Size effect between concrete interfaces under shear load

The retrofitting of the existing RC structures with added concrete layer crossed by post installed rebars is strongly related to the behaviour of the interface between the new and the old concretes. The overall strength of the connection depends on several mechanisms such as friction and dowel action between the two concrete layers, as well as the type of loading. In the past, attention was given to understand these mechanisms considering several types of specimens, usually characterized by small dimensions. Nevertheless, it is well known that size effect is often crucial in concrete elements. In this paper, with reference to a specimen geometry already employed for assessing the shear strength between old to new concrete interface, the influence of the size effect on the overall response is analysed. Based on the results of an experimental campaign, a numerical model is adopted and validated. Therefore, specimens with three different dimensions were numerically analysed to define the suitable specimen size accounting also the effect of the different concrete strengths.