JP6933930B2 - How to predict the ultimate value of drying shrinkage strain of concrete - Google Patents

Description

The present invention predicts the ultimate value of the dry shrinkage strain of concrete from the characteristic value of the coarse aggregate by using the relational expression between the final value of the dry shrinkage strain of concrete and the characteristic value of the coarse aggregate used for the concrete. Regarding the method.

Since concrete has low tensile strength, cracks (shrink cracks) may occur due to the shrinkage of concrete. This shrinkage crack not only spoils the aesthetic appearance of the concrete structure, but also causes a decrease in the durability of the structure such as a decrease in the watertightness and airtightness of the concrete and corrosion of the reinforcing bar. Therefore, in order to ensure the durability of concrete, it is necessary to control shrinkage cracks.
The main cause of this shrinkage crack is the drying shrinkage strain of concrete. As shown in FIG. 8, the strain includes a strain caused by external restraint of concrete and a strain caused by internal restraint. Therefore, in order to control shrinkage cracks in concrete, it is necessary to grasp the drying shrinkage strain, which is the main cause, in advance.

It is known that the drying shrinkage strain of concrete has a high correlation with the dynamic elastic modulus and Young's modulus of the coarse aggregate and the drying shrinkage strain of the coarse aggregate itself.
For example, in Patent Document 1, the following equation (1) is shown as a relational expression between the drying shrinkage strain of concrete and the kinematic elastic modulus of a coarse aggregate (claim 3).
y = ax-b …… (1)
(In the formula, y represents the drying shrinkage strain (× ^10-6 ) of concrete in the drying period of 26 weeks, x represents the dynamic elastic modulus (kN / mm ² ) of the coarse aggregate, and a represents the coarse aggregate. Is 11.536 in the case of igneous rock, 21.195 in the case of sedimentary rock, and b is 1201.6 in the case of igneous rock and 1812.2 in the case of sedimentary rock.)

Further, Patent Document 2 describes the following equations (2) and the following equations as the relational expression between the dry shrinkage strain of concrete and the Young's modulus of coarse aggregate and the relational expression between the dry shrinkage strain of concrete and the dry shrinkage strain of coarse aggregate, respectively. Equation (3) is shown (claims 2 and 3, respectively).
εc = A × Eg + B …… (2)
(In the formula, εc represents the drying shrinkage strain (× ^10-6 ) of concrete in the drying period of 26 weeks, Eg represents the Young's modulus of coarse aggregate (kN / mm ² ), and A is the coarse aggregate. If the rock type is sedimentary rock, it is 14.0, if it is not sedimentary rock, it is 5.3, and if the rock type of coarse aggregate is sedimentary rock, it is -1700, and if it is not sedimentary rock, it is -1035.)

εc = C × εg + D …… (3)
(In the formula, εc represents the drying shrinkage strain (× ^10-6 ) of concrete in a drying period of 26 weeks, εg represents the drying shrinkage strain of ^{coarse aggregate (× 10-6} ), and C is the coarse aggregate. When the rock type is sedimentary rock, it is 0.9, when it is not sedimentary rock, it is 0.8, and when the rock type of coarse aggregate is sedimentary rock, it is -520, and when it is not sedimentary rock, it is -563. )

Further, in Patent Document 3, the relational expression between the water absorption rate of the coarse aggregate and the dry shrinkage strain of the coarse aggregate, which is easier to measure, is used to determine the dry shrinkage strain of the coarse aggregate from the water absorption rate of the coarse aggregate. After obtaining the predicted value, a method of predicting the drying shrinkage strain of concrete from the predicted value and the relational expression between the drying shrinkage strain of coarse aggregate and the drying shrinkage strain of concrete is shown (claims 1 and 2).

In each of the above relational expressions, the drying shrinkage strain of concrete and various characteristic values of coarse aggregate are actually measured, and the relational expression (regression formula) is obtained by using these measured values as objective variables and explanatory variables, respectively. However, if equation (1) is to be applied to the prediction of drying shrinkage strain of concrete using coarse aggregates other than igneous rock and sedimentary rock, it is necessary to obtain the relational equation (return coefficient and constant term) again, but concrete. The measurement of the drying shrinkage strain is performed in accordance with JIS A 1129-1 to 3 "Method for measuring the length change of mortar and concrete", and it is necessary to wait 1 to 2 years to obtain the final value of the drying shrinkage strain. Must be (see FIGS. 13 and 14). Further, also in the equations (2) and (3), when a relational expression is newly obtained in order to improve the prediction accuracy, it is necessary to wait for the same period in order to obtain the final value of the drying shrinkage strain.
In order to obtain the final value of the drying shrinkage strain, it is necessary to wait for such a long period of time, but this is not practical. Therefore, in Patent Documents 1 and 2, 80 to 90% of the final value of the drying shrinkage strain is obtained. A drying period of 26 weeks is adopted, which is a drying period in which a degree of drying shrinkage strain can be obtained.
As described above, there is a problem that the work of finding the relational expression requires a long period of time.

Japanese Unexamined Patent Publication No. 2012-251965 Japanese Unexamined Patent Publication No. 2012-103057 Japanese Unexamined Patent Publication No. 2013-071850

Therefore, an object of the present invention is to provide a method capable of easily measuring the ultimate value of the drying shrinkage strain of concrete in a short period of time and accurately predicting the ultimate value of the drying shrinkage strain of concrete.

