Types and sources of salts causing exfoliation and efflorescence in stone relics at Yongling Mausoleum

The Yongling Mausoleum in Chengdu contains stone statues that provide valuable insights into the art and culture of the Five Dynasties and Ten Kingdoms period. The sandstone, primarily composed of quartz, calcite, and potassium feldspar, has suffered severe forms of deterioration, including exfoliation and efflorescence, mainly due to salt weathering. This study analyzed salts in exfoliation and efflorescence powder using IC, OM, μ-RS, FTIR, and SEM-EDS, identifying gypsum as the predominant salt. ESEM-EDS and XRD further confirmed that the surface crystals were gypsum and thenardite. Combined with the structural degradation, waterborne ions, and atmospheric pollutants, Na⁺ and SO₄²⁻ primarily originated from historical water accumulation, seepage, and sulfur dioxide exposure. Notably, the sulfate concentration in the efflorescent stone powder reached 0.922%, indicating an extremely severe level of salt damage. These findings clarify the deterioration mechanisms and provide a scientific basis for future conservation efforts.