United States Department of Transportation
i
Design and evaluation of high-volume fly ash (HVFA) concrete mixes, report A : evaluation of HVFA cementitious paste and concrete mixtures.
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2012-10-01
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Abstract:In the Paste Screening Study, 25 combinations of five Type I/II portland cements
and five Class C fly ashes commonly used in Missouri were tested in paste form with no
chemical or powder additives. Testing procedures included semi-adiabatic calorimetry,
Vicat setting time, miniature slump, and compressive strength at one and 28 days. The
two most reactive and two least reactive combinations (defined by one day strengths)
were further evaluated in the Paste Main Effects Study. Eighty mixtures were examined.
In the Paste Main Effects Study, the effects of two levels each of WR/HRWR,
gypsum, calcium hydroxide (lime), rapid set cement (RSC), and gypsum-lime, and
gypsum-RSC were determined. Except for the WR/HRWR dosage level experiment, all
other mixtures contained a low WR/HRWR dosage. Except for the gypsum level
experiment, all other mixtures contained 4% gypsum. The lime levels were 5 and 10%
and the RSC levels were 10 and 20%. All percentages are by mass of fly ash. Sixty-four
mixtures were examined.
The objective of the Concrete Properties Study was to scale up from paste to
concrete the most promising powder additive combinations and then evaluate the
mixtures in terms of plastic and hardened properties. Thus the mixture matrix included
ordinary portland cement (OPC)-fly ash blends at two levels (same as in the Paste Main
Effects Study) and fly ash at three levels (zero, 50 and 70%). WR dosage (nominal
dosage), gypsum content (4%), lime content (10%), and RSC content (20%) were held
constant. Ten concrete mixtures were evaluated.
At the 50% fly ash level, one day strengths were low no matter which powder
additives was used, but good strengths were achieved by day 3. At the 70% fly ash level, the concrete was weaker than at zero and 50% fly ash, but reasonable strengths were
reached at 28 days. At 50% fly ash, abrasion resistance was somewhat lower. At 70% the
effect was much worse. In regard to drying shrinkage, it appears that HVFA mixtures
shrink less than their OPC counterparts. In a comparison to OPC mixtures, rapid chloride
permeability (RCP) was lower for 50% fly ash mixtures, but 70% fly ash mixtures are
more permeable. All HVFA mixtures had greater freeze-thaw Durability Factors than the
OPC mixtures, and were at 93 or above. However, all fly ash mixtures did poorly in
regard to salt scaling. Reaction time (calorimeter curve time, setting time, stiffening time)
varied as a function of characteristics of the OPC and fly ash in conjunction with each
other, type and level of powder additives used, dosage of WR/HRWR, and the type of
test method used for evaluation.
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