Neutral solidifying material

Abstract

To provide a neutral solidifying material enabling formation of improved soil having pH kept around neutral and strength less likely to decrease during reuse.SOLUTION: The neutral solidifying material of the present invention contains alumina cement and an alkaline earth metal compound. The neutral solidifying material contains 2 mass% or more and less than 40 mass% of the alumina cement. The neutral solidifying material preferably contains at least one alkaline earth metal compound selected from the group consisting of gypsum and calcium carbonate. The neutral solidifying material preferably contains 0.1 mass% or more and 20 mass% or less of a polymer flocculant. The neutral solidifying material may also preferably contain 0.1 mass% or more and 70 mass% or less of a sulfate containing at least one cation selected from the group consisting of iron ions, aluminum ions, and ammonium ions.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a neutral solidification material used for soil improvement. [Background technology]

[0002] Soil solidification materials are used to improve the strength of soft soil generated during civil engineering works such as road and tunnel construction, making it easier to remove and reuse it. Soil solidification materials are known to be classified into cement-based, lime-based, and gypsum-based materials. In recent years, neutral solidification materials that can maintain the pH of improved soil near neutral have been used, taking into consideration the preservation of the surrounding environment, such as water quality and vegetation. Cement-based and lime-based solidification materials have room for improvement because they cause the soil to have an alkaline pH. Gypsum-based solidification materials have room for improvement because they do not develop sufficient strength.

[0003] For the purpose of improving soil strength with a solidification material, Patent Document 1, for example, discloses a soil solidification material that contains magnesium oxide, aluminum sulfate and / or iron sulfate, with the remainder being gypsum. Patent Document 2 discloses a neutral solidification material containing 30 to 80 parts by mass of alumina cement and 20 to 70 parts by mass of anhydrous aluminum sulfate. Also known is a neutral solidifying material having insolubilizing properties, which is obtained by adding calcium carbonate and acidic sulfate compounds such as aluminum sulfate and ferrous sulfate to light-burned magnesia or light-burned magnesia partially hydrated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-109829 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-210255 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the improved soil obtained by treating soft soil with the above-mentioned solidification materials is excavated and reused after being cured for a certain period of time, the strength of the improved soil may be lower than it was immediately after improvement. None of the above-mentioned documents considers this point at all. Therefore, an object of the present invention is to provide a neutral solidification material that can obtain improved soil that is less likely to lose strength when reused while maintaining a pH close to neutral. [Means for solving the problem]

[0006] As a result of intensive research conducted by the present inventors to solve the above problems, it was found that it is effective to use an alumina cement-based solidifying agent and to use a specific amount of alumina cement in combination with other components. The present invention is based on the above findings, Alumina cement and an alkaline earth metal compound; The alumina cement is contained in an amount of 2% by mass or more and less than 40% by mass. The above problem is solved by providing a neutral solidification material. [Effects of the Invention]

[0007] By treating soft soil with the neutral solidification material of the present invention, the pH of the solidified soil can be maintained near neutral, and the strength of the soil is less likely to decrease when it is reused. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described below based on preferred embodiments thereof. The neutral solidification material of the present invention is a material that can be mixed with the soil to be improved to obtain improved soil that maintains a pH in the neutral range and is resistant to loss of strength when reused. Examples of soil that can be solidified include wet soil such as soft soil containing water, and construction waste soil and construction sludge that are generated secondarily during various construction works such as road construction, tunnel construction using the shield tunneling method, and building construction. The neutral solidification material of the present invention is suitable for solidifying at least one of wet soil, construction waste soil, and construction sludge. In the following description, "improved soil" refers to soil that has been improved by adding the neutral solidification material of the present invention to the soil that is the target of solidification treatment.

