Estudio de la fluencia de una calcarenita: la Piedra de San Julián (Alicante)

La fluencia de las rocas tiene gran importancia en la evaluación del comportamiento a largo plazo de elementos construidos con estos materiales. En este trabajo, se ha caracterizado física y mecánicamente una calcarenita porosa bien conocida localmente como Piedra de San Julián. Se han realizado ensayos de compresión uniaxial de 96 h. a carga constante. Se ha utilizado un modelo de fluencia bien conocido, el Código-modelo CEB-FIP 2010, usado para modelizar otro material pétreo (hormigón). Además, se ha propuesto un modelo reológico. El objetivo principal de este trabajo es investigar la posibilidad de aprovechar la gran experiencia acumulada en el estudio del hormigón, con el fin de obtener un enfoque para el comportamiento de la roca, para tiempos de prueba muy largos difíciles de implementar en laboratorio. Se propone una función de fluencia adaptada a la roca estudiada dependiente sólo de sus características elásticas y mecánicas.

Single-walled carbon nanotube buckypapers as electrocatalyst supports for methanol oxidation

This work studies the use of various single-walled carbon nanotube (SWCNT) buckypapers as catalyst supports for methanol electro-oxidation in acid media. Buckypapers were obtained by vacuum filtration from pristine and oxidized SWCNT suspensions in different liquid media. Pt–Ru catalysts supported on the buckypapers were prepared by multiple potentiostatic pulses using a diluted solution of Pt and Ru salts (2 mM H2PtCl6 + 2 mM RuCl3) in acid media. The resulting materials were characterized via SEM, TEM, EDX and ICP-OES analysis. Well dispersed rounded nanoparticles between 2 and 15 nm were successfully electrodeposited on the SWCNT buckypapers. The ruthenium content in the bimetallic deposits was between 32 and 48 at. %, while the specific surface areas of the catalysts were in the range of 72–113 m2 g−1. It was found that the solvent used to prepare the SWCNT buckypaper films has a strong influence on the catalyst dispersion, particle size and metal loading. Cyclic voltammetry and chronoamperometry experiments point out that the most active electrodes for methanol electro-oxidation were prepared with the buckypaper supports that were obtained from SWCNT dispersions in N-methyl-pyrrolidone.

Estudio de la influencia de la temperatura en las propiedades físicas y mecánicas de la calcarenita de San Julián

En este trabajo se muestran los resultados de una serie de ensayos de laboratorio realizados para estudiar el efecto de las altas temperaturas en las propiedades físicas y mecánicas de una calcarenita muy usada como material de construcción en edificios y monumentos históricos de la ciudad de Alicante. El objetivo es evaluar el daño térmico producido en el material al exponerlo a diferentes temperaturas y la influencia de los diferentes procesos de enfriamiento (al aire y por inmersión en agua), así como la viabilidad del diagnóstico del daño mediante métodos no destructivos (ultrasonidos). Se han utilizado probetas cilíndricas extraídas de bloques de roca sobre las que se han realizado ensayos de caracterización del material intacto obteniendo la porosidad, velocidades de propagación de las ondas P y S, módulos dinámicos y estáticos y resistencia a compresión uniaxial. El calentamiento se ha efectuado en horno eléctrico a temperaturas de entre 105 y 600ºC, en intervalos de 100ºC. Para cada temperatura (excepto 105 ºC) se han calentado diez probetas, enfriándolas posteriormente mediante dos procesos diferentes, obteniendo datos de un total de 55 probetas sometidas a diferentes condiciones de temperatura y método de enfriamiento. Finalmente, se han determinado de nuevo las propiedades de las probetas tras su calentamiento, comparando y correlacionando las diferentes variables. Las conclusiones principales destacan un acusado descenso de los valores de las propiedades medidas con la temperatura (excepto la porosidad que aumenta). Este descenso se acelera notablemente con enfriamiento por agua. Los ensayos no destructivos detectan el deterioro producido en el proceso de igual forma que los destructivos.

