Roadbed material and method for manufacturing roadbed material

Abstract

Provided are a roadbed material containing granulated carbonated steelmaking slag and raw material blocks having a carbon fixation ability, and a method for manufacturing the roadbed material, without granulating the carbonated steelmaking slag and the raw material blocks. In the roadbed material, the content of at least one of the carbonated steelmaking slag, a wooden material, a synthetic resin, and a natural fiber is 1 mass% or more and 90 mass% or less.

Description

Technical Field

[0001] This invention relates to roadbed materials and methods for manufacturing roadbed materials. Background Technology

[0002] To achieve carbon neutrality, various decarbonization technologies are being researched. Among them, carbonate and concrete-related technologies based on CO2 utilization are easier to implement and have high potential for CO2 fixation compared to other CO2 utilization technologies. Patent document 1 discloses a roadbed material formed by using calcium carbonate and magnesium carbonate generated through a carbonation reaction as binders to solidify and block up slag.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 11-21153 Summary of the Invention

[0004] The problem that the invention aims to solve In the roadbed material disclosed in Patent Document 1, carbon dioxide or a gas containing carbon dioxide is blown into the slag stockpile or filling layer to solidify and lump the granular slag, and the particle size of the lumps is adjusted through crushing, screening, etc., to manufacture the roadbed material. However, the method in Patent Document 1, which involves lumping the granular slag and then crushing the lumps to manufacture the roadbed material, presents a problem with a very high production burden.

[0005] The present invention was made in view of the problems of the prior art, and its object is to provide a roadbed material containing the granular carbonated steelmaking slag and the raw materials with carbon fixation ability without lumping them, and a method for manufacturing the roadbed material.

[0006] Methods for solving problems The methods used to solve the above problems are as follows.

[0007] [1] Roadbed material, wherein the content of at least one of acidified steelmaking slag, wood material, synthetic resin and natural fiber is more than 1% by mass and less than 90% by mass.

[0008] [2] As described in [1], the aforementioned carbonated steelmaking slag is carbonated steelmaking slag micro powder with a particle size of less than 1 mm. The aforementioned carbonated steelmaking slag micro powder contains more than 1% by mass of carbonates.

[0009] [3] The roadbed material as described in [1] or [2], wherein the aforementioned wood material is at least one of wood flour, wood chips, wood fibers, wood fibers, pulp, semi-carbide, carbide, cellulose nanofiber, carbon nanofiber and carbon fiber.

[0010] [4] The roadbed material as described in any one of [1] to [3], wherein the aforementioned synthetic resin is at least one of synthetic rubber scraps, waste tires, polyvinyl chloride scraps, polyethylene scraps and synthetic fiber scraps, which are synthetic polymer compounds.

[0011] [5] The roadbed material as described in any one of [1] to [4], wherein the aforementioned natural fiber is at least one of plant fiber and animal fiber.

[0012] [6] The roadbed material as described in any one of [1] to [5], wherein the aforementioned carbonated steelmaking slag is at least one of carbonated converter slag, carbonated secondary refining slag, carbonated molten iron pretreatment slag and carbonated electric furnace slag.

[0013] [7] The roadbed material as described in any one of [1] to [6], wherein the aforementioned carbonized steelmaking slag is slag made by carbonizing steelmaking slag micro powder with a particle size of less than 1 mm.

[0014] [8] A method for manufacturing roadbed material, comprising: a mixing step, wherein at least one of carbonated steelmaking slag, wood material, synthetic resin and natural fiber is mixed with steelmaking slag, wherein the mixing step is carried out in such a way that the content of at least one of the aforementioned carbonated steelmaking slag, wood material, synthetic resin and natural fiber is 1% by mass or more and 90% by mass or less.

[0015] [9] The method for manufacturing roadbed material as described in [8], wherein the aforementioned carbonized steelmaking slag is carbonized steelmaking slag micro powder manufactured by carbonizing steelmaking slag micro powder with a particle size of less than 1 mm.

