Composite mineral binder based on lime and slag

Abstract

FIELD: road construction.SUBSTANCE: invention can be used in compositions for strengthening base soils during the construction, reconstruction and major repairs of highways. The composite mineral binder on a lime-slag base is a product of combined grinding of converter slag from the Chelyabinsk Metallurgical Plant and a mineral product of soda production heat-treated at a temperature of 900-950 °C with the following ratio of components, wt.%: slag 70; mineral product of soda production 30. The invention makes it possible to obtain a composite clinker-free binder without the use of clinker minerals based on converter slag and heat-treated mineral product of soda production (HTMP), which ensures increased strength and water resistance of the reinforced soil.EFFECT: composite clinker-free binder.1 cl, 2 tbl, 1 ex

Description

[0001] The invention relates to the field of road construction and can be used in compositions for strengthening base soils (underlayment) during the construction, reconstruction and major repairs of highways.

[0002] A road construction ash primer (Patent RU 2779688, published 29.12.2021) is known, comprising Portland cement, ash and slag mixture, soil, and water. The ash and slag mixture contains no more than 10% calcium oxide by weight, and the primer is coarse gravel soil with light loam or sand in the following ratio of components, by weight: 75.20% ash and slag mixture, 18.8% ash and slag mixture, 6.00% Portland cement, and 13.26% water, based on the dry soil weight.

[0003] The disadvantages of this fly ash primer for road construction include the need for an ash and slag mixture with a low calcium oxide content (no more than 10% by weight). Most fly ash generated from coal combustion has a calcium oxide content of 15% by weight or more, significantly complicating the search for suitable raw materials. Furthermore, the use of coarse gravel with light loam or sand in the soil composition significantly limits its application in areas where sandy loam and clay loam are used as the soil. Achieving a homogeneous mixture also requires powerful mixing equipment capable of mixing coarse soil and finely dispersed components. Furthermore, fly ash mixtures contain active alkali metal sulfates, which can cause corrosion on metal equipment components.Also, the properties of the ash and slag mixture can vary significantly depending on the type of coal burned and the operating mode of the thermal power plant, which creates the possibility of instability of the final product.

[0004] A raw material mixture is known (Patent KR102565271 B1, published on 09.08.2023), which contains, per 100 wt. % polysilicon sludge, from 30 to 60 wt. % fly ash, from 100 to 500 wt. % steelmaking slag, from 30 to 60 wt. % ash from burning paper sludge, from 30 to 60 wt. % steelmaking slag, from 5 to 10 wt. % gypsum, from 1 to 5 wt. % blast furnace slag, from 1 to 5 wt. % additives.

[0005] A disadvantage of this raw mix is ​​its complex structure, requiring the mixing and milling of a large number of raw components with widely varying degrees of abradability. This creates significant challenges in grinding them to the required fineness. Furthermore, ensuring a homogeneous mixture requires high-power and sophisticated industrial equipment; otherwise, significant heterogeneity in the specific surface area of ​​the components can lead to mixture segregation. Furthermore, each component of the raw mix has an unstable chemical and particle size distribution, necessitating constant adjustments to the recipe. Furthermore, the waste materials used (polysilicon sludge, ash from the incineration of paper sludge) are generated by rare industrial processes, significantly limiting the scale of production and forcing it to be localized.Also, the use of such a quantity of different wastes can lead to unpredictable consequences during hardening, associated with chemical reactions occurring between the components: the high content of alkali oxides in the steel slag, combined with reactive silicon from the sludge, can lead to an alkali-silica reaction, causing destructive processes and cracks in the cement soil over time.

[0006] A raw mix (Patent KR102694665 B1, published on August 14, 2024) is known for strengthening soft soil, in which fine blast furnace slag powder is used as the main material to minimize the amount of ordinary Portland cement CEM1 and bentonite, which are most widely used as binders, as well as coal tar, a by-product of the steel production process, as a raw material, and calcination dust generated during the production of coke and pitch coke, as a stimulator.

