Exfoliation microcracks in building granite. Implications for anisotropy

Granite is found in many world heritage monuments and cities. It continues to be one of the most widely used stones in today's construction, given its abundance, uniformity and durability. Quarrymen traditionally cut this rock along its orthogonal slip planes, where splitting is easier. Ranked by ease of splitting, these planes are rift, grain and hardway. Granite is traditionally quarried along the rift plane where coplanar exfoliation microcracks coalesce developing a flat surface. This splitting surface minimizes the cost and effort of subsequent hewing. Rift plane was predominantly used on the fair face of ashlars in heritage buildings worldwide. Determining the petrographic and petrophysical behaviour of these three orthogonal splitting planes in granite is instrumental to understanding decay in ashlars and sculptures. The decay of building granite is different in each splitting plane. Alpedrete granite was the stone selected for this study based on the orientation and distribution of exfoliation microcracks and the characterisation of their implications for the anisotropy of petrophysical properties such as ultrasonic wave propagation, capillarity, air permeability, micro-roughness and surface hardness. Inter- and intracrystalline microcrack length and spacing were also measured and quantified. The findings show that the splitting planes in Alpedrete granite are determined by the orientation of exfoliation microcracks, which as a rule are generally straight and intracrystalline and determine the anisotropy of the petrophysical properties analysed. Splitting planes are the orientation that should be applied when performing laboratory tests for the petrographic and petrophysical properties of building granite.This study was funded by the Regional Government of Madrid, Spain, in the framework of the GEOMATERIALS-2CM [S2013/MIT-2914] programme.Peer reviewe

Thermal stress-induced microcracking in building granite

Microcracking induced by wide fluctuations in temperature affects granite quality and durability, making the stone more vulnerable to decay. Determining the extent of that effect is not always straightforward, however, given the excellent durability of these materials. Four types of construction granite quarried in the region of Madrid, Spain, and frequently used in both the built heritage and in de novo construction (Alpedrete, Cadalso de los Vidrios, Colmenar Viejo and Zarzalejo) were exposed to 42 thermal cycles (105–20 °C; UNE-EN, 14066, 2003). Petrographic and petrophysical properties were analysed using both destructive and non-destructive techniques. Microcracking generated in the granite stones by 42 thermal cycles had barely any impact on their petrophysical properties, which are the parameters normally assessed to establish material quality and durability. Their petrographic properties, which are not generally assessed in this type of studies, were affected, however. This study contends that petrographic analysis is needed to objectively quantify the actual quality and durability of the most highly resistant materials when petrophysical studies are inconclusive. Petrographic and fluorescence microscopy, along with fractography, are among the most prominent techniques for petrographic exploration. Thanks to the deployment of these techniques, mineral microcracking could be monitored throughout the present tests conducted. The microscopic findings revealed substantial micro-textural and microstructural change in and around the granite minerals, which play a prominent role in decay. The findings showed that pre-existing microcracks coalesced and generated further microcracking as decay progressed. Microcracking was most intense in Zarzalejo granite due to its textural characteristics determined by its high feldspar content. Microscopic observation revealed that the microstructure of feldspar minerals, with their crystallographic anisotropies and secondary mineral phases, favoured microcrack development. Zarzalejo granite exhibited lower quality and durability than Colmenar Viejo and Cadalso de los Vidrios granites, which were more resistant to heat treatment.This study was funded by the project GEOMATERIALES 2 (S2013/MIT-2914).Peer reviewe

Causes of scaling on bush-hammered heritage ashlars: a case study—Plaza Mayor of Madrid (Spain)

Masons have traditionally used granite anisotropy to cut and lay the stone. Scaling, a common type of granite decay, is observed worldwide. This study explored the relationship between weathering and cut planes in heritage ashlars, specifically in the stone on Madrid’s Plaza Mayor, whose construction dates back to 1590. The 71 rectangular granite columns that support its porticoes are oriented towards the four cardinal points. All 71 have one exposed side that faces the square, one protected side facing inward and two semi-protected sides perpendicular to the other two. The sides of the columns are also oriented to the points of the compass. This study aimed to identify the prevailing orientation of scaling, if any, in the granite ashlars and to determine how this process is affected by climate, microclimate (orientation), use, hewing and exfoliation microcracks. All four sides of the 71 columns were mapped (284 in all) to analyse scaling height, distribution and orientation. The findings showed that the microcracks are vertically oriented and decline in density and length with depth from the surface. Scaling was observed on the lower ashlars in the columns to a maximum depth of 3 mm. Determining the direction of exfoliation microcracks is imperative to understanding decay mechanisms in granite ashlars and sculptures and that information must be taken into consideration when applying conservation treatments.This study was funded by the Community of Madrid under the GEOMATERIALS (S2009/MAT-1629) and GEOMATERIALS-2CM (S2013/MIT-2914) research programmes and Project 921349 awarded to the Complutense University of Madrid’s Research Group ‘Alteración y Conservación de los Materiales Pétreos del Patrimonio’Peer reviewe

Estimación de la dispersión Compton en Fluorescencia de Rayos X: Aplicación al estudio de rocas carbonáticas

