Structural efficiency of blast furnace steel slag aggregate concrete for strengthening RC flat slabs

Abstract This study investigates blast furnace steel slag concrete as a sustainable strengthening layer for reinforced concrete (RC) flat slabs, with natural aggregates fully replaced by slag in the overlay. Five slabs (1500 × 1500 × 100 mm) were tested under static loading and compared against FRP, steel fiber-reinforced concrete, and high-performance concrete strengthening methods. The slag overlay increased ultimate load by 29.9% and first-crack load by 15.7%, while reducing ultimate deflection by 56.4% compared to the control slab. A validated ANSYS finite element model was used to conduct 22 parametric configurations examining overlay thickness, slab aspect ratio, and bottom reinforcement corrosion. Results show that increasing the aspect ratio from 1.2 to 2.0 reduces ultimate load by 73%, and 25–100% bottom mesh corrosion reduces ultimate load from 233 kN to 61.5 kN. An overlay of 20–30% of slab thickness is recommended as the optimal strengthening configuration.