Karls Geopolymer Experiments

[Deleted]

I have made some more experiments.

Silica gel cat litter ball miled for faster disolution by shaking with steel balls in a jar.
Cannot be milled fine enough this way to be used without prior dissolution in lye.
Fine milling would require a rotating ball mill.
Trass cement (60% OPC 40% trass, five years over time) instead of lime,
as I have had no more lime.
Due to low remaining reactivity the law prohibits the use of such old stuff
as a hydraulic binder in buildings.
Zeolithe (Clinopthilolit) milled the same way.

If the zeolithe powder is mixed with lye powder and water is added,
the reaction is even more violent as with pure lye,
because gas is created by the reaction with the zeolithe powder.
The gas release by the reaction with the zeolithe is temperature dependant,
a significant amount will be released only at elevated temperatures.
Can be used instead of aluminium powder for foaming,
due to the temperature dependance the gas release is controllable.
Fine milled zeolithe will likely produce more gas, but still less than aluminium powder.

If only lye and waterglass is used, regardles of homemade or commercial waterglass,
the mixture must be very precise, just slightly to much water and the chemistry will fail.
Due to higher reactivity metakaolin is a bit more forgiving than fly ash or grog.

With lime ( or trass cement this time) one can mix the incredients without a scale by eye and experience.

About 50% of the binder pozzolan can be replaced by natural clay.
Organic matter like saw dust can be added without problems.

Quick lime should be used for short pot times to prevent segregation,
if the density of the mixtrure incredients is very different especially if something with a plasticier effect
like fly ash is contained, eg if the mixture conteins expanded perlite or something very heavy like pure alumina.

[Deleted]

A binder made of ball milled (shaked) perlite and natural clay works just fine.

I have made water glass from silica gel cat litter and ordinary drain cleaner
which contains sodium hydroxide flakes, nitrate, sodium carbonate and aluminum grains.
The price of the ordinary drain cleaner is less than half the price of the pure sodium hydroxide.
I have not observed negative effects on hardening.

Because of the nitrate the water has to be added outdoor.

[terryeh]

Jun 17, 2014 17:46:14 GMT -8 @karl said:

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).

As you have noted , according to "Nath and Sarker" in the above white paper; higher CaO leads to shorter curing time and stronger concrete.

"For example Class C fly ash generally contains more than 20% lime (CaO)"   !?!?  The statement of the year ! (because that's how long I've been wondering about this)

Nath and Sarker employ various amounts of slag, from 10% to 30% of the binder. The slag contains 43% CaO
This means the total mix at 10% has 6% CaO overall; and the total mix at 30% has 14% averall. (with fly ash "F"-1.8% CaO)
Fly ash "C" has 20% CaO ! So why are we bothering with ground slag at all ?
Using a binder of 100% fly ash "C" give's us 20% CaO and... a simpler, and cheaper recipie.
6%=1/17, 14%=1/7, 20%=1/5

I further point out that while higher water lowers strength and lengthens cure times (which is what higher CaO is countering); It gets us the holly grail of precast, A fast curing WET MIX.

[Deleted]

Yes, if you can get class C fly ash you do not need anything else for the binder.
Due to the spherical shape it needs only small amounts of water.

[pyrophile]

I am not understanding everything (because of my english and chemics knowledge) but I find all this very interesting, as far as I understand!
Thank you Karl!

[terryeh]

Jul 1, 2015 4:51:02 GMT -8 @karl said:

Yes, if you can get class C fly ash you do not need anything else for the binder.
Due to the spherical shape it needs only small amounts of water.

Thanks Karl:

Iam looking further in to fly ash. I have found that fly ash F is 10% or less CaO and fly ash C is 10% or greater CaO
My last idea is that maybe you could have very precise control (repeatability) by thoroughly mixing in quicklime (CaO), with the dry fly ash, to total aproximately 15% (as per "Nath and Sarker" with 30% slag)
To a 2-4% CaO fly ash (fly ash F) it would be something like 1% quicklime (of total ingredients) Which is  a few cents per cubic foot.
I will also investigate safer alternatives and the "shock" issue of setting to quickly
I don't understand how, if you get the amount right and well premixed; It can be a problem as apossed to adding it through slag.

[Deleted]

Wikipedia gives more than 20% CaO for class C fly ash.
Unfortunately ASTM C618: 1 is behind a paywall.
The Canadian Standards Association (CSA) defines two types of class C fly ash.

Like in portland cement the CaO in fly ash or slag is usually not free.
While PC contains more than 60% CaO only about 1% is unbound.
The CaO is bound in Tricalcium silicate, Dicalcium silicate and Tricalcium aluminate.
The bound CaO does not react in the same way as the free CaO.

The reactivity also depends on the kind of bound.

[talltuk]

Hi Karl. I was interested in experimenting with your tinkerers geopolymer. I have 59kgs of fireclay and 200l of perlite. Just need lime and sodium silicate. What sort of ratio have you used binder to aggregate? My first test will be a 5l tin aprovecho cook stove.

