ASSESSMENT OF ATMOSPHERIC POLLUTION IMPACT ON THE MICROSTRUCTURE OF MARBLE SURFACES

Abstract

In this work, digital processing of SEM images is utilized in order to assess the impact of atmospheric pollution on the microstructure of pentelic marble surfaces. The investigation samples were collected by the pentelic marble surfaces of the historic buildings of National Archaeological Museum and National Library in Athens, Greece. The investigated surfaces disclosed the representative decay patterns of black-grey crusts, washed out surfaces, etc, that usually develop in polluted urban atmosphere like the Athens’ centre. Beside the mineralogical/ morphological and chemical investigation that took place by the means of SEMEDX, SEM-image-analysis program EDGE was applied for the estimation of three evaluation parameters of marble microstructure. EDGE program, which was developed by the US Geological Survey, is a computer program which analyzes scanning-electron-microscopy images for measuring the fractal dimension of the exposed surfaces of stone specimens cut in cross section. The near-surface fracture density of the stone can also be computed, while the shape factor, a surface roughness factor, results from the traced fractal dimension. Moreover, the parameter of friability index is introduced, representing the physicochemical and physicomechanical stability of the stone surface. The combined use of SEM-EDX and EDGE program provided results which can classify the presented decay patterns not only according to their chemical composition and morphological characteristics, but regarding the micro-structural parameters of surface roughness, near-surface fracture density and surface friability as well. Therefore, a better and more thorough description of the impact of atmospheric pollution on marble microstructure is accomplished, leading to better decision making on conservation planning of decayed stones.