The use of Polyethylene Terephthalate (PET) as an additive in the stabilization of swelling soils is a sustainable option considering the increasing environmental pollution caused by improper disposal of plastic waste. Given the limited capacity of recycling programs, incorporating these materials in construction can be a viable solution. In the conducted study, compacted mixtures of soil-lime-PET were prepared at different dry unit weights (14, 15 and 16 kN/m³). Micronized PET was used with percentages of 5% and 10%, while hydrated lime was added at 0%, 2%, 4%, and 6%, both by dry mass. These mixtures were subjected to one-dimensional swelling tests. The results showed that the PET content, lime content, and porosity are significant factors influencing the behavior of compacted mixtures. The index porosity/volumetric lime content adjusted by an exponent (ƞ/(Liv)-0,26) can link the one-dimensional swelling behavior. The combination of both materials creates a sustainable solution for controlling soil swelling.

A cal e a cinza do bagaço da cana-de-açúcar (CBCA), apresentam-se como alternativa para estabilização química do solo, promovendo melhoria de suas propriedades mecânicas. Entretanto, as reações pozolânicas entre esses materiais apresentam desenvolvimento lento. A adição de cloreto de sódio catalisa essas reações, reduzindo o tempo necessário para um ganho significativo de resistência. Nesse contexto, a água residual de dessalinização por osmose reversa (ARD) apresenta uma elevada concentração salina, com destaque para o cloreto de sódio. Diante disso, o objetivo deste trabalho é avaliar a ARD como um catalisador no processo de ganho de resistência de uma areia estabilizada com cal e CBCA. A mistura 75% areia 25% CBCA foi estabilizada com 6%, 8% e 10% de cal hidratada. Os pesos específicos secos utilizados nas amostras foram de 15, 16 e 17 kN/m³, com a umidade de compactação fixada em 13,5%. A água utilizada nos ensaios teve duas fontes distintas: o abastecimento público e a ARD. As amostras foram submetidas ao ensaio de compressão simples. Os resultados mostraram que a resistência aumenta à medida que o teor de cal aumenta, bem como, a resistência é crescente quando a porosidade diminui. Os resultados mostraram que a ARD não acelerou o ganho da resistência mecânica para 28 dias de cura. No entanto, a ARD ainda possui potencialidade para estabilização de solos, por apresentar resultados semelhantes à água do abastecimento público, permitindo uma economia de água potável e aumento a sustentabilidade do processo.

The disposal of tailings has become a challenge for the mining sector, environmental agencies, and society. This research aims to analyze the geomechanical and environmental behavior of cemented bauxite tailings (BT) for use in cemented dry tailings piles, a new trend for tailing disposal. The experimental program consisted of a series of unconfined compression tests and splitting tensile tests in BT with addition of 2%, 4%, and 6% of Portland Cement (Ci), and compacted at 18 kN/m3, 19 kN/m3, and 20 kN/m3. Leachability and solubilization tests were done with specimens with 20 kN/m3 and Ci of 0%, 4%, and 6%. All samples were done with water content of 18% and cured for 7 days. Increasing in Portland cement content and dry units of weight increases unconfined compressive strength (qu) and splitting tensile strength (qt); therefore, the increase in porosity decreases these mechanical properties. The importance of those parameters was confirmed by ANOVA and Tukey test analysis. The porosity/Portland cement content index allowed the prediction of qu and qt of BT-Portland cement blends; however, the qt/qu remained constant (0.14) and independent of this index. The environmental analysis showed that the addition of Portland cement to BT reduced the concentration of manganese in the leachate and the concentrations of chromium, iron, and sodium in the solubilized extract, complying with the toxicity and drinking water standards recommended by the USEPA. However, it also increased the concentration of aluminum in both extracts, exceeding the limit set by CONAMA 460 (Brazilian standard).

Swelling soils pose significant geotechnical challenges due to their volumetric instability during seasonal variations in water content, which can cause damage to overlying structures. Lime stabilization is widely employed to mitigate this; however, a rationalized dosage for lime is still required. The initial unsaturated condition of swelling soils tends to govern their expansive properties, with the initial water content ( w i ) dictating the initial hydration of clay minerals and the initial suction influencing the soil’s water adsorption affinity. Although the adjusted porosity/volumetric lime content index ( η / L i v ) has proven effective for describing swelling properties, a knowledge gap persists regarding the influence of w i on this dosage. Thus, this study investigates the influence of initial w i and total suction on the swelling behavior of a lime-stabilized soil. A series of vertical swell, swelling pressure, and total suction tests were performed on samples compacted at dry unit weights of 13.5, 14.5, 15.5, and 16.5 kN / m 3 , hydrated lime contents of 2%, 3%, and 4%, initial water contents of 16%, 19.5%, and 23%, following a full factorial design approach. The results showed that increasing the initial water content reduces the magnitude of soil swelling. Lower values of initial suction ( < 5,500 kPa ) have a significant effect on swelling properties; beyond this threshold, the effect becomes less pronounced. The application of the η / ( L i v ) α index revealed a separate dosage curve for each w i value. The normalization of these curves yields a relationship between swelling pressure ( P S ) and vertical swelling ( ε S ), enabling the prediction of P S based on ε S and vice versa, thereby minimizing laboratory labor. These observations were corroborated by an analysis of variance (ANOVA) and scanning electron microscopy analyses. In summary, this work presents a rational and practical framework for assessing the influence of w i and total suction on swelling properties of soils stabilized with hydrated lime.