Green low-carbon concrete based on lithium slag composite admixture and preparation method thereof

Abstract

The application provides green low-carbon concrete based on lithium residue composite admixture and a preparation method thereof, and belongs to the technical field of green low-carbon concrete. The concrete comprises raw materials: cement, lithium residue composite admixture, sand, CO2 pre-carbonized recycled coarse aggregate, gravel, water, water reducing agent and composite mineralization regulator. The lithium residue composite admixture comprises components: lithium residue powder, carbonized recycled cement micro powder, lightly calcined dolomite powder, metakaolin, synthetic lithium smectite, hemihydrate gypsum and diethanol mono-isopropanol amine. The composite mineralization regulator comprises polyaspartic acid sodium, magnesium lactate and sodium metaaluminate. The synergistic system of the lithium residue composite admixture, the composite mineralization regulator and the low-carbon aggregate interface optimization improves the problems of poor workability of high-mixing lithium residue concrete, weak interface transition zone, insufficient strength and durability and the like, and improves the utilization value of solid waste such as lithium residue, recycled cement micro powder and recycled coarse aggregate in the concrete.

Description

Technical Field

[0001] This invention relates to the field of green and low-carbon concrete technology, specifically to a green and low-carbon concrete based on lithium slag composite admixture and its preparation method. Background Technology

[0002] Concrete is currently the most widely used building material in engineering construction, and its production process consumes large amounts of resources such as cement and natural sand and gravel. Cement clinker production is not only energy-intensive but also generates significant amounts of carbon dioxide emissions. Under the current context of green building, utilizing industrial solid waste, low-value mineral powders, and recycled aggregates to partially replace cement and natural aggregates has become an important technological direction for the ready-mixed concrete industry to reduce carbon emissions, decrease the consumption of natural resources, and promote the resource utilization of solid waste.

[0003] Lithium slag is a large-scale industrial solid waste generated during lithium salt production. Rich in silicon and aluminum components such as SiO2 and Al2O3, it exhibits pozzolanic activity. Using lithium slag as a mineral admixture in concrete can partially replace cement, reducing carbon emissions from cementitious materials and mitigating land occupation and environmental risks caused by long-term lithium slag storage. Therefore, the resource utilization of lithium slag in low-carbon concrete has significant engineering application value.

[0004] However, the direct application of lithium slag to concrete presents several technical drawbacks. Lithium slag particles are often loose, porous, and irregular in shape, with a large specific surface area and high water absorption rate. When directly added to concrete, they readily absorb mixing water, leading to a decrease in initial slump, increased slump loss over time, and increased slurry viscosity, thus affecting pumpability. Although lithium slag contains active SiO2 and Al2O3, the early pozzolanic reaction is slow to initiate, and under high admixture conditions, it is prone to problems such as insufficient early strength and unstable later strength development. Furthermore, the sulfates, alkali metals, and associated trace elements in lithium slag may affect the cement hydration process, volume stability, and long-term durability; simply grinding or directly compounding it makes it difficult to simultaneously meet the requirements of workability, strength development, and durability.

[0005] Existing lithium slag concrete technologies mostly employ mechanical grinding, alkali or sulfate activation, mineral powder or fly ash compounding, and polymer coating to improve lithium slag performance. While these methods can improve lithium slag activity or fresh mix performance to some extent, they still have the following shortcomings: First, most technologies mainly focus on modifying the lithium slag powder itself, without systematically designing reaction pathways from the perspective of the directional generation of cement hydration products; second, some technologies simply superimpose multiple powders or admixtures, lacking a clear ion release sequence and hydration product reconstruction mechanism; third, sand and stone aggregates are usually still treated as inert skeleton materials, failing to fully utilize the influence of the mineral composition, surface micro-powder, and old mortar layer of sand and stone on the interface transition zone and hydration product generation of lithium slag concrete.

[0006] Therefore, based on the above problems, it is urgent to develop a synergistic regulation technology for high-content lithium slag concrete. This technology involves systematically designing and optimizing lithium slag composite admixtures, specific chemical regulation components, and aggregates to improve the poor workability, insufficient early strength, weak interfacial transition zone, and unstable durability of high-content lithium slag concrete. This will enable the production of green concrete with balanced performance and reliable service, thus promoting the transition of lithium slag from "low-value disposal" to "high-value utilization". Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a green, low-carbon concrete based on lithium slag composite admixtures and its preparation method. This invention first prepares the lithium slag composite admixture, and then further constructs a synergistic system of lithium slag composite admixture, composite mineralization regulator, and low-carbon aggregate interface optimization to solve problems such as poor workability, weak interface transition zone, and insufficient strength and durability in high-content lithium slag concrete. Specifically, the lithium slag composite admixture improves the problem of rapid water absorption and slow early reaction when lithium slag powder is used alone; the composite mineralization regulator regulates the dispersion, release, and nucleation processes of components such as calcium, magnesium, aluminum, and silicon; and low-mud dolomite manufactured sand and CO2 pre-carbonized recycled coarse aggregate optimize the structure of the interface transition zone between fine and coarse aggregates. Through the synergistic effect of the above material system, this invention significantly improves the comprehensive performance of high-content lithium slag concrete, while also promoting the high-value utilization of low-value solid waste resources in concrete.

[0008] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0009] This invention provides a green low-carbon concrete based on lithium slag composite admixture, comprising the following raw materials in parts by weight: 160-210 parts cement, 120-190 parts lithium slag composite admixture, 820-850 parts sand, 600-780 parts CO2 pre-carbonized recycled coarse aggregate, 270-450 parts crushed stone, 150-170 parts water, 6-9 parts water-reducing agent, and composite mineralization regulator;

[0010] The lithium slag composite admixture comprises the following components in parts by weight: 65-80 parts lithium slag powder, 8-18 parts carbonized recycled cement powder, 3-8 parts lightly calcined dolomite powder, 4-8 parts metakaolin, 0.2-0.8 parts synthetic lithium saponite, 1-3 parts hemihydrate gypsum, and 0.05-0.15 parts diethanol monoisopropanolamine.

[0011] The dosage of the composite mineralization regulator is 0.20%-0.70% of the total mass of the cementitious materials. The composite mineralization regulator includes sodium polyaspartate, magnesium lactate, and sodium aluminate. The total mass of the cementitious materials is the sum of the masses of cement and lithium slag composite admixture.

[0012] Furthermore, the preparation method of the lithium slag composite admixture is as follows: lithium slag powder, carbonized recycled cement powder and lightly calcined dolomite powder are mixed evenly; then metakaolin, hemihydrate gypsum and synthetic lithium saponite are added and mixed evenly again; finally, diethanol monoisopropanolamine is added, mixed evenly, and then sieved to obtain the lithium slag composite admixture.

[0013] Further, in the composite mineralization regulator, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate is 1:(4.5-7.0):(1.8-3.0). This invention uses sodium polyaspartate, magnesium lactate, and sodium aluminate as a composite mineralization regulator in green low-carbon concrete based on lithium slag composite admixtures, wherein the sodium polyaspartate is used to adjust the Ca... 2+ Mg 2 + The release and precipitation process in the cement pore solution controls the nucleation and growth of calcium carbonate and magnesium-containing hydration products, reducing early coarse precipitation and local flocculation; the magnesium lactate provides a mild magnesium source, allowing magnesium ions to gradually participate in the reaction during cement hydration; the sodium aluminate can supplement the early soluble aluminum phase and promote the formation of carbonate hydration products and magnesium-aluminum hydration products.

[0014] Furthermore, the lithium slag powder is a powder obtained by drying, crushing, and grinding lithium slag produced during the lithium salt production process; the Blaine specific surface area of ​​the lithium slag powder is 300-350 m². 2 / kg, moisture content ≤ 1.0%, D 50 The particle size is 10-30 μm. By mass percentage, the lithium slag powder contains 50%-60% SiO2, 18%-25% Al2O3, 3%-8% CaO, and ≤8% SO3. The lithium slag powder provides an active silica-alumina phase, which reacts with Ca(OH)2 and soluble calcium and magnesium components in the later stages of cement hydration to generate CASH gel and magnesium-containing hydration products.

