JP2020128316A - Construction method of tunnel lining concrete - Google Patents

Abstract

To provide a construction method of tunnel lining concrete having high initial strength development at a low temperature, even in the case of tunnel lining concrete using blast furnace cement, and capable of suppressing crack caused by dry shrinkage.SOLUTION: In a construction method of tunnel lining concrete, the tunnel lining concrete is constructed under an environment of 15°C or lower, which contains an expansive admixture having a Blaine specific surface area of 4,000-7,000 cm/g, one or more kinds of nitrite salts selected from a nitrite salt of an alkali metal and a nitrite salt of an alkaline earth metal, and blast furnace cement.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for constructing tunnel lining concrete.

In many cases, the tunnel lining concrete is constructed by repeating the following steps (i) and (ii) to splice the concrete.
(I) After installing the Centle formwork in the tunnel using the Centle cart, concrete is poured into the Centle formwork.
(Ii) After the concrete has hardened, the trolley truck moves forward and moves to the next section.
And in the construction of tunnel lining concrete, "Centre formwork must not be removed until the driven concrete reaches the required strength, and it should be done about 12 to 20 hours after the completion of concrete driving. In many cases, the compressive strength of concrete during demolding is set to ² to 3 N/mm ² as a standard” (Non-Patent Document 1).

By the way, in recent years, mixed cement such as blast furnace cement and fly ash cement has been attracting attention as an alternative to Portland cement from the viewpoint of effective utilization of by-products and suppression of generation of carbon dioxide which is a main causative agent of global warming. There is. Of these, blast furnace cement is a mixture of blast furnace slag fine powder, which is a by-product of the steel mill, and ordinary Portland cement, and the amount of blast furnace slag fine powder mixed, the amount of cement clinker used, and thus the production amount (firing amount). ) Can be reduced, the effect of suppressing the production of carbon dioxide is large in the production of cement.
In addition, the concrete using blast furnace cement has almost the same strength at 28 days of age as the concrete using normal Portland cement and is excellent in long-term strength development, and in recent years, has the effect of suppressing salt damage and alkali-aggregate reaction. It is also proven to be high.
Therefore, if blast-furnace cement can be used for tunnel lining concrete, the use of blast-furnace cement will be expanded, and it will contribute to effective utilization of by-products and suppression of carbon dioxide generation. Since the initial strength development is low, especially in a low temperature environment, there are many problems in using blast furnace cement in an actual construction.

Conventionally, various methods for increasing the strength of concrete have been proposed. For example, in terms of materials,
Patent Document 1 proposes a method for constructing a tunnel in which water is mixed with a cement composition containing cementum, fluoroauin, an inorganic sulfate, and a setting modifier as main components, and lining is performed in-situ. Then, the method is said to exert strength early after filling the concrete while securing the fluidity of the concrete for a certain period of time by the action of the rapid hardening material (fluoroauin and inorganic sulfate) and the setting modifier. There is.
Patent Document 2 proposes a cement composition containing anhydrous gypsum, aluminum sulfate, an alkali metal aluminate, and nitrates. When the admixture is used, a cement hardened product having good strength development can be obtained, so that steam curing is unnecessary.
Patent Document 3 proposes a hydraulic composition composed of blast furnace slag fine powder, limestone fine powder, and two or more kinds of stimulants having different elution rates of calcium ions. The hydraulic composition is said to have a setting time and a strength-developing property equivalent to those of ordinary cement, even though it contains blast furnace slag.

On the other hand, in terms of manufacturing,
Patent Document 4 proposes a method of heating the ends of the center that are overlapped in the next step to develop a required compressive strength.
Patent Document 5 proposes a method for placing tunnel lining concrete, in which two movable centles are advanced in the tunnel excavation direction in the same direction to construct lining concrete. This method shortens the construction period of the lining concrete while ensuring demolding strength by providing a time difference between the placing timings of the respective centles when manufacturing the tunnel lining concrete using the two centles. It is said to be possible.

