Study of Physical and Mechanical Properties of High-Strength Concrete Made with Varying Dosages of Silica Fume

High-strength concrete (HSC) is increasingly used in modern infrastructure for its superior load-carrying capacity and durability, yet OPC-based production carries high embodied carbon and durability concerns such as elevated heat of hydration and early-age cracking. Supplementary cementitious materials (SCMs) can address both issues, but controlled comparisons within a single high-strength mix remain limited, restricting transferable mix-design conclusions. This study examines the physical and mechanical performance of M65 grade HSC incorporating fly ash (fixed at 20% of binder) and silica fume (varied 0–10% in 2% increments) at a water-to-binder ratio of 0.3 with a PCE-based superplasticizer. Seven constituent materials were characterised per relevant IS specifications before mix proportioning. Specimens were cast, water-cured, and tested for workability, fresh density (both in fresh state), and compressive, splitting tensile, and flexural strength (all in hardened state) at 7 and 28 days per IS 516, IS 5816, and IS 1199. The programme identifies the optimum silica fume level balancing workability, density, and strength development, addressing the scarcity of controlled SCM comparisons in existing literature. Findings support rational SCM selection in HSC mix design, offering practical guidance for balancing performance and sustainability while promoting lower-cement construction practices.