JPH08334446A - Early strength measuring method for shotcrete - Google Patents

Abstract

PURPOSE: To provide a simple, precise early strength measuring method for shotcrete. CONSTITUTION: A drive element 2 is driven by a constant impact energy at all times, its resilience speed is detected by a detection part 3 so that the resilience values according to strength are calculated, and in this case, the diameter of drive face 2a of the drive element 2 is so set as hard to be affected by recessed/projecting faces of concrete, so that the striking impact energy is set to 15Nmm to 700Nmm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring early strength of sprayed concrete for measuring early strength of concrete sprayed on a portion to be sprayed.

[0002]

2. Description of the Related Art Conventionally, the early strength of shotcrete is measured, for example, on concrete shot on the surface of an excavated tunnel. By knowing the strength of the sprayed concrete at an early stage, the conditions of the sprayed concrete can be changed thereafter. That is, it is possible to know whether or not the ratio of the quick-setting admixture mixed in the sprayed concrete is appropriate, and if appropriate, the subsequent spraying can be performed without changing the conditions. The spraying can be performed by correcting the deviation.

As described above, the measurement of early strength of shotcrete is important for quality control of concrete on site, and conventionally, it was measured by pull-out test.
In this pull-out test, as shown in FIG. 5, an appropriate number of molds 20 to which pins 21 are fixed are prepared.
Spray the concrete C to be tested so that the pin 21 is embedded in it. Then, after a predetermined time, from the other side, pin 2
1 was pulled out, at this time, the shear strength was obtained from the pulling force P and the shearing surface A of the breaking cone, and this was converted into compressive strength.

[0004]

However, since the pull-out test is a destructive type, concrete must be sprayed separately from the part to be sprayed, and the work becomes complicated, so it is suitable for daily management tests on site. There was a problem of not having. Moreover, the detection accuracy was also poor.

An object of the present invention is to reliably solve the above-mentioned conventional problems, and to provide a simple and accurate method for measuring early strength of shotcrete.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for measuring early strength of concrete sprayed on a portion to be sprayed, in a method for measuring early strength of concrete to be sprayed onto the portion to be sprayed. For the attached concrete,
The impact element is always impacted with a constant impact energy, and the repulsion speed is detected by the detection unit to calculate the repulsion value according to the strength, in which case the impact surface of the impact element has a diameter that is not easily affected by the irregularities of concrete. And the impact energy of the impact is set to 15 Nmm to 700 Nmm.

Further, the present invention is effective when the measurement is performed after the measurement surface of the concrete sprayed on the sprayed portion is flattened.

[0008]

EXAMPLE The early strength measurement of shotcrete is often used under adverse conditions near the face of the tunnel. Therefore, the measurement is required to satisfy the following conditions.

20 to 100 for measuring the strength of the 1-day age
It is possible to measure in the range of kg / cm ² , be able to obtain an average value, be a portable type, be a waterproof type, be a battery type, and be able to print out on site.

It is extremely difficult to satisfy all of these conditions, and even if the conventional non-destructive repulsive concrete strength tester can measure low strength, it is 100 kg / cm ²
As described above, the measurement range of 20 to 100 kg / cm ² cannot be accurately measured.

The inventor of the present application has made various studies on the reason why the conventional repulsion tester is not suitable for measuring the early strength of concrete. As a result, it was found that in the repulsion type concrete strength tester, the strength of the object to be measured is small, and therefore the object to be measured is dented by the impact of the impacting element, and the repulsion according to the strength cannot be obtained. Therefore, the impact force of the striker was weakened, but this time, even if the strength of the measured object was different, the difference in repulsion did not occur, and the measurement error became too large, so it could not be used at all. found.

Therefore, according to the present invention, for measuring the early strength of concrete, as shown in FIG. 1, for example, a hitting element 2 having a built-in magnet (not shown) is always hit with a constant impact energy of 15 Nmm to 700 Nmm. For example, the measuring device 1 that detects the repulsion speed by the detection unit 3 including a coil is used. The measuring device 1 will be described. When the loading tube 4 is lowered, the catch chuck 7 is lifted via the rack 5 and the gear 6, and when the impact spring 8 is compressed to a certain point, the catch chuck 7 moves the hitting element 2 onto the hitch 2. The impacting element 2 strikes the surface to be measured by the impacting element 8 when the impacting element 8 is released. When the striker 2 having a built-in magnet passes through the detection unit 3, a voltage corresponding to the speed is induced at the time of impact and rebound, a repulsion value is calculated from the speed difference, and a compression strength is calculated from the repulsion value. Can be guided. In this case, in the measuring instrument 1, the impact surface 2a of the impact element 2 has a diameter that is not easily affected by the unevenness of concrete, for example, a diameter of 4 mm or more, and the unevenness is flattened with a trowel or a grinder. I tried to measure it. In addition, this measurement is as shown in FIG.
Positioning is performed so that the striking direction is substantially perpendicular to the concrete surface C on which the measuring device 1 is measured.

