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Since 1989 this laboratory has had good success using X-ray fluorescence (XRF) methods to determine the amount of fly ash that is present in portland cement-fly ash mixtures. The method has been used on mixtures of dry cementitious constituents prior to batching, and also on portland cement-fly ash mortars and concretes. The method is based on the determination of the concentration of barium (Ba) and strontium (Sr) present in the construction materials. Since these two elements are greatly enriched in Iowa fly ashes they act as “finger prints” for the presence of fly ash, and if the proper criteria are satisfied, they also allow for the quantification of the amount of fly ash in a given mixture. The method works best when it can be calibrated with materials taken directly from a given jobsite. The method is very quick since samples can normally be analyzed in less than 10 min. The sample preparation process does not involve extraction techniques that use hazardous solvents. With a modern, computer-controlled X-ray fluorescence spectrometer the method can also be extended to determine many other elements present in the sample, such as sulfur (S) and chlorine (Cl), which may be of importance to investigations concerning the chemical attack of portland cement-based materials.
Scientist, Iowa State University, Materials Analysis and Research Laboratory (MARL), Ames, IA
Geologist, Iowa Department of Transportation, Ames, IA
Stock #: CCA10339J