Applications of Image Analysis to Marble Samples

The study of natural stone decay is useful in the field of modern building, but also for the protection and recovery of artistic and architectural heritage. The presence of voids in compact rock is one of the main features that drive the processes of decay of stone materials. In particular, the pore characteristics, such as their volume, their network connectivity and their distribution inside the stone are key parameters to better study and understand the weathering of natural stone. For this reason, image analysis (jPOR for ImageJ) on thin sections cut from different portion of ten kinds of marble specimens have been performed. The results obtained show that different crystal habits and the presence of subgrains are correlated with mechanical strength and durability of the stone. Also a correlation between Total Optical Porosity (TOP) and water absorption for marbles in natural state have been found. The analysis of TOP of marble artificially and naturally weathered has given the explanation of the different variations in water absorption obtained from natural to artificial ageing. In particular it seems that the naturally decay is more aggressive that the artificial one (performed according to EN 16306: 2013). In fact, for marble with polygonal contour and no subgrains, it seems to be a different distribution of porosity on the specimens naturally aged respect those artificially aged.