[0015] Furthermore, the carbonized recycled cement powder is obtained by CO2 carbonization treatment of recycled cement stone powder from waste concrete. The CO2 carbonization conditions are: CO2 volume fraction of 70%-90%, relative humidity of 50%-70%, temperature of 40-60 ℃, and carbonation time of 6-8 h. The carbonized recycled cement powder originates from recycled cement stone in waste concrete, possessing both a calcium carbonate phase and retaining the microstructure of carbonized cement stone and some residual hydration product structures. It serves as a nucleation substrate for hydration products in cement paste and participates in aluminate reactions to generate aluminocarbonate hydration products, thereby improving the early reaction efficiency and paste density of the lithium slag composite admixture. Compared to uncarbonized recycled cement stone powder, the carbonized recycled cement powder has a lower free Ca(OH)2 content, lower early water absorption and volume stability risks, making it more suitable as a nucleation filler in high-content lithium slag systems, and providing conditions for the formation of aluminocarbonate hydration products in the presence of the aluminum phase.

[0016] Specifically, the process of obtaining carbonized recycled cement stone powder by CO2 carbonization of recycled cement stone powder from waste concrete is as follows: The waste concrete is selectively crushed, sieved, and impurities are removed to obtain recycled cement stone particles; the recycled cement stone particles are dried and ground to obtain recycled cement stone powder; the Blaine specific surface area of ​​the recycled cement stone powder is 400-500 m². 2 / kg, D 50 The particle size is 8-25 μm; the recycled cement stone powder is placed in an environment with a CO2 volume fraction of 70%-90%, a relative humidity of 50%-70%, and a temperature of 40-60 ℃ for 6-8 h to obtain carbonized recycled cement powder; the CaCO3 content in the carbonized recycled cement powder is 25%-55%, the free Ca(OH)2 content is ≤ 5%, and the moisture content is ≤ 1.0%.

[0017] Furthermore, the lightly calcined dolomite powder is obtained by lightly calcining dolomite at 700-850 °C for 0.5-2 h and then grinding it, and its Blaine surface area is 350-400 m². 2 / kg, D 50 The particle size is 5-20 μm. By mass percentage, the light-calcined dolomite powder contains 15%-35% active MgO, 20%-40% CaO, and has a loss on ignition of 10%-25%, with satisfactory stability. The light-calcined dolomite powder provides a slowly released magnesium and calcium source, and synergistically interacts with the active silica-alumina phase in lithium slag powder and metakaolin to promote the formation of magnesium-containing hydration products and aluminate hydration products, thereby improving the compactness and interfacial structure of concrete in its later stages.

[0018] Furthermore, the metakaolin is obtained by calcining and activating kaolin, and its D... 50Particle size is 2-8 μm, specific surface area is 600-800 m² 2 / kg. The metakaolin contains 35%-45% Al2O3 and 45%-55% SiO2 by mass percentage. This invention incorporates metakaolin into lithium slag composite admixtures to supplement the early-stage active aluminum-silicon phase, thereby improving the problem of slow early-stage reaction in lithium slag. Simultaneously, the metakaolin can synergistically promote the formation of CASH gel, aluminate hydration products, and magnesium-aluminum hydration products with the calcium carbonate phase in carbonized recycled cement powder, lightly calcined dolomite powder, and magnesium and aluminum sources in the composite mineralization regulator.

[0019] Furthermore, the synthesized lithium saponite is a layered magnesium silicate material, D 50 Particle size ≤ 15 μm, moisture content ≤ 8%. Introducing synthetic lithium saponite into lithium slag composite admixtures can improve the fresh mixing stability of high-content lithium slag systems; its lamellar structure can form a weak thixotropic network in the static state of the mixture, reducing bleeding, segregation and particle settling; under the action of stirring and pumping shearing, this weak network can be partially destroyed without significantly reducing the fluidity of concrete, ensuring construction fluidity.

[0020] Furthermore, the D of the hemihydrate gypsum 50 The particle size is 5-20 μm, SO3 content is ≥ 35%, and moisture content is ≤ 1.0%. The hemihydrate gypsum can provide an appropriate amount of sulfate phase to regulate the early hydration process of cement, and together with the aluminum and calcium phases, it forms fine ettringite, which is beneficial to improving the early paste structure.

[0021] Furthermore, the diethanol monoisopropanolamine, as a dispersing and early hydration promoting component, is beneficial to improving the dispersion uniformity of various powders in lithium slag composite admixtures and promoting early cement hydration.

[0022] Furthermore, the sand is low-mud dolomite manufactured sand; the fineness modulus of the low-mud dolomite manufactured sand is 2.6-3.0, the stone powder content is 5%-10%, the methylene blue value is ≤ 1.4 g / kg, and the mud content is ≤ 1.0%. By mass percentage, the total content of CaCO3 and MgCO3 in the low-mud dolomite manufactured sand is ≥ 80%, and the equivalent MgO content is ≥ 8%. In the green low-carbon concrete of this invention, the sand is mainly used as fine aggregate. Specifically, the selected low-mud dolomite manufactured sand has dolomite stone powder adhering to its surface containing calcium and magnesium carbonate components, which can play a role in micro-filling, nucleation, and interface transition refinement in the mortar interface zone, facilitating the uniform deposition of hydration products on the sand grain surface and improving the pore structure of the mortar interface zone.

[0023] Furthermore, the CO2 precarbonized recycled coarse aggregate is obtained from waste concrete through crushing, screening, impurity removal, moisture conditioning and CO2 carbonization treatment. Its particle size is 5-25 mm, water absorption rate ≤ 5.0%, crushing value ≤ 15%, needle-like and flaky particle content ≤ 8%, and mud content ≤ 0.8%.

[0024] Specifically, the preparation method of the CO2 pre-carbonized recycled coarse aggregate is as follows:

[0025] Waste concrete is crushed, screened, and impurities (mud, bricks, sawdust, and lightweight impurities) to obtain recycled coarse aggregate in the 5-25mm particle size range. The recycled coarse aggregate is then conditioned to a moisture content of 3.0%-4.0% and treated in a CO2 carbonization environment to obtain CO2 pre-carbonized recycled coarse aggregate. The CO2 carbonization conditions are: CO2 volume fraction 80%-99%, relative humidity 50%-70%, temperature 20-60 ℃, and carbonization time 8-14 h. After CO2 pre-carbonization treatment, the Ca(OH)2, CSH decalcified phase, and calcium-containing components in the old mortar on the surface of the recycled coarse aggregate undergo a carbonization reaction, generating CaCO3 and filling the pores of the old mortar, thereby reducing water absorption and increasing surface density.

[0026] Furthermore, the crushed stone is natural limestone crushed stone; the particle size of the natural limestone crushed stone is 5-25 mm, the crushing value is ≤ 10%, the mud content is ≤ 1.0%, and the content of needle-like and flaky particles is ≤ 8%. This invention combines natural limestone crushed stone with CO2 pre-carbonized recycled coarse aggregate, which can reduce the fluctuations in water absorption and strength that may occur when large quantities of recycled aggregate are used.

[0027] Furthermore, the water-reducing agent is a polycarboxylate water-reducing agent; the water reduction rate of the polycarboxylate water-reducing agent is 25%-30%, the solid content is 18%-25%, and the air content is ≤ 3.0%.

[0028] The present invention also provides a method for preparing the above-mentioned green low-carbon concrete based on lithium slag composite admixture, comprising the following steps:

[0029] M1: Preparation of lithium slag composite admixture:

[0030] Weigh out the following components by weight: lithium slag powder, carbonized recycled cement powder, lightly calcined dolomite powder, metakaolin, synthetic lithium saponite, hemihydrate gypsum, and diethanol monoisopropanolamine.

[0031] Lithium slag powder, carbonized recycled cement powder and lightly calcined dolomite powder are added to a high-speed powder mixing equipment and mixed at 600-1000 r / min for 5-10 min at room temperature to initially disperse the three components.

[0032] Then add metakaolin, hemihydrate gypsum and synthetic lithium saponite, and continue mixing for 8-15 minutes;

[0033] Finally, add diethanol monoisopropanolamine and continue mixing for 2-5 minutes, controlling the material temperature to not exceed 45 ℃ during the mixing process. After mixing, sieve the resulting material through a 0.30 mm sieve to obtain lithium slag composite admixture.

