JP5685004B2 - Soil improvement method - Google Patents

Description

The present invention is a soil improvement which suppresses elution of heavy metals or improves strength by mixing an environmental load reducing cement composition which can be suitably used for improving contaminated soil and soft ground into the soil and ground. It is about the method.

  Blast furnace slag obtained as a by-product when producing metallic iron from iron ore using a blast furnace has performance similar to that of cement, such as latent hydraulic properties, and is produced in large quantities. It has been widely used in the civil engineering / architecture field, but it is also used in various ways as a constituent material for ground improvement materials and soil improvement materials.

As a strength improvement material for soft ground, for example, Patent Document 1 discloses “a solidified material composed of cement-based solidified material, anhydrous gypsum, granulated blast furnace slag, and alumina sludge”, and Patent Document 2 discloses a “C ₃ S content”. Has a mineral composition of 35 to 65% by weight, C ₃ A content of 10 to 20% by weight, Fe ₂ O ₃ content of 2% by weight or less, Al ₂ O ₃ / Fe ₂ O ₃ Is a ground improvement material consisting of 100 parts by weight of a cement composition having a weight ratio of 3 or more, 10 to 300 parts by weight of gypsum, and 10 to 300 parts by weight of blast furnace slag.

  Moreover, as an improving material (insolubilizing agent) that suppresses elution of heavy metals such as hexavalent chromium from contaminated soil, Patent Document 3 describes “an insolubilizing agent made of blast furnace cement having a slag content of 31 to 70%”. Yes. Furthermore, Patent Document 4 describes “a ground improvement material comprising hydraulic material, blast furnace slag and gypsum” as a consideration of both the elution suppression of heavy metals and strength development.

  On the other hand, following the reduction of greenhouse gas emissions based on the Kyoto Protocol issued in February 2005 and the resolution of the G8 Summit in July 2009, the cement industry and the construction industry are also one of the greenhouse gases. There is a need to work on reducing emissions.

  Under such circumstances, the basic unit of carbon dioxide at the time of cement production is 788 kg / t, which is extremely large as compared with 24.1 kg / t of the basic unit generated when blast furnace slag is generated. Therefore, recently, in consideration of the environmental problems as described above, cement-based solidified materials used for ground improvement and soil improvement are being further decemented, reduced in cement, and increased in blast furnace slag. .

  Under such circumstances, cement-based solidification mainly composed of blast furnace slag such as “heavy metal dissolution inhibitor containing 1 to 42 parts by weight of Portland cement or lime with respect to 100 parts by weight of blast furnace slag” as shown in Patent Document 5. Materials have also been developed.

  On the other hand, as shown in Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9, and the like, conventionally, various soil improvement materials containing magnesium-containing materials such as light-burned magnesia, magnesium oxide, and burned dolomite. (Heavy metal elution inhibitor) is also known.

JP 05-311170 A JP 2005-105234 A JP 2001-321756 A JP 2001-348571 A JP 2005-162862 A JP 2003-013063 A JP 2004-292568 A JP 09-279142 A JP 2009-155414 A

  Conventionally, as shown in Patent Documents 1 to 3, cement-based "soft ground strength improving material" including blast furnace slag and "improvement of suppressing elution of heavy metals such as hexavalent chromium from contaminated soil" Various materials (insolubilizers) have been developed, but none of them considers both strength and suppression of elution of heavy metals, nor does it consider the above environmental problems.

  Although what is shown by patent document 4 considers both the intensity | strength and the elution suppression of heavy metal, the said environmental problem is not considered at all.

  Although what is shown in Patent Document 5 considers both strength and elution suppression of heavy metals, and because it is mainly made of blast furnace slag, it seems to correspond to the environmental problem, If the amount of cement contained in the heavy metal elution inhibitor is small or the amount of the heavy metal elution inhibitor added to the soil is small, the effect of inhibiting the elution of heavy metal may not be sufficiently exerted or sufficient strength may not be obtained.

  In Patent Documents 6 to 9, no consideration is given to the environmental problem.

