JP2011020921A - Concrete material for placing in cold weather, and concrete structure using the material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concrete material for placing in a cold weather which is capable of suppressing or preventing the occurrence of crack being initial defect caused by dry shrinkage in a surface member constituting a structure such as a slab or wall surface particularly to be constructed in the cold weather, and to provide a concrete structure using the material. <P>SOLUTION: The concrete material used for placing in the cold weather includes a moderate-heat portland cement, a low-addition type expanding material and an aggregate. The relation of the mass ratio X (mass%) of water to be mixed to the total mass of the moderate-heat portland cement and the low-addition type expanding material incorporated in the concrete material, and the unit amount Y (kg/m<SP>3</SP>) of the low-addition type expanding material per concrete structure unit volume (m<SP>3</SP>) satisfies 27.5-0.25X≤Y≤37.5-0.25X. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-placed concrete material to be applied to a reinforced concrete structure to be constructed in a cold region or cold, and a concrete structure using the concrete material. A concrete material that can be suitably used for surface members such as slabs and the like, and that can suppress or prevent cracks caused by drying shrinkage and temperature shrinkage, which are initial defects of these structures and surface members, is used. It relates to a concrete structure.

In recent years, in the field of building structures such as reinforced concrete structures and steel-framed reinforced concrete structures, higher durability is required from the viewpoint of improving earthquake resistance.
In order to increase the durability of such a concrete structure, it is necessary to prevent cracks, which are initial defects, and these cracks are particularly likely to occur in surface members such as walls and slabs of concrete structures. The main causes are drying shrinkage and temperature stress.
Therefore, in these surface members, it is necessary to mainly suppress or prevent cracks caused by drying shrinkage and temperature stress in the initial curing process.

Focusing on these viewpoints, in order to reduce temperature stress, "Study on practical application of ultra high strength concrete using low heat Portland cement", Abstracts of Architectural Institute of Japan, 2000, A-1 (Materials) Construction), p. In 919-920 (Non-Patent Document 1), a low heat generation type cement improved from a conventional cement is proposed and put into practical use.
In order to reduce the drying shrinkage, “Concrete Self Shrinkage Research Committee Report” September 2002, Japan Concrete Institute, p. In 207-210 (Non-Patent Document 2), an expansion material and a shrinkage reducing agent are proposed and put into practical use.

  However, in conventional concrete structures, shrinkage and thermal stress are intertwined and cracks occur. Therefore, if individual measures such as reducing shrinkage or reducing thermal stress are adopted separately, they will occur in concrete structures. It has been difficult to effectively prevent cracking.

Recently, attempts have been made to prevent temperature cracks in concrete structures by using a concrete material that is a combination of low heat Portland cement and an expansion material or shrinkage reduction material.
In this case, in order to compensate for the shrinkage of the concrete structure, the “Expanded Concrete Design and Construction Guidelines” of the Japan Society of Civil Engineers set the constrained expansion rate of the concrete to which the expansion material is added to 150 × 10 ⁻⁶ to 250 × 10. ^-6 .

However, in the case of a concrete material that is significantly affected by shrinkage, from the viewpoint of cracking prevention, it is necessary to grasp the performance of each constituent material of each concrete material and carefully consider the optimum usage amount of each constituent material. Cracks cannot be effectively suppressed or prevented.
In particular, in the case of concrete structures with significant drying shrinkage, there is a method of increasing the amount of expansion material contained in the concrete material in order to suppress or prevent the occurrence of cracks. If constrained, chemical prestress and densification of the hardened body structure can be achieved, so that the original effect against cracks can be fully exerted. When the restraint is small or equal due to the directivity, excessive expansion may occur, the hardened body structure may loosen, and fine cracks may occur.

