Laboratorial Study of the Combined Effect of SO2 and High-Temperature Ageing on the Physical and Mechanical Properties of Encostinha Marble, a Portuguese Stone.

The effects of SO₂, high temperature (600°C) and cooling type (slow and rapid) were investigated in this study as decay factors of a building stone (Encostinha Marble). Changes in colour, gloss, apparent density, open porosity, capillary water absorption and ultrasonic pulse velocity were assessed, complemented with SEM observations and XRD analysis. SO₂ did not significantly react with the marble; no neoformed products were identified and only superficial changes were registered. Specimens became darker and duller. The increase in size of pre-existing microcracks and the development of new ones caused by high temperature, with a consequent increase in open porosity, was the main cause of the marked degradation of physical and mechanical properties. The cooling type was also shown to influence the physical and mechanical characteristics of the marble. A more pronounced increase in open porosity and capillary water absorption in specimens cooled by total immersion in tap water was observed. This increase was not in line with the corresponding decrease in ultrasonic parameter values. [ABSTRACT FROM AUTHOR]