WSU researchers use coal waste to create sustainable concrete
New coal concrete reduces energy demand, greenhouse emissions
PULLMAN, Wash. – Washington State University researchers have created a sustainable alternative to traditional concrete using coal fly ash, a waste product of coal-based electricity generation.
The advance tackles two major environmental problems at once by making use of coal production waste and by significantly reducing the environmental impact of concrete production.
Xianming Shi, associate professor in WSU’s Department of Civil and Environmental Engineering, and graduate student Gang Xu, have developed a strong, durable concrete that uses fly ash as a binder and eliminates the use of environmentally intensive cement. They report on their work in the August issue of the journal, Fuel.
Reduces energy demand, greenhouse emissions
Production of traditional concrete, which is made by combining cement with sand and gravel, contributes between five and eight percent of greenhouse gas emissions worldwide. That’s because cement, the key ingredient in concrete, requires high temperatures and a tremendous amount of energy to produce.
Fly ash, the material that remains after coal dust is burned, meanwhile has become a significant waste management issue in the United States. More than 50 percent of fly ash ends up in landfills, where it can easily leach into the nearby environment.
While some researchers have used fly ash in concrete, they haven’t been able to eliminate the intense heating methods that are traditionally needed to make a strong material.
“Our production method does not require heating or the use of any cement,” said Xu.
Molecular engineering
This work is also significant because the researchers are using nano-sized materials to engineer concrete at the molecular level.
“To sustainably advance the construction industry, we need to utilize the ‘bottom-up’ capability of nanomaterials,” said Shi.
The team used graphene oxide, a recently discovered nanomaterial, to manipulate the reaction of fly ash with water and turn the activated fly ash into a strong cement-like material. The graphene oxide rearranges atoms and molecules in a solution of fly ash and chemical activators like sodium silicate and calcium oxide. The process creates a calcium-aluminate-silicate-hydrate molecule chain with strongly bonded atoms that form an inorganic polymer network more durable than (hydrated) cement.
Aids groundwater, mitigates flooding
The team designed the fly ash concrete to be pervious, which means water can pass through it to replenish groundwater and to mitigate flooding potential.
Researchers have demonstrated the strength and behavior of the material in test plots on the WSU campus under a variety of load and temperature conditions. They are still conducting infiltration tests and gathering data using sensors buried under the concrete. They eventually hope to commercialize the patented technology.
“After further testing, we would like to build some structures with this concrete to serve as a proof of concept,” said Xu.
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The research was funded by the U.S. Department of Transportation’s University Transportation Centers and the WSU Office of Commercialization.
even IF fly ash had needed high heat to work would that still not have been acceptable?
would have at least gotten rid of the fly ash.
have not had chance to read up on it much, anyone know how compression strength is compared to standard concrete mixes?
There was this building block called cinderblock…
Graphene oxide (aka graphite oxide) is another form of TheMagicMolecule!!
And where does graphite come from?
joelobryan
“And where does graphite come from?”
The Moon?
OK, I give in, where does graphite come from?
The high grade stuff is mined. Low grade amorphous “lampblack” is made from petroleum coke.
OK, I am a chemist by UCBerkeley training, and have some modest hands-on experience in cement chemistry while taking Materials Science electives. So… what’s the REAL story here?
Before I got to the critical two words (sodium silicate), I was wondering “how on Earth are they getting FLY ASH to bind in a classic cement hydration-and-crosslinking chemical reaction with graphene oxide?” I was reading slowly, and I thought “well, maybe they’re using a strong glassy binder like sodium silicate, and probably augmented with a ‘classic’ cement hydration-and-crosslinking compound like refactory quicklime/burnt lime (calcium/magnesium oxides)”.
Then but a paragraph later, “sodium silicate” and “calcium oxide” are slipped in.
THING IS — that as soon as you add “water glass” (Na₂SiO₄ sodium silicate) and “quicklime/burnt lime” (CaO calcium oxide) in some portion to fly ash, you are again making cement by an alternate route. The CaO does its job turning to various intermolecular bridge compounds thru slow hydration and water-mediated cross-linking. The Na₂SiO₄ does its work quickly, donating the silicate anion to cross-linking, binding to the various refactories of fly ash.
The graphene oxide … to me … seems to be a 3 dollar bill. It might act as a rate-related catalyst, causing a slurry of the interrelated compounds to ‘set’ faster, or ‘set’ in a more crystalline (strength) fashion. But itself, it appears to not have a structural component. Moreover, if “graphene oxide” works as a catalyst, there are a number of other cheap, traditional cement-chemistry catalysts well documented in the literature and industrial practice.
_______
Point is, that there is another problem that is going for the asking.
