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Salt efflorescence is one of the major hazards to cultural heritages, masonries, and highways etc. It is now generally accepted that damages caused by salt efflorescence are mainly due to continuous cycles of salt crystallization/dissolution or hydration/dehydration in confined spaces. The position where salt efflorescence occurs and its type are closely related to the degree of damages caused by salt efflorescence. It is known that water is the key environmental factor determining the salt crystallization position. But influence of the correlation between water supply and evaporation on the position of salt crystallization is still not clearly understood. In this work, a set of experiments are designed to investigate salt efflorescence in porous matrix. It is found that the types and positions of salt efflorescence have little to do with nucleation, but are mainly governed by crystal growth, which is controlled by the rates of water evaporation, water and salt supply, capillary forces and surface properties of the porous matrices. [ABSTRACT FROM AUTHOR]

Salt weathering is a common deterioration phenomenon that affects outdoor cultural properties, and it is important to precisely predict the heat, moisture, and salt transfer in porous materials to suppress salt weathering. Osmosis and osmotic pressure were considered in the field of soil research, especially in clay research, but not in the field of outdoor cultural properties and building materials, which are the main target of salt weathering. Osmosis in clay is supposed to be caused by its surface charge. However, it has been suggested that sandstones and bricks that constitute cultural properties and buildings also have surface charge as clay. Thus, osmosis and osmotic pressure can occur in building materials, which may lead to materials degradation. In this study, we derive basic equations, based on nonequilibrium thermodynamics, for the simultaneous heat, dry air, water vapor, liquid water, cation, and anion transfer in building materials by considering osmosis. This equation was compared with existing model for heat and moisture transfer equations as well as models that considered the salt transfer. Based on the previous research for osmosis in clay, we summarized conditions under which osmosis occurs in building materials and presented an outlook for modeling the physical properties of materials related to osmosis. [ABSTRACT FROM AUTHOR]

The study is concerned with the rate of evaporation from porous rock, including the second stage of evaporation characterised by the existence of a dry surface layer separated from the wet capillary zone by a sharp evaporation front. The main objective is to investigate the relationship between the depth of evaporation front and the rate of evaporation as the drying process progresses, and to compare measured evaporation rate with the corresponding calculated values. Sandstone core samples saturated with water were allowed to dry naturally under room conditions, while the changes in the evaporation rate and the depth of evaporation front, among other quantities, were measured. We demonstrate that the evaporation rate can be very accurately determined from the depth of the evaporation front and the ambient air temperature and relative humidity using Fick's law for water-vapor diffusion. During the second stage of evaporation, the diffusion flux through the dry surface layer is computed using the water-vapor diffusion coefficient of the rock, determined from a separate wet cup experiment. In order to cover the first stage of evaporation, an additional parameter characterising the diffusion layer of air above the surface is required, either determined by the best fit to the measured evaporation rates, or adopted from previous studies. The calculated evaporation rate was in good agreement with measurements, with Pearson correlation coefficient 0.98 and relative error of the calculations averaging 15% over the evaporation front depths ranging from 0 to 29 mm. A workflow for determining the evaporation rate from sandstone outcrops is suggested, along with possible applications in sandstone weathering research. [ABSTRACT FROM AUTHOR]

Abstract Salt efflorescence is one of the major hazards to cultural heritages, masonries, and highways etc. It is now generally accepted that damages caused by salt efflorescence are mainly due to continuous cycles of salt crystallization/dissolution or hydration/dehydration in confined spaces. The position where salt efflorescence occurs and its type are closely related to the degree of damages caused by salt efflorescence. It is known that water is the key environmental factor determining the salt crystallization position. But influence of the correlation between water supply and evaporation on the position of salt crystallization is still not clearly understood. In this work, a set of experiments are designed to investigate salt efflorescence in porous matrix. It is found that the types and positions of salt efflorescence have little to do with nucleation, but are mainly governed by crystal growth, which is controlled by the rates of water evaporation, water and salt supply, capillary forces and surface properties of the porous matrices.

Abstract The different salt weathering issues of the sandstone in the Nankan Grotto have significantly influenced their preservation conditions. This work aimed to evaluate the petrography and environment constraints for salt weathering of three typical sandstones: yellow sandstone, cyan sandstone, and gray sandstone in the Nankan Grotto. Salt resistance test and acid leaching test were conducted on these three sandstones. In addition, the mineralogy, geochemical mass balance, micro-structure, and water transport properties of these sandstones were also analyzed. It is found that yellow sandstone had high quartz concentration, porosity, and water transport ability. Cyan sandstone had low calcite concentration, high porosity and medium water transport ability. Gray sandstone had high calcite concentration, low porosity and water transport ability. The decay of sandstones in the salt resistance test at 20 °C was faster than those at 5 °C and 35 °C. In addition, yellow sandstone was the most resistant to the salt resistance test, followed by cyan sandstone, and gray sandstone was the most vulnerable to the salt resistance test. In the H2SO4 acid leaching test, efflorescence pattern was the most likely type of decay in yellow and cyan sandstones. Thenardite was the exclusive salt in the yellow sandstone, while gypsum was the mainly salt in the cyan sandstone. Gypsum crust and subflorescence were the most common types of decay for gray sandstone. In the HNO3 acid leaching test, yellow and cyan sandstones did not show obvious variations. For gray sandstone, the secondary minerals were gypsum and dolomite, and crust pattern was observed. In general, the salt weathering of gray sandstone was more severe than yellow and cyan sandstones. The differences in petrography (mainly calcite concentration) and micro-structure of sandstone and the external environment leaded to the differences in the types, amounts, and locations of the salt crystallization in the acid leaching tests. These contributed to the different development of efflorescence, subflorescence, and crust patterns. Our research reveals the petrographic, micro-structural, and environmental constraints for different salt weathering processes of sandstones in the Nankan Grotto.

Due to lithological and environmental differences, the weathering degree of stone heritage varies even within the same area. Various factors dominate the weathering process at different stages. Implementing preventive measures has reduced the impact of controllable factors such as human activities. However, salt weathering caused by atmospheric pollutants, water, and salt migration in rock formations has emerged as a major contributor to the deterioration of stone heritage. Understanding the re-weathering characteristics of stone cultural heritage at different weathering degrees is crucial for preventive protection. This study investigated the weathering status of Nanshiku Temple and designed an experimental scheme based on field monitoring data. By controlling the number of freeze-thaw cycles, stones with different weathering degrees were prepared, and sulfate weathering simulations were conducted. The results revealed severe damage to sandstone due to Na2SO4 crystallization. Higher initial weathering degrees resulted in more pronounced deterioration and faster weathering rates. Surface hardness analysis approximated the decay process using a logarithmic function within a certain range but could not fully capture the overall weathering of the stone. Uniaxial compressive strength showed a strong correlation with weathering indices like p-wave velocity. These findings provide a theoretical basis for preventive protection efforts in stone cultural heritage.

