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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]

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]

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]

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]

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]

Grottoes encounter significant challenges, such as weathering and water erosion, seriously threatening their preservation. Current laboratory research on grotto deterioration predominantly centers on characterizing the deterioration process, making it challenging to conduct cross-scale quantitative analysis of the intricate rock evolution process. This study examines sandstone from Baoding Mountain in Dazu and employs a cross-scale experimental approach to conduct dry–wet cycle tests on salt weathering. By integrating particle flow numerical simulation and inorganic salt deliquescence theory, the study elucidates the mechanism of aging degradation of sandstone caused by various salt solutions. The results indicate that the hierarchical order of the influence of salt solution types on rock degradation, ranked from highest to lowest, is as follows: sodium sulfate, magnesium sulfate, and sodium carbonate. The sandstone samples exhibited significant damage after 7 and 18 cycles of medium and high-concentration sodium sulfate solutions, respectively. In contrast, the strength of sandstone samples decreased by only 5.3% on average after 20 cycles of medium and low-concentration sodium carbonate solution. Subsequently, particle flow was analyzed numerically using the variable stiffness theory. The influence of salt solution on sandstone’s strength, deformation characteristics, internal pores, and fracture development can be quantitatively evaluated by examining five core mesoscopic parameters. Furthermore, the study highlights that the relative humidity required for the deliquescence of sodium sulfate and magnesium sulfate crystals exceeds 80%, making these crystals vulnerable to the repetitive dissolution–migration–precipitation processes in the climate conditions of Baoding Mountain, thereby accelerating the deterioration of rocks in the region. [ABSTRACT FROM AUTHOR]

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]

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]

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]

Dimension and ornamental stones used for built heritage are frequently affected, under all climates, by intense weathering induced by the transport of saline solutions. Accordingly, researchers addressed the weathering mechanisms induced by salts (primarily Na2SO4), the stresses generated in the host material, and the durability of ornamental and dimension stones. This study investigates the behaviour of four sedimentary lithotypes, differing in texture and structure (Breccia Aurora, Rosso Verona, and fine- and coarse-grained Vicenza Stone) exposed to a selection of saline solutions, aiming at evaluating their susceptibility to weathering and the influence of petrographic features on durability. The chosen Na2SO4, MgSO4, Na2CO3, NaCl, and KNO3 solutions include the anions characterizing the major saline sources affecting built heritage: capillary rise, acid rain, atmospheric particulate deposition, bird or other animal scat, and de-icing salt contamination. The petrophysical properties of unweathered and salt-weathered samples were characterized by relative mass variation estimation, capillary rise, and hygroscopic absorption-based porosimetry. Scanning Electron Microscopy coupled with microprobe allowed studying the morphological changes triggered by weathering and analysing the chemical composition of the efflorescence crust. The whole of data, consistently with literature, allowed inferring pore type and distribution as the main intrinsic parameters controlling salt weathering susceptibility. Moreover, Na2SO4 and Na2CO3 proved to be the most harmful, probably due to their ability to crystallize in different hydration stages at room temperature. The comparative analysis of the induced weathering can help to choose suitable dimension stones for new buildings or restoration replacements. [ABSTRACT FROM AUTHOR]

The textural properties of a rock and the characteristics of its pore network are intrinsic variables to consider when investigating the resistance of rock to weathering. To establish the influence of these variables on the effectiveness and progression of weathering processes, two lithotypes of a limestone were analyzed with respect to their texture and porosity, and to their performance during artificial weathering experiments. The studied rock is Vicenza Stone, a bioclastic limestone with heterogeneous texture, variable grain size from fine to coarse, and high levels of open porosity (27–28%). Two sets of samples were obtained from a quarry, defining coarse-grained (CGV) and fine-grained (FGV) lithotypes of Vicenza Stone. Multiple techniques (optical microscopy, scanning electron microscopy, image analysis, mercury intrusion porosimetry, hygroscopicity, ultrasound, and water absorption) were used to characterize the texture and porosity of the limestone. The sample sets were subjected to freeze–thaw (UNI 11186:2008, Cultural heritage—Natural and artificial stone—Methodology for exposure to freeze-thawing cycles, 2008) and salt-crystallization (partial continuous immersion method with a Na2SO4-saturated saline solution) weathering experiments to investigate the processes and progression of mechanical and chemical weathering. Differences in freeze–thaw-induced micro-cracks and in the deposition of secondary micrite between the lithotypes show that the CGV has an overall higher susceptibility to freeze–thaw weathering than FGV. Salt-weathering processes induced micro-crack formation, material dissolution, and secondary precipitation, suggesting the simultaneous occurrence of mechanical stress and chemical dissolution–precipitation processes. FGV is more prone to salt-induced weathering than CGV, whereas CGV is susceptible to the wide thermal excursions of freeze–thaw weathering. [ABSTRACT FROM AUTHOR]

To assess salt damage risks in building materials and geomaterials, the key components to identify are the accumulation of salts and the damage propagation. Experimental data combining both are scarce but offer an additional richness for understanding the coupling between transport and mechanics in the context of salt crystallization in porous media. Here, we quantify the drying of sodium sulfate and sodium chloride solutions from Savonnières limestone together with the damaging character of anhydrous sodium sulfate and halite precipitation, respectively. Repeated wetting–drying cycles are performed, by using salt solutions in the rewetting phase and by drying at an elevated temperature of 45 °C. The drying and deformation dynamics are characterized by means of high-resolution neutron radiography, with a moisture content resolution of 0.04 kg/m3 and a spatial resolution of 13.5 μm/pixel. Precipitation occurs inside the specimen by treating the upper volume of the specimen hydrophobically. High Peclet numbers are found, representing a long first drying stage leading to salt accumulation in a localized zone, increasing the damage risk. In-pore crystallization of halite during drying of 5.8 molal sodium chloride solutions is particularly damaging for our type of samples. Large deformations are observed already during the first cycle, indicative of crack formation. With 1.4 molal sodium sulfate solutions, no damage is observed upon precipitating the anhydrous sodium sulfate crystal, but the drying rate decreases with every cycle due to augmented pore clogging. [ABSTRACT FROM AUTHOR]

