JP5383964B2 - Soil hardening material - Google Patents

Description

  The present invention relates to a soil solidifying material, and particularly to a soil solidifying material useful for solidifying soft soil.

  One of the uses of magnesium oxide is as a solidifying material for soft soil. Magnesium oxide is less alkaline than calcium oxide, which is also used as a soil-solidifying material, and therefore has an advantage that the load on the environment is small. However, magnesium oxide has a problem that the solidification reaction rate is slow and the solidification ability of the soil is slightly inferior to calcium oxide. For this reason, adding a sulfate etc. to magnesium oxide as a soil-solidification reaction promoter has been studied to increase the soil-solidification ability.

  Patent Document 1 discloses a magnesium oxide-containing soil solidifying material using sulfate as a reaction accelerator. This patent document includes calcium sulfate and magnesium sulfate as examples of sulfates.

Patent Document 2 discloses a magnesium oxide-containing soil solidifying material using at least one of phosphate, sulfate, carbonate, and organic acid as a reaction accelerator. In this patent document, as an example of phosphate, superphosphate lime, heavy superphosphate lime, dissolved phosphorus fertilizer, and calcined phosphorus fertilizer, sulfate examples include anhydrous gypsum, dihydrate gypsum, potassium sulfate, sulfuric acid Aluminum, ammonium sulfate, potassium alum, and sodium alum include sodium carbonate, sodium bicarbonate, and organic acids as examples of carbonates, citric acid, tartaric acid, lactic acid, and oxalic acid, respectively.
JP 2003-193050 A JP 2003-193462 A

Magnesium oxide is weaker alkali than calcium oxide, but considering the environmental load after solidification treatment, it is preferable that the amount of magnesium oxide added for soil solidification is small.
Therefore, an object of the present invention is to develop a soil solidifying material having a higher soil solidifying capacity than conventional magnesium oxide-containing soil solidifying materials, and to achieve a high soil solidifying effect by adding as little magnesium oxide as possible. Is to make it.

  As a result of studying a magnesium oxide-containing soil solidifying material containing magnesium oxide and sulfate, the present inventor further increases the solidification ability of the soil by adding a predetermined amount of phosphate and calcium carbonate. I found out that it would be possible.

In the present invention, magnesium oxide is 20 to 60% by mass, magnesium, calcium and / or aluminum sulfate is 1 to 50% by mass, phosphate is 0.1 to 10% by mass, and calcium carbonate is 20 to 60% by mass. It is in the soil solidification material containing 1%.

Preferred embodiments of the present invention are as follows.
(1) Furthermore, calcium oxide and / or light-burned dolomite are included in the range of 1 to 90 parts by mass with respect to 100 parts by mass of magnesium oxide.
(2) Magnesium, calcium and / or aluminum sulfate is contained in the range of 1/50 to 1 mass times that of magnesium oxide.
(3) A phosphate is included in the range of 1/100 to 1/10 mass times of magnesium oxide.
(4) Calcium carbonate is contained in the range of 1/3 to 3 times the mass of magnesium oxide.
(5) Magnesium oxide has an average periclase crystallite diameter in the range of 10 to 50 nm, a BET specific surface area in the range of 5 to ²⁰ m ² / g, an average particle diameter in the range of 1 to 5 μm, and particles The proportion of particles having a diameter exceeding 10 μm does not exceed 10% by volume, and the apparent density is in the range of 0.3 to 0.8 g / cm ³ .

  The soil solidifying material of the present invention has higher soil solidifying ability than the conventional magnesium oxide-containing soil solidifying material. For this reason, since the quantity of the magnesium oxide added to soft soil can be reduced by using the soil solidification material of this invention, the load to an environment can be reduced.

The soil-solidifying material of the present invention comprises four essential components: sulfate, phosphate and calcium carbonate of one or more metals selected from the group consisting of magnesium oxide, magnesium, calcium and aluminum.
The content of magnesium oxide is in the range of 20 to 60% by mass, preferably in the range of 25 to 60% by mass with respect to the total amount of essential components. If the content of magnesium oxide is less than the above range, the solidification ability of the soil is lowered.

  Magnesium, calcium and aluminum sulfates, phosphates and calcium carbonate act as magnesium oxide reaction promoters. Magnesium, calcium and aluminum sulfates are weakly acidic and have an effect of suppressing the increase in pH of the soil after the solidification treatment. Since calcium carbonate is weaker alkaline than magnesium oxide, the load on the soil after the solidification treatment is small.

