Preparation method of inert steel slag aggregate and road asphalt mixture using aggregate

Abstract

The invention relates to a preparation method of an inert steel slag aggregate, which comprises the following steps of: crushing hot-stuffy steel slag serving as a raw material, and performing strong magnetic separation at the magnetic field intensity of not less than 8000 gauss to obtain a magnetic steel slag aggregate and a steel slag aggregate rich in silicate mineral phase; the magnetic steel slag aggregate is ground, stripped and shaped through a rod mill, so that silicate mineral phases attached to the surface of the magnetic steel slag aggregate are stripped, and the particle morphology of the steel slag aggregate is improved; and carrying out weak magnetic separation on the rod-milled material at the magnetic field intensity not higher than 4000 gauss to obtain the inert steel slag aggregate with the RO phase content not lower than 30%. According to the preparation method of the inert steel slag aggregate, a synergistic process chain of crushing, high-intensity magnetic separation, rod mill stripping and low-intensity magnetic separation is constructed, a traditional long-term aging or stabilizer external adding method is replaced, the volume stability problem of the steel slag is synchronously solved in a short time, enrichment of active mineral phases is achieved, the pavement performance of the aggregate is optimized, and the service life of the aggregate is prolonged. The method has the remarkable advantages of high treatment efficiency, controllable effect and high resource utilization rate.

Description

Technical Field

[0001] This invention belongs to the field of steel slag resource utilization and road engineering aggregate preparation technology, and specifically relates to a method for preparing inert steel slag aggregate and a road asphalt mixture using the aggregate. Background Technology

[0002] Steel slag, used as aggregate in road asphalt mixtures, can improve pavement durability, skid resistance, wear resistance, driving safety, and comfort at a relatively low cost. However, steel slag raw materials have a loose and porous surface and a high water absorption rate, which usually does not meet the water absorption requirements specified in the standards. Furthermore, it contains unevenly distributed free calcium oxide, periclase, and other expanding components. When these components undergo hydration or oxidation, the steel slag raw material will experience significant volume expansion, leading to defects such as expansion, arching, cracking, and spalling on the surface of cement concrete or asphalt concrete.

[0003] To overcome the drawback of poor volume stability of steel slag and achieve the goal of using steel slag as a high-quality aggregate in road engineering on a large scale, the current inert modification measures mainly include two methods: aging treatment and improved steel slag. However, due to their respective bottlenecks, these two methods have not been adopted at the industrial level, as detailed below: (1) The aging treatment of steel slag involves natural aging and heat treatment processes. Natural aging takes several months to a year or even longer and requires a large amount of land. Although accelerated aging methods such as steam aging and heat treatment can shorten the treatment time, they increase energy consumption and equipment investment, thereby increasing costs. Moreover, the treatment effect is affected by various factors such as steel slag composition and particle size distribution, making it difficult to ensure that the treatment effect of each batch of steel slag is completely consistent.

[0004] (2) Modification of steel slag mainly involves adding stabilizers and blending with other materials. Adding stabilizers or using them in combination with other materials increases material costs. Although modification can solve the problem of volume instability, the added stabilizers or other materials will affect other properties of the mixture (such as strength and durability). Some modifiers are also harmful to the environment, especially after rainwater runoff or long-term use, which can cause environmental pollution problems.

[0005] Meanwhile, the performance of the mixture is not only affected by the elemental materials, but also by the interactions between different materials at the interface (such as adsorption, penetration, and diffusion). It is influenced by factors such as material composition, surface properties, and temperature. Asphalt and inert steel slag aggregates are two materials with different properties, and there is a transitional weak zone at their interface. Moreover, the composition and morphology of the material in the interface region differ from those in the matrix, and its structure is relatively loose with lower strength. Under the influence of external factors, cracks are prone to appear in this region. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing inert steel slag aggregate and a road asphalt mixture using the aggregate. This method addresses the problems of long treatment cycles, large land occupation, high costs, and quality fluctuations associated with the inertization of steel slag in the prior art. It achieves effective separation of the magnetic phase and silicate mineral phase in steel slag and enriches the RO phase to obtain inert steel slag aggregate. Simultaneously, the silicate phase is recovered to prepare steel slag micro powder as a filler, which is used together to prepare road asphalt mixture. Except for asphalt, the other components in the road asphalt mixture are derived from intermediate and final products prepared from inert steel slag aggregate, achieving the performance indicators of a standardized product with simple components.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing inert steel slag aggregate, comprising the following steps: Step 1: Using hot-quenched steel slag as raw material, crush it and then perform strong magnetic separation with a magnetic field strength of not less than 8000 Gauss to obtain magnetic steel slag aggregate and steel slag aggregate rich in silicate mineral phase. Step 2: The magnetic steel slag aggregate is subjected to rod milling and shaping to remove the silicate mineral phase attached to its surface and improve the particle morphology of the steel slag aggregate. Step 3: The material after rod milling is subjected to weak magnetic separation with a magnetic field strength of no more than 4000 Gauss to obtain inert steel slag aggregate with an RO phase content of no less than 30% (based on XRD semi-quantitative analysis).

[0008] This invention presents a method for preparing inert steel slag aggregate, constructing a synergistic process chain of "crushing-strong magnetic separation-bar milling and peeling-weak magnetic separation." After separating magnetic steel slag aggregate through strong magnetic separation, this process innovatively introduces a controllable bar milling and peeling step. This aims to precisely remove the silicate mineral phases adhering to the aggregate surface, optimize particle morphology, and create conditions for the efficient enrichment of the RO phase through subsequent weak magnetic separation. This process strictly controls the grinding intensity and time, achieving surface cleaning and edge improvement while effectively avoiding the damage to the inherent rough and porous structure of the steel slag caused by excessive grinding. This integrated process replaces traditional long-term aging or external stabilizer methods, simultaneously solving the volume stability problem of steel slag, achieving the enrichment of active mineral phases, and optimizing the road performance of the aggregate in a short time. It has significant advantages such as high processing efficiency, controllable effects, and high resource utilization.

