Experimental Fatigue Test for Pre-Qualification of Repair Mortars Applied to Historical Masonry

Restoration work on historical masonry buildings requires new repair materials capable of providing adequate durability over time. The interface between strengthening mortar and historical masonry can be the site of various stresses due to mechanical and thermohygrometric actions, also causing delamination actions. At the Non-Destructive Testing Laboratory of the Politecnico di Torino, an experimental methodology has been developed through static, freezing-thawing and cyclic tests on mixed mortar-bricks specimens. The aim of the laboratory tests was to select a durable and compatible repair mortar before the application. Fatigue tests simulated all main stresses that can be generated at the interface between repair mortar and original masonry, both mechanical and thermo-hygrometric aspects. The experimental results were interpreted by evaluating the variation of deformation parameters over time during the tests. From a range of four strengthening mortars, the experimental procedure was able to select the one with the greatest guarantees of durability and compatibility. A similar experimental procedure has also been developed to test the durability of dehumidified mortars suitable for the recovery of historical plasters subjected by rising dump effects. The same selected mortars have been used successfully at prestigious restoration sites, demonstrating their validity over time.