Utilising cement kiln dust as a sustainable cementitious alternative for recycled asphalt pavement materials: a mechanical, economic, and environmental study

This study investigated the mechanical, microstructural, and environmental performance of recycled asphalt pavement materials stabilised with ordinary Portland cement (OPC) and cement kiln dust (CKD) as sustainable alternatives for full-depth reclamation (FDR) applications. Unconfined compressive strength (UCS), indirect tensile strength (ITS), flexural strength (FS), resilient modulus (MR), and wet–dry durability were evaluated for various reclaimed asphalt pavement (RAP) blends. Results showed that CKD at 15% maximised strength, the UCS increased up to 9.7 times compared to unstabilised blends and matched 3% OPC in up to 80% RAP blends, with similar ITS, FS, and MR trends before declining at higher dosages. However, CKD mixtures exhibited greater strength loss under wet–dry cycles than OPC mixes. Microstructural analysis revealed cementitious product formation, microstructural densification, elevated chloride/alkali content, and chloro-aluminate hydrates that explain CKD's performance limits. Lifecycle assessment showed CKD can cut CO₂ emissions by up to 89% and reduced costs by 36% versus OPC, supporting its use as a sustainable stabiliser in low- to medium-traffic FDR designs when properly dosed.