As a result of studying a prediction method that meets the above object, the present inventor can accurately measure the ultimate value of the drying shrinkage strain of concrete in a short period of time by using a specific drying shrinkage strain measuring device using a laser. The above equations (1) to (3), which were obtained by using the final value of the dry shrinkage strain and various characteristic values of the coarse aggregate, were found to be able to predict the dry shrinkage strain with high accuracy, and completed the present invention. ..
That is, the present invention is a method for predicting the ultimate value of the drying shrinkage strain of concrete having the following constitution.

[1] A step of obtaining a relational expression between the final value of the dry shrinkage strain of concrete measured using the following dry shrinkage strain measuring device (E ₁ ) and the characteristic value of the coarse aggregate (A) used for the concrete. ,
A step of substituting the characteristic value of the coarse aggregate (B) into the relational expression to predict the ultimate value of the drying shrinkage strain of concrete using the coarse aggregate (B).
A method for predicting the ultimate value of dry shrinkage strain of concrete, including at least.
However, the relational expression is any one selected from the following equations (1) to (3).
y = ax-b …… (1)
(In the formula, y represents the drying shrinkage strain (× ^10-6 ) of concrete in the drying period of 26 weeks, x represents the dynamic elastic modulus (kN / mm ² ) of the coarse aggregate, and a represents the coarse aggregate. Is 11.536 in the case of igneous rock, 21.195 in the case of sedimentary rock, and b is 1201.6 in the case of igneous rock and 1812.2 in the case of sedimentary rock.)
εc = A × Eg + B …… (2)
(In the formula, εc represents the drying shrinkage strain (× ^10-6 ) of concrete in the drying period of 26 weeks, Eg represents the Young's modulus of coarse aggregate (kN / mm ² ), and A is the coarse aggregate. If the rock type is sedimentary rock, it is 14.0, if it is not sedimentary rock, it is 5.3, and if the rock type of coarse aggregate is sedimentary rock, it is -1700, and if it is not sedimentary rock, it is -1035.)
εc = C × εg + D …… (3)
(In the formula, εc represents the drying shrinkage strain (× ^10-6 ) of concrete in a drying period of 26 weeks, εg represents the drying shrinkage strain of ^{coarse aggregate (× 10-6} ), and C is the coarse aggregate. When the rock type is sedimentary rock, it is 0.9, when it is not sedimentary rock, it is 0.8, and when the rock type of coarse aggregate is sedimentary rock, it is -520, and when it is not sedimentary rock, it is -563. )
Further, when the coarse aggregate (A) and the coarse aggregate (B) are coarse aggregates of the same rock type and the coarse aggregate is a mixture of a plurality of rock types, the coarse aggregate (A) and the coarse aggregate (A) are coarse. The aggregate (B) is a coarse aggregate of the same type of rock, and is a mixture of coarse aggregates having the same mixing ratio.
The characteristic value of the coarse aggregate (A) and the characteristic value of the coarse aggregate (B) are selected from the dynamic elastic modulus of the coarse aggregate, the Young's modulus of the coarse aggregate, and the drying shrinkage strain of the coarse aggregate. , Any one.
<Dry shrinkage strain measuring device (E ₁ )>
A drying shrinkage strain measuring device including at least one laser displacement meter, a pedestal for mounting a specimen for measuring drying shrinkage strain, and a positioning jig for the specimen.
However, when the specimen has a disk shape, the diameter of the specimen is 10 to 30 cm, and the thickness of the specimen is 5 to 20 mm.
When the specimen has a square plate shape, the length of one side of the square plate is 10 to 30 cm, and the thickness of the square plate-shaped specimen is 5 to 20 mm.

In the method for predicting the ultimate value of the drying shrinkage strain of concrete of the present invention, the ultimate value of the drying shrinkage strain of concrete can be accurately measured in a short period of time (within 50 days) by using a specific drying shrinkage strain measuring device using a laser. The final values of the dry shrinkage strain can be predicted with high accuracy by the above equations (1) to (3) obtained by using the final value and various characteristic values of the coarse aggregate.

