Method for manufacturing concrete specimen

Abstract

In a concrete specimen 100 in which a crack 110 has been introduced in advance to an exposure surface 120, a load is applied to two end parts such that a surface on the opposite side corresponding to the crack 110 serves as a fulcrum 32. A surface of the concrete specimen 100 other than the exposure surface 120 is reinforced in a state in which the crack 110 has reached a desired width, and the load is released after the reinforcement. After the reinforcement, the two end parts are cut off, leaving a prescribed size centered on the crack 110.

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 Mikio 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," Japan Industrial Standards

[0005] In the case of prestressed concrete specimens, cracks introduced by the prestress of the internal rebars close. In Non-Patent Document 1, a three-point bending fixture is used to maintain the crack width. To maintain a certain crack width, a large bending stress must be applied to the specimen, so the fixture must be made of strong steel, which makes it difficult to secure experimental space and prepare a large number of specimens.

[0006] One possible method is to insert a spacer into the cracked area while the crack is open, but this would mean partially closing the cracked area, so there is room for improvement.

[0007] The present disclosure has been made in consideration of the above, and aims to provide a concrete specimen with controlled crack width that does not take up much space during experiments.

[0008] A method for manufacturing a concrete specimen according to one embodiment of the present disclosure involves applying a load to both ends of a concrete specimen, with a crack previously introduced into the exposed surface of the concrete specimen, using the opposite surface of the concrete specimen corresponding to the crack as a fulcrum, reinforcing the surfaces of the concrete specimen other than the exposed surface once the crack has reached a desired width, and then releasing the load after the reinforcement.

[0009] According to the present disclosure, it is possible to provide a concrete specimen with controlled crack width that does not take up much space during experiments.

[0010] 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. Fig. 3 is a side view showing an example of a concrete specimen fixed to a fixing jig. Fig. 4 is a top view showing an example of a concrete specimen fixed to a fixing jig. Fig. 5 is a side view showing an example of a concrete specimen fixed to a fixing jig. Fig. 6 is a diagram showing an example of a concrete specimen.

[0011] An example of a method for manufacturing a concrete specimen according to this embodiment will be described with reference to FIG.

[0012] In step S1, a worker fixes the concrete specimen with cracks introduced to a fixing jig.

[0013] FIG. 2 shows an example of a concrete specimen 100. The concrete specimen 100 is a concrete piece cut from a cylindrical prestressed concrete structure (e.g., a utility pole) with a crack 110 introduced into it. 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 a concrete piece cut from a utility pole is used, the short direction of the concrete specimen 100 is curved, and reinforcing bars are present within the concrete specimen 100.

[0014] If multiple cracks occur in the concrete specimen 100, the bending stress that occurs when a load is applied to both ends of the concrete specimen 100 is dispersed, making it difficult to control the crack width. For this reason, it is desirable for the concrete specimen 100 to have only one crack. To prepare a concrete specimen 100 with only one crack introduced into the exposed surface 120, it is advisable to reinforce both ends of the exposed surface 120 (the surface shown in FIG. 2 ) with resin 130, and then apply stress so that only one crack 110 occurs on the exposed surface 120 in the center of the concrete specimen 100.

[0015] 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 between the base 31 and the metal plate 33. The base 31 and the metal plate 33 are connected with bolts 34.

[0016] In step S2, 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 crack reaches the desired crack width.

[0017] In step S3, while controlling the crack width with the fixture 30, the worker reinforces the surfaces of the concrete specimen 100 other than the exposed surface in the experiment. FIG. 4 shows the reinforced concrete specimen 100. In the example shown in FIG. 4, the concrete specimen 100 is reinforced by applying epoxy resin 140 to the side of the concrete specimen 100. The side here refers to the side when the exposed surface 120 is the front. Paint is applied uniformly to the side of the concrete specimen 100. The paint film thickness is preferably 30 μm or more. Similar effects can be achieved with paints with a higher Young's modulus than epoxy resins, such as unsaturated polyester resins or polyurethane resins. Alternatively, metal plates with a higher Young's modulus and strength than concrete may be attached to the side of the concrete specimen 100 with resin or the like.

[0018] After reinforcing the concrete specimen 100, in step S4, the worker loosens the bolts 34 to release the load, and removes the concrete specimen 100 from the fixing jig 30.

[0019] In step S5, the worker cuts off both ends of the concrete specimen 100, leaving the exposed surface 120 including the crack 110. To reduce the force that attempts to close the crack 110 due to prestress from the rebar away from the crack 110, it is recommended to cut off both ends immediately after removing the concrete specimen 100 from the fixture 30. FIG. 6 shows an example of a concrete specimen 100 with both ends cut off. In the example shown in the figure, both ends were cut off, leaving the entire exposed surface 120 and a small amount of resin 130. The sides of the concrete specimen 100 are reinforced with epoxy resin 140. Because the effects of surfaces other than the crack 110 must also be evaluated experimentally, it is recommended to leave at least 100 mm of the exposed surface 120 of the concrete specimen 100. Note that it is not necessary to cut off both ends of the concrete specimen 100.

[0020] As described above, the method for manufacturing a concrete specimen of this embodiment involves applying a load to both ends of concrete specimen 100, with crack 110 previously introduced into exposed surface 120, using the surface opposite crack 110 as fulcrum 32, and once crack 110 has reached a desired width, reinforcing the surfaces of concrete specimen 100 other than exposed surface 120, and then releasing the load. This eliminates the need to continue fixing concrete specimen 100 with fixing jig 30, making it possible to provide a concrete specimen with a controlled crack width that does not take up much space during experiments.

[0021] In the method for manufacturing a concrete specimen according to this embodiment, after reinforcement, both ends are cut off, leaving a predetermined size centered on the crack 110. This reduces the force that tries to close the crack 110 due to the prestress of the reinforcing bars.

[0022] 100 Concrete specimen 110 Crack 120 Exposed surface 130 Resin 140 Epoxy resin 30 Fixing jig 31 Base 32 Support 33 Metal plate 34 Bolt

Claims

1. A method for manufacturing a concrete specimen, comprising the steps of: applying loads to both ends of a concrete specimen, with a crack previously introduced into the exposed surface of the specimen, using the surface opposite the crack as a fulcrum; reinforcing the surfaces of the concrete specimen other than the exposed surface when the crack has reached a desired width; and releasing the load after the reinforcement.

2. A method for manufacturing a concrete specimen according to claim 1, in which only one crack is introduced into a concrete piece cut out from a prestressed concrete structure.

3. A method for manufacturing a concrete specimen according to claim 2, comprising the steps of: cutting both ends of the concrete specimen after reinforcement, leaving a predetermined size centered on the crack.

4. A method for manufacturing a concrete specimen according to any one of claims 1 to 3, comprising the steps of applying a resin to the side surface of the concrete specimen when the exposed surface is the front surface, thereby reinforcing the side surface of the concrete specimen.

5. A method for manufacturing a concrete specimen according to claim 4, comprising applying an epoxy resin to the concrete specimen for reinforcement.

6. A method for manufacturing a concrete specimen according to any one of claims 1 to 3, comprising reinforcing the concrete specimen by attaching a plate of a material having a higher Young's modulus and strength than concrete.

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