JP2023033380A - Neutral solidifier and treatment method of soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a neutral solidifier which can ameliorate soil to have high strength while keeping pH near neutrality.

SOLUTION: A neutral solidifier contains magnesium oxide, at least one kind of sulfate chosen from aluminum sulfate, ferrous sulfate and gypsum, and a macromolecule flocculant having acrylic amide unit and sodium acrylate unit. The composition ratio of the acrylic amide unit constructing the macromolecule flocculant is 55-90 mol%. Containing 1-8 mass% of macromolecule flocculant is suitable. Containing 10-50 mass% of magnesium oxide is suitable.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a neutral solidification material and a soil treatment method.

In order to facilitate the carrying out and reuse of soft soil, soil generated from construction work, and the like, a soil solidification material that improves the strength of the soil is used. Soil solidification materials are classified into cement-based, lime-based, and gypsum-based, etc., according to their constituents. A gypsum-based soil solidifying material is used that can maintain the pH of the soil near neutrality. However, gypsum-based soil solidifying materials may not exhibit sufficient strength compared to cement-based ones, and there is room for improvement in this respect.

For the purpose of improving the strength of improved soil when using a soil solidification material, Patent Document 1 discloses a soil solidification material composed of magnesium oxide, aluminum sulfate and/or iron sulfate, and the balance being gypsum. Further, Patent Document 2 discloses a soil improver containing auxiliary materials such as hemihydrate gypsum in addition to metal salts such as metal sulfates, magnesium-containing substances and polymeric thickening materials.

JP-A-2000-109829 JP 2008-100313 A

However, the soil improvement materials described in Patent Documents 1 and 2 were able to maintain the pH of the improved soil near neutral, but the strength development was not sufficient and the strength could not be improved to the desired level. was there.

Improved soil obtained by solidifying construction-generated soil may be reused at the site where the construction-generated 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 surplus soil was generated, and then brought to the site where it is to be reused. At this time, the strength of the improved soil may be reduced due to the excavation, loosening, and other steps. As a result, it may not be possible to exhibit sufficient strength at the place where it is reused. The soil conditioners described in Patent Literatures 1 and 2 are not examined at all for improving such points.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a neutral solidifying material capable of obtaining improved soil which is less susceptible to a decrease in strength due to excavation and disentanglement while maintaining pH near neutrality.

As a result of intensive studies to solve the above problems, the present inventors found that by using a polymer flocculant having a specific composition, it is possible to maintain both the pH of improved soil and high strength. came to form

That is, the present invention provides magnesium oxide,
at least one sulfate of aluminum sulfate, ferrous sulfate and gypsum; and
and a polymer flocculant having an acrylamide unit and a sodium acrylate unit,
The present invention provides a neutral solidifying material in which the composition ratio of acrylamide units constituting the polymer flocculant is 55 to 90 mol %.

Further, as a preferred aspect of the present invention, there is provided a neutral solidifying material containing 1 to 8% by mass of the polymer flocculant.

Further, as a preferred aspect of the present invention, there is provided a neutral solidifying material containing 10 to 50% by mass of the magnesium oxide.

Furthermore, the present invention comprises a step of curing a mixture of soil to be treated and a neutral solidification material until the cone index measured according to JIS A1228 is 800 kN/m ² or more,
The neutral solidifying material includes magnesium oxide, at least one sulfate salt selected from aluminum sulfate, ferrous sulfate, and gypsum, and a polymer flocculant containing polyacrylamide and sodium acrylate as main components. Provided is a method for treating soil, wherein the composition ratio of acrylamide units constituting a polymer flocculant is 55 to 90 mol %.

Further, as a preferred aspect of the present invention, there is provided a soil treatment method for treating the soil containing a foaming agent.

According to the present invention, it is possible to improve the soil to exhibit high strength while maintaining the pH near neutrality, so that the improved soil can be reused in a wide range of applications, leading to effective utilization of resources. .

FIG. 1 is a schematic cross-sectional view showing an example of a soil treatment method using a neutral solidifying material together with an example of a shield machine used in a bubble shield construction method.