For concrete structures with such remarkable drying shrinkage, in order to ensure a sufficiently large expansion coefficient in a range where the hardened body structure does not loosen more than before, the selection of the expansion coefficient is important. JP-A-2004-217514 includes a low heat generation type cement, a low additive type expansive material and an aggregate, and the low additive type expansive material is 12.5 to 27.5 kg / m ³ , thereby curing. The expansion rate on the 7th day is in the range of 150 × 10 ^{−6 to} 750 × 10 ⁻⁶ , and cracks due to drying shrinkage, which is an initial defect, are also formed in the surface members constituting concrete structures such as slabs and walls. It is described that it can be suppressed or prevented.

However, although the proposed concrete material can be sufficiently applied in a temperature range of 10 ° C. or higher, application to a concrete structure driven in a cold temperature of 10 ° C. or lower cannot effectively suppress or prevent cracks. The current situation is difficult.
That is, when the temperature is low at 10 ° C. or lower, the curing of the low heat Portland cement is extremely delayed, so that the stress due to the expansion of the expansion agent contained in the cement appears, and the stress is compensated by the strength obtained by the cement curing. In some cases, cracking due to expansion may occur, and the strength development of the low heat generation type cement deteriorates, resulting in a long construction period of the concrete structure.

  However, a concrete material that has overcome the problems such as poor strength development of the concrete structure to be driven in cold weather and requires long-term curing, and has effectively improved crack resistance especially in cold weather. The current situation is not.

JP 2004-217514 A

“Study on the practical application of ultra-high strength concrete using low heat Portland cement”, Abstracts of Academic Lectures of Architectural Institute of Japan, 2000, A-1 (Material Construction), p. 919-920 “Report of the Research Committee on Self-Shrinkage of Concrete”, September 2002, Japan Concrete Institute, p. 207-210

  The object of the present invention relates to a concrete material applied to a reinforced concrete structure that is constructed in cold weather, a concrete structure using the concrete material, and a manufacturing method thereof, and more particularly, a reinforced concrete constructed in cold weather. A concrete material that can be suitably used for surface members such as walls and slabs of structures, etc., has excellent strength development, and can effectively suppress or prevent cracks caused by drying shrinkage and temperature shrinkage, which are initial defects. The present invention provides a concrete structure using the concrete material and a method for manufacturing the same.

  In constructing a concrete structure in cold weather, the present inventors have difficulty in using low heat Portland cement, which is slow in hardening of the cement, because the strength expression of the concrete is inferior. When combined with additive-type expansive material, when cold, especially in cold regions of 10 ° C or less, the time of strength development of medium-heated Portland cement matches the time of expansion of the expansive material, and construction is performed when cold. It is possible to obtain excellent crack suppression or prevention that cannot be obtained at room temperature against cracks caused by drying shrinkage, which is an initial defect, in concrete members that make up concrete structures, especially slabs and walls. And reached the present invention.

That is, the cold-placed concrete material of the present invention is a cold-placed concrete material applied for cold-working, and includes medium-heated Portland cement, a low addition type expansion material, and an aggregate ( However, fatty acids and / or their salts, and blast furnace chilled slag are not included), the mass ratio of water to be mixed with the total mass of medium-heated Portland cement and low addition type expansion material contained in the concrete material X (mass%) and the unit amount Y (kg / m ³ ) of the low addition type expansion material contained per unit volume (m ³ ) of the concrete structure are represented by the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
It is characterized by satisfying the relationship.

Preferably, the concrete material of the present invention is characterized in that the low addition type expansion material is an ettringite-lime composite expansion material.
More preferably, the concrete material of the present invention further includes a water reducing agent.

In addition, the concrete structure of the present invention has an expansion rate of 150 × 10 after the 7th day of curing at 5 ° C. under water after the concrete material obtained by kneading the concrete material of the present invention and water is mixed. and at ^-6, and is characterized in that in curing 14 days at 600 × ^{10 -6} in the following range.

