Date of Award

Spring 1996

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Wenzel, Thomas H.

Second Advisor

Crovetti, James

Third Advisor

Vinnakota, Sriramulu

Abstract

This thesis examined the actual strength contribution of a specific weight of Class C or Class F fly ash when added to an ordinary portland cement (OPC) in a concrete mixture. This was accomplished by determining and applying a cementing efficiency index (EI) for fly ash. EI is defined as the gain in compressive strength of a fly ash concrete over an OPC concrete at the same age with the same slump per pound of fly ash added to an OPC concrete mixture. This index will allow designers to take a standard mixture and add fly ash and increase its strength with little increased cost. A reliable cementing efficiency index (EI) was determined by statistical analysis on existing portland cement concrete and fly ash concrete compressive strength and mixture data which had age, slump, and fly ash addition level as variables. Using these variables, a statistical regression was performed for EI. From this analysis, reliable regression equations were developed for EI, the cementing efficiency index. Verification mixtures were performed to test the validity of the regression against the strength gain of an entirely different mixture than that of the original regression data. The verification mixtures were proportioned for a target compressive strength. An increase in strength for each pound of fly ash added was expected as given by the regression equations for EI. The strengths for these verification mixtures were recorded for the 7 and 28 day ages. This analysis and verification attempted to quantify a strength contribution for a certain quantity of fly ash. This led to the development of an Efficiency Index (E.I.) for a specific addition level of fly ash. This index assigned a strength gain for a weight of fly ash added or substituted in a concrete mixture under specific conditions of slump, fly ash type, and age. Conclusions are made concerning the effectiveness of the mixture proportioning method from the actual verification mixtures. Recommendations are made for further research in this area with respect to refining the use of the cementing Efficiency Index in mixture proportioning.

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