Carbonized wet-ground steel slag-lithium slag-based composite admixture and application thereof

Abstract

The invention relates to a carbonized wet-ground steel slag-lithium slag-based composite admixture and application thereof, and belongs to the technical field of solid waste recycling and green building materials. The composite admixture is liquid slurry prepared from steel slag powder and lithium slag powder through a carbonization-wet grinding synergistic activation process. According to the main process, mechanical grinding and chemical carbonization reaction are synchronously carried out, and microbubbles generated by decomposition of ammonium bicarbonate are supplemented to enhance mass transfer. In the process, free oxides in the steel slag are converted into stable carbonate, a silicon-aluminum network of the lithium slag is depolymerized, and the stable carbonate and the lithium slag cooperate to generate compact gelling products such as calcite, ettringite and AFm-like substances, so that the material activity is improved, and meanwhile, the problems of poor stability and high-sulfur expansion risks are fundamentally solved. The product can be used as a functional liquid cementing material, and is added instead of part of mixing water during concrete mixing, and high-performance low-carbon concrete is prepared after curing; and large-scale high-value utilization of the steel slag and the lithium slag is realized.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and relates to solid waste resource utilization and green building materials technology; specifically, it relates to a carbonized wet-milled steel slag-lithium slag-based composite admixture and its application. Background Technology

[0002] The production of silicate cement consumes large amounts of limestone and releases CO2, making it one of the main sources of carbon emissions in the construction sector. To achieve low-carbon development, utilizing industrial solid waste to prepare mineral admixtures to replace part of the cement clinker has become an important technological path for reducing the carbon footprint. Steel slag and lithium slag, as typical bulk solid wastes, are produced in large quantities but have low utilization rates. However, due to their potential cementitious components, they have been widely studied for use in cement-based materials in recent years.

[0003] Steel slag is mainly composed of CaO and SiO2, containing hydraulic minerals such as dicalcium silicate. However, due to the slow cooling after smelting, C2S mainly exists in the thermodynamically stable γ-crystal form, with significantly lower hydration activity than β-C2S in ordinary cement. Simultaneously, steel slag contains a large amount of inert RO phase, making it difficult to participate in hydration reactions. A more prominent problem is that it often contains free calcium oxide and free magnesium oxide, which slowly hydrate in the later stages of concrete hardening, causing volume expansion and affecting long-term volume stability, thus limiting its safety in engineering applications.

[0004] Lithium slag is mainly composed of amorphous SiO2 and Al2O3, possessing some pozzolanic activity but lacking self-hydraulic properties. It requires an external alkaline environment to activate the reaction, resulting in slow early strength development. Some lithium slag has a high SO3 content, which can exert a sulfate-activating effect when appropriate, but excessive amounts increase the water demand of the slurry, deteriorate workability, and induce delayed ettringite formation under temperature and humidity changes, leading to irreversible expansion and cracking. In addition, the coarse particles and porous structure of lithium slag result in a large specific surface area, but insufficient reaction can weaken the matrix density, adversely affecting the durability properties of concrete, such as impermeability and frost resistance.

[0005] Given the significant performance deficiencies of single solid waste materials, preparing composite mineral admixtures by blending steel slag and lithium slag has become a feasible strategy. This strategy aims to improve overall cementitious performance and reduce clinker content through the complementarity of their chemical composition and physical properties. However, existing technologies still have shortcomings in terms of activation efficiency, volume stability control, and engineering applicability.

[0006] For example, Chinese invention patent application CN117105554A discloses a method for preparing lithium slag and steel slag by co-milling to 400-500 mesh, and controlling the SO3 content of the mixture to ≤3.0% to reduce the risk of expansion. This method relies on physical milling to achieve particle refinement and component dilution, but it does not effectively chemically activate the inert γ-C2S and RO phases in the steel slag, and it fails to eliminate the risk of delayed ettringite formation during long-term service in a high sulfate environment. As a result, the early activity improvement of the blend is limited, and its effect on improving the microstructure density and durability is insufficient.

[0007] Chinese invention patent CN115724608B uses a phosphoric acid / alcohol solution and an organosilane coupling agent to modify the surface of steel slag, and then combines it with AOD slag, nickel-iron slag, fly ash, and a small amount of lithium slag. Although this improves the reactivity to some extent, the process is complex, the reagent cost is high, and the introduction of organic matter may bring environmental burden, which is not conducive to industrial promotion. At the same time, the proportion of lithium slag is low, and its synergistic effect with steel slag has not been fully explored.

[0008] Chinese invention patent CN114213051B utilizes the 4.2%-5.8% sulfate naturally present in specific lithium slag to activate steel slag. This method has strict requirements for raw material sources and poor adaptability; furthermore, the high sulfate content in the system still poses a risk of delayed ettringite formation leading to expansion. In addition, it lacks effective control measures for the stability of f-CaO / f-MgO in the steel slag, making it difficult to balance early activity with long-term volume stability.

[0009] While some other solutions achieve higher mechanical properties, their high dependence on cement clinker weakens their carbon reduction benefits. For example, the ternary system of phosphorus slag-lithium slag-steel slag proposed by Chinese invention patent CN115321898B still requires the addition of 5%-10% silicate cement clinker as an early strength component. Essentially, it is still dominated by clinker and fails to reflect the design concept of low-carbon cementitious materials based on industrial solid waste.

