JP2020051812A - Measuring method of heat expansion coefficient of concrete - Google Patents

Abstract

To provide a method capable of easily and accurately measuring a heat expansion coefficient of concrete in a short period.SOLUTION: In a measuring method of a heat expansion coefficient of concrete, using a length change measuring apparatus Eor E, the length change of a concrete specimen per unit temperature change is measured, and a heat expansion coefficient of concrete is acquired.<Length change measuring apparatus E>is a length change measuring apparatus that at least includes one or more laser displacement gauges, a pedestal for supporting a specimen for length change measurement, and a positioning tool of the specimen.<Length change measuring apparatus E>is a length change measuring apparatus that at least includes two or more laser displacement gauges, three or more support members for supporting a specimen for length change measurement, and a pedestal in which a part of the support members is buried.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a method for easily and accurately measuring the thermal expansion coefficient of concrete in a short period of time.

The linear expansion coefficient of concrete is a characteristic value of concrete obtained by measuring a length change occurring when a temperature change is given to concrete and converting the length change per unit temperature change. At present, methods for measuring the coefficient of linear expansion of concrete have not been standardized, and thus many methods have been proposed (Non-Patent Document 1). Among these, the conventional method of measuring the coefficient of linear expansion of concrete is as follows. A concrete specimen of 10 cm × 10 cm × 40 cm, in which drying shrinkage has converged, is sealed with an aluminum tape, placed in a thermostat, and subjected to temperature history. And measuring the change in the length of the concrete with an embedded strain gauge in the specimen, and calculating the change in the length of the concrete per unit temperature change (hereinafter, referred to as “conventional method”). However, in this method, the rate of temperature rise and fall of the specimen is extremely low at 1 ° C./hour in order to prevent temperature cracks, and in order to make the temperature inside the concrete and the surface layer uniform, as shown in FIG. In addition, each time the temperature is raised and lowered by 5 ° C., the temperature must be maintained for 5 hours, and the measurement requires a long time.
In Non-Patent Document 2, the linear expansion coefficient and the like of weak material age of concrete are measured using a laser displacement meter. However, the specimen is as large as 10 × 100 × 400 mm, and can measure only cement paste and simulated concrete (actually, mortar). In addition, the length is measured while changing the water temperature while the specimen is immersed in water. Therefore, only one standard specimen can be measured per apparatus.

"Research Committee Report on Crack Control of Mass Concrete", Edited by the Japan Society of Mixed Concrete Engineers, Architectural Institute of Japan, 91 pages (Table-3.3.2), published February 22, 2006 Teramoto et al., “Study on the Young's Age Linear Expansion Coefficient of Ultra-High Strength Concrete”, Annual Journal of Concrete Engineering, Vol. 29, no. 1, pp. 633-638, 2007

  Therefore, an object of the present invention is to provide a method capable of easily and accurately measuring the thermal expansion coefficient of concrete in a short period of time.

The present inventor has studied a measurement method that meets the above-described object, and as a result, has found that the above object can be achieved by measuring a change in the length of concrete per unit temperature change using a specific length change measurement device. Completed the invention.
That is, the present invention is a method for measuring the thermal expansion coefficient of concrete having the following configuration.

[1] below with reference to the length change measuring device E ₁ or E _2, to obtain a thermal expansion coefficient of the concrete by measuring the length change of the concrete specimen per unit temperature change, method of measuring the thermal expansion coefficient of the concrete .
<Length change measuring device E ₁ >
A length change measuring device including at least one or more laser displacement gauges, a pedestal for mounting a specimen for measuring a length change, and a jig for positioning the specimen <Length change measuring device E ₂ >
Length change measurement including at least two or more laser displacement gauges, three or more support members for supporting a specimen for length change measurement, and a pedestal having a part of the support member embedded therein. Apparatus [2] The method for measuring the thermal expansion coefficient of concrete according to [1], wherein the specimen is a specimen of concrete that has been dried and shrunk, and is a specimen whose entire surface is sealed.
[3] The specimen is a disk-shaped specimen having a diameter of 10 to 30 cm and a thickness of 5 to 20 mm, or a square plate having a length of one side of 10 to 30 cm and a thickness of 5 to 20 mm. The method for measuring the thermal expansion coefficient of concrete as described in [1] or [2] above, which is a sample.

  The method for measuring the thermal expansion coefficient of concrete according to the present invention can easily and accurately measure the thermal expansion coefficient of concrete in a short period of time.

