis for green building materials and carbon neutrality applications.

[0034] In summary, this invention, through two-step ball milling and graded centrifugation of the early-strength agent, forms a three-tiered particle size distribution structure of 0.5~2 μm, 3~10 μm, and 10~20 μm. This effectively achieves rapid improvement in early strength while maintaining long-term mechanical property stability, significantly shortens the setting and hardening time (4.0~4.5 h), effectively increases the 3-day compressive strength (reaching 22~26 MPa), and maximizes the maintenance of the 28-day compressive strength (46~50 MPa). It significantly improves the early strength development speed of solid waste cementitious materials while ensuring long-term strength stability over 28 days. Furthermore, the introduction of nano-calcium carbonate and magnesium carbonate as CO2-capturing components into the early-strength agent effectively accelerates ion migration and reaction rates within the system, significantly improving the carbon recycling efficiency of solid waste cementitious materials, and providing technical support for green building materials and carbon-neutral applications.

[0035] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An early-strength agent, characterized in that, By mass, it includes the following components: 40-60 parts high-calcium component, 10-20 parts silica fume, 15-25 parts aluminate cement, 5-10 parts desulfurized gypsum, 0.5-2 parts triisopropanolamine, and 5-20 parts CO2 capturing component; The high-calcium component includes 25-35 parts quicklime and 15-25 parts carbide slag; the CO2 capturing component includes 3-12 parts nano-calcium carbonate and 2-8 parts magnesium carbonate. The preparation of the early strength agent includes the following steps: The high-calcium component was dissolved in water and stirred to react. After centrifugation, the supernatant was collected. Desulfurized gypsum, triisopropanolamine, silica fume, and aluminate cement were added to the supernatant, stirred, and the pH was adjusted. The mixture was subjected to a first hydrothermal reaction to form a high-calcium silicon-aluminum-silicon composite precursor phase. The mixture was ultrasonically dispersed, filtered, and the filter residue was dried. The filter residue was mixed evenly with the CO2 capturing component and subjected to a first grinding treatment. The mixed particles were subjected to a second hydrothermal reaction, dried, sieved, and subjected to a second grinding treatment. The mixed particles were then graded and centrifuged to obtain an early-strength agent. The first grinding process involves a mixture of particles with diameters of 10-20 μm and 3-10 μm; the second grinding process involves particles with diameters of 0.5-10 μm.

2. The early-strength agent according to claim 1, characterized in that, The stirring time was 15-30 min, and the stirring speed was 1500-1800 rpm; the centrifugation speed was 3000-5000 rpm, and the centrifugation time was 10-15 min; the pH was adjusted using 1.0 mol·L⁻¹. -1 The pH is adjusted to 13.5-14.5 using an aqueous sodium hydroxide solution.

3. The early-strength agent according to claim 1, characterized in that, The temperature of the first hydrothermal reaction is 120~160℃, and the hydrothermal reaction time is 3~5 h.

4. The early-strength agent according to claim 1, characterized in that, The ultrasonic dispersion time is 10-20 min; the drying temperature is 60-80℃ and the drying time is 1-3 h.

5. The early-strength agent according to claim 1, characterized in that, The first grinding process involves mixing grinding media balls with diameters of 10 mm and 3 mm for ball milling; the mass ratio of grinding media balls to material is 6:1 to 8:1; the rotation speed of the ball mill is 300 to 600 rpm; the first grinding time is 30 to 120 minutes for grinding, after which the mixture is homogeneous, and grinding continues for another 30 to 120 minutes.

6. The early-strength agent according to claim 1, characterized in that, The temperature of the second hydrothermal reaction is 120~150℃; the time of the second hydrothermal reaction is 4~12 h.

7. The early-strength agent according to claim 1, characterized in that, The sieve aperture size is 10 μm, retaining particles with a diameter of 10~20 μm. Particles with a diameter <10 μm are subjected to a second grinding process. The second grinding process is carried out by ball milling with grinding media balls of diameters of 1 mm and 0.3 mm. The mass ratio of grinding media balls to material is 10:1~15:

1. The second grinding process takes 30~120 min. The rotation speed of the second grinding process is 60~100 rpm. The rotation speed of the centrifuge is 2000~4000 rpm.

8. The application of an early-strength agent as described in any one of claims 1-7, characterized in that, It is used in the fields of concrete structures and green building materials.

9. The application of the early-strength agent according to claim 8, characterized in that, It is used in the preparation of solid waste cementitious materials.

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