Variability and Trends in Iowa Fly Ashes
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VARIABILITY AND TRENDS IN IOWA FLY ASHES SCOTT SCHLORHOLTZ, KEN BERGESON and TURGUT DEMIREL Department of Civil Engineering, Iowa State University, Ames, IA, Received 1 November,
50011
1986; refereed
ABSTRACT An investigation has been made of the variability of physical and chemical properties of high-calcium (Class C) fly ashes from four Iowa power plants. The investigation summarizes results obtained from three years (1983 through 1985) of monitoring of the various power plants. All four of the power plants burn low-sulfur, sub-bituminous coal from Wyoming. Fly ash samples were obtained from the power plants in accordance to the procedures described in ASTM C 311. Laboratory testing methods were similar to those specified by ASTM C 311. During the three year period, 102 samples were subjected to chemical and physical analysis while an additional 349 samples were subjected to physical analysis only. In general, the four power plants produce fly ashes of similar mineralogy and chemical composition. The observed time variation of the chemical composition of fly ash from a single power plant was quite small. The sulfur content consistently showed the largest coefficient of variation of the 10 elements studied. Physical characteristics of the fly ashes (as measured by ASTM tests) were also fairly uniform over long periods of time, when considered on an individual power plant basis. Fineness, when measured by wet washing using a 325 mesh sieve, consistently exhibited the largest coefficient of variation of any of the physical properties studied. INTRODUCTION The characterization of high-calcium fly ashes has steadily improved in the last few years. Before the late 1970's little was known about the chemical and physical properties of such fly ashes [1,2]. Today the literature abounds with papers concerning high-calcium fly ashes (see for example MRS Symposia 1981, 1984, 1985, and International Ash Symposia 1976, 1979, 1982, 1985). General agreement has been reached on the major crystalline compounds normally encountered in fly ashes of different origins [2-7]. Glass composition and content are currently being investigated. Chemical analysis of fly ash has suffered from two basic problems: (1) lack of adequate standard reference materials for calibration of analytical techniques; (2) misinterpretation of the results obtained from such chemical analyses. It is hoped that the first problem will be solved by late 1986 when the National Bureau of Standards releases three new fly ash standards [8]. The second problem is simply one of confusion about the type of data obtained from the chemical analyses specified in ASTM C 311 [9]; it is hoped that future work will help to eliminate such misunderstandings. Simple correlations between the chemical composition of fly ash and its influence on the strength and durability characteristics of portland cement pastes, mortars and concretes have been pursued for many years [10-17], but to date these have not been adequately defined. The purpose of this paper is to present the results
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