WHAT KIND OF FLY ASH? Coal ash. The problem? Radioactivity potential. Some (many, actually) fly ashes from coal sourced in the US are so radiactive that they set off radiation detectors while being driven by truck to waste sequestration facilities. They’re considered a potential ORE for uranium and thorium. “Cinder blocks” — the ubiquitous construction grey or tan blocks — made before 1985 when tough anti-radiation laws went into effect, were one of the strongest sources of airborne radon gas that bedeviled below-grade basement air domestically.
That then is the problem.
ALSO the “other three dollar bill” is that the claim of “not being energy intensive like conventional concrete(s)” is disingenuous: it takes substantial energy to kiln-convert limestone/dorite (calcium carbonate, magnesium carbonate, as a mixture) into calcium/magnesium oxide (“quicklime / burnt lime”). If the fly ash is a SIGNIFICANT (majority) component to the structural integrity of the cement-reaction, then that is good. If it is a stochiometrically modest amount, then the cost (energy) of producing quicklime and sodium silicate quite easily could offset the Green Ballyhoo marketing potential.
Just saying
GoatGuy
Goatguy
That was a great chemical tour. I have seen some geopolymers and was very impressed. Applications needing less than 700 C can be made from two waste streams from industrial processes – both of which they will pay you to take away. High alkali bonded glass materials in high temperature coal ash makes a great geopolymer. I have seen a sheet somewhat akin to drywall that was foamed in the centre with tiny bubbles. Hit with a hammer, it dented and did not crack at all. Amazing stuff. Amazing insulation, amazing strength, no cement content, low price. If your ash has too much uranium, you can import ash from India, Africa and China. Heh heh…
Crispin (father of materials engineer)
Let’s not forget the smash hit the Chinese had with dry wall.
It would be nice to find a valuable use for fly ash. May be that use in a concrete like application will work for some applications. But beware!
I have a friend who had to dig out part of his concrete driveway against his garage due to fly ash expanding 15 years later and uplifting the entrance 8″ – 12″. Not sure if he placed any under the house foundation. There were other examples I heard about.
I bid on a contract related to removal of fly ash from a local landmark hotel where fly ash was used under the new construction of a major addition. The floors were raised several inches, doors jammed, glass curtain wall breaking, etc. Not sure if it was fly ash from a local steel mill or coal burning. It took a few years to manifest itself. Cost was major.
There was portion of I-81 in Virginia that was built using concrete due to Federal Regulations because a cement mfg was located in that county. Uplifting was severe and remedy took years but I don’t know if any fly ash was used in the base.
Anyway, if a waste product can be utilized that is a good thing. But don’t take a nano look and create a mega issue.
eyesonu
“Anyway, if a waste product can be utilized that is a good thing. But don’t take a nano look and create a mega issue.”
Doesn’t that personify science in general, and AGW specifically.
Great comment.
Permeable is terrible for anything in the frost zone.
As already mentioned, fly ash already has many uses.
https://en.m.wikipedia.org/wiki/Fly_ash
Sounds good. Is there an academic paper on it yet?
Cheers
Roger
Well, this is not exactly news, is it?
“The process creates a calcium-aluminate-silicate-hydrate molecule chain with strongly bonded atoms that form an inorganic polymer network more durable than (hydrated) cement.”
These are collectively known as geopolymers. When I was in Potchefstroom I visited the producer of such materials who was making high accuracy coal stove components for us. It is not mentioned in the article that these materials have a very high melting temperature – they can be used in some cases up to 1400 C. Essentially it is a reaction between the glass in the ash and a high pH material (>11 will do).
There are a couple of new items on the market that are very interesting substitutes for refractories. One is phosphate bonded alumina using aluminum dihydrogen phosphate and another is aluminum orthophosphate. Both make refractory materials without firing the product in a kiln.
Something else not mentioned is that the fly ash has to have been subjected to temperatures above 1300 C so it is in a glassy phase. Your basic coal stove doesn’t produce the right raw material. It has to come from a power station or large boiler. The big attraction is the cost: far cheaper than cement, and I’d say it is worth burning coal to get the ash in some cases.
Look for this at your modern construction sites. It can be foamed to make strong, insulative products. The research in South Africa is being funded by PPC (obviously) to get on top of these materials before someone else does. I saw kerb stones being made from it. It is strong and impervious to heat from a cutting torch.
Multiple papers are available on the chemical mechanisms involved.
“The research was funded by the U.S. Department of Transportation’s University Transportation Centers and the WSU Office of Commercialization.”
It seems to me that research funded by the gov’t ought not be patented except for international use and mfg. We the People paid for, it belongs to us. The academics are doing work for hire.
