Composition and properties of the ancient mortar for masonry pagodas in Sichuan and Shaanxi Provinces, China

Masonry mortar is one of the primary building materials for ancient masonry pagodas and plays a crucial role in maintaining the structural stability of ancient pagodas. The components of masonry mortar from 21 ancient masonry pagodas of different historical periods in Sichuan and Shaanxi provinces were analyzed. X-ray diffraction was used to analyze the mineral composition of the mortar, while chemical indicators including iodine-iodide reagent, Benedict's reagent, and Coomassie brilliant blue solution, were employed to detect the types of organic additives present in the mortar. Microscopic observation was used to identify the plant fibers mixed in the mortar. Compression tests on the reconstituted specimens were conducted to understand the mechanical properties of masonry mortar with different compositions. The research results show that the mineral components of most masonry mortars include quartz, feldspar, mica, calcite, and gypsum, with the primary raw materials being loess and lime. Some ancient pagoda mortars contain reducing sugars and protein-based organic additives, and a few were found to have, barley straw added. Compression tests on the reconstituted specimens show that among various masonry mortars, loess mortar has greater compressive strength and smaller elastic modulus compared to lime mortar. The addition of egg white can significantly increase the compressive strength and elastic modulus, and the addition of straw can enhance the compressive strength of the mortar.