A method for preparing a low-carbon cementitious material for soil stabilization and applications thereof

Abstract

The application relates to the technical field of building materials, and discloses a preparation method of low-carbon cementitious material for soil solidification of a foundation and application thereof, raw materials include, in weight fractions, 450-550 parts of finely ground iron tailing powder, 300-350 parts of slag powder, 100-200 parts of ordinary Portland cement, 50-100 parts of steel slag powder, 20-30 parts of sulphoaluminate cement, 50-100 parts of desulfurization gypsum, and 10-50 parts of calcium carbide slag; wherein the particle size D10 of the finely ground iron tailing powder is less than or equal to 2 microns, the specific surface area is 680-850 m2 / kg, and the finely ground iron tailing powder contains 0.2%-0.5%wt of a composite grinding aid; the finely ground iron tailing powder is a kind of powder material with cementitious activity; the cementitious material prepared by taking the finely ground iron tailing powder as a main component is used for soil solidification in foundation engineering, and replaces the use of traditional cement; the engineering cost is greatly reduced, and the carbon emission in the engineering is also greatly reduced.

Description

[0001] This application is a divisional application of application filed on December 1, 2025, with application number 202511789792X and invention title "Preparation and Application Method of Low-Carbon Cementitious Material for Foundation Soil Solidification". Technical Field

[0002] This invention relates to the field of building materials technology, specifically to a method for preparing a low-carbon cementitious material for foundation soil solidification and its application. Background Technology

[0003] In the construction of infrastructure such as highways, railways, airports, and industrial and civil buildings, foundation treatment is a crucial step in ensuring the safety and stability of the project. Geotechnical engineering typically requires the consumption of large amounts of solidifying agents (or cementing materials) to improve weak soils and enhance their bearing capacity and stability. Traditionally, silicate cement has dominated the field of soil solidification due to its excellent consolidation strength, good water resistance, and mature application technology.

[0004] However, the production of silicate cement is a high-energy-consuming and high-emission process, emitting approximately 0.8-0.9 tons of carbon dioxide per ton of cement clinker produced. With the increasingly severe global climate change problem, my country has proposed the "3060" dual-carbon strategy (peak carbon emissions by 2030 and carbon neutrality by 2060), which requires all industries, especially the building materials industry, to transform towards green and low-carbon practices. Therefore, limiting and gradually replacing high-carbon-emission cement and developing new low-carbon cementitious materials have become an inevitable trend and research hotspot in the industry.

[0005] Currently, the comprehensive utilization rate of metal tailings is only 33%, with the utilization rate of fine-grained tailings, which are the most difficult to dispose of, being as low as 5%. How to dispose of metal tailings on a large scale and with high added value is a major challenge to achieving the construction of "tailings-free mines" and the sustainable development of the mining industry.

[0006] Metal tailings, especially those containing iron, copper, and gold, are primarily composed of silicon dioxide (SiO2) and aluminum oxide (Al2O3), similar to traditional pozzolanic materials such as fly ash and slag, theoretically possessing the potential to serve as cementing materials. Therefore, many scholars have attempted to apply metal tailings to the building materials field. However, most studies treat tailings as an inert micro-aggregate or filler, utilizing their filling effect to improve the density of concrete or mortar. In this application model, the chemical activity of the tailings is not effectively activated, and their dosage is typically limited to below 15%, otherwise, it leads to a significant decrease in material strength. This low-dosage, low-value utilization method is largely ineffective for disposing of massive amounts of tailings and fails to fundamentally solve the problem.

[0007] Therefore, there is an urgent need to develop a technology that can effectively stimulate the cementitious activity of metal tailings and achieve their high utilization rate, and based on this, to prepare a soil stabilizer that can replace cement on a large scale, meet engineering performance requirements, and has both low carbon, environmental protection and economic benefits. Summary of the Invention

[0008] This invention provides a method for preparing a low-carbon cementitious material for foundation soil solidification and its application. Through a mechanical-chemical composite activation method, iron tailings powder material with cementitious activity is activated to prepare a cementitious material with this material as the main component. This material is used for soil solidification in foundation engineering, replacing traditional cement and significantly reducing engineering costs while also substantially reducing carbon emissions. To achieve the above objectives, this invention adopts the following technical solution: A low-carbon cementitious material for foundation soil solidification, characterized in that its raw materials comprise, by weight, the following: 450-550 parts of finely ground iron tailings powder; 300-350 parts of slag powder; 100-200 parts of ordinary Portland cement; 50-100 parts of steel slag powder; 20-30 parts of sulfoaluminate cement; 50-100 parts of desulfurized gypsum; 10-50 parts of calcium carbide slag; The finely ground iron tailings powder is prepared by mixing and grinding raw iron tailings with a composite grinding aid. The finely ground iron tailings powder has a particle size D10≤1.2μm and a specific surface area of ​​750-850m² / kg. The composite grinding aid activator is composed of diethanol monoisopropanolamine, sodium hexametaphosphate, and sodium formate in a mass ratio of 1:5:8, and the addition amount is 0.3%-0.5% of the iron tailings mass. The surface of the finely ground iron tailings powder particles has an amorphous ferrosilicon activation layer with a thickness of 10-20 nm, and under alkaline activation environment, the iron element in the finely ground iron tailings powder participates in the hydration reaction to generate iron-based ettringite. The sodium formate in the composite grinding aid activator forms an iron ion complex system with diethanol monoisopropanolamine, which is used to promote the dissolution of Fe3+ in iron tailings.