Preferably, the concrete structure of the present invention is a mass ratio X (mass%) of the water with respect to the total mass of the moderately heated cement and the low additive expansion material contained in the concrete material of the present invention, The unit amount Y (kg / m ³ ) of the low addition type expansion material contained per unit volume (m ³ ) of the concrete structure is the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
It is characterized by satisfying the relationship.

In the method for producing a concrete structure of the present invention, when the concrete material containing the concrete material of the present invention and water is driven in a cold temperature of 10 ° C. or less, the moderately hot Portland cement contained in the concrete material and the low The mass ratio X (mass%) of the water with respect to the total mass of the additive expansion material, and the unit amount Y (kg / m ³ ) of the low additive expansion material contained per unit volume (m ³ ) of the concrete structure Is the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
A concrete structure is constructed by using a concrete material prepared so as to satisfy the above conditions by driving in a cold state of 10 ° C. or lower.

The cold-placed concrete material of the present invention includes medium-heated Portland cement, a low additive-type expansion material, and an aggregate. The concrete material obtained by kneading the concrete material and water is finally poured. The unit amount of the low-addition type expansive material contained per 1 m ^{3 of the} finished concrete structure obtained in the above is set to a specific blending ratio, so that it can be used for driving in cold, particularly at 10 ° C. or less. It is possible to effectively suppress or prevent cracks resulting from drying shrinkage, which is an initial defect.

  In addition, the concrete structure of the present invention has an expansion rate within a certain range after the concrete material is placed, so that cracks due to drying shrinkage of the concrete structure placed at a temperature of 10 ° C. or less are remarkable in cold weather. Even in a surface member constituting a structure such as a slab or a wall, cracks due to drying shrinkage that are initial defects can be effectively suppressed or prevented.

  The method for producing a concrete structure of the present invention uses a medium-heated Portland cement, a low additive expansion material, and a concrete material prepared by adjusting the amount of water so that the concrete material satisfies a certain relationship. In particular, since it is used to drive a concrete structure at 10 ° C. or lower, it is possible to construct a concrete structure in which cracks due to drying shrinkage do not occur.

Low addition type contained per unit volume (1 m ³ ) of concrete structure with respect to the total mass X (mass%) of water / (medium moderately heated cement + low addition type expansive material) in the concrete material for placing during cold of the present invention It is a figure which shows the effective range of unit amount Y (kg / m < ³ >) of an expandable material. It is a figure which shows the uniaxial constrained expansion coefficient in the age (day) at the time of low temperature placing of the concrete material (No. 3, 16-19) for placing at the time of cold. It is a figure which shows the uniaxial restraint expansion coefficient in the age (day) at the time of the low temperature placing of the concrete material for placement (No. 8, 20) in cold conditions. It is a figure which shows the compressive strength in the age (day) at the time of low temperature implantation of the concrete material (No. 8, 20) for placement under cold conditions. It is a figure which shows the uniaxial restraint expansion coefficient in the age (day) at the time of low temperature implantation of the concrete material (No.1, 2, 4, 5) for placement under cold conditions. It is a figure which shows the uniaxial constrained expansion coefficient in the age (day) at the time of low temperature implantation of the concrete material for placement (No. 6, 7, 9, 10) under cold conditions. It is a figure which shows the uniaxial constrained expansion coefficient in the age (day) at the time of low temperature implantation of the concrete material for placement (No. 11, 12, 14, 15) under cold conditions. It is a figure which shows the compressive strength in the age (day) at the time of the low temperature placing of the concrete material for placement (No. 1, 2, 4, 5) under cold conditions. It is a figure which shows the compressive strength in the material age (day) at the time of low temperature placing for the concrete material for placement (No. 6, 7, 9, 10) under cold conditions. It is a figure which shows the compressive strength in the age (day) at the time of low temperature placement of the concrete material for placement (No. 11, 12, 14, 15) under cold conditions.

