A paving process for steel slag roads

Abstract

The present invention discloses a paving process for steel slag roads, which combines the resource utilization technology of converter steel slag, LF refining slag, and tundish waste slag from continuous casting machines with the highway construction in areas with abundant rainfall and heavy snowfall. After optimizing the compositions of tundish waste slag and molten steel refining slag, according to the characteristics of different road structural layers and taking advantage of the different properties of different steel slags, steel slag roads are paved. This not only solves the road safety problems caused by excessive f-MgO in tundish waste slag from continuous casting machines and excessive f-CaO in converter steel slag during the process of using steel slag for road construction, but also optimizes the technological properties of steel slag roads, demonstrating the power of technological innovation.

Description

Technical Field

[0001] The present invention relates to a paving process for a steel slag road. Background Art

[0002] Referring to the literature: (1) Gan Wanggui published a paper titled "Research on the Use of Steel Slag for Filling Highway Subgrades" in the journal "WISCO Technology" in the 4th issue of 2007. The paper states that "through a series of tests on WISCO steel slag, the chemical composition, physical and mechanical properties, mineral phase composition, soundness, and harmfulness of the steel slag were comprehensively analyzed. The results show that when the storage period of the steel slag is 12 months, its crushing value, free calcium oxide content, soundness, and harmfulness tests all meet the relevant national and industry standards. Therefore, steel slag stored for more than 12 months can be used as highway subgrade materials."; (2) Xue Ming and Feng Shunxiang published a paper titled "Research on the Application of Converter Steel Slag in Subgrades" in the journal "Iron & Steel" in Volume 31 of 1996. The paper states that "the steel slag mixture should have a suitable gradation. When the steel slag treatment process of Anyang Steel has not changed significantly, that is, it will not significantly affect the existing stability and gradation of the steel slag, large pieces of steel slag larger than 50 mm should be screened out, and then the steel slag mixture should be composed of coarse aggregate (d > 10 mm): fine aggregate (d < 10 mm) = 70% - 80%: 30% - 20% by proportion. The content of free calcium oxide in the steel slag should be preferably 3% - 6% and not more than 6.5%."; (3) Pan Fang, Li Jun, etc. published a paper titled "Application of Steel Slag in Asphalt Pavement Base Courses" in the journal "Journal of Hefei University of Technology" in the 6th issue of 2002. The paper states that "studies have shown that steel slag mixtures with a certain gradation and a certain activity (free calcium oxide content) can be self-compacted into a whole after compaction. The CBR value of steel slag mixtures with a certain gradation can reach 250% - 400% of the standard value, and the immersion expansion rate is also small. In particular, the mixture with a mix ratio of crushed stone (16 - 19 mm): coarse steel slag (> 10 mm): fine steel slag (< 10 mm) = 1:7:2 can be used for constructing asphalt pavement base courses."

[0003] According to the above literature, there is currently no literature mentioning the process method of using refining slag and tundish waste slag from continuous casting machines in the construction of steel slag roads. Summary of the Invention

[0004] The purpose of the present invention is to provide a paving process for a steel slag road, which can not only digest a large amount of steel slag for highway construction, but also effectively optimize the quality of highway construction.

[0005] The technical solution adopted by the present invention is a paving process for a steel slag road, which is divided into four aspects: the pretreatment process of refining slag, the processing process of tundish waste slag of a continuous casting machine, the treatment process of converter steel slag, and the paving process of the steel slag road structure layer. The specific construction process is as follows:

[0006] A. Pretreatment process of molten steel refining slag:

[0007] 1). After the refining slag is overturned according to the traditional process, the remaining steel blocks are selected, and the tail slag is stored separately.

[0008] 2). Transport fly ash to the storage point of the refining slag and store it separately for later use.

[0009] 3). Mix the refining slag and fly ash in a mass percentage ratio of 80:20, and process them to 200 meshes as a cementitious material for later use.

