JP5565019B2 - Ground improvement method and method for producing solidified material for re-digging used therefor - Google Patents

Description

  The present invention relates to a ground improvement method that can be easily re-excavated and can reduce the elution amount of hexavalent chromium, and a method for producing a solidified material for re-excavation used therefor.

Conventionally, cement-based solidification materials are frequently used to improve soil quality in soft ground. The ground that has been improved is required to exhibit a predetermined solidification strength at a relatively early stage. For example, the solidification strength generally required for improvement of the roadbed and temporary construction is about 300 to 500 kN / m ² with a uniaxial compressive strength at a material age of 7 days. On the other hand, in the ground where pipes and the like are buried in the ground, the ground may be excavated again after construction for the purpose of repairing buried objects. Backhoe is mainly used for excavation of the improved ground, and generally the ground strength that can be excavated is 500 to 1000 kN / m ² in terms of uniaxial compressive strength.

However, when a cement-based solidified material is used, when the target ground is sandy soil or silty soil, the initial solidified strength may be 1000 kN / m ² or more with a small amount of solidified material added. Furthermore, when the target ground is cohesive soil, a pozzolanic reaction takes place over a long period of time, and the strength of the improved ground increases with time to 1000 kN / m ² or more, making it difficult to re-excavate with a backhoe. In such a case, a special excavator such as a breaker is required.

In order to control the solidification strength appropriately, there is a method to reduce the addition amount of solidification material, but in the ground with good strength development by adding a small amount of solidification material such as sandy soil and silty soil, addition of solidification material If the amount is reduced, there is a problem that the solidified strength becomes non-uniform in terms of the mixing accuracy of the soil and the solidified material. For this reason, in ground improvement using cement-based solidified material, the minimum amount of solidified material added is specified to be 50 kg or more per 1 m ³ of the target ground in order to ensure uniformity of mixing on site (Non-patent Document 1). ). In addition, when the target ground is cohesive soil, it is difficult to obtain the necessary solidification strength in the initial stage if the amount of solidification material added is reduced.

In order to cope with the above problems, various studies have been made on cement-based solidified materials on the premise of re-excavation of improved ground. For example, Patent Document 1 discloses that a composition containing a fast-hardening admixture, a long-term strength suppressing material, and a fluidizing material in a cement-based material has good initial strength development and little strength enhancement at later ages. It is disclosed. Moreover, in patent document 2, the appropriate intensity | strength of 300-1000 kN / m < ² > is uniaxial compressive strength by adding 140-200 kg per 1 m < ³ > of a mixture with normal Portland cement, fly ash, and limestone powder. Is obtained, and it can be improved to a ground of uniform strength. Furthermore, Patent Document 3 discloses that long-term strength can be appropriately suppressed by adding an admixture such as calcium carbonate, fly ash, and blast furnace slag powder to the fast-hardening soil improvement material of cementitious material.

  Patent Document 4 discloses a solidified material in which Portland cement and half-water gypsum are combined. By utilizing the rapid hydration process that is characteristic of semi-water gypsum, it is easy to create a ground that can be easily re-excavated even at long-term ages. In addition, the strength of the improved ground is easy to control because the initial and long-term strengths hardly change even when the amount of the solidified material increases.

  By the way, when the above-mentioned solidified material premised on re-digging is used, the strength of the improved ground is likely to be smaller than that of a general improved ground. In this case, cement hydrate is not sufficiently formed, and hexavalent chromium tends to be eluted, and there is a concern about the influence on the environment. Many studies have been made on the method for suppressing elution of hexavalent chromium from a solidified soil using a cement-based solidified material. For example, in Patent Document 5, various reducing agents are added to cement to obtain a solution from the solidified soil. A method for reducing the elution of hexavalent chromium is disclosed.

  In order to reliably reduce the hexavalent chromium elution amount, it is also effective to reduce the hexavalent chromium content in the cement clinker. As the method, for example, an appropriate amount of reducing sulfide sulfur is contained by setting the oxygen partial pressure inside and near the surface of the cement clinker particles at the time of manufacturing the cement clinker (Patent Document 6). ), A method of reducing the hexavalent chromium content in the cement clinker by using a reducing action by combustibles in the cement clinker firing step (Patent Document 7). In addition, by adjusting the angle and installation position of the kiln burner, the angle and installation position of the auxiliary burner, and firing the cement clinker as a flame film, a manufacturing method that reduces the ratio of hexavalent chromium generation to the total chromium content (Patent Document) 8) etc. are proposed.

