JP6780946B2 - Uniaxial restraint crack test concrete specimen and its preparation tool - Google Patents

Description

The present invention relates to a constrained concrete specimen used for a uniaxially constrained crack test of concrete, and a tool for making the same.

Conventionally, the uniaxial restraint test of concrete has been evaluated by JIS A 1151 “Dry shrinkage crack test method for restrained concrete (hereinafter referred to as JIS method)” (see, for example, Non-Patent Document 1).
Specifically, as shown in FIG. 5A, the strain of the restraint steel 52 is measured by attaching the sample strain measuring gauge 53 to the center of each of the restraint steel 52 from both sides of the concrete member 51 of the specimen 50. Then, as shown in FIG. 5B, the time when the strain value suddenly decreases or the time when dry cracks are visually confirmed is defined as the time when the cracks occur. The strain measurement interval is every 1 to 4 hours, from the start of drying of the concrete to the occurrence of cracks.

Tsuzuki, Sakai, Ichinose, Hirata; Uniaxial restraint crack test in concrete using limestone aggregate and expansion material; Annual Proceedings of Concrete Engineering, Vol. 34, No. 1 2012

However, the above JIS method is suitable for measuring the drying shrinkage strain of general concrete in the range of 600 × 10 ^{-6 to} 800 × 10 ^-6 , but the drying shrinkage strain is 400 × 10 ^-6. Regarding the concrete reduced below, there are problems that it is difficult to measure the drying shrinkage crack itself, and even if it can be measured, the measurement period becomes long.

The present invention has been made in view of the conventional problems, and is a concrete specimen for a uniaxial restraint crack test capable of evaluating drying shrinkage cracks in a relatively short time even for concrete having a small drying shrinkage strain. It is an object of the present invention to provide the manufacturing tool.

In the present invention, when the direction of connecting the rectangular restraint portions in plan view located at both ends and the two restraint portions is the length direction, the free contraction is narrower than the restraint portion located between the restraint portions. A flat steel member having a portion, a connecting portion in which the width connecting the restraining portion and the free contracting portion expands from the free shrinking portion toward the restraining portion, and an outer side in the width direction of the restraining portion. Two restraint shaped steels that are attached to and extend in the length direction, and one end of the restraint shaped steel of one of the two restraint shaped steels and one of the restraining portions of the restraining portion side. They are respectively connected to the other of the one restraint portion of the restraining section steel, and the other end with one side connecting rods of the two embedded in restraint portion of the one, one end of the restraining section steel of the two One of the restraint shaped steels is connected to the other restraint portion side of the restraint portion and the other restraint portion side of the other restraint shaped steel, and the other end is embedded in the other restraint portion. a two other side connecting rod and uniaxial restraint cracking test concrete specimen having a that is, the at one of the restraining portion, is disposed between one side connecting rod of the two, of the other at restraining portion, is disposed between the two other side the connecting rod, wherein embedded in the center of the concrete member, comprising a rod-shaped steel extending the lengthwise, the rod-shaped steel, the Both ends located on the restraint portion side are fixed to the steel of the concrete member, and the central portion located on the free contraction portion side is embedded in the concrete member without contacting the concrete of the concrete member, and the restraint at one side and the other side of the section, characterized in that it is respectively fixed to the other ends of said two other side connecting rod on one side the connecting rod of the two.
In this way, a rod-shaped steel material is embedded in the center of the concrete member so that the central portion does not come into contact with the concrete member, and the rod-shaped steel material is integrally reinforced with the connecting rod to reinforce the degree of restraint of the concrete member. It is possible to evaluate the drying shrinkage cracks of concrete in a short period of time because the cracks are easily generated. In addition, it is possible to accurately evaluate the drying shrinkage cracks of concrete having a small drying shrinkage strain.
Further, since the rod-shaped steel material is made of round steel having a cross-sectional area of 2.8% to 16.1% of the cross-sectional area of the central portion of the concrete member, drying shrinkage cracks of concrete can be efficiently evaluated.

