Multi-analytical Studies of the Lime Mortars from the Yanxi Hall in the Yangxin Palace of the Palace Museum (Beijing)

For centuries, the architecture of the Palace Museum represented the highest standard of Chinese architecture. The Yangxin Palace of the Palace Museum consisted of 18 masonry buildings built using bricks, wood, roof tiles and various mortars. In 2016, a five-year project was initiated to work on the maintenance and restoration of the Yangxin Palace buildings. The characterization of the construction materials has become of primary importance, in order to obtain information about the raw ingredients and building technology of the mortars, and the history of possible previous restorations. In this paper, 12 different samples representing three types of mortar-based materials-namely, jointing mortars between the bricks on the wall, and surface plasters as well as mortars used on the roof-were collected for analysis from the Yanxi Hall of the Yangxin Palace. Analysis into the composition, grain-size distribution, organic and fibre additives and testing of the mortar density and water absorption were performed. Starch, protein and plant fibres were identified in some of the samples. Brucite, mullite and ettringite were detected within most mortars on the roof, possibly originating from the furnace slag added into the raw materials for restoration purposes. The analytical results will serve as a critical reference for the maintenance and restoration of the buildings in the Yangxin Palace.