JP2006083354A - Water-proofing sealant for seam and water-blocking layer-forming material, consisting of bentonite slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bentonite slurry improved with waterproof property and durability made as capable of installing a high concentration bentonite in a good flowing property on stopping water at a seam part of a precast concrete by using the bentonite slurry or forming a water-blocking layer by using the bentonite slurry. <P>SOLUTION: This waterproof sealant for the seam of the precast concrete consists of the bentonite slurry obtained by forming the slurry of bentonite with carbonate ion-containing water. The water-blocking layer-forming material consists of the bentonite slurry obtained by forming the slurry of the bentonite with the carbonate ion-containing water. The bentonite slurry shows ≤6 liquid to solid ratio (liquid/solid ratio) and 150-300 mm cylinder flow value, since it contains carbonate ion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a seam sealing material and a water shielding layer forming material using bentonite slurry.

  Bentonite slurry has been widely used as a stabilizing liquid and a grout material for the borehole wall. For example, as described in Patent Document 1, a swelling layer is used to form a water-stopping layer such as a waste disposal site. It has been proposed to be used for the material to be formed. In this case, a water shielding layer is formed by filling bentonite slurry between two sheets of synthetic resin or rubber.

In the radioactive waste geological disposal site business, the use of bentonite as an artificial barrier material has been proposed. At that time, even when bentonite slurry is used to seal water in concrete or to build a water barrier layer, even if distilled water is added to bentonite to create bentonite slurry, the liquid / It is difficult to prepare a slurry (fluid slurry) having a low solid ratio (high bentonite concentration). In addition, bentonite slurry to which a fluidizing agent is added in order to impart fluidity contains organic substances and is difficult to apply in the field of radioactive waste geological disposal sites.
JP-A-10-128268

  In view of the above circumstances, the present invention has an object to suppress the swelling performance of bentonite by distilled water. As a result, by suppressing the swelling performance of bentonite, the construction of the joint water stop and the water shielding layer of the concrete is achieved. It is an object to improve the durability and high durability.

  According to the present invention, there is provided a seam-sealing material for precast concrete made of bentonite slurry obtained by slurrying bentonite with carbonate ion-containing water. At that time, when the precast concrete contains γ belite, the γ belite is carbonated and densified by carbonate ions in the bentonite slurry, so that the water stoppage can be further improved. According to the present invention, there is also provided a water shielding layer forming material comprising bentonite slurry obtained by slurrying bentonite with carbonate ion-containing water. The bentonite slurry according to the present invention preferably has a liquid / solid ratio (liquid / solid ratio) of 6 or less and a cylinder flow value of 150 to 300 mm.

  When building a concrete structure by laying or stacking precast concrete, the bentonite slurry is filled as a water-stopping material at the joint. In the present invention, water containing carbonate ion is added to the bentonite to make a slurry. One feature is that a bentonite slurry is used. This water-stopping material can also be applied to ordinary concrete structures, but it can be advantageously applied especially to the construction of underground structures using precast concrete in radioactive waste geological disposal site projects. Typical examples of carbonate ion-containing water include aqueous solutions of sodium hydrogen carbonate and sodium carbonate.

  It was found that when a sodium hydrogen carbonate aqueous solution (sodium bicarbonate water) was added to bentonite to form a slurry, a higher flow value could be obtained with a smaller liquid / solid ratio than when distilled water was added to make a slurry. This relationship is shown in FIG.

FIG. 1 shows that when changing the liquid / solid ratio (actually, the weight ratio of water / bentonite) to slurry bentonite, distilled water, 2 wt% NaHCO ₃ , 5 wt% NaHCO ₃ or saturated NaHCO ₃ are used as liquid components. It shows the result of examining how the cylinder flow value changes when using. Generally, if the cylinder flow value of bentonite slurry is less than 150, the fluidity of the slurry is poor and unsuitable for filling, and if it exceeds 300 mm, material separation occurs, so it is optimal that the cylinder flow value be in the range of 150 to 300 mm. It is.

