Neutral solidification material and soil processing method

Abstract

To provide a neutral solidifying material capable of improving to soil which developed high strength while maintaining pH close to neutrality.SOLUTION: A neutral solidifying material of the present invention contains magnesium oxide, ferrous sulfate, and a polymer flocculant having an acrylamide unit and a sodium acrylate unit. A mass ratio of the ferrous sulfate to the magnesium oxide in terms of anhydrous is 1.50 to 2.50. A composition ratio of the acrylamide units constituting the polymer flocculant is 35 to 98 mol %. The neutral solidifying material is also preferable to further contain gypsum. The present invention also provides a soil treatment method using the neutral solidifying material.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a neutral solidification material and a soil treatment method. [Background technology]

[0002] Soil solidification materials are used to improve soil strength and make it easier to transport and reuse soft soil and construction waste soil, etc. It is desirable for such soil solidification materials to maintain the pH of the soil after soil improvement near neutral while also providing sufficient strength, taking into consideration the conservation of the surrounding environment, such as water quality and vegetation.

[0003] For the purpose of improving the strength of improved soil when a soil solidification material is used, Patent Document 1 discloses a soil solidification material consisting of magnesium oxide, aluminum sulfate and / or ferrous sulfate, with the remainder being gypsum. Patent Document 2 discloses a soil improvement material that contains auxiliary materials such as hemihydrate gypsum in addition to metal salts such as metal sulfates, magnesium-containing substances, and polymer-based thickening materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-109829 A [Patent Document 2] JP 2008-100313 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the soil improvement materials described in Patent Documents 1 and 2 have room for improvement in terms of maintaining the pH of the improved soil near neutral while sufficiently increasing the strength development.

[0006] In addition, the improved soil obtained by performing a solidification treatment on construction waste soil may be reused either at the site where the construction waste soil was generated or at another site. In the latter case, the improved soil is typically cured for a certain period of time at the site where the construction waste soil was generated and then transported to the site where it will be reused. At this time, the strength of the improved soil may decrease due to the steps of excavation and loosening. As a result, the soil may not be able to achieve sufficient strength at the site where it is to be reused. The soil improvement materials described in Patent Documents 1 and 2 do not consider any improvement in such points.

[0007] Therefore, an object of the present invention is to provide a neutral solidification material that can obtain improved soil that maintains a pH level close to neutral and is less susceptible to a decrease in strength due to excavation and loosening. [Means for solving the problem]

[0008] The present invention relates to a polymer flocculant comprising magnesium oxide, ferrous sulfate, and a polymer flocculant having an acrylamide unit and a sodium acrylate unit, a mass ratio of the ferrous sulfate to the magnesium oxide in terms of anhydrous is 1.50 to 2.50; The present invention provides a neutral solidification material, in which the composition ratio of the acrylamide units constituting the polymer flocculant is 35 to 98 mol %.

[0009] The present invention also includes a step of mixing the soil to be treated with a neutral solidification material, The neutral solidification material includes magnesium oxide, ferrous sulfate, and a polymer flocculant having an acrylamide unit and a sodium acrylate unit; and a mass ratio of the ferrous sulfate to the magnesium oxide in terms of anhydrous is 1.50 to 2.50; The present invention also provides a method for treating soil, wherein the polymer flocculant has a composition ratio of acrylamide units of 35 to 98 mol %. Effect of the Invention

[0010] According to the present invention, soil can be improved to have high strength while maintaining the pH close to neutral, so that the improved soil can be reused for a wide range of applications, leading to effective use of resources. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a method for treating soil using a neutral solidification material, together with an example of a shield machine used in the air bubble shield method. [Diagram 2] FIG. 2 is a graph showing the relationship between the composition ratio of the acrylamide unit in the neutral solidification materials of Examples 1, 3 and 4 and Comparative Example 4 and the cone index of the improved soil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A preferred embodiment of the present invention will be described below. Note that the present invention is not limited to the following embodiment. In the following description, when it is written "X to Y[Z]" (X and Y are arbitrary numbers, and [Z] is a unit added as necessary), it means "X[Z] or more and Y[Z] or less" or "X or more and Y or less" unless otherwise specified.

