Ground improvement material and method for manufacturing ground improvement material

Abstract

The present invention provides a ground improvement material and a method for manufacturing the ground improvement material that can reduce CO2 emissions. [Solution] A ground improvement material containing a solidifying agent and water, wherein the solidifying agent contains either cement or slaked lime, or both, blast furnace slag fine powder, and carbonated steelmaking slag powder, and the carbonated steelmaking slag powder contains calcium carbonate.

Description

[Technical Field]

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

[0002] With growing awareness of global environmental protection, low-carbon materials are in demand for construction materials. In conventional ground improvement methods, cement and water are mixed to create a ground improvement material, which is then mixed with in-situ soil to form soil cement, thereby stabilizing and improving the strength of the improved ground.

[0003] However, because cement, which is included in ground improvement materials, emits a large amount of carbon dioxide during its manufacture, there is a growing need to reduce the amount of cement used in ground improvement materials from the perspective of protecting the global environment. 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 a ground improvement material, nor does it address environmental protection or CO2 emission reduction as a ground improvement 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 ground improvement material and a method for manufacturing the ground improvement 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 ground improvement material containing a solidifying agent and water, The solidifying agent contains cement or slaked lime, or both, blast furnace slag fine powder, and carbonated steelmaking slag powder. The aforementioned carbonated steel slag powder is a ground improvement material containing calcium carbonate. [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 A ground improvement material as described in [1] that satisfies the following formula (i). 30.0≦W / (C+CH+GGBFS+CGGSS)×100≦300.0 ···(i) However, in formula (i), C is the mass (kg) of the cement, CH is the mass (kg) of the slaked lime, GGBFS is the mass (kg) of the fine powder of blast furnace slag, CGGSS is the mass (kg) of the carbonated steelmaking slag powder, and W is the mass (kg) of the water. [3] The ground improvement 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), The ground improvement 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 ground improvement material according to [1], further satisfying the following formula (ii). 5.0 ≦ CGGSS / (GGBFS + CGGSS) × 100 ≦ 30.0 ···(ii) However, in formula (ii), GGBFS is the mass (kg) of the fine powder of blast furnace slag, and CGGSS is the mass (kg) of the carbonated steelmaking slag powder. [6] The ground improvement material according to [1], wherein the cement is any one of ordinary Portland cement, ultra-early strength Portland cement, early strength Portland cement, medium heat Portland cement, and low heat Portland cement. [7] The ground improvement material according to [1], further comprising fine powder of steelmaking slag in the solidifying material. [8] A method for manufacturing a ground improvement material, comprising a step of kneading the solidifying material and the water to produce the ground improvement material according to any one of [1] to [7]. [9] Kneading the solidifying material and the water at a construction site, A method for manufacturing a ground improvement material, wherein the ground improvement material according to any one of [1] to [7] is produced at the construction site.

Advantages of the Invention

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

Embodiments for Carrying Out the Invention

[0011] Conventional ground improvement materials used are those containing cement as a solidifying agent and water. When performing ground improvement, the ground improvement material is injected into the ground and stirred and mixed with the in-situ soil to form soil cement, thereby achieving ground stabilization and strength improvement. 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 achieve low carbonization of the ground improvement material.

[0012] The inventors of the present invention have intensively studied a ground improvement material that enables reduction of the amount of cement used, suppression of elution of hexavalent chromium into the ground, and enables the soil cement formed by mixing the ground improvement material and the in-situ soil to have appropriate strength. As a result, they have found that ground improvement materials can be produced by using fine powder of blast furnace slag and carbonated steelmaking slag powder as solidifying agents.

[0013] The inventors of the present invention have further found that by using fine powder of blast furnace slag and carbonated steelmaking slag powder as solidifying agents, calcium in calcium carbonate contained in the carbonated steelmaking slag powder elutes as an alkaline component into water, and this alkaline component stimulates the fine powder of blast furnace slag, which is a glassy hydraulic material, so that a predetermined strength is exhibited in the soil cement. They have also found that elution of hexavalent chromium can be suppressed by the action of the fine powder of blast furnace slag. Hereinafter, a ground improvement material and a method for producing the same according to an embodiment of the present invention will be described.

[0014] The ground improvement material of the present embodiment is a ground improvement material containing a solidifying agent and water, the solidifying agent contains one or both of cement or slaked lime, fine powder of blast furnace slag, and carbonated steelmaking slag powder, and the carbonated steelmaking slag powder contains calcium carbonate.

[0015] The ground improvement material of the present embodiment can form soil cement by being mixed with in-situ soil. Hereinafter, the blending components of the ground improvement material will be described.

