Reactivity of precursors for geopolymerization studied by isothermal calorimetry

The paper deals with analyzes of Isothermal Conduction Calorimetry response obtained during the alkaline activation of four types of precursors (metakaolin, slag and two kinds of waste ceramic powders) to geopolymers. The first two precursors are traditionally used, while the latter two are emerging materials and knowledge of their alkaline activation might have high importance in the recycling of Construction and Demolition Waste. The studied precursors differ each to other not only in the chemical composition, but also in the phase composition—the waste ceramic precursors are highly crystalline. It was found that the total reaction heat evolved in the geopolymerization is directly proportional to the amorphous matter content as well as to the compressive strength of the activated product. This finding can be used as fast evaluation tool in searching of new potential geopolymer precursors. The dissolution and polycondensation steps were observed in all experiments and their kinetics was described by Jander’s equation. While the rate of dissolution step is not dependent on temperature, the polycondensation has been accelerated by the higher temperature. The level of the rate acceleration was described by apparent activation energy; these findings can be useful in tuning of geopolymers curing procedure.