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

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

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

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

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

Piedras artificiales: morteros y hormigones. El cemento como máximo representante de estos materiales de construcción

12 págs, 7 fig.-- Publicado en el libro "Ciencia, Tecnología y Sociedad" dentro del programa Maternas financiado por la Comunidad de Madrid, en colaboración con la Asociación Restauradores sin Fronteras (RSF).[EN] From the dawn of architecture to the present day, artificial stones have been the most in-demand building material. Natural stones, because of their beauty, fine quality, etc., are now favoured over artificial stones, but the use of the latter has always been indispensable. The most representative group of artificial stones is that of mortars and concrete. These mortars are obtained from the mixture of natural dry materials with a binding material and water. The binding materials may be common (lime, plaster, clay, etc) or hydraulic (hydraulic lime and cements). Over the last two centuries, 19th and 20th, the prominence of hydraulic mortars and concrete has been enormous and has given cement the starring role in modern construction.[ES] Desde los albores de la arquitectura y hasta el día de hoy, piedras artificiales han sido las más demandadas dentro de los materiales de construcción. Las piedras naturales, debido a su belleza, gran calidad, etc, han sido mejor valoradas que las piedras artificiales, pero el uso de estas últimas siempre ha sido indispensable. El grupo más representativo de piedras artificiales es el de los morteros y hormignones. Estos morteros se obtienen a partir de la mezcla de un árido natural seco con un aglomerante y agua. Los aglomerantes pueden ser de materiales comunes (cal, yeso, arcilla, etc) o hidráulicos (cal hidráulica y cementos). En los últimos dos siglos, XIX y XX, la utilización de morteros hidráulicos y hormigones ha ido en aumento, lo que implica que el cemento juega un papel importante en la construcción moderna.Proyecto Maternas financiado por la Comunidad de Madrid (Referencia S-0505/MAT-0094)

Integración de datos de termografía de infrarrojos y otras técnicas no destructivas en detección de humedades y sales

La humedad es una de las principales preocupaciones en relaci&oacute;n con la conservaci&oacute;n del patrimonio arquitect&oacute;nico. La humedad cataliza reacciones qu&iacute;micas y favorece el crecimiento biol&oacute;gico. Adem&aacute;s, el agua puede estar cargada en sales, que se transportan en soluci&oacute;n y pueden generar da&ntilde;os por cristalizaci&oacute;n e hidrataci&oacute;n - deshidrataci&oacute;n. La humedad en muros y otras estructuras solo se puede medir directamente con metodos &quot;gravim&eacute;tricos&quot;. Estos m&eacute;todos, necesitan la extracci&oacute;n de una peque&ntilde;a muestra, por lo que, a vees, en el contexto de propiedades patrimoniales, es conveniente considerar el uso de T&eacute;cnicas no Destructivas, como los sensores el&eacute;ctricos o la termograf&iacute;a de infrarrojos para la determinaci&oacute;n de los focos de humedad. Estos m&eacute;todos necesitan una interpretaci&oacute;n pues hay otros factores como el contenido de sales o la porosidad que afectan a sus lecturas. En este trabajo se presenta un experimento de laboratorio en el que se estudian materiales p&eacute;treos con distintas porosidades saturados en agua y, en un caso, con sales mediante Medidores de Humedad Port&aacute;tiles y Termograf&iacute;a de Infrarrojos durante el proceso de evaporaci&oacute;n. Esto se realiza como paso previo para establecer un protocolo de utilizaci&oacute;n conjunta de sensores el&eacute;ctricos y termograf&iacute;a de infrarrojos para la evaluaci&oacute;n de humedades en elementos patrimoniales reales

Non-destructive testing for the assessment of granite decay in heritage structures compared to quarry stone

Several types of granite found in two architectural heritage monuments were assessed with two non-destructive, portable techniques: Schmidt hammer rebound and ultrasound velocity (Vp). Similar assessments were conducted on the rock from which the granite was originally quarried for comparison. The results obtained, which revealed the existence of a direct correlation, constitute a useful indication of decay, particularly if the approximate dates of construction are known. And conversely, if they are not, such stone assessments may provide a rough estimate of when the structure was built. Both of these convenient, portable and non-destructive techniques may be used as reliable indicators of the degree of stone decay

The measurement of surface roughness to determine the suitability of different methods for stone cleaning

Trabajo presentado a la EGU General Assembly 2011.In order to select the best bead blasting based method to clean the stone masonry of specific areas of the Cathedral of Segovia (Segovia, Spain), measurements of the roughness of the stone surface were performed, before and after cleaning processes.Peer reviewe