A delayed-strengthening steel slag-based cementitious material and a preparation method thereof

Abstract

This invention discloses a late-strengthened steel slag-based cementitious material and its preparation method, specifically relating to the field of solid waste resource utilization and cementitious material preparation technology. The method first involves drying and grinding converter steel slag, desulfurization gypsum, and slag; then, the materials are proportioned and the water-cement ratio and water-reducing agent dosage are controlled; next, the powders are premixed, and a combination of water-reducing agent pre-dissolution, stepwise liquid addition, and high-speed or high-shear stirring is used to form a non-Newtonian fluid state with certain self-supporting capacity and continuous flowability; finally, molding and standard curing are performed to obtain the late-strengthened steel slag-based cementitious material. This invention can improve the dispersibility, formability, and long-term strength gain of high-content steel slag systems without relying on strong alkali activators.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and cementitious material preparation technology, and more specifically, to a late-strengthening steel slag-based cementitious material and its preparation method. Background Technology

[0002] Steel slag, desulfurized gypsum, and blast furnace slag are all bulk industrial solid wastes generated by industries such as metallurgy and power generation. Steel slag contains mineral components such as dicalcium silicate, tricalcium silicate, RO phase, and free calcium oxide, exhibiting certain potential cementitious activity. Blast furnace slag has high potential hydraulic properties and can participate in subsequent reactions under suitable conditions. Desulfurized gypsum can provide sulfate ions, playing a regulatory role in the reaction process and product formation of the system. Therefore, constructing a complete solid waste cementitious material system using steel slag, desulfurized gypsum, and blast furnace slag has high engineering application value and practical significance for improving the resource utilization level of solid waste and reducing the dependence of traditional cementitious materials on natural resources and high-carbon clinker systems.

[0003] Currently, some research has been conducted on steel slag-slag-gypsum cementitious systems. However, existing technologies generally suggest that the steel slag content should not be too high. Steel slag is typically used as an auxiliary component, while the mechanical properties and hardening effect of the system are ensured by increasing the proportion of slag, introducing clinker components, or adding alkaline activators. The main reason for this is that the activity release of steel slag is relatively slow. When the steel slag content is high, the system is prone to problems such as insufficient early reaction, poor slurry uniformity, difficulty in controlling the flow state, insufficient molding stability, and slow subsequent densification, thus affecting the material's strength development and performance.

[0004] Furthermore, existing preparation methods for steel slag-based cementitious materials largely follow conventional slurry or mortar mixing techniques. Process design primarily focuses on mixing, molding, and curing under typical water-cement ratio conditions, with insufficient attention paid to controlling particle aggregation, interfacial contact, and dispersion under high steel slag content conditions. Especially under low liquid phase or even ultra-low water-cement ratio conditions, if ordinary liquid addition and conventional stirring methods are still used, it is often difficult to form a stable, uniform, and moldable slurry structure. This can easily lead to agglomeration, bleeding, segregation, or localized liquid deficiency, thus limiting the potential performance of the high steel slag system.

[0005] On the other hand, existing technologies still fall short in their research and utilization of the long-term performance of high-strength steel slag systems. Many technical solutions focus more on early strength or performance at normal ages, while paying insufficient attention to the continuous enhancement characteristics that high-strength steel slag systems may exhibit under longer curing periods. There is a lack of preparation methods and process control pathways adapted to the development patterns of such performance. Therefore, how to improve the dispersibility, formability, and long-term performance growth capacity of high-strength steel slag systems without relying on strong alkali activators has become a pressing technical problem to be solved in this field.