Further, the present invention comprises a rectangular plate-shaped bottom plate, end plates erected at both ends in the length direction, which is a direction parallel to the long side of the bottom plate, and a straight portion composed of a straight line parallel to the long side. It is provided with a straight or curved bend that gradually separates from both ends of the straight portion, so that the distance between the bends increases toward the end in the longitudinal direction at a position separated from the end plate by a predetermined distance. A mold with two side plates erected on the bottom plate, and two restraint-shaped steels extending in the length direction, each of which is arranged so as to abut the side plates on the outside of the side plates of the bottom plate. And one end plate side of the end plate and one end portion of the other side plate than one end portion of one side plate of the two side plates of the restrained steel having two ends. are respectively connected to one end plate side of, and two one-side connecting rod the other end extending in the width direction of the bottom plate from the restraint shaped steel each one end is connected, one end of two captive shaped steel of the other end plate side of the end plate than the other end portion of one side plate of the two side plates, and each connected to the other end plate side than the other end portion of the other side plate is, the other end a two second side connecting bar and the uniaxial constrained cracking test concrete specimen prepared instrument having a extending in the width direction of the bottom plate from the restraint shaped steel each one end of which is connected, the two the width direction center of the side plate, and at one end the one end plate side than the side plates, are arranged between the two first side connecting bar, the other end plate side than the other end portion of the side plate In the straight portion of the side plate of the rod-shaped steel material extending in the length direction and the rod-shaped steel material arranged between the two connecting rods on the other side, or at least a part of the straight portion and the bent portion. covering the portion surrounded by, with rod-shaped steel material and a contact-preventing member for preventing the contact with the concrete, rod-shaped steel material, than the one end portion of the side plate at one end plate side, 2 is fixed to the other ends of one side connecting rod of the present, at the other end plate side than the other end portion of the side plate is fixed that in each of the other ends of the two other side connecting bar It is characterized by.
By using such a concrete specimen for uniaxial restraint crack test, it is possible to reliably fabricate a concrete specimen for uniaxial restraint crack test in which a rod-shaped steel material is embedded in the center of a concrete member.

The outline of the present invention does not enumerate all the necessary features of the present invention, and subcombinations of these feature groups can also be inventions.

It is a figure which shows the concrete specimen for the uniaxial restraint crack test by this invention. It is a figure which shows the concrete specimen making tool for a uniaxial restraint crack test. It is a figure which shows the result of having investigated the number of days of crack occurrence when the diameter of a round steel was changed. It is a figure which shows the result of having investigated the number of days of crack occurrence when the shrinkage amount of concrete was changed. It is a figure which shows the uniaxial restraint crack test method of the conventional concrete.

1 (a) to 1 (c) are views showing a concrete specimen 10 for a uniaxial restraint crack test according to the present embodiment, (a) is a plan view, (b) is a side view, and (c) is a view. The figure is a cross-sectional view taken along the line AA of FIG.
The concrete specimen for uniaxial restraint crack test (hereinafter referred to as the specimen) 10 includes a flat plate-shaped concrete member 11, a restraint device 12 for restraining the concrete member 11, and a round steel 13 embedded in the center of the concrete member 11. The outer strain gauge 14 attached to each of the two restraint shaped steels 121 constituting the restraint device 12, the Teflon sheet 15 (Teflon: registered trademark) that covers the central portion of the round steel 13 from the outside, and the round steel 13 are attached. The inner strain gauge 16 is provided.
The concrete member 11 is a flat plate-shaped member including a restraint portion 111, a free contraction portion 112, and a connecting portion 113. Hereinafter, the thickness direction of the flat plate is defined as the thickness direction, the direction connecting the two restraint portions 111 is defined as the length direction, and the direction perpendicular to the length direction and the thickness direction is defined as the width direction.
The restraint portion 111 has a rectangular shape in a plan view and is located at both ends of the concrete member 11.
The free contraction portion 112 has a rectangular shape that is long in the plan view length direction and has a width narrower than the width of the restraint portion 111, and is located at the central portion of the concrete member 11. The restraint portion 111 and the free contraction portion 112 are connected by a connecting portion 113 whose width gradually expands from the free contraction portion 112 side to the restraint portion 111 side, respectively. In this example, the length of the free contraction portion 112 is set longer than the length of the restraint portion 111. The width and thickness of the free contraction portion 112 are the same dimensions.
As will be described later, the restraint portion 111, the free contraction portion 112, and the connecting portion 113 are integrally formed.

