Effect of mixed vs single brine composition on salt weathering in porous carbonate building stones for different environmental conditions

• We study stone weathering induced by single brine composition and by complex mixture of salts.
• We compare the effect of crystallization/dissolution and deliquescence/precipitation cycles.
• We investigate the effects of environmental conditions and microstructure on stone durability.

The influence of different factors, brine composition, environmental conditions and pore structure, on salt weathering of porous carbonate building stones is investigated. The main goal of this study is to highlight the differences in weathering between single salts and a mixture of different salts. Two kinds of weathering mechanism are studied, the crystallization pressure and the deliquescence/recrystallization process. To achieve this purpose wetting and drying cycles and cycles varying relative humidity on samples containing salts were performed. The effect of total salt content with different salts and mixtures is simulated by weathering tests with solution of different compositions (NaCl, 6% in weight, Na2SO4·10H2O, 6% in weight, CaSO4 at saturation, and a mixture of them at total concentration of 6.2%). Weathering tests were performed at room temperature and 50 °C and under low and high relative humidity.The results show that the final weathering depends on a complex combination of three parameters: (i) environmental conditions, (ii) salt composition and (iii) petrophysical properties of stones, and general conclusions on the impact of each parameter can be drawn. An important result is that salt mixtures have a lesser impact on weathering during crystallization cycles: single salt brines, especially sodium sulphate, produce more weathering than complex brine compositions during wetting and drying cycles. Conversely during variations on RH, samples with salt mixtures suffer more damage than samples weathered with a brine of single salt composition.