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Abstract Volcanic rocks have been used for building activity by the inhabitants of important cities located on the slopes of Mt. Etna, Italy. In this paper, the potential use of volcanic residues (code 20 03 03—“Municipal waste” residues from road cleaning in the European Waste Catalogue (EWC)) for the production of alkali activated material, especially devoted to the restoration of buildings belonging to the Baroque Sicilian architecture, was investigated. In particular, large volcanic pyroclastic deposits of recent eruptions considered waste materials were studied and a volcanic paleo-soil, locally named ghiara, widely used for mortars and plaster production in XVII–XVIII century with good pozzolanic features, was also considered. Both volcanic materials were activated using different mixtures of NaOH and Na 2 SiO 3 . Furthermore, formulations with different amount of metakaolin addition (10–25 wt%) were prepared due to low reactivity of volcanic materials and to allow the activation at room temperature. X ray diffraction revealed the formation of small quantities of zeolites as a result of the alkali activation process. The mechanical-physical results evidenced that the mechanical strength is strongly dependent on the metakaolin amount (10–38 MPa); accessible porosity average 25% and an average pore diameter of 0.06 µm; water absorption range 9–15%, eluates conductivity in the range 20–350 µS/m. These results confirm the occurring of alkali activation and the good potential for these pyroclastic wastes for valorization in the restoration field. Graphic Abstract
Abstract Alkali‐activated materials (AAMs) and “geopolymers” are inorganic polymeric materials obtained by mixing of solid aluminosilicate precursors with an alkaline solution (generally, KOH or NaOH and Na 2 SiO 3 mixed in various ratios). This class of aluminosilicate materials has emerged as a greener alternative to traditional concrete, for large‐scale as well as for niche applications such as conservation and restoration of built heritage. In this work we apply Raman spectroscopy both to aluminosilicate precursors (metakaolin, pumice, volcanic ash, volcanic soils, clayey sediments, ceramic waste) and to the respective AAMs. In the field of vibrational spectroscopy, Raman is much less employed in the literature with respect to Fourier transform infrared (FTIR) to have insights into the alkali activation process from a molecular point of view. The aim of this paper is to investigate the potentiality of a Raman approach to the comparison of the employed raw materials with the respective AAMs. Raman analyses during the first hours of geopolymerization were also carried out on the clayey sediments and ceramic waste‐based products. The results, differentiated according to the employed precursors, exhibit spectra relative to crystalline and amorphous phases that can give an indication about the newly formed aluminosilicate gel.
This paper analyses the net social benefits deriving from the medium-scale production of geopolymers based on volcanic ash compared to traditional cementitious materials used in construction and restoration sectors. In contrast to the existing literature grounded on the physical and mechanical characterization of geopolymers, our analysis considers two aspects: public finance savings from avoiding the disposal of volcanic ash in landfills and environmental benefits deriving from reduction in CO2 releases due to the production process at room temperature. Our case study focuses on the reuse of natural waste, namely the volcanic ash of the Mt. Etna volcano (Italy), whose disposal involves significant costs for society. Its use in the alkaline activation process avoids the exploitation of natural resources. Considering the huge amount of volcanic ash from Mt. Etna that falls on the urban areas of Eastern Sicily, the results show relevant economic benefits, in terms of both avoided costs and tax reductions for the citizens. Alongside these, significant environmental benefits are evidenced thanks to the release of up to 78% lower CO2 emissions by synthesised materials with volcanic ash than by traditional cementitious ones. Overall, the social cost savings compared to traditional materials is 0.339 EUR/kg for geopolymer.
Mortars, like any other natural and artificial stone materials, are subject to atmospheric weathering agents which affect their durability according to the intrinsic characteristics of the material, such as mineralogical composition, texture and pore structure. This paper aims to investigate the physical-chemical durability of lime-based mortars made with two different volcanic aggregates, locally known as azolo and ghiara, peculiar of the historic built heritage of Catania (Eastern Sicily, Italy). An experimental approach has been used, based on the reproduction in laboratory of historic mortars by using ancient recipes. The experimental samples have been characterized from a physical point of view and then subject to accelerated aging tests. Specifically, the samples have undergone: i) mineralogical investigations through X-ray diffraction (XRD); ii) thin section analysis by polarized optical microscopy; iii) pore structure analysis through mercury intrusion porosimetry (MIP); iii) water absorption by capillarity; iii) water vapor permeability test; iv) accelerated aging test by salt crystallization; v) decay by sulfur dioxide. Results obtained highlight that the higher microporosity which characterizes the ghiara mortars is certainly responsible for their greater water absorption by capillarity as well as for their lower resistance to salt crystallization and exposure to sulfur dioxide, with respect to azolo-based ones.
