B. Liguori

Coal Combustion Wastes Reuse in Low Energy Artificial Aggregates Manufacturing

Sustainable building material design relies mostly on energy saving processes, decrease of raw materials consumption, and increase of waste and by-products recycling. Natural and lightweight artificial aggregates production implies relevant environmental impact. This paper addresses both the issues of residues recycling and energy optimization. Particularly, three coal combustion wastes (Weathered Fly Ash, WFA; Wastewater Treatment Sludge, WTS; Desulfurization Device Sludge, DDS) supplied by the Italian electric utility company (ENEL) have been employed in the manufacture of cold bonded artificial aggregates. Previously, the residues have been characterized in terms of chemical and mineralogical compositions, water content, particle size distribution, and heavy metal release behavior. These wastes have been used in the mix design of binding systems with the only addition of lime. Finally, the artificial aggregates have been submitted to physical, mechanical, and leaching testing, revealing that they are potentially suitable for many civil engineering applications.

A preliminary investigation on kinetics of zeolite A crystallisation using optical diagnostics

Abstract Preliminary data concerning the monitoring in situ of the zeolite A crystallisation from clear solutions are reported. Experiments were performed at 60 and 70°C with fresh and aged solutions having the following composition: 8.6Na 2 O·0.18SiO 2 ·Al 2 O 3 ·150H 2 O. The formation of early phases in the crystallisation process were followed using diagnostics such as dynamic light scattering (DLS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The comparison of the available data seems to indicate the formation of a precursor phase (like gel) in the case of not aged solution. Conversely, crystallisation in aged solution seems to proceed without intermediate phases. At the same time, an investigation on the kinetics aspects of the zeolite A crystallisation was carried out. As far as the reproducibility test is concerned, the chemical system selected showed good results on a large number of tests.

Synergistic effect of vegetable protein and silicon addition on geopolymeric foams properties

Organic–inorganic hybrid foams based on an alkali alumino-silicate matrix were prepared using different foaming methods. Firstly, silico-aluminate inorganic matrix, activated through a sodium silicate solution, was prepared at room temperature. The obtained viscous paste was expanded by means of silicon metal redox reaction in alkaline media in combination with protein-assisted foaming. The foamed systems were hardened at defined temperature and time and then characterized by FTIR, scanning electron microscopy, and compression tests. The high temperature behavior and specific surface area were also evaluated. The experimental findings highlighted that the combination of silicon metal and vegetable protein allowed tailoring hybrid foams with enhanced properties: good yield strength and thermal resistance typical of geopolymeric foam with a ductile behavior (toughness) and low density typical of organic foams.

Hybrid geopolymeric foams with diatomite addition: Effect on chemico-physical properties

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.

Safe trapping of Cs in heat-treated zeolite matrices. Part 2

Abstract Safe trapping of cesium was investigated by heat-treating at various temperatures a Slovakian clinoptilolite-rich tuff sample, previously subjected to exhaustive exchange with Cs + . The influence of temperature on the process effectiveness was studied and the mechanism of Cs + immobilization explained. Treating the Cs-exchanged material, at 1000°C results in zeolite breakdown and the formation of an amorphous, likely glassy, phase, which safely encapsulates the polluting cation, as it has been demonstrated by standard leaching tests. This study indicates that clinoptilolite-rich tuff is a good candidate for immobilization of cesium, taken up by ion exchange.

Binders alternative to Portland cement and waste management for sustainable construction—part 1:

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.

Ion exchange kinetics and thermodynamics of hydrosodalite, a narrow pore zeolite

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.

Setting up the production process of diatomite-based ceramic foams

ABSTRACT 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.

Hemp reinforcement in lightweight geopolymers

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.

Organic-inorganic hybrid foams with diatomite addition: Effect on functional properties

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.