[0013] The neutral solidification material of the present invention is a material used to obtain soil that maintains a neutral pH and exhibits high strength by mixing with the soil to be improved. Examples of soil to be improved include water-containing soil such as soft soil containing water, and construction waste soil and construction sludge, which are generated secondarily from various construction works such as road construction, tunnel construction using the shield tunneling method, and building construction work. In other words, the neutral solidification material of the present invention is suitably used to solidify at least one of water-containing 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 to be improved.

[0014] In the present invention, "neutral" refers to "the pH of the improved soil is 5.8 or more and 8.6 or less." This is the value shown in the section on "discharge into public water areas other than sea areas" in the effluent pH standard stipulated in the Water Pollution Control Act. Therefore, improved soil containing the neutral solidification material of the present invention complies with the effluent standard even if, for example, rainwater that has permeated the improved soil flows into groundwater or a river, and the improved soil can be reused with reduced environmental impact without being limited by its application or place of use.

[0015] The neutral solidification material of the present invention contains the following components (1) to (3). (1) Magnesium oxide. (2) Ferrous sulfate. (3) A polymer flocculant having an acrylamide unit and a sodium acrylate unit.

[0016] The neutral solidification material of the present invention contains magnesium oxide, which is a component that is mainly mixed to solidify the soil to be improved. Examples of magnesium oxide include lightly burned magnesium oxide obtained by burning magnesium hydroxide or magnesium carbonate at 600 to 900°C.

[0017] The content of magnesium oxide in the neutral solidification material is preferably 2 to 41 mass %, more preferably 3 to 30 mass %, further preferably 4 to 21 mass %, and even more preferably 15 to 21 mass %, calculated as anhydrous. By setting the magnesium oxide content as described above, it is possible to achieve a high level of strength development of the soil to be improved and to maintain the pH at neutral. In addition, when improving soil contaminated with heavy metals, etc., it is possible to insolubilize the heavy metals and suppress the elution of the heavy metals from the improved soil. As a result, there is also an advantage that the environment around the improved soil can be preserved.

[0018] The neutral solidification material of the present invention contains ferrous sulfate. Ferrous sulfate is a component that is mainly mixed to maintain the pH of the soil to be improved at neutral.

[0019] The content of ferrous sulfate in the neutral solidification material is preferably 2.8 to 70 mass%, more preferably 5 to 50 mass%, further preferably 10 to 40 mass%, and even more preferably 30 to 40 mass%, calculated as anhydrous. The conditions for these contents are that the mass ratio of ferrous sulfate to magnesium oxide (S / M ratio) described below is satisfied, and that the sum of the contents of magnesium oxide and polymer coagulant is 100 mass% or less. By setting the ferrous sulfate content as described above, the pH of the soil to be improved can be maintained neutral while the soil exhibits higher strength. In addition, when improving soil contaminated with heavy metals, the heavy metals can be reduced and insolubilized, thereby suppressing the elution of the heavy metals from the improved soil.

[0020] The mass ratio of ferrous sulfate to magnesium oxide (S / M ratio) is preferably 1.50 to 2.50, more preferably 1.60 to 2.45, even more preferably 1.70 to 2.40, and even more preferably 1.70 to 2.0, based on the mass of each in anhydrous terms. By setting the mass ratio in this range, soil such as water-containing soil and mud, which has been difficult to reuse with conventional techniques, can be made to exhibit sufficient strength suitable for reuse, and resources can be used effectively.

[0021] The neutral solidification material of the present invention contains a polymer flocculant having an acrylamide unit and a sodium acrylate unit. The polymer flocculant is a component that is mainly mixed to aggregate the soil particles to be improved and increase the strength of the improved soil. The polymer flocculant is preferably a single component or a mixture of organic polymers. In the present invention, the "unit" refers to a monomer unit that constitutes the chemical structure of a polymer.

[0022] A specific embodiment of the polymer flocculant contained in the neutral solidification material is, for example, a copolymer obtained by polymerizing acrylamide as a first monomer and sodium acrylate as a second monomer. The copolymer may be at least one of the following: an alternating copolymer in which each monomer is polymerized alternately, a random copolymer in which the arrangement of each monomer is random, a block copolymer having a structural unit in which the same type of monomer is polymerized continuously, and a graft copolymer in which a polymer made of one monomer is branched and bonded to a polymer made of the other monomer. In any of the above embodiments, the polymer flocculant has an acrylamide unit and a sodium acrylate unit in its chemical structure.