The present invention has been made in view of the above problems, and its object is to achieve the effective use of blast furnace slag, and to elute heavy metals from contaminated soil even if the amount of incorporation into the soil and ground is small. An object of the present invention is to provide a soil improvement method by mixing a low-cement environmental load-reducing cement composition , which is effective for restraint and capable of improving strength against soft ground, into the target soil.

As a result of intensive investigations to solve the above problems, the present inventors have reduced the amount of cement used and increased the amount of blast furnace slag to reduce the cement content. While controlling, if necessary, using an appropriate amount of anhydrous gypsum and an appropriate amount of magnesium-containing material, it is possible to suppress elution of heavy metals (especially hexavalent chromium) from contaminated soil even if the amount of mixing is small, and The present inventors have completed the present invention by finding a soil improvement method using an environmental load-reducing cement composition capable of obtaining improved soil having good strength development.

That is, the present onset Ming, a cement composition containing a magnesium content of a specific amount consists specified amount of blast furnace slag with a specific amount of cement, as required, a specific amount of magnesium-containing material and a specific amount of anhydrite It is a soil improvement method in which a specific amount of a cement composition of a reduced environmental load containing is mixed with target soil. More specifically, the invention is shown below .

One aspect of the present invention is “ 1-50 mass% of cement composition comprising 20-40 mass% of Portland cement and 60-80 mass% of blast furnace slag with respect to 1 m ^{3 of} soil to be improved. Cement composition with a low cement content mainly composed of blast furnace slag, wherein the magnesium content in the cement composition containing the magnesia-containing material is 8.4 to 15% by mass in terms of MgO. A soil improvement method characterized by mixing 50 to 450 kg of a product .

Thus, while controlling the content of active magnesium content in suppressing elution of heavy metals, Ru with a low cement reduce environmental impact cement composition in combination with cement, blast furnace slag and magnesia inclusions in a particular formulation it allows even small mixing amount Ru good modified soil suppressing elution of the possible development of strength of the heavy metals is obtained from contaminated soil.

  Moreover, since blast furnace slag is used in large quantities, the effective use of blast furnace slag can be expanded. The “environmental load reduction type” in the present invention is a type that contributes to environmental problems such as suppression of carbon dioxide emission and reduction of industrial waste disposal.

One of the present invention is “ a cement composition 100 comprising 20 to 40 mass% of Portland cement, 50 to 80 mass% of blast furnace slag, and 15 mass% or less of anhydrous gypsum with respect to 1 m ^{3 of} soil to be improved. A blast furnace slag comprising 1 to 50 parts by mass of a magnesia-containing material with respect to parts by mass, wherein the magnesium content in the cement composition containing the magnesia-containing material is 5.0 to 15% by mass in terms of MgO. A soil improvement method characterized in that 50 to 450 kg of a low-cemented cement composition as a main component is mixed.
By combining cement and blast furnace slag with anhydrous gypsum added as necessary in a specific formulation, it is possible to increase the effect of suppressing the elution of heavy metals from contaminated soil and the strength development.

In the present invention , 1 to 50 parts by mass of magnesia-containing material is mixed with 100 parts by mass of the total amount of Portland cement and blast furnace slag or 100 parts by mass of Portland cement, blast furnace slag and anhydrous gypsum. .

Magnesia inclusions but are intended to be added pressure for the purpose of improving the effect of suppressing the elution of heavy metals, in general, the purpose is achieved easily in the present invention by the mix design.

One preferred that magnesia inclusions in the present invention is Ru dolomite fired product der.

  A dolomite fired product containing CaO or MgO as an alkali stimulator for blast furnace slag is one of the preferred magnesium-containing materials. By using this, the object of the present invention can be easily achieved by the above-described blending design. The dolomite fired product referred to in the present invention is generally called calcined dolomite, soft calcined dolomite, light calcined dolomite, calcined dolomite, or the like.

Preferred another one of those magnesia inclusions in the present invention is Ru light burned magnesia der.

