Rebound Hammer test

Rebound Hammer test :

Rebound Hammer test is a Non-destructive testing method of concrete which provide a convenient and rapid indication of the compressive strength of the concrete. The rebound hammer is also called as Schmidt hammer that consist of a spring controlled mass that slides on a plunger within a tubular housing.

Objective of Rebound Hammer Test :

1. To determine the compressive strength of the concrete by relating the rebound index and the compressive strength
2. To assess the uniformity of the concrete
3. To assess the quality of the concrete based on the standard specifications
4. To relate one concrete element with other in terms of quality

Rebound hammer test method can be used to differentiate the acceptable and questionable parts of the structure or to compare two different structures based on strength.

Rebound Hammer Positions for Testing Concrete Structure :

Points to Remember in Rebound Hammer Test :

1. The concrete surface should be smooth, clean and dry.
2. Ant loose particles should be rubbed off from the concrete surface with a grinding wheel or stone, before hammer testing.
3. Rebound hammer test should not be conducted on rough surfaces as a result of incomplete compaction, loss of grout, spalled or tooled concrete surface.
4. The point of impact of rebound hammer on concrete surface should be at least 20mm away from edge or shape discontinuity.
5. Six readings of rebound number is taken at each point of testing and an average of value of the readings is taken as rebound index for the corresponding point of observation on concrete surface 

Quality of Concrete for different values of rebound number :

Factors Influencing Rebound Hammer Test :

1. Type of Aggregate
2. Type of Cement
3. Surface and moisture condition of the concrete
4. Curing and Age of concrete
5. Carbonation of concrete surface

Advantages of Rebound hammer test

1. Apparatus is easy to use
2. Determines uniformity properties of the surface
3. The equipment used is inexpensive
4. Used for the rehabilitation of old monuments

Disadvantages of Rebound Hammer Test :

1. The results obtained is based on a local point
2. The test results are not directly related to the strength and the deformation property of the surface
3. The probe and spring arrangement will require regular cleaning and maintenance
4. Flaws cannot be detected with accuracy.

                                     

                                                                   Rebound hammer

                                     

                                                               Parts of Rebound hammer

Rebound hammer test at Elamakkara site :