JP4271676B2 - Premix powder cement composition for ground improvement - Google Patents

Description

  Conventionally, as a ground improvement method in soft ground improvement construction, a jet grout method in which cement milk is jetted deeply into the ground and mixed with soil has been adopted. This is because multiple pipes are inserted into the ground, and while rotating the pipes, cement milk is injected into the ground at high pressure from the vicinity of the tip of these pipes to cut the soil in the ground. This is a method of stabilizing the ground by replacing the ground with slime while discharging the mixed soil cement slurry (hereinafter referred to as slime) to the ground. However, when clay-rich clay or clay is mixed with cement milk, the soil particles and cement aggregate to lose fluidity, the viscosity increases greatly, and the injection becomes incomplete, cutting the ground. There was a problem that the slime generated at the time was not discharged to the ground, which hindered ground improvement work. Therefore, as a result of adding water so that the slime can easily rise on the ground or increasing the injection rate of cement milk into the ground, the amount of slime increases as construction sludge, and the processing cost is reduced. There was a problem of increasing.

  On the other hand, the cement milk to be injected is usually manufactured at or near the construction site by adding a cement-based solidifying material and an admixture of water and liquid. There was a problem that the work became complicated.

  For this reason, a premix type powder solidifying material that has been dry-mixed in advance with a cement-based solidified powder additive that can give the slime excellent fluidity and reduce the slime viscosity is strongly desired. ing. The present invention relates to a premix powder cement composition for ground improvement that can meet such a demand.

  Conventionally, methods using various additives are known as techniques for reducing the viscosity of slime (see, for example, Patent Documents 1 to 9). However, these conventional methods have a problem that they cannot sufficiently meet the above-described requirements. In addition, it is known that a liquid dispersant for cement is mixed with an inorganic fine powder to form a powder dispersant (see, for example, Patent Documents 10 to 12). However, all of the conventionally proposed dispersants for cement are intended for the cement concrete field, and are not effective in dispersing soil for the purpose of improving the ground. There is a problem that you can not.

Japanese Patent Laid-Open No. 6-256056 Japanese Patent Publication No. 6-4875 Japanese Patent Publication No. 7-96675 JP-A-10-95976 JP-A-11-254425 Japanese Patent Laid-Open No. 11-256161 JP 2001-172629 A JP 2004-143041 A Japanese Patent Laid-Open No. 2004-175989 Japanese Patent No. 2666961 Japanese Patent Laid-Open No. 10-45451 Japanese Patent No. 3619196

  The problem to be solved by the present invention is a process of using a ground improvement method, particularly a jet grout method, and cutting and mixing the ground in a short time by spraying compressed air and cement milk while rotating into the ground at ultra high pressure. 1) Premix powder cement for ground improvement that can simultaneously satisfy 1) improving the fluidity of the slime to ensure sufficient workability, and 2) ensuring the required predetermined early strength. It is in providing the composition.

  As a result, the present inventors have studied to solve the above-mentioned problems. As a result, the ground improvement agent containing a predetermined amount of a powder additive composed of a mixture of a specific vinyl copolymer aqueous solution and porous silica fine powder. We have found that a premix powder cement composition is correctly suitable.

That is, the present invention is a ground improvement powder additive (hereinafter also referred to as a powder additive) in which 25 to 75% by mass of the following A component and 75 to 25% by mass (100% by mass in total) of the following B component are mixed. Is a premix powder cement composition for ground improvement, characterized by containing 0.2 to 10 parts by mass with respect to 100 parts by mass of the cement-based solidified material.
Component A: an aqueous solution comprising a vinyl copolymer having a mass average molecular weight of 2000 to 50000 obtained by alkaline hydrolysis of a copolymer of olefin having 3 to 8 carbon atoms and maleic anhydride, and having a solid content concentration of 10 to 80% by mass Component B: porous silica fine powder

  The premix powder cement composition for ground improvement according to the present invention described above is easy to manage in the field work of ground improvement work, and in particular 50 fine particles having a ground soil particle diameter of 75 μm or less. Remarkable fluidity can be imparted to soil containing a large amount of fine particles, that is, containing 20% by mass or more of clay or silt of 5 μm or less, that is, highly viscous soil. As a result, it is not necessary to increase the injection rate of cement milk into the ground, or it can be reduced as necessary, so that it is possible to suppress the generation amount of slime that becomes construction sludge, and at the same time, cement milk and soil By promoting the uniform mixing property, it is possible to sufficiently develop the initial strength and long-term strength of the ground improved soil necessary for ensuring workability.

