Sandstone Monuments Research Articles

Glycidyl polyhedral oligomeric silsesquioxane-enhanced flexible aminosiloxanes to protect sandstone monuments

To protect weathered ancient stone monuments from surface cracking and surface damage by powders, strong materials containing flexible chains are required. Herein, a facile strategy was proposed to produce hybrid octa-glycidyl polyhedral oligomeric silsesquioxane (GPOSS)-enhanced flexible siloxanes by the ring-opening reaction of GPOSS using three aminosiloxanes (bis(3-aminopropyl) terminated poly (dimethyl siloxane) (NH2-PDMS), 3-aminopropyltriethoxysilane (APTS), and N-(6-aminohexyl) aminopropyl trimethoxysilane (AHAPTMS). This produced three different protective materials (POSS-PDMS, POSS-APTS, and POSS-AHAPTMS) that greatly improved the weather resistance of sandstone monuments, especially their resistance to water, salt, temperature, and humidity. All three protective materials presented an adhesion of up to 2.4 MPa. The resistance of freeze-thaw aging cycles was much higher for the protected sandstone (104–133 cycles) compared with the unprotected sandstone (20 cycles). The three protective materials improved the salt weather resistance of protected sandstone (9–60 cycles) compared with unprotected sandstone (3 cycles), with the long-chain aminosiloxane AHAPTMS providing the best protection. The hydrophobicity of three protective materials on the sandstone surface was improved. Furthermore, the water absorption, water vapor permeability, pore size distribution, mechanical strength, light transmittance, and glass transition temperature (Tg), were all improved. The three GPOSS-enhanced flexible siloxanes are novel and eco-friendly materials for protecting sandstone monuments.

Implementation of a non-destructive method to assess weathering deterioration of sandstones in cultural heritage

This paper proposes a non-destructive approach based on the Equotip hardness tester to assess weathering deterioration in a protected sandstone monument located in the historic centre of Camerino (Italy). The approach is tested on one sandstone column, where various forms of weathering, such as discolouration, scaling and loss of stone volume, are observed. The mechanical characterisation with Equotip was performed on 24 measuring points, systematically distributed in the column. Innovatively, the two probes available from Proceq (Proceq© 2010) were used to assess differences among surface and in-depth hardness values of the column. In addition, an un-weathered rock core from the original extraction site was also analysed and compared with the rock matrix of the column. The obtained results show a 15% hardness reduction from depth to the surface of the column and a 25% overall hardness reduction with respect to the fresh sandstone core samples. Equotip results were coupled with grain size analyses, mercury intrusion porosimetry, scanning electron microscopy and X-ray diffractometry results, and a correlation between hardness and grain size was evaluated. By combining these approaches, it was possible to identify the processes that occurred during weathering: (a) freeze-thaw cycles that caused a decrease in micropore volume and an increase in macropores connected with low Equotip values; (b) iron oxide and sulphuric acid released from pyrite oxidation contribute to the dissolution and precipitation of calcium carbonate, which can be rearranged in the outer and surface macroporosity. The quantitative approach proposed in this study may be a valid low-cost and quick tool to assess weathering heterogeneities on building stone materials and to provide insights for effective preservation strategies of historical monuments.

Sandstone monuments still standing after storms: Waterproofing and durability protection

Using the Surface waterproofing to solve moisture expansion which leads to the acceleration of surface weathering of sandstone relics is a hot topic. This study focuses on surface coating protection because of the special status of cultural relics. The fluorinated ZnO/SiO2 nano-coating was applied on the sandstone matrix in this work. The loading of the fluorinated ZnO/SiO2 in the nano-coating, the penetration depth of the nano-coating in the sandstone matrix, and the waterproofing effect of the sandstone surface were investigated within the limitation of the color difference systematically. The freeze-thaw cycles, light exposure, water absorption, and aging tests were carried out to evaluate the environmental durability of the nano-coating in a simulated humid environment of southwestern of China. All the tests meet the criteria for the heritage protection color difference. When the loading of fluorinated ZnO/SiO2 nano-coating is 0.4%, the water contact angle (WCA) and oil contact angle (OCA) are significantly improved, which are larger than 160° and 140°, respectively. The WCA and OCA have little changed after freeze-thaw cycle for three weeks, and the WCA only decreases only 7% after 300 h UV aging treatment. This significantly enhanced stability is due to the good penetration depth of the fluorinated ZnO/SiO2 nano-coating on the sandstone matrix. Moreover, the excellent air permeability is achieved as well to ensure substrate breathing. This work would provide a new idea for the long-term protection of sandstone heritage in practical environment.

