Evaluation device for evaluating characteristics of concrete, and method for evaluating characteristics of concrete

Abstract

Provided is an evaluation device that is capable of acquiring a variety of physical property values necessary for evaluating thermal cracking risk while using a concrete composed of the same material as a concrete to be used at a site.　This evaluation device comprises: a strength testing unit that includes a plurality of first cylindrical bodies; an unrestrained testing unit that includes a first bottomed rectangular frame-shaped body; a restrained testing unit that includes a second bottomed rectangular frame-shaped body and has both longitudinal ends thereof restrained by a restraining steel material having a thermal expansion coefficient of less than 1×10-6 / °C; a heat-insulating housing container that covers the strength testing unit, the unrestrained testing unit, and the unrestrained testing unit; and a thermometer that is capable of measuring a change in the temperature within the housing container. The unrestrained testing unit has a first strain sensor provided inside the first rectangular frame-shaped body, and the restrained testing unit has a second strain sensor provided to the restraining steel material.

Description

Evaluation device for evaluating concrete characteristics and method for evaluating concrete characteristics

[0001] The present invention relates to an evaluation device for evaluating the properties of concrete, and a method for evaluating the properties of concrete using this device.

[0002] In general, concrete used in large-scale (large-scale, large-section) structures (mass concrete) is prone to thermal strain due to temperature changes in parts. Thermal strain can cause thermal cracking in mass concrete. For this reason, it is important to evaluate the risk of thermal cracking in mass concrete.

[0003] A device known as a TSTM (Thermal Stress Testing Machine) is known as a device used for experimentally evaluating the thermal cracking properties of concrete. This device is a uniaxial confinement-type testing device that can arbitrarily control the temperature and constraint conditions of concrete under adiabatic conditions. The TSTM device can perform two types of tests: a confinement test in which the temperature conditions are changed under constraint to evaluate the properties of concrete, and an unconstrained test in which the temperature conditions are changed under unconstrained conditions to evaluate the properties of concrete.

[0004] However, the TSTM device requires water flow control for temperature management, more specifically, the control of water temperature and water volume, which results in a large device scale. Furthermore, in order to maintain a high level of accuracy in the test results, maintenance of the control mechanism and the like is necessary. For these reasons, the TSTM device is usually installed in a large testing room, making it difficult to evaluate concrete that will actually be used on-site.

[0005] Patent Document 1 discloses a test device that is easy to handle and can test the mechanical properties of concrete under conditions that reproduce an adiabatic state.

[0006] JP 2019-078614 A

[0007] When assessing the risk of thermal cracking in mass concrete, a method is generally adopted in which various concrete properties are acquired and then the temperature stress is calculated by numerical analysis using these data as input values. This numerical analysis requires a variety of concrete properties, typical examples of which include compressive strength, tensile strength, Young's modulus, temperature rise, autogenous shrinkage strain, and thermal expansion coefficient.

[0008] Although the test equipment disclosed in Patent Document 1 can be used to obtain information on thermal insulation characteristics and mechanical characteristics such as compressive strength, the data is insufficient to assess the risk of thermal cracking.

[0009] In view of the above-mentioned problems, the present invention aims to provide an evaluation device that can acquire various physical property values ​​necessary for evaluating the risk of thermal cracking while using concrete made of the same material as the concrete used in the field. Another object of the present invention is to provide a method for evaluating the properties of concrete using the evaluation device.

[0010] The evaluation device according to the present invention is an evaluation device for evaluating the characteristics of concrete that is a measurement target, and includes: a strength test section including a plurality of first cylindrical bodies into which the concrete can be poured; an unconstrained test section including a first rectangular frame-shaped body with a bottom into which the concrete can be poured; and a second rectangular frame-shaped body with a bottom into which the concrete can be poured, both ends in the longitudinal direction of the second rectangular frame-shaped body having a thermal expansion coefficient of 1×10 -6 / °C; a heat-insulating container that covers the strength test section, the unconstrained test section, and the unconstrained test section; and a thermometer that can measure temperature changes inside the container, wherein the unconstrained test section has a first strain sensor installed inside the first rectangular frame, and the constrained test section has a second strain sensor installed in the constraining steel.

[0011] The evaluation device is used in a state where a plurality of test specimens, each formed by pouring concrete to be evaluated into a first cylindrical body, a first rectangular frame body, and a second rectangular frame body, are placed in an insulated storage container. Here, the concrete to be evaluated can be concrete poured on-site, or concrete supplied from a concrete factory and made of the same material as the concrete to be poured on-site can be used.

[0012] A plurality of test specimens (strength test specimens) obtained by pouring concrete into the first cylindrical body are placed in a storage container.

[0013] For example, each time a predetermined age is reached, a strength test specimen at a target age among the plurality of strength test specimens is removed from the container and a Young's modulus measurement test is performed on the strength test specimen at the target age, thereby calculating the change in Young's modulus of concrete over time. The Young's modulus measurement test is performed, for example, in accordance with JIS A 1149:2017 "Test method for static elastic modulus of concrete."

[0014] As a more specific example, the strength test specimen is removed from the storage container every time the material age reaches 1 day, 3 days, 7 days, 14 days, and 28 days, and the above test is performed. At this time, a heat-insulating filler may be placed in the storage container so as to fill the gap (the area occupied by the original strength test specimen) that is created when the strength test specimen is removed. Typical heat-insulating fillers that can be used include foam beads, polystyrene foam, rock wool, glass wool, and urethane foam.

[0015] Furthermore, by conducting a compressive strength test on the target age strength test specimen, the change in the compressive strength of the concrete over time can be calculated. The compressive strength test is conducted, for example, in accordance with JIS A 1108:2018 "Test method for compressive strength of concrete." The compressive strength test may be conducted in parallel with the Young's modulus measurement test. The concrete compressive strength and Young's modulus for each age obtained in this manner may be used to derive a correlation between the two.

[0016] Furthermore, by performing a splitting tensile strength test on the target age strength test specimen, it is possible to calculate the change in the splitting tensile strength of the concrete over time. The splitting tensile strength test is performed, for example, according to JIS A 1113:2018 "Test method for splitting tensile strength of concrete."

[0017] When compressive strength tests and splitting tensile strength tests are performed on strength test specimens of the same age, it is preferable to prepare at least twice as many strength test specimens as the number of different ages. For example, two or more strength test specimens are removed from the storage container each time the age reaches 1 day, 3 days, 7 days, 14 days, and 28 days, and compressive strength tests and splitting tensile strength tests are performed on them. The compressive strength test and the Young's modulus measurement test may be performed in parallel on the same strength test specimen.

[0018] In addition, the same test may be performed on multiple strength test specimens of the same material age, and the value obtained by calculation based on the obtained measurement values ​​(e.g., average value) may be used as the measurement value obtained from the test results.

[0019] As described above, the strength test specimens are removed from the storage container each time the material age timing is reached. On the other hand, the unrestrained and restrained test specimens are placed in the storage container for a long period of time (for example, 25 days or more). From this perspective, in order to facilitate the removal of the strength test specimens, it is preferable that the storage container be made of a heat insulating material and have a removable lid, and that the strength test specimens be placed in the storage container above the unrestrained and restrained test specimens (closer to the lid).

[0020] As a more detailed example, the storage container may have a bottom portion installed in a position opposite the lid portion and sides covering the bottom portion on all sides, the unconstrained test section and the constrained test section may be arranged in a direction along the bottom portion, and the multiple first cylindrical bodies included in the strength test section may be arranged in a direction along the bottom portion while being placed directly above the first rectangular frame-shaped body included in the unconstrained test section and the second rectangular frame-shaped body included in the constrained test section.

