Ground improvement material and method for manufacturing ground improvement material

Abstract

This invention provides a ground improvement material that can reduce CO2 emissions and a method for manufacturing the same. [Solution] A ground improvement material comprising a solidifying agent containing blast furnace slag fine powder and steelmaking slag fine powder, and water, wherein the steelmaking slag fine powder contains at least one or more of the following: free lime, calcium hydroxide, calcium ferrite, calcium silicate, and dicalcium silicate.

Description

[Technical Field]

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

[0002] The increasing density of buildings due to population concentration in urban areas, and the weight of disaster prevention facilities themselves due to the enhancement of disaster prevention facilities as part of national resilience measures, are leading to a growing demand for higher bearing capacity in the steel pipe piles and concrete piles that constitute the foundation structures of these buildings and facilities.

[0003] By the way, when driving steel pipe piles or concrete piles into soft ground, ground improvement is necessary beforehand. It is common practice to use ground improvement materials to stabilize and strengthen soft ground.

[0004] Cement grout is sometimes used as a ground improvement material. When cement grout is injected into the ground, it is mixed with the existing soil to form soil cement, which is said to be able to stably maintain the improved ground.

[0005] However, because cement production generates a large amount of carbon dioxide, there is a growing need to reduce the amount of cement used in cement slurry 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.

[0006] 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.

[0007] 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.

[0008] 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]

[0009] [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]

[0010] This invention has been made in view of the above circumstances, and aims to provide a ground improvement material that can reduce CO2 emissions and a method for manufacturing the same. [Means for solving the problem]

[0011] To solve the above problems, the present invention adopts the following configuration. (1) A ground improvement material comprising a solidifying material containing blast furnace slag fine powder and steelmaking slag fine powder, and water. The ground improvement material in which the steelmaking slag fine powder contains at least one or two or more of free lime, calcium hydroxide, calcium ferrite, calcium silicate, and dicalcium silicate. (2) The specific surface area of the blast furnace slag fine powder is 3000 cm 2 / g or more and 10000 cm 2 / g or less, The specific surface area of the steelmaking slag fine powder is 3000 cm 2 / g or more and 10000 cm 2 / g or less, The ground improvement material according to (1), which satisfies the following formula (i). 30.0 ≦ W / (GGBFS + GGSS)×100 ≦ 300.0 ···(i) However, in formula (i), GGBFS is the mass (kg) of the blast furnace slag fine powder, GGSS is the mass (kg) of the steelmaking slag fine powder, and W is the mass (kg) of the water. (3) Furthermore, it contains a admixture, The ground improvement material according to (1), in which the admixture is a chemical admixture containing one or two or more of lignin sulfonic acid, lignin sulfonate, oxycarboxylic acid, oxycarboxylate, polycarboxylic acid, polycarboxylate, or silicofluoride. (4)[[ID=3I]] The ground improvement material according to (1), which further satisfies the following formula (ii). 5.0 ≦ GGSS / (GGBFS + GGSS)×100 ≦ 30.0 ···(ii) (5) A method for manufacturing a ground improvement material, including a step of kneading at least the steelmaking slag fine powder, the blast furnace slag fine powder, and the water to manufacture the ground improvement material according to any one of (1) to (4). (6) At least the blast furnace slag fine powder, the steelmaking slag fine powder, and water are kneaded at the construction site, A method for manufacturing a ground improvement material, which manufactures the ground improvement material according to any one of (1) to (4) at the construction site.

Advantages of the Invention

[0012] 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.

Brief Description of the Drawings

[0013] [Figure 1] A diagram showing the evaluation results of the ground improvement material according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0014] Conventional ground improvement materials use those containing cement as a solidifying material and water. When performing ground improvement, the ground improvement material is stirred and mixed with in-situ soil to form soil cement, thereby stabilizing the improved ground and improving its strength. However, since cement emits 755.5 kg of CO2 per ton during its production, in order to reduce the carbon footprint of the ground improvement material, it was necessary to reduce the amount of cement used.

[0015] The present inventors earnestly studied to minimize the cement content in the ground improvement material, and found that by using fine powder of blast furnace slag and fine powder of steelmaking slag as solidifying materials, the CO2 emissions can be reduced, and furthermore, the elution of hexavalent chromium into the ground can be suppressed.

