As a simple, but robust, conclusion, the presence of soluble Na and K salts can also cause, by precipitation of poorly soluble calcium salt (with portlandite, CH) or anion exchange reactions (with phases related to C-A-H), the release of anions into solution. Therefore, the presence of any salts of Na and K in cement pore water is undesirable and the measurements of Na and K elements is a good proxy (indicator) for the maximal concentration of in pore solution. This is why the total alkali equivalent content () of cement can simply rely on the measurements of Na and K ("e.g.", by ICP-AES, AAS, XRF measurements techniques).