  The powder additive in the present invention comprises an A component and a B component. The component A is an aqueous solution of a vinyl copolymer obtained by alkaline hydrolysis of a copolymer of an olefin having 3 to 8 carbon atoms and maleic anhydride. Examples of the olefin having 3 to 8 carbon atoms include propylene, n-butene, isobutylene, n-pentene, cyclopentene, 2-methyl-1-butene, n-hexene, 2-methyl-1-pentene and 3-methyl- Examples thereof include 1-pentene, 4-butyl-1-pentene, 2-ethyl-1-butene, 1-octene, diisobutylene, and mixtures thereof, among which olefins having 4 carbon atoms are preferable, and isobutylene is particularly preferable.

A copolymer of an olefin having 3 to 8 carbon atoms and maleic anhydride can be obtained by a known method. For example, ethylbenzene, maleic anhydride, a radical chain transfer agent and a radical initiator as a solvent are charged into an autoclave, the reaction system is purged with nitrogen, and an olefin having 3 to 8 carbon atoms is injected, and the pressure is 0 to 60 to 120 ° C. The copolymer can be obtained as a precipitate by radical copolymerization reaction for 2 to 10 hours under the condition of 2 to 0.5 N / mm ² .

  In order to obtain a desired copolymer, the type and amount of radical initiator and radical chain transfer agent, the type and amount of solvent, polymerization temperature, polymerization time and the like are appropriately selected. Examples of the radical initiator used here include azo initiators such as azobisisobutyronitrile and 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), benzoyl peroxide, lauroyl peroxide, Non-aqueous initiators such as cumene hydroperoxide are listed.

  In the copolymer of olefin having 3 to 8 carbon atoms and maleic anhydride, the copolymerization ratio of both is olefin having 3 to 8 carbon atoms / maleic anhydride = 45 to 55/55 to 45 (molar ratio). Preferably, the ratio is close to 50/50 (molar ratio).

  The vinyl copolymer contained in the aqueous solution of the component A is obtained by alkaline hydrolysis of the copolymer of olefin having 3 to 8 carbon atoms and maleic anhydride described above. As the alkali when alkali-hydrolyzing the copolymer of olefin having 3 to 8 carbon atoms and maleic anhydride, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide are preferable, Such an aqueous solution of an alkali metal hydroxide is more preferable, and an aqueous sodium hydroxide solution is particularly preferable from an industrial standpoint. Further, the water-soluble vinyl copolymer contained in the aqueous solution of the component A may be a partially neutralized product obtained by alkaline hydrolysis of a copolymer of olefin having 3 to 8 carbon atoms and maleic anhydride, or a completely neutralized product. It may be.

  The vinyl copolymer in the aqueous solution of the vinyl copolymer as the component A has a mass average molecular weight of 2000 to 50000, but preferably 3000 to 35000. Here, the mass average molecular weight means a pullulan-converted mass average molecular weight measured by gel permeation chromatography (hereinafter simply referred to as GPC method).

  A component contains 10-80 mass% of said vinyl copolymers by solid content concentration.

The porous silica fine powder used as the component B is amorphous silicic acid having a composition of SiO ₂ · nH ₂ O. As the porous silica fine powder, what is called wet silica, in which water glass is neutralized with an acid such as hydrochloric acid, and the deposited precipitate is washed with water and dried to form a powder, is preferable. Among these porous silica fine powders, the component B preferably has a specific surface area of 50 to 450 m ² / g and an average particle size of 0.1 to 500 μm, and particularly oil absorption (JIS-K5101-19). (The amount of oil absorption by A) exceeds 100 ml / 100 g.

  The powder additive in the present invention comprises the A component and the B component described above, and comprises 25 to 75% by mass of the A component and 75 to 25% by mass of the B component (total 100% by mass). What consists of A component 55-65 mass% and B component 45-35 mass% (total 100 mass%) is preferable. A component is an aqueous solution of a vinyl copolymer, but by simply mixing the A component and the B component at room temperature, a dry and crushed, non-blocking, smooth feel and uniform powder additive is obtained. This is to obtain a premix powder cement composition capable of imparting excellent fluidity and initial strength to the cement-based solidified material to which a predetermined amount thereof is added.

  The powder additive according to the present invention can be produced by first charging the B component and then charging the A component little by little into a mixer equipped with stirring blades. The product is usually a powder having a particle size of 3000 μm or less, but when such a powder additive is used in a premix powder cement product, it is preferable that the particle size is uniform, and the particle size is 2000 μm. It is preferable to classify using a classifier such as a sieve so that the average particle size is 1 to 1500 μm.

