What is the minimum and maximum setting time of Geopolymer concrete and what is the minimum Reaction time between the solution of sodium hydroxide and sodium silicate, how long it will take for those chemicals to polymerize, after addition of fly ash what would be the reaction and setting time?
Dear Bala,
geopolymers are strongly depending on :
- quality and granulometry of powder precursors
- type of alkaline liquid hardener chosen (MR, concentration and so on)
- extra water content
- temperature when tested
- hardeners Must be done industrially not “at home” because only using autoclave all reactions can be stabilized
- fly ash only class F
- but fly ash even class F, are a waste so very inconstant so isn’t possible to answer precisely because depends even on calcining temperature of fly ash (mandatory at least more than 1300°C)
- mix design (if you mix like Portland cement materials, you will never obtain a Geopolymer, maybe an alkali activated material , that isn’t a synonym and on contrary is completely different technology).
You May understand that like Portland cement changes if produced in Italy , with our carbonate , clay and gypsum or in India , with totally different raw materials even though are the same minerals (different quarries, different secondary minerals, different sulphate that could be gypsum or anhydrite and different kilns) ; fly ash can vary a lot, consequently its reactivity and geopolymerization process can go on at different speed. In any case fly ash only can’t be used alone at room temperature or mechanical resistance will remain quite low and setting time very long .
Best regards
Alex Reggiani
Polymerization reaction as other chemistry reaction depends on the size of particles and the reaction rate is fast if the particle is finess that means the time of reaction is short. To answer in your question, you must do the kinetic of the polymerisation to determine the time.
Dear Charles ,
geopolymerization process is strongly dependent on quality of powder precursor, so not only the size (that of course is important, because only fine powder can react well) but the mineralogy involved.
For example if you compare at the same size fly ash class F (burned at least at 1300°C or more ) or metakaolin (750°C calcined) , Geopolymerization will be extremely more efficient using the second raw material.
Even at room temperature, with very long setting time for fly ash (more than 10h because is only superficial reaction on spherical particles) , while setting time for metakaolin could be long ,but variable according to its mineralogy and faster than fly ash because metakaolin reacts totally , foil after foil .
So this reaction is promoted by correct amorphous mineralogy not only by micronization f reactive powders.
In my experience compressive strength of this mortar with very fine fly ash at room temperature remains very low , within 20 MPa . Using metakaolin you can obtain almost easily more than 50 or 60 MPa.
All the best
Alex Reggiani
The setting time of Geopolymer mortar due to different curing temperature has been determined. The initial setting time and final setting time ranged from 129 minutes to 270 minutes. The higher the curing temperature, less setting time is required.
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https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29MT.1943-5533.0001157
Article Effects of Parameters on the Setting Time of Fly Ash Based G...
Conference Paper Effect of adding acid solution on setting time and compressi...
http://www.ijirset.com/upload/2013/special/environmental/42_SETTING.pdf
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