[0021] The test specimen (unconstrained test specimen) obtained by pouring concrete into the first rectangular frame has a first strain sensor embedded therein. For example, an embedded strain gauge can be used as the first strain sensor. By acquiring the change over time in the measurement value of the first strain sensor, the change over time in the unconstrained strain of the concrete being measured can be obtained.

[0022] The test specimen (restrained test specimen) obtained by pouring concrete into the second rectangular frame had a thermal expansion coefficient of 1 × 10 -6 The constraining steel material is, for example, an invar steel material (with a thermal expansion coefficient of 0.5×10 -6 / °C) can be used. A second strain sensor is installed in the restraining steel. In a more detailed example, a threaded portion of the restraining steel is machined and then the second strain sensor is fixed in place. For example, a strain gauge can be used as the second strain sensor. By acquiring the change over time in the measurement value of the second strain sensor, the change over time in strain under restraint of the concrete being measured can be obtained.

[0023] The unrestrained and restrained specimens are housed in an insulated container along with multiple strength test specimens. As these specimens age, hydration reactions progress, generating heat, which causes the temperature inside the container to rise. After that, as the hydration reactions reach a saturation point, the rate of temperature rise inside the container slows, and over time, the temperature eventually drops to the same temperature as the outside air temperature. In other words, the unrestrained and restrained specimens are subjected to the same temperature history inside the insulated container.

[0024] The measurement value of the first strain sensor corresponds to the free strain value, which reflects the strain due to temperature history and the autogenous shrinkage strain. Meanwhile, the measurement value of the second strain sensor installed on the restraining steel corresponds to the steel strain, which is the strain value in the restrained state, which reflects the strain due to temperature history and the autogenous shrinkage strain. Therefore, the restrained strain value can be obtained based on the measurement values ​​of the first strain sensor and the second strain sensor, more specifically, based on the difference between the measurement values ​​of the first strain sensor and the second strain sensor. In other words, the change over time in the restrained strain of the concrete being measured can be obtained.

[0025] Based on the relationship between the balance of forces between the restraining steel and the concrete and the strain compatibility conditions, the restraint stress generated in the concrete can be calculated by a calculation based on the ratio of the restraining steel in the restrained test specimen (steel ratio), the Young's modulus of the restraining steel, and the value of strain in the restrained state. As described above, the value measured by the second strain sensor can be used as the value of strain in the restrained state. The Young's modulus of the restraining steel can be the physical property value of the steel used as the restraining steel. The steel ratio can be the ratio between the area of ​​the end in the longitudinal direction of the second rectangular frame that constitutes the restraint test section and the cross-sectional area of ​​the restraining steel.

[0026] In this way, once the time-dependent changes in the restraint strain and the time-dependent changes in the restraint stress of the concrete being measured are obtained, the apparent Young's modulus can be calculated based on the correlation between the two, both during heating and cooling. The restraint stress and the restraint strain exhibit a nearly linear correlation during both heating and cooling. Therefore, by linearly approximating each correlation using, for example, the least squares method and deriving the slope, the apparent Young's modulus of the concrete being measured during heating and cooling can be determined. This apparent Young's modulus can be considered to be a Young's modulus that takes into account both elastic strain and creep strain under constantly changing restraint stress.

[0027] On the other hand, as described above, by performing Young's modulus measurement tests on multiple strength test specimens of different ages, the actual change in Young's modulus over time of the concrete being measured can be obtained. According to the Japan Concrete Institute's "Guidelines for Crack Control of Mass Concrete 2016" (hereinafter simply referred to as the "Control Guidelines"), the effect of creep is considered as a decrease in stiffness due to the effective Young's modulus, which is the Young's modulus multiplied by a reduction factor. Therefore, the reduction factor of the Young's modulus (at each temperature increase and decrease) of the concrete being measured can be calculated from the ratio between the actual Young's modulus obtained by the Young's modulus measurement test and the apparent Young's modulus (at each temperature increase and decrease).

[0028] According to the above control guidelines, the same Young's modulus reduction coefficient is used for both rising and falling temperatures, regardless of the type and blend of cement used in the concrete. In contrast, the evaluation device according to the present invention can obtain a Young's modulus reduction coefficient specific to the concrete being measured, and by using this value in numerical analysis, it becomes possible to more accurately evaluate the risk of thermal cracking in mass concrete.

[0029] The evaluation device is also equipped with a thermometer capable of measuring temperature changes inside the container. Therefore, the effective material age can be calculated by acquiring the history of changes in the thermometer's measurements. In other words, the relationship between the material age at the time the strength test specimen was removed from the container and the effective material age can be obtained.

[0030] Various correlation information can be obtained using the information obtained in this manner on the correlation between the age of the strength test specimens when they were removed from the storage container and the effective age of the concrete. For example, a correlation between the change in the compressive strength of the concrete over time and the effective age of the concrete can be obtained by performing a compressive strength test on the strength test specimens removed at each age. Also, a correlation between the change in the splitting tensile strength of the concrete over time and the effective age of the concrete can be obtained by performing a splitting tensile strength test on the strength test specimens removed at each age.

[0031] After 25 days or more have passed since the specimen was placed in the storage container, the unrestrained specimen may be removed from the storage container, and the measurement value of the first strain sensor may be read while subjecting the specimen to a temperature change (for example, from the outside temperature to approximately 60°C) in an insulated environment, thereby obtaining the relationship between the temperature and the measurement value of the first strain sensor.

[0032] It is believed that even if an unconstrained test specimen is subjected to a temperature change after 25 days or more has passed, additional autogenous shrinkage strain associated with the hydration reaction will not occur. In other words, by subjecting an unconstrained test specimen after 25 days or more has passed to a temperature change and obtaining a correlation between the temperature and the measurement value of the first strain sensor, information regarding the temperature strain of the concrete can be obtained. In particular, the thermal expansion coefficient of the concrete can be obtained from the relationship between the temperature and the measurement value of the first strain sensor. Typically, the correlation between the temperature and the measurement value of the first strain sensor is approximately linear. Therefore, for example, the correlation between the temperature and the measurement value of the first strain sensor can be linearly approximated based on the least squares method, and the slope of the linear approximation can be calculated to obtain the thermal expansion coefficient of the concrete.

[0033] On the other hand, the measurement value of the first strain sensor attached to the unconstrained test specimen placed in the containment vessel reflects the temperature strain and autogenous shrinkage strain based on the temperature history inside the containment vessel. The value of the temperature strain occurring in the unconstrained test specimen placed in the containment vessel can be derived by multiplying the value of the temperature change when the unconstrained test specimen is placed in the containment vessel by the thermal expansion coefficient of the concrete calculated using the above method. Therefore, by subtracting the value of the temperature strain from the measurement value of the first strain sensor attached to the unconstrained test specimen placed in the containment vessel, the change in the autogenous shrinkage strain of the unconstrained test specimen over time can be obtained. This autogenous shrinkage strain is the autogenous shrinkage strain of the concrete being measured.

[0034] Therefore, based on the information on the correlation between the material age and the effective material age obtained by the above-mentioned method, the correlation between the effective material age and the autogenous shrinkage strain of the concrete being measured can be obtained. The information on the correlation between the effective material age and the autogenous shrinkage strain of the concrete can be used to evaluate the risk of thermal cracking in an actual structure constructed using that concrete using 3D-FEM analysis.

[0035] In the evaluation device, the thermometer may be installed in any position as long as it measures the temperature inside the container, but from the viewpoint of accurately measuring the temperature of the concrete, it is preferable that the thermometer be installed in at least one of the strength test section, the unconstrained test section, and the constrained test section. However, as described above, since strength test specimens are removed at each age, if a thermometer is to be installed in the strength test section, it is preferable to install it in the strength test specimen that is removed from the container latest.

