JP5362171B2 - Soil hardening material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium oxide-containing soil solidifier having a high soil solidifying capacity. <P>SOLUTION: The soil solidifier comprises 20 to 60 mass% magnesium oxide having 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<SP>2</SP>/g, an average particle diameter in the range of 1 to 5 &mu;m, a proportion of particles of a particle diameter of above 10 &mu;m in the range of below 10 vol.%, and an apparent density in the range of 0.3 to 0.8 g/cm<SP>3</SP>, 1 to 50 mass% sulfate of magnesium, calcium and/or aluminum, and 10 to 60 mass% calcium carbonate. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

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 has an average periclase crystallite diameter in the range of 10 to 50 nm and a BET specific surface area of 5 to 5. In the range of 20 m ² / g, the average particle size is in the range of 1 to 5 μm, the proportion of particles having a particle size exceeding 10 μm does not exceed 10% by volume, and the apparent density is 0.3 to 0 It has been found that by using magnesium oxide in the range of 0.8 g / cm ³ and further adding a predetermined amount of calcium carbonate, the solidification ability of the soil can be further enhanced.

Therefore, the present invention 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, 20 to 60% by mass of magnesium oxide and magnesium and / or calcium 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 . 1 to 50 wt% sulfuric acid salts, and certain calcium carbonate in soil solidifying material comprising 20 to 60 wt%.

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 and / or sulfates of calcium, including at 1 / 50-1 times mass range of magnesium oxide.
(3) Calcium carbonate is contained in the range of 1/3 to 3 times the mass of magnesium oxide.

  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, by using the soil solidifying material of the present invention, the amount of magnesium oxide added to the soft soil can be reduced, and the load on the environment after the solidification treatment can be reduced.

Soil solidifying material of the present invention are magnesium oxide, magnesium and calcium or Ranaru mono- or di-or more metal sulfate selected from the group, and three calcium carbonate as an essential component.
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.

Sulfate and calcium carbonate act as a reaction accelerator for solidification of magnesium oxide. Further, sulfates of magnesium and calcium in the weakly acidic, there is also the effect of suppressing the increase in the pH of the soil after solidification. 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 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 and calcium carbonate is less than the above range, the effect as a reaction accelerator becomes insufficient.

Magnesium oxide used in the soil solidifying material of the present invention 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, and an average particle diameter in the range of 1 to 5 μm. Thus, the proportion of particles having a particle 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 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 smaller than the above range, the reactivity becomes too high. On the other hand, when the average periclase crystallite diameter is larger than the above range, the onset of soil solidification is delayed.

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 smaller than the above range, the onset of soil solidification is delayed.

  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 larger than the above range, it is difficult to uniformly disperse when the soil is soft. On the other hand, when the average particle diameter is smaller than the above range, the handling property is lowered.

  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 exceeds 10% by volume, it is difficult to uniformly disperse in the soil solidified material.

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 smaller than the above range, the handling property is lowered. On the other hand, when the apparent density is larger than the above range, it is difficult to uniformly disperse in the soil solidified material.

  Magnesium oxide used in the soil solidifying material of the present invention is fired at a temperature of 650 to 900 ° C., preferably 680 to 900 ° C., by forming magnesium hydroxide particles generated by adding alkali such as calcium hydroxide to seawater. Can be manufactured. 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.

Sulfates of magnesium and calcium used for soil solidifying material of the present invention may be anhydrous salt, or a salt hydrate. The sulfate preferably contains 35% by mass or more of a sulfuric acid component (SO ₄ ²⁻ ). Examples of sulfate, magnesium sulfate anhydrous, magnesium heptahydrate sulfate, anhydrous calcium sulfate (gypsum anhydride), calcium 0.5 hydrate (hemihydrate gypsum) sulfate, which soil solidify calcium dihydrate sulfate The well-known sulfate used for materials can be mentioned. A sulfate may be used individually by 1 type, and may use 2 or more types together.

  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 Magnesium hydroxide particles are produced by adding a 15% strength by weight calcium hydroxide suspension to seawater so that the molar ratio of calcium to the amount of magnesium in seawater is 0.9. To obtain a magnesium hydroxide suspension. 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 sulfate heptahydrate (3) Calcium sulfate (anhydrous gypsum)

(4) Calcium carbonate (manufactured by Ube Materials Corporation)
Particle size: 100 mesh sieve 90% by mass pass (5) Calcium oxide (manufactured by Ube Materials Co., Ltd.)
Particle diameter: 200 mesh sieve 95% by mass pass

[Examples 1-3, Comparative Examples 1-3]
The above raw materials were mixed at a mass ratio shown in Table 1 below to prepare a soil solidifying material. In Table 1, 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
────────────────────────────────────────
Example 1 Comparative example 1 Example 2 Comparative example 2 Example 3 Comparative example 3
────────────────────────────────────────
Magnesium oxide 30 30 45 45 40 40
Magnesium sulfate ・ 7 water salt 15 15 5 5 − −
Calcium sulfate 5 5 10 10 10 10
Calcium carbonate 50-35-20-
Calcium oxide-5 5 30 30
────────────────────────────────────────
Alkali component content 30.0 60.0 50.0 76.9 70.0 87.5
(mass%)
────────────────────────────────────────

[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 added at a rate of each ^{30kg / m 3, 70kg / m} 3, 100kg / m 3, the solidification soil mixed was prepared. In Table 2, the amount (kg / m ³ ) of the alkaline material 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. Table 2 shows 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 2
────────────────────────────────────────
Example 1 Comparative example 1 Example 2 Comparative example 2 Example 3 Comparative example 3
────────────────────────────────────────
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 21.0 26.3
Cone index (kN / m ² ) 105 512 394 625 316 368
pH (-) 8.7 8.9 9.0 8.9 9.3 9.3
────────────────────────────────────────
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 49.0 61.3
Cone index (kN / m ² ) 1257 2311 2293 4129 1870 1631
pH (-) 8.9 8.8 9.1 9.0 10.5 10.9
────────────────────────────────────────
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 70.0 87.5
Cone index (kN / m ² ) 2250 3620 4880 6662 3185 3340
pH (-) 8.9 8.9 9.1 9.2 11.3 11.5
────────────────────────────────────────

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.
As is apparent from the graphs of FIGS. 1 to 3, the solidified soil to which the soil solidifying material containing calcium carbonate (Examples 1 to 3) is added is the soil solidifying material not containing calcium carbonate (Comparative Examples 1 to 3). It can be seen that the corn index tends to show a higher value relative to the amount of alkaline material added to the soil than the solidified soil added with 3).

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.

Claims (4)

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. ratio not exceed 10% by volume, and apparent density of 0.3 to 0.8 g / cm ³ 20 to 60 wt% of magnesium oxide in the range of, magnesium and / or sulfates of calcium 1 A soil solidifying material containing 50% by mass and 20 to 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. Magnesium and / or mosquitoes Rushiu sulfate beam, soil solidifying material according to claim 1 comprising at 1 / 50-1 times mass range 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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