Preparation of low-carbon cementitious material for ground soil solidification and method of application thereof

Abstract

The application relates to the technical field of building materials, and discloses a low-carbon cementing material for soil solidification of a foundation and a preparation and application method thereof, raw materials of which include, in terms of 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 m 2 / kg, and the finely ground iron tailing powder contains 0.2%-0.5%wt of a composite grinding aid, so that the iron tailing becomes a kind of powder material with cementing activity; the cementing material prepared by taking the iron tailing as a main component is used for soil solidification in foundation engineering, replaces the use of traditional cement, greatly reduces the engineering cost, and greatly reduces the carbon emission of the engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a low-carbon cementitious material for soil solidification and a preparation method and application method thereof. BACKGROUND

[0002] In the construction of highways, railways, airports, and industrial and civil buildings, foundation treatment is a key link to ensure the safety and stability of the project. In geotechnical engineering, a large amount of solidifying agent (or cementitious material) is usually consumed to improve soft soil and improve its bearing capacity and stability. Traditionally, Portland cement dominates the field of soil solidification due to its excellent solidification strength, good water resistance, and mature application technology.

[0003] However, the production of Portland cement is a high-energy and high-emission process, with about 0.8-0.9 tons of carbon dioxide emitted per ton of cement clinker produced. 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.

[0004] At present, the comprehensive utilization rate of metal tailings is only 33%, and the utilization rate of fine-grained tailings, which is the most difficult to dispose, is as low as 5%. How to large-scale and high-value disposal of metal tailings is a major challenge to realize "no tailings mine" construction and sustainable development of mining industry.

[0005] Metal tailings, especially iron, copper, and gold tailings, are mainly composed of silicon dioxide (SiO2) and aluminum oxide (Al2O3), similar to traditional pozzolanic materials such as fly ash and slag, and theoretically have the potential to be used as cementitious materials. Therefore, many scholars have attempted to apply metal tailings to the building materials field. However, most studies consider tailings as an inert micro-aggregate or filler, using its filling effect to improve the density of concrete or mortar. In this application mode, the chemical activity of tailings is not effectively activated, and its dosage is usually limited to less than 15%, otherwise it will cause a significant decrease in material strength. This low-dosage and low-value utilization method has little effect on disposing large amounts of tailings and has not fundamentally solved the problem.

[0006] Therefore, it is urgent to develop a technology that can effectively activate the cementitious activity of metal tailings and achieve high-proportion utilization, and based on this, to prepare a soil solidifying agent that can replace cement on a large scale, meet the performance requirements of engineering, and have low carbon, environmental protection, and economic benefits. SUMMARY

[0007] The application provides a low-carbon cementing material for ground soil solidification and a preparation and application method thereof.

[0008] A low-carbon cementing material for ground soil solidification, characterized in that raw materials thereof include, by weight fraction:

[0009] finely ground iron tailings powder 450-550 parts;

[0010] slag powder 300-350 parts;

[0011] ordinary Portland cement 100-200 parts;

[0012] steel slag powder 50-100 parts;

[0013] sulphoaluminate cement 20-30 parts;

[0014] desulfurized gypsum 50-100 parts;

[0015] carbide slag 10-50 parts;

[0016] The finely ground iron tailings powder is prepared by mixing and grinding raw iron tailings with a composite grinding activator, the particle size D10 of the finely ground iron tailings powder is less than or equal to 1.2 microns, and the specific surface area is 750-850 m 2 / kg.

[0017] The composite grinding 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 mass of the iron tailings;

[0018] The finely ground iron tailings powder has an amorphous silicon-iron activation layer with a thickness of 10-20 nm on the surface of the particles, and in an alkaline excitation environment, the iron element in the finely ground iron tailings powder participates in the hydration reaction to generate iron-based ettringite;

[0019] The sodium formate in the composite grinding activator forms an iron ion complex system with the diethanol monoisopropanolamine to promote the dissolution of Fe3+ in the iron tailings.

[0020] The ternary system of diethanol monoisopropanolamine-sodium formate-sodium hexametaphosphate in the application not only plays a grinding role, but also constitutes a physical dispersion-chemical complexation dual system.

[0021] Diethanol mono-isopropanol amine: adsorbed on the broken surface of the fine particles through a special alcohol amine structure, providing steric hindrance, effectively solving the problem of electrostatic agglomeration of D10≤1.2 μm superfine powder in a physical way.

[0022] Sodium formate and sodium hexametaphosphate: synergistically act on the magnetite and hematite phases on the surface of iron tailings, induce non-stoichiometric dissolution of Fe 3+ , and the dissolved active Fe 3+ reacts with Ca(OH)2 and SO4 2- provided by the sulphoaluminate cement and calcium carbide slag in the system to generate ettringite in situ.

[0023] Compared with ordinary ettringite, the iron-containing ettringite has higher density and microsclerite hardness, and its crystal growth form can better fill the micro-nano pores in the foundation soil. In the present application, the iron tailings are no longer inert fillers, but chemical components that directly contribute to strength.

[0024] Because there is a significant natural potential difference between the finely ground iron tailings (containing magnetite) and the steel slag powder (mainly containing RO phase and a small amount of metallic iron).

