Cement for Severe Environments - Cementitious Materials And Pozzolans, Industrial Projects, Sustainability - Concrete Construc
As should be apparent from our many reports on the topic, the science and technology for utilizing Coal Ash in the manufacture of Portland-type Cement, PC, and Portland-type Cement Concrete, PCC, is becoming very well established, and appears now to be growing at an accelerating pace.
That pace is creating changes in the Cement and Concrete industry that we, with our isolated and disabled circumstances, are wholly unable to keep up with and report accurately; that, especially so since some major natural resources companies have begun to take notice and invest in smaller companies who have developed Coal Ash utilization technologies, with resultant changes in corporate names and headquarters locations.
Further, some innovators in Cement technology, who are employing more Coal Ash in their formulations in concert with technology that's proprietary, but not qualified for patent protection, treat their compounds and processes as trade secrets, with only associated and required Material Safety Data Sheets revealing the presence of "aluminosilicate" materials that one could presume to be, or be derived from, Coal Ash.
And, thus, there isn't much substantive we can make report on in those cases.
We will do our best to keep you apprised of what we are beginning to perceive as a "mini", or focused, industrial revolution in the field of Cement and Concrete manufacturing, where Coal Ash really does seem to be playing an increasingly larger role; and, to that end, we introduce you herein to yet another player in the field of high-performance Coal Ash-based Cement.
First, we again remind you, as seen, for just one example, in:
West Virginia Coal Association | Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development; concerning: "United States Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; Assignee: New Jersey Institute of Technology; Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction and other applications, which hardenable mixtures demonstrate significant levels of acid and sulfate resistance";
that, the various Cements and Concretes which can be made from Coal Ash will, typically, have a far greater resistance to chemical attack and corrosion than conventional PC and PCC formulations.
And, such chemical resistance of Coal Ash Cement is, to a certain extent, the focus of our dispatch herein, as introduced by excerpts from the initial link to:
"Cement for Severe Environments; Concrete Construction; February, 2012
by: Peter VanderWerf (president of consulting firm Building Works Inc. and a professor at Boston College)
New cement chemistry creates concrete that withstands chemical attack and high temperatures.
Many concrete customers in industrial applications are turning to a new family of nonportland cements to increase the life of their physical plant and cut repair costs and downtime. Based instead on pozzolanics, these cements create concrete with a durability that outperforms conventional concrete in laboratory tests and in the field. When repair is necessary, their rapid set times bring facilities back to service faster.
Concrete is usually thought of as a durable building material. But in some severe environments, portland cement-based concrete is not tough enough. Acids present in petrochemical production, food processing, and wastewater steadily eat away at portland cement concretes in floors and containment structures until they become unusable. Extreme heat of metal processing eventually decomposes the cement paste.
Users of these high-demand applications are searching for new mixes, admixtures, and coatings that make concrete last longer in corrosive and high-temperature conditions. And they have a strong economic incentive. Concrete deterioration can make processes inefficient in the short run, and eventually force concrete repairs or replacement. The cost of repair can be substantial, but the indirect cost of stopping production to make repairs is worse. The facility loses output and revenue, schedules may be missed, and the effect ripples through the entire operation.
A variety of methods have been used to improve the durability of conventional concrete made with portland cement. Unfortunately, these alternatives have their limits. Adding inert, fine-particulate minerals, such as fly ash or silica fume, is a common practice intended to increase durability for portland cement concrete that comes into contact with corrosive liquids and gases. These minerals fill the capillaries within the concrete crystal structure, which reduces the penetration of fluids and slows their attack, but does not stop it.
(Note in the above that they are talking about just adding Coal Ash to the Concrete as an aggregate, which is still a pretty good practice, not making the Cement itself from Coal Ash.)
Another alternative is to put a chemically resistant coating, usually an epoxy, over the exposed concrete surfaces. These modern coatings stand up well to corrosives, but the cost is so high that use is restricted to a few areas considered most vulnerable. Also, it can be difficult to achieve and maintain an effective seal.
In all of these cases of chemical deterioration, the weak link in the mix is the portland cement. Durable aggregates typically are available if needed. However, the paste produced by portland cement is composed principally of calcium hydroxide and calcium silicate hydrates. These break down in the presence of corrosive and caustic chemicals—even when using a Type II or Type V portland cement.
Measures to resist heat run into similar roadblocks. The calcium silicate hydrates of portland cement decompose when exposed to temperatures above 250 F (120 C). Some minerals improve concrete’s heat resistance by increasing the density of the paste, but as with chemical corrosion, the calcium silicate hydrate is still vulnerable. As the cement paste loses strength, eventually both it and the aggregates it is intended to bind with begin falling off in pieces
The new industrial cements are the product of materials company, Ceratech Inc. They consist of entirely different compounds, more like the pozzolanics used in the ancient Roman Coliseum and aqueducts that are still standing today. Ceratech cements are 95% fly ash, combined with chemical activators that give them a robust cementing action. This chemistry replaces all of concrete’s portland cement with recycled material, something that greatly decreases the concrete’s carbon footprint.