[0016] In the following explanation, cement or slaked lime, or both, along with blast furnace slag powder and carbonated steelmaking slag powder, may be collectively referred to as "solidifying agents."

[0017] The cement is preferably one of the following: ordinary Portland cement, ultra-high-early-strength Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, or low-heat Portland cement. Alternatively, blended cements such as blast furnace cement or fly ash cement may be used.

[0018] There are no particular restrictions on the amount of slaked lime used.

[0019] In this embodiment, quicklime may be used instead of cement or slaked lime.

[0020] Since cement and slaked lime emit large amounts of carbon dioxide during their manufacture, it is desirable that their use be limited in the ground improvement material of this embodiment. Specifically, the proportion of cement included in the solidifying agent is preferably in the range of 3 to 20% by mass of the total amount of solidifying agent. More preferably, it should be in the range of 4 to 17% by mass. Furthermore, the proportion of slaked lime contained in the solidifying agent is preferably in the range of 3 to 20% by mass relative to the total amount of the solidifying agent. More preferably, it is in the range of 4 to 17% by mass.

[0021] By mixing cement or slaked lime with the ground improvement material, alkaline components leach from the cement or slaked lime. The leached alkaline substances stimulate the blast furnace slag powder, a glassy hydraulic material, and accelerate its hardening. As a result, the ground improvement material can exhibit the required strength.

[0022] 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 incorporating blast furnace slag fine powder into ground improvement materials, the leaching of hexavalent chromium into the ground can be suppressed.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] When this type of carbonated steel slag powder is mixed into a ground improvement material, the calcium from the calcium carbonate contained in the carbonated steel 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.

[0030] 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.

[0031] The ground improvement 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 steelmaking slag fine powder exemplified as a raw material for carbonated steelmaking slag powder.

[0032] When incorporating steelmaking slag powder into a ground improvement material, it may be included by substituting a portion of the carbonated steelmaking slag powder with the steelmaking slag 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 powder. This supplies a larger amount of the alkaline components necessary for the hydration reaction of the blast furnace slag powder, making the hydration reaction of the blast furnace slag powder more active. As a result, soil cement with higher uniaxial compressive strength can be obtained.

[0033] 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.

[0034] The ratio of water to the amount of solidifying agent in the ground improvement material (total amount of cement or slaked lime, blast furnace slag fine powder, and carbonated steelmaking slag powder) preferably satisfies the following formula (i).

[0035] 30.0≦W / (C+CH+GGBFS+CGGSS)×100≦300.0 ···(i)

[0036] In formula (i), C is the mass of cement (kg), CH is the mass of slaked lime (kg), GGBFS is the mass of blast furnace slag powder (kg), CGGSS is the mass of carbonated steelmaking slag powder (kg), and W is the mass of water (kg). 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.

[0037] If W / (C+CH+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 sufficiently 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.

[0038] The ratio of carbonated steel slag powder to the total amount of blast furnace slag fine powder and carbonated steel slag powder in the ground improvement material is preferably such that it satisfies the following formula (ii).

[0039] 5.0≦CGGSS / (GGBFS+CGGSS)×100≦30.0 (ii)

[0040] If CGGSS / (GGBFS+CGGSS)×100 is 5.0 or higher, that is, if the ratio of carbonated steelmaking slag powder to the total amount of blast furnace slag fine powder and carbonated steelmaking slag powder is 5.0% or higher, then appropriate strength can be obtained due to the alkaline components leached from the carbonated steelmaking slag powder. If CGGSS / (GGBFS+CGGSS)×100 is 30.0 or lower, that is, if the ratio of carbonated steelmaking slag powder to the total amount of blast furnace slag fine powder and carbonated steelmaking slag powder is 30.0% or lower, the risk of hexavalent chromium contained in carbonated steelmaking 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.

[0041] 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.

[0042] Furthermore, the ground improvement material of this embodiment may contain admixtures. In this embodiment, the admixture may be formulated primarily for the purpose of improving the fluidity of the ground improvement 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.

[0043] 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.

[0044] The ratio of admixture to solidifying agent in a ground improvement material is preferably such that it satisfies the following formula (iii).

[0045] 0≦SP / (C+CH+GGBFS+CGGSS)×100≦5 …(iii)

[0046] 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.

[0047] SP / (C+CH+GGBFS+CGGSS)×100 may be 0, but it may be 0.1 or higher in order to obtain the desired effect of the admixture. That is, if the admixture ratio to the solidifying agent is 0.1% or higher, the effects of the admixture in reducing the hardening speed, improving fluidity, and reducing the amount of water can be fully exerted. On the other hand, if SP / (C+CH+GGBFS+CGGSS)×100 exceeds 5.0, that is, if the admixture ratio to the solidifying agent exceeds 5.0%, the effect of adding the admixture saturates. The range of SP / (C+CH+GGBFS+CGGSS)×100 may be 0.1 or higher, or 0.2.0 or higher and 4.0 or lower, or 0.5 or higher and 3.0 or lower, or 1.0 or higher and 2.0 or lower.