  Examples of the cement-based solidifying material used in the present invention include various portland cements such as ordinary portland cement, early-strength cement, ultra-early-strength cement, medium-heated cement, mixed cement such as blast furnace cement, fly ash cement, and silica cement. One of these can be used alone, or a mixture of two or more can be used as appropriate. Although not limited, usually Portland cement or blast furnace cement is usually used. In addition, fine powder admixtures such as blast furnace slag fine powder, fly ash, silica fume, limestone fine powder and gypsum may be contained within a range of 70% by mass or less of various Portland cements.

  The premix powder cement composition for ground improvement according to the present invention contains the powder additive described above in a proportion of 0.2 to 10 parts by mass with respect to 100 parts by mass of the cement-based solidified material. When the amount is less than 0.2 parts by mass, the fluidity is insufficient. On the other hand, when the amount exceeds 10 parts by mass, the setting delay is increased and the initial strength is lowered, and the intended sufficient effect cannot be obtained. Preferably, it contains in the ratio of 1.0-6.0 mass parts. Furthermore, it is more preferable to select appropriately within the range of the content ratio as described above in relation to the properties of the soil.

  Moreover, when using the premix powder cement composition for ground improvement which concerns on this invention, another agent can be used together purposefully. Examples of such other agents include antifoaming agents, preservatives, setting retarders, setting accelerators, and waterproofing agents.

  Next, the usage method of the premix powder cement composition for ground improvement of this invention is demonstrated. That is, basically, the ground improvement premix powder cement composition of the present invention containing the ground improvement powder additive in a predetermined ratio is 100 to 300%, preferably 125 to 100% of its mass using a mixer. This is a method of preparing a ground improvement premix powder cement composition slurry by mixing with 275% kneaded water, pouring the slurry into the ground to be improved, mixing, and curing. In the jet grouting method, usually 0.3 to 1.5 times the volume of the soil to be improved, preferably 0.5 to 1.2 times the volume of cement milk is injected into the ground using a high-pressure pump.・ Used after being jetted and mixed.

  Hereinafter, in order to make the configuration and effects of the present invention more specific, examples and the like will be described. However, the present invention is not limited to the examples. In the following examples and the like, unless otherwise indicated,% means mass%, and part means mass part.

(1) Test Category 1 (Synthesis of vinyl copolymer in component A of ground additive powder additive)
<Synthesis of vinyl copolymer (a-1)>
A 2-liter autoclave was charged with 98 g (1 mol) of maleic anhydride, 640 g of ethylbenzene as a solvent, 0.6 g of 3-mercaptopropionic acid as a molecular weight regulator, and 2 g of azobisisobutyronitrile as a polymerization initiator while stirring. After uniformly dissolving, the atmosphere was replaced with nitrogen. Next, after 59 g (1.05 mol) of isobutylene was injected, the temperature of the reaction system was heated to 85 ° C., and the radical polymerization reaction was continued for 6 hours while maintaining the temperature at 85 ° C. to complete the reaction. After the completion of the polymerization reaction, the temperature of the reaction system was cooled to room temperature, and after deaeration, stirring was stopped and the precipitated polymer was taken out, filtered and dried to obtain 141 g of a light yellow powdery polymer. As a result of analysis, it was an isobutylene and maleic anhydride copolymer having a composition ratio of maleic anhydride / isobutylene = 50/50 (molar ratio). Next, 50 g of this copolymer, 51 g of a 30% aqueous sodium hydroxide solution and 20 g of tap water are placed in a flask equipped with a stirrer and a cooling condenser, heated with stirring to dissolve uniformly, and both isobutylene and maleic anhydride are mixed. A vinyl copolymer aqueous solution having a solid content concentration of 50% by mass comprising a salt (a-1) of an alkali hydrolyzate of the polymer was obtained. When the molecular weight of this was measured by GPC, the mass average molecular weight was 19500 (in pullulan conversion).

<Synthesis of vinyl copolymers (a-2) to (a-4) and (ar-1) to (ar-3)>
In the same manner as in the synthesis of (a-1), salts (a-2) to (a-4) and (ar-1) of alkali hydrolysates of olefins having 3 to 8 carbon atoms and maleic anhydride copolymer are used. ) To (ar-3) were synthesized to obtain a vinyl copolymer having a solid concentration of 50% by mass. The contents of the vinyl copolymer synthesized above are shown in Table 1.

