diminishing returns
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2022 ◽  
Vol 9 ◽  
Omar Abdelrahman ◽  
Nishant Garg

To address the high CO2 footprint associated with cement production, many alternative, sustainable binders are now gaining worldwide attention–including alkali-activated materials. The alkali-activation reaction of metakaolin is a fairly complex process involving transformation of one amorphous reactant (precursor metakaolin) into another amorphous product or products (N-A-S-H gel and/or disordered zeolite type phases). In spite of this complexity, researchers in the past 2 decades have gained significant knowledge on the nature of this reaction at multiple scales. Understanding and developing a clear relationship between the alkalinity of the mix and the extent of reaction is of high interest for practical applications. However, detailed and thorough investigations on this important relationship are limited. Here, in this study, we address this gap by systematically investigating a series of alkali-activated materials samples with a wide range of Na/Al ratios (0.5–1.8) using seven different yet complementary analytical techniques (isothermal calorimetry, FTIR, XRD, TGA, NMR, and Raman imaging). Applied in tandem, these tools reveal a clear but non-linear relationship between the Na/Al ratio and the extent of alkali-activation reaction indicating diminishing returns at higher Na/Al ratios, where higher Na/Al ratios cause an increase in the degree of reaction until a certain point at which the increase in Na/Al ratio does not significantly affect the reaction kinetics, but may affect the gel polymerization. These findings could potentially aid decision making for commercial applications of AAMs where alkalinity of the mix is an important parameter for performance as well as safety.

2021 ◽  
pp. 18-22
Lucy F Donaldson ◽  
Ramiro Alberio ◽  
Jennifer Batson ◽  
Frances Henson ◽  
Roger Lemon ◽  

2021 ◽  
Vol 13 (21) ◽  
pp. 11712
Tjerk Jan Schuitmaker-Warnaar ◽  
Callum J. Gunn ◽  
Barbara J. Regeer ◽  
Jacqueline E. W. Broerse

Unsustainability in health care comprises diminishing returns and misalignment between the health care regime and the needs of the population. To deal with complex sustainability problems, niche solutions can be collaboratively designed and implemented through reflexive methods. For second-order sustainability, however, the institutionalization of the reflexive element itself is also needed. This paper aims to provide insight into the possibilities of embedding reflexivity into institutions to support second-order sustainability by reporting on two consecutive participatory research programs that sought to address unsustainability in terms of misalignment and diminishing returns. The first case study reflexively monitored the system’s innovation toward an integrated perinatal care system. Reflection within the project and implementation was supported successfully, but for stronger embedding and institutionalization, greater alignment of the reflexive practices with regime standards was needed. Building on these lessons, the second case study, which was part of the IMI-PARADIGM consortium, collaboratively built a structured tool to monitor and evaluate “the return on engagement” in medicine development. To institutionalize reflexivity, the creation of “reflexive standards” together with regime actors appears to be most promising. Broader and deeper institutionalization of reflexive standards can be attained by building enforcement structures for reflexive standards in the collaborative process as part of the reflexive methodologies for addressing complex sustainability problems.

IEEE Spectrum ◽  
2021 ◽  
Vol 58 (10) ◽  
pp. 50-55
Neil C. Thompson ◽  
Kristjan Greenewald ◽  
Keeheon Lee ◽  
Gabriel F. Manso

2021 ◽  
Xuchen Guo ◽  
Peijian Shi ◽  
Ülo Niinemets ◽  
Dirk Hölscher ◽  
Rong Wang ◽  

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