Evaluation of Stress-Induced Microstructural Changes in Concrete Using Ultrasonic Pulse Velocity (UPV) with Variable Transducer Sizes

Abstract

The Ultrasonic Pulse Velocity (UPV) test is a non-destructive method used to evaluate the structural integrity, homogeneity, and compressive strength of concrete. It is based on the principle that the propagation speed of high-frequency sound waves correlates with the elastic properties and density of the material. In this study, two transducer sizes—28 mm (150 Hz) and 49.7 mm (54 Hz)—are employed to examine the influence of sensor size on signal propagation. A transmitting transducer generates a mechanical pulse, while a receiving transducer on the opposite surface records it. The transit time is measured to calculate pulse velocity using V=L/T, where V is velocity (m/s), L is the direct path length (m), and T is travel time (s). UPV serves as a key indicator of concrete quality: higher velocities suggest sound material, whereas lower values indicate cracks, voids, or weak zones. The study explores the relationship between incremental compressive stress and UPV in 64 concrete cubes across eight mix grades (M10–M45). Specimens are divided equally between the two transducer types for direct comparison under identical conditions. After 28 days of curing, samples undergo monotonic axial loading to failure, with UPV readings recorded at each stress stage. The investigation aims to correlate pulse velocity attenuation with increasing stress, anticipating a gradual decline in UPV as compressive stress rises. Findings will enhance understanding of stress-induced microstructural changes in concrete, demonstrating UPV’s capability as a sensitive, non-destructive evaluation tool for detecting internal deterioration under load.