Editorial to the topical collection “Building stones and geomaterials through history and environments: from quarry to heritage. Insights on the conditioning factors - The Rolf Snethlage-Volume”

Under the umbrella of “building stones”, a wide range of research topics are possible. A vast interdisciplinary scientific community provides valuable information that should be considered at several levels. These are the extraction of the stone from the quarry to their application on buildings, and the implementation of conservation measures when necessary. The present special issue contains 44 articles on the research into natural building stones. The editorial intention is to present the main highlights of each paper, which are grouped into the following sections in order to better understand the overall content: Quarrying, Physical–Mechanical Properties, Heritage and Weathering, Restoration and Techniques, Miscellaneous. This volume is dedicated to the memory of Professor Rolf Snethlage. The international community of applied geosciences has lost an important researcher and teacher. Therefore, a brief description of importance of the research carried out by Rolf Snethlage is presented at the end of the Editorial.


Introduction
Today, there are fewer and fewer buildings, structures, or monuments that are built with natural rocks, materials such as cement, bricks, and even synthetic materials have been replacing them. However, past human history shows that this was not always the case. The oldest evidence of hominids using stone tools goes back around one million years. This continued with the first groups of nomadic hunter-gatherers using natural rocks to make their sophisticated hunting tools, and furthermore, using natural rock formations as shelters. Since the first sedentary settlements, humans built their spiritual and ceremonial centers, worship centers, temples, churches, and even dwellings using the most accessible material, i.e., natural stones. Over time, the techniques of extraction, transportation, carving, and reworking of the rock were perfected to the point of erecting impressive buildings, monuments, and even entire cities all with natural rocks. Fortunately, for many of us today, large numbers are still standing to be admired and appreciated and are now considered part of all of humanity's cultural heritage.
Building stones are available everywhere and their varieties are related to the geological setting. These stones can be purchased at a low price and are environmentally friendly. Therefore, their extraction and application will probably continue to show a high rate of growth. Several conditioning factors need to be considered during the assessment of this important economic activity. These are the quarrying, the processing of the dimensional stones, their application, which also includes environmental constrains and weathering.
The natural fracturing of the rock mass controls how the stone is extracted from the quarry. Previous evaluations before the opening of a quarry are crucial for maximizing the yield and minimizing the impact to the environment. To increase the productivity of the quarry, the technical staff need to maintain updated information about the main joint sets and their distribution in newly exposed quarry walls. New techniques of acquiring information and software programs are powerful tools with increasing utilization by the quarry owners and operators. The use of aerial photos together with the modeling of the joint sets will become more frequent in the coming years.
Physical and mechanical properties are one of the most important factors to be considered in the building stone industry. The color and texture are still the main controlling factors for the choice of a building stone, whereas the requirements for the physical and mechanical properties established by international standards should be given more weight. There are no inferior building stones, but flawed utilizations, when not taking the set of physical-mechanical properties of a specific stone into account. Different rock types have a wide range of properties, which need to be taken into account when utilizing natural stones. Knowing the physical and mechanical properties will allow one to choose the best material for a specific utilization and to define the type of maintenance required through time.
Environmental factors will act on the natural stone minerals, once the stone has been applied to a specific structure, e.g., a building façade or monument, etc., which leads to a possible degradation. Durability studies should be performed to assess the stone's behavior under the action of water, salt and ice, the most aggressive elements affecting the composition of a stone. When necessary protective or conservation measures need to be implemented, especially in highly porous materials used in historical buildings or monuments.
It is important and necessary to protect, care for and conserve the constructions, structures, and historical buildings that are part of humanity's cultural heritage, which different cultures have left us at different times in history and under different environmental conditions. Once a building has been built, it will be exposed to physical and chemical deterioration agents that can damage the structure to different degrees under different rates of weathering. All these factors must be studied and analyzed not only to know why and how this happens, but also to know how to lessen and control them, and if necessary, how to restore and conserve them. To do this, it is essential to understand all the processes that are required, starting from the extraction in a quarry, processing, and eventually becoming a cultural heritage construction.
The present special issue contains current articles on the research into natural building stones. In the following sections, a summary of the 44 papers is presented.