[0009] In one embodiment, the hot-quenched steel slag is obtained by hot-quenching molten steel slag through a closed water spray system, and the generated steam is used to digest free calcium oxide and magnesium oxide.

[0010] The unique feature of the inert steel slag aggregate preparation method employed in this invention lies in the construction of a synergistic process chain of "crushing-strong magnetic separation-bar milling and peeling-weak magnetic separation". After separating the magnetic steel slag aggregate through strong magnetic separation, this process innovatively introduces a controllable bar milling and peeling step. In specific implementation, the mill speed is set at 71 r / min, each batch processes approximately 3 kg of material, and approximately 10 kg of forged steel is used as the peeling medium, with a medium-to-material mass ratio of approximately 3.33:1. The peeling time is strictly controlled to approximately 5 minutes. This step aims to precisely peel off the silicate mineral phases adhering to the aggregate surface, optimize particle morphology, and create conditions for the subsequent efficient enrichment of the RO phase through weak magnetic separation.

[0011] This set of parameters constitutes a high-energy-input, short-duration abrasive system. Its purpose is to achieve selective surface treatment through precisely controlled impact and abrasion: effectively stripping silicate mineral phases from the aggregate surface and optimizing particle morphology and angularity, while strictly preventing damage to the inherent rough and porous structure of steel slag, excessive generation of harmful fine powder, and wear of particle edges due to overtreatment. This creates conditions for subsequent weak magnetic separation and enrichment of the RO phase, ultimately ensuring the core mechanical and interfacial properties of the resulting inert steel slag aggregate as an asphalt mixture aggregate. This integrated process replaces traditional long-term aging or external stabilizer methods, simultaneously solving the volume stability problem of steel slag, enriching the active mineral phase, and optimizing the road performance of the aggregate in a short time. It has significant advantages such as high processing efficiency, controllable effects, and high resource utilization.

[0012] In one embodiment, the inert steel slag aggregate is screened and graded to include at least one of the following particle size ranges: 0–2.36 mm, 2.36–4.75 mm, 4.75–9.5 mm, 9.5–13.2 mm, or 13.2–16 mm.

[0013] In one embodiment, the water absorption rate of the inert steel slag aggregate is ≤3.0%.

[0014] In one embodiment, the weak magnetic separation, in addition to obtaining inert steel slag aggregate, also yields a steel slag product with a low RO phase content. This product differs from the target aggregate in chemical composition and mineral composition, and mainly serves as an intermediate product of this invention or a byproduct of the RO phase enrichment process. It possesses the potential for resource utilization of bulk solid waste. Based on its specific physicochemical properties, further research can be conducted on its feasibility as roadbed filler, cement admixture, or other building material raw materials, thereby achieving a wider range of graded and high-value utilization of steel slag resources. In the context of this invention, it is particularly suitable as roadbed filler.

[0015] In a second aspect, the present invention provides a road asphalt mixture composed of asphalt and aggregates, wherein the aggregates are composed of filler and inert steel slag aggregates obtained by the preparation method described in the first aspect, and the filler is steel slag powder obtained by grinding steel slag aggregates rich in silicate mineral phases obtained by the preparation method described in the first aspect to below 200 mesh.

[0016] Based on the total mass of road asphalt mixture, the asphalt content is 4.0%-6.0%, the aggregate content is 94.0%-96.0%, and the filler content in the aggregate is 4.0%-8.0%.

[0017] The road asphalt mixture of this invention has a closed-loop composition, consisting of asphalt, steel slag powder, and inert steel slag aggregate, without any other fillers, aggregates, or modifiers. This design achieves full-component, high-efficiency utilization of steel slag resources in the asphalt mixture, with excellent chemical and physical compatibility among the components. Asphalt, as a binder, accounts for 4.0% to 6.0% of the total mass of the mixture; steel slag powder, as a functional filler, accounts for 4.0% to 8.0% of the total mass of the aggregate, and is obtained by grinding steel slag aggregate rich in silicate mineral phases to below 200 mesh, leveraging its high specific surface area and alkaline surface to enhance interfacial bonding and water stability; inert steel slag aggregate, as a skeleton material, accounts for a high proportion and is prepared by the method described in the first aspect, possessing a rough surface, high angularity, and high RO phase content, completely replacing natural aggregates, together forming a high-performance steel slag asphalt mixture.

[0018] Compared with existing aging or external stabilizer improvement methods, this invention achieves directional separation of mineral phases and enrichment of RO phases through the coupling of "strong magnetic separation + rod milling and shaping + weak magnetic separation". It has the advantages of short processing cycle, small footprint, controllable results and high resource utilization rate, and is suitable for industrial continuous production.

[0019] This invention utilizes a synergistic process to obtain inert steel slag aggregate and steel slag powder, exhibiting significant advantages in the preparation of road asphalt mixtures. The resulting inert steel slag aggregate, with its extremely low free calcium oxide (f-CaO) content (≤0.5%), fundamentally overcomes the inherent volume stability problem of traditional steel slag, ensuring the long-term dimensional stability of the mixture. Simultaneously, the aggregate's rough, porous surface, sharp edges, and high alkalinity enable it to form strong mechanical and chemical bonds with asphalt, significantly improving interfacial adhesion. The steel slag powder, as a highly active filler, further enhances the adhesion and cohesion of the asphalt mastic. The synergistic effect of these two components gives the resulting asphalt mixture excellent mechanical strength, durability, and resistance to water damage. This technology achieves high-value utilization of all components of steel slag, with a closed-loop process and good system compatibility. It can replace natural aggregates on a large scale, offering significant environmental benefits and engineering economics, aligning with the development direction of green and low-carbon road materials. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the inert steel slag preparation process of the present invention.

