any geopolymer -flyash-concrete in USA yet? 1

[davefitz]

I have recently read several reports from India and Australia regarding their use of geopolymer-flyash concrete . Results indicate that 28 day compressive strength is over 50 MPa( over 7250 psi), and zero portland cement is utilized. Basically , class F flyash + sodium hydroxide plus sodium silcate are used as replacement binders in lieu of portland cement. CO2 credits associated with this is 1 ton of carbon credited per ton of this concrete.

We have 50 yrs accumulation of flyash from our coal fired plants, and viewing this flyash as of equivalent value as portland cement might lead one to think we are now sitting on a gold mine.

Are there any USA applications of this technology ?

 

[concretemasonry]

I am sure they do have it in India, although the Indian fly ash is extremely variable in properties. The Indians are very good technically and creative and can conduct excellent studies on small volumes.

Any old fly ash in the U.S., even if possibly acceptable to make it usable for any high volume since it obviously is not stored in bins, but on the ground or used to fill large holes or swamp lands. In the U.S., properties are determined by the fuel used and the type of collection methods. Both type C and type F have been available, but the good fly ash is already under long term contract to the cement companies as a raw material or the international admixture companies for use as an admix.

What many people around power plants see is "bottom ash", which is course, contains some heavy metals and needs to be processed.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[markmc]

I have followed the development of materials known as geopolymers for a few years now. I have created various formulae for GP mixes after I saw a sample about ten years ago. It has some unusual properties that could be useful in many different fields. But... So far, the commercialization has been very limited. There was a company in Texas (where I am) that produced an early cure, high strength GP OPC blend for a while in the early to mid 90's. There is a batch plant currently producing GP concrete in Australia. There are also niche products around the world. Although there are tons of research and academic papers written, replacing OPC is a tall order. OPC is second only to potable water as a man made material. Try changing the course of that ship!

I was working on a less ambitious application, still am, as time permits.
I used Class F fly ash from a plant in the four corners area. It worked well. The fly ash does not even need to be particularly clean, although an old deposit would be a lot of work to use. I have read that Class C might not work as well due to interference with the polymerization process from the additional CaO present. I have not tried to use Class C fly ash personally.

 

[davefitz]

The research papers claim extraordinary properties , depending on the curing method and aggragate/flyash properties, including:
a) 2-4 times the compressive strength and up to 10 times the tensile stength of OPC
b) directly bonds to reinforcement filament wires, leading to a true composite material, suitable for many deense related purposes
c) fireproof, strong to 1000 C, stable to 1600 C
d) very short initial curing period, to >10 MPa in 4 hrs ( used as emergency runway cement repair patch )
e) non-leaching of heavy metals for a large family of metals, may be considered as an alternative to vitrification for some metals
f) very low CO2 footprint, may qualify for 1 ton of carbon for each tonof concrete used.

My own limited application is to convert flyah deposits to beneficial use while consuming FGD purge wastewater. Maybe paving bricks or highway barriers as final product.

It has potential to be a "disruptive" technology.

 

[markmc]

I can vouch for several of the properties you mention, especially b, the stuff is really "sticky" and will bond well with a broad range of other materials. The applications that you mention are ones that I am interested in looking into. The fun part is that it's all new. My recipes are as good as anybody's because there aren't any cookbooks. In which part of the country are you? Also, is your fly ash Class C or F or both? How old? Perhaps we could work together on producing some samples from your mountain of fly ash.

 

[davefitz]

Markmc:

we have class F flyash- 50 yrs accumulation from several plants. More important we have a wastewater stream of 1500 gpm from the fFGD purge. At issue is whether this wastewater can be used with the dry NaOH , as it contains 10,000 ppm chlorides and also boron and selenium, 2 metals tha may leach from geopolymer concrete. Also,the purge has high levels calcium sulphate- perhaps we will need to soften the wastewater and remove the Se with a bioreactor prior to mixing with NaOH , etc.

 

[markmc]

I think the waste stream is too complex to guess. Off hand, I think it could be used as the water source. Although, you will have to make more than a few bricks to use all of that waste stream. As far as the boron and selenium leaching, there is a lot of research and experimental data on the use of GP as a means of encapsulating hazardous wastes, even in situ. If the reaction goes right, you end up with the boron and selenium ions tied up in something like granite.

 

[davefitz]

markmc:

I forgot to mention- we would be reducing the wastewater flowrate by a factor of 9:1 by first using a falling film evaporator. The resulting wastewater flow would be in the range of 150-200 gpm, with a chloride content up to 90,000 ppm. The concentration of heavy metals to be similarly increased.

Some published papers suggest the Se and B will leach out, so the Se to be first reduced via a bioreactor and the B maybe reduced via electro coagulation.

The slow increase in US adoption of GPC geopolymer concrete ( compared to india, china, Mideast) appears to be due to the massive investment the existing concreet industy has in the status quo. Developing countries have a cleaner sheet to start with, and may have less difficulty lobbying their standards organizations to accept the new technology.

 

[Ryb01]

Not too sure about the mix composition but have heard about this product that may be of some interest. Hope this helps.

http://www.grancrete.net/