[0009] The ternary system of "diethanol monoisopropanolamine-sodium formate-sodium hexametaphosphate" contained in this invention not only plays a grinding aid role, but also constitutes a dual-effect system of "physical dispersion-chemical complexation": Diethanol monoisopropanolamine: Through its special amine structure, it adsorbs onto the broken bond surface of fine particles, providing steric hindrance, and physically effectively solves the problem of electrostatic agglomeration of ultrafine powders with D10≤1.2μm.

[0010] Sodium formate and sodium hexametaphosphate: synergistically act on the magnetite and hematite phases on the surface of iron tailings, inducing non-stoichiometric dissolution of Fe³⁺. The dissolved active Fe³⁺ enters the liquid phase, reacting with Ca(OH)₂ and SO₄ provided by sulfoaluminate cement and carbide slag in the system. 2- The reaction produces iron-containing ettringite in situ.

[0011] Compared to ordinary ettringite, iron-bearing ettringite has higher density and microhardness, and its crystal growth morphology is better able to fill the micro- and nano-pores of the foundation soil. In this invention, the iron tailings are no longer inert fillers, but rather a chemical component that directly contributes to strength.

[0012] There is a significant natural potential difference between finely ground iron tailings powder (containing magnetite) and steel slag powder (mainly containing RO phase and a small amount of metallic iron).

[0013] When the two are mixed and come into contact with pore water (electrolyte), countless microscopic galvanic cells are formed inside the mixture. This micro-cell effect accelerates electron transfer on the surface of the steel slag, causing the glassy network of the steel slag to depolymerize rapidly, and the reaction rate is 3-5 times higher than that of traditional chemical excitation.

[0014] This invention enables the achievement of rapid early strength even with low cement content.

[0015] The sulfoaluminate cement meets the requirements of rapid-hardening (R·SAC) grade 42.5 and above in the standard "Ssulfoaluminate Cement" (GB 20472-2006). The sulfoaluminate cement clinker used conforms to the standard GB / T37125-2018, with an alkalinity coefficient of 0.9-1.0 and an aluminum-sulfur ratio of 3.0-4.0. The sulfoaluminate cement can rapidly generate a large number of fine ettringite grains in the early stages of cementitious material hydration, providing the nuclei needed for the hydration of iron tailings powder to form ettringite, and increasing the expansion component in the hardened cementitious material.

[0016] This invention, through the relationship between iron tailings grinding time and specific surface area, reveals that without the addition of grinding aids, reverse grinding easily occurs, leading to material agglomeration and making it difficult to further increase the specific surface area. Using the composite grinding aid activator of this invention effectively delays the onset of the reverse grinding stage, prevents premature material agglomeration, significantly improves grinding efficiency, and ensures that the specific surface area of ​​the iron tailings meets the activation requirements.

[0017] During the mechanical activation process of iron tailings, the diethanol monoisopropanolamine improves grinding fluidity by reducing electrostatic adsorption between solid material particles, and forms a "slow-release shell" on the surface of the iron tailings using grinding aids, thereby optimizing the distribution of powder particles and increasing the specific surface area. During the hydration process of the curing agent, it can continuously stimulate the activity of the mixture of slag, steel slag, and finely ground iron tailings powder, thereby improving the 28-day strength.

[0018] The sodium hexametaphosphate plays a grinding aid role in the ultrafine grinding process of iron tailings, eliminating the agglomeration of ultrafine particles, and preventing sedimentation and bleeding in concrete mixtures, effectively improving the workability of the mixtures.

[0019] During the hydration process of the soil stabilizer, the sodium formate can continuously stimulate the depolymerization and hydration of the silicon-aluminum network in the slag powder and steel slag powder through multi-stage hydrolysis.

[0020] Preferably, the chemical composition and mass percentage of the finely ground iron tailings powder are as follows: SiO2 45%-60%, Al2O3 5%-15%, Fe2O3 8%-20%, CaO 3%-10%, MgO 3%-10%, K2O 1%-3%, Na2O 2%-4%, SO3 0%-4%, and other unavoidable impurities 2%-4%.

[0021] Preferably, the mineral composition of the finely ground iron tailings powder includes 35%-45% quartz, 15%-25% potassium feldspar, 10%-20% sodium feldspar, 10%-15% mica, 5%-10% chlorite, and 10%-15% other minerals.

[0022] Preferred, the slag powder is S95 grade slag powder with a specific surface area of ​​420-450 m² / kg. It participates in the secondary hydration of iron tailings powder, slowly releasing and supplementing the active silica-alumina components required for the hydration of iron tailings powder-based low-carbon cementitious materials. The steel slag powder is finely ground steel slag powder with a specific surface area of ​​500-550 m² / kg. Steel slag contains a large amount of high-temperature molten silicate minerals, which have hydration activity after grinding. It can form a synergistic effect with the clinker mineral components in the silicate cement in the curing agent, effectively supplementing the active mineral components for the later hydration of the curing agent. The ordinary silicate cement is P.O42.5 grade cement with a specific surface area ≥300 m² / kg and a clinker ratio of not less than 75 wt%. The ordinary silicate cement selected in this invention generates strength through its own hydration in the early stage, and more importantly, provides the calcium components required for the hydration of the surface active silica-alumina components of iron tailings powder. In addition, it also plays a role in stimulating the depolymerization and secondary hydration of the glassy structure in the slag powder. The desulfurized gypsum is an industrial by-product with an SO3 content greater than 35% and a specific surface area of ​​200-250 m² / kg. It can provide the SO4 required in the hydration process of iron tailings powder and slag powder. 2- Ions stimulate the dissolution and hydration of active SiO2 and Al2O3 in iron tailings powder and slag powder.

