Anti-expansion cracking steel slag asphalt concrete and preparation method thereof

Abstract

The application discloses anti-expansion and anti-cracking steel slag asphalt concrete and a preparation method thereof. The aggregate of the anti-expansion and anti-cracking steel slag asphalt concrete comprises steel slag with a content of particles of 0.075 mm or less on the surface of 1.0%, an angularity index of 35 s or more, and porosity of 4.5%-6.5%. Compared with traditional steel slag asphalt concrete, the anti-expansion and anti-cracking steel slag asphalt concrete has an oil film residual area ratio of 90% or more and an immersion expansion rate of 1.5% or less, has good anti-expansion and anti-cracking performance caused by surface expansion and cracking of oil film drop, solves the technical problem that the traditional steel slag asphalt concrete is prone to surface expansion and cracking caused by oil film drop, meanwhile, the excellent performance of the steel slag as a road material is retained, and a win-win result of resource utilization of industrial solid waste and improvement of road performance is achieved.

Description

Technical Field

[0001] This invention belongs to the field of asphalt concrete and its preparation technology, and more specifically, relates to an anti-expansion cracking steel slag asphalt concrete and its preparation method. Background Technology

[0002] Research on steel slag as an aggregate for asphalt concrete has progressed from "feasibility verification" to "performance optimization" and then to "high-value utilization." Existing research generally agrees that the volume stability of steel slag remains the core bottleneck restricting its large-scale application. Focusing on controlling f-CaO content (≤2%) and expansion rate (≤1.8%), a series of steel slag treatment technologies have been developed, including natural aging, heat treatment, and acid treatment, to reduce the f-CaO content in steel slag. This reduces the likelihood of internal microcracks caused by volume expansion due to the hydration reaction of f-CaO in the steel slag within the asphalt concrete.

[0003] However, in practical engineering applications and long-term service, it has been found that steel slag aggregate asphalt concrete prepared using these technologies as aggregate exhibits expansion cracking on the surface of its subgrade or base course. This manifests as large-scale longitudinal cracks or wavy deformation, primarily due to early and uneven detachment of the asphalt binder (oil film) from the steel slag aggregate surface. After the oil film detaches, the pavement structure deteriorates rapidly under the combined effects of vehicle loads and moisture. Specific defects include localized bulging deformation—"bumps"—and aggregate spalling, forming potholes. Therefore, even reducing the f-CaO content in the steel slag to meet standard requirements cannot completely solve the problem of oil film detachment in steel slag aggregate asphalt concrete pavements, leading to bulges and potholes.

[0004] Furthermore, steel slag has a complex chemical composition, with main components including CaO, SiO2, Fe2O3, Al2O3, and MgO. Its mineral phases include dicalcium silicate (C2S), tricalcium silicate (C3S), RO phase, and free calcium oxide (f-CaO). The composition of steel slag varies significantly depending on its source, and there are no unified standards for the morphology, angularity, and porosity control technologies of steel slag aggregates, making it difficult to directly apply existing technologies. Therefore, developing an asphalt concrete and its preparation method that can effectively prevent the asphalt film from peeling off steel slag aggregates, thereby avoiding bulges and potholes in road surfaces, is a pressing application challenge in this field. Summary of the Invention

[0005] To address the aforementioned technical deficiencies or improvement needs, this invention provides an anti-expansion cracking steel slag asphalt concrete and its preparation method. The aim is to improve the oil film detachment resistance of steel slag aggregate asphalt concrete pavement by controlling the morphology and physical parameters of the steel slag. It has been found that steel slag with a surface coating of particles smaller than 0.075mm (<1%), an angularity index ≥35s, and a porosity of 4.5%-6.5% exhibits strong adhesion to asphalt. Asphalt concrete prepared using steel slag as aggregate exhibits an oil film residual area ratio ≥90%, significantly improving the oil film detachment resistance of asphalt concrete pavement. Preferably, the addition of an appropriate amount of polyester fiber further reinforces and toughens the concrete, enhancing its resistance to temperature cracking and load deformation. This solves the technical problem of oil film detachment easily occurring in existing asphalt concrete pavements prepared using steel slag as aggregate.

[0006] To achieve the above objectives, according to a first aspect of the present invention, an anti-expansion cracking steel slag asphalt concrete is provided, which is used to resist surface expansion cracking caused by the shedding of oil film on asphalt concrete pavement. The anti-expansion cracking steel slag asphalt concrete has an oil film residual area ratio of ≥90%, and its aggregate includes steel slag with a surface coating of particles smaller than 0.075mm and a content of <1%, an angularity index of ≥35s, and a porosity of 4.5%-6.5%.

