Effect of different loading systems on acousto-ultrasonic characteristics of concrete under axial compression

Abstract

Abstract In order to study the effects of different loading systems and stress history on the damage evolution of concrete, the acoustic emission characteristic parameters, the acoustic emission release rate, acousto-ultrasonic pulse wave velocity and the Rv value were compared and analyzed in the process of axial compression damage of concrete with different water cement ratios under step and intermittent loading. In this paper, the intermittent period led to a certain degree of “closure” in the internal microcracks of concrete, thus in the same HB to HD holding period, the acoustic emission release rate, mean value of acoustic emission characteristic parameters and mean acousto-ultrasonic pulse wave velocity under intermittent loading were all higher than that of step loading. The acousto-ultrasonic pulse wave velocity decreased with the increasing of the stress level and increased during the IA to ID intermittent period. Among them, with the decreasing of water cement ratio (from 0.6 to 0.4), the acoustic emission cumulative hits and the acoustic emission release rate increased, while the acousto-ultrasonic pulse wave velocity increased, and there were some differences in the acoustic emission release rate of the two loading systems at different water cement ratios. Furthermore, the Rv value decreased with the decreasing of water cement ratio in the IA to IC intermittent period and in the ID intermittent period, the Rv value increased with the decreasing of water cement ratio, thus the Rv value could reflect the evolution law of concrete with different water cement ratios during the intermittent period. The obtained results show that the acoustic emission and acousto-ultrasonic characteristic parameters are not consistent under two different loading systems, so research in this paper can provide a theoretical basis for the damage identification and analysis of concrete structures under cyclic loading based on the acousto-ultrasonic technology in practical engineering.