United States Department of Transportation
i
Design and evaluation of high-volume fly ash (HVFA) concrete mixes.
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2012-10-01
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[PDF-796.37 KB]
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Edition:Final report.
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Abstract:Concrete is the world’s most consumed man-made material. Unfortunately, the production of portland cement, the active
ingredient in concrete, generates a significant amount of carbon dioxide. For each pound of cement produced, approximately one
pound of carbon dioxide is released into the atmosphere. With cement production reaching nearly 6 billion tons per year
worldwide, the sustainability of concrete is a very real concern.
Since the 1930’s, fly ash – a pozzolanic material – has been used as a partial replacement of portland cement in concrete to
improve the material’s strength and durability, while also limiting the amount of early heat generation. From an environmental
perspective, replacing cement with fly ash reduces concrete’s overall carbon footprint and diverts an industrial by-product from
the solid waste stream (currently, about 40 percent of fly ash is reclaimed for beneficial reuse and 60 percent is disposed of in
landfills).
Traditional specifications limit the amount of fly ash to 25 or 30 percent cement replacement. Recent studies, including those
by the investigators, have shown that higher cement replacement percentages – even up to 75 percent – can result in excellent
concrete in terms of both strength and durability. Referred to as high-volume fly ash (HVFA) concrete, this material offers a
viable alternative to traditional portland cement concrete and is significantly more sustainable. By nearly doubling the use of
reclaimed fly ash in concrete, HVFA concrete aligns well with MoDOT’s green initiative on recycling.
However, HVFA concrete is not without its problems. At all replacement rates, fly ash generally slows down the setting time
and hardening rates of concrete at early ages, especially under cold weather conditions, and when less reactive fly ashes are used.
Furthermore, with industrial by-products, some variability in physical and chemical characteristics will normally occur, not only
between power plants but also within the same plant. Consequently, to achieve the benefits of HVFA concrete, guidelines are
needed for its proper application in bridges, roadways, culverts, retaining walls, and other transportation-related infrastructure
components.
The objective of this research was to design, test, and evaluate HVFA concrete mixtures. The study focused on the hardened
properties of HVFA concrete containing aggregates and fly ash indigenous to the state of Missouri and developed guidelines on
its use in infrastructure elements for MoDOT.
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