A steel slag internal curing aggregate, its preparation method and application; a concrete composition, its preparation method and application.

Abstract

This invention relates to the field of building materials technology, specifically to a steel slag internal curing aggregate, its preparation method and application, and a concrete composition, its preparation method and application. The invention involves mixing a stability modifier containing silica and aluminum components, a pore-forming agent, and a binder, followed by granulation. The resulting granules are then mixed with molten steel slag, heat-treated, and cooled to obtain the steel slag internal curing aggregate. The steel slag internal curing aggregate prepared by this invention has a low free calcium oxide content and exhibits characteristics such as lightweight, high volume stability, and high water absorption. It can partially replace natural aggregates in the preparation of high-strength concrete. The addition of the steel slag internal curing aggregate can significantly reduce shrinkage cracks in concrete and improve its mechanical properties and durability.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a steel slag internal curing aggregate and its preparation method and application, and a concrete composition and its preparation method and application. Background Technology

[0002] Steel slag is a major solid waste generated in the steel industry, and its resource utilization is of great significance for promoting a circular economy and sustainable development. However, free calcium oxide (C₂O₃) is commonly found in steel slag. f -CaO) and free magnesium oxide ( f Overburned mineral phases such as MgO undergo slow hydration reactions upon contact with water (e.g., CaO + H2O → Ca(OH)2, MgO + H2O → Mg(OH)2), accompanied by a significant volume expansion effect. This characteristic leads to serious volume stability problems when steel slag is used as an aggregate or admixture in cement concrete and building materials. The resulting internal stress accumulation can cause cracking, deformation, and even structural failure in cement concrete materials in the later stages, affecting not only the quality and durability of the project but also posing a potential safety risk. This severely restricts the large-scale, high-value-added utilization of steel slag in the building materials field. Summary of the Invention

[0003] Therefore, the purpose of this invention is to provide an internally cured steel slag aggregate. The internally cured steel slag aggregate prepared by this invention... f - Low CaO content and high volume stability mean that when added to concrete, it can significantly reduce shrinkage cracks and improve the mechanical properties and durability of concrete.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing steel slag internal curing aggregate, comprising the following steps: A stability modifier, a pore-forming agent, and a binder containing silicon and aluminum components are mixed and granulated to obtain granular material. The granular material is then mixed with molten steel slag, heat-treated, and cooled to obtain steel slag internal curing aggregate.

[0005] Preferably, the stability modifier includes one or more of coal gangue, fly ash, and pozzolanic materials; The stability modifier has a particle size ≤2mm; The stability modifier accounts for 5-20% of the mass of the molten steel slag.

[0006] Preferably, the pore-forming agent includes one or more of bituminous coal, anthracite, lignite, sub-bituminous coal, graphite, activated carbon, coke, silicon carbide, starch, sawdust, and rice husk ash; The particle size of the pore-forming agent is ≥100 mesh; The mass of the pore-forming agent accounts for 2 to 10% of the mass of the molten steel slag.

[0007] Preferably, the binder comprises an aqueous solution of carboxymethyl cellulose and / or water glass; The water glass has a modulus of 2.0 to 3.3 and a Baume degree of 30 to 40. The mass concentration of the carboxymethyl cellulose aqueous solution is 0.5-2%; The mass of the binder accounts for 0.5 to 1.5% of the total mass of the stability modifier and the pore-forming agent.

[0008] Preferably, the heat treatment temperature is 1400~1700℃ and the time is 10~24h.

[0009] Preferably, the steps further include: sequentially crushing, shaping and screening the steel slag internal curing aggregate to obtain steel slag internal curing fine aggregate and steel slag internal curing coarse aggregate; the particle size of the steel slag internal curing fine aggregate is ≤4.75mm, and the particle size of the steel slag internal curing coarse aggregate is 4.75~9.5mm and not 4.75mm.

[0010] The present invention also provides a steel slag internal curing aggregate prepared by the preparation method described above, wherein the steel slag internal curing aggregate has a porous structure.

[0011] The present invention also provides a concrete composition, the raw materials of which include the steel slag internal curing aggregate, cementitious material, fine aggregate, coarse aggregate and water as described in the above technical solution.

[0012] Preferably, the cementitious material includes cement, slag powder, and fly ash; The raw materials for preparing the concrete composition also include thermo-shrinkable fibers; The steel slag internal curing aggregate consists of fine steel slag internal curing aggregate with a particle size of 0~4.75mm and coarse steel slag internal curing aggregate with a particle size of 4.75~9.5mm. The fine aggregate includes sand with a particle size ≤ 4.75 mm; The coarse aggregate includes crushed stone, and the particle size of the crushed stone is 4.75~10mm; The volume of the fine aggregate cured in the steel slag accounts for 10-40% of the total volume of the fine aggregate cured in the steel slag and the fine aggregate. The volume of the coarse aggregate cured in the steel slag accounts for 10-20% of the total volume of the coarse aggregate and coarse aggregate cured in the steel slag.

