An Experimental Study on the Compressive Strength of Recycled Stone Aggregate Concrete

The volume of construction and demolition (C&D) waste generated worldwide continues to rise sharply, which undermines efforts to meet long-term sustainability targets. Converting demolished concrete into aggregate offers a practical route to limit landfill disposal and preserve natural raw materials. In Bangladesh, crushed brick chips are the conventional coarse aggregate for concrete, whereas demolished substructure elements such as pile caps usually contain stone chips and can therefore supply stone-based recycled concrete aggregate (RCA) of high strength. In this work, natural coarse aggregate (NCA) was substituted with stone-based RCA at levels of 0%, 20%, 40%, 60%, 80%, and 100%, and the resulting recycled aggregate concrete (RAC) was examined. The aim was to identify an acceptable RCA substitution level that does not impair concrete performance. Six batches of cylindrical specimens (100 mm × 200 mm) were prepared with a mix proportion of 1: 1.1: 3.1, designed following the British Standard method, and a constant w/c ratio of 0.50. Tests on the coarse aggregates indicated that the collected RCA was of better quality than the brick-based NCA, with a higher SSD unit weight (1493 kg/m 3 versus 1338 kg/m 3 ) and a much lower water absorption (10.32% versus 23.16%). Consequently, compressive strength rose progressively with RCA content up to 80% substitution, where it exceeded that of the control mix by 47%. At full (100%) substitution, the gain over the control dropped to 33.8%. This decline is linked to the larger quantity of old mortar attached to the aggregate surface, which produces a weaker interfacial transition zone (ITZ).