Pressure jig for concrete test piece and freezing and thawing test method using the same

Abstract

To provide a pressure jig for a concrete test piece that can externally apply stress in a compression direction to a concrete test piece and can quantitatively evaluate the influence of repeated freezing and thawing actions on the concrete test piece, and a freezing and thawing test method using the same.SOLUTION: A pressure jig for a concrete test piece 1 externally applies stress in a compression direction to a concrete test piece 10 used for a freezing and thawing test of concrete, and has: a first binding plate 2 on which the concrete test piece 10 is placed; a plurality of guide rails 3 that is erected on the outer peripheral edges of the first binding plate 2; a second binding plate 4 that slides along the guide rails 3 to bind the concrete test piece 10 with the first binding plate 2; and pressure application and removal means 5 that presses the second binding plate 4 to apply a pressure to the concrete test piece 10, and releases the pressing force to remove the pressure applied to the concrete test piece 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressure tool for concrete specimens for measuring deterioration caused by repeated freezing and thawing of concrete, and in particular to a freeze-thaw test method using the same for performing freeze-thaw tests on concrete specimens to which compressive stress is applied from the outside. [Background technology]

[0002] Concrete is an artificial stone made by mixing cement with aggregates such as sand and gravel and water, and is used in a variety of structures such as building foundations and irrigation channels.

[0003] However, concrete can deteriorate rapidly depending on the conditions of use and the environment. Frost damage in cold regions is one such deterioration phenomenon, in which the water contained in concrete repeatedly freezes and thaws, causing cracks and peeling.

[0004] Various measures have been taken against such frost damage in the past. For example, JP 2015-83767 A proposes a method for inhibiting frost / salt scaling, which comprises spraying on the surface of the hardened cement body an antifreeze agent which contains at least one type selected from the group consisting of sodium salts, potassium salts, and calcium salts and does not contain magnesium, and a water-soluble metal salt which contains at least one type of metal selected from the group consisting of magnesium, iron, and aluminum and reacts with an alkaline aqueous solution to become the hydroxide of the metal, thereby forming a coating made of the hydroxide of the metal between the surface of the hardened cement body and the ice adhering to the surface of the hardened cement body (Patent Document 1).

[0005] In addition, JP 2019-156700 A proposes an invention relating to a frost damage inhibitor consisting of a hardened cement body containing antifreeze polysaccharide in order to reduce the possibility of corrosion caused by the use of salts as in the invention described in Patent Document 1 (Patent Document 2).

[0006] Furthermore, the Japanese Industrial Standards (JIS) have established an underwater freezing and thawing test method (JIS A1148A method) as a standard for evaluating the performance of concrete that has been treated to protect against frost damage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-83767 A [Patent Document 2] JP 2019-156700 A Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, the inventors have previously conducted research into the actual state of frost damage deterioration of concrete structures and have found that when compressive stress is applied to concrete from the outside, cracks and other defects caused by frost damage are less likely to occur.

[0009] However, the existing underwater freeze-thaw test method (JIS A1148A method) does not specify a test method for concrete in which compressive stress is applied from the outside. Because of this, it is not possible to quantitatively evaluate the degree of pressure applied from the outside or the relationship between that pressure and the composition of concrete, and so there is a growing need for a quantitative evaluation method.

[0010] The present invention has been made to solve the above-mentioned problems, and aims to provide a pressure tool for concrete specimens, which can apply compressive stress to a concrete specimen from the outside and can quantitatively evaluate the effects of repeated freezing and thawing of the concrete specimen, and a freeze-thaw test method using the same. [Means for solving the problem]

[0011] The pressure applying tool for concrete specimens according to the present invention is a pressure applying tool for concrete specimens that applies a compressive stress from the outside to a concrete specimen used in a concrete freeze-thaw test, in order to solve the problem of being able to apply pressure in a compressive direction to a concrete specimen from the outside and to remove that pressure. The pressure applying tool has a first constraining plate on which the concrete specimen is placed, a plurality of guide rails erected on the outer periphery of the first constraining plate, a second constraining plate that slides along the guide rails and restrains the concrete specimen together with the first constraining plate, and a pressure applying / removing means for applying pressure to the concrete specimen by pressing the second constraining plate, or removing pressure from the concrete specimen by releasing the pressing.

[0012] In addition, as one aspect of the present invention, in order to solve the problem of easily applying pressure to and removing pressure from a concrete specimen, the first constraining plate and the second constraining plate may be formed in a substantially square shape when viewed in a plane, the guide rails may be erected at the four corners of the first constraining plate, the second constraining plate may have an insertion hole formed therein that is slidable along the guide rails, and the pressure application / removal means may include a pressure plate that is slidable along the guide rails above the second constraining plate and can be fixed at any height, and has a female threaded hole that penetrates in the vertical direction at its central position, and a pressure bolt that is screwed into the female threaded hole of the pressure plate and has its tip pressed downwardly against the central position of the upper surface of the second constraining plate to apply pressure to the concrete specimen.

