Cement-based solidification material

Abstract

To provide a cement-based solidification material capable of preparing ground improvement soil that hardly elutes hexavalent chromium.SOLUTION: A cement-based solidification material contains cement clinker powder, gypsum powder, and blast furnace slag powder. An L value of the pulverized blast furnace slag powder in the Hunter Lab color space is 80.23 or more and 86.29 or less, and / or a b value of the pulverized blast furnace slag powder in the Hunter Lab color space is 2.80 or more and 4.89 or less. Preferably, a water-soluble hexavalent chromium content of the cement clinker powder is 27 ppm or less, a hydraulic modulus of the cement clinker powder is 2.26 or more, a SO3 content of the blast furnace slag powder is 4.00 mass% or less, and a content of blast furnace slag powder in the cement-based solidification material is 25.0 mass% or more and 45.0 mass% or less, and the SO3 content of the cement-based solidification material is 4.5 mass% or more and 8.0 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Patent Document 1 below describes a cement-based solidification material containing cement clinker powder, gypsum dihydrate powder, anhydrous gypsum powder, and ground granulated blast furnace slag. According to this document, the amount of hexavalent chromium eluted from ground improvement soil (a mixture of cement-based solidification material, water, and soil to be improved) can be reduced by setting the hydraulic ratio of the cement clinker powder to 2.00 to 2.10, the free lime content of the cement clinker powder to 0.1 to 1.0 mass%, the total chromium content in the cement clinker powder to 200 ppm or more, the proportion of water-soluble hexavalent chromium in the total chromium content to 3 mass% or less, and the proportion of SO3 in the cement-based solidification material to 3.5 to 15 mass%.

[0003] In Japan, the standard amount of hexavalent chromium contained in tap water (tap water) has been lowered from 0.05 mg / L to 0.02 mg / L in recent years. However, hexavalent chromium eluted from ground improvement soil may be mixed into tap water via groundwater. Therefore, in order to reduce the amount of hexavalent chromium contained in tap water to 0.02 mg / L or less, it is considered preferable to reduce the amount of hexavalent chromium eluted from ground improvement soil to 0.02 mg / L or less.

[0004] In the technology described in Patent Document 1 below, in a hexavalent chromium elution test (Test Example 4) using the above cement-based solidification material, the amount of water-soluble hexavalent chromium contained in the cement clinker powder was 10.7 ppm, and the amount of water-soluble hexavalent chromium contained in the ground improvement target soil was 10.7 ppm. 3 The amount of cement-based solidification material mixed in the soil is 70 kg, and the amount of hexavalent chromium eluted from the soil improvement soil is 0.02 mg / L. Therefore, if the amount of water-soluble hexavalent chromium contained in the cement clinker powder exceeds 10.7 ppm, or if the amount of water-soluble hexavalent chromium eluted in the soil improvement soil exceeds 1 m 3If the amount of cement-based solidification material mixed exceeds 70 kg, the soil will contain more hexavalent chromium (contained in the cement-based solidification material) than in Test Example 4 above, and it is thought that the amount of hexavalent chromium leaching from the soil may exceed 0.02 mg / L. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-169260 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, the present inventors have conducted various studies on cement-based solidification materials capable of producing improved soil from which hexavalent chromium is less likely to be eluted. As a result, they have found that the amount of hexavalent chromium eluted from improved soil can be reduced by adjusting the L value or b value of the ground granulated blast furnace slag contained in the cement-based solidification material to fall within a predetermined range. Based on this finding, an object of the present invention is to provide a cement-based solidification material capable of producing improved soil from which hexavalent chromium is less likely to be eluted. [Means for solving the problem]

[0007] A cement-based solidification material according to a first aspect of the present invention comprises cement clinker powder, gypsum powder, and ground granulated blast furnace slag. The ground granulated blast furnace slag has an L value of 80.23 or more and 86.29 or less in the Hunter Lab color space, and / or a b value of 2.80 or more and 4.89 or less in the Hunter Lab color space. Hereinafter, the L value, a value, and b value in the Hunter Lab color space will be simply referred to as the L value, a value, and b value, respectively. The gypsum powder may be, for example, any one of gypsum dihydrate powder, gypsum hemihydrate powder, and gypsum anhydrite powder, or a mixture of two or more thereof.

