Effectiveness of Fly Ash and Lime in Cement-Stabilised Base Mixtures Using Recycled and Natural Aggregates

The rising generation of construction and demolition waste, along with the depletion of natural aggregates, demand sustainable alternatives for pavement construction. The aim of this study is to investigate the performance of cement-treated base and subbase mixtures containing recycled concrete aggregate (RCA), fly ash, and hydrated lime as partial substitutes for cement. RCA substitution levels were 0%–100%, and cement contents (4–6%) mixed with fly ash + lime (10% + 20% and 20% + 10%). The results include mechanical properties such as compaction characteristics, unconfined compressive strength (UCS), durability index, elastic modulus, modulus of rupture and resilient modulus, and microstructural studies. The results indicate that combining RCA and lime increases the optimum moisture content while causing a marginal decrease in maximum dry density. The 28-day UCS for mixes ranged from 4.86 to 8.95 MPa, meeting IRC:37-2018 parameter requirements; all durability index values were greater than 0.80. Resilient modulus values ranged from 335 to 491 MPa, with stress-dependent behaviour and high R²= 0.9474.