WO2024257174A1 - Method for manufacturing concrete test piece - Google Patents

Abstract

This method involves: reinforcing both end parts of an exposed surface 120 of a concrete test piece 100, to which a crack is to be introduced, while leaving the central part of the exposed surface; introducing one crack 110 into the central part of the exposed surface 120 by applying bending stress to the concrete test piece 100 having said both end parts reinforced; and controlling the crack width by applying loads onto said both end parts of the concrete test piece 100 while setting a surface of the concrete test piece 100 oppositely corresponding to the crack 110 as a fulcrum 32.

Description

Manufacturing method of concrete specimen

This disclosure relates to a method for manufacturing a concrete specimen.

In concrete structures, the reinforcing bars inside the concrete will not corrode as long as the concrete remains alkaline, but if the concrete becomes neutral or salt penetrates into the concrete, the reinforcing bars will begin to corrode. If cracks appear in the concrete, the concrete becomes more susceptible to neutralization and salt penetration. Therefore, in order to maintain and manage concrete structures, it is important to understand the deterioration of the concrete structure over time when cracks appear in the concrete.

In order to evaluate the deterioration of concrete structures over time, concrete specimens are manufactured with cracks introduced in advance and the width of the cracks controlled. Non-Patent Document 1 describes concrete specimens in which cracks of 0.1 mm and 0.3 mm width were introduced into prestressed concrete cut from utility poles.

Shunsuke Otani, Toru Wakabayashi, and Mikio Ichiba, "Study on corrosion monitoring of rebars inside utility poles," 64th Materials and Environment Review Meeting (2017), B-102 "Test method for bending strength of concrete JIS A 1106:2018", Japan Industrial Standards "Injectable epoxy resin for architectural repair JIS A 6024:2008", Japan Industrial Standards

As with Non-Patent Document 1, when cracks are introduced into a concrete specimen using a three-point bending test jig, there is a problem in that numerous cracks often occur, making it difficult to control the crack width to 0.3 mm or more.

This disclosure has been made in consideration of the above, and aims to provide a concrete specimen with a larger crack width.

In one embodiment of the method for manufacturing a concrete specimen disclosed herein, both ends of the exposed surface of the concrete specimen where the crack is to be introduced are reinforced, leaving the central portion of the exposed surface, and bending stress is applied to the concrete specimen with both ends reinforced to introduce a single crack in the central portion of the exposed surface. The crack width is controlled by applying loads to both ends of the concrete specimen using the opposite surface of the concrete specimen corresponding to the crack as a fulcrum.

This disclosure makes it possible to provide concrete specimens with larger crack widths.

FIG. 1 is a flow chart showing an example of a process flow of a method for manufacturing a concrete specimen. FIG. 2 is a diagram showing an example of a concrete specimen having reinforced both ends. FIG. 3 is a diagram showing an example of a concrete specimen having a crack. FIG. 4 is a side view showing an example of a concrete specimen fixed to a fixing jig. FIG. 5 is a top view showing an example of a concrete specimen fixed to a fixing jig.

With reference to Figure 1, an example of a method for manufacturing a concrete specimen according to this embodiment will be described.

In step S1, the worker reinforces both ends of the concrete specimen 100.

The concrete specimen 100 is a piece of concrete cut out from a cylindrical prestressed concrete structure (e.g., a utility pole). The length of the long side of the concrete specimen 100 is preferably 150 mm to 600 mm. To satisfy the standards of the bending strength test method for concrete described in Non-Patent Document 2, it is preferable that the span when bending stress is applied is 3 times the thickness of the specimen ±20% or more. When using a concrete piece cut out from a utility pole, the short side of the concrete specimen 100 is curved, and reinforcing bars are present inside the concrete specimen 100.

Figure 2 shows an example of a concrete specimen 100 with reinforced ends. In the example of Figure 2, both ends of the exposed surface 120 (the surface where cracks will occur) of the concrete specimen 100 are reinforced with epoxy resin 130, leaving the central portion of the concrete specimen 100. The exposed surface 120 that is not reinforced with epoxy resin 130 is the part where cracks will occur on the surface. Since it is necessary to experimentally evaluate the effects of the surface other than cracks, it is recommended to reinforce both ends of the exposed surface 120 of the concrete specimen 100, leaving at least 100 mm. In Non-Patent Document 1, the surface other than the exposed surface is covered with epoxy resin paint, but in this embodiment, both ends of the exposed surface 120 are covered with epoxy resin 130, which is different.