Quarrying
Joint set geometry and density are key parameters in quarrying yield, since this regulates the volume and shape of the natural blocks. Modern processing technologies demand large unfractured blocks, up to ten cubic meters that can be further dimensioned into various sized blocks. Bogdanowitsch et al. (2022) used information both collected in the field and from unmanned aerial vehicles, namely, digital surface models, orthophotos, and threedimensional models to assess the fracturing in quarries of 21 quarries of granite, limestone, marble, and slate from Portugal. Modelling the fracturing in quarry fronts with software programs such as 3D-BlockExpert helps in quarry management, by modelling the trend of joint surfaces and computing the shape and volume of the in-situ blocks and the quarry yield. Furthermore, the effect of changing the cutting direction by a small shift in the cutting angle can improve the number and volume of the final blocks.
Profitable dimensional stone production mainly depends on the effective number of extracted blocks with a predefined size. The regularity and volume of the blocks are of critical importance. Schneider-Löbens et al. (2022) applied a joint analysis as an important tool for optimizing block extraction of natural stones. For the optimal use of a deposit and a sustainable protection of resources, a detailed evaluation of the deposit including assessment of geological characteristics is necessary. Regarding deposits of natural building stones, in many cases, however, there is a lack of sufficient geological assessment that meets the necessary requirements for such an evaluation. 3D-BlockExpert computer code provides a forward-looking approach for sustainable quarry management using the fracture spacing and fracture orientation. A large number of investigations were carried out in quarry areas with different lithologies in Germany and Spain, such as sandstones, limestones, slates and granites.

Physical-mechanical properties
Building stones should meet the required standards to support the mechanical actions when used for different applications. Furthermore, the physical-mechanical properties regulate the rate of degradation under severe environmental conditions. The previous evaluation of the building stone behavior is a key factor in avoiding further degradations beyond those related to the natural weathering process that affects all materials.
Two research studies are presented that investigate the physical-mechanical properties in carbonate rocks. Salvini et al. (2023) utilize 11 different carbonate rocks to analyze them according to their texture and durability. These rocks were measured by accelerated aging tests which reproduced freeze-thaw and salt crystallization cycles. Eleven limestones from different locations in Portugal were also subjected to different tests and analyses, including the description of their mineralogical composition, grain size, and texture, as well as their bowing behavior to assess the main factors that control their physical-mechanical properties and durability ). The results from both research studies show that the texture and porosity of carbonates play a major role in their deterioration rate.
The study of nine granites from Pakistan highlights the importance of textural and petrographic features for the assessment of stone behavior (Ahmed et al. 2021). The strength properties of the granites are related to texture, quartz percentage, mineralogy and alteration of minerals, volume of void spaces, the occurrence of micro-fractures and grain size.
The presence of clay minerals can affect the properties of the building stones, as pointed out by Pires et al. (2022) in a limestone. In contact with water or moisture, alterations in color, increased fracturing, and swelling, which leads to the loss of material are common typical degradation patterns, especially when stratification and stylolites are parallel to the surface of the slabs. This study highlights the importance of proper stone selection to avoid facade degradation, and hence contributes to the prevention of accidents and promote user safety as well as economic aspects. Domingos et al. (2021) simultaneously measured the 222Rn and 220Rn exhaled per unit mass and emanation coefficient in granitic rock samples collected in the Central Iberian Zone and shows that it is possible to identify a priori the areas with higher potential of radiation exposure. Dealing with the same topic, Siegesmund et al. (2022a) selected 82 building stones covering a wide range regarding the mineralogy and the geological background to measure their radioactivity and calculate the resulting annual equivalent doses and radon exhalation values. The activity concentration of radon, thorium and potassium, A 226 Ra, A 232 Th and A 40 K, for most of the samples, is below the upper limits of normal activities (A 226 Ra and A 232 Th < 100 Bq kg −1 and A 40 K < 1000 Bq kg −1 ) for construction materials (European Commission 1999). The felsic rocks show the highest exhalation rates for both 222 Rn and 220 Rn, followed by metamorphic rocks, while the mafic rocks, limestones and travertines have the lowest values. In some cases, like a small and poor ventilated room covered by thick tiles, the modelling of the annual equivalent dose rates and radon exposure can reach the maximum values. The values obtained characterize unrealistic cases, but allows one to have an idea about the possible harmful use of the building material. Both consumers, producers and market organizations should be aware of this new challenge. Çetintaş et al. (2023) investigated the variations in capillary water absorption and porosity of some limestones during the ongoing weathering process under salt action and air pollutants. They discuss an assessment of the effects that salt crystallization and the reaction of air pollutants (SO 2 , NO 2 ) with moist or wet rock surfaces have on the porosity and pore radii distributions of selected limestones. The physical-mechanical of the stones are influenced by the environmental conditions. Ye et al. (2002) studied the creep behavior of sandstone under saturated and dry conditions under different driving stress ratio. They found that under an identical driving stress ratio, the dry specimens' creep strain and steady-state creep rate are relatively higher than those of the saturated ones. Furthermore, a method for predicting the time-to-failure based on short-term creep test results is proposed.
