We've documented in a few recent reports, such as:
Federal Highway Administration Recommends Fly Ash Concrete | Research & Development;
that, Coal fly ash can be utilized as a raw material in the making of Portland-type cement, as a substitute for other minerals; and, that such use of Coal fly ash actually makes the resulting cement and concrete products stronger and more durable.
Such use of Coal ash takes advantage of its properties as a "pozzolan", which is actually a technical term used in the concrete industry to describe a class of "siliceous" minerals that exhibit a certain type of reactive cementitious properties, when properly blended and treated with other minerals, specifically Calcium Oxide, as it is made, through roasting in kilns, from limestone, i.e., Calcium Carbonate.
For the sticklers in our audience, we acknowledge that Magnesium Carbonate can be/usually is also involved, but the natural sources and chemical reactions are nearly identical.
In any case, the word "pozzolan" is derived from an old Italian label that was applied long, long ago to certain types of volcanic ash that exhibit such cementitious properties; and, more about it all can be learned via:
Fly Ash Resource Center-Pozzolan Page; wherein we're told that: "Pozzolan is a finely-divided material that reacts with calcium hydroxide and alkalies to form compounds possessing cementitious properties."
A more extended discussion, including some of the history, is accessible via:
Pozzolan - Wikipedia, the free encyclopedia; which does confirm that pozzolans are used "to increase the long-term strength and other material properties of Portland cement concrete"; and, that they are "siliceous materials which react with calcium hydroxide to form calcium silicates".
But, the use of Coal fly ash as a chemical building block of cement isn't what this report is about.
As anyone who has worked on any kind of "construction" project, even if it's just anchoring the legs of the kids' swing set in the ground, almost instinctively knows, to get any kind of real strength out of cement, you have to add some large solid particles of stuff to it. Gravel and crushed stone will leap into the minds of anyone who has ever worked with the stuff, or seen broken chunks of it around construction projects.
That's one big reason we have "sand and gravel" companies.
The river "gravel", or crushed stone, are the larger chunks of hard stuff, the "aggregate", that, as the cement into which it has been blended sets, and shrinks just a little bit, creates the internal stresses that make the resulting concrete so much stronger than just the cement, by itself, would be.
And, just as Coal fly ash can be used in the making of the cement, it can also be utilized to make the aggregate that turns that cement into concrete.
As confirmed by our very own Consolidation Coal Company, Consol, in excerpts, with an additional links and excerpts appended, from the initial link in this dispatch to:
"United States Patent 5,364,572 - Process for Making High-Strength Synthetic Aggregates
Date: November, 1994
Inventors: Muh-Cheng Wu and George Wasson, PA
Assignee: Consolidation Coal Company, Pittsburgh
Abstract: A process for making high-strength aggregates including hydrating calcium oxide containing coal combustion ash for a sufficient period of time to convert a high percentage of the calcium oxide to calcium hydroxide prior to forming the aggregates and curing the aggregates in high humidity. The moisture of the hydrated material is monitored to vary the hydration moisture to the desired set point. Further, the process involves producing high-strength aggregates from calcium hydroxide containing FGD ashes such as generated from duct sorbent injection and spray dryer processes.
(Note, that, as we believe we have documented in previous reports, but, as we will affirm in reports to follow, compounds of Calcium and Sulfur, i.e., Calcium Sulfate, as can be formed by Flue Gas Desulfurization, "FGD", devices and scrubbers, can also be utilized in the making of cement and concrete, in addition to "coal combustion ash" itself. And, in fact, those compounds are crucial to this Consol process. They are needed, and, thus, in combination with siliceous fly ash, this represents a way in which two potentially objectionable Coal combustion byproducts can be utilized.)
Claims: Method of producing high-strength aggregates from calcium oxide (CaO) containing coal combustion ash (by) hydrating the ash (as described) so that at least 80% of the calcium oxide is hydrated to calcium hydroxide (and) adding enough water to the ash in the hydrator to densify the ash (and) pelletizing the hydrated ash from the hydrator with a rotary pelletizing disc.; and, curing the pelletized products at a temperature between 120 and 212 F in a curing chamber at a high humidity, greater than 90%, for 6 to 48 hours to develop high pellet strength.
(Basically, for "high humidity", at "212 F", you just boil water under it.)
Method of producing high strength synthetic aggregates from ... coal combustion ash.
Background and Filed: This invention relates to a process for producing high-strength synthetic aggregates from calcium oxide (CaO) containing flue gas desulfurization (FGD) ashes ... .
Summary: High-strength synthetic aggregates can be produced from CaO containing coal combustion ashes, such as those generated from a fluidized-bed combustion (FBC) unit and the Limestone Injection Multistage Burner (LIMB) process, and from the Ca(OH)2 containing coal combustion ashes, such as those generated from duct sorbent injection and spray dryer processes.