[0013] The present invention also provides the application of the steel slag internal curing aggregate or the concrete composition described in the above-mentioned technical solutions in building materials.

[0014] This invention has found that during the mixing of powdered stabilizers with molten steel slag, the stabilizers are easily and rapidly encapsulated by the high-temperature molten steel slag, forming localized high-temperature reaction zones or reaction dead zones. This results in the SiO2, Al2O3, and other components in the stabilizer not having enough time to diffuse fully, and instead only reacting with the surface of the steel slag. f -CaO reaction, while the interior of steel slag f -CaO cannot come into contact with stabilizers. f - The residual CaO content can reach 1~1.5 wt%. f - High CaO residue; the significant density difference between the powdered stabilizer and the steel slag leads to uneven mixing and the formation of stabilizer-rich zones in certain areas, resulting in an uneven internal structure of the prepared steel slag internal curing aggregate. When the powdered pore-forming agent is directly added to the high-temperature steel slag, it is quickly covered by the molten slag, and the gases produced during combustion escape directly from the steel slag system. This prevents the formation of stable pores in the prepared steel slag internal curing aggregate, resulting in low porosity and significantly weakened internal curing function. Furthermore, when using powdered stabilizers, they are prone to floating and stratification during mixing with molten steel slag. The high viscosity of molten steel slag at high temperatures makes uniform mixing with the powdered stabilizer difficult, leading to large fluctuations in the content of active minerals (e.g., C3S, C2S) in different batches of steel slag internal curing aggregate.

[0015] This invention first uses the binding agent to form the stability modifier and pore-forming agent into granules, so that most of the stability modifier and pore-forming agent are encapsulated within the granules. When in contact with molten steel slag, a "slow reaction interface" is formed, allowing the residual heat of the molten steel slag to gradually penetrate into the interior of the granules. f -CaO reacts fully with Al2O3 and SiO2 in the stabilizer to produce calcium aluminum feldspar (C2AS), anorthite, active components of calcium silicate, active components of calcium aluminate, enstatite, forsterite, etc. f The reaction conversion rate of CaO can reach over 95%, and the final steel slag internal curing aggregate contains... f The CaO content is <0.5wt%, which fundamentally optimizes the mineral composition of steel slag, significantly reduces the content of free calcium oxide and free magnesium oxide, and improves the volume stability of steel slag. The granular material contains pore-forming agents, forming a porous material upon contact with molten steel slag. The granular material prepared by this invention has a small density difference with molten steel slag, allowing the granules to uniformly fill the gaps in the molten steel slag. This avoids localized compositional deviations caused by the agglomeration of powdered stabilizers and pore-forming agents, resulting in a more uniform mineral composition of the cured aggregate within the steel slag.

[0016] Furthermore, when using a pore-forming agent containing carbon components, the carbon components in the pore-forming agent undergo a reduction reaction with oxides (such as free calcium oxide and free magnesium oxide) in the steel slag, releasing gas. Because the molten steel slag has a high viscosity, the gas is not easily discharged, thus forming a porous material.

[0017] The steel slag internal curing aggregate prepared by this invention has a porous structure and a high water absorption rate. When used to prepare concrete, it can slowly release the internally stored water in the concrete, effectively alleviating the shrinkage caused by hydration and self-drying inside the concrete, and reducing the 28-day drying shrinkage rate of the concrete by more than 10%.

[0018] Furthermore, this invention controls the particle size of the stability modifier to ≤2mm and the particle size of the pore-forming agent to ≥200 mesh. The difference in particle size between the two results in a granular material with a porous structure. When molten steel slag is mixed with the granular material, heat permeates through the pores of the granular agent, which facilitates the full utilization of the stability modifier and the pore-forming agent, thereby promoting the achievement of… f -Deep elimination of CaO.

[0019] The steel slag internal curing aggregate prepared by this invention f - It has low CaO content and features lightweight, high volume stability, and high water absorption. It can partially replace natural aggregates in the preparation of high-strength concrete. The addition of steel slag internal curing aggregate can significantly reduce shrinkage cracks in concrete, improve the mechanical properties and durability of concrete, resulting in high engineering quality and low potential engineering safety risks. It significantly improves the large-scale, high-value-added utilization rate of steel slag in the building materials field.

[0020] As shown in the test results of the examples, the steel slag internal curing aggregate prepared in this invention exhibits... f -CaO content < 0.5wt%, porosity 14.8~18.4%.