[0025] When the two are mixed and contact with pore water (electrolyte), countless micro-batteries are formed inside the mixture. This micro-battery effect accelerates the electron transfer on the surface of the steel slag, rapidly depolymerizes the steel slag glass network, and the reaction rate is 3-5 times higher than that of traditional chemical activation.

[0026] Therefore, the present application can still obtain very fast early strength at low cement content.

[0027] The sulphoaluminate cement meets the standard fast-hardening type (R·SAC) 42.5 grade and above grade index requirements in the standard “Sulphoaluminate Cement” (GB 20472-2006), the sulphoaluminate cement clinker meets the GB / T37125-2018 standard, the alkalinity coefficient is 0.9-1.0, and the aluminum-sulfur ratio is 3.0-4.0. The sulphoaluminate cement can rapidly generate a large amount of fine ettringite grains in the early hydration of the cementitious material, provide the crystal nucleus required for the hydration of the iron tailings powder to generate ettringite in the cementitious material, and increase the swelling component in the hardened cementitious material.

[0028] The present application finds that, without adding grinding aids, the grinding is prone to reverse grinding phenomenon, the material agglomerates, and the specific surface area is difficult to improve. After using the composite grinding activator of the present application, the appearance time of the reverse grinding stage is effectively delayed, the material agglomeration is avoided, the grinding efficiency is greatly improved, and the specific surface area of the iron tailings reaches the activation requirement.

[0029] The diethanol mono-isopropanol amine can improve the grinding flowability by reducing the electrostatic adsorption between the solid material particles during the mechanical force activation of the iron tailings, form a "slow-release shell" on the surface of the iron tailings by using grinding aids, optimize the powder particle distribution, and increase the specific surface area; and can continuously stimulate the activity of mixed materials such as slag, steel slag, and finely ground iron tailings powder during the hydration process of the solidifying agent, and increase the 28d strength.

[0030] The sodium hexametaphosphate plays a role in grinding during the superfine grinding of the iron tailings, eliminates the agglomeration phenomenon of superfine particles, and plays a role in preventing settlement and bleeding in the concrete mixture, effectively improving the workability of the mixture.

[0031] The sodium formate can continuously stimulate the depolymerization and hydration of the silicon-aluminum network in the slag powder and steel slag powder in the soil solidifying agent through multi-stage hydrolysis during the hydration process of the soil solidifying agent.

[0032] Preferably, the chemical composition and mass percentage of the finely ground iron tailings powder are as follows: SiO2 is 45%-60%, Al2O3 is 5%-15%, Fe2O3 is 8%-20%, CaO is 3%-10%, MgO is 3%-10%, K2O is 1%-3%, Na2O is 2%-4%, SO3 is 0%-4%, and other unavoidable impurities are 2%-4%.

[0033] Preferably, the mineral composition of the finely ground iron tailings powder includes 35%-45% of quartz, 15%-25% of potassium feldspar, 10%-20% of sodium feldspar, 10%-15% of mica, 5%-10% of chlorite, and 10%-15% of other minerals.

[0034] Preferably, the slag powder is S95 grade powder with a specific surface area of 420-450m 2 / kg, participates in the secondary hydration of the iron tailings powder, and slowly releases and supplements the active silicon-aluminum components required for the hydration of the low-carbon cementitious material based on the iron tailings powder. The steel slag powder is finely ground steel slag powder with a specific surface area of 500-550m 2 / kg, contains a large amount of silicate minerals melted at high temperature, has hydration activity after being finely ground, can form a synergistic effect with the clinker mineral components in the Portland cement in the solidifying agent, and effectively supplements the active mineral components for the hydration of the solidifying agent in the later stage. The Portland cement is P.O42.5 grade cement with a specific surface area of ≥300m 2 / kg, the proportion of clinker in cement is not less than 75wt%, the ordinary portland cement selected by the application generates strength in early stage through self-hydration, more importantly, provides calcium component required by surface active silicon aluminum component of iron tailings powder for hydration, and additionally plays a role of stimulating glass structure depolymerization and secondary hydration in slag powder. The desulfurization gypsum is an industrial byproduct, the mass content of SO3 is greater than 35%, the specific surface area is 200-250m 2 / kg, and can provide SO4 2- ions required in the hydration process of iron tailings powder and slag powder, and stimulate dissolution and hydration of active SiO2 and Al2O3 in iron tailings powder and slag powder.

[0035] Preferably, the particle size median D50 of the fine iron tailings powder is 4-6μm. In the grinding process, with the decrease of D50 value, the number of "unsaturated bonds" on the surface of iron tailings powder particles increases, causing the non-crystalline transformation of silicon aluminum components on the surface of crystal minerals, from inert state to active state, and having hydration activity.

[0036] The application further discloses a preparation method of the low-carbon cementitious material for soil solidification.

