Stoichiometry of Slag Hydration with Calcium Hydroxide

The stoichiometry of the reaction between ground granulated blast furnace slag (GGBFS) having an empirical formula of C 7.88 S 7.39 M 3 A and calcium hydroxide (CH) was investigated. Scanning electron microscopy (SEM) was used to determine the slag consumption as well as the Ca/Si ratio in calcium silicate hydrate gel (C‐S‐H) products. A tentative stoichiometric ratio of 2.6 mol of 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 C‐S‐H gel product, a range for the molar stoichiometry between 1.65 and 3.42 was found. 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 gel around slag grains, a calcium‐to‐silica ratio of 1.3 to 1.4 was found for both slag/CH and slag/cement systems.