Neutral solidifying material

Abstract

To provide a neutral solidifying material capable of enhancing the strength of soil subjected to solidification treatment and of keeping the pH around 7.SOLUTION: The neutral solidifying material according to the present invention comprises slaked lime, magnesium oxide, superphosphate of lime, calcium carbonate, a polymer flocculant, and a metal sulfate. Preferably, the metal sulfate is ferrous sulfate. The polymer flocculant preferably includes an acrylamide unit and a sodium acrylate unit. It is also preferable that the content of slaked lime is in the range of 3-10 mass% inclusive, that the content of magnesium oxide is in the range of 2-10 mass% inclusive, and that the content of superphosphate of lime is in the range of 5-10 mass% inclusive.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 soil strength and facilitate the removal and reuse of soft soil and construction waste soil. Taking into consideration the preservation of the surrounding environment, such as water quality and vegetation, it is desirable for these soil solidification materials to maintain the pH of the improved soil near a neutral range while also achieving sufficient strength.

[0003] Soil solidification materials are required to have the ability to solidify the soil while also neutralizing it to meet wastewater standards, so soil solidification materials containing calcium superphosphate as a pH adjuster have been proposed. For example, Patent Document 1 discloses that a solidification material to be mixed with mud to solidify the mud contains superphosphate lime, magnesium oxide and / or calcium oxide. Patent Document 2 discloses a soil solidification material containing magnesium oxide and a metal salt selected from magnesium sulfate, magnesium hydroxide, magnesium chloride, calcium sulfate, aluminum sulfate, ferrous sulfate, polyaluminum chloride, alum, calcined alunite, superphosphate, and zinc sulfate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-203962 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-154735 Summary of the Invention [Problem to be solved by the invention]

[0005] However, soil solidification materials that use slaked lime as the solidification material are strongly alkaline, so there is a risk that the pH of the solidified soil will not meet the wastewater standards. Even if the soil meets the discharge standards immediately after solidification, it may not meet them over the long term. Therefore, it is desirable to control the pH to as close to 7 as possible immediately after solidification. Therefore, the object of the present invention is to provide a neutral solidification material that can increase the strength of solidified soil and maintain the pH near the neutral range, particularly near pH 7. [Means for solving the problem]

[0006] The present invention provides a neutral solidification material containing slaked lime, magnesium oxide, superphosphate, calcium carbonate, a polymer flocculant, and a metal sulfate. [Effects of the Invention]

[0007] According to the present invention, there is provided a neutral solidification material that can increase the strength of solidified soil and maintain the pH at around 7. According to the present invention, it is possible to increase the strength of soil, particularly immediately after solidification. Furthermore, according to the present invention, there is provided a neutral solidification material that has a pH of around 7 or less. 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 soil to be improved to maintain a pH in the neutral range and obtain soil with high strength. Examples of soil to be solidified include wet soil such as soft soil containing water, and construction waste soil and construction sludge that are generated as by-products of 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) to (6): (1) Slaked lime (2) Magnesium oxide (3) Superphosphate (4) Calcium carbonate (5) Polymer flocculants (6) Metal sulfates Each component will be described below.

[0011] (1) Slaked lime The neutral solidification material of the present invention contains slaked lime (calcium hydroxide, Ca(OH)2) as one of its constituent components. The content of slaked lime in the neutral solidification material is preferably 3% by mass or more, and more preferably 4% by mass or more. The content of slaked lime in the neutral solidification material is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. By setting the content of slaked lime within the above range, the improved soil treated with the neutral solidification agent of the present invention can develop sufficient strength. The slaked lime used in the present invention may be produced by adding quicklime and water to soil and hydrating it. In this case, the neutral solidification material of the present invention may contain unreacted quicklime.