[0037] Step one: mixing the dried iron tailings with the composite grinding and activating agent;

[0038] Step two: performing mechanical force chemical activation grinding by using a high-energy ball mill, controlling the grinding temperature at 50-70℃ to prevent the volatilization failure of the organic grinding agent, and grinding to D10≤1.2μm and the powder rheological index>1.2, to obtain the fine iron tailings powder;

[0039] Step three: uniformly mixing the fine iron tailings powder obtained in step one with slag powder, ordinary portland cement, steel slag powder, sulphoaluminate cement, desulfurization gypsum and carbide slag, to obtain the low-carbon cementitious material.

[0040] Preferably, in step one, the drying temperature is 100-110℃, the drying time is 4-6h, the grinding speed is 45-55r / min, the grinding time is 60-90min, and the water content of the dried iron tailings is ≤1.5wt%. 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 fully ground, and if the grinding time is too long, the internal cracks of the iron tailings powder particles begin to appear "compaction" and "welding" phenomenon, resulting in the decrease of the specific surface area of the iron tailings and the decrease of the reaction activity.

[0041] Preferably, in step one, the particle size D50 of the fine iron tailings powder obtained by grinding is 4-6μm, and the specific surface area is 680-850m 2 / kg, the total leaching concentration of Si+Al elements in the alkali solution is greater than or equal to 100 mg / L, and the 28d activity index is greater than or equal to 75%. By adding modified components such as slag powder, ordinary Portland cement and sulphoaluminate cement, the activity can be increased to more than 95%.

[0042] The application further discloses an application method of the low-carbon cementitious material for ground soil solidification.

[0043] The application further discloses an application of the low-carbon cementitious material for ground soil solidification in ground engineering, which is used for roadbed soil solidification, ground pile solidification or soft soil ground reinforcement.

[0044] The application has the following beneficial effects:

[0045] 1. The application provides a low-carbon cementitious material for ground soil solidification and an application method thereof, wherein the total content of cement clinker in the ground soil solidification agent prepared by a non-calcination composite activation method is less than 15%, the content of the ground fine iron tailings powder is more than 45%, and other component materials are industrial solid wastes such as steel slag, calcium carbide slag and desulfurization gypsum; the carbon emission is only less than 35% of that of traditional cement; and the strength index of the obtained low-carbon cementitious material can reach the standard of 42.5-grade cement. The cementitious material can be used as a soil solidification agent to consolidate ground soil in ground engineering, including roadbed soil and various ground pile solidification, and the effect reaches that of traditional cement, and the cost and carbon emission are greatly reduced. The application solves the problem of high cost in ground engineering and improves the proportion of fine particle metal tailings, thereby solving the problem of tight storage capacity of metallurgical mines. The solidified soil prepared by the ground fine iron tailings powder-based solidification agent prepared by the application can meet the index requirements of engineering application, and the mechanical properties and durability of the solidified body can reach and be better than those of P.S.A 42.5 reference cement.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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

[0050] Figure 1 This is an image showing the appearance of the iron tailings powder-based cementitious material in an embodiment of the present invention.

[0051] Figure 2 This is a mineral phase composition analysis diagram of the original iron tailings in an embodiment of the present invention;

[0052] Figure 3 This is a microscopic morphology diagram of the original iron tailings in an embodiment of the present invention;

[0053] 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.

[0054] Figure 5 This is a graph showing the change in crystallinity during the iron tailings grinding process in an embodiment of the present invention;

[0055] Figure 6A micro-morphology graph of the unconsolidated soil in the embodiment of the present application;

[0056] Figure 7 A micro-morphology graph of the 7-day hydration process of the iron tailings powder-based cementitious material in the embodiment of the present application;

[0057] Figure 8 A micro-morphology graph of the 28-day hydration process of the iron tailings powder-based cementitious material in the embodiment of the present application;

[0058] Figure 9 A micro-morphology graph of the 28-day test piece of the cement-consolidated soil in the embodiment of the present application

[0059] Figure 10 A micro-morphology graph of the 28-day test piece of the iron tailings powder-based cementitious material-consolidated soil in the embodiment of the present application. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0061] A low-carbon cementitious material for soil consolidation, raw materials of which include, by weight fraction:

[0062] Fine iron tailings powder 450-550 parts;

[0063] Slag powder 300-350 parts;

[0064] Ordinary portland cement 100-200 parts;

[0065] Steel slag powder 50-100 parts;

[0066] Sulphoaluminate cement 20-30 parts;

[0067] Desulfurized gypsum 50-100 parts;

[0068] Carbide slag 10-50 parts;

[0069] The fine iron tailings powder is prepared by mixing and grinding the raw iron tailings with a composite grinding and activating agent, the particle size D10 of the fine iron tailings powder is ≤1.2 μm, and the specific surface area is 750-850 m 2 / kg;

[0070] The composite grinding and activating agent 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 mass of the iron tailings.

[0071] The ground fine iron tailings powder has an amorphous ferrosilicon activation layer with a thickness of 10-20 nm on the surface of the particles, and in an alkaline excitation environment, the iron element in the ground fine iron tailings powder participates in the hydration reaction to generate iron-based ettringite.

[0072] The sodium formate in the composite grinding and excitation agent forms an iron ion complex system with diethanol monoisopropanolamine to promote the dissolution of Fe3+ in the iron tailings.