The best mode for carrying out the present invention will be described below, but the present invention is not limited thereto.
The concrete material of the present invention is a concrete material used for driving in cold weather, and includes medium-heated Portland cement, a low additive type expansion material, and an aggregate (however, fatty acids and / or salts thereof, blast furnace) (Slow cooling slag is not included).
Generally, moderately hot Portland cement is inferior in crack resistance in a normal temperature range, and it is difficult to obtain a desired crack reduction effect even when combined with an expansion material.
However, in the present invention, when it is cold, particularly in a cold region of 10 ° C. or less, the strength expression time of medium-heated Portland cement coincides with the time of expansion expression of the expansion material, so it cannot be obtained in the normal temperature region. It became possible to obtain excellent crack suppression or prevention.

The moderately hot portland cement used for the concrete material of the present invention has a low heat of hydration and can be struck as concrete even in cold weather to exhibit strength, and is standardized in Japanese Industrial Standards: JIS R5210 Any one or more of them can be used.
Further, the low addition type expansion material used for the concrete material of the present invention compensates for the shrinkage of the concrete structure after placing, for example, lime-based expansion material, ettringite expansion material, ettringite-lime composite expansion material One or more of these are preferably used.
As the ettringite-lime composite expansion material, for example, an expansion material containing 50% by mass of free lime, 20% by mass of Irwin (3CaO.3Al ₂ O ₃ .CaSO ₄ ), and 30% by mass of anhydrous gypsum is preferable. It is done.

The blending amount of the low addition type expansive material contained in the concrete material of the present invention is the mass of water mixed with the total mass of the moderately heated Portland cement and the low addition type expansive material contained in the concrete material. The ratio X (mass%) and the unit amount Y (kg / m ³ ) of the low addition type expansion material contained per unit volume (m ³ ) of the concrete structure are represented by the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
It is necessary to have a relationship that satisfies
Here, the concrete structure refers to a concrete structure that is driven and cured using a concrete material obtained by kneading the above concrete material and water.

This is because if the blending amount of the low addition type expansion material is less than the range represented by the above formula, the addition effect of the expansion material is small, and a sufficient expansion effect against drying shrinkage cannot be obtained. This is because it becomes difficult to compensate for the shrinkage of the structure, and if the blending amount is larger than the range represented by the above formula, excessive expansion may occur, resulting in the concrete structure. This is because fine cracks may occur.
For example, when the concrete material and water are mixed and then kneaded to prepare a concrete material, the mixing mass ratio of water to the total mass of the moderately-heated Portland cement and the low addition type expansion material is 0.5 ( 50 mass%), the blending amount of the low addition type expansive material contained in the concrete material is 15 to 25 kg / m ³ per unit volume (m ³ ) of the finished concrete structure. When each is 0.4 (40 mass%), it is preferable to set it as 17.5-27.5 kg / m < ³ >.

Furthermore, the aggregate used in the concrete material of the present invention is not particularly limited as long as it is blended with ordinary concrete, and as fine aggregate, river sand, land sand, crushed sand, etc. Further, as the coarse aggregate, river gravel, land gravel, crushed stone and the like can be suitably used.
Additives such as a water reducing agent may be added to the concrete material as necessary (however, fatty acids and / or salts thereof, and blast furnace slow cooling slag are not included).
As the water reducing agent, for example, an AE water reducing agent, a high performance water reducing agent, a high performance AE water reducing agent and the like are preferably used.

Further, the concrete material of the present invention can be added by mixing the above-described concrete material of the present invention and water, specifically, medium-heated Portland cement, low-addition type expansion material and aggregate, and if necessary, It is obtained by mixing water reducing agent and water.
The mass ratio X (mass%) of water with respect to the total mass of the medium-heated Portland cement and the low additive expansion material contained in the concrete material, and the low content contained per unit volume (m ³ ) of the finished concrete structure The unit amount Y (kg / m ³ ) of the additive-type expansion material is the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
Is satisfied.

