Soil improvement material, soil improvement method, and soil improvement soil

Abstract

To provide a soil improvement material which suppresses the emission of carbon dioxide.SOLUTION: The soil improving material comprises blast furnace slag fine powder, slaked lime and anhydrous gypsum. The mass ratio of the blast furnace slag fine powder is 55-60%, the mass ratio of the slaked lime to the blast furnace slag fine powder is 33-60%, the mass ratio of the anhydrous gypsum to the blast furnace slag fine powder is 17-45%, and the total of the mass ratios of the blast furnace slag fine powder, the slaked lime and the anhydrous gypsum is 100% (improved soil 1-4 and 1-5).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground improvement material, a ground improvement method, and improved soil. [Background technology]

[0002] Cement-based ground improvement materials are commonly used for ground improvement. Patent Document 1 describes a ground improvement material containing ordinary Portland cement, anhydrous gypsum, and ground granulated blast furnace slag. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-134925 Summary of the Invention [Problem to be solved by the invention]

[0004] Since cement emits carbon dioxide during its production, there is a demand for ground improvement materials that reduce carbon dioxide emissions. [Means for solving the problem]

[0005] The ground improvement material of the present invention is composed of ground granulated blast furnace slag, slaked lime, and anhydrous gypsum. The mass ratio of the ground granulated blast furnace slag is 55% to 60%, the mass ratio of slaked lime to the ground granulated blast furnace slag is 33% to 60%, the mass ratio of anhydrous gypsum to the ground granulated blast furnace slag is 17% to 45%, and the total mass ratio of the ground granulated blast furnace slag, slaked lime, and anhydrous gypsum is 100%. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a soil improvement material that reduces carbon dioxide emissions. [Brief explanation of the drawings]

[0007] [Figure 1]1 is a graph showing the uniaxial compressive strength of Example 1. [Figure 2] 1 is a graph showing the amount of hexavalent chromium eluted in Example 1. [Figure 3] 1 is a graph showing the uniaxial compressive strength of Example 2. [Figure 4] 1 is a graph showing the amount of hexavalent chromium eluted in Example 2. [Figure 5] 1 is a graph showing the uniaxial compressive strength of Example 3. [Figure 6] 1 is a graph showing the amount of hexavalent chromium eluted in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be explained below using examples. Table 1 provides an overview of the ground improvement materials and soils S1 to S3 used in Examples 1 to 3, and Figure 2 shows the specifications of soils S1 to S3. Volcanic ash clayey soils (soils S1 and S2) and clayey soil (soil S3) with different water contents were used as soils S1 to S3. Ground improvement material A or B was added to these soils S1 to S3 and solidified to create the improved soils of Examples 1 to 3, respectively. The soil classification is based on the Geotechnical Society's JGS-0051-2020 "Engineering Classification System for Soil Materials."

[0009] [Table 1]

[0010] [Table 2]

[0011] Example 1 Table 3 shows the composition of the improved soil in Example 1, as well as the measurement results of the unconfined compressive strength and hexavalent chromium elution amount. Improved soils 1-1 to 1-7 were prepared by adding only a non-cement-based solidification material (ground improvement material A) to soil S1 as the ground improvement material. Improved soil 1-8 was prepared by adding only a cement-based solidification material (ground improvement material B) to soil S1 as the ground improvement material. Ground granulated blast furnace slag BF, which forms the skeleton of the solidified body, was added to improved soils 1-1 to 1-7. Because ground granulated blast furnace slag BF exhibits hydraulic properties in a highly alkaline environment, slaked lime CH, which has the effect of raising the pH, was added to improved soils 1-2 to 1-7. Slaked lime CH also has the effect of reacting with clay minerals in the soil to cause a pozzolanic reaction. Anhydrous gypsum GP forms ettrinoid together with slaked lime CH. For this reason, anhydrous gypsum GP was added to improved soils 1-3 to 1-7. Therefore, improved soil 1-1 contained only ground granulated blast furnace slag BF, improved soil 1-2 contained ground granulated blast furnace slag BF and hydrated lime CH, and improved soils 1-3 to 1-7 contained ground granulated blast furnace slag BF, hydrated lime CH, and anhydrous gypsum GP. The mixing ratios of ground granulated blast furnace slag BF, hydrated lime CH, and anhydrous gypsum GP were changed for improved soils 1-3 to 1-7.

