Mineralogical and chemical study of the salt alteration of masonry blocks in the baths of Antoninus ruins at Carthage, Tunisia

The coastal archaeological site of Carthage in Tunisia (36°51′16′′ N, 10°20′06′′ E) is a valuable cultural heritage that requires conservation efforts. The presence of salt-related decay in the baths of Antoninus ruins (162 AD) is threatening their aesthetic appearance and structural stability. The buildings show various aspects of deterioration: honeycombs and black crusts. We provide a characterization of the deterioration mechanism caused by salt using X-ray diffraction, ion chromatography, inductively coupled plasma emission spectroscopy, digital and scanning electron microscopy with EDS analysis, helium porosimetry, and analysis with an optical microscope. The results indicate that the building material is calcarenite, heavily contaminated by halite, gypsum, and traces of nitrates. These contaminants originate from sea spray, dry and wet deposits of atmospheric pollutants, and saline groundwater via capillary rise. Under a seasonally variable Mediterranean climate, they contribute significantly to the physical and chemical limestone masonry deterioration.