Consideraciones sobre la datación de morteros de cal mediante 14C

A pesar de que pueden existir dudas por parte de algunos investigadores sobre la inclusión de las técnicas de datación dentro de la caracterización de los morteros históricos, aportar su antigüedad de fabricación o elaboración permite la adscripción cronológica del elemento constructivo del que forma parte (muros, fábricas, revestimientos, etc.), información importante para complementar las hipótesis históricas o arqueológicas, por lo que parece lógica su integración dentro de la herramientas arqueométricas de caracterización de estos materiales de construcción. Dentro de las técnicas instrumentales disponibles actualmente que datan mediante 14C, se expondrá la espectrometría de masas con acelerador de partículas AMS (Accelerator Mass Spectrometry), que se vale de la determinación del cociente isotópico 14C/12C para el cálculo de la edad. Es el método más moderno y que consigue medidas de mayor calidad, empleando a su vez menos cantidad de muestra (decenas de miligramos). Con esta metodología es posible fechar muestras de hasta 50.000 años de antigüedad, siendo un sistema de datación totalmente afianzado en la comunidad científica. Se indicarán los componentes del mortero de cal conteniendo 14C que son susceptibles de datar, las precauciones durante la toma de muestras y los errores intrínsecos y extrínsecos que se deben considerar en el análisis de los resultados

Brick durability and conservation treatment (Santa María de Jesús chapel portal, Seville, Spain)

Se ha estudiado la alteración diferencial de los 2 tipos de ladrillo de la iglesia de Santa María de Jesús (Sevilla) y 2 tratamientos para su restauración. Se han caracterizado por DRX y SEM, así como sus propiedades físicas, hídricas y mecánicas. Probetas preparadas de ladrillos de la iglesia se han sometido a ensayo de cristalización de sales para determinar las causas y los mecanismos de alteración. El ladrillo rojo es el que presenta menor temperatura de cocción, menor porosidad y mayor proporción de microporos. Las propiedades físicas y mecánicas de ambos ladrillos no varían significativamente con los tratamientos, sólo las propiedades hídricas cambian con el hidrófugo. En el ensayo de alteración mejora mucho el comportamiento del ladrillo amarillo, mientras que en el rojo no varía la morfología de alteración (características de materiales con microporos) ni la durabilidadDurability differences of 2 types of brick from Santa María de Jesús Chapel (Sevilla) and 2 treatments for its restoration have been studied. They have been characterizad using XRD and SEM, as well as their physical, hydric and mechanical properties. Samples prepared with bricks from the chapel have been submitted to salt crystallization test, to identify decay causes and mechanisms. The red brick present the lowest firing temperature, lower porosity and a great proportion of micropores. Physical and mechanical properties don’t change significantly with the treatments, only hygric properties vary with the water repellent. The accelerated aging test revealed significant improvement in the behaviour of yellow brick, but no change in the decay mechanism of red brick (Typical of microporous materials) or its durability is observe

Methodology for characterising microlayers in historical plasterwork

The study of (micro)layer structure in walls is a fundamental tool for expanding our knowledge of historical buildings and developing suitable proposals for intervention and restoration. In materials such as plasterwork, the (micro)layer sequence can be confusing, resulting in the need for a more detailed analysis in order to accurately determine the materials and interventions carried out on a given decorative element in the past. This work presents a methodological proposal based on optical microscopy, XRD, micro-XRD, SEM-EDAX, FTIR, and 14C dating to accurately identify the structure and composition of the different types of microlayers comprising the plasterwork. The resulting data are of great use in decision-making for restoration and can be compared with historiographic information in order to confirm hypotheses or clarify gaps in chronological adscription

Influencia de asfaltenos y resinas en la viscosidad de petróleos bituminosos utilizables como pinturas asfálticas de imprimación

