A low-carbon composite cementitious material modified by spherical materials and a preparation method thereof

Abstract

The present application relates to the field of low-carbon composite cementitious material, and particularly relates to a kind of spherical material modified low-carbon composite cementitious material and a preparation method thereof.The raw material of the low-carbon composite cementitious material prepared by the present application includes core functional component, auxiliary cementitious component, composite activation system and functional additive;the core functional component is the combination of spherical active powder and fine aggregate;the composite activation system is compounded by desulfurized gypsum and alkali composite activator;the functional additive contains polycarboxylic acid water reducing agent, compounded retarder, defoaming agent and nano modifier;the preparation is classified grinding of spherical material, raw material pretreatment, mixing of basic component, composite activation compounding and homogenization.The present application has high industrial solid waste content, low carbon emission per ton, excellent mechanical properties, durability and working performance of cementitious material, good volume stability, suitable preparation process for existing production line, no high-temperature calcination, realizes high-value utilization of steel slag solid waste, suitable for various environments, and has good application prospect in industrial production direction.

Description

Technical Field

[0001] This invention relates to the field of preparation of low-carbon composite cementitious materials, specifically to a spherical material modified low-carbon composite cementitious material and its preparation method. Background Technology

[0002] Traditional silicate cement production consumes large amounts of resources such as limestone and coal, with approximately 0.8 tons of carbon emissions per ton of cement. It also faces challenges such as resource shortages and environmental pollution. Existing low-carbon cementitious materials primarily use industrial solid wastes such as slag, fly ash, and steel slag as raw materials to achieve carbon reduction by replacing cement clinker. However, this method faces many difficulties in industrialization. For example, industrial solid wastes have low hydration activity, requiring a high proportion of cement clinker or strong activators to ensure mechanical properties, resulting in solid waste content typically below 50%, limiting the low-carbon effect. Traditional steel slag has high levels of free calcium oxide and free magnesium oxide, leading to poor stability; its content in cementitious materials is limited to no more than 15%. The irregular morphology and unreasonable gradation of solid waste particles result in low density of the cementitious system, poor durability properties such as impermeability, freeze-thaw resistance, and wear resistance, and a short service life. Furthermore, existing solid waste-based cementitious materials have complex preparation processes, high energy consumption, poor component compatibility, difficulty in controlling product performance stability, high equipment modification costs, and significant challenges in industrialization.

[0003] Therefore, inventing a low-carbon composite cementitious material with high solid waste content, high performance, and low emissions has great potential for production and application. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a solid waste-based homogeneous slurry and its preparation method. The raw materials for the low-carbon composite cementitious material prepared by this invention include a core functional component, an auxiliary cementitious component, a composite activation system, and functional additives. The core functional component is a combination of spherical active powder and fine aggregate. The composite activation system is a compound of desulfurized gypsum and an alkaline composite activator. The functional additives include polycarboxylate superplasticizer, compound retarder, defoamer, and nano-modifier. The preparation process involves spherical material classification and grinding, raw material pretreatment, basic component mixing, and composite activation and homogenization. This invention features high industrial solid waste content, low carbon emissions per ton, excellent mechanical, durability, and workability properties of the cementitious material, good volume stability, and a preparation process compatible with existing production lines. It eliminates the need for high-temperature calcination, enabling high-value utilization of steel slag solid waste. It is suitable for various environments and has excellent application prospects in industrial production.

[0005] This invention discloses a low-carbon composite cementitious material modified with spherical material, which is composed of the following components in parts by weight:

[0006] The core functional component is 40-70 parts, the auxiliary gelling component is 20-45 parts, the composite activation system is 3.8-13.8 parts, and the functional additive is 0.8-3.3 parts.

[0007] Preferably, the core functional component is a spherical material, consisting of 25-45 parts of spherical active powder and 15-25 parts of spherical fine aggregate.

[0008] Preferably, the auxiliary cementitious components include 15-30 parts of granulated blast furnace slag powder, 5-10 parts of high-calcium fly ash, and 0-5 parts of silicate cement clinker.