[0023] Preferably, the median particle size D50 of the ground iron tailings powder is 4-6 μm. During the grinding process, as the D50 value decreases, the number of unsaturated bonds on the surface of the iron tailings powder particles increases continuously, causing the silicon and aluminum components on the surface of the crystalline minerals to undergo an amorphous transformation, changing from an inert state to an active state, and acquiring hydration activity.

[0024] This invention also discloses a method for preparing a low-carbon cementitious material for foundation soil solidification, comprising the following steps: Step 1: Mix the dried iron tailings with the composite grinding aid activator; Step 2: Use a high-energy ball mill for mechanochemical activation grinding, control the grinding temperature at 50-70℃ to prevent the organic grinding aid from volatilizing and becoming ineffective, grind until D10≤1.2μm and powder rheological index>1.2 to obtain finely ground iron tailings powder; Step 3: Mix the finely ground iron tailings powder obtained in Step 1 with slag powder, ordinary silicate cement, steel slag powder, sulfoaluminate cement, desulfurized gypsum and carbide slag evenly to obtain a low-carbon cementitious material.

[0025] Preferably, in step one, the drying temperature is 100-110℃, the drying time is 4-6 hours, the grinding speed is 45-55 r / min, the grinding time is 60-90 minutes, and the moisture content of the dried iron tailings is ≤1.5 wt%. By controlling the speed and grinding time, the iron tailings powder with the highest activity can be obtained. If the grinding time is too short, the iron tailings powder cannot be ground sufficiently; if the grinding time is too long, the internal cracks of the iron tailings powder particles begin to show "compaction" and "welding" phenomena, resulting in a decrease in the specific surface area of ​​the iron tailings and thus a decrease in reaction activity.

[0026] Preferably, in step one, the finely ground iron tailings powder has a particle size D50 of 4-6 μm, a specific surface area of ​​680-850 m² / kg, a total Si+Al leaching concentration of ≥100 mg / L in alkaline solution, and a 28-day activity index ≥75%. By adding modifying components such as slag powder, ordinary silicate cement, and sulfoaluminate cement, its activity can be increased to over 95%.

[0027] This invention also discloses an application method for a low-carbon cementitious material for foundation soil solidification, which is used for soil solidification in foundation engineering. The raw materials include, by weight, 100-200 parts of low-carbon cementitious material, 300-380 parts of water, and 1500-1650 parts of foundation soil. After being mixed and stirred evenly, the mixture is poured into a mold or construction site, compacted, and cured to obtain solidified foundation soil.

[0028] This invention also discloses the application of a low-carbon cementitious material for foundation soil solidification in foundation engineering, used for roadbed soil solidification, foundation pile solidification, or soft soil foundation reinforcement. The dosage of the soil solidification agent is 5%-10% of the mass of the foundation soil, which can completely replace the traditional construction method of cement solidification of foundation soil.

[0029] The present invention has the following beneficial effects: 1. This invention provides a method for preparing a low-carbon cementitious material for foundation soil solidification and its application. Through a non-calcining composite activation method, the total cement clinker content in the manufactured finely ground iron tailings powder-based solidifier is less than 15%, the finely ground iron tailings powder content exceeds 45%, and other components are industrial solid wastes such as steel slag, carbide slag, and desulfurization gypsum. Carbon emissions are only less than 35% of traditional cement, and the strength index of the obtained low-carbon cementitious material can reach the standard of 42.5 grade cement. This cementitious material can be used as a soil solidifier in foundation engineering to consolidate foundation soil, including roadbed soil and various foundation piles, achieving the same effect as traditional cement while significantly reducing cost and carbon emissions. This invention solves the problem of high costs in foundation engineering and also increases the utilization rate of fine-grained metal tailings, addressing the problem of limited storage capacity in metallurgical mining enterprises. The solidified soil prepared using the fine iron tailings powder-based solidifier prepared by this invention can meet the requirements of engineering applications in all aspects. When solidified soil is prepared by replacing P·S·A42.5 cement in the same proportion, the mechanical properties and durability of the solidified body can meet or exceed the indicators of P·S·A42.5 reference cement.

[0030] 2. Compared with the traditional use of cement as a curing agent in foundation engineering, the above-mentioned finely ground iron tailings powder-based curing agent provided by the present invention can completely replace slag silicate cement in foundation engineering and achieve a comprehensive performance superior to cement consolidation. This greatly reduces the consumption of cement and other cementitious materials, lowers the construction cost of foundation engineering, reduces carbon emissions, and increases the proportion of resource-based disposal and utilization of metal tailings, thus achieving the goal of low-carbon, safe, and efficient production.

