Salt damage at Petra, Jordan: a study of the effects of wind on salt distribution and crystallisation.

Abstract

The crystallisation of salts in porous building materials is a principle agent of decay in historic monuments and archaeological sites, including the World Heritage Site of Petra, Jordan. Nonetheless, the mechanism of salt damage is still inadequately understood. This research was undertaken in order to examine the role of wind speed in the salt damage process. The first aim of the research was to evaluate the role of wind speed in salt crystallisation and distribution. The second aim was to monitor the microclimate conditions and salt distribution at selected monuments in Petra, in order to understand the extent and mechanism of salt damage at these monuments. The monitoring of the microclimate conditions included spot readings for wind speed, temperature and relative humidity taken during four fieldwork visits as well as continuous logging. The salt distribution was assessed by analysis of samples that were collected from different locations, depths and heights at the same monuments. The research also took into account the role of clay minerals in salt damage. The third aim of the research was to develop a salt simulation test that would include the effects of wind. The tests were undertaken with sandstone and limestone specimens under controlled environmental conditions, including low, high and fluctuating wind speed. The results have shown that wind speed has a significant impact on salt crystallisation and distribution in porous materials, and thus on decay rates, and that fluctuating wind speed enhances salt damage more than steady speeds. In addition, the research has suggested an unexpected relationship between pore structure and the behaviour of salts under different environmental conditions. The thesis concludes with recommendations for the conservation of the site of Petra. These include proposals for reducing the salt content of certain monuments and for protection against the effects of wind