Pressure jig for concrete specimen and freeze-thaw 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 jig for concrete specimens used to measure deterioration of concrete due to repeated freezing and thawing, and in particular to a freeze-thaw test method using the same for concrete specimens to which external compressive stress is applied. [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 agricultural irrigation channels.

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

[0004] Various countermeasures have been taken to prevent such frost damage. For example, Japanese Patent Application Laid-Open No. 2015-83767 proposes a method for preventing frost and salt scaling, which comprises spraying, on the surface of the hardened cement body, an antifreeze agent that contains at least one selected from the group consisting of sodium salts, potassium salts, and calcium salts but does not contain magnesium, and a water-soluble metal salt that contains at least one metal selected from the group consisting of magnesium, iron, and aluminum and reacts with an alkaline aqueous solution to form 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, Patent Publication No. 2019-156700 proposes an invention relating to a frost damage inhibitor consisting of a hardened cement body containing antifreeze polysaccharides 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) has established a water freeze-thaw test method (JIS A1148A method) as a standard for evaluating the performance of concrete that has been treated to prevent frost damage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-83767 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-156700 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, the inventors have conducted a survey of 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 caused by frost damage are less likely to occur.

[0009] However, the current underwater freeze-thaw test method (JIS A1148A method) does not specify a test method for concrete in which external compressive stress is applied. As a result, 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 the concrete, and 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 jig for concrete specimens, which can apply compressive stress to concrete specimens from the outside and can quantitatively evaluate the effects of repeated freezing and thawing of the concrete specimens, and a freeze-thaw test method using the same. [Means for solving the problem]

[0011] The pressure jig for concrete specimens of the present invention is a pressure jig for concrete specimens that applies compressive stress from the outside to concrete specimens used in concrete freeze-thaw tests, in order to solve the problem of being able to apply compressive pressure to concrete specimens from the outside and also be able to remove that pressure.The pressure jig for concrete specimens of the present invention applies compressive stress from the outside to concrete specimens used in concrete freeze-thaw tests, and has the following features: a first constraining plate on which the concrete specimen is placed; a plurality of guide rails erected on the outer edge 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 pressure application / removal means that applies pressure to the concrete specimen by pressing the second constraining plate, or removes pressure from the concrete specimen by releasing that pressure.

[0012] In addition, as one aspect of the present invention, in order to solve the problem of easily applying pressure to and releasing pressure from a concrete specimen, the first constraining plate and the second constraining plate may be formed in an approximately square shape when viewed from above, 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 allows it to slide 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 center, and a pressure bolt that is screwed into the female threaded hole of the pressure plate and whose tip presses downward against the center 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 of the present invention is a freeze-thaw test method using a concrete specimen pressurizing jig to solve the problem of quantitatively evaluating the effects of repeated freezing and thawing of a concrete specimen to which external compressive stress has been applied using the concrete specimen pressurizing jig, and includes a specimen initial value measurement step of measuring a numerical value that serves as an index of the strength of the concrete specimen before freezing and thawing, a specimen pressurizing step of sandwiching the concrete specimen between the first confining plate and the second confining plate to restrain it and apply a predetermined pressure, a test liquid injection step of placing the concrete specimen in a test tank in a state where it is restrained and pressurized by the concrete specimen pressurizing jig, and injecting 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 to a second temperature lower than zero and a thawing process from the second temperature to the first temperature are one cycle, and repeatedly freezing and thawing the concrete specimen a predetermined number of times, and a predetermined 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 jig 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 cycling step has exceeded a predetermined number; a relative dynamic modulus of elasticity calculation step for calculating a relative dynamic modulus of elasticity 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 modulus of elasticity determination step for determining whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined numerical value; and if the relative dynamic modulus of elasticity is not equal to or less than a predetermined numerical value, the concrete specimen is restrained by the concrete specimen pressure jig and a predetermined pressure is applied to the concrete specimen, and the freeze-thaw cycling step is performed; 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 modulus of elasticity is equal to or less than a predetermined numerical value in the relative dynamic modulus of elasticity determination step.