[0031] 3. This invention significantly improves the activity of iron tailings powder through a mechanical-chemical composite activation method. The content of finely ground iron tailings powder in the cementitious material exceeds 45%, the total content of cement clinker is within 15%, and other component materials are industrial solid wastes such as steel slag, carbide slag, and desulfurization gypsum. 90% of the raw materials are industrial solid waste materials, which greatly improves the utilization rate of fine-grained metal tailings.

[0032] The strength index of the finely ground iron tailings powder-based low-carbon cementitious material prepared by this invention can reach the standard of 42.5 grade cement. The 7-day unconfined compressive strength of the solidified soil prepared with it is 51.6%-96.4% higher than that of cement-solidified soil, and the 28-day unconfined compressive strength is 27.03%-98.34% higher, with significantly improved mechanical properties.

[0033] 4. The low-carbon cementitious material prepared by this invention has a slow-release shell structure. In the initial stage of mixing with the foundation soil, this shell prevents the rapid adsorption of calcium ions in the gel material by clay minerals, avoiding the phenomenon of "false coagulation" and ensuring the fluidity and permeability of the slurry. When mixing is completed and static solidification begins, the high pH environment in the soil hydrolyzes away this protective shell, releasing the encapsulated highly active micro-powders, which react at the contact points with the soil particles. This solves the industry problem of traditional curing agents being difficult to disperse evenly and easily encapsulated by clay, leading to their failure. Attached Figure Description

[0034] Figure 1 This is an image showing the appearance of the iron tailings powder-based cementitious material in an embodiment of the present invention. Figure 2 This is a mineral phase composition analysis diagram of the original iron tailings in an embodiment of the present invention; Figure 3 This is a microscopic morphology diagram of the original iron tailings in an embodiment of the present invention; Figure 4 This is a diagram showing the change in specific surface area during the iron tailings grinding process in an embodiment of the present invention. Figure 5 This is a graph showing the change in crystallinity during the iron tailings grinding process in an embodiment of the present invention; Figure 6 This is a microscopic morphology diagram of unconsolidated foundation soil in an embodiment of the present invention; Figure 7 This is a microscopic morphology image of the iron tailings powder-based cementitious material during the 7-day hydration process in an embodiment of the present invention. Figure 8 This is a microscopic morphology diagram of the 28-day hydration process of the iron tailings powder-based cementitious material in an embodiment of the present invention. Figure 9 This is a microscopic morphology image of a cement-consolidated foundation soil specimen after 28 days, as shown in this embodiment of the invention. Figure 10 This is a microscopic morphology image of a 28-day specimen of foundation soil consolidated with iron tailings powder-based cementitious material in an embodiment of the present invention. Detailed Implementation

[0035] 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.

[0036] A low-carbon cementitious material for foundation soil solidification, comprising the following raw materials in parts by weight: 450-550 parts of finely ground iron tailings powder; 300-350 parts of slag powder; 100-200 parts of ordinary Portland cement; 50-100 parts of steel slag powder; 20-30 parts of sulfoaluminate cement; 50-100 parts of desulfurized gypsum; 10-50 parts of calcium carbide slag; The finely ground iron tailings powder is prepared by mixing and grinding raw iron tailings with a composite grinding aid. The finely ground iron tailings powder has a particle size D10≤1.2μm and a specific surface area of ​​750-850m² / kg. The composite grinding aid activator is composed of diethanol monoisopropanolamine, sodium hexametaphosphate, and sodium formate in a mass ratio of 1:5:8, and the addition amount is 0.3%-0.5% of the iron tailings mass. The surface of the finely ground iron tailings powder particles has an amorphous ferrosilicon activation layer with a thickness of 10-20 nm, and under alkaline excitation environment, the iron element in the finely ground iron tailings powder participates in the hydration reaction to generate iron-based ettringite.

[0037] The sodium formate in the composite grinding aid activator forms an iron ion complex system with diethanol monoisopropanolamine, which is used to promote the dissolution of Fe3+ in iron tailings.

[0038] The chemical composition and mass percentage of the finely ground iron tailings powder are as follows: SiO2 45%-60%, Al2O3 5%-15%, Fe2O3 8%-20%, CaO 3%-10%, MgO 3%-10%, K2O 1%-3%, Na2O 2%-4%, SO3 0%-4%, and other unavoidable impurities 2%-4%.

[0039] The mineral composition of the finely ground iron tailings powder includes 35%-45% quartz, 15%-25% potassium feldspar, 10%-20% sodium feldspar, 10%-15% mica, 5%-10% chlorite, and 10%-15% other minerals.

[0040] The slag powder is S95 grade slag powder with a specific surface area of ​​420-450 m² / kg; the steel slag powder is finely ground steel slag powder with a specific surface area of ​​500-550 m² / kg; the ordinary Portland cement is P.O42.5 grade with a specific surface area ≥300 m² / kg and a clinker ratio of not less than 75 wt%; the desulfurized gypsum has an SO3 content greater than 35% and a specific surface area of ​​200-250 m² / kg.

