Effect and characterization of the nucleation C-S-H seed on the reactivity of granulated blast furnace slag powder

Abstract It is still uncertain whether nucleation calcium silicate hydrate (C-S-H) seed can really improve the reactivity of granulated blast-furnace slag (GGBS) powder and accelerate the strength development. In this work, various pastes and mortars were prepared with cement, GGBS and C-S-H seed, and their compressive and flexural strengths, chemical shrinkages, the characteristics of hydration heat liberations and CH content in the hardened pastes, and reactivity indexes and reaction degrees of the GGBS in the presence of nucleation C-S-H seed were investigated. The results show that C-S-H seed notably increases the 1, 3, 7 and 28 d strength of the 50% GGBS and 50% cement mortar. The hardened pastes with nucleation C-S-H seed provide the greater strength reactivity index than the control at 7 and 28 d, especially 0.6, 1 and 2% C-S-H seed have more significant role on this index. It also enhances the chemical shrinkage and the more significantly increased chemical shrinkage is related to the higher content of nucleation C-S-H seed as the greater chemical shrinkage implies more hydration or reaction. It shortens the induction period, cut down the acceleration stage, accelerates the conversion of AFt to AFm and enhances the total hydration heat. It reduces the calcium hydroxide (CH) content in the hardened paste, and reaction degrees of the GGBS were investigated in order to further determine the role of nucleation C-S-H seed on the reactivity of GGBS, the results show that it improves the 1, 3, 7 and 28 d reaction degrees of GGBS, 1 and 2% C-S-H seed increase the percentages of the reacted GGBS at 1, 3, 7 and 28 d about 66% and 134%, 56% and 94%, 101% and 200%, 41.7% and 46.1% respectively by the control. These results will provide a reference for the more widely application of nucleation C-S-H seed as well as the activation of GGBS reactivity.