The correlation of different surface hardness values with the rock's compressive strength (UCS) is a very important value that has been studied by Gireson et al. (2023). They found a decrease at various rates under the effect of freeze-thaw (FT) cycles. However, the proposed equation of carbonate building stones in practical engineering applications needs to be further elaborated upon. Valido et al.'s (2023a) study an ignimbrite from island of Tenerife (Spain) exploited as natural stone with four chromatic varieties. They found that the properties vary depending on the depth of the stratigraphic volcanic level, a high degree of correlation between the physical properties and a significant impact of the petrographic characteristics.
The physical-mechanical and durability was assessed in two varieties of the same type of rock from Arucas (Gran Canaria Island) (Valido et al. 2023b). The porosity stands out as the property with the higher difference, influencing the durability of the stones and, therefore, the possible utilizations. In the Canary archipelago, only nine building stones are extracted, distributed in three islands. This research intends to be a step towards the recognition of the social and economic importance connected to quarry activity and a contribution to the designation of "Piedra Chasnera" as a Global Heritage Stone Resource (GHSR).
Through all cultures and epochs worldwide, tuffs have been used as construction material for the creation of buildings, artworks and sculptures . As popular as the material is, however, it is often very sensitive to weathering, and the reasons for their fast deterioration are manifold and have been the subject of many studies. Pötzl et al. (2022b) identified key parameters that may be useful in the estimation of the strength and durability of tuffs by analyzing a data set of more than 500 samples from the literature. Fifteen selected tuffs were investigated in more detail. Tuffs exhibit a great mineralogical and fabric heterogeneity, and along with this heterogeneity, they show a wide range of technical parameters and responses to weathering. Especially, the porosity, water absorption, and hydric expansion can exceed values multiple times higher than other rock types.
Microcracks, grain-boundary cracks or intracrystalline cracks control, among other things, the weathering behavior of crystalline marbles (Siegesmund et al. , 2022a. The extreme anisotropy of thermal dilatation of calcite (subordinately also dolomite) and the resulting buildup of thermal stresses are probably primary causes of marble weathering. These lead to the build-up of tensile, compressive or shear stresses when the temperature increases, depending on the crystallographic directional relationships between neighboring grains, which presumably lead primarily to the opening of grain boundaries. Ultrasonic wave velocities are a powerful and sensitive tool for the damage assessment of marble. Ongoing experimental alteration approaches were used to document the state of deterioration using Vp-systematics. In addition, thermal expansion and the residual strain values after applying thermal impacts were used to introduce a new quantitative measure based on experimental length changes and volume changes. To quantify such volume changes, a so-called quantitative decay index for marbles was proposed.
To identify the primary cause of the moisture expansion due to swelling, swelling experiments were performed and discussed with respect to the mineralogical composition, the rock fabrics and additional petrophysical properties (Siegesmund et al. 2023). Clay minerals and zeolites that expand due to the influence of a high relative humidity or uptake of moisture play a significant and decisive role in the damage and deterioration of natural stones, such as volcanic tuffs and sandstones. These factors are of crucial importance, because the investigated hydric swelling processes are, as far as is known, either caused by intracrystalline swelling clay minerals or a cleavage pressure triggered by the interaction of surface forces at high micropore fractions in the nanometer range (Siegesmund et al. 2023).
