Physical and mechanical properties of the repaired sandstone ashlars in the facing masonry of the Charles Bridge in Prague (Czech Republic) and an analytical study for the causes of its rapid decay

0364644 - ÚSMH 2012 RIV DE eng J - Článek v odborném periodiku
Přikryl, R. - Weishauptová, Zuzana - Novotná, M. - Přikrylová, J. - Šťastná, A.
Physical and mechanical properties of the repaired sandstone ashlars in the facing masonry of the Charles Bridge in Prague (Czech Republic) and an analytical study for the causes of its rapid decay.
Environmental Earth Sciences. Roč. 63, 7/8 (2011), s. 1623-1639. ISSN 1866-6280. E-ISSN 1866-6299
Grant CEP: GA ČR GA205/08/0676
Výzkumný záměr: CEZ:AV0Z30460519
Klíčová slova: natural stone * weathering * water soluble salts
Kód oboru RIV: AL - Umění, architektura, kulturní dědictví
Impakt faktor: 1.059, rok: 2011

The facing masonry of the Gothic Charles Bridge in Prague (Czech Republic) has been largely altered during nineteenth and twentieth century repairs, due to extensive replacements of weathered sandstone ashlar blocks. Natural stone varieties used during these replacements show different responses to a variety of weathering processes which lead to their rapid decay. The decay of the newer stone has been accelerated by use of Portland cement paste as the binding and fill material, instead of the original hydraulic lime-based and cocciopesto-type mortars. The hardened Portland cement paste makes an almost impermeable barrier, with permeability three to four orders of magnitude lower, compared to the original mortars and natural stone. The low permeability of this new alien material results in the accumulation of water-soluble salts (specifically nitrates, but also sulphates and chlorides) in the facing masonry ashlars, with their crystallisation coming in the form of both sub- and efflorescence, as well as the development of various decay forms (blistering, granular disintegration and/or scaling and flaking). The source of the water-soluble salts can be traced back to previous restoration attempts. These included chemical cleaning (black crust removal) by nitric acid, ammonium hydroxide (‘ammonium water’), or ammonium hydrogen carbonate, all which can be linked to high nitrate content in the efflorescence.
Trvalý link: http://hdl.handle.net/11104/0200075