[0009] As used herein, "neutral" means that the pH of the improved soil is between 5.8 and 8.6. This is the value shown in the section on "discharge into public waters other than the sea" in the pH standards for wastewater stipulated in the Water Pollution Control Act. Therefore, improved soil containing the neutral solidification material of the present invention complies with the wastewater standards, even if, for example, rainwater that has permeated the improved soil flows into groundwater or a river. Therefore, improved soil treated with the neutral solidification material of the present invention is not limited in its application or location of use. Furthermore, improved soil treated with the neutral solidification material of the present invention has a reduced environmental impact and can be easily reused.

[0010] The neutral solidification material of the present invention is a composition containing the following components (1) and (2): (1) Alumina cement. (2) Alkaline earth metal compounds. Each component will be described below.

[0011] (1) Alumina cement The neutral solidification material of the present invention contains alumina cement as one of its constituent components. There are several types of alumina cement, including those for fire resistance and building materials, and any type can be used in the present invention. From the viewpoint of improving workability and solidification strength, the alumina cement preferably contains 10% by mass or more and 70% by mass or less of Al2O3, and more preferably 30% by mass or more and 60% by mass or less.

[0012] The alumina cement content in the neutral solidification material is preferably 2% by mass or more, more preferably 4% by mass or more, and even more preferably 6% by mass or more. By setting the alumina cement content in this manner, the soil to be treated can be solidified with sufficient strength. The alumina cement content in the neutral solidification material is preferably less than 40% by mass, more preferably less than 35% by mass, and even more preferably less than 25% by mass. By setting the alumina cement content in this manner, the strength of the improved soil treated with the neutral solidification material of the present invention can be sufficiently increased, and the pH of the improved soil can be maintained near neutral.

[0013] Alumina cement has the mineral composition CA (CaO·Al2O3), C 12 It may contain at least one selected from A7(12CaO·7Al2O3), C4AF(4CaO·Al2O3·Fe2O3), C2AS(2CaO·Al2O3·SiO2), C2S(α)(2CaO·SiO2), C2S(β)(2CaO·SiO2), CaTiO3 and Fe3O4. In addition to the mineral composition above, aluminous cement contains FeO and Ca4Al6O 12 It may contain at least one selected from SO4.

[0014] CA and C in aluminous cement 12 The content ratio of A7 is set to a value that satisfies the following requirements: CA and C, from the viewpoint of sufficiently increasing the strength of the improved soil treated with the neutral solidification material of the present invention and maintaining the pH of the improved soil near neutral. 12The total content of A7 is preferably 30% by mass or more and 70% by mass or less, more preferably 35% by mass or more and 65% by mass or less, and even more preferably 40% by mass or more and 60% by mass or less.

[0015] The content of each mineral component mentioned above can be measured by Rietveld analysis of the powder X-ray diffraction pattern of the alumina cement. The measurement conditions were as follows: a BrukerAXS D2 PHASER X-ray diffractometer, tube voltage: 30 kV, tube current: 10 mA, tube: Cu, scan range: 2θ = 5 to 70°, step width: 0.02°, scan speed: 1.4° / min. The Rietveld analysis was performed using a BrukerAXS TOPAS.

[0016] The alumina cement may contain at least one element selected from Al, Si, Fe, Ca, Mg, and S. When alumina cement is chemically analyzed in accordance with JIS R5020:2010, it is found that the alumina cement contains aluminum, calculated as Al2O3, in an amount of preferably 10% by mass to 70% by mass. By including aluminum in this amount, the soil solidification strength can be increased sufficiently.

[0017] Alumina cement is used to ensure that the specific surface area of ​​the soil is 1500 cm² in order to sufficiently increase the solidification strength of the soil. 2 / g or more, and 2 / g or more, 2500cm 2 It is more preferable that the saturation coefficient is 1 / g or more.

