From material to structure: Multi-scale damage and fracture interpretation using acoustic emission and integrated experimental techniques

The interpretation of damage and fracture processes in cement-based materials and structures remains a fundamental challenge for ensuring the safety and durability of civil infrastructure. This paper presents a coherent synthesis of original experimental research unified by a methodological framework: the integration of Acoustic Emission (AE) monitoring with complementary techniques, including Digital Image Correlation (DIC), mechanical testing, and advanced signal analysis, to investigate fracture phenomena across multiple scales. This work presents a clear progression from material-scale behaviour to element-level response and full-scale structural applications. At the material scale, size effects and ductile-to-brittle transitions in plain concrete under compression are examined, revealing fractal energy emission characteristics. At the element scale, the damage process in GFRP-bar reinforced concrete beams is analysed through multi-technical approaches, including RA-AF analysis, natural time analysis, AE entropy, and the novel Method of Critical Fluctuations-Based (MCF-B). At the structural scale, two case studies demonstrate the practical application of AE monitoring: UHPC-strengthened RC beams after 24 years of sustained loading, and crack evolution monitoring on the UHPC deck layer of a long-span cable-stayed bridge during construction. Across all scales, AE parameters, including b -value, β t coefficient, natural time variance, and entropy, consistently provide robust precursors to critical damage states. The synthesis demonstrates that fracture processes, from microcrack nucleation to macro-crack propagation and structural instability, follow scale-invariant patterns that can be captured through AE monitoring. This integrated, multi-scale perspective offers a physically grounded framework for structural health monitoring and damage assessment, demonstrating that consistent damage indicators can be interpreted across scales within a unified methodology.