The pellet strength (meets specified) abrasion requirements for use in road construction. In addition to high strength, the pellets have several other useful properties for use as synthetic aggregates in road and structural construction. For example, the synthetic aggregates ... have suitable unit weight, grain size distribution, (specified) abrasion and soundness indices for use as coarse aggregates in road base, asphalt concrete and Portland cement concrete in road construction (and) synthetic aggregates from ... spray dryer ashes have suitable unit weight, grain size distribution for use as coarse lightweight aggregates in concrete masonry units."
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Consol actually covers a lot of somewhat disparate ground in the full Disclosure, as you might surmise even from our relatively brief and overly-condensed excerpts. Civil and concrete engineers could do a far better job of explaining and summarizing it all for anyone who's genuinely interested; and, if you live in Coal Country, you should be.The point of it all is that Coal combustion ashes arising from different points in a Coal exhaust stream can be utilized to manufacture both coarse and fine aggregates for concrete.
All as Consol a little later confirmed, in the subsequent:
"United States Patent: 6054074 - Manufactured Aggregates from Coal Combustion By-Products
Date: April, 2000
Inventors: Muh-Cheng Wu and George Wasson, PA
Assignee: Consol, Incorporated, Pittsburgh
Abstract: This is a method of producing manufactured aggregates from coal combustion by-products having sulfur. Recycle fines containing calcium hydroxide, an aluminum-containing material, and water are mixed together to form a feed mix which is agglomerated into an agglomerated product. The agglomerated product is combined with curing fines which contain calcium oxide which together form a blended mix. The blended mix is cured using the moisture in the blended mix which is used to exothermally hydrate the calcium oxide in the blended mix to form calcium hydroxide and which autogenically provides the required heat for curing and converts the calcium oxide in the blended mix to a dry calcium hydroxide-containing material to form aggregate products and dry fines. The aggregate products are separated from the dry fines, the dry fines are recycled to the mixing step and the aggregates are taken and used as a useful product for other purposes.
Claims: Method of producing manufactured aggregates from a combustion by-product (and) wherein the combustion by-product comprises fluidized-bed combustion by-product and ... pulverized coal fly ash.
Field: Aggregates, traditionally made from natural and crushed stone and sand, constitute about 80% by volume of concrete in structural materials and road construction. The consumption of natural aggregates in the United States is well over one billion tons per year. This invention relates to a process for producing manufactured aggregates from coal combustion by-product. The manufactured aggregates meet standard commercial specifications for road, lightweight and concrete aggregates, making them suitable for use in construction and agricultural applications. The replacement of natural aggregates with aggregates manufactured from coal combustion by-product could provide an opportunity for the high-volume use of and substantially expand the market for coal combustion byproduct.
Summary: We provide a method of producing manufactured aggregates from combustion byproduct. Combustion by-product containing sulfur are combined with recycle dry fines containing calcium hydroxide, an aluminum-containing material, and water. We mix the recycle dry fines containing calcium hydroxide, combustion by-product, aluminum-containing material, and the water to form a feed mix. We then agglomerate the feed mix into an agglomerated product. We then combine the agglomerated product with curing fines which contain between 5%-30% calcium oxide by weight of the curing fines and this produces a blended mix. We then cure the blended mix in a curing vessel to form aggregates and create recycled dry fines for recycling, during which moisture in the blended mix exothermally hydrates calcium oxide in the blended mix to form a dry calcium hydroxide-containing material and autogenically provides all of the required heat for curing and no external source of heat is required. We then separate the aggregates and the recycle dry fines and we then recycle the recycle dry fines which contain calcium hydroxide to the mixing step and the cycle is repeated.
We preferably provide that the combustion by-product comprises wet flue gas desulfurization sludge, and that the aluminum-containing material comprises fly ash."
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And, that is the essence of the thing: We can mix Coal "fly ash" with Coal exhaust "desulfurization sludge" and make little rocks out of 'em.
Then, we can sell those little rocks into a market that, according to Consol, uses "over one billion tons" of those little rocks "per year".
And, if that estimate seems high to you, consider that our United States Government's Geologic Survey, in:
http://minerals.usgs.gov/
projects, that, by "2020 U.S. production of crushed stone ... will be about 1.6 billion metric tons, while production of sand and gravel will be just under 1.1 billion metric tons".
Folks, that's a lot of danged fly ash we could potentially be putting to good, constructive use.
Even more so when you consider that's just for use in the aggregate.
If the Cement itself, as we have documented to be feasible and practical, and as we will further document to in coming reports to be so, were made in part of cementitious "pozzolans" derived from Coal ash, the total potential consumption of Coal Combustion Byproducts in various cement and concrete applications would be absolutely staggering.
Objections would be raised, of course. And, most of the ones we can foresee would be specious conjecture, which could be easily, and authoritatively, refuted.
The only question to be answered, really, is the same as that concerning the conversion of Coal, and the recycling of Carbon Dioxide, into hydrocarbons:
The technology to get it done is clear and established, so:
Why aren't we doing it?