Estimation method of physical property value of concrete

Abstract

To provide a method for estimating physical property values of concrete, including a reduction coefficient of Young's modulus, while taking into account the property of the concrete to be measured.SOLUTION: This estimation method includes the steps of placing multiple test specimens obtained by pouring concrete to be measured in an insulated storage container having a temperature history, calculating the change in Young's modulus over time, calculating a constrained strain value based on a first strain value of a strain sensor attached to the unconstrained test specimen and a second strain value of a strain sensor attached to the constrained test specimen constrained by constraint steel, calculating a constrained stress based on the value based on the constraint steel and the second strain value, calculating an apparent Young's modulus at each of the time of heating and cooling based on the correlation between the constrained strain value and the constrained stress, and deriving a reduction coefficient of Young's modulus at each of the time of heating and cooling based on the ratio between the Young's modulus and the apparent Young's modulus.SELECTED DRAWING: Figure 18

Description

Technical Field

[0001] The present invention relates to a method for estimating physical property values of concrete, including a reduction coefficient of Young's modulus of concrete.

Background Art

[0002] Generally, concrete (mass concrete) used in large-scale (large-sized, large cross-section) structures is likely to generate thermal strain due to temperature changes in the part. Thermal strain can cause thermal cracking of mass concrete. Therefore, it is important to evaluate the risk of thermal cracking of mass concrete.

[0003] As an apparatus used for experimentally evaluating the behavior of thermal cracking of concrete, an apparatus called TSTM (Thermal Stress Testing Machine) is known. This apparatus is a uniaxial restraint type test apparatus capable of arbitrarily controlling the temperature condition and the restraint condition of concrete in an adiabatic state. According to the TSTM apparatus, it is possible to perform a restraint test for evaluating the behavior of concrete by changing the temperature condition under restraint and an unrestrained test for evaluating the behavior of concrete by changing the temperature condition in an unrestrained state.

[0004] However, due to circumstances such as the need for water flow control for temperature management, more specifically, control of water temperature and water volume, the scale of the TSTM apparatus becomes large. In addition, in order to maintain the accuracy of test results at a high level, maintenance of the above control mechanism and the like is necessary. Due to such circumstances, the TSTM apparatus is usually installed in a test room having a large space, and it is difficult to evaluate concrete actually used on site.

[0005] Patent Document 1 discloses a test apparatus that is excellent in handleability and can perform a test on the mechanical properties of concrete in a state where an adiabatic state is reproduced.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2019-078614 Summary of the Invention Problems to be Solved by the Invention

[0007] When evaluating the risk of thermal cracking of mass concrete, generally, after obtaining various concrete physical properties, a method of calculating thermal stress by numerical analysis using these data as input values is adopted. In this numerical analysis, various physical property values of concrete are required. Typical examples include physical property values such as compressive strength, tensile strength, Young's modulus, temperature rise, autogenous shrinkage strain, and coefficient of thermal expansion.

[0008] By the way, among the physical properties of concrete, it is difficult to obtain the creep characteristics through experiments or numerical analysis. Therefore, the influence of creep is often evaluated and used by a reduction coefficient of Young's modulus.

[0009] On the other hand, it is not easy to determine the reduction coefficient of Young's modulus for individual concrete. For this reason, currently, it is normal that the reduction coefficient of Young's modulus presented in the "Cracking Control Guidelines for Mass Concrete 2016" of the Japan Concrete Institute (hereinafter simply abbreviated as "Control Guidelines") and the like is applied to all concrete.

[0010] However, in reality, it is expected that the value of the reduction coefficient of Young's modulus will change according to the type and composition of cement used in concrete. Therefore, if the value of the reduction coefficient of Young's modulus defined in the above control guidelines is uniformly adopted and the risk of thermal cracking of mass concrete is evaluated based on this value, it is also possible that the accuracy of the risk evaluation is not sufficiently guaranteed.

[0011] In view of the above problems, an object of the present invention is to provide a method for estimating physical property values of concrete including a reduction coefficient of Young's modulus in consideration of the properties of the concrete to be measured.

Means for Solving the Problems

[0012] The estimation method according to the present invention is a method for estimating physical property values of concrete to be measured, a step (a) of installing a plurality of test specimens obtained by placing the concrete in one or more heat-insulating containers having a temperature history including temperature rise and temperature drop; a step (b) of performing a Young's modulus measurement test on a strength test specimen belonging to the plurality of test specimens every time a predetermined age timing arrives to calculate a time-dependent change pattern of the Young's modulus of the concrete; a step (c) of obtaining a first strain value which is a measured value of a first strain sensor attached to an unconstrained test specimen obtained by placing the concrete in a frame in an unconstrained state among the plurality of test specimens; a step (d) of obtaining a second strain value which is a measured value of a second strain sensor attached to a constrained test specimen obtained by placing the concrete in a frame constrained by a constraint steel material among the plurality of test specimens; a step (e) of calculating a time-dependent change pattern of the constrained strain value of the concrete based on the first strain value and the second strain value; a step (f) of calculating a time-dependent change pattern of the constrained stress of the concrete based on a value based on the constraint steel material of the constrained test specimen and the second strain value; a step (g) of calculating an apparent Young's modulus at the time of temperature rise and temperature drop based on a correlation between the constrained strain value and the constrained stress; and a step (h) of deriving a reduction coefficient of Young's modulus at the time of temperature rise and temperature drop based on a ratio between the Young's modulus obtained in the step (b) and the apparent Young's modulus obtained in the step (g).

[0013] Here, as the concrete to be evaluated, it is possible to use the concrete placed on site, or it is also possible to use the same material concrete as the concrete planned to be placed on site and supplied from a concrete plant.

[0014] For example, every time a predetermined age timing arrives, by taking out the strength test specimen from the storage container and performing a Young's modulus measurement test, the change pattern of the Young's modulus of the concrete over time can be calculated. The Young's modulus measurement test is performed, for example, by a method compliant with JIS A 1149:2017 "Test Method for Static Elastic Modulus of Concrete". As a more specific example, every time the ages of 1 day, 3 days, 7 days, 14 days, and 28 days have elapsed, the strength test specimen is taken out from the storage container and the above test is performed.

[0015] In addition, the same test may be performed on a plurality of strength test specimens of the same age, and a value (for example, an average value) obtained by calculation based on the obtained measured values may be used as the measured value obtained from the test results.

[0016] An unrestrained test specimen is a test specimen obtained by placing concrete in a frame in an unrestrained state with a first strain sensor attached. More specifically, the unrestrained test specimen can be obtained by placing concrete so as to embed the first strain sensor in a state where the first strain sensor is installed inside the frame in an unrestrained state. As the first strain sensor, for example, an embedded strain gauge can be used. In step (c), by acquiring the change over time of the measured value of the first strain sensor, the change over time of the unrestrained strain of the concrete to be measured can be obtained.

