Assessment of fresh properties of self-compacting concrete incorporating GGBS and recycled concrete aggregate

Self-compacting concrete (SCC) shows a promising way towards sustainable construction with the addition of industrial by-products and recycled materials. This research study focuses on the fresh behaviour of SCC using ground granulated blast-furnace slag (GGBS) as a cement replacement (15%, 30%, 45%) and recycled concrete aggregate (RCA) as a coarse aggregate replacement (20–100%). Twenty-four SCC mixes were made and tested with slump flow, T500, J-ring, L-box, U-box, and V-funnel tests. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results indicate that GGBS exhibits an amorphous and angular morphology, which enhances the volume of the paste and its reactivity. In contrast, RCA had high roughness and adherent mortar, resulting in lower flowability at higher replacement values. Results showed that GGBS up to 30% had a consistent effect on flowability, with slump flow improved by 15–21 mm, and T500 reduced by as much as 0.5 s. In contrast, an RCA above 80% had a significant detrimental effect on flow and passing ability. Optimal performance was achieved with 30% GGBS mixed with RCA in the range of 40–60%, striking a balance between sustainability and desirable SCC fresh properties.