Effect of Wetting and Drying Cycle on the Behavior of Teff Straw Ash-Stabilized Expansive Soil

This study explores the impact of wetting and drying cycles on teff straw ash-stabilized expansive soil, with a focus on enhancing its mechanical properties for road subgrade applications. Expansive soil, characterized by continuous swell and shrink behavior, undergoes cyclic testing to establish equilibrium and critical density. The mitigating effects of teff straw ash on soil damage and its influence on expansive soil’s mechanical attributes are investigated. Laboratory results classify natural expansive soil as A-7-5 and CH according to AASHTO and USCS standards, respectively. Using a one-dimensional odometer apparatus, six wetting–drying cycles are conducted on teff straw ash-stabilized expansive soil to observe its behavior at equilibrium. Scanning electron microscopy reveals a disordered bond between soil particles and teff straw ash, intensifying with increased wetting–drying cycles. X-ray diffraction analysis is performed on samples subjected to different curing times, indicating heightened cation exchange and pozzolanic reactions as curing duration increases, thereby reducing soil expansiveness. A 96-hr socked California Bearing Ratio (CBR) test assesses subgrade strength. The CBR values for natural soil fall below the Ethiopian Road Authority (ERA) standards for low-volume roads. In contrast, expansive soil stabilized with teff straw ash at 10%, 15%, and 20% exhibits substantial increases in CBR values (3.7, 6.7, and 8.9, respectively), meeting the ERA standards. This suggests that teff straw ash stabilization renders expansive soil suitable for low-volume road subgrades, aligning with ERA standards. This comprehensive study provides valuable insights into the potential use of teff straw ash as an effective stabilizer for expansive soils, offering sustainable solutions for road construction in regions characterized by expansive soil challenges.