[0021] This invention also provides a concrete composition, the raw materials of which include the steel slag internal curing aggregate, cementitious materials, fine aggregate, coarse aggregate, and water as described in the above-mentioned technical solution. The steel slag internal curing aggregate used in this invention has the characteristics of being lightweight, having high volume stability, and high water absorption, and can partially replace natural aggregates (such as coarse aggregate and fine aggregate) in the preparation of high-strength concrete. The addition of steel slag internal curing aggregate can significantly reduce shrinkage cracks in concrete and improve the mechanical properties and durability of concrete.

[0022] Furthermore, by adding thermo-shrinkable fibers to the concrete composition, the present invention can stimulate its shrinkage through the exothermic reaction of hydration, thereby applying three-dimensional micro-prestress to the concrete and improving its crack resistance. Attached Figure Description

[0023] Figure 1 A photograph of the steel slag internal curing aggregate prepared in Example 1; Figure 2 This is a photograph of the steel slag internal curing aggregate prepared in Example 2. Detailed Implementation

[0024] This invention provides a method for preparing steel slag internal curing aggregate, comprising the following steps: mixing a stability modifier, a pore-forming agent and a binder containing silicon and aluminum components and granulating them to obtain granular material; mixing the granular material with molten steel slag, subjecting it to heat treatment and then cooling it to obtain steel slag internal curing aggregate.

[0025] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0026] In this invention, the stability modifier contains a silicon-aluminum component, and the stability modifier may include one or more of coal gangue, fly ash, and pozzolanic materials. In this invention, the particle size of the stability modifier can be ≤2mm. In this invention, the mass of the stability modifier can account for 5-20% of the mass of the molten steel slag, and can also be 10-15%, specifically 5%, 6%, 7%, 8%, 9%, 10%, 11%, 11.25%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. During subsequent heat treatment, the free calcium oxide and free magnesium oxide in the steel slag react chemically with the silicon-aluminum component in the stability modifier under the residual heat of the molten steel slag to generate calcium silicate, calcium aluminate minerals, enstatite, forsterite, etc., which essentially optimizes the mineral composition of the steel slag and significantly reduces the free calcium oxide content. f The content of CaO (<0.5%) and free magnesium oxide improves the volume stability of steel slag.

[0027] In this invention, the pore-forming agent contains a carbon component and may include one or more of bituminous coal, anthracite, lignite, sub-bituminous coal, graphite, activated carbon, coke, silicon carbide, starch, sawdust, and rice husk ash. In this invention, the particle size of the pore-forming agent may be ≥100 mesh, or 100-400 mesh, or further 200-300 mesh. In this invention, the mass of the pore-forming agent may account for 2-10% of the mass of the molten steel slag, or 3-6%, specifically 2%, 3%, 3.75%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. In this invention, the mass ratio of the stability regulator to the pore-forming agent may be 1-4:1, or 2-3:1, specifically 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. When the pore-forming agent is omitted, the stabilizer and conditioner, when added directly, will completely participate in the mineral reaction (such as the conversion of SiO2 in fly ash to C2S), without the formation of additional pores, resulting in a low porosity of the prepared steel slag internal curing aggregate. In this invention, a pore-forming agent is added, and the pore-forming agent and stabilizer are prepared into granules. During subsequent heat treatment, the carbon component in the pore-forming agent undergoes a reduction reaction with the oxides in the steel slag, releasing gases (such as CO2 and CO). Due to the high viscosity of the molten steel slag, the gases are not easily released, thus forming a porous material. Moreover, the pore-forming agent is encapsulated inside the granules, and the gases (such as CO2 and CO) generated during combustion are confined by the outer shell of the granules (molten steel slag), forming interconnected pores, resulting in a porous structure in the prepared steel slag internal curing aggregate. The starch used in this invention is a finely granular organic pore-forming agent, which is uniformly dispersed in the matrix as discrete particles, physically occupying space. At high temperatures, it undergoes gelatinization, melting, and thermal oxidative decomposition, generating gases such as CO2 and H2O that escape. Near-spherical, uniformly sized pores are formed at the original starch particle locations. Low dosages result in mainly isolated closed pores, while high dosages can form interconnected open pores. The sawdust used in this invention is a fibrous woody biomass composed of cellulose, hemicellulose, and lignin, interwoven in the matrix in a fibrous form. At high temperatures, the fibers pyrolyze, burn, and completely ablate, releasing a large amount of gas. Controlled by the fiber morphology, it forms elongated, fissure-like, highly interconnected pores with a wide pore size distribution and high open porosity. The rice husk used in this invention is a shell-shaped hard biomass, and the core pore-forming method is the thermal decomposition and burning of organic components. Its shell-shaped structure and lamellar morphology not only form cavities where the organic phase disappears after burning, but also retain interstitial pores between the shell layers. Finally, irregular, multi-level, large-diameter, highly interconnected macroscopic pores are formed, with a disordered pore structure and strong permeability.

