JP7461708B2 - How to measure expansion strain - Google Patents

Description

The present invention relates to an expansion strain measuring method and an expansion strain measuring device that can easily and efficiently measure the expansion strain of concrete, such as ASR (alkali silica reaction), DEF (delayed ettringite formation), and the residual expansion of concrete structures.

ASR is a phenomenon in which the silica in reactive aggregate reacts with the alkali metal ions in concrete under high pH conditions to produce alkaline silica gel, which then absorbs water and expands, causing cracks in the concrete. This ASR is known to be one of the main causes of reduced durability of concrete. Therefore, in order to ensure the durability of concrete, it is necessary to predict the occurrence of cracks and take measures such as reinforcement in advance.

DEF is a phenomenon in _{which ettringite} ([ _Ca6Al2 (OH) _12.24H2O ]( _SO4 ) _3.2H2O ), which is formed by hydration of cement, expands in concrete after several months to several years, causing cracks in the concrete. Since the entire cement paste is the expansion matrix in DEF, the expansion strain is several times larger than _that in ASR, in which the reactive aggregate is the expansion matrix.

Here, methods for determining the alkali-silica reactivity of concrete include JCI-S-101-2017 "Test method for alkali-silica reactivity of concrete" and JASS 5N T-603 "Test for reactivity of concrete." The method of JCI-S-101-2017 involves pouring concrete with a total alkali content of 5.5 kg/ ^m3 of concrete converted to _Na2O , demolding it 24 hours after it is placed, and then moist curing the resulting 100 x 100 x 400 mm test specimen at 40°C, and measuring the change in length of the test specimen 1 to 6 months, 9 months, and 12 months after demolding using the dial gauge method. In addition, the method of JASS 5N T-603 involves pouring concrete with total alkali amounts of 1.2, 1.8, and 2.4 kg/ ^m3 of concrete calculated as _Na2O , preparing test specimens of the same size in the same manner as in the JCI standard, curing them in the same manner, measuring the change in length six months after demolding using the dial gauge method, calculating the critical alkali amount at which the expansion strain is 0.1%, and judging the alkali-silica reactivity of the concrete based on this critical alkali amount.

However, as mentioned above, the JCI-S-101-2017 method requires large test specimens, dedicated formwork, tools, and measuring equipment, and the test period is long, at least one year. As mentioned above, the JASS 5N T-603 method requires three levels of alkali content to be set and test specimens to be prepared. Furthermore, a common problem with the JCI-S-101-2017 and JASS 5N T-603 methods is that for test specimens measuring 100 x 100 x 400 mm, in concrete with a large amount of expansion such as that accompanied by the pessimum phenomenon, the test specimens may twist or distort due to the aggregate amount or alkali leaching, resulting in large individual variation and making it difficult to measure using a dial gauge.
In general, shrinkage strain of concrete occurs relatively uniformly and can be regarded as a one-dimensional displacement in the longitudinal direction, with a maximum of about 0.1%, but expansion strain shows non-uniform behavior, and when unconstrained, twisting and distortion may occur during expansion, some of which may cause expansion of 1 to 2%. Therefore, there was a problem that expansion strain such as ASR and DER cannot be accurately measured because there is a large variation between individuals.

Furthermore, the conventional DEF accelerated evaluation method also uses test specimens of the same size as the ASR judgment method, 100 x 100 x 400 mm or φ100 x 200 mm, so the expansion strain is often excessive, on the order of several percent, and no standardized evaluation method exists.
In addition, for structures that are at risk of ASR, it is necessary to estimate the future extent of expansion, and the aforementioned residual expansion amount is the estimated value of this "future extent of expansion." One of the methods for testing the residual expansion amount is JCI-DD2. In this test method, the core is specified to be, in principle, 100 mm in diameter and approximately 250 mm in length. However, in reality, it is difficult to extract a core of this size due to reinforcing bars in the concrete, etc.

Therefore, methods for continuously tracking ASR and DEF and methods for early detection have been proposed. For example,
The method of continuously tracking cracks caused by ASR described in Patent Document 1 involves drilling a small-diameter monitoring hole in a concrete structure, scanning the wall surface of the hole with a first sensor, performing a primary diagnosis of ASR by image analysis, and if a follow-up investigation is necessary, inspecting the remaining load-bearing capacity, and if the remaining load-bearing capacity is equal to or greater than the required load-bearing capacity, further monitoring the progression of the cracks by installing a second sensor on the wall surface of the hole in order to confirm the progression of ASR, etc. However, this method requires drilling the concrete structure, and the tracking work is cumbersome.
The method for determining DEF described in Patent Document 2 is a method for determining that DEF does not occur when the difference between the relative intensity of powder X-ray diffraction of ettringite in a hydrated sample taken from a cement composition before high-temperature curing and the relative intensity of powder X-ray diffraction of ettringite in a hydrated sample taken from a cement composition after high-temperature curing is 5% or less. However, this method is based on observation at the time of sample collection, and cannot observe the change over time in expansion behavior after high-temperature curing, and the equipment is expensive.