[0009] Preferably, the composite activation system includes 3-8 parts of desulfurized gypsum and 0.8-5.8 parts of alkaline composite activator, wherein the alkaline composite activator is composed of sodium hydroxide, water glass and sodium carbonate in a mass ratio of 2:3:1.

[0010] Preferably, the functional additives include 0.2-0.6 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.08-0.3 parts of retarder, 0.02-0.4 parts of defoamer, and 0.5-2 parts of nano-modifier.

[0011] Preferably, the spherical active powder is prepared by closed-circuit grinding of spherical material, which is composed of 31% dicalcium silicate, 10% tricalcium aluminate, 26% magnesium iron tetroxide, 27% iron tetroxide, 4% manganese tetroxide, and 2% chromium tetroxide.

[0012] Preferably, the particle size of the spherical fine aggregate is 0.15~1.18mm.

[0013] Preferably, the retarder is composed of sodium gluconate and sodium citrate in a mass ratio of 3:1.

[0014] This invention also discloses a method for preparing a low-carbon composite cementitious material modified with spherical material, the method comprising the following steps: S1 Raw Material Pretreatment: Spherical materials are sieved through a multi-stage grading sieve to obtain spherical materials of different particle sizes. Spherical materials with a particle size of 0.15~1.18mm are used as spherical fine aggregates; spherical materials smaller than 0.15mm are prepared into spherical active powders by closed-circuit milling; auxiliary cementing components are dried; and nano-modifiers are dispersed. S2 Primary Mixing: Mix the core functional components and pretreated auxiliary cementitious components according to the weight parts to obtain a uniform basic mixture; S3 Composite Activation and Compounding: Add the composite activation system and functional additives to the basic mixture obtained in step S2 according to the weight ratio, mix evenly, and then homogenize. After homogenization, a spherical modified low-carbon composite cementitious material is obtained.

[0015] Preferably, in step S1, the multi-stage grading screen is a three-layer stacked vibrating screen with screen apertures of 1.18mm, 0.5mm, and 0.15mm from top to bottom, a screen body vibration frequency of 45Hz, and an amplitude of 3mm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: A low-carbon composite cementitious material modified with spherical material and its preparation method thereof, which has the following characteristics: (1) The total amount of industrial solid waste in cementitious materials is as high as 70%~90%, of which spherical materials account for 40%~70%, which can effectively replace general silicate cement. Compared with traditional cement production, the carbon emission per ton of product is ≤120kg, and the carbon emission is reduced by 65%~88%. At the same time, it realizes the large-scale high-value utilization of molten steel slag solid waste, solves the resource waste and environmental pollution problems caused by traditional steel slag stockpiling, and achieves low carbon.

[0017] (2) The spherical material contains 31% dicalcium silicate, 10% tricalcium aluminate and other hydration-active minerals, which rapidly hydrate to form CSH gel, ettringite and other hydration products under the action of the composite activation system; its 323 kg / cm³ 3 The high compressive strength and dense packing characteristics of the material significantly improve the density of the cementitious system. The spherical active powder and fine aggregate work synergistically to optimize the cementitious system. Therefore, the prepared low-carbon composite cementitious material has a 3-day compressive strength ≥16MPa, a 7-day compressive strength ≥25MPa, a 28-day compressive strength ≥42.5MPa, and a 90-day compressive strength ≥55MPa. Its early strength meets construction requirements, and its later strength continues to increase. Its mechanical properties are superior to traditional solid waste-based low-carbon cementitious materials and meet the standards of traditional silicate cement of the same grade.

[0018] (3) The spherical material has no free calcium oxide or free magnesium oxide, and the water absorption rate is only 0.06%, and the actual water content is only 0.03%. Combined with the filling effect of the nano modifier, the drying shrinkage rate of the cementitious material is ≤0.035% after 28 days, with no risk of shrinkage and cracking, which solves the problem of poor volume stability of traditional steel slag-based cementitious materials.

[0019] (4) The spherical material is a black spherical solid particle with a sphericity of ≥90%. The smooth spherical shape produces a significant ball effect. Combined with its continuous and reasonable particle size distribution, the water requirement for the standard consistency of the cementitious material is reduced by 18% compared with traditional solid waste cementitious materials. When combined with polycarboxylate high-efficiency water-reducing agent, the product has a flowability of ≥180mm, a water retention of ≥90%, an initial setting time of 160~220min, and a final setting time of 240~300min. It can be adapted to various construction scenarios such as pumping, cast-in-place, precast, and plastering.

