R. Fort

Sedimentology and geochemistry of carbonates from lacustrine sequences in the Madrid Basin, central Spain

Abstract Lacustrine and alluvial carbonate facies have been investigated in Middle Miocene successions of the western side of the Madrid Basin in order to evaluate paleoenvironments in which carbonates formed. Carbonate facies are varied and include: (1) calcrete and dolocrete; (2) pond deposits; (3) lake margin dolostone; (4) mudflat carbonate; and (5) open-lake carbonate facies. The dominant mineralogy of these is dolomite and/or low-Mg calcite. No high-Mg calcite or aragonite have been detected in any sample. δ 18 O- and δ 13 C-values range from −8.20 to −1.80% PDB and −10.25 to −0.70% PBD, respectively. More negative δ 18 O- and δ 13 C-values correspond to predominantly calcite calcretes and to carbonate deposited in ponds at the foot of arkosic alluvium. Higher δ 18 O-values are from both lacustrine carbonate and dolocrete. This latter lithofacies has strong geochemical similarities to dolostones deposited in a lake margin environment. Mudflat carbonate, deposited on shallow platforms subject to lake water oscillation, shows great heterogeneity in both stable isotope value and trace-element content. The mineralogy of these carbonates is dominated by calcite and the limestones contain molds of gypsum. Occurrence of calcitized dolomite textures in these facies suggests the influence of fresher water during expanding lacustrine cycles or further interaction with less saline groundwater. Trace-element contents are considered to be potential indicators of the different carbonate facies types, thus aiding the paleoenvironmental interpretation. However, discrimination among carbonate facies on the basis of trace-element contents appears to be dependent on the statistical method utilized for treatment of data. More information is needed to ascertain their use as paleoenvironmental indicators.

Pore size distribution and the durability of a porous limestone

Abstract A comparison of durability estimations based on mercury porosimeter data and experimental salt crystallization tests carried out on Bateig Stone from Alicante, Spain, establish that the main factor in the salt crystallization durability test is the ‘ink bottle’ pore system, identified by the presence of residual mercury in large pores after porosity testing. In addition, the results suggest that the commonly used indirect durability tests may not be considered a scientific definition of building stone behaviour.

Determination of anisotropy to enhance the durability of natural stone

Anisotropy is a petrophysical property of natural stone and other construction materials that determines their quality and resistance to decay due to a variety of agents, such as water. A study was conducted on nine types of stone widely used in Spains built heritage, using six previously defined anisotropy indices. These indices can be used to determine the degree of anisotropy, which helps explain the differential decay observed in stone materials quarried in the same bed and used to build the same structure. The conclusion reached is that anisotropy should be determined in the natural stone used both to restore the architectural heritage and in new construction, since the appropriate choice of material quality ensures greater resistance to decay and, therefore, increased durability. Materials with the lowest possible anisotropy should be selected, as this property governs their hydraulic behaviour: the lower the anisotropy in a material, the better its behaviour in relation to water and the longer its durability.

Evolution in the use of natural building stone in Madrid, Spain

Many types of stone have been used for construction in Madrid. In historical times, their use was determined by the proximity of the geological resources, the ease of quarrying and transportation links to the city. More recently, as transport connections and quarrying techniques have improved, quality and durability have become key determinants of building stone selection. Local flint was used intensively from the ninth to the eleventh century, when it was replaced by Redueña dolostone, used in turn until the seventeenth century. Granitic rocks from the Guadarrama Mountain Range that crop out in the northern and western area of the province increasingly began to be used in the city from the sixteenth century. Traditionally known as Berroqueña stone, this building stone was quarried in a number of areas; the primary point of supply was Zarzalejo, and from the eighteenth century the granite used was mainly quarried in the Alpedrete area. Eighteenth century advances in underground quarrying made it possible to extract a limestone (Colmenar stone) located in the southeastern part of the region. Together with Berroqueña stone, this limestone became one of Madrid’s traditional building stones, and both, highly esteemed for their excellent petrophysical properties and durability, are still used today.

Impacts of fire on stone-built heritage

Abstract Fire is a major threat to stone-built cultural heritage and this paper is a review of the existing research into fire damage on building stone. From early research based on anecdotal evidence of macroscopic observations, scientists have moved on to develop various techniques for approaching the investigation of fire damage to stone (high-temperature heating in ovens, lasers, real flame tests), different aspects of the damage that fire does have been learned from each, developing understanding of how microscopic changes affect the whole. This paper seeks to highlight the need for a greater awareness of the threat that fire poses (and the need to take precautionary measures in the form of fire-suppression systems), of the immediate effects, and of the long-term management issues of natural stone structures which have experienced fire.

Soluble salt minerals from pigeon droppings as potential contributors to the decay of stone based Cultural Heritage

This paper describes the salt content and pH evolution in solutions produced by the water-soluble extraction of accumulated pigeon droppings. Results demonstrate that these accumulations contain 4 % of soluble salts. Therefore, they are a plausible source of salts commonly found on buildings. These salts comprise halite, sylvite, potassium calcium sulphate, aphthitalite, apatite group minerals, weddellite and gypsum. The interaction of solutions formed from pigeon droppings with porous limestone was also studied. A noticeable deterioration in limestone due to acid attack was observed, including surface etching of rock-forming minerals.

