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

Abstract

To provide a solidified soil construction method and a soil paving material preparation set capable of acquiring solidified soil which can maintain a smooth surface, and can suppress occurrence of cracking and swelling due to freezing.SOLUTION: A solidified soil construction method is configured so that: a soil paving material including a soil component, magnesium oxide, and at least one kind of an additive agent selected from magnesium chloride and magnesium sulfate, is constructed for acquiring a soil paving layer; then, the soil paving layer is exposed to a below zero temperature and is solidified.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for applying solidified soil and a set for preparing a soil paving material, and more particularly to a method for applying solidified soil and a set for preparing a soil paving material that can be used in sub-freezing environments. [Background technology]

[0002] Magnesium oxide-based soil solidification materials are known (see, for example, Patent Document 1). The soil solidification material 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-316967 [Patent Document 2] Patent No. 5897067 Summary of the Invention [Problem to be solved by the invention]

[0004] Unlike solidification materials used to improve industrial waste, soil paving materials must satisfy the aesthetic needs of users, such as surface finishing. For this reason, even if physical properties such as strength are met, if the aesthetics are marred by cracks and swelling, the user's needs cannot be met. Even in the Pacific coastal areas from Kanto to Kyushu, where 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 swelling in the soil paving roads immediately after construction, which have not yet developed their strength, and solidifies in that state when the temperature rises during the day. This raises the risk of marring the aesthetics.

[0005] An object of the present invention is to provide a method for applying solidified soil, which can obtain solidified soil that can maintain a smooth surface by suppressing the occurrence of cracks and blisters due to freezing, and a soil paving material preparation set. [Means for solving the problem]

[0006] The solidified soil construction method of 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 constructed to obtain a soil paving layer, and the soil paving layer is solidified by exposing it to below freezing point.

[0007] The solidified soil construction method of the present invention is characterized in that a mixture of soil components and magnesium oxide is constructed to obtain a soil pavement layer to which no additives have been added, an aqueous additive solution 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 layer is solidified by exposing it to below freezing points.

[0008] The soil paving material preparation set of the present invention is characterized in that it comprises 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. Effect of the Invention

[0009] According to the present invention, it is possible to provide a solidified soil application method that can obtain solidified soil that can suppress the occurrence of cracks and swelling due to freezing and maintain a smooth surface, and a soil paving material preparation set. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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 maintaining a smooth surface while suppressing the occurrence of cracks and blisters caused by volume expansion due to freezing. Hereinafter, an embodiment of the present invention will be described in detail.

[0011] <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.

[0012] 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 include granite, Kanto loam, black soil, red soil, and silt soil. Magnesium oxide is said to solidify mainly through the pozzolanic reaction, and is compatible with soil containing amorphous silica. It has a BET specific surface area of ​​5m 2 Magnesium oxide is not particularly limited as long as it is magnesium oxide powder having a molecular weight of at least 10000 / g. For example, magnesium hydroxide (Mg(OH)2) produced by adding an alkali such as calcium hydroxide to seawater or magnesite ore (MgCO3) particles are calcined at a temperature of 650 to 900°C, preferably at a temperature of 680 to 900°C, for 10 to 120 minutes.

[0013] Magnesium oxide solidifies by reacting with water. The content of magnesium oxide in the soil paving material is preferably 2 to 20 mass% based on the soil components. If the amount of magnesium oxide is too small, the desired effect cannot be obtained. On the other hand, if the amount is too large, the pH tends to be high in addition to the cost and color. The content of magnesium oxide is more preferably 3 to 15 mass% based on the soil components.

[0014] 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 mass% of the soil paving material. If the amount of the additive is too small, the desired effect cannot be obtained, and if the amount is too large, it is not preferable from the viewpoint of cost and workability when preparing the aqueous solution. The content of the additive is more preferably 2 to 15 mass% of the soil paving material.

[0015] The soil paving material can be prepared, for example, by mixing soil components and 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 and 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.

[0016] Along with 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 added, it is possible to change the color tone by coloring.

[0017] 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% relative to 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 water, rather than as an aqueous solution.

[0018] The soil paving material is spread evenly and applied by roller compaction 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 application site can be, for example, a flat or sloped surface that has been leveled and has been root removed. It is preferable to apply the spread paving material so that it is about 1 to 7 cm thick from the ground.

[0019] 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. - The minimum temperature must be below freezing and the maximum temperature must be above 0°C within 3 days after installation. - Within 14 days after installation, there are 7 or more days when the minimum temperature is below freezing.