Preferred embodiments of the invention are described below. In addition, this invention is not limited to the following embodiment. In the following description, when described as "X to Y [Z]" (X and Y are arbitrary numbers and [Z] is a unit), unless otherwise specified, "X [Z] or more Y [ Z] means "less than or equal to".

The neutral solidifying material of the present invention is a material that is used to obtain soil that maintains a neutral pH and develops high strength by being mixed with the soil to be improved. The soil to be improved is, for example, water-containing soil such as soft soil containing water, or mud, etc., which is secondarily generated by various construction works such as road construction, tunnel construction by shield construction method, etc. construction soil and construction sludge. That is, the neutral solidification material of the present invention is suitably used for solidifying at least one of water-containing soil, construction soil and construction sludge.
In the following description, "improved soil" refers to soil that has been improved by adding the neutral solidifying material of the present invention to the soil to be improved.

"Neutral" in the present invention means that "the pH of the improved soil is 5.8 or more and 8.6 or less". This is the numerical value shown in the section "Discharged into public water areas other than sea areas" in the effluent standard pH specified in the Water Pollution Control Law. Therefore, the improved soil containing the neutral solidifying material of the present invention satisfies the drainage standards even when rainwater permeated into the improved soil flows into groundwater or rivers, so the use of the improved soil and It can be reused with reduced environmental impact without being restricted by the place of use.

The neutral solidifying material of the present invention contains the following components (1) to (3).
(1) Magnesium oxide (2) Sulfate of at least one of aluminum sulfate, ferrous sulfate and gypsum (3) Polymer flocculant having an acrylamide unit and a sodium acrylate unit

The neutral solidifying material of the present invention contains magnesium oxide. Magnesium oxide is a component that is mainly blended to solidify the soil to be improved.
Examples of magnesium oxide include light burned magnesium oxide obtained by burning magnesium hydroxide or magnesium carbonate at 600 to 900°C.

The content of magnesium oxide in the neutral solidifying material is preferably 10 to 50% by mass, more preferably 10 to 47% by mass, and still more preferably 10 to 45% by mass in terms of anhydride. By setting the content of magnesium oxide to the above-described level, it is possible to achieve both strength development of the soil to be improved and maintenance of a neutral pH at a high level. In addition, when soil contaminated with heavy metals or the like is to be improved, heavy metals can be insolubilized to suppress elution of heavy metals from the improved soil. As a result, there is also the advantage that the surrounding environment can be preserved using the improved soil.

The neutral solidifying material of the present invention contains at least one sulfate salt of aluminum sulfate, ferrous sulfate and gypsum. Sulfate is a component that is mainly blended to maintain neutral pH of the soil to be improved.

The sulfate contained in the neutral solidifying material may be any one of aluminum sulfate, ferrous sulfate, or gypsum, or may contain two kinds of aluminum sulfate, ferrous sulfate, and gypsum, It may contain all of aluminum sulfate, ferrous sulfate and gypsum.
From the viewpoint of achieving both strength development of the soil to be improved and maintaining pH neutral at a high level, the sulfates contained in the neutral solidification material are aluminum sulfate, ferrous sulfate and gypsum. It preferably contains at least two of them, more preferably contains at least aluminum sulfate and ferrous sulfate, and still more preferably contains all of aluminum sulfate, ferrous sulfate and gypsum.

The total sulfate content in the neutral solidifying material is preferably 42 to 89% by mass, more preferably 44 to 87% by mass, and still more preferably 46 to 84% by mass in terms of anhydride.
By adjusting the content of the sulfate as described above, it is possible to develop the strength of the soil to be improved and to keep the pH neutral and stably.

When aluminum sulfate is contained as a sulfate, the content of aluminum sulfate in the neutral solidifying material is preferably 0 to 65% by mass, more preferably 0 to 60% by mass, more preferably 0 to 60% by mass, in terms of anhydride. 0 to 55% by mass. That is, as long as the total sulfate content satisfies the above range, aluminum sulfate may not be contained.
By setting the content of aluminum sulfate as described above, it is possible to maintain the pH neutral and stably while developing the strength of the soil to be improved.