[0073] The chemical composition and mass percentage of the ground fine iron tailings powder are as follows: SiO2 is 45%-60%, Al2O3 is 5%-15%, Fe2O3 is 8%-20%, CaO is 3%-10%, MgO is 3%-10%, K2O is 1%-3%, Na2O is 2%-4%, SO3 is 0%-4%, and other unavoidable impurities are 2%-4%.

[0074] The mineral composition of the ground fine iron tailings powder includes 35%-45% of quartz, 15%-25% of potassium feldspar, 10%-20% of sodium feldspar, 10%-15% of mica, 5%-10% of chlorite, and 10%-15% of other minerals.

[0075] The slag powder is S95 grade powder with a specific surface area of 420-450 m 2 / kg; the steel slag powder is ground steel slag powder with a specific surface area of 500-550 m 2 / kg; the ordinary portland cement is P.O42.5 grade with a specific surface area of ≥300 m 2 / kg, and the clinker proportion in the cement is not less than 75wt%; the SO3 mass content in the desulfurization gypsum is greater than 35%, and the specific surface area is 200-250 m 2 / kg.

[0076] A preparation method of a low-carbon cementitious material for soil solidification, comprising the following steps:

[0077] Step one: mix the dried iron tailings with the composite grinding and excitation agent;

[0078] Step two: perform mechanical chemical activation grinding using a high-energy ball mill, control the grinding temperature at 50-70℃ to prevent the organic grinding aid from volatilizing and failing, and grind to D10≤1.2μm and a powder rheological index >1.2 to obtain ground fine iron tailings powder;

[0079] Step three: uniformly mix the ground fine iron tailings powder obtained in step one with slag powder, ordinary portland cement, steel slag powder, sulphoaluminate cement, desulfurization gypsum, and carbide slag to obtain a low-carbon cementitious material.

[0080] In the step one, the drying temperature is 100-110 DEG C, the drying time is 30-45 min; the grinding speed is 45-55 r / min, the grinding time is 60-90 min, and the moisture content of the iron tailings after drying is less than or equal to 1.5 wt%.

[0081] In the step two, the particle size D50 of the ground iron tailings powder is 4.6 mu m, and the total leaching concentration of Si+Al elements in the alkali solution is greater than or equal to 100 mg / L, and the 28d activity index is greater than or equal to 75%.

[0082] An application method of a low-carbon cementitious material for soil solidification of a foundation, which is used for soil solidification in foundation engineering, and raw materials include, by weight fraction, 100-200 parts of a low-carbon cementitious material, 300-380 parts of water, and 1500-1650 parts of foundation soil.

[0083] An application of a low-carbon cementitious material for soil solidification of a foundation in foundation engineering, which is used for subgrade soil solidification, foundation pile solidification, or soft soil foundation reinforcement, and the mixing amount of the low-carbon cementitious material is 5%-10% of the mass of the foundation soil.

[0084] In the embodiment of the present application, the specific preparation method of the low-carbon cementitious material includes:

[0085] S1, taking the wet-based iron tailings after pressure filtration, drying in a drying box until the moisture content is less than 1.50%, and then taking out and airing to room temperature for standby.

[0086] S2, stirring and compounding diethanol monoisopropanolamine, sodium hexametaphosphate and sodium formate according to a mass ratio of 1:5:8 to prepare a composite grinding activator;

[0087] S3, adding the composite grinding activator to the original iron tailings after drying, and grinding by a ball mill to obtain superfine iron tailings powder;

[0088] S4, uniformly mixing the superfine iron tailings powder with ordinary Portland cement, fast-hardening sulphoaluminate cement, mineral powder, steel slag powder, desulfurization gypsum and carbide slag to obtain the iron tailings powder-based cementitious material for soil solidification.

[0089] The embodiment of the present application also provides a foundation solidified soil test piece preparation method made of the above-mentioned iron tailings powder-based soil solidification agent, and raw materials include, by weight fraction, 100-200 parts of the above-mentioned iron tailings powder-based solidification agent, 300-380 parts of water, and 1500-1650 parts of foundation soil.

[0090] The embodiment of the present application is further described in the following multiple embodiments.

[0091] In the following embodiments, the XRD pattern of the iron tailings powder is as follows:Figures 1-10 As shown, the content of quartz is 24.2%, the content of potassium feldspar is 31.1%, the content of sodium feldspar is 23.8%, the content of biotite is 6.2%, and the balance is other minerals; the chemical composition and mass percentage in the iron tailings powder are: 58.9% of SiO2, 14.3% of Al2O3, 15.6% of Fe2O3, 3.0% of CaO, 2.2% of MgO, 2.1% of K2O, 2.4% of Na2O and 2.3% of SO3. The test mill used is a 5kg cement test mill, model Ø500x500. The dry basis raw iron tailings are obtained by drying the wet basis fine particle grade iron tailings after pressure filtration in a forced air oven for 6 hours, and the drying temperature is 110°C, and the moisture content after drying is ≤1.5wt%.