[0015] The freeze-thaw test method according to the present invention is a freeze-thaw test method using a concrete specimen pressurizing jig to solve 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 concrete specimen pressurizing jig, and includes a specimen pressurizing step of sandwiching and restraining a concrete specimen before freezing and thawing between the first and second restraining plates and applying a predetermined pressure, a specimen initial value measuring step of measuring a numerical value that serves as an index of the strength of the concrete specimen in a state pressurized by the concrete specimen pressurizing jig, a test liquid injection step of placing the concrete specimen in a state restrained and pressurized by the concrete specimen pressurizing jig in a test tank and injecting test liquid until the concrete specimen is entirely submerged, and a temperature management step of controlling the temperature of the test liquid to perform a freezing process from a first temperature higher than zero to a second temperature lower than zero and a thawing process 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 post-freeze-thaw measurement step of measuring the numerical value of the index while applying pressure with the concrete specimen pressure jig after a predetermined number of freeze-thaw 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 modulus of elasticity calculation step of calculating a relative dynamic modulus of elasticity 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 modulus of elasticity determination step of determining whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined numerical value. If the relative dynamic modulus of elasticity is not equal to or less than the predetermined numerical value, the freeze-thaw cycling step is performed with the concrete specimen restrained by the concrete specimen pressure jig and a predetermined pressure 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 modulus of elasticity is equal to or less than the predetermined numerical value in the relative dynamic modulus of elasticity determination step. [Effects 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 explanation 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. [Figure 2] 1 is a front view showing a pressure jig for a concrete specimen according to the first embodiment. FIG. [Figure 3] 1 is a plan view showing a pressure jig for a concrete specimen according to the first embodiment of the present invention. FIG. [Figure 4] FIG. 2 is a bottom view showing the pressure jig for a concrete specimen of the first embodiment. [Figure 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. 10 is a flowchart showing the procedure of a second embodiment of the freeze-thaw test method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[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 concrete specimen pressurizing jig 1 is a jig used in freeze-thaw tests of concrete, and is capable of applying compressive stress to a concrete specimen 10 from the outside. As shown in FIG. 1 , the concrete specimen pressurizing jig 1 in this first embodiment includes 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 that pressure, and a strain gauge 6 that measures the applied 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, together with second constraining plate 4, clamps and constrains concrete specimen 10. First constraining plate 2 in this first embodiment is formed in a substantially square shape in plan view so that it can be installed in a test tank used in conventional freeze-thaw testing methods, and is formed from a square steel plate with a side length of approximately 100 mm and a thickness of approximately 5 mm.

[0021] In addition, insertion holes are opened at the four corners of the first restraint plate 2 for inserting the guide rail 3, 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 constraining plate 2 are not particularly limited, and may be selected appropriately depending on the size of the test tank used in the freeze-thaw test method.

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

[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 is screwed onto a long nut that becomes the leg portion 21, thereby erecting the guide rail 3.

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

[0026] The second constraint plate 4 slides along the guide rails 3 to constrain the concrete specimen 10 together with the first constraint plate 2, and in this first embodiment, is formed from a square iron plate with sides of approximately 100 mm and a thickness of approximately 5 mm, similar to the first constraint plate 2. Insertion holes 41 having an inner diameter large enough to insert the guide rails 3 are opened at the four corners of the second constraint plate 4 at positions corresponding to the guide rails 3. By inserting the guide rails 3 into each insertion hole 41, the second constraint plate 4 can move up and down 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 selected appropriately 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 for releasing that pressure, and in this first embodiment, as shown in Figure 1, it has a pressure plate 51 installed above the second constraining plate 4 and a pressure bolt 52 screwed into this pressure plate 51.

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

[0030] In addition, a female screw hole 511 that penetrates in the vertical direction is formed at the center position of the pressure plate 51 for screwing in the pressure bolt 52, and in this first embodiment, a female screw hole 511 that can screw in an M12 bolt 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 capable of sliding along the guide rail 3 and applying pressure to press down on the first restraint plate 2.

[0032] Pressure bolt 52 is a bolt that is screwed into female threaded 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, it 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 has threaded portion 521, where a male thread is formed approximately 30 mm from the head side, and the portion distal to threaded portion 521 is an unthreaded portion 522 without a thread for providing strain gauge 6.

[0033] The shape of the pressure bolt 52 is not limited to a hexagonal bolt, and may be appropriately selected from a square bolt that is square when viewed from above, a bolt with a hexagonal recess in the center of the top surface into which a hexagonal wrench can be inserted, or a bolt with 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 push down the second restraint plate 4, such as a hydraulic jack, and can release that pressure.