FIG. 1 illustrates the above formula per unit volume (m ³ ) of a finished concrete structure with respect to water / (medium moderately hot Portland cement + low additive expansion material) X (mass%) in the concrete material of the present invention. The range of the unit amount Y (kg / m ³ ) of the low addition type expansion material contained is illustrated.
In FIG. 1, the upper limit value and the lower limit value of the low additive-type expansion material amount Y are shown by two straight lines.

In the figure, “O” indicates a preferred embodiment in which no cracks due to expansion or drying shrinkage are observed, and “X” indicates an embodiment in which cracks due to expansion are observed, or the expansion rate after implantation is 150 × 10. Each of them is less than ⁻⁶ and may be cracked due to drying shrinkage.
Further, the straight line L ₁ in FIG. 1 the upper limit, the straight line L ₂ represents the lower limit, respectively.
Note that cracks in the region above the straight line L _{1 (upper} limit) is due to the expansion of the concrete, cracking in the region below the straight line L _{2 (lower} limit) is due to the drying shrinkage of the concrete .

The evaluation of such cracks is as follows: water / (medium-heated Portland cement + low addition type expansion material) X (mass%) and the unit amount of low addition type expansion material contained per unit volume (m ³ ) of the finished concrete structure After preparing a plurality of concrete materials each having a different value from Y, and preparing three columnar concrete structure specimens having an outer diameter of 10 cm and a height of 20 cm for each concrete material, The surface of each concrete structure specimen was visually observed to check for cracks due to expansion or drying shrinkage.

According to FIG. 1, the mass ratio (% by mass) of water with respect to the total mass of the medium-heated Portland cement and the low additive expansion material contained in the concrete material and the finished concrete structure unit when the concrete material is driven in the cold The range of the unit amount Y (kg / m ³ ) of the low addition type expansion material contained per volume (m ³ ) is within the range of these straight lines L ₁ and L ₂ , that is,
27.5-0.25X ≦ Y ≦ 37.5-0.25X
If it satisfies the above, it can be seen that no cracks due to expansion or drying shrinkage, which are initial defects, are observed.

The concrete structure of the present embodiment is constructed by driving the above-described concrete material when it is cold at 10 ° C. or lower and then curing for a predetermined period.
In this way, the concrete structure has an expansion rate of 150 × 10 ⁻⁶ or more after the 7th day of curing after the concrete material is placed in the cold state, that is, when it is cold, and is expanded on the 14th day of the curing. The rate is preferably in the range of 600 × 10 ⁻⁶ or less.
The range of this expansion coefficient is the uniaxial constrained expansion test method (“Test Method Targeting Expansion and Shrinkage” of Method B of “Appendix 2 Japanese Industrial Standards JIS A 6202 Appendix 2 Constrained Expansion and Shrinkage Test Method of Expanded Concrete”). The uniaxially constrained expansion rate of the hardened concrete material on the 7th day at 5 ° C. wet curing is 150 × 10 ⁻⁶ or more, and the expansion rate on the 14th day of curing is 600 × 10 ⁻⁶ or less. It means that it is within the range.

Here, the reason for limiting the expansion rate after the age of 7 days to a range of 150 × 10 ⁻⁶ or more is that if the expansion rate is less than 150 × 10 ⁻⁶ , the drying shrinkage cannot be sufficiently compensated, This is because cracks due to drying shrinkage tend to occur, and when the expansion rate at the age of 14 days exceeds 600 × 10 ⁻⁶ , cracks due to excessive expansion are likely to occur in the concrete structure. It is.

In order to manufacture such a concrete structure, the mass ratio X (mass%) of water with respect to the total mass of the medium-heated Portland cement and the low-addition-type expansion material, and the low content contained per unit amount of finished concrete (m ³ ). The unit amount Y (kg / m ³ ) of the additive-type expansion material is the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
In order to satisfy the above conditions, medium-heated Portland cement, low-addition type expansion material, aggregate, water, and water reducing agent as needed are weighed and put into a mixer. Kneaded thoroughly until fully dispersed uniformly to prepare a concrete material.

