Abstract
This review undertakes rigorous analysis of much of the copious literature available to the scientific community on the use of alkali-activated binders (AABs) in construction. The authors’ main intention is to categorically refute arguments of that part of the scientific community underestimating or even dismissing the actual potential of AABs as alternatives to Portland cement (PC). The main premise invoked in support of those arguments is a presumed lack of material resources for precursors that would make AAB industrial-scale production unfeasible anywhere on the planet (a substantial number of scientific papers show that the raw materials required for AAB manufacture are in abundance worldwide). The review also analyses the role of alkaline activators in the chemistry of AABs; it is important to clarify and highlight that alkaline activators are not, by any means, confined to the two synthetic products (caustic soda and waterglass) mostly employed by researchers; other sustainable and efficient products are widely available. Finally, the review deals with the versatility of AAB production processes. The technologies required for the large scale manufacturing of AABs are mostly already in place in PC factories; actually no huge investment is required to transform a PC plant in a AAB factory; and quality and compositional uniformity of Alkaline Cements (binders produced through an industrial process) would be guaranteed. The last conclusions extracted from this review-paper are related with: i) the low carbon footprint of one-part AABs and ii) the urgent need of exploring standardization formulas allowing the commercial development of (sustainable) binders different from PC.
Highlights
According to reports issued by the United Nations Climate Change Conference (COP 25) held at Madrid, Spain in December 2019, the ice cap in Greenland is melting seven times more quickly than in the nineteen nineties and onefourth of the world’s population is at risk of water shortage in the near future
The literature identifies a broad spectrum of industrial, mining and agroforestry by-products or waste and a series of aluminosilicate minerals as precursors (Fernández-Jiménez et al, 2005a; Provis et al, 2015; Van Deventer, 2017; Rivera et al, 2020), whilst caustic alkalis and/or alkaline silicates are frequently used as activators (Provis and Van Deventer, 2014a; Hamidi et al, 2016; Atabey et al, 2020; Garcia-Lodeiro et al, 2020; Zhang et al, 2020)
Most studies, conducted with liquid hydroxide or alkaline salt activators (Figure 8) mixed with a solid precursor, pursue aims relating to OH- concentration, type of alkaline cation or the SiO2/Na2O ratio (Fernández-Jiménez and Palomo, 2005a)
Summary
According to reports issued by the United Nations Climate Change Conference (COP 25) held at Madrid, Spain in December 2019, the ice cap in Greenland is melting seven times more quickly than in the nineteen nineties and onefourth of the world’s population is at risk of water shortage in the near future. The literature identifies a broad spectrum of industrial, mining and agroforestry by-products or waste and a series of aluminosilicate minerals as precursors (Fernández-Jiménez et al, 2005a; Provis et al, 2015; Van Deventer, 2017; Rivera et al, 2020), whilst caustic alkalis and/or alkaline silicates are frequently used as activators (Provis and Van Deventer, 2014a; Hamidi et al, 2016; Atabey et al, 2020; Garcia-Lodeiro et al, 2020; Zhang et al, 2020).
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