JP5822202B2 - Concrete quality control test method - Google Patents

Description

  The present invention relates to a concrete quality control test method, and a strain gauge is attached to a cylindrical lightweight steel mold used for a concrete strength test, and the strain of the mold is measured. In the test that made it possible to confirm the presence or absence of the expansion material and shrinkage reducing agent in the target concrete and to roughly grasp the amount of the expansion material, the concrete linear expansion coefficient and the compensation linear expansion coefficient of the strain gauge The present invention relates to a concrete quality control test method in which the temperature correction is performed in consideration of the above, and the strain fluctuation during the age of the material is reduced to increase the accuracy of each evaluation described above.

  Applicant is a lightweight columnar material used for concrete strength test as a concrete management test method that can grasp and evaluate the quality of expansive concrete and cracking concrete mixed with the purpose of suppressing cracking at an early stage. A strain gauge is attached to the center of the steel mold in the height direction, and the initial expansion strain of expanded concrete is evaluated by measuring the strain of the mold, and a test method that can be used for quality control is proposed (patent) Reference 1). With this test method, it has become possible to confirm the presence or absence of mixing of an expansion material and a shrinkage reducing agent into the concrete to be tested and a rough estimate of the amount of expansion material mixed in the concrete construction site.

  FIG. 1 is an explanatory view showing an embodiment in which a strain gauge is affixed to the surface of the above-described lightweight steel cylindrical mold frame 10 and the amount of strain is measured in this test method. As this cylindrical mold 10, for example, an off-the-shelf product (trade name: lightweight mold SUMMIT) made of a tin-plated thin steel sheet having a thickness of about 0.3 mm processed into a cylindrical shape was used. The strain gauges were attached so that the position and direction of the strain gauge were the center position in the height direction of the mold and the longitudinal direction of the strain gauge matched with the circumferential direction of the mold. A butyl rubber sheet 12 is pasted so as to cover the surface of the strain gauge 11 to perform waterproofing. A lead wire 13 (shown as a single diagram for the sake of simplicity) is extended from the strain gauge 11 to the measuring device 14, and each level of concrete C is placed in the cylindrical mold 10 by the measuring device 14. The strain change of the cylindrical form frame 10 immediately after the casting is placed until a predetermined age is continuously measured to grasp the expansion property of the concrete. In the figure, a mold notch line 15 is formed on the outer surface of the mold. The formwork can be cut off by this formwork cutout line 15, and the concrete specimen can be easily removed from the mold.

JP2011-169894A

  By the way, it is assumed that this quality control test method can be easily performed at a concrete construction site or the like. Therefore, in addition to the type of concrete and the type of additive, it is necessary to consider the effect of the environmental temperature at the concrete placement site and to know the appropriate strain amount of the concrete that hardens under that environmental temperature. .

  For example, for concrete with different aggregates (hard sandstone crushed stone, limestone crushed stone) with respect to time-dependent changes in strain in concrete hardening in a constant temperature room such as a 20 ° C environment, the age from concrete placement to age 7 days FIG. 2 shows an example of the relationship between the strain and the expansion strain (strain gauge measurement value). In this way, at a constant ambient temperature (20 ° C.), it is recognized that most of the strain change occurs until the first day of aging, and then shows a generally bilinear type change with time, which stabilizes almost flat after that. ing.

  However, in an environment such as a site where actual concrete placement work is performed, there is generally a case where there is a temperature change in one day. The time-dependent change in concrete strain assuming such a change in temperature (daily difference) is reproduced with a temperature history (maximum temperature of about 33 ° C./day, minimum temperature of about 17 ° C./day) as shown in FIG. 3, for example. And the time-dependent change (concrete casting-material age 7 days) of the cast concrete was measured. As a result, as shown in FIG. 4, it was confirmed that the concrete strain accompanying the aging of the material fluctuates in conjunction with the temperature history (temperature fluctuation).

  It is expected that the concrete strain based on this temperature history behaves in combination with the strain variation of the concrete itself in the mold and the strain (strain gauge measured value) variation of the lightweight steel mold. For this reason, it is necessary to perform measurement that appropriately indicates the concrete strain even in the measurement values obtained by strain gauges having different linear expansion coefficients. Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art and correct the temperature of the measured strain with respect to the change in the environmental temperature over the age of the concrete specimen when it is cured. The object is to provide a concrete quality control test method capable of measuring strain.

In order to achieve the above object, the present invention is a strain gauge affixed to the outer surface of a thin-walled cylindrical formwork in which concrete has been placed, and measures the amount of strain from immediately after placing the concrete to a predetermined material age. In a concrete quality control test method for evaluating whether the concrete is a concrete in which a predetermined additive or additive is appropriately mixed from the change over time, the linear expansion coefficient of the concrete and the compensation linear expansion coefficient of the strain gauge Is corrected by the temperature difference between the concrete temperature at the time of each measurement up to the predetermined age and the concrete temperature immediately after placing, to correct the strain over time, and the strain after the correction It is characterized in that the evaluation is performed using a change with time .

