Supplementary Cementitious Materials (SCMs) are materials used in concrete to replace a portion of the Portland cement, enhance the properties of the concrete, and contribute to sustainability goals. Common SCMs include fly ash, silica fume, slag, and natural pozzolans. These materials interact with Portland cement in concrete through pozzolanic or hydraulic reactions, where SCMs react with calcium hydroxide released during cement hydration to form additional calcium silicate hydrate (C-S-H) phases. This process not only enhances the strength and durability of concrete but also reduces the permeability and enhances chemical resistance, making the concrete more robust against environmental attacks.