Resin formwork for concrete strength test specimens and boss formwork using the same

Abstract

To facilitate demolding work after concrete filling in a resin formwork for creasing a boss specimen.SOLUTION: A resin formwork 1 comprises: a formwork body 2 whose one face is defined as an opening part and which is made of four lateral faces 4A-4D in the circumferential direction and a bottom face 5; a flange part 3 provided along the circumferential direction so as to surround the opening part A of the formwork body 2; a plurality of strips of ribs 6 continuously formed at prescribed intervals on the outer peripheral surface of the framework body 2; and, at the flange part 3, a plurality of slit grooves 8a-8 formed over a section from the edge of the opening A to the outer edge of the flange part 3, and notch grooves 9a and 9b thinned into a V-shaped cross section formed on the outer surface 2 over a section to the bottom face 5 so as to be substantially continued from the slit grooves 8a-8e.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resin formwork for producing a concrete strength test specimen (hereinafter also referred to as a boss specimen) that is integrally molded with structural concrete, and a boss formwork using the same. [Background technology]

[0002] The quality of concrete poured into structures is affected by the environmental conditions (climate, season), construction conditions (pouring and compaction), curing conditions, etc. at the site where it is poured, even if it is produced using the same mix plan. For this reason, the quality inspection of structural concrete must be carried out by checking the quality of the hardened structural concrete after pouring.

[0003] Against this background, in 2005, the Japanese Society for Non-Destructive Inspection (JSNDI) established the standard "Methods for Preparing BOSS Specimens and Testing Compressive Strength" (NDIS 3424:2011) as a test method for directly inspecting the strength of structural concrete. This involves casting specimens under the same environmental and construction conditions as the structural concrete, curing them, and then extracting them from the structural concrete without damaging it, in order to conduct more accurate strength tests. A BOSS specimen is a rectangular specimen in which a boss formwork is attached to the structural formwork before the concrete is poured, and when concrete is poured into the structural formwork, the boss formwork is simultaneously filled with concrete, forming an integral part of the surface layer of the structural concrete. "BOSS" stands for Broken Off Specimens by Splitting.

[0004] Chiyoda Construction Co., Ltd. has traditionally sold boss formwork for producing boss specimens. However, this boss formwork is made up of multiple steel parts and screws and nuts, so it was necessary to either purchase a fully assembled product or purchase the parts and assemble them on-site.

[0005] Therefore, in order to reduce the weight of the boss formwork and at the same time eliminate the labor required for assembly, the present applicants have proposed in Patent Document 1 listed below a lightweight resin formwork for forming specimens for concrete strength tests, in which the sides and bottom are formed into a box shape that is molded integrally from synthetic resin, flanges of different widths are formed on the outer periphery of the top surface of the box shape, and multiple ribs are formed continuously at required intervals on the outer periphery of the side and bottom surfaces, with the flange that becomes the upper surface when in use being wider than the other flanges and having multiple jig holes formed therein. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2009-190225 Summary of the Invention [Problem to be solved by the invention]

[0007] In the resin formwork of Patent Document 1, in order to facilitate removal of the formwork after filling with concrete, a pair of V-shaped cut grooves are provided close to each other at the four outer corners of the box-shaped section, extending from the side surface to the flange section, and the four corners are peeled off from the concrete by tearing the cut grooves. However, this formwork removal work is laborious as it requires manual tearing of the resin formwork, and there has been a demand for easier formwork removal work.

[0008] Furthermore, in the above-mentioned resin formwork, although the formwork body is made of resin, the molding plates and slit plates attached to the flange surfaces remain made of steel, which has led to problems such as increased weight and high manufacturing costs.

[0009] Therefore, a main object of the present invention is to facilitate the removal of resin formwork for producing boss specimens after filling them with concrete.

[0010] Secondly, by using resin for the molding plate and slit plate, it is possible to reduce the weight and manufacturing costs. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention according to claim 1 provides a box-shaped resin formwork for preparing a concrete strength test specimen, The resin formwork is composed of a formwork main body having four circumferential side surfaces and a bottom surface, one surface of which is an opening, and a flange portion provided along the circumferential direction so as to surround the opening of the formwork main body, and a plurality of ribs are continuously formed at predetermined intervals on the outer peripheral surface of the formwork main body, A resin formwork for concrete strength test specimens is provided, characterized in that a plurality of slit grooves are formed in the flange portion over the section from the edge of the opening to the outer edge of the flange portion, and a thinned cut groove with a V-shaped cross section is formed on the outer surface of the formwork main body over the section to the bottom surface so that it is substantially continuous with the slit grooves.

