V. G. Ruiz de Argandoña

Characterization by computed X-ray tomography of the evolution of the pore structure of a dolomite rock during freeze-thaw cyclic tests

Abstract The study of the pore structure of rocks is very important for the interpretation of their behaviour when subjected to weathering. In the case of rocks used in historic buildings or in objects of art where other techniques can not be applied, the Non-Destructive Testing method (NDT) for determining porosity, such as X-ray computed tomography (X-ray CT), becomes a very interesting alternative. In this paper this technique has been used for imaging textural features and the internal pore structure of a dolomitic rock used as building material in Oviedo Cathedral, Spain. The reconstructed 3D image shows a non uniform distribution of porosity. The rock has been subjected to freeze-thaw cycles to evaluate its durability. The evolution of the void structure has also been studied by X-ray CT and the images obtained allow one to follow the progressive decay and to assess the internal depth of the damage. Because of the low resistance to weathering of the rock, damage, mainly in the form of fissures, was observed even in the initial tests (third cycle in some of the specimens). Breakdown of the rock appeared as early as cycle 12 in some specimens.

Rock Matrix Diffusion as a Mechanism of Radionuclide Retardation: A Natural Analogue Study of El Berrocal Granite, Spain

Blocks and cores of El Berrocal granite intersected by hydrogeologically-active fractures have been studied in order to determine (1) the extent to which diffusion of natural radionuclides has taken place from fractures into the rock matrix, and (2) the microstructural controls of diffusion. The results suggest that, in many granitic rocks, matrix diffusion (of uranium, at least) may be limited to a zone extending only a few cm from water-conducting fractures and that not all of the rock may be available for diffusion. This should be taken into account in establishing radionuclide migration/retardation models for repository sites.

Characterization by X-ray computed tomography of water absorption in a limestone used as building stone in the Oviedo Cathedral (Spain)

Abstract Water plays a fundamental role in rock weathering processes. Its penetration and movement inside rocks greatly influences the nature and intensity of damage affecting building stones. X-ray computed tomography (CT) is a useful technique for non-destructive mapping of water penetration. For the reported study, CT was used to investigate the internal structure and water penetration patterns for the Piedramuelle Stone, a Cretaceous limestone used as building material in the Oviedo Cathedral (North of Spain). X-ray CT provides good images of the internal structure of the samples: the sedimentary layering due to differences in composition and porosity is clearly seen, as well as other textural features. The movement and penetration rate of water was monitored during standard free absorption water tests. The images that were obtained show a clear difference between dry and wet zones in the interior of the sample. Water movement is related to the petrographic characteristics of the rock, mainly to layering which controls the direction of water penetration. Hounsfield Unit numbers provide a quantitative approach for assessing the penetration rate of water.

NON-DESTRUCTIVE ULTRASONIC PROCEDURE TO EVALUATE IN SITU THE RELATIVE DETERIORATION OF MONUMENTAL STONES: PRELIMINARY RESULTS

To evaluate in-situ the relative deterioration of monumental stones, a non-destructive ultrasonic procedure is under development: ultrasonic waves are introduced into the rock and after travelling through it are processed for evaluation of their Vp, amplitude, duration, energy and count number. The procedure was applied to two Spanish Monasteries, one built with a granodiorite (El Escorial, Madrid, which results are included here) and the other built with sandstone (Sta. Maria de Ripoll, Gerona). Laboratory ageing tests, involving monitoring of the above mentioned ultrasonic parameters, were performed as a basis for interpreting the in-situ measurements. The energy seems to be the most sensitive parameter as an indicator of the rock deterioration, so, the value obtained for a masonry block in the monument can be used to classify the rock into one of preset deterioration groups.

Mechanical Stresses Generated by Crystallization of Salts Inside Treated and Non-Treated Monumental Stones; Monitoring and Interpretation by Acoustic Emission / Microseismic Activity.

The crystallization of salts in building stones is one of the most common and severe deteriorating phenomencndeveloped on Historic Buildings. To evaluate their mechanical effects in treated and non-treated stones, experimental salt crystallization tests and the monitoring of the corresponding acoustic emission / microseismic activity, AE/MS, have been planned. Salt crystallization tests have therefore been performed on a high porosity (30%) limestone used in the building of the Cathedral of Murcia (Spain). Each test consisted of 11 and 20 cycles (for the non-treated and treated specimens, respectively) of immersion of specimens in salt solution (14% Na 2 SO 4 . 10H 2 O) for 4 h., drying in an oven at 60 °C for 14 h. and final cooling at room temperature for 6 h. The treated specimens were consolidated by total immersion in ethyl silicate -Tegovakon V- and protected with a water repellent, oligomeric polysiloxane -Tegosivin HL- 100-, (both from Th. Goldschmidt, FRG). The AE/MS, was monitored in the 100-300 KHz range. The preliminary results show a very different AE/MS behaviour between the non-treated and the treated specimens.

Durabilidad en ambientes húmedos de la Arenisca de La Marina (Jurásico superior de Asturias)

Se ha estudiado la alterabilidad de dos variedades (gris y amarilla) de una roca ornamental asturiana, denominada Arenisca de la Marina, perteneciente a la Formacion Lastres (Jurasico Superior). Ademas de las clasicas tecnicas de microscopia, para el estudio textural se han utilizado la velocidad de propagacion de ondas elasticas y la tomografia axial computerizada de rayos-X. Se ha determinado la variacion de algunas propiedades fisicas (densidad, porosidad abierta y velocidad de propagacion de ondas elasticas) antes y despues de los ensayos de alterabilidad (humedad-sequedad, hielo-deshielo y cristalizacion de sales), comprobandose que los ciclos de cristalizacion de sales son los mas agresivos y que la variedad amarilla es mas susceptible al deterioro que la variedad gris. La textura ejerce una gran influencia en la durabilidad de ambas muestras, de modo que las bandas con mas matriz y mayor porosidad presentan una mayor desagregacion superficial, determinandose la existencia de un comportamiento anisotropo, mas marcado en el caso de la variedad amarilla que en la gris.