[0048] Furthermore, as an admixture, the following may be included in place of or together with the above-mentioned chemical admixture: AE agents, high-performance water-reducing agents, AE water-reducing agents, fluidizing agents, etc.

[0049] Furthermore, ground improvement materials can also contain additives. Examples of additives include pozzolanic materials, hydraulic alumina components, hydraulic additives such as ultrafast-setting cement or gypsum, and lime components such as light-calcined dolomite or hydroxide dolomite. By adding these, ground improvement materials can be suitably used even if the soil type of the ground is high-organic soil, sludge, or other special soils.

[0050] In this embodiment, it is desirable that the soil cement formed by the ground improvement material exhibits the following properties.

[0051] [Uniaxial compressive strength of soil cement at 28 days of age] There are no particular restrictions on the uniaxial compressive strength of soil cement. It is desirable to change the application of the ground improvement material depending on the uniaxial compressive strength of the soil cement. For example, when forming soil cement that is integrated with steel, such as in steel pipe soil cement piles, the soil cement should have a compressive strength of 1000 kN / m² at the point of adhesion to the ground. 2 Preferably, 2000 kN / m2 The above compressive strength is required. If it is lower than this strength, the appropriate strength cannot be maintained as a foundation structure.

[0052] Also, when the ground improvement material is used for temporary ground stabilization treatment after removing underground obstacles, etc., the strength of the soil cement is preferably kept low in order to re-drill the improvement location, and it is 10 kN / m 2 or more and 1000 kN / m 2 or less. If the strength is too high, it will become an obstacle to re-drilling in the subsequent process. On the other hand, if the strength is too weak, the ground cannot be effectively stabilized. Therefore, it is desirable to fall within the above low-strength range.

[0053] The uniaxial compressive strength is measured in accordance with JIS A 1216:2020 (Method for Uniaxial Compression Test of Soil).

[0054] [Hexavalent chromium elution value: 0.05 mg / L or less] The material contained in the ground improvement material may contain hexavalent chromium. In the present invention, the carbonated steel slag powder may contain hexavalent chromium. Hexavalent chromium is a specific harmful substance under the Soil Pollution Countermeasures Law, and it is necessary to suppress the elution into the ground to 0.05 mg / L or less as the reference value of the Environmental Notice No. 46 test.

[0055] [P funnel flow-down time (test standard: JSCE-F 521-2018)] The shorter the P funnel flow-down time of the ground improvement material, the better the workability, and when the ground improvement material is pumped into the ground, troubles such as clogging of the pumping pump are less likely to occur. Generally, if the P funnel flow-down time of the ground improvement material is 14 seconds or less, it is considered that such troubles are less likely to occur.

[0056] [Penetration test (test standard: JIS A 1147:2019 (Proctor 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:

[0057] As described above, the ground improvement material of this embodiment contains blast furnace slag powder and carbonated steelmaking slag powder as solidifying agents, along with cement or slaked lime. When the carbonated steelmaking slag powder, which contains 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, by mixing the ground improvement material, which uses less cement or slaked lime, with in-situ soil, soil cement can be formed, and CO2 emissions can be kept low.

[0058] Furthermore, since all the solidifying agents that contribute to the hardening of the soil cement are industrial by-products, the use of the ground improvement material of this embodiment can reduce the environmental burden. Furthermore, by controlling the amount of solidifying agent mixed in, the strength of the soil cement after hardening can be controlled, making it possible to obtain a ground improvement 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.

[0059] According to the ground improvement material of this embodiment, by using a chemical admixture whose admixture mainly consists of one or more of polycarboxylic acids, polycarboxylic acid salts, ligninsulfonic acid, ligninsulfonate salts, oxycarboxylic acids, oxycarboxylic acid salts, or silicogenic compounds, particularly effective performance can be achieved in terms of fluidity and strength.

[0060] According to the ground improvement material of this embodiment, by further incorporating steelmaking slag fine powder into the solidification material, 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 is provided.

[0061] According to the ground improvement material of this embodiment, since the cement is ordinary Portland cement or the like, the alkaline component is effectively supplied as a stimulant to the blast furnace slag fine powder, and good quality soil cement can be formed.

[0062] Furthermore, with the ground improvement material of this embodiment, by mixing the ground improvement material at the construction site, it is possible to mix a ground improvement material that is suitable for the detailed ground conditions at the site, which become clear during the construction phase, and to carry out construction using a ground improvement material that is more appropriate for the ground at the site.