(A) is a figure which shows the pattern of the temperature history (temperature rise and temperature fall) in the conventional method, (B) is the temperature of the concrete using ordinary Portland cement and the rate of change of the length of the specimen measured by the conventional method. FIG. On the one length change measuring device E ₁ having a laser displacement meter, a schematic diagram showing an example of a state of mounting the specimen, a plan view of the left figure the measuring device, the right diagram FIG. 2 is a side view of the measuring device. On the length change measuring device E ₁ with two laser displacement meter, a schematic diagram showing an example of a state of mounting the specimen, a plan view of the left figure the measuring device, the right diagram FIG. 2 is a side view of the measuring device. Some of the lower portion of the support member, on a support member of length change measuring device E ₁ formed by installing a state embedded in the pedestal, a schematic diagram showing an example of a state of mounting the specimen, The left drawing is a plan view of the measuring device, and the right drawing is a side view of the measuring device. However, the description of the laser displacement meter is omitted in FIG. Two laser displacement meter, a schematic diagram showing an example of formed by arranging opposite length change measuring device E _2, plan view of the left figure the measuring device, the right figure the measuring device FIG. FIG. 9 is a schematic diagram showing an example of a length change measuring device E2 in which _two laser displacement meters are arranged so that lasers emitted from the laser displacement meters intersect at an angle of 90 °. Is a plan view of the measuring device, and the right diagram is a side view of the measuring device. However, the description of the laser displacement meter located behind the paper is omitted. Four laser displacement meter, a laser irradiated from the laser displacement meter is arranged so as to intersect at an angle of 90 °, a schematic diagram showing an example of length change measuring device E _2, left Is a plan view of the measuring device, and the right diagram is a side view of the measuring device. However, the laser displacement gauges located forward and backward with respect to the paper surface are omitted. The length change measuring device E _2, is a photograph showing a state of mounting the specimen. Note that the pin at the center of the pedestal in (A) is not a supporting member but a screw for fixing the pedestal. (A) and (B) are diagrams illustrating the relationship between the temperature and the rate of change of the length of the test sample in Examples 1 and 2, respectively. Also, the regression coefficients in each figure represent the linear expansion coefficients. (C) and (D) are diagrams showing the relationship between the temperature and the rate of change of the length of the test sample in Examples 3 and 4, respectively. Also, the regression coefficients in each figure represent the linear expansion coefficients. (E) and (F) are diagrams showing the relationship between the temperature and the rate of change of the length of the test sample in Examples 5 and 6, respectively. Also, the regression coefficients in each figure represent the linear expansion coefficients. (G) is a diagram showing the relationship between the temperature and the rate of change of the length of the test piece in Example 7. Also, the regression coefficients in each figure represent the linear expansion coefficients.

The present invention is, using said length change measuring device E ₁ or E _2, to obtain a thermal expansion coefficient of the concrete by measuring the length change of concrete per unit temperature change, the measuring method of the coefficient of thermal expansion of the concrete is there.
Hereinafter, the present invention will be described in detail with respect to a length change measuring device and a method for measuring the coefficient of thermal expansion of concrete.

1. Change the length measuring device E ₁
As illustrated in FIGS. 2 to 4, the length change measuring device E ₁ includes one or more laser displacement meters 4, a pedestal 2 on which a test piece for measuring a length change is mounted, and the test piece 1. It is a device including at least the positioning jig 3 of FIG.
The laser displacement meter is not particularly limited, and examples thereof include a commercially available laser displacement meter such as a reflection type or a transmission type. In the present invention, if the number of laser displacement meters is increased, the number of data is increased, and the measurement accuracy is improved accordingly, but the cost of the apparatus is high. Therefore, the number of laser displacement meters is preferably 1 to 4, more preferably. Preferably, the number is 2 to 4. The laser displacement meter is installed so as to be able to irradiate a laser toward the center of a disk-shaped (FIGS. 2 to 4) or square-plate-shaped specimen placed on a base. The installation position of the laser displacement meter is, for example, the position shown in FIGS. 2 and 3.