[0023] One of the characteristics of the polymer flocculant contained in the neutral solidification material is that the acrylamide units constituting the polymer flocculant have a specific composition ratio. In detail, the composition ratio of the acrylamide units constituting the polymer flocculant is preferably 35 to 98 mol%, more preferably 40 to 98 mol%, even more preferably 50 to 97 mol%, even more preferably 55 to 97 mol%, and even more preferably 65 to 75 mol%. By using a polymer flocculant in which the acrylamide units are composed in such a ratio, it is possible to achieve a high level of both the strength development of the soil to be improved and the maintenance of a neutral pH.

[0024] The reason why the use of a polymer flocculant having acrylamide units in the above-mentioned ratio can be modified to improve strength is not clear, but the present inventors speculate as follows. Generally, in the neutral to alkaline pH range (i.e., pH range of 5.8 or higher), the mineral particles that make up the soil particles have a low isoelectric point, so the particles are negatively charged and electrostatic repulsion is likely to occur between the water and the soil particles. Therefore, the soil particles are less likely to form aggregates such as coagulation, and as a result, the strength of the entire soil tends to be low. When the above-mentioned polymer flocculant is added, first, the amide groups derived from the acrylamide units are adsorbed onto the soil particle surface. Next, the carboxyl groups derived from the sodium acrylate units repel each other, spreading the molecular chains of the polymer flocculant, which then embraces (takes in) the soil particles and water. As a result, the soil particles are effectively aggregated, and water is retained between the soil particles, which is thought to improve the strength of the improved soil. In particular, the process of developing strength by adding the above-mentioned polymer flocculant is believed to proceed in the following order: (i) adsorption of the flocculant onto the surface of the soil particles, (ii) cross-linking between the soil particles, and (iii) agglomeration of the soil particles. It is believed that by adjusting the composition ratio of the acrylamide units contained in the polymer flocculant to the above-mentioned suitable ratio, the above-mentioned processes (i) and (ii), which are important for developing strength, can be carried out in a balanced and effective manner.

[0025] The content of the acrylamide unit constituting the polymer flocculant can be calculated, for example, by measuring the elements of carbon, hydrogen and nitrogen which are the constituent elements of the polymer flocculant, and using the following method. In detail, about 2 mg of the polymer flocculant to be measured is precisely weighed out and introduced into an elemental analyzer (e.g., Microcorder JM10, manufactured by J Science Labs) to quantitatively measure the mass of each element. For example, antipyrine (carbon element: 70.2 mass%, hydrogen element: 6.4 mass%, nitrogen element: 14.9 mass%) can be used as the standard.

[0026] The mass ratio (mass%) of carbon element measured by the above-mentioned method is designated as C1, and the mass ratio (mass%) of nitrogen element is designated as N1. From these values, the composition ratios of acrylamide units and sodium acrylate units are calculated by the following method. First, the acrylamide unit has the chemical formula "-CH2-CH(CO-NH2)-", and the unit has 3 carbon atoms and 1 nitrogen atom. In addition, the sodium acrylate unit has the chemical formula "-CH2-CH(COONa)-", and the number of carbon atoms in the unit is 3 and the number of nitrogen atoms in the unit is zero.

[0027] The composition ratio (mol%) of the acrylamide unit in the polymer flocculant is "A", the composition ratio (mol%) of the sodium acrylate unit in the polymer flocculant is "100-A", and based on the number of carbon and nitrogen in each unit, the composition ratio (mol%) of the carbon in the acrylamide unit is expressed as "3×A", and the composition ratio (mol%) of the nitrogen in the acrylamide unit is expressed as "A". The composition ratio (mol%) of the carbon in the sodium acrylate unit is expressed as "3×(100-A)".