[0017] A restrained test specimen is a test specimen obtained by placing concrete in a frame restrained by restraining steel with a second strain sensor attached. More specifically, the restrained test specimen can be obtained by placing concrete so as to embed the restraining steel in a state where the second strain sensor is fixedly attached to the restraining steel.

[0018] As the restraint steel material, a material with an extremely low coefficient of thermal expansion is preferably used, and preferably, the coefficient of thermal expansion is less than 1×10 -6 / °C. As such a restraint steel material, for example, invar steel material (coefficient of thermal expansion is about 0.5×10 -6 / °C) can be used.

[0019] As a detailed example, after machining a part of the threaded portion of the restraint steel material, the second strain sensor is fixedly installed. For example, a strain gauge can be used as the second strain sensor. In step (d), by obtaining the change over time of the measured value of the second strain sensor, the change over time of the strain under the restraint of the concrete to be measured can be obtained.

[0020] The unrestrained test specimen and the restrained test specimen are placed under the same temperature history in a heat-insulating container.

[0021] The measured value of the first strain sensor corresponds to the value of the free strain in which the strain associated with the temperature history and the autogenous shrinkage strain are reflected. On the other hand, the measured value of the second strain sensor installed on the restraint steel material is the steel strain and corresponds to the value of the strain in the restrained state in which the strain associated with the temperature history and the autogenous shrinkage strain are reflected. Therefore, in step (e), based on the measured value of the first strain sensor and the measured value of the second strain sensor, the value of the restrained strain can be obtained. As a specific method for step (e), a method of calculating the difference value between the measured value of the first strain sensor and the measured value of the second strain sensor can be used. By this step (e), the change over time of the restrained strain of the concrete to be measured can be obtained.

[0022] In step (f), by utilizing the force balance between the restraint steel and the concrete and the relationship regarding the strain compatibility condition, the restraint stress generated in the concrete is calculated from the second strain value obtained in step (d), i.e., the strain value in the restrained state. More specifically, the restraint stress generated in the concrete can be calculated by an operation based on the ratio of the restraint steel in the restraint test body (steel ratio), the Young's modulus of the restraint steel, and the strain value in the restrained state. As the Young's modulus of the restraint steel, the physical property value of the steel used as the restraint steel can be utilized. As the steel ratio, for example, the value of the ratio of the area of the end portion of the frame body constituting the restraint test body in the extending direction of the restraint steel to the cross-sectional area of the restraint steel can be utilized.

[0023] In this way, when the time-dependent change pattern of the restrained strain of the concrete to be measured and the time-dependent change pattern of the restraint stress are obtained, in step (g), the apparent Young's modulus at the time of temperature rise and temperature drop is calculated based on the correlation between the two. The restraint stress and the restrained strain exhibit a nearly linear correlation at the time of temperature rise and temperature drop, respectively. Therefore, by linearly approximating each correlation, for example, based on the least squares method, and deriving the slope, the apparent Young's modulus of the concrete to be measured at the time of temperature rise and temperature drop can be obtained. This apparent Young's modulus can be regarded as the Young's modulus considering both the elastic strain and the creep strain under the restraint stress that changes moment by moment.

[0024] As described above, in step (b), for a plurality of strength test specimens with different ages, Young's modulus measurement tests are respectively performed, whereby the temporal change in the actual Young's modulus of the concrete to be measured can be obtained. According to the control guidelines, the influence of creep is considered as a reduction in rigidity due to the effective Young's modulus obtained by multiplying the Young's modulus by a reduction coefficient. From this, in step (h), based on the ratio between the actual Young's modulus obtained by the Young's modulus measurement test and the apparent Young's modulus (for each of the heating and cooling processes), the reduction coefficient of the Young's modulus of the concrete to be measured (for each of the heating and cooling processes) is calculated. The reduction coefficient of the Young's modulus calculated in this way is a value that reflects the specific properties of the concrete to be measured. Therefore, for example, by using this value in numerical analysis, it becomes possible to more accurately evaluate the risk of thermal cracking of mass concrete.

[0025] The step (a) is a step of installing a plurality of the strength test specimens, one or more of the unrestrained test specimens, and one or more of the restrained test specimens in the same housing container. The temperature history may be obtained based on the heat generation from a plurality of the strength test specimens installed in the housing container.

[0026] In this case, the unrestrained test specimens and the restrained test specimens are accommodated together with a plurality of strength test specimens in the same heat-insulating housing container. Since these test specimens generate heat as the age elapses and the hydration reaction progresses, the temperature inside the housing container rises due to this heat generation. Thereafter, when the progress of the hydration reaction reaches a saturated state, the rate of temperature rise inside the housing container is mitigated, and after a further period of time, it eventually drops to a temperature equivalent to the outside air temperature. That is, the unrestrained test specimens and the restrained test specimens are placed under the same temperature history inside the heat-insulating housing container.

[0027] Therefore, according to the above method, it is not necessary to prepare in advance a plurality of housing containers in which the same temperature history is set for each, and the preparation process for estimation is simplified.

[0028] As a specific example, the following evaluation device can be used. That is, the evaluation device includes a strength test section including a plurality of first cylindrical bodies into which the concrete can be placed; an unconfined test section including a bottomed first rectangular frame body into which the concrete can be placed; a confined test section including a bottomed second rectangular frame body into which the concrete can be placed, and both ends in the longitudinal direction of the second rectangular frame body being confined by a restraint steel material with a coefficient of thermal expansion of less than 1×10 -6 / °C; the strength test section, the unconfined test section, and a heat-insulating storage container covering the unconfined test section; and a thermometer capable of measuring temperature changes in the storage container. The unconfined test section has a first strain sensor installed inside the first rectangular frame body. The confined test section is characterized by having a second strain sensor installed on the restraint steel material.

[0029] When using the above evaluation device, a heat-insulating filler may be installed in the storage container so as to fill the gap (the occupied area of the original strength test specimen) generated by removing the strength test specimen from the storage container. As the heat-insulating filler, typically, expanded beads, expanded polystyrene, rock wool, glass wool, urethane foam, etc. can be used.

[0030] In addition, by performing a compressive strength test on the strength test specimen taken out from the storage container, it is also possible to calculate the time-dependent change mode of the compressive strength of the concrete. The compressive strength test is performed, for example, in accordance with the method specified in JIS A 1108:2018 "Method of Test for Compressive Strength of Concrete". The compressive strength test may be performed in parallel with the above Young's modulus measurement test. In addition, using the compressive strength of the concrete and the Young's modulus of the concrete for each age obtained in this way, it is also possible to derive the correlation between the two.

[0031] Furthermore, by performing a splitting tensile strength test on the strength test specimens taken out from the storage container, the time-dependent change pattern of the splitting tensile strength of the concrete may be calculated. The splitting tensile strength test may be performed, for example, in accordance with the method specified in JIS A 1113:2018 "Method of Test for Splitting Tensile Strength of Concrete".

