DOI: 10.5593/SGEM2015/B12/S2.115


A. Antao, M. Quinta-Ferreira
Friday 7 August 2015 by Libadmin2015

References: 15th International Multidisciplinary Scientific GeoConference SGEM 2015, www.sgem.org, SGEM2015 Conference Proceedings, ISBN 978-619-7105-32-2 / ISSN 1314-2704, June 18-24, 2015, Book1 Vol. 2, 863-872 pp

The research developed aimed to quantify and understand the evolution of the physical properties of the Guarda granite, Portugal, related with weathering. Samples were collected in selected outcrops representative of the different weathering grades, and when necessary were prepared in the laboratory to be tested with nondestructive techniques. The grades of weathering were defined considering the macro and microscopic observations of the samples combined with the properties measured. It was found that porosity and water absorption tend to increase with increasing weathering, while a reduction in ultrasound velocity occurs. Moreover, it was found that the density of the rock showed no major changes during the weathering sequence, not allowing an easy differentiation of the weathering grades. This is due to the type of weathering imposed on these granites that are essentially of physical nature, without significant variations in the density of the rock. The analysis of the type of porosity was very important in understanding the geometric characteristics of the pore space. Being the granite a material of low porosity, small variations of the property lead to large variations in the behavior of the material. As the increase of porosity in granites indicates major changes, it can be used for a first assessment of rock characteristics. Good correlations were obtained between ultrasound velocity and other parameters like: dry density, porosity, water absorption by capillarity and permeability to oxygen. It was concluded that the texture and the average grain size are important factors to consider in the water absorption by capillary. The relations obtained allow a fast characterization of this granite along its weathering profile.

Keywords: Granite, weathering, physical properties, Portugal