Abstract
Ultrasonic Pulse Velocity (UPV) is widely used for evaluating concrete quality and estimating in situ compressive strength. However, its suitability for structural acceptance assessment remains questionable when workmanship-related defects are present. This study investigates the limitations of UPV-based strength estimation through a case study involving 38 reinforced concrete columns exhibiting segregation, geometric irregularities, twisting, out-of-plumbness, and suspected construction joint defects. The investigation included visual inspection, review of 45 concrete cylinder test results, 570 UPV measurements, development of a project-specific UPV-strength correlation using five calibration specimens, and 75 apparent crack-depth measurements. The concrete cylinder tests satisfied the specified design strengths, while UPV results generally classified the concrete as Medium/Fair to Good according to IS 13311 (Part 1):1992. However, UPV-based strength estimates ranged from 3.27 MPa to 73.31 MPa, indicating considerable uncertainty, which may also reflect the limited calibration dataset. Apparent crack-depth evaluation showed that 80% of the calculated values exceeded the physical dimensions of the tested columns, indicating that these results should be interpreted as evidence of loss of continuity, lack of bond, or construction joint discontinuities rather than actual crack depths. The findings demonstrate that satisfactory concrete strength and acceptable UPV classifications do not necessarily indicate satisfactory structural acceptability. Therefore, UPV-based strength estimation should not be used as the sole basis for acceptance assessment, and structural decisions should incorporate visual inspection, construction quality, and evidence of structural continuity.