EXPERIMENTAL STUDY OF FACTORS AFFECTING ULTRASONIC PULSE TIME IN FIBER-REINFORCED CONCRETE

Abstract

This study investigates factors affecting ultrasonic pulse propagation time (UPPT) in high-performance fiber-reinforced concrete (HPFRC). Steel fiber contents (0.0, 0.5, 1.0, and 2.0 vol%), specimen sizes (40×40×160 mm³ and 150×150×600 mm³), the presence of cracks, and different measurement methods on UPPT in HPFRC, were considered. Bending and compression tests were used to determine both the UPPT and mechanical properties of matrices. Steel fibers significantly affect the UPPT of HPFRC, especially under post-loading conditions, by improving crack bridging and preserving structural integrity, thus delaying pulse attenuation. HPFRC without steel fibers fails to transmit pulses after loading as a result of severe cracking, whereas HPFRC with 0.5%, 1.0%, and 2.0% steel fibers increases pulse propagation time, with higher fiber content providing better resistance to crack propagation. Besides, larger specimens exhibit longer UPPT due to energy attenuation, wave interaction, and material heterogeneity, but this effect diminishes as fiber content exceeds 1.0%. Furthermore, the direct measurement method consistently produces lower UPPT than the indirect measurement method due to shorter pulse travel distances. In addition, vertical notches also impact UPPT, with longer propagation times as cracks widen. Under increasing bending stress, UPPT becomes unstable, and excessive crack expansion disrupts signal transmission.