[0036] The constrained specimen contains concrete and constraining steel, which has a different specific heat, thermal conductivity, and heat capacity than the concrete. On the other hand, the unconstrained specimen does not contain constraining steel. Therefore, from the perspective of accurately measuring the temperature of the concrete, it is more preferable to install a thermometer on the unconstrained specimen than on the constrained specimen.

[0037] Furthermore, as described above, when determining the autogenous shrinkage strain of the unconstrained test specimen, it is calculated from the value of the temperature strain that occurred in the unconstrained test specimen, so from the viewpoint of improving this accuracy, it is more preferable to install a thermometer on the unconstrained test specimen.Furthermore, from the viewpoint of measuring the thermal expansion coefficient by performing an adiabatic test on the unconstrained test specimen removed from the container, it is more preferable to install a thermometer on at least the unconstrained test section.

[0038] The constrained and unconstrained specimens placed in the containment vessel are given a temperature history resulting from heat generation due to the hydration reaction of multiple strength test specimens placed in the same vessel. For example, if a thermometer is installed on the constrained or unconstrained specimen, the temperature change pattern for each material age can be obtained. Therefore, by performing an inverse analysis of the relationship between the material age and the measured values ​​of the thermometer attached to the constrained or unconstrained specimen, the adiabatic temperature rise characteristics of the concrete being measured can be obtained. Information on the adiabatic temperature rise characteristics of concrete can be used to evaluate the risk of thermal cracking when an actual structure is constructed using that concrete using 3D-FEM analysis.

[0039] However, among the physical properties of concrete, the creep characteristics are difficult to obtain through experiments or numerical analysis. Therefore, the effect of creep is often evaluated using the reduction factor of Young's modulus.

[0040] On the other hand, it is not easy to determine the Young's modulus reduction factor for each concrete. For this reason, the Young's modulus reduction factor presented in the Japan Concrete Institute's "Guidelines for Crack Control of Mass Concrete 2016" (hereinafter simply referred to as "Control Guidelines") is currently generally applied to all concrete.

[0041] However, in reality, it is expected that the value of the reduction factor for Young's modulus will vary depending on the type and mix of cement used in concrete. Therefore, if the value of the reduction factor for Young's modulus specified in the above control guidelines is uniformly adopted and the risk of thermal cracking of mass concrete is evaluated based on that value, the accuracy of the risk assessment may not be fully guaranteed.

[0042] The above-mentioned evaluation device can be used as one of the methods for estimating the physical properties of concrete, including the reduction factor of Young's modulus, while taking into consideration the properties of the concrete to be measured. However, the method for estimating the physical properties of concrete can also be implemented without using the above-mentioned evaluation device. This estimation method will be described below.

[0043] This estimation method is a method for estimating physical property values ​​of concrete to be measured, and includes the steps of: (a) placing a plurality of test specimens obtained by pouring the concrete in one or more heat-insulated storage containers having a temperature history including temperature rises and falls; (b) performing a Young's modulus measurement test on strength test specimens belonging to the plurality of test specimens each time a predetermined material age is reached, and calculating the change in Young's modulus of the concrete over time; (c) acquiring a first strain value which is a measurement value of a first strain sensor attached to an unconstrained test specimen obtained by pouring the concrete into a frame in an unconstrained state among the plurality of test specimens; (d) acquiring a second strain value which is a measurement value of a second strain sensor attached to a constrained test specimen obtained by pouring the concrete into a frame constrained by constraining steel among the plurality of test specimens; and (e) calculating the change in the constrained strain value of the concrete over time based on the first strain value and the second strain value. The method is characterized by comprising a step (f) of calculating the change in the restraint stress of the concrete over time based on the value based on the restraint steel possessed by the restraint test specimen and the second strain value; a step (g) of calculating the apparent Young's modulus during heating and cooling based on the correlation between the restraint strain value and the restraint stress; and a step (h) of deriving a reduction coefficient of the Young's modulus during heating and cooling based on the ratio between the Young's modulus obtained in step (b) and the apparent Young's modulus obtained in step (g).

[0044] Here, the concrete to be evaluated can be concrete poured on-site, or concrete supplied from a concrete factory that is made of the same material as the concrete to be poured on-site.

[0045] For example, by removing a strength test specimen from a storage container and conducting a Young's modulus measurement test each time a predetermined age is reached, it is possible to calculate the change in Young's modulus of concrete over time. The Young's modulus measurement test is conducted, for example, in accordance with JIS A 1149:2017 "Test method for static elastic modulus of concrete." As a more specific example, the strength test specimen is removed from the storage container each time the age reaches 1 day, 3 days, 7 days, 14 days, and 28 days, and the above test is conducted.

[0046] In addition, the same test may be performed on multiple strength test specimens of the same material age, and the value obtained by calculation based on the obtained measurement values ​​(e.g., average value) may be used as the measurement value obtained from the test results.

[0047] The unconstrained test specimen is a test specimen obtained by pouring concrete into an unconstrained frame with a first strain sensor attached. More specifically, the unconstrained test specimen is obtained by placing the first strain sensor inside the unconstrained frame and pouring concrete so that the first strain sensor is embedded. For example, an embedded strain gauge can be used as the first strain sensor. In step (c), the time-dependent change in the measurement value of the first strain sensor is acquired, thereby obtaining the time-dependent change in the unconstrained strain of the concrete being measured.

[0048] The restrained test specimen is a test specimen obtained by pouring concrete into a frame restrained by restraining steel members with the second strain sensor attached. More specifically, the restrained test specimen is obtained by pouring concrete so as to bury the restraining steel members with the second strain sensor fixedly attached to the restraining steel members.

[0049] As the restraining steel material, a material with an extremely low thermal expansion coefficient is preferably used, and preferably, the thermal expansion coefficient is 1×10 -6 / °C. Such a restrained steel material is, for example, an invar steel material (the thermal expansion coefficient of which is 0.5 × 10 -6 / ℃) can be used.

[0050] In a specific example, a threaded portion of the restraining steel is machined, and then a second strain sensor is fixedly installed. For example, a strain gauge can be used as the second strain sensor. In step (d), the change over time in the measured value of the second strain sensor is acquired, thereby obtaining the change over time in the strain of the concrete under restraint.

[0051] The unrestrained and restrained specimens are subjected to the same temperature history in an insulated containment vessel.

[0052] The measurement value of the first strain sensor corresponds to the free strain value, which reflects the strain due to temperature history and the autogenous shrinkage strain. Meanwhile, the measurement value of the second strain sensor installed on the restraining steel corresponds to the steel strain, which is the strain value in the restrained state, which reflects the strain due to temperature history and the autogenous shrinkage strain. Therefore, in step (e), the restrained strain value can be obtained based on the measurement values ​​of the first strain sensor and the second strain sensor. As a specific method for step (e), a method of calculating the difference between the measurement values ​​of the first strain sensor and the second strain sensor can be used. This step (e) allows the change in the restrained strain of the concrete being measured over time to be obtained.

[0053] In step (f), the restraint stress generated in the concrete is calculated from the second strain value obtained in step (d), i.e., the value of strain in the restrained state, by utilizing the relationship between the balance of forces between the restraint steel and the concrete and the strain compatibility conditions. More specifically, the restraint stress generated in the concrete can be calculated by a calculation based on the ratio of the restraint steel in the restrained test specimen (steel ratio), the Young's modulus of the restraint steel, and the value of strain in the restrained state. The Young's modulus of the restraint steel can be calculated using the physical properties of the steel used as the restraint steel. The steel ratio can be, for example, the ratio between the area of ​​the end of the frame constituting the restraint test specimen in the extension direction of the restraint steel and the cross-sectional area of ​​the restraint steel.