[0021] Figure 2 Photos of inert steel slag with different particle sizes.

[0022] Figure 3 This is a schematic diagram of XRD analysis at different stages of the steel slag inertization process.

[0023] Figure 4 This is the gradation curve for inert steel slag aggregate.

[0024] Figure 5 This is the gradation curve for diabase aggregate.

[0025] Figure 6 This is the gradation curve for limestone aggregate.

[0026] Figure 7 The graph shows the various indicators of the Marshall test for inert steel slag-asphalt mixture.

[0027] Figure 8 The graph shows the various indicators of the Marshall test for diabase-asphalt mixture.

[0028] Figure 9 The graph shows the various indicators of the Marshall test for limestone-asphalt mixture. Detailed Implementation

[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0030] This invention discloses a process for preparing inert steel slag. Using hot-quenched steel slag as raw material, the process involves sequential pretreatment crushing, strong magnetic separation, silicate phase grinding and recovery, magnetic steel slag rod milling and shaping, and weak magnetic separation enrichment of the RO phase. This yields inert steel slag aggregate with a high RO phase content, and the byproduct steel slag powder is used as a filler in asphalt mixtures. This process, through the coupling of "two-stage magnetic separation + grinding and shaping," achieves efficient separation of the magnetic phase and silicate mineral phase and enrichment of the RO phase in the steel slag. It has advantages such as short processing cycle, small footprint, controllable results, and high resource utilization rate, making it suitable for continuous industrial production. The specific process is as follows: Figure 1 As shown, it includes: S1 Raw material selection: Hot-quenched steel slag is selected as the raw material.

[0031] Hot-quenched steel slag is produced by hot-quenching molten steel slag in a closed system with water spray. The steam generated during the process dissolves free calcium oxide and magnesium oxide, thereby significantly improving the volume stability of the steel slag. Compared with untreated steel slag, it is suitable for use as road aggregate.

[0032] S2 Pre-treatment crushing: Jaw crusher is used to perform preliminary crushing of steel slag, so that the particle size is controlled below 19 mm.

[0033] This step crushes the steel slag to a particle size of ≤19mm, which helps improve the separation efficiency of the subsequent magnetic separation process and provides a suitable feed particle size for rod mill shaping, ensuring effective stripping of silicate mineral phases and optimization of particle morphology.

[0034] S3 Strong Magnetic Separation: The crushed steel slag is subjected to strong magnetic separation with a magnetic field strength of 8000 Gauss to obtain magnetic steel slag aggregate and steel slag aggregate rich in silicate mineral phase.

[0035] This step employs a high-intensity magnetic separator. The purpose of high-intensity magnetic separation is to achieve efficient separation of magnetic steel slag aggregate from steel slag rich in silicate minerals. The principle is to utilize the difference in magnetic susceptibility between ferromagnetic minerals (such as ferromagnetic FeO) and silicate minerals in the steel slag in a strong magnetic field for separation. A magnetic field strength of 8000 Gauss is selected to ensure sufficient adsorption force on the magnetic components, thereby achieving efficient separation and providing a suitable material basis for subsequent rod milling and weak magnetic separation processes.

[0036] S4 (Optional) Silicate Phase Resource Utilization Grinding: Grind steel slag aggregate rich in silicate mineral phase to below 200 mesh to obtain steel slag micro powder, which can be used as filler in asphalt mixture.

[0037] S5 Rod Mill Shaping and Peeling: Magnetic steel slag aggregate is fed into a rod mill for grinding and shaping to remove the silicate mineral phase attached to its surface and improve the particle morphology.

[0038] Specifically, this step uses a rod mill for grinding and shaping. During rod milling, approximately 3 kg of magnetic steel slag aggregate is added per batch, and the processing time in the rod mill is controlled to be approximately 5 minutes. This process aims to achieve two key objectives: first, to effectively remove the silicate mineral phases adhering to its surface, improve particle morphology, and enhance the cleanliness and angularity of the aggregate surface; second, to precisely control the grinding time to prevent over-grinding from damaging the inherent rough and porous surface structure of the steel slag aggregate, generating excessive harmful fine powder, or causing excessive wear of particle edges, thereby ensuring its core mechanical and interfacial bonding advantages as an asphalt mixture aggregate.

[0039] S6 Weak magnetic separation enrichment of RO phase: Weak magnetic separation is used on the material after rod milling with a magnetic field strength of 4000 Gauss to separate inert steel slag aggregate with a high RO phase content (not less than 30%) and steel slag product with a low RO phase content.

[0040] This step uses a weak magnetic separator. The purpose of weak magnetic separation is to further enrich the RO phase to obtain highly inert steel slag aggregate. The separation principle is that under a set low magnetic field strength, the weaker magnetic RO phase (such as FeO) can still be effectively adsorbed, while non-magnetic minerals such as silicates are separated. By selecting a magnetic field strength of 4000 Gauss, the target RO phase can be effectively retained while separating the weaker magnetic impurity phase, thereby achieving efficient enrichment of the RO phase and improving the inertization quality of the steel slag.

[0041] S7 (Optional) Grading and Screening: Standard grading and screening of inert steel slag aggregates to obtain aggregate products with different particle size ranges to meet the gradation requirements of different asphalt mixtures.

[0042] S8 (Optional) Quality Characterization: Perform XRF and / or XRD analysis on the products of each process to determine the chemical composition and mineral phase composition for quality control.

