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The issue of samples shape and size effect on the destructive strength of concrete returns from time to time because the compliance of conversion factors proposed by various authors is not satisfactory. Modern drilling equipment encourages to take samples from the structure and to conduct tests of concrete compressive strength based on the destruction of cylinders. This paper presents the ultrasound test methodology for determination of ‘d’ conversion factor from samples obtained, e.g., from structure for strength determined on other samples. First, the velocities of longitudinal ultrasound waves were reduced to a fixed base because samples of various sizes from Ø4 to Ø32cm were tested. Regression curves for the tested samples were determined, separately for each size. Based on these, for various ultrasound velocities and various sizes of samples strengths and relations between strengths was calculated. Formulas were given, which allow to convert the strength from sample of any diameter to the different one. The example of ultrasound testing method for the evaluation of mortar strength in joints between bricks was also presented

Determination of the Influence of Cylindrical Samples Dimensions on the Evaluation of Concrete and Wall Mortar Strength Using Ultrasound Method