Published Paper Details:

Underwater concrete (UWC) is widely used in marine and hydraulic structures; however, its performance is often compromised by cement washout, loss of cohesion, and significant strength reduction during underwater placement. This study evaluates the fresh and hardened properties of selected underwater concrete mixtures incorporating silica fume and a hybrid combination of silica fume and fly ash, in comparison with a conventional control mix. The experimental program focused on assessing workability, washout resistance, air content, and compressive strength under both air and underwater casting conditions. The results demonstrate that the control mix suffered severe washout and substantial strength loss, confirming its unsuitability for underwater applications. The inclusion of silica fume significantly improved washout resistance and strength retention due to enhanced matrix densification and refined pore structure; however, it led to increased viscosity and reduced flowability. In contrast, the hybrid silica fume-fly ash mixture provided a more balanced performance, achieving improved workability, reduced air content, and satisfactory strength retention, particularly at later ages. The findings confirm that optimized combinations of supplementary cementitious materials can effectively enhance the stability and durability of underwater concrete. The hybrid silica fume and fly ash system is shown to be a promising solution for achieving improved overall performance in underwater construction while maintaining acceptable workability.