The pedestal 2 is used for mounting a specimen for measuring a change in length. The shape of the pedestal is not particularly limited, and is, for example, a square plate shape or a disk shape shown in FIGS. Further, it is preferable that the pedestal be kept horizontal to improve the measurement accuracy.
Further, the pedestal is preferably manufactured using an Invar steel material in order to prevent deformation due to heat or impact. Further, the pedestal may be provided with a support member 5 for supporting the specimen. When the support member is provided, the transfer of heat between the specimen and the pedestal can be cut off or reduced, so that the measurement accuracy of the length change is improved.
The shape of the support member is not particularly limited, and examples thereof include a spherical shape as shown in FIG. 4 (in FIG. 4, a part of the lower portion of the support member is embedded in the pedestal), a columnar shape, and the like. When the support member is formed in a columnar shape, preferably, the surface of the support member in contact with the specimen is made hemispherical so as to come into contact with the specimen at a point.
The number of the support members is preferably three or more so that the specimen can be stably mounted. It should be noted that if the number of support members is increased, it takes time and effort to manufacture the apparatus. Therefore, the number of support members is preferably three or four. In addition, it is preferable that the support member is installed so as to form an equilateral triangle or a square in order to stably mount the specimen. FIG. 4 shows an example in which the support members are installed so as to form a square. Further, the support member is preferably manufactured using an Invar steel material in order to prevent deformation due to heat or impact.

The positioning jig 3 is used to determine and fix the mounting position of the specimen when measuring the length change of the specimen. For example, as shown in FIG. 2 and FIG. For example, two pins or the like which are installed in an inverted state are exemplified. In FIGS. 2 and 3, when the disk-shaped specimen is placed on the pedestal, the positioning jig of the disk-shaped specimen is adjusted so that the center of the disk-shaped specimen coincides with the center of the pedestal. Install in a position where it comes into contact with the surrounding side surface. In addition, the said positioning jig may be installed in the outer side of a pedestal other than on a pedestal. Further, the positioning jig is preferably manufactured using an Invar steel material in order to prevent deformation due to heat or impact.
Further, it is preferable that the length change measuring device (E ₁ ) is configured by integrally integrating the laser displacement meter, the pedestal, and the positioning jig using the base. The laser displacement meter, the pedestal, the positioning jig, and the base used to install them are preferably manufactured using invar steel to prevent deformation due to heat or impact.

2. Measurement method The method of measuring the length change with length change measuring device E ₁ has, on a length change measuring device E ₁ base, a specimen of the disk-shaped or rectangular plate, surrounding該供piece After placing it so that the side of the sample comes in contact with the positioning jig, irradiate the laser to the side surface around the specimen using a laser displacement meter, and measure the distance between the laser displacement meter and the side surface around the sample. This is a method of measuring the change in the length of the test sample by measuring.
When the specimen has a disk shape, if the diameter of the specimen is 10 to 30 cm, the production of the specimen is easy, and, as described later, the inside and the surface of the specimen which is left standing in a thermostat. Temperature becomes uniform in a short time. The diameter of the specimen is more preferably 10 to 20 cm. Further, if the thickness of the specimen is 5 to 20 mm, the specimen is unlikely to be broken, and the temperature of the inside and the surface of the specimen which is left in a constant temperature bath becomes uniform in a short time. The thickness of the test piece is more preferably 6 to 18 mm, further preferably 7 to 15 mm, and particularly preferably 8 to 12 mm.
When the specimen is a square plate, the length of one side of the square plate is preferably 10 to 30 cm, more preferably 10 to 20 cm, and still more preferably 10 to 30 cm. It is a square, particularly preferably a square having a side length of 10 to 20 cm. If the length of one side is 10 to 30 cm square, the production of the specimen is easy, and the temperature of the inside and the surface of the specimen which is left in the constant temperature bath becomes uniform in a short time. Further, the thickness of the square plate-shaped specimen is preferably 5 to 20 mm, more preferably 6 to 18 mm, still more preferably 7 to 15 mm, and particularly preferably 8 to 12 mm. If the thickness of the test piece is 5 to 20 mm, the test piece is hard to crack, and the temperature of the inside and the surface of the test piece that is left standing in the thermostat becomes uniform in a short time.
Incidentally, when the support member to the length change measuring device E ₁ seat is installed, on the support member, as the side surface of the periphery of the specimen of the disk-shaped or rectangular plate is in contact with the positioning jig Then, the specimen is placed.

