Silicon dioxide, or silica, is a primary component of many types of aggregates and supplementary cementitious materials used in concrete, such as sand, quartz, and fly ash. In the context of cement chemistry, the solubility of SiO 2 refers to its ability to dissolve in the alkaline pore solution of concrete, primarily influenced by the pH level and the presence of other chemical species. The dissolution of SiO 2 is a critical factor in pozzolanic reactions, where dissolved silica reacts with calcium hydroxide (a byproduct of cement hydration) to form additional calcium silicate hydrate (C-S-H), thereby enhancing the concrete’s strength and durability.