A new approach for semi-automatic rock mass joints recognition from 3D point clouds

Rock mass characterization requires a deep geometric understanding of the discontinuity sets affecting rock exposures. Recent advances in Light Detection and Ranging (LiDAR) instrumentation currently allow quick and accurate 3D data acquisition, yielding on the development of new methodologies for the automatic characterization of rock mass discontinuities. This paper presents a methodology for the identification and analysis of flat surfaces outcropping in a rocky slope using the 3D data obtained with LiDAR. This method identifies and defines the algebraic equations of the different planes of the rock slope surface by applying an analysis based on a neighbouring points coplanarity test, finding principal orientations by Kernel Density Estimation and identifying clusters by the Density-Based Scan Algorithm with Noise. Different sources of information —synthetic and 3D scanned data— were employed, performing a complete sensitivity analysis of the parameters in order to identify the optimal value of the variables of the proposed method. In addition, raw source files and obtained results are freely provided in order to allow to a more straightforward method comparison aiming to a more reproducible research.

Relationship between static and dynamic elastic modulus of calcarenite heated at different temperatures: the San Julián's stone

The San Julián’s stone is the main material used to build the most important historical buildings in Alicante city (Spain). This paper describes the analysis developed to obtain the relationship between the static and the dynamic modulus of this sedimentary rock heated at different temperatures. The rock specimens have been subjected to heating processes at different temperatures to produce different levels of weathering on 24 specimens. The static and dynamic modulus has been measured for every specimen by means of the ISRM standard and ultrasonic tests, respectively. Finally, two analytic formulas are proposed for the relationship between the static and the dynamic modulus for this stone. The results have been compared with some relationships proposed by different researchers for other types of rock. The expressions presented in this paper can be useful for the analysis, using non-destructive techniques, of the integrity level of historical constructions built with San Julián’s stone affected by fires.

Assessment of corrective measures for alleviating slope instabilities in carbonatic Flysch formations: Alicante (SE of Spain) case study

As is well known, in order to select remediation measures to correct or prevent slope instabilities, it is essential to identify and characterize the instability mechanisms. This task is especially complex for heterogeneous rock masses such as Flysch formations. This paper addresses the assessment of corrective measures used in carbonate Flysch formations by classifying and grouping field data reported in an available database in order to associate this data with various instability mechanisms and stratigraphic column types as well as with the corrective measures taken to stabilise them. For this purpose, 194 slopes have been geomechanically characterized, mainly by considering the observed instability mechanisms. The corrective measures that were applied have been evaluated for their suitability and performance, and, if applicable, the causes of their malfunction have been also studied. As a result, some guidelines based on the observed behaviour and the suitability of the correction measure as a function of instability type are proposed for similar slopes.

Characterization of the instability mechanisms affecting slopes on carbonatic Flysch: Alicante (SE Spain), case study

The studied Flysch sequence of Alicante occupies a widely populated area crossed by main communication routes. The slopes existing on this area usually suffer slope instabilities that cause substantial damage and a very high maintenance cost. In order to assess the type of instability mechanisms affecting these heterogeneous carbonatic slopes, in this paper a wide inventory of 194 Flysch rock slopes has been performed, reporting the existing lithologies, their competence and their relative arrangement and the geometrical relationship between bedding and the slope and the associated instability mechanism. All these data have been jointly used for performing an instability mechanisms characterization. For systematically characterizing the wide type of complex rock exposures existing in the study area, they are divided into basic units referred as lithological pattern columns to which the different observed instability mechanisms are associated. Inventoried instability mechanisms are diverse and sometimes are combined with each other. Rockfalls are a very common instability mechanism associated to the differential weathering and sapping of the marly lithologies which are present in a wide number of geometrical combinations. The other instability mechanisms closely depend on the combination of the geometrical and lithological parameters. Therefore, this work provides a new basic tool which can be easily used during preliminary project stages for knowing the instability mechanisms which can affect rock slopes excavated on carbonatic Flysch heterogeneous geological formations.