[0043] Specifically, each batch of product must undergo X-ray fluorescence spectroscopy (XRF) analysis to ensure that the free calcium oxide (f-CaO) content is ≤0.5% and the Fe2O3 content is ≥30%; simultaneously, X-ray diffraction (XRD) analysis must be performed to confirm that the RO phase ratio is ≥30%. In addition, road performance indicators such as water absorption rate (≤3.0%), crushing value (≤20%), and Los Angeles abrasion (≤20%) must be tested according to the "Specifications for Testing Aggregates for Highway Engineering" (JTG 3432-2024), and can only be put into use after all of them pass the tests.

[0044] In a specific embodiment 1 of the present invention, the steel slag raw material selected is hot-quenched steel slag produced by Shaanxi Hancheng Longmen Steel Plant. This type of steel slag is obtained by subjecting high-temperature molten steel slag to closed-loop water spray hot quenching treatment. The principle is to use the steam generated during the treatment process to dissolve the free calcium oxide and magnesium oxide in the steel slag, thereby effectively solving the problem of the volume stability of the steel slag and finally obtaining slag material with stable performance.

[0045] In the steel slag pretreatment stage, a jaw crusher is first used to pre-crush the steel slag raw material to control its particle size to below 19 mm. Subsequently, 8000 Gauss high-intensity magnetic separation technology is used to separate the crushed steel slag, obtaining two products: one is pre-treated steel slag aggregate with magnetic properties, and the other is steel slag aggregate rich in silicate mineral phases.

[0046] For steel slag raw materials rich in silicate mineral phases, they are ground to below 200 mesh and used as filler in asphalt mixtures. For magnetic steel slag raw materials, they are fed into a rod mill for processing. The main function of this step is to shape the steel slag aggregate and remove the silicate mineral phases adhering to its surface. After grinding, a weak magnetic separation process at 4000 Gauss is used for further separation to obtain inert steel slag aggregate with a high RO phase content and steel slag with a low RO phase content, respectively.

[0047] The asphalt mixture prepared in this embodiment uses inert steel slag aggregate, with limestone aggregate and diabase aggregate used as control groups. The aggregates used in this experiment were subjected to standard sieve analysis to obtain aggregate particles in different size ranges, specifically five gradations: 0-2.36 mm, 2.36-4.75 mm, 4.75-9.5 mm, 9.5-13.2 mm, and 13.2-16 mm.

[0048] The inert steel slag aggregate prepared in this embodiment has a rough and porous surface, often exhibiting a honeycomb structure; its color is mixed, mainly dark gray and brownish-gray, often with obvious metallic luster spots; the particles have sharp edges, and the cross-section shows mineral phases and air bubbles of varying shades, presenting an overall uneven, mixed-color appearance. Figure 2 The mineral phase composition of different processes in the steel slag inert modification process was analyzed by X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD). Figure 3 The chemical composition of different steel slags is shown in Table 1.

[0049] Table 1. Comparison of chemical composition at different stages of the steel slag inerting process

[0050] The mechanical properties of inert steel slag aggregate, limestone aggregate, and diabase aggregate are shown in Table 2. The aggregate performance was tested according to the requirements of the "Specifications for Testing Aggregates in Highway Engineering" (JTG 3432-2024). All performance indicators met the specifications.

[0051] Table 2 Mechanical property tests of inert steel slag, limestone, and diabase Testing items Inert steel slag limestone diabase Technical indicators relative density of hair volume 3.20 2.86 2.84 —— Apparent relative density 3.45 2.94 2.21 ≥2.90 Water absorption rate (%) 2.26 0.84 0.85 ≤3.0 Needle-like particle content (%) 4.75-9.5：6.939.5-13.2：2.4713.2-16：8.39 4.75-9.5：5.159.5-13.2：3.3313.2-16：6.96 4.75-9.5：10.069.5-13.2：8.613.2-16：7.7 ≤12 Crushing value (%) 14.4 22.9 18.7 ≤26 Los Angeles wear (%) 12.49 20.28 12.78 ≤26 Inert steel slag aggregate, limestone aggregate, and diabase aggregate were selected as the research objects, and three types of tests were completed: appearance characteristics, chemical composition, and road performance. In terms of appearance, inert steel slag aggregate is dark gray / brown with a honeycomb-like porous surface; limestone aggregate is grayish-white / light yellow with a rough surface; and diabase aggregate is dark gray / dark green with a dense structure. Regarding chemical composition, the contents of key components such as CaO and Fe2O3 in the three types of aggregates were determined by XRF analysis. Inert steel slag aggregate had a CaO content of 33.8% and a Fe2O3 content of 31.6%, exhibiting significant alkalinity. Its surface alkaline components can form stable chemical bonds with the acidic functional groups in asphalt, thereby improving the adhesion between the asphalt and aggregate interface. Limestone aggregate contained 96.02% CaO and 0.12% Fe2O3, while diabase aggregate contained 9.33% CaO and 16.1% Fe2O3.

[0052] In terms of road performance, the density, water absorption rate, crushing value and other indicators were tested according to the "Specifications for Testing Aggregates in Highway Engineering" (JTG 3432-2024). The results showed that the bulk relative density of inert steel slag aggregate was 3.20, the crushing value was 14.4%, the Los Angeles abrasion was 12.49%, and the adhesion to asphalt was grade 5. All of these met the specifications and were better than limestone (crushing value 22.9%) and in some aspects better than diabase (Los Angeles abrasion 12.78%).

[0053] Furthermore, the inert steel slag aggregate of the present invention is mainly used as an aggregate component in road asphalt mixtures, and the aforementioned steel slag powder can be used as a filler to form road asphalt mixtures together with asphalt.