[0010] B. Pretreatment process of tundish waste slag of a continuous casting machine:

[0011] 1). Store the tundish waste slag of the continuous casting machine separately.

[0012] 2). Mix the separately stored tundish waste slag of the continuous casting machine with brine MgCl 2 ·6H 2 O, where the addition amount of the brine is 5% - 8% of the weight of the tundish waste slag of the continuous casting machine. After mixing evenly, use a ball mill or a vertical mill to process it to 250 meshes as a subgrade cushion material for later use.

[0013] C. Pretreatment process of converter steel slag:

[0014] 1). The converter steel slag is processed according to the normal converter steel slag treatment process. After magnetic separation to extract iron, the tail slag is crushed and processed, and the steel slag is processed to less than 50 mm. It is classified according to different particle sizes d. The classification treatment standards are as follows: ① For the part where 37.5 mm < d < 50 mm, it is stored as a subgrade cushion material; ② Screen out the part with particle size d in the range of 5 - 17.5 mm as asphalt concrete surface layer material or aggregate; ③ After selecting the asphalt concrete surface layer material, the remaining part with particle size d in the range of 0.075 - 37.5 mm is used as a water stable layer material as a whole; ④ The converter steel slag with particle size d < 0.075 mm is used as an alternative to alkaline stone powder for asphalt concrete surface layer material.

[0015] 2). The converter steel slag is not stored mixed with the refining slag and the tundish waste slag of the continuous casting machine.

[0016] D. Paving process of the steel slag road structure layer:

[0017] 1), after the roadbed excavation, first mix the converter steel slag with a particle size d > 37.5mm with the processed waste slag and brine mixture from the continuous caster tundish in a mass percentage ratio of 6:4. After mixing evenly, it is used as the material for stone dumping and squeezing silt and the cushion layer for the wet and soft foundation. The paving meets the design requirements. After paving, leveling and compaction, sprinkle water for curing for 3 - 7 days;

[0018] 2), after the cushion layer is cured, mix the converter steel slag with a particle size d in the range of 0.075 - 37.5mm and the processed refining slag in a mass percentage ratio of 85 - 95:5 - 15. After mixing evenly, it is used as the material for the water-stable layer to pave the water-stable layer. The paving of the water-stable layer meets the design requirements. During this construction period, the problems of particle size and gradation are not considered. After the water-stable layer is paved, it is leveled by a leveling machine, compacted by a roller, and sprinkled with water for curing for 3 - 7 days;

[0019] 3), in areas with abundant precipitation and heavy snowfall in winter, the asphalt concrete adopts the AC-16 structure, and the paving thickness meets the design requirements. During this process, the converter steel slag with a particle size d < 0.075mm is used as a substitute for the alkaline stone powder in the asphalt concrete surface layer material. All the aggregates are converter steel slag with a particle size d of 5 - 17.5mm. The particle size of the asphalt concrete surface layer material meets the gradation requirements of AC-16.

[0020] The technical content of this case is based on the following scientific discoveries:

[0021] 1. Through scientific research and summarizing the existing failed cases of using steel slag for road construction, the inventor found that modern steelmaking enterprises not only produce converter steel slag, but also produce steel refining slag, waste slag from the continuous caster tundish, etc. The production volume of converter steel slag is 10% - 20% of the steel output, the production volume of refining slag is 0.9% - 1.5% of the steel output, and the production volume of waste slag from the continuous caster tundish is 0.15% - 0.3% of the steel output. Among them, the f-CaO content in the refining slag is about 10%, and the waste slag from the continuous caster tundish mainly contains MgO, and the f-MgO content in it is very high. Due to the lack of clear resource utilization channels, most enterprises mix the steel refining slag and waste slag from the continuous caster tundish with the converter steel slag for stacking and overall resource utilization, which is the main factor for the unstable performance in the process of using steel slag for road construction. The traditional process method to eliminate these unstable factors is the aging and digestion of steel slag, but this causes the stacking of steel slag and affects the surrounding environment;

