Search for: All records

Alkali-activated materials (AAMs) are one type of sustainable alternative for ordinary Portland cement (OPC), providing significant reductions in CO2 emissions. AAMs based on fly ash or metakaolin are found to possess good fire performance, where the binder gels crystallize and form ceramic phases on heating. However, the ambient temperature setting properties and short-term strength development of select low-calcium AAMs are unfavorable, requiring the optimization of the mix design and a re-evaluation of the chemical, mechanical and physical properties at elevated temperatures (i.e., fire conditions). In this investigation, the influence of calcium hydroxide on the thermal evolution of alkali-activated metakaolin has been assessed, where gel crystallization and restructuring have been evaluated using X-ray diffraction and Fourier transform infrared spectroscopy. It is found that the 10 wt. % replacement of metakaolin with calcium hydroxide, together with a reduction in silicate activator concentration from 10 to 5M, does not adversely impact the phase evolution on heating since similar crystalline phases are seen to emerge. However, the exact location of calcium in the high temperature phases of silicate-activated metakaolin remains unknown.