Non Destructive Testing of Concrete and It's Types With Diagram

Non Destructive Testing of Concrete

These tests are performed on the hardened concrete of R.c.c structures. No separate specimen is prepared for these tests. The information gathered through such tests is in fact related to the original structure. Whereas the information collected through other tests relate only to the specimen concerned. There is certainly some difference between the results of the specimen and the original structure. However between the results of the specimen and the original structure however precautions are taken in the preparation of the specimen.
According to this fact, the information from the Non Destructive Testing of Concrete Are reliable. No damage is done to a structure in this test. Albeit minor scratches many be there. These will not damage the strength of the structure.
Since these tests are performed at the site, so no time is wasted in the report writing. Thus a construction work is done briskly depending upon the tests. In addition to this information about the structure can be had after intervals of time. Also the information regarding strength of some old constructions can also be obtained. The generally performed tests of this type are as follows:

• Rebound Hammer Test
• Penetration Resistance Test
• Break Off Test
• Ultra sonic Pulse Velocity Test.

Now start to know about Non Destructive Testing of Concrete types with explanation with diagram.

• Rebound HAMMER TEST

by this test, the compressive strength of prepared concrete work is found out. The instrument used in this test is called Rebound Hammer. It is also called Schmitt Hammer.

This is put on the surface of the prepared concrete and then pressed and released. By this action the dynamic mass in this instrument moves by the springs inside the instrument. In this way it shows some reading on the instrument. This reading is called Rebound Number. The stronger the concrete is the more reading will be shown on the instrument this experiment is repeated 6 times and their average is calculated. Then this strength is compared to some standard graph. This instruments is based on the principle that if some elastic matter is stricken against some hard surface then it will rebound with the same intensity. In other words according to

Newton’s Third Law of Motion”

"Action and reaction are equal and act in the opposite direction"
In there is some big piece of stone near the concrete surface them the instrument will show the reading of the stone instead of that of the concrete. Such reading should not be considered. This test does not show accurate results on the open textured surface of the concrete also this test should not be performed on a rough surface. If this is to be done on a rough surface then the roughness of the surface should be removed first and then apply the test. During the test the instrument should be placed perpendicular to the surface. It is to be noted that the instrument many be placed horizontally in the case of a wall or a column while vertical in case of floor or slab. The results obtained in the two cases of the instrument regarding strength of concrete are shown by three graphs A, B and C. these values will be considered separately for the respective surfaces. These days modern instrument have been invented which give the reading printed on the paper like a fax machine.

Instrument                               Value read on the instrument

Inclination                                        10. 20. 30. 40. 50. 60

45 UP                                              -   -3.5 -3.1 -2.6 -2.1 -1.6

45 Down                                 +2.4  +2.5 +2.3 +2.0 +1.6 +1.3

• PENETRATION RESISTANCE TEST

This test is useful for finding the compressive strength of concrete. This can be used successfully to find the strength of the concrete before removing the form work. A steel rod is used in this test. This rod is penetrated in the concrete with some particular force. This rod will penetrate to much depth in a weak concrete. While less depth in case of strong concrete. Taking in to account this principle different departments have designed different rods for this purpose, also instruments have been incented to penetrate the rod in concrete for a fixed interval of time. a graph has also been prepared for each rod. This can be used to find the strength of concrete according to the penetrated depth of the rod. The marks of the concrete surface can be removed by filling mortar in them..

• BREAK OFF TEST

This test is performed to find the flexural strength of concrete. In this test a round bore of some particular dia meter is grooved in concrete. This bore is carried out in the hard concrete with the help of a drill machine. In addition to this a tube of desired size is placed in the concrete at the time of placing of concrete then a after a desired number of days. This test is performed. A jack increased for this testing. A vertical force is applied on the bore with the help of this jack the force is increase gradually. In this ways some part of the concrete breaks down. The force acting on the bore in this position gives the strength of concrete. Different departments have prepared different graphs related to this test. These graphs help to compare the flexural strength of concrete. The bore is then filled with concrete.

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• ULTRASONIC PLUSE VELOCITY TEST

This test is used to find compressive strength of concrete. This compressive strength of both the fresh and hardened concrete can be found out with the help of this test. In addition to this the information about the fitness or otherwise of pre-cast elements can also be found out. By this test the strength of concrete after freezing and firing can also be found out. The thickness of concrete can also be found out by this test. In formation regarding voids in concrete and cracks can also be had by this test.
In this compressive waves are passed through concrete. The time of passing these waves is calculated. In this way velocity of waves can be calculated.
 The instrument used for this purpose is called transducer. This instrument comprises many attachments like amplifier, time measuring circuit and pulse generator. The frequency of pulse generator is 10 to 150 HZ. Two transducers are fitted at two places of concrete Waves are produced at tone transducer and then sent to the other. The time consumed is noted.
Then velocity of waves is calculated. This is velocity has deep reaction with the mass of unit volume of concrete. The ultrasonic velocity and strength of concrete are shown by a graph with is provided by the instrument manufacturer. These days such instruments have been invented which show the ultrasonic velocity automatically.