[0028] This invention controls the particle size of the stability modifier to ≤2mm and the particle size of the pore-forming agent to ≥100 mesh. The difference in particle size between the two results in a granular material with a porous structure. When molten steel slag is mixed with the granular material, heat permeates through the pores of the granular material, which facilitates the full utilization of the stability modifier and the pore-forming agent, thereby promoting the achievement of… f -Deep elimination of CaO.

[0029] In this invention, the binder may include an aqueous solution of carboxymethyl cellulose and / or water glass. In this invention, the mass concentration of the aqueous carboxymethyl cellulose solution may be 0.5-2%, or 1-1.5%, specifically 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, or 2%. In this invention, the mass of the binder may account for 0.5-1.5% of the total mass of the stabilizer and pore-forming agent, or 0.5-1%, specifically 0.5%, 0.8%, 1%, 1.2%, or 1.5%. In this invention, the modulus of the water glass may be 2.0-3.3, or 2.4-3, specifically 2.0, 2.4, 2.6, 2.8, 3, 3.2, or 3.3; the Baume degree of the water glass may be 30-40, specifically 30, 32, 34, 35, 36, 38, or 40.

[0030] In this invention, mixing the stability modifier, pore-forming agent and binder may include: mixing the stability modifier and the pore-forming agent, and mixing the resulting mixture with the binder.

[0031] This invention does not impose any particular limitation on the granulation process, as long as it produces granules with a particle size ≤ 5 mm. In this invention, the particle size of the granules can be 0.15~5 mm, or 1~4 mm, or even 2~3 mm. In this invention, the dry density of the granules can be 1.3~1.8 g / cm³. 3 It can also be 1.35~1.5g / cm³. 3 Specifically, it can be expressed as 1.3 g / cm³. 3 1.35g / cm 3 1.38g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 Or 1.8g / cm 3 .

[0032] After granulation, the present invention may further include drying the granules obtained from granulation to obtain granulated material. The present invention does not have specific limitations on the drying method and conditions; drying to a constant weight is sufficient.

[0033] In this invention, mixing the granular material with molten steel slag may include: pouring the molten steel slag into a slag pan containing the granular material. This invention utilizes the weight and impact force of the molten steel slag to mix the molten steel slag with the granular material, which facilitates forced turbulent mixing of the molten steel slag and granular material, eliminates component stratification, localized high-temperature reaction zones, and mixing dead zones, and improves the compositional uniformity and performance stability of the composite material.

[0034] In this invention, the temperature of the heat treatment can be 1400~1700℃, or 1500~1600℃, specifically 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃, or 1700℃; the time of the heat treatment can be 10~24h, or 15~20h, specifically 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h; the heat treatment is performed using the residual heat of molten steel slag.

[0035] In this invention, the density of the molten steel slag can be 3.0~3.5 g / cm³. 3 It can also be 3.1~3.4 g / cm³. 3 It can be further increased to 3.2~3.3 g / cm³. 3 In this invention, the molten steel slag is obtained by melting steel slag. This invention does not have a special limitation on the source of the steel slag; any steel slag well known to those skilled in the art can be used, such as converter steel slag.

[0036] In the present invention, the cooling may include segmented cooling, and the segmented cooling may include high-temperature cooling, medium-temperature cooling, and low-temperature cooling carried out in sequence; when the temperature of the system after heat treatment (denoted as T) > 700 °C, high-temperature cooling is adopted, when 400 °C < T ≤ 700 °C, medium-temperature cooling is adopted, and when T ≤ 400 °C, low-temperature cooling is adopted. In the present invention, the cooling rate of the high-temperature cooling may be 10 to 20 °C / min, or may also be 12 to 18 °C / min, and may specifically be 10 °C / min, 11 °C / min, 12 °C / min, 13 °C / min, 14 °C / min, 15 °C / min, 16 °C / min, 17 °C / min, 18 °C / min, 19 °C / min or 20 °C / min; the time of the high-temperature cooling may be 5 to 10 min, and may specifically be 5 min, 6 min, 7 min, 8 min, 9 min or 10 min; the high-temperature cooling may include air cooling, and the wind speed of the air cooling may be 0.8 to 1.2 m / s, and may specifically be 0.8 m / s, 0.9 m / s, 1 m / s, 1.1 m / s or 1.2 m / s. In the present invention, the cooling rate of the medium-temperature cooling may be 5 to 10 °C / min and not 5 °C / min, and may specifically be 5.1 °C / min, 5.5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min; the time of the medium-temperature cooling may be 30 to 40 min, and may specifically be 30 min, 32 min, 34 min, 35 min, 36 min, 38 min, 40 min; the medium-temperature cooling may include air cooling, and the wind speed of the air cooling may be 0.3 to 0.5 m / s, and may specifically be 0.3 m / s, 0.35 m / s, 0.4 m / s, 0.45 m / s or 0.5 m / s. In the present invention, the cooling rate of the low-temperature cooling may be ≤ 5 °C / min, or may also be 0.5 to 5 °C / min, and may specifically be 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min; the time of the low-temperature cooling may be 60 to 120 min, or may also be 80 to 100 min, and may specifically be 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min; the low-temperature cooling may be natural ventilation cooling. The present invention adopts the above-mentioned segmented cooling method. The high-temperature section is cooled relatively quickly, can quickly pass through the high-temperature zone, can inhibit abnormal grain growth, avoid over-sintering or oxidation, and ensure uniform internal structure of the material; the medium-temperature section is cooled at a moderate rate, which is beneficial to matching the phase change and structure stability range of the material, reducing thermal shock and internal defect generation; the low-temperature section is cooled slowly, which can fully release the residual thermal stress, significantly improve the dimensional stability and mechanical properties of the material, and reduce the risk of cracking and deformation.This invention controls the cooling rate to below 20℃ / min and does not use direct water quenching, which can avoid the formation of through cracks or damage to the pore structure inside the aggregate.