[0020] (5) The combination of the compacting effect of spherical material and nano-modifier reduces the porosity of the cementitious hardened body by more than 25%, achieving an impermeability grade ≥ P12 and a chloride ion permeability coefficient ≤ 1.2 × 10⁻⁶. -12 m 2 / s; The high content of iron-based minerals can improve the resistance to sulfate attack, and the sulfate attack resistance coefficient is ≥0.96 after 150 dry and wet cycles; The high hardness spherical particles improve the wear resistance and thus extend the service life, making it suitable for engineering applications in harsh environments such as construction, marine, and roads.

[0021] (6) The low-carbon composite cementitious material prepared by the method provided by this invention has a low water-soluble chloride content, no risk of chloride salt corrosion, and can be safely used in reinforced concrete structures; the preparation process has no wastewater or waste gas emissions, and the dust emission concentration is ≤10mg / m³. 3 It meets national environmental protection emission standards and produces no secondary pollution.

[0022] (7) The preparation method provided by the present invention does not require a high-temperature calcination process. It can be prepared by grading, grinding and mixing at room temperature. The process is short, the energy consumption per ton of product is low, the preparation process can be directly adapted to existing process equipment, the product has stable performance and can be mass-produced. Detailed Implementation

[0023] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0024] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0025] The raw materials used in the examples meet the following standards: Spherical material: The basic phase composition by mass percentage is 31% dicalcium silicate, 10% tricalcium aluminate, 26% magnesium iron tetroxide, 27% iron tetroxide, 4% manganese tetroxide, and 2% chromium tetroxide; the harmful substance indicators meet the following requirements: lead, copper, arsenic, mercury, and cadmium content are all <1mg / kg, hexavalent chromium content is 0.39mg / kg, free silicon content is 0.97%, and water-soluble chloride (Cl-) is ≤0.002%.

[0026] Granulated blast furnace slag powder: meets the requirements of GB / T 18046-2017 S95 grade, with a specific surface area ≥400m2 / kg and a 28d activity index ≥95%.

[0027] High-calcium fly ash: meets the requirements of GB / T 1596-2017 Grade I, with CaO content ≥30% and water requirement ratio ≤95%.

[0028] Silicate cement clinker: meets the relevant technical requirements of GB / T 21372-2008.

[0029] Desulfurized gypsum: Industrial by-product desulfurized gypsum, SO3 content ≥45%, attached water ≤5%.

[0030] Alkaline composite activator: It is composed of sodium hydroxide (flakes, purity ≥98%), water glass (modulus 1.8~2.2, solid content ≥40%), and sodium carbonate (powder, purity ≥99%) in a mass ratio of 2:3:1.

[0031] Polycarboxylate superplasticizer: water reduction rate ≥28%, chloride-free.

[0032] Retarder: It is a mixture of sodium gluconate and sodium citrate in a mass ratio of 3:1.

[0033] Defoamer: It is a compound of organosilicon and polyether defoamers in a mass ratio of 1:2.

[0034] Nano-modifier: It is a compound of nano-silica with a particle size of 20~50nm and nano-calcium carbonate with a particle size of 50~100nm in a mass ratio of 2:1.

[0035] Example 1: A low-carbon composite cementitious material modified with spherical material, composed of the following components by weight: The composition comprises 40 parts core functional components, 20 parts auxiliary cementitious components, 3.8 parts composite activation system, and 0.81 parts functional additives. The core functional component is spherical material, specifically composed of 25 parts spherical active powder and 15 parts spherical fine aggregate; the particle size of the spherical material and fine aggregate is 0.15~1.18mm. The auxiliary cementitious components include 15 parts granulated blast furnace slag powder, 5 parts high-calcium fly ash, and 0 parts silicate cement clinker. The composite activation system includes 3 parts desulfurized gypsum and 0.8 parts alkaline composite activator. The functional additives include 0.2 parts polycarboxylate-based high-efficiency water-reducing agent, 0.08 parts retarder, 0.03 parts defoamer, and 0.5 parts nano-modifier.

