following

Dear Prakash, alkali activation permits high strength but you need to use strong alkali systems, with very high pH (lot of Soda or Potassa content, user hostile and corrosive system ) but you haven’t repeatable structure so alkali cations may migrate on surface so leaching and chemical stability (specially under acid attack) may create big problems and durability will be incostant .In alkali activated materials you use slag and fly ash as powder precursors, but to have good strength you must use heat curing and high amount of slag (check at work of Glukowsky and Kirilenko to have an idea of what I’m talking about). When you add strong alkali you destroy the precursors, but is difficult to be sure that everything react so unreacted powders act like pozzolana materials creating CSH gel , very weak and with hydrates minerals that will grow up (these minerals will be destroyed , due to water vapor formation , when you do fire proof test).

With geopolymerization Prof . Davidovits has demonstrated that the best raw material to show this chemical reaction at ambient temperature (isn’t necessary heat curing, if you realize a mortar) is metakaolin, specially If burned at 750°C in flash kiln. The pH of system may be alkali but user friendly so less alkaline and comparable with lime and Portland systems (you can touch these silicates , they aren’t corrosive but only irritant). Geopolymerization can occur also in acid pH , using phosphoric acids , but alkali systems are preferable because of costs. Alkali cations remains inside the matrix of geopolymer so is very difficult to be leached and acids can’t attack because metakaolin hasn’t calcium and magnesium inside.

Geopolymer technology could use also wastes materials of course, like fly ash , slag and microsilica but ratio between them and mix design is completely different compared to alkali activated materials.

I’m working with geopolymer technology from more than 6 years following Prof Davidovits methods and mechanical strength that is possible to reach can pass 100-120 MPa in compression, by the way, usually these strengths aren’t too much if you know that most used concretes in buildings are M30-35, so structural (>25MPa) but quite stable and cheap. Airports roads are made with flexural strength of 5MPa and compressive of 32-35MPa usually. So if You are curious to learn more about geopolymer technology, please come to next Geopolymer Camp from 9 to 11th of July in Saint Quentin de Picardie (north east of France) we will speak about directly.

Check on Geopolymer Institute site more informations or check on my company site (geomits.com) to see video and presentations that I’ve showed at last Geopolymer Camps .

With my best regards

Alex Reggiani

Thank you Mr. Reggiani for your excellent answer.

Is metakolin important for creating good geopolymer?.

I am working on creating low cost geopolymer building blocks so I must concentrate on reducing the cost and ease of manufacturing so it can be effectively used in developing countries. Metakolin is not widely available like flyash.

Dear Prakash ,

metakaolin is the best to observe geopolymerization but isn’t cheap like waste materials of course, so if you have to create geopolymer concrete you may use fly ash class F. Is necessary doing quality checks because class F isn’t the only parameter to respect. You must check temperature of production for your fly ash, because is a waste and depending on plant could be obtained from 950° to 1600°C. You must use only fly ashes calcined at least after 1300°C to have the most reactive mineralogy without sulfur , coal particles or other pollutions that may interfer with geopolymerization process. Using fly ash you may have weak performances , but in India temperature is high almost ever so you will reach however enough resistance .

Metakaolin isn’ everywhere this is true, but clay minerals and feldspar rocks are worldwide , there are several ways to obtain metakaolin mineral from rocks, with low cost process.

Other big issue is mixing system and mixing procedure. How do you want to mix ? If you wrong the method you will obtain at best an alkali activated materials. You must learn the basis of this technology and Geopolymer Camp is the best school you may find . I warmly suggest to come , after that 3 days everything will be more clear and if you have doubts you will find all the experts , first of all Prof Davidovits and his son Ralph , that will answer . Doing geopolymer is quite easy if you follow some rules , there are 6 main rules to be able to produce correct Geopolymer.

Hoping to see you in France , there are big discounts for students , specially if you partecipate at all 3 days of Camp.

Alex Reggiani

Unfortunately, I cant attend the Geopolymer camp this year. I hope I can attend next year.

Thank you again Mr. Reggiani for your quick and excellent answer.

Don’t worry see you

Regards

Alex Reggiani

Hi, you might find the below resources of relevance:

1) Rafeet et al. "Guidelines for mix proportioning of fly ash/GGBS based alkali activated concretes", Construction and Building Materials, 147, 2017, pp.130-142

2) A. McIntosh, S. E. M. Lawther, J. Kwasny, M. N. Soutsos, D. Cleland & S. Nanukuttan (2015) Selection and characterisation of geological materials for use as geopolymer precursors, Advances in Applied Ceramics, 114:7, 378-385, DOI: 10.1179/1743676115Y.0000000055

3) Raffeet et al. "Alkali activated fuel ash and slag mixes: optimization study from paste to concrete building blocks", Conference: 34th cement and concrete science conference, At: Sheffield, UK, 2014.