[0006] Therefore, there is an urgent need to provide a steel slag-based cementitious material and its preparation method for high steel slag content conditions, so as to improve the problems of insufficient utilization of high-value steel slag with high admixture, weak preparation method targeting, and insufficient long-term performance exploration in the existing technology. Summary of the Invention

[0007] To overcome the aforementioned deficiencies of the prior art, this invention provides a delayed-strengthening steel slag-based cementitious material and its preparation method. The material employs a high steel slag formulation system, combined with an ultra-low water-cement ratio, pre-dissolved water-reducing agent in stepwise addition, and high-shear stirring control, to enable the slurry to form a non-Newtonian fluid state and achieve continuous strengthening over a long period, thereby solving the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A late-strength steel slag-based cementitious material is prepared by the following method: Step 1: The converter steel slag, desulfurized gypsum and slag are dried and ground respectively to obtain converter steel slag powder, desulfurized gypsum powder and slag powder. Step 2: Weigh out 75%–92% of converter steel slag powder, 6%–15% of desulfurized gypsum powder, and 0%–15% of slag powder based on the total mass of the cementitious components. Also weigh out the mixing water and water-reducing agent, wherein the water-cement ratio is 0.10–0.14, and the water-reducing agent dosage is 0.8%–2.0% of the total mass of the cementitious materials. Step 3: Add converter steel slag powder, desulfurized gypsum powder and slag powder to a mixing device for premixing to obtain dry-mixed cementitious material; Step 4: Dissolve the water-reducing agent in the mixing water beforehand. First, mix 70% to 90% of the total mixing water with the water-reducing agent to form an initial liquid phase. Add the initial liquid phase to the dry-mixed cementitious material and stir at low speed to initially wet the powder. Then, stir at high speed or high shear. Add the remaining mixing water 1 to 2 times and continue stirring to make the slurry form a non-Newtonian fluid state. Step 5: The slurry obtained in Step 4 is poured or spread to form a sample or product blank. Step six: Place the sample or product blank obtained in step five under standard curing conditions and cure it to the predetermined age to obtain a late-strengthening steel slag-based cementitious material.

[0009] The resulting late-strengthened steel slag-based cementitious material is a solidified body after molding and curing. It has a good dense structure and a long-term strength growth characteristic, and can be used as a base cementitious phase in a neat cementitious matrix or a high-density cementitious system.

[0010] As a further embodiment of the present invention, the converter slag in step one is converter slag that has been crushed, magnetically separated and aged, the desulfurized gypsum is gypsum produced as a by-product of flue gas desulfurization, and the slag is granulated blast furnace slag powder.

[0011] As a further embodiment of the present invention, the specific surface area of ​​the converter steel slag powder, desulfurized gypsum powder and slag powder in step one is 350-450 m² / kg.

[0012] As a further embodiment of the present invention, in step two, the amount of converter steel slag powder is 75% to 92% by weight of the total mass of the cementing components, the amount of desulfurized gypsum powder is 6% to 15%, and the amount of slag powder is 0% to 15%.

[0013] As a further embodiment of the present invention, the water-reducing agent in step two is a polycarboxylate-based high-efficiency water-reducing agent, and the dosage of the water-reducing agent is 0.8% to 2.0% of the total mass of the cementitious material.

[0014] As a further embodiment of the present invention, the stirring equipment in step three is a planetary mixer, a vertical shaft mixer, or a high-shear powder mixing equipment, and the premixing process is to first stir at low speed for 30-60 seconds, and then stir at medium speed for 60-180 seconds.

[0015] As a further embodiment of the present invention, in step four, after the initial liquid phase is added to the dry-mixed gelling material, it is first stirred at low speed for 30-90 seconds, then stirred at high speed or high shear for 90-300 seconds, and then stirred for 60-180 seconds after adding the remaining mixing water. The entire stirring process is controlled to be completed within 5-15 minutes.

[0016] As a further embodiment of the present invention, the non-Newtonian fluid state in step four is that the slurry has a certain self-supporting ability under stirring, shearing or external force, has continuous fluidity in a static state, and the slurry is uniform as a whole, without obvious bleeding, segregation or coarse particle agglomeration.

