Internal Damping Ratio of Normal- and High-Strength Concrete Considering Mechanical Damage Evolution

This paper significantly extends investigations into internal damping ratios in both undamaged and damaged conditions for normal-strength concretes (NSCs) and high-strength concretes (HSCs). This study examines concretes with compressive strengths ranging from 42 to 83 MPa. Cyclic loads were applied using a servo-controlled hydraulic testing machine, and for each cyclic step, the dynamic elastic modulus (Ed) and internal damping ratio (xi) were determined through acoustic tests. The results show that the normal-strength concretes (fc=42 MPa) exhibited an undamaged internal damping ratio of xi=0.5%, reaching a maximum of xi=2.5% at a damage index of 0.8. Conversely, the high-strength concrete mixtures (fc=83 MPa) showed an undamaged internal damping ratio of xi=0.29%, with a peak value of xi=0.93% at a damage index of 0.32. The initial internal damping values are influenced by porosity and transition zones, which affect the material behavior under cyclic loads. Progressive damage leads to increased Coulomb damping due the cracking process. Few studies have quantified and comprehended the internal damping ratio under cyclic loading-induced damage, and this research advances our understanding of NSC and HSC behavior under dynamic excitation and damage evolution, especially in impact scenarios.