The different salt weathering issues of the sandstone in the Nankan Grotto have significantly influenced their preservation conditions. This work aimed to evaluate the petrography and environment constraints for salt weathering of three typical sandstones: yellow sandstone, cyan sandstone, and gray sandstone in the Nankan Grotto. Salt resistance test and acid leaching test were conducted on these three sandstones. In addition, the mineralogy, geochemical mass balance, micro-structure, and water transport properties of these sandstones were also analyzed. It is found that yellow sandstone had high quartz concentration, porosity, and water transport ability. Cyan sandstone had low calcite concentration, high porosity and medium water transport ability. Gray sandstone had high calcite concentration, low porosity and water transport ability. The decay of sandstones in the salt resistance test at 20 °C was faster than those at 5 °C and 35 °C. In addition, yellow sandstone was the most resistant to the salt resistance test, followed by cyan sandstone, and gray sandstone was the most vulnerable to the salt resistance test. In the H2SO4 acid leaching test, efflorescence pattern was the most likely type of decay in yellow and cyan sandstones. Thenardite was the exclusive salt in the yellow sandstone, while gypsum was the mainly salt in the cyan sandstone. Gypsum crust and subflorescence were the most common types of decay for gray sandstone. In the HNO3 acid leaching test, yellow and cyan sandstones did not show obvious variations. For gray sandstone, the secondary minerals were gypsum and dolomite, and crust pattern was observed. In general, the salt weathering of gray sandstone was more severe than yellow and cyan sandstones. The differences in petrography (mainly calcite concentration) and micro-structure of sandstone and the external environment leaded to the differences in the types, amounts, and locations of the salt crystallization in the acid leaching tests. These contributed to the different development of efflorescence, subflorescence, and crust patterns. Our research reveals the petrographic, micro-structural, and environmental constraints for different salt weathering processes of sandstones in the Nankan Grotto. [ABSTRACT FROM AUTHOR]

Solute fluxes in Antarctic meltwaters indicate microbial processes influence chemical weathering. Antarctic cyanobacterial mats dominated by Leptolyngbya glacialis enhance weathering rates at 12 °C. Yet, their effects on nutrient fluxes in colder, nutrient-limited conditions, similar to the McMurdo Dry Valleys environments, are unknown. Here, we investigate biotic and abiotic weathering rates of glaciofluvial sediments at 4 °C and compare results to previous experiments at 12 °C. We also examine the effects of nutrient and salt concentrations on weathering fluxes by comparing the effects of different media concentrations (0.1X and 0.001X: 10 and 1000 times diluted) at both temperature conditions. Our results show limited evidence of biologically mediated silica release at 4 °C, yet microbe-mineral interactions still affect nutrient fluxes, particularly for Ca, Mg, Mn, P, and N. However, a higher initial salt concentration (0.1X media) increased the concentration of solutes released under abiotic conditions. These results indicate that aqueous solutes, temperature and microbial processes are all important factors controlling weathering rates and nutrient fluxes in cold settings. [ABSTRACT FROM AUTHOR]

• The impacts of main factors on salt weathering were revealed. • The thermodynamic crystallization behavior of salt mixture was presented by ECOS-RUNSALT model. • A quantitative method to evaluate the salt weathering damage potential for sandstone grottoes were proposed. A large number of exquisite sandstone grottoes remaining along the Silk Road in Northwest China suffer from severe salt damage due to the vulnerability of the sandstone materials used and long-term continuous fluctuation of environmental conditions. Exploring the mechanism of salt weathering is crucial for the conservation of these grottoes. This study aims to quantitatively analyze the damage potential and the main impact factors of salt weathering in 14 grottoes along the Silk Road that were selected and investigated by using visual evaluation, salt analysis including thermodynamic modeling, and a comprehensive evaluation based on the entropy weight method. The results indicate that salt weathering of the sandstone grottoes is primarily characterized by efflorescences, peeling, and powdering. The overall salt content within the weathering layer typically exceeds a threshold of 1 %. Within the semi-arid area, the humidity fluctuations critical for significant volume changes in crystalline salts fall within the ranges 46–76 % and 16–30 %. In the semi-humid area, these ranges are 58–90 %, 42–50 %, and 16–30 %. A total of 14 salts can precipitate in the study area with NaCl, NaNO 3 , KNO 3 , Na 2 SO 4 · x H 2 O and several double salts occuring most frequently. Generally, the damage degree of sandstones grottoes in the semi-humid area is more serious than that in the semi-arid area. Through a comparison of visual inspection and more comprehensive quantitative evaluation, it has been confirmed that the salt damage is primarily influenced by the factors salt content, salt type, and environmental conditions. Furthermore, the order of influence for each factor on salt weathering can be ranked as follows: salt content > salt type > environmental conditions. This study quantitatively reveals the impact of various factors on salt weathering and proposes a method to evaluate the salt damage potential, which is of great significance for the preventive conservation of sandstone grottoes. [ABSTRACT FROM AUTHOR]

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Rising damp is one of the main problems affecting historical masonry structures worldwide, as it affects the appearance of heritage architecture and reduces strength. In this study, to reproduce the pathologies as much as possible and explain the mechanism, the aging test was set up with the climate data (temperature, humidity, etc.) derived from the real environment in nature at the location of the White Temple Tower, which was the object of this study. The tests mimicked the temperature, humidity, and types of salt solutions as closely as possible. Unlike the traditional aging test (producing specimens in accordance with some standards), two samples of blue brick carvings and blue brick cubes were used for the test. The results show that brick carvings suffered more severe surface degradation than brick cubes under various circumstances. Brick specimens' mechanical characteristics, such as wave velocity and compressive strength, were greatly diminished, and there was a fluctuating trend in surface hardness and color difference. The data indicate a size effect on the weathering between brick carvings and brick cubes, with the former displaying a faster rate of weathering under identical conditions. The experiment successfully simulates some of the phenomena observed in the field and provides an idea for studying the weathering of brick artifacts.

Abstract The fossils of Hamipterus tianshanensis (Wang et al. in Curr Biol 24:1323–1330, 2014) and their eggs have important scientific significance because they can provide unique information about the reproduction, development, and evolution of pterosaurs. The fossils and the rock surrounding them have, however, been weathered, which including powdering and flaking, since they were relocated from Xinjiang to Beijing. The high content of soluble salts is a significant factor in fossil deterioration because the dissolution–recrystallization process can generate tremendous pressure and lead to decreased mechanical strength. This study evaluated the electrokinetic desalination performance for the fossils, and two types of poultices employed including paper pulp from Bioline® and CKS121 (cellulose: kaolin: sand = 1:2:1, w/w). Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), ion chromatography (IC), and other methods were applied to evaluate the desalination effect. The surface salt content reduction by applied direct current (DC) was about 70%, and the inner salt content reduction was about 80%. The experimental results suggest that the electrokinetic method is a promising way to desalinate fossils. Nonetheless, cracks appeared in the surrounding rock crack after electrokinetic desalination, which can be explained by the montmorillonite swelling-induced stresses. Pre-consolidation, especially for electro-chemical method may solve the cracking problem for the clay-rich sandstone desalination.