Most importantly for industrial applications, these cements create a paste entirely out of fine, inert materials. The concrete is denser, without the interconnected capillaries of conventional concrete, making it resistant to both chemicals and heat.
This cement in a typical mix can achieve a 28-day compressive strength of about 8000 psi. All the cements in this company’s line offer greater chemical and heat resistance than portland cement, but some are formulated specifically to increase one property or another. Concrete made with the most chemically resistant product (known as Kemrok) maintained its material mass and compressive strength sharply longer than portland cement concrete in a series of exposure tests with sulfuric, nitric, acetic, and hydrochloric acids. Concrete with the most heat-resistant cement (Firerok) withstands sustained temperatures of 570 F (300 C) and intermittent temperatures of 1850 F (1000 C).
The relatively rapid set time of this cement is a plus in repair situations. According to Ceratech’s president Jon Hyman, “Depending on the product used, 24-hour compressive strengths of concrete mixes range from 2100 to 4800 psi. One of the great things about this cement chemistry is that it produces both high early and high ultimate strengths without extra measures. If we can get a million-dollar-per-week wastewater plant or industrial production facility online a day or two faster, the payoff is huge.”
Precasters have begun to develop wastewater containment structures made with the new cements. The traditional approach in this application is to apply coatings over the concrete surfaces that will be most exposed to high-sulfate water. But with pozzolanic cements they can create a monolithic product that is resistant to sulfates everywhere, eliminating concerns over the cost and quality of the coating work.
The sustainability of the new cements is a side benefit. They use 95% recycled material (fly ash) and 5% renewables (curing activators). “Besides keeping coal ash out of landfills, our products are entirely carbon neutral,” says Hyman. “We don’t burn fossil fuels and release carbon dioxide the way portland cement does.” Greener concrete is a plus in today’s sustainable-construction market. “We like being able to work with a ‘green’ product that offers superior performance”.
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As a full read of the above article will affirm, even "Ceratech", who confess that their Cement is "95%" Coal Ash, are mum, to certain extent, about that remaining "5%". But, what they do say about all of it should be encouraging to anyone interested in Coal, and all associated Coal-use industries, as we can learn on Ceratech's web site:
Ceratech Inc.;
"Can Be Used For Virtually Any Application That Currently Utilizes Portland Cement;
Outperforms Portland Cement For Durability, Sustainability and Value!
Profound Environmental Implications: Ceratech's revolutionary carbon neutral cement technology utilizes no portland cement nor does it require extensive amounts of raw minerals and energy resources to produce.
Certatech's cement eliminates one ton of CO2 for every ton of portland cement it displaces while producing a highly durable, high performance concrete."
(As we've previously documented for you a number of times, the calcination of limestone, CaCO3, to produce Portland Cement, primarily Calcium Oxide, generates Carbon Dioxide via the equation:
CaCO3 + Heat = CaO + CO2.
Thus, for each molecule of limestone we can replace or displace, we prevent at least one molecule of Carbon Dioxide from being generated. We say "at least" since the source of heat for the calcination process is likely to be generating CO2 of it's own.)
Incorporated in 2002, Ceratech, Inc. is a clean technology company that has successfully developed and commercialized the world's first carbon neutral "green" cement.
Ceratech's core technology converts industrial waste by-products produced by coal-fired power generation plants into hydraulic cements that are an alternative to portland cement for the production of concrete.
Ceratech's carbon neutral cement is the most environmentally responsible cement available in the market today. Our cement meets and/or exceeds the most stringent engineering requirements, is compatible with all existing batch, delivery, placing and finishing techniques, and provides exceptional durability for infrastructure and industrial applications.
It is our mission to develop and deliver to the market, carbon neutral cements that deliver superior performance at a competitive price. We are committed to sustainable development that meets the needs of the present, without comprising the ability of future generations to meet their own needs by delivering products to the market that are carbon neutral, comprised principally of industrial by products (>90%) and are more durable than traditional materials.
Sustainability Technology: What is Carbon Neutral, Green Cement? A cementitious material that incorporates and optimizes recycled materials, therefore reducing the impact on natural raw materials, water, consumption of energy, and green house gas emissions like CO2. In practice, the manufacturing of Green Cement will be accomplished by reducing and ideally eliminating, the production of damaging green house gasses. Green Cement's performance characteristics must by definition meet or exceed, the functional performance capabilities of conventional cementitious materials for concrete and concrete products.