Swelling clay minerals are of interest for diverse areas of geotechnical engineering, in particular, the stability of slopes, foundations, tunnels, and boreholes (Wangler 2023). They are of particular interest as well in the field of conservation of built cultural heritage, as they often appear in the matrix of sandstones and other stones used in historical buildings and monuments, where wetting and drying cycles can lead to damage. Wangler (2023) discusses the potential damage mechanism in the Swiss molasse sandstone. The Molasse de Villarlod is a fine-to-medium-grained Miocene sandstone that occurs in three different varieties. There are some implications of this work for the conservation of built cultural heritage constructed with Villarlod molasse, primarily when it comes to understanding and mitigating the swelling behavior. The fact that the swelling is predominantly crystalline points again to treatment strategies that target this, such as ion exchange with species that induce lower swelling. For an ongoing discussion on the Villarlod sandstone, the reader is also referred to Siegesmund et al. (2023).
Damages due to fire occurred on many monuments and affected building sandstones (Franzen et al. 2022). Cottatype sandstone is a variety of Elbe sandstone that has been widely used over centuries, preferably for sculptures and ornamental decoration on façades like the ashlars in massive stonework for the baroque Dresden Zwinger (Germany). The results are useful hints for understanding the processes running at the grain size scale in clay-bearing sandstones during heating to elevated temperatures. This might help to better assess and understand mechanical properties of sandstone surfaces that were affected by fire attack. The remnant compressive strengths of parts of a massive sandstone building after fire incidents are crucial for planning restoration and reconstruction measures.
Abrasion is an important test method for assessing the suitability of rock materials used as natural stone. Kolgitti and Çelik (2022) propose the use of the Wide Wheel Abrasion test on core samples and half-cut core samples, because the values obtained are useful for estimating the rock material properties as in the uniaxial compressive strength. Moreover, Sari and Yavuz (2023) propose a new empirical equation to predict the abrasion resistance of fresh and after freeze-thaw tests of limestones based on the basic material properties without performing Böhme abrasion and freeze-thaw tests. The results showed that Böhme abrasion values of fresh limestones and those which were treated during freeze-thaw tests can be reliably predicted. However, studies should be carried out on more diverse limestone types and different natural stone types to improve and evaluate the obtained results.

Heritage and weathering
Natural rocks and other geomaterials can be used collectively for architectural works, i.e., that show specific features: the color, its sculpturing, the architectural style, origin and its history. Heritage buildings are composed of individual stone elements, which have specific mineralogical characteristics, structures, fabrics, etc. and these are the parameters that make the rock susceptible to deterioration. Moreover, the rock parameters have a significant control on the conservation strategies.
Many regional examples of the geological-geochemical, lithological, and geomechanical properties of heritage rocks, as well as examples of possible alternative rocks for restoration are presented in the topical collection. Examples of these are the dacite, trachydacite, and trachyandesite of the Binbir Church in the Karaman province of Turkey (Horasan Page 5 of 11 415 et al. 2022), the restoration works, and the search for possible alternative rocks for the Hong Nang Temple Sida in Lao PDR, which was built with sandstone and siltstone (Park et al. 2021), the documentation and structural analysis of the water supply canal system of Dezful city in Iran utilizing a three-dimensional model based on multi-image photogrammetry (Attarian et al. (2022), or the study of the provenance of the conglomerate and sandstone ashlars used in the construction of the Lyrbe city in Antalya, Turkey (Aksoy et al. 2021).
Examples of volcanic tuffs used as construction rock in heritage buildings are those describing the material characteristics of a deteriorated five-story stone pagoda and were compared with those of fresh rocks from its quarrying site in Korea (Jo and Lee 2022). Similar lithology (a porous and soft acid tuff from Japan) was investigated, where the volcanic tuff appears extensively affected by the efflorescence of gypsum, mirabilite, and thenardite, whose development depends on the stone-environment interaction (Germinario and Oguchi 2022).
Non-destructive techniques are excellent tools to be applied when historical buildings are studied. Orenday-Tapia et al. (2021) found a close relation between the velocity propagation of seismic waves and the density of the masonry in historical buildings. Chabas et al. (2022) used a combination of low-to-non-invasive methods associating microclimatic measurements, mineralogical, petrophysical, chemical and isotopic analyses to determine the composition and the source of salts in a restored dovecote. The results show that efflorescences are derived from organic nitrogen.