With a strain gauge affixed to the outer surface of a thin-walled cylindrical formwork in which concrete has been placed, the amount of strain from immediately after placing the concrete to a predetermined age is measured. In a concrete quality control test method for evaluating whether or not the concrete is properly mixed with an additive, the predetermined material is used for a numerical difference between a linear expansion coefficient of the concrete and a compensation linear expansion coefficient of the strain gauge. The time-dependent change of the strain amount is corrected by multiplying the difference between the temperature at the time of each measurement up to the age and the temperature immediately after placement, and the evaluation is performed using the time-dependent change of the strain amount after the correction. To do.

  The linear expansion coefficient of the concrete is preferably obtained in advance by a concrete length change test, and a strain gauge having a compensated linear expansion coefficient having a small numerical difference from the linear expansion coefficient is preferably used.

  It is preferable to use a thin steel plate mold as the thin cylindrical mold.

  As described above, according to the present invention, in a concrete construction site or the like, confirmation of the presence or absence of mixing of an expansion material and a shrinkage reducing agent into the concrete to be tested, and a general grasp of the amount of expansion material mixed The effect of using a strain gauge with a compensation linear expansion coefficient that matches the linear expansion coefficient of the concrete type in the quality control test to be performed, reducing the effect of temperature changes during the age of the material, and improving the test accuracy Play.

The schematic explanatory drawing of the apparatus structure of the concrete quality control test method of this invention. A concrete strain time-dependent change figure in a 20 degreeC environment (after casting-material age 7 days). Temperature history chart in the strain measurement test tank (after casting to material age 7 days). FIG. 4 is a time-dependent change diagram of the concrete (coarse aggregate: limestone crushed stone) strain under the temperature history shown in FIG. The temperature history pattern figure in a tank at the time of a linear expansion coefficient measurement. Test concrete for measuring linear expansion coefficient (coarse aggregate: hard sandstone crushed stone) Actual strain change with time (material age 25-30 days). Test concrete for measuring linear expansion coefficient (coarse aggregate: limestone crushed stone) Actual strain change with time (material age 25-30 days). FIG. 4 is a time-dependent change diagram of concrete strain measurement with a strain gauge having four types of compensated linear expansion coefficients under the temperature history shown in FIG. 3 (coarse aggregate: hard sandstone crushed stone, after placing to material age 7 days). FIG. 4 is a time-dependent change diagram of concrete strain measurement with a strain gauge having four types of compensated linear expansion coefficients under the temperature history shown in FIG. 3 (coarse aggregate: limestone crushed stone, after placement to material age 7 days). The concrete strain time-dependent change figure calculated | required by carrying out the distortion correction | amendment using the correction | amendment formula (Formula 1) by concrete temperature about the concrete strain measurement result by the strain gauge of each compensation linear expansion coefficient shown in FIG. The concrete strain time-dependent change figure calculated | required by carrying out the distortion correction | amendment using the correction | amendment formula (Formula 1) by concrete temperature about the concrete strain measurement result by the strain gauge of each compensation linear expansion coefficient shown in FIG. The concrete strain time-dependent change figure calculated | required by carrying out the distortion correction | amendment using the correction | amendment formula (Formula 2) by the temperature (temperature in a tank) about the concrete strain measurement result by the strain gauge of each compensation linear expansion coefficient shown in FIG. FIG. 10 is a concrete strain chronological change diagram obtained by correcting the concrete strain measurement result of each compensated linear expansion coefficient shown in FIG. 9 using a strain gauge by using a correction formula (Formula 2) based on an air temperature (tank temperature).

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

  It is thought that the above-mentioned fluctuation of concrete strain with the lapse of age shows a complex fluctuation with respect to environmental temperature change because the linear expansion coefficient of concrete and the linear expansion coefficient of lightweight steel formwork are different. . Therefore, the following experiment was conducted to obtain the coefficient of linear expansion of the concrete with respect to environmental temperature changes, and the extent of fluctuation due to the difference in the compensation linear expansion coefficient of the strain gauge used in the concrete quality control test method of the present invention. It was decided to set.

