JP2013015382A - Method for testing quality management of crack suppression control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply estimate mixing/non-mixing of an addition material (additive) to a drying shrinkage crack suppression concrete and estimate a substantial amount of the mixture.SOLUTION: A strain gauge with a predetermined gauge length is stuck to the lateral surface of a thin-wall cylindrical molding to measure an amount of strain of the gauge immediately after the concrete installation to a predetermined material age, and whether the addition material or the additive for shrinkage crack suppression is appropriately mixed in the concrete or not is determined. It is preferable to measure the circumferential strain by sticking a strain gauge with the gauge length 10 mm or more to a height-directional central position of the thin-wall cylindrical molding.

Description

  The present invention relates to a quality control test method for crack-suppressing concrete, and is added to suppress the occurrence of shrinkage cracks in concrete carried into the concrete placement site. The present invention relates to a quality control test method for crack-suppressing concrete capable of easily determining whether or not a reducing agent is mixed.

  In 2009, the JASS5 regulations were revised. Among them, regarding the regulation of drying shrinkage in quality control of concrete, the contractor performs trial kneading before starting construction to obtain the drying shrinkage, and confirms that it is below the specified shrinkage or specified value. Requirements such as must be specified. In response to such regulations, an expansion material and a shrinkage reducing agent are mixed as an additive (agent) that is expected to have a shrinkage reducing effect on concrete, and a shrinkage crack (hereinafter referred to as a shrinkage crack in this specification is simply called a crack) It is thought that concrete with controlled generation will increase in the future.

  For example, as for the test of concrete mixed with an expansion material to suppress shrinkage cracking (hereinafter referred to as expanded concrete), the uniaxial restraint specified in JIS A 6202 Annex 2 (reference) is used as the expansion test. There is an expansion test method for expanded concrete in a state (test method in which only expansion is symmetric: hereinafter referred to as A method test). Moreover, regarding the strength test and the like, a quality control method devised according to the type of cement has been proposed (Patent Document 1).

JP 2006-177808 A

  However, although the above-mentioned A method test is a test prescribed in the JIS standard, a large specimen for bending test is used, and a concrete restraint device is buried in the mold to produce a test specimen. And the amount of expansion in the hardening process of the concrete in the restraint state in a formwork is measured with a length measuring device. For this reason, it was difficult to adopt as a field test. The purpose of quality control in Patent Document 1 is to control the strength of concrete. The quality of quality is determined by quickly verifying the presence or absence of the expansion material in the ready-mixed concrete received at the concrete placement site and the amount of expansion material used. It is not suitable to be applied as a test method that can be managed.

  This is due to the mixing amount and components of the concrete expansion material and the measurement method of the expansion amount. In other words, the amount of the expanded material mixed in the expanded concrete is a very small amount of less than 1% of the volume of the concrete, so it cannot be judged from the appearance characteristics of the ready-mixed concrete, and the expanded material component is cement. Similarly, since it is calcium, it is difficult to determine the presence or absence of contamination in the component analysis. In addition, analytical measurements are highly specialized, such as the need for dedicated equipment, making it difficult to apply at each site.

  Moreover, since the shrinkage reducing agent generally contains a nonionic surfactant as a main component, it is necessary to perform a qualitative analysis of concrete or the like in order to confirm that it has been added. Therefore, it was difficult to simply confirm the presence or absence of a shrinkage reducing agent at each site.

  The applicant has already measured the amount of strain on the outer surface of the cylindrical form frame from immediately after placing the concrete to a predetermined material age, grasps the change over time in the amount of strain indicating the expansion tendency during that time, A proposal has been made to confirm the presence or absence of a shrinkage reducing agent and to estimate the amount (see Japanese Patent Application No. 2011-11421). Cylindrical formwork used for the measurement of strain is not a durable cast cylindrical formwork that is used repeatedly, but a thin wall made by processing or resin molding a thin iron plate that is supposed to be used only once. It is a cylindrical formwork. A strain gauge is affixed to the outer surface of the thin cylindrical mold frame, and the amount of strain is measured. In that case, an error is expected to occur in the measured strain due to the difference in gauge length of the strain gauge to be attached. Therefore, the object of the present invention is to solve the problems of the conventional techniques described above, and in concrete construction sites, etc., by using a simple test method, whether or not the expansion material and the shrinkage reducing agent are mixed in the concrete to be tested. Quality control test of crack-suppressing concrete that measures the appropriate amount of strain of the cylindrical form, which is the object of measurement, and manages the amount of strain appropriately so that confirmation and approximate estimation of the amount of expanded material can be performed It is to provide a method.

