Efeito do rejeito de caulim na estabilização de solo/cimento.

Abstract

The management of industrial solid waste is one of the main contemporary challenges for sustainable development. In the mining context, kaolin processing in the Seridó region (PB/RN, Brazil) generates a significant volume of waste, often improperly disposed of, resulting in substantial environmental liabilities. Simultaneously, the scarcity of natural aggregates and the demand for low environmental impact geotechnical solutions drive the search for alternative materials. This research evaluated the technical performance of Kaolin Processing Waste (KPW) as a filler material in sandy soil stabilized with Portland cement. The experimental program consisted of physical, chemical, and mineralogical characterization of the materials, followed by molding specimens with KPW contents of 0%, 10%, 20%, and 30% (replacing soil), CP V-ARI cement contents of 3%, 5%, and 7%, and different dry unit weights (17.5, 18.0, and 18.5 kN/m³). Initially, all combinations were subjected to unconfined compressive strength tests (7 days curing) to identify the most influential variables. Based on these results, the 5% cement content and dry unit weight of 18.0 kN/m³ were selected as reference conditions for the complementary tests of flexural tensile strength, durability (12 wetting and drying cycles), and hydraulic conductivity, allowing the evaluation of mixture behavior in scenarios of greater practical relevance. The results demonstrated that KPW addition promoted compressive strength gains of up to 40% for mixtures with 3% cement. This increase results from the synergistic action among constituents: cement acts as a chemical binder, forming C-S-H bridges between grains; adequate compaction (γd) reduces void volume, bringing particles closer together; and KPW, through the filler effect, fills residual macropores, refining the microstructure and optimizing cemented contact points. In tension, the increase reached 78% with 30% KPW (322 kPa), raising the tensile/compressive strength ratio from 18.8% to 30.1%, indicating greater composite toughness. Durability was significantly improved, with accumulated mass loss reduced from 56.06% (control mixture) to 8.51% (30% KPW), representing an 85% reduction. Hydraulic conductivity decreased by approximately 800 times (from 3.24×10⁻⁴ m/s to 3.99×10⁻⁷ m/s), proving the filler effect in clogging capillary channels. The dosage methodology based on the porosity/cement volumetric content index (η/Civ) proved applicable, with high correlation coefficients (R² > 0.90). It is concluded that the optimal global content is 30% KPW, as it maximizes toughness, durability, and impermeability, transforming an environmental liability into a high-value input for sustainable geotechnical applications, aligned with the Sustainable Development Goals (SDG 9, 12, 13, and 15).