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A FAU-X-rich porous monolith has been obtained by means of an unconventional two-stage method consisting of the production of a foamed geopolymeric precursor and its subsequent conversion by means of a hydrothermal method. The influence of the conversion process parameters, such as NaOH concentration (0.1–2 M), treatment temperature (40–80 °C) and time (24–72 h) on the FAU-X crystallization was studied. Collected data revealed that the highest yield in terms of zeolite content and FAU-X/LTA ratio was obtained performing the hydrothermal treatment with a 0.5 M NaOH solution at 60 °C. The crystallization kinetics of FAU-X inside the geopolymer precursor was investigated by means of Synchrotron Radiation X-Ray Diffraction Quantitative Phase Analysis (SR-XRD-QPA). Results showed that the crystallization starts after an induction time of about 3 days, and the weight percentage of the zeolite in the sample raises up to about 78% after 20 days of treatment. The highest yield in terms of zeolite content, about 80% of FAU-X and 6% of LTA, was reached at 20 days. Finally, Scanning Electron Microscopy (SEM) analysis showed the presence of well-defined octahedral crystals either on the pore surface or in the bulk of the sample starting from 3 days of hydrothermal treatment.

Graffiti vandalism represents an aesthetic and structural phenomenon of degradation both for buildings and cultural heritage: the most used sprays and markers can permeate the stone materials exposing them to degradation. Hence, great attention is being currently devoted to new non-invasive chemical approaches to face this urgent problem. This work is aimed at deeply examining the effects of some of the most sustainable chemical protective methods on the physical properties of natural building materials (e.g., tuff and limestone) by testing two commercial anti-graffiti products. It was found that the nanotechnological product Ector (E) was more effective than Nord Resine (NR) in anti-graffiti applications even if its permanent character hinders its application to the cultural heritage. Conversely, the less performant NR could be used in this field due to its sacrificial behavior, according to the guidelines of the Italian Ministry of Cultural Heritage and Activities and Tourism. The findings highlight the importance of developing new sustainable methods for the preservation of cultural and building materials from vandal graffiti, which should combine the high hydrophobia, the ecological characteristics, and the effectiveness of E, with the sacrificial properties of NR.

Demolition activity plays an important role in the total energy consumption of the construction industry in the European Union. The indiscriminate use of non-renewable raw materials, energy consumption, and unsustainable design has led to a redefinition of the criteria to ensure environmental protection. This article introduces an experimental plan that determines the viability of a new type of construction material, obtained from crushed brick waste, to be introduced into the construction market. The potential of crushed brick waste as a raw material in the production of building precast products, obtained by curing a geopolymeric blend at 60 °C for 3 days, has been exploited. Geopolymers represent an important alternative in reducing emissions and energy consumption, whilst, at the same time, achieving a considerable mechanical performance. The results obtained from this study show that the geopolymers produced from crushed brick were characterized by good properties in terms of open porosity, water absorption, mechanical strength, and surface resistance values when compared to building materials produced using traditional technologies.

Promoting the use of gypsum and gypsum-based materials in construction is a successful strategy from an environmental point of view, it allows a lower energy demand with a sensible reduction in carbon dioxide emissions. At the same time, the manufacturing of gypsum products can represent an interesting sector to redirect and manage the large amount of autoclaved aerated concrete (AAC) waste. In this paper a sustainable application of AAC granulate waste in gypsum-based building materials was proposed. The intrinsic compatibility derived their chemical composition and allowed it to partially substitute raw gypsum with the waste up to 30% without affecting the functional and structural properties of the final product. Physical characterization and sound absorption data confirmed that the addition of AAC waste does not significantly alter the typical porosity of the gypsum composite. Finally, all of the composites reached mechanical performances suitable for different building application as gypsum plaster.

Ceramic adhesives are an interesting alternative to traditional methods to join metal to ceramics such as fastening, vacuum brazing and gluing. Ceramic adhesives are made of an inorganic matrix with a filler (alumina, zirconia, silica, etc.), and they require a thermal cure cycle in order to establish adhesion. In this work, the adhesion between two different adhesive and Ti6Al4V is studied in details and the influence of the curing cycle is analyzed. Two different adhesives have been used, the first made of a phosphate matrix with an alumina filler, the second made of a silicate matrix wit an alumina filler. The results indicates that in the case of the first adhesive a high temperature cure it is necessary in order to establish a strong adhesion with the metal; on the contrary the second adhesive is capable to create a strong bonding already at low temperature.

