Characterization and Stabilization of Collapsible Soils in Arid Regions Using Lime–Ceramic Waste Blends

Collapsible soils, commonly found in arid and semi-arid regions, present significant geotechnical challenges: moisture induces collapse of their metastable structure, causing sudden settlement that jeopardizes infrastructure integrity. This study investigates the effectiveness of a composite binder consisting of 3 % lime and 4–8 % finely ground ceramic waste for stabilizing reconstituted collapsible soils representative of semi-arid and arid regions worldwide, using locally sourced North African materials. Specimens composed of 80 % Boussaâda sand and 20 % Djebel Debbagh kaolin were prepared, cured for 7 d under sealed conditions at 20°C ± 2°C, and evaluated using Atterberg limits, Standard Proctor compaction, one-dimensional oedometer flooding, and unconsolidated–undrained triaxial tests. The addition of 3 % lime combined with increasing ceramic-waste content progressively reduced soil plasticity, with the plasticity index decreasing from 8.66 % for untreated soil to 3.19 % at 8 % ceramic waste + 3 % lime, whereas the 6 % ceramic waste combination restored the maximum dry density to 1.91 g cm−3 at a reduced optimum moisture content. Collapse potential, under one-dimensional oedometer flooding at 200 kPa, was reduced to less than 0.05 % at 8 % ceramic waste with 60-blow compaction energy, reclassifying the treated soil as non-collapsible. Cohesion increased substantially from 16 to 95 kPa, whereas the friction angle varied within approximately 35°–40° across the tested mixtures, suggesting cohesion was the primary driver of the strength gain, consistent with a contribution from cementation and bonding mechanisms. Microstructural analyses using scanning electron microscopy–energy-dispersive X-ray spectroscopy provide evidence consistent with the formation of calcium silicate hydrate (C–S–H) and calcium aluminate hydrate (C–A–H) phases, resulting in denser matrices, thicker interparticle bonds, and reduced porosity. The 3 % lime dosage consistently provided the alkalinity and calcium supply necessary to activate pozzolanic reactions in the ceramic fines, offering an effective, locally valorizable ground-improvement approach.