Composition and properties of Indiana flyashes

Carol Louise Kilgour, Purdue University

Abstract

A suite of representative Indiana flyashes was characterized to provide background to chemical, physical and physicochemical parameters that might affect their use in concrete. Of the 14 flyashes, 12 could be characterized as Class F in accordance with ASTM C 618. The majority of these flyashes (8 out of 12) had almost identical chemistry, typically SiO$\sb2$, Al$\sb2$O$\sb3$, and Fe$\sb2$O$\sb3$ (combined content = 90%) and CaO $\sp\sim$2%. This denotes these flyashes were derived from a uniform coal source, in this case perhaps an Illinois Basin deposit. Investigations on the activities of the flyashes in both the standard pozzolanic activity index test with portland cement (which varies water content as required) and for a modified test at constant water content, were carried out. The effects of different flyashes on water demand of the cement mortars were variable, some, especially those of higher carbon contents or coarse size distributions, increased, rather than decreased water demand. Some of the variability of strengths measured in flyash mortars was related to the degree of "overwatering" and "underwatering" effects, with respect to water content needed for optimum flow. It appears that 10 of the 12 flyashes would pass ASTM C 618 specification. Magnetically separated fractions of Class F flyashes were found to be composed primarily of ferrite spinel, hematite, and sometimes maghemite, with little quartz or mullite. X-ray diffraction bands were not detectable or weak, but indirect evidence indicates the glass in these magnetically separated particles would have a glass band maxima of around 27$\sp\circ$ 2$\theta$ if they were detectable. The dissolution behavior of a subset of three class F flyashes seems to indicate the composition of material eventually dissolved in a simulated pore solution is practically identical to the composition dissolved almost immediately in 1% HF treatment when the latter are recalculated to exclude the iron oxide liberated by HF. The compositions of such solutions give a good indication of the average composition of the glass. Addition of a small amount of solid Ca(OH)$\sb2$ to the simulated pore solution radically changes the response of the flyash. Any dissolved material is subsequently precipitated as amorphous or crystalline calcium-bearing compounds. (Abstract shortened with permission of author.)

Degree

Ph.D.

Advisors

Diamond, Purdue University.

Subject Area

Civil engineering

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