Bricks vulnerability to detrimental reactions promoted by salt contaminated solutions in natural environment: experimental evidences

The rising damp of salt contaminated groundwater is a very frequent phenomena affecting historical masonry. For bricks involved in this contamination process, no wideworld-appreciated interventions for stopping the decay are available. This is also due to a lack of widely shared identification strategies of micro-structural and mechanical parameters affecting brick vulnerability, linked to the level of contamination. In this work, it has been studied the behaviour of bricks contaminated by sulphates solutions at low concentrations, that is concentrations similar to groundwater promoted detrimental reactions in real structures. In a wide experiment carried out in Bologna, natural outdoors climate (warm and hot seasons) governed the speed of the ageing processes in the brick masonry specimens has been studied. Starting from the same ageing treatment and thermodynamic boundary conditions, the comparison between the damage promoted in bricks as part of masonry elements or bricks tested as single units has shown to be very interesting. Aspects such as the microstructure and the pore distribution of the material have been linked to the salt amount able to trigger the decay processes. This quantitative information was evaluated from dust sampling and Ion-Chromatography analysis. NDT and micro-destructive measurements of the residual stiffness on the treated bricks lead to understand how deep was the damage produced by the salt crystallization process into the brick units.