Flexural performance of RC slabs strengthened by UHTCC/CFRP hybrid materials considering PE debonding effects

Flexural behavior of six reinforced concrete (RC) slabs was investigated. The slabs were strengthened by different lengths of externally bonded (EB) CFRP sheets using sprayed ultra-high toughness cementitious composite (UHTCC) as bonding layers to induce plate end (PE) debonding. The structural performances including failure mode, load-deflection/strain response, toughness, and interfacial stress were analyzed. A three-parameter elastic foundation model was proposed to quantify interfacial stresses and predict structural flexural behaviors. The results reveal that debonding substantially degrades load-bearing capacity (38.20–66.99 %), ultimate deflection (57.77–88.08 %), and toughness (73.50–96.24 %), and severely limits CFRP utilization ratio to only 12.35–40.29 %. For equal-length UHTCC/CFRP layers, Interface I (concrete-UHTCC) reaches maximum stress at the end, while Interface II (UHTCC-FRP) exhibits peak stress at locations between midspan and ends, with both interfacial stresses decreasing as strengthening length increases. When UHTCC length is larger than CFRP, both interfaces reach their peak stresses at the end. However, Interface I end stress becomes CFRP-length-independent, while Interface II peak stress reduces by 94.13 % as CFRP length increases from 100 mm to 400 mm. The theoretical model accurately predicts the debonding locations and provides reasonable estimations of initial stiffness and ultimate deflection. However, the elastic framework results in overestimated load-carrying capacity predictions. • The effects of PE debonding on the flexural performance of UHTCC/CFRP-strengthened RC slabs were systematically investigated. • A three-parameter elastic foundation model was proposed to analyze interfacial stresses in UHTCC/CFRP-strengthened systems. • A predictive model for structural flexural behavior was developed based on the derived interfacial stress solutions.