Analysis on Engineering Behavior of Dense Bituminous Mixes Using Coal Ash with Natural Fiber Reinforcement

Bituminous mixtures generally consist of coarse aggregates, fine aggregates, filler, and a binder. Hot Mix Asphalt (HMA) refers to bituminous mixtures in which all components are heated, mixed, placed, and compacted at elevated temperatures. HMA can be categorized into dense‐graded mixes (Bituminous Concrete, BC) and gap‐graded mixes such as Stone Matrix Asphalt (SMA). SMA typically requires stabilizing additives—cellulose fibres, mineral fibres, or polymers—to prevent drain-down. In the present study, slow-setting emulsion (SS1)–coated sisal fibre was incorporated at varying dosages of 0, 0.25, 0.5, 0.75, and 1% by weight of the mix, with fibre lengths of 0, 5, 10, 15, and 20 mm. The optimum composition—comprising the optimum bitumen content, fibre content, and fibre length—was identified based on the test results. Marshall characteristics were evaluated to determine the optimum binder and fibre parameters. A maximum Marshall stability of 15 kN was achieved at an optimum bitumen content of 5.57%, an optimum sisal fibre content of 0.5%, and a fibre length of 10 mm. To further assess pavement performance, additional tests such as moisture susceptibility, indirect tensile strength (ITS), creep behaviour, and tensile strength ratio (TSR) were conducted. Considering the environmental concerns associated with coal ash disposal, its use as a partial replacement for natural sand and stone dust offers a sustainable and economical alternative. Performance evaluation through ITS, moisture susceptibility, TSR, and retained stability confirmed the suitability of the modified bituminous mixes..