Geopolymerization of Expansive Black Cotton Soils with Alkali-Activated Binders

Black cotton soil (BCS) is highly expansive in nature when it is exposed to moisture. This property renders BCS unsuitable for use in geotechnical applications. Cement stabilization is one of the most popular methods for reducing the swelling properties of BCS. However, the production of cement leads to the emission of greenhouse gases, which is a threat to modern society. Hence, the present study aims to make use of two waste materials, fly ash and ground granulated blast furnace slag (GGBS) for stabilizing BCS. The study proposes a method of geopolymerizing BCS with alkali-activated binders (AAB). AAB is produced by the reaction of an aluminosilicate precursor (fly ash and/or GGBS) with an alkaline activator solution containing sodium silicate and sodium hydroxides. The water-to-solid (w/s) ratio is varied from 0.3 to 0.5 in this study. To identify the variations in chemical characteristics and surface morphology for both untreated BCS and BCS treated with AAB, mineralogical and chemical characterizations are performed through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The index and shear strength properties before and after the treatment of BCS with AAB are compared. It is observed that the effect of geopolymerization in BCS significantly increases the UCS and CBR value and reduces the free swell and plasticity index. Recommendations on the practical implementation of this technique for stabilization of expansive soils are proposed based on the findings of this study.