JP 2014-189961 A JP 2010-223634 A

The present invention aims to provide a method for easily and efficiently measuring the expansive strain of concrete caused by ASR, DEF, etc., and an expansive strain measuring device.

As a result of extensive research into a method for measuring expansion strain that would achieve the above-mentioned objective, the inventors discovered that the above-mentioned objective could be achieved by using a laser to measure the expansion of a test specimen of a specific shape, and thus completed the present invention.
That is, the present invention provides an expansion strain measuring method and an expansion strain measuring device having the following configurations.

[1] (A) one or more laser displacement meters, (B) a base for placing a specimen for measuring expansion strain, and (C) a positioning jig for the specimen. After placing the specimen on a base of an expansion strain measuring device,
A method for measuring expansive strain in which a laser displacement meter is used to irradiate a laser onto the peripheral side of a specimen and measure the distance between the laser displacement meter and the peripheral side of the specimen, thereby measuring the expansive strain of the specimen.
However, the test specimen is a hardened concrete body, and the thickness of the test specimen is greater than the maximum dimension of the coarse aggregate.
[2] A method for measuring expansion strain described in [1], in which the specimen is placed on a base of the expansion strain measuring device so that the peripheral side of the specimen is in contact with a positioning jig.
[3] The method for measuring expansive strain described in [1] or [2], wherein the specimen is disc-shaped or polygonal-shaped.
[4] The method for measuring expansive strain described in any one of [1] to [3], wherein the specimen is rotated clockwise or counterclockwise to measure the distance between the laser displacement meter and the peripheral side of the specimen multiple times, and the average value of these distances is calculated as the expansive strain of the specimen.
[5] The method for measuring expansive strain according to any one of [1] to [4], wherein the thickness of the specimen is 15 to 25 mm.
[6] The method for measuring expansive strain according to any one of [1] to [5] above, wherein the test specimen is placed on a pedestal and the expansive strain is measured every time a predetermined period of time has elapsed.
[7] The method for measuring expansive strain according to any one of [1] to [ ₆ ] above, wherein a metal plate (base plate) having the same shape and dimensions as the specimen before expansion is placed on a base, the distance (L 1 ) between the laser displacement meter and the peripheral side of the metal plate is measured, and then the specimen is placed on the base in place of the metal plate, the distance (L ₂ ) between the laser displacement meter and the peripheral side of the specimen is measured, and the difference between L ₁ and L ₂ (L ₁ -L ₂ ) is defined as the expansive strain.
[8] A method for measuring expansive strain described in any one of [1] to [6] above, comprising placing a metal plate (base plate) having the same shape and dimensions as the specimen before expansion on a base, measuring the distance between a laser displacement meter and the peripheral side of the metal plate, setting the distance (indicated as ) to zero, and then placing the specimen on the base in place of the metal plate, measuring the distance between the laser displacement meter and the peripheral side of the specimen, and determining the expansion strain.

The method and device for measuring expansion strain according to the present invention have the following advantages.
(i) The expansive strain of concrete caused by ASR, DEF, etc. can be measured simply and efficiently.
(ii) Since the installation of gauge plugs or instruments is not required and the length of the specimen can be measured directly, there is no limit to the change in length. Specifically, in the conventional contact gauge method, the measurable range of the expansion strain of the measuring device is about ±0.5 mm, and expansion strains exceeding this range cannot be measured. In addition, in the method of installing gauge plugs, if twisting or distortion occurs, the gauge plugs do not align with each other, so measurement is not possible. On the other hand, in the present invention, the measurable range of the laser displacement meter is as large as about ±5 mm, and even if twisting or distortion occurs, the expansion strain can be easily measured by simply irradiating a laser onto the side surface around the disk specimen.
(iii) The specimen used in the present invention is smaller and lighter than the specimens used in the JCI-S-101-2017, JASS 5N T-603, and JCI-DD2 methods, making it easier to move the specimen and perform other operations. Furthermore, many test levels can be performed, and the tests can be completed in a relatively short period of time.