Salt weathering is considered one of the most important factors leading to the damage of Petra's monuments. Inhabiting or limiting the crystallization of these salts could therefore prevent/slow down the destruction of Petra's sandstones. Using of sodium ferrocyanide as a salt crystallization inhibitor has been proved in the past as a prospective treatment measure against salt weathering. This study is the first to investigate the effectiveness of salt crystallization inhibitor on a stone material loaded with a salt mixture. The effect of sodium ferrocyanide on the crystallization of salt mixtures inside sandstone samples from Petra has been studied. The results showed that using of inhibitor changes the crystal morphology of salts from cubic to dendrites, which makes the drying time faster than that of pure salt solution. Therefore, allows the salt to crystallize on the surface of the stone in the form of harmless efflorescence rather than destructive sub-florescence. [ABSTRACT FROM AUTHOR]

In recent years, with the increasing frequency of human engineering activities, the phenomenon of sodium sulfate erosion has been widely observed in the Loess Plateau. This not only leads to difficulties in land reclamation but also affects human health, posing a significant risk to the investment environment in the Northwest region of China. In this study, three types of loess were treated with sodium sulfate to prepare remolded soil samples with salt content levels of 0%, 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%. Observations and tests were conducted at multiple scales. The results indicate significant differences in the structural characteristics of the three types of loess under the influence of sodium sulfate. The higher the salt content in the loess, the greater the degree of structural damage. Subsequently, macroscopic mechanical properties were determined through direct shear tests, and it was found that as the salt content in the loess increased, the strength decreased. The resulting macroscopic mechanical properties showed a strong correlation with the microstructural characteristics. This study provides valuable insights for soil and water conservation and geological disaster prevention in the Loess Plateau region. [ABSTRACT FROM AUTHOR]

The fossils of Hamipterus tianshanensis (Wang et al. in Curr Biol 24:1323–1330, 2014) and their eggs have important scientific significance because they can provide unique information about the reproduction, development, and evolution of pterosaurs. The fossils and the rock surrounding them have, however, been weathered, which including powdering and flaking, since they were relocated from Xinjiang to Beijing. The high content of soluble salts is a significant factor in fossil deterioration because the dissolution–recrystallization process can generate tremendous pressure and lead to decreased mechanical strength. This study evaluated the electrokinetic desalination performance for the fossils, and two types of poultices employed including paper pulp from Bioline® and CKS121 (cellulose: kaolin: sand = 1:2:1, w/w). Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), ion chromatography (IC), and other methods were applied to evaluate the desalination effect. The surface salt content reduction by applied direct current (DC) was about 70%, and the inner salt content reduction was about 80%. The experimental results suggest that the electrokinetic method is a promising way to desalinate fossils. Nonetheless, cracks appeared in the surrounding rock crack after electrokinetic desalination, which can be explained by the montmorillonite swelling-induced stresses. Pre-consolidation, especially for electro-chemical method may solve the cracking problem for the clay-rich sandstone desalination. [ABSTRACT FROM AUTHOR]

Abstract The mineralogy, geochemical mass balance, sulfur isotope, and micro-structure of the sandstone in the Nankan Grotto were analyzed to explore the weathering mechanisms of the subflorescence and crust patterns. The results revealed that the mineralogical compositions of the rock samples from the subflorescence and crust sites were quartz, feldspar, calcite, and clay minerals. The calcite content was much higher in the crust site than that in the subflorescence site. Based on the microscopic petrographic evidence, the crystallization stress of the thenardite and calcite and the swelling/shrinking stress of the clay minerals led to the detachment of the outer rock layer, after which subflorescence became visible on the newly exposed surface. Solution migration carried Ca2+ from the interior of the rock to the surface, where it combined with CO3 2− and SO4 2− to produce gypsum and calcite on the surface during the drying process, resulting in the formation of the crust. Therefore, the mineralogical composition (especially the calcite content) laid the foundation for the distinct development of the subflorescence and crust. In addition, the microstructure and external environment influenced the amount and location of salt crystallization, eventually leading to thenardite crystallizing within the rock in the subflorescence site while the gypsum precipitated on the surface as a crust. The sulfur isotope analysis revealed that the sulfur in the subflorescence and crust sites was most likely derived from detergents and from the combustion of oil and natural gas. Our research revealed the microscopic weathering mechanisms of the subflorescence and crust patterns in the Nankan Grotto, providing insights on salt weathering mechanisms for stone heritage sites around the world.

Using high-precision CT scanning equipment, two series of tests on frost and salt weathering were conducted to investigate the characteristics of pore change in tuff. Experiments on frost and salt aging were performed with pieces of tuff from the same area of southeast China. One set of tuff samples was soaked in saturated sodium sulfate or magnesium sulfate solutions for 60 days. Another set of tuff samples were subjected to 60 freeze–thaw cycles after being submerged in saturated sodium sulfate or magnesium sulfate solutions for 48 h. Our study demonstrates that processes such as salt erosion and freeze–thaw affect the pore evolution of tuffs significantly. Tuff lost 1.56% of its mass after being submerged in magnesium sulfate solutions for 60 days, while tuff submerged in sodium sulfate solutions gained a negative 0.33% of its mass. After 60 freeze–thaw cycles, the mass loss of tuff samples immersed in sodium sulfate, magnesium sulfate, and distilled water solutions was 3.52%, 3.58%, and 3.82%, respectively. The average porosity of the magnesium sulfate and sodium sulfate test groups increased by 6.59% and 4.14%, respectively, when the number of days of salt erosion was extended from 10 to 60 days. The average porosity of tuff samples immersed in magnesium persulfate and sodium sulfate solutions increased by 2.25% and 2.18%, respectively, as the number of freeze–thaw cycles went from 10 to 60. [ABSTRACT FROM AUTHOR]

The mineralogy, geochemical mass balance, sulfur isotope, and micro-structure of the sandstone in the Nankan Grotto were analyzed to explore the weathering mechanisms of the subflorescence and crust patterns. The results revealed that the mineralogical compositions of the rock samples from the subflorescence and crust sites were quartz, feldspar, calcite, and clay minerals. The calcite content was much higher in the crust site than that in the subflorescence site. Based on the microscopic petrographic evidence, the crystallization stress of the thenardite and calcite and the swelling/shrinking stress of the clay minerals led to the detachment of the outer rock layer, after which subflorescence became visible on the newly exposed surface. Solution migration carried Ca2+ from the interior of the rock to the surface, where it combined with CO32− and SO42− to produce gypsum and calcite on the surface during the drying process, resulting in the formation of the crust. Therefore, the mineralogical composition (especially the calcite content) laid the foundation for the distinct development of the subflorescence and crust. In addition, the microstructure and external environment influenced the amount and location of salt crystallization, eventually leading to thenardite crystallizing within the rock in the subflorescence site while the gypsum precipitated on the surface as a crust. The sulfur isotope analysis revealed that the sulfur in the subflorescence and crust sites was most likely derived from detergents and from the combustion of oil and natural gas. Our research revealed the microscopic weathering mechanisms of the subflorescence and crust patterns in the Nankan Grotto, providing insights on salt weathering mechanisms for stone heritage sites around the world. [ABSTRACT FROM AUTHOR]