As is apparent from the results of FIG. 1, in order to obtain a slurry having a cylinder flow value of 150 to 300 mm, the slurry using distilled water needs to have a liquid / solid ratio of about 6.5 to 8.0. In contrast, in a slurry using saturated NaHCO ₃ , this can be achieved by setting the liquid / solid ratio to about 1.4 to 2.0. Even a slurry using 2% NaHCO ₃ can be achieved at a liquid / solid ratio of about 3.5 to 4.3. That is, when bentonite is slurried using an aqueous solution of sodium bicarbonate, good fluidity is exhibited even if the bentonite concentration is increased. The higher the concentration of sodium bicarbonate in the aqueous solution, the higher the bentonite concentration.

  This phenomenon can be explained as follows. In the slurry to which distilled water is added, the bentonite swells and the fluidity deteriorates. Therefore, in order to obtain a cylinder flow value of 150 to 300 mm, it is necessary to add distilled water 6.5 to 8.0 times that of bentonite, whereas in the case of water added with sodium hydrogen carbonate (sodium bicarbonate water), bentonite Therefore, good fluidity can be maintained even with the addition of a small amount of water. Such a tendency shows the same effect with sodium carbonate instead of sodium bicarbonate.

  Therefore, for example, when the bentonite slurry according to the present invention is applied as a joint material for building an underground structure by laying and stacking precast concrete in a radioactive waste geological disposal site project, it has a high bentonite concentration during construction. Since good fluidity is maintained so that the joint can be filled (applied), a bentonite packed layer having a high bentonite concentration is formed over the entire joint. And as sodium bicarbonate water is diluted into groundwater, the original swelling / water-stop function of bentonite is restored, and high water-stopping ability can be exhibited.

In particular, bentonite slurries applied (filled) to the joints of precast concrete penetrate into the concrete and the bentonite fine particles and carbonate ions become dense, and the concrete in the vicinity of the joint becomes dense and exhibits good water-stopping properties. At that time, when a high load is applied to the joint, about 10 to 35 wt% of silica sand may be mixed in the slurry. In addition, carbonate ions permeating into the concrete from the slurry at the joints act as a CO ₂ source for causing carbonation of the concrete, and the water stoppage is further improved by densification and neutralization of the concrete by this carbonation, Elution of Ca ions from concrete can also be suppressed. FIG. 2 shows this diagrammatically.

  As shown in FIG. 2, a densified region having a certain depth is formed in the concrete from the seam surface by the baking soda bentonite slurry filled in the seam of the precast concrete. FIG. 3 shows the results of an experimental investigation of how this densified region is formed. The experiment was performed as follows.

[Preparation of paste]: The water-cement ratio was 40 wt%, 60 wt%, and 80 wt%, and the mixture was kneaded using a hand mixer and a Hobart mixer. Chemical admixture was not used, ordinary Portland cement made by Taiheiyo Cement was used for cement, and purified water was used for water. Kneading was carried out with a hand mixer from the introduction of the material to 1 minute before completion of the addition, and after confirming the dispersion state, the mixture was mixed for 1 minute with the Hobart mixer.

[Preparation of molded body]: Each paste that has been kneaded is placed in a mold so as to form a molded body of 40 × 40 × 40 mm, and is cured in a humid atmosphere at 40 ° C. and 95% humidity for 1 day. Medium curing was performed for 6 days, for a total of 7 days, and used as test specimens.

[Immersion test in bentonite slurry]: A sodium bicarbonate bentonite slurry having a liquid / solid ratio of 1.8 and a cylinder flow value of 250 mm was obtained by slurrying bentonite using a 5 wt% aqueous solution of sodium bicarbonate. Each said compact | molding | casting was immersed in this baking soda bentonite slurry at room temperature for 10 weeks.

[Measurement of porosity]: A surface layer sample having a depth of 2 mm on the surface was collected from each specimen after immersion, and the porosity was measured by mercury porosimetry. For comparison, a sample at the center of each specimen was taken and the porosity was measured in the same way. The results are shown in FIG. 3 in comparison with each paste compact.