The Tropea cliff (southern Calabria, Italy), affected by fast weathering processes and landslides, has needed various interventions of slope consolidation aimed at reducing hazard conditions. These interventions were performed with low environmental impact techniques in order to preserve the architecture and the landscape of the area. In 1998, a consolidant resin was tested on a limited portion of the Tropea sandstone cliff. The purpose of this test was checking the resin behavior against erosion processes. Previous researches showed a good resistance to erosion with only a slight opacification of the treated sandstone portion. This paper aims at studying the behavior of the consolidant resin after 17 years from its application. The research was performed by several laboratory tests. The Fourier transform infrared spectroscopy analysis has indicated that the consolidant product was an epoxy resin. The scanning electron microscopy analysis has shown that the resin has penetrated into the rock up to 2 mm. The chemical analysis further testified that the tested surface is characterized by higher content of soluble salts than the non-treated surface. The salt content is mainly related to the infiltration of water enriched in soluble salts, due to the marine aerosol. The soluble salts, crystallizing in the rock pores and between the mica sheets, produce an increase of physical stress that is responsible of the exfoliation processes of the resin. Therefore, the use of epoxy resin on the tested sandstone rocks increases the strength on the outer rock surface, with a consequent good resistance to erosion processes just in a restricted period. Overtime, water infiltration introduces dangerous soluble salts below the treated surface, causing salt crystallization with important exfoliation processes of the treated rock surface. [ABSTRACT FROM AUTHOR]

The disintegration of rocks by weathering plays an important role in the occurrence of Acid Mine Drainage (AMD), which is the environmental problem caused by the exposure of sulfide minerals to water and oxygen. The weathering of rocks is, generally, classified into physical or chemical weathering. However, there are few studies that focus on the complex interaction between physical and chemical weathering of rocks and on the effects of the interaction on the occurrence of AMD. This paper elucidates the complex interrelation between physical and chemical weathering of rocks as well as the progress of AMD through leaching test and weathering test with argillaceous rocks taken in open-cast coal mine in Indonesia in addition to sample analysis before and after the wetting and drying cycle: the rock samples were exposed to oxygen and water during the cycle. The results indicated that the argillaceous rocks which consist of sulfide and/or sulfate caused chemical weathering with micro-cracks on the surface of rocks through the dissolution of soluble iron and sulfur during the occurrence of AMD. Additionally, physical weathering of rocks due to clay minerals was accelerated by chemical weathering with the development of cracks with the occurrence of AMD in the argillaceous rocks containing kaolinite and pyrite. Although weathering of rocks also accelerated AMD, it was concluded that the sulfur content, the form of sulfur and iron in rocks, and the supply of oxygen significantly contributed to the occurrence of AMD. [ABSTRACT FROM AUTHOR]

The deterioration of a stone material is related to its pore structure, which affects the interaction between surface and environmental agents. Indeed, salt crystallization is one of the most dangerous weathering agents in porous building materials. The crystallization pressure of salt crystals, growing in confined pores, is found to be the main cause for damage. The consolidation of such degraded stone materials represents a crucial issue in the field of restoration of cultural heritage. This paper presents the results of a laboratory experimentation carried out on Modica stone, a limestone largely used in the Baroque architecture of eastern Sicily. Several specimens, collected from a historical quarry near the city of Modica, were artificially degraded by salt crystallization tests. Then, degraded samples were treated with three different consolidating products: a suspension of nanolime in alcohol, a suspension of nanosilica in water, and ethyl silicate dispersed in white spirit. A systematic approach, including mercury intrusion porosimetry, peeling tests and point load test, was used to evaluate the correlation between the salt crystallization and the micro-structural features of the limestone, as well as the efficacy of treatments. The consolidating behavior of the tested products was also appraised by repeating salt crystallization tests after consolidation, in order to assess the resistance of treated stone to further salt crystallization phenomena. Results showed that nanolime provides a good resistance to the stone; conversely, ethyl silicate, although inducing an enhancement of stone cohesion, leads to an increase of the crystallization pressure, which generates dangerous susceptibility to weathering. [ABSTRACT FROM AUTHOR]

Salt crystallization is a strong weathering agent in porous building materials. The crystallization pressure exerted by salt crystals, growing in confined pores, is found to be one of the main causes for damage. This paper presents the results of laboratory experimentation carried out on the Neapolitan Tuff, a pyroclastic rock largely used in Campanian architecture. Several specimens, collected from a historical quarry near the city of Naples, were treated with two different consolidating products: a suspension of nanosilica in water (Syton X30) and ethyl silicate (Estel 1000) dispersed in organic solvent (TEOS). Untreated and treated samples were then artificially degraded using salt crystallization tests in order to assess the effectiveness of consolidation treatments. A systematic approach, including mercury intrusion porosimetry, peeling tests and point load test, was employed to evaluate the correlation between the salt crystallization and the micro-structural features of the tuff. In addition, in order to make a correlation between porous structure of materials and susceptivity to salt crystallization, the calculation of the crystallization pressures was performed. In all samples, at the early stage of crystallization, the presence of gypsum was revealed, coming from the precipitation of sulphate ions, introduced during the test, and sodium ions, coming from the zeolites within the stone. Results showed that both consolidants increase the resistance of tuff to salt crystallization, although they induce an increase in crystallization pressure. Ethyl silicate, however, shows a better behaviour in terms of superficial cohesion, even after several degradation cycles. [ABSTRACT FROM AUTHOR]

