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Alternative (i.e., non-Portland) cements, such as alkali-activated materials, have gained significant interest from the scientific community due to their proven CO2 savings compared with Portland cement together with known short-term performance properties. However, the concrete industry remains dominated by Portland cement-based concrete. This Letter explores the technical and non-technical hurdles preventing implementation of an alternative cement, such as alkali-activated materials, in the concrete industry and discusses how these hurdles can be overcome. Specifically, it is shown that certain technical hurdles, such as a lack of understanding how certain additives affect setting of alkali-activated materials (and Portland cement) and the absence of long-term in-field performance data of these sustainable cements, can be mitigated via the use of key molecular- and nano-scale experimental techniques to elucidate dominant material characteristics, including those that control long-term performance. In the second part of this Letter the concrete industry is compared and contrasted with the electricity generation industry, and specifically the transition from one dominant technology (i.e., coal) to a diverse array of energy sources including renewables. It is concluded that financial incentives and public advocacy (akin to advocacy for renewables in the energy sector) would significantly enhance uptake of alternative cements in the concrete industry. 

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.