Backfill material and method for manufacturing backfill material

Abstract

The present invention provides a backfill material and a method for manufacturing the backfill material that can reduce CO2 emissions. [Solution] A backfill material is used that contains a solidifying agent containing blast furnace slag fine powder and carbonated steelmaking slag powder, and water, wherein the carbonated steelmaking slag powder contains calcium carbonate.

Description

[Technical Field]

[0001] This invention relates to backfill material and a method for manufacturing backfill material. [Background technology]

[0002] With growing awareness of global environmental protection, low-carbon materials are in demand for construction materials. For example, backfill materials are used when temporarily backfilling the ground after removing fluidized soil or underground obstacles. When backfilling, for example, cement and water are mixed to prepare the backfill material, which is then mixed with the in-situ soil to form soil cement, and this soil cement is then backfilled into the ground.

[0003] However, since cement contained in backfill materials produces a large amount of carbon dioxide during its manufacture, there is a growing need to reduce the amount of cement used in backfill materials from the perspective of global environmental protection. Furthermore, cement can contain hexavalent chromium. If this hexavalent chromium leaches from soil cement into the ground, it can trigger environmental problems.

[0004] Herein, Patent Document 1 describes a hydrated solidified body for underwater submersion, which is obtained by hydrating and hardening raw materials, with powdered steelmaking slag as the main aggregate and blast furnace slag fine powder as the main binder, and is characterized in that it contains nitrogen-containing organic matter as part of the raw materials.

[0005] Furthermore, Patent Document 2 describes a method for obtaining a hydrated solidified body by kneading and hardening a composition containing aggregate including steelmaking slag, a binder including blast furnace slag fine powder, and water, wherein the steelmaking slag includes steelmaking slag fine aggregate, and the calcium ion concentration in the test solution obtained by performing the "test in its usable form" described in JIS K 0058-1:2005 "Test methods for chemical substances of slags - Part 1: Elution test method" is 30 mg / L or higher, and the amount of steelmaking slag fine aggregate blended is 800 kg / m³. 3 The above describes a method for producing a hydrated solidified product.

[0006] However, the hydrated solidified material for underwater submersion described in Patent Document 1 is for use in marine areas. Furthermore, the hydrated solidified material described in Patent Document 2 is for use in concrete applications. Therefore, neither Patent Document 1 nor 2 mentions its use as backfill material, nor does it address environmental protection or CO2 emission reduction as a backfill material. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2009-045006 [Patent Document 2] Japanese Patent Publication No. 2024-012841 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention has been made in view of the above circumstances, and aims to provide a backfill material and a method for manufacturing the backfill material that can reduce CO2 emissions. [Means for solving the problem]

[0009] To solve the above problems, the present invention adopts the following configuration. [1] A solidifying agent containing blast furnace slag fine powder and carbonated steelmaking slag powder, and water, The aforementioned carbonated steelmaking slag powder contains calcium carbonate as a backfill material. [2] The specific surface area of ​​the blast furnace slag fine powder is 3000 cm². 2 / g or more, 10000cm 2 It is less than / g The backfill material described in [1] that satisfies the following formula (i). 30.0≦W / (GGBFS+CGGSS)×100≦300.0 (i) However, in formula (i), GGBFS is the mass (kg) of the blast furnace slag fine powder, CGGSS is the mass (kg) of the carbonated steelmaking slag powder, and W is the mass (kg) of the water. [3] The backfill material according to [1], wherein the particle size of the carbonated steelmaking slag powder is 600 μm or less. [4] Further comprising a mixing agent (SP), [1] The backfill material according to [1], wherein the mixing agent is a chemical mixing agent containing one or more of lignin sulfonic acid, lignin sulfonate, oxycarboxylic acid, oxycarboxylate, polycarboxylic acid, polycarboxylate or silicofluoride. [5] The backfill material according to [1], which further satisfies the following formula (ii). 5.0 ≦ CGGSS / (GGBFS + CGGSS)×100 ≦ 30.0 ···(ii) [6] The backfill material according to [1], wherein the solidifying material further contains steelmaking slag fine powder. [7] A method for producing a backfill material, comprising a step of kneading at least the blast furnace slag fine powder, the carbonated steelmaking slag powder and the water to produce the backfill material according to any one of [1] to [6]. [8] Kneading at least the blast furnace slag fine powder, the carbonated steelmaking slag powder and the water at a construction site, A method for producing a backfill material, wherein the backfill material according to any one of [1] to [6] is produced at the construction site.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a backfill material capable of reducing CO2 emissions and a method for producing the same.