An internal recycling mechanism between ammonia/ammonium and nitrate driven by ammonia-oxidizing archaea and bacteria (AOA, AOB, and Comammox) and DNRA on Angkor sandstone monuments

The ancient Angkorian sandstone monuments in Cambodia are well known for biodeterioration of the sandstone under tropic climate. This study examined ammonia oxidizing bacteria (AOB and Comammox) and archaea (AOA) in stone-dwelling microbiome from three important Angkor monuments, namely Angor Wat, Bayon of Angkor Thom, and Preah Vihear, by DNA-based metagenomics analysis, RNA-based functional gene reverse-transcriptional (RT)-qPCR quantification, and N-15 isotope analysis. Our metagenomics datasets on these three monuments reveal a rich microbiome and abundant microbial nitrogen transforming reactions of ammonia oxidation and nitrite oxidation, Comammox and dissimilatory nitrate reduction to ammonium (DNRA), and these results support an internal recycling mechanism between ammonia/ammonium and nitrate by AOA, AOB, Comammox and DNRA on the stone monuments to support the microbial community. Though a wide range of AOB and AOA lineages together with Comammox were retrieved from these metagenomes as the potential ammonia-oxidizers, only AOA and Comammox were most abundant, likely to contribute to the biochemical processes of ammonia oxidation. The RNA-based qPCR quantification of the functional gene amoA in this study showed that AOA were the more active ammonia oxidizers over AOB in the microbiome of these Angkor sandstone monuments. In addition, a rich population of nitrite/nitrate producing AOA and Comammox drove the sequestration of CO2 onto the stone and this process was in turn supported by DNRA to provide the substrate ammonia/ammonium for a further cyclic reaction to take place continuously between ammonia/ammonium and nitrate. This model is further supported by the high enrichment of stable isotope 15N signature of NO3− in sandstone surface biofilms. The findings of this study are insightful for elucidation of nitrate accumulation by an internal N cycling mechanism proposed, and are important for understanding the sustainable microbial community and protection management of stone cultural heritage.

Silica-based hybrids for adhesive coatings and their anti-salt damage in the protection of ancient sandstone

Hybrid coatings have been used as the protective materials on sandstone monuments for many decades. But the protective performance is strongly depended on the adhered interface between protective coating and matrix. To find out how the hybrid coatings affect the adhesive performances and anti-salt damage behaviors during Na2SO4 salt-loaded hygrothermal aging (SLHA) cycles, the surface/mechanical properties of three silica-based hybrid coatings (S1-S3) and their anti-salt damage results (surface weathering appearance, mass change, porosity, water absorption and morphology of pore structures) of the sandstones adhered by these hybrid coatings have been evaluated and discussed. The results reveal that dendritic Na2SO4 crystals cover on the sand grains in both natural and hydrophilic silica/PVA (S1) adhered sandstones, which makes the adhered sandstone perform the least damage. Owing to the high adhesive and mechanical strength, S1-adhered sandstones perform the best anti-salt damage during Na2SO4 SLHA cycles. While the needle-like and cumulate ellipsoidal Na2SO4 crystals precipitate in the pores and interstices result to much severe salt damaged in adhered sandstones by hydrophobic P(GMA-MAPOSS) (S2) and PGMA-g-P(MA-POSS) (S3) during Na2SO4 SLHA cycles, although they enhanced the strength of adhesive pore walls. Actually, the macro salt damage behaviors on the sandstones treated by different hybrid coatings are proved to be a competition result of different crystallization patterns. Therefore, the pore interface adjusted by protective coatings should be one of the decisive factors for anti-salt damage during the sandstone protection.

