Ground improvement material and ground improvement method using the same
A cement-based ground improvement material with antimony(III) compounds addresses the instability of blast furnace slag powder by reducing hexavalent chromium leaching and enhancing ground strength, ensuring effective ground treatment without slag powder.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TAIHEIYO CEMENT CORP
- Filing Date
- 2022-02-24
- Publication Date
- 2026-07-23
AI Technical Summary
The supply of blast furnace slag powder, used to reduce hexavalent chromium leaching from cement-based ground improvement, is unstable, and existing methods fail to effectively suppress hexavalent chromium leaching and maintain ground strength when its use is limited or absent.
A ground improvement material comprising a cement-based solidifying agent and an antimony(III) compound, with specific proportions of cement, gypsum, and optionally other admixtures, is used to enhance strength and reduce hexavalent chromium elution.
The material effectively suppresses hexavalent chromium leaching and enhances ground strength, even without blast furnace slag powder, by incorporating antimony(III) compounds, achieving improved unconfined compressive strength and environmental compliance.
Smart Images
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Abstract
Description
[Technical Field]
[0001] The present invention relates to a ground improvement material and a ground improvement method using the same. [Background technology]
[0002] One known method for improving ground conditions involves adding and mixing cement-based solidifying agents to the ground to increase its strength (for example, unconfined compressive strength). On the other hand, when ground improvement treatment (solidification treatment) is performed using cement-based solidification materials, there is a problem that hexavalent chromium may leach out of the improved ground due to reasons such as the cement containing trace amounts of hexavalent chromium compounds. Patent Document 1 describes a heavy metal immobilization material used to prevent the leaching of heavy metals in a material made of gypsum, the heavy metal immobilization material having slag fine powder as its main component. Furthermore, Patent Document 2 describes a hexavalent chromium formation inhibitor that uses particles obtained by crushing and classifying the roasted body of a waste lithium-ion battery as an active ingredient. [Prior art documents] [Patent Documents]
[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-169816 [Patent Document 2] Japanese Patent Publication No. 2021-146317 [Overview of the project] [Problems that the invention aims to solve]
[0004] It is known that blast furnace slag powder is used to reduce hexavalent chromium leached from cement into harmless trivalent chromium. However, in recent years, there have been concerns that the supply of blast furnace slag powder may decrease or become unstable. The object of the present invention is to provide a ground improvement material that can suppress the amount of hexavalent chromium leached out, even when blast furnace slag fine powder is not used or is used in small amounts, and that exhibits excellent strength development, as well as a ground improvement method using the same. [Means for solving the problem]
[0005] As a result of diligent research to solve the above problems, the inventors of the present invention have found that the above objectives can be achieved by using a ground improvement material containing a cement-based solidifying agent and an antimony(III) compound, and have completed the present invention. In other words, the present invention provides the following [1] to [8]. [1] A ground improvement material characterized by containing a cement-based solidifying agent and an antimony(III) compound. [2] The ground improvement material according to [1], wherein the amount of antimony(III) in the antimony(III) compound per 100 parts by mass of the cement-based solidifying material is 0.002 parts by mass or more. [3] The ground improvement material according to [1] or [2] above, wherein the antimony(III) compound is one or more selected from the group consisting of antimony trichloride, potassium antimony tartrate, sodium antimony tartrate, diantimony trioxide, antimony trifluoride, and diantimony trisulfide.