The classic Elbe sandstones, such as the Cotta sandstone, the Posta sandstone and the Reinhardtsdorfer sandstone, which have been extracted specifically for building purposes in Saxony (Germany) since the thirteenth century, are not missing in the literature on dimensional stones. The Pläner (Lehr 2022), however, is often overlooked not only in Saxony. According to Lehr (2022), Pläner in the petrographic sense are sandy-marly siltstones, sandy-silty marlstones, silicified marlstones and marly silicites. They are characterized by cyclically deposited sediments in large areas of the Bohemian-Saxonian and Münsterland Cretaceous Basins. The aim of this paper is to illustrate the similarities and differences of the Pläner stones used as a building material from the Cretaceous basins considered here. Four different types of Pläners can be classified based on their primary facies and early diagenetic characteristics, but also the limestones that are called Pläners, which occur within the Pläner sequences and the residuals of these Pläners are considered. The historically dominant stone of Prague is the "Golden Pläner" (zlatá opuka). It owes its name to the warm reddish-yellow coloration.
Small historical churches in rural villages like St. Johannis Chapel Lütgenrode near Goettingen (Lower Saxony, Germany), which dates to the thirteenth century, are mainly functional buildings, lacking spectacular architectural or ornamental features (Siegesmund et al. 2022c). Of the ten stratigraphic intervals with natural building stones listed in the above work of the Goettingen area, nine can be found in the walls of the Lütgenrode Chapel. In addition, two fragments of marine lower Jurassic siltstones occur exclusively here. Based on detailed mapping of the lithology and decay features the most important rock types were sampled as far as possible from old, abandoned quarries and then investigated with respect to important material parameters. Furthermore, onsite investigations on strength and water absorption were carried out. According to existing estimates, approximately 550,000 EUR will be necessary for the complete repair work. The largest share will be for the restoration of the south facade and the interior, where the greatest damage prevails. The emergency protection on the south side will stop the collapse of the already extremely warped facade for a few more years. Siegesmund et al. (2022b) investigated 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. Volcanic rocks have been used, since the first cultures appeared in Mesoamerica. As designated by UNESCO, Mexico is one of the countries with the largest number of world heritage sites. Of these sites, the vast majority are constructions consisting of pyramids, colonial churches, or historical buildings, which were erected with natural stones. The stones used for the construction of these buildings were mostly rocks from the surroundings, so their lithology is dependent on the geology of each site. The results of the quality assessment on the tuffs from Mexico, despite their strong heterogeneity, indicate some general trends and allow for some general statements regarding their technical properties and material behavior. Siegesmund et al. (2022b), therefore, directly formulate some observations and recommendations when dealing with this extremely diverse material, which may potentially help categorize the material and estimate weathering resistance and construction suitability. Novaković et al (2023) studied the intensities of degradation processes present on the kersantite rock built into the monument "Small Staircase" in Belgrade (Serbia). Kersantite is an important architectural building stone of Serbia and is a striking feature of the capital's architecture in the first half of the twentieth century. It was widely used in the construction of Belgrade buildings until the Second World War. The investigations were conducted on sound rock from the quarry and damaged stone used for the monument. While some staircase parts were underground for 90 years, most of the stone elements were exposed to different environmental conditions and anthropogenic influences. The results of Novaković et al (2023) confirm the importance of understanding and perceiving the synergistic action of the properties of the used material, the monument's architecture, its micro-environmental conditions and all the influences and mechanisms that lead to the degradation of cultural monuments built of stone. García-Solís et al. (2023) studied the petrographic and microfacial characterization of the building stones of buildings, monuments, and quarries of the archeological site of Calakmul to document aspects of composition, lithologies, and stone exploitation. Microfacial analysis shows that the used building rocks are highly recrystallized biosparudites with the presence of reef and shallow water fauna and come from different quarries. These results determined by García-Solís et al. (2023) help to identify the origin of the rocks, their use in the buildings and monuments studied, and contribute to the knowledge of their lithological characteristics and their response to weathering in a tropical context. Such aspects are crucial in the decision making for future conservation processes.

Restoration and techniques
The conservation of rocks as a measure of protection and care of the structures built with natural rocks has generated a series of state-of-the-art methodologies that are advancing rapidly in the direction of being sustainable, environmentally and landscape friendly.