I think Fly Ash Concrete might arrive in your Home Depot (or be used to make concrete blocks for your next office building) about the same time my Flying Car is delivered.
I’m concreting at the moment and coal flyash is listed as one of the ingredient in the Portland cement.
call me crazy – isn’t this why they are called “cinder” blocks? This doesn’t seem like a new idea.
I’m truly astounded, cement made from fly ash ? This ‘discovery’ has been in active use for a VERY long time already. Cement is the ‘active’ ingredient of concrete.
I’ve been following this site for quite some time. I’m here to learn.
Reading this particular thread, some of you are as bad as climate alarmists.
How many of you are/were involved in building? You all sound like experts?
I’ve been building for 40+ years.
The house I live in has a so-called cinder block foundation (60+ years). The major addition we did 15 years ago has a block foundation. Not a crack in either the old or the newer.
I’m not going to get into what you need for a deeper foundation, but if properly instituted, a cinder-block foundation is MORE THAN ADEQUATE. Ultimately, it depends on the footing you place your block foundation upon. All my projects had great footings!!
I’m not going to post my education credentials because that’s really beside the point.
AH
Well, I’ve been in construction for +40 years too and also studied material science in the 70s. Foundations / footings are designed dependant on soil mechanics. Concrete core-filled concrete (cinder) blocks reinforced with steel rod are commonly used everywhere in the world in a variety of applications long lasting and without consequence. My educational credentials somewhat exceed my professional needs … but that is beside the point.
I’d never laid a block until 3 months ago, now I’ve laid 860, N12/16 core-filled, all on nice chunky footings, about to render with exposed aggregate…also beside the point.
Theyll should use that ash to forests, to prevent asidification of forests and lakes. When timber is taken from forest it takes minerals from the ground. If you don’t put those minerals back to forest in some way ….
Nothing new, coal ash has been used in concrete and pavement for decades. How much of our tax money was pissed away on this boondoggle?
The US funded this technology …in China? WTF?
Please read the first paragraph. “Washington State University researchers ….”
I worked at a coal fired power plant for many years and the plant sold fly ash to a concrete manufacturer almost from the day it started operation. There are two problems, first the ash must be low in carbon, ie carbon must be almost all burnt in the combustion process. This itself is a problem because burning more of the carbon in the coal requires higher temps in the furnace and that increases the formation of nitric oxides (NOX) in the flue gas, NOX is a problem pollutant. So this requires careful control to efficiently burn the carbon while keeping NOX production low.
The other problem is that flyash is somewhat radioactive, containing uranium and thorium. When concrete made with flyash was used in building construction (making cinder blocks IIRC) this led to radon buildup in the buildings. Not acceptable of course. So the concrete made with flyash is generally used here for highway construction.
Flyash may become a more valuable product since I understand that experiments are underway to extract rare earth elements from flyash. I understand that the concentration of rare earths is somewhat lower than the clays used in China but still usable.
Exactly, I worked at a industrial plant (coal fired spreader stoker steam boiler) and the fly ash (fabric filter baghouse) was just too high in unburnt carbon. We did reduce the carbon content with some refurbishments and readjustments, but it was very difficult to keep the carbon content low constantly, in order to sell the flyash to a cement manufacturer.
I prefer using fly ash blend cement for my backyard projects.
It is typically called builders cement in Australia and is slightly cheaper and just as strong.
It contains up to 25% fly ash, usually from blast furnaces.
No, no, no. Can’t use graphene oxide. Graphine oxide is made up of oxygen, hydrogen and (drum roll) that nasty CARBON. We could also discuss the oxidizers that are used in processing graphene oxide.
‘….molecule chain with strongly bonded atoms that form an inorganic polymer network more durable than (hydrated) cement.’ “After further testing, we would like to build some structures…” Add a Three D Printer and……” In China they are building houses with Three D Printers.
Yes, yes, fly ash has been added to concrete for thousands of years, in varying quantities. But this process, they say, “…eliminates the use of…cement…” Granted, they are still in the R&D phase, but it shows promise, its characteristics differ from concrete enough that many of the issues cited by other commenters may not be issues after all. Its performance also differs enough that I can immediately think of applications where this material could be better. Of course every graduate engineer’s research has invented the greatest thing since sliced bread, but they’re not all wrong. As an engineer, I’m intrigued. I might even agree that spending some of my tax dollars on further development could be worthwhile. Maybe we should just agree to check back with them in a year or two?
Try substituting Idaho sourced pumice in the cement mix to reduce use of the Portland. The Roman cement recipe would set and retain strength with salty sea water. Required much lower temperature to prepare the ingredients saving energy. Pumice variant does not leave an excess of sodium hydroxide dispersed in the cured concrete as does typical cement mixtures.