[0016] Invention Effects According to the present invention, roadbed materials can be produced by mixing raw materials with carbon-fixing capabilities without lumping them. Therefore, the roadbed material of the present invention is a roadbed material with low production burden and easy to manufacture. Furthermore, by using this roadbed material, roadbed materials with CO2 fixation can be easily manufactured, thus contributing to the realization of carbon neutrality. Detailed Implementation

[0017] [Implementation Method 1] The present invention will now be described through embodiments thereof. Regarding the roadbed material according to this embodiment, a portion of the amount of the mixed material incorporated into the roadbed material is replaced with a substance containing CO2 to obtain the roadbed material. Thus, a roadbed material containing fixed CO2 is obtained. As Embodiment 1, a roadbed material containing carbonated steelmaking slag will be described.

[0018] The roadbed material according to Embodiment 1 includes carbonated steelmaking slag. Regarding the roadbed material containing carbonated steelmaking slag according to Embodiment 1, a mixing step is performed to mix the carbonated steelmaking slag with at least one of uncarbonated steelmaking slag, blast furnace slag, and electric furnace slag. Alternatively, these materials can be manufactured by crushing and blending them to meet the CS-40 particle size distribution specified in JIS A5015:2018 "Steelmaking Slag for Road Use".

[0019] In carbonated steelmaking slag, it is preferable to use carbonated steelmaking slag powder with a particle size of less than 1 mm, which is manufactured by carbonated treatment of steelmaking slag powder with a particle size of less than 1 mm. That is, carbonated steelmaking slag is preferably slag produced by carbonated steelmaking slag powder with a particle size of less than 1 mm. A particle size of less than 1 mm refers to a particle size that can be sieved through a sieve with a mesh opening of 1 mm. By using carbonated steelmaking slag powder with a particle size of less than 1 mm, a reaction-promoting effect is achieved due to the increased reaction interface area during carbonated treatment, thus increasing the CO2 fixation content of the carbonated steelmaking slag.

[0020] Carbonated steelmaking slag can be manufactured by adding steam to the steelmaking slag, introducing a gas containing CO2, and performing a carbonation treatment for at least 10 minutes. Alternatively, instead of adding steam to the steelmaking slag, carbonated steelmaking slag can be manufactured by maintaining the steelmaking slag in water, introducing a gas containing CO2 into the water, and performing a carbonation treatment for 1 day. Alternatively, instead of adding steam to the steelmaking slag, carbonated steelmaking slag can be manufactured by diluting water into the steelmaking slag, introducing a gas containing CO2, and performing a carbonation treatment for 1 day. The CO2 concentration of the introduced CO2-containing gas should be 1% by volume or more. As the CO2-containing gas, exhaust gas with a CO2 concentration of 10% by volume or more discharged from the manufacturing process equipment in the steel plant can also be used. The steelmaking slag used in the manufacture of carbonated steelmaking slag is at least one of converter slag, secondary refining slag, molten iron pretreatment slag, and electric furnace slag.

[0021] The carbonated steelmaking slag contains carbonates introduced through the aforementioned carbonation treatment. Examples of carbonates include calcium carbonate, calcium carbonate hydrate, magnesium carbonate, and magnesium carbonate hydrate. Preferably, the carbonation treatment of the steelmaking slag is performed such that the content of carbonates in the carbonated steelmaking slag is 1% by mass or more. Because carbonates contain CO2, a higher content of carbonates in the carbonated steelmaking slag will increase the CO2 fixed in the subgrade material. Therefore, it is preferable to use carbonated steelmaking slag with a carbonate content of 1% by mass or more as a raw material for subgrade materials, thereby increasing the amount of CO2 fixed in the subgrade material. The higher the content of carbonates in the carbonated steelmaking slag, the greater the amount of CO2 fixed in the subgrade material; therefore, an upper limit for the carbonate content is not specified.

[0022] Carbonated steel slag is mixed into the subgrade material in such a way that the content of carbonated steel slag is 1% by mass or more. This allows CO2 to be fixed in the subgrade material, thus contributing to carbon neutrality. The carbonated steel slag is then mixed into the subgrade material in such a way that the content of carbonated steel slag in the subgrade material is 90% by mass or less. By making the content of carbonated steel slag 90% by mass or less, the bearing capacity of the subgrade material is improved, and the modified CBR of the subgrade material can be 60 or more. Here, the modified CBR test refers to the CBR of the material obtained by compacting the subgrade material to 95% of its maximum dry density.

[0023] In this case, regarding the roadbed material containing carbonated steelmaking slag according to Embodiment 1, since CO2 is fixed in the roadbed material, the use of this roadbed material can contribute to the realization of carbon neutrality. Furthermore, it not only becomes a roadbed material with high support strength, ensuring a modified CBR of 60 or higher, but also, since calcium carbonate and the like are included in the carbonated steelmaking slag, it can also suppress alkali leaching.