[0010] In summary, the existing steel slag-lithium slag composite admixture technology generally has the following problems: (1) There is a lack of effective chemical activation methods for the γ-C2S and RO phases in steel slag, and the volume stability risk caused by f-CaO / f-MgO is not well controlled; (2) The activity activation of lithium slag volcanic ash is insufficient, and the hidden danger of delayed expansion caused by high SO3 has not been fundamentally solved; (3) It relies heavily on mechanical grinding or complex modification processes, making it difficult to achieve a balance between activity, stability and economy; (4) High-performance systems often require the addition of cement clinker, which limits the solid waste substitution rate and carbon emission reduction potential.

[0011] Therefore, there is an urgent need to develop a new synergistic activation technology that, under low or no clinker conditions, can efficiently activate the potential activity of steel slag through the synergistic effect of physical activation and chemical activation, suppress the risk of expansion, fully release the reaction potential of lithium slag, and prepare a low-carbon composite mineral admixture with high activity, good volume stability and excellent durability. Summary of the Invention

[0012] To address the key technical challenges of existing steel slag-lithium slag composite admixtures in practical applications, such as insufficient activity activation, poor volume stability, and potential expansion risks caused by the high SO3 content in lithium slag, this invention aims to provide a carbonized wet-milled steel slag-lithium slag-based composite admixture and its applications. This composite admixture is a liquid slurry, prepared from industrial solid waste steel slag powder and lithium slag powder as core raw materials through a carbonization wet milling process. The product can be directly used as a functional cementitious component in concrete production, suitable for preparing high-performance low-carbon concrete.

[0013] This invention not only achieves large-scale, high-value-added resource utilization of two typical industrial solid wastes, but also actively fixes CO2 during the preparation process, significantly reducing carbon emissions and demonstrating outstanding environmental benefits. More importantly, through the synergistic design of material composition and process parameters, this invention constructs a self-driven reaction system that achieves efficient activation without the need for additional cement clinker or complex chemical modifiers, thus promoting the development of mineral admixtures towards "high activity, high stability, and high carbon reduction."

[0014] The objective of this invention is achieved through the following technical solution:

[0015] On one hand, the present invention provides a carbonized wet-milled steel slag-lithium slag-based composite admixture, wherein the composite admixture is a liquid slurry prepared by simultaneous carbonization-wet milling reaction of the following components in parts by weight, water, and optionally a polycarboxylate-based high-efficiency water-reducing agent; the liquid-to-solid mass ratio in the liquid slurry is (1.5-2.5):1: Lithium slag powder: 60-70 parts; Steel slag powder: 30-40 parts; Ammonium bicarbonate: 1-3 parts. The amount of ammonium bicarbonate used should be controlled within 1-3 parts. If the amount is too low, the CO2 and NH3 produced by decomposition will be insufficient, and the promoting effect on the carbonation reaction will not be sufficient. If the amount is too high, due to the limitations of solubility and decomposition rate, the excess component will not be able to participate in the reaction in time and completely. The residue will decompose and produce too much gas after being added to the concrete with the paste, resulting in increased porosity inside the concrete and reduced density and strength.

[0016] As one implementation, the initial median particle size D of the steel slag powder 50 The initial median particle size D of the lithium slag powder is 45-55 μm. 50The median particle size D of the solid phase of the resulting composite admixture slurry is 25-35 μm. After processing using the process described in this invention, the median particle size D of the solid phase of the composite admixture slurry is... 50 Effectively controlling the size within the 3-5 μm range is beneficial for improving its dispersibility and reaction kinetics.

[0017] As one implementation scheme, the main original chemical composition of the steel slag powder, by mass fraction of the total weight of the steel slag powder, includes: SiO2 14.0-18.0%, Al2O3 4.0-6.0%, Fe2O3 24.0-28.0%, CaO 3 6.0-40.0%, and MgO 6.0-8.0%, which conforms to the physicochemical characteristics of typical converter steel slag.

[0018] As one implementation scheme, the main original chemical composition of the lithium slag powder, by mass fraction of the total weight of the lithium slag powder, includes: SiO2 56.0-60.0%, Al2O3 18.0-22.0%, Fe2O3 1.0-2.0%, CaO 6.0-8.0%, SO3 6.0-8.0%, reflecting its high silicon and aluminum and sulfur-rich characteristics, which are derived from acid-roasted lithium slag.

[0019] As one implementation, the polycarboxylate superplasticizer in the composite admixture accounts for 0.3%-0.5% of the total solid mass.

[0020] On the other hand, the present invention also provides a method for preparing the aforementioned composite admixture, the method comprising the following steps: S1. Raw material premixing: Lithium slag powder and steel slag powder are dry-mixed evenly to obtain a mixture. Specifically, lithium slag powder and steel slag powder can be placed in a dry mixing device according to the above ratio for dry mixing and thorough stirring to obtain a homogenized mixture.

