JP4883390B2 - Solidifying material for ground improvement and solidified soil using the same - Google Patents

Description

The present invention relates to a solidifying material for ground improvement and a solidified soil using the same , and more particularly, in a ground improvement work using, for example, cement or a cement-based solidified material, a high-strength improved soil can be obtained and It aims at providing the solidification material for ground improvement which can suppress elution of a valence chromium, and the solidification processing soil using this .

  While soil contamination problems were being addressed, it was found that hexavalent chromium was eluted from the soil improved by cement and cement-based solidified material depending on the conditions of the soil. Therefore, in March 2000, the former Ministry of Construction, the former Ministry of Transportation, the Ministry of Agriculture, Forestry and Fisheries issued a notification regarding the immediate use of cement and cement-based solidification materials for ground improvement and reuse of improved soil. It was done. After that, the amount of hexavalent chromium eluted from the improved soil was reduced by using a special soil (for hexavalent chromium countermeasure) cement-based solidification material sold by a cement company. Thus, although this problem is less likely to occur, it has not been completely solved.

Incidentally, the general soil improvement for solidifying material, cement-based material to produce a crystal of ettringite by adding sulfate _{(3CaO · Al 2 O 3 ·} 3CaSO 4 · 32H 2 O) a, restraint of the soil particles It is a material that has improved. As the sulfate, anhydrous gypsum or dihydrate gypsum is mainly used.
As a conventional solidifying material for ground improvement, for example, “ground improvement material” of Patent Document 1 is known. This is to reduce elution of hexavalent chromium by the action of blast furnace slag in ground improvement materials including hydraulic materials, blast furnace slag and gypsum. Specifically, a ground improvement material containing 5 parts by weight or more of blast furnace slag and 2 parts by weight or more of gypsum in terms of anhydrous gypsum with respect to 100 parts by weight of a hydraulic material is prepared and used from the improved soil. This is intended to suppress elution of valent chromium.

Moreover, as patent document 2, 40-80 volume% of things with a particle diameter of 10 micrometers or less are contained, and it is high intensity | strength by using a sulfate powder with a specific surface area of 0.5-1.0 m < ² > / g. Those that can achieve good workability have been developed.
JP 2001-348571 A JP 2004-137322 A

  However, in Patent Document 1, although the elution amount of hexavalent chromium is suppressed by the action of blast furnace slag, the effect cannot be expected unless a large amount of blast furnace slag is added. That is, it is said that elution can be suppressed by including 5 parts by weight or more of blast furnace slag, but in the examples, the smallest amount of blast furnace slag added is 42.9 parts by weight of blast furnace slag. The effect of adding less than that in parts by weight is unknown. However, it can be easily predicted that the effect of suppressing the elution of hexavalent chromium will decrease as the amount of blast furnace slag added decreases.

  Moreover, in patent document 2, although it is supposed that high intensity | strength and favorable workability | operativity will be obtained by using the limited gypsum, about the elution of hexavalent chromium, it is described that blast furnace cement B type is used. Yes. However, if the blast furnace cement type B is used, there arises a problem that the strength is greatly lowered depending on the type of soil.

Therefore, as a result of intensive research, the inventors have found that when 0.3 g is added to 100 mL of cement clinker or hydraulic material and distilled water having a water temperature of 25 ° C., the calcium ion concentration becomes 200 ml / L or more 10 minutes after the addition. We have found that the use of a solidifying material for ground improvement containing anhydrous gypsum reduces the elution amount of hexavalent chromium in the improved soil to an environmental standard value or less, and further improves the strength of the improved ground. .

The object of the present invention is to provide a ground improvement solidifying material in which the amount of hexavalent chromium elution from the improved soil is below the environmental standard value and the improved ground has high strength, and a solidified soil using the same.

The invention according to claim 1 is a cement clinker or hydraulic material and gypsum added to the cement clinker or hydraulic material, and when 0.3 g is added to 100 mL of distilled water at a water temperature of 25 ° C. A solidifying material for ground improvement containing anhydrous gypsum whose calcium ion concentration becomes 200 mg / L or more in 10 minutes.

