Thaumasite as decay product of cement mortar in brick masonry of a church near Venice
2003; Elsevier BV; Volume: 25; Issue: 8 Linguagem: Inglês
10.1016/s0958-9465(03)00159-8
ISSN1873-393X
AutoresF. Veniale, Massimo Setti, Carlos Rodríguez‐Navarro, S. Lodola, W. Palestra, A. Busetto,
Tópico(s)Calcium Carbonate Crystallization and Inhibition
ResumoThaumasite has been recognized as constituent of salt efflorescences occurring within the cementitious mortar connecting the brick framework. It gives rise to swelling fissures and scaly detachments; furthermore, to heaving, curving and spalling of the perimeter walls. The sand aggregate of the mortar contains carbonates (calcite 25–40%, dolomite 20–35% and aragonite 5–20%). The bricks rarely contain negligible amounts of gypsum, whereas, together with Mg–calcite and dolomite, it constitutes very thin patinas covering some bricks exposed to south: probably, such patinas originated by precipitation from solution percolating through the joint mortar. It is noteworthy that thaumasite efflorescences are mainly located at the north-side of the perimeter masonry, and their amount is higher (up to 30%) on the internal walls where lack of direct sun-radiation, narrow range of temperature changes and dew-condensation conditions actually keep up a rather constant and relatively high room moisture ratio, and low temperature. The most probable source of pollutants should be discharges (exhaust gases, as sulphur oxides) from the large petrol-chemistry industrial area located in the neighbourhood of Mestre town, inside the Venice lagoon. Morphological features and air drying behaviour of the thaumasite crystals, as observed by Environmental-SEM, indicate that their growth took place in conditions far from equilibrium, e.g. at different supersaturation values.
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