[0028] Based on the above-mentioned ratios, the ratio (C5 / N5) of the carbon element composition ratio (C5) to the nitrogen element composition ratio (N5) in the polymer flocculant is calculated by the following formula (I). (C5 / N5)={(3×A)+3×(100-A)} / A=300 / A ···(I)

[0029] Here, C5 / N5 corresponds to "{(C1) / (carbon atom amount)} / {(N1) / (nitrogen atom amount)}" (carbon atom amount = 12, nitrogen atom amount = 14). Therefore, the composition ratio A of the acrylamide unit is calculated by the following formula (II). Composition ratio A of acrylamide units (mol%) = 300 / (C5 / N5) = 300 / {(C1) / (amount of carbon atoms)} / {(N1) / (amount of nitrogen atoms)} (II)

[0030] The composition ratio of the sodium acrylate unit is calculated by the following formula (III). Composition ratio of sodium acrylate unit (mol%) = 100-A (III)

[0031] The composition ratio of the sodium acrylate unit constituting the polymer flocculant is preferably 2 to 65 mol%, more preferably 2 to 60 mol%, even more preferably 3 to 50 mol%, even more preferably 3 to 45 mol%, and even more preferably 25 to 35 mol%. By using a polymer flocculant in which the sodium acrylate unit is constituted in such a ratio, it is advantageous because the strength reduction due to excavation and loosening is unlikely to occur after the neutral solidification material of the present invention is mixed with soil on site, after curing for a certain period of time, or when it is transported to a place where it will be reused.

[0032] The total content of the polymer flocculant in the neutral solidification material is preferably 1 to 8 mass%, more preferably 1 to 7 mass%, further preferably 1 to 6 mass%, and even more preferably 1 to 3 mass%, calculated on anhydrous basis. By using such a content, sufficient strength can be obtained in the improved soil, and the material cost can be reduced.

[0033] The neutral solidification material of the present invention may be free of gypsum (i.e., 0 mass %), or alternatively, may further contain gypsum. From the viewpoint of further increasing the strength of the improved soil by utilizing the hydraulic properties of the gypsum itself, it is preferable that the neutral solidification material further contains gypsum.

[0034] When gypsum is contained, the gypsum content in the neutral solidification material is preferably more than 0 mass% and not more than 94 mass%, more preferably 40 to 91 mass%, still more preferably 40 to 88 mass%, even more preferably 40 to 85 mass%, and still more preferably 40 to 50 mass%, calculated as an anhydride content. By setting the gypsum content within the above range, it is possible to achieve a high level of both soil strength development and maintaining a neutral pH. In addition, when gypsum is contained, it is also preferable from the viewpoint of strength expression that the content of gypsum in the neutral solidification material be the remainder when the contents of magnesium oxide, ferrous sulfate, and polymer coagulant are each within the above-mentioned ranges.

[0035] When the neutral solidification material contains gypsum, the gypsum can be at least one of anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum, etc. Gypsum specified in JIS R9151 can also be used. Of these, it is preferable to use hemihydrate gypsum as the gypsum from the viewpoint of achieving a reduction in production costs in addition to improving the strength and maintaining the pH of the soil to be improved.

[0036] The magnesium oxide, sulfate and polymer flocculant may each independently be in the form of a powder, or in the form of a liquid or slurry dissolved or dispersed in a solvent such as water. The magnesium oxide and sulfate may each independently be in the form of anhydride or hydrate. From the viewpoint of improving the ease of handling and workability during transportation and use of the neutral solidification material, it is preferable that the magnesium oxide, sulfate and polymer flocculant are all in a powder form. From the same viewpoint, the neutral solidification material of the present invention is preferably in powder form.

[0037] The Blaine specific surface area of ​​magnesium oxide is preferably 6000 to 20000 cm 2 / g, and more preferably 7000 to 20000 cm 2 / g, and more preferably 8000 to 20000 cm 2 / g. By setting the Blaine specific surface area in this range, the workability of the neutral solidification material can be improved, and the strength of the improved soil can be improved by increasing the solidification property of the soil to be improved due to its high hydration activity. In addition, it is preferable that the above-mentioned range of Blaine specific surface area is satisfied when light-burned magnesium oxide is used as the magnesium oxide, since this allows both improvement of workability and improvement of the strength of the improved soil to be achieved at a high level. The Blaine specific surface area of ​​magnesium oxide can be measured, for example, according to JIS R5201:1997 "Physical testing methods for cement" using a Blaine air permeability device.

