The replacement ratio in concrete refers to the proportion of a primary component (typically Portland cement) that is substituted with an alternative material, such as fly ash, slag, or silica fume. These materials, known as supplementary cementitious materials (SCMs), are used to enhance the concrete’s properties and reduce the environmental footprint of cement production. The mechanism by which SCMs enhance concrete includes chemical reactions that contribute to the hydration process, improving the material’s strength and durability. For instance, silica fume can react with calcium hydroxide (a byproduct of cement hydration) to form additional calcium silicate hydrate, the primary binding phase in concrete, which enhances the density and strength of the material.