Abstract In the last decades, particular attention has been aimed to innovative materials class with high-tech features to apply in conservation-restoration of Cultural Heritage, ensuring both aesthetic compatibility and adequate properties with regards to the original rock substrate. AGM for CuHe project aims to valorise Sicilian raw materials, natural and industrial by-products, for the development of alkali-activated materials, as geopolymers. These materials are produced by the activation of an aluminosilicate precursors in alkaline environment. Volcanic raw materials (volcanic ash, volcanic paleo-soils and pumice) and ceramic industrial waste were mixed with an alkaline solution and cured at room temperature. In some cases, small quantities of metakaolin were added to the mixture to increase the reactivity of the precursors. In order to obtain the geopolymeric reaction, the precursors need to be fully characterized. A similar approach is also applied to the synthesized geopolymers in order to understand its behaviour in relation to the original building materials. Therefore, a multi-analytical approach is proposed: chemical and mineralogical studies (XRF and XRD), combined with spectroscopic (FT-IR) and morphological (SEM and μCT) analyses. These preliminary results confirm the feasibility of this eco-friendly class of materials using the proposed local raw materials.
Abstract The investigation on the reticulation degree of volcanic alkali-activated materials, AAMs, were experimentally determined in terms of chemico-physical properties: weight loss after leaching test in water, ionic conductivity and pH of the leachate and compressive strength. Artificial neural network (ANN) was successfully applied to predict the chemical stability of volcanic alkali-activated materials. Nine input data per each chemico-physical parameter were used to train each ANN. The training series of specific volcanic precursors were tested also for the other one. Excellent correlations between experimental and calculated data of the same precursor type were found reaching values around one. The evidence of strong effect on chemical stability of the alkaline activator SiO 2 /Na 2 O molar ratio as well as the Si/Al ratio of precursor mixtures on the reticulation degree of ghiara-based formulation with respect to volcanic ash-based materials is presented. It must be noted that such effect was much less pronounced on the compressive strength values, appearing more insensitive the molar ratio of the alkaline activator. The comparison of the ANN results with more conventional multiple linear regression (MLR) testifies the higher prediction performance of the first method. MLRs results, less significant, are useful to confirm the powerful capacity of ANNs to identify the more suitable formulation using a set of experimental AAMs. This study, as few others, on the correlation between chemical stability and compressive strength of AAMs provide a great contribution in the direction of durability and in-life mechanical performance of these class of materials. Graphic abstract
Abstract Zeolites are present in numerous outcrops of volcanites of different ages in Sicily (Italy). Some of these outcrops are important because they constitute the ideal genesis conditions of some of these minerals, which represent geological indicators of chemical and geothermal gradients involved during their formation. For this purpose, a group of zeolites coming from areas of the Ionian coast and Palagonia village (Eastern Sicily) was investigated by means of Raman spectroscopy. In the geological record, these areas have been influenced by intense volcanic events that produced mineralization of hydrothermal origin. Sicilian zeolite samples were analysed in situ using different mobile Raman apparatus, directly on the outcrops of Aci Castello and the nearby Lachea Island, or in local collections where they are preserved. Some of these samples have been then analysed using laboratory micro‐Raman to compare the results and identify the zeolite types. The strength and weakness points of each instrument have been highlighted. Often, the Raman spectra of zeolites are affected by broad fluorescence, making them of difficult interpretation. However, satisfying results were obtained with portable devices, whose identifications were confirmed by micro‐Raman, discerning zeolites of different groups, such as analcime, chabazite, natrolite and phillipsite. The use of portable instruments has demonstrated the possibility to obtain identification of zeolites and related minerals both on site and in the laboratory, whose results match with the geological setting of the considered areas.
In the present study, porous inorganic polymers were synthetized by alkaline activation of volcanic ash and 'ghiara' paleosoil using Al swarf and Al commercial powder as pore inducing agent. The Alkali Activated Foams (AAFs) were characterized in terms of mineralogy, macro- and microstructure, by synchrotron X-ray diffraction, electron microscopy, infrared spectroscopy, and X-ray computed microtomography. The obtained porous matrices show different microstructures; the size and extent of the pores vary according to the type, size and amount of the foaming agent and to the viscosity of the pastes. Addition of Al swarf to the volcanic ash based slurry generates expansion of the paste, whereas ghiara based one do not expand due to a lower viscosity of the slurry. Moreover, results indicate that the Al addition procedure during the synthesis affects the pore characteristics: Al powder added directly to the volcanic ash-based slurry triggers an incipient pore nucleation, whereas AAFs prepared adding Al powder to the solid mix do not develop an extended pore network. Results of this research show that porosity can be efficiently tailored in volcanic based AAFs by regulating the amount and type of Al.
