Exploring Lime Mortar Microstructure: Investigating the Impact of Mixed-in Additives and their Role in Salt Efflorescence Inhibition

This study presents the analysis of the crystallization impact in four lime-based mortar mixtures in order to determine the extent of decay during salt crystallization, affected by the use of additives and change in microstructure. For this purpose, non-destructive micro-computed tomography was used to monitor salt crystallization in lime mortar cores. This technique allowed tracking of salt precipitation after accelerated weathering steps and further enabled the localization of damage due to salt crystallization in both time and space. Results indicate that the internal 3D microstructure of the lime mortars is greatly influenced by the type and the amount of additive used. Polyacrylic acid (PAA) acted as a superplasticizer and air entrainer in the mixture, resulting in the formation of larger air voids, which led to a decrease in compressive strength. Mobilization of salts within the mortar matrix was observed, causing accumulation and cracking of the mortar wall towards the end of the weathering experiment.