[0012] (2) Magnesium oxide The neutral solidification material of the present invention contains magnesium oxide (MgO) as one of its components. Magnesium oxide is a component that is mainly mixed to solidify the soil to be improved. When magnesium oxide is mixed into the soil to be improved, it undergoes a hydration reaction, and then becomes magnesium hydroxide, which is then carbonated by carbon dioxide in the air to become magnesium carbonate. This reaction solidifies the soil. Light-burned magnesium oxide and burnt magnesium oxide are known as magnesium oxide, and light-burned magnesium oxide is preferred from the viewpoint of reactivity. Light-burned magnesium oxide can be obtained, for example, by burning magnesium hydroxide or magnesium carbonate in air at 600°C to 900°C.

[0013] The content of magnesium oxide in the neutral solidification material is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more, expressed in terms of anhydrous. The content of magnesium oxide in the neutral solidification material is preferably 10% by mass or less, and more preferably 6% by mass or less, expressed in terms of anhydrous. By setting the magnesium oxide content within the above range, it is possible to impart sufficient strength to the soil to be improved and maintain the pH of the soil in a neutral range after treatment. In addition, when improving soil contaminated with heavy metals, the heavy metals can be insolubilized and prevented from leaching out from the improved soil. As a result, there is also the advantage that the environment surrounding the improved soil can be protected.

[0014] (3) Superphosphate The neutral solidification material of the present invention contains superphosphate as one of its components. Superphosphate is known as a phosphate fertilizer, but in the present invention, it is added to maintain the pH of the soil to be improved in a neutral range. Superphosphate is a mixture of monocalcium phosphate (Ca(H2PO4)2·H2O) and calcium sulfate (gypsum, CaSO4) made by treating phosphate rock or bone meal with sulfuric acid to make the phosphorus soluble. Superphosphate is acidic because it contains soluble phosphoric acid. This property contributes to maintaining the pH of the soil to be improved in a neutral range. From this perspective, the soluble phosphoric acid content in superphosphate is preferably 17% by mass or more, more preferably 18% by mass or more, and preferably 19% by mass or less. Furthermore, the content of water-soluble phosphoric acid components in the soluble phosphoric acid components is preferably 14% by mass or more, more preferably 16% by mass or more, and also preferably 19% by mass or less.

[0015] The content of superphosphate in the neutral solidification material is preferably 5% by mass or more, and more preferably 7% by mass or more. The content of superphosphate in the neutral solidification material is preferably 10% by mass or less, and more preferably 9% by mass or less. By setting the content of superphosphate within the above range, the pH of the improved soil treated with the neutral solidification material of the present invention can be maintained in the neutral range.

[0016] (4) Calcium carbonate The neutral solidification material of the present invention contains calcium carbonate as one of its constituent components. Calcium carbonate is used primarily as a bulking agent in the neutral solidification material of the present invention. The content of calcium carbonate in the neutral solidification material can be the remainder obtained by subtracting the total content (mass %) of all components constituting the neutral solidification material of the present invention from 100 mass %. This allows the bulking effect to be fully exerted.

[0017] (5) Polymer flocculants The neutral solidification material of the present invention contains a polymer flocculant as one of its components. The polymer flocculant is used in the neutral solidification material of the present invention to absorb moisture in the soil to be improved and increase the strength of the soil. The polymer flocculant preferably comprises a homopolymer or copolymer of one or more polymerizable monomers having a hydrophilic functional group. Examples of the polymerizable monomer include acrylamide, acrylic acid, sodium acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, etc. These polymerizable monomers can be used alone or in combination of two or more.

[0018] The content of the polymer flocculant in the neutral solidification material is preferably 1% by mass or more, and more preferably 2% by mass or more. The content of the polymer flocculant in the neutral solidification material is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. By setting the content of the polymer flocculant within the above range, it is possible to develop sufficient strength in the soil to be improved, and also to maintain the pH of the soil after treatment in a neutral range.