[0034] First, lithium slag powder, carbonized recycled cement powder, and lightly calcined dolomite powder are premixed to preferentially disperse the carbonized recycled cement powder and lightly calcined dolomite powder on the surface of lithium slag powder particles. Then, metakaolin, hemihydrate gypsum, and synthetic lithium saponite are added for secondary mixing. Finally, diethanol monoisopropanolamine is added for short-term dispersion treatment. This invention uses a segmented mixing method to allow the nucleating and filling components, aluminum-silicon compensating components, and thixotropic stabilizing components to function independently, avoiding local agglomeration caused by mixing multiple components at once. The Blaine specific surface area of ​​the mixed and sieved lithium slag composite admixture is 350-450 m². 2 / kg, moisture content ≤ 1.0%.

[0035] M2: Preparation of composite mineralization regulator solution:

[0036] Add sodium polyaspartate and magnesium lactate to water accounting for 40%-60% of the total mixing water mass, and stir until completely dissolved to obtain the first conditioning solution;

[0037] Add sodium aluminate to water that accounts for 10%-20% of the total mixing water mass, and stir until completely dissolved to obtain the second conditioning solution; reserve the remaining mixing water for the concrete mixing stage.

[0038] M3: Concrete mixing:

[0039] Add sand, CO2 pre-carbonized recycled coarse aggregate and crushed stone into a forced mixer and dry mix for 20-40 seconds;

[0040] Then add cement and lithium slag composite admixture, and continue dry mixing for 30-60 seconds to ensure that the cementitious material is evenly coated on the surface of the aggregate.

[0041] Then add the first conditioning solution and water-reducing agent, and stir for 40-60 seconds; then add the second conditioning solution and continue stirring for 60-120 seconds.

[0042] Finally, add the remaining mixing water and continue stirring until the mixture is uniform to obtain green low-carbon concrete based on lithium slag composite admixture.

[0043] In this invention, a stepwise mixing method is adopted, first adding sodium polyaspartate and magnesium lactate, and then adding sodium aluminate. The purpose is to first treat the Ca... 2+ Mg 2+Dispersion and complexation are regulated to reduce early disordered precipitation and powder agglomeration; then a soluble aluminum phase is introduced so that the aluminum phase, magnesium phase, calcium carbonate phase and lithium slag silica-alumina phase gradually participate in the reaction during cement hydration, thereby improving the uniformity of hydration product formation.

[0044] The mechanism of the technical solution of this invention is as follows:

[0045] Lithium slag powder itself contains a large amount of SiO2 and Al2O3, which are the main sources of pozzolanic reaction in the later stage of concrete. However, directly adding it to concrete will result in decreased workability and insufficient early strength due to its porous particles, high water absorption, and slow early reaction. Therefore, this invention combines lithium slag powder with carbonized recycled cement powder, lightly calcined dolomite powder, metakaolin, synthetic lithium saponite, hemihydrate gypsum, and diethanol monoisopropanolamine, so that lithium slag powder no longer undertakes the reaction alone, but forms a continuous hydration reaction process with other components. Among them, carbonized recycled cement powder provides a fine calcium carbonate phase and a nucleation substrate for carbonized cement stone, promoting the deposition of cement hydration products and participating in the formation of carbon aluminate hydration products; metakaolin provides an early-reactive aluminum-silicon phase to compensate for the insufficient early activity of lithium slag; hemihydrate gypsum provides an appropriate amount of sulfate phase, which, together with the calcium and aluminum phases, forms fine ettringite, improving the early pore structure; lightly calcined dolomite powder provides slowly released active MgO and CaO, providing a reaction source for the formation of magnesium-containing hydration products; synthetic lithium saponite improves the suspension stability of the slurry through its layered structure, reducing bleeding, segregation, and particle sedimentation caused by lithium slag powder and recycled powder; diethanol monoisopropanolamine is used to improve the dispersion uniformity of various powders in the lithium slag composite admixture and promote early cement hydration.

[0046] Specifically, in the early hydration stage, the calcium carbonate phase in the carbonated recycled cement powder, the sulfate phase provided by hemihydrate gypsum, and the aluminum phase provided by sodium aluminate and metakaolinite jointly participate in the reaction to generate fine ettringite and aluminate hydration products. These products preferentially form around lithium slag powder, recycled cement powder, and cement particles, filling the early pores between particles and improving the initial structural stability of the slurry, thereby addressing the problem of low early strength in high-lithium slag content systems. With increasing age, the active SiO2 and Al2O3 in the lithium slag powder and metakaolinite continue to undergo secondary hydration and pozzolanic reactions with Ca(OH)2 generated from cement hydration and the calcium, magnesium, and aluminum sources in the system, promoting the continuous generation of CASH-type gels, aluminate hydration products, and magnesium-containing hydration products. These hydration products can further fill capillary pores, reduce the proportion of interconnected pores, and improve the density of the slurry in the later stages.

[0047] Meanwhile, the composite mineralization regulator is key to regulating the reaction process in this invention. The composite mineralization regulator includes sodium polyaspartate, magnesium lactate, and sodium aluminate. Among them, the sodium polyaspartate molecule contains carboxyl groups and other coordinating groups, which can react with Ca in the cement pore solution.2+ Mg 2+ It produces a certain complexing and dispersing effect, which slows down the precipitation of calcium and magnesium ions in the early stage of mixing, thereby reducing slurry flocculation and slump loss. At the same time, sodium polyaspartate also participates in regulating the nucleation and growth of calcium carbonate and magnesium-containing hydration products, making them tend to be fine and dispersed, rather than forming coarse and locally concentrated precipitates. Magnesium lactate provides a mild magnesium source. After magnesium ions are gradually released in the alkaline environment of cement, they, together with the silicon and aluminum components released from lithium slag powder and metakaolin, as well as the calcium and carbonate phases in the system, promote the formation of magnesium-containing hydration products and aluminate hydration products, thereby improving the later compactness and pore structure stability of the slurry. Sodium aluminate provides an early soluble aluminum phase, which on the one hand promotes the formation of carbonaluminate hydration products from the calcium carbonate phase in carbonized recycled cement powder and dolomite powder, and on the other hand provides an aluminum source for the formation of magnesium-aluminate hydration products. This invention utilizes the combined regulatory effects of sodium polyaspartate, magnesium lactate, and sodium aluminate to promote the more uniform participation of calcium, magnesium, aluminum, and silicon components in the system in the reaction, thereby enabling CSH / CASH gels, aluminate hydration products, and magnesium-containing hydration products in the slurry to be generated and distributed more evenly, thus improving the slurry's binding capacity and pore-filling effect.

[0048] The lithium slag composite admixture and composite mineralization regulator of this invention both incorporate calcium, magnesium, aluminum, and carbonate phases, ensuring that the formation of hydration products and optimization of interfacial structure occur not only within the slurry but also are closely related to the surface characteristics of the aggregates. In concrete formulation design, the low-mud dolomite manufactured sand used in this invention contains an appropriate amount of dolomite powder on its surface. The calcium and magnesium carbonate micropowder within it can play a role in micro-filling, nucleation, and interfacial transition zone refinement in the mortar interface, promoting the uniform deposition of hydration products on the sand grain surface. This, along with CSH / CASH-type gels, aluminocarbonate hydration products, and magnesium-containing hydration products generated in the slurry, improves the interfacial pore structure. In contrast, the main mineral component of ordinary river sand is quartz, lacking calcium and magnesium carbonate micropowder on its surface, making it difficult to provide similar interfacial nucleation and micro-filling effects. Furthermore, the clay components in manufactured sand with high mud content easily adsorb water-reducing agents and mixing water, potentially exacerbating slump loss and slurry instability in high-mud-content lithium slag systems. Therefore, the low-mud dolomite manufactured sand in this invention also plays a role in interfacial auxiliary strengthening. CO2 pre-carbonization of recycled coarse aggregate, combined with a lithium slag composite admixture system, improves the interface zone of the coarse aggregate. This invention, through CO2 pre-carbonization treatment, converts Ca(OH)2 and some decalcification hydration products in the old slurry layer on the surface of the recycled coarse aggregate into CaCO3, filling the pores of the old slurry, reducing water absorption, and increasing surface density. This calcium carbonate-modified old slurry layer can serve as an interface substrate for the deposition of new hydration products, forming a tighter interfacial bond with the CASH gel, aluminate hydration products, and magnesium-containing hydration products generated by the lithium slag composite admixture and composite mineralization regulator.

