Geopolymer Concrete Protects against Corrosion
We've previously documented that Coal Ash can serve both as a raw material for making Portland-type Cement and as a fine aggregate for that Cement, to make Portland-type Cement Concrete; as seen, for two examples, in our reports of:
West Virginia Coal Association | Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development; concerning: "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998; Assignee: Dravo Lime Company, Pittsburgh (PA); Abstract: Cement is produced by forming a moist mixture of a flue gas desulfurization process waste product containing 80-95 percent by weight calcium sulfite hemihydrate and 5-20 percent by weight calcium sulfate hemihydrate, aluminum, iron, silica and carbon, agglomerating the moist mixture while drying the same to form a feedstock, and calcining the dry agglomerated feedstock in a rotary kiln (and) wherein said source of aluminum and iron comprises fly ash"; and:
West Virginia Coal Association | "Concrete of the Future" Made with Coal Ash | Research & Development; concerning the 2012 article: "'Benefits of High Volume Fly Ash: New Concrete Mixtures Provide Financial, Environmental and Performance Gains'; High volume fly ash (HVFA) concrete mixtures offer many benefits, including reduced cost, reduced energy content, enhanced environmental sustainability, and improved long-term performance".
And, as indicated in the above "Benefits of High Volume Fly Ash", the use of Coal Ash in Portland-type Cement Concrete offers a number of advantages, primary among them "improved", for reasons pertaining to greater strength and higher corrosion resistance, "long-term performance".
However, as we have begun to document in a few previous reports, there is a "new" type of construction material, which, with potentially better properties and better, more time- and energy-efficient processing characteristics, has been under development over just the last decade or so.
"Geopolymers" are a class of mineral-based compositions arising from alkali-silicate reactions that can serve in many or all of the traditional applications for Portland Cement Concrete, PCC, and seem to offer even greater improvements on the performance of even PCC utilizing Fly Ash as a fine aggregate. In point of fact, they seem to be taking the chemical reactions that occur in PCC filled with Coal Ash aggregate a step further, making them the foundation of the solidification process.
More information concerning "Geopolymers", and their benefits, is made available by the Federal Highways Administration, in their Concrete Pavement Technology Program's "Tech Brief":
http://www.fhwa.dot.gov/
Even more about them can be learned via:
Geopolymer Institute and Geopolymer - Wikipedia, the free encyclopedia; "Geopolymers are new materials for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation and new cements for concrete".
Among our few past reports on Geopolymers made with Coal Ash is:
West Virginia Coal Association | Louisiana Coal Ash Protects Concrete from Corrosion | Research & Development; concerning: "United States Patent Application 20120156381 - Geopolymer Mortar and Method; 2012; Inventors: Erez Allouche and Carlos Montes, Louisiana; (Presumed eventual Assignee of Rights: Louisiana Tech University); Abstract: A geopolymer mortar formed by mixing about 35% to about 45% by weight pozzolanic material, about 35% to about 45% by weight silicon oxide source, about 15% to about 20% by weight alkaline activator solution, and about 0.3% to about 2.5% by weight copper ion source. The pozzolanic material may be fly ash and the silicon oxide source may be sand".We'll have more on the above "Application 20120156381 - Geopolymer Mortar and Method" presently; but, since Louisiana Tech University, based on related information, was the presumed eventual Assignee of Rights to that method of making Geopolymer from Coal Ash, following, as excerpted from the initial link in this dispatch, is a report, from Louisiana Tech, describing some of their advantages:
"'Geopolymer Concrete Protects against Corrosion'; By Jay Landers; May 29, 2012; (The headline is followed by a photograph of concrete embedded with rebar, and bears the caption: "In tests in which samples were exposed to a chloride environment, steel reinforcement embedded in concrete made with geopolymers exhibited far less corrosion than those embedded in concrete made with portland cement. Courtesy of Louisiana Tech University’s Trenchless Technology Center".) A new form of concrete made with geopolymer binders rather than portland cement exhibits high strength, low permeability, and high resistance to corrosion and heat.