[0024] [Implementation Method 2] Next, as Embodiment 2, a roadbed material containing wood will be described. By using wood as a raw material for the roadbed material, CO2 can be fixed in the roadbed material. The wood material is, for example, at least one of wood flour, wood chips, wood fibers, wood fibers, pulp, semi-carbon, carbides, cellulose nanofibers, carbon nanofibers, and carbon fibers.

[0025] Regarding the roadbed material containing wood-based material according to Embodiment 2, a mixing step is performed to mix the wood-based material with uncarbonated steelmaking slag. Alternatively, these materials can be manufactured by pulverizing and blending them to meet the CS-40 particle size distribution specified in JIS A 5015:2018 "Steelmaking Slag for Roads". The wood-based material is mixed in such a way that the wood content in the roadbed material is 1% by mass or more and 90% by mass or less. This allows CO2 to be fixed in the roadbed material, and enables the modified CBR of the roadbed material to be 60 or more.

[0026] By using wood as a raw material for roadbed materials, the specific gravity of the manufactured roadbed material can be adjusted. High-density roadbed materials with a low wood content are suitable for applications such as parking lots. Conversely, low-density roadbed materials with a high wood content are suitable for applications such as paving materials for solar power generation equipment. Using low-density roadbed materials with a high wood content simplifies construction, thus shortening the construction period.

[0027] Wood has high water absorption, which helps to suppress the separation of fine powder materials in the subgrade during construction. Therefore, subgrade materials containing wood have a higher infill ratio during construction, resulting in subgrade materials with high support strength. Furthermore, subgrade materials containing wood can absorb the expansion of the subgrade material, making them highly elastic. If the elastic modulus of the subgrade material increases, the modified CBR of the subgrade material increases; therefore, subgrade materials containing wood have a higher modified CBR than subgrade materials without wood.

[0028] Due to its high water absorption, the natural moisture content of the roadbed material in its stockpile state is 2-3% by mass, compared to 6-7% by mass, while that of the roadbed material containing wood is 0.5% by mass. Because of this difference in natural moisture content, the generation of dust and other pollutants is suppressed in the stockpile state of the roadbed material containing wood, compared to the roadbed material without wood.

[0029] Furthermore, the wood material preferably contains at least one of semi-carbides and carbides. Semi-carbides and carbides contain more pores, thus further increasing the water absorption of the wood material. Therefore, roadbed materials containing wood materials with at least one of semi-carbides and carbides have a higher filling rate during construction, resulting in roadbed materials with higher support strength. Semi-carbides can be manufactured by heating the wood material in an anaerobic or low-oxygen reducing atmosphere at a temperature above 200°C and below 300°C. Carbides can be manufactured by heating the wood material in an anaerobic or low-oxygen reducing atmosphere at a temperature above 300°C and below 1000°C.

[0030] [Implementation Method 3] Next, as Embodiment 3, a roadbed material containing synthetic resin will be described. By using synthetic resin as a raw material for the roadbed material, CO2 can be fixed in the roadbed material. The synthetic resin is, for example, at least one of synthetic rubber scraps, waste tires, polyvinyl chloride scraps, polyethylene scraps, and synthetic fiber scraps, which are synthetic polymer compounds. The synthetic fiber scraps are, for example, polyester-based, polyurethane-based, polyvinyl alcohol-based, polyacrylonitrile-based, and polypropylene-based synthetic fiber scraps, excluding nylon resin fiber scraps, which are polyamide-based.

[0031] Regarding the roadbed material containing synthetic resin according to Embodiment 3, a mixing step is performed to mix the synthetic resin with uncarbonated steelmaking slag. Alternatively, these materials can be manufactured by pulverizing and blending them to meet the CS-40 particle size distribution specified in JIS A 5015:2018 "Steelmaking Slag for Roads". The synthetic resin is mixed in such a way that the content of synthetic resin in the roadbed material is 1% by mass or more and 90% by mass or less. This allows CO2 to be fixed in the roadbed material, and enables the modified CBR of the roadbed material to be 60 or more.