Mineral production continues to be necessary for economic development, consequently also the management of mining and mineral-processing wastes represent a considerable issue in terms of recycling and economic strategies for the future. One of the most promising reuses for coarse-grained mining wastes, especially barren waste rocks from coal and metal mining, is their application in the building and construction sector. An experimental research has been developed with the aim of studying the possible reuse of waste rocks – coming from mining activities-as fine aggregates in a fly ash based geopolymer: physical, chemical and mechanical tests have been carried out in order to analyze in detail the interaction between the geopolymer binder and the rock waste aggregates. All the mixtures, characterized by an aggregate/binder/ratio ranging between 0.05 and 1, showed a final microstructure characterized by a rather homogeneous geopolymer matrix embedding the mining waste rock. The geopolymeric matrix governs the overall mechanical behavior of the system, thanks also to the strong interaction at the interface between matrix and aggregates (mining waste). Moreover, all the geocomposites satisfy the prescribed limit for inert or non-hazardous waste.

The present paper assesses petrographic, mineralogical, chemical, and technological features of different zeolitic tuff samples from various western USA districts of the Basin and Range Province containing mainly erionite, mordenite, clinoptilolite/heulandite and phillipsite. The aim of this characterization is to evaluate the pozzolanic activity of these samples according to European normative UNI-EN 196/5 (Fratini test) to program a possible use as addition for blended cements. Petrographic and mineralogical results show that the two phillipsite-bearing tuffs have a higher theoretical Cation Exchange Capacity (CEC) than the other samples; technological characterization shows a pozzolanic behavior for all the samples but higher for the tuff samples containing phillipsite, which shows a higher reactivity with CaO. All the samples could be thus advantageously employed for the preparation of blended cements, potentially reducing CO2 emissions by 70–90%.

The present study is focused on the development and characterization of innovative cementitious-based composite sensors. In particular, multifunctional cement mortar composites with enhanced functional, piezo-resistive, properties are designed with Multiwall Carbon Nanotube-MWCNTs and reduced Graphene Oxide-rGO dispersed in a natural-rubber latex aqueous dispersion, by exploiting both the concept of confining of the conductive filler in the polymeric phase. The manufactured cement-based composites were characterized by means of Inelastic Neutron Scattering to assess the hydration reactions and the interactions of natural rubber with the hydrated cement phases and by Electron Scanning Microscopy and X-Ray diffraction to evaluate the morphological and mineralogical structure, respectively. Piezo-resistive properties to assess electro-mechanical behavior in strain condition are also measured. The results show that the presence of natural-rubber latex permits to obtain a three-dimensional rGO/MWCNTs segregate structure which catalyzes the formation of hydrated phases of the cement and increases the piezo-resistive sensitivity of mortar composites, representing a reliable approach in developing innovative mortar-based piezoresistive strain sensors.

Water pollution is one of the biggest environmental issues of our times. To address such a huge challenge, the full involvement of everyone is required. In this context, we report the results of outreach hands-on activities aimed at presenting to the general public two classes of materials with high potential in the removal of common water pollutants, such as heavy metals and dyes: zeolites and chitosan-based aerogels. Under the guidance of young students of materials science and engineering, participants have performed safe, fast, and easy to understand experiments for the removal of copper ions and dye molecules from water. The discussion of the results, which was adapted time by time to the knowledge and age of the audience, provided all participants with a general understanding of the two phenomena underlying water purification, namely, ion exchange for zeolites and molecular adsorption for chitosan aerogels. Besides raising awareness of young people about water pollution and, more in general, about environmental issues, the proposed activity highlights the key role of materials scientists in providing smart and feasible solutions to tackle everyday problems.

An innovative and facile synthesis of cobalt based inorganic pigment was carried out by means of a low energy thermal conversion of a cobalt-exchanged zeolite. The Na-A [LTA] zeolite was used, since it is a low cost and easily available raw material. The ion exchange mechanism allowed to control, at microscopic level, the composition of the zeolitic precursor. Several chromatic effects could be obtained by varying the treatment temperature and/or the cobalt concentration in the contact solution. The reliability of these new zeolite-based pigments was tested in porcelain manufacture, in collaboration with the Institute for the Capodimonte porcelain “Giovanni Caselli”. The developed cobalt pigments were successfully tested either in the porcelain mixture to obtain a coloured product or in the decoration step (such as ingobbio, colored glazes and “third fire decoration”).

