Microstructural Characterization of Black Cotton Soil Stabilized with Agricultural Waste Materials

Expansive soil is primarily impervious and shows swelling and shrinkage behavior when exposed to moisture fluctuation, making it incompatible with geomechanical applications. Recently, waste materials and fibers have been used to improve sustainable solutions in designing new soil reinforcing and stabilizing materials. In many rice-producing countries, rice husk (RH) is one of the most extensively available agricultural wastes. This study shows a detailed microstructural investigation of black cotton soil (BCS) stabilized with 3–15% rice husk ash (RHA) containing a high amount of amorphous silica needed for employing pozzolanic action in weak soils. The reorganized soil structure due to the treatment is researched through a series of microstructural tests, including scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray fluorescence (XRF). The microstructural analyses 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 improved hydrophobic nature of the clay mixture. The XRD tests unveiled the amorphous nature of RHA. The XRF tests revealed 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.