A novel form of concrete made from geopolymer binder technology developed by researchers at Louisiana Tech University is stronger and more resistant to corrosion and high temperatures than portland cement, potentially offering an ideal product for replacing the traditional construction material in harsh environments. For example, the geopolymer concrete recently performed well serving as a refractory surface at a facility used to test rocket engines.
Because its main ingredient is an industrial by-product, the geopolymer binder technology requires much less energy to produce and results in significantly less carbon dioxide emissions relative to portland cement, making it a more environmentally sustainable option as well.Geopolymers represent a class of cementitious materials that harden and gain strength without the use of portland cement.
Although a variety of materials may be used to create geopolymers, the basic components are a fine-powdered material rich in aluminum and silica - - including fly ash ... - - and sodium hydroxide, potassium hydroxide, or another alkali to cause the aluminum and silica to leach out of the powdered material. “We can use a variety of waste products or natural sources to get the powder that we are looking for,” says Erez Allouche, Ph.D., P.E., M.ASCE, the director of Louisiana Tech University’s Trenchless Technology Center.
Fly ash has turned out to be the main ingredient of choice for Allouche and his colleagues.
A by-product of coal combustion, fly ash represents a readily available material in the United States ... .Geopolymers differ from portland cement in that their setting mechanism depends on polymerization rather than hydration. As a result, geopolymers can achieve their significant maximum strength within 3 to 5 days, depending on the curing effort applied, whereas portland cement typically may require as much as a month to achieve most of its strength and an entire year to achieve full completion.
While offering the same ease of application as portland cement, geopolymer technology provides such benefits as early high compressive and tensile strengths, low permeability, and high resistance to corrosive agents and elevated temperatures.
Although the concept of geopolymer binders has existed since the early 1950s, efforts to commercialize the technology have yet to succeed on a widespread basis. “It’s a very novel technology, with substantial challenges in taking the concept from the lab to the field,” Allouche says. Among the major challenges that he and his colleagues have had to overcome is the variability of fly ash, which, as a byproduct of coal combustion, can possess varying characteristics depending on such factors as the type and quality of the coal source and how it is burned and cooled.
To address this variability, the researchers collected approximately 60 fly ash samples from around the world. After characterizing the materials within each sample, the researchers created a geopolymer formulation suitable for each. Based on this work, the researchers developed a database summarizing the different properties of the various fly ash samples and created software that enables them to predict certain mechanical properties of geopolymer binders made from different fly ash samples. In this way, the researchers can account for the variability associated with the use of an industrial byproduct, enabling them to create an “engineered product that has predictable properties,” Allouche says.
Allouche and his colleagues have also developed various admixtures for use in manipulating the material so as to enable it to be applied in different ways or to achieve certain setting times or mechanical strengths. Geopolymer concrete can be used in structural and nonstructural applications and made either by precast, cast-in-place, or spray-applied methods.
(The) geopolymer technology can be produced using essentially the same equipment and processes as that used to create portland cement.
For its part, the geopolymer concrete is a “more finicky material” than portland cement, Allouche acknowledges, as it requires greater precision during the process of mixing ingredients.
However, geopolymer concrete offers certain clear advantages from an environmental standpoint. For example, portland cement production requires significant quantities of energy and generates billions of tons of carbon dioxide annually. By comparison, production of some formulations of geopolymer binder technology requires 90 percent less energy and 85 percent less carbon dioxide emissions.In terms of mechanical properties, geopolymer technology can achieve a compressive strength of up to 16,000 psi in as little as 24 hours, while resisting corrosion by acids and sulfates as well as temperatures of up to 3,200°F.
With its high strength and resistance to corrosion and extreme temperatures, geopolymer technology offers a potentially favorable alternative to portland cement in certain specialized applications. For example, geopolymer technology shows considerable promise in applications for which portland cement requires the use of an epoxy or other coating to protect against corrosion. If such coatings fail, they typically do so because of a problem with the bond, or the interface between the protective layer and the underlying portland cement, Allouche says. However, geopolymer technology is a single component that does not rely on an outer coating for protection. “There’s no interface to fail,” Allouche notes.