[0021] S2. Simultaneous Carbonization-Wet Milling Activation: Transfer the mixture obtained in step S1 to the sealed grinding jar of a ball mill, and add water to adjust the liquid-solid mass ratio to (1.5-2.5):1. Then, (from the top of the grinding jar) introduce carbon dioxide (CO2) gas with a purity of not less than 99.5%, and maintain the gauge pressure inside the jar at a stable 0.1-0.3 MPa using a pressure control system. Before starting the ball mill, add ammonium bicarbonate and 0.3%-0.5% (by weight of total solids) of a polycarboxylate-based high-efficiency water-reducing agent to the grinding system. Start the ball mill (running continuously at a speed of 300-600 rpm) to allow the material to undergo simultaneous mechanical grinding and carbonization reactions. The entire process lasts 40-60 minutes.

[0022] S3. Post-processing of product: After the reaction is completed, stop ball milling and take out the obtained uniform and stable slurry, which is the composite admixture product of the present invention; immediately transfer it to a sealed container for storage to prevent moisture evaporation, component sedimentation or uncontrolled secondary carbonization, and ensure product performance stability.

[0023] As one implementation, in step S2, the grinding media used is zirconia balls, and the ratio of their total mass to the mass of the mixture obtained in step S1 is (1-2):1.

[0024] As one implementation, the zirconia grinding balls have a particle size range of 0.6-1.4 mm, and the sum of the stacked volume of the zirconia grinding balls and the volume of the slurry formed by the mixture and water obtained in step S1 accounts for 60%-75% of the effective volume of the ball mill jar.

[0025] In another aspect, the present invention also provides the application of the above-mentioned carbonized wet-milled steel slag-lithium slag-based composite admixture in the preparation of high-performance low-carbon concrete as a functional liquid cementitious material.

[0026] As one implementation, the composite admixture is added to replace part of the mixing water during concrete mixing.

[0027] Furthermore, the present invention also provides a method for preparing high-performance, low-carbon coagulation, the method comprising the following steps: A1. Component preparation: The composite admixture slurry prepared above is used as a liquid cementitious material. At the same time, cement clinker (general silicate cement or other cement clinker), aggregate (coarse and fine aggregate) and (conventional concrete) admixtures are prepared. A2. Slurry addition and dosage control: During concrete mixing, the composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water; wherein, based on the mass of the solid phase contained in the slurry, its addition amount is 15%-20% of the total cementitious material mass; A3. Replenish mixing water and homogenize the mixture: Add the remaining mixing water and other admixtures to the mixing system. The total mixing time shall not be less than 120 seconds until a homogeneous concrete mixture with good fluidity and no bleeding is obtained and without segregation is obtained. A4. Molding and Curing: The mixture is poured, vibrated, and compacted, and then cured to obtain high-performance low-carbon concrete. Specifically, the mixture can be poured into a designated mold, compacted using a vibrating table or immersion vibrator to remove internal air bubbles; then cured to obtain high-performance low-carbon concrete with excellent mechanical properties and durability.

[0028] The core innovation of this invention lies in the deep integration of the synergistic effect of the "steel slag-lithium slag" material and the synergistic effect of the "wet grinding-carbonization" process. At the material level, steel slag and lithium slag form a complementary system: steel slag is rich in Ca... 2+ and OH -Not only is it efficiently activated in a carbonized environment, but it also promotes the depolymerization of the high-polymerization silicon-aluminum network in lithium slag, releasing a large amount of active SiO2 and Al2O3; while the lithium slag consumes Ca(OH)2 in the system and provides Al 3+ With SO4 2- Together, they promote the formation of dense ettringite (AFt) and mono / semi-carbonate type AFm phases.

[0029] At the process level, the simultaneous wet milling and carbonization produce a significant synergistic effect: ammonium bicarbonate decomposes in an alkaline environment to produce NH3 and CO2, locally increasing the pH and CO2 solubility, which helps to accelerate the carbonization process; on this basis, the carbonization reaction guides the formation of thermodynamically stable calcite (CaCO3) and AFm-like phases, promoting the early formation of ettringite, thereby resolving the volume stability risks caused by the delayed formation of ettringite; at the same time, the wet milling process breaks the inert structure of γ-C2S and RO phases in steel slag, accelerates the prehydration and carbonization conversion of free calcium oxide and free magnesium oxide, significantly improves their reactivity, optimizes particle morphology and gradation, and greatly enhances the density of the hardened slurry.

[0030] This invention employs an integrated process of "wet grinding and carbonization simultaneously," fundamentally different from the traditional carbonization-only approach. Under the forced deagglomeration effect of mechanical grinding, both steel slag and lithium slag continuously expose fresh, active surfaces. Their silicon-aluminum / silicon-calcium networks are disrupted in real time, leading to immediate material exchange and coupling reactions, rather than passively waiting for CO2 diffusion as inert particles within a molded specimen. Specifically, the lithium slag effectively regulates the liquid-phase ion balance by actively consuming the Ca(OH)2 released from the hydrolysis of the steel slag in the system, and the dissociated Al... 3+ With SO4 2- Coupled with calcium ions dissolved from steel slag, it promotes the in-situ formation of dense ettringite (AFt) and thermodynamically stable mono / semi-carbonate AFm-like phases. This mechanism transforms the previously troublesome high SO3 content in lithium slag from a potential expansion hazard into a raw material advantage for the formation of dense AFt, realizing a fundamental shift in lithium slag from "physical filling" to "chemical co-construction".

