Cement-based solidification material

Abstract

To provide a cement-based solidification material that prevents the elution of heavy metals from solidified improved soil (a blend of soil and solidification material) and significantly increases the strength of the solidified improved soil (such as uniaxial compressive strength).SOLUTION: A cement-based solidification material comprises cement, gypsum powder, ground granulated blast furnace slag, and magnesium compound powder. The magnesium compound powder is at least one selected from the group consisting of magnesium nitrate powder, magnesium chloride powder, and magnesium sulfate powder. The amount of the magnesium compound powder is 0.6-10.0 pts.mass relative to a total of 100 pts.mass of the cement, gypsum powder, and ground granulated blast furnace slag.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a cement-based solidification material. [Background technology]

[0002] A known method for solidifying soil involves adding a solidifying material such as cement to the soil, mixing it, and then hydrating it to solidify, thereby increasing the strength of the mixture of soil and solidifying material (solidified and improved soil). For example, Patent Document 1 describes a solidification material that is excellent in initial strength development and ease of handling, which is made of hydraulic powder and is characterized by containing moisture in an amount such that the mass loss when heated for 5 minutes at a temperature of 90°C in a windless atmosphere is 0.28 to 0.76 parts by mass per 100 parts by mass of the hydraulic powder.

[0003] On the other hand, as an insolubilizing material for suppressing the elution of heavy metals from soil contaminated with heavy metals, for example, Patent Document 2 describes an insolubilizing material mainly composed of light-burned magnesia, characterized in that the forsterite content is 6.0 mass% or less and the fluorine (F) content is 0.045 mass% or less in a total amount (100 mass%) of the insolubilizing material. Furthermore, Patent Document 3 describes a fluorine elution inhibitor that contains a cement-based solidification material and further contains lime as a fluorine elution inhibitor that can inhibit the elution of fluorine from improved soil under specific conditions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-115048 A [Patent Document 2] JP 2017-113703 A [Patent Document 3] JP 2018-172526 A Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a cement-based solidification material that can suppress the leaching of heavy metals from solidified and improved soil (a mixture of soil and solidification material) and can sufficiently increase the strength (e.g., uniaxial compressive strength) of the solidified and improved soil. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned object can be achieved by a cement-based solidification material containing cement, gypsum powder, ground granulated blast furnace slag, and one or more magnesium compound powders selected from the group consisting of magnesium nitrate powder, magnesium chloride powder, and magnesium sulfate powder, in which the amount of the magnesium compound powder is 0.6 to 10.0 parts by mass per 100 parts by mass of the total of the cement, gypsum powder, and ground granulated blast furnace slag, and have completed the present invention. That is, the present invention provides the following [1] to [6]. [1] A cement-based solidification material comprising cement, gypsum powder, ground granulated blast furnace slag, and a magnesium compound powder, wherein the magnesium compound powder is one or more selected from the group consisting of magnesium nitrate powder, magnesium chloride powder, and magnesium sulfate powder, and the amount of the magnesium compound powder is 0.6 to 10.0 parts by mass per 100 parts by mass of the total of the cement, the gypsum powder, and the ground granulated blast furnace slag. [2] The cement-based solidification material according to [1], wherein, in a total of 100% by mass of the cement, the gypsum powder, and the ground granulated blast furnace slag, the proportion of the cement is 10 to 80% by mass, the proportion of the gypsum powder is 1 to 40% by mass in terms of SO3, and the proportion of the ground granulated blast furnace slag is 5 to 70% by mass. [3] The cement-based solidification material according to [1] or [2], wherein the gypsum powder is anhydrous gypsum powder.

[0007] [4] A method for producing the cement-based solidification material according to any one of [1] to [3] above, comprising: a cement composition preparation step of mixing the cement, the gypsum powder, and the ground granulated blast furnace slag to obtain a cement composition; and a cement-based solidification material preparation step of mixing the cement composition and the magnesium compound powder to obtain the cement-based solidification material. [5] A method for solidifying soil containing heavy metals using the cement-based solidification material described in any one of [1] to [3] above, characterized in that the cement-based solidification material is added to and mixed with soil containing heavy metals to obtain solidified improved soil. [6] The solidification method according to [5], wherein the soil has a water content of 80% or more and an ignition loss of 10% by mass or more. Effect of the Invention

