Optimization of the Use of Buton Rock Asphalt Reviewed from the Influence of Filler Composition

Natural asphalt from Buton Island, particularly Buton Rock Asphalt (BRA), is widely used as a partial substitute for oil asphalt and rock ash filler in Hot Mix Asphalt (HMA). With asphalt content reaching 30–45% of the aggregate, the required oil asphalt can be reduced to 1–4%. Waste engine oil, containing up to 15%, serves as a softener similar to hard asphalt. BRA and engine oil waste supports the utilization of local resources while enhancing environmental sustainability by reducing oil asphalt needs from 5–6% to 2–3%. Fine BRA particles can act as fillers, though they have lower strength than rock ash. Increasing BRA by 5% raises the filler content by 0.633% and gradually replaces rock ash. At 45% BRA, oil asphalt becomes unnecessary but results in a high VIM value of 8.739%. The optimal performance is achieved at 40% BRA and 2% oil asphalt, yielding a VIM of 4.105% and stability of 1,148.86 kg. However, increasing BRA to 45% lowers stability to 782.11 kg, indicating the threshold for effective use. Excess BRA reduces structural integrity due to high fine particle content, highlighting the need for balance in its application.