Bonding assessment of semi-precast slabs subjected to flexural load and differential shrinkage

Adequate bonding at the interface between a cast in-situ concrete topping and a precast concrete base is essential for a composite concrete structure to resist the interface shear due to loading and differential shrinkage. Inadequate bonding arising from cracks, slippage, delamination, debonding at interface, etc. may reduce the composite action and weaken the structural performance. This paper presents the bonding assessment of composite structure including performance assessment and compatibility assessment. Performance assessment aims to assess the flexural performance and to evaluate the composite behavior under loading. Compatibility assessment aims to investigate the risk of debonding due to differential shrinkage through estimating the interface force by the restrained shrinkage strains from measurements. The above is applied to two types of semi-precast slabs (SPS) using (a) 50 mm precast plank with nanosilica and (b) 70 mm precast plank without nanosilica, and both with in-situ concrete topping to achieve a total thickness of 160 mm. Both performance assessment and compatibility assessment have shown that there is sufficient bonding at the interface of SPS to resist the interface shear without the need to provide reinforcement crossing the interface. The bonding assessment proposed in this study has provided a method to evaluate the bonding at the interface of a composite structure when subjected to loading and differential shrinkage.