The active microbes and biochemical processes contributing to deterioration of Angkor sandstone monuments under the tropical climate in Cambodia – A review

Abstract Angkor monuments/temples in the Southeast Asia are UNESCO World Cultural Heritage of the Khmer Civilization and they require preservation and protection from destruction. In this article, activity- and process-based approaches are used to present the current available results on the active microorganisms and their biochemical processes associated with the biodeterioration of sandstone cultural heritage under the tropical climate in Cambodia. Such information is important for effectively protection and management. Severe deterioration of sandstone monuments is a result of weathering processes of a combination of physical, chemical and biological forces, including both natural and anthropogenic ones. Given the fact that water is an important natural factor affecting the stability of sandstone cultural heritage under the tropical regions, subsequent microbial colonization and contribution to the deterioration of sandstone have been investigated with both culture-dependent and culture-independent techniques to provide information about the microbiota associated with the sandstone. Recent data show that both sulfur and nitrogen cycles are active biochemical processes by specific microorganisms on sandstone temples/monuments in the tropical region. Both sulfur-oxidizing bacteria and fungi are active involved and, more recently, ammonia-oxidizing archaea (AOA) are implicated with higher abundance than ammonia-oxidizing bacteria (AOB) on sandstone monuments. It is clear that a research paradigm shift is taking place on microbiology of cultural heritage, and the active, and biochemically and physiologically functional microbes are focused to advance our fundamental understanding and knowledge on the biodeteriogens for a better protection and management of cultural heritage. Biochemically and physiologically functional and important microorganisms, as well as the biochemical mechanisms involved, shall be focused in order to advance the basic research on cultural heritage, while providing essential information for its protection, including Angkor sandstone temples and monuments.

The Curious Case of the Octagonal Temple

Abstract The Muṇḍeśvarī temple near Bhabuā in southwest Bihar is an octagonal, sandstone monument without a spire. Scholars have dated the temple to the first half of the seventh century, primarily on account of early inscriptions from the site and the style of the door frames. Few monuments survive from this nascent stage of structural North Indian temple architecture, and the Muṇḍeśvarī temple is intriguing because it is an anomaly in terms of its size, composition, and the shape of its plan. This study argues that the Muṇḍeśvarī temple has been misdated, and presents a systematic architectural analysis that highlights multiple features and irregularities that are incompatible with early North Indian design. The paper proposes that, rather than being seventh century, the octagonal shrine was built about a millennia later, in the sixteenth–seventeenth century, incorporating doorways and moldings salvaged from the ruins of the seventh century temples that once graced the hilltop. The latter part of the article considers how the Muṇḍeśvarī temple came to be buried by the end of the eighteenth century, and questions whether the Archaeological Survey of India might have altered the temple's appearance during the reconstructive work they undertook at the start of the twentieth century.

Microbiome and nitrate removal processes by microorganisms on the ancient Preah Vihear temple of Cambodia revealed by metagenomics and N-15 isotope analyses

Preah Vihear temple is one of the most significant representatives of the ancient Angkorian temples listed as United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Sites. The surfaces of this Angkor sandstone monument are covered with deteriorated materials, broadly called "sediments" here, resulting from a long time of weathering of the sandstone. The sediments might adversely affect the ancient sandstone substratum of this cultural heritage, and the potential risk from them is essential information for current strategies and on-going protection and management. The extracted DNA from the sediment samples of this temple was used for Illumina high-throughput sequencing analysis, resulting in approximately 12 Gb of metagenomic dataset. The results of this shotgun metagenomic analysis provided a thorough information of the phylogenetic groups presented in the microbiome of the sediment samples, indicating that potential metabolic activities, involving different geomicrobiological cycles, may occur in this microbiome. The phylogenetic result revealed that the majority of metagenomic reads were affiliated with Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes at the phylum level. The metabolic reconstruction results indicated that the important geomicrobiological cycling processes include carbon sequestration, and nitrogen and sulfur transformation as the potentially active ones in the sediments of the sampling sites. Specifically, the dissimilatory nitrate reduction to ammonium (DNRA) and the newly discovered complete ammonia oxidation (comammox) were retrieved from this metagenomic dataset. Furthermore, the genetic information on the presence of acid-producing processes by sulfur- and ammonia-oxidizing bacteria and archaea in this metagenomic dataset suggested that the microbial flora in these samples has the potential to participate in the degradation of sandstone cultural heritage by producing acids. N-15 isotope amendment and incubation analysis results confirmed the presence of active denitrification, but not anammox activity at this temple. These results are important for our knowledge on the microbial community composition and microbial biodeterioration processes affecting this sandstone cultural heritage and will aid in the protection and management of the ancient Preah Vihear temple.Key Points• Microbiota on Preah Viher temple was analyzed using NGS.• Nitrate-N transformation by DNRA, comammox, and denitrifcation was detected.• N-15 isotope analysis confirmed the active denitrifcation, but not Anammox.• Accumulation of nitrate is a result of less active removal by denitrification.