[0008] The cement-based solidification material according to the second item of the present invention is the cement-based solidification material according to the first item, wherein the water-soluble hexavalent chromium content of the cement clinker powder is 27 ppm or less, the hydraulic coefficient of the cement clinker powder is 2.26 or more, the SO3 content of the ground granulated blast furnace slag is 4.00 mass% or less, the content of the ground granulated blast furnace slag in the cement-based solidification material is 25.0 mass% or more and 45.0 mass% or less, and the SO3 content of the cement-based solidification material is 4.5 mass% or more and 8.0 mass% or less. [Effects of the Invention]

[0009] According to the first aspect of the present invention, it is possible to prepare improved soil that is less likely to elute hexavalent chromium. According to the second aspect of the present invention, it is possible to prepare improved soil that is even more unlikely to elute hexavalent chromium and has high strength. DETAILED DESCRIPTION OF THE INVENTION

[0010] A cement-based solidification material according to one embodiment of the present invention will be described. The cement-based solidification material according to this embodiment contains cement clinker powder, gypsum powder, and ground granulated blast furnace slag.

[0011] The mineral composition of the cement clinker powder of this embodiment is, for example, a C3S content of 64.9 mass% or more and 73.8 mass% or less, a C2S content of 5.4 mass% or more and 12.9 mass% or less, a C3A content of 8.8 mass% or more and 9.6 mass% or less, and a C4AF content of 7.5 mass% or more and 8.6 mass% or less.

[0012] In order to minimize the amount of hexavalent chromium eluted from the ground improved soil prepared using the cement-based solidification material according to this embodiment (hereinafter simply referred to as "hexavalent chromium elution amount"), it is preferable that the hydraulic modulus (HM) of the cement clinker powder according to this embodiment is 2.26 or more and the content of water-soluble hexavalent chromium is 27 ppm or less. In this embodiment, for example, the hydraulic modulus is 2.26 or more and 2.36 or less, and the content of water-soluble hexavalent chromium is 10 ppm or more and 27 ppm or less.

[0013] As the gypsum powder of this embodiment, for example, any one of gypsum dihydrate powder, gypsum hemihydrate powder, and anhydrous gypsum powder, or a mixture of two or more thereof, can be used.

[0014] In order to minimize the amount of hexavalent chromium eluted, the ground granulated blast furnace slag used in this embodiment satisfies the following condition (1) or (2), and preferably satisfies both of these conditions. (1) The L value of the ground granulated blast furnace slag is 80.23 or more and 86.29 or less. (2) The b value of the ground granulated blast furnace slag is 2.80 or more and 4.89 or less. The a value of the ground granulated blast furnace slag of this embodiment is, for example, −0.14 or more and 0.38 or less.

[0015] In order to minimize the amount of hexavalent chromium elution, the SO3 content of the ground granulated blast furnace slag of this embodiment is preferably 4.00% by mass or less, and the proportion of ground granulated blast furnace slag in the cement-based solidification material of this embodiment is preferably 25% by mass or more. In this embodiment, for example, the SO3 content is 0.08% by mass or more and 4.00% by mass or less. Furthermore, in order to increase the strength of the ground improvement soil of this embodiment, the proportion of ground granulated blast furnace slag in the cement-based solidification material of this embodiment is preferably 45% by mass or less.

[0016] The specific surface area of ​​the ground granulated blast furnace slag of this embodiment is, for example, 3000 cm 2 / g or more 10000cm 2 / g or less. In this specification, the specific surface area means the specific surface area measured using a Blaine air permeation device. The specific method for measuring this specific surface area is specified in "JIS R 5201."

[0017] In order to reduce the amount of hexavalent chromium elution, the total SO content of the cement-based solidification material according to this embodiment is preferably 4.5% by mass or more and 8.0% by mass or less. The specific surface area of ​​the cement-based solidification material according to this embodiment is, for example, 3000 cm 2 / g or more 10000cm2 / g or less.

[0018] Volume of soil to be improved [m 3 The mixing amount [kg] of the cement-based solidification material according to this embodiment relative to the 3 More than 300kg / m 3 The following is the result.

