Alkalis in concrete comes from a variety of sources, both internal and external. All concrete constituents can contribute alkalis, but Portland cement is the major source of alkalis to concrete. These alkalis come from the raw materials used to make clinker and from fuels. Only a portion of the alkalis in cement are readily soluble and are highly dependent on the constituents of the clinker. Sulfate alkalis are considered readily soluble. Alkalis can come from concrete constituents such as mixing water, admixtures, aggregates, and SCMs, fibers, and can even be recycled through the products of the alkali-silica reaction. Alkalis can also come from external sources such as alkaline or sea water, fertilizers, industrial residues and de-icing products. Finally, electrochemical treatments affect the distribution of alkalis within the material. There are many sources of alkalis, and the alkalis of each component must be considered.