We investigated the behaviour of salt solutions during the drying process in porous stone and the extraction of salts by paper pulp poultices (PPP). The investigations were carried out at a 300 year old boundary wall of the Worcester College in Oxford, UK, as well as under laboratory conditions. The laboratory blocks of porous, bioclastic limestone (Aflenzer stone, Austria) were cut into stone cubes and prisms (5 × 5 × 5 and 5 × 5 × 20 cm) and soaked first with ultrapure HO and second with different concentrations (0.1, 0.5 and 1 mol l) of a saline solution of NaCl and NaSO to determine their behaviour during the dehydration process under different conditions. After determining the capillary absorption coefficient and the capillary rise behaviour of the stone cubes, we sampled material by PPP and by drilling. The samples were immersed in ultrapure water and the salt ion content was measured via conductivity and ion chromatography (IC). The main aim of the laboratory analysis was to investigate the effectivity of the PPP in extracting salts from the stone and to derive a semi-quantitative calibration (PPP results vs. original salt content). The field work at the college boundary wall comprised sampling (PPP and stone surface material) at surfaces of different weathering features. Finally, the field work results were compared to the laboratory work. The lab experiment results show that approximately 24% of the salts within a 100% saturated stone cube moved into the poultice within the 1 h of application. At 75% and lower saturation degrees, only 14-11% of the salts moved into the respective poultices. For the field setting, the amount of anions extracted by PPP is 6-63% (mean 20.7%) of the amount found in the stone samples. The spatial distribution of salt ion concentrations, collected by poultices, corresponds with the 'hot spots' of weathering. [ABSTRACT FROM AUTHOR]

The reconstituted stone used in the Orval Abbey is highly susceptible to salt weathering. It was produced from debris of natural stones (which were at that time in short supply) by craftsmen working in the Abbey and its composition is highly variable. The major salt involved in weathering is sodium sulfate (NaSO). This study focused on the thermal behavior of a reconstituted stone with various degrees of weathering observed on-site and it was studied by passive and active infrared thermography (IRT), and on the evolution of reconstituted-stone samples in a salt uptake experiment in the laboratory. On-site, the thermal responses of salt-weathered and unweathered zones were different. IRT allowed to detect unweathered though highly salt-laden zones, although correlations between thermal response and salt concentration are difficult to establish due to the influence of surface properties (color and roughness). In the laboratory, samples of the reconstituted stone were submitted to successive immersion-drying cycles in solutions of NaSO with 7, 14 and 26 % concentration and characterized by weighing, surface colorimetry and active IRT. Results showed that the thermal response (increase in surface temperature due to flash excitation: T) increased with salt concentration and with the number of cycles, as long as sample disintegration had not started. Then, it decreased and stabilized, whatever the salt concentration. Those results indicated that an increase in the thermal response of building materials (in active IRT) can be interpreted as an indicator of salt accumulation, possibly leading to damage. IRT proved to be an interesting non-destructive technique in this respect. [ABSTRACT FROM AUTHOR]

Ancient monuments are significant for the cultural identity of countries and they are also very important from economical point of view. There are a lot of environmental damages that affect building materials and monuments. Therefore, the preservation of the monuments has become a vital challenge. Gradual natural destructive factors including freezing and thawing, heating and cooling, salt weathering and acidic rainfall play an important role in destruction of monuments. In this study, for assessment of weathering effects on engineering properties of Hamedan granitic monuments, heating and cooling (up to 600 cycles), freezing and thawing (up to 300 cycles), and salt weathering (up to 50 cycles) tests have been performed. Also, in order to estimate the deterioration of the Ganjnameh inscriptions, four inscriptions were prepared and subjected to heating and cooling (up to 600 cycles), freezing and thawing (up to 300 cycles), magnesium sulfate salt weathering (up to 60 cycles), and acidic rain (up to 1 year time) tests. The results showed that when compared with that of salt weathering, the effects of heating-cooling and freezing-thawing weathering were negligible. Also, deterioration effect of magnesium sulfate on weight loss has been observed more remarkably than that of sodium sulfate. The deterioration effect of sodium sulfate on loss of engineering properties was evaluated more effectively than that of magnesium sulfate. Simulation of the Ganjnameh inscriptions behavior subjected to the weathering tests indicated that deterioration effect of sulfate solution was more effective than that of other weathering processes. [ABSTRACT FROM AUTHOR]

This work considers the crystallisation mechanisms of the most common and aggressive salts that generate stress in porous building stones as a result of changing ambient conditions. These mechanisms include the salt crystallisation that result from decreasing relative humidity and changes in temperature and, in hydrated salts, the dissolution of the lower hydrated form and the subsequent precipitation of the hydrated salt. We propose a new methodology for thermodynamic calculations using PHREEQC that includes these crystallisation mechanisms. This approach permits the calculation of the equilibrium relative humidity and the parameterization of the critical relative humidity and crystallisation pressures for the dissolution-precipitation transitions. The influence of other salts on the effectives of salt crystallisation and chemical weathering is also assessed. We review the sodium and magnesium sulphate and sodium chloride systems, in both single and multicomponent solutions, and they are compared to the sodium carbonate and calcium carbonate systems. The variation of crystallisation pressure, the formation of new minerals and the chemical dissolution by the presence of other salts is also evaluated. Results for hydrated salt systems show that high crystallisation pressures are possible as lower hydrated salts dissolve and more hydrated salts precipitate. High stresses may be also produced by decreasing temperature, although it requires that porous materials are wet for long periods of time. The presence of other salts changes the temperature and relative humidity of salt transitions that generates stress rather than reducing the pressure of crystallisation, if any salt has previously precipitated. Several practical conclusions derive from proposed methodology and provide conservators and architects with information on the potential weathering activity of soluble salts. Furthermore, the model calculations might be coupled with projections of future climate to give as improved understanding of the likely changes in the frequency of phase transitions in salts within porous stone. [ABSTRACT FROM AUTHOR]

Diagnosing the weathering of stones used in built heritage is essential for their preservation. Samples taken from the surface and the core stones of Al-Ziggurat walls in the archaeological city of Al-Nimrud (North Iraq) were characterized. Stone samples from a quarry believed to be the origin of the stones used in the construction of Al-Nimrud were also characterized. Physical properties, pore space system, mineralogical and chemical compositions and microstructural properties of historic, fresh and weathered stones were determined by various complementary techniques at the microscopic level. Results show that the main damage observed on the stone surface of Al-Ziggurat walls is due to salt weathering. Gypsum is the predominant salt and probably originated from the soil in contact with the stones during burial of the walls. Results also indicate that the characteristics of samples of the core of historic stone are quite similar to those of the fresh stone extracted from the quarry, demonstrating that the core of the historic stone is unweathered and that this quarry was probably the source of the construction material for Al-Ziggurat. This means that these fresh stones could be used in future restoration work. [ABSTRACT FROM AUTHOR]

