Durability of masonry systems: A laboratory study

We deal with the textural aspects, porometry and hydric behaviour of combinations of building materials and their durability under attack by salt crystallisation and freezing. We selected 4 types of lime mortar (pure lime mortar, lime mortar + air-entraining agent, lime mortar + pozzolana and lime mortar + air-entraining agent + pozzolana) which were used in combination with either brick or calcarenite stone. Lime mortars were chosen because they are compatible with traditional building materials, including the bricks and calcarenites that were widely used in the historical buildings that make up our architectural heritage. There are more similarities between the pore size ranges in calcarenites and mortars than there are between those in bricks and mortars. In all cases, a fine layer of calcite microcrystals develops at the contact surface between the mortar and the stone or brick. This is produced by the transformation of the portlandite, which concentrates in this area due to capillary moisture migration. This surface may on the one hand represent an obstacle to the flow of water between the different parts of the system formed by these materials, but on the other it may also favour greater adherence between the components, especially in the calcarenite + mortar combination, which proved to be the most resistant to deterioration in the freeze–thaw tests.