[0032] By using synthetic resins in the raw materials of roadbed materials, roadbed materials with high thermal insulation properties can be manufactured. Furthermore, by using synthetic resins in the raw materials of roadbed materials, lightweight roadbed materials and roadbed materials with high elastic modulus can be manufactured. If the elastic modulus of the roadbed material increases, the modified CBR of the roadbed material increases; therefore, roadbed materials containing synthetic resins have a higher modified CBR than roadbed materials without synthetic resins.

[0033] [Implementation Method 4] Next, as embodiment 4, a roadbed material containing natural fibers will be described. By using natural fibers as the raw material for the roadbed material, CO2 can be fixed in the roadbed material. Natural fibers include, for example, at least one of plant fibers such as cotton, hemp, flax, rice husks, palm shells, and banana peels, and animal fibers such as wool, cashmere, and silk.

[0034] Regarding the natural fiber-containing subgrade material according to Embodiment 4, a mixing step is performed to mix the natural fibers with uncarbonated steelmaking slag. Alternatively, these materials can be manufactured by pulverizing and blending them to meet the CS-40 particle size distribution specified in JIS A 5015:2018 "Steelmaking Slag for Roads". The natural fibers are mixed in such a way that the content of natural fibers in the subgrade material is 1% by mass or more and 90% by mass or less. This allows CO2 to be fixed in the subgrade material, and enables the modified CBR of the subgrade material to be 60 or more.

[0035] By using natural fibers in the raw materials of roadbed materials, high-strength roadbed materials can be manufactured. Furthermore, using natural fibers in the raw materials of roadbed materials can also produce lightweight roadbed materials with a high modulus of elasticity. If the modulus of elasticity of the roadbed material increases, the modified coefficient of elasticity (CBR) of the roadbed material increases. Therefore, roadbed materials containing natural fibers have a higher modified CBR than roadbed materials without natural fibers.

[0036] In embodiments 1 to 4, examples of roadbed materials comprising carbonated steelmaking slag, wood materials, synthetic resins, or natural fibers were described, but the methods are not limited to these. Roadbed materials can be manufactured using wood materials together with carbonated steelmaking slag, synthetic resins together with carbonated steelmaking slag, or natural fibers together with carbonated steelmaking slag. Furthermore, roadbed materials can be manufactured using synthetic resins together with wood materials, using natural fibers together with wood materials, or using natural fibers together with synthetic resins.

[0037] The roadbed material involved in this embodiment is a roadbed material comprising at least one of carbonated steelmaking slag, wood materials, synthetic resins, and natural fibers, wherein the content of at least one of carbonated steelmaking slag, wood materials, synthetic resins, and natural fibers is 1% by mass or more and 90% by mass or less. Thus, the roadbed material involved in this embodiment can be manufactured by mixing and adjusting these raw materials to a specified particle size without causing the carbonated steelmaking slag, wood materials, synthetic resins, and natural fibers to become lumpy. Therefore, it is a roadbed material with a lower production burden and easier to manufacture than conventional roadbed materials.

[0038] Example Next, an example will be described using carbonized steelmaking slag, wood materials, synthetic resins, and natural fibers as mixed raw materials with fixed CO2, adjusting the mixing ratio of these raw materials, and manufacturing a roadbed material with a particle size distribution meeting CS-40. The types of mixed raw materials, mixing ratios, maximum particle size, natural moisture content of the roadbed material, modified CBR of the roadbed material, strength assessment results, and CO2 fixation amount of the roadbed material are shown in Table 1 below. The composition of each steelmaking slag used in the examples is shown in Table 2 below.

[0039] [Table 1] [Table 2] In Table 1 above, "mixing ratio" refers to the percentage (by mass) of the mixed raw materials contained in the subgrade material. "Maximum particle size of the mixed raw materials" means that the entire quantity passes through a sieve with the nominal mesh opening specified in JIS Z 8801-1:2019 corresponding to the maximum particle size (mm).

[0040] "Modified CBR" refers to the CBR at 95% of the maximum dry density. CBR is the load expressed as a percentage of the standard load when a 5.0 cm diameter piston penetrates the surface of the subgrade material to 2.5 mm or 5.0 mm. For the standard load, it is 13.4 kN for 2.5 mm penetration and 19.9 kN for 5.0 mm penetration. Regarding "strength assessment," if the modified CBR is 60 or higher, it indicates sufficient support for the subgrade material and is assessed as "0"; if the modified CBR is less than 60, it indicates insufficient support for the subgrade material and is assessed as "×".