[0018] (2) Alkaline earth metal compounds The neutral solidification material of the present invention contains an alkaline earth metal compound as one of its constituent components. The alkaline earth metal compound is used for the purpose of filling voids in the soil and increasing the solidification strength of the improved soil. Examples of the alkaline earth metal compound include calcium compounds and magnesium compounds. Examples of calcium compounds include calcium salts, calcium hydroxides, and calcium oxides, etc. Specific examples include calcium carbonate, calcium hydroxide, calcium oxide, and calcium sulfate (gypsum). Examples of magnesium compounds include magnesium salts, magnesium hydroxides, and magnesium oxides, and specifically, magnesium oxide. Although it depends on the properties of the soil to be improved, it is preferable to use calcium carbonate as the alkaline earth metal compound from the viewpoint of neutralizing the pH of low-pH soil and stably maintaining the pH in the neutral range, and it is also preferable to use gypsum as the alkaline earth metal compound from the viewpoint of further increasing the solidification strength of high-pH soil.

[0019] As the gypsum used as the alkaline earth metal compound, at least one of gypsum anhydride, gypsum hemihydrate, gypsum dihydrate, etc. can be used. Gypsum specified in JIS R9151 can also be used. Of these, it is preferable to use gypsum hemihydrate as the gypsum from the viewpoint of achieving an improvement in the strength of the soil to be treated.

[0020] In the present invention, the various alkaline earth metal compounds described above may be used alone or in any combination of two or more thereof. In particular, it is preferred that the alkaline earth metal compound contains at least one selected from the group consisting of gypsum and calcium carbonate.

[0021] The alkaline earth metal compounds are selected from those with a Blaine specific surface area of ​​100 cm2 in order to fill the voids in the soil to be treated and increase the solidification strength. 2 / g or more 50000cm 2 / g or less, and 2 / g or more 10000cm 2 / g or less is more preferable, and 2 / g or more 8000cm 2When the alkaline earth metal compound is, for example, a mixture of gypsum and calcium carbonate, the Blaine specific surface area of ​​the alkaline earth metal compound means the Blaine specific surface area of ​​the mixture.

[0022] The content of the alkaline earth metal compound in the neutral solidification material is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The content of alkaline earth metal compounds in the neutral solidification material is preferably 95% by mass or less, more preferably 92% by mass or less, and even more preferably 90% by mass or less. By setting the content ratio of the alkaline earth metal compound in this manner, the pH of the improved soil treated with the neutral solidification material of the present invention can be maintained in the neutral range.

[0023] (3) Other ingredients The neutral solidification material of the present invention may contain other components in addition to the above-mentioned components, as necessary. Such components include polymer flocculants and sulfates (excluding gypsum).

[0024] (3-1) Polymer flocculant The polymer flocculant is a component that is mainly added to agglomerate soil particles to increase the strength of the improved soil, and is preferably a polymer compound consisting of a single component or a mixture of organic polymers. From this perspective, the total content of the polymer flocculant in the neutral solidification material is preferably 0.1% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 15% by mass or less, and even more preferably 1% by mass or more and 10% by mass or less.

[0025] It is preferable that the polymer flocculant is at least one polymer compound selected from the group consisting of acrylamide and sodium acrylate, since this further enhances the flocculation effect of the soil particles to be treated. From the viewpoint of making this advantage even more pronounced, it is preferable that the polymer flocculant is, for example, a copolymer obtained by polymerizing acrylamide as the first monomer and sodium acrylate as the second monomer.

[0026] When the polymer flocculant is a copolymer formed by polymerizing acrylamide and sodium acrylate, the composition ratio of the acrylamide units in the copolymer is preferably 55 mol% to 90 mol%, more preferably 60 mol% to 85 mol%, and even more preferably 60 mol% to 80 mol%. By using a polymer flocculant with acrylamide units in such a ratio, it is possible to achieve a high level of both the strength development of the soil to be treated and the maintenance of a neutral pH range. The composition ratio of the acrylamide unit in the copolymer can be measured by the method described in JP 2021-134320 A, a previous application filed by the applicant.

