Influence of rift and bedding plane on the physico-mechanical properties of granitic rocks. Implications for the deterioration of granitic monuments

The influence of the natural planes in granitic rocks (rift and bedding pla ne) on some of their physico-mechanical properties was evaluated with a vie w to establishing how the disposition of these planes in granitic construct ion materials affects the deterioration of granitic monuments. Blocks were cut from three granites that have been widely used in construction and rest oration in Santiago de Compostela (Galicia, NW Spain), and their capillarit y, permeability to water vapour, thermal expansion and expansion upon immer sion in water, and compressive and bending strength were determined in thre e different orientations with respect to a reference plane. The results sho wed that the granitic rocks were strongly anisotropic and that this anisotr opy was reflected in the values of most of the measured properties, especia lly thermal expansion, expansion upon immersion in water, and mechanical re sistance. The disposition of the natural planes was clearly identified for only one of the granites; for the other two, the relation between these pla nes was less straightforward and its identification would require the use o f a more exhaustive sampling strategy than that used here. The variation in the physical properties with the orientation of the granite blocks suggest ed that blocks positioned with the rift vertically oriented would be partic ularly prone to deterioration. (C) 2000 Elsevier Science Ltd. All rights re served.