It is a schematic diagram showing an example of a state in which a specimen is placed on a drying shrinkage strain measuring device (E ₁ ) having one laser displacement meter, and the left figure is a plan view of the measuring device, and the right is a plan view of the measuring device. Is a side view of the measuring device. It is a schematic diagram showing an example of a state in which a specimen is placed on a drying shrinkage strain measuring device (E ₁ ) having two laser displacement meters, and the left figure is a plan view of the measuring device and the right is a plan view of the measuring device. Is a side view of the measuring device. Some of the lower portion of the support member, on a support member formed by installing a state embedded in the pedestal drying shrinkage strain measurement device (E _1), a a schematic view showing an example of a state of mounting the specimen The left figure is a plan view of the measuring device, and the right figure is a side view of the measuring device. However, in FIG. 3, the description of the laser displacement meter is omitted. _{It is a schematic diagram showing an example of a drying shrinkage strain measuring device (E 2} ) in which two laser displacement meters are arranged so as to face each other. The left figure is a plan view of the measuring device, and the right figure is the said. It is a side view of the measuring device. It is a schematic diagram which shows an example of _{the drying shrinkage strain measuring apparatus (E 2} ) in which two laser displacement meters are arranged so that the lasers radiated from the laser displacement meters intersect at an angle of 90 °. The left figure is a plan view of the measuring device, and the right figure 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 a drying shrinkage strain measurement device (E ₂₎ The left figure is a plan view of the measuring device, and the right figure is a side view of the measuring device. However, the laser displacement meters located in front of and behind the paper are omitted. The drying shrinkage strain measurement device (E _2), is a photograph showing a state of mounting the specimen. The pin at the center of the pedestal (A) is not a support member but a screw for fixing the pedestal. It is a conceptual diagram which shows the drying shrinkage strain and the drying shrinkage stress of concrete generated by the internal restraint and the external restraint. It is a figure which shows the measurement state of the ultrasonic wave propagation time in a coarse aggregate. It is a schematic diagram which shows the relationship between the longitudinal strain and the stress of a coarse aggregate, and is the schematic diagram which shows the relationship between the stress of 1/3 or less of the maximum load, and the longitudinal strain. It is a schematic diagram which shows the time-dependent change of the drying shrinkage strain of a coarse aggregate. It is a figure which shows the time-dependent change of the drying shrinkage strain of the specimen made using various cements, (A) is ordinary Portland cement, (B) is blast furnace cement type B, (C) is moderate heat Portland cement, and (D) shows the drying shrinkage strain of the specimen using low heat Portland cement. The curve shown by "the present invention" in the figure is a curve of the drying shrinkage strain measured _{by using the drying shrinkage strain measuring device (E 1} ), and the curve shown by the "JIS method" in the figure is JIS A. It is a curve of the drying shrinkage strain measured using 1129-2 "Measurement method for length change of mortar and concrete Part 2: Contact gauge method". It is a figure which shows the drying shrinkage strain of the specimen of formulation 1, (A) shows the drying shrinkage strain with a drying period of up to 460 days, (B) is the drying shrinkage strain of (A) with a drying period of up to 20 days. Is enlarged and shown. The curve shown by "the present invention" in the figure is a curve of the drying shrinkage strain measured _{by using the drying shrinkage strain measuring device (E 2} ), and the curve shown by the "JIS method" in the figure is the JIS. It is a curve of the drying shrinkage strain measured using A 1129-2. The same applies to FIG. 14 below. It is a figure which shows the drying shrinkage strain of the specimen of formulation 2, (A) shows the drying shrinkage strain with a drying period of up to 460 days, (B) is the drying shrinkage strain of (A) with a drying period of up to 20 days. Is enlarged and shown.

As described above, the present invention presents the ultimate value of the dry shrinkage strain of concrete measured using the dry shrinkage strain measuring device (E ₁ ) or the dry shrinkage strain measuring device (E _{2), and the coarse aggregate used for the concrete.} The step of obtaining the relational expression of the characteristic value of (A) and the final value of the drying shrinkage strain of concrete using the coarse aggregate (B) by substituting the characteristic value of the coarse aggregate (B) into the relational expression. It is a method for predicting the ultimate value of the drying shrinkage strain of concrete, which includes at least the step of predicting. Hereinafter, the present invention will be described in detail separately for a drying shrinkage strain measuring device, a method for measuring the ultimate value of the drying shrinkage strain, a method for measuring the characteristic value of coarse aggregate, and the like.

1. 1. Dry shrinkage strain measuring device (E ₁ )
As illustrated in FIGS. 1 to 3, the drying shrinkage strain measuring device (E ₁ ) includes one or more laser displacement meters 4, a pedestal 2 for mounting a specimen for measuring drying shrinkage strain, and the same. It is an apparatus including at least the positioning jig 3 of the specimen 1.
The laser displacement meter is not particularly limited, and examples thereof include commercially available laser displacement meters such as a reflection type and 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. The number is preferably 2-4. The laser displacement meter is installed so that the laser can be irradiated toward the center of the disk-shaped or square plate-shaped specimen placed on the pedestal. Examples of the installation position of the laser displacement meter include the positions shown in FIGS. 1 and 2.

Further, the pedestal 2 is used for placing a specimen for measuring drying shrinkage strain. The shape of the pedestal is not particularly limited, and is, for example, a square plate shape or a disk shape shown in FIGS. 1 and 2. Further, in order to improve the measurement accuracy, it is preferable that the pedestal is kept horizontal.
Further, the pedestal is preferably manufactured using 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. By installing the support member, the heat transfer between the specimen and the pedestal can be reduced, so that the measurement accuracy of the drying shrinkage strain is improved.
The shape of the support member is not particularly limited, and examples thereof include a spherical shape as shown in FIG. 3 (in FIG. 3, 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 columnar, the surface of the support member in contact with the specimen is preferably hemispherical so as to make point contact with the specimen.
The number of support members is preferably 3 or more because the specimen can be stably placed. It should be noted that the number of support members is more preferably 3 to 4, because it takes time and effort to manufacture the device when the number of support members is increased. Further, the support member is preferably installed so as to form an equilateral triangle or a square in order to stably place the specimen. FIG. 3 shows an example in which the support members are installed so as to form a square. Further, the support member is preferably manufactured using 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 drying shrinkage strain of the specimen. For example, as shown in FIGS. 1 and 2, the positioning jig 3 is placed on a pedestal. Examples include two pins installed in an inverted state. In FIGS. 1 and 2, when the disk-shaped specimen is placed on the pedestal when the drying period is 0 (zero) days, the center of the disk-shaped specimen and the center of the pedestal coincide with each other. The positioning jig is installed at a position where it comes into contact with the side surface around the disk-shaped specimen. The positioning jig may be installed outside the pedestal in addition to the pedestal. Further, the positioning jig is preferably manufactured using Invar steel material in order to prevent deformation due to heat or impact.
Further, the drying shrinkage strain measuring device (E ₁ ) preferably includes a laser displacement meter, a pedestal, and a positioning jig integrally by using a base. The laser displacement meter, pedestal, positioning jig, and the substrate used to install them are preferably manufactured using Invar steel material in order to prevent deformation due to heat or impact.

