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The greyish coloured sandstone with light blue veins, shows some differences in colour and compactness once machined. The grain is sometimes fine, sometimes coarse. All of this because the rocks appearing in the Upper Savio valley originates from two distinct geological formations. The more compact stone, harder and with a finer grain, is extracted from the so-called Autochthonous formation, say from rock layers which sedimented in the same area where they appear. The more coarse, less hard and more easily machinable sandstone originates from the Allochthonous formation, say rocky complexes subject to horizontal translation motions which sometimes appear on surface hundreds of kilometres far from the sedimentation basin.
The Autochthonous formation involving the upper Savio valley, and especially the Para-Lastreto territory (belonging to the municipalities of Verghereto and Sarsina) is presently quarried at various levels. The sandstone extracted here shows good chemical, mineralogical and mechanical characteristics and the variety of the stone levels offers a suitable diversification of the product and can meet the most different demands of the market.
The following stratigraphic column resumes the main arenaceous levels of this territory:
- about 40 cm under the ground level, we find the "slabs" of grey-light blue sandstone used once for the roofs;
- under this first layer, there is the so-called "colombino", a whitish, hard and highly fractured calcareous rock;
- this calcareous layer is followed by the "bozze", say splinters of grey-light blue sandstone with medium-coarse grain;
- finally, at the fourth level, we find the "alberese" bank, a hard and massive grey-light blue sandstone with medium-fine granulometry.
Samples of the stone underwent some laboratory tests. The results obtained proved that sandstone, and especially the "alberese" bank, the stone of the Upper Savio valley, has excellent values in terms of compressive and bending strength and resistance to wear, imbibition and frost.
Additionally, various studies and laboratory tests demonstrated the perennial indeformability of the stone, subject to a constant load, with respect to other materials used for building purposes like, for instance, concrete which, once under stress, shows exactly the opposite behaviour. The tests conducted aimed at understanding how the time factor could affect the deformation behaviour of the treated material.
The comparison of the diagrams illustrating the time-related deformation behaviour of sandstone and concrete allows to notice that sandstone, once submitted to stress, suffers from a minimum initial deformation which keeps constant over the time without reaching the breaking point, since plastic deformations always remain below the limit of elasticity. On the contrary, the deformation of concrete is constant and endless.
The large use of this strong and durable material is in continuous evolution in both building and restoration and urban refurbishment fields. The paving of squares, streets and pavements in the town-centres is one of the sectors which most largely make use of this stone. Thanks to the resistance to wear and the machinability, the use of the stone slabs to pave outdoor environments allows for a series of technical and esthetical solutions, hardly offered by other materials. The stone can be machined in various ways. The most common machining types are: "chiselling" resulting in diagonal, straight or herring-bone machined slabs; "bush-hammering" which results in a coarse and non-skid surface; "piercing" which creates a hollow and irregular surface; and finally "flaming" characterised by an uneven yet more uniform surface.
The stone machined is subject to losses of compressive strength of roughly 200 kg per sqcm.
The combination of the different machining types can be an enriching element for town repaving projects.
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