Method for manufacturing concrete test piece

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

[0001] The present disclosure relates to a method for manufacturing a concrete specimen.

[0002] 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 concrete structures over time when cracks appear in the concrete.

[0003] In order to evaluate the deterioration of concrete structures over time, concrete specimens are manufactured by introducing cracks in advance and controlling the crack width. 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 out from utility poles.

[0004] Shunsuke Otani, Toru Wakabayashi, and Motoyuki Ichiba, "Study on Corrosion Monitoring of Steel Bars Inside Utility Poles," 64th Materials and Environment Review Meeting (2017), B-102 "Test Method for Bending Strength of Concrete JIS A 1106:2018," JIS "Injection Epoxy Resin for Building Repair JIS A 6024:2008," JIS

[0005] As in Non-Patent Document 1, when cracks are introduced into a concrete specimen using a three-point bending test jig, countless cracks often occur, and there is a problem that it is difficult to control the crack width to 0.3 mm or more.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a concrete specimen with a larger crack width.

[0007] A method for manufacturing a concrete specimen according to one embodiment of the present disclosure involves reinforcing both ends of the exposed surface of a concrete specimen, leaving the central portion of the exposed surface where a crack is to be introduced, applying bending stress to the concrete specimen with the reinforced ends to introduce a single crack in the central portion of the exposed surface, and applying loads to both ends of the concrete specimen using the opposite surface of the concrete specimen corresponding to the crack as a fulcrum to control the crack width.

[0008] According to the present disclosure, a concrete specimen with a larger crack width can be provided.

[0009] Fig. 1 is a flowchart 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 with reinforced ends. Fig. 3 is a diagram showing an example of a concrete specimen with cracks. 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.

[0010] An example of a method for manufacturing a concrete specimen according to this embodiment will be described with reference to FIG.

[0011] In step S1 , the worker reinforces both ends of the concrete specimen 100 .

[0012] The concrete specimen 100 is a concrete piece cut from a cylindrical prestressed concrete structure (e.g., a utility pole). The length of the concrete specimen 100 in the long direction is preferably 150 mm to 600 mm. To satisfy the standard of the concrete bending strength test method described in Non-Patent Document 2, the span when bending stress is applied should be at least 3 times the thickness of the specimen ±20%. When using a concrete piece cut from a utility pole, the short direction of the concrete specimen 100 is curved, and reinforcing bars are present within the concrete specimen 100.

[0013] FIG. 2 shows an example of a concrete specimen 100 with reinforced ends. In the example of FIG. 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 not reinforced with epoxy resin 130 is the portion 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 of the exposed surface 120. While Non-Patent Document 1 covers the surface other than the exposed surface with epoxy resin paint, this embodiment differs in that both ends of the exposed surface 120 are coated with epoxy resin 130.

[0014] Since concrete cracks easily appear in areas other than the center during bending tests, it is believed that cracks originate from small defects on the concrete surface. Therefore, concrete reinforcement should be achieved by reinforcing the concrete surface without gaps. Specifically, rather than reinforcing the concrete surface with tape, it is desirable to use a material that penetrates the concrete surface and adheres to it for reinforcement. Resins with high concrete permeability, such as epoxy resins classified as low viscosity (viscosity 100 to 1000 mPa·s) as described in Non-Patent Document 3, can be used. Any resin that can reinforce the concrete specimen 100 is acceptable, not just epoxy resins. The thicker the resin is applied, the greater the reinforcing effect. Because even small defects on the concrete surface can become crack initiation points, a paint film thickness of 30 μm or more is desirable to ensure no areas are left uncoated.

[0015] 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, the bending stress is applied to the concrete specimen 100 until a single crack appears. The bending stress may be applied to the concrete specimen 100 using a bending tester capable of precise load control, or the bending stress may be applied to the concrete specimen 100 using a fixing jig described below. The occurrence of a crack may be confirmed visually, or by detecting acoustic emissions. If acoustic emissions are detected, the bending stress can be reliably released before multiple cracks appear.

[0016] 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 and number of cracks that occur can be easily controlled.

[0017] In step S3, the worker fixes the concrete specimen with the cracks introduced to a fixing jig.

[0018] 3 and 4 show the concrete specimen 100 fixed to the fixing jig 30. FIG. 3 is a side view, and FIG. 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 concrete specimen 100 in the long direction between the base 31 and a 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.

[0019] 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 of Figure 3, the worker tightens the bolts 34 and applies a load to both ends of the concrete specimen 100 until the desired crack width is reached.

[0020] As explained above, both ends of the exposed surface 120 of the concrete specimen 100 where 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 the reinforced both ends to introduce a single crack 110 in the central portion of the exposed surface 120. The crack width is controlled by applying a load to both ends of the concrete specimen 100 using the surface of the concrete specimen 100 opposite to the crack 110 as a fulcrum 32. This makes it possible to provide a concrete specimen with a larger crack width.

[0021] 100 Concrete specimen 110 Crack 120 Exposed surface 130 Epoxy resin 30 Fixing jig 31 Base 32 Support 33 Metal plate 34 Bolt

Claims

1. A method for manufacturing a concrete specimen, comprising: reinforcing both ends of an exposed surface of a concrete specimen in which a crack is to be introduced, leaving the central portion of the exposed surface; applying bending stress to the concrete specimen with both ends reinforced to introduce a single crack in the central portion of the exposed surface; and applying a load to both ends of the concrete specimen, using the opposite surface of the concrete specimen corresponding to the crack as a fulcrum, to control the width of the crack.

2. A method for manufacturing a concrete specimen according to claim 1, comprising applying a resin coating to both ends of the exposed surface to reinforce the exposed surface.

3. A method for manufacturing a concrete specimen according to claim 2, comprising applying an epoxy resin to both ends of the exposed surface to reinforce the exposed surface.

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