[0036] A method for preparing a low-carbon composite cementitious material modified with spherical material includes the following steps: S1 raw material pretreatment: S1-1 Spherical Material Grading Pretreatment: Spherical materials are processed using a 3-layer stacked vibrating screen with screen apertures of 1.18mm, 0.3mm, and 0.15mm from top to bottom. The screen vibration frequency is set at 45Hz, the amplitude at 3mm, and the processing capacity is 10t / h. The spherical materials are fed uniformly into the top screen via a screw conveyor. During the screening process, a high-pressure airflow back-blowing automatic screen cleaning device is activated with a back-blowing pressure of 0.4MPa, back-blowing once every 30 minutes for 10 seconds each time. Large particles on the 1.18mm screen are sent to a jaw crusher for crushing and then returned to the screening system. Particles with a diameter of 0.15~1.18mm are sent to a special bin as spherical fine aggregate. Fine materials under the 0.15mm screen are transported to the grinding process bin through a negative pressure pipeline with a conveying air velocity of 12m / s. The grinding process silo is a vertical roller mill system, with the roller pressure set at 8MPa, the grinding disc speed at 30r / min, and the hot air temperature at 120℃. The feed rate is automatically adjusted according to the mill current, controlling the current fluctuation to ±5%. After grinding, the material is classified by an air classifier at a speed of 1800r / min. The coarse powder is returned to the mill for re-grinding. During the grinding process, the temperature inside the mill is controlled to be ≤80℃ through a cold air valve. Sampling and testing are conducted every hour to control the specific surface area of ​​the obtained spherical active powder to be 380~420m2 / kg and the particle size distribution D50=18~22μm. The qualified fine powder is collected by a cyclone dust collector and sent to a special active powder silo.

[0037] S1-2 Auxiliary Cementitious Component Drying: Granulated blast furnace slag powder, high-calcium fly ash, and desulfurized gypsum are fed into a rotary dryer via a quantitative screw conveyor. The dryer speed is set to 3 r / min, the inclination angle to 3°, the inlet air temperature to 200°C, and the outlet air temperature to 80°C. After drying, the materials are cooled to 32°C via a cooling screw conveyor. After sampling and testing, the moisture content is ≤0.5%, and the materials are sent to their respective sealed silos. The desulfurized gypsum is crushed to a particle size ≤2mm after drying.

[0038] S1-3 Nano Modifier Pre-dispersion Treatment: Weigh nano-silica and nano-calcium carbonate according to the formula, put them into a high-speed mixer, set the speed to 1500 r / min, and pre-mix for 5 min; add spherical active powder accounting for 10% of the total mass of nano powder, and continue mixing for 10 min. The particles are coated by mechanical shearing to prevent the nano particles from agglomerating; the pre-mixed powder is sent to an airflow pulverizer, set the airflow pressure to 0.7 MPa, and the pulverizing chamber temperature to ≤60℃, and further dispersed to obtain nanocomposite powder, which is stored in a special sealed silo with a 20 r / min stirring device.

[0039] S2 Primary Mixing: The core functional components, pretreated auxiliary cementitious components, and desulfurized gypsum, after pretreatment in step S1, are fed into a double-helix conical mixer at a rate of 0.5 t / min by weight. The mixing time is set to 30 r / min and 12 min to obtain the basic mixture.

[0040] S3 Composite Activation and Compounding: Sodium hydroxide, water glass, and sodium carbonate are mixed in a mass ratio of 2:3:1, then deionized water is added to control the solid-liquid ratio at 1:0.8. The stirring speed is set to 60 r / min, and stirring is carried out for 30 min until completely dissolved to obtain an alkaline composite activator. Polycarboxylate superplasticizer, retarder, and defoamer are mixed to obtain a functional additive, which is then diluted with deionized water at a ratio of 5 times the mass of the functional additive. The basic mixture prepared in step S2 is fed into a biaxial zero-gravity mixer with a speed of 40 r / min. The alkaline composite activator solution is atomized and sprayed in at a pressure of 0.3 MPa using a metering pump, with a particle size of 50-100 μm and a spraying time of 3 min. After mixing for another 2 min, the diluted liquid additive complex is sprayed in for another 2 min. Finally, a nano-modifier is added, and mixing is continued for another 8 min to obtain the mixture. The mixture is subjected to a magnetic separator with a magnetic field strength of 10000Gs to remove metal impurities. After impurity removal, it is homogenized by an air homogenizer for 2 hours. After homogenization, a spherical modified low-carbon composite cementitious material is obtained.

