Alkali modulus, often referred to as the alkali ratio or alkali–silica ratio, is a critical parameter in the chemistry of cement and concrete, determining the ratio of alkali oxides (Na 2O and K 2O) to silica (SiO 2) in cementitious materials. This ratio is pivotal because it influences the hydration reactions, setting time, and durability of concrete, especially under severe environmental conditions. An optimal alkali modulus can enhance the performance and longevity of concrete structures by managing the reactivity of the cement with the aggregates and minimizing deleterious reactions such as alkali–silica reaction (ASR), which can lead to expansive damage and structural failure.