JP7195962B2 - Construction method of tunnel lining concrete - Google Patents

Description

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

Tunnel lining concrete is often constructed by repeating the following steps (i) and (ii) to lay concrete.
(i) After installing the center formwork in the tunnel using the center trolley, pour concrete into the center formwork.
(ii) After the concrete hardens, the center truck moves forward and moves to the next section.
In the construction of tunnel lining concrete, it is said that the center formwork should not be removed until the poured concrete reaches the required strength, and it should be done about 12 to 20 hours after the concrete is poured. The compressive strength of concrete at the time of demolding is set at 2 to 3 N/mm ² as a guideline” (Non-Patent Document 1).

By the way, in recent years, mixed cement such as blast furnace cement and fly ash cement has attracted attention as an alternative to Portland cement from the viewpoint of effective utilization of by-products and suppression of the production of carbon dioxide, which is the main cause of global warming. there is Of these, blast-furnace cement is a mixture of granulated blast-furnace slag, a by-product of ironworks, and ordinary Portland cement. ) can be reduced, so the effect of suppressing the production of carbon dioxide is large in the production of cement.
Concrete using blast-furnace cement has almost the same strength at 28 days of age as concrete using ordinary Portland cement, and has excellent long-term strength development. It has also been proven to be high.
Therefore, if blast-furnace cement can be used for tunnel lining concrete, the applications of blast-furnace cement will expand, contributing to the effective utilization of by-products and the suppression of carbon dioxide generation. Because of the low initial strength development, especially in a low temperature environment, there are many problems in using blast furnace cement for actual structures.

Conventionally, various methods have been proposed for increasing the strength of concrete. For example, in terms of materials,
Patent Literature 1 proposes a tunnel construction method in which a cement composition containing cementitious material, fluoroain, an inorganic sulfate, and a setting modifier as main components is mixed with water and cast-in-place lining is performed. In this method, the action of the rapid hardening materials (fluoroain and inorganic sulfate) and the setting modifier ensures the fluidity of the concrete for a certain period of time, and after the concrete is filled, the strength is developed at an early stage. there is
Patent Document 2 proposes a cement composition containing anhydrous gypsum, aluminum sulfate, alkali metal aluminate and nitrates. The use of such an admixture yields a hardened cement product with good strength development, so steam curing is not required.
Patent Document 3 proposes a hydraulic composition comprising ground granulated blast furnace slag, ground limestone, and two or more stimulants with different calcium ion elution rates. Although the hydraulic composition contains blast furnace slag, it is said to have the same setting time and strength development as ordinary cement.

On the other hand, in terms of manufacturing,
Patent Document 4 proposes a method of heating the ends of the center to be overlapped in the next step to develop the required compressive strength.
Patent Document 5 proposes a tunnel lining concrete casting method in which two mobile centers are advanced in the same tunnel excavation direction to construct lining concrete. In this method, when the tunnel lining concrete is manufactured using two centers, by providing a time difference between the casting times in each center, the demolding strength is secured and the construction period of the lining concrete is shortened. It is said to be possible.

However, the inventions of Patent Documents 1 to 5 are concerned about the following problems. i.e.
In the invention of Patent Document 1, it is difficult to determine the addition amount of the condensation modifier and to adjust the fluidity in accordance with changes in the environmental temperature.
In the invention of Patent Document 2, since some of the aluminate alkali salts are designated as deleterious substances, caution is required in the storage and management of the materials. It is difficult to adjust the freshness of the resin and adjust the curing time.
In the invention of Patent Document 3, curing is delayed at low temperatures, and the initial strength development is particularly low. In addition, since there is a large amount of powder to be handled, the work at the ready-mixed concrete factory becomes complicated. Furthermore, when a large amount of an alkaline stimulant is used, the drying shrinkage of concrete increases, and cracks are likely to occur.
The invention of Patent Document 4 can secure the necessary strength in the part where the reaction force is applied when the center moves, but the strength development is low in other parts, and it requires special equipment, so it is not versatile. low.
Since the invention of Patent Document 5 uses two centers, the tunnel must be of a certain scale, and the construction site is limited to areas and places where ready-mixed concrete shipping capacity is high.

