Abstract

Author:
Mattia Latini, Sara Mattiello, Roberto Ercoli, Paola Stabile, Carlo Santulli, Eleonora Paris

Doi: 10.26480/jwbm.02.2025.34.40

This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

The increasing production of sea-derived waste connected with the catering industry could be used as a secondary source of raw materials, thus reducing the burden of its accumulation, which accounts for millions of tons per year, thus offering a circular economy approach. This study focuses on the possibility of retrieving calcium carbonate from seashells waste, including oysters, mussels and clams bivalve mollusks from the Adriatic Sea farming to use them into geopolymer matrices. Seashells were analyzed by means of X-ray Powder Diffraction (XRPD), and Raman spectroscopy, highlighting compositional differences, spanning from almost pure calcite for oysters and pure aragonite for clams with mussels shells having an intermediate composition (76% calcite, 24% aragonite). Up to 50 wt.% seashells were inserted into metakaolin-based geopolymer matrices as aggregate, using grain sizes from 80 microns to 2 millimeters. Mechanical tests showed that oyster-based samples have the highest flexural resistance (8 ± 0.4 MPa) at 28 days curing, whilst clam-based samples display the highest compressive resistance (60.2 ± 2.9 MPa) in the same conditions. Furthermore, physical properties, including density and open porosity of the geopolymers, indicate that clam-based samples are denser compared to oysters and mussels samples, which in turn display slightly higher porosities. The results indicate that geopolymers can incorporate high quantities of seashell waste and may be suitable for construction industry, in replacement of Portland concrete, with only limited difference in properties among the geopolymers filled by various seashell powders. This suggests even the possibility to use these waste aggregates without preliminary separation by species.