  Light calcined magnesia, which is an alkali stimulant for blast furnace slag and has a high elution suppression effect on heavy metals as well as the above-mentioned calcined dolomite, is also one of the preferred magnesium-containing materials. The purpose is easily achieved.

Soil improvement method of the present invention, with respect to the soil (target soil) 1 m ³ as a target of improvements, a soil improving how formed by 50~450kg mixing the cement composition.

Thus, in the soil improvement method of the present invention, a predetermined amount of the cement composition of the present invention is mixed with target soil such as contaminated soil or soft soil to suppress elution of heavy metals or to reinforce strength. Even when a relatively small amount of 50 to 100 kg of 100 kg or less is mixed with 1 m ^{3 of the} target soil, it is possible to suppress elution of heavy metals while ensuring a certain level of strength.
In the case of mixing in such a small amount, the magnesium content in the cement composition is, for example, 13.6 to 15% by mass (a system not containing gypsum) or 11.5 to 15% by mass (anhydrous gypsum in terms of MgO). It is preferable to increase the number of systems including

  In addition, the said target soil said by this invention is contaminated soil by heavy metal (especially hexavalent chromium), volcanic ash clay soil, sandy soil, humus soil, highly hydrous soil, other soft soil, organic soil, highly organic soil. , Black me, silt, cohesive soil, etc.

  According to the cement composition of the present invention, it is effective in suppressing the elution of heavy metals (especially hexavalent chromium) from contaminated soil even if the amount of incorporation into soil and ground is relatively small, and the strength can be improved with respect to soft ground. A cement composition for soil improvement and ground improvement can be easily obtained.

  In addition, the cement composition of the present invention is a blast furnace slag-based, low-cement environmental load reducing type for effective use of blast furnace slag, and it is a recent environment such as carbon dioxide emission suppression and industrial waste effective use. It also contributes to solving problems.

Further, according to the soil improvement method of the present invention, both strength and suppression of elution of heavy metals (especially hexavalent chromium) can be improved only by mixing the cement composition of the present invention with the target soil. Even when the cement composition of the present invention is mixed in a relatively small amount of 100 kg or less with respect to 1 m ³ of the target soil, elution of heavy metals can be suppressed while securing a certain level of strength, and it is environmentally friendly.

  Hereinafter, the cement composition and the soil improvement method of the present invention will be described more specifically.

  The cement composition of the present invention contains a small amount of cement and a large amount of blast furnace slag, and if necessary, contains an appropriate amount of anhydrous gypsum and an appropriate amount of magnesia-containing material.

  The cement is a commercially available Portland cement such as ordinary Portland cement, early-strength Portland cement, or moderately hot Portland cement. Ordinary Portland cement is preferred in terms of price and supply.

  These Portland cements usually contain 1 to 2.5% magnesium in terms of MgO. Although this magnesium content is also small, it seems to influence the elution inhibitory effect of heavy metals.

Blast furnace slag is a commercially available blast furnace granulated slag powder conventionally used as a material for blast furnace cement and cement admixture. The fineness is not particularly limited, but those having a brain value of 3000 to 8000 cm ² / g are preferable. Within this range, it is easy to obtain at an affordable price, and the object of the present invention can be sufficiently achieved.

  Blast furnace slag is an industrial waste in the case of iron making that has latent hydraulic properties that are hydraulically driven by an alkali stimulant, and contributes to both strength development and suppression of elution of heavy metals. In particular, from the viewpoint of suppressing elution of heavy metals, it is preferable to use blast furnace slag containing a large amount of magnesium (5 to 8% in terms of MgO in the blast furnace slag).

Anhydrous gypsum (CaSO ₄ ) has been conventionally used as a material for cement admixtures, and these can be used. If it contains 90% by weight or more of anhydrous gypsum, other gypsum may be included a little. Use of waste materials such as waste gypsum board or a fired product thereof is preferable from the environmental viewpoint. The fineness of anhydrous gypsum is not particularly limited as long as it is a powder.

  Anhydrous gypsum contributes to the development of initial strength due to ettringite formation, and is added when the required strength cannot be ensured with the cement and the blast furnace slag alone.