[0092] The specific surface area of the S95 grade mineral powder in the following examples is 430m 2 / kg, the specific surface area of the steel slag powder is 545m 2 / kg; the sulphoaluminate cement meets the index requirements of the fast-hardening type (R·SAC) 42.5 grade in the standard “Sulphoaluminate Cement” (GB 20472-2006), the sulphoaluminate clinker used is standard GB / T37125-2018, the basicity coefficient (cm) is 0.98, and the aluminum-sulfur ratio (Ps) is 3.5; the ordinary portland cement meets the index requirements of P·O42.5 grade cement in the national standard “General Portland Cement” (GB175-2023); the desulfurization gypsum and the carbide slag are both industrial by-products, and are powdery materials, the specific surface area of the desulfurization gypsum is 280m 2 / kg, and the specific surface area of the carbide slag is 336m 2 / kg; the sodium hexametaphosphate is powdery, and the specific surface area is 220m 2 / kg; the sodium formate is powdery, and the specific surface area is 200m 2 / kg; and the diethanol mono-isopropanol amine is a viscous yellow transparent liquid.

[0093] Example 1

[0094] The present application provides a preparation method of a low-carbon cementitious material for soil solidification:

[0095] The dried raw iron tailings are put into the test mill for grinding, the rotational speed of the test mill is 45r / min, the grinding time is 3min, which plays a role of dispersing and dispersing the additives, and a fine particle grade raw iron tailings powder is obtained; the specific surface area is 313m 2 / kg, and the median particle size (D50) is 16.21μm

[0096] Take 200 parts of dry basis original fine particle grade iron tailings, 450 parts of S95 grade slag powder, 50 parts of steel slag powder, 200 parts of P042.5 cement, 30 parts of fast hardening sulphoaluminate cement, 50 parts of desulfurization gypsum, and 20 parts of carbide slag, mix the materials in a mixer to obtain iron tailings based cementitious material A1.

[0097] Example 2

[0098] The embodiment of the present application provides a preparation method of a low-carbon cementitious material for ground soil solidification:

[0099] According to the proportion of 0.5% of the dry basis iron tailings, a composite grinding activator (diethanol mono-isopropanol amine + sodium hexametaphosphate + sodium formate) is taken, and the dried original iron tailings are put into a test mill for grinding, the rotating speed of the test mill is 45r / min, and the grinding time is 40min, so as to obtain fine iron tailings powder, and the specific surface area is 582 m 2 / kg, and the median particle size (D50) is 6.23um;

[0100] Take 300 parts of dry basis original fine particle grade iron tailings, 350 parts of S95 grade slag powder, 50 parts of steel slag powder, 200 parts of P042.5 cement, 30 parts of fast hardening sulphoaluminate cement, 50 parts of desulfurization gypsum, and 20 parts of carbide slag, mix the materials in a mixer to obtain iron tailings based cementitious material A2.

[0101] Example 3

[0102] The embodiment of the present application provides a preparation method of a low-carbon cementitious material for ground soil solidification:

[0103] According to the proportion of 0.5% of the dry basis iron tailings, a composite grinding activator (diethanol mono-isopropanol amine + sodium hexametaphosphate + sodium formate) is taken, and the dried original iron tailings are put into a test mill for grinding, the rotating speed of the test mill is 45r / min, and the grinding time is 80min, so as to obtain fine iron tailings powder, and the specific surface area is 792 m 2 / kg, and the median particle size (D50) is 4.40um;

[0104] Take 400 parts of dry basis original fine particle grade iron tailings, 250 parts of S95 grade slag powder, 50 parts of steel slag powder, 200 parts of P042.5 cement, 30 parts of fast hardening sulphoaluminate cement, 50 parts of desulfurization gypsum, and 20 parts of carbide slag, mix the materials in a mixer to obtain iron tailings based cementitious material A3.

[0105] Example 4

[0106] The embodiment of the present application provides a method for preparing solidified soil in roadbed engineering by using iron tailings powder based cementitious material:

[0107] Step a: take iron tailings powder-based curing agent (A1) 100 parts, water 300 parts, silty clay 1660 parts by mass fraction. Prepare materials;

[0108] Step b: put the prepared materials into a concrete mixer in turn, and stir evenly to obtain a cured foundation soil mixture.

[0109] Step c: then the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 15%, and after 48h demolding, the molded product is cured under standard curing conditions (20±2℃, 95%±5% relative humidity), to obtain a cured soil test piece B1-1.

[0110] Example 5

[0111] The embodiment of the present application provides a method for preparing cured soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0112] Step a: take iron tailings powder-based curing agent (A1) 100 parts, water 340 parts, silty clay 1620 parts by mass fraction. Prepare materials;

[0113] Step b: put the prepared materials into a concrete mixer in turn, and stir evenly to obtain a cured foundation soil mixture.

[0114] Step c: then the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 17%, and after 48h demolding, the molded product is cured under standard curing conditions (20±2℃, 95%±5% relative humidity), to obtain a cured soil test piece B1-2.

[0115] Example 6

[0116] The embodiment of the present application provides a method for preparing cured soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0117] Step a: take iron tailings powder-based curing agent (A1) 100 parts, water 380 parts, silty clay 1580 parts by mass fraction. Prepare materials;

[0118] Step b: put the prepared materials into a concrete mixer in turn, and stir evenly to obtain a cured foundation soil mixture.

