Cement-based solidification material for organic soil, solidification treatment method for organic soil, and manufacturing method for cement-based solidification material

Abstract

To provide a cement solidification material that can increase the strength of organic soil to be treated, particularly the initial strength of it.SOLUTION: A cement solidification material for organic soil contains Portland cement, ground granulated blast furnace slag, gypsum and acidic sulfate. The solidification material has the SO3 / Al2O3 molar ratio of 0.9-1.65. The ground granulated blast furnace slag has a basicity of 1.75 or more. Preferably, the content of the acidic sulfate is 1 pt.mass or more and 5 pts.mass or less relative to 100 pts.mass of the total of the Portland cement, ground granulated blast furnace slag, gypsum and acidic sulfate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a cement-based solidification material for organic soil and a method for solidifying organic soil, and further to a method for producing the cement-based solidification material. [Background technology]

[0002] As a method for solidifying soil contained in soft ground, a method of adding a solidifying material such as a cement-based solidifying material is adopted. In particular, organic soil such as peat, which has a high water content, contains a lot of humic substances such as humic acid and fulvic acid as organic matter. When solidifying organic soil, the humic substances react with calcium hydroxide produced by the hydration reaction of cement, inhibiting the hydration of cement. As a result, the solidification performance of the cement may not be fully demonstrated.

[0003] As a means for solidifying such organic soil, for example, there is a method using a solidification material in which a sulfate is added to a mixture of cement and gypsum (Patent Document 1), or a method using cement and a clayey soil having a Blaine specific surface area of ​​8000 cm 2 Disclosed are a method using a solidification material containing gypsum and ground granulated blast furnace slag with a concentration of 100 / g or more (Patent Document 2), and a method using a solidification material containing a cement-based solidification material and ferrous sulfate (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-70150 A [Patent Document 2] JP 2018-193515 A [Patent Document 3] JP 2019-48938 A Summary of the Invention [Problem to be solved by the invention]

[0005] The solidification materials described in Patent Documents 1 to 3 are capable of improving the strength of organic soil by solidification treatment, but the strength after solidification treatment is insufficient, leaving room for improvement.

[0006] Therefore, an object of the present invention is to provide a cement-based solidification material and a solidification method capable of increasing the strength of improved soil in the treatment of organic soil. [Means for solving the problem]

[0007] As a result of intensive research into the above-mentioned problems, the present inventors have found that a method for producing a concrete mixture containing Portland cement, ground granulated blast furnace slag, gypsum, and acid sulfate and having a specific basicity is used, and a specific solidification material, SO 3 / Al 2 O 3 The inventors discovered that by using a solidification material adjusted to achieve the above molar ratio in the solidification treatment of organic soil, the resulting improved soil can exhibit high strength, which led to the completion of the present invention.

[0008] That is, the present invention provides: Contains Portland cement, ground granulated blast furnace slag, gypsum and acid sulfates. SO 3 / Al 2 O 3 The molar ratio is 0.9 to 1.65, The present invention provides a cement-based solidification material for organic soil, in which the basicity of ground granulated blast furnace slag is 1.75 or more.

[0009] The present invention also provides A method for solidifying organic soil comprising a step of mixing the cement-based solidification material with organic soil, Organic soil contains humus, The humic substance comprises at least one selected from humic acid and fulvic acid; The present invention provides a method for solidifying organic soil, in which the total amount of humic acid and fulvic acid is 5 mass % or more. Effect of the Invention

[0010] According to the cement-based solidification material of the present invention, the strength, particularly the initial strength, of the organic soil to be treated can be increased. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] A preferred embodiment of the present invention will be described below. In the following description, when it is written "X to Y[Z]" (X and Y are arbitrary numbers, and [Z] is a unit), it means "X[Z] or more and Y[Z] or less" unless otherwise specified.

[0012] The "organic soil" in the present invention refers to soil classified as "organic soil" in the book "Methods and Commentary of Soil Material Testing" (Geotechnical Society, published November 2009, pages 53-79). Specifically, the organic soil in the present invention includes organic soil classified as O (O), such as organic clay and organic volcanic ash soil, and highly organic soil classified as Pt, such as peat and black mud. These soils contain organic matter. Organic soil has an organic matter content of less than 20% by mass, and highly organic soil has an organic matter content of 20% by mass or more. The organic matter content can be the value of the ignition loss described later. In the following explanation, unless otherwise specified, "organic soil" will be used as a general term for these soils.

