Geochemistry of the built environment : alteration products of stony materials

Abstract

It is presented a review addressing the geochemical evolution of materials surfaces in the built environment, focusing namely on the geochemical diversity of decay products. The same geochemical weathering processes that affect natural rock outcrops act on stony materials after their emplacement on the built structures, enhanced by higher concentration of pollutants related to the urban environment and to specific geometric configurations of architectural works. These processes lead to the formation of alteration products that could cause the mobilization of substances of the original materials and the formation of new substances. Two major categories of alteration products will be considered in this review: coatings and erosive features. Coatings can result from neoformations related to pollutants and the reactions between pollutants and the substrate. In the discussion of erosive features will be included processes that imply the loss of material or that create conditions for that loss (fissuring). These erosive features can result from several processes that involve the chemical instability of the original phases of the materials, as well as physical consequences related to the interaction with pollutants, such as expansion and crystallization inside the pore network. The alteration products of stony materials in the built environment present specific geochemical aspects related to the specific conditions and its study is paramount for the definition of qualitative and quantitative relationships between pollutants and alteration features.