Japanese Patent Laid-Open No. 10-158049 JP-A-2-34546 Japanese Patent Laid-Open No. 11-35939 JP-A-8-109377 JP 2000-86322 A Japanese Patent Laid-Open No. 2003-171152 Japanese Patent Application Laid-Open No. 11-1000024 JP 2008-137826 A

Cement Association: Ground Improvement Manual Third Edition with Cement-Based Solidifying Material, p48, 2005.

As described above, although cement-based solidified materials based on re-excavation of improved ground have been developed so far, in Patent Documents 1 to 3, the long-term age is about 28 days, and the strength after that The suppression effect of the promotion is not specifically shown. Further, solidifying material described in these documents, in order to obtain the required strength in the general ground the lowest solidifying material amount in the improved target soil 1 m ³ per 50kg or more, fly ash, limestone powder, blast furnace slag or the like Used as an extender. However, when blast furnace slag and cement are used in combination, long-term strength may increase due to the latent hydraulic properties of the slag. In general, the initial and long-term strength developability of the solidified material varies depending on the type of the target soil, and it is difficult to suppress the strength to allow re-excavation for all target soils. This is because when the moisture content of the target soil is high and the amount of solidifying material added to obtain the initial strength increases, the long-term strength tends to increase.

  In addition, the solidifying material composition described in Patent Document 4 has a large amount of addition necessary to obtain the required strength as compared with cement-based solidifying material, and is intended for soil with a high water content ratio such as viscous soil In particular, a large amount of addition is required. For this reason, there was still room for improvement in terms of processing costs.

  In view of such a situation, the present invention can obtain a predetermined solidification strength at an initial stage after the improvement work of the soft ground, and can sufficiently suppress the increase of the solidification strength thereafter, and can reduce the elution amount of hexavalent chromium from the improved ground. An object of the present invention is to provide a ground improvement method that can be made sufficiently small and a method for producing a solidified material for re-excavation used therefor.

The present invention has a hydraulic modulus (HM) of 2.20 to 2.35, a silicic acid ratio (SM) of 2.50 to 2.90 and an iron ratio (IM) of 2.50 to 3.50 and A solidified material for re-digging containing 83 to 93% by mass of cement clinker having a total chromium content of 30 to 70 mg / kg and 7 to 17% by mass of gypsum has a pozzolanic activity of 15 to 25% and a natural water content of mass. Provided is a ground improvement method comprising a step of adding and mixing 40 to 100 kg per 1 m ³ of target soil of 30 to 50% on a ratio basis.

  According to the above ground improvement method, the ratio of cement clinker and gypsum satisfying the above requirements is set within a predetermined range, and the soil with pozzolanic activity and natural water content is within a predetermined range is used as the target soil. After the construction, the initial solidification strength is sufficiently high, and thereafter the increase in solidification strength can be sufficiently suppressed. In addition, the elution amount of hexavalent chromium from the improved ground can be made sufficiently small.

According to the study by the present inventors, it is preferable to satisfy at least one of the following conditions from the viewpoint of obtaining the effect of the present invention more stably and highly.
(1) The hexavalent chromium content of the cement clinker is 20 to 45 mg / kg.
(2) The target soil is at least one selected from silt, sandy soil, and cohesive soil.
(3) The wet density of the target soil is 1.5 to 2.5 g / cm ³ .
(4) The target soil contains 0 to 20% by mass of gravel, 10 to 40% by mass of sand, and 50 to 80% by mass of fine particles.

  Moreover, this invention provides the manufacturing method of the solidification material for re-digging used for the said ground improvement method. That is, the method for producing a solidified material for re-digging according to the present invention comprises 1100 to 1300 kg of limestone, 150 to 400 kg of coal ash, 10 to 100 kg of construction generated soil, and 10 to 100 kg of sewage sludge per ton of cement clinker. A first mixing step of using 10 to 50 kg to obtain a mixture, a firing step of firing the mixture to obtain a cement clinker, and a second mixing step of mixing the cement clinker and gypsum to obtain a solidified material for re-excavation. Prepare. Cement clinker having a hydraulic modulus (HM) of 2.20 to 2.35, a silicic acid ratio (SM) of 2.50 to 2.90, and an iron ratio (IM) of 2.50 to 3.50 in the firing step. In the first mixing step, the mixing ratio of limestone, coal ash, construction generated soil and sewage sludge is adjusted. In the second mixing step, 83 to 93 parts by mass of cement clinker and 7 to 17 parts by mass of gypsum are mixed with 100 parts by mass of the solidified material for re-digging.

In order to obtain a cement clinker having an Al ₂ O ₃ content of 5.0 to 7.0 mass% and an Fe ₂ O ₃ content of 1.4 to 2.8 mass% in the firing step, the first It is preferable to adjust the mixing ratio of limestone, coal ash, construction generated soil, and sewage sludge in the mixing step.