[0013] Furthermore, as one aspect of the present invention, in order to solve the problem of accurately measuring the pressure applied to a concrete specimen, a pair of strain gauges may be provided at axisymmetric positions on the axial side of the pressure bolt to measure the amount of axial contraction of the pressure bolt in response to the pressure.

[0014] The freeze-thaw test method according to the present invention is a freeze-thaw test method using a pressurizing tool for concrete specimens, for solving the problem of quantitatively evaluating the influence of repeated freezing and thawing of a concrete specimen to which a compressive stress has been applied from the outside using the pressurizing tool for concrete specimens, the freeze-thaw test method using the pressurizing tool for concrete specimens comprising: a specimen initial value measuring step of measuring a numerical value serving as an index of the strength of the concrete specimen before freezing and thawing; a specimen pressurizing step of restraining the concrete specimen between the first restraining plate and the second restraining plate and applying a predetermined pressure; a test liquid injecting step of placing the concrete specimen in a test tank in a state where it is restrained and pressurized by the pressurizing tool for concrete specimens, and injecting a test liquid until the concrete specimen is entirely submerged; a freeze-thaw circulation step of controlling the temperature of the test liquid to perform temperature management in which a freezing process from a first temperature higher than zero degrees to a second temperature lower than zero degrees and a thawing process from the second temperature to the first temperature are set as one cycle, and repeating freezing and thawing of the concrete specimen a predetermined number of cycles; the concrete specimen is subjected to a predetermined number of freeze-thaw cycles, and then the concrete specimen is removed from the concrete specimen pressure tool and the numerical value of the index is measured; a step number determination step for determining whether the number of steps in the freeze-thaw circulation step has exceeded a predetermined number; a relative dynamic elastic modulus calculation step for calculating a relative dynamic elastic modulus from the numerical value of the index before the freeze-thaw cycle and the numerical value of the index after the freeze-thaw cycle if the predetermined number of steps has not been exceeded in the step number determination step; and a relative dynamic elastic modulus determination step for determining whether the calculated relative dynamic elastic modulus is equal to or less than a predetermined numerical value; and if the relative dynamic elastic modulus is not equal to or less than the predetermined numerical value, the concrete specimen is restrained by the concrete specimen pressure tool and a predetermined pressure is applied to the concrete specimen, and the freeze-thaw circulation step is terminated if the predetermined number of steps has been exceeded in the step number determination step or if the relative dynamic elastic modulus is equal to or less than the predetermined numerical value in the relative dynamic elastic modulus determination step.

[0015] The freeze-thaw test method according to the present invention is a freeze-thaw test method using a pressurizing jig for a concrete specimen, for solving the problem of quantitatively evaluating the influence of repeated freezing and thawing of a concrete specimen to which a compressive stress has been applied from the outside using the pressurizing jig for a concrete specimen, the freeze-thaw test method using the pressurizing jig for a concrete specimen comprising a specimen pressurizing step of sandwiching and restraining a concrete specimen before freezing and thawing between the first restraining plate and the second restraining plate and applying a predetermined pressure, a specimen initial value measuring step of measuring a numerical value that is an index of the strength of the concrete specimen in a state pressurized by the pressurizing jig for a concrete specimen, a test liquid injecting step of placing the concrete specimen in a state restrained and pressurized by the pressurizing jig for a concrete specimen in a test tank and injecting test liquid until the concrete specimen is entirely submerged in water, and a temperature management step of controlling the temperature of the test liquid to perform a freezing step from a first temperature higher than zero degrees to a second temperature lower than zero degrees and a thawing step from the second temperature to the first temperature as one cycle, and the concrete specimen is subjected to a predetermined number of freezing and thawing cycles. a step number determination step of determining whether the number of steps in the freeze-thaw cycling step has exceeded a predetermined number; a relative dynamic elastic modulus calculation step of calculating a relative dynamic elastic modulus from the numerical value of the index before the freeze-thaw and the numerical value of the index after the freeze-thaw, if the predetermined number of steps has not been exceeded in the step number determination step; and a relative dynamic elastic modulus determination step of determining whether the calculated relative dynamic elastic modulus is equal to or less than a predetermined numerical value. If the relative dynamic elastic modulus is not equal to or less than the predetermined numerical value, the freeze-thaw cycling step is performed in a state in which the concrete specimen is restrained by the concrete specimen pressure jig and a predetermined pressure is applied, and the freeze-thaw test is terminated if the predetermined number of steps has been exceeded in the step number determination step, or if the relative dynamic elastic modulus is equal to or less than the predetermined numerical value in the relative dynamic elastic modulus determination step. Effect of the Invention

[0016] According to the present invention, it is possible to apply compressive stress to a concrete specimen from the outside, and to quantitatively evaluate the influence of repeated freezing and thawing of the concrete specimen. [Brief description of the drawings]