2. Method for measuring dry shrinkage strain using a dry shrinkage strain measuring device (E ₁ ) The measuring method is to place a disk-shaped or square plate-shaped specimen on the pedestal of the dry shrinkage strain measuring device (E _1). After placing the specimen so that the peripheral side surface of the specimen is in contact with the positioning jig, the laser displacement meter is used to irradiate the peripheral side surface of the specimen with a laser to obtain the laser displacement meter and the peripheral side surface of the specimen. This is a method of measuring the drying shrinkage strain of a specimen by measuring the distance between them.
When the specimen is in the shape of a disk, if the diameter of the specimen is 10 to 30 cm, it is preferable that the specimen is easy to manufacture and the specimen dries quickly. 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 not easily cracked and the specimen dries even faster, which is preferable. The thickness of the specimen is more preferably 6 to 18 mm, further preferably 7 to 15 mm, and particularly preferably 8 to 12 mm.
When the specimen has a square plate shape, the length of one side of the square plate is preferably 10 to 30 cm, more preferably 10 to 20 cm, and even more preferably 10 to 30 cm on one side. A square, particularly preferably a square with a side length of 10 to 20 cm. If the square has a side length of 10 to 30 cm, the specimen can be easily manufactured and the specimen can be dried quickly. 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 specimen is 5 to 20 mm, the specimen is hard to crack and the specimen dries even faster.
When a support member is installed on the pedestal of the drying shrinkage strain measuring device (E ₁ ), the peripheral side surface of the disk-shaped or square plate-shaped specimen comes into contact with the positioning jig on the support member. As such, the specimen is placed.

The measuring method is a method of measuring the drying shrinkage strain by placing the specimen on a pedestal every predetermined drying period. Then, in order to improve the measurement accuracy of the drying shrinkage strain, preferably, the specimen has a disk shape, and the specimen is rotated clockwise or counterclockwise so that the peripheral side surface of the specimen is positioned. In contact with the tool, measure the distance between the laser displacement meter and the peripheral side surface of the specimen at least twice, preferably 3-5 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 90 ° clockwise to measure the point c. The average value of the points is calculated as the drying shrinkage strain.
In the measuring method of the present invention, the measurement interval of the drying shrinkage strain is arbitrary, but the measurement interval of the drying shrinkage strain is preferable in order to obtain the final value of the drying shrinkage strain at an early stage and to reduce the time and effort for measurement. The drying period is every 1 to 10 days, more preferably every 1 to 7 days.

Further, in the measuring method of the present invention, in order to measure the drying shrinkage strain more accurately, a metal plate (base length plate) having the same shape and dimensions as the specimen before drying is placed on a pedestal and a laser is used. _{After measuring the distance (L 1} ) between the displacement meter and the side surface of the metal plate, the specimen is placed on a pedestal in place of the metal plate, and between the laser displacement meter and the side surface of the specimen. This is a method of measuring the _{distance (L 2} ) and obtaining the final value of the drying shrinkage strain based on the difference between _{L 1} and L _{2 (L 1 −} L _2).
Further, when using a measuring device in which the measured distance is displayed on the screen, the measuring method of the present invention mounts a metal plate (base length plate) having the same shape and dimensions as the specimen before drying on the pedestal. Place it, measure the distance between the laser displacement meter and the side surface of the metal plate, set the distance (indication) to zero, and then place the specimen on the pedestal in place of the metal plate. This is a method of measuring the distance between the laser displacement meter and the side surface of the specimen to determine the drying shrinkage strain.
The metal plate (base length 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 more preferably Invar in order to prevent deformation due to heat or impact. It is a steel material.

3. 3. Dry shrinkage strain measuring device (E ₂ )
As illustrated in FIGS. 4 to 7, the drying shrinkage strain measuring device (E ₂ ) includes two or more laser displacement meters 4, and three or more supporting members 5 for supporting the specimen for measuring the drying shrinkage strain. , And a device including at least a pedestal 2 formed by embedding a part of the support member.
The laser displacement meter is the same as the laser displacement meter of the drying shrinkage strain measuring device (E ₁ ). Further, in order to improve the measurement accuracy of the drying shrinkage strain, two or more laser displacement meters are installed. With one laser displacement meter, the measurement accuracy of drying shrinkage strain may decrease. Further, if the number of laser displacement meters is increased, the number of data is increased, and the measurement accuracy is further improved by that amount, but the cost of the device is increased. Therefore, 2 to 6 laser displacement meters are preferably installed, and 2 to 4 laser displacement meters are more preferably installed.
Since the laser displacement meter improves the measurement accuracy of drying shrinkage strain and makes it easy to place the specimen, it is preferable to irradiate the laser at positions equilaterally spaced from the center of the equilateral triangle or square formed by the support member. Install with the surface facing the center. Further, in order to further improve the measurement accuracy of the final value of the drying shrinkage strain, more preferably, 2 to 6 of the laser displacement meters are crossed by the laser irradiated from the laser displacement meter at an angle of 60 to 300 °. Arrange to do so.
In the mode of installing the laser displacement meter, when two laser displacement meters are installed, for example, the laser displacement meters are installed facing each other as shown in FIG. 4, or the laser is 90 ° as shown in FIG. When four laser displacement meters are installed so as to intersect at the angle of the above, two sets of laser displacement meters are installed facing each other as shown in FIG.