[0019] Next, test examples for illustrating the performance of the cement-based solidifying material according to one embodiment of the present invention will be described with reference to Tables 1 to 4.

[0020] [Table 1]

[0021] [Table 2]

[0022] [Table 3]

[0023] [Table 4]

[0024] 1. Experimental methods for each test example (Production of cement-based solidification material) In each test example (test examples A1 to A40 shown in Table 2, test examples B1 to B8 shown in Table 3, and test examples C1 to C10 shown in Table 4), cement clinker powder, gypsum powder, and granulated blast furnace slag were mixed to prepare a cement-based solidification material.

[0025] (Analysis of materials used in cement-based solidification materials) However, before preparing the cement-based solidification material, the chemical composition of the cement clinker powder to be used was measured in accordance with JIS R 5204:2019, the modulus of this cement clinker powder (Equation 1 below) was calculated based on the above chemical composition, and the mineral composition of this cement clinker powder was calculated using the Bogue formula (Equation 2 below) based on the above chemical composition. In addition, the SO3 content, L value, a value, and b value of the ground granulated blast furnace slag to be used were measured. The SO3 content was measured in accordance with JIS R 5202:2010. (Formula 1) HM = CaO / (SiO2 + Al2O3 + Fe2O3) SM = SiO2 / (Al2O3 + Fe2O3) IM=Al2O3 / Fe2O3 (Formula 2) C3S=(4.07×CaO)-((7.60×SiO2)+(6.72×Al2O3)+(1.43×Fe2O3)+(2.85×SO3)) C2S = (2.87 × SiO2) - (0.754 × C3S) C3A=(2.65×Al2O3)-(1.69×Fe2O3) C4AF = (3.04 × Fe2O3)

[0026] (Analysis of cement-based solidification materials) The SO3 content and specific surface area of ​​the prepared cement-based solidification material were also measured. The SO3 content was measured in accordance with JIS R 5204:2019.

[0027] (First experiment on cement-based solidification materials) (Step 1: Preparation of the specimen) A test specimen (corresponding to the improved soil) was prepared by mixing powdered cement-based solidification material, sample soil (corresponding to the soil to be improved), and solvent water. The method for preparing the test specimen was based on "JCAS L-01:2006: Strength test method for improved soil using cement-based solidification material." In preparing the test specimen, the volume of the sample soil [m 3 ], the amount of cement-based solidification material mixed [kg] to 100 kg / m 3The sample soil used was Kanto loam from Kawasaki City, Kanagawa Prefecture. The sample soil had a water content of 102.1% and a wet density of 1.391 g / cm. 3 The particle size composition of the sample soil was 0.6% gravel, 9.0% sand, and 90.4% fine particles.

[0028] (First experiment on cement-based solidification materials) (Step 2: Test piece performance measurement) When the specimen was 7 days old, a uniaxial compressive strength test based on "JIS A 1216:2020: Uniaxial compression test method for soil" and a hexavalent chromium elution test based on "Environmental Agency Notification No. 46 of August 23, 1991: Environmental Standards for Soil Contamination" were conducted on the specimen.

[0029] (Second experiment on cement-based solidification materials) The second experiment differed from the first experiment in the following respects, and was similar to the first experiment in respects not specified below. That is, in the second experiment, Instead of adding cement-based solidification material to the soil in powder form, we use a slurry made by adding water to the cement-based solidification material and stirring it well. Volume of sample soil [m 3 ], the amount of cement-based solidification material mixed [kg] to 100 kg / m 3 rather than 300 kg / m 3 year, The method for preparing the specimens was based on "JGS 0821-2009: Method for preparing specimens without compaction of stabilized soil" rather than "JCAS L-01:2006." Here, the slurry cement-based solidification material is a mixture of 100 mass % of cement-based solidification material and 60 mass % of water.

[0030] 2. Experimental results for each test example Table 1 shows the composition of the cement clinker powder used in each test example. In each test example, a cement-based solidification material was produced using one of the cement clinker powders Cli-1 to Cli-6 shown in Table 1. In Table 1, the items "SiO2" to "MnO" indicate the chemical composition (unit: mass%) of the cement clinker powder, the item "Total" indicates the total value of the values ​​in the items "SiO2" to "MnO", the items "HM" to "IM" indicate the modulus of the cement clinker powder, and the items "C3S" to "C4AF" indicate the mineral composition (unit: mass%) of the cement clinker powder.