[0038] The BET specific surface area of ​​magnesium oxide is preferably 5 to 30 m2 / g, more preferably 7 to 30m 2 / g, more preferably 8 to 30m 2 / g. By setting the range in this way, the workability of the neutral solidification material can be improved, and the strength of the improved soil can be improved by increasing the solidification property of the soil to be improved due to its high hydration activity. In addition, it is preferable that the above-mentioned range of Blaine's specific surface area is satisfied when light-burned magnesium oxide is used as the magnesium oxide, since this allows both improvement of workability and improvement of the strength of the improved soil to be achieved at a high level. The BET specific surface area of ​​magnesium oxide can be measured by a constant volume gas adsorption method using, for example, a high-precision gas adsorption apparatus (BELSORP-mini, manufactured by BEL Japan Co., Ltd.).

[0039] The MgO content in the magnesium oxide is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. This content makes it difficult for the pH buffering ability of the surrounding environment of the improved soil to decrease, and can improve the strength of the improved soil.

[0040] The CaO content in magnesium oxide is preferably 3 mass % or less, more preferably 2 mass % or less, and even more preferably 1 mass % or less. This content makes it easier to maintain the pH of the environment surrounding the improved soil neutral, and also improves the strength of the improved soil.

[0041] The MgO content and CaO content in the above-mentioned magnesium oxide can be measured in accordance with JIS M8853:1998 "Method of chemical analysis of aluminosilicate raw materials for ceramics".

[0042] As long as the effects of the present invention are achieved, the neutral solidification material may further contain additives other than the above-mentioned magnesium oxide, ferrous sulfate, and polymer flocculant, depending on the properties of the soil to be improved.

[0043] Examples of the additive include at least one of sulfates other than ferrous sulfate and gypsum, such as aluminum sulfate, calcium aluminate minerals, such as hydrotalcite and hydrocalumite, silicon-containing minerals, such as silica stone, carbonates, such as magnesium carbonate and limestone, porous bodies, such as sepiolite, perlite, zeolite, and silica, and chelating agents.

[0044] The above-mentioned various additives may each independently be in the form of a powder, or in the form of a liquid or slurry dissolved or dispersed in a solvent such as water. Furthermore, each of the various additives may be independently in the form of anhydride or hydrate. It is preferable to carry out a blending test in advance and determine whether or not various additives are added and the mixing amounts based on the results.

[0045] 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 solidification treatment is carried out to improve the soil. The neutral solidification material when mixed with the soil to be improved may be in the form of a powder or a slurry. In addition, 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 simultaneously, or one of the neutral solidification material and the soil to be improved may be added to the other.

[0046] 1m of soil to be improved 3 The amount of neutral solidification material added per unit area can be changed as appropriate depending on the type and properties of the soil to be improved and the desired developed strength. From the viewpoints of achieving uniform mixing, improved developed strength, and reduced processing costs, the amount is preferably 20 to 200 kg / m. 3 More preferably, it is 20 to 150 kg / m 3 and more preferably 20 to 75 kg / m 3 It is.

[0047] The equipment used to mix the neutral solidification material with the soil to be improved can be any mixing equipment commonly used in the art, such as a backhoe, a backhoe equipped with a mixing bucket, a stabilizer, a self-propelled soil improvement machine, a stationary mixer, a trencher-type agitation mixer, a deep layer mixing machine, a power blender, and a plant mixer.

[0048] An example of a method for treating soil using the neutral solidification material of the present invention will be described below with reference to Fig. 1. The neutral solidification material of the present invention can be used for excavated soil such as mud discharged by shield methods such as the mud pressure shield method and the air bubble shield method as the soil to be treated for improvement.

[0049] The shield machine 1 shown in Fig. 1 is typically used in the air bubble shield method. The shield machine 1 includes a disk-shaped cutter 11 with a plurality of holes penetrating in the excavation direction, and a motor 12 connected to the cutter 11 for rotating the cutter 11. The direction in which the drive shaft of the motor 12 extends coincides with the excavation direction. The shield machine 1 shown in the figure also includes a screw conveyor 3. The screw conveyor 3 is located behind the cutter 11 in the excavation direction, and is used to transport the excavated soil excavated by the cutter 11 backward in the excavation direction.