[0017] [Figure 1] 1 is a perspective view showing a first embodiment of a pressurizing jig for a concrete specimen according to the present invention, in which a concrete specimen is restrained. FIG. [Diagram 2] FIG. 2 is a front view showing the concrete specimen pressing jig of the first embodiment. [Diagram 3] FIG. 2 is a plan view showing the pressure jig for a concrete specimen of the first embodiment. [Figure 4] FIG. 2 is a bottom view showing the pressure jig for a concrete specimen of the first embodiment. [Diagram 5] FIG. 1 is a flow chart showing the procedure of a first embodiment of a freeze-thaw test method according to the present invention. [Figure 6] FIG. 11 is a flow chart showing the procedure of a second embodiment of the freeze-thaw test method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a first embodiment of a pressurizing jig for a concrete specimen and a freeze-thaw test method using the same according to the present invention will be described with reference to the drawings.

[0019] The pressure jig 1 for a concrete specimen is a jig used in a freeze-thaw test of concrete, and can apply a compressive stress to a concrete specimen 10 from the outside. As shown in Fig. 1, the pressure jig 1 for a concrete specimen in this first embodiment has a first constraining plate 2 on which the concrete specimen 10 is placed, a plurality of guide rails 3 erected on the outer periphery of the first constraining plate 2, a second constraining plate 4 that slides along the guide rails 3 and constrains the concrete specimen 10 together with the first constraining plate 2, a pressure applying / removing means 5 that applies pressure to the concrete specimen 10 or removes the pressure, and a strain gauge 6 that measures the pressure applied by the pressure applying / removing means 5. Each component will be described in detail below.

[0020] First constraining plate 2 is a plate material on which concrete specimen 10 is placed and which clamps and constrains said concrete specimen 10 together with second constraining plate 4. First constraining plate 2 in this first embodiment is formed in a substantially square shape in a plan view so that it can be installed in a test tank used in a conventional freeze-thaw test method, and is formed from a square iron plate with one side of approximately 100 mm and a thickness of approximately 5 mm.

[0021] In addition, insertion holes for inserting the guide rails 3 are opened at the four corners of the first restraint plate 2, and the underside of the inserted guide rail 3 is configured as a leg 21 whose height can be adjusted by screwing a long nut into it.

[0022] The shape and dimensions of the first restraining plate 2 are not particularly limited, and may be appropriately selected depending on the size of the test tank used in the freeze-thaw test method.

[0023] The guide rail 3 is a rail for guiding the second constraining plate 4 so that it can slide up and down, and is erected on the outer periphery of the first constraining plate 2. The guide rail in this first embodiment is formed of a long bolt with a length of approximately 530 mm so that it can be installed in a test tank used in a conventional freeze-thaw test method.

[0024] 1, in the first embodiment, a total of four guide rails 3 are erected, one at each of the four corners of the first constraining plate 2. Specifically, each guide rail 3 is inserted into an insertion hole opened at the four corners of the first constraining plate 2 and screwed into a long nut that becomes the leg portion 21, thereby erecting the guide rail 3.

[0025] The guide rail 3 is not limited to being formed by a long bolt, but may be appropriately selected from round bar material or square bar material without male threads.

[0026] The second constraint plate 4 slides along the guide rail 3 to constrain the concrete specimen 10 together with the first constraint plate 2, and in this first embodiment, is formed of a square iron plate with a side length of about 100 mm and a thickness of about 5 mm, similar to the first constraint plate 2. At the four corners of this second constraint plate 4, insertion holes 41 having an inner diameter that allows the guide rail 3 to be inserted therethrough are opened at positions corresponding to the guide rail 3. Then, by inserting the guide rail 3 into each insertion hole 41, the second constraint plate 4 is configured to be movable in the vertical direction while remaining parallel to the first constraint plate 2.

[0027] The shape and dimensions of the second constraining plate 4 are not particularly limited, and like the first constraining plate 2, may be appropriately selected depending on the size of the test tank used in the freeze-thaw test method.

[0028] The pressure application / removal means 5 is a means for applying pressure to push down the second constraining plate 4 and releasing that pressure, and in this first embodiment, as shown in Figure 1, has a pressure plate 51 installed above the second constraining plate 4 and a pressure bolt 52 screwed into this pressure plate 51.

[0029] The pressure plate 51 serves as a base for applying pressure to the second constraining plate 4, and in this first embodiment is formed from a substantially square iron plate with one side of about 100 mm and a thickness of about 10 mm so that it can be installed in a test tank used in a conventional freeze-thaw test method. In order to configure this pressure plate 51 so that it can slide along the guide rail 3 above the second constraining plate 4 and can be fixed at any height, in this first embodiment, insertion holes through which the guide rail 3 can be inserted are formed at the four corners, and the pressure plate is fastened and fixed by nuts screwed onto the guide rail 3 so as to sandwich it from above and below.

