New Material Provides Strong and Lightweight Alternative to Concrete – without Cement
We've earlier made report on the development, at Georgia Tech University, and other places, of processes wherein "fly ash", the residues of Coal combustion, primarily from electrical power generation plants, could be reclaimed and utilized in the production of a replacement for traditional cement.
Herein, via the above and following links, we wanted to affirm, and to provide a little more information about, those potentials; and, to highlight what might be one unrecognized benefit of them.
Comment, with additional links and excerpts, follows excerpts from the initial link to:
"New Use for Coal Ash: Material Provides Strong and Lightweight Alternative to Concrete – without Cement
Each year, coal-burning power plants, steel factories and similar facilities in the United States produce more than 125 million tons of waste, much of it fly ash and bottom ash left over from combustion. Mulalo Doyoyo has plans for that material.
An assistant professor in Georgia Tech’s School of Civil and Environmental Engineering, Doyoyo, has developed a new structural material based on these leftovers from coal burning. Known as Cenocell (TM), the material offers attributes that include high strength and light weight – without the use of cement, an essential ingredient of conventional concrete.
With broad potential applications and advantages such as good insulating properties and fire resistance, the “green” material could replace concrete, wood and other materials in a broad range of applications in construction, transportation and even aerospace.
“Dealing with the ash left over from burning coal is a problem all over the world,” said Doyoyo. “By using it for real applications, our process can make the ash a useful commodity instead of a waste product. It could also create new industry and new jobs in parts of the world that need them badly.”
Because it uses what is now considered a waste material to replace cement – which generates carbon dioxide, a greenhouse gas – the new material is considered an asset to the environment. The material can have a wide range of properties that make it competitive with concrete."
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The above article only hints at another advantage of using Coal fly ash in place of "cement - which generates carbon dioxide"; and, we'll address that a little more, following additional confirmation of the fact, that, Coal combustion ash can be utilized in the manufacture of structural products that replace such conventional, "Portland"-type cement.
Comment continues, following the link to, and excerpts from:
"United States Patent Application: 0100071597 - Fly Ash-Based Lightweight Cementitious Composition
Date: March, 2010
Inventor: Marianela Perez-Pena, IL
Assignee: United States Gypsum Company, Chicago
Abstract: A method of making a rapid setting lightweight cementitious composition with improved compressive strength for products such as boards is disclosed. The method mixes fly ash, alkali metal salt of citric acid and lightweight aggregate with water. Compositions which include fly ash, alkali metal salts of citric acid and lightweight aggregate are also disclosed.
Claims: A method of providing a lightweight cementitious mixture having improved compressive strength and water durability comprising:mixing water, reactive powder, an alkali metal salt of citric acid, and lightweight aggregate wherein the ... reactive powder (comprises) 75 to 100 wt. % fly ash, and 0 to 25 wt. % hydraulic cement and gypsum.
(And/or) wherein the reactive powder comprises 88.5 to 100% fly ash, no hydraulic cement and no gypsum, based upon weight of the reactive powder.
(So, note: Conventional "hydraulic cement" and "gypsum" aren't really needed, just "fly ash".)
(And) wherein the cementitious reactive powder further comprises silica fume.
(We note that Coal ash can contain quite a bit of "silica fume".)
Background and Field: This invention relates generally to fast setting cementitious compositions that can be used for a variety of applications in which rapid hardening and attainment of early strength is desirable. In particular, the invention relates to cementitious compositions that can be used to make boards with excellent moisture durability for use in wet and dry locations in buildings. Precast concrete products such as cement boards are made under conditions which provide a rapid setting of the cementitious mixture so that the boards can be handled soon after the cementitious mixture is poured into a stationary or moving form or over a continuously moving belt. Ideally, this setting of the cement mixture may be achieved as soon as about 20 minutes, preferably as soon as 10 to 13 minutes, more preferably as soon as 4 to 6 minutes, after mixing the cement mixture with a suitable amount of water.
(Note: The Coal fly-ash product being disclosed is for structural, water-resistant "wall board", more like "cement board", for those familiar with the construction trades, as opposed to "gypsum board" or "dry wall", which isn't really structural, and which isn't resistant to moisture. This ash-based product can, it seems, be used anywhere cement-based products could be used.)
The ... reactive powder blend of the cementitious composition is typically free of externally added lime.
A shorter setting time and higher early age compressive strength helps to increase the production output and lower the product manufacturing cost.
The very fast setting cementitious compositions of this invention can be used for a variety of applications in which rapid hardening and attainment of early strength is desirable. Using the alkali metal salt of citric acid, such as potassium citrate and/or sodium citrate, to accelerate setting of the cementitious composition, when the slurry is formed at elevated temperatures, makes possible increased rate of production of cementitious products such as cement boards.
A typical cementitious reactive powder of this invention comprises 75 to 100 wt % fly ash ... ."
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In other words, we can manufacture a high early strength cement-type structural material, suitable "for use in wet and dry locations in buildings", which could be composed of "75 to 100 wt %" of Coal plant "fly ash".
Aside from the fact that such Coal ash-based material would be replacing concrete, consider that it could, when cured, also replace wood in some applications, and we wouldn't have to cut down so many trees.
But, as we have previously documented, the process of making traditional, Portland-type, cement, by "calcining" Limestone in cement kilns, generates truly astonishing amounts of Carbon Dioxide.
Replacing Limestone in the manufacture of cement, with Fly Ash, actually results in a net reduction of overall Carbon Dioxide emissions from the processes of cement manufacture and Coal-power generation, if the amounts of CO2 arising from each were accounted separately and then totaled.
Documentation of that fact can be found in:
http://www.watancon.com/documentation/technical/Malhotra_-_Role_of_Fly_Ash_in_reducing_GGE.pdf
"Role of Fly Ash In Reducing Greenhouse Gas Emissions During The Manufacturing Of Portland Cement
V.M. Malhotra, Scientist Emeritus, Advanced Concrete Program, CANMET, Natural Resources Canada
Synopsis: This paper gives a global review of portland cement production and greenhouse gas emissions during its manufacturing. It is emphasized in the paper that fly ash is and will remain the major supplementary cementing materials for decades to come, and the concrete industry must concentrate its major efforts for the increased use of fly ash in concrete.
Not only is the manufacturing of portland cement highly energy intensive, it also is a significant contributor of the greenhouse gases.
The production of one tonne of cement contributes about 1 tonne of CO2 to the atmosphere.
(And, about) half of the CO2 emissions are due to the calcination of limestone."
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There are some estimates provided of the total amount of Cement made in the world, and, thus, the amount of Carbon Dioxide emitted by all of that associated cement-making. And that total is, especially with the contributions to it being made by developing countries, rather enormous.
The point is:
If we were to replace Limestone in the making of cement, "75 to 100 wt %" of it, with Coal plant "fly ash", then the total Carbon Dioxide emissions from both processes, taken together, could be reduced to almost just the total amount, maybe 25% more, of the CO2 emitted by generating electrical power through the combustion of Coal.
More than that, such practice would eliminate, or at least reduce, the need, and expense, of developing and implementing programs that are intended and designed to simply get rid of Fly Ash.
As with Carbon Dioxide, we can, and should, be looking at it as a resource, rather than as a waste.