This is a schematic diagram showing an example of a state in which a test specimen is placed on an expansion strain measuring device of the present invention having one laser displacement meter, where the left figure is a plan view of the measuring device and the right figure is a side view of the measuring device. This is a schematic diagram showing an example of a state in which a test specimen is placed on an expansion strain measuring device of the present invention having two laser displacement meters, where the left figure is a plan view of the measuring device and the right figure is a side view of the measuring device. This is a schematic diagram showing an example of a state in which a test specimen is placed on a support member that is installed with a part of the lower part of the support member embedded in a pedestal, the left figure being a plan view of the measuring device, and the right figure being a side view of the measuring device. However, in Fig. 3, the laser displacement meter is omitted. 3 shows the expansion strain of the disk specimens after a storage period of 182 days, measured using the expansion strain measuring device shown in FIG. 2.

The present invention is the method for measuring expansion strain and the expansion strain measuring device as described above. The present invention will be described in detail below in the order of the expansion strain measuring device and the method for measuring expansion strain.

1. Expansion Strain Measuring Device (A) Laser Displacement Gauge The laser displacement gauge 4 used in the present invention is not particularly limited, and examples thereof include commercially available laser displacement gauges of the reflection type and transmission type.
In the present invention, increasing the number of laser displacement meters increases the amount of data and improves the measurement accuracy accordingly; however, the cost of the device increases, so the number of laser displacement meters is preferably 1 to 4, and more preferably 1 to 2.
The laser displacement meter is installed so that a laser can be irradiated toward the center of a disk-shaped or square plate-shaped specimen 1 placed on a pedestal. The laser displacement meter can be installed at any of the positions shown in Figs. 1 and 2, for example.

(B) Pedestal The pedestal 2 used in the present invention is used to place a specimen for measuring expansive strain. The shape of the pedestal is not particularly limited, and may be, for example, a square plate or a disk as shown in Figures 1 and 2. In order to improve the measurement accuracy, it is preferable that the pedestal be kept horizontal.
Furthermore, the base is preferably manufactured using Invar steel to prevent deformation due to heat or impact.

Furthermore, the base may be provided with a support member 5 for supporting a specimen for measuring the expansive strain. By providing the support member, the transfer of heat between the specimen for measuring the expansive strain and the base can be reduced, thereby improving the measurement accuracy of the expansive strain.
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 part of the support member is embedded in the base), a columnar shape, etc. When the support member is columnar, it is preferable that the upper part is hemispherical.
The number of support members is preferably three or more because the specimen can be stably placed on the support member, but the number of support members increases the time and effort required to manufacture the device. Therefore, the number of support members is preferably three to four. In order to stably place the specimen on the support member, the support members are preferably arranged to form an equilateral triangle or a square. Figure 3 shows an example in which the support members are arranged to form a square.
Furthermore, the support member is preferably manufactured using Invar steel to prevent deformation due to heat or impact.

(C) Positioning jig The positioning jig 3 used in the present invention is used to determine and fix the placement position of the specimen when measuring the expansion strain of the specimen, and may be, for example, two pins installed in an inverted state on a pedestal as shown in Figures 1 and 2. In Figures 1 and 2, when a disk-shaped specimen is placed on the pedestal at the start of measurement, the positioning jig is placed in a position where it comes into contact with the peripheral side of the disk-shaped specimen so that the center of the disk-shaped specimen coincides with the center of the pedestal. This arrangement allows the irradiation position of the peripheral side of the specimen to be measured to be accurately fixed, improving the expansion accuracy of the expansion strain.
Furthermore, the positioning jig is preferably manufactured using Invar steel to prevent deformation due to heat or impact.

The expansion strain measuring device of the present invention is preferably constructed by integrating the laser displacement gauge, the base, and the positioning jig using a base. In this case, the base used to install the laser displacement gauge, the base, and the positioning jig is preferably manufactured using Invar steel to prevent deformation due to heat or impact.