[0035] The strain gauge 6 is used to measure the amount of axial contraction 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., which receives the output electrical signal and inputs it into a mathematical formula corresponding to the strain gauge 6, thereby making it possible to calculate the applied force.

[0036] 1 and 2, in the first embodiment, a pair of strain gauges 6 are provided at axisymmetric positions on the axial side 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 each strain gauge 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 for measuring the applied pressure is not limited to using the strain gauge 6, but 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, and the like.

[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 uses a concrete specimen pressure jig 1 and includes the following steps: a specimen initial value measurement step S1 for measuring a numerical value that serves as 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 into the concrete specimen 10 until the concrete specimen 10 is completely submerged; a freeze-thaw cycling step S4 for repeatedly freezing and thawing the concrete specimen 10 a predetermined number of times; 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 freeze-thaw cycles; a step number determination step S6 for determining the number of steps in the freeze-thaw cycling 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 is described below.

[0040] The specimen initial value measurement step S1 is a step for measuring a numerical value that serves as an indicator of the strength of the concrete specimen 10. In this first embodiment, the concrete specimen 10 is a vertically elongated rectangular parallelepiped-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 concrete strength index, and is a value used to calculate the relative dynamic modulus of elasticity. In this 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] 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 against 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 it.

[0045] The strain gauge 6 measures the amount of shrinkage of the pressure bolt 52, which shrinks in response to the pressure (applied pressure) applied to the concrete specimen. Specifically, the strain gauge 6 outputs an electrical signal corresponding to the amount of shrinkage of the pressure bolt 52 and transmits it to a computer or the like. The computer or the like calculates the applied pressure from the received electrical 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 applied 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, and even if the pressure bolt 52 is bent and deformed by the pressure, 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, making it possible to accurately calculate the pressure.

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

[0048] The test tank in this first embodiment is large enough to accommodate multiple concrete specimen pressurizing jigs 1, making it possible to simultaneously perform freeze-thaw tests on multiple pressurized concrete specimens 10. The test liquid used in this first embodiment is Nybrine liquid, which contains ethylene glycol and propylene glycol as its main components.

[0049] Furthermore, 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, and the output value of the strain gauge 6 is confirmed in a state in which the temperature of the test liquid is set to a first temperature, which will be described next.

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

[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 per 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 is set to 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 in which, after a predetermined number of freeze-thaw cycles, the primary resonance frequency is measured as an index value, and in this first embodiment, the concrete specimen 10 is removed from the concrete specimen pressurizing jig 1 to perform the measurement in accordance with the measurement conditions of the specimen initial value measurement step S1. Because 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 pressure bolts 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, the same as the first temperature, so that the temperature of the concrete specimen 10 does not exceed the first temperature before the next freeze-thaw cycle step S6.

[0055] The step number determination step S6 is a step for determining whether a first condition for terminating the freeze-thaw test is met, 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 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 (30 cycles x 10 steps = 300 cycles), and if the number of cycles per step is 34, the predetermined number of steps is 9 (34 cycles x 9 steps) = 306.

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

[0058] If it is determined in the step number determination step S6 that the number of steps exceeds the predetermined number (S6: YES), the freeze-thaw test is terminated. On the other hand, if it is determined that the number of steps does not exceed the predetermined number (S6: NO), the process proceeds to the relative dynamic 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 of concrete deterioration. In this first embodiment, the relative dynamic modulus of elasticity is calculated by comparing the primary resonance frequency before freeze-thaw measured in the specimen initial value measurement step S1 with the primary resonance frequency after freeze-thaw measured in the most recent post-freeze-thaw measurement step S5. The calculated relative dynamic modulus of elasticity is expressed as a percentage.

[0060] The relative dynamic modulus of elasticity 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 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 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 again constrained 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 constraining 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 it is determined in the relative dynamic modulus of elasticity determination step S8 that the relative dynamic modulus of elasticity is below a predetermined value (60%) (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 sufficiently deteriorated due to freeze-thawing, and the freeze-thaw test is terminated.