[0013] The solidification material of the present invention is a cement-based material as described below. The solidification material of the present invention is preferably used for the solidification treatment of wet organic soil, and is particularly preferably used for the solidification treatment of wet highly organic soil. The wet state refers to a water content ratio of more than 0%, as described below. The solidification material of the present invention is used for solidification treatment of organic soil having a water content of preferably 100% or more, more preferably 150% or more, and preferably 1000% or less. The moisture content is the ratio of the mass of water in the soil to the dry mass of the soil being measured, expressed as a percentage, and can be measured, for example, in accordance with JIS A1203:2009. By using the solidification material of the present invention for soil having such a water content, it is possible to make the soil, which was previously difficult to develop strength, develop high strength.

[0014] The organic soil to which the solidification material of the present invention is applied preferably contains humic substances in a water-containing state. Humic substances are components that constitute the organic matter contained in organic soil, and examples of such components include humic acidic components such as humic acid and fulvic acid, humin, and bitumen. The solidification material of the present invention is preferably used for solidification treatment of organic soil containing humic substances in an amount of preferably 5% by mass or more, more preferably 7% by mass or more, and preferably 20% by mass or less. The content of humic substances is defined as the ratio to the mass of the organic soil in a water-containing state. By using the solidification material of the present invention on organic soil containing humus in such a proportion, the solidification reaction is less likely to be inhibited by humus, making it possible to efficiently promote the solidification reaction even in soil that has previously been difficult to develop strength, and allowing the soil to develop high strength after solidification treatment.

[0015] In particular, the solidifying material of the present invention is preferably used for organic soil containing at least one type of humic substance selected from humic acid and fulvic acid. When organic soil containing at least one selected from humic acid and fulvic acid is to be solidified, it is preferable to use the solidification material of the present invention for organic soil in which the total amount of humic acid and fulvic acid is preferably 5% by mass or more, more preferably 7% by mass or more, and preferably 20% by mass or less. The content of humic acid and fulvic acid is the ratio to the mass of the organic soil in a water-containing state. By using the solidification material of the present invention on organic soil containing humic acid and fulvic acid in such a ratio, neutralization of the alkali in the solidification material with acidic components such as humic acid and fulvic acid is unlikely to occur, and the solidification reaction by alkali is unlikely to be inhibited. As a result, it is possible to efficiently proceed with the solidification reaction even in organic soil that has previously been difficult to develop strength, and the soil after solidification can develop high strength.

[0016] The presence or absence and content of humic substances, humic acid and fulvic acid can be measured, for example, by the method described in the Examples below.

[0017] The organic soil to be treated has an ignition loss of preferably 20 to 90% by mass, more preferably 25 to 70% by mass. The ignition loss of the organic soil can be measured, for example, in accordance with JIS A1226:2009. By using the solidification material of the present invention for organic soil having such an ignition loss, it is possible to make the soil exhibit high strength after the solidification treatment.

[0018] An example of organic soil that satisfies at least one of the above-mentioned humus or humus acidic component content, water content, and ignition loss is high organic soil. In other words, the solidification material of the present invention is particularly suitable for use in the solidification treatment of high organic soil. High organic soil is soil in which dead plants and the like have accumulated over many years. Examples of high organic soil include peat (subcategory symbol [Pt] in the above book), which is undecomposed and fibrous, and black charcoal (subcategory symbol [Mk] in the above book), which is black due to the decomposition of sediments. It is preferable that high organic soil satisfies at least one of the above-mentioned humus content, water content, and ignition loss at the time of collection in order to increase the work efficiency during the solidification treatment.

[0019] The solidifying material of the present invention is a cement-based material containing Portland cement, ground granulated blast furnace slag, gypsum, and acid sulfate. The solidification material of the present invention is SO 3 / Al 2 O 3 The molar ratio is preferably 0.9 to 1.65, more preferably 1.2 to 1.6. 3 / Al 2 O 3 The molar ratio can be adjusted by the content of gypsum in the solidification material. 3 / Al 2 O 3By setting the molar ratio to 0.9 or more, hydrates such as ettringite are effectively generated, improving strength development. 3 / Al 2 O 3 Setting the molar ratio to 1.65 or less also effectively produces hydrates such as ettringite, improving strength development.

