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Saturation Factors for Calcium Hydroxide and Calcium Sulfates in Fresh Portland Cement Pastes
Author(s) -
GARTNER ELLIS M.,
TANG FULVIO J.,
WEISS STUART J.
Publication year - 1985
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.1151-2916.1985.tb10122.x
Subject(s) - portlandite , saturation (graph theory) , calcium hydroxide , gypsum , portland cement , mineralogy , cement , materials science , calcium , chemistry , composite material , metallurgy , combinatorics , mathematics
Aqueous extracts from five cement pastes at w/c = 0.5 were analyzed for Ca 2+ , SO 2– 4 , Na + , and K + . Degrees of saturation with respect to portlandite, gypsum, and syngenite were determined at ages from 6 min to 3 h, taking into account ionic association effects. Portlandite saturation is usually attained within a few minutes of mixing, but rates of saturation vary. The maximum degree of saturation is 2 to 3 times the equilibrium value and is attained within 2 h. Initial super‐saturation with respect to gypsum, and in some cases syngenite, occurs at very early ages and declines to the saturation level within 12 min. Results are interpreted by use of a solution‐precipitation model for cement hydration. The calculated critical size of portlandite nuclei at early ages is ∼0.1 μm. Slow growth of portlandite nuclei suggests a surface poisoning phenomenon.