During the weathering of stone monuments, salt accumulation and crystallization lead to salt damage. In this study, we investigated the evolution of heritage sandstone salt accumulation, considering the porous system of the stone and humidity conditions. Two types of heritage sandstone were collected from the North Grotto Temple (NGT sandstone, coarse sandstone) and the Leshan Giant Buddha (LGB sandstone, fine sandstone) to conduct a salt weathering test simulating the continuous wick effect under different relative humidity conditions. We monitored the sandstone evaporation rate and macroscopic surface phenomena during the simulation test. We analyzed the sandstone after 10, 20, 40, 80, and 160 days of salt solution rise (capillary action) to investigate the salt accumulation within different stone sections and on the stone surface. Additionally, ultrasonic wave velocity tests were conducted to determine salt damage within the sandstones. Results showed that salt accumulation increased over time in both sandstone types and increased along the direction of capillary rising height, but showing different increasing gradients (i.e. with increasing height, salt accumulation increased only slightly in the NGT sandstone but rapidly in the LGB sandstone). Notably, different salt distributions in sandstones further affected the development of salt damage and variations in the evaporation rate. This study aims to comprehensively understand weathering and salt accumulation in monumental rocks, providing valuable suggestions to effectively preserve these monuments. [ABSTRACT FROM AUTHOR]

This study was dedicated to evaluating the durability of the carbonatic stones of Crac des Chevaliers castle against salt crystallization. Crac des Chevaliers castle is a UNESCO world heritage site located in Syria and is considered one of the most important crusader castles built in the 12th century. Salt efflorescence is a common decay type detected on the stone blocks of this building, so six dolomite stone lithotypes with various structures tested under salt aging in three different salt solutions; sodium chloride, magnesium sulfate, and sodium sulfate. Among those lithotypes were two microbioclastic wackstone and four microcrystalline dolomite. The microbioclastic wackstone had low open porosity (18 and 11 v/v%) compared to the microcrystalline dolomites of about 28v/v% open porosity. Two of the microcrystalline dolomite lithotypes had bimodal pore networks and around 4 v/v% closed pores, however, the other two exhibited very small closed porosity (around 0.35 v/v%). The results revealed that even though the great effect of the open porosity on the durability of the specimens, the closed porosity also had a major role and the weathering form depended on the salt composition and the stone porosity properties. The primary decay type of the specimens in sodium sulfate solution was granular disintegration while pitted surfaces formed in sodium chloride solution, and the exfoliation of the stone surface into thin layers was observable after the aging with magnesium sulfate solution. The effect of NaCl crystallization on the specimen was not as aggressive as that of the sulfates. [ABSTRACT FROM AUTHOR]

Honeycomb weathering is a common phenomenon found on various rock surfaces all around the world. However, honeycomb formation mechanisms are still poorly understood. In this study, we propose a model describing moisture transport within the sandstone and erosion resulting from salt deposition during evaporation of moisture off the rock surface. The moisture transport model is based on the non-linear diffusion equation, where the volumetric moisture content is a combined parameter accounting for the moisture and gas (vapor) content. The moisture transport model accounts for the several-orders-of-magnitude decrease in moisture diffusivity, observed during drying. It was assumed that erosion occurs when the evaporation front is located close to the rock surface. The depth of erosion is proportional to the moisture flow rate through the drying surface. The ABAQUS finite-element software suite was used for numerical solution of the non-linear diffusion equation. The iterative scheme of erosion simulation for different drying cycles was implemented using the Python programming language. Computations were conducted in the 2D setting for the square model with dimensions of 50 mm × 50 mm. Simulation results demonstrate the possibility of obtaining various landform shapes (honeycombs, tafoni) by varying only the value of the distribution of moisture content at the bottom side, simulating the rate of internal wetting of rock. [ABSTRACT FROM AUTHOR]

Climate change is causing damage to infrastructure, ecosystems, and social systems, including cultural heritage sites. In the European part of Russia, there are 20 UNESCO-listed cultural heritage sites situated in different climatic conditions. This study assesses the impact of climate change on these sites by using ERA5 re-analysis data to calculate two frost damage indices and two salt weathering indices for the period 1960–2020. The findings indicate a rise in frost damage and salt weathering at cultural heritage sites in northern Europe, primarily due to changes in air temperature and water in the atmosphere, which are the main parameters responsible for the destruction of stone and brick structures. Given the observed and predicted trends in the main meteorological parameters, the detrimental destructive impact of climate change on cultural heritage sites will only increase. In view of the significant length of Russia from north to south and the difference in climatic conditions, measures for the adaptation and protection of cultural heritage sites must be adapted to local conditions and consider the material from which the object is made. [ABSTRACT FROM AUTHOR]

The present study aimed to discuss the impact of sabkha on the natural and human environments in the study area. It acts as an obstacle to many human activities and development. The study adopted many scientific approaches, such as regional approach and applied approach. Some methodologies, such as the quantitative, morphometric and cartographic methods, focus on the use of GIS environment in analyzing and deducing topographic maps and spatial images using several software’s, such as ArcGIS V.10.5 and ENVI 5.3. A multi-criteria evaluation model (MCEM) was built to assess the sabkha hazardous effect on the urban expansion in the study area. The extent, physical properties and the impact of the sabkhas on the human activities are investigated during the field visits. The sabkha area and the salt weathering are considered as the most effective impacts, where the impact of salt weathering appeared on the buildings in Suez and Ras Gharib. Moreover, the rise of the subsurface water which can increase the subsidence rate are also noticed and recorded. Fourteen localities of sabkhas occupy an area of 156 km² representing about 30% of the total area. Finally, the present study reported the characteristics of sabkhas and discussed their environmental effects on the urban expansion in the study area. [ABSTRACT FROM AUTHOR]

• Hydric (liquid water) dilatation decreases with increasing salinity of pore water. • Salt contamination reverses hygric (water vapour) dilatation phases of clay-rich rocks. • Crystallisation of NaCl develops higher strain than hydration of clay interlayers. • Changes in volume occur more frequently once clay-rich rocks are exposed to salts. • Salt weathering of clay-rich rocks produces granular disintegration and scaling. The mechanisms through which crystallisation of salts and hydration of swelling clays cause deterioration of rocks are generally understood. However, how these two decay mechanisms operate synergistically is less clear. In this study, we investigated the impact of a salt (NaCl) on the deterioration of clay-rich basaltic scoria from which the churches forming the UNESCO World Heritage Site of Lalibela in Ethiopia are hewn. The basaltic scoria is rich in smectite (swelling clay) and zeolitic minerals which have micropores and an affinity for efficient water absorption. Hydric and hygric swelling experiments were carried out on 50 mm cube quarry samples and continuous measurements were taken with Linear Variable Displacement Transformers (LVDT). Hydric (liquid water) tests involved partially submerging the samples in deionised and saline solutions. Hygric (water vapour) tests were done in an environmental cabinet where the RH fluctuated between 60% to 90% RH with salt-free and salt-contaminated samples. The results showed that contamination with salts alters both hydric and hygric behaviour. Hydric swelling was reduced in most samples when contaminated with salt, while the expansion and contraction phases in hygric tests were reversed after contamination with NaCl. Continuous measurement of dilatation allowed us to quantify the strain developed during the phase transition of NaCl. Due to the crystallisation pressure, hygric dilatation increased significantly in salt-contaminated samples. Salt-contaminated samples also showed frequent episodic changes in volume that corresponded both with the hydration/dehydration of clay interlayers and crystallisation/dissolution of NaCl. These volume changes correspond with the damage profile on the surface of the samples, i.e., contour scaling and granular disintegration. The results indicate that the mechanism through which salt contamination accelerates the decay of clay-rich rocks is via an increase in the frequency and degree of hygric dilatation. [ABSTRACT FROM AUTHOR]