Abstract In recent years, there has been a growing interest in one-part alkali-activated materials, which utilize solid-form alkali activators, within the construction industry. This approach is becoming popular due to its simpler and safer application for cast-in-situ purposes, as compared to the conventional two-part method. At this purpose, we have pioneered the use of volcanic deposits of Mt. Etna volcano (Italy) as precursor for the synthesis of a unique one-part formulation. This was done to assess its performance against both traditional and two-part alkali-activated materials. The study employed a comprehensive range of investigative techniques including X-ray powder diffraction, Fourier transform infrared spectroscopy, hydric tests, mercury intrusion porosimetry, ultrasound, infrared thermography, spectrophotometry, contact angle measurements, uniaxial compressive strength tests, as well as durability tests by salt crystallization and freeze–thaw cycles. The key findings on the studied samples are as follows: i) small size of pores and slow absorption-drying cycles; ii) satisfying compactness and uniaxial compressive strengths for building and restoration interventions; iii) high hydrophily of the surfaces; iv) lower heating dispersion than traditional materials; v) significant damage at the end of the salt crystallization test; vi) excellent resistance to freeze–thaw cycles. These newly developed materials hold promises as environmentally friendly options for construction applications. They offer a simplified mixing process in contrast to the conventional two-part alkali-activated materials, thus providing an added advantage to this class of materials.
Abstract Due to the surprising lack of knowledge concerning raw materials and production technology employed to make mosaics after the twelfth century, an archaeometric investigation was carried out on the materials constituting the mosaic decoration of the South aisle wall of Monreale Cathedral (Italy), taking advantage of a conservation intervention. In this work, fallen coloured or gilded glass tesserae to be repositioned were studied by means of a combination of a molecular technique (Raman spectroscopy) and an elemental one (portable X-ray Fluorescence, pXRF); also, efflorescences affecting the general conservation state and samples of the respective bedding mortar were analysed with the former technique and with X-ray diffraction (XRD). The raw materials used and, consequently, the different compositions characterizing gilded vs. coloured glass tesserae were highlighted with the vibrational spectroscopy; chromophores and trace elements were detected by pXRF. This complementary approach allowed to disclose clues about glass-manufacturing technique and raw materials. The nature of the salts was also ascertained through Raman spectroscopy and XRD, for the benefit of the conservation procedure, and connected to the mortars’ composition.
In the view of the recycling and upscaling processes of waste materials, three different precursors, namely metakaolin, fly ash and volcanic ash, were mixed with Na- or K-silicate to produce binders aimed for the synthesis of geopolymer mortars based on construction and demolition wastes (CDWs). These later, used as aggregates in amount of 50 wt.%, were sampled in two geologically different Italian areas. A comparative study was carried out through a multidisciplinary approach using mineralogical–chemical analyses and physical–mechanical tests for the characterization of six binders and twelve mortars. The aim was to verify the effects of CDW interactions on binders as well as the extent of their compositional influences on the final properties. The chemical and mineralogical results evidenced strong compositional differences among the CDWs, differently influencing the physical–mechanical performances (i.e., compressive strength, density, water absorption and porosity) of the mortar samples. Regardless of the types of precursors and CDWs used, a better influence of K-silicate than sodium on the synthetised samples was observed. Furthermore, the higher versatility of metakaolin mortars with any type of CDW used was noted. Contrary, fly ash and volcanic ash mortars showed better properties with CDWs based on their high silica content and volcanic minerals. The study highlighted the critical roles of the CDW composition and precursor selection in mortar production. It confirmed that CDWs can be recycled for geopolymeric synthesis through proper characterisation and binder selection. Optimising these parameters allows for the successful integration of CDWs into geopolymeric materials. This process supports the advancement of a circular economy in the construction industry.
Abstract This work involved the use of neutron imaging for the study of the mechanism and rate of capillary water uptake within alkali-activated materials (geopolymers) synthesized starting from natural and industrial waste precursors of the Sicilian territory, to be applied to the conservation of cultural heritage. In detail, the materials were produced starting from Mt. Etna Volcanic ash, basalt cutting sludges and industrial ceramic tiles wastes; the starting formulations were also enriched with different types of additives (calcium-rich or reinforcing fibres); furthermore, all the samples were investigated both as such and after preliminary weathering treatment inducing sodium chloride crystallization. The aqueous solutions transfer capability of the products was investigated, with important implications in the possible formation of efflorescence. This is vital when prospecting a conservation intervention and evaluating the suitability of the materials for this scope. The study during water uptake was conducted by means of neutron radiography continuously acquiring images integrated on 10 s, while the wet samples of the ceramic-based geopolymers group were studied also by means of neutron tomography with the aim of observing the porous structures/the formed fractures in 3 dimensions. The data were treated and the sorptivity of the materials was obtained, giving some indications about the advisable formulations (e.g. with calcium-based additive) and those to be avoided for cultural heritage conservation (e.g. ceramic-based without additive).