  According to the present invention, a predetermined solidification strength can be obtained at the initial stage after improvement work on soft ground, and then the increase in solidification strength can be sufficiently suppressed, and the elution amount of hexavalent chromium from the improved ground can be sufficiently reduced. it can.

  Hereinafter, preferred embodiments of the present invention will be described. The solidification material for re-digging used in the ground improvement method according to this embodiment includes 83 to 93 mass% of cement clinker and 7 to 17 mass% of gypsum.

<Solidification material for re-digging>
(Cement clinker)
The cement clinker according to the present embodiment has an effect of imparting strength to the solidified ground. The cement clinker used has a hydraulic modulus (HM) of 2.20 to 2.35, a silicic acid ratio (SM) of 2.50 to 2.90, and an iron ratio (IM) of 2.50 to 3 in the cement clinker. .50 and the total chromium content is 30-70 mg / kg.

As described above, the hydraulic modulus (HM) of the cement clinker is 2.20 to 2.35, preferably 2.22 to 2.30, more preferably 2.24 to 2.29. More preferably, it is 2.25 to 2.28. When the hydraulic modulus (HM) is less than 2.20, it is difficult to obtain a predetermined strength when improving the soft ground, and when it exceeds 2.35, the calcination property of the cement clinker decreases. The hydraulic modulus (HM) of the cement clinker is calculated by the following formula (1).
HM = CaO / (SiO ₂ + Al ₂ O ₃ + Fe ₂ O ₃ ) (1)

As described above, the cement clinker has a silicic acid ratio (SM) of 2.50 to 2.90, preferably 2.55 to 2.80, more preferably 2.60 to 2.75. More preferably, it is 2.65 to 2.70. When the silicic acid ratio (SM) is less than 2.50, it is difficult to obtain a cement clinker having an appropriate composition, and when it exceeds 2.90, the production cost of the cement clinker increases. The silicic acid ratio (SM) of the cement clinker is calculated by the following formula (2).
SM = SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) (2)

As described above, the iron ratio (IM) of the cement clinker is 2.50 to 3.50, preferably 2.70 to 3.40, more preferably 2.80 to 3.30, Preferably it is 2.90-3.25. When the iron ratio (IM) is less than 2.50, the effect of reducing the total chromium content becomes small. From the viewpoint of improving the hexavalent chromium elution suppression, it is desirable that the iron ratio (IM) is as high as possible. However, when the iron ratio (IM) exceeds 3.50, it is difficult to prepare the raw material. The iron ratio (IM) of the cement clinker is calculated by the following formula (3).
IM = Al ₂ O ₃ / Fe ₂ O ₃ (3)

  The total chromium content of the cement clinker is 30 to 70 mg / kg as described above. Here, the total chromium content means the total content of all chromium having different valences such as trivalent chromium and hexavalent chromium contained in the cement clinker. The total chromium content is preferably as low as possible. However, when the total chromium content in the cement clinker is less than 30 mg / kg, the amount of industrial by-products and industrial waste as a raw material for cement clinker decreases, and the manufacturing cost of the cement clinker increases. On the other hand, if the total chrome content in the cement clinker exceeds 70 mg / kg, when solidifying volcanic ash clay such as Kanto Loam, the amount of hexavalent chromium eluted from the solidified soil may depend on the solidification conditions. May increase. The total chromium content in the cement clinker is preferably 40 to 65 mg / kg, more preferably 43 to 62 mg / kg, from the viewpoint of achieving both a sufficiently low production cost and a sufficiently low hexavalent chromium elution amount. More preferably, it is 45-61.

  The hexavalent chromium content in the cement clinker is preferably 20 to 45 mg / kg. As with the total chromium content, the hexavalent chromium content is preferably as low as possible. However, if the hexavalent chromium content in the cement clinker is less than 20 mg / kg, the amount of industrial by-products and industrial waste that can be used for the cement clinker raw material There is a tendency for manufacturing costs to increase. On the other hand, when the hexavalent chromium content in the cement clinker exceeds 45 mg / kg, the amount of hexavalent chromium eluted from the solidified soil depending on the solidification conditions when solidifying volcanic ash clay such as Kanto Loam. Tend to increase. The hexavalent chromium content in the cement clinker is preferably 25 to 40 mg / kg, more preferably 30 to 35 mg / kg from the viewpoint of achieving both a sufficiently low production cost and a sufficiently low elution amount of hexavalent chromium. Yes, and more preferably 30-33.

  The raw material basic unit per ton of cement clinker is preferably 1100 to 1300 kg of limestone, 150 to 400 kg of coal ash, 10 to 100 kg of construction generated soil, and 10 to 50 kg of sewage sludge. Here, the raw material basic unit per ton of cement clinker means the blending amount of raw materials for producing 1 ton of cement clinker.