[0031] Compared with the prior art, the present invention has the following outstanding advantages: (1) Significantly improved activation efficiency: Through the dual synergistic mechanism of "materials-process", the deep activation of steel slag and lithium slag was achieved, which significantly improved the potential gelling activity of the composite system, solved the technical bottleneck of low activity of single solid waste and slow early strength development after compounding, and enhanced the growth potential of later strength.

[0032] (2) Fundamental guarantee of volume stability: Under the synergistic effect of wet grinding and carbonization, f-CaO and f-MgO in steel slag are rapidly and thoroughly converted into stable calcium carbonate and magnesium carbonate during the preparation stage, realizing the pre-disinfection of harmful components and eliminating the risk of cracking and damage caused by hydration expansion in the later stage from the source.

[0033] (3) Effective conversion of high SO3 risk and synergistic enhancement of durability: This invention cleverly utilizes the "carbonization-dominated" reaction pathway to transform the high SO3 content in lithium slag from a disadvantage to an advantage. The dense calcite preferentially generated by the system competitively consumes calcium ions with the mono / semi-carbonate type AFm-like phase, inhibiting the formation of harmful expansion phases; at the same time, the early AFt and AFm-like phases generated in situ can effectively fill capillary pores, optimize pore size distribution, and significantly improve the long-term durability of concrete.

[0034] (4) Multifunctional synergistic effect of key additives: The introduced ammonium bicarbonate decomposes in the alkaline grinding environment, producing additional NH3 and CO2. This process not only locally increases the pH and replenishes the CO2 required for the carbonization reaction on-site, strengthening the carbonization atmosphere, but also the micro bubbles generated by its decomposition can play a role in internal circulation stirring and enhancing mass transfer, effectively breaking up material agglomeration, promoting the uniform dispersion and contact of reactants, thereby further accelerating the carbonization reaction kinetics and improving the overall activation efficiency.

[0035] (5) The green, low-carbon and economic advantages are prominent: the whole process is simple and efficient, no high-temperature calcination is required, and energy consumption is low; the additives used are inexpensive, safe and environmentally friendly, and easy to obtain; the whole process actively fixes CO2, which has significant carbon emission reduction benefits and industrialization prospects. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0037] The raw materials used in the following embodiments are shown below: (1) Converter steel slag powder: Commercially available steel slag powder from a certain place in Shanghai, with the main chemical composition of SiO2 16.2%, Al2O3 5.1%, Fe2O3 25.8%, CaO 38.5%, MgO 7.0%, and median particle size D 50 It is 48μm; (2) Lithium slag powder: Commercially available lithium slag powder from a certain region in Jiangsu Province, produced by acid roasting, has the following main chemical composition: SiO2 58.3%, Al2O3 20.1%, Fe2O3 1.5%, CaO 7.2%, SO3 6.1%, and median particle size D.50 It is 30μm; (3) Carbon dioxide (CO2) gas: industrial grade, purity ≥99.5%; (4) Ammonium bicarbonate (NH4HCO3): Industrial grade, purity ≥99.0%; (5) Polycarboxylate superplasticizer: Zhongjian New Materials brand, solid content 15%, water reduction rate 25%; (6) Zirconia spheres: particle size range of 0.6-1.4 mm; (7) Cement clinker: Commercially available P·O42.5 ordinary Portland cement; (8) Mineral powder: Commercially available S95 mineral powder; (9) Aggregates: Fine aggregates are manufactured sand with a fineness modulus of 2.6, MB of 0.8, and stone powder content of 6.6%; coarse aggregates are 5-20mm continuously graded crushed stone. (10) Mixing water: ordinary tap water.

[0038] The carbonized wet-milled steel slag-lithium slag-based composite admixture used in the various embodiments of the present invention is prepared through the following steps: S1. Raw material premixing: Weigh lithium slag powder and steel slag powder according to the weight parts, and dry mix them in a dry mixer for 10 minutes to obtain a homogenized mixture.

[0039] S2, Carbonization-Wet Milling Activation: Transfer the mixture obtained in step S1 to a sealed ball mill jar equipped with a pressure control system, and add water to adjust the liquid-to-solid mass ratio to 2:1. Introduce CO2 gas from the top of the jar, and maintain the gauge pressure inside the jar at a stable 0.2 MPa using the pressure control system. Before starting the ball mill, add ammonium bicarbonate and a polycarboxylate-based high-efficiency water-reducing agent (0.4% of the total solid mass) to the grinding system. The grinding media used are zirconia balls (particle size range 0.6-1.4 mm), with a total mass ratio of zirconia balls to the mixed slurry mass of 1.5:1, and the sum of the volumes of the zirconia balls and the slurry occupying 70% of the effective volume of the ball mill jar. Start the ball mill and run it continuously at 450 rpm for 50 minutes to allow the material to simultaneously complete the mechanical grinding and chemical carbonization reactions.

[0040] S3. Product Post-processing: After the reaction is complete, immediately remove the resulting homogeneous and stable slurry and transfer it to a sealed container for storage. The median particle size D of the solid phase of the obtained composite admixture slurry was determined. 50 It is 4.2 μm.