[0037] In this invention, after obtaining the steel slag internal curing aggregate, the invention may further include: sequentially crushing, shaping and screening the steel slag internal curing aggregate to obtain steel slag internal curing fine aggregate and steel slag internal curing coarse aggregate respectively; the particle size of the steel slag internal curing fine aggregate is <4.75mm, and the particle size of the steel slag internal curing coarse aggregate is 4.75~9.5mm and not 4.75mm.

[0038] The steel slag internal curing aggregate prepared by this invention has the characteristics of being lightweight, having high volume stability, and having high water absorption. It can partially replace natural aggregates in the preparation of high-strength concrete. The addition of steel slag internal curing aggregate can significantly reduce shrinkage cracks in concrete and improve the mechanical properties and durability of concrete. It has a very good application prospect as a building material.

[0039] This invention also provides a steel slag internal curing aggregate prepared by the method described in the above technical solution, wherein the steel slag internal curing aggregate has a porous structure. In this invention, the porosity of the steel slag internal curing aggregate can be 10-20%, or 12-18%, specifically 10%, 11%, 12%, 13%, 14%, 14.8%, 15%, 16%, 16.2%, 17%, 18%, 18.4%, 19%, or 20%. In this invention, the dry density of the steel slag internal curing aggregate is 2.0-2.4 g / cm³. 3 Specifically, it can be expressed as 2.0 g / cm³. 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 Or 2.4g / cm 3 , The present invention also provides a concrete composition, the raw materials of which include the steel slag internal curing aggregate, cementitious material, fine aggregate, coarse aggregate and water as described in the above technical solution.

[0040] In this invention, the cementitious material may include cement, slag powder, and fly ash. In this invention, the mass fraction of cement in the cementitious material may be 40-60%, or 45-50%, specifically 50%; the cement may include one or more of PO52.5 cement, PII52.5 cement, and PII42.5 cement. In this invention, the mass fraction of slag powder in the cementitious material may be 10-30%, or 15-25%, specifically 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, or 30%; the volume average particle size (D[4,3]) of the slag powder may be 16-22 μm, specifically 16 μm, 17 μm, 18 μm, 18.2 μm, 19 μm, 20 μm, 21 μm, or 22 μm. In this invention, the mass fraction of fly ash in the cementitious material can be 20-40%, or 25-35%, specifically 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, or 40%; the volume average particle size (D[4,3]) of the fly ash can be 20-30 μm, or 24-28 μm, specifically 20 μm, 22 μm, 22.2 μm, 24 μm, 25 μm, 26 μm, 28 μm, or 30 μm. In this invention, the amount of cementitious material in the concrete composition can be 450-500 kg / m³. 3 Specifically, it can be 450 kg / m 3 460kg / m 3 470kg / m 3 480kg / m 3 490kg / m 3 Or 500kg / m 3 In this invention, the water-cement ratio of the concrete can be 0.28 to 0.32, specifically 0.28, 0.29, 0.3, 0.31, or 0.32.

[0041] In this invention, the steel slag internal curing aggregate is a fine steel slag internal curing aggregate with a particle size of <4.75mm and a coarse steel slag internal curing aggregate with a particle size of 4.75~9.5mm and not 4.75mm.

[0042] In this invention, the fine aggregate may include sand; the particle size of the sand may be ≤4.75mm. In this invention, the coarse aggregate may include crushed stone, specifically gravel, the particle size of which may be 4.75~10mm, or even 5~10mm. In this invention, the mass ratio of the fine aggregate to the total mass of the fine and coarse aggregates (i.e., the sand ratio) may be 36~45%, or even 38~42%, specifically 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%.