[0119] Step c: then the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 18%, and after 48h demolding, the molded product is cured under standard curing conditions (20±2℃, 95%±5% relative humidity), to obtain a cured soil test piece B1-3.

[0120] Example 7

[0121] The embodiment of the present application provides a method for preparing cured soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0122] Step a: Take iron tailings powder-based cementitious material (A2) 100 parts, water 300 parts, and silty clay 1660 parts by mass fraction. Prepare the materials;

[0123] Step b: Put the prepared materials into a concrete mixer in turn, and mix uniformly to obtain a solidified foundation soil mixture.

[0124] Step c: Then, the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 15%, and after 48 hours, the mold is removed and formed, and the standard curing conditions (20±2℃, 95%±5% relative humidity) are used for curing to obtain a solidified soil test piece B2-1.

[0125] Example 8

[0126] The embodiment of the present application provides a method for preparing solidified soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0127] Step a: Take iron tailings powder-based cementitious material (A2) 100 parts, water 340 parts, and silty clay 1620 parts by mass fraction. Prepare the materials;

[0128] Step b: Put the prepared materials into a concrete mixer in turn, and mix uniformly to obtain a solidified foundation soil mixture.

[0129] Step c: Then, the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 17%, and after 48 hours, the mold is removed and formed, and the standard curing conditions (20±2℃, 95%±5% relative humidity) are used for curing to obtain a solidified soil test piece B2-2.

[0130] Example 9

[0131] The embodiment of the present application provides a method for preparing solidified soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0132] Step a: Take iron tailings powder-based cementitious material (A2) 100 parts, water 380 parts, and silty clay 1580 parts by mass fraction. Prepare the materials;

[0133] Step b: Put the prepared materials into a concrete mixer in turn, and mix uniformly to obtain a solidified foundation soil mixture.

[0134] Step c: Then, the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 19%, and after 48 hours, the mold is removed and formed, and the standard curing conditions (20±2℃, 95%±5% relative humidity) are used for curing to obtain a solidified soil test piece B2-3.

[0135] Example 10

[0136] The embodiment of the present application provides a method for preparing solidified soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0137] Step a: according to the mass fraction, iron tailings powder-based cementitious material (A3) 100 parts, water 300 parts, silty clay 1660 parts are taken.

[0138] Step b: the materials are sequentially placed into a concrete mixer, and the solidified foundation soil mixture is obtained after uniform stirring.

[0139] Step c: then the mixture is loaded into a mold, and after tamping and compaction, reinforced clay with a water content of 15% is obtained, and after 48h demolding, the standard curing condition (20±2 DEG C, 95%±5% relative humidity) is carried out, and the solidified soil test piece B3-1 is obtained.

[0140] Example 11

[0141] The embodiment of the present application provides a method for preparing solidified soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0142] Step a: according to the mass fraction, iron tailings powder-based cementitious material (A3) 100 parts, water 340 parts, silty clay 1620 parts are taken.

[0143] Step b: the materials are sequentially placed into a concrete mixer, and the solidified foundation soil mixture is obtained after uniform stirring.

[0144] Step c: then the mixture is loaded into a mold, and after tamping and compaction, reinforced clay with a water content of 17% is obtained, and after 48h demolding, the standard curing condition (20±2 DEG C, 95%±5% relative humidity) is carried out, and the solidified soil test piece B3-2 is obtained.

[0145] Example 12

[0146] The embodiment of the present application provides a method for preparing solidified soil in roadbed engineering by using iron tailings powder-based cementitious material:

[0147] Step a: according to the mass fraction, iron tailings powder-based cementitious material (A3) 100 parts, water 380 parts, silty clay 1580 parts are taken.

[0148] Step b: the materials are sequentially placed into a concrete mixer, and the solidified foundation soil mixture is obtained after uniform stirring.

[0149] Step c: then the mixture is loaded into a mold, and after tamping and compaction, reinforced clay with a water content of 17% is obtained, and after 48h demolding, the standard curing condition (20±2 DEG C, 95%±5% relative humidity) is carried out, and the solidified soil test piece B3-3 is obtained.

[0150] Comparative Example 1

[0151] The present comparative example provides a method for testing the strength of cement prepared from solidified soil in roadbed engineering:

[0152] Step a: 450 parts of 42.5 grade slag portland cement, 225 parts of water, and 1350 parts of ISO standard sand were weighed according to the mass fraction. The materials were prepared;

[0153] Step b: The prepared materials were sequentially placed into a mortar mixer according to the strength testing method in GB to prepare a cement mortar mixture.

[0154] Step c: Then the mixture was loaded into a mold for molding, and after being vibrated and compacted, the cement mortar test piece was obtained. After 24 hours, the mold was removed, and the cement mortar test piece CC for solidified soil was obtained under standard curing.

[0155] Comparative Example 2

[0156] The present comparative example provides a method for preparing a cement for solidified soil in roadbed engineering:

[0157] Step a: 100 parts of 42.5 grade slag portland cement, 300 parts of water, and 1660 parts of silty clay were weighed according to the mass fraction. The materials were prepared;

[0158] Step b: The prepared materials were sequentially placed into a concrete mixer to obtain a solidified foundation soil mixture.

