When two concretes are cast against each other, a bond is formed between the two. The shear strength of this bond is dependent on the transfer of shear stresses between substrate and overlay as a result of four mechanisms, namely: adhesion, mechanical interlock, friction and dowel action [1]. It is known that overlay and substrate characteristics and interface reinforcement influence these mechanisms and hence the shear strength of the bond [2]. In the absence of an adequate bond forming between substrate and overlay, composite action of the two will not develop and the substrate and overlay will behave as two separate elements [3]. Alternatively, if a good bond does form, with significant shear transfer capacity, the components will behave monolithically [4].
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