JP7644736B2 - A method for solidifying soil in sub-freezing environments and a material preparation set for soil paving - Google Patents

Description

The present invention relates to a method for applying solidified soil and a set for preparing materials for soil paving, and in particular to a method for applying solidified soil and a set for preparing materials for soil paving that can be used in environments where the temperature drops below freezing.

Magnesium oxide-based soil solidification materials are known (see, for example, Patent Document 1). The soil solidification materials described therein can rapidly solidify soil, such as soil generated at construction work sites. In addition, a composition containing a magnesium oxide solidification material that suppresses frost damage has been proposed (see, for example, Patent Document 2). This composition can form a soil solidification layer on the ground surface that is highly stable against repeated temporary freezing.

Japanese Patent Application Publication No. 10-316967 Patent No. 5897067

Unlike solidification materials used to improve industrial waste, etc., soil paving materials must satisfy the user's aesthetic needs for surface finishing, etc. For this reason, even if physical properties such as strength are met, if the aesthetics are marred by cracks, blistering, etc., the user's needs cannot be met. Even in the Pacific coastal areas from Kanto to Kyushu, in winter when temperatures exceed 0°C during the day but drop below freezing at night, moisture from construction can freeze at night. The expansion of the material due to freezing causes cracks and blistering in the soil paving road immediately after construction, which has not yet developed its strength, and the material solidifies in this state when the temperature rises during the day. This raises the risk of marring the aesthetics.

The present invention aims to provide a method for applying solidified soil that can suppress the occurrence of cracks and swelling due to freezing and obtain solidified soil that can maintain a smooth surface, and a soil paving material preparation set.

The method for applying solidified soil according to the present invention is characterized in that a soil paving material containing soil components, magnesium oxide, and at least one additive selected from magnesium chloride and magnesium sulfate is applied to obtain a soil paving layer, and the soil paving layer is solidified by exposing it to below freezing point.

The method for applying solidified soil according to the present invention is characterized in that a mixture of soil components and magnesium oxide is applied to obtain a soil pavement layer to which no additives have been added, an aqueous solution of additives containing at least one additive selected from magnesium chloride and magnesium sulfate is supplied to the soil pavement layer to which no additives have been added, and then the soil pavement layer is solidified by exposing it to below freezing point.

The soil paving material preparation set according to the present invention is characterized by including a first material consisting of a mixture of soil components and magnesium oxide, and a second material that is packaged separately from the first material and consists of at least one additive selected from magnesium chloride and magnesium sulfate.

The present invention provides a method for applying solidified soil that can suppress the occurrence of cracks and swelling due to freezing and obtain solidified soil that can maintain a smooth surface, and a soil paving material preparation set.

Through extensive research, the present inventors have discovered that by incorporating at least one additive selected from magnesium chloride and magnesium sulfate, it is possible to obtain solidified soil that is capable of suppressing the occurrence of cracks and blisters due to volume expansion caused by freezing and capable of maintaining a smooth surface.
Hereinafter, an embodiment of the present invention will be described in detail.

<Solidified soil construction method>
The solidified soil construction method of the present invention can use a soil paving material containing soil components, magnesium oxide, and at least one additive selected from magnesium chloride and magnesium sulfate. In this case, the soil paving material is first constructed to obtain a soil paving layer, and then the soil paving layer is solidified while being exposed to below freezing point, thereby carrying out the solidified soil construction method of the present invention.

The soil components contained in the soil paving material are the main components that make up the soil when it is provided on the ground surface, and examples thereof include masami soil, Kanto loam, black soil, red soil, and shirass soil. Magnesium oxide is said to solidify mainly by pozzolanic reaction, and is compatible with soil containing amorphous silica. There is no particular restriction on magnesium oxide as long as the magnesium oxide powder has a BET specific surface area of 5 m ² /g or more. For example, magnesium hydroxide (Mg(OH) ₂ ) produced by adding an alkali such as calcium hydroxide to seawater, or magnesite ore (MgCO ₃ ) particles are calcined at a temperature of 650 to 900°C, preferably 680 to 900°C, for 10 to 120 minutes.

Magnesium oxide solidifies by reacting with water. The magnesium oxide content in soil paving materials is preferably 2 to 20% by mass based on the soil components. If there is too little magnesium oxide, the desired effect cannot be obtained. On the other hand, if there is too much, there are problems in terms of cost and color tone, as well as a tendency for the pH to become high. The magnesium oxide content is more preferably 3 to 15% by mass based on the soil components.