[0041] The application of the carbonized wet-milled steel slag-lithium slag-based composite admixture in the various embodiments of the present invention includes the following steps: A1. Component preparation: The composite admixture slurry prepared above is used as a liquid cementitious material, and cement clinker, aggregates and admixtures are prepared at the same time. A2. Slurry addition and dosage control: During concrete mixing, the composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water; wherein, based on the mass of the solid phase contained in the slurry, its addition amount is 15%-20% of the total cementitious material mass; A3. Replenish mixing water and homogenize the mixture: Add the remaining mixing water and other admixtures to the mixing system. The total mixing time shall not be less than 120 seconds until a homogeneous concrete mixture with good fluidity and no bleeding is obtained and without segregation is obtained. A4. Molding and curing: The mixture is poured, vibrated and compacted, and then cured to finally produce concrete.

[0042] Example 1 A carbonized wet-milled steel slag-lithium slag-based composite admixture is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 65 parts; Steel slag powder: 35 parts; Ammonium bicarbonate: 2 parts; An application of a carbonized wet-milled steel slag-lithium slag-based composite admixture is provided: During concrete mixing, the prepared composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water. The amount added, based on the mass of the solid phase in the slurry, is 15% of the total cementitious material mass. The remaining mixing water and other admixtures are added, and the total mixing time is no less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0043] Example 2 A carbonized wet-milled steel slag-lithium slag-based composite admixture is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 60 parts; Steel slag powder: 40 parts; Ammonium bicarbonate: 1 part; An application of a carbonized wet-milled steel slag-lithium slag-based composite admixture is provided: During concrete mixing, the prepared composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water. The amount added, based on the mass of the solid phase in the slurry, is 18% of the total cementitious material mass. The remaining mixing water and other admixtures are added, and the total mixing time is no less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0044] Example 3 A carbonized wet-milled steel slag-lithium slag-based composite admixture is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 70 parts; Steel slag powder: 30 parts; Ammonium bicarbonate: 3 parts; An application of a carbonized wet-milled steel slag-lithium slag-based composite admixture is provided: During concrete mixing, the prepared composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water. The amount added, based on the mass of the solid phase in the slurry, is 20% of the total cementitious material mass. The remaining mixing water and other admixtures are added, and the total mixing time is no less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0045] Comparative Example 1 A carbonized wet-milled steel slag-lithium slag-based composite admixture without added ammonium bicarbonate is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 70 parts; Steel slag powder: 30 parts; Its preparation method includes the following steps: A1. Raw material premixing: Weigh lithium slag powder and steel slag powder according to the weight parts, and dry mix them in a dry mixer for 10 minutes to obtain a homogenized mixture.

[0046] A2. Carbonization-Wet Milling Activation: Transfer the mixture obtained in step A1 to a sealed ball mill jar equipped with a pressure control system, and add water to adjust the liquid-to-solid mass ratio to 2:1. Introduce CO2 gas from the top of the jar, and maintain the gauge pressure inside the jar at a stable 0.2 MPa using the pressure control system. Before starting the ball mill, add a polycarboxylate-based high-efficiency water-reducing agent (0.4% of the total solid mass) to the grinding system. The grinding media used are zirconia balls (particle size range 0.6-1.4 mm), with a total mass ratio of zirconia balls to the mixed slurry mass of 1.5:1, and the sum of the volumes of the zirconia balls and the slurry occupying 70% of the effective volume of the ball mill jar. Start the ball mill and run it continuously at 450 rpm for 50 minutes to allow the material to simultaneously complete the mechanical grinding and chemical carbonization reactions.

[0047] A3. Product post-processing: After the reaction is completed, immediately remove the obtained uniform and stable slurry and transfer it to a sealed container for storage.

[0048] An application of a carbonized wet-milled steel slag-lithium slag-based composite admixture without added ammonium bicarbonate is provided: During concrete mixing, the prepared composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water. The amount added, based on the mass of the solid phase in the slurry, is 20% of the total cementitious material mass. The remaining mixing water and other admixtures are added, and the total mixing time is no less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0049] Comparative Example 2 A composite admixture of steel slag and lithium slag that has only undergone wet milling but has not been carbonized is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 70 parts; Steel slag powder: 30 parts; Ammonium bicarbonate: 3 parts; Its preparation method includes the following steps: B1. Raw material premixing: Weigh lithium slag powder and steel slag powder according to the weight parts, and dry mix them in a dry mixer for 10 minutes to obtain a homogenized mixture.

[0050] B2. Wet Milling Activation: Transfer the mixture obtained in step A1 to the sealed grinding jar of a ball mill, and add water to adjust the liquid-to-solid mass ratio to 2:1. Before starting the ball mill, add ammonium bicarbonate and polycarboxylate-based high-efficiency water-reducing agent (0.4% of the total solid mass). The grinding media used are zirconia balls (particle size range 0.6-1.4 mm), with a total mass ratio of zirconia balls to the mixed slurry of 1.5:1, and the sum of the volumes of the zirconia grinding balls and the slurry occupying 70% of the effective volume of the ball mill jar. Start the ball mill and run it continuously at 450 rpm for 50 minutes to allow the material to complete only the mechanical grinding process in an atmospheric pressure air environment.

