The C-S-H gel of Portland cement mortars: Part I. The interpretation of energy-dispersive X-ray microanalyses from scanning electron microscopy, with some observations on C-S-H, AFm and AFt phase compositions

Journal Article · Mon Sep 01 04:00:00 EDT 2003 · Cement and Concrete Research

DOI:https://doi.org/10.1016/S0008-8846(03)00064-4· OSTI ID:20658326

Famy, C; Brough, A R; Taylor, H F W

Scanning electron microscopy (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 atom 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 we consider to be a highly substituted ettringite of probable composition C{sub 6}A{sub 2}S-bar{sub 2}H{sub 34} or {l_brace}Ca{sub 6}[Al(OH){sub 6}]{sub 2}{center_dot}24H{sub 2}O{r_brace}(SO{sub 4}){sub 2}[Al(OH){sub 4}]{sub 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.

• OSTI ID: 20658326
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Journal Issue: 9 Vol. 33; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINATES
CALCIUM SILICATES
GELS
HYDRATION
MORTARS
PORTLAND CEMENT
SCANNING ELECTRON MICROSCOPY
SULFATES
X RADIATION