[0030] Further, at the central position of the pressure plate 51, a female threaded hole 511 is formed which penetrates in the vertical direction for screwing in the pressure bolt 52, and in this first embodiment, a female threaded hole 511 into which an M12 bolt can be screwed is formed.

[0031] The shape and dimensions of the pressure plate 51 are not particularly limited, and may be appropriately selected from shapes that are slidable along the guide rail 3 and that can apply pressure to press down on the first restraint plate 2.

[0032] Pressure bolt 52 is a bolt that is screwed into female screw hole 511 of pressure plate 51 to apply pressure to second restraint plate 4, and in this first embodiment, as shown in Figures 1 and 3, is an M12 hexagonal bolt with a head that is hexagonal in plan view and a shaft length of approximately 90 mm. The side of pressure bolt 52 is threaded portion 521 with a male thread formed about 30 mm from the head side, and the tip side of threaded portion 521 is an unthreaded portion 522 without a thread in order to provide strain gauge 6.

[0033] The bolt shape of the pressure bolt 52 is not limited to a hexagonal bolt, and may be appropriately selected from among a square bolt that is square when viewed from above, a bolt having a hexagonal recess in the center of the top surface into which a hexagonal wrench can be inserted, or a bolt having a cross hole into which a screwdriver can be inserted.

[0034] Furthermore, the pressure application / removal means 5 is not limited to a configuration consisting of a pressure plate 51 and a pressure bolt 52, but may be appropriately selected from means that can apply pressure to press down the second restraint plate 4, such as a hydraulic jack, and can release that pressure.

[0035] The strain gauge 6 is for measuring the amount of contraction in the axial direction of the pressure bolt 52 according to the applied pressure (applied force), and is capable of outputting the amount of contraction as an electrical signal. Although not shown, it is connected to an analog / digital converter or a computer, etc., and by receiving the output electrical signal and inputting it into a mathematical formula corresponding to the strain gauge 6, the applied force can be calculated.

[0036] 1 and 2, in the first embodiment, a pair of strain gauges 6 are provided at axisymmetric positions on the axial side surface of the unthreaded portion 522 of the pressure bolt 52. In this way, in the first embodiment, by providing a pair of strain gauges 6 at axisymmetric positions and using the average value of the values ​​measured by the strain gauges 6 when calculating the pressure, it is possible to suppress the influence of measurement errors of the strain gauges 6 caused by bending deformation of the pressure bolt 52 when pressure is applied.

[0037] The method of measuring the applied pressure is not limited to using the strain gauge 6, and may be appropriately selected from a method based on the tightening torque value of the pressure bolt 52, an angle method based on the tightening angle, an ultrasonic bolt axial force method that measures the expansion and contraction of the pressure bolt 52 using ultrasonic waves, etc.

[0038] Next, the function of each component of the pressurizing jig 1 for a concrete specimen of the first embodiment will be described together with the freeze-thaw test method of the first embodiment.

[0039] The freeze-thaw test method of the first embodiment is a freeze-thaw test method using a pressure tool 1 for a concrete specimen, and includes a specimen initial value measurement step S1 for measuring a numerical value that is an index of the strength of the concrete specimen 10, a specimen pressurization step S2 for applying a predetermined pressure to the concrete specimen 10, a test liquid injection step S3 for placing the concrete specimen 10 in a test tank and injecting a test liquid until the concrete specimen 10 is entirely submerged, a freeze-thaw circulation step S4 for repeating freezing and thawing the concrete specimen 10 a predetermined number of cycles, a post-freeze-thaw measurement step S5 for measuring the numerical value of the index of the concrete specimen 10 after the predetermined number of cycles of freezing and thawing, a step number determination step S6 for determining the number of steps in the freeze-thaw circulation step S4, a relative dynamic modulus calculation step S7 for calculating the relative dynamic modulus of elasticity, and a relative dynamic modulus determination step S8 for determining whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined value. Each step will be described below.

[0040] The specimen initial value measurement step S1 is a step for measuring a numerical value that is an index of the strength of the concrete specimen 10. In this first embodiment, the concrete specimen 10 is a long rectangular prism-shaped concrete specimen, and the primary resonance frequency of the concrete specimen 10 is measured before it is frozen and thawed and before a predetermined pressure is applied.

[0041] The primary resonance frequency is a value measured during non-destructive testing of a value that is an index of the strength of concrete, and is a value used to calculate the relative dynamic modulus of elasticity. In the first embodiment, the resonance frequency of the flexural vibration is measured as the primary resonance frequency. In addition to the resonance frequency of the flexural vibration, the mass and ultrasonic propagation time of the concrete specimen 10 are also measured.

[0042] In addition, the numerical value that indicates the strength of concrete is not limited to the primary resonance frequency. The ultrasonic propagation time is also a numerical value that indicates the strength and can be used to calculate the relative dynamic modulus of elasticity.