[0041] A method for preparing a low-carbon cementitious material for foundation soil solidification includes the following steps: Step 1: Mix the dried iron tailings with the composite grinding aid activator; Step 2: Use a high-energy ball mill for mechanochemical activation grinding, control the grinding temperature at 50-70℃ to prevent the organic grinding aid from volatilizing and becoming ineffective, grind until D10≤1.2μm and powder rheological index>1.2 to obtain finely ground iron tailings powder; Step 3: Mix the finely ground iron tailings powder obtained in Step 1 with slag powder, ordinary silicate cement, steel slag powder, sulfoaluminate cement, desulfurized gypsum and carbide slag evenly to obtain a low-carbon cementitious material.

[0042] In step one, the drying temperature is 100-110℃ and the drying time is 30-45 min; the grinding speed is 45-55 r / min and the grinding time is 60-90 min; and the moisture content of the iron tailings after drying is ≤1.5 wt%.

[0043] In step two, the particle size D50 of the ground iron tailings powder is 4.6 μm, the total leaching concentration of Si+Al elements in the ground iron tailings powder in alkaline solution is ≥100 mg / L, and the activity index is ≥75% after 28 days.

[0044] A method for applying a low-carbon cementitious material for foundation soil solidification, used for soil solidification in foundation engineering, the raw materials include by weight: 100-200 parts of low-carbon cementitious material, 300-380 parts of water and 1500-1650 parts of foundation soil, after being mixed and stirred evenly, it is poured into a mold or construction site, compacted and cured to obtain solidified foundation soil.

[0045] The application of a low-carbon cementitious material for foundation soil solidification in foundation engineering, used for roadbed soil solidification, foundation pile solidification or soft soil foundation reinforcement, wherein the dosage of the soil solidification agent is 5%-10% of the mass of the foundation soil.

[0046] In the embodiments of this application, the specific preparation method of the low-carbon cementitious material includes: S1. Take the wet iron tailings after pressure filtration, dry them in a drying oven until the moisture content is less than 1.50%, then take them out and let them air dry to room temperature for later use.

[0047] S2. Diethanol monoisopropanolamine, sodium hexametaphosphate and sodium formate are mixed and compounded in a mass ratio of 1:5:8 to prepare a composite grinding aid activator. S3. Add the composite grinding aid to the dried original iron tailings and grind them in a ball mill to obtain ultrafine iron tailings powder. S4. Mix the ultrafine iron tailings powder with the ordinary silicate cement, rapid hardening sulfoaluminate cement, mineral powder, steel slag powder, desulfurized gypsum and carbide slag evenly to obtain the soil-solidified iron tailings powder-based cementitious material.

[0048] This invention also provides a method for preparing a foundation solidified soil specimen made with the above-mentioned iron tailings powder-based soil solidifier, wherein the raw materials include, by weight, 100-200 parts of the above-mentioned iron tailings powder-based solidifier, 300-380 parts of water and 1500-1650 parts of foundation soil.

[0049] The embodiments of the present invention will be further described below with reference to several examples.

[0050] In the following examples, the XRD patterns of iron tailings powder are shown as follows: Figures 1-10 As shown, the quartz content is 24.2%, potassium feldspar content is 31.1%, sodium feldspar content is 23.8%, biotite content is 6.2%, and the balance is other minerals. The chemical composition and mass percentage of the iron tailings powder are: 58.9% SiO2, 14.3% Al2O3, 15.6% Fe2O3, 3.0% CaO, 2.2% MgO, 2.1% K2O, 2.4% Na2O, and 2.3% SO3. The test mill used was a 5kg cement test mill, model Ø500×500. The dry-basis undisturbed iron tailings were obtained by drying the wet-basis fine-grained iron tailings after pressure filtration in a forced-air drying oven for 6 hours at a drying temperature of 110℃, and the moisture content after drying was ≤1.5wt%.

[0051] The S95 grade mineral powder in the following examples has a specific surface area of ​​430 m². 2 / kg, steel slag powder specific surface area 545m² 2 / kg; Sulfoaluminate cement meets the requirements of rapid-hardening (R·SAC) grade 42.5 in the standard "Sulfoaluminate Cement" (GB 20472-2006), and the sulfoaluminate clinker used meets the standard GB / T37125-2018, with an alkalinity coefficient (cm) of 0.98 and an aluminum-sulfur ratio (Ps) of 3.5; Ordinary Portland cement meets the requirements of P·O 42.5 grade cement in the national standard "General Portland Cement" (GB175-2023); Desulfurized gypsum and carbide slag are both industrial by-products, powdery materials, and the specific surface area of ​​desulfurized gypsum is 280m². 2 / kg, the specific surface area of ​​carbide slag is 336m² 2 / kg; Sodium hexametaphosphate is in powder form with a specific surface area of ​​220m². 2 / kg; Sodium formate is in powder form with a specific surface area of ​​200m². 2 / kg; Diethanol monoisopropanolamine is a viscous, yellow, transparent liquid. Example

[0052] This invention provides a method for preparing a low-carbon cementitious material for foundation soil solidification: The dried undisturbed iron tailings were placed in a test mill and ground at a speed of 45 r / min for 3 minutes. This process was sufficient to disperse the tailings and aids, resulting in fine-grained undisturbed iron tailings powder. The tested specific surface area was 313 m². 2 / kg, median particle size (D50) is 16.21μm. Take 200 parts of dry, unprocessed fine-grained iron tailings, 450 parts of S95 grade slag powder, 50 parts of steel slag powder, 200 parts of PO42.5 cement, 30 parts of rapid-hardening sulfoaluminate cement, 50 parts of desulfurized gypsum, and 20 parts of carbide slag. Put the materials into a mixer and mix them evenly to obtain iron tailings-based cementitious material A1. Example

