Evaluation method for concrete

Abstract

To provide an evaluation method for more accurately measuring air permeability of concrete.SOLUTION: A method for evaluating concrete formed of a concrete composition includes: arranging a plurality of linear binding reinforcing-bars so as to form a network structure in which the reinforcing-bars perpendicularly intersect each other; filling the network structure with the concrete composition; preparing a tabular solid concrete test piece having vertical length and longitudinal length of 240 to 520 mm and thickness of 40 to 100 mm; and evaluating the concrete using the concrete test piece.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for evaluating concrete.

Background Art

[0002] In recent years, in the civil engineering field and the construction field, the use of concrete expansion agents in concrete compositions for the purpose of reducing tensile stress generated by drying shrinkage and the like has been increasing.

[0003] When forming expansive concrete using such an expansion agent, usually, restraint reinforcement (such as steel bars) is disposed inside it. There is a report that such expansive concrete having restraint reinforcement inside forms a hardened body with high water tightness when the concrete is consolidated. On the other hand, when the restraint reinforcement corrodes, the concrete may deteriorate and the durability may also decrease. Concrete is generally alkaline, but when air containing carbon dioxide penetrates into the concrete, it is neutralized, and as a result, the restraint reinforcement is likely to corrode. For this reason, it is desirable to control the air permeability of concrete, and there is a desire to provide a composition capable of forming concrete with controlled air permeability. And in order to control the air permeability of concrete, it is necessary to accurately evaluate the air permeability.

[0004] As a method for evaluating the air permeability of concrete, the Torrent method is generally known. This Torrent method is generally used to check the air permeability of the surface layer part at the time of completion of a concrete structure and evaluate the quality of the actual structure. That is, the Torrent method itself is used for evaluating a structure, and it is hard to say that it is established as a method for evaluating the air permeability of concrete itself.

[0005] Therefore, although there are reports on evaluating the air permeability of expansive concrete based on the Torrent method, the evaluation methods used are not exactly the same for each report, and it has been difficult to sufficiently compare concretes or the compositions for forming them with each other and obtain sufficient findings because the evaluation method for the air permeability of concrete has not been standardized.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of the above problems, the present invention provides a method for more appropriately evaluating the air permeability of concrete in a constrained state.

Means for Solving the Problems

[0008] That is, the present invention is as follows [1] to [6]. [1] A method for evaluating concrete formed from a concrete composition, placing a plurality of linear restraint reinforcing bars so as to form a mesh structure in which they are perpendicular to each other, enclosing the mesh structure with the concrete composition, and preparing a plate-shaped solid concrete specimen having a longitudinal length and a transverse length of 240 to 520 mm each and a thickness of 40 to 100 mm, the method comprising evaluating the concrete using the concrete specimen. [2] The method according to [1], wherein the ratio of the restraint reinforcement bars is 0.2 to 3.6%. [3] The method according to [1] or [2], wherein the restraint reinforcement bars are deformed reinforcement bars. [4] The method according to any one of [1] to [3], wherein the mesh structure is arranged near the center in the thickness direction of the concrete specimen. [5] A method for evaluating the air permeability of concrete formed from a concrete composition, placing a plurality of linear restraint reinforcement bars so as to form a mesh structure in which they are perpendicular to each other, enclosing the mesh structure with the concrete composition, and preparing a solid rectangular parallelepiped concrete specimen, wherein the longitudinal length and the transverse length of the rectangular parallelepiped are each 240 to 520 mm, and the thickness is 40 to 100 mm, after curing the concrete specimen, the method comprising allowing air to permeate from the bottom surface to the upper surface of the concrete specimen.

Advantages of the Invention

[0009] According to the present invention, the air permeability of concrete in a restrained state can be more appropriately evaluated.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments of the present invention are not limited by this description.

[0012] <Concrete Specimen> The concrete specimen according to the present invention includes restraint reinforcing bars of a specific shape. FIG. 1 is a perspective view of an embodiment of a concrete specimen that can be used in the evaluation method according to the present invention.