[0032] When performing a compressive strength test and a splitting tensile strength test on strength test specimens of the same age, it is preferable to prepare strength test specimens that are at least twice the number of types of age. For example, every time the age reaches 1 day, 3 days, 7 days, 14 days, and 28 days, two or more strength test specimens are taken out from the storage container, and a compressive strength test and a splitting tensile strength test are performed. The compressive strength test and the Young's modulus measurement test may be performed in parallel on the same strength test specimen.

[0033] In addition, when all of the strength test specimens, the unconstrained test specimens, and the constrained test specimens are stored in the same storage container, while the strength test specimens are taken out from the storage container every time the age timing arrives, the unconstrained test specimens and the constrained test specimens are placed in the storage container for a long period (for example, a number of days of 25 days or more). From such a viewpoint, in order to easily take out the strength test specimens, the storage container is made of a heat insulating material and has a removable lid, and it is preferable to place the strength test specimens above (closer to the lid) the unconstrained test specimens and the constrained test specimens in the storage container.

[0034] As a more detailed example, The storage container has a bottom portion installed at a position facing the lid portion, and side portions covering the bottom portion from four sides. The unconstrained test portion and the constrained test portion are arranged in a direction along the bottom portion. The plurality of the first cylindrical bodies included in the strength test portion may be arranged in a direction along the bottom portion in a state of being placed directly above the first rectangular frame body included in the unconstrained test portion and the second rectangular frame body included in the constrained test portion.

[0035] In addition, the above evaluation device is equipped with a thermometer capable of measuring temperature changes inside the storage container. Therefore, by obtaining the change history of the measured values of the thermometer, the effective age can be calculated. That is, the relationship between the age of the material when the strength test specimen is taken out from the storage container and the effective age can be obtained.

[0036] Using the information regarding the correlation between the age of the material when the strength test specimen is taken out from the storage container and the effective age obtained in this way, it is also possible to obtain various correlation information. For example, the correlation between the time-dependent change pattern of the compressive strength of concrete and the effective age of concrete can be obtained by performing a compressive strength test on the strength test specimens taken out at each age of the material. Also, for example, the correlation between the time-dependent change pattern of the splitting tensile strength of concrete and the effective age of concrete can be obtained by performing a splitting tensile strength test on the strength test specimens taken out at each age of the material.

[0037] After 25 days or more have passed since it was installed in the storage container, the unrestrained test specimen is taken out from the storage container, and the measured value of the first strain sensor is read while applying a temperature change (for example, from the outside air temperature to about 60°C) in a heat-insulated environment. It may also be considered to obtain the relationship between the temperature and the measured value of the first strain sensor.

[0038] It is considered that no additional autogenous shrinkage strain due to the hydration reaction occurs in the unrestrained test specimen after 25 days or more have passed, even if a temperature change is applied thereafter. That is, by causing a temperature change in the unrestrained test specimen after 25 days or more have passed and obtaining the correlation between the temperature and the measured value of the first strain sensor, information regarding the temperature strain of concrete can be obtained. Specifically, the coefficient of thermal expansion of concrete can be obtained from the relationship between the temperature and the measured value of the first strain sensor. Typically, since the temperature and the measured value of the first strain sensor exhibit a substantially linear correlation, for example, the coefficient of thermal expansion of concrete can be obtained by linearly approximating the correlation between the temperature and the measured value of the first strain sensor based on the least squares method and deriving its slope.

[0039] On the other hand, the measured value of the first strain sensor provided on the unrestrained test specimen installed in the storage container is a value that reflects the thermal strain and the autogenous shrinkage strain based on the temperature history in the storage container. By multiplying the value of the temperature change in the state where the unrestrained test specimen is installed in the storage container by the coefficient of thermal expansion of the concrete calculated by the above method, the value of the thermal strain generated in the unrestrained test specimen installed in the storage container can be derived. Therefore, by subtracting the value of the thermal strain from the measured value of the first strain sensor provided on the unrestrained test specimen installed in the storage container, the time-dependent change pattern of the autogenous shrinkage strain of the unrestrained test specimen can be obtained. This autogenous shrinkage strain is the autogenous shrinkage strain of the concrete to be measured.

[0040] Therefore, based on the information regarding the correlation between the age and the effective age obtained by the method described above, the correlation between the effective age and the autogenous shrinkage strain of the concrete to be measured can be obtained. The information regarding the correlation between the effective age and the autogenous shrinkage strain of the concrete can be used when evaluating the temperature cracking risk by 3D-FEM analysis in the case of constructing an actual structure using the concrete.

[0041] In the above evaluation device, the installation position of the thermometer is irrelevant as long as the temperature in the storage container is measured. However, from the viewpoint of accurately measuring the temperature of the concrete, it is preferable that the thermometer is attached to at least one of the strength test section, the unrestrained test section, and the restrained test section. However, as described above, since the strength test specimens are taken out for each age, when installing a thermometer in the strength test section, it is preferable to install it in the strength test specimen with the latest timing of being taken out from the storage container.

[0042] Note that the restrained test specimen contains concrete and restrained steel, and the restrained steel has different specific heat, thermal conductivity, and heat capacity compared to the concrete. On the other hand, the unrestrained test specimen does not contain restrained steel. Therefore, from the viewpoint of accurately measuring the temperature of the concrete, it is more preferable to install the thermometer on the unrestrained test specimen rather than on the restrained test specimen.

[0043] Furthermore, as described above, when obtaining the autogenous shrinkage strain of the unrestrained specimen, it is calculated from the value of the thermal strain that occurred in the unrestrained specimen. Therefore, when a thermostatic bath capable of applying a predetermined temperature history from the outside is not used as the storage container, it is more preferable that a thermometer is installed in the unrestrained specimen from the viewpoint of improving the accuracy of the measured temperature. Furthermore, as described above, from the viewpoint of measuring the adiabatic test for the unrestrained specimen taken out from the storage container in order to measure the coefficient of thermal expansion, it is more preferable that a thermometer is attached at least to the unrestrained test section.

[0044] As described above, when the strength specimen, the restrained specimen, and the unrestrained specimen are installed in the same storage container, a temperature history due to the heat generation caused by the hydration reaction of each specimen is given to these specimens. For example, when a thermometer is installed in the restrained specimen or the unrestrained specimen, the mode of temperature change for each age can be obtained. Therefore, by performing inverse analysis of the relationship between the age and the measured value of the thermometer attached to the restrained specimen or the unrestrained specimen, the adiabatic temperature rise characteristics of the concrete to be measured can be obtained. Information regarding the adiabatic temperature rise characteristics of the concrete can also be used when evaluating the temperature cracking risk in the actual structure constructed using the concrete by 3D-FEM analysis.