This study explores the feasibility of utilizing granite sawing sludge (FC) as a precursor to produce alkali-activated materials (AAMs). To enhance the reactivity of the system, metakaolin (MK) was added and binary mixtures were synthetized. A multidisciplinary approach, including mineralogical, chemical and mechanical analysis, was employed to assess the suitability of these precursors to produce AAMs. X-Ray diffraction (XRD) and Fourier-Transform Infrared spectroscopy (FT-IR) confirmed the occurred activation reaction with the consequent increase in the amorphous content. Raman spectroscopy was used to further explore the mineralogical composition of the consolidated specimens, helping in the detection of salts, whose formation is ascribed to secondary carbonatation processes. Morphological analysis (SEM-EDS) displayed relatively uniform microstructures for all specimens. Compressive strength tests revealed that MK rich samples achieved best values compared to FC rich formulations, which exhibited reduced strength resistance. This study highlights, for the first time, the benefits of incorporating Cuasso al Monte granite sawing sludges into alkali-activated binders. Results suggested that the incorporation of FC is recommended for both environmental and economic advantages.
From the 9th to the 11th century, Sicily has been part of the Islamic oecumene, the dār al-Islām. Up until now, very few studies have been carried out on the centres of pottery production of this period, and most of them concern the Emiral capital of the isle, Palermo. The archaeometric data obtained with chemical and minero-petrographic analyses on Islamic pottery found in Paternò – a town situated in the southwestern slope of Mt. Etna – has provided a certain number of issues of very important matter. The selection of the samples has been made among the archaeological finds coming from the excavation near the church of Cristo al Monte, on the hilltop, which represented the inner part of the medieval madīna. The mineralogical and chemical characterization of the ceramic body has been attained using optical microscopy on thin sections and X-ray fluorescence respectively, in order to define the probable provenance of each sample. Further information of technological matter has been provided using X-Ray diffraction on powdered samples, which furnishes mineralogical data useful to hypothesise the firing temperatures: the main task attained on this issue was the focus on the self-slipped ware with salted water, one of the main technological class in Islamic Sicily. Finally, energy dispersive X-Ray fluorescence was adopted for a preliminary investigation of pigments used to decorate the lead glazed pottery. The issues related to both the local and imported pots – the latter represented almost completely by Palermo"s products – provided some important historical and archaeological information about the means of Sicilian pottery production during this important period.
Food counterfeiting is an emerging problem worldwide and the increasing consumption of fake products has brought food safety into major focus. In recent years, several analytical approaches were developed to prevent food counterfeiting. Among them, X-ray Fluorescence spectroscopy (XRF) is emerging as a fast and simple screening tool for food elemental analysis, with important applications in the agri-food sector. The present work explores the feasibility of using portable XRF device to verify the quality and the geographical origin of pistachio samples coming from different growing areas of Sicily (Italy), including pistachio samples form Bronte and Raffadali districts, recognized by the European Union with the Protected Designation of Origin (PDO) label. The XRF spectra and the yields extracted for the main identified elements were compared with each other by using Principal Component Analysis (PCA). Statistical analysis highlighted that pistachio samples clustered into distinct groups accordingly with their territory of origin, having a different elemental profile. Among the elements, K and Ca appear to act as discriminant markers, followed by Rb and Fe. Potassium mainly characterized the samples originating from Agrigento and Messina, whereas Ca, Rb and Fe the pistachio seeds harvested in Catania. Based on these results, the elemental composition detectable through XRF analysis could be used as a fingerprint to disentangle foodstuffs of different origin and to hinder the occurrence of food counterfeits concerning the branded products, in support of the traceability system. The possibility of assessing quality and traceability quickly, easily and in-situ, gives solid perspectives for a large-scale application of the XRF technique at all stages of the food chain.
Abstract In this study, binary alkali-activated pastes based on volcanic ash from Mount Etna (Italy) and borosilicate waste glass were synthesized for the first time using potassium hydroxide (KOH) at different molarities (i.e., 7 M and 9 M) and moderate temperature (60 °C). This work aims to define how the reactants involved in the mix design, specifically the solution concentration and solid proportions of the waste precursors, influence the final microstructure and subsequently their physical and mechanical properties. For this purpose, a multidisciplinary approach, including mineralogical, molecular, chemical, and morphological investigations, was applied to elucidate these properties. The physical-mechanical parameters, including density, uniaxial compressive strengths, porosity, pH, and leaching resistance, determined by boiling tests, were quantified. Increasing KOH molarity from 7 M to 9 M contributes to the formation of a more stable Si-O-Si/Al network, enhancing the compressive strength resistance (~21 to 23 MPa) and reducing both weight loss (~7 to 9%) and the open porosity (~20%). The combined effect of higher molarity and waste glass proportion positively influenced the mechanical response, as a result of the formation of a denser and more compact microstructure. Results confirmed that sustainable materials can be produced using potassium-based binders made from volcanic ash and waste glass.