  The magnesia-containing material contains 10 to 100% MgO, and is added when the magnesia content in the cement composition is insufficient only with cement and blast furnace slag. Examples of the magnesia-containing material include a dolomite fired product, a light fired magnesia, a magnesia cement, and a magnesia clinker, among which a dolomite fired product and a light fired magnesia are preferable.

  The fineness of the magnesia-containing material is not particularly limited, but in order to efficiently play the role of both an alkali stimulant for suppressing leaching of heavy metals and blast furnace slag, particles having a particle size of 5 mm or less are preferable.

The dolomite fired product is obtained by firing dolomite (CaMg (CO ₃ ) ₂ ) at 750 to 1000 ° C. to decarboxylate dolomite. A so-called hard-burned dolomite fired product fired above 1000 ° C. may not be able to fix heavy metals. The dolomite fired product includes calcined dolomite obtained by decarboxylating CaCO ₃ and MgCO ₃ and semi-fired dolomite obtained by decarboxylating only MgCO ₃ . In addition to calcined dolomite, calcined dolomite, soft calcined dolomite, and light calcined dolomite are also included. The components are, for example, CaO: 65.6% and MgO: 32.1%, and some impurities such as silica and calcium carbonate are included.

  If the total amount of CaO and MgO is 95% or more, a commercially available product may be used. The dolomite fired product is preferable because it can effectively serve as both an alkali suppressant for heavy metal elution suppression and blast furnace slag, and can be stably supplied at a relatively low price.

  Light-burned magnesia is made of MgO obtained by firing raw materials such as magnesium hydroxide at 300 to 400 ° C. As with the above dolomite fired product, it can effectively serve as both an inhibitor of heavy metal elution and an alkali stimulant for blast furnace slag, but it is particularly preferred when it is desired to increase the elution suppression effect of heavy metal.

  In the present invention, it is necessary to limit the ratio of the Portland cement and blast furnace slag, which are the main components of the cement composition, in the cement composition such that the amount of blast furnace slag is larger. If there is more blast furnace slag than Portland cement, strength enhancement by MgO can be expected.

  Portland cement is 20 to 40% by mass in the cement composition. If the amount is less than 20% by mass, the amount of cement is too small and the strength development becomes worse. If it exceeds 40% by mass, the content of blast furnace slag is reduced, so that the elution suppressing effect of heavy metals is deteriorated and it is difficult to become an environmental load reducing type cement composition.

  The blast furnace slag is 50 to 80% by mass in the cement composition. If it is less than 50% by mass, the effect of suppressing elution of heavy metals is deteriorated, and the amount of cement is increased, so that it is difficult to become an environmental load reducing type cement composition. Moreover, when it exceeds 80 mass%, the amount of cement will decrease too much and strength development will worsen.

  Anhydrous gypsum is 0 to 15% by mass in the cement composition and does not necessarily need to be contained in the cement composition. It is added when strength development is insufficient only with Portland cement, blast furnace slag, and magnesia-containing material added as necessary.

  The upper limit of the amount added needs to be 15% by mass. If it exceeds 15% by mass, the effect of inhibiting the elution of heavy metals will deteriorate, the expression of long-term strength will deteriorate, or abnormal expansion will occur, making it difficult to obtain a cement composition with stable performance.

  In the cement composition of the present invention, the content of magnesium in the cement composition needs to be 3 to 15% by mass in terms of MgO in the above blending ratio. If it is less than 3 mass%, the elution suppression effect of a heavy metal may worsen. When it exceeds 15 mass%, it becomes difficult to ensure sufficient strength depending on the target soil. By setting the content in the above range, it becomes easy to stably obtain both the heavy metal elution suppression effect and good strength development. When only the Portland cement and blast furnace slag cannot produce MgO in the above range, a magnesia-containing material is added.

  The magnesia-containing material is mixed when it is desired to enhance the elution control effect of heavy metals, but the mixed amount is the total amount of Portland cement, blast furnace slag, and anhydrous gypsum (the mixture is called ECM cement) added as necessary. It is preferable to set it as 1-50 mass parts with respect to a mass part.

