Avaliação geotécnica do uso de misturas de solo com resíduo de construção e lodo de estação de tratamento de água em camadas de cobertura de aterros sanitários.

Abstract

In Brazil, large quantities of waste are generated daily from construction activities, municipal solid waste management, and drinking water treatment processes. In this context, the development and application of reuse methodologies for these materials are essential to mitigate the environmental impacts associated with the extraction of virgin raw materials and the improper disposal of waste. An alternative approach is the use of recycled residues in landfill cover layers, which must exhibit geotechnical behavior compatible with the criteria established by technical standards and specialized literature. This research aimed to evaluate the mineralogical analysis, geotechnical characterization, and hydromechanical behavior of mixtures of natural soil with recycled construction and demolition waste (RCD-R) and water treatment plant sludge (WTP sludge or LETA), for application in landfill cover layers. The soil used in this study was collected from a sanitary landfill located in Guapó, Goiás, Brazil. The RCD-R (gray sand) was obtained from a company specialized in processing construction waste from the cities of Goiânia and Aparecida de Goiânia, while the sludge originated from the João Leite Water Treatment Plant, in Goiânia, Goiás. Mixtures containing 20% and 40% of RCD-R (SRC20 and SRC40) and 20% and 40% of LETA (SLE20 and SLE40), by dry mass, were prepared. The samples were subjected to X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), environmental tests, geotechnical characterization, permeability tests, unconfined compressive strength tests, as well as absorption and shrinkage tests. The mineralogical analysis showed consistency among the applied methods, identifying a silico-aluminous composition with quartz and clay minerals in the soil; a predominance of kaolinite and goethite with high Al₂O₃ and Fe₂O₃ contents in the LETA; and high SiO₂ and CaO contents in the RCD-R, associated with cementitious products and calcite. Environmental tests classified the RCD-R and the LETA as compliant with the environmental quality limits established by the applicable standards. The results of the geotechnical characterization indicated that mixtures containing RCD-R (SRC20 and SRC40) exhibited reduced plasticity and an increase in the sandy fraction, whereas mixtures containing LETA (SLE20 and SLE40) showed higher fines content and elevated liquid limits. Regarding permeability, all mixtures presented coefficients compatible with technical standards, except for SRC40. Unconfined compressive strength values exceeded 200 kPa for the SRC20, SLE20, and SLE40 mixtures. In terms of volumetric variation, only SRC20 and SLE40 maintained shrinkage values below 4% under all tested environmental conditions. The SRC20 and SLE40 mixtures demonstrated the most satisfactory technical performance, combining low permeability, adequate mechanical strength, and suitable volumetric stability for use as landfill cover materials. However, SLE40 showed limitations related to its low plasticity index and Unified Soil Classification System (USCS) classification, highlighting the need for complementary analyses that consider the characteristics of tropical soils. Overall, this research provides technical and environmental support for the reuse of RCD-R and LETA, promoting waste diversion from landfills, conservation of natural resources, and the advancement of sustainable practices in solid waste management.