Non-destructive and mechanical evaluation of environmental decay effects in masonry

The experimental work presented in this paper results from the need to accurately evaluate the health-state and evolution of damage in masonry structures exposed to aggressive environmental agents such as moisture and salts. The activity has started in the framework of a 7FP EU research project - SMooHS - recently concluded and it has continued with a PhD. Environmental agents such moisture and salt, although at low initial concentration, trigger the damage first by propagating through the material capillary pores and secondly by repeated cycles of hydration/crystallization of the dissolved salts. These cycles, which occur in specific microclimatic conditions, cause aesthetical and substantial changes to the material character (such as expulsion of material flakes, micro-cracks, powdering or decay of the physical-chemical and alteration of mechanical properties) which, in the long term, may also seriously compromise the reliability of the built structures. These damages, although common in historic and existing masonry structures, result from a complicated interaction between the structure itself and the specific micro-climate to which it belongs; due to the complexity of the phenomenon, further investigations on real cases in real conditions are necessary. At this purpose, a vast experimental research in Bologna considered different series of masonry specimens subjected to natural (outdoors exposure and low-concentrated brine capillary rise) or accelerated ageing processes (total immersion in high-concentrated brine and treatment in climatic cell to force crystallization). Outdoors ageing was performed on large scale brick walls as well as on smaller 0.5 x 0.5 x 0.12 m3 specimens. The evolution over time of weathering processes in these specimens was repeatedly monitored. Here, the decay effects were qualitatively and quantitatively evaluated via non-destructive tests. Instead, on accelerated aged specimens, mechanical tests in compression were performed after visual inspection and sonic tests. This paper will present an overview of the main phases of the experimental campaign including innovative examples of monitoring the masonry destructive tests by means of optical image correlation.