When ferrous sulfate is included as a sulfate, the content of ferrous sulfate in the neutral solidifying material is preferably 0 to 30% by mass, more preferably 0 to 25% by mass, in terms of anhydride. , more preferably 0 to 20% by mass. In other words, ferrous sulfate may not be contained as long as the total content of sulfates satisfies the above range.
By adjusting the content of ferrous sulfate to the above range, it is possible to develop a higher strength while maintaining the pH of the soil to be improved at a neutral level. In addition, when soil contaminated with heavy metals or the like is to be improved, heavy metals can be reduced and made insoluble, thereby suppressing elution of heavy metals from the improved soil.

When gypsum is included as a sulfate, at least one of anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum can be used as gypsum. Gypsum specified in JIS R9151 can also be used. Among these, it is preferable to use gypsum hemihydrate 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.
When gypsum is contained as a sulfate, the content of gypsum in the neutral solidifying material is preferably 0 to 75% by mass, more preferably 0 to 70% by mass, more preferably 0 to 70% by mass, in terms of anhydride. 65% by mass. That is, as long as the total sulfate content satisfies the above range, gypsum may not be contained.
By setting the content of gypsum to the above-mentioned level, the strength of the improved soil can be further enhanced due to the hydraulic property of the gypsum itself.

The neutral solidifying 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 added to increase the strength of the improved soil by flocculating particles of the soil to be improved, and is preferably a single component or a mixture of organic polymers. The total content of the polymer flocculant in the neutral solidifying material is preferably 1-8% by mass, more preferably 1-7% by mass, and still more preferably 1-6% by mass.
A "unit" in the present invention refers to a monomer unit that constitutes a polymer.

A specific embodiment of the polymer flocculant contained in the neutral solidifying material is, for example, a copolymer obtained by polymerizing acrylamide, which is the first monomer, and sodium acrylate, which is the second monomer. etc., which have an acrylamide unit and a sodium acrylate unit in the polymer flocculant.
In addition, the copolymer is an alternating copolymer in which each monomer is alternately polymerized, a random copolymer in which the arrangement of each monomer is disordered, and a block copolymer having structural units in which the same type of monomers are continuously polymerized. , and graft copolymers in which a polymer of one monomer is branched and bound to a polymer of the other monomer.

One of the characteristics of the polymer flocculant contained in the neutral solidifying material is that the acrylamide units constituting the polymer flocculant have a specific composition ratio.
Specifically, the composition ratio of the acrylamide unit contained in the polymer flocculant is preferably 55 to 90 mol%, more preferably 60 to 85 mol%, still more preferably 60 to 80 mol%. By using a polymer flocculant having such a ratio of acrylamide units, it is possible to achieve both strength development of the soil to be improved and maintenance of a neutral pH at a high level.

Although it is not clear why the use of a polymer flocculant having the acrylamide unit in the above-mentioned ratio can improve the strength, the present inventors speculate as follows.
In general, in the neutral to alkaline pH range (that is, the pH range of 5.8 or higher), the mineral particles that make up the soil particles are negatively charged due to their low isoelectric points. It is easy for electrostatic repulsion to occur between water and soil particles. As a result, the soil particles are less likely to be agglomerated, and as a result, the strength of the soil as a whole tends to decrease.
When the above-mentioned polymer flocculant is added, first, the amide group derived from the acrylamide unit adsorbs to the surface of the soil particles, and then the carboxy group derived from the sodium acrylate unit repels each other, resulting in molecules of the polymer flocculant. By spreading the chains and holding (taking in) the soil particles and water by the spread, the soil particles can be effectively aggregated and the water can be retained between the soil particles, improving the strength of the improved soil. It is considered possible. In particular, the strength development process by the addition of the above-mentioned polymer flocculant includes (i) adsorption of the flocculant to the surface of the soil particles, (ii) cross-linking of the soil particles, and (iii) aggregation of the soil particles. It is considered that the processes of (i) and (ii), which are important for strength development, are balanced by setting the composition ratio of the acrylamide unit contained in the polymer flocculant to preferably 55 to 90 mol%. It is thought that it can progress well.

Carbon, hydrogen and nitrogen contained in the polymer flocculant can be measured, for example, by the following methods. Specifically, about 2 mg of the polymer flocculant to be measured is accurately weighed, and this is introduced into an elemental analyzer (for example, Microcoder JM10 manufactured by J Science Lab Co., Ltd.) to quantitatively measure the mass of each element. do. Antipyrine (carbon element: 70.2% by mass, hydrogen element: 6.4% by mass, nitrogen element: 14.9% by mass), for example, can be used as the sample.