  The manufacturing method of the cement clinker in the present embodiment includes a mixing step of preparing limestone, coal ash, construction generated soil, and sewage sludge at a predetermined mixing ratio, and in the mixing step, the hydraulic modulus (HM) of the cement clinker. ) Is 2.20 to 2.35, the silicic acid ratio (SM) is 2.50 to 2.90, and the iron ratio (IM) is 2.50 to 3.50. .

As described above, hydraulic modulus (HM), rate silicate (SM) and Tetsuritsu (IM) is a value calculated by the equation (1) ~ (3), Al 2 O contained in the cement clinker ₃ , determined by the amounts of Fe ₂ O ₃ , SiO ₂ and CaO. Therefore, when producing cement clinker, the contents of Al ₂ O ₃ , Fe ₂ O ₃ , SiO ₂ and CaO in limestone, coal ash, construction generated soil and sewage sludge are analyzed, and based on the analysis results, It is preferable to adjust the mixing ratio of limestone, coal ash, construction generated soil, and sewage sludge so that the hydraulic ratio (HM), silicic acid ratio (SM), and iron ratio (IM) are within the predetermined ranges.

  In the above mixing step, it is preferable to prepare 1 ton of cement clinker in a mixing ratio of 1100 to 1300 kg of limestone, 150 to 400 kg of coal ash, 10 to 100 kg of construction generated soil, and 10 to 50 kg of sewage sludge. .

In the above mixing step, as _Al 2 _{O 3} content in the cement clinker is 5.0 to 7.0 mass% and _Fe 2 _{O 3} content is 1.4 to 2.8 mass%, limestone It is preferable to adjust the blending ratio of coal ash, construction generated soil and sewage sludge.

When the content of Al ₂ O ₃ in the cement clinker is less than 5.0% by mass, it tends to be difficult to sufficiently reduce the total chromium content. When the content exceeds 7.0% by mass, the raw material is procured. In addition, raw material preparation tends to be difficult. The Al ₂ O ₃ content is more preferably 5.5 to 6.5% by mass, still more preferably 5.7 to 6.3% by mass, and even more preferably 5.9 to 6.2% by mass. %.

It is difficult to control the Fe ₂ O ₃ content in the cement clinker to less than 1.4% by mass, and the production cost increases. On the other hand, if the Fe ₂ O ₃ content exceeds 2.8% by mass, the Al ₂ O ₃ content needs to be 7.0% by mass from the above formula (3). In this case, it is difficult to procure raw materials and prepare raw materials, and the amount of liquid phase generated in the cement clinker increases, which tends to cause manufacturing inconvenience. The Fe ₂ O ₃ content in the cement clinker is more preferably 1.6 to 2.6% by mass, still more preferably 1.8 to 2.4% by mass, and still more preferably 1.9 to 2.2% by mass.

  The cement clinker of the present embodiment is characterized in that the amount of coal ash blended at the time of manufacturing the cement clinker is larger than that of a normal Portland cement clinker. The type of coal ash is not particularly limited, and is generated from, for example, a coal-fired power plant, and fly ash, bottom ash, and the like can be used.

  The amount of coal ash used for producing 1 ton of the cement clinker is dry basis, preferably 150 to 400 kg. When the amount of coal ash blended is less than 150 kg, the manufacturing cost increases, and the iron ratio (IM) of the cement clinker tends to be too small. When the amount exceeds 400 kg, blending of raw materials tends to be difficult. The amount of coal ash blended is more preferably 180 to 365 kg, still more preferably 210 to 330 kg, and even more preferably 240 to 335 kg.

  The blending amount of limestone per ton of the cement clinker is preferably 1100 to 1300 kg on a dry basis. When the blending amount of limestone is less than 1100 kg, a predetermined hydraulic modulus is difficult to obtain, and when it exceeds 1300 kg, the calcination property is remarkably lowered. The blending amount of limestone is more preferably 1170 to 1290 kg, still more preferably 1230 to 1280 kg, and still more preferably 1235 to 1270 kg.

  The amount of construction generated soil per ton of the cement clinker is preferably 10 to 100 kg on a dry basis. In addition, as said construction generation | occurrence | production soil, the soil etc. which generate | occur | produce as a by-product in building construction, civil engineering, etc. are mentioned, for example. The amount of construction generated soil is more preferably 12 to 90 kg, still more preferably 14 to 80 kg, and still more preferably 16 to 70 kg.

  The preparation amount of sewage sludge per ton of the cement clinker is preferably 10 to 50 kg on a dry basis. The preparation amount of sewage sludge is more preferably 12 to 48 kg, still more preferably 14 to 46 kg, and still more preferably 16 to 44 kg.