  In order to achieve the above object, the present invention attaches a strain gauge having a predetermined gauge length to the outer surface of a thin cylindrical mold frame, measures the strain amount of the strain gauge from immediately after placing concrete to a predetermined age, From the change over time in the amount of strain, it is characterized in that it is determined whether the concrete is appropriately mixed with an additive or additive for suppressing shrinkage cracking.

  The strain amount is preferably measured by applying a strain gauge having a gauge length of 10 mm or more to the center position in the height direction of the thin cylindrical mold frame and measuring the strain in the circumferential direction.

  As for the amount of strain, it is preferable that a strain gauge having a gauge length of 5 mm or more is attached to the central position in the height direction of the thin cylindrical mold frame, and the axial strain is measured.

  Determining that the expansion material is mixed by the amount of strain showing a steep rise immediately after concrete placement and until one day of material age, and gradually increasing or almost constant to a predetermined value at the subsequent material age. Can do.

  As the thin-walled cylindrical mold, it is preferable to use a disposable mold for a cylindrical specimen for a concrete strength test.

  It is preferable to use a thin steel plate mold for the disposable mold for a cylindrical specimen.

  The amount of strain is the amount of strain determined by the expansion test method of expanded concrete in a uniaxial restraint state defined in JIS A 6202 Annex 2 (reference) with respect to the equivalent amount of additive or additive for suppressing shrinkage cracking. The strain amount obtained by the expansion test method of the expanded concrete in the linear regression relation and in the uniaxial constraint state can be obtained by multiplying the strain amount measured by the test method of the present invention by 1.1.

  As mentioned above, when conducting quality control of concrete mixed with expansive material, a strain gauge with an appropriate gauge length is affixed to a thin cylindrical formwork, and the change in strain is measured, making it easy on site. In addition, it is possible to determine whether or not the expansion material is mixed, and in the predetermined blending range, it is possible to roughly grasp the initial expansion amount when the standard amount of the expansion material is mixed.

Explanatory drawing which showed the external appearance shape of the thin cylindrical formwork, and the sticking position of a strain gauge (the 1). Explanatory drawing which showed the external appearance shape of the thin-walled cylindrical formwork, and the sticking position of a strain gauge (the 2). The graph which showed the relationship between the age from implantation | striking in 1 mm of gauge length, and the amount of measurement strain. The graph which showed the relationship between the age from implantation | striking in 5 mm of gauge length, and the amount of measurement distortion. The graph which showed the relationship between the age from implantation | striking in the gauge length of 10 mm, and the amount of measurement distortion. The graph which showed the relationship between the age from implantation | striking in 30 mm of gauge length, and the amount of measurement distortion. The figure which showed the distortion amount (average value) by each gauge length in 7 days of age, and dispersion | variation. The relationship graph of the amount of mold distortion at the time of using a steel mold, and age. The relationship graph of the amount of mold distortion at the time of using a resin mold, and age. The relationship graph of the amount of mold distortion in each mixing amount of expansion material, and material age. (Water cement ratio = 55%) The relationship graph of the amount of mold distortion in each mixing amount of expansion material, and material age. (Water cement ratio = 45%) The relationship graph of the amount of mold distortion in each mixing amount of expansion material, and material age. (Water cement ratio = 35%) The relationship graph of the amount of mold distortion and material age in a contrast test with a JIS standard test. (Expansion material amount 20, 25kg / m ³ ) The relationship graph of the amount of mold distortion and material age in each level which applied the present invention to A field. The relationship graph of the amount of mold distortion and material age in each level which applied the present invention to B field. The relationship graph of the amount of mold distortion and material age in each level which applied the present invention to C field. The relationship graph (each test body data) with the amount of mold distortion and material age for every level at the time of mixing an expansion material and a shrinkage reducing agent. The relationship graph (experiment average value) of the amount of mold distortion for every level at the time of mixing an expansion material and a shrinkage reducing agent. The graph which showed the distortion amount in this invention, and the relationship between the distortion amount in A method test.

  Hereinafter, the following examples will be described with reference to the accompanying drawings as modes for carrying out the quality control test method for crack-suppressing concrete of the present invention.