[0007] Preferably, in the anti-expansion cracking steel slag asphalt concrete, the content of particles smaller than 0.075mm coated on the surface of the steel slag is ≤0.8%, and the angularity index is ≥35s.

[0008] Preferably, the steel slag in the anti-expansion cracking steel slag asphalt concrete is prepared by the following method: After crushing, shaping, and screening, the unaged steel slag raw material is washed for 30-45 seconds under the condition of water flow velocity of 0.5-2.5m / s, with the mass-to-volume ratio of unaged steel slag to water being 1:8-15, to obtain steel slag aggregate.

[0009] According to a second aspect of the present invention, a method for preparing anti-expansion cracking steel slag asphalt concrete as described in the present invention is also provided, comprising the following steps: Steel slag with a surface coating of particles smaller than 0.075 mm (<1.0%), an angularity index ≥35s, and a porosity of 4.5%-6.5% was used as aggregate. By mass ratio, the mix consists of 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, 0.25%~0.3% polyester fiber, and 5.5%-5.6% modified asphalt. Before preparation, heat the steel slag aggregate to 180℃~200℃ and the asphalt to 155℃~160℃. During mixing, first mix the steel slag aggregate and polyester fiber in a mixing tank at 170℃~180℃ for 8s-10s (dry mixing), then add the asphalt, mineral powder and steel slag aggregate and mix for 40s-50s (wet mixing). The asphalt mixture should have the asphalt mortar evenly coating the surface of the aggregate, and the mixture should have a bright and uniform color, no white spots, good cohesion and a certain degree of fluidity.

[0010] Preferably, in the preparation method, the steel slag raw material is unaged steel slag, which is pretreated as follows: After being crushed, shaped, and screened, the steel slag raw material is washed for 40-45 seconds under the condition of a water flow velocity of 0.5-2.5 m / s, with the mass-to-volume ratio of unaged steel slag to washing liquid being 1:8-15. The steel slag aggregate is screened into 10-15mm steel slag aggregate, 5-10mm steel slag aggregate and 3-5mm steel slag aggregate.

[0011] Preferably, in the preparation method, the steel slag raw material is pretreated according to its particle size as follows: The unaged steel slag raw material is 3-5mm in size, and the steel slag is washed at a flow rate of 0.5-1.0m / s for 40-45s. The unaged steel slag raw material is 5-10mm in size, and is flushed with the steel slag at a flow rate of 1.5-2.0m / s for 40-45s. The unaged steel slag raw material is 10-15mm in size, and is flushed with the steel slag at a flow rate of 2.0-2.5m / s for 40-45s.

[0012] Preferably, in the preparation method, the pH value of the washing solution is 4-5.

[0013] Preferably, in the preparation method, the washing solution is adjusted to a pH of 4-5 using a weakly acidic chemical agent, wherein the weakly acidic chemical agent does not include any one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0014] Preferably, in the preparation method, the weakly acidic chemical agent includes one or more combinations of oxalic acid, acetic acid, and carbonic acid.

[0015] Preferably, in the preparation method, the weakly acidic chemical agent is a combination of oxalic acid and acetic acid.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: The steel slag asphalt concrete provided by this invention comprises steel slag with a surface coating of particles smaller than 0.075mm (<1%), an angularity index of ≥35s, and a porosity of 4.5%-6.5%. The asphalt concrete prepared has an oil film residual area ratio of ≥90% and an expansion rate of ≤1.5%, exhibiting good resistance to oil film peeling and meeting the requirements of some highway paving projects with high performance requirements. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] To enhance the adhesion between steel slag aggregate and asphalt film, we attempted to study the optimization of the physical morphology of the steel slag surface. The results showed that the angularity and porosity of the steel slag do not have a simple positive correlation with adhesion. Appropriate angularity can enhance mechanical anchoring, and moderate surface opening can create a "glue nail" effect. However, excessive porosity (especially closed pores) and oil absorption rate can lead to insufficient effective oil film thickness, thus reducing long-term adhesion durability. Therefore, the key to the steel slag pretreatment in this invention lies in controlling the pore structure (retaining beneficial anchoring pores and sealing harmful pores) and optimizing the angular morphology, rather than simply pursuing high angularity or high porosity.