[0053] This invention provides a method for preparing a low-carbon cementitious material for foundation soil solidification: A composite grinding aid (diethanolamine monoisopropanolamine + sodium hexametaphosphate + sodium formate) was prepared at a ratio of 0.5% by mass of dry iron tailings and ground with the dried undisturbed iron tailings in a test mill. The mill speed was 45 r / min and the grinding time was 40 min, resulting in finely ground iron tailings powder with a tested specific surface area of ​​582 m². 2 / kg, with a median particle size (D50) of 6.23μm; Take 300 parts of dry, unprocessed fine-grained iron tailings, 350 parts of S95 grade slag powder, 50 parts of steel slag powder, 200 parts of PO42.5 cement, 30 parts of rapid-hardening sulfoaluminate cement, 50 parts of desulfurized gypsum, and 20 parts of carbide slag. Put the materials into a mixer and mix them evenly to obtain iron tailings-based cementitious material A2. Example

[0054] This invention provides a method for preparing a low-carbon cementitious material for foundation soil solidification: A composite grinding aid (diethanol monoisopropanolamine + sodium hexametaphosphate + sodium formate) was prepared at a ratio of 0.5% by mass of dry iron tailings and ground with the dried undisturbed iron tailings in a test mill. The mill speed was 45 r / min, and the grinding time was 80 min, resulting in finely ground iron tailings powder with a tested specific surface area of ​​792 m². 2 / kg, with a median particle size (D50) of 4.40 μm; Take 400 parts of dry, unprocessed fine-grained iron tailings, 250 parts of S95 grade slag powder, 50 parts of steel slag powder, 200 parts of PO42.5 cement, 30 parts of rapid-hardening sulfoaluminate cement, 50 parts of desulfurized gypsum, and 20 parts of carbide slag. Put the materials into a mixer and mix them evenly to obtain iron tailings-based cementitious material A3. Example

[0055] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts by weight of iron tailings powder-based solidifying agent (A1), 300 parts by weight of water, and 1660 parts by weight of silty clay. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0056] Step c: Then, the mixture is put into a mold and compacted to obtain reinforced clay with a moisture content of 15%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B1-1. Example

[0057] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts of iron tailings powder-based solidifying agent (A1), 340 parts of water, and 1620 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0058] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B1-2. Example

[0059] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts of iron tailings powder-based solidifying agent (A1), 380 parts of water, and 1580 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0060] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 18%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B1-3. Example

[0061] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts by weight of iron tailings powder-based cementitious material (A2), 300 parts by weight of water, and 1660 parts by weight of silty clay. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0062] Step c: Then, the mixture is poured into a mold and compacted to obtain reinforced clay with a moisture content of 15%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B2-1. Example

[0063] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts of iron tailings powder-based cementitious material (A2), 340 parts of water, and 1620 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0064] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B2-2. Example

[0065] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts of iron tailings powder-based cementitious material (A2), 380 parts of water, and 1580 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0066] Step c: Then, the mixture is poured into a mold and compacted to obtain reinforced clay with a moisture content of 19%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B2-3. Example

[0067] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts by weight of iron tailings powder-based cementitious material (A3), 300 parts by weight of water, and 1660 parts by weight of silty clay. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0068] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 15%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B3-1. Example

[0069] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts of iron tailings powder-based cementitious material (A3), 340 parts of water, and 1620 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0070] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B3-2. Example

[0071] This invention provides a method for preparing solidified soil in roadbed engineering using iron tailings powder-based cementitious materials: Step a: Weigh out 100 parts by weight of iron tailings powder-based cementitious material (A3), 380 parts by weight of water, and 1580 parts by weight of silty clay. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0072] Step c: Then, the mixture is put into a mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain consolidated soil specimen B3-3.

[0073] This comparative example provides a method for testing the strength of cement prepared from solidified soil in roadbed engineering: Step a: Weigh out 450 parts of 42.5 grade slag silicate cement, 225 parts of water, and 1350 parts of ISO standard sand according to the specified weight proportions. Prepare the materials; Step b: The prepared materials are put into the mortar mixer in sequence according to the strength test method in GB to prepare cement mortar mixture.

[0074] Step c: Then, the mixture is poured into a mold to form a cement mortar specimen. After compaction, it is leveled to obtain a cement mortar specimen. After 24 hours, it is demolded and cured according to standard to obtain a cement mortar specimen CC for solidified soil.

[0075] This comparative example provides a method for using cement in roadbed engineering to prepare solidified soil: Step a: Weigh out 100 parts of 42.5 grade slag silicate cement, 300 parts of water, and 1660 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0076] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 15%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain the consolidated soil reference specimen SCL-1.

[0077] This comparative example provides a method for using cement in roadbed engineering to prepare solidified soil: Step a: Weigh out 100 parts of 42.5 grade slag silicate cement, 340 parts of water, and 1620 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0078] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain the consolidated soil reference specimen SCL-2.