[0017] As a further embodiment of the present invention, the molding method in step five is either injection molding or spreading molding, and slight vibration for venting or surface leveling can be used during the molding process. The molded slurry is left to stand in the mold for 12 to 24 hours before being demolded.

[0018] As a further embodiment of the present invention, the standard curing conditions in step six are a temperature of 20±2℃, a relative humidity of not less than 95%, and a curing period of 7 days, 14 days, 28 days, 90 days, or more.

[0019] The technical effects and advantages of the late-strengthening steel slag-based cementitious material and its preparation method of the present invention are as follows: This invention uses high-volume converter steel slag as the main cementing component, and combines it with desulfurized gypsum and a small amount of slag to construct a steel slag-based cementing system. Stable preparation and performance of the high steel slag system can be achieved without relying on strong alkali activators. This invention overcomes the problems of limited steel slag content and insufficient resource utilization in existing technologies, and significantly improves the bulk disposal capacity and high-value utilization level of steel slag.

[0020] This invention effectively improves the wetting uniformity, particle deagglomeration ability, and overall slurry dispersion of the high steel slag system under ultra-low water-cement ratio conditions by pre-dissolving the water-reducing agent in the mixing water and adding the initial liquid phase first and then replenishing the remaining mixing water in stages, combined with low-speed wetting and high-speed or high-shear stirring programs. It also reduces the agglomeration, bleeding, segregation, and local liquid shortage phenomena that are prone to occur under conventional processes.

[0021] This invention utilizes the synergistic control of a high steel slag formulation window, an ultra-low water-cement ratio, and a specific mixing process to enable the slurry to form a non-Newtonian fluid state with a certain self-supporting capacity and continuous flowability before molding. This state is beneficial for enhancing particle packing density, improving inter-particle contact and encapsulation effects, and ensuring that the slurry maintains good formability, uniformity, and structural continuity during casting or spreading molding.

[0022] The steel slag-based cementitious material prepared by this invention exhibits significant long-term continuous strengthening characteristics under standard curing conditions, especially maintaining a high strength increase over a long curing period, demonstrating a delayed strengthening effect. This method provides a specialized preparation route for exploring the long-term performance of high-strength steel slag cementitious materials, and can be further applied to high-density cementitious paste matrices, high-performance matrix materials, and related precast product systems. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing a late-strengthening steel slag-based cementitious material according to the present invention.

[0024] Figure 2 This is a schematic diagram of the appearance of the slurry when it reaches a non-Newtonian fluid state in Embodiment 1 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment was conducted under actual operating conditions in the preparation of a high-density cementitious matrix on a comprehensive utilization test line for converter steel slag in a steel enterprise in Hebei Province. In this case, the converter steel slag was taken from the steel slag treatment system of the enterprise's converter steelmaking process. After coarse and fine crushing within the plant, magnetic separation equipment was used to remove recoverable metallic iron and some iron impurities. It was then aged in an open-air stockpile for later use. The desulfurization gypsum was taken from the dewatering by-product gypsum of the enterprise's flue gas desulfurization system for its coal-fired power units. The slag used was S95 grade granulated blast furnace slag powder. The preparation process corresponding to this condition is as follows: Figure 1 As shown, the process includes six steps in sequence: raw material pretreatment, raw material batching, dry mixing and homogenization, step-by-step liquid addition and high-shear mixing, molding and standard curing. Each step is connected sequentially and carried out continuously.

[0028] In the raw material pretreatment stage, converter steel slag, desulfurized gypsum, and slag were dried separately. The purpose of drying was to minimize the impact of free water on the powder surface and localized moisture fluctuations on the mixing state under low water-to-binder ratio conditions. The drying temperature was controlled at 105℃ and maintained until the mass remained essentially constant. The dried converter steel slag, desulfurized gypsum, and slag were then fed into ball mills for grinding, and the specific surface area of ​​the ground powders was measured. The test results showed that the specific surface area of ​​the converter steel slag powder was 403 m² / kg, the desulfurized gypsum powder was 389 m² / kg, and the slag powder was 421 m² / kg, all within the range of 350–450 m² / kg, and generally close to the optimal fineness level of 400 m² / kg. This particle size distribution is beneficial for improving the particle contact efficiency of the high-solids system and the dispersion uniformity under subsequent low-liquids conditions. The three powders, after grinding, were all grayish-white or gray fine powders, with no obvious clumping. They were sealed and stored separately for later use.