In the drying shrinkage strain measuring device (E ₂ ), the support 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, the specimen dries homogeneously and early, so that the ultimate value of the drying shrinkage strain can be measured early.
The shape, number, arrangement shape (position shape), and material of the support members are the same as those of the drying shrinkage strain measuring device (E ₁ ).

The pedestal is formed by burying and fixing a part (lower part) of the support member. Incidentally, the pedestals shown in FIGS. 4 to 6 have a square plate shape, and the pedestals shown in FIG. 7 have a disk shape. Incidentally, the pedestal is preferably being kept horizontal, the material it Invar steel is preferable is the same as the drying shrinkage strain measurement device (E _1).

In the drying shrinkage strain measuring device (E ₂ ), a specimen mounting auxiliary jig may be used in order to facilitate mounting of the specimen on the support member. Examples of the specimen mounting auxiliary jig include two pins installed on the outside of the pedestal as shown in FIG. 7. On a support member of the drying shrinkage strain measurement device of FIG. 7 (E ₂₎ supporting, for example, when placing a disc-shaped specimens having a diameter of 10 cm, the specimen to contact the two pins When placed on the member, the specimen can be placed so that the center of the specimen and the center of the square formed by the support member coincide with each other.
The specimen mounting auxiliary jig may be installed on the outside of the pedestal as shown in FIG. 7, or may be installed on the pedestal. Further, the specimen mounting auxiliary jig is preferably manufactured using Invar steel material in order to prevent deformation due to heat or impact.

The drying shrinkage strain measuring device (E ₂ ) is also configured by integrating two or more laser displacement meters, a pedestal, and, if necessary, a specimen mounting auxiliary jig, as shown in FIGS. 4 to 7. do. The material of such pedestal that Invar steel is preferable is the same as the drying shrinkage strain measurement device (E _1).

4. Method of measuring dry shrinkage strain using a dry shrinkage strain measuring device (E ₂ ) In this measuring method, the center of a disk-shaped or square columnar specimen is placed on the support member of the dry shrinkage strain measuring device (E _2). After placing the support member so as to coincide with the center of the regular triangle or square formed by the support member, a laser displacement meter is used to irradiate the side surface around the specimen with a laser to irradiate the side surface around the specimen with the laser displacement meter and the circumference of the specimen. This is a method of determining the drying shrinkage strain of a specimen by measuring the distance between the sides of the specimen.
For example, as shown in FIG. 7, a disk-shaped specimen is placed on the support members (four spherical points on the pedestal) of _{the drying shrinkage strain measuring device (E 2), and the center and the support member of the specimen are placed.} After placing the squares to be formed so that the centers of the squares coincide with each other (FIG. 7 (B)), the side surface around the specimen is irradiated with a laser using a laser displacement meter, and the laser displacement meter and the periphery of the specimen are subjected to laser irradiation. The drying shrinkage strain of the specimen is determined by measuring the distance between the sides.
The shape, size, and thickness of the specimen are the same as in the method of measuring the drying shrinkage strain using the drying shrinkage strain _{measuring device (E 1).}

The measurement method is different from (a) a method in which the specimen is dried with the specimen still placed on the support member and the drying shrinkage strain is obtained every predetermined drying period, and (b) another method. Any method of obtaining the drying shrinkage strain by placing the specimen dried in the place on the support member at a predetermined drying period is possible, but the labor of work is reduced and the measurement accuracy is improved. From the point of view, the method (a) is preferable.
The measurement interval of the drying shrinkage strain is the same as that of the method of measuring the drying shrinkage strain using the drying shrinkage strain _{measuring device (E 1).}
As described above, if the drying shrinkage strain measuring device (E ₁ ) or (E ₂ ) is used _, the final value of the drying shrinkage strain can be accurately obtained in a short period of time.

5. Method for Measuring Dynamic Elastic Modulus of Coarse Aggregate The measuring method is a method including at least the following steps (A) and (B).
(A) The transmitter of the ultrasonic propagation time measuring instrument is brought into contact with one end of the longest diameter of the coarse aggregate having the longest diameter of 15 mm or more, and the receiving of the measuring instrument is made at the other end of the longest diameter of the coarse aggregate. Step of measuring the propagation time of ultrasonic waves in the coarse aggregate with the children in contact (B) Using the value of the ultrasonic propagation time obtained in the step (A) above, the following equation (1) was used. step for calculating a dynamic elastic modulus of crude aggregate based ^{_{E d = (L / T)}} 2 · ρ ...... (1)
(Wherein, E _d represents the dynamic elastic modulus, L represents a longest diameter of coarse aggregate, T is shows an ultrasonic propagation time, [rho bone dry the coarse aggregate was determined in accordance with JIS A 1110 Represents density.)
According to this measuring method, the measurement error (fluctuation) of the ultrasonic propagation time can be reduced, and the kinematic elastic modulus of the coarse aggregate can be accurately obtained.

