Long-term monitoring of decay evolution in bricks and lime mortar affected by salt crystallisation

The consequences of moisture and dissolved salt capillary rise in porous construction materials are major causes of aesthetic and mechanical decay in masonry. Given the limitations of the present esting standards related with construction materials ageing, work is necessary to reduce some of the gaps. For a better comprehension of the evolution of this complex phenomenon and of its effects, an experimental work was initiated some years back in the Building Science group in Bologna University, Italy, aimed at monitoring environmental degradation in masonry materials typical of historic structures. Of particular interest is natural ageing with low-concentration brines and long-term monitoring. To achieve this aim, a first step is to know the mechanical and hygrothermal properties of masonry’s constituent materials, in at least two rather different stages in the structure’s lifetime, together with the environmental conditions endured during that timeframe. Knowing in quantitative terms how the physical and load-bearing properties may have decreased, can help in establishing degradation indexes to predict the rate of material decay. The contribution reports on the outcome of capillary water absorption tests conducted in a controlled environment on solid brick units and lime mortar prisms. The materials were tested twice: as-new and after five summer seasons of natural outdoor exposure in southern European climate together with provoked capillary rise either by tap water or by lowconcentrated sodium chloride or sodium sulphate brines. The values of the absorption rate determined for the different materials and salts are compared with the pre- and postexperimental ultrasonic signal velocities. By means of thin section analysis, alterations of the different materials during the long term monitoring were observed. The obtained values are of interest from different viewpoints, such as to evaluate possible changes in the masonry material’s diffusivity, to create a database or as input for numerical simulations.