Monitoring the bonding behavior of GFRP-concrete interface using piezo-based integrated electromechanical impedance and guided-wave techniques

The durability of glass fibre-reinforced polymer (GFRP)-reinforced concrete (RC) members in harsh environments depends heavily on bond interface mechanics, and understanding stress distributions is essential. Prior studies primarily attached sensors outside the bond zone, limiting detection critical interfaces. The present study investigates the bond zone development and deterioration mechanisms using guided wave (GW) techniques and electromechanical impedance (EMI)-based interface-bonded embedded sensor (IBES) and embedded smart aggregate (ESA) sensors, respectively. EMI-based conductance signatures and statistical indices investigate early, intermediate, and long-term interfacial bond growth. Afterwards, pullout tests monitored bond degradation and associated stress transfer mechanisms using EMI signal norms and GW-based band frequency energy parameters. Results indicate IBES and ESA sensors effectively detect interfacial bond development and degradation, through conductance spectra variations. EMI signal norm were parameters highly sensitive to bond damage progression from 20% to 80% of peak stress. GW-based indices identified advanced debonding stages but showed limited sensitivity during the early development. The present study also introduced normalised Shannon and fuzzy entropy indexes to localise bond strength deterioration. The IBES-based fuzzy entropy index demonstrates higher sensitivity, enabling consistent localisation of failure load thresholds. Findings indicate combined EMI and GW techniques exhibit strong correlation with rebar slip, facilitating accurate characterisation and early-stage damage assessment.