[0054] Once the time-dependent changes in the restraint strain and the time-dependent changes in the restraint stress of the concrete to be measured are obtained in this way, in step (g), the apparent Young's modulus is calculated for each of the temperature rise and the temperature fall based on the correlation between the two. The restraint stress and the restraint strain exhibit a nearly linear correlation during both the temperature rise and the temperature fall. Therefore, by linearly approximating each correlation using, for example, the least squares method and deriving the slope, the apparent Young's modulus of the concrete to be measured during each of the temperature rise and the temperature fall can be determined. This apparent Young's modulus can be considered to be a Young's modulus that takes into account both elastic strain and creep strain under constantly changing restraint stress.

[0055] As described above, in step (b), a Young's modulus measurement test is performed on multiple strength test specimens of different ages, thereby obtaining the change in the actual Young's modulus of the concrete being measured over time. According to the control guidelines, the effect of creep is considered as a decrease in stiffness due to the effective Young's modulus, which is the Young's modulus multiplied by a reduction factor. Therefore, in step (h), a reduction factor for the Young's modulus (at each temperature increase and decrease) of the concrete being measured is calculated based on the ratio between the actual Young's modulus obtained in the Young's modulus measurement test and the apparent Young's modulus (at each temperature increase and decrease). The reduction factor for the Young's modulus calculated in this manner reflects the specific properties of the concrete being measured. Therefore, for example, by using this value in a numerical analysis, the risk of thermal cracking of mass concrete can be more accurately evaluated.

[0056] The step (a) is a step of placing 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 storage container, and the temperature history may be obtained based on heat generated from the plurality of strength test specimens placed in the storage container.

[0057] In this case, the unrestrained and restrained specimens are housed in the same insulated storage container along with multiple strength test specimens. As these specimens age, the hydration reaction progresses, generating heat, which causes the temperature inside the storage container to rise. After that, when the hydration reaction reaches a saturation point, the rate of temperature rise inside the storage container slows, and after a certain period of time, the temperature eventually drops to the same temperature as the outside air temperature. In other words, the unrestrained and restrained specimens are exposed to the same temperature history inside the insulated storage container.

[0058] Therefore, according to the above method, it is not necessary to prepare in advance a plurality of storage containers, each having the same temperature history set therein, and the preparation process for estimation is simplified.

[0059] According to the evaluation device of the present invention, it is possible to obtain a variety of concrete property values ​​using a simple method while using concrete made of the same material as the concrete used on-site.

[0060] 1 is a perspective view schematically showing the structural appearance of one embodiment of an evaluation device according to the present invention. FIG. 2 is a schematic cross-sectional view of the evaluation device shown in FIG. 1. FIG. 3 is a schematic plan view of the evaluation device shown in FIG. 1 with a lid removed. FIG. 4 is a schematic plan view of the evaluation device shown in FIG. 3 with a strength test specimen removed. FIG. 5 is a perspective view schematically showing the structure of a strength test specimen. FIG. 6 is a plan view schematically showing the structure of an unconstrained test specimen. FIG. 7 is a plan view schematically showing the structure of a constrained test specimen. FIG. 8 is a graph schematically showing the correlation between the number of days elapsed and Young's modulus. FIG. 9 is a graph showing the correlation between effective age and Young's modulus measured using the concrete of Example 1. FIG. 10 is a graph showing the correlation between effective age and compressive strength measured using the concrete of Example 1. FIG. 11 is a graph showing the correlation between compressive strength and Young's modulus measured using the concrete of Example 1. FIG. 12 is a graph showing the correlation between compressive strength and splitting tensile strength measured using the concrete of Example 1. FIG. 13 is a graph schematically showing the manner of change over time in the measured values ​​of the first strain sensor and the second strain sensor. 1 is a graph showing changes over time in the measured values ​​of the first strain sensor and the second strain sensor when the concrete of Example 1 is used. FIG. 2 is a graph showing changes over time in the confinement stress. FIG. 3 is a graph showing the correlation between the confinement stress and the confinement strain. FIG. 4 is a graph showing the correlation between the confinement stress and the confinement strain calculated based on the measured values ​​of the first strain sensor and the second strain sensor when the concrete of Example 1 is used. FIG. 5 is a graph showing the correlation between the Young's modulus reduction coefficient and the effective material age, derived based on the correlation between the confinement stress and the confinement strain measured using the concrete of Example 1 and the correlation between the effective material age and the Young's modulus. FIG. 6 is a graph showing the relationship between the measured values ​​of the first strain sensor and the temperature when an insulation test was conducted on the concrete of Example 1. FIG. 7 is a graph showing the relationship between the autogenous shrinkage strain and the effective material age, derived based on the measured values ​​using the concrete of Example 1. FIG. 8 is a graph showing the relationship between the age and the temperature rise of the concrete to be measured placed in a storage container. 22 is a graph schematically showing the adiabatic temperature rise characteristics of the concrete being measured, obtained by back-analyzing the results shown in FIG. 21 .

[0061] The evaluation device according to the present invention is a device for evaluating the properties of concrete as a measurement target. Specifically, the evaluation device is used in a state where a plurality of test specimens each having concrete as a measurement target poured into a predetermined area are housed inside the device.

[0062] Hereinafter, embodiments of an evaluation device and a method of using the same according to the present invention will be described with reference to the accompanying drawings. However, the drawings are schematic, and the dimensional ratios in the drawings do not necessarily match the actual dimensional ratios. Furthermore, the dimensional ratios between the drawings do not necessarily match.

[0063] [Configuration of Evaluation Device] Fig. 1 is a perspective view showing a schematic appearance of the evaluation device. The evaluation device 1 includes a lid 2 and a storage container 3. The lid 2 and the storage container 3 are both made of a heat insulating material, for example, polystyrene foam. The lid 2 is detachable from the storage container 3.

[0064] In the following description, the X-Y-Z coordinate system shown in FIG. 1 will be referenced. In addition, in the following description, when a direction is expressed and a positive or negative direction is to be distinguished, it will be described with a positive or negative sign, such as "+Z direction" or "-Z direction." In addition, when a direction is expressed without distinguishing between positive and negative directions, it will be simply referred to as "Z direction." In other words, in this specification, when simply referring to "Z direction," it includes both the "+Z direction" and the "-Z direction." Typically, the +Z direction is the vertically upward direction.

[0065] Fig. 2 is a schematic cross-sectional view of the evaluation device 1 shown in Fig. 1 cut along the X-Z plane at a predetermined Y coordinate position. Fig. 3 is a schematic plan view of the evaluation device 1 shown in Fig. 1 with the lid 2 removed, viewed from the +Z side in the -Z direction.

[0066] As shown in Figures 2 and 3, the storage container 3 has a bottom 3b installed in a position opposite the lid 2 in the Z direction, and side portions 3a that cover the top of the bottom 3b from all sides, and each test specimen (10, 20, 30) is installed inside the area surrounded by the side portions 3a and the bottom 3b.

[0067] The evaluation device 1 is used with a strength test specimen 10, an unconstrained test specimen 20, and a constrained test specimen 30 placed in a storage container 3. As shown in Figures 2 and 3, in the evaluation device 1 of this embodiment, the multiple strength test specimens 10 are placed closer to the lid 2 than the unconstrained test specimens 20 and the constrained test specimens 30. Figure 3 shows an example in which 30 strength test specimens 10 are placed in the evaluation device 1.

[0068] Figure 4 is a schematic plan view of the evaluation device 1 when the plurality of strength test specimens 10 are removed from the state shown in Figure 2 and viewed from the +Z side in the -Z direction. As shown in Figures 2 and 4, in the evaluation device 1 of this embodiment, the unconstrained test specimens 20 and the constrained test specimens 30 are located on the bottom 3b side and arranged along the surface of the bottom 3b (X-Y plane). Figure 4 shows an example in which two unconstrained test specimens 20 and two constrained test specimens 30 are installed in the evaluation device 1.