  The technical feature of the present invention is that the amount of strain generated on the outer surface of a thin-walled cylindrical form made of various materials used for the strength test of concrete using a cylindrical specimen is measured from immediately after placing the concrete to about 7 days of age. From the tendency of the change over time, the presence or absence of the expansion material and the shrinkage reducing agent and the amount of mixing are roughly estimated. By applying the quality control test of the present invention, the quality control of the crack-suppressing concrete mixed with the expansion material and the shrinkage reducing agent can be easily performed at a construction site or the like.

  In the present invention, in order to achieve the predetermined effect of the present invention, it is premised that the amount of strain can be accurately measured on the surface of the above-described cylindrical frame. Therefore, the thin-walled cylindrical form used as a form for a cylindrical specimen for a concrete strength test was used. The thickness of the existing thin cylindrical form is appropriately set according to the strength of the material used (steel plate, synthetic resin, waterproof paper). For example, as a material used for the existing thin-walled cylindrical form, it is about 0.3 mm for a steel plate and about 1.5 to 2.5 mm for a synthetic resin and a paper material. In the present invention, the thickness of the material is set so that the mold has a strength to maintain a predetermined specimen size at the time of preparation of the concrete specimen, and the amount of distortion on the surface of the mold that changes during the concrete hardening process can be accurately measured. What is necessary is just to set and it is just about t / r <= 0.1 (t: plate | board thickness, r: test body radius (internal dimension radius of a formwork)) in various materials. In the present embodiment, a thin-walled cylindrical mold (hereinafter referred to as a disposable mold) is used as a test cylindrical mold, which is used only for producing a test specimen once and discarded after the concrete specimen is removed from the mold. However, it is needless to say that the quality control test according to the present invention can be carried out even in a thin cylindrical mold that can be used repeatedly.

  Hereinafter, as a verified test example (example), an example according to the type of each disposable mold as the thin cylindrical mold to be used, a validity verification test of the gauge length used, the amount of intumescent material mixed and the amount of strain in the circumferential direction The result of the comparison test with the test for obtaining the relationship with the test and the test based on the JIS standard will be described.

[1. Verification of effectiveness of form type and form strain measurement direction]
Hereinafter, with respect to two examples using different types of disposable molds, the verification results of the accuracy of each material property and the difference in strain measurement direction will be described with reference to the drawings and tables.
(Example 1: Thin steel plate form-strain gauge application direction = circumferential direction, axial direction)
(Example 2: Synthetic resin mold-strain gauge sticking direction = circumferential direction, axial direction, bottom surface)

(Example 1: Thin steel plate form-strain gauge application direction = circumferential direction, axial direction)
(1) Material used and measurement direction The thin steel plate form 10 (hereinafter referred to as a steel mold) used in this example is a cylindrical shape obtained by processing the tin plated thin steel plate illustrated in FIG. It is an off-the-shelf product (trade name: lightweight mold SUMMIT) used as a mold for test specimens, and the cylindrical side surface has a single steel plate, and the bottom plate has a double structure to ensure smoothness. In this example, a steel mold for a test specimen of φ100 × height 200 mm was used. Further, in order to measure the deformation (strain) of the steel mold 10, the measurement positions and directions shown in FIGS. 1A and 1B (hereinafter, the direction of (a) is the circumferential direction, (b ) Direction is referred to as the axial direction.) Strain gauges 11 and 12 are affixed to each of the strain gauges 11 and 12 and lead wires 13 (shown as a single diagram for the sake of simplicity). The strain change (circumferential direction, axial direction) of the mold 10 between a predetermined age and immediately after the concrete C of each level is placed in the mold 10 is extended to the measuring apparatus 14. Measurements were made continuously to determine the expansion properties of concrete.
(2) Concrete blending and fresh properties Tests are conducted with an example of blending concrete containing expansive material (hereinafter simply referred to as expansive concrete) among crack-controlling concrete. The fresh properties were as shown in Table 1-1 and Table 1-2, and the amount of the expanded material mixed was set to the standard use amount (20 kg / m ³ ).