"Improving quality of lining concrete using two lining centers": The 67th Annual Conference of the Japan Society of Civil Engineers, pp.9-10, VI-005, 2012

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

Therefore, in view of the above problems, the present invention provides a construction method for tunnel lining concrete that can exhibit high initial strength at low temperatures and can suppress cracking due to drying shrinkage even in tunnel lining concrete using blast furnace cement. intended to provide

The inventors of the present invention have studied a tunnel lining concrete construction method that meets the above object, 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 construction method for tunnel lining concrete having the following configuration.

[1] Contains an expansive material having a Blaine specific surface area of 4000 to 7000 cm ² /g, one or more nitrites selected from alkali metal nitrites and alkaline earth metal nitrites, and blast furnace cement ,
Tunnel lining concrete in which the addition amount of the expansive agent is 10 to 50 kg/m ³ and the addition rate of the nitrite is 1.0 to 8.0% by mass with respect to the blast furnace cement is heated to 15 ° C. or less. Construction method of tunnel lining concrete, which is constructed under the environment of
[2] The addition rate of the nitrite and the addition amount of the expansion material are
(A) When the environmental temperature is 5°C or less, select from the area surrounded by the curve drawn by the following formula (1) and y = 50 and x = 3.2,
(B) When the environmental temperature is more than 5°C and 10°C or less, the curve drawn by the following formula (1) (excluding the curve) and the curve drawn by the following formula (2), y = 50 and x = 3. Select from the area enclosed by 2,
(C) When the environmental temperature is above 10°C and 15°C or less, the curve drawn by the following formula (2) (excluding the curve) and the curve drawn by the following formula (3), y = 50 and x = 3. Select from the area enclosed by 2,
The method for constructing the tunnel lining concrete according to the above [1].
y= 104.58 ×x ^−1.079 (1)
y=60.147×x− ^0.952 (2)
y= ^24.59 ×x− 0.77 (3)
However, the above y is the addition amount (kg/m ³ ) of the expansion material, and the above x is the addition rate (C×mass %) of the nitrite (solid content).

The tunnel lining concrete used in the present invention can maintain a slump for 60 minutes or more even in an environment of 15 ° C. or less, and has a compressive strength of 2 N / mm ² or more, which is a strength that can be demolded at an age of 18 hours. Therefore, according to the tunnel lining concrete construction method of the present invention, the lining concrete can be constructed using a mobile formwork.

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

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

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 expansion material that is usually used has a low Blaine specific surface area of about 2500 to 3500 cm ² /g. If the Blaine specific surface area is high, the expansion development property is low. Therefore, an expanding material having a Blaine specific surface area of 4000 cm ² /g or more has been rarely used until now. However, the present inventors have found that if an expansive material with a Blaine specific surface area of 4000 to 7000 cm ² /g is used together with blast furnace cement and nitrite, a strength of 2 N/mm ² that can be removed from the mold at 18 hours of material age can be obtained. I found out that it can be done. The Blaine specific surface area of the expansion material is preferably 4500 to 6000 cm ² /g.
The Blaine specific surface area is determined using the Blaine air permeation device specified in JIS R 5201 "Physical test method for cement", and the flow rate of the air passing through the cement-packed cell is determined by the change time of the solution head, and the standard sample and Calculate by comparison.
The unit amount of the expansive material is 10-50 kg/m ³ . If the unit amount of expansive agent is within this range, a shrinkage-compensated concrete having a constrained expansion coefficient of 150 to 250×10 ⁻⁶ can be obtained.
The expanding material includes one or more selected from lime-based expanding materials and calcium sulfoaluminate-based expanding materials. Among these, the lime-based expanding material is preferred because of its high expansion property.
The lime-based expansive material contains expansive calcined material containing free quicklime (CaO) and gypsum. The expansive fired product is obtained by firing a mixture of calcium raw materials such as calcium carbonate, slaked lime, and quicklime, silica raw materials, alumina raw materials, iron oxide raw materials, and gypsum raw materials in an electric furnace, rotary kiln, or the like. After pulverizing with a ball mill or the like, the material is classified to adjust the particle size.
The lime-based expansive material is produced by mixing powdered gypsum and pulverized expansive calcined material in a mixer or the like, or by mixing gypsum and expansive calcined material and then pulverizing the mixture. The gypsum is not particularly limited, but is preferably anhydrite and type II anhydrite, and more preferably type II anhydrite, because of its high swelling property.