In Table 1,
* 1: Type of monomer that forms the structural unit * 2: Isobutylene * 3: Mixture of isobutylene / 1-pentene = 60/40 (molar ratio) * 4: Diisobutylene

(2) Test Category 2 (Manufacture of powder additives for ground improvement)
<Production Example 1> Production of ground additive powder additive (M-1) 4 kg of porous silica fine powder (Tokuyama NR manufactured by Tokuyama Corporation, specific surface area 180 m ² / g, average particle size 85 μm) as component B The ribbon mixer was charged. Next, 6 kg of an aqueous solution of a vinyl copolymer (a-1) having a solid content concentration of 50% by mass as component A was added in portions while stirring into the ribbon mixer and mixed thoroughly, and then using a sieve. Classification was performed to obtain 10 kg of a ground additive powder additive (M-1) having a particle size of less than 500 μm and an average particle size of 90 μm.

<Production Examples 2 to 6 and Comparative Production Examples 1 to 3> Production of (M-2) to (M-6) and (R-1) to (R-5) Powder additive for ground improvement of Production Example 1 ( In the same manner as in the preparation of M-1), powder additives for ground improvement (M-2) to (M-6) and (R-1) to (R) in Production Examples 2 to 6 and Comparative Production Examples 1 to 5 were used. -5) was obtained. Table 2 summarizes the contents of the ground improvement powder additives prepared in the above examples.

In Table 2,
・ A-1 to a-4: Vinyl copolymer synthesized in test category 1 ・ The average particle size is a powder photograph taken with a scanning electron microscope, and 100 particles are arbitrarily selected from this photographed image. The long diameter (longest diameter d1 passing through the center of the particle) and short diameter (shortest diameter d2 passing through the center of the particle) were measured for each selected particle, and the average value of (d1 + d2) / 2 was obtained.
Since Comparative Examples 4 and 5 did not become powdery, the average particle size was not measured.
* 5: The vinyl copolymer is used as an aqueous solution with a solid content concentration of 50% by mass.
* 6: Silica fume fine powder with specific surface area of 20 m ² / g and average particle diameter of 0.3 μm * 7: Calcium carbonate fine powder with specific surface area of 0.8 m ² / g and average particle diameter of 2.5 μm

(3) Test category 3 (production of premix powder cement composition for ground improvement)
<Production Examples 7 to 18 and Comparative Production Examples 6 to 12> (PM-1) to (PM-12) and (PR-1) to (PR-7)
Among the ground improvement powder additives manufactured in Test Category 2, those in a state of powder were used. The cement-based solidified materials are ordinary Portland cement (NC, density = 3.16 g / cm ³ , the same shall apply hereinafter), and ordinary Portland cement 30% by mass and blast furnace cement B type (BB, density = 3.04 g / cm ³ , hereinafter not applicable). Same) 70% by weight of a mixture (NC + BB, total 100% by weight) was used. First, 1000 parts of cement-based solidification material is put into a 2 L Hobart mixer, and then the ground improvement powder additive produced in Test Category 2 is added in a range of 10 to 60 parts, and dry mixed to the ground. An improved premix powder cement composition was prepared. The obtained ground improvement premix powder cement composition is summarized in Table 3.

In Table 3,
・ NC: Ordinary Portland cement ・ NC + BB: Mixture consisting of 30% by mass of ordinary Portland cement and 70% by mass of blast furnace cement type B

(4) Test category 4 (Preparation and evaluation of premix powder cement composition slurry for ground improvement)
Using the ground improvement premix powder cement composition prepared in Test Category 3, a slurry was prepared and evaluated as follows.
<Examples 1-9 and Comparative Examples 3-8> Formulation Nos. Listed in Table 4 using premix powder cement compositions for ground improvement. Ground improvement cement composition slurry according to 1 or 2 The ground improvement premix powder cement composition and water described in Table 3 were weighed according to Table 4, and mixed in a Hobart mixer to prepare cement milk. To this cement milk, 1630 g of excavated soil (Osaka Marine Clay) having physical properties shown in Table 5 was added and mixed to prepare a ground improved cement composition slurry.
About the prepared ground improvement cement composition slurry, the viscosity of this slurry and the uniaxial compressive strength of the hardened | cured material of this slurry were measured, and the result was shown in Table 6.

<Comparative Examples 1-2> The premix powder cement composition for ground improvement is not used. Preparation of ground improvement cement slurry by 3 or 4 Ordinary Portland cement or a mixture of 30% by weight of ordinary Portland cement and 70% by weight of Blast Furnace Cement B and water are weighed according to Table 4 and placed in a Hobart mixer and mixed uniformly. Cement milk was prepared. To this cement milk, 1630 g of excavated soil (Osaka Marine Clay) having physical properties shown in Table 5 was added and mixed to prepare a ground improved cement slurry.
About the prepared ground improvement cement composition slurry, the viscosity of this slurry and the uniaxial compressive strength of the hardened | cured material of this slurry were measured, and the result was shown in Table 6.

