Abstract
Abstract The main target of SEEDS is to recover selected industrial sediments currently classified and treated as waste and re-use them into the production cycle of construction materials for building and infrastructure. More in detail, the idea is to use waste sediments as “reagents” in partial replacement of virgin raw materials to produce geopolymers and alkali-activated materials (AAMs), improving the eco-sustainability of the building materials production chain, but without compromising (indeed possibly increasing) the performance of the final products. Furthermore, the project will be integrated with parallel toxicity and carcinogenic studies, by effect-directed analysis (EDA) approach. The project is in line with the objectives of the Italian “Piano Nazionale di Ripresa e Resilienza (PNRR)”, in particular with the missions “Green revolution and ecological transition” and “Infrastructures for a sustainable mobility”. To this aim, a multidisciplinary method is proposed encompassing mineralogical, materials science, engineering and toxicological knowledge to gain eco-sustainable building materials with suitable characteristics for each specific application. Firstly, mineralogical knowledge on the selected sediments is necessary to develop suitable mixtures to produce the target materials; after, as these materials must satisfy the mechanical properties disciplined by specific standards, engineering knowledge is required. In fact, the use of sediments in the geopolymer matrix undoubtedly will lead to the modification of some properties of the consolidated material (e.g., strength, durability, technical performance, etc.); nevertheless, these modifications could be linked to mineralogical composition, which in turn can be properly modulated in mixture design. It should also be stressed that the materials produced will be carefully characterized considering not only their chemical and physical properties, but also their safeness to assess the absence of risks for both human health and the environment, a step which is mandatory to plan technology transfer. The SEEDS project aims at obtaining laboratory validation of the sediment-based products (Technology readiness level, TRL, of 4), with possible extension to preliminary industrial evaluations (TRL 5). Thus, SEEDS is not a mere methodological approach to a looming problem, but it is a new way of rethinking our waste.
Results achieved
The objectives outlined in the project proposal have been successfully achieved, and in various aspects, surpassed. A systematic characterization of Italian quarry waste, sediments, and by-products was performed, by using specific methodologies and protocols, facilitating the development of innovative geomaterials. The scope of their development and application was focused to geopolymer-based construction materials. Then, the research was broadened also to agronomic solutions and CO2 sequestration technologies. As planned, the project involved the toxicological characterization of the waste geomaterials before transformation into new materials. The toxicological safety assessment was also performed for some new products obtained by the re-use of the waste materials. In addition, the project addressed safety concerns by characterizing imported raw materials within the Italian supply chain for potential contaminants, including asbestos and unregulated fibrous minerals. For the development of geopolymer-based construction materials, preliminary reactivity assessment of quarry waste and sediments in alkali environments (specifically sodium hydroxide and sodium silicate) was performed: they indicated that both the clayey silt and the quartz sand residues were not suitable as primary precursors for alkali-activated materials, differently from basalt powders. The effect of different process key parameters was explored and finally two formulations based on basalt waste were selected for deep investigation, due to promising results in terms of consolidation and stability. The first (1) is based on 100% basalt as raw material and is activated with sodium hydroxide. The second formulation (2) is based on a mixture of basalt powder and a small fraction of metakaolin (approximately 10 wt.% of the solid precursor), activated with a sodium silicate solution. Post thermal treatments at 200 °C and post infiltration with silicates solutions are however required to improve the performance of both materials. The best basalt-only hydroxide- activated system (1) reached compressive strength around 64 MPa, while the optimized basalt–metakaolin silicate-activated system (2) reached compressive strength up to approximately 59 MPa. Moreover, both selected systems exhibited high thermal stability up to 1000 °C, in line with the formation of inorganic binding gels and the intrinsic stability of basalt-derived phases. This thermal robustness supports the suitability of the developed binders not only as alternative cementitious matrices but also as candidates for applications requiring resistance to elevated temperatures. The economic feasibility of the proposed geopolymer formulations was assessed through a detailed cost analysis. The results confirmed that basalt-based formulations offer a clear economic and environmental advantage, combining lower material and energy costs with reduced embodied energy compared to conventional geopolymer systems. To satisfy the project objective of valorising multiple waste streams and increasing the circularity of the developed materials, additional secondary resources were also investigated. In particular, construction and demolition waste (CDW) powders were incorporated into basalt-based metakaolin geopolymer systems. CDW was selected because it represents one of the largest and most widely available waste streams in the construction sector, with significant availability both geographically and over time. The integration of CDW allowed the development of mixed precursor systems capable of producing mechanically resistant alkali-activated materials while maintaining a high waste-derived content. The incorporation of CDW in the basalt-based systems was therefore explored not to replace the already effective basalt precursor, but rather to evaluate the possibility of combining different waste streams in a single alkali-activated matrix. This approach allowed the valorisation of heterogeneous construction residues while maintaining adequate mechanical and microstructural properties of the resulting materials. The potential to incorporate construction and demolition waste further strengthens the circularity of the proposed approach, while maintaining acceptable performance standards for sustainable construction applications. Activities of the project involved also the parallel screening of quarry waste and by-products for agronomic valorisation, and recovery strategies for quarry-derived silicate dusts. A detailed toxicological assessment of the industrial waste materials chosen at the beginning of the project, namely quartz sand residues, basalt waste powders, and clayey silt was performed. All three waste materials showed significant cyto- and genotoxicity across different cell lines and eliciting both acute and chronic inflammatory responses in immune cells. Among the tested materials, the clayey silt exhibited the highest cytotoxicity. These results highlighted the importance of setting up inertization or transformation processes for these materials in order to preserve human health from the detrimental effects due to accidental contact/inhalation. Furthermore, the project encompassed the toxicological assessment of two tobermorite-rich materials synthesized from the upcycling of quarry- derived silicate dusts high in crystalline silica. These findings underscore the critical importance of conducting adequate and predictive toxicological evaluations to guarantee the environmental and occupational safety of any novel material engineered for industrial application. Indeed, the results suggested that predicting biological impact solely from the physical and chemical characteristics of a novel substance remains highly challenging. Consequently, direct experimental assessments targeting specific toxicity markers remain of primary importance to ensure safety. The project underlined the general awareness of effective waste eco-recycling, also leveraging synergies with external projects and industrial stakeholders. This aspect has facilitated the valorisation of both the cited quarry waste and other End-of-Waste processes derived material that had hitherto remained unexploited.Project details
Unibo Team Leader: Giovanni Valdrè
Unibo involved Department/s:
Dipartimento di Scienze Biologiche, Geologiche e Ambientali
Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali
Coordinator:
ALMA MATER STUDIORUM - Università di Bologna(Italy)
Total Eu Contribution: Euro (EUR) 211.601,00
Total Unibo Contribution: Euro (EUR) 69.862,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
27/02/2026