[0159] Step c: Then the mixture was loaded into a mold, and after being compacted, a reinforced clay with a water content of 15% was obtained. After 48 hours, the mold was removed and molded, and the standard test piece SCL-1 for solidified soil was obtained under standard curing conditions (20±2℃, 95%±5% relative humidity).

[0160] Comparative Example 3

[0161] The present comparative example provides a method for preparing a cement for solidified soil in roadbed engineering:

[0162] Step a: 100 parts of 42.5 grade slag portland cement, 340 parts of water, and 1620 parts of silty clay were weighed according to the mass fraction. The materials were prepared;

[0163] Step b: The prepared materials were sequentially placed into a concrete mixer to obtain a solidified foundation soil mixture.

[0164] Step c: Then the mixture was loaded into a mold, and after being compacted, a reinforced clay with a water content of 17% was obtained. After 48 hours, the mold was removed and molded, and the standard test piece SCL-2 for solidified soil was obtained under standard curing conditions (20±2℃, 95%±5% relative humidity).

[0165] Comparative Example 4

[0166] The present comparative example provides a method for preparing a cement for solidifying soil in roadbed engineering:

[0167] Step a: 100 parts of 42.5 grade slag portland cement, 380 parts of water, and 1580 parts of silty clay are weighed according to the mass fraction. Prepare the materials;

[0168] Step b: The prepared materials are sequentially placed into a concrete mixer and uniformly stirred to obtain a solidified foundation soil mixture.

[0169] Step c: Then the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 19%, and after 48 hours, the mold is removed and formed. The standard curing conditions (20±2℃, 95%±5% relative humidity) are used for curing, and the solidified soil reference specimen SCL-3 is obtained.

[0170] Comparative Example 5

[0171] The present comparative example provides a method for preparing a cement for solidifying soil in roadbed engineering:

[0172] Step a: 140 parts of 42.5 grade slag portland cement, 300 parts of water, and 1620 parts of silty clay are weighed according to the mass fraction. Prepare the materials;

[0173] Step b: The prepared materials are sequentially placed into a concrete mixer and uniformly stirred to obtain a solidified foundation soil mixture.

[0174] Step c: Then the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 17%, and after 48 hours, the mold is removed and formed. The standard curing conditions (20±2℃, 95%±5% relative humidity) are used for curing, and the solidified soil reference specimen SCL-3 is obtained.

[0175] Comparative Example 6

[0176] The present comparative example provides a method for preparing a cement for solidifying soil in roadbed engineering:

[0177] Step a: 140 parts of 42.5 grade slag portland cement, 340 parts of water, and 1580 parts of silty clay are weighed according to the mass fraction. Prepare the materials;

[0178] Step b: The prepared materials are sequentially placed into a concrete mixer and uniformly stirred to obtain a solidified foundation soil mixture.

[0179] Step c: Then the mixture is loaded into a mold and compacted to obtain reinforced clay with a water content of 17%, and after 48 hours, the mold is removed and formed. The standard curing conditions (20±2℃, 95%±5% relative humidity) are used for curing, and the solidified soil reference specimen SCL-3 is obtained.

[0180] Comparative Example 7

[0181] The present comparative example provides a method for preparing a cement for solidifying soil in roadbed engineering:

[0182] Step a: 140 parts of 42.5 grade slag portland cement, 380 parts of water, and 1540 parts of silty clay were weighed according to the mass fraction.

[0183] Step b: The prepared materials were sequentially placed in a concrete mixer and stirred uniformly to obtain a solidified foundation soil mixture.

[0184] Step c: Then the mixture was loaded into a mold and compacted to obtain reinforced clay with a water content of 17%, and after 48 hours, the mold was removed and formed, and the standard curing conditions (20±2℃, 95%±5% relative humidity) were used for curing to obtain a solidified soil standard test specimen SCH-3.

[0185] Test Example

[0186] 1. The solidified agent and foundation solidified soil test specimens of Examples 1-12 and Comparative Examples 1-7 were subjected to mechanical property detection according to the "Cement Mortar Strength Test Method" (GB / T17671-2021) and the "Highway Engineering Inorganic Binder Stabilized Material Test Specification" (JTG3441-2024), and the results are shown in Table 1.

[0187] Table 1: Mechanical property test results

[0188]

[0189] 2. The solidified soil test specimens of Examples 4-12 and Comparative Examples 2-3 were subjected to setting time influence coefficient, water stability coefficient, and 28-day frost resistance detection according to the "Soil Solidification Agent Application Technology Standard" (CJJ / T286-2018) and the "Highway Engineering Inorganic Binder Stabilized Material Test Specification" (JTG3441-2024), and the results are shown in Table 2.

