Stoichiometry and Kinetics of Slag Hydration in the Presence of Calcium Hydroxide.
Stoichiometry and Kinetics of Slag Hydration in the
Presence of Calcium Hydroxide.
(706 K)
Richardson, J. M.; Biernacki, J. J.; Stutzman, P. E.;
Bentz, D. P.
Journal of the American Ceramic Society, Vol. 85, No.
4, 947-953, 2002.
Keywords:
calcium silicate hydrate; stag hydration; stoichiometry;
cements; kinetics
Abstract:
The reaction between ground granulated blast furnace
slag (GGBFS) having an empirical formula of
C7.88S7.39M3A and calcium hydroxide (CH) was
investigated. The stoichiometry of the reaction and
kinetics were explored. Thermogravimetric analysis was
used to monitor the consumption of CH from which rate
constants were determined. Scanning electron microscopy
(SEM) was used to determine the slag consumption as well
as the Ca/Si ratio in C-S-H products. A tentative
stoichiometric ratio of 2.6 moles CH consumed per mole
of slag reacted was determined using two methods. By
combining consumption data determined separately for
slag and CH a molar stoichiometry of 2.79 was found.
Similarly, by directly determining the Ca/Si ratio in
the calcium silicate hydrate (C-S-H) product a range for
the molar stoichiometry between 1.65 and 3.42 was found.
Knudsen activation energies of 14.5, 17.9, and 22.6
kJ/mole were determined for three different mass ratios
of slag and CH reacted over a temperature range of 15
{degrees}C to 50 {degrees}C and hydrated for a period of
time from 0 days to 32 days. Finally, a comparison of
the stoichiometry of the slag/CH reaction was made with
slag/Portland cement hydration. The basic features of
both appear similar. In the C-S-H around slag grains, a
calcium to silica ratio of 1.3 to 1.4 was found for both
slag/CH and slag/cement systems.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899