Important things about rebound hammer test

Dnyan Deshmukh

Staff member
Rebound hammer test specifications are given in IS 13311 part 2 1992.

Every one know about it and knows how to do rebound hammer test, many had gone through the IS codes, posts on blogs and some interview questions.

One of my friend ask me, how i should do the rebound hammer test, as per IS code the strength of concrete is represented by average of 6 rebound numbers.

I am not going detailed in process of rebound hammer test which is already available in IS Code.

Is Really rebound hammer number represents, actual strength of my concrete?

It depends on many factors, as the rebound number is simply result of hardness of surface.
if surface is hard like stone / rock - you will most probably get a higher reading.
if surface is soft like cement paste on surface with voids behind it - you will most probably get a lower reading.

Concrete is homogeneous mixtcher of cement, sand, aggregates and water.

and we expect the same is poured in structure, structure has steel in it to.
The pouring of concrete in homogeneous for depends on many factors like, mix design, structure size, reinforcement congestion and compaction etc.

so there is a chance, when we do rebound hammer test it may take few points on a soft surface with void behind it and on too hard surface like stone.

Averaging of that 6 numbers will result in nothing but the failure of concrete (which is not fail actually)

What to do to get that 6 numbers which are right.

Well instead of 6 readings you can take the 14 reading at one location.

after that remove the lowest and upper 4 readings to get the most probably representing 6 nos of rebound.

Then average out that 6 nos to interpolate the strength of actual concrete.

There are many errors involve in test, so results of test have the tolerance of + / - 25 %.
Such tolerance is very high, one can not rely on it 100% to assume concrete is fail or pass.
Some more additional test requires to back up the rebound hammer result to show the concrete is good.