THERMAL EXPANSION AND ITS CONTROL ON THE DURABILITY OF MARBLES

Abstract

Marbles as ornamental stones as well as in their natural environments show complex weathering phenomena. The physical weathering of marbles due to thermal treatment is often discussed as the initial stage of deterioration. Eighteen different well-known marble types were selected to quantify experimentally the effect of heating and cooling within the temperature range of 20°C to 85°C while three different ramps at 40°C, 60°C and 85°C destination temperature were performed. The marbles differ in composition from calcitic to dolomitic as well as in their fabrics. The average grain size varies from 50mm up to 3mm, while the grain boundary geometry differs from a granoblastic foam structure to those with weakly inequigranular-amoeboid structure. The lattice preferred orientation ara also highly different in c-axis and a-axis distribution. With respect to the heating and cooling cycles three different groups of marbles can be distinguished: Type I is characterized by an isotropic thermal expansion and large isotropic residual strain (permanent length change); Type II exhibits an anisotropic expansion and no or small isotropic residual strains; Type III shows an anisotropic expansion and am anisotropic residual strain. Most samples show deteriorations due to thermal treatment, which cannot be understood without taking into account the rock fabric. The magnitude and directional dependence of the thermal expansion is mainly controlled by a lattice and shape preferred orientation. The composition, grain size, grain boundary geometry and pre-existing microcracks modify in a more complex way the progressive loss of cohesion due to dilatancy caused by the anisotropic thermal expansion.