[0022] 2. The inventor found that during the slag treatment process, when the converter steel slag is processed to less than 5mm, the f-CaO in the converter steel slag is converted into CaO with hydration reaction activity under the action of mechanical force chemical reaction, and there is no longer the harm of expansion;

[0023] 3. The inventor found through research that the tundish slag from the continuous casting machine contains 65% - 85% MgO. During the operation of the tundish, these MgO are affected by high-temperature liquid steel for a long time, resulting in coarse grains, dense structure between crystals, slow hydration reaction, and similar properties to f-MgO in converter steel slag. The reaction activity can be improved and the hazards can be eliminated by using the mechanical force chemical reaction pretreatment method.

[0024] 4. The inventor found through practice and research that the content of f-CaO in the refining slag is high and the refining slag is seriously polluted by pulverization. Adding fly ash to the refining slag and then mixing and processing it to about 200 mesh, the f-CaO in the refining slag can react with SiO 2 and Al 2 O 3 in the fly ash to undergo a hydration reaction and eliminate the instability of the refining slag.

[0025] Based on the above findings, the inventor utilized the characteristics of the refining slag and the tundish slag from the continuous casting machine to develop a process for producing road materials such as magnesia-rich cement and portland cement using the refining slag from the steel mill and the tundish slag from the continuous casting machine. The produced materials are applied to road construction in areas with abundant rainfall and heavy snowfall. While eliminating the hazards of f-CaO in the refining slag and f-MgO in the waste coating of the tundish of the continuous casting machine, the process of paving the steel slag road is optimized.

[0026] To sum up, the innovation points of the present invention are as follows:

[0027] 1. The inventor found that when f-CaO in the converter steel slag and the refining steel slag undergoes a hydration reaction, it can cause a volume expansion of 98%. This expansion effect can eliminate road hazards such as shrinkage cracks and pavement deflection caused by inappropriate aggregate gradation, and developed a steel slag road construction technology using discontinuous graded steel slag aggregates for road construction;

[0028] 2. The inventor found that by adding fly ash to the refining slag and processing it to about 200 mesh using a mill, the f-CaO in the refining slag becomes reactive and reacts with SiO 2 and Al 2 O 3 in the fly ash during road construction to undergo a hydration reaction, eliminating the instability of the refining slag, and developed a process technology for mixing and processing the refining slag and fly ash, eliminating the unstable factors in the process of resource utilization of the refining slag;

[0029] 3. The MgO in the tundish coating of the continuous casting machine has coarse grains and slow hydration reaction after being affected by the high temperature of molten steel for a long time. Using the principle of mechanical force chemical reaction, after processing the waste coating of the tundish of the continuous casting machine to 250 mesh, adding a part of bittern (MgCl 2 ·6H 2O), which can convert the waste tundish coating of the continuous casting machine into magnesia cement and eliminate the expansion hazard caused by f-MgO in the tundish waste slag of the continuous casting machine;

[0030] 4. Screen the converter steel slag, select the steel slag with a particle size of 30 - 50 mm as the cushion material for the subgrade in the shallow water area and the aggregate for treating the wet and soft foundation, and use the refining slag and the tundish waste slag of the continuous casting machine as the filling material to lay a cushion layer of 100 - 500 mm, which can effectively prevent the upward seepage of groundwater in the shallow water area;

[0031] 5. Crush the converter steel slag to the range of 0.075 - 37.5 mm, and use the treated refining slag as the cementitious material for laying the water-stable layer of the road. The gradation problem of the converter steel slag does not need to be considered in this process. The dosage of the refining slag is determined according to the gradation requirements of the granular materials in the converter steel slag. Among them: 1. When the coarse aggregate (d > 10 mm) in the steel slag aggregate is greater than the fine aggregate (d < 10 mm), the dosage of the refining slag accounts for 15% of the aggregate amount (when the refining slag is insufficient, it is replaced by Portland cement); 2. When the coarse aggregate (d > 10 mm) in the steel slag aggregate is less than the fine aggregate (d < 10 mm), the dosage of the refining slag accounts for 5 - 10% of the aggregate amount (when the refining slag is insufficient, it is replaced by Portland cement). Utilize the hydration reaction expansion effect of f-CaO in the converter steel slag to make up for the short board caused by the shrinkage of the water-stable layer due to the discontinuous gradation of the aggregate.