[0054] Based on the technical requirements for medium-density graded asphalt mixtures (AC type) in the "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40-2004), AC-16 medium-grained asphalt mixture was selected as the target gradation type, with a nominal maximum particle size of 16mm, suitable for the upper and middle layers of road surface courses. The engineering design gradation range refers to the passing rate limits for AC-16 in the specification (e.g., 35% ~ 55% passing through a 4.75 mm sieve, and 4% ~ 8% passing through a 0.075 mm sieve) to ensure the mixture has a suitable dense skeleton structure. The specific gradation design method is as follows: (1) Calculate the aggregate mix proportion The trial-and-error method (approximating the target gradation step by step based on the mass balance equation) or the graphical method (gradation curve superposition method) is adopted, with the median value of the engineering design gradation range as the target, to initially determine the mass percentage of each grade of mineral material. The specific steps include: ① Selecting key control sieve apertures (such as 2.36 mm, 4.75 mm, 0.075 mm); ② Adjusting the blending ratio through linear interpolation or curve fitting so that the synthesized gradation curve falls within the allowable deviation range of the specification (±3%-5%); ③ Verifying whether the void ratio (VMA) of the mineral material and the interlocking state of the coarse aggregate skeleton meet the requirements.

[0055] (2) Mix ratio verification and optimization The preliminary aggregate mix proportions were verified through synthetic gradation, with a focus on checking: ① the absolute deviation (≤ ±2%) of the passing rate of key sieve openings (4.75 mm, 2.36 mm, 0.075 mm) from the design target; ② the continuity of the synthetic gradation curve (avoiding humps or gaps); ③ whether the aggregate gradation parameters (such as coarse aggregate ratio CA, fine aggregate ratio FA, and filler ratio FF) meet the requirements of the AC-16 gradation theoretical model. If the verification fails, the blending ratios need to be readjusted and iteratively calculated until all technical indicators are met. The mix proportions of inert steel slag, limestone, and diabase as aggregates are shown in Tables 3, 4, and 5, respectively. Table 3. Aggregate mix proportions of inert steel slag-asphalt mixture

[0056] Table 4. Aggregate proportioning results of diabase-asphalt mixture

[0057] Table 5. Results of aggregate proportions for limestone-asphalt mixtures

[0058] The aggregate gradation design of this invention ensures that the final gradation curve falls within the specified gradation range of AC-16 type asphalt mixture and is as close as possible to the median line.

[0059] Based on the AC-16 gradation specification (JTG F40-2004), the mix design of inert steel slag / diabase / limestone-asphalt mixture was completed using the skeleton-dense design concept. The composite gradation curve is shown in [reference needed]. Figure 4 , Figure 5 and Figure 6 The estimated oilstone quantities are shown in Table 6 below: Table 6 Estimated Asphalt-Aggregate Ratio for Inert Steel Slag / Diabase / Limestone-Asphalt Mixture

[0060] Based on the above theory, the preparation process of the asphalt mixture of the present invention is as follows: (1) Aggregate pretreatment (taking inert steel slag as an example) According to the preset mass ratio, 0-16 mm inert steel slag aggregate (divided into five grades: 0-2.36 mm, 2.36-4.75 mm, 4.75-9.5 mm, 9.5-13.2 mm, and 13.2-16 mm) and steel slag powder (specific surface area ≥500 m² / kg) were weighed and placed in a forced convection oven and heated to 160-170 ℃ and kept at a constant temperature for 4 h to eliminate water adsorbed on the aggregate surface and improve the asphalt coating effect.

[0061] (2) Preheating of SBS modified asphalt Transfer the finished SBS modified asphalt to a constant temperature heating container and heat it to 170-180 ℃ at a rate of 2 ℃ / min, ensuring that it is within the optimal mixing viscosity range (0.28 ± 0.03 Pa·s).

[0062] (3) Hot mixing of aggregates and asphalt The preheated steel slag aggregate of grade 5 was put into the laboratory asphalt mixing pot (capacity 15 L) according to the design ratio in Table 3. The dry mixing mode (speed 50 r / min) was started and premixed for 10 s. Then, the SBS modified asphalt with the target asphalt-aggregate ratio was injected, and the wet mixing mode (speed 75 r / min) was switched and continuously stirred for 90 s to ensure that the asphalt uniformly coated the surface of the aggregate.

[0063] (4) Filler mixing and final mixing Add the predetermined mass of steel slag powder (accounting for 5% of the total mass of the aggregate) to the mixing pot, and continue to mix in wet mixing mode for 90 seconds to ensure that the filler is fully dispersed in the asphalt mortar. The total wet mixing time should be strictly controlled within 180 seconds to avoid asphalt aging or temperature segregation. (5) Molding and demolding The well-mixed material was quickly transferred to a Marshall mold (Φ101.6 mm×63.5 mm) preheated to 145 ℃, and compacted on both sides 75 times each using an automatic compactor. After molding, the specimen was placed at room temperature (25 ± 2 ℃) to cool for 12 h, and finally demolded non-destructively using a hydraulic demolding machine (demolding rate 5 mm / min) to obtain a standard cylindrical specimen.

[0064] To determine the optimal asphalt-aggregate ratio, this invention employs the wax-sealing method to measure the bulk density of Marshall specimens, simultaneously measuring specimen stability and flow value, and calculating parameters such as porosity, aggregate void ratio, and asphalt saturation. A systematic analysis of the above test data is then conducted, and relevant trends and patterns can be identified through… Figure 7 Presented intuitively.

[0065] To determine the effective relative density of the aggregate, this invention uses a vacuum method to measure the maximum relative density of unmodified asphalt mixtures mixed with an estimated optimal asphalt-aggregate ratio, and takes the average value. Then, the effective relative density of the synthesized aggregate is calculated using the following formula:

[0066] In the formula: The effective relative density of the synthetic mineral; The percentage of asphalt used in the experiment (in the total mixture) is %. The maximum relative density measured under the experimental asphalt dosage conditions is dimensionless. The relative density of asphalt (25 ℃ / 25 ℃) is dimensionless.