Molecular Identification of deteriorating Aspergillus spp. from sandstone monuments

Biodeterioration is irreversible damage that is caused by the colonization of bio communities on the surface of sandstone monuments. Out of all bio communities, fungi play the most vital role in the deterioration of sandstone. Fungi can colonize on the surface of sandstone and by releasing many types of inorganic and organic acids, pigments and enzymes, can changing not only the surface of the materials but the color of the sandstone. Moreover, mycelia of fungi can penetrate into the internal surface of sandstone and change the interior chemical contents of sandstone. This study was focused on the identification of fungi that were colonized on the sandstone monument. The samples were collected from different monument places built during different time periods and analyzed using cellophane tape methods and swabbing & serial dilution methods. A sampling of stone was carried out to identify inhibiting microorganisms. Biochemical and microscopic methods were used for isolated strains of samples. In addition, the Polymerase Chain Reaction (PCR) and sequencing of the PCR products were done. Finally, the phylogenic tree was constructed base on the sequences of ITs region. We identify high microbial diversity in fungal groups . The fungal commodity structure differed among the samples. The inhabiting fungi which isolated from sandstone monuments belong to high microbial diversity fungal groups. The result revealed that the strain exhibited a high level of 18S rRNA similarity with Aspergillus costaricaensis, Aspergillus luchuensis was identified as a close relative to Aspergillus spp.

Photoactive and hydrophobic nano-ZnO/poly(alkyl siloxane) coating for the protection of sandstone

Poly(alkyl siloxane) containing photoactive nano-ZnO (0.5 wt%) has been studied as a protective coating of glauconitic sandstone. Effect on visual appearance, hydrophobicity, porosity, water absorption/evaporation, and self-cleaning ability of the sandstone was measured. The results were evaluated in comparison with uncoated and poly(alkyl siloxane)-coated sandstone. Static contact angle of water reached 89° ± 3° and 128° ± 2° for poly(alkyl siloxane) and nano-ZnO/poly(alkyl siloxane) coating, respectively. Poly(alkyl siloxane) and nano-ZnO/poly(alkyl siloxane) coatings led to increased reduction in water absorption (>50%) for ∼18 h and ∼8 h, respectively, compared to the uncoated sandstone. The shorter time is compensated by self-cleaning ability: photodegradation of methylene blue on the nano-ZnO/poly(alkyl siloxane) coating after 5 h of UV irradiation was observed. This coating is a promising candidate for practical use in sandstone monuments protection.

Combined effects of salt, cyclic wetting and drying cycles on the physical and mechanical properties of sandstone

Salt weathering has considerable effects, and it has recently become the subject of interest among researchers and engineers, especially in terms of sandstone heritage buildings and sandstone monuments. However, the impacts of salt weathering on sandstone after wetting-drying cycles have been neglected in the literature. Under the conditions of the long-term or gradual underground seepage of water into sandstone heritage buildings and monuments, salt accumulation and recrystallization occur in sandstone when the rate of evaporation is sufficiently high, and they reduce rock stability. In view of this problem, experiments subjecting sandstone to up to 50 wetting-drying cycles were conducted using water and solutions containing concentrations of 4%, 6% or 8% magnesium sulfate (MgSO4). The physical and mechanical properties were tested after different wetting-drying cycles. The results show that the wetting-drying cycles impacted the sandstone samples soaked in a salt solution more than the samples that were soaked in only water. Thirty cycles is the threshold number in terms of changes in P-wave velocity, thermal conductivity and tensile strength. A correlation analysis was conducted, and it showed that both color lightness and thermal conductivity are good parameters for evaluating tensile strength. The results contribute to the evaluation process and protection of sandstone heritage buildings and monuments against salt weathering.