[0012] In the invention described in claim 1, a plurality of slit grooves are formed in the flange portion of the resin form over the section from the edge of the opening to the outer edge of the flange portion, and thinned cut grooves with a V-shaped cross section are formed in the outer surface of the form body over the section to the bottom surface so as to be substantially continuous with the slit grooves. Therefore, since the slit grooves are formed in the flange portion that is most difficult to tear and is cut from the beginning, the divided flange pieces can be easily removed by pinching them with pliers or the like and pulling them apart.

[0013] As a second aspect of the present invention, there is provided a resin formwork for concrete strength test specimens as set forth in claim 1, wherein the resin formwork is made of ABS resin, polyethylene resin or polypropylene resin.

[0014] The invention described in claim 2 above provides a suitable example of a material for the resin formwork. The resin formwork is preferably made of, for example, ABS resin, polyethylene resin, or polypropylene resin.

[0015] As the present invention according to claim 3, there is provided a resin formwork for concrete strength test specimens according to either claim 1 or 2, in which the slit grooves are formed in two rows on each of a pair of opposing side portions of the flange portion, with two rows on each side, either upper and lower or left and right.

[0016] The invention described in claim 3 shows one example of a pattern for forming slit grooves. As shown in the embodiment described later, the slit grooves can be formed in two rows, one above the other or two below the other, on each of a pair of opposing side portions of the flange portion. The flange piece portion sandwiched between these two slit grooves can be easily removed from the mold by pinching it with pliers or the like and pulling it apart.

[0017] The present invention according to claim 4 provides a resin formwork for concrete strength test specimens according to either claim 1 or 2, in which the slit grooves are formed in two rows, one on each of two opposing pairs of side portions of the flange portion, in two rows, one above the other, and in two rows, one on each of the other pairs of side portions, in two rows, one on each side.

[0018] The invention described in claim 4 shows another example of the formation pattern of the slit grooves. As shown in the embodiment described later, the slit grooves are formed in two rows, one on each of two opposing pairs of both sides of the flange, with two rows in two rows, one on each of two sides, one on each of two sides, and two rows in two rows, one on each of two sides, with the other, with the flange pieces sandwiched between the two slit grooves being pinched with pliers or the like and pulled apart, thereby making it possible to easily remove from the mold.

[0019] The present invention, as claimed in claim 5, provides a boss formwork characterized in that a resin molded plate having the same external dimensions as the flange portion and an opening inside is arranged on the surface side of the flange portion of the resin formwork described in any one of claims 1 to 4, and a resin slit plate having a greater thickness than the molded plate and a sharp lower edge is arranged on the surface side of the molded plate above the opening in the molded plate, and these components are integrated by a connecting means.

[0020] In the invention described in claim 5, the boss form is composed of the resin form, the resin molding plate, and the resin slit plate. By using resin for all the components, it is possible to reduce the weight and manufacturing costs.

[0021] As the present invention according to claim 6, there is provided a boss formwork according to claim 5, in which a screw hole is formed in the slit plate for screwing in a breaking bolt for breaking off a concrete strength test specimen from structural concrete.

[0022] In the invention described in claim 6 above, since the entire boss formwork of the present invention is made of resin, the screw holes for threading the breaking bolts are formed in the slit plate with the greatest thickness. This is to ensure sufficient strength, since a breaking force is applied to the threaded engagement portion as the breaking bolt is threaded forward.

[0023] The present invention as claimed in claim 7 provides a boss formwork as claimed in either claim 5 or 6, in which, when a molding plate and a slit plate are arranged in the resin formwork, nail holes are provided at four locations, at both upper corners of the slit plate and at both lower corners of the molding plate, for attachment to a formwork for pouring concrete.