[0020] The Portland cement contained in the solidifying material of the present invention may be, for example, ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, etc. From the viewpoint of versatility and early strength development, it is preferable to use high-early-strength Portland cement.

[0021] The content of Portland cement in the solidification material of the present invention is SO 3 / Al 2 O 3 The molar ratio is determined by taking into account the balance between the contents of gypsum and acid sulfate so that it is the above-mentioned value. In general, the content of Portland cement in the solidification material is preferably 20 to 49 mass%, more preferably 24 to 40 mass%. Within this range, SO 3 / Al 2 O 3 The molar ratio tends to fall within the ranges mentioned above.

[0022] The ground granulated blast furnace slag contained in the solidifying material of the present invention is obtained by water-cooling and pulverizing slag generated secondarily in blast furnaces of steelworks, etc., to obtain a powder having an average particle size of 5 to 20 μm. The average particle size is measured in the same manner as the average particle size of acid sulfates, which will be described later. As the ground granulated blast furnace slag, for example, commercially available granulated blast furnace slag or that specified in JIS A6206:2013 can be used. Ground granulated blast furnace slag has a high content of alumina components, which contributes to an alumina source for increasing the amount of ettringite produced, and can improve the strength of soil after solidification. Furthermore, ground granulated blast furnace slag has latent hydraulic properties that harden when stimulated by alkali contained in cement, etc., and due to this, when organic soil in a hydrated state is solidified, the strength of the soil after solidification can be improved.

[0023] By the way, it is known that basicity is generally used as a measure of reactivity when ground granulated blast furnace slag is used as cement. The higher the basicity of ground granulated blast furnace slag, the greater its reactivity. Basicity is the ratio of (CaO+MgO+Al) in the components of ground granulated blast furnace slag. 2 O 3 ) / SiO 2 The basicity of the ground granulated blast furnace slag used in the present invention is preferably 1.75 or more, more preferably 1.79 or more, from the viewpoint of high reactivity. The upper limit of the basicity is about 2.00. As described later, the basicity of the ground granulated blast furnace slag is not constant but varies depending on the lot and brand, so the basicity of the blast furnace slag generated from the blast furnace is continuously measured, and if the basicity of the blast furnace slag is 1.75 or more, the blast furnace slag is collected for use as a raw material for the solidification material of the present invention. The Blaine specific surface area of ​​the ground granulated blast furnace slag is preferably 3000 to 7000 cm 2 / g, and more preferably 3500 to 6000 cm 2 The Blaine specific surface area of ​​ground granulated blast furnace slag can be measured in accordance with JIS R5201:2015 "Physical testing methods for cement." By using ground granulated blast furnace slag having such basicity and Blaine specific surface area, it is possible to reduce the manufacturing costs of the cement-based solidification material and the costs required for the solidification treatment, while at the same time imparting high strength to the soil after the solidification treatment.

[0024] The sulfide sulfur content of the ground granulated blast furnace slag is preferably 0.5 mass% or more, more preferably 0.6 mass% or more, further preferably 0.75 mass% or more, and preferably 1.5 mass% or less. The sulfide sulfur content can be measured in accordance with JIS R5202:2010 "Methods for chemical analysis of cement". Since the sulfide sulfur content of the blast furnace slag powder is within this range, if the solidification material contains heavy metals such as hexavalent chromium, the heavy metals can be reduced to trivalent chromium by the sulfide sulfur, and the leaching of heavy metals from the soil after solidification can be suppressed to below environmental standards.

[0025] From the viewpoint of further enhancing the solidification performance of organic soil by bringing about a good balance between the latent hydraulic properties of the ground granulated blast furnace slag and the alkali hydration reaction of cement, the content of ground granulated blast furnace slag in the solidification material of the present invention is preferably 40 to 65 mass%, more preferably 45 to 60 mass%. By setting the content to 40 mass% or more, it is possible to suppress the decrease in strength development at long-term material ages. Furthermore, by setting the content to 65 mass% or less, the Portland cement content is not excessively reduced, so that it is possible to suppress the decrease in strength development at early material ages. Furthermore, within such a range, the amount of SO 3 / Al 2 O 3 The molar ratio tends to fall within the ranges mentioned above.