[0190] Table 2: Setting, water stability, and frost resistance test results

[0191]

[0192] As can be seen from Table 1, the iron-silicon-aluminum type metal tailings powder-based soil solidification agent prepared by the present application has good cementing activity. The 28d mortar compressive strength of solidification agent A3 reaches 47.7MPa, close to the level of 49.8MPa of P·S·A42.5 cement. The unconfined compressive strength of the solidified soil prepared by the solidification agent of the present application is significantly better than that of the solidified soil prepared by the same amount of cement. Especially the solidification agents A2 and A3 prepared by finely ground iron tailings powder, under the same conditions:

[0193] The 7d strength of the consolidated soil sample in Example 7 is increased by 51.60% compared with the cement solidified soil (SCL-1), and the 28d strength is increased by 27.03%;

[0194] The 7d strength of the consolidated soil sample in Example 10 is increased by 71.53% compared with the cement solidified soil (SCL-1), and the 28d strength is increased by 72.09%;

[0195] Even compared with the high cement content solidified soil (SCH-1), the 28d strength of the consolidated soil sample in Example 10 is still increased by 50.0%.

[0196] As can be seen from Table 2, the solidified soil prepared in the application has excellent durability performance:

[0197] The 4h setting time influence coefficient reaches 103%-121%, indicating that the early strength development is good;

[0198] The water stability coefficient reaches 108%-124%, which is obviously better than that of the cement solidified soil;

[0199] The 28d frost resistance index reaches 81.77%-92.66%, and the mass loss rate is only 1.24%-3.86%, and the frost resistance performance is excellent.

[0200] Although the metal tailings are rich in silicate and aluminate mineral components, the crystallinity is high, and the activity is low under normal conditions. A composite activation method needs to be used to make it have cementitious activity. At the same time, after activation, the silicate and aluminate components in the metal tailings need to consume a large amount of calcium and sulfur components to form hydration products C-(A)-S-H and AFt in the hydration process, and in the process of generating hydration products, the nucleation of hydration products needs a high energy barrier. When the number of nucleation in the system is small, it is difficult to overcome this barrier to form a large number of crystal nuclei. Therefore, a small amount of sulphoaluminate cement is added to provide the AFt crystal nucleus needed in the hydration process and accelerate the dissolution and hydration process of the active silicate and aluminate components. The addition of slag powder is to supplement the active silicate and aluminate components in the early stage system. Combined with ordinary Portland cement and desulfurized gypsum, the AFt is supplemented, and a large number of dispersed C-(A)-S-H crystal nuclei are also provided, which helps the low polymer generated after the glass body of the slag is released to improve the cementing strength of the iron tailings powder-based cementitious material hydration system. Steel slag contains a large amount of silicate minerals melted at high temperature, which has hydration activity after being ground, but the activity is lower than that of cement clinker due to the complete and coarse crystallization, and the hydration speed is relatively slow. It can form a synergistic effect with the mineral components of the ordinary cement in the solidifying agent to effectively supplement the active mineral components in the later hydration of the solidifying agent.

[0201] Although the fine metal tailings have the basic conditions of cementitious activity in mineral composition and chemical composition, the current disposal means under non-calcination conditions cannot release its activity, and the utilization rate is not high, so the activity of the fine metal tailings is further improved by using the composite modification method.

[0202] The fine metal tailings are modified by the composite grinding activator in the grinding process, the activity of the modified ultra-fine metal tailings powder is significantly improved, the production of the soil stabilizer and the solidification of the foundation soil are met, and the use amount of cement is reduced.

[0203] The above only describes the preferred embodiments of the present application, and it should be noted that the ordinary skilled in the art can make several improvements and refinements without departing from the technical principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A low-carbon cementitious material for solidifying foundation soil, 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 ≤ 1.2 μm and a specific surface area of ​​750-850 m². 2 / 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 strength. The aluminum element participates in the hydration reaction to generate aluminum-doped hydrated calcium silicate, which improves the durability of the cementitious material.

2. The low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, The sodium formate in the composite grinding aid activator forms an iron ion complex system with diethanol monoisopropanolamine, which is used to promote the Fe ion concentration in iron tailings. 3+ Dissolution.

3. The 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%.

4. A low-carbon cementitious material for foundation soil solidification according to claim 1 or 3, 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.

5. A low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, The slag powder is S95 grade mineral powder with a specific surface area of ​​420-450 m². 2 / kg; the steel slag powder is finely ground steel slag powder with a specific surface area of ​​500-550m². 2 / kg; the ordinary Portland cement is grade P.O42.5, with a specific surface area ≥300m². 2 / kg, the clinker ratio in the cement is not less than 75wt%; the SO3 content in the desulfurized gypsum is greater than 35%, and the specific surface area is 200-250m². 2 / kg.

6. A method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 1, characterized in that, 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.

7. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 6, 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%.

8. The method for preparing a low-carbon cementitious material for foundation soil solidification according to claim 7, characterized in that, In step one, the particle size D50 of the finely ground iron tailings powder is 4.6 μm, the total leaching concentration of Si+Al elements in the finely ground iron tailings powder in alkaline solution is ≥100 mg / L, and the activity index is ≥75% after 28 days.

9. A method for applying a 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.

10. The application method of the low-carbon cementitious material for foundation soil solidification according to claim 9 in foundation engineering, characterized in that, The low-carbon cementitious material is used for roadbed soil solidification, foundation pile solidification, or soft soil foundation reinforcement, and the dosage of the low-carbon cementitious material is 5%-10% of the mass of the foundation soil.

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