Thermal stress in the Apuan Marbles: relationship between microstructure and petrophysical characteristics

Apuan marbles originating from different zones of the Apuan metamorphic complex have been characterized form the chemical, petrographical, microstructural and physical point of view. All samples were subjected to accelerated ageing by thermal cycling and their petrographical parameters evaluated. After a accelerated ageing, all samples show an increase in total open porosity and/or porosity evaluated with HG porosimeter in the range of pore size between 0.0037 and 150 mm. The greates variations were recorded in the coarse and fine-grained marbles with straight grain boundaries. Two trends werw observed in variation of the ratio of Hg-porosity to total open porosity after thermal ciclyng: either an increase on total open porosity not followe by a proportional increase in HG-porosity or an increase in Hg-porosity proportional to an incerase in total open porosity. During total immersionn tests, an increase of the water absorption was observed for those samples characyerised by a high ratio Hg-porosity/total open porosity with a unimodal distribution of Hg-porosity. In the case of water absorption through capillarity, the samples that suffer high increase are those characterised by a unimodal pore size distribution, even if they posses low Hg-porosity. This behaviour underlines that in the aged samples, subjected to the two different mechanisms of water absorption, the pore size distribution play an important role.