Influence of moisture on ultrasonic propagation, acoustic emission activity, and failure mechanism in concrete media

Abstract

Free water in a concrete medium significantly influences its bearing capacity and failure mechanism. In this study, the mechanical properties and failure mechanism in concrete specimens with different moisture contents were investigated with the objective of enhancing the safety of concrete structures. Uniaxial compression tests were employed to study bearing capacity, ultrasonic propagation, acoustic emission activity and failure mechanism of concrete specimens with moisture contents of 0%, 2%, 4%, and 5.5%. The results implied that the crack initiation stress and compressive strength of concrete first increased and then decreased with the increase in moisture content, and the elastic modulus and Poisson’ s ratio first decreased and then increased. The inflection points were observed in the fitting curves for moisture contents within 1.15–1.65%. With the increase in the moisture in the concrete specimens, the ultrasonic propagation velocity in the material increased, the acoustic emission activity decreased, and the proportion of high-frequency acoustic emission signals decreased. The acoustic emission activity in the concrete specimens was observed predominantly in the failure stage under the influence of uniaxial stress. Based on the moment tensor inversion of acoustic emission, the proportion of shear damage in the failure process of concrete increased with the increase in moisture content. The failure mechanism was analyzed by obtaining the ISO and DC values of acoustic emission events, the moment tensor T–k diagram, and the P–T diagram. The geometric orientation of the acoustic emission events was consistent with the macroscopic fracture mode of the specimens. The ultrasonic propagation, acoustic emission characteristics and the deterioration mechanism of bearing capacity in water-saturated concrete were analyzed. The findings of this study can be applied in health monitoring and for the safe operation of concrete structures in water environments.