Damage evolution and fracture characteristics of fiber‐reinforced manufactured sand concrete columns: Axial compression tests and acoustic emission monitoring

The increasing scarcity of natural sand (NS) has accelerated the adoption of manufactured sand (MS) in construction. Nevertheless, experimental studies focusing on the structural behavior of manufactured sand concrete (MSC) columns remain limited. This study employs acoustic emission monitoring during uniaxial compression tests to investigate the internal damage evolution of MSC columns. Four key parameters—MS replacement ratio, reinforcement ratio, slenderness ratio, and steel fiber content—were systematically examined to assess their influence on damage behavior. Results indicate that failure modes correlate with concrete strength, with the MS replacement ratio exerting the most pronounced effect. Under axial compression, specimens with a 100% MS replacement ratio demonstrated a 9.3% increase in ultimate bearing capacity relative to the NS‐only control group. While the fundamental failure pattern remained unchanged, the incorporation of steel fibers contributed to enhanced mechanical performance—specifically, by restraining cover spalling and improving both compressive strength and post‐peak ductility. This enhancement is attributed to increased shear‐frictional resistance at localized regions, which delays failure and improves energy dissipation. The b ‐value evolution effectively captured damage progression, enabling real‐time tracking of microcrack initiation and macrocrack development. Damage thresholds were established using the historical index and severity index ( S r ), with a critical safety boundary defined at (9, 3). By coupling Gaussian mixture modeling with SVM, this study achieved quantitative classification of crack types in MSC columns, which supports early‐stage damage warning and structural safety evaluation for axially loaded MSC members.