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.
Non-destructive Testing of Solid Brick Compression Strength in Structures
Solid burnt brick sized 290 × 140 × 65 mm or 303 × 145 × 70 mm respectively, represents one of most widespread brick building material, both structural and nonbearing ones, in Czech historical buildings. During their rebuilding and reconstruction, we frequently ask for brickwork material strength. Most exact method is to take test samples just from the construction and put them to trial nevertheless; such method is inapplicable in principle due to damage of the construction under testing. Other potentiality consists in collection of test samples just from brickwork and preparation of small test specimens. However; currently there is no sufficient number of data for elaboration of correct rates for conversion coefficients as to compression/tensile bending strength for small test specimens and whole brick failure strength. Brick strength can be detected also by means of non-destructive testing method such as ultrasonic pulse method. Practically, it appears that non-destructive testing and ultrasonic pulse method are optimal. This paper evaluates efficiency of these methods for brick strength evaluation; It also describes – for selected methods – testing methodology and test result evaluation along with calibration correlations to determine strength based on non-destructive testing parameter. The set of 300 values for each of parameter under monitoring is adequate to specify appropriate calibration correlation. Defined correlation coefficients for given calibration are high enough (more than 0.9) so presented correlations are usable in practice.
USING OF ULTRASONIC PULSE METHOD FOR PREDICTION OF STRENGTH OF BLENDED CEMENTS
One of the ways how to rationalize the experimental work is to put to use the non-destructive testing methods. In case of the strength testing of the various age cement specimens the usage of the ultrasonic pulse method appears to lead to decrease the necessary amount of tested samples. Application of this method requires fixed initial conditions like constant proportion of components, identical testing samples and constant sample’s condition during the testing. The methodology of testing and also the calibration correlations for the compressive strength or tensile bending strength and propagation velocity of ultrasonic pulses, are mentioned in this paper.