Acoustic emission and digital image correlation evidence of size effects on the compression failure of concrete

Compression failure of concrete without effective confinement may show brittle failure modes, and size effects are crucial for understanding catastrophic behaviours. In this study, acoustic emission (AE) and digital image correlation techniques were innovatively combined to investigate the energy release characteristics and crack propagation patterns in concrete specimens under compression. Plain concrete specimens of base size 75, 150 and 300 mm and slenderness ratios of 0.5, 1.0 and 2.0 were tested under compression. The results showed that the compressive strength and ductility of the concrete specimens exhibited significant size and slenderness effects. With an increase in the specimen size or slenderness ratio, a ductile-to-brittle transition occurred and the post-peak behaviour shifted from softening to catastrophic failure, which was accompanied by local and global instability phenomena. This study also highlights the fractal characteristics of AE signals, with a fractal dimension of 2.19, indicating that energy release is primarily concentrated on the surface. This research has significant implications for the structural reliability and safety of concrete structures, reducing the risk of catastrophic failure.