JP5861874B2 - 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. Use a strain gauge with a compensated linear expansion coefficient suitable for the concrete type in a test that enables confirmation of the presence or absence of the expansion material and shrinkage reducing agent in the target concrete, and the approximate amount of expansion material mixed in. Further, the present invention relates to a concrete quality control test method in which the influence of temperature change during the age of the material is reduced to improve the test accuracy.

  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 columnar mold, for example, a ready-made 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, with regard to the time-dependent change of strain in concrete hardening under a 20 ° C environment such as a constant temperature room, for concrete using different aggregates (hard sandstone crushed stone, limestone crushed stone), 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. Therefore, it is necessary to perform measurement such that the measurement value by the strain gauge appropriately indicates the concrete strain. Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art, paying attention to the linear expansion coefficient of the target concrete and the compensated linear expansion coefficient of the strain gauge, the material at the time of curing the concrete specimen An object of the present invention is to provide a concrete quality control test method capable of measuring an appropriate concrete strain over time.

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 a predetermined additive or an additive is appropriately mixed from a change in quantity over time, the concrete corresponding to a change in temperature over time of the strain amount of the concrete The strain amount is measured using a strain gauge having a compensation linear expansion coefficient that minimizes the strain fluctuation of the strain gauge.

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 close to 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 the concrete (coarse aggregate: hard sandstone crushed stone) strain measurement using a strain gauge of each compensation linear expansion coefficient under the temperature history shown in FIG. FIG. 4 is a time-dependent change diagram of the concrete (coarse aggregate: limestone crushed stone) strain measurement using a strain gauge with each compensation linear expansion coefficient under the temperature history shown in FIG. FIG. 9 is a time-dependent change diagram of concrete strain measurement with a strain gauge having a linear expansion coefficient α = 11.8 in FIG. 8 (after casting to material age 7 days). FIG. 10 is a time-dependent change diagram of concrete strain measurement with a strain gauge having a linear expansion coefficient α = 8.1 in FIG. 9 (after casting to material age 7 days).

  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 performed to set a situation where the strain measurement value stably changed with respect to the environmental temperature change.

（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.

[Strain gauge selection evaluation test according to concrete type]
It is known that the linear expansion coefficient of concrete is generally about α = 6 to 11. As the numerical difference of the linear expansion coefficient depending on the type of coarse aggregate, it is known that when limestone crushed stone is used, it is small, and when hard sandstone crushed stone is used, it becomes larger than limestone crushed stone. It was confirmed that it matched. 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 can be assumed that the effect of temperature change in this test method can be reduced by using a strain gauge having a compensation linear expansion coefficient comparable to the concrete strain assumed by the coarse aggregate used. Therefore, the verification was performed by the following test. In this specification, “compensated linear expansion coefficient” is one of the strain gauge standards and specifications specified for products based on the linear expansion coefficient due to the thermal output of the target strain gauge. Refers to an index of selection.

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 the results of the quality control test method in which the temperature history shown in FIG. 3 is used, and the strain gauges having the respective compensation linear expansion coefficients shown in Table 2 are used for the concrete types using the hard sandstone crushed stone. It is the graph which showed the time-dependent change by the strain gauge from immediately after concrete placement to 7 days of age. Regardless of which strain gauge is used, a predetermined strain fluctuation appears corresponding to the concrete temperature change. Of these, FIG. 10 shows the behavior of the strain gauge with the smallest fluctuation. The strain of the strain gauge having the compensation linear expansion coefficient (α = 11.8) is 1/3 to 4 of the fluctuation of the strain gauge having other compensation linear expansion coefficients, and the fluctuation with respect to the temperature change is the smallest. This can be attributed to the fact that the rigidity of the concrete is sufficiently larger than that of the lightweight steel formwork, and that the linear expansion coefficient of the concrete and the compensation linear expansion coefficient of the strain gauge are close, that is, the numerical difference between the two is small.

  FIG. 9 shows the results of the quality control test method in which the temperature history shown in FIG. 3 is used, and a strain gauge having each compensation linear expansion coefficient shown in Table 2 is used for the concrete type using limestone crushed stone. It is the graph which showed the time-dependent change by the strain gauge from immediately after concrete placement to age 7 days. Regardless of which strain gauge is used, a predetermined strain fluctuation appears corresponding to the concrete temperature change. Among them, FIG. 11 shows the behavior of the strain gauge with the minimum fluctuation. The strain of the strain gauge having the compensation linear expansion coefficient (α = 8.1) is 1/3 to 6 of the fluctuation of the strain gauge having another compensation linear expansion coefficient, and the fluctuation with respect to the temperature change is the smallest. Also in this case, it was confirmed that the linear expansion coefficient of the concrete using the limestone crushed stone was close to the value of the compensation linear expansion coefficient of the strain gauge.

  In this way, by selecting a strain gauge with a compensation linear expansion coefficient that is close to the linear expansion coefficient of the concrete type, that is, with a small numerical difference, fluctuations due to temperature changes in the measured concrete strain can be reduced, and more accurate evaluation can be performed. It was recognized that we could do it.

  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 (3)

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,
A concrete quality control test method comprising: measuring a strain amount using a strain gauge having a compensation linear expansion coefficient that minimizes a strain variation of the strain gauge corresponding to a temperature change with time of the strain amount of the concrete. . The concrete quality control test method according to claim 1, wherein a 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 close to the linear expansion coefficient is used.   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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