JP6118129B2 - Linear expansion coefficient test method - Google Patents

Description

  The present invention relates to a linear expansion coefficient test method for determining a linear expansion coefficient of concrete or the like.

  In a structure such as a reinforced concrete structure, when a mass concrete member having a large cross-sectional dimension is used, there is a problem that temperature cracking occurs due to the temperature rise and fall of concrete due to the heat of hydration of cement.

  One of the physical properties of concrete that greatly affects such temperature cracks is the coefficient of linear expansion. The coefficient of linear expansion means the amount of change in length that occurs when the temperature changes by 1 ° C. The smaller the value, the less likely the temperature cracks to occur. The linear expansion coefficient of general concrete is about 10μ / ° C, but it has been revealed that it varies greatly due to the influence of aggregates and cement types, blending, etc., and the linear expansion of concrete during construction of mass concrete members It is important to know the coefficients.

  As a method for measuring the linear expansion coefficient, for example, there is one defined as JIS A 1325 “Method for measuring linear expansion coefficient of building materials”. In addition, a strain gauge installed in a stress-free container that cuts off the edge of the actual structure or full-scale mock test specimen is embedded in the process of temperature rise and fall due to the heat of hydration of concrete. There is also a method of calculating the linear expansion coefficient from the behavior of temperature and strain. Thereby, the linear expansion coefficient which directly affects the temperature crack of mass concrete is obtained (refer nonpatent literature 1).

  Further, Patent Document 1 discloses a mold for covering the outer surface with an air layer forming body and pouring a hydraulic material into the internal space for curing and solidifying, and a thermometer and strain provided in the internal space of the mold. An apparatus for calculating the linear expansion coefficient of a hydraulic material provided with a meter is described.

  By the way, inside the mass concrete as described above, only the heat of hydration generated from the concrete material becomes the heating source of the concrete. As an example of simulating such a state, Patent Document 2 describes that a concrete specimen after kneading is placed in an internal space sealed with a heat insulating material wall to perform heat insulation curing. Describes a method of estimating the structure strength by covering the small specimen immediately after placement with a heat insulating material to insulate, measuring the strength of the small specimen by giving a temperature history close to that of a large section concrete structure Has been.

Takahiro Shigaki, Kenji Funamoto, Manabu Terahara, Tetsuaki Kameya, Tomohiro Tsuda, Hirotoshi Ishuin, Shusuke Kuroiwa: Temperature and stress measurement of buildings using low heat Portland cement, Summary of Academic Lectures of Architectural Institute of Japan, A-1 497-502, 2008.7

JP 2009-58326 A JP-A-6-201548 JP-A-2-3000064

  The conventional linear expansion coefficient measuring method has a problem that it is difficult to apply at a practical level. For example, JIS A 1325 “Measuring method of linear expansion coefficient of building materials” requires special equipment that varies the environmental temperature. Further, in the method using a full-scale simulation test body or the like as in Non-Patent Document 1, a large-scale experiment space is required. Therefore, it is difficult to use these methods at a construction site or a ready mixed concrete factory at a practical level.

  On the other hand, the linear expansion coefficient calculating device of Patent Document 1 does not simulate the thermal environment inside mass concrete where only the heat of hydration serves as a heating source. In Patent Documents 2 and 3, the concrete is cured in an adiabatic state. However, the linear expansion coefficient of concrete could not be measured.

  The present invention has been made in view of the above-described problems, and its purpose is to provide a linear expansion coefficient test method that can perform a test imitating the thermal environment in mass concrete and easily obtain the linear expansion coefficient. It is to be.

In order to achieve the above-mentioned object, the present invention arranges a specimen made of a hardened cement body in which a thermometer and a strain gauge are embedded in a heat insulating curing container using a heat insulating material, and generates water generated inside the hardened cement body. This is a linear expansion coefficient test method characterized by measuring the change over time in temperature and strain due to sum heat , linearly approximating the change in strain when the temperature drops, and calculating the slope as the linear expansion coefficient .