Due to precipitation and groundwater level changes, rocks often cycle between dry and wet states. This can cause weathering, which may be exacerbated by the presence of salt. Sandstone is a widely used material in ancient and modern buildings, so the effects of salt during wet-dry cycling are, therefore, of great interest. It is also important in geotechnical engineering to understand its effects on the physical properties of rock. In this paper, sandstone from Wanzhou District, Chongqing, China, was soaked in 0%, 2%, 4%, 6%, or 8% NaCl solutions for 200 dry–wet cycles. The quality, chromaticity, and roughness of the sandstone were measured, and changes in the internal pore structure were studied using nuclear magnetic resonance. The sandstone exhibited three stages of mass loss: a decrease (0–10 cycles), a slow increase (10–140 cycles), and a sharp increase (140–200 cycles). In the third stage, the chromaticity, roughness, porosity, and pore size change significantly. Higher NaCl concentrations cause more serious rock weathering. Salt crystallization increases the pore size, which indirectly accelerates the weathering rate. [ABSTRACT FROM AUTHOR]

Salt weathering resistance is a critical parameter governing the durability of coastal masonry units and mortars. Accelerated weathering cycles are employed at the laboratory to investigate the responses of substrates and mortars upon exposure to salt, moisture, temperature fluctuations and humidity. In this paper, the individual and synergistic performances of bricks and mortar formulations when exposed to accelerated salt weathering cycles are investigated, incorporating the influence of wind on their resilience. The study examines the behaviour of brick-mortar sandwich specimens and separate specimens of bricks and mortar mixtures comprising cement, dry hydrated lime, fly ash, and limestone. These specimens are exposed to repeated weathering cycles in a 5 % sodium sulphate solution. Along with the mass variations during each weathering cycle, physicomechanical, microstructural, mineralogical and morphological characterization of the specimens are used to compare their salt weathering resistance. The results highlight that the responses of individual masonry components might not collectively translate to the overall performance of the combined system due to hygric resistance, which is minimal when the components have comparable pore size distribution. Higher microporosity (pores of diameter between 0.1 μm and 10 μm) and mechanical strength enough to resist the crystallization stresses together provide better resistance to salt weathering to the individual mortars. However, pore structure compatibility and pore fraction similarity between the components govern the behaviour of the combined system and, therefore, reflect the better performance of sandwich specimens with brick and lime mortars. The study demonstrated that wind accelerates material degradation during salt weathering through progressive erosion, accelerated evaporation and subsequent formation of isolated thenardite. • Microporosity and substrate strength govern the salt-weathering performance. • Small pores aid cryptoflorescence; larger pores aid efflorescence. • Wind-driven erosion and evaporation aggravate material loss during weathering. • Accelerated drying causes rapid supersaturation & heterogeneous salt distribution. • Individual units weather differently from masonry systems due to hygric resistance. [ABSTRACT FROM AUTHOR]

Detrital quartz grains extracted from sebkha sediments in southeastern Tunisia underwent scanning electron microscopy analysis to identify sediment sources and assess the influence of the saline environment on the grains. Core sediments collected from Sebkha el Melah and Sebkha Mhabeul cover the last 5000 and 2000 BP, respectively. The uppermost Unit III, present in both cores, exhibits two distinct facies based on the mechanical microtextures of its quartz grains. The aeolian facies sediments are characterized by quartz grains with rounded outlines, upturned plates, and crescentic percussion marks. In contrast, the fluvial facies sediments are associated with quartz grains featuring subangular outlines, v-shaped percussion cracks, conchoidal fractures. Observations on the quartz grains of the sebkhas suggest multiple transportation and processing events, indicating long-distance transport and rapid deposition rates. The majority of quartz grains appear to originate from the surrounding terrain, reflecting the dynamic geological history of the region. This study delves into the connection between microtexture variations on quartz grain surfaces and specific historical climatic conditions in the sebkhas. By examining geochemical variations along the cores, facies with elevated salt concentrations corresponding to warmer periods reveal extensively weathered quartz grains. This substantial chemical alteration is evident through microtextures such as oriented etch pits, anastomosed dissolution networks and solution crevasses. The profound dissolution has significantly impacted the quartz lattice, resulting in the decomposition of the grains and the formation of "cauliflower" or "spongy" shapes, erasing prior microtextures. Conversely, during less warm periods, quartz dissolution was less severe, thereby preserving microtextures. Sand grain surfaces are notably sensitive to both transport processes and variations in the physicochemical environment. In the hypersaline and confined environments of sebkhas in southeastern Tunisia, potent post-sedimentary processes can obliterate and obscure the original microtextures recorded on grains from previous environments due to highly fluctuating physicochemical conditions. • Quartz grain microtextures have been analyzed to identify sediment sources in Tunisian sebkhas. • Fluvial deposits show angular grains with v-shaped cracks, indicating water transport. • Aeolian deposits show rounded grains with crescentic percussion marks, indicating wind transport. • High salt concentrations recorded during warm periods enhance chemical weathering on quartz grains. • Hypersaline conditions can obscure previous textures on quartz grain surfaces. [ABSTRACT FROM AUTHOR]

Using high-precision CT scanning equipment, two series of tests on frost and salt weathering were conducted to investigate the characteristics of pore change in tuff. Experiments on frost and salt aging were performed with pieces of tuff from the same area of southeast China. One set of tuff samples was soaked in saturated sodium sulfate or magnesium sulfate solutions for 60 days. Another set of tuff samples were subjected to 60 freeze–thaw cycles after being submerged in saturated sodium sulfate or magnesium sulfate solutions for 48 h. Our study demonstrates that processes such as salt erosion and freeze–thaw affect the pore evolution of tuffs significantly. Tuff lost 1.56% of its mass after being submerged in magnesium sulfate solutions for 60 days, while tuff submerged in sodium sulfate solutions gained a negative 0.33% of its mass. After 60 freeze–thaw cycles, the mass loss of tuff samples immersed in sodium sulfate, magnesium sulfate, and distilled water solutions was 3.52%, 3.58%, and 3.82%, respectively. The average porosity of the magnesium sulfate and sodium sulfate test groups increased by 6.59% and 4.14%, respectively, when the number of days of salt erosion was extended from 10 to 60 days. The average porosity of tuff samples immersed in magnesium persulfate and sodium sulfate solutions increased by 2.25% and 2.18%, respectively, as the number of freeze–thaw cycles went from 10 to 60.