2. Nitrite The nitrite used in the present invention includes one or more selected from alkali metal nitrites and alkaline earth metal nitrites. Specifically, sodium nitrite, potassium nitrite, lithium nitrite, One or more selected from calcium nitrite, magnesium nitrite, and the like can be mentioned. By combining these nitrites with an expansive material having a specific Blaine specific surface area, even when blast furnace cement is used, it can be 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. Among these nitrites, calcium nitrite is particularly preferred from the viewpoint of early strength development.
The addition rate of nitrite (solid content) is preferably 0.4 to 3.2% by mass relative to the blast furnace cement from the viewpoint of securing initial strength development and fluidity.
Nitrite is preferably used in the form of an aqueous solution. The combination of the powder-based expanding material and the liquid-based curing accelerator is easy to handle, so it can be used in ready-mixed concrete factories, agitator vehicles, construction sites, and the like. The concentration of nitrite in the aqueous nitrite solution is preferably 10 to 50% by mass for ease of handling, and the aqueous nitrite solution is used as a part of the unit water volume.
In the present invention, the addition rate of the nitrite and the addition amount of the expansion agent 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 linear areas.
y=a×x- ^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. , 60.147 at 10°C and 24.59 at 15°C, and b is 1.079 at 5°C, 0.952 at 10°C and 0.77 at 15°C.
Concrete containing nitrite and an expansive agent at an addition rate (amount) selected from this region exhibits high strength development even in a low-temperature environment.

3. Blast-furnace cement The blast-furnace cement used in the present invention is a mixture of Portland cement and quenched ground granulated blast-furnace slag. JIS A 6206 "Grounded blast furnace slag for concrete" classifies blast furnace cement into types A, B, and C according to the mixing ratio of the ground blast furnace slag. In particular, the blast furnace cement used for the tunnel lining concrete used in the present invention is not particularly limited, but since it has high strength development, the B type in which the mixing ratio of ground granulated blast furnace slag is more than 30% and 60% or less is recommended. preferable.

4. Other Materials Used in the Tunnel Lining Concrete of the Present Invention Aggregates used in the present invention are not particularly limited, and are fine aggregates and coarse aggregates used in ordinary concrete, such as river sand, sea sand, mountain sand, 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, recycled coarse aggregate, and the like. The amount (unit amount) of the aggregate is preferably 1,300 to 2,000 kg/m ³ . When the amount of the aggregate is within this range, it is easy to achieve a balance between suppression of heat generation and drying shrinkage of concrete and workability of concrete. The blending amount of the aggregate is more preferably 1500-1800 kg/m ³ . Further, the fine aggregate ratio (s/a: ratio of fine aggregate volume/total aggregate volume) is preferably 35 to 60%. Workability can be ensured if the fine aggregate ratio is within this range.
The water used in the present invention is not particularly limited, and examples thereof include tap water, supernatant water of fresh concrete sludge, and the like. The blending amount (unit amount) of water is preferably 150 to 250 kg/m ³ in order to ensure material separation resistance. Also, 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 hydration heat and secure compressive strength.
Furthermore, the tunnel lining concrete may contain admixtures (materials) used in ordinary mortar and concrete, as long as 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, a rust inhibitor, an air entrainment agent, an antifoaming agent, a foaming agent, a waterproof agent, Water repellents, anti-efflorescence agents, setting modifiers, pigments, fibers, silica fume, and the like.

