David Benavente

The combined influence of mineralogical, hygric and thermal properties on the durability of porous building stones

It is a common practice to test building stones against an isolated decay factor when assessing the durability of building stones. Accordingly, the interpretation of results is often driven by the considerations of a limited number of properties thought as relevant to the action of that specific decay factor. In this way, the role of the synergies of decay processes and agents is often neglected. Contrarily, when different decay factors are included in the same experiment and the stone properties are examined conjunctly, the difficulties of isolating the effects of a specific decay factor or of isolating the contribution of “relevant” stone properties become apparent. The aim of this paper is to assess the combined contribution of mineralogical, hygric and thermal properties to the durability of different stones after exposure to laboratory-simulated cyclic decay combining wetness and temperature variations. For this purpose, 10 stone types were selected to emphasize the impact of the mineralogical heterogeneity on stone decay, in particular the coexistence of calcareous and siliceous grains and the occurrence of clays. The results emphasize the importance of considering the relations between decay factors and highlight how stone properties must be considered as a whole in order to assess and understand the durability of building stones.

Quantification of salt weathering in porous stones using an experimental continuous partial immersion method

Abstract In this study, an experimental salt weathering simulation and porous stone durability classification are proposed. There are many laboratory tests that quantify durability against salt crystallisation weathering action. These are usually based on the total immersion of samples into a saline solution, which is not representative of the salt weathering mechanism. An experimental test based on partial immersion is suggested. This is a comparable study of weight loss and degradation of visual appearance due to salt crystallisation using, on the one hand, a standard durability test (UNE), and, on the other, the proposed durability test. The weight loss and visual appearance in our test is comparable to the degradation of building stone. The differences between weight loss data in both tests depend on the petrophysical properties: porous media and degree of coherence. From this testing, a new durability classification as a function of dry weight loss in the partial immersion test is proposed. Four divisions of different types of materials can be made in this classification, which quantifies salt weathering action mainly in environments and mild climatic conditions.

Predicting the Capillary Imbibition of Porous Rocks from Microstructure

The kinetics of capillary imbibition into porous rocks is studied experimentally and theoretically. The Washburn law is modified by introducing various corrections relating to the microstructure of the rocks, such as tortuosity, pore shape (obtained experimentally), and applying the effective medium approximation (EMA) in order to calculate the effective radius that defines the hydraulic conductance and the topology of the capillary imbibition. The application of the EMA shows that capillary imbibition is mainly produced in 1-D, and the pore structure is constituted by different pore throats in series, linked by chamber pores. The capillary process has been discussed as a function of their petrography and pore structure. Our study of the Washburn equation and the addition of correction factors for the pore structure allows a very accurate prediction of the weight rate.

Paleolithic Art in Peril: Policy and Science Collide at Altamira Cave

Despite evidence of damaging human impacts, cave paintings may again be threatened if visitors are allowed access. In the last decade, considerable attention has been paid to the deterioration of the caves that house the worlds most prominent Paleolithic rock art. This is exemplified by the caves of Lascaux (Dordogne, France) (1) and Altamira (Cantabria, Spain), both declared World Heritage Sites. The Altamira Cave has been closed to visitors since 2002. Since 2010, reopening the Altamira Cave has been under consideration. We argue that research indicates the need to preserve the cave by keeping it closed in the near future.

Comparison of the static and dynamic elastic modulus in carbonate rocks

Young’s modulus is one of the most important mechanical parameters in building materials used to assess both the appropriateness of a material as well as its mechanical stability. The paper reports a study to predict the elastic modulus for ten carbonate rocks using the ultrasonic technique. The rocks varied from homogeneous limestones to rocks with abundant stylolite, veins and fissures and were subjected to both salt crystallization and thermal weathering tests in order to modify the number and features of their discontinuities. The dynamic and static elastic moduli were measured in both weathered and unweathered samples. The results confirmed the poor relationship between the static and dynamic moduli for the studied rocks. A new equation is proposed which uses both dynamic elastic modulus and spatial attenuation of compressive waves to provide an accurate prediction of static Young’s modulus. As spatial attenuation is highly sensitive to the presence of rock defects, the correlation is very useful for rocks with fractures, voids and/or which have suffered weathering.RésuméLe module d’Young est l’un des plus importants paramètres mécaniques des matériaux de construction. Il est utilisé pour évaluer à la fois l’adéquation d’un matériau et sa stabilité mécanique. L’article présente une étude visant à prévoir le module d’élasticité de dix roches carbonatées à partir de la technique des ultrasons. Les roches testées allaient des calcaires homogènes aux calcaires avec de nombreux stylolites, veinules et fissures. Elles furent soumises à des tests de cristallisation de sels et d’altération thermique afin de modifier le nombre et les caractéristiques de leurs défauts. Les modules statiques et dynamiques furent mesurés à la fois pour les échantillons sains et pour les échantillons altérés. Les résultats ont confirmé les relations faibles entre module statique et module dynamique pour les roches étudiées. Une nouvelle équation est proposée qui, à partir du module d’élasticité dynamique et de l’atténuation spatiale des ondes de compression, fournit une prévision du module d’Young statique. Du fait que l’atténuation spatiale des ondes de compression est hautement sensible à la présence de défauts dans les roches, la corrélation établie est très utile pour les roches contenant des fissures et des vides ou qui ont été soumises à de l’altération.

