Alkalis in cement and concrete refer primarily to sodium and potassium compounds that are present in the cement mix, either as part of the raw materials or added during the manufacturing process. These alkalis can react with certain siliceous aggregates to form alkali–silica gel, which can absorb water and expand, leading to alkali–silica reaction (ASR). This reaction is one of the most significant concerns related to the presence of alkalis in concrete, impacting its longevity and structural integrity.