[0050] First, the ground is excavated by the shield machine 1. In this embodiment, an air bubble injection pipe 15 is provided for injecting air bubbles into the soil to be excavated in order to increase the fluidity of the excavated soil when excavating the ground. One end of the air bubble injection pipe 15 is connected to an air bubble supplying device (not shown) such as a pump, and the other end opens to the cutter 11 side. The air bubble supplying device may supply air bubbles together with an air bubble agent that promotes the formation of air bubbles and stabilizes the air bubbles.

[0051] The excavated soil generated by excavating the ground is transported in the opposite direction to the excavation direction by the chamber 2 and the screw conveyor 3 in the shield machine 1 through holes provided in the cutter 11. The excavated soil containing the air foaming agent has high fluidity and is easy to transport. During transportation by the screw conveyor 3, in order to prevent eruptions caused by pressure changes when the excavated soil is discharged from the screw conveyor 3, an anti-eruption material may be added inside the screw conveyor 3 using a dosing device 4 provided on the front side of the screw conveyor 3 in the excavation direction, and the material may be mixed with the excavated soil 10 while being transported.

[0052] Next, the excavated soil 10 transported backward in the excavation direction by the screw conveyor 3 is discharged onto the belt conveyor 5 through a gate 31 located on the rear side of the screw conveyor 3 in the excavation direction, and is transported in the opposite direction to the excavation direction.

[0053] The excavated soil 10 transported by the belt conveyor is then placed in a bucket 6, the neutral solidification material of the present invention is added to the excavated soil 10 from a solidification material adding device 20, the soil is mixed by a mixer 30, and the soil is preferably cured for a certain period of time. These operations may be carried out after the excavated soil 10 is transported to the ground through a dump or a vertical shaft, or may be carried out at the tunnel construction site.

[0054] Since the neutral solidification material of the present invention can exhibit sufficient strength even immediately after mixing with the soil to be treated, the improved soil may be subjected to the subsequent process without curing. Alternatively, curing may be performed depending on the desired strength and the acceptance conditions of the destination. When curing is performed, the period may be preferably about 1 to 14 days, more preferably about 1 to 7 days.

[0055] In addition, when curing, in order to enable the soil to be used immediately after it has developed strength without any special treatment, the soil to be treated is mixed with the neutral solidification material, and the cone index measured according to JIS A1228 is preferably 400 kN / m 2 This index is the on-site cone index of the "Class 3 construction generated soil" described below, and such a cone index allows efficient reuse at other construction sites and ensures sufficient strength.

[0056] Through the above steps, improved soil that has developed strength can be obtained. The cured soil is then transported to the desired location, such as a treatment plant or a reuse site, using transport equipment such as a dutch or truck, and is reused or disposed of as necessary. Since the improved soil has a strength that is improved to a level that allows it to be reused, it can be transported as construction material and can be used effectively.

[0057] In this way, by using the neutral solidification material of the present invention, construction waste soil, which in conventional technology would have been treated as industrial waste or soil with limited uses due to its insufficient strength, can be solidified before being transported outside the site where the construction waste soil was generated, and the improved soil can be reused as construction material at the same or a different construction site.

[0058] In particular, when improved soil is used at a construction site different from the one where the construction generated soil was generated, the improved soil is cured for a certain period of time before being transported to the other construction site, but improved soil solidified using the neutral solidification material of the present invention can be transported with its strength adequately maintained even if it is excavated or loosened at the time of transportation.In addition, the improved soil can be reused as it is at the other construction site where it was transported without going through any special process, so it has high workability. In addition, soil containing an aerating agent has higher fluidity than soil not containing an aerating agent, making it difficult to handle or reuse in its current state. However, improving soil containing an aerating agent with a neutral solidification material has the advantage of achieving high levels of strength and pH control, improving handleability, and allowing the improved soil to be effectively used for a variety of purposes.