  The content of sulfate is in the range of 1 to 50% by mass, preferably in the range of 10 to 30% by mass, based on the total amount of essential components. Furthermore, the sulfate content is preferably in the range of 1/50 to 1 mass times that of magnesium oxide, and more preferably in the range of 1/10 to 3/4 mass times.

  The content of phosphate is in the range of 0.1 to 10% by mass, preferably in the range of 0.5 to 5% by mass with respect to the total amount of essential components. Furthermore, the phosphate content is preferably in the range of 1/100 to 1/10 mass times that of magnesium oxide, and more preferably in the range of 1/50 to 1/20 mass times.

The content of calcium carbonate, based on the total amount of the essential components, in the range of 20 to 60 wt%. Furthermore, the content of calcium carbonate is preferably in the range of 1/3 to 3 times by mass of magnesium oxide, and more preferably in the range of 1/3 to 2 times by mass.
When the content of sulfate, phosphate and calcium carbonate is less than the above range, the effect as a reaction accelerator becomes insufficient.

The magnesium oxide used in the soil solidifying material of the present invention is preferably light-burned magnesium oxide. Particularly preferred magnesium oxide has an average periclase crystallite size in the range of 10 to 50 nm, a BET specific surface area in the range of 5 to ²⁰ m ² / g, an average particle size in the range of 1 to 5 μm, Is a magnesium oxide in which the proportion of particles exceeding 10 μm does not exceed 10% by volume and the apparent density is in the range of 0.3 to 0.8 g / cm ³ .

  The average periclase crystallite diameter of magnesium oxide is in the range of 10 to 50 nm, preferably in the range of 20 to 40 nm. The average periclase crystallite diameter is an average diameter of crystallites forming the magnesium oxide particles. The average periclase crystallite diameter is one of the indexes representing the reactivity of magnesium oxide. When the average periclase crystallite diameter is in the above range, the reactivity of magnesium oxide is increased, and the onset of soil solidification is accelerated.

BET specific surface area of the magnesium oxide is in the range of 5 to 20 m ² / g, preferably in the range of 10 to 20 m ² / g. The BET specific surface area is one of the indexes representing the reactivity of magnesium oxide. When the BET specific surface area is in the above range, the reactivity of magnesium oxide increases and the onset of soil solidification is accelerated.

  The average particle diameter of magnesium oxide is in the range of 1 to 5 μm. The average particle size is one of the indexes that represent the dispersibility and handling properties of magnesium oxide. When the average particle size is in the above range, magnesium oxide is easily dispersible in the soil to be solidified, and handling properties are improved.

  The proportion of particles with a magnesium oxide particle size exceeding 10 μm is less than 10% by volume. The distribution of the particle diameter of magnesium oxide is one of the indexes representing dispersibility. When the ratio of the particles having a particle diameter exceeding 10 μm is in the above range, the magnesium oxide is easily dispersible in the soil to be solidified, and handling properties are improved.

Apparent density of the magnesium oxide is in the range of 0.3 to 0.8 g / cm ^3, preferably in the range of 0.5~0.8g / cm ^3. The apparent density is one of the indexes representing the dispersibility and handling properties of magnesium oxide. When the apparent density is in the above range, magnesium oxide can be easily dispersed in the soil to be solidified, and handling properties are improved.

  The magnesium oxide is produced by firing magnesium hydroxide particles produced by adding alkali such as calcium hydroxide to seawater at a temperature of 650 to 900 ° C, preferably 680 to 900 ° C. Can do. Since magnesium hydroxide particles obtained from seawater incorporate sulfate radicals in seawater, the magnesium oxide obtained by firing the magnesium hydroxide particles in the above temperature range usually has a sulfate radical of 0.00. It is included in an amount in the range of 5 to 2.5% by mass. The firing time varies depending on factors such as the firing temperature and the magnesium hydroxide particle size, but is generally 10 to 120 minutes.

The magnesium, calcium and aluminum sulfates used in the soil solidifying material of the present invention may be anhydrous salts or hydrated salts. The sulfate preferably contains 35% by mass or more of a sulfuric acid component (SO ₄ ²⁻ ). Examples of sulfates include anhydrous magnesium sulfate, magnesium sulfate, heptahydrate, anhydrous calcium sulfate (anhydrous gypsum), calcium sulfate, 0.5 hydrate (hemihydrate gypsum), calcium sulfate, dihydrate, anhydrous aluminum sulfate And publicly known sulfates used for soil solidifying materials such as aluminum sulfate and 18 hydrate. A sulfate may be used individually by 1 type, and may use 2 or more types together. As the sulfate, magnesium and calcium sulfates are preferably used.