Salt crystallization in pore spaces will usually cause major damage to natural sandstone. Salt distribution and movement are hard to detect in the field within a small scale. Understanding salt generation and transportation in semi-arid regions can help to protect natural cultural relics and control the salt weathering damage. Salt transportation behavior and deposition processes in Yungang Grotto were studied through a detailed hydrochemistry analysis within the context of the atmosphere-rock-water environmental system. Changes of salt types in different media were analyzed according to the sequence of water and salt transportation, integrating the results of atmospheric dry and wet deposition, soil in the aeration area and sandstone, and salt on the rock surface. The study shows the generation of salt is related to vertical transport in the soil and rock weathering zone. Salt transportation originates from soil cover, passes through the sandstone weathering zone, and finally accumulates in the grottoes. Due to coal burning pollution, acid deposits leading to sulfate bind to the soil. Salt generation in soil is the result of neutralization among sulfate, carbonate, and carbonate minerals, leading to cations of soluble salt that give priority to bonding with Ca and Mg, while the anions are mainly HCO and SO. Salt in sandstone weathered crust is not only impacted by soil, but also carbonate dissolution from CO-rich water, its inverse process, and feldspar dissolution. Rock surfaces in the inner grottoes suffer intense evaporation, resulting in salt accumulation, and carbonate and sulfate mineral deposition or dissolution, producing the salt type of MgSO or NaSO, while HCO and Ca are heavily consumed. The result can provide a scientific basis for engineering measures that reduce the hazard of salt accumulation. [ABSTRACT FROM AUTHOR]

Yungang Grottoes in north of China are the classical masterpieces of Chinese Buddhists, dating from the Northern Wei Dynasty 1,500 years ago. This rock art is threatened by weathering processes that has been accelerated due to coal mining. The dominant weathering processes occurring on the rock surface are collapse, flaking, and efflorescence. Salt crystal growth plays a major cause of these deteriorations, and it has a close relationship with water movement. The major salt on the rock surface are sulfates, with a primary composition of epsomite, thenardite, and gypsum. In addition, carbonate minerals are found, mostly calcite and nesquehonite. In this paper, three grottoes in the eastern part have been investigated via measuring the rock surface moisture and recording the surface temperature and humidity. These nondestructive techniques are used for the first time in China on cultural relics. The movement of moisture has been calculated and mapped, and then analyzed for its relationship with the weathering process. Three main sources of water transport in the sandstone are adopted to explain the moisture content patterns. The aim of this study is to help rock art conservation in Yungang Grottoes, thus to provide a better understanding regarding the driving processes of internal moisture transport, which results in significant weathering processes. The evidence shows that the natural character of sandstone, water transport mechanism, and continental semi-arid conditions are the major causes of rock deterioration. Meanwhile, air pollution due to coal mining is also an important factor in driving the weathering process. [ABSTRACT FROM AUTHOR]

Sodium sulfates are well known to be the most damaging salts in building materials and rocks. Unfortunately, the crystallization processes of sodium sulfates are not completely understood. In addition, the metastable heptahydrate has long been neglected in scientific works on salt damage until recently. In this study, we use temperature monitoring and differential scanning calorimetry to detect and identify the crystallization of sodium sulfate hydrates (i.e., mirabilite and heptahydrate) upon cooling/heating a bulk solution. The presence of impurities seems to play a major role in the crystallization sequence and can explain the crystallization of mirabilite and ice close to −10 °C. The crystallization of heptahydrate does not seem to be sensitive to the presence of impurities and does not always occur prior to the crystallization of mirabilite as commonly observed. The heptahydrate and mirabilite show different and characteristic thermal signatures that enable to distinguish each other. The shape, the intensity and the duration of the peak of temperature due to the crystallization depict these differences. Therefore, the thermal signatures can be used in further experimental studies to estimate the role of the different sodium sulfate hydrates involved in the salt weathering of rocks. [ABSTRACT FROM AUTHOR]

Precipitation of salts in confined spaces is the key mechanism for rock weathering and damage to building materials. To date there is no comprehensive study of the parameters influencing the reduction of pore space by salt crystals and the consequences for transport and damage by crystallization pressure. A novel method is presented to quantify pore clogging (i.e., the degree to which crystallization of salts interferes with transport of solution in porous materials). After drying capillary-saturated stone specimens containing salt solutions, the rate of capillary uptake of decane into the salt-contaminated specimens is measured. By treating the salt-contaminated material as a bilayer, the width of the crystallization front and the degree of pore filling can be determined. Two model materials with different pore size distributions (Indiana and Highmoor limestone) and three salts (sodium chloride, sodium sulfate and magnesium sulfate) are selected for this study. It is shown that pore clogging results from the interplay between pore size distribution and salt properties. Different scenarios are discussed to link pore clogging with salt damage. [ABSTRACT FROM AUTHOR]

Salt weathering is a crucial process that brings about a change in stone, from the scale of landscapes to stone outcrops and natural building stone façades. It is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture, where repeated oscillations in these parameters can cause re-crystallisation, hydration/de-hydration of salts, bringing about stone surface loss in the form of, for example, granular disaggregation, scaling, and multiple flaking. However, this 'traditional' view of how salt weathering proceeds may need to be re-evaluated in the light of current and future climatic trends. Indeed, there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general. Building on contemporary research on the 'deep wetting' of natural building stones, it is proposed that (as stone may be wetter for longer), ion diffusion may become a more prominent mechanism for the mixing of molecular constituents, and a shift in focus from physical damage to chemical change is suggested. Data from ion diffusion cell experiments are presented for three different sandstone types, demonstrating that salts may diffuse through porous stone relatively rapidly (in comparison to, for example, dense concrete). Pore water from stones undergoing diffusion experiments was extracted and analysed. Factors controlling ion diffusion relating to 'time of wetness' within stones are discussed, (continued saturation, connectivity of pores, mineralogy, behaviour of salts, sedimentary structure), and potential changes in system dynamics as a result of climate change are addressed. System inputs may change in terms of increased moisture input, translating into a greater depth of wetting front. Salts are likely to be 'stored' differently in stones, with salt being in solution for longer periods (during prolonged winter wetness). This has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone (especially in more mobile constituents), leading to a weakening of the stone matrix/grain boundary cementing. The 'output' may be mobilisation and precipitation of elements leading to, for example, uneven cementing in the stone. This reduced strength of the stone, or compromised ability of the stone to absorb stress, is likely to make crystallisation a more efficacious mechanism of decay when it does occur. Thus, a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens. [ABSTRACT FROM AUTHOR]

Gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones. To quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone. Different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles. During drying two different temperatures (50 and 25 °C) and relative humidity (low, 25 % at 50 °C and 65 % at 25 °C, and high, 99 %) have been applied. The acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts. Our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions, and also higher when drying at 50 °C than at room temperature. Microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature, gypsum crystallizes not on the sample surface, like in the other samples, but deeper in the inner part of the sample, in good agreement with previously published data. We show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory. [ABSTRACT FROM AUTHOR]

Following automation of lighthouses around the coastline of Ireland, reports of accelerated deterioration of interior granite stonework have increased significantly with an associated deterioration in the historic structure and rise in related maintenance costs. Decay of granite stonework primarily occurs through granular disintegration with the effective grusification of granite surfaces. A decay gradient exists within the towers whereby the condition of granite in the lower levels is much worse than elsewhere. The lower tower levels are also regions with highest relative humidity values and greatest salt concentrations. Data indicate that post-automation decay may have been triggered by a change in micro-environmental conditions within the towers associated with increased episodes of condensation on stone surfaces. This in turn appears to have facilitated deposition and accumulation of hygroscopic salts (e.g. NaCl) giving rise to widespread evidence of deliquescence in the lower tower levels. Evidence indicates that the main factors contributing to accelerated deterioration of interior granite stonework are changes in micro-environmental conditions, salt weathering, chemical weathering through the corrosive effect of strongly alkaline conditions on alumino-silicate minerals within the granite and finally, the mica-rich characteristics of the granite itself which increases its structural and chemical susceptibility to subaerial weathering processes by creating points of weakness within the granite. This case study demonstrates how seemingly minor changes in micro-environmental conditions can unintentionally trigger the rapid and extensive deterioration of a previously stable rock type and threaten the long-term future of nationally iconic operational historic structures. [ABSTRACT FROM AUTHOR]

This article is based on field investigations carried out at Ta Keo and Banteay Srei temples (Angkor, Cambodia), which have similar environmental histories and display the same recurrent decorative pattern (lotus petal) in three different sandstone lithotypes. Based on two original scales of mechanical and chemical weathering, the degree of deterioration of c.2000 sandstone petals was visually assessed, resulting in the proposal of a durability scale. An explanatory scheme was provided, based on laboratory analyses of stone materials (ICP-AES, XRD, SEM-EDS, polarizing microscopy and mercury injection). The key drivers of sandstone durability are both mineralogical and petrophysical. The remarkable preservation of the pink sandstone is due to the quartzose nature of its clasts, the non-swelling clay content of its abundant matrix (kaolinite) and its porosity structure (large connected pores and probable non-connected porosity). The overall good preservation of the green sandstone is due to its extremely low porosity and specific surface area, associated with its strong cementation. The severe deterioration of the grey sandstone is due to its laminated structure (oriented biotites), the susceptibility to hygric swelling and solution of its binding agents (chlorite/smectite and calcite) and its porosity structure, which evolves during a two-stage weathering sequence. The first stage is characterized by a bimodal porosity due to the partial clogging of macropores by swelling clays, and the second stage by a substantial increase in porosity and the penetration of salts (barite and anhydrite). Conversely, oxidation phenomena associated with weathering can lead to a drastic reduction of porosity. [ABSTRACT FROM AUTHOR]

San Jerónimo Monastery (Granada, Spain) was selected as a case study for the investigation of the effect of indoor environmental conditions on salt weathering and for on-site testing of a remediation treatment using crystallization inhibitors on account of the extreme salt damage affecting both the building stone, a biomicritic limestone, calcarenite and wall paintings. A methodology combining several analysis techniques, phenomenological observations, salt and moisture analysis, environmental monitoring and thermodynamic simulations, was adopted in order to study the salt damage problems affecting this building. Within the collected samples, the majority of salts were found to be magnesium sulphate in the form of either hexahydrite or epsomite, depending on the climate conditions, together with minor amounts of gypsum, nitrates and chlorides. Comparison of empirical observations with thermodynamic simulations of the salt mixture behaviour clearly showed that salt-induced damage events take place during the seasonal changes from spring to summer and winter to spring. An aqueous solution of an organic phosphonate, which in laboratory experiments was found to be an effective inhibitor of magnesium sulphate crystallization, was sprayed over a selected test area of unpainted stonework at the site. Preliminary results seem to indicate that after the application of the treatment both the amount of efflorescence and ongoing damage to the stone support is reduced. However, long-term monitoring of the future condition of the test area is needed to confirm whether indeed this treatment is appropriate and effective in reducing salt damage at this case study site. The outcome of this study extends beyond the particular problems at San Jerónimo Monastery, as it demonstrates a methodological approach for the study and evaluation of salt weathering problems affecting cultural heritage. [ABSTRACT FROM AUTHOR]

The Orval Abbey, a major monument of southern Wallonia, Belgium, was partly destroyed and rebuilt several times between the Middle Ages and the present time. The oldest parts are made of natural stones of local origin (Bajocian and Sinemurian limestones) and the most recent parts are mostly made of reconstituted stone. The process of reconstituted stone making is not known. Although confronting the same environmental conditions, the reconstituted stone is much more susceptible to weathering than the natural limestones, especially to salt crystallisation. The present study compared the mineralogical and petrophysical properties of these building materials to gather information on the making of the reconstituted stone and to understand the difference in salt susceptibility between natural and reconstituted stones. Microscopic observations and petrophysical measurements showed that the reconstituted stone is composed of debris of Sinemurian and Bajocian limestone and cement, and the salt efflorescences were thenardite. Within the cement, amorphous grains were found that may correspond to grains of clinker, which have not reacted during stone making. Although its porosity and water transfer properties were close to that of the Bajocian limestone, its pore access distribution was centred around 0.1 μm. Furthermore, the details of the pore size distribution allowed calculating salt susceptibility indices that were very high in the case of the reconstituted stone. Thus, the composition of the cement and the pore size distribution are likely the two factors explaining a high susceptibility of the reconstituted stone to salt weathering. [ABSTRACT FROM AUTHOR]

