Deliverables WP3
DELIVERABLE 3.1: ‘Report on manufacturing and mechanical characterization of highly porous bodies’
Glass and mixtures of glass and ‘active’ supplementary residues, studied during WP1, were considered for foaming and printing experiments, by engineering of gelation conditions, according to rheological studies.
At UniPD (Università degli Studi di Padova), alongside traditional direct foaming methods, where porosity is generated during the drying of alkali-activated suspensions due to gas evolution within the hardening matrix, the salt templating method was enhanced and broadened. This approach, initially developed for Opal glass, was successfully extended to other types of waste glass, including Basg (both clean and dirty) and SLG. By incorporating up to 120 wt% sodium chloride with varying particle sizes into the activated suspensions, and by increasing the molarity of the alkaline activator, was possible to produce mechanically stronger structures with porosity above 80%. The washing step following hardening ensured the complete removal of salt, resulting in a well-developed porous network.
In parallel, additive manufacturing technologies were further implemented. Initial challenges in producing lattice structures using direct ink writing (DIW) with activated glass pastes were addressed by shifting to an approach based on polymer replicas. These scaffolds, fabricated using Digital Light Processing (DLP), were subsequently coated with activated glass suspensions. This method eliminated the need for sintering or thermal decomposition of the polymer, simplifying the process and improving structural integrity. Particularly promising results were obtained with samples printed using Vitrolite, a glass-ceramic photosensitive resin. The resulting glass coatings were homogeneous have withstood immersion in boiling water. This is probably due to stronger interactions between the glass particles within the suspension and the ceramic resin. These advanced manufacturing techniques, initially tailored for Opal glass, were then successfully applied to other glass waste (Basg and SLG) with encouraging results.
The porous structures produced by salt templating and polymer replica have been shared with UniMORE and UniCaLV for further testing, including leaching assessments and cytotoxicity assays.
DELIVERABLE 3.2: ‘Report on stabilization of pollutants, according to leaching and cytotoxicity studies’
Basg waste products release pollutants, including metals and glass components, when they stagnate in water. This is due to the instability of the gel phase that forms during the activation process. To overcome this problem, washing and drying cycles of the samples were introduced to remove the soluble secondary phases. The results of leaching tests demonstrate that samples subjected to subsequent immersions in boiling water significantly reduce the release of pollutants into solution. The boiled samples are also non-cytotoxic, in fact washing step allows to eliminate most of the alkali which form soluble hydrated carbonates, thus reducing the alkalinity of the environment which has negative effects on cell viability. Opal glass-based products, on the other hand, are extremely stable, in fact the activation process leads to the formation of additional amorphous phase which resists boling tests, also explaining the exceptional compressive strength of the consolidated samples (~33 MPa). Leaching tests confirm the chemical stability of the Opal glass products; the concentrations of metals released are lower than the limit values established by law for inert materials (according to D.M. of 27 September 2010).
Extensive leaching and cytotoxicity studies, conducted by UniMORE and UniCaLV, were also performed on porous materials produced through salt templating method by adding salt particles to activated opal glass slurries (Unipd). The process was then extended to other glass waste including SLG and WEEE glass obtaining encouraging results for both chemical stability and mechanical resistance.