[0016] The present inventors further found that by using fine powder of blast furnace slag and fine powder of steelmaking slag as solidifying materials, calcium compounds contained in the fine powder of steelmaking slag elute as an alkali and stimulate the fine powder of blast furnace slag, which is a glassy hydraulic material, so that a predetermined strength is exhibited as a ground improvement material. It was also found that the elution of hexavalent chromium can be suppressed by the action of the fine powder of blast furnace slag. Hereinafter, the ground improvement material according to an embodiment of the present invention and its manufacturing method will be described.

[0017] The ground improvement material of this embodiment is a ground improvement material comprising a solidifying agent containing blast furnace slag fine powder and steelmaking slag fine powder, and water, wherein the steelmaking slag fine powder contains at least one or more of the following: free lime, calcium hydroxide, calcium ferrite, calcium silicate, and dicalcium silicate. The ground improvement material of this embodiment can form soil cement by being mixed with in-situ soil. In the following explanation, blast furnace slag powder and steelmaking slag powder may be collectively referred to as "solidifying agent."

[0018] 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.

[0019] In this embodiment, blast furnace slag fine powder is used, with a specific surface area of ​​3000 cm². 2 / g or more, 10000cm 3 It is preferable that the specific surface area is in the range of / g or less. If the specific surface area is below the upper limit, the hardening reaction of the soil cement will not proceed too rapidly, the viscosity after mixing the materials will be suitably controlled, and favorable fluidity for construction will be exhibited. If the specific surface area is above the lower limit, the hardening reaction of the soil cement will proceed at an appropriate rate, and the hardening time to reach the desired hardness will not be prolonged.

[0020] Steelmaking slag fine powder can be exemplified by the pulverization of 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] The steelmaking slag fine powder contains one or more substances among free lime, calcium hydroxide, calcium ferrite, calcium silicate, and dicalcium silicate. By blending such steelmaking slag fine powder into a ground improvement material, calcium contained in the steelmaking slag fine powder can dissolve into water, stimulate the glassy substance of the blast furnace slag fine powder, and enable the blast furnace slag fine powder to exhibit hydraulicity. As a result, a soil cement suitable for a predetermined use and extremely excellent in environmental performance can be formed.

[0022] A part of the steelmaking slag fine powder may be replaced with carbonated steelmaking slag powder. The carbonated steelmaking slag powder refers to a material in which a part or all of the calcium composition in the steelmaking slag fine powder reacts with CO2 to immobilize CO2. It is presumed that CO2 is immobilized in the state of calcium carbonate. Also, the CO2 used for the production of the carbonated steelmaking slag powder is preferably the CO2 generated from each process of steelmaking in the steelworks.

[0023] In this embodiment, as the steelmaking slag fine powder, the specific surface area is preferably in the range of 3000 cm 2 / g or more and 10000 cm 3 / g or less. If the specific surface area is below the upper limit value, the curing reaction of the soil cement does not proceed rapidly, and the material exhibits appropriate fluidity for construction without showing flash setting properties. If the specific surface area is above the lower limit value, the curing reaction of the soil cement proceeds moderately, and the curing time until reaching the desired hardness does not become long.

[0024] The mixing ratio of water to the amount of the solidifying material (total amount of blast furnace slag fine powder and steelmaking slag fine powder) in the ground improvement material preferably satisfies the following formula (i).

[0025] 30.0≦W / (GGBFS+GGSS)×100≦300.0 ···(i)

[0026] In equation (i), GGBFS is the mass (kg) of blast furnace slag powder, GGSS is the mass (kg) of steelmaking slag powder, and W is the mass (kg) of water.

[0027] When W / (GGBFS+GGSS)×100 is 30 or more, that is, when the water content relative to the total amount of solidifying agent is 30% or more, the moisture content is appropriate, and by maintaining appropriate fluidity during soil cement production, sufficient mixing with in-situ soil is easily achieved. When W / (GGBFS+GGSS)×100 is 300 or less, that is, when the water content relative to the total amount of solidifying agent is 300% or less, the moisture content is appropriate, and the material can maintain appropriate strength as a structural material.

[0028] The proportion of steelmaking slag fine powder in the solidification agent of the ground improvement material is preferably such that it satisfies the following formula (ii).

[0029] 5.0≦GGSS / (GGBFS+GGSS)×100≦30.0 (ii)

[0030] If GGSS / (GGBFS+GGSS)×100 is 5 or greater, that is, if the proportion of steelmaking slag powder in the solidification material is 5% or greater, appropriate strength can be obtained due to the alkaline substances leached from the steelmaking slag powder. If GGSS / (GGBFS+GGSS)×100 is 30 or less, that is, if the proportion of steelmaking slag powder in the solidification material is 30% or less, the risk of hexavalent chromium contained in the steelmaking slag powder leaching into the ground can be reduced. Note that GGSS / (GGBFS+GGSS)×100 may be between 10 and 25, or between 15 and 20.