[0051] B3. Product post-processing: After the reaction is completed, immediately remove the obtained uniform and stable slurry and transfer it to a sealed container for storage.

[0052] An application of a steel slag-lithium slag composite admixture that has only undergone wet milling but not carbonization is provided: During concrete mixing, the prepared composite slurry is directly added to the mixing equipment, replacing part of the mixing water. The amount added, based on the mass of the solid phase contained in the slurry, is 20% of the total cementitious material mass. The remaining mixing water and other admixtures are added, and the total mixing time is not less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0053] Comparative Example 3 A steel slag-lithium slag composite admixture that has only undergone carbonization but not wet grinding is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 70 parts; Steel slag powder: 30 parts; Ammonium bicarbonate: 3 parts; Its preparation method includes the following steps: C1. Raw material premixing: Weigh lithium slag powder and steel slag powder by weight, and dry mix them in a dry mixer for 10 minutes to obtain a homogenized mixture.

[0054] C2. Carbonization and Activation: Transfer the mixture obtained in step C1 to a sealed reactor, and add water to adjust the liquid-to-solid mass ratio to 2:1. Introduce carbon dioxide gas with a purity of not less than 99.5% from the top of the reactor, and maintain the gauge pressure inside the reactor at a stable 0.2 MPa using a pressure control system. Before starting the agitator, add ammonium bicarbonate and a polycarboxylate-based high-efficiency water-reducing agent (0.4% of the total solid mass) to the system. Start the low-speed agitator and continuously stir at 60 rpm for 50 minutes, ensuring that the material undergoes only a chemical carbonization reaction in a pressurized CO2 environment, without mechanical grinding or activation.

[0055] C3. Product Post-processing: After the reaction is complete, the resulting uniform and stable slurry is immediately removed and transferred to a sealed container for storage. Testing shows that the median particle size D50 of the solid phase of the obtained composite admixture slurry remains within the range of 35-45 μm (close to the initial particle size of the raw materials).

[0056] An application of a steel slag-lithium slag composite admixture that has only undergone carbonization but not wet grinding is provided: During concrete mixing, the prepared composite admixture slurry is directly added to the mixing equipment, replacing part of the mixing water. The amount added, based on the mass of the solid phase contained in the slurry, is 20% of the total cementitious material mass. The remaining mixing water and other admixtures are added, and the total mixing time is not less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0057] Comparative Example 4 A dry-mixed steel slag-lithium slag composite admixture is provided, which is prepared from the following components in parts by weight: Lithium slag powder: 70 parts; Steel slag powder: 30 parts.

[0058] Its preparation method includes the following steps: C1. Dry mixing of raw materials: Weigh the lithium slag powder and steel slag composite admixture according to the weight parts, and dry mix them in a dry mixer for 10 minutes to obtain homogenized dry mixed powder.

[0059] An application of a physically compounded dry-mixed steel slag-lithium slag composite admixture is provided: During concrete mixing, the composite powder obtained from the above dry mixing process is added to the mixing equipment along with cement and other cementitious materials. The amount added, based on the powder's mass, is 20% of the total cementitious material mass. Subsequently, mixing water and other admixtures are added, and the total mixing time is no less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, vibrated to compact it, and placed in a standard curing room for curing to the specified age, after which its performance is tested.

[0060] Comparative Example 5 A commercially available S95 grade slag powder is used as a mineral admixture in concrete mixing. The powder is added directly to the mixing equipment as a mixing agent. The amount added, based on its powder weight, is 20% of the total cementitious material weight. Remaining mixing water and other admixtures are added, and the total mixing time is no less than 120 seconds to form a homogeneous concrete mixture. The mixture is then poured into molds, compacted, and placed in a standard curing room for curing to the specified age before its performance is tested.

[0061] The concrete mix proportions prepared in each embodiment and comparative example are shown in Table 1 below: Table 1. Mix proportions of concrete used in the examples and comparative examples (unit: kg / m³) 3 )

[0062] Volumetric stability was tested according to the "Test Method for Dry Shrinkage of Cement Mortar" (JC / T603-2004) and the "Test Method for Expansion Rate of Expansive Cement" (JC / T313-2009). Length change was measured using a length comparator with a dial gauge graduation of 0.01 mm. Mortar specimens (25 mm × 25 mm × 280 mm) were molded and cured for 1 day before demolding. The measuring heads on both sides were immediately wiped clean with anhydrous ethanol, and the initial length L0 was measured in a constant temperature chamber (20 ± 2℃). The specimens were then placed in a standard curing chamber for water curing. After 28 days, the specimens were removed, the surface moisture was wiped off with a damp cloth, and the length L0 was measured immediately. 28 The linear rate of change ε ​​(%) is calculated according to equation (1), accurate to 0.001%: (1); In the formula: L is the effective measurement length of the specimen (250mm); a positive value indicates expansion, and a negative value indicates contraction.

[0063] Mechanical properties were tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the compressive strength was determined after standard curing for 7 days and 28 days.

[0064] The electrical flux was tested according to the standard GB / T50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete" to test the electrical flux over 28 days.