[0064] According to the first embodiment described above, the following effects can be achieved. 1. By using the pressure jig 1 for concrete specimens, freeze-thaw tests can be performed while applying compressive stress from the outside to the concrete specimen 10, allowing for quantitative evaluation of the effects of repeated freezing and thawing. 2. The concrete specimen pressure jig 1 can restrain the concrete specimen 10 and apply pressure to it, and can also be easily removed. 3. The concrete specimen 10 can be easily restrained and removed using the pressure jig 1 for the concrete specimen, so that measurements of numerical values ​​that serve as indicators of strength after freezing and thawing in freeze-thaw tests can be carried out smoothly. 4. The pair of strain gauges 6 can accurately measure the applied pressure, and the concrete specimen 10 can be restrained with an equal pressure even when it is repeatedly attached and detached. 5. The numerical values ​​of the above indexes can be measured before and after freezing and thawing without being restrained by the pressure jig 1 for concrete specimens, so that 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. Note that, among the components and steps of this second embodiment, components and steps that are the same as or correspond to the components of the first embodiment described above will be assigned 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 that serves as an index of strength for calculating the relative dynamic modulus of elasticity while the concrete specimen 10 is pressurized by the concrete specimen pressurizing jig 1, and is a method for performing a freeze-thaw test without removing the specimen when measuring the numerical value that serves as an index of strength after freeze-thaw. That is, as shown in Fig. 6, the specimen pressurizing step S2' is performed before the specimen initial value measuring step S1', and in the post-freeze-thaw measuring step S5', the index value is measured while the concrete specimen 10 is pressurized by the concrete specimen pressurizing jig 1.

[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 constrained, and a predetermined pressure is applied. A strain gauge 6 is used to control the applied pressure.

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

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

[0070] Next, the process proceeds to test liquid injection step S3 and freeze-thaw cycling 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 using the concrete specimen pressure jig 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 cycling 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 (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 thaw measurement step S5' are both for the concrete specimen 10 in a pressurized state, so the relative dynamic modulus of elasticity can be calculated by comparing them.

[0075] Then, in the relative dynamic modulus of elasticity determination step S8, it is determined whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined value. 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 process returns to the freeze-thaw circulation step S4, and steps S5 to S8 are repeated.

[0076] In this second embodiment, the concrete specimen 10 remains restrained by the pressure jig 1 for the concrete specimen, so that it can be returned to the freeze-thaw circulation step S4 as is, and the work can be carried out smoothly.

[0077] On the other hand, if 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 with the first embodiment, it is possible to quantitatively evaluate the effects of repeated freezing and thawing of a 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, which continues to apply a constant pressure, the effect on strength caused by the release of pressure during the test is eliminated, and the work of attachment and detachment is no longer necessary, which has the effect of allowing the test to be performed more smoothly.

[0079] The pressure jig 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 shapes of the first constraining plate 2 and the second constraining plate 4 that constrain and apply pressure to the concrete specimen 10 are not limited to square, but may be selected appropriately from rectangular, circular, or other shapes to match 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, but the widthwise direction may be constrained and pressure may be applied, and the effects of the resulting repeated freezing and thawing action may be quantitatively evaluated. [Explanation of symbols]

[0081] 1. Pressure jig for concrete specimens 2 First restraint plate 3 Guide rails 4 Second restraint plate 5. Pressure application / relief means 6 Strain gauges 10 Concrete specimen 21 Legs 41 Insertion hole 51 Pressure plate 52 Pressure bolt 511 female screw hole 521 Threaded part 522 Screwless part

Claims

1. A pressure jig for a concrete specimen that applies compressive stress from the outside to a concrete specimen used in a freeze-thaw test of concrete, a first restraint plate on which the concrete specimen is placed; a plurality of guide rails provided upright on an outer peripheral 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; and 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 upright at four corners of the first constraining plate, and an insertion hole is formed in the second constraining plate such that the second constraining plate can slide along the guide rails, The pressure application / relief means a pressure plate that is slidable along the guide rail above the second restraint plate and can be fixed at any height, and that has a female screw hole that penetrates in the vertical direction at a central position; a pressure bolt that is screwed into the female screw hole of the pressure plate and that presses downward with its tip the center position of the upper surface of the second restraint plate to apply pressure to the concrete specimen; The pressure jig for a concrete specimen, comprising:

2. 2. A pressure jig for a concrete specimen as described in claim 1, wherein a pair of strain gauges are 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.