[0041] The semi-carbonized material, as a wood-based material, is manufactured by treating wood flour with a particle size of less than 1 mm at 250°C for 10 minutes using superheated steam. The carbonized material, as a wood-based material, is manufactured by treating wood flour with an average particle size of less than 300 μm at 300°C for 20 minutes using superheated steam.

[0042] As shown in Examples 1-23 of Table 1, roadbed materials comprising at least one of the following—carbonated steelmaking slag, wood materials, synthetic resins, and natural fibers—within a particle size distribution range of 1% to 90% by mass, exhibit good balance between coarse and fine particles, resulting in increased filler density and a higher modified carbon density (CBR). Based on these results, the roadbed materials of Examples 1-23 are confirmed to be high-supporting materials capable of fixing CO2 and achieving a modified CBR of 60 or higher. Furthermore, by using these roadbed materials, it is possible to contribute to the realization of carbon neutrality.

[0043] On the other hand, for roadbed materials that do not contain carbonated steel slag, wood materials, synthetic resins, or natural fibers (Comparative Example 5), although the modified CBR value is 60 or higher, CO2 is not fixed in the roadbed material. For roadbed materials that contain more than 90% by mass of carbonated steel slag, wood materials, synthetic resins, or natural fibers in 95% by mass, the high proportion of mixed raw materials increases the proportion of fine particles within the CS-40 particle size range, reduces the filling rate of the roadbed material, and lowers the modified CBR to less than 60%. Based on these results, it is confirmed that although the roadbed materials involved in Comparative Examples 1 to 4, which contain more than 90% by mass of carbonated steel slag, wood materials, synthetic resins, or natural fibers, are able to fix CO2 in the roadbed material, the modified CBR becomes less than 60, and the support strength of the roadbed material is reduced.

[0044] It was confirmed that the roadbed material mixed with wood has a higher natural moisture content and a larger modified CBR compared to other roadbed materials. In addition, due to the increased natural moisture content, fine dust is adsorbed, thus, when storing roadbed materials containing wood in stockpiles, the generation of dust and other pollutants can be suppressed compared to other roadbed materials.

Claims

1. Roadbed materials, among which, The content of at least one of the following—carbonated steelmaking slag, wood materials, synthetic resins, and natural fibers—is more than 1% by mass and less than 90% by mass.

2. The roadbed material as described in claim 1, wherein, The carbonated steelmaking slag is a carbonated steelmaking slag micro powder with a particle size of less than 1 mm. The carbonated steelmaking slag micro powder contains more than 1% by mass of carbonates.

3. The roadbed material as described in claim 1 or 2, wherein, The wood material is at least one of wood flour, wood chips, wood fibers, wood fibers, pulp, semi-carbide, carbide, cellulose nanofibers, carbon nanofibers and carbon fibers.

4. The roadbed material as described in any one of claims 1 to 3, wherein, The synthetic resin is at least one of synthetic rubber scraps, waste tires, polyvinyl chloride scraps, polyethylene scraps, and synthetic fiber scraps, which are used as synthetic polymer compounds.

5. The roadbed material as described in any one of claims 1 to 4, wherein, The natural fiber is at least one of plant fiber and animal fiber.

6. The roadbed material as described in any one of claims 1 to 5, wherein, The carbonated steelmaking slag is at least one of the following: carbonated converter slag, carbonated secondary refining slag, carbonated molten iron pretreatment slag, and carbonated electric furnace slag.

7. The roadbed material as described in any one of claims 1 to 6, wherein, The carbonized steelmaking slag is a slag formed by carbonizing steelmaking slag micro powder with a particle size of less than 1 mm.

8. A method for manufacturing roadbed materials, which has the following characteristics: In the mixing step, at least one of the following is mixed with the carbonated steelmaking slag, wood materials, synthetic resins, and natural fibers: In the mixing step, the mixture is carried out in such a way that the content of at least one of the carbonated steelmaking slag, wood material, synthetic resin and natural fiber is more than 1% by mass and less than 90% by mass.

9. The method for manufacturing roadbed material as described in claim 8, wherein, The carbonated steelmaking slag is a carbonated steelmaking slag powder manufactured by carbonating steelmaking slag micro powder with a particle size of less than 1 mm.

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