(1) Coarse Aggregate The longest diameter of the coarse aggregate to be measured in the step (A) is usually 15 mm or more, preferably 20 mm or more, and more preferably more than 25 mm. When the longest diameter of the coarse aggregate is less than 15 mm, the propagation distance of ultrasonic waves is short, so that the error of the measured value of the ultrasonic wave propagation time tends to be large.
Here, the longest diameter is a rectangular parallelepiped in which one coarse aggregate fits, and is the longest line and its line among the three types of orthogonal lines (vertical line, horizontal line and height line) that form this rectangular parallelepiped. The length of.

Further, the state of the coarse aggregate to be measured in the step is preferably an air-dried state, and more preferably an absolutely dry state. Here, the absolutely dry state means a state in which the coarse aggregate is dried until the mass becomes constant. When the state of the coarse aggregate is shown by the water content, the coarse aggregate having a water content of 2.0% by mass or less is preferable, 1.0% by mass or less is more preferable, and 0.1% by mass or less is further preferable. When the water content exceeds 2.0% by mass, the error of the measured value of the ultrasonic propagation time tends to be large.

(2) Measurement of Ultrasonic Propagation Time In the measurement, as shown in FIG. 9, the transmitter 6 of the ultrasonic propagation time measuring device 8 is brought into contact with one end of the longest diameter of the coarse aggregate, and the coarse aggregate is measured. With the receiver 7 of the measuring instrument in contact with the other end of the longest diameter of the measuring instrument, the propagation time of ultrasonic waves in the coarse aggregate is measured. In this measuring method, the work of flattening both ends of the longest diameter of the coarse aggregate becomes unnecessary, and the working time of the measurement can be significantly shortened as compared with the conventional method.
The number of coarse aggregates used for measuring the ultrasonic propagation time is preferably 10 or more. When the number of coarse aggregates measured is 10 or more, the average of the measured values tends to converge to the average of the measured values of the coarse aggregate population.

The outer diameter of the transmitter and receiver of the ultrasonic propagation time measuring device used here depends on the size of the coarse aggregate and the shape of the end of the longest diameter of the coarse aggregate. When the end of the longest diameter is sharp, the outer diameter is preferably 50 mm or less, more preferably 25 mm or less, still more preferably 15 mm or less. When the outer diameter is 50 mm or more, the error of the measured value of the ultrasonic propagation time tends to be large.
When the temperature at the time of measuring the ultrasonic propagation time is the environmental temperature at which concrete is normally placed, for example, about 60 ° C. or less, the fluctuation of the measured value is small and is not particularly limited, but generally, 10 to 10 The range of 40 ° C. is preferable.

6. Method for measuring Young's modulus of coarse aggregate (1) Coarse aggregate The absolute dry density of coarse aggregate ^{is preferably 1.5 g / cm 3} or more, more preferably 2.0 g / cm ³ or more, and 2.5 g / cm. ³ or more is more preferable. If the value is ^{less than 1.5 g / cm 3} , the prediction accuracy tends to decrease.

(2) Method for measuring Young's modulus of coarse aggregate In the measurement method, a core having a diameter of 32 mm and a length of 64 mm is extracted from the rough aggregate, and then compressed and loaded on the core of the coarse aggregate, and a strain gauge is used. (For example, the inspection length is 30 mm. PFL-30 manufactured by Tokyo Sokki Kenkyusho) is used to measure the longitudinal strain of the coarse aggregate to obtain a stress-longitudinal strain curve. Next, from the stress-strain curve, the gradient (Young's modulus) of the line segment connecting the stress corresponding to 1/3 of the maximum load and the stress when the longitudinal strain is 50 × ^{10-6 is obtained (Fig.).} 10).

7. Method for measuring dry shrinkage strain of coarse aggregate The method for measuring dry shrinkage strain of coarse aggregate is as follows (a) to (d).
(A) One surface of a coarse aggregate (aggregate grain of about 15 to 20 mm) is polished with a polishing machine (for example, a grinder or sandpaper) to make a smooth surface (flat surface), and then a strain gauge (a strain gauge (for example) is applied to the smooth surface. For example, the inspection length is 2 mm. FLA-2) manufactured by Tokyo Institute of Instrument Research is pasted.
(B) After waterproofing the pasted portion, the waterproofed coarse aggregate is immersed in water at 20 ± 2 ° C. for 7 days.
(C) After 7 days have passed, the coarse aggregate is taken out, and the coarse aggregate is allowed to stand in a room at a temperature of 20 ± 3 ° C. and a relative humidity of 60 ± 5% for 12 days to dry.
(D) The amount of change in the strain of the coarse aggregate during the 12 days is defined as the drying shrinkage strain of the coarse aggregate (see FIG. 11).

8. Types of coarse aggregates The types of coarse aggregates used for the various measurements are not particularly limited, but are igneous rocks such as basalt, anthropite, rhemic rock, granite, keratinite, and mottled rock, limestone, hard sandstone, and tuff. At least one species selected from sedimentary rocks such as sandstone and tuff, and gravel can be mentioned. The coarse aggregate may be a natural aggregate or a regenerated aggregate. Of these coarse aggregates, limestone, hard sandstone, slate and tuff are included in sedimentary rocks.

