| Resumo : |
The production of Portland cement (PC) requires high amount of energy, consumes non-renewable resources and emitting large amounts of carbon dioxide. Due to the necessity for sustainable development, the search for alternative, low-cost, and widely available materials, represents a significant challenge for researchers. This thesis focuses on the development and performance evaluation of a novel binder: magnesium aluminosilicate cement produced using water treatment plant sludge ash (WTPSA) as an alternative aluminosilicate source. WTPSA is a by-product generated in water treatment plants processes and requires appropriate disposal due to the presence of potentially hazardous substances that pose risks to both human health and the environment. A secondary objective of this work is to validate a novel processing approach based on the combined calcination of raw materials, aimed at enhancing material reactivity and cement performance. The results demonstrated that the combined calcination methodology significantly improved particle adhesion and distribution, leading to a denser microstructure. Mortars produced with this method achieved a compressive strength of 42 MPa after 28 days - 223% higher than the 13 MPa obtained with cement prepared using separately calcined materials. Hydration products identified in cements derived from both kaolinite clay and WTPSA included magnesium-aluminosilicate hydrate (M-A-S-H), brucite (Mg(OH)?), and hydrotalcite-like phases. SEM/EDS analysis confirmed the incorporation of aluminum into the M-A-S-H structure and further indicated that the combined calcination process produced a more compact and homogeneous matrix. In evaluating the performance of different WTPSA sources, pastes P1-50/50, P2-60/40, and P3-60/40 (named according to the type of WTPSA produced (1, 2, or 3) and the MgCO?/WTPSA ratio) showed higher formation of reactive hydration phases, denser microstructures, and superior mechanical performance - achieving compressive strengths of 40, 31, and 33 MPa, respectively, after 28 days. Despite differences in geographic origin and treatment processes, all three WTPSA samples exhibited consistent behavior in terms of hydration products and mechanical performance. These findings confirm the technical viability and environmental potential of WTPSA as a sustainable aluminosilicate precursor for MgO-SiO? cement. Moreover, the study validates the combined calcination methodology as a promising low-energy approach for the production of eco-friendly cementitious materials using both industrial kaolinite clay and WTPSA. |