[0032] 6. In areas with abundant rainfall and heavy snowfall, when laying the asphalt concrete surface layer of the road, adopt the AC-16 structure, use the converter steel slag as the aggregate, and use the ground granulated blast-furnace slag powder equivalent to replace the commonly used limestone powder as the filler of the asphalt mixture to enhance the waterproof damage ability of the asphalt concrete, optimize the freeze-thaw resistance performance of the road surface, and improve the anti-skid function of the road surface.

[0033] The beneficial contributions of the present invention are as follows: 1. In the construction process of treating soft and wet subgrades and cushion layers in the present invention, magnesia cement can react rapidly when encountering water to form a cementitious material, preventing the infiltration and erosion of groundwater. The heat released by the reaction of magnesia cement can be rapidly conducted downward to solidify the roadbed, reducing cracks and fissures in the cushion layer. The f-CaO remaining in the converter steel slag and the f-MgO remaining in the tundish slag of the continuous casting machine, the thermal stress generated by their expansion effect, can continue to extrude the soft and wet subgrade of the roadbed, playing the role of strengthening and squeezing silt; 2. In the construction process of the water-stable layer, by utilizing the cementitious effect of the refined slag, the consumption of cement is omitted, and the CBR value of the water-stable layer can reach more than 250. By using the expansion effect of f-CaO, the problem of discontinuous aggregate particle gradation is solved, and common problems such as shrinkage cracks and unevenness in the construction of the water-stable layer are eliminated; 3. For the asphalt concrete surface layer constructed by using the present invention, in areas with abundant rainfall and large snowfall, problems such as poor road surface anti-skid performance, low anti-freezing and thawing ability of the road surface, and poor anti-water damage performance can be effectively solved, improving the service life of the road; 3. For the tundish slag of the continuous casting machine, except for returning it to the steelmaking production of magnesium balls, there is no clear resource utilization process in the current industry. The present invention provides a highly competitive process method for the resource utilization of the tundish slag of the continuous casting machine. Detailed implementation mode

[0034] A paving process for a steel slag road, which is divided into four aspects: the pretreatment process of refined slag, the processing process of tundish slag of the continuous casting machine, the treatment process of converter steel slag, and the paving process of the steel slag road structure layer. The specific construction process is as follows:

[0035] A. Pretreatment process of molten steel refined slag:

[0036] 1). After the refined slag is turned over according to the traditional process, the remaining steel blocks are selected, and the tail slag is stored separately;

[0037] 2). Transport fly ash to the refined slag storage point and store it separately for use;

[0038] 3). Mix the refined slag and fly ash in a mass percentage ratio of 80:20, and process it to 200 meshes for use as a cementitious material;

[0039] B. Pretreatment process of tundish slag of the continuous casting machine:

[0040] 1). Store the tundish slag of the continuous casting machine separately;

[0041] 2). Mix the separately stored tundish slag of the continuous casting machine with brine MgCl 2 ·6H 2 O, wherein the addition amount of the brine is 5% - 8% of the weight of the tundish slag of the continuous casting machine. After mixing evenly, use a ball mill or a vertical mill to process it to 250 meshes for use as a roadbed cushion material;

[0042] C. Pretreatment process of converter steel slag:

[0043] 1). The converter steel slag is processed according to the normal converter steel slag treatment process. After magnetic separation for iron extraction, the tail slag is crushed and processed. The steel slag is processed to less than 50 mm and classified according to different particle sizes d. The classification criteria are as follows: ① For the part where 37.5 mm < d < 50 mm, it is stored as subgrade cushion material; ② The part with a screened particle size d in the range of 5 - 17.5 mm is used as asphalt concrete surface layer material or aggregate; ③ After selecting the asphalt concrete surface layer material, the remaining part with a particle size d in the range of 0.075 - 37.5 mm is used as a whole as the water-stable layer material; ④ The converter steel slag with a particle size d < 0.075 mm is used as a substitute for the alkaline stone powder of the asphalt concrete surface layer material;

[0044] 2). The converter steel slag is not mixed and stored with the refining slag and the tundish waste slag of the continuous casting machine;

[0045] D. Paving process of the steel slag road structure layer:

[0046] 1). After the roadbed of the road is excavated, first, the converter steel slag with a particle size d > 37.5 mm is mixed evenly with the processed tundish waste slag of the continuous casting machine and the brine mixture in a mass percentage ratio of 6:4, and used as the material for stone throwing and silt squeezing and the cushion material of the wet soft foundation. It is paved to meet the design requirements. After paving, leveling and compaction, it is watered and cured for 3 - 7 days;

[0047] 2). After the cushion is cured, the converter steel slag with a particle size d in the range of 0.075 - 37.5 mm is mixed evenly with the processed refining slag in a mass percentage of 85 - 95:5 - 15, and used as the water-stable layer material to pave the water-stable layer. The paving of the water-stable layer meets the design requirements. During this construction period, the particle size and gradation problems are not considered. After the water-stable layer is paved, it is leveled by a leveling machine, compacted by a roller, and watered and cured for 3 - 7 days;

[0048] 3). In areas with abundant precipitation and large winter snowfall, the asphalt concrete adopts the AC - 16 structure, and the paving thickness meets the design requirements. During this process, the converter steel slag with a particle size d < 0.075 mm is used as a substitute for the alkaline stone powder of the asphalt concrete surface layer material, and all the aggregates are the converter steel slag with a particle size d of 5 - 17.5 mm. The particle size of the asphalt concrete surface layer material meets the gradation requirements of AC - 16. Example

[0049] The implementation of the present invention is illustrated by taking the steel slag of Bayi Iron & Steel Co., Ltd. of Baowu Group as an example:

[0050] 1. Transport the fly ash generated by Yili Iron & Steel Co., Ltd. to the storage point of refined steel slag in Yigang. After mixing it evenly according to the mass percentage of refined steel slag to fly ash of 80:20, process it to 200 mesh for standby.

[0051] 2. Mix the tundish waste slag from the continuous casting machine in the steelmaking plant of Yili Iron & Steel Co., Ltd. with bittern. The addition amount of bittern is 5% - 8% of the tundish waste slag. After mixing the two evenly, process it to 250 mesh for standby.

[0052] 3. Screen the converter steel slag into multiple grades. After selecting sufficient asphalt concrete aggregates, screen and select the converter steel slag with a particle size d < 0.075mm as a substitute for the alkaline stone powder in the asphalt concrete surface layer material, and use the remaining part as aggregate for standby; Aggregate is a large amount of material.

[0053] 4. After the roadbed is excavated, according to the groundwater and subgrade conditions, mix the part with a particle size d > 37.5mm with the aggregate processed from the tundish waste slag of the continuous casting machine according to the mass percentage of 6:4, and use it as the replacement material and cushion material for treating the wet and soft foundation. The thickness of the cushion or replacement meets the relevant design and specification requirements of road construction.

[0054] 5. After the cushion construction is completed, mix the converter steel slag in the particle size range of d = 0.075 - 37.5mm with the treated refined steel slag evenly according to the mass percentage of 85:15, and use it as the water-stable layer material to pave the water-stable layer. The paving thickness of the water-stable layer meets the relevant design and specification requirements of road construction.