However, the inventions of Patent Documents 1 to 5 are concerned about the following problems. That is,
In the invention of Patent Document 1, it is difficult to determine the addition amount of the coagulation modifier and adjust the fluidity in accordance with the change in the ambient temperature.
In the invention of Patent Document 2, since a part of the alkali aluminate salt is designated as a deleterious substance, attention must be paid to the storage and management of the material, and since many kinds of materials are used, concrete can be used at various temperatures. It is difficult to adjust the fresh properties and curing time.
In the invention of Patent Document 3, curing is delayed at a low temperature, and in particular, initial strength development is low. Moreover, since many powders are handled, the work in the ready-mixed concrete factory becomes complicated. Furthermore, when a large amount of alkaline stimulant is used, the drying shrinkage of the concrete becomes large, so that cracks easily occur.
The invention of Patent Document 4 can secure necessary strength in a portion to which a reaction force is applied when the center moves, but strength development is low in other portions, and since special equipment is required, versatility is high. Low.
Since the invention of Patent Document 5 uses two centers, the tunnel requires a certain scale, and the construction site is limited to an area or place where the shipping capacity of ready-mixed concrete is high.

"Upgrading the quality of lining concrete using two lining centres": 67th Annual Conference of JSCE, pp. 9-10, VI-005, 2012

JP-A-2-293360 JP-A-8-165154 JP, 2014-148434, A JP 2001-123794A JP, 2013-129991, A

Therefore, in view of the above problems, the present invention, even in tunnel lining concrete using blast furnace cement, high initial strength expression at low temperature, also, a method of constructing a tunnel lining concrete that can suppress cracking due to drying shrinkage. The purpose is to provide.

The inventors of the present invention have studied the construction method of the tunnel lining concrete that meets the above purpose, and have found that the above object can be achieved by using a specific expansive material and nitrite, and have completed the present invention. That is, the present invention is a method for constructing tunnel lining concrete having the following configuration.

[1] A tunnel cover containing an expansive material having a Blaine specific surface area of 4000 to 7000 cm ² /g, at least one nitrite selected from alkali metal nitrites and alkaline earth metal nitrites, and blast furnace cement. A construction method for tunnel lining concrete, in which the construction concrete is constructed in an environment of 15°C or lower.
[2] The above [1], wherein the addition rate of the nitrite and the addition amount of the expansive material are selected from a curve drawn by the following formula (1) and a region surrounded by y=50 and x=3.2. Tunnel lining concrete construction method.
y=ax− ^b ... (1)
However, in the formula (1), y is the amount of expansion material added (kg/m ³ ), x is the addition rate of nitrite (solid content) (C×mass %), and a is 104.degree. 58, 60°C at 10°C, 24.59 at 15°C, b is 1.079 at 5°C, 0.952 at 10°C, 0.77 at 15°C.

The tunnel lining concrete used in the present invention can hold a slump for 60 minutes or more even under an environment of 15° C. or less, and has a compressive strength of 18 hours when the demolding strength is 2 N/mm ² or more. Therefore, according to the tunnel lining concrete construction method of the present invention, the lining concrete can be constructed using the movable formwork.

It is a graph which shows the relationship between a nitrite (solid content) addition rate and a lime type expansive material addition amount.

As described above, the tunnel lining concrete construction method of the present invention is one or more selected from expansive materials having a Blaine specific surface area of 4000 to 7000 cm ² /g, and alkali metal nitrites and alkaline earth metal nitrites. Is a method of constructing a tunnel lining concrete containing a hardening accelerator containing nitrite and blast furnace cement in an environment of 15° C. or lower.
Hereinafter, the expansive material, the nitrite, and the blast furnace cement will be separately described in detail.

1. Expanding Material The expanding material used in the present invention has a Blaine specific surface area of 4000 to 7000 cm ² /g. Incidentally, the expansive material which is usually used has a low Blaine specific surface area of about 2500 to 3500 cm ² /g. When the Blaine specific surface area is high, the expansion developability is low. Therefore, until now, an expansion material having a Blaine specific surface area of 4000 cm ² /g or more has hardly been used. However, the present inventors obtained 2N/mm ² which is the demoldable strength at the age of 18 hours by using the expansive material having a Blaine specific surface area of 4000 to 7000 cm ² /g together with blast furnace cement and nitrite. I found that The Blaine specific surface area of the expansive material is preferably 4500 to 6000 cm ² /g.
The Blaine specific surface area was determined by using the Blaine air permeation device specified in JIS R 5201 “Physical test method for cement”, and determining the flow velocity of air passing through the cell filled with cement with the change time of the solution head, and comparing with the standard sample. Calculate by comparing.
The unit amount of the expansion material is 10 to 50 kg/m ³ . When the unit amount of the expansive material is within this range, shrinkage-compensating concrete having a constrained expansion coefficient of 150 to 250×10 ⁻⁶ can be obtained.
Examples of the expansive material include one or more selected from lime expansive materials and calcium sulphoaluminate expansive materials. Among these, a lime-based expansive material is preferable because it has a high expansibility of expansion.
The lime-based expansive material contains an expansive fired product containing free quick lime (CaO) and gypsum. Then, the expansive calcined product is a mixture of calcium carbonate, slaked lime, calcium-based raw materials such as quick lime, siliceous raw material, alumina-based raw material, iron oxide raw material, and gypsum raw material after firing in an electric furnace or a rotary kiln. After crushing with a ball mill or the like, classification is performed to adjust the particle size.
The method for producing the lime-based expansive material is to mix powdered gypsum and the pulverized product of the expandable fired product with a mixer or the like, or to mix the gypsum and the expanded fired product and then pulverize. The gypsum is not particularly limited, but it is preferably anhydrous gypsum and type II anhydrous gypsum, and more preferably type II anhydrous gypsum because of its high swelling expression.