[0067] For modified asphalt and SMA and other difficult-to-disperse mixtures, the effective relative density should be directly calculated from the synthetic bulk relative density and synthetic apparent relative density of the aggregates using the following formula: ,

[0068] The asphalt absorption coefficient C is determined by the material's water absorption rate using the formula... Seeking, .

[0069] The synthetic water absorption rate of the material is calculated using the following formula: .

[0070] In the formula: ρ is the effective relative density of the synthetic mineral aggregate; C is the bitumen absorption coefficient of the synthetic mineral aggregate; The water absorption rate of the synthetic mineral is %; The bulk relative density of the mineral is dimensionless. ρ is the synthetic apparent relative density of the mineral, dimensionless.

[0071] To determine the maximum relative density of the mixture, the maximum theoretical relative density of the mixture with different asphalt content should be calculated using the following formula for modified asphalt or SMA mixtures:

[0072] The maximum theoretical relative density of the asphalt mixture is given relative to the calculated asphalt content Pb, and is dimensionless. The calculated asphalt-aggregate ratio in the asphalt mixture is %; ρ is the relative density of asphalt (25℃ / 25℃), dimensionless.

[0073] The test was conducted according to the Asphalt Mixture Density Test (Weight Method in Water) in the Highway Engineering Asphalt and Asphalt Mixture Test Procedure, measuring the porosity, aggregate void ratio, and effective asphalt saturation of the specimens as shown in the following formulas: , ,

[0074] In the formula: VV is the void ratio (%) of the asphalt mixture specimen; VMA is the aggregate void ratio (%) of the asphalt mixture specimen; VFA is the effective asphalt saturation ratio (%) of the asphalt mixture specimen. It is the sum of the percentages of various mineral aggregates in the total mass of the asphalt mixture (%).

[0075] Based on the above process, the data obtained by the present invention are shown in Tables 7, 8, 9, 10, 11 and 12.

[0076] Table 7. Marshall test bulk density of inert steel slag-asphalt mixture oilstone ratio 4.3% 4.8% 5.3% 5.8% 6.3% Hair volume density 2.80 2.81 2.85 2.84 2.85 Table 8 Marshall Stability of Inert Steel Slag-Asphalt Mixture oilstone ratio 4.3% 4.8% 5.3% 5.8% 6.3% Stability 14.99 16.73 17.83 15.32 15.23 Table 9 Marshall test flow values ​​of inert steel slag-asphalt mixture oilstone ratio 4.3% 4.8% 5.3% 5.8% 6.3% Stream value 3.34 3.57 3.61 4.09 4.8 Table 10 Marshall test porosity of inert steel slag-asphalt mixture oilstone ratio 4.3% 4.8% 5.3% 5.8% 6.3% Porosity / % 7.6 6.3 4.0 3.7 2.3 Table 11 Marshall Test Aggregate Intermittency Rate for Inert Steel Slag-Asphalt Mixture oilstone ratio 4.3% 4.8% 5.3% 5.8% 6.3% Mineral aggregate porosity / % 16.18 16.20 15.50 16.10 16.30 Table 12 Marshall test asphalt saturation of inert steel slag-asphalt mixture oilstone ratio 4.3% 4.8% 5.3% 5.8% 6.3% Saturation / % 53.0 61.0 74.2 77.0 85.8 To calculate the optimal asphalt-aggregate ratio, in the experiments of this invention, the asphalt-aggregate ratio or asphalt content is used as the abscissa, and the various indicators of the Marshall test are used as the ordinate. The test results are plotted on a graph and connected to form a smooth curve. The asphalt content range OACmin ~ OACmax that meets the technical standards for asphalt mixtures specified in this specification is determined. The selected asphalt content range must cover the entire range of the design void ratio and, as far as possible, the required range of asphalt saturation, and ensure that the density and stability curves show peaks. If the entire range of the design void ratio is not covered, the test must be repeated with an expanded asphalt content range.

[0077] (1) The calculation of the asphalt-aggregate ratio of inert steel slag-asphalt mixture is shown in Table 13 and Table 14.

[0078] Table 13 Four indicators for determining OAC1 in inert steel slag-asphalt mixtures: a1, a2, a3, and a4 a1 a2 a3 a4 oilstone ratio 5.39% 5.22% 5.49% 5.15% Where a1 is the bulk density of the hair (g / cm³) 3 a1 is the asphalt-aggregate ratio at the maximum value; a2 is the asphalt-aggregate ratio at the maximum value of stability (kN); a3 is the median value of the asphalt-aggregate ratio within the target porosity (%) range; a4 is the median value of the asphalt-aggregate ratio within the asphalt saturation (%) range.

[0079] Table 14 Marshall Test Parameters for AC-16 Densely Mixed Asphalt Mixture Stability (kN) Porosity (%) Asphalt saturation (%) Flow value (mm) Gap ratio (%) Indicator Requirements >8 3～6 65～75 2～4 >13.5 oilstone ratio 4.3～6.3% 4.87%～6.1% 4.94%～5.36% 4.3%～5.74% 4.3%～6.3%

[0080]

[0081]

[0082] (2) The calculation of the asphalt-aggregate ratio of diabase-asphalt mixture is shown in Tables 15, 16, 17, 18, 19, 20 and 21.