  The phosphate used for the soil solidifying material of the present invention includes orthophosphate, condensed phosphate and a mixture thereof. Examples of phosphates include sodium phosphate, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, lime superphosphate, heavy superphosphate, dissolved phosphorus fertilizer, and calcined phosphorus manure. A phosphate may be used individually by 1 type and may use 2 or more types together. As the phosphate, sodium hexametaphosphate is preferably used.

  In the soil solidifying material of the present invention, normal powdered or granular calcium carbonate can be used as the calcium carbonate. The particle size of calcium carbonate is preferably 50% by mass or more, more preferably 80% by mass or more under 100 mesh sieve.

In the soil solidification material of the present invention, calcium oxide and / or light calcined dolomite [oxidation obtained by firing dolomite (magnesium and calcium double carbonate) in order to improve the soil solidification effect and accelerate the development of soil solidification. A composite of magnesium and calcium oxide] may be added. Since calcium oxide and lightly burned dolomite are more strongly alkaline than magnesium oxide, the amount of calcium oxide and / or lightly burned dolomite is 100 parts by weight of magnesium oxide in consideration of the environmental load after solidification treatment. It is preferable that it exists in the range of 1-90 mass parts with respect to. In particular, when adding calcium oxide and / or light burned dolomite to the soil solidified material, the total content of alkaline materials (magnesium oxide, calcium oxide and light burned dolomite ) in the soil solidified material is 25 to 80% by mass. It is preferable to be in the range.

  The soil solidification material of this invention can be manufactured by mixing said each component using well-known mixing apparatuses, such as a mixer, for example.

The soil solidifying material of the present invention may be added in the form of powder to the soft soil to be solidified, or may be added in the form of a suspension dispersed in water. The amount of the soil-solidifying material added to the soft soil varies depending on the softness and moisture content of the soil and cannot be determined uniformly, but is usually in the range of 20 to 150 kg with respect to 1 m ^{3 of} soil.

A soil solidifying material was prepared using the following materials.
(1) Magnesium oxide A
A calcium hydroxide suspension having a concentration of 15% by mass is added to seawater so that the molar ratio of calcium to the amount of magnesium in seawater is 0.9, thereby producing magnesium hydroxide particles. A suspension was obtained. The obtained magnesium hydroxide suspension was concentrated so that the solid content concentration was 35% by mass. The concentrated magnesium hydroxide suspension was washed with industrial water, then filtered and dried to obtain magnesium hydroxide. The average particle diameter of the obtained magnesium hydroxide was 3.3 μm. This magnesium hydroxide was baked for 30 minutes at a temperature of 700 ° C. in a rotary kiln baking furnace to obtain magnesium oxide.
The obtained magnesium oxide has a periclase crystallite diameter of 31 nm, a BET specific surface area of 15.8 m ² / g, an average particle diameter of 3.3 μm, a ratio of particles having a particle diameter exceeding 10 μm, 7% by volume, and an apparent density. was 0.66 g / cm ^3, purity of 95.88 mass%, the content of the sulfate was 1.82 wt%. The periclase crystallite diameter of magnesium oxide, the average particle diameter, the ratio of particles having a particle diameter exceeding 10 μm, and the apparent density were measured by the following methods.

[Average periclase crystallite diameter]
The X-ray diffraction pattern of the (200) plane of the magnesium oxide periclase crystallite is measured under the conditions of a tube voltage of 40 kV and a tube current of 20 mA using an X-ray diffractometer to determine the average periclase crystallite diameter. Silicon is used as the standard sample.

[Average particle diameter, ratio of particles having a particle diameter exceeding 10 μm]
Magnesium oxide is added to ion-exchanged water, and after ultrasonic dispersion treatment is performed for 30 seconds, the particle size distribution is measured using a laser diffraction particle size distribution analyzer (SK Laser LMS-30, manufactured by Seishin Enterprise Co., Ltd.). Then, the average particle diameter and the ratio of the particles having a particle diameter exceeding 10 μm are obtained.