Effects of the Invention

[0045] According to the present invention, it is possible to derive an estimated value of the reduction coefficient of the Young's modulus specific to the concrete to be measured. Furthermore, using the reduction coefficient of the Young's modulus, it is possible to accurately evaluate the risk of temperature cracking of a structure (mass concrete) using the concrete.

Brief Description of the Drawings

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[0047] The estimation method according to the present invention relates to an estimation method of physical properties of concrete including a reduction coefficient of Young's modulus of the concrete to be measured.

[0048] [First Embodiment] The first embodiment of the estimation method according to the present invention will be described with reference to the drawings as appropriate. However, the following drawings are schematically shown, and the dimensional ratios on the drawings do not match the actual dimensional ratios. Also, the dimensional ratios do not necessarily match between the drawings.

[0049] This embodiment corresponds to an embodiment in which a reduction coefficient of Young's modulus of concrete is estimated while using a predetermined evaluation device for evaluating the characteristics of the concrete to be measured. Specifically, it is used in a state where a plurality of test specimens in which the concrete to be measured is driven into a predetermined region are accommodated inside.

[0050] <Configuration of the Evaluation Device> FIG. 1 is a perspective view schematically showing the external appearance of the evaluation apparatus used in the present embodiment. The evaluation apparatus 1 includes a lid portion 2 and a storage container 3. Both the lid portion 2 and the storage container 3 are made of a heat insulating material, for example, formed of styrofoam. The lid portion 2 is removable from the storage container 3.

[0051] In the following description, the X - Y - Z coordinate system shown in FIG. 1 is referred to. Further, in the following description, when distinguishing positive and negative directions when expressing a direction, it is described with positive and negative signs, such as “+Z direction” and “−Z direction”. When expressing a direction without distinguishing positive and negative directions, it is simply described as “Z direction”. That is, in this specification, when simply described as “Z direction”, both “+Z direction” and “−Z direction” are included. Typically, the +Z direction is the vertically upward direction.

[0052] FIG. 2 is a schematic cross - sectional view when the evaluation apparatus 1 shown in FIG. 1 is cut along the X - Z plane at a position of a predetermined Y coordinate. FIG. 3 is a schematic plan view when the lid portion 2 is removed from the evaluation apparatus 1 shown in FIG. 1 and the evaluation apparatus 1 is viewed from the +Z side in the -Z direction.

[0053] As shown in FIGS. 2 to 3, the storage container 3 has a bottom portion 3b installed at a position facing the lid portion 2 in the Z direction, and side portions 3a covering the upper part of the bottom portion 3b from four directions. Inside the region surrounded by the side portions 3a and the bottom portion 3b, each test body (10, 20, 30) is installed.

[0054] The evaluation apparatus 1 is used with the strength test body 10, the unconstrained test body 20, and the constrained test body 30 installed in the storage container 3. As shown in FIGS. 2 to 3, in the evaluation apparatus 1 of the present embodiment, a plurality of strength test bodies 10 are installed closer to the lid portion 2 than the unconstrained test body 20 and the constrained test body 30. FIG. 3 shows an example in which 30 strength test bodies 10 are installed in the evaluation apparatus 1.

[0055] FIG. 4 is a schematic plan view when a plurality of strength test specimens 10 are removed from the state of FIG. 2 and the evaluation apparatus 1 is viewed from the +Z side in the -Z direction. As shown in FIGS. 2 and 4, in the evaluation apparatus 1 of the present embodiment, the unconstrained test specimens 20 and the constrained test specimens 30 are located on the bottom 3b side and arranged along the plane (X-Y plane) of the bottom 3b. FIG. 4 illustrates an example in which two unconstrained test specimens 20 and two constrained test specimens 30 are installed in the evaluation apparatus 1.

[0056] FIG. 5 is a perspective view schematically showing the configuration of the strength test specimen 10. The strength test specimen 10 has, for example, a cylindrical tubular body 11 made of tinplate or plastic, and concrete to be measured is driven into the internal space 12 of the tubular body 11 to form it. The dimensions of the tubular body 11 are arbitrary. As an example, the diameter is 10 cm and the height is 20 cm. FIG. 3 shows a state in which 30 strength test specimens 10 in which concrete of the same material to be measured is driven into the internal space 12 of the tubular body 11 of the same dimensions are installed in the storage container 3. The tubular body 11 corresponds to the "first tubular body".

[0057] As shown in FIGS. 2 to 3, between the plurality of strength test specimens 10, for the purpose of ensuring the heat insulation of the internal space 12 of the tubular body 11, a heat-insulating filler 6 made of foamed beads, expanded polystyrene molded into the shape of the internal space 12, spray-type urethane foam, rock wool, glass wool, etc. is filled.

[0058] FIG. 6 is a plan view schematically showing the configuration of the unconstrained test specimen 20. The unconstrained test specimen 20 has a bottomed rectangular frame body 21 made of wood or plywood, etc., and a first strain sensor 25 is installed in the internal space 23 of the frame body 21. Then, the unconstrained test specimen 20 is formed by driving the concrete to be measured into the internal space 23 of the frame body 21 so as to embed the first strain sensor 25. As the first strain sensor 25, for example, an embedded strain gauge can be used. The frame body 21 corresponds to the "first rectangular frame body".

[0059] The dimensions of the frame body 21 are arbitrary. As an example, it has a rectangular parallelepiped shape of 10 cm × 10 cm × 80 cm.

[0060] From the viewpoint of suppressing the deformation of the concrete by the frame body 21, a buffer board made of polystyrene or the like may be attached to the side surface in the longitudinal direction of the frame body 21, and a buffer film made of polyester or the like may be attached to the side surface and the bottom surface in the short side direction.

[0061] In the example of FIG. 6, a signal line 27 is attached to the first strain sensor 25, and the measured value of the first strain sensor 25 is configured to be continuously or intermittently readable. However, as long as the measured value of the first strain sensor 25 can be continuously or intermittently read, it is not limited to a wired connection and may be a wireless connection.

[0062] The first strain sensor 25 is preferably composed of an embedded strain gauge equipped with a temperature measurement function. When the first strain sensor 25 does not have a temperature measurement function, a thermocouple (not shown) may be mounted on the frame body 21 so that the temperature of the unconstrained test specimen 20 can be measured.

[0063] FIG. 7 is a plan view schematically showing the configuration of the constrained test specimen 30. The constrained test specimen 30 is formed into a bottomed rectangular frame body by a pair of side plates 31 arranged to face each other in the short side direction, a pair of end plates 32 arranged to face each other in the longitudinal direction, and a bottom plate (not shown). This frame body corresponds to the "second rectangular frame body".

[0064] The pair of end plates 32 are fixedly connected by the constraint steel material 34. The end plate 32 and the constraint steel material 34 are fixed by welding, for example. The side plates 31 and the bottom plate are made of wood or plywood, for example. Also, the end plates 32 and the constraint steel material 34 are made of a steel material with an extremely low coefficient of thermal expansion of less than 1×10 -6 / °C. As a specific example, the end plates 32 and the constraint steel material 34 are made of invar steel, tungsten, etc., and preferably made of invar steel.