The additive is selected from magnesium chloride and magnesium sulfate, and lowers the freezing point of water in the soil paving material and increases the strength after solidification. An example of magnesium chloride is magnesium chloride hexahydrate, and an example of magnesium sulfate is magnesium sulfate heptahydrate. The content of the additive is preferably 1 to 20% by mass of the soil paving material. If the amount of additive is too small, the desired effect cannot be obtained, and if the amount is too large, it is not preferable from the standpoint of cost and workability when preparing the aqueous solution. The content of the additive is more preferably 2 to 15% by mass of the soil paving material.

Soil paving materials can be prepared, for example, by mixing soil components with magnesium oxide to obtain a mixture, and then adding additives to the mixture. A known mixing device such as a mixer can be used to mix the soil components with the magnesium oxide. Since the soil components and magnesium oxide can be mixed uniformly, the occurrence of unevenness is suppressed. Moreover, it becomes possible to mix the soil components and magnesium oxide in a factory, etc., which leads to a reduction in on-site work.

In addition to magnesium oxide, pavement coloring pigments such as iron oxide, titanium oxide, and chromium oxide, pigment dispersants, etc. may be added to the soil components. For example, when about 0.05 to 1 mass % of iron oxide pigment is included, it is possible to change the color tone by coloring.

The additive can be added as an aqueous solution to the mixture of soil components and magnesium oxide. Examples of water include tap water, seawater, river water, etc. from which impurities have been removed, and are not particularly limited. The additive can be added to water and mixed with a ladle or hand mixer to prepare an aqueous solution. The concentration of the additive in the aqueous solution is not particularly limited, and can be, for example, about 1 to 20 mass% of the soil paving material. It is desirable to appropriately select the concentration of the additive in the aqueous solution and the amount of the aqueous solution added to the mixture so that the content of the additive in the soil paving material is within the above-mentioned range. The additive may be added to the mixture before or together with the water, rather than as an aqueous solution.

The soil paving material is spread evenly and then rolled with a roller to obtain a compacted soil paving layer with a smooth surface. The roller weight for roller compaction is not particularly limited, but is usually about 5 to 30 kg. The construction site can be, for example, a flat or sloped surface that has been leveled and has had its roots removed. It is preferable to apply the paving material so that it is about 1 to 7 cm thick from the ground.

The soil pavement layer thus constructed solidifies while being exposed to below freezing points, resulting in solidified soil. In this specification, "solidification" refers to a state in which plasticity has been lost, and "solidified soil" refers to a soil pavement layer whose compressive strength has increased due to the reaction of magnesium oxide and other substances contained therein. "Exposing to below freezing points" specifically refers to the following conditions, and is intended to be used mainly outdoors in winter in temperate zones.
- Within 3 days after installation, the minimum temperature will be below freezing and the maximum temperature will be above 0°C. - Within 14 days after installation, there will be 7 or more days with the minimum temperature below freezing.

Even if the solidified soil applied by the method of the present invention is exposed to below freezing during solidification, the freezing point drop caused by the additives prevents cracks and swelling caused by freezing. This allows the surface to remain smooth as if it had been applied with a roller or the like, maintaining its aesthetic appearance. In addition, after solidification, the strength increase due to the reaction of magnesium oxide and the strength increase due to the additives prevents cracks and swelling even when the soil is loaded onto the road surface.

The presence or absence of cracks and blisters can be determined by a Schmidt hammer test. Any Schmidt hammer can be used as long as it can be used to measure the strength and compaction of soil, etc. If the Schmidt hammer test results in a specified strength, it is deemed that no cracks or blisters have occurred. In other words, the solidified soil has a good, aesthetic appearance.

The soil paving material used in the above-mentioned method contains magnesium oxide as well as at least one additive selected from magnesium chloride and magnesium sulfate. By using such a soil paving material, the reaction between magnesium oxide, magnesium chloride, etc. and water is promoted, which increases the strength of the applied soil paving layer after solidification and suppresses cracks and swelling.