[0024] In the invention described in claim 7, when the shaped plate and the slit plate are disposed in the resin formwork, nail holes are provided at each of the upper corners of the slit plate and the lower corners of the shaped plate for attaching it to a concrete pouring formwork. In this invention, multiple slit grooves are formed in the flange portion of the resin formwork, allowing each flange piece to move freely. In this state, there is a possibility that a sufficient sealing function will not be achieved when concrete is filled, so when the boss formwork is set in the concrete pouring formwork, nails are driven into the four corners and the flange pieces are clamped by the shaped plates, thereby ensuring a sufficient sealing function. [Effects of the Invention]

[0025] As explained above in detail, according to the present invention, it is possible to facilitate the removal of resin formwork for producing boss specimens after filling them with concrete.

[0026] Furthermore, by using resin for the molded plate and slit plate, it is possible to reduce the weight and manufacturing costs. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a perspective view showing a resin formwork 1 according to the present invention with the opening facing upward. [Figure 2] FIG. 2 is a front view of the resin formwork 1. [Figure 3] FIG. 2 is a plan view of the resin formwork 1. [Figure 4] FIG. 2 is a side view of the resin formwork 1. [Figure 5] FIG. 2 is a rear view of the resin formwork 1. [Figure 6] 1 is a perspective view showing an assembly procedure for a resin mold 1, a forming plate 12, and a slit plate 13. FIG. [Figure 7] FIG. [Figure 8] FIG. 2 is a front view of the forming plate 12 showing the assembled state. [Figure 9]FIG. [Figure 10] 1 shows a slit plate 13, (A) being a front view and (B) being a side view. [Figure 11] FIG. 10 is a front view showing a modified example of the resin formwork 1. [Figure 12] 10 is a longitudinal cross-sectional view of a main part showing another example of the means for connecting the resin formwork 1, the forming plate 12, and the slit plate 13. FIG. [Figure 13] 1 is a side view showing the state in which the boss formwork is attached to the concrete pouring formwork 30. FIG. [Figure 14] FIG. 10 is an intermediate cross-sectional view showing the completed state of concrete pouring. [Figure 15] FIG. 10 is a diagram showing how to break down a boss specimen. [Figure 16] FIG. 10 is a side view showing an example of attaching a cap bolt 34 in a second embodiment, showing a state in which a boss form is attached to a concrete pouring form 30. [Figure 17] FIG. 10 is a perspective view showing an assembly procedure for a resin mold 1, a forming plate 12, and a slit plate 13 in a third embodiment. [Figure 18] 1 is a side view showing the state in which the boss formwork is attached to the concrete pouring formwork 30. FIG. [Figure 19] 1 is a plan view showing the state in which the boss formwork is attached to the concrete pouring formwork 30. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0029] The boss formwork for obtaining boss specimens that can directly inspect the quality of structural concrete is composed of a resin formwork 1, a forming plate 12, and a slit plate 13, as shown in Figure 6.

[0030] The resin formwork 1 is a box-shaped formwork made from synthetic resins such as ABS resin, which has excellent heat resistance, mechanical strength, oil resistance, impact resistance, gloss, and processability, or polyethylene resin, which has good releasability from concrete, preferably high-density polyethylene resin or polypropylene resin. Among these, ABS resin is preferable in terms of mechanical strength, impact resistance, and processability. The resin formwork 1 will be described in detail below with reference to Figures 1 to 5.

[0031] As shown in Figure 1, the resin formwork 1 is composed of a formwork main body 2, one of whose faces is an opening A, which has four circumferential side surfaces 4 and a bottom surface 5, and a flange portion 3 provided along the circumferential direction so as to surround the opening A of the formwork main body 2, and multiple ribs 6 are formed continuously at predetermined intervals on the outer peripheral surface of the formwork main body 2.