On the use of wooden beams as an anti-seismic device in stone masonry in Qasr el-Bint, Petra, Jordan

Timber string-courses have clearly been used to strengthen stone ashlar buildings in Petra, Jordan. These embedded beams, used as a form, held the brittle stone ashlars together, especially during earthquakes. In this study, tied and frictional surfaces were used to represent the interaction between the masonry blocks and the embedded wooden beams. Micro and macro modelling were used to evaluate the effect of using the embedded wooden beams on the integrity of the sandstone monument Qasr el-Bint. The traction-separation behaviour of the cohesive element was employed to model the mortar joints. A continuum, plastic-based, damage constitutive model (CDP) was used to represent the behaviour of the masonry walls. The results of these investigations demonstrated the role of the embedded wood string-courses as an anti-seismic device in reducing the shear stress of the stone masonry structure by up to 33%. The repairing and preserving of these beams that function as anti-seismic devices are needed to strengthen the structure against potential earthquakes.

A comprehensive approach to conservation of ancient graffiti at El Kurru, Sudan

ABSTRACTThis paper describes conservation and preservation of ancient Meroitic graffiti in a rock-cut temple at the site of El Kurru in Sudan. The temple and its graffiti provide important material evidence for the African empire of Kush, but El Kurru's sandstone monuments suffer from granular disintegration and other serious condition problems. Although the conservation of archaeological heritage is often complicated, it is especially challenging in Sudan due to a fragile national economy and, until October 2017, United States sanctions against the country. A comprehensive, investigation-based approach has been used in conservation planning for the graffiti. Work began with a criterion-anchored rating condition survey designed to identify, prioritize, and monitor condition issues. Chemical analysis of the stone was conducted, and treatment options including alkoxysilane consolidation and grout injection were explored. Preventive conservation strategies for the temple, including a protective shelter and increased community education, have also been examined. Finally, reflectance transformation imaging was used to document the graffiti's condition and create a virtual, visual catalog. In description of these activities, the paper emphasizes key principles for guiding conservation at archaeological sites: practicality, flexibility, sustainability, and placing a high value on the contributions and wishes of stakeholders.

More wide occurrence and dominance of ammonia-oxidizing archaea than bacteria at three Angkor sandstone temples of Bayon, Phnom Krom and Wat Athvea in Cambodia

The Angkor monuments of Khmer civilization in Cambodia are suffering from serious deterioration by physical and chemical mechanisms as well as biological attack. The objectives of this study were to analyze the community of ammonia-oxidizing microorganisms as a biodeteriogen and the environmental factors contributing to biodeterioration of these sandstone monuments. A total of 34 samples were taken from three different temples in Siem Reap of Cambodia, including Phnom Krom, Wat Athvea, and Bayon of Angkor Thom. Our results showed that ammonia-oxidizing archaea (AOA) were detectable in 30 samples of all three sites, while ammonia-oxidizing bacteria (AOB) were detected in only 10 samples by polymer-chain reaction (PCR) amplification of the ammonia monooxygenase subunit A gene, amoA. Community analysis by constructing AOA and AOB clone libraries of the amoA gene revealed that the AOA community composition were more complex than that of AOB and related to at least three groups, Nitrosopumilus sp. from Group I.1a, Nitrosotalea sp. from Group I.1a-associated, and Nitrosophaera sp. from Group I.1b. AOB sequences obtained from samples in this study were clustered with the Nitrosospira lineage. Besides the higher diversity of AOA than AOB observed, AOA were also detected much higher abundance than AOB in majority of the samples based on the quantitative real-time PCR analysis. AOA and AOB had positive correlation with the sample pH values among the environmental variables analyzed in this study. Acidity may interact with minerals causing dissolution and crystallization regulated through wet and drying cycle. Overall, AOA were the dominating members over AOB in the nitrifying community and may play an important role in the biodeterioration of the monument sandstones via nitrogen cycling.