[0007] A disadvantage of this raw mix is ​​the use of coal tar, which is a hazardous waste due to its content of carcinogenic polycyclic aromatic hydrocarbons (PAHs), phenols, and other toxic substances. Therefore, its use in construction without thorough pre-treatment is risky. Furthermore, the chemical composition of calcination dust can vary significantly and contain undesirable impurities. Furthermore, it is a highly specialized material, making it difficult to supply to production facilities. Mixing coal tar and calcination dust can lead to groundwater contamination, making it unsuitable for use near water sources or in residential areas. Furthermore, the combination of viscous coal tar with finely dispersed calcination dust and slag creates difficulties in creating a homogeneous composition, which in turn can lead to the formation of tar clumps and subsequent uneven soil stabilization.Coal tar, being an organic substance, can interfere with the normal hydration and hardening processes of inorganic binders, acting as a hardening retarder. Oxidation and leaching of the tar are possible, leading to a loss of the bearing capacity of the reinforced soil. Furthermore, granulated blast furnace slag, unlike converter slag, is a more scarce and expensive material due to the need for costly granulation of the liquid melt immediately after tapping.

[0008] The closest analogue to the claimed invention in technical essence is a complex binder presented in a patent for reinforced clay soil (Patent RU 2645316 C1, published on 18.01.2017), where steel-smelting converter slag from the Novolipetsk Metallurgical Plant is used as the main component of the complex binder, and Portland cement or slag Portland cement of a strength grade of at least M300 is used as a hardening activator with the following ratio of components by solid phase, wt. %: the said steel-smelting slag 10-69, the said Portland cement or slag Portland cement 3-7, soil 28-83 and additionally - the chemical additive "Chimston" in an amount of 0.175% of the weight of Portland cement or slag Portland cement.

[0009] A disadvantage of the prototype is the use of a significant amount of Portland cement, which prevents it from achieving maximum environmental efficiency through complete waste recycling. The selected range of the main component content (from 10 to 69 wt.%) is extremely broad, indicating that the formulation is not universal and may lead to unpredictable fluctuations in the strength and technological properties of the binder. The binder content, depending on the soil, ranges from 20 to 50% or more by weight, which significantly exceeds the recommended dosages (in particular, according to the document "Methodological Recommendations for the Consumption Rates of Binders for Strengthening Materials Used in the Construction of Road Layers," cement-based soil for road construction, depending on the soil type, should contain from 5 to 12% cement and other similar types of hydraulic binders).Using binders in quantities exceeding 15% of the soil's mass to stabilize soils significantly complicates the mixing process, creating a viscous mixture with high internal resistance. The large surface area of ​​the binder, while accelerating the initial setting, prevents the resulting mixture from being thoroughly mixed and compacted before it loses its plasticity.

[0010] The technical problem of the invention is to obtain a composite clinker-free binder without the use of clinker minerals (cement and lime) based on converter slag and heat-treated mineral product of soda production (HTMP), which ensures increased strength and water resistance of the reinforced soil.

[0011] The use of MPSP heat-treated at 900-950°C as a lime substitute in a binder for strengthening cohesive soils reduces plasticity, lowers the moisture content of waterlogged clay soils, improves the compactibility of clay soils, virtually eliminates shrinkage and swelling, significantly increases compressive strength, especially under full water saturation, and improves the water resistance of soils strengthened with this binder. The presence of 11 wt.% MgO in MPSP positively affects the hardening rate of the strengthened soil, and anhydrite (anhydrous calcium sulfate) serves as an additional structure-forming component. To increase the efficiency of heat-treated MPSP, converter slag is added, which promotes the formation of the main structure-forming components - calcium hydrosilicates.A lime-slag binder, prepared by co-milling metallurgical slag and heat-treated mineral by-product of soda production, can impart the necessary strength, water resistance, frost resistance, and other required physical and mechanical properties to these reinforced soils. This binder is used in quantities of 12-14% by weight of the dry soil mass. Adding heat-treated mineral by-product of soda production in quantities exceeding 14% by weight is economically impractical, as it leads to an unjustified increase in the cost of the finished mixture without a proportional increase in strength. Furthermore, excessive binder content increases the viscosity of the mixture, which significantly reduces its compactibility in the field and requires the use of heavier equipment.

