Date of Award

5-31-1993

Document Type

Dissertation

Degree Name

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

Department

Civil and Environmental Engineering

First Advisor

Methi Wecharatana

Second Advisor

John W. Liskowitz

Third Advisor

C.T. Thomas Hsu

Fourth Advisor

Jay N. Meegoda

Fifth Advisor

Anthony E. Cerkanowicz

Abstract

Fly ash, a by-product of coal burning power plants, is produced in large quantities each year. It is commonly known that fly ash possesses pozzolanic behavior which can enhance the properties of concrete. Due to a lack of proper understanding on the formation of fly ash and its performance in concrete, the question of quality assurance has frequently been a major concern of engineers using fly ash in their construction projects. As a result, much fly ash is disposed of as waste material in landfills. Recent environmental concerns and a shortage of landfill space have rapidly escalated the disposal cost of fly ash and therefore, the need to seek better utilization of fly ash in concrete is then critical.

The objective of this investigation is to study the effect of fly ash on the strength development of mortar and concrete and to develop models to predict its performance in these cementitious composites. The fly ash used was carefully selected and defined as to its origination, formation, physical and chemical compositions, and the storage condition. The original fly ash was fractionated into six particle size ranges, each having a relatively uniform particle size, with maximum sizes ranging from 5 to 300 microns. The rate of strength gain of these fly ash concretes was monitored from 1 to 180 days. The compressive strength for each series was correlated to the conditions of fly ash used to determine the major parameters affecting the performance of fly ash in mortar and concrete.

The results from this study show that the particle size of fly ash has a significant effect on the strength development of concrete. The combustion condition in the boiler has some influence on the performance of fly ash in cementitious composites. Of particular importance is the finding that certain portions of fly ash when used as cement replacement can improve the strength of concrete beyond normal cement as early as 14 days. A correlation to predict the compressive strength of fly ash concrete is proposed and provides good agreement with experimental results both from this study as well as from other investigators.

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