[0012] Each of these improved soils 1-1 to 1-8 contains multiple samples containing different amounts (addition amounts) of ground improvement material A or B. The unconfined compressive strength of improved soils 1-1 to 1-8 at 7 days was measured according to JIS A 1216:2020 "Unconfined Compression Test Method for Soil." Additionally, the amount of hexavalent chromium leaching from improved soils 1-1 to 1-8 at 7 days was measured according to Ministry of the Environment Notification No. 46. The hexavalent chromium concentration was quantified according to JIS K0102 65.2.1 "Diphenylcarbazide Absorptiometry Method."

[0013] [Table 3]

[0014] Figure 1 shows the unconfined compressive strength of Example 1 at 7 days of age, and Figure 2 shows the amount of hexavalent chromium eluted at 7 days of age for Example 1. Improved soils 1-4 and 1-5 exhibited higher unconfined compressive strength than improved soil 1-8, which used a cement-based solidification material as ground improvement material B. Improved soils 1-1 to 1-3 and 1-6 to 1-7 exhibited lower unconfined compressive strength than improved soil 1-8. Improved soil 1-4 contains ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP in a mass ratio of 6:3:1, and improved soil 1-5 contains ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP in a mass ratio of 6:2:2. The amount of hexavalent chromium leaching was measured for improved soils 1-4, 1-6, and 1-8. The amount of hexavalent chromium leaching from improved soils 1-4 and 1-6 was virtually zero, while that from improved soil 1-8 was significantly higher than the guideline value of 0.05 mg / L (Appendix to Environment Agency Notification No. 46). This is thought to be because the hexavalent chromium content in cement is much higher than the hexavalent chromium content in ground granulated blast furnace slag BF, hydrated lime CH, and anhydrous gypsum GP. Therefore, the amount of hexavalent chromium leaching from improved soils 1-1 to 1-3, 1-5, and 1-7 is also thought to be virtually zero.

[0015] Example 2 Table 4 shows the composition of the improved soil in Example 2, as well as the measurement results of the unconfined compressive strength and hexavalent chromium elution amount. Improved soils 2-1 to 2-7 were prepared by adding only a non-cement-based solidification material (ground improvement material A) to soil S2 as the ground improvement material. Improved soil 2-8 was prepared by adding only a cement-based solidification material (ground improvement material B) to soil S2 as the ground improvement material. Improved soil 2-1 contained only ground granulated blast furnace slag BF and slaked lime CH, while improved soils 2-2 to 2-7 contained ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP. The blending ratios of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP were changed in improved soils 2-2 and 2-7. Ground improvement material A in improved soil 2-2 contained ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP in a ratio of 7:2:1. Ground improvement material A for improved soil 2-3 contains ground granulated blast furnace slag (BF), slaked lime CH, and anhydrous gypsum GP in a ratio of 65:15:20. Ground improvement material A for improved soil 2-4 has the same composition as ground improvement material A for improved soil 1-4 in Example 1, containing ground granulated blast furnace slag (BF), slaked lime CH, and anhydrous gypsum GP in a ratio of 6:3:1. Ground improvement material A for improved soil 2-5 has the same composition as ground improvement material A for improved soil 1-5 in Example 1, containing ground granulated blast furnace slag (BF), slaked lime CH, and anhydrous gypsum GP in a ratio of 6:2:2. Ground improvement material A for improved soil 2-6 contains ground granulated blast furnace slag (BF), slaked lime CH, and anhydrous gypsum GP in a ratio of 55:20:25. The soil improvement material A of improved soil 2-7 contains ground granulated blast furnace slag BF, hydrated lime CH, and anhydrous gypsum GP in a ratio of 55:33:12. The unconfined compressive strength and the amount of hexavalent chromium elution were measured using the same method as in Example 1.