The restraint device 12 includes two restraint shaped steels 121 extending in the length direction of the concrete member 11 and a plurality of reinforcing rods 122 extending in the thickness direction welded to the restraint portion 111 side of the restraint shaped steel 121, respectively. And a connecting rod 123 that connects the two restraint shaped steels 121 on the restraint portion 111 side, and the concrete member 11 is restrained by the restraint portion 111. The reinforcing rod 122 and the connecting rod 123 are embedded in the concrete of the restraint portion 111.
The restrained shaped steel 121 is a vertical piece 121a extending in the thickness direction of the concrete member 11 and a horizontal piece extending outward from the end of the vertical piece 121a (the side opposite to the side facing the other restrained shaped steel 121). A U-shaped steel material having a piece 121b and extending in the length direction. Vertical pieces 121a facing each other are connected to each other by a connecting rod 123 at both ends of the restraint section steel 121.
Further, a wire strain gauge (outer strain gauge 14) is attached to each of the two restraint shaped steels 121 at the center in the length direction.
The round steel 13 is a bar having a circular cross section that extends in the length direction and is embedded in the concrete member 11, and is screwed so as to be located at both ends in the length direction and fixed to the concrete of the concrete member 11. It includes a fixed portion 131 that has been provided, and a non-fixed portion 132 that is covered with a Teflon sheet 15 and does not come into contact with the concrete of the concrete member 11. The Teflon sheet 15 functions as a contact preventive material for preventing the surface of the round steel 13 from coming into contact with concrete.
The fixing portion 131 is located in a region from the end of the concrete member 11 to the center side of the restraining portion 111 and on the end side of the free shrinking portion 112, and the non-fixing portion 132 is connected to the free shrinking portion 112 and the connecting portion 113. It is located in the area up to the center of. The length of the non-fixed portion 132 is preferably approximately twice or more the length of the fixed portion 131.
A wire strain gauge (inner strain gauge 16) is attached to the inside of the Teflon sheet 15 at the center of the round steel 13 in the length direction, which is the center of the non-fixed portion 132.
In this embodiment, as shown in FIG. 1 (c), the fixing portion 131 of the round steel 13, by welding or the like, since the reinforced by one conjugated with connecting rod 123 of the restraint 12, the fixing unit 131 and the concrete Even if the contact length of the member with the concrete is short, the round steel 13 can surely restrain the restraining portion 111 of the concrete member 11.

The strain measurement of the specimen 10 is performed every 1 to 4 hours using both the outer strain gauge 14 attached to the restraint shaped steel 121 and the inner strain gauge 16 attached to the round steel 13.
In this example, the time when the strain value measured by one of the outer strain gauge 14 and the inner strain gauge 16 suddenly decreases is defined as the time when the crack occurs. It is preferable to visually confirm the dry cracks at the same time.
As described above, in the uniaxial restraint crack test concrete specimen 10 of the present invention, the concrete member 11 is restrained not only on both sides of the restraint portion 111 but also at the center, so that the degree of restraint can be increased. Therefore, the drying shrinkage cracks of concrete can be evaluated in a short period of time, and the drying shrinkage cracks of concrete having a small drying shrinkage strain can be evaluated accurately.
It is preferable to use the round steel 13 having a cross-sectional area of 2.8% to 16.1% of the cross-sectional area of the free shrinkage portion 112 of the concrete member 11. Specifically, when the cross section of the free shrinkage portion 112 is 100 mm × 100 mm, the preferable diameter of the round steel 13 is 19 mmφ to 48 mmφ.
When the cross-sectional area of the round steel 13 is less than 2.8% of the cross-sectional area of the free shrinkage portion 112, the restraint on the concrete member 11 becomes small, so that the period until the occurrence of cracks cannot be sufficiently shortened. Because. Further, when the cross-sectional area of the round steel 13 exceeds 16.1% of the cross-sectional area of the free shrinkage portion 112, the volume of the concrete of the free shrinkage portion 112 decreases, so that unnecessary cracks occur, and as a result, the concrete It is difficult to accurately evaluate dry shrinkage cracks (in the explanation that the factor that limits the maximum diameter is the diameter of the coarse aggregate, the free shrinkage portion 112 has a cross-sectional area of 100 mm × 100 mm. I chose the above reason because it is necessary).