[0049] This invention proposes a synergistic technology system using lithium slag composite admixture as the main reaction carrier, composite mineralization regulator as the means of regulating hydration reaction, and low-mud dolomite manufactured sand and CO2 pre-carbonized recycled coarse aggregate as interface auxiliary strengthening components. Specifically, the lithium slag composite admixture mainly undertakes the functions of active silicon-aluminum reaction, carbonization nucleation, magnesium phase replenishment, and slurry stabilization; the composite mineralization regulator mainly regulates the release and reaction processes of calcium, magnesium, and aluminum components; and the low-mud dolomite manufactured sand and CO2 pre-carbonized recycled coarse aggregate mainly improve the structure of the mortar interface zone and the coarse aggregate interface zone. Through the synergistic effect between the components, high-content lithium slag concrete can achieve relatively stable performance improvements in the fresh mixing stage, early hardening stage, and later strength development stage.

[0050] Compared with the prior art, the advantages of the present invention are:

[0051] (1) This invention constructs a composite admixture system with lithium slag powder as the main component, which improves the problems of poor workability, slow reaction, and unstable strength development when lithium slag is used alone. This invention combines lithium slag powder, carbonized recycled cement powder, lightly calcined dolomite powder, metakaolin, synthetic lithium saponite, hemihydrate gypsum, and diethanol monoisopropanolamine, so that the system simultaneously has the functions of active silicon-aluminum reaction, carbonation nucleation, magnesium phase regulation, early sulfate regulation, and slurry stabilization. Among them, carbonized recycled cement powder provides fine calcium carbonate phase and nucleation matrix, lightly calcined dolomite powder provides slow-release magnesium source, metakaolin supplements early active aluminum-silicon phase, and synthetic lithium saponite improves slurry suspension stability. The synergistic effect of the above components effectively reduces the negative impact of high lithium slag content on concrete workability, improves the early hydration product generation capacity, and promotes the formation of later CASH gel and magnesium-containing hydration products.

[0052] (2) This invention employs a composite mineralization regulator composed of sodium polyaspartate, magnesium lactate, and sodium aluminate to regulate the reaction process of calcium, magnesium, aluminum, and silicon components, resulting in a more uniform and stable formation of hydration products. Sodium polyaspartate can regulate the reaction of calcium, magnesium, aluminum, and silicon components. 2+ and Mg 2+ It plays a role in complexation, dispersion, and mineralization regulation, avoiding rapid ion precipitation in the early stages of mixing that could cause slurry flocculation and slump loss. Magnesium lactate provides a mild magnesium source, allowing the magnesium phase to gradually participate in the lithium slag silica-alumina phase reaction. Sodium aluminate replenishes the early soluble aluminum phase, promoting the formation of carbon aluminate hydration products and magnesium-aluminate hydration products. Through this composite regulation, it promotes the formation and uniform distribution of CSH / CASH gels, carbon aluminate hydration products, and magnesium-containing hydration products within the concrete, thereby improving slurry density, later-stage strength, impermeability, and resistance to ion intrusion.

[0053] (3) This invention uses low-mud dolomite manufactured sand and CO2 pre-carbonized recycled coarse aggregate as interfacial synergistic aggregates, further extending the effects of lithium slag composite admixtures and composite mineralization regulators to the aggregate interface zone. The surface of the low-mud dolomite manufactured sand contains an appropriate amount of calcium magnesium carbonate powder, which can play a role in micro-filling, nucleation, and interface transition zone refinement in the mortar interface zone, which is conducive to the uniform deposition of slurry hydration products on the sand grain surface and improves the pore structure of the mortar interface zone; the surface of the CO2 pre-carbonized recycled coarse aggregate forms a relatively dense calcium carbonate interface after carbonization of the old slurry, which can reduce the water absorption rate of the recycled aggregate and provide an interface substrate for the deposition of new hydration products. Together with the lithium slag composite admixture and composite mineralization regulator, the two improve the structure of the mortar interface zone and the coarse aggregate interface zone, thereby improving the compactness of concrete, interfacial bonding ability, and green and low-carbon benefits. Detailed Implementation

[0054] To enable those skilled in the art to clearly and completely understand the technical solution of the present invention, the present invention will be further described in detail below with reference to embodiments. Obviously, the embodiments described herein are only for explaining the present invention and are not intended to limit the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0055] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the raw materials, methods and equipment used in this invention are conventional raw materials, methods and equipment in the art.

[0056] This invention provides a green low-carbon concrete based on lithium slag composite admixture, comprising the following raw materials in parts by weight: 160-210 parts cement, 120-190 parts lithium slag composite admixture, 820-850 parts sand, 600-780 parts CO2 pre-carbonized recycled coarse aggregate, 270-450 parts crushed stone, 150-170 parts water, 6-9 parts water-reducing agent, and composite mineralization regulator;

[0057] The lithium slag composite admixture comprises the following components in parts by weight: 65-80 parts lithium slag powder, 8-18 parts carbonized recycled cement powder, 3-8 parts lightly calcined dolomite powder, 4-8 parts metakaolin, 0.2-0.8 parts synthetic lithium saponite, 1-3 parts hemihydrate gypsum, and 0.05-0.15 parts diethanol monoisopropanolamine.

[0058] The dosage of the composite mineralization regulator is 0.20%-0.70% of the total mass of the cementitious materials. The composite mineralization regulator includes sodium polyaspartate, magnesium lactate, and sodium aluminate. The total mass of the cementitious materials is the sum of the masses of cement and lithium slag composite admixture.

[0059] In some examples, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate in the composite mineralization regulator is 1:(4.5-7.0):(1.8-3.0).

[0060] In some examples, the lithium slag powder is a powder obtained by drying, crushing, and grinding lithium slag produced during the lithium salt production process; the Blaine surface area of ​​the lithium slag powder is 300-350 m². 2 / kg, moisture content ≤ 1.0%, D 50 The particle size is 10-30 μm. By mass percentage, the lithium slag powder contains 50%-60% SiO2, 18%-25% Al2O3, 3%-8% CaO, and ≤ 8% SO3.

[0061] In some examples, the carbonized recycled cement powder is obtained by CO2 carbonization treatment of recycled cement stone powder from waste concrete; the conditions for CO2 carbonization treatment are: CO2 volume fraction of 70%-90%, relative humidity of 50%-70%, temperature of 40-60 ℃, and carbonization time of 6-8 h; the CaCO3 content in the carbonized recycled cement powder is 25%-55%, the free Ca(OH)2 content is ≤ 5%, and the moisture content is ≤ 1.0%.

[0062] In some examples, the lightly calcined dolomite powder is obtained by calcining dolomite at 700-850 °C for 0.5-2 h and then grinding it, resulting in a Blaine surface area of ​​350-400 m². 2 / kg, D 50 The particle size is 5-20 μm; by mass percentage, the active MgO content in the lightly calcined dolomite powder is 15%-35%, the CaO content is 20%-40%, and the loss on ignition is 10%-25%.

[0063] In some examples, the metakaolin is obtained by calcining and activating kaolin, and its D 50 Particle size is 2-8 μm, specific surface area is 600-800 m² 2 / kg. The metakaolin contains 35%-45% Al2O3 and 45%-55% SiO2 by mass percentage.

[0064] In some examples, the synthetic lithium saponite is a layered magnesium silicate material, D 50 Particle size ≤ 15 μm, moisture content ≤ 8%.

[0065] In some examples, the D of the hemihydrate gypsum 50 The particle size is 5-20 μm, the SO3 content is ≥ 35%, and the moisture content is ≤ 1.0%.

[0066] In some examples, the sand is low-mud dolomite manufactured sand; the fineness modulus of the low-mud dolomite manufactured sand is 2.6-3.0, the stone powder content is 5%-10%, the methylene blue value is ≤ 1.4 g / kg, and the mud content is ≤ 1.0%; by mass percentage, the total content of CaCO3 and MgCO3 in the low-mud dolomite manufactured sand is ≥ 80%, and the equivalent MgO content is ≥ 8%.