In bending tests, concrete cracks can easily appear in places other than the center, so it is believed that cracks in concrete originate from small defects on the concrete surface. Therefore, to reinforce concrete, it is better to adopt a method of reinforcing the concrete surface without any gaps. Specifically, rather than reinforcing the concrete surface with something like tape, it is preferable to use something that can penetrate the concrete surface and adhere to it for reinforcement. It is sufficient to use a resin that has high permeability to concrete, such as an epoxy resin classified as having a low viscosity (viscosity 100 to 1000 mPa·s) as described in Non-Patent Document 3. It is not limited to epoxy resin, but any resin that can reinforce the concrete specimen 100 will do. The thicker the resin is applied, the greater the reinforcing effect. If even a small defect remains on the concrete surface, it can become the starting point of a crack, so it is desirable to have a paint film thickness of 30 μm or more so that no part is left unpainted.

After the epoxy resin has hardened, in step S2, the worker applies a bending stress to the concrete specimen 100 with both ends reinforced, causing a crack in the concrete specimen 100. At this time, the stress is released before multiple cracks appear. In other words, bending stress is applied to the concrete specimen 100 until a single crack appears. Bending stress may be applied to the concrete specimen 100 using a bending tester capable of precise load control, or bending stress may be applied to the concrete specimen 100 using a fixed jig, which will be described later. The occurrence of a crack may be confirmed visually, or by detecting acoustic emissions. If acoustic emissions are detected, bending stress can be reliably released before multiple cracks appear.

Figure 3 shows an example of a concrete specimen 100 with a crack 110. The concrete specimen 100 in Figure 3 has only one crack on the exposed surface 120 that is not reinforced with epoxy resin 130. By reinforcing both ends of the exposed surface 120 of the concrete specimen 100 with epoxy resin 130, the location of the crack and the number of cracks can be easily controlled.

In step S3, the worker fixes the concrete specimen with the cracks introduced to the fixture.

Figures 3 and 4 show the concrete specimen 100 fixed to the fixing jig 30. Figure 3 is a side view, and Figure 4 is a top view. The worker places the concrete specimen 100 on the base 31 with the fulcrum 32 against the back side of the crack 110, and sandwiches both ends of the long side of the concrete specimen 100 between the base 31 and the metal plate 33. The base 31 and the metal plate 33 are connected with bolts 34. The fixing jig 30 is not limited to the one shown in the figure, and may have any structure that can apply a load to both ends of the concrete specimen 100 and fix it.

In step S4, the worker uses the center of the concrete specimen 100 as a fulcrum and applies a load to both ends of the concrete specimen 100 until the crack 110 reaches the desired crack width. When using the fixing jig 30 in FIG. 3, the bolts 34 are tightened and a load is applied to both ends of the concrete specimen 100 until the crack reaches the desired crack width.

As explained above, both ends of the exposed surface 120 of the concrete specimen 100 in which a crack is to be introduced are reinforced, leaving the central portion of the exposed surface, and bending stress is applied to the concrete specimen 100 with both ends reinforced to introduce a single crack 110 in the central portion of the exposed surface 120. The opposite surface of the concrete specimen 100 corresponding to the crack 110 is used as a fulcrum 32, and a load is applied to both ends of the concrete specimen 100 to control the crack width. This makes it possible to provide a concrete specimen with a larger crack width.

REFERENCE SIGNS LIST 100 Concrete specimen 110 Crack 120 Exposed surface 130 Epoxy resin 30 Fixing jig 31 Base 32 Support 33 Metal plate 34 Bolt

Claims (3)

The exposed ends of the concrete specimen are reinforced, leaving the central portion of the exposed surface in which the cracks are to be introduced.
A bending stress is applied to the concrete specimen having reinforced both ends to introduce a single crack in the central portion of the exposed surface;
A method for manufacturing a concrete specimen, comprising: applying loads to both ends of the concrete specimen using the opposite surface of the concrete specimen corresponding to the crack as a fulcrum, thereby controlling the crack width. A method for producing a concrete specimen according to claim 1,
A method for manufacturing a concrete specimen, comprising the steps of: applying a resin coating to both ends of the exposed surface to reinforce the surface. A method for producing a concrete specimen according to claim 2,
A method for manufacturing a concrete specimen, comprising the steps of: applying epoxy resin to both ends of the exposed surface to reinforce it.

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