United States Department of Transportation
i
Laboratory evaluation of 100 percent fly ash cementitious systems : final report 573.
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2016-12-01
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[PDF-1.27 MB]
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Edition:Final report
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Abstract:Long-lasting, durable concrete is a must have for Departments of Transportation (DOT’s) in today’s construction and economic climate. Many entities are
turning to alternative concrete mixtures to ensure long-term durability such as ternary mixtures, lower w/cm ratios, lower cementitous materials contents,
and alternative binders such as Ekkomaxx. The use of fly ash as a sole binder production of portland cement concrete can be difficult and the
aforementioned product allows the control of the set times to allow better usage of class C fly ash as the sole binder.
Thirty-six mixtures were prepared and duplicated in the laboratory to determine the effects of activator dosage, fly ash content, and water content. The
fresh properties of slump, air content, and set time were measured. Hardened properties tested included compressive and flexural strength, length change,
and surface resistivity.
The slump results show that the w/a ratio affect the slump greater than the admixture dosage rate. Generally, the slump increases as dosage rate increases,
but the trend would be considered fair as the w/a changes between the different admixture dosage rates.
The time between initial and final set was very short. This is of concern to the authors due to the fact that this is the period in which the concrete material
has to be finished and textured. In a controlled laboratory environment, this can be completed rather easily. In an ambient environment, many effects
come into play such as wind speed, temperature, and relative humidity. The short window may be a barrier to full-scale implementation. Overdosing the
admixture has a negative effect of producing concrete that does not set within a 24-hour time period, and sometimes not even within 36 hours.
The hardened concrete properties show that many of the mixtures will meet or exceed Louisiana Department of Transportation and Development (DOTD)
requirements for compressive strength and surface resistivity. The results show that the overall strength is dependent upon admixture dosage rate, followed
by the w/a ratio and ash content, respectively. Although these mixtures will meet or exceed requirements, care should be exercised when utilizing this
material; a trial batch is recommended for all applications.
The authors recommend that a discussion between the materials administrator, AML representatives for concrete materials, and the PRC be held to discuss
future usage of this product. Key points in the discussion will be to designate the product under the chemical admixture or cement designation(s).
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