  The cement clinker according to the present embodiment has good initial strength development, and the amount of cement clinker for obtaining a predetermined strength in the initial stage can be reduced, so that the increase in long-term strength due to the progress of the pozzolanic reaction can be suppressed. It is advantageous. Moreover, since the elution amount of hexavalent chromium from the solidified soil is caused by the chromium content in the cement clinker, it is advantageous that the amount of hexavalent chromium in the cement clinker is small or the amount of cement clinker is small.

  The cement clinker content of the solidified material for re-digging is 83 to 93% by mass, preferably 85 to 91% by mass, more preferably 87 to 90% by mass, based on the total mass of the solidified material for re-digging. More preferably, it is 88-89 mass%. If the cement clinker content is less than 83% by mass, the amount of solidification material added to obtain a predetermined solidification strength is likely to increase. If it is more than 93% by mass, it is necessary to obtain a predetermined solidification strength in soil with a high water content ratio. There is a possibility that the amount of solidification material added increases and the strength increases with long-term aging.

(Gypsum)
As the gypsum to be added to the solidified material for re-digging, one or more kinds selected from anhydrous gypsum, half-water gypsum and 2-water gypsum can be mixed and used. Gypsum has the role of generating a large amount of ettringite, which is a hydrate of cement, and increasing the solidification strength. Of these, anhydrous gypsum is preferred. Anhydrous gypsum produces ettringite, which is a hydrate of cement, in a large amount at the initial age, so it is advantageous that a small amount of solidifying material is added even to soil with a high water content.

  The gypsum content of the solidified material for re-digging is 7 to 17% by mass, preferably 9 to 15% by mass, more preferably 10 to 13% by mass, based on the total mass of the solidified material for re-digging. Yes, more preferably 11 to 12% by mass. If the gypsum content is less than 7% by mass, the amount of solidification material added to obtain a predetermined solidification strength in a soil with a high water content ratio increases, and there is a risk that the strength will increase with long-term aging. On the other hand, if the gypsum content is more than 17% by mass, the amount of solidifying material added to obtain a predetermined solidification strength tends to increase.

  The solidified material for re-digging according to the present embodiment may contain a hydration accelerator in order to suppress cement hydration reaction in a long-term age. As the hydration accelerator, for example, general cement accelerators such as sodium carbonate and potassium sulfate can be used. The total amount of cement clinker and gypsum in the solidified material for re-digging is preferably 90.0 to 99.9% by mass, more preferably 93.0 to 10%, based on the total mass of the solidified material for re-digging. It is 99.9 mass%.

  Since the solidified material for re-digging can be prepared by mixing powdery raw materials, no special equipment or means is required for the preparation. Therefore, the said solidification material can be obtained using the apparatus (for example, mixer) for well-known powder mixing.

<Ground improvement method>
In the ground improvement method according to the present embodiment, 40 to 100 kg of the above-mentioned solidification material for re-digging is added to 1 m ³ of the target soil having a pozzolanic activity of 15 to 25% and a natural water content of 30 to 50%, a backhoe, etc. The process of mixing using is provided.

  In the solidified material using cement as a hydraulic material, when calcium hydroxide is liberated by hydration of the cement, the pozzolanic reaction with the soil proceeds and the long-term strength is enhanced. In addition, as the amount of cement increases, the amount of free calcium hydroxide increases and promotes the pozzolanic reaction. The higher the moisture content of the target soil, the more the amount of solidifying material added must be increased in order to obtain a predetermined strength in the initial stage, and as a result, the pozzolanic reaction proceeds. For this reason, the said solidification material for re-digging cannot obtain a desired intensity | strength characteristic with respect to all the soils. That is, it is one of the points of the present invention to use a predetermined amount of the solidification material for re-digging for the target soil having a predetermined range of pozzolanic activity and natural water content.

  Here, the pozzolanic activity of soil is described in “Pozora activity of fly ash in recent years and its rapid quantification method”: Takakura, Ikuno, Shirakata; 43rd Cement Technology Conference Lecture, pp 212-217, 1989. It is the value measured by applying the method for measuring the pozzolanic activity of the fly ash applied to the soil. The measurement method is specifically as follows.

The target soil is pulverized after oven drying at 110 ° C. for 24 hours, 0.2 g of this pulverized target soil, 0.2 g of quick lime and 20 ml of pure water are placed in a pressure vessel, shaken sufficiently, and then heated to 120 ° C. Leave it in the dryer for 4.5 hours. After cooling this to room temperature, the contents are taken out while washing the inside of the pressure vessel with 120 ml of 0.2N hydrochloric acid, filtered through a 0.45 μm membrane filter, and Si, Al and Fe in this filtrate are analyzed by atomic absorption spectrometry. The mass% per dry soil is determined, and the total value (SiO ₂ mass% + Al ₂ O ₃ mass% + Fe ₂ O ₃ mass%) is defined as the pozzolanic activity of the soil.