[0065] The sulfate resistance test was conducted according to the standard GB / T50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete", which tested the compressive strength and corrosion resistance coefficient after 150 cycles of wet and dry sulfate treatment.

[0066] Table 2 Performance Test Results

[0067] Comparative analysis of Examples 1 to 3 reveals that the carbonized wet-milled steel slag-lithium slag-based composite admixture of the present invention exhibits good controllability in its component ratio and dosage in concrete. While ensuring excellent volume stability of the concrete, by rationally adjusting the formulation and dosage of this composite admixture, the early and later mechanical properties of the concrete can be synergistically optimized, and its resistance to ion penetration and sulfate attack can be simultaneously improved, demonstrating excellent engineering applicability and performance adjustability.

[0068] The comparison between Example 3 and Comparative Example 1 shows that the composite admixture prepared in Comparative Example 1 without the addition of ammonium bicarbonate exhibits significantly inferior volume stability, mechanical properties, and durability in concrete compared to Example 3. This indicates that ammonium bicarbonate plays a crucial role in enhancing mass transfer and supplementing carbon sources in the "carbonation-wet grinding" system. Adding ammonium bicarbonate to the admixture allows for a synergistic improvement in performance and stability at a relatively low cost, highlighting the economic efficiency and advanced nature of the present invention.

[0069] The comparison between Example 3 and Comparative Example 2 shows that while conventional wet grinding processes can activate the materials to some extent through physical action, the lack of chemical activation and stabilization mechanisms fails to effectively convert unstable components such as free calcium oxide and free magnesium oxide in the steel slag, and also fails to fully eliminate the potential expansion risk posed by the high SO3 content in the lithium slag. This results in a significantly increased linear expansion rate of the prepared concrete, insufficient microstructural density, poor volume stability, and severely weakened long-term durability. In contrast, this invention utilizes a synergistic activation process of "carbonation-wet grinding," simultaneously conducting mechanical grinding and chemical reactions. This process preferentially converts f-CaO / f-MgO in the steel slag into stable carbonates, guiding the system to generate dense calcite, ettringite (AFt), and AFm-like phases. This not only achieves higher strength but also fundamentally solves the volume stability problem, highlighting the technical advantages of this invention in ensuring the long-term dimensional stability of materials.

[0070] The comparison between Example 3 and Comparative Example 3 shows that if only carbonation treatment is performed without mechanical wet grinding activation, although ammonium bicarbonate and CO2 can promote the conversion of free oxides to some extent, the inert components inside the steel slag and lithium slag particles cannot be fully exposed because they have not undergone mechanical crushing. The carbonation reaction is mainly limited to the particle surface. This limitation leads to slow early strength development of concrete, and the unrefined coarse particles weaken the compactness of the transition zone between the paste and aggregate, ultimately causing significant adverse effects on mechanical properties and durability. The above results further verify the necessity and effectiveness of the "mechanical-chemical coupling" activation mechanism proposed in this invention: by exposing fresh active surfaces in real time through mechanical grinding, and by stabilizing harmful components in a timely manner through carbonation reaction, the two work synergistically to achieve simultaneous improvement in reaction efficiency and material properties.

[0071] The comparison results of Example 3 and Comparative Example 4 show that simply dry-mixing steel slag powder and lithium slag powder cannot achieve deep particle refinement or effectively activate their potential cementitious activity, resulting in a significant lag in both early and late strength development of the concrete. More importantly, the untreated f-CaO / f-MgO and high-sulfur components in the raw materials continue to hydrate and react in the later stages of concrete hardening, causing severe volume expansion, resulting in a loose and porous internal structure, and ultimately leading to a sharp deterioration in durability. This invention, through a dual synergistic mechanism of "materials-process," utilizes steel slag to provide alkalinity and calcium sources, and lithium slag to provide a silicon-aluminum network and sulfate ions, combined with the synergistic effect of wet grinding and carbonization, to achieve deep activation of the two solid wastes and pre-decomposition of harmful components. This comprehensively overcomes the insufficient activity and stability risks caused by simple compounding, powerfully verifying the necessity and advancement of the "waste-to-waste, synergistic efficiency" technical path of this invention.

[0072] The comparison results between Example 3 and Comparative Example 5 show that the composite admixture prepared by this invention surpasses traditional high-quality mineral admixtures in key performance indicators. It not only exhibits superior early activity in 7-day compressive strength but also demonstrates comparable or even better volume stability in linear expansion rate. More importantly, it shows superior performance in long-term durability indicators such as 28-day electrical flux and corrosion resistance coefficient after sulfate wet-dry cycling. This fully demonstrates that this invention successfully transforms two originally low-activity, high-risk industrial solid wastes into a high-performance, high-stability functional liquid cementitious material through a green and low-carbon synergistic activation process, without requiring additional cement clinker, thus possessing significant environmental benefits and outstanding engineering application value.