[0065] In the restraint test specimen 30, the steel ratio of the restraint steel 34 is preferably 0.5% to 6%. Here, the steel ratio of the restraint steel 34 can be the value of the ratio of the cross-sectional area of the restraint steel 34 to the area of the end plate 32.

[0066] A second strain sensor 35 is installed on the restraint steel 34. As the second strain sensor 35, for example, a strain gauge can be used. Also, in the example of FIG. 7, a thermometer 36 composed of a thermocouple is attached to the restraint steel 34. However, whether the restraint test specimen 30 has the thermometer 36 or not is arbitrary.

[0067] The outer dimensions of the bottomed frame body formed by the side plates 31, the end plates 32, and the bottom plate are arbitrary. For example, it has a rectangular parallelepiped shape of 10 cm × 10 cm × 80 cm. The restraint test specimen 30 is formed by driving the concrete to be measured into the internal space 33 of this bottomed frame body so as to embed the restraint steel 34.

[0068] A buffer film made of polyester or the like may be attached to the side plates 31 and the bottom plate. The end plate 32 is provided for the purpose of receiving the expansion force by the end plate 32 and accurately measuring the expansion stress when the concrete expands due to heat generation at the initial stage after the concrete is driven in.

[0069] In the example of FIG. 7, a signal line 37 is attached to the second strain sensor 35, and the measured value of the second strain sensor 35 is configured to be continuously or intermittently readable. However, as long as the measured value of the second strain sensor 35 can be continuously or intermittently read, it is not limited to a wired connection and may be a wireless connection. Note that the temperature information measured by the thermometer 36 may also be configured to be continuously or intermittently readable in the same manner as the measured value of the second strain sensor 35.

[0070] As described above, in the state before the concrete is placed, inside the storage container 3 that constitutes the heat-insulating storage container, a plurality of cylindrical bodies 11, a frame body 21 in which the first strain sensor 25 is installed in the internal space 23, and a frame body (31, 32) in which a restraint steel material 34 to which the second strain sensor 35 is attached is fixed in the internal space 33 are arranged.

[0071] The cylindrical body 11 constitutes a strength test section, and by placing the concrete to be evaluated in the internal space 12 of the cylindrical body 11, a strength test specimen 10 is formed. The frame body 21 and the first strain sensor 25 constitute an unconstrained test section, and by placing the concrete to be evaluated in the internal space 23 of the frame body 21, an unconstrained test specimen 20 is formed. The frame body (31, 32), the restraint steel material 34, and the second strain sensor 35 constitute a constrained test section, and by placing the concrete to be evaluated in the internal space 33 of the frame body (31, 32), a constrained test specimen 30 is formed.

[0072] In FIG. 4, in the X-Y plane direction, by arranging the unconstrained test specimen 20 and the constrained test specimen 30, it is shown that the internal space surrounded by the side surface of the storage container 3 is almost blocked. The outer dimensions of the storage container 3 may be appropriately set according to the outer dimensions of the frame body 21 constituting the unconstrained test specimen 20 and the outer dimensions of the frame body (31, 32) constituting the constrained test specimen 30. However, when the unconstrained test specimen 20 and the constrained test specimen 30 are arranged without gaps in the X-Y plane direction and a gap is generated between the side portion 3a of the storage container 3 and each test specimen (20, 30), the gap may be filled with a heat-insulating filler 6.

[0073] [Method of Using the Evaluation Device] When using the evaluation device 1, each test specimen (strength test specimen 10, unconstrained test specimen 20, constrained test specimen 30) formed by placing the concrete to be evaluated in each test section is installed in the inner space of the storage container 3 of the evaluation device 1. Then, the lid portion 2 is arranged to cover the upper part of the storage container 3.

[0074] More specifically, the unrestrained test specimen 20 and the restrained test specimen 30 are placed on the surface of the bottom 3b. Then, a plurality of strength test specimens 10 are arranged along the X-Y plane direction on the upper surfaces of these test specimens (20, 30). A buffer film made of, for example, polyester or the like may be attached to the open surface on the +Z side of the unrestrained test specimen 20 and the restrained test specimen 30.

[0075] After each test specimen (10, 20, 30) is placed in the evaluation device 1, the strength test specimen 10 is taken out every time a predetermined age timing arrives. After the strength test specimen 10 is taken out, it is preferable to place the heat-insulating filler 6 in the storage container 3 so as to fill the gap generated by taking out the strength test specimen 10.

[0076] For example, the strength test specimen 10 is taken out of the storage container every time the ages of 1 day, 3 days, 7 days, 14 days, and 28 days have passed. By performing a Young's modulus measurement test using the strength test specimens 10 of each taken-out age, the relationship between the Young's modulus and the age of the concrete to be measured can be obtained (see, for example, FIG. 8). The Young's modulus measurement test can be performed by a method conforming to, for example, JIS A 1149:2017 "Test Method for Static Elastic Modulus of Concrete".

[0077] As described above, at least one of the unrestrained test specimen 20 and the restrained test specimen 30 placed in the storage container 3 is equipped with a temperature measurement function (thermometer). Since the internal space of the storage container 3 is covered with a heat-insulating member, for example, the temperature history read from the first strain sensor 25, which is an embedded strain gauge equipped with a temperature measurement function and mounted on the unrestrained test specimen 20, can be regarded as the temperature history inside the storage container 3. Also, for example, the temperature history read from the thermometer 36 mounted on the restrained test specimen 30 can be regarded as the temperature history inside the storage container 3. As another example, a separate thermometer may be mounted inside the storage container 3. In this case, the temperature history read from the thermometer can be regarded as the temperature history inside the storage container 3.

[0078] That is, according to the evaluation device 1, information regarding the temperature history in the storage container 3 can be obtained. Based on this information regarding the temperature history, the relationship between the installation period (actual age) of the test specimen installed in the storage container 3 and the effective age can be obtained. As an example, based on the Arrhenius law of the following formula (1) defined in the cracking control guidelines for mass concrete, the effective age t e is calculated.

[0079]

Equation

[0080] Note that in formula (1), △t i represents the period (days) during which the temperature of a predetermined concrete continues, and T(△t i ) represents the temperature (°C) of the concrete that continues over △t i .

[0081] As an example, concrete containing the materials shown in Table 1 below in the proportions shown in Table 2 was placed in each test section as the concrete to be evaluated to produce test specimens (10, 20, 30), which were then installed in the evaluation device 1.

[0082]

Table 1

[0083]

Table 2

[0084] Using the concrete of Example 1, each test specimen was installed in the evaluation device 1, and based on the temperature history measured by the thermometer, the relationship between the age (installation period) and the effective age in the evaluation device 1 was obtained. Then, for the strength test specimen 10 taken out from the storage container 3 every time a predetermined age arrived, a Young's modulus measurement test was performed to obtain the correlation between the measured Young's modulus and the effective age. Fig. 9 shows the correlation between the Young's modulus and the effective age.