According to the first aspect of the present invention, when 0.3 g is added to 100 mL of distilled water having a water temperature of 25 ° C. as the gypsum added to the cement clinker or the hydraulic material, 10 g of calcium (ion) is contained in the gypsum. The ground is improved by using a solidifying material for ground improvement that employs anhydrous gypsum that dissolves 200 mg / L or more per minute. As a result, high-strength improved soil can be obtained, and elution of hexavalent chromium from the improved soil can be suppressed.

The action of reducing the elution of hexavalent chromium according to the present invention is to produce calcium silicate hydrate and calcium aluminate hydrate by cement, exhibit solidification strength, and fix hexavalent chromium to reduce elution. It can be mentioned.
However, it is known that in volcanic ash cohesive soils and the like, there is a relatively large amount of hexavalent chromium leaching from the improved soil by cement or cement-based solidifying material. One of the causes is considered to be allophane contained in large quantities in the volcanic ash clay. Allophane is an amorphous clay mineral having a hollow sphere shape with a diameter of about 5 nm, containing a large amount of non-free water therein, and having no significant X-ray recovery peak. Since allophane has the property of adsorbing a large amount of calcium ions, the calcium ions in the solidified material are adsorbed by the allophane in the soil during the solidification treatment of the soil, making it difficult to produce cement hydrate. When cement hydration does not proceed, it is considered that the expression of solidification strength is reduced and hexavalent chromium cannot be fixed to cement hydrate.

When the ground is improved, ettringite (3CaO.Al ₂ O ₃ .3CaSO ₄ ..3) is obtained by hydrolysis of C ₃ S (3CaO.SiO ₂ ), C ₃ A (3CaO.Al ₂ O ₃ ), gypsum, etc. immediately after the improvement. 32H ₂ O) is generated, and calcium ions are released from the surface of C ₃ S and the surface of C ₃ A, respectively.
Therefore, when gypsum is added to the cement clinker or hydraulic material which is the gist of the present invention, a large amount of calcium ions can be supplied at the initial stage of the solidification treatment by using anhydrous gypsum with a high dissolution rate of calcium ions. Become. Thereby, the calcium ion adsorption amount of allophane is saturated at the initial stage of the solidification treatment, and surplus calcium ions promote the formation of hydrates that contribute to the development of strength and the fixation of hexavalent chromium.

As a method for determining the dissolution rate of calcium ions, 0.3 g of gypsum is added to 100 mL of water at a water temperature of 25 ° C., and the calcium ions are dissolved at a rate of 200 mg / L or more in 10 minutes using a magnetic stirrer and a stirrer. The method using anhydrous gypsum is adopted . In addition, if the rotational speed of the stirrer is about 100 to 600 rpm, there is no significant difference in the calcium ion concentration.

Here, the water temperature was set to 25 ° C., and 0.3 g of anhydrous gypsum was added to 100 mL of water because a difference in the effect of gypsum tends to occur and gypsum can be differentiated. If the amount of anhydrous gypsum added is 3 g, the dissolution rate of calcium ions is 200 mg / L or more in 10 minutes in most gypsum and cannot be differentiated.

Furthermore, the measurement time is set to 10 minutes because dissolved calcium ions increase with time and cannot be distinguished.
The reason why the dissolved amount of calcium ions is 200 mg / L or more is that when the amount is less than 200 mg / L, the strength of the improved soil is low and the amount of hexavalent chromium eluted is large. A preferable dissolution amount of calcium ions is 200 mg / L. If it is this value, the further improvement effect that the strength expression of improved soil is high and the elution amount of hexavalent chromium is small will be acquired.

In addition, hydrates such as calcium silicate and calcium aluminate are generated in the long term due to the pozzolanic reaction between calcium contained in the hydraulic material and silica and aluminum in the soil, increasing the strength of the ground-improved part. Is done.
The amount of the ground improvement solidifying material added to the target soil can be easily determined by conducting a preliminary test based on the required strength at the site. Thereby, required intensity | strength expression can be obtained.