[0031] 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 fluidity. The admixture may also be formulated for the purpose of reducing the hardening rate of the soil cement. Moreover, the admixture may be formulated for the purpose of reducing the amount of water while maintaining fluidity.

[0032] The admixture is more preferably a chemical admixture containing one or more of 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 is reduced, and it can exhibit favorable fluidity for construction.

[0033] The mixing ratio of the admixture to the amount of solidifying agent (total amount of blast furnace slag fine powder and steelmaking slag fine powder) in the ground improvement material preferably satisfies the following formula (iii).

[0034] 0≦SP / (GGBFS+GGSS)×100≦5 …(iii)

[0035] In equation (iii), SP is the mass (kg) of the admixture.

[0036] SP / (GGBFS+GGSS)×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 is added at a ratio of 0.1% or more to the total amount of blast furnace slag powder and steelmaking slag powder, 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 / (GGBFS+GGSS)×100 exceeds 5, that is, if the admixture is added at a ratio of 5% or more to the total amount of blast furnace slag powder and steelmaking slag powder, the effect of adding the admixture becomes saturated. The range of SP / (GGBFS+GGSS)×100 may be 0.1 or more, or 0.2 or more and 4 or less, or 0.5 or more and 3 or less, or 1 or more and 2 or less.

[0037] Furthermore, as an admixture, the above-mentioned chemical admixture may be replaced with, or together with, an AE agent, a high-performance water-reducing agent, an AE water-reducing agent, a fluidizing agent, etc.

[0038] 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 quicklime, slaked lime, lightly calcined dolomite, or dolomite hydroxide. 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.

[0039] In this embodiment, it is desirable that the soil cement formed by the ground improvement material exhibits the following properties.

[0040] [Uniaxial compressive strength of soil cement at 28 days of age] It is desirable to vary the application of the ground improvement material depending on its compressive strength. For example, when ground improvement materials are used in a composite structure integrated with steel and concrete as part of a foundation structure such as a steel pipe soil-cement pile, the soil-cement ground improvement material must have a compressive strength of 1000 kN / m² at the point of adhesion to the ground. 2 ~2000kN / m 2 The above compressive strength is desirable. Furthermore, the strength of ground improvement materials used for temporary ground stabilization after the removal of underground obstacles should be kept low because drilling will be required again at the improvement site, ideally around 1000 kN / m 2 The following is desirable: If the strength is too high, it will hinder subsequent re-drilling processes; on the other hand, if the strength is too low, the ground cannot be effectively stabilized. Therefore, it is desirable for the strength to fall within the low-strength range described above.

[0041] [Hexavalent chromium elution level: 0.05 mg / L or less] The materials used in ground improvement materials may contain hexavalent chromium. In the present invention, hexavalent chromium may be present in the steelmaking slag fine 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.

[0042] [P funnel flow time (Test standard: JSCE-F 521-2018)] The shorter the flow time of the cement milk in the P funnel, the better the workability, and the less likely problems are to occur, such as clogging of the pump when the ground improvement material is pumped into the ground. Generally, it is thought that such problems are less likely to occur if the flow time of the P funnel is 14 seconds or less.

[0043] [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:

[0044] As described above, the ground improvement material of this embodiment contains blast furnace slag fine powder and steelmaking slag fine powder. Therefore, CO2 emissions can be kept low. In addition, 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, the strength of the soil cement after hardening can be controlled by adjusting the amount of solidifying agent, making it possible to obtain a ground improvement material that exhibits the necessary performance depending on the application. Moreover, from the perspective of environmental pollution risk, the inclusion of blast furnace slag fine powder can suppress the elution of hexavalent chromium, which is an environmentally harmful substance.

[0045] 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.

[0046] 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 soil conditions of the site that become clear during the construction phase, and construction can be carried out using a ground improvement material that is more appropriate for the ground at the site.

[0047] 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 stabilizing the ground in shallow, intermediate, and deep layers; underground wall construction methods that construct underground walls by integrating structural steel, steel sheet piles, etc., with soil cement; and construction methods that construct foundation structures by integrating steel pipes, steel sheet piles, concrete piles, etc., with soil cement. [Examples]

[0048] 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. 9 shown in Table 1 were manufactured by mixing a solidifying agent consisting of blast furnace slag powder and steelmaking slag powder with water and an admixture in predetermined proportions. The blast furnace slag powder had a surface area of ​​4110 cm². 2 The sample used was one containing 1g of steelmaking slag. The steelmaking slag fine powder had a surface area of ​​4110 cm². 2 I used the one that was / g. Next, cohesive soil (simulated soil) was mixed with the ground improvement materials No. 1 to No. 9 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 moisture content was set to 75.5%.

