Natural and accelerated weathering of two coloured sicilian building stones

Among many coloured stones employed as "marbles" in the rich baroque architecture in Sicily, the dark grey Breccia di Billiemi and the Rosso di Piana degli Albanesi are of widespread use. Nowadays they are also exported in Northern Europe and in Arabian countries. Both stones were employed outdoor and indoor as slabs and for structural elements, such as columns, but when exposed outdoor, they undergo significant alteration processes, affecting not only their chromatic aspect but also the state of aggregation. Aim of this experimental work is to investigate some alteration processes induced by weathering in order to understand the mechanism of their evolution. The effects of accelerated weathering in laboratory are compared with natural ageing in the urban environment. The study of such stones includes the description of lithofacies, the characterisation by means of petrographic and physical-chemical techniques - optical and electronic microscopy, XRD - and finally accelerated weathering experiments on both lithotypes - UV radiation plus dew, thermal treatments, washout, exposition to both oxidative and acid environment.