With regards to strength and durability which geopolymer concrete paste provides superior quality a) synthesized with 100% fly ash with some effect of temperature curing or b) synthesized at ambient temperatures using fly ash + GGBS
Usually FA + GGBS has more CaO, so final product contains C-A-S-H gel which is more durable then N-A-S-H. But you must take into account what sort of activator solution is used, for example NaOH with water glass is more effective then pure NaOH solution. The properties of activator solution (molarity, type etc.) has vital importance on final product. To know which combination of raw materials is better it should be clear what sort of activator is used.
Dear Vytautas. Thank you for your comments. Do you have any articles where they compare the properties of C-A-S-H gel andN-A-S-H gel..
B) synthesized at ambient temperatures using fly ash + GGBS
In general all the constitutent material does not have same properties.
Rather going for single material we have to concentrate on complex material.
Because all the material available are not in their purest form.
Fly ash consists of rich carbon content because it is a by product of coal.
Similarly GGBS consists of properties similar to iron ore.
So combination of Fly ash and GGBS gives better result.
Dear Nabil,
geopolymers aren’t alkali activated materials , because alkali activation can’t produce polymerization . Other reason is that geopolymerization process can occur in acidic medium so KASH and NASH don’t exist inside geopolymer matrix , CASH is only CSH from pozzolanic reaction between precursor not reacted or activated (because you are doing alkali activation not geopolymerization ) and salts (cations) that migrate into water to surface . In geopolymer alkaline cations are strictly engaged inside the matrix so can be leached . This fact produce strong durability. There aren’t gels or other hydrated materials. Fly ash Geopolymers (only class F fly ash, because using class C is only possible to have alkali activation) to develop strength at room temperature need heat curing, after that their durability become very long . Of course because you are talking about concrete so curing needs to be under ambient temperature, fly ash plus GGBS is better, about strength development.
Carbonation will be comparable to OPC concrete (usually lower, but depends on type and amount of slag used) but durability will be very prolonged (little lower however than fly ash geopolymer concrete heat cured) due to resistance to corrosion and to sea salt and to chemical attacks in general.
Please don’t confuse more geopolymer with alkali activated materials, these technologies are really different and never can be used as synonyms of each other.
Alkali activation is quite known process , similar to Portland technology, but is not stable for long time. Russian studies showed this and instability comes out when you stress these materials immersing in water (losing till 50-60% of strength) , in contact with sulphates (expansion) , or simply in presence of humidity with bloomings and strong salty efflorescences that grow on surface creating high risk of Alkali - Silica reactions...alkaline cations can migrate so leached out.
Please check on geopolymer.org videos and articles that clarify my words.
I’m using geopolymer technology because of stability of this technology and is completely different world from alkali activation. Piramids are still here and they are the biggest testimony of durability of geopolymer materials.
Come next year in July at next geopolymer camp in France , we might meet and talk directly with my friend professor Joseph Davidovits and his son Ralph . I’m sure that everythings will be more clear . By the way if you want doing alkali activated materials it’s ok, but please use correct terminology . I think that scientists must diffuse information at best possible not creating misunderstandings.
All the best
Happy new year to all
Alex Reggiani
Dear, Alex Reggiani
I thought Geopolymer paste synthesized with GGBS+Flyash gives promising results rather than Flyash. Because of the properties of GGBS is much better compared to Flyash. And Strength obtained at ambient temperature is more important rather than heat curing, when it comes to implementation part. So its better to be blend with GGBS and Flaysh.
Thanks & Regards,
Basavakiran
Dear Basavakiran,
I ‘m agree with you, but mechanical strength isn’t only parameter to be considered, because durability is probably important like strength development. What is important is to find the right dosages and methods to blend raw materials without losing any property, maintaining constancy of yield.
I think this is the only way to develop the best geopolymer concretes .
All the best
Alex Reggiani
Experiments conducted at our lab : GPC mixes involving fly ash and GGBS were casted and cured at ambient temperatures. And we found that the combination of fly ash + GGBS provides us better strength development, proper setting time and a good durability in comparison to GPC mixes with flyash alone.
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