[0020] Even if the solidified soil applied by the method of the present invention is exposed to below freezing during solidification, the occurrence of cracks and swelling due to freezing is suppressed due to the freezing point drop caused by the additive. Therefore, the surface can be kept in a smooth state as applied by a roller or the like, and the beauty of the soil can be maintained. Furthermore, after solidification, the occurrence of cracks and swelling is suppressed even if the soil is loaded on the road surface due to the increase in strength caused by the reaction of magnesium oxide and the increase in strength caused by the additive.

[0021] 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 predetermined strength, it is considered that no cracks or blisters have occurred. In other words, the solidified soil has a good appearance and is excellent in appearance.

[0022] The soil paving material used in the above-mentioned method contains at least one additive selected from magnesium chloride and magnesium sulfate in addition to magnesium oxide. By using such soil paving material, the reaction between magnesium oxide, magnesium chloride, etc. and water is promoted, so that the strength of the laid soil paving layer after solidification is increased and cracks and swelling can be suppressed.

[0023] 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, the 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 applied to the soil paving layer to which no additives have been added by surface spraying, and then the soil paving layer is solidified while being exposed to below freezing point, thereby implementing the solidified soil application method of the present invention.

[0024] The raw materials used, such as soil components, are the same as those described above, and construction can be performed in the same manner as described above. However, what is obtained by construction is a soil pavement layer to which no additives have been added. A soil pavement layer containing additives can be obtained by supplying an aqueous solution of additives to the soil pavement layer. 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 content of additives in the solidified soil is 2 to 5 mass %.

[0025] The soil pavement layer containing the additive aqueous solution solidifies while being exposed to below freezing points, as described above. As described above, even when exposed to below freezing points, the additive causes the freezing point to drop, suppressing the occurrence of cracks and blistering 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 that of a pavement constructed using only magnesium oxide, so that cracks and blistering are suppressed even when the pavement is loaded on the road surface. Another advantage is that the amount of work required is reduced, since only the aqueous solution needs to be sprayed after construction.

[0026] <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.

[0027] The first material contains the above-mentioned soil components and magnesium oxide in the above-mentioned ratio. 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 will not harden, and workability will not be impaired.

[0028] 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 consisting 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 in a moist state. This allows the surface to be kept smooth and the beauty of the surface to be maintained. EXAMPLES

[0029] Specific examples of the present invention will be described below, but the present invention is not limited to these.

[0030] <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 Materials) 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)

[0031] (Preparation of the mixture) Magnesium oxide (10 mass %) and iron oxide (0.1 mass %) were added to the sand soil and mixed to prepare a mixture of soil components and magnesium oxide.

[0032] (Test Example 1) Magnesium chloride hexahydrate was added at 2% by mass to the mixture, 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.

[0033] (Test Example 2) Magnesium chloride hexahydrate was added to the mixture at 3% by mass, and tap water at 10% by mass was added and 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 2.

[0034] (Test Example 3) Magnesium chloride hexahydrate was added at 5% by mass to the mixture, 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 3.

[0035] (Test Example 4) Magnesium chloride hexahydrate was added to the mixture at 10% 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 4.

[0036] (Test Example 5) Magnesium chloride hexahydrate was added to the mixture at 15% 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 5.

[0037] (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.

[0038] (Test Example 7) Magnesium sulfate heptahydrate was added to the mixture at 5% 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 7.

[0039] (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.

[0040] An unconfined compression test (JIS A1216) was carried out on the specimens of Test Examples 1 to 8 on the 7th day of material age. The results are summarized in the following Table 1. The strength ratio when the average unconfined compressive strength of the specimens of Test Example 1 was taken as 100 was defined as strength ratio 1, and the strength ratio when the average unconfined compressive strength of the specimens of Test Example 8 was taken as 100 was defined as strength ratio 2, and are also shown in Table 1.

[0041] [Table 1]

[0042] 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 improves the unconfined compressive strength. The unconfined compressive strength of the specimen in Test Example 8, which does not contain any additive, is only 61% of that in Test Example 1, based on strength ratio 1.

[0043] An unconfined compression test (JIS A1216) was carried out on the specimens of Test Example 1 and Test Example 8 at 28 days of age. The obtained results are shown in Table 2 below as Test Example 9 and Test Example 10, respectively. The strength ratio when the average unconfined compressive strength of the specimens of Test Example 9 was taken as 100 was taken as strength ratio 1, and the strength ratio when the average unconfined compressive strength of the specimens of Test Example 10 was taken as strength ratio 2, and are also shown in Table 2.