[Apparent density]
After slowly putting magnesium oxide into a 50 cm ³ graduated cylinder gradually up to the 50 cm ³ marked line of the graduated cylinder, the mass of magnesium oxide in the graduated cylinder is weighed, and the apparent density is calculated by the following formula.
Apparent density (g / cm ³ ) = mass of magnesium oxide (g) / 50 (cm ³ )

(2) Magnesium oxide B
The periclase crystallite is 58 nm, the BET specific surface area is 12.9 m ² / g, the average particle size is 15.8 μm, the proportion of particles having a particle size exceeding 10 μm is 67% by volume, and the apparent density is 0.68 g / cm ³ . China light burned magnesium oxide with a purity of 96.94% by mass and a sulfate radical content of 0.03% by mass

(3) Magnesium sulfate, heptahydrate (4) Calcium sulfate (anhydrous gypsum)
(5) Sodium hexametaphosphate

(6) Calcium carbonate (manufactured by Ube Materials Corporation)
Particle size: 100 mesh sieve 90% by mass pass (7) Calcium oxide (manufactured by Ube Materials Corporation)
Particle diameter: 200 mesh sieve 95% by mass pass

[Examples 1-4, Comparative Examples 1-4]
The said raw material was mixed by the mass ratio shown in the following Table 1 and Table 2, and the soil solidification material was prepared. In Tables 1 and 2, the alkali component content (% by mass) is the weight percentage of the alkaline material (magnesium oxide, calcium oxide) contained in the soil solidifying material.

Table 1
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Example 1 Comparative Example 1 Example 2 Comparative Example 2
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Magnesium oxide A 30 30 45 45
Magnesium sulfate heptahydrate 15 15 5 5
Calcium sulfate 5 5 10 10
Sodium hexametaphosphate 1-1
Calcium carbonate 49-34-
Calcium oxide − − 5 5
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Alkali component content (mass%) 30.0 60.0 50.0 76.9
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Table 2
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Example 3 Comparative Example 3 Example 4 Comparative Example 4
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Magnesium oxide A 40 40 − −
Magnesium oxide B − − 40 40
Calcium sulfate 10 10 10 10
Sodium hexametaphosphate 1 1 1 1
Calcium carbonate 19-19-
Calcium oxide 30 30 30 30
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Alkali component content (mass%) 70.0 86.4 70.0 86.4
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[Solidification treatment]
Soft soil (Kanto loam, moisture content: 133% by mass, wet density: 1.331 g / cm ³ , dry density: 0.797 g / cm ³ , pH: 6.5) 1 m ³ , soil solidification obtained above Material was respectively added at a ratio shown in Table 3 and 30kg / m ³ shown in Table ^{4, 70kg / m 3, 100kg} / m 3 below, the solidification soil mixed was prepared. In Tables 3 and 4, the amount of the alkaline material (kg / m ³ ) added to the soil is the amount of the alkaline material (magnesium oxide and calcium oxide) contained in the soil solidifying material added to the soil. Tables 3 and 4 show the evaluation results of strength and pH of the solidified soil. Soil strength was evaluated by corn index. The corn index and pH were measured by the following methods.

[Measuring method of cone index]
A specimen was prepared in accordance with JGS-0716 “Consolidated soil cone index test method”, stored in a sealed container, and stored in a constant temperature and humidity chamber (20 ° C., 80% RH). The corn index (kN / m ² ) was measured 14 days after age. The higher the value of the corn index, the higher the strength of the soil.

[Measurement method of pH]
The solidified soil was stored in an airtight container and stored in a constant temperature and humidity chamber (20 ° C., 80% RH), and after 14 days of material age, it complied with JGS-0211 “pH test method for soil suspension”. In this method, 10 g of a sample obtained by the non-drying method was put into 50 g of pure water, stirred for 1 hour, allowed to stand for 1 hour, and the pH of the water was measured.