（試験方法）
鋼製型枠（供試体寸法＝100×100×400（mm））に埋込み型ひずみ計を設置してコンクリートを打込み、線膨張係数の測定を行った。コンクリート打設後は、封緘状態にして図３に示したのと同様の温度履歴を与えて養生した。その後、材齢２０日程度で脱型し、アルミ粘着テープを用いて封緘養生を続け、材齢２３日頃から図５に示すような温度履歴における養生を行った。
（試験結果）
各コンクリートの埋込み型ひずみ計の実ひずみと温度変化の結果を図６，図７に示す。コンクリート実ひずみおよび温度が一定になった時の測定値を用いて線膨張係数αを算出した（コンクリートの長さ変化試験方法（JIS A1129 ）の計算方法に準拠）。この結果、（以下、線膨張係数の表示：α×１０^-6）としたとき、
硬質砂岩砕石コンクリート：α＝１１．７
石灰岩砕石コンクリート ：α＝ ８．３
を得た。 [Test to determine the linear expansion coefficient of concrete]
The linear expansion coefficient of each concrete using coarse aggregate (hard sandstone crushed stone, limestone crushed stone) used in the subsequent tests is calculated from each actual strain obtained by the length change test.
(Concrete type)
Table 1 shows the concrete mix and fresh properties (slump value, flow value, air volume, measurement temperature) of two levels (two types of coarse aggregate: hard sandstone crushed stone and limestone crushed stone).

(Test method)
An embedded strain gauge was installed in a steel mold (specimen size = 100 × 100 × 400 (mm)), and concrete was driven in to measure the linear expansion coefficient. After placing the concrete, it was cured in a sealed state with the same temperature history as shown in FIG. Thereafter, the mold was removed at about 20 days of age, and sealing curing was continued using an aluminum adhesive tape, and curing at a temperature history as shown in FIG.
(Test results)
6 and 7 show the actual strain and temperature change results of the embedded strain gauges of each concrete. The linear expansion coefficient α was calculated using the measured values when the actual concrete strain and temperature became constant (based on the calculation method of the concrete length change test method (JIS A1129)). As a result, (hereinafter referred to as linear expansion coefficient display: α × 10 ⁻⁶ )
Hard sandstone crushed concrete: α = 11.7
Limestone crushed concrete: α = 8.3
Got.

[Verification test of relationship between concrete type and strain coefficient compensated linear expansion coefficient]
It is known that the linear expansion coefficient of concrete is generally about α = 6 to 11. As a numerical difference of the coefficient of linear expansion due to the type of coarse aggregate, it is known that when limestone crushed stone is used, it is small, and when using hard sandstone crushed stone, it is larger than the case of limestone crushed stone, It was confirmed that it was consistent with the test results. At this time, in the case of the quality control test method proposed by the applicant described above, the rigidity of the concrete is sufficiently larger than that of the lightweight steel formwork, so that the strain value is determined by the behavior of the concrete inside the formwork. Therefore, it was decided to confirm the fluctuations that occur when using a strain gauge with a compensation linear expansion coefficient different from that of concrete. It can be assumed that the effect of temperature changes in this test method can be reduced. Therefore, the verification was performed by the following test.

Using strain gauges (4 levels) with different compensation linear expansion coefficients and concrete (2 levels) with different linear expansion coefficients, strain measurement was performed in this quality control test method at a predetermined temperature history. There are 8 types of test combinations as shown in Table 2. An ettringite-lime composite expansion material was used as the expansion material. The concrete mix is the same as shown in Table 1.

  FIG. 8 shows a test using a strain gage using a strain gauge having each of the compensation linear expansion coefficients shown in Table 2 for a concrete type using a hard sandstone crushed stone in a test conducted with the temperature history shown in FIG. It is the graph which showed a time-dependent change (from immediately after concrete placement to the age of 7 days). Regardless of which strain gauge is used, a predetermined strain fluctuation appears corresponding to the concrete temperature change.

FIG. 9 is a graph showing a time-dependent measurement using a strain gauge having a coefficient of linear expansion as shown in Table 2 for a concrete type using limestone crushed stone in a test conducted with a temperature history shown in FIG. It is the graph which showed the change. Also in this case, for the same reason as in FIG. 8, different strain fluctuations occur for each strain gauge having each compensation linear expansion coefficient corresponding to the age of the concrete accompanying the concrete temperature change.
[Evaluation of strain considering temperature change and material linear expansion coefficient]

  The strain variation shown in FIGS. 8 and 9 may be caused by two points: a concrete temperature under a temperature history, and a numerical difference between the linear expansion coefficient of the concrete and the compensation linear expansion coefficient of the strain gauge. Therefore, by calculating the correction formula using the temperature at each age, the target concrete, and the compensation linear expansion coefficient of the strain gauge used as variables, we can calculate the corrected concrete strain with reduced strain variation and evaluate the concrete strain. It was.

