Geotechnical Performance of Red Soil Stabilized with Fly Ash and Reinforced with Polypropylene Fibres

The environmentally conscious and viable alternative to the traditional binders like lime and cement includes the sustainable use of industrial by-products for soil stabilization. This study proposes an innovative solution beyond the sole use of fly ash for geotechnical applications such as Class F fly ash (15–30%) and polypropylene fibres (0.5–2%) in high-plasticity red soils. The laboratory testing, including compaction, Unconfined Compressive Strength (UCS), stiffness, and strength ratio, allows us to discern the changes in density, strength, and ductility. The findings from the study showed that the addition of fly ash to the mixtures increased the strength and stiffness significantly, with the best result obtained using 20% fly ash. The reasons for such an increase in properties are the pozzolanic reactions taking place and causing the soil to become denser. Polypropylene fibres improved ductility, crack resistance, and post-peak performance but diminished the efficiency of compacting and stiffness at high dosages (> 1.5%). The optimum mix was 20–25% fly ash with 1% polypropylene fibre, which significant combined improvement in strength, ductility, and workability. Such results of combining fly ash and artificial fibres in the stabilization will have practically resulted in the application of poor-quality road sub-grades and other infrastructure projects on poor soils.