Karls Geopolymer Experiments

[lawry]

Karl I have some fly ash but no blast furnace slag?
I also have 200 mesh grog and clay. What's a good replacement for the slag?

[Deleted]

Granulated blast furnace slag ist just a cheap pozzolan with self cementing properties due to high calcium content.
Easy to get in the UK.
No replacement required.

[Deleted]

I have got 25Kg high alumina schamotte GWE 43 <63µm (250 mesh) from Gottfried.de
Enough for a lot of small experiments.
I love experiments.
Maybe I will build a small J-stove by layered shell technique
around cardboard and use it for some calcining experiments.

I have also got 3kg low grade (85% purity) pottassium hydroxide at Ebay
for a price usually requested for just 1 Kg of the same grade, which I could not resist.
I have used it to make waterglass from silica gel cat litter.

[keithturtle]

These folks run specials on NaOH and KOH on occasion www.essentialdepot.com/

Less than 2 turtlebuks a pound for lye, but I reckon shipping to EU would be quite a bit

Always good stuff, has been my experience with this supplier based in central Florida USA

Turtle

[lawry]

I've been experimenting with some of the suggested mixes in the papers and ive had SOME promising results. In all my tests the samples end up with this white deposit.... What is it? Is it safe? Should it be there?
See pictures

[Deleted]

That is efflorescence caused by water soluble alkalis
respectively their salts.
Efflorescence may happen with masonry too.
Waterglass or lye may not have reacted completely
or it is something in the clay.
In the case of Waterglass or lye unreacted material
may react with CO2 from air and form carbon salts.
It will stop once the material is dried.

The more reactive the used pozzolan and the lower
the alkali content of the pozzolan respectively clay
and the better the geopolymer is cured the less likely
it will happen

Efflorescence: Cause and Control.
www.masonryinstitute.org/pdf/612.pdf

[lawry]

Thanks Karl. I am also hand mixing my samples I suspect that this may also cause this problem. I really want an ambient curing recipe. I will keep trying.

[lawry]

I have done some tests. On the left is a Fly Ash and aggregate brick. The middle one has FA, small size aggregate and perlite. The dark brick has FA, Clay and aggregate. I cured them after 24 hrs at 90⋅C left them overnight in the oven. these bricks are rock hard!
The fly ash only brick does well at ambient curing. After seven days I couldn't break it by hand.
I m trying an ambient cured perlite brick currently. I will update once it's dry.



The structural ones will be for the body of my stove. I plan to get them mix tested at a lab for strength. The perlite will be for the riser.

[Deleted]

Class F fly ash contains usually about 4-6% CaO,
which is the reason it cures well under ambient conditions.
Most of the CaO in fly ash is sintered and thus reacts
a bit slower than the free form of CaO.

Calcium oxide or calcium hydroxide is usually the key
for ambient curing.
An extremely large surface as by metakaolin
may allow ambient curing without (very low) calcium.

[firewatcher]

Karl,

In your "Geopolymer for low-tech tinkerer" thread, you said the following...

"For a binder with water glass:
45% pulverized perlite or vermiculite, 45% natural clay and 10% lime.
Add water glass until you get consistency like cream, then fill it with coarse aggregates,
or just thicken it with more clay.
Porous aggregates like scoria, porous grog, perlite or vermiculite are preferable,
as they will support drying and firing."

My question is...is there a good rule to follow with regard to the ratio of aggregate to binder for the mix that you outlined (specifically I'll be using perlite)?

I've seen about as many different "ideal" ratios (binder:aggregate) as I have recipes for refractory. I was just wondering if you could share your experience with this mix and suggest a known "optimal" ratio using perlite as the aggregate. Some ratios that I've used in the past are around the 1:3 ratio binder to aggregate (by volume). For successful hardening at ambient temperature I don't really have a good guess at a starting ratio so as not to waste materials.

[Deleted]

The possible ratio of aggregate/binder depends on the particle size of the aggregate
and its liquid demand.
One can add more aggregate with low liquid demand.
The smaller the size the smaller the ratio,
as weight increases/decreases by three dimensions,
but surface only by two.

Binder with very small particles are more effective.

[firewatcher]

Lawry's post above looks promising...i've also been unable to find fly ash though. Am i just looking in the wrong places or asking the wrong questions when looking for these supplies? It seems like all these materials should be fairly available to the public. ?

[lawry]

firewatcher the fly ash is available at "modern" coal fired power plants, which use either a fabric filter plant or precipitate especially to collect the fly ash. The older plants might be using a wet ashing system that mixes the coarse and fly ashes.
Can't you just call a nearby power plant and ask?

[firewatcher]

Unless i'm misunderstanding, i don't think i'll be able to get fly ash then...our plants nearby are nuclear.

[lawry]

Yes you wont get from there. What about the other materials that Karl is trying?