[0019] (6) Metal sulfates The neutral solidification material of the present invention contains a metal sulfate as one of its components. The metal sulfate is mainly added to maintain the pH of the soil to be improved at neutral. The metal sulfate is also added to lower the pH of the neutral solidification material itself. Examples of metal sulfates include sulfates of iron and aluminum, specifically ferrous sulfate and aluminum sulfate (aluminum sulfate). In particular, it is preferable to use ferrous sulfate as the metal sulfate, from the viewpoint of being able to stably maintain the pH of the soil in a neutral range after treatment.

[0020] The content of the metal sulfate in the neutral solidification material is preferably 8% by mass or more, and more preferably 9% by mass or more. The content of metal sulfate in the neutral solidification material is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 18% by mass or less. By setting the content of metal sulfate within the above range, the pH of the soil to be improved can be stably maintained in the neutral range, while the soil strength can be increased. In addition, when improving soil contaminated with heavy metals, the heavy metals can be insolubilized by reduction, thereby suppressing their elution from the soil.

[0021] (7) Other ingredients The neutral solidification material of the present invention may further contain other components in addition to the above-mentioned components, such as porous materials such as sepiolite, perlite, zeolite, and silica, slag, anhydrous gypsum, hemihydrate gypsum, talc, unburned dolomite, silica powder, fly ash, and chelating agents.

[0022] 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 near the neutral range, it is preferable that the neutral solidification material of the present invention consists of hydrated lime, magnesium oxide, superphosphate, calcium carbonate, a polymer coagulant and a metal sulfate, with the remainder being unavoidable impurities.

[0023] 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.

[0024] 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. In addition to the preparation method of mixing the above-mentioned components, quicklime (calcium oxide, CaO) can be used instead of slaked lime, and quicklime, magnesium oxide, superphosphate, calcium carbonate, a polymer coagulant, and a metal sulfate can be mixed to form a mixture. By adding an appropriate amount of water to this mixture, slaked lime can be generated from the quicklime in the mixture, and the neutral solidification material of the present invention can be obtained.

[0025] 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 improved and the soil is improved by solidification treatment. The neutral solidification material may be in the form of a powder or a slurry when mixed with the soil to be improved. Furthermore, when mixing the neutral solidification material with the soil to be improved, the neutral solidification material and the soil to be improved may be mixed at the same time, or one of the neutral solidification material and the soil to be improved may be added to the other.

[0026] 1m of soil to be improved 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 preferably 20 kg / m 3 More than 200kg / m 3 More preferably, it is 20 kg / m or less. 3 Less than 150kg / m 3 More preferably, it is 20 kg / m or less. 3 More than 75kg / m 3 The following is the result.

[0027] Examples of equipment for mixing the neutral solidification material with the soil to be improved 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.

[0028] By using the neutral solidification material of the present invention, construction waste soil, which in the conventional technology was treated as industrial waste or soil with limited uses due to its insufficient strength, can be solidified before being transported from the site where the construction waste soil was generated to increase its strength, and the improved soil can be reused as construction material at the same or a different construction site. The strength of soil treated with the neutral solidification material of the present invention is 200 kN / m, as expressed in the cone index test qc of compacted soil measured in accordance with JIS A1228. 2 In particular, the cone index test qc of the compacted soil immediately after treatment with the neutral solidification material of the present invention is 200 kN / m or more. 2 It is preferable that this is equal to or greater than this.

[0029] Furthermore, because soil improved with the neutral solidification material of the present invention exhibits high strength, it can be suitably used, for example, as "Type 3 construction generated soil" as defined in the soil classification standards of the Ministry of Land, Infrastructure, Transport and Tourism's notice "Regarding Generated Soil Utilization Standards," or as "Type 3 treated soil" as defined in the quality standards of the Ministry of Land, Infrastructure, Transport and Tourism's notice "Construction Sludge Treatment Level Utilization Technical Standards." In particular, soil improved with the neutral solidification material of the present invention can be suitably used in a wide range of civil engineering or construction applications, 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]

[0030] 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."

