Date of Award

Spring 1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Methi Wecharatana

Second Advisor

C.T. Thomas Hsu

Third Advisor

Dorairaja Raghu

Fourth Advisor

Jay N. Meegoda

Fifth Advisor

William Librizzi

Abstract

Grinding process is introduced to provide fine particles of coal fly ash that enhances the strength gain of cement mortars. It is discovered that grinding can make all the studied fly ashes more suitable for concrete use at higher replacement value than previously anticipated even when the effect of high carbon content is considered.

In this study, new mechanisms for strength gain of fly ash mortars are proposed. They are dispersion and nucleation, which are results from the presence of fly ash in the cement mortar. These effects are shown to enhance the hydration of cement. The pozzolanic action of fly ash contributes strength at a later stage. Pozzolanic activity of fly ash is shown to increase with fineness of the ground fly ash.

Several types of fly ashes, wet bottom, dry bottom and low NOx, fly ashes are chosen as representative of the waste products of existing and the new burner technology. They were ground to different particle size distributions. Tests were conducted to determine the physical properties of these fly ashes and their performance in cement mortars. Optimum ranges of the grinding process were explored along with particle size analysis, chemical composition, mineralogy, and morphological aspects of raw and ground fly ash.

In order to see whether these processed fly ashes can be used at high percentages in cementitious products, the performance of mortars made from these fly ashes is examined. The strength contribution of fly ash in cement mortars through dispersion, nucleation, and pozzolanic action were investigated and found to perform equally or better than normal cement mortars as early as seven days. Furthermore, the study on the properties of mortars made of high-carbon ground fly ash from low NOx, furnace also showed similar strength enhancement. The major conclusion of this study is that grinding is a suitable mean to increase utilization of fly ash as cement replacement. The processing technique has economically been demonstrated to yield quality fly ash for us in concrete, thus reducing the amount of fly ash that needs to be disposed of in landfills.

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