Regards

Thank you Mr.Kanavaris I will check it out.;

Dear: Prakash Kumar Sekar ,

The main difference between geopolymer and alkali activated cement is the localization of Na cations. In case of alkali activated cement Na+ attaches with the terminal oxygen (ortho position), which can move to build free alkali, and consequently, results in a significant loss in cement stability. Due to the high alumina content in geopolymer, Na cations are neutralized the negative charge on tetrahedral alumina within geopolymeric structure, yielding hardened materials with high stability.

We can lead a long discussion on this issue but I personally think that the main difference is that alkali activated materials exist but geopolymers does not exist.

There is no one XRD, SEM, EDS or anything what could confirm existing of geopolymers, except theories od porf. Davidovitz, which I don't really accept.

Dear Lukasz ,

I think that Prof Davidovits has already demonstrated scientifically the existence of geopolymer base structure as nano material, it's a fact, universally accepted. You can see by yourself his results and the same results were found from Prof. Kriven from Urbana University of Illinois, just to remind other one of most important people about this technology. I've chosen to work only on geopolymers because, every day, I confirm their studies with stable results for industrial uses, not only to do research in the laboratory, that can produce "close systems". So I respect your thinking , of course, but can't accept your explanation because from several years have been produced all scientific proofs about geopolymer technology , not only from Prof. Davidovits or Prof. Kriven.

I know that alkali activated materials exist , but please show me an industrial application , a part precasting (where you heat at 70-90°C) , where these products are stable and durable (every time you put in water their mechanical strength and stability decrease and not constantly , sometime you lost 40-50% of strength obtained by air, sometime less , sometime more till 60%. Efflorescence never stopped , I have Russian colleagues that may confirm this, we saw the building realized at Moscow using AASlag with NaOH during the 80' , that still create sodium beard of carbonation depending on humidity of air...and the color of walls varies from green to whitish not regularly). If you want to work with alkali activated materials , come on, it's ok, continue to do and good luck. But I think the topic of this question is to find and explaining what are the differences between these binders, because they are completely different , even if precursors could be similar raw materials. Mix design, control quality about precursors, temperature of calcining of these precursors and the using of correct hardener (in geopolymer technology there aren't activators...because powder precursors are already very reactive, so they need only the correct way to have the precise ratio of salts to react) that isn't corrosive for skin and breath like soda used for alkali activation, are different . Are you agree about this?

By the way , sorry for the length , this is only my point of view .

Kind regards

Alex Reggiani

Dear Alex,

A I said before, we can lead really long discussion about geopolymers.

Of course, I respect your opinion. Many people work with geopolymers, including myself. My PhD thesis was about geopolymers, and I work with that kind of materials since over 20 years and this is the mine reason that I changed my opinion.

If you are curious why I changed my mind about geopolymers we can discuss privately, not here.

Best regards.

Dear Lukasz , my personal email is [email protected] , if you want go deeper about the discussion .

Thank you again

Alex Reggiani

The discussion following this question is always fun. Most entertaining is the discussion between prof. Davidovits and prof. Provis on Wikipedia: https://en.wikipedia.org/wiki/Talk:Geopolymer

As far as my opinion matters, no simple statements can be made regarding a comparison between geopolymer's and alkali-activated materials' properties. Although these are mention often as a benefit of one or the other, it most of the times has nothing to do with the material itself. Furthermore, the properties are very much dependent on the mixture, more than being dependent whether or not you call it a geopolymer or alkali-activated material. To Łukasz Gołek , I think geopolymers do exist, but that they not necessarily look exactly how the theory of Davidovits describes them. But well, this might rather be a philosophical discussion and we might mean the same thing.

Now to incite some discussion :D I think the main discussion and confusion out there is about the 2 possible definitions of the word "alkali-activated material". (1) It is a latent hydraulic material, for which you speed up the reactions after adding an alkali and (2) It is any material which forms a network after an alkali was added to a precursor. Although the difference might be small in words, (2) is much wider, geopolymer fits in (2) and not in (1). While the "Provis school" follows the wide definition (2), Davidovits follows (1), resulting into his aggrevation in calling the geopolymer and alkali-activated material.

Hmm, sorry, in the end it did not become a direct answer to your question Prakash Kumar Sekar, but I hope I contributed to this topic anyhow.

for me geopolymer is subset of alakli activated materials

I would rather say that it's commercial name for alkali activated materials, which is promoted in some companies and organizations as new kind of material. But its my opinion.

Dear Cyriaque,

if is true what are you saying try to realize an Alkali activated materia using acidic medium. I’m already doing acid geopolymer mortars , so I think that reactions are “quite“ different.