Cavernous weathering is commonly found on sandstone slopes in different environments. Either a single dominant process or polygenetic agents require to be invoked in order to interpret the development. The Yongningshan hill of the central Loess Plateau is representative of cliff dwellings in Northwest China, which is characterized by well‐developed cavernous weathering features and provides a good opportunity for the better understanding of sandstone weathering in the Loess Plateau. Multiple methods, including field survey, in‐situ rock strength measurement, along with experiments on samples for microscopic observation, element composition and salt chemistry, were employed to investigate the controlling factors of cavernous weathering. The results show that cavern development is different on the four slopes with the western slope hosting massive honeycombs, tafoni and hardened surfaces. The porous and permeable aeolian sandstones are fundamental, because they provide space and pathways for the transportation of water and salt, honeycombs dominantly aligning within the lamination of cross‐beds. The environmental factors such as the seasonal wetting and drying cycle, aeolian salt, moisture and water vapor are key factors for the development of cavernous weathering forms. The northern and northwestern wind‐blown dust storms have brought abundant salts, the lengthier dry periods of the wetting and drying cycle being beneficial for salt accumulation within caverns, favoring salt weathering. [ABSTRACT FROM AUTHOR]

The Santo Domingo Diocesan School (Orihuela, SE Spain) is a singular case study that relates air quality monitoring and stone conservation. The monument suffers severe damage due to salt crystallization by rising damp, which is related to the indoor environment dynamics, high groundwater salt content, and microstructure, the building's porous stone (biocalcarenite). Results revealed that 222Rn concentration in indoor air is low due to the building's high ventilation rate, despite the medium-low geogenic radon potential in the area. Wavelets analysis showed that ventilation is caused by outdoor and indoor temperature variations and directly affects the 222Rn and CO2 dynamics inside the church. CO2, as well as relative humidity (RH), presented periodicities with intermediate frequencies (5–8 days) related to visits. These RH and temperature (T) variations intensified the salt damage by increasing the frequency of dissolution-crystallization cycles. The mineralogical characterization and geochemical calculations concluded that chlorides (halite and sylvite), sulfates (thenardite, epsomite, hexahydrite and aphthitalite) and nitrates (niter) present from dissolution forms to whiskers and hopper-type morphologies. This indicates high saturation values and, therefore, higher crystallization pressure values within the porous media of the biocalcarenite. On the contrary, the near-equilibrium crystal shape and incongruent precipitation reaction for humberstonite suggest a lower alteration for this salt on the building stone. [ABSTRACT FROM AUTHOR]

Cavernous weathering (honeycombs, tafoni) is a common weathering feature of both natural and artificial exposures. Honeycombs are known from various environments but are best developed in coastal areas. There are several theories as to their origin, with salt weathering currently being the most favoured by the geomorphological community. To test if the drying pattern of salt‐laden moisture results in honeycombs (the theory of Huinink et al., Earth Surface Processes and Landforms, 29(10), 1225–1233, 2004), coastal honeycombs in the metasandstone of Tuscany (Italy) were studied both in the field and with a laboratory evaporation experiment. The depth of the evaporation front was measured by the 'uranine‐probe' method in the honeycomb pits and lips. The evaporation rate was calculated from the depth of the evaporation front as well as the climatic conditions at the study site. Lastly, the amounts of precipitated salts were estimated based on the evaporation rate of seawater. In the evaporation experiment, the evaporation front retreated faster in the lips than in the pits, and the field measured evaporation front was closer to the surface in the pits (2 mm) than in the lips (7 mm). Thus, the calculated evaporation rate was higher in the pits than in the lips (16.1 and 4.6 mm/yr, respectively). Similarly, the amount of salts precipitated was also higher in the pits (0.7 kg/m2/yr compared to 0.2 kg/m2/yr in lips). Faster salt deposition in the pits as well as the evaporation front position fits well with the theory of Huinink et al. Based on surface tensile strength measurements, case hardening is not protecting the honeycomb lips. [ABSTRACT FROM AUTHOR]

The structural damage caused by salt weathering in loess soil is a crucial factor leading to soil erosion and geological disasters in the Loess Plateau region of China. However, the impact of salt weathering on the structural damage and strength degradation of soil under unidirectional dehumidification conditions remains unclear. To gain a comprehensive understanding of the structural damage process and strength characteristics of soil under salt weathering, this study focuses on Q 2 loess (silt loam, a loose aeolian deposit) in Fugu County, Shaanxi Province. Multiscale observations tests and direct shear tests were conducted on samples with varying sodium sulfate contents. The research findings indicate that at the macroscopic scale, The 3.0 % salt content sample experienced the most severe salt weathering, exhibiting characteristics of powdering and disintegration. Moreover, it exhibited the highest expansion displacement, reaching 22 mm. In addition, all samples go through three stages during the entire salt weathering process, namely budding, growth, and stable stages. At the mesoscopic scale, the displacements and expansions caused by salt crystallization growth on soil particles and pores were captured in real-time. Furthermore, the crystallization behavior of sodium sulfate differs on the surface and near-surface of samples as water content decreases, resulting in four distinct layering structures. At a microscopic scale, salt weathering leads to the formation of aggregates and the generation of numerous expansion pores within samples. Not only that, the shear behavior of samples transitioned from strain-softening to strain-hardening after salt weathering, with the peak strength significantly weakened compared to the residual strength. Additionally, before a salt content of 1.5 %, the cohesion of samples experiences the greatest decline, gradually slowing down thereafter, ultimately decreasing by 16 kPa. However, the decrease in the friction angle is less significant, with only a decrease of 4.8°. In summary, an increase in sodium sulfate content exacerbates the occurrence of "salt crystallization-induced expansion" and "soil drying-induced coagulation" phenomena in saline soils, resulting in severe damage to soil structure and strength. This study will provide valuable insights for soil and water conservation as well as disaster prevention in the Loess Plateau region, serving as a crucial reference for future research and engineering practices in the region. The samples were sheared after undergoing salt weathering. The expansion displacement of samples was obtained. The crystallization behavior of salt in samples was directly observed. The phenomenon of crystallization differentiation was explained. The damage characteristics and mechanisms of soil structures were revealed. [ABSTRACT FROM AUTHOR]

Climate change is causing damage to infrastructure, ecosystems, and social systems, including cultural heritage sites. In the European part of Russia, there are 20 UNESCO-listed cultural heritage sites situated in different climatic conditions. This study assesses the impact of climate change on these sites by using ERA5 re-analysis data to calculate two frost damage indices and two salt weathering indices for the period 1960–2020. The findings indicate a rise in frost damage and salt weathering at cultural heritage sites in northern Europe, primarily due to changes in air temperature and water in the atmosphere, which are the main parameters responsible for the destruction of stone and brick structures. Given the observed and predicted trends in the main meteorological parameters, the detrimental destructive impact of climate change on cultural heritage sites will only increase. In view of the significant length of Russia from north to south and the difference in climatic conditions, measures for the adaptation and protection of cultural heritage sites must be adapted to local conditions and consider the material from which the object is made.