[0067] In some examples, the CO2 precarbonized recycled coarse aggregate is obtained from waste concrete after crushing, screening, impurity removal, moisture conditioning and CO2 carbonization treatment. Its particle size is 5-25 mm, water absorption rate ≤ 5.0%, crushing value ≤ 15%, needle-like and flaky particle content ≤ 8%, and mud content ≤ 0.8%.

[0068] In some examples, the crushed stone is natural limestone crushed stone; the particle size of the natural limestone crushed stone is 5-25 mm, the crushing value is ≤ 10%, the mud content is ≤ 1.0%, and the content of needle-like and flaky particles is ≤ 8%.

[0069] In some examples, the water-reducing agent is a polycarboxylate water-reducing agent; the water reduction rate of the polycarboxylate water-reducing agent is 25%-30%, the solid content is 18%-25%, and the air content is ≤ 3.0%.

[0070] The specifications and sources of the raw materials used in the following specific implementation cases are shown in Table 1 below.

[0071] Table 1: Specifications and sources of raw materials used in the examples

[0072]

[0073] Example 1

[0074] This embodiment provides a green low-carbon concrete based on lithium slag composite admixture, comprising the following raw materials in parts by weight: 185 parts cement, 150 parts lithium slag composite admixture, 835 parts low-mud dolomite manufactured sand, 690 parts CO2 pre-carbonized recycled coarse aggregate, 350 parts natural limestone crushed stone, 158 parts water, 7.2 parts polycarboxylate superplasticizer, and 1.35 parts composite mineralization regulator (0.40% of the total mass of cement and lithium slag composite admixture); wherein, in the composite mineralization regulator, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate is 1:4.94:2.00; the lithium slag composite admixture comprises the following components in parts by weight: 72 parts lithium slag powder, 12 parts carbonized recycled cement powder, 5 parts lightly calcined dolomite powder, 6 parts metakaolin, 0.5 parts synthetic lithium saponite, 2 parts hemihydrate gypsum, and 0.10 parts diethanolmonoisopropanolamine.

[0075] The preparation method of the lithium slag composite admixture is as follows: First, lithium slag powder, carbonized recycled cement powder, and lightly calcined dolomite powder are added to a high-speed powder mixer and mixed at 800 r / min for 8 min at room temperature to initially disperse the three components; then, metakaolin, hemihydrate gypsum, and synthetic lithium saponite are added, and mixing continues for 12 min; finally, diethanol monoisopropanolamine is added, and mixing continues for 3 min, controlling the material temperature during mixing to not exceed 45 ℃; after mixing, the resulting material is sieved through a 0.30 mm sieve to obtain the lithium slag composite admixture; the Blaine specific surface area of ​​the obtained lithium slag composite admixture is 410 m². 2 / kg, with a moisture content of 0.7%.

[0076] The preparation method of the green low-carbon concrete based on lithium slag composite admixture is as follows: Sodium polyaspartate and magnesium lactate are added to water accounting for 50% of the total mixing water mass and stirred until completely dissolved to obtain a first conditioning solution; sodium aluminate is added to water accounting for 15% of the total mixing water mass and stirred until completely dissolved to obtain a second conditioning solution; low-mud dolomite manufactured sand, CO2 pre-carbonized recycled coarse aggregate, and natural limestone crushed stone are added to a forced mixer and dry-mixed for 30 s; then cement and lithium slag composite admixture are added and dry-mixed for another 45 s; then the first conditioning solution and polycarboxylate superplasticizer are added and stirred for 50 s; then the second conditioning solution is added and stirred for another 90 s; finally, the remaining mixing water is added and stirred evenly to obtain the green low-carbon concrete based on lithium slag composite admixture.

[0077] Example 2

[0078] This embodiment provides a green low-carbon concrete based on lithium slag composite admixture. Compared with Embodiment 1, this embodiment increases the amount of lithium slag composite admixture and reduces the amount of cement, verifying the applicability of higher lithium slag composite admixture dosage. The green low-carbon concrete based on lithium slag composite admixture in this embodiment includes the following raw materials in parts by weight: 170 parts cement, 180 parts lithium slag composite admixture, 830 parts low-mud dolomite manufactured sand, 730 parts CO2 pre-carbonized recycled coarse aggregate, 310 parts natural limestone crushed stone, 162 parts water, 8.0 parts polycarboxylate superplasticizer, and 1.65 parts composite mineralization regulator (0.47% of the total mass of cement and lithium slag composite admixture); wherein, in the composite mineralization regulator, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate is 1:5.83:2.33; the lithium slag composite admixture includes the following components in parts by weight: 68 parts lithium slag powder, 16 parts carbonized recycled cement powder, 6 parts lightly calcined dolomite powder, 7 parts metakaolin, 0.6 parts synthetic lithium saponite, 2.5 parts hemihydrate gypsum, and 0.12 parts diethanolmonoisopropanolamine.

[0079] The preparation method of the lithium slag composite admixture is the same as in Example 1, and the Blaine specific surface area of ​​the prepared lithium slag composite admixture is 425 m². 2 / kg, with a moisture content of 0.8%.

[0080] The preparation method of the green low-carbon concrete based on lithium slag composite admixture is the same as in Example 1.

[0081] Example 3

[0082] This embodiment provides a green low-carbon concrete based on lithium slag composite admixture. Compared with Embodiment 1, this embodiment has a higher cement content and a lower lithium slag composite admixture content, which is used to verify the applicability of the present invention under medium lithium slag composite admixture content. The green low-carbon concrete based on lithium slag composite admixture in this embodiment includes the following raw materials in parts by weight: 200 parts cement, 130 parts lithium slag composite admixture, 845 parts low-mud dolomite manufactured sand, 640 parts CO2 pre-carbonized recycled coarse aggregate, 430 parts natural limestone crushed stone, 156 parts water, 6.8 parts polycarboxylate superplasticizer, and 0.96 parts composite mineralization regulator (0.29% of the total mass of cement and lithium slag composite admixture); wherein, in the composite mineralization regulator, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate is 1:6.00:2.60; the lithium slag composite admixture includes the following components in parts by weight: 78 parts lithium slag powder, 10 parts carbonized recycled cement powder, 4 parts lightly calcined dolomite powder, 5 parts metakaolin, 0.3 parts synthetic lithium saponite, 1.5 parts hemihydrate gypsum, and 0.08 parts diethanolmonoisopropanolamine.

[0083] The preparation method of the lithium slag composite admixture is the same as in Example 1, and the Blaine specific surface area of ​​the prepared lithium slag composite admixture is 392 m². 2 / kg, with a moisture content of 0.6%.

[0084] The preparation method of the green low-carbon concrete based on lithium slag composite admixture is the same as in Example 1.

[0085] Example 4

[0086] This embodiment provides a green low-carbon concrete based on lithium slag composite admixture. Compared with Example 1, this embodiment appropriately increases the amount of lightly calcined dolomite powder and magnesium lactate to verify the magnesium phase regulation and enhancement effect. The green low-carbon concrete based on lithium slag composite admixture in this embodiment includes the following raw materials in parts by weight: 180 parts cement, 160 parts lithium slag composite admixture, 835 parts low-mud dolomite manufactured sand, 710 parts CO2 pre-carbonized recycled coarse aggregate, 320 parts natural limestone crushed stone, 160 parts water, 7.6 parts polycarboxylate superplasticizer, and 1.85 parts composite mineralization regulator (0.54% of the total mass of cement and lithium slag composite admixture); wherein, in the composite mineralization regulator, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate is 1:6.25:2.00; the lithium slag composite admixture includes the following components in parts by weight: 70 parts lithium slag powder, 14 parts carbonized recycled cement powder, 7 parts lightly calcined dolomite powder, 6 parts metakaolin, 0.5 parts synthetic lithium saponite, 2 parts hemihydrate gypsum, and 0.10 parts diethanolmonoisopropanolamine.

[0087] The preparation method of the lithium slag composite admixture is the same as in Example 1, and the Blaine specific surface area of ​​the prepared lithium slag composite admixture is 420 m². 2 / kg, with a moisture content of 0.8%.

[0088] The preparation method of the green low-carbon concrete based on lithium slag composite admixture is the same as in Example 1.

