EVALUATION OF CALCULATION CORRELATION EFFICIENCY AS MENTIONED IN en 13791 IN ORDER TO DETERMINATION CONCRETE COMPRESSION STRENGTH BY NONDESTRUCTIVE TESTING

The paper presents evaluation of correlations for calculation of concrete compression strength using nondestructive testing parameters for both impact and ultrasonic pulse methods, as listed in EN 13791:2007. This standard indicates procedures relating to compression strength determination in construction and building elements. These procedures relate to compression strength evaluation based either on test specimens (drill cores) or combination of NDT and drill core testing. These nondestructive methods are not covered by procedures taking into account only nondestructive testing parameter pursuant to common calibration correlation. Correlation based on Schmidt impact hammer rebound does not respect various positions of this instrument although positioning of the same is essential for rebound value. No specific type of impact hammer is given for particular calculation correlation. In addition, another challenge is preparation of test surface along with evaluation of impact hammer measurement according to EN 12504-2 as compared with EN 13791. Dispersion of significant values varies between 15 % and 50 % depending upon specific values of impact hammer rebound. Calculation correlation based on ultrasonic pulse velocity implies that – at 4 km/s – concrete compression strength is equal to zero which is absurd conclusion, indeed. We indicate confrontation with calibration correlation as stated by technical bibliography and technical standards as well.