Uso combinado de fibras de polipropileno e cinza leve de carvão mineral para controle de retração e fluxo de gás em camadas de cobertura de aterros sanitários

Abstract

The final disposal of municipal solid waste (MSW) in sanitary landfills poses challenges, particularly regarding the control of biogas emissions. Final cover layers act as barriers to water infiltration and gas migration; however, their performance may be compromised by the shrinkage and cracking of compacted soils. This thesis evaluated the hydromechanical and environmental behavior of mixtures composed of cover soil, coal fly ash, and polypropylene fibers for application in sanitary landfills. The experimental program comprised 24 formulations, including reference materials, soil–fiber mixtures with 6 and 12 mm fibers, soil–ash mixtures containing 10%, 20%, and 30% residue, and ternary compositions. Physicochemical, mineralogical, microstructural, environmental, and geotechnical characterizations were performed, along with compaction, consistency, shrinkage, hydraulic conductivity, intrinsic air permeability, unconfined compression, indirect tensile strength by diametral compression, image-monitored drying, and numerical modeling using the Vadose/W software. The ash reduced plasticity and volumetric and linear shrinkage, particularly at higher contents; however, it decreased densification and increased water and air transport. In the environmental tests, the leaching extract did not indicate hazardous characteristics, whereas the solubilized extract classified the ash as a non-inert material, making its use conditional upon control of dosage, confinement, and contact with water. The 12 mm fibers increased strength, deformability, and absorbed energy, but higher contents favored agglomeration, loss of homogeneity, and greater pore connectivity. Among the ternary mixtures, the matrix containing 20% ash showed the most favorable mechanical interaction with the fibers, although it remained less advantageous in terms of transport properties. The multicriteria assessment identified S0.75F12, composed of soil and 0.75% of 12 mm fibers, as the formulation with the best overall performance. The mixture reached 544 kPa in unconfined compression and 56.23 kPa in indirect tension, reduced volumetric shrinkage to 32.9%, and exhibited a hydraulic conductivity of 1.86 × 10⁻⁷ cm/s. The modeling indicated similar responses for the soil, S0.50F12, and S0.75F12. It is concluded that ash and fibers produce complementary, although not necessarily synergistic, effects. S0.75F12 is the main candidate for validation at a larger scale, whereas the ash-containing mixtures show potential for controlled-dosage or multilayer systems.