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Content archived on 2024-04-16

Granitic materials and historical monuments : study of the factors and mechanisms of weathering and application historical heritage conservation


The objective is to improve a scientific basis for decisions on restoration and maintenance procedures for granitic monuments in Europe.
Deterioration processes of granitic materials are being studied in a continental climate (the Spanish Plateau), in a humid climate (French Bretagne) and under industrial pollution conditions (Porto Area, Portugal). A few representative monuments from each area are examined together with samples from the quarries from which the building materials originated.

In Bretagne, crystallization of salts and biological degradation are the 2 paramount factors for degradation. A study of the microflora, lichen development, action of nitrifying bacteria and fermenting sugar bacteria are being carried out.
In the Porto zone, the effect of industrial pollution is determined by comparative studies of monument weathering in areas with different climate and atmospheric contamination (Porto and Braga). The work implies rain water causes stone degradation by the dissolution of granite components and salt crystallization.

In Spain, 3 types of granite employed in historical buildings construction have been studied: one typical sain granite, one porous facies with smectite and another silicified granite, rich in opal. The agents responsible for degradation seem to be the strong thermal oscillations in this area, salt crystallization, especially in the lower parts of the buildings and dissolution of opal in areas with mortar influence.

The study of artificial ageing of the different types of granite has been carried out in simulation chambers, under controlled humidity and temperature conditions. The treatment of unaltered and altered materials in chambers is currently done with consolidating products, determining in each case the changes in the material properties during and after the ageing and/or treatments process.
Deterioration processes of granitic materials are studied in a continental climate (the Spanish Plateau), in a humid climate (French Bretagne) and under severe contaminating conditions (Porto Area, Portugal). A few representative monuments from each area are examined, chosen in view of their importance to cultural heritage, the materials they are made from, and the existence (or absence) of restoration already carried out. A study will be simultaneously carried out on the quarries from which their building materials originate and, if they have already been used up, quarries with similar rocks will be utilized.

The broad scientific content of this project is as follows.
Characterization of granite materials used in the areas to be studied, using appropriate experimental techniques. A comparative study will be performed of fresh stones (from quarries) and corresponding weathered stones from different parts of monuments.
Studies of the behaviour and response of the different materials under selected environmental conditions and in chambers under controlled conditions, as well as their response to different types of treatment for cleaning and for maintenance.
Acquisition of knowledge of the factors governing degradation processes and the main mechanisms involved. The effect of different factors (physical, chemical and biological) on every component of the rocks and on their texture and structure will be identified.


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