EIS Field Investigation in an Archaeological Site

Nydam Mose is an area rich in archaeological artefacts from the Iron Age. Excavations have been conducted in this area since 1859. Environmental changes and probably disturbances caused by excavating the area are now expected to have lead to an accelerated rate of deterioration of both wood and metal objects.

The area has been anaerobic and the corrosion rate has been very low for the metal objects to be preserved for so long, but it is now a major concern, whether the artefacts will further on be preserved in the area or will now corrode away. The National Museum is now monitoring the environmental changes and changes in corrosion rate.

The aim of this investigation is to determine which parameters and which techniques that are necessary and applicable in order to characterise the corrosivity of an archaeological site in view of in situ preservation of archaeological artefacts. There are large differences between the state of preservation of an artefact found in one specific area to another illustrating the diversity of the environment and the effect of the different history of the artefacts.

This combined with general difficulties related to monitoring in soil makes it an ambitious task to produce data representative for the actual precorroded objects. However, in an attempt to characterise the corrosivity of the present environment electrochemical soil corrosion probes with carbon steel electrodes have been buried at 1-m depth.

Results of electrochemical impedance spectroscopy measurements, electrical resistance corrosion rate measurements and weight loss data from the initial 15 months exposure will be presented and discussed as well as some practical aspects of field monitoring.