Thereafter, the concrete material is immediately driven into a mold having a predetermined shape, and sufficient curing is performed.
Desirably, the period necessary for the curing is preferably longer than the warm period in consideration of the outside air temperature when it is cold, and is at least 7 days.
By this curing, the low-addition type expansion material exerts an expansion effect and compensates for the drying shrinkage of the concrete, whereby the concrete structure maintains a desired shape without causing excessive drying shrinkage or excessive expansion. However, the mechanical strength can be sufficiently expressed.

The present invention will be specifically described with reference to the following examples and comparative examples, but the present invention is not limited to these examples.
A. Unconfined expansion rate and expansion cracking of concrete (1) “Evaluation of cement type and expansion characteristics”
As shown in Table 1, the type of cement, the water in the concrete material / (cement + low-additive expansion material) X (mass%), and the unit expansion material amount Y (kg) contained per unit volume of the concrete structure In order to confirm the expansion characteristics of the combination of the cement type and the low additive type expansion material among the 20 types of concrete materials obtained by variously setting (/ m ³ ), no. 3 and no. The uniaxial restraint expansion coefficient of the concrete structure specimen which was driven at 5 ° C. using 16-19 concrete materials and then cured in water at 5 ° C. was measured.
In addition, the measurement of the uniaxial restraint expansion rate is based on the B method “Test method for expansion and contraction” of “Appendix 2 of Japanese Industrial Standards JIS A 6202, Annex 2 Restraint Expansion and Shrinkage Test of Expanded Concrete” except for the curing temperature. Was made to comply.

The results are shown in FIG.
From FIG. 2, in the combination of the cement type and the low additive type expansion material, an appropriate expansion was obtained as compared with the time of placing, and the concrete structure specimen with less drying shrinkage thereafter was No. 3 (Cement type; moderately hot Portland cement) and No. 3 19 (cement type; low heat Portland cement).

  In Table 1, medium-heated Portland cement, ordinary Portland cement, early strong Portland cement, blast furnace cement Type B and low heat Portland cement are all made by Sumitomo Osaka Cement Co., Ltd. Used an ettringite-lime composite expansion material (manufactured by Sumitomo Osaka Cement Co., Ltd .; product name: Super Sax Type S).

(2) “Evaluation of concrete materials for placement in cold weather”
<Concrete uniaxial restraint expansion coefficient and strength development test>
Using concrete materials of No. 8 (cement type; moderately hot Portland cement) and No. 20 (cement type; low-heat Portland cement) in Table 1 above, the expansion of the concrete structure specimen and the expression of strength in the placement during cold weather The concrete structure specimens that were driven at a temperature of 5 ° C. were tested by water curing at 5 ° C.
The two types of concrete specimens No. 8 and No. 20 were measured for uniaxially restricted expansion, and the results are shown in FIG. In addition, the uniaxial restraint expansion coefficient was measured by the method similar to the said test method.
Further, the strength development properties of the concrete structure specimens No. 8 and No. 20 were tested.
The strength development was tested according to JIS A 1108 “Concrete Compressive Strength Test Method”. The result is shown in FIG.

No. 8 and no. No. 20 concrete structure specimen can be properly expanded. In the structure using the concrete material of No. 8, the compressive strength becomes 10 N / mm ² or more at any age. It was revealed that the compressive strength of the concrete structure using 20 concrete materials is not sufficient, and it may be difficult to demold the concrete structure driven in the cold.

Subsequently, the uniaxial restraint expansion coefficient of each concrete structure specimen produced by using concrete materials (Nos. 1 to 15) and driving at 5 ° C. was measured. The measurement of the uniaxial restricted expansion rate was performed in the same manner as the above test method.
In addition, the uniaxial restraint expansion coefficient in each material age of each specimen which performed 5 degreeC water curing as a curing condition was measured.
Moreover, the compressive strength of these specimens was also measured.