2. Nitrite The nitrite used in the present invention includes one or more selected from nitrites of alkali metals and nitrites of alkaline earth metals, specifically, sodium nitrite, potassium nitrite, lithium nitrite, One or more selected from calcium nitrite, magnesium nitrite and the like. By combining these nitrites and an expansive material having a specific Blaine specific surface area, even when blast furnace cement is used in a low temperature environment (15°C or less) without impairing the fluidity of concrete. It is possible to enhance the initial strength development of the. Among these nitrites, calcium nitrite is particularly preferable from the viewpoint of developing the initial strength.
From the viewpoint of ensuring initial strength development and fluidity, the addition rate of nitrite (solid content) is preferably 0.4 to 3.2 mass% with respect to blast furnace cement.
Nitrite is preferably used in the form of an aqueous solution. Since the combination of the powder-type expansion material and the liquid-type curing accelerator is easy to handle, it can be used in ready-mixed concrete plants, agitator cars, construction sites, etc. The concentration of nitrite in the aqueous nitrite solution is preferably 10 to 50% by mass because it is easy to handle, and the aqueous nitrite solution is used by converting it as a part of the unit amount of water.
In the present invention, the addition rate of the nitrite and the addition amount of the expansive material are preferably selected from the curve drawn by the following formula (1) and the region surrounded by y=50 and x=3.2. However, the area includes a line.
y=ax− ^b ... (1)
However, in the formula (1), y is the amount of expansion material added (kg/m ³ ), x is the nitrite (solid content) addition rate (C×mass %), and a is 104.58 at an environmental temperature of 5° C. It is 60.147 at 10°C, 24.59 at 15°C, and b is 1.079 at 5°C, 0.952 at 10°C, and 0.77 at 15°C.
The concrete containing the nitrite and the expansive material in the addition ratio (amount) selected from the region has high strength development even in a low temperature environment.

3. Blast furnace cement The blast furnace cement used in the present invention is a cement formed by mixing Portland cement and rapidly cooled blast furnace slag fine powder. JIS A 6206 “Blast furnace slag fine powder for concrete” classifies blast furnace cement into A type, B type, and C type according to the mixing ratio of the blast furnace slag fine powder. In particular, the blast-furnace cement used for the tunnel lining concrete used in the present invention is not particularly limited, but since the strength development is high, there is B type having a mixing ratio of the blast-furnace slag fine powder of more than 30% and 60% or less. preferable.

4. Other materials used in the tunnel lining concrete of the present invention, the aggregate used in the present invention is not particularly limited, is a fine aggregate and coarse aggregate used in normal concrete, for example, river sand, sea sand, mountain sand, Examples thereof include crushed sand, artificial fine aggregate, slag fine aggregate, recycled fine aggregate, silica sand, river gravel, land gravel, crushed stone, artificial coarse aggregate, slag coarse aggregate, and recycled coarse aggregate. The amount (unit amount) of the aggregate is preferably 1300 to 2000 kg/m ³ . When the content of the aggregate is within the range, it is easy to balance the heat generation and drying shrinkage of the concrete with the workability of the concrete. The blending amount of the aggregate is more preferably 1500 to 1800 kg/m ³ . The fine aggregate ratio (s/a: volume ratio of fine aggregate/volume ratio of total aggregate) is preferably 35 to 60%. If the fine aggregate ratio is within this range, workability can be secured.
The water used in the present invention is not particularly limited, and examples thereof include tap water and clear water of raw conus sludge. The blending amount (unit amount) of water is preferably 150 to 250 kg/m ³ in order to secure the material separation resistance. The concrete kneader is preferably a concrete mixer. The water-cement ratio (W/C) is preferably 40 to 65%, more preferably 45 to 60% in order to reduce the heat of hydration and secure the compressive strength.
Further, the tunnel lining concrete may contain an admixture (material) used for ordinary mortar or concrete within a range in which the effects of the present invention are not substantially lost. The admixture (material) includes a water reducing agent, an AE water reducing agent, a high performance water reducing agent, a fluidizing agent, a shrinkage reducing agent, a water retention agent, an anticorrosive agent, an air entraining agent, an antifoaming agent, a foaming agent, a waterproofing agent, Water repellents, anti-whitening agents, setting regulators, pigments, fibers, silica fumes, and the like.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.
1. Materials Used Table 1 shows the materials used.

