activation of flyash

Dear Mr Dekmush,

do you mean European standards then its EN 197?

I have not done alkali activation of fly ash myself and its not done in
Holcim yet but I have done a literature review, the summary I have
attached. To activate Class F fly ash as in India will be quite difficult
as its a relatively coarse and low reactiv fly ash. You need high
percentages of activators which might cause problems with regards to
standard limits on Cl and alkalies and in application e.g. corrosion and
ASR reaction. Therefore we will test this new combination of grinding aids
and quality improvers from South Africa as send to you as it seems to work
quite well. Fly ash content could be increased from 32 to 38% at same
perfomance.

Economically its difficult to say if grinding or activation is more
economic as it depends on the % and type of activator and the Blaine.
Grinding has a certain limit for activation of fly ash cement as beyond
around 4000 Blaine the activation effect through surface increase is
compensated by higher water demand in the concrete. So beyond a certain fly
ash content it should be probably a combination of both mechanical and
chemical activation. The cheapest activator is NaCl which mainhly acts on
the clinker, NaOH is more fly ash specific but also more costly.
Coarse fly ashes with a high reactive SiO2 content >30% react very well on
grinding, we have seen it in some of our Eastern European plants.

Another promising option are multiple blends like fly ash/slag or fly
ash/limestone blends. They combine very well and when ground separately
fineness of the components can be adjusted to maximise performance. But I
think the IS does not allow it right now, may be in the future.

Generally you can say its possible to activate each fly ash its just a
matter of concentration and thats also the problem. The majority of R&D was
on either activation via suspension or at elevated temperatures or US
specific Class C fly ashes were used which have cement like properties,
there are Class C fly ash based binders in US marketed as shown in the
file. Except HolcimAct admixture which should work also with your
clinker/FA, I do not see a magic powder which will push the fly ash
activity, I see more a combination of measures be it even another grinding
system like vibrating mills, one large scale operational in Texas and use
of certain activators partially activating the clinker and partially
activating fly ash. May be it should be also mentioned that Lafarge did
tests with injecting HCl in the finished mill to activate fly ash by
etching the surface of fly ash particles but problem in this case was
corrosion of mill parts. Another option of course would be air
classification of fly ash to increase fineness and thus reactivitiy but
this requires CAPEX and has about 5USD/t operation cost and you have to
take care of the residue as well.

So all together I do not have a final solution, sorry. I would certainly
start with HolcimAct first and see if it works.

What is your current project and program and what are the targets you want
to achieve?

Best regards

Stefan Dietz

(See attached file: Fly_ash_maximation Holcim.ppt)(See attached file: EN
197-1 en.pdf)(See attached file: Fly ash standards.ppt)
_____________________

Stefan Dietz
Holcim Group Support Ltd
Corporate Commercial Services
Product Innovation and Development
Im Schachen
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Phone +41 58 858 64 12
Fax +41 58 858 64 09
Mobile +41 79 373 7983
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