Modes for Carrying Out the Invention

[0011] Conventional backfill materials used are those containing cement as a solidifying agent and water. When backfilling the ground, the backfill material is mixed with the in-situ soil to form soil cement, and the formed soil cement is backfilled to stabilize the ground. However, since cement emits 755.5 kg of CO2 per ton during its production, it was necessary to reduce the amount of cement used in order to reduce the carbon footprint of the backfill material.

[0012] The inventors of the present invention conducted extensive research to minimize the cement content in the backfill material. As a result, they found that by using blast furnace slag fine powder and carbonated steelmaking slag powder as the solidifying agent in the backfill material, it is possible to reduce the CO2 emissions while stabilizing the ground, and further suppress the elution of hexavalent chromium into the ground.

[0013] The inventors of the present invention further found that when blast furnace slag fine powder and carbonated steelmaking slag powder are used as the solidifying agent, calcium in calcium carbonate contained in the carbonated steelmaking slag powder elutes as an alkaline component into water, and this alkaline component stimulates the blast furnace slag fine powder, which is a glassy hydraulic material, to exhibit a predetermined strength in the soil cement. They also found that the action of the blast furnace slag fine powder can suppress the elution of hexavalent chromium. Hereinafter, the backfill material and its manufacturing method according to the embodiments of the present invention will be described.

[0014] The backfill material of the present embodiment includes a solidifying agent containing blast furnace slag fine powder and carbonated steelmaking slag powder, and water, and is a backfill material in which the carbonated steelmaking slag powder contains calcium carbonate.

[0015] The backfill material of the present embodiment can form soil cement by mixing with in-situ soil. Hereinafter, the blending components of the backfill material will be described. In the following description, the blast furnace slag fine powder and the carbonated steelmaking slag powder may be collectively referred to as "solidifying agent" for explanation.

[0016] Blast furnace slag fine powder is obtained by rapidly cooling molten slag, which is formed simultaneously with pig iron in a blast furnace, with water to produce water-granulated slag, and then crushing the water-granulated slag. By mixing blast furnace slag fine powder with backfill material, the leaching of hexavalent chromium into the ground can be suppressed.

[0017] In this embodiment, blast furnace slag fine powder is used, with a specific surface area of ​​3000 cm². 2 / g or more, 10000cm 2 It is preferable to use a specific surface area within the range of / g or less. If the specific surface area is above the lower limit, the hardening reaction of the soil cement is not suppressed, the hardening rate is improved, the hardening time to reach the desired hardness is shortened, and problems such as material segregation are less likely to occur, which is preferable. Also, if the specific surface area is below the upper limit, the hardening of the soil cement does not proceed too rapidly, and the strength of the soil cement does not increase excessively, which is preferable.

[0018] Carbonated steelmaking slag powder refers to steelmaking slag powder in which CO2 is immobilized by reacting part or all of the calcium composition in the steelmaking slag powder with CO2. Part or all of the CO2 immobilized in carbonated steelmaking slag powder is immobilized in the form of calcium carbonate.

[0019] It is desirable that the calcium carbonate content in the carbonated steelmaking slag powder be greater than 0% by mass. The presence of calcium carbonate facilitates the elution of calcium as an alkaline component, thereby enabling the water-hardening properties of the blast furnace slag fine powder to be exhibited.

[0020] The steelmaking slag fine powder, which is the raw material for carbonated steelmaking slag powder, can be exemplified by crushing various types of slag, such as pre-treatment slag generated in the molten iron pre-treatment process, converter slag generated in processes such as decarburization and desilicate in converters, electric furnace slag such as reduction slag and oxidation slag generated in electric furnace processes, ingot slag generated in the casting process, and secondary refining slag generated in the secondary refining process. These may be included individually or as a mixture of two or more types.

[0021] Furthermore, the CO2 used in the production of carbonated steelmaking slag powder should be the CO2 generated from each stage of steelmaking at a steel mill.

[0022] The steelmaking slag fine powder contains one or more of the following substances: free lime, calcium hydroxide, calcium ferrite, calcium silicate, and dicalcium silicate. Carbonated steelmaking slag powder can be obtained by reacting such steelmaking slag fine powder with CO2 in the presence of water.