[0079] This comparative example provides a method for using cement in roadbed engineering to prepare solidified soil: Step a: Weigh out 100 parts of 42.5 grade slag silicate cement, 380 parts of water, and 1580 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0080] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 19%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain the consolidated soil reference specimen SCL-3.

[0081] This comparative example provides a method for using cement in roadbed engineering to prepare solidified soil: Step a: Weigh out 140 parts of 42.5 grade slag silicate cement, 300 parts of water, and 1620 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0082] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain the consolidated soil reference specimen SCH-1.

[0083] This comparative example provides a method for using cement in roadbed engineering to prepare solidified soil: Step a: Weigh out 140 parts of 42.5 grade slag silicate cement, 340 parts of water, and 1580 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0084] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain the consolidated soil reference specimen SCH-2.

[0085] This comparative example provides a method for using cement in roadbed engineering to prepare solidified soil: Step a: Weigh out 140 parts of 42.5 grade slag silicate cement, 380 parts of water, and 1540 parts of silty clay according to the specified weight proportions. Prepare the materials; Step b: Place the prepared materials into the concrete mixer in sequence and mix evenly to obtain a solidified foundation soil mixture.

[0086] Step c: Then, the mixture is put into the mold and compacted to obtain reinforced clay with a moisture content of 17%. After 48 hours, it is demolded and cured under standard curing conditions (20±2℃, 95%±5% relative humidity) to obtain the consolidated soil reference specimen SCH-3.

[0087] 1. The mechanical properties of the curing agent and foundation solidified soil specimens of Examples 1-12 and Comparative Examples 1-7 were tested in accordance with the Test Method for Strength of Cement Mortar (GB / T17671-2021) and the Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering (JTG3441-2024). The results are shown in Table 1.

[0088] Table 1. Mechanical property test results

[0089] 2. The solidified soil specimens of Examples 4-12 and Comparative Examples 2-3 were tested for setting time influence coefficient, water stability coefficient and 28-day frost resistance in accordance with the "Technical Standard for Application of Soil Stabilizers" (CJJ / T286-2018) and the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG3441-2024). The results are shown in Table 2.

[0090] Table 2 Results of tests on condensation, water stability and antifreeze properties

[0091] As shown in Table 1, the iron-silicon-aluminum type metal tailings powder-based soil stabilizer prepared in this invention exhibits good cementitious activity. The 28-day compressive strength of stabilizer A3 reaches 47.7 MPa, approaching the 49.8 MPa level of P·S·A42.5 cement. The stabilized soil prepared using the stabilizer of this invention shows significantly better unconfined compressive strength than stabilized soil prepared with the same amount of cement. In particular, stabilizers A2 and A3, prepared using finely ground iron tailings powder, under the same conditions: The 7-day strength of A2 solidified soil (B2-1) is 51.60% higher than that of cement-solidified soil (SCL-1), and the 28-day strength is 27.03% higher. The 7-day strength of A3 solidified soil (B3-1) is 71.53% higher than that of cement-solidified soil (SCL-1), and the 28-day strength is 72.09% higher. Even compared to high-dosage cement-stabilized soil (SCH-1), the 28-day strength of A3-stabilized soil (B3-1) is still increased by 50.0%.

[0092] As can be seen from Table 2, the solidified soil prepared by this invention exhibits excellent durability performance: The influence coefficient of 4-hour setting time reaches 103%-121%, indicating good early strength development; The water stability coefficient reaches 108%-124%, which is significantly better than that of cement-stabilized soil. The 28-day antifreeze index reached 81.77%-92.66%, and the mass loss rate was only 1.24%-3.86%, demonstrating excellent antifreeze performance.

[0093] Although metal tailings are rich in aluminosilicate minerals, they have high crystallinity and low activity under normal conditions. A complex activation method is required to induce cementitious activity. Furthermore, the activated aluminosilicate components in the metal tailings consume large amounts of calcium and sulfur during hydration to form hydration products C-(A)-SH and AFt. The nucleation of these hydration products requires a high energy barrier, which is difficult to overcome when the number of nuclei in the system is low. Therefore, this study adds a small amount of sulfoaluminate cement to provide the necessary AFt nuclei for hydration, accelerating the dissolution and hydration of the active aluminosilicate components. The addition of slag powder replenishes the active aluminosilicate components in the initial stage of the system. Combined with ordinary silicate cement and desulfurized gypsum as activation materials, it replenishes AFt while also providing a large number of dispersed C-(A)-SH nuclei. This helps the oligomers released after the glassy structure in the slag disintegrates to form hydration products, thereby improving the bonding strength of the iron tailings powder-based cementitious material hydration system. Steel slag contains a large amount of high-temperature molten silicate minerals, which have hydration activity after being ground. However, due to their complete and coarse crystals, their activity is lower than that of cement clinker, and their hydration rate is relatively slow. They can form a synergistic effect with the mineral components of ordinary cement in the curing agent, effectively supplementing the active mineral components for the later hydration of the curing agent.

[0094] Although finely ground metal tailings possess the basic conditions for gelling activity in terms of mineral composition and chemical composition, current non-calcination treatment methods cannot release their activity, resulting in low utilization. Therefore, this invention utilizes a composite modification method to further enhance their activity.

