Damage quantification of built stone on Dark Gate (Belgrade, Serbia): sample of damage index application for decay rate evaluation

摘要

The Dark Gate is the monument of culture, part of the cultural and historical complex of the Belgrade Fortress. It is constructed of limestone blocks that after 270 years of exposure to environmental conditions and different anthropogenic influences show wide ranges of decay forms. During 2007, detail registration of all built limestone microfacies and weathering forms was done using tools of monument mapping. A correlation scheme "intensity-damage category'' was made according to the type, intensity, and distribution of damage forms. For quantification of decay rate of the Dark Gate, damage indices were calculated on the bases of mapping results. Calculated values of damage indices (>3) reflected differences between separate zones of the gate (south-north facades, east-west oriented parts of the gate). This approach allowed assessment and comparison of weathering rates according to the gate's position and the exposure of the stone to environmental influences. The linear damage index showed that the moderate damage is the dominant category on the entire monument, while the progressive damage index implies to the need of urgent intervention. After 7 years, re-evaluation of these parameters was done. New data of weathering mapping and recalculated values of damage indices reflected significant acceleration in decay rate. By comparing weathering maps and values of damage indices from 2007 and 2014, the eastern part of the gate was separated as the zone of the monument that had suffered the heaviest damage. Differences among the values of damage indices showed that the position of the gate is one of the main causes of the present state of stone blocks built in the Dark Gate. They also showed that a carefully made damage category scheme is a key diagnostic tool in each restoration project.