In the solidified soil application method of the present invention, a mixture of soil components and magnesium oxide can be used instead of the above-mentioned soil paving material. In this case, first, a mixture of soil components and magnesium oxide is applied to obtain a soil paving layer to which no additives have been added. Next, an additive aqueous solution containing at least one additive selected from magnesium chloride and magnesium sulfate is supplied to the soil paving layer to which no additives have been added by surface spraying, and then the soil paving layer is solidified by exposing it to below freezing, thereby carrying out the solidified soil application method of the present invention.

The raw materials used, such as soil components, are the same as those described above, and construction can be carried out using the same methods as those described above. However, what is obtained by construction is a soil pavement layer to which no additives have been added. By supplying an aqueous solution of additives to the soil pavement layer, a soil pavement layer containing additives can be obtained. The aqueous solution of additives can be prepared in the same manner as described above. It is desirable to supply the aqueous solution of additives in an amount such that the additive content in the solidified soil is 2 to 5 mass %.

As mentioned above, the soil pavement layer containing the additive aqueous solution solidifies when exposed to below freezing temperatures. As mentioned above, even when exposed to below freezing temperatures, the additive causes the freezing point to drop, suppressing the occurrence of cracks and swelling caused by freezing. This allows the surface to be kept smooth and the aesthetic appearance to be maintained. In addition, after solidification, the additive increases the strength compared to construction using only magnesium oxide, so even if a load is placed on the road surface, the occurrence of cracks and swelling is suppressed. Another advantage is that after construction, only the aqueous solution needs to be sprayed, reducing the amount of work.

<Soil paving material preparation set>
The soil paving material preparation set of the present invention includes a first material consisting of a mixture of soil components and magnesium oxide, and a second material packaged separately from the first material and consisting of at least one additive selected from magnesium chloride and magnesium sulfate.

The first material contains the soil components and magnesium oxide as described above in the ratios described above. The second material, which is made of additives such as magnesium chloride, is packaged separately from the first material, which contains soil components such as granite. Therefore, due to the deliquescence of magnesium chloride, the granite and other soil components do not harden, and workability is not impaired.

The first material and the second material are mixed to prepare a soil paving material, which can be used in the solidified soil construction method of the present invention. Alternatively, the second material, which is made of an additive, can be made into an aqueous solution, which can be used to carry out the solidified soil construction method of the present invention. In either case, since the obtained soil paving layer contains the additive, the occurrence of cracks and swelling due to freezing is suppressed even if it is exposed to below freezing points while still containing moisture. This allows the surface to be kept smooth and beautiful.

Specific examples of the present invention are given below, but the present invention is not limited to these.

<Preliminary Examination>
First, a test specimen was prepared by adding additives to a mixture of soil components and magnesium oxide, and the effects of the additives on the curing at constant temperature and humidity were examined. Magnesium chloride or magnesium sulfate was used as the additive. Iron oxide was also added to the mixture as a coloring agent. The following materials were used for each test.
Magnesium oxide: Paving Master (manufactured by Ube Material Industries)
Magnesium chloride: Magnesium chloride hexahydrate, special grade (manufactured by Hayashi Pure Chemical Industries, Ltd.)
Magnesium sulfate: Magnesium sulfate heptahydrate special grade (manufactured by Hayashi Pure Chemical Industries, Ltd.)
Iron oxide: BAYFERROX960 (manufactured by LANXESS)

(Preparation of Mixture)
Magnesium oxide (10 mass %) and iron oxide (0.1 mass %) were added to the granular sand and mixed to prepare a mixture of soil components and magnesium oxide.

(Test Example 1)
Magnesium chloride hexahydrate was added to the mixture at 2% by mass, and tap water was added at 10% by mass, and the mixture was kneaded to obtain a raw material composition. This was molded into a cylindrical shape with a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 1.

(Test Example 2)
Magnesium chloride hexahydrate was added in an amount of 3% by mass to the mixture, and tap water was added in an amount of 10% by mass to the mixture, followed by kneading to obtain a raw material composition, which was then molded into a cylindrical shape having a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 2.

(Test Example 3)
Magnesium chloride hexahydrate was added in an amount of 5% by mass to the mixture, and tap water was added in an amount of 10% by mass to the mixture, followed by kneading to obtain a raw material composition, which was then molded into a cylindrical shape having a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 3.

(Test Example 4)
Magnesium chloride hexahydrate was added to the mixture in an amount of 10% by mass, and tap water was added in an amount of 10% by mass, and the mixture was kneaded to obtain a raw material composition. This was molded into a cylindrical shape with a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 4.