[0031] Example 1 The neutral solidification material was prepared by mixing the components shown in Table 1 below. Details of each component are as follows. Slaked lime: Produced by adding water to quicklime (Ube Material Industries, Ltd.) under 5 mm in size and allowing it to react. Magnesium oxide: Light-burned magnesium oxide (MgO content 91.1%) manufactured by Ube Material Industries, Ltd. Superphosphate: Taki 17.0 superphosphate manufactured by Taki Chemical Co., Ltd. Calcium carbonate: Ube Material Industries, Ltd. Polymer flocculant: Sanflock AH-4SFA manufactured by Sanyo Chemical Industries, Ltd. Metal sulfate: Ferrous sulfate monohydrate manufactured by LOMON (China)

[0032] [Examples 2 to 8 and Comparative Example 1] A neutral solidification material was prepared in the same manner as in Example 1, except that the blending ratio of each component was as shown in Table 1.

[0033] 〔evaluation〕 The pH of the neutral solidification agents obtained in the Examples and Comparative Examples was measured using the following method. The pH of the mixed soil immediately after mixing the neutral solidification agents obtained in the Examples and Comparative Examples with the soil described below, and the cone index test QC of the compacted soil were also measured using the following method. The results are shown in Table 1.

[0034] [pH of neutral solidification material] Measurements were made in accordance with JGS 0211.

[0035] [pH of mixed soil] Sandy soil was used as the raw soil. The water content of this soil measured in accordance with JIS A1203 was 32.7%, and the wet density measured in accordance with JIS A1210 was 1.739 g / cm. 3 It was. The neutral solidification materials obtained in the examples and comparative examples were added to this soil at a rate of 20 kg / m 3 The soil was mixed using a mortar mixer. The pH of the mixed soil was measured immediately after mixing in accordance with JGS 0211.

[0036] [Cone index strength qc of mixed soil] The cone index strength (qc) of the compacted mixed soil after measuring the pH was measured. The measurement was carried out in accordance with JIS A1288. The penetration device was placed vertically at the center of the top surface of a 100mm molded specimen with a diameter of 100mm and a height of 127mm, and penetrated at a speed of 10mm / s. The penetration resistance force was calculated from the load meter reading when the tip of the cone penetrated 50mm, 75mm, and 100mm from the top of the specimen. The cone index strength qc was calculated from the penetration resistance force obtained by the penetration device and the base area of ​​the tip of the cone used.

[0037] [Table 1]

[0038] As is clear from the results shown in Table 1, the neutral solidification materials of each example have a low pH by themselves, and by treating the soil with these neutral solidification materials, it is possible to obtain sufficient strength and maintain the pH in the neutral range. In particular, it is clear that the use of ferrous sulfate as the metal sulfate can bring the pH closer to neutral. The neutral solidification material of Comparative Example 1 itself had a high pH.

Claims

1. A neutral solidification material containing slaked lime, magnesium oxide, superphosphate, calcium carbonate, polymer flocculant, and metal sulfate.

2. 2. The neutral solidification material according to claim 1, wherein the metal sulfate is ferrous sulfate.

3. The superphosphate contains a soluble phosphate content of 17% by mass or more and 19% by mass or less, The neutral solidification material according to claim 1, wherein the soluble phosphate content is 14% by mass or more and 19% by mass or less of water-soluble phosphate content.

4. The content of the slaked lime is 3% by mass or more and 10% by mass or less, The content of the magnesium oxide is 2% by mass or more and 10% by mass or less, The content of the superphosphate is 5% by mass or more and 10% by mass or less, The content of the polymer flocculant is 1% by mass or more and 5% by mass or less, 3. The neutral solidification material according to claim 1, wherein the content of the metal sulfate is 8% by mass or more and 30% by mass or less.

5. 3. The neutral solidification material according to claim 1, comprising the slaked lime, the magnesium oxide, the superphosphate, the calcium carbonate, the polymer coagulant, and the metal sulfate, with the remainder being inevitable impurities.

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