Dredging activities of harbours and rivers are becoming very important in many countries all over the world and, as a consequence, the disposal of dredged sediments is a critical concern from an environmental point of view. In order to facilitate the disposal or the reuse of large volume of dredged soils, usually under-consolidated and with a high water content, an electrokinetic treatment can be adopted with the goal to dewater and strengthen the sediments. This paper presents the results of some electrokinetic tests performed on reconstituted clayey specimens at different pore fluid salinities (0.2 < sc < 30 g/l) treated with electrokinetic (EK) technique. The results indicate that the presence of small quantities of salts in the pore fluid enhances the electro-osmotic consolidation. On the contrary, for high salt concentrations of the pore fluid the electro-osmotic dewatering is significantly reduced. The mechanical behaviour of treated specimens has been investigated at the micro (SEM) and macro scale (triaxial and oedometer tests). The experimental results highlighted the relevant and expected contribution of the pore fluid characteristic on the effectiveness of the treatment as ground improvement technique.

The latest tendency of the scientific community regards the development of different classes of green materials able to solve pollution problems caused by industrial and human activity. In this paper, chitosan and diatomite were used to produce a broad-spectrum hybrid adsorbent, either in powder or in monolithic form for environmental pollutant removal. Diatomite&ndash, chitosan-based powders and porous diatomite&ndash, chitosan hybrids were prepared and characterized by chemical-physical, thermal and morphological analysis. Moreover, their adsorbent capacity towards anionic dye (Indigo Carmine) was also evaluated. Obtained data showed that chitosan improves the adsorption capacity of both systems, increasing the uptake of dye in both diatomite&ndash, chitosan systems.

The subsoil consolidation in the archaeological sites or in areas with historic existing buildings (e.g. Pompeii) needs the use of ground improvement techniques that must guarantee the safeguarding of such relevant areas and structures. One of the best approaches in such cases is low pressure grouting. An experimental multidisciplinary study was carried out with the aim to design and characterize a sustainable chemical grout sodium silicate-based catalysed by NaHCO3. The evolution from sol-to-glassy phase of the grouts was carefully investigated, furthermore the effectiveness of the grout has been verified either by lab tests or by real-scale field trials. The experimental findings suggested that it is possible to properly control the viscosity and gel-time of the grout modulating the amount of catalyst without affecting the final consolidation performances. Furthermore, the results at real-scale validate the safety of the above approach in cultural heritage applications, since it allowed a complete permeation of the soil without worsening its final properties. (C) 2019 Elsevier Ltd. All rights reserved.

Motivated by the hierarchical micro and nanoscale features in terms of porosity of diatomite, the production of ceramic-graded porous foams with tailored porosity, obtained by using it as raw material, has been proposed. The main challenge during the foam-production process has been the preservation of diatomite nanometric porosity and the addition of other levels of hierarchical porosity. The coupled use of two techniques of direct foaming (chemical and mechanical), combined with the use of 3D printing inverse replica method, assured the achievement of porosity of, respectively, microscopic and macroscopic dimensions. Optical and scanning electron microscopies have been performed for an in-depth characterization of the final microstructure. XRD analysis has been carried out to check the influence of sacrificial templates on the matrix mineralogical composition. The porosity of the diatomite-based foams has been investigated by means of nitrogen-adsorption analysis and mercury-intrusion porosimetry. The experimental tests confirmed the presence of different porous architectures ranging over several orders of magnitudes, giving rise to complex systems, characterized by hierarchical levels of porosity. The presence of porosity of graded dimensions affects the final mechanical performances of the macroporous diatomite-based foams, while their mineralogical composition does not result to be affected by the addition of templates., Scientific Reports, 10 (1), ISSN:2045-2322

In the last decades, the use of natural fibers as replacement to synthetic fibers in reinforced composites has become a trending practice due to their attractive features. The main drawbacks associated with the use of natural fibers are the hydrophilic nature and the weak interaction between fiber and binder matrix, so they are often subjected to pre-treatments before their utilization. The use of chemical treatments may improve the adhesion between fiber and matrix, but it involves a dangerous impact on the environment. In this study, biologically treated hemp fibers were proposed as reinforcement in plasterboards. The effect of the bio-treatment was evaluated by SEM, DTA, FT-IR and XRD analysis in comparison with traditional chemically treated fibers. These analyses showed that both the treatments involve in similar modifications on fiber's morphology and composition. In addition, a strong reduction of treated fibers' water absorption was measured. Three-point bending test and low impact behavior revealed an enhanced toughness and a damage reduction of the fiber-reinforced plasters, so indicating a comparable efficacy of the biologically treated fibers respect to a chemically treated ones.

