Mechanical, durability, and microstructural study of dispersive soil stabilized by alkali-activated rice husk ash and natural fiber
Amir Ghanbari Astaneh, Mehdi Abbasi, Iman Hosseinpour, Meghdad Payan, Mahdi Salimi
Abstract
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 ( E u ), 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.