Let C1 be the mass ratio (% by mass) of the carbon element and N1 be the mass ratio (% by mass) of the nitrogen element measured by the above method. From these values, each composition ratio of the acrylamide unit and the sodium acrylate unit is calculated by the following method.
First, the acrylamide unit has a chemical formula of " _--CH.sub.2 --CH(CO-- _NH.sub.2 )--", where the number of carbon atoms in the unit is 3 and the number of nitrogen atoms in the unit is 1.
Further, the sodium acrylate unit has the chemical formula of " _--CH.sub.2 --CH(COONa)--", the number of carbon atoms in the unit is 3, and the number of nitrogen atoms in the unit is zero.

The composition ratio (mol%) of the acrylamide unit in the polymer flocculant is set to "A", the composition ratio (mol%) of the sodium acrylate unit in the polymer flocculant is set to "100-A", and the carbon of each unit Based on the numbers and nitrogen numbers, the composition ratio (mol%) of carbon in the acrylamide unit is expressed as "3×A", and the composition ratio (mol%) of nitrogen in the acrylamide unit is expressed as "A". Also, the composition ratio (mol %) of carbon in the sodium acrylate unit is expressed as "3×(100−A)".

Based on the respective ratios described above, the ratio (C5/N5) of the composition ratio of the carbon element (C5) to the composition ratio of the nitrogen element (N5) in the polymer flocculant is calculated by the following formula (a). be.
(C5/N5)={(3×A)+3×(100−A)}/A=300/A (a)

Here, C5/N5 is expressed as "{(C1)/(carbon atomic weight)}/{(N1)/(nitrogen atomic weight)}" (carbon atomic weight = 12, nitrogen atomic weight = 14), so the acrylamide unit The composition ratio A of is calculated by the following formula (b).
Composition ratio A (mol%) of acrylamide units
=300/{(C1)/(carbon atomic weight)}/{(N1)/(nitrogen atomic weight)} (b)

Moreover, the composition ratio of the sodium acrylate unit is calculated by the following formula (c).
Composition ratio of sodium acrylate unit (mol%) = 100-A (c)

The composition ratio of the sodium acrylate unit contained in the polymer flocculant is preferably 10 to 45 mol%, more preferably 15 to 40 mol%, still more preferably 20 to 35 mol%.

The properties of magnesium oxide, sulfate and polymer flocculant may be independently powdery, or liquid or slurry dissolved or dispersed in a solvent such as water. Magnesium oxide and sulfate may each independently be an anhydride or a hydrate.
From the viewpoint of improving the handleability during transportation and use of the neutral solidifying material, it is preferable that all of the magnesium oxide, the sulfate, and the polymer flocculant be in the form of powder.
From the same point of view, the neutral solidifying material of the present invention is preferably powdery.

The Blaine specific surface area of magnesium oxide is preferably 6,000 to 20,000 cm ² /g, more preferably 7,000 to 20,000 cm ² /g, still more preferably 8,000 to 20,000 cm ² /g.
By setting the Blaine specific surface area to such a range, it is possible to improve the workability of the neutral solidification material, and to improve the solidification property of the soil to be improved due to its high hydration activity. Strength can be improved. In addition, it is preferable that the above-mentioned range of Blaine specific surface area is satisfied when light-burnt magnesium oxide is used as magnesium oxide in that both improvement of workability and improvement of strength of improved soil can be achieved at a high level.
The Blaine specific surface area of magnesium oxide can be measured using a Blaine air permeation device, for example, according to JIS R5201:1997 "Physical Test Method for Cement".

The BET specific surface area of magnesium oxide is preferably 5 to 30 m ² /g, more preferably 7 to 30 m ² /g, still more preferably 8 to 30 m ² /g.
By setting it in such a range, the workability of the neutral solidification material can be improved, and the solidification property of the soil to be improved due to high hydration activity is increased, and the strength of the improved soil is improved. be able to. In addition, it is preferable that the above-mentioned range of Blaine specific surface area is satisfied when light-burnt magnesium oxide is used as magnesium oxide in that both improvement of workability and improvement of strength of improved soil can 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 Bell Japan).