[0027] (3-2) Sulfate Sulfates not only act as a neutralizer for alumina cement, but also react with alumina cement to produce various hydrates, solidifying the soil to be improved. Sulfates also have the effect of immobilizing heavy metals, such as arsenic, contained in the soil to be improved. From this perspective, it is preferable to use sulfates containing at least one cation selected from the group consisting of iron ions, aluminum ions, and ammonium ions. Specifically, it is preferable to use at least one sulfate selected from the group consisting of ferrous sulfate, aluminum sulfate, and ammonium sulfate. These sulfates can be used alone or in combination. When using aluminum sulfate, either its anhydride or hydrate can be used.

[0028] The content of sulfates (excluding gypsum if the alkaline earth metal compound contains gypsum) in the neutral solidification material is preferably 0.1 mass% or more, more preferably 1 mass% or more, and even more preferably 2 mass% or more, expressed as the total amount of sulfates (excluding gypsum), from the viewpoint of bringing the pH of the soil to be treated into the neutral range and increasing the strength of the soil. From a similar viewpoint, the content of sulfates (excluding gypsum) in the neutral solidification material is preferably 70 mass% or less, expressed as the total amount of sulfates (excluding gypsum), more preferably 50 mass% or less, and even more preferably 25 mass% or less.

[0029] (3-3) Other components other than polymer flocculants and sulfates The neutral solidification material of the present invention may contain other components in addition to the above-mentioned components, such as porous materials such as sepiolite, perlite, and zeolite, slag, talc, unburned dolomite, fly ash, and chelating agents.

[0030] From the viewpoint of further increasing the strength of soil treated with the neutral solidification material of the present invention and maintaining the pH stably in the neutral range, it is preferable that the neutral solidification material of the present invention consists of alumina cement, alkaline earth metal compound, polymer coagulant, sulfate, and the remainder unavoidable impurities.

[0031] Each of the above-mentioned components is preferably in a powder form. Furthermore, if each component can form a hydrate, it may be in the form of a hydrate or an anhydrous form.

[0032] The neutral solidification material of the present invention can be prepared by mixing the above-mentioned components in predetermined amounts using a known dry mixer.

[0033] The neutral solidification material of the present invention can be used in a soil treatment method in which the neutral solidification material is mixed with the soil to be treated and solidified to improve the soil. The neutral solidification material may be in the form of a powder or a slurry when mixed with the soil to be treated. Furthermore, when mixing the neutral solidification material with the soil to be treated, the neutral solidification material and the soil to be treated may be mixed simultaneously, or one of the neutral solidification material and the soil to be treated may be added to the other.

[0034] 1m of soil to be treated 3 The amount of neutral solidification material added per m of soil to be improved can be changed as appropriate depending on the type and properties of the soil to be improved and the desired strength of the soil. From the viewpoints of uniformity of mixing, improvement of strength of the soil to be improved, and reduction of processing costs, it is necessary to 3 The amount of neutral solidification material added per unit area is, for example, 20 kg / m 3 More than 200kg / m 3 It may be the following:

[0035] Examples of equipment for mixing the neutral solidification material with the soil to be treated include mixing equipment commonly used in the technical field, such as backhoes, backhoes equipped with mixing buckets, stabilizers, self-propelled soil improvement machines, stationary mixers, trencher-type agitation mixers, deep mixing machines, power blenders, and plant mixers.

[0036] By using the neutral solidification material of the present invention, soil that would have been treated as industrial waste or soil with limited uses due to its insufficient strength in the prior art can be reused as improved soil with increased strength by solidifying it before being transported from the site of generation. According to the present invention, a decrease in strength of the improved soil can be avoided when it is reused.

[0037] The strength of soil treated with the neutral solidification material of the present invention is expressed as the cone index of compacted soil measured in accordance with JIS A1228 (Cone Index Test Method for Compacted Soil), and is 200 kN / m regardless of the age of the material. 2 In particular, the cone index of the compacted soil immediately after treatment with the neutral solidification material of the present invention is preferably 400 kN / m or more. 2 It is preferable that this is equal to or greater than this.