  In the present invention, by using a heat-insulating curing container having high heat insulation performance, only the heat of hydration reproduces the thermal environment inside the mass concrete that becomes a heating source, so that the container itself can be miniaturized and a small amount of cement can be cured. The body's heat of hydration can provide a temperature history similar to that inside the full-scale simulated specimen. In this way, by measuring the temperature and strain in the process of temperature rise and fall due to heat of hydration of the hardened cement body, it is possible to easily conduct tests at construction sites, ready mixed concrete factories, etc., and obtain the linear expansion coefficient . In addition, since the test can be performed indoors by downsizing the test apparatus, highly accurate evaluation can be performed without being affected by the outside air temperature. As described above, according to the present invention, a low-cost and simple linear expansion coefficient test method that can be carried out at a practical level is realized, high-accuracy analysis can be performed for temperature cracks in mass concrete, and cracks in mass concrete can be reduced. It is possible to select concrete mixes that are effective in

  A plurality of specimens in which a hardened cement body is placed in a mold are arranged inside the heat insulation curing container, and at least one of the plurality of specimen bodies includes a thermometer and a strain gauge embedded in the hardened cement body. It is desirable.

  The test can be easily performed by using a specimen in which a hardened cement body is placed on a mold. Moreover, when a plurality of specimens are placed and the number of hardened cement bodies in the heat-insulating curing container is increased, a remarkable temperature increase due to heat of hydration can be obtained as compared with the case where a single specimen is arranged.

It is desirable to determine the total amount of the hardened cement body to be arranged inside the heat insulation curing container by the following formula.
V ≧ −0.62 · R + 22
here,
V: Total amount of hardened cement (L)
R: Thermal resistance value of heat insulating material (m ² · K / W)

  In the heat-insulating curing container, the amount of necessary cement hardened body can be reduced and the heat-insulating curing container can be downsized as the heat insulating material having higher heat insulating performance is used. The amount of hardened cement required depends on the heat resistance value of the heat insulating material, and by setting as described above, a temperature history comparable to that of a full-scale simulated test specimen can be obtained.

  It is desirable that a thermometer and a strain gauge are embedded in the hardened cement body in each of the specimen located closer to the center in the heat insulation curing container and the specimen farther from the center.

  Thereby, a linear expansion coefficient can be evaluated based on the difference in the test result by the arrangement | positioning conditions of the test body in an insulation curing container. For example, when the results of a plurality of specimens are averaged, the linear expansion coefficient can be evaluated more suitably.

  It is desirable to arrange a heat insulating material in a space other than the specimen in the heat insulating curing container.

  If the remaining space in which the specimen is placed in the heat-insulating curing container is filled with a heat insulating material such as polystyrene foam beads, the heat insulating performance can be further improved, and the linear expansion coefficient test can be performed more suitably.

  ADVANTAGE OF THE INVENTION According to this invention, the test which simulated the thermal environment inside mass concrete can be performed, and the linear expansion coefficient test method which can obtain | require a linear expansion coefficient simply can be provided.

Perspective view of heat insulation curing container 1 Cross section of heat insulation curing container 1 Cross section of specimen 2 The figure which shows typically the change over time of the temperature and strain amount of the cement hardened body 20 The figure which shows another example of this embodiment The figure explaining Example 1 The figure explaining Example 1 The figure explaining Example 2 The figure which shows the full-scale simulation specimen 30 The figure which shows the heat insulation curing container 40 The figure which shows an example of the temperature history of cement hardening body, and the change over time of the temperature and strain amount of the cement hardening body The figure explaining Example 2

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(1. Insulation curing container)
The heat insulation curing container 1 used with the linear expansion coefficient test method of this embodiment is demonstrated using FIG. FIG. 1 is a perspective view of the heat insulating curing container 1, FIG. 1 (a) shows a state in which the lid portion 13 is opened, and FIG. 1 (b) shows a state in which the lid portion 13 is closed.

  As shown in FIG. 1, the heat-insulating curing container 1 is composed of a box-shaped main body portion 11 having an upper portion as an opening and a lid portion 13. A heat insulating material is used for each surface of the main body 11 and the lid 13. As the heat insulating material, for example, a material having high heat insulating performance such as polystyrene foam, urethane foam, vacuum heat insulating material or the like is used.