[0049] The obtained soil cement was cured by sealing at a temperature of 20°C and a humidity of 90% or higher. The uniaxial compressive strength at 28 days of age, the hexavalent chromium leaching value at 7 days of age, and the hexavalent chromium leaching value at 28 days of age were measured for the cured soil cement. These measurements were performed as described above. The results are shown in Table 1.

[0050] Table 1 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 for cement and blast furnace slag powder was 40.21 kg-CO2 / t and 40.21 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. Since there is no unified definition for the CO2 intensity of steelmaking slag powder, the same value as for blast furnace slag powder was used. Table 2 shows the CO2 intensity for each raw material of the ground improvement material.

[0051] CO2 emissions (kg / m 3 ) = {40.21 × amount of steelmaking slag fine powder added (kg / m³ 3 ) + 40.21 × amount of blast furnace slag fine powder added (kg / m³ 3 )} / 1000 …(A)

[0052] [Table 1]

[0053] [Table 2]

[0054] As shown in Table 1, in all examples incorporating blast furnace slag powder and steelmaking slag powder, favorable values ​​were observed for P funnel flow time, hexavalent chromium leaching amount, and needle penetration test values. Regarding compressive strength, Figure 1 shows the relationship between the uniaxial compressive strength value and W / P at 28 days of age. Solidifying agent addition amount: 500 kg / m 3 The results show that the uniaxial compressive strength increases linearly as the W / P ratio decreases, suggesting that once the amount of solidifying agent added exceeds a certain level, the material exhibits properties where the strength improves as the amount of solidifying agent increases. (Solidifying agent added: 300 kg / m³) 3The results also show that the unconfined compressive strength increases linearly as the W / P ratio decreases. Thus, similar to general soil cement using cement, the unconfined compressive strength tends to increase with decreasing W / P, suggesting that the blast furnace slag powder is stimulated by the alkaline substances supplied from the steelmaking slag powder, resulting in the material exhibiting hardening properties. Furthermore, the unconfined compressive strength to be exhibited can be designed based on the W / P ratio. It is also possible to achieve higher strength by increasing the amount of solidifying agent added. In terms of strength, as shown in the test results, it is suitable for structural applications where adhesion to the ground is expected, and for temporary backfill materials where low strength is required. By increasing the amount of solidifying agent added, it is considered applicable to areas requiring higher strength. In this embodiment, soil cement was prepared for cohesive soil, which is relatively difficult to strengthen; it is thought that higher strength would be exhibited in sandy soil. Also, the ground improvement material 1m 3 CO2 emissions per unit area are 50 kg / m³ 3 The following findings indicate that replacing cement with blast furnace slag powder and steelmaking slag powder can reduce CO2 emissions from the production of ground improvement materials, thus contributing to the preservation of the global environment.

[0055] Based on the above results, it was found that the ground improvement material of the present invention can exhibit excellent performance.

Claims

1. A ground improvement material containing a solidifying agent containing blast furnace slag fine powder and steelmaking slag fine powder, and water. The aforementioned steelmaking slag fine powder contains at least one or more of the following: free lime, calcium hydroxide, calcium ferrite, calcium silicate, and dicalcium silicate.

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 specific surface area of ​​the aforementioned steelmaking 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 / (GGBFS+GGSS)×100≦300.0...(i) However, in formula (i), GGBFS is the mass of the blast furnace slag powder (kg), GGSS is the mass of the steelmaking slag powder (kg), and W is the mass of the water (kg).

3. Furthermore, it contains admixtures, 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.

4. Furthermore, the ground improvement material according to claim 1, which satisfies the following formula (ii). 5.0≦GGSS / (GGBFS+GGSS)×100≦30.0...(ii)

5. A method for producing a ground improvement material, comprising the step of kneading at least the steelmaking slag fine powder, the blast furnace slag fine powder, and the water to produce the ground improvement material according to any one of claims 1 to 4.

6. At least the blast furnace slag powder, the steelmaking slag powder, and water are mixed together at the construction site. A method for manufacturing a ground improvement material, comprising manufacturing the ground improvement material described in any one of claims 1 to 4 at the aforementioned construction site.

Images