[0055] 6. After the water-stable layer construction is completed, use the converter steel slag with a particle size d < 0.075mm as a substitute for the alkaline stone powder in the asphalt concrete surface layer material. Use the converter steel slag with a particle size d in the range of 5 - 17.5mm as aggregate. After mixing with asphalt, pave the asphalt concrete surface layer. The paving thickness meets the relevant design and specification requirements of road construction.

[0056] 7. After the surface layer paving is completed, under the same conditions, the road traffic can be opened about 3 days in advance.

Claims

1. A paving process for steel slag roads, characterized in that this process is divided into four aspects: the pretreatment process of refining slag, the pretreatment process of tundish waste slag of continuous casting machine, the pretreatment process of converter steel slag, and the paving process of steel slag road structure layer. The specific construction process is as follows: A. Pretreatment process of refining slag: 1). After the refining slag is overturned according to the traditional process, the remaining cast steel blocks are selected, and the tail slag is stored separately; 2). Transport fly ash to the storage point of refining slag and store it separately for use; 3). Mix the refining slag and fly ash in a mass percentage ratio of 80:20, and process it to 200 meshes for use as a cementitious material; B. Pretreatment process of tundish waste slag of continuous casting machine: 1). Store the tundish waste slag of the continuous casting machine separately; 2), Mix the tundish slag of the continuous casting machine stored separately with brine MgCl 2 ·6H 2 O. The addition amount of the brine is 5% - 8% of the weight of the tundish slag of the continuous casting machine. After mixing evenly, use a ball mill or a vertical mill to process it to 250 meshes and use it as a subgrade cushion material for standby; C. Pretreatment process of converter steel slag: 1). The converter steel slag is processed according to the normal converter steel slag treatment process. After magnetic separation to extract iron, the tail slag is crushed and processed. The steel slag is processed to less than 50 mm and classified according to different particle sizes d. The classification treatment standards are as follows: ① For the part where 37.5 mm < d < 50 mm, it is stored as subgrade cushion material; ② Screen out part of the particle size d in the range of 5 - 17.5 mm as asphalt concrete surface layer material or aggregate; ③ After selecting the asphalt concrete surface layer material, the remaining part with particle size d in the range of 0.075 - 37.5 mm is used as the water stable layer material as a whole; ④ The converter steel slag with particle size d < 0.075 mm is used as a substitute for alkaline stone powder in the asphalt concrete surface layer material; 2). The converter steel slag is not mixed and stored with the refining slag and the tundish waste slag of the continuous casting machine; D. Paving process of steel slag road structure layer: 1). After the roadbed is excavated, first mix the converter steel slag with particle size d > 37.5 mm with the processed mixture of tundish waste slag of continuous casting machine and bittern in a mass percentage ratio of 6:4, and use it as the material for throwing stones to squeeze silt and cushion material for wet and soft foundation. Spread it to meet the design requirements. After spreading, leveling and compaction, sprinkle water for curing for 3 - 7 days; 2). After the cushion is cured, mix the converter steel slag with particle size d in the range of 0.075 - 37.5 mm and the treated refining slag in a mass percentage of 85 - 95:5 - 15, and use it as the water stable layer material to pave the water stable layer. The paving of the water stable layer meets the design requirements. During this construction period, the particle size and gradation are not considered. After the water stable layer is spread, level it with a leveling machine, compact it with a roller, and sprinkle water for curing for 3 - 7 days; 3). In areas with sufficient precipitation and heavy snowfall in winter, the asphalt concrete adopts the AC - 16 structure, and the paving thickness meets the design requirements. During this process, the converter steel slag with particle size d < 0.075 mm is used as a substitute for alkaline stone powder in the asphalt concrete surface layer material, and all the aggregates are converter steel slag with particle size d of 5 - 17.5 mm. The particle size of the asphalt concrete surface layer material meets the gradation requirements of AC - 16.