As part of a recent examination of its refractory capabilities, the geopolymer binder technology was applied as test patches within a concrete plume trench at the John C. Stennis Space Center, a facility in Hancock County, Mississippi, that is used by the U.S. National Aeronautics and Space Administration (NASA) to test rocket engines. Subjected to extremely high temperature and thrust loads during testing of the rocket engines, the plume trenches must be made of very strong materials. During the first test of the geopolymer technology in early May, the test patches were subjected to temperatures of roughly 2,700°F to more than 4,500°F, as well as up to 400,000 lb of thrust from the rocket engines. The geopolymer patches held well during the test, showing little wear and no sign of melting. “From an aesthetic prospective, the geopolymer surface looked even better following the test,” Allouche says. Future tests of the material at the site are planned beginning this summer.
Among a handful of other installations to date, the technology also has been used with success to construct an acid spill pad at an Arkansas manufacturing facility, Allouche says. The manufacturer needed to protect its loading dock against corrosion, which frequently resulted when acidic materials used as part of the production process leaked onto the dock. Since being installed on the loading dock in July 2011, the geopolymer technology has prevented corrosion. “So far, so good,” Allouche says. As for other potential applications in corrosive environments, the geopolymer technology likely would work well as bridge decking in marine environments, such industrial applications as petrochemicals and food processing, and pipelines, manholes, and storage facilities for wastewater, Allouche says.
As one of the most well-established construction products around, portland cement enjoys considerable economies of scale, helping to lower production costs. Therefore, geopolymer concrete is not intended to replace portland cement, Allouche says. Rather, the technology, with its unique mechanical characteristics, is expected to “supplement” its more conventional counterpart, he notes. Although geopolymer concrete is more expensive to make, it has been shown to come within 10 to 30 percent of the cost of portland cement on certain applications, Allouche says.
With its strength and resistance to extreme temperatures and corrosion, geopolymer technology could help engineers in their efforts to design and construct more enduring facilities. Because of the high cost associated with replacing critical infrastructure, care should be taken to construct such infrastructure using materials that will last much longer than what is currently considered possible, Allouche says. “We have to use materials that last hundreds of years, not tens of years,” he says."
------------------
Well, we don't know. If Coal Ash Geopolymer costs, maybe, "30 percent" more to make than conventional Portland Cement and Concrete, but, as in "materials that last hundreds of years, not tens of years", lasts a whole order of magnitude of time longer than PCC, how, in the world, could the slight additional expense not be easily justified, especially when such use would make unnecessary otherwise required expenses, with no return, for Ash disposal?
Clearly: Geopolymer made from Coal Ash is a viable alternative to conventional Portland-type Cement Concrete, especially so in some more or less severe environments.
Much of that is again confirmed via:
Louisiana Tech University researcher wins Governor's Technology Product of the Year award; "'Louisiana Tech University Researcher Wins Governor's Technology Product of the Year Award'; September 24, 2012; Dr. Erez Allouche, associate professor of civil engineering and director of the Trenchless Technology Center at Louisiana Tech University, has been honored by the Louisiana Technology Council with the 2012 Louisiana Technology Product of the Year award for his innovative "green" geopolymer concrete technology. "This award is a great honor," says Allouche. "I view it as recognition of the value and commercial potential of the technology by Louisiana's business community, and a strong affirmation that our technology development efforts are on the right track." ... In May, Allouche received the "eWARD" for his geopolymer concrete technology for the Shreveport/Bossier City Northern Louisiana region from the Louisiana Technology Council and the North Louisiana Economic Partnership. "Dr. Allouche has received strong support for his novel geopolymer research from utility companies, product manufacturers, contractors and government agencies," said Dr. Les Guice, executive vice president and vice president for research and development at Louisiana Tech. "His innovations are already attracting global commercial interests." Over the past few years, Allouche has led a team of researchers at Louisiana Tech to develop patented geopolymer binder technology with recent emphasis on commercialization in the field of high-end