Uso de lodo de estação de tratamento de água para produção de tijolos ecológicos

Abstract

The reuse of sludge from water treatment plants as an input in civil construction represents a promising strategy to reduce environmental impacts, add value to waste that is difficult to dispose of, and promote sustainable practices in the sector. In this context, this study investigated the feasibility of incorporating sludge from a Water Treatment Plant (LETA), heat-treated at 650ºC (LETA650), as a partial substitute for Portland cement in the manufacture of ecological bricks. The research involved the physical, chemical, and mineralogical characterization of the sludge and soil used, as well as the experimental evaluation of compositions with different levels of cement replacement by LETA (0, 5, 10, 20, and 40%). The bricks produced were subjected to compressive strength, mass loss, and water absorption tests. An experimental design with a factorial statistical approach was applied to optimize the proportions, culminating in the definition of the formulation with the best performance. The ideal composition was analyzed for durability, thermal conductivity, and morphological behavior, in addition to mechanical, physical, chemical, and mineralogical properties. The results indicated that LETA presents characteristics of a silty-sandy soil with low plasticity and total thermal mass loss of 34.51% up to 1000 °C. Thermogravimetric analysis and X-ray diffraction demonstrated the presence of pozzolanic activity from 100 °C, with a peak of reactivity at 650 °C, evidenced by the pozzolanic activity index (PAI) of 88.5%. LETA presented a content of 81.39% of oxides (SiO2, Al2O3, and Fe2O3), meeting the normative chemical composition requirements for pozzolans. Among the tests performed, the replacement of 5% of the cement by LETA650 presented better mechanical performance, with improved reduction in water absorption and mass loss. Substitutions of up to 10% did not significantly impact the brick characteristics. Statistical analysis confirmed the predictive capacity of the proposed mathematical model. The findings show that the addition of calcined LETA to soil-cement bricks constitutes a technically viable and environmentally advantageous solution, favoring the valorization of waste and reducing the demand for conventional cement in the construction industry.