Sustainable Stabilization of Expansive Soils Using Lime Sludge and Sodium Chloride: A Circular Economy Approach

Expansive soils represent one of the major challenges in geotechnical engineering due to their unpredictable shrink–swell behavior, which compromises the structural stability of buildings and complicates their use in construction projects. This phenomenon, influenced by seasonal climate variations, is expected to worsen under projected climate change, which is characterized by extreme precipitation and greater thermal variability, significantly increasing the risk of structural damage.

Conventional stabilization methods, such as the exclusive use of lime or salts, present limitations: they require large quantities of material, generate environmental impacts, and do not always guarantee sustainable improvements. This study proposes an innovative approach that combines sodium chloride (NaCl) and lime sludge (LS), a by-product from water treatment plants, to improve the properties of expansive soils while aligning with circular economy principles. Mixtures were prepared with 3%, 6%, and 9% NaCl and 5%, 10%, and 15% LS. Laboratory tests—including Atterberg limits, free swell, swelling pressure, swelling percentage, and infiltration—were conducted to evaluate changes in the soil’s swelling characteristics.

The results show reductions of up to 35% in liquid limit and 65% in free swell. Furthermore, the reduction in plasticity index was up to 36%. In addition, infiltration was 40 mm at the beginning and became 25mm, contributing to better hydraulic stability. Many tons of lime sludge were utilized in the project. By incorporating the lime sludge directly into the treated soil, the material was diverted from potential landfill disposal, thereby reducing the volume of waste generated and lowering the emissions normally associated with conventional waste management practices.

This approach offers a more efficient, cost-effective, and sustainable technical solution, distinguished by its dual action (chemical and recycling) and its contribution to waste valorization. Future research will focus on validating the method at the pilot scale and assessing its performance under extreme climatic conditions, consolidating its applicability in resilient infrastructure projects.