The effect of high curing temperature on the reaction kinetics in MK/lime and MK-blended cement matrices at 60 °C

It is well known that the pozzolanic reaction between metakaolin (MK) and calcium hydroxide produces CSH, C 2ASH 8 (stratlingite), C 4AH 13 and C 3ASH 6 (hydrogarnet). However, the presence or absence of these hydrated phases depends on different parameters, such as curing temperature, matrix used, etc. This paper shows the results of a study in order to know the effect of high curing temperature (60 °C) on the kinetics of the pozzolanic reaction in different matrices. MK/lime (calcium hydroxide) and MK-blended cement matrices were studied in samples stored and cured at 60 °C and up to 123 days of hydration. The nature, sequence and crystallinity of the hydrated phases were analysed using differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Results showed that the sequence and formation of the hydrated phases was different in both matrices cured at 60 °C. In an MK/lime matrix, C 2ASH 8, C 4AH 13 and C 3ASH 6 were the main hydrated phases; while in an MK-blended cement, stratlingite was the sole hydrated phase issued from pozzolanic reaction. The DTA and XRD data also reveal an important fact: there is no evidence of the presence of hydrogarnet in blended cements.