[0031] In addition, Tables 2 to 4 do not specify the type of cement clinker powder used in each test example (any of Cli-1 to Cli-6 shown in Table 1), but by comparing the "HM" shown in Table 1 with the "HM" shown in Tables 2 to 4, the type of cement clinker powder used in each test example can be determined.

[0032] The meanings of the items in Tables 2 to 4 are as follows: "HM": HM (hydraulic hardness) of cement clinker powder "Cr 6+ ": Water-soluble hexavalent chromium content of cement clinker powder "SO3": SO3 content of ground granulated blast furnace slag "L value": L value of ground granulated blast furnace slag "a value": a value of ground granulated blast furnace slag "b value": b value of ground granulated blast furnace slag "Ratio": Mass percentage of ground granulated blast furnace slag to cement-based solidification material "Total SO3": SO3 content of cement-based solidification material "Specific surface area": ​​The specific surface area of ​​the cement-based solidification material Unconfined compressive strength (addition amount 100 kg / m 3 )": Measured value of unconfined compressive strength test in the first experiment Unconfined compressive strength (addition amount 300 kg / m 3 )": Measurement value of unconfined compressive strength test in the second experiment Hexavalent chromium elution amount (addition amount 100 kg / m 3 )": Measurement value of hexavalent chromium elution test in the first experiment Hexavalent chromium elution amount (addition amount 300 kg / m 3 )": Measurement values ​​of hexavalent chromium elution test in the second experiment

[0033] As shown in Table 2, in Test Examples A1 to A40, "HM" was 2.26 or more and 2.36 or less, and "Cr 6+ " is 10 ppm or more and 27 ppm or less, "SO3" is 0.08 mass% or more and 4.00 mass% or less, "L value" is 80.23 or more and 86.29 or less, "a value" is -0.14 or more and 0.38 or less, "b value" is 2.80 or more and 4.89 or less, "ratio" is 25 mass% or more and 45 mass% or less, "total SO3" is 4.5 mass% or more and 8.0 mass% or less, and "specific surface area" is 3850 cm 2 / g or more 4200cm 2 / g or less. In the following, these items are collectively referred to as "condition items."

[0034] Furthermore, as shown in Table 2, in test examples A1 to A40, the "uniaxial compressive strength (addition amount 100 kg / m 3 ) is 269kN / m 2 More than 370kN / m 2 Hereafter, "uniaxial compressive strength (addition amount 300 kg / m 3 )" is 1880kN / m 2 More than 2300kN / m 2 The following is the "amount of hexavalent chromium elution (addition amount 100 kg / m 3 ) and "Hexavalent chromium elution amount (addition amount 300 kg / m 3 ) is below 0.02 mg / L.

[0035] As shown in Table 3, in test examples B1 to B4, only the "L value" of the condition items is outside the range of test examples A1 to A40, and in test examples B5 to B8, only the "b value" of the condition items is outside the range of test examples A1 to A40. 3 ) and "Uniaxial compressive strength (addition amount 300 kg / m 3) is within the range of test examples A1 to A40, but the amount of hexavalent chromium elution (addition amount 100 kg / m 3 ) and "Hexavalent chromium elution amount (addition amount 300 kg / m 3 )" is outside the range of test examples A1 to A40.

