Decay of the Campanile limestone used as building material in Tudela Cathedral (Navarra, Spain)
O. Buj, J. Gisbert, B. Franco, N. Mateos, B. Bauluz, 2010. "Decay of the Campanile limestone used as building material in Tudela Cathedral (Navarra, Spain)", Limestone in the Built Environment: Present-Day Challenges for the Preservation of the Past, B. J. Smith, M. Gomez-Heras, H. A. Viles, J. Cassar
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A characterization is presented of the building materials used in the Cathedral of Tudela, as well as of the different forms of decay, with the aim of establishing the cause and mechanisms of this decay. The Cathedral of Tudela was built mainly with Campanile limestone from the upper Miocene. The campanile limestone is a wackestone, with a terrigenous content of 2.6% and 1.5–2.5% of organic matter.
After a detailed investigation of all the different forms of stone decay, our conclusion is that the main type of damage affecting Campanile limestone has morphologies similar to a mechanical fracture with breakages of convex surfaces and resulting very sharp edges. The process of decay is caused by the expansion of the rock during the drying process, which has a very rapid and aggressive effect on the rock.
Laboratory tests showed that through extreme drying in the presence of a magnesium sulphate solution, the salt crystallization inside the stone generates a strength greater than the tensile strength of the stone, thus causing a fracture and the loosening of rock fragments. The materials introduced in recent restorations (sandstone and Portland cement) provide the necessary magnesium for the development of this weathering in Campanile limestone.