Flexural strength enhancement of prestressed concrete flooring units using structural topping

Abstract

The combination of precast prestressed concrete elements and in situ topping is becoming an increasingly popular structural system of choice. However, for this structural system to be fully effective a sufficient bond between the two elements must be ensured. If this is not achieved then the system risks the friction which is present at the interface to be overcome by the horizontal shear stress produced by flexural loading. As a result such a system may experience premature failure induced by slippage and eventually delamination. Previous work investigated the horizontal shear capacity of various interfaces which had a different degree of roughness. This study continues on such research, however, it focuses on how the surface treatment affects the overall behaviour of such elements when subjected to a bending action. Thus, a total of ten samples were produced, where the main variable was the surface treatment. The samples were made up of a thin prestressed layer with an equally thin concrete topping of a lower compressive strength. These samples were then tested under a four-point symmetrical loading arrangement to achieve the bending moment required. During testing the vertical deflections, strains and slippage experienced by each sample were recorded. The results obtained suggested that when the surface roughness was quite low, the specimen experienced a brittle mode of failure induced by delamination between the two layers. Thus, only a flexural mode of failure was experienced when sufficient roughness was achieved. The rate of roughness also seems to influence the composite action of the samples.