[0085] The Young's modulus measurement test and the compressive strength test can be carried out in parallel. Therefore, for the strength test specimens 10 taken out for each age of the material, by performing the compressive strength test, the relationship between the compressive strength and the age of the concrete to be measured can be obtained. The compressive strength test is carried out, for example, in accordance with the method specified in JIS A 1108:2018 "Method for Compressive Strength Test of Concrete". Furthermore, since the relationship between the age of the material and the effective age can be obtained as described above, the relationship between the compressive strength and the effective age can be obtained. Fig. 10 is a graph showing the correlation between the compressive strength and the effective age measured using the concrete of Example 1. Also, based on the results shown in Figs. 9 and 10, the correlation between the Young's modulus and the compressive strength may be derived. Fig. 11 is a graph showing the correlation between the compressive strength and the Young's modulus measured using the concrete of Example 1.

[0086] The strength test specimens 10 may be taken out from the storage container 3 at the same age as the age at which the compressive strength test is carried out, and the splitting tensile strength test may be carried out using the strength test specimens 10 of each age. In this case, from the viewpoint of performing the splitting tensile strength test and the Young's modulus measurement test (and the compressive strength test) on the strength test specimens 10 of the same age, it is preferable to install in the evaluation device 1 a number of strength test specimens 10 that is at least twice the number of types of ages for which the test is carried out.

[0087] The splitting tensile strength test is carried out, for example, in accordance with the method specified in JIS A 1113:2018 "Method for Splitting Tensile Strength Test of Concrete". As described above, since the relationship between the age of the material and the effective age can be obtained, the relationship between the splitting tensile strength and the effective age can be obtained.

[0088] Therefore, by comparing the compressive strength and the splitting tensile strength at the same effective age, the relationship between the compressive strength and the splitting tensile strength can also be obtained. Fig. 12 shows the correlation between the compressive strength and the splitting tensile strength measured using the concrete of Example 1.

[0089] The storage container 3 is held in a heat-insulated state, and a plurality of test specimens (10, 20, 30) are arranged inside. Since these test specimens (10, 20, 30) generate heat as the age progresses and the hydration reaction proceeds, the temperature inside the storage container 3 rises due to this heat generation. Then, when the progress of the hydration reaction reaches a saturated state, the rate of temperature rise inside the storage container 3 is alleviated, and after a further period elapses, it drops to the same temperature as the outside air temperature. That is, the unconstrained test specimen 20 and the constrained test specimen 30 are placed under the same temperature history inside the heat-insulating storage container 3.

[0090] The change over time of the strain value read from the first strain sensor 25 mounted on the unconstrained test specimen 20 corresponds to the change over time of the unconstrained strain of the concrete to be measured under the state placed under the above temperature history. The change over time of the strain value read from the second strain sensor 35 mounted on the constrained test specimen 30 corresponds to the change over time of the strain under restraint of the concrete to be measured placed under the above temperature history. FIG. 13 is a graph schematically showing the change modes of the measured values of the first strain sensor 25 and the change modes of the measured values of the second strain sensor 35. Further, FIG. 14 is a graph showing the change modes of the measured value S1 of the first strain sensor 25 mounted on the unconstrained test specimen 20 using the concrete of Example 1 and the change modes of the measured value S2 of the second strain sensor 35 mounted on the constrained test specimen 30 using the concrete of Example 1.

[0091] The measured value S1 of the first strain sensor 25 corresponds to the value of the free strain in which the strain associated with the above temperature history and the autogenous shrinkage strain are reflected. On the other hand, the measured value S2 of the second strain sensor 35 corresponds to the value of the strain in the constrained state in which the strain associated with the temperature history and the autogenous shrinkage strain are reflected. Therefore, by calculating the difference value S3 between the measured value S1 of the first strain sensor 25 and the measured value S2 of the second strain sensor 35, the change over time of the constrained strain ε s of the concrete to be measured can be obtained.

[0092] Moreover, the restraint stress can be obtained from the force balance relationship between the restraint steel 34 and the concrete placed in the restraint specimen 30. For example, the restraint stress F can be calculated by the following equation (2). In equation (2), E s corresponds to the Young's modulus of the restraint steel 34, p corresponds to the steel ratio of the restraint steel 34 in the restraint specimen 30, and s2 corresponds to the measured value of the second strain sensor 35 mounted on the restraint specimen 30. In equation (2), tensile stress is represented as a positive value and compressive stress as a negative value. F = -E s ·p·s2…(2)

[0093] For example, by performing the calculation of the above equation (2), the time-dependent change pattern of the restraint stress F in the concrete placed in the restraint specimen 30 can be obtained. Fig. 15 is a graph schematically showing the change pattern of the restraint stress F.

[0094] A correlation is recognized between the change pattern of the restraint stress F obtained in this way and the change pattern of the restraint strain ε s Fig. 16 is a graph schematically showing the correlation between the restraint stress and the restraint strain.

[0095] As schematically shown in Fig. 16, the restraint stress and the restraint strain show a nearly linear correlation at the time of temperature rise (curve Eca1) and temperature drop (curve Eca2), respectively. Therefore, by linearly approximating each correlation based on, for example, the least squares method and deriving its slope, the apparent Young's modulus of the concrete to be measured at the time of temperature rise and temperature drop can be obtained. This apparent Young's modulus can be regarded as a Young's modulus considering both the elastic strain and the creep strain due to the time-varying restraint stress.

[0096] Fig. 17 is a graph showing the correlation between the restraint stress and the restraint strain calculated based on the results shown in Fig. 14. In the case of the results in Fig. 17, the apparent Young's modulus of the concrete to be measured at the time of temperature rise is 4.8 kN / mm 2, the apparent Young's modulus of the concrete to be measured during cooling is 29.4 kN / mm 2 and are respectively obtained.

[0097] On the other hand, as described above with reference to FIG. 9, by performing a Young's modulus measurement test on the strength test specimens 10 taken out from the evaluation device 1 for each age, the change over time of the Young's modulus of the concrete to be measured can be obtained. Based on the ratio between this measured Young's modulus and the apparent Young's modulus derived by calculation using the above method, the reduction coefficient of the Young's modulus of the concrete to be measured can be determined. FIG. 18 is a graph showing the relationship between the reduction coefficient of the Young's modulus calculated by the above calculation and the effective age. In practice, the average value of the reduction coefficient of the Young's modulus during the temperature rise period can be used as the reduction coefficient of the Young's modulus of the concrete to be measured during temperature rise. Similarly, the average value of the reduction coefficient of the Young's modulus during the temperature drop period can be used as the reduction coefficient of the Young's modulus of the concrete to be measured during temperature drop. In the example of FIG. 18, the reduction coefficient of the Young's modulus of the concrete to be measured can be determined to be 0.28 during temperature rise and 1.00 during temperature drop, respectively.

