C-S-H gel of portland cement mortars. Pt.1. The interpretation of energy-dispersive x-ray ...

Summary

SEM microanalyses of the calcium-silicate-hydrate (C-S-H) gel in Portland cement pastes rarely represent single phases.  Essential experimental requirements are summarised and new procedures for interpreting the data are described.   These include, notably, plots of Si/Ca against other atomic ratios, 3D plots to allow three such ratios to be correlated  and solution of linear simultaneous equations to test and quantify hypotheses regarding the phases contributing to individual microanalyses.  Application of these methods to the C-S-H gel of a 1-day-old mortar identified a phase with Al/Ca = 0.67 and S/Ca = 0.33, which is considered to be a highly substituted ettringite of probable composition C6A2barS2H34 or {Ca6[Al(OH)6]2.24H2O}(SO4)2[Al(OH)4]2.  If this is true for Portland cements in general, it might explain observed discrepancies between observed and calculated aluminate concentrations in the pore solution.  The C-S-H gel of a similar mortar aged 600 days contained unsubstituted ettringite and an AFm phase with S/Ca = 0.125.  34 refs.

Primary author(s): Famy C; Brough A R; Taylor H F W

                            Lafarge Laboratoire Central de Recherche; Leeds,University

Source: Cem.Concr.Res.

            33,No.9,2003,p.1389-1398


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