Concrete compressive strength extracted from existing buildings

The evaluation of seismic safety of existing buildings is an increasingly important topic in earthquake engineering, especially in light of the provisions subscribed in recent national and international building codes. For rc buildings that assessment is not possible without the definition of concrete mechanical properties and, in particular, the definition of its compressive strength. Since the '90s of previous century, the Tuscany Region has launched a campaign of diagnostic on-site tests as prescribed by the Tuscan Regional Program VSCA (Reinforced Concrete Buildings Seismic Vulnerability) for determining the quality of concrete in public rc buildings. In this paper, two buildings - selected from those investigated by the Tuscany Region and now demolished after being declared unsafe are analyzed. In particular, some issues related to the concrete mechanical characterization both on-site and in laboratory are addressed considering the method of extraction of cylindrical specimens and the size of the sample obtained by grinding the core.