Anhydrous gypsum can be used for both natural products and by-products. What mixed impurities, such as a clay mineral, may be used.
As the hydraulic material, a material containing at least one of Portland cement, lime, mixed cement, solidifying material for soil improvement, and special cement is desirable.
  Among these, as Portland cement, for example, ordinary Portland, early-strength Portland cement, low heat Portland, and the like can be employed.

As the lime, quick lime, slaked lime, limestone powder and the like can be employed.
As the mixed cement, for example, mixed cement, silica cement, fly ash cement and the like can be employed.
As the special cement, for example, alumina cement, magnesia cement, gypsum cement (Keans cement) or the like can be employed.

The cement clinker preferably contains at least one of ordinary Portland cement clinker, early-strength Portland cement clinker and low heat Portland cement clinker.

Invention of Claim 2 uses the solidification material for ground improvement of Claim 1 for volcanic ash clay, and the elution amount of hexavalent chromium on the age of 28 days is 0.01-0.03 mg / L. It is solidified soil .

According to the solidification material for ground improvement and the solidified soil using the same according to claim 1, in the construction method for ground improvement with cement or cement-based solidification material, when adding gypsum to cement clinker or hydraulic material In addition, by using anhydrous gypsum in which calcium ion dissolves at least 200 mg / L (test to add 0.3 g of gypsum to 100 mL of distilled water at a water temperature of 25 ° C.) in 10 minutes, high strength improved soil is obtained. Can do. Moreover, elution of hexavalent chromium from the improved soil can be suppressed.

  Examples of the present invention will be specifically described below. However, the present invention is not limited to these.

As the target soil for the solidification treatment, volcanic ash clay soil (collected from Kamifukuoka City, moist / cm ² , 1.35 g / cm ³ , moisture content of 114.2%) was employed.
Usable materials (cement clinker or hydraulic material) include ordinary Portland cement (manufactured by Ube Mitsubishi Cement Co., Ltd., symbol NC), quick lime (manufactured by Ryoko Lime Industry Co., Ltd., symbol CaO), blast furnace cement type B (Ube Mitsubishi Cement) Manufactured by Co., Ltd., symbol BB), general soft soil cement-based solidifying material youth stabilizer 10 (manufactured by Ube Mitsubishi Cement Co., Ltd., symbol US10), ordinary Portland cement clinker (manufactured by Ube Mitsubishi Cement Co., Ltd., symbol N), Hayao Portland cement A clinker for a cement (Ube Mitsubishi Cement Co., Ltd., symbol H) and a low heat Portland cement clinker (Ube Mitsubishi Cement Co., Ltd., symbol L) were employed.

As the gypsum, Asahi Glass Co., Ltd. hydrofluoric anhydride gypsum (density 2.94 g / cm ³ , specific surface area 4410 cm ² / g, symbol An-A), Nippon Light Metal Co., Ltd. hydrofluoric anhydride gypsum (density 2.96 g / cm) ³ , specific surface area 4460 cm ² / g, symbol An-N), Thai natural anhydrous gypsum T (density 2.94 g / cm ³ , specific surface area 4490 cm ² / g, symbol An-T), another lot of Thai natural anhydrous Gypsum S (density 2.92 g / cm ³ , specific surface area 3940 cm ² / g, symbol An-S), Daikin Industries, Ltd. hydrofluoric anhydride gypsum (density 2.99 g / cm ³ , specific surface area 6240 cm ² / g, symbol An-D), dihydrate gypsum (density 2.32 g / cm ³ , specific surface area 2080 cm ² / g, symbol G) manufactured by Kanto Science Co., Ltd. was employed.

  According to the tests shown in Tables 1 and 2, 100 mL of distilled water having a water temperature of 25 ° C. was put into a 200 mL beaker, the ion electrode was inserted into distilled water, and 3.0 g (Table 1) and 0.3 g of the above-mentioned gypsum. (Table 2) Add each, and stir and mix immediately at a speed of 500 rpm using a magnetic stirrer (manufactured by Tokyo Seisakusho Co., Ltd.) and a stirrer (manufactured by ASONE Co., Ltd.) for a predetermined time shown in Table 1 and Table 2. went. Then, the density | concentration of the calcium ion melt | dissolved in these solutions was measured with time by the ion electrode (Toa Denpa Kogyo KK make, HS-305).