[0043] In this invention, the volume of the fine aggregate for internal curing of steel slag can account for 10-40% of the total volume of the fine aggregate and fine aggregate for internal curing of steel slag, or it can be 20-30%, specifically 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38% or 40%.

[0044] In this invention, the volume of the coarse aggregate cured in the steel slag can account for 10-20% of the total volume of the coarse aggregate and coarse aggregate cured in the steel slag, or it can be 10-15%, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0045] In this invention, the raw materials for preparing the concrete composition may further include thermo-shrinkable fibers, which may include polyolefin fibers; the number average molecular weight of the polyolefin fibers may be 180,000 to 250,000 g / mol, specifically 180,000 g / mol, 190,000 g / mol, 200,000 g / mol, 210,000 g / mol, 220,000 g / mol, 230,000 g / mol, 240,000 g / mol or 250,000 g / mol; the weight average molecular weight of the polyolefin fibers may be 350,000 to 500,000 g / mol, specifically 350,000 g / mol, 380,000 g / mol, 400,000 g / mol, 420,000 g / mol, 450,000 g / mol, 480,000 g / mol or 500,000 g / mol. In this invention, the length of the thermoshable fiber can be 8-12 mm, specifically 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm; the diameter of the thermoshable fiber can be 0.15-0.25 mm, or 0.18-0.22 mm, specifically 0.15 mm, 0.16 mm, 0.17 mm, 0.18 mm, 0.19 mm, 0.2 mm, 0.21 mm, 0.22 mm, 0.23 mm, 0.24 mm, or 0.25 mm. In this invention, the amount of thermoshable fiber used in the concrete composition can be 1-3 kg / m³. 3 It can also be 1~2kg / m 3 Specifically, it can be 1 kg / m 3 1.5kg / m 3 2kg / m 3 2.5kg / m 3 Or 3kg / m 3 .

[0046] The present invention also provides the application of the steel slag internal curing aggregate described in the above technical solution or the concrete composition described in the above technical solution in building materials. The steel slag internal curing aggregate provided by the present invention has the characteristics of light weight, high volume stability, high water absorption rate, etc., and can partially replace natural aggregates to prepare high-strength concrete. The addition of the steel slag internal curing aggregate can significantly reduce the shrinkage cracks of concrete and improve the mechanical properties and durability of concrete. The steel slag internal curing aggregate and the concrete composition provided by the present invention have good application prospects as building materials.

[0047] In the following examples and comparative examples, the steel slag used is the converter steel slag of Shaoguan Iron and Steel Company, and its chemical composition is shown in Table 1.

[0048] Table 1 Chemical composition of converter steel slag (wt%)

[0049] In order to further illustrate the present invention, the steel slag internal curing aggregate provided by the present invention, its preparation method and application, the concrete composition, its preparation method and application will be described in detail below in conjunction with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0050] Example 1 (1) Preparation of steel slag internal curing aggregate Mix coal gangue (particle size less than 1.18 mm) and anthracite (fineness of 150 mesh) evenly according to a mass ratio of 2:1 to obtain a mixed powder. Add a binder (an aqueous carboxymethyl cellulose solution with a concentration of 1.5 wt%) to granulate the mixed powder (particle size ≤ 5 mm), and dry it to constant weight at 105 °C to obtain granular material (dry density of 1.38 g / cm 3 ). Spread the granular material on the bottom of the slag pot, pour molten steel slag (1650 °C), mix, and perform heat treatment using the waste heat in the system. The heat treatment time is 24 h, and it is cooled in stages by air cooling to obtain the steel slag internal curing aggregate. The obtained steel slag internal curing aggregate is crushed, shaped, and screened by a counterattack crusher to obtain steel slag internal curing fine aggregate (particle size < 4.75 mm) and steel slag internal curing coarse aggregate (particle size of 4.75 - 9.5 mm and not 4.75 mm). Among them, the mass of the binder accounts for 0.5% of the total mass of the mixed powder; the mass of the granular material accounts for 15% of the total mass of the converter steel slag. Staged air cooling: High temperature section (when T > 700 °C): The cooling rate is 15 °C / min, the time is 8 min, and the wind speed is 1.0 m / s; Medium temperature section (400 °C < T ≤ 700 °C): The cooling rate is 8 °C / min, the time is 35 min, and the wind speed is 0.4 m / s; Low temperature section (T ≤ 400 °C): The cooling rate is 5 °C / min, the time is 90 min, and natural ventilation is used.

