Lime mortar with mixed in crystallization modifiers to mitigate salt damage

Abstract

Although salt crystallization damage is a widespread damage process in the porous materials of our built cultural heritage, no definite solution yet exists to improve the durability of materials with respect to salt crystallization. Most research focuses on improving material properties, whereas only few studies concentrate on changing the crystallization process in order to make it less harmful.Within this last trend, recently the use of salt crystallization modifiers has been considered. Crystallization modifiers are ions or molecules that promote or inhibit crystal growth and/or change the crystal habit, thereby possibly reducing salt damage.We give in this paper experimental evidence that borax is a promising crystallization modifier for sodium sulfate and that it might mitigate salt crystallization damage when mixed in lime-based mortars. Lime-based mortars are chosen as a model system, since they are especially prone to salt crystallization damage due to their limited mechanical strength and bi-modal pore size distribution.