The AFm phase in Portland cement

Journal Article · Thu Feb 15 04:00:00 EST 2007 · Cement and Concrete Research

DOI:https://doi.org/10.1016/j.cemconres.2006.10.010· OSTI ID:20995360

Matschei, T ^[1]; Lothenbach, B ^[2]; Glasser, F P ^[1]

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1. Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Old Aberdeen, AB24 3UE Scotland (United Kingdom)
2. EMPA, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Concrete and Construction Chemistry, Ueberlandstrasse 129, CH-8600 Duebendorf (Switzerland)

The AFm phase of Portland cements refers to a family of hydrated calcium aluminates based on the hydrocalumite-like structure of 4CaO.Al{sub 2}O{sub 3}.13-19 H{sub 2}O. However OH{sup -} may be replaced by SO{sub 4} {sup 2-} and CO{sub 3} {sup 2-}. Except for limited replacement (50 mol%, maximum) of sulfate by hydroxide, these compositions do not form solid solutions and, from the mineralogical standpoint, behave as separate phases. Therefore many hydrated cements will contain mixtures of AFm phases. AFm phases have been made from precursors and experimentally-determined phase relationships are depicted at 25 deg. C. Solubility data are reported and thermodynamic data are derived. The 25 deg. C stability of AFm phases is much affected by the nature of the anion: carbonate stabilises AFm and displaces OH and SO{sub 4} at species activities commonly encountered in cement systems. However in the presence of portlandite, and as carbonate displaces sulfate in AFm, the reaction results in changes in the amount of both portlandite and ettringite: specimen calculations are presented to quantify these changes. The scheme of phase balances enables calculation of the mineralogical balances of a hydrated cement paste with greater accuracy than hitherto practicable.

• OSTI ID: 20995360
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Journal Issue: 2 Vol. 37; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINATES
CALCIUM COMPOUNDS
HYDROXIDES
PORTLAND CEMENT
SOLUBILITY
STABILITY
SULFATES
THERMODYNAMICS