An overview of some traditional materials used in linear fortification structures in coastal regions of China: implications for their analytical study and conservation

Coastal forts in China were mainly built during the Ming and Qing dynasties. Their distribution from north to south along China’s coastline illustrates their use as coastal defence from foreign invasion. Despite many recent efforts to investigate and conserve coastal ruins in China, many coastal fortresses continue to undergo significant damage, which poses a major challenge to their long-term conservation. In this study, the development of structures for coastal defence is comprehensively reviewed, and their construction materials, including earth soil, bricks, natural stone, and composite materials with air lime binder and additives, are summarized. Furthermore, we focus on differences in chemical composition between European and American natural hydraulic lime and traditional Chinese hydraulic lime and note the applicability of traditional Chinese hydraulic lime in the restoration of geotechnical heritage. Detailed information about representative techniques, such as direct ramming, plate ramming, and the adobe stacking method, is also provided. In addition to the review and summary of conservation and research, two typical restoration cases conducted by the Chinese Academy of Cultural Heritage (CACH) are highlighted. Although these priceless treasures are currently in a state of severe deterioration, it is gratifying to see more interdisciplinary and international attention given to studying and protecting these ancient structures.