What factors contribute to high mechanical strength of tabia? Case study of the tabia from coastal forts sites at Zhejiang, China

Tabia is one of the most widely used construction materials in ancient China. In this work, the tabia samples from three coastal defense fort sites at Zhejiang Province, China, we analyzed to determine their component composition and physiochemical properties. The results show that these tabia samples exhibited high compressive strength, which could be as high as 4–9 MPa. Furthermore, the systematic analysis demonstrated that the high compressive strength was related to the following factors: (1) a suitable mass ratio of sand, lime, and clay; (2) an appropriate sand particle size ratio; and (3) the formation of hydrated calcium silicate (C-S-H). Moreover, sticky rice was also detected in the tabia samples. These findings are fundamentally important, which could be beneficial to further study of the craftsmanship of the coastal defense forts and could further provide essential guidance for the protection and restoration of the tabia relics.