(2. Specimen)
2 is a cross-sectional view of the heat-insulating curing container 1, FIG. 2 (a) is a horizontal cross-sectional view along line BB in FIG. 2 (b), and FIG. 2 (b) is a cross-sectional view of FIG. It is sectional drawing of the perpendicular direction along line AA. As shown in FIG. 2, a plurality of specimens 2 are arranged in the internal space of the main body 11. In the illustrated example, a total of nine rows are arranged in three vertical rows and three horizontal rows.

  FIG. 3 is a diagram showing in detail the cross section of the specimen 2 in the vertical direction. As shown in FIG. 3 (a), the specimen 2 is obtained by placing a hardened cement body 20 after kneading inside a lightweight mold 24. The lightweight mold 24 is a cylindrical mold having an open top, such as tin or plastic.

  The hardened cement body 20 is concrete, mortar, cement paste, or the like, and the temperature rise due to heat of hydration using Portland cement as a binder, or an additive such as blast furnace slag or fly ash added to the binder. Refers to all that can be expected.

  In at least one of the specimens 2, as shown in FIG. 3B, a strain gauge 21 and a thermometer 23 are embedded in the hardened cement body 20. The strain gauge 21 is, for example, a strain gauge, and the thermometer 23 is, for example, a thermocouple. In the present embodiment, a strain gauge 21 and a thermometer 23 are embedded in the hardened cement body 20 with a specimen 2a (see FIG. 2A) in the center of the container.

(3. Linear expansion coefficient test method)
As the linear expansion coefficient test, as shown in FIG. 1 (b), the lid 13 of the heat-insulating curing container 1 is closed, and the strain cement 21 and the thermometer 23 are used to immediately after placing the hardened cement body 20. In the course of temperature increase and decrease due to heat of hydration, the change over time of the temperature and strain amount of the hardened cement body 20 is measured.

  FIG. 4 schematically shows changes over time in the temperature and strain amount of the hardened cement body 20. In the present embodiment, the strain change at the time of temperature drop can be linearly approximated from the change over time shown in the figure, and the slope can be calculated as the linear expansion coefficient.

  Note that the strain gauge 21 and the thermometer 23 can be provided by a plurality of specimens 2. In this case, it is preferable to provide the strain gauge 21 and the thermometer 23 at least with the specimen 2 located closer to the center in the heat-insulating curing container 1 and the specimen 2 located farther from the center. For example, in FIG. 2 (a), the strain gauge 21 and the specimen 2 at the corner and the specimen 2 at the corner, or the specimen 2 at the center of the side and the specimen 2 at the corner. A thermometer 23 is provided.

  Thereby, a linear expansion coefficient can be evaluated based on the difference in the test result by the arrangement | positioning conditions of the test body 2 in the heat insulation curing container 1. FIG. For example, if the linear expansion coefficient of the cement cured body 20 in each specimen 2 is averaged, the linear expansion coefficient can be evaluated more accurately.

  As described above, in the present embodiment, by using the heat insulating curing container 1 having high heat insulating performance, the temperature condition inside the mass concrete where only the heat of hydration is a heating source is reproduced, so the container itself is downsized. In addition, the hydration heat of a small amount of the hardened cement body 20 can provide a temperature history comparable to that of the actual full-scale simulated test body. By measuring the temperature and strain in the process of temperature rise and fall due to heat of hydration of the hardened cement body 20 in this way, it is possible to easily conduct tests at construction sites, ready mixed concrete factories, etc., and obtain linear expansion coefficients. it can. In addition, since the test can be performed indoors by downsizing the test apparatus, highly accurate evaluation can be performed without being affected by the outside air temperature.

  From the above, a low-cost and simple linear expansion coefficient test method that can be carried out at a practical level is realized, high-accuracy analysis of temperature cracks in mass concrete is possible, and concrete mixing is effective in reducing cracks in mass concrete. Selection becomes possible.

  Further, in the present embodiment, the test can be easily performed by using the lightweight mold 24 stuffed with the hardened cement body 20 as the specimen 2. Further, when a plurality of specimens 2 are arranged in the container and the number of the hardened cement bodies 20 is increased, a remarkable temperature increase due to heat of hydration can be obtained as compared with the case where a single specimen 2 is arranged. This has also been confirmed in examples described later.

