Grey cast iron as construction material of bridges from the 18^th and 19^th century

Many bridges and railroad viaducts, which have been operated at the western and southern regions of Poland, were erected at the end of the 18^th or beginning of the 19^th century. In recent years they undergo overhauls and renovations requiring familiarity with the construction materials they have been made of. It is necessary for estimation of their load capacity (possible reinforcements) and determining their suitability for further utilisation. Among the materials in the old bridges the puddled steels and cast irons predominate. Aim of the work is identification and documentation of microstructure and selected properties of the cast irons used for production of parts for the bridge in Łażany, the Old Mieszczański Bridge in Wrocław, the hanging bridge in Ozimek, as well as the columnar piers of the railroad viaduct in Wrocław. Using the methods of light microscopy and scanning electron microscopy, as well as the results of hardness measurements and chemical analysis, it has been shown that the objects have been built of grey cast iron with flake graphite having the ferritic-pearlitic or pearlitic matrix. The diversification of their chemical analysis resulting from the type, size and geometry of the cast parts was indicated. The tested materials fulfil requirements of the contemporary standards related to grey cast irons of the EN-GJL-100 and EN-GJL-150 grades.