Experimental Example The experimental method is as follows within the range of strength of 25 to 100 kgf / cm ² .
10 kinds of materials are used, and the test piece is 15 × 15 × 1
As a 5 cm cube, 9 points x 3 faces = 27 points were hit. As the measuring device 1, the impact surface 2 of the impact element 2 is used.
The diameter of a was 9 mm, the weight of the striker 2 was 20 g, and the impact energy of the striker 2 was 160 Nmm. The results are shown in Table 1.

[0014]

[Table 1]

Focusing on the coefficient of variation of each sample from Table 1, it is within about 10%, but the minimum and maximum range of each measured value is shown in FIG. 3 and has a considerable range. I understand. Further, since data below the target intensity was obtained in this experiment, regression was performed using a quadratic curve to obtain the following regression equation.

Σ = 0.014R ² -0.17R + 5.2 Correlation coefficient: 0.98 The relationship between the data and the regression equation is shown in the graph of FIG.

As stated above, the experiment yielded decent results. Considering the reason, if the repulsion type tester detects the repulsion speed instead of the repulsion level, the speed will be according to the concrete compressive strength even if the impact energy is small, and the early strength of the concrete It seems that it is possible to detect the range of 20 to 100 kg / cm ² which is necessary for the measurement.

Since the measuring instrument 1 makes an electrical measurement, it can be connected to a computer to output an average value of measured values,
Processing such as automatically excluding abnormal values can be performed. Further, the measuring device 1 is a portable type, can be of a battery type, and the measured values can be printed out on site. In addition, as a waterproof and dustproof measure, a felt is attached to the opening portion of the striker 2, and the measuring device 1
The space between the detection unit 3 and the loading tube 4 may be covered with a bellows. Further, the measuring instrument 1 may cover the whole of the striking element 2 except for the opening that appears in the striker 2.

[0019]

According to the structure of the first aspect of the present invention, the impact element containing the magnet is always impacted with a constant impact energy against the concrete sprayed on the sprayed portion, and the repulsion speed is detected by the coil. The impact value for impact is set to 15 Nmm to 700 Nmm because the impact surface of the impact element has a diameter that is not easily affected by the unevenness of concrete, and the impact energy is set to 15 Nmm to 700 Nmm. The measurement range of ^{20 to} 100 kg / cm ² can be accurately measured, and the early strength measurement of shotcrete can be easily and accurately performed by the nondestructive method.

According to the structure of claim 2, since the measurement is performed after the measurement surface of the concrete sprayed on the sprayed portion is flattened, the measurement error is small and the accuracy can be increased.

[Brief description of drawings]

FIG. 1 is a sectional view of a measuring instrument applied to the present invention.

FIG. 2 is an explanatory diagram showing a state during measurement.

FIG. 3 is a graph showing data of experimental results.

FIG. 4 is a graph showing the relationship between experimental result data and a regression equation.

FIG. 5 is an explanatory diagram showing a conventional pullout test.

[Explanation of symbols]

 1 Measuring instrument 2 Impact element 3 Detector

Claims (2)

[Claims] 1. A method for measuring early strength of sprayed concrete for measuring early strength of concrete sprayed on a sprayed part, wherein a striker is always impacted with a constant impact energy on the concrete sprayed on the sprayed part. Then, calculate the repulsion value according to the strength by detecting the repulsion speed in the detection unit, at which time the impact surface of the impact element has a diameter that is not easily affected by the irregularities of concrete, the impact energy to impact is An early strength measuring method for shotcrete characterized by being set to 15 Nmm to 700 Nmm. 2. The method for measuring early strength of sprayed concrete according to claim 1, wherein the measurement is performed after flattening the measurement surface of the concrete sprayed onto the sprayed portion. Method for measuring early strength of concrete.