Alkali-activated materials: the role of molecular-scale research and lessons from the energy transition to combat climate change

Abstract

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.

A Roadmap for Production of Cement and Concrete with Low-CO2 Emissions

“…[107]). The higher activator concentration used for metakaolin (Na2SiO3 activator with Na2O concentration equivalent to 10M NaOH, [107]) compared to FA (Na2SiO3 activator [106] with Na2O concentration equivalent to ~2M NaOH) and associated availability of free silica will likely have promoted more extensive dissolution of the precursor and amount of gel precipitated, leading to a more refined pore structure, although there is no direct evidence in the literature on this behaviour. However, when metakaolin is activated using a hydroxide-based activator (28 wt.…”

“…% Na2O relative to metakaolin with a water-to-solid ratio of 0.9) a very open connected pore structure evolves, consisting of pores that are ~100 nm in size after 1 year of curing (at ambient temperature, unpublished MIP data similar to data reported in ref. [107]).…”