[0041] Example 2: A low-carbon composite cementitious material modified with spherical material, composed of the following components by weight: The composition comprises 45 parts core functional components, 25 parts auxiliary cementitious components, 5.8 parts composite activation system, and 1.3 parts functional additives. The core functional component is spherical material, specifically composed of 27.5 parts spherical active powder and 17.5 parts spherical fine aggregate; the particle size of the spherical material and fine aggregate is 0.15~1.18mm. The auxiliary cementitious components include 18 parts granulated blast furnace slag powder, 6 parts high-calcium fly ash, and 1 part silicate cement clinker. The composite activation system includes 4 parts desulfurized gypsum and 1.8 parts alkaline composite activator. The functional additives include 0.3 parts polycarboxylate-based high-efficiency water-reducing agent, 0.18 parts retarder, 0.12 parts defoamer, and 0.7 parts nano-modifier.

[0042] The preparation method of a spherical material modified low-carbon composite cementitious material is the same as that in Example 1.

[0043] Example 3: A low-carbon composite cementitious material modified with spherical material, composed of the following components by weight: The composition comprises 50 parts core functional components, 30 parts auxiliary cementitious components, 7.8 parts composite activation system, and 1.8 parts functional additives. The core functional component is spherical material, specifically composed of 30 parts spherical active powder and 20 parts spherical fine aggregate; the particle size of the spherical material and fine aggregate is 0.15~1.18mm. The auxiliary cementitious components include 21 parts granulated blast furnace slag powder, 7 parts high-calcium fly ash, and 2 parts silicate cement clinker; the composite activation system includes 5 parts desulfurized gypsum and 2.8 parts alkaline composite activator; and the functional additives include 0.4 parts polycarboxylate-based high-efficiency water-reducing agent, 0.28 parts retarder, 0.22 parts defoamer, and 0.9 parts nano-modifier.

[0044] The preparation method of a spherical material modified low-carbon composite cementitious material is the same as that in Example 1.

[0045] Example 4: A low-carbon composite cementitious material modified with spherical material, composed of the following components by weight: The composition comprises 55 parts core functional components, 35 parts auxiliary cementitious components, 9.8 parts composite activation system, and 2.3 parts functional additives. The core functional component is spherical material, specifically composed of 32.5 parts spherical active powder and 22.5 parts spherical fine aggregate; the particle size of the spherical material and fine aggregate is 0.15~1.18mm. The auxiliary cementitious components include 24 parts granulated blast furnace slag powder, 8 parts high-calcium fly ash, and 3 parts silicate cement clinker. The composite activation system includes 6 parts desulfurized gypsum and 3.8 parts alkaline composite activator. The functional additives include 0.5 parts polycarboxylate-based high-efficiency water-reducing agent, 0.13 parts retarder, 0.37 parts defoamer, and 1.3 parts nano-modifier.

[0046] The preparation method of a spherical material modified low-carbon composite cementitious material is the same as that in Example 1.

[0047] Example 5: A low-carbon composite cementitious material modified with spherical material, composed of the following components by weight: The composition comprises 60 parts core functional components, 40 parts auxiliary cementitious components, 11.8 parts composite activation system, and 2.8 parts functional additives. The core functional component is spherical material, specifically composed of 35 parts spherical active powder and 25 parts spherical fine aggregate; the particle size of the spherical material and fine aggregate is 0.15~1.18mm. The auxiliary cementitious components include 27 parts granulated blast furnace slag powder, 9 parts high-calcium fly ash, and 4 parts silicate cement clinker; the composite activation system includes 7 parts desulfurized gypsum and 4.8 parts alkaline composite activator; and the functional additives include 0.6 parts polycarboxylate-based high-efficiency water-reducing agent, 0.25 parts retarder, 0.35 parts defoamer, and 1.6 parts nano-modifier.

