Setting of alkali-activated slag cement. Influence of activator nature

The objective of this work was to determine the mechanisms that govern the setting times of alkali-activated slag (AAS) cement pastes, as a function of the nature of the alkaline activator used. For this purpose three different activators were used: waterglass (Na2SiO2.nHaOH with a SiO2/NaO ratio equal 1·5), NaOH and Na2CO3. The concentration of all solutions was constant = 3% of Na2O by mass of the slag. The pastes were studied through isothermal conduction calorimetry, FTIR and 29Si and 27Al MAS-NMR. Results indicate that pastes activated with waterglass develop faster setting due to the formation of an initial calcium silicate hydrate. Setting, in pastes activated with NaOH is due to the formation of a more polymerised calcium silicate hydrate. Pastes activated with Na2CO3 show longer setting times due to the initial formation of a sodium calcium carbonate which retard the reaction processes.