<Examples 10 to 12 and Comparative Examples 9 to 11> Formulation Nos. Listed in Table 4 using a premix powder cement composition for ground improvement. Preparation of ground improvement cement composition slurry according to No. 5 The ground improvement premix powder cement composition and water described in Table 3 were weighed according to Table 4, and mixed in a Hobart mixer to prepare cement milk. To this cement milk, 1630 g of excavated soil (Osaka Marine Clay) having physical properties shown in Table 5 was added and mixed to prepare a ground improved cement composition slurry.
About the prepared ground improvement cement composition slurry, the viscosity of this slurry and the uniaxial compressive strength of the hardened | cured material of this slurry were measured, and the result was shown in Table 6.

<Comparative example 12> Mixing No. of Table 4 which does not use the premix powder cement composition for ground improvement is used. Preparation of ground improvement cement slurry according to No. 6 323 g of cement-based solidified material consisting of 30% by mass of ordinary Portland cement and 70% by mass of Blast Furnace Cement B (total 100% by mass) and 646 g of water are mixed uniformly in a Hobart mixer. Milk was prepared. To this cement milk, 1630 g of excavated soil (Osaka Marine Clay) having physical properties shown in Table 5 was added and mixed to prepare a ground improved cement slurry.
About the prepared ground improvement cement composition slurry, the viscosity of this slurry and the uniaxial compressive strength of the hardened | cured material of this slurry were measured, and the result was shown in Table 6.

In Table 4,
* 8: capacity ratio of cement milk to be injected into the injection rate = excavated soil 1m ³ per (%)
* 9: Formulation No. 3 is NC, blending no. 4 and no. 6 is NC + BB

In Table 5,
* 10: Fine particles having a particle size of less than 5 μm * 11: Silt particles having a particle size of from 5 μm to less than 75 μm * 12: Sand particles having a particle size of from 75 μm to 2 mm

<Evaluation of physical properties of ground improvement cement composition slurry>
The viscosity of the ground improvement cement composition slurry and the uniaxial compressive strength of the cured product of the slurry were determined as follows.

  Viscosity: Using a B-type viscometer, the viscosity was measured at 20 ° C. immediately after kneading and after 30 minutes. The smaller the measured value, the smaller the viscosity and the better the fluidity. In order to obtain a ground improved cement composition slurry having fluidity that can be injected, sprayed, and mixed at the construction site, the viscosity value of the prepared ground improved cement composition slurry is preferably 10,000 mPa · S or less.

-Uniaxial compressive strength test: Compressive strength (kN / m ² ) of materials 1 day, 7 days and 28 days for molded products formed using a mold with a diameter of 50 mm and a height of 100 mm in accordance with JIS-A1108 Was measured.

In Table 6,
* 13: A copolymer of maleic acid and methoxypoly (30 mol) ethylene glycol allyl ether used as a dispersant for cement, the copolymer used in the premix powder cement composition (PM-2) of the present invention. Except having replaced with (weight average molecular weight 23000), the thing of the completely same composition was used.
* 14: The same composition as described above was used except that it was replaced with a cement dispersant (Tupol HP-11 manufactured by Takemoto Yushi Co., Ltd.).

Claims (6)

The powder additive for ground improvement in which 25 to 75% by mass of the following A component and 75 to 25% by mass (100% by mass in total) of the following B component are mixed is 0.2 to 100 parts by mass of the cement-based solidified material. The premix powder cement composition for ground improvement characterized by containing in the ratio of -10 mass parts.
Component A: an aqueous solution comprising a vinyl copolymer having a mass average molecular weight of 2000 to 50000 obtained by alkaline hydrolysis of a copolymer of olefin having 3 to 8 carbon atoms and maleic anhydride, and having a solid content concentration of 10 to 80% by mass Component B: porous silica fine powder The premix powder cement composition for ground improvement according to claim 1, which is used in a jet grout method. The premix powder cement composition for ground improvement according to claim 1 or 2, wherein the olefin having 3 to 8 carbon atoms is isobutylene having 4 carbon atoms. The premix powder cement composition for ground improvement according to any one of claims 1 to 3, wherein the component B is a fine porous silica powder having a specific surface area of 50 to 450 m ² / g and an average particle size of 0.1 to 500 µm. . An aqueous solution having a solid content concentration of component A of 40 to 60% by mass, and a powder additive comprising 35 to 65% by mass of component A and 65 to 35% by mass of component B (100% by mass in total). The premix powder cement composition for ground improvement in any one of 1-4. The premix powder cement composition for ground improvement according to any one of claims 1 to 5, wherein ordinary Portland cement and / or blast furnace cement is used as the cement-based solidifying material.