Stabilization of Expansive Black Cotton Soil Using Alkali-Activated Binder with Glass and Polypropylene Fiber

Expansive soil exhibits high swelling and shrinkage behavior when moisture fluctuation occurs; this volumetric variation in black cotton soil (BCS) renders unsuitable for use in geotechnical applications. The present paper emphasizes an experimental investigation on the effect of discrete polypropylene (PP) and glass fiber (GF) with alkali-activated binder (AAB) on geomechanical properties of BCS. Hence, the present study aims to compare the geoengineering and microstructural characteristics between PP and glass fiber on AAB treated BCS. PP and GF were varied from 0 to 0.4% with 5% AAB in the BCS. AAB is produced by the reaction between alkali-activator solution (sodium hydroxide and sodium silicate) and aluminosilicate precursor (Class-F fly ash/slag). Microstructural analysis for AAB treated BCS reinforced with both PP and GF is performed through a stereomicroscope, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The unconfined compressive strength (UCS), indirect tensile strength (ITS) California Bearing Ratio (CBR) and linear shrinkage tests for glass fiber-AAB and PP fiber-AAB treated BCS are carried out. The influences of varying percentages of different fiber with AAB content in the BCS show a significant improvement in geoengineering properties, especially tensile strength. It is observed that the addition of 5% AAB with 0.3% of glass fiber and PP fiber reduces the linear shrinkage by 12–15% while CBR and ITS values are increased by 20–30%. From the results, it is observed that the PP fiber-AAB treated BCS achieves maximum mechanical strength when compared to glass fiber-AAB treated BCS.