[0083] Table 15 Marshall Test Bulk Density of Diabase-Asphalt Mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Hair volume density 2.46 2.57 2. 65 2.64 2.64 Table 16 Marshall test porosity of diabase-asphalt mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% porosity % 12.46 7.55 3.99 3.65 2.94 Table 17. Marshall Test Aggregate Void Ratio of Diabase-Asphalt Mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Gap ratio % 19.82 16.63 14.44 15.17 15.57 Table 18 Marshall test asphalt saturation of diabase-asphalt mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% saturation% 37.1 54.6 72.4 75.9 81.1 Table 19 Marshall Stability of Diabase-Asphalt Mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Stability 14.73 15.51 15.46 15.34 16.48 Table 20 Marshall test flow values ​​of diabase-asphalt mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Stream value 2.05 2.63 3.29 3.81 4.39 Table 21 Four indicators for determining OAC1 in diabase-asphalt mixtures: a1, a2, a3, and a4 a1 a2 a3 a4 oilstone ratio 5.11% 4.70% 5.32% 5.02%

[0084]

[0085]

[0086] (3) The calculation results of the asphalt-aggregate ratio of limestone-asphalt mixture are shown in Tables 22, 23, 24, 25, 26, 27 and 28.

[0087] Table 22 Marshall Test Bulk Density of Limestone-Asphalt Mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Hair volume density 2.32 2.34 2. 39 2.38 2.38 Table 23 Marshall test porosity of limestone-asphalt mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% porosity % 7.94 6.40 4.02 3.64 2.86 Table 24 Marshall test gap ratio of limestone-asphalt mixture oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Gap ratio % 15.02 14.69 13.58 14.06 14.47 Table 25 Marshall test asphalt saturation of limestone-asphalt mixtures oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% saturation% 47.1 56.4 70.4 74.1 80.2 Table 26 Marshall Stability of Limestone-Asphalt Mixtures oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Stability 13.6 14.23 14.10 11.07 11.86 Table 27 Marshall test flow values ​​of limestone-asphalt mixtures oilstone ratio 4.0% 4.5% 5.0% 5.5% 6.0% Stream value 2.05 2.63 3.29 3.81 4.39 Table 28 Four indicators for determining OAC1 in diabase-asphalt mixtures: a1, a2, a3, and a4 a1 a2 a3 a4 oilstone ratio 5.11% 4.70% 5.32% 5.02%

[0088]

[0089]

[0090] Based on the above experiment: The inert steel slag-asphalt mixture of this invention: OAC1 = 5.3125% was calculated using a1 (peak bulk density asphalt-aggregate ratio 5.39%), a2 (peak stability asphalt-aggregate ratio 5.22%), a3 (median target void ratio asphalt-aggregate ratio 5.49%), and a4 (median asphalt saturation asphalt-aggregate ratio 5.15%). Combined with OACmin = 4.94% and OACmax = 5.36%, OAC2 = 5.15%, and finally, OAC = 5.23%; that is, Furthermore, the mass percentage of asphalt in the mixture of the present invention can be obtained as follows: .

[0091] Diabase-asphalt mixture: OAC1=5.038%, OAC2=5.015%, final OAC=5.03%.

[0092] Limestone-asphalt mixture: OAC1=4.94%, OAC2=5.0%, final OAC=4.97%.

[0093] The beneficial effects of this invention are specifically manifested in the following ways: (1) The steel slag inert modification process effectively solves the problem of volume stability and the modified aggregate has excellent performance.

[0094] Through a "crushing-magnetic separation-bar milling and shaping" process, the free calcium oxide (f-CaO) content of steel slag is effectively reduced. Furthermore, the mechanical properties of inert steel slag aggregate are superior to those of natural aggregate: the crushing value of inert steel slag is 14.4% (limestone 22.9%, diabase 18.7%), and the Los Angeles abrasion is 12.49% (limestone 20.28%), demonstrating outstanding resistance to crushing and abrasion; its bulk relative density is 3.20, higher than that of limestone (2.86) and diabase (2.84), indicating stronger skeletal support.

[0095] (2) The properties of the asphalt and filler are matched to meet the design requirements of the mixture. The IC type SBS modified asphalt used in the test has a ductility of 611.1 mm (≥300 mm) at 10℃ and a softening point of 61.9℃ (≥60℃), exhibiting excellent low-temperature crack resistance and high-temperature stability; the 70# base asphalt has a ductility of 214.9 mm (≥200 mm) at 10℃ and a softening point of 48.75℃ (≥40℃), making it suitable for different pavement requirements.

[0096] Steel slag powder, prepared by grinding steel slag with a high silicate mineral content, has a specific surface area of ​​574.75 m² / kg, which is much higher than that of ordinary mineral powder. It can fully adsorb the lightweight components of asphalt. Its CaO content is 42.45%, which can react with the acidic components of asphalt to form chemical bonds, while filling the gaps between aggregates and improving the density of asphalt mixtures.

[0097] (3) The inert steel slag-asphalt mixture has a reasonable gradation and good compatibility with the optimal asphalt-aggregate ratio. The synthetic gradations of the three types of mixtures all meet the AC-16 gradation range in JTG F40-2004. The passing rate of key sieves (4.75mm, 2.36mm, 0.075mm) deviates from the median by ≤±2%, with no gaps. They can form a stable structure of "coarse aggregate interlocking skeleton + fine aggregate and asphalt mortar filling".

[0098] The optimal asphalt-aggregate ratio exhibits excellent compatibility: the optimal asphalt-aggregate ratio for inert steel slag-asphalt mixtures is 5.23%, higher than that for diabase (5.03%) and limestone (4.97%). This is because its honeycomb-like porous structure requires more asphalt coating. At this asphalt-aggregate ratio, the specimens exhibit a porosity of 4.0% (meeting the 3-6% specification requirement), stability of 17.83 kN (diabase 15.51 kN, limestone 14.23 kN), and flow value asphalt saturation of 74.2% (65-75% optimal range), achieving the best balance between mechanical properties and density.