[0006] [4] The ground improvement material according to any one of [1] to [3] above, wherein the proportion of cement in the ground improvement material is 40% by mass or more. [5] The ground improvement material according to any one of [1] to [4] above, wherein the cement-based solidifying material contains gypsum, and the proportion of gypsum in the cement-based solidifying material is 1.0% by mass or more on an anhydrous basis. [6] The ground improvement material according to any one of [1] to [5] above, wherein the cement-based solidification material does not contain blast furnace slag fine powder, or the proportion of blast furnace slag fine powder in the cement-based solidification material is 40% by mass or less. [7] A method for improving the ground using the ground improvement material described in any of [1] to [6] above, characterized in that the ground improvement material is added to the ground and mixed to obtain improved ground. [8] The ground improvement method according to [7], wherein the ground is volcanic ash clay containing allophane in a proportion of 10.0 to 55.0% by mass. [Effects of the Invention]
[0007] The ground improvement material of the present invention can suppress the elution of hexavalent chromium even when blast furnace slag fine powder is not used or is used in small amounts, and exhibits excellent strength development. Furthermore, according to the ground improvement method of the present invention, the amount of hexavalent chromium leaching from the ground can be suppressed, and the strength of the ground (for example, unconfined compressive strength) can be increased. [Modes for carrying out the invention]
[0008] The ground improvement material of the present invention contains a cement-based solidifying agent and an antimony(III) compound. The cement-based solidifying agent used in the present invention refers to a material that contains cement as the main material (usually 40% by mass or more, preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 65% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more), and also contains admixtures that can be optionally blended. Examples of cements used in cement-based solidification materials include various types of Portland cement such as ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement, as well as blended cements such as blast furnace cement, fly ash cement, and silica cement, and eco-cement, white cement, and ultrafast-setting cement. Among these, various types of Portland cement are preferred from the standpoint of ease of availability. From the viewpoint of improving strength development, the proportion of cement in the ground improvement material is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 65% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more.
[0009] Examples of admixtures that can be arbitrarily added to cement-based solidifying agents include blast furnace slag powder, gypsum, quicklime, slaked lime, fly ash, limestone powder, and silica fume. These may be used individually or in combination of two or more. From the viewpoint of obtaining the effect of the present invention, which is that the amount of hexavalent chromium leaching can be suppressed even when blast furnace slag fine powder is not used or is used in small amounts, it is preferable that the cement-based solidifying material does not contain blast furnace slag fine powder as an admixture, or that the proportion of blast furnace slag fine powder in the cement-based solidifying material is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 25% by mass or less, and particularly preferably 10% by mass or less. In the case that the cement contained in the cement-based solidifying material is blast furnace cement, the above proportion of blast furnace slag fine powder shall not include the blast furnace slag fine powder contained in the blast furnace cement.
[0010] Furthermore, from the viewpoint of improving strength development, cement-based solidifying agents that contain gypsum as an admixture are preferred. The proportion of gypsum in the cement-based solidifying agent is preferably 1.0% by mass or more, more preferably 3.0 to 20.0% by mass, even more preferably 5.0 to 18.0% by mass, and particularly preferably 8.0 to 15.0% by mass, on an anhydrous basis. Note that the above proportion of gypsum does not include gypsum contained in the cement. Examples of the above-mentioned gypsum include anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum, or mixtures thereof. The proportion of admixtures in the cement solidifying material (in the case of those containing two or more kinds of admixtures, the total thereof) is preferably 60% by mass or less, more preferably 55% by mass or less, still more preferably 50% by mass or less, still more preferably 35% by mass or less, particularly preferably 20% by mass or less, from the viewpoint that the proportion of cement relatively increases and the strength development property is improved.
[0011] An antimony(III) compound is a compound containing trivalent antimony. Examples of the antimony(III) compound include antimony trichloride, potassium antimonyl tartrate, sodium antimonyl tartrate, antimony trioxide, antimony trifluoride, and antimony trisulfide. These may be used alone or in combination of two or more. Among them, antimony trioxide is preferable from the viewpoint of easy availability and the like. The amount of antimony(III) in the antimony(III) compound with respect to 100 parts by mass of the cement-based solidifying material is preferably 0.002 parts by mass or more, more preferably 0.010 parts by mass or more, still more preferably 0.015 parts by mass or more, still more preferably 0.020 parts by mass or more, still more preferably 0.030 parts by mass or more, still more preferably 0.045 parts by mass or more, particularly preferably 0.060 parts by mass or more, from the viewpoint of further suppressing the elution amount of hexavalent chromium. Also, from the viewpoint of preventing excessive increase in cost and preventing reduction in strength development property, the above amount is preferably 0.100 parts by mass or less, more preferably 0.090 parts by mass or less, still more preferably 0.080 parts by mass or less, particularly preferably 0.070 parts by mass or less.