[0012] The specified technical result is achieved in that the composite mineral binder on a lime-slag base based on converter slag, according to the invention, is a product of the combined grinding of converter slag from the Chelyabinsk Metallurgical Plant and a mineral product of soda production heat-treated at a temperature of 900-950°C in the following ratio of components, wt. %:

[0013] specified slag 70;

[0014] mineral product of soda production 30.

[0015] The technological process for the production of a composite clinker-free binder without the use of clinker minerals (cement and lime) for soil stabilization in transport construction includes the following production cycles: collection and preparation of raw materials to the required technological level; dosage; mixing of dry components.

[0016] The following materials were used to produce a composite clinker-free binder without the use of clinker minerals (cement and lime) for soil strengthening in transport construction:

[0017] 1. Mineral product of soda production (MPSP) produced by JSC BSC (TU 2149-334-00203312-2015) is a solid, lumpy, non-combustible gray material with a mass fraction of (CaCO3 + MgCO3) of at least 60% and a mass fraction of moisture of no more than 35%.

[0018] The technological process for the formation of a mineral product of soda production is based on the thickening and sedimentation of the solid phase of the distillation liquid, filtration of the thickened liquid under pressure, storage of the filtered sediment - a mineral product of soda production (MPSP), followed by shipment. According to the results of X-ray phase analysis, the mineralogical composition of the MPSP is represented mainly by calcium carbonate CaCO3 (from 49 to 61 wt.%), also present are carbonate minerals monohydrocalcite CaCO3 * H2O in an amount of 2 to 4.5 wt. %, magnesian calcite (Mg 0.03 Sa 0.97 )(СО3) in an amount from 1.2 to 5 wt. %, magnesite MgCO3 in an amount from 0.1 to 3.3 wt. %. Total content of Ca and Mg oxides (CaO+MgO) акт is in the range from 5 to 8 wt.%, but the content of MgO is greater than the content of CaO. A fairly significant content of gypsum dihydrate CaSO4*2H2O and hemihydrate CaSO4*0.5 H2O (in total from 10 to 15 wt.%).

[0019] The mineralogical composition of the MPSP after heat treatment at a temperature of 900-950°C is as follows: total content of free oxides (CaO+MgO) актis 68.9 wt.%, of which free calcium oxide CaO is 57.3 wt.%, free magnesium oxide MgO is 11.64 wt.%, which is significantly higher than the permissible values ​​for lime according to GOST 9179-2018. The composition includes dicalcium silicate C2S (13.5 wt.%) and tricalcium silicate C3S (3.8 wt.%), as well as anhydrite CaSO4 in the amount of 5.4 wt.%. The optimal heat treatment range for MPSP is 900-950°C, determined by phase transformations: at temperatures below 900°C, CaCO3 decarbonation is incomplete, reducing the binder's activity. Above 950°C, the decomposition of magnesium-containing carbonates leads to the formation of periclase (MgO), which is characterized by delayed hydration and is accompanied by volumetric expansion at late stages of hardening, causing the destruction of the hardened composite. Heat treatment of MPSP at 900-950°C is an advantage over the temperature used for calcining lime (1000-1200°C) and cement (1450-1500°C).This results in significant energy savings, reduced carbon emissions and allows for the use of lower temperature, simpler and cheaper processing plants.

[0020] 2. Converter slag is a waste product of the Chelyabinsk Metallurgical Plant and is a dry, dispersed, dark-gray material. The moisture content of the converter slag sample was 0.2 wt.%. The converter slag sample consisted primarily of grains ranging in size from 2.5 to 10 mm.

[0021] According to the results of X-ray phase analysis, the slag particles have a mixed structure, the degree of crystallinity is 64%, the remaining 36% is an amorphous phase. The mineralogical composition of the crystalline part of the converter slag is mainly represented by tricalcium silicate C3S (10 wt.% of the total slag weight), dicalcium silicate C2S (10 wt.% of the total slag weight), and tricalcium aluminate C3A (11 wt.% of the total weight), there are also dicalcium ferrite C2F (11 wt.% of the total slag weight), trivalent iron oxide Fe2O3 (8 wt.%), free calcium oxide CaO (3.5 wt.%) and calcium hydroxide Ca(OH)2- about 3 wt.%. The total content of calcium and magnesium oxide is 36-38 wt.%, the content of aluminum oxide is 5-6 wt. %, iron oxide - 18-20 wt. %, silicon oxide content - about 22-24 wt. %. Based on the chemical composition, converter slag is classified as a basic slag.