[0023] When this type of carbonated steelmaking slag powder is mixed into backfill material, the calcium from the calcium carbonate contained in the carbonated steelmaking slag powder dissolves into the water. This dissolved calcium becomes an alkaline component that stimulates the glassy properties of the blast furnace slag fine powder, allowing the blast furnace slag fine powder to exhibit its hydraulic properties. As a result, a soil cement that is suitable for its intended use and has excellent environmental properties can be formed.

[0024] The particle size of the carbonated steel slag powder is preferably 600 μm or less. If the particle size is 600 μm or less, the hardening reaction of the soil cement is not suppressed, the hardening rate does not decrease, the hardening time to reach the desired hardness is shortened, and problems such as material separation can be prevented. The particle size of the carbonated steel slag powder may be 0.1 μm or more. Note that the particle size of the carbonated steel slag powder refers to the maximum particle size.

[0025] The backfill material of this embodiment may contain steelmaking slag fine powder as a solidifying agent. In this case, the steelmaking slag fine powder can be the same type as the steelmaking slag fine powder exemplified as a raw material for carbonated steelmaking slag powder.

[0026] When steelmaking slag fine powder is to be included in the backfill material, it may be included by substituting a portion of the carbonated steelmaking slag powder with the steelmaking slag fine powder. That is, more than 0% by mass and less than 100% by mass of the carbonated steelmaking slag powder may be replaced with steelmaking slag fine powder. This supplies a larger amount of the alkaline components necessary for the hydration reaction of the blast furnace slag fine powder, making the hydration reaction of the blast furnace slag fine powder more active. As a result, a backfill material with higher uniaxial compressive strength can be obtained.

[0027] When replacing a portion of the carbonated steelmaking slag powder with steelmaking slag fine powder, the steelmaking slag fine powder has a specific surface area of ​​3000 cm². 2 / g or more, 10000cm 2 It is preferable to use a material with a specific surface area in the range of / g or less. If the specific surface area is above the lower limit, the hardening reaction of the soil cement will not be suppressed, the hardening speed will improve, the hardening time to reach the desired hardness will be shortened, and defects such as material segregation can be prevented. On the other hand, if the specific surface area is below the upper limit, the hardening of the soil cement will not proceed too rapidly, and there is no risk of the strength of the soil cement increasing excessively.

[0028] The ratio of water to the amount of solidifying agent in the backfill material (total amount of blast furnace slag fine powder and carbonized steelmaking slag powder) preferably satisfies the following formula (i).

[0029] 30.0≦W / (GGBFS+CGGSS)×100≦300.0 (i)

[0030] In formula (i), GGBFS is the mass (kg) of blast furnace slag powder, CGGSS is the mass (kg) of carbonated steelmaking slag powder, and W is the mass (kg) of water. Note that if a portion of the carbonated steelmaking slag powder is replaced with steelmaking slag powder, CGGSS in formula (i) may be the total amount of carbonated steelmaking slag powder and steelmaking slag powder.

[0031] If W / (GGBFS+CGGSS)×100 is 30.0 or higher, that is, if the water content relative to the total amount of solidifying agent is 30.0% or higher, then the backfill material and in-situ soil can be thoroughly mixed during the production of soil cement. If W / (GGBFS+CGGSS)×100 is 300.0 or lower, that is, if the water content relative to the total amount of solidifying agent is 300.0% or lower, then the soil cement can maintain an appropriate unconfined compressive strength.

[0032] The proportion of carbonated steelmaking slag powder in the solidification agent of the backfill material is preferably such that it satisfies the following formula (ii).

[0033] 5.0≦CGGSS / (GGBFS+CGGSS)×100≦30.0 (ii)

[0034] If CGGSS / (GGBFS+CGGSS)×100 is 5.0 or higher, that is, if the proportion of carbonated steel slag powder in the solidification material is 5.0% or higher, appropriate strength can be obtained due to the alkaline components leached from the carbonated steel slag powder. If CGGSS / (GGBFS+CGGSS)×100 is 30.0 or lower, that is, if the proportion of carbonated steel slag powder in the solidification material is 30.0% or lower, the risk of hexavalent chromium contained in the carbonated steel slag powder leaching into the ground can be reduced. Note that CGGSS / (GGBFS+CGGSS)×100 may be between 10.0 and 25.0, or between 15.0 and 20.0.

