Microstructural Characterization of Expansive Soil Stabilized with Agricultural Waste Materials

Expansive soil is predominantly impervious and exhibits swelling and shrinkage behavior when exposed to moisture fluctuation, making it unsuitable for geomechanical applications. Recently, waste materials and fibers have been used to develop sustainable solutions in designing new soil reinforcing and stabilizing materials. In many rice-producing countries, rice husk (RH) is one of the most widely available agricultural wastes. This study presents a detailed microstructural analysis of black cotton soil (BCS) stabilized with 3–15% rice husk ash (RHA) containing a high amount of amorphous silica needed for implementing pozzolanic action in weak soils. The reconstituted soil structure due to the treatment is studied through a series of microstructural tests, including scanning electron microscopy (SEM), X-ray diffraction (XRD), stereomicroscope, Fourier transform infrared (FTIR) spectroscopy, and X-ray Fluorescence (XRF). The microstructural studies revealed that with the increase in RHA content, new compounds containing functional groups such as silanol and siloxanes (Si–OH and Si–O–Si–OH) got introduced into the BCS + RHA mixture, leading to an enhanced hydrophobic nature of the clay mixture. The XRD tests revealed the amorphous nature of RHA. The XRF tests indicated an increment of 76% in the elemental composition of Silica (SiO2). The FTIR and SEM analyses reveal RHA's specific functional groups and surface characteristics.