3. A freeze-thaw test method using a pressurizing jig for a concrete specimen that applies compressive stress from the outside to a concrete specimen used in a freeze-thaw test of concrete, the pressurizing jig for a concrete specimen having 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 constrains the concrete specimen together with the first constraining plate, and a pressure applying / removing means that applies pressure to the concrete specimen by pressing the second constraining plate, or removes pressure from the concrete specimen by releasing the pressing force, a test piece initial value measurement step for measuring a numerical value that is an indicator of the strength of the concrete test piece before freezing and thawing; a specimen pressurizing step of sandwiching and restraining the concrete specimen between the first constraining plate and the second constraining plate and applying a predetermined pressure; a test liquid injection step of placing the concrete specimen restrained and pressurized by the concrete specimen pressurizing jig in a test tank and injecting test liquid into the test tank until the entire concrete specimen is submerged; a freeze-thaw cycle step in which the temperature of the test liquid is controlled to perform a temperature management cycle consisting of a freezing step from a first temperature higher than zero to a second temperature lower than zero and a thawing step from the second temperature to the first temperature, 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 the number of steps of the freeze-thaw cycle step has exceeded a predetermined number; If the number of times does not exceed a predetermined number in the step number determination step, a relative dynamic modulus of elasticity calculation step of calculating a relative dynamic modulus of elasticity from the numerical value of the index before the freeze-thaw and the numerical value of the index after the freeze-thaw; a relative dynamic modulus of elasticity determination step of determining whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined value, If the relative dynamic modulus of elasticity is not equal to or less than the predetermined value, the freeze-thaw circulation step is continued while the concrete specimen is restrained by the pressure jig for the concrete specimen and a predetermined pressure is applied, the concrete specimen is removed from the pressure jig for the concrete specimen and the post-freeze-thaw measurement step is continued, the number of steps determination step, the relative dynamic modulus of elasticity calculation step, and the relative dynamic modulus of elasticity determination step are continued, The freeze-thaw test method, wherein while the freeze-thaw circulation step, the post-freeze-thaw measurement step, the step number determination step, the relative dynamic elastic modulus calculation step, and the relative dynamic elastic modulus determination step are being performed, the freeze-thaw test is terminated if the step number determination step exceeds a predetermined number, or if the relative dynamic elastic modulus becomes equal to or less than a predetermined value in the relative dynamic elastic modulus determination step.

4. A freeze-thaw test method using a pressurizing jig for a concrete specimen that applies compressive stress from the outside to a concrete specimen used in a freeze-thaw test of concrete, the pressurizing jig for a concrete specimen having 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 constrains the concrete specimen together with the first constraining plate, and a pressure applying / removing means that applies pressure to the concrete specimen by pressing the second constraining plate, or removes pressure from the concrete specimen by releasing the pressing force, a specimen pressurizing step of sandwiching and restraining a concrete specimen before freezing and thawing between the first restraint plate and the second restraint 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 jig in a test tank and injecting test liquid into the test tank until the entire concrete specimen is submerged; a freeze-thaw cycle step in which the temperature of the test liquid is controlled to perform a temperature management cycle consisting of a freezing step from a first temperature higher than zero to a second temperature lower than zero and a thawing step from the second temperature to the first temperature, 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 with the concrete specimen pressure jig after a predetermined number of freeze-thaw cycles; a step number determination step of determining whether the number of steps of the freeze-thaw cycle step has exceeded a predetermined number; If the number of times does not exceed a predetermined number in the step number determination step, a relative dynamic modulus of elasticity calculation step of calculating a relative dynamic modulus of elasticity from the numerical value of the index before the freeze-thaw and the numerical value of the index after the freeze-thaw; a relative dynamic modulus of elasticity determination step of determining whether the calculated relative dynamic modulus of elasticity is equal to or less than a predetermined value, If the relative dynamic modulus of elasticity is not equal to or less than the predetermined value, the concrete specimen is constrained by the pressure jig for the concrete specimen and a predetermined pressure is applied, and the freeze-thaw cycling step, the post-freeze-thaw measurement step, the step number determination step, the relative dynamic modulus of elasticity calculation step, and the relative dynamic modulus of elasticity determination step are continued; The freeze-thaw test method, wherein while the freeze-thaw circulation step, the post-freeze-thaw measurement step, the step number determination step, the relative dynamic elastic modulus calculation step, and the relative dynamic elastic modulus determination step are being performed, the freeze-thaw test is terminated if the step number determination step exceeds a predetermined number, or if the relative dynamic elastic modulus becomes equal to or less than a predetermined value in the relative dynamic elastic modulus determination step.

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