  If it is less than 1 part by mass, it is difficult to obtain a mixing effect. If the amount exceeds 50 parts by mass, no increase in effect is observed even if the amount is increased. On the other hand, strength development may be worsened. For example, when a dolomite fired product or lightly burned magnesia is mixed as described above, a cement composition having a magnesium content of 3 to 15% by mass in terms of MgO can be easily obtained.

  The cement composition of the present invention comprises the above-mentioned Portland cement and blast furnace slag as main components, and comprises anhydrous gypsum and a magnesia-containing material added as necessary, and is used as a premix product obtained by premixing these. However, Portland cement and blast furnace slag, or Portland cement, blast furnace slag and anhydrous gypsum are premixed (preparing several types of ECM cement as a base), and magnesia-containing materials are used at the time of construction. You may mix and use.

  By doing in this way, since the kind and mixing amount of a magnesia containing material can be adjusted according to target soil and a use purpose, the use range of the cement composition of this invention is expanded, and it becomes easy to use.

  The method for producing the cement composition of the present invention is not particularly limited. What is necessary is just to premix the said material suitably by the conventional method, or to mix and use it at the time of construction. The blending ratio is determined according to the type of the target soil and the purpose of use of the cement composition. For example, when the main purpose is to suppress the elution of heavy metals, the formulation increases the amount of anhydrous gypsum and the content of magnesium, and when the purpose is to improve the strength of soft ground and to manufacture soil cement, Or a formulation that increases the content of anhydrous gypsum.

  In any case, at least the aluminum content, sulfuric acid content, and magnesium content in each of the above materials should be analyzed and grasped in advance, and a preliminary test for determining the composition of the sampled target soil and the cement composition of the present invention should be conducted. It is preferable to carry out the conventional method.

In the soil improvement method of the present invention, an appropriate addition amount differs depending on the type of the target soil to 1 m ^{3 of} the soil (target soil) to be improved with the cement composition of the present invention, but 50 to 450 kg is mixed. It will be.

  As mentioned above, as mentioned above, contaminated soil with heavy metals (especially hexavalent chromium), volcanic ash clay, sandy soil, humus soil, highly hydrous soil, other soft soil, organic soil, highly organic soil, Kuroboku , Silt, and clay soil.

The cement composition of the present invention is mixed with these target soils. Although an appropriate addition amount varies depending on the type of the target soil, 50 to 450 kg is mixed with 1 m ^{3 of} the target soil. For example, it is preferable to add 50 to 200 kg for sandy soil and silt, 100 to 300 kg for viscous soil, and 250 to 450 kg for volcanic ash clay, humus soil, Kuroboku, and highly organic soil.

  For the purpose of improving strength, (a) use a cement composition with a high cement content, (b) include anhydrous gypsum in the cement composition, and (c) mix the cement composition with the target soil. Take measures such as increasing the amount.

  For the purpose of suppressing elution of heavy metals, (a) Use a cement composition with a high blast furnace slag content, (b) Increase the amount of cement admixed and increase the amount of cement hydrate to increase the amount of fixed heavy metal. And (c) include a magnesia-containing material in the cement composition to increase the magnesium content in the cement composition.

When aiming at both improvement of strength and suppression of elution of heavy metals, use an intermediate blending of the above measures. A preferable blending example of the improved soil in the soil improvement for both the above purposes is a mixture of 20 to 30% by mass of Portland cement, 70 to 60% by mass of blast furnace slag and 10% by mass of anhydrous gypsum with respect to 1 m ³ of the target soil. (ECM cement) is mixed with 200 to 300 kg and calcined dolomite is mixed with 20 to 50 kg.

  In addition, since the amount of blast furnace slag, which has an effect of suppressing heavy metal elution, decreases in the target soil when the amount of cement composition mixed in the target soil is small, it is better to supplement with the magnesia-containing material.

  The ground improvement methods include shallow layer improvement and deep layer improvement depending on the depth from the ground, and addition methods include powder addition and slurry addition. The method of ground improvement is the same as in the case of a conventional cement-based solidified material mixed with soil, and is not particularly limited.