[0069] FIG. 5 is a perspective view showing a schematic configuration of the strength test specimen 10. The strength test specimen 10 has a cylindrical body 11 made of, for example, tinplate or plastic, and is formed by pouring concrete to be measured into the internal space 12 of the body 11. The dimensions of the body 11 are arbitrary, but 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, each of which has the same dimensions and has concrete of the same material to be measured poured into the internal space 12 of each cylinder 11, are placed in the storage container 3. The body 11 corresponds to the "first cylindrical body."

[0070] As shown in Figures 2 and 3, the spaces between the multiple strength test specimens 10 are filled with insulating filler 6 made of foam beads, polystyrene foam molded to the shape of the internal space 12, spray-type urethane foam, rock wool, glass wool, etc., in order to ensure the insulation of the internal space 12 of the cylindrical body 11.

[0071] 6 is a plan view showing a schematic configuration of the unconstrained test specimen 20. The unconstrained test specimen 20 has a rectangular frame 21 with a bottom made of wood, plywood, or the like, and a first strain sensor 25 is installed in the internal space 23 of the frame 21. The unconstrained test specimen 20 is formed by pouring concrete to be measured into the internal space 23 of the frame 21 so that the first strain sensor 25 is embedded in the frame 21. An embedded strain gauge, for example, can be used as the first strain sensor 25. The frame 21 corresponds to the "first rectangular frame-shaped body."

[0072] The frame 21 may have any dimensions, but as an example, it has a rectangular parallelepiped shape measuring 10 cm x 10 cm x 80 cm.

[0073] In order to prevent the concrete from being deformed by the frame body 21, a buffer board made of polystyrene or the like may be attached to the longitudinal sides of the frame body 21, and a buffer film made of polyester or the like may be attached to the lateral sides and bottom surfaces of the lateral sides.

[0074] 6, a signal line 27 is attached to the first strain sensor 25, and the measurement value of the first strain sensor 25 can be read out continuously or intermittently. However, as long as the measurement value of the first strain sensor 25 can be read out continuously or intermittently, the connection is not limited to a wired connection and may be a wireless connection.

[0075] The first strain sensor 25 is preferably an embedded strain gauge equipped with a temperature measurement function. If the first strain sensor 25 does not have a temperature measurement function, a thermocouple (not shown) may be mounted on the frame 21 to measure the temperature of the unconstrained test specimen 20.

[0076] 7 is a plan view showing a schematic configuration of the restraint test specimen 30. The restraint test specimen 30 has a rectangular frame body with a bottom formed by a pair of side plates 31 arranged opposite each other in the short direction, a pair of end plates 32 arranged opposite each other in the long direction, and a bottom plate (not shown). This frame body corresponds to the "second rectangular frame body."

[0077] The pair of end plates 32 are fixedly connected to each other by restraining steel members 34. The end plates 32 and the restraining steel members 34 are fixed to each other by, for example, welding. The side plates 31 and the bottom plate are made of, for example, wood or plywood. The end plates 32 and the restraining steel members 34 have a thermal expansion coefficient of 1×10 -6 / ° C. As a specific example, the end plates 32 and the restraining steel members 34 are made of invar steel, tungsten, or the like, and preferably made of invar steel.

[0078] In the restraint 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 defined as the ratio of the cross-sectional area of ​​the restraint steel 34 to the area of ​​the end plate 32.

[0079] A second strain sensor 35 is installed on the restraining steel member 34. A strain gauge, for example, can be used as the second strain sensor 35. In the example of Fig. 7, a thermometer 36 consisting of a thermocouple is attached to the restraining steel member 34. However, it is optional whether or not the restraining test specimen 30 has the thermometer 36.

[0080] The outer dimensions of the bottomed frame formed by the side plates 31, end plates 32, and bottom plate are arbitrary, but for example, it is a rectangular parallelepiped shape of 10 cm × 10 cm × 80 cm. The confined specimen 30 is formed by pouring the concrete to be measured into the internal space 33 of this bottomed frame so as to embed the confining steel members 34.

[0081] The side plates 31 and bottom plate may be fitted with a buffer film made of polyester or the like. The end plates 32 are provided to absorb the expansion force when the concrete expands due to heat generation in the early stages after being poured, thereby enabling accurate measurement of the expansion stress.

[0082] 7, a signal line 37 is attached to the second strain sensor 35, and the measurement value of the second strain sensor 35 can be read out continuously or intermittently. However, as long as the measurement value of the second strain sensor 35 can be read out continuously or intermittently, the connection is not limited to a wired connection and may be a wireless connection. Note that, like the measurement value of the second strain sensor 35, the temperature information measured by the thermometer 36 may also be read out continuously or intermittently.

[0083] As described above, before concrete is poured, the evaluation device 1 has, inside the storage container 3 that constitutes an insulating storage container, a plurality of cylindrical bodies 11, a frame body 21 in which a first strain sensor 25 is installed in the internal space 23, and a frame body (31, 32) in which a restraining steel member 34 to which a second strain sensor 35 is attached is fixed in the internal space 33.

[0084] The cylindrical body 11 constitutes the strength test section, and concrete to be evaluated is poured into the internal space 12 of the cylindrical body 11 to form a strength test specimen 10. The frame body 21 and the first strain sensor 25 constitute the unconstrained test section, and concrete to be evaluated is poured into the internal space 23 of the frame body 21 to form an unconstrained test specimen 20. The frame bodies (31, 32), confining steel 34, and the second strain sensor 35 constitute the constrained test section, and concrete to be evaluated is poured into the internal space 33 of the frame bodies (31, 32) to form a constrained test specimen 30.

[0085] 4 shows that the unrestrained test specimens 20 and the restrained test specimens 30 are arranged in the X-Y plane to substantially close the internal space surrounded by the side surfaces of the storage vessel 3. The external dimensions of the storage vessel 3 may be set appropriately depending on the external dimensions of the frame 21 constituting the unrestrained test specimen 20 and the external dimensions of the frame bodies (31, 32) constituting the restrained test specimen 30. However, if gaps are generated between the side portions 3 a of the storage vessel 3 and each test specimen (20, 30) when the unrestrained test specimens 20 and the restrained test specimens 30 are arranged without gaps in the X-Y plane, the gaps may be filled with a heat-insulating filler material 6.

[0086] [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 pouring concrete to be evaluated into each test section is placed in the inner space of the storage container 3 of the evaluation device 1. Then, the lid 2 is arranged to cover the top of the storage container 3.

[0087] More specifically, the unconstrained test specimen 20 and the constrained test specimen 30 are placed on the surface of the bottom portion 3b. Then, on the upper surfaces of these test specimens (20, 30), a plurality of strength test specimens 10 are arranged along the X-Y plane. The unconstrained test specimens 20 and the constrained test specimens 30 may have a buffer film made of, for example, polyester attached to the open surface on the +Z side.

[0088] After each test specimen (10, 20, 30) is placed in the evaluation device 1, the strength test specimen 10 is removed each time a predetermined material age timing is reached. After the strength test specimen 10 is removed, it is preferable to place a heat insulating filler 6 in the storage container 3 so as to fill the gap created by removing the strength test specimen 10.

[0089] For example, strength test specimens 10 are removed from the container every time 1 day, 3 days, 7 days, 14 days, and 28 days have passed. A Young's modulus measurement test is performed using the strength test specimens 10 at each age, thereby obtaining the relationship between Young's modulus and age for the concrete being measured (see, for example, FIG. 8). The Young's modulus measurement test can be performed, for example, according to JIS A 1149:2017 "Test method for static elastic modulus of concrete."

