The relationships between ultrasonic P and S wave velocities and resistivity in reinforced concrete

Concrete strength is an important parameter in structural seismic design. This parameter can be determined directly by destructive tests and indirectly by non-destructive tests. In this study, the uniaxial compressive strength test was used as a destructive method, while ultrasonic and resistivity methods were used as non-destructive methods to estimate concrete strength and physical properties of concrete. The novelty of this study is that it presents a non-linear mathematical model of the relationships between ultrasonic velocities (P and S) and resistivity values in reinforced concretes with different strengths, reinforcement diameters, and pore saturation types. Firstly, in this study, the relationships between resistivities and ultrasonic velocities were shown separately for low- and high-strength reinforced concretes. In these, relationships were obtained linearly when the concrete strength remained in a narrow range. In addition, due to the low determination coefficient of relationship in the linear relationships and the resistivity values affected by the pore saturation type, it would be thought that more accurate results are obtained as a result of establishing non-linear equations. Therefore, when concrete strengths varying in a wide range (low- and high-strength) are evaluated together, a new non-linear relationship between ultrasonic velocities and resistivity is revealed. As a result, ultrasonic velocities could be calculated from resistivity values with Root Mean Square Error (RMSE) of 0.02 km/s. It was also revealed that the diameter of the reinforcement did not significantly affect the resistivity-ultrasonic velocity relationships obtained, while the concrete’s strength and saturation type were quite effective in these relationships. As a result, the saturation degrees of reinforced concrete determined from both the measured P and S wave velocities and the velocities calculated from the resistivity values were compared. According to this, the RMSE values were obtained between 0.04 and 0.08 for low- and high-strength reinforced concrete.