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Post by Deleted on Jun 12, 2014 8:53:53 GMT -8
Geopolymer concrete for ambient curing condition asec2012.conference.net.au/papers/028.pdfThe above paper deals with fly ash. Significant calcium monoxide (CaO, burnt lime) content, especialy in type C, is the main difference to other kinds of aluminosilicates. One needs only to add some calcium monoxide to other kinds of aluminosilicates, to get much faster setting times. The Paper uses 14M (40%) sodium hydroxide solution, which is extremely dangerous. Sodium silicate/sodium hydroxide ratios varied as 1.5, 2.0 and 2.5. No extra water added. In my experiments I have used sodium hydroxide powder in much smaller amounts. I have mixed the koalinic clays with calcium monoxide and sodium hydroxide powder, then added water. Kaolinic clays and grog Ball-Clay Hymod Prima (the finest kaolinic clay) White fat clay (not as fine as ball clay but much finer as kaolin) China Clay Grolleg (a bit finer than kaolin 233) Cement fine white grog (a cheap kind of metakaolin with only 18% alumina) The China Clay, despide relatively large particles, is definitely pozzolanic as it reacts with calcium monoxide, mixing in some cement fine grog results in very fast setting times. Natural kaolinic clays, without calcium monoxide, have very long setting times at ambient temperatures, beyond my patience by far. Very high amounts of sodium hydroxide, as in the paper, rather prolong setting times. The results have meet my expectations. |
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Post by Deleted on Jun 12, 2014 12:10:47 GMT -8
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Post by photoman290 on Jun 12, 2014 13:28:30 GMT -8
davidiots warns against using caustic mixtures of that concentration in one of his talks. he advocates low caustic content in his mixes.
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Post by Deleted on Jun 13, 2014 4:44:03 GMT -8
While all testet kaolinic clays have shown pozzolanic poperties,
it is not enough for ambient curing in a reasonable time.
Some cement fine grog, fine metakaolin powder, fly ash or natural pozzolan eg. trass powder is also required.
If mixes contain also waterglass the use of calcium monoxide may cause pot times of a few minutes,
calcium hydroxide is less reactive.
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Post by Deleted on Jun 13, 2014 6:15:31 GMT -8
For general safety I recommend to avoid the use of caustic low viscosity liquids.
Even a PH 12 liquid like waterglass is dangerous.
To optimize the dissolution of NaOH and small particles:
Clay powder, diatomaceous earth, NaOH and water can be mixed 24 hours prior
to the addition of calcium oxide/hydroxide and more reactive pozzolan.
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Post by Deleted on Jun 17, 2014 17:46:14 GMT -8
Have made some experiments with curing at 70°C-80°C.
Mixtures for warm curing can be made with quite low viscosity and still harden within a relatively short time,
which will result in lower density and thus lower heat conductivity.
According to most papers ambient curing will have similar strength after 28 days,
but thats a rather long time.
Raising the calcium oxide content from 1/9 to 1/7 or 1/6 would shorten ambient curing for low viscosity too.
For example Class C fly ash generally contains more than 20% lime (CaO).
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Post by Deleted on Jun 17, 2014 20:54:09 GMT -8
A quite well working mix.
9 parts cement fine grog or metakaolin
1 part calcium oxide powder
1 part sodium hydroxide powder
As little water as possible,
for warm curing it can be significantly more water.
If the particles are very fine waterglass can be omitted.
Parts of the cement fine grog or metakaolin can be replaced
with natural kaolinic clay, more for warm curing.
Warm curing is like baking cakes.
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Post by Deleted on Jun 19, 2014 7:22:40 GMT -8
Conclusion
It is possible to replace parts of the cement fine grog/metakaolin
with natural clay.
However natural clay delays hardening due to less reactivity
and will likely cause less final strength, which may increase at firing.
By warm curing something with the consistency of condensed milk
or cream can be hardened within a few hours.
Low viscosity allows casting of complicated and thin walled things.
Building a ceramic shell could be shortened significantly,
by painting and chemical hardening instead immersing and drying.
Waterglass caused more problems for me than it solved.
Likely it will make the resulting geopolymer more dense
and thus also stronger.
However high density is for refractories not as desirable as for building parts.
In Germany starting at:
Cement fine white grog ~ 1.1€/1kg, 29€/50kg, 22€/20kg
white grog 0-1 mm ~ 0.95€/1kg, 20€/50kg
sodium hydroxide powder ~ 5€/1kg, 20€/5kg, 10€/2kg
fine white lime ~ 5€/1kg, 6,25€/2kg,
24kg mixture ~ 39€ + shipping ~ 21€ = ~ 60€
Natural clay could be calcined DIY with a stove.
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Post by Deleted on Jun 21, 2014 10:06:32 GMT -8
Some densities once all water is gone away.
cement fine grog with 300ml water/kg mix 1.27g/cm3
Same with 660ml/kg (very low viscosity) 0.95g/cm3 (warm curing required)
Half of the grog replaced with china clay 660ml/kg 0.82g/cm3 (warm curing recommended)
Half of the grog replaced with white fat clay 660ml/kg 0.85g/cm3 (warm curing recommended)
A quite low thermal conductivity can be expected from this.
The densest piece feels like stoneware and is about as hard.
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Post by photoman290 on Jun 23, 2014 10:29:27 GMT -8
hi karl, do you have any figures for shrinkage from the low viscosity mix probably not so important for a j tube but could be useful to know if using it for complex shapes.
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Post by Deleted on Jun 26, 2014 2:27:44 GMT -8
do you have any figures for shrinkage from the low viscosity mix There was no measurable shrinkage for any of the mixtures. |
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Post by Deleted on Jun 26, 2014 4:07:34 GMT -8
The pieces with very fine powdered clay in the mix got small cracks while drying.
No problems with china clay (kaolin) or alumina in the mix also not with pure fine grog.
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Post by Deleted on Jun 29, 2014 1:24:47 GMT -8
From the texts above one may have got the impression pure natural clays do not work, but they do.
However, hardening of natural clays is very slow under ambient curing.
The reaction of natural clays under warm curing is quite fast.
I have made some more warm curing experiments with pure natural clays.
For some pieces I have used cat litter (manufactured from sand) as a filler, which works great.
Obviously the amount of alumina and magnesia in the clays is more important than particle size,
thus there is no need to opt for the very fine, fat (plastic) varieties of clays.
The meager, non plastic varieties of clays are simpler to handle,
as they require significant less water than the fat ones.
Provided the alumina content is high enough even local clays may work.
It is possible to take the cheap route to geopolymers,
however the cheap route requires more patience for hardening and drying.
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Post by pyrophile on Jul 4, 2014 15:45:24 GMT -8
Great!
Thank You Karl for all these practical details!
Grog -refractory or not- and also metakaolin can be found in shops specialised for potters in rather big cities or internet, of course.
Benoit
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Post by Deleted on Jul 8, 2014 7:03:55 GMT -8
Once I have adviced the creation of the best ever HD silencer/cooler In German www.silenthardware.de/2008/06/14/sechs-festplattendammboxen-im-test/From the experiments for it I have had some remaining calcined alumina 99,5% Al2O3 and some ultrafine F 1200 fused alumina (corundum). Both hardened quite fast under ambient curing. The resulting geopolymers should be good for 1600°C to 1700°C. The melting point of alumina is 2050°C. Silicon carbide geopolymers should be good for up to 2000°C The industry is offering virtualy any kind of minerals in calcined or fused form. Eg. calcined talc is used to build heat excangers. A speciality are lightweight cenospheres which are extracted from fly ash. |
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