[0043] The specimen pressurizing step S2 is a step in which the concrete specimen 10 is restrained by the concrete specimen pressurizing jig 1 and a predetermined pressure is applied. Specifically, as shown in Fig. 1, the concrete specimen 10 is sandwiched between the first restraining plate 2 and the second restraining plate 4 of the concrete specimen pressurizing jig 1. At this time, the height at which the pressurizing plate 51 is fixed is adjusted as necessary.

[0044] Then, the pressure bolt 52 is rotated in the tightening direction, and its tip is used to press downward the center of the upper surface of the second constraining plate 4. The second constraining plate 4 slides downward along the guide rail 3 while remaining parallel to the first constraining plate 2. As a result, the concrete specimen 10 is constrained by the first constraining plate 2 and the second constraining plate 4, and pressure is applied to the concrete specimen 10.

[0045] The strain gauge 6 measures the amount of contraction of the pressure bolt 52, which contracts in response to the pressure (pressure) applied to the concrete specimen. Specifically, the strain gauge 6 outputs an electric signal corresponding to the amount of contraction of the pressure bolt 52, and transmits it to a computer or the like. The computer or the like calculates the pressure from the received electric signal, and displays it on a monitor or the like. In this first embodiment, the pressure applied to the concrete specimen 10 is managed based on the pressure displayed on a monitor or the like.

[0046] Furthermore, in this first embodiment, a pair of strain gauges 6 are provided at axially symmetric positions on the unthreaded portion 522 of the pressure bolt 52. Even if the pressure bolt 52 is bent and deformed by the pressure force, the effect of the bending deformation can be cancelled out by using the average value of the values ​​based on the electrical signals of each strain gauge 6, and an accurate pressure force can be calculated.

[0047] The test liquid injection step S3 is a step in which the concrete specimen 10 restrained and pressurized by the concrete specimen pressurizing jig 1 is placed in the test tank, and test liquid is injected until the entire specimen is submerged.

[0048] The test tank in the first embodiment has a size in which a plurality of pressurizing jigs 1 for concrete specimens can be installed, and a freeze-thaw test can be performed at one time on a plurality of pressurized concrete specimens 10. As the test liquid in the first embodiment, Nybrine liquid containing ethylene glycol and propylene glycol as main components is used.

[0049] In addition, in this first embodiment, although not shown, the concrete specimen 10 in a state of being restrained and pressurized by the concrete specimen pressurizing jig 1 is placed in a test tank, and the concrete specimen 10 is entirely submerged in test liquid. The output value of the strain gauge 6 is confirmed in a state where the temperature of the test liquid is set to a first temperature, which will be described next.

[0050] The freeze-thaw circulation step S4 is a step in which the concrete specimen 10 is repeatedly frozen and thawed a predetermined number of cycles. Specifically, the temperature of the test liquid is controlled to perform temperature management in which a freezing process from a first temperature higher than zero to a second temperature below zero, and a thawing process from the second temperature to the first temperature constitute one cycle, and freezing and thawing are repeated a predetermined number of cycles.

[0051] In this first embodiment, the first temperature is 5° C., the second temperature is −18° C., and the temperature of the test liquid is controlled so that the time required for one cycle is 3 hours or more and 4 hours or less in accordance with the JISA1148A method. At this time, the temperature of the center of the concrete specimen 10 at the first temperature is within a range of 5±2° C., and the temperature of the center of the concrete specimen 10 at the second temperature is within a range of −18±2° C.

[0052] The number of cycles does not exceed 36 cycles in accordance with the JISA1148A method, and in this first embodiment, the number of cycles is appropriately selected from 30 cycles, 32 cycles, 34 cycles, or 36 cycles.

[0053] The post-freeze-thaw measurement step S5 is a step of measuring the primary resonance frequency as an index value after a predetermined number of freeze-thaw cycles, and in this first embodiment, in order to match the measurement conditions of the specimen initial value measurement step S1, the concrete specimen 10 is removed from the concrete specimen pressurizing jig 1 and measurement is performed. Since the concrete specimen 10 is restrained by the concrete specimen pressurizing jig 10 of this first embodiment, it can be easily removed from the concrete specimen pressurizing jig 10 by loosening the pressurizing bolt 52.

[0054] Then, the primary resonance frequency (resonance frequency of flexural vibration) of the removed concrete specimen 10 is measured. In this first embodiment, the mass and ultrasonic propagation time are also measured. At this time, it is preferable to measure the primary resonance frequency and the like in an indoor environment where the temperature of the concrete specimen 10 is controlled to 5° C., which is the same as the first temperature, so that the temperature of the concrete specimen 10 does not become equal to or higher than the first temperature before the next freeze-thaw cycle step S6.

[0055] The step number determination step S6 is a step for determining the first condition for terminating the freeze-thaw test, and determines whether the number of steps in the freeze-thaw cycling step S4 has exceeded a predetermined number. In the step number determination step S6 in the first embodiment, the number of cycles is set to 300 cycles or the smallest number of steps exceeding 300 cycles.