The use of modern biological methods such as the ureolytic microbial-induced calcite precipitation, utilizes urease active bacteria to precipitate calcium carbonate to act as a binding material (Mori and Uday 2021). In other cases, conservation methods already known and used around the world are analyzed, such as the application of hydrophobic agents in the form of organosilicon compounds, applied to the Baumberger sandstone to evaluate their influence on the weathering processes during long-term exposure. These analyses showed however, that hydrophobic surface treatment did not lead to a significant decrease of weathering or damages, therefore a hydrophobic surface treatment of the Baumberger sandstone seems to be unsuitable (Orlowsky et al. 2022). Many times, the restoration involves the use of some type of mortar or even the use of artificial rocks.
For the modern-day conservation of historical monuments, the main goal is to try and preserve the original material as much as possible. When tuff stones are not available for restoration measures, be it localized repair work or complete natural stone replacement, the information determined from the mineralogical and rock mechanical investigations of volcanic tuffs, can help in giving us parameters by which stone replacement materials (e.g., mortars or artificial stones) can be matched to the available inventory. Stone replacement mortars or artificially optimized replacement stones should be developed and tested as a conservation measure. Menningen et al. (2022) present a paper on the development of mortars and artificial tuff rocks manufactured using materials rejected during the quarrying of tuff rocks. They use source material from Mexico and Armenia. Utilizing this material, the production of replacement products with optimized properties for the restoration and repair of severely damaged natural stones represents a resourcesaving measure for the preservation of these buildings. Franzen and Fischer (2022) studied three sculpted figures made from Cotta limestone, which presented a visual aspect that resembled a more iron-like casting with the typical reddish-brown color of rust, like the products of iron corrosion. Studies of this deterioration showed that the origin of the rust was the dissolution of iron in the groundwater (Franzen and Fischer 2022).
Tuff rocks from Armenia, Germany and Mexico were treated with two commercially available consolidants based on a silicic acid ester, as well as different pretreatments with an anti-swelling agent and/or primer components (Pötzl et al. 2022a). The main goals of this study are to identify a general suitability of different consolidating treatments for different types of tuffs, evaluating tartaric acid as a primer component for tuff consolidation and to pursue the approach of finding a molecular answer for the apparent tuff consolidation problematics, by testing a consolidation agent with smaller molecules than products currently on the market, e.g., tetramethoxysilane (TMOS).
Since the 1970s, the weathering of marble, with regard to its loss of cohesion between the individual grains, has been focused on monument conservation and has achieved an increased level of importance . Until today, there were several materials developed, like the acrylic resin total impregnation or its optimized formulation. In Italy, the application of the so-called Bologna cocktail was very common. Another consolidation material often chosen is the tetra orthosilicate (TEOS/KSE), while the bonding to calcitic surfaces causes problems. Menningen et al. (2021) also show that, for various types of marble with different properties, a reduction in residual strain after thermal cycles can be achieved by treatment with aqueous solutions of diammonium hydrogen phosphate (DAP). Because of the formation of hydroxyapatite among calcite grains, marble cohesion is increased, and the bowing tendency is decreased after treatment with DAP. While for some types of marble, bowing was low even after 30 heating-cooling cycles after consolidation; in other cases, a progressive loss in cohesion and resistance to bowing was registered. Further tests are in progress to affirm the effectiveness and to ascertain the long-term behaviour of DAP-treated marbles.
Many historically valuable buildings and cultural monuments made of natural stone are severely threatened in their existence. The cleaning of natural stone surfaces can be a simple protective approach (Koch et al. 2023). The overriding principle here is caution and care, because on one hand, the unique cultural heritage of the past should not suffer irreparable damage or even be destroyed by improper cleaning applications. When a hot-water high-pressure cleaner with its massive cleaning aggregate is driven to the front of a delicate sandstone facade, even civil engineers feel extremely uneasy. In fact, the steam generated by this unit has a smaller mechanical effect on the surface than a toothbrush, and the "particle size" of this cleaning medium is infinitely smaller than that of the finest abrasive used by a micro-jet system. Such misconceptions can only be countered with a thorough scientific understanding of the work. The quantitative comparison of different cleaning methods for different types of building stone is a complex matter and presented by Koch et al. (2023). The resulting water pressure on the surface is significantly influenced by the cleaning distance, but also by the equipment used and the respective flow rate, which is also dependent on the cleaning process.

