New Insights into the Retarding Effect of Aluminates on C3S Hydration

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Title: New Insights into the Retarding Effect of Aluminates on C3S Hydration

Author(s): E. Pustovgar, M. Palacios, J.-B. d’Espinose de Lacaillerie, T. Matschei, N. Ruffray, R. Verel, and R.J. Flatt

Publication: Special Publication

Volume: 320

Issue:

Appears on pages(s): 14.1-14.12

Keywords: aluminates; C3S; hydration; isothermal calorimetry; NMR

Date: 8/1/2017

Abstract:
Clinker replacement by supplementary cementitious materials (SCMs) is one of the most effective routes to reduce the environmental impact of Portland cement. However, increasing amounts of alumina-rich SCMs can reduce the reactivity and early mechanical strength of concrete. The reason of the lower strength includes a lower reactivity of the SCMs, but possibly also a passivation induced by the aluminates released from the SCMs on the silicates hydration. In this study, we have investigated the effect of the aluminate ions on the hydration of tricalcium silicate (C3S) by using a combination of several analytical techniques such as isothermal calorimetry, nuclear magnetic resonance (NMR) and scanning electron microscopy. It has been revealed that the initial and total dosages of aluminates play an important role on the length of the induction period and the time of the main peak position. Results are consistent with C3S dissolution being rate limiting. Finally, the influence of Na2SO4 on the passivation induced by the aluminates has been studied.