The paper describes the analyses and the tests carried out on representative slabs of white Carrara marble which have highlighted the correlation between the microfabrics and physical and mechanical parameters. The aim is to determine the conditions which indicate the triggering and evolution of the deformation phenomena. La note ecrit l'analyse et les epreuves effectuee sur un echantillon representatif de nombreuses dalles en marbre de Carrara. Les etudes montrent la correlation entre la mineralogie et les paramètres physiques et mecaniques. Le but est determiner les conditions qui indiquent l'amorçage et l'evolutions des phenomènes de deformation. Diese Arbeit gibt eine Beschreibung der experimentalen Untersuchungen und der Analysen ueber die Marmorplatten von Carrara. Daraus resultiert, dass die Charakterisierung der Mineralogie und die Porositat der Gesteinsmaterialien die physikalische mechanische Degradation beurteilen und die Kruemmungen bestimmen.

Introduction

Many cases of time-dependent mechanical decay affecting stone materials, represented mainly by marble, used in architecture, historical buildings and monuments are reported in literature. These processes are mainly related to the bending of marble-slabs and architectural elements which are involved by creep processes, generally in load conditions due exclusively to their own weight (Winkler 1975). These time-dependent deformation phenomena are often triggered off by the effects of stress release, due, in turn, to residual stress (Voight 1966). The latter is connected to the tectonic and geomorphological history, to the effects of new environmental conditions and to the new geometry of the stone elements. It is important to identify and study these phenomena as it has already been proven that they play an important role in controlling and increasing the effects due to natural weathering and atmospheric pollution. At the same time, in many cases, creep processes are the vehicle for more rapid, and sometimes obvious, effects of bowing type deformation, caused by thermal cycles or by the incorrect fixing of slabs. We have had some well known cases in recent architectural works which present bending phenomena in the covering material, e.g. the Amoco Tower (Chicago), the Arc de la Defense (Paris), the Finland House (Helsinki). Other cases are related to ancient monuments, e.g. the many façades and external walls of Romanesque and gothic churches, particularly in Tuscany. In many cases we have a modest deformation effect, however micro-deformations, and sometimes micro-cracks, are present in the intergranular and transgranular structure of the marble and they are a vehicle of degradation processes. On this ground, it is clear that it is necessary, not only to continue the studies and the tests for characterizing and modelling creep phenomena, with the identification of the constitutive laws, but also to examine and apply analyses and forecasting methods to small scale processes, in order to find the relationship between physical properties and microfabric features. As it is well known there are many types of marble (Ertag 1980) and their behaviour can differ greatly even if they come from the same geostructural basin. Indeed previous experiences (Barsottelli et al. 1999) have clearly shown that "identical" marbles, classified as such according to technical.

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