[0029] In this embodiment, converter steel slag is used as the main cementing component, desulfurized gypsum as the sulfate regulating component, and slag as the active compensating component. Based on the total mass of the cementing components, 85.0% converter steel slag powder, 10.0% desulfurized gypsum powder, and 5.0% slag powder are weighed. For ease of implementation, this embodiment assumes a total cementing component volume of 1000g per batch, resulting in 850g of converter steel slag powder, 100g of desulfurized gypsum powder, and 50g of slag powder. The mixing water is controlled at a water-cement ratio of 0.12, corresponding to a total water addition of 120g. A polycarboxylate-based high-efficiency water-reducing agent is used, with a dosage of 1.5% of the total mass of the cementing materials, i.e., 15g. No clinker, sodium hydroxide, water glass, or other strong alkaline activators are added in this embodiment. The system relies on the high steel slag main component, the desulfurized gypsum regulating component, a small amount of slag compensating component, and a specific rheological control preparation process to achieve subsequent performance. The main ingredient parameters are shown in Table 1.

[0030] Table 1 Main ingredient parameters for Example 1

[0031] In the dry mixing and homogenization stage, the weighed converter steel slag powder, desulfurized gypsum powder, and slag powder were jointly added to a planetary mixer with high shear capacity. The mixture was first stirred at low speed for 45 seconds, then at medium speed for 120 seconds, allowing the three powders to undergo spatial pre-dispersion and uniform mixing before the addition of liquid. This pre-mixing procedure ensured that the desulfurized gypsum and slag were evenly distributed within the high-steel-slag powder system, thus creating conditions for subsequent uniform wetting and particle deagglomeration under low-liquid-phase conditions. After dry mixing, the powder state was observed; the overall color was uniform, with no obvious areas of uneven color depth or localized concentrations of coarse particles, indicating good pre-mixing effect.

[0032] In the stepwise addition and high-shear stirring stage, all 15g of polycarboxylate superplasticizer was first added to 120g of mixing water and stirred at room temperature until completely dissolved, forming a homogeneous superplasticizer solution. Then, 80% of the total mixing water, i.e., 96g, was taken and used together with the entire superplasticizer solution as the initial liquid phase, with the remaining 24g of mixing water reserved as the supplementary liquid. The planetary mixer was started at low speed, and the 96g of the initial liquid phase was slowly added to the dry-mixed gelling agent along the inner wall of the mixing drum, while maintaining low-speed stirring for 60s to allow the powder to gradually complete the initial wetting. In this stage, the dry powder gradually transformed into a highly viscous wet state, and a preliminary liquid film formed on the surface of some particles. The system transitioned from loose powder to a wet agglomerate with a certain degree of cohesion, but the overall system still maintained strong cohesive resistance.

[0033] After low-speed wetting, switch the mixer to high-speed mode and maintain it for 180 seconds. High-speed mixing promotes further deagglomeration of the previously formed wetted agglomerates, allowing the water-reducing agent to distribute more fully on the surfaces of various particles, enhancing the lubrication, slippage, and rearrangement capabilities between particles. After high-speed mixing, the remaining 24g of mixing water is added twice, 12g each time. After the first addition, continue mixing for 60 seconds to further adjust the flow state of the system; after the second addition, continue mixing for 90 seconds to stabilize the rheological state of the slurry and make it more homogeneous. The total mixing time is controlled at 9 minutes, falling within the process control range of 5–15 minutes.