Next, a method of manufacturing the concrete specimen 10 for the uniaxial restraint crack test will be described.
First, as shown in FIG. 2A, the mold 20 is assembled.
The dimensional length of the mold 20 is based on JIS.
The mold 20 includes a rectangular plate-shaped bottom plate 21, an end plate 22, and a side plate 23.
The bottom plate 21 is a rectangular plate-shaped member of 960 mm (length) × 250 mm (width) × 10 mm (thickness), and the direction parallel to the long side is the length direction and the direction parallel to the short side is the width direction. ..
The end plate 22 is a rectangular plate-shaped member of 250 mm (width) × 100 mm (length) × 10 mm (thickness), and is erected at both ends of the bottom plate 21 in the length direction.
The side plate 23 includes a straight portion 23a formed of a straight line parallel to the long side and a curved portion 23b formed of a smooth curve gradually separated from the straight line from both ends of the straight line portion. It is erected on the bottom plate 21 at a position separated from the end plate 22 at the center of the bottom plate 21 by a predetermined distance so that the distance between the curved portions 23b increases toward the end plate 22.
In this example, the length of the straight portion 23a of the side plate 23 is 300 mm, the R of the bent portion 23b is 350 mm, and the length in the length direction between the ends is 600 mm.
The bottom plate 21 and the side plate 23 are preferably made of steel so as not to be deformed when the specimen is produced. The end plate 22 may be plywood.
As a method of assembling the formwork 20, after two side plates 23 are erected on the bottom plate 21, the end plate 22 may be attached to the end portion in the length direction of the bottom plate 21.

Next, as shown in FIG. 2B, two restraint shaped steels 121 are placed on the outside of the side plate 23 so that the surface of the vertical piece 121a opposite to the horizontal piece 121b abuts on the side plate 23. After arranging them so as to be parallel to each other, the two restraint shaped steels 121 are fixed to the bottom plate 21 with bolts, nuts or the like with one horizontal piece 121b, respectively.
The length of the restraint section 121 is 960 mm, the thickness of the vertical piece 121a is 100 mm, and the length of the horizontal piece 121b is 40 mm.
Since the length of the restraint shaped steel 121 is the same as the length of the bottom plate 21, both ends of the two restrained shaped steels 121 in the length direction abut on the end plates 22 respectively.
The restraint-shaped steels 121 are connected to each other by a connecting rod 123 on the end plate 22 side of the side plate 23 so that the two restraint-shaped steels 121 are parallel to each other and have the same distance. Both ends of the connecting rod 123 are threaded, and the restraint shaped steel 121 and the connecting rod 123 are connected by nuts from the inside and the outside of the vertical piece 121a.
Further, a plurality of reinforcing rods 122 extending in the thickness direction are attached by welding between the side plate 23 and the end plate 22 inside the restraint shaped steel 121.
In order to make the distances between the restraint shaped steels 121 the same, it is preferable to connect the restraint shaped steels 121 to each other and then fix them to the restrained shaped steels 121 of the bottom plate 21.

Next, as shown in FIG. 2C, the non-fixed portion 132 is covered with the Teflon sheet 15, and the round steel 13 having the inner strain gauge 16 attached to the inside of the Teflon sheet 15 is placed in the mold 20. By arranging and attaching the outer strain gauge 14 to the restraint shaped steel 121, a concrete specimen preparation tool for uniaxial restraint crack test (hereinafter referred to as preparation tool 1), which is a preparation tool for manufacturing the specimen 10, is obtained. ..
The round steel 13 is arranged in the form 20 by fixing the fixing portion 131 to the connecting rod 123 of the restraint device 12 by welding or the like.
Specifically, the connecting rod 123 is cut in the middle of the rod, the fixing portion 131 of the round steel 13 is arranged in the cut space, and the connecting rod 123 is welded and integrated with the cut both ends.
Since the connecting rod 123 is connected to the vertical piece 121a of the restrained section 121a from the inside and the outside by nuts at both ends, distortion of the restrained section 121 due to cutting and welding can be minimized. it can.
After mounting the round steel 13, the outer strain gauges 14 are mounted at the centers of the two restraint shaped steels 121 in the length direction, respectively.

