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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. 

Cryo-electron microscopy (cryo-EM) single particle analysis (SPA) has revolutionized biology, revealing the hydrated structure of numerous macromolecules. Yet, the potential of SPA to study inorganic materials remains largely unexplored. An area that could see great impact is solution-processed device materials, where solution changes affect everything from crystal morphology for perovskite photovoltaics to stability of photoluminescent quantum dots. While with traditional microscopy, structures underlying these effects can only be analyzed after drying, cryo-EM allows characterization of in-solution structures, revealing how features arise during processing. A top candidate for such characterization is found in chalcogenide glasses (ChGs), which researchers in the 1980s proposed take on solvent-dependent solution nanostructures whose morphologies have yet to be confirmed. Here we show that cryo-EM can directly image ChGs in solution and combine with other techniques to connect solution structure to film characteristics. Our results bring closure to a long open question in optoelectronics and establish SPA as a tool for solution-processed materials.

 

In this study, in situ quasi-elastic neutron scattering (QENS) has been employed to probe the water dynamics and reaction mechanisms occurring during the formation of NaOH- and Na 2 SiO 3 -activated slags, an important class of low-CO 2 cements, in conjunction with isothermal conduction calorimetry (ICC), Fourier transform infrared spectroscopy (FTIR) analysis and N 2 sorption measurements. We show that the single ICC reaction peak in the NaOH-activated slag is accompanied with a transformation of free water to bound water (from QENS analysis), which directly signals formation of a sodium-containing aluminum-substituted calcium–silicate–hydrate (C–(N)–A–S–H) gel, as confirmed by FTIR. In contrast, the Na 2 SiO 3 -activated slag sample exhibits two distinct reaction peaks in the ICC data, where the first reaction peak is associated with conversion of constrained water to bound and free water, and the second peak is accompanied by conversion of free water to bound and constrained water (from QENS analysis). The second conversion is attributed to formation of the main reaction product ( i.e. , C–(N)–A–S–H gel) as confirmed by FTIR and N 2 sorption data. Analysis of the QENS, FTIR and N 2 sorption data together with thermodynamic information from the literature explicitly shows that the first reaction peak is associated with the formation of an initial gel (similar to C–(N)–A–S–H gel) that is governed by the Na + ions and silicate species in Na 2 SiO 3 solution and the dissolved Ca/Al species from slag. Hence, this study exemplifies the power of in situ QENS, when combined with laboratory-based characterization techniques, in elucidating the water dynamics and associated chemical mechanisms occurring in complex materials, and has provided important mechanistic insight on the early-age reactions occurring during formation of two alkali-activated slags.