  For example, W / P = 1 (weight ratio) cement milk is prepared with a premixed material (P) and water (W) made of Portland cement, blast furnace slag and anhydrous gypsum of a predetermined composition, and stirred while being stirred. A fixed amount of calcined dolomite powder is added to produce cement milk made of the cement composition of the present invention.

  A predetermined amount of the cement milk is mixed with a predetermined amount of target soil by a mechanical stirring method and a jet stirring method to improve the soil. The target soil by the soil improvement method of the present invention can be expanded to construction waste such as construction generated soil, and the obtained improved soil can be used as a reinforcing material and a soil cement pillar, sandbag, seismic reinforcement, ground subsidence prevention, and other various fields. Can be used as a filler.

  Next, the performance of the trial improvement soil using the cement composition of the present invention is shown in Test Examples A to D.

[Test Example A]
(1) Materials used Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement)
Blast-furnace slag: Seramento (Dai Shi Co., Ltd .: Brain value 4000 cm ² / g product)
Anhydrous gypsum: manufactured by Dei Shi Co., Ltd .: Brain value 4000 cm ² / g
Firing dolomite: manufactured by Yoshizawa Lime Co., Ltd. (MgO: 32.1%)
Target soil: Silt (water content: 41.1%, wet density is 1716 kg / m ³ )

(2) Production of trial improvement soil Cement and blast furnace slag, cement, blast furnace slag and anhydrous gypsum were mixed to obtain a mixture (ECM cement) having a predetermined composition shown in Table 1. Water was added thereto at a ratio of water / ECM cement = 1 (mass ratio), and the mixture was stirred and mixed by a Hobart mixer to obtain a cement slurry.

  The blending ratio shown in Table 1 is adjusted so that the cement slurry and the calcined dolomite mixed as necessary are mixed with the target soil and kneaded with a soil mixer, and the obtained kneaded product is adjusted to 5φ × 10 cm. A specimen for a uniaxial compressive strength test was obtained by molding.

Incidentally, mixing amount of burnt dolomite and ECM cement shown in Table 1 (unit amount: kg / m ³⁾ is the kg per target soil 1 m ^3.
Further, the magnesium content in the cement composition in Table 1 was determined according to JIS R 5202.

(3) Performance test
(i) Uniaxial compressive strength test A uniaxial compressive strength test was conducted on the 7th and 28th days of the material age in accordance with the provisions of JIS A1216.
(ii) Hexavalent chromium elution test Hexavalent chromium elution test was performed in accordance with the provisions of the Environmental Agency Notification No. 46, using the crushed pieces after the uniaxial compressive strength test.

(4) Test results Table 1 shows the test results. Test No. 1-6 and test no. 13-18 or test no. 7-12 and test no. As can be seen by comparing 13 to 18, by using the cement composition of the present invention, the strength equivalent to that of a conventional blast furnace cement can be obtained even with a low cement. Further, the strength can be improved even if the amount of the cement composition mixed in the silt is relatively small (even if the amount of cement is relatively small).

  Furthermore, in conventional blast furnace cement, when the magnesium content effective for suppressing elution of heavy metals increases (mixed with calcined dolomite), the strength decreases. However, in the cement composition of the present invention, the strength improves. By using the composition, elution of heavy metals can be effectively suppressed and strength can be improved.

[Test Example B]
(1) Materials used Same as Test A except for the target soil. Kanto Loam (water content: 134.3%, wet density 1350 kg / m ³ ) was used as the target soil.

(2) Manufacture of trial improvement soil It adjusted so that it might become a mixture ratio shown in Table 2, and it manufactured similarly to Test Example A.

(3) Performance test Same as Test example A.

(4) Test results Table 2 shows the test results. What departs from the scope of the present invention is test no. As shown in FIG. 22, in the case where the magnesium content is small, the elution suppression of hexavalent chromium may be insufficient even if the strength can be secured.