Ba0.75Sr0.25 Al2Si2O8 (BSAS) ceramic was synthetized starting from a (Ba, Sr)-exchanged zeolite A. The substitution of Ba with Sr promoted the transformation of hexacelsian to monocelsian, which was attained by a 5 h thermal treatment at 1200 °C. BSAS systems were structurally and dielectrically characterized. In particular, the evaluation of dielectric properties was performed by impedance spectroscopy in a.c. The study of the dielectric and the spectroscopic characteristic was investigated in the frequency range (100 Hz - 1 MHz). The dependence of the dielectric constant on the frequency has been explained on the basis of the mechanism Maxwell-Wagner, comparing BSAS systems with commonly used ceramic materialsin radome manufacturing, such as fused silica (SiO2) and silicon nitride (Si3N4).Electrochemical Impedance Spettroscopy (EIS) also provides useful information about the microstructure of the ceramic materials. The curve of permittivity vs frequency showedthat the BSAS has a constant performance in the frequency range investigated with lower value of permittivity compared to the other materials investigated.

Mesoporous silica nanoparticles are among the most promising nanovectors for controlled release of active compounds. In this work we design a mesoporous silica-based delivery system in which the release of the active compound is controlled by specific pore/wall interactions and can also be triggered by an external stimulus, such as the simple addition of water into the surrounding releasing medium. Due to its reversibility in presence of water, imine bond formation between amino groups and aldehydes has been proposed as a valuable approach to reach this scope. The amino-group is provided by the amino-functionalized mesoporous silica which has been obtained through the functionalization of Santa Barbara Amorphous (SBA)-15 with aminopropyltrietoxysilane. Whereas the aldehyde is represented by the active compound itself: the natural antimicrobial vanillin. The obtained particles have been embedded into PCL-based films. The amino-functionalization of mesoporous silica has been confirmed through NMR analysis and X-ray diffraction. Imine bond formation and evolution has been followed by 13C NMR before and after the contact of mesoporous silicas with water. Release kinetics of vanillin show that the diffusion of vanillin from films containing the functionalized mesoporous silica is delayed by about 20% and 75% with respect to films containing free vanillin, in water and in ethanol respectively. The most significant feature of the system is the stepwise behavior which shows that the release of the amount of vanillin bound to the NH2 groups of functionalized SBA is triggered only after the addition of water to the surrounding ethanolic solution. These findings give an important insight into the use of pristine and functionalized mesoporous silicas for the development of polymer films for active responsive packaging materials.

In this study, the suitability of a nano-silica based consolidant for the conservation of a volcanic tuff was evaluated. The consolidant consists of an aqueous suspension of nano-silica particles (diameter of 10 ÷ 20 nm) and despite its lower penetration capacity than ethyl-silicate–based consolidants, takes advantage of less toxicity, a fast-enough setting time. Moreover, it induces not - relevant chromatic alterations on specimens’ surface. For this purpose, two series of specimens have been dipped one or two times in the consolidating solution (1:1 dilution). After treatment by immersion, a considerable amount of solvent evaporated, but a continuous silica gel film permeated the pores of stone surface layers, thereby reducing the stone susceptibility to decay mechanisms related to the action of water, mainly the water absorption by capillarity and permeability. The consolidating action promoted also a moderate strengthening effect, increasing the cohesion of tuff as evidenced by unconfined compressive and flexural strength tests. Finally, ageing tests (freeze-thaw cycles) have provided additional data that support the suitability of silica nanoparticles for conservation/restauration of tuff.

A great challenge of research is the utilization of natural or synthetic zeolites, in place of natural pozzolans, for manufacturing blended cements. The difficulties of interpretation of the pozzolanic behavior of natural zeolite-rich materials and the role played by their nature and composition can be overcome by studying more simple systems, such as pure synthetic zeolites. This study aims at investigating the pozzolanic ability of isostructural zeolites with different framework compositions, such as three sodium zeolites of the faujasite (FAU) framework type: LSX, X, and Y. The pozzolanic activity has been estimated by thermogravimetry and X-ray diffraction analysis. The overall outcome of the investigation is that the zeolite structure affects its pozzolanic activity, as zeolites with similar framework densities exhibit distinct abilities to fix lime. Moreover, the framework composition is effective either from a kinetic point of view or on the total amount of fixed lime. Zeolite X appears to possess the best average features.