The content of MgO in magnesium oxide is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more. With such a content ratio, it becomes difficult for the pH buffering capacity of the surrounding environment of the improved soil to decrease, and the strength of the improved soil can be improved.

The content of CaO in magnesium oxide is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. With such a content ratio, the pH of the surrounding environment of the improved soil can be easily maintained neutral, and the strength of the improved soil can be improved.

The MgO content and CaO content in the magnesium oxide described above are JIS M
8853: 1998 "Method for chemical analysis of aluminosilicate raw material for ceramics".

As long as the effects of the present invention are exhibited, the neutral solidification material may further contain additives according to the properties of the soil to be improved. Examples of additives include calcium aluminate minerals such as hydrotalcite and hydrocalumite, silicon-containing minerals such as silica stone, carbonates such as magnesium carbonate and limestone, and porous materials such as sepiolite, perlite, zeolite and silica. , and at least one of chelating agents and the like can be used.
The various additives may independently be in the form of powder, or may be in the form of liquid or slurry dissolved or dispersed in a solvent such as water.
Moreover, each additive may independently be an anhydride or a hydrate.
It is preferable to conduct a blending test in advance and determine the presence or absence of addition of various additives and the amount to be mixed based on the results.

The neutral solidification material of the present invention can be used in a solidification method in which the neutral solidification material and soil to be improved are mixed and solidified.
The state of the neutral solidifying material when mixed with the soil to be improved may be powder or slurry.
In addition, the neutral solidification material and the soil to be improved may be mixed at the same time, and one of the neutral solidification material and the soil to be improved may be mixed with the other. may be added.

The amount of neutral solidification material added per 1 m ³ of the soil to be improved can be changed as appropriate according to the type and properties of the soil to be improved and the desired strength of expression, but the uniformity of mixing and the strength of expression It is preferably 20 to 200 kg/m ³ , more preferably 20 to 150 kg/m ³ , still more preferably 20 to 75 kg/m ³ from the viewpoint of both improvement and reduction of treatment costs.

Equipment for mixing the neutral solidification material and the soil to be improved includes, for example, a backhoe, a backhoe equipped with a mixing bucket, a stabilizer, a self-propelled soil improvement machine, a stationary mixer, a trencher-type stirring mixer, a deep mixing machine, and a power Equipment commonly used in the art, such as blenders and plant mixing, can be used.

An example of a soil treatment method using the neutral solidifying material of the present invention will be described below with reference to FIG. The neutral solidification material of the present invention can be used for excavated soil such as mud discharged by a shield construction method such as a mud pressure shield construction method or a bubble shield construction method, as soil to be improved.
A shield machine 1 shown in FIG. 1 is typically used for a bubble shield construction method. The shield machine 1 includes a disc-shaped cutter 11 having a plurality of holes penetrating in the excavating 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 direction of excavation. The shield machine 1 shown in the figure also includes a screw conveyor 3 located behind the cutter 11 in the excavation direction and for conveying the excavated soil excavated by the cutter 11 backward in the excavation direction.

First, the ground is excavated by the shield machine 1 . In this embodiment, a bubble injection pipe 15 for injecting bubbles into the soil to be excavated is provided for the purpose of increasing the fluidity of the excavated soil when excavating the ground. One side of the bubble injection tube 15 is connected to a bubble supply device (not shown) such as a pump, and the other side opens toward the cutter 11 side. The foam supply device may, for example, supply the foam together with the foaming agent.

Excavated soil generated by excavating the ground is conveyed in a direction opposite to the excavation direction by the chamber 2 and the screw conveyor 3 of the shield machine 1 through a hole provided in the cutter 11 . Excavated soil containing a foaming agent has high fluidity and is easy to convey.
During transport by the screw conveyor 3, a loading device 4 provided on the front side of the screw conveyor 3 in the excavation direction for the purpose of preventing ejection due to pressure changes when excavated soil is discharged from the screw conveyor 3. A blowout prevention material may be added to the inside of 3 and mixed with the excavated soil 10 for transportation.
Subsequently, the excavated soil 10 conveyed rearward in the excavation direction by the screw conveyor 3 is discharged onto the belt conveyor 5 via the gate 31 located on the rear side in the excavation direction of the screw conveyor 3 and conveyed.