Se describe un método, para la determinación de elementos traza por Fluorescencia de Rayos X, basado en la estimación de los coeficientes de absorción de masa (μ) en patrones de rocas carbonáticas a partir de la medida de la intensidad del pico denominado Compton con un tubo de wolframio. Este método permite, utilizando un patrón internacional (BCR-1), el análisis de elementos traza en sedimentos y rocas carbonáticas. Para el estroncio y el zinc, los errores tienen un valor máximo de ±5 por 100. En longitudes de onda superiores al eje de absorción del hierro, es necesario establecer una corrección basada en el contenido en hierro, lo que permite la determinación del hierro y manganeso. Este método tiene una limitación relacionada con el coeficiente de absorción de la muestra: no es aplicable a materiales con un μ muy bajos (μ¡,,9<7) o muy altos (μ¡.,9<20). No obstante, comúnmente los sedimentos y rocas carbonáticas presentan valores de μ incluidos en dicho rango

Experimental assessment of a wireless communications platform for the built and natural heritage

Wireless sensor networks have become extremely popular in a number of fields in recent years, the cultural heritage among them. To date, however, communications quality has not been technically validated in any of the various built (churches, museums, archaeological sites) or natural (caves, lava tubes) heritage scenarios. The present study establishes methodology for assessing the quality of wireless communications and validating the network used, both of which are essential to guaranteeing accurate long-term monitoring in heritage scenarios. Parameters such as signal strength, link quality, range and success rate were analysed with a view to preventing transmission failure and ensuring reliable monitoring for the preventive conservation of the cultural heritage.The present study was funded under projects CGL2011-27902, GEOMATERIALES 2 (S2013/MIT-2914).Peer reviewe

Durabilidad y conservación de geomateriales del patrimonio construido : Reunión científica del Programa Geomateriales, 9 de octubre de 2013

El presente volumen recoge las ponencias presentadas en la Reunión Científica del Programa Geomateriales, celebrada el 9 de octubre de 2013. Estas ponencias se organizaron fundamentalmente en base a los objetivos científicos del programa, incidiendo en las principales actividades realizadas y resultados obtenidos, y apostando por los jóvenes investigadores incorporados. En los resúmenes incluidos se pretende resaltar, por un lado, los resultados científicos de mayor relevancia, las investigaciones que han generado el desarrollo de patentes, las colaboraciones establecidas entre los diferentes grupos y/o empresas y las previsiones futuras. Por otro, aspectos relacionados con los objetivos de formación, como la realización de tesis doctorales y movilidad de investigadores, así como la participación conjunta en los objetivos de difusión y en actividades de gestión de los diferentes miembros del programa. [ABSTRACT] This volume contains the papers presented at the Scientific Meeting of Geomaterials Programme, hold on October 9, 2013. These contributions were organized mainly based on the scientific objectives of the program, focusing on the major activities accomplished and results reached and standing up for young researchers incorporated. The abstracts included aim to highlight the most important scientific results, research that has led to the development of patents, collaborations established between different groups and/or companies and future prospects. Furthermore, aspects related with training objectives, such as doctoral thesis and researchers mobility, as well as joint participation in the objectives of dissemination and management activities carried out by the members of the program

Rutas Geomonumentales: la geología para la enseñanza y difusión del patrimonio arquitectónico.

Las Rutas Geomonumentales constituyen una novedosa metodología de abordar la divulgación del patrimonio arquitectónico con una clara intencionalidad didáctica, permitiendo conocer de cerca los materiales geológicos que lo configuran, la relación que guardan con los edificios, su conservación y sus causas de deterioro. El patrimonio arquitectónico es difundido desde una perspectiva cultural y científica, permitiendo la interacción entre disciplinas como la historia, geología, química, arquitectura, ingeniería, arte y sociología

Innovación en la conservación del Patrimonio Arquitectónico

La construcción y la restauración se preparan para la revolución que supondrá la llegada de los nuevos materiales basados en la nanotecnología. Gracias a ellos, las viejas piedras y los antiguos elementos cerámicos serán capaces de adaptarse a las necesidades concretas de cada proyecto de edificación

Evolución geoquímica de la salmuera de la laguna de Alcahazo, Pedro Muñoz (Ciudad Real).

La Mancha, por sus condiciones climáticas y geomorfológicas, es una región natural en la que se forman frecuentes encharcamientos que derivan hacia sistemas tipo "sebkha" en los que se produce precipitación de sales por evaporación. En la laguna se han determinado las siguientes fases minerales: sulfato magnésico (epsomita, hexahidrita, pentahidrita y kieserita), sulfato cálcico (yeso), cloruro sódico (halita) y cloruro magnésico (bischofita). Las aguas de la laguna, en el período de máxima dilución, presentan una composición marcadamente sulfatada, con alto contenido en cloruros, magnesio y sodio. En laboratorio se ha realizado el seguimiento de la evolución de la salmuera en condiciones equivalentes a las naturales, estableciéndose su correlación con la secuencia teórica de precipitación según VALYASHKO. Por último, se hace una valoración más detallada de los contenidos en estroncio, lo que permite establecer la hipótesis, en función de los aportes, de que esta laguna funciona como un sistema cerrado con recargas limitadas a aportes de lluvia en su cuenca de recepción