The authors make wrong assumptions about the sustainability of geopolymers. This authors forgot or are not aware that geopolymers based on alkaline activators like sodium silicate and sodium hydroxide that are known not only for their high cost but also for their high carbon fooprint. Provis et al. (2015) already emphasized that geopolymers “are not intrinsically or fundamentally ‘low-CO2’ unless designed effectively to achieve such performance”. Recently The et al. (2017) confirmed that OPC binders have less carbon emissions than geopolymers Provis, J.L.; Palomo, A.; Shi, C. (2015) Advances in understanding alkali-activated materials. Cement and Concrete Research 78: 110-125. The, S.; Wiedmann, T.; Castel, A.; de Burgh, J. (2017) Hybrid life cycle assessment of greenhouse gas emissions from cement, concrete and geopolymer concrete in Australia. Journal of Cleaner Production 152, 312-320. Also Pade and Guimaraes (2007) estimate that for a 100 years life concrete structures can store around 28% of CO2 during 70 years life time and as much as 58% after demolition during 30 years. And a very recent study by Xi et al. (2016) showed that “a cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO2 emissions from production of cement over the same period”. Pade, C.; M. Guimaraes, M. (2007) The CO2 uptake of concrete in a 100 year perspective. Cem. Concr. Res. 37, 1348–1356. Xi et al. (2016) Substantial global carbon uptake by cement carbonation. Nature Geoscience 9, 880-883.

Provis and Van Deventer (2009) mentioned that the sialate nomenclature of Davidovits “implies certain aspects of the geopolymer gel structure which do not correspond to reality”. Provis, J.L.; Van Deventer, J.S.J. (eds.) (2009) Geopolymers: Structure, Processing, Properties and Industrial Applications, Woodhead Publishing, Cambridge, UK,

Provis (2014) has provided a more suitable definition of geopolymers:Geopolymers constitute a small group of the larger alkali activated binder family. They are low calcium binder materials produced though the reaction of an aluminosilicate powder (precursor) with an alkaline activator, usually composed by hydroxide, silicate, carbonate or sulfate leading to the formation an amorphous aluminosilicate gel and secondary nano crystalline zeolite-like structures. Provis, J.L. (2014) Geopolymers and other alkali activated materials: why, how, and what ? Materials and Structures 47, 11-25.