Influence of Surface Preparation Method on the Concrete Rebound Number obtained from Impact Hammer Test

For concrete strength detection in structures different testing procedures are being used. For nondestructive testing of concrete strength built in the construction the most used impact hammers in technical practice are those of Schmidt system. The hammer rebound value on concrete is influenced by number of factors, these includes the treatment of the test area. In the article there are presented testing results of concrete by rebound hammer type Schmidt N and L made on the test surface treated by two different ways (according to CSN 73 1373 and EN 12504-2). Hardness test methods are indirect methods of determining the strength of concrete, i.e. compressive strength of concrete is determined from the calibration relationship between parameter of nondestructive testing and strength of concrete. The basic factors affecting the hammer rebound value are: test area treatment, concrete composition, concrete humidity, hammer position, age of concrete, carbonation. Test area preparation according to EN 12504-2 Using the abrasive stone, grind heavily textured or soft surfaces, or surfaces with loose mortar, until they are smooth. Smooth-formed or trowelled surfaces may be tested without grinding. Remove any water present on the surface of the concrete. Areas exhibiting honeycombing, scaling, rough texture, or high porosity should be avoided. Test area preparation according to CSN 73 1373 the test area is cleared of carbonated concrete layers and is dry grinded so that the concrete structure is visible. There was demonstrated single valued effect of the test area treatment method on hammer rebound values. Test surface preparation according to EN 12504-2 is simpler though, but for this type of testing is not optimal.