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Trabajo presentado en el 16º Congresso Nacional de Geotecnia, celebrado en Açores (Portugal), del 27 al 30 de mayo de 2018, [EN] Lapilli tuff has been widely used in architectural heritage as construction material and ornamental stone in Madeira. Some of its quarries have been depleted, its exploitation was forbidden decades ago and stocks of the original quarries are getting increasingly scarce. The present study investigates the coupled effect of pore structure, PS, and water transport properties, WTP, on its decay. Urban fieldwork was conducted in order to identify common stone damage mechanisms, and salt weathering was found to be the most common. 36 cylindrical specimens of two representative facies, belonging to two distinct volcanostratigraphic units with different textural characteristics were studied: a highly porous and a porous facies. Petrographic features and mineralogical composition were analysed. PS properties were quantified by effective porosity, mean pore radius and water saturation coefficient, whilst WTP were described through permeability and capillarity. Sharp Front analysis was applied to model liquid transport in unsaturated conditions. Salt durability test was performed on the same specimens and its effects were quantified by means of the percentage of dry weight loss, DWL, due to salt crystallisation. The results of PS, WTP and DWL, were analysed through advanced statistical methods. Urban fieldwork and laboratory experiments demonstrated that the most significant parameters affecting durability of lapilli tuff are porosity, mean pore radius, rock components distribution and its inadequate use. Major deterioration problems observed were related to the presence of small constructions that act as water reservoir. The principal component analysis revealed that there is a negative correlation between WTP and DWL. As WTP are intimately linked to pore space, these petrophysical parameters can be considered as quality indicators of lapilli stone durability. Powerful model for estimating permeability from capillarity is presented. It is the first time that this kind of model gives a high correlation coefficient (R²=0.9822) in highly heterogeneous rocks., [PT] Os tufos de lapilli têm sido utilizados no património arquitetónico na Madeira como materiais de construção e rochas ornamentais. Algumas pedreiras têm-se esgotado, a sua exploração foi proibida há décadas e as existências nas pedreiras originais são escassas. Este estudo investiga o efeito simultâneo da estrutura do poro, EP, e das propriedades de transporte da água, PTA, na sua alteração. A partir duma campanha de campo urbana, identificou-se a precipitação de sais como um dos mecanismos de alteração mais comuns. De seguida foram estudados, 36 provetes cilíndricos de duas fácies representativas, pertencentes a duas unidades vulcano-estratigráficas diferentes, com características texturais distintas: altamente porosa e porosa. As características petrográficas e a composição mineralógica foram estudadas. A EP foi quantificada mediante porosidade aberta, radio medio do poro e coeficiente de absorção de água. As PTA foram caracterizadas mediante permeabilidade e capilaridade. Nesta última, foi aplicada a análise Sharp Front para modelizar o transporte do líquido. Sobre os mesmos provetes realizou-se a determinação da resistência à cristalização de sais, quantificada pela percentagem da perda de massa inicial, PMS. Os resultados de EP, PTA e PMS foram analisados utilizando métodos estatísticos avançados. A campanha de campo e as experiencias de laboratório demostraram que os parâmetros significativos que afeitam a durabilidade são a porosidade, o radio medio do poro, a distribuição dos componentes da rocha e o seu uso inadequado. As principais alterações observadas relacionam-se com pequenas construções que atuam como reservatório de água. As análises dos componentes principais revelaram uma correlação negativa entre as PTA e a PMS. Devido à relação existente entre as PTA e o espaço poroso, estes parâmetros podem ser utilizados como indicadores da durabilidade. Um modelo para estimar a permeabilidade a partir da capilaridade com um coeficiente alto (R²=0.9822) é presentado pela primeira vez em rocas heterogéneas.

This paper compares different experimental methods for measuring water permeability in 17 different porous building rocks. Both commercial apparatus and specially made designed permeameters are used for characterising intrinsic permeability and hydraulic conductivity, k, of rocks in the range of 10−12 to 10−4 m/s (~ 10−19−10−11 m2 or ~ 10−4−104 mD). We use both falling head and constant head permeameter methods including the triaxial and modified triaxial tests and a classical constant head permeameter. Results showed that for very low and low permeability samples (k< 10−6 m/s), triaxial conditions were found the most accurate procedures and they provided similar or slightly lower permeability values than constant and falling head methods. The latter techniques were highly recommended for permeable and high permeable porous building materials. Water permeability values were also linked to effective porosity and interpreted in terms of interparticle and vugs porosity. Finally, some modifications in the apparatus and procedures were carried out in order to assess water permeability in soft materials, which involve the use of non-saturated samples., Se comparan diferentes métodos experimentales para la medida de la permeabilidad al agua en rocas porosas usadas como material de construcción. Se usaron diferentes permeabilímetros, (comerciales y desarrollados específicamente) empleando los métodos triaxial, triaxial modificado, carga constante y carga variable. Se caracterizó la permeabilidad intrínseca y conductividad hidráulica, k, con valores que var.an desde 10−12 a 10−4 m/s (~ 10−19−10−11 m2 or ~ 10−4−104 mD). Para muestras poco y muy poco permeables el ensayo con célula triaxial fue el mas reproducible. Los ensayos de carga constante son muy recomendables para rocas porosas de construcción permeables y muy permeables. Además, se definen los parámetros experimentales más apropiados para caracterizar la permeabilidad de rocas de construcción. La permeabilidad al agua se relaciona con la porosidad efectiva y se interpreta en términos de porosidad tipo interpartícula y vugs. Finalmente, se modificaron los equipos y procedimientos para poder estimar la permeabilidad en materiales blandos.

This study aims to understand the effect of salt and frost crystallisation on the petrophysical and durability properties of representative types of travertine and carbonate tufas. Results demonstrate that the studied travertines and tufas exhibit a very high durability against salt and ice crystallisation cycles, compared to carbonates rocks with similar porosity values. The variation of the loss of mass, effective porosity, capillary absorption coefficient, ultrasonic wave velocity and attenuation, and compressive strength was scarce during weathering tests. The evolution of petrophysical properties was slightly more intense after 30 cycles of salt crystallisation than 100 cycles of freeze–thaw. Petrophysical and durability properties of the travertines and carbonate tufas depend on porosity fraction and on the manner in which the vuggy porosity is connected. In the travertine facies, vuggy macropores show little connection and can be considered as separate-vug porosity. Their addition to interparticle porosity increases effective porosity and reduces their mechanical strength but does not significantly increase capillary transport and the effectiveness of salt and ice action over the stone. On the contrary, in the carbonate tufas, vugs act as touching-vug pores, as capillary imbibition coefficients reveal. However, scanning electron microscopy displays that they underwent microcracking processes related mainly to both thermal stresses and/or ice and salt pressures. These microcracks present little connection, and they do not enhance noticeably the water flow or decrease the mechanical properties. These results are finally discussed in terms of a nonlinear decay pattern, which with long periods of apparent stability might be followed by rapid and catastrophic decay., This study was financed by the Spanish Ministry of Education and Science (MEC) through the Research Project CGL2006-05027/BTE and Community of Madrid (S2023/MIT 2914). A pre-doctoral research fellowship was awarded to N. Cueto by the MEC.