[0051] Figure 1The image shows a physical picture of the steel slag internal curing aggregate. As can be seen, the steel slag internal curing aggregate prepared by this invention has a porous structure.

[0052] (2) Preparation of high-strength concrete Raw materials for preparation: 490 kg / m³ of cementitious material 3 The following materials are used for internal curing of steel slag: fine aggregate (particle size < 4.75 mm), sand (particle size ≤ 4.75 mm), coarse aggregate (particle size 4.75~9.5 mm), gravel (particle size 5~10 mm), and thermoshrunk fiber (polyolefin fiber with a weight average molecular weight of 450,000 g / mol, a number average molecular weight of 200,000 g / mol, a diameter of 0.2 mm, and a length of 10 mm) at a rate of 1.5 kg / m³. 3 The cementitious material composition is 50wt% PO52.5 cement, 20wt% slag powder (D[4,3]=18.2μm), and 30wt% fly ash (D[4,3]=22.2μm). The volume of the steel slag-cured fine aggregate accounts for 20% of the total volume of the steel slag-cured fine aggregate and sand. The volume of the steel slag-cured coarse aggregate accounts for 10% of the total volume of the steel slag-cured fine aggregate and 5~10mm crushed stone. The water-cement ratio of the high-strength concrete is 0.3, and the sand ratio is 41%.

[0053] The preparation steps for high-strength concrete are as follows: Pre-wet the steel slag-cured aggregate to a moisture content of 6.7% to obtain pre-wetted steel slag-cured aggregate; dry-mix the pre-wetted steel slag-cured coarse aggregate and fine aggregate for 30 seconds, add cement, slag powder, and fly ash and dry-mix for 30 seconds, add mixing water and liquid admixtures and wet-mix for 60-90 seconds, add thermo-shrinkable fibers and wet-mix for 30-60 seconds to obtain high-strength concrete. The total mixing time should be ≥150 seconds to ensure no dry lumps and a uniform slurry.

[0054] Example 2 Steel slag internal curing aggregate and high-strength concrete were prepared according to the method of Example 1. The only difference from Example 1 is that the mixed powder composition is coal gangue:coke mass ratio = 3:1, the particle size of coal gangue is less than 1.18 mm, and the fineness of coke is 100 mesh. Figure 2 The image shows a physical picture of the steel slag internal curing aggregate. As can be seen, the steel slag internal curing aggregate prepared by this invention has a porous structure.

[0055] Example 3 Steel slag internal curing aggregate and high-strength concrete were prepared according to the method of Example 1. The only difference from Example 1 is that the mixed powder composition is coal gangue: fly ash: silicon carbide mass ratio = 3:1:1, the particle size of coal gangue is less than 1.18 mm, and the fineness of silicon carbide is 120 mesh.

[0056] Comparative Example 1 The only difference from Example 1 is that no pore-forming agent is added.

[0057] Comparative Example 2 The only difference from Example 1 is that the mixed powder is not granulated and is directly mixed with molten steel slag.

[0058] Test Example 1 Testing of steel slag internal curing aggregates prepared in the examples and comparative examples Chemical composition test: YB / T 140-2009 "Chemical Analysis Methods for Steel Slag", test results are shown in Table 2.

[0059] Physical performance indicators: GB / T 17431.1-2010 "Lightweight aggregates and their test methods Part 1: Lightweight aggregates", test results are shown in Table 2.

[0060] Table 2 Chemical composition and porosity of steel slag internal curing aggregates prepared from raw steel slag, examples, and comparative examples.

[0061] As shown in Table 2, the dry density of the steel slag internal curing aggregates prepared in Examples 1-3 is between 2.0 and 2.4 g / cm³. 3 Compared to ordinary limestone aggregates and river sand, it is lightweight; its water absorption rate is ≤6.7%, which provides internal curing during concrete preparation; and f - The CaO content was less than 0.5 wt%, which significantly improved the volume stability of the steel slag aggregate. Compared with Example 1, the porosity and water absorption of the steel slag aggregate prepared in Comparative Example 1 decreased significantly, while the dry density increased; the chemical composition of the steel slag aggregate prepared in Comparative Example 2 fluctuated greatly. f High CaO and MgO content reduces stability, and the material exhibits low water absorption and high dry density. The porosity of the steel slag internal curing aggregates prepared in Examples 1-3 ranged from 14.8% to 18.4%. A comparison between Example 3 and Comparative Example 1 revealed that the incorporation of a pore-forming agent can effectively improve the porosity of the steel slag aggregates.

[0062] Test Example 2 Performance testing of concrete prepared in the examples and comparative examples Compressive strength test: The test results are shown in Table 3 of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019).

[0063] Drying shrinkage test: The test results are shown in Table 3 of the "Standard for Test Methods of Long-term Performance and Durability of Concrete" (GB / T50082-2024).