[Table 1-1]

[Table 1-2]

(Example 2: Synthetic resin mold-strain gauge sticking direction = circumferential direction, axial direction, bottom surface)
(1) Material used and measurement direction The synthetic resin mold (hereinafter referred to as resin mold) used in this example is a resin molded product formed into a cylindrical shape, and is a cylindrical type for a cylindrical specimen. As shown in FIG. 1 (c), a flange 10a is formed on the bottom surface of the mold, which is an off-the-shelf product (trade name: plastic mold (φ100 × 200 mm): manufactured by Floric Co., Ltd.). A bottom steel plate 15 is fixed to the flange 10a. Thereby, the smoothness of the end face of the specimen is ensured. The mold dimensions are the same as in Example 1. Also in this resin mold, in order to measure deformation (strain), as shown in FIGS. 1A and 1B, strain gauges 11 and 12 are attached in the circumferential direction and the axial direction, respectively. The lead wires 13 are extended from the respective strain gauges 11 and 12 to the measuring device 14, and the molds between immediately after each level of concrete C is placed in the mold 10 by the measuring device 14 until a predetermined age. It was decided to continuously measure the strain change of the concrete and grasp the expansion property of the concrete. Furthermore, in Example 2, the strain gauge 16 was affixed also to the bottom steel plate 15, and the expansion | swelling property in the bottom face was grasped | ascertained (FIG.1 (c)).
(2) Concrete mix and fresh properties The mix and fresh properties of the used expansive material-mixed concrete (hereinafter simply referred to as expansive concrete) are the same as in Table 1-1 and Table 1-2. Standard usage (20 kg / m ³ ) was set.
[2. Strain gauge proper gauge length verification test]
In Example 1 described above, strain gauge lengths of different gauge lengths (referred to as strain-measurable range lengths in this specification) are pasted on the surface of a thin steel plate formwork, and the amount of strain is applied. Verify the measurement error and set the gauge length of the strain gauge suitable for the following test.
(1) Material used, measurement direction In order to measure the deformation (strain) of the steel mold 10 using the steel mold used in Example 1, as shown in FIGS. The strain gauges 11 and 12 (6 sheets in total) were affixed at three locations (approximately 120 ° intervals) in the circumferential direction, with the circumferential direction and the axial direction as a set. The wiring of the lead wire 13 to the measuring device 14 is the same as that in the first embodiment. In the verification test, the strain gauge gauge length (La: axial gauge length, Lc: circumferential gauge length) is set to 4 levels of La = Lc = (1, 5, 10, 30) mm. The strain change (circumferential direction, axial direction) of the mold 10 immediately after the concrete C was placed in the mold 10 up to a predetermined age (7 days) was continuously measured. FIG. 2 (c) shows an example in which a strain gauge having a gauge length (La = Lc) of 10 mm is attached to the outer surface of the mold for explanation.
(2) Concrete mix and fresh properties The mix and fresh properties of the concrete used for the validity verification test of the gauge length used are as shown in Table 2-1 and Table 2-2. The standard usage (20 kg / m ³ ) was set as in Examples 1 and 2.

[Table 2-1]

[Table 2-2]

[About the mold length and strain gauge length used in the verification test]
(1) Strain amount measurement test results and knowledge based on the difference in gauge length of strain gauges Each test specimen (with respect to four levels of strain gauge gauge length (La = Lc) 1, 5, 10, 30 mm) 3 to 6 show the measurement results of strain amounts in the respective measurement directions (circumferential direction and axial direction) from immediately after placing the concrete to 7 days of age in 3 specimens for 1 level). Show. Moreover, the distortion amount (average value) and variation by each gauge length in the age of 7 days are shown in FIG. The following knowledge was obtained from the above results.
・ The variation in the amount of strain in the circumferential direction differs greatly when the gauge length (Lc) is 5 mm or less and 10 mm or more, and when Lc = 10 mm or more, there is almost no data variation. Therefore, the measurement error between the specimens can be reduced by setting the gauge length to 10 mm or more in the circumferential direction.
-Since the variation in the axial direction is generally smaller than that in the circumferential direction, the gauge length can be 5 mm or more.
(2) Test results and knowledge to verify the difference in formwork a) Each measurement direction (circumferential direction, axis) immediately after placing concrete (with or without expandable material) in steel mold until age 7 days The measurement results of the strain amount in the (direction) are shown in FIGS. The + side of the strain amount in the graph is the expansion side. The following knowledge was obtained from the above results.
-The expansion side can be confirmed when the expansion material is used, and the contraction side distortion can be confirmed when the expansion material is not used, so that the presence or absence of the expansion material can be clearly determined.
・ The difference between levels is small and the accuracy is good.
・ When comparing the circumferential direction and the axial direction, the amount of strain is larger in the circumferential direction.
b) Measurement results of strain in each measurement direction (circumferential direction, axial direction, bottom surface) from immediately after placing concrete (with or without expansion material) to resin mold until age 7 days are shown in FIG. a) to (f). In addition, like FIG. 8 each figure, the + side of the strain amount in the graph is the expansion side. The following knowledge was obtained from the above results.
-When an expansion material is used, since a larger strain amount than that of a steel mold can be confirmed on the expansion side, the presence or absence of the expansion material is easy.
・ There is a slight variation between levels, and there is a level with large fluctuations after a certain age.
・ When no expansion material is mixed, a peak on the contraction side appears in the initial stage.
・ Although not noticeable, the presence or absence of the expansion material can also be confirmed by the amount of strain of the bottom steel plate.
(3) Summary From the above points,
-When a strain gauge is attached in one direction, the circumferential direction is preferred, and the gauge length of the strain gauge is preferably Lc = 10 mm.
-When measuring the strain amount in the axial direction, a strain gauge with a gauge length La = 5 mm can be used.
-It is preferable to use a steel mold as the cylindrical mold, to determine whether or not the expansion material is mixed, and to estimate the mixing amount. Although it was confirmed that the resin mold is expected to be applied at a young age, the following verification test is for conducting tests up to about 7 days of material age. As is clear from the above-described verification test, any resin mold or steel mold can be adopted as long as the appropriate material age is selected.

