Development of pseudo-ductile permanent formwork for durable concrete structures

The present investigation focuses on a new approach for the construction of durable concrete structures. Using Pseudo-ductile Cementitious Composites (PDCC) of relatively low water/binder ratio, permanent formworks are first fabricated. Normal concrete is then cast to make structural components. With low permeability and high crack resistance, the permanent formwork acts as effective surface cover to prevent the corrosion of steel reinforcements. The formwork can be made with PDCC alone, or with the incorporation of Glass Fiber Reinforced Plastics (GFRP) rods. In some structural components, the GFRP reinforcements will be sufficient to provide the necessary load-carrying capacity. When higher loads are to be carried, steel reinforcements can be added to produce a component with very high durability (due to the thick cover to steel) as well as ductile behavior. This paper focuses on mechanical aspects of this construction concept. The development of PDCC for formwork fabrication is first described. The bond between PDCC and concrete, in relation to various surface treatment methods, will be investigated with beam specimens. Test results on concrete beams made with GFRP reinforced PDCC formwork are then presented and compared to theoretical predictions. A design example is performed to demonstrate the use of GFRP/PDCC permanent formwork for constructing the deck of a footbridge. The results of this investigation show promise of the technology for practical applications.