[0090] As described above, at least one of the unconstrained test specimen 20 and the constrained test specimen 30 installed in the storage vessel 3 is equipped with a temperature measurement function (thermometer). Since the internal space of the storage vessel 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 is installed in the unconstrained test specimen 20, can be considered to be the temperature history inside the storage vessel 3. Furthermore, for example, the temperature history read from the thermometer 36 installed in the constrained test specimen 30 can be considered to be the temperature history inside the storage vessel 3. As another example, a separate thermometer may be installed in the storage vessel 3, and in this case, the temperature history read from the separate thermometer can be considered to be the temperature history inside the storage vessel 3.

[0091] That is, the evaluation device 1 can obtain information about the temperature history inside the container 3. Based on this information about the temperature history, it is possible to obtain the relationship between the installation period (actual age) of the test specimen installed inside the container 3 and the effective age. As an example, based on the Arrhenius law of the following equation (1) defined in the Guidelines for Controlling Cracks in Mass Concrete, the effective age t e is calculated.

[0092]

[0093] In addition, in equation (1), Δt i indicates the period (days) during which the temperature of the concrete remains constant, and T(△t i ) is △t i This refers to the temperature (℃) of the concrete that continues over a period of time.

[0094] As an example, concrete containing the materials shown in Table 1 below in the proportions shown in Table 2 was poured into each test section as the concrete to be evaluated, and test specimens (10, 20, 30) were produced and placed in the evaluation device 1.

[0095]

[0096]

[0097] Using the concrete of Example 1, each test specimen was placed in the evaluation device 1, and the relationship between the material age (installation period) and the effective material age in the evaluation device 1 was obtained based on the temperature history measured by the thermometer. Then, a Young's modulus measurement test was performed on the strength test specimen 10 taken out of the storage container 3 each time a predetermined material age was reached, and the correlation between the measured Young's modulus and the effective material age was obtained. Figure 9 shows the correlation between the Young's modulus and the effective material age.

[0098] The Young's modulus measurement test and the compressive strength test can be performed in parallel. Therefore, by performing a compressive strength test on strength test specimens 10 extracted at each age, the relationship between compressive strength and age for the concrete being measured can be obtained. The compressive strength test is performed, for example, according to JIS A 1108:2018 "Test Method for Compressive Strength of Concrete." Furthermore, since the relationship between age and effective age is obtained as described above, the relationship between compressive strength and effective age can also be obtained. Figure 10 is a graph showing the correlation between compressive strength and effective age measured using the concrete of Example 1. Furthermore, the correlation between Young's modulus and compressive strength may be derived based on the results shown in Figures 9 and 10. Figure 11 is a graph showing the correlation between compressive strength and Young's modulus measured using the concrete of Example 1.

[0099] It is also possible to remove strength test specimens 10 from the container 3 at the same age as the age at which the compressive strength test will be performed, and to perform a splitting tensile strength test using the strength test specimens 10 of each age. In this case, from the viewpoint of performing a splitting tensile strength test and a Young's modulus measurement test (and a compressive strength test) on strength test specimens 10 of the same age, it is preferable to place in the evaluation device 1 the number of strength test specimens 10 that is at least twice the number of types of age at which the test will be performed.

[0100] The splitting tensile strength test is performed, for example, by a method conforming to JIS A 1113:2018 "Test method for splitting tensile strength of concrete." As described above, since the relationship between the material age and the effective material age can be obtained, the relationship between the splitting tensile strength and the effective material age can also be obtained.

[0101] 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 be obtained. Figure 12 is a graph showing the correlation between the compressive strength and the splitting tensile strength measured using the concrete of Example 1.

[0102] The storage container 3 is maintained in an insulated state, and multiple test specimens (10, 20, 30) are placed inside. These test specimens (10, 20, 30) generate heat as the hydration reaction progresses with the passage of material age, and this heat generation causes the temperature inside the storage container 3 to rise. Thereafter, when the progress of the hydration reaction reaches a saturated state, the rate of temperature rise inside the storage container 3 slows, and after a further period of time, the temperature drops to the same temperature as the outside air temperature. In other words, the unconstrained test specimen 20 and the constrained test specimen 30 are placed under the same temperature history inside the insulated storage container 3.

[0103] The change over time in the strain value read from the first strain sensor 25 mounted on the unconstrained test specimen 20 corresponds to the change over time in the unconstrained strain of the concrete being measured under the above-mentioned temperature history. The change over time in the strain value read from the second strain sensor 35 mounted on the constrained test specimen 30 corresponds to the change over time in the constrained strain of the concrete being measured under the above-mentioned temperature history. Figure 13 is a graph schematically showing the change in the measured value of the first strain sensor 25 and the change in the measured value of the second strain sensor 35. Figure 14 is a graph showing the change in 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 in the measured value S2 of the second strain sensor 35 mounted on the constrained test specimen 30 using the concrete of Example 1.

[0104] The measured value S1 of the first strain sensor 25 corresponds to the value of free strain, which reflects the strain due to the temperature history and the autogenous shrinkage strain. On the other hand, the measured value S2 of the second strain sensor 35 corresponds to the value of strain in a constrained state, which reflects the strain due to the temperature history and the autogenous shrinkage strain. 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 constrained strain ε of the concrete to be measured can be calculated. s The change over time can be obtained.

[0105] Furthermore, the restraint stress can be calculated from the balance of forces between the restraint steel 34 and the concrete placed in the restraint test 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 restraining steel 34, p corresponds to the steel ratio of the restraining steel 34 in the restrained test specimen 30, and s2 corresponds to the measurement value of the second strain sensor 35 mounted on the restrained test specimen 30. In addition, in equation (2), tensile stress is expressed as a positive value and compressive stress is expressed as a negative value. F = -E s ・p・s2 …(2)

[0106] For example, by performing the calculation of the above equation (2), it is possible to obtain the change over time in the restraint stress F in the concrete placed in the restraint test specimen 30. Fig. 15 is a graph that schematically shows the change in the restraint stress F.

[0107] The change in the restraint stress F and the restraint strain ε s 16 is a graph showing a schematic correlation between the restraint stress and the restraint strain.

[0108] As shown schematically in Figure 16, the restraint stress and restraint strain exhibit a nearly linear correlation during both the temperature rise (curve Eca1) and temperature fall (curve Eca2). Therefore, by linearly approximating each correlation using, for example, the least squares method and deriving the slope, the apparent Young's modulus of the concrete being measured during both the temperature rise and the temperature fall can be determined. This apparent Young's modulus can be considered to be a Young's modulus that takes into account both the elastic strain and creep strain due to the restraint stress, which change over time.

[0109] Fig. 17 is a graph showing the correlation between restraint stress and restraint strain calculated based on the results shown in Fig. 14. In the results of Fig. 17, the apparent Young's modulus of the concrete being measured at elevated temperature was 4.8 kN / mm 2 , the apparent Young's modulus of the concrete being measured when cooled is 29.4 kN / mm 2 and are required respectively.

[0110] On the other hand, as described above with reference to FIG. 9 , a Young's modulus measurement test is performed on strength test specimens 10 removed from the evaluation device 1 at each age, thereby obtaining the change in Young's modulus of the concrete being measured over time. The reduction factor of the Young's modulus of the concrete being measured can be calculated by the ratio of the measured Young's modulus to the apparent Young's modulus calculated by the above method. FIG. 18 is a graph showing the relationship between the Young's modulus reduction factor calculated by the above calculation and the effective age. In practice, the average value of the Young's modulus reduction factor over the heating period can be used to determine the Young's modulus reduction factor of the concrete being measured during heating. Similarly, the average value of the Young's modulus reduction factor over the cooling period can be used to determine the Young's modulus reduction factor of the concrete being measured during cooling. In the example of FIG. 18 , the reduction factors of the Young's modulus of the concrete being measured during heating can be calculated as 0.28 and 1.00, respectively.

