The rebound hammer method could be used for:
(i) assessing the likely compressive strength of concrete with the help of suitable corelations between rebound index and compressive strength,
(ii) assessing the uniformity of concrete,
(iii) assessing the quality of the concrete in relation to standard requirements, and
(iv) assessing the quality of one element of concrete in relation to another.
When the plunger of rebound hammer is pressed against the surface of the concrete, the spring- controlled mass rebounds and the extent of such rebound depends upon the surface hardness of concrete. The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete. The rebound is read off along a graduated scale and is designated as the rebound number or rebound index.
Fig. 1: Rebound Hammer
It consists of a spring controlled mass that slides on a plunger within a tubular housing. The impact energy required for rebound hammers for different applications is given in Table 1.
|S. No.||Application||Approx. Impact Energy required for Rebound hammer (Nm)|
|1||For Testing Normal Weight Concrete||2.25|
|2||For light-weight concrete or small and impact sensitive parts of concrete||0.75|
|3||For testing mass concrete for example, in roads, air field pavements and hydraulic structures||2.25|
Table 1 : Impact Energy for Rebound hammer for different Applications.
Fig. 2: Schematic of Rebound Hammer
IS-13311 (Part 2):1992 (Reaffirmed- May 2013) “Non Destructive Testing of Concrete-Methods of Test (Rebound hammer)”.