[0008] The object of the present invention is to provide a cement-based solidification material that can suppress the leaching of heavy metals from solidified and improved soil and can sufficiently increase the strength (e.g., uniaxial compressive strength) of the solidified and improved soil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The cement-based solidification material of the present invention is a cement-based solidification material containing cement, gypsum powder, ground granulated blast furnace slag, and magnesium compound powder, wherein the magnesium compound powder is one or more selected from the group consisting of magnesium nitrate powder, magnesium chloride powder, and magnesium sulfate powder, and the amount of the magnesium compound powder is 0.6 to 10.0 parts by mass per 100 parts by mass of the total of the cement, gypsum powder, and ground granulated blast furnace slag. The details are explained below. Examples of cements that can be used in the present invention include various types of Portland cements, such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement, as well as mixed cements, such as blast-furnace cement, fly ash cement, and silica cement, alumina cement, and ecocement, etc. These may be used alone or in combination of two or more. Among these, from the viewpoints of cost, versatility, etc., various types of Portland cement are preferred, and ordinary Portland cement is more preferred. Furthermore, when blast furnace cement is used as the cement, the ground granulated blast furnace slag contained in the blast furnace cement corresponds to the "ground granulated blast furnace slag" used in the present invention. In other words, only the cement contained in the blast furnace cement (the material obtained by excluding ground granulated blast furnace slag from blast furnace cement) corresponds to the "cement" used in the present invention. Furthermore, the amount of ground granulated blast furnace slag contained in the blast furnace cement is not included in the amount of "cement" used in the present invention, but is included in the amount of "ground granulated blast furnace slag" used in the present invention.

[0010] Furthermore, when cement contains gypsum, the gypsum is not included in the "gypsum powder" used in the present invention. The proportion of gypsum in cement is usually 0.1 to 5.0 mass%, preferably 0.5 to 4.0 mass%, and more preferably 1.0 to 3.0 mass%, calculated as SO3. The gypsum contained in the cement is not particularly limited, but is usually gypsum dihydrate, gypsum hemihydrate, or a mixture of gypsum dihydrate and gypsum hemihydrate. The Blaine specific surface area of ​​the cement is preferably 2,500 to 4,000 cm 2 / g, more preferably 3,000 to 3,800 cm 2 / g, and particularly preferably 3,200 to 3,600 cm 2 / g. The above Blaine specific surface area is 2,500 cm 2 If the specific surface area of ​​the Blaine is 4,000 cm or more, the strength of the solidified improved soil can be increased. 2If the content is 1 / g or less, the materials are easily available, and an increase in the cost of the materials can be prevented.

[0011] The proportion of cement in the cement-based solidification material, which is a total of 100% by mass of cement, powdered gypsum, and ground granulated blast furnace slag, is preferably 10 to 80% by mass, more preferably 25 to 65% by mass, and particularly preferably 40 to 53% by mass. If the proportion is 10% by mass or more, the strength of the solidified and improved soil can be increased. If the proportion is 80% by mass or less, an increase in the cost of the cement-based solidification material can be prevented.

[0012] Examples of the types of gypsum powder used in the present invention include powders of natural dihydrate gypsum, flue gas desulfurized gypsum, phosphate gypsum, titanic gypsum, hydrofluoric gypsum, etc. These may be used alone or in combination of two or more. Examples of the form of gypsum (whether hydrated or not) include gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. The gypsum powder may be a powder consisting of only one type of form, or may be a powder containing two or more types of forms. Among these, anhydrous gypsum is preferred from the viewpoints of further suppressing the elution of heavy metals from the solidified and improved soil and increasing the strength of the solidified and improved soil. The Blaine specific surface area of ​​the gypsum powder is preferably 2,000 to 12,000 cm 2 / g, more preferably 2,500 to 6,000 cm 2 / g, and more preferably 2,800 to 5,000 cm 2 / g, and particularly preferably 3,000 to 4,000 cm 2 / g. The above Blaine specific surface area is 2,000 cm 2 If the specific surface area of ​​the Blaine is 12,000 cm / g or more, the strength of the solidified improved soil can be increased. 2 If the content is 1 / g or less, the materials are easily available, and an increase in the cost of the materials can be prevented.

