Non-destructive strength estimation of vintage clay bricks based on rebound hardness in architectural heritage buildings

Abstract

Assessment of masonry structures by rebound hammer is easy to be performed and does not require special preparations. The operating principle of the rebound hammer makes possible to collect direct information about the damping properties of the tested substrate near the surface that can be related to the compressive strength. In the technical literature multiple applications of the rebound hammers are reported for field testing of masonry, but there is no consensus about the reliability of the strength estimation of vintage clay bricks based on rebound hammer testing. Aims of this research were to collect detailed information about the inherent (local) variability of the rebound index based on a comprehensive statistical analysis and to compare the variability differences between different rebound hammers (L-type and N-type) for vintage clay bricks, similarly to that has already been demonstrated for concrete in the technical literature. Further aim of the research was to clarify if there is a direct relationship between the colour, the compressive strength and the surface hardness of vintage clay bricks. The research also targeted to refine the strength estimation proposals available in the literature and to clarify the potential influencing parameters for such relationships.