Modelización y estimación de la durabilidad de materiales pétreos porosos frente a la cristalización

Source: OAI

ABSTRACT 291 pp.-- Tesis desarrollada en el Departamento de Ciencias de la Tierra y del Medio Ambiente, Facultad de Ciencias, Universidad de Alicante (2002). [EN] In this Thesis, different mechanisms of salt crystallisation are evaluated, and stone durability against salt crystallisation is also quantified. These stones are widely used not only in architectural and cultural heritage but also in modern buildings, used as building material. Three salt crystallisation mechanisms are studied: evaporation process of brines from porous media of rocks; the influence of porous media on the mineral precipitation sequence; and, finally, the crystallisation pressure that mineral growth produces over the pore wall. In order to quantify stone durability, a salt crystallisation test, based on partial immersion of the materials, is proposed. For this purpose, nineteen porous stones have been chosen for their different petrophysical and petrographic characteristics (mainly bioclastic rocks with different grain size); and two brines have also been used for their abundance and aggresiveness: NaCl and Na2SO4. Finally, a durability theoretic estimator is proposed, including parameters of porous media and mechanical properties of rocks. [ES] Los objetivos de esta tesis son (i)modelizar la cristalización de sales en medios porosos mediante el estudio de la saturación de los diferentes minerales que van a crecer en el seno de rocas porosas por evaporación, la determinación experimental de la secuencia de precipitación que se produce en los poros de las rocas proponiendo las ecuaciones básicas que rigen dicho proceso y la determinación de la variación del sistema poroso de la roca por la presión de cristalización, evaluando mediante las ecuaciones teóricas planteadas por Scherer (1999) la influencia de los parámetros más importantes que definen dicha presión: el volumen molar, la tensión superficial cristal-salmuera y la interacción cristal-superficie de la roca. Adicionalmente, esta Tesis pretende cuantificar la durabilidad de las rocas porosas, (i) proponiendo un nuevo ensayo acelerado de cristalización de sales más acorde con las observaciones reales, en contraposición a los ensayos basados en ciclos de inmersión total de la roca en salmuera y (ii) definiendo estimadores teóricos de durabilidad acordes con los mecanismos de degradación de las rocas porosas de construcción por la acción de la cristalización de sales evaluados y cuantificados a lo largo de la tesis doctoral. Esta Tesis ha sido financiada por una beca de formación de personal investigador de la Generalitat Valenciana y por los proyectos: PB96-0321, GV97-RN14-3 y MAT2000-074. Peer reviewed

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    ABSTRACT: The combined influence of rock fabric, pore geometry and mineralogy (petrological parameters) on transport properties in complex and heterogeneous naturally fractured rocks was studied experimentally. As fissure geometry quantification has rarely been addressed in most theoretical studies of transport properties, emphasis was placed on the effects of fissure geometry on both non-saturated media (capillary rise) and saturated media (permeability).We proved that prediction of transport properties in complex rocks is not guaranteed by the estimation of the classic micro-structural variables considered in the literature and that accurate prediction can only be attained when petrological parameters are first quantified in depth, and then combined.Principal component analysis and the regression models proposed here clearly demonstrated on the one hand that, a meaningful porous network in non-saturated media must be modelled with a combination of different geometrical capillary tubes representing the matrix (cylindrical) and the fissure (rectangular prism) and on the other hand, that in saturated media a well-in-deep fissure size quantification enabled a more accurate prediction of permeability to be made.The experimental data confirm that transport properties and its anisotropy are closely dependent on fissure typology, textural characteristics, mineralogy and spatial distribution of the whole rock fabric elements. Enlarged-fissures weakly exert capillary suction due to the retarding effect of gravitational forces, but they are vital in controlling permeability. Cracklebreccias with small clasts, high dolomite cement content and high inter-clast fissure density exhibit strong capillary suction. However, high calcite cement produces abnormally low rates of capillary rise, due to possible pore surface contamination, together with a high contact angle effect. Good agreement between permeability and geometric factors provided a suitable basis for identifying preferred permeable directions. Additionally, we found a critical fissure density which defined the isotropic matrix permeability. We also present a new practical and simple linear model relating permeability to capillarity with meaningfully and easily estimated petrological parameters.Results obtained in the present study demonstrated the correct identification and use of more directly related petrological variables for modelling transport properties. Moreover, the analysis of these results using multivariate analysis is considerably more demanding compared to the conventional approaches.
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    ABSTRACT: Three kinds of brecciated dolostones (BD) from the Betic Cordillera (Spain) marketed as commercial marble and extensively used as construction and building materials were studied in order to describe their water transport properties. Water permeability and capillary imbibition test were undertaken in order to determine the influence of pore structure on water transport within these types of stones. These BD are commonly known in the commercial sector as Marrón Emperador (ME), Beige Serpiente (BS) and Amarillo Triana (AT). In general terms, they are all mesocrystalline dolostones with different degrees of fissure density. These fissure systems are frequently filled with mineral calcite and dolomite cement and sometimes present evidence of strong dissolution processes. Spatial distribution of textural components differs significantly according to the variety studied. A correlation between water permeability and other physical properties is discussed, including both pore structure (porosity and pore size distribution) and fissure geometry (width and density). Since permeability is a directional quantity, it has been measured in three orthogonal directions, together with the other parameters. In order to establish a relationship between all parameters, multivariate statistical tools have been applied. The mercury intrusion porosimetry results defined two kinds of porous family: matrix/cement (porous space) and fissures. Moreover, we found that the permeability logarithm correlates with fissure density (~70%) and is independent of both porosity and fissure width. Furthermore, principal component analysis corroborates permeability dependence on fissure density and suggests strong influence of mean porous size on permeability. The anisotropic index estimated for ME and AT is quite some distance from 1, indicating strong anisotropic permeability, whereas for BS it is nearer to 1, denoting isotropic permeability behaviour.
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