[0059] In addition, the soil improved by the neutral solidification material of the present invention has high strength, and can be suitably used, for example, as "Class 3 construction generated soil" as specified in the soil classification standard of the notification "Standards for Utilization of Generated Soil" by the Ministry of Land, Infrastructure, Transport and Tourism, or as "Class 3 treated soil" as specified in the quality standard of the notification "Technical Standards for Utilization of Construction Sludge Treatment Level" by the Ministry of Land, Infrastructure, Transport and Tourism. In detail, the soil improved by the neutral solidification material of the present invention can be suitably used in a wide range of applications, such as backfilling of structures, backfilling of buildings, backfilling of civil engineering structures, embankments for roads, embankments, land development, railway embankments, airport embankments, and water surface reclamation, and for civil engineering or construction work. EXAMPLES

[0060] The present invention will be described in more detail below with reference to examples. The scope of the present invention is not limited to these examples. In the following description, "%" stands for "mass %" unless otherwise specified. In the following tables, "-" indicates non-containment.

[0061] [Examples 1 to 2 and Comparative Examples 1 to 5] <1. Preparation of construction waste soil samples> Powdered sample soil was used as the raw soil. The moisture content of this sample soil measured in accordance with JIS A1203 (hereinafter simply referred to as moisture content) was 5.8%, and the pH measured in accordance with JGS 0211-2000 was 5.1. Other physical properties of the sample soil are shown in Table 1 below. Next, water, an air foaming agent (Magical Lasting Foam, an excavation additive, manufactured by TAC Co.) and an eruptive prevention material (Alka Super Rock, a mud modifier, manufactured by Taiko Bussan Co.) were added to the sample soil in the proportions shown in Table 1 below to obtain a construction generated soil replica sample (mud-like sample) with the physical properties shown in Table 1 below. In Table 1, the wet density was measured in accordance with JIS A1210.

[0062] [Table 1]

[0063] <2. Preparation of neutral solidification material> As raw materials, magnesium oxide, ferrous sulfate, and polymer flocculants with different mol% contents of acrylamide units and sodium acrylate units shown below were mixed in the ratios shown in Table 2 below to prepare powdered neutral solidification materials indoors. All raw materials used were in powder form. Comparative Example 4 did not contain the polymer flocculant, and instead gypsum was added as the balance.

[0064] (raw materials) Magnesium oxide: Light-burned magnesium oxide (MgO content 91.1% by mass), manufactured by Ube Material Industries, Ltd. Ferrous sulfate: Ferrous sulfate monohydrate, from China. Gypsum: Hemihydrate gypsum manufactured by Chiyoda Ute. Polymer flocculant: Sanfloc AH-4SFA, manufactured by Sanyo Chemical Industries, Ltd. (acrylamide unit composition ratio measured by the method described above: 72 mol%).

[0065] <3. Preparation of improved soil> Powdered neutral solidification material, 90kg / m 3 The pH of each improved soil was maintained neutral.

[0066] [Soil strength evaluation] The cone index (kN / m) of each material immediately after mixing was measured for the generated soil samples and improved soil in accordance with JIS A1228. 2 ) was measured. The strength of soil is judged as 500 kN / m 2 Those with a cone index of 500 kN / m or more (a standard equivalent to Class 3 construction soil indoors) are rated as good (indicated with the symbol "O" in the table). 2 The results are shown in Table 2.

[0067] [Table 2]

[0068] As shown in Table 2, the neutral solidification materials of Examples 1 and 2, which use magnesium oxide, sulfate, and a polymer flocculant with a specific acrylamide unit composition ratio and have a specific range of S / M ratio, are able to fully develop the strength of improved soil compared to the materials of each comparative example. This is supported by the fact that the cone index of the generated soil sample, which was a value that would be classified as Class 4 construction generated soil in the soil classification standard of the notification "Regarding standards for using generated soil," was improved to an improved soil with a cone index equivalent to Class 3 construction generated soil by adding the neutral solidification material.

[0069] [Examples 3 to 4] In this example, the relationship between the acrylamide unit composition ratio and strength development was evaluated using powdered polymer flocculants with different acrylamide unit composition ratios, while keeping the blending ratio of each raw material the same as in Example 1. The polymer flocculants used in Examples 3 and 4 are shown below.

