Stabilization of Expansive Clays by Combined Effects of Geopolymerization and Fiber Reinforcement

Expansive soil exhibits significantly low volumetric stability when exposed to moisture fluctuations, rendering it unsuitable for use in geotechnical applications. The present study emphasizes the stabilization of expansive black cotton soil (BCS) using envirosafe alkali-activated binders (AAB) with the inclusion of polypropylene (PP) fiber. AAB is produced by the reaction between an aluminosilicate precursor (Class F fly ash and/or slag) and an alkaline activator solution containing sodium silicate and sodium hydroxide. A water-to-solid (w/s) ratio of 0.4 is maintained for the AAB used in the present study. Physical, microstructural, and mineralogical characterizations for both untreated BCS and fiber-reinforced-AAB-treated BCS are performed through a stereomicroscope, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis. The indirect tensile strength (ITS), swell/shrink test, California bearing ratio (CBR), and unconfined compressive strength for both untreated BCS and fiber-reinforced-AAB-treated BCS are carried out for different fly ash and GGBS (slag) proportions in the AAB mixture. The additions of varying percentages of fiber to AAB-treated BCS show a significant improvement in the geomechanical behavior of the soil. It is observed that the replacement of 5% of BCS mass by AAB prepared with 70% fly ash + 30% slag and containing 0.3% of PP fiber reduces the swelling pressure by 35–40%. The corresponding CBR and ITS values are found to increase by 40–45%. Recommendations for the practical implementation of fiber-reinforced AAB to treat BCS are provided based on the observations from this study.