The Stress Effect on the Ultrasonic Velocity Variations of Concrete under Repeated Loading

Abstract

This paper presents a study on the histories of ultrasonic velocity variations of concrete specimen during repeated compressive loading tests. The slight longitudinal velocity variation caused by compressive stress was measured by calculating the cross correlation of longitudinal wave-front signal. Results showed that the slight ultrasonic velocity change of concrete specimen under repeated loading could be determined accurately. Results also showed that the total wave velocity change of the mortar specimen at the stress-free state decreases with the decreasing of w/c ratios. The compressive stress-induced velocity change of concrete is larger than that of the mortar specimen. This effect further demonstrates that the coarse aggregate and its interfacial area do result in the initiation of microcracks, and in turn, decrease the ultrasonic wave velocity. The results and the measurement method developed in this paper can serve as an important reference for further studying the fracture process of concrete materials.