[0099] (4) The physicochemical properties of inert steel slag improve the interface and overall performance of the mixture. Enhanced physical properties improve mechanical interlocking: Inert steel slag has a rough surface and sharp edges, resulting in a larger contact area with asphalt compared to natural stone, leading to stronger mechanical interlocking. Furthermore, compared to traditional natural aggregates, inert steel slag has more pores, allowing for a tighter bond with asphalt.

[0100] Chemical properties enhance interfacial adhesion: Inert steel slag is strongly alkaline (CaO content 33.8%), and the calcium ions on its surface can form chemical bonds with acidic components of asphalt (such as carboxylic acids), which increases the adhesion of asphalt mixtures by about 20% compared to natural stone. In addition, the alkaline environment can slow down the volatilization of lightweight molecules during the aging process of asphalt, maintain the flexibility and ductility of the mixture, and delay the brittle cracking of the pavement.

[0101] (5) The use of inert steel slag as a substitute for natural aggregates is feasible and meets the requirements of green development. The Marshall test results of inert steel slag-asphalt mixtures are comprehensively superior to those of limestone mixtures, and in some aspects superior to those of diabase mixtures: stability 17.83 kN (limestone 14.23 kN), aggregate void ratio 15.50% (>13.5% of the specification requirement), and porosity 4.0% (within a reasonable range), proving that it can replace natural aggregates such as basalt and limestone for asphalt pavements.

Claims

1. A method for the preparation of inert steel slag aggregates, characterized by, Comprising the following steps: Step 1, using hot leached steel slag as raw material, crushing it and then performing strong magnetic separation at a magnetic field strength of not less than 8000 Gauss to obtain magnetic steel slag aggregate and steel slag aggregate rich in silicate mineral phase; Step 2, rod milling and stripping shaping of the magnetic steel slag aggregate to strip the silicate mineral phase attached to its surface and improve the particle morphology of the steel slag aggregate; Step 3, weak magnetic separation of the rod-milled material at a magnetic field strength of not more than 4000 Gauss to obtain inert steel slag aggregate with RO phase content of not less than 30%.

2. The method for preparing the inert steel slag aggregate according to claim 1, characterized in that, The rod milling and stripping shaping is set at a mill speed of 71 r / min, each batch of material is about 3 kg, about 10 kg of steel forging is used as stripping medium, the mass ratio of medium to material is about 3.33:1, and the stripping time is strictly controlled at about 5 minutes.

3. The method for preparing the inert steel slag aggregate according to claim 1, characterized in that, The inert steel slag aggregate is classified by screening, and at least one of the following particle size intervals is included: 0-2.36 mm, 2.36-4.75 mm, 4.75-9.5 mm, 9.5-13.2 mm, 13.2-16 mm.

4. The method of claim 1, wherein the inert steel slag aggregate is prepared by the steps of: The water absorption of the inert steel slag aggregate is ≤3.0%. ​ 5. The method for preparing inert steel slag aggregate according to claim 1, characterized in that, In addition to obtaining the inert steel slag aggregate, the weak magnetic separation also obtains a steel slag product with less RO phase content, which is used as a roadbed filler.

6. A road asphalt mixture, characterized in that Composed of asphalt and mineral aggregate; the mineral aggregate is composed of filler and inert steel slag aggregate obtained by the preparation method of claim 1; the filler is steel slag micropowder obtained by grinding the steel slag aggregate rich in silicate mineral phase obtained by the preparation method of claim 1 to 200 mesh or less; The asphalt content is 4.0%-6.0% and the mineral aggregate content is 94.0%-96.0% based on the total mass of the road asphalt mixture, and the mass content of the filler in the mineral aggregate is 4.0%-8.0%.

7. The road asphalt mixture according to claim 6, characterized in that, The asphalt content is 4.97% and the mineral aggregate content is 95.03% based on the total mass of the mixture; the inert steel slag aggregate content is 90% and the filler content is 5% based on the total mass of the mineral aggregate; the inert steel slag aggregate accounts for the following mass percentage of the total mass of the mineral aggregate: 13.2-16 mm particle size accounts for 11%, 9.5-13.2 mm particle size accounts for 14%, 4.75-9.5 mm particle size accounts for 22%, 2.36-4.75 mm particle size accounts for 23%, and 0-2.36 mm particle size accounts for 25%, and the mineral aggregate synthetic gradation meets the AC-16 median gradation range.

8. A method of producing the road asphalt mixture according to claim 6, characterized in that, Comprising the following steps: Step (1), according to the gradation, different particle sizes of inert steel slag aggregate are weighed, and the steel slag micropowder is placed in a forced convection oven and heated to 160-170 ℃ and kept constant for 4 h±0.5 h; Step (2), the finished SBS modified asphalt is transferred to a constant temperature heating container, and the temperature is raised to 170-180 ℃ at a rate of 2 ℃ / min; Step (3), the preheated inert steel slag aggregate is dry mixed and then injected into the SBS modified asphalt for wet mixing to ensure that the asphalt uniformly covers the surface of the aggregate; Step (4), add the preheated steel slag micropowder and continue wet mixing to make the filler fully dispersed in the asphalt paste; Step (5), using the material obtained in step (4) to form and demould.

9. The method of claim 8, wherein the road asphalt mixture is prepared by, In the step (1), the inert steel slag aggregate is graded into five grades of 0-2.36 mm, 2.36-4.75 mm, 4.75-9.5 mm, 9.5-13.2 mm and 13.2-16 mm.

10. The method for preparing road asphalt mixture according to claim 8, characterized in that, In the step (3) and step (4), the wet mixing time is 90s±5s respectively, and the total wet mixing time is strictly controlled within 180s.

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