Multianalytical study of neapolitan yellow tuff rotting: Archaeological park of herculaneum as a representative case of study

Abstract

The eruption of Mount Vesuvius in 79 CE buried Herculaneum under volcanic material, preserving its structures and organic materials remarkably well. Today, this site is known as the Archaeological Park of Herculaneum. Unfortunately, exposure to environmental factors has led to the degradation of Neapolitan Yellow Tuff (NYT), a material commonly used in Roman buildings, through a process known as rotting. This study, conducted by the Herculaneum Archaeological Park (PAERCO) and the Herculaneum Conservation Project (HCP) in collaboration with the IBeA research group (Research and Innovation in Analytical Chemistry, University of the Basque Country UPV/EHU), aimed to understand the tuff rotting process. By combining in-situ non-destructive analyses with laboratory investigations, it was determined, that NYT rotting is caused by the capillary ascent of saline-rich ground humidity, leading to internal stress from salt crystallization, with sodium sulphate identified as a critical threat. Furthermore, the analyses indicated that salts chemically react with NYT's minerals, causing the selective loss of its cementing material (zeolites). The study of soil samples revealed that the risk of rotting varies across the park due to differences in salt concentration and composition. These insights will help PAERCO and HCP identify high-risk areas and implement preventive measures, including the use of portable XRF instruments for ongoing monitoring and preservation of the site's historic structures.