  However, this invention is not restricted to this, For example, as shown to Fig.5 (a), a cement hardening body can be laid in the whole inside of the heat insulation curing container 1, and it can also be set as the test body 2. FIG. Moreover, as shown in FIG.5 (b), the heat insulation performance can be improved further by stuffing heat insulation materials 25, such as beads made from a polystyrene foam, in the space other than the specimen 2 in the heat insulation curing container 1, and more suitable. A linear expansion coefficient test can be performed.

  Next, the results of studying the linear expansion coefficient test method of the present invention will be described as examples. However, the present invention is not limited to this.

[Example 1; relationship between thermal resistance value of heat insulating material and quantity of hardened cement body]
In Example 1, the test for examining the optimal value was conducted about the relationship between the heat resistance value of the heat insulating material of a heat insulation curing container and the quantity of hardened cement bodies.

  In Example 1, a plurality of different levels were prepared for the thermal resistance value of the heat insulating material and the quantity of the hardened cement body, and the internal temperature was measured immediately after placing the hardened cement body to compare the maximum temperatures. As a specimen, an experiment was performed by placing a cement hardened body BL having a composition shown in FIG. 6A on the lightweight mold described in FIG.

  As the heat insulation container, as shown in FIG.6 (b), the three heat insulation containers A, B, and C from which the heat resistance value of a heat insulating material differs were prepared. In addition, the number of hardened cement bodies was changed in four ways as shown in FIG. 6B by changing the number of specimens arranged in the heat insulation curing container.

  Further, as a comparative example, a simulated test body was prepared in which a hardened cement body having a size of 1000 mm long × 1000 mm wide × 800 mm high was placed in a mold. A thermometer was placed in the hardened cement body, and the maximum temperature obtained from the internal temperature history immediately after placement was regarded as the true value.

  The result is shown in the item “maximum temperature” in FIG. The maximum temperature of the cement-cured body of the specimen in each heat-insulating curing container is approximately close to the maximum temperature of the simulated specimen, and the temperature history inside the cement-cured body of the full-scale simulated specimen is insulated. It was found that the specimens in the curing container were successfully simulated.

  Among these, No. 6 in FIG. The maximum temperature of the hardened cement body under the conditions indicated by 1, 2, 5, 6, 7, 9, and 10 is 90% or more of the maximum temperature of the simulated test body, which is particularly good. I understand that.

  FIG. 7 shows the above results in a graph with the thermal resistance value of the heat insulating material as the horizontal axis and the quantity of the hardened cement body as the vertical axis. The plot indicated by the circle in FIG. 1, 2, 5, 6, 7, 9, 10 are shown, and the plots shown by squares are No. The data of 3, 4, 8, 11, 12 are shown.

Here, the straight line in the graph indicates the condition for separating both data, and the following equation (1)
V = −0.62 × R + 22 (1)
It was found that V is the quantity (L) of hardened cement, and R is the thermal resistance value (m ² · K / W) of the heat insulating material.

  As described above, from the test results of Example 1, as the thermal resistance value R of the heat insulating material is larger and the quantity V of the hardened cement body is larger, a temperature history closer to a full-scale simulated specimen is obtained. It was found that a particularly preferable condition in is represented by V ≧ −0.62 × R + 22.

[Example 2; Verification of accuracy of linear expansion coefficient]
As Example 2, a test for verifying the accuracy of the linear expansion coefficient obtained by the linear expansion coefficient test method of the present invention was performed.

  In Example 2, three types of hardened cement NS, NL, and BL whose formulation is shown in FIG. 8 were used for the test. For each hardened cement body, the linear expansion coefficient obtained from the linear expansion coefficient test using a full-scale simulated specimen was regarded as a true value, and this was compared with the linear expansion coefficient obtained from the linear expansion coefficient test of the present invention. .

  FIG. 9 shows a full-scale simulation specimen 30. 9A is a horizontal cross-sectional view along line DD in FIG. 9B, and FIG. 9B is a vertical cross-sectional view along line CC in FIG. 9A. is there. The simulated test body 30 was a cement cured body having a length of 1000 mm × width of 1000 mm × height of 800 mm, and this was placed in a mold (not shown). Styrofoam 32 was disposed on the upper and lower surfaces of the simulated specimen 30 as a heat insulating material.