[0064] Table 3. Test results of compressive strength and drying shrinkage of concrete prepared in the examples and comparative examples.

[0065] As shown in Tables 2-3, by comparing Examples 1-3, it was found that the incorporation of the stability modifier and the pore-forming agent can effectively reduce the free calcium oxide content in the steel slag (<0.5wt%), and the porosity is between 14.8% and 18.4%. By comparing Example 3 and Comparative Example 1, it was found that the incorporation of the pore-forming agent can effectively increase the porosity of the concrete. The steel slag internal curing aggregate prepared by this invention has a good curing effect. The compressive strength of the high-strength concrete 28 prepared with it increased by 8.7%, the drying shrinkage rate decreased by 11%, and the crack resistance of the concrete was significantly improved.

[0066] The above results demonstrate that this invention utilizes a uniformly mixed stabilizer and pore-forming agent to subject steel slag to a high-temperature reaction. Using the residual heat of the molten steel slag, the free calcium oxide and free magnesium oxide in the slag react chemically with the silica-alumina components in the stabilizer to generate calcium silicate and calcium aluminate minerals. This fundamentally optimizes the mineral composition of the steel slag, reduces the free calcium oxide content, and improves the volume stability of the steel slag. Furthermore, using the residual heat of the steel slag, the carbon components in the pore-forming agent undergo a reduction reaction with the oxides in the steel slag, releasing CO and / or CO2 gases, thereby forming a porous material. The steel slag internal curing aggregate prepared by this invention is lightweight, has high volume stability, and high porosity, and can partially replace natural aggregates in the preparation of high-strength concrete. It can reduce shrinkage cracks in high-strength concrete and improve its mechanical properties and durability.

[0067] 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 principle 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 steel slag internal curing aggregate, characterized in that, Includes the following steps: A stability modifier, a pore-forming agent, and a binder containing silicon and aluminum components are mixed and granulated to obtain granular material. The granular material is then mixed with molten steel slag, heat-treated, and cooled to obtain steel slag internal curing aggregate.

2. The preparation method according to claim 1, characterized in that, The stability modifier includes one or more of coal gangue, fly ash, and pozzolanic materials; The stability modifier has a particle size ≤2mm; The stability modifier accounts for 5-20% of the mass of the molten steel slag.

3. The preparation method according to claim 1, characterized in that, The pore-forming agent includes one or more of bituminous coal, anthracite, lignite, sub-bituminous coal, graphite, activated carbon, coke, silicon carbide, starch, sawdust, and rice husk ash; The particle size of the pore-forming agent is ≥100 mesh; The mass of the pore-forming agent accounts for 2 to 10% of the mass of the molten steel slag.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The binder comprises an aqueous solution of carboxymethyl cellulose and / or water glass; The water glass has a modulus of 2.0 to 3.3 and a Baume degree of 30 to 40. The mass concentration of the carboxymethyl cellulose aqueous solution is 0.5-2%; The mass of the binder accounts for 0.5 to 1.5% of the total mass of the stability modifier and the pore-forming agent.

5. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 1400~1700℃, and the time is 10~24h.

6. The preparation method according to claim 5, characterized in that, The steps further include: sequentially crushing, shaping and screening the steel slag internal curing aggregate to obtain steel slag internal curing fine aggregate and steel slag internal curing coarse aggregate; the particle size of the steel slag internal curing fine aggregate is ≤4.75mm, and the particle size of the steel slag internal curing coarse aggregate is 4.75~9.5mm and not 4.75mm.

7. The steel slag internal curing aggregate prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The steel slag internal curing aggregate has a porous structure.

8. A concrete composition, characterized in that, The raw materials for preparation include the steel slag internal curing aggregate, cementing material, fine aggregate, coarse aggregate and water as described in claim 7.

9. The concrete composition according to claim 8, characterized in that, The cementing material includes cement, slag powder, and fly ash; The raw materials for preparing the concrete composition also include thermo-shrinkable fibers; The steel slag internal curing aggregate consists of fine steel slag internal curing aggregate with a particle size of 0~4.75mm and coarse steel slag internal curing aggregate with a particle size of 4.75~9.5mm. The fine aggregate includes sand with a particle size ≤ 4.75 mm; The coarse aggregate includes crushed stone, and the particle size of the crushed stone is 4.75~10mm; The volume of the fine aggregate cured in the steel slag accounts for 10-40% of the total volume of the fine aggregate cured in the steel slag and the fine aggregate. The volume of the coarse aggregate cured in the steel slag accounts for 10-20% of the total volume of the coarse aggregate and coarse aggregate cured in the steel slag.

10. The application of the steel slag internal curing aggregate of claim 7 or the concrete composition of claim 8 or 9 in building materials.

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