In Europe, large amounts of materials are dredged annually to maintain channels and harbour activities. Consolidation processes in dredged sediments take very long-time due to the high-water content, much more than those considered in the typical problems of geotechnical engineering. The electrokinetic treatment (EK) can be an effective technique to accelerate the dewatering of these sediments and, at the same time, to improve their mechanical properties. An experimental research is under course at the University of Napoli Federico II with the aim to analyse the effects induced by EK treatments on the physic-chemical and mechanical properties of two different soils. Some laboratory tests have been carried out in a special apparatus (special oedometer) adopting two different pore fluids (tap water and sea water). The laboratory results show that the effect of EK treatment, both in terms of induced water flow and improvement of soil mechanical properties, is affected by the chemical properties of the pore fluid and by the physical and mineralogical characteristics of the particles. The results obtained at the macro-scale (specimen) have been analysed at the micro-scale by means of X-ray diffraction analysis and Scanning Electron Microscopy, comparing the microstructures of treated and untreated soils specimens.

Many industrial applications need supporting or shaping powdery zeolites. Since geopolymers can be considered the amorphous counterpart or precursors of crystalline zeolites, it is possible to promote zeolite crystallization inside the geopolymeric matrix by tuning pH, temperature and time of the geopolymerization reaction. In this paper, combining zeolite crystallization with a foaming process initiated by silicon, a multifunctional self-supporting zeolitic material has been obtained with pores ranging from the micro to the macro range. Geopolymerization and crystallization have been realized simultaneously curing the samples at specific temperature and humidity conditions. Every specimen obtained at curing time higher than two days, regardless relative humidity and silicon content, contained zeolite A [LTA] and X [FAU] as the only crystalline phases. Finally, the porosity generated by the foaming process promotes the zeolite nucleation mainly on the surfaces of the pores, whereas the struts remain amorphous.

The management of huge amounts of waste deriving from several anthropogenic activities, such as manufacturing, construction, mining and quarrying, dredging, represents a great contemporary environmental challenge for many countries worldwide. Among the different recycling possibilities, the use of the excavated soils, obtained from operations such as tunneling, excavations, mining, dredging etc., which are generally considered as soil waste, in the production of innovative eco-sustainable building materials represents an interesting alternative to their disposal. In fact, considering especially their chemical composition, low cost and easy availability, soil wastes seem to be the ideal candidates to be used as secondary raw materials for the manufacture of geopolymer-based materials. The paper intends to present a review of the recent scientific literature regarding the use of different types of soil waste to produce geopolymeric binders. Particular attention is focused on mining waste (deriving from various types of mining industries) and dredged sediments coming from marine harbors and natural and artificial water reservoirs, in order to understand and critically discuss the limits of their disposal approach and, at the same time, show perspectives and challenges for possible future research activities in this field. The production of geopolymer-based building components, starting from mining waste and reservoir sediments, is widely discussed thanks to the numerous scientific findings, while the recycling of marine dredged sediments through geopolymerization represents a completely new and innovative trend in research activity, in fact only few related papers were found in literature. It can be strongly stated that geopolymerization can significantly contribute to a sustainable improvement of soil waste management systems.

This paper reports the characterization of Sr-, Zn- and Cd-exchanged zeolitic materials as water vapor adsorbents, in order to evaluate the influence of the extraframework species on their adsorption properties. Both synthetic and natural substrates are taken into account. Water vapor adsorption isotherms on each ion-exchanged sample have been obtained at 298, 318, 338, and 358 K and have then been modeled using the Dubinin-Astakhov equation. Focusing on the possible implementation of such adsorbents in thermodynamic cycles, an estimation of their specific heat storage densities has been expressed. Results revealed that adsorbents of natural origin are not suitable for a valid employment in thermodynamic cycles, while FAU-type zeolite X samples exchanged with Sr2+ or divalent transition metal ions (i.e., Zn2+ or Cd2+) show a significant potential as heat storage media. The same trend of the specific heat storage density with the cationic content of the adsorbent can be identified for both series of synthetic and naturally originating materials (i.e., Zn > Sr > Cd > Na), confirming how ion exchange allows effective tuning of zeolitic substrates when employed in thermodynamic cycles based on the reversible adsorption of water vapor.