The United States GREEN Building Council (USGBC), defines sustainable construction as "the ability to meet present needs without compromising the ability of future generations to meet their needs."
Ceratech's cement technology clearly and profoundly accomplishes these objectives and definitions via a simple, near zero energy processs of combining an abundant and sustainable waste stream with a rapidly renewable, agriculturally based product.
Ceratech's cement technolgy has been described as "triple green," due to its substantial reduction in landfillling of coal ash, CO2 greenhouse gas mitigation by the displacement of portland cement, elimination of virgin mineral resources, 50% reduction in mix water requirements and its virtually energy free production process.
In its 12 year history, Ceratech has displaced more CO2 than all other alternative cement technologies combined.
To Date, Ceratech Has Diverted Over 100K Tons of Waste Ash From Landfills & Eliminated 100K Tons of CO2 Greenhouse Gas Through The Displacement of Portland Cement."
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In honesty, "100K Tons of Waste Ash" diverted from landfills and "100K Tons of CO2" emission prevented ain't, in the grand scheme of things, that big of a bunch.
But, it is a start, God bless 'em. And, the size of the potential market for Coal Ash in PC and PCC is vast. We could, if we put our minds to it, use up virtually all of the Coal Ash we produce, and prevent a lot of CO2 from being generated in the making of Portland-type Cement.
And, we do note that Ceratech are at work developing their own, enhanced technology for utilizing Coal Ash in the making of their "Triple Green ... carbon neutral cements", as seen, for one example, in:
"United States Patent: 8186106 - High Strength Cement ... and Concrete Including Industrial By-Products
(High strength cement, mortar and concrete including industrial by-products - CeraTech, Inc.)
Date: May, 2012
Inventors: Glenn Schumacher, et. al., MD
Assignee: CeraTech, Inc., VA
Abstract: Cementitious compositions in which the cementitious properties of fly-ash are carefully controlled. The cementitious compositions may be substantially free harsh acids and bases such as citric acids and alkali metal activators including alkali hydroxides and metal carbonates. The use of these harsh chemicals creates acid base reactions during use of the products. Instead of these harsh chemicals, a citric salt, for example potassium citrate, may be used as a reaction accelerator. Boric compounds may be used as a retarder in the compositions.
Claims: An article of manufacture comprising a hydrated and hardened cement composition comprising a pozzolan powder; two or more activators, at least one of which has a pH between 6 and 9; and a retarder, wherein the hydratable cement has a calcium content expressed as the oxides of 15 wt % or more based on the total weight of the hydratable cement; and wherein said activator having a pH of between about 6 and about 9 accounts for greater than 50% of the total weight of activators in said hydratable cement.
An article of manufacture comprising a hydrated and hardened cement composition comprising a pozzolan powder; one or more pH neutral activators; and a retarder, wherein the hydratable cement has a calcium content expressed as the oxides of 15 wt % or more based on the total weight of the hydratable cement, and wherein the pH neutral activators account for greater than 50% of the total weight of activators in said hydratable cement; and wherein the hydratable cement has less than 20% by weight Portland cement based on the total weight of the hydratable cement.
Background and Field: A novel family of compositions is disclosed for the production of blended hydraulic cementitious materials and their concrete and mortar derivatives for original construction, repair, precast block, armor, spray and other applications.
These materials exhibit controlled reactions of calcium-containing industrial byproducts with chemical activators, retarders, bond enhancers and mechanical strength modifiers.
Materials with pozzolanic properties contain glassy silica and alumina that will, in the presence of water and free lime, react with the calcium in the lime to produce calcium silicate hydrates. There are both natural and industrial pozzolans.
Industrial pozzolans are produced during industrial processes and include, for example, Class C and Class F fly-ashes. These fly-ashes are produced during the combustion of coal."
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And, again, note that the disclosed Coal Ash-based "Cement" is considered to be "High Strength", in addition to, as implied by the accompanying articles, being "resistant to sulfates everywhere" and even notably "heat-resistant", all while being "Triple Green" and very nearly "carbon neutral".
That's sounding kind of tough to beat, ain't it?
In any case, there will be more to follow on "CeraTech, Inc." and their Coal Ash-based Cement technology.
But, again, that is because there is good information about them "out there" that we, with our sadly limited capacities, can access and work with.
There is a lot, relative to the productive utilization of our Coal Ash, "going on". And, it all goes to prove, that, rather than being some sort of "hazardous" waste, Coal Ash is valuable mineral resource.
We can, according to all the information provided herein, consume and utilize Coal Ash in the making of replacements for Portland Cement and Portland Cement Concrete; replacements and substitutes consisting of "95%" Coal Ash that are better, in terms of final properties, economics and environmental impact than those traditional, conventional Cement and Concrete materials.