Three Portuguese limestones (two grainstones, Semi-rijo and Moca Creme commercial types, and a travertine) were subjected to salt crystallisation test (EN 12370:1999). Grainstones specimens showed higher weight loss than the travertine ones. Results are discussed, using parametric and nonparametric statistics, in relation to pore space characteristics that have been considered durability predictors, evaluated at the macroscopic (water imbibition) and microscopic (mercury injection porosimetry) levels. Several of the pore-space parameters indicate differences between grainstones and travertine, but these differences are much lower than the differences in weight loss. Results of the durability dimensional estimator (DDE) seem to present a discrepancy, with higher values in the rock type having lower weight loss (travertine). Additionally, weathering patterns of travertine samples show marked irregularities (a feature that is not assessed by weight loss). These irregularities are attributed to heterogeneous spatial distribution of detritic components (a feature that is not assessed by pore-space parameters). Comparing the grainstones, Moca Creme showed higher values of mass loss and several durability predictors suggested noteworthy differences in relation to Semi-rijo. However, these differences are much lower than differences in weight loss. Calculated crystallisation pressures are even higher for Semi-rijo. It is proposed that petrographical aspects of Moca Creme, namely heterogeneity related to the presence of bioclasts and veinlets, could contribute to explain the higher weathering susceptibility of this rock type. These results highlight the need to include petrographical features in assessments of durability and the usefulness of visual description on the characterization of salt weathering. [ABSTRACT FROM AUTHOR]

Local sandstone used in nineteenth century buildings in Sydney has been affected by salt weathering and surface crust formation. This study trialled two approaches, namely washing-and-vacuuming and poulticing, to salt-removal treatment of weathered sandstone blocks from the Sydney Hospital and Australian Museum. Both treatments removed solutes from the stones in laboratory tests. ICP/titration of sampled scrapings at depths of 0-2, 2-5 and >50 mm showed substantial between-sample variation, with no significant difference being recorded in solute levels after treatment (Mann-Whitney U test), except for sulfur and sodium. Sulfur levels increased at the surface (0-2 mm) following washing-and-vacuuming but not poulticing for the Hospital and Museum samples. Sodium levels increased at the surface (0-2 mm) following poulticing but not washing-and-vacuuming for the Hospital samples. The presence of surface crusts may have contributed to some of the variation in desalination responses. [ABSTRACT FROM AUTHOR]

The City of Adelaide suffers from rapid damage to historic building materials due to salts, rising damp, and damp-proof course failures. Adelaide City Council has partially funded repairs to over 400 buildings in the past 15 years. To begin to examine the scope of this problem and the effectiveness of various treatments, 24 historic buildings in Adelaide were examined, with a focus on the building materials, historic interventions and current treatments applied to treat rising damp and salt decay. Analysis of 90 samples found high levels of sodium sulfate, sodium chloride and sodium nitrate in cellars, ground water and building materials, suggesting a clear example of rising damp. Samples of disintegrating masonry, depth profiles acquired by drilling, poultices and damp proof courses (DPC) were analyzed by Ion Chromatography (IC) and Environmental Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (ESEM/EDS). Mercury Intrusion Porosimetry (MIP) and capillarity test were carried out in the building materials and DPCs showing that porous materials with high porosity, small pores and low strength are more prone to salt weathering. The City of Adelaide is a natural laboratory for comparing and analyzing different treatments of salt-laden masonry, with hundreds of treated buildings of the same age, in the same environment, and with similar building materials. [ABSTRACT FROM AUTHOR]

Surficial and bulk samples of historical bricks of different age (from XII to XVIII centuries) recovered from a campaign of archaeological excavations recently carried out at the site of a medieval monastery in the S. Giacomo in Paludo Island in theVenice Lagoon have been characterised by FT-IR, TGA-DTG and DTA, XRD, SEM + EDS. The samples belong to a particular brick type commonly used in the Venice region: the " altinella brick". The bulk relative abundance of primary (i.e. calcite and dolomite) and secondary firing minerals (i.e. diopside and wollastonite) in the bricks coupled with their relative geometrical dimensions allows placing the samples in a chronological sequence according to known historical changes in brickmaking firing temperatures and practices. Most of the bricks were used as paving material and have been exposed to the action of seawater salts (chlorides and sulphates) due to periodical submersion following high tide episodes. Salt-laden (gypsum, halite, mirabilite) surficial patinas are indeed present but salt weathering does not appear to have affected the overall structural soundness of the bricks in this now abandoned island as it is the case with brickwork located in other more populated (and polluted) areas in Venice and its lagoon. [ABSTRACT FROM AUTHOR]

Salt weathering is now known to be as much a widespread problem as corrosion of embedded steel in reinforced concrete structures exposed to aggressive marine environments. A growing shortage of good quality uncontaminated aggregates and mixing water free of chlorides, especially in the coastal regions of the world, means that chlorides may get trapped in the concrete well before it is exposed to hot, marine environments. The integrity and the durable service life of concrete structures under these conditions then very much depend on the ability and performance of salt contaminated concrete to resist further intrusion of chlorides from external sources. The overall aim of this paper is to present some of the critical engineering and durability properties of concrete made with and without slag, and with or without chlorides when exposed to salt laden environments. The tests reported include compressive and flexural strength development, swelling and shrinkage, water and chloride absorption and oxygen permeability after exposure up to 250 days. It is shown that the immediate effect of exposure to such environments is long-term loss of strength, expansive strains, and vulnerability to internal microcracking leading to enhanced permeability and long-term lack of durability of concrete. [ABSTRACT FROM AUTHOR]

