Chemical and Microscopic Investigation of Ancient Mortar and Plaster from the Middle Elamite Period Tepti Ahar's Vaulted Tomb, Southwestern Iran

摘要

The Haft Tappeh archaeological site, located in southwestern Iran, includes remains of the Middle Elamite period city, Kapanak (ca. 1400 BC). The archaeological excavations retrieved architectural remnants, the most significant of which being the tomb of Tepti Ahar in the northern area. The tomb is constructed of brick with mortar and plaster. The bricks are more deteriorated than mortar and plaster, and it is interesting to know the reasons behind durability of mortar/plaster in time. The aim of the article is characterization of mortar/plaster of the Tepti Ahar's tomb. X-ray powder diffraction, X-ray fluorescence, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy were employed throughout. Samples are prevalently made of gypsum with anhydrite, and in some cases bassanite and quartz, soil minerals, and calcite as impurities. The crystal's shape is large in size with rounded edges as a result of long-term natural weathering. The micromorphological features, with coarse grain sizes, have improved physical and mechanical properties of the material. The dehydration channels in the gypsum crystals suggest the influence of moisture changes in the environment within the burial interval. Thus, long-term natural weathering has rendered a dense microstructure as the main reason for the stability of the mortar-plaster in time.