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New insights into tricalcium silicate hydration in paste
Author(s) -
Sowoidnich Thomas,
Bellmann Frank,
Damidot Denis,
Ludwig HorstMichael
Publication year - 2019
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/jace.16133
Subject(s) - aqueous solution , precipitation , calcium silicate , phase (matter) , silicate , chemistry , isothermal process , calorimetry , silicon , metastability , cement , conductivity , calcium , mineralogy , chemical engineering , materials science , thermodynamics , metallurgy , organic chemistry , physics , meteorology , engineering
The knowledge of the aqueous phase composition during the hydration of tricalcium silicate (C 3 S) is a key issue for the understanding of cement hydration. A new in situ method of computing calcium ion concentration from the measurement of the electrical conductivity on paste was coupled to isothermal calorimetry and BET measurements to get new insights on the early hydration of C 3 S. Ion concentrations of the aqueous phase are mainly dependent on the degree of hydration and the water to C 3 S ratio. In the case of C 3 S paste, the calcium and silicon concentrations determined at low degrees of hydration can be related to the equilibrium curve of C‐S‐H having C/S = 1.27 and named C 1.27 SH y . It is expected that C 1.27 SH y thermodynamically controls the aqueous phase composition at this early stage. Indeed, the formation of C 1.27 SH y is quasi‐immediate when C 3 S is in contact with water inducing a very rapid increase of the specific surface area that remains constant during the induction period. At higher degrees of hydration, the aqueous phase composition departs from the C 1.27 SH y equilibrium curve. C 1.27 SH y appears to be a metastable C‐S‐H that could be related to an intermediate phase previously reported. The quasi‐immediate precipitation of C 1.27 SH y on C 3 S surface explains why calcium and silicon concentrations remain low during early hydration even though C 3 S is strongly undersaturated. This also agrees with the control of the end of the induction period by the nucleation and growth of more stable C‐S‐H.