Temperature influence on the physical and mechanical properties of a porous rock: San Julian's calcarenite

This work discusses the results from tests which were performed in order to study the effect of high temperatures in the physical and mechanical properties of a calcarenite (San Julian's stone). Samples, previously heated at different temperatures (from 105 °C to 600 °C), were tested. Non-destructive tests (porosity and ultrasonic wave propagation) and destructive tests (uniaxial compressive strength and slake durability test) were performed over available samples. Furthermore, the tests were carried out under different conditions (i.e. air-cooled and water-cooled) in order to study the effect of the fire off method. The results show that uniaxial compressive strength and elastic parameters (i.e. elastic modulus and Poisson's ratio), decrease as the temperature increases for the tested range of temperatures. A reduction of the uniaxial compressive strength up to 35% and 50% is observed in air-cooled and water-cooled samples respectively when the samples are heated to 600 °C. Regarding the Young's modulus, a fall over 75% and 78% in air-cooled and water-cooled samples respectively is observed. Poisson's ratio also declines up to 44% and 68% with the temperature in air-cooled and water-cooled samples respectively. Slake durability index also exhibits a reduction with temperature. Other physical properties, closely related with the mechanical properties of the stone, are porosity, attenuation and propagation velocity of ultrasonic waves in the material. All exhibit considerable changes with temperature.

Steam reforming of ethanol over bimetallic RhPt/La2O3: Long-term stability under favorable reaction conditions

Recently, the steam reforming of biofuels has been presented as a potential hydrogen source for fuel cells. Because this scenario represents an interesting opportunity for Colombia (South America), which produces large amounts of bioethanol, the steam reforming of ethanol was studied over a bimetallic RhPt/La2O3 catalyst under bulk mass transfer conditions. The effect of temperature and the initial concentrations of ethanol and water were evaluated at space velocities above 55,000 h−1 to determine the conditions that maximize the H2/CO ratio and reduce CH4 production while maintaining 100% conversion of ethanol. These requirements were accomplished when 21 mol% H2O and 3 mol% C2H5OH (steam/ethanol molar ratio = 7) were reacted at 600 °C. The catalyst stability was assessed under these reaction conditions during 120 h on stream, obtaining ethanol conversions above 99% during the entire test. The effect of both H2 and air flows as catalyst regeneration treatments were evaluated after 44 and 67 h on stream, respectively. The results showed that H2 treatment accelerated catalyst deactivation, and air regeneration increased both the catalyst stability and the H2 selectivity while decreasing CH4 generation. Fresh and spent catalyst samples were characterized by TEM/EDX, XPS, TPR, and TGA. Although the Rh and Pt in the fresh catalyst were completely reduced, the spent samples showed a partial oxidation of Rh and small amounts of carbonaceous residue. A possible Rh–Pt–Rh2O3 structure was proposed as the active site on the catalyst, which was regenerated by air treatment.

Measuring the effective focal length and shape factor of a thick lens using a microscope

The optical power of a thick spherical lens and its Coddington shape factor are essential magnitudes that characterize its image quality. Here, we propose an experimental procedure and apparatus that allow accurate determination of those magnitudes for any spherical lens from geometrical measurements. The performance of the technique and the used instruments are simple since it only requires a microscope and an optical mouse. The propose overcomes the drawbacks of other devices that need of the refractive index or may damage the lens surfaces, like spherometers, and provides similar results to those from commercial lensmeters.

An approach for characterising the weathering behaviour of Flysch slopes applied to the carbonatic Flysch of Alicante (Spain)

Various studies indicate that most of the slope instabilities affecting Flysch heterogeneous rock masses are related to differential weathering of the lithologies that make up the slope. Therefore, the weathering characteristics of the intact rock are of great importance for the study of these types of slopes and their associated instability processes. The main aim of this study is to characterise the weathering properties of the different lithologies outcropping in the carbonatic Flysch of Alicante (Spain), in order to understand the effects of environmental weathering on them, following slope excavation. To this end, 151 strata samples obtained from 11 different slopes, 5–40 years old, were studied. The lithologies were identified and their mechanical characteristics obtained using field and laboratory tests. Additionally, the slaking properties of intact rocks were determined, and a classification system proposed based on the first and fifth slake cycles (Id1 and Id5 respectively) and an Index of Weathering (IW5), defined in the study. Information obtained from the laboratory and the field was used to characterise the weathering behaviour of the rocks. Furthermore, the slaking properties determined from laboratory tests were related to the in-situ weathering properties of rocks (i.e., the weathering profile, patterns and length, and weathering rate). The proposed relationship between laboratory test results, field data, and in-situ observations provides a useful tool for predicting the response of slopes to weathering after excavation during the preliminary stages of design.

