Abstract
The research aim was to investigate phase development after pozzolanic reaction between metakaolin (MK) and calcium hydroxide (CH) with alkaline and thermal activations. The CH to MK ratio (C/M) of 0.4 generating CaO/SiO2 of 1.18 was selected in this study. Various concentrations of NaOH solutions (0.01, 0.1, 1, 3, 5 and 10 M) were used. The alkali activated samples were thermally activated at 25 °C, 70 °C, 90 °C and 130 °C for 4 h. Phase development under thermal activation of alkali activated metakaolin based system were investigated. At every temperature, C/M mixtures with 0.01 and 0.1 M NaOH promoted the formations of poorly crystalline calcium silicate hydrate (C-S-H(I)) and calcium aluminosilicate hydrate (CASH) compounds. With 3 and 5 M NaOH activations, sodium aluminosilicate hydrate (NASH) and sodium calcium silicate hydrate (NCSH) was formed. 1 M NaOH was found to be a boundary of phase transformation from C-S-H(I) and CASH to NASH and NCSH. In addition, zeolite X and sodalite appeared when NaOH solution reached 10 M. Thermal activation significantly affected phase development at high concentration of alkaline activation (1-10 M). At 1 M NaOH, NASH compounds in a form of gmelinite and zeolite ZK-14 were found at 70-90 °C. At 3-5 M, katoite was found at 70-130 °C. At 10 M, zeolite X was found at 70-90 °C. Sodalite was also found at 130 °C with 10 M NaOH.
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