The Effect of Temperature on the Formation of Hydrogarnet in Matrices Made with Metakaolin/Lime Mixtures


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Title: The Effect of Temperature on the Formation of Hydrogarnet in Matrices Made with Metakaolin/Lime Mixtures

Author(s): M. Was, M. I. Snchez de Rojas, and J. Rivera

Publication: Special Publication

Volume: 199


Appears on pages(s): 757-768

Keywords: high curing temperature; hydrogarnet; lime; reaction kinetics; metakaolin

Date: 6/1/2001

The effect of temperature on the acceleration of the pozzolanic reaction rate is well known. In the case of the pozzolanic reaction between MK and calcium hydroxide, the researches have been focused on the hydrated phases and mainly on their stability, taking into account the possible transformation from metastable phases (C2ASH8 and C4AH13) to cubic phase C3ASH6, with the corresponding risk on durability.This paper reports a study to evaluate the influence of temperature on the formation of hydrogarnet (C3ASH6) in metakaolin (MK)/lime matrices subjected to 60°C curing temperature. The MIS and lime were mixed in a ratio of 1 :l by weight, stored and cured at 60°C and up to 123 days of hydration time. The kinetics of the pozzolanic reaction, sequence of appearance of different reaction products, quantities and crystallinity of the hydrogarnet as well as other hydrated phases, has been investigated using thermal (TG and DTA) and diffraction (XRD) analysis. The results showed that under the conditions tested here the hydrogarnet is formed very quickly in the first hours of curing (after 30 hours of hydration). This phase coexists at the same time with C2Ash8 (gehlenite) and C4AH13. The formation and amount of the hydrogarnet was closely related to the calcium hydroxide content in mixtures. There was not any evidence that the hydrogarnet was formed from a transformation reaction, but it was a result of the reaction between MK and lime.