Al-hambra is an immense and valuable archaeological site in Spain built on Sabika hill with red brick and natural sandy limestone. It exhibits weathering features indicating salt weathering process. The main aim of this study is to examine weathering processes and intensity acting on Al-hambra. Rock petrography and mineralogical composition have been examined using thin sections, scanning electron microscope, X-ray diffraction and X-ray fluorescence; limits of rock’s physical parameters using ultrasonic waves and mercury porosimeter; rock salt content through hydrochemical analysis. Salts attacking this structure are mainly from wet deposition of air pollutants on the long term chemical alteration of rock’s carbonate content to its equivalent salts. The salts’ concentration limit within the examined rock samples is considerably low but it is effective on the long run through hydration of sulphate salts and/or crystallization of chloride salts. Rock texture type and its silica as well as clay content reduces its resistance to internal stresses by salts as well as wetting and drying cycles at such humid area. The recession in limits of physical parameters examined for deep seated and weathered limestone samples quantitatively reflects weathering intensity on Al-hambra. [ABSTRACT FROM AUTHOR]

Saline solution properties, viscosity in particular, are shown to be critical in salt weathering associated with sodium and magnesium sulfate crystallization in porous limestone. The crystallization of sodium and magnesium sulfate within a porous limestone has been studied at a macro- and microscale using different techniques, including mercury intrusion porosimetry, environmental scanning microscopy and X-ray computed tomography. Such analysis enabled the visualization of the crystallization process in situ, and at high magnification, yielding critical information as to where and how salts crystallize. Sodium sulfate decahydrate (mirabilite) tends to crystallize in large pores as euhedral micron-sized crystals formed at low supersaturation near to the surface of the stone. In contrast, magnesium sulfate heptahydrate (epsomite) tends to precipitate as anhedral wax-like aggregates formed at high supersaturation and distributed homogeneously throughout the stone pore system filling large and small pores. While the former crystallization behavior resulted in scale formation, the latter led to crack development throughout the bulk stone. Ultimately, the contrasting weathering behavior of the two sulfates is explained by considering differences in flow dynamics of solutions within porous materials that are mainly connected with the higher viscosity of magnesium sulfate saturated solution (7.27 cP) when compared with sodium sulfate saturated solution (1.83 cP). On the basis of such results, new ways to tackle salt weathering, particularly in the field of cultural heritage conservation, are discussed. [ABSTRACT FROM AUTHOR]

Historic sandstone structures carry an inheritance, or a ‘memory’, of past stresses that the stone has undergone since its placement in a façade. This inheritance, which conditions present day performance, may be made up of long-term exposure to a combination of low magnitude background environmental factors (for example, salt weathering, temperature and moisture cycling) and, superimposed upon these, less frequent but potentially high magnitude events or ‘exceptional’ factors (for example, lime rendering, severe frost events, fire). The impact of complex histories on the decay pathways of historic sandstone is not clearly understood, but this paper seeks to improve that understanding through the use of a laboratory ‘process combination’ study. Blocks of quartz sandstone (Peakmoor, from NW England) were divided into subsets that experienced different histories (lime rendering and removal, fire and freeze–thaw cycles in isolation and combination) that reflected the event timeline of a real medieval sandstone monument in NE Ireland, Bonamargy Friary (McCabe et al. ). These subsets were then subject to salt weathering cycles using a 10% salt solution of NaCl and MgSO4 that represents the ‘every-day’ stress environment of, for example, sandstone structures in coastal, or polluted urban, location. Block response to salt weathering was monitored by collecting, drying and weighing the debris that was released as blocks were immersed in the salt solution at the beginning of each cycle. The results illustrate the complexity of the stone decay system, showing that seemingly small variations in stress history can produce divergent response to salt weathering cycles. Applied to real-world historic sandstone structures, this concept may help to explain the spatial and temporal variability of sandstone response to background environmental factors on a single façade, and encourage conservators to include the role of stress inheritance when selecting and implementing conservation strategies. [ABSTRACT FROM AUTHOR]

The influence of pore structure, water transport properties and rock strength on salt weathering is evaluated by means of a thorough rock characterisation and a statistical analysis. The pore structure was described in terms of its porosity, pore size distribution (quantified by mean pore radius) and specific surface area, density and water transport was characterised by means of water permeability (saturated flow) and capillary imbibition (unsaturated flow); whilst the rock strength test was carried out using uniaxial compressive strength, compressional and shear wave velocities, dynamic elastic constants and waveform energy and attenuation were obtained from the digital analysis of the transmitted signal. A principal component analysis and a stepwise multiple regression model was carried out in order to examine the direct relationships between salt weathering and petrophysical properties. From the principal component analysis, two main components were obtained and assigned a petrophysical meaning. The first component is mostly linked to mechanical properties, porosity and density whereas the second component is associated with the water transport and pore structure. Salt weathering, quantified by the percentage of weight loss after salt crystallisation, was included in both principal components, showing its dependence on their petrophysical properties. The stepwise multiple regression analysis found that rock strength has a predominant statistical weight in the prediction of salt weathering, with a minor contribution of water transport and pore structure parameters. [ABSTRACT FROM AUTHOR]

Three geo-archaeological sites at the North Coast and Alexandria, namely, the Alexandria wall (El Shalalat Park site), Abu Soir temple, and Marina excavations, were investigated to determine the negative impact of a salty environmental condition. The monuments suffer from rock decay of different rates. The geo-archaeological sites were built mainly from oolitic limestone blocks (i.e., the Alexandria wall at the El Shalalat Park site and Abu Soir temple) or excavated on them (i.e., Marina excavations). Field inspection and a lab analysis were carried out to understand the weathering mechanism. Salt weathering criteria such as disintegration, pitting, scaling, exfoliation, and honeycomb are observed on the Alexandria wall and upper parts of the Abu Soir temple, while dangerous cracks are detected on the Marina excavation tombs. The petrographic study of the oolitic limestone samples shows that they consist mainly of oolities and drusy sparite as a cement (oolitic grainstone). Some oolities have quartz grains as nuclei. Hydrochemical analysis shows that the total dissolved salts of extracted solutions of the North Coast quarry samples range from 539 to 686 ppm and dramatically increase (i.e., ten times) for extracted solutions from monument samples, ranging from 5395 to 6880 ppm. The dominant cation is sodium while the dominant anion is chlorine. Acid insoluble residue analysis shows that the carbonate content ranges from 89.2% to 96.4% for fresh samples from quarries and from 9.2% to 94.8% for weathered monument samples. The weight loss of the quarry oolitic limestone samples range from 30.7% to 32.7% and its physical and mechanical properties become worse after being subjected to 15 cycles of a durability simulation soundness test (using a sodium sulphate solution). Our main recommendations are to use suitable grouting for binding the cracks, high durability reconstruction rocks, and suitable cleaning methods to remove salts from the monuments. [ABSTRACT FROM AUTHOR]

