Rebound hammer tests on mortar

The rebound hammer test on mortar constitutes a non-destructive investigation method capable of providing information on the quality of the masonry mortar, measuring its surface hardness and correlating this to its resistance using empirical functions. The method is used to estimate the resistance of the surface or pseudo-surface mortar of masonry walls, investigate the degree of homogeneity of the mechanical properties of the same, delineate zones or areas of poor quality or degraded. The methodology is however not intended as a substitute for the compression test on mortar specimens obtained by standard method. The mortar rebound hammer consists of a cylindrical body equipped with a rod that protrudes from one end of the casing and is loaded by a spring. The rod – with a smaller diameter than that of the concrete hammer or “N” type to be able to fit into the mortar joints of reduced height – is pressed onto the surface to be tested until it reaches the limit of its stroke. An internal mass hits then the ring nut rigidly fixed to the rod, which in turn is in contact with the surface under test. The mass, after hitting the rod, bounces to a certain height shown by an index placed on a graduated scale. The rebound height is proportional to the surface hardness of the mortar (the link between hardness and resistance has a purely empirical and probabilistic nature, the impact energy is lower than the concrete sclerometer, and is equal to 0.169J / 0.169N/ mm2).
Measuring range 1.4 – 25 N/mm2 (Mpa)
Reference standards: RILEM MS.D.7; ASTM C 805.