  The correction based on the temperature change uses either the correction based on the concrete temperature or the correction based on the air temperature (curing temperature, tank temperature) as a variable. It can be said that the use of concrete temperature is the basic idea for correction due to temperature changes, but in order to measure concrete temperature over time at the site where the concrete has been placed, a thermocouple, temperature sensor, etc. Additional measuring means are required. For this reason, it is also preferable to perform correction using the air temperature (curing temperature, tank temperature) that causes the concrete temperature change. In this case, it is possible to solve the problem in the correction due to the concrete temperature.

図８，図９に示したコンクリートひずみの経時変化を、式（１）で補正して示したコンクリート温度補正後のコンクリートひずみの経時変化を図１０，図１１に示す。図８に対して、ひずみ変動は大幅に小さくなり、また異なる補償線膨張係数を有するひずみゲージ間の数値差もほとんどなくなり、コンクリート温度を利用してひずみを補正することで、ひずみの変動を十分に抑えることができ、ひずみゲージの補償線膨張係数の数値差を考慮に入れたコンクリートの膨張ひずみの評価が行うことが可能となることが確認できた。 (1) Correction by concrete temperature Correction by concrete temperature was performed using the following formula (1).

FIGS. 10 and 11 show the time-dependent changes in the concrete strain after the concrete temperature correction shown by correcting the time-dependent changes in the concrete strain shown in FIGS. 8 and 9 by the equation (1). Compared to FIG. 8, the strain fluctuation is greatly reduced, and there is almost no numerical difference between strain gauges having different compensation linear expansion coefficients. By correcting the strain using the concrete temperature, the fluctuation of the strain is sufficient. It was confirmed that it was possible to evaluate the expansion strain of concrete taking into account the numerical difference of the compensation linear expansion coefficient of the strain gauge.

  Further, if this equation (1) is used, if the compensation linear expansion coefficient of the strain gauge is known, the concrete temperature and strain when a predetermined temperature change is applied are measured, so that an approximate line of the concrete can be obtained. An expansion coefficient can be determined.

図８，図９に示したコンクリートひずみの経時変化を、式（２）で補正して示したコンクリート温度補正後のコンクリートひずみの経時変化を図１２，図１３に示す。図９に対して、ひずみ変動は小さくなり、また異なる補償線膨張係数を有するひずみゲージ間の数値差も小さくなる。なお、コンクリート温度を利用してひずみを補正した場合（図１０．図１１）に比べ、その変動はやや大きいが、コンクリート温度による補正の場合と同様に、コンクリートの膨張ひずみの評価が行うことが可能となる。 (2) Correction by air temperature Correction by air temperature (curing temperature, temperature in the tank) was made using equation (2).

FIGS. 12 and 13 show the time-dependent changes in the concrete strain after the concrete temperature correction shown by correcting the time-dependent changes in the concrete strain shown in FIGS. Compared to FIG. 9, the strain variation is reduced, and the numerical difference between strain gauges having different compensation linear expansion coefficients is also reduced. Although the variation is slightly larger than when the strain is corrected using the concrete temperature (FIGS. 10 and 11), the expansion strain of the concrete can be evaluated as in the case of the correction based on the concrete temperature. It becomes possible.

  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 Lightweight steel cylindrical formwork (cylindrical formwork)
11 Strain gauge 14 Measuring device

Claims (4)

With a strain gauge affixed to the outer surface of a thin-walled cylindrical formwork in which concrete has been placed, the amount of strain from immediately after placing the concrete to a predetermined age is measured. In the concrete quality control test method for evaluating whether the concrete is properly mixed with additives,
The numerical difference between the linear expansion coefficient of the concrete and the compensation linear expansion coefficient of the strain gauge is multiplied by the temperature difference between the concrete temperature at the time of each measurement up to the predetermined age and the concrete temperature immediately after placing. A concrete quality control test method comprising correcting a change in strain over time and performing the evaluation using a change in strain after the correction. With a strain gauge affixed to the outer surface of a thin-walled cylindrical formwork in which concrete has been placed, the amount of strain from immediately after placing the concrete to a predetermined age is measured. In the concrete quality control test method for evaluating whether the concrete is properly mixed with additives,
The numerical difference between the linear expansion coefficient of the concrete and the compensation linear expansion coefficient of the strain gauge is multiplied by the difference between the temperature at the time of each measurement up to the predetermined age and the temperature immediately after placing , A concrete quality control test method comprising correcting a change with time and performing the evaluation using a change with time of the strain after the correction.   The linear expansion coefficient of the concrete is obtained in advance by a concrete length change test, and a strain gauge having a compensated linear expansion coefficient having a small numerical difference from the linear expansion coefficient is used. Concrete quality control test method.   The concrete quality control test method according to claim 1 or 2, wherein a thin steel plate mold is used for the thin cylindrical mold.

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