JPH032542A - Testing machine for initial strength of concrete - Google Patents

Abstract

PURPOSE:To easily and accurately find the initial strength of placed concrete by controlling the displacement of a drawing pin in its drawing direction by a detachable member. CONSTITUTION:When a framework is removed at a predetermined time, a testing machine is selected to judge the appropriateness of the time, and a cap 7 screwed in a holder 5 is detached. As a result, the drawing pin 3 pushes away the concrete between an end 3A and a lid 8 by the drawing force based on the load of a spring 6 and tends to protrude to the outside from the framework 1. Drawing resistance is exerted mainly on the end 3A against the drawing force by the concrete being set, and the pin 3 tends to be retained at the original position. Accordingly, if the spring constant of the coil spring 6 and the initial load are appropriately preset, whether the compressive strength of the concrete is sufficient for the removal of the framework 1 or not is easily confirmed by the fact that the pin 3 after the cap 7 is detached remains in the concrete or not.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to means for determining the initial strength of concrete, which is used when it is desired to quickly remove a poured concrete formwork.

(Conventional technology) In the sliding 7-ohm method, in which reinforcing bars are assembled and concrete is poured alternately while the yoke supporting the inner and outer formwork is slid upward by jacks, the poured concrete remains uncured. If you slide the formwork while the concrete is still in the formwork, the concrete exposed from the formwork may collapse, while if you slide the formwork after it has hardened too much, the concrete may crack due to the frictional resistance between the formwork and the concrete. Therefore, in order to obtain high-quality concrete, it is necessary to accurately judge the timing of sliding the formwork.

In addition, in the two-in-place cast-in-place construction method in which lining concrete is poured using a shield tail immediately after a tunnel is excavated by a shield type excavator, the end formwork of the poured concrete must be removed as soon as possible to move on to the next process. Although this is desirable in terms of work efficiency, it is necessary to carefully judge whether or not the formwork can be removed to prevent the poured concrete from collapsing.

To make such a judgment, it is essential to understand the compressive strength of the concrete at that point in time.For this purpose, conventionally, for example, test pieces taken during concrete pouring were subjected to a compressive strength test, and the test results were used to make decisions. I used it as a basis.

In addition, a part of the formwork was removed, the exposed concrete surface was observed, and the compressive strength was estimated by applying pressure to the surface with one's fingers or penetrating the concrete with a rod-shaped object and measuring the resistance.

(Problem to be solved by the invention) However, in the case of the former method that uses a test piece, the test results of the test piece may be inaccurate due to the difference in the curing environment between the concrete 1 and the test piece. There was a problem that the strength did not necessarily match the strength of concrete 1-.

In addition, the latter method, which is based on observation, requires skill and is not reliable, as the penetration resistance changes greatly when a rod-shaped object penetrates into concrete and comes into contact with coarse aggregate, which may lead to erroneous judgments. I disliked being lacking.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a testing machine that can easily and accurately determine the initial strength of poured concrete.

(Means for Achieving the Object) To this end, the present invention provides a pull-out pin having a predetermined shape that penetrates the formwork and projects into the concrete-casting part, and a pull-out pin that is pulled out from the concrete-casting part. It includes a spring disposed outside the formwork that biases the pull-out pin in the pull-out direction, and a removable member that restricts displacement of the pull-out pin in the pull-out direction.

(Function) During concrete I pouring, the pull-out pin is biased in the pull-out direction by a spring, and its displacement in the pull-out direction is regulated by a regulating member. When concrete is poured and the regulating member is removed after a predetermined period of time has elapsed, the pull-out pin is displaced in accordance with the balance between the pull-out force based on the spring load of the spring and the pull-out resistance due to the concrete in the middle of hardening. Since pull-out resistance and compressive strength are closely related,
The initial strength of the concrete can be determined from the displacement of the pull-out pin at this time.

(Example) Embodiments of the present invention are shown in FIGS. 1 to 3.

In FIG. 1, reference numeral 1 indicates a formwork (weir plate), and a pull-out pin 3 is supported at the center of a circular hole 2 formed in the formwork 1 at right angles to the formwork 1.

The pull-out pin 3 has disk-shaped both ends 3A and 3B, and is attached to the formwork 1.
It freely slides through the tip of the support member 4 extending in the shape of an arm toward the center of the hole 2, and the other end 3A protrudes from the hole 2 into the inside of the formwork 1, that is, into the concrete pouring area. do.

