Colour and Roughness Measurements as NDT to Evaluate Ornamental Granite Decay

Granitoids are selected for ornamental purposes due to their texture and colour. The determination of granitoid durability has been slightly neglected since most of standard weathering tests have been developed for stones with more than 5% porosity. In addition, the evaluation of the decay is commonly focused on loss of mass or fracturation. In this study, the decay of granitoids was assessed with NDT such as colour and roughness. For this research, four granitoids commonly used as ornamental stones have been studied. They show differences in colour and texture, thought porosity is similar. Four weathering tests were carried out: salt crystallization, Freeze-Thaw cycles, SO2 exposure and heating to different temperatures. Standard test were adapted to focus the damage on the surface. Colour and roughness measurements were carried out before and after the tests. We concluded that, in the decay tests in which chemical reactions were not involved, roughness measurements gave accurate information about the decay. In the decay tests in which chemical reactions are produced, such as SO2 interaction or mineral transformation due to high temperatures, both colour and roughness could evidence the decay, even if colour change is faster and easier to observe and measure.