  Inside the simulated test body 30, a thermometer and a strain gauge (not shown) installed in a stress-free container 31 that cuts the edge with the surrounding cemented body was embedded at the position shown in the figure. And the linear expansion coefficient at the time of temperature fall was calculated | required from the change over time of the temperature and the strain amount in the process of the temperature rise by the heat | fever of hydration of a cement hardening body, and a fall.

  The heat insulation curing container 40 used in Example 2 is shown in FIG. 10A is a horizontal cross-sectional view along line FF in FIG. 10B, and FIG. 10B is a vertical cross-sectional view along line EE in FIG. 10A. is there.

In Example 2, the heat insulation curing container 40 of width 350mm x length 255mm x height 300mm comprised by the main-body part 41 and the cover part 43 was used. A heat insulating material having a thermal resistance value of 25 m ² · K / W was used for each surface of the heat insulating curing container 40.

  In the heat-insulating curing container 40, six specimens 50 in which a hardened cement body was placed in a cylindrical lightweight mold with an upper part having a diameter of 100 mm and a height of 200 mm were arranged as shown in the figure. The total number of hardened cement bodies was 9.4L.

  In Example 2, a thermometer and a strain gauge are arranged on each of the three specimens 50a to 50c arranged along the lateral side (corresponding to the horizontal direction in the drawing), and The temperature and strain were measured immediately after installation. A thermocouple was used for the thermometer, and a strain gauge was used for the strain gauge.

  An example of the temperature history of the hardened cement body of the specimen 50 and the change over time of the temperature and strain is shown in FIGS. 11 (a) and 11 (b), respectively. In Example 2, the linear expansion coefficient when the temperature of the hardened cement body is lowered is determined by the slope of the straight line indicated by the dotted line in FIG. 11B by using the change over time in the temperature and strain amount shown in FIG. Calculated. In the example shown in the figure, the linear expansion coefficient was calculated to be 9.09 (about 9.1) μ / ° C. from the slope of the straight line.

  The result of Example 2 is shown in the item “Test Result” in the table of FIG. For the simulated test specimen 30 (comparative example), the maximum temperature and linear expansion coefficient obtained by the thermometer and strain gauge placed in each of the two unstressed containers 31 (see FIG. 9), and their average values are Indicated.

  For the specimen 50 (example of the present invention), the maximum temperature and the linear expansion coefficient of each cemented body of the three specimens 50a to 50c, and the average value thereof were shown.

  As shown in the figure, in Example 2, the maximum temperature of the cement-hardened body of the specimen 50 is the same as that of the full-scale simulated specimen 30, and the linear expansion coefficient value is equivalent. It was. From the above, it was confirmed that the maximum temperature and the linear expansion coefficient equivalent to the full-scale simulation specimen were obtained by the present invention.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

1, 40 ............ Insulation curing container 2, 50 ...... Specimen 20 ...... Cement cured body 21 ...... Strain meter 23 ...... Thermometer 24 ...... Lightweight formwork 25 ...... Insulation 30 ……… Mock test specimen

Claims (5)

Inside a heat-insulating curing container using a heat insulating material, place a specimen with a hardened cement body embedded with a thermometer and strain gauge,
A line characterized by measuring a change in temperature and strain over time due to heat of hydration generated inside the hardened cement body , linearly approximating the change in strain when the temperature drops, and calculating the slope as a linear expansion coefficient Expansion coefficient test method. Inside the heat-insulating curing container, a plurality of specimens in which a hardened cement body is placed in a mold are arranged,
The linear expansion coefficient test method according to claim 1, wherein a thermometer and a strain gauge are embedded in the hardened cement body in at least one of the plurality of specimens. The linear expansion coefficient test method according to claim 1 or 2, wherein a total amount of the hardened cement body to be disposed inside the heat insulation curing container is determined by the following formula.
V ≧ −0.62 · R + 22
here,
V: Total amount of hardened cement (L)
R: Thermal resistance value of heat insulating material (m ² · K / W)   The thermometer and the strain gauge are embedded in the hardened cement body in each of the specimen closer to the center in the heat insulation curing container and the specimen farther from the center, respectively. The linear expansion coefficient test method according to claim 3.   The linear expansion coefficient test method according to claim 1, wherein a heat insulating material is disposed in a space other than the specimen in the heat insulating curing container.

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