  In addition, Test No. As shown in FIGS. 23 and 24, where the magnesium content is high, the strength is lower than that of the present invention (Test Nos. 20 and 21) even though the elution of hexavalent chromium can be suppressed.

  If the cement composition of the present invention is used, it is possible to stably ensure strength and suppress elution of heavy metals regardless of the magnesium content (variation).

[Test Example C]
(1) Materials used Same as Test A except for the target soil. The target soil was sandy soil (water content: 34.0%, wet density 1844 kg / m ³ ).

(2) Manufacture of trial improvement soil Cement, blast furnace slag, and anhydrous gypsum were mixed to obtain a mixture (ECM cement) having a predetermined composition shown in Table 3. This mixed powder and calcined dolomite powder mixed as necessary are mixed with the target soil and kneaded with a soil mixer, and the obtained kneaded material is formed into 5φ × 10 cm and is a specimen for a uniaxial compressive strength test. Got. Others are the same as in Test Example A.

(3) Performance test Same as Test example A.

(4) Test results Table 3 shows the test results. When the cement composition of the present invention is used, the test No. As shown in 27, 29 and ³⁰ , the strength can be ensured even when the amount of incorporation into the target soil is relatively small at about 100 kg / m ³ .

[Test Example D]
(1) Materials used Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement)
Blast-furnace slag: Seramento (Dai Shi Co., Ltd .: Brain value 4000 cm ² / g product)
Anhydrous gypsum: manufactured by Dei Shi Co., Ltd .: Brain value 4000 cm ² / g
Firing dolomite: manufactured by Yoshizawa Lime Co., Ltd. (MgO: 32.1%)
Light-burned magnesia: Takei Kogyo Co., Ltd. (MgO: 49.0%)
Soil: Clay (water content: 54.5%) and No. 6 silica sand (water content: 0.05%) mixed in a mass ratio of 1: 1 (sample water content: 27.3%, wet) Density: 2002kg / m ³ )

In addition, this trial object soil included hexavalent chromium in the cement so as to be 300 mg / kg with the first grade reagent CaCrO ₄ .2H ₂ O, and used as contaminated soil with hexavalent chromium.

(2) Manufacture of trial improvement soil Cement and blast furnace slag, cement, blast furnace slag and anhydrous gypsum were mixed to obtain a mixture (ECM cement) having a predetermined composition shown in Tables 4 and 5. Water was added thereto at a ratio of water / ECM cement = 1 (mass ratio), and the mixture was stirred and mixed by a Hobart mixer to obtain a cement slurry.

The blending ratio shown in Table 4 and Table 5 is adjusted, and the above-mentioned cement slurry and calcined dolomite or light calcined magnesia mixed as necessary are mixed in the soil for trial production and kneaded with a soil mixer. The kneaded product was molded into 5φ × 10 cm to obtain a specimen for a uniaxial compressive strength test.

(3) Performance test Same as Test example A.

(4) Test results Table 4 shows the test results using the calcined dolomite, and Table 5 shows the test results using the light calcined magnesia. Test No. in Table 4 31-38 and test no. 47-54, or test no. 39-46 and test no. As can be seen by comparing 47 to 54, the one using the cement composition of the present invention develops strength higher than that of the blast furnace cement blended material despite being low cement, and elution of hexavalent chromium is also possible. It is suppressed. It can be seen that it is also effective against soil contaminated with hexavalent chromium.

  In addition, Test No. As shown in Nos. 47 to 54, where the amount of cement deviates from the range of the present invention and the content of magnesium increases, the strength expression deteriorates. As shown in 31-46, it does not fall as much as the blast furnace cement blend.

  In addition, test No. in Table 5 As can be seen from 55 to 62, in the cement composition of the present invention, even when the magnesia-containing material is changed to the calcined dolomite and light calcined magnesia is used, good strength expression and hexavalent chromium elution suppression can be achieved. As in the case of using the calcined dolomite, even if the magnesium content increases, the strength expression does not deteriorate and becomes slightly better.