[0013] The concrete specimen used in the present invention has a plate-like shape, and restraint reinforcing bars are arranged inside the solid concrete. Here, "plate-like" refers to a structure having a substantially constant thickness and relatively large upper and lower surfaces in a direction perpendicular to the thickness direction. Typically, it has a cuboid shape with rectangular upper and lower surfaces, but the shapes of the upper and lower surfaces are not limited to rectangles and may be circular, elliptical, etc. In FIG. 1, a cuboid-shaped concrete specimen is exemplified for convenience. Since the concrete specimen is plate-like, when measuring air permeability, only the gas permeating from the bottom surface to the upper surface is easy to measure, enabling a more accurate air permeability evaluation.

[0014] The concrete specimen used in the present invention has a longitudinal length and a transverse length of 240 to 520 mm and a thickness of 40 to 100 mm, respectively. Here, when the concrete specimen has a cuboid shape as shown in FIG. 1, the longitudinal, transverse, and thickness directions can be defined as the x direction, y direction, and z direction shown in FIG. 1. If the upper and lower surfaces of the concrete specimen are not rectangular, the longitudinal length and the transverse length of the rectangle circumscribing the projection surface are taken as the longitudinal length and the transverse length of the concrete specimen.

[0015] The restraint reinforcement is composed of a plurality of straight reinforcing bars, and the plurality of reinforcing bars are arranged in a mesh pattern. In FIG. 1, a plurality of straight reinforcing bars are arranged in the x direction, and a plurality of straight reinforcing bars are arranged in the y direction perpendicular thereto. Here, the intersecting reinforcing bars do not necessarily contact each other. Also, even when the intersecting reinforcing bars contact each other, they do not need to be fixed by binding or the like. This is because each reinforcing bar only needs to exhibit the effect of restraining expansion or contraction in the x direction or the y direction. In FIG. 1, the direction of the restraint reinforcement is arranged to be parallel to the longitudinal direction or the lateral direction of the rectangular parallelepiped, but it may be arranged obliquely so as to have a certain angle with respect to the longitudinal direction or the lateral direction.

[0016] Also, it is preferable that the mesh structure formed by the restraint reinforcement is arranged near the center in the thickness direction of the plate-shaped concrete specimen. That is, in FIG. 1, the length in the z direction of the concrete specimen is the thickness, and it is preferable that the mesh structure is arranged at the portion that is half of the length. More specifically, the mesh structure includes restraint reinforcement arranged to intersect vertically, and the intermediate portion between the upper restraint reinforcement and the lower restraint reinforcement can be arranged to be at the position of half in the z direction. Furthermore, it is preferably arranged parallel to the upper surface of the concrete specimen.

[0017] Also, the restraint reinforcement is preferably arranged substantially evenly throughout the concrete specimen. Specifically, when looking at the concrete specimen from above, it is preferable that the restraint reinforcement is arranged at equal intervals in the width direction. This is because the restraint force is evenly exerted on the entire concrete specimen. To adjust the position of the restraint reinforcement in the concrete specimen, it is preferable to fix it to the formwork with wire or binding wire. The wire or binding wire is not particularly limited as long as it can fix the restraint reinforcement to the approximate center of the concrete specimen.

[0018] The concrete specimen is provided with a plurality of restraint reinforcing bars, which are adjusted according to the size of the concrete specimen, the thickness of the restraint reinforcing bars, etc., and the number thereof is not particularly limited. In the concrete specimen illustrated in FIG. 1, 10 restraint reinforcing bars are described, but for example, about 6 to 20 restraint reinforcing bars can be provided. And when manufacturing the concrete specimen provided with this restraint reinforcing bar, it is preferable that the reinforcement ratio is 0.2 to 3.6%, and more preferably 0.5 to 2.0%.

[0019] As the reinforcing bars constituting the restraint reinforcing bars used in the present invention, for example, deformed bars, round steel bars, deformed bars, stainless steel bars, etc. can be used, but deformed bars are preferably used. Also, as the material of the reinforcing bars, an appropriate one can be selected from known materials such as SR235, SD295A, SD345, etc. and used. The thickness of the steel material can be appropriately selected within a range that does not hinder the function of the present invention, and for example, a reinforcing bar with a diameter of 6 mm can be mentioned.

