Changes of C-S-H gel in strong chloride solution

C-S-H paste was investigated after 28 months' immersion in strong chloride solution with Mg²⁺. In the outer, altered layer, about 3 mm thick, C-S-H gel became very compact and highly decalcified with a CaO—SiO₂ molar ratio (C/S) of 0·48. New phases, brucite and basic magnesium chlorides, were formed, the latter principally in microcracks. In the otherwise unaltered internal zone the concentration of chloride ions was high, being equal to the concentration in the external layer. But the C/S was unchanged and the concentration of magnesium ions was very small, The beginning of the densification process of C-S-H phase can be observed in the transition zone.