(Test Example 5)
Magnesium chloride hexahydrate was added to the mixture in an amount of 15% by mass, and tap water was added in an amount of 10% by mass, and the mixture was kneaded to obtain a raw material composition. This was molded into a cylindrical shape with a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 5.

(Test Example 6)
Magnesium sulfate heptahydrate was added to the mixture at 2% by mass, and tap water was added at 10% by mass, and the mixture was kneaded to obtain a raw material composition. This was molded into a cylindrical shape with a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 6.

(Test Example 7)
Magnesium sulfate heptahydrate was added in an amount of 5% by mass to the mixture, and tap water was added in an amount of 10% by mass to the mixture, followed by kneading to obtain a raw material composition, which was then molded into a cylindrical shape having a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 7.

(Test Example 8)
The mixture was mixed with 10% by mass of tap water and kneaded to obtain a raw material composition, which was then molded into a cylindrical shape with a diameter of 5 cm and a height of 10 cm to prepare a specimen for Test Example 8.

Unconfined compression tests (JIS A1216) were conducted on the specimens of test examples 1 to 8 on the seventh day of material age. The results are summarized in Table 1 below. The strength ratio when the average unconfined compressive strength of the specimens of test example 1 is taken as 100 is strength ratio 1, and the strength ratio when the average unconfined compressive strength of the specimens of test example 8 is taken as 100 is strength ratio 2, both of which are shown in Table 1.

As shown in strength ratio 2 in Table 1 above, it was confirmed that the inclusion of an additive selected from magnesium chloride and magnesium sulfate improved the unconfined compressive strength. The unconfined compressive strength of the specimen in test example 8, which did not contain any additive, was only 61% of that of test example 1, based on strength ratio 1.

A uniaxial compression test (JIS A1216) was conducted on the specimens of Test Example 1 and Test Example 8 on the 28th day of material age. The results are shown in Table 2 below as Test Example 9 and Test Example 10, respectively. The strength ratio when the average uniaxial compressive strength of the specimens of Test Example 9 is taken as 100 is set as strength ratio 1, and the strength ratio when the average uniaxial compressive strength of the specimens of Test Example 10 is taken as 100 is set as strength ratio 2, and are also shown in Table 2.

The specimen of Test Example 10, which does not contain any additive, shows a strength of 48% of that of Test Example 9 at 28 days, even when cured at constant temperature and humidity.

Example 1
The same raw material composition (mixture, magnesium chloride, water) as in Test Example 1 was used as the soil paving material, and a soil paving layer was constructed by the method of the present invention.
The soil paving material was prepared by adding magnesium chloride to the mixture in the same manner as in Test Example 1, adding 10% by mass of tap water, and then kneading. This was spread evenly over a 40 cm x 60 cm section with a thickness of 5 cm, and compacted with a 25 kg roller to form a soil paving layer. The soil was then solidified by exposing it to below freezing points to obtain solidified soil.

Example 2
First, the mixture prepared in the preliminary test was spread evenly in a section measuring 40 cm x 60 cm with a thickness of 5 cm. As the additive aqueous solution, an aqueous solution with a water content of 10 mass % was prepared by adjusting magnesium chloride hexahydrate to 2 mass % relative to the mixture.
The aqueous solution of the additive was sprayed onto the spread mixture, which was then rolled with a 25 kg roller to form a soil pavement layer, which was then solidified by exposing it to below freezing point to obtain solidified soil.

Example 3
First, the mixture prepared in the preliminary test was spread evenly in a section measuring 40 cm x 60 cm with a thickness of 5 cm. As the additive aqueous solution, an aqueous solution with a water content of 10 mass % was prepared by adjusting magnesium chloride hexahydrate to 2 mass % relative to the mixture.
Tap water was sprayed onto the spread mixture, which was then rolled with a 25 kg roller, and then an aqueous solution of additives was sprayed onto the mixture to form a soil paving layer. The soil was then solidified by exposing the mixture to below freezing point to obtain a solidified soil.

<Comparative Example 1>
First, the mixture prepared in the preliminary test was spread evenly in a 40 cm x 60 cm section with a thickness of 5 cm. 10% by mass of tap water was sprayed on the spread mixture, and the mixture was compacted with a 25 kg roller to form a soil pavement layer. The soil was then exposed to below freezing point to solidify, and solidified soil was obtained.