Miscellaneous
The reuse of marble and granite cutting waste to produce facade panels with thermal insulation properties by alkaliactivation was studied by Bruschi et al. (2022). Both wastes are viable precursors to produce facade panels with appropriate strength and thermal conductivity. Regarding the thermal behavior, a range between 1.63 and 1.97 W/m 2 °C was obtained, which is lower than the thermal conductivity values shown by current insulation materials with similar density, indicating the suitability of the proposed solution for thermal insulation.
Porous limestone was quarried in subsurface areas for dimension stone from the nineteenth century in the Budapest region. Zenah et al. (2022) assessed the stability of a cellar system under surface by computing the critical depth and Fig. 1 Rolf Snethlage (right) with Siegfried Siegesmund at the official book presentation of the textbook "Naturstein in der Kulturlandschaft" (2013) at the German Federal Environmental Foundation in Osnabrück critical width of pillars under critical load for this type of limestone. The strength reduction factor was calculated for several geometries, indicating the changes in the stability of these underground quarries and pointing out the importance of cellar geometries. Bruno et al. (2023) presented another example of underground construction, a huge underground space used as a water reservoir named Palombaro Lungo, located in the city of Matera. The hypogeum is dug into a Plio-Pleistocene rock called Gravina Calcarenite. It is a calcareous sandstone and a weak rock with good mechanical properties, low permeability and easy to be excavated. The internal geometry of the hypogeum and the rock thicknesses above the caves was reconstructed by the integration of topographic and GPR surveys. The results from numerical simulations showed a stress-strain state compatible with the fractures detected in situ and confirmed the absence of instability problems in the groundwater reservoir.
Jamal-ud-din et al. (2023) assessed the vulnerability of an urban area to earthquake hazards by using Geographical Information Systems (GIS) and Multi-Criteria Decision Making (MCDM) techniques. Twenty-four distinct indicators of earthquake vulnerability were included in this study, grouped into the socio-economic, structural, systematic, and geological components. The results of this study may be helpful for urban planners and authorities by protecting human life, mitigating seismic risk, and identifying the risk zones, and resource allocation by targeting vulnerable locations and groups and deciding on development control interventions.
This volume is dedicated to the memory of Professor Rolf Snethlage (Fig. 1). The international community of applied geosciences loses an important researcher and teacher. Through his research with its main emphasis on "Archaeometry" (Volkswagen Foundation), Rolf Snethlage became the first scientist at a state office for the preservation of monuments in the central laboratory in Munich (Germany). From then on, stone conservation was his research topic. Through him, Munich very quickly became a center of national and international restoration research.
Since the 1970s, the loss of cultural assets induced by environmental contamination was increasing in the public's awareness, along with forest death due to atmospheric pollution. If one considers today's discussions on climate change and its influences on valuable cultural assets, it becomes clear that half a century later there are actually even more massive problems that seemed to have been solved. From 1985 to 1995, Rolf Snethlage was actively involved in the research project "Stone Decay-Stone Conservation" sponsored by the German Federal Ministry of Research and  (1998), (Snethlage, Ed) Technology (BMFT) and, as the project progressed, became the responsible manager. This BMFT project marked the beginning of scientific research into questions of weathering and conservation in Germany. It was Rolf Snethlage who, as editor, made the results available to a wide audience in the "Jahresberichten Steinzerfall-Steinkonservierung" and in the books "Denkmalpflege und Naturwissenschaft: Natursteinkonservierung 1 und II" (Fig. 2). The number of publications by Rolf Snethlage is impressive (Fig. 3). Among restorers, building planners and stonemasons, his "Leitfaden Steinkonservierung" (in the 5th edition with Dr. Pfanner) is the standard work in the daily practice of monument conservation. The book by Siegesmund & Snethlage. (eds.) "Stone in Architecture-Properties, Durability", now in its 5th edition, has been introduced worldwide and has become a classic.
Internationally, Rolf impressed many people by his activities in a variety of European projects, at ICOMOS, RILEM or EUROCARE EUROMARBLE. On behalf of the German government, he was active in China in the conservation of the clay figure army of the emperor Quin Shihuan, in Petra (Jordan) or the Temple of God at Dafosi, etc.. Rolf Snethlage liked to mingle in the circle of his colleagues and students very much. At conferences and social gatherings, he was always very balanced, witty, unagitated and cordial. Rolf Snethlage leaves a gap that cannot be filled in any way. Fig. 3