Reaction mechanism of alkali-activated brick clay mill residues

Abstract

The need for low-carbon and low-cost building materials has become increasingly urgent in these years due to the concern over climate change. Clay-based geopolymer or alkali-activated materials can be one possibility to meet the need. Some researchers have reported the synthesis of high-strength alkali-activated materials from untreated clay sources. However, the investigation into the reaction mechanism of the alkali-activated clay is still limited. This would be one reason why this method has not been adopted in practice yet. Thus, this paper attempted to elucidate the reaction mechanism of a kind of alkali-activated material derived from brick clay mill residues. Both the FTIR and XRD results revealed that the clay minerals, muscovite/illite and kaolinite, within the mill residues indeed participated into the alkali activation process. The elevated curing temperature played a vital role in activating these two minerals. The dissolution of both the muscovite/illite and kaolinite at 65 °C was weak because the movement of the water molecules of the alkaline activator was not sufficiently intense to cleave the interlayer spacing of the two mineral crystals as identified by XRD. As the curing temperature increased, the dissolution of both the minerals were enhanced. The best temperature for kaolinite was found at 110 °C, and for muscovite/illite, it was 155 °C. The results also showed that the ingredient of the alkaline activator impacted the alkali activation of the mill residues. According to the changes in chemical bonds identified by FTIR, the dissolution of kaolinite was found to be more intense when the alkalinity of the activator was stronger. In comparison, the favorable alkalinity for dissolving muscovite/illite could neither be excessively high nor low. This study proposed a schematic mechanism of the alkali-activated mill residue in the end.