Higher diversity and abundance of ammonia-oxidizing archaea than bacteria detected at the Bayon Temple of Angkor Thom in Cambodia

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are two groups of the ammonia-oxidizing microorganisms responsible for conversion of ammonia to nitrite, producing acidity and damaging building materials, including valuable cultural heritage stone structures. In this study, the molecular biomarker of amoA gene of archaea and bacteria was applied in polymerase chain reaction (PCR) amplification and quantitative real-time (RT) PCR (qPCR) to detect the abundance of AOA and AOB at 4 locations (Pond, Entrance, Gallery and Central Tower) of Bayon temple at Angkor Thom, Cambodia. The results showed that both AOA and AOB were positively detected at all locations and the diversity index suggested that AOA were more diverse than AOB. Sequences of AOA were mainly distributed in Group I.1b and few clustered in Group I.1a and Group I.1a-associated, while AOB were all closely related to β-proteobacteria (Nitrosospira). Based on the qPCR results, AOA outnumbered AOB clearly, the gene copy numbers of AOA amoA gene ranged from 1.35 × 106 to 2.52 × 108 copies per gram of dry materials, while, in comparison, AOB amoA gene copy numbers from 6.54 × 105 to 4.52 × 106 copies per gram of dry materials. In addition, the abundance of amoA gene from galleries was the highest than other locations. At gallery section, gene abundance, NH4+ and NO3− agreed well with the intensity of biofilm development. Based on the community and abundance analysis, nitrogen cycling plays an important role in contributing to deterioration of sandstone monuments at Angkor Thom in Cambodia under tropical climate.

Bacterial Rhizosphere Biodiversity from Several Pioneer Desert Sand Plants Near Jizan, Saudi Arabia

Life in arid regions and, in particular, hot deserts is often limited due to their harsh environmental conditions, such as large temperature fluctuations and low amounts of water. These extreme environments can influence the microbial community present on the surface sands and any rhizosphere members surrounding desert plant roots. The Jizan desert area, located in Saudi Arabia, supports particular vegetation that grows in the large sandy flat terrain. We examined five different samples, four from the rhizosphere of pioneer plants plus a surface sand sample, and used pyrosequencing of PCR-amplified V1-V3 regions of 16S rDNA genes from total extracted DNA to reveal and compare the bacterial population diversity of the samples. The results showed a total of 3,530 OTUs in the five samples, calculated using ≥ 97% sequence similarity levels. The Chao1 estimation of the bacterial diversity fluctuated from 637 to 2,026 OTUs for a given sample. The most abundant members found in the samples belong to the Bacteroidetes, Firmicutes and Proteobacteria phyla. This work shows that the Jizan desert area of Saudi Arabia can contain a diverse bacterial community on the sand and surrounding the roots of pioneer desert plants. It also shows that desert sand microbiomes can vary depending on conditions, with broad implications for sandstone monument bacterial communities

Gravity-induced stress as a factor reducing decay of sandstone monuments in Petra, Jordan

Abstract Recent work has shown that gravity-induced stress within a landform due to vertical loading reduces weathering and erosion rates, contrary to commonly held hypotheses. The purpose of this investigation is to evaluate the negative feedback between stress and weathering of sandstone monuments at the Petra World Heritage Site in Jordan via field observations, salt weathering experiments, and physical and numerical modeling. Previous studies on weathering of Petra monuments have neglected the impact of stress, but the ubiquitous presence of stress-controlled landforms in Petra suggest that it has a substantial effect on weathering and erosion processes on manmade monuments and natural surfaces. Laboratory salt weathering experiments with cubes of Umm Ishrin sandstone from Petra demonstrated the inverse relationship between stress magnitude and decay rate. Physical modeling with Střelec locked sand from the Czech Republic was used to simulate weathering and decay of Petra monuments. Sharp forms subjected to water erosion decayed to rounded shapes strikingly similar to weathered tombs in Petra. The physical modeling results enabled visualization of the recession of monument surfaces in high spatial and temporal resolution and indicated that the recession rate of Petra monuments was far from constant both in space and time. Numerical modeling of stress fields confirmed the physical modeling results. This novel approach to investigate weathering clearly demonstrates that increased stress decreases the decay rate of Petra monuments. To properly delineate the endangered zones of monuments, the potential damage caused by weathering agents should be combined with stress modeling and verified by documentation of a real damage.