As described above, the pozzolanic activity of the target soil is 15 to 25%, preferably 17 to 24%, more preferably 19 to 23%, and still more preferably 20 to 22%. If pozzolanic activity of the soil is less than 15%, solidifying material amount for obtaining a predetermined intensity in the early ages is generally the lowest solidifying material amount of the target soil 1 m ³ per 50kg follows becomes ground improved in construction is not It may be uniform. On the other hand, if the pozzolanic activity of the soil exceeds 25%, it is necessary to add 60 kg or more of solidifying material in order to obtain a predetermined strength at the initial age, and due to the pozzolanic reaction between the soil and the solidifying material in the long-term age, Long-term aging strength may increase and re-digging may become difficult.

As described above, the amount of the solidification material for re-excavation with respect to 1 m ³ of the target soil is 40 to 100 kg, preferably 45 to 80 kg, more preferably 50 to 70 kg, and further preferably 52 to 60 kg. is there. If the amount of solidification material for re-digging is less than 50 kg, the improved ground may be uneven. If it exceeds 60 kg, the long-term strength of the long-term age will be increased due to the pozzolanic reaction between the soil and the solidified material in the long-term age. It may increase and it may be difficult to re-dig.

As described above, the natural water content of the target soil is 30 to 50%, preferably 35 to 49%, more preferably 40 to 49%, and still more preferably 43 to 49%. In the present invention, the preferable range of the natural water content ratio of the target soil is defined because the present inventors have found that the pozzolanic activity of the soil is correlated with the natural water content ratio of the soil. If the natural water content ratio of the soil is less than 30%, solidifying material amount for obtaining a predetermined intensity in the early ages is generally the lowest solidifying material amount of the target soil 1 m ³ per 50kg follows becomes ground improved in construction is not It may be uniform. On the other hand, if the natural moisture content of the soil exceeds 50%, it is necessary to add 60 kg or more of solidifying material in order to obtain a predetermined strength at the initial age, and due to the pozzolanic reaction between the soil and the solidifying material in the long-term age, Long-term aging strength may increase and re-digging may become difficult.

  Here, the natural moisture content of the soil is the moisture content that the soil holds in its natural state, and is measured by JIS A 1203: 1999 “Soil moisture content test method”.

The target soil is at least one selected from silt, sandy soil and cohesive soil, and preferably has a specific wet density and particle size. The wet density of the target soil is preferably 1.5 to 2.5 g / cm ³ , more preferably 1.7 to 2.3 g / cm ³ , and still more preferably 1.8 to 2.2 g / cm ^3. It is. Here, the wet density is a mass per unit volume of the soil, and is measured by JIS A 1225: 2000 “Method for testing wet density of soil”.

  The target soil is preferably a soil containing gravel, sand and fine particles. The gravel content is 0 to 20% by mass, preferably 5 to 15% by mass, and more preferably 5 to 10% by mass.

  The sand content is 10 to 40% by mass, preferably 20 to 35% by mass, and more preferably 25 to 30% by mass.

  The fine particle content is 50 to 80% by mass, preferably 55 to 75% by mass, and more preferably 60 to 70% by mass.

  Here, the amount of gravel, sand and fine particles contained in the target soil is the distribution of the soil particle diameter expressed as a percentage by mass, according to JIS A 1204: 2000 “Soil Particle Size Test Method”. taking measurement.

  If it is the range of the wet density of the above-mentioned soil and a particle size, moderate intensity | strength will be obtained at the early age of age, subsequent strength increase is small, and it can re-dig.

  Hereinafter, specific examples will be shown and the present invention will be described in more detail. However, the present invention is not limited to these examples.

(1) Manufacture and analysis of cement clinker First, the raw materials of cement clinker used in each example and each comparative example (limestone, meteorite, blast furnace dust, copper gravel, coal ash, construction generated soil, sewage sludge, deiron slag, The chemical composition of incineration ash was determined. Table 1 shows the chemical composition of each raw material.

  Using the raw materials described above, adjusting the raw material basic unit so that the hydraulic modulus (HM), the silicic acid rate (SM), and the iron rate (IM) become predetermined values, the cement clinkers K1 and K2 are respectively Prepared. Specifically, the cement clinker was prepared as follows.