[0019] Experimental results show that steel slag with a surface coating of less than 1% particles smaller than 0.075mm, an angularity index ≥35s, and a porosity of 4.5%-6.5% as aggregate can significantly enhance its long-term adhesion performance with asphalt. In particular, steel slag with a surface coating of less than 0.8% particles smaller than 0.075mm, an angularity index ≥35s, and a porosity of 4.5%-6.5% as aggregate can produce asphalt concrete with good anti-oil film peeling effect. In practical applications, it can avoid local bulging deformation ("bulge"), aggregate peeling, and pothole formation ("potholes") in steel slag aggregate asphalt concrete pavement, thus solving the problem of base surface expansion and cracking caused by oil film peeling in actual engineering applications and long-term service of steel slag aggregate asphalt concrete.

[0020] This invention provides an anti-expansion cracking steel slag asphalt concrete, which is used to resist surface expansion cracking caused by the shedding of oil film on asphalt concrete pavement. The anti-expansion cracking steel slag asphalt concrete has an oil film residual area ratio of ≥90%, and its aggregate includes steel slag with a surface coating of particles smaller than 0.075mm and a content of <1%, an angularity index of ≥35s, and a porosity of 4.5%-6.5%.

[0021] In some embodiments, asphalt concrete is prepared by partially or completely replacing natural aggregates with steel slag; the oil film residual area ratio of the expansion-cracking resistant steel slag asphalt concrete is ≥90%.

[0022] Steel slag with a surface coating of particles smaller than 0.075 mm of ≤0.8%, an angularity index of ≥35s, and a porosity of 4.5%-6.5% is preferred as aggregate. Steel slag aggregate can partially or completely replace natural aggregate in the preparation of asphalt concrete; in particular, steel slag aggregate can completely replace natural aggregate in the preparation of asphalt concrete.

[0023] In some embodiments, the steel slag aggregate is prepared by the following method: (1) After crushing and shaping the steel slag raw material, the steel slag sand with a particle size ≤ 2.36 mm is removed by screening to obtain the screened steel slag (2.36 mm < particle size ≤ 16 mm). (2) The steel slag after shaping and screening is washed and dust removed and calcium is fixed by liquid flushing. The steel slag raw material is 3-5mm, and the steel slag is flushed at a flow rate of 0.5-1.0m / s for 40-45s. The steel slag raw material is 5-10mm, and the steel slag is flushed at a flow rate of 1.5-2.0m / s for 40-45s; The steel slag raw material is 10-15mm, and the steel slag is flushed at a flow rate of 2.0-2.5m / s for 40-45s.

[0024] Preferably, the steel slag aggregate is prepared according to the following method: (1) After crushing and shaping the steel slag raw material, the steel slag sand with a particle size ≤ 2.36 mm is removed by screening to obtain the screened steel slag (2.36 mm < particle size ≤ 16 mm). (2) A weak acidic chemical agent is dissolved in water to prepare an acidic washing solution; the weak acidic chemical agent includes one or more of oxalic acid, acetic acid and carbonic acid, but does not contain any one or more of hydrochloric acid, phosphoric acid, nitric acid and sulfuric acid.

[0025] (3) The steel slag after screening is washed with water to remove dust and solidify calcium by liquid flushing. The steel slag raw material is 3-5mm, and the washing liquid with pH value range of 4-5 is used to flush the steel slag for 45s. The steel slag raw material is 5-10mm, and a water washing solution with a pH value range of 4-5 is used to rinse the steel slag for 45 seconds. The steel slag raw material is 10-15mm thick. A water washing solution with a pH value range of 4-5 is used to wash the steel slag for 45 seconds.

[0026] A method for preparing steel slag asphalt concrete resistant to expansion and cracking includes the following steps: Steel slag with a surface coating of particles smaller than 0.075 mm and a content of <1%, an angularity index of ≥35s, and a porosity of 4.5%-6.5% was used as aggregate. By mass ratio, the aggregate is prepared as follows: 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, and 5.4%-5.5% asphalt. The mixture is dry-mixed for 30-40 seconds, then wet-mixed for 30-50 seconds to ensure that the asphalt evenly coats the aggregate before paving and compaction.

[0027] The preferred mix composition, by mass ratio, is 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, 0.25%~0.3% polyester fiber, and 5.5%-5.6% modified asphalt. Before preparation, heat the steel slag aggregate to 180℃~200℃ and the asphalt to 155℃~160℃. During mixing, first mix the steel slag aggregate and polyester fiber in a mixing tank at 170℃~180℃ for 8s-10s (dry mixing), then add the asphalt, mineral powder and steel slag aggregate and mix for 40s-50s (wet mixing). The asphalt mixture should have the asphalt mortar evenly coating the surface of the aggregate, and the mixture should have a bright and uniform color, no white spots, good cohesion and a certain degree of fluidity.

