Reflection: Little amorphous waste used in geopolymeric synthesis contributes to the formation of a new phase or would it just be a charge?
We synthesize geopolymers with an amorphous source material of Al and Si (flint kaolin) and we also use waste such as red mud and fly ash, but a line of researchers is categorical in saying that these waste, because they are little amorphous, act only as a charge. Would it be simplistic in this way? or do these waste contribute to the formation of a new phase (zeolite) characteristic of the waste used in the synthesis? Reflection ...
Dear André,
your doubt is one of the main consequences of wrong information about geopolymer technology on internet.
Your precursors aren’t the best to obtain real geopolymerization , but could work if you are doing alkali activated materials.
Geopolymer isn‘t Alkali activated material , at all!
Geopolymerization isn’t only a reaction about chemistry, but is a chemical reaction that occurs at low temperature (less 100°C ) or at ambient temperature but involved amorphous minerals . This means that right mineralogy is the key factor to obtain geopolymers or not. Zeolite is weak minerals generated from alkali activation of fly ash, it is true , it is pH alkaline reaction, but isn’t a mineral polymer = geo-polymer.
So to obtain geopolymerization you must use the correct alumina silicates (reactive , because amorphous so don’t need any alkali activation! These powders , calcined at specific temperature became useful for Geopolymer technology: 750°C in flash kiln for metakaolins (kaolin is already crystalline mineral so less reactive even if its chemistry was perfect. Calcination creates amorphous conditions that will react with alkali silicates , this process is alkalination not alkali activation) , > 1300°C (to eliminate all coal and sulphur particles) for fly ashes class F only, class C can’t be used for Geopolymers and so on.
Prof. Davidovits demonstrated to me and to all participants of his geopolymer camp (2 weeks ago the last edition) why we must follow 6 rules to be sure about procedure to obtain geopolymer mortars, geopolymer concretes , geopolymer foams and other types of geopolymer mortars.
Check on geopolymer.org site of Geopolymer Institute about how to distinguish from Geopolymer and alkali activated material (4 videos have been dedicated).
So the answer about your doubt is... yes , if you use a non amorphous material to create geopolymer binder, you don’t obtain a mineral polymer. Wastes with lot of Silica or Alumina have easy reaction in high alkaline pH, but this Reaction can’t create repetitive units that permit stable results and long durability of hardened products .
You may verify immersing in water (also boiling water, that is the hardest test to understand if the product is geopolymerized or not) , immersing in acid or in sulphate solutions and checking frost - defrost cycles . Every tests need that mechanical strength remains almost similar compared to standard curing .
Remember that metakaolin, the best powder precursor to obtain geopolymerization (if silicates used to react have the correct molar ratio...of course and this is other big difference from geopolymer and alkali activated material. Usually geopolymer pH is user friendly) is reactive even in acidic medium, so is not possible to confuse geopolymer technology with alkali activation technology.
I’m sorry for the long speech but is very important that in scientific portals like Research Gate , terminology is correctly reported .
Wastes that you use are low reactive so you can destroy their structure using strong alkali, but you will obtain very little part of geopolymer (the correct amorphous fraction) and unreactive Part acts like weak zeolitic structure, not properly like a charge , but more or less.
I hope that some principles now will be more clear about Geopolymer world.
Isn’t easy to do , but following precise rules is mandatory .
All the best , have a nice work
Alex Reggiani
Dear André,
your doubt is one of the main consequences of wrong information about geopolymer technology on internet.
Your precursors aren’t the best to obtain real geopolymerization , but could work if you are doing alkali activated materials.
Geopolymer isn‘t Alkali activated material , at all!
Geopolymerization isn’t only a reaction about chemistry, but is a chemical reaction that occurs at low temperature (less 100°C ) or at ambient temperature but involved amorphous minerals . This means that right mineralogy is the key factor to obtain geopolymers or not. Zeolite is weak minerals generated from alkali activation of fly ash, it is true , it is pH alkaline reaction, but isn’t a mineral polymer = geo-polymer.
So to obtain geopolymerization you must use the correct alumina silicates (reactive , because amorphous so don’t need any alkali activation! These powders , calcined at specific temperature became useful for Geopolymer technology: 750°C in flash kiln for metakaolins (kaolin is already crystalline mineral so less reactive even if its chemistry was perfect. Calcination creates amorphous conditions that will react with alkali silicates , this process is alkalination not alkali activation) , > 1300°C (to eliminate all coal and sulphur particles) for fly ashes class F only, class C can’t be used for Geopolymers and so on.
Prof. Davidovits demonstrated to me and to all participants of his geopolymer camp (2 weeks ago the last edition) why we must follow 6 rules to be sure about procedure to obtain geopolymer mortars, geopolymer concretes , geopolymer foams and other types of geopolymer mortars.
Check on geopolymer.org site of Geopolymer Institute about how to distinguish from Geopolymer and alkali activated material (4 videos have been dedicated).
So the answer about your doubt is... yes , if you use a non amorphous material to create geopolymer binder, you don’t obtain a mineral polymer. Wastes with lot of Silica or Alumina have easy reaction in high alkaline pH, but this Reaction can’t create repetitive units that permit stable results and long durability of hardened products .
You may verify immersing in water (also boiling water, that is the hardest test to understand if the product is geopolymerized or not) , immersing in acid or in sulphate solutions and checking frost - defrost cycles . Every tests need that mechanical strength remains almost similar compared to standard curing .
Remember that metakaolin, the best powder precursor to obtain geopolymerization (if silicates used to react have the correct molar ratio...of course and this is other big difference from geopolymer and alkali activated material. Usually geopolymer pH is user friendly) is reactive even in acidic medium, so is not possible to confuse geopolymer technology with alkali activation technology.
I’m sorry for the long speech but is very important that in scientific portals like Research Gate , terminology is correctly reported .
Wastes that you use are low reactive so you can destroy their structure using strong alkali, but you will obtain very little part of geopolymer (the correct amorphous fraction) and unreactive Part acts like weak zeolitic structure, not properly like a charge , but more or less.
I hope that some principles now will be more clear about Geopolymer world.
Isn’t easy to do , but following precise rules is mandatory .
All the best , have a nice work
Alex Reggiani
Thank you very much Alex Reggiani . Excellent explanation.
All the best, André
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