Resistance of consolidated lime mortars to freeze–thaw and salt crystallization cycles by different accelerated durability tests

The present study aimed at evaluating the performance of untreated and consolidated lime mortars, in terms of durability and possible “delayed incompatibility” of the consolidants. Lime mortars samples were treated by an aqueous solution of diammonium hydrogen phosphate (DAP treatment) and a dispersion of nanolimes (NL treatment). The samples were then subjected to accelerated ageing by different methods: (1) freeze–thaw cycles; (2) salt crystallization cycles based on the European standard EN 12370 (often considered as highly aggressive); (3) salt crystallization cycles according to a new recommendation proposed by the RILEM TC 271-ASC (designed to provide less aggressive and more reliable ageing). The results of the study showed that the DAP-based treatment was able to significantly reduce damage caused by freeze–thaw cycles and salt weathering cycles by the RILEM procedure. In the case of salt weathering by the EN procedure, some risk of “delayed incompatibility” was highlighted for DAP, which can be considered an outcome of the combination between the salt weathering procedure itself and the consolidating treatment. For both freeze–thaw and salt weathering by either procedure, the residual mechanical properties of DAP samples at the end of the cycles were significantly higher than those of the untreated references and of the NL samples, for which the effects of the NL treatment were very modest.