Buton Asphalt Modified with Natural Zeolite for Warm Mix Production and CO₂ Emission Reduction

This study evaluates the use of Indonesian natural zeolite as a sustainable warm-mix additive for Thin Layer Asphalt Concrete incorporating Pure Asbuton B-50/30. Unlike most Warm Mix Asphalt (WMA) studies that rely on commercial synthetic additives and petroleum binders, this study investigates locally sourced clinoptilolite zeolite as a mineral foaming additive for Asbuton asphalt mixtures. The optimum asphalt content was determined as 5.95% using the Marshall mix design method, while natural zeolite was incorporated at 1.5% of the total mixture weight. The addition of natural zeolite enabled the mixture to be produced at 145°C, lower than the conventional Asbuton mixing temperature of 165-170°C specified in the 2025 Indonesian Highway Specifications. The zeolite modified mixture achieved a Marshall stability of 1,179.56 kg and a Marshall Quotient of 410.99 kg/mm, indicating adequate structural performance under reduced temperature production. The improved workability is attributed to the release of crystalline water from the zeolite framework, which generates a temporary foaming effect that lowers binder viscosity and enhances aggregate coating. A production stage emission assessment showed that the normalized CO₂ reduction was approximately 4.88 kg CO₂ per ton of asphalt mixture. Under a theoretical national scale overlay scenario, this corresponds to an upper bound reduction potential of approximately 2.04 billion kg CO₂ compared with conventional hot mix asphalt production. These findings demonstrate that regional natural zeolite can serve as a technically feasible and environmentally beneficial alternative to commercial synthetic WMA additives for Asbuton pavement applications.