[0035] Furthermore, if a portion of the carbonated steelmaking slag powder is replaced with fine steelmaking slag powder, CGGSS in formula (ii) may be the total amount of carbonated steelmaking slag powder and fine steelmaking slag powder.

[0036] Furthermore, the backfill material of this embodiment may contain an admixture. In this embodiment, the admixture may be formulated primarily for the purpose of improving the fluidity of the backfill material. Alternatively, the admixture may be formulated for the purpose of reducing the hardening rate of the soil cement. Furthermore, the admixture may be formulated for the purpose of reducing the amount of water while maintaining the fluidity of the soil cement.

[0037] The admixture is more preferably a chemical admixture containing one or more of the following: ligninsulfonic acid, ligninsulfonate, oxycarboxylic acid, oxycarboxylic acid salt, polycarboxylic acid, polycarboxylic acid salt, or silicogenic fluoride. By using the above chemical admixture as the admixture, the hardening rate of the soil cement can be reduced, and the strength of the soil cement after hardening can be prevented from becoming excessively high.

[0038] The mixing ratio of the admixture to the amount of solidifying agent in the backfill material (total amount of blast furnace slag fine powder and carbonized steelmaking slag powder) preferably satisfies the following formula (iii).

[0039] 0≦SP / (GGBFS+CGGSS)×100≦5.0 …(iii)

[0040] In formula (iii), SP is the mass (kg) of the admixture. Note that if a portion of the carbonated steelmaking slag powder is replaced with fine steelmaking slag powder, CGGSS in formula (iii) may be the total amount of carbonated steelmaking slag powder and fine steelmaking slag powder.

[0041] SP / (GGBFS + CGGSS)×100 may be 0, but in order to obtain the desired effects of the admixture, it may also be 0.1 or more. That is, if the blending ratio of the admixture with respect to the total amount of the fine powder of blast furnace slag and the powder of carbonated steelmaking slag is 0.1% or more, the effects of reducing the curing rate, improving the fluidity, and reducing the water content by the admixture can be fully exerted. On the other hand, when SP / (GGBFS + CGGSS)×100 exceeds 5.0, that is, when the blending ratio of the admixture with respect to the total amount of the fine powder of blast furnace slag and the powder of carbonated steelmaking slag exceeds 5.0%, the addition effect of the admixture saturates. The range of SP / (GGBFS + CGGSS)×100 may be 0.1 or more, or 0.2 or more and 4.0 or less, may be 0.5 or more and 3.0 or less, or may be 1.0 or more and 2.0 or less.

[0042] Also, as the admixture, instead of the above chemical admixture or together with the above chemical admixture, an AE agent, a high-performance water reducer, an AE water reducer, a fluidizing agent, etc. may be contained.

[0043] Furthermore, the backfill material can also contain an additive. Examples of the additive include pozzolanic materials, hydraulic alumina components, hydraulic admixtures such as super rapid hard cement or gypsum, lime components such as quicklime, slaked lime, lightly burned dolomite or hydrated dolomite. By adding these, even if the soil quality of the ground is high organic matter soil, sludge, or other special soils, the backfill material can be suitably used.

[0044] It is desirable that the backfill material used in this embodiment exhibits the following performance for the soil cement formed.

[0045] [Uniaxial compressive strength of soil cement at 28 days of age] After the removal of underground obstacles, the strength of the soil cement used for temporary ground stabilization treatment is preferably suppressed to a low strength for re-drilling the backfill location, and it may be 50 kN / m 2 or less. More preferably, it is 4.0 kN / m 2 or more and 50 kN / m 2The following is desirable: Uniaxial compressive strength is measured in accordance with JIS A 1216:2020 (Uniaxial Compression Test Method for Soil).

[0046] [Hexavalent chromium elution level: 0.05 mg / L or less] The materials contained in backfill may contain hexavalent chromium. In this invention, hexavalent chromium may be contained in the carbonated steel slag powder. Hexavalent chromium is a specified hazardous substance under the Soil Contamination Countermeasures Act, and its leaching into the ground must be kept below 0.05 mg / L, which is the standard value for the Environmental Notification No. 46 test.