[0022] The binder is produced as follows: after heat treatment of the MPSP and drying of the converter slag, the raw components are combined and ground. The feed to the mill for grinding is carried out using a bucket elevator through intermediate bins. From the intermediate bins, the resulting mixture of MPSP and converter slag is fed via a screw conveyor to the mill for combined fine grinding of the components using dosing units. The fine grinding mill is a combination of a high-speed impact mill and an air-centrifugal classifier and is designed to produce mineral powders with a fraction of 0.06-0.07 mm. The estimated mill capacity is 10-15 m 3 per hour and depends on the physical and mechanical properties of the raw materials and the required grinding fineness. The mixture of MPSP and slag, ground to a size of 0.06-0.07 mm, is fed by a belt conveyor to a silo (finished product storage area).

[0023] Example.

[0024] Pre-treated mineral product of soda production (MPSP) (heat-treated at a temperature of 900-950°C followed by grinding (crushing) to a fraction of 0-5 mm) was subjected to joint grinding with converter slag in a laboratory ball mill in the ratio: converter slag - 70 wt. %, mineral product of soda production (MPSP) after heat treatment - 30 wt. %, until the residue on a sieve No. 0.08 mm was no more than 5% by weight.

[0025] The specific surface area of ​​the obtained mineral binder, determined by the air permeability method using the PSKh-12 device, was about 5300 cm 2 / g. Combined grinding was carried out in a laboratory double-drum ball mill, the grinding duration was about 8 hours.

[0026] Tests were also carried out on prototype samples using converter slag, Portland cement and the chemical additive "Chimston".

[0027] The compositions of the test samples are shown in Table 1.

[0028]

[0029] After 7 and 28 days of normal hardening, the activity (compressive strength) of the samples was determined according to the method of GOST 30744-2001 “Cements. Test methods using polyfractional sand”. The test results are given in Table 2.

[0030]

[0031] From the data provided, it follows that the maximum strength values ​​of hardened samples of the composite binder are achieved with the following components in the binder composition, wt. %: mineral product of soda production - 30, converter slag - 70. When introducing a mineral product of soda production and converter slag in quantities less (composition 1) and more (composition 3) than those indicated in Table 1, a decrease in the compressive strength indicator is observed.

[0032] The composite mineral binder obtained according to the proposed invention is completely clinker-free and waste-free, as it is created exclusively from industrial waste, which in turn makes it possible to solve environmental problems, contributing to the reduction of the carbon footprint.

[0033] The use of a heat-treated mineral product from soda production, containing active oxides and clinker minerals (C2S, C3S), enables high binder activity and compressive strength comparable to traditional cements. Furthermore, after heat treatment, the MPSP already contains calcium sulfate (anhydrite) CaSO4, eliminating the need for gypsum in the developed binder.

[0034] The use of converter slag containing active minerals (C2S, C3A, C2F) and an amorphous phase, along with alkaline activation by calcium and magnesium oxides from MPSP and sulfate activation by anhydrite, facilitates the formation of durable hydrosilicate, hydroaluminate, and ettringite phases, providing the binder with effective curing, high final strength, density, and chemical resistance comparable to cement. Ettringite, a harmful component in heavy-duty concrete with dense aggregates, has no harmful effects when used with the developed binder for soil stabilization, as clay conglomerates are not highly durable, are easily deformed, and do not impede the growth of ettringite crystals or create internal stress.

[0035] Thus, the proposed solution makes it possible to obtain a composite mineral binder on a lime-slag base for strengthening the base soils (subgrade) during the construction, reconstruction and major repairs of highways, helping to reduce the consumption of high-grade Portland cement for these purposes.

Claims

A composite mineral binder on a lime-slag base based on converter slag, characterized in that it is a product of the combined grinding of converter slag from the Chelyabinsk Metallurgical Plant and a mineral product of soda production heat-treated at a temperature of 900-950°C in the following ratio of components, wt. %: the specified slag 70; mineral product of soda production 30

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