[0026] The acid sulfate contained in the solidification material of the present invention can be, for example, ferrous sulfate or aluminum sulfate. When organic soil containing water is treated with the solidification material of the present invention, the acid sulfate is used to suppress the dissolution of a large amount of humic substances in the organic soil due to high alkalinity caused by calcium hydroxide generated after the cement in the solidification material comes into contact with the water in the soil, to prevent the hydration of cement from being inhibited by the humic substances, and to increase the amount of ettringite produced by supplying sulfate ions, thereby improving the strength of the soil after the solidification treatment. In addition, ferrous sulfate has the advantage of reducing hexavalent chromium contained in cement and suppressing the elution of hexavalent chromium from the soil after the solidification treatment to below the environmental standard.

[0027] The ferrous sulfate usable in the acidic sulfate contained in the solidifying material of the present invention may be anhydrous or may be a hydrate such as a monohydrate, a tetrahydrate, a pentahydrate, a heptahydrate, etc. From the viewpoint of reducing the production cost of the solidifying material of the present invention and obtaining a highly versatile cement-based solidifying material, the ferrous sulfate is preferably a hydrate, which is an economical and inexpensive substance, and more preferably a monohydrate.

[0028] The ferrous sulfate is preferably in a powder form. In this case, the maximum particle size of the particles constituting the ferrous sulfate powder is preferably 1000 μm or less, more preferably 900 μm or less. The average particle size of the particles constituting the ferrous sulfate powder is preferably 10 to 70 μm, more preferably 15 to 65 μm. When the ferrous sulfate is in the form of particles having such a particle size, the dissolution of humic substances by high alkali is suppressed, and the supply of sulfate ions proceeds at an appropriate rate, resulting in the effect of improving strength. Ferrous sulfate having such a particle size can be obtained, for example, from a commercially available product or by crushing, sieving, etc.

[0029] The maximum particle size and average particle size of ferrous sulfate can be measured, for example, by the following method. Specifically, the maximum particle size and average particle size can be measured using a laser diffraction particle size distribution measuring device (e.g., Mastersizer 3000 manufactured by Malvern Instruments, and a dry dispersion unit AERO S (dispersion conditions: sample circulated at an air pressure of 4 bar). The maximum particle size is the maximum particle size measured by this device, and the average particle size is the cumulative 50% particle size D 50 It can be said that:

[0030] The aluminum sulfate used as the acidic sulfate contained in the solidifying material of the present invention may be anhydrous or may be a hydrate, for example, a 13-17 hydrate.

[0031] The content of the acid sulfate in the solidifying material of the present invention is preferably 1 to 5 mass %, more preferably 1.5 to 4.5 mass %. By having the content of the acid sulfate in such a range, soil with high strength can be obtained. The content of the acid sulfate is preferably 1 part by mass or more and 5 parts by mass or less, more preferably 1.5 parts by mass or more and 4.5 parts by mass or less, and even more preferably 1.8 parts by mass or more and 4.2 parts by mass or less, when the total of the Portland cement, the ground granulated blast furnace slag, the gypsum, and the acid sulfate is taken as 100 parts by mass. By setting the content of the acid sulfate to 1 part by mass or more, the dissolution of a large amount of humic substances in the organic soil due to high alkalinity caused by calcium hydroxide generated after the cement in the solidification material comes into contact with the water in the soil is suppressed, and the inhibition of hydration of the cement by the humic substances is effectively prevented, and the amount of ettringite produced can be increased early by supplying sulfate ions. Furthermore, by setting the content of the acid sulfate to 5 parts by mass or less, the inhibition of hydration of the cement due to the excessive addition of the acid sulfate is effectively suppressed, and the dissolution of the humic substances in the organic soil can be suppressed and the amount of ettringite produced can be increased.

[0032] As the gypsum contained in the solidifying material of the present invention, for example, at least one of anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum can be used. From the viewpoint of efficiently improving the strength of organic soil, the gypsum is preferably at least one of anhydrous gypsum and dihydrate gypsum, and more preferably anhydrous gypsum.

[0033] The content of gypsum in the solidification material of the present invention is SO 3 / Al 2 O 3 The molar ratio is determined by the balance between the contents of Portland cement and acid sulfate so that it is the above-mentioned value. In general, the content of gypsum in the solidifying material is preferably 10 to 18 mass%, more preferably 12 to 16 mass%. Within this range, SO 3 / Al 2 O 3 The molar ratio tends to fall within the ranges mentioned above.