[0048] The preparation method of a spherical material modified low-carbon composite cementitious material is the same as that in Example 1.

[0049] Example 6: A low-carbon composite cementitious material modified with spherical material, composed of the following components by weight: The composition comprises 70 parts core functional components, 45 parts auxiliary cementitious components, 13.8 parts composite activation system, and 3.3 parts functional additives. The core functional component is spherical material, specifically composed of 45 parts spherical active powder and 25 parts spherical fine aggregate; the particle size of the spherical material and fine aggregate is 0.15~1.18mm. The auxiliary cementitious components include 30 parts granulated blast furnace slag powder, 10 parts high-calcium fly ash, and 5 parts silicate cement clinker. The composite activation system includes 8 parts desulfurized gypsum and 5.8 parts alkaline composite activator. The functional additives include 0.6 parts polycarboxylate-based high-efficiency water-reducing agent, 0.3 parts retarder, 0.4 parts defoamer, and 2 parts nano-modifier.

[0050] The preparation method of a spherical material modified low-carbon composite cementitious material is the same as that in Example 1.

[0051] Example 7: The core functional components are all composed of spherical fine aggregates, and the remaining raw materials and steps are the same as in Example 4.

[0052] Example 8: The core functional components are all composed of spherical active powders, and the remaining raw materials and steps are the same as in Example 4.

[0053] Example 9: The composite activation system is composed entirely of desulfurized gypsum, and the remaining raw materials and steps are the same as in Example 4.

[0054] Example 10: No nano-modifier was added to the functional additives, and the other raw materials and steps were the same as in Example 4.

[0055] Example 11: The core functional components were replaced with 25 parts of ordinary converter steel slag powder and 15 parts of ordinary river sand. The remaining raw materials and steps were the same as in Example 4.

[0056] The low-carbon composite cementitious materials prepared in Examples 1-11 were subjected to performance testing, and the test results are shown in Tables 1-3 below: Table 1

[0057] Table 2

[0058] Table 3

[0059] From the data in Tables 1-3 above, we can see that: (1) The total amount of industrial solid waste in Examples 1-6 is 89.3-97.5%, of which spherical material accounts for 52.4-61.9% of the total mass; the carbon emission per ton of product is only 91-112 kg. This invention uses spherical material prepared from molten steel slag as the core functional component, which replaces silicate cement clinker with high carbon emission in a large proportion. It does not require a high-temperature calcination process and can be prepared by simply classifying, grinding and mixing at room temperature, which greatly reduces carbon emissions from the source. At the same time, it realizes the large-scale high-value utilization of molten steel slag solid waste and solves the resource waste and environmental pollution problems caused by traditional steel slag stockpiling.

[0060] (2) The 7-day compressive strength of Examples 1-6 was 25.3-31.2 MPa, and the 90-day compressive strength was 55.4-64.2 MPa, of which the 7-day compressive strength of Example 4 was 31.2 MPa and the 90-day compressive strength was 64.2 MPa. This is because the spherical material contains 31% dicalcium silicate, 10% tricalcium aluminate and other hydration-active minerals. Under the synergistic effect of the alkaline gypsum composite activation system, it can quickly break the glass structure, release the active silica-alumina components, and hydrate to generate a large amount of high-strength CSH gel and ettringite. At the same time, the spherical active powder and the spherical fine aggregate work together to achieve the compact packing of the cementitious system. The high compressive strength spherical particles, as the skeleton, further improve the density and mechanical properties of the hardened body.

[0061] (3) The mortar fluidity of Examples 1-6 is 182-215 mm; the water retention is 90.2-94.8%; the initial setting time is 180-218 min and the final setting time is 256-298 min. This is because the spherical material is a smooth spherical particle with a sphericity of ≥90%, which produces an obvious ball effect in the cementitious system, greatly reducing the frictional resistance between particles and reducing the water requirement for standard consistency; combined with a high water-reducing polycarboxylate-based high-efficiency water-reducing agent, the fluidity and water retention of the slurry are further optimized; at the same time, the setting time can be controlled and adjusted by the regulation of sodium gluconate and sodium citrate compound retarder, which can be adapted to various construction scenarios such as pumping, cast-in-place, precast, and plastering.

