Deliverables WP1

DELIVERABLE 1.1

In agreement with the objectives of WP1: ‘Material Selection’, the following glasses waste sensitive to weak alkali activation (not exceeding 3M) were identified and characterized: pharmaceutical boro-alumino-silicate glass (having different degrees of contaminations from other materials), Opal glass, LCD glass at Unipd and WEEE glasses (Waste from Electrical and Electronic Equipment like glasses from dismissed photovoltaic plants and fluorescent lamps) at UniMORE. All these glasses have been ground into fine powders and activated by addition of alkaline solution. The resulting slurries were dried through cold consolidation (40-75°C) combined with microwave heating. The hardened monoliths are boiling resistant and have density and compression strength characteristics that make them competitive with many building materials currently on the market such as concrete, bricks and cement.

The above-mentioned residues have undergone a systematic characterization, in terms of chemical composition and mineralogy, before and after activation. The alkaline environment of the solution results in the partial dissolution of the glass particles surface with consequent formation of a cross-linked structure featuring strong Si-O-Si, Si-O-Al and Al-O-Al bonds [1,2]. All glass components in solution form secondary phases, also by interaction with atmosphere (formation of carbonate and hydrate carbonate). Immersion of weak alkali activated samples in boiling water removes carbonates and secondary soluble phases but leaves the bonds between particle surfaces intact.

The application of microwave heating in combination with low temperature drying in the oven has allowed to considerably reduce curing times and energy consumption which is of considerable interest in the perspective of industrial exploitation [3]. It is generally agreed that MW heating is more efficient, prevents the formation of temperature gradients through volumetric heating of the material and, above all, requires less energy compared to other processes [3,4]. In the case of BASG and Opal glass, the microwave treatment also improved the strength of the consolidated material while leaving the density virtually unchanged.

Selection has aimed at separating ‘active’ from ‘passive’ supplementary residues, according to the reactivity, in turn due to granulometry and/or chemical composition and/or mineralogy. The addition of fine particles (below 75 μm) of Al2O3-rich residues such as volcanic ashes (pumice and lapillus) has considerably increased the stability and the mechanical properties of the final product [5]. The development of new glass-based formulations implementing fine pumice and lapillus tailings as matrix components was in accordance with the task M1.2: Identification of combinations of supplementary inorganic residues and glasses forming stable gels of WP1.

The release of pollutants and glass components into solution has been investigated by leaching tests conducted on activated materials. The detection of specific elements (such as metals and Ba in the case of BASG) is closely related to the stability of the gel phase formed between glass particles during activation process. This phenomenon was considerably reduced by subjecting the material to successive boiling and drying cycles.

Finally, infrared spectroscopy analisys, antimicrobial (gram positive and negative bacteria) and cytotoxicity (Keratinocytes HaCaT cells) studies conducted at UniCaLV on all materials produced supported leaching tests results. All compositions were found to have antimicrobial activity with differences depending on the alkaline activator (NaOH or KOH) and molarity. Non-cytotoxic formulations were selected for further investigation.

References

[1] M. Mahmoud, J. Kraxner, A. Mehta, H. Elsayed, D. Galusek, E. Bernardo, Alkali activation-induced cold consolidation of waste glass: Application in organic-free direct ink writing of photocatalytic dye destructors, Journal of the European Ceramic Society 44 (9) (2023), https://doi.org/10.1016/j.jeurceramsoc.2023.12.023.

[2] G. Tameni, F. Cammelli, H. Elsayed, F. Stangherlin, E. Bernardo, Upcycling of boro-alumino-silicate pharmaceutical glass in sustainable construction materials, Detritus 20 (2022), 10.31025/2611-4135/2022.15218.

[3] J. Aschoff, S. Partschefeld, J. Schneider, A. Osburg, Effect of Microwaves on the Rapid Curing of Metakaolin and Aluminum Orthophosphate-Based Geopolymers. Materials 17 (463) (2024), https://doi.org/10.3390/ma17020463.

[4] B. Horvat, M. Pavlin, V. Ducman, Influence of microwaves in the early stage of alkali activation on the mechanical strength of alkali-activated materials,Ceramics International 49 (14) (2023), https://doi.org/10.1016/j.ceramint.2022.12.133.

[5] F. Altimari, I. Lancellotti, C. Leonelli, F. Andreola, H. Elsayed, E. Bernardo, L. Barbieri, Green materials for construction industry from Italian volcanic quarry scraps, Materials Letters 333 (2023), https://doi.org/10.1016/j.matlet.2022.133615.