Self-compacting concrete (SCC) mix design conventionally requires a high binder content to achieve the required flowability and segregation resistance, thereby increasing the risk of shrinkage at both early and later ages. The present study explores the synergistic effect of incorporating nanosilica (NS) and ultrafine blast furnace slag (UFBFS) on the fresh and hardened properties of M60 grade SCC, including durability and shrinkage performance, by optimizing the binder content without compromising SCC performance requirements. Preliminary experimental investigations revealed that UFBFS enhances workability and strength properties, while NS increases paste viscosity and uniformity. The results of the experiments showed that a 5–8% replacement of the UFBFS-to-OPC ratio could be considered optimal for enhancing compressive strength. Integrating UFBFS and NS allowed for optimizing the binder content at 565 kg/m³ while meeting SCC flow requirements, reducing it from 600 kg/m³. The modified SCC demonstrated a 28-day compressive strength of 70 MPa and exhibited better durability, such as high resistance to water penetration, low water absorption, and low chloride permeability. The drying shrinkage was reduced by 38% in the modified SCC, and cracking due to plastic shrinkage was avoided in the modified SCC. The work clearly illustrates how UFBFS and NS can be used to prepare a durable SCC at lower binder content and with good shrinkage resistance.