[0028] In some embodiments, steel slag asphalt concrete resistant to expansion cracking is prepared according to the following method: The steel slag raw material is unaged steel slag. After crushing, shaping and screening, it is washed for 30-45 seconds under the condition of water flow velocity of 0.5-2.5m / s, with the mass-to-volume ratio of unaged steel slag to washing liquid being 1:8-15. The sieving results are 10-15mm steel slag aggregate, 5-10mm steel slag aggregate and 3-5mm steel slag aggregate.

[0029] The raw materials are added sequentially to the mixing pot in the following proportions: 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, and 5.4%-5.5% asphalt content. The mixture is then dry-mixed for 30-40 seconds, followed by wet-mixing for 30-50 seconds to ensure uniform asphalt coating of the aggregates. The finished mixture is stored in a storage silo or loaded onto trucks, covered with tarpaulins for insulation, and transported to the site for paving and compaction as quickly as possible.

[0030] Preferably, the steel slag raw material is 3-5mm, and the steel slag is flushed at a flow rate of 0.5-1.0m / s for 40-45s; the steel slag raw material is 5-10mm, and the steel slag is flushed at a flow rate of 1.5-2.0m / s for 40-45s; the steel slag raw material is 10-15mm, and the steel slag is flushed at a flow rate of 2.0-2.5m / s for 40-45s.

[0031] In some embodiments, rinsing is performed using a washing solution with a pH of 4-5; the washing solution is adjusted to a pH of 4-5 using a weakly acidic chemical agent, which includes one or more combinations of oxalic acid, acetic acid, and carbonic acid, but excludes any one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0032] In some embodiments, the weakly acidic chemical agent used is a combination of oxalic acid and acetic acid.

[0033] The following are examples. Example 1: Preparation of steel slag aggregate asphalt concrete resistant to oil film peeling Using steel slag (with a surface coating of particles smaller than 0.075 mm of less than 1%, an angularity index of 36s, and a porosity of 4.5%-6.5%) as aggregate (free calcium oxide content of 1.2%), asphalt concrete resistant to oil film detachment was prepared according to the following method: After pretreatment of the raw materials, the following proportions are made by weight: 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, 0.25%~0.3% polyester fiber, and 5.5%-5.6% modified asphalt. Before preparation, heat the steel slag aggregate to 180℃~200℃ and the asphalt to 155℃~160℃. During mixing, first mix the steel slag aggregate and polyester fiber in a mixing tank at 170℃~180℃ for 8-10 seconds (dry mixing), then add the asphalt, mineral powder, and steel slag aggregate and mix for 40-50 seconds (wet mixing). The asphalt mixture should have a uniform coating of asphalt mortar on the aggregate surface, a bright and uniform color, no white spots, good cohesiveness, and a certain degree of fluidity. Store the finished mixture in a storage silo or load it onto a truck, cover it with tarpaulin for insulation, and transport it to the site for paving and compaction as soon as possible. Specifically, in this embodiment, after pretreatment of the raw materials, the mixture is prepared by weight ratio as follows: 45% 10-15mm steel slag aggregate, 30% 5-10mm steel slag aggregate, 5% 3-5mm steel slag aggregate, 10% 0-3mm diabase manufactured sand, 10% limestone mineral powder, 0.3% polyester fiber, and 5.5% modified asphalt. Before preparation, the steel slag aggregate is heated to 200℃ and the asphalt is heated to 155℃. During mixing, the steel slag aggregate and polyester fiber are first mixed in a mixing tank at 170℃ for 10 seconds (dry mixing), and then the asphalt, mineral powder, and steel slag aggregate are added and mixed together for 50 seconds (wet mixing). The asphalt mixture should have a uniform coating of the aggregate surface, a bright and uniform color, no white spots, good cohesiveness, and a certain degree of fluidity. The finished mixture is stored in a storage silo or loaded onto a truck, covered with tarpaulin for insulation during transportation, and transported to the site for paving and compaction as soon as possible.