[0047] [P funnel flow time (Test standard: JSCE-F 521-2018)] The shorter the flow time of the backfill material through the P-funnel, the easier the work is, and the less likely problems are to occur, such as clogging of the pump when the backfill material is pumped into the ground. Generally, it is thought that such problems are less likely to occur if the flow time of the backfill material through the P-funnel is 14 seconds or less.

[0048] [Penetration test (Test standard: JIS A 1147:2019 (Proctor's penetration resistance test))] After forming soil cement in the ground, steel materials such as steel pipe piles and steel sheet piles, and concrete structures such as concrete piles are sometimes erected within the soil cement. If the soil cement hardens too much, it can hinder the penetration of such core materials. Therefore, a needle penetration test result of 2.0 N / mm after 8 hours of mixing is required. 2 The following is preferable:

[0049] As described above, the backfill material of this embodiment contains blast furnace slag powder and carbonated steelmaking slag powder as solidifying agents instead of cement. When carbonated steelmaking slag powder containing calcium carbonate is mixed with water, the calcium dissolves into the water as an alkali, stimulating the glassy properties of the blast furnace slag powder, causing the blast furnace slag powder to exhibit hydraulic properties. As a result, soil cement can be formed by mixing the backfill material with in-situ soil without using cement, thereby keeping CO2 emissions low.

[0050] Furthermore, since all the solidifying agents that contribute to the hardening of the soil cement are industrial by-products, the use of the backfill material in this embodiment can reduce the environmental burden. Furthermore, the strength of the soil cement after hardening can be controlled by adjusting the amount of solidifying agent, making it possible to obtain backfill material that exhibits the necessary performance depending on the application. Furthermore, from the perspective of environmental pollution risk, the inclusion of blast furnace slag fine powder can suppress the leaching of hexavalent chromium, which is an environmentally harmful substance.

[0051] According to the backfill material of this embodiment, by using a chemical admixture whose main components are one or more of the following: polycarboxylic acid, polycarboxylic acid salt, ligninsulfonic acid, ligninsulfonate, oxycarboxylic acid, oxycarboxylic acid salt, or silicogenic fluoride, particularly effective performance can be achieved in terms of fluidity and strength.

[0052] In this embodiment of the backfill material, by further incorporating steelmaking slag fine powder into the solidification agent, a larger amount of alkaline substances necessary for the hydration reaction of blast furnace slag fine powder is supplied, and the hydration reaction of blast furnace slag fine powder becomes more active. As a result, a backfill material with higher uniaxial compressive strength can be provided.

[0053] Furthermore, with the backfill material of this embodiment, by mixing the backfill material at the construction site, it is possible to mix a backfill material that is suitable for the detailed soil conditions of the site that become clear during the construction phase, and construction can be carried out using a backfill material that is more appropriate for the ground conditions at the site.

[0054] The backfill material of this embodiment can be applied to a variety of uses, including general ground improvement methods aimed at improving the strength and stabilization of the ground, underground wall construction methods that build underground walls by integrating structural steel or steel sheet piles with soil cement, and construction methods that build foundation structures by integrating steel pipes, steel sheet piles, concrete piles with soil cement. [Examples]

[0055] The present invention will be specifically described below with reference to examples. Backfill materials No. 1 to No. 9 shown in Table 1 were produced by mixing a solidifying agent consisting of blast furnace slag fine powder and carbonated steelmaking slag powder with water and an admixture in predetermined proportions at an ambient temperature of 20°C. The blast furnace slag fine powder had a surface area of ​​4110 cm². 2 I used the one that was / g.

[0056] Carbonated steelmaking slag powder was produced by contacting steelmaking slag fine powder with CO2 in the presence of water. Specifically, the specific surface area was 4110 cm². 2 Carbonated steelmaking slag powder containing 17% by mass of calcium carbonate was produced by contacting the steelmaking slag powder with an atmosphere containing 5% CO2 and the remainder being oxygen and nitrogen, while maintaining a state where 100 to 300 g of water was contained per 1 kg of steelmaking slag powder. This carbonated steelmaking slag powder was then mixed into the backfill material.

[0057] Next, backfill materials No. 1 to No. 9 were mixed with cohesive soil (simulated soil) as in-situ soil to create soil cement. 1 m of in-situ soil 3 The amount of solidifying agent added per unit was set at 500 kg or 300 kg. The simulated soil consisted of 100% kaolin clay, with a wet density of 1.518 g / cm³. 3 The dry density is 0.865 g / cm³. 3 The water content used was 75.5%.

