Dear Omar,

I think you are right about the sentence that Geopolymer Technology is feasible and sustainable…but something of very wrong is written in the article.

First of all, geopolymerization isn’t the same than alkali activation. There is nothing to be activated in GP technology while that term is correct if you are thinking about AAMs.

I try to explain very simply Geopolymer material is the result of poly condensation and it’s a mineral polymer. Who drives the reaction is the precursor that is selected raw material aluminum silicate but amorphous so the liquid part, is called reagent or hardener because just balance the mineralogy inside the precursor (the reactive alumina) and could be alkaline or acidic but never is an hydraulic reaction. Geopolymers were proposed by Professor Davidovits because of their mineral nature so completely fireproof like natural stones not for substituting the ordinary Portland cement to do concrete. This because depending on the geography and the connected sourcing the raw materials necessary to do a cheap GP concrete aren’t still worldwide diffused. Maybe in Russia, India, China and U.S. this technology can be used also for concrete applications but thinking that fly ash are sustainable should be discussed. In fact it is necessary to burn 28 tons of coal to obtain 1 ton of fly ash and only type F, from Antracite coal can be used, so I don’t know if you have considered how much CO2 can generate burning 28 tons of coal, but roughly I think more than the CO2 capturing of fly ash GP concrete during its life. Of course if you have already huge deposits (dumped) fly ash F could be wasted if enough amorphous but not alone because is too weak about strength development (due to mineralogy and because fly ash is an empty sphere). Geopolymerization doesn’t come from a dissolution because nothing of regular and homogeneous can exit from random process like that. Geopolymer mix design is specific for all types of GP materials and starts with alkalination (if using alkaline medium) or acidification (if using acidic medium) then when the precursor is depolymerized into base monomers can proceed the correct reaction till the condensation (hardening). This process is hydrophilic so it remains stable when occurred even if the material is immersed in water or in boiling water. There is no leaching or efflorescence because the alkalis are used to create new feldspar minerals with the hardening.

Alkali activation instead is still a hydraulic process so isn’t a polymer, at all and you can find OH groups into the final minerals. This means that GP and AAM aren’t synonyms. How to explain an Acid Alkali Activated Material? GP aren’t subset of AAM, simply can be alkaline. It’s like you try to compare OPC with hydrate or hydraulic limes. I think all people know that both are alkaline, limes even more but no one can confuse about they are different binders. AAMs are mixed following a process that is close to Portland based materials so I can understand they are studied from long time as alternatives to do concrete.

But from Glukovsky to now, why those studies are still not operative? All scientists in their articles said that are more convenient that OPC (less CO2 using wastes and so on, possible to be activated by solid admixtures so just add water technology like OPC market is requiring) so why are still not on the industrial markets , neither where the costs allow their use?

Maybe because AAMs are more dangerous for users (because of super high alkaline pH, classified corrosive. I mean the NaOH part of the activators that use 12, 16 or 20 Molar !) and aren’t balanced materials so there are problems of efflorescence (the over saturated alkaline activators cannot be stabilized so lot of free Na or K ions migrate to the surface capturing CO2 forming carbonates much more soluble than CaCO3 that is normally produced by OPC materials) or leaching in water (the migrate alkaline ions can be leached out from the material because still well soluble in water) so the strength of the material is strongly affected, with important losing till sometime to the failure. Activator is fundamentally the glue that keep all together but AAMs don’t harden properly but they mainly dry. If the activation is made in a oven the reaction is more closed but the over saturated particles remain outside the structure and can be solubilized by water (rain, humidity of the air or water immersion), while at ambient temperature is used GGBS that let reach very high strength but hasn’t the necessary mineralogy to be stable under water again (If not stabilized in some way).

If the aim is to substitute Portland cement I think the new binder used should be stable at the same conditions where OPC is used or it is non sense.

I just want to say that from the article there is a lack about knowledge on genuine Geopolymer technology, starting from the technical words. This can explain why there is written that GP are weak about tensile or Flexural strength because I never have found this weakness even without fibers or heat curing.

Obviously fiber addiction can help specially if the aim is realizing a lightweight panel or a thermal insulated block even with good phono absorbing. Hemp or straw are useful to lightweight the material but are most important the binder nature, the mix design and the industrial process (vibration and compaction).

From my experience about Geopolymer technology the real brake to the explosion is properly this lack of knowledge that put all materials with alkaline pH at same level.

So there is fear to change because there are confused ideas and industrially speaking bad results. But GP materials aren’t so high in alkalinity because reaction doesn’t need so caustic ambient to happen and GP are user friendly, classified like Portland and lime. For this reason I agree with you that GP can be the binders for the present and for the future, like they already worked well in the past.

Sorry for my long speech but I think it‘s time to clarify what is what because there are applications and applications so Geopolymer materials and AAMs can be used at their best for specific purposes contributing both to proceed about the green transition.

Best regards

Alex Reggiani

Dear Alex

Thank you for your insightful comment. It is clear that you have a good understanding of Geopolymer technology and the differences between Geopolymers and Alkali Activated Materials (AAMs). It is true that AAMs have some limitations in terms of their stability and strength, as well as their potential health hazards. It is important to note that Geopolymer technology can provide a sustainable alternative to traditional cement production, with the potential for lower CO2 emissions and the use of waste materials in production. However, it is important for researchers and industry professionals to have a clear understanding of the technology and its limitations, in order to promote its safe and effective use in various applications.

King Regards

Omar Tanane

100% agree

Best regards

Hi,

The Geopolymer Camp 2023 was on 3D printing with geopolymer. Alex made several conferences on those topics: https://geopolymer.org/fichiers/?dir=gpcamp-2023