[0056] For example, if the number of cycles per step is 30, the predetermined number of steps is 10 steps (30 cycles x 10 steps = 300 cycles), and if the number of cycles per step is 34, the predetermined number of steps is 9 steps (34 cycles x 9 steps) = 306 cycles.

[0057] That is, in the first embodiment, when the number of cycles in one step is 30 to 33, the predetermined number of steps is 10, and when the number of cycles in one step is 34 to 36, the predetermined number of steps is 9.

[0058] Then, in the step number determination step S6, if it is determined that the step number exceeds the predetermined number (S6: YES), the freeze-thaw test is terminated. On the other hand, if it is determined that the step number does not exceed the predetermined number (S6: NO), the process proceeds to the relative dynamic elastic modulus calculation step S7.

[0059] The relative dynamic modulus of elasticity calculation step S7 is a step for calculating the relative dynamic modulus of elasticity, which is one of the indicators showing deterioration of concrete, and in this first embodiment, the primary resonance frequency before freezing and thawing measured in the specimen initial value measurement step S1 is compared with the primary resonance frequency after freezing and thawing measured in the most recent post-freezing and thawing measurement step S5 to calculate the relative dynamic modulus of elasticity. The calculated relative dynamic modulus of elasticity is expressed as a percentage.

[0060] The relative dynamic elastic modulus can also be calculated from the ratio of the ultrasonic propagation time before freezing and thawing to the ultrasonic propagation time after freezing and thawing.

[0061] The relative dynamic modulus of elasticity determination step S8 is a step for determining a second condition for terminating the freeze-thaw test when the number of steps does not exceed a predetermined number, and determines whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined value. In the relative dynamic modulus of elasticity determination step S8 in the first embodiment, it is determined whether the relative dynamic modulus of elasticity is equal to or less than 60%.

[0062] If it is determined in the relative dynamic modulus of elasticity determination step S8 that the relative dynamic modulus of elasticity is not equal to or less than the predetermined value (60%) (S8: NO), the concrete specimen 10 is restrained again by the concrete specimen pressure jig 1, a predetermined pressure is applied (S9), and the process returns to the freeze-thaw circulation step S4, and steps S5 to S8 are repeated. In this first embodiment, the pressure restraining the concrete specimen 10 is measured and managed by a pair of strain gauges 6 that can accurately measure the applied pressure, so that the freeze-thaw test can be performed again under the same pressurizing conditions.

[0063] On the other hand, if the relative dynamic elastic modulus is determined to be below a predetermined value (60%) in the relative dynamic elastic modulus determination step S8 (S8: YES), even if the number of steps in the freeze-thaw circulation step S4 does not exceed the predetermined number, it is determined that the concrete specimen 10 has been sufficiently deteriorated due to freezing and thawing, and the freeze-thaw test is terminated.

[0064] According to the first embodiment as described above, the following effects can be obtained. 1. By using the pressure jig 1 for concrete specimens, a freeze-thaw test can be performed while applying compressive stress from the outside to the concrete specimen 10, and a quantitative evaluation of the effects of repeated freezing and thawing can be performed. 2. The pressure jig 1 for concrete specimens can restrain the concrete specimen 10 and apply pressure to it, while also allowing easy removal. 3. Since the concrete specimen 10 can be easily restrained and removed using the pressure jig 1 for the concrete specimen, measurements of numerical values ​​that serve as indicators of strength after freezing and thawing in a freeze-thaw test can be smoothly carried out. 4. The pressure can be accurately measured by the pair of strain gauges 6, and the concrete specimen 10 can be restrained with an equal pressure even when it is repeatedly attached and detached. 5. Since the numerical values ​​of the above-mentioned indexes can be measured before and after freezing and thawing without being restrained by the pressure jig for concrete specimens 1, an accurate relative dynamic modulus of elasticity can be calculated.

[0065] Next, a second embodiment of the freeze-thaw test method according to the present invention will be described. Among the configurations and steps of the second embodiment, those that are equivalent or correspond to those of the first embodiment described above are given the same reference numerals and will not be described again.

[0066] The freeze-thaw test method of the second embodiment is a method for measuring a numerical value serving as an index of strength for calculating the relative dynamic modulus of elasticity while the concrete specimen 10 is pressurized by the pressurizing jig 1 for concrete specimen, and the freeze-thaw test is performed without removing the specimen when measuring the numerical value serving as an index of strength after freezing and thawing. That is, as shown in Fig. 6, a specimen pressurizing step S2' is performed prior to the specimen initial value measuring step S1', and in the post-freezing and thawing measuring step S5', the numerical value of the index is measured while the concrete specimen 10 is pressurized by the pressurizing jig 1 for concrete specimen.