In the measurement method, for example, after the specimen is allowed to stand in a constant temperature bath, the inside of the constant temperature bath is 30 ° C. → 50 ° C. → 70 ° C. → 50 ° C. → 30 ° C. in the order of 1 to 3 hours, preferably 1.5 ° C. The sample is held for up to 2.5 hours, and at the end of the holding time at each temperature, the change in the length of the test sample is measured to determine the rate of change in the length. Further, in order to eliminate the influence of drying shrinkage, the sample is preferably a sample whose drying shrinkage has been completed (saturated) and whose entire surface is sealed. The test specimen can be sealed, for example, by covering it with an aluminum tape.
Then, in order to improve the measurement accuracy of the change in length, the specimen is preferably disk-shaped, and the specimen is rotated clockwise or counterclockwise, and the side surface around the specimen is positioned. While in contact with the tool, measure the distance between the laser displacement meter and the peripheral side surface of the specimen twice or more, preferably 3 to 5 times. For example, after measuring the point a of the specimen shown in FIG. 1, the specimen is rotated 90 ° clockwise to measure the point b, and further rotated clockwise 90 ° to measure the point c. The average value of the points is determined as a change in length.

Further, in order to more accurately measure the change in length, the measuring method of the present invention places a metal plate (base plate) having the same shape and dimensions as the specimen on the pedestal, and uses a laser displacement meter. After measuring the distance (L ₁ ) between the side surfaces of the metal plate, the specimen is placed on a pedestal instead of the metal plate, and the distance (L ₁ ) between the laser displacement meter and the side surface of the specimen is measured. ₂ ) is measured, and a change in length is obtained based on the difference (L ₁ −L ₂ ) between L ₁ and L ₂ .
In addition, when using a measuring device in which the measured distance is displayed on a screen, the measuring method of the present invention includes placing a metal plate (base plate) having the same shape and dimensions as the specimen on a pedestal. After measuring the distance between the laser displacement meter and the side surface of the metal plate, setting the distance (indicated by zero) to zero, placing the specimen on a pedestal in place of the metal plate, This method measures the distance between the displacement meter and the side surface of the specimen to determine the change in length.
The metal plate (base plate) is preferably a metal of the same material as the pedestal so that the change in length due to a change in temperature is the same, and in order to prevent deformation due to heat or impact, more preferably an invar steel material It is.

3. Change the length measuring device E ₂
Length change measurement unit E _2, as illustrated in Figures 5-8, two or more laser displacement gauge 4, the support member of the above three points for supporting the specimen for length change measurements 5, and And a pedestal 2 in which a part of the support member is embedded.
The laser displacement meter is the same as the laser displacement meter length change measuring device E _1. In addition, two or more laser displacement meters are installed in order to improve the measurement accuracy of the length change. With one laser displacement meter, there is a possibility that the measurement accuracy of the length change is reduced. Further, if the number of laser displacement meters is increased, the number of data is increased, and the measurement accuracy is further improved, but the cost of the apparatus is increased. Therefore, two to six laser displacement meters are preferably installed, and more preferably two to four laser displacement meters are installed.

Since the laser displacement meter improves the measurement accuracy of the change in length and facilitates the placement of the specimen, it is preferable to irradiate the laser at a position equidistant from the center of the equilateral triangle or square formed by the support member. Place the surface facing the center. Further, in order to further improve the measurement accuracy of the length change, more preferably, two to six of the laser displacement meters, so that the laser emitted from the laser displacement meter intersects at an angle of 60 to 300 °. Deploy.
When two laser displacement meters are installed, for example, when two laser displacement meters are installed, the laser displacement meters are installed facing each other as shown in FIG. 5 or the laser is moved 90 ° as shown in FIG. When four laser displacement meters are installed so as to intersect with each other at two angles, as shown in FIG. 7, two sets of laser displacement meters are installed facing each other.

In the length change measuring device (E ₂ ), the supporting member is an indispensable jig, and is used to separate the specimen from the pedestal and provide a space between the specimen and the pedestal. By providing this space, it is possible to reduce a decrease in the temperature of the specimen when measuring the change in length.
The shape of the support member, the number, arrangement to form (the shape of the position), and the material is the same as the length change measuring device E _1.

The pedestal is formed by burying and fixing a part (lower part) of the support member. Incidentally, the pedestal shown in FIGS. 5 to 7 has a square plate shape, and the pedestal shown in FIG. 8 has a disk shape. Incidentally, it is preferable that the base is kept horizontal, the material it Invar steel is preferable is the same as the length change measuring device E _1.