[0034] The steel slag is prepared using a wet process, as detailed below: (1) Pretreatment, crushing and shaping of steel slag raw materials Impurities in the aggregated steel slag are removed by a sluice screen. The steel slag is unaged and its chemical index (f-CaO) and physical index (expansion rate) are unstable, with a free calcium oxide content of 5.2%. A magnetic separator is installed on the belt conveyor below the sluice screen to remove iron from the aggregated steel slag. Subsequently, a vertical shaft impact crusher is used to crush the large pieces of steel slag to a particle size suitable for subsequent processing (D). max<30mm), after crushing, the steel slag particles are shaped by an impact crusher. The shaping machine uses the high-speed impact principle of "stone against stone" and is combined with closed-circuit screening to "grind" irregular steel slag particles into cubes. During this process, residual metal is strictly removed, and the final product is high-quality aggregate that meets the requirements of high-grade asphalt pavement. After shaping, the content of needle-like and flaky particles in the material is reduced to less than 5%, and the angularity index of the material is 32s. After crushing and shaping, steel slag sand with a particle size ≤2.36mm is removed by screening. The content of particles with a particle size ≤0.075mm on the surface of the steel slag material after primary screening is 3.5%, and the free calcium oxide content is 5.2%.

[0035] (2) Water washing for dust removal and calcium fixation The shaped steel slag is washed and dust removed and calcium is fixed by liquid flushing. The aggregate particles are washed under the vibration of a negative angle linear vibrating screen, and the steel slag is impacted by a jet of water pressure of 0.15~0.4MPa. The steel slag aggregate particle size is 9.5~16mm, and the steel slag is flushed with water pressure of 0.3~0.4MPa for 30~35s; the steel slag aggregate particle size is 4.75~9.5mm, and the steel slag is flushed with water pressure of 0.2~0.3MPa for 35~40s; the steel slag aggregate particle size is 2.36~4.75mm, and the steel slag is flushed with water pressure of 0.15~0.2MPa for 40~45s. In this embodiment, the steel slag aggregate particle size is 9.5~16mm, and the steel slag is washed with 0.3MPa water pressure for 30s; the steel slag aggregate particle size is 4.75~9.5mm, and the steel slag is washed with 0.2MPa water pressure for 35s; the steel slag aggregate particle size is 2.36~4.75mm, and the steel slag is washed with 0.2MPa water pressure for 40s. After washing, the surface of the steel slag material is coated with particles smaller than 0.075mm with a content of 0.9%, free calcium oxide content of 1.2%, angularity index of 36s (tested by flow time method), porosity of 5.0%, polishing value of 52, and texture index of 430.

[0036] (3) Grading and screening A multi-layer vibrating grading screen is used for grading and screening. The screening machine is equipped with a vibrating screen with square screen holes. The screen mesh is made of wear-resistant steel alloy steel. (The screen mesh size is calculated based on product specifications, vibrating screen working angle, screening efficiency, etc. The vibrating screen mesh size b=d / cosθ, where b—net width of screen hole, mm; d—aggregate particle size, mm; θ—vibrating screen mesh working angle, degrees) to ensure grading accuracy and efficiency. After dehydration and drying, steel slag aggregates of various grades are obtained: 2.36~4.75mm fine aggregate, 4.75~9.5mm medium aggregate, and 9.5~16mm coarse aggregate.

[0037] (4) Categorized storage The coarse aggregate (9.6-16mm) is stored in a cool, ventilated place for 120-168 hours; the medium aggregate (4.75-9.5mm) is stored in a cool, ventilated place for 96-144 hours; and the fine aggregate (2.36-4.75mm) is stored in a cool, ventilated place for 72-120 hours. In this embodiment, the coarse aggregate (9.6-16mm) is stored in a cool, ventilated place for 168 hours; the medium aggregate (4.75-9.5mm) is stored in a cool, ventilated place for 144 hours; and the fine aggregate (2.36-4.75mm) is stored in a cool, ventilated place for 120 hours.

[0038] Example 2

[0039] Using steel slag with a surface coating of particles smaller than 0.075 mm (≤0.8%), an angularity index of 38s, and a porosity of 4.5%-6.5% as aggregate (free calcium oxide content ≤1.5%), asphalt concrete resistant to oil film detachment is prepared according to the following method: After pretreatment of the raw materials, they are added to the mixing pot in the following proportions by mass: 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone powder, and 5.4%-5.6% asphalt content. The mixture is then dry-mixed for 30-40 seconds, followed by wet-mixing for 30-50 seconds to ensure uniform asphalt coating of the aggregates. The finished mixture is stored in a storage silo or loaded onto trucks, covered with tarpaulins for insulation, and transported to the site for paving and compaction as quickly as possible. Specifically, in this embodiment, after pretreatment of the raw materials, they are mixed according to the following proportions: 40% 10-15mm steel slag aggregate, 35% 5-10mm steel slag aggregate, 5% 3-5mm steel slag aggregate, 10% 0-3mm diabase manufactured sand, 10% limestone mineral powder, 0.3% polyester fiber, and 5.6% modified asphalt. These are then sequentially added to a mixing pot and dry-mixed for 10 seconds, followed by wet mixing for 35 seconds to ensure uniform asphalt coating of the aggregates. The finished mixture is stored in a storage silo or loaded onto trucks, covered with tarpaulins for insulation, and transported to the site for paving and compaction as quickly as possible.