[0098] Also, after a period during which it is considered that the hydration reaction has sufficiently progressed, the unconstrained test specimen 20 may be taken out from the storage container 3 and a separate heat insulation test may be performed. As the timing for taking out the unconstrained test specimen 20 from the storage container 3, it is the timing when the temperature of the storage container 3 has dropped until the indicated value of the thermometer installed in the storage container 3 and the temperature of the atmosphere where the storage container 3 is installed are approximately the same. For example, it can be the timing when 25 days or more have passed.

[0099] The unconstrained test specimen 20 is installed, for example, in a thermostatic bath programmed to generate a temperature history set within the range of 20°C to 60°C, and the correlation between the measured value of the first strain sensor 25 attached to the unconstrained test specimen 20 and the temperature is obtained.

[0100] An example of the temperature history is as follows. 20°C (held for 3 hours) → temperature increase at 5°C / hour → 30°C (held for 3 hours) → temperature increase at 5°C / hour → 40°C (held for 3 hours) → temperature increase at 4°C / hour → 50°C (held for 3 hours) → temperature increase at 5°C / hour → 60°C (held for 3 hours) → temperature decrease at 5°C / hour → 50°C (held for 3 hours) → temperature decrease at 5°C / hour → 40°C (held for 3 hours) → temperature decrease at 5°C / hour → 30°C (held for 3 hours) → temperature decrease at 5°C / hour → 20°C (held for 3 hours)

[0101] The above temperature increase and decrease are regarded as one cycle. For example, a temperature change of 2 cycles is applied to the unrestrained specimen 20. Then, under the above temperature history, at each time period when the temperature is held (for example, 20°C, 30°C, 40°C, 50°C, 60°C), the measured value of the first strain sensor 25 is read when the indicated value of the thermometer mounted on the unrestrained specimen 20 becomes stable.

[0102] FIG. 19 is a graph showing the relationship between the measured value of the first strain sensor 25 and the temperature when the above-described heat insulation test was performed on the unrestrained specimen 20 using the concrete of Example 1.

[0103] As described above, this heat insulation test was performed on the unrestrained specimen 20 after a period in which the hydration reaction was considered to have sufficiently progressed. Therefore, even if a temperature change is applied to the unrestrained specimen 20 in the heat insulation test, it is considered that no additional autogenous shrinkage strain due to the hydration reaction occurs in the concrete placed in the unrestrained specimen 20. Thus, it can be said that the correlation between the measured value of the first strain sensor 25 and the temperature shown in FIG. 19 is information reflecting the temperature strain of the concrete placed in the unrestrained specimen 20. As shown in FIG. 19, since the temperature and the measured value of the first strain sensor 25 show a substantially linear correlation, for example, by linearly approximating the two based on the least squares method and deriving the slope, the coefficient of thermal expansion of the concrete placed in the unrestrained specimen 20, that is, the concrete to be measured, can be obtained.

[0104] The measured value S1 of the first strain sensor 25 of the unrestrained test specimen 20, measured in the state of being installed in the storage container 3 (see FIGS. 13 to 14), is a value reflecting the thermal strain and the autogenous shrinkage strain based on the temperature history in the storage container 3. As described above at the location where the effective age is derived, according to the evaluation device 1, information regarding the temperature history in the storage container 3 can be obtained. Therefore, by multiplying the temperature change value due to the temperature history by the coefficient of thermal expansion of the concrete to be measured, the value of the thermal strain of the concrete to be measured based on the temperature history in the storage container 3 can be obtained. By subtracting this value of the thermal strain from the measured value S1 of the first strain sensor 25 of the unrestrained test specimen 20, measured in the state of being installed in the storage container 3, the time-dependent change pattern of the autogenous shrinkage strain of the unrestrained test specimen 20, that is, the time-dependent change pattern of the autogenous shrinkage strain of the concrete to be measured can be obtained.

[0105] And, as described above, based on the temperature change in the storage container 3, the correlation between the age and the effective age of the material in the storage container 3 has been obtained. Therefore, the correlation between the autogenous shrinkage strain of the concrete to be measured and the effective age of the concrete can be obtained. FIG. 20 is a graph showing the correlation between the autogenous shrinkage strain and the effective age of the concrete of Example 1, derived based on the results shown in FIGS. 14 and 19. The information regarding the correlation between the effective age and the autogenous shrinkage strain of the concrete obtained by the above method can be used when evaluating the temperature cracking risk in the case of constructing an actual structure using the concrete by 3D-FEM analysis.

[0106] Furthermore, as described above, since the temperature change in the storage container 3 has been obtained, for example, as schematically shown in FIG. 21, the relationship Ta between the age of the concrete to be measured and the amount of temperature rise can be obtained. Therefore, by inversely analyzing this relationship Ta, the adiabatic temperature rise characteristic Tb of the concrete to be measured, as schematically shown in FIG. 22, can be obtained.

[0107] As described above, according to the evaluation device 1, various physical property values can be obtained, including the reduction coefficient of the Young's modulus of the concrete to be measured. By performing numerical analysis using many physical property values obtained in this way, it is possible to accurately evaluate the risk of thermal cracking of a structure (mass concrete) using the concrete to be measured.

[0108] Hereinafter, a modification example of the present embodiment will be described.

[0109] 〈1〉 In the present embodiment, every time a predetermined age timing arrives, the lid portion 2 is opened and the strength test specimen 10 is taken out upward. However, the direction of taking out the strength test specimen 10 is not limited to upward. For example, the position of the lid portion 2 may be set to the side, and the strength test specimen 10 may be taken out from the side.

[0110] 〈2〉 In the storage container 3, a number of strength test specimens 10 that is larger than the number of specimens to be taken out for each age and subjected to the above tests may be installed. The extra strength test specimens 10 installed are used for the purpose of causing a hydration reaction in the storage container 3 and raising the temperature in the storage container 3.

[0111] 〈3〉 When a plurality of restraint test specimens 30 are installed in the storage container 3, the average value of the restraint stress for each restraint test specimen 30, which is derived based on the measured values of the second strain sensors 35 mounted on each restraint test specimen 30, may be used as the restraint stress F.

[0112] Furthermore, in the above, the steel ratios of the restraint steel materials 34 mounted on the respective restraint test specimens 30 may be made different from each other. In this case, when calculating the restraint stress F, it is derived based on the measured values of the second strain sensors 35 mounted on the respective restraint test specimens 30 and the steel ratios of the restraint steel materials 34 mounted on the corresponding restraint test specimens 30. And the average value of the restraint stress for each restraint test specimen 30 derived in this way may be used as the restraint stress F.

[0113] 〈4〉The number of the unrestrained test specimens 20 installed in the storage container 3 may be one. Similarly, the number of the restrained test specimens 30 installed in the storage container 3 may be one.