In length change measuring device E _2, to facilitate the placement of the specimen onto the supporting member, it may be used specimen mounting-interpolation Sukeji tool. As the test object placing auxiliary jig, there are two pins installed outside the pedestal as shown in FIG. On the length change measuring device E ₂ of the support member of FIG. 8, for example, when placing a disc-shaped specimens having a diameter of 10 cm, the supporting member the specimen to contact the two pins By placing the sample on the sample, the sample can be placed so that the center of the sample matches the center of the square formed by the support member.
In addition, as shown in FIG. 8, the test object placing auxiliary jig may be installed on the outside of the pedestal, or may be installed on the pedestal. In addition, the test piece placing auxiliary jig is preferably manufactured using an invar steel material in order to prevent deformation due to heat or impact.

As shown in FIGS. 5 to 8, the length change measuring device (E ₂ ) also includes two or more laser displacement gauges, a pedestal, and, if necessary, a test object mounting assisting jig. Is preferred. The material of the pedestal such that Invar steel is preferable is the same as the length change measuring device E _1.

4. Measurement method The method of measuring the length change with length change measuring device E ₂ comprises a support member of the length change measuring device E _2, the center of the disk-shaped or square pillar of the specimen, the support member After placing it so that it coincides with the center of the equilateral triangle or square formed by the laser, irradiate the laser to the side surface around the specimen using a laser displacement meter, and place it between the laser displacement meter and the side surface around the specimen. Is a method of obtaining a change in the length of a test specimen by measuring the distance of the specimen.
For example, as shown in FIG. 8, on the support member length change measuring device E ₂ (4 points spherical on the base), the specimen of the disk-shaped, is formed around the support member該供piece After placing so that the centers of the squares coincide (FIG. 8 (B)), a laser is applied to the side surface around the specimen using a laser displacement meter, and the laser displacement meter and the side surface around the specimen are irradiated. By measuring the distance between them, the length change of the specimen is measured.
The shape, size, and thickness of the specimen are the same as those in the case of the method of measuring the length change using the length change measuring device (E ₁ ).
In the measurement method, for example, after the specimen is allowed to stand in a constant temperature bath, the inside of the constant temperature bath is 30 ° C. → 50 ° C. → 70 ° C. → 50 ° C. → 30 ° C. in order of 1 to 3 hours, preferably 1 to 3 hours. The sample is held for 0.5 to 2.5 hours, and at the end of the holding time at each of the above temperatures, the change in the length of the specimen is measured, and the rate of change in the length is obtained. Further, in order to eliminate the influence of drying shrinkage, the sample is preferably a sample whose drying shrinkage has been completed (saturated) and whose entire surface is sealed. The test specimen can be sealed, for example, by covering it with an aluminum tape.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.
1. Materials used (1) Cement (i) Ordinary Portland cement (abbreviation: NC)
(Ii) Blast furnace cement type B (abbreviation: BB)
(Iii) Moderate heat Portland cement (abbreviation: MC)
(Iv) Low heat Portland cement (abbreviation: LC)
The cements are all manufactured by Taiheiyo Cement Corporation.
(2) Expanding material (abbreviation: EX)
Pacific Hyperexpan (Pacific Materials)
(3) Shrinkage reducing agent (abbreviation: SR)
Tetraguard AS21 (manufactured by Taiheiyo Materials Corporation)
(4) Fine aggregate (abbreviation: S)
Mountain sand, surface dry density 2.56 g / cm ³
(5) Coarse aggregate (i) Crushed sandstone, surface dry density 2.61 g / cm ³ (abbreviation: G1)
(Ii) Lime crushed stone, surface dry density 2.71 g / cm ³ (abbreviation: G2)
(6) Water (abbreviation: W)
Tap water (7) water reducing agent (abbreviation: LS)
Lignin sulfonic acid AE water reducing agent, trade name Pozzolith No. 70 [registered trademark], BASF (8) AE agent Trade name Master Air 404 [registered trademark], manufactured by BASF

2. Preparation of Concrete Specimen for Measurement of Length Change According to the composition shown in Table 1, the above-mentioned materials were collectively charged into a pan-type mixer having a capacity of 50 liters and kneaded for 2 minutes. The concrete was obtained by casting into a mold having a height of 20 cm. The amount of the AE agent was adjusted so that the amount of air in the concrete was 4.5% and the slump was 15 cm.
Next, the concrete was subjected to wet-air curing at 20 ° C. for 1 day, then demolded, and further cured in water at 20 ° C. for 7 days. After curing in water, the vicinity of the center in the height direction of the concrete was cut off, and three concrete disks each having a diameter of 10 cm and a thickness of 1 cm were prepared for each composition, for a total of 6 × 3 = 18.
Until the drying shrinkage of the disk is completed, the disk is dried in an environment of 20 ° C. and a relative humidity of 60 ± 5% for 56 days except for the compound N-SR. After drying in an environment at 60 ° C. and a relative humidity of 60% for 91 days, the entire surface of the disk was covered with an aluminum tape to prepare a specimen for measuring a change in length.