[0012] According to the ground improvement material of the present invention, the strength of the ground (for example, uniaxial compressive strength) can be increased, and the elution amount of hexavalent chromium from the ground can be suppressed. As an example of a method for improving the ground using the above ground improvement material, there is a method of adding the ground improvement material to the ground to be improved, mixing it, and obtaining the improved ground. Examples of methods for adding and mixing a ground improvement material to the ground include a dry addition method in which the ground improvement material is added to the ground in powder form and mixed, and a slurry addition method in which water is added to the ground improvement material to form a slurry, and then the slurry is added to the ground and mixed. Further, according to the ground improvement material of the present invention, even in the case of a ground where volcanic ash clay (e.g., Kanto loam) that easily elutes hexavalent chromium is the target ground for improvement, elution of hexavalent chromium can be sufficiently suppressed.
[0013] Also, from the viewpoint that excellent strength development can be expected, the above ground may preferably contain allophane at 1.0 to 60.0% by mass, more preferably 5.0 to 55.0% by mass, and particularly preferably 10.0 to 30.0% by mass. According to the ground improvement material of the present invention, even if the above ratio is 1.0% by mass or more, the strength of the improved ground can be made sufficient. If the above ratio is 60.0% by mass or less, the strength of the improved ground can be increased more, and the elution amount of hexavalent chromium can be suppressed more. Note that the above ratio is a conversion value in dry soil. Examples of the ground containing allophane include volcanic ash clay containing allophane at a ratio of 10.0 to 55.0% by mass (preferably 12.0 to 30.0% by mass). Allophane is a kind of amorphous silicate aluminum clay mineral contained in a large amount in volcanic ash clay, and the ratio of allophane can be measured, for example, in accordance with the description of the "acid oxalate extraction method" (Journal of Dairy Science University, 28(1), pp. 7 - 45 (2003)).
[0014] Also, the above ground may contain humus (humic acid, fulvic acid, or bitumen). In the ground, the ratio of humic acid is preferably 0.1 to 10.0% by mass, more preferably 1.0 to 5.0% by mass, the ratio of fulvic acid is preferably 0.5 to 20.0% by mass, more preferably 8.0 to 16.0% by mass, and the ratio of bitumen is preferably 5.0% by mass or less, more preferably 3.0% by mass or less. According to the ground improvement material of the present invention, even in the case of a ground containing humus, the strength of the improved ground can be made sufficient.
[0015] Ground to be improved: 1 meter 3 The amount of ground improvement material to be added per unit area varies depending on the properties of the target ground, the amount of hexavalent chromium contained in the ground, the construction conditions, and the required strength of the improved ground obtained after treatment, but for ground to be improved, 1 m 3 The amount per unit is preferably 50-450 kg, more preferably 100-400 kg, and particularly preferably 150-300 kg. If the amount is 50 kg or more, the strength of the improved ground can be further increased, and the leaching of hexavalent chromium can be further suppressed. If the amount is 450 kg or less, an excessive increase in costs can be prevented. [Examples]
[0016] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Cement; commercially available, high-early-strength Portland cement (2) Blast furnace slag fine powder (indicated as "blast furnace slag" in Table 2); manufactured by Day-C Company, trade name "Cerament" (3) Gypsum; anhydrite (4) Antimony(III) compounds; commercially available, antimony trioxide solution (antimony trioxide content: 10% by mass) (5) Soils 1-4: Table 1 shows the types of soils and the proportions of allophane, humic acid, fulvic acid, and bitumen in the soil. The proportion of allophane was measured according to the acidic oxalate extraction method described above.