[0034] The solidifying material of the present invention can be obtained, for example, by mixing the respective materials in a known mixer. The solidifying material thus obtained is preferably in a powder form.

[0035] The method for solidifying the water-containing organic soil to be treated using the solidification material having the above-mentioned structure will be described below. In the following description, the above-mentioned descriptions regarding the solidification material and the organic soil to be solidified are appropriately applied.

[0036] The soil solidification method of the present invention includes a step of mixing a solidification material with soil to be treated. The soil to be treated can be organic soil in a water-containing state, particularly highly organic soil in a water-containing state.

[0037] In the present method, the mixing method may involve adding one of the solidification material and the soil to be treated to the other, or the solidification material and the soil to be treated may be mixed simultaneously. The solidification material to be mixed may be in powder form, or may be in the form of a slurry dispersed in a dispersion medium such as water.

[0038] The amount of solidification material to be mixed can be changed as appropriate depending on the type and properties of the soil to be treated. 3 The amount is preferably 100 to 500 kg, more preferably 200 to 450 kg, and even more preferably 300 to 400 kg, relative to the soil. By mixing in such a range, ettringite can be efficiently generated in the soil while suppressing the treatment cost, and the strength of the soil after solidification treatment can be increased. In addition, with the improvement in strength, the elution of heavy metals such as arsenic and hexavalent chromium into the environment can be further reduced. The volume of the soil to be treated is the value in a wet state.

[0039] The solidification material can be mixed with the soil to be treated using a mixing device or method commonly used in this technical field, such as a backhoe, a backhoe equipped with a mixing bucket, a stabilizer, a self-propelled soil improvement machine, a stationary mixer, a Hobart mixer, a trencher type agitation mixer, a deep layer mixer, a power blender, or a plant mixer.

[0040] Next, a method for manufacturing the solidifying material of the present invention will be described. The ground granulated blast furnace slag contained in the solidifying material of the present invention contributes to long-term strength development due to the formation of ettringite and its latent hydraulic properties. Such strength development depends on the reactivity of the ground granulated blast furnace slag. This reactivity is indicated by the basicity of the ground granulated blast furnace slag, and the higher the basicity, the better the strength development. The basicity of ground granulated blast furnace slag is not constant and varies depending on the lot and brand, so it is difficult to use it in a limited manner. However, even if the basicity is low, the strength development can be compensated for by increasing the content of ground granulated blast furnace slag in the solidifying material. Therefore, in the present invention, the basicity of the blast furnace slag generated from the blast furnace is continuously measured, and if the basicity of the blast furnace slag is 1.75 or more, the blast furnace slag is collected to be used as a raw material for the solidifying material of the present invention. Then, in order to obtain the required strength, the content of ground granulated blast furnace slag in the solidifying material is determined. The content of ground granulated blast furnace slag in the solidifying material is determined as follows in relation to the basicity. That is, when the basicity is high, the content of ground granulated blast furnace slag in the solidifying material is adjusted to be low, and when the basicity is low, the content of ground granulated blast furnace slag is adjusted to be high. The content of ground granulated blast furnace slag in the solidifying material is preferably 40 to 65 mass%, and for example, when the basicity is 1.75, it is good to make it 60 to 65 mass%, and when the basicity is 1.80, it is good to make it 53 to 58 mass%. The collected blast furnace slag is finely ground, and then mixed with Portland cement, gypsum, and acid sulfates in a content according to its basicity. The contents of Portland cement, gypsum, and acid sulfates in the solidification material are determined by the following formula: 3 / Al 2 O 3 The molar ratio is adjusted to 0.9 to 1.65. This makes it possible to increase the strength of organic soil even when using a solidification material that uses ground granulated blast furnace slag with low basicity, in other words, low reactivity. EXAMPLES

[0041] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0042] <Materials used in cement-based solidification materials> High-early-strength Portland cement (manufactured by Ube Mitsubishi Cement Co., Ltd.), ground granulated blast furnace slag 1 (basicity 1.844; domestically produced), ground granulated blast furnace slag 2 (basicity 1.799; domestically produced), ground granulated blast furnace slag 3 (basicity 1.812; domestically produced), anhydrous gypsum, ferrous sulfate (monohydrate; produced in China), and aluminum sulfate (tetrahydrate; manufactured by Taimei Chemical Industry Co., Ltd., industrial product) were mixed to obtain cement-based solidification materials with different compositions.