[0089] Comparative Example 1

[0090] The concrete provided in this comparative example differs from that in Example 1 in that: this comparative example does not use lithium slag composite admixture, but instead uses lithium slag powder of equal mass to replace the lithium slag composite admixture in Example 1; and no composite mineralization regulator is added. Specifically, the concrete in this comparative example comprises the following raw materials in parts by weight: 185 parts cement, 150 parts lithium slag powder, 835 parts low-mud dolomite manufactured sand, 690 parts CO2 pre-carbonized recycled coarse aggregate, 350 parts natural limestone crushed stone, 158 parts water, and 7.2 parts polycarboxylate superplasticizer.

[0091] This comparative example illustrates the impact of undisturbed lithium slag powder on workability and strength development when directly applied to concrete.

[0092] Comparative Example 2

[0093] The concrete provided in this comparative example differs from that in Example 1 in that the lithium slag composite admixture does not contain carbonized recycled cement powder, and an equal mass of lithium slag powder replaces the carbonized recycled cement powder. Specifically, the lithium slag composite admixture in this comparative example comprises the following components in parts by weight: 84 parts lithium slag powder, 5 parts lightly calcined dolomite powder, 6 parts metakaolin, 0.5 parts synthetic lithium saponite, 2 parts hemihydrate gypsum, and 0.10 parts diethanolmonoisopropanolamine. The composition of other raw materials and the preparation method are the same as in Example 1.

[0094] This comparative example is used to illustrate the carbonation nucleation effect and calcium carbonate phase regulation effect of carbonated recycled cement powder.

[0095] Comparative Example 3

[0096] The concrete provided in this comparative example differs from that in Example 1 in that: the lithium slag composite admixture does not contain light-burned dolomite powder, and an equal mass of lithium slag powder replaces the light-burned dolomite powder; simultaneously, the composite mineralization regulator does not contain magnesium lactate. Specifically, the lithium slag composite admixture in this comparative example comprises the following components in parts by weight: 77 parts lithium slag powder, 12 parts carbonized recycled cement powder, 6 parts metakaolin, 0.5 parts synthetic lithium saponite, 2 parts hemihydrate gypsum, and 0.10 parts diethanolamine monoisopropanol; the amount of composite mineralization regulator in this comparative example remains 1.35 parts, and the mass ratio of sodium polyaspartate to sodium aluminate in the composite mineralization regulator is 1:2.00. The composition and preparation method of the other raw materials are the same as in Example 1.

[0097] This comparative example illustrates the impact of the absence of magnesium lactate and the magnesium phase control system provided by lightly calcined dolomite powder on the later-stage strength development, pore structure densification, and durability of concrete, provided that the total amount of regulator is kept constant.

[0098] Comparative Example 4

[0099] The concrete provided in this comparative example differs from that in Example 1 in that the composite mineralization regulator does not contain sodium polyaspartate. That is, the amount of composite mineralization regulator used in this comparative example remains 1.35 parts, and the mass ratio of magnesium lactate to sodium aluminate in the composite mineralization regulator is 4.94:2.00. The composition and preparation method of the other raw materials are the same as in Example 1.

[0100] This comparative example illustrates the effect of the absence of sodium polyaspartate on calcium and magnesium ion dispersion regulation, early flocculation control, slump maintenance, and fresh slurry stability, while maintaining a consistent total amount of regulator.

[0101] Comparative Example 5

[0102] The concrete provided in this comparative example differs from that in Example 1 in that the composite mineralization regulator does not contain sodium aluminate. That is, the amount of composite mineralization regulator in this comparative example remains 1.35 parts, and the mass ratio of sodium polyaspartate to magnesium lactate in the composite mineralization regulator is 1:4.94. The composition and preparation method of the other raw materials are the same as in Example 1.

[0103] This comparative example illustrates the effect of the absence of the early soluble aluminum phase provided by sodium aluminate on the formation of aluminate hydration products, magnesium-aluminate hydration products, early strength development, and pore structure densification, while maintaining a consistent total amount of regulator.

[0104] Comparative Example 6

[0105] The concrete provided in this comparative example differs from that in Example 1 in that the lithium slag composite admixture does not contain synthetic lithium saponite, and uses an equal mass of lithium slag powder instead of synthetic lithium saponite. Specifically, the lithium slag composite admixture in this comparative example comprises the following components in parts by weight: 72.5 parts lithium slag powder, 12 parts carbonized recycled cement powder, 5 parts lightly calcined dolomite powder, 6 parts metakaolin, 2 parts hemihydrate gypsum, and 0.10 parts diethanolmonoisopropanolamine. The composition of other raw materials and the preparation method are the same as in Example 1.

[0106] This comparative example is used to illustrate the effect of synthetic lithium saponite on the stability and anti-segregation properties of freshly mixed slurry.

[0107] Comparative Example 7

[0108] The concrete provided in this comparative example differs from that in Example 1 in that ordinary river sand is used instead of the low-mud dolomite manufactured sand in Example 1. The fineness modulus, gradation, and mud content of the ordinary river sand are similar to those of the low-mud dolomite manufactured sand. Specifically, the concrete in this comparative example comprises the following parts by weight of raw materials: 185 parts cement, 150 parts lithium slag composite admixture, 835 parts ordinary river sand, 690 parts CO2 pre-carbonized recycled coarse aggregate, 350 parts natural limestone crushed stone, 158 parts water, 7.2 parts polycarboxylate superplasticizer, and 1.35 parts composite mineralization regulator (0.17 parts sodium polyaspartate, 0.84 parts magnesium lactate, and 0.34 parts sodium aluminate; representing 0.40% of the total mass of cement and lithium slag composite admixture). The composition and preparation method of other raw materials are the same as in Example 1.

[0109] This comparative example is used to illustrate the interfacial auxiliary role of low-mud dolomite manufactured sand in the system of this invention.

[0110] Comparative Example 8

[0111] The concrete provided in this comparative example differs from that in Example 1 in that it uses recycled coarse aggregate that has not undergone CO2 carbonization treatment instead of the CO2 pre-carbonized recycled coarse aggregate in Example 1. Specifically, the concrete in this comparative example comprises the following raw materials in parts by weight: 185 parts cement, 150 parts lithium slag composite admixture, 835 parts low-mud dolomite manufactured sand, 690 parts recycled coarse aggregate, 350 parts natural limestone crushed stone, 158 parts water, 7.2 parts polycarboxylate superplasticizer, and 1.35 parts composite mineralization regulator (0.17 parts sodium polyaspartate, 0.84 parts magnesium lactate, and 0.34 parts sodium aluminate; representing 0.40% of the total mass of cement and lithium slag composite admixture). The recycled aggregate is obtained by crushing, screening, and removing impurities from waste concrete, and then adjusting the moisture content to 3.5%. The composition and preparation methods of other raw materials are the same as in Example 1.

[0112] This comparative example illustrates the effect of CO2 pre-carbonized recycled coarse aggregate on improving the workability and interfacial properties of fresh aggregate.

[0113] Comparative Example 9

[0114] The concrete provided in this comparative example differs from that in Example 1 in that the preparation method of the lithium slag composite admixture is different. This comparative example does not use a segmented mixing method, but instead mixes the raw materials in one step to prepare the lithium slag composite admixture. Specifically, the preparation method of the lithium slag composite admixture in this comparative example is as follows: lithium slag powder, carbonized recycled cement powder, lightly calcined dolomite powder, metakaolin, synthetic lithium saponite, hemihydrate gypsum, and diethanolmonoisopropanolamine are added to a high-speed powder mixer at once and mixed at 800 r / min for 23 min at room temperature. The resulting lithium slag composite admixture is then sieved through a 0.30 mm sieve before use. Other raw material compositions and concrete preparation methods are the same as in Example 1.

[0115] This comparative example illustrates the impact of segmented mixing process of lithium slag composite admixture on powder dispersion uniformity, water demand, activity index, and concrete workability.

[0116] Experimental Example: Performance Testing of Lithium Slag Composite Admixture and Concrete

[0117] Performance tests were conducted on the concrete prepared in Examples 1-4 and Comparative Examples 1-9. Among them, the powder performance tests were conducted only on lithium slag powder, lithium slag composite admixtures prepared in Examples 1-4 and lithium slag composite admixtures prepared in Comparative Examples 2, 3, 6 and 9.

