Environmentally-friendly bedding mortars for repair of historical buildings

In this work, the possibility of using environmentally-friendly mortars (with crushed bricks replacing sand) as bedding mortars for repair of historical building was studied. When bedding mortars are used for intervention on historical building a compatibility issue can emerge. Indeed, if masonry containing sulphate salts is restored by using mortars based on hydraulic binders the risk of failure is high. For this reason, as binders alternatively a blended cement and a hydraulic lime were used, both proving to be unsensitive to sulphates. Two crushed brick aggregates were alternatively added to the mortars by fully replacing virgin sand; they showed different grain size distributions and, consequently, a different content of very fine materials. All the environmentally-friendly mortars were characterized from a mechanical point of view, and also their ability to adhere to two different kinds of bricks was investigated. Then, their physical behaviour was studied through microstructure characterization, as well as through the evaluation of both resistance to the vapour permeability and capillary water absorption. Results obtained showed that the use of recycled bricks instead of virgin sand, if finely ground, could allow to strongly improve mortar-brick bond strength; while, if roughly ground, it could allow to achieve a good compromise between vapour permeability and capillary absorption of mortar.