Multi-scale nondestructive characterisation and acoustic emission quantitative index for brittle–ductile damage discrimination of glass fibre cement composites

Conventional destructive mechanical tests cannot capture real-time full-process damage evolution or distinguish brittle and ductile failure states of glass fibre reinforced cement composites (GFCM). This study establishes a multi-scale non-destructive testing (NDT) framework integrating acoustic emission (AE) monitoring, X-CT scanning and SEM characterisation, and proposes a quantitative index, energy dissipation power (η), to identify the brittle-to-ductile transition. Fibre proportion (0.2%–1.0%) and length (10–50 mm) were varied, with five replicates per condition; ANOVA and error bars ensure statistical validity. A PCI-2 AE system with 150 kHz sensors recorded ringing counts and dissipated energy during uniaxial compression. Low fibre dosage produced instantaneous concentrated AE pulses indicating brittle collapse, whereas fibres of at least 0.8% and 40 mm generated stepwise signals from interfacial debonding and pull-out. The index, defined as total dissipated energy divided by damage duration, reaches an optimal ductile threshold at 0.8% fibre proportion. X-CT revealed fibre agglomeration at high dosages and SEM quantified crack suppression by fibre–matrix bonding. Borehole CT inspection at an underground site validated the framework.