I have added silica fume to alkali activated slag mortars. Two types of alkaline activators are tested for geopolymer mortars : NaOH + sodium silicate and KOH + sodium silicate.
Silica fume addition didn't improved the compressive strength of mortars (in some cases even lowered it). The silica fume was added to the mixtures in the form of liquid (mixed with alkaline activator).
I am asking about possible reasons of such trend. I have attached the results of 3 and 7 day compressive strength of mortars here.
Best,
Hello Amin
Interesting results. How about the effect on ductility?
The effect on the compressive strength depends on the dosage used. The following is a good source of reading where some comprehensive research was undertaken. I hope it will be of some help:
https://researchbank.rmit.edu.au/view/rmit:6112/Adam.pdf
Best wishes
Dear Amin,
first of all, you have to understand that if you correctly write that you are working on alkali activated slag you can't speak about geopolymer mortars , because aren't the same technologies, at all. You can't have a geopolymer using only slag as powder binder, it's totally impossible because mineralogy of slag is incomplete for geopolymerization , while it's very useful for alkali activating (specially if you do heat aging at 60-70°C to fix the sulphur content of the slag to avoid oxidation that will change your product color, see Glukovsky huge works in Ukraine). But In Geopolymer technology there isn't any "activator" but only a liquid hardener or reagent that permits dissolution and recondensation so geopolymerization process. This because what is very reactive is the powder that you use as binder (already calcined at high temperature as Fly ash or slag, but you can't use alone, or as microsilica , while calcined at 750°C for the best metakaolins you may use) and process is named alcalination not activation, so isn't necessary so high pH you obtain using NaOH and KOH as in your report, but only pH quite similar to cementitious or lime based products. I put my fingers inside liquids that I use , without any risk of corrosion.
Microsilica is perfect for increasing strength but depends on the type you use and of course depends on your mix design. Probably wasn't a good idea to put microsilica into the liquid...
Come to next Geopolymer Camp in France in July, we will talk directly if you are interested in Geopolymer technology. But is necessary for first that you understand what kind of products you want to develop, if you chose alkali activated slag don't talk about geopolymers and of course if you want to realize geopolymers you must follow the correct terminology and procedures (choice of reactive powders, setting of alkali or why not acid liquid hardener and respect mix design).
Hoping to be useful to your future research.
Best regards
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