The System Na ₂ O‐CaO‐SiO ₂ ‐H ₂ O

Abstract

A portion of the quaternary phase diagram for Na 2 O‐CaO‐SiO 2 ‐H 2 O has been constructed. Plotting concentrations as their 10th roots allows compounds having solubilities which differ by several orders of magnitude to be represented on a single diagram. The compositional relationships among sodium‐substituted calcium silicate hydrate, calcium‐substituted sodium silicate hydrate, calcium bydroxide, a quaternary compound of approximate composition 0.25Na 2 O · CaO · SiO 2 · 3H 2 O, sodium hydroxide monohydrate, and miscellaneous sodium silicate hydrates are presented. The quaternary diagram constructed shows the quaternary compound to exist in equilibrium with sodium‐substituted calcium silicate hydrate and calcium hydroxide. Conditions in concrete pore solutions which favor the formation of this quaternary compound may also favor the occurrence of the alkali‐silica reaction.