Objective
The aim of this research project is to contribute to a better knowledge of the degradation phenomena and of the conservation procedures of granitic rocks, in general, and to the specific aspects related to the conservation of megalithic monuments in particular.
In the Iberian Peninsular there are a very large number of monuments made of granitic rocks. Megalithic monuments, castra and other prehistoric and proto-historic monuments, Roman structures, cathedrals, churches and an immense number of civil buildings constitute a vast heritage which needs to be preserved. Granitic rocks present several characteristics that give them some peculiarities and reduce, or even nullify, the possibilities of extrapolating to them, knowledge concerning other types or rocks, such as limestones and sandstones, more often the object of interest by the international scientific community. Granitic rocks are polimineralic and their constituents have very physical and chemical properties. Their behaviour as regards weathering is distinct as well. Granitic rocks, when fresh, are compact, highly resistant, and have low porosity and permeability, but they undergo a significant decrease in quality, for increments of these two parameters, even if they are small. Granitic rocks are mainly composed of quartz and feldspars (alkaline and/or plagioclase) and may contain significant amounts of other minerals. Different grain sizes lead to differences in rock behaviour and small amounts of secondary minerals may accelerate the degradation of these rocks. Voids are mainly of the fissure type and their role in reducing permeability is much more efficient than a similar volume of voids of the pore type. Selection of treatments for granitic rock is very difficult because of its low porosity and permeability greatly hinder the penetration of treatment products. Assessment of treatment efficacy is also difficult, owing to the small quantities of products that can be absorbed and to their distribution through extremely small voids, which demands very accurate and powerful testing equipment to detect and characterize the products. Assessment of treatment durability raises some intricate problems in any type of rock. Several aspects are involved such as: chemical and mechanical properties of the treatment products, stability in time, of their relevant physical properties, as well as properties of the new composite material made up of the rock plus the treatment product. Accelerated ageing tests in laboratory conditions, though useful, have not been sufficient to overcome the scarcity of experience gathered with treatment products in their still short existence. Direct involvement of industrial partners is considered very important. Supply of treatment products and cooperation in the development of the new formulations are some key issues coming from their participation. For PORTUGAL this has a specific interest because conservation practice is quite incipient and there is a great difficulty in obtaining conservation products. In the course of the project some benefits are expected to come out of it for the conservation practitioners, taking into account that research support for these specialised teams is almost absent in PORTUGAL. Although in a less critical manner, the situation in SPAIN as regards the conservation industry is also unsatisfactory.
Programme(s)
Topic(s)
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LISBOA
Portugal