Then, the excavated soil 10 conveyed by the belt conveyor is placed in the bucket 6, the neutral solidifying material of the present invention is added to the excavated soil 10 from the solidifying material addition device 20, mixed by the mixer 30, and preferably cured for a certain period of time. do. These operations may be performed after the excavated soil 10 has been carried out to the ground through a pit or shaft, or may be performed at the tunnel construction site. The curing period can be appropriately changed according to the desired strength and the acceptance status of the export destination, but it is preferably about 1 to 14 days, more preferably about 1 to 7 days.

Through the above steps, it is possible to obtain improved soil in which strength is expressed in the soil to be treated. After that, the soil after curing is transported to a target site such as a treatment plant or a recycling site by using a transporting facility such as a trolley or a truck, and reused or discarded as necessary. Since the strength of this improved soil is improved to a reusable level, it can be carried out as a construction material and can be effectively used.

In this way, by using the neutral solidifying material of the present invention, construction-generated soil, which has been treated as industrial waste or soil with limited uses due to insufficient strength in the prior art, can be removed from the site where construction-generated soil is generated. The improved soil can be reused as a construction material at the same or a different construction site by solidifying it before transporting it to a factory.

In particular, when improved soil is used at a construction site different from the construction site where construction-generated soil is generated, the neutral solidification material of the present invention is used when the improved soil is transported to another construction site after curing for a certain period of time. The solidified improved soil can be carried out in a state in which the strength of the improved soil is sufficiently maintained even if excavation or loosening is performed at the time of carrying out. In addition, even at other construction sites where the improved soil has been brought in, the improved soil can be reused as it is without going through any special steps.

In addition, since the soil improved by the neutral solidification material of the present invention exhibits high strength, for example, the Ministry of Land, Infrastructure, Transport and Tourism stipulates in the soil classification criteria of the notification "Regarding the use of generated soil" "Second It can be suitably used as "second-class treated soil" specified in the quality standards of the "technical standards for the use of construction sludge treatment" notified by the Ministry of Land, Infrastructure, Transport and Tourism. Specifically, the soil improved by the neutral solidifying material of the present invention is used, for example, for backfilling of structures, backfilling of buildings, backfilling of civil engineering structures, embankments for roads, embankments, land development, and railway embankments. , civil engineering work such as airport embankment and water surface reclamation, or a wide range of uses such as construction.

EXAMPLES The present invention will be described in more detail below with reference to examples. The scope of the invention is not limited to such examples. In the following description, "%" represents "% by mass" unless otherwise specified.

[Examples 1 to 6 and Comparative Examples 1 to 5]
<1. Preparation of Construction Excavated Soil Reproduction Sample>
Powdered mudstone was used as the original soil. This mudstone has a water content ratio of 29.9% measured according to JIS A1203 (hereinafter also simply referred to as "water content ratio"), and a wet density measured according to JIS A1210 of 1.75 g/ cm ³ and the pH measured according to JGS 0211-2000 was 8.4.
Next, water, a foaming agent (OK-1, manufactured by Taiheiyo Shield Mechanics Co., Ltd.) and an anti-ejection agent (SP-α, manufactured by Taiheiyo Shield Mechanics Co., Ltd.) were added to the mudstone in the proportions shown in Table 1 below. , two types of construction soil samples (mud-like samples) with different water content ratios were obtained. Hereinafter, these construction-generated soil reproduction samples are also referred to as "generated soil sample 1" and "generated soil sample 2."