[0043] The chemical composition of each material used in the preparation of the cement-based solidification material is shown in Table 1 below. The chemical composition of the high-early-strength Portland cement was measured in accordance with JIS R 5202:2010 "Methods for chemical analysis of cement." The chemical composition of anhydrous gypsum was measured in accordance with JIS R9101:2018 "Method for chemical analysis of gypsum." The chemical compositions of the ground granulated blast furnace slag and ferrous sulfate monohydrate were measured in accordance with JIS M8853:1998 "Methods for chemical analysis of aluminosilicate raw materials for ceramics." The Blaine specific surface area of ​​each material was measured in accordance with JIS R5201:2015 "Physical testing methods for cement."

[0044] [Table 1]

[0045] <Sample soil> The sample soils to be solidified were peat A, B, and C collected in Hokkaido. The physical properties of the sample soils are shown in Table 2 below. All of these sample soils are highly organic soils in a moist state, containing more than 20% by mass of organic matter.

[0046] The moisture content of the sample soil was measured in accordance with JIS A1203:2009 "Testing method for moisture content of soil." The wet density of the sample soil was calculated by filling a mold with a diameter of 5 cm and a height of 10 cm with the sample soil and multiplying the mass of the filled sample (g) by the volume of the mold (cm 3 ) was subtracted to obtain the result. The ignition loss of the sample soil was measured in accordance with JIS A1226:2009 "Test method for ignition loss of soil."

[0047] The humus content of the sample soil was measured according to the following procedure, citing Figure 4 in "The Influence of Organic Matter on the Soil Stabilization Effect and Organic-Resistant Solidification Materials" by Shigeyuki Kumato and Noboru Shimatani, Civil Engineering Test Book Monthly Report No. 402, November 1986, pp. 15-26. Humic acid is a humic substance that is insoluble in a mixed solvent of benzene and alcohol, soluble in alkali, and insoluble in acid. Fulvic acid is a humic substance that is insoluble in a mixed solvent of benzene and alcohol, soluble in acid and alkali. Bitumen is a humic substance that is soluble in a mixed solvent of benzene and alcohol, and insoluble in acid and alkali. First, the wet sample soil to be measured was stirred in a Hobart mixer and its mass in the wet state was measured. The sample soil was then sieved through a 2 mm standard mesh sieve and allowed to dry naturally indoors to prepare a sample for extraction. Next, a certain amount (10 g) of the sample for extraction was placed in a cylindrical filter paper, and the bitumen was extracted with a mixture of ethanol and benzene (mass ratio 1:1) in a Soxhlet extraction apparatus placed on a hot water bath. This extraction was continued until the solvent in the extractor became colorless. After the extraction was completed, the extract in the receiver was dried at a constant temperature of 50°C, and the dried product was weighed to obtain the amount of bitumen. Next, the sample for extraction after bitumen extraction was air-dried, and the sample was immersed in a 0.5N NaOH aqueous solution for 48 hours, after which a 0.5N HCl aqueous solution was added to obtain a mixed solution. This mixed solution was then centrifuged to separate the filtrate and the precipitate. The above-mentioned process using a 0.5N NaOH aqueous solution and a 0.5N HCl aqueous solution was repeated for the obtained precipitate, and the obtained precipitate was washed again with pure water to obtain a liquid phase containing humic acid. This liquid phase was dried in an oven at 90°C, and the dried product was weighed to obtain the amount of humic acid. The alkali-insoluble component was determined by separately drying the precipitate obtained by the above-mentioned centrifugation at a constant temperature and then weighing it. The measured ignition loss of the sample soil was used as the organic matter content of the sample soil, and the amount of fulvic acid was calculated by subtracting the amounts of bitumen, humic acid, and alkali-insoluble components (excluding soil particles) from this organic matter content. The mass ratio of humic substances to the sample soil in a wet state is shown in Table 2 below.

