Desenvolvimento de compósitos álcali-ativados reforçados com fibras de vidro para impressão 3D

Abstract

The construction industry is seeking more sustainable alternatives to Portland cement, a major CO2 emitter. In this context, alkali-activated cements (AACs) or geopolymers stand out for their use of industrial byproducts, thereby reducing environmental impact and potentially enhancing mechanical properties. Additionally, 3D printing is emerging as a disruptive technology for the sector, enabling the creation of complex geometries, process automation, and reductions in waste and costs.The objective of this thesis was to develop and evaluate the physical and mechanical behavior of alkali-activated composites reinforced with glass fibers for 3D printing applications. The methodology included the characterization of precursors (metakaolin, blast furnace slag, and steel slag) and an activator (sodium metasilicate). The "one-part" alkali-activation method was chosen, mixing the dry materials – precursor, activator, and 6 mm AR glass fibers (0%, 1.0%, 1.5%, and 2.0%) – before adding water. A 2 k factorial design assisted in defining the optimal dosage. Preliminary tests revealed that slag-based matrices were unfeasible for 3D printing with the available equipment, leading to the selection of metakaolin (MK) as the main precursor. The optimal dosage for MK was established with molar ratios of SiO₂/Al₂O₃ = 3,2, SiO₂/Na₂O = 4,0, and Na₂O/Al₂O₃ = 0,8. Fresh-state properties were analyzed by setting time tests (Vicat and calorimetry) and rheology tests (Squeeze Flow). In the hardened state, axial compressive strength (cubic specimens) and four- point flexural strength (160x40x20 mm prisms) were evaluated for both molded and 3D printed samples. Linear interleaved (perpendicular) and honeycomb infill patterns, both with 50% infill, were investigated, and a cementitious plate prototype inspired by the Victoria Regia structure was also developed. Results showed that fiber-reinforced molded samples exhibited an increase in rupture load (up to 125% with 2.0% fibers) and post-cracking residual load capacity, indicating higher toughness. 3D printed samples with a linear interleaved pattern also showed an increase in rupture load with fiber addition (around 21.4%). Notably, most of these printed samples showed higher Specific Energy Absorption (SEA) than molded ones, highlighting the benefit of fiber alignment promoted by extrusion. In contrast, the honeycomb infill pattern resulted in a significant reduction in peak load (67.6%) and toughness, due to the non-alignment of fibers with the main stress direction. The Victoria Regia-inspired prototype was successfully printed, validating the feasibility of complex geometries, although it requires optimization of printing parameters. It is concluded that the thesis demonstrated the feasibility of developing metakaolin-based alkali-activated composites reinforced with glass fibers for 3D printing. The addition of glass fibers significantly improved the post-cracking mechanical behavior and toughness of the composites, both molded and printed, with a content between 1.0% and 1.5% being the most suitable for maintaining print quality.