[0070] Example 3: Sanfloc AH-9S, manufactured by Sanyo Chemical Industries, Ltd. (acrylamide unit composition ratio measured by the above-mentioned method: 60 mol %). Example 4: Acofloc A-220, manufactured by MT Aquapolymer Co., Ltd. (acrylamide unit composition ratio measured by the above-mentioned method: 96 mol %).

[0071] For Examples 3 and 4, improved soil was prepared in the same manner as in Example 1, and the soil strength was measured and evaluated using the Cone Index in the same manner as described above. The results are shown in Table 3 below, along with the acrylamide unit composition ratio in the polymer flocculant. Table 3 lists the compositions and results of Example 1 and Comparative Example 4 again.

[0072] [Table 3]

[0073] As shown in Table 3, Examples 1, 3 and 4, in which the acrylamide unit composition ratio in the polymer flocculant is within a specified range, are able to fully develop soil strength to the extent that the improved soil has a cone index equivalent to Type 3 construction waste soil, compared to the comparative example.

[0074] The relationship between the acrylamide unit composition ratio and cone strength shown in Table 3 is shown in Figure 2 together with a linear approximation line (shown by a dashed line). As shown in Figure 2, it can be seen that there is a correlation in which the cone strength increases as the acrylamide unit composition ratio in the polymer flocculant increases. Furthermore, a cone index threshold of 500 kN / m 2 In this case, the composition ratio of the acrylamide unit is estimated to be about 35 mol %. Based on this knowledge, the present invention has been completed by setting the preferable range of the composition ratio of the acrylamide unit as described above.

[0075] As described above, the neutral solidification material of the present invention can improve the soil to be improved into soil with high strength while maintaining the pH near neutral, so that the improved soil can be reused for a wide range of purposes, leading to effective use of resources.

Claims

1. The present invention relates to a flocculating agent for a sintered material comprising magnesium oxide, ferrous sulfate, a polymer flocculant having an acrylamide unit and a sodium acrylate unit, and gypsum; a mass ratio of the ferrous sulfate to the magnesium oxide in terms of anhydrous is 1.50 to 2.50; The magnesium oxide is contained in an amount of 2 to 41% by mass in terms of anhydrous. The ferrous sulfate is contained in an amount of 2.8 to 40% by mass in terms of anhydrous. The polymer flocculant is contained in an amount of 1 to 8 mass% in terms of anhydrous substance, The gypsum is contained in an amount of 40 to 94% by mass in terms of anhydrous. The composition ratio of the acrylamide unit constituting the polymer flocculant is 55 to 97 mol %, A neutral solidification material used to treat soil containing foaming agents.

2. A neutral solidification material as described in claim 1, wherein the composition ratio of sodium acrylate units constituting the polymer flocculant is 2 to 65 mol %.

3. A neutral solidification material as described in claim 1 or 2, wherein the MgO content in the magnesium oxide is 80 mass% or more.

4. The method includes a step of mixing the soil to be treated with a neutral solidification material, The neutral solidification material includes magnesium oxide, ferrous sulfate, a polymer flocculant having an acrylamide unit and a sodium acrylate unit, and gypsum; a mass ratio of the ferrous sulfate to the magnesium oxide in terms of anhydrous is 1.50 to 2.50; The neutral solidification material contains 2 to 41 mass% of the magnesium oxide in terms of anhydrous basis, The neutral solidification material contains 2.8 to 40 mass% of the ferrous sulfate in terms of anhydrous. The neutral solidification material contains the polymer flocculant in an amount of 1 to 8 mass% in terms of anhydrous. The neutral solidification material contains 40 to 94% by mass of the gypsum in terms of anhydrous. The composition ratio of the acrylamide unit constituting the polymer flocculant is 55 to 97 mol %, A method for treating soil, the method comprising treating the soil containing an aerating agent.

5. A soil treatment method as described in claim 4, wherein the composition ratio of the sodium acrylate units constituting the polymer flocculant is 2 to 65 mol %.

6. A method for treating soil as described in claim 4 or 5, wherein the MgO content in the magnesium oxide is 80 mass% or more.

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