Is there any method being used to test the compressive strength of the concrete without destructing?
Yes, there is.
The Rebound hammer test (Non-destructive test) is widely used to determine the compressive strength of the concrete elements, also called as Schmidt hammer test.
We have already discussed some of the destructive tests such as the compressive strength of concrete cube & Tensile strength of concrete cube.
Rebound Hammer Test is a Non-Destructive Test method widely used to measure the quality, uniformity & compressive strength of the concrete.
It is a straightforward test and can get the results immediately without any problematic calculation.
Mostly the rebound hammer test is suggested in the following scenarios.
The Rebound hammer test will be performed as per IS Code 13311 Part -2.
The process of carbon dioxide from air penetrating the concrete is known as carbonation.
A rebound hammer test machine is required, as shown in the picture below.
It is more like throwing a rubber ball against the wall. If you throw the ball to the hard surface with a high
Assume the plunger as the ball and the rebound hammer pressure as your hand force and the ball back bounces are rebounds numbers.
The hardness of the concrete & rebound is related to the compressive strength of the concrete. The bounce is measured from the scale, and it is called the rebound number or rebound index.
Before doing the test, the rebound hammer should be calibrated through a testing anvil and ensure the result is trusty. The anvil should be steel & having Brinell hardness 5000N/Sqmm.
The impact energy required for rebound hammers for different applications is given in the below table as per IS 13311 part 2.
Application | Approx Impact Energy required for Rebound Hammer in Nm |
Normal Weight Concrete | 0.75 |
Lightweight Concrete | 2.25 |
Mass Concrete | 30 |
The result will be finalized through correlating the value of rebound number and compressive strength of concrete by using the rebound hammer graph.
The accuracy of the rebound hammer result may differ from ±25% to the compressive strength of concrete by the destructive test method.
SI | Date | Test Point | Crushing Value in N/Sqmm | Rebound Number |
1 | Point 1 | |||
2 | Point 2 | |||
3 | Point 3 | |||
4 | Point 4 | |||
5 | Point 5 | |||
6 | Average |
From the above graph, you may see the relationship between the rebound number and the compressive strength of concrete. The compressive strength value increases when the rebound number increases.
For example, if the rebound number value is 35 downward vertical position, then the compressive strength value is 31 N/Sqmm.
Generally, this graph is given the backside of the rebound hammer machine so we can correlate the value on that.
The recommended rebound number values are given in the below table to check the quality of concrete.
Average Rebound Value | Quality of concrete |
>40 | Very good |
30 to 40 | Good |
20 to 30 | Fair |
<20 | Poor concrete |
0 | Delamination |
The main advantage of the Rebound hammer test is that it can be applied on the concrete surface by horizontal, vertical downward & upward direction.
SI | Advantages | Disadvantages |
1 | Inexpensive | Regular maintenance required |
2 | Helps to find the strength of the old structure | Need to correlate the rebound value to the crushing strength value. |
3 | Instant Results | Difficult to find if defects happened in the machine. |
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