Soluble salt minerals from pigeon droppings as potential contributors to the decay of stone based Cultural Heritage

This paper describes the salt content and pH evolution in solutions produced by the water-soluble extraction of accumulated pigeon droppings. Results demonstrate that these accumulations contain 4 % of soluble salts. Therefore, they are a plausible source of salts commonly found on buildings. These salts comprise halite, sylvite, potassium calcium sulphate, aphthitalite, apatite group minerals, weddellite and gypsum. The interaction of solutions formed from pigeon droppings with porous limestone was also studied. A noticeable deterioration in limestone due to acid attack was observed, including surface etching of rock-forming minerals.

Salt influence on evaporation from porous building rocks

The evaporation process of saline solutions within porous building rocks has been studied. Twelve different porous rocks saturated in pure water and a NaCl solution, were dried in a moisture balance. The influence of pore structure, environmental relative humidity and saline solution on the evaporation process has been studied from the experimental results. In order to explain the influence of these parameters simultaneously on the evaporation process, a detailed study of the thermodynamic equations is realised. This study explains the evaporation process in 0.01–100 μm pore size interval, predicting that saline solutions remain a long time within porous media, and therefore, intensify weathering processes.

Subterranean atmospheres may act as daily methane sinks

In recent years, methane (CH4) has received increasing scientific attention because it is the most abundant non-CO2 atmospheric greenhouse gas (GHG) and controls numerous chemical reactions in the troposphere and stratosphere. However, there is much that is unknown about CH4 sources and sinks and their evolution over time. Here we show that near-surface cavities in the uppermost vadose zone are now actively removing atmospheric CH4. Through seasonal geochemical tracing of air in the atmosphere, soil and underground at diverse geographic and climatic locations in Spain, our results show that complete consumption of CH4 is favoured in the subsurface atmosphere under near vapour-saturation conditions and without significant intervention of methanotrophic bacteria. Overall, our results indicate that subterranean atmospheres may be acting as sinks for atmospheric CH4 on a daily scale. However, this terrestrial sink has not yet been considered in CH4 budget balances.

Peroxodisulfate as a chemical initiator for methacrylate-ester monolithic columns for capillary electrochromatography.

Organic monolithic stationary phases for CEC were synthesized in situ in fused‐silica capillaries. Polymerization mixtures were composed of butyl methacrylate, ethylene dimethacrylate, and [2‐(methacryloyloxy)ethyl]trimethyl ammonium chloride in the presence of a porogenic solvent, using ammonium peroxodisulfate as chemical initiator, and N,N,N′,N′‐tetramethylethylenediamine to activate the reaction. The influence of the amount of initiator, temperature, and composition of porogenic solvent on the physical and chromatographic properties of monolithic stationary phases has been investigated. A minimum plate height of 14.5 μm was obtained at 18 wt% of 1,4‐butanediol in the polymerization mixture. The produced monolithic stationary phases exhibited a good repeatability and batch‐to‐batch and mixture‐to‐mixture reproducibility, with RSD values below 5.6% in the electrochromatographic parameters studied. A comparison with columns prepared by thermal initiation with α,α′‐azobisisobutyronitrile (AIBN) was also performed. The most efficient column initiated with peroxodisulfate showed better efficiencies and selectivities than that prepared with AIBN at the same composition mixture.

A GIS-based methodology to quantitatively define an Adjacent Protected Area in a shallow karst cavity: the case of Altamira cave.

Different types of land use are usually present in the areas adjacent to many shallow karst cavities. Over time, the increasing amount of potentially harmful matter and energy, of mainly anthropic origin or influence, that reaches the interior of a shallow karst cavity can modify the hypogeal ecosystem and increase the risk of damage to the Palaeolithic rock art often preserved within the cavity. This study proposes a new Protected Area status based on the geological processes that control these matter and energy fluxes into the Altamira cave karst system. Analysis of the geological characteristics of the shallow karst system shows that direct and lateral infiltration, internal water circulation, ventilation, gas exchange and transmission of vibrations are the processes that control these matter and energy fluxes into the cave. This study applies a comprehensive methodological approach based on Geographic Information Systems (GIS) to establish the area of influence of each transfer process. The stratigraphic and structural characteristics of the interior of the cave were determined using 3D Laser Scanning topography combined with classical field work, data gathering, cartography and a porosity-permeability analysis of host rock samples. As a result, it was possible to determine the hydrogeological behavior of the cave. In addition, by mapping and modeling the surface parameters it was possible to identify the main features restricting hydrological behavior and hence direct and lateral infiltration into the cave. These surface parameters included the shape of the drainage network and a geomorphological and structural characterization via digital terrain models. Geological and geomorphological maps and models integrated into the GIS environment defined the areas involved in gas exchange and ventilation processes. Likewise, areas that could potentially transmit vibrations directly into the cave were identified. This study shows that it is possible to define a Protected Area by quantifying the area of influence related to each transfer process. The combined maximum area of influence of all the processes will result in the new Protected Area. This area will thus encompass all the processes that account for most of the matter and energy carried into the cave and will fulfill the criteria used to define the Protected Area. This methodology is based on the spatial quantification of processes and entities of geological origin and can therefore be applied to any shallow karst system that requires protection.