[0067] Specifically, in the specimen pressurizing step S2' in the second embodiment, the concrete specimen 10 before freezing and thawing is sandwiched between the first constraining plate 2 and the second constraining plate 4 to be restrained, and a predetermined pressure is applied. A strain gauge 6 is used to manage the applied pressure.

[0068] In the second embodiment, the specimen initial value measuring step S1' measures a numerical value that is an index of strength while the concrete specimen 10 is attached to the concrete specimen pressurizing jig 1. In the second embodiment, the ultrasonic propagation time is measured as a numerical value that is an index of strength. This is preferably performed in an indoor environment that is temperature-controlled to 5° C., which is the same as the first temperature.

[0069] The numerical value serving as an index of strength is not limited to the ultrasonic propagation time, but may be the first resonance frequency as in the first embodiment.

[0070] Next, the process proceeds to a test liquid injection step S3 and a freeze-thaw cycle step S4.

[0071] In the post-freeze-thaw measurement step S5', after a predetermined number of freeze-thaw cycles, the concrete specimen 10 is pressurized by the concrete specimen pressurizing tool 1 and the ultrasonic propagation time is measured as a numerical value that serves as an indicator of strength.

[0072] The number of steps in the freeze-thaw circulation step S4 is determined in the step number determination step S6. If the step number determination step S6 determines that the number of steps exceeds a predetermined number (S6: YES), the freeze-thaw test is terminated.

[0073] On the other hand, if it is determined that the number of steps does not exceed the predetermined number of times (S6: NO), the process proceeds to the relative dynamic elastic modulus calculation step S7.

[0074] The relative dynamic modulus of elasticity calculation step S7 is a step for calculating the relative dynamic modulus of elasticity. In this second embodiment, the ultrasonic propagation time before freezing and thawing measured in the specimen initial value measurement step S1' and the ultrasonic propagation time after freezing and thawing measured in the post-freezing and thawing measurement step S5' are both for the concrete specimen 10 in a pressurized state, so that the relative dynamic modulus of elasticity can be calculated by comparing them.

[0075] In the relative dynamic elastic modulus determination step S8, it is determined whether the calculated relative dynamic elastic modulus is equal to or less than a predetermined value. If it is determined in the relative dynamic elastic modulus determination step S8 that the relative dynamic elastic modulus is not equal to or less than the predetermined value (60%) (S8: NO), the process returns to the freeze-thaw circulation step S4, and steps S5 to S8 are repeated.

[0076] In this second embodiment, since the concrete specimen 10 remains restrained by the pressurizing jig 1 for a concrete specimen, it is possible to return directly to the freeze-thaw circulation step S4, and the work can be carried out smoothly.

[0077] On the other hand, when it is determined in the relative dynamic modulus of elasticity determination step S8 that the relative dynamic modulus of elasticity is equal to or less than the predetermined value (S8: YES), the freeze-thaw test is terminated.

[0078] As described above, according to the freeze-thaw test method of the second embodiment, as in the first embodiment, it is possible to quantitatively evaluate the influence of repeated freezing and thawing of the concrete specimen 10 to which a compressive stress is applied from the outside. In particular, since the test is performed while the concrete specimen 10 is restrained by the pressure jig 1 for concrete specimens to which a constant pressure is continuously applied, it is possible to eliminate the influence on strength caused by the release of pressure during the test, and since the work of installation and removal is unnecessary, it is possible to obtain the effect of enabling the test to be performed more smoothly.

[0079] The pressurizing tool for a concrete specimen and the freeze-thaw test method using the same according to the present invention are not limited to the above-described embodiments, and can be modified as appropriate.

[0080] For example, the shape of the first constraining plate 2 and the second constraining plate 4 that constrain and apply pressure to the concrete specimen 10 is not limited to a square shape, and may be appropriately selected from a rectangular shape, a circular shape, or the like, in accordance with the shape of the concrete specimen 10. Furthermore, the direction in which the concrete specimen 10 is constrained and pressure is applied is not limited to the longitudinal direction of the concrete specimen 10, and the width direction may be constrained and pressure may be applied, and the effect of the repeated freezing and thawing action caused thereby may be quantitatively evaluated. [Explanation of symbols]

[0081] 1. Pressure fixture for concrete specimens 2 First restraint plate 3 Guide rail 4 Second restraint plate 5. Pressure relief means 6 Strain Gauges 10 Concrete specimen 21 Legs 41 Insertion hole 51 Pressure plate 52 Pressure bolt 511 Female thread hole 521 Thread part 522 Screwless part

Claims

1. A pressure jig for a concrete specimen used in a freeze-thaw test of concrete, which applies a compressive stress from the outside to a concrete specimen, A first restraint plate on which the concrete specimen is placed; A plurality of guide rails provided upright on an outer circumferential edge portion of the first restraint plate; A second constraining plate that slides along the guide rail and constrains the concrete specimen together with the first constraining plate; a pressure applying / relieving means for applying pressure to the concrete specimen by pressing the second restraint plate, or for removing pressure from the concrete specimen by releasing the pressing force; The pressure jig for a concrete specimen.