[0016] [Table 4]

[0017] Figure 3 shows the unconfined compressive strength of Example 2, and Figure 4 shows the amount of hexavalent chromium eluted in Example 2. Improved soil 2-4 and improved soil 2-5 were treated with an additive amount of 150 kg / m 3 In the range up to 200 kg / m, the unconfined compressive strength was equivalent to that of improved soil 2-8 using soil improvement material B. 3In the case of Improved Soil 2-1, the unconfined compressive strength was at a level that would not pose a problem in practical use. In contrast, even when the amount added was increased, almost no increase in unconfined compressive strength was observed. This indicates that soil improvement material A in Improved Soils 2-4 and 2-5 (Improved Soils 1-4 and 1-5 in Example 1) is also effective for soil S2. Improved Soils 2-6 and 2-7 also exhibited unconfined compressive strength equivalent to that of Improved Soil 2-8. The amount of hexavalent chromium eluted from Improved Soils 2-4 and 2-5 was virtually zero. The amount of hexavalent chromium eluted from Improved Soil 2-8 was reduced compared to Improved Soil 1-8 in Example 1, but still exceeded the target value of 0.05 mg / L. The reasons for these results are thought to be the same as those in Example 1.

[0018] Example 3 Table 5 shows the composition of the improved soil in Example 3, as well as the measurement results of the unconfined compressive strength and hexavalent chromium elution amount. Improved soil 3-1 was prepared by adding only a non-cement-based solidification material (ground improvement material A) to soil S3 as the ground improvement material. Improved soil 3-2 was prepared by adding only a cement-based solidification material (ground improvement material B) to soil S3 as the ground improvement material. Ground improvement material A in improved soil 3-1 has the same composition as ground improvement material A in improved soil 1-4 in Example 1, containing ground granulated blast furnace slag BF, hydrated lime CH, and anhydrous gypsum GP in a ratio of 6:3:1. The unconfined compressive strength and hexavalent chromium elution amount were measured using the same method as in Example 1.

[0019] [Table 5]

[0020] Figure 5 shows the unconfined compressive strength of Example 3, and Figure 6 shows the amount of hexavalent chromium leaching in Example 3. Improved soil 3-1 exhibited the same unconfined compressive strength as improved soil 3-2, which used ground improvement material B. This indicates that ground improvement material A was effective for improved soil 3-1 (improved soil 1-4 in Example 1) even for soil S3. The amount of hexavalent chromium leaching was essentially zero for improved soil 3-1. Improved soil 3-2 was below the target value of 0.05 mg / L, but this is thought to be due to the smaller leaching effect of the clayey soil (soil S3) compared to the volcanic ash clayey soils (soils S1 and S2), and no significant difference was observed in the amount of hexavalent chromium leaching.

[0021] From the above-described Examples 1 to 3, the ground improvement material is composed of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP, and it is preferable that the mass ratio of ground granulated blast furnace slag BF is 55% to 60%, the mass ratio of slaked lime CH to ground granulated blast furnace slag BF is 33% to 60%, the mass ratio of anhydrous gypsum GP to ground granulated blast furnace slag BF is 17% to 45%, and the total mass ratio of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP is 100%. The ground improvement material of the examples does not contain any components other than ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP, but may contain trace amounts (for example, 5% or less by mass) of additives. In this case, the mass ratio of ground granulated blast furnace slag BF is preferably 55% to 60%, the mass ratio of slaked lime CH to ground granulated blast furnace slag BF is 33% to 60%, the mass ratio of anhydrous gypsum GP to ground granulated blast furnace slag BF is 17% to 45%, and the total mass ratio of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP to the ground improvement material is preferably 95% to less than 100%. The additives are not particularly limited as long as they do not cause a decrease in strength or an increase in the amount of hexavalent chromium leaching. While the examples were focused on volcanic ash clayey soil (soils S1 and S2) and clayey soil (soil S3), the ground improvement material with the above composition is also effective for sandy soil.

[0022] Alternatively, when the ground improvement material is composed of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP, the mass ratio of the ground granulated blast furnace slag BF may be 55% to 60%, the mass ratio of slaked lime CH may be 20% to 33%, the mass ratio of anhydrous gypsum GP may be 10% to 25%, and the total mass ratio of the ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP may be 100%. Also, when the ground improvement material contains a powder composed of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP, and trace amounts of additives other than the powder, the mass ratio of the ground granulated blast furnace slag BF to the powder may be 55% to 60%, the mass ratio of slaked lime CH to the powder may be 33% to 60%, the mass ratio of anhydrous gypsum GP to the powder may be 17% to 45%, and the mass ratio of the powder to the ground improvement material may be 95% to less than 100%.

