Non-destructive assessment of lime and nano-alumina oxide stabilized clay for new material development

The rapid expansion of civil engineering projects and the growing need to utilize problematic soils have highlighted the importance of developing innovative approaches for soil improvement and performance evaluation. In this study, the combined effects of lime and nano-aluminum oxide (nano-Al₂O₃) as supplementary additives were investigated for stabilizing highly plastic clay (CH). To evaluate the mechanical and microstructural properties of the treated soils, a series of tests was conducted, including standard Proctor compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV) as a non-destructive test, and scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that the addition of nano-Al₂O₃ caused a decrease in the maximum dry density (MDD) and an increase in the optimum moisture content (OMC), which is attributed to changes in the soil structure and the occurrence of pozzolanic reactions between the lime and nanoparticles. The optimal mixture of 9% lime and 1.2% nano-Al₂O₃, after seven days of curing, resulted in 42% and 26% increases in UCS and ITS, respectively. Furthermore, the UPV value for this mixture increased by approximately 72% compared with lime-stabilized soil, indicating higher density and improvement in the fine-grained structure of the soil. Increasing the curing time to 90 days also resulted in a continuous growth in UCS and UPV by 97% and 113%, respectively, demonstrating the continuation of pozzolanic reactions and a gradual improvement of the soil structure. Moreover, microstructural results confirmed enhanced formation of hydration products and a denser cementitious matrix in the optimized mixture. Based on data analysis, exponential correlations were established between UPV and mechanical parameters (UCS and ITS), with coefficients of determination of R2 = 0.84 and R2 = 0.79, respectively. These results indicate that the non-destructive UPV test can be used as an efficient tool for in-situ monitoring and prediction the strength of soils stabilized with lime and nanoparticles.