The effect of temperature on the hydration rate and stability of the hydration phases of metakaolin–lime–water systems

Abstract

[EN]The paper presents the results of a study carried out to determine the effect of curing temperature on the kinetics of reaction of a metakaolin (MK)/lime mixture. MK and analytical grade Ca(OH)2 were mixed in a ratio of 1:1 by weight and with a water/binder ratio of 2.37. Specimens were cured at 20 and 60 °C. In the first case, the curing time varied from 2 h up to 180 days and, in the second case, from 2 h up to 123 days. A mathematical model was applied to calculate the rate constant for the hydration reaction. The identity and the amount of the phases present were determined from thermal analysis (TG and DTA) data. The results showed that the rate constant for the samples cured at 60 °C was 68 times greater than the rate constant at 20 °C for the same curing period (up to 9 days). At 20 °C, the sequence of appearance of the hydrated phases was C–S–H, C2ASH8 and C4AH13; while at 60 °C, the sequence was C–S–H, C2ASH8, C4AH13 and hydrogarnet (C3ASH6). There is no evidence of further C2ASH8 and C4AH13 transformation into hydrogarnet in the mixture studied for 123 days at 60 °C.