Next, concrete is placed in the space surrounded by the thick frame shown in FIG. 2C (the space surrounded by the mold 20 of the manufacturing tool 1 and the restraint shaped steel 121). Then, after curing for a predetermined period (for example, 7 days), the concrete member 11 is formed into a flat concrete member 11 having a round steel 13 embedded therein and a restraining device 12 for restraining the concrete member 11 by removing the mold. Body 10 can be obtained.

[Example]
The table of FIG. 3 shows the results of preparing specimens 10 having different diameters of the round steel to be buried and examining the number of days of crack occurrence. The number of survey days was set to half a year, and if no cracks had occurred after half a year, it was set to "no cracks".
Materials used are as follows.
Water (W); Tap water cement (C); Ordinary Portland cement Fine aggregate (S1); River sand Fine aggregate (S2); Crushed sand Coarse aggregate (G1); Limestone crushed coarse aggregate (G2); Hard sandstone crushed stone Shrinkage reducing agent (Sr); Polyether derivative system The preparation conditions for concrete are shown in Table 1 below.
The water-cement ratio (W / C) is 50%, the fine aggregate ratio (s / a) is 47.4%, and the unit water amount (W) is 170 kg / cm ³ .

The concrete of the specimens 1-1 to 1-4 has a coarse aggregate of hard sandstone crushed stone (G2) and an actual shrinkage rate of 787 × 10 ^-6 . The shrinkage reducing agent (Sr) is not blended.
Concrete trial body 1-5～1-8 is the coarse aggregate is limestone (G1), both, shrinkage reducing agent (Sr) obtained by 10 kg / cm ³ formulation, actual shrinkage 434 × 10 ^- It is ⁶ .
The specimens 1-1 and 1-5 are conventional specimens on which no round steel is arranged, and the specimens 1-2 to 1-4 and the specimens 1-6 to 1-8 have diameters, respectively. Is a specimen according to the present invention in which round steels of 13 mm, 19 mm, and 32 mm are arranged.
As can be seen from the table in FIG. 3, in the free sample having an actual shrinkage rate of 787 × 10 ^-6 , the period until cracking of the free sample according to the present invention is shorter than that in the conventional free sample. I understand.
Further, the larger the diameter of the round steel, the shorter the period until cracks occur.
On the other hand, in the free sample having an actual shrinkage rate of 434 × 10 ^-6 , cracks occurred only when the diameter of the round steel was 32 mm, and no cracks occurred when the diameters were 13 mm and 19 mm. Since the number of days was short, it is estimated that if the number of survey days is extended, the same result as the sample with an actual shrinkage rate of 787 × 10 ^-6 can be obtained.
As a result, if a specimen is used in which a rod-shaped steel material is buried in the center of the concrete member with both ends fixed to the concrete and the central part does not come into contact with the concrete, cracks are likely to occur, and as a result, the concrete It was confirmed that the dry shrinkage cracks of concrete can be evaluated in a short period of time.

Further, the table of FIG. 4 shows the results of investigating the number of days of crack occurrence when the diameter of the round steel was kept constant (32 mm) and the shrinkage rate of the concrete was changed.
In this experiment, a formulation using an expansion material was also carried out. Further, in order to accelerate the occurrence of cracks, a notch with a depth of 10 mm is provided in the center of the concrete member.
As can be seen from the table of FIG. 4, it was also confirmed that by arranging the round steel, cracks could be generated regardless of the type of concrete.

Although the present invention has been described above with reference to the embodiments and examples, the technical scope of the present invention is not limited to the scope described in the embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the claims that forms with such modifications or improvements may also be included in the technical scope of the invention.