[0040] The steel slag is prepared using a wet process, as detailed below: Raw steel slag (of which the steel slag is unaged, with high f-CaO content and unstable expansion rate from converter steel slag) is crushed and shaped after being removed by a magnetic separator to remove iron and other substances. After shaping, it is screened in multiple stages using a multi-layer vibrating screen and a linear vibrating screen. Fine aggregates, medium aggregates, and coarse aggregates are washed and dust removed and calcium is fixed by liquid flushing. A weakly acidic chemical agent (one or more of oxalic acid, acetic acid, and carbonic acid, but excluding any one or more of hydrochloric acid, phosphoric acid, nitric acid, and sulfuric acid) is dissolved in water to form a washing solution with a pH of 4-5.

[0041] The washing solution has a pH of 4 (formed by dissolving oxalic acid and acetic acid in water). The shaped steel slag is washed and dust removed, and calcium is fixed using a liquid flushing method. The aggregate particles are washed under the vibration of a negative-angle linear vibrating screen, and the steel slag is impacted by a jet at a water pressure of 0.15~0.4MPa. Specifically, for steel slag aggregates with a particle size of 9.5~16mm, the slag is flushed at 0.3~0.4MPa for 30s; for aggregates with a particle size of 4.75~9.5mm, the slag is flushed at 0.2~0.3MPa for 35s; and for aggregates with a particle size of 2.36~4.75mm, the slag is flushed at 0.15-0.2MPa for 45s. In this embodiment, the steel slag aggregate particle size is 9.5~16mm, and the steel slag is washed with 0.4MPa water pressure for 30s; the steel slag aggregate particle size is 4.75~9.5mm, and the steel slag is washed with 0.3MPa water pressure for 35s; the steel slag aggregate particle size is 2.36~4.75mm, and the steel slag is washed with 0.2MPa for 45s. After washing, the content of particles smaller than 0.075mm coated on the surface of the steel slag material is reduced from 3% to 0.6%, the free calcium oxide (f-CaO) content is significantly reduced to below 0.8%, the angularity index is 38s, the porosity is 4.8%, the polishing value is 52, and the texture index is 440.

[0042] A multi-layer vibrating grading screen is used for grading and screening. The screening machine is equipped with a vibrating screen with square screen holes. The screen mesh is made of wear-resistant steel alloy steel. (The screen mesh size is calculated based on product specifications, vibrating screen working angle, screening efficiency, etc. The vibrating screen mesh size b=d / cosθ, where b—net width of screen hole, mm; d—aggregate particle size, mm; θ—vibrating screen mesh working angle, degrees) to ensure grading accuracy and efficiency. After dehydration and drying, steel slag aggregates of various grades are obtained: 2.36~4.75mm fine aggregate, 4.75~9.5mm medium aggregate, and 9.5~16mm coarse aggregate.

[0043] The coarse aggregate (9.6-16mm) is stored in a cool, ventilated place for 120-168 hours; the medium aggregate (4.75-9.5mm) is stored in a cool, ventilated place for 96-144 hours; and the fine aggregate (2.36-4.75mm) is stored in a cool, ventilated place for 72-120 hours. In this embodiment, the coarse aggregate (9.6-16mm) is stored in a cool, ventilated place for 144 hours; the medium aggregate (4.75-9.5mm) is stored in a cool, ventilated place for 120 hours; and the fine aggregate (2.36-4.75mm) is stored in a cool, ventilated place for 96 hours.