This study deals with stone deterioration in underground cultural heritage and geoheritage, correlating the origin, compositional features, and space–time changes of salt weathering with the rock properties (petrography and geochemistry) and environmental setting (microclimate and chemistry of rainwater and groundwater). The material of study is Oya-ishi, one of the best-known building stones of Japan; it is a porous and soft acid tuff with a long tradition of use in historical and modern architecture. A number of underground sites of cultural or commercial significance was investigated in central Japan, where Oya stone appears extensively affected by efflorescence growth. The efflorescences are composed of mixed sulfates, including gypsum, mirabilite, and thenardite, whose development depends on the stone–environment interaction. The underground environment is extremely humid and water is the main driving force of salt weathering, having a twofold function. First, it conveys the alteration of the rock components, in particular pyrite, glass (pumice, fiamme, and shards), zeolites (clinoptilolite), clay minerals (smectites), and feldspars, which release SO42−, Na+, and Ca2+ ions. Second, water controls the salt stability and cycles of crystallization/deliquescence and hydration/dehydration, depending on the site depth and seasonal microclimate fluctuations; in this regard, knowing the specific thermodynamic behavior of the phases involved can help predicting where and when salt weathering and the resulting stone damage are most severe. [ABSTRACT FROM AUTHOR]

Salt crystallization and phase change in porous media cause significant deterioration of cultural heritage made of stones and bricks. In this study, laboratory experiments on salt weathering of sandstone from the Dazu rock carvings (DRC) in Chongqing, southwest China, were carried out by exposing them to cycles of temperature and humidity change. Mirabilite, the main component of the salts in DRC that readily undergoes phase change, was utilized for the study. Three groups of Dazu sandstone (DS) samples with high (2.4 mol/L), moderate (1.5 mol/L) and low concentrations (1.0 mol/L) of sodium sulphate were prepared; and two conditions, high‐temperature with low‐humidity and low‐temperature with high‐humidity, were designed to simulate the fluctuations of temperature and humidity in the Dazu area. After several cycles, the dehydration and moisture absorption of DS under these two conditions forces the phase change of sodium sulphate between thenardite (Na2SO4) and mirabilite (Na2SO4·10H2O), causing different levels of damage. A combination results of sample length, weight, microstructure, and mechanical property variations show that the damage effect of the thenardite formed during dehydration is more significant than that of mirabilite in moisture absorption. During these cycles, there is noticeable salt migration and the local concentration of salts is influenced by the microstructure of the stone and the distribution of clay minerals. Samples with high salt content show disintegration of the stone into powder, while those with moderate salt concentration show flaking and salt accumulation on the surface. These types of damage correspond with observations of natural weathering in the field. The experiment shows that no obvious damage takes place when the salt content is lower than 0.67%. These results contribute to a better understanding of the effects of salt weathering on sandstone and provide references for choosing correct prevention and protection measures for the world heritage site DRC. [ABSTRACT FROM AUTHOR]

The presence of salts during cyclic wet and dry conditions can cause weathering of rock and is the main cause of damage to ancient and modern buildings. Accordingly, salt weathering, especially of granite, has aroused great interest. Determining the relationship between wet–dry cycling and the physical properties of rock is of great significance to geotechnical engineering. In this paper, granite samples were processed into two shapes (round and semicircular) and subject to 0, 10, 20, 30, 40 and 50 wet–dry cycles, with the wetting achieved with 0%, 5%, 10% or 20% concentrations of Na2SO4 solution. The mass loss, roughness and indentation hardness of granite samples all changed to some extent with cycle number, with greater changes occurring at higher salt concentrations. Rock shape also affects the extent of weathering damage, as surface area and features such as corners facilitate the ingress of salt solution. [ABSTRACT FROM AUTHOR]

Cellulose poulticing is a widespread method of desalination in practice for removal of salts from ancient structures. Optimization of the process is essential, considering that poulticing/desalination is the prime step during the protection of existing structures in the coastal zones. Even though poulticing is widely used in European countries, it is not common in India, because the principle and efficacy of the method have not been studied so far for masonry materials in the ancient Indian structures with specific microstructure. The present study analyses the effect of cellulose poulticing in bricks considering the role of pore size in the substrates and the removal of different types of salts depending upon the pore distribution. The process was found around 74% more efficient in removing Na2SO4 than NaCl in materials with more micropores (pore size <1 µm), as demonstrated from scanning electron microscopy images and analysis of pore structure using mercury intrusion porosimetry on brick samples. Interesting results on the unsuitability of cellulose poulticing in certain materials and the reasons for the same were obtained, which are based on the predominant transport mechanisms for salt removal. The study would be a reference for initiating cellulose poulticing as an effective desalination method in the ancient structures of coastal southern India. [ABSTRACT FROM AUTHOR]

Over the past 10 years, our research team has holistically studied the environmental aspects of the conservation and restoration of the Hagia Sophia, which is suffering from severe degradation of its wall paintings, including the exfoliation of wall paintings and inner finishing materials, mainly due to salt crystallisation. In the present study, we investigated the influence of environmental factors and wall composition on the hygrothermal behaviour in the structure, such as moisture accumulation and evaporation within the walls, which significantly affect salt crystallisation. The differences in distribution of high moisture content at second cornice are depending on the azimuth, and the high correlation between high moisture content and deterioration severity is significant. A two-dimensional numerical model of the simultaneous transfer of heat and moisture considering the measured material physical properties and wall composition of the exedra wall is developed to quantitatively investigate the influence of environmental factors on moisture accumulation. Numerical results show that infiltrated rainwater tends to accumulate because the original builders used connection mortar, which has a much larger moisture diffusivity than that of modern mortar, and the accumulated water at the bottom of the wall is difficult to drain owing to the shape of the wall. In the northwest exedra, the influence of wind-driven rain on water accumulation is similar to that of runoff rainwater from the upper roofs, which probably causes deterioration over a wide area. In addition, the effect of the deterioration suppression measure by the re-covering of the outer surfaces of the west wall in 2013 is verified, and an appropriate suppression measure against water permeation is examined using a numerical model. [ABSTRACT FROM AUTHOR]

Abstract The Buddhist sacred site of Taya Caves is a gem hidden underground in Yokohama, Japan. The caves were excavated and sculpted into bare rock by Shingon Buddhist monks from the Kamakura until the Edo period (thirteenth–nineteenth century), and dedicated to ascetic training, rituals, and pilgrimage. They are a maze of halls and galleries decorated with hundreds of rock-cut reliefs, picturing deities and masters of Buddhism, temples and shrines, real and fantastic animals, vegetal motifs, mandalas, zodiac signs, family crests, etc. The history and rock art of Taya Caves and the urge to preserve their cultural value led to this first-ever scientific investigation, dealing with the stone properties, deterioration, and environmental setting. Textural, mineralogical, geochemical, and petrophysical investigations were combined with a microclimate monitoring and chemical analyses of groundwater and rainwater. The caves are excavated into a clay-rich fossiliferous siltstone, extremely soft and porous and highly susceptible to water-driven weathering. Water represents a constant in Taya Caves, either flowing, dripping, and stagnant; or rising from the subsoil; or related to the extremely high relative humidity. Crusts and efflorescences represent important indicators of mineral dissolution and mobilization. The crusts are made of gypsum, crystallized from the dissolution of calcareous bioclasts and oxidation of pyrite, with minor calcite. The efflorescences are composed of chlorides, phosphates, sulfates, and carbonates, possibly deriving from agrochemicals and the surface vegetation cover. The salt weathering is strictly related to the microenvironmental variables and physico-chemical properties of the phases and waters involved. Rock-water interaction is particularly damaging even considering just the physical mechanisms. The stone is strongly sensitive to water absorption, hygroscopic adsorption, and slaking: the stresses generated by in-pore water and air movement and the swelling clay minerals may lead to rapid disintegration, especially during cyclic processes. This research is expected to raise concerns about the safeguard of Taya Caves and support future monitoring and conservation plans, and to foster a wider promotion and valorization of this heritage site.