refractory materials. The unique process uses a sodium silicate based polymer to convert a waste by-product, specifically fly ash from coal-fired power plants, into a high performance refractory and corrosion resistant material. Compared to Portland cement, which is an industry standard in concrete construction, geopolymer technology reduces the "carbon-footprint" by 90 percent and energy consumption by 85 percent. Allouche has also developed methods for dry casting, extruding, and spraying geopolymer concrete to create a variety of products ranging from precast pipes to manhole coatings. One of the most notable products is a high-temperature product known as HTGeopolymerTM that can be used in refractory products or used as a corrosion resistant material".-------------------
The advantages of Coal Ash-based Geopolymer are further highlighted in:
'Green' Research Results In New Geopolymer Concrete Technology; "'Green' Research Results In New Geopolymer Concrete Technology; 2009; Dr. Erez Allouche, assistant professor of civil engineering at Louisiana Tech University and associate director of the Trenchless Technology Center, is conducting innovative research on geopolymer concrete and providing ways to use a waste byproduct from coal fired power plants and help curb carbon dioxide emissions. Inorganic polymer concrete (geopolymer) is an emerging class of cementitious materials that utilize "fly ash", one of the most abundant industrial by-products on earth, as a substitute for Portland cement, the most widely produced man-made material on earth. Portland cement production is a major contributor to CO2 emissions as an estimated five to eight percent of all human-generated atmospheric CO2 worldwide comes from the concrete industry. Production of Portland cement is currently toping 2.6 billion tons per year worldwide and growing at 5 percent annually. Geopolymer concrete has the potential to substantially curb CO2 emissions (and to) produce a more durable infrastructure capable of design life measured in hundreds of years instead of tens. In comparison to ordinary Portland cement (OPC), geopolymer concrete (GPC) features greater corrosion resistance, substantially higher fire resistance (up to 2400° F), high compressive and tensile strengths, a rapid strength gain, and lower shrinkage. Perhaps Geopolymer concrete's greatest appeal is its life cycle greenhouse gas reduction potential; as much as 90% when compared with OPC".
-----------------------
And, finally, given all the above economic and environmental advantages of substituting a "Geopolymer" made from Coal Ash for "OPC" - "Ordinary Portland Cement" and Portland Cement Concrete, we learn that our government's technical experts in the US Patent and Trademark Office just recently confirmed the practicality of the process disclosed in Dr. Erez Allouche's "United States Patent Application 20120156381 - Geopolymer Mortar and Method", via issuance of:
United States Patent: 8512468 - Geopolymer Mortar and Method
Patent US8512468 - Geopolymer mortar and method - Google Patents
Date: August 20, 2013
Inventors: Erez Allouche and Carlos Montes, LA
Assignee: Louisiana Tech University Research Foundation, Ruston, LA
Abstract: A geopolymer mortar formed by mixing about 35% to about 45% by weight pozzolanic material, about 35% to about 45% by weight silicon oxide source, about 15% to about 20% by weight alkaline activator solution, and about 0.3% to about 2.5% by weight copper ion source. The pozzolanic material may be fly ash and the silicon oxide source may be sand. The alkaline activator solution may be a sodium hydroxide solution containing sodium silicate. The geopolymer mortar may have a viscosity in the range of about 25,000 to about 50,000 centipoise. The geopolymer mortar may be formed by further mixing one or more additives, such as surfactants, thermal spheres, anti-sagging agents, adhesion primers, or fibers. The geopolymer mortar may be applied as a protective coating on a surface of a structure.
(Concerning the above "thermal spheres", and what they might be, see, for one example, our report of:
West Virginia Coal Association | Georgia Tech Recycles Coal Utilization Byproducts | Research & Development; concerning: "United States Patent 8,057,594 - High Strength Pozzolan Foam Materials and Methods of Making Same; 2011; Assignee: Georgia Tech Research Corporation, Atlanta, GA; Abstract: The various embodiments of the present invention relate generally to high strength foam materials and methods of making the same. More particularly, various embodiments of the present invention relate to high strength foam materials comprising pozzolans, such as cenospheres derived from fly ash".)
Claims: A composition of matter formed by the mixing of the components comprising:
(a) about 35% to about 45% by weight fly ash;
(b) about 35% to about 45% by weight sand;
(c) about 15% to about 20% by weight alkaline activator solution;
(d) about 0.3% to about 2.5% by weight copper ion source; and:
(e) about 0% to about 2.2% by weight fibers.
