Concrete testing is one of the most important processes in determining the quality of concrete. These tests come in many forms with different concrete conditions. Some testing is necessary when the concrete is wet (for example, workability testing), some test is needed when the concrete begins to harden (for example, setting time, cube strength, etc.), and some testing is necessary when the concrete is already in place. Because of the different types of tests, the ultimate goal of these tests is to make sure that the particular one selected and used will be able to fulfill its full capacity.
Testing concrete in its fresh state is not a problem at all, and even testing the cured properties of concrete using test specimens such as cubes and cylinders is also not a difficult task. However, testing a specific structure that already exists is a completely different transaction. As a rule, these tests fall into two main categories, both destructive testing and non-destructive testing. As the name sounds, you can figure out how to do it. Let me reserve a discussion of the destructive test for another article. In this article we will deal with a more non-destructive test, and in this article, in particular, the Rebound Hammer method will be discussed in more detail.
The jackhammer test, which is also widely known as the Schmidt Hammer test, is one of the most commonly used non-destructive tests for hardened concrete. This is probably also one of the easiest methods. The concept of this method is to compare the surface hardness of a concrete surface with the compressive strength of concrete. When a Schmidt hammer is pressed against a concrete surface, the resulting rebound mass is discarded in a scale attached to the hammer. This value is then used to assess the strength of the concrete using a correlation graph, which is usually provided by hammer manufacturers. However, it should be remembered that the strength obtained as a result of this test using the correlation graph is intended only for testing the target. In addition to evaluating strength, the hammer rebound test is also widely used to test the homogeneity of a concrete surface. With the value obtained from the Schmidt hammer, it is possible to determine whether the corresponding area of concrete has a homogeneous amount of compact or not. An area that is not well compacted will give a lower rebound number than a well-compacted area.
There are several other factors that will affect the value of a Schmidt hammer. First, the surface condition of the test area. According to standard requirements, the test should be clean and smooth. In addition, the angles of the hammer when you press the test pad also affect the number of rebounds. The number of revolutions is also influenced by voids near the concrete surface, a large aggregate near the surface, etc. To reduce the influence of these factors, it is usually necessary to take an average value from 10 to 12 values from different points on the test area.