EXAMPLES The present invention will be described below 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 constrained expansion rate According to the formulation shown in Table 2, the materials shown in Table 1 were put into a concrete mixer at once and mixed for 2 minutes. It was cured in water at 20°C for 7 days. Constraint expansion rate of the cured concrete was measured according to JIS A 6202 "expanding material for concrete". Concrete with a constrained expansion rate of 150 to 250×10 ⁻⁶ was determined as shrinkage compensation 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).
Table 3 shows the results. As shown in Table 3, the constrained expansion coefficients of the concretes of formulations 1-2 to 1-6 satisfy the above criteria, and are shrinkage-compensating concretes.

3. Measurement of slump According to the formulation shown in Table 4, concrete was kneaded in the same manner as in the restrained expansion test, and then immediately after kneading (0 minutes) and 60 minutes after kneading in accordance with JIS A 1101 "Concrete slump test method". The slump of the post-concrete was measured. Concrete with a slump of 10 cm or more after 60 minutes elapsed was determined to be suitable for construction as tunnel lining concrete. The addition ratio of the admixture in Table 4 is the same as in Table 2.
Table 5 shows the results. As shown in Table 5, since the changes in slump of the concretes of formulations 2-1 to 2-5 with time satisfy the above criteria, the concretes of formulations 2-1 to 2-5 can be constructed 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 restrained expansion test, and then the kneaded concrete was poured into a mold. The concrete was removed from the mold by hand, and the compressive strength of the concrete at a material age of 18 hours was measured according to JIS A 1108 "Concrete Compressive Strength Test Method". Then, the strength that can be demolded is set to 2 N / mm ² , and at each temperature of 5 ° C, 10 ° C, and 15 ° C, the compressive strength of concrete at the age of 18 hours is ² N / mm A relational expression between the addition rate (% by mass) of the expansion agent and the addition amount of the expansion agent was obtained. FIG. 1 shows the relational expression and the curve drawn by the relational expression.
As shown in Figure 1, the area above the curve indicated by the triangle points at 5°C, the area above the curve indicated by the square points at 10°C, and the area above the curve indicated by the diamond points at 15°C. In the area of , the compressive strength of concrete meets the above criteria. Therefore, by selecting the addition rate (amount) of nitrite and expansive agent from the region above the curve at each temperature shown in FIG.

Claims (2)

An expansive material having a Blaine specific surface area of 4000 to 7000 cm ² /g, one or more nitrites selected from alkali metal nitrites and alkaline earth metal nitrites, and blast furnace cement ,
Tunnel lining concrete in which the addition amount of the expansive agent is 10 to 50 kg/m ³ and the addition rate of the nitrite is 1.0 to 8.0% by mass with respect to the blast furnace cement is heated to 15 ° C. or less. Construction method of tunnel lining concrete, which is constructed under the environment of The addition rate of the nitrite and the addition amount of the expansion material are
(A) When the environmental temperature is 5°C or less, select from the area surrounded by the curve drawn by the following formula (1) and y = 50 and x = 3.2,
(B) When the environmental temperature is more than 5°C and 10°C or less, the curve drawn by the following formula (1) (excluding the curve) and the curve drawn by the following formula (2), y = 50 and x = 3. Select from the area enclosed by 2,
(C) When the environmental temperature is above 10°C and 15°C or less, the curve drawn by the following formula (2) (excluding the curve) and the curve drawn by the following formula (3), y = 50 and x = 3. Select from the area enclosed by 2,
The construction method of the tunnel lining concrete according to claim 1.
y= 104.58 ×x ^−1.079 (1)
y=60.147×x− ^0.952 (2)
y= ^24.59 ×x− 0.77 (3)
However, the above y is the addition amount (kg/m ³ ) of the expansion material, and the above x is the addition rate (C×mass %) of the nitrite (solid content).

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