Investigation of Weathering Resistance and Damage Manifestations of Mortar Formulations for Heritage Structures in Saline Environment

Abstract

ABSTRACT Salt, moisture, wind, relative humidity, and temperature fluctuations accelerate the deterioration of heritage masonry mortars. The salt entering the structure crystallizes on water evaporation, resulting in efflorescence and cryptoflorescence. As the conservation of built heritage primarily focuses on protecting the structure’s functionality, durability, and compatibility with the materials, salt weathering resistance must be emphasized when choosing a repair material for conservation. This study investigates the resistance of five different mortar compositions to salt exposure. Mortar cubes of size 50 mm were cast using five different binder compositions — dry hydrated lime, lime aged for one month, lime aged for one year, lime mortar with 20% Ordinary Portland Cement by weight and lime mortar with 50% Ordinary Portland Cement by weight. Alternate wetting and drying cycles were simulated by immersing the cubes in a 10% anhydrous sodium sulphate solution followed by drying. Physicomechanical characterization of the mortar was conducted before weathering. X-ray diffraction and Scanning Electron Microscopy provided the mineralogical and morphological alterations of the mortar specimens with weathering, respectively. Along with the microstructural assessment, observations on the mass change during the weathering cycles indicated that the partial replacement of lime with cement improved the weathering resistance of the mortar by changing the pore structure of the matrix. However, salt weathering resistance was unaffected by the changes in the ageing duration of lime. The study provides options for alternative lime-based systems with enhanced salt weathering resistance and investigates the role of the compositional differences and their impact on the pore structure and strength of the matrix, which in turn governs the salt weathering resistance.