© The Geological Society of London 2006 1 Deterioration-related changes in physical properties and mineralogy of limestone monuments

Abstract: Many public buildings were constructed from limestone in Budapest. The deterioration and the changes in physical and mineralogical properties of two texturally and physically different limestone types have been compared. The first type, that is used on the facades of monuments, is a porous limestone (oolitic) with an effective porosity of up to 36 % and having a very low compressive strength (2-11 MPa). The second type is a freshwater limestone (travertine) with effective porosity of generally less than 10 % and with a compressive strength of up to 120 MPa. These textural differences and the variable physical properties are well expressed in the differences of decay phenomena. Schmidt hammer rebound, Duroscope rebound, water absorption and mineralogical composition (XRD, DTA-DTG) were measured and compared. The porous limestone shows intense black and white crust formation. The strength of the crust is related to the thickness, to the mineral composition, to the crust morphology and to the capacity of water absorption. Calcite-rich, impermeable, thick white crusts have the highest strength, which is followed by gypsum-rich laminar black crusts alongside with thin gypsum-rich white crusts. The crusts are prone to scaling and/or flaking that is followed by rapid material loss and back-weathering. During the removal of the crust not only does the surface with its gypsum-rich crust chip off but also a detachment layer with the substrate. As