The composition of matter ... wherein the fly ash is predominantly class C or class F fly ash.
Description and Background: Corrosion and deterioration of concrete pipes, manholes, wet wells, chambers, tunnels, diversion boxes, pump stations, drop structure reservoirs and treatment basins due to sulfuric acid attack is a major concern associated with wastewater conveyance and treatment facilities. Traditional cementitious materials such as Portland cement are inexpensive, but do not offer longevity under wastewater conveyance and treatment conditions. Concrete pipes are chemically attacked when subjected to acids with pH values of 6.5 or lower for extended periods of time. The pH in sewer lines can reach values of 2 or 3, and in some extreme cases 0.5. The highly acidic environment in sewer pipe lines and wastewater treatment facilities significantly reduces the life of these buried structures, causing significant financial losses.
Efforts have been made to address issues with concrete and brick surfaces in wastewater collection and treatment systems such as susceptibility to corrosion, cracking, and lack of long-term durability in harsh environments. For example, additives have been added to Portland cement in an effort to enhance the corrosion resistance of the Portland cement. Attempted additives include silica fume, fly ash, and blast furnace slag.
Another example of an attempted method of protecting concrete surfaces is the addition of a thin layer of chemically resistant material (e.g., polyurethane, polyurea, epoxy, mortar epoxy, high alumina cement, or asphalt) on the inner surface of concrete pipes or other concrete surfaces. Difficulties with the addition of these thin layers include issues with ensuring adequate bonds between a spray-on coating and the host concrete surface, formation of pinholes that allow sulfuric acid and/or bacteria to penetrate the coating and destroy the bond between the coating and the host concrete surface, ensuring proper coverage at joints of concrete pipes, and construction related damage to the coating during installation. Also, both of these efforts significantly increased costs of construction and operation.
Geopolymers are inorganic alumino-silicate amorphous polymers formed by chemical reactions under highly alkaline conditions between an active pozzolanic material, such as fly ash ... and an activator solution (e.g., a mixture of sodium hydroxide and an alkaline silicate such as sodium silicate or potassium silicate). Polymeric chains form when a pozzolanic material comes in contact with an alkaline activator solution. The geopolymer net consists of SiO4 and AlO4 tetrahedra linked together by shared oxygen atoms.
Geopolymers exhibit excellent compressive resistance (up to 120 MPa) and rapid strength gain, with 95% of their ultimate strength achieved in as little as three days under proper curing conditions. Geopolymers also exhibit low vulnerability to chemical attacks, and are practically inert to attack by sulfate salts because they are not based on calcium silicate. Because they are composed of an alkaline silicate net, geopolymers are also inert to alkali-aggregate reaction, which is a common concern with Portland cement.
Summary: A geopolymer mortar formed by mixing about 34% to about 46% by weight pozzolanic material, about 34% to about 46% by weight silicon oxide source, and about 15% to about 20% by weight alkaline activator solution, and about 0.3% to about 2.5% by weight copper ion source. The pozzolanic material may be fly ash or metakaolin. The silicon oxide source may be sand. The alkaline activator solution may be composed of a liquid sodium silicate and a sodium hydroxide solution. The geopolymer mortar may be applied to concrete or brick surfaces, and may serve as a corrosion resistant barrier. The copper ion source may provide a bactericidal property to the geopolymer mortar. The geopolymer mortar may have a suitable viscosity for spray application. The geopolymer mortar may be formed by further mixing in one or more additives including, but not limited to, surfactants, thermal spheres, colloidal silicas, adhesion primers, and fibers.
The various embodiments of the geopolymer coating offer high corrosion resistance, bactericidal properties, low costs of production, and rapid and easy application. The geopolymer coating may have enhanced viscosity and surface tension suitable for its application as a mortar coating using manual or mechanical means.