[0032] The formwork main body 2 is made of resin and has a thickness of at least 3 mm, preferably 3 to 5 mm. For ease of explanation, the upper surface when attached to the concrete pouring formwork is referred to as the upper surface 4A, the lower surface as the lower surface 4B, and the two side surfaces as the left and right side surfaces 4C and 4D. To improve the overall rigidity (strength) of the formwork main body 2, a plurality of ribs 6, 6... of a required width and height are continuously formed at predetermined intervals on the outer periphery of the side surfaces 4A to 4D and the bottom surface 5. Specifically, the ribs 6 are formed as a plurality of ribs 6a, ten in the illustrated example, extending continuously from the upper surface 4A to the opposing lower surface 4B along the outer surface of the bottom surface 5 at predetermined intervals in the horizontal direction. Meanwhile, a plurality of ribs 6b, four in the illustrated example, extending continuously from the left surface 4C to the opposing right surface 4D along the outer surface of the bottom surface 5 at predetermined intervals in the horizontal direction. The ribs 6a, 6a... formed continuously on the upper and lower side surfaces 4A, 4B and the bottom surface 5, and the ribs 6b, 6b... formed continuously on the left and right side surfaces 4C, 4D and the bottom surface 5, intersect in a lattice pattern on the outer surface of the bottom surface 5, as shown in Fig. 5, and the presence of such a large number of ribs 6 greatly enhances the strength and rigidity of the formwork main body 2. As also shown in Fig. 3, the upper surface 4A has a plurality of air vent holes 4a, 4a... formed at predetermined intervals in the vertical and horizontal directions, and an air-permeable sheet 14 is stretched on the inner surface of the upper surface 4A, as shown in Fig. 6.

[0033] On the other hand, the flange portion 3 is also made of resin with a thickness of at least 3 mm, preferably about 3 to 5 mm. For ease of explanation, as shown in Figure 2, when attached to the concrete pouring formwork, the upper portion is referred to as the upper flange 3A, the lower portion as the lower flange 3B, and the two side portions as the left and right flanges 3C and 3D. In the illustrated example, the upper flange 3A and the left and right flanges 3C and 3D have approximately the same width, and the width of the lower flange 3B is smaller. Note that the rectangular line shown in Figure 2 is the border of an opening formed in the concrete pouring formwork to attach the boss formwork to the concrete pouring formwork.

[0034] In order to facilitate demolding after filling and hardening of concrete, a plurality of slit grooves 8 are formed in the flange portion 3 from the edge of the opening A to the outer edge of the flange portion 3. Furthermore, a thinned, V-shaped cut groove 9 is formed in the side surface 4 of the formwork body 2 so as to be substantially continuous with the slit grooves 8 and extend to the bottom surface 5. Specifically, as shown in FIG. 2, slit grooves 8a, 8b (8c, 8d) are formed in two horizontal rows, one above the other, in a pair of opposing side portions 3C, 3D of the flange portion 3. As shown in FIG. 4, thinned, V-shaped cut grooves 9a, 9b are formed in the side surface 3 of the formwork body 2 so as to be continuous with the opening end of the slit groove 8 or its vicinity (within 2 mm) and extend to the bottom surface 5. The phrase "substantially continuous" refers to a shape that continues from the vicinity (within 2 mm) of the opening end of the slit groove 8 as well as a shape that continues from the opening end of the slit groove 8.

[0035] As described above, by forming multiple slit grooves in the flange portion of the resin formwork and forming cut grooves 9a, 9b in a section that is substantially continuous from this to the bottom surface, when the boss formwork is split off and the resin formwork 1 is peeled off to remove the boss specimen, each flange piece that has been divided into several pieces by the slit grooves can be easily removed by picking it up with pliers or the like and peeling it off as is.

[0036] Furthermore, in the flange portion 3, connecting pins 10 are erected on the left and right sides of the upper flange 3A as connecting means for combining with a forming plate 12 and a slit plate 13, which will be described later. The connecting pins 10 are generally cylindrical pin members, and are divided into four parts in a cross direction so that they can expand and contract in the radial direction. Furthermore, the upper flange 3A is formed with two insertion holes 11 for inserting bolts to break the boss formwork out of the structural concrete.

[0037] 6, a forming plate 12 and a slit plate 13 are assembled to the resin formwork 1 to complete a boss formwork. Specifically, a resin forming plate 12 having the same external dimensions as the flange portion 3 and an opening therein is disposed on the surface side of the flange portion 3 of the resin formwork 1, and a resin slit plate 13 having a greater thickness than the forming plate 12 and a sharp lower edge is disposed on the surface side of the forming plate 12 in a position substantially corresponding to the upper flange portion 3A.

[0038] The forming plate 12 is made of synthetic resin such as ABS resin, high-density polyethylene resin, polypropylene resin, polycarbonate resin, etc., similar to the resin formwork 1. Among these, it is particularly preferable to use polycarbonate resin, as it has sufficient rigidity to withstand the pressure of pouring concrete.

