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Many cultural heritage sites in Mexico have been built with volcanic tuff rocks from the earliest Central American civilizations to the time of the Spanish conquest and up to the present. Throughout this long period of time, the stones have been subjected to progressive weathering as evidenced by different types of damage phenomenon such as scaling, sanding, crumbling, sugaring and salt efflorescence. This study utilizes a collection of 53 tuffs from different regions in Mexico that show a diverse range of colors, rock compositions and mineralogy, and heterogeneous rock fabrics indicative of their volcanic origin. Comprehensive investigations have been done that include detailed petrographic analyses, cathodoluminescence, clay mineral analyses, and the determination of a wide range of petrophysical properties (e.g., porosity, capillary water uptake, water absorption, sorption, hydric and thermal expansion, and mechanical properties). All analyzed data combined are used for derivation of some general trends concerning the suitability/durability of tuffs applied as natural building stones. [ABSTRACT FROM AUTHOR]

Small historical churches in rural villages are mainly functional buildings, lacking spectacular architectural or ornamental features. This is also true for the St. Johannis Chapel Lütgenrode near Göttingen (Lower Saxony, Germany), which dates back to the 13th century. The use of ca. 10 different natural building stones (Triassic sandstone and limestone, Holocene fresh water carbonate), scattered roof tiles and bricks result in a highly heterogeneous character of the chapel's ascending walls. In addition, various repairs over the last centuries, using inadequate materials, amplified damages and produced critical stability problems, in particular at the southern wall. Here, the suitability of the dimensional stones are evaluated for construction and replacement purposes. A semi-quantitative distribution of lithotypes was performed, and weathering forms were mapped in detail. On-site analyses (micro-drilling resistance, the Schmidt hammer rebound test, capillary water absorption) provide data on the deterioration state of the main lithologies. The petrophysical data show that stratigraphically comparable building stones exhibit different technical characteristics and weathering behavior. All data serve to characterize the state of weathering and provide the data set to plan for future restoration work. The amount needed for restoration work has been estimated to be approximately 435,000–550,000 EUR. Because the local church authorities evaluate the significance of a church based on the frequency of its use, a secular use would be able to save the Lütgenrode chapel, but then the church political leaders would have to act quickly. [ABSTRACT FROM AUTHOR]

Volcanic tuffs naturally show a strong heterogeneity in their petrography and petrophysical properties. The arrangement of the components in tuffs can create a very wide spectrum of porosities and fabrics, which in turn can lead to a highly differential weathering behavior. Considerable amounts of clay minerals and zeolites are common and can contribute to a high sensitivity to expansional processes and salt crystallization. Understanding the influence of the rock properties on material behavior and durability can help to make predictions on future material behavior and evaluate the suitability of the material for construction purposes. This study presents the petrographic and petrophysical data of 15 selected tuffs and 513 tuffs from the literature used as building stones. Regression analysis show if parameters are comparable and if key parameters can be identified. Key parameters can potentially be used for the estimation of the material behavior, without the use of expensive analytics or weathering simulations. [ABSTRACT FROM AUTHOR]

Decay of trachyte used as building stone in urban environment was investigated through the analysis of crusts and patinas found on trachyte of the Euganean Hills in the Renaissance city walls of Padua, northeastern Italy. Mineralogical and microstructural characteristics of the alteration products, as well as major- and trace-element chemical composition, were determined by optical microscopy, SEM-EDS and X-ray mapping, XRPD, and LA-ICPMS. The results are discussed referring to environmental parameters, in particular concerning air quality and anthropic pollution sources. The influence of composition of the stone and other neighboring materials on specific weathering processes is also debated. The formation of crusts and patinas turns out to be mainly due to exogenous processes. Enrichment in heavy metals and carbonaceous matter derives from the deposition of particulate emitted during fuel combustion by road vehicles, domestic heating and, secondarily, industrial activities. The particulate is typically cemented by calcite, mainly mobilized after dissolution from nearby mortar joints, or iron, released by leaching from iron-bearing minerals, reprecipitated according to pH fluctuations. Gypsum layers were rarely observed. Generally, composition of the weathering crusts and patinas of Euganean trachyte proves to be an informative marker for the relevant environmental conditions and their evolution. [ABSTRACT FROM AUTHOR]