3D-structured silica exoskeletons-diatomite was used as reactive inorganic ingredient, with and without metakaolin to produce sustainable multifunctional diatomite-based geopolymeric foams. Suitable amount of Silicon powder and vegetable surfactant were used as foaming agents, while polysilicate solution was used as reactive crosslinker. The resulting porous materials, characterized by hierarchical porosity ranging from macro to nano-scale, were fabricated at 40 °C for 24 h and characterized by means of chemical and morphological investigations, contact angle, thermal and acoustic properties and fire reaction. The presence of diatomite in the produced foams provides an increase of thermal inertia, and the thermal insulation performance firstly due to the intrinsically low thermal conductivity of diatomite and also because silicon and vegetable surfactant are able to promote the formation of a co-continuous mesoporous structure. Furthermore, the created morphological structure provides a good acoustic absorption coefficient in a wide range of frequency. Finally, due to their hydrophilicity/oleophobicity character, diatomite-based geopolymeric foams could, potentially, be proposed as oil/water separation membranes. Keywords: Sustainable chemical-Diatomite, Porous material, Silicate solution, Wettability, Thermal-acoustic insulation

The paper represents the “state of the art” on sustainability in construction materials. In Part 1 of the paper, issues related to production, microstructures, chemical nature, engineering properties, and durability of mixtures based on binders alternative to Portland cement were presented. This second part of the paper concerns the use of traditional and innovative Portland-free lime-based mortars in the conservation of cultural heritage, and the recycling and management of wastes to reduce consumption of natural resources in the production of construction materials. The latter is one of the main concerns in terms of sustainability since nowadays more than 75% of wastes are disposed of in landfills.

Wastewater treatments by using low cost adsorbents is becoming a topic of primary interest. In the present work, the efficiency of a diatomite-based composite ceramic foam for cadmium adsorption was analyzed, in order to propose it as low-cost heavy metal absorber. Kinetic data showed a faster cadmium uptake capacity for the foamed sample, due to enhancement of the specific surface area obtained by foaming. Moreover, adsorption isotherms showed that the cadmium adsorption depends on the temperature for both materials and, in particular, this dependence is linear and higher for diatomite based composite foam.

The requirement for environmentally friendly construction materials for sustainable development is nowadays an important issue and the geopolymer technology provides a good solution to replace, as binder, the ordinary cement materials for green building. Fly ash, an industrial by-product currently disposed of as waste, can be used as feedstock for geopolymers with an excellent greenness. In order to preserve the eco-friendly nature of the fly ash based geopolymer and enhance the mechanical properties that represent a weak point of the cementitious materials, limiting their application fields, a new fly ash based geopolymer composite was introduced. For this purpose, inorganic, organic and natural short fibers, i.e. E-glass, aramid and hemp respectively, were considered as reinforcement. The mechanical response of these composites under quasi-static and dynamic load conditions was investigated and compared to plain geopolymers, drawing the attention to the hemp reinforced ones, because of their low coast and eco-friendly nature.

Due to the large latent heat related to dehydration into hemihydrate and anhydrite, gypsum is largely used to make firebreak systems. During a fire exposure, the dehydration can induce cracks inside the panels, since the loss of bound-water molecules leads to a large thermal shrinkage. In this study, hemp fibers were added into the plaster, acting as thermo-mechanical reinforcement of the gypsum panels and hindering the cracks formation. The effect of hemp fibers on the thermal behavior of gypsum panels was studied in terms of thermo-mechanical properties in isothermal conditions. Change in chemical composition and morphology of the gypsum matrix after the thermomechanical test were analysed by thermogravimetry (TGA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Hemp fibers, even at high temperatures, preserved their “bridge action” between the fracture surfaces, increasing the tenacity of plaster and preventing its fragile collapse.

Natural fibres have been widely studied as environment-friendly alternative to synthetic ones in composite manufacturing; they can be considered as reinforcement of geopolymeric foams for use as insulating materials. In this regard, the paper focuses on lightweight geopolymers reinforced with hemp fibre grids. These novel composite materials, produced in different ways, are characterized by means of wide experimental tests and their properties are compared with the ones of the plain geopolymer. Morphological analysis shows good bonding between the matrix and the hemp reinforcement; in addition, the main physical properties of the foam are not negatively affected by the presence of hemp fibres. From a mechanical point of view, the composites when subjected to quasi-static load conditions do not collapse in a brittle manner, and show improved flexural strength under dynamic load conditions. Finally, from thermal analysis, they guarantee a good thermal stability.

