Experimental Study on the Effects of Coal Ash and Emulsion Coated-Sisal Fibers in Hot Mix Asphalt

India’s coal-fired thermal power plants produce substantial amounts of fly ash and bottom ash, leading to critical environmental and disposal challenges. This experimental study investigates the integration of these waste by-products into Hot Mix Asphalt (HMA) by utilizing fly ash as a mineral filler and bottom ash as a fine aggregate. Emulsion-coated natural sisal fibers were incorporated to improve the mix performance and provide a sustainable alternative to conventional materials. Dense graded bituminous mixes (DBM) were prepared as per MORTH (2013) specifications, using VG-30 bitumen and a nominal maximum aggregate size (NMAS) of 26.5 mm. Sisal fibers coated with SS-1 emulsion were added at varying contents (0%–1%) and lengths (5 mm–20 mm). The Marshall Mix Design method was employed to evaluate the optimal binder content, fiber dosage, and fiber length. The optimum mix, with 5.57% binder, 0.5% fiber content, and 10 mm fiber length, achieved a peak Marshall Stability of 15 kN. Performance evaluation through tensile strength ratio (TSR), indirect tensile strength (ITS), static creep, and moisture susceptibility tests indicated marked improvements in mechanical properties. The results affirm that the combined use of coal ash and treated sisal fiber not only enhances pavement performance but also presents a cost-effective and environmentally responsible method of ash utilization.