[0044] Comparative Example 1 Steel slag aggregate was prepared using the dry process described in patent CN109678368A, resulting in aggregate with 2.1% of particles coated with particles smaller than 0.075mm, an angularity index of 30s, and a free calcium oxide content of 2.6%. The steel slag obtained by the dry process was then used to prepare asphalt concrete. The specific preparation process is as follows: After pretreatment of the raw materials, the following proportions are made by weight: 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, 0.25%~0.3% polyester fiber, and 5.5%-5.6% modified asphalt. Before preparation, heat the steel slag aggregate to 180℃~200℃ and the asphalt to 155℃~160℃. During mixing, first mix the steel slag aggregate and polyester fiber in a mixing tank at 170℃~180℃ for 8-10 seconds (dry mixing), then add the asphalt, mineral powder, and steel slag aggregate and mix for 40-50 seconds (wet mixing). The asphalt mixture should have a uniform coating of asphalt mortar on the aggregate surface, a bright and uniform color, no white spots, good cohesiveness, and a certain degree of fluidity. Store the finished mixture in a storage silo or load it onto a truck, cover it with tarpaulin for insulation, and transport it to the site for paving and compaction as soon as possible. Specifically, in this comparative example, after pretreatment of the raw materials, the proportions by weight are as follows: 40% 10-15mm steel slag aggregate, 35% 5-10mm steel slag aggregate, 5% 3-5mm steel slag aggregate, 10% 0-3mm diabase manufactured sand, 10% limestone mineral powder, 0.3% polyester fiber, and 5.6% modified asphalt. Before preparation, the steel slag aggregate is heated to 200℃ and the asphalt is heated to 155℃. During mixing, the steel slag aggregate and polyester fiber are first mixed in a mixing tank at 170℃ for 10 seconds (dry mixing), and then the asphalt, mineral powder, and steel slag aggregate are added and mixed together for 50 seconds (wet mixing). The asphalt mixture should have a uniform coating of the aggregate surface, a bright and uniform color, no white spots, good cohesiveness, and a certain degree of fluidity. The finished mixture is stored in a storage silo or loaded onto a truck, covered with tarpaulin for insulation during transportation, and transported to the site for paving and compaction as soon as possible.

[0045] The steel slag used as aggregate is prepared using the following dry method: The raw material steel slag is converter steel slag that has been naturally aged for more than 6 months (free calcium oxide content 2.6%), and is prepared into steel slag aggregates of various grades according to the method in CN109678368A: 2.36~4.75mm fine aggregate, 4.75~9.5mm medium aggregate, and 9.5~16mm coarse aggregate.

[0046] The anti-oil film peeling effects of steel slag asphalt concrete prepared in Example 1, Example 2 and Comparative Example 1 are compared as follows: The steel slag aggregates from Examples 1, 2, and Comparative Example 1 were sieved, and particles with a diameter of 9.5-13.2 mm were collected. The aggregates were poured into asphalt and immediately mixed evenly with a metal shovel for 1-1.5 minutes. Twenty aggregates coated with asphalt were transferred to a glass plate and cooled at room temperature for 1 hour. The glass plate was then immersed in a constant temperature water bath at 80℃±1℃ for 30 minutes. The asphalt that had peeled off and floated on the water surface was removed, and the glass plate was carefully removed from the water and immersed in cold water to observe the peeling of the asphalt film. The peeling degree of the three types of asphalt is shown in Table 1 below: Table 1 Comparison of asphalt stripping degree under different treatment methods

[0047] As shown in Table 1, the stripping degree of steel slag prepared by the traditional dry method and mixed with asphalt was 12.8%, while the stripping degree of steel slag prepared by the wet method of this invention and mixed with asphalt was 9.1% and 7.3%, respectively. Compared with existing steel slag, the steel slag of this invention with a surface coating of particles smaller than 0.075mm <1%, an angularity index of ≥35s, and a porosity of 4.5%-6.5% has good resistance to oil film stripping. As an aggregate, it can be used to prepare asphalt concrete resistant to oil film stripping.

[0048] Steel slag asphalt concrete precast blocks were prepared according to Examples 1, 2, and Comparative Example 1. The steel slag aggregate and asphalt were mixed evenly according to the designed gradation and optimal asphalt-aggregate ratio. The mixtures were then molded into specimens measuring 101.6 mm (diameter) × 63.5 mm (height) using a standard Marshall compactor. A portion of the Marshall specimens were cut off by 5 mm from each end of their height, and then cut in half to prepare circular slice specimens measuring 101.6 mm (diameter) × 25 mm (height).