[Deleted]

Like with concrete the ratio of binder to aggregate depends on the aggregate size.
With large aggregate size one needs less binder than with fine aggregate.

You neede to pulverize the perlite to use it as a pozzolan.
In the UK metakaolin (Argical M1000), PFA (Pulverised Fuel Ash) or GBFS (Ground Furnace Slag) are pretty cheap.
Available in many shops for traditional building materials.

Eg.
www.chalkdownlime.com/products/pozzolans-additives.html?limit=24
www.ecohousestore.co.uk/product/Argical_M-1000_pozzolan_LPLR0110025

[jliebler]

FWIW Here is a recipe from Joseph Davodovits book, Geopolymer chemistry and applications.
20 parts by weight MK750, 20 parts by weight ground granulated blast furnace slag, 24 parts K-silicate with MR 1.25 and 50% concentration, 56 parts by weight fly ash class F,29 parts by weight water. Mix is cast, covered and allowed to harden at room temperature. Compressive strength is 65MPA after 28 days.

I have Agsil 16H which is 26.56% K, 24.6% Si, 52.8% SiO2 that I hope to use for the K-silicate, is it close enough? I'm also thinking of substituting cenospheres for all of the fly-ash to make an easily cast insulative geo-polymer for a batch firebox.

[Deleted]

26.56% K and 24.6% Si gives a MR Si/K of ~ 1.29.
Cenospheres are usualy just fly ash selected by size, density or color.
White cenospheres contain only very small amounts of iron oxides.

[djsalvo]

Could I use blast furnace slag (3/4" to fines) as my aggregate fill in place of perlite?

[Deleted]

No, not for insulation.
Blast furnace slag has a density in the range of common vulcanic rock,
ten times or more denser than expanded perlite.

It is commonly used for sandblasting.

Rapidly cooled blast furnace slag, finely grinded, has pozzolanic properties
and thus can be used to make a binder.

[andyd]

Hello, everyone! Hello, Karl! I am a new person for this forum. And while surfing the web, found this forum and was surprised by the professional talks here I am very interested in geopolymers and its different application, but unfortunately have lack of knowledge in chemistry. Thanks to this forum I have finally understood what is molarity of KOH and NOH, but one question remains unclear for me, I hope someone of you can help. In Davidovits books, articles and in other sources of information concerning geopolymers, they speak about Si:Al ratio and if you have Si:Al = 1 this material is suitable for brick and ceramics (as far as I understand from your forum the more Alumina in the recipe the higher the melting point of the final product and thus this is good for ceramics), if you have Si:Al = 2 (1.5...2.5) this is good for cement and concrete applications, waste incapsulation and if Si:Al = 20 and more (15...40) this is good for fireproof, for resins, aeronautics etc. application. So the question is simple: How to calculate this Si:Al ratio, knowing the chemical compositions of materials (metakaolin, fly-ash and GGBS). Do we need to take into account water glass and it's SiO2 content or not? How to change Si:Al ratio in one recipe by changing the amount of raw materials in the recipe? For instance, we have per 100%: Metakaolin: - 10% and FA - 30% and GGBS 10% - what will be the Si:Al ratio in this case? To calculate easily, let's take the chemical composition of MK as SiO2 = 53%, Al2O3 = 43,8%; Fly-Ash: SiO2 = 58,23% and Al2O3 = 25,3% and for GGBS: SiO2 = 39,6% and Al2O3 10,4% with CaO = 39,5%. 

[Deleted]

The ratios given refer to molecules respectively atoms.
To calculate the weight ratios one needs the molar mass of the individual molecules.
Molar mass and mass percent can be obtained by molar mass calculators like this one:
www.caymanchem.com/chemAssistant/Tool/4002

Silica (SiO2)
molar mass (g/mol): 60.08439
mass percentage: silicon (Si) 46.74347 % and oxygen (O) 53.25653 %.

Alumina (Al2O3)
molar mass (g/mol): 101.96136
mass percentage: aluminium (Al) 52.9250 3% and oxygen (O) 47.07498 %.

Si:Al = 1 means a mass ratio of (2xSiO2)/Al2O3 2x60.08439/101.96136 ~ 1.18.
Si:Al = 2 means a mass ratio of (4xSiO2)/Al2O3 4x60.08439/101.96136 ~ 2.36.

A precise calculation needs to include everything that is involved in the chemical reaction.
Thus yes, for a precise calculation you need to take into account water glass and it's SiO2 content.

With this information you can answer your last question yourself.


BTW
You can make waterglass by dissolving silica gel in water and lye at 90°C
by the following formulas, where n is a number between 1 and 5.
The higher the number the less caustic the waterglass will be.

Potassium silicate
n SiO2 + 2 KOH → K2O•nSiO2 + H2O

Sodium silicate
n SiO2 + 2 NaOH → Na2O•nSiO2 + H2O

Caution: Hot lye is extremely dangerous.