Dottorato in INGEGNERIA ELETTRICA, DEI MATERIALI E DELLE
NANOTECNOLOGIE

Titolo della tesi: Additive manufacturing technology and materials optimization for civil engineering applications: eco-sustainability approach in materials and process

To date, the global cement and concrete industry is projected towards achieving eco-sustainability goals to mitigate the emission of climate-altering gases and reduce the consumption of natural and non-renewable resources. Investing in “greener” cementitious binders, promoting the use of recycled materials and industrial by-products as secondary raw materials, and implementing the digital fabrication in the construction sector represent some of the principal actions required by the new international policies to pursue these sustainability objectives. The present PhD project embraces these topics by combining them in a single research work. Specifically, the thesis deals with the study and investigations of novel cement and geopolymer mixes optimized for 3D printing processes incorporating ground waste tire rubber, as total replacement of mineral aggregates. Many studies have clearly highlighted the peculiarities in the use of recycled tire rubber in cementitious matrices both in environmental (natural resource saving and cleaner disposal of end-of-life tires) and engineering (lightweight, mechanical ductility, durability, thermo-acoustic efficiency) terms. However, very few research works have focused on integrating rubber-concrete mixes with geopolymer technology, which represent a new generation of binder more eco-effective than ordinary concrete materials. Furthermore, successfully implementing rubberized mixtures in additive manufacturing processes would result in multiple benefits: eco-design, architectural flexibility, and optimized production. Starting from Portland and geopolymer mix designs optimally tailored for 3D printing processes, four different rubberized formulations were produced for partial (50% v/v) and total (100% v/v) replacement of the mineral aggregate (sand) of the reference cement mortar with the two fractions of ground waste tire (0-1 mm rubber powder and 1-3 mm rubber granules). Concerning the ordinary cement composites, after optimizing the mix designs by evaluating the main fresh-state printability requirements, a comprehensive experimental campaign was conducted based on physical, mechanical, microstructural, and thermo-acoustic characterization aimed at evaluating the influence of the polymer aggregate on both print quality of composites and engineering behaviour. Then, ground waste tire rubber was implemented in novel geopolymer-based composites, with the purpose of developing “concrete” materials with improved eco-sustainability deriving from both the low-carbon matrix and implementation of waste products as functional aggregates. First, the experimentation was aimed at evaluating the influence of rubber addition on geopolymer material’s performance (microstructural compatibility, physical properties, mechanical behavior, and thermo-acoustic properties) obtained by conventional mold-casting method. Secondly, comprehensive rheological tests were performed to optimize the rubberized geopolymer mixes for 3D printing. Preliminary print quality analysis and mechanical characterization were then carried out on the printed samples. Throughout the experimental investigation conducted on the rubber-geopolymer composites, a comparative performance analysis with the Portland-based mixes was performed to explore the potential of the two binders both in terms of technological properties and cost-emissions impact.