A method for evaluating the onset time and velocity of S-wave in concrete materials

The well-established ultrasonic pulse velocity (UPV) technique can be correlated to the strength of concrete materials by the measurement of P-wave. However, S-wave seems to be more sensitive to the solid matrix connectivity. Here, we reported a method for evaluating the onset time and velocity of S-wave in concrete materials, developed based on the continuous wavelet transform and covariance models. To verify its effectiveness, we characterized the hydration process of six U-shaped cement mortar specimens with different water/cement (w/c) ratios and cement grades by using the ultrasonic pulse velocity (UPV) technique. The extracted onset time and velocity of the S-wave based on the developed method is comparable to the results measured by the commercial Freshcon system. For both methods, similar results were got: with the increase of the w/c ratio, the velocity values of the S-wave decreased, and the variations in the specimens made of cement grade 42.5 were larger than that of cement grade 32.5. By taking the velocity values calculated by the commercial Freshcon system as standard, the percentage deviations of the velocity values, calculated by the developed method, in the specimens made of cement grade 32.5 are less than 14%, and in the specimens made of cement grade 42.5 are less than 16%.