[0017] [Table 1]
[0018] [Examples 1-11, Comparative Examples 1-5] A ground improvement material was obtained by mixing a cement-based solidifying agent in which the proportions of cement, blast furnace slag powder, and anhydrous gypsum are as shown in Table 2, with a diantimony trioxide solution in which the amount of antimony(III) (indicated as "Sb2O3" in Table 2) relative to the cement-based solidifying agent is as shown in Table 2. The above-mentioned ground improvement material and the types of soil shown in Table 1 are used in a soil mixture of 1 m³. 3 The soil was improved by adding and mixing a soil improvement material in an amount of 200 kg per m³. 3 The reason for lowering the value compared to the previous value is to make it easier to observe the trend in the amount of hexavalent chromium leached out. The uniaxial compressive strength of the obtained ground-improved soil at 7 days was measured in accordance with "JIS A 1216:2020 (Uniaxial Compression Test Method for Soil)". Furthermore, a hexavalent chromium leaching test was conducted on the improved soil after the unconfined compressive strength measurement, in accordance with Environmental Agency Notification No. 46, and the amount of hexavalent chromium leached from the improved soil was measured in accordance with "JIS K 0102:2016 (Test Methods for Industrial Wastewater)". The results are shown in Table 2.
[0019] [Table 2]
[0020] Table 2 shows that when comparing Examples 1-4 with Comparative Example 1, the amount of hexavalent chromium leached (0.01-0.05 mg / liter) when using a cement-based solidification material containing antimony(III) compounds (Examples 1-4) is smaller than the amount of hexavalent chromium leached (0.13 mg / liter) when using a cement-based solidification material without antimony(III) compounds (Comparative Example 1). This indicates that using a ground improvement material containing antimony(III) compounds can further reduce the amount of hexavalent chromium leached. Similar trends were observed in the comparisons of Example 5 and Comparative Example 2, Examples 6-8 and Comparative Example 3, Example 9 and Comparative Example 4, and Example 10 and Comparative Example 5. Furthermore, the uniaxial compressive strength of Examples 1-4 (109-127 kN / m) 2) and the uniaxial compressive strength of Comparative Example 1 (117 kN / m 2 ), the comparison of the uniaxial compressive strength of Example 5 (250 kN / m 2 ) and the uniaxial compressive strength of Comparative Example 2 (253 kN / m 2 ), and the comparison of the uniaxial compressive strengths of Examples 6 to 8 (501 to 608 kN / m 2 ) and the uniaxial compressive strength of Comparative Example 3 (534 kN / m 2 ), the comparison of the uniaxial compressive strength of Example 9 (492 kN / m 2 ) and the uniaxial compressive strength of Comparative Example 4 (500 kN / m 2 ), the comparison of the uniaxial compressive strength of Example 10 (478 kN / m 2 ) and the uniaxial compressive strength of Comparative Example 5 (490 kN / m 2 ), it can be seen that the ground improvement material of the present invention has the same strength development property as the ground improvement material containing no antimony (III) compound. Also, from Examples 6 to 11 (where the blending ratio of fine blast furnace slag powder is 0% by mass), it can be seen that according to the ground improvement material of the present invention, the elution amount of hexavalent chromium from the ground can be reduced even though it does not contain fine blast furnace slag powder. Furthermore, it can be seen that when the ground to be improved contains allophane at a ratio of 13.9 to 50.2% by mass (Examples 1 to 9), the elution amount of hexavalent chromium from the ground can be reduced to below the environmental standard value.
Claims
[Claim 1] A ground improvement material containing a cement-based solidifying agent and an antimony (III) compound, The amount of antimony(III) in the antimony(III) compound per 100 parts by mass of the cement-based solidifying material is 0.015 to 0.070 parts by mass. The above antimony (III) compound is antimony trioxide. The proportion of cement in the above-mentioned ground improvement material is 55% by mass or more. The above cement-based solidifying agent contains gypsum, and the proportion of the above gypsum in the above cement-based solidifying agent is 1.0 to 15.0% by mass on an anhydrous basis. A method for improving ground using a ground improvement material in which the above-mentioned cement-based solidification material does not contain blast furnace slag fine powder, or the proportion of blast furnace slag fine powder in the above-mentioned cement-based solidification material is 40% by mass or less, A ground improvement method characterized by adding the above-mentioned ground improvement material to ground having an allophane content of 1.0 to 1.4% by mass, a humic acid content of 0.1 to 5.0% by mass, a fulvic acid content of 0.5 to 3.7% by mass, and a bitumen content of 5.0% by mass or less, and mixing it to obtain improved ground.