This review presents “a state of the art” report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1—the present paper—focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

The management of reservoirs for water supply is a great environmental problem, since regular de-silting operations produce huge quantities of sediments. Among the recycling possibilities, the use of clay sediments for the manufacture of geopolymer-based materials seems to be an interesting alternative to disposal, due to their low cost and easy availability. In particular, two sediments, coming from reservoirs located in Southern Italy, were firstly characterized by X-ray diffraction, differential thermogravimetry, Fourier transformed infrared (FTIR) spectroscopy and 27 Al and 29 Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. The reactivity of raw and thermally treated clay sediments in alkaline media was also investigated. Finally, geopolymeric samples were produced and chemically, physically and mechanically characterized. The results showed that the calcined clay sediments can be suitable source materials in polycondensation reactions and that the increase of the calcination temperature from 400 to 750 °C resulted in an increased reactivity. Moreover, good mechanical properties were obtained by all the geopolymers prepared with heat-treated sediments.

The design of the production process of diatomite-based ceramic foams, starting from different percentages of metakaolin, diatomite, and sodium silicate solution as reactive ingredients and vegetable surfactant and silicon powder as blowing agents, has been set up. The foams were obtained using the double effect of different foaming approaches: mechanical stirring and chemical foaming. Six systems were prepared fixing the amount of diatomite (100%) and adding in the starting mixture of different percentages (0.05, 0.1, 0.25, 0.5, 0.75, and 1 wt%) of silicon metal. Once the optimal percentage of silicon metal (0.05%) is chosen thanks to XRD analysis, other three systems were prepared only changing the amount of diatomite (50, 70, and 100 wt%) in starting formulation. The foam obtained with 100% of diatomite results to be the optimized final formulation, as it shows a hierarchical porosity with a high homogeneity of the matrix at the same time. The results highlighted that the best performances in terms of lightness, high porosity as well as homogenous microstructure were obtained using, with respect to the total amount, 6 wt% of mechanical stirred vegetable surfactant together with 0.05 wt% of Si as physical and chemical blowing agents, respectively.

Organic–inorganic hybrid foams were prepared by using metakaolin or diatomite as a partial (or total) replacement of metakaolin, as precursor and metal silicon and whipped protein as blowing agents. The foamed systems were cured at defined temperature and time and then characterized by chemical point of view through Fourier transformed infrared spectroscopy and X-ray diffraction and by mechanical and morphological point of view by compression tests and scanning electron microscopy. The experimental findings highlighted that the replacement of diatomite in the formulation affected the morphological structure of the foams and consequently their mechanical properties, due to a different chemism between the sodium silicate and the solid phase. In particular, the consolidation mechanism in the diatomite based-hybrid foams changed from geopolymerization to a silicate polycondensation. Consequently, mechanical performances enhanced with increase of the diatomite content.

Physical and chemical properties of raw materials used in additive manufacturing deeply influence process outcomes in terms of product quality. Therefore, a good production policy should mandatorily consider the availability of measurement facilities that provide ad hoc characterizations of raw materials. At the same time, structure and defect analysis is a crucial step in the optimization of AM process as well as for the quality control of final products. For this reason, a laboratory of materials and products characterization has been identified as one of key-facilities of the Digital Manufacturing Hub that the University of Napoli Federico II is establishing at CeSMA (Centro di Servizi Metrologici e tecnologici Avanzati) as support for the development of an additive manufacturing industry in Campania Region and Southern Italy.

In this paper fly ash based geopolymer mortars have been prepared and their thermal behavior evaluated in order to assess the suitability of fly ash based alkali-activated binders for thermal energy storage in solar thermal plants. Different parameters, such as binder/aggregate ratio, percentage of fly ash replaced by slag, temperature and curing time, have been changed and optimized using the Design Of Experiments (DOE) approach. In order to estimate the thermal cycling stability of geopolymeric mortars at elevated temperatures, mechanical strength and weight loss of each sample subjected to different thermal cycles in the temperature range 150–550 °C were evaluated. Finally, thermal conductivity of some of the mixtures, selected on basis of the thermal stability test results, have been measured. Fly ash based geopolymeric mortars remained stable after each thermal treatment and specimens treated at elevated temperatures retained acceptable compressive strength. The thermal stability was preserved also after repeated thermal cycles, proving that fly ash based geopolymers are suitable materials for thermal energy storage concretes.