Los crudos extrapesados procedentes del área Machete (Venezuela) son materiales de consistencia blanda o fluida, por lo que se salen del campo en el que normalmente se aplica el ensayo de penetración a productos asfálticos según el mé- todo ASTM D-5 (1), cuyo límite máximo es 30 mm, y pueden ser utilizados como pinturas asfálticas de imprimación. Al igual que otros productos asfálticos, estos petróleos son químicamente una mezcla de numerosos hidrocarburos nafténicos, parafínicos, aromáticos y compuestos heterocíclicos que contienen azufre, nitrógeno, oxígeno, etc. Están compuestos por una fase pesada y otra de aceites malténicos que, además de los hidrocarburos naturales empleados como aditivos, actúa a modo de fluidificante volátil. La primera fase se describe como una mezcla de asfalten~ o susta,ncias complejas de alto peso molecular, insoluble en hidrocarburos parañnicos y soluble en compuestos aromáticos como el benceno; la segunda es descrita como una mezcla de resinas y otros hidrocarburos. Estas dos fases constituyen un sistema coloidal. En este trabajo se presentan los resultados experimentales del efecto de la proporción de asfaltenos y resinas en la viscosidad de tales crudos, con vista a su aplicación como materiales imprimadores. Los experimentos se realizaron en un reactor batch marca Parr en una atmósfera de nitrógeno yempleando n-heptano como disolvente. Una vez precipitados los asfaltenos a partir de las muestras utilizadas y, seguidamente, de la fracción de maltenos obtenida, se separaron las resinas. Al comparar los resultados obtenidos, se encontró que los asfaltenos eran responsables de las características estructurales y de consistencia del vehículo, mientras las resinas le proporcionan propiedades aglutinantes y los aceites malténicos actúan como disolventesThe bituminous crude from the Machete/ Venezuela/ area/ which has such a fluid consistency thatitfalls outside the normalscope of the A5TM o-s (1) penetration tes~ exceeding the 3D-mm ceiling specified in that standar~ and can be used as an asphaltprimer: Like other asphaltproducts/ these materials are -chemically speaking- a mix ofnumerous naphtheni~ paraffinic and aromatic hydrocarbons and heterocyc/ic compounds containing sulphur, nitrogen/ oxygen and so on. They have a dense and a malthene Ol'l phase which/ along with the natural hydrocarbons additives usedin these products/ acts as a volatile fluidizer: The former is described as a mix of asphaltenes: comple~ high mo/ecular weight substances that are insolub/e in paraffinichydrocarbons andsoluble in aromatic compounds such as benzene. The malthene oilphase/ in turn/ consists in a mix of resins and hydrocarbons and together the two constitute a colloida/system. The experiments discussedin thepresentpaper were conducted to determine the effect of the proportion of asphaltenes and resin oils on the viscosity ofsuch bituminous crude emulsions/ with a view to their use as primers. These experiments were run in a Parr batch reactor in a nitrogen atmosphere using n-heptane as a solvent. The resins were separated after the asphaltenes precipitated from the samples and subsequently from the malthene fraction obtained. The results showed that the asphaltenes account for the structural characteristics and consistency ofthe medium and the resin oils for its cohesive properties/ the malthene oils act as solvent

Plasterwork in the Ambassadors Hall (Salon de Embajadores) of the Real Alcazar of Seville (Spain): Graphic reconstruction of polychrome work by layer characterization

This work examines a polychrome plasterwork in one of the most important scalloped arches in the Ambassadors Hall (Salón de Embajadores), which is the most outstanding room in the Mudéjar Palace of the Real Alcázar of Seville (Spain). Characterization by stratigraphy, XFR, XRD, and FTIR studies has supplied data on changes in the composition and colors in this building element. The research is complemented with historical information on the most significant interventions in this hall. Graphic analysis and the modeling of decorative geometric elements in 3D with BIM software were used to simulate its evolution from its original state. The results characterize the base plasterwork and the polychromies constituted by 1–3 microlayers with a thickness between 5 and 300 lm, formed of blue (19.88% Cu-azurite), vermilion (19.00% Pb-massicot and 5.34% Hg-cinnabar), and golden layers (68.93% Au). The colors were obtained through the use of mineral pigments such as azurite, cinnabar-litharge, and gold-leaf, respectively. The rich colors visible in this hall now have varied over time

An argument for using alizarine yellow R and indigo carmine to determine in situ the degree of alkalinity in reinforced concrete

The commonest way of determining the passivation of steel in reinforced concrete is to spray a pH indicator onto the surface of a reinforced concrete specimen. To do so, the traditional indicator used has been phenolphthalein in ethanol, which shifts from colourless to purple in the pH range of 8.5–10.0. If the concrete encasing the rebar turns purple, it indicates it is passivated; that is, it has a film of iron oxide impermeable to oxygen that protects it from oxidation. However, the reduction in the pH of the concrete due to carbonation (between 11.4 and 8.5) indicates, despite the reddish-purple colour, the disappearance of the passive layer of the steel. Consequently, we propose a novel in situ technique for determining with a high degree of reliability, the passive state (pH over 11.7) and the active state (pH under 11.4) using two reactants: alizarine yellow R and indigo carmine

Considerations on the physical and mechanical properties of lime-stabilized rammed earth walls and their evaluation by ultrasonic pulse velocity testing

This study examines the influence of moulding moisture content on the compressive strength, dry density and porosity of a rammed earth wall, using ultrasound as a complementary technique. Non-parametric and multivariate statistical techniques were applied to analyse the behaviour of variables with a sufficiently large population. The statistical analysis demonstrated that excessive or insufficient moulding moisture content directly determines the physical-mechanical properties of such walls. Ultrasound was confirmed as a valid technique for assessing the quality of a wall, since its response, albeit with certain limitations, was consistent with physical-mechanical properties