Longitudinal waves for evaluation of large concrete blocks after repair

The present paper discusses the repair characterization of large concrete blocks based on the propagation of low-frequency elastic waves. A common repair method applied in damaged structures is cement injection. As a result, cracks and voids are eliminated; however, due to the poor initial mechanical properties of fresh cement, pulse velocity does not recover immediately, complicating the assessment. Results of P-wave velocity measured through the thickness of a large structure show that only after a suitable hydration period wave parameters increase. Laboratory tests were also conducted in order to extract information under more controlled conditions. It is concluded that velocity, frequency and amplitude of the ultrasonic waves are sensitive to the repair condition and the hardening of the injection material, while slight dispersion trends are eliminated after proper repair.