[0023] Ground improvement materials consisting of granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP, as well as ground improvement materials containing granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP as the main components, can be stored in a mixed state for long periods. Gypsum dihydrate and hemihydrate contain water molecules, and gypsum dihydrate in particular is often stored in a hydrous state, i.e., with excess water on the surface, which may cause solidification when mixed with granulated blast furnace slag BF and slaked lime CH. Therefore, in the case of ground improvement materials containing gypsum dihydrate or gypsum hemihydrate, multiple materials must usually be mixed on-site, which can be difficult to work with and control the mixing ratio. In contrast, anhydrous gypsum GP does not contain water, so there is little risk of solidification. The ground improvement material of the present invention can be mixed in advance in a factory or other facility in a predetermined ratio, making it easy to work with and to control the mixing ratio.

[0024] The present invention is not limited to soil improvement materials. The scope of the present invention also includes a soil improvement method that includes injecting a soil improvement material into the ground, and soil improved with soil containing the soil improvement material. In these inventions, the soil improvement material is composed of ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP, with the mass ratio of the ground granulated blast furnace slag BF being 55% to 60%, the mass ratio of the slaked lime CH to the ground granulated blast furnace slag BF being 33% to 60%, the mass ratio of the anhydrous gypsum GP to the ground granulated blast furnace slag BF being 17% to 45%, and the total mass ratio of the ground granulated blast furnace slag BF, slaked lime CH, and anhydrous gypsum GP being 100%. When the ground improvement material contains blast furnace slag powder BF, slaked lime CH, and anhydrous gypsum GP as the main components, the mass ratio of the blast furnace slag powder BF is 55% or more and 60% or less, the mass ratio of slaked lime CH to the blast furnace slag powder BF is 33% or more and 60% or less, the mass ratio of anhydrous gypsum GP to the blast furnace slag powder BF is 17% or more and 45% or less, and the total mass ratio of the blast furnace slag powder BF, slaked lime CH, and anhydrous gypsum GP to the ground improvement material is 95% or more and less than 100%. [Explanation of symbols]

[0025] BF Ground granulated blast furnace slag CH slaked lime GP anhydrite S1, S2 Volcanic ash clay soil S3 clayey soil

Claims

1. A ground improvement material comprising ground granulated blast furnace slag, slaked lime, and anhydrous gypsum, wherein the mass ratio of the ground granulated blast furnace slag is 55% or more and 60% or less, the mass ratio of the slaked lime to the ground granulated blast furnace slag is 33% or more and 60% or less, the mass ratio of the anhydrous gypsum to the ground granulated blast furnace slag is 17% or more and 45% or less, and the total mass ratio of the ground granulated blast furnace slag, the slaked lime, and the anhydrous gypsum is 100%.

2. A ground improvement method comprising injecting into the ground a ground improvement material comprising ground granulated blast furnace slag, slaked lime, and anhydrous gypsum, wherein the mass ratio of the ground granulated blast furnace slag is 55% or more and 60% or less, the mass ratio of the slaked lime to the ground granulated blast furnace slag is 33% or more and 60% or less, the mass ratio of the anhydrous gypsum to the ground granulated blast furnace slag is 17% or more and 45% or less, and the total mass ratio of the ground granulated blast furnace slag, the slaked lime, and the anhydrous gypsum is 100%.

3. 3. The ground improvement method according to claim 2, wherein the ground is clayey soil, volcanic ash clayey soil, or sandy soil.

4. a ground improvement material comprising ground granulated blast furnace slag, slaked lime, and anhydrous gypsum, wherein the mass ratio of the ground granulated blast furnace slag is 55% or more and 60% or less, the mass ratio of the slaked lime to the ground granulated blast furnace slag is 33% or more and 60% or less, the mass ratio of the anhydrous gypsum to the ground granulated blast furnace slag is 17% or more and 45% or less, and the total mass ratio of the ground granulated blast furnace slag, the slaked lime, and the anhydrous gypsum is 100%; The ground into which the soil improvement material has been injected; Ground improvement soil with the following properties.

5. A ground improvement material comprising ground granulated blast furnace slag, slaked lime, and anhydrous gypsum, wherein the mass ratio of the ground granulated blast furnace slag is 55% or more and 60% or less, the mass ratio of the slaked lime to the ground granulated blast furnace slag is 33% or more and 60% or less, the mass ratio of the anhydrous gypsum to the ground granulated blast furnace slag is 17% or more and 45% or less, and the total mass ratio of the ground granulated blast furnace slag, the slaked lime, and the anhydrous gypsum is 95% or more and less than 100%.

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