[0036] As shown in Table 4, in test example C1, only "HM" among the condition items was outside the range of test examples A1 to A40, and in test examples C2 and C3, only "Cr" among the condition items was outside the range of test examples A1 to A40. 6+ In test examples C4 and C5, only "SO3" out of the condition items is outside the range of test examples A1 to A40, in test examples C6 and C7, only "ratio" out of the condition items is outside the range of test examples A1 to A40, and in test examples C8 to C10, only "total SO3" out of the condition items is outside the range of test examples A1 to A40. 3 ) and "Uniaxial compressive strength (addition amount 300 kg / m 3 ) is within the range of test examples A1 to A40, but the amount of hexavalent chromium elution (addition amount 100 kg / m 3 ) and "Hexavalent chromium elution amount (addition amount 300 kg / m 3 )" exceeds the range of test samples A1 to A40. In test samples C7 to C10, the "elution amount of hexavalent chromium (addition amount 100 kg / m 3 ) and "Hexavalent chromium elution amount (addition amount 300 kg / m 3 ) is within the range of test examples A1 to A40, but the "uniaxial compressive strength (addition amount 100 kg / m 3 ) and "Uniaxial compressive strength (addition amount 300 kg / m 3 )" is below the range of test examples A1 to A40.

[0037] 3. Discussion The above experimental results can be considered as follows. (1) When the L value of the blast furnace slag powder contained in the cement-based solidification material is in the range of 80.23 or more and 86.29 or less (Test Examples A1 to A40), the amount of hexavalent chromium leaching from the ground improvement soil can be reduced compared to when it is not in this range (Test Examples B1 to B4), provided that all other conditions are similar. (2) When the b value of the blast furnace slag powder contained in the cement-based solidification material is in the range of 2.80 or more and 4.89 or less (Test Examples A1 to A40), the amount of hexavalent chromium leaching from the ground improvement soil can be reduced compared to when it is not in this range (Test Examples B5 to B8), provided that all other conditions are similar. (3) When the hydraulic ratio of the cement clinker powder contained in the cement-based solidification material is in the range of 2.26 or more (Test Examples A1 to A40), the amount of hexavalent chromium leaching from the ground improvement soil can be reduced compared to when it is not in this range (Test Example C1), provided that the conditions other than the hydraulic ratio are similar. (4) When the water-soluble hexavalent chromium content of the cement clinker powder contained in the cement-based solidification material is in the range of 27 ppm or less (Test Examples A1 to A40), the amount of hexavalent chromium leaching from the ground improvement soil can be reduced compared to when it is not in this range (Test Examples C2 and C3), provided that all other conditions are similar. (5) When the SO3 content of the blast furnace slag powder contained in the cement-based solidification material is in the range of 4.00 mass% or less (Test Examples A1 to A40), the amount of hexavalent chromium leaching from the ground improvement soil can be reduced compared to when it is not in this range (Test Examples C4 and C5), provided that all conditions other than the SO3 content are similar. (6) When the content of blast furnace slag powder in the cement-based solidification material is in the range of 25 mass% or more (Test Examples A1 to A40), the amount of hexavalent chromium leaching from the ground improvement soil can be reduced compared to when it is not in this range (Test Example C6), provided that all other conditions are similar. (7) When the content of blast furnace slag powder in the cement-based solidification material is in the range of 45 mass% or less (test examples A1 to A40), the strength of the ground improvement soil can be increased compared to when it is not in this range (test example C7), provided that all other conditions are the same. (8) When the SO3 content of the cement-based solidification material is in the range of 4.5 mass% or more and 8.0 mass% or less (test examples A1 to A40), the strength of the ground improvement soil can be increased compared to when it is not in this range (test examples C8 to C10), provided that all conditions other than the SO3 content are similar.

Claims

1. A cement-based solidification material containing cement clinker powder, gypsum powder, and ground granulated blast furnace slag, the L value of the ground granulated blast furnace slag in the Hunter Lab color space is 80.23 or more and 86.29 or less, and / or the b value of the ground granulated blast furnace slag in the Hunter Lab color space is 2.80 or more and 4.89 or less, The cement clinker powder has a water-soluble hexavalent chromium content of 27 ppm or less, The hydraulic coefficient of the cement clinker powder is 2.26 or more, The ground granulated blast furnace slag has an SO 3 content of 4.00 mass% or less, The content of the ground granulated blast furnace slag in the cement-based solidification material is 25.0% by mass or more and 45.0% by mass or less, The cement-based solidification material has an SO 3 content of 4.5 mass % or more and 8.0 mass % or less.

2. The cement-based solidification material according to claim 1, characterized in that the gypsum powder is any one of gypsum dihydrate powder, gypsum hemihydrate powder, and anhydrous gypsum powder, or a mixture of two or more thereof.

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