Formulation and characterization of repair mortars for sandstone with lightweight aggregates made from masonry rubble

This paper deals with the study of different lime-based repair mortars for the conservation of sandstone objects in the context of monument preservation. New types of lightweight aggregates, which were manufactured from masonry rubble, were used to develop these repair mortars. This allows for recycling of construction and demolition waste while helping to conserve natural resources. As part of this work, the mortars were comprehensively characterised in terms of their chemical, physical, mechanical and hygric properties, such as bulk density, pore structure, strength, water absorption, shrinkage and carbonation. All mortars are lightweight mortars with bulk densities of about 1300 kg/m³ . They achieve high porosities of around 50 %. At the same time, the mortars exhibit sufficient compressive strengths ranging from 1.8 to 11.3 MPa. The compressive strength depends on the degree of carbonation of the mortars and increases with sample age. The analysis of the pore structure shows that the mortars mainly contain macropores. The large number of capillary pores, with sizes ranging from 0.1 to 1000 μm, results in a good water absorption behaviour. The evaluation of the results proves that the repair mortars are compatible with Cotta sandstone. • Investigation of resource-saving repair mortars for the conservation of sandstone. • Mortars produced with lightweight aggregates made by recycling of construction and demolition waste. • Extensive characterisation in terms of chemical, physical, mechanical and hygric properties. • Compatibility with Cotta sandstone experimentally proven.