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Stoichiometry and Kinetics of Slag Hydration in the Presence of Calcium Hydroxide.


pdf icon 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.