[0039] As shown in Figure 9, the external dimensions (length x width) are the same as those of the flange portion 3 of the resin formwork 1, and an opening 12A is formed inside. As shown in Figure 8, a front view of the completed assembly state, the opening 12A is formed smaller in both length and width than the opening A of the resin formwork 1. Rectangular openings 15, 15 are formed on the upper side of the forming plate 12 at positions corresponding to the connecting pin 10 formed on the flange portion 3, and an insertion hole 16 of the same shape is formed at a position corresponding to the insertion hole 11. In addition, nail holes 17, 17... are formed at four locations at both upper corners and both lower corners for attaching the boss formwork to a concrete pouring formwork.

[0040] On the other hand, the slit plate 13 is made of synthetic resin such as ABS resin, high-density polyethylene resin, polypropylene resin, polycarbonate resin, etc., just like the resin formwork 1. Among these, it is particularly desirable to use polycarbonate resin, not only because of its ability to peel off concrete, but also because it has the strength to transmit strength firmly when breaking up the specimen, making the breaking up smooth.

[0041] As shown in Figure 10, the horizontal dimension is the same as that of the forming plate 12, and the vertical dimension is approximately the same as the width dimension of the flange portion above the opening 12A of the forming plate 12 (see Figure 8). The standard portion has a thickness greater than that of the forming plate 12, specifically at least 6 mm or more, preferably 6 to 12 mm, and the lower edge 13a is sharp. This slit plate 13 is a transmission member for applying a splitting force when splitting the boss form from the structural concrete, and generates cracks in the concrete using the sharp lower edge 13a as the base point.

[0042] This slit plate 13 needs to be thick to provide rigidity, but does not need to be heavy, so as shown in the example, it has a lattice-shaped recess to reduce weight and cost.

[0043] In the slit plate 13, rectangular openings 18, 18 are formed at positions corresponding to the connecting pins 10 formed in the flange portion 3, and screw holes 19, 19 are formed at positions corresponding to the insertion holes 11, for threading in breaking bolts for breaking out concrete strength test specimens together with the resin formwork from the structural concrete. In addition, nail holes 20, 20 are provided at both upper corners, respectively, for attaching the boss formwork to a concrete pouring formwork.

[0044] In the above-mentioned Patent Document 1, the screw holes for the splitting bolts are formed in a molded plate (made of metal), but in the present invention, the molded plate 12 is made of resin, which may prevent sufficient strength from being secured. Therefore, the screw holes for the splitting bolts are formed in a slit plate 13 which has a relatively large thickness.

[0045] 6, the assembly is performed by stretching a breathable sheet 14 on the inner surface of the upper surface 4A of the resin formwork 1. As the breathable sheet 14, a breathable nonwoven fabric or porous film can be suitably used.

[0046] Then, the forming plate 12 is overlapped on the surface side of the flange portion 3 of the resin formwork 1. At this time, the connecting pin 10 formed on the flange portion 3 is inserted into the rectangular opening 15 of the forming plate 12. The outer diameter of the connecting pin 10 is formed slightly larger than the opening 15, and the connecting pin 10 is fitted into the opening 15 while shrinking in the radial direction, thereby being integrated.

[0047] Next, the slit plate 13 is placed on the front surface of the forming plate 12, above the opening 12A of the forming plate 12. At this time, the connecting pin 10 formed on the flange portion 3 is inserted into the rectangular opening 18 of the slit plate 13. The outer diameter of the connecting pin 10 is slightly larger than the opening 18, and the connecting pin 10 is fitted into the opening 18 while shrinking in the radial direction, thereby becoming one piece.

[0048] Assembly is completed in the above manner, and the boss formwork is completed.

[0049] [Other examples] (1) In the above embodiment, slit grooves 8a, 8b (8c, 8d) are formed horizontally in two upper and lower rows in each of the pair of opposing side portions 3C, 3D of the flange portion 3. However, slit grooves may be formed vertically in two left and right rows in each of the pair of opposing side portions 3A, 3B of the flange portion 3. Furthermore, by combining these, as shown in FIG. 11 , in the two pairs of opposing side portions 3C, 3D (3A, 3B) of the flange portion, one side portion 3C, 3D may have two slit grooves 8a, 8b (8c, 8d) in two upper and lower rows, and the other side portion 3A, 3B may have two slit grooves 8e, 8g (8f, 8h) in two left and right rows. In this embodiment, slit grooves are formed on both sides so as to straddle the corners of the opening A, which improves ease of peeling at the corners, which are the most difficult to peel. (2) In the above embodiment, the flange portion 3, the molding plate 12, and the slit plate 13 are connected by inserting the connecting pin 10 provided on the flange portion 3. However, as shown in FIG. 12(A), these components may be connected by screwing in a countersunk screw 21, or as shown in FIG. 12(B), these components may be connected by a bolt and nut 22.

