CHALCEDONITE-BASED REPAIR MORTARS APPLICABLE IN HISTORIC BUILDINGS � SALT CRYSTALLIZATION RESISTANCE

Abstract

Increasing demands on the thermal performance of the building envelope play a crucial role in the design of buildings in order to maintain a quality indoor climate with reduced energy consumption. In case of repair mortars development, the necessary thermal insulation improvement can be effectively achieved by using lightweight aggregates. However, the application of new materials to historical buildings might be problematic due to their incompatibility with materials originally used in the past. In this paper, two lime-based mortars have been prepared and studied in terms of their basic structural, thermal and mechanical properties with emphasis on the mechanical performance after salt crystallization. In terms of design, the first mortar mixture used silica sand as aggregate. In the second mixture, the sand was fully replaced by crushed chalcedonite. The samples were subjected to 10 wetting/drying cycles, immersed in NaCl solution and distilled water. The results confirmed that the application of porous chalcedonite aggregate caused significant increase in material porosity followed with the drop of thermal conductivity and compressive strength compared to the reference mortar with silica sand. On the other hand, residual compressive strength retained after the crystallization test exceeded the initial value before crystallization. Based on the results of the conducted experimental analyses it was concluded that the use of chalcedonite as aggregate in lime-based repair mortars might be beneficial due to the improved thermal insulation performance and resistance to salt crystallization.