Properties of Mortars with Recycled Stone Aggregate for the Reconstruction of Sandstone in Historic Buildings

The research concerned the mortars with recycled stone aggregate used for the reconstruction of historic objects. The face of stone walls is exposed to atmospheric, chemical, and biological factors, causing its destruction. The aim of the research was to develop a mortar that would be compatible with the stone both in terms of its external appearance as well as its physical and mechanical properties. For this purpose, three mortars based on recycled sandstone aggregate with three different gradations were prepared. The compatibility of stone and mortar was tested in terms of the physical and mechanical properties as well as the resistance to salt and frost corrosion. The mortars reflect the properties of sandstone and offer great opportunities to adjust them as desired. The frost resistance of the mortars was consistent, with practically no weight loss after 25 test cycles. They achieved lower compression strength than stone, which is an important feature in avoiding destruction by using an excessively strong mortar. Moreover, the absorbability of the mortars turned out to be favorable (max. 25%). Mortars were resistant to the destructive effect of salt and did not show the ability to whitewash and desalinate.