[0044] [Table 2]

[0045] It can be seen that the strength of the specimen of Test Example 10, which does not contain any additive, at 28 days after curing at constant temperature and humidity is low, at 48% of that of the specimen of Test Example 9.

[0046] <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 40cm x 60cm section with a thickness of 5cm, and compacted with a 25kg roller to create a soil paving layer. The soil was then solidified by exposing it to below freezing points to obtain solidified soil.

[0047] <Example 2> 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. As the additive solution, an aqueous solution with a water content of 10 mass% was prepared by adjusting magnesium chloride hexahydrate to 2 mass% of the mixture. The additive solution was sprayed on the spread mixture, which was then rolled with a 25 kg roller to form a soil pavement layer. The soil was then exposed to below freezing temperatures to solidify, yielding a solidified soil.

[0048] <Example 3> 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. As the additive solution, an aqueous solution with a water content of 10 mass% was prepared by adjusting magnesium chloride hexahydrate to 2 mass% of the mixture. Tap water was sprayed onto the spread mixture, which was then compacted with a 25 kg roller. An aqueous solution of additive was then sprayed onto the mixture to form a soil pavement layer, which was then solidified by exposure to below freezing points to obtain solidified soil.

[0049] <Comparative Example 1> First, the mixture prepared in the preliminary test was spread evenly over a 40cm x 60cm section with a thickness of 5cm. 10% tap water was sprayed onto the spread mixture, and the mixture was compacted with a 25kg roller to create a soil pavement layer. The soil was then exposed to below freezing temperatures to solidify, and solidified soil was obtained.

[0050] In both the working example and the comparative example, 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.

[0051] 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), cube compressive strength (kg / cm 2 ), and cylindrical compressive strength (kN / m 2 ) are explained below.

[0052] (Average rebound hardness) The resilience value is read using a Schmidt hammer. Five measurements are taken, and the top and bottom values ​​are removed and the average is calculated. The average rebound hardness is considered to pass if it is 38 or more at 28 days of age.

[0053] (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. The cube compressive strength is 40 (kg / cm 2 ) or higher is a pass.

[0054] (Cylinder Compressive Strength) Multiply the cube compressive strength value by 0.85 and then convert it to kg / cm 2 from kN / m 2 This is the unit converted value (multiplied by 98.07). The compressive strength of the cylinder is 3300 (kN / m 2 ) or higher is a pass.

[0055] If all the results are acceptable, the solidified soil is deemed to have no cracks or blisters and to have a good appearance. The results are summarized in Table 3 below.

[0056] [Table 3]

[0057] The solidified soil of the Example had a good appearance with no cracks observed even two months after application. In contrast, the solidified soil of Comparative Example 1 showed cracks two weeks after application, and the cracks had expanded two months after application.

[0058] 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 strength of each solidified soil at 28 days.

[0059] [Table 4]

[0060] The strength of the solidified soil in Comparative Example 1 was significantly reduced to 18% of that in Example 1. Comparing with 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 melting due to rising temperatures during the day was repeated, 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.

[0061] In the cases of Examples 1 and 2, magnesium chloride was included as an additive, so the freezing point of the soil pavement layer was lowered. 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 solidified soil.

Claims

1. 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.

2. The soil paving material is mixing the soil component and the magnesium oxide to obtain a mixture; by adding the additive to the mixture.

2. The method for solidifying soil according to claim 1.

3. 3. The method of claim 2, wherein the additive is added to the mixture as an aqueous solution or together with water.

4. A mixture of soil components and magnesium oxide is applied to obtain a soil pavement layer without additives; An aqueous additive solution containing at least one additive selected from magnesium chloride and magnesium sulfate is supplied to the soil pavement layer to which no additive has been added, and then the soil pavement layer is solidified by exposing the soil pavement layer to a temperature below freezing. A method for solidifying soil.

5. 5. The method for solidifying soil according to claim 1, wherein the soil component is decomposed granite.

6. 5. The method for applying solidified soil according to claim 1, wherein the additive is used in an amount of 2 to 5% by mass of the soil paving material.

7. a first material comprising a mixture of soil components and magnesium oxide; a second material that is packaged separately from the first material and that is made of at least one additive selected from magnesium chloride and magnesium sulfate; A soil paving material preparation set comprising:

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