Mechanical performance and durability of asphalt mixtures incorporating coal fly ash filler for sustainable pavement applications

This study investigates coal fly ash (CFA), a by-product of coal combustion, as a filler material in asphalt mixtures. Four mixtures containing 0%, 2%, 4%, and 6% CFA were evaluated through a comprehensive laboratory testing program, including Marshall Properties, Indirect Tensile Strength (ITS), Cantabro Loss, Resilient Modulus, Dynamic Creep, and Wheel Tracking tests. The incorporation of CFA resulted in consistent improvements in mechanical performance. At 6% CFA content, Marshall stiffness increased by 63% (from 4,728 to 7,697 N/mm), rut depth decreased by 24% (from 2.1 to 1.6 mm), and ITS increased significantly (from 1,006 to 1,970 kPa), indicating enhanced load-bearing capacity, deformation resistance, and tensile strength. Cantabro loss was reduced by 40% (from 8.5% to 5.1%), demonstrating improved abrasion resistance, while resilient modulus values at both 25 °C and 40 °C confirmed increased stiffness across service temperatures. Dynamic creep results further showed reduced permanent strain and higher creep stiffness with increasing CFA content. Overall, the findings demonstrate that CFA is an effective filler for enhancing the mechanical performance and durability of asphalt mixtures while enabling the beneficial reuse of industrial by-products.