FRP stay-in-place participating formwork: design considerations and preliminary testing

The research presented in this paper focuses upon FRP stay-in-place participating formwork for use in floor slab construction. Ease of construction is the prime motivation for the development of such a system. Time saving on site can be achieved by elimination of hand laying of internal reinforcement and provision of temporary support since all reinforcement is built into the formwork itself and is self-supporting. The crucial part of this research is investigating the most appropriate method of achieving robust bond between concrete and FRP formwork. The failure of conventional adhesive bonds is brittle and failure may occur without any warning. Therefore a more robust mechanical interlock at the interface between concrete and FRP is required to allow sufficient deformability to be created in this composite system with a more gradual failure mode. This might be achieved via transverse reinforcement in the concrete, integral with the formwork. To study the behaviour of both pultruded GFRP grid and moulded GFRP grating as mechanical shear connectors to achieve such bond between the formwork and concrete, a series of push-out tests on 300 × 400mm slab specimens have been conducted. From the resulting stress-slip curves, the longitudinal shear behaviour of both systems has been established. The test results indicate the feasibility of using moulded grating with vertical rods as shear-keys with reasonable ductility. The result of the tests will be used to provide guidance for the design of full slabs.