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 from the chemical, petrographical, microstructural and physical points of view. All samples were subjected to accelerated ageing by thermal cycling and their petrophysical parameters evaluated. After accelerated ageing, all samples show an increase in total open porosity and/or porosity evaluated with Hg porosimeter in the range of pore sizes between 0.0037 and 150 mm. The greatest variations were recorded in the coarse and fine-grained marbles with straight grain boundaries. Two trends were observed in variation of the ratio of Hg-porosity to total open porosity after thermal cycling: either an increase in total open porosity not followed by a proportional increase in Hg-porosity or an increase in Hg-porosity proportional to an increase in total open porosity. During total immersion tests, an increase of the water absorption was observed for those samples characterised by a high ratio Hg-porosity/total open porosity with a unimodal distribution of Hgporosity. In the case of water absorption through capillarity, the samples that suffer a higher increase are those characterised by a bimodal pore size distribution, even if they possess low Hg-porosity. This behaviour underlines that in the aged samples, subjected to the two different mechanisms of water absorption, the pore size distribution plays an important role.