2. the first constraining plate and the second constraining plate are formed in a substantially square shape in a plan view, the guide rails are provided at four corners of the first constraining plate, and an insertion hole slidable along the guide rails is formed in the second constraining plate, The pressure application / relief means is a pressure plate that is slidable along the guide rail above the second restraint plate and can be fixed at any height, and has a female screw hole that penetrates in the vertical direction at a center position; a pressure bolt that is screwed into the female screw hole of the pressure plate and that presses down the center position of the upper surface of the second restraint plate with its tip to apply pressure to the concrete specimen; The pressure jig for a concrete specimen according to claim 1 .

3. 3. A pressure jig for a concrete specimen as described in claim 2, wherein a pair of strain gauges for measuring the amount of axial contraction of the pressure bolt in response to a pressure force are provided at axially symmetric positions on the axial side of the pressure bolt.

4. A freeze-thaw test method using the pressure jig for concrete specimens according to claim 1, A specimen initial value measurement step of measuring a numerical value that is an index of the strength of a concrete specimen before freezing and thawing; a specimen pressurizing step of sandwiching and restraining the concrete specimen between the first restraint plate and the second restraint plate and applying a predetermined pressure; A test liquid injection step of placing the concrete specimen restrained and pressurized by the concrete specimen pressurizing tool in a test tank and injecting a test liquid until the entire concrete specimen is submerged in water; a freeze-thaw circulation step in which a temperature of the test liquid is controlled to perform a temperature management in which a freezing process from a first temperature higher than zero degrees to a second temperature lower than zero degrees and a thawing process from the second temperature to the first temperature are set as one cycle, and the concrete specimen is repeatedly frozen and thawed a predetermined number of times; A post-freeze-thaw measurement step of removing the concrete specimen from the concrete specimen pressurizing jig after a predetermined number of freeze-thaw cycles and measuring the numerical value of the index; a step number determination step of determining whether or not the number of steps of the freeze-thaw circulation step exceeds a predetermined number; A relative dynamic elastic modulus calculation step of calculating a relative dynamic elastic modulus from the numerical value of the index before the freezing and thawing and the numerical value of the index after the freezing and thawing when the predetermined number of times is not exceeded in the step number determination step; and a relative dynamic elastic modulus determination step of determining whether the calculated relative dynamic elastic modulus is equal to or less than a predetermined value, If the relative dynamic modulus of elasticity is not equal to or less than a predetermined value, the concrete specimen is restrained by the pressure jig for the concrete specimen and a predetermined pressure is applied thereto, and the freeze-thaw circulation step is performed in this state; The freeze-thaw test method, wherein the freeze-thaw test is terminated when the step number determination step exceeds a predetermined number of times, or when the relative dynamic elastic modulus determination step determines that the relative dynamic elastic modulus is equal to or less than a predetermined value.

5. A freeze-thaw test method using the pressure jig for concrete specimens according to claim 1, a specimen pressurizing step of sandwiching and restraining a concrete specimen before freezing and thawing between the first restraining plate and the second restraining plate and applying a predetermined pressure; A test piece initial value measurement step of measuring a numerical value that is an index of the strength of the concrete test piece in a state pressurized by the concrete test piece pressurizing jig; A test liquid injection step of placing the concrete specimen restrained and pressurized by the concrete specimen pressurizing tool in a test tank and injecting a test liquid until the entire concrete specimen is submerged in water; a freeze-thaw circulation step in which a temperature of the test liquid is controlled to perform a temperature management in which a freezing process from a first temperature higher than zero degrees to a second temperature lower than zero degrees and a thawing process from the second temperature to the first temperature are set as one cycle, and the concrete specimen is repeatedly frozen and thawed a predetermined number of times; A post-freeze-thaw measurement step of measuring the numerical value of the index while applying pressure to the concrete specimen by the pressure jig after a predetermined number of freeze-thaw cycles; a step number determination step of determining whether or not the number of steps of the freeze-thaw circulation step exceeds a predetermined number; A relative dynamic elastic modulus calculation step of calculating a relative dynamic elastic modulus from the numerical value of the index before the freezing and thawing and the numerical value of the index after the freezing and thawing when the predetermined number of times is not exceeded in the step number determination step; and a relative dynamic elastic modulus determination step of determining whether the calculated relative dynamic elastic modulus is equal to or less than a predetermined value, If the relative dynamic modulus of elasticity is not equal to or less than a predetermined value, the concrete specimen is restrained by the pressure jig for the concrete specimen and a predetermined pressure is applied thereto, and the freeze-thaw circulation step is performed in this state; The freeze-thaw test method, wherein the freeze-thaw test is terminated when the step number determination step exceeds a predetermined number of times, or when the relative dynamic elastic modulus determination step determines that the relative dynamic elastic modulus is equal to or less than a predetermined value.

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