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    Sustainable use of waste hazelnut shell ash in road construction to stabilize expansive subgrade
    (Elsevier Ltd., 2024) Tanyıldızı, Muhammed; Nasıroğlu, Sema; Zeybek, Abdulhakim; Gökalp, İslam
    Expansive (shrinkage-swelling) soils tend to suffer significant volume changes with fluctuations in moisture content. The volume instability of expansive soils causes considerable damage to the road pavements, resulting in significant economic losses. This study examines the usage of waste hazelnut shell ash (WHSA) as an alternative sustainable stabilizer to improve the geotechnical properties of expansive road subgrade soils. For this purpose, WHSA was added to expansive soil specimens prepared at ratios of 2%, 4%, 6%, 8%, and 10% by dry weight of the soil. Consistency limit, swell-shrink, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), direct shear, fall cone, consolidation, and wetting-drying experiments were conducted to investigate the influence of WHSA on the physical, mechanical, and durability characteristics of expansive soil. The experimental results indicated that the addition of WHSA caused a reduction in the UCS and the undrained shear strength of the soil. On the other hand, the UCS of specimens containing WHSA appeared to steadily increase after they were cured for various periods ranging from 7 to 90 days. A significant reduction was observed in the plasticity and swell-shrink potential when WHSA increased from 0% to 10%. The CBR of the soil increased from 2.47% to 16.71% by adding 10% WHSA, indicating that the thickness of the subbase layer can be reduced by approximately 55%. The cohesion of the soil appeared to decrease, whereas the international friction angle increased. A considerable improvement was achieved in the wetting-drying performance of the soil by increasing the WHSA content. Moreover, the consolidation-induced settlement was reduced up to a certain WHSA ratio. These results show that the WHSA can be a reliable, environmentally friendly, and cost-effective alternative material for the stabilization of expansive road subgrade soils.