[0095] This invention utilizes a composite grinding aid activator to modify metal tailings during the grinding process. The modified ultrafine metal tailings powder exhibits significantly enhanced activity, meeting the requirements for soil stabilizer production and foundation soil solidification, thereby reducing cement usage and responding to the national "dual-carbon" strategy. Simultaneously, it can also address the challenge of storing large quantities of low-activity metallurgical solid waste in my country, promoting the implementation of a multi-industry collaborative mechanism for solid waste resource utilization.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-carbon cementitious material for foundation soil solidification, characterized in that, Its raw materials, by weight, include: 450-550 parts of finely ground iron tailings powder; 300-350 parts of slag powder; 100-200 parts of ordinary Portland cement; 50-100 parts of steel slag powder; 20-30 parts of sulfoaluminate cement; 50-100 parts of desulfurized gypsum; 10-50 parts of calcium carbide slag; The finely ground iron tailings powder is prepared by mixing and grinding raw iron tailings with a composite grinding aid. The finely ground iron tailings powder has a particle size D10≤1.2μm and a specific surface area of ​​750-850m² / kg. The composite grinding aid activator is composed of diethanol monoisopropanolamine, sodium hexametaphosphate, and sodium formate in a mass ratio of 1:5:8, and the addition amount is 0.3%-0.5% of the iron tailings mass. The surface of the finely ground iron tailings powder particles has an amorphous ferrosilicon activation layer with a thickness of 5-10 nm. Under alkaline activation environment, the iron element in the finely ground iron tailings powder participates in the hydration reaction to generate iron-based ettringite, which has higher density and micro hardness. It fills the micro-nano pores of the foundation soil, so that the iron tailings are no longer an inert filler, but a chemical component that directly contributes to the strength. The aluminum element participates in the hydration reaction to generate aluminum-doped hydrated calcium silicate, which improves the durability of the cementitious material. The sodium formate in the composite grinding aid activator forms an iron ion complex system with diethanol monoisopropanolamine, which is used to promote the dissolution of Fe3+ in iron tailings. The preparation method of low-carbon cementitious materials includes the following steps: Step 1: Mix the dried iron tailings with the composite grinding aid activator; Step 2: Use a high-energy ball mill for mechanochemical activation grinding, control the grinding temperature at 50-70℃ to prevent the organic grinding aid from volatilizing and becoming ineffective, grind until D10≤1.2μm and powder rheological index>1.2 to obtain finely ground iron tailings powder; Step 3: Mix the finely ground iron tailings powder obtained in Step 1 with slag powder, ordinary silicate cement, steel slag powder, sulfoaluminate cement, desulfurized gypsum and carbide slag evenly to obtain a low-carbon cementitious material.

2. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, The chemical composition and mass percentage of the finely ground iron tailings powder are as follows: SiO2 45%-60%, Al2O3 5%-15%, Fe2O3 8%-20%, CaO 3%-10%, MgO 3%-10%, K2O 1%-3%, Na2O 2%-4%, SO3 0%-4%, and other unavoidable impurities 2%-4%.

3. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, The mineral composition of the finely ground iron tailings powder includes 35%-45% quartz, 15%-25% potassium feldspar, 10%-20% sodium feldspar, 10%-15% mica, 5%-10% chlorite, and 10%-15% other minerals.

4. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, The slag powder is S95 grade slag powder with a specific surface area of ​​420-450 m² / kg; the steel slag powder is finely ground steel slag powder with a specific surface area of ​​500-550 m² / kg; the ordinary Portland cement is P.O42.5 grade with a specific surface area ≥300 m² / kg and a clinker ratio of not less than 75 wt%; the desulfurized gypsum has an SO3 content greater than 35% and a specific surface area of ​​200-250 m² / kg.

5. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 4, characterized in that, In step one, the drying temperature is 100-110℃ and the drying time is 30-45 min; the grinding speed is 45-55 r / min and the grinding time is 60-90 min; and the moisture content of the iron tailings after drying is ≤1.5 wt%.

6. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 5, characterized in that, In step one, the particle size D50 of the ground iron tailings powder is 4.6 μm, the total leaching concentration of Si+Al elements in the ground iron tailings powder in alkaline solution is ≥100 mg / L, and the activity index is ≥75% after 28 days.

7. An application method of the preparation method of the low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, For soil solidification in foundation engineering, the raw materials include, by weight, 100-200 parts of low-carbon cementitious material, 300-380 parts of water and 1500-1650 parts of foundation soil. After mixing and stirring evenly, the mixture is poured into molds or construction sites, compacted and cured to obtain solidified foundation soil. Due to the natural potential difference between finely ground iron tailings powder and steel slag powder; When the two are mixed and come into contact with pore water, countless micro-galvanic cells are formed inside the mixture, creating a micro-battery effect that accelerates electron transfer on the surface of the steel slag, causing the glassy network of the steel slag to depolymerize rapidly, increasing the reaction rate, and achieving early strength with low cement content.

8. The application method of the low-carbon cementitious material for foundation soil solidification according to claim 7 in foundation engineering, characterized in that, The soil stabilizer is used for roadbed soil solidification, foundation pile solidification, or soft soil foundation reinforcement. The dosage of the soil stabilizer is 5%-10% of the mass of the foundation soil.

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