[0049] Marshall specimens and circular slice specimens were immersed in a 60°C constant temperature water bath. The specimens were removed after 3, 7, 14, and 21 days, and the surface particles of the circular slice specimens were tested to see if they swelled, cracked, or pulverized. The diameter and height of the Marshall specimen were measured using vernier calipers, and its volume change was calculated. The results are shown in Table 2 below: Table 2 Comparison of immersion swelling rates under different treatment methods

[0050] According to the JT / T1086-2016 standard "Steel Slag for Asphalt Mixtures", the water immersion swelling rate of steel slag aggregate used in asphalt concrete should not exceed 1.8%. Although the water immersion swelling rate of the steel slag aggregate in Comparative Example 1 met the requirements, its Marshall specimens showed obvious swelling or pulverization on the surface. In contrast, the steel slag used in this invention, with a surface coating of particles smaller than 0.075 mm (<1%), an angularity index ≥35s, and a porosity of 4.5%-6.5%, as the aggregate for asphalt concrete, did not show swelling or pulverization on the surface of the prepared Marshall specimens. The oil film residual area ratio was ≥90%, and the water immersion swelling rate was ≤1.5%, demonstrating good resistance to oil film peeling and reducing the risk of pavement expansion and cracking.

[0051] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A steel slag asphalt concrete resistant to expansion and cracking, characterized in that, For use in preventing surface expansion cracking caused by oil film peeling from asphalt concrete pavement, the oil film residual area ratio of the steel slag asphalt concrete for preventing expansion cracking is ≥90%, and by mass ratio, it includes 40%-45% of 10-15mm steel slag aggregate, 30%-35% of 5-10mm steel slag aggregate, 5%-8% of 3-5mm steel slag aggregate, 10%-12% of 0-3mm diabase manufactured sand, 8%-10% of limestone mineral powder, 0.25%~0.3% of polyester fiber and 5.5%-5.6% of modified asphalt; The steel slag aggregate comprises steel slag with a surface coating of particles smaller than 0.075 mm, a particle size of 0.6%-0.9%, an angularity index of 36s-38s, and a porosity of 4.8%-5.0%. The steel slag is unaged steel slag, and it is pretreated as follows: After crushing, shaping, and screening, the raw material, unaged steel slag, is washed for 40-45 seconds under a water flow velocity of 0.5-2.5 m / s, with a mass-to-volume ratio of unaged steel slag to washing liquid of 1:8-15. The sieving results are divided into 10-15 mm steel slag aggregate, 5-10 mm steel slag aggregate, and 3-5 mm steel slag aggregate. The washing solution is neutral water or a washing solution with a pH value of 4-5. The unaged steel slag has a particle size of 3-5 mm and is washed at a flow rate of 0.5-1.0 m / s for 40-45 s; the unaged steel slag has a particle size of 5-10 mm and is washed at a flow rate of 1.5-2.0 m / s for 40-45 s; the unaged steel slag has a particle size of 10-15 mm and is washed at a flow rate of 2.0-2.5 m / s for 40-45 s.

2. The anti-expansion cracking steel slag asphalt concrete as described in claim 1, characterized in that, The steel slag aggregate, as an anti-slip and wear-resistant aggregate, has a surface coating of 0.6% particles smaller than 0.075mm, an angularity index of 38s, and a porosity of 4.8%.

3. A method for preparing anti-expansion cracking steel slag asphalt concrete as described in claim 1 or 2, characterized in that, Includes the following steps: Steel slag with a surface coating of particles smaller than 0.075 mm of 0.6%-0.9%, an angularity index of 36s-38s, and a porosity of 4.8%-5.0% was used as aggregate. By mass ratio, the mix consists of 40%-45% 10-15mm steel slag aggregate, 30%-35% 5-10mm steel slag aggregate, 5%-8% 3-5mm steel slag aggregate, 10%-12% 0-3mm diabase manufactured sand, 8%-10% limestone mineral powder, 0.25%~0.3% polyester fiber, and 5.5%-5.6% modified asphalt. Heat the steel slag aggregate to 180℃~200℃ and the asphalt to 155℃~160℃. During mixing, first dry mix the steel slag aggregate and polyester fiber at 170℃~180℃ for 8s-10s; then add the modified asphalt, limestone powder and steel slag aggregate and wet mix for 40s-50s; so that the asphalt mortar evenly coats the surface of the aggregate.

4. The preparation method according to claim 3, characterized in that, The pH value of the washing solution is 4-5.

5. The preparation method according to claim 4, characterized in that, The washing solution is adjusted to a pH of 4-5 using a weakly acidic chemical agent, which does not include any one or more of hydrochloric acid, sulfuric acid, and nitric acid.

6. The preparation method according to claim 5, characterized in that, The weakly acidic chemical agent includes one or more combinations of oxalic acid, acetic acid, and carbonic acid.

7. The preparation method according to claim 6, characterized in that, The weakly acidic chemical agent is a combination of oxalic acid and acetic acid.

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