[0062] (4) The 28-day shrinkage rates of Examples 1 to 6 were only 0.025% to 0.034%, all meeting the design requirement of ≤0.035%, with no risk of shrinkage cracking. Among them, the shrinkage rate of Example 4 was as low as 0.025%, with the best volume stability. The spherical material has no free calcium oxide or free magnesium oxide, thus avoiding the volume expansion and stability problems caused by the post-hydration of f-CaO and f-MgO in traditional converter steel slag; at the same time, its own water absorption rate is only 0.06% and water content is only 0.03%, which can significantly reduce the hydration shrinkage of the cementitious system; combined with the micro-filling effect of the nano-modifier, it can effectively fill the capillary pores of the hardened body, further reducing the shrinkage deformation.

[0063] (5) The impermeability grades of Examples 1 to 6 reach P12 to P16; the chloride ion permeability coefficient is 0.72 to 1.18 × 10⁻⁶. -12 m 2 / s; the sulfate resistance coefficient after 150 wet-dry cycles is 0.961~0.985. The synergistic effect of the dense packing effect of the spherical material and the micro-filling effect of the nano-modifier reduces the porosity of the cementitious hardened body by more than 25%, refines the pore structure, blocks water seepage and chloride ion penetration channels, and improves the impermeability and chloride ion penetration resistance. At the same time, the high iron content in the spherical material can effectively improve the sulfate resistance of the cementitious system, and the high hardness of the spherical particles can significantly improve the wear resistance of the material and extend the service life of the project. It is suitable for harsh environment engineering such as construction, marine, and road.

[0064] (6) In Example 7, without the addition of spherical active powder, the low-carbon composite cementitious material prepared had low compressive strength, and its fluidity, setting time, shrinkage rate, and resistance to seepage and erosion were all unqualified. This is because the spherical fine aggregate is used as a physical skeleton filler. When spherical active powder is not added, the hydration of only a small amount of auxiliary cementitious components cannot generate sufficient CSH gel and ettringite, thus failing to form a high-strength three-dimensional cementitious structure. Moreover, the porosity will increase significantly, resulting in a decrease in the mechanical properties and other properties of the final product.

[0065] (7) In Example 8, no spherical fine aggregate was added. Although the strength of the low-carbon composite cementitious material prepared was relatively high at 7 days, the compressive strength at 90 days was only 48.6 MPa. This is because the fully active powder hydrates quickly in the early stage and has high early strength. However, without the skeleton support of spherical fine aggregate, the cementitious system cannot achieve close packing, which leads to an increase in the porosity of the hardened body and a decrease in strength in the later stage.

[0066] (8) In Example 9, without the addition of the alkaline composite activator, all aspects of performance decreased. The strongly alkaline environment provided by the alkaline composite activator can quickly break the glassy network structure of spherical materials, slag, and fly ash, releasing the active silica-alumina components, which then react synergistically with the sulfate ions provided by the desulfurized gypsum to generate ettringite and promote CSH gel growth. Using only desulfurized gypsum as a single component cannot provide a sufficient alkaline environment, the glassy structure of the active minerals cannot be effectively broken, the hydration reaction is insufficient and the process is slow, ultimately leading to a comprehensive deterioration of all performance aspects. (9) In step 10, no nano-modifier was added. Nano-modifiers can provide growth sites for hydration products, promoting uniform and dense growth of hydration products. Nanoparticles can fill the capillary pores of gel hydration products, refining the pore structure, reducing porosity, and improving the density of the system. After removing the nano-modifier, the proportion of harmful pores in the gel system increased, and the number of capillary pores increased, ultimately leading to an increase in drying shrinkage, a decrease in water retention, and a deterioration in impermeability and erosion resistance.

