Morphology and detachment mechanism of weathering crusts of porous limestone in the urban environment of Budapest

Török, Ákos (2007) Morphology and detachment mechanism of weathering crusts of porous limestone in the urban environment of Budapest. Central European Geology, 50 (3). pp. 225-240. ISSN 1788-2281

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Abstract

Abstract A fine-grained and a medium-grained oolitic limestone of Miocene age were studied on ashlars of monuments in Budapest. The studied buildings are located in a polluted urban environment. The surface alteration is characterized by the presence of white (thin and thick) and black (laminar and framboidal) weathering crusts. Flaking, scaling and blistering are common crust detachment forms. Crust detachment is followed by rapid surface loss in the form of granular disintegration or of secondary crusts stabilizing the stone surface. Non-destructive in situ mechanical tests such as Schmidt hammer rebound and Duroscope clearly document the presence of thin and thick weathering crusts, and the degradation of underlying fine-and medium-grained limestone. Crust formation is associated with a textural change, since precipitation of pore-occluding calcite and gypsum and reduction of porosity in the crust zone has been recorded. Crust detachment is attributed to the crystallization pressure of air pollution-related gypsum, to freeze/thaw cycles, and to differences in mechanical properties of crust and host rock.

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