[0034] After the above procedures are completed, as follows: Figure 2As shown, the slurry transforms from a highly viscous and wet state to a homogeneous slurry with a continuous surface, no significant free water exudation, and a certain degree of overall support. Macroscopically, this slurry does not exhibit the characteristics of a typical high water-to-binder ratio flowing slurry, nor does it appear as a dry, hard, discontinuous agglomerate. Instead, it presents a non-Newtonian fluid state suitable for casting or spreading. In this state, the slurry can move and rearrange itself when subjected to external forces such as stirring, trowel pushing, or low-amplitude vibration, and maintains a certain degree of morphological continuity after the external force is removed, without significant bleeding or coarse particle separation.

[0035] To further confirm this state, the operational status of the slurry after stirring was recorded in this embodiment. When the slurry was placed on a metal tray and lifted with a spatula, a continuous slurry band was formed without obvious breakage; the local accumulation height of the slurry could be maintained at approximately 9 mm, indicating that it has a certain self-supporting capacity after external force; the edges slowly expanded after standing for 30 seconds without obvious bleeding, indicating that it has continuous fluidity in a static state; after low-amplitude vibration for 10 seconds, the slurry surface became further smooth, with no coarse particle stratification or segregation, indicating that the system is uniformly dispersed. The relevant observation results are shown in Table 2. Therefore, it can be determined that the slurry has a certain self-supporting capacity under stirring, shearing, or external force, has continuous fluidity in a static state, and is uniform overall, without obvious bleeding, segregation, or coarse particle agglomeration, meeting the requirements for a non-Newtonian fluid state.

[0036] Table 2 Observation Record of Slurry State in Example 1

[0037] In the molding stage, the mixed slurry was poured into a 40mm×40mm×160mm mold for casting. The molding was done in two layers, with each layer being gently vibrated for 8-10 seconds to remove internal air bubbles after filling. The surface was then leveled. This embodiment primarily employs pouring molding, gentle vibration for venting, and surface leveling to complete the molding process. This entire process is compatible with the non-Newtonian fluid state of the slurry, ensuring that the molded sample has good appearance integrity and structural continuity. After standing in the mold for 18 hours, the molded slurry was demolded. Upon demolding, the sample surface was intact, with clear edges and corners, and no obvious honeycomb, pitting, or chipped corners, indicating that the slurry still has good moldability under ultra-low water-cement ratio and high steel slag conditions.

[0038] During the curing stage, the demolded samples were placed in a standard curing room for curing at a temperature of 20±2℃ and a relative humidity of not less than 95%. Compressive strength tests were conducted at 7d, 14d, 28d, and 90d, with three parallel samples tested at each age. The average value was taken as the test result, and the test results are shown in Table 3.

[0039] Table 3. Compressive strength results at different ages in Example 1

[0040] Table 3 shows that the cementitious material prepared under these conditions achieved stable strength at 7 days, continued to increase at 14 and 28 days, further increased to 63.8 MPa at 90 days, and increased by 14.5 MPa from 28 to 90 days, exhibiting a clear long-term continuous strengthening characteristic. To facilitate a direct comparison of strength development at different ages, the stage increase can be further calculated: 7.7 MPa from 7 to 14 days, 9.2 MPa from 14 to 28 days, and 14.5 MPa from 28 to 90 days. This indicates that under standard curing conditions, the system did not achieve full performance release in the early stages, but maintained a high growth rate over a relatively long curing period, demonstrating a late-strength characteristic.

[0041] To further enhance the completeness of the implementation conditions, this embodiment also observed the appearance during the molding and mechanical testing processes. The 7-day-old specimen already possessed a complete appearance and a stable load-bearing foundation; the 14-day-old specimen surface was denser than the 7-day specimen; the 28-day-old specimen showed a significant reduction in cross-sectional porosity; and the 90-day-old specimen's cross-section was even denser. These phenomena correspond to the strength test results, indicating that through the synergistic control of high steel slag main components, ultra-low water-cement ratio, stepwise addition of water-reducing agent, and high-shear stirring, it is possible to achieve a non-Newtonian fluid state similar to ultra-high performance concrete mixtures under standard curing conditions without relying on strong alkali activators, and on this basis, gradually achieve sustained long-term strength growth.