9. Derivation of relational expressions and prediction of dry shrinkage strain of concrete Regression analysis (fitting) of regression coefficients using the above formulas (1) to (3) from the final value of the dry shrinkage strain of concrete and the characteristic value of coarse aggregate. The relational expression is derived by calculating by. The relational expression thus obtained can be widely applied to concretes having different types of cements and aggregates, and different formulations, and is highly versatile. Then, the characteristic value of the coarse aggregate is substituted into the derived relational expression to obtain the final value of the drying shrinkage strain.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.
1. 1. Measurement of the ultimate value of dry shrinkage strain of concrete using a dry shrinkage strain measuring device (E ₁ ) (1-1) Materials used (i) Cement (abbreviation: C, all manufactured by Taiheiyo Cement Co., Ltd.)
Ordinary Portland cement (abbreviation: NC)
Blast furnace cement type B (abbreviation: BB)
Moderate heat Portland cement (abbreviation: MC)
Low-grade Portland cement (abbreviation: LC)
(Ii) Fine aggregate (abbreviation: S): Mountain sand (surface dry density 2.56 g / cm ³ )
(Iii) Coarse aggregate (abbreviation: G): Surface dry density 2.61 g / cm ³
(Iv) Water (abbreviation: W): Tap water (v) AE water reducing agent: Ligno sulfonic acid-based AE water reducing agent, trade name Pozoris No. 70 [registered trademark], manufactured by BASF, Ltd.
(Vi) AE agent: Brand name Master Air 404 [registered trademark], manufactured by BASF

(1-2) Preparation of Specimen for Drying Shrink Strain Measurement According to the formulation shown in Table 1, each of the above materials was put into a pan-type mixer having a capacity of 50 liters in a batch, kneaded for 2 minutes, and then the kneaded product was kneaded. It was cast into a mold having an inner diameter of 10 cm and a height of 20 cm and molded to obtain concrete. Next, the concrete was wet-air-cured at 20 ° C. for 1 day, then demolded, and further water-cured at 20 ° C. for 7 days. After curing in water, the vicinity of the central portion in the height direction of the concrete was cut to prepare three specimens for measuring drying shrinkage strain having a diameter of 10 cm and a thickness of 1 cm.

(1-3) Measurement of Dry Shrinkage Strain of Specimen Specimen 1 for measurement of dry shrinkage strain was dried under the conditions of room temperature 20 ± 2 ° C. and relative humidity 60 ± 5%. Then, every 7 days during the drying period, the specimen for measuring the drying shrinkage strain is placed on the pedestal 2 so that the side surface around the specimen comes into contact with the positioning jig 3 of the drying shrinkage strain measuring device shown in FIG. After placement, the distance between the laser displacement meter and the peripheral side surface of the specimen was measured using the laser displacement meter 4. In this embodiment, the distance between the laser displacement meter and the side surface around the specimen is measured at three points (points a, b, and c in FIG. 1) for one specimen. , This average value is calculated as the final value of the drying shrinkage strain of the specimen, and further, the drying shrinkage strain (average value) of these three specimens is averaged to calculate the final value of the entire drying shrinkage strain. bottom. The results are shown in FIGS. 12 and 2 (however, in FIG. 12, a part of the data after the drying period of 56 days is omitted).
For comparison, the drying shrinkage strain of concretes A to D was measured in accordance with JIS A 1129-2 "Mortar and concrete length change measurement method Part 2: Contact gauge method" (JIS method). .. The results are shown in FIG. 12 and Table 2.

As shown in FIG. 12, the final value of the drying shrinkage strain of any concrete cannot be obtained by the JIS method until the drying period has passed for one year or more, whereas according to the present invention, the specimen is dried. Due to the high speed, the final value of the drying shrinkage strain can be accurately obtained as early as the drying period is within 50 days.

2. Measurement of the ultimate value of dry shrinkage strain of concrete using a dry shrinkage strain measuring device (E ₂ ) (2-1) Materials used (i) Cement (abbreviation: C): Ordinary Portland cement (manufactured by Taiheiyo Cement)
(Ii) Fine aggregate (abbreviation: S): Mountain sand (surface dry density 2.56 g / cm ³ )
(Iii) Coarse aggregate A (abbreviation: G): Surface dry density 2.71 g / cm ³
(Iv) Coarse aggregate B (abbreviation: G): Surface dry density 2.61 g / cm ³
(V) Water (abbreviation: W): Tap water (vi) Water reducing agent (abbreviation: SP): Polycarboxylic acid-based high-performance AE water reducing agent, trade name Master Grenium SP8SV [registered trademark], manufactured by BASF, Ltd.
(Vii) Air volume adjuster: Product name Master Air 404 (manufactured by BASF)

(2-2) Preparation of Specimen for Dry Shrink Strain Measurement The method for preparing a specimen for dry shrinkage strain measurement is the same as that described in paragraph 0039 for dry shrinkage strain measurement, except that the formulations shown in Table 3 are used. It is the same as the method for producing the specimen.