[3. Relationship between amount of expansion material mixed and mold strain]
We will investigate the water cement ratio of concrete and the amount of mixed expansion material, clarify the relationship between the amount of expanded material mixed and the amount of strain in the mold, and grasp the qualitative expansion properties of expanded concrete.
(1) Test level and concrete mix Table 3 shows the test level and concrete mix. The water powder ratio {water / (cement + expansion material)} was set to three levels of 55%, 45%, and 35%. Also, the amount of expansion material mixed is 0 kg / m ³ (no contamination), 10 kg / m ³ (0.5 times the standard usage), 20 kg / m ³ (standard usage), 30 kg / m ³ (standard usage) (1.5 times), and 12 (3 × 4) level. Each fresh property is shown in Table 4.

[Table 3]

[Table 4]

(2) Test results and knowledge FIGS. 10 to 12 show the test results of the strain amount of each mold immediately after concrete placement (injection) to 7 days of age. The plus side in the graph is the expansion side. The following knowledge was obtained from the above results.
-Since all the levels show a sharp rise tendency of the strain amount up to the first day of material age, a general tendency can be grasped by the tendency of strain change up to the first day of material age and the subsequent change in age of the material.
-For each water powder ratio, the amount of strain on the expansion side increases as the amount of the expanded material mixed increases.
・ For each water powder ratio, when the standard amount (20 kg / m ³ ) of the expanded material is mixed, the mold strain amount reaches between 100 and 200 μ at 7 days of age.
・ When the water powder ratio is 35%, the mold strain is smaller than other levels due to the effect of self-shrinkage during curing.

[4. Validity verification of this test by comparison with JIS standard test]
Contrast the results of the above test (hereinafter referred to as the main test) with the existing test already defined in the JIS standard (JIS A 6202 Annex 2 (Reference) Restraint Expansion Test A Method for Expanded Concrete). The validity of this study was verified.
(1) Test level and concrete mix Table 5 shows the test level and concrete mix. The water-cement ratio is about 45% for both levels. The amount of the expanded material mixed was set at two levels of 20 kg / m ³ (standard usage) and 25 kg / m ³ (1.25 times the standard usage). Each fresh property is shown in Table 6.

[Table 5]

[Table 6]

(2) Test results and findings A method test (JIS A 6202 Annex 2 (Reference) restraining expansion test of the expansion concrete) by the test results, about 200μ in 20 kg / m ^3, about 280μ in 25 kg / m ^3, It was also confirmed by the JIS standard test that both levels satisfied the target value. On the other hand, the measurement result of each mold distortion | strain amount from immediately after concrete placement to the age of material 7 by this test is shown in FIG. The following knowledge was obtained from the above results.
-It was confirmed that this test is a test that can confirm the influence due to the difference in the amount of the expanded material mixed, as in the method A test (JIS standard test).
-In this test, when only the standard use amount of the expansion material is mixed, the mold strain at the age of 7 days is about 250 μm.

