Time change for the propagation of ultrasonic vibrations in concrete under changing the conditions of measurements

The determination of physicomechanical characteristics of the material of the structures in operation using non-destructive testing methods has significant limitations. These restrictions are caused by differences in the composition of concrete, the parameters of the construction of the structure as well as the conditions of measurement. The human factor depends on the level of training of the specialist who carries out the measurements. Рurpose. To evaluate the impact of ultrasonic devices pressing during the "dry contact" and the need to comply with the requirements of device manufacturers regarding the size of the force of pressing the device. Methods. The measurement of the propagation time of ultrasonic vibrations was carried out using the «Pulsar 1.1» device with a change in the force of pressing the device to the concrete of the sample in the range recommended by the device manufacturer and less. Statistical processing of the results obtained (with visualization) was performed using the EXEL software package. Results. Studies have confirmed the need to take into account the magnitude of the force pressing the device to the concrete surface when measuring the propagation time of ultrasonic vibrations. It has been established that with a change in the magnitude of the pressing force of the device to the concrete surface, several intervals can be distinguished for which the dependence “propagation time of ultrasonic vibrations − the pressing force of the device” is approximated linearly. The dimensions and interposition of such intervals substantially depend on changes in the surface parameters of the concrete structure, change in the composition of the concrete mix and its properties, conditions of concrete molding and hardening. For all tests (when viewing the entire series of samples), the sample size is larger than the limits of the confidence interval. When considering each of the samples separately from the rest of the sample size is within the limits of the confidence interval. Conclusions. Studies have confirmed the effect on the measurement results of the pressure of the device to the surface, the composition and properties of the concrete mix, the molding conditions and the hardening of the concrete. Improving the accuracy of determining the physicomechanical characteristics of the material of the structures is possible taking into account the mentioned above factors.