[0114] 〈5〉The installation methods of the strength test specimens 10, the unrestrained test specimens 20, and the restrained test specimens 30 in the storage container 3 described above in this embodiment are merely examples, and the present invention is not limited to the illustrated arrangement modes. For example, the strength test specimens 10, the unrestrained test specimens 20, and the restrained test specimens 30 may all be arranged along the surface of the bottom 3b. Further, for example, the unrestrained test specimens 20 and the restrained test specimens 30 may be arranged along the vertical direction.

[0115] [Second Embodiment] In the above first embodiment, the case where each physical property value is measured with the strength test specimens 10, the unrestrained test specimens 20, and the restrained test specimens 30 installed in the same storage container 3 was described. This is intended to realize the same temperature history by the temperature rise due to the heat generation accompanying the hydration reaction generated from these test specimens and the temperature drop due to the convergence of the progress of the hydration reaction by accommodating a plurality of test specimens including the strength test specimens 10, the unrestrained test specimens 20, and the restrained test specimens 30 in the storage container 3 having the same heat insulation property.

[0116] In other words, as long as each test specimen (strength test specimen 10, unrestrained test specimen 20, and restrained test specimen 30) can be installed under the same temperature history in the heat-insulated storage container, it is not necessarily required to install these test specimens in the same storage container 3. For example, with each test specimen accommodated in a thermostatic bath programmed to generate a predetermined temperature history, the reduction coefficient of the Young's modulus of concrete may be derived by a method according to the first embodiment. Further, in this case, with respect to the physical property values of concrete other than the reduction coefficient of the Young's modulus, they may be derived according to the method described above in the first embodiment.

[0117] [Alternative Embodiment] Hereinafter, alternative embodiments will be described.

[0118] 〈1〉In each of the above embodiments, the case of deriving physical property values of concrete other than the reduction coefficient of the Young's modulus of concrete has also been described. However, for the reduction coefficient of the Young's modulus of concrete and physical property values other than the physical property values necessary for deriving this reduction coefficient, derivation is not necessarily required.

[0119] 〈2〉The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for better understanding of the present invention, and are not necessarily limited to those having all the configurations described. The scope of the present invention is indicated by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0120] 1: Evaluation device 2: Lid portion 3: Storage container 3a: Side portion of the storage container 3b: Bottom portion of the storage container 6: Filling material 10: Strength test specimen 11: Cylindrical body 12: Internal space 20: Unrestrained test specimen 21: Frame body 23: Internal space 25: First strain sensor 27: Signal line 30: Restrained test specimen 31: Side plate 32: End plate 33: Internal space 34: Restraining steel material 35: Second strain sensor 36: Thermometer 37: Signal line

Claims

1. A method for estimating physical property values of concrete to be measured, comprising: Step (a) of installing a plurality of test specimens obtained by placing the concrete in one or more heat-insulating containers having a temperature history including a temperature rise and a temperature drop; Step (b) of, every time a predetermined age timing arrives, performing a Young's modulus measurement test on a strength test specimen belonging to the plurality of test specimens to calculate a change pattern over time of the Young's modulus of the concrete; Step (c) of obtaining a first strain value, which is a measured value of a first strain sensor attached to an unconstrained test specimen obtained by placing the concrete in a frame in an unconstrained state, among the plurality of test specimens; Step (d) of obtaining a second strain value, which is a measured value of a second strain sensor attached to a constrained test specimen obtained by placing the concrete in a frame constrained by a constraint steel material, among the plurality of test specimens; Step (e) of calculating a change pattern over time of the constrained strain value of the concrete based on the first strain value and the second strain value; Step (f) of calculating a change pattern over time of the constrained stress of the concrete based on a value based on the constraint steel material of the constrained test specimen and the second strain value; Step (g) of calculating an apparent Young's modulus at the time of temperature rise and temperature drop respectively based on a correlation between the constrained strain value and the constrained stress; Step (h) of deriving a reduction coefficient of the Young's modulus at the time of temperature rise and temperature drop respectively based on a ratio between the Young's modulus obtained in step (b) and the apparent Young's modulus obtained in step (g). A method for estimating physical property values of concrete, characterized by comprising the above steps.

2. Step (a) is a step of installing a plurality of the strength test specimens, one or more of the unconstrained test specimens, and one or more of the constrained test specimens in the same container; The method for estimating physical properties of concrete according to claim 1, wherein the temperature history is obtained based on heat generation from a plurality of the strength test specimens installed in the storage container.

3. The method for estimating physical properties of concrete according to claim 1 or 2, wherein the step (a) includes a step of obtaining the unconstrained test specimen by placing the concrete so as to embed the first strain sensor while the first strain sensor is installed inside a frame in an unconstrained state.

4. The method for estimating physical properties of concrete according to claim 1 or 2, wherein the step (a) includes a step of obtaining the constrained test specimen by placing the concrete so as to embed the restraint steel material while the second strain sensor is fixedly attached to the restraint steel material.

5. The method for estimating physical properties of concrete according to claim 1 or 2, further comprising a step (i) of calculating the effective age of the strength test specimen to be the object of execution of the step (b) at the age timing based on the temperature change in the storage container measured by a thermometer.

6. After 25 days or more have elapsed since the step (a), taking out the unconstrained test specimen from the storage container, applying a temperature change in a heat-insulated environment, and obtaining the coefficient of thermal expansion of the concrete from the relationship between the temperature and the measured value of the first strain sensor (step (j)); calculating a time-dependent change pattern of autogenous shrinkage strain of the concrete based on the change pattern of temperature strain obtained by multiplying the coefficient of thermal expansion by the time-dependent change pattern of the temperature measured by the thermometer and the change pattern of the first strain value obtained in the step (c) (step (k)); The method for estimating physical properties of concrete according to claim 5, further comprising a step (l) of obtaining the relationship between the effective age and the autogenous shrinkage strain of the concrete based on the results of the step (i) and the step (k).

7. Each time the material age timing arrives, a compressive strength test is performed on the strength test specimen to obtain the time-dependent change pattern of the compressive strength of the concrete (step m); A method for estimating physical property values of concrete according to claim 5, comprising: a step (n) of obtaining the relationship between the effective age and the compressive strength of the concrete based on the results of the step (i) and the step (m).

8. Each time the material age timing arrives, a splitting tensile strength test is performed on the strength test specimen to obtain the time-dependent change pattern of the compressive strength of the concrete (step o); A method for estimating physical property values of concrete according to claim 5, comprising: a step (p) of obtaining the relationship between the effective age and the splitting tensile strength of the concrete based on the results of the step (i) and the step (o).

9. A method for estimating physical property values of concrete according to claim 5, characterized by having a step (q) of inversely analyzing the relationship between the age of the concrete and the measured value of the thermometer to obtain the adiabatic temperature rise characteristics of the concrete.

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