Workability and Flexural Strength of Binary Blended Concrete made with Recycled Aggregates and Marble Dust under Two-Point Loading

The increasing demand for sustainable construction materials has increased interest in utilizing industrial waste products in concrete production. This research explores the combined effect of recycled coarse aggregates (RCA), obtained from demolished concrete, and marble dust (MD), a byproduct of marble processing, on workability and flexural strength of concrete. Both materials are widely available construction wastes that pose significant disposal challenges. In this study, RCA was used to replace 50% of conventional coarse aggregates, while marble dust replaced cement in varying proportions from 1–10%, at 1% intervals. A total of twelve concrete mixes were prepared using a standard 1:2:4 mix ratio and a constant water-binder ratio of 0.55. Among these, ten mixes contained both RCA and MD, one served as a control mix with all conventional aggregates and no MD, and one contained RCA but no MD. Workability was evaluated using the slump test, and flexural strength was assessed using standard prisms (100 mm × 100 mm × 500 mm) tested under two-point loading after 28 days of curing. The results revealed a clear trend of decreasing slump values with increasing marble dust content, indicating reduced workability due to higher water demand. Flexural strength generally declined with higher MD content, but the mix with 7% MD and 50% RCA achieved a balanced performance, exhibiting only a 15% reduction in strength compared to the control mix, while improving central deflection by 11%. These findings demonstrate that a binary blend of RCA and MD can yield eco-efficient concrete with acceptable structural performance, supporting broader adoption of waste materials in construction. The results also highlight the importance of optimized blending ratios to balance strength, ductility, and workability in sustainable concrete applications.