The geopolymer coating may be used as a protective coating for the rehabilitation and reconstruction of concrete or brick surfaces of structures used for the transportation, storage, and treatment of wastewater streams from municipal and industrial sources including, but not limited to, pipes, manholes, wet wells, chambers, tunnels, diversion boxes, pump stations, drop structures, reservoirs, clarifiers, and primary and secondary retention and treatment basins. The geopolymer coating may also be used as a coating for tunnels and mine shafts where acidic conditions are the main source of deterioration of the supporting structures. The geopolymer coating may be applied using conventional techniques for cementitious linings including, but not limited to, spraying, pumping, flooding, and trowelling.
A geopolymer mortar formed by mixing about 34% to about 46% by weight pozzolanic material, about 34% to about 46% by weight silicon oxide source, and about 15% to about 20% by weight alkaline activator solution, and about 0.3% to about 2.5% by weight copper ion source. The pozzolanic material may be fly ash or metakaolin. The silicon oxide source may be sand. The alkaline activator solution may be composed of a liquid sodium silicate and a sodium hydroxide solution. The geopolymer mortar may be applied to concrete or brick surfaces, and may serve as a corrosion resistant barrier. The copper ion source may provide a bactericidal property to the geopolymer mortar. The geopolymer mortar may have a suitable viscosity for spray application. The geopolymer mortar may be formed by further mixing in one or more additives including, but not limited to, surfactants, thermal spheres, colloidal silicas, adhesion primers, and fibers.
The geopolymer coating is a mixture of a pozzolanic material, an alkaline activator solution, a silicon oxide source, and a copper ion source. The pozzolanic material may be class C fly ash, class F fly ash (and) capable of forming a corrosion-resistant and chemically-resistant geopolymer when mixed with an alkaline activator solution. The alkaline activator solution may be a mixture of an alkaline silicate and a sodium hydroxide solution or a mixture of an alkaline silicate and a potassium hydroxide solution. The alkaline silicate may be sodium silicate or potassium silicate.
(Tests) performed on geopolymer samples prepared with ... class F fly ash exhibited good early compressive strength and high corrosion resistance to sulfuric acid. Geopolymer samples formed with class C fly ash displayed high compressive strength at an early stage.
The various embodiments of the geopolymer coating offer high corrosion resistance, bactericidal properties, low costs of production, and rapid and easy application. The geopolymer coating may have enhanced viscosity and surface tension suitable for its application as a mortar coating using manual or mechanical means.
The geopolymer coating may be used as a protective coating for the rehabilitation and reconstruction of concrete or brick surfaces of structures used for the transportation, storage, and treatment of wastewater streams from municipal and industrial sources including, but not limited to, pipes, manholes, wet wells, chambers, tunnels, diversion boxes, pump stations, drop structures, reservoirs, clarifiers, and primary and secondary retention and treatment basins. The geopolymer coating may also be used as a coating for tunnels and mine shafts where acidic conditions are the main source of deterioration of the supporting structures. The geopolymer coating may be applied using conventional techniques for cementitious linings including, but not limited to, spraying, pumping, flooding, and trowelling."
-----------------------
Our excerpts, we know, are far too long; but, the importance of the technology embodied within the included documents likely can't be overemphasized:
Starting with Coal Ash, we can manufacture a coating and a reconstruction "mortar" for our concrete infrastructure that will resist chemical attack and thermal stress far better than Ordinary Portland Cement Concrete, "OPC".
Further, the Coal Ash Geopolymer disclosed herein can be even stronger than OPC; and, used as a protective or restorative coating for concrete structures, it performs at least as well as, but is far less expensive than, the various polymers, like epoxies, that have traditionally been used.
Moreover, if used as a direct replacement for some or all of the OPC in new construction, the Coal Ash Geopolymer would result in structures that could last as much as ten times longer; require much less energy to be used in manufacturing the materials of their construction; and, be responsible for the emission of much less, perhaps 90% less, CO2 in the manufacturing of those conventional materials.
All of those advantages have been recognized by others; and, as we will see in reports to follow, the manufacture of Geopolymers, and the demand for raw materials such would entail, could well change our perception of Coal Ash, from noxious solid waste we must, at some great expense, somehow dispose of, to valuable raw material resource, from which we can construct an enduring, economically and environmentally better, infrastructure.