[0042] The cementitious material obtained in this embodiment can be used directly as a neat cementitious paste matrix, or further as a base cementitious phase in a high-density cementitious system, used in high-performance matrix materials, precast component cementitious phases, grouting material matrices, or other high-density cementitious material systems. In specific applications, the proportions and process parameters can be finely adjusted according to the activity of converter steel slag, grinding fineness, compatibility with water-reducing agents, and target flow state. However, the parameter combination used in this embodiment can stably obtain a uniform slurry, good forming state, and significant delayed strengthening effect.

[0043] Example 2

[0044] This embodiment uses converter steel slag, desulfurized gypsum, slag, and polycarboxylate-based high-efficiency water-reducing agent from the same sources as in Example 1. The raw material pretreatment method is the same as in Example 1. All three powders are dried and ground before use, and the specific surface area is controlled within the range of 350-450 m² / kg. Strong alkali activators are also not added in this embodiment.

[0045] Based on the total mass of the cementitious components, weigh out 88.0% converter steel slag powder, 8.0% desulfurized gypsum powder, and 4.0% slag powder. For 1000g of cementitious components, this equates to 880g of converter steel slag powder, 80g of desulfurized gypsum powder, and 40g of slag powder. The mixing water is controlled at a water-cement ratio of 0.11, with a total amount of 110g. A polycarboxylate-based high-efficiency water-reducing agent is used, with a dosage of 1.4% of the total mass of the cementitious materials, corresponding to 14g.

[0046] Three powders were added to a vertical shaft mixer and stirred at low speed for 40 seconds, followed by medium speed for 150 seconds to obtain a dry-mixed gelatin. Then, 14g of water-reducing agent was pre-dissolved in 110g of mixing water, with 77g of water forming an initial liquid phase (70% of the total mixing water). This initial liquid phase was slowly added to the dry-mixed gelatin and stirred at low speed for 50 seconds to initially wet the powders. Then, high-speed stirring was performed for 210 seconds. The remaining 33g of mixing water was added in two batches: 16g after the first addition and stirring for 70 seconds, and 17g after the second addition and stirring for 80 seconds. The entire stirring process was completed within 10 minutes. After stirring, the slurry maintained a certain packing profile, exhibited continuous fluidity after settling, and showed no significant bleeding or segregation.

[0047] The slurry was poured into a 40mm×40mm×160mm mold, cast, and the surface was leveled. After standing for 20 hours, the mold was removed, and then the mold was cured under standard conditions of 20±2℃ and relative humidity not less than 95%. The compressive strength test results at different ages are shown in Table 4.

[0048] Table 4. Compressive strength results at different ages in Example 2

[0049] This embodiment can still form a uniform slurry that meets the molding requirements under conditions of higher steel slag ratio and lower water-cement ratio, and achieves a compressive strength of 61.5 MPa at 90 days, indicating that the method of the present invention is also applicable to high steel slag and low liquid phase conditions.

[0050] Example 3

[0051] This embodiment illustrates that the method of the present invention can still be implemented when the amount of slag is 0. The raw materials are still converter steel slag after crushing, magnetic separation and aging, flue gas desulfurization by-product gypsum and polycarboxylate-based high-efficiency water-reducing agent. The raw material pretreatment method is the same as in Example 1, and strong alkali activator is also not added in this embodiment.

[0052] Based on the total mass of the cementitious components, weigh out 90.0% converter steel slag powder, 10.0% desulfurized gypsum powder, and 0% slag powder. For 1000g of cementitious components, this equates to 900g of converter steel slag powder and 100g of desulfurized gypsum powder. The mixing water is controlled at a water-cement ratio of 0.13, with a total amount of 130g; the water-reducing agent dosage is 1.8% of the total mass of the cementitious materials, corresponding to 18g.