[0118] The powder performance tests included the Blaine specific surface area, 30-minute water absorption rate, water demand ratio, 7-day activity index, and 28-day activity index of lithium slag powder and lithium slag composite admixtures. The 30-minute water absorption rate was tested using a weighing method: 100 g of dry powder was weighed, soaked in water for 30 minutes, filtered, and the mass of the powder after water absorption was measured, and the water absorption rate was calculated. The water demand ratio and activity index were tested using conventional methods for mineral admixtures. The test results are shown in Table 2.

[0119] The performance tests for freshly mixed concrete included initial slump, initial spread, slump loss at 1 hour, slump loss at 2 hours, and bleeding rate. The test results are shown in Table 3.

[0120] Mechanical property tests included compressive strength at 3 days, 7 days, 28 days, and 56 days. The test results are shown in Table 4.

[0121] Routine durability tests included 28-day electrical flux, 56-day electrical flux, 28-day chloride ion migration coefficient, 56-day chloride ion migration coefficient, and water permeability resistance rating. Test results are shown in Table 5.

[0122] Table 2: Performance Test Results of Lithium Slag Powder and Lithium Slag Composite Admixture

[0123]

[0124] Table 2 shows that the water absorption rate of pure lithium slag powder after 30 minutes is 18.4%, and the water demand ratio is 116%, indicating that lithium slag powder has the problems of high water absorption rate and large water demand. However, the water absorption rate of the lithium slag composite admixture prepared in Examples 1-4 is reduced to 9.2%-10.8% after 30 minutes, and the water demand ratio is reduced to 101%-104%. This indicates that by combining lithium slag powder with carbonized recycled cement powder, lightly calcined dolomite powder, metakaolin, synthetic lithium saponite, and hemihydrate gypsum, the present invention can significantly reduce the rapid adsorption of mixing water by lithium slag powder.

[0125] From the activity index, the lithium slag composite admixtures prepared in Examples 1-4 showed an activity index of 78%-83% at 7 days and 94%-99% at 28 days, both significantly higher than that of lithium slag powder. This indicates that the lithium slag composite admixture of the present invention can improve the problem of insufficient early-stage reaction of lithium slag and enhance its later-stage activity.

[0126] Comparative Example 2, which did not contain carbonized recycled cement powder, had a significantly higher 30-minute water absorption rate and water demand ratio than Example 1, while its 7-day and 28-day activity indices were lower than those of Example 1. This indicates that the fine calcium carbonate phase and carbonized cement stone nucleation matrix provided by the carbonized recycled cement powder help improve powder properties and increase reactivity. Comparative Example 3, lacking lightly calcined dolomite powder, had a lower 28-day activity index than Example 1, indicating that the magnesium phase component promotes the later reaction. Comparative Example 6, lacking synthetic lithium saponite, showed little change in powder activity index, but a slightly increased water demand ratio, indicating that synthetic lithium saponite mainly functions in slurry stabilization and water retention. Comparative Example 9 used the same lithium slag composite admixture components as Example 1, but mixed all components at once. Its 30-minute water absorption rate was 11.6%, and its water demand ratio was 105%, both higher than Example 1; its 7-day and 28-day activity indices were lower than those of Example 1. This indicates that under the same component conditions, staged mixing is beneficial for further reducing powder water demand and improving activity efficiency.

[0127] The test results of Comparative Examples 2, 3, 6 and 9 further illustrate that the present invention does not simply dilute lithium slag powder with low water absorption powder, but improves the performance of lithium slag composite admixture through the synergistic effect of carbonization nucleation components, magnesium phase regulating components, slurry stabilizing components and segmented mixing process.

[0128] Table 3: Performance Test Results of Freshly Mixed Concrete

[0129]

[0130] As shown in Table 3, the initial slump of the fresh concrete in Examples 1-4 was 210-225 mm, the initial spread was 525-550 mm, the slump loss after 2 hours was 24-35 mm, and the bleeding rate was 0.4%-0.6%, indicating that the concrete prepared by the present invention has good initial workability and retention performance over time.

[0131] Comparative Example 1 used an equal mass of lithium slag powder to directly replace the lithium slag composite admixture, without adding a composite mineralization regulator. The initial slump of its fresh concrete was only 165 mm, the slump loss after 2 hours reached 92 mm, and the bleeding rate reached 1.5%. This indicates that directly applying lithium slag powder to concrete can easily lead to a significant decrease in the workability of the concrete due to its high water absorption rate and poor particle dispersion.

[0132] The composite mineralization regulator in Comparative Example 4, which did not contain sodium polyaspartate, resulted in a slump loss of 68 mm in freshly mixed concrete after 2 hours, significantly higher than that in Example 1. This indicates that, under the condition of consistent total regulator dosage, the relative increase in the dosage of magnesium lactate and sodium aluminate cannot compensate for the adverse effects of the lack of sodium polyaspartate. Sodium polyaspartate can effectively regulate Ca2+. 2+ Mg 2+The release, dispersion and sedimentation process reduces slump retention and stability of freshly mixed slump, thereby improving slump retention and stability.

[0133] Comparative Example 6, which does not contain synthetic lithium saponite, has a higher bleeding rate and 2-hour slump loss than Example 1. This indicates that synthetic lithium saponite mainly improves the fresh mixing stability of the high-content lithium slag system through its lamellar thixotropic structure, thereby reducing bleeding and time-related losses.

[0134] In Comparative Example 7, ordinary river sand was used instead of low-mud dolomite manufactured sand. The initial slump and spread of the freshly mixed concrete did not change significantly, indicating that ordinary river sand is not necessarily detrimental to the fluidity of freshly mixed concrete. However, the lack of the calcium-magnesium carbonate interface on the surface of the dolomite manufactured sand resulted in a less effective improvement in the subsequent strength and durability of the concrete compared to Example 1.

[0135] The concrete in Comparative Example 8, which used recycled coarse aggregate without CO2 carbonation treatment, had significantly lower initial slump and slump retention performance than that in Example 1. This indicates that the recycled coarse aggregate without carbonation treatment has a higher water absorption rate, which can easily exacerbate the loss of workability of fresh concrete.

[0136] The lithium slag composite admixture in Comparative Example 9, produced using a one-time mixing process, showed significantly worse workability indicators in its fresh concrete compared to Example 1. The results indicate that, under the same raw material composition, segmented mixing is beneficial for improving the dispersion uniformity of each powder component and reducing the adverse effects of localized agglomeration on the long-term workability and paste stability of the concrete.

[0137] Table 4: Test Results of Mechanical Properties of Concrete

[0138]

[0139] As shown in Table 4, the 3-day compressive strength of the concrete in Examples 1-4 was 20.4-23.2 MPa, the 7-day compressive strength was 32.1-35.5 MPa, the 28-day compressive strength was 45.5-49.2 MPa, and the 56-day compressive strength was 52.2-56.3 MPa, all showing good early and late strength development.

[0140] Comparative Example 1, which directly replaced lithium slag composite admixture with lithium slag powder, showed significantly lower 3-day, 7-day, 28-day, and 56-day strengths in its concrete compared to Example 1. This indicates that lithium slag powder alone exhibits slow early-stage reaction and insufficient later-stage strength development. In contrast, this invention, through the synergistic effect of lithium slag composite admixture and composite mineralization regulator, can significantly improve the strength level of high-lithium slag-content concrete. Comparative Example 2, which did not contain carbonized recycled cement powder, showed significantly reduced 3-day and 7-day strengths. This suggests that the fine calcium carbonate phase and microstructure of carbonized cement stone in the carbonized recycled cement powder contribute to the nucleation of hydration products, thereby improving early-stage strength. The composite mineralization regulator in Comparative Example 5 does not contain sodium aluminate, but the total amount of composite mineralization regulator is the same as that in Example 1. Its compressive strength at 3 days, 7 days, 28 days and 56 days is still significantly lower than that in Example 1. This indicates that the early soluble aluminum phase provided by sodium aluminate is conducive to the formation of carbon aluminate hydration products and magnesium-aluminate hydration products, thereby promoting early strength development and slurry densification.

