Characterization of historical mortar from Huilongguan temple site in Wudang Mountain, Hubei province, China

As the royal Taoist buildings of the Ming dynasty (1368–1644 CE), the Huilongguan temple site of Wudang Mountain represents the highest level of art and architecture of that era. Thanks at least in part to the quality and durability of building mortar materials, the part buildings of the Huilongguan temple site are still well preserved after 500 years of erosion by wind and rain. The present study conducted muti-analytical techniques to explore the characterization of eight mortars from the Huilongguan temple site. The results indicate that the material formulae of these mortars from construction phases I–IV of the Ming dynasty were all sticky rice as the organic additive incorporated into the magnesian lime base, which originated from the calcination of dolomitic limestone. The contents of Ca carbonate in the studied mortar samples are about 39–66%; the design of mortar groundmass presents differences due to various building purposes. Different from sharp-edged rhombohedral calcite crystals of pure lime mortar, irregular nano-scale calcite crystals were found in the studied samples due to sticky rice slurry regulating the growth of Ca carbonate as an inhibitor and template, which formed more compact organic–inorganic composite microstructures.