2. Expansion strain measurement method of the present invention is a method for measuring the expansion strain of a specimen by placing a disk-shaped or square plate-shaped specimen on the base of the expansion strain measurement device so that the peripheral side surface of the specimen is in contact with a positioning jig, and then irradiating the peripheral side surface of the specimen with a laser using a laser displacement meter to measure the distance between the laser displacement meter and the peripheral side surface of the specimen.
The specimen is a hardened cement composition such as concrete or mortar.
In the case where the specimen is disc-shaped, the diameter of the specimen is preferably 10 to 30 cm, since the specimen can be easily manufactured. The diameter of the specimen is more preferably 10 to 20 cm. Furthermore, if the thickness of the specimen is 5 mm or more, the specimen is less likely to break, and if it is 50 mm or less, the workability is good, which is preferable. The thickness of the specimen is more preferably 8 to 40 mm, further preferably 10 to 30 mm, and particularly preferably 15 to 25 mm. In the case where the specimen is concrete, the thickness is preferably larger than the maximum dimension of the coarse aggregate specified by JIS. If the thickness of the specimen is smaller than the maximum dimension of the coarse aggregate, the expansive gel of the ASR may leak out, and the expansive strain may not be accurately captured.
In addition, 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 even more preferably, the square has a side length of 10 to 30 cm, and particularly preferably, the square has a side length of 10 to 20 cm. If the length of one side is 10 to 30 cm, the specimen can be easily manufactured. In addition, the thickness of the square plate specimen is preferably about the maximum dimension of the coarse aggregate, more preferably 8 to 40 mm, even more preferably 10 to 30 mm, and particularly preferably 15 to 25 mm. If the thickness of the specimen is 8 mm or more, the specimen is less likely to crack, and if it is 40 mm or less, the workability is good. If the thickness of the specimen is smaller than the maximum dimension of the coarse aggregate, the expansive gel of the ASR may leak out, and the expansive strain may not be accurately captured.
In addition, when a support member is installed on the base of the expansion strain measuring device of the present invention, the disk-shaped or square plate-shaped specimen is placed on the support member so that the peripheral side of the specimen is in contact with the positioning jig.

In the measurement method of the present invention, the specimen is placed on a pedestal and the expansion strain is measured every predetermined period. In order to improve the measurement accuracy of the expansion strain, the specimen is preferably disk-shaped, and the specimen is rotated clockwise or counterclockwise to measure the distance between the laser displacement meter and the side surface of the specimen, with the side surface of the specimen in contact with the positioning jig, multiple times, preferably 3 to 5 times. For example, after measuring point a of the specimen shown in FIG. 1, the specimen is rotated 90° clockwise to measure point b, and then rotated 90° clockwise to measure point c, and the average value of the three points is obtained as the expansion strain. Specifically, the disk specimen is considered to expand relatively uniformly in all directions, but even if it expands non-uniformly, the length in different diameter directions can be measured by rotating and measuring, so that the measurement value is stable and the accuracy is improved by using the average value.
In the measurement method of the present invention, the interval for measuring the expansion strain is arbitrary, but in order to reduce the labor required for measurement, it is preferably every 1 to 10 days, more preferably every 1 to 7 days.

Furthermore, in order to measure the expansion strain more accurately, the measurement method of the present invention involves placing a metal plate (base plate) having the same shape and dimensions as the specimen before expansion on a pedestal, measuring the distance (L ₁ ) between the laser displacement meter and the peripheral side of the metal plate, and then placing the specimen on the pedestal in place of the metal plate and measuring the distance (L ₂ ) between the laser displacement meter and the peripheral side of the specimen, and the difference between L ₁ and L ₂ (L ₁ -L ₂ ) is the expansion strain.
In addition, when using a measuring device that displays the measured distance on a screen, the measuring method of the present invention is a method in which a metal plate (base plate) having the same shape and dimensions as the specimen before expansion is placed on a pedestal, the distance between the laser displacement meter and the peripheral side of the metal plate is measured, the distance (displayed) is set to zero, and then the specimen is placed on the pedestal in place of the metal plate, and the distance between the laser displacement meter and the peripheral side of the specimen is measured to obtain the expansion strain. Specifically, by using the metal plate (base plate), the device can be calibrated and errors from the previous measurement can be corrected.
The base plate is desirably made of a metal that is not easily affected by temperature, humidity, wear, etc., and is preferably made of Invar steel to prevent deformation due to heat or impact.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
1. Materials used (1) Cement (abbreviation: C): Ordinary Portland cement, manufactured by Taiheiyo Cement Corporation.
(2) Fine aggregate (abbreviation: S): mountain sand.
(3) Coarse aggregate (abbreviation: G1): Reactive aggregate (andesite) with a maximum dimension of 20 mm. Andesite contains a large amount of highly reactive silica minerals (cristobalite, tridymite, small crystal quartz, and amorphous volcanic glass).
(4) Coarse aggregate (abbreviation: G2): Crushed stone (hard sandstone) with a maximum dimension of 20 mm.
(5) Water (abbreviation: W): tap water.
(6) AE water reducing agent (abbreviation: AD): a lignin sulfonic acid-based AE water reducing agent, the product name of which is Pozzolith No. 70 [registered trademark] (manufactured by BASF Corporation).
(7) NaOH (abbreviation: Na): A reagent of sodium hydroxide.
The reactive aggregate is an aggregate containing highly reactive minerals (such as silica minerals), and examples thereof include volcanic rocks such as andesite and sedimentary rocks such as chert.