[0038] In addition, soil improved with the neutral solidification material of the present invention has a cone index of 400 kN / m 2 If the soil meets the above criteria, it can be suitably used as, for example, "Type 3 construction generated soil" as defined in the soil classification criteria of the Ministry of Land, Infrastructure, Transport and Tourism's notification "Regarding Generated Soil Utilization Standards," or "Type 3 treated soil" as defined in the quality criteria of the Ministry of Land, Infrastructure, Transport and Tourism's notification "Construction Sludge Treatment Level Utilization Technical Standards." In detail, soil improved with the neutral solidification material of the present invention can be suitably used in a wide range of applications, such as for civil engineering or construction work, such as backfilling of structures, backfilling of buildings, backfilling of civil engineering structures, road embankments, embankments, land development, railway embankments, airport embankments, and water surface reclamation. [Example]

[0039] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass." Before describing the Examples and Comparative Examples in detail, the alumina cement and alkaline earth metal compound used in the Examples and Comparative Examples will be described in detail. Tables 1 to 3 show the mineral composition (Rietveld analysis value), chemical composition (JIS R5020:2010), density, and Blaine specific surface area of ​​the alumina cements used in the examples and comparative examples, respectively.

[0040] [Table 1]

[0041] [Table 2]

[0042] [Table 3]

[0043] Table 4 shows the density, Blaine specific surface area and particle size of the alkaline earth metal compounds used.

[0044] [Table 4]

[0045] Table 5 shows the density, Blaine specific surface area and particle size of the ferrous sulfate used.

[0046] [Table 5]

[0047] Examples 1-7 and Comparative Examples 1-6 The solidification material was prepared by mixing the components shown in Table 7 below. The values ​​for each component in the table represent "mass %." The polymer flocculant used was Sanfloc AH-4SFA (acrylamide unit: 72 mol%) manufactured by Sanyo Chemical Industries, Ltd.

[0048] 〔evaluation〕 The solidification materials obtained in the examples and comparative examples were applied to the sample soil described below at a rate of 50 kg / m 3 Test specimens for measuring the cone index of the improved soil immediately after mixing with the amount of addition were prepared, and the cone index was measured in accordance with JIS A1228. In addition, to confirm the effect of re-kneading, the same improved soil was loosened and placed in a polyethylene bag, and after one day and seven days of curing, test specimens for measuring the cone index were prepared, and the cone index was measured for each. Furthermore, after one day and seven days of curing, the improved soil was thoroughly loosened by hand, and its pH was measured in accordance with JGS0211-2009. The results are shown in Table 7.

[0049] [Sample soil] Clayey soil and sandy soil were mixed and adjusted to the particle size distribution shown in Table 6. Water was added to the soil so that the water content was 30.0%, and foaming agent TS-foam (manufactured by Onoda Chemico Co., Ltd.) was added at a concentration of 0.4% to create a volume of 200 L / m 3(20kg / m 3 After adding the scouring agent, the mixture was mixed at low speed for 1.5 minutes using a soil mixer. Next, the eruption prevention agent SP-α (manufactured by Onoda Chemico Co., Ltd.) was added and mixed at low speed for 1.5 minutes using a soil mixer to prepare the sample soil.

[0050] [Table 6]

[0051] [Table 7]

[0052] As is clear from the results shown in Table 7, the improved soil treated using the gypsum-based solidification material of Comparative Example 3-5 had a cone index ratio of less than 0.9 both 1 day / immediately after and 7 days / immediately after, meaning that the cone index was lower than immediately after treatment. In contrast to this, the improved soils treated using the solidification materials of Examples 1-7 containing a specified amount of alumina cement all had cone index ratios of 0.9 or higher, and the cone indexes were maintained or increased one day and seven days later compared to those immediately after treatment, demonstrating excellent strength development. Comparative Example 6 used Portland cement, and even when ferrous sulfate, an acidic material, was added, the pH exceeded 9 after 1 day or 7 days, not satisfying the pH range of 5.0 to 9.0. Thus, compared to Portland cement, improved soils treated with alumina cement showed a lower pH, and all improved soils treated with the solidification materials of Examples 1-7 containing a specified amount of alumina cement had a pH within the range of 5.0 to 9.0.