[0063] The ground improvement 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 construct underground walls by integrating structural steel or steel sheet piles with soil cement, and construction methods that construct foundation structures by integrating steel pipes, steel sheet piles, concrete piles with soil cement. [Examples]

[0064] The present invention will be specifically described below with reference to examples. At an ambient temperature of 20°C, ground improvement materials No. 1 to No. 13 shown in Table 1 were manufactured by mixing a solidifying agent consisting of either ordinary Portland cement or slaked lime, blast furnace slag fine powder and carbonated steelmaking slag powder, water, and an admixture in predetermined proportions. The blast furnace slag fine powder had a surface area of ​​4110 cm². 2 I used the one that was / g.

[0065] 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. 2Carbonated 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.

[0066] Next, cohesive soil (simulated soil) was mixed with the ground improvement materials No. 1 to No. 13 as in-situ soil to create soil cement. 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%.

[0067] 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, the hexavalent chromium leaching value at 7 days, the hexavalent chromium leaching value at 28 days, and the needle penetration strength were measured for the cured soil cement. The flow time of the ground improvement material through a P funnel was also measured. These measurements were performed as described above. The results are shown in Table 1.

[0068] Table 1 also shows the CO2 emissions during the manufacturing of each ground improvement material. These CO2 emissions were calculated using the following formula (A), assuming that the CO2 intensity of ordinary Portland cement, slaked lime, blast furnace slag powder, and carbonated steel slag powder were as follows: ordinary Portland cement: 755.5 kg-CO2 / t, slaked lime: 755.5 kg-CO2 / t, blast furnace slag powder: 40.21 kg-CO2 / t, and carbonated steel slag powder: -75.59 kg-CO2 / t.

[0069] The CO2 intensity for cement is based on the cement variety inventory data list in "Overview of Cement LCI Data," published on April 1, 2024, by the Japan Cement Association. Since there is no unified definition for the CO2 intensity of slaked lime, it was treated as the same as cement. 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, it was assumed that the CO2 intensity of steelmaking slag powder is the same as that of blast furnace slag powder. As the amount of CO2 immobilized in the carbonated steelmaking slag powder used in this example was 115.7 kg per ton of steelmaking slag powder, the CO2 intensity for carbonated steelmaking slag powder was calculated as 40.21 - 115.7 = -75.59 kg. Table 2 shows the CO2 intensity of each raw material for the ground improvement materials.

[0070] CO2 emissions (kg / m 3 ) = {755.5 × cement mix ratio (kg / m 3 )+755.5×slaked lime content (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)

[0071] [Table 1]

[0072] [Table 2]

[0073] 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 1000 kN / m² in all cases. 2 The above results show that the desired strength has been achieved. Furthermore, ND in the needle penetration test indicates a needle penetration strength of 0.1 N / mm² 8 hours after mixing. 2This indicates that the desired state has been achieved.

[0074] Based on the above results, it was found that the ground improvement material of the present invention can exhibit excellent performance.

Claims

1. It is a ground improvement material containing a solidifying agent and water. The solidifying agent contains cement or slaked lime, or both, blast furnace slag fine powder, and carbonated steelmaking slag powder. The aforementioned carbonated steel slag powder is a ground improvement material containing calcium carbonate.

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, A ground improvement material according to claim 1, satisfying the following formula (i). 30.0≦W / (C+CH+GGBFS+CGGSS)×100≦300.0...(i) However, in formula (i), C is the mass of the cement (kg), CH is the mass of the slaked lime (kg), 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 ground improvement material according to claim 1, wherein the particle size of the carbonated steel slag powder is 600 μm or less.

4. Furthermore, it contains admixtures (SP), The ground improvement 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 ground improvement material according to claim 1, which satisfies the following formula (ii). 5.0≦CGGSS / (GGBFS+CGGSS)×100≦30.0...(ii) However, in formula (ii), GGBFS is the mass (kg) of the blast furnace slag fine powder, and CGGSS is the mass (kg) of the carbonated steelmaking slag powder.

6. The ground improvement material according to claim 1, wherein the cement is any of ordinary Portland cement, ultra-rapid strength Portland cement, rapid strength Portland cement, moderate heat Portland cement, or low heat Portland cement.

7. The ground improvement material according to claim 1, wherein the solidifying material contains steelmaking slag fine powder.

8. A method for manufacturing a ground improvement material, comprising the step of kneading the solidifying agent and the water to manufacture the ground improvement material according to any one of claims 1 to 7.

9. The solidifying agent and the water are mixed together at the construction site. A method for manufacturing a ground improvement material, comprising manufacturing the ground improvement material according to any one of claims 1 to 7 at the aforementioned construction site.

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