INTRODUCTION The application of ultrasonic waves for measurements in buildings and facilities construction is a relatively new method. It began tobe used at the end of the last century. In the last years the ultrasonic pulse velocity method is one of the most frequently and widely used methods for non-destructive control of properties of building materials and the quality of performance of concrete and reinforced concrete structures. In this method is measured the time or velocity of distribution of ultrasonic pulses into the mass of tested structural elements. This method is easy to use and the results could be obtained fast in place. The measurements are carried out with specialized portable devices, which consist of:

In this paper are described the experimental researches for determining the modulus of elasticity of concrete by the measured velocity of ultrasonic pulse, using the Non-Destructive Ultrasonic Pulse Velocity Method. Knowing the modulus of elasticity is necessary to be ensured service suitability and acceptable appearance of the designed reinforced concrete structures. The researches were performed on standard test specimens tested on different age of concrete between 3 days and 1126 days.

Failures occur in the structures of reinforced concrete buildings and facilities during their continuous exploitation, without being overloaded or exposed to extreme impacts, the most common being cracks. Their detection and change in time are related to the assessment of the state of the structures, their safety, and reliability during their construction and especially for their safety exploitation. This paper describes the results of the experimental studies conducted by authors aiming to verify the possibility of using the non-destructive ultrasonic pulse velocity method (NDUPVM) for detection and evaluation of cracks. Results of an experimental study of 12 reinforced concrete beams are presented. In previous experiments, some of them were subjected to bending until the maximum crack width of 0.3 mm was reached and others until yielding of the longitudinal reinforcement. The results obtained from the measurements of the depths of the normal cracks with different widths with NDUPVM were compared with the visually measured ones. In the present research cracks with the same width and with a similar depth were chosen. The influence of extreme external conditions to the accuracy of the measured crack depths by the NDUPVM was investigated. Non-destructive ultrasonic research was done by a portable device Proceq TICO.

In this article are presented the author's experimental studies for determining the dynamic modulus of elasticity of concrete in tests of reinforced concrete beams at the age of concrete 1926 days. For two years the reinforced concrete elements were indoors, and for the next more than three years they were left outdoors, exposed to external atmospheric influences. The results of the measured velocities of P-longitudinal and S-transverse waves generated by piezoelectric transducers are presented. The research used a combination of two modern non-destructive methods in the study of concrete - ultrasonic pulse velocity and ultrasonic pulse echo. The dynamic Poisson's ratio and the dynamic modulus of elasticity of concrete are determined on the basis of the measured velocities of the longitudinal and transverse waves. The measurements were made respectively by means of portable instruments Proceq Tico and Pundit Live Array Pro of the company Proceq. The obtained results are compared with the theoretically calculated modulus of elasticity according to BDS EN 1992-1-1:2005/NA:2015.

Determining the compressive strength of concrete is important in all phases of construction and in diagnosing the technical condition of existing reinforced concrete buildings and facilities during their service. In this article, the author presents the experimental results from research conducted over 6 years. The following non-destructive methods were used in the tests—elastic rebound, ultrasonic, SonReb and destructive methods, and the results of the latter were used as a reference. The tests were carried out on specimens prepared on the day of laying the concrete mix in the reinforced concrete beams or cores taken from the beams. The results of the determination of the probabilistic compressive strength using the different methods at concrete ages of 28, 244, 280, 293, 342, 1126 and 1926 days, are presented. The relative error, predicted strength and accuracy were determined and compared. Isocurves were drawn to determine the compressive strength for each point of a reinforced concrete structure based only on measurements obtained using non-destructive methods. The results obtained via SonReb and via the method assessing ultrasonic pulse velocity and its relationship to the dynamic and static modulus of elasticity were the closest to the reference compressive strength values.