1. Concrete specimens tested shall be at least 10 cm thick and fixed within structure. Smaller
specimens must be rigidly supported.
2. A test area shall be at least 15 cm in diameter. Heavily, soft, or surface with loose mortar shall be
ground smooth with the abrasive prior to testing. A surface exhibiting honeycombing, scaling, or high
porosity should be avoided.
3. The test area is divided at least 10 points and each point shall be closer together than 2.5 cm as
shown in Fig. 4.
4. Hold the hammer firmly and make sure that the plunger is perpendicular to the test surface as shown
in Fig. 5. Gradually push the hammer toward the test surface until the hammer impact. After that,
maintain pressure in the hammer and, if necessary, depress the button on the side of the hammer to
lock the plunger in its retracted position. Estimate the rebound number on the scale to the nearest
whole number and record the rebound number.
5. The average of ten readings is calculated. Discard readings differing from the average of 10 reading
by more than 6 units and determine the average of the remaining readings. If more than 2 readings
differ from the average by 6 units, discard the entire set of readings and determine rebound numbers
at 10 new readings within the test area.
6. Find the compressive strength of concrete specimens from rebound number using calibration
diagram supplied with manufacturer.