The ion-exchange properties of a synthetic hydrosodalite (Na-hS) have been investigated by kinetic and thermodynamic analysis of exchange reactions of the original sodium form for lithium, potassium and calcium forms. Kinetic curves, modelled by a Langmuir-type equation, revealed that exchange rate for lithium and for potassium are of the same order, whereas they are two order faster than for calcium. Thermodynamic analysis of the cation exchange isotherms pointed out that sodalite is selective for sodium over the other three cationic forms examined, which is consistent with the preference exhibited by the sodalite type for sodium environments, either in natural or in laboratory crystallization. Na/Li and Na/Ca exchanges are incomplete, whereas unexpectedly Na/K exchange turns out to be complete, even though K+ dimension exceeds the width of the access window to sodalite cages. The obtained results have been discussed in terms of Eisenman–Sherry theory, pointing out agreements and discrepancies.

In this paper artificial aggregates based on recycled plastic materials, mostly polyolefin and polyethylene terephthalate waste, were used as partial replacement of natural aggregates for manufacturing hydraulic mortars. In particular, different amounts (10–50% by weight) of siliceous sand were substituted by the same weight of the above plastic waste, to obtain six mortars with different composition. The influence of plastic addition on physical and mechanical properties (density, porosity, compressive and flexural behavior and water vapour permeability) was studied. Moreover the thermal conductivity of the obtained mortars was evaluated. Recycled plastic substitution enhances the open porosity, causing a decrease in flexural and compressive strength, with an increase in water vapour permeability. Nevertheless, the presence of plastic aggregate leads to a significant reduction in thermal conductivity, which improves the thermal insulation performances of the mortar. For this reason the addition of recycled plastic aggregate in the manufacturing of hydraulic mortars can be considered a way to reduce the growing environmental impact of polymers and, at the same time, it allows the development of increasingly eco-sustainable building materials.

In order to design binding materials able to historical buildings restoration, physical–mechanical properties and microstructure of fibre-reinforced lime-based hydraulic mortars, have been studied, in comparison with a reference hydraulic lime-based mortar with no addition. Fibre-reinforced mortars, even characterised by larger porosity and lower mechanical strength than the reference, pointed up a clear improvement in the post-cracking behaviour and, regardless of nature and concentration of fibres, turned from brittle materials to ductile materials. It was demonstrated that the addition of as low as 2% of glass fibres leads to a toughening of the mortar and jointly to an improvement of the flexural load.

Dredging activity in harbours and channels produces huge quantities of sediments, generally considered as waste soil (WS) to be disposed: the management of such sediments is a great environmental problem for many countries worldwide. Among the recycling possibilities, the use of dredged sediments for the manufacture of geopolymer-based materials seems to be an interesting alternative to disposal, due to their low cost and easy availability. In order to analyse the possibility to use these geopolymer materials as building materials - for instance as precast construction elements in maritime projects - a multi-disciplinary research activity has been developed at the Federico II University of Napoli (Italy). Some experimental tests have been carried out on different geopolymeric specimens made by mixing sediments from Napoli 'harbour and industrial fly ashes produced by a power plant in the South of Italy. A siliceous sand was used for comparison as an inert reference material. Chemical, morphological and mechanical properties of different specimens have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and finally unconfined compression tests. The experimental results highlight that the use of dredged sediments in combination with fly ash can lead to geopolymeric matrices with interesting mechanical performances. Some differences in the microstructure of the geocomposite built with the siliceous sand or the dredged materials were found. In terms of environmental impacts, on the basis of standard leaching tests and according to Italian thresholds, the adopted dredged mixtures satisfy the prescribed limit for inert or non hazardous waste.

Organic–inorganic hybrid foams were prepared by using metakaolin, diatomite as a partial (or total) replacement of metakaolin, as matrix, silicon and whipped protein as pore forming. The foamed systems were hardened at defined temperature and time and then characterized by mechanical point of view through compression tests and by functional point of view through fire reaction and acoustic tests. The experimental findings highlighted that the replacement of diatomite in the formulation affected the morphological structure of the foams and consequently their mechanical properties. In particular, the consolidation mechanism in the diatomite based-hybrid foams changed from geopolymerization to a silicate polycondensation mechanism. Therefore, mechanical performances enhanced with increasing of the diatomite content. Fire reaction tests, such as non-combustibility and cone calorimeter tests, showed positive thermal inertia of samples regardless of the content of diatomite.