[0053] Converter slag powder and desulfurized gypsum powder were added to a planetary mixer and stirred at low speed for 50 seconds, followed by medium speed for 160 seconds. 18g of water-reducing agent was pre-dissolved in 130g of mixing water, and 104g of this was used as the initial liquid phase, accounting for 80% of the total mixing water. This initial liquid phase was added to the dry-mixed cementitious material and stirred at low speed for 70 seconds, followed by high speed for 200 seconds. The remaining 26g of mixing water was then added twice, with stirring times of 70 seconds and 90 seconds after each addition, respectively. The entire stirring process was completed within 11 minutes. The resulting slurry had a continuous surface, maintained its basic outline after molding, and showed no obvious bleeding or coarse particle stratification after settling. It still possessed a certain degree of self-support and continuous fluidity.

[0054] Samples were prepared by spreading and molding the slurry. After molding, the samples were allowed to stand for 24 hours before demolding. Then, they were cured under standard conditions of 20±2℃ and relative humidity of not less than 95%. The results of compressive strength tests at different ages are shown in Table 5.

[0055] Table 5. Compressive strength results at different ages in Example 3.

[0056] Under these conditions, it is still possible to obtain a formable, curable steel slag-based cementitious material with long-term strengthening characteristics, indicating that the method of the present invention is still feasible even when the slag powder content is 0.

[0057] Comparative Example 1 This comparative example is consistent with Example 1 in terms of raw material type, powder fineness, proportion, water-cement ratio, type and dosage of water-reducing agent, molding method, and curing conditions. Specifically, it uses 85.0% converter steel slag powder, 10.0% desulfurized gypsum powder, and 5.0% slag powder, with a water-cement ratio of 0.12. The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent at a dosage of 1.5%, and no strong alkali activator is added. The difference lies in the use of a one-time addition method for mixing. Specifically, all 120g of mixing water and 15g of water-reducing agent are mixed at once and directly added to the dry-mixed gelling agent. Then, it is first stirred at low speed for 60 seconds, followed by high speed for 180 seconds. The remaining mixing water is not added in stages, and the other steps remain the same.

[0058] During the mixing process, numerous agglomerates with wet exteriors and dry interiors were observed in the slurry. After mixing, localized free water was visible on the surface, indicating poor slurry uniformity. Localized water bleeding was observed on the surface of the molded samples. The compressive strength test results at different ages are shown in Table 6.

[0059] Comparative Example 2 This comparative example is consistent with Example 1 in terms of raw material type, powder fineness, proportion, water-cement ratio, type and dosage of water-reducing agent, step-by-step liquid addition method, molding method, and curing conditions, and also does not contain a strong alkali activator. The difference is that the high-speed or high-shear stirring stage is omitted, and only ordinary low-speed and medium-speed stirring is used. Specifically, 96g of the initial liquid phase is first added to the dry-mixed gelatin, stirred at low speed for 60s, and then stirred at medium speed for 120s. The remaining 24g of mixed water is then added twice, and stirred at medium speed for 60s and 80s after each addition. High-speed or high-shear stirring is not performed throughout the process, and the other steps are the same.

[0060] After mixing, although the slurry could basically take shape, small local agglomerates could still be observed with the naked eye, indicating weak stacking and retention capabilities. The surface uniformity after vibration was not as good as in Example 1. The results of compressive strength tests at different ages are shown in Table 6.

[0061] Table 6 Comparison of compressive strength between the examples and the comparative examples.

