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Chemistry of the Aqueous Phase of Ordinary Portland Cement Pastes at Early Reaction Times
Author(s) -
Kelzenberg Anthony L.,
Tracy Sharon L.,
Christiansen Bruce J.,
Thomas Jeffrey J.,
Clarage Matthew E.,
Hodson Simon,
Jennings Hamlin M.
Publication year - 1998
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1998.tb02631.x
Subject(s) - ettringite , portland cement , gypsum , chemistry , cement , calcium hydroxide , calcium silicate , sodium sulfate , mineralogy , aqueous solution , portlandite , sulfur , sulfate , precipitation , calcium , clinker (cement) , inorganic chemistry , chemical engineering , sodium , metallurgy , materials science , organic chemistry , physics , meteorology , engineering
The chemistry of the aqueous phase of ordinary portland cement paste at early ages (<2 h) has been analyzed in terms of the concentrations of the elemental components in the pore fluid. The concentrations of calcium, sulfur, aluminum, and silicon are rationalized by plotting the data on “phase diagrams.” To simplify the analysis, the portland cement system is described using two subsystems: (i) CaO‐Al 2 O 3 ‐CaSO 4 ‐H 2 O, modified by the presence of sodium and potassium, and (ii) CaO‐SiO 2 ‐H 2 O. During the first 10 min of hydration, the calcium, sulfur, and aluminum concentrations all decrease, roughly in proportion, which suggests a precipitation process, a conversion of calcium sulfate hemihydrate to gypsum, and the initial formation of ettringite. The CaO‐Al 2 O 3 ‐CaSO 4 ‐H 2 O subsystem seems to move from a phase assemblage of gypsum, Al 2 O 3 ·3H 2 O, and ettringite to an assemblage of gypsum, calcium hydroxide, and ettringite during the first 15‐30 min after the water and the cement are mixed. The silicate equilibrium is approached more slowly. The intensity of mixing has relatively little effect on the concentrations beyond the first few minutes.