  From the results of FIG. 3, it can be seen that in the case of pastes having a water cement ratio of 60% and 80%, the porosity of the surface layer portion is lower than that in the interior, and the hardened paste is densified. Therefore, in the case of the precast concrete as shown in FIG. 2, the hardened cement matrix portion is densified at the seam surface layer portion in contact with the baking soda bentonite slurry, which shows that the durability of the concrete is improved.

When the precast concrete contains γ belite (2CaO · SiO ₂ ), this densification is performed better. In mortar or concrete containing γ-belite, it is known that when γ-belite is exposed to a CO ₂ source, it is carbonated and the porosity is reduced to become dense (for example, Concrete Engineering Vol.26. 2004.6 , Kosuke Yokoseki et al. “Chloride shielding effect of mortar with carbonation curing by mixing γ2CaO · SiO ₂ ”). Therefore, when the present invention is applied to precast concrete containing γ belite using this phenomenon, that is, when the carbonate ion-containing bentonite slurry of the present invention is filled in the joint portion, the carbonate ion becomes the CO ₂ source. As a result, the gamma belite in the concrete can be carbonated, and the concrete in the vicinity of the joint can be further densified, thereby further improving the water stoppage and durability.

  Furthermore, the carbonate ion-containing bentonite slurry of the present invention is also useful as a material for forming a water shielding layer in the ground. For example, in the radioactive waste geological disposal site project, the formation of an artificial barrier layer by bentonite, such as the construction of the bentonite layer at the bottom and the bentonite layer at the side of the concrete pit, is being studied. It may be necessary to form. In such a case, as described above, the bentonite slurry of the present invention containing carbonate ions exhibits good fluidity at a high bentonite concentration, so that bentonite can form a high-concentration impermeable layer with good workability. it can.

  Also in the case of forming a water shielding layer, the carbonate ion-containing bentonite slurry has a liquid-solid ratio (liquid / solid ratio) of 6 or less and a cylinder flow value of 150 to 300 mm as in the case of the water blocking material. Good. As the carbonate ion source, baking soda is the most appropriate from the viewpoint of price and availability, and the concentration of baking soda should be 1 wt% or more and saturated water.

FIG. 4 shows that powder containing 30% by weight of silica sand in bentonite is slurried by changing the liquid / solid ratio using saturated NaHCO ₃ water, and water is passed through the slurry (1 per 25 cm ³ volume of the specimen). The change in hydraulic conductivity when water flow was continued at a flow rate of 0.0 to 5.0 mL was investigated. As can be seen from the results of FIG. 4, the hydraulic conductivity decreases with the elapsed time. This indicates that the original swelling / waterstop function of bentonite is restored as NaHCO ₃ in the slurry is diluted with water.

It is the figure which showed the relationship between the liquid / solid ratio of the carbonate ion containing bentonite slurry, and the cylinder flow value as compared with that of the bentonite containing distilled water. It is a conceptual diagram which shows the densification area | region when the carbonate ion containing bentonite slurry is inserted in the joint part of precast concrete. It is a figure which shows the result of the densification test of the paste by the bentonite slurry containing carbonate ion. It is the figure which showed the change of the water permeability coefficient when water-flowing to the bentonite slurry (silica sand 30 weight% containing) containing carbonate ion.

Claims (4)

  A joint water-sealing material for precast concrete made of bentonite slurry obtained by slurrying bentonite with carbonate ion-containing water.   The joint water stop material according to claim 1, wherein the precast concrete is a concrete containing γ belite.   A material for forming a water shielding layer comprising bentonite slurry obtained by slurrying bentonite with carbonate ion-containing water.   4. The water shielding layer forming material according to claim 1, wherein the bentonite slurry has a liquid / solid ratio (liquid / solid ratio) of 6 or less and a cylinder flow value of 150 to 300 mm.