[0050] [Construction example] Next, a method for producing a boss specimen using the boss form and a procedure for breaking it will be described in detail with reference to FIGS.

[0051] First, as shown in Fig. 13, an opening 30a for installing a boss form is formed at a predetermined location in the concrete pouring formwork 30. The size of this opening 30a is the size shown by the dashed line 7 in Fig. 2.

[0052] Next, a boss formwork is brought in, and the formwork body 2 of the resin formwork 1 is protruded from the inside of the concrete pouring formwork 30 through the opening 30a to the outside, and the back surface of the flange portion 3 is brought into contact with the concrete pouring formwork 30. Then, nails 23 are driven into the nail holes 20, 17 formed in the four corners of the boss formwork to fix the boss formwork in place.

[0053] After completing the above preparations, concrete is poured into the concrete pouring formwork 30. As shown in Figure 14, the poured concrete flows into the resin formwork 1 through the opening 12A in the forming plate 12, and the presence of the air holes 4a allows the air inside the resin formwork 1 to pass through the breathable sheet 14 and be discharged to the outside, eliminating air pockets inside the resin formwork 1 and allowing the concrete to fill every corner of the resin formwork 1. The poured concrete is cured and hardened for the required time in the same environment inside the concrete pouring formwork 30 and the resin formwork 1.

[0054] After a predetermined time has passed and the structural concrete has completely hardened, the concrete pouring formwork 30 is removed. Then, as shown in FIG. 15 , the threaded portion of a splitting bolt 31 is inserted through the insertion hole 11 in the flange portion 3 and the insertion hole 16 in the forming plate 12, and the splitting bolt 31 is screwed into the threaded hole 19 in the slit plate 13. Then, a wrench or ratchet wrench 32 is brought in and the splitting bolt 31 is further turned in the tightening direction. After the tip of the threaded portion of the splitting bolt 31 contacts the structural concrete, the slit plate 13 is moved in a reactionary direction in which it peels off, and a crack 33 is formed at the position of the opening 12A in the forming plate 12, starting from the tip (sharp portion) of the slit plate 13. This crack 33 allows the resin formwork 1, along with the slit plate 13 and forming plate 12, to be split (separated) from the structural concrete.

[0055] Then, the resin formwork 1 is removed in the same manner as described above, to obtain a concrete strength test specimen (boss specimen) integrally formed with the structural concrete.

[0056] The box-shaped resin formwork 1 in the above embodiment is lightweight and does not deform during operations such as pouring and compacting concrete, and transporting, allowing specimens of the intended dimensions to be formed with high precision. The box-shaped resin formwork 1 can be a resin formwork for specimens that are rectangular, with dimensions of, for example, 75 mm x 75 mm x 150 mm, 100 mm x 100 mm x 100 mm, 100 mm x 100 mm x 200 mm, or 125 mm x 125 mm x 250 mm in length, width, and length.

[0057] [Second embodiment] In the above example of construction, concrete ends up filling the space formed by the insertion hole 11 in the flange portion 3, the insertion hole 16 in the forming plate 12, and the screw hole 19 in the slit plate 13, resulting in extra work being required to remove this concrete. Therefore, as shown in Figure 16, the opening 30a of the concrete pouring formwork 30 is formed to include the insertion hole 11 portion of the flange portion 3, and a cap bolt 34 is inserted from the outside to fill the spaces between the insertion holes 11, 16 and the screw hole 19 with the threaded portion, thereby preventing concrete from filling the spaces and enabling the break-out bolt 31 to be inserted smoothly.

[0058] [Third embodiment] Next, the third embodiment will be described in detail with reference to FIGS.