[0058] The obtained soil cement was cured by sealing at a temperature of 20°C and a humidity of 90% or higher. The unconfined compressive strength at 28 days of age, the hexavalent chromium leaching value at 7 days of age, the hexavalent chromium leaching value at 28 days of age, and the needle penetration strength were measured for the cured soil cement. The flow time of the backfill material through a P funnel was also measured. These measurements were performed as described above. The results are shown in Table 1.

[0059] Table 1 also shows the CO2 emissions during the manufacturing of each backfill material. These CO2 emissions were calculated using the following formula (A), assuming that the CO2 intensity for blast furnace slag powder and carbonated steel slag powder were 40.21 kg-CO2 / t and -75.59 kg-CO2 / t, respectively. The CO2 intensity for blast furnace slag powder is based on the Japan Concrete Institute's Research Committee Report on Environmental Impact Assessment of Cement and Concrete, published in September 2024. Furthermore, since there is no unified definition for the CO2 intensity of carbonated steelmaking slag powder, assuming that the CO2 intensity of steelmaking slag fine powder is the same as that of blast furnace slag fine powder, and given that the amount of CO2 immobilized in the carbonated steelmaking slag powder used in this example was 115.7 kg per ton of steelmaking slag fine powder, the CO2 intensity of carbonated steelmaking slag powder was calculated as 40.21 - 115.7 = -75.59 kg. Table 2 shows the CO2 intensity of each raw material in the backfill.

[0060] CO2 emissions (kg / m 3 ) = {40.21 × amount of blast furnace slag fine powder added (kg / m³ 3 ) + (-75.59 × Carbonated steel slag powder blending amount (kg / m 3 )} / 1000 …(A)

[0061] [Table 1]

[0062] [Table 2]

[0063] As shown in Table 1, it can be seen that CO2 emissions decrease as the proportion of carbonated steelmaking slag powder increases. Furthermore, the unconfined compressive strength was 50 kN / m² in all cases. 2 The results are as follows, indicating that the desired strength has been achieved. Furthermore, ND in the needle penetration test means that the needle penetration strength 8 hours after mixing is 0.1 N / mm². 2 This indicates that the desired state has been achieved.

[0064] Based on the above results, it was found that the backfill material of the present invention can exhibit excellent performance.

Claims

1. A solidifying agent containing blast furnace slag fine powder and carbonated steelmaking slag powder, and water, The aforementioned carbonated steelmaking slag powder contains calcium carbonate as a backfill material.

2. The specific surface area of ​​the aforementioned blast furnace slag fine powder is 3000 cm². ２ / g or more, 10000cm ２ / g or less, The backfill material according to claim 1, satisfying the following formula (i). 30.0≦W / (GGBFS+CGGSS)×100≦300.0...(i) However, in formula (i), GGBFS is the mass of the blast furnace slag powder (kg), CGGSS is the mass of the carbonated steelmaking slag powder (kg), and W is the mass of the water (kg).

3. The backfill material according to claim 1, wherein the particle size of the carbonated steelmaking slag powder is 600 μm or less.

4. Furthermore, it contains admixtures (SP), The backfill material according to claim 1, wherein the admixture is a chemical admixture containing one or more of ligninsulfonic acid, ligninsulfonate, oxycarboxylic acid, oxycarboxylic acid salt, polycarboxylic acid, polycarboxylic acid salt, or silicophilic acid.

5. Furthermore, the backfill material according to claim 1, which satisfies the following formula (ii). 5.0≦CGGSS / (GGBFS+CGGSS)×100≦30.0...(ii)

6. Furthermore, the backfill material according to claim 1, wherein the solidifying agent contains steelmaking slag fine powder.

7. A method for producing backfill material, comprising the step of kneading at least the blast furnace slag fine powder, the carbonated steelmaking slag powder, and the water to produce the backfill material according to any one of claims 1 to 6.

8. At least the blast furnace slag fine powder, the carbonated steelmaking slag powder, and the water are mixed together at the construction site. A method for manufacturing backfill material, comprising manufacturing the backfill material according to any one of claims 1 to 6 at the aforementioned construction site.

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