2. Measurement of Restraint Expansion Rate According to the composition shown in Table 2, the materials shown in Table 1 were put into a concrete mixer all at once, and after kneading for 2 minutes, the kneaded concrete was placed in a mold and demolded. It was cured in water at 20° C. for 7 days. For the concrete after curing, the restraint expansion coefficient was measured according to JIS A 6202 “Expansion material for concrete”. It should be noted that concrete having a restricted expansion coefficient of 150 to 250×10 ⁻⁶ was determined as shrinkage-compensating concrete. The addition rate of the admixture (AD) in Table 2 is the addition rate (% by mass) of the calcium nitrite aqueous solution to the cement (C).
The results are shown in Table 3. As shown in Table 3, the constrained expansion rate of the concretes of the formulations 1-2 to 1-6 satisfies the above criteria, and is therefore shrinkage-compensating concrete.

3. Measurement of slump After kneading concrete according to the composition shown in Table 4 in the same manner as in the constrained expansion test, immediately after kneading (0 minutes) and 60 minutes elapsed in accordance with JIS A 1101 "Slump test method for concrete". The later concrete slump was measured. In addition, it was determined that the concrete with a slump of 10 cm or more after 60 minutes can be applied as tunnel lining concrete. The addition rate of the admixture in Table 4 is the same as in Table 2.
The results are shown in Table 5. As shown in Table 5, the change over time of the slump of the concrete of mixes 2-1 to 2-5 satisfies the above criteria, and therefore the concrete of mixes 2-1 to 2-5 can be applied as tunnel lining concrete.

3. Measurement of Compressive Strength According to the composition shown in Table 6, at each temperature of 5° C., 10° C., and 15° C., the concrete was kneaded in the same manner as in the constrained expansion test, and then the kneaded concrete was placed in a mold. Then, the compressive strength of the concrete at the age of 18 hours was measured according to JIS A 1108 "Test method for compressive strength of concrete". Then, the demoldable strength is set to ² N/mm ² , and at each temperature of 5° C., 10° C., and 15° C., the nitrite (solid content) at which the compressive strength of concrete at the age of 18 hours becomes ² N/mm ^2. The relational expression between the addition rate (mass %) of (min) and the addition amount of the expansion material was determined. FIG. 1 shows the relational expression and the curve drawn by the relational expression.
As shown in FIG. 1, at 5° C., the area above the curve indicated by the triangular points, at 10° C. above the curve indicated by the square points, and at 15° C. above the curve indicated by the diamond points. In this region, the compressive strength of concrete satisfies the above criteria. Therefore, if the addition rate (amount) of the nitrite and the expansive material is selected from the region above the curve at each temperature shown in FIG. 1, the tunnel lining concrete exhibiting demoldable strength can be manufactured.

Claims (2)

A tunnel lining concrete containing an expansive material having a Blaine specific surface area of 4000 to 7000 cm ² /g, at least one nitrite selected from alkali metal nitrites and alkaline earth metal nitrites, and blast furnace cement. , Construction method for tunnel lining concrete, which is constructed in an environment of 15°C or lower. The tunnel lining according to claim 1, wherein the addition rate of the nitrite and the addition amount of the expansive material are selected from a curve drawn by the following formula (1) and a region surrounded by y=50 and x=3.2. Concrete construction method.
y=ax− ^b ... (1)
However, in the formula (1), y is the amount of expansion material added (kg/m ³ ), x is the nitrite (solid content) addition rate (C×mass %), and a is 104.58 at an environmental temperature of 5° C. It is 60.147 at 10°C, 24.59 at 15°C, and b is 1.079 at 5°C, 0.952 at 10°C, and 0.77 at 15°C.