Design of Innovative, Eco-Friendly, and “Made in Italy” Architectural Components Using Marble Sludge and Disposed Fishnets

Western Sicily hosts two significant and largely unresolved waste challenges: the marble processing industry of the Custonaci quarrying basin (Trapani) generates large volumes of calcium carbonate sludge without many established valorisation routes, while the Mediterranean fishing economy produces abandoned, lost, or otherwise discarded fishing gear (ALDFG), which persist in the marine environment for decades. Both streams are locally abundant, spatially proximate, and underexploited as secondary raw materials.This doctoral research investigates whether these two waste streams can be combined into a technically viable composite material, supporting circular economy. Starting from the hypothesis that recycled polypropylene from Mediterranean fishing nets, compounded with marble dust from the Custonaci basin, can be mixed to manufacture a composite material suitable for contraction, the research develops a proof-of-concept — rPP+MD — through a multi-stage experimental programme covering chemical characterisation, composite fabrication, and mechanical testing across three independent fishing net batches of different geographic origin and exposure history.The structural application is grounded in the observation that the mechanical profile of rPP+MD — low stiffness and adequate ductility — is particularly suited for the reinforcement of historic masonry vaults, more specifically thin vaults, a typology widespread in the built heritage of Western Sicily and the broader Mediterranean. Unlike high-modulus fibre-reinforced composites, a stiffness-compatible material can bridge cracks and restore structural continuity without disrupting the membrane behaviour on which the vault’s structural efficiency depends. This is investigated through a finite element modelling (FEM) study of a cracked realina trough vault in Partinico (Palermo, Sicily), through a comparison with the unreinforced cracked condition and a CFRP benchmark solution.The research contributes an original waste-to-composite pathway rooted in the productive identities of Western Sicily, a replicable multi-batch characterisation protocol for heterogeneous recycled polymer feedstocks, and a performance-based FEM methodology for stiffness-compatible reinforcement in heritage masonry. The outcomes were formalised in a patent application filed with the Italian Patent and Trademark Office (UIBM) under number 102026000002521 on 03/02/2026.