Scanning electron microscopy studies of neoformations on stony materials of modern building works

Abstract

The built environment is subjected to several pollutants under variable environmental conditions defining diverse geochemical systems. These geochemical systems promote the occurrence of neoformations that can have a detrimental effect on surfaces of the building materials. Hence, the study of neoformations helps in the understanding of weathering processes that affect built elements. In the present paper is presented a scanning electron microscopy study of macroscopic manifestations of neoformations detected on an extensive visual survey of several modern architectural works in urban aggregates of northern and central Portugal. The studies performed suggest that cementitious materials play an important role as sources of pollutants for the commonest neoformations such as carbonate rich stains and coatings as well as salt efflorescences of alkaline sulphates and carbonates. There are also indications of contributions from organic sources for alkaline nitrates and atmospheric pollution for gypsum-rich black crusts. Other less common neoformations include phosphate aggregates and silica stains that while having a global negligible impact on the studied built elements represent interesting indicators on the geochemical systems of the built environment. In the case of the carbonate-rich coatings were detected indications of recurrence related to the circulation of carbonate forming solutions that will be relevant for maintenance of the built surfaces.