[0073] In summary, the carbonized wet-milled steel slag-lithium slag-based composite admixture provided by this invention is a liquid slurry, prepared from steel slag powder and lithium slag powder through a carbonization-wet milling synergistic activation process. The key process involves simultaneous mechanical grinding and chemical carbonization reactions in a ball mill, supplemented by microbubbles generated from the decomposition of ammonium bicarbonate to enhance mass transfer. During this process, free oxides in the steel slag are converted into stable carbonates, and the silica-alumina network of the lithium slag is depolymerized. Both synergistically generate dense calcite, ettringite, and AFm-like cementitious products, thereby fundamentally solving the problems of poor stability and high-sulfur expansion risks while improving material activity. This product can be used as a functional liquid cementitious material, replacing part of the mixing water during concrete mixing, and after curing, produces high-performance, low-carbon concrete. This invention achieves large-scale, high-value utilization of steel slag and lithium slag, actively fixing carbon dioxide during the production process without the need for external cement clinker, truly achieving the goal of "treating waste with waste, green and low-carbon," and possessing significant environmental benefits and promising engineering applications.

[0074] Although the present invention has been described in detail above, it should be understood that those skilled in the art can make appropriate adjustments or improvements to the above embodiments without departing from the core concept of the present invention. All such equivalent transformations or substitutions based on the basic principles of the present invention should be considered to fall within the protection scope defined by the claims of the present invention.

Claims

1. A carbonized wet-milled steel slag-lithium slag-based composite admixture, characterized in that, The composite admixture is a liquid slurry prepared by simultaneous carbonization-wet milling reaction of the following components in parts by weight, water, and optional polycarboxylate-based high-efficiency water-reducing agent; the liquid-solid mass ratio in the liquid slurry is (1.5-2.5):1; Lithium slag powder: 60-70 parts; Steel slag powder: 30-40 parts; Ammonium bicarbonate: 1-3 parts.

2. The composite admixture according to claim 1, characterized in that, The initial median particle size D of the steel slag powder 50 The initial median particle size D of the lithium slag powder is 45-55 μm. 50 The median particle size D of the solid phase of the slurry obtained after carbonization and wet milling is 25-35 μm. 50 It is 3-5μm.

3. The composite admixture according to claim 1 or 2, characterized in that, The original chemical composition of the steel slag powder, by mass fraction of the total weight of the steel slag powder, includes: SiO2 14.0-18.0%, Al2O3 4.0-6.0%, Fe2O3 24.0-28.0%, CaO 36.0-40.0%, MgO 6.0-8.0%; the original chemical composition of the lithium slag powder, by mass fraction of the total weight of the lithium slag powder, includes: SiO2 56.0-60.0%, Al2O3 18.0-22.0%, Fe2O3 1.0-2.0%, CaO 6.0-8.0%, SO3 6.0-8.0%.

4. The composite admixture according to claim 1 or 2, characterized in that, The polycarboxylate-based high-efficiency water-reducing agent in the composite admixture accounts for 0.3%-0.5% of the total solid mass.

5. A method for preparing the composite admixture as described in any one of claims 1-4, characterized in that, The method includes the following steps: S1. Raw material premixing: Dry mix lithium slag powder and steel slag powder evenly to obtain a mixture; S2, Carbonization-Wet Grinding Activation: Transfer the mixture obtained in step S1 to the sealed grinding jar of the ball mill, add water to adjust the liquid-solid mass ratio to (1.5-2.5):1; introduce carbon dioxide gas with a purity of not less than 99.5% into the grinding jar, and stabilize the gauge pressure inside the jar at 0.1-0.3MPa through the pressure control system; before starting the ball mill, add ammonium bicarbonate and 0.3%-0.5% of polycarboxylate-based high-efficiency water-reducing agent by the total mass of solids into the grinding system; start the ball mill to allow the material to undergo mechanical grinding and carbonization reactions simultaneously, the whole process lasting 40-60 minutes; S3. Product post-processing: After the reaction is completed, take out the obtained uniform and stable slurry, seal it and store it for later use.

6. The preparation method according to claim 5, characterized in that, In step S2, the grinding media used are zirconia balls, and the ratio of their total mass to the mass of the mixture obtained in step S1 is (1-2):

1.

7. The preparation method according to claim 6, characterized in that, The particle size range of the zirconia grinding balls is 0.6-1.4 mm, and the sum of the stacked volume of the zirconia grinding balls and the volume of the slurry formed by the mixture and water obtained in step S1 accounts for 60%-75% of the effective volume of the ball mill jar.

8. The application of the composite admixture as described in any one of claims 1-4 in the preparation of high-performance low-carbon concrete as a functional liquid cementitious material.

9. The application according to claim 8, characterized in that, The composite admixture is added to replace part of the mixing water during concrete mixing.

10. A method for preparing high-performance, low-carbon coagulation, characterized in that, The method includes the following steps: A1. Component preparation: The composite admixture as described in any one of claims 1-4 is prepared together with cement clinker, aggregate and admixture as a liquid cementitious material; A2. Slurry addition and dosage control: During concrete mixing, the composite admixture is directly added to the mixing equipment, replacing part of the mixing water; wherein, based on the mass of the solid phase contained in the slurry, its addition amount is 15%-20% of the total cementitious material mass; A3. Homogenization and mixing: Add the remaining mixing water and admixtures, and mix for a total time of not less than 120 seconds until a uniform concrete mixture without segregation is obtained. A4. Molding and curing: The mixture is poured, vibrated and compacted, and then cured to finally produce high-performance low-carbon concrete.

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