Assessment of the technical, economic, and carbon reduction potential of recycled concrete aggregate for sustainable roads in Saudi Arabia

Construction and demolition (C&D) waste has been creating significant environmental and economic challenges associated with landfill disposal and depletion of natural resources. In Saudi Arabia, the growing volume of C&D waste highlights the need for sustainable recycling strategies that support the objectives of Vision 2030 and circular economy principles. This study evaluated the feasibility of utilizing recycled concrete aggregate (RCA) as a substitute for natural aggregate in both hot-mix asphalt (HMA) and base layer applications for road construction. RCA was obtained from a landfill in Buraidah, Saudi Arabia, processed, and evaluated through aggregate suitability tests, Marshall mix design, Proctor compaction, and California Bearing Ratio (CBR) testing. Economic performance was assessed using construction and life-cycle cost calculations, while construction-stage CO₂ emissions were estimated using a scenario-based carbon-screening approach. A multi-criteria ranking framework integrating engineering, economic, and carbon-performance indicators was also applied to compare RCA alternatives. The RCA satisfied the specified aggregate requirements, although its water absorption (7.83%) and abrasion loss (40.55%) were higher than those of the natural aggregate. In HMA mixtures, RCA contents up to 20% showed comparatively favorable volumetric and mechanical performance within the tested binder range, whereas mixtures containing 30–50% RCA exhibited elevated air voids and reduced VFA, indicating the need for further binder optimization. For base layers, increasing RCA content reduced maximum dry density from 2.29 to 1.73 g/cm³ and increased CBR from 96.8% for the control to 172.5% at 100% RCA, while swell decreased from 0.45 to 0.004%. Economic analysis indicated net savings of 2.35–9.73% for HMA mixtures, with the highest savings at 10% RCA, while base-layer costs decreased by up to 25.1% at 100% RCA. The estimated construction-stage CO₂ reduction increased from 4.67% to 23.37% for HMA and from 23.07 to 79.02% for base layers with increasing RCA content. Under the adopted equal-weight multi-criteria framework, 10% RCA provided the most favorable HMA option considering technical feasibility and overall performance, whereas 100% RCA ranked highest for the base layer. Overall, the findings indicate that RCA has substantial potential for sustainable pavement construction in Saudi Arabia, particularly in base-layer applications, while higher RCA contents in HMA require further optimization and durability validation.