1 Concrete specimen preparation tool for uniaxial restraint crack test,
10 Concrete specimen for uniaxial restraint crack test, 11 Concrete member,
111 Restraint part, 112 Free contraction part, 113 Connection part,
12 Restraint device. 121 restraint shaped steel, 122 reinforcing rod, 123 connecting rod,
13 Round steel, 131 fixed part, 132 non-fixed part, 14 outer strain gauge,
15 Teflon sheet, 16 inner strain gauge.

Claims (3)

When the direction in which the rectangular restraint portions in plan view located at both ends and the two restraint portions are connected to each other is the length direction, the free contraction portion having a width narrower than the restraint portion located between the restraint portions and the said A flat-plate-shaped concrete member having a connecting portion in which the width connecting the restraining portion and the free contracting portion expands from the free shrinking portion toward the restraining portion is attached to the outside of the restraining portion in the width direction. Of the two restraint shaped steels extending in the length direction and one of the two restraint shaped steels at one end , one of the restraint sections and the other are respectively connected to the one restraint portion of the restraining section steel, and one side connecting rod of the two other end of which is embedded in the restricted portion of the one, while the one of the two captive shaped steel end The restraint-shaped steel of No. 1 was connected to the other restraint portion side of the restraint portion and the other restraint portion side of the other restraint-shaped steel, and the other end was embedded in the other restraint portion. A concrete specimen for uniaxial restraint crack testing equipped with a connecting rod on the other side of the book .
On the one restraint side, it is arranged between the two one-side connecting rods, and on the other restraint side, it is arranged between the two other-side connecting rods, and is the center of the concrete member. is embedded in, provided with a rod-shaped steel extending the lengthwise,
The rod-shaped steel material is
Both ends located on the restraint side are fixed to the concrete of the concrete member,
The central portion located on the free contraction portion side is embedded in the concrete member in a state where the central portion is not in contact with the concrete of the concrete member.
And uniaxial wherein at one side and the other side of the restraining portion, characterized in that each fixed to the other end of one side connecting rod of the two on the other end of the two other side connecting bar Concrete specimen for restraint crack test. The uniaxial restraint crack test according to claim 1, wherein the rod-shaped steel material is a round steel having a cross-sectional area of 2.8% to 16.1% of the cross-sectional area of the central portion of the concrete member. Concrete specimen. A rectangular plate-shaped bottom plate and
The end plates erected at both ends in the length direction, which is the direction parallel to the long side of the bottom plate,
A straight portion formed of a straight line parallel to a long side and a bent portion formed of a straight line or a curved line gradually distant from both ends of the straight portion are provided, and the bent portion is located at a position separated from the end plate by a predetermined distance. A mold with two side plates erected on the bottom plate so that the distance increases toward the end in the length direction.
On the outside of the side plate of the bottom plate, two restraint shaped steels extending in the length direction, each of which is arranged so as to abut the side plate,
One end of the restraining section steel of the two, the two one end plate side of the one said end plate from the end of one side plate of the side plate, and, one end of the other side plate Two one-sided connecting rods that are connected to one end plate side of the portion and the other end extends in the width direction of the bottom plate from the restraint shaped steel to which each one end is connected.
One end of the two restraint shaped steels is closer to the other end plate of the end plate than the other end of one side plate of the two side plates , and the other end of the other side plate. Two other-side connecting rods that are connected to the other end plate side of the portion and the other end extends in the width direction of the bottom plate from the restraint shaped steel to which each one end is connected.
It is a concrete specimen preparation tool for uniaxial restraint crack test equipped with
It is arranged between the two one-side connecting rods at the center of the two side plates in the width direction and on the one end plate side of the one end of the side plates, and the other end of the side plates. wherein at the other end plate side than the disposed between the two other side connecting rod, and the rod-shaped steel extending in the longitudinal direction,
Contact prevention for preventing the rod-shaped steel material from coming into contact with concrete, which covers the straight portion of the side plate or the portion surrounded by at least a part of the straight portion and the bent portion of the rod-shaped steel material. With wood,
The rod-shaped steel product, at one end the one end plate side of said side plate, is fixed to the other ends of one side connecting rod of the two, than the other end portion of the side plate wherein at the other end plate side, the two other side respectively connected uniaxial restraint cracking test concrete specimen prepared device, characterized in that it is fixed to the other end of the bar.

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