United States Department of Transportation
i
Detection of fly ash in Portland cement fly ash concrete : final report.
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1991-12-01
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[PDF-6.70 MB]
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Alternative Title:Detection of fly ash in Portland cement fly ash-concrete.
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Abstract:The chemical composition, phases present, and textural characteristics of suite of 113 fly ashes were studied. The fly ashes came from Gifford-Hill & Co., Inc. power plants in Cason, TX; Gentry, AR; Westlake, LA; Boyce, LA; Choteau, OK and Oologah, OK. Two ordinary Portland cement (OPC) concrete samples, with 7:3 aggregate to cement weight ratio, and 51 samples with Portland cement partially replaced by fly ash (producing a 70:25.5:4.5 weight ratio) were also studied. The water to pozzolan ratio was 0.4 for both groups.
X-ray diffractometry was used to identify the mineralogy and the glass structure of the fly ashses. Special data reduction techniques were developed to establish the mineralogy of individual ashes and the typical specimen, Quartz, anhydrite, melilite, lime, tricalcium, aluminate, dicalcium silicate, merwinite, periclase, ferrie spinel, hematite, and possibly brownmillerite were found. The average structure of the glassy component was studied by examining the maximum of the broad hump in the background. The hump was found to be remarkably constant in its location at approximately 32.0o2Θ.
Minor but significant mineralogical differnces, such as amount of ettringite, were observed between the concrete samples with OPC and CPC and fly ash. The glassy in the Portland cement concrete was relatively symmetric and positioned at 33.0o2Θ, whereas the hump for the Portland cement-fly ash concrete was asymmetric with a maximum at 30.0o2Θ. The average structure of the nearly amorphous C-S-H in Portland cement-fly ash concrete is thus different from that in pure Portland cement concrete. The differences in minor mineralogy and the nature of C-S-H between Portland cement and Portland cement-fly ash can be exploited to develop an analytical method for the detection of fly ash in concrete.
Chemical analysis and evaluation of the results by discriminant function and factor analysis revealed little variation in the composition of the ashes from a given power plant sampled. The oxides of Ca and Al were used to formulate a quantitative technique that estimates fly ash at the 4.5 weight percent level in concrete with a total analytical error ±0.1 weight percent when the sources of fly ash and other concrete components are known. If the mean fly ash composition of all samples is used as a reference, the maximum error of estimation increases to ±1.0 weight percent.
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