The 500th anniversary of European arrival in Brazil was celebrated in 2000 and highlighted the need to review the condition of the country’s remaining colonial built heritage. This revision is particularly apposite in the adjacent cities of Rio de Janeiro and Niterói, where the heritage that survived twentieth century reconstruction has done so largely because of ownership by the church or military. However, whilst this may have protected buildings from demolition, detailed fabric can be neglected or abused. This paper investigates this possibility through an examination of two forts, built primarily of local augen gneiss, that guard the entrance to Guanabara Bay. Natural outcrops exposed to the same humid sub-tropical maritime environment show that this rock is susceptible to slow disaggregation through salt weathering. Surveys suggest that stonework in the forts that is sheltered from rainwash is heavily loaded with salt and has passed a threshold, wherein stresses accumulated over centuries of apparent stability, combined with the effects of a more recent increase in atmospheric pollution and apparently inappropriate intervention (re-pointing), have triggered rapid breakdown that requires immediate intervention. [ABSTRACT FROM AUTHOR]

Digital image processing is applied to X-ray element maps and back-scattered electron (BSE) images obtained with scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), to quantify and identify salts and porosity with depth in porous media. Until now, only salt chemical composition with depth has been characterised and salt mineral composition inferred, so that no salt quantification was possible. The method we present can be used stand-alone or integrated with other techniques to fill certain gaps in our knowledge. It can be used to quantify texture and porosity of clay minerals, with implications in petroleum research. Also, salts may be identified and quantified with depth in porous media; this is important when selecting among salt extraction procedures in order to conserve cultural heritage. Finally, the method can help in interpreting salt weathering processes and links between stone decay forms at different scales, with consequences for geomorphology. To demonstrate the method, salt and pore percentages with depth are determined in two limestone types from monuments in the Aunis province, SW France: i) Crazannes sparite, showing alveolisation and black crust, and ii) La Pallice micrite, suffering from micro-delamination. In most of the micrites no salts are identified. Porosity data show that micro-fissures are confined between the surface and 9 mm depth in LPAM5, the only micrite with loading salts with depth (NaCl = 1.9% at the surface versus 1.4% at 18 mm; and Na2SO4 · H2O and MgCl2 ∼ 0.02% in the first 3 mm). In the sparites, those samples with no crust display an alveolisation zone with lower porosity and higher diversity and percentage of salts. In CRZM6, the stone crust-alveolisation front lies at a depth of 9 mm. In the crust, porosity is lower than in the alveolisation zone (12%). Salt concentration, by contrast, is higher in the crust (2.91% versus 0.14% in the alveolisation zone). [ABSTRACT FROM AUTHOR]

Discusses genetic engineering of japonica rice and salt tolerance of the plant. Increase in salt tolerance with the overexpression of the yeast HAL2 gene; Introduction of rice HAL2-1ike (RHL) gene into a japonica rice cultivar HJ19 with Agrobacterium tumefaciens-mediated transformation; Selection of transgenic plants in R0 generation on the principle of GUS-positive, RHL gene PCR-positive and normal growth; Indication that hygromycin-resistant plants of some transgenic lines increased salt tolerance during the seedling and booting stage; Finding they were less damaged in the cytomembrane and stronger in leaf tissue viability; Southern analysis of transgenic lines tolerant to salt in R[sub 1] generation showing the RHL gene expression cassette was successfully integrated into rice genome.

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. [ABSTRACT FROM AUTHOR]

When rain impacts a building façade, it is essential that once it has entered, it leaves by evaporation to help the building dry out. Accumulation of moisture can lead to internal dampness, mould and decay of valuable masonry by salt weathering. In a solid masonry wall where the stone is of low permeability, such as granite which is found in many historic buildings, rain water mainly enters and leaves through mortar joints. If granite stone masonry needs repointing, the repair mortar must allow the overall masonry to dry out. This study evaluates the drying response of various lime-based repointing mortars mixes in small granite stone masonry constructions (test walls) subjected to a simulated intense short rain event and then left to dry. It determines the moisture movement through mortar joints, the influence of materials, joint types and workmanship, and whether repointing could mitigate moisture ingress and help masonry dry out. This study developed a novel experimental protocol which allowed comparison of the drying response of different mortar types in a low-porosity stone masonry system and the effect of repointing. Five test walls were built of Cornish granite with five different lime mortar mixes combining NHL 3.5 (St Astier) gauged with non-hydraulic quicklime (Shap), quartz and calcitic sand and biomass wood ash as additives. Simulated intense rain was sprayed on each wall over a 3.25 h spell. Drying was monitored over a week with a microwave moisture device (MOIST350B). Measurements were done at surface and depth on both mortar joints and granite units. Each wall was then repointed with the same mortar mix initially used when built and the same rain simulation was performed to evaluate differences repointing could make to the moisture dynamics. The importance of mortar in dealing with moisture movements in the test wall and absorbing moisture from the stones was demonstrated. Gauged binder and wood ash additives decreased the capillary absorption capacity of mortars while retaining a good drying rate. This study has also showed that after repointing water did not penetrate as deep under the same conditions. Therefore repointing reduces the threat of water ingress and shows that it could be a suitable conservation intervention to mitigate water ingress and accelerate drying. [ABSTRACT FROM AUTHOR]