[0059] In this third embodiment, there is a concern that the threads of the screw holes 19 formed in the slit plate 13 may be crushed when the formwork is broken away from the structural concrete because they are made of resin. To prevent this, it is desirable to form a hexagonal hole 24 in place of the screw holes 19, as shown in Figure 17, and to fit a steel nut 25 into this hexagonal hole 24. Therefore, even when the breaking-away bolt 31 is screwed in and broken away, the threads of the steel nut 25 will not be crushed, and the resin formwork 1 can be broken away (separated) from the structural concrete without any problems.

[0060] In addition, in the first embodiment, the slit plate 13, the molding plate 12, and the resin formwork 1 are assembled using a connecting pin 10 formed on the flange portion 3 of the resin formwork 1. However, in order to firmly integrate the slit plate 13, the molding plate 12, and the resin formwork 1, in this third embodiment, a bolt 26 may be used, and the threaded portion of this bolt 26 may be inserted through the insertion hole 11 formed in the flange portion 3 and the insertion hole 16 of the molding plate 12, and then screwed onto the steel nut 25, thereby integrating these three components.

[0061] 18 and 19 show the state in which the boss formwork according to the third embodiment is attached to a formwork 30. As shown in these figures, in order to facilitate peeling from the concrete when breaking it up after the concrete has hardened, a taper 27 sloping inward (toward the center of the resin formwork 1) toward the concrete space may be provided on the top and side surfaces of the assembled resin formwork 1, forming plate 12, and slit plate 13. [Explanation of symbols]

[0062] 1...plastic formwork, 2...formwork main body, 3...flange portion, 4A to 4D...side surface, 5...bottom surface, 6 (6a and 6b)...rib, 8 (8a to 8h)...slit groove, 9 (9a and 9b)...cut groove, 10...connecting pin, 11...insertion hole, 12...molded plate, 13...slit plate, 14...breathable sheet, 15...rectangular opening, 16...insertion hole, 17...nail hole, 18...rectangular opening, 19...screw hole, 20...nail hole, 21...countersunk head screw, 22...bolt and nut, 23...nail, 30...concrete pouring formwork, 30a...opening, 31...breaking bolt, 32...spanner or ratchet wrench, 33...crack, 34...cap bolt, 24...hexagonal hole, 25...steel nut, 26...bolt, 27...taper

Claims

1. A box-shaped resin formwork for preparing a concrete strength test specimen, The resin formwork is composed of a formwork main body having four circumferential side surfaces and a bottom surface, one surface of which is an opening, and a flange portion provided along the circumferential direction so as to surround the opening of the formwork main body, and a plurality of ribs are formed continuously at predetermined intervals on the outer peripheral surface of the formwork main body, A resin formwork for concrete strength test specimens, characterized in that a plurality of slit grooves are formed in the flange portion over the section from the edge of the opening to the outer edge of the flange portion, and a thin-walled cut groove with a V-shaped cross section is formed on the outer surface of the formwork main body over the section to the bottom surface so that it is substantially continuous with the slit grooves.

2. 2. A resin formwork for concrete strength test specimens according to claim 1, wherein said resin formwork is made of ABS resin, polyethylene resin or polypropylene resin.

3. A resin formwork for concrete strength test specimens as described in either claim 1 or 2, wherein the slit grooves are formed in two rows on each of the opposing pair of both sides of the flange portion, in two rows, one above the other or two below the other, or in two rows, one left and one right.

4. A resin formwork for concrete strength test specimens as described in either claim 1 or 2, wherein the slit grooves are formed in two rows, one on each side, in two rows, one above the other, on the two opposing pairs of both sides of the flange portion, and in two rows, one on each side, in two rows, one on the left and one on the right.

5. A boss formwork characterized in that a resin molded plate having the same external dimensions as the flange portion and an opening inside is arranged on the surface side of the flange portion of the resin formwork described in any one of claims 1 to 4, and a resin slit plate having a thickness greater than that of the molded plate and a sharp lower edge is arranged on the surface side of the molded plate above the opening of the molded plate, and these components are integrated by a connecting means.

6. 6. A boss form according to claim 5, wherein said slit plate has a screw hole for threading in a breaking bolt for breaking off a concrete strength test specimen from structural concrete.

7. A boss formwork as described in either claim 5 or 6, wherein when a molding plate and a slit plate are arranged in the resin formwork, nail holes are provided at four locations, at both upper corners of the slit plate and at both lower corners of the molding plate, for attachment to a concrete pouring formwork.

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