Artificial Weathering of Portuguese Granites Exposed to Salt Atmosphere: Variations of Mechanical Properties

Five types of granites [SPI, Cinzento Santa Eulália (CE), Cinzento Arronches (CA), Rosa Santa Eulália (RE) and Rosa Arronches (RA)] from the Portalegre region (SE Portugal) have been extensively used as ornamental rocks and building stones. Fresh specimens of these granite types were sampled from their quarries and exposed to 150 cycles of sodium chloride atmosphere (SCA). The visual mineral changes in the surfaces and the percentage of mass losses were monitorized every 15 cycles. The petrographic and major mechanical properties were determined before and after the SCA exposure. Water absorption under vacuum and at atmospheric conditions as well as uniaxial compressive strength tests, pre and post-SCA, were performed to determine variations in the characteristic values. Mass losses were registered after the exposure to SCA, varying between a minimum of 0,18% for SPI granite and a maximum of 0,23% for CA granite. Water absorption and porosity increased for each granite type, with most favourable values obtained for SPI (12% of increase) and the worse for RA granite (77% of increase). The uniaxial compressive strength after exposure to SCA decreased for the five granite types, with the best results being achieved by the SPI granite and the worse by the CA granite. Although the values of mass losses were smaller in the CE and SPI granites, the visible mineralogical changes were higher in CE granite, shown mostly through severe chromatic changes. The CA, RA and RE granites presented worse results in porosity and uniaxial compressive strength tests after the SCA exposure, rather than the CE and SPI. The data obtained so far suggest that the variations in the mechanical properties due to salt crystallization are smaller on fine to medium coarse granites and larger on medium to coarse granites.