Characterization of rock slopes through slope mass rating using 3D point clouds

Rock mass classification systems are widely used tools for assessing the stability of rock slopes. Their calculation requires the prior quantification of several parameters during conventional fieldwork campaigns, such as the orientation of the discontinuity sets, the main properties of the existing discontinuities and the geo-mechanical characterization of the intact rock mass, which can be time-consuming and an often risky task. Conversely, the use of relatively new remote sensing data for modelling the rock mass surface by means of 3D point clouds is changing the current investigation strategies in different rock slope engineering applications. In this paper, the main practical issues affecting the application of Slope Mass Rating (SMR) for the characterization of rock slopes from 3D point clouds are reviewed, using three case studies from an end-user point of view. To this end, the SMR adjustment factors, which were calculated from different sources of information and processes, using the different softwares, are compared with those calculated using conventional fieldwork data. In the presented analysis, special attention is paid to the differences between the SMR indexes derived from the 3D point cloud and conventional field work approaches, the main factors that determine the quality of the data and some recognized practical issues. Finally, the reliability of Slope Mass Rating for the characterization of rocky slopes is highlighted.

Educación para la salud en la escuela primaria: opinión del profesorado de la ciudad de Alicante

Objetivo: Explorar la opinión del profesorado de educación primaria de la ciudad de Alicante sobre las actividades de salud realizadas en la escuela. Método: Estudio exploratorio mediante análisis de contenido cualitativo. Se formaron tres grupos de discusión (8-9 participantes) con profesorado de educación primaria (14 mujeres y 11 hombres) procedentes de 14 escuelas públicas y 7 concertadas de la ciudad de Alicante. La información se obtuvo preguntando a los/las participantes sobre las actividades de salud realizadas en el aula o en el centro escolar. Resultados: El profesorado diferenció las actividades que forman parte de las programaciones escolares de educación para la salud de las que proceden de programas de otras instituciones públicas o privadas. Consideró que los programas externos son impuestos, no tienen continuidad y responden a modas pasajeras. Aunque mostró una actitud más favorable y comprometida con las actividades y programaciones escolares, identificó la educación para la salud como una tarea secundaria. En su opinión, incrementar su formación en salud, implicar a los padres y las madres, profesionales sanitarios y la administración educativa fomentaría la educación para la salud en la escuela. Conclusiones: El profesorado muestra una opinión más favorable y un mayor compromiso hacia las actividades de salud que complementan y facilitan su tarea educativa. Su programación docente y opinión deben tenerse en cuenta para maximizar la eficiencia de las actividades de promoción y educación para la salud promovidas por instituciones, compañías y fundaciones externas a la escuela.

A simple method to predict elastic settlements in foundations resting on two soils of differing deformability

This paper shows the analysis results obtained from more than 200 finite element method (FEM) models used to calculate the settlement of a foundation resting on two soils of differing deformability. The analysis considers such different parameters as the foundation geometry, the percentage of each soil in contact with the foundation base and the ratio of the soils’ elastic moduli. From the described analysis, it is concluded that the maximum settlement of the foundation, calculated by assuming that the foundation is completely resting on the most deformable soil, can be correlated with the settlement calculated by FEM models through a correction coefficient named “settlement reduction factor” (α). As a consequence, a novel expression is proposed for calculating the real settlement of a foundation resting on two soils of different deformability with maximum errors lower than 1.57%, as demonstrated by the statistical analysis carried out. A guide for the application of the proposed simple method is also explained in the paper. Finally, the proposed methodology has been validated using settlement data from an instrumented foundation, indicating that this is a simple, reliable and quick method which allows the computation of the maximum elastic settlement of a raft foundation, evaluates its suitability and optimises its selection process.