Mechanical Properties and Durability of CNT Cement Composites

In the present paper, changes in mechanical properties of Portland cement-based mortars due to the addition of carbon nanotubes (CNT) and corrosion of embedded steel rebars in CNT cement pastes are reported. Bending strength, compression strength, porosity and density of mortars were determined and related to the CNT dosages. CNT cement paste specimens were exposed to carbonation and chloride attacks, and results on steel corrosion rate tests were related to CNT dosages. The increase in CNT content implies no significant variations of mechanical properties but higher steel corrosion intensities were observed.

Conformational changes of dissolved humic and fulvic superstructures with progressive iron complexation

Conformational changes of a humic acid (HA) and a fulvic acid (FA) induced by iron complexation were followed by high-performance size exclusion chromatography (HPSEC) with both UV–vis and refractive index (RI) detectors. Molecular size distribution was reduced for HA and increased for FA with progressive iron complexation. Since interactions of Fe with humic components are electrostatic, it is likely that the triple-charged Fe ions formed stronger complexes with the more acidic hydrophilic and hydrated FA than with the less acidic and more hydrophobic HA. The large content of ionized carboxyl groups in FA, thus favored the formation of intra- or intermolecular bridges between the negatively charged fulvic acid molecules, and led to more compact and larger size network than for HA. Conversely, iron complexation with HA disrupted the humic conformational arrangements stabilized by only weak hydrophobic bonds into smaller-size aggregates of greater conformational stability due to formation of strong metal complexes. These results confirmed that humic molecules in solution were organized in supramolecular associations of relatively small molecules loosely bound together by dispersive interactions and hydrogen bonds, and they specifically responded to chemical changes brought about by metal additions. The present study revealed the molecular changes occurring in superstructures of natural organic matter when in metal complexes and contributed to understand and predict the environmental behavior in waters and soil of metal complexes with natural organic matter.

¿Qué está pasando en el proceso de enseñanza-aprendizaje de Ciencias Básicas en nuestro sistema educativo?

Se ha creado una red multidisciplinar que agrupa profesorado de distintas etapas educativas con el objetivo de analizar debilidades en la enseñanza de asignaturas de Ciencias básicas y experimentales (en todas las etapas formativas) y proponer actuaciones de innovación docente que subsanen esas debilidades. El trabajo realizado hasta ahora se ha centrado en tres objetivos específicos: 1) Identificar debilidades y fortalezas en la docencia de Matemáticas, Químicas, Física, Biología y Geología. Para ello, se han analizado tanto las prácticas docentes más habituales como las innovaciones más recientes (TICs, programa EntusiasMAT, etc.); 2) Diseñar estrategias de comunicación y trabajo colaborativo que mejoren el flujo de comunicación e información entre docentes de Ciencias de distintas etapas educativas; 3) Proponer protocolos, estrategias y buenas prácticas para la mejora de la docencia en Ciencias en todas las etapas educativas (por ejemplo, se plantea el diseño e implementación de talleres para que los más pequeños aprendan cuestiones relativas a ciencias naturales mediante el juego). Entre las conclusiones obtenidas destacan: 1) se sigue empleando de forma mayoritaria la clase teórica magistral aún a pesar de las interesantes propuestas de innovación docente existentes; 2) el aprendizaje es más eficiente cuando se basa en experiencias prácticas.

Compositional signatures of the Cenozoic sedimentary succesions of the Malaguide Complex (Betic Cordillera, Spain)

The studied Cenozoic sedimentary successions consist of deposits from continental/shallow-water to deep-marine environments of the Malaguide Complex (Betic Cordillera) outcropping in the Sierra Espuña area (SE Spain). The aim of this study is to characterize the composition, source area(s) provenance and weathering processes of these sedimentary successions from the pre-orogenic (Paleocene-Early Oligocene) to the syn-orogenic (Late Oligocene-Early Miocene) stage using petrological and geochemical methodologies. The studied sandstones are mainly quartzolithic with abundant metamorphic and sedimentary lithic fragments. In particular, the composition of samples from the pre-orogenic cycle is mainly carbonate with important siliciclastic components that occur within the medium to fine grained arenites. The composition of samples from the syn-orogenic cycle is characterized by a sharp change from carbonate to siliciclastic terms. Thus, the composition of the overall sandstone samples is very heterogeneous and suggests a source area mainly characterized by the Malaguide basement and lower units of the Internal Betic Zone, that partially compose the Mesomediterranean Microplate. The geochemical proxies suggest a provenance mainly from felsic source area with a minor supply from mafic rocks in some samples of the syn-orogenic stage. Furthermore, palaeoweathering indices indicate low to moderate weathering conditions for the sources. The Cenozoic sedimentary successions of the Malaguide Complex played an important role in the geodynamic evolution of the Betic Cordillera that represents the key tectonic element of the western domains of the Mesomediterranean Microplate.