Mechanical, durability, and microstructural study of dispersive soil stabilized by alkali-activated rice husk ash and natural fiber

This study aims to investigate the stabilization efficiency of dispersive soil using alkali-activated rice husk ash (RHA) in combination with hemp fiber (HF) as randomly distributed reinforcement. Various contents of RHA (i.e., 0 %, 2.5 %, 5 %, 7.5 %, and 10 %) and HF (i.e., 0 %, 0.5 %, 1 %, 1.5 %, and 2 %) were incorporated into the dispersive soil, along with NaOH solutions at concentrations of 2 M and 4 M. The treated specimens were cured for 7 and 28 days and then exposed to freeze–thaw (F–T) cycles. A wide range of mechanical and microstructural tests, including standard compaction, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), indirect tensile strength (ITS), pinhole testing, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), were conducted to evaluate the performance of the stabilized soil. According to the results, stabilized specimens exhibited significant mechanical improvement, with the optimized mixture (5 % RHA + 1 % HF, activated with 4 M NaOH) achieving a UCS of 778.9 kPa and retaining approximately 67.5 % of its strength after eight F-T cycles. The inclusion of HF further improved the performance of the RHA-stabilized soils by promoting particle interlocking, leading to enhancement in energy absorption (Eu), while reducing the secant modulus (E₅₀). The results also demonstrate the transformation of soil behavior from dispersive to transitional and, eventually, non-dispersive conditions. Microstructural observations confirm the formation of cementitious gels and chemical compounds, consistent with the macro-scale mechanical improvements.