[0020] In the present invention, since the restraint reinforcing bars restrain the expansion or contraction of the concrete, it is preferable that the restraint reinforcing bars penetrate the concrete specimen and their ends are exposed so that the effect can be fully exerted. By adopting such a structure, the effect of the restraint reinforcing bars can be obtained over the entire length direction. However, if necessary, the restraint reinforcing bars can be made not to be exposed on the surface of the concrete specimen. Even in such a case, in order to sufficiently obtain the effect of the restraint reinforcing bars, it is preferable that the length of the restraint reinforcing bars is 90% or more of the longitudinal or transverse length of the concrete specimen.

[0021] The concrete specimen used in the present invention is manufactured, for example, by the following procedure. First, a formwork for the concrete specimen, straight restraining reinforcement bars, and a concrete composition are prepared. As the formwork, an iron formwork, a wooden formwork, etc. can be used. It is preferable that grooves or holes for fixing the restraining reinforcement bars are provided on the side surface of the formwork. And when pouring the concrete composition into the formwork, it is preferable to adjust the positions of the grooves or holes so that the restraining reinforcement bars can be fixed near the center in the thickness direction. Thereby, the restraining reinforcement bars can be arranged near the center of the concrete specimen. When no grooves or holes are provided, the restraining reinforcement bars and the formwork can be adhered with an adhesive or the like so as to be arranged near the center in the thickness direction of the concrete specimen. The concrete composition is prepared by blending cement, aggregate, water, admixtures, and admixture agents, etc., and thoroughly kneading with a concrete mixer or the like. When evaluating the properties of expansive concrete, an expansive agent for concrete specified in JIS A 6202 is used as the admixture. Next, in the formwork, the restraining reinforcement bars are arranged in a mesh structure, and the concrete composition is poured thereinto and cured in a state where the restraining reinforcement bars are encapsulated by the concrete composition, whereby the concrete specimen is manufactured. It is preferable to fill the formwork with the concrete composition while applying vibration using a table vibrator or the like. The cover of the reinforcement bars is preferably 10 to 30 mm, for example, about 20 mm. When filling the concrete composition, it is preferable that the size is such that there is a gap for the aggregate to enter between the restraining reinforcement bars and the formwork, and by setting the cover to such a size, the uneven distribution of the aggregate in the concrete specimen can be prevented.

[0022] After the concrete specimen is sufficiently cured, it is taken out of the formwork and, if necessary, cured for a predetermined period and then used for evaluation. In addition, when using a hygroscopic formwork such as a wooden formwork as the formwork, a moisture-impermeable sheet such as a polyester sheet may be installed in the formwork in advance to prevent moisture absorption from the concrete specimen.

[0023] <Method for Evaluating Permeability of Concrete> The concrete evaluation method according to the present invention is particularly suitable for evaluating the air permeability of concrete. For the evaluation of air permeability, methods such as the drilling method, the single-chamber method, and the double-chamber method (TRENT method) are known. Among these, the TRENT method is preferably used as a method for evaluating the air permeability from the bottom surface to the upper surface of a concrete structure.

[0024] In addition, the procedure for evaluating the air permeability of concrete according to the present invention is placing a plurality of linear restraint reinforcing bars so as to form a mesh structure in which they are perpendicular to each other, enclosing the mesh structure with the concrete composition, and preparing a plate-shaped solid concrete specimen having a longitudinal length and a transverse length of 240 to 520 mm each and a thickness of 40 to 100 mm, after curing the concrete specimen, allowing air to permeate from the bottom surface to the upper surface of the concrete specimen, and the air permeability is evaluated by measuring the amount of permeated air by the double-chamber method (TRENT method). Such an evaluation is preferably performed in a standardized procedure so that many measurement results can be compared with each other. In the present invention, it is preferable to perform in accordance with JCI-DD5 "Oxygen Diffusion Coefficient Test Method (Draft)" by the Japan Concrete Institute. The measurement part of the measuring device used in the double-chamber method (TRENT method) has a structure having an inner chamber and an outer chamber, and the air permeability is evaluated by the pressure in the inner chamber. By controlling the pressure in the inner chamber and the pressure in the outer chamber to be equal, the inflow of air from the outside to the inner chamber is physically excluded, and as a result, a plug flow (air flow) from the bottom surface to the upper surface of the concrete specimen is formed under the inner chamber. From this plug flow, the air permeability coefficient kt of the concrete can be measured by the following formula (1).