[0111] Alternatively, the unconstrained test specimen 20 may be removed from the storage container 3 after a period of time during which the hydration reaction is considered to have progressed sufficiently, and a separate insulation test may be performed. The timing for removing the unconstrained test specimen 20 from the storage container 3 is when the temperature of the storage container 3 has decreased to the point where the reading of a thermometer installed in the storage container 3 is approximately the same as the temperature of the atmosphere in which the storage container 3 is installed. For example, this may be when 25 days or more have passed.

[0112] The unconstrained test specimen 20 is placed in a thermostatic chamber programmed to generate a temperature history set within a range of, for example, 20°C to 60°C, and the correlation between the measurement value of the first strain sensor 25 attached to the unconstrained test specimen 20 and the temperature is obtained.

[0113] 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).

[0114] The above-mentioned temperature increase and decrease constitute one cycle, and for example, two cycles of temperature change are applied to the unconstrained test specimen 20. Then, under the above-mentioned temperature history, in each time period in which the temperature is maintained (for example, 20°C, 30°C, 40°C, 50°C, and 60°C), the measurement value of the first strain sensor 25 is read at the time when the reading of the thermometer mounted on the unconstrained test specimen 20 becomes stable.

[0115] FIG. 19 is a graph showing the relationship between the measurement value of the first strain sensor 25 and the temperature when the above-mentioned insulation test was performed on the unconstrained test specimen 20 using the concrete of Example 1.

[0116] As mentioned above, this adiabatic test was performed on the unconstrained specimen 20 after a period of time during which the hydration reaction was considered to have progressed sufficiently. Therefore, even if a temperature change is applied to the unconstrained specimen 20 during the adiabatic test, it is considered that additional autogenous shrinkage strain due to the hydration reaction will not occur in the concrete poured into the unconstrained specimen 20. Therefore, the correlation between the measurement value of the first strain sensor 25 and the temperature shown in FIG. 19 can be said to be information reflecting the temperature strain of the concrete poured into the unconstrained specimen 20. As shown in FIG. 19, the temperature and the measurement value of the first strain sensor 25 show an approximately linear correlation. Therefore, the thermal expansion coefficient of the concrete poured into the unconstrained specimen 20, i.e., the concrete to be measured, can be obtained by linearly approximating the correlation between the two using, for example, the least squares method and deriving the slope.

[0117] The measurement value S1 (see FIGS. 13 and 14 ) of the first strain sensor 25 of the unconstrained test specimen 20, measured while the specimen is installed in the storage container 3, reflects the temperature strain and autogenous shrinkage strain based on the temperature history within the storage container 3. As described above in the section on deriving the effective material age, the evaluation device 1 obtains information about the temperature history within the storage container 3. Therefore, by multiplying the temperature change value due to the temperature history by the thermal expansion coefficient of the concrete being measured, the temperature strain value of the concrete being measured, based on the temperature history within the storage container 3, is obtained. By subtracting this temperature strain value from the measurement value S1 of the first strain sensor 25 of the unconstrained test specimen 20, measured while the specimen is installed in the storage container 3, the change in the autogenous shrinkage strain of the unconstrained test specimen 20 over time, i.e., the change in the autogenous shrinkage strain of the concrete being measured over time, can be obtained.

[0118] As described above, a correlation between the age of the concrete in the storage container 3 and the effective age is obtained based on the temperature change inside the storage container 3. Therefore, a 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 in Example 1, which was derived based on the results shown in FIGS. 14 and 19. Information about the correlation between the effective age and autogenous shrinkage strain of the concrete obtained by the above method can be used to evaluate the risk of thermal cracking when an actual structure is constructed using the concrete, using a 3D-FEM analysis.

[0119] Furthermore, as described above, since the temperature change inside the container 3 is obtained, the relationship Ta between the age of the concrete to be measured and the amount of temperature rise can be obtained, for example, as shown schematically in Fig. 21. Therefore, by performing an inverse analysis of this relationship Ta, the adiabatic temperature rise characteristic Tb of the concrete to be measured can be obtained, as shown schematically in Fig. 22.

[0120] As described above, the evaluation device 1 according to the present invention can directly obtain a variety of physical property values ​​related to the concrete to be measured, and can also obtain many more physical property values ​​by performing arithmetic processing using the obtained physical property values. By performing numerical analysis using the many physical property values ​​thus obtained, it is possible to accurately evaluate the risk of thermal cracking in a structure (mass concrete) that uses the concrete to be measured.

[0121] Second Embodiment This embodiment corresponds to an embodiment in which a reduction coefficient of Young's modulus of concrete is estimated while utilizing a predetermined evaluation device for evaluating the properties of concrete to be measured. Specifically, the device is used in a state in which a plurality of test specimens, each having concrete to be measured poured into a predetermined area, are housed inside. When evaluating the properties of the concrete to be measured, the evaluation device 1 described above in the first embodiment can be used. Explanations of the evaluation device 1 and how to use it will be omitted to avoid redundancy.

[0122] As described above, various physical property values, including the reduction coefficient of Young's modulus of the concrete to be measured, can be obtained by the evaluation device 1. By performing numerical analysis using the many physical property values ​​thus obtained, it is possible to accurately evaluate the risk of thermal cracking in a structure (mass concrete) that uses the concrete to be measured.

[0123] In the first embodiment, a case has been described in which physical property values ​​of concrete other than the reduction coefficient of Young's modulus of concrete are derived using the evaluation device 1. However, it is not necessarily necessary to derive physical property values ​​other than the reduction coefficient of Young's modulus of concrete and the physical property values ​​necessary to derive this reduction coefficient.

[0124] Furthermore, the method of installing the strength test specimens 10, unconstrained test specimens 20, and constrained test specimens 30 in the container 3 of the evaluation device 1 described above in the first embodiment is merely an example, and the present invention is not limited to the illustrated arrangement. For example, the strength test specimens 10, unconstrained test specimens 20, and constrained test specimens 30 may all be arranged along the surface of the bottom 3b. Furthermore, for example, the unconstrained test specimens 20 and constrained test specimens 30 may also be arranged along the vertical direction.

[0125] Furthermore, in the above-described first embodiment, a case has been described in which the respective physical property values ​​are measured with the strength test specimen 10, the unconstrained test specimen 20, and the constrained test specimen 30 placed in the same storage container 3. This is intended to realize the same temperature history by storing multiple test specimens, including the strength test specimen 10, the unconstrained test specimen 20, and the constrained test specimen 30, in the same thermally insulated storage container 3, through the temperature rise due to heat generation accompanying the hydration reaction occurring in these test specimens and the temperature decrease due to the convergence of the progress of the hydration reaction.

[0126] In other words, as long as each test specimen (strength test specimen 10, unconstrained test specimen 20, and constrained test specimen 30) can be placed under the same temperature history in the insulated container, these test specimens do not necessarily need to be placed in the same container 3. For example, each test specimen may be placed in a thermostatic chamber programmed to generate a predetermined temperature history, and the reduction factor of Young's modulus of concrete may be derived by a method similar to that of the first embodiment. Furthermore, in this case, physical properties of concrete other than the reduction factor of Young's modulus may also be derived by the method described above in the first embodiment.

[0127] Another embodiment will now be described.

[0128] <1> In the above embodiment, the lid 2 is opened and the strength test specimen 10 is removed upward each time the predetermined material age is reached. However, the direction in which the strength test specimen 10 is removed is not limited to the upward direction. For example, the lid 2 may be positioned to the side, and the strength test specimen 10 may be removed from the side.