(2-3) Measurement of Dry Shrinkage Strain of Specimen The center of the test piece is attached to a support member fixed to the pedestal of the _{dry shrinkage strain measuring device (E 2} ) shown in FIG. 7 for measuring the dry shrinkage strain. The product was dried under the conditions of room temperature of 20 ± 2 ° C. and relative humidity of 60 ± 5% while being placed so that the centers of the squares formed by the support members coincided with each other. Then, every day during the drying period, the drying shrinkage strains at the four points of the specimens are measured using two sets of laser displacement meters facing each other, and the average value of the final values of the drying shrinkage strains of the three specimens. Was calculated.
For comparison, the drying shrinkage strain of the concrete of Formulation 1 and Formulation 2 is based on JIS A 1129-2 "Mortar and Concrete Length Change Measurement Method Part 2: Contact Gauge Method" (JIS method). The final value of was measured. The measurement results of the final values of the drying shrinkage strains of the concrete of Formulation 1 and Formulation 2 are shown in FIGS. 13 and 14, respectively.

The final value of the drying shrinkage strain of the concrete of Formulation 1 measured using the drying shrinkage strain measuring device (E ₂ ) was 760μ, and the drying shrinkage strain of 460 days in the JIS method was 745μ. Incidentally, in the JIS method using the compound 1, the error of the drying shrinkage strain at 460 days is considered to be ± 100μ, so the drying shrinkage strain at 460 days may be considered as the final value. The final value (760μ) × 0.9 of the drying shrinkage strain measured in the present invention is 684μ, and the measured value (702μ) of the drying shrinkage strain with a drying period of 6 months measured according to the JIS method is They match by a small margin of 2.6% (= 100 × (702-684) / 702).
The final value of the drying shrinkage strain in the present invention using Formulation 2 was 1260μ, and the drying shrinkage strain having a drying number of 460 days in the JIS method was 1250μ. The final value (1260μ) × 0.9 of the drying shrinkage strain measured in the present invention is 1134μ, which is 4 from the measured value (1185μ) of the drying shrinkage strain measured according to the JIS method for a drying period of 6 months. It is a close match of 0.3% (= 100 × (1185-1134) / 1185).

1 Specimen 2 Pedestal 3 Positioning jig 4 Laser displacement meter (However, the black arrow indicates the laser)
5 Support member 6 Transmitter 7 Receiver 8 Ultrasonic propagation time measuring instrument

Claims (1)

A step of obtaining a relational expression between the final value of the dry shrinkage strain of concrete measured using the following dry shrinkage strain measuring device (E ₁ ) and the characteristic value of the coarse aggregate (A) used for the concrete.
A step of substituting the characteristic value of the coarse aggregate (B) into the relational expression to predict the ultimate value of the drying shrinkage strain of concrete using the coarse aggregate (B).
A method for predicting the ultimate value of dry shrinkage strain of concrete, including at least.
However, the relational expression is any one selected from the following equations (1) to (3).
y = ax-b …… (1)
(In the formula, y represents the drying shrinkage strain (× ^10-6 ) of concrete in the drying period of 26 weeks, x represents the dynamic elastic modulus (kN / mm ² ) of the coarse aggregate, and a represents the coarse aggregate. Is 11.536 in the case of igneous rock, 21.195 in the case of sedimentary rock, and b is 1201.6 in the case of igneous rock and 1812.2 in the case of sedimentary rock.)
εc = A × Eg + B …… (2)
(In the formula, εc represents the drying shrinkage strain (× ^10-6 ) of concrete in the drying period of 26 weeks, Eg represents the Young's modulus of coarse aggregate (kN / mm ² ), and A is the coarse aggregate. If the rock type is sedimentary rock, it is 14.0, if it is not sedimentary rock, it is 5.3, and if the rock type of coarse aggregate is sedimentary rock, it is -1700, and if it is not sedimentary rock, it is -1035.)
εc = C × εg + D …… (3)
(In the formula, εc represents the drying shrinkage strain (× ^10-6 ) of concrete in a drying period of 26 weeks, εg represents the drying shrinkage strain of ^{coarse aggregate (× 10-6} ), and C is the coarse aggregate. When the rock type is sedimentary rock, it is 0.9, when it is not sedimentary rock, it is 0.8, and when the rock type of coarse aggregate is sedimentary rock, it is -520, and when it is not sedimentary rock, it is -563. )
Further, when the coarse aggregate (A) and the coarse aggregate (B) are coarse aggregates of the same rock type and the coarse aggregate is a mixture of a plurality of rock types, the coarse aggregate (A) and the coarse aggregate (A) are coarse. The aggregate (B) is a coarse aggregate of the same type of rock, and is a mixture of coarse aggregates having the same mixing ratio.
The characteristic value of the coarse aggregate (A) and the characteristic value of the coarse aggregate (B) are selected from the dynamic elastic modulus of the coarse aggregate, the Young's modulus of the coarse aggregate, and the drying shrinkage strain of the coarse aggregate. , Any one.
<Dry shrinkage strain measuring device (E ₁ )>
A drying shrinkage strain measuring device including at least one laser displacement meter, a pedestal for mounting a specimen for measuring drying shrinkage strain, and a positioning jig for the specimen.
However, when the specimen has a disk shape, the diameter of the specimen is 10 to 30 cm, and the thickness of the specimen is 5 to 20 mm.
When the specimen has a square plate shape, the length of one side of the square plate is 10 to 30 cm, and the thickness of the square plate-shaped specimen is 5 to 20 mm.

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