Equation

[0025] By adopting the method standardized in this way, it becomes possible to compare the air permeability of concrete specimens formed from various concrete compositions with each other, even if they are separated in distance or time.

[0026] Hereinafter, the present invention will be described with examples as follows. It should be noted that the present invention is not limited by the following examples.

Example

[0027] 1. Preparation of concrete specimens Using the materials shown in Table 1, a concrete composition for preparing concrete specimens was prepared. Also, using those materials, four types of concrete compositions with different mixing conditions of admixtures (expansive agents) were prepared as shown in Table 2. The admixture (expansive agent) was used as a replacement for fine aggregate and was used at a standard addition amount of 20 kg / m 3 . The fresh properties of each concrete composition were set to a target slump of 15 ± 2.5 cm and a target air content of 4.5 ± 1.5%.

[0028]

Table 1

[0029]

Table 2

[0030] Concrete specimens were prepared using each concrete composition. First, deformed bars with a diameter of 6 mm were combined in a mesh pattern in a formwork and arranged such that the mesh structure was near the center in the thickness direction of the concrete specimen. Then, the concrete composition kneaded for 2 minutes with a concrete mixer was filled into the formwork while applying vibration using a table vibrator and cured to prepare the specimen shown in Fig. 1. The size of the specimen was 300 mm in the x-direction length and y-direction length and 60 mm in the z-direction thickness as shown in Fig. 1, and the reinforcement ratio was 0.88%. Also, concrete specimens without reinforcement were prepared using each concrete composition.

[0031] 2. Test Results 2-1 Air Permeability Test The concrete specimens demolded from the formwork at 1-day age were cured in water until 7-day age and then cured in a sealed can for 182 days. After the curing was completed, the air permeability of the concrete specimens was evaluated. The obtained results were as shown in Table 3.

Table 3

[0032] From the comparison between Examples 1 and 2 and Examples 3 and 3, it can be seen that when concrete is made from a concrete composition mixed with an admixture (expansive material), the air permeability coefficient tends to be smaller. When the restrained reinforcement is not included in the concrete specimen, the difference is small and it is difficult to distinguish by the air permeability grade. On the other hand, from the comparison between Examples 5 and 6 and Examples 7 and 8, it can be seen that in the concrete specimens having the structure specified in the present invention, the difference is shown to be clear. That is, by applying restraint conditions when preparing the concrete specimens, a clear difference due to the presence or absence of the admixture was confirmed.

Explanation of Signs

[0033] 10 Concrete Specimen 11 Concrete 12 Restrained Reinforcement

Claims

1. A method for evaluating concrete formed from a concrete composition, comprising: placing a plurality of straight restraint reinforcing bars so as to form a mesh structure in which they are perpendicular to each other, enclosing the mesh structure with the concrete composition, and preparing a plate-shaped solid concrete specimen having a longitudinal length and a transverse length of 240 to 520 mm each and a thickness of 40 to 100 mm; evaluating the concrete using the concrete specimen.

2. The method according to claim 1, wherein the reinforcement ratio of the restraint reinforcing bars is 0.2 to 3.6%.

3. The method according to claim 1 or 2, wherein the restraint reinforcing bars are deformed reinforcing bars.

4. The method according to claim 1 or 2, wherein the mesh structure is disposed near the center in the thickness direction of the concrete specimen.

5. A method for evaluating the air permeability of concrete formed from a concrete composition, comprising: placing a plurality of straight restraint reinforcing bars so as to form a mesh structure in which they are perpendicular to each other, enclosing the mesh structure with the concrete composition, and preparing a plate-shaped solid concrete specimen having a longitudinal length and a transverse length of 240 to 520 mm each and a thickness of 40 to 100 mm; after curing the concrete specimen; allowing air to permeate from the bottom surface to the top surface of the concrete specimen.

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