[0053] Examples 8-13 The alumina cements used were those shown in Table 8 below. These alumina cements were mixed with the components shown in the same table. Except for these, the solidification materials were prepared in the same manner as in Example 1. The values ​​for each component in the table mean "mass%." The obtained solidifying material was used to carry out the same evaluation as in Example 1. The results are shown in Table 8. As is clear from the results shown in Table 8, the improved soil treated using the solidification material of each example containing a specified amount of alumina cement all had a cone index ratio of 1.2 or more, and the cone index was maintained or increased one day and seven days later compared to immediately after treatment, demonstrating excellent strength development. In addition, the improved soil treated with the solidification materials of each example showed a low pH.

[0054] [Table 8]

[0055] Example 14 The solidification material was prepared by mixing the components shown in Table 10 below. The values ​​for each component in the table represent "mass %." The obtained solidification material was applied to simulated arsenic-contaminated soil at a rate of 60 kg / m 3 The improved soil was then evaluated for the degree of arsenic immobilization. The improved soil was sealed in a polyethylene bag and cured at 20°C for one day, after which the concentration of eluted arsenic was measured in accordance with Ministry of the Environment Notification No. 18. The results are shown in Table 10. The same table also shows the results for Examples 1-3 and Comparative Example 5. The arsenic-contaminated soil was prepared as follows.

[0056] [Simulated arsenic-contaminated soil] A specified amount of disodium hydrogen arsenate heptahydrate (Na2HAsO4·7H2O, Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution was added to soil made from hard sandstone crushed to particles of 2 mm or less, and the soil was mixed at low speed using a soil mixer for 1.5 minutes, after which any soil adhering to the container and paddle was scraped off. After further mixing at low speed for 1.5 minutes, the mixture was sealed in a polyethylene bag and left to cure for one day to create simulated contaminated soil. The properties of the simulated contaminated soil prepared are shown in Table 9 below. The moisture content was measured in accordance with JIS A 1203 "Testing Method for Moisture Content of Soil." The wet density was calculated by filling a mold 5 cm in diameter and 10 cm high with the simulated contaminated soil and calculating the mass of the filled soil and the volume of the mold. The pH was measured using the test solution prescribed in Ministry of the Environment Notification No. 46. The amount of arsenic leaching was measured in accordance with Ministry of the Environment Notification No. 18.

[0057] [Table 9]

[0058] [Table 10]

[0059] The amount of arsenic elution from the improved soil treated with the solidification material of Comparative Example 5 was 0.018 mg / L, which was lower than the 0.061 mg / L elution amount from the simulated arsenic-contaminated soil. However, it exceeded the soil elution standard of 0.01 mg / L. In contrast to this, in improved soil treated with a solidification material containing a specified amount of alumina cement, the amount of arsenic leaching was below the soil leaching standard of 0.01 mg / L, demonstrating excellent arsenic leaching suppression effects.

Claims

1. Alumina cement and an alkaline earth metal compound; The alumina cement is contained in an amount of 2% by mass or more and less than 40% by mass. Neutral solidifying material.

2. 2. The neutral solidification material according to claim 1, wherein the alkaline earth metal compound comprises at least one selected from the group consisting of gypsum, calcium carbonate, calcium oxide, calcium hydroxide, and magnesium oxide.

3. The neutral solidification material according to claim 1 or 2, containing 0.1 mass % or more and 20 mass % or less of a polymer flocculant.

4. The neutral solidification material according to claim 3, wherein the polymer flocculant is at least one polymer compound selected from the group consisting of acrylamide and sodium acrylate.

5. 3. The neutral solidification material according to claim 1, comprising 0.1% by mass or more and 70% by mass or less of a sulfate containing at least one cation selected from the group consisting of iron ions, aluminum ions, and ammonium ions.

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