United States Department of Transportation
i
Design and Application of High-Volume Fly Ash Self-Consolidating Concrete With the Incorporation of Nanoparticles
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2012-01-01
[PDF-4.10 MB]
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TRIS Online Accession Number:01493465
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Edition:Final Report
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Abstract:Fly ash, a byproduct of coal combustion, has been used in Portland cement concrete for decades, and is widely accepted in the industry as a replacement for cement in amounts up to approximately 20% by mass. Addition of fly ash reduces the environmental impact of concrete by simultaneously consuming an otherwise unused waste product and by replacing cement, which is the most polluting and energy intensive component of concrete (an estimated 5% of all manmade CO2 emissions are due to cement production). Fly ash also improves the properties of concrete in several ways: improved fluidity during mixing and placing, higher strength, improved dimensional stability, and increased longevity of concrete structures. In spite of these improvements, challenges associated with the use of fly ash have prevented its cement replacement level from increasing beyond 20%. Currently, only about 40% of the fly ash that is available is used by the concrete industry; the remainder is stored in large landfill-type enclosures. In 2008, one such enclosure at the Tennessee Valley Authority (TVA)’s Kingston Fossil Plant ruptured and spilled approximately 5.4 million cubic yards of impounded coal fly ash slurry onto the surrounding land and into the adjacent Emory River. It was the worst environmental disaster of its kind in United States history. Public opinion is often shaped by disasters of this type, which in this case highlight the seemingly negative impacts of fly ash use. It is incumbent upon leaders of research in infrastructure, construction, and materials science to highlight the benefits of fly ash, to facilitate its maximum use, and to communicate its importance to the wider community. Therefore, the goal of this proposed research is to reduce the environmental impact of concrete construction through innovative materials use and production techniques, resulting in dramatic increases in the percentage of fly ash used in widespread construction. One of the most promising avenues for maximizing the use of fly ash is to incorporate it into self-consolidating concrete (SCC), which requires a relatively large amount of fine particles to produce. Studies have shown that with proper mix design, high-volume fly ash (HVFA) SCC mixes (cement replacements with fly ash of 30 – 70% by mass) can exhibit comparable workability and compressive strength development to conventional SCC, and even increased durability and decreased drying shrinkage. It is hypothesized that nanoparticles (e.g. nanosilica and nanolimestone) will facilitate the use of fly ash by maintaining early-age strength gain while nanoclays will facilitate the use of HVFA-SCC for cast-in-place applications by developing green strength. Fresh-state and early-age properties will be closely evaluated, where fresh-state is considered before set while early-age is after set. With proper proportioning of fly ash, clays, and nanoparticles, the authors expect to develop a material with the potential to revolutionize cast-in-place SCC applications from both a construction and sustainability standpoint. Specific objectives include the following: 1. Evaluate the influence of clays on HVFA-SCC so as to effectively use them to tailor its rheological properties; 2. Explore test methods to appropriately characterize HVFA-SCC; and 3. Evaluate the fresh-state and early-age properties of HVFA-SCC.
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