[0067] (10) Example 11 uses commonly used materials in the prior art. The low-carbon composite cementitious materials prepared are inferior to the products prepared by the preparation method provided by the present invention in terms of performance. Common converter steel slag commonly used in the prior art contains a large amount of free calcium oxide and free magnesium oxide, with low hydration activity and poor volume stability, and is prone to expansion and cracking in the later stage; ordinary river sand is an irregular particle without spherical morphology, which cannot produce a ball effect, requires a large amount of water and has poor workability; at the same time, the active mineral content of ordinary steel slag is much lower than that of spherical material, and there is no high content of iron-based minerals, resulting in insufficient hydration reaction and poor erosion resistance.

[0068] In summary, the low-carbon composite cementitious material prepared by the method provided by this invention not only achieves large-scale, high-value utilization of molten steel slag solid waste, but also solves the environmental problems associated with traditional steel slag stockpiling. Furthermore, the preparation process is simple, low-carbon, and low-consumption, showing great promise for industrialized production. Among these, Example 4 exhibits the best ratio of active powder to fine aggregate and optimal matching of the composite activation system dosage, resulting in the best overall performance.

[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A low-carbon composite cementitious material modified with spherical material, characterized in that, Composed of the following components by weight: The core functional component is 40-70 parts, the auxiliary gelling component is 20-45 parts, the composite activation system is 3.8-13.8 parts, and the functional additive is 0.8-3.3 parts.

2. The low-carbon composite cementitious material modified with spherical material according to claim 1, characterized in that, The core functional component is a spherical material, consisting of 25-45 parts of spherical active powder and 15-25 parts of spherical fine aggregate.

3. The low-carbon composite cementitious material modified with spherical material according to claim 1, characterized in that, The auxiliary cementitious components include 15-30 parts of granulated blast furnace slag powder, 5-10 parts of high-calcium fly ash, and 0-5 parts of silicate cement clinker.

4. The low-carbon composite cementitious material modified with spherical material according to claim 1, characterized in that, The composite activation system includes 3-8 parts of desulfurized gypsum and 0.8-5.8 parts of alkaline composite activator, wherein the alkaline composite activator is composed of sodium hydroxide, water glass and sodium carbonate in a mass ratio of 2:3:

1.

5. The low-carbon composite cementitious material modified with spherical material according to claim 1, characterized in that, The functional additives include 0.2-0.6 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.08-0.3 parts of retarder, 0.02-0.4 parts of defoamer, and 0.5-2 parts of nano-modifier.

6. The low-carbon composite cementitious material modified with spherical material according to claim 2, characterized in that, The spherical active powder is prepared by closed-circuit grinding of spherical material, which consists of 31% dicalcium silicate, 10% tricalcium aluminate, 26% magnesium iron tetroxide, 27% iron tetroxide, 4% manganese tetroxide, and 2% chromium tetroxide.

7. The low-carbon composite cementitious material modified with spherical material according to claim 2, characterized in that, The spherical fine aggregate has a particle size of 0.15~1.18 mm.

8. The low-carbon composite cementitious material modified with spherical material according to claim 5, characterized in that, The retarder is composed of sodium gluconate and sodium citrate in a mass ratio of 3:

1.

9. A method for preparing a low-carbon composite cementitious material modified with spherical material, characterized in that, Includes the following steps: S1 Raw Material Pretreatment: Spherical materials are screened through a multi-stage grading screen to obtain spherical materials of different particle sizes. Spherical materials with a particle size of 0.15~1.18mm are used as spherical fine aggregates. Spherical active powder was prepared by closed-circuit milling of spherical material smaller than 0.15 mm; the auxiliary cementitious component was dried; and the nano-modifier was dispersed. S2 Primary Mixing: Mix the core functional components and pretreated auxiliary cementitious components according to the weight parts to obtain a uniform basic mixture; S3 Composite Activation and Compounding: Add the composite activation system and functional additives to the basic mixture obtained in step S2 according to the weight ratio, mix evenly, and then homogenize. After homogenization, a spherical modified low-carbon composite cementitious material is obtained.

10. The method for preparing a spherical material-modified low-carbon composite cementitious material according to claim 9, characterized in that, In step S1, the multi-stage grading screen is a three-layer stacked vibrating screen with screen apertures of 1.18mm, 0.5mm, and 0.15mm from top to bottom, respectively, a screen body vibration frequency of 45Hz, and an amplitude of 3mm.

Images