2. Preparation of specimens for measuring expansive strain According to the formulations shown in Table 1, for each formulation, the above-mentioned materials were all charged into a 50-liter pan-type mixer, mixed for 2 minutes, and then cast into a cylindrical formwork to obtain a concrete specimen with a diameter of 10 cm, a height of 20 cm, and a total alkali content of 5.5 kg/ ^m3 of concrete in terms of _Na2O . Next, the concrete was sliced to a thickness of 2 cm to prepare three disk specimens for measuring expansive strain. These nine specimens were named specimen No. 1, No. 2, and No. 3 for each formulation.

3. Measurement of Expansion Strain of Specimen The disk specimen was wet cured at 20° C. for a storage period (material age) of 56 days, then switched to wet curing at 40° C., and the length of the specimen was measured every 7 days to calculate the expansion strain. Specifically, the disk specimen was placed on the base of the expansion strain measuring device so that the peripheral side of the specimen was in contact with the positioning jig, and then a laser was irradiated to the peripheral side of the specimen using a laser displacement meter to measure the distance between the laser displacement meter and the peripheral side of the specimen.
For reference, the expansion strain of a rectangular column specimen measuring 100 x 100 x 400 mm was measured in accordance with the method of JCI-S-101-2017.
The results are shown in Table 2 and FIG.

As shown in Table 2 and Figure 4, when the JCI method was used with rectangular column specimens, large expansive strain occurred in mixes 1 and 3, and ASR gel due to reactive aggregate was also observed. On the other hand, the expansive strain after 182 days of storage for mixes 1 and 3 of 2 cm thick disk specimens was about 800 to 600 x ^10-6 on average for specimens No. 1 to 3, with little variation, and the expansive strain was able to be captured.
Furthermore, since the present invention can compare expansion strains relatively, it is possible to easily grasp and compare the evaluation of pessimums with different mixing ratios of reactive aggregates, such as comparing Mix 1 and Mix 3. It is also possible to evaluate differences in the type of reactive aggregate and the influence of environments such as temperature and humidity.
The present invention is not limited to expansion strain caused by ASR, but can also be applied to expansion strain caused by DEF.

1 Test specimen 2 Pedestal 3 Positioning jig 4 Laser displacement meter (note that the black arrow indicates the laser.)
5 Support member

Claims (8)

(A) one or more laser displacement meters, (B) a base for placing a specimen for measuring expansion strain, and (C) a positioning jig for the specimen. The specimen is placed on a base of an expansion strain measuring device,
A method for measuring expansive strain in which a laser displacement meter is used to irradiate a laser onto the peripheral side of a specimen and measure the distance between the laser displacement meter and the peripheral side of the specimen, thereby measuring the expansive strain of the specimen.
However, the test specimen is a hardened concrete body, and the thickness of the test specimen is greater than the maximum dimension of the coarse aggregate. The method for measuring expansion strain according to claim 1, wherein the specimen is placed on the base of the expansion strain measuring device so that the peripheral side of the specimen is in contact with a positioning jig. The method for measuring expansion strain according to claim 1 or 2, wherein the specimen is disc-shaped or polygonal-shaped. The method for measuring expansive strain according to any one of claims 1 to 3, in which the specimen is rotated clockwise or counterclockwise to measure the distance between the laser displacement meter and the peripheral side of the specimen multiple times, and the average of these distances is calculated as the expansive strain of the specimen. The method for measuring expansion strain according to any one of claims 1 to 4, wherein the thickness of the test specimen is 15 to 25 mm. A method for measuring expansion strain according to any one of claims 1 to 5, in which a test specimen is placed on a pedestal and the expansion strain is measured every time a predetermined period of time has elapsed. 7. The method for measuring expansive strain according to claim 1, further comprising the steps of: placing a metal plate (base plate) having the same shape and dimensions as a specimen before expansion on a pedestal; measuring the distance (L ₁ ) between a laser displacement meter and the peripheral side of the metal plate; placing the specimen on the pedestal in place of the metal plate; measuring the distance (L ₂ ) between the laser displacement meter and the peripheral side of the specimen; and determining the difference (L ₁ -L ₂ ) between L ₁ and L ₂ as the expansive strain. The method for measuring expansive strain according to any one of claims 1 to 6, comprising placing a metal plate (base plate) having the same shape and dimensions as the specimen before expansion on a base, measuring the distance between a laser displacement meter and the peripheral side of the metal plate, setting the distance (indicated as) to zero , and then placing the specimen on the base in place of the metal plate, and measuring the distance between the laser displacement meter and the peripheral side of the specimen to obtain the expansive strain.

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