After hardening of your material alkali activated, try to cure under water immersion till 28 days . Compare strength development with air curing and let me know your results. Using geopolymer mortars I usually obtain the same resistance or even little more higher (with very low tolerances , within 10-15%, that depends on shape of sample).

Take pictures about efflorescence if you have .

Best regards

Alex Reggiani

I will turn the situation a little bit and ask another question - what is this article about? About geopolymers or alkali activated materials?

https://authors.elsevier.com/a/1YdVh3QCo9Up~E

I am sorry that I have not written to you yet, but as soon as I have some time, I email you.

Regards.

Hi Lukasz,

don’t worry I write during night because I also haven‘t time, so I understand your words.

About the article this is 100% alkali activation process, there isn’t the correct mineralogy to have Geopolymerization . The author explains how is generated hydration reaction and in geopolymer there aren’t hydrate minerals . Raw materials are useless for creating geopolymer , fly ash class C, high in CaO, are similar to slag but are less constant and used as precursor can create problems of flash setting . In particular Alumina and Silica are too low, but is wrong to check only chemistry, Geopolymerization is chemical reaction between minerals, not only inorganic or amorphous raw materials. Waste glass isn’t constant, it’s amorphous but without the reactivity necessary , so maybe it can react but to do that will be necessary too much alkaline solution or too high pH. Geopolymer are created from super reactive powders where hardener permits the good diffusion of salts , necessary to react, so alkali remain inside the geopolymer matrix and durability will be prolonged (while efflorescence are almost zero) and stability remains the same batch after batch. Silicates that I’m using aren’t corrosive so user hostile , but user friendly .

Waste glass in my experience isn’t geopolymer precursor .

Regards

Alex Reggiani

I would like to join again :) I would say the material in the paper of dr. Golek is neither a geopolymer nor an alkali-activated material. I would call it quite general a cementitious binder, as the main binding phases are CSH and ettringite (right?) and you don't add alkalis, just water. But I don't really care how you call it, it is genius: you put two waste streams together and it becomes hard. Nice work! Also to get into the "user friendlyness" discussion, I think water is also not corrosive.

There is still a lot to discuss, but I will keep it focused on one of the points of dr. Regianni: The need for more alkalis in alkali activated materials vs. geopolymers. This is so mixture-dependent that it does not make sense arguing about it. You can make an alkali-activated material with liquid/solid 0.3 and wt% Na2O in the liquid of 5, while you can also make it with liquid/solid 1 and wt% Na2O of 20. If you make a geopolymer starting from metakaolin, you are actually at the higher side of the range, because you need a lot of liquid to be able to mix the clay and a lot of Na to charge balance all of the Al.

Thank you Arne Peys , I appreciate your nice words.

According to your explanation - I agree with it. From my work and my colleague last examination we noticed that in some specific conditions the alkali activation (or just hydration process) is proceeding even if the pH is neutral. It mean that the alkalization level of environment and concentration of activators are not the only factors which decide about progress of reaction. In nearest future we would like to publish our examinations.

Dear Arne, my surname is Reggiani , like parmigiano cheese from my country , but doesn’t matter. 😅

I wanted just to clarify that I’m not against AAM and I really appreciate the work of Dr. Golek even though I don’t know the details about it, (water of course isn’t corrosive , but what water can dissolve inside the powders , like sodium carbonate for example, may become quite caustic after certain dosages...) but I’m against who creates confusion at scientific level. I’m agree with you that there are different type of alkaline activation, but geopolymers aren’t one of them. Also mix design is very different.

I have enough experience of Portland cement technology, using every type of special cements (CAC, CSA, belite cements , limes and gypsum) and for sure I respect different point of view, this is normal and necessary to have good exchange of knowledge . By the way , with my comment I want only clarify that geopolymer are different material from alkali activated . I’m also working on geopolymer made in acidic medium for field of work completely different from building materials. So can’t be an alkali activated the same of that geopolymer , or not ? are you agree ?

Kind regards

Alex Reggiani

Oops, sorry for the typo in your name!

I definitely agree that alkali-activated materials are not the same as geopolymers. However, what I do believe is that there is an overlap between the two families of materials if you take the definition of alkali-activated material in the way Provi and van Deventer use it (this does not count for the definition that Davidovits uses), in the sense that alkaline geopolymers (so not the phosphate acid activated ones) are formed by mixing a powder precursor with an alkali. What I do agree on is that geopolymers are quite distinct in properties from other alkali-activated materials, like alkali-activated blast furnace or copper slag, in terms of molecular structure, resulting properties and ideal applications for the material.

I think people should embrace the confusion in the naming, acknowledge that different definitions exist for the same term and mention which one is meant to lift the confusion before saying what is not part of what.