FIG. 1 to 5 are diagrams showing uniaxial restrained expansion rates at respective ages (days). 6 to 10 are diagrams showing uniaxial restrained expansion rates at respective ages (days) of 6 to 10, respectively. It is a figure which shows the uniaxial restraint expansion coefficient in each material age (day) of 11-15 each.
Further, FIG. 1 to 5 are diagrams showing the compressive strength at each age (day). It is a figure which shows the compressive strength in each age (day) of each 6-10, FIG. It is a figure which shows the compressive strength in each material age (day) of 11-15 each.

(Evaluation criteria)
Even when concrete is driven in a cold condition, it is required that cracks due to expansion and cracks due to drying shrinkage do not occur.
In order to prevent cracking due to shrinkage, if an expansion amount of 150 × 10 ⁻⁶ or more is generated by 7 days after implantation, it has resistance due to shrinkage cracking. It is also suggested in the Japan Society of Civil Engineers "Guidelines for Design and Construction of Expanded Concrete".
From this, it can be seen that the specimens No. 1 and No. 6 have an expansion rate of 150 × 10 ⁻⁶ or less on the 7th, and are inappropriate as concrete during cold weather.

On the other hand, cracks due to expansion are caused by adding a large amount of an expanding material, thereby inhibiting the development of concrete strength, causing concrete cracks due to excessive expansion, and further reducing the strength.
In concrete cast in the cold, it was confirmed from the above test results that cracks due to expansion would not occur if the expansion rate on the 14th day was 600 × 10 ⁻⁶ or less.
Here, the reason why the expansion rate on the 14th day was set as a standard is that there was almost no increase in the expansion after the 14th day even in cold weather.
Specimens No. 10 and 15 had an expansion rate of 14 × 10 ⁻⁶ or more on the 14th day, and cracks due to expansion were confirmed.

From FIG. 1 and these figures, when using a combination of moderately-heated Portland cement and a low addition type expansion material blended at a certain ratio at the time of cold, the concrete material that reduces cracks due to drying shrinkage is as follows: to compensate for the causes of the cracking by the expansion action of low added-type expansion member contracts contained in such materials, low added-type expansion material a concrete structure unit volume 1 m ³ per lower limit of the linear L ₂ in FIG. 1 By using more than the addition amount shown by a value, it turns out that the expansion coefficient of 150x10 < ^-6 > or more is obtained by age 7 days.
Therefore, by setting the blending range of the low additive type expansion material as described above, it has resistance to cracks caused by drying shrinkage.

Table 2 shows the results of a test for confirming expansion cracks in the unconstrained state of the concrete material (No. 1 to 15).
In such a confirmation test, each concrete material (No. 1 to 15) was driven at 5 ° C., and three pieces of each were produced, each having a columnar concrete structure specimen having an outer diameter of 10 cm and a height of 20 cm. Then, the mold is removed from the mold on the first day of the wet curing at the temperature, and each concrete structure specimen is immersed in water at 5 ° C., and then the surface of each concrete structure specimen is visually observed every day. It was observed and examined for the presence of expansion cracks.

From Table 2, no. In the concrete structure specimens of 1, 2, 4 to 7, 9, 11, 12, and 14, no expansion crack was observed even 6 days after immersion in water (7 days after preparation of the specimen). On the other hand, no. In the concrete specimens 10 and 15, cracks occurred by 6 days after immersion in water (7 days after preparation of the specimen).
Moreover, the strength expression property of the concrete structure specimen was tested.
The strength development was tested according to JIS A 1108 “Concrete Compressive Strength Test Method”. The results are shown in FIGS.