  As described above, the cement composition of the present invention has a strength development effect that is higher than that of a conventional blast furnace cement, and has a heavy metal (hexavalent chromium), despite having a low cement content with a reduced environmental load. Elution suppression effect is also high.

  Further, in the case of a conventional blast furnace cement blend with a high cement content, the strength expression becomes worse when the magnesium content increases, and the strength expression becomes unstable due to the magnesium content, but the cement composition of the present invention The product is not greatly affected by the magnesium content, and the strength can be secured stably.

  Furthermore, depending on the target soil, the objective can be achieved with a relatively small amount of mixing, and there may be an advantage in terms of economy.

[Test Example E]
An aqueous solution having a Cr ⁶⁺ concentration of 10 ppm and a cement composition shown in Table 6 were mixed at a water powder ratio of 10, and the Cr ⁶⁺ concentration was measured at a material age of 7 days. In addition, the dolomite baked material was mixed with ECM cement in an external ratio.

The calcined dolomite used was made of MgO, the main component calcined at 750 ° C. for 4 hours in an electric furnace by covering the crucible with raw dolomite (Ube Material Co., Ltd., clay lime) (carbon dioxide partial pressure 0.1 atm). CaCO ₃ semi-fired dolomite (CaO = 42.4%, MgO = 23.0%, ig.loss = 33.9%). In all cases, the Cr ⁶⁺ concentration was fixed to the limit of quantification or less.

  The cement composition of the present invention is a novel blast furnace slag-magnesia solidified material that has both a heavy metal elution suppression effect from soil, a good and stable strength development performance, and is effective in improving contaminated soil and soft ground. The soil can be improved simply by mixing the cement composition with the target soil. In addition, improved soil prepared by mixing this cement composition with construction generated soil can be used for soil cement pillars, sandbags, and the like.

Claims (5)

For 1 m ^{3 of} soil to be improved, 1 to 50 parts by mass of magnesia-containing material is mixed with 100 parts by mass of cement composition consisting of 20 to 40% by mass of Portland cement and 60 to 80% by mass of blast furnace slag. 50 to 450 kg of a cement composition composed mainly of blast furnace slag and having a low cement content, in which the magnesium content in the cement composition containing the magnesia-containing material is 8.4 to 15% by mass in terms of MgO. The soil improvement method characterized by this. 1 to 50 mass% of cement composition consisting of 20 to 40 mass% of Portland cement, 50 to 80 mass% of blast furnace slag, and 15 mass% or less of anhydrous gypsum with respect to 1 m ^{3 of} soil to be improved. Cement composition with a low cement content mainly composed of blast furnace slag, wherein the magnesium content in the cement composition containing the magnesia-containing material is 5.0 to 15% by mass in terms of MgO. A method for improving soil, comprising mixing 50 to 450 kg of a product. For 1 m ^{3 of} soil to be improved, 1 to 50 parts by mass of magnesia-containing material is mixed with 100 parts by mass of cement composition consisting of 20 to 40% by mass of Portland cement and 60 to 80% by mass of blast furnace slag. The cement composition containing the magnesia-containing material has a magnesium content of 13.6 to 15% by mass in terms of MgO , and 50 to 100 kg of a cement composition composed mainly of blast furnace slag and reduced to cement is mixed. The soil improvement method characterized by this. 1 to 50 mass% of cement composition consisting of 20 to 40 mass% of Portland cement, 50 to 80 mass% of blast furnace slag, and 15 mass% or less of anhydrous gypsum with respect to 1 m ^{3 of} soil to be improved. Cement composition with a low cement content mainly composed of blast furnace slag, wherein the magnesium content in the cement composition containing the magnesia-containing material is 11.5 to 15% by mass in terms of MgO. A soil improvement method, comprising mixing 50 to 100 kg of a product. 200 to 300 kg of a mixture of 20 to 30% by weight of Portland cement, 70 to 60% by weight of blast furnace slag, and 10% by weight of anhydrous gypsum is mixed with 1 m ^{3 of} soil to be improved, and calcined dolomite is applied during construction. A soil improvement method comprising mixing 20 to 50 kg.