Detachment analysis of dehumidified repair mortars applied to historical masonry walls

An innovative laboratory procedure for the pre-qualification of repair mortars is described. The tested mortars are suitable for use with new dehumidified plasters applied to historical masonry walls. Long-term plaster detachment frequently occurs because of the mechanical incompatibility of mortar. The procedure consists of the application of static loads to mixed stone block-mortar specimens with particular characteristics, in terms of geometry and adhesion at the interface. A numerical simulation based on the cohesive crack model was used to follow the experimental data, in order to describe the evolutionary phenomenon of detachment as a function of a small number of parameters. The methodology is currently being used at Sacro Monte di Varallo Special Natural Reserve (UNESCO heritage site) in Piedmont (Italy

Mechanically affected zone in AFM force measurements — Focus on actual probe tip geometry

International audienceThe estimation of a mechanically affected zone (MAZ) during AFM force measurements on polymers or composites requires a precise knowledge of the probe tip geometry. A new calibration method is proposed to determine the tip geometry from force measurements on reference materials. The test is then modelled by finite element method in order to validate the probe geometry and to determine the (MAZ) on these materials. The numerical simulation is used to show the influence of test parameters and sample elastic modulus on the impacted volume. The evolution of MAZ diameter and depth with Young's modulus and sample displacement can be correctly described by two analytical models. It is then possible to predict the lateral resolution or depth penetration associated to an AFM force measurement on a given polymer. The aim is to optimize test parameters to characterize mechanical interphases at nanometre scale in multiphase materials and to measure polymer surfaces modulus in thin layer systems