FI68913C - CONSTRUCTION TESTING WITH TRYCKHAOLLFASTHET HOS BETONG I EN KONSTRUKTION - Google Patents

Description

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DEVICE FOR TESTING THE COMPRESSION STRENGTH OF STRUCTURAL CONCRETE

Testing of the compressive strength of the concrete of the structure is performed either using test pieces removed from the structure or directly from the structure. The following 5 methods are known for testing the compressive strength of concrete directly from structures: 1. Surface hardness measurement - Williams test gun - Frank spring hammer - Einbeck pendulum hammer 10 2. Elasticity measurement - Schmidt elastic hammer 3. Penetration measurement - Simbi hammer - Spit hammer 15 - Windsor hammer 15 - Windsor 5. Vibration methods 6. Combined methods

Said methods are either difficult to use in site conditions, expensive in terms of equipment and operating costs, or rather unfavorable in terms of reliability, which is why their use in site conditions is rather low.

In the present invention, the compressive strength of concrete is measured in particular by a penetration method well suited for early strength testing of concrete with a device that is simple and easily available on site. The invention is characterized by the features of the claims.

In the method, one or more thinner pins, preferably made of steel, are mounted on the surface of the structure or directly on the impact piece. The pins are subjected to impact as in the surface hardness measurement method 2 6391 3 described above (Einbeck's pendulum hammer), but the impact load is so strong that the pins penetrate deep into the concrete in the same way as in the Windsor penetration test described above. The difference with the Windsor test is that the impact of the pin is achieved by a gravity body whose mass and drop height can be optimized for different types of applications and different concretes to best suit each.

The advantages of the method and the device compared to the previously known methods are its simplicity and suitability for site conditions, the cheapness of the device and the speed of the testing itself, the reliability of the operation and the almost free operating cost of the devices. The device is particularly suitable for determining the demolition strength of concrete, which is especially important in winter concreting. When the compressive strength of concrete can be easily assessed immediately before the demolition of the molds, the damage and collapse that sometimes occurs during the demolition of the molds is easily avoided.

15 The penetration method is based on the fact that the penetration resistance k of a pin in concrete correlates with the compressive strength of the concrete.

The solution is obtained from the energy balance equation. When the gravity is determined by means of a self-falling mass, the equation is of the form J mv2 = kx (1) 20 where m is the falling mass (kg) mass velocity at the moment of impact on the concrete surface g ground traction acceleration (^) h mass drop height (m) s 25 k pin penetration resistance to concrete (kN) x penetration depth of the pin into concrete (m)

The starting point of formula (1) is that the penetration resistance k is constant, k can be determined experimentally. If k is a function of the penetration depth, the integral J * k (x) dx appears to the right of Equation (1).

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The penetration resistance k is solved, for example, from equation (1), giving k = -212L- (kN) (2)

The compressive strength of concrete is obtained by the penetration resistance k from the experimentally determined equation s K = f (k) (3) where K is the nominal strength of the concrete f experimentally determined function The size of the mass used depends on the thickness of the structure to be tested, the be-10 strength and the pin used. A suitable mass per pin may be about 1 ... 5 kg when the drop height is about 1 m.

The accompanying drawings illustrate a device according to the invention, in which Figure 1 shows the principle of the device and Figure 2 shows the operating principle of the device in the horizontal and vertical structure of concrete testing.

The principle of the device is shown in Figure 1. The device comprises a stand 1, an impact piece 2 consisting of one piece or a combination of several separate impact pieces, sliding and support rails 3, 2o of the printing piece, removable penetration pins 4, possible penetration pin mounting plate 5 and support rail swivel limiters 6. When only one penetrating pin 4 is used, a separate penetrating pin mounting plate is not required, but the pin can be attached directly to the impacting drawing.

The principle of operation of the device in the testing of horizontal and vertical concrete is shown in Figure 2. At the beginning of the test, the stand is mounted on a horizontal base, which in the case of a horizontal structure may be the structure to be tested and in the case of a vertical structure, for example a horizontal structure or scaffolding. In the absence of support, the device can also be attached to the vertical structure 30 under test, for example by means of kill aids.

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In the case of a horizontal structure, the impactor is fixed to the support rails at a predetermined height and, if separate penetration pins are used, the pins are fixed to the surface of the structure to be tested by means of a mounting plate. In another model, the penetration pin or pins may be attached to the impactor. The impactor attachment is abruptly removed, causing the impactor to fall and cause the pin to penetrate.

Penetration is measured from each pin.

When using a mounting plate, the penetration can be measured by movement with respect to the mounting plate. When the penetration pin is attached to the impact piece 10, the penetration can be determined, for example, through a hole made in the impact piece next to the pin with a dipstick.

In the case of a vertical structure, the impactor or parts thereof are fixedly attached to the support rails and raised to a predetermined height by the support rails and their swivel limiters 6, after which the impactor is either fixed in position and abruptly disengaged or released directly, causing the impactor to strike the pin with potential energy. Also in this case, the penetration pin or pins can also be attached to the impactor itself. The penetration of the pins is measured as in the case of a horizontal structure.

20 The experiment is repeated the desired times so that the result can be refined.

The compressive strength of concrete can be estimated from the penetration results using the dependences between the compressive strength and the penetration depth according to the preliminary studies.

The drawings and the related description are intended to illustrate the idea of the invention. The details of the device according to the invention may vary within the scope of the claims.

Claims (1)

Apparatus for testing the compressive strength of a concrete structure, comprising a stand (1), an impact piece (2) consisting of one or more parts, sliding and support rails (3) for a printing piece, removable penetration pins (4) and support rail swivel limiters (6) that the impact of the pin is produced by the gravity body (2) by gravity either using a free fall or by differently controlling or converting the falling movement into e.g. a oscillating movement, whereby the sliding and support rails (3) of the printing body (2) are in a vertical position so that the distance of the push piece (2) from the penetration pin mounting plate (5) is adjustable for the required test force, and that when testing vertical concrete, the support rails (3) of the push piece (2) are in a horizontal position from the measuring point end with the swivel limiters (6) ) distant the center of the support rail acting as a pendulum bar is adjusted to the required impact force for testing, and that the penetrating pins (4) are directly attached to either the impactor (2) or the mounting plates (5).