[0048] [Table 2]

[0049] <Production of solidified soil using cement-based solidification materials> Each component shown in Table 1 above is 3 / Al 2 O 3 The cement-based solidification materials of Examples 1 to 14 and Comparative Examples 1 to 5 shown in Table 3 were obtained by mixing so that the molar ratios were as shown in Table 3. 3 The soil was added at a rate of 400 kg per 1000 ml of soil. The soil was then mixed for 90 seconds using a Hobart mixer. After mixing, the soil was scraped off and mixed for another 90 seconds to produce the soil after solidification treatment (hereinafter, this will also be referred to as solidification-treated soil).

[0050] <Strength measurement of solidified treated soil> The strength of the obtained solidified treated soil was measured by the following method. First, the solidified soil obtained using the solidification materials of the Examples and Comparative Examples was molded in accordance with JGS 0821 "Test specimen preparation method for stabilized soil without compaction" to obtain cylindrical specimens with a diameter of 5 cm and a height of 10 cm. These specimens were cured for 7 days in a sealed state at a temperature of 20°C and a humidity of 90% RH. Next, the unconfined compressive strength (kN / m 2 ) was measured in accordance with JIS A1216 "Unconfined Compression Test Method for Soil." The higher the value of the unconfined compressive strength, the higher the strength of the solidified treated soil. The results are shown in Table 3 below.

[0051] [Table 3]

[0052] The target peat A contains high-early-strength Portland cement, ground granulated blast furnace slag, gypsum and aluminum sulfate 14-hydrate, and also contains SO 3 / Al 2 O 3 The cement-based solidification materials (Examples 1 to 5) in which the molar ratio and basicity of the ground granulated blast furnace slag are within the range of the present invention are 3 / Al 2 O 3 It is clear that the strength is higher than that of the comparative examples 1 and 2, which have molar ratios outside the range of the present invention. In addition, for peat B and C, high-early-strength Portland cement, ground granulated blast furnace slag, gypsum, and ferrous sulfate monohydrate were included, and SO 3 / Al 2 O 3 It can be seen that the strength is high even in the cement-based solidification materials (Examples 6 to 13) in which the molar ratio and basicity of the ground granulated blast furnace slag are within the range of the present invention. In addition, peat C contains high-early-strength Portland cement, ground granulated blast furnace slag, gypsum, and ferrous sulfate monohydrate, and also contains SO 3 / Al 2 O 3 It can be seen that the cement-based solidification material (Example 13) in which the molar ratio and basicity of the ground granulated blast furnace slag are within the range of the present invention has higher strength than the cement-based solidification materials (Comparative Examples 3 to 5) in which ferrous sulfate is not added. In addition, when Examples 11, 13 and 14 are compared, 3 / Al 2 O 3 Even if the molar ratio is about the same, it is presumed that if the basicity of the ground granulated blast furnace slag is lower, the strength will also be lower, and if the basicity is 1.75 or less, the strength will be insufficient.

Claims

1. Contains Portland cement, ground granulated blast furnace slag, gypsum and acid sulfates. SO ３ / Al ２ O ３ The molar ratio is 0.9 to 1.65, A cement-based solidification material for organic soil, the basicity of which is 1.75 or more for ground granulated blast furnace slag, The organic soil contains humic substances; The humic substance comprises at least one selected from humic acid and fulvic acid; A cement-based solidification material having a total amount of humic acid and fulvic acid of 5 mass% or more.

2. 2. The cement-based solidification material according to claim 1, wherein the content of the acid sulfate is 1 part by mass or more and 5 parts by mass or less when the total amount of the Portland cement, the ground granulated blast furnace slag, the gypsum, and the acid sulfate is 100 parts by mass.

3. 3. The cement-based solidification material according to claim 1, wherein the acid sulfate comprises at least one selected from the group consisting of ferrous sulfate and aluminum sulfate.

4. A method for solidifying organic soil, comprising the step of mixing the cement-based solidification material according to any one of claims 1 to 3 with the organic soil.

5. 1m of organic soil ３ The solidification method according to claim 4, wherein 100 to 500 kg of cement-based solidification material is mixed with the raw material.

6. A method for producing the cement-based solidification material according to any one of claims 1 to 3, A method for producing a cement-based solidification material, comprising the steps of: measuring the basicity of blast furnace slag generated from a blast furnace; sampling blast furnace slag having a basicity of 1.75 or more; and mixing the sampled blast furnace slag with Portland cement, gypsum, and acid sulfate.

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