  First, the above-described raw materials were dried and pulverized at 250 to 300 ° C. until a predetermined particle size was obtained using a vertical mill. Thereafter, the dried and crushed raw material was fed from above the suspension preheater, preheated and calcined in the preheater, and fired in a rotary kiln at a high temperature of about 1450 ° C. Then, cement clinker K1 and K2 were prepared by quenching with a cooler.

  Table 2 and Table 3 show the raw material basic units and main chemical compositions of the cement clinker K1 and K2. The chemical composition of the cement clinker was measured according to JIS R 5202: 1999 “Chemical analysis method of Portland cement”. F. The amount of CaO was measured according to JCAS I-01: 1997 “Method for Quantifying Free Calcium Oxide” of the Cement Association Standard Test Method.

From the chemical compositions of the cement clinker K1 and K2 in Table 3 above, the hydraulic modulus (HM), silicic acid rate (SM) and iron rate (IM) were calculated by the following formulas (1) to (3). The values are shown in Table 4.
HM = CaO / (SiO ₂ + Al ₂ O ₃ + Fe ₂ O ₃ ) (1)
SM = SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) (2)
IM = Al ₂ O ₃ / Fe ₂ O ₃ (3)

Table 4 also shows the total chromium content and hexavalent chromium content in the cement clinker K1 and K2. The total chromium content in the cement clinker was measured in accordance with JCAS I-52 “Analyzing Method of Trace Components in Cement by ICP Emission Spectroscopic Analysis and Electric Heating Atomic Absorption Spectroscopy” of the Cement Association Standard Test Method. Further, the hexavalent chromium content in the cement clinker is determined by dissolving the cement clinker in ethylenediaminetetraacetic acid disodium (EDTA) solution adjusted to pH 13 to obtain trivalent chromium in the cement clinker as chromium hydroxide (Cr (OH) ₃ ) Precipitation (solubility product (22 ° C.): 6.3 × 10 ⁻³¹ ) as ₃ ), and measurement was performed using the property that only hexavalent chromium remains in the solution. An ICP emission spectroscopic analyzer was used for the quantification of hexavalent chromium.

(2) Preparation of cement-based solidification material (solidification material for re-digging) A solidified material was prepared by mixing the trially produced K1 or K2 cement clinker and hydrofluoric acid anhydrous gypsum manufactured by Central Glass Co., Ltd.

(3) Target soil Table 5 shows the properties of the target soil.

(4) Soil pozzolanic activity test The target soil was pulverized after oven drying at 110 ° C. for 24 hours, and 0.2 g of this pulverized target soil, 0.2 g of quicklime and 20 ml of pure water were placed in a pressure vessel and shaken thoroughly. After that, it was left in a dryer heated to 120 ° C. for 4.5 hours. After cooling this to room temperature, the contents are taken out while washing the inside of the pressure vessel with 120 ml of 0.2N hydrochloric acid, filtered through a 0.45 μm membrane filter, and Si, Al and Fe in this filtrate are analyzed by atomic absorption spectrometry. To determine the mass% per dry soil. The total value of these (SiO ₂ mass% + Al ₂ O ₃ mass% + Fe ₂ O ₃ mass%) was defined as the pozzolanic activity of the soil.

(5) Solidification test To the target soil shown in Table 5, after adding the solidification material prepared in (2) and mixing with a Hobart mixer for 3 minutes, JCAS L-01: 2006 “cement system for sandy soil and silt According to JGS 0821-2000 “Test specimen preparation method without stabilizing compacted soil” for viscous soil (1) and viscous soil (2) A cylindrical specimen of × 10 cm was produced. The specimen was sealed with a polywrap, cured at room temperature of 20 ° C. and a humidity of 90%, and uniaxial compressive strength was measured at a predetermined age according to JIS A1216 “Soil Uniaxial Compression Test Method”. Here, the target strength of the solidified soil is uniaxial compressive strength of 300 kN / m ² or more required for general roadbed or temporary improvement, and long-term material age of 28 to 365 days at material age of 7 days. Then, it was 1 to 1.5 times the strength of the material 7 days old.

Usually, in the solidifying material blending design, soil and solidifying material are mixed in a room to produce a solidified soil, the strength is measured, and the amount of solidifying material added to obtain the required strength is determined. However, since the mixing accuracy is different from the actual construction, the site / indoor strength ratio of 0.5 is often used for designing. That is, the design strength if 300 kN / ^{m 2,} sets the solidifying material amount, such as strength of 600 kN / ^{m 2} is obtained. In that case, the improved ground has an average strength of 300 kN / m ² . Since the target value of the long-term material age strength in the present invention is assumed to be a portion where the strength is increased, the target value is set to 1 to 1.5 times the material age 7 days.