[0062] As shown in Table 6, under the condition of basically the same raw material system, Examples 1-3, which adopted stepwise liquid addition and high-shear stirring, all achieved better strength development, especially showing more obvious continuous strengthening characteristics in the 28-90 day stage. In contrast, when Comparative Example 1 used a one-time liquid addition method, the slurry homogeneity decreased, and the later strength growth was significantly weakened. In Comparative Example 2, although it could still be molded after the high-speed or high-shear stage was eliminated, particle deagglomeration and slurry homogeneity were insufficient, and the overall strength level was lower than that of Example 1. The above results indicate that through the synergistic control of a high steel slag formulation window, ultra-low water-cement ratio, stepwise liquid addition, and high-shear stirring, the slurry can reach a specific non-Newtonian fluid state before molding and form a significant delayed strengthening effect under standard curing conditions.

[0063] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0064] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The material is prepared by the preparation method according to any one of claims 2 to 10.

2. A method for preparing a late-strengthened steel slag-based cementitious material, characterized in that, Includes the following steps: Step 1: The converter steel slag, desulfurized gypsum and slag are dried and ground respectively to obtain converter steel slag powder, desulfurized gypsum powder and slag powder. Step 2: Weigh out 75%–92% of converter steel slag powder, 6%–15% of desulfurized gypsum powder, and 0%–15% of slag powder based on the total mass of the cementitious components. Also weigh out the mixing water and water-reducing agent, wherein the water-cement ratio is 0.10–0.14, and the water-reducing agent dosage is 0.8%–2.0% of the total mass of the cementitious materials. Step 3: Add converter steel slag powder, desulfurized gypsum powder and slag powder to a mixing device for premixing to obtain dry-mixed cementitious material; Step 4: Dissolve the water-reducing agent in the mixing water beforehand. First, mix 70% to 90% of the total mixing water with the water-reducing agent to form an initial liquid phase. Add the initial liquid phase to the dry-mixed cementitious material and stir at low speed to initially wet the powder. Then, stir at high speed or high shear. Add the remaining mixing water 1 to 2 times and continue stirring to make the slurry form a non-Newtonian fluid state. Step 5: The slurry obtained in Step 4 is poured or spread to form a sample or product blank. Step six: Place the sample or product blank obtained in step five under standard curing conditions and cure it to the predetermined age to obtain a late-strengthening steel slag-based cementitious material.

3. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The converter slag in step one is converter slag that has been crushed, magnetically separated and aged; the desulfurized gypsum is gypsum produced as a by-product of flue gas desulfurization; and the slag is granulated blast furnace slag powder.

4. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The specific surface area of ​​the converter steel slag powder, desulfurized gypsum powder, and slag powder in step one is 350-450 m² / kg.

5. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The water-reducing agent in step two is a polycarboxylate-based high-efficiency water-reducing agent, and the dosage of the water-reducing agent is 0.8% to 2.0% of the total mass of the cementitious material.

6. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The mixing equipment in step three is a planetary mixer, a vertical shaft mixer, or a high-shear powder mixing equipment. The premixing process involves first mixing at low speed for 30-60 seconds, and then mixing at medium speed for 60-180 seconds.

7. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, In step four, after adding the initial liquid phase to the dry-mixed gelling agent, the mixture is first stirred at a low speed for 30-90 seconds, then stirred at a high speed or high shear for 90-300 seconds. After adding the remaining mixing water, the mixture is stirred for another 60-180 seconds, and the entire stirring process is completed within 5-15 minutes.

8. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The non-Newtonian fluid state in step four refers to a slurry that has a certain self-supporting ability under stirring, shearing or external force, has continuous fluidity in a static state, and is uniform in overall composition without obvious bleeding, segregation or coarse particle agglomeration.

9. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The molding method in step five is either injection molding or spreading molding. During the molding process, slight vibration can be used to vent air or level the surface. After molding, the slurry is left to stand in the mold for 12 to 24 hours before being demolded.

10. The method for preparing a delayed-strength steel slag-based cementitious material according to claim 2, characterized in that, The standard curing conditions in step six are a temperature of 20±2℃, a relative humidity of not less than 95%, and a curing period of 7 days, 14 days, 28 days, 90 days, and above.

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