In both the examples and the comparative examples, the minimum temperature was below freezing on the day of application and on the third day after application, and the minimum temperature was 13 days out of the 28 days after application. In addition, the maximum temperature difference between the day after the freezing point and the previous day was +7.9°C, and the maximum temperature was above 0°C.

The strength of the solidified soil of the Example and Comparative Example at age 28 was measured by a Schmidt hammer test. The test machine used was a Schmidt concrete hammer PT model manufactured by Proceq. The average rebound hardness (R), cubic compressive strength (kg/ ^cm2 ), and cylindrical compressive strength (kN/ ^m2 ) are described below.

(Average rebound hardness)
The resilience value is read using a Schmidt hammer. Five measurements are taken, and the top and bottom values are excluded, and the average of the three measurements is calculated.
The average rebound hardness is acceptable if it is 38 or more at 28 days of age.

(cube compressive strength)
This value was calculated from the average rebound hardness using Proceq's rebound-compression strength standard conversion chart for the relationship between rebound hardness and cube compression strength.
A cube compressive strength of 40 (kg/cm ² ) or more is acceptable.

(Cylinder Compressive Strength)
This value is calculated by multiplying the cube compressive strength by 0.85 and then converting the value from kg/ ^cm2 to kN/ ^m2 (multiplying by 98.07).
A cylindrical body compressive strength of 3300 (kN/m ² ) or more is acceptable.

If all results are acceptable, the solidified soil is deemed to have no cracks or swelling and to have a good appearance. The results are summarized in Table 3 below.

The solidified soil of the Example showed no cracks even two months after application and had a good appearance. In contrast, the solidified soil of Comparative Example 1 showed cracks two weeks after application, and the cracks were confirmed to have expanded two months after application.

The strength ratios, assuming the cylindrical compressive strength of the solidified soil in Example 1 at 28 days is 100, are summarized in Table 4 below, along with the cylindrical compressive strengths of each solidified soil at 28 days.

The strength of the solidified soil in Comparative Example 1 was significantly reduced to 18% of that in Example 1. Comparing it to the results in Table 2 above, it was shown that exposure to below freezing temperatures caused a greater reduction in strength than curing at constant temperature and humidity. Exposure to below freezing temperatures during solidification caused the moisture in the voids between the particles in the soil pavement layer to freeze and expand, and this cycle was repeated during the day as the temperature rose, weakening the bonds between the particles in the soil pavement layer. This is presumably the cause of the reduction in strength in Comparative Example 1.

In the cases of Examples 1 and 2, magnesium chloride was included as an additive, which caused a drop in the freezing point of the soil pavement layer. It is presumed that even when exposed to temperatures below freezing, the moisture in the voids in the soil pavement layer was prevented from freezing and expanding, and the bonds between the particles in the soil pavement layer were solidified without being weakened, resulting in the production of solidified soil.

Claims (7)

a soil paving material containing a soil component, magnesium oxide, and at least one additive selected from magnesium chloride and magnesium sulfate is applied to obtain a soil paving layer;
A method for solidifying soil, comprising the steps of: exposing the soil pavement layer to below freezing point to solidify the soil pavement layer. The soil paving material is
mixing the soil component and the magnesium oxide to obtain a mixture;
2. The method for applying solidified soil according to claim 1, wherein the mixture is prepared by adding the additive to the mixture. The method for applying solidified soil according to claim 2, characterized in that the additive is added to the mixture as an aqueous solution or together with water. A mixture of soil components and magnesium oxide is applied to obtain a soil pavement layer without additives;
A method for solidifying soil, comprising the steps of: supplying an aqueous solution of an additive containing at least one additive selected from magnesium chloride and magnesium sulfate to a soil pavement layer to which no additive has been added; and then solidifying the soil pavement layer by exposing the soil pavement layer to a temperature below freezing. The method for solidifying soil according to any one of claims 1 to 4, characterized in that the soil component is granite. The method for applying solidified soil according to any one of claims 1 to 4, characterized in that the additive is used in an amount of 2 to 5 mass % of the soil paving material. a first material comprising a mixture of soil components and magnesium oxide;
A soil paving material preparation set comprising a second material packaged separately from the first material and comprising at least one additive selected from magnesium chloride and magnesium sulfate.