Deterioration caused by dimensional change in stone (EBD pathology): the role of the organic matter — pore network — salt combination

We have studied a pathology produced by dimensional changes in Miocene lacustrine limestones of the Ebro basin with very low clay content (Briviesca and Tudela stone). The samples studied come from stone blocks of the Cathedrals of Burgos and Tudela and their respective original quarries. Three additional rocks that present a pattern of similar deterioration are also characterised. The pathology, known as “Expansion by Drying (EBD)”, looks like a mechanical fracture and is produced by important dimensional changes of the material. We have carried out a detailed study of the rocks with Mercury Intrusion Porosimetry (MIP) and establish four different porous systems in the materials studied. A relationship is found between the type of porous system and the presence of the pathology. In order to develop, EBD pathology needs a porosimetry like the one defined for group IV. On the other hand, oxidation of the organic matter present in the rock (proven by aging the rock with ozone) changes the porosimetry of group IV rocks, converting them into a porous network of group III. These facts explain why EBD pathology develops in oxidized rocks of historical buildings and not in fresh quarry rocks. In addition, we characterise dimensional changes of the rock by the intrusion of liquid water (conventional hydric expansion) and water vapour adsorption. These data have been relevant to understand the mechanisms of the dimensional change in the rocks studied.