  As is clear from Table 1, when the amount of gypsum is 3.0 g, the dissolution rate of calcium ions in any gypsum (An-A, An-N, An-T, An-S, An-D, G). There was no noticeable difference. All gypsum had a calcium ion concentration of 200 mg / L or more 5 minutes after addition to distilled water (immersion time 5 minutes), and a calcium ion concentration of 300 mg / L or more 30 minutes after addition. The theoretical dissolution amount is about 500 mg / L for anhydrous gypsum and about 590 mg / L for dihydrate gypsum.

  Further, as is apparent from Table 2, when the gypsum amount was 0.3 g, a difference was observed in the dissolution rate of calcium ions. In particular, in 10 minutes after immersion, An-A, An-N, and An-T that have a calcium ion concentration of less than 200 mg / L, and An-S, An-D, and G that have a calcium ion concentration of 200 mg / L or more. Divided into groups.

In the tests shown in Table 3, the composition of the solidified soil (target soil) was 60% water solidified material, and the amount of solidified material for ground improvement was 300 kg / m ³ with respect to 1 m ³ of wet soil. The composition of the solidifying material for ground improvement was such that the ratio of NC to anhydrous gypsum was 90:10, and the ratio of NC to dihydrate gypsum was 10% in terms of anhydrous gypsum. Thereafter, specimens were produced in accordance with JGS 0821-2000 “Method for producing specimens without compaction of stabilized soil”.
Next, uniaxial compressive strength was measured at a material age of 7 days and a material age of 28 days in accordance with JIS A 1216 “Soil Uniaxial Compression Test Method”. For samples after the uniaxial compression test, a hexavalent chromium dissolution test was performed according to the Cement Association Standard Test Method JCAS L-02-2004 "A Hexavalent Chromium Dissolution Test Method Using Cement and Cement-Based Solidifying Materials" It was.

  As is clear from Table 3, the ground improvement solidified material using gypsum whose calcium ion concentration becomes 200 mg / L or more 10 minutes after the addition has good strength development and a small amount of hexavalent chromium elution. I was able to confirm.

In the test shown in Table 4, the composition of the solidified soil was dry (water solidified material ratio 0%) added, and the amount of the ground improving solidified material added was 200 kg / m ³ with respect to 1 m ³ of wet soil. The composition of the solidifying material for ground improvement is 90:10 for quick lime and anhydrous gypsum, 90:10 for blast furnace cement and anhydrous gypsum, and 40:50:10 for alumina cement, NC and anhydrous gypsum. The ratio of US10 and anhydrous gypsum was 90:10. Other test methods were carried out in the same manner as in Table 3.

  As is apparent from Table 4, when a solidifying material for ground improvement in which the type of hydraulic material is changed is added to gypsum whose calcium ion concentration is 200 mg / L or more in 10 minutes after the addition, strength development is good, It was confirmed that the elution amount of hexavalent chromium was small.

  In the test shown in Table 5, anhydrous gypsum was added to cement clinker, and a solidified material for ground improvement was prepared by mixing and grinding. The composition of the obtained solidifying material for ground improvement was set to be 10% added in terms of anhydrous gypsum. Other test methods were carried out in the same manner as in Table 3.

  As is apparent from Table 5, when the cement clinker is changed to gypsum whose calcium ion concentration becomes 200 mg / L or more in 10 minutes after the addition and mixed and pulverized, the strength development is good and the elution amount of hexavalent chromium is small. I was able to confirm that.

Claims (2)

Cement clinker or hydraulic material ,
Gypsum added to the cement clinker or hydraulic material, and when 0.3 g is added to 100 mL of distilled water having a water temperature of 25 ° C., anhydrous gypsum having a calcium ion concentration of 200 mg / L or more 10 minutes after the addition Including solidification material for ground improvement. Use the ground improvement solidification material of claim 1 for volcanic ash cohesive soil,
Solidified soil having an elution amount of hexavalent chromium of age 28 on the order of 0.01 to 0.03 mg / L.