[0141] The lithium slag composite admixture in Comparative Example 3 did not contain lightly calcined dolomite powder, and the composite mineralization regulator did not contain magnesium lactate. However, the total amount of composite mineralization regulator was the same as in Example 1, and its 28-day and 56-day compressive strengths were still lower than those in Example 1. This indicates that, under the condition of consistent total amount of composite mineralization regulator, simply increasing the amount of sodium polyaspartate and sodium aluminate cannot replace the magnesium phase regulation system composed of lightly calcined dolomite powder and magnesium lactate. The introduction of an appropriate amount of magnesium source is beneficial to the continuous generation of magnesium-containing hydration products and the densification of pore structure, thereby promoting the later-stage strength development of concrete. Example 4 appropriately increased the magnesium phase composition, and its 56-day compressive strength reached 56.3 MPa, which was higher than other examples, further demonstrating that magnesium phase regulation is helpful for later-stage strength development.

[0142] Comparative Examples 7 and 8 used ordinary river sand and recycled coarse aggregate without CO2 carbonization treatment, respectively. The strength of their concrete was lower than that of Example 1. This shows that although low-mud dolomite manufactured sand and CO2 pre-carbonized recycled coarse aggregate are not the core reactive components of this invention, they can improve the overall strength of concrete through interfacial reinforcement.

[0143] Comparative Example 9, a lithium slag composite admixture prepared using a one-time mixing method, showed lower early and later compressive strengths than Example 1. This indicates that even with identical raw material components, without a segmented mixing process, the nucleation and filling components, aluminum-silicon compensation components, magnesium phase regulating components, and thixotropic stabilizing components are difficult to form a uniform and synergistic distribution, leading to a decrease in the early hydration product formation efficiency and the later pore filling effect.

[0144] Table 5: Test Results of Concrete Durability Performance

[0145]

[0146] As shown in Table 5, the 28-day and 56-day electrical flux of the concrete in Examples 1-4 were lower than those in the comparative example, and the chloride ion migration coefficient was also significantly reduced. The water permeability resistance grade reached P12, indicating that the present invention improved the pore structure and interface structure of the concrete, thereby enhancing its impermeability and resistance to chloride ion intrusion. Specifically, the 56-day electrical flux of the concrete in Example 4 was 760 C, and the 56-day chloride ion migration coefficient was 3.4 × 10⁻⁶. -12 m 2 / s, which is superior to other embodiments, indicates that after appropriately increasing the magnesium source content, the magnesium-containing hydration products generated in the later stage of the system have a better effect on pore filling and ion transport blocking.

[0147] Comparative Example 3, containing lithium slag composite admixture lacking light-burned dolomite powder and composite mineralization regulator lacking magnesium lactate, exhibited significantly higher electrical flux and chloride ion migration coefficients than Example 1. This indicates that the absence of a magnesium phase regulation system composed of light-burned dolomite powder and magnesium lactate weakens the formation of magnesium-containing hydration products and pore-filling effects in the later stages, thereby reducing the concrete's resistance to chloride ion intrusion and its impermeability. Comparative Example 5, lacking sodium aluminate in its composite mineralization regulator, also showed significantly reduced concrete durability, indicating that soluble aluminum phase promotes the formation of aluminate and magnesium-aluminate hydration products, helping to improve the pore structure of the paste and the density of the interfacial transition zone. Comparative Example 8, using recycled coarse aggregate without CO2 carbonization treatment, exhibited poor concrete durability, indicating that the high interfacial porosity of ordinary recycled coarse aggregate is detrimental to impermeability and chloride ion intrusion resistance. Comparative Example 9 generally showed inferior durability compared to Example 1. This indicates that, under the same raw material composition conditions, the lithium slag composite admixture prepared stepwise by the present invention is beneficial to the uniform generation of hydration products inside the slurry and at the interface, thereby further improving the pore structure and resistance to ion intrusion.

[0148] In summary, this invention, through the combined design of "lithium slag composite admixture - composite mineralization regulator - interface synergistic aggregate", effectively improves the problems of poor workability, low early strength, unstable later strength development and weak interface structure in high lithium slag concrete, and enhances the utilization value of solid waste or low-value resources such as lithium slag, recycled cement powder, recycled coarse aggregate and manufactured sand and gravel powder in concrete.

[0149] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A green, low-carbon concrete based on lithium slag composite admixture, characterized in that, The raw materials include the following parts by weight: 160-210 parts cement, 120-190 parts lithium slag composite admixture, 820-850 parts sand, 600-780 parts CO2 pre-carbonized recycled coarse aggregate, 270-450 parts crushed stone, 150-170 parts water, 6-9 parts water-reducing agent, and composite mineralization regulator. The lithium slag composite admixture comprises the following components in parts by weight: 65-80 parts lithium slag powder, 8-18 parts carbonized recycled cement powder, 3-8 parts lightly calcined dolomite powder, 4-8 parts metakaolin, 0.2-0.8 parts synthetic lithium saponite, 1-3 parts hemihydrate gypsum, and 0.05-0.15 parts diethanol monoisopropanolamine; the carbonized recycled cement powder is obtained by CO2 carbonization treatment of recycled cement stone powder from waste concrete; the conditions for CO2 carbonization treatment are: CO2 volume fraction of 70%-90%, relative humidity of 50%-70%, temperature of 40-60 ℃, and carbonization time of 6-8 h; The dosage of the composite mineralization regulator is 0.20%-0.70% of the total mass of the cementitious material, and the composite mineralization regulator includes sodium polyaspartate, magnesium lactate and sodium aluminate. The CO2 pre-carbonized recycled coarse aggregate is obtained from waste concrete after crushing, screening, impurity removal, moisture conditioning and CO2 carbonization treatment; the CO2 carbonization treatment conditions are: CO2 volume fraction 80%-99%, relative humidity 50%-70%, temperature 20-60 ℃, carbonization time 8-14 h.

2. The green low-carbon concrete based on lithium slag composite admixture according to claim 1, characterized in that, In the composite mineralization regulator, the mass ratio of sodium polyaspartate, magnesium lactate, and sodium aluminate is 1:(4.5-7.0):(1.8-3.0).

3. The green low-carbon concrete based on lithium slag composite admixture according to claim 1, characterized in that, The lithium slag powder is a powder obtained by drying, crushing and grinding lithium slag produced during the lithium salt production process.

4. The green low-carbon concrete based on lithium slag composite admixture according to claim 1, characterized in that, The lightly calcined dolomite powder is obtained by lightly calcining dolomite at 700-850 ℃ for 0.5-2 h and then grinding it.

5. A green low-carbon concrete based on lithium slag composite admixture according to claim 1, characterized in that, The synthetic lithium saponite is a layered magnesium silicate material, D 50 Particle size ≤ 15 μm, moisture content ≤ 8%.

6. A green low-carbon concrete based on lithium slag composite admixture according to claim 1, characterized in that, The sand is low-mud dolomite manufactured sand; the mud content of the low-mud dolomite manufactured sand is ≤ 1.0%, the total content of CaCO3 and MgCO3 is ≥ 80%, and the equivalent content of MgO is ≥ 8%.

7. A green low-carbon concrete based on lithium slag composite admixture according to claim 1, characterized in that, The crushed stone is limestone crushed stone.

8. The method for preparing green low-carbon concrete based on lithium slag composite admixture according to any one of claims 1-7, characterized in that, Includes the following steps: Preparation of lithium slag composite admixture: Lithium slag powder, carbonized recycled cement powder and lightly calcined dolomite powder are mixed evenly; then metakaolin, hemihydrate gypsum and synthetic lithium saponite are added and mixed evenly again; finally, diethanol monoisopropanolamine is added, mixed evenly and then sieved to obtain lithium slag composite admixture. Preparation of composite mineralization regulator solution: Sodium polyaspartate and magnesium lactate are dissolved in water accounting for 40%-60% of the total mixing water mass to obtain the first regulator solution; sodium aluminate is dissolved in water accounting for 10%-20% of the total mixing water mass to obtain the second regulator solution; Concrete mixing: Dry mixing of sand, CO2 precarbonized recycled coarse aggregate and crushed stone; Then add cement and lithium slag composite admixture and continue dry mixing to make the cementitious material evenly coat the surface of the aggregate. Add the first regulating solution and water-reducing agent, mix well; then add the second regulating solution, mix well; finally add the remaining mixing water, mix well, and obtain green low-carbon concrete based on lithium slag composite admixture.

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