This study investigates the use of cast-iron slag in ternary blended binders as part of the concrete industry’s transition toward sustainable and environmentally friendly practices. With a focus on reducing the carbon footprint of traditional Portland cement, the research examines the physical properties, compressive strength, and microstructural characteristics of binders comprising cast-iron slag (CIS), ground granulated blast furnace slag (GGBS), and Portland cement. A total of 18 distinct binder mixtures were systematically designed and evaluated to explore the effects of varying proportions of cast-iron slag, GGBS, and cement. The experimental program aimed to optimize binder compositions for improved performance and sustainability. Compressive strength tests were conducted on specimens cured under standard conditions at 7, 14, and 28 days. Among the tested mixtures, Mix M4 exhibited supaerior compressive strength compared to the others, while M4, M6, and M8 were selected for detailed microstructural analysis. Microstructural investigations, were conducted to study the morphology, crystalline phases, and chemical bonds within the binders. Replacing 30% of cement with equal parts of slag significantly reduced air voids, as observed in SEM images, resulting in a denser and more durable material.