Petrography and geochemistry of Pharaonic sandstone monuments in Tall San Al Hagr, Al Sharqiya Governorate, Egypt: implications for provenance and tectonic setting

Petrographic and major and trace element compositions of Tanis sandstones from Tall San Al Hagr, Al Sharqiya Governorate, Egypt, have been investigated to determine their source, provenance, intensity of paleoweathering of the source rocks, and tectonic setting. Tanis sandstones are yellowish brown in color, siliceous, partly calcareous, and originated from sands deposited in fluvial channels. Texturally, Tanis sandstones are medium- to very coarse-grained, mature, and moderately sorted. Scarcity of feldspars indicates that the sandstone is extensively recycled from a distant source. Their average modal composition (Q99.75F0.03L0.22) classifies them as quartz arenites (quartzite), which is consistent with the geochemical study. Chemical analyses revealed that sandstones have high SiO2 and Fe2O3t and low Al2O3 and TiO2 values, which are consistent with the modal data. Sandstone samples are enriched in most trace elements such as Zr and Ba, and they are depleted in V, Pb, Sc, Rb, U, and Th. The petrography and geochemistry results suggest that Tanis sandstones were deposited in an intracratonic basin or a passive continental margin of a synrift basin. They were mainly derived from deeply weathered granitic-gneissic sources, supplemented by recycled sands from an associated platform. The CIA and CIW values (60.2 and 87.74, respectively) of the Tanis sandstones indicate moderate to intensive weathering either of the original source or during transport before deposition, and may reflect low-relief and warm humid climatic conditions in the source area. The heavy-mineral and trace element results reveal that the Gebel Ahmar quarry is the probable source for the Tanis sandstones.

Dispersions of Surface Modified Calcium Hydroxide Nanoparticles with Enhanced Kinetic Stability: Properties and Applications to Desalination and Consolidation of the Yungang Grottoes

ABSTRACTCalcium hydroxide (Ca(OH)2) is one of the most interesting materials used to consolidate stone sculptures, monuments, mortars or wall paintings. In this study, we reported on the synthesis and characterization of surface modified Ca(OH)2 nanoparticles as a dispersion with enhanced kinetic stability and the applications for the conservation of sandstone monuments. Uniform hexagonal Ca(OH)2 nanoparticles (∼35nm) were obtained by mixing NaOH and NaCl aqueous solutions at 100∼175oC using homogeneous-phase reactions. It was further demonstrated that 3-(Methacryloyloxypropane oxygen) trimethoxysilane surfactant agent can significantly reduce agglomeration and simultaneously improve specific surface area of as-synthesized Ca(OH)2 nanoparticles. Brunauer-Emmett-Teller (BET) measurement showed that specific surface area of modified Ca(OH)2 nanoparticles reaches up to ∼48.78m2/g, about 2.5 and 3.4 times higher than that of unmodified and commercial ones, respectively. The kinetic stability of Ca(OH)2 despersion can be further enhanced and its viscosity can be decreased by optimizing the ratio of ethanol and n-propanol. Especially, a technique, which combined the Ferroni-Dini method and dispersion of Ca(OH)2 nanoparticles with enhanced kinetic stability, was proposed to effectively desalinate and consolidate the decayed stone, as evidenced by significant decreases of the porosity and concentration of detrimental Cl- and SO42- ions in the severely decayed sandstone samples from the Yungang grottoes.

MYCO-ECOLOGICAL STUDY OF HISTORICAL SANDSTONE MONUMENTS, WITH SPECIAL REFERENCE TO MAMA BHANJA TEMPLE OF CHHATTISGARH

Historical sand stone monuments, is subjected to degradation induced by diverse mycoflora. Fungi are among the most active microorganisms in these processes. Fungal ability in production of pigments and organic acids have crucial role in discoloration and degradation of different types of sandstone in historical monuments. This investigation focuses on myco-ecological analyses of microbial bio-film from Mama Bhanja temple of Chhattisgarh State. The seven (07) fungal organisms with specific distribution on sandstone monuments were isolated. Fungi from Ascomycotina as well as Deuteromycotina were more frequent. The most frequent isolated fungal species from these historical sandstone monuments are Aspergillus niger, Curvularia lunata, Rhizoctonia solani and Aspergillus flavus. Aspergillus niger was common in almost all the sandstone structures of this monument. The frequency and relative frequency of these fungal organisms associated with deteriorated sandstone monuments site provides valuable data for future studies. KEY WORDS:- Degradation, Deterioration, Sandstone monument, Myco-ecological, Biofilm.