3. After the specimen with length change measuring device E ₁ measuring the specimen length change allowed to stand for 1 hour at 20 ° C., the side surface surrounding the該供specimen is, length change measuring apparatus shown in FIG. 2 so as to contact the positioning jig 3 of E _1, while placing the specimen 1 to the base 2, using a laser displacement gauge 4, the distance between the peripheral side surface of the specimen with a laser displacement meter ( Base length) was measured. Next, after the specimen was allowed to stand in a thermostat, the interior of the thermostat was maintained in the order of 30 ° C. → 50 ° C. → 70 ° C. → 50 ° C. → 30 ° C. for 2 hours, respectively. Was measured and the rate of change in length was determined. In this example, the distance between the laser displacement gauge and the side surface around the test sample was measured at three places (points a, b, and c in FIG. 2) for one test sample. The average value was calculated as a change in the length of the test sample, and the changes in the length (average value) of the three test samples were averaged to obtain the linear expansion coefficients (per unit temperature) of Examples 1 to 7. Of the specimen).
For comparison, a specimen (10 cm × 10 cm × 40 cm) whose drying shrinkage had converged was sealed with an aluminum tape and placed in a thermostat using a conventional method, and the temperature history shown in FIG. Given, measure the change in length of the specimen using an embedded strain gauge in the specimen, calculate the change in length of the specimen per unit temperature change, and determine the linear expansion coefficients of Comparative Examples 1 to 7. Was.
The results are shown in Table 2 and FIGS.

As shown in Table 2, the linear expansion coefficient of the concrete is very small at 3.9% or less between the method of measuring the thermal expansion coefficient of the present invention and the conventional method, and almost the same value is obtained. In the conventional method, the measurement time of the length change rate requires 7 days as shown in FIG. 1A, but in the present invention, it is 18 hours (= 30 ° C. → 50 ° C. → 70 ° C. → 50 ° C. → 30 ° C.). The temperature is maintained for 2 hours in the order of ° C., and the temperature rise and fall of the constant temperature bath is completed in an extremely short time of 8 hours (rate of temperature rise and fall of 10 ° C./hr).
In addition, in the conventional method, since the measurement requires seven days, from the start to the end of the measurement, the hydration of the concrete progresses, and the physical properties of the concrete change, and as shown in FIG. A different straight line is obtained in the process and the cooling process, and a difference occurs in the coefficient of thermal expansion (the slope of the straight line). On the other hand, in the present invention, since the measurement time is as short as 12 hours, the difference in the coefficient of thermal expansion is small.

1 Specimen 2 Pedestal 3 Positioning jig 4 Laser displacement meter (However, black arrow indicates laser.)
5 Supporting members

Claims (3)

Using the following length change measuring device E ₁ or E _2, to obtain a thermal expansion coefficient of the concrete by measuring the length change of the concrete specimen per unit temperature change, method of measuring the thermal expansion coefficient of the concrete.
<Length change measuring device E ₁ >
A length change measuring device including at least one or more laser displacement gauges, a pedestal for mounting a specimen for measuring a length change, and a jig for positioning the specimen <Length change measuring device E ₂ >
Length change measurement including at least two or more laser displacement gauges, three or more support members for supporting a specimen for length change measurement, and a pedestal having a part of the support member embedded therein. apparatus   The method for measuring the thermal expansion coefficient of concrete according to claim 1, wherein the specimen is a concrete specimen whose drying and shrinkage has been completed, and a specimen whose entire surface is sealed.   The specimen is a disk-shaped specimen having a diameter of 10 to 30 cm and a thickness of 5 to 20 mm, or a square plate-shaped specimen having a length of one side of 10 to 30 cm and a thickness of 5 to 20 mm. The method for measuring the coefficient of thermal expansion of concrete according to claim 1 or 2.