[5. Application example on site]
An example in which this test (test for confirming the presence or absence of expansion material mixing in expanded concrete using a steel mold) is applied to a plurality of sites using expanded concrete is shown below.
(1) Site A (1st floor slab concrete placement site for reinforced concrete building construction)
Table 7 shows the concrete mix. Table 8 shows the fresh properties at each level. FIG. 14 shows the measurement results of the strain amounts, the concrete temperature and the air temperature from the termination to the age of 7 days.

[Table 7]

[Table 8]

(2) Site B (waist wall concrete placement site for reinforced concrete building construction)
Table 9 shows the mix of concrete. Table 10 shows the fresh properties at each level. FIG. 15 shows the measurement results of the strain amounts, the concrete temperature and the air temperature from the termination to the age of 7 days.

[Table 9]

[Table 10]

(3) Site C (slab concrete placement site for steel reinforced concrete building construction)
Table 11 shows the concrete mix. Table 12 shows the fresh properties at each level. FIG. 16 shows the measurement results of the respective strain amounts, the concrete temperature and the air temperature from the termination to the age of 7 days.

[Table 11]

[Table 12]

  In addition, the expansion material of a different manufacturer was used in C field. It has been confirmed from the manufacturer-provided data that the expansion rate of the expansion material used at the A site and the B site is the same as that of the expansion material used at the C site.

[Judgment results applied to the site]
In applying this test, there is a need to consider the effects of temperature during concrete placement and curing, but at all levels of the target site, the amount of strain is abrupt from just after concrete placement to one day of age. In the subsequent age, the amount of strain gradually increased to a predetermined value between 100 μm and 300 μm and reached a substantially constant value. Thereby, as a result of using this test, it was confirmed that the concrete used at these sites was an appropriate expanded concrete mixed with an appropriate amount of an expanding material.

[6. Verification test using shrinkage reducing agent]
In the above, the verification test using an expansion material as an additive for crack-suppressing concrete and the effect confirmation when applied to the field were explained. By the way, with regard to the presence or absence of the use of an additive for suppressing cracking, it is recognized that the presence or absence of mixing can be confirmed by a similar test even with a shrinkage reducing agent. As the verification, as follows, additive-free concrete (standard), standard expansion material usage (20kg / m ³ ) (level 2), standard usage of shrinkage reducing agent (6kg / m ³ ) (level 3) The following tests were conducted. Thereby, also about the shrinkage reducing agent, it was decided to grasp | ascertain the behavior in the test body produced using the steel mold.
(1) Material used and measurement direction The above-mentioned disposable steel mold is used for the mold, and a strain gauge is applied in the circumferential direction of the steel mold, and each level of concrete is placed in the mold 10. The change in the amount of strain of the mold was measured continuously from immediately after that until the predetermined age (7 days) (see FIG. 1 (a)).
(2) Test level and concrete mix Table 13 shows the test level and concrete mix. As shown in the table, the water powder ratio {water / (cement + expansion material, shrinkage reducing agent)} is 43%, no additive (standard), expansion material 20 kg / m ³ (standard usage), shrinkage Three levels of reducing agent 6 kg / m ³ (standard usage) were set.

[Table 13]

(2) Test results and knowledge Fig. 17 and Fig. 18 show the test results of the strain amount of each mold immediately after concrete placement (injection) to 7 days of age. FIG. 18 shows the average value of the specimens at each level, and shows the tendency at that level. The change in the strain amount at levels 1 and 2 was equivalent to the additive-free (equivalent to standard) and expanded material standard use amount (20 kg / m ³ ) in FIGS. 10 and 5, and met the target values for each formulation. The value is shown. It can be seen that the tendency when the shrinkage reducing agent shown in level 3 is added shows a change tendency clearly different from levels 1 and 2. The plus side in the graph is the expansion side. The following knowledge was obtained from the above results.
-The distinction of each level (no addition (standard), expansion material addition, shrinkage reduction agent addition) can be generally grasped at the age of one day.
The presence or absence of a shrinkage reducing agent can be grasped by confirming that the same transition is shown by a value shifted to the expansion side by a predetermined strain amount with respect to the transition with time of the additive-free (standard) specimen. As shown in FIGS. 17 and 18, it was recognized that the strain amount showed a positive value from immediately after the concrete placement to the age of 2 days, and showed a temporal change showing a negative value at the later age. With this point, it can be determined that the shrinkage reducing agent is mixed. During this time, the amount of strain gradually increases and shows an expansion tendency. However, depending on the amount of shrinkage reducing agent used, the tendency changes when the strain becomes positive strain (expanded state) or remains the negative strain amount (shrinked state). There is also a case. In any case, it was confirmed by a plurality of specimens that the change with time in the subsequent age was a negative value close to zero. Therefore, it is preferable to determine the presence or absence of the shrinkage reducing agent by grasping the tendency of the change with time.
・ As a quantitative trend, when a standard amount of shrinkage reducing agent (6 kg / m ³ ) is mixed, there is no sudden strain change at 1-2 days of age, and the amount of strain at that time is It was confirmed that 0 to -20 μ was gradually changed at the age of 4 to 7 days.