(6) Elution test of hexavalent chromium from solidified soil After preparing the solidified soil and sealing and curing as in (5), the Environment Agency Notification No. 46 (August 23, 1991) at 7 days of age The elution test was conducted according to the above, and the hexavalent chromium was quantified by diphenylcarbazide spectrophotometry of the filtrate after shaking. The target value of the hexavalent chromium elution amount was set to 0.05 mg / L or less which is the elution amount standard defined in the Soil Contamination Countermeasures Law.

  The results are shown in Table 6.

As shown in Example 1, the solidified material composed of trial cement clinker K1 and gypsum had an age of 7 by adding 52 kg of solidified material per 1 m ³ of soil when the pozzolanic activity of the soil was within the range of the present invention. It can be seen that a uniaxial compressive strength of 300 kN / m ² is obtained per day, and thereafter the solidification strength of the material age 28 to 365 is 1.5 times or less of the material age 7 days.

On the other hand, as shown in Comparative Examples 1 and 3, when the pozzolanic activity of the soil is lower than the range of the present invention, the required amount of the solidifying material for obtaining the target strength at the age of 7 days is 50 kg which is the minimum solidifying material addition amount. / M ³ or less. As shown in Comparative Example 2, when 50 kg per 1 m ^{3 of} soil, which is the minimum solidification material addition amount, is added to sandy soil whose pozzolanic activity is below the range of the present invention, re-excavation becomes difficult at 7 days of age. It exceeds the uniaxial compressive strength of 1000 kN / m ² . Moreover, as shown in Comparative Example 5, when the pozzolanic activity of the soil is higher than the range of the present invention, the solidification strength at ages 186 and 365 is 1.5 times or more at the age 7 days. Furthermore, as shown in Comparative Example 5, when the pozzolanic activity of the soil is higher than the range of the present invention, the solidification strength of the long-term age becomes 1.5 times or more of the age of 7 days.

  The elution amount of hexavalent chromium from the solidified soil is 0.05 mg / L or less of the environmental standard for the solidified material composed of the trial cement clinker K1 and gypsum shown in Example 1, whereas in Comparative Example 4, It can be seen that the solidified material composed of the trial cement clinker K2 and gypsum shown exceeds the environmental standard of 0.05 mg / L.

Claims (7)

In the cement clinker, the hydraulic modulus (HM) is 2.20 to 2.35, the silicic acid rate (SM) is 2.50 to 2.90, and the iron rate (IM) is 2.50 to 3.50. A solidification material for re-digging containing 83 to 93% by mass of cement clinker having a chromium content of 30 to 70 mg / kg and 7 to 17% by mass of gypsum has a pozzolanic activity of 15 to 25% and a natural moisture content of 30 to 30%. A ground improvement method comprising a step of adding and mixing 40 to 100 kg per 1 m ^{3 of} 50% target soil.   The ground improvement method of Claim 1 whose hexavalent chromium content of a cement clinker is 20-45 mg / kg.   The ground improvement method according to claim 1 or 2, wherein the target soil is at least one selected from silt, sandy soil, and cohesive soil. The ground improvement method as described in any one of Claims 1-3 whose wet density of object soil is 1.5-2.5 g / cm < ³ >.   The ground improvement method according to any one of claims 1 to 4, wherein the target soil contains 0 to 20 mass% of gravel, 10 to 40 mass% of sand, and 50 to 80 mass% of fine particles. A first mixing step of obtaining a mixture using 1100 to 1300 kg of limestone, 150 to 400 kg of coal ash, 10 to 100 kg of construction generated soil, and 10 to 50 kg of sewage sludge on a dry basis per ton of cement clinker;
A firing step of firing the mixture to obtain a cement clinker;
A second mixing step of mixing the cement clinker and gypsum to obtain a solidified material for re-digging;
With
In the firing step, the hydraulic ratio (HM) is 2.20 to 2.35, the silicic acid ratio (SM) is 2.50 to 2.90, and the iron ratio (IM) is 2.50 to 3.50. In order to obtain a cement clinker having a total chromium content of 30 to 70 mg / kg, the mixing ratio of limestone, coal ash, construction generated soil and sewage sludge is adjusted in the first mixing step,
The manufacturing method of the solidification material for re-digging which mixes cement clinker 83-93 mass parts and 7-17 mass parts of plaster with 100 mass parts of solidification materials for re-digging in the said 2nd mixing process. In order to obtain a cement clinker having an Al ₂ O ₃ content of 5.0 to 7.0 mass% and an Fe ₂ O ₃ content of 1.4 to 2.8 mass% in the firing step, the first The method for producing a solidified material for re-digging according to claim 6, wherein the mixing ratio of limestone, coal ash, construction generated soil, and sewage sludge is adjusted in the mixing step.