The expansion processes that develop in building stones upon changes of moisture content may be an important contributing factor for their deteriorations. Until recently, few data could be found in the literature concerning this parameter and weathering processes. Moreover, the processes that may be responsible for the moisture related expansion of natural building stones are not yet completely understood. To further elucidate this process, extensive mineralogical, petrophysical and fabric investigations were performed on eight German sandstones in order to obtain more information regarding the weathering process and its dependence on the rock fabric. The analysed sandstones show a wide range of pore size distributions and porosities. A positive correlation with the fabric and the pore space can be found for all studied petrophysical parameters. The intensity of the expansion and related swelling pressure cannot be attributed only to the swelling of clay minerals. The investigations suggest that the micropores and the resulting disjoining pressure during wet/dry cycles also play an important role. The results obtained suggest that the mechanism is related to the presence of liquid water within the porous material. [ABSTRACT FROM AUTHOR]

The present study documents the results of an inter-disciplinary model project that was planned with the aim of developing an innovative winter covering system for marble statuaries located on the Schlossbrücke (Berlin). Such a system would need to fulfil the various requirements for structural stability, aesthetics, climate and practical use. This applied research represents the first complex scientific study of the sustainability of a winter covering system. The study is characterised by the use of complex scientific instruments such as special laboratory analysis and numerical simulation tools. The interaction between the environment and the artefacts in connection with the innovative winter covering structures were studied by extensive climatic monitoring. [ABSTRACT FROM AUTHOR]

novel approach of studying dust, black crust and host limestones by using various techniques is presented in this paper. Samples were collected from limestone monuments located in rural, urban and industrial areas in Germany and Hungary. The paper focuses on differences in the mineralogical composition, major and trace element distribution of materials and their total polyaromatic hydrocarbons (PAH) concentration having different exposure to air pollutants. High concentration of gypsum was found in laminar and dendritic black crusts and even in the dust of both urban and rural areas, despite the low concentration of SO in rural atmospheric environments. The black crusts show a typical microfabric with distinct layers of various gypsum-calcite mineral associations, silt-sized mineral fragments and black particle content. In dust, newly formed gypsum crystals were found along with mineral fragments, and siliceous and, less frequently, carbonaceous fly ash particles. High concentration of lead was found both in the samples of urban and rural areas of Germany and Hungary. Lead mostly accumulates in dust and also in the black crust. Highest lead concentrations were found not on the surface of the black crust, but close to the crust/limestone boundary according to LA-ICPMS analyses. It indicates that despite the ban of leaded petrol, lead is still present in the dust and the in the soiled zones of the built environment. Similarly to lead, no significant difference in the total PAH content of dust and crust samples were found in the two countries. Dusts are equally enriched in PAH in both countries, whereas black crusts contain fewer amounts. Most of the aqueous extracts of the samples were saturated with respect to sulphate, which also indicate the presence of gypsum, whilst in some German samples unsaturated conditions were detected. In summary, by using a combination of these analytical techniques, it was possible to distinguish rural and urban samples and to outline the role of dust in bringing pollutants to the stone surface. It is suggested that the analysed dust and stone samples indicate not only present, but also the past, pollution fluxes and as a consequence stones similar to sediments or surface waters can be used as environment indicators. [ABSTRACT FROM AUTHOR]

Salt and ice crystallisation in the pore spaces causes major physical damage to natural building stones. The damaging effect of these processes can be traced back to physically induced stress inside of the rock while crystallizing. The increasing scientific research done during the past century has shown that there are numerous parameters that have an influence on the weathering resulting from these processes. However, the working mechanisms of the stress development within the rock and its material dependency are still subject to discussion. This article gives an overview of salt and ice weathering. Additionally, laboratory results of various sandstones examined are presented. Salt crystallisation tests and freeze/thaw tests were done to obtain information about how crystallisation weathering depends on material characteristics such as pore space, water transportation, and mechanical features. Simultaneous measuring of the length alternating during the salt and ice crystallisation has revealed detailed information on the development of crystal in the pore spaces as well as the development of stress. These findings can help to understand the damaging mechanisms. [ABSTRACT FROM AUTHOR]

An introduction to articles published within the issue is presented, including articles on stone weathering and atmospheric pollution.