Some aspects of measuring the time of propagation of ultrasonic vibrations in concrete

Determination of the physicomechanical characteristics of concrete with the use of ultrasonic vibrations simultaneously with simplicity has great uncertainty, which depends on a number of technological operations and environmental conditions. Modern ultrasonic devices use mainly the so-called “dry” contact between surface and device, which does not always allow to get unambiguous results. Рurpose. To evaluate the effect of differences in the structure of concrete on the propagation time of ultrasound in concrete with changing measurement conditions. Methods. Measurements are made using the instrument "Novotest IPSM-U". During testing, samples of concrete with various aggregate granulometric composition were used. The pressing force of the device to the sample concrete did not exceed the device recommended by manufacturers. Statistical processing of the results obtained (with visualization) was performed using the EXEL software package. Results. For each sample, the measurement results are within the confidence interval with a security of 0.95. The dependences of the “propagation time of ultrasonic vibrations − the force of pressing the device” and the boundaries of intervals with linear changes are determined. Attempts to establish the dependence of changes in the boundaries of the established intervals on changes in the concrete composition of the samples led to significantly non-linear dependencies with low confidence of the approximation. For fine-grained concrete, the effect of pressing the device to concrete on the measurement results was confirmed. Samples of fine-grained concrete showed greater uniformity than samples of heavy concrete. That still does not allow the use of a generalized relationship to determine the physic-mechanical characteristics of concrete from the results of measuring the propagation time of ultrasonic vibrations during a “dry” contact between the device and concrete. Conclusions. The analysis of these results confirmed the need to improve the existing methodology for determining the physic-mechanical characteristics of concrete using ultrasonic devices. The improvement of the accuracy of the technique can be achieved by reducing the influence of heterogeneity of concrete composition, conditions of its manufacture and operation.