Mechanical assessment of epoxy‑bonded timber-concrete-composite shear specimens

Timber-concrete composite (TCC) floors are promoted as low-carbon alternatives to reinforced concrete slabs, with their structural reliability governed by the performance of the timber-concrete interface. This study provides a systematic assessment of the shear behaviour of adhesively bonded TCC joints through small-scale testing. Three test configurations were compared under short-term loading. Among these, the Vertical Slip-Block (VSB) test exhibited the lowest scatter (coefficient variation 12%) compared with the Inclined Slip-Block (23%) and Vertical Push-Out (19%) tests and consistently produced substrate-cohesive failures. VSB was therefore adopted to evaluate five structural epoxy formulations: a reference resin, two ductile variants with enhanced fracture strain, and two particle-filled variants (glass fibres, microspheres). Ductile formulations achieved up to 35% higher shear strength relative to the baseline and promoted a favourable shift in failure mode from adhesive debonding to cohesive failure in timber and concrete. This transition reflects improved stress redistribution and enhanced robustness of the bonded interface. The results establish formulation-specific performance thresholds and provide data to inform analytical design approaches, including potential adaptations of the Eurocode γ-method. Overall, the study demonstrates the potential of adhesive design to deliver reliable and damage-tolerant TCC connections, thereby advancing sustainable floor construction.