This paper reports the characterization of internal damping ratio (
factor of ultrahigh-performance fiber-reinforced concrete (UHPFRC) using acoustic tests for undamaged and damaged samples excited by an impact. Ratio
is a nondimensional parameter that measures the material capacity to dissipate vibration, and the
factor is physically interpreted as inverse attenuation, measuring the undamped characteristics of an oscillator. A servohydraulic testing machine was used for straining the samples cyclically, and at the end of each cycle the acoustic tests were made to measure
. Furthermore, scanning electron microscopy (SEM) was performed in samples extracted from the damaged specimens. From results, undamaged samples presented average
around 0.35% with maximum and minimum values of 0.50% and 0.15%, respectively. The analysis of damaged samples showed that the internal damping gave a small variation in the first two load cycles and achieved 0.8% after the peak stress. Low values of
found in the present study suggest that UHPFRC structures are more susceptible to excessive vibrations than normal-strength concrete structures. Moreover, SEM images showed damage mechanisms that are the probable reasons for the increase of
after severe loading.