Modification of the porous network by salt crystallization in experimentally weathered sedimentary stones

The aim of this study is to understand how the porous network of a stone is modified by the crystallization of sodium sulphate. Samples of five different stones have been experimentally weathered and evaluated thanks to mercury porosimetry in three different states: fresh, weathered by salt and weathered cleaned from the salts. Optical and electronic microscopy observations have also been led to complete these measurements. The results show that porosity and the general aspect of the porous network remain quite similar after weathering. Nevertheless, crystals tend to grow on all the grains regardless of the size of the related voids (pores or cracks), and these crystallizations seem to be harmful for the stone: a lot of voids of different entry sizes (from 10 nm to 20 mu m) have been affected by the accelerated ageing tests. This study confirms that generally stones with a high amount of small pores (up to several mu m) are the most susceptible to suffer from salt damage. Nevertheless, the influence of a few other features (high porosity, pore shape and pre-existent intragranular cracks) on the long-term behaviour of the stones suffering from salt decay is discussed.