<2. Preparation of neutral solidifying material>
As raw materials, magnesium oxide, aluminum sulfate and ferrous sulfate shown below, and polymer flocculants with different mol% contents of acrylamide units and sodium acrylate units were mixed in the ratios shown in Table 2 below, and totaled. Ten types of powdery neutral solidifying materials were prepared.
・Magnesium oxide: Ube Material Co., Ltd., light burnt magnesium oxide ・Aluminum sulfate: Made in China, aluminum sulfate 14 hydrate ・Ferrous sulfate: Made in China, ferrous sulfate monohydrate ・Polymer aggregation Agent:
(1) Neutral solidification materials B and H: Akoflock A-150UH manufactured by MT Aquapolymer Co., Ltd.
(2) Neutral solidifying material C: SANFLOCK AH-9S manufactured by Sanyo Chemical Industries, Ltd.
(3) Neutral solidification materials D and I: SANFLOCK AH-4SFA manufactured by Sanyo Chemical Industries, Ltd.
(4) Neutral solidifying materials E and J: Akoflock A-125 manufactured by MT Aquapolymer Co., Ltd.
(5) Neutral solidifying material F: Water Flock PA-041 manufactured by Technica Co., Ltd.
(6) Neutral solidification material G: Akofloc A-220 manufactured by MT Aquapolymer Co., Ltd.

<3. Preparation of improved soil>
A powdery neutral solidification material was added to the generated soil sample 1 in an amount of 30 kg/m ³ and mixed, and to the generated soil sample 2 in an amount of 40 kg/m ³ and mixed. , the desired improved soil was obtained. The pH of each improved soil was maintained neutral.

[Soil strength evaluation]
The cone index was measured according to JIS A1228 for the generated soil samples and improved soil.
Immediately after mixing each material, specimens for cone index measurement were prepared from the generated soil samples, and the cone index was measured.
In the improved soil, in order to confirm the effect of kneading, the same improved soil was repeatedly used 1 day after curing and 7 days after curing, and immediately before the test, test specimens for cone index measurement in each curing period were prepared. index was measured.
Soil strength is determined by multiplying the cone index value measured after curing indoors for the above period by 0.9, taking into consideration the impact of strength reduction during excavation and unraveling of improved soil and differences in the surrounding environment. This value is used as the estimated strength of the improved soil at the site, and the estimated value of 800 kN/m ² or more (Type 2 construction surplus soil or more) is evaluated as good (indicated by “○” in Table 3). , and those with an estimated value of less than 800 kN/m ² were evaluated as poor (indicated by "x" in Table 3). The results are shown in Tables 1 and 3.

As shown in Table 3, the neutral solidifying material of the example using magnesium oxide, sulfate, and a polymer flocculant having a predetermined acrylamide unit composition ratio has a higher curing rate than the comparative example. It can be seen that the strength of the improved soil can be fully expressed regardless of the period. This is because the cone index of the generated soil sample was a value that was classified as "Type 4 construction generated soil" in the soil classification criteria of the above-mentioned notice "Regarding the use of generated soil", but the neutral solidification It is also supported by the fact that the addition of timber improved the soil to have a cone index equivalent to that of type 2 construction soil.
In particular, the neutral solidification materials of Examples 1 to 4, in which the content of the polymer flocculant in the neutral solidification material is set in a suitable range, can further increase the strength of the improved soil, and can be used by excavation and loosening. It is also found that the improved soil can be suitably reused even after curing for a certain period of time after the addition of the neutral solidifying material, since the strength is less affected by the decrease.

As described above, the neutral solidifying material of the present invention can improve the soil to be improved to maintain the pH near neutral and express high strength, so the improved soil can be reused in a wide range of applications. This can lead to effective use of resources.

Claims (5)

magnesium oxide;
at least one sulfate of aluminum sulfate, ferrous sulfate and gypsum; and
and a polymer flocculant having an acrylamide unit and a sodium acrylate unit,
A neutral solidifying material, wherein the composition ratio of the acrylamide unit constituting the polymer flocculant is 55 to 90 mol %. The neutral solidifying material according to claim 1, containing 1 to 8% by mass of the polymer flocculant. The neutral solidifying material according to claim 1 or 2, containing 10 to 50% by mass of said magnesium oxide. A step of curing a mixture of soil to be treated and a neutral solidifying material until the cone index measured according to JIS A1228 reaches 800 kN/m ² or more,
The neutral solidifying material contains magnesium oxide, a sulfate salt of at least one of aluminum sulfate, ferrous sulfate and gypsum, and a polymer flocculant having an acrylamide unit and a sodium acrylate unit; A method for treating soil, wherein the composition ratio of the acrylamide unit constituting the flocculant is 55 to 90 mol %. 5. The soil treatment method according to claim 4, wherein said soil containing a foaming agent is treated.

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