From the compressive strength shown in FIG. 9 and FIG. It can be seen that the concrete structure specimens of Nos. 10 and 15 are significantly inferior in strength development due to cracks as compared with other specimens in which no cracks occurred.
Accordingly, from FIGS. 5 to 7, FIGS. 9 and 10, and Table 2, the expansion coefficient at the upper limit of the added amount of the unit expanded material (kg / m ³ ) that does not cause expansion cracks in the placement of the concrete material at the time of cold is It can be seen that it may be 600 × 10 ⁻⁶ or less at the age of 14 days.

From the above results, in FIG. 1, in order to obtain an expansion coefficient of 150 × 10 ⁻⁶ or more that provides resistance to cracking due to drying shrinkage, the unit expansion of the low addition type expansion material per unit volume of the concrete structure The material amount (kg / m ³ ) range may be equal to or greater than the straight line L ₁ shown in FIG. 1, and the added amount of the unit expanded material amount (kg / m ³ ) that does not generate expansion cracks may be within the range of the straight line L _2. I understand that.

B. Crack resistance of concrete In a concrete structure actually constructed, tensile stress is generated by the shrinkage being restrained by reinforcing bars embedded in the concrete or existing concrete structures, and this tensile stress is applied to the concrete structure. When the tensile strength is exceeded, a phenomenon occurs in which the concrete structure is cracked.
As described above, if the uniaxial restraint expansion coefficient at the age of 7 days after implantation is less than 150 × 10 ⁻⁶ , there is a possibility of cracking due to drying shrinkage in a concrete structure restrained by a reinforcing bar or the like The fact that the "Design Guidelines for Expanded Concrete" of the Japan Society of Civil Engineers cannot be cleared is the same at cold and normal temperatures.

  According to the present embodiment, by using a medium-heated Portland cement and a low additive type expansion material in combination with a concrete material to be poured in the cold, not only the predetermined expansion rate is satisfied, but also the initial expansion crack and drying shrinkage It is clear that it has become possible to produce cracking-reduced concrete for driving in cold weather that can suppress cracking due to aging.

  The present invention is a concrete material that can be effectively applied particularly when driven in cold weather, and a concrete structure manufactured by such a concrete material has excellent strength development and cracks due to drying shrinkage, slabs, walls, etc. Since the cracks caused by drying shrinkage, which is an initial defect, can be effectively suppressed or prevented in the surface members constituting the construction structure of the construction, further improvement in durability and further improvement in earthquake resistance can be achieved during cold weather. It becomes possible to improve, and it can be effectively applied to a reinforced concrete structure or a steel reinforced concrete structure that is driven in cold weather.

Claims (5)

It is a concrete material used for driving in the cold, and includes medium-heated Portland cement, a low additive type expansion material, and aggregates (however, fatty acids and / or salts thereof, and blast furnace slow cooling slag are not included) Contained per unit mass (m ³ ) of mass ratio X (mass%) of water mixed with the total mass of medium-heated Portland cement and low additive expansion material contained in the concrete material The unit amount Y (kg / m ³ ) of the low addition type expansion material to be used is the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
A concrete material for placing in cold weather, characterized by satisfying the relationship.   The concrete material for pouring during cold according to claim 1, wherein the low additive type expansive material is an ettringite-lime composite expansive material.   3. A cold-placed concrete material according to claim 1 or 2, further comprising a water reducing agent. The expansion coefficient after pouring the concrete material obtained by kneading the concrete material for cold placing according to any one of claims 1 to 3 and water is 150 × after 7 days of 5 ° C water curing. A concrete structure characterized by being 10 ⁻⁶ or more and within a range of 600 × 10 ⁻⁶ or less on the 14th day of curing. 5. The concrete structure according to claim 4, wherein a mass ratio X (mass%) of the water with respect to a total mass of the moderately-heated cement and the low addition type expansion material contained in the concrete material, and a concrete structure unit volume (m ³ ) The unit amount Y (kg / m ³ ) of the low addition type expansion material contained per unit is the following formula:
27.5-0.25X ≦ Y ≦ 37.5-0.25X
A concrete structure characterized by satisfying the following requirements.

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