Table 3
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Example 1 Comparative Example 1 Example 2 Comparative Example 2
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Amount of soil hardening material added to soil: 30 kg / m ³
Amount of alkaline material added to soil (kg / m ³ ) 9.0 18.0 15.0 23.1
Cone index (kN / m ² ) 100 512 526 625
pH (-) 9.0 8.9 8.6 8.9
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Soil solidifying material addition amount: 70 kg / m ³
Amount of alkaline material added to soil (kg / m ³ ) 21.0 42.0 35.0 53.9
Cone index (kN / m ² ) 1195 2311 3302 4129
pH (-) 9.1 8.8 9.1 9.0
────────────────────────────────────────
Soil hardener addition amount: 100 kg / m ³
Amount of alkaline material added to soil (kg / m ³ ) 30.0 60.0 50.0 76.9
Cone index (kN / m ² ) 2138 3620 5172 6662
pH (-) 9.0 8.9 9.1 9.2
────────────────────────────────────────

Table 4
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Example 3 Comparative Example 3 Example 4 Comparative Example 4
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Amount of soil hardening material added to soil: 30 kg / m ³
Amount of alkaline material added to soil (kg / m ³ ) 21.0 25.9 21.0 25.9
Cone index (kN / m ² ) 596 701 590 613
pH (-) 9.3 9.5 9.5 9.7
────────────────────────────────────────
Soil solidifying material addition amount: 70 kg / m ³
Amount of alkaline material added to soil (kg / m ³ ) 49.0 60.5 49.0 60.5
Cone index (kN / m ² ) 2256 2536 1510 1239
pH (-) 10.4 11.0 10.5 11.0
────────────────────────────────────────
Soil hardener addition amount: 100 kg / m ³
Amount of alkaline material added to soil (kg / m ³ ) 70.0 86.4 70.0 86.4
Cone index (kN / m ² ) 4705 3659 2174 1987
pH (-) 11.1 11.5 11.3 11.4
────────────────────────────────────────

FIG. 1 is a graph showing the relationship between the amount of alkaline material added to soil and the corn index of the solidified soil in the soil solidification treatment of Example 1 and Comparative Example 1. FIG. 2 is a graph showing the relationship between the amount of alkaline material added to the soil and the corn index of the solidified soil in the soil solidification treatment of Example 2 and Comparative Example 2. FIG. 3 is a graph showing the relationship between the amount of alkaline material added to the soil and the corn index of the solidified soil in the soil solidification treatment of Example 3 and Comparative Example 3. FIG. 4 is a graph showing the relationship between the amount of alkaline material added to the soil and the corn index of the solidified soil in the soil solidification treatment of Example 4 and Comparative Example 4.
As is apparent from the graphs of FIGS. 1 to 4, the solidified soil to which the soil solidifying material (Examples 1 to 4) containing both phosphate and calcium carbonate is added is more preferable for phosphate and calcium carbonate. It turns out that it exists in the tendency for the cone index with respect to the quantity of the alkaline material added to soil to show a high value compared with the solidification process soil which added the soil solidification material (Comparative Examples 1-4) which does not contain both.

It is a graph which shows the relationship between the quantity of the alkaline material added to soil, and the corn index of solidification processing soil in the soil solidification processing of Example 1 and Comparative Example 1. FIG. In the soil solidification process of Example 2 and Comparative Example 2, it is a graph which shows the relationship between the quantity of the alkaline material added to soil, and the corn index of the solidification process soil. It is a graph which shows the relationship between the quantity of the alkaline material added to soil, and the corn index of solidification processing soil in the soil solidification processing of Example 3 and Comparative Example 3. FIG. In the soil solidification process of Example 4 and Comparative Example 4, it is a graph which shows the relationship between the quantity of the alkaline material added to soil, and the corn index of the solidification process soil.

Claims (5)

Particles having an average periclase crystallite diameter of 10 to 50 nm, a BET specific surface area of 5 to ²⁰ m ² / g, an average particle diameter of 1 to 5 μm, and a particle diameter of more than 10 μm. 20 to 60% by mass of magnesium oxide having a proportion not exceeding 10% by volume and an apparent density in the range of 0.3 to 0.8 g / cm ³ , 1 of magnesium, calcium and / or aluminum sulfate A soil-solidifying material containing -50% by mass, 0.1-10% by mass of phosphate, and 20-60% by mass of calcium carbonate.   Furthermore, the soil solidification material of Claim 1 which contains a calcium oxide and / or a light-burning dolomite in the range of 1-90 mass parts with respect to 100 mass parts of magnesium oxide.   The soil-solidifying material according to claim 1, comprising magnesium, calcium and / or aluminum sulfate in a range of 1/50 to 1 times mass of magnesium oxide.   The soil solidification material of Claim 1 which contains a phosphate in the range of 1/100-1/10 mass times of magnesium oxide.   The soil-solidifying material according to claim 1, comprising calcium carbonate in a range of 1/3 to 3 times by mass of magnesium oxide.

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