Overview of recent knowledge of patinas on stone monuments: the Spanish experience

Abstract The historic treatment of stonework has often been linked to the artificial application of patinas, mainly for aesthetic and protective reasons. Increasingly, however, researchers have identified a possible combined origin for patinas that has linked natural, biological processes to those associated with an artificial, man-made origin. This suggests that, although coatings may have been initially applied on purpose, they transform over time with the aid of micro-organisms and other chemical interactions. The original mixture applied to create a patina could include lime and/or gypsum, water, natural pigments and organic additives. However, their present-day mineralogy is varied and includes a wide range of minerals from calcium carbonates to calcium sulphates, calcium oxalates, calcium phosphates, silicates (quartz, feldspar, clay minerals) and iron oxides/hydroxides. Patinas have been studied in detail in Greece and Italy, but rarely in Spain. In this paper, existing knowledge on Spanish patinas is co-ordinated and previous and current research summarized. Emphasis is placed on artificial patinas initially applied to protect stone. These both appear to effectively protect the stone substrates on which they were applied and provide an insight into historical techniques of stone conservation. Because of this their preservation should be a strong consideration in restoration projects. Ongoing research focuses on the challenges of reproducing patinas, based on historical references.

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

The roughness of stone surface was measured, before and after bead blasting-based cleaning methods, to select the most efficient one to be used in masonry and stonework of specific areas of the Cathedral of Segovia (Spain). These types of cleaning methods can, besides the removal of soiling and surface deposits, leave a rougher surface, which would mean higher and more rapid water retention and deposit accumulation due to a specific surface increase, therefore accelerating stone decay. Or, in contrast, the cleaning method can be so aggressive that it can smooth the surface by reducing its roughness, a fact that usually corresponds to excessive material removal—soot and deposits–-but also part of the stone substrate. Roughness results were complemented with scanning electron microscopy observations and analyses and colour measurements. Finally, it was possible to select the best cleaning method among the six that were analysed, for different areas and different stone materials. Therefore, this study confirms the measurement of surface roughness as a reliable test to determine the suitability of stone cleaning methods; it is a non-destructive technique, portable and friendly to use, which can help us to rapidly assess—together with other techniques—the efficacy and aggressiveness of the stone cleaning method.

Synthesis, Photocatalytic, and Antifungal Properties of MgO, ZnO and Zn/Mg Oxide Nanoparticles for the Protection of Calcareous Stone Heritage

More recently, the biological colonization of stone heritage and consequently its biodeterioration has become the focus of numerous studies. Among all microorganisms, fungi are considered to be one of the most important colonizers and biodegraders on stone materials. This is why the development of new antifungal materials requires immediate action. ZnMgO nanoparticles (NPs) have several exciting applications in different areas, highlighting as an efficient antimicrobial agent for medical application. In this research, the application of Zn-doped MgO (Mg1-xZnxO, x = 0.096) NPs obtained by sol-gel method as antifungal coatings on dolomitic and calcitic stones has been explored as a means to develop effective protective coatings for stone heritage. Moreover, the photocatalytic and antifungal activity of Mg1-xZnxO NPs were comparatively studied with single ZnO and MgO NPs. Thus, compared to the MgO and ZnO nanomaterials, the Mg1-xZnxO NPs exhibited an enhanced photocatalytic activity. After UV irradiation for 60 min, 87% methylene blue was degraded over Zn-doped MgO NPs, whereas only 58% and 38% of MB was degraded over ZnO and MgO NPs, respectively. These nanoparticles also displayed a better antifungal activity than that of single pure MgO or ZnO NPs, inhibiting the growth of fungi Aspergillus niger, Penicillium oxalicum, Paraconiothyrium sp., and Pestalotiopsis maculans, which are especially active in the bioweathering of stone. The improved photocatalytic and antifungal properties detected in the Mg1-xZnxO NPs was attributed to the formation of crystal defects by the incorporation of Zn into MgO. The application of the MgO- and Zn-doped MgO NPs as protective coatings on calcareous stones showed important antifungal properties, inhibiting successfully the epilithic and endolithic colonization of A. niger and P. oxalicum in both lithotypes, and indicating a greater antifungal effectiveness on Zn-doped MgO NPs. The use of Zn-doped MgO NPs may thus represent a highly efficient antifungal protection for calcareous stone heritage.

Assessment of Different Methods for Cleaning the Limestone Façades of the Former Workers Hospital of Madrid, Spain

Abstract Five different methods for cleaning the limestone façades on what was originally the Workers Hospital in Madrid are analyzed in this paper. Due to the pollution in the surrounding air, just 20 years after a prior cleaning operation, sulfate crusts had developed on the entire stone surface of the building. The gypsum mortar used in the original masonry constituted an additional source of sulfur. Limestone is a traditional building material in Madrid and its surroundings. The petrography, mineralogy and petrophysical properties of the biomicrite, pelmicrite and biopelmicrite varieties of limestone identified in the hospital walls were determined. Analysis of a black layer on the stone surface showed that it consisted primarily of sulfate crusts. The cleaning methods tested were alkaline gels (sodium hydroxide and potassium hydroxide), pressurized hot water, glass bead blasting and latex peeling. The criteria for assessing the effectiveness and potential risks of the various cleaning systems included changes in the chromatic parameters of the stone, the formation of alteration products (i.e. salts) and modification of the stone surface. The stones cleaned with the three most effective methods, together with a rain-washed stone as a reference, were washed with water to generate an artificial runoff. The collected drain water was analyzed to determine the presence of any by-products from the cleaning process. The method found to be most effective and which caused the least alteration to the stone surface was glass bead blasting, particularly after adjustment of the bead size and pressure conditions used for the test.