[0013] The proportion of gypsum powder (SO3 equivalent) in the total of 100% by mass of cement, gypsum powder, and ground granulated blast furnace slag contained in the cement-based solidification material is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, and particularly preferably 13 to 25% by mass. If the proportion is 1% by mass or more, the workability (particularly ensuring a sufficiently long workable time) when mixing the cement-based solidification material with soil is improved. If the proportion is 40% by mass or less, the strength development of the cement-based solidification material is further improved.

[0014] Examples of the ground granulated blast furnace slag used in the present invention include fine powders such as granulated slag obtained by quenching with water and crushing molten slag, which is a by-product of pig iron production in a blast furnace, and slowly cooled slag obtained by crushing the molten slag. These may be used alone or in combination of two or more. The Blaine specific surface area of ​​the ground granulated blast furnace slag is preferably 3,000 to 10,000 cm 2 / g, more preferably 3,200 to 8,000 cm 2 / g, and more preferably 3,500 to 6,000 cm 2 / g, and particularly preferably 3,800 to 5,000 cm 2 / g. The above Blaine specific surface area is 3,000 cm 2 / g or more, the strength development of the solidification material can be further improved. 2 If the molecular weight is less than 1 / g, the materials are easily available and the cost is not excessively high.

[0015] The proportion of ground granulated blast furnace slag in the total of 100% by mass of cement, gypsum powder, and ground granulated blast furnace slag contained in the cement-based solidification material is preferably 5 to 70% by mass, more preferably 10 to 65% by mass, even more preferably 25 to 58% by mass, and particularly preferably 35 to 55% by mass. If the proportion is 5% by mass or more, the initial strength of the solidified improved soil (e.g., less than 28 days old) can be increased. If the proportion is 70% by mass or less, the long-term strength of the solidified improved soil (e.g., 28 days or more old) can be increased.

[0016] The magnesium compound powder used in the present invention is at least one selected from the group consisting of magnesium nitrate powder, magnesium chloride powder, and magnesium sulfate powder. Among them, magnesium sulfate powder is preferable from the viewpoint of increasing the strength of the solidified improved soil, magnesium chloride powder is preferable from the viewpoint of further reducing the amount of fluorine eluted from the solidified improved soil, and magnesium nitrate powder is preferable from the viewpoint of further reducing the amount of arsenic eluted from the solidified improved soil.

[0017] The amount of magnesium compound powder relative to 100 parts by mass of the total of cement, gypsum powder, and ground granulated blast furnace slag is 0.6 to 10.0 parts by mass, preferably 0.8 to 8.0 parts by mass, more preferably 1.5 to 7.0 parts by mass, even more preferably 2.5 to 6.5 parts by mass, and particularly preferably 4.0 to 6.0 parts by mass. If the amount is less than 0.6 parts by mass, the amount of heavy metals eluted from the solidified improved soil increases. If the amount exceeds 10.0 parts by mass, the strength of the solidified improved soil may decrease. In addition, the cost of materials becomes excessively high.

[0018] The cement-based solidification material of the present invention may contain other materials as long as the effects of the present invention are not affected. Examples of other materials include fly ash and limestone powder. The ratio of other materials in the cement-based solidification material is not particularly limited, but is usually 10% by mass or less, preferably 5% by mass or less. The cement-based solidification material of the present invention is in powder form. The Blaine specific surface area of ​​the cement-based solidification material is preferably 3,000 to 12,000 cm 2 / g, more preferably 4,000 to 10,000 cm 2 / g, and particularly preferably 5,000 to 8,000 cm 2 / g. The above Blaine specific surface area is 3,000 cm 2 If the specific surface area of ​​the Blaine is 12,000 cm / g or more, the strength of the solidified improved soil can be increased. 2 If the content is 1 / g or less, the materials are easily available, and an increase in the cost of the materials can be prevented.

[0019] The cement-based solidification material of the present invention can be produced by appropriately mixing the above-mentioned raw materials. An example of the method for producing the cement-based solidification material of the present invention includes a method including a cement composition preparation step of mixing cement, gypsum powder, and ground granulated blast furnace slag to obtain a cement composition, and a cement-based solidification material preparation step of mixing the cement composition obtained in the above step with magnesium compound powder to obtain a cement-based solidification material.