A coil spring 6 having a predetermined spring constant is interposed between the other end 3B of the pull-out pin 3 and the support member 4. The coil spring 6 is housed inside a cylindrical holder 5 formed at the tip of the support member 4, and urges the pull-out pin 3 in the direction of pulling out Fj% from the concrete placement part. Further, a cap 7 screwed onto the top of the holder 5 as a removable regulating member abuts the end 3B of the pull-out pin 3,
Displacement of the pull-out pin 3 in the pull-out direction is regulated against the coil spring 6.

In addition, in order to close the hole 2 around the pull-out pin 3, the pull-out pin 3
A two-piece lid 8 having a notch through which it passes is attached to the formwork 1.

Next, the effect will be explained.

As shown in FIG. 1, this testing machine is set in a formwork 1 prior to concrete pouring. For that, formwork 1
Before assembling, select the number of formwork pieces in advance to form holes 2, and attach the support member 4 with the pull-out pin 3, coil spring 6, and cap 7 assembled to the formwork 1 in the state shown in Figure 1.
It is best to attach it to the holder and cover hole 2 with M8. It is desirable to install multiple testing machines for each concrete pouring section.

Figure 2 shows the condition of the testing machine after concrete pouring. That is, although the pull-out pin 3 is urged in the pull-out direction by the coil spring 6, the displacement in the pull-out direction is restricted by the cap 7, so unless the cap 7 is removed, the pull-out pin 3 will not touch the poured concrete. It does not exert any force. Therefore, the concrete around the pull-out pin 3 hardens under the same conditions as the concrete in other parts.

Now, when the scheduled time for removing the formwork has arrived, a testing machine is selected to determine whether or not the formwork can be removed, and the cap 7 screwed onto the holder 5 is turned and removed. As a result, the restriction on displacement in the pulling direction is lifted, and the pulling pin 3 uses the pulling force based on the spring load of the spring 7 to push away the concrete between the end 3A and the lid 8 and protrude outward from the formwork 1. try to. Against this pulling force, the hardening concrete exerts a pulling resistance mainly on the end portion 3A, and tries to keep the pulling pin 3 in its original position.

It has been confirmed through experiments that there is a linear correlation between the pulling force p (=pulling resistance) of the pulling pin 3 and the compressive strength σ of the concrete, as shown in the graph of FIG.

This graph uses an M6 fully threaded bolt for the pull-out pin 3,
This is based on the results of an experiment in which the area of the end portion 3A is "J", Cl62, and the depth of embedding the pull-out pin 3 into concrete is 4c+n.

Therefore, if the spring constant and initial load of the coil spring 6 are properly set, the cap 7
Whether the compressive strength of the concrete is sufficient for dismantling the formwork 1 can be easily determined by whether or not the pull-out pin 3 remains inside the concrete after being removed.

That is, if the pull-out pins 3 remain inside the concrete, the concrete will not collapse even if the formwork 1 is dismantled, so the formwork 1 can be immediately removed.

Conversely, if the pull-out pin 3 falls outside the formwork 1,
Since the concrete had not yet hardened to a strength sufficient to remove formwork 1, after curing for a certain period of time, the same test was conducted using another testing machine installed at another location within the pouring area, and the formwork was removed. It is determined again whether or not 1 can be dismantled.

Note that the pulling force applied to the pulling pin 3 changes depending on the spring constant and initial load of the coil spring 6, so it is possible to use a coil spring 6 with a different spring constant or adjust the initial load by adjusting the screwing amount of the cap 7. By doing so, it is possible to perform tests targeting various strengths.

(Effects of the Invention) As described above, the present invention reduces the displacement of the pull-out pin in the pull-out direction by the force that biases the pull-out pin protruding into the concrete placement space through the formwork in the pull-out direction using a spring. Since a removable regulating member is provided, the initial strength of concrete can be determined from the displacement of the pull-out pin when the regulating member is removed. Therefore, it is possible to accurately and easily judge whether or not the formwork should be dismantled or moved.

[Brief Description of the Drawings] Figure 1 is a perspective view of an initial strength testing machine showing an embodiment of the present invention, Figure 2 is a sectional view of the same, and Figure 3 is a diagram showing the relationship between the pulling force of the pull-out pin and the compressive strength of concrete. It is a graph showing a relationship. 1... Formwork, 3... Pull-out pin, 4... Support member,
6...Coil spring, 7...Cap.

Claims (1)

[Claims] A pull-out pin with a predetermined shape that penetrates the formwork and protrudes into the concrete placement area; a spring disposed outside the formwork that biases the pull-out pin in a direction to pull it out from the concrete placement area; A concrete initial strength testing machine consisting of a removable member that regulates the displacement of the pin in the pulling direction.