Evaluating Cold Joint Damage in Concrete Using Surface Wave Dispersion Velocity Profiles: A Field Study

This study introduces a rapid, on-site method to evaluate cold joint severity in concrete using surface wave group velocity dispersion curves. We examined a concrete plate where an untreated pouring surface, created seven days after a formwork failure, resulted in a severe cold joint. To assess this, we positioned two sensors: one directly over the cold joint and another on an unaffected section. Both recorded displacement waveforms generated by a single impact source equipped with piezoelectric material for precise impact timing. Group velocity dispersion curves were then generated using short-time Fourier transform and reassignment. The results showed that the dispersion curve passing through the cold joint displayed a notable wave velocity reduction and dispersion. These findings aligned with both numerical and experimental analyses. Furthermore, swapping the receiver positions produced consistent results, demonstrating the method's independence from instrumental calibration. This is a significant advantage over amplitude-based techniques for detecting cold joints.