Dear Arne,

comparing experiences of Russian colleagues to mine, we arrived to understand that Alkali Activated are very good for precasting, because of heating that close the reaction.

What is wrong in your definition ,of geopolymer, is that isn’t enough to mix powder precurso with alkali to have geopolymer. If silicate isn’t correct in terms of Molar Ratio and powder hasn’t the right mineralogy you will not obtain polymerization of new minerals also called Geopolymerization.

This is the main difference.

This is also the reason why during water immersion, salts are leached out from alkali activated structure and bonding of material becomes weak , with strong reducing of strength or at worst expansion and failure , like pictur below. Geopolymers even after more days of immersion are stable and I don’t lost any strength (no leaching) , check the water of both pictures.

I think there is a reason if Davidovits created 4 videos and last number 25 paper at geopolymer.org (download for free), to explain technically what change and why technologies are very different, from several point of view.

Even hydraulic lime and OPC are alkaline but with very different performances . By the way I appreciate this kind of discussion where respect to other point of view is maintained.

Thanks

Alex Reggiani

Picture 1. Alkali activated after 2 days immersion

Picture 2. Alkali activated after 8 days immersion

Picture 3. Geopolymers after 28 days immersion

Wow, the samples in the picture look quite bad. That kind of cracking is not a system property of alkali-activated materials, but mixture specific.

I was not clear enough I believe, because what you say that my definition for geopolymers is, is my definition for alkali-activated materials. The alkali-activated material is in this definition a material obtained from mixing a powder with an alkali, I don't claim that this is the definition of the geopolymer. I do say that some geopolymers fall within this category: you mix metakaolin (= a powder) with sodium silicate (= an alkali) using the right ratios and you will obtain both a geopolymer and alkali-activated material. I attach a figure that tries to clarify this.

I also like this discussion. Trying to give good arguments instead of personal attacks brings us closer to the truth (and to each other? :D).

Best regards,

Arne

Dear Arne,

I know the “new” definition from Provis, but can you explain where is polymerization in these materials, if only have to add alkaline solution at some reactive powder?

If it was so easy to realize geopolymer products like this graphic teaches , why AAM are still so unstable and geopolymer from Davidovits is are stable at every condition?

And last question , why Ukrain school of standard alkali activated slag from several years of testing (from ‘50) has permitted to realize one building only (covered of sodium carbonate beards and other colors of efflorescence) ?

I think that the best application for AAM remains precasting because the process uses heating at 60 to 90°C , that allows to finish the reaction and after cooling products are well balanced.

Thanks for so interesting discussion even from different point of view.

Best regards

Alex Reggiani

Dear Alex,

There is not necessarily polymerization in all alkali-activated materials within this definition, only in those that also happen to be inorganic polymers or geopolymers. If the powder is metakaolin and alkaline solution is an alkali silicate, you will have polymerization. If the powder is blast furnace slag and the alkali sodium sulfate, probably not.

I do not really follow the second question. It is super easy to obtain geopolymer products. You just have to mix sodium silicate and reactive metakaolin and make sure you have a Na/Al of 1 (and according to some Si/Al of 2 for pure geopolymers). And, as I said before, the stability of AAMs is mixture dependent, sure, you can make crappy samples, but that does not prove that all of the materials are bad.

The Ukranian case is again more a matter of sample specific behavior than a proof of failure of the system.

BUT, all of these things are not relevant to my point. Even though you mention that you know the definition that Provis uses, every mention of AAM in your text refers to the definition of Davidovits. I respect your choice of consistently using the latter.

As a general conclusion, I believe it would enhance the clarity in the research community if it is always mentioned which definition of AAM is used.

Cheers,

Arne

According to literature, what differentiates alkali activated from geopolymer is whether or not they need elevated temperature for curing. Geopolymer is claimed no to need elevated temperature for curing, while alkali activated does.

In general, I find both to be the same.

Dear Sulaem,

aren’t the same. Try to do an Alkali Activated Material using acidic medium. Using Geopolymer technology is possible and you obtain a ceramic like product. But of course the cost for acid medium is high so this way is good for dental application. While alkaline medium is better for low tech market like alternative to Portland for mortars and concretes.

AAM are hydraulic materials like Portland, geopolymers aren’t hydraulic and set true polycondensation

But for newcomers can be similar and lot of scientific papers create confusion because aren’t correctly done.

All the best

Alex Reggiani

such an enlightening discussion! i must thank all the participants who indirectly contributed to clear my doubts

MANY THANKS TO ALL STUDENT AND PROFESSORS ENRICH THIS DISCUSSION WITH VAKUABLE INFO.

Dear Prakash Kumar Sekar ,

Geopolymers are consist of silicate and aluminates. However, calcium is the major constituent in Alkali activated binder.