[0129] <2> A greater number of strength test specimens 10 than the number of specimens to be taken out at each age and subjected to the above-mentioned tests may be placed in the storage container 3. These extra strength test specimens 10 are used to cause a hydration reaction in the storage container 3 and raise the temperature inside the storage container 3.

[0130] <3> When multiple restraint test specimens 30 are installed in the storage container 3, the restraint stress F may be the average value of the restraint stress for each restraint test specimen 30 derived based on the measurement values ​​of the second strain sensors 35 installed on each restraint test specimen 30.

[0131] Furthermore, in the above, the steel ratios of the restraint steel members 34 mounted on the respective restraint test specimens 30 may be different from each other. In this case, the restraint stress F is calculated based on the measurement values ​​of the second strain sensors 35 mounted on the respective restraint test specimens 30 and the steel ratios of the restraint steel members 34 mounted on the corresponding restraint test specimens 30. The average value of the restraint stresses for each restraint test specimen 30 thus derived may be used as the restraint stress F.

[0132] <4> The number of unconstrained test specimens 20 placed in the storage vessel 3 may be one. Similarly, the number of constrained test specimens 30 placed in the storage vessel 3 may be one.

[0133] <5> 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 to provide a better understanding of the present invention, and the present invention is not necessarily limited to those having all of the configurations described. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0134] REFERENCE SIGNS LIST 1: Evaluation device 2: Lid 3: Storage container 3a: Side of storage container 3b: Bottom of storage container 6: Filler 10: Strength test specimen 11: Cylindrical body 12: Internal space 20: Unconstrained test specimen 21: Frame 23: Internal space 25: First strain sensor 27: Signal line 30: Constrained test specimen 31: Side plate 32: End plate 33: Internal space 34: Constraining steel material 35: Second strain sensor 36: Thermometer 37: Signal line

Claims

1. An evaluation device for evaluating the characteristics of concrete to be measured, comprising: a strength test section including a plurality of first cylindrical bodies into which the concrete can be poured; an unconstrained test section including a first rectangular frame-shaped body with a bottom into which the concrete can be poured; and a second rectangular frame-shaped body with a bottom into which the concrete can be poured, both ends of the second rectangular frame-shaped body in the longitudinal direction being thermally expanded to a thermal expansion coefficient of 1×10 -6 / °C; an insulating containment vessel covering the strength test section, the unconstrained test section, and the unconstrained test section; and a thermometer capable of measuring a temperature change within the containment vessel, wherein the unconstrained test section has a first strain sensor installed inside the first rectangular frame-shaped body, and the constrained test section has a second strain sensor installed on the constraining steel.

2. The evaluation device described in claim 1, characterized in that the storage container is made of a thermal insulating material and has a removable lid, and the strength test section is located closer to the lid than the unconstrained test section and the constrained test section.

3. The evaluation device described in claim 2, characterized in that the storage container has a bottom installed in a position opposite the lid portion and sides covering the bottom from all sides, the unconstrained test section and the constrained test section are arranged in a direction along the bottom, and the multiple first cylindrical bodies included in the strength test section are arranged in a direction along the bottom while being placed directly on top of the first rectangular frame body included in the unconstrained test section and the second rectangular frame body included in the constrained test section.

4. The evaluation device described in claim 1 or 2, characterized in that the strength testing section includes the first cylindrical bodies in a number equal to or greater than twice the number of types of age of concrete to be subjected to the strength test.

5. The evaluation device according to claim 1 or 2, further comprising a heat insulating filler material filled in the spaced apart portions of the plurality of first cylindrical bodies.

6. The evaluation device according to claim 1 or 2, characterized in that the thermometer is attached to the unconstrained test section.

7. A method for evaluating characteristics of concrete using the evaluation device according to claim 1, comprising the steps of: (a) placing, in the storage vessel, an unconstrained test specimen obtained by pouring the concrete into the first rectangular frame-shaped body, a constrained test specimen obtained by pouring the concrete into the second rectangular frame-shaped body, and a plurality of strength test specimens obtained by pouring the concrete into a plurality of the first cylindrical bodies; (b) removing a target age strength test specimen belonging to the plurality of strength test specimens from the storage vessel each time a predetermined age timing arrives, and performing a Young's modulus measurement test on the target age strength test specimen, thereby calculating the change over time in the Young's modulus of the concrete; and (c) calculating the change over time in the constrained strain value of the concrete based on a first strain value which is a measurement value of the first strain sensor possessed by the unconstrained test section in a state where it is placed in the storage vessel, and a second strain value which is a measurement value of the second strain sensor possessed by the constrained test section in a state where it is placed in the storage vessel; A method for evaluating characteristics of concrete, comprising the steps of: (d) calculating a change in the restraint stress of the concrete over time based on a steel ratio, which is the ratio of the restraint steel in the restraint test piece, the Young's modulus of the restraint steel, and the second strain value; (e) calculating an apparent Young's modulus at each of the time of heating and cooling based on the correlation between the restraint strain value and the restraint stress; and (f) deriving a reduction coefficient of the Young's modulus at each of the time of heating and cooling based on the ratio between the Young's modulus obtained in (b) and the apparent Young's modulus obtained in (e).

8. A method for evaluating the characteristics of concrete as described in claim 7, characterized in that it comprises a step (g) of calculating the effective age of the target age strength test specimen at the age timing based on the temperature history inside the storage container measured by the thermometer, and a step (h) of obtaining a correspondence between the age of the concrete corresponding to the age timing and the effective age obtained by step (g).

9. A method for evaluating the characteristics of concrete as described in claim 8, characterized by comprising: a step (i) of conducting a compressive strength test on the target age strength test specimen to obtain a change in the compressive strength of the concrete over time; and a step (j) of obtaining a relationship between the effective age of the concrete and the compressive strength based on the results of the steps (h) and (i).

10. A method for evaluating the characteristics of concrete as described in claim 9, characterized in that it comprises a step (k) of obtaining a relationship between the compressive strength and the Young's modulus of the concrete based on the results of the steps (b) and (i).

11. A method for evaluating the characteristics of concrete as described in claim 9, characterized by comprising: a step (l) of performing a splitting tensile strength test on the target age strength test specimen to obtain the change in the splitting tensile strength of the concrete over time; and a step (m) of obtaining the relationship between the compressive strength and the splitting tensile strength of the concrete based on the results of steps (i) and (l).

12. The method for evaluating characteristics of concrete as described in claim 8, characterized in that it comprises the steps of: (n) removing the unconstrained test specimen from the storage container 25 days or more after step (a), subjecting the specimen to a temperature change in an insulated environment, and obtaining a thermal expansion coefficient of the concrete from the relationship between the temperature and the measurement value of the first strain sensor; (o) calculating a change in temperature strain over time of the concrete based on the change in temperature measured by the thermometer multiplied by the thermal expansion coefficient and the change in the first strain value obtained in step (c); and (p) obtaining a relationship between the effective age of the concrete and the autogenous shrinkage strain based on the results of steps (g) and (o).

13. The method for evaluating the characteristics of concrete as described in claim 7, characterized in that the thermometer is attached to at least one of the unconstrained test section and the constrained test section, and further comprising a step (q) of inversely analyzing the relationship between the age of the concrete and the measurement value of the thermometer to obtain the adiabatic temperature rise characteristics of the concrete.

14. A method for evaluating the characteristics of concrete as described in claim 7, characterized in that the storage container is made of insulating material and has a removable lid, the strength test section is located closer to the lid than the unconstrained test section and the constrained test section, and step (b) includes a step of opening the lid each time the material age timing arrives, removing the target age strength test specimen from the storage container, and placing an amount of insulating filler material in the storage container corresponding to the area occupied by the removed target age strength test specimen.

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