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The Santo Domingo Diocesan School (Orihuela, SE Spain) is a singular case study that relates air quality monitoring and stone conservation. The monument suffers severe damage due to salt crystallization by rising damp, which is related to the indoor environment dynamics, high groundwater salt content, and microstructure, the building’s porous stone (biocalcarenite). Results revealed that 222Rn concentration in indoor air is low due to the building’s high ventilation rate, despite the medium-low geogenic radon potential in the area. Wavelets analysis showed that ventilation is caused by outdoor and indoor temperature variations and directly affects the 222Rn and CO2 dynamics inside the church. CO2, as well as relative humidity (RH), presented periodicities with intermediate frequencies (5–8 days) related to visits. These RH and temperature (T) variations intensified the salt damage by increasing the frequency of dissolution-crystallization cycles. The mineralogical characterization and geochemical calculations concluded that chlorides (halite and sylvite), sulfates (thenardite, epsomite, hexahydrite and aphthitalite) and nitrates (niter) present from dissolution forms to whiskers and hopper-type morphologies. This indicates high saturation values and, therefore, higher crystallization pressure values within the porous media of the biocalcarenite. On the contrary, the near-equilibrium crystal shape and incongruent precipitation reaction for humberstonite suggest a lower alteration for this salt on the building stone.

Tafoni are a type of cavernous weathering features widespread in different climate zones around the world, but their origin has not been fully understood. Little attention was paid on tafoni in conglomerates. Danxiashan UNESCO Global Geopark, located within the subtropic humid region of South China, has a landscape of large tafoni that occur on cliffs of red conglomerates. Both the Dinosaur Rock and Pagoda Peak of the geopark were selected to investigate the formation mechanisms of tafoni in conglomerates. During the field investigation, the size, rock hardness, and the external and internal meteorology of tafoni were measured and tested. The texture and composition of rock samples were observed, and the ion chromatography experiments were performed as well. Results show that tafoni have well ellipsoidal openings. Clasts of the conglomerates are largely sub-rounded and poorly sorted, and the cement is dominantly composed of calcite and iron oxide. The hardness of the lips is almost equal to that of the columns, and both are slightly higher than the backwalls. Compared with the external intense environmental changes, the interior of the tafoni is characterized by smaller temperature and relative humidity ranges and windless condition. Therefore, the porous and permeable conglomerates provide favorable lithology for tafoni development, and the micro-environment within the caverns is conducive to improving water utilization efficiency and enhancing salt weathering. The salts mainly consist of sulfates and nitrates, which might be derived from frequent raining, water evaporation and red beds as well. Consequently, tafoni are the result of the synergistic effects by multiple factors, rather than a single mechanism. [ABSTRACT FROM AUTHOR]

The current study aims to assess the compatibility between tuffeau and Richemont stone exposed to salt weathering, the most frequent physical-mechanical weathering process. Different experimental tests, both in macro- and in micro- scale, were performed on the aged stone samples underwent 20 wetting-drying cycles using salt solution of sodium chloride. The results of the aged samples were then compared with the already results belonged to the fresh samples. In the accelerated ageing tests the stone samples were situated in two different methods: the isolated stone samples and the pair of stone samples, i.e. one tuffeau sample linked to one Richemont sample. The linked test method was adopted to simulate the in-situ situation of the stones. The main results show that the microstructural characteristics of the stone (pore size distribution, water transfer properties and tensile strength) strongly reflect the stone resistance versus the salt weathering. Moreover, the results indicate that the integrity of tuffeau stone samples increased when linked to the Richemont stone samples referring to the presence, in partial way, the compatibility between the two stones. However, the limited conditions of the salt crystallization test (i.e. only 20 wetting-drying cycles) were not sufficient to detect the complete behavior of the two stones towards the salt weathering. Therefore, the current results confirm that the compatibility assessment between the stones cannot be judged based on the results presented in this study.

Salt-induced deterioration of architectural heritage is accelerated drastically in marine environments. This paper investigates the deterioration mechanism of the Shore Temple using various analytical techniques. Deteriorated and pristine stone samples were analyzed using X-ray fluorescence spectroscopy (XRF), thin section studies, and SEM in order to understand the deterioration mechanism. The meteorological and micro-climatic conditions of Shore Temple in the tropical Indian climate were studied, as they have played a vital role in the deterioration of the stone matrix. The sides of the temple that face the sea as well as the upper part of the temple show intense alveolarization and the stone variety was petrologically identified as “garnetiferous hornblende biotite granite”. The evaluation of results in terms of the efficacy of ethyl silicate consolidation of stone after desalination is very difficult due to continuous sea sprays. The compatible lime rendering evidenced in the shelter area and then scientifically examined during this study may be applied as a protective layer to safeguard and conserve the lone Pallava edifice on the seashore from deterioration in tropical and hygric saline conditions.

Salt weathering is a significant process affecting the deterioration and conservation of stone‐built heritage in many locations and environments. While much research has focused on the impact of salt weathering under arid or coastal conditions with characteristic climatic conditions and salt types, many sites found to be experiencing salt‐induced deterioration, such as sandstone rock‐hewn cave temples in Gansu Province, China and sandstone buildings in the northern UK, experience high humidities, moderate temperature ranges, and different salt types. To evaluate the impact of salt weathering on sandstone‐built heritage under such mild humid environmental conditions, a lab simulation experiment was designed. The experiment was carried out on three types of sandstone (used in the northern UK and Gansu Province, China) and utilized a realistic diurnal humidity and temperature cycle (85% RH/16°C + 60% RH/22°C), and three widespread damaging salts, that is, Na2SO4, MgSO4, and the mixture of Na2SO4–MgSO4. The nature and extent of deterioration was monitored by photography, weight loss, and the changes in petrophysical properties measured using hardness, ultrasonic pulse velocity (P‐wave velocity), water absorption coefficient by capillarity, open porosity, and apparent density. All three sandstones were found to be susceptible to MgSO4 and the mixture of Na2SO4–MgSO4, but weakly affected by Na2SO4 under mild humid environmental conditions. [ABSTRACT FROM AUTHOR]