Recycling bottom ash in cement-stabilized pavement materials: Mechanical performance and environmental feasibility

This study investigates the feasibility of utilizing bottom ash (BTA), a by-product of coal combustion, as a sustainable partial replacement for sand in cement-stabilized mixtures for pavement applications. Cement-stabilized mixtures incorporating BTA (0–50%) and cement (1–7%) were evaluated for their mechanical and durability performance through unconfined compressive strength, splitting tensile strength, California bearing ratio, and wetting-drying resistance tests. Microstructural analyses, including X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectrometry, were conducted to elucidate hydration mechanisms and structural transformations governing strength development. A predictive model for unconfined compressive strength was established, demonstrating a strong correlation (R² = 0.8364) with curing time, cement, and BTA content. The optimal mix, comprising 20% BTA and 7% cement, achieved a 6.6 MPa unconfined compressive strength at 120 days, significantly outperforming the control sample (3.2 MPa). California bearing ratio tests yielded a peak value of 727%, indicating superior load-bearing capacity. Environmental assessment confirmed that heavy metal leaching from BTA-cement-stabilized mixtures remained within regulatory safety limits. The findings demonstrate that stabilized mixtures meet or exceed the Department of Highways, Thailand standards for subbase and base layers, with 20% BTA and 7% cement suitable for soil-cement base applications and 30% BTA with 3% cement viable for subbase layers. This study highlights the potential of BTA as a cost-effective, sustainable alternative in pavement construction, promoting resource efficiency and circular economy principles in the construction sector.