[7. Relationship between test according to the present invention and method A]
The present invention is a simple test method as described above (hereinafter referred to as a simple method test). By examining the relationship with the A method test according to the JIS standard, the validity of the test method of the present invention can be verified. Perform verification.
(1) Method A test specimen For comparison with the measurement result of strain amount according to the present invention, in the method A test, the test specimen seals the casting surface so that moisture does not escape after the concrete is cast. Then, demolding was performed at a material age of 1 day, followed by underwater curing. In the simple method test, a disposable steel mold was used, a strain gauge having a gauge length of 10 mm was attached in the circumferential direction, and the strain was measured.
(2) Experimental level and strain measurement The water binding ratio of concrete is 45%. In the A method test test, the expansive material consumption (10, 20, 30, 50 kg / m ³ ) is 4 levels. Test specimens were prepared at five levels of the amount of expansion material used (0, 10, 20, 30, 50 kg / m ³ ), and the change over time in the expansion amount of each specimen (up to 7 days of age) was measured.
(3) Relationship of strain amount change FIG. 19 is a plot of the relationship between the strain amount in the simple method test and the strain amount in the A method test at the age of 7 days for each amount of expanded material used. As shown in the figure, the simple method test result and the A method test result according to the present invention can be shown by a linear regression line, and the simple method test result is multiplied by 1.1 under the above test conditions. It was confirmed that an equivalent value of the test result of the A method test can be obtained. Accordingly, it can be said that the simple method test of the present invention can be effectively applied as a test method in place of the A method test (JIS A 6202 Annex 2 (Reference) Restrained Expansion Test of Expanded Concrete).

  In addition, this invention is not limited to the Example mentioned above, A various change within the range shown to each claim is possible. In other words, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

10 Formwork (Mold)
11, 12, 16 Strain gauge 13 Lead wire 14 Measuring device

Claims (8)

  A strain gauge with a predetermined gauge length is affixed to the outer surface of a thin-walled cylindrical formwork, and the strain amount of the strain gauge is measured from immediately after placing the concrete to a predetermined material age. A quality control test method for crack-suppressing concrete, characterized in that it is determined whether the concrete is appropriately mixed with any additive or additive.   2. The crack suppression according to claim 1, wherein a strain gauge having a gauge length of 10 mm or more is affixed to a central position in a height direction of the thin cylindrical mold frame, and a strain in a circumferential direction is measured. Concrete quality control test method.   2. The crack-suppressing concrete according to claim 1, wherein the strain is measured by attaching a strain gauge having a gauge length of 5 mm or more to a central position in the height direction of the thin cylindrical mold frame and measuring axial strain. Quality control test method.   Determining that the expansion material is mixed by the amount of strain showing a steep rise immediately after concrete placement and until one day of material age, and gradually increasing or almost constant to a predetermined value at the subsequent material age. The quality control test method for crack-suppressing concrete according to any one of claims 1 to 3.   The method for quality control testing of crack-suppressing concrete according to any one of claims 1 to 4, wherein a disposable form for a column test body for a concrete strength test is used for the thin-walled cylinder form.   The quality control test method for crack-suppressing concrete according to claim 5, wherein a mold made of a thin steel plate is used for the disposable mold for the cylindrical specimen.   The amount of strain is the amount of strain determined by the expansion test method of expanded concrete in a uniaxial restraint state specified in JIS A 6202 Annex 2 (reference) with respect to the equivalent amount of additive or additive for suppressing shrinkage cracking. The quality control test method for crack-suppressing concrete according to claim 1, wherein the method has a linear regression relationship.   The crack-suppressing concrete according to claim 7, wherein the strain amount obtained by the expansion test method of the expanded concrete in the uniaxial constraint state is obtained by multiplying the strain amount in the linear regression relationship by 1.1. Quality control test method.

Images