[0020] According to the cement-based solidification material of the present invention, it is possible to suppress the amount of heavy metals leaching from soil containing heavy metals to be solidified, and to sufficiently increase the strength (e.g., unconfined compressive strength) of the soil. Here, heavy metals are any of the following: cadmium and its compounds, hexavalent chromium compounds, cyanide, mercury and its compounds, selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds (listed as Type 2 specified hazardous substances in the Soil Contamination Countermeasures Act (2003)). Note that fluorine and boron are not heavy metals, but fluorine and its compounds, and boron and its compounds are considered to be included in heavy metals. Two or more of these may be contained in the above soil. One example of a method for solidifying soil containing heavy metals using the cement-based solidification material of the present invention is a method in which the cement-based solidification material is added to and mixed with soil containing heavy metals to obtain solidified improved soil. Examples of methods for adding and mixing a cement-based solidification material to soil include a dry addition method in which the cement-based solidification material is added in powder form to the soil and mixed, and a slurry addition method in which a slurry containing the cement-based solidification material and water is added to the soil and mixed. In addition, the above-mentioned slurry includes a slurry obtained by mixing a cement-based solidification material with water, as well as a slurry obtained by mixing a mixture of cement, gypsum powder, and ground granulated blast furnace slag with water, and a slurry obtained by adding water to a magnesium compound powder.

[0021] Soil containing heavy metals that is the subject of solidification treatment is not particularly limited, but examples include clayey soil (for example, Kanto loam) and organic soil. Furthermore, from the viewpoint of being able to perform sufficient solidification treatment and insolubilization treatment of heavy metals even in soils in which solidification treatment and insolubilization treatment of heavy metals was difficult using conventional solidification materials, it is preferable to target soils with a water content of 80% or more (more preferably 100% or more, and particularly preferably 200% or more) and an ignition loss of 10% by mass or more (more preferably 20% by mass or more, and particularly preferably 40% by mass or more) for solidification treatment. From the viewpoint of ensuring sufficient strength of the solidified and improved soil, the water content is preferably 500% or less, and more preferably 400% or less. From the viewpoint of ensuring sufficient strength of the solidified improved soil, the ignition loss is preferably 60 mass % or less, and more preferably 50 mass % or less.

[0022] Before carrying out the above-mentioned solidification method, an evaluation method for evaluating the suitability of the solidification method, which includes a measuring step and a judging step, may be carried out. By carrying out the evaluation method in advance, it is possible to carry out an efficient solidification treatment of soil containing heavy metals. [Measurement process] This step is a step for measuring the water content and loss on ignition of soil containing heavy metals. This process makes it possible to obtain the properties of soil containing heavy metals. In this process, at least one of the type and amount of elution of the heavy metals may be measured. Also, the type of magnesium compound powder contained in the cement-based solidification material may be determined according to the type of heavy metals measured. For example, if the soil contains fluorine and the amount of elution is large (environmental standards are not met), magnesium chloride powder may be selected as the magnesium compound powder. If the soil contains arsenic and the amount of elution is large (environmental standards are not met), magnesium nitrate powder may be selected as the magnesium compound powder.

[0023] [Judgment process] This step is a step of determining that if the water content and ignition loss of the soil obtained in the measurement step satisfy specific values ​​(e.g., a water content of 80% or more and an ignition loss of 10% by mass or more), the soil is to be subjected to solidification treatment by mixing with the cement-based solidification material of the present invention, and that if the water content and ignition loss do not satisfy specific values ​​(e.g., a water content of 80% or more and an ignition loss of 10% by mass or more), the soil is not to be subjected to solidification treatment by mixing with the cement-based solidification material of the present invention. In addition, if it is determined in the determination process that the above soil is not to be subjected to solidification treatment, sufficient solidification treatment can be performed without using the cement-based solidification material of the present invention, so from the viewpoint of reducing the cost of solidification treatment, solidification treatment can be performed using a general solidification material.

[0024] 1m of soil to be solidified 3 The amount of cement-based solidification material to be added per m of soil to be improved varies depending on the properties of the soil, the amount of heavy metals contained in the soil, the conditions of application, and the strength required for the solidified improved soil obtained after treatment. 3 The weight is preferably 50 to 500 kg, more preferably 100 to 400 kg, and particularly preferably 150 to 300 kg. If the amount is 50 kg or more, the strength of the solidified improved soil can be increased and the elution of heavy metals can be further suppressed, whereas if the amount is 500 kg or less, an excessive increase in costs can be prevented. EXAMPLES

[0025] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Cement: Ordinary Portland cement; percentage of gypsum (mixture of gypsum dihydrate and hemihydrate) in cement: 2.0% by mass (SO3 equivalent); manufactured by Taiheiyo Cement Corporation; Blaine specific surface area: 3,340 cm 2 / g (2) Blast furnace slag powder (shown as "blast furnace slag" in Tables 2 and 3); manufactured by Dice Corporation, product name "Cerament", Blaine specific surface area: 4,000 cm 2 / g (3) Anhydrous gypsum powder (shown as "anhydrous gypsum" in Tables 2 and 3); manufactured by Kokusai Shoji Co., Ltd., natural anhydrous gypsum, Blaine specific surface area: 3,200 cm 2 / g (4) Magnesium compound powder (shown as "magnesium compound" in Tables 2 and 3) A: Magnesium chloride hexahydrate, manufactured by Naikai Salt Co., Ltd., reagent (purity: 95% by mass or more) (5) Magnesium compound powder B; magnesium sulfate anhydrate, Fujifilm Wako Pure Chemical Industries, Ltd., reagent (purity: 95% by mass or more) (6) Magnesium compound powder C; magnesium nitrate hexahydrate, Fujifilm Wako Pure Chemical Industries, Ltd., reagent (purity: 98% by mass or more) (7) Soil A: Clay soil (details are shown in Table 1) (8) Soil B: organic soil (details are shown in Table 1).

[0026] [Table 1]

[0027] [Examples 1 to 6, Comparative Examples 2 to 4] A cement composition was obtained by mixing cement, ground granulated blast furnace slag, and anhydrous gypsum powder in the amounts shown in Table 2. Next, magnesium compound powder of the type and amount shown in Table 2 was mixed into the obtained cement composition until the materials became homogenous, to obtain a cement-based solidification material. In Tables 2 and 3, the amount of anhydrous gypsum powder is an SO3 equivalent value, and the amount of magnesium compound powder is an anhydrous equivalent value. The obtained cement-based solidification material was applied to soil A (clay soil) and 1 m 3 The cement-based solidification material was added in the amounts shown in Table 2 per unit, and mixed to obtain solidified improved soil. The unconfined compressive strength of the obtained solidified and improved soil at an age of 7 days was measured in accordance with JIS A 1216:2020 (Unconfined compression test method for soil). The solidified improved soil was sealed and cured for 7 days at approximately 20°C. The amount of fluorine and its compounds eluted from the solidified improved soil after curing was measured in accordance with Notification No. 18 of the Ministry of the Environment.

[0028] [Comparative Example 1] A solidified and improved soil was obtained in the same manner as in Example 1, except that no magnesium compound powder was used and a cement composition was used as the cement-based solidification material. The unconfined compressive strength of the obtained solidified and improved soil at an age of 7 days and the amount of fluorine and its compounds eluted from the solidified and improved soil after curing were measured in the same manner as in Example 1. [Comparative Example 5] Solidified improved soil was obtained in the same manner as in Example 1, except that the ground granulated blast furnace slag and the powdered anhydrous gypsum were not used. The unconfined compressive strength of the obtained solidified and improved soil at an age of 7 days and the amount of fluorine and its compounds eluted from the solidified and improved soil after curing were measured in the same manner as in Example 1. The results are shown in Table 2.

[0029] [Table 2]

[0030] From Table 2, the unconfined compressive strength (269 to 452 kN / m) of the solidified and improved soil in Examples 1 to 6 using the cement-based solidification material of the present invention at a material age of 7 days was 2 ) is the unconfined compressive strength (152-225 kN / m) at 7 days of the solidified improved soil in Comparative Example 1 (similar to Examples 1-3 except that it does not contain magnesium compound powder) and Comparative Example 5 (similar to Example 1 except that it does not contain ground granulated blast furnace slag and anhydrous gypsum powder). 2 ) is found to be larger than Furthermore, it can be seen that the elution amounts of fluorine and its compounds from the solidified improved soils in Examples 1 to 6 using the cement-based solidification material of the present invention (0.65 to 0.79 mg / liter) meet the environmental standard value (0.8 mg / liter or less) and are smaller than the elution amounts of fluorine and its compounds from the solidified improved soils in Comparative Examples 1 to 5 (0.85 to 1.20 mg / liter).

[0031] [Examples 7 to 11, Comparative Examples 7 to 9] A cement composition was obtained by mixing cement, ground granulated blast furnace slag, and anhydrous gypsum powder in the amounts shown in Table 3. Next, magnesium compound powder of the type and amount shown in Table 3 was mixed into the obtained cement composition until the materials became homogenous, to obtain a cement-based solidification material. The obtained cement-based solidification material was applied to soil B (organic soil) by 1 m 3 The cement-based solidification material was added in the amounts shown in Table 3 per unit, and mixed to obtain solidified improved soil. The unconfined compressive strength of the obtained solidified and improved soil at an age of 7 days was measured in accordance with JIS A 1216:2020 (Unconfined compression test method for soil). The solidified and improved soil was sealed and cured for 7 days at approximately 20°C. The amount of arsenic and its compounds eluted from the solidified and improved soil after curing was measured in accordance with Notification No. 18 of the Ministry of the Environment.

[0032] [Comparative Example 6] A solidified and improved soil was obtained in the same manner as in Example 7, except that no magnesium compound powder was used and a cement composition was used as the cement-based solidification material. The unconfined compressive strength of the obtained solidified and improved soil at an age of 7 days and the amount of arsenic and its compounds eluted from the solidified and improved soil after curing were measured in the same manner as in Example 7. [Comparative Example 10] Solidified improved soil was obtained in the same manner as in Example 7, except that the ground granulated blast furnace slag and the powdered anhydrous gypsum were not used. The unconfined compressive strength of the obtained solidified and improved soil at an age of 7 days and the amount of arsenic and its compounds eluted from the solidified and improved soil after curing were measured in the same manner as in Example 7. The results are shown in Table 3.

[0033] [Table 3]

[0034] From Table 3, the unconfined compressive strength (407-602 kN / m) of the solidified improved soil in Examples 7-11 using the cement-based solidification material of the present invention at a material age of 7 days was 2 ) is the unconfined compressive strength (254 kN / m) of the solidified improved soil in Comparative Example 10 (which is the same as Example 7 except that it does not contain ground granulated blast furnace slag and anhydrous gypsum powder and the amount of magnesium compound is 9 parts by mass) at 7 days of age. 2 ) is found to be larger than In addition, the amount of arsenic and its compounds leached from the solidified improved soil in Examples 7 to 11 using the cement-based solidification material of the present invention (0.005 to 0.009 mg / liter) satisfies the environmental standard value (0.01 mg / liter or less) and is smaller than the amount of arsenic and its compounds leached from the solidified improved soil in Comparative Examples 6 to 10 (0.011 to 0.020 mg / liter).

Claims

1. A cement-based solidification material comprising cement, gypsum powder, ground granulated blast furnace slag, and magnesium compound powder, The magnesium compound powder is at least one selected from the group consisting of magnesium nitrate powder, magnesium chloride powder, and magnesium sulfate powder, A cement-based solidification material, characterized in that the amount of the magnesium compound powder is 0.6 to 10.0 parts by mass per 100 parts by mass of the total of the cement, the gypsum powder, and the ground granulated blast furnace slag.

2. The ratio of the cement is 10 to 80 mass % of the total of the cement, the gypsum powder, and the ground granulated blast furnace slag, and the ratio of the gypsum powder is SO ３ 2. The cement-based solidification material according to claim 1, wherein the content of the ground granulated blast furnace slag is 5 to 70 mass % in terms of the total mass of the cement-based solidification material.

3. 2. The cement-based solidification material according to claim 1, wherein the gypsum powder is anhydrous gypsum powder.

4. A method for producing the cement-based solidification material according to any one of claims 1 to 3, comprising: a cement composition preparation step of mixing the cement, the gypsum powder, and the ground granulated blast furnace slag to obtain a cement composition; A method for producing a cement-based solidification material, comprising the step of preparing a cement-based solidification material by mixing the cement composition and the magnesium compound powder to obtain the cement-based solidification material.

5. A method for solidifying